Patent Application
20140054292
This disclosure relates generally to multiple-polymeric-layer thermoformable materials and articles formed from such materials. In one aspect, the present disclosure relates generally to containers for hygienically containing food, including containers having multiple peelable layers on a surface which contacts the food, such that the same container can be used multiple times to hygienically contain food without the need to sanitize the food-contacting surface between uses.
The disclosure also relates to other containers having peelable surface layers, such as paint trays.
Paint Trays
Paint is commonly applied to walls and other surfaces with a paint roller comprised of a roll of napped textile material or other paint absorbent substrate carried on a handle, and a metal or plastic paint-holding tray into which the roller is placed to load the roll with paint. While useful in quickly applying a uniform paint coating to large surfaces, a major disadvantage of the use of this system is the required messy and time consuming chore of cleaning the roller and tray after use. The present application relates to an improved tray that enables the user to avoid tray cleaning, and to a tray with two wells divided by a flat section designed specifically to properly distribute paint on the roller nap. The tray configuration is also designed to lend itself to thermoforming.
In an attempt to minimize cleaning, the prior art describes a preformed paint tray liner that is placed into the interior of a paint tray. Generally, these liners are thermoformed from a plastic sheet having a thickness of from about 0.008 to about 0.03 inches. The paint is poured into this liner, which is removed and discarded along with any adhered paint after the paint job is completed. While effective in eliminating the need to clean the paint tray, these preformed liners are sufficiently expensive that many users attempt to clean and reuse the liners. Their thickness adds significantly to environmental waste upon disposal and require significant amounts of energy to produce. The preformed tray liners also require separate additional storage prior to use.
Other prior art as exemplified by U.S. published patent application no. 2004/0112902 to Campbell and U.S. published patent application no. 2006/0037960 to Rosa manually presses an impervious plastic sheet having a thickness of from about 0.5 to about 5 mils and an adhesive backing into a previously formed paint tray so that the sheet approximately conforms to the tray. The sheet is peeled away and discarded after use. While using less material than preformed tray liners, these sheets are awkward and time consuming to individually hand press into place and do not provide a functional liner that exactly conforms to the tray interior, especially in the corners of the tray.
Food Service Containers
Food is commonly held in bins, trays, pans, and other containers during its preparation, presentation, and serving. In order to minimize transmission of food-borne illnesses and to comply with applicable regulations regarding food sanitation, food and food-implement containers must be frequently sanitized. This is particularly true in situations in which food containers are used over long periods, refilled, or accessed frequently by individuals removing items therefrom. Examples of containers of these types include pans used in buffet or steam tables, bins recessed in a food preparation surface, salad bar pans, bulk condiment containers, cutlery bins, hot and cold soup kettles, and chafing dish inserts. In food service settings, it is desirable to maintain hygienic conditions even for containers that do not hold food or implements intended for human consumption (e.g., bins used for busing tables and other utility bins).
Some food service situations require use of many food storage containers to separately contain different food items. Examples of such situations include salad and buffet displays at restaurants, cafeterias, and groceries at which customers select food desired for purchase from the containers. Other examples include food preparation stations (e.g., food preparation tables such as those shown in U.S. Pat. No. 6,385,990) located in restaurant, cafeteria, or grocery settings, at which an employee of the establishment selects food (e.g., sandwich components and condiments) from a variety of trays accessible to the employee in response to requests from a customer. In these settings, containers having standardized sizes are frequently used to facilitate replacement of a used container with a fresh one. Retailer food service practices or government regulations often specify how frequently used containers must be sanitized or replaced, rather than simply refilled with new food items or implements. Frequently, the containers are not refilled, and are instead removed and sanitized prior to being refilled with food and reused, or are simply discarded.
Food storage containers are used to hold foods that must be maintained at cool temperatures (e.g., perishable products such as meats, cheeses, lettuce, tomatoes, and yogurts), foods that are maintained at warm or hot temperatures (e.g., soups or cooked entrees), and food service items that are maintained at ambient temperatures (e.g., breads and crackers, eating utensils, and foods intended for near-immediate consumption). For food storage containers in which heat transfer (either into or from the food contained therein) is desired, it is known to make the containers from materials that exhibit thermal conductivity and heat capacity characteristics suited to the desired use of the container.
Conventional food service containers have a variety of shapes, such as rectangular and circular pans having an open top. A flange or rim typically extends around the perimeter of the open pan top to hold the container in a fitting, such as a frame or rack. When used in a heated or chilled table setting, the flange can also provide a seal around the perimeter of the container, improving energy efficiency (i.e., by preventing loss of heating or cooling medium) and appearance. The flange can also act as a convenient surface for lifting, supporting, and carrying the container. When used in a steam table, buffet table, salad bar, or the like, the body (e.g., the portion containing the food) and flange of a container are typically dimensioned so that the body of the container is received into an opening in the table or bar and is supported by its flange resting upon the edges of the table or bar opening or upon a frame or rack fitted to the bar or table.
Food storage containers sometimes have corresponding lids that are adapted to fit an orifice of the container (e.g., a soup tureen having a fitted lid, optionally with a recessed section to accommodate the handle of a ladle when the tureen and lid are assembled). The lid can serve to exclude contaminants, to prevent gain or loss of heat, or some combination of these functions.
Reusable food service containers of these types are made from a variety of materials, and are frequently made from either metals (e.g., stainless steel) or relatively durable plastics (e.g., polycarbonates). However, disposable food containers made from lower-cost plastics (e.g., various polyethylenes, polyesters, and polypropylenes) are also used.
Regardless of whether reusable or disposable food storage containers are employed, use of the containers typically involves generation of significant quantities of waste. Disposable containers both preclude cost savings that are realized with re-usable containers (since a new container must be used each time) and generate solid waste which must be disposed of properly. Although reusable containers avoid the economic waste of single use containers, they require sanitation procedures that are costly, time consuming, and generate significant quantities of (usually liquid) waste materials. Furthermore, sanitation of reusable food containers tends to generate solid and liquid wastes (e.g., food particles, fats, and greases) that are not soluble in water and for which disposal in wastewater systems tends to be regulated. Thus, commercial scale sanitation of reusable food containers often requires investment in equipment that isolates such wastes (e.g., grease traps), inspections to monitor compliance with applicable regulations, or both. In general, disposal of solid wastes (which are generally removed by truck, rather than by cloggable pipes and sewers) is less regulated and more flexible than disposal of liquid wastes containing non-water-soluble components, in addition to conserving water used for washing.
Others have proposed fitting disposable liners to food service containers in order to alleviate the waste and inconvenience associated with cleaning reusable food service containers. Such liners can be difficult to install and to remove in a sanitary fashion. Also, they are susceptible to bypass if food products from the interior of the liner are spilled or migrate beneath the liner. When such liners are not adapted specifically to the food service container, problems of fitting and use arise from the unmatched dimensions of the liners and containers. For example, non-fitted liners can fold or crease to create pockets in which food products can accumulate or be hidden, leading to spoilage or bacterial growth that can contaminate food products in the remainder of the container. Fitted liners have the drawback that they fit only a specific container, but not others. Inserted liners also have the drawback that they tend to move or slide around in the food service container when foodstuffs are manipulated therein. Furthermore, known liners also have disadvantages stemming from the fact that they are formed (like plastic bags) by welding, adhering, or otherwise sealing plastic sheets along a seam. The seams can often leak or tear, defeating the purpose of the liner. Insertable liners also tend to be relatively unsightly and expensive.
There is a continuing need for a food container that can hygienically contain food and food service items and that can be rapidly and conveniently recycled for multiple uses, preferably without generation of excessive waste materials and while presenting a favorable appearance. The subject matter of the present disclosure addresses this need.
Various types of subject matter are described in this disclosure.
In prior related applications (U.S. patent applications No. 12/620,460, filed 17 Nov. 2009 and Ser. No. 11/734,285, filed 12 Apr. 2007, and U.S. provisional patent applications 60/794,409, filed 24 Apr. 2006 and 60/855,597, filed 31 Oct. 2006), use of technology similar to that described herein was described in the context of making articles such as paint trays for use in applying paint to a surface with a paint roller, and in particular to a paint tray having a one or more layers of a peelable surface film, whereby the paint tray can be cleaned after use by peeling away the upper film surface. Those applications also related to methods for converting multiple layers of material into a stack or roll and forming the paint tray or other container with adhered layers. It was recognized that those methods could lend themselves to a number of markets other than paint trays, i.e., trash cans, buckets, metal paint trays, cat litter containers, camping plates, medical trays, etc.
In one aspect, the subject matter described herein relates to a peelable, multi-use food service container. The container includes a relatively rigid sheet of a thermoformable polymer and at least one, and preferably a plurality of, second sheets of a polymer, each second sheet having a sanitary face and an adhesion face. A first surface of the rigid sheet has a conformation adapted for holding, supporting, or containing a food service item. Each of the second sheets overlaps the rigid sheet at the first surface and conforms to the shape of the first surface. Interposed between the rigid sheet and the adjacent second sheet is a first barrier composition that adheres (e.g., peelably) the rigid sheet and the adhesion face of the adjacent second sheet. A second barrier composition (identical to or different from the first) is interposed between the adhesion and sanitary faces of adjacent second sheets. The second barrier composition peelably adheres the second sheets to one another. The container thus has one or a plurality of hygienic second sheets peelably adhered to a surface adapted for holding, supporting, or containing a food service item. In one embodiment, the second barrier composition is identical between all second sheets. In another embodiment, a second sheet more distal from the rigid sheet is more easily peeled from the second sheet underlying it than is a second sheet more proximal to the rigid sheet. The container can have a protective coat layer applied atop the uppermost second sheet to prevent contamination of and physical damage to the second sheet(s), such as might occur during manufacture, storage, shipping, or installation of the container.
In another aspect, the disclosure relates to method of operating a food station. The method involves assembling one or more first food products (e.g., a sandwich or salad) from components stored in multiple food containers, including at least one selected component that is held in a peelable food container described herein. After assembling first food product(s) (for example, when the ingredients in the container are depleted, at the end of a business day or shift, or after a pre-selected period of time), a second sheet is peeled from the peelable food container (revealing a sanitary surface that can be contacted with fresh food components), and more of the selected component is added to the peelable food container. One or more second food products (identical to or different from the first food products) are then assembled from components stored in the food containers, including at least the selected component.
In this disclosure, terms such as horizontal, upright, vertical, above, below, beneath, and the like, are used solely for the purpose of clarity in illustrating the subject matter disclosed herein, and should not be taken as words of limitation. The drawings are for the purpose of illustrating the subject matter disclosed herein and are not intended to be to scale.
The subject matter of this disclosure relates to various embodiments.
Thermoformable Stack
In one embodiment, the subject matter of this disclosure relates to a thermoformable stack. The stack includes a first sheet of a thermoformable polymer and at least a second polymeric sheet (sometimes referred to herein as a “liner” sheet) that overlaps the first sheet at an overlapping region. The first and second sheets can have the same composition and thickness, or these characteristics can be different. The stack can include multiple second polymeric sheets (made of the same or different polymers and having the same or different thicknesses). The stack can also include sheets of other materials, such as metal sheets. A layer of a first barrier composition is interposed between faces of the first and second sheets in at least a portion of the overlapping region, preferably including substantially all of the first surface. The first barrier composition prevents fusion of the surfaces of the first and second sheets at the thermoforming condition. When the stack is subjected to the thermoforming condition, the first sheet assumes a thermoformed shape, the shape of the second sheet conforms to the shape of the first sheet, and the first and second sheets do not fuse in the portion of the overlapping region.
When the stack includes at least one pressure-deformable sheet, such as a metal sheet, as a first and/or second sheet, the stack can be shaped using ordinary bending, stamping, and other pressure-based shaping methods. Such stacks preferably include first and second sheets that can withstand pressure, shear, deformation, and stretching forces inherent in pressure-based shaping methods without tearing or becoming punctured. By way of example, thin, stretchable nylon sheets can be adhered to an aluminum sheet, with a first barrier composition interposed between the aluminum sheet and the adjacent nylon sheet and a second barrier composition interposed between adjacent nylon sheets. Such an aluminum/nylon stack can be subjected to a press that deforms the aluminum sheet into a desired shape, with the nylon sheets stretching to match the shape without becoming substantially de-adhered from the surface of the aluminum sheet or from one another. In this manner, shaped metal objects having peelable polymeric layers can be made, as can articles made from other pressure-deformable materials (e.g., uncured ceramic pastes).
The second sheet is made of a material that is selected such that it is capable of maintaining its structural integrity at a thermoforming condition at which the first sheet can be thermoformed. The second sheet is capable of conforming to the shape of the first sheet as the first sheet is thermoformed at the thermoforming condition. If desired, the second sheet can be a material that is also thermoformable at the thermoforming condition, but this is not a requirement. However, if a non-thermoformable second sheet is used, the second sheet may detach, deform, or pull away from the first sheet following thermoforming. Even if the second sheet is thermoformable, these behaviors can nonetheless manifest themselves if the first and second sheets are made of different materials (owing, for example, to different coefficients of thermal expansion). When the second sheet is a non-thermoformable material, the characteristics of the second sheet and any adhesive in the adjacent barrier compositions should be selected to retain the desired configuration of first and second sheets in the finished article. By way of example, if one or more of the second sheets is an elastic material, then the elastic material should be selected such that it can temporarily deformed at the thermoforming conditions, the adhesive(s) should be selected such that they will adherently oppose the tendency of the elastic material to resume its original shape after thermoforming, or some combination of these. An adhesive in the interposed barrier composition can thereby cause a second sheet to remain conformed to the shape of the underlying thermoformed surface, even if the second sheet itself is not thermoset at the thermoforming temperature.
One or more tabs can be interposed between the first sheet and second sheets. If a tab extends beyond an edge of either sheet, the tab can be used to facilitate separation of the first and second sheets after thermoforming. The tab can be adhered to either sheet or to neither.
In one embodiment, the tab is relatively fixedly adhered to the second sheet and either peelably adhered to or not adhered to the first sheet, such that the second sheet can be peeled from the first by grasping the tab and pulling the second sheet away from the first by way thereof.
In a second embodiment, the tab is relatively fixedly adhered to the first sheet and either peelably adhered to or not adhered to the second sheet, such that the second sheet can be peeled from the first by scratching (e.g., with a fingernail or an edged instrument, such as the tine of a fork) the edge of the second sheet that overlies the tab to begin partial peeling of the second sheet at the location of the tab, and then grasping the partially peeled portion of the second sheet and manually peeling the remainder of the second sheet away from the first by pulling on the partially peeled portion. In this second embodiment, if the second sheet is peelably adhered to the tab (i.e., rather than not adhered at all to the tab), then adhesion of the second sheet to the tab can exclude materials (e.g., dust, liquids, or food particles) from the space between the tab and second sheet, rendering the tab surface clean upon peeling the second sheet therefrom. This can be of particular significance in applications (e.g., in food service containers) in which preservation of a sanitary surface upon peeling is desired.
Although a loose stack of polymeric sheets can be thermoformed using the materials and methods described herein, it can be convenient to bind the first and second sheets to one another (and to bind multiple second sheets together, where multiple second sheets are present) prior to thermoforming (e.g., to facilitate combination, storage, shipping, handling, manufacture, and alignment of the sheets). The means used to bind the sheets to one another is not critical, but preferably does not affect the properties of the sheets in the region(s) of the sheets that are to be thermoformed. By way of example, the sheets can be bound together using a glue applied to a common edge of the first and second sheets, by fusion of a common edge of the first and second sheets, by stapling the first and second sheets together, by adhering the sheets together using an adhesive applied between the sheets at an inter-sheet area distinct from the shaped section of the sheets, or by other means.
In order to prevent detachment or deformation of the second sheet away from the first sheet after thermoforming, the first barrier composition can include an adhesive that peelably adheres the first and second sheets. By incorporating such an adhesive into the first barrier composition, thermoformed articles can be made in which the second sheet can be peeled away from the first sheet, preferably (i.e., by judicious selection of an adhesive) without tearing either of the first and second sheets. All, or only a portion, of the overlapping region can be coated with the adhesive-containing first barrier composition. When a tab is interposed between polymer sheets, the tab can be adhered to the adhesive and used to pull the edge of the sheet to which the tab is adhered away from the adjacent sheet to which the tab is not adhered. In alternative configurations, the adhesive can be incorporated into the barrier composition or the adhesive can be a composition discrete from the barrier compositions. By way of example, a barrier composition having perforations or holes therethrough can be interposed between sheets and a separate adhesive interposed between the sheets on one side of the barrier composition (i.e., the adhesive contacting both sheets through the holes or perforations), with the adhesive preventing fusion of the sheets, but adhering them where it is present and the barrier composition preventing fusion of the sheets where the adhesive is not present.
An important embodiment of the subject matter disclosed herein is a stack (sometimes referred to herein as a “master pad roll” when provided in the form of a rolled stack) of overlapping polymeric sheets. This stack includes the first sheet, which is a thermoformable polymer, and at least one, and preferably a plurality (e.g., 2, 3, 6, 10, or 20), of second polymeric sheets. Each second sheet overlaps the first sheet at the overlapping region, is capable of maintaining its structural properties (i.e., each sheet maintains its integrity and, preferably, its pliability and approximate thickness) at the thermoforming condition, is capable of conforming to the shape of the first sheet as the first sheet is thermoformed at the thermoforming condition, and has a layer of a second barrier composition interposed between it and each adjacent second sheet in a portion of the overlapping region. The first barrier composition prevents fusion of the surfaces of the first sheet and the adjacent second sheet at the thermoforming condition. The second barrier composition (which may be identical to the first) prevents fusion of the surfaces of adjacent second sheets at the thermoforming condition. When the stack is subjected to the thermoforming condition, the first sheet assumes a thermoformed shape, the shape of each of the second sheets conforms to the shape of the first sheet, and the sheets do not fuse in the portion of the overlapping region. In this embodiment, each of the second sheets can have different, identical, or substantially the same composition. Likewise, the compositions of the first sheet and any or all of the second sheets can be different, identical, or substantially the same.
As with the first barrier composition, the second barrier composition can include an adhesive (i.e., the same adhesive as the first or a different adhesive). Such a second barrier composition peelably adheres adjacent second sheets. An article made by thermoforming a stack of this sort will have multiple peelable layers. Such articles are desirable when, for example, a renewably clean and/or sanitary surface is required of an article, and particularly in situations in which cleaning of the surface is difficult, time-consuming, distasteful, or hazardous. In one embodiment, an article having a relatively thick (e.g., 10 to 40 mils) base (substrate) layer made from a thermoformed polymer can have multiple thin (e.g., 1 to 7 mils) peelable layers that are separately peelably adhered to the base in a stacked configuration. The base can provide shape and rigidity to the article (e.g., a paint tray, a toilet seat, or a food service container), and the peelable layers can provide a renewably clean surface upon peeling of individual layers.
The stack described herein has at least one second sheet on at least one face of the first sheet, as described above. Multiple second sheets can be arranged on the first sheet, adjacent one another, at a distance from one another, overlapping one another, or any combination of these. The second sheets can be stacked atop one another, with the edges of the stacked second sheets coinciding perfectly or nearly perfectly with one another, with the edges of each stacked second sheet completely covering one or more edges of the sheet over which it is stacked, with the edges of each stacked sheet receded away from one or more edges of the sheet over which it is stacked, or any combination of these. Furthermore, second sheets can be arranged on one or both faces of the first sheet. On each face of the first sheet, there can be a single second sheet, multiple non-overlapping second sheets, multiple partially-overlapping second sheets, or multiple stacked second sheets.
When tabs are interposed between adjacent sheets, at least a portion of the tab should extend beyond an edge of one of the adjacent sheets, to facilitate grasping of the tab, the edge of the sheet, or both. If an adhesive is interposed between the adjacent sheets, the tab can facilitate peeling of the adjacent sheets, particularly if the adhesive completely fills the gap (i.e., all the way to the edges of the sheets) between the adjacent sheets. If no adhesive is interposed between the adjacent sheets, the tab can nonetheless facilitate separation of the adjacent sheets by relieving any pressure or electrostatic attraction in the inter-sheet gap, by providing a region in which electrostatic forces between the sheet surfaces are disrupted, or simply by providing a mechanical lever by which expansion of the inter-sheet gap can be initiated.
In an advantageous embodiment, tabs are interposed between sheets in such a manner that the tabs between sheets alternate between one side of the shaped article (or stack) and the other side, for example so that peeling a sheet using a tab interposed between the top sheet and the next (i.e., underlying) sheet on the right side of the shaped article exposes a tab interposed between the next sheet and the third sheet on the left side of the shaped article. (See, e.g.,
In one embodiment, tabs extend beyond the edges of both adjacent sheets between which the tab is interposed. In this embodiment, the tab can be grasped independently of the sheets and used to initiate peeling. While this embodiment has the advantages of ease of use and visibility, it has the disadvantages that the tabs can be unsightly and compromise sanitation (e.g., by providing a spot at which sheets can be inadvertently peeled and an otherwise-sanitary surface between the peeled sheets can be exposed to environmental contaminants).
In another embodiment, the tab is fixedly adhered to one of two adjacent sheets and peelably adhered to the other sheet, which does not completely cover the tab. In this embodiment, the tab is not used as a handle or grasping point for peeling either sheet to which it is attached. Instead, the tab provides a surface (e.g., a scratch-resistant surface) from which a portion of the sheet that is peelably adhered thereto can be peeled by scratching, abrading, or picking the edge of that sheet at the tab surface. When a plurality of such tabs are used in a stack of sheets, the tabs can, for example, be arranged such that the tab for facilitating peeling of the uppermost (relative to the first sheet) second sheet runs down the right of the stack, with the uppermost second sheet completely obscuring the tab for facilitating peeling of the underlying second sheet, which runs down the left of the stack. Upon peeling of the uppermost sheet, the tab for facilitating peeling of the uppermost sheet will be completely exposed (i.e., because the portion of that tab that was partially obscured by the uppermost sheet prior to peeling will now be exposed), and the tab for facilitating peeling of the underlying second sheet will be partly exposed (part of that tab being obscured by that underlying second sheet, which can be peeled therefrom in like manner as for the uppermost sheet). A similar side-to-side alternating arrangement can be used for multiple second sheets, with the width of the sheets increasing with proximity to the first sheet (i.e., such that each second sheet completely obscures all but one of the tabs underlying it and partially obscures that remaining tab (at which peeling of the sheet can be initiated).
In embodiments in which a tab is peelably adhered to and partially covered by an upper second sheet and relatively fixedly adhered to an underlying (relative to the first sheet) second sheet, it can be convenient to include on the tab indicia for indicating the operability of the tab. For instance, because the tab is partially covered by the upper sheet, the non-covered portion of the tab can be imprinted with the first designation “̂̂̂̂ PEELHERE ̂̂̂̂”, with the upper portion of the letters adjacent the overlying edge of the upper sheet, to indicate the edge of the upper sheet which should be peeled from the tab. The obscured portion of the tab can be imprinted with the second designation “vvvv DO NOT vvvv” immediately above the first, so that when the upper sheet has been peeled from the tab (i.e., when the tab is no longer useful), the full indicium
(i.e., a combination of the first and second designations) is visible. Other suitable indicia can be used.
The stack described herein can be prepared and provided in the form of multi-sheet leaves, folded bundles, or rolls, for example. In many polymer-processing operations, rolls of polymeric materials are preferred for ease of handling. Rolls of the stack described herein can be prepared simply by winding the stack about itself, or about a core such as a paper or wooden tube or cylinder, in a rotary fashion. In order to minimize unintended interactions between the bottom of the stack in one layer of the roll and the top of the stack in an adjacent layer of the roll, a release agent can be interposed between layers of stack as it is rolled. In one embodiment, the release agent is a sheet of a material such as paper or waxed paper. In another embodiment, the release agent is an oil or other liquid agent which inhibits or prevents irreversible interaction of stack layers. By way of example, a thin film of a silicone-based compound (e.g., a liquid polysiloxane-containing composition, such as a silicone oil) can be applied to the top, bottom, or both top and bottom of the stack as it is rolled. The release agent should either be an agent which does not affect thermoforming operations on the stack or an agent which can be separated from the stack prior to thermoforming operations.
Images, text, designs, or other printed matter can be included on one or more of the sheets of the stack and articles made by thermoforming the stack. By way of example, label text and graphics can be printed on the outermost second sheet (i.e., the second sheet on the “top” of the stack, having no other second sheets atop it). Such label information can be printed on the exterior of the sheet (i.e., on the surface of the product) or, if the outermost second sheet is not opaque, the information can be printed on the inner surface (i.e., first-sheet-side) of that sheet. Such printed matter should encapsulated between the sheet and the barrier composition that is interposed between the outermost sheet and the adjacent sheet. Encapsulation of the printed matter can ensure that the printed matter is peeled off with the outermost sheet (i.e., does not adhere to the adjacent sheet) when the outermost sheet is peeled away from the adjacent sheet. Printed matter can be applied to the inner and/or outer faces of any of the sheets described herein in the same manner. Judicious selection of surface treatments (e.g., Corona treatment) and adjacent adhesives can ensure that the printed matter remains bound to a desired surface when the adjacent adhesive (and any polymeric or other sheet adhered to the desired surface by the adhesive) is peeled away.
When printed matter is included on a surface of the shaped articles described herein, the precise materials and methods used to print the matter on the surface are not critical, other than that they should be selected such that the printed matter will remain attached to the surface to which it is applied during normal use of the shaped article (unless detachment of the printed matter is considered acceptable). By way of example, in one embodiment of the thermoformed, multiple-peelable-layer paint tray disclosed herein, the outermost peelable layer is transparent and the printed matter is applied to the underside of that layer (i.e., the face of the layer that is adhered to the underlying surface) such that an adhesive in the barrier composition between that layer and the underlying surface adheres to the printed matter (and thence to the outermost layer) when the outermost layer is peeled away from the underlying surface. In another embodiment, the penultimate peelable layer (i.e., the second sheet adjacent the first sheet) is transparent and the printed matter (e.g., text reading, “This is the final peelable layer!”) is applied to the underside of that layer (i.e., the face of the layer that is adhered to the surface of the first sheet) such that the printed matter is removed, together with any adhesive present in the first barrier composition, when the penultimate peelable layer is peeled away from the first sheet.
Included in embodiments of this disclosure are shaped articles that include multiple, substantially identically-shaped sheets of thermoformable polymers that overlap at an overlapping region. Interposed between each pair of sheets, in at least a portion of the overlapping region, is a layer of a barrier composition. Because the barrier composition prevents the sheets from fusing across their entire faces (i.e., the sheets do not fuse at the portions of the overlapping region at which the barrier composition is present when the sheets are thermoformed) the article is separable into multiple, substantially identically-shaped subarticles upon separation of the sheets. The barrier composition can be omitted from at least a portion of the gap at the overlapping portion of the sheets in order to form an article in which the substantially identically-shaped subarticles remain bound together at the overlapping portion that lacked the barrier composition during thermoforming. Alternatively, that portion of the gap can be filled with an adhesive to (reversibly or irreversibly) bind the overlapping portions corresponding to the sub-articles. Such bundles of subarticles can often be stored, shipped, handled, manufactured, and used more conveniently and more energy-efficiently than an equivalent number of separate subarticles, and the subarticles can be separated from one another at a convenient time and place simply by breaking, cutting, or otherwise separating individual articles from the bound overlapping portion. Such an article can include multiple (e.g., 2, 6, 10, or 20) discrete egg cartons, cookie trays, cups, blister packs, computer keyboard covers, food containers, or paint tray liners that can be separated from one another as desired. The multiple items can have substantially the same thickness, different thicknesses, or a combination thereof.
The subject matter described in this disclosure includes a shaped article that includes a shaped thermoformable polymer sheet, a plurality of second polymer sheets, and first and second barrier compositions. The second sheets overlap the thermoformable sheet at an overlapping region and conform to the shape of the thermoformable sheet at substantially the entire overlapping region. The first barrier composition is interposed between and peelably adheres the thermoformable sheet and the adjacent second sheet. The second barrier composition is interposed between and peelably adheres adjacent second sheets. In an article of this type, the second sheets are peelably removable from the article. The article can include tabs interposed between adjacent second sheets and a tab between the thermoformable sheet and the adjacent second sheet. By way of example, the shaped article can be a paint tray having peelable liner layers, as described herein. Further by way of example, the shaped article can be a food service container, as described herein.
Further details of the materials and methods suitable for use in the articles, methods, and compositions described herein are provided in the ensuing sections of this disclosure.
Thermoformable Polymer Sheets
The identity and composition of thermoformable polymer sheets used in the articles and methods described herein are not critical. A skilled artisan will recognize that substantially any thermoformable polymeric material can be used. Examples of suitable thermoformable polymeric materials include polyethylene terephthalates, polyesters, polyethylenes (including high density polyethylenes and high molecular weight polyethylenes), polypropylenes, polyvinylchlorides, polystyrenes, nylons, copolymers of these, and combinations of these.
A skilled artisan can select a thermoformable polymeric material, or combinations of such materials, suitable for use in substantially any application by considering such properties as the shrink rate, crystallinity, heat deflection temperature, tear strength, draw ratio, thickness, rigidity, melt temperature, thermal conductivity, heat capacity, and polymer backbone orientation of the material(s). Selection of materials can also be guided by properties that do not necessarily directly impact the thermformability of the materials, such as cost, color, opacity, recycled material content, environmental impact, surface energy, chemical resistance, and surface sheen of the materials.
In selecting appropriate materials, an artisan should consider at least two sets of conditions: the environmental conditions to which the finished, shaped article will be subjected (e.g., during transportation, storage, and use) and the conditions that the materials will experience during the thermoforming process. Materials should be selected so as to exhibit the desired color, shape, strength, rigidity, and peelability, for example, once the materials have been shaped in the thermoforming process into their final, desired form. The materials should also be selected, together with the thermoforming conditions, so as to allow assembly and shaping of the materials into their final, desired form using thermoforming conditions available to the artisan.
Peelable Polymer Sheets
The identity and composition of peelable polymer sheets used in the articles and methods described herein are not critical. A skilled artisan will recognize that substantially any peelable polymeric material can be used.
In some embodiments, peelable sheets preferably have sufficient structural integrity that they do not tear or significantly stretch when subjected to forces necessary to peel them from surfaces to which they are adhered with a peelable adhesive. For example, when a paint tray having peelable surface layers is made as described herein, each of the peelable surface layers can preferably be peeled from the underlying surface as a single, integral sheet (i.e., no holes or tears) while containing paint coating its non-adhered surface. Peelable sheets that tear, stretch, or puncture are acceptable in embodiments in which containment of liquid within the peelable sheet is not required. For food service containers, as described herein, the maker should consider the characteristics of the peelable sheets at the temperature at which the sheets are likely to be peeled (e.g., either room temperature or a higher or lower temperature used, respectively, for storing heated or cooled foods).
The peelable sheets are preferably thin (e.g., 1 to 4 mils, preferably 1-2 mils thick) and highly flexible. Sheets having a thickness in excess of 8 mils can be difficult to peel, and so sheets thicker than 8 mils are not preferred. The peelable sheets can be made from substantially any polymeric material(s) and by substantially any sheet-forming process. By way of example, suitable polymer sheets can be made by blowing, molding, casting, or extruding suitable polymer materials, or by some combination of these processes. When made of thermoformable materials, the peelable sheets are preferably thermoformed simultaneously with the substrate sheet of thermoformable material to which they are adhered. When made of non-thermoformable materials, the peelable sheets should be capable of maintaining their structural integrity at a thermoforming conditions at which the substrate sheet to which they are adhered is thermoformable. Examples of suitable polymers for peelable sheets include polyethylenes, polypropylenes, polyethylene terephthalates, nylons, polyvinyl chlorides, copolymers of these, and combinations of these.
Peelable sheets can be selected to be rigid (i.e., retain their shape after peeling, e.g., akin to prior art molded paint tray liners that can be lifted out of a paint tray and retain their shape when subjected to small forces) or substantially non-rigid (e.g., blown polymeric sheets such as the material used in trash can liners and trash bags).
The peelable nature of an individual peelable sheet can derive from surface attraction between the peelable sheet and the surface underlying it. Preferably, however, an adhesive is interposed between the sheet and the surface (e.g., in the barrier composition) and the peelable nature of the sheet derives primarily from the adhesive forces exerted by the adhesive upon the sheet and the surface. An adhesive can be selected (e.g., based on the chemical identity or the surface treatment of the peelable sheet or the surface to which it is adhered) so that, upon peeling of the peelable sheet, the adhesive preferentially remains adhered to the peelable sheet, or to the surface. For instance, when the function of the peelable sheet is to expose the surface free of adhesive and other contaminants, the adhesive can be selected so that it both adheres the peelable sheet and the surface and adheres more strongly (i.e., more tenaciously) to the peelable sheet so that, upon peeling, the adhesive is removed from the surface along with the peelable sheet.
Differences in the tenacity with which an adhesive binds the opposed surfaces of two polymer sheets can be controlled in a number of ways, including by coating one or more portions of one surface with a composition that inhibits binding of the adhesive to the surface. Preferably, however, differences in the tenacity of adhesive-binding are controlled by selecting or treating the polymer sheets such that their opposed surfaces exhibit a difference in surface energies. If the difference between the surface energies of the two surfaces is relatively large—at least 5 Dynes—then the adhesive will bind significantly more tenaciously to one surface than the other. As the difference in surface energies of the two surfaces increases beyond 5 Dynes, the likelihood that all of the adhesive will remain with one sheet when the two sheets are separated increases. A difference of 5 to 14 Dynes between the adhered surfaces of the two sheets is considered appropriate.
It may be possible to separate two surfaces having an adhesive interposed between them, even if the surface energies of the surfaces differ by less than 5 Dynes. In this situation, the adhesive may adhere to each of the two surfaces with roughly equal tenacity, meaning that the adhesive may adhere to both surfaces (at various portions) after the two surfaces are separated from one another. In many applications, it is desirable to have most or all of the adhesive to adhere to the surface of only a single one of the polymer sheets (usually the one being peeled away from the remaining sheets or substrate). For such applications, the two surfaces contacted by the adhesive should preferably have surface energies that differ by at least about 5 Dynes.
The amount of force needed to separate peelable sheets from their underlying surface is not critical, but is preferably sufficiently small to prevent tearing and substantial stretching of the peelable sheet upon manual peeling of the sheet from the surface. The amount of separation force needed is a function of the materials selected for the peelable sheets, the underlying surface, and any barrier composition or adhesive interposed between them. Practically speaking, the tenacity of adhesion between a peelable sheet and the underlying surface should be selected so that the sheet can be peeled away from the surface using normal human strength, but not so tenacious that the sheet must be torn or punctured by a person peeling the sheet from the surface. A skilled artisan recognizes that the numerous variables (e.g., the angle at which the sheet is pulled from the surface, whether fingernails are applied to the sheet surface, the speed with which the sheet is peeled, the temperature of the shaped article at the time of peeling) can affect the peeling characteristics of the sheet, and the materials described herein include all materials that are operable under the ambient conditions corresponding to anticipated uses of the materials and shaped articles.
To the extent that an objective measure of the force needed to peel a sheet from an underlying substrate surface is desired, a standardized test of peel strength can be used. An example of a suitable test is ASTM D3330/D3330M, which is a standardized test for peel adhesion of pressure-sensitive tape. A modification of this procedure (e.g., substituting a sheet of the substrate material in place of the standard steel sheet in ASTM D3330/D3330M and selecting a peel angle appropriate for the intended use of the shaped article being tested) can also be used. In each case, the characteristics of the shaped article or stack should be selected such that the peel strength of the finished article is within the limits of human strength.
Various surface treatments and polymer sheet ingredients can be used to affect the surface energy
In one embodiment of the stack and shaped articles described herein, multiple adjacent polymer sheets are made of the same material. Unless treated non-identically, the two faces of a polymer sheet will normally have the same surface energy. Therefore, in stacks and articles which include multiple identical polymer sheets, it is important that the two faces of the identical polymer sheets (e.g., the adhesion and sanitary faces of second sheets of food service containers described herein) be treated differently, so as to yield a polymer sheet having different surface energy values for each of its two faces. Such sheets are preferably treated such that the surface energies of their faces differ by 5 Dynes or more. Many compositions and methods for affecting the surface energy of polymer sheets are known to skilled artisans in this field, and substantially any of those methods may be employed. Such methods include conventional surface finishing techniques such as grinding and polishing, annealing processes, Corona treatment, and plasma contact techniques such as atmospheric, chemical, and flame plasma techniques. Compositions for affecting the surface energy of a surface of a polymer sheet are also well known, and include compounds that can be contacted or reacted with the surface to modify its chemical or physical properties (affecting its surface energy).
An example of a suitable surface treatment is the process known as Corona treatment or Corona discharge treatment, which involves application to a surface of a high-frequency, high voltage electrical discharge. Corona treatment raises the surface energy of a polymeric surface. Applied to one face of a polymer sheet having two otherwise identical faces, Corona treatment will raise the surface energy of the face, relative to the opposite face of the sheet. The power applied in a Corona treatment can be controlled to limit the treatment substantially to one side of a sheet. At very high power, the treatment can raise the surface energy of both faces of the same sheet which, in the absence of other surface treatments, will not yield a polymer sheet having different surface energies on its two faces. If a polymer sheet is Corona treated at or near the time it is formed, the surface energy-raising effects of the treatment can endure for weeks, months, or years. If the sheet is Corona treated days, weeks, or later after the sheet is made, the surface energy-raising effects of the treatment can be more transitory (e.g., enduring only for days or weeks). Polymer sheets that are Corona treated at or very near the time they are formed can be used in the stacks and articles described herein. Polymer sheets can also be “bump-treated” (i.e., be Corona treated regardless of how long it has been since the sheet was formed) shortly before making the stacks and articles described herein.
Peelable sheets can be made from clear, translucent, or colored materials, ingredients and method for imparting each of these characteristics being known in the art. Colorants and opacity agents should be selected in view of the intended use of the container. By way of example, non-toxic, and preferably substantially non-leaching, agents should be used in food service containers as described herein. Where a shaped article is desired to have a selected color, that can be achieved by making the peelable sheets that color, or by making the rigid sheets that color and the peelable sheets clear or substantially transparent.
Barrier Compositions
The identity and composition of barrier compositions interposed between polymer sheets used in the articles and methods described herein are not critical. A skilled artisan will recognize that substantially any material can be used as a barrier composition between two polymers, so long as it substantially prevents fusion of two polymers under conditions at which at least one of the polymers can be thermoformed. A wide variety of such compositions are known for this purpose.
Examples of suitable barrier compositions include adhesives (e.g., peelable adhesives such as pressure-sensitive adhesives), known polymer release agents, a polymeric or paper film interposed between polymer layers, and various liquids, including low-viscosity silicone oils.
A composition interposed between two surfaces (e.g., between the first and second polymer sheets, or between two second polymer sheets, as described herein) can act as a barrier composition between the two surfaces if the composition coats at least one of the two surfaces at a thermoforming condition, thereby preventing surface-to-surface contact and fusion of the two surfaces at the thermoforming condition.
A barrier composition prevents fusion of opposed polymeric surfaces only when it is interposed between the surfaces at the thermoforming condition. For that reason, the barrier composition must be interposed between the surfaces over the entire area for which fusion between the surfaces is not desired. This can be achieved in various ways, including use of liquid and solid barrier compositions. When a stack is to be thermoformed to make a plurality of shaped objects that are not fused over some portions, but fused at at least one portion (e.g., a stack of cookie trays fused only at a single, frangible extension of the trays at one corner), the barrier composition is interposed among the polymer sheets in the non-fused areas, but is not interposed between the polymer sheets in the area in which fusion is desired. Multiple barrier compositions can be interposed between different portions of a pair of sheet such that, together, the barrier compositions cover at least one surface of the two sheets at every overlapping portion and prevent fusion between the two sheets. If desired, certain portions can be left uncovered by barrier compositions, such that those portions fuse or adhere to one another upon thermoforming (e.g., if peeled sheets are to remain attached to the surface from which they are peeled).
Liquid barrier compositions should be selected such that they completely coat (i.e., wet) at least one of the surfaces over the entire area for which fusion is not desired. This can be achieved by selecting a liquid barrier composition (i.e., a composition that is a liquid at at least the thermoforming condition, regardless of whether it is a liquid at which it is contacted with the surface) that has a surface tension significantly greater (i.e., at least 2 Dynes, and preferably at least 10 Dynes greater) than the surface energy of the surface with which it is contacted. This surface energy difference should ensure that the liquid barrier composition completely wets (i.e., coats) the area of the surface for which fusion is not desired. Preferably, the liquid barrier composition has a surface tension significantly greater than the surface energy of both surfaces, so that the liquid is not displaced from between the surfaces at points at which the two surfaces are urged tightly against one another.
Solid barrier compositions (e.g., polymer sheets) should be selected so that the solid covers the entire area for which fusion is not desired. The identity of the solid is not critical, so long as it does not prevent the portions of a polymer sheet that are to be thermoformed from reaching the thermoforming condition. Solid barrier compositions can prevent fusion of the surfaces (and/or) fail to fuse to one or both surfaces for a variety of reasons, any of which are sufficient to render a material suitable as a solid barrier composition. Some solids can be predicted to act as suitable barrier compositions, while other may require empirical testing (e.g., thermoforming two sheets of the polymer with the solid interposed between them) in order to determine their suitability. Either way, selection of an appropriate solid barrier composition is within the ken of a skilled artisan in this field.
Another type of barrier composition that can be used is a composition incorporated as an additive into one or both of the polymer sheets. These compositions melt and “bloom” to the surface of a polymer when heated, pressed, stretched, or otherwise manipulated. If such a composition is included in one or both of the polymer sheets such that the composition blooms at the surface of at least one sheet at the thermoforming condition and prevents contact between the polymer sheets themselves, then the composition can be used as a barrier composition in the articles and methods described herein. A wide variety of compositions that exhibit such blooming behavior are known in the art.
Adhesives
The identity and composition of adhesive interposed between polymer sheets used in the articles and methods described herein are not critical. A skilled artisan will recognize that substantially any material can be used as an adhesive between two polymers, so long as it reversibly binds the two polymer layers (at least when peelability of the two sheets is desired) and requires no more force to separate the polymer layers than can be practically applied to the polymer layers by a person of ordinary strength. A wide variety of such compositions are known for this purpose.
The adhesives used between a peelable polymer sheet and an underlying surface are preferably peelable, meaning that the polymer sheet can be peeled from the surface by a person of ordinary strength, preferably without tearing or substantially stretching the sheet. Preferably, an adhesive having a coat weight of roughly 0.6 to 15 ounces per inch is used to adhere a peelable sheet to an underlying surface. A skilled artisan in this field is able to select a standard coat weight for a given adhesive, empirically determine an appropriate coat weight, or both. Thus, selection of an appropriate amount of adhesive is well within the ken of an ordinarily-skilled artisan in this field.
A wide variety of suitable adhesives are known in the art and can be used as described herein. Pressure-sensitive adhesives are among the suitable adhesives that can be used. Likewise, adhesives that adhere preferentially to one of two adhered surfaces, upon peeling of one of the surfaces away from the other) are suitable and are preferred in certain embodiments. By way of example, if an adhesive adheres more strongly to a peelable polymer sheet than to a surface to which the sheet is adhered by the adhesive, the adhesive will tend to remain with the sheet when it is peeled from the surface.
Various compounds and surface treatments can be used to reduce the force needed to pull an adhesive from a surface, and such compounds and treatments can be used to modulate adhesion of an adhesive to a surface described herein.
Specific examples of adhesives that can be used in the articles described herein include polysiloxane-based adhesives, rubber cement, and acrylic adhesives (e.g., waterborne pressure-sensitive, acrylic adhesives of the MULTI-LOK™ brand family of acrylic adhesives manufactured by National Adhesives of Bridgewater, N.J.).
Printing
Text, images, or other graphical material can be printed onto one or more faces of one or more of the polymer sheets described herein. A wide variety of materials and methods can be used to print such material onto the surface of a polymer sheet. A difficulty inherent in printing on polymer materials is that the printed matter can often easily be displaced from the polymer surface by heat, light, or mechanical abrasion, leading to reduced print quality. Furthermore, it can be undesirable for the materials used for printing to contact materials that will be in contact with the polymer. For example, it can be undesirable to have printing inks contact paint on the interior surface of a paint tray or food on the interior surface of a food service container. These effects can be avoided by applying a clear polymer sheet or layer over top of the printed matter, thereby securing it in place and preventing its displacement. However, the clear layer often cannot be peeled off without severely damaging the printed matter and/or leaving portions of the printed matter on the peeled sheet and the underlying surface.
In one embodiment of the stacks and shaped articles described herein, printed matter is incorporated between polymer sheets and is peelable coherently with one sheet. In this embodiment, the printed matter is printed (preferably “reverse” printed, in that the printed matter is intended to be viewed through the sheet, rather than by viewing the printed surface of the sheet) onto the face of a clear (or at least translucent or not-completely-opaque) polymer sheet, and that face of the clear sheet is adhered to an underlying sheet. The tenacity with which the printed matter clings to the clear sheet and the tenacity to which adhesive overlying the printed matter clings to the printed matter (and thence to the clear sheet) is greater than the tenacity with which the adhesive overlying the printed matter adheres to the underlying sheet. Thus, when the clear sheet is peeled away from the underlying sheet, the printed matter (and the adhesive overlying it) come away with the clear sheet, leaving the underlying surface free of adhesive and/or printed matter.
The tenacity of binding of printed matter to a polymer sheet can, as described herein for adhesives, be affected by surface treatment of the polymer sheet prior to printing upon it. Corona treatment and plasma discharge techniques, for example, can raise the surface energy of a polymer surface, rendering it susceptible to more tenacious binding by the printed matter. Likewise, surface treatment (e.g., Corona treatment) of a polymer surface having printed matter thereon can raise the surface energy of the surface (including the portion on which the printed matter appears). By applying to the printed portion of the surface an adhesive that adheres more tenaciously to the printed portion than to the opposed underlying surface, adhesion of the adhesive with the printed matter can be maintained upon peeling of the sheet carrying the printed matter from the underlying surface.
In another embodiment, a release agent can be interposed between adhesive contacting a sheet having printed matter carried thereon and an opposed surface. The release agent overlies the printed matter and prevents (or weakens) binding between the adhesive that contacts that printed matter and the portion of the opposed surface that is adjacent the printed matter on the sheet. When the sheet is peeled from the surface, the poor (or lack of) adhesion between the sheet and the surface in the region where the printed matter occurs prevents damage to the printed matter, which is peeled off with the sheet.
Thermoforming Apparatus and Conditions
The articles described herein can be made using known thermoforming apparatus and conditions. Of course, the apparatus and conditions should be selected based on the identity and the characteristics of the materials to be processed. Selection of appropriate thermoforming conditions, based on the identity(ies) of the materials to be processed is within the ken of a skilled artisan in this field.
Paint Trays and Other Thermoformed Articles
In one embodiment, the subject matter disclosed herein includes a paint tray with a plurality of peelable liners that are simultaneously thermoformed with the tray, with the liners being thermoformed to the shape of the tray interior surface at the same time the tray is formed. As used herein, the term “thermoformed” is intended to encompass various methods of shaping a thermoplastic sheet or stacked sheets by heating the sheet and applying a pressure differential to the opposed side of the sheet to conform the sheet to the shape of a mold surface.
While the subject matter of this disclosure is occasionally described in terms of the preferred embodiment of simultaneously thermoforming a substrate and a plurality of liner sheets or simultaneously thermoforming a plurality of similar thin wall substrates with a release agent/barrier on the inner or bottom surface, it will be understood after reading the disclosure that the subject matter also includes simultaneously forming a substrate and a single liner sheet, and shaping the liner sheets and substrate by other means, e.g., by stamping, injection molding or blow molding. The substrate, while preferably a thermoformable plastic, may also be of other materials, e.g., metals.
In one example of thermoforming known as vacuum molding, a sheet is positioned adjacent a female (or male) mold section and a vacuum is applied to draw the sheet against the mold surface. A male mold section may be pressed against the sheet on the opposite side of the sheet from the female mold section to assist in conforming the sheet to the shape of the female mold section. In other processes, such as pressure forming, the heated sheet is pressed against a male mold section (or, more frequently, into a female mold section), usually with the assistance of a vacuum to conform the sheet to the mold shape.
In a preferred embodiment of the subject matter disclosed herein, at least one, and preferably a plurality of stacked planar sheets of thin plastic serving as disposable liners (“liner sheets”) are positioned on a surface of a planar substrate sheet of a greater thickness to be formed into a paint tray or other shaped article (e.g., a food service container). The combination of liner sheets and a single substrate makes a “stack” (as disclosed elsewhere herein) or “tray sheet” when the stack is used for making trays. The liner sheets will preferably be significantly thinner than the substrate sheet, e.g., the liner sheets may be from about 1 mil to about 6 mils thick, while the substrate sheet may be from about 10 mils to about 40 mils thick.
Each liner sheet has an adhesive on its inner or bottom surface to secure the liner sheets to the immediately adjacent sheet, with the innermost or bottom liner sheet being adhered to the top surface of the substrate sheet. Preferably, the adhesive backing is a uniform coating of adhesive over the entire inner surface of the sheets except where tear tabs are located. While applying the adhesive in making the liner sheets, the tabs can be added in line, anywhere in part or whole around the perimeter of where the tray will be formed. This can be done by deadening the adhesive. Tabs are applied to each liner sheet to facilitate separation of the sheets. Suitable adhesives will be apparent to one skilled in the art, the requirement being that the adhesive is a peelable adhesive, i.e., an adhesive that will permit separation of one liner sheet from another liner sheet or the substrate without tearing the liner sheet.
The tray sheets can be shipped in either sheet form or roll form. For convenience in shipping, storage, and thermoforming, the tray sheet may be provided to the thermoformer in a continuous roll form (“master pad roll”). The roll can be continuously fed through the thermoformer, with each length of tray sheet being indexed, then thermoformed into a shape, i.e., paint tray. The roll length and width can be as desired. For example, the master pad roll can be 5″ to 48″ in width. As another example, the master pad roll can be 60″ in width.
The combined stack of sheets (i.e., stack or tray sheets), is thermoformed as a unit into the shape of the desired product, e.g., a paint tray with the liner sheets being on the interior of the paint tray. Upon cooling, the tray sheet maintains its thermoformed configuration due to the thickness of the substrate sheet, while the configuration of the liner sheets is assisted by the presence of the adhesive backing.
The paint tray is used like one would use an ordinary paint tray that does not have a liner. However, unlike the prior art trays described above, there is no need to place a preformed liner into the tray or attempt to hand shape a sheet of thin plastic to conform to the tray interior. After use, the upper liner sheet can be simply peeled away along with the paint residue, exposing the next liner sheet as a clean paint tray ready for use.
The mold, and thereby the thermoformed tray system, can be of various shapes. Generally, the resultant tray will have an open-top interior cavity with a floor and continuous side walls. The paint tray may include at least one paint well and a flat section, normally ridged, for removal of excess paint from a roller dipped into paint within the paint well. In a preferred embodiment, the improved tray may be comprised of two paint wells divided by a horizontal, flat central section so that paint can be placed in both wells. The flat section is connected to opposed ramps tapering upwardly from the paint wells.
In another embodiment of the subject matter disclosed herein, multiple containers such as plastic egg cartons, cookie trays, dessert gelatin containers, blister packs, rigid paint tray liners etc., are produced by simultaneously thermoforming multiple layers of plastic sheets having the same thickness. Sheets used in this application are generally from about 0.006″ to about 0.025″ thick. Preferably, a stack of sheets, e.g., from 4 to 6 sheets, are provided to the thermoformer in roll form. A release agent, e.g., a coating, adhesive barrier or release film is applied between the sheets to prevent the sheets from melting/bonding together during the thermoforming process, and to allow the finished containers to be separated easily (e.g., a form of silicone may be introduced between the layers of sheets. A zone coat of adhesive (e.g., 1 inch wide) may be applied along the edge of the substrate to allow for easier transport of the rolls of substrates and sheets by keeping the material together in roll form more effectively. Stacks of sheets are thermoformed by being drawn or pressed into a mold having the desired cavity shape.
As illustrated in
As illustrated in
The resultant product is a thermoformed tray system comprised of a substrate sheet in the shape of the desired tray, with a plurality of liner sheets stacked thereon and held in place by adhesive layers, both natural or man made, between the liner sheets and the lowermost liner sheet and the upper surface of the substrate sheet. All sheets are molded into the shape of the desired tray.
A preferred paint tray 30 is illustrated in
Various other means may be used to include tabs to facilitate separation of the tapes. For example, as shown in
In another alternative shown in
Yet another alternative as shown in
Yet another alternative is shown in
While the subject matter disclosed in this section is described primarily in terms of the manufacture of a paint tray with a stack of thermoformed sheet liners conforming to the interior dimensions of the paint tray, it will be apparent that the broad concept of the subject matter disclosed herein can be modified for other applications. For example, as illustrated in
In another alternative illustrated in
By way of example, this simultaneous multi-article thermoforming process can thermoform a stack that is 3 to 6 layers thick (i.e., 3-6 thermoformable plastic layers having appropriate barrier compositions therebetween) and delivered in roll form. A greater number of thermoformable sheets (e.g., 10) can also be simultaneously formed and thereafter separated. However, the process can be limited by the thickness of the stack, whereby a stack that cannot practically be heated to a thermoformable temperature within a commercially reasonable time, without melting exterior layers, or that is too thick to be thermoformed may be impractical. The upper limit on the thickness and number of sheets in the stack depends on the materials used in the stack layers and can both be understood by a skilled artisan in this field and empirically determined through ordinary trial and error procedures. For instance, the maximum practical thickness of a stack of materials that exhibits a relatively low thermal conductivity may be about 50 mils, while the maximum practical thickness of a stack of materials that exhibits a greater thermal conductivity may be about 70-80 mils. A coating, adhesive barrier, release agent, or film can be applied to or placed in between the sheets where needed and in any combination to prevent the sheets from melting/bonding together in the thermoforming process, and for allowing the finished products to be separated easily (e.g., a form of silicone may be introduced between the layers of sheets while a zone coat of adhesive (e.g., 1 inch wide) may be applied along the edge of the substrate). This adhesion allows for easier transport of the roll of sheets by keeping the material together in roll form more effectively. Multiple sheets of approximate thickness 0.010″ each are stacked together with a barrier/adhesion between each layer. The multi-sheet layers are rolled together and then sold to various thermoforming companies. Ultimately time and money are saved by the thermoformers, allowing them to be more efficient. Sheets 90 are thermoformed by being drawn or pressed into a mold 92 having the desired cavity shape.
Food Service Containers
An important embodiment of the subject matter disclosed herein relates to peelable food service containers that are made using the thermoformable stack described herein.
For practical uses, food service containers must have sufficient rigidity to contain their intended contents under their intended conditions of use. For example, cutlery bins can be free standing (i.e., having the capacity to contain cutlery without breaking or substantially sagging without the assistance or support of a rack or other frame or container) or held within a rack (in which case, the support provided by the rack can render the rigidity of the bin relatively unimportant, so long as the bin is sufficiently rigid to contain cutlery without its sides collapsing within the rack and preventing access to its contents). Further by way of example, pans configured to be suspended within a rack (e.g., a wire or shaped metal frame, a countertop, or table top) of a buffet table, sandwich assembly station, or steam table need to be sufficiently rigid that they the can support foods that are placed within them when installed on the rack without collapsing or falling through the rack. Such suspended food containers typically have a flange or rim that surrounds one or more cavities defined by the peelable surface of the container, such that some or all of the weight of the container and its contents is borne by the rack when the container is installed therein. Food service containers must therefore be relatively rigid, the rigidity required being a function of the intended uses of the containers and readily understood by skilled artisans in this field.
Food service containers are sometimes used in situations in which heat transfer into of from the food service items therein is desired. The food service containers described herein can be used in such situations, with the materials used and number of peelable layers being selected to facilitate desired or required heat transfer characteristics (e.g., thermal conductivity and heat capacity of the materials) for the container. Such selection and construction is within the ordinary level of skill in this field, in view of the disclosure made herein.
Food service containers must also present a sanitary surface for contacting food service items such as foods, components of foods, and utensils used for preparing or consuming food. Such surfaces must be hygienic such that they are free of filth and pathogens which could present health hazards upon contact with food service items. These health hazards can be physical, microbiological, biological, or chemical agents of disease. A thorough review of food sanitation is beyond the scope of this disclosure. However, it is recognized that surfaces that contact food and other food service items during processing, preparation, storage, serving, and consumption of foods should be free from pathogens and potentially pathogenic wastes. Relevant wastes that should be excluded include human and animal feces, residues of food that previously contacted the surface, residues of washing and sanitizing reagents, residues from industrial processes for making the container, airborne dirt and grime, mold, mildew, microbial growth (including both microbes themselves and materials on or in which microbes can survive and reproduce), and contaminants that may contact the surface during manufacturing, shipping, handling, and installation of the container.
It is well known to make reusable food service containers from materials (e.g., stainless steel, porcelain, glass, and plastics) that exhibit formability, durability, and resistance to cleaning- and sanitizing-agents. Such containers can be used multiple times and sanitized between uses to maintain the sanitary state of the surface that contacts the food or other food service item. By way of example, baking pans and salad bar component trays are often made of metal and their food-contacting surface is washed and sanitized between individual uses. It is also well known to make single-use containers having a sanitary food-contacting surface, where the container is used only a single time and discarded. Hybrid products are known, such as baking trays having disposable inserts (e.g., paper cups inserted into depressions in muffin baking trays). Use of disposable liners for food service containers not expressly made to receive them is also known, such as when baking dishes are lined with aluminum foil, temperature resistant plastic sheets, or paper liners.
Reusable food containers have the disadvantage that they must be cleaned and sanitized. Disposable single-use food containers lack that shortcoming, but can be uneconomical and generate significant amounts of waste, since the entire container is discarded following each use. Use of disposable liners in a reusable base mitigates the shortcomings of both types of containers, but presents the difficulty of matching or shaping liners to fit the re-usable base. Disposable liners also have the shortcoming that they must be constructed of relatively thick materials in order to facilitate handling and installation. Relative to the peelable layers of food service containers described herein, such liners require substantially more polymeric material and energy to fabricate, leading to significantly greater costs. Disposable liners are typically made by joining one or more sheets of plastic material into a bag-like structure, and they include seams that can puncture, tear, of fail to join. Furthermore, disposable liners do not adhere to the food service container across substantially the entire food-contacting surface of the container, meaning that tilting or inversion of the container can displace the liner from the container, limiting or eliminating its usefulness.
Disclosed herein are food service containers that have peelable, disposable liners “built in” to a reusable base. Such containers do not require matching or fitting of liners and permit multiple uses of the same base. Furthermore, after the supply of liners is exhausted, the base can be either reused (i.e., like an ordinary reusable container) or recycled to make a new container having disposable liners assembled therewith. Such a peelable, multi-use food service container is believed to represent a substantial advance over existing reusable and disposable food service containers and liners.
The peelable, multi-use food service container disclosed herein is formed from a relatively rigid sheet of a thermoformable polymer and has at least one, and preferably a plurality (e.g., 2, 5, 10, or 20) of thin second sheets of a polymer peelably attached thereto. Each of the second sheets can be individually peeled from the container, yielding a sanitary surface upon each peeling. The container can thus be reused relatively rapidly, since a soiled surface can be sanitized simply by peeling a second sheet from the surface to expose a fresh, sanitary surface ready for reuse.
Describing the thermoformable polymer sheet as “relatively rigid” means that the container formed from the sheet exhibits sufficient rigidity and integrity to contain food service items without rupturing or spilling its contents under its intended conditions of use. This sheet is referred to herein as the “rigid” sheet to differentiate it from the peelable “second” sheets, which need not exhibit any significant rigidity.
By way of example, a tray holding sliced meats or cheese during assembly of sandwiches ordinarily becomes soiled upon contact with the meats or cheese. Prior to reusing the tray, sanitary practice requires cleaning and sanitation of the tray. Where this is achieved by washing, the delay in reusing the tray is typically caused by removing the tray to the site of washing, by rinsing, washing, rinsing again, sanitizing, and drying the tray, returning the tray to the site of use, and refilling. This process also generates considerable liquid wastes which must be disposed of in a sewer, septic, or other system. If a peelable, multi-use tray as described herein is used in its place, sanitation of the tray can be achieved simply by peeling a second sheet from the tray (optionally without even removing the tray from its place at the sandwich-assembly station or any remaining food or residue from the tray), and the tray can be immediately refilled. The soiled second sheet can be disposed of with other solid wastes (e.g., in a wastebasket), and the entire operation can be performed without the sandwich assembler leaving his station.
Thus, in one aspect, the subject matter described herein relates to a peelable, multi-use food service container. The container includes a substantially rigid sheet of a thermoformable polymer and one or a plurality of second sheets of a polymer, each second sheet having a sanitary face and an adhesion face. A first surface of the rigid sheet has a conformation adapted for holding a food service item. Each of the second sheets overlaps the rigid sheet at the first surface and conforms to the shape of the first surface. Interposed between the rigid sheet and the adjacent second sheet is a first barrier composition that adheres (e.g., peelably or permanently) the rigid sheet and the adhesion face of the adjacent second sheet. A second barrier composition (identical to or different from the first) is interposed between the adhesion and sanitary faces of adjacent second sheets. The second barrier composition peelably adheres the second sheets to one another. The container thus has a plurality of hygienic second sheets peelably adhered to a surface adapted for holding a food service item.
In one embodiment, the second barrier composition is identical between all second sheets. In another embodiment, a second sheet more distal from the rigid sheet is more easily peeled from the second sheet underlying it (i.e., by using a less tenacious adhesive, or a lower concentration of the same adhesive, between the sheets) than is a second sheet more proximal to the rigid sheet. Alternatively, portions of the adhesive in barrier compositions between more distal second sheets can be deadened or omitted by applying a non-adhesive barrier composition at those portions, resulting in a lower force necessary to separate the two adjacent second sheets.
As with other containers described in this disclosure, the first and second barrier compositions can be applied to a single portion of the rigid and second sheets or as a grid or pattern of dots (or other shapes and conformations). In an important embodiment, the first barrier composition is interposed between the rigid sheet and the adjacent second sheet over substantially the entire surface of the second sheet. In another important embodiment, the second barrier composition is interposed between adjacent second sheets over at least substantially the entire portion of the first surface. The remainder of the second sheets in this important embodiment can be free (i.e., grippable), or they can be adhered to the underlying sheet, especially about their perimeter, optionally with a tab interposed between the second sheet and the underlying surface at one or more portions along the perimeter.
The food service containers described herein can have movable or removable lids that cover an orifice of the container. The lid can be simply a unitary piece of material (e.g., the same material as the rigid sheet) or, alternatively, it can have peelable second sheets adhered thereto in at least the portion of the lid that covers the orifice.
In one embodiment of the food service container, the first surface of the rigid sheet is sanitary and the adjacent second sheet is peelably adhered to the sanitary first face of the rigid sheet. In this embodiment, the rigid sheet can be permitted to contact the food service item (i.e., because the first surface is sanitary) prior to recycling, discarding, or cleaning and sanitizing the rigid sheet.
In another embodiment, the first surface is not necessarily a sanitary surface, but the first barrier composition is selected such that the second sheet adjacent the rigid sheet cannot be (or cannot conveniently be) peeled from the rigid sheet under the normal operating conditions (e.g., room temperature) of the container. In this embodiment, the rigid sheet is not intended to be contacted with the food service item during normal use, it being shielded therefrom by the adjacent second sheet, which has a sanitary face. Preferably, the first barrier composition is selected such that the adjacent second sheet can be easily removed (e.g., peeled) from the rigid sheet under selected (e.g., relatively high temperature) conditions, such as conditions that would be encountered during recycling of the materials used to make the rigid sheet. In this way, the adjacent second sheet can be segregated from the rigid sheet materials and the two materials handled separately. If the first barrier composition remains associated with the second sheet, this also improves the relative purity of the material used to make the rigid sheet during recycling of that rigid sheet.
The container includes at least one, and preferably two or more, second sheets. When multiple second sheets are present, the second sheets have interposed between them a second barrier composition that peelably adheres adjacent second sheets to one another. Each second sheet has a sanitary face and an adhesive face. When assembled, the adhesive face of each second sheet is nearer (more proximal to) the rigid sheet than is the sanitary face. Thus, for adjacent second sheets, the sanitary face of the more proximal second sheet is nearer the rigid sheet than is the interposed second barrier composition, which itself is nearer the rigid sheet than is the adhesive face of the more distal second sheet. The characteristics of each of the sanitary face of the more proximal sheet, the interposed second barrier composition, and the adhesive face of the more distal sheet is selected so that when the more distal sheet is peeled away from the more proximal sheet, the second barrier composition remains substantially (preferably virtually exclusively) with the adhesive face of the more distal sheet. This leaves a sanitary face that is substantially free of the second barrier composition. Because the sanitary face is substantially free of the second barrier composition, potential interactions between that second barrier composition and any food service items placed in the container are minimized. This can be achieved, for example, by controlling the surface energies (e.g., by selecting materials in multi-layer composite second sheets or by corona treatment or other surface treatments of the second sheets) of the sanitary and adhesive faces of second sheets such that the difference in surface energy between the two faces is at least about 5 Dynes.
The container can have one or more tabs associated with the second sheets. The tabs can, for example, be interposed between adjacent second sheets for facilitating separation of the adjacent second sheets. In one embodiment, the tab is interposed between adjacent second sheets and simply prevents the two second sheets from tightly adhering to one another (i.e., regardless of whether one or both second sheets adhere to the tab). The tab creates a region at which the adjacent second sheets can be manually separated from one another. In one embodiment, the tab adheres to the adhesion face of one of a pair of adjacent second sheets, but does not adhere to the sanitary face of the other adjacent second sheet. If the second sheets are cut across the area including the tab, a user can pull the two second sheets apart by grasping the tab and the second sheet to which it adheres and pulling these away from the other second sheet (to which the tab does not adhere). If desired, the user can insert an object (e.g., the tip of a fingernail or a knife) between the tab and the non-adhered second sheet to facilitate the separation.
The tab can also extend beyond the edges of one or both second sheets, which provides a convenient surface for grasping and pulling by a user. In a food service environment, however, tabs that extend beyond the sanitary surfaces of second sheets can provide opportunities for soiling and cross-contamination between layers of second sheets, and it is recognized that tabs that are not obscured by an over-lying second sheet are not appropriate for all food service uses. In such situations, tabs are preferably completely overlaid by a second sheet or, at least, do not extend beyond the edge of an over-lying second sheet.
For food service containers, it is desirable to maintain a clean and sanitary face on an underlying surface prior to when an overlying second sheet is peeled therefrom. Separation or peeling of an overlying second sheet during manufacture, shipping, or storage offers an opportunity for environmental contaminants to contact the underlying surface. Tabs that are not adhered to both an overlying second sheet and the underlying surface present an opportunity for such separation or peeling to occur. In order to prevent this, tabs are preferably adhered to both overlying second sheet(s) and the underlying surface in the food service containers described herein. Tabs should be peelably adhered to at least one of the adjacent surfaces, to facilitate peeling of second sheets (and, optionally, the tabs).
In one embodiment, a container having multiple second sheets has tabs interposed between those second sheets to facilitate their peeling from the container. Each tab is peelably adhered to one of the adjacent second sheets, preferably at least along substantially the entire portion of the tab that is overlapped by that second sheet. The tab is also adhered (either peelably or relatively fixedly, such as by fusion or tenacious adhesion) to the other adjacent second sheet, again preferably along substantially the entire portion of the tab that overlaps that other second sheet. Such an arrangement facilitates peeling of a second sheet from the container, either by peeling a second sheet from the tab and thence from the container or by peeling the tab attached to an overlying second sheet away from an underlying second sheet and using the partially peeled tab as a handle to peel the overlying sheet from the underlying sheet. If the tab is peelably attached to both adjacent second sheets (either with equal or unequal tenacity), then one second sheet can be peeled from the other by aid of the tab, and the tab can thereafter be peeled from the second sheet to which it remains attached.
By way of example, a tab can be peelably adhered across its entire surface to a portion of a proximal (relative to the first sheet) second sheet near one edge of the container and peelably adhered across only the overlapping portion of a distal second sheet that overlaps the tab at one edge of the distal second sheet. In this conformation, the gap between the proximal and distal second sheets contains the tab at the edge of the distal second sheet and is sealed both above and below the tab by the peelable adhesive (the second barrier composition). Thus, the gap resists introduction of contaminants between the proximal and distal second sheets prior to peeling of the distal second sheet. The distal second sheet can be peeled from the proximal sheet by drawing an instrument (e.g., a fingernail or the edge of a spatula) across the edge of the distal sheet where it overlaps the tab, thereby initiating peeling of the distal sheet from the tab. By pulling on the distal sheet using the thus-displaced edge thereof, the distal sheet can be peeled from the container, leaving the proximal sheet attached thereto, with the tab remaining attached to the proximal sheet. If desired, the tab can be peeled from the proximal sheet.
When tabs are included in a container as described herein, the tabs can be aligned with one another, such that peeling of one second sheet and its associated tab reveals another tab located at the same location on the container (albeit one second sheet-layer closer to the rigid sheet). However, this aligned arrangement of tabs can cause difficulty, in that a user desiring to peel only the upper-most second sheet (i.e., the one most distal from the rigid sheet) may inadvertently disturb multiple sheets while attempting to manipulate only the tab associated with the upper-most sheet. This difficulty can be avoided if the tabs corresponding to different second sheets are placed at different locations along (or near) the perimeter of the container. If these tabs are physically separated from one another (e.g., tabs separated left-to-right, when viewing the container from the distal surface), a user may be able to more easily manipulate only the tab corresponding to the upper-most second sheet without disturbing the tabs (and the sanitary surface) corresponding to other second sheets.
The tabs can be the same color and composition as a second sheet and can, in fact, be simply an extension of one of the second sheets (i.e., the second sheet that is peeled when the tab is pulled). However, tabs are preferably made a different color and from a different material, so that they can be more easily identified and manipulated by a user. In one embodiment, each tab is made from a material that is different in color from and attached to the adhesion face of the second sheet that is peeled upon pulling the tab. One or more of the tabs can also include an indicium of the number of second sheets that remain attached to the container. By way of example, each second sheet can have a tab attached to the adhesion face thereof, with the tab bearing a numeral equal to the number of second sheets that remain adhered to the rigid sheet upon peeling the sheet to which the tab is attached. By way of an alternative example, all tabs can be white, with the tab associated with the second sheet that is adjacent the first sheet being red or bearing a star, the text “Last Use,” or the like.
As with the tabs, the colors of the rigid and second sheets are immaterial, yet selectable. In instances in which either the rigid sheet or the second sheets will be viewed by customers (e.g., at a sandwich assembly station at a restaurant in which customers stand within view of the station), it may be desirable to select sheets having particular colors (e.g., matching the decor of the restaurant) or appearances. In one embodiment, the rigid sheet has a color selected for a particular purpose (e.g., consistency with the color scheme of a food service station such as a buffet table), and the second sheets adhered thereto are substantially clear, so that the container has substantially the appearance of the rigid sheet, regardless of how many second sheets remain adhered thereto. For functional reasons (e.g., keeping track of how many peelable layers remain), it can also be desirable to impart a color or appearance to different layers of the container. By way of example, if it is desired that the rigid layer not be used to contact food service items, then the rigid layer can be made from materials having one color (e.g., black), while the second sheets that are peelably adhered to the rigid sheet are made from materials having a different color (e.g., white). Thus, in this example, if a white surface is revealed upon peeling a second sheet, the user knows that the revealed surface is that of a desirable second sheet, while the user knows that if the revealed surface is black, then the revealed surface is the non-desired rigid sheet. Although printing is generally not used on surfaces used for food contact, the printing methods described herein can nonetheless be used to print images, text, or other indicia on the second sheets of the container described herein.
Food service containers are sometimes intended to facilitate heat transfer either into or away from food service items held in the container. By way of example, forks held in a compartment at a salad bar are often chilled, as are lettuce, dressings, and other salad components. Soups, cooked entrees intended for consumption while warm, and steam tray contents are often heated. Other components (e.g., crackers and breads) may be neither heated nor cooled. Such heating and cooling is typically effected by contacting a fluid (e.g., air, steam, or water) against the surface of the container on the face opposite the face that contacts the food service item contained therein.
Where heating or cooling of container contents is desired, the materials used to make the food service container should be selected to facilitate the anticipated operating conditions and the desired heat flux characteristics. Thus, in situations in which relatively high heat flux is desired, materials which have relatively high thermal conductivity should be used and the number of second sheet layers should be controlled. Selection of appropriate materials is both within the ken of the ordinary designer and determinable through routine empirical observation.
A wide variety of polymer materials may be used to form the rigid and second sheets for food service containers as described herein. Selection of appropriate materials is within the level of skill of an ordinary artisan in the field of thermoforming. An important consideration when selecting materials for use in food service containers is statutes, regulations, and other requirements that are relevant to materials used in contact with food in the locale in which the container is to be used. By way of example, in the United States, materials used to contact food during manufacture, shipping, storage, and preparation are regulated by the Food and Drug Administration's Center for Food Safety and Applied Nutrition. In addition to processes for applying for approval for contacting food service items with various materials, most relevant regulatory agencies maintain lists of materials that are generally approved for use in contacting foods. In the U.S., such materials are referred to as “Generally Regarded as Safe” (GRAS), and lists of GRAS materials for food contact substances are maintained by the U.S. Food and Drug Administration. Many of these materials can be used to make the rigid and second sheets and barrier compositions described herein.
Materials useful for making the containers described herein can also be selected from materials identified and/or described by private or non-profit standard-setting organizations (e.g., NSF International of Ann Arbor, Mich.), that report or recommend materials safe for contact with food and food-preparation surfaces.
Likewise, a wide variety of barrier compositions can be used in the food service containers described herein. The barrier compositions should provide sufficient adhesion between the second sheet and the underlying sheet that the second sheet is not disturbed or peeled by normal air currents and handling operations. It is sufficient, for example, if the barrier composition provides only sufficient adhesive strength to keep a substantially rigid peelable sheet from falling out of the container when the container is inverted. At the same time, the adhesion provided by the barrier compositions must not be so great that the second sheet cannot be peeled from the underlying surface without damaging the second sheet or the underlying surface. The barrier compositions should also be selected for chemical and physical compatibility with the food service items and environmental conditions that the containers are likely to encounter. By way of example, barrier compositions intended for use in food service containers for holding hot soup should maintain their adhesive properties at anticipated soup temperatures, should not substantially dissolve in aqueous fluids (i.e., in the event the soup contacts the barrier composition near an edge of or through a breach through a second sheet), and should preferably be peelable both at anticipated soup temperatures and at 20 degrees Celsius. A variety of GRAS barrier compositions are available and, provided they conform with the other characteristics described herein, suitable for use in the containers.
For containers intended for use in contact with consumable food items, good manufacturing processes, consistent with practices common in the food industry for maintaining sanitation, should be used to make, package, ship, store, and use the food service containers described herein.
In an important embodiment, the food service container has a standardized shape and conformation. Standardized containers are used in a wide variety of settings in the food and restaurant industries. Examples include salad bars, sandwich assembly stations, steam tables, chafing dishes, cafeteria serving counters, cafeteria utensil stands, and buffet tables. The sizes and conformations of food service containers used in such settings are widely known and often vary by manufacturer of the setting furniture. An advantage of the food service containers described herein is that they can be manufactured to fit substantially any known standardized racks or furniture. They can also be used to form free-standing containers, such as baking pans, serving trays, and cookie sheets.
The food service containers described in this section are made in substantially the same ways as other containers described in this application (except that more sanitary manufacturing requirements may be necessary than are used, for example, for making paint trays). For relatively shallow containers (e.g., those in which the most-displaced portions of the thermoformed stack are displaced only 1-2 inches from the pre-thermoforming position of the stack), standard thermoforming apparatus and procedures are appropriate. For deeper containers (e.g., those in which one or more portions of the thermoformed stack are displaced >6 inches from the pre-thermoforming position of the stack or in which relatively steep sides are formed), standard thermoforming methods can lead to creasing, overlapping, excessive thinning, puncture, or some combination of these, of one or more sheets in the stack, including the relatively thinner second sheets. To avoid this, it is desirable to control the conformation of the stack during the forming operation, so that when the stack is engaged by the thermoforming mold, it is not creased, folded, excessively thinned, or punctured.
In one method of controlling the conformation during forming, a stack including the rigid sheet and multiple second sheets is assembled and heated to about a temperature appropriate for thermoforming. Prior to engaging the heated stack with the thermoforming mold, pressure (negative or positive) is applied to one face of the stack, so that the stack is deflected by atmospheric pressure into a shape that roughly approximates the shape of the thermoforming mold while maintaining the stack in a smooth conformation. The pressure is preferably applied by adjusting the atmospheric or the gas pressure at the stack face, for example by applying a vacuum. Apparatus for applying such pressure are well known and include, for example, devices commonly referred to as “vacuum boxes” and “pressure boxes.” Any apparatus used to apply such pressure preferably does not physically contact any portion of the stack that is to be thermoformed (to avoid heat transfer that would affect the thermoformability of the contacted portion). After the stack has been pressure-deformed, the stack is contacted with one or more thermoforming molds, per normal thermoforming procedures. As in standard thermoforming procedures, the stack can be drawn against a mold by application of negative pressure on the face of the stack that contacts the mold, forced against a mold by application of positive pressure on the face opposite that which contacts the mold, or both.
In one embodiment of the food service containers described herein, the rigid sheet is made from a recyclable polymeric material, while the second sheets are made from thin, disposable polymer that preferably degrades relatively quickly in landfill conditions. This embodiment relates to a container that significantly reduces waste generation corresponding to use of food service containers. Each second sheet can be simply discarded with solid wastes (i.e., garbage) after use. The rigid sheet that supports the second sheets can be recycled, either through a municipal recycling service provider or by returning it to the manufacturer to be re-melted and again formed into rigid plastic sheeting (or other materials for which recycled food containers may be more appropriate). In one version of this embodiment, the first barrier composition is selected such that it relatively tightly adheres the adjacent second sheet to the rigid sheet, so that that adjacent second sheet cannot be easily removed from the rigid sheet during normal use. When returned to a recycler, the adjacent second sheet (which may be soiled from use) can either be recycled together with the rigid sheet (especially if it is made of the same polymer as the rigid sheet) or it can be removed by subjecting the container to a condition (e.g., high temperature) at which the first barrier composition adheres the adjacent second sheet less tenaciously to the rigid sheet, permitting removal of the second sheet prior to recycling of the rigid sheet. In this embodiment, the level of impurities in the recycled rigid sheet materials can be significantly improved by removing the potentially soiled second sheets therefrom.
The peelable, multi-use food service container described herein can be used as a component of a food service station, such as a salad bar or a sandwich assembly station. In such a station, a rack, countertop, or other apparatus has a conformation adapted to hold at least one peelable container. The station can, of course, hold multiple peelable containers of the same or different sizes and shapes. In normal food storage and dispensing operations, such a station is essentially indistinguishable from stations having non-peelable containers. However, when cleaning or sanitation of one of the containers is desired, a difference becomes apparent. Rather than removing a container and either replacing it with another container or washing and replacing the same container, as in a traditional station, a peelable container can be cleaned and sanitized simply by peeling a second sheet from the first surface thereof. The peeled container can thereafter be refilled and immediately re-used, with the peeled sheet discarded. The cleaning and sanitation achieved by peeling both improves the rapidity with which the station can be maintained and reduces the waste associated with maintaining it.
In some instances, containers at food service stations are refilled in a kitchen or other food preparation area prior to being brought to the station to replace soiled containers. In such instances, the peelable containers described herein can nonetheless be advantageous, in that they reduce the time and waste associated with cleaning soiled containers, whether that cleaning is performed at the station itself or in a kitchen or other preparatory area.
In another aspect, the disclosure relates to method of operating a food station. The method involves assembling one or more first food products from components stored in multiple food containers, including at least one selected component that is held in a peelable food container described herein. After assembling first food product(s), a second sheet is peeled from the peelable food container (revealing a sanitary surface that can be contacted with fresh food components), and more of the selected component is added to the peelable food container. One or more second food products (identical to or different from the first food products) are then assembled from components stored in the food containers, including at least the selected component.
The peelable food service containers described herein will typically be manufactured at a site distant from the location at which they will be used, transported between the manufacture and use locations, and stored at one or more intermediate locations. At each of these steps, the containers can be exposed to environmental contaminants (e.g., dirt, dust, rodents, liquids) that are not compatible with maintenance of sanitary surfaces. When a peelable food service container as described herein is contacted with such contaminants, the outermost second sheet (i.e., the one which will have contacted the contaminant) can simply be peeled off to remove the contamination and reveal a fresh, sanitary face useful for food service. However, it is preferable to avoid manufacturing, storage-, and transportation-contamination in the first place.
In order to prevent contamination of the sanitary face of the outermost second sheet, the containers can be packaged in a wrapper, box, or the like. Alternatively, a protective coat layer can be included as the uppermost (i.e., most distal from the rigid sheet) layer in the stack. The protective coat should overlap the uppermost second sheet, at least over the first surface (i.e., the portion of the uppermost second sheet that will contact food service items), and should be relatively easily removable therefrom, for example by peeling or rinsing with water. Because the purpose of the protective coat is simply to prevent contact between environmental contaminants and the uppermost second sheet, the composition, color, and thickness of the protective coat are not critical, and any relatively inexpensive material can be used. The protective coat contacts the uppermost second sheet over substantially the entire sanitary face of that second sheet. The protective coat can be held in place simply by electrostatic attraction, and is preferably peelably adhered to the second sheet. The protective coat can also be made from a material that resists scratching, whereby the protective coat can protect the container from both contamination and physical damage. The protective coat material can be selected such that it can be printed upon or accepts adhesive labels, so that the protective coat can provide both shielding and marketing or labeling functions. The protective coat can be peeled from the container and discarded (or recycled) by the user prior to filling the container with a food service item for the first time.
A food service container designed to be inserted into a rack for holding multiple food service containers as a part of a sandwich assembly station was fabricated. The concave interior portion of the container had the approximate conformation of a tapered rectangular cuboid having rounded edges and dimensions of about 10½ inch length (tapering to about 11¾ inch at the opening)×about 4¾ inch width (tapering to about 5¾ inch at the opening)×5½ inch depth. The corners of the interior cuboid had radii of about ⅞ inch. A flange extended about the opening, having a length of about 12¾ inches and a width of about 6⅞ inches, with rounded corners (about ¾ inch radius).
In this embodiment, the rigid sheet was composed of PET (polyethylene terephthalate), black in color, approximately 30 mils (i.e., ca. 0.03 inch) in thickness. The container included ten second sheets peelably adhered to the rigid sheet. Each of the second sheets was composed of polyethylene, was white in color, and approximately 2 mils in thickness. Interposed between each of the second sheets was a second barrier composition that was composed of a water-based acrylic pressure sensitive adhesive, which was flood coated on the adhesive face of each second sheet. A first barrier composition identical in composition to the second was interposed between the rigid sheet and the adjacent second sheet, and was present by virtue of the adhesive face of the adjacent second sheet having been flood coated therewith.
Tabs were interposed between at least several pairs of adjacent second sheets at one of the corners of the flange. The tabs extended diagonally across the corner of the flange and were trimmed flush with the edges of the second sheets between which they were interposed. Each tab was peelably adhered to the second sheet that overlaid the tab and was not adhered to the second sheet beneath (i.e., more proximal to the rigid sheet) the tab. Second sheets could be peeled from the container by scratching or picking at the tab beneath the uppermost second sheet to begin peeling the tab and uppermost second sheet from the second sheet underlying them. By pulling the sheet and tab approximately across the cavity in the container (i.e., generally tangentially across the top of the container), the uppermost second sheet could be peeled therefrom without substantially disturbing any of the other second sheets of the container. This could be done multiple times, once for each of the second sheets of the container. The lowermost second sheet could similarly be peeled from the rigid sheet.
The appropriateness of the container for holding and storing food service products was tested by pouring food products with easily detected residues (i.e., pickles with brine, oils, etc.) into the cavity of the container, permitting them to remain there for about one day, and then removing the food products. Upon peeling the second sheet that contacted the food products, no residue could be detected by its characteristic scent or by wiping the interior of the cavity after peeling the top sheet. This confirmed that the containers so tested contained the food products without permitting them to leak after about 24 hours—a longer period than the normal period of storage for food service containers of this type in, for example, a buffet or steam table.
Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/32111 | 4/12/2011 | WO | 00 | 7/25/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61323239 | Apr 2010 | US | |
| 60855597 | Oct 2006 | US | |
| 60794409 | Apr 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12762887 | Apr 2010 | US |
| Child | 13641056 | US | |
| Parent | 11734285 | Apr 2007 | US |
| Child | 12762887 | US | |
| Parent | 12620460 | Nov 2009 | US |
| Child | 11734285 | US |
