Patent Application
20070151685
Embodiments of the present disclosure relate generally to cellulose based substrates encapsulated with polymeric films.
Containers made from fibreboard are used widely in many industries. For example, fibreboard containers are used to ship products that are moist or packed in ice such as fresh produce or fresh seafood. It is known that when such containers take up moisture, they lose strength. To minimize or avoid this loss of strength, moisture-resistant shipping containers are required.
Moisture-resistant containers used to date have commonly been prepared by saturating container blanks with melted wax after folding and assembly. Wax-saturated containers cannot be effectively recycled and must generally be disposed of in a landfill. In addition, wax adds a significant amount of weight to the container blank, e.g., the wax can add up to 40% by weight to the container blank.
Other methods for imparting moisture resistance to container blanks have included impregnation with a water-resistant synthetic resin or coating the blank with a thermoplastic material. In the latter case, forming water-resistant seals around container blank peripheral edges and edges associated with slots or cutouts in the container blank has been an issue. When seals along these edges are not moisture resistant or fail, moisture can be absorbed by the container blank with an attendant loss of strength. In addition, obtaining consistent and reproducible bonding of the thermoplastic material to the container blank and around edges has been a challenge.
Faced with the foregoing, the present inventors developed a cellulose based substrate encapsulated with a polymeric film that is recyclable and lighter in weight than previous wax-saturated containers and does not suffer from inconsistent bonding, sealing, and conformance of a film to the substrate. The encapsulated container is generally set forth in co-pending U.S. patent application Ser. No. 10/879,846, filed on Jun. 29, 2004, from which priority is claimed in the present application.
Upon further research, the inventors discovered an additional problem related to cellulose based substrate encapsulation. While encapsulated cellulose based containers have improved moisture resistance, their moisture-resistant characteristics are compromised if the encapsulating film is not sealed correctly during manufacture or is subsequently punctured during manufacture or use. Hence, a problem associated with encapsulated, corrugated, cellulose based containers is that if the encapsulating polymeric film allows moisture to enter the encapsulation, the moisture wicks throughout the container and renders the container weakened or, worse yet, inoperable.
Therefore, there exists a need for a moisture-resistant encapsulated container having improved moisture wicking resistance.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In accordance with one embodiment of the present disclosure, a cellulose based substrate is provided. The cellulose based substrate includes a cellulose based sheet having a corrugated medium spanning between first and second linerboards, wherein the corrugated medium includes at least one sizing agent for moisture wicking resistance. The cellulose based substrate further includes a polymeric film encapsulating at least a portion of the cellulose based sheet.
In accordance with another embodiment of the present disclosure, a container is provided. The container includes a cellulose based sheet having a corrugated medium spanning between first and second linerboards, wherein the corrugated medium includes at least one sizing agent for moisture wicking resistance. The container further includes a polymeric film encapsulating at least a portion of the cellulose based sheet.
In accordance with yet another embodiment of the present disclosure, a container is provided. The container includes a cellulose based sheet having a corrugated medium spanning between first and second linerboards, wherein the corrugated medium includes a sizing agent for moisture wicking resistance and a reactive cationic cross-linking type resin for improved wet strength. The container further includes a polymeric film encapsulating at least a portion of the cellulose based sheet.
The patent or application file contains at least one photograph executed in color. Copies of this patent or patent application publication with color photographs will be provided by the Office upon request and payment of the necessary fee.
The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
As used herein, the following terms have the following meanings.
Fibreboard refers to fabricated paperboard used in container manufacture, including corrugated fibreboard.
Container refers to a box, receptacle or carton that is used in packing, storing, and shipping goods.
Moisture-resistant film refers to polymeric films that are substantially impervious to moisture. Such films are not necessarily totally impervious to moisture, although this is preferred, but the amount of moisture capable of passing through the film should not be so great that such moisture reduces the strength or other properties of the cellulose based substrate to below acceptable levels.
Thermobondable refers to a property of a material that allows the material to be bonded to a surface by heating the material.
Thermoplastic refers to a material, usually polymeric in nature, that softens when heated and returns to its original condition when cooled.
Panel refers to a face or side of a container.
Score refers to an impression or crease in a cellulose based substrate to locate and facilitate folding.
Flaps refer to closing members of a container.
Peeling refers to separation of one film from another film along a bond formed between the films.
Creep refers to movement of the film-to-film bond line that occurs when the films peel from each other when the bond is subjected to stress.
The present invention provides for the encapsulation of a cellulose based substrate with polymeric films. Cellulose based substrates are formed from cellulose materials, such as wood pulp, straw, cotton, bagasse, and the like. Cellulose based substrates useful in the present invention come in many forms, such as fibreboard, containerboard, corrugated containerboard, and paperboard. The cellulose based substrates can be formed into structures such as container blanks, tie sheets, slip sheets, and inner packings for containers. Examples of inner packings include shells, tubes, partitions, U-boards, H-dividers, and corner boards.
The following discussion proceeds with reference to an exemplary cellulose based substrate in the form of a containerboard blank, but it should be understood that the present invention is not limited to containerboard blanks.
Referring to
Overlying and underlying container blank 20 are polymeric films 43 adhered to the container blank and bonded and sealed to each other around the container blank periphery 36 by an adhesive. Polymeric films 43 are also bonded and sealed to each other by an adhesive adjacent the exposed blank edges that define slots 32 and cutouts 42. As used herein, the term “sealed” means that overlapping portions of the film adjacent the top surface and the film adjacent the bottom surface are bonded to each other by an adhesive in a manner that substantially prevents moisture from passing through the seal. Areas 31, identified with the stippling, correspond to locations on container blank 20 where additional adhesive can be applied in order to further strengthen and reinforce films 43, as described below in more detail.
Container blank 20 can be folded and secured into a container as illustrated in
Referring to
Containerboard is one example of a cellulose based substrate useful in the present invention. Particular examples of containerboard include single face corrugated fibreboard, single-wall corrugated fibreboard, double-wall corrugated fibreboard, triple-wall corrugated fibreboard and corrugated fibreboard with more walls. The foregoing are examples of cellulose based substrates and forms the cellulose based substrates may take that are useful in accordance with the methods of the present invention; however, the present invention is not limited to the foregoing forms of cellulose based substrates.
Portions of the cellulose based substrate can be crushed before applying the polymeric films. Crushing of the cellulose based substrate adjacent its peripheral edges, and the edges within cutouts and slots, has been observed to result in improved conformance of the film to the shape of the edges. Crushing of the edges can be achieved by passing the edges through a nip to temporarily reduce the caliper of the substrate and reduce its resilience to deformation. Crushing of the edges is commonly achieved by placing stiff rubber rollers adjacent to cutting knives.
Polymeric films useful in accordance with the present invention include thermobondable and thermoplastic films that are moisture-resistant. The films should cooperate with the adhesives, described below in more detail, to bond the films together and provide moisture-resistant seals between the overlapping portions of the films. The adhesive may additionally bond the films to the cellulose based substrate. Useful films may be a single-layer or may be a multi-layer, e.g., a two or more layer film. Single-layer films are preferred. The choice of a specific film composition and structure will depend upon the ultimate needs of the particular application for the cellulose based substrate. Films should be chosen so that they provide the proper balance between properties such as flexibility, moisture resistance, abrasion resistance, tear resistance, slip resistance, color, printability, and toughness.
In certain embodiments, co-extruded multi-layer polymeric films can be used. Multi-layer films provide the ability to choose an inner layer composition that cooperates with the adhesive while at the same time providing an outer layer that has properties more appropriate for the exposed surfaces of the encapsulated container.
Exemplary films include linear low density polyethylene (LLDPE) blended with low density polyethylene (LDPE), blends of LLDPE and ethylene vinyl acetate (EVA) copolymer, blends of LLDPE and ethylene acrylic acid (EAA), coextruded films comprising LLDPE and EVA layers, coextruded films of an LLDPE-LDPE blend and EVA, coextruded films having an LLDPE layer and an EAA or ethylene methacrylic acid (EMA) layer, or coextruded films having an LLDPE-LDPE layer and an EAA or EMA layer. Examples of other useful film layers include those made from metallocene, Surlyn® thermoplastic resins from DuPont Company, polypropylene, polyvinylchloride, or polyesters or combination thereof in a monolayer or multi-layer arrangement.
Film thickness can vary over a wide range. The film should not be so thick that when it is applied to a container blank it will not conform to changes in topography along the surface of the container blank created by such things as the peripheral edges, edges defined by the slots, and edges defined by the cutouts. The films should be thick enough to survive normal use conditions without losing their moisture-resistance. Exemplary film thicknesses range from about 0.7 mil (0.018 mm) to about 4.0 mil (0.10 mm).
The moisture-resistant polymeric film applied to the inner and outer surfaces of the container blank can be the same, or different films can be applied to different surfaces. Choosing different films for the respective surfaces would be desirable when the particular properties needed for the respective surfaces of the container blank differ. Examples of film properties that might be chosen to be different on the respective surfaces of the container blank have been described above. In addition to being colored, it is possible that graphics may be preprinted on the polymeric film. For food applications, the film is preferably approved for use by the United States Food and Drug Administration.
Adhesives useful in accordance with the present invention include those that cooperate with the films to bond the films together and optionally to the underlying cellulose based substrate. The adhesive and film combination should be such that the two are able to conform to the exposed edges of the container blank. Preferably, once the adhesive and film are conformed to the edges of the container blank and the adhesive has set, any peeling of the films and creep adjacent such edges is minimal. The adhesive and films should be chosen so that the bond between the films formed by the adhesive has a cohesive strength that is greater than the stresses that the bonds are exposed to during manufacturing and use of the encapsulated container. For example, the film and adhesive should be chosen so that the bond between the films formed by the adhesive has a cohesive strength that is greater than the stresses that promote peeling of the films adjacent the container blank edges. By choosing the films and adhesives so that the bond between the films formed by the adhesive has a cohesive strength greater than the stresses promoting peeling, creep of the peeling can be minimized. Preferably, the adhesive will remain with the polymeric films when the encapsulated container blank is re-pulped, e.g., during recycling. Exemplary types of adhesives are known as hot melt adhesives, and include elastic styrene-isopropene-styrene block copolymers. Other useful adhesives include ethylene vinyl acetate adhesives, amorphous polyolefin adhesives, polypropylene adhesives, and pressure sensitive adhesives. Preferably, the adhesives have a viscosity ranging from about 1,000 to 15,000 centipoise at the application temperature. While hot melt adhesives are preferred, it should be understood that non-hot melt adhesives may find utility in the present invention and that other compositions of adhesives may also be used.
Referring to
Container blank 50 can be folded and secured into a container as illustrated in
Referring to
In the embodiment of
The location where the adhesive is applied can vary; however, when the adhesive is heated, it is preferable to add the adhesive as close to the nip formed by rollers 54 as possible in order to avoid premature cooling of the adhesive. In order to facilitate wetting of the film surfaces by the adhesive, the film surfaces can be treated such as by corona treatment (not shown). The adhesive should be applied at temperatures that do not adversely affect the moisture-resistant properties of the film and do not damage the film or the underlying container blank. The application rate for the adhesive can vary. Exemplary application rates include about 1 gram per square meter to 15 grams per square meter. When necessary, more adhesive can be applied to those areas where added bond strength is desirable such as areas prone to tears or where added thickness can reduce abrasion damage. After the adhesive is applied, film 56 is provided adjacent upper first surface 38 of container blank 20, and film 58 is provided adjacent lower second surface 40 of container blank 20. Films 56 and 58 have a width dimension measured in the cross-machine direction that is greater than the width of container blank 20. Thus, portions of the films 56 and 58 extend beyond the edges of the blanks that are parallel to the direction that the blanks travel. In the direction that the blanks travel through the process, individual blanks are spaced apart. Accordingly, films 56 and 58 bridge the space between the trailing edge of one blank and the leading edge of the next blank.
The combination of container blank 20, first film 56 and second film 58 passes through the nip formed by rollers 54. The nip formed by rollers 54 defines an inlet to a pressure chamber 60. Pressure chamber 60 is in fluid communication with a pump 62 capable of increasing the pressure within pressure chamber 60. Pressure chamber 60 also includes a plurality of rollers 64 for supporting the combined container blank 20, first film 56 and second film 58 through pressure chamber 60. Pressure chamber 60 is operated at a pressure greater than the pressure outside pressure chamber 60. As described below in more detail, the elevated pressure within pressure chamber 60 promotes the conformance of films 56 and 58 to container blank 20 around the container blank peripheral edges as well as within any slots or cutouts provided in the container blank. The container blank 20 and films 56 and 58 exit chamber 60 through the nip created by rollers 66. The nips created by rollers 54 and 66 are preferably as airtight as possible in order to maintain the elevated pressure within chamber 60. Alternative means can be used besides the rollers to prevent pressure loss from chamber 60, such as air locks and the like. From pressure chamber 60, container blanks 20 encapsulated by films 56 and 58 pass to trimming stage 78 described below in more detail.
As noted above, films 56 and 58 are dimensioned such that the respective films extend beyond the container blank periphery in the cross machine direction perpendicular to the travel of the container blank 20. In this manner, film 56 comes into contact with film 58 adjacent the container blank periphery and within slots and cutouts where the films overlap. The presence of adhesive between these overlapping portions of the film causes the films to be held together. As the adhesive cools, the cohesive strength of the bond formed by the adhesive between the films increases. Preferably, the adhesive bonds the films to each other at substantially all points where the films overlap. In this manner, the films form an envelope that substantially encapsulates the container blank. As described below in more detail, the envelope is formed in a manner such that a pressure differential may be provided between the environment inside the envelope and the environment outside the envelope. An envelope formed around the container blank is suitable so long as it encapsulates the blank in a manner that is capable of supporting a pressure differential between the inside of the envelope and the outside. For example, two films bonded to each other adjacent the leading and trailing edges of a container blank, but not the parallel side edges, would not substantially encapsulate a blank so as to be able to support a pressure differential between an environment between the films and an environment outside the films; however, an envelope formed by the films wherein the films are intermittently or reversibly bonded around all exposed edges of the container blank would be satisfactory, because a pressure differential can be created between the interior of the envelope and the environment exterior to the envelope.
Conformance of the two films to the container blank periphery, slots, and cutouts, is promoted by providing a pressure differential between an environment within the envelope described above and the environment exterior of such envelope. More specifically, the container blank and films are treated so that there is a point in the manufacturing process after the adhesive has been applied to at least one of the films where the pressure within the envelope is lower than the pressure exterior to the envelope. Satisfactory conformance of the films is evidenced by an absence of air bubbles at the interface between the films and the container blank, as well as robust and continuous seals around the exposed edges of the container and the edges exposed within the cutouts and slots. The degree of the conformance of the films to the container blank can be evaluated by assessing the distance between the film-to-film bond line and the exposed edge of the container blank. As the distance between the film-to-film bond line and the container blank edge increases, the degree of conformance of the film to the container blank edge decreases. Shorter distances between the container blank edge and the film-to-film bond line are more desirable than larger distances.
As used herein, the phrase “pressure differential” refers to a difference in pressure between the inside of the envelope and the exterior of the envelope that is attributable to more than the pressure differential that would be observed by simply reducing the temperature of gas within the envelope without a phase change. For example, in the context of the present invention, a pressure differential can be provided by moving the envelope from a low pressure environment to a higher pressure environment, with or without cooling of the gas within the envelope.
Pressure within pressure chamber 60 can vary and should be chosen so that crushing of the container blank is avoided while at the same time, conformance of the film to the blanks is high. The pressure in chamber 60 should not be so high that excessive gas loss cannot be prevented by rollers 54 and 66. Rollers 54 and 66 should be operated at a pressure that is high enough to minimize gas loss while at the same time not being so high that unwanted crushing of the container blank occurs. Examples of suitable rollers include silicone rubber rollers that are either patterned or non-patterned. The particular pressure within the chamber will depend upon a number of factors, including the thickness and malleability of the film. Thinner more malleable films will conform to the container blank with less pressure than thicker, stiffer films. The chamber should be long enough so that the adhesive is able to gain adequate cohesive strength through cooling as it passes through pressure chamber 60. As discussed above, an adequate cohesive strength is one that is greater than the tension force that promotes peeling of the films from each other. The length of pressure chamber will also depend upon the speed of the blanks passing through the chamber. Exemplary pressures within the pressure chamber can range from about 2 to 20 pounds per square inch. Blank speeds ranging from about 1 to 500 feet (0.3 to 150 meters) per minute are exemplary.
Within trimming stage 78, sensor 80 and laser 82 cooperate to trim away excess polymeric film around the container blank periphery and within the slots and cutouts without compromising the water-resistant seals. In order to ensure the accuracy of the film trimming, trimming stage 78 preferably employs a conveyance system 83, such as a vacuum belt that minimizes movement of the container blank and films during the laser trimming process. Alternatives to laser trimming include die cutting or hand trimming.
By trimming away portions of the polymeric films within the cutouts, openings can be provided for ventilation, drainage, or for allowing the cutouts to serve as handles for the container. It is preferred that trimming of the films within the cutouts and slots be carried out as soon as possible after the adhesive forms the film-to-film bonds. Peeling of the films occurs when the tension on the films is greater than the cohesive strength of the film-adhesive-film bond. When the films conform to the contour of the edges of the container blank, the films are put under tension that can cause peeling. Peeling is evidenced by the films separating along the line where the upper film meets the lower film. As the films begin to peel, this line begins to creep away from the edge of the container blank. As peeling may increase over time, it is preferable to minimize the time between when the encapsulated blank leaves the pressure chamber and the time when the trimming occurs. The films adjacent the exposed edges should be trimmed as close as possible to the container blank edges without compromising the film-to-film bond at the time of trimming. The distance between the edge of the container blank and the edge of the trimmed film should be great enough that any peeling of the films does not extend to the trimmed edge of the films and compromise the seal between the films.
Referring to
Vacuum chamber 84 is an air tight chamber in fluid communication with vacuum pump 88. The inlet of vacuum chamber 84 includes rollers 94 defining a nip designed to allow a container blank 20 and associated films 56 and 58 to pass into chamber 84 without compromising the reduced pressure therein. Upstream from rollers 94 are a pair of rollers 92 that receive films 56 and 58 and container blank 20. Films 56 and 58 are positioned adjacent to the upper and lower surface of blank 20 at rollers 92. When container blank 20 includes corrugated fibreboard and the flutes are oriented parallel to the direction of travel of the blanks, when the leading edge of the container enters vacuum chamber 84, a suction is created at the trailing end of the container blank. This suction draws films 56 and 58 against the trailing end of container blank 20 and serves to create a seal that prevents air from being drawn into vacuum chamber 84 through the corrugated flutes of container 20.
Vacuum chamber 84 includes a conveyor belt 96 for transporting blanks 20 through vacuum chamber 84. Vacuum chamber 84 also includes a combination of rollers 98, 100 and 102 for separating films 56 and 58 from container blank 20 and delivering the films to an adhesive applicator 104 where adhesive is applied to a surface of the films 56 and 58 before they are recombined with blanks 20. As noted above, in the illustrated embodiment, adhesive is shown as being applied to surfaces of both films 56 and 58; however, this embodiment is not limited to applying adhesive to both films and accordingly, adhesive can be applied to either film 56 or 58. The exit of vacuum chamber 84 includes a pair of rollers 106 defining an air tight nip at the exit of chamber 84.
In accordance with this process employing a vacuum chamber, container blanks 20 are combined with films 56 and 58 at film application stage 86. The web comprising the container blank 20 and films 56 and 58 enter vacuum chamber 84 at the nip formed by rollers 94. As films 56 and 58 enter vacuum chamber 84, they are separated from container blank 20 and delivered to adhesive applicators 104 where adhesive is applied to the surface of at least one of the films. As soon as possible after adhesive applicators 104, films 56 and 58 are recombined with container blanks 20. The amount of time between when adhesive is applied to the films and when the films are applied to the container blank should be minimized in order to avoid the adhesive losing its adhesive properties due to cooling.
The combination of films 56 and 58 and the adhesive form an envelope encapsulating container blank 20. Pressure within this envelope will be approximately equal to the pressure within vacuum chamber 84. Accordingly, as the envelope exits vacuum chamber 84, it will be exposed to the environment outside vacuum chamber 84 which preferably is atmospheric pressure. The pressure differential between the internal environment within the envelope and the environment outside the envelope promotes the conformance of the film to the container blank, including the exposed edges around the container blank periphery and edges defined within cutouts and slots. After the adhesive cools, the web of films, adhesive, and container blank is delivered to trimming stage 78 where the encapsulated blank is processed as described above.
In the process illustrated in
Exemplary vacuum conditions within vacuum chamber 84 can range from about 200 mm Hg to about 300 mm Hg. Vacuum within vacuum chamber 84 should be chosen so that it is far enough below the pressure outside vacuum chamber 84 so that acceptable conformance of films 56 and 58 to container blank 20 is achieved after the encapsulated blank exits the vacuum chamber. Vacuum within vacuum chamber 84 should not be so low that film damage occurs, the container blank experiences loss of caliper or the vacuum cannot be maintained by the seals at the inlet and outlet of the vacuum chamber. The description regarding the types of films, adhesives, film properties, adhesive properties, adhesive loading, line speeds and the like described above with respect to
Although not illustrated, other methods of promoting the conformance of the polymeric films to the container blank can be used. One example of such method includes a hot air knife capable of delivering a focused stream of air at the encapsulated container blank as it leaves the pressure chamber 60 of
With the reference to
The present invention has been described above in the context of a containerboard blank encapsulated with a polymeric film. The containerboard blank can be formed and secured to provide a moisture-resistant container. In addition, such a moisture-resistant container can be combined with other structural components such as inner packings, described above, that may be encapsulated with a polymeric film, or may not be encapsulated with a polymeric film. Furthermore, containers can be provided wherein the container body is not encapsulated with a polymeric film while certain inner packing structural components are encapsulated with a polymeric film. In addition, cellulose based inner packings encapsulated with a polymeric film can be combined with non-cellulosic based container bodies and cellulose based container bodies encapsulated with polymeric film can be combined with non-cellulosic inner packing structural components.
The moisture wicking resistance properties of the flutes or corrugated medium 48 in accordance with the present disclosure will now be described in greater detail. Embodiments of the present disclosure achieve moisture wicking resistance in the container 20 while maintaining adhesive properties between the corrugated medium 48 and the linerboards 44 and 46. In that regard, the corrugated medium 48 is treated with at least one additive designed to enhance the sizing of the corrugated medium 48.
As described above, the container or container blank 20 is suitably formed from a cellulose based sheet having flutes or corrugated medium 48 spanning between the first and second linerboards 44 and 46. The container or container blank 20 includes a polymeric film encapsulating at least a portion of the cellulose based sheet. In some instances, there will be holes in the container encapsulation films, whether from film manufacturer defects, the container manufacturing process, or container packing and handling issues. As described in greater detail in the Examples provided below, a container that has such a hole (or holes) and is exposed to free water will wick water, so long as there is free water to be absorbed or until the total saturation point of the container is reached, unless the corrugated sheet (including the linerboard and the corrugated medium) has low-wicking properties. Moreover, as described in the Examples provided below, encapsulated containers tend to wick water more readily that unencapsulated containers.
Most corrugated cellulose based containers are formed from cellulose based sheets having a corrugated medium spanning between the first and second linerboards. The corrugated medium is typically adhered to the first and second linerboards using a water-based adhesive. Conventional practice in the field of corrugated cellulose based containers is to manufacture the first and second linerboards with a sizing agent, which provides some moisture-resistance in the first and second linerboards, but to manufacture the corrugated medium with little to no sizing, as compared to the first and second linerboards.
It was believed that such manufacturing processes allow the water-based adhesive to sufficiently penetrate the corrugated medium and provide a suitable bonding site between the corrugated medium and the linerboards. However, such manufacturing processes allow for water or moisture to wick through the corrugated medium and spread to the linerboards. After water has wicked throughout an encapsulated cellulose based container, the container will be damaged and will likely fail under the load of the contents within the container.
Therefore, conventional practice in the field of corrugated cellulose based containers has been to manufacture the corrugated medium with little or no sizing agents. Contrary to conventional practice, the sized corrugated medium, in accordance with the present disclosure, provides moisture wicking resistance to the container while still obtaining a suitable adhesive bond. Moreover, such a bond can be improved by increasing the roughness factor of the corrugated medium.
It should further be appreciated that water-resistant adhesives are also within the scope of the present disclosure. Water resistant adhesives obtain a suitable bond between the corrugated medium and linerboards while further improving the moisture resistance of the corrugated cellulose based containers described herein.
In one embodiment, the corrugated medium 48 includes alum, which is an additive designed to size the natural resins to form hydrophobic groups within the cellulosic fiber. Alum is generally added to virgin cellulose fiber, as opposed to recycled fiber. Regarding recycled fiber, the natural resins in the fiber tend to break down in the drying and/or repulping process. For this reason, alternative agents are added to secondary or recycled fiber.
In another embodiment, the corrugated medium 48 includes a sizing agent. As a nonlimiting example, the sizing agent is a reactive sizing agent, such as alkyl ketene dimer (AKD), alkenyl ketene dimer emulsion (ALKD), alkenyl succinic anhydride (ASA), or any blends of the foregoing additives, such as ASA/ALKD blends. It should be appreciated, however, that non-reactive sizing agents (such as rosin and paraffin wax emulsions) and other surface treatments (such as styrene maleic anhydride (SMA), styrene acrylic emulsion (SAE), polyacrylamides (PAE), colloidal silica, and cellulosics) are also sizing agents within the scope of the invention.
In accordance with embodiments described herein, the reactive sizing agent is present in the corrugated medium in an amount in the range of about 0.1 to about 10.0 lbs/ton. In another embodiment, the reactive sizing agent is present in the corrugated medium in an amount in the range of about 0.1 to about 4.0 lbs/ton. Variations in the amount of reactive sizing agent are generally a result of variations in amount of virgin fiber versus secondary or recycled fiber used in the product, as well as the papermaking conditions.
Linerboards of a corrugated substrate generally have moisture wicking resistance properties similar to the corrugated medium described herein, whether sized by alum or the sizing agents described herein.
It should be apparent that the principles of including a sizing agent for moisture wicking resistance in the corrugated medium described herein are not limited to container encapsulation methods by adhesive bonding, but also extend to other encapsulation methods. It should further be appreciated that the principles of including a sizing agent for moisture wicking resistance in the corrugated medium are not limited to encapsulated containers, but also extend to unencapsulated containers.
In another embodiment, the cellulosic pulp is treated with both a sizing treatment, as discussed above, and a wet strength resin, such as cationic polyamide-epichlorohydrin reaction products (PAE resins). Methods of enhancing the strength of cellulosic products with PAE resins is described in U.S. Pat. No. 5,830,320, the disclosure of which is hereby expressly incorporated by reference. As described in U.S. Pat. No. 5,830,320, a cellulosic fiber product comprises about 5-40% of the cellulosic fiber treated with 0.5-5.0% of a reactive crosslinking-type wet strength resin additive substantially uniformly blended with 95-60% of untreated fiber.
The PAE resin is at least partially crosslinked and may be selected from the following: urea-formaldehyde condensation products, melamine-urea-formaldehyde condensation products, and polyamide-epichlorohydrin reaction products.
In addition to improving wet strength, such treatment with PAE resin increases the dry strength of the cellulosic fiber product and improves the repulpability of the fibers when recycled. Therefore, in another embodiment, 10-30% of the cellulosic fiber is treated with 0.5-5.0% of a reactive crosslinking-type wet strength resin additive. In another embodiment, the cellulosic fiber product contains from about 0.1-0.6% by weight of the resin based on the total amount of cellulosic fiber in the product.
Advantages of moisture wicking resistance properties in the corrugated medium in accordance with the present disclosure include increased container integrity and strength when exposed to water and/or water migration. For example, in produce-packing applications, water or ice is added to produce to keep the produce fresh during transportation. If the encapsulation structure is damaged and allows moisture to enter the encapsulation, the embodiments disclosed herein prevent water from wicking throughout the encapsulated cellulose based substrate or sheet. Therefore, the wicking resistance properties of the container described herein provide for wicking prevention and maintain container integrity even if water enters the encapsulation structure.
Examples 1-6 that follow illustrate the improved strength of containers constructed in accordance with embodiments of the present disclosure as compared to previously developed (or “control”) containers. Specifically, the Examples indicate that water tends to wick significantly less in Low Wicking Medium container board, as compared to Control container board. Moreover, wicking in the Low Wicking Medium was observed to be more prevalent in encapsulated samples than in unencapsulated samples, indicating that encapsulation encourages wicking. In addition, the Examples indicate that the moisture wicking directly impacts the top-to-bottom strength of the container and that the Low Wicking Medium containers have superior strength performance over the Control Medium containers. In that regard, the Low Wicking Medium encapsulated containers only lost 25% of their top-to-bottom strength when exposed to a water mist shower for seven days. The Control Medium encapsulated containers, on the other hand, lost 73% of their top-to-bottom strength.
The basis for the wicking testing provided in this example is in accordance with the Springfield Wick Test W-30. Several modifications were made to accommodate the use of combined corrugated container board rather than the individual paper samples that the test is designed for. The first modification was to cut the samples to a size of 11 inches×2 inches to be large enough for the encapsulation process (described below in Example 3). As seen in
The “Control Medium” samples were cut from a C-flute corrugated container board, having standard low-wicking linerboards and a standard medium (i.e., without a sizing agent). The “Low-Wicking Medium” samples were also cut from a C-flute corrugated container board from the same manufacturer under the same manufacturing conditions, but having standard low-wicking linerboards and a low-wicking medium (i.e., with a sizing agent).
As seen in
During testing, it was observed that the Control Medium samples began to wick water immediately on contact with the water pool. The Low-Wicking Medium samples had no immediate wicking. In all cases, the linerboards of the samples wicked very little water compared to the corrugated medium. Most of the wicking was completed within less than 2 hours of testing. Water did continue to wick after that initial period, but at a significantly reduced rate.
The Control Medium samples wicked water a distance of approximately 5.8 cm above the level of the water pool, while the Low-Wicking Medium samples wicked approximately 1-2 mm above the level of the water pool. As seen in
As seen in
The test that was run over a 72-hour period had similar results to the 3-hour test. As seen in
Two sets of nine, 4″×4″×4″ regular slotted containers manufactured from the same materials used for the wicking testing in Example 1 were die cut. (Regular slotted containers in accordance with the present disclosure include flaps all having the same length, with the two outer flaps being one half of the container width to meet in the middle.) The nine Control Medium containers were marked with a “C” and sent with the nine Low-Wicking Medium containers to be encapsulated. The bottom flaps and the manufacturer's joint were closed using hot melt, and two 1 mm holes were punched into consecutive bottom slots of all of the containers. As seen in
After seven days the containers were removed from the cooler and taken directly to be top-to-bottom compression tested. The results in Table 1 below show a significant difference in compression results between containers made from the Control Medium container board (126.67 lbf average) and containers made from the Low-Wicking Medium container board (171.22 lbf average).
The largest contributing factor to the Control Medium sample containers having low average results was that two of the Control Medium sample containers were completely saturated with water inside the encapsulation. In that regard, the containers had wicked water into the whole structure of the container. These two saturated containers had peak force readings of 23 lbf and 28 lbf. However, even with those two containers disregarded from the average test results, the remaining Control Medium sample containers averaged 155.57 lbf, still significantly less than the compression strength of the Low-Wicking Medium sample containers at 171.22 lbf. These results suggest that the containers having a Low-Wicking Medium provide additional strength, as compared to containers with a medium that wicks, because the Low-Wicking Medium does not “pull” (or wick) free water into the structure of the container.
Therefore, incorporating a medium having low-wicking properties into an encapsulated container apparently improves the ability of the finished container to continue to provide structural strength when the encapsulation is compromised and the container is exposed to free water.
An additional wick test was done using the same corrugated material as used in Example 1, except in encapsulated form (see
The basis for the wicking portion of the testing was again the Springfield Wick Test W-30, with the same modifications described above in Example 1. Again, 450 ml of deionized water was added to the pool at the bottom of the testing apparatus.
From the same materials as the samples used in the previous examples, the encapsulated Control Medium samples were cut from an encapsulated C-flute corrugated container board, having standard linerboards and a standard medium. The encapsulated Low-Wicking Medium sample were cut from an encapsulated C-flute corrugated container board, having standard linerboards and a Low-Wicking Medium. As seen in
Unlike the unencapsulated samples in Example 1, the encapsulation materials in this example prevented measurements of water wicking at interim times during the 72-hour test.
The encapsulated Low-Wicking Medium samples on the right include one sample having a water mark approximately 1-2 mm above the level of the water pool and one sample having no indication of a water mark. Neither sample has any water staining along the flute lines, as observed in the Control Medium samples.
Referring to
Referring to
Notably, the encapsulated Low-Wicking Medium sample that wicked water drew considerably more water than the unencapsulated counterparts previously described in Example 1 (4.2 cm versus 1-2 mm). Both samples were cut from the same piece of container board; therefore, these results indicate that the encapsulation or the process of encapsulation encourages wicking. It is believed that the encapsulated Low-Wicking Medium sample that did not wick water was not adequately prepared with puncture holes. For example, the puncture holes may have been closed off by the excess material from the encapsulating film that deformed when it touched the bottom of the water pool.
The encapsulated Control Medium samples also wicked considerably more water than their unencapsulated counterparts described in Example 1 (21.2 cm versus 5.0 cm). Again, both samples were cut from the same piece of board; therefore, these results further indicate that the encapsulation or the process of encapsulation has an enhancement effect on water wicking.
Two samples of encapsulated broccoli containers were obtained. A hole was punctured in the top flap locking hole. In an effort to determine how a large quantity of penetrating water affects an encapsulated container in terms of container strength and water migration, 400 ml of deionized water was poured down the exposed flutes of the container.
Both sample containers had the same 69# liners from the same rolls: mottled white on the double back side and standard kraft for the single face. The difference between the two containers was the corrugated medium. The first sample container is the Control Medium container having a 36# FPT Medium (Spec. No. 4490). The second sample container is the Low-Wicking Medium container having a 36# FPT Low-Wicking Medium (Spec. No. 4491).
Using a squeeze bottle, 400 ml of deionized water was injected into each container over a 10-minute period into one corner of the container opposite the manufacturer's joint. As seen in
Both containers were allowed to stand for 44 hours. Referring to
The Control Medium container (
Referring to
This example shows that the Low-Wicking Medium container does not “pull” water into the container much above the level of the standing pool of water it may be in. On the other hand, the Control Medium container, when exposed to a constant source of free water, continues to “pull” that water into the container structure until equilibrium is reached (i.e., when the container structure completely saturated). There is a maximum amount of water, which will produce container failure regardless of the paper combination used in an encapsulated container.
In conjunction with Example 4, a second trial was conducted with sample containers from the same materials as those described in Example 4. In this example, ten containers of each of the two medium types (Control and Low-Wicking Mediums) were placed in a standing pool of water. Each container stood in approximately 1 inch of water. The pool was continually fed a small stream of water to maintain a constant depth. Each container had a hole intentionally created in a bottom corner with sandpaper, not at the manufacturing joint. All of the containers were weighted from above to keep them in the water and prevent floating.
After three plus days, five containers of each type were removed from the pool with the intention of doing top-to-bottom compression testing. However, all the containers were so wetted out on the bottom that doing top-to-bottom tests was infeasible. Upon removing the containers from the pool, observations were made about the different wetness areas. In that regard, the containers having the Low-Wick Medium were completely saturated on all the bottom flaps and approximately 1 to 1.5 inches up all the sidewalls. These containers only minimally wicked water above the level of the pool, which is consistent with the results described in the previous examples.
Of the five Control Medium samples, the bottom flaps on all of these containers were completely saturated as well. In addition, water wicked up to a minimum of 3 inches on all panels with a majority of the panels having water halfway or more up the sidewalls of the panels.
The other ten samples (five of each type of medium—Control and Low-Wick) were allowed to soak for three additional days. The Low-Wick Medium samples had no further take up of water beyond 0.5 inch level above the level of the pool. The remaining Control Medium containers continued to wick all the way up the sidewall and onto the top flaps of the containers.
Ten samples of the encapsulated broccoli container containing 36# Low-Wick Medium (Spec. No. 4491) and ten sample containers containing 36# Control Medium (Spec. No. 4490) were subjected to testing. Holes were formed in two bottom corners of each container. Each container was then filled with 35 pounds of roll cores which were enclosed in a plastic bag, and the containers were closed. Each set of ten containers was then stacked on its own pallet. Three layers were built using four containers on the bottom and middle layers and two containers on the top layer. The two pallets were placed directly underneath their own spray head.
Initially, each container was hand watered, using a garden hose to simulate the initial soaking a container would receive in a spray or a clamshell applicator. Then, the spray nozzles were turned on at a controlled rate of 0.14 gallons/minute. The containers were left for seven days under the shower.
The containers were emptied of the roll cores and taken to the lab for top-to-bottom compression testing. Table 2 displays the results of the compression testing.
Dry containers were also tested to compare to the watered containers and averaged 1050 pounds force average. Therefore, the containers with Low-Wick Medium lost an average 25% of their top-to-bottom strength, while the containers with Control Medium lost 73% of their top-to-bottom strength.
The differences between the two types of container were even more apparent when the containers were handled. The containers with Control Medium were almost entirely soaked. All panels were partially, if not completely wet. The containers with Low-Wick Medium had only small areas of wetness, with the exception of one container, which had some larger areas of wetness. In the one exception container, water had penetrated other holes that were in the container prior to the test and had not been made as a uniform testing condition. Due to the Low-Wick Medium, however, the water that entered these holes also did not spread through the entire panel of the container. The data in Table 2 shows the differences in water take-up in grams on average.
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure.
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/879,846, filed on Jun. 29, 2004, the disclosure of which is hereby expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10879846 | Jun 2004 | US |
| Child | 11650601 | Jan 2007 | US |
