Patent Application
20240301249
This invention relates to compositions comprising (co)polyester resins and antifog agents suitable for use as a heat seal layer for use as part of a film to be used as a flexible bag or part of a lidding laminate for a container, such as polyester trays and for use as part of a film to be used as a flexible bag or lidding laminate also having a pressure sensitive adhesive layer to allow for resealing the container. Such compositions are suitable for use as part of films to be used as flexible bags or part of a lidding laminate to seal containers for food, consumer products, and medical devices.
Multilayer laminates in the form of films are known to be used to seal containers, such as containers used in the food industry for packaging perishable foods, in particular fresh products. Such films may be referred to as “heat seal films,” and (co)polyester resins have been known to be a constituent of such heat seal films. As used herein, the terms “heat-seal”, “heat-sealing”, “heat-sealable”, and the like refer to a first portion of a film surface (i.e., formed from a single layer or multiple layers) which is capable of forming a fusion bond to a second portion of a film surface. A heat-seal layer is capable of fusion bonding by conventional indirect heating means which generate sufficient heat on at least one film contact surface for conduction to the contiguous film contact surface and formation of a bond interface therebetween without loss of the film integrity. It should be recognized that heat sealing can be performed by any one or more of a wide variety of manners, such as using a heat seal technique (e.g., melt-bead sealing, thermal sealing, impulse sealing, ultrasonic sealing, hot air, hot wire, infrared radiation).
It is important to ensure that a strong initial bond strength exists between the heat seal film and the container or to itself to ensure that the contents of the container (or bag) remain well-preserved. The initial force needed to separate the layers is relatively strong before the package is opened in order for the seal area also to withstand the expected abuse during the packaging operation, distribution, and storage. Moreover, the bond is considered “resealable” if the consumer may simply engage the two exposed film surfaces together-by finger pressure to cause the seal between the layers to re-establish. The means of forming peelable/resealable bonds and their use in packaging applications are disclosed in the art.
U.S. Pat. No. 7,422,782 describes a multilayer film suitable for use in packaging comprising a heat sealable water insoluble polyester polymeric layer and a pressure-sensitive adhesive layer that is peelable and resealable. The multilayer film described therein may be used as a lidding laminate for a container or tray or may be used to be adhered to itself and serve as a flexible bag or pouch. The peelable/resealable bond may include both an initial first peel strength and a re-tack second peel strength. Preferably, the initial first peel strength (sometimes referred to herein as the “lockseal”) may be greater than the re-tack second peel strength. It is also desirable to use the same film to reseal the container after the container is opened initially. Since these films are used in food packaging, it is desirable that the heat seal film, as well as the packaging film and tray stocks, be food contact compliant according to the applicable governmental agency, such as the Food and Drug Administration (FDA).
Such containers or trays are generally referred to as polyester containers or trays. This terminology could be used to mean a container or tray which is made entirely of polyester or is made of another material but has a polyester coating. One material often used for such containers or trays is amorphous polyethylene terephthalate (APET). Another material used for such containers or trays is crystalline polyethylene terephthalate (CPET), which may be coated with APET or recycled polyethylene terephthalate (PET). Typically, such containers have a minimum thickness of 100 μm, generally between 200 and 1000 μm. The container may be thermoformed to provide a flat bottom on which the food rests and a perimeter at the top in the form of a flat band or lip, often parallel to the bottom. Sealing between the heat seal film and the container is performed by the application of heat typically on the heat seal side, pressure, and dwell time to the film on the container, typically at the lip. Similar processes may be used to heat seal a heat seal layer to itself to serve as a bag or pouch to contain a product, such as food, consumer products, or medical devices. By “sealing to itself,” one portion of the heat seal layer may be sealed to another portion of the heat seal layer.
Another important feature is that the film avoids fogging. Fogging tends to limit the visibility of the contents of the container to a consumer due to moisture condensating on the inside of the film. Also, the film is transparent or, at worst, only slightly hazy. Consumers may wish to be able to view the contents of a container clearly to assess for freshness. Antifog agents have been known to be incorporated into heat seal films for this purpose.
A number of attempts have been made to provide heat seal films for containers. U.S. Patent Application Publication No. 2013/0224411 discloses antifog films useful for packaging food, and more particularly to antifog films that can be used as lidding films in trays made of APET. The films may include at least one base layer or film, such as a polyester film, and a heat seal layer.
U.S. Patent Application Publication No. 2019/0077137 describes a coated polyester film equipped on at least one side with permanent antifog coating. The film of the invention is suitable for the production of greenhouse blinds and has specific transparency properties, permanent antifog properties, and high UV resistance.
German Patent Application No. DE 10 2009 021 713 discloses a coextruded seal and peel biaxial oriented polyester film with a base layer (B) and a heat sealable and peelable surface layer (A). The surface layer (A) contains a low sealing, peelable polymer, while the base layer (B) contains polyethylene terephthalate and polyethylene isophthalate at a chosen ratio. An antifog coating is applied to the surface layer (A).
European Patent Application No. EP 3 366 471 relates to a sealant antifog composition for polyester films comprising anionic and nonionic surfactants in a mixture of amorphous and (semi)crystalline polyesters. The invention also relates to a multi-layer film comprising a sealant layer having the above composition, to the use of such films in food packaging, and to packages obtained therefrom.
International Patent Application Publication No. WO 2018/132442 A1 provides a semicrystalline copolyester resin composition formed by twin screw extrusion of various ingredients including copolyester resins and antiblock, slip, and antifog additives. This semicrystalline copolyester resin can be extruded on to a polyethylene terephthalate (PET) film or coextruded with PET resin to form clear PET films with antifog properties. These films with antifog properties are produced in a single step without the use of solvent and do not involve any secondary step for coating a separate antifog layer. This process minimizes the cost and time required by a converter to make such clear antifog films. These films containing the heat seal copolyester resin can be heat sealed to clear APET trays. Embodiments of the resin composition disclosed therein are FDA and EU compliant for direct food contact application.
U.S. Patent Application Publication No. 2018/0215522 relates to a multilayer film comprising a layer of an extrudable hot-melt self-adhesive composition, for example based on a styrene block copolymer, a completable thin layer consisting of a thermoplastic, and a heat-sealable and cleavable layer comprising at least 95 wt % of at least one linear copolyester resin. It also relates to a process for producing the film, which comprises co-extrusion blow-molding and to resealable packagings using as a lid the multilayer film described therein.
The prior art describes the use of (co)polyester in heat seal films. The chemistry has been widely known and used as lidstock for amorphous polyester containers or trays. The need for an improved antifog film or lidding laminate to serve as a heat seal lidding laminate for a container or as a bag remains. Also desirable is an improved antifog film or lidding laminate that has reseal functionality. In addition, it is desirable that such heat seal films are transparent, with little or no haze.
In order to meet at least some of the needs described herein, the present invention provides a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin. The composition may be used to form a heat seal layer containing an antifog agent.
According to another embodiment of the invention, a laminate in the form of a film for sealing a container or sealing to itself to form a flexible bag comprises: (a) a heat seal layer adapted to be adhered to the container and comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin; and (b) a core layer adhered to the heat seal layer.
According to another embodiment of the invention, a laminate in the form of a film for sealing a container or sealing to itself to form a flexible bag comprises: (a) a heat seal layer adapted to be adhered to the container (or itself, in the case of a bag) and comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin; (b) a pressure sensitive adhesive layer adhered to and in direct contact with the heat seal layer; and (c) a core layer adhered to the pressure sensitive adhesive layer.
According to another embodiment of the invention, a method of sealing a container comprises the steps of: (a) forming a lidding laminate comprising a core layer and a heat seal layer comprising a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin, wherein the laminate optionally has a pressure sensitive adhesive layer between the core layer and the heat seal layer and in direct contact with the heat seal layer; and (b) heat sealing the laminate to the container.
According to another embodiment of the invention, a method of forming a bag comprises the steps of: (a) forming a laminate comprising a core layer and a heat seal layer comprising a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin, wherein the laminate optionally has a pressure sensitive adhesive layer between the core layer and the heat seal layer and in direct contact with the heat seal layer; and (b) heat sealing the heat seal layer to itself.
According to still another embodiment of the invention, a package comprises a container and a lidding laminate comprising: (a) a heat seal layer adhered to the container and comprising a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin; (b) optionally, a pressure sensitive adhesive layer adhered to the heat seal layer; and (c) a core layer adhered to the pressure sensitive adhesive layer when present or to the heat seal layer when the pressure sensitive adhesive layer is not present.
According to still another embodiment of the invention, a package comprises a flexible bag or pouch comprising: (a) a heat seal layer adhered to itself and comprising a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and having a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C.; and an antifog agent, wherein the composition has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin; (b) optionally, a pressure sensitive adhesive layer adhered to the heat seal layer; and (c) a core layer adhered to the pressure sensitive adhesive layer when present or to the heat seal layer when the pressure sensitive adhesive layer is not present.
The present invention may be understood more readily by reference to the attached drawing, in which:
The present invention may be understood more readily by reference to the following detailed description of certain embodiments of the invention and the working examples.
The term “(co)polyester” is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids or esters (i.e., diacids or diesters) with one or more difunctional hydroxyl compounds (i.e., diols), and is generic to both polyesters and copolyesters. A polyester is the reaction product of one diacid or diester with one diol, whereas a copolyester is the reaction product of multiple diacids or diesters with one diol, multiple diols with one diacid or diester, or multiple diacids or diesters with multiple diols.
The term “reaction product” or residue as used herein refers to any product of an esterification or transesterification reaction of any of the monomers used in making the (co)polyester, including an oligomer or the final (co)polyester, reacted to a certain intrinsic and melt viscosities. The term “reaction product” also includes a monomer formed in situ by the reaction of other monomers which may become part of the (co)polyester backbone. Typically, the relative amounts of the monomer residues making up the (co)polyester product are the same as or very similar to the relative amounts of the monomers used in the charge to make the product. In some conditions, however, other monomers are formed during the production of the (co)polyester and such formed monomers may become part of the final product. When ethylene glycol is used, for example, some amount of diethylene glycol may be formed at a low level in situ and its residue may become part of the (co)polyester backbone, as is known in the art.
As used herein, the phrase “peel strength” refers to: (1) in embodiments in which no pressure sensitive adhesive layer is used (i.e., as shown in
In the embodiment described in which no pressure sensitive adhesive is present, the force required to cause the failure shown in
As used herein, the phrase “peelable/resealable bond” as used herein refers to at least one bond between two adjacent film layers which is adapted to easily separate or delaminate by manually pulling apart the film, and reseal or re-adhere to itself by bringing the separated portions of film together by application of manual finger pressure.
As used herein, the phrase “innermost film layer” as applied to film layers of the present invention refers to the film layer which is closest to the product relative to the other layers of the multilayer film. An innermost film layer may serve as a food-contact layer and is referred to herein as the heat seal layer. The phrase “outermost film layer,” as used herein refers to the exterior-film layer which is furthest from the product relative to the other layers of the multilayer film and is referred to herein as the core layer, which may be a single layer or be made up of sub-layers.
As used herein, the phrase “food-contact layer” as applied to film layers refers to any film layer of a multilayer film which is in direct contact with the food product packaged in the film. This is the heat seal layer as described herein.
As used herein, the phrase “pressure sensitive adhesive” refers to adhesives which are tacky upon the application of pressure without its tackiness being essentially dependent upon temperature elevation.
As used herein, the phrase “direct contact” as applied to film layers, is defined as adhesion of the subject film layer surface directly to another film layer surface (including all or substantially all the entire planar surfaces) when the laminate is sealed together.
An embodiment of the invention pertains to a composition comprising a (co)polyester resin comprising the reaction product of at least one diol and at least one diacid or diester and an antifog agent. The (co)polyester resin has a heat of fusion of 0.1 to 8 J/g, preferably 0.2 to 5 J/g, most preferably 0.5 to 3 J/g and a glass transition temperature between about 50° C. and 100° C., preferably between about 60° C. and about 90° C., and most preferably between about 65° C. and about 85° C. The composition has a heat of fusion greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin. Thus, the (co)polyester resin and antifog agent are selected such that, when mixed, the mixture has a higher heat of fusion value and a lower glass transition temperature relative to those values of the (co)polyester resin alone.
Heat of fusion values provided herein are determined according to ASTM E793-01 “Standard Test Method for Enthalpies of Fusion and Crystallization by Differential Scanning Calorimetry,” except with one modification to the test in that a scanning temperature of 15° C. per minute instead of 10° C. per minute was used. As is known in the art, heat of fusion values are obtained and reported herein as the values obtained upon the first heat of the sample. The glass transition temperature values provided herein are determined in accordance with ASTM E1356-08. As is known in the art, glass transition temperature values are obtained and reported herein as the values obtained upon the second heat of the sample. Preferably, the heat of fusion of the composition is 7.5 to 30 J/g, preferably 10 to 25 J/g, most preferably 12.5 to 20 J/g. The glass transition temperature of the composition is preferably between about 40° C. and 80° C., preferably between about 45° C. and about 75° C., and most preferably between about 50° C. and about 70° C. In a preferred embodiment, the value of the melt peak of the (co)polyester resin is substantially the same as the value of the melt peak of the composition. As used herein, the value of the melt peak is determined by _ASTM E793-01, except with one modification to the test in that a scanning temperature of 15° C. per minute instead of 10° C. per minute was used. In this context of the relative melt peak values of the mixture and the (co)polyester resin alone, “substantially the same as” shall mean that the two temperatures are within 5° C., preferably 3° C., most preferably 2° C. of one another.
The composition is suitable for use as a heat seal resin capable of being extruded on to PET films or coextruded with PET resins to produce a clear heat sealable laminate with anti-fogging properties. This laminate may be used for packaging fresh produce, meats, or other food products or other items that could potentially contain moisture or otherwise produce fog. This laminate may be used as a pouch or bag in which event it is sealed to itself, specifically with the heat seal layers being sealed to itself as shown, for example, in FIG. 2 of U.S. Pat. No. 7,422,782, which is incorporated herein by reference. The laminate may also be used as a lidding laminate in which event it is sealed to a tray or container. The usual container for such food products is clear amorphous PET trays. The overall concept of the packaging is to help the consumer see the food in the tray or in the bag or pouch. If there are water droplets or fogging is present on the surface of the film, the overall effect of the packaging is lost and the consumer satisfaction will be impaired. Fog develops in numerous ways as a result of changing climate or variation in temperature conditions such as freezing or humidity. When warm air, which holds moisture, meets a colder surface, water can condense and settle on to the colder surface. When too much moisture settles, this leads to water accumulation that needs to go somewhere, resulting in fog. The principle behind using anti-fog heat seal resins is to create a hydrophilic surface by altering the degree of wetting on the surface of the film when the heat seal coating is formed. The antifog heat seal layer improves the wettability of the surface and, when this surface attracts and absorbs moisture, it creates a non-scattering or a thin layer of film of water without impeding vision through the layer.
The laminate of embodiments of the invention have also been found to have low haze. Having a low haze is desirable so that consumers can easily see through the laminate to view the product within the sealed container or bag. Preferably, the haze of the laminate, as determined in accordance with ASTM D1003, is less than about 5%, preferably less than about 3%, and most preferably less than about 2%.
According to an embodiment of the invention, the at least one diacid or diester is mostly, substantially all, or all aromatic. As used herein in this context, the term “mostly” means more than fifty (50) mole percent and substantially all means at least ninety-five (95) mole percent. In a preferred embodiment of the invention, the at least one diacid or diester comprises, consists essentially of, or consists of one of dimethyl terephthalate, terephthalic acid, or a blend thereof. In still another preferred embodiment, the at least one diacid or diester consists of dimethyl terephthalate, terephthalic acid, or a blend thereof, and the at least one diol consists of ethylene glycol and diethylene glycol or a blend thereof.
According to another embodiment of the invention, the (co)polyester resin comprises the reaction product of at least one diol and at least two diacids or diesters. Preferably, the at least two diacids or diesters are mostly, substantially all, or all aromatic and preferably comprise, consist essentially of, or consist of dimethyl terephthalate, terephthalic acid, isophthalic acid, dimethyl isophthalate, or blends thereof. In the embodiment in which the at least two diacids or diesters consist of dimethyl terephthalate and isophthalic acid, these monomers are preferably used in a molar ratio of greater than about 60:40, preferably between about 65:35 and about 95:5, and most preferably between about 70:30 and about 90:10.
According to another embodiment of the invention, the at least one diol is mostly, substantially all, or all aliphatic or cycloaliphatic. Preferably, the least one diol comprises, consists essentially of, or consists of ethylene glycol. In a preferred embodiment, the at least one diol consists of ethylene glycol and the at least two diacids or diesters consist of dimethyl terephthalate and isophthalic acid, preferably in in a molar ratio of greater than about 60:40, preferably between about 65:35 and about 95:5, and most preferably between about 70:30 and about 90:10.
In another embodiment of the invention, the amorphous (co)polyester resin has a Brookfield Thermosel melt viscosity at 255° C. of between 100,000 and 350,000 cP, preferably between about 125,000 cP to 275,000 cP, with a #27 spindle at rotational speed between about 0.3 and 2 rpm. In yet another embodiment of the invention, the intrinsic viscosity of the (co)polyester resin is between about 0.1 dl/g to about 0.7 dl/g, preferably between about 0.45 dl/g to about 0.66 dl/g. As used herein, intrinsic viscosity is determined in accordance with ASTM D5225-14. The viscosity of the (co)polyester resin increase as the reaction progresses. The amorphous (co)polyester resin may have a melt flow index within a range of 7 to 50 g/10 min, as measured in accordance with ASTM D1238-20 at a temperature of 190° C. and using a weight of 2.16 kg.
The (co)polyester used in the present invention may be produced by any conventional method for producing a (co)polyester by a transesterification method or a direct esterification method. However, in consideration of food applications, use of heavy metals or compounds that pose a problem in hygiene as catalysts and additives should be avoided or limited. The (co)polyesters used in the present invention typically can be prepared from diacids or diesters and diols which react in substantially equal proportions and are incorporated into the (co)polyester polymer as their corresponding residues. As is well-known, the diols are added in excess, because unreacted diols are more easily evaporated than unreacted diacids or diesters. The (co)polyesters of the present invention, therefore, can contain substantially equal molar proportions of diacid or diester residues and diol residues. The mole percentages provided in the present disclosure, therefore, may be based on the total moles of diacid and diester residues or the total moles of diol residues.
Suitable methods include, but are not limited to, the steps of reacting one or more dicarboxylic acids with two or more diols at a temperature of 100° C. to 315° C. at a pressure of 0.1 to 760 mm Hg for a time sufficient to form a polyester. U.S. Pat. No. 3,772,405, incorporated herein by reference, describes suitable methods of producing (co)polyesters. In one process for making the (co)polyester resin, the process comprises: (I) heating a mixture comprising the selected monomers useful in any of the (co)polyesters of the invention in the presence of a catalyst at a temperature of 150 to 255 C for a time sufficient to produce an initial polyester; (II) heating the initial polyester of step (I) at a temperature of 240 to 320° C. for 1 to 4 hours; and (III) removing any unreacted glycols.
Suitable catalysts for use in this process include, but are not limited to, organo-zinc, titanium, or tin compounds, although organo-tin compounds are not preferred for food packaging applications. The use of this type of catalyst is well-known in the art. Examples of catalysts useful in the present invention include, but are not limited to, zinc acetate dihydrate, butyltin tris-2-ethylhexanoate, dibutyltin diacetate, titanium (IV) 2-ethylhexyloxide, titanium (IV) butoxide and/or dibutyltin oxide. Other catalysts may include, but are not limited to, those based on manganese, lithium, germanium, and cobalt. Catalyst amounts can range from 10 ppm to 20,000 ppm or 10 to 10,000 ppm, or to 5000 ppm or 10 to 1000 ppm or 10 to 500 ppm, or 10 to 300 ppm or 10 to 250 based on the catalyst metal and the weight of the final polymer. The process can be carried out in either a batch or continuous process. In embodiments of the invention, the reaction is continued until the product has a Brookfield Thermosel melt viscosity at 255° C. of between 100,000 and 350,000 cP, preferably between about 125,000 cP to 275,000, with a #27 spindle at rotational speed between about 0.3 and 2 rpm. In another embodiment of the invention, the reaction is continued until the product has an intrinsic viscosity of between about 0.1 dl/g to about 0.7 dl/g, preferably between about 0.45 dl/g to about 0.66 dl/g. The reaction is stopped in a known way, for example by stopping the vacuum and heat upon obtaining a measurement of the torque on the agitator which would correspond to the desirable viscosity of the (co)polyester melt.
As mentioned above, the composition of the present invention comprises an antifog agent. The antifog agent is selected such that the composition comprising the (co)polyester resin and the antifog agent (either alone or with other additives) has a heat of fusion of greater than the heat of fusion of the (co)polyester resin and a glass transition temperature less than the glass transition temperature of the (co)polyester resin. In a preferred embodiment, the antifog agent is selected from the group consisting of a sorbitan ester, a glycerol ester, and blends thereof. Embodiments of the invention using this additive impart excellent antifog ability when the film is exposed to either hot fog or cold fog conditions, in some cases leading to instantaneous antifog performance at 3° C. to 10° C. Preferably, the antifog additive, like the other constituents of the composition, are safe for food if the item to be contained is a food item. Several antifog additives provided by Croda Polymer Additives are suitable, such as Atmer™ 100 (a liquid sorbitan ester), Atmer™ 1440 (a glycerol ester liquid), and Atmer™ 1010 (glycerol ester paste), and Atmer™ 116 (ethoxylated sorbitan ester liquid), Atmer™ 122 (a glycerol ester microbead). Other antifog additives with similar chemistry, performance, and properties can also be used. Preferably, the antifog additive migrates to the surface of the PET film and raises the surface energy of the PET film and lowers the surface energy of the water droplets forming a continuous and uniform transparent layer of water once water condenses on the surface of the PET film. In embodiments of the invention, the antifog additive is present in an amount suitable to achieve the necessary antifog properties, without impacting the adhesive properties of the composition. In embodiments, the antifog agent is present in the composition between about 1% to about 12% by weight of the fully formulated heat seal resin composition, preferably about 2% to about 10%, and most preferably about 3% to about 7%.
Embodiments of compositions of the present invention for forming the heat seal layer may optionally contain one or more additives conventionally used in the manufacture of polymeric films. Examples of such additives are pigments, lubricants, antioxidants, free radical scavengers, UV absorbers, thermal stabilizers, anti-blocking agents, surface active agents, slip aids, optical brighteners, gloss improvers, and viscosity modifiers, among other additives.
According to an embodiment of the invention, a laminate for sealing a container (also referred to herein as a “lidding laminate”) or for serving as a flexible bag comprises a heat seal layer adapted to be adhered to the container (or sealed to itself) and comprising any composition described herein; an optional pressure sensitive adhesive layer adhered to the heat seal layer; and a core layer adhered to the pressure sensitive adhesive layer when present or to the heat seal layer when the pressure sensitive adhesive layer is not present. Embodiments of the invention also include a package, such as a sealed container with the lidding laminate adhered to the container or such as a bag or pouch formed by sealing the heat seal layer of the laminate to itself. In one embodiment, the package comprises a container, such as a tray, and a laminate comprising: a heat seal layer adhered to the container and comprising any of the compositions described herein; optionally, a pressure sensitive adhesive layer adhered to and in direct contact with the heat seal layer; and a core layer adhered to the pressure sensitive adhesive layer when present or to the heat seal layer when the pressure sensitive adhesive layer is not present.
The embodiment of the invention shown in
In an embodiment of the invention, the peel strength between the container and the heat seal layer is at least about 1.1, preferably at least about 1.25, more preferably at least about 1.5, and most preferably at least 2 times stronger than the peel strength between the pressure sensitive adhesive layer and the heat seal layer. This permits the adhesive failure between the cleave lines 29a and 29b, as shown in
As described above, pressure sensitive adhesive layer 26 may be an SBC-based adhesive. Such adhesives are commercially available under the trademark M-Resin™ from the assignee hereof. Such adhesives are also described in U.S. Patent Application Publication No. 2018/0215522, incorporated herein by reference. In embodiments herein, the pressure sensitive adhesive layer comprises a hot-melt self-adhesive composition which has a melt flow index, measured in accordance with ASTM D1238-20 for a temperature of 190° C. using a weight of 2.16 kg, ranging from 0.01 to 200 g/10 minutes and which comprises:
The pressure sensitive adhesive composition may comprise one or more styrene block copolymers, having a weight-average molar mass Mw of generally between 50 kDa and 500 kDa. Unless otherwise indicated, the weight-average molar masses Mw that are given in the present text are expressed in daltons (Da) and are determined by Gel Permeation Chromatography, the column being calibrated with polystyrene standards. These styrene block copolymers may consist of blocks of various polymerized monomers including at least one polystyrene block, and are prepared by radical-polymerization techniques. The triblock copolymers include 2 polystyrene blocks and 1 elastomer block. They can have various structures: linear, star (also called radial), branched or else comb. The diblock copolymers include one polystyrene block and one elastomer block. The triblock copolymers have the general formula: ABA (I), in which:
The diblock copolymers have the general formula: A-B (II), in which A and B are as defined previously.
When the composition comprises several triblock styrene copolymers, the latter being chosen from the group comprising SIS, SBS, SEPS, SIBS and SEBS, it is understood that triblocks can belong to just one or to several of these 5 copolymer families. The same is true for the diblock copolymers.
It is preferred to use a composition comprising a triblock copolymer and a diblock copolymer having the same elastomer block, owing in particular to the fact that such blends are commercially available. According to one particularly preferred implementation variant, the content of diblock copolymer in the composition al can range from 40% to 90%, preferably from 50% to 90%, even more preferentially from 50% to 60%. According to one particularly advantageous embodiment, the composition of the pressure sensitive adhesive consists of an SIS triblock copolymer and of an SI diblock copolymer. In this case, the total content of styrene units in the composition al preferably ranges from 10% to 20%. The triblock copolymers included in the composition al preferably have a linear structure. The styrene block copolymers comprising an elastomer block, in particular of SI and SIS type, that can be used in the composition are commercially available, often in the form of triblock/diblock blends, including:
As mentioned above, the pressure sensitive adhesive composition also comprises one or more tackifying resins having a softening temperature of between 5 and 140° C. The tackifying resin(s) that can be used have weight-average molar masses Mw of generally between 300 and 5000 Da and are chosen in particular from:
According to one preferred embodiment, use is made of resins belonging to categories (ii) or (iii) above for which mention may be made, as examples of commercially available resin, of:
According to a preferred embodiment, the pressure sensitive adhesive composition comprises:
According to another preferred variant, the pressure sensitive adhesive composition comprises:
According to yet another preferred embodiment, the pressure sensitive adhesive composition further comprises one or more stabilizers (or antioxidants). These compounds are introduced in order to protect the composition against degradation resulting from a reaction with oxygen which is capable of forming from the action of heat, light, or residual catalysts on certain raw materials such as tackifying resins. These compounds can include primary antioxidants, which trap free radicals and which may be substituted phenols, such as Irganox® 1010 from Ciba. The primary antioxidants can be used alone or in combination with other antioxidants, such as phosphites, for instance Irgafos® 168 also from Ciba, or else with UV-stabilizers such as amines.
The pressure sensitive adhesive composition can also comprise a plasticizer, and, if present, preferably not in an amount exceeding 5%. As plasticizer, use may be made of a paraffinic and naphthenic oil (such as Primol® 352 from the company ESSO) optionally comprising aromatic compounds (such as Nyflex 222B). Finally, the composition may also comprise mineral or organic fillers, pigments, or dyes.
The pressure sensitive adhesive composition can be prepared, in the form of granules or pellets having a size between 1 and 10 mm, preferably between 2 and 5 mm, by simple hot-mixing of its ingredients, between 150 and 200° C., preferably at approximately 160° C., by means of a twin-screw extruder equipped with a tool for cutting the extruded product as it leaves the die.
Aspect 1. A composition comprising:
Aspect 2. The composition of Aspect 1, wherein the heat of fusion of the composition is 7.5 to 30 J/g, preferably 10 to 25 J/g, most preferably 12.5 to 20 J/g.
Aspect 3. The composition of Aspects 1 or 2, wherein the glass transition temperature of the composition is between about 40° C. and 80° C., preferably between about 45° C. and about 75° C., and most preferably between about 50° C. and about 70° C.
Aspect 4. The composition of any of Aspects 1-3, wherein the value of the melt peak of the (co)polyester resin is substantially the same as the value of the melt peak of the composition.
Aspect 5. The composition of any of Aspects 1-4, wherein the at least one diacid or diester is mostly, substantially all, or all aromatic.
Aspect 6. The composition of Aspect 5, wherein the at least one diacid or diester is terephthalic acid or dimethyl terephthalate.
Aspect 7. The composition of any of Aspects 1-6, wherein the (co)polyester resin comprises the reaction product of at least one diol and at least two diacids or diesters.
Aspect 8. The composition of Aspect 7, wherein the at least two diacids or diesters are mostly, substantially all, or all aromatic.
Aspect 9. The composition of Aspect 8, wherein the at least two diacids or diesters comprise, consist essentially of, or consist of dimethyl terephthalate and isophthalic acid.
Aspect 10. The composition of Aspect 8, wherein the at least two diacids or diesters consist of dimethyl terephthalate and isophthalic acid in a molar ratio of greater than 60:40, preferably between about 65:35 and about 95:5, and most preferably between about 70:30 and about 90:10.
Aspect 11. The composition of any of Aspects 1-10, wherein the at least one diol is mostly, substantially all, or all aliphatic or cycloaliphatic.
Aspect 12. The composition of Aspect 11, wherein the least one diol comprises, consists essentially of, or consists of ethylene glycol.
Aspect 13. The composition of any of Aspects 1-12, wherein the antifog agent is selected from the group consisting of a sorbitan ester, a glycerol ester, and blends thereof.
Aspect 14. A laminate comprising:
Aspect 15. The laminate of Aspect 14, wherein the laminate is a lidding laminate and is suitable for sealing a container and the heat seal layer is adapted to be adhered to the container.
Aspect 16. The laminate of Aspect 14, wherein the laminate is suitable for use as a bag and the heat seal layer is adapted to be adhered to itself.
Aspect 17. The laminate of any of Aspects 14-16, wherein the pressure sensitive adhesive layer is present and comprises a hot-melt self-adhesive composition which has a melt flow index, measured for a temperature of 190° C. using a weight of 2.16 kg, ranging from 0.01 to 200 g/10 minutes and which comprises:
Aspect 18. The laminate of any of Aspects 14-17, wherein the pressure sensitive layer is present and the peel strength between the container and the heat seal layer is at least about 1.1, preferably at least about 1.25, more preferably at least about 1.5, and most preferably at least 2 times stronger than the peel strength between the pressure sensitive adhesive layer and the heat seal layer.
Aspect 19. The laminate of any of Aspects 14-18, wherein the haze of the laminate is less than about 5%, preferably less than about 3%, and most preferably less than about 2%, as determined in accordance with ASTM D1003.
Aspect 20. A method of sealing a container comprising the steps of:
Aspect 21. A method of forming a bag comprising the steps of:
Aspect 22. The method of Aspects 20 or 21, wherein the laminate further comprises a pressure sensitive adhesive layer between the core layer and the heat seal layer.
Aspect 23. A package comprising a container; and a laminate comprising:
Aspect 24. The package of Aspect 23, wherein the pressure sensitive adhesive layer is present and the laminate has an initial peel strength of at least about 7 N/15 mm as measured in accordance with ASTM D903.
Aspect 25. The package of Aspect 23, wherein the pressure sensitive adhesive layer is present and the laminate has a re-tack peel strength of at least about 0.5 N/15 mm, preferably at least about 0.7 but at most about 5 N/15 mm, preferably at most about 3 N/15 mm, tested after the third cycle of opening and re-sealing.
The following examples demonstrate several aspects of certain preferred embodiments of the present invention, and are not to be construed as limitations thereof.
A copolyester heat seal coating composition, Example 1, was prepared using Vitel 1100, manufactured by Bostik, Inc., which is a semi-crystalline copolyester resin with a Tg of 74° C., a Tm of 205° C., and a heat of fusion of 1.4 J/g. The heat seal copolyester was made by combining 97% by weight of V1100 copolyester, 1.5% by weight of Atmer 1010 (a glycerol ester paste), and 1.5% by weight of Atmer 116 (a ethoxylated sorbitan ester liquid). Both Atmer products are commercially available from Croda. The components were mixed using a twin screw extruder and pelletized. The heat seal resin hence extruded was cooled using a water bath and pelletized to yield the solid pellets. The pellets were then dried and packaged to be used either for extrusion or co-extrusion process. The thickness of the heat seal layer was about 7 μm.
The physical properties of the heat seal copolyester resin Example 1 are provided in below in Table 1. All of the Examples 1-5 described herein were coextruded with M-Resin, such as MX660, M650, M651, which are styrene block copolymer-based pressure sensitive adhesives in pellet form, and LDPE as a core layer on a multi-layer blown film line. The co-extruded blown film possessed a multi-layer laminated structure with copolyester as heat seal layer having anti-fog properties, and the M-resin serves as a reclosable pressure sensitive adhesive layer. The properties of the film samples produced using the Examples 1—5 are provided below in Tables 2 and 3.
A copolyester heat seal coating composition, Example 2, was made by combining 96% by weight of Vitel 1100 copolyester, 2% by weight of Atmer 1010, and 2% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized using Leistritz MIC 27 6L/400 equipment as described above in Example 1. The physical properties of the heat seal copolyester resin Example 2 are provided in Table 1, and the resealability and antifog properties of the film are provided below in Tables 2 and 3.
A copolyester heat seal coating composition, Example 3, was made by combining 95% by weight of Vitel 1100 copolyester, 2.5% by weight of Atmer 1010, and 2.5% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above in Example 1. The physical properties of the heat seal copolyester resin Example 3 are provided in Table land antifog properties of the film are provided below in Table 3.
A copolyester heat seal coating composition, Example 4, was made by combining 94% by weight of Vitel 1100 copolyester, 3% by weight of Atmer 1010, and 3% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above in Example 1. The physical properties of the heat seal copolyester resin Example 4 are provided in Table 1.
A copolyester heat seal coating composition, Example 5, was made by combining 93% by weight of Vitel 1100 copolyester, 3.5% by weight of Atmer 1010, and 3.5% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above in Example 1. The physical properties of the heat seal copolyester resin Example 5 are provided in Table 1.
aGlass transition temperature determined by ASTM E1356-08 using DSC
bHeat of fusion determined by ASTM E-793-01 using DSC
cMelting point determined by ASTM D7138 using DSC
dIntrinsic viscosity determined by ASTM D5225-14
eMFI determined by ASTM D1238-20
aPeel strength determined by ASTM D903
A copolyester heat seal coating composition, Example 6, was made by combining 97% by weight of Vitel 1100 copolyester, 1.500 by weight of Atmer 1010, and 1.50% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above. The heat seal resin hence extruded was cooled using a water bath, and pelletized to yield the solid pellets. Examples 6-8 were then dried and packaged to be used for cast co-extrusion as sheets with PET resins (Indorama RAMAPET N180). The co-extruded bilayer films were subsequently biaxial oriented stretched off-line or in-line at 3.2×3.2 stretch ratio at 95° C. for 40 seconds and annealed at 200° C. for 5 seconds. The sample film properties are listed in Table 4 below.
A copolyester heat seal coating composition, Example 7, was made by combining 96% by weight of Vitel 1100 copolyester, 2% by weight of Atmer 1010, and 2% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above. The heat seal resin hence extruded was cooled using a water bath, and pelletized to yield the solid pellets. The copolyester was then coextruded with PET on a cast extrusion line. The co-extruded bilayer films were subsequently biaxial oriented stretched off-line or in-line at 3.2×3.2 stretch ratio at 95° C. for 40 seconds and annealed at 200° C. and for 5 seconds. The sample film properties were listed in Table 4.
A copolyester heat seal coating composition, Example 8, was made by combining 95% by weight of Vitel 1100 copolyester, 2.5% by weight of Atmer 1010, and 2.5% by weight of Atmer 116. The components were mixed using a twin screw extruder and pelletized as described above. The heat seal resin hence extruded was cooled using a water bath, and pelletized to yield the solid pellets. The copolyester was then coextruded with PET on a cast extrusion line. The co-extruded bilayer films were subsequently biaxial oriented stretched off-line or in-line at 3.2×3.2 stretch ratio at 95° C. for 40 seconds and annealed at 200° C. and for 5 seconds. The sample film properties were listed in Table 4.
Heat Seal Test Description: The heat seal was conducted on a Gradient heat seal tester, Model GHS-03, manufactured by Labthink International, Inc., Medford, MA. Heat seal pressure was 40 psi and the dwell time was 0.5 second (ASTM F88). The heat seals were made with heat seal coating facing the APET sheet. The APET sheet selected for this study has a thickness of 457 μm. Three sealing temperatures were selected for the current study. The temperatures for sealing were 135° C., 149° C., and 163° C. Other conditions of sealing could be used. Once sealed, the samples were conditioned at room temperature (25° C. and 32% RH) for 24 hrs. The testing data at the two different seal dwell time up to five opening are reported in Table 2 as peel strengths in using Instron 5543, following ASTM D903. The testing was conducted at room temperature (25° C. and 32% RH). The peel speed was 12 inches per minutes. The initial peel strength and reseal strength values are listed in Table 2.
Antifog test: The antifog effectiveness of the PET film produced using the heat seal coating was assessed by the following method. Cold fog: Clear APET trays 2 inch tall were used for the testing. A white paper towel was laid in the inside of the tray and it was filled with 20 mL of distilled water at room temperature. The paper towel would hold the water and prevented the water from being spilled when the tray was sealed or moved around to be placed in the refrigerator. The lip of the tray was about ¼ inch. The APET tray was placed inside a silicone mold for proper alignment during sealing. PET film about 4 inch in diameter containing the heat seal coating was then laid face down on the tray, meaning the heat seal coating faced the inside of the tray. The PET film was then sealed to the tray using a low temperature press at 150° C. to achieve a very good seal. The pressure on the press was about 40 psi. Dwell time was 1 sec. A picture of the tray after sealing was taken to represent time zero point. See
aHaze determined by ASTM D1003
The anti-fog scores were rated as follows: Anti-fog score 1-very poor: opaque layer of small fog droplets; score 2-poor: opaque or transparent layer of large droplets; score 3-acceptable: complete layer of large transparent droplets; score 4-good: randomly distributed or large transparent droplets; score 5-excellent: transparent film without visible water. The films of Examples 6-8 demonstrated very low haze values. As can be seen in
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/000380 | 6/29/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63216575 | Jun 2021 | US |
