Patent Description:
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.

<CIT> 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 <NUM>, generally between <NUM> and <NUM>. 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. <CIT> 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.

<CIT> 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. <CIT> 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. <CIT> 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. <CIT> 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.

<CIT> 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 complexable thin layer consisting of a thermoplastic, and a heat-sealable and cleavable layer comprising at least <NUM> 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM> , and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM> , and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM> , and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM> , and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>; 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>; 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: (<NUM>) in embodiments in which no pressure sensitive adhesive layer is used (i.e., as shown in <FIG>), the cohesive strength of the heat seal layer; and (<NUM>) in embodiments in which the pressure sensitive adhesive layer is present (i.e., as shown in <FIG>), the bond or adhesive strength between the heat-sealable, innermost film-layer (also referred to herein as the heat seal layer) and the pressure sensitive adhesive layer in direct contact therewith. In embodiments in which the pressure sensitive adhesive layer is present, the peel strength depends primarily on the chemical similarity or dissimilarity of the materials which form the two layers in direct contact with one another. Peel strength of known materials may also be affected by production conditions, packaging machine conditions, and environmental conditions during film fabrication, the packaging process, and storage. The multilayer film according to the present invention may be heat-sealed to itself such that two portions of the innermost layer are brought into contact with each other using heat-seal jaws and by applying a pressure (force) for an appropriate time and temperature, for example a pressure of <NUM> psi for <NUM> second at a temperature of between <NUM>-<NUM>° C. The innermost layer may then be separated or delaminated from an adjacent adhesive layer (a polymeric second layer) and the force required to separate these layers may be measured in accordance with the test method described in ASTM D903. This is referred to as the "first peel strength" or the "initial peel strength. " After delamination, the separated portions of film may be manually rejoined by applying a manual force at this seal region of the film. The external innermost layer may further be re-separated or delaminated from an adjacent adhesive layer and the force required to separate these layers may be measured in accordance with the test method described in ASTM D903. This is referred to as the "re-tack peel strength.

In the embodiment described in which no pressure sensitive adhesive is present, the force required to cause the failure shown in <FIG> (which includes cohesive failure of the heat seal layer) may be measured in accordance with the test method described in ASTM D903.

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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>. 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-<NUM> "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 <NUM> per minute instead of <NUM> 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-<NUM>. 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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g. The glass transition temperature of the composition is preferably between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>. 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-<NUM>, except with one modification to the test in that a scanning temperature of <NUM> per minute instead of <NUM> 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 <NUM>, preferably <NUM>, most preferably <NUM> 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> of <CIT>. 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 <NUM>%, preferably less than about <NUM>%, and most preferably less than about <NUM>%.

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 (<NUM>) mole percent and substantially all means at least ninety-five (<NUM>) 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 <NUM>:<NUM>, preferably between about <NUM>:<NUM> and about <NUM>:<NUM>, and most preferably between about <NUM>:<NUM> and about <NUM>:<NUM>.

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 <NUM>:<NUM>, preferably between about <NUM>:<NUM> and about <NUM>:<NUM>, and most preferably between about <NUM>:<NUM> and about <NUM>:<NUM>.

In another embodiment of the invention, the amorphous (co)polyester resin has a Brookfield Thermosel melt viscosity at <NUM> of between <NUM>,<NUM> and <NUM>,<NUM> cP, preferably between about <NUM>,<NUM> cP to <NUM>,<NUM> cP, with a #<NUM> spindle at rotational speed between about <NUM> and <NUM> rpm. In yet another embodiment of the invention, the intrinsic viscosity of the (co)polyester resin is between about <NUM> dl/g to about <NUM> dl/g, preferably between about <NUM> dl/g to about <NUM> dl/g. As used herein, intrinsic viscosity is determined in accordance with ASTM D5225-<NUM>. 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 <NUM> to <NUM>/<NUM>, as measured in accordance with ASTM D1238-<NUM> at a temperature of <NUM> and using a weight of <NUM>.

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 <NUM> to <NUM> at a pressure of <NUM> to <NUM> Hg for a time sufficient to form a polyester. <CIT> 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 <NUM> to <NUM> C for a time sufficient to produce an initial polyester; (II) heating the initial polyester of step (I) at a temperature of <NUM> to <NUM>° C for <NUM> to <NUM> hours; and (III) removing any unreacted glycols.

Suitable catalysts for use in this process include, but are not limited to, organozinc, 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-<NUM>-ethylhexanoate, dibutyltin diacetate, titanium (IV) <NUM>-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 <NUM> ppm to <NUM>,<NUM> ppm or <NUM> to <NUM>,<NUM> ppm, or to <NUM> ppm or <NUM> to <NUM> ppm or <NUM> to <NUM> ppm, or <NUM> to <NUM> ppm or <NUM> to <NUM> 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 <NUM> of between <NUM>,<NUM> and <NUM>,<NUM> cP, preferably between about <NUM>,<NUM> cP to <NUM>,<NUM>, with a #<NUM> spindle at rotational speed between about <NUM> and <NUM> rpm. In another embodiment of the invention, the reaction is continued until the product has an intrinsic viscosity of between about <NUM> dl/g to about <NUM> dl/g, preferably between about <NUM> dl/g to about <NUM> 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 <NUM> to <NUM>. 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™ <NUM> (a liquid sorbitan ester), Atmer™ <NUM> (a glycerol ester liquid), and Atmer™ <NUM> (glycerol ester paste), and Atmer™ <NUM> (ethoxylated sorbitan ester liquid), Atmer™ <NUM> (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 <NUM>% to about <NUM>% by weight of the fully formulated heat seal resin composition, preferably about <NUM>% to about <NUM>%, and most preferably about <NUM>% to about <NUM>%.

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.

<FIG> show a cross-sectional view of the embodiment of the lidding laminate <NUM> without any pressure sensitive adhesive layer. In particular, lidding laminate <NUM> comprises a heat seal layer <NUM> and a core layer <NUM>. Heat seal layer <NUM> is formed from (e.g., by being extruded from) a composition comprising any of the (co)polyester resin/antifog agent compositions described herein. In embodiments of the invention, core layer <NUM> itself may comprise multiple sub-layers laminated together. In a preferred embodiment, heat seal <NUM> layer consists of the single layer of the (co)polyester/anti-fog agent compositions described herein. The thickness of heat seal layer <NUM> may vary over a wide range depending on the application, and may range from <NUM>-<NUM>, preferably from <NUM>-<NUM>, and most preferably from <NUM>-<NUM>. Core layer <NUM> may also be a single layer or may be a multilayer film itself, such as a three-layer film of a PET sub-layer, polyurethane laminating adhesive (PU) sub-layer, and polyethylene (PE) sub-layer. Core layer <NUM> may also comprise a barrier or print sub-layer. Preferably, the PE sub-layer is adjacent to a tie layer, to which heat seal layer <NUM> is adhered. The thickness of core layer <NUM> may vary over a wide range depending on the application, and may range from <NUM>-<NUM>, preferably from <NUM>-<NUM>, and most preferably from <NUM>-<NUM>. Lidding laminate <NUM> may be formed in any way, such as by: (i) extrusion of each layer followed by lamination or (ii) coextrusion. <FIG> show container or tray <NUM>, which can be any known material as described above, such as APET.

<FIG> shows lidding laminate <NUM> adhered to container <NUM>; such adhesion may be done by heat sealing in a conventional way, which involves applying pressure to a heated lidding laminate <NUM> against the lip of container <NUM> and allowing it to cool and thereby form a bond with container <NUM>. After peeling off lidding laminate <NUM> from container <NUM>, substrate failure (or cohesive failure) occurs within both heat seal layer <NUM> and core layer <NUM>, as shown in <FIG> shows a straight vertical cleave line 19a across both heat seal layer <NUM> and core layer <NUM> and a straight horizontal cleave line 19b across heat seal layer <NUM>. In practice, the failure path may actually be irregular in shape, but will extend from the top of core layer <NUM> to the outside (left-hand side, as shown in <FIG>) of heat seal later <NUM>. In this embodiment, the initial bond between heat seal layer <NUM> and core layer <NUM> is viewed as a "lockseal," and it has a peel strength (or "initial peel strength" which, because this embodiment is not resealable, is the only peel strength) of greater than <NUM>,<NUM> gli (<NUM> N/<NUM>) or about <NUM> N/<NUM>, as measured according to ASTM D903.

<FIG> show a cross-sectional view of the embodiment of the invention having a pressure sensitive adhesive layer <NUM> as part of a lidding laminate <NUM>, which also comprises heat seal layer <NUM> and core layer <NUM>. In this embodiment, heat seal layer <NUM>, core layer <NUM>, and container <NUM> are analogous to and have the same materials and properties as heat seal layer <NUM>, core layer <NUM>, and container <NUM>, respectively. In a preferred embodiment, pressure sensitive adhesive layer <NUM> comprises an adhesive based on styrene block copolymers (SBCs), as described in more detail below. Pressure sensitive adhesive layer <NUM> may be any suitable pressure sensitive adhesive layer (e.g., an SBC-based adhesive) or may itself comprise multiple sub-layers, such as a trilaminate, or two or more such multilaminates. For example, pressure sensitive adhesive layer <NUM> may comprise a trilaminate having a pressure sensitive adhesive sub-layer as the innermost sub-layer in direct contact with heat seal layer <NUM>, a laminating sub-layer of low density polyethylene (LDPE) on other side of the pressure sensitive adhesive sub-layer, and a sealing layer of PET on the other side of the LDPE layer in direct contact with core layer <NUM>. The thickness of pressure sensitive adhesive sublayer may vary over a wide range depending on the application, such as from <NUM>-<NUM>, preferably from <NUM>-<NUM>, and most preferably from <NUM>-<NUM>. In the event that the pressure sensitive adhesive layer <NUM> is a trilaminate with the particular pressure sensitive adhesive sublayer being one of the three layers of the trilaminate, the thickness of pressure sensitive adhesive layer <NUM> may range from <NUM>-<NUM>, preferably from <NUM>-<NUM>, and most preferably from <NUM>-<NUM>.

<FIG> shows lidding laminate <NUM> adhered to container <NUM>; and such adhesion is done by heat sealing in a conventional way, which may involve applying pressure to a heated lidding laminate <NUM> against the lip of container <NUM> and allowing it to cool and thereby form a bond with container <NUM>. After initially peeling off lidding laminate <NUM> from container <NUM>, adhesive failure occurs between heat seal layer <NUM> and pressure sensitive adhesive layer <NUM>, and heat seal layer <NUM> cleaves along cleave lines 29a and 29b, Although shown as straight vertical lines in <FIG>, the fault path in actuality may be irregular, but does extend throughout the entire height of heat seal layer <NUM> from a vertical location adjacent the tray <NUM> to a vertical location adjacent the interface with pressure sensitive adhesive layer <NUM>. In this embodiment, the initial bond between heat seal layer <NUM> and pressure sensitive adhesive layer <NUM> is viewed as a lockseal, as described above, namely having an initial peel strength of greater than <NUM>,<NUM> gli (<NUM> N/<NUM>) or about <NUM> N/<NUM>, as measured according to ASTM D903.

The embodiment of the invention shown in <FIG> also provides for a "reseal" function, meaning that, after the initial opening of the container from its state after being heat sealed, the pressure sensitive layer <NUM> can be resealed to the heat seal layer <NUM> with only finger pressure sufficient to re-engage the two surfaces to provide a re-tack peel strength of at least about <NUM> N/<NUM>, preferably at least about <NUM> but at least about <NUM> N/<NUM>, preferably at least about <NUM> N/<NUM>, tested after the third cycle of opening and re-sealing. Preferably, these re-tack peel strengths are achieved despite the presence of some contamination between the two layers, such as food particles or residues. It is recognized that re-tack peel strength will generally decrease with an increasing number of opening (or peeling) and re-tacking cycles Preferably, the re-tack peel strength remains at at least about <NUM> N/<NUM> after <NUM> cycles, preferably after <NUM> cycles and most preferably after <NUM> cycles. To achieve the reseal function, lidding laminate <NUM> must have heat seal layer <NUM> placed in direct contact with pressure sensitive adhesive layer <NUM> (or sub-layer, in the event that layer <NUM> includes multiple sub-layers) to provide an interface of those two layers, which will become the point of adhesive failure after the initial peel. Stated another way, if layer <NUM> is comprised of multiple sub-layers, the sub-layer of layer <NUM> which contains the pressure sensitive adhesive must be positioned in direct contact with heat seal layer <NUM>; in this way, the sub-layers of layer <NUM> which are not the layer containing the pressure sensitive adhesive (e.g., tie layers, printing layer) are positioned so as not to obstruct the heat seal/pressure sensitive layer interface that can be resealed.

In an embodiment of the invention, the peel strength between the container and the heat seal layer is at least about <NUM>, preferably at least about <NUM>, more preferably at least about <NUM>, and most preferably at least <NUM> 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 <FIG>.

As described above, pressure sensitive adhesive layer <NUM> 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 <CIT>. 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-<NUM> for a temperature of <NUM> using a weight of <NUM>, ranging from <NUM> to <NUM>/<NUM> 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 <NUM> kDa and <NUM> 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 <NUM> polystyrene blocks and <NUM> 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 <NUM> 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 <NUM>% to <NUM>%, preferably from <NUM>% to <NUM>%, even more preferentially from <NUM>% to <NUM>%. 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 <NUM>% to <NUM>%. 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 <NUM> and <NUM>. The tackifying resin(s) that can be used have weight-average molar masses Mw of generally between <NUM> and <NUM> 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® <NUM> from Ciba. The primary antioxidants can be used alone or in combination with other antioxidants, such as phosphites, for instance Irgafos® <NUM> 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 <NUM>%. As plasticizer, use may be made of a paraffinic and naphthenic oil (such as Primol® <NUM> 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 <NUM> and <NUM>, preferably between <NUM> and <NUM>, by simple hot-mixing of its ingredients, between <NUM> and <NUM>. , preferably at approximately <NUM>° C, by means of a twin-screw extruder equipped with a tool for cutting the extruded product as it leaves the die.

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 <NUM>, was prepared using Vitel <NUM>, manufactured by Bostik, Inc. , which is a semi-crystalline copolyester resin with a Tg of <NUM>, a Tm of <NUM>, and a heat of fusion of <NUM> J/g. The heat seal copolyester was made by combining <NUM>% by weight of V1100 copolyester, <NUM>% by weight of Atmer <NUM> (a glycerol ester paste), and <NUM>% by weight of Atmer <NUM> (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 <NUM>.

The physical properties of the heat seal copolyester resin Example <NUM> are provided in below in Table <NUM>. All of the Examples <NUM>-<NUM> 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 <NUM> - <NUM> are provided below in Tables <NUM> and <NUM>.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. The components were mixed using a twin screw extruder and pelletized using Leistritz MIC <NUM><NUM>/<NUM> equipment as described above in Example <NUM>. The physical properties of the heat seal copolyester resin Example <NUM> are provided in Table <NUM>, and the resealability and antifog properties of the film are provided below in Tables <NUM> and <NUM>.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. The components were mixed using a twin screw extruder and pelletized as described above in Example <NUM>. The physical properties of the heat seal copolyester resin Example <NUM> are provided in Table <NUM> and antifog properties of the film are provided below in Table <NUM>.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. The components were mixed using a twin screw extruder and pelletized as described above in Example <NUM>. The physical properties of the heat seal copolyester resin Example <NUM> are provided in Table <NUM>.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. 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 <NUM> - <NUM> 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 <NUM> × <NUM> stretch ratio at <NUM> for <NUM> seconds and annealed at <NUM> for <NUM> seconds. The sample film properties are listed in Table <NUM> below.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. 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 <NUM> × <NUM> stretch ratio at <NUM> for <NUM> seconds and annealed at <NUM> and for <NUM> seconds. The sample film properties were listed in Table <NUM>.

A copolyester heat seal coating composition, Example <NUM>, was made by combining <NUM>% by weight of Vitel <NUM> copolyester, <NUM>% by weight of Atmer <NUM>, and <NUM>% by weight of Atmer <NUM>. 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 <NUM> × <NUM> stretch ratio at <NUM> for <NUM> seconds and annealed at <NUM> and for <NUM> seconds. The sample film properties were listed in Table <NUM>.

Heat Seal Test Description: The heat seal was conducted on a Gradient heat seal tester, Model GHS-<NUM>, manufactured by Labthink International, Inc. , Medford, MA. Heat seal pressure was <NUM> psi and the dwell time was <NUM> 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 <NUM>. Three sealing temperatures were selected for the current study. The temperatures for sealing were <NUM>, <NUM>, and <NUM>. Other conditions of sealing could be used. Once sealed, the samples were conditioned at room temperature (<NUM> and <NUM>% RH) for <NUM> hrs. The testing data at the two different seal dwell time up to five opening are reported in Table <NUM> as peel strengths in using Instron <NUM>, following ASTM D903. The testing was conducted at room temperature (<NUM> and <NUM>% RH). The peel speed was <NUM> inches per minutes. The initial peel strength and reseal strength values are listed in Table <NUM>.

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 <NUM> inch tall were used for the testing. A white paper towel was laid in the inside of the tray and it was filled with <NUM> 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 <NUM> 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 <NUM> to achieve a very good seal. The pressure on the press was about <NUM> psi. Dwell time was <NUM> sec. A picture of the tray after sealing was taken to represent time zero point. The sealed tray is placed in a refrigerator at <NUM> (<NUM> °F). The antifog property of the film is then assessed after <NUM>, <NUM> hour, <NUM> hour, up to <NUM> hour (<NUM> day) to <NUM> hours (<NUM> days) and about <NUM> days. Each time, pictures were taken for comparison. Representative pictures are shown in <FIG> for Examples <NUM> and <NUM> tested at <NUM> day and <NUM> weeks. Hot fog: Glass jar containing <NUM>% internal volume of water was covered with the PET film containing the heat seal antifog coating face down on top of the jar. Rubber bands were used to secure the film to the jar. The water in the jar was then warmed to <NUM> using a water bath for <NUM> minutes and up to <NUM> minutes. The antifog ability of the films were then assessed by visual inspection. The hot fog ability of the films looked very good with mostly clear medium sized drops. Example <NUM> in the left column of <FIG> shows only a few small areas of fog, and therefore received a rating of <NUM>. The right column of <FIG> is clear of any fog (at least in the original samples and photographs). Therefore, these samples received a rating of <NUM>. Any apparent haziness or fog shown in the right-hand column of <FIG> is caused by the conversion of the original photographs pdf. The PET film without antifog heat seal coating fogged immediately with fine foggy drops.

Claim 1:
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 <NUM> to <NUM> J/g, preferably <NUM> to <NUM> J/g, most preferably <NUM> to <NUM> J/g and a glass transition temperature between about <NUM> and <NUM>, preferably between about <NUM> and about <NUM>, and most preferably between about <NUM> and about <NUM>; 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 heat of fusion is the value upon the first heat, determined according to ASTM E793-<NUM>, except that the scanning temperature is <NUM> per minute instead of <NUM> per minute, and the glass transition temperature is the value upon the second heat of the sample, determined according to ASTM E1356-<NUM>.