WO2000022031A1 - Easily heat sealable nylon film - Google Patents

Abstract

A film for manufacturing heat sealable packages for single or multiple use applications in a high temperature environment, wherein the sealant layer or film comprises the following components: i) at least one polyamide resin selected from aliphatic and semi-aromatic polyamides that can be either semi-crystalline or amorphous in structure having a number average molecular weight of at least about 5000, having graft sites and forming the continuous phase of the composition, wherein the semi-crystalline polyamides have a melting point greater than 200 °C; ii) at least one ethylene copolymer, E/X/Y, where E is ethylene and is at least 50 % by weight of E/X/Y, X is from 1-35 % by weight of an acid containing unsaturated mono-carboxylic acid, and Y is 0-49 % by weight of a moiety derived from at least one alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof where the alkyl groups contain 1-12 carbon atoms, and further wherein the acid groups in the acid-containing moiety are neutralized by from 0-100 % by weight of a metal ion; iii) at least one polymeric grafting agent which contains reactive groups selected from at least one of epoxides, isocyanates, aziridines, silanes, alkyl halides, alpha-halo ketones and aldehydes, or oxazoline, which reacts with the acid-containing moieties in component ii) and additionally react with the graft sites of component i), and iv) at least one C2-C20 polyolefin selected from polyethylene, polypropylene, ethylene propylene diene terpolymer, copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof upon which are grafted from about 0.05 to about 5 % by weight of monomers or mixtures of monomers selected from ethylenically unsaturated acidic monomers or their derivatives thereof, with the proviso that a flame retardant is always present.

Description

TITLE

Easily Heat Sealable Nylon Film FIELD OF THE INVENTION

This application claims the benefit of U.S. Provisional Application No. 60/103,835 filed on October 9, 1998.

The present invention relates to heat sealable polyamide film for single or multiple use packaging in high temperature environment applications. The film may be used in multilayer film structures as the sealant film or as a monolayer film structure. It is particularly useful in circumstances where barrier properties, chemical resistance and heat tolerance are required. The polyamide layer or film provides a relatively inert film that may be used to package a variety of substances. BACKGROUND OF THE INVENTION

The prior art has proposed the use of nylon in or as the resin of choice for producing film for packaging for use in high temperature environments, in particular bags. There have been problems in producing such bags, as nylon has not been found to be suitable for producing heat sealable film on a production scale. The film has not been capable of providing a tough durable seal when sealed to itself, and adhesives and/or solvents have been required to seal it, either by application to the seal interface areas or by the use of an adhesive or tie layer in the film structure. The sealing window has also been quite narrow which meant production was difficult.

Traditional nylon films can be heat sealed but the heat seal temperature range (seal temperature to burn through temperature) is small. Furthermore, the resultant seal tends to be brittle because the material is heated to its melting point and then cools slowly, resulting in a severe increase in the crystallinity of the base material. For all practical purposes, nylon has not been regarded as being capable of providing a tough durable seal.

A commercial process to heat seal nylon was developed in the late 1970's by Peter Gray at DuPont Canada Inc. using a solvent application at the seal interface. This effectively reduced the sealing temperature without causing crystallization. This process was used commercially for a few years. There is a commercial advantage in using heat sealable films because there is a great number of low cost high productivity machinery readily available to produce products, e.g. bags and pouches as well as machinery to package products in situ e.g. vertical and horizontal form and fill machines. This has been standard practice with polyethylene films for many years. Since nylon films have many unique advantages in oxygen, flavour and solvent barrier, it has been customary to laminate nylon film to polyethylene film in order to achieve heat sealability while achieving barrier properties. However this approach is more costly and does not necessarily provide the properties required for high temperature environment packaging applications.

While there are many high temperature environments in which polyamide film packaging would have practical application, the following are examples of well known applications. Dry cleaning methods involve the use of non-aqueous based solvents which remove oily stains and soiling, but are less effective for removing protein based stains and particulates such as clay soils. Thus the non- aqueous based solvents, usually hydrocarbons may be combined with other substances in order to effect total cleaning of a garment. Typically the garments or clothing that are dry cleaned are comprised of wool, silk or blends of such fabrics, or delicate fabrics, or garments of complex or delicate construction that are not easily subjected to aqueous cleaning methods.

Commercial dry cleaning is quite costly and thus there has been an interest in developing home dry cleaning products. Since the dry cleaning process not only removes soiling and stains from garments, but also freshens the garments and removes hair and lint and the like, there has been a need to develop home dry cleaning methods that would mimic to a great extent the methods used commercially. Thus the home methods which have been proposed have involved the use of a domestic hot air clothes dryer using a containment bag for the articles to be dry cleaned.

Apparently conventional laundry dryers which may function quite normally can reach air and surface temperatures that are far greater than those expected for such an appliance. In particular, the dryer drum can reach temperatures ranging from about 120°C to about 150°C, and surface temperatures varying from about 175 °C to 200°C. These temperatures are much higher than the programmed temperatures which are typically from about 39°C to about 120°C. Given that the development of these high temperatures is sufficiently widespread, it is essential that any home dry cleaning system be able to function in such an environment.

A typical home dry cleaning system can comprise a substrate or carrier sheet, which contains various cleaning agents contained within a plastic bag. The garments to be cleaned are placed in the plastic bag, together with the substrate or sheet containing the solvents and the like, with the bag being sealed and then placed in a clothes dryer for tumbling at a temperature which will allow the cleaning solvents to penetrate the garments for removal of soiling and staining from, and for refreshment of the garments.

Under the circumstances, the plastic bag or package that is used for this dry cleaning operation must therefore be heat resistant, have barrier properties, be chemically resistant, be tough and durable enough to withstand multiple use applications, and not stick to the dryer surfaces or to itself, and remain integral in use. RELATED PRIOR ART

In U.S. Patent No. 5,681,355 issued October 28, 1997 to Davis et al, the disclosures of which are incorporated herein by reference, there is described a containment bag which uses heat resistant polymers, such as nylon, to avoid unanticipated hot spots in a clothes dryer. In this patent, there are numerous references to various patents which describe cleaning processes some of which are for use in a domestic clothes dryer. Suitable structures for the containment bag are shown in this patent. The containment bag may be constructed of a polymer which is either nylon or polyester or combinations thereof. This patent contains no information as to the exact nature of the nylon film used in constructing or in manufacturing the containment bag. However, the patent details the types of cleaning agents used, the substrates that may be employed to contain the cleaning agents, the type of fabric that may be subjected to the dry cleaning process, and the actual method of dry cleaning employing the bag. In U.S. Patent No. 5,547,476 issued August 20, 1996 to Siklosi et al, the disclosures of which are incorporated herein by reference, there is described a home dry cleaning process. In this instance, the containment bag is referred to as a flexible bag. In particular, the flexible container at col. 6, line 59 to col. 7, line 14 is described. The container should be large enough to contain the fabrics to be cleaned. It may be manufactured from any economical material such as polyester, polypropylene, and the like, with the proviso that it must not melt if used in contact with a hot air dryer. The walls of the container should be substantially impermeable to water vapour and solvent vapour under the intended use conditions and the package may be sealed by means such as strings or wires or various snap closures. ZIPLOC^® closures and NELCRO^® type closures are proposed, although contact adhesives, adhesive tape, zipper type closures and the like are also proposed. The container can be of any convenient size but should not be so large as to interfere with the operation of the dryer. In particular, it should not be so large as to block any air vents. At col. 10, line 29 further discussion of the bag is found. A nylon film is proposed as the material. The proposal is for using nylon only bags, or core extruded nylon and/or polyester or nylon and/or polyester outer and/or inner layers surrounding a less thermally suitable inner core such as polypropylene. It is also proposed that the bag be constructed using a non-woven outer shell comprising a heat resistant material such as nylon or polyethylene terepthalate and an inner sheet of a polymer which provides a vapour barrier. It is proposed that whatever the bag structure, it must be capable of retaining its integrity under conditions of thermal stress at temperatures up to at least about 204 °C to 260 °C. U.S. Patent No. 5,681,355 issued October 28, 1997 to Davis et al, the disclosures of which are incorporated herein by reference, describes a further home dry cleaning process which is conducted in a hot air clothes dryer using a containment bag. This patent describes the containment bag also and mentions the materials mentioned above, in particular the nylon and nylon combinations. In this instance, reference is also made to the thickness of the bag as ranging from about 1-3 mil thickness, although thicker sheets can be used if rigidity of the bag is desired. The size of the bag is such that the internal volume will range from about 10,000 to about 25,000 cm³. Other examples of containment bags for use in high temperatures environments are the type generally known as cook-in films or bags. Examples of such bags are found in U.S. Patents Nos. 3,995,084 issued November 30, 1976 to Berger et al, 4,855,183 issued August 8, 1989 to Oberle and 5,213,900 issued May 25, 1993 to Friedrich, the disclosures of which are incorporated herein by reference. These bags are somewhat different from the bags employed in a dry cleaning process, since they are not normally meant for multiple use, and are not closed in the same fashion as is required for a dry cleaning operation. In addition, because these bags come into contact with food, the regulatory requirements surrounding them dictate to a considerable extent the composition of the film used to manufacture the bags. However, it is to be noted that polyamide is frequently found in films of this type and these patents represent examples of such combinations.

To date the production of a self sealing polyamide film has proved to be problematic. In recent years formulations have been developed that have high resulted in films that may be used in high temperature applications and have good sealing properties. Examples of such films are found in the following documents.

In Ng and Farkas PCT Patent Application No. CA94/00667 filed December 7, 1994, the disclosure of which is hereby incorporated herein by reference, there is disclosed a heat-sealable polyamide film which may be used in multilayered structures for use in packaging. Generally these polyamides comprise at least one pendant alkyl branch having 1 to 3 carbon atoms within at least two amide linkages along the polymer backbone and at least one sequence of at least seven consecutive carbon atoms, excluding carbon atoms in pendant alkyl branches, if any, within at least two amide linkages along the polymer backbone. Specifically, they are referred to as low temperature Nylons (LTN).

In Saltman, U.S. Patent No. 5,091,478 issued February 25, 1992, the disclosure of which is hereby incorporated herein by reference, there are disclosed partially grafted flexible thermoplastic compositions formed by melt blending under high shear, a thermoplastic material having available graft sites, said thermoplastic material being at least one continuous phase of the composition, an ethylene copolymer containing an unsaturated mono-carboxylic acid, and a polymeric grafting agent having reactive groups capable of reacting with the mono-carboxylic acid in the ethylene copolymer and with the available graft sites in the thermoplastic material. These compositions have use in a wide range of molding, coating and adhesive applications, including various automotive applications, wire and cable coating applications and high temperature adhesive applications.

In Epstein, U.S. Patent No. 4,174,358 issued November 13, 1979, the disclosure of which is incorporated herein by reference, there is disclosed toughened multiphase thermoplastic compositions consisting of essentially one phase containing 60 to 99 percent by weight of a polyamide matrix resin of number average molecular weight of at least 5000, and 1 to 40 percent by weight of at least one other phase containing particles of at least one polymer having a particle size in the range of 0.01 to 3.0 microns and being adhered to the polyamide, the at least one polymer having a tensile modulus in the range of 1.0 to 20,000 psi, the ratio of the tensile modulus of the polyamide matrix to tensile modulus of said at least one polymer being greater than 10 to 1. The polymer is either branched or straight chain, but the nylon is conventional nylon. The toughened polymer is useful for making molded and extruded parts. In PCT Patent Application No. CA97/00200 filed March 24, 1997 in the name of Farkas, the disclosure of which is incorporated herein by reference, there is described a heat formable laminating film which is used to produce embossed laminates. The film is formed from a multiphase thermoplastic resin composition which may include low temperature nylon, the presence of which significantly improves heat sealability and formability of the resin formulation. It has now been found that some of the above disclosed formulations have particular utility in producing film for packages that are for use in high temperature environments. However, the films must be produced by modifying the typical production methods in order to control the crystallinity of the film so that it possesses the heat sealability. SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a film for manufacturing heat sealable packages for use in a high temperature environment, wherein the sealant layer or film comprises the following components: i) at least one polyamide resin selected from aliphatic and semi-aromatic polyamides that can be either semi-crystalline or amorphous in structure having a number average molecular weight of at least about 5000, having reactive sites and forming the continuous phase of the composition, wherein the semi- crystalline polyamides have a melting point greater than 200°C; ii) at least one ethylene copolymer, E/X/Y, where E is ethylene and is at least 50 % by weight of E/X/Y, X is from 1-35 % by weight of an acid containing unsaturated mono-carboxylic acid, and Y is 0-49 % by weight of a moiety derived from at least one alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof where the alkyl groups contain 1-12 carbon atoms, and further wherein the acid groups in the acid-containing moiety are neutralized by from 0-100% by weight of a metal ion; iii) at least one polymeric grafting agent which contains reactive groups selected from at least one of epoxides, isocyanates, aziridines, silanes, alkyl halides, alpha-halo ketones and aldehydes, or oxazoline, which reacts with the acid-containing moieties in component ii) and additionally react with the graft sites of component i), and the weight percent of the monomer(s) containing the reactive groups is 0.5-15 weight percent of the polymeric grafting agent, and the remainder of the polymeric grafting agent contains at least 50 % by weight of ethylene and from 0-49 % by weight of a moiety derived from at least one alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof where the alkyl groups contain 1-12 carbon atoms; and iv) at least one C₂-C₂₀ polyolefm selected from polyethylene, polypropylene, ethylene propylene diene terpolymer, copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof upon which are grafted from about 0.05 to about 5% by weight of monomers or mixtures of monomers selected from ethylenically unsaturated acidic monomers or their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5-norborene-2,3-dicarboxylic acid, maleic anhydride, monomethyl fumarate and monomethyl maleate; and from ethylenically unsaturated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4- vinyl pyridine, vinyltriethyloxysilane and allyl alcohol; the components being combined in accordance with one of the following formulation combinations:

A. from about 29 to about 54% by weight of component i), from about 8 to about 70% by weight of component ii), and from about 0.8 to about 45% by weight of component iii); B. from about 55 to about 90% by weight of component i), from about 10 to about 45% by weight of components ii) or iv) or mixtures thereof; and C. from about 30 to about 91 % by weight of component i), from about 1.5 to about 70% by weight of component ii), and from about 0.15 to about 45 % by weight of component iii).

The present films approach polyethylene films with respect to heat sealability, but their thermal stability is higher than polyolefin films. In addition, the heat sealing temperature window and forming window are sufficiently broad to permit their use in many commercial applications. Typically, the film for such uses would pass an oven test at 200°C for one hour. The film formulation may include additional optional ingredients selected from flame retardants, heat stabilizers, antioxidants, anti-blocking agents, slip additives, pigments or dyes, processing aids, plasticizers and ultra-violet blocking agents. Of these optional ingredients, most desired are heat stabilizers, antioxidants and flame retardants.

The amount of antioxidants, heat stabilizers and mixtures thereof that may be included in the film formulation may range from 0.05 to 5.0% by weight, more preferably, the range is from 0.05 to 2.0% by weight.

The flame retardant may comprise from about 1% to about 40% by weight of the total resin composition and is selected preferably from organic halogen based retardants, metal hydroxides, melamine chemistry based retardants, and red phosphorus can also be used in combination with a synergist to enhance flame retardancy. Synergists include antimony trioxide, zinc, borate, zinc stannate and powdered silicone are also preferably present. The selection of the synergist is based on the intended application. The amount of synergist may be about 10%, e.g. 2 parts flame retardant to 1 part synergist. More preferably, the flame retardant comprises from about 5% to about 30% by weight of the total resin composition.

In another aspect of the present invention, there is provided an improved method for producing a film wherein the formulation for the resin is as set out above and the resin is extruded and passed through a die to form a film or film layer and the film is optionally subjected to a print treatment, the improvement comprising a) intimately mixing the components of the resin formulation for the film to ensure thorough mixing and uniformity of melt blend; b) subjecting the film as it exits the die to quenching at a temperature as low as 20 °C to solidify the formulation to as low a crystallinity as possible; and c) reheating the solidified film to a temperature of from just above the quench temperature up to about 90 °C to increase its crystal structure in a controlled way in order to stabilize the film. The quenching occurs preferably at a temperature of about 30°C. Preferably the reheating occurs at a temperature of between about 50 °C to about 80 °C. In another aspect, the invention provides a package that may be used in a high temperature environment and is manufactured from a film having the formulation as set out above. The bag is heat sealed to itself along at least one of its sides and has an opening through which product to be packaged may be placed. The film could be produced as a flat web and then formed into a tube by using a lap seal. In this way only the bottom of the bag would be permanently sealed with the top or free end having a resealable closure, if desired, applied thereto. Alternatively, the bag could be made from a flat web that is folded in half on itself, with the side and one end being permanently sealed.

The opening of the bag may be sealed in any conventionally known manner. Thus it may be permanently sealed so that the bag requires destruction of the seal to open, or it may be provided with a closure that permits it to be opened and closed any number of times, thus allowing the package to be reused. The package may be sealed by means such as strings or wires or various snap closures. ZIPLOC^® closures and VELCRO^® type closures may be proposed, although contact adhesives, adhesive tape, zipper type closures and the like may also be employed.

In yet another aspect of the present invention, there is provided a single or multiple use heat resistant dry cleaning bag for use in a domestic clothes dryer for a dry cleaning operation, the bag being heat sealed to itself along at least one of its outer edges, and having a reclosable opening for placing items to be dry cleaned in the bag, the bag being formed from a film having a formulation as set forth above, and having barrier properties so as to permit dry cleaning substances to be placed therein and the bag may be tumbled in a domestic dryer for dry cleaning the items. The bag can be of any convenient size but should not be so large as to interfere with the operation of the dryer. In particular, it should not be so large as to block any air vents.

The film may be selected from films of suitable thickness such as, for example, 1 to 3 mils thick. The presence of the nylon in the film ensures that the bag has the required vapour and moisture barrier properties and is also chemically resistant to the cleaning substances that may be selected for incorporation into the bag. It is important that the closure have the same properties as the film used in the bag and this must be considered when selecting the type of closure for the bag. The bags can be manufactured using conventional bag manufacturing equipment or such equipment suitably modified.

The types of cleaning products and the substrates upon which they are placed or applied to are well known in the art and need not be described here as they do not form part of the present invention. The previously referenced patents contain these details.

In the following tables there are set out the various combinations of components that may comprise the different formulation combinations set out earlier.

Table I - Formulation A

* Any ratio may be used

Table πi - Formulation C

Please note that for all of the compositions listed for Formulation A, B and C, these are the starting formulations going into the extruder. Because of the various reactions that occur during melt processing, the composition of the film coming out of the extruder might not be exactly the same. For Formulation C, which is the blend of Zytel^® FN and conventional polyamide, and which encompasses preferred film examples, the following preferred formulations apply:

The broadest range encompasses blends of conventional nylon and Zytel^® FN with from 1 to 80% weight conventional nylon. The preferred range encompasses from 10 to 70 % weight of conventional nylon. The most preferred range encompasses from 30 to 60% weight of conventional nylon in the blend.

For the above formulations, it is important to note that the combination of the three components i) and ii) and iii) is such that the polyamide must be the continuous phase in the formulation. If the polyolefm phase is the continuous phase, then the film will have a low melting point.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are used to illustrate the present invention: Figures 1 to 3 illustrate DSC (Differential Scanning Calorimetry) curves for film used to make packages in accordance with the present invention; and

Figure 4 is a schematic representation of a cast film production line that may be used to manufacture the film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

COMPONENT i)

The polyamide of component i) embraces those semi-crystalline and amorphous resins having a number average molecular weight of at least 5000 and commonly referred to as nylons. Suitable polyamides include those described in U.S. Patents Nos. 2,071,250; 2,071,251; 2,130,523; 2,130,948; 2,241,322; 2,312,966; 2,512,606; and 3,393,210. The polyamide resin can be produced by condensation of equimolar amounts of an aliphatic or aromatic dicarboxylic acid containing from 4 to 12 carbon atoms with a diamine, in which the diamine contains from 4 to 14 carbon atoms. Excess diamine can be employed to provide an excess of amine end groups over carboxyl end groups in the polyamide. Examples of polyamides include poly hexamethylene adipamide (Nylon 66), polyhexamethylene azelaamide (Nylon 69), polyhexamethylene sebacamide (Nylon 610), and polyhexamethylene dodecanoamide (612 Nylon), the polyamide produced by ring opening of lactams, i.e., polycaprolactam, polylauric lactam, poly-11-aminoundecanoic acid, bisφaraaminocyclohexyl) methane dodecanoamide. It is also possible to use in this invention polyamides prepared by the copolymerization of two of the above polymers or terpolymerization of the above polymers or their components, e.g., 6T/DT, a copolymer of terephthalic acid (T) and 2-methylpentamethylenediamine (D) and hexamethylenediamine (6). Preferably the polyamides are semi-crystalline and aliphatic or semi-aromatic with a melting point in excess of 200?C, or they are amorphous.

Preferred polyamides include Nylon 6,6, Nylon 6, Nylon 612, Nylon 11, Nylon 12, Nylon 1212, amorphous nylons, Nylon 6/6,6 copolymers.

Most preferred polyamides include Nylon 6,6, Nylon 612 and Nylon 6. It is to be understood that this component may comprise blends of two or more nylons. COMPONENT ii) Suitable ethylene copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methyaorylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylaic acid/n- butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/ethyl vinyl ether, ethylene/methacrylic acid/butyl vinyl ether ethylene/acrylic acid/-methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, ethylene/acrylic acid/n- butyl methacrylate, ethylene/methacrylic acid/ethyl vinyl ether and ethylene/acrylic acid/butyl vinyl ether.

Preferred ethylene copolymers that contain a monocarboxylic acid moiety for use in the compositions of the present invention include ethylene/methacrylic acid, ethylene/acrylic acid, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate and ethylene/acrylic acid/methylacrylate copolymers. The most preferred ethylene copolymers for use in the compositions of the present invention are ethylene/methacrylic acid, ethylene/acrylic acid copolymers, ethylene/methacrylic acid/n-butyl acrylate and ethylene/methacrylic acid/methylacrylate terpolymers.

Surlyn® is an example of a suitable commercially available product. Zinc- neutralized Surlyn® is preferred for nylon over sodium-neutralized Surlyn®. COMPONENT iii)

These polymeric grafting agents include ethylene copolymers copolymerized with monomers containing one or more reactive moieties said monomers selected from unsaturated epoxides of 4-11 carbon atoms, such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, vinyl glycidyl ether, and glycidyl itaconate, unsaturated isocyanates of 2-11 carbon atoms, such as vinyl isocyanate and isocyanato-ethyl methylacrylate, aziridine and monomers containing, silanes such as alkoxy or alkyl silanes, alkylating agents such as alkyl halides, or alpha-halo ketones or aldehydes or oxazoline, and the polymeric grafting agent may additionally contain an alkyl acrylate, alkyl methacrylate, carbon monoxide, sulfur dioxide and/or alkyl vinyl ether, where the alkyl groups contain 1-12 carbon atoms.

Preferred polymeric grafting agents for use in the compositions of the present invention include ethylene/glycidyl acrylate, ethylene/n-butyl acrylate/glycidyl acrylate, ethylene/methylacrylate/glycidyl acrylate, ethylene/glycidyl methacrylate, ethylene/n-butyl acrylate/glycidyl methacrylate and ethylene/methylacrylate/glycidyl methacrylate copolymers. The most preferred grafting agents for use in the compositions of the present invention are copolymers derived from ethylene/n-butyl acrylate/glycidyl methacrylate and ethylene/glycidyl methacrylate.

It should be noted that the level of reactive component e.g. glycidyl methacrylate will affect the degree of crosslinking with the nylon, and may be adjusted appropriately to the desired level as known by those skilled in the art. COMPONENT iv)

The graft monomers, and mixtures thereof, used to prepare the graft polymers can be selected from the group consisting of ethylenically unsaturated acidic monomers or their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5-norbornene-2,3- dicarboxylic acid, maleic anhydride, monosodium maleate, disodium maleate, itaconic anhydride, citraconic anhydride, monomethyl fumarate and monomethyl maleate. Also, the graft monomers can be selected from ethylenically unsaturated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4- vinyl pyridine, vinyltriethoxysilane and allyl alcohol. The grafting monomers, and mixtures thereof, can be present in the graft polymer in an amount of from 0.05 to 5% wt. and would be grafted onto a C₂-C₂₀ polyolefm including polyethylene, polypropylene, ethylene propylene diene terpolymer, as well as copolymers of ethylene with, but not limited to, vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof.

This component acts as an alternative toughener in the formulation. Grafted polyethylene, grafted polypropylene, and grafted rubber, may be used as noted earlier, and these may be used in combination with non-grafted polyethylenes, polypropylenes and rubbers. This component may be used interchangeably with component ii) in Formulation B. FILM FORMATION

The heat-sealable polyamide film may be formed by a cast film process or by a blown film process. Both types of film processes are known in the art of manufacture of polyamide films. Furthermore, the film may be a monolayer film or a multilayer film, the film being for example an extrusion coated, a coextruded film or a laminate. Either the monolayer film or the coextruded film may be in an unoriented condition, in the form of monoaxially oriented film or in the form of biaxially oriented film. It will be understood by persons skilled in the art that the properties of such polyamide films will depend on several factors including, but not limited to, extruder hold-up time and screw design, melt processing temperature, quenching rate and degree of quenching, film thickness, the amount of and type of additional components, as well as the amount of and type of the particular polyamide as described herein.

The polyamide resins described herein may also be coextruded or laminated with polyolefins or grafted polyolefm, particularly polyethylene, grafted polyethylene or grafted polypropylene, especially using tie or adhesive layers between the polyamide and polyolefm. The heat-sealable polyamide films may be laminated to polyolefins or other barrier polymers using conventional processes. In addition, the heat-sealable polyamides may be coated with poly vinylene dichloride (PVDC), EVOH, PVOH or other suitable barrier coatings and then laminated to itself to form a higher barrier heat-sealable structure. BLENDING OF FORMULATION COMPONENTS

The compositions of the present invention, especially when in the form of layers e.g. films or sheets, may be treated with a corona discharge (ED) in order to improve the properties of the resins with respect to bonding of coatings, inks, adhesives or the like. In addition, the additives such as, but not limited to, moisturizing agents, heat stabilizers, flame retardants, fillers, anti-blocking agents, slip additives, pigments or dyes, processing aids, anti-oxidants, plasticizers or ultra violet blocking agents may be melt blended with each other under high shear. The various ingredients may first be combined with one another in what is commonly referred to as a "salt and pepper" blend, i.e., a pellet blend, of each of the ingredients, or they may be combined with one another via simultaneous or separate metering of the various components, or they may be divided and blended in one or more passes into one or more sections of mixing equipment such as an extruder, Banbury, Buess Kneader, Ferrell continuous mixer, or other mixing equipment. For example, one can use an extruder with two or more feed zones into which one or more of the ingredients may be added sequentially. In this case, it is sometimes advantageous that the thermoplastic and polymeric grafting component be combined first, then the acid-containing copolymer be added downstream. This helps promote the grafting reaction(s) between the thermoplastic and polymeric grafting components, prior to the reaction(s) between the polymeric grafting component and acid-containing copolymer. However, the order of addition is such that the components ii) and iii) would never be added to the extruder without the nylon, as otherwise, a crosslinked non-extrudable material would result. The high shear insures proper dispersion of all the components such as would be necessary to carry out the grafting reaction. In addition, sufficient mixing is essential to achieve the morphology which is necessary in the compositions of the present invention. The morphology required for the compositions of the present invention is that at least one of continuous phases must be the thermoplastic, i.e., component i). Note that the thermoplastic, component i), is at least one of the continuous phases in all of the compositions of the present invention even though the thermoplastic, component i) comprises less, and in fact, in some cases substantially less than 50 volume %.

In the following examples, there are described embodiments of the invention, which are for illustrative purposes only. These should not be used to limit the scope of the appended claims. EXAMPLE

Seven films (four films without flame retardant and three with flame retardant) were produced in accordance with the present invention. These are all C formulations as will be apparent. All films are 3mil thickness. All the films were formed to heat seal well on conventional heat seal equipment and all the films had strong, tough seals. Film Formulation:

The films were made from a Zytel™ FN727 resin and a Nylon 6 resin mixture in the following combinations:

Film #1: 60% / 40% Zytel™ FN727 resin / Nylon 6 resin mixture Film #2: 70% / 30% Zytel™ FN727 resin / Nylon 6 resin mixture

Film #3: 50% / 50% Zytel™ FN727 resin / Nylon 6 resin mixture Film #4: 40% / 60% Zytel™ FN727 resin / Nylon 6 resin mixture Film #5: 50% / 50% with 9% by weight flame retardant mix (6% BPS and 3 % antimony trioxide) Film #6: 50% / 50% with 18% flame retardant mix 12% by weight BPS* and 6% by weight Antimony Trioxide (flame retardant mix)

Film #7: 50% / 50% with flame retardant 12% BPS flame retardant * BPS is brominated polystyrene flame retardant. A commercial example is FERRO PYROCHEK™ 68PB. The antimony trioxide is AMPSEC. Zytel™ FN727 is a DuPont toughened heat stabilized Nylon 6 based resin.

Other resins in the Zytel™ family some of which are Nylon 6,6 based are also considered to be useful in the present formulations.

The DSC results shown in the accompanying Figures 1 to 3 are for the film of Sample Film #4. Referring to Figure 4, there is illustrated a cast filmline shown generally at 1 that represents the preferred method for producing the film la of the invention. The cast film line comprises a twin screw compounding extruder 12 which achieves an intimate mixture of recipe components delivered to the extruder 12 from hopper 10 and feeder 11. This intimate mixing can be achieved in other ways usually involving separate steps, which can be more costly and time corisuming. Next is a melt pump 12a, a filter 13, a die 14, an ultra low temperature quench roll 15 which helps to achieve the desired amorphous structure. The annealing roll 16 follows, to heat treat the film la to control the level of crystallinity. The final quench roll 17 reduces the film temperature to room temperature for final windup on winder 33. Slit device 20 allows the film to be edge trimmed to a suitable width or slit as required. Pull roll 31 maintains tension, through the line prior to final windup, after which the cross web Beta Gauging System 18 provides the data for cross web die profile correction. The steam cabinet 19 provides an optional process to stabilize moisture content in the film. Finally the high energy corona print treatment 29 makes the film more receptive to printing inks and laminating adhesives. The resin recipe of the present invention inhibits crystal growth and in combination with the film process forms a film with a low initial crystallinity. The resulting film heat seals easily and makes a tough, strong and durable heat seal that allows production of a bag for use in high temperature environments. The following Tables IV and N are included to provide some comparison between the properties of the films of the present invention and standard polyamide films such as Nylon 6 and Nylon 6,6.

TABLE IV

Typical Physical Properties (25/t Film) for Nylon 6 and Nylon 6,6

All of these properties were measured using standard ASTM methods as noted.

* DSC method is not an ASTM method. Heat sample from room temperature to 290 °C isothermally for 5 minutes. Cool down sample to room temperature at a ramp rate of 10°C/minute. Then hold the sample at room temperature for 5 minutes. Then increase temperamre again up to 290 °C at same ramp rate. This provides data for DSC.

TABLE V SUMMARY OF FILM SAMPLE PROPERTIES

TABLE VI SUMMARY OF DSC TESTS FOR FILM SAMPLES

DISCUSSION OF TEST DATA FOR HEAT SEALABLE NYLON FILM OF THE PRESENT

INVENTION

DSC CURVES

Table VI sets out the data that is plotted in Figures 1 to 3. Each sample has 3 data curves

1) Initial Heating a) Melting point b) And energy required to melt.

2) Cooling From The Melt a) Crystallization temperature b) Energy dissipated on crystallization

3) Reheating The Sample a) Melting Point b) Energy required to melt the second time The tabulated DSC data shows all 6 data points for the sample.

The very first thing to notice about the data is that the melting energy per unit weight for pure nylon 6 and pure nylon 6,6 is very much larger than for the Film Samples (#1 through #7) of the present invention. The pure nylon films do not heat seal well because of their inherent crystallinity and brittleness.

PHYSICAL PROPERTY DATA

The data shows that the lower crystallinity films also have: a) Lower modulus of elasticity b) Higher elongation to break These properties are considered to be desirable in films for the intended application. HEAT SEAL TESTING OF FILM SAMPLES

These DSC's show that the major melting peak is the nylon peak, even when other components are present. If this were not so, this could cause the film to stick to itself or other surfaces during use when manufactured into a bag for use in high temperature environments.

The heat sealing properties of the various film samples produced were tested using a Vertrod Impulse Sealer

The two parameters that can be controlled on this tester are the "Dwell Time" (i.e. the amount of time the electric impulse is applied to the material) and the amount of "Heat" (electric impulse) applied. On the Vertrod Sealer both parameters are controlled by way of calibrated knobs and in our test the knobs were set at predetermined values and each sample sealed at those conditions.

The strength of the obtained seals were then checked using an Instron. The values obtained when setting Dwell Time and Heat at the chosen values are listed in the Table (expressed in g/1").

TABLE VII

The essence of the method of the present invention resides in the following steps of the method: The 3 roll process with the annealing roll is unique in the cast film industry.

The annealing temperature is used in combination with the cast temperature to achieve the unique physical properties of the film of the invention.

In its most preferred form, the formulation for the film comprises a total polyamide component of Nylon 6 that may range from about 70 to about 95 % by weight, more preferably 80 to 90% by weight. The ethylene copolymer may comprise from about 7.5% to about 20% by weight, more preferably about 3.75% to about 15% by weight. The polymeric grafting component may comprise from about 1.25% to about 10% by weight, more preferably about 2.5% to about 5.0% by weight. The invention may be varied in any number of ways as would be apparent to a person skilled in the art and all obvious equivalents and the like are meant to fall within the scope of this description and claims. The description is meant to serve as a guide to interpret the claims and not to limit them unnecessarily.

Claims

WE CLAIM:

1. A film for manufacturing heat sealable packages for single or multiple use applications in a high temperature environment, wherein the sealant layer or film comprises the following components: i) at least one polyamide resin selected from aliphatic and semi-aromatic polyamides that can be either semi-crystalline or amorphous in structure having a number average molecular weight of at least about 5000, having graft sites and forming the continuous phase of the composition, wherein the semi-crystalline polyamides have a melting point greater than 200°C; ii) at least one ethylene copolymer, E/X/Y, where E is ethylene and is at least 50 % by weight of E/X/Y, X is from 1-35 % by weight of an acid containing unsaturated mono-carboxylic acid, and Y is 0-49 % by weight of a moiety derived from at least one alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof where the alkyl groups contain 1-12 carbon atoms, and further wherein the acid groups in the acid-containing moiety are neutralized by from 0-100% by weight of a metal ion; iii) at least one polymeric grafting agent which contains reactive groups selected from at least one of epoxides, isocyanates, aziridines, silanes, alkyl halides, alpha- halo ketones and aldehydes, or oxazoline, which reacts with the acid-containing moieties in component ii) and additionally react with the graft sites of component i), and the weight percent of the monomer(s) containing the reactive groups is 0.5-15 weight percent of the polymeric grafting agent, and the remainder of the polymeric grafting agent contains at least 50 % by weight of ethylene and from 0-49 % by weight of a moiety derived from at least one alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof where the alkyl groups contain 1-12 carbon atoms; and iv) at least one C₂-C₂₀ polyolefm selected from polyethylene, polypropylene, ethylene propylene diene terpolymer, copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof upon which are grafted from about 0.05 to about 5% by weight of monomers or mixtures of monomers selected from ethylenically unsaturated acidic monomers or their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5-norborene-2,3-dicarboxylic acid, maleic anhydride, monomethyl fumarate and monomethyl maleate; and from ethylemcally unsatorated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4- vinyl pyridine, vinyltriethyloxysilane and allyl alcohol; the components being combined in accordance with one of the following formulation combinations:

A. from about 29 to about 54% by weight of component i), from about 8 to about 70% by weight of component ii), and from about 0.8 to about 45% by weight of component iii);

B. from about 55 to about 90% by weight of component i), from about 10 to about 45% by weight of components ii) or iv) or mixtures thereof;

C. from about 30 to about 91 % by weight of component i), from about 1.5 to about 70% by weight of component iii), and from about 0.15 to about 45% by weight of component iv); thereof, with the proviso that a flame retardant is always present.

2. The film as claimed in Claim 1 wherein additional optional ingredients are present selected from antioxidants, heat stabilizers, flame retardants, anti-blocking agents, slip additives, pigments or dyes, processing aids, plasticizers, ultra-violet blocking agents and mixtures thereof.

3. The film as claimed in Claim 1 wherein the amount of antioxidants, heat stabilizers and mixtures thereof ranges from 0.05 to 5.0% by weight.

4. The film as claimed in Claim 3 wherein the range is from 0.05 to 2.0% by weight.

5. The film as claimed in Claim 1 wherein the flame retardant comprises from about 1% to about 30% by weight of the total resin composition and is selected from organic halogen based retardants, metal hydroxides, melamine chemistry based retardants, and red phosphorus.

6. The film as claimed in Claim 5 wherein the flame retardant comprises from about 1% to about 5% by weight of the total resin composition.

7. An improved method for producing a packaging film as claimed in claim 1 wherein the formulation is extruded and passed through a die to form a film or film layer and the film is optionally subjected to a high energy Corona print treatment, the improvement comprising a) intimately mixing the components of the resin formulation to ensure thorough mixing and uniformity of melt blend; b) subjecting the melt to quenching at a temperature as low as 20 °C to solidify the formulation to as low a crystallinity as possible; and c) reheating the solidified film to a temperature of from above the quench temperature about 90 °C from the die to increase its crystal structure in a controlled way in order to stabilize the film.

8. The method as claimed in claim 7 wherein the quenching occurs at a temperature of about 30°C.

9. The method as claimed in claim 8 wherein the reheating occurs at a temperature of between about 50 °C to about 80°C.

10. A package that may be used in a high temperature environment and is manufactured from a film formulation as claimed in Claim 1, the bag being heat sealed to itself along at least one of its sides and having an opening through which product to be packaged may be placed.

11. The package as claimed in Claim 10 wherein the bag is for multiple use and includes a reclosable closure at its open end.

12. The film as claimed in claim 1 wherein the formulation comprises from about 30 to about 91% by weight of conventional polyamide; from about 1.5 to about 70% by weight of E/X/Y ethylene copolymer; and from about 0.15 to about 45% by weight of polymeric grafting agent and the polyamide is the continuous phase.

13. The film as claimed in claim 1 wherein the formulation comprises from about 38 to about 86% by weight of conventional polyamide; from about 5.5 to about 59% by weight of E/X/Y ethylene copolymer; and from about 1 to about 28% by weight of polymeric grafting agent and the polyamide in the continuous phase.

14. The film as claimed in claim 1 wherein the formulation comprises from about 52 to about 84% by weight of conventional polyamide; and from about 2 to about 14.5% by weight of polymeric grafting agent and the polyamide is the continuous phase.

15. A single or multiple use heat resistant, chemical resistant, vapour and liquid barrier dry cleaning bag for use in a domestic clothes dryer for a dry cleaning operation, the bag being heat sealed to itself along at least one of its outer edges, and having a reclosable opening for placing items to be dry cleaned in the bag, the bag being formed from a film having a formulation as claimed in Claim 1, the bag may be tumbled in a domestic dryer for dry cleaning the items.