JPH06210810A - Multilayer film capable of back seaming - Google Patents

Abstract

PURPOSE: To generate a backseamed skin by providing a heat sealing layer containing a blend of a specific wt.% of a copolymer based on propylene and a specific wt.% of a uniform ethylene/α-olefin copolymer having specific density to perform molding. CONSTITUTION: A thermoplastic film fitted to cook-in packaging has an inner sealing layer, a food contact layer, a nylon layer and an outside layer or an inner sealing layer, a food contact layer, a nylon layer, a barrier layer and an outside layer. The heat sealing layer of the inner sealing layer and the contact layer comprises a blend consisting of about 50-95 wt.% a copolymer based on propylene and about 5-50 wt.% of a uniform ethylene/α-olefin copolymer having a density of below about 0.9 g/cc. Since the thermoplastic film is biaxially oriented, it shrinks during cooking to be closely fitted to food and elastic recovery characteristics are applied by the nylon layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The field of this invention is bags and casings that exhibit improved structural integrity as well characterized as "cook-ins".
Is a packaging film for producing. As used herein, the term "cook-in" is intended to describe a packaging material that is structurally resistant to exposure to time-temperature conditions while containing food.

The present invention relates generally to thermoplastic films suitable for cook-in packaging, and more particularly to food cook-in films. These films may exhibit food contact surface properties that promote bond adhesion to the food products contained therein during cook-in. The films of the present invention exhibit improved heat and cold seal strength, improved optical properties, and are easier to process than known films. The invention is particularly backseamed (ba
ckseamed) intended to be a jacket.

[0003]

BACKGROUND OF THE INVENTION Cook-in packaged foods essentially include foods that are cooked in a package, where they are consumed after they have been delivered to a consumer and are then consumed without heating. obtain. Cook-in time temperature conditions typically represent long, slow dishes, for example about 5
It represents immersion in hot water at 5 to about 65 ° C. for about 1 to about 4 hours. These conditions are representative of customary cooking requirements. About 70 ° C to about 10 for about 12 hours
Soaking at 0 ° C represents the limit. Under such conditions, the cook-in packaging material must retain the integrity of the seal, i.e. any heat s
Ealed seams should also be resistant to being torn off during cook-in. This film also
There is a need for itself to be heat sealable, and the packaging film should essentially be compatible with the food product it contains. Preferably, this intrinsic compatibility is achieved by the film exhibiting a heat shrinkage which results in a tightly packed package under the above conditions, i.e. the film is subjected to such time-temperature conditions. It should be heat shrinkable and should have sufficient shrink energy so that when the packaged food is submerged in hot water, the packaging film shrinks snugly around the product contained therein. Yes, and in particular, should have a uniaxial and / or biaxial shrinkage rate of up to about 55%.

The film also limits the "cook-out" or collection of juice during cooking in between the food product contained therein and the food contact surface of the packaging material. May exhibit food adhesion, which increases product yield by. More specifically, in a multilayer film of the type in which the first "sealing and food contact" layer in the cook-in is made of a type of material that adheres to the food product it is contained, this first layer is an alternative. Can be referred to as an "adhesive layer". As used herein, the term "adhesion" is sufficient to prevent the food-contacting surface of the film from becoming substantially intrinsic during the cook-in to prevent fluid buildup between the film and the products contained therein. Is intended to mean to bind to the food contained in.

US Pat. No. 4,469,742 to Oberle et al.
A heat-shrinkable cook-in film is described, which comprises a first "sealing or food contact" layer consisting of a non-lipophilic polymeric material having a higher softening point than that of the next shrink layer; this first layer A second layer consisting of a homopolymer or copolymer of ethylene melt-bonded to; a third or adhesive layer melt-bonded to this second layer, which is radiation-crosslinkable and compared to the next barrier layer. A chemically modified polyethylene having functional groups exhibiting a strong affinity); a fourth or barrier layer composed of a copolymer of hydrolyzed ethylene and vinyl acetate melt-bonded to this third layer A fifth or adhesive layer the same as the third layer melt bonded to the fourth layer; and a sixth or abuse layer melt bonded to the fifth layer. In one embodiment, this first "sealing and food contact" layer is a metal salt neutralized ionomer, a copolymer of olefins and carboxylic acids, a typical example of which is meat contained therein during cook-in. It is Surlyn (TM), a type of material that adheres to products.
This Surlyn (TM) layer also functions as a layer that adheres to proteins. In another embodiment, the sealing layer is a propylene-ethylene random copolymer containing 1 to 6 wt% ethylene. This patent also discloses a method of making a film that involves total co-extrusion and selective irradiation and orientation.

[0006] A common method for producing heat-shrinkable films, as described by Oberle et al., Uses a tubular orientation method, in which a bubble is created to create an internal pressure to produce a lateral pressure. The first tube of the film is biaxially oriented by stretching in the direction and stretching in the machine direction by using pinch rolls of different speeds. The films of the present invention can be easily oriented with minimal and sometimes no bubble breakage during orientation. The latter is then used to produce bags, for example, by flattening the seamless tubular film by collapsing the stretched bubble to flatten it, for example, typically flattening the tubular article. An end-seal bag is manufactured by transversely heat-sealing the width of an object such that the lateral seal of the tubing forms the bottom of the bag, or Heat seals form the sides of the bag and one edge of the tubing forms the bottom of the bag. The bags are typically filled with food in the bag, degassed the bag, and heat sealed the mouth of the bag or put the mouth of the bag together, It is used by attaching a metal clip around the mouth of this combined bag to create a seal. Alternatively, the collapsed tube may be divided into one film or two or more films depending on the desired width. The film may then be folded longitudinally around a forming shoe and the opposite ends joined as a lap seal to produce a backseamed jacket. This backseamed jacket is used when, due to process limitations, it is not possible to produce an oriented tube, or a diameter that is small enough for a given cook-in application. Is often desired. However, the overlying seals of the jacket require that the inner layer (optionally an adhesive layer) of the cook-in material be heat sealable to its outermost layer. Such required sealing compat
Compatibility is most easily achieved by providing inner and outer layers having the same chemical composition. However, as long as the individual compositions exhibit sufficient compatibility to produce peel resistant seals under severe cook-in conditions,
These inner and outer layers need not be the same.
The production of backseamed tubing with the film may be a continuous or intermittent process. With this intermittent method,
The film is typically sealed to produce tubing having the length required for a given end use application, followed by transverse cutting. By indexing the film forward and repeating the sealing and cutting steps, a set of tubular jackets with the desired diameter and length is obtained. One end of these jackets is clipped and then stuffed and the opposite end is clipped, or they are similar to the manufacture of bags from seamless tubing. Alternatively, it may be treated by heat sealing. Alternatively, it is also possible to use an interrupted method that results in a continuous tube, as long as the independently created seals have at least some overlap. In the continuous method, the entire length of the film is sealed to produce a continuous tube, which is then clipped, stuffed and then clipped.

The cook-in tubing, whether seamless or back-seamed, may be pleated, ie folded or unfolded to provide a relatively short length. The handling may be facilitated during the packing. Regardless of the method of manufacture, the bag or jacket is then placed at about the same temperature as the film was stretched and oriented, typically about 160 to 2
Immerse in hot water of 05 degrees F (61 to 96 ° C),
This hot water dip is one of the fastest and most economical means of transferring sufficient heat to the film to shrink it uniformly. Alternatively, the bag, film or jacket may be used as a liner in a cooking mold.

Schirmer US Pat. No. 4,606,922
Adhesive plastic cook-in packaging, eg jacket,
And a method for enhancing the yield of cooked-in packaged meat products is described. The method comprises a cohesive cook-in container that includes a soft thermoplastic casing that is inherently compatible with the meat product contained therein and that has an internal meat-contacting surface made of selectively irradiated ionomer. First, and then adapting the container around the meat product of choice to cook the packaged product, at which time the interior surface of the casing is applied to the meat product. The bonding essentially prevents the fluid from being cooked out.

Thompson US Pat. No. 4,411,919
Disclosed are soft plastic cook-in packages that adhere, as well as methods of enhancing the yield of cook-in packaged meat products. The method involves providing a cohesive cook-in package that includes a flexible plastic container that is essentially compatible with the meat product of choice and that is provided with a meat product contacting surface composed of polymeric olefins. The meat product in the cook-in is subjected to an energy-radiating surface treatment in the presence of oxygen sufficient to adhere its internal surface to the container, which container is hot bl
own) made from tubular film. After the packaging is fitted around the meat product of choice, the packaged product is cooked, at which point it is essential that the fluid be cooked out by adhering the interior surface to the meat product. To prevent.

Erk et al., US Pat. No. 4,303,711, for packaging of a biaxially stretched plastic material for packaging and encasing paste type foodstuffs which are heated after packaging or packaged in a hot fluid state. And tubular films for jackets are described. This film has at least 1
A mixture of about 50-99 parts by weight of an aliphatic polyamide and about 1-50 parts by weight of one or more members of the group consisting of ionomer resins, modified ethylene vinyl acetate copolymers and modified polyolefins.

US Pat. No. 4,601,929 to Erk et al. Relates to a single layer of polyamide film for packaging and encasing foodstuffs in paste form, especially foodstuffs that are packaged hot or subjected to post-packaging heat treatment. .

US Patent No. 4,568,580 to Ghiradello et al.
Relates to a product for packaging food products comprising a first film part provided with at least one surface comprising a copolyamide obtained by random copolymerizing at least two different polyamide precursor monomers. is there. This product includes a second film portion comprising a film having a surface containing the above-described copolyamide, and at least one heat weld between the copolyamide surfaces of the first film portion and the second film portion. . The product should be at 70 ° C to 120 ° C for at least 10 minutes without damage from this heat welding.
Can withstand heat treatment at temperatures of.

Oberle US Pat. No. 4,855,183 discloses a cook-in film provided with a first food contact layer comprising a polyamide composition.

Oberle US Pat. No. 4,762,748 discloses a cook-in shrink film characterized by having an ethylene alkyl acrylate copolymer in the core and overuse layers, the adhesive layer, or both. There is. The sealing layer is selected from the group consisting of propylene ethylene copolymers, ionomers, blends of low density linear polyethylene and ionomers, and blends of low density linear polyethylene and ethylene acrylic acid copolymers.

Schirmer US Pat. No. 4,448,792 describes
A cook-in shrink bag provided with a sealing and food contact layer consisting of a propylene homopolymer or copolymer, preferably a low ethylene content propylene ethylene copolymer, is described. The core layer adjacent to the sealing layer is a blend of propylene homopolymers or copolymers. Also, a barrier layer,
It has an overuse layer and an adhesive layer sandwiching this barrier layer.

Oberle US Pat. No. 4,879,124 describes a perforated cook-in shrink bag. Suitable materials for this sealing layer include ethylene-acrylic acid copolymers, ethylene methacrylic acid copolymers, ionomers, and blends of the above.

Schirmer US Pat. No. 4,608,302 describes
Oriented films derived from propylene copolymers and unplasticized Saran suitable for use in packaging prepared foods are disclosed. The core layer may consist of an ethylene vinyl acetate copolymer having a vinyl acetate content of 10 to 12% by weight and a fractional melt index. The core layer is a homopolymer or copolymer of propylene (which may be a copolymer of propylene and ethylene)
Adjacent to the sealing layer is.

Bekele US Pat. No. 4,909,726 describes an impact resistant film for chub packaging.
The various layers may include a polymeric material having a fractional melt index.

Mueller, US Pat. No. 4,977,922, describes a barrier stretch film with at least one interior layer which may consist of an ethylene vinyl acetate copolymer having a fractional melt index.

Schirmer US Pat. No. 4,937,112 describes
A core comprising an olefin sealing layer and a polymeric material adjacent to the sealing layer having a high molecular weight and a fractional melt index selected from the group consisting of high density polyethylene, low density polyethylene and ethylene vinyl acetate copolymer. Chub wrapping films with layers are described.

US Pat. No. 4,495,24 issued to Ohya et al.
9 is a multilayer laminated film with a core layer of hydrolyzed ethylene-vinyl acetate copolymer and two outer layers of a mixture of copolymers of ethylene and vinyl acetate and copolymers of propylene and ethylene or low density linear polyethylene. Is disclosed. The multilayer laminated film of this document allows it to exhibit heat-shrinkability and it exhibits gas barrier properties.

US Pat. No. 4,182,457 (Yamada et al.) Discloses a container provided with a core of EVOH, an adhesive layer, and an additional layer of, for example, polypropylene or ethylene propylene copolymer.

US Pat. No. 4,511,610 (Yazaki et al.) Discloses a container with a core of EVOH, an adhesive layer, and an additional layer of, for example, polypropylene or ethylene propylene copolymer.

US Patent No. issued to Christensen et al.
4,405,667 is clearly a low density linear polyethylene heat seal layer, a second layer consisting of a blend of low density linear polyethylene and a propylene ethylene copolymer, any third, fourth and fifth consisting of a propylene ethylene copolymer. Layer, sixth layer made of anhydride modified polypropylene, seventh layer made of nylon, EVO
A retortable pouch comprising an eighth layer of H and a ninth layer or nylon is disclosed.

US Patent No. 4,532,1 issued to Mueller
89 discloses a shrink film with two skin layers, each containing, for example, a blend of polypropylene and an ethylene propylene copolymer.

Also of interest is US Pat. No. 4,400,428 issued to Rosenthal et al.
A multi-layer comprising a gas barrier layer consisting of a hydrolyzed ethylene vinyl acetate copolymer, a layer adjacent to this base film and a heat-sealable outer layer which may be, for example, a modified propylene / ethylene copolymer. Disclosed is a composite film comprising a biaxially oriented polypropylene based film (BOPP) laminated on at least one surface having a structure.

EPO Patent Application No. 0149321 discloses a gas barrier layer consisting of a copolymer of vinylidene chloride, an outer layer consisting of a polyolefin such as ethylene propylene copolymer, polypropylene and mixtures thereof, at least one intermediate layer consisting of a polyamide, and A heat-shrinkable tubular film is disclosed that comprises an adhesive layer disposed between any of the layers.

British Patent Application GB 2,139,948A includes a surface layer of heat-sealable polymer, eg LLDPE blended with low density linear polyethylene or other polymers such as EVA, and an EVOH layer. A multilayer, preferably coextruded, fiber-layer heat-sealable film with a layer of polypropylene is disclosed. These layers may be adhered with a polymer adhesive tie layer.

British Patent Application GB 2,221,649 contains 70-1
An improved core layer comprising a copolymer of propylene with a beaker softening point of 10 ° C. and one or more alpha olefins, and two outer layers comprising a crystalline polypropylene resin having a melting point of 135-150 ° C. Composite films are disclosed that exhibit excellent heat shrink properties.

EPO Patent Application No. 435498-A is intended for a heat-shrinkable multilayer film provided with a heat sealing layer which is a copolymer of propylene and at least two other alpha-olefins.

Japanese patent application 3063133-A is intended for a heat-shrinkable multilayer film provided with at least one layer which is a blend of an aliphatic polyamide and an amorphous polyamide.

Japanese patent application 3121842-A describes polyamide /
It is intended for a packaging material that includes an inner layer that is a blend of polyethylene.

German patent application 3943024-A is intended for a single layer jacket which is a blend of nylon 6 and copolyamide.

Therefore, one object of the present invention is to provide a novel cook-in film which is easily biaxially oriented.

A still further object of the present invention is a novel cook exhibiting improved biaxial orientation as a tube, using a bubble-forming means with essentially minimal or no bubble breakage. To provide in-film.

A still further object of the present invention is to provide a method of making the above novel cook-in film whose sealing layer comprises a blend of a propylene-based copolymer and an ethylene alpha-olefin copolymer. is there.

A still further object of the present invention is to provide a method of making the above novel cook-in film wherein the outermost layer comprises a blend of a propylene-based copolymer and an ethylene alpha-olefin copolymer. .

Yet another object of the present invention is to provide a cook-in film that exhibits good elastic recovery to give a dense packaging appearance.

A further object of the present invention is to provide a cook-in film which can be molded to produce a backseamed envelope.

Some of the additional objects and advantages of the invention are set forth in the following description, and in part will be apparent to those skilled in the art from this description or practice of the invention. Can be mastered in. The objects and advantages of the invention may be realized and attained by means of the methods and combinations particularly pointed out in the appended claims.

[0041]

SUMMARY OF THE INVENTION In addition to these objects, another object is to provide a homogeneous ethylene alpha-copolymer in which the propylene-based copolymer is from about 50 to about 95% by weight and has a density of less than about 0.90 g / cc. This is accomplished by providing a heat-shrinkable multilayer film with a heat sealing layer of the blend where the olefin copolymer is about 5 to about 50% by weight. The above objects are further achieved by providing said film with at least one layer comprising a polyamide, a copolyamide, an amorphous copolyamide, or a blend of the above.

[0042]

DETAILED DESCRIPTION OF THE INVENTION The present invention generally comprises a heat sealing layer which is a blend of a propylene-based copolymer and a homogeneous ethylene alpha-olefin copolymer having a density of less than about 0.90 g / cc. Intended for a heat-shrinkable multilayer film. In particular, a film exhibiting improved processability and heat seal properties according to the present invention has the structure: (inner sealing and food contact layer) / (nylon layer) / (outer sealing layer) or (inner seal and food contact layer). ) / (Nylon layer) / (barrier layer) / (outer sealing layer). Here again, the inner sealing and food contact layer is a blend of an ethylene alpha-olefin copolymer having a density of less than about 0.90 g / cc and a propylene-based copolymer. The propylene-based copolymer is preferably about 94 to about 99.
An ethylene propylene copolymer having a weight percent propylene and from about 1 to about 6 weight percent ethylene.

Alternatively, the propylene-based copolymer may be a copolymer of propylene, ethylene and butene. The copolymer of ethylene, propylene and butene should preferably include about 90 to about 99 wt% propylene, about 1 to about 6 wt% ethylene and about 1 to about 10 wt% butene. is there.
It is noted that for the purposes of this specification, the term "copolymer" is intended to broadly describe the polymerization products of two or more comonomers.

The heat sealing layer may, in any case, contain from 50 to about 95% by weight of the above propylene-based copolymer, with a more preferred range being 70.
To about 85%, with 75% of the heat sealing layer being the optimum amount of the copolymer. As mentioned above, this propylene-based copolymer was prepared with about 0.90 g / c.
Blend with a homogeneous ethylene alpha-olefin copolymer having a density less than c.

Ethylene alpha-olefins are generally speaking copolymers of ethylene with one or more comonomers selected from C ₃ to about C ₁₀ alpha olefins, but especially C Included are copolymers of ethylene with ₄ to about C ₁₀ alpha olefins such as butene-1, pentene-1, hexene-1, octene-1 and the like, wherein these polymer molecules are:
It contains long chains with few side chains or branches, and is sometimes called linear polymers. These polymers are obtained by low pressure polymerization processes, and the side chain branching present is shorter than the non-linear ethylenes. Ethylene / alpha-olefin copolymers are about 0.860 g / c
It has a density ranging from c to about 0.940 g / cc. The term "low density linear polyethylene" is generally understood to include the group of ethylene / alpha-olefin copolymers that fall within the density range of about 0.915 to about 0.940 g / cc. Sometimes linear polyethylene in the density range of about 0.926 to about 0.940 is called medium density linear polyethylene (LMDPE). The lower density ethylene alpha olefins
Very low density polyethylene (VLDPE, typically used to represent ethylene and butene copolymers supplied by Union Carbide) and very low density polyethylene (ULDPE, typically Dow Are used for the purpose of representing the copolymers of ethylene and octene supplied by the company). VLDP here
Although specific density ranges for E, ULDPE, LLDPE and LMDPE have been mentioned, it is not possible to draw a clear line for density classification and the above is noted to vary by supplier.

To date, conventional ethylene alpha-olefins have been produced by Ziegler-Natta catalyzed polymerization. Traditional Ziegler-Natta homogeneous systems include metal halides activated with metal alkyl catalysts. They have different metal oxidation states, as well as different ligand environments depending on where the site of the ligand is located in this catalyst, all of which are relatively It generally results in a heterogeneous composition with a broad molecular weight distribution. Generally speaking, Ziegler-Natta catalysts have weak incorporation of comonomers thereby yielding some polymers with many comonomers and other polymers with essentially less. For example, with a conventional Ziegler-Natta catalyst, linear ethylene alpha with an average of 10% comonomer is used.
The olefin may exhibit a comonomer range of 0 to 40% in any of the individual chains provided.

Recently, a new class of ethylene-based linear polymers has been introduced. These new resins are those prepared by metallocene-catalyzed polymerization, and they have narrower or more homogeneous compositional characteristics, such as molecular weight distribution, than resins prepared by conventional Ziegler-Natta polymerization processes. Characterized by having. Conventional Ziegler-Natta polymerization systems have a catalyst composition difference considered, which is illuminated as different catalytic reaction sites with different reaction rates and selectivities at each site. The metallocene catalyst system has been characterized as a single identifiable chemotype that exhibits remarkable selectivity. Therefore,
Conventional systems produce resins that reflect the specific properties exhibited by different catalytic sites, whereas resins made with metallocene systems reflect a single catalytic site. However, it is noted that at least some of the ethylene-based linear polymers previously available exhibit the physical and compositional properties achieved using the present metallocene-catalyzed polyolefins. The above copolymers were not made with a metallocene catalyst, but were made with a nonmetallocene single-site catalyst that yields a resin that achieves the homogeneity exhibited by the resin using metallocene as a catalyst. The above example is a resin marketed by Mitsui under the trademark Tafmer (TM). Metallocene catalyzed ethylene alpha olefins and Tafmer type resins are suitable for use in the heat sealing layer of the present invention.

Thus, the ethylene alpha-olefin of the present heat sealing layer is a homogeneous metallocene catalyzed resin, or at least a single site catalyzed resin, such as Tafmer. The density is limited to less than about 0.90 g / cc in order to aid the processability exhibited by the overall film structure and to obtain improved sealing. The homogeneous ethylene alpha-olefin used is preferably a copolymer of ethylene and butene or a copolymer of ethylene and propylene, which shows excellent compatibility with propylene-based resins. The ethylene alpha-olefin is present in the heat sealing layer from about 5 to about 5
It constitutes 0% by weight, most preferably 15 to 30% by weight.

The film structure is provided with a layer containing at least one polyamide or nylon. The layer is present for the purpose of providing elastic recovery properties throughout the structure. Specifically, in cook-in applications such as those described above, food products are literally cooked in film packaging. Because the film is biaxially oriented, it shrinks during cooking and fits closely with the food product it contains. After cooking, the product is typically cooled, which often results in product shrinkage, at least for meat products. It is desirable for the film to exhibit good elastic recovery in order to closely fit the meat during such contraction.

It is generally known that nylons impart the above elastic recovery properties to thermoplastic films. By investigating various combinations of polyamides, copolyamides and amorphous nylons for the purposes of the present invention, a suitable combination of processability, stiffening properties and elastic recovery was determined. It has been found that a layer of nylon 6/12 gives the optimum combination of properties for the present invention.

Accordingly, the present invention preferably has the previously indicated (inner sealing and food contact layer) / (nylon layer).
/ (Outer sealing layer), and in a further embodiment, the structure: (inner sealing and food contact layer) /
It contains (nylon layer) / (barrier layer) / (outer sealing layer). Each of these layers may also optionally be adhered to each other with a tie layer.

The food contact layer may optionally be subjected to energy radiation treatments including, but not limited to, corona discharge, plasma, flame, ultraviolet and high energy electron treatments. For example, the food contact layer may be selectively irradiated with energetic electrons, which is advantageous during irradiation of the entire multilayer film structure due to cook-in integrity as discussed in more detail below. Can be achieved. Radiation doses are expressed herein in terms of radiation units "RAD", and million RADs or megarads are expressed as "MR". The proper dose of high energy electrons is
It is less than about 12 MR, more preferably in the range of about 2 to about 9 MR.

The adhesive or tie layer also includes any polymer that exhibits excellent adhesion to the barrier layer and the core layer, or to the abuse layer, or both the core layer and the abuse layer. You can leave. Various polyethylenes including the copolymers of polyethylene and the copolymers of ethylene and vinyl acetate as described herein are useful as tie layers for use in accordance with the present invention. Preferably, the tie layer comprises anhydride modified alpha-olefin copolymers having rubber moieties, such as those contained in the core layer discussed above. A suitable resin is Morton Internation.
Tymor 1203 manufactured by al. Also suitable is By Pont made by Byn
el 4107. However, any of the various adhesives well known in the film manufacturing art, such as Chempl
It is also possible to use Plexar (TM) adhesive or the like supplied by ex Co.

The term "ethylene vinyl acetate copolymer" (EVA) as used herein as one type of polyethylene
Is a copolymer derived from ethylene and vinyl acetate monomers, wherein the ethylene-derived units are present in major amounts in the copolymer and the vinyl acetate-derived units are present in minor amounts in the copolymer. Is represented. EVA is known not only to have similar structural strength as ethylene alpha-olefin polymers, but also to provide excellent adhesion to adjacent layers, which reduces the need for "adhesives". Or it can be eliminated. By hydrolyzing EVA copolymers, copolymers of ethylene and vinyl alcohol (E
VOH) can be produced and these are mainly used as barrier layers according to the invention. Orientation
Modifiers such as ethylene / acrylic acid ester / maleic anhydride terpolymers may be blended into the present EVOH barrier layer for the purpose of enhancing its ability.

The term "oriented" is also used herein in an interchangeable manner with the term "indicating heat shrinkability", which essentially refers to the stretched dimension of a material after it has been stretched. It represents the material that was cured by cooling it while maintaining it at. Oriented (ie, heat-shrinkable) materials exhibit a tendency to return to their original unstretched (unexpanded) dimensions when heated to a suitable elevated temperature.

The cook-in film of the present invention is preferably oriented and is produced by extrusion methods, especially coextrusion methods known in the art. It is first cooled, for example with a cascade of water quenches, and then it is oriented again by heating and stretching it within its orientation temperature range. Stretching for orientation can be accomplished in a number of ways, such as "blown bubble" technology or "tenter framing." These methods are well known to those skilled in the art and can be used to cross or cross the material (TD).
And / or is called an orienting operation that stretches in the machine or machine direction (MD). After stretching, the film is cured or fixed in its oriented molecular structure by rapid quenching to cool the film rapidly while maintaining essentially its stretched dimensions.

If a film with little or no orientation is desired, such as a non-oriented or non-heat-shrinkable film, the film may be formed from a non-oriented material, or If it arises from an oriented material, it may be "hot blown". When producing a hot blown film,
The film is not cooled immediately after being extruded or coextruded, but is stretched for a short period after it is first extruded while the film is still at a high temperature above the orientation temperature range of the material. Then the film is cooled in a well known manner. It is well known to those skilled in the art that the above method is familiar and that the resulting film exhibits essentially unoriented properties. Other methods of producing unoriented films are also well known, such as cast extrusion or cast coextrusion methods.

As indicated, these film layers can be produced by coextrusion, where subsequent multilayers are extrusion coated with additional layers to produce a multilayer film. It is also possible to make two multi-layer tubes and later extrusion coat or laminate one of these tubes onto the other. In the production of films where it is desired to subject one or more layers of this film to treatment, which can be detrimental to one or more of the other layers, rather than coextruding the entire film, The coating method is preferred. It is desirable to irradiate one or more layers of the film with high energy electrons, and the film is one of vinylidene chloride.
If one or more copolymers (eg Saran (TM)) are included, such as a barrier layer such as vinylidene chloride and vinyl chloride or vinylidene chloride and methyl acrylate, and vinylidene chloride and ethyl acrylate or acrylonitrile, do the above. be able to.

Films of this type include, for example, films in which the barrier layer is a Saran (TM) layer in addition to or in place of the EVOH layer.
The technicians in this field generally understand that irradiation with high-energy electrons generally causes the saran (TM) to deteriorate and discolor and become brown when exposed to the saran (TM) barrier layer composition. I am aware that it is harmful. Therefore, for films with a barrier layer containing a Saran (TM) layer, when the multilayer structure is irradiated with high-energy electrons after the overall coextrusion, this irradiation is carefully performed at low levels. Needs to be done. Alternatively, extrude the first layer or layers, subject this layer or layers to high-energy electron irradiation, then attach a saran (TM) barrier layer, and from that, extrude and pre-irradiate The above is avoided by sequentially attaching other layers (which may or may not be irradiated) to the outer surface of the tubing. By using such a sequence, the Saran (TM) barrier layer is not subjected to harmful discoloration,
It becomes possible to perform high-energy electron irradiation of the first layer or layers.

Accordingly, the terms "extrude" or "extrude" as used herein are intended to include coextrusion, extrusion coating, or a combination thereof.

A general outline for the film production shown above is that the method is described in US Pat. Nos. 4,274,900; 4,229,24.
1 ;, 4,194,039; 4,188,443; 4,048,428; 3,821,182 and 3,022,543, as they are well known and are not intended to be all inclusive.

[0062]

EXAMPLES Attempts were made to produce the film structures shown below. The polyamide composition of the inner layer was believed to provide good elastic recovery properties to conventional inner sealant / bond / barrier / bond / outer sealant structures. However, it has been found that orientation of these comparative film structures is difficult and sometimes impossible. The relative percent thickness for each layer is also shown.

[0063]

[Table 1]

[0064]

[Table 2]

The film structures shown below, all of which contained a blend of propylene-based copolymer and ethylene alpha-olefin in its sealant, were both easy to process and There was little or no difficulty in orienting. It is noted that the structure of this example contains a polyamide-containing layer having a thickness comparable to that of Comparative Examples 1-9 above. In those earlier structures, the polyamide was split to create two separate layers sandwiching the barrier layer to produce the same film structure from above and below. Caused. The symmetrical structure was thought to prevent bending. However, in this example, it was confirmed that the hardness of the barrier layer was balanced with that of a single polyamide-containing layer to prevent bending.

[0066]

[Table 3]

[0067]

[Table 4]

[0068]

[Table 5]

[0069]

[Table 6]

In the examples given above, the following materials were used:

EPC-1 Fina 847 commercially available from Fina
3, Propylene / Ethylene Copolymer with 3.1% Ethylene EPC-2 Elva KS 409 sold by Solvay, Propylene Ethylene Copolymer with 3.2% ethylene EPB Sumitomo W531D, Ethylene Propylene Butene Copolymer R-AD ethylene alpha-olefin copolymer, Tymor (TM) 1 commercially available from Morton International
203, grafted with rubber and maleic anhydride Bynel E302 marketed by P-AD DuPont, polypropylene PA grafted with anhydride or 8209FN marketed by PA-1 Allied, nylon 6 PA-2 Huls Vestami marketed by America, Inc.
d L1940 Natural, Irganox 1098, containing antioxidants and calcium stearate APA DuPont commercially available Selar PA 3426, amorphous nylon CPA-1 Emser commercially available XE 3303, nylon 6
6/610 CPA-2 Emser sells CF62BSE, nylon 6
/ 69 CPA-3 BASF marketed Ultramid C35, nylon 666 CPA-4 Emser marketed Grilon CF6S, nylon 6/12 EVOH ethylene vinyl alcohol copolymer, Eva
Eval LC-E105A EVOH-2 ethylene vinyl alcohol copolymer commercially available from l of America, Eva
ECG-156B M ethylene-acrylic acid ester-maleic anhydride copolymer modifier marketed by l of America Tafmer A-4085 marketed by EAO-1 Mitsui, homogeneous ethylene butene copolymer, density = 0.85 g / C
c Low density ethylene alpha-olefin copolymer ATTANE (TM) 4203, commercially available from EAO-1 Dow Chemical,
Ethylene polymerized with 1-octene having a density of 0.905 g / cc EAO-2 Dow Chemical commercially available ethylene-1
-Octene copolymer Dowlex (TM) 2045 EBA sold by Quantum Chemical Company
A 705-009, ethylene butyl acrylate copolymer with a butyl acrylate content of 5% by weight COLOR-1 white concentrate, commercially available from Teknor Color E
PE 10214-C, 50% TiO ₂ /50% LDPE Blends The above description of preferred embodiments of the invention has been given for purposes of description and description. This is not exhaustive, i.e., not intended to limit the invention to the precise form described, and modifications and variations may be made in light of the above teachings, or It is possible to obtain them from the practice of the invention. Illustrating the principles of the invention and its practical application, various modifications are made available to those skilled in the art to enable various embodiments of the invention and to suit their particular intended use. The specific examples have been selected and described in order to enable the present invention to be utilized. For example, although back seamed envelopes have been discussed herein, thermoplastic films in which the present seal layer and other structural layers are used are also within the scope of the invention.
It is intended that the scope of the invention be limited by the claims appended hereto and their equivalents.

Claims (15)

[Claims] 1. A propylene-based copolymer is about 5 parts by weight.
A heat sealing layer comprising a blend of from 0 to about 95 wt% and from about 5 to about 50 wt% of a homogeneous ethylene alpha-olefin copolymer having a density of less than about 0.90 g / cc. Heat shrinkable multilayer film. 2. The propylene-based copolymer is about 70 to about 85% by weight and the homogeneous ethylene alpha-olefin copolymer is about 15 to about 30.
The heat-shrinkable multi-layer film according to claim 1, wherein the heat-sealing layer contains a blended material in a weight percentage. 3. The heat-shrinkable multi-layer film according to claim 1, wherein the propylene-based copolymer is a copolymer of propylene and one or more other alpha-olefins. 4. The heat-shrinkable multilayer film according to claim 3, wherein the propylene-based copolymer is a copolymer of propylene and ethylene. 5. The heat-shrinkable multilayer film according to claim 4, wherein the propylene-based copolymer is a copolymer of propylene, ethylene and butene. 6. The heat shrinkable multilayer film of claim 4, wherein the propylene-based copolymer comprises about 94 to about 99 wt% propylene and about 1 to about 6 wt% ethylene. 7. The propylene-based copolymer comprises about 90 to about 99 wt% propylene, about 1 to about 6 wt% ethylene, and about 1 to about 10 wt% butene. The heat-shrinkable multilayer film described. 8. The heat-shrinkable multilayer film according to claim 1, further comprising an outer layer heat-sealable on the heat-sealing layer. 9. The heat-shrinkable multilayer film according to claim 1, further comprising at least one inner layer comprising a polyamide, a copolyamide, or a blend thereof. 10. The heat-shrinkable multilayer film according to claim 9, wherein the polyamide is amorphous. 11. The heat-shrinkable multilayer film according to claim 1, further comprising a barrier layer. 12. The heat-shrinkable multi-layer film according to claim 1, further comprising one or more adhesive bonding layers. 13. The heat-shrinkable multilayer film according to claim 1, wherein the film is corona-treated. 14. An internal heat sealing layer comprising a blend comprising from about 5 to about 50% by weight of a homogeneous ethylene alpha-olefin copolymer having a density of less than about 0.90 g / cc, and about 0.90 g / cc. A heat-shrinkable multi-layer film having an outer heat sealing layer comprising a blend comprising from about 5 to about 50% by weight of a homogeneous ethylene alpha-olefin copolymer having a density of less than. 15. The heat shrink of claim 14 further comprising at least one inner layer comprising a polymeric material selected from the group consisting of polyamides, copolyamides, amorphous polyamides and blends thereof. Multi-layer film.