JPH049673B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to oriented thermoplastic films for packaging. More particularly, the present invention relates to coextruded multilayer oriented films with high oxygen barrier properties. Thermoplastic films, particularly polyolefin materials, are used in connection with the packaging of various articles, including food products, which require resistance to abuse and stress, attractive appearance and protection from the environment during storage and distribution cycles. used for a period of time. Excellent heat-sealing strength is a characteristic of thermoplastic films used in applications where the contained product is heat-sealing, e.g., stressing the lateral seals of pouches, bags, and other packaging made from such films. This is an essential prerequisite for Therefore, it would be advantageous to produce packaging films that have improved seal strength at a given sealing temperature and a lower sealing temperature range. Suitable optical properties are also desirable for inspection of packaged products after packaging, in the distribution chain, and ultimately at the point of sale. Optical properties, such as high gloss, high clarity, and low haze,
Aesthetically appealing packaging materials and packaged products contribute to increasing the appeal of the product to consumers. To lower the permeation of gases with the aim of reducing the permeation of oxygen through packaging films, thereby delaying spoilage and extending the shelf life of products such as food products that are sensitive to oxygen. A variety of polymeric materials have been used. Ethylene vinyl alcohol copolymer (EVOH) is well known as an oxygen barrier material and has been used in combination in multilayer packaging films in the past. EVOH also provides excellent protection against fragrance and fragrance. It is also desirable to impart shrinkage properties to the packaging film, ie, the ability of the film to shrink upon exposure to heat, or, when constrained, to create shrinkage tension within the packaging film.
This property is imparted to the film by orienting the film during its manufacture. Typically, the produced film is stretched in the machine (machine) direction, in the transverse direction, or in both directions to varying degrees to provide shrinkage potential upon subsequent heating. After being so stretched, the film is quenched and
This shrinkage potential is imparted to the resulting film. One advantage of shrinkable films is the tight, smooth appearance of the resulting packaged product, which provides aesthetic packaging as well as protects the packaged product from environmental abuse. A variety of food and non-food products can and have been packaged with shrink film. Sometimes, it is also desirable to orient the packaging film and then heat set the film by heating the film near its orientation temperature. This produces a film that has substantially less shrinkage while retaining many of the advantages of orientation, such as improved modulus and optical properties. U.S. Pat. No. 4,064,296 to Bornstein et al. discloses that hydrolyzed ethylene vinyl acetate (HEVA) is formed by coextruding, for example, an outer layer of ethylene vinyl acetate copolymer (EVA). The film is disclosed. U.S. Patent No. 4,464,443 to Farrell et al.
No. 1, which describes the use of EVOH in multilayer polymer structures, and includes desiccants such as dibasic sodium phosphate and calcium chloride. Although EVOH is an excellent barrier material, it is moisture sensitive and loses much of its barrier properties at high relative humidity. US Patent No. to Newsome
No. 4,457,960 discloses the use of EVOH and blends of EVOH in multilayer films.
The film can be made as a heat shrinkable film and can be melt extruded. The outer layer of the multilayer film can be a blend of linear low density polyethylene (LLDPE) and EVA. U.S. Pat. No. 4,495,249 to Ohya et al. discloses a multilayer film having a core layer of a saponified copolymer of ethylene and vinyl acetate and comprising two outer layers of a mixture of EVA and LLDPE. ing. The multilayer laminated film of this US patent can be heat shrinkable and has gas barrier properties. U.S. Patent No. 4501797 to Super et al.
No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, 2006, 1, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, and 4 disclose a non-equilibrium oriented multilayer film comprising an inner layer of anhydride-modified polypropylene and a barrier layer of ethylene vinyl alcohol and nylon. U.S. Patent No. to Koschak et al.
No. 4,501,798 discloses the use of blends of EVOH and nylon and non-balanced multilayer polymer films that also include LLDPE or EVA in the sealant layer. An adhesive layer of a material having carboxy moieties, preferably an anhydride derivative, is present. The films of this US patent are characterized by having a high barrier to gas permeation, high gloss, transparency and stiffness. US Pat. No. 4,347,332 to Odorzynski et al. discloses a film having a blend of nylon and ethylene vinyl alcohol copolymer. U.S. Patent No. 4,551,4465 to Schoenberg et al. covers LLDPE, LMDPE and EVA
and a four-component surface layer of LLDPE, LMDPE and EVA with a UV stabilizer. It is an object of the present invention to provide a coextruded thermoplastic multilayer film characterized by excellent oxygen barrier properties over a wide range of humidity conditions. It is also an object of the present invention to provide a coextruded thermoplastic multilayer film that is substantially free of voids in the blend material of the film. Another object of the present invention is to provide an aesthetic appearance with excellent clarity and other desirable optical properties.
An object of the present invention is to provide a thermoplastic multilayer film. Another object of the invention is to provide a thin thermoplastic multilayer film with excellent toughness and abrasion resistance. It is still another object of the present invention to produce a coextruded film that can be fully coextruded and oriented to produce a film with excellent shrink properties and excellent oxygen barrier properties over a wide range of humidity conditions. An object of the present invention is to provide a thermoplastic multilayer film. Another object of the invention is to provide a thermoplastic multilayer film that has excellent heat sealing properties and can be heat sealed at relatively low temperatures. The present invention comprises a crosslinked core layer of ethylene vinyl alcohol copolymer, two crosslinked inner layers each of adhesive polymeric material, and each of a blend of linear low density polyethylene and very low density polyethylene. The present invention relates to an oriented multilayer film characterized in that it comprises two crosslinked outer layers. In another aspect, a method of making an oriented multilayer film includes a core layer of ethylene vinyl alcohol copolymer, two intermediate layers of adhesive materials, and a blend of linear low density polyethylene and very low density polyethylene. co-extruding the two outer layers of and rapidly cooling the co-extruded film;
The process consists of crushing the cooled film, heating the crushed film to its orientation temperature range, and stretching and orienting the heated film. Definitions "Interlayer" and "inner layer" and the like are used herein to define a layer in a multilayer film that is surrounded on both sides by an outer layer. The term "ethylene vinyl alcohol copolymer",
"EVOH" and the like are used herein to encompass saponified or hydrolyzed products of ethylene vinyl acetate copolymers. The term "racking" is used here to mean
Stretching the coextruded and reheated film by tenter framing and blown bubble processes;
Used to define well-known methods. Term "Linear Low Density Polyethylene", "LLDPE"
are used herein to refer to copolymers of ethylene and one or more comonomers selected from _C4 to _C10 alpha olefins, e.g. butene-1, octene, etc., and herein copolymers The molecule consists of long chains with few side chain branches or cross-links. This molecular structure distinguishes it from ordinary low-density or medium-density polyethylene, which is more highly branched than its respective counterpart. "LLDPE," as defined herein, typically has a density ranging from about 0.916 g/cm ^<3> to about 0.925 g/cm ^<3> . The term "very low density polyethylene",
"VLDPE" etc. are usually about 0.910g/
cm ³ to about 0.860 g/cm ³ . The terms "oriented", "oriented", etc. are used herein to refer to stretching a resinous polymeric thermoplastic material heated to its orientation temperature and then cooling to freeze the alignment of the molecules of the material in the direction of stretching. The following is used to describe the method and the properties of the resulting polymers. The orientation temperature range for a given film will vary with the different primary lipid thermoplastic materials or blends thereof that make up the film. These temperature ranges are generally
Above about room temperature and below the melting point of the thermoplastic material or blend of thermoplastic materials. Such ranges are well known to those skilled in the art. Uniaxial orientation results from a stretching force applied in one direction. Biaxial orientation results from stretching forces applied in two directions. All crude percentages here are by weight
Calculated according to standards. The term "polyamide" and the like refers to high molecular weight polymers having amide bonds along the molecular chain, and more specifically refers to synthetic polyamides, such as nylon. A more detailed explanation will be given with reference to the only attached drawing. Referring specifically to FIG. 1, there is shown a schematic cross-sectional view of a preferred embodiment of the coextruded multilayer oriented film of the present invention. The structure of the film is a multilayer film with the generalized structure A/B/C/B/A, where A is the outer layer;
B is the intermediate adhesive layer and C is the core layer containing barrier material. Preferably, each of the outer layers A comprises about 35% of the total multilayer film thickness, the middle layer B comprises about 10% of the film thickness, and
The barrier layer C then constitutes about 10% of the total film thickness. The total thickness of the multilayer film is preferably about 0.5-2.0 mils, more preferably about 0.75-1.5 mils.
It is. Even more preferably, the multilayer film of the present invention is about 1 mil thick. Preferably, core layer 10 is about 0.00127 to 0.0254
mm (about 0.05-1 mil), more preferably about 0.00254
mm (approximately 0.1 mil) thick. Approximately 0.00127 (approximately 0.05
Thicknesses less than mil) result in very thin films that can cause voids in the barrier material. about
Thicknesses greater than 0.0254 mm (about 1 mil) create films that are difficult to stretch or latch, and also increase cost due to expensive barrier components. A suitable EVOH is EVALH, commercially available from EVALCA. It has been found that it is difficult to orient EVOH to produce heat-shrinkable films. During the stretching or racking process to orient such films, EVOH can sometimes develop voids. This development causes some loss of oxygen barrier properties, which affects the useful shelf life of food packaged in EVOH film, i.e.
It may be reduced. EVOH like this
The presence of voids in the layer can also discolor food products, such as processed meats, and therefore reduce the appearance and market value of the packaged food product. Therefore, blending the EVOH of the core layer with 1-20% polyamide resin is desirable in some applications. The polyamide can be a polymer or a copolymer containing polyamide comonomers. When using such blends, the EVOH is preferably about 80-99% of the blend.
% by weight, and the polyamide comprises about 1-20% by weight of the blend. More preferably, the blend consists of about 90% by weight ethylene vinyl alcohol copolymer and about 10% by weight polyamide. Intermediate layers 12 and 14 are preferably acid or anhydride modified polymeric materials and may bond core layer 10 to outer layers 16 and 18. This material is preferably a polyolefin, such as polyethylene or ethylene-
Includes blends of ester copolymer substrates and graft copolymers of unsaturated carboxylic acids or acid anhydrides with polyolefins, such as polyethylene, or ethylene-ester copolymers. Outer layers 16 and 18 preferably include:
It is a blend of LLDPE and VLDPE. These outer layers preferably contain from about 70 to about 80% by weight
Contains LLDPE and about 20 to about 30% by weight VLDPE. More preferably, outer layers 16 and 18 are about
75% by weight LLDPE and approximately 25% by weight VLPDE
including. The film is preferably irradiated with about 3 to 13 Megarads (MR), more preferably about 5 to 10M.
Orient after irradiation with R. irradiation. Orientation is accomplished by racking or stretching the film in the machine (machine) and transverse directions at a racking ratio of about 3.0 to about 5.0 times its original length. To orient the film, for example by blowing, the coextruded and cooled tube is heated to the orientation temperature range. These ranges are well known for many polymeric materials and are generally below the melting point of formation. Preferably, the film made according to the present invention is heated to 90°C to 140°C, more preferably 105°C to 115°C. Example 1 75% LLDPE (Dowlex 2045) and 25%
Sample films were prepared by blending VLDPE (DFDA 1137) and blending with a masterbatch concentrate containing approximately 2% slip and antiblock agents. This outer blend layer is composed of approximately 90% EVOH (EVAL H) and 10% nylon 6/nylon 12 copolymer (Grillon CA-
6) and an intermediate adhesive layer (Norchem Plqxar 3150). Doelex) 2045 can be obtained from the Dow Chemical Company. This is a particularly preferred LDPE for use in the present invention.
is a copolymer of ethylene and octene, and has a density of about 0.920 g/cm ² and a melt flow index (ASTM-D-1238, E-28) of about 0.7 to about 1.2 g/10 min at 23°C. has.
LLDPE imparts toughness to the film. VLDPE has a preferred density of 0.900-0.910 g/ ^cm2 . A preferred resin is DFDA- available from Union Carbide Corporation.
1137, this resin has a density of approximately 0.906g/ ^cm2 ,
It has a melt flow index of 0.721 g/10 min and a melting point of 118°C (244〓). This material is a butene-based copolymer. The EVOH of the core blend layer is EVAL H,
It is available from Eval Company of America and has an ethylene content of about 38% by weight and a melt flow index of about 1.5 g/10 min. Other suitable EVOH resins are EVAL
E, EVAL F, and EVAL K, and blends thereof, and preferably such resins or blends have a melt flow index (ASTM D 1238) of about 1 to 4 g/10 min.
has. Grillon CA-6 is available from Emsar Industries and blended with EVOH. Grillon CA-6
is a nylon copolymer having about 60% by weight nylon 6 and about 40% by weight nylon 12. Nylon 12 may be effective alone as a blend material in the core layer, but it is a relatively expensive material. Nylon 6 may be effective as a blend material, but is somewhat difficult to process. Certain blends have excellent blocking properties related to EVOH,
Moreover, it has been found to be very advantageous in making core blends with the processing and drawing advantages of nylon. Other suitable nylon copolymers include Grillon CR, which has 20-30% by weight nylon 6 and 70-80% by weight nylon 12.
-9. The intermediate adhesive layer, Norchem Dlexar 3150, is an anhydride modified resin based on low density polyethylene manufactured by Norchem. Other anhydride modified resins, e.g.
CXA-E162 (DuPont) can also be used as an intermediate adhesive layer. The polymer melt from the coextrusion die was then cooled and cast into a solid tape, which was irradiated with approximately 8 megarads of radiation. The tape was then heated in an oven to about 110°C and blown into bubbles. The bubble was expanded both mechanically (longitudinally) and laterally to approximately 3.5 times its original dimensions, then deflated and plyed into a single wound roll of film. The final film has a thickness of approximately 0.0254 mm (1 mil) and, in addition to the shrink properties imparted by orientation, has excellent toughness, excellent optical properties, burnout resistance, tear resistance, and It showed heat sealability. The film also exhibited excellent abuse resistance and the necessary stiffness and low tack required for packaging applications, and there were virtually no voids in the EVOH/polyamide blend layer. Example 2 Another sample film was manufactured with a similar construction to the sample film of Example 1 and by a similar method. The LLDPE used in the outer layer of the sample was Exxon LL-3001. The physical properties of the two sample films are listed in Table 1 below.

【table】

Table: To determine the seal strength of the films of the present invention, sample films were prepared similar to those of Example 1, but using CXA-E162 as the intermediate adhesive layer and without polyamide. . This film is designated as film A in Table 2 below. For comparison, another film was made with substantially the same composition as Film A, but with a different outer blend layer. This film is designated as Film B in Table 2 below. This outer layer is 50% by weight
of linear low density polyethylene, 25% by weight linear medium density polyethylene, and about 25% by weight ethylene vinyl acetate copolymer. The heat seal strengths shown in Table 2 are in pounds per inch (kg/cm) and were tested on a Vertrod heat seal apparatus (ASTM F 88) at seal rod temperatures as indicated. 10 samples of film A and 10 samples of film B were made and heated to 149°C (300〓) and 204°C (400〓).
The heat seal strength was tested at each of two different temperatures. The results are shown in Table 2.

[Table] Film A weighs 0.95Kg/at 149℃ (300〓)
cm (5.3 lb/in) and a heat seal strength of 0.96 Kg/cm (5.4 bond/in) at 204°C (400〓). In contrast, film B
0.80 Kg/cm (4.5 lb/in) at 149°C (300〓) and 0.89 at 204°C (400〓)
Has a heat seal strength of Kg/cm (5.0 lb/in). This is an approximately 18% improvement in heat seal strength at 149°C (300〓) and 204°C (400〓).
〓), it is calculated that the heat seal strength is improved by about 8%. Film B has a thickness of about 100 gauge (ie, about 1 mil), whereas Film A has a thickness of about 90 gauge. At these thicknesses, thicker materials generally form a somewhat stronger heat seal at a given temperature.
Taking this into consideration, the relative improvement in film A according to the present invention would be greater than shown above. Obvious modifications to the invention will occur to those skilled in the art without departing from the spirit and scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a preferred embodiment of the invention. 10...core layer, 12...middle layer, 14...middle layer,
16...outer layer, 18...outer layer.

Claims (1)

Claims: 1 Components: (a) a crosslinked core layer consisting of an ethylene vinyl alcohol copolymer, (b) two crosslinked inner layers each consisting of an adhesive polymeric material, and (c) each having a linear (d) two crosslinked outer layers comprising a blend of low-density polyethylene and very low-density polyethylene; Extruded multilayer film. 2 Components: (a) a crosslinked core layer consisting of an ethylene vinyl alcohol copolymer, (b) two crosslinked inner layers each consisting of an adhesive polymeric material, and (c) each containing (1) about 70% by weight. two crosslinked outer layers consisting of a blend of ~80% by weight linear low density polyethylene and (2) from about 20% to about 30% by weight very low density polyethylene. Oriented multilayer film. 3 Components: (a) a crosslinked core layer consisting of an ethylene vinyl alcohol copolymer, (b) two crosslinked inner layers each consisting of an acid-modified polymeric material or an acid anhydride-modified polymeric material, and (c) each of two crosslinked outer layers consisting of a blend of (1) about 75% by weight linear low density polyethylene and (2) about 25% by weight very low density polyethylene. multilayer film. 4. The film according to claim 3, wherein the core layer further contains polyamide. 5 The core layer comprises (1) about 80% to 99% by weight ethylene vinyl alcohol copolymer and (2) about 1% by weight.
5. The film of claim 4 comprising a blend of ~20% by weight polyamide. 6. The film of claim 4, wherein the core layer comprises a blend of (1) about 90% by weight ethylene vinyl alcohol copolymer and (2) about 10% by weight polyamide. 7. The film of claim 3 which is oriented by racking in both the machine and transverse directions with a racking ratio of about 3.0 to about 5.0. 8. The film of claim 3 which is oriented by racking in both the machine and transverse directions with a racking ratio of about 3.5. 9 Steps: (a) Coextruding a core layer of ethylene vinyl alcohol copolymer, two middle layers of adhesive material, and two outer layers of a blend of linear low density polyethylene and very low density polyethylene. (b) rapidly cooling the extruded film, (c) crushing the cooled film, (d) heating the crushed film to the orientation temperature range, and (e) stretching and orienting the heated film. , A method for producing an oriented multilayer film, comprising: 10. The method of claim 9, wherein the coextruded film is cooled to about room temperature. 11. The method of claim 9, wherein the heated film is oriented by racking in both the machine and transverse directions at a racking ratio of about 3.0 to about 5.0. 12. The method of claim 9, wherein the heated film is oriented by racking in both the machine and transverse directions at a racking ratio of about 3.5. 13. The method of claim 9, further comprising the step of reheating the oriented film to about its orientation temperature to obtain a substantially non-shrinkable film.