JPH0334852A - Multi-layer film and manufacture thereof - Google Patents

Abstract

PURPOSE: To realize a packaging of excellent gloss, high transparency and good sense without wrinkle by incorporating a first core layer having an LLDPE or a VLDPE, two outer layers each containing an ionomer and another core layer further containing an olefin polymer or copolymer between the first core layer and the outer layer and between the second core layer and the outer layer. CONSTITUTION: A film having first core layer containing an LLDPE or a VLDPE, a second core layer containing a VLDEP or an LLDPE, two outer layers each containing an ionomer and a further other core layer containing an olefin polymer or copolymer between the first core layer and the outer layer and between the second core layer and the outer layer is co-extrusion molded. The extrusion molded film is cooled, the cooled film is pressed to be flat. The molded film can be emitted with an ionizing radiation or the like such as high energy electrons. The radiation for bringing about crosslinking is normally conducted before stretching and orienting the film. If the film has a barrier layer made of a polyvinylidene chloride-polyvinyl chloride copolymer, its radiation emitting for crosslinking is conducted before providing the barrier layer.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to packaging films, and more particularly to films useful for packaging foods, particularly frozen meat.

Hitherto, thermoplastic films, particularly films made from polyolefin materials, have been used to package a variety of products, including perishable foods, that require protection from the surrounding environment. This film should withstand physical and environmental abuse during storage and distribution, and be beautiful.
It is i< that presents a pleasing appearance. The optical properties of such packaging materials, such as good gloss, high transparency, and low haze, contribute to the aesthetic appeal to consumers of the product wrapped in the packaging material T.1. Also, if the optical properties are excellent, it becomes possible to appropriately inspect the packaged product during the distribution cycle and at the point of purchase by the end user.

During the manufacturing process of thermoplastic film, it is ``stretched and oriented'' (
The film can be given a 1:1 shrinkability by adjusting the film orientation. By being stretched and oriented, the film may shrink when exposed to heat, e.g. in a hot water bath or by exposure to hot air, or may be fixed/in the case of shrinkage stress in the packaging film. may occur. - A common method is to stretch the formed film to varying degrees in the machine direction or in a direction perpendicular to the machine direction, or both, i.e. in the longitudinal direction and in the transverse direction. To,
Provides shrinkability so that it will shrink to a desired degree when heated later. 2. After the stretching operation, the film 11 is rapidly cooled, thereby imparting a shrinkage potential to the resulting film. The shrinkable film has some additional toughness so that the film can withstand abuse, tightening and clearing the appearance of the product.

Naturally, it is desirable that the film maintain excellent optical properties even after shrinking.

Heat absorption 1i! ff: Bags made of polymeric films are acceptable for packaging meat, especially raw and processed meat.

Bags made of heat-shrinkable film are supplied to meat packaging and shipping sites with one end sealed and the other end left open to receive the meat product. The bag containing the pieces of meat is usually evacuated and the open end sealed by heat sealing or by attaching a metal clip. This step can be carried out conveniently in a vacuum chamber, with degassing and clip attachment or heat sealing taking place automatically.

The bag removed from the chamber is heat-shrinked, for example, by immersing the contents in a hot water bath or by passing hot air through a channel.

In a typical distribution chain, whole primal or subprimal cuts of food animals are packaged in shrink bags as described above. The packaged meat is transported from the central abattoir where the packaging is carried out A) to a retail supermarket where the bags are opened and the meat is cut into pieces for retail sale. That is, bags of this type must meet several needs imposed by both the slaughterhouse or meat packaging and shipping plant and the bag user. Additionally, products packaged in bags may be displayed for retail sale to consumers. It is therefore desirable to provide aesthetically pleasing packaging in which the bag contracts relatively completely around the product so that the bag does not wrinkle and blood and juices do not collect in the folds of the wrinkles. Therefore, the film constituting the bag as described above should have relatively high shrinkability and, in particular, good optical properties after shrinkage.

It is also important that the bag be physically able to withstand the processes of receiving its contents, degassing, sealing, sealing, heat shrinking, cartoning, shipping, unloading, and storage for retail sale. Many polymeric films are unsuitable for such abuse. A polymeric film with excellent toughness is required.4 It must also be strong enough to withstand the handling associated with moving the packaged meat, which can weigh as much as 45 kg or more. In particular, when meat is packed into bags, the seal at the bottom of the bag must be able to withstand impact forces.

The present invention provides a three-layer film that has poor toughness, relatively high shrinkage, and has optical properties such as excellent clarity even after shrinkage. This multilayer film/Lm is
For example, it can be produced by a known method such as extrusion molding and then stretching and orientation to form a shrinkable film.

The present invention therefore provides: (a) a first core layer comprising LLDPE, preferably c, fVLDr'E, and optionally a second core layer comprising VLD["E, or (b) two outer 17J (outer 1Bers) each containing io and nomer; (c) located between the first cardiac layer and the outer layer and between the second cardiac layer and the outer layer; and a further core layer comprising an olefin polymer or copolymer.

This multilayer film preferably comprises an olefin polymer or copolymer between the first core layer and the second core layer (=1 advantageously also having an additional core layer).

The olefin in the olefin polymer or copolymer is preferably ethylene, with ethylene vinyl acetate copolymer being preferred. It is also possible to use modified polymers to improve glabellar adhesion.

A multilayer film L, for example, includes a first core layer, a second core layer and J
] In between may also have an oxygen barrier layer, such as a layer of polyvinylidene chloride (PVDC) or ethylene hynyla/L-col (EVOII) polymer or copolymer.

The present invention also provides a method of making a multilayer film, the method comprising: (a) a first core layer comprising LLDPE, preferably VLDPE, and optionally VLDPE;
a second core layer preferably comprising LLDPE; (b) two outer layers each comprising an ionomer; and (c) between the first core layer and the outer layer and between the second core layer and the outer layer. Co-extruding the film with a further core layer comprising an olefin polymer or copolymer, cooling the formed film, and pressing the cooled film flat (cot tapsinH) 1 including.

The first and second core layers C of the film according to the invention typically include:
Each layer has a thickness of 5 to 15 μm. The outer layers typically each have a thickness of 8 to 35 μm. Further core layer thicknesses are typically 2-10 to 41 nm.

For example, a coextruded film may have 1 (to, 15M)
Ionizing radiation such as high energy key electrons can be irradiated with a dose of F.F.rad. Such irradiation to induce crosslinking is usually carried out before stretch orientation of the film.

When the film has a barrier layer of polyvinylidene chloride-polychloride copolymer, the radiation exposure for crosslinking is carried out prior to providing the barrier layer in the film body. It is known that barrier materials such as those mentioned above are adversely affected by radiation exposure, for example discoloration.

If the film has a barrier layer of EVOH or polyvinylidene chloride-methyl acrylate copolymer, it is possible to irradiate the entire multilayer film.

For the production of stretched oriented films, the method of the present invention has been
Depending on the situation, the pressed and flattened film is irradiated with radiation and then heated to the stretching orientation temperature range.
It also includes stretching and orienting the heated film.

Stretch orientation is carried out by stretching or stretching the film 7 in the longitudinal direction (machine direction) and the transverse direction at a stretching rate of about 2 to 5 times the original size of the film. For the stretch orientation of the film l, for example the blow expansion method (blo
Then, the cooled tube is heated to its stretching orientation temperature range. The stretch orientation temperature range is well known for many polymeric materials and is usually below the melting point of the film. Preferably 1. ,l,
The film according to the invention is heated to 85-95°C, more preferably 87-92°C.

The above content regarding the production of multilayer films is mainly based on Chi J, -
Bubble co-extrusion molding and inflation method 3 (tr111] ped bubble Lecbniq
In connection with the drawing process described in UE), a multilayer film is molded by extrusion from S1'' Jtsu I to 01 from Tie, and the resulting film is stretched using a tenter. It is also possible to apply manufacturing methods.

The stretched oriented multilayer film according to the invention has excellent abuse resistance, excellent optical properties, especially after shrinkage, and excellent f'S sealing properties, making it suitable for packaging food products, especially frozen meat products. Especially suitable for 1j. The carcass may be imported frozen, as in the case of New Zealand F lamb, or frozen in stratification at the point of origin. The meat is then cut into pieces while still frozen and packaged in shrink bags for retail sale. By stretch-orienting the multilayer film, toughness and improved (i.e., reduced) oxygen permeability can be obtained. The films of the present invention also typically have a relatively low modulus and excellent stretch processability, making processing steps easier, for example during bag manufacturing.

4. As used herein, the term "core layer" refers to a layer that is attached to both sides or other layers of a multilayer film.

The term "oricnt, cd" is used to define a polymeric material that has been heated and pulled together (or even rearranged in molecular arrangement) by stretching or blow-expansion techniques, but only in one direction. Thermoplastic materials to be stretched (i-axis stretch oriented, material f+ stretched both in the longitudinal and transverse directions) are biaxially stretch oriented.

The term "rackiB'" is used herein to mean
The same 11'7 extrusion 1) is then reheated and the multilayer film is extruded using a deniter or by the blow expansion method in a manner known in the art.

As used herein, 'LLDPE' and 'Linear Low Density Polyethylene' are selected from among ethylene and C4-CIO-17 fins such as G-1-1 and octene. Refers to a copolymer with more than one species of comonomer 5-, the molecules of which contain long chains with few stranded or cross-linked structures.The molecular structure is much more branched than the normal In contrast to the molecular structure of low-density polyethylene, L D P E also has the characteristic that it can be produced by low-pressure and low-temperature processes.
D P E varies from about 0.916H/cc to about 0.916H/cc.
If the density is within the range of 925H/cc.

As used herein, the term "VLDPE" or "very low density polyethylene" generally has a
Refers to a linear polyethylene:7 polymer having a density of less than 2 B/cc and greater than or equal to about 0.860 H/cc. As used herein, the terms ``IEV8'' and ``ethylene-vinyl acetate monomer'' refer to a copolymer consisting of ethylene and vinyl acetate monomer, which contains a large amount of ethylene-vinyl acetate monomer. Preferably about 60 to 9 total
Contains 8% polyamide, while vinyl acetate: Nyl Yamaki Crab Chive I.
refers to a copolymer containing a small amount, preferably about 2 to 40% by weight.

In this specification, the term ``ionomer'' refers to vinyl monomers which also carry acid groups, such as ethylene and usually basic ethylenic unsaturation/L-phonic acid, such as acrylic acid or methacrylic acid. = 1 polymer. It is to be understood that the term "ionomer" as used herein refers to both the free and ionic forms. The ionic form is preferred over the free acid form. - Any suitable metal ion such as an alkali metal ion such as ion, alkali metal ion, or other polyvalent metal ion is suitable. Preferably, the ionomer has a relatively small null index.

When the ionomer is used in its free acid form, poly(ethylene-co-methacrylic acid: EM^) and poly(ethylene-=1-acrylic acid E8) are used.1.
stomach.

Honmei #lT! The term "ethylene vinyl alcohol copolymer" or "'EVOII'" used in the book refers to the saponified or hydrolyzed ethylene-vinyl chloride copolymer, and the ethylene comonomer. 1-alcopolymer.Such copolymers are prepared by, for example, hydrolyzing the alcoholic acid cenyl alcohol, or by chemically reacting it with polyhydric alcohol. The degree of decomposition is preferably at least 50%, more preferably at least 852≦.The ethylene comonomer is typically about 15% to about 65% degraded.

The term "polychlorinated nylidene" used in this specification is sold by Dour Chemica 1 in the United States under the brand name "S aran".
9 letters containing at least 502 hydrogen chloride monomers and common? - as vinyl chloride,
Also meant is a vinyl chloride 8 d 7 polymer containing methyl acrylate or other suitable monomers.

In the present invention, the total thickness of the multilayer film is usually 50 to 1
It is 50μIll. It is possible to use a thick fill j1, but the cost of J% tr fee/L＼ is binary. Film resistance is normally 70-], 10 μto
If it is 70-90 μIll, it is very feminine. The film should not be so thin that it cannot withstand losses, for example when packaging bone-in meat pieces, nor should it be so thick that it becomes unnecessarily difficult to stretch orient and process.

As set forth herein, including each claim,
The copper weight is calculated based on weight unless otherwise specified.

The invention is illustrated by the following examples.

Examples of multilayer films according to the invention are shown in Table I below. In the table (i), the thickness of each layer is shown in parentheses in μm.

Io, Nomer 1 is commercially available from Du I'onL'lt, SURLYN 1.605, an ethylene methacrylic acid copolymer containing methacrylic acid 15χ, and the cation is lithium. be. This =
1 polymer has a Menototo index of 28.

(ill) Ionomer is D uP on 1
It is an ethylene-methacrylic acid copolymer ``ζ'', which is commercially available from Co., Ltd. and has an S-order number 1y1.11.601 containing 10% methacrylic acid, and is a cationic (storium) polymer.

The mel-intex of this copolymer is 13.

(iv) ILDPIE has a density of 9.20H/
(This is linear low-density polyethylene, which is used as a material for manufacturing and manufacturing.)

(v) LLDI'E2 has a density of 9.17H/cc
and Meltoy>Tex 23, a linear low-density polyethylene.

(vi) The EVA is a standard EVA of 7J containing 182 vinyl acids and has a null l-index of 20.
do.

〉 (-,, 7I/L-mu with the usual Chi-J-bu simultaneous extrusion technique (4・
The duplex was produced by extrusion and cooled to form a duplex. The expanded tube was passed through a hot water bath at a temperature of 87 to 89° C., and the tip taken out from the bath was expanded by blowing fluid to give the expanded tube a wall thickness of about 70 tm. This inflation method is true! j'S name is known. After that, Chifu, -bu,
Cool rapidly to fix the stretching orientation, and then roll it up.
A desired stretched and oriented multilayer film was obtained.

1 It! +! When compared with the alternating film/L film, it was found that the optical properties of the present invention, Fino 11, and Fino 11 (of the comparative film 7) were all excellent.
't'l is jl[(1' was added), and its abuse resistance is 11. is the same as that of the comparative film;
(J is poor, but the workability is good.7):.

Akuta Fino 1〕\J) Actual thickness 7 mm (unit: μm, nominal I7
(J70μ+11) and the free contraction () in the longitudinal direction (1,) and the transverse direction (T>) per centimeter are shown in kH.

Enter-” [- film comparison 1 Example 1 Example 2 Thickness (actual) 1 5 4 contraction Comparative example Example 3 Example 4 Length■15 Ratio 1I 121 column Example 6 Example 7

Claims (23)

[Claims] (1) (a) a first core layer comprising LLDPE or VLDPE; (b) two outer layers each comprising an ionomer;
c) A multilayer film having a further core layer comprising an olefin polymer or copolymer located between the first core layer and the outer layer and between the second core layer and the outer layer. 2. The film of claim 1, wherein the first core layer comprises VLDPE. 3. The film of claim 1 or 2, further comprising a second core layer comprising VLDPE or LLDPE. (4) The film of any one of claims 1 to 3, wherein the second core layer comprises LLDPE. (5) further comprising an additional core layer comprising an olefin polymer or copolymer between the first core layer and the second core layer. film. (6) The film according to claim 5, wherein the olefin in the olefin polymer or copolymer is ethylene. (7) The film according to claim 5 or 6, wherein the olefin polymer or copolymer is an ethylene-vinyl acetate copolymer. (8) The film according to any one of claims 1 to 7, further comprising an oxygen barrier layer. (9) A film according to claim 8, characterized in that the oxygen barrier layer is a polymer or copolymer of polyvinylidene chloride or ethylene vinyl alcohol. (10) The film according to any one of claims 1 to 9, wherein the first and second core layers have a thickness of 5 to 15 μm. (11) The film according to any one of claims 1 to 10, wherein the outer layer has a thickness of 8 to 35 μm. (12) The film according to any one of claims 1 to 11, wherein the thickness of the further core layer is 2 to 10 μm. (13) The film according to any one of claims 1 to 12, having a total thickness of 50 to 150 μm. (14) The film according to any one of claims 1 to 13, having a total thickness of 70 to 90 μm. (15) The film according to any one of claims 1 to 14, wherein the ionomer is an ethylene-methacrylic acid copolymer containing sodium as a neutralizing cation. (16) The film according to claim 15, wherein the ionomer has a small melt index. (17) The film according to any one of claims 1 to 16, which has been irradiated with ionizing radiation. (18) The film according to any one of claims 1 to 17, wherein the film is stretched and oriented. 19. The film of claim 1, wherein the film is substantially as described herein. (20) (a) A first comprising LLDPE or VLDPE
cardiac layer, and in some cases VLDPE or LLD
(b) two outer layers each containing an ionomer; (c) a second core layer between the first core layer and the outer layer;
coextruding a film having a further core layer comprising an olefin polymer or copolymer located between the core layer and the outer layer; cooling the formed film; and pressing the cooled film. A method of manufacturing a multilayer film including flattening. (21) Claim 20, further comprising heating the pressed and flattened film to a temperature range for stretching and orientation, and stretching the heated film to stretch and orient it.
The method described in. (22) The method according to claim 20 or 21, further comprising crosslinking the film by irradiation with radiation before stretching and orientation. 23. The method of claim 20, wherein the method is substantially as described in any one of Examples 1-7 herein.