CA1170159A

CA1170159A - Laminate film

Info

Publication number: CA1170159A
Application number: CA000388676A
Authority: CA
Inventors: Yoshiharu Nishimoto; Kengo Yamazaki
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1980-10-31
Filing date: 1981-10-26
Publication date: 1984-07-03
Also published as: KR860000648B1; EP0051480B1; EP0051480B2; EP0051480A1; JPS5775856A; KR830007253A; JPS64216B2; US4456646A; AU7694781A; AU544001B2; ZA817295B; DE3168538D1

Abstract

TITLE OF THE INVENTION:
LAMINATE FILM

ABSTRACT OF THE DISCLOSURE:
Described is a laminate film excellent in oil-resistance, heat-resistant sealing ability and gas-barriering property having a percentage of heat-shrinkage of larger than 15 % at 90°C
comprising a center layer consisting of a copolymer(I) of vi-nylidene chloride and both two outermost layers consisting of a mixture of 20 to 70 % by weight of a copolymer(II) of ethylene and alpha-olefin of density of 0.900 to 0.950 and of crystalline melting point of 110 to 125°C and 80 to 30 % by weight of a copolymer(III) of ethylene and vinyl acetate with the proviso that the content of the copolymer(II) in the total amount of copolymers in both the two outermost layers is less than 65 %
by weight and showing a structure of having an adhesive layer between the center layer and the outermost layer.

Description

1 1 70 .~ 5 !~

BACKGROUND OF THE INVENTION: ;
The present invention relates to a heat-shrinkable laminate film having a center layer of a copolymer of vinylidene chloride (hereinafter referred to as PVDC), both two outermost layers of a mixture of a copolymer of ethylene and alpha-olefin of a crystalline melting point of llO to 125C and a copolymer of ethylene and vinyl acetate (hereinafter referred to as EVA) of a crystalline melting point of 85 to 103C and two adhesive layers each of which is inserted between the- center layer and the outermost layer.
~ eat-shrink packaging is industrially most convenient as packing for foodstuffs having irregular shapes such as raw meats, cooked meats, cheeses and other ~a-tty foodstuffs. In addition, since a long period of preser~atlon is required to these packed foodstuffs, gas-barrier property is necessary for such a packaging material. Moreover, since i~ is necessary to subject the packed foodstuffs to heat-treatment for a certain time period for sterilization in the case where the foodstuff is cooked meat (for instance, for at least 8 minutes at 90C
against Escherichia coli), oil-resistance and peel-resistant of the sealed parts in the heat shrinkage (hereinafter referred to as peel-resistant) are required to the packing material.
More in detail, there are problems in packing and sterilizing the fatty foodstuffs of breaking the thinly stretched outermost layer which is softened by fats and heat and of breaking the seal part or its viciDity of the packins material due t~ the : '' l ~ 01~9 . ,,' heat-shrinking stress generating at the time of thermal sterili-zation or at the time of packing, and accordingly, a packaging material (film) of excellent oil-resistance and peel-resistant is keenly demanded in such a case.
As a hea-t-shrinkable film of gas-barrier property, a film consisting solely of PVDC, a laminate film of construction of EVA/PVDC/EVA disclosed in Canadian Patent No. 982,923, and a cylindrically formed laminate film of construction of EVA/
PVDC/irradiated EVA by radioactive rays disclosed in Japanese Patent Application Laying Open No. 34565/72, etc. are enumerable.
~ owever, the film consisting solely of PVDC has defects ¦ of causing hygienically undesirable cases-where the additives such as plasticizers and stabilizers .in the f~ilm migrate into the packed foodstuff according to the kinds of the packed foodstuffs and becoming an undesirable state for preserving the foodstuffs due to the reduction of gas-barrier property owing to the relatively large amount of the additives for maintaining cold-resistant strength of the film, etc.
Since the laminate film of the construction of EVA/

PVDC/EVA has the EVA layer as the outermost layer which is high in cold-resistant strength, it is not necessary to add a large amount of the additive into PVDC and accordingly, the problem of reduction of gas-barrier property has been solved, however, EVA has a defect of being poor in oil-reslstance and peel-resistant.

, _ _ .

1 170tS9 In Japanese Patent Application Laying Open No. 34565/72, a cross-l.inked EVA by radioactive rays is used for the purpose of improving the oil-resistance, however, only as one of the outermost layers for the fear of causing decomposition of PVDC in the center layer by the raclioactive irradiation. In addition, heat-resistant seal ability is not improved by the cross-linking by radioactive irradiation on EVA.
In order to obtain the laminate film excellent in oil-resistance, it is desirable to use a polymer of alpha-olefin of, for instance, a crystalline melting point o~ higher than 110C
as the two outermost layers. However, since the polymer of alpha-olefin of the crystalline melting point of higher than 110C is poor in stretchability, it is impossible to uniformly stretch after being laminated wlth a PVDC lay-er, and accordingly, ¦
heat-shrinkable laminate film can not be available.
In addition, in cases where polyethylene of low density ¦¦ of a crystalline melting point of lower than 110C or an ionomer ¦¦ is used, there is a defect of poor heat-resistant seal ability.
According to the above-mentioned reasons, a heat-shrinkable film excellent in oil-resistance, peel-resistant : and gas-barrier property has been demanded in the field of food-packaging.
As a result of elaborated studies, the present inventors have found that the laminate film comprising a center layer of a copolymer(I) of vinylidene chloride, both the two outermost layer3 of a mixture of 20 to 70 ~ by weight o' a copolymer(II~

3 17~3~5g , . . I
of ethylene and alpha-olefln of a density of 0.900 to 0.950 and of a crystalline melting point of 110 to 125C and ~0 to 30 %
~by weight of a copolymer(III) of ethylene and vinyl acetate of la crystalline melting point of 85 to 103C and adhesive layer !between the center layer and the outermost layer and having a percentage of heat-shrinkage of larger than 15 % at 90C, with the proviso that the content of the copoly~.er(II) in the total weight of both the two outermost layers is less than 65 %, is excellent in oil-resistance, peel-resistant and gas-barrier property.
It is an object of the present inventlon to provide a new heat-shrinkable laminate film for packaging foodstuff.
It is another object of the present invention to provide a new ¦¦heat-shrinkable laminate film, having an excellent properties in oil-resistance, peel resistant and gas barrier-ing properties.
BRIEF EXPLANATION OF THE DRAWINGS:
.
¦ In the drawings, Fig. 1 shows the range of composition of l the copolymer(III) of ethylene and vinyl acetate, the ordinate showing the melt index of the copolymer (g/10 min) and the absci-ssa showing the content (% by weight) of vinyl acetate units in the copolymer, and Fig. 2 shows a general chart of the process for preparing the laminate film of the present invention.
I DETAI~ED DESCRIPTION OF THE INVENTION:
The present invention relates to a heat-shrinkable film excellent in oil-resistance and peel-resistant and uniformly stretchable without giving minute local necking.
The heat-shrinkable film according to the present invention comprises a center layer of PVDC and two outermost ` _ 4 _ 70~59 layers both of which consist of a mixture of at least 20 % by ~weight of a copolymer of ethylene and alpha-olefin having a Icrystalline melting point of 110 to 125C and EVA of a ¦crystalline melting point of 85 to 103C and relatively rich in stretchability, and the film accord:ing to the present invention is superior in oil-resistance and peel resistant as compared to the laminate film having a polymer of alpha-olefin of a crystal-line melting point equal to the mean value of the crystalline melting points of the above-mentioned polymers of alpha-olefin as the two outermost layers.
In order that EVA of a crystalline melting point of 85 to 103C plays a role of improving the stretchability, it is ¦Inecessary that such EVA is contained in each of the two outermost layers in an amount of at least 30 % by weight. Accordingly, the resin of the two outermost layers consist-s of a mixture of 20 to 70 % by weight of a copolymer(II) of ethylene and alpha-¦olefin of a crystalline melting point of 110 to 125C and 80 to ! 30 % by weight of a copolymer(III). Besides, in order to carry l~out the heat-shrinking packing conveniently in industrial scale, the film having a rate of heat-shrinkage of higher than 15 ~
at a temperature of 90C is desirable. In order to prepare a film of a rate of heat-shrinkage of higher than 15 %, it is necessary to maintain the temperature at stretching as low as possible. For that purpose, it is necessary that EVA of a crystalline melting point of 85 to 103C which is rich in stretchability at a low temperature is contained in an amount of at least 35 % to the total amount of polymers in both the two outermost layers, and the amount of copolymer(II) in the total amount of polymers in both of the two outermost layers ll i _ 5 _ Il .

' I

~:~7(~15~ ~
.

should be less than 65 % by weight.
As the copolymer(II) of ethylene and alpha-olefin of a crystalline melting point of 110 to 125C, copolymers of ethylene and a small amount (1.0 to 30 % by weight) oE alpha- !
olefin of carbon number of less than 18, for lnstance, butene-l, pentene-l, 4-methylpentene-1, hexene-l, octene-l, etc. are used.
These copolymers are those referred to as linear low-density polyethylene (L-LDPE) of a density of 0.900 to 0.950 g/cc and of a cry~talline~melting point of 110 to 125C, for instance, ULTZEX, NEOZEX (both made by Mitsul Petrochemical Co.) and DOWLEX (made by Dow Chemical Co.), and are produced by copolymerization by using a catalyst consisting mainly of a transition metal. These copolymers are r-ich in stretchability in spite of their relatively high crystalline melting point and moreover, they are tenacious and rich in a~ti-stress-l cracking property.
`~ As EVA which is mixed with the above-mentioned copoly mer(II) of ethylene and alpha-olefin, those of the content of i vinyl acetate units of 3 to 12 % by weight are used. EVA
selected from these ranges of properties is fairly compatible with the copolymer(II~ to be rich in transparency and is oil-resistant, peel resistant, and easily stretchable~
Among such EVA, those included in the pentagonal range made by connecting the five points in Eig. 1, i.e., W-I (3,0.2), W-II (3,4.0), X-II (5,4.0), Z-III (12,1.5) and Z-I (12,0.2) with linear lines are preferable because of their excellent oil-resistance after mixing with the copolymer(II) of ethylene ll ~ 1 70~

nd alpha-ole in. Moreover, those included in the heptagonal range made by connecting the seven points i.n Fig. 1, i.e , W-I (3,002), W-II (3,4.0), X-II (5,4.0), X-I (5,2.0), Y-I (9~0~5)0 Z-II (12,0.5) and Z-I (12,0.2) with linear lines are most pre-ferable because of their excellent peel-resistant plus excellent oil-resistance after mixing with -the copolymer(II).
The above-mentioned melt-.index of the polymers is measured by the method is ASTM D-1238-79 (cf. Japanese Industrial Standard K-6730-1973), and their crystalline melting point is the temperature of the highest peak in the melting curve obtained by determining the melting point of the polymer with a differ ential scanning calorimeter (Type IB, made by Perkin-Elmer CoO) at a temperature rise rate of 8C/min.
PVDC for use in the present invention is a copolymer of 65 to 95 % by weight of vinylidene chloride and 5 to 35 %
by weight of at least one of unsaturated monomers polymerizabl.e with vinylidene chloride. As the copolymerizable monomer with vinylidene chloride, for instance, vinyl chloride, acrylonit-rile and alkyl acrylate of 1 to 18 carbon atoms in the alkyl ~roup are enumerable. Into PVDC, publicly known plast:i.clzerO
stabilizer, etc. may be added if necessaryO
Since a copolymer(II) of ethylene and alpha-olefin is originally not compatible with PVDC, the :Lam:ina-te made ~y piling the layer of PVDC and that of the copolymer(II) is apt to be exfoliated. Particularly, since there are many cases according to the present invention where it is necessary to ~ ~:170:~59 soak the laminate in hot water for a long period for sterili-zation, the laminate with weak mutual adhesion is apt to be exfoliated thus spoiling the appearance with additional reduction of peel-resistance.
Accordingly, it is necessary in the present invention to provide a layer of strong adhesion between the outermost layer and the center layer to prevent the e~foliation. As the material for such a layer of strong adhesion, polyolefin modified by carboxylic acid, copolymers of ethylene and vinyl acetate, block copolymer of styrene and bu*adiene and the like are used, and particularly, a copolymer of ethylene and vinyl acetate containing 13 to 25 % by weight of vinyl acetate units or a mixture of copolymers of ethylene and vinyl acetate ¦ containing in total of 13 to 25 % by-weight of vinyl acetate units is preferable. The preferable thickness of such a ~¦ layer of 1 to 3 microns.
¦¦ It is preferable to have the thickness of e~ch of the ¦ outermost layers of more than 18 % of the total thickness of the laminate, and the kinds of the copolymer(II) and EVA, the ratio of mixing of the copolymer(II) to EVA and the thickness of one of the outermost layers may be the same to or different from those of the other of the outermost layers.
In the case where the thickness of the layer playing the role of sealing is less than 18 % of the total thickness of the lamlnate (at least one of the two outermost layers in the ca e Of clasp-sealing and o h of the two outerl~ost lay-rs -.

:

ll 1170159 in the case of envelope-sealing), there is a tendency of giving poor peel-resistant. Total thickness of the laminate is pre^
ferably about 20 to 100 microns in generalO It is necessary to have at least 2 microns of the thlckness of the center layer for granting gas-barriering property and the thickness is preferably less than 30 % of the total thickness of the laminate because of a tendency of reducing the impact strength in the case of more than 30 %.
The cylindrically formed laminate film according to the present invention is extruded by using a circular die similar to that disclosed in Japanese Patent Application Laylng Open No. 82888/78 while supplying the melt materials from the nu~ber of extruders corresponding to the number of laminate layers.
The each layer of the flat laminate film according to the present invention is extruded by using a publicly known T--die while . supplying eaçh material from each extruder, and then laminated together.
A representative process ~or preparing the cylindrically formed laminate-film will be explained as follows while refer-ring to FigO 2 The mixture of copolymer(II) and (III)~ adhesi.ve re~inand PVDC are respectively extruded from the separate extruders (1)~ (1') and (1"~ and are supplied to the co-extruding circular die (2) to be a cylindrically formed laminated film (3), which is taken by the pair of nip-rollers (5) installed in a cooling bath (6) containing ~ater maintained at a temperature of low~r 1~0~59 than 40C to be an envelope-formed folded laminate film while being immediately quenched by water in the bath (6) and having a liquid (4) enclosed within the cylindrically formed part of I the laminate film (3) squeezed by the nip-rollers ~5), the ¦ liquid having been introduced for preventing the adhesion of ¦ the both two inner walls of the envelope-formed folded laminate film.
Then, the thus quenched envelope-formed laminate film Il is continuously pulled up from the bath (6) and transferred 10ll into a heating bath (8) containing hot water ~aintained at, for instance, 80 to 110C and/or an oven maintained at the same temperature (the oven is omitted from Fig. 2) and passed 1~ through the second pair of nip-rollers installed in the bath (8) ¦i or the oven while being heated.
Thereafter, the folded laminate film was inflated I between the second pair of nip-rollers (9) and the third pair j of nip-rollers (12) rotating at a speed of a few times, for instance 1.5 to 4.0 times, of that of the rotation of`the second I¦ pair of nip-rollers (9) by the air introduced and enclosed 201 between the both two internal walls of the envelope-formed laminate film while being cooled by the ambient atmosphere at ordinary temperature. By this inflation, a biaxial stretch-ing both 1.5 to 4.0 times into longitudinal direction and diametral direction is simultaneously carried out on the laminate film to prepare a heat-shrinkable laminate film (11) of t~e present inve~tion . . .

1 J 7~59 In the case of preparing the flat laminate film, the film extruded from the T-die is once cooled by the chilling rolls right below the die, and then, after being heated to a predetermined temperature, stretched between the pair of rolls into the direction of material flow and stretched into the direction of width by a tenter in a successive biaxial stretching, or stretched simultaneously into both directions of flow-direction and width-direction by a different tenter to be a heat-shrinkable film.
The heat-shrinkable stretched laminate film according to the present invention obtained by the above-mentioned process is excellent in oil-resistance, heat-resistant seal ability and gas-barriering property and desirably used for packing fatty foodstuffs requiring sterilization at a high temperature.
The present invention will be explained more in detail while referring to non limitativ~ examples as follows:
EXAMPLES 1- ~ 15:
. ~ .
By using a plurality o extruders corresponding to each combination of resins shown in Table 2 (refer to each member of polymers in Table 1), respective resins of each combination were extruded from the xespective extruders and these extruded resins were co-extruded via the co-extruding die to be a cylindrically formed laminate with the desired combination.
The thus extruded cylindrically formed laminate was quenched in a cooling bath at about 20C to be cylinder of 120 mm in folded width and of 250 ~ 980 microns in thickness.

137V~59 In the thus extruded cylindrically formed laminate, a suitable amount of soybean oil had been enclosed in advance of quenching for the prevention of adhesion of both the inner surfaces of the laminate when it was folded. Then, the cylinder was heated for about 12 sec in a hot water bath maintained at a temperature shown in Table 2 while beillg transferred in the bath at a rate of 5 m/min and passed betwe-e.~.-the first nip-rollers of a revoluting rate of 5 m/min. Thereafter, the I heated cylinder was stretched by 3 times into the longitudinal 10l direction while being stretched into transvers directlon by inflating the cylinder with an air supplied into the cylinder 3.3 times of the original diameter until pa-ssing between the second nip-rollers of a revoluting rate of 1-5 m/min while being cooled by an ambient atmosphere at ordinary temperature.
The thus obtained biaxially stretched laminate film was about i 360 mm in folded width and about 25 ~ 98 mi-crons in thickness.
Table 1 shows the physical properties of each polymer used for preparing the laminate film with an index; Table 2 1I shows the composition and constitution of the laminate film 20,¦ prepared as above; Table 3 shows the test met-hods of physical ¦¦ properties of the laminate film and Table 4 shows the test ~esults of the 1a~in~te ~ilm.

~ 12 -,, 11 1 17~159 Table 1: Polymers and Copolymers . _~
Index of Polymers Melt index Density Content of Crystalline polymer and melt. point copolymers (g/10 min) (g/cc) VAc(wt.%) (C) A r Tr ~ ~

C L-LDPE 2.5 0.922 _ 122 D L-LDPE ~ 2.5 0.93 _ 122 E L-LDPE 0.7 0.922 _ 120 0 F L-LDPE 1.8 0.935 122 G Low-density 1.2 0.922 _ 107 pleoneye thy- . . __ .

H EVA 0.3 0.93 3 103 I EVA 3.8 0.93 3.5 101 J EVA 0.5 0.93 5 97 K EVA 2.0 0.93 5 .97 L EVA 1.1 0.93 5.5 96 M EVA 3.3 O.93 6 95 N EVA - 0.2 0.93 8 94 O EVA 0.5 0.93 9 93 _ ~
P EVA 1.5 0.93 10 91 Q EVA 3 0.93 10 90 R EVA 0.35 0.94 12 85 S EVA 0.8 0.94 12 85 .. : to be continued Table 1: (Continued) , Index of ¦ Polymers Melt index¦ Density ¦ Content of ¦ Crystalline polymer and melt. point copolymers (g/10 min) (g/cc) VAc(wt.~) (C) i _ _ .__ _ _ jl T EVA 3 O . 94 15 82 I l 1~ EVA 6 O . 9 5 2 8 _ V modif ed 15 0.97 19 _ carboxylic 0~; acid . ~ . ___ I Notes: A is a composition of 100 part-s of copolymer of vinylidene chloride and vinyl chloride of 80:20 ! and 1 part of epoxyfied soybean oiL.
Il B is a composition of 100 parts of copolymer of il vinylidene chloride and vinyl-c~l-orld-e of 85 15 and 'j 0.5 part of epoxyfied soybean oil.
C and D: Linear low-dens~y polye-thylene, commercial name of ULTOZEX. (-~ts~i- Pe-trochemical Co.) ll E and F: Linear low-density polyethylene, commercial 20', name of NEOZEX ~ (Mitsui Petrochemical Co.) ,i V lS resin for an adhesive, commercial name of ADMER.
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,11 117~159 Table 3: Me-thods of Determination Item Method . __ A specimen of 10 cm in length and also in width cut out from the laminate fil~
is immersed into hot water a-t 90C in a relaxed state for one minu-te. The Rate of shrinkage rate of linear shrinkage of the film in hot water into direction of length, and that into direction of width were respectively expressed by L and T in percentage as compared to the original dimensions.

. .. _____ __ _ Vacuum-packed meat loaf with the speci-men is immersed into hot water a-t 90C
on which surface an oil is intentional-ly floated for 8 min, or vacuum-packed Oil-resisiance loast pork (Chinese style) with the specimen is-immersed into the same manner for lO mini. After cooling the foodstuff, the damage of the outermost layer is observed.
Heat-sealed specimen (c~asp-type seal-~eat-resistan-t seal ing or envelope-type sealing) is abiIity stretched onto an embroidary frame with about 5% of reserve, and after pain~ing lard on the specimen, it is immersed into hot water of 85C. The time until the seal part is broken is measured in sec.
....____ i . ..

1 17~59 Table 4: Test Results of Laminate Film _ Example Stretch- Rate of Oil-resistance Heat- Gas-barrier- iability heat- of the layers resistant ing property I
. (%, L/Tl~) First Fifth ability (cc/cm2 day 1 possible 42/47 1 2 ¦ 2 ~ 42 I

2 possible 37/41 1 1 ¦ 2 ~ 42 I

3 possible 39/42 1 1 ¦ 2 ¦ 42 ¦

4 possible 40/45 1 1 ¦ 2 ¦ 42 .
10 1 5 possible 30/36 1 1 ! 1 1 42 i . l l 6 possible 35/39 1 1 1 42 7 possible 33/41 1 1 1 42 il 8 possible 36/38 1 1 . 42 9 possible 32/37 1 1 1 15 ~I 10 possible 37/42 1 1 1 52 ., 11 possible 37/40 1 1 1 52 I
., 12 possible 28/35 1 1 1l) 68 ,,. 13 possible 32/35 1 1 1l) 68 il 14 poss.ible 35/39 1 1 1 34 20,¦ 15 possible 38/43 2 1 2 42 l ~ i , Comparative l .
Example l , 1 possible 43/47 3 3 ¦ 3 42 2 with minute 32/36 1 1 ¦ 2 42 necking l ll 3 possible 42/46 1 2 ¦ 3 42 ¦¦ . to be continued - 18 - :

,11 ~ 5 9 Table 4: ~Continued) Example Stretch- Rate of Oil-resistance Peel- ¦ Gas-barrier-ability heat- of the layersResis- ing property shrinkage tant(cc/cm2 day.
(%, L/Tl)) First Fi:fth ability atom.) 4 hardly _ ~ _ _ stretchable possible 44/48 3 2 2 42 6 possible 45/48 3 3 _ 0 Note: Oil-resistance is evaluated as: 1 no change found on meatloaf and pork; 2 no chanye found on meatloaf;
3 breakage found on the outermost layer.
Peel-resistant ability is evaluated as: 1 over 60 sec, 2 less than 60 sec and more -than 10 sec, and 3 less than 10 sec.
1) envelope-type sealing. The remalnder is clasp-type sealing.
In the case of clasp-type sealing, the fifth layer becomes to be the seal surface.

11 1 170~

As are seen in Examples 1 to 15 in Table 4, the laminate film according to the present invention showed excellent stretch-ability, oil-resistance, peel-resistant and gas-barrier property.
The laminate film of Comparative Example 1 showed i breaking in oil-resistance test, and showed poor peel-resistant ! because of the content of the copolymer(II) in the first layer of less than 10 ~ by weight, and of the crys-talline melting point of the low-density polyethylene of lower than 110C.

10~ The laminate film of Comparative Example 2 showed ` poor stretchability with minute neckings bec-ause of the content of EVA in the first layer of less than 30 ~ by weight.
The laminate ~ilm of Comparative ExampLe 3 showed poor peel-resistant ability because of the lac~ oE any adhesive ;
layers~
The laminate film of Comparative Example 4 was impos-sible to be obtained because both the first and the fifth layers were to be composed of low-density polyethy]ene without using any adhesive layers.
The laminate film of Comparative Example 5 was poor in oil-resistance because of the content of the copolymer(II) in the first layer of 10 ~ by weight.
The laminate film of Comparative Example 6 was poor in oil-resistance because of the crystalline melting point of EVA in the first layer and the fifth layer of as low as 82C, and poor in peel-resistant.

!
.:

Claims

WHAT IS CLAIMED IS:

1. A laminate film of the rate of heat-shrinkage at 90°C of higher than 15 % comprising the center layer consisting of a copolymer(I) of vinylidene chloride and both the outer-most layers consisting of a mixture of 20 to 70 % by weight of a copolymer(II) of ethylene and alpha-olefin of a crystalline melting point of 110 to 125°C and 80 to 30 % by weight of a copolymer(III) of ethylene and vinyl acetate of a crystalline melting point of 85 to 103°C with the proviso that the content of said copolymer(II) in the total amount of copolymers in both the outermost layers is less than 65 % by weight and having an adhesive layer between the center layer and the outermost layer.

2. A laminate film according to claim 1, wherein said copolymer(I) of vinylidene chloride comprises 65 to 95 % by weight of vinylidene chloride and 35 to 5 % by weight of at least one of unsaturated monomers copolymerizable with vinylidene chloride.

3. A laminate film according to claim 1, wherein said copolymer(II) of ethylene and alpha-olefin is a copolymer of ethylene and one or more alpha-olefins selected from the group consisting of butene-l, pentene-l, 4-methylpentene-1, hexene-l and octene-l.

4. A laminate film according to claim 1, wherein said copolymer(III) of ethylene and vinyl acetate falls in the pentagonal range defined in Fig. 1 by linear lines respectively connecting the respective points of (W-I), (W-II), (X-II), (Z-III) and (Z-I).

5. A laminate film according to claim 1, wherein said adhesive layer comprises a polymer or a mixture of polymers selected from the group consisting of polyethylene modified by a carboxylic acid, a copolymer of ethylene and vinyl acetate.

6. A laminate film according to claim 1 or claim 5 wherein the thickness of said adhesive layer is in the range of 1 to 3 microns.