JPH11105222A - Heat-shrinkable multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-vinyl chloride-based shrink film, which is excellent in transparency, glossiness and with which even a commodity having corner parts can be packed without wrinkle. SOLUTION: This film is a multilayered film having at least three layers. Both the outer layers are made of poly(trimethylene terephthalate), the degree of crystallization of each of which is 30% or less. The inner layer is made of at least one polymer selected from the group consisting of a man-rigid polymer made of polypropylene-based polymer, polyethylene-based polymer, ethylene- vinylacetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylate copolymer and ethylene-α-olefin copolymer, an ionic crosslinkable copolymer, a block copolymer of vinyl aromatic hydrocarbon and conjugated dien derivative and its derivative.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a packaging film,
Particularly, the present invention relates to a heat-shrinkable multilayer film which is useful as a shrinkable film for packaging and has excellent elasticity, low-temperature shrinkage, sealability, optical properties, impact resistance and the like.

[0002]

2. Description of the Related Art A heat-shrinkable film for packaging produced by stretching a thermoplastic resin film is capable of tightly wrapping its contents by shrinking by applying heat such as hot air. Applications, such as sundries, food, toys,
It is used for the packaging of various kinds of goods such as fruits and vegetables and raw textiles. Currently, the film used for shrink wrapping is
Films made of resins such as polyvinyl chloride, polyethylene, polypropylene, and nylon can be used. However, each of these films has disadvantages.

[0003] That is, among the above films, a polyvinyl chloride shrinkable film (hereinafter referred to as PVC) having the highest evaluation.
The film is abbreviated as a film, is hard, has good gloss and transparency, has relatively good sealing properties, has a relatively low shrinkage temperature, and has a wide temperature range. The seal strength is a little weak, and careful sealing is required.Resin decomposes during fusing and sealing, generating toxic gas and corroding packaging machinery. Because the strength is reduced or the impact strength is reduced, especially at low temperatures (below -10 ° C), the impact resistance is greatly reduced, and most of them contain a large amount of plasticizer. It has the drawbacks that the dimensions and physical properties change over time, the contents are stained by migration of the plasticizer, and the gloss is reduced due to excessive bleeding on the surface.

[0004] Polyethylene-based heat-shrinkable films have high impact strength and high seal strength, but are inferior in gloss and permeability to polyvinyl chloride and poor in low-temperature shrinkage, and therefore have an appropriate shrinkage temperature of polyvinyl chloride. 20-50 ° C than vinyl
It has the disadvantage of being expensive. Even with polyethylene films,
A film that has been highly stretched at a high temperature by highly cross-linking molecules using an electron beam or the like has a large maximum shrinkage and maximum shrinkage stress, and has better optical properties such as transparency and heat resistance than ordinary polyethylene-based films. Although it is excellent, the transparency after shrinkage and the strength after shrinkage tend to deteriorate due to the high shrinkage temperature, it is difficult to heat seal due to cross-linking, there is no elongation, and the tear strength is weak.

[0005] Polypropylene-based heat-shrinkable films have the advantages of relatively good transparency and gloss, relatively stiffness, and high shrinkage stress, but have a low maximum shrinkage and a high proper shrinkage temperature. The upper limit has disadvantages such as easy melting and a narrow appropriate temperature range. Nylon-based heat-shrinkable film has relatively good transparency, stiffness, large shrinkage stress, and excellent impact resistance, but has a lower shrinkage and higher shrinkage temperature than polyvinyl chloride film. Disadvantages such as poor sealability.

[0006] A high shrinkage or a high shrinkage stress can be exhibited with respect to the above-mentioned existing film, good transparency so that the package contents can be easily confirmed, and good gloss that can enhance the commercial value. Having a good elasticity (high waist strength and surface hardness) necessary for improving the workability when performing high-speed automatic packaging, Japanese Patent Publication No. 5-33896 proposes a film satisfying sufficient impact resistance and tear strength at the time of packaging and at the stage of distribution of goods. Example 1 of the publication discloses a three-layer film of a substantially amorphous polyester (hereinafter referred to as Co-PET) having a Vicat softening point of 82 ° C and a polyolefin-based resin composition (hereinafter referred to as PO). (Co-PE
T / PO / Co-PET) has been proposed. But,
The reality is that the film is not sufficient.

[0007]

For example, when a video tape or the like is pillow-shrink-wrapped, it can be neatly wrapped with a PVC film, whereas the above three-layer film (hereinafter referred to as a conventional Co-PET / PO / Co-PET) is used. Film), the overall finish is good, but fine wrinkles tend to remain at the corners of the videotape. As a result of the study by the present inventors, it was found that the cause was a difference in the heat shrinkage characteristics between the two films. FIG. 2 compares the heat shrinkage rates of the two. In FIG. 2, the vertical axis indicates the shrinkage rate (%), and the horizontal axis indicates the temperature (° C.) at which the shrinkage rate was measured. According to FIG. 2, the shrinkage rate of the PVC film gradually increases from around 40 ° C. with respect to the temperature, whereas the conventional Co-PET / PO / Co-PET is reduced.
In the film, the curve of the shrinkage rate sharply rises from around 70 ° C.

[0008] Here, shrink wrapping such as video tape is 10% to 30% of the circumference of the product in both the vertical and horizontal directions.
The product is wrapped gently with a film having a margin (hereinafter, referred to as a margin ratio) and passed through a hot air shrink tunnel set at a temperature of about 70 to 120 ° C. (passing time is about 1 to 5 seconds). By doing so, the film is shrunk to a tight finish. The PVC film begins to shrink immediately after entering the tunnel, and gradually shrinks as the film temperature rises, as in a curve of the heat shrink characteristic shown in FIG.

On the other hand, conventional Co-PET / PO
The / Co-PET film hardly shrinks until it reaches a temperature exceeding 70 ° C., and starts to shrink sharply as soon as the temperature exceeds 70 ° C. At this time, heat shrinkage stress is suddenly generated. However, if there is a corner such as a video tape, the stress is concentrated on the corner, and radial wrinkles around the corner are likely to occur.
Also, wrinkles are likely to occur when the hot air is blown differently or when the film temperature is slightly different (such as a portion where the film is in contact with a product and a portion where the film is not in contact). Therefore, the present invention provides a conventional Co-PET / PO / Co
-By maintaining the transparency, gloss and elasticity of PET film while maintaining the heat shrinkage characteristics of a PVC film, shrink wrapping is possible even for products with corners such as video tapes. It is intended to provide a film.

[0010]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object, and as a result, has accomplished the present invention. That is, the present invention is a multilayer film comprising at least three layers, both outer layers of which are made of poly (trimethylene terephthalate) having a crystallinity of 30% or less, and an inner layer of which is a polypropylene-based polymer or a polyethylene-based film. Polymer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, soft polymer composed of ethylene-α-olefin copolymer, A heat-shrinkable multilayer film comprising at least one polymer selected from the group consisting of an ion-crosslinkable copolymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative and a derivative thereof.

Hereinafter, the present invention will be described in detail. First, in the present invention, it is essential to use poly (trimethylene terephthalate) (hereinafter abbreviated as PTT) having a crystallinity of 30% or less for both outer layers. Here, PTT is
Although a straight polymer of poly (trimethylene terephthalate) may be used, another component may be copolymerized with an acid component or a glycol component for the purpose of controlling the crystallization rate and crystallinity. For example, as the acid component,
Examples thereof include aromatic acids such as phthalic acid and isophthalic acid, and aliphatic acids such as adipic acid. Examples of the glycol component include ethylene glycol, butylene glycol, and 1,4.
-Cyclohexane dimethanol, bisphenol A and the like may be copolymerized. In that case, the copolymer component is 10 mol%.
It is often better to keep them below.

[0012] Both outer layers of the multilayer film of the present invention are PT
The technical significance of using T will be described in comparison with conventional techniques and the like. FIG. 1 shows the heat shrinkage characteristics of the four types of multilayer films. In FIG. 1, the vertical axis indicates the shrinkage rate (%).
And the horizontal axis shows the temperature (° C.) at which the shrinkage was measured. Also,
In FIG. 1, the film of the present invention (Example 1 described later)
Corresponds to the above-mentioned conventional Co-PET / PO / Co
A PET film (corresponding to Comparative Example 1 described later), a comparative film using poly (butylene terephthalate) (hereinafter abbreviated as PBT) for both outer layers (corresponding to Comparative Example 2 described later), and a PVC film described above. Show.

As is apparent from FIG. 1, the film () of the present invention shows the heat shrinkage characteristic closest to that of the PVC film (). When a video tape was shrink-wrapped (the margin rate was 12% in both the vertical and horizontal directions) using the film described below, the film could be packaged neatly without any small wrinkles at the corners. In contrast, the conventional Co-
In the PET / PO / Co-PET film (), both outer layers have a Vicat softening point (ΔTg: glass transition point) of 82 ° C.
Because of the Co-PET, the shrinkage onset temperature was as high as 70 ° C., and the heat shrinkage rate sharply increased at 70 ° C. as described above. Therefore, when the video tape is shrink-wrapped, wrinkles are generated at the corners as described above.

Further, the comparative film () using PBT having a Tg of about 30 ° C. for both outer layers starts to shrink at a low temperature of about 40 ° C., but has a small maximum shrinkage rate of less than 30%. Did not finish tightly, and the film had a dull feeling. Thus, the packaging was performed with the above-mentioned margin ratio reduced to about 5%, but the finish was not tight. In addition, the margin ratio of 5% is a level that is difficult in actual packaging, and it was found that the comparative film () is not suitable for practical use. Incidentally, the reason why the maximum shrinkage ratio of the comparative film () is as small as less than 30% is considered to be due to the fact that the crystallization speed of PBT is high and the crystallization speed is increased by stretching orientation.

As described above, PTT having a Tg of 45 to 65 ° C.
Is used for both outer layers of the film of the present invention is a conventional Co-P
Compared with the ET / PO / Co-PET film, the curve of the heat shrinkage characteristic has a gentle rise, and the maximum shrinkage ratio exceeds 30%. It can be seen that even products having corners can be tightly packed without wrinkles. In addition, the film of the present invention is superior in dimensional stability during storage as compared with the PVC film.

Therefore, both outer layers of the present invention have a crystallinity of 30.
% Of PTT. As described above, in the case of Co-PET whose glycol component is mainly composed of ethylene glycol, the Tg is as high as 81 ° C., so that the curve of the heat shrinkage characteristic sharply rises, and in the case of PBT whose glycol component is butylene glycol, the Tg is high. Is as low as about 30 ° C., the dimensional stability is poor, and the crystallization rate is high, so that the maximum shrinkage is less than 30%.

PTT used in the multilayer film of the present invention
Needs to be 30 ° C. or less. If it exceeds 30%, the maximum shrinkage remains below 30%. If the crystallinity is less than 10%, a problem may occur in dimensional stability. Therefore, the crystallinity is preferably 10 to 30%. The intrinsic viscosity (measurement conditions will be described later) of PTT used in the multilayer film of the present invention is preferably 0.7 or more, and more preferably 0.8 to 1.6 from the viewpoint of film forming properties.

In the outer layers of the multilayer film of the present invention, other kinds of polymers can be mixed with the above-mentioned PTT as long as the effects of the present invention are not impaired. In this case, the mixing amount of the other polymer is preferably 30% by weight or less. Further, the outer layer of the multilayer film of the present invention is mixed with additives such as an antistatic agent and an anti-fogging agent, a plasticizer, an auxiliary agent, a dye or a light-absorbing substance as long as the effects of the present invention are not impaired. Alternatively, a coating process may be performed.

Next, in the multilayer film of the present invention, the inner layer is formed from the viewpoints of transparency, stretching film forming stability, and heat shrinkage characteristics.
Polypropylene-based polymer, polyethylene-based polymer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-α-olefin copolymer At least one selected from the group consisting of a soft polymer comprising an union, an ion-crosslinkable copolymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative, and a derivative thereof.
It is necessary to consist of a kind of polymer.

Examples of the above-mentioned polypropylene-based polymer include homopolypropylene, a random copolymer of α-olefin (excluding propylene) such as ethylene and butene-1, and propylene, and a block copolymer thereof. Random copolymer of α-olefin (excluding propylene) and propylene, Cataloy (flexible grade, terpolymer type) of Montell-JPO, CAP of Ube Lexen, Tokuyama P.
E. FIG. An elastic propylene polymer such as R is preferable because it has excellent stretchability, transparency, impact strength (dart impact strength, piercing strength, etc.) and the like. Examples of the polyethylene polymer include a low-density polyethylene, a medium-high-density polyethylene, and a linear copolymer having a density of 0.89 to 0.93 g / cm ³ in which ethylene is copolymerized with an α-olefin having 3 or more carbon atoms. Low-density polyethylene (particularly preferred is one polymerized with a single-site catalyst such as a metallocene catalyst or a Brookhart catalyst). Examples of the ethylene-aliphatic unsaturated carboxylic acid copolymer and the ethylene-aliphatic unsaturated carboxylic acid ester copolymer include an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, and an ethylene-acrylic acid ester (methyl, Ethyl, butyl, etc.)
Copolymer, ethylene-methacrylic acid ester (methyl,
Ethyl, butyl, etc.) copolymers.

The soft polymer comprising the ethylene-α-olefin copolymer is defined as a soft copolymer of ethylene and one or more α-olefins selected from α-olefins having 3 to 12 carbon atoms. And α-olefins as propylene, butene-1, hexene-1, heptene-1, 4-methyl-1-pentene, octene-1,
Others, preferably ethylene and hexene-polymerized using a single site catalyst such as a metallocene catalyst.
1 or octene-1. Further, a small amount of a non-conjugated diene derivative may be copolymerized as a third component in the soft polymer comprising the ethylene-α-olefin copolymer. The ethylene content of the copolymer is 10 to 95
Mol%, preferably in the range of 40 to 93 mol%. The soft polymer composed of these ethylene-α-olefin copolymers has a crystallinity of 30% or less by a DSC method, and includes a soft thermoplastic polymer or a soft elastomer.

The above-mentioned ion-crosslinkable copolymer is an ionomer resin obtained by saponifying at least a part of an ethylene-methacrylic acid ester copolymer or an ethylene-acrylic acid ester copolymer and further ionically bonding a part thereof. . The above-mentioned block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative and a derivative thereof are a block copolymer comprising a block of a vinyl aromatic hydrocarbon represented by styrene and a block of a conjugated diene such as butadiene and isoprene. Or hydrogenated conjugated double bonds of these copolymers, or those obtained by acid-modifying these copolymers.

Among the above polymers that can be used in the multilayer film of the present invention, the most preferable is (A) a polyethylene-based polymer and an ethylene-vinyl acetate copolymer as a main component, and an ethylene-α-olefin copolymer. And (B) a linear low-density polyethylene, an ultra-low-density polyethylene, an ethylene-vinyl acetate copolymer (with a vinyl acetate group content of 5% by weight). ２５25% by weight, melt index 0.2０．２10
A) an ethylene-α-olefin soft copolymer other than the above, or a composition obtained by further mixing 5 to 30% by weight of a soft elastomer composed of the ethylene-α-olefin copolymer, or (A) (B) Both groups 100
The composition is a composition in which 5 to 30% by weight of a crystalline polypropylene is mixed with respect to part by weight. These have the effect of not only improving the stretchability of the material itself but also significantly improving the stretchability of the outer layer. It also has the effect of preventing necking stretching of the outer layer during stretching.

Further, the above preferred mixed composition has an interlayer adhesive strength that does not cause practical delamination between the outer layer and the outer layer.
Synergies that do not cause stretching strain due to the difference between the resins that make up each layer (these strains occur because the optimal stretching conditions are different when used alone), and conversely increase the width of the stretching optimal conditions as a whole and make the whole more stable It is effective. As a result, not only is the stretching property of all layers improved,
Particularly, the stretching effect of the outer layer is remarkably improved. For example, under the condition that the outer layer alone can be stretched only up to 6 times in area stretching ratio, for example, in a low temperature region, the addition of the inner layer enables stretching up to 10 times. In addition, even when the stretched multilayer film is heat-treated, the inner layer has an effect that a decrease in strength is small.

In the multilayer film of the present invention, it is possible to further provide an adhesive layer between the outer layer and the inner layer for more positively increasing the interlayer adhesive strength. In this case, as the resin for the adhesive layer, among the above resins, a higher ethylene-vinyl acetate copolymer having a copolymerization ratio of a component other than ethylene, or an ethylene-aliphatic unsaturated carboxylic acid copolymer may be used. Good. In this case, a preferred example is a vinyl acetate content of 40 to 5 as an ethylene-vinyl acetate copolymer.
0% by weight, and an ethylene-aliphatic unsaturated carboxylic acid copolymer having an acrylic acid content of 10 to 20% by weight. Further, an acid-modified polyolefin resin can also be preferably used. The acid-modified polyolefin resin may be added to the inner layer.

The multilayer film of the present invention preferably has a thickness of 60
１５０150 kg / mm ² , more preferably 80-130 k
g / mm ² . Tensile modulus is 60k
If it is less than g / mm ² , the film tends to be insufficient in stiffness and hardness, and the film tends to cause problems in handling, wrinkling, and the like. On the other hand, when the tensile modulus exceeds 150 kg / mm ² , the film tends to be too hard, and is likely to be torn or inconvenient to handle.

The multilayer film of the present invention preferably has a thickness of 50
５００500 g / mm ² , more preferably 100-300 g
/ Mm ² . Further, in the multilayer film of the present invention, a preferable temperature at which the above-mentioned heat shrinkage stress value is developed is in the range of 60 to 160 ° C, more preferably 60 to 140 ° C, and still more preferably 60 to 120 ° C. If the heat shrinkage stress value is less than 50 g / mm ² ,
The fit of the film after shrinkage may be insufficient, and wrinkles and wrinkles tend to occur easily after packaging.
On the other hand, if the heat shrinkage stress value exceeds 500 g / mm ² , some of the contents of the package may be deformed, impairing the appearance after packaging, and causing a tendency for the seal portion to be damaged. If the heat shrinkage stress developing temperature range is less than 60 ° C., the dimensional stability of the film at the distribution stage or the like is liable to decrease.
If the temperature exceeds 60 ° C., the film may be deteriorated or adversely affect the contents to be packed.

The multilayer film of the present invention preferably has a thickness of 30
It has a saturated heat shrinkage value in the range of ７０70%, more preferably 40-60%. The values in these ranges are preferably from 60 to 160 ° C, more preferably from 60 to 160 ° C.
Expressed in the 140 ° C. range. Saturation heat shrinkage value of 30
If it is less than%, the fit after shrinkage tends to be insufficient, which may cause wrinkles or lumps after packaging. On the other hand, if the saturated heat shrinkage value exceeds 70%, after shrinkage, some contents may be deformed or tear may occur in the seal portion. On the other hand, when the shrinkage onset temperature is lower than 60 ° C., a problem may occur in the dimensional stability in the distribution or storage stage of the film. On the other hand, when the shrinkage onset temperature exceeds 120 ° C., the film may deteriorate or adversely affect the contents to be packed.

In the multilayer film of the present invention, the thickness of the outer layer is generally from 6 to 60%, preferably from 6 to 45%, more preferably from 6 to 30% based on all layers of the multilayer film.
%, Most preferably 8 to 25%. At less than 6%
There is a tendency that the fit to the contents after shrinkage becomes insufficient due to the decrease in film elastic modulus (hip), shrinkage stress, etc., wrinkles and wrinkles may occur, or the sealing strength may be insufficient, From the processing surface, the co-stretchability deteriorates, and in particular, the thickness accuracy of the outer layer also has a problem. on the other hand,
If it exceeds 60%, the elastic recovery rate may be poor, the material may be easily broken, the content may be deformed after the shrinkage, the seal may be broken, or the co-extrusion property may be problematic.

The multilayer film of the present invention has an overall thickness of generally 5 to 100 μm, preferably 6 to 80 μm. If it is less than 5 μm, there may be a problem in workability during handling, particularly during packaging. On the other hand, if it exceeds 100 μm, the stiffness of the film becomes too high, and the fit may be poor. In addition, the responsiveness of shrinkage may deteriorate, and the finish may be impaired.

The multilayer film of the present invention has an interlayer adhesive strength that does not cause a practical problem without peeling of the outer layer and the inner layer during actual use, that is, after contraction and sealing, as well as during distribution and storage. Preferably, the adhesive strength between layers is 75 g / 10 mm or more.
Here, the measurement of the interlayer adhesive strength is performed according to JIS-Z-0237-8, and is represented by the peeling force between the outer layer and the inner layer per 10 mm width of the film.

Next, a preferred method for producing the multilayer film of the present invention will be described. The polymer corresponding to each layer of the multilayer film is melted by an extruder, coextruded with a multilayer die, and cooled and solidified to a predetermined temperature using a liquid refrigerant or the like to obtain a raw multilayer film. Here, the temperature for cooling and solidifying is preferably around Tg of both outer layer resins.
The range of 0-60 degreeC is preferable. The extrusion method is not particularly limited, and a multilayer T-die method, a multilayer circular method, or the like can be used, and the latter method is preferable. Next, the obtained multilayer film raw material is heated, and the area stretch ratio is 5 to at least one axis at a stretching temperature (T ° C) satisfying the condition of Tg−20 ≦ T ≦ Tg + 35 with respect to Tg of the outer layer film. 5
The heat-shrinkable film is manufactured by stretching the film to be 0 times. More specifically, the simultaneous biaxial stretching method is more preferred, and the more preferred stretching temperature (T ° C.) is Tg−15 ≦ T ≦ T
g + 20, and the preferred area stretching ratio is 10 to 36 times. Such stretching conditions are necessary in order to obtain the above-mentioned preferable characteristics of the multilayer film, and to maintain the stability of the stretching process, and to keep the film thickness unevenness and the like in a good state.

The film of the present invention may be subjected to a crosslinking treatment with an energy beam such as an electron beam. Such a cross-linking treatment is effective in expanding the packaging range, particularly the upper temperature limit, without impairing the heat sealability at all, and improving tear strength and the like,
It is effective for improving packaging wrinkles due to stress loss. Methods for measuring and evaluating physical properties in the present invention are as follows. (1) Crystallinity of Outer Layer Resin The crystallinity in the present invention is the crystallinity in a state of constituting a multilayer film. The method of finding it followed the following method.

First, samples having different degrees of crystallinity are prepared from resin alone under arbitrary conditions. This sample was pulverized while cooling with liquid nitrogen, and the pulverized data was obtained by using a Rotaflex RU-200B manufactured by Rigaku Corporation (using a graphite monochromator) at an acceleration voltage of 50 KV and a tube current of 160 mA (target: Cu). , 2θ: 5-36
Measurements were made in °. Further, a sample whose crystallinity was clarified by the above method was obtained by DSC (DSC manufactured by PerkinElmer).
-2: heating rate = 10 ° / min, sample amount = 10 mg,
Calculate the calorific value using indium as a standard) to determine the heat of fusion and create a calibration curve. Next, DSC measurement was performed on the multilayer film, the heat of fusion was determined from the area of the peak appearing at 220 to 230 ° C, and the crystallinity was determined from the composition ratio of each layer using the above calibration curve.

(2) Intrinsic Viscosity (IV) A 1: 1 mixture of methylene chloride and trifluoroacetic acid is used as a solvent, and the concentration of the solution is set to 25 ± 0.
It was measured at 5 ° C. with a capillary solution viscometer. (3) Tensile modulus It was carried out in accordance with ASTM-882-67 and expressed as a value obtained by converting the stress at 2% elongation to 100%. (4) Heat shrinkage rate A 100 mm square film sample was placed in a thermostat set at a predetermined temperature, and heat-treated for 30 minutes in a freely shrinkable state. Then, the shrinkage amount of the film was determined, and the percentage of the value obtained by dividing by the original dimension was obtained. It was expressed by. In the case of uniaxial stretching, the average is taken in the stretching direction, and in the case of preferred biaxial stretching, the average is taken in the longitudinal and transverse directions. (5) Heat shrinkage stress The film was sampled into a strip having a width of 10 mm.
It was set without loosening, immersed in silicon oil heated to each temperature, and the generated stress was detected. At a silicon oil temperature of 80 ° C. or lower, the value after 20 seconds of immersion, and when the temperature exceeds 80 ° C., the value after 10 seconds was adopted, and the values were expressed in the same manner as in the case of the shrinkage ratio.

(6) Transparency Transparency was evaluated according to the following criteria using a HAZE value measured according to ASTM-D-1003-52. Symbol Standard ◎ HAZE (%) <1.0 １．０ 1.0 ≦ HAZE (%) <2.0 Δ2.0 ≦ HAZE (%) <3.0 × HAZE (%) ≧ 3.0 (7) Gloss The glossiness was evaluated according to the following criteria using a GLOSS value measured according to ASTM-D-2454-65T. Symbol Standard ◎ GLOSS (%)> 150 １５０ 130 <GLOSS (%) ≦ 150 △ 100 <GLOSS (%) ≦ 130 × GLOSS (%) ≦ 100

(8) Packing property Sample film was 240 m long using an L-type sealer.
A bag having a size of mx 145 mm in width was prepared, and a video tape (about 190 mm in length x 105 mm in width x 25 mm in height) in a case was put in the bag so as to come to the center of the bag. In this case, the margins in the vertical and horizontal directions are about 12%. Length 80 with the length of the bag containing the video tape set to 80 ° C
The film was passed through a 2 cm hot air shrink tunnel in about 2 seconds to shrink the film. The obtained package was evaluated according to the following criteria. Symbol Criteria ◎ The corners of the wrap case are clean with no wrinkles.タ イ ト There is a slight lack of tightness but no wrinkles. (The above is the acceptable level.) △ Wrinkles are noticeable at the corners, but even if you touch the surface with your hands, you will not be bothered. × There is a scratch when taking out the stacked products due to the corner wrinkles. XX The film has a dull feeling due to insufficient shrinkage. Or the seal part etc. has been torn due to shrinkage.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. First, polymers used in Examples and Comparative Examples are shown below. PTT1: poly (trimethylene terephthalate) [intrinsic viscosity = 1.0, Tg by DSC = 60 ° C., melting point = 2
25 ° C.] PTT2: poly (trimethylene terephthalate / isophthalate) [acid components are 90 mol% of terephthalic acid and 10 mol% of isophthalic acid, intrinsic viscosity = 0.9, Tg by DSC method = 45 ° C., melting point = 220 ° C.] PTT3: poly (trimethylene / butylene terephthalate) [glycol component is trimethylene glycol (1,
3-propanediol) 95 mol% and butylene glycol (1,4-butanediol) 5 mol%, intrinsic viscosity =
1.1, Tg by DSC method = 50 ° C., melting point = 225
° C] Co-PET: a substantially amorphous copolymerized polyester [the acid component is terephthalic acid, the glycol components are 70 mol% of ethylene glycol, 30 mol% of 1,4-cyclohexanedimethanol, and the intrinsic viscosity is 0. .8, Tg = 81 ° C. by DSC method (PET manufactured by Eastman Kodak Company)
G6763 equivalent)] PBT: poly (butylene terephthalate) [intrinsic viscosity = 1.0, Tg by DSC method = 30 ° C., melting point = 225]
° C, (Duranex 600F, manufactured by Polyplastics)
ER: ethylene-octene-1 copolymer [octene-1 = 25% by weight, density = 0.87 g / cm ³ , melting point =
56 ° C, melt index (190 ° C, load 2.16
kg) = 0.5 g / 10 min (ENGA manufactured by Dow Chemical Company)
GE: EG8150 equivalent)] PP: propylene-ethylene random copolymer [ethylene = 4% by weight, density = 0.90 g / cm ³ , melting point =
131 ° C., melt flow rate (230 ° C., load 2.1
EVA: Ethylene-vinyl acetate copolymer [vinyl acetate = 14% by weight, density = 0.934 g / cm ³ , melting point = 9]
3 ° C, melt index (190 ° C, load 2.16k
g) = 2.0 g / 10 minutes]

[0039]

EXAMPLE 1 For both outer layers (S), use was made of PTT1 containing 0.1% by weight of stearic acid amide and 0.2% by weight of silica having an average diameter of 4 μm. The inner layer (B) was EVA.
Is 70% by weight, 15% by weight of PP and 15% by weight of ER, each polymer is melted by a respective extruder, and S / B / S = 15% / 70% / 15% thickness Co-extrusion from a circular multilayer (three-layer) die to achieve the ratio,
After being quenched and solidified by warm water at 40 ° C., it was folded with a pair of pinch rolls to obtain a 250 μm-thick raw tubular film. At this time, a surfactant was injected into the tube between the annular die and the pair of pinch rolls from a pipe provided in the center of the annular die mandrel, and a thin film of the surfactant was formed on the inner surface of the tube. This tubular material is passed between two pairs of differential nip rolls, heated to 80 ° C. in a heating zone, and stretched in a stretching zone (under a multi-stage hood) under the same atmosphere, at a stretching ratio of 5.0 times and 5.0 times horizontally. The film was biaxially stretched at the same time, and cooled by air at 20 ° C. in a cooling zone to perform bubble stretching. 60 ° C
5% in the vertical direction in the hot air oven set in the relaxation rate,
The film was relaxed by taking 7% in the horizontal direction to obtain a film having a thickness of 11 μm. The obtained film was slit at the ears (both ends) and wound into a roll by a winder as two films.

[0040]

Comparative Examples 1 and 2 In Example 1, PTT1 was replaced with Co-
The same experiment as in Example 1 was repeated, except that PET was used, the hot water temperature was 70 ° C., and the stretching heating zone temperature was 100 ° C., to obtain a multilayer film having a thickness of 11 μm (Comparative Example 1). Next, in Example 1, the same experiment as in Example 1 was repeated except that PTT1 was PBT, and the thickness was 11 μm.
m was obtained (Comparative Example 2). The multilayer films of Example 1, Comparative Examples 1 and 2 were evaluated under the above conditions. Table 1 shows the results. Using Table 1 and FIG. 1, the following describes that the present invention is superior to the prior art. FIG. 1 shows the heat shrinkage characteristics of each multilayer film. In FIG. 1, the vertical axis indicates the shrinkage rate (%), and the horizontal axis indicates the temperature (° C.) at which the shrinkage rate was measured. FIG. 1 shows a PVC film (in FIG. 1) together with the multilayer film of Example 1 (in FIG. 1), the multilayer film of Comparative Example 1 (in FIG. 1), and the multilayer film of Comparative Example 2 (in FIG. 1). 1 (in FIG. 1).

As apparent from FIG. 1, the multilayer film () of Example 1 of the present invention exhibited the heat shrinkage characteristic closest to that of the PVC film (). Example 1
As shown in Table 1, the film had a packaging property of “◎”. On the other hand, the multilayer film () of Comparative Example 1
The shrinkage rate sharply increased from 0 ° C., and as shown in Table 1, the packaging property was “×”.

The multilayer film of Comparative Example 2 was heated at 40 ° C.
It begins to shrink from a low temperature, and the rise of the curve is gradual, but the shrinkage rate remains at about 25% at maximum,
As shown in Table 1, the packaging property was “xx”. These differences are attributable to differences in the properties of the resins used for the outer layers, and are the properties that can be exhibited only by using PTT as in the present invention. From the above, it can be seen that the multilayer film of the present invention exerts a much better effect than the conventional multilayer film.

[0043]

Embodiments 2 and 3 In Embodiment 1, PTT1 is replaced with PTT.
The same experiment as in Example 1 was repeated except that the film thickness was changed to 2, and a multilayer film having a thickness of 11 μm was obtained (Example 2). Moreover, in Example 1, PTT1 was set to PTT2, and a multi-stage roll (passing time of 10
The same experiment as in Example 1 was repeated except that the heat setting was performed in (sec), and a multilayer film having a thickness of 11 μm was obtained (Example 3).

[0044]

Example 4 The same experiment as in Example 1 was repeated except that PTT1 was changed to PTT3.
A μm multilayer film was obtained (Example 4).

[0045]

Comparative Example 3 The same experiment as in Example 3 was repeated except that PTT2 was changed to PTT3, and the thickness was reduced to 11 mm.
A μm multilayer film was obtained (Comparative Example 3). Example 2
4. The multilayer film of Comparative Example 3 was evaluated under the above conditions. Table 2 shows the results. With reference to Table 2, the necessity that the crystallinity of both outer layers is 30% or less in the present invention will be described below. First, as is clear from Table 2, Examples 2 to
All of the multilayer films of No. 4 were excellent in transparency, glossiness and packaging property. Here, the film of Example 2 showed the heat shrinkage characteristic closest to the PVC film in this example, but the crystallinity was as small as 10% or less, and the shrinkage at 40 ° C. was in the longitudinal direction / horizontal direction. = 3% / 1% and shrunk even at 40 ° C., indicating that there was some difficulty in dimensional stability during storage and the like.

The film of Example 3 had a crystallinity of 30% and a shrinkage ratio at 120 ° C. of 35 in the vertical / horizontal direction.
% / 28%, and there was little tightness in the packaging. On the other hand, in Comparative Example 3 having a crystallinity of 35%,
Shrinkage at 120 ° C. is 28% / 22% in the vertical / horizontal direction
And the packaging property was "x". From the above,
It is understood that the crystallinity of both outer layers needs to be 30% or less.

[0047]

Examples 5-6 and Comparative Example 4 In Example 1, except that the thickness ratio of both outer layers was 30% (Example 5), 6% (Example 6) and 0% (Comparative Example 4), The same experiment as in Example 1 was repeated to obtain a multilayer film having a thickness of 11 μm,
These were evaluated under the above conditions. Table 3 shows the results.

In the multilayer film of Example 5, the thickness ratio of both outer layers is 30%, and the thickness ratio of the intermediate layer is 40% and 50%.
% Of the film. Although all evaluations were at acceptable levels, stretching was unstable in the film forming method shown in this example. Next, the film of Example 6 is a film in which the thickness ratio of both outer layers is 6%. All evaluations were at the “〇” level. However, the tensile modulus was as small as 60 kg / mm ^2, and the stiffness of the film was felt weak, and handling was somewhat difficult. The multilayer film of Comparative Example 4 was a film in which both outer layers were not formed and only the intermediate layer was formed.
All of the packaging properties were "x".

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

According to the present invention, the conventional Co-PET /
It is possible to provide a non-vinyl chloride-based multilayer film that can be shrink-wrapped without wrinkles even for products having corners such as video tapes while maintaining the transparency, glossiness, and tensile modulus, which are characteristics of the PO / Co-PET film. In addition, the multilayer film of the present invention is not limited to non-food pillow shrink packaging such as video tape, food pillow shrink packaging,
Furthermore, it is also suitable for overlap shrink packaging, twist packaging, and the like, and is also useful as a base material for a laminate film such as a drawing.

[Brief description of the drawings]

FIG. 1 is a drawing showing heat shrinkage characteristics of a multilayer film of the present invention and a conventional film.

FIG. 2 is a drawing showing heat shrinkage characteristics of a conventional Co-PET / PO / Co-PET film and a PVC film.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B32B 27/32 103 B32B 27/32 103 B65D 65/40 B65D 65/40 D 71/08 71/08 A

Claims (1)

[Claims] 1. A multilayer film comprising at least three layers, both outer layers of which are made of poly (trimethylene terephthalate) having a crystallinity of 30% or less, and an inner layer of which is a polypropylene polymer or a polyethylene polymer. Copolymer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, soft polymer composed of ethylene-α-olefin copolymer, ion A heat-shrinkable multilayer film comprising at least one polymer selected from the group consisting of a crosslinkable copolymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative and a derivative thereof.