Heat-shrinkable multi-layered film

Abstract

The present invention aims to provide a heat shrinkable multilayer film capable of providing a heat shrinkable label that can be easily torn along the perforation in both the TD and MD and also has excellent impact resistance and transparency. Provided is a heat shrinkable multilayer film including: front and back layers; an interlayer; and adhesive layers, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, the front and back layers each contain a polyester resin, and the interlayer contains a polystyrene resin in an amount of 80 to 99% by weight and a polyester resin in an amount of 1 to 20% by weight.

Claims

1. A heat shrinkable multilayer film comprising: front and back layers; an interlayer; and adhesive layers, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, the front and back layers each contain a polyester resin, the interlayer contains an aromatic vinyl hydrocarbon-conjugated diene copolymer in an amount of 80 to 99% by weight and a polyester resin in an amount of 1 to 20% by weight, the aromatic vinyl hydrocarbon-conjugated diene copolymer in the interlayer represents all of a styrene-containing polymer in the interlayer, and the aromatic vinyl hydrocarbon-conjugated diene copolymer constituting the interlayer is a mixed resin of 50 to 99% by weight of an aromatic vinyl hydrocarbon-conjugated diene copolymer having a Vicat softening temperature of lower than 80° C. and 1 to 50% by weight of an aromatic vinyl hydrocarbon-conjugated diene copolymer having a Vicat softening temperature of 80° C. or higher.

2. The heat shrinkable multilayer film according to claim 1, wherein the adhesive layers each contain a polystyrene resin, a polyester resin, a styrene elastomer, or a polyester elastomer.

3. The heat shrinkable multilayer film according to claim 1, wherein the interlayer further contains a styrene elastomer or a polyester elastomer.

4. The heat shrinkable multilayer film according to claim 1, wherein the polyester resin constituting the interlayer has a glass transition temperature of 30° C. to 95° C.

5. A heat shrinkable label comprising the heat shrinkable multilayer film according to claim 1.

Description

DESCRIPTION OF EMBODIMENTS

(1) The following will describe the present invention in detail referring to examples, but the present invention should not be limited to these examples.

(2) The following materials were used in examples and comparative examples.

(3) (Polyester Resin)

(4) Polyester resin A: polyester resin (glass transition temperature: 69° C.) containing a dicarboxylic acid component (component derived from terephthalic acid: 100 mol %) and a diol component (component derived from ethylene glycol: 65 mol %, component derived from diethylene glycol: 20 mol %, component derived from 1,4-cyclohexanedimethanol: 15 mol %) (Polystyrene resin)

(5) Polystyrene resin A: styrene-butadiene copolymer (styrene content: 81.3% by weight, butadiene content: 18.7% by weight, Vicat softening temperature: 81° C.)

(6) Polystyrene resin B: styrene-butadiene copolymer (styrene content: 77.7% by weight, butadiene content: 22.3% by weight, Vicat softening temperature: 71° C.)

(7) Polystyrene resin C: styrene-butadiene copolymer (styrene content: 72% by weight, butadiene content: 28% by weight, Vicat softening temperature: 76° C.)

(8) (Polyester Elastomer)

(9) Elastomer A: non-modified polyester-polyether block copolymer containing a polyester as a hard segment and a polyether as a soft segment (durometer hardness: 55, glass transition temperature: 45° C., Vicat softening temperature: 126° C., melting point: 191° C., specific gravity: 1.17)

Example 1

(10) An amount of 100% by weight of polyester resin A was used as a resin to constitute the front and back layers.

(11) A mixed resin containing 30% by weight of elastomer A and 70% by weight of polystyrene resin C was used as a resin to constitute the adhesive layers.

(12) A mixed resin containing 15% by weight of polyester resin A, 25% by weight of polystyrene resin A, and 60% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(13) These resins were fed into extruders having a barrel temperature of 160° C. to 250° C., extruded into a five-layer sheet through a multilayer die at 250° C., and cooled and solidified on a take-up roll at 30° C. Subsequently, the sheet was stretched at stretching ratio of 6 times in a tenter stretching machine with a preheating zone set at 105° C., a stretching zone set at 90° C., and a heat setting zone set at 85° C., and then wound with a winder. Thus, a heat shrinkable multilayer film was obtained in which the direction perpendicular to the main shrinkage direction was the MD and the main shrinkage direction was the TD.

(14) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and had a five-layer structure (front layer (5.7 μm)/adhesive layer (0.7 μm)/interlayer (27.2 μm)/adhesive layer (0.7 μm)/back layer (5.7 μm)).

Example 2

(15) An amount of 100% by weight of polyester resin A was used as a resin to constitute the front and back layers.

(16) A mixed resin containing 65% by weight of elastomer A and 35% by weight of polystyrene resin C was used as a resin to constitute the adhesive layers.

(17) A mixed resin containing 15% by weight of polyester resin A, 25% by weight of polystyrene resin A, and 60% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(18) These resins were fed into extruders having a barrel temperature of 160° C. to 250° C., extruded into a five-layer sheet through a multilayer die at 250° C., and cooled and solidified on a take-up roll at 30° C. Subsequently, the sheet was stretched at stretching ratio of 6 times in a tenter stretching machine with a preheating zone set at 105° C., a stretching zone set at 90° C., and a heat setting zone set at 85° C., and then wound with a winder. Thus, a heat shrinkable multilayer film was obtained in which the direction perpendicular to the main shrinkage direction was the MD and the main shrinkage direction was the TD.

(19) The obtained heat shrinkable multilayer film had a total thickness of 50 μm and had a five-layer structure (front layer (7 μm)/adhesive layer (1 μm)/interlayer (34 μm)/adhesive layer (1 μm)/back layer (7 μm)).

Example 3

(20) A heat shrinkable multilayer film was obtained as in Example 1 except that a mixed resin containing 5% by weight of polyester resin A, 28% by weight of polystyrene resin A, and 67% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

Example 4

(21) A heat shrinkable multilayer film was obtained as in Example 1 except that a mixed resin containing 10% by weight of polyester resin A, 27% by weight of polystyrene resin A, and 63% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

Comparative Example 1

(22) An amount of 100% by weight of polyester resin A was used as a resin to constitute the front and back layers.

(23) A mixed resin containing 30% by weight of elastomer A and 70% by weight of polystyrene resin C was used as a resin to constitute the adhesive layers.

(24) A mixed resin containing 30% by weight of polystyrene resin A and 70% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(25) These resins were fed into extruders having a barrel temperature of 160° C. to 250° C., extruded into a five-layer sheet through a multilayer die at 250° C., and cooled and solidified on a take-up roll at 30° C. Subsequently, the sheet was stretched at stretching ratio of 6 times in a tenter stretching machine with a preheating zone set at 105° C., a stretching zone set at 90° C., and a heat setting zone set at 85° C., and then wound with a winder. Thus, a heat shrinkable multilayer film was obtained in which the direction perpendicular to the main shrinkage direction was the MD and the main shrinkage direction was the TD.

(26) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and had a five-layer structure (front layer (5.7 μm)/adhesive layer (0.7 μm)/interlayer (27.2 μm)/adhesive layer (0.7 μm)/back layer (5.7 μm)).

(27) (Evaluation)

(28) The heat shrinkable multilayer films obtained in the examples and the comparative examples were evaluated as follows.

(29) Table 1 shows the results.

(30) (1) Tear Strength in MD and TD

(31) The tear strength in the MD and the TD was measured in conformity with ISO 6383-2 using HEIDON TYPE:17 produced by Shinto Scientific Co., Ltd.

(32) (2) Puncture Resistance

(33) The puncture resistance was measured in conformity with ISO 3036:1975 using a film impact tester produced by Toyo Seiki Seisaku-Sho, Ltd.

(34) (3) Ease of Tearing Along Perforation

(35) Thirty plastic bottles to which shrink labels were attached (without delamination or wrinkles) were prepared. For each bottle, the shrink label was removed by tearing with hands along the perforation. The state at this time was observed and the ease of tearing along perforation was evaluated in accordance with the following criteria.

(36) Good: The shrink labels were torn along the perforation in the MD and TD and easily removed.

(37) Poor: At least one of the shrink labels was not torn along the perforation and difficult to remove.

(38) (4) Haze

(39) The haze was measured in conformity with ISO 14782 using NDH5000 produced by Nippon Denshoku Industries Co., Ltd.

(40) TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 3 4 1 Heat shrinkable Front and back Polyester resin Polyester resin A 100 100 100 100 100 multilayer film layers (% by weight) (glass transition temperature: 69° C.) Thickness (μm) 5.7 7 5.7 5.7 5.7 Adhesive layers Polyester elastomer Elastomer A 30 65 30 30 30 (% by weight) (glass transition temperature: 45° C. Vicat softening temperature: 126° C.) Polystyrene resin Polystyrene resin C 70 35 70 70 70 (% by weight) (Vicat softening temperature: 76° C.) Amount of styrene component 72 72 72 72 72 (% by weight) Amount of conjugated diene 28 28 28 28 28 component (% by weight) Thickness (μm) 0.7 1 0.7 0.7 0.7 Interlayer Polyester resin Polyester resin A 15 15 5 10 — (% by weight) (glass transition temperature: 69° C.) Polystyrene resin Polystyrene resin A 25 25 28 27 30 (% by weight) (Vicat softening temperature: 81° C.) Polystyrene resin B 60 60 67 63 70 (Vicat softening temperature: 71° C.) Amount of styrene component 78.8 78.8 78.8 78.8 78.8 (% by weight) Amouont of conjugated diene 21.2 21.2 21.2 21.2 21.2 component (% by weight) Apparent Vicat softening 74 74 74 74 74 temperature (° C.) Thickness (μm) 27.2 34 27.2 27.2 27.2 Total thickness (μm) 40 50 40 40 40 Evaluation Tear strength (mN) MD 1201 2193 1221 1226 665 TD 129 164 160 158 196 Puncture resistance (J) 0.82 0.89 0.79 0.80 0.44 Ease of tearing along perforation Good Good Good Good Poor Haze (%) 6.3 6.5 4.5 5.5 4.3

INDUSTRIAL APPLICABILITY

(41) The present invention can provide a heat shrinkable multilayer film capable of providing a heat shrinkable label that can be easily torn along the perforation in both the TD and MD and also has excellent impact resistance and transparency.