Heat-shrinkable multilayer film and heat-shrinkable label

Abstract

The present invention provides a heat shrinkable multilayer film which has excellent adhesiveness between front and back layers and an interlayer not only at normal temperature but also at low temperature to effectively prevent delamination and is less likely to have residual white streaks along creases. The present invention also provides a heat shrinkable label including the heat shrinkable multilayer film. The present invention relates to a heat shrinkable multilayer film including: front and back layers each containing a polyester resin; an interlayer containing a polystyrene resin; and adhesive layers, the front and back layers and the interlayer being stacked with the adhesive layers interposed therebetween, the adhesive layers each containing 20 to 65% by weight of a polystyrene resin and 35 to 80% by weight of a polyester elastomer.

Claims

1. A heat shrinkable multilayer film comprising: front and back layers each consisting of a polyester resin; an interlayer consisting of a polystyrene resin; and adhesive layers each consisting of a polystyrene resin and a polyester elastomer, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, the polyester resin in the front layer and the back layer is an aromatic polyester resin derived from condensation polymerization of at least one diol component and at least one dicarboxylic acid component comprising terephthalic acid in a range of 55 mol % or more in the at least one dicarboxylic acid component as 100 mol %, the polystyrene resin in the interlayer is a styrene-butadiene copolymer having a styrene content in a range from 78 to 84% by weight and butadiene content in a range from 16 to 22% by weight, the adhesive layers each consists of from 30 to 49% by weight of the polystyrene resin and from 51 to 70% by weight of the polyester elastomer, the polystyrene resin in the adhesive layer a styrene-butadiene copolymer having a styrene content in a range from 65 to 71% by weight and a butadiene content in a range from 29 to 35% by weight, the polyester elastomer in the adhesive layers is a block copolymer comprising an aromatic polyester as a hard segment and a polyalkylene ether glycol as a soft segment, and the polyester elastomer has a glass transition temperature in a range from 70 C. to 0 C.

2. The heat shrinkable multilayer film according to claim 1, wherein the polyester elastomer contained in the adhesive layers has a melting point in a range from 120 C. to 200 C.

3. The heat shrinkable multilayer film according to claim 1, wherein the polyester elastomer contained in the adhesive layers has a specific gravity in a range from 0.95 to 1.20.

4. The heat shrinkable multilayer film according to claim 1, wherein the polyester elastomer contained in the adhesive layers is modified by an ,-ethylenically unsaturated carboxylic acid.

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

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view illustrating how to peel a film in evaluation of the interlaminar strength.

(2) FIG. 2 is a schematic view illustrating how to peel a film in evaluation of the interlaminar strength.

(3) FIG. 3 is a schematic view illustrating a heat shrinkable multilayer film in which peeling occurs at the interface between an interlayer and an adhesive layer.

(4) FIG. 4 is a schematic view illustrating a heat shrinkable multilayer film in which peeling occurs at the interface between a front layer and an adhesive layer.

(5) FIG. 5 is a schematic view illustrating a heat shrinkable label used for evaluation of the flexibility of a label.

(6) FIG. 6 is a photograph showing an exemplary case where crease-whitening is not observed in evaluation of crease-whitening.

(7) FIG. 7 is a photograph showing an exemplary case where crease-whitening is observed in evaluation of crease-whitening.

DESCRIPTION OF EMBODIMENTS

(8) Embodiments of the present inventions are described below in detail with reference to examples. The present invention is not limited to the examples.

(9) Materials used in the examples and comparative examples are listed below.

(10) (Polyester Resin)

(11) PET-1: an aromatic polyester random copolymer resin (glass transition temperature: 69 C.) containing a dicarboxylic acid component (100 mol % of terephthalic acid) and diol components (65 mol % of a component derived from ethylene glycol, 12 mol % of a component derived from diethylene glycol, 23 mol % of a component derived from 1,4-cyclohexane dimethanol) and having a tensile modulus of elasticity of 2000 MPa

(12) PET-2: an aromatic polyester random copolymer resin (glass transition temperature: 85 C.) containing a dicarboxylic acid component (100 mol % of terephthalic acid) and diol components (68 mol % of a component derived from ethylene glycol, 2 mol % of a component derived from diethylene glycol, 30 mol % of a component derived from 1,4-cyclohexane dimethanol) and having a tensile modulus of elasticity of 1950 MPa

(13) (Polystyrene Resin)

(14) PS-1: styrene-butadiene copolymer (78% by weight of styrene, 22% by weight of butadiene, Vicat softening temperature: 72 C., MFR: 5.6 g/10 min)

(15) PS-2: styrene-butadiene copolymer (80% by weight of styrene, 20% by weight of butadiene, Vicat softening temperature: 75 C., MFR: 5.5 g/10 min)

(16) PS-3: styrene-butadiene copolymer (84% by weight of styrene, 16% by weight of butadiene, Vicat softening temperature: 75 C., MFR: 6.2 g/10 min)

(17) PS-4: styrene-butadiene copolymer (80% by weight of styrene, 20% by weight of butadiene, Vicat softening temperature: 76 C., MFR: 9.7 g/10 min)

(18) PS-5: styrene-butadiene copolymer (71% by weight of styrene, 29% by weight of butadiene, Vicat softening temperature: 72 C., MFR: 6.1 g/10 min)

(19) PS-6: styrene-butadiene copolymer (72% by weight of styrene, 28% by weight of butadiene, Vicat softening temperature: 78 C., MFR: 7.2 g/10 min)

(20) PS-7: styrene-butadiene copolymer (76% by weight of styrene, 24% by weight of butadiene, Vicat softening temperature: 80 C., MFR: 8.4 g/10 min)

(21) PS-8: styrene-ethylene-butylene copolymer (67% by weight of styrene, 33% by weight of ethylene-butylene, MFR: 5.3 g/10 min, JIS-D hardness: 71)

(22) (Polyester Elastomer)

(23) TPE-1: polyester elastomer (melting point: 163 C., specific gravity: 1.15, JIS-D hardness: 40, glass transition temperature: 35 C., tensile modulus of elasticity: 38 MPa) composed of a polyester as a hard segment and a polyalkylene ether glycol as a soft segment

(24) TPE-2: polyester elastomer (melting point: 183 C., specific gravity: 1.07, JIS-D hardness: 39, glass transition temperature: 47 C., tensile modulus of elasticity: 35 MPa) composed of a polyester as a hard segment and a polyalkylene ether glycol as a soft segment and modified with maleic acid

(25) The glass transition temperature of each polyester resin was measured by a method in conformity with JIS K 7121 (1987) using a differential scanning calorimeter (DSC-60, Shimadzu Corporation).

(26) The Vicat softening temperature was measured in accordance with JIS K 7206 (1999). Specifically, a specimen was taken from each of the above polystyrene resins. Then, a needle-shaped indenter was placed on the specimen, and the temperature was raised at 120 C./h while applying a load of 10 N to the indenter. The temperature at which the needle-shaped indenter entered the specimen by 1 mm was measured as the Vicat softening temperature.

(27) The MFR was measured by a method in conformity with ISO 1133. Specifically, each polystyrene resin was molten at 200 C. and the amount of resin ejected at a load of 5 kg for each 10 minutes was measured.

(28) The melting point of each polyester elastomer was measured by a method in conformity with JIS-K 7121 (1987) using a differential scanning calorimeter (DSC-60, Shimadzu Corporation) at a rate of temperature rise of 10 C./min.

(29) The specific gravity of each polyester elastomer was measured in conformity with JIS K 7112 (1999) by a water displacement method in which ethanol was used as an immersion liquid (electron specific gravity meter MD-300S, Alfa Mirage Co., Ltd.).

(30) JIS-D hardness of each polyester elastomer was measured by a method in conformity with JIS-K 6235 (2012) using a durometer (Asker durometer (type-D), Kobunshi Keiki Co., Ltd.).

(31) The glass transition temperature of each polyester elastomer was measured by a method in conformity with JIS K 7244 (1999) using a dynamic viscoelasticity measuring device (Q800, TA Instruments, Japan.) in a tensile mode.

(32) The tensile modulus of elasticity was measured by a method in conformity with ASTM-D882. Specifically, a non-stretched sheet of each of the polyester resins and the polyester elastomers was subjected to measurement using Strograph VE10 (Toyo Seiki Seisakusho, Ltd.).

Example 1

(33) The resin used for the front and back layers was the polyester resin (PET-1).

(34) The resin used for the interlayer was the polystyrene resin (PS-1).

(35) The resins used for the adhesive layers were 60% by weight (60 parts by weight) of the polystyrene resin (PS-5) and 40% by weight (40 parts by weight) of the polyester elastomer (TPE-1).

(36) The resins were put in an extruder with a barrel temperature of 160 C. to 250 C., and extruded through a multilayer die at 250 C. into a five-layer sheet. The sheet was cooled and solidified on take-up rolls at 30 C. Subsequently, the sheet was stretched at a stretch ratio of six times in a tenter stretching machine with a preheating zone (105 C.), a stretching zone (90 C.), and a heat setting zone (85 C.). The stretched sheet was wound on a winder. Thus, a heat shrinkable multilayer film was obtained in which the direction orthogonal to the main shrinkage direction was MD, and the main shrinkage direction was TD.

(37) The heat shrinkable multilayer film had a five-layer structure of front or back layer (4.0 m)/adhesive layer (0.8 m)/interlayer (25.4 m)/adhesive layer (0.8 m)/front or back layer (4.0 m), with a total thickness of 35 m.

Example 2

(38) A film having a five-layer structure of front or back layer (3.7 m)/adhesive layer (0.7 m)/interlayer (26.2 m)/adhesive layer (0.7 m)/front or back layer (3.7 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resins used for the adhesive layer were 60% by weight of the polystyrene resin (PS-6) and 40% by weight of the polyester elastomer (TPE-1).

Example 3

(39) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.7 m)/interlayer (23.6 m)/adhesive layer (0.7 m)/front or back layer (5.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the interlayer was the polystyrene resin (PS-2) and the resins used for the adhesive layers were 50% by weight of the polystyrene resin (PS-5) and 50% by weight of the polyester elastomer (TPE-2).

Example 4

(40) A film having a five-layer structure of front or back layer (4.0 m)/adhesive layer (0.8 m)/interlayer (25.4 m)/adhesive layer (0.8 m)/front or back layer (4.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the interlayer was the polystyrene resin (PS-2) and the resins used for the adhesive layers were 40% by weight of the polystyrene resin (PS-5) and 60% by weight of the polyester elastomer (TPE-1).

Example 5

(41) A film having a five layer structure of front or back layer (5.0 m)/adhesive layer (0.8 m)/interlayer (23.4 m)/adhesive layer (0.8 m)/front or back layer (5.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the interlayer was the polystyrene resin (PS-3) and the resins used for the adhesive layers were 40% by weight of the polystyrene resin (PS-5) and 60% by weight of the polyester elastomer (TPE-2).

Example 6

(42) A film having a five-layer structure of front or back layer (3.5 m)/adhesive layer (0.8 m)/interlayer (26.4 m)/adhesive layer (0.8 m)/front or back layer (3.5 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the front and back layers was the polyester resin (PET-2), the resin used for the interlayer was the polystyrene resin (PS-4), and the resins used for the adhesive layers were 20% by weight of the polystyrene resin (PS-5) and 80% by weight of the polyester elastomer (TPE-2).

Example 7

(43) A film having a five-layer structure of front or back layer (4.0 m)/adhesive layer (0.8 m)/interlayer (25.4 m)/adhesive layer (0.8 m)/front or back layer (4.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the front and back layers was the polyester resin (PET-2), the resin used for the interlayer was the polystyrene resin (PS-3), and the resins used for the adhesive layers were 50% by weight of the polystyrene resin (PS-6) and 50% by weight of the polyester elastomer (TPE-1).

Example 8

(44) A film having a five-layer structure of front and back layer (3.5 m)/adhesive layer (0.8 m)/interlayer (26.4 m)/adhesive layer (0.8 m)/front or back layer (3.5 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the front and back layers was the polyester resin (PET-2), the resin used for the interlayer was the polystyrene resin (PS-2), and the resins used for the adhesive layers were 25% by weight of the polystyrene resin (PS-7) and 75% by weight of the polyester elastomer (TPE-2).

Example 9

(45) A film having a five-layer structure of front or back layer (4.5 m)/adhesive layer (0.9 m)/interlayer (29.2 m)/adhesive layer (0.9 m)/front or back layer (4.5 m) with a total thickness of 40 m was produced in the same manner as in Example 1, except that the resin used for the front and back layers was the polyester resin (PET-1), the resin used for the interlayer was the polystyrene resin (PS-1), and the resins used for the adhesive layers were 20% by weight of the polystyrene resin (PS-5), 15% by weight of the polystyrene resin (PS-8) and 65% by weight of the polyester elastomer (TPE-1).

Comparative Example 1

(46) A film having a five-layer structure of front or back layer (5.5 m)/adhesive layer (0.8 m)/interlayer (27.4 m)/adhesive layer (0.8 m)/front or back layer (5.5 m) with a total thickness of 40 m was produced in the same manner as in Example 1, except that the resins used for the adhesive layers were 75% by weight of the polystyrene resin (PS-5) and 25% by weight of the polyester elastomer (TPE-1).

Comparative Example 2

(47) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.7 m)/interlayer (23.6 m)/adhesive layer (0.7 m)/front or back layer (5.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the interlayer was the polystyrene resin (PS-2) and the resins used for the adhesive layers were 15% by weight of the polystyrene resin (PS-6) and 85% by weight of the polyester elastomer (TPE-2).

Comparative Example 3

(48) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.7 m)/interlayer (23.6 m)/adhesive layer (0.7 m)/front or back layer (5.0 m) with a total thickness of 35 m was produced in the same manner as in Example 1, except that the resin used for the front and back layers was the polyester resin (PET-2), the resin used for the interlayer was the polystyrene resin (PS-2), and the resin used for the adhesive layers was the polyester elastomer (TPE-2).

Comparative Example 4

(49) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.8 m)/interlayer (28.4 m)/adhesive layer (0.8 m)/front or back layer (5.0 m) with a total thickness of 40 m was produced in the same manner as in Example 1, except that the resins used for the adhesive layers were 25% by weight of the polystyrene resin (PS-5) and 75% by weight of the polyester resin (PET-1).

Comparative Example 5

(50) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.8 m)/interlayer (28.4 m)/adhesive layer (0.8 m)/front or back layer (5.0 m) with a total thickness of 40 m was produced in the same manner as in Example 1, except that the resins used for the adhesive layers were 25% by weight of the polystyrene resin (PS-1) and 75% by weight of the polyester resin (PET-1).

Comparative Example 6

(51) A film having a five-layer structure of front or back layer (5.0 m)/adhesive layer (0.8 m)/interlayer (28.4 m)/adhesive layer (0.8 m)/front or back layer (5.0 m) with a total thickness of 40 m was produced in the same manner as in Example 1, except that the resins used for the adhesive layers were 75% by weight of the polystyrene resin (PS-1) and 25% by weight of the polyester resin (PET-1).

(52) (Evaluation)

(53) The heat shrinkable multilayer films obtained in the examples and comparative examples were evaluated for the following parameters. Table 1 shows the structure of the heat shrinkable multilayer films and the evaluation results.

(54) (1) Heat Shrinkage

(55) The heat shrinkable multilayer film was cut into a size of 100 mm in the main shrinkage direction (TD)100 mm in the direction orthogonal to the main shrinkage direction (MD), whereby a sample was prepared. The sample was immersed in hot water at 70 C. for 10 seconds. Then the sample was taken out and immediately immersed in tap water for 10 seconds. The length (L) of one side along the TD of the sample was measured, and the heat shrinkage in TD was calculated by Equation (1) below.
Heat shrinkage (%)={(100L)/100}100(1)

(56) This measurement was performed for three samples (n=3), and the average value thereof was taken as the shrinkage. The heat shrinkage in the case of immersion in hot water at 80 C. and that in the case of immersion in boiling water were also measured in the same manner.

(57) (2) Interlaminar Strength at Normal Temperature

(58) The heat shrinkable multilayer film was cut into a size of 100 mm in length10 mm in width, whereby a sample was prepared. A film end of the sample was partly delaminated as illustrated in FIG. 1. The strength (N/10 mm) when the sample was peeled at normal temperature (23 C.) in the 180-degree direction in the lengthwise direction of the sample as illustrated in FIG. 2 at a tension rate of 500 ram/min was measured with a peeling tester (Peeling TESTER HEIDON-17, Shinto Scientific Co., Ltd.). FIGS. 1 and 2 each are a schematic view illustrating how to peel the film in evaluation of interlaminar strength.

(59) The test was performed in such a manner that the lengthwise direction was the main shrinkage direction (TD) or the direction (MD) orthogonal to the main shrinkage direction.

(60) The test was performed 10 times for each of the MD and TD directions, and the average interlaminar strength in each direction was obtained.

(61) The interlaminar strength in each of the MD and TD directions was evaluated using the obtained average values based on the following criteria. The film rated as 0 (good) can suppress defects such as peeling of a heat shrinkable label upon attachment of the label to a container.

(62) (Interlaminar Strength in MD Direction)

(63) The average interlaminar strength of 0.50 N/10 mm or higher was rated (good) and the average interlaminar strength of less than 0.50 N/10 mm was rated x (poor).

(64) (Interlaminar Strength in TD Direction)

(65) The average interlaminar strength of 0.50 N/10 mm or higher was rated (good) and the average interlaminar strength of less than 0.50 N/10 mm was rated x (poor).

(66) (3) Evaluation of Peeled Surface at Normal Temperature

(67) In measurement of the delamination strength at normal temperature, the delaminated interface in measurement in the TD direction was observed and evaluated based on the following criteria.

(68) (Evaluation of Peeled Surface)

(69) A case where the film was delaminated at the interface between the interlayer and the adhesive layer was rated 0 (good). A case where the film was delaminated at the interface between the front or back layer and the adhesive layer was rated x (poor).

(70) When the heat shrinkable label is attached to a container, a flaw may be made in the surface layer on the outer side of the heat shrinkable label due to a load applied upon folding of the label by a label-attaching machine or the like. The flaw in the surface layer may become a starting point of delamination. In the worst case, the label may be peeled after the attachment. Whether or not the label is peeled depends on which interface suffers delamination in the heat shrinkable multilayer film. FIG. 3 is a schematic view illustrating a heat shrinkable multilayer film in which peeling occurs at the interface between the interlayer and the adhesive layer. FIG. 4 is a schematic view illustrating a heat shrinkable multilayer film in which peeling occurs at the interface between the front layer and the adhesive layer.

(71) In the case where delamination occurs at the interface between the interlayer and the adhesive layer as illustrated in FIG. 3, even if a flaw is made by a label-attaching machine, delamination does not progress, provided that the flaw does not penetrate through the front layer and the adhesive layer. In such a case, peeling of the label is not likely to occur. In the case where delamination occurs at the interface between the front layer and the adhesive layer as illustrated in FIG. 4, a flaw made in the surface layer causes progress of the delamination, leading to peeling of the label.

(72) (4) Presence or Absence of Zipping at Normal Temperature

(73) The heat shrinkable multilayer film was cut into a size of 100 mm in length10 mm in width, and left at normal temperature (23 C.) for 10 minutes. A film end of the sample was partly delaminated in the same manner as in the evaluation of the interlaminar strength. The presence or absence of zipping was evaluated based on the following criteria. When the zipping is determined to be present, the interlaminar strength is not uniform.

(74) When the interlaminar strength is not uniform, the peeling resistance is high at a part where the interlaminar strength is high and the peeling resistance is low at a part where the interlaminar strength is low. When a heat shrinkable multilayer film with nonuniform peeling resistance is peeled, a part where delamination stops and a part where delamination rapidly progresses are regularly or irregularly present therein, and such a state of the film is referred to as zipping.

(75) (Presence or Absence of Zipping)

(76) Present: A stripe pattern was left on the peeled front or back layer.

(77) Absent: A stripe pattern was not left on the peeled front or back layer.

(78) (5) Interlaminar Strength at Low Temperature

(79) The heat shrinkable multilayer film was cut into a size of 100 mm in length10 mm in width, and left at low temperature (5 C.) for 10 minutes. Then, the interlaminar strength (N/10 mm) thereof was determined. The measurement was performed in the same manner as in the evaluation of the interlaminar strength at normal temperature, except that the temperature was set to 5 C.

(80) In each measurement, the interlaminar strength in the TD direction and the minimum value thereof were determined. The measurement was performed 10 times, and the average of the obtained 10 values of the interlaminar strength in the TD direction was determined as the average value in the TD direction. Similarly, the average of the obtained 10 minimum values was determined as the average minimum value in the TD direction. Evaluation at low temperature, especially, measurement of the interlaminar strength in the TD direction shows the resistance of a heat shrinkable label against delamination under a load in the TD direction by a label-attaching machine or the like in a low-temperature environment. Determination of the average and the minimum value of the interlaminar strength in the TD direction show the degree of variation in the delamination strength in a low-temperature environment.

(81) (Interlaminar Strength in TD Direction)

(82) The average interlaminar strength of 0.50 N/10 mm or more was rated 0 (good). The average interlaminar strength of less than 0.50 N/10 mm was rated x (poor).

(83) (6) Evaluation of Peeled Surface at Low Temperature

(84) In measurement of the delamination strength in the TD direction at low temperature, the delamination interface was observed and evaluated based on the same criteria as those in the evaluation of the peeled surface at normal temperature.

(85) (7) Presence or Absence of Zipping at Low Temperature

(86) The heat shrinkable multilayer film was cut into a size of 100 mm in length10 mm in width, and left at low temperature (5 C.) for 10 minutes. A film end of the sample was partly delaminated in the same manner as in the evaluation of the interlaminar strength. The presence or absence of zipping was evaluated based the same criteria as those for the evaluation of the presence or absence of zipping at normal temperature.

(87) (8) Evaluation of Delamination after Bending Label

(88) The obtained heat shrinkable multilayer film was cut at a width of 227 mm in the TD direction. A solvent prepared by mixing 100 parts by weight of 1,4-dioxolan and 30 parts by weight of cyclohexane was applied to the film in a width of 3 mm in a direction parallel with the MD direction. The film was bent flatly and both end portions were bonded to each other to form a cylinder with a width of 108 mm in the TD direction. The cylindrical heat shrinkable multilayer film was cut at a width of 100 mm in the MD direction as illustrated in FIG. 5, thereby preparing a heat shrinkable label. FIG. 5 is a schematic view illustrating a heat shrinkable label used in the evaluation of flexibility. A part where the both end portions of the label was sealed with the solvent is also referred to as solvent-sealed portion.

(89) Then, both ends of the solvent-sealed portion of the heat shrinkable label were held with fingers under a low-temperature (5 C.) atmosphere, and bent 20 times in such a manner that the stress was applied in the TD direction. The label was bent at six portions, thereby preparing a bent heat shrinkable label.

(90) The bent heat shrinkable label was attached to a 275-g round metal bottle (diameter: about 66 mm) and immersed in boiling water for 10 seconds, so that the label was heat-shrunk to cover the container. The appearance of the solvent-sealed portions of the resulting label was evaluated based on the following criteria.

(91) (good): Delamination did not occur at any solvent-sealed portion in all the 10 labels.

(92) (acceptable): Delamination occurred at solvent-sealed portions in 1 or 2 labels among 10 labels.

(93) x (poor): Delamination occurred at solvent-sealed portions in 3 or more labels among 10 labels.

(94) (9) Evaluation of Crease-Whitening

(95) The heat shrinkable multilayer film (film width: 500 mm) was subjected to gravure printing using Finestar (black) (Toyo Ink Co., Ltd.) followed by gravure printing using Finestar (white) (Toyo Ink Co., Ltd.). In this manner, the heat shrinkable multilayer film with bicolor back print (black/white) was prepared. The printing plate used was prepared by direct laser platemaking with an engraving depth of 30 m and the number of lines of 175.

(96) Then, the heat shrinkable multilayer film was cut in a black print portion into a rectangle with a size of 100 mm in the MD direction200 mm in the TD direction, whereby a cut sample was prepared. The obtained cut sample was folded in such a manner that the printed face is inside, and rubber roller was pressed to the cut sample twice at a normal temperature (23 C.) in a direction parallel with the MD direction at a load of 2 kg and a rate of 2 seconds/100 mm. In this manner, the cut sample got a crease. The cut sample was unfolded, and the rubber roller was further pressed once at a load of 2 kg and a rate of 2 seconds/100 mm to smooth the crease. Then, the sample was immersed in hot water at 75 C. for seven seconds using a jig that can control the shrinkage in the TD direction. The sample was shrunk 5% in the TD direction. The appearance of the crease was evaluated based on the following criteria.

(97) In the evaluation of the appearance, the sample was illuminated by a fluorescent lamp from a 45-degree oblique direction against the sample, and visually observed by ten persons on the opposite side of the fluorescent lamp from a 45-degree direction relative to the sample. FIG. 6 shows an exemplary case where crease-whitening is not observed. FIG. 7 shows an exemplary case where crease-whitening is observed.

(98) (Evaluation of Crease-Whitening)

(99) (good): All the ten persons could not observe crease-whitening.

(100) (acceptable): One or two of the ten persons observed crease-whitening.

(101) x (poor): Three or more of the ten persons observed crease-whitening.

(102) (10) Change in Transparency after Heat Treatment

(103) The haze value of the heat shrinkable multilayer film was measured before and after the heat treatment, and the change rate thereof was obtained. The heat treatment was performed by the same method as that in the measurement of the heat shrinkage under the conditions of immersion in boiling water for 10 seconds. The haze value was measured in conformity with ASTM D-1003 using a haze meter NDH5000 (Nippon Denshoku Industries Co., Ltd.).

(104) The change rate was calculated by the following equation.
Change rate=(Haze value after heat treatment/haze value before heat treatment)100

(105) (good): Change rate of less than 400%.

(106) x (poor): Change rate of 400% or more.

(107) (Comprehensive Evaluation)

(108) (good): The film was not rated x (poor) in any of the evaluations (1) to (10).

(109) x (poor): The film was rated x (poor) at least once in the evaluations of (1) to (10).

(110) TABLE-US-00001 TABLE 1 Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- am- am- am- am- am- am- am- am- am- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 9 Consti- Front and Polyester PET-1 100 100 100 100 100 100 tuting back layers resin PET-2 100 100 100 resin Interlayer Polystyrene PS-1 100 100 100 (% by resin PS-2 100 100 100 weight) PS-3 100 100 PS-4 100 Adhesive Polystyrene PS-1 layer resin PS-5 60 50 40 40 20 20 PS-6 60 50 PS-7 25 PS-8 15 Polyester TPE-1 40 40 60 50 65 elastomer TPE-2 50 60 80 75 Polyester PET-1 resin Evalu- Heat 70 C. 10 sec 39 40 38 38 40 21 22 22 42 ation shrinkage 80 C. 64 64 63 63 64 59 60 61 65 (%) Boiling 80 80 80 80 80 75 75 76 80 water Interlaminar Average value in MD direction 1.00 1.04 0.91 0.89 1.03 0.93 0.91 1.11 0.99 strength Evaluation of interlaminar strength at normal Average value in TD direction 0.91 0.94 0.82 0.77 0.80 0.81 0.83 0.92 0.96 temperature Evaluation of (23 C.) interlaminar strength (N/10 mm) Peeled surface upon measurement Between interlayer and adhesive layer of delamination strength at normal temperature (23 C.) in TD direction Evaluation of peeled surface at normal temperature (23 C.) Presence or absence of zipping Absent Absent Absent Absent Absent Absent Absent Absent Absent at normal temperature (23 C.) Interlaminar Average value in TD direction 1.23 1.11 1.15 0.90 0.93 0.96 1.10 0.88 1.18 strength Minimum value in TD direction 0.90 0.89 1.00 0.73 0.75 0.81 0.93 0.71 0.94 at low Evaluation of temperature interlaminar strength (5 C.) (N/10 mm) Peeled surface upon measurement Between interlayer and adhesive layer of delamination strength at low temperature (5 C.) in TD direction Evaluation of peeled surface at low temperature (5 C.) Presence or absence of zipping Absent Absent Absent Absent Absent Absent Absent Absent Absent at low temperature (5 C.) Evaluation of delamination after bending label 1/10 0/10 0/10 0/10 0/10 0/10 0/10 0/10 0/10 Evaluation of flexibility Evaluation of crease-whitening Change rate of transparency after heat treatment (%) 280 278 285 290 290 390 287 380 310 Evaluation based on change rate of transparency Comprehensive evaluation Com- Com- Com- Com- Com- Com- par- par- par- par- par- par- ative ative ative ative ative ative Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Consti- Front and Polyester PET-1 100 100 100 100 100 tuting back layers resin PET-2 100 resin Interlayer Polystyrene PS-1 100 100 100 100 (% by resin PS-2 100 100 weight) PS-3 PS-4 Adhesive Polystyrene PS-1 25 75 layer resin PS-5 75 25 PS-6 15 PS-7 PS-8 Polyester TPE-1 25 elastomer TPE-2 85 100 Polyester PET-1 75 75 25 resin Evalu- Heat 70 C. 10 sec 40 38 22 39 38 40 ation shrinkage 80 C. 63 62 59 63 62 64 (%) Boiling 80 79 74 80 79 81 water Interlaminar Average value in MD direction 0.97 1.03 1.16 0.80 0.21 0.43 strength Evaluation of interlaminar strength x at normal Average value in TD direction 0.97 0.82 0.76 0.75 0.34 0.59 temperature Evaluation of x (23 C.) interlaminar strength (N/10 mm) Peeled surface upon measurement Between interlayer and adhesive layer of delamination strength at normal temperature (23 C.) in TD direction Evaluation of peeled surface at normal temperature (23 C.) Presence or absence of zipping Absent Absent Absent Absent Absent Absent at normal temperature (23 C.) Interlaminar Average value in TD direction 0.48 0.98 0.95 0.26 0.14 0.22 strength Minimum value in TD direction 0.00 0.74 0.77 0.00 0.00 0.00 at low Evaluation of x x x x temperature interlaminar strength (5 C.) (N/10 mm) Peeled surface upon measurement Between front Between interlayer and adhesive layer Between front of delamination strength at or back layer or bach layer low temperature (5 C.) in TD direction and adhesive and adhesive layer layer Evaluation of peeled surface x at low temperature (5 C.) Presence or absence of zipping Present Absent Absent Present Present Present at low temperature (5 C.) Evaluation of delamination after bending label 7/10 0/10 0/10 5/10 4/10 7/10 Evaluation of flexibility x x x x Evaluation of crease-whitening x x Change rate of transparency after heat treatment (%) 290 578 580 302 295 280 Evaluation based on change rate of transparency x x Comprehensive evaluation x x x x x x

(111) The heat shrinkable multilayer films obtained in Examples 1 to 9 were favorably rated in all of the evaluations. Even if delamination occurs in the heat shrinkable multilayer film, the delamination occurs at the interface between the interlayer and the adhesive layer, and therefore, peeling of the label does not occur.

(112) In the case of Comparative Examples 1 to 6 in which the mixing ratio of the resins for the adhesive layers does not fall within the range specified in the present invention, the interlaminar strength was lowered at low temperature, the appearance was impaired due to whitening of creases which occurred when the film was strongly folded in the solvent sealing step, and/or delamination occurred due to the impact upon attachment thereof to a container. In addition, zipping occurred at low temperature.

INDUSTRIAL APPLICABILITY

(113) The present invention can provide a heat shrinkable multilayer film which has excellent adhesiveness between front and back layers and an interlayer not only at normal temperature but also at low temperature to effectively prevent delamination and is less likely to have residual white streaks along creases. The present invention can also provide a heat shrinkable label including the heat shrinkable multilayer film.

REFERENCE SIGNS LIST

(114) 1: Front or back layer 2: Interlayer 3: Adhesive layer