Heat-shrinkable multilayer film and heat shrinkable label

Abstract

The present invention provides a heat shrinkable multilayer film that has excellent adhesiveness between front and back layers and an interlayer, effectively prevents delamination, and is less likely to have white creases on folds. The present invention also provides a heat shrinkable label formed from 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, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, and the adhesive layers each contain 50 to 95% by weight of a polystyrene resin and 5 to 50% by weight of a polyester elastomer.

Claims

1. A heat shrinkable multilayer film, comprising: front and back layers each comprising a polyester resin; an interlayer comprising a polystyrene resin; and adhesive layers, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, each of the adhesive layers consists of from 55 to 85% by weight of a polystyrene resin and from 15 to 45% by weight of a polyester elastomer, the polyester resin is obtained by polycondensation of a dicarboxylic acid component and a diol component, the diol component comprises a component derived from 1, 4-cyclohexane dimethanol, the polystyrene resin of the adhesive layer is different from the polystyrene resin of the interlayer, the polystyrene resin of the interlayer is a styrene-butadiene copolymer having a styrene content of 78 to 90% by weight and a butadiene content of 10 to 22% by weight, the polystyrene resin of the adhesive layer is a styrene-butadiene copolymer having a styrene content of 50 to 76% by weight and a butadiene content of 24 to 50% by weight, and the polyester elastomer is a block copolymer consisting of a polyester and a polyalkylene ether glycol, the block copolymer comprising a polyalkylene ether glycol segment in an amount from 55 to 90% by weight, wherein the film does not form crease-whitening when the film is treated by being folded and pressed twice with a rubber roller at a load of 2 kg and a speed of 2 sec/100 mm in parallel to a machine direction of the film, and wherein the film has an adhesive strength in the machine direction of 100 to 200 g/cm, the adhesive strength being measured via separation at an angle of 180° and a tensile speed of 200 mm/min.

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

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

4. A heat shrinkable label formed of the heat shrinkable multilayer film according to claim 1.

5. The heat shrinkable multilayer film according to claim 1, wherein the polyester forming the block copolymer in the polyester elastomer is an aromatic polyester.

6. The heat shrinkable multilayer film according to claim 1, wherein in the polyester elastomer, the polyester of the block copolymer forms a hard segment and the polyalkylene ether glycol of the block copolymer forms a soft segment.

7. The heat shrinkable multilayer film according to claim 1, wherein the polyester resin comprises a component derived from terephthalic acid as the dicarboxylic acid component, and the adhesive layer has a thickness in a range from 0.3 μm to 3.0 μm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view showing a state of separating a film in evaluation of interlaminar strength.

(2) FIG. 2 is a schematic view showing a state of separating a film in evaluation of interlaminar strength.

(3) FIG. 3 is a photograph showing one example where no crease-whitening is observed in evaluation of crease-whitening.

(4) FIG. 4 is a photograph showing one example where crease-whitening is observed in evaluation of crease-whitening.

DESCRIPTION OF EMBODIMENTS

(5) The following will describe embodiments of the present invention in detail referring to examples, but the present invention is not limited to these examples.

(6) The materials used in the examples and comparative examples are listed below.

(7) (Polyester Resin)

(8) PEs-1: a polyester resin (Vicat softening temperature: 69° C.) that contains a dicarboxylic acid component (100 mol % of terephthalic acid) and a diol component (65 mol % of a component derived from ethylene glycol, 12 mol % of a component derived from diethylene glycol, and 23 mol % of a component derived from 1,4-cyclohexane dimethanol)

(9) PEs-2: a polyester resin (Vicat softening temperature: 85° C.) that contains a dicarboxylic acid component (100 mol % of terephthalic acid) and a diol component (68 mol % of a component derived from ethylene glycol, 2 mol % of a component derived from diethylene glycol, and 30 mol % of a component derived from 1,4-cyclohexane dimethanol)

(10) (Polystyrene Resin)

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

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

(13) PS-3: a styrene-butadiene copolymer (Asaflex 830, produced by Asahi Kasei Chemicals Corporation, Vicat softening temperature: 72° C., MFR: 6.1 g/10 min)

(14) PS-4: a styrene-butadiene copolymer (CLEAREN 220M, produced by DENKI KAGAKU KOGYO KABUSHIKI KAISHA, Vicat softening temperature: 78° C., MFR: 7.2 g/10 min)

(15) PS-5: a styrene-butadiene copolymer (CLEAREN 210M, produced by DENKI KAGAKU KOGYO KABUSHIKI KAISHA, Vicat softening temperature: 80° C., MFR: 8.8 g/10 min)

(16) (Polyester Elastomer)

(17) TPE-1: an elastomer consisting of a polyester as a hard segment and a polyether as a soft segment (PRIMALLOY A 1600N produced by Mitsubishi Chemical Corporation, melting point: 160° C., specific gravity: 1.00)

(18) TPE-2: an elastomer consisting of a polyester as a hard segment and a polyether as a soft segment (Hytrel 4057 produced by DU PONT-TORAY CO., LTD., melting point: 163° C., specific gravity: 1.15)

(19) (Polystyrene Elastomer)

(20) TPE-3: a maleic anhydride-modified styrene-ethylene/butylene-styrene block copolymer (styrene content: 30% by weight, addition amount of maleic anhydride: 0.5% by weight, MFR: 4.0 g/10 min)

(21) The Vicat softening temperatures were determined by a method in accordance with JIS K 7206 (1999). Specifically, a specimen was taken out from each polyester resin and from each polystyrene resin, a needle-shaped indenter was placed on the specimen, and a load of 10N was applied to the needle-shaped indenter and the temperature was raised at 120° C./h. The temperature at which the needle-shaped indenter was inserted into the specimen by 1 mm was considered as the Vicat softening temperature.

(22) The MFRs were determined by a method in accordance with ISO 1133, by melting each polystyrene resin at 200° C. and measuring the ejection amount of the resin at a load of 5 kg for 10 min.

(23) The melting points were determined by raising the temperature of each polyester elastomer at 10° C./min using a differential scanning calorimeter (DCS-60, produced by Shimadzu Corporation).

(24) The specific gravity of each polyester elastomer was determined by a method in accordance with JIS K 7112 (1999), that is, by liquid displacement using ethanol as an immersion liquid (an electronic hydrometer MD-300S, produced by Alfa Mirage Co., Ltd.).

Example 1

(25) A polyester resin (PEs-1) was used for a resin forming front and back layers.

(26) A polystyrene resin (PS-1) was used for a resin forming an interlayer.

(27) For resins forming adhesive layers, 85% by weight (85 parts by weight) of a polystyrene resin (PS-3) and 15% by weight (15 parts by weight) of a polyester elastomer (TPE-1) were used. The resins were charged 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 in take-up rolls at 30° C. Subsequently, the sheet was stretched at a stretch ratio of six times in a tenter stretching machine having a preheating zone of 105° C., a stretching zone of 90° C., and a heat setting zone of 85° C. The stretched sheet was wound on a winder. Thus, a heat shrinkable multilayer film in which the direction orthogonal to the main shrinkage direction was MD and the main shrinkage direction was TD was obtained.

(28) The heat shrinkable multilayer film had a five-layer structure of front or back layer (8 μm)/adhesive layer (1 μm)/interlayer (32 μm)/adhesive layer (1 μm)/front or back layer (8 μm), with a total thickness of 50 μm.

Example 2

(29) A polystyrene resin (PS-2) was used for a resin forming an interlayer.

(30) For resins forming adhesive layers, 70% by weight of a polystyrene resin (PS-3) and 30% by weight of a polyester elastomer (TPE-1) were used.

(31) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (10 μm)/adhesive layer (0.8 μm)/interlayer (28.4 μm)/adhesive layer (0.8 μm)/front or back layer (10 μm) was obtained.

Example 3

(32) For resins forming adhesive layers, 50% by weight of a polystyrene resin (PS-3) and 50% by weight of a polyester elastomer (TPE-2) were used.

(33) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (5 μm)/adhesive layer (0.6 μm)/interlayer (23.8 μm)/adhesive layer (0.6 μm)/front or back layer (5 μm), with a total thickness of 35 μm was obtained.

Example 4

(34) For resins forming adhesive layers, 70% by weight of a polystyrene resin (PS-3) and 30% by weight of a polyester elastomer (TPE-2) were used.

(35) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (7 μm)/adhesive layer (1.0 μm)/interlayer (24 μm)/adhesive layer (1.0 μm)/front or back layer (7 μm), with a total thickness of 40 μm was obtained.

Example 5

(36) A polyester resin (PEs-2) was used for a resin forming front and back layers.

(37) For resins forming adhesive layers, 75% by weight of a polystyrene resin (PS-4) and 25% by weight of a polyester elastomer (TPE-2) were used. A stretching process was performed at a stretch ratio of 5.5 times in a tenter stretching machine having a preheating zone at 110° C., and a stretching zone at 90° C. and a heat setting zone at 85° C. The stretched sheet was wound on a winder. Thereby, a heat shrinkable multilayer film in which the direction orthogonal to the main shrinkage direction was MD and the main shrinkage direction was TD was obtained.

(38) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (5 μm)/adhesive layer (1.0 μm)/interlayer (28 μm)/adhesive layer (1.0 μm)/front or back layer (5 μm), with a total thickness of 40 μm was obtained.

Example 6

(39) For resins forming adhesive layers, 75% by weight of a polystyrene resin (PS-5) and 25% by weight of a polyester elastomer (TPE-2) were used.

(40) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (10 μm)/adhesive layer (1.0 μm)/interlayer (18 μm)/adhesive layer (1.0 μm)/front or back layer (10 μm), with a total thickness of 40 μm was obtained.

Comparative Example 1

(41) For a resin forming adhesive layers, 100% by weight of a polystyrene resin (PS-3) was used.

(42) Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (7 μm)/adhesive layer (1.0 μm)/interlayer (24 μm)/adhesive layer (1.0 μm)/front or back layer (7 μm), with a total thickness of 40 μm was obtained.

Comparative Example 2

(43) For a resin forming adhesive layers, 100% by weight of a polyester elastomer (TPE-1) was used. Other processes were performed in the same manner as in Example 5. Thus, a five-layer film consisting of front or back layer (8 μm)/adhesive layer (1.0 μm)/interlayer (32 μm)/adhesive layer (1.0 μm)/front or back layer (8 μm), with a total thickness of 50 μm was obtained.

Comparative Example 3

(44) For a resin forming adhesive layers, a polystyrene elastomer (TPE-3) was used. Other processes were performed in the same manner as in Example 5. Thus, a five-layer film consisting of front or back layer (6.5 μm)/adhesive layer (0.9 μm)/interlayer (30.2 μm)/adhesive layer (0.9 μm)/front or back layer (6.5 μm), with a total thickness of 45 μm was obtained.

Comparative Example 4

(45) For resins forming adhesive layers, 25% by weight of a polystyrene resin (PS-3) and 75% by weight of a polyester elastomer (TPE-2) were used. Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (8 μm)/adhesive layer (1.0 μm)/interlayer (32 μm)/adhesive layer (1.0 μm)/front or back layer (8 μm), with a total thickness of 50 μm was obtained.

Comparative Example 5

(46) For resins forming adhesive layers, 50% by weight of a polystyrene resin (PS-1) and 50% by weight of a polyester resin (PEs-1) were used. Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (6 μm)/adhesive layer (0.8 μm)/interlayer (26.4 μm)/adhesive layer (0.8 μm)/front or back layer (6 μm), with a total thickness of 40 μm was obtained.

Comparative Example 6

(47) For resins forming adhesive layers, 75% by weight of a polystyrene resin (PS-3) and 25% by weight of a polyester resin (PEs-1) were used. Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (6 μm)/adhesive layer (1.0 μm)/interlayer (36 μm)/adhesive layer (1.0 μm)/front or back layer (6 μm), with a total thickness of 50 μm was obtained.

Comparative Example 7

(48) For resins forming adhesive layers, 97% by weight of a polystyrene resin (PS-3) and 3% by weight of a polyester elastomer (TPE-2) were used. Other processes were performed in the same manner as in Example 1. Thus, a five-layer film consisting of front or back layer (6 μm)/adhesive layer (1.0 μm)/interlayer (26 μm)/adhesive layer (1.0 μm)/front or back layer (6 μm), with a total thickness of 40 μm was obtained.

(49) (Evaluation)

(50) The heat shrinkable multilayer films obtained in the examples and the comparative examples were evaluated as follows. Table 1 shows the results.

(51) (1) Adhesive Strength (Adhesiveness) Before Printing

(52) The heat shrinkable multilayer film was cut into a size of 100 mm (in length)×10 mm (in width), and part of the film edge was delaminated as shown in FIG. 1. The layers were separated at a 180° angle at a tensile speed of 200 mm/min in the longitudinal direction of the sample as shown in FIG. 2. The strength at this time was measured using a peel tester (Peeling Tester HEIDON-17, produced by Shinto Scientific Co., Ltd.).

(53) The test was performed 10 times in the both MD and TD. Thereby, the adhesive strengths in the MD and in the TD were determined. Also, the average of the both adhesive strengths in the MD and TD was determined so as to be able to prevent delamination caused by diagonally tearing the film when the film was tried to be torn along perforations.

(54) If the measured values fluctuated due to zipping, the initial peak value was considered as the adhesive strength because the strength initiating delamination should be focused on.

(55) The average adhesive strengths in the MD and in the TD and the average value of the both adhesive strengths in the MD and TD were evaluated according to the following criteria. If these values are evaluated as “o”, delamination of the film caused by diagonally tearing the film when the film is tried to be torn along perforations may be prevented.

(56) (Adhesive Strength in MD)

(57) An adhesive strength of 100 g/cm or more was evaluated as “o”, and an adhesive strength of less than 100 g/cm was evaluated as “x”.

(58) (Adhesive Strength in TD)

(59) An adhesive strength of 50 g/cm or more was evaluated as “o”, and an adhesive strength of less than 50 g/cm was evaluated as “x”.

(60) (Average Value in Both MD and TD)

(61) An average value of 80 g/cm or more was evaluated as “o”, and an average value of less than 80 g/cm was evaluated as “x”.

(62) (2) Adhesive Strength (Adhesiveness) after Printing

(63) A black image was printed on the heat shrinkable multilayer film (film width: 500 mm) using Fine Star black (TOYO INK CO., LTD.), and then a white image was printed using Fine Star white (TOYO INK CO., LTD.), each by gravure printing. This provided a heat shrinkable multilayer film with a two-color-printed (black and white) back face. The printing plate was one produced by direct laser engraving with a plate depth of 30 μm and 175 lines.

(64) The printed heat shrinkable multilayer film was cut into a size of 100 mm (in length)×10 mm (in width), and part of the film edge was delaminated as shown in FIG. 1. The layers were separated at a 180° angle at a tensile speed of 200 mm/min in the longitudinal direction of the sample as shown in FIG. 2. The strength at this time was measured using a peel tester (Peeling Tester HEIDON-17, produced by Shinto Scientific Co., Ltd.).

(65) The test was performed 10 times in the both MD and TD, and the adhesive strengths in the MD and in the TD, and the average of the strengths in the both MD and TD were determined based on the average values of the measurement results. The film was evaluated according to the following criteria.

(66) If the measured values fluctuated due to zipping, the initial peak value was considered as the adhesive strength because the strength initiating delamination should be focused on.

(67) The adhesive strengths in the MD and in the TD and the average of the strengths in the both MD and TD were evaluated according to the following criteria. If these values are evaluated as “o”, the film has sufficient anti-printability, which enables to prevent delamination caused by diagonally tearing the film when the film is tried to be torn along perforations.

(68) (Adhesive Strength in MD)

(69) An adhesive strength of 100 g/cm or more was evaluated as “o”, and an adhesive strength of less than 100 g/cm was evaluated as “x”.

(70) (Adhesive Strength in TD)

(71) An adhesive strength of 50 g/cm or more was evaluated as “o”, and an adhesive strength of less than 50 g/cm was evaluated as “x”.

(72) (Average of the Strengths in Both MD and TD)

(73) An average of 80 g/cm or more was evaluated as “o”, and an average of less than 80 g/cm was evaluated as “x”.

(74) (3) Evaluation of Crease-Whitening

(75) A black image was printed on the heat shrinkable multilayer film (film width: 500 mm) using Fine Star black (TOYO INK CO., LTD.), and then a white image was printed using Fine Star white (TOYO INK CO., LTD.), each by gravure printing. This provided a heat shrinkable multilayer film with a two-color-printed (black and white) back face. The printing plate was one produced by direct laser engraving with a plate depth of 30 μm and 175 lines.

(76) Then, the heat shrinkable multilayer film was cut into a rectangle with a size of 100 mm (in MD)×200 mm (in TD) from the black printed part. This cutout sample was folded with the printed face inside and pressed twice by a rubber roller at a load of 2 kg and a speed of 2 sec/100 mm in parallel to the MD, so that a crease was formed. Then, the cutout sample was unfolded and pressed once by the rubber roller at a load of 2 kg and a speed of 2 sec/100 mm, so that the crease was smoothed out. Thereafter, the sample was immersed in warm water at 75° C. for 7 seconds using a jig capable of controlling the shrinkage rate in the TD, and thereby the film was shrunk by 5% in the TD. The appearance of the crease at this time was evaluated based on the following criteria.

(77) The appearance of the crease was evaluated as follows: light of a fluorescent lamp was applied onto the sample from an angle of 45°, and 10 persons visually observed the sample from the opposite side to the lamp at an angle of 45°. FIG. 3 shows one example where no crease-whitening was observed, and FIG. 4 shows one example where crease-whitening was observed.

(78) ∘: None of the 10 persons observed crease-whitening.

(79) Δ: One or two of the 10 persons observed crease-whitening.

(80) x: Three or more of the 10 persons observed crease-whitening.

(81) (4) Sealing Strength in MD

(82) The heat shrinkable multilayer film was sealed using a solvent containing 40 parts by weight of cyclohexane for 100 parts by weight of 1,4-dioxolan, whereby forming a sealed portion in parallel to the MD with a width of 3 mm. The heat shrinkable multilayer film was cut into a size of 10 cm (in MD)×5 cm (in TD) such that the solvent sealed portion was placed in the center, and then part of the sealed edge was separated. The layers were separated at a 180° angle at a tensile speed of 200 mm/min in the longitudinal direction of the sample. The sealing strength at this time was measured using a peel tester (Peeling Tester HEIDON-17, produced by Shinto Scientific Co., Ltd.).

(83) The test was performed ten times in the MD, and the average value was calculated. The average value was evaluated according to the following criteria. If the film was evaluated as “oo” or “o”, separation at the sealed portion may be prevented even by an external force in the MD by a labeler or the like.

(84) A sealing strength of 60 g or more was evaluated as “oo”, a sealing strength of 40 g or more and less than 60 g was evaluated as “o”, a sealing strength of 25 g or more and less than 40 g was evaluated as “Δ”, and a sealing strength of less than 25 g was evaluated as “x”.

(85) (Total Evaluation)

(86) ∘: no “x” in the evaluations (1) to (4)

(87) x: one or more “x” in the evaluations (1) to (4)

(88) TABLE-US-00001 TABLE 1 Compar- Compar- Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative ative ative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Composition Front and back layers PEs-1 100 100 100 100 — 100 100 — — 100 100 100 100 of resin PEs-2 — — — — 100 — — 100 100 — — — — (parts by Interlayer PS-1 100 — — 100 100 100 100 100 100 100 100 100 100 weight) PS-2 — 100 100 — — — — — — — — — — Adhesive Polystyrene PS-3 85 70 50 70 — — 100 — — 25 — 75 97 layers resin PS-4 — — — — 75 — — — — — — — — PS-5 — — — — — 75 — — — — — — — PS-1 — — — — — — — — — — 50 — — Polyester TPE-1 15 30 — — — — — 100 — — — — — elastomer TPE-2 — — 50 30 25 25 — — — 75 — — 3 Polystyrene TPE-3 — — — — — — — — 100 — — — — elastomer Polyester PEs-1 — — — — — — — — — — 50 25 — resin Evaluation Adhesive MD 142 150 137 144 126 150 36 142 134 140 61 45 35 strength Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ ◯ ◯ x x x before TD 88 136 122 136 119 68 45 124 123 120 103 53 51 printing Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ ◯ ◯ ◯ ◯ x (g/cm) Average of MD 115 143 130 140 123 109 41 133 128 130 82 49 43 and TD Adhesive Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ ◯ ◯ ◯ x x strength MD 159 163 158 166 167 174 42 167 34 163 84 51 38 after Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ x ◯ x ◯ x printing TD 71 120 135 124 98 52 32 145 58 141 67 37 44 (g/cm) Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ ◯ ◯ ◯ x x Average of MD 115 142 147 145 133 113 37 156 46 152 76 44 41 and TD Evaluation ◯ ◯ ◯ ◯ ◯ ◯ x ◯ x ◯ x x x Evaluation of crease-whitening ◯ ◯ Δ ◯ ◯ ◯ ◯ x ◯ x ◯ ◯ ◯ Sealing MD 42 60 68 62 52 55 15 80 38 70 21 24 15 strength Evaluation ◯ ◯◯ ◯◯ ◯◯ ◯ ◯ x ◯◯ Δ ◯◯ x x x (g) Total evaluation ◯ ◯ ◯ ◯ ◯ ◯ x x x x x x x

(89) The heat shrinkable multilayer films obtained in the examples achieved good results in all the evaluation items. In contrast, in the cases where the mixing ratio of the resins forming adhesive layers is out of the range specified by the present invention, such as in Comparative Examples 1 to 7, the films had low adhesive strengths, or left white creases caused by folding the films with a strong pressure in a solvent sealing process for attaching the films to containers, which resulted in poor appearance.

INDUSTRIAL APPLICABILITY

(90) The present invention can provide a heat shrinkable multilayer film that has excellent adhesiveness between front and back layers and an interlayer, effectively prevents delamination, and is less likely to have white creases on folds. The present invention can also provide a heat shrinkable label formed from the heat shrinkable multilayer film.

REFERENCE SIGNS LIST

(91) 1: interlayer 2: front and back layers