HEAT-SHRINKABLE MULTILAYER FILM AND HEAT-SHRINKABLE LABEL

Abstract

The present invention provides a heat shrinkable multilayer film which has excellent printability and also has good finish quality after attachment. The present invention relates to a heat shrinkable multilayer film, including front and back layers each containing a polyester resin, an interlayer, and adhesive layers, the front and back layers and the interlayer being stacked with the adhesive layers interposed therebetween. The interlayer contains a styrene homopolymer and a plasticizer. The interlayer contains the plasticizer in an amount of 5 to 35% by weight.

Claims

1. A heat shrinkable multilayer film, comprising: front and back layers each containing a polyester resin; an interlayer; and adhesive layers, the front and back layers and the interlayer being stacked with the adhesive layers interposed therebetween, the interlayer containing a styrene homopolymer and a plasticizer, the interlayer containing the plasticizer in an amount of 5 to 35% by weight.

2. The heat shrinkable multilayer film according to claim 1, wherein the interlayer contains the styrene homopolymer in an amount of 10 to 90% by weight.

3. The heat shrinkable multilayer film according to claim 1, wherein the interlayer contains an aromatic vinyl hydrocarbon-conjugated diene copolymer.

4. The heat shrinkable multilayer film according to claim 3, wherein the interlayer contains the aromatic vinyl hydrocarbon-conjugated diene copolymer in an amount of 60% by weight or less.

5. The heat shrinkable multilayer film according to claim 1, wherein the plasticizer is an ester compound or an epoxidized vegetable oil.

6. The heat shrinkable multilayer film according to claim 1, wherein the adhesive layers each contain at least one selected from the group consisting of a polyester elastomer, a styrene elastomer, and an aromatic vinyl hydrocarbon-conjugated diene copolymer.

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

Description

DESCRIPTION OF EMBODIMENTS

[0123] Embodiments of the present inventions are described below in detail with reference to examples. The present invention is not limited to the examples.

[0124] Materials used in the examples and comparative examples are listed below.

(Polyester Resin)

[0125] PET-1: polyester resin (glass transition temperature: 74 C.) containing dicarboxylic acid components (79 mol % of a component derived from terephthalic acid and 21 mol % of a component derived from isophthalic acid) and diol components (86 mol % of a component derived from ethylene glycol, 2 mol % of a component derived from diethylene glycol, and 12 mol % of a component derived from neopentyl glycol)

[0126] PET-2: polyester resin (glass transition temperature: 68 C.) containing dicarboxylic acid components (96 mol % of a component derived from terephthalic acid and 4 mol % of a component derived from isophthalic acid) and a diol component (100 mol % of a component derived from ethylene glycol)

(Polystyrene Resin)

[0127] PS-1: styrene homopolymer (Vicat softening temperature: 94 C., MFR=7.5 g/10 min)

[0128] PS-2: styrene-butadiene copolymer (70% by weight of styrene and 30% by weight of butadiene, Vicat softening temperature: 88 C., MFR=10 g/min)

[0129] PS-3: styrene-butadiene copolymer (70% by weight of styrene and 30% by weight of butadiene, Vicat softening temperature: 72 C., MFR=6 g/10 min)

(Polyester Elastomer)

[0130] TPE-1: polyether-ester type polyester elastomer (Hytrel 2401, produced by Du Pont-Toray Co., Ltd.) having a polyester segment (hard segment) prepared from an aromatic dicarboxylic acid and a short chain glycol and a polyether segment (soft segment) prepared from an aromatic dicarboxylic acid and a polyalkylene glycol (long chain glycol)

[0131] The Vicat softening temperature was measured in accordance with JIS K 7206 (1999). Specifically, a specimen was taken from each of the above polyester resins and the 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.

Example 1

[0132] As resins for the front and back layers, 70% by weight of the polyester resin (PET-1) and 30% by weight of the polyester resin (PET-3) were used.

[0133] As resins for the interlayer, 34% by weight of the polystyrene resin (PS-1) and 60% by weight of the polystyrene resin (PS-2) were used, and 6% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0134] As resins for the adhesive layers, 60% by weight of the polyester elastomer (TPE-1) and 40% by weight of the polystyrene resin (PS-3) were used.

[0135] 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 with 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.

[0136] The heat shrinkable multilayer film had a five-layer structure of front or back layer (5 m)/adhesive layer (1 m)/interlayer (28 m)/adhesive layer (1 m)/front or back layer (5 m), with a total thickness of 40 m.

Example 2

[0137] As resins for the interlayer, 40% by weight of the polystyrene resin (PS-1) and 49% by weight of the polystyrene resin (PS-2) were used, and 11% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0138] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 3

[0139] As resins for the interlayer, 40% by weight of the polystyrene resin (PS-1) and 49% by weight of the polystyrene resin (PS-2) were used, and 11% by weight of diisononyl phthalate (DINP) was added to the resins for the interlayer.

[0140] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 4

[0141] As resins for the interlayer, 35% by weight of the polystyrene resin (PS-1) and 50% by weight of the polystyrene resin (PS-2) were used, and 15% by weight of epoxidized soybean oil (epoxidized fatty acid glyceride, Adekacizer O-130P, produced by Adeka Corporation) was added to the resins for the interlayer.

[0142] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 5

[0143] As resins for the interlayer, 50% by weight of the polystyrene resin (PS-1) and 35% by weight of the polystyrene resin (PS-2) were used, and 15% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0144] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 6

[0145] As resins for the interlayer, 50% by weight of the polystyrene resin (PS-1) and 30% by weight of the polystyrene resin (PS-2) were used, and 20% by weight diisononyl phthalate (DINP) was added to the resins for the interlayer.

[0146] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 7

[0147] As resins for the interlayer, 50% by weight of the polystyrene resin (PS-1) and 25% by weight of the polystyrene resin (PS-2) were used, and 25% by weight diisononyl adipate (DINA) was added to the resins for the interlayer.

[0148] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 8

[0149] As resins for the interlayer, 60% by weight of the polystyrene resin (PS-1) and 25% by weight of the polystyrene resin (PS-2) were used, and 15% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0150] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 9

[0151] As resins for the interlayer, 75% by weight of the polystyrene resin (PS-1) and 10% by weight of the polystyrene resin (PS-2) were used, and 15% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0152] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 10

[0153] As resins for the interlayer, 80% by weight of the polystyrene resin (PS-1) and 9% by weight of the polystyrene resin (PS-2) were used, and 11% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0154] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Example 11

[0155] As resins for the interlayer, 89% by weight of the polystyrene resin (PS-1) and 11% by weight of diisononyl adipate (DINA) were used.

[0156] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Comparative Example 1

[0157] As a resin for the interlayer, 100% by weight of the polystyrene resin (PS-2) was used.

[0158] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Comparative Example 2)

[0159] As resins for the interlayer, 50% by weight of the polystyrene resin (PS-1) and 46% by weight of the polystyrene resin (PS-2) were used, and 4% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0160] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

Comparative Example 3

[0161] As resins for the interlayer, 50% by weight of the polystyrene resin (PS-1) and 10% by weight of the polystyrene resin (PS-2) were used, and 40% by weight of diisononyl adipate (DINA) was added to the resins for the interlayer.

[0162] Other processes were performed in the same manner as in Example 1, whereby a five-layer structure film was obtained.

(Evaluation)

[0163] 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.

(1) Heat shrinkage

[0164] 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 warm 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 Formula (1) below.

Heat shrinkage (%)={(100L)/100}100(1)

[0165] 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 warm water at 80 C. for 10 seconds and that in the case of immersion in warm water at 100 C. for 10 seconds were also measured in the same manner.

(2) Spontaneous Shrinkage

[0166] 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 allowed to stand in a low temperature incubator (IL-82, produced by Yamato Scientific Co., Ltd.) set at 40 C. for seven days. The spontaneous shrinkage was measured in the same manner as the heat shrinkage. Only the spontaneous shrinkage in TD was measured. Evaluation criteria were as follows.

(Good): 2.0% or less
(Poor): 2.1% or more

(3) Printability

[0167] Printing was performed on the obtained heat shrinkable multilayer film using a five-color gravure printing machine.

Film width: 900 mm
Printing inks: OSM-type sepia, red, yellow, blue, and white (base portion), produced by Dainichiseika Color & Chemicals Mfg. Co., Ltd.
Ink viscosity: 15 sec (Zahn cup method, Zahn cup #3)
Plate: color chart plates prepared by engraving platemaking
Printing speed: 150 m/min.

[0168] The number of missing ink spots per 1 m.sup.2 of the heat shrinkable multilayer film was measured using a defect detector (produced by Futec Inc.). Evaluation criteria were as follows.

(Good): 5 or less

(Fair) : 6 to 10

[0169] (Poor): 11 or more

(4) Shrink Finish Quality

[0170] Two ends of the obtained heat shrinkable multilayer film were bonded to each other with a solvent such that the main shrinkage direction corresponded to the circumferential direction, whereby a tubular heat shrinkable label (flat width: 114 mm, length: 160 mm) was prepared. The obtained tubular heat shrinkable label was slipped over a round (polygonal) 500-ml PET bottle having a diameter of about 65 mm, and shrunk using a steam tunnel (SH-5000 produced by Fuji Astec, Inc). The steam pressures in the zones were 0.06 MPa, 0.08 MPa, and 0.1 MPa, the set temperatures were 80 C., 85 C., and 95 C., and the tunnel transit time was seven seconds. The attachment evaluation was performed in accordance with the following criteria.

(Good): No crease, sliding-up, or distortion was observed.
(Poor): At least one of crease, sliding-up, and distortion was observed.

TABLE-US-00001 TABLE 1 Ex- Ex- Ex- Ex- Ex- Ex- Ex- ample ample ample ample ample ample ample 1 2 3 4 5 6 7 Resin Front and back Polyester resin PET-1 70 70 70 70 70 70 70 (% by layers PET-2 30 30 30 30 30 30 30 weight) Interlayer Polystyrene resin PS-1 34 40 40 35 50 50 50 PS-2 60 49 49 50 35 30 25 Proportion (% by weight) of styrene 76 74.3 74.3 70 74.5 71 67.5 Proportion (% by weight) of butadiene 18 14.7 14.7 15 10.5 9 7.5 Plasticizer DINA 6 11 15 25 DINP 11 20 Epoxidized 15 soybean oil Adhesive Polyester elastomer TPE-1 60 60 60 60 60 60 60 layer Polystyrene resin PS-3 40 40 40 40 40 40 40 Evaluation Heat 70 C. 10 sec TD 9 21 17 18 33 24 30 shrinkage 80 C. 10 sec TD 35 47 44 42 57 53 55 (%) 100 C. 10 sec TD 62 62 62 60 66 62 63 Spontaneous 40 C. 7 days TD 0.5 0.7 0.6 0.6 0.8 0.7 0.8 shrinkage (%) Evaluation Printability (Number of missing 7 5 5 4 2 1 1 ink spots/m.sup.2) Evaluation Shrink finish quality Ex- Ex- Ex- Ex- Compar- Compar- Compar- ample ample ample ample ative ative ative 8 9 10 11 Example 1 Example 2 Example 3 Resin Front and back Polyester resin PET-1 70 70 70 70 70 70 70 (% by layers PET-2 30 30 30 30 30 30 30 weight) Interlayer Polystyrene resin PS-1 60 75 80 89 50 50 PS-2 25 10 9 100 46 10 Proportion (% by weight) of styrene 77.5 80.5 86.3 89 70 82.2 57 Proportion (% by weight) of butadiene 7.5 4.5 2.7 0 30 13.8 3 Plasticizer DINA 15 15 11 11 4 40 DINP Epoxidized soybean oil Adhesive Polyester elastomer TPE-1 60 60 60 60 60 60 60 layer Polystyrene resin PS-3 40 40 40 40 40 40 40 Evaluation Heat 70 C. 10 sec TD 31 29 26 25 12 9 49 shrinkage 80 C. 10 sec TD 55 53 51 50 36 28 72 (%) 100 C. 10 sec TD 64 62 61 60 60 54 82 Spontaneous 40 C. 7 days TD 0.8 0.8 0.7 0.7 0.9 0.5 2.5 shrinkage (%) Evaluation x Printability (Number of missing 1 1 0 0 16 4 0 ink spots/m.sup.2) Evaluation x Shrink finish quality x

INDUSTRIAL APPLICABILITY

[0171] The present invention provides a heat shrinkable multilayer film which has excellent printability and also has good finish quality after attachment. The present invention also provides a heat shrinkable label including the heat shrinkable multilayer film.