Heat-shrinking multilayer film and heat-shrinking label

Abstract

The present invention provides a heat shrinkable multilayer film that can prevent layer misalignment at a center seal portion and thereby provide a labelled container having excellent appearance when the film is attached to a container as a heat shrinkable label for dry heat shrinking, and a heat shrinkable label including the heat shrinkable multilayer film as a base film. Provided is 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 heat shrinkable multilayer film has a maximum shrinkage stress of 3.5 to 11 MPa when immersed in hot water at 80° C. for 30 seconds.

Claims

1. A heat shrinkable multilayer film comprising: front and back layers each containing a polyester resin; an interlayer containing a polystyrene resin; and adhesive layers each containing a styrene-butadiene copolymer, which is a copolymer consisting of a component derived from styrene as an aromatic vinyl hydrocarbon and a component derived from 1,3-butadiene as a conjugated diene, wherein the front and back layers and the interlayer are stacked with the adhesive layers interposed therebetween, the heat shrinkable multilayer film has a maximum shrinkage stress of 3.5 to 11 MPa, which is measured by immersing in hot water at 80° C. for 30 seconds, the polystyrene resin constituting the interlayer is a mixed resin containing a styrene-butadiene copolymer (A) having a Vicat softening temperature of 80° C. or higher and a styrene-butadiene copolymer (B) having a Vicat softening temperature of lower than 80° C., the interlayer contains 1 to 35% by weight of the styrene-butadiene copolymer (A) and 65 to 99% by weight of the styrene-butadiene copolymer (B), wherein the styrene-butadiene copolymer (A) and the styrene-butadiene copolymer (B) in the interlayer represents all of the polystyrene resin in the interlayer, and the styrene-butadiene copolymer constituting the adhesive layers has a higher butadiene content than all of the styrene-butadiene copolymers constituting the interlayer.

2. The heat shrinkable multilayer film according to claim 1, wherein the polyester resin constituting the front and back layers has a glass transition temperature of 55° C. to 95° C.

3. The heat shrinkable multilayer film according to claim 1, wherein the adhesive layer contains the styrene-butadiene copolymer in an amount of 35 to 70% by weight and a polyester elastomer in an amount of 30 to 65% by weight.

4. 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 of a center seal portion of a heat shrinkable label.

(2) FIG. 2 is a schematic view of layer misalignment at a center seal portion of a heat shrinkable label.

(3) FIG. 3 is a schematic view of a measurement sample for dry heat shrinkage ratio measurement.

(4) FIG. 4 is a schematic view showing a method for dry heat shrinkage ratio measurement.

DESCRIPTION OF EMBODIMENTS

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

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

(7) (Polyester Resin)

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

(9) (Polystyrene Resin)

(10) Polystyrene resin A: styrene-butadiene copolymer having a styrene content of 81.3% by weight and a butadiene content of 18.7% by weight (Vicat softening temperature: 81° C.)

(11) Polystyrene resin B: styrene-butadiene copolymer having a styrene content of 77.7% by weight and a butadiene content of 22.3% by weight (Vicat softening temperature: 71° C.)

(12) Polystyrene resin C: styrene-butadiene copolymer having a styrene content of 72% by weight and a butadiene content of 28% by weight (Vicat softening temperature: 76° C.)

(13) (Polyester Elastomer)

(14) Elastomer A: Hytrel 2521, produced by Du Pont-Toray Co., Ltd., durometer hardness 55

Example 1

(15) Polyester resin A was used as a resin to constitute the front and back layers.

(16) 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.

(17) A mixed resin containing 10% by weight of polystyrene resin A and 90% by weight of polystyrene resin B was used as a resin constituting the interlayer.

(18) These resins were fed into extruders having a barrel temperature of 160° C. to 250° C., extruded into a three-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 roll-stretched in MD at stretching ratio of 1.5 times, then stretched in TD at a stretching ratio of 6 times in a tenter stretching machine with a preheating zone set at 112° C. (transit time: 5.3 seconds), a stretching zone set at 100° C. (transit time: 7.8 seconds), and a heat setting zone set at 102° C. (transit time: 5.3 seconds). The sheet was then wound with a winder, whereby a heat shrinkable multilayer film having a total thickness of 40 μm and a five-layer structure was obtained (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

(19) Polyester resin A was used as a resin to constitute the front and back layers.

(20) 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.

(21) A mixed resin containing 15% by weight of polystyrene resin A and 85% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(22) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(23) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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 3

(24) Polyester resin A was used as a resin to constitute the front and back layers.

(25) 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.

(26) 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.

(27) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(28) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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 4

(29) Polyester resin A was used as a resin to constitute the front and back layers.

(30) 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.

(31) A mixed resin containing 45% by weight of polystyrene resin A and 55% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(32) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(33) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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 5

(34) Polyester resin A was used as a resin to constitute the front and back layers.

(35) 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.

(36) A mixed resin containing 50% by weight of polystyrene resin A and 50% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(37) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(38) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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 6

(39) Polyester resin A was used as a resin to constitute the front and back layers.

(40) 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.

(41) A mixed resin containing 10% by weight of polystyrene resin A and 90% by weight of polystyrene resins B was used as a resin to constitute the interlayer.

(42) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

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

Example 7

(44) Polyester resin A was used as a resin to constitute the front and back layers.

(45) 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.

(46) A mixed resin containing 15% by weight of polystyrene resin A and 85% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(47) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

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

Example 8

(49) Polyester resin A was used as a resin to constitute the front and back layers.

(50) 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.

(51) 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.

(52) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

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

Example 9

(54) Polyester resin A was used as a resin to constitute the front and back layers.

(55) 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.

(56) A mixed resin containing 45% by weight of polystyrene resin A and 55% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(57) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

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

Example 10

(59) Polyester resin A was used as a resin to constitute the front and back layers.

(60) 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.

(61) A mixed resin containing 50% by weight of polystyrene resin A and 50% by weight of polystyrene resin B was used as a resin to constitute the interlayer.

(62) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

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

Comparative Example 1

(64) Polyester resin A was used as a resin to constitute the front and back layers.

(65) 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.

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

(67) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(68) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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)).

Comparative Example 2

(69) Polyester resin A was used as a resin to constitute the front and back layers.

(70) 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.

(71) Polystyrene resin A was used as a resin to constitute the interlayer.

(72) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(73) The obtained heat shrinkable multilayer film had a total thickness of 40 μm and 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)).

Comparative Example 3

(74) Polyester resin A was used as a resin to constitute the front and back layers.

(75) 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.

(76) Polystyrene resin B was used as a resin to constitute the interlayer.

(77) A heat shrinkable multilayer film was obtained as in Example 1 except that these resins were used.

(78) The obtained heat shrinkable multilayer film had a total thickness of 30 μm and a five-layer structure (front layer (3.2 μm)/adhesive layer (0.7 μm)/interlayer (22.2 μm)/adhesive layer (0.7 μm)/back layer (3.2 μm)).

(79) (Evaluation)

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

(81) (1) Shrinkage Stress

(82) The obtained heat shrinkable multilayer film was cut to 200 mm×10 mm such that TD (main shrinkage direction) corresponded to the long side, whereby a measurement sample was obtained. One end of this measurement sample was fixed at a chuck distance of 100 mm, and the other end was connected to a load cell to measure the load (the output signals from the load cell were recorded by a recorder).

(83) The measurement sample along with the chucks was immersed in hot water adjusted to 80° C. for 30 seconds. The shrinkage stress when the measurement sample was shrunk was measured. Here, the maximum value during 30 seconds was taken as the measurement value.

(84) (2) Dry Heat Shrinkage Ratio

(85) The heat shrinkable multilayer film was cut to 300 mm×25 mm such that the TD (main shrinkage direction) corresponded to the long side. A gauge length of 200 mm was marked on the film, whereby a measurement sample was prepared (see FIG. 3). Both ends of the measurement sample were then fixed to a 520-mm-long pointer. The fixed heat shrinkable multilayer film was bent with the front layer on the outside (see FIG. 4). The measurement sample was then placed, from a side hole, into a constant-temperature and constant-humidity chamber (produced by Nagano Science Co., Ltd., LH31-12M) set at a temperature of 70° C. or 100° C. and a humidity of 25%. After 10 seconds from placing, the heat shrinkable multilayer film was taken out and the gauge length was measured. The shrinkage ratio of the gauge length was calculated by the following formula.
Dry heat shrinkage ratio={(200−gauge length after shrinking (mm))/200}×100

(86) The average of measurement results of three measurement samples was used as the dry heat shrinkage ratio. Values that were 2% or more away from the average were not counted.

(87) (3) Layer Misalignment

(88) The obtained heat shrinkable multilayer film was cut to 100 mm×200 mm such that TD (main shrinkage direction) corresponded to the long side. The film was solvent-sealed using a solvent mixture containing 100 parts by weight of 1,4-dioxolane and 40 parts by weight of cyclohexane such that the center seal portion was 5 mm wide and in parallel with MD (direction perpendicular to the main shrinkage direction). The film was then folded flat with the center seal portion positioned in the middle, whereby a tubular heat shrinkable label was obtained.

(89) Thereafter, the heat shrinkable label was immersed in hot water at 100° C. for 30 seconds using a fixture capable of regulating the shrinkage ratio in TD, whereby the label was shrunk by 5% in TD.

(90) The appearance of the center seal portion at this time was observed to examine misalignment between the interlayer and a front or back layer. The layer misalignment was evaluated according to the following criteria.

(91) Good: The misalignment between the interlayer and a front or back layer at the center seal portion was smaller than 0.1 mm.

(92) Poor: The misalignment between the interlayer and a front or back layer at the center seal portion was 0.1 mm or greater.

(93) (4) Attachability

(94) Labels having a lay flat width of 132 mm and a length of 110 mm were produced using the heat shrinkable multilayer films obtained in Examples 1 to 10 and Comparative Examples 1 to 3.

(95) A covering type shrink tunnel K-1000 (produced by Kyowa Denki Co., Ltd.) was set at a tunnel temperature of 95° C., an air flow of 20 Hz, and a belt speed of 25 Hz (transit time: 25 seconds) and used as tunnel 1.

(96) Separately, a covering type shrink tunnel K-100 (produced by Kyowa Denki Co., Ltd.) was set at a tunnel temperature of 100° C., an air flow of 40 Hz, a belt speed of 25 Hz (transit time: 25 seconds) and used as tunnel 2.

(97) Subsequently, each obtained label was attached to a spray bottle (Kabi Killer® spray bottle, capacity: 400 mL, width: 102 mm, depth: 57 mm, height: 164 mm), and passed through tunnel 1, then a room temperature atmosphere for 7 seconds, and then tunnel 2. The label was thus shrunk and attached to the container.

(98) The label attachability (attachment finish) was evaluated as follows.

(99) Good: No appearance defect due to insufficient shrinking or the like was observed.

(100) Poor: An appearance defect due to insufficient shrinking or the like was observed at the upper end of the label or any other portion.

(101) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 8 9 10 1 2 3 Heat Front and Polyester resin A 100 100 100 100 100 100 100 100 100 100 100 100 100 shrinkable back layers (% by weight) multilayer Thickness (μm) 5.7 5.7 5.7 5.7 5.7 7 7 7 7 7 5.7 5.7 3.2 film Adhesive Elastomer A 30 30 30 30 30 65 65 65 65 65 30 30 30 layer (% by weight) Polystyrene resin C 70 70 70 70 70 35 35 35 35 35 70 70 70 (% by weight) Thickness (μm) 0.7 0.7 0.7 0.7 0.7 1 1 1 1 1 0.7 0.7 0.7 Interlayer Polystyrene resin A 10 15 30 45 50 10 15 30 45 50 70 100 — (% by weight) Polystyrene resin B 90 85 70 55 50 90 85 70 55 50 30 — 100 (% by weight) Thickness (μm) 27.2 27.2 27.2 27.2 27.2 34 34 34 34 34 27.2 27.2 22.2 Total thickness (μm) 40 40 40 40 40 50 50 50 50 50 40 40 30 Evaluation Shrinkage stress (MPa) 6.5 8.3 8.8 9.5 10 5.4 6.8 7.2 7.6 8 12 12.5 3 Dry heat  70° C. 20 21 20 20 20 20 20 20 20 20 19 19 16 shrinkage 100° C. 77 77 76 75 75 76 75 74 73 74 72 72 68 ratio (%) Layer misalignment Good Good Good Good Good Good Good Good Good Good Poor Poor Good Attatchability Good Good Good Good Good Good Good Good Good Good Good Good Poor

INDUSTRIAL APPLICABILITY

(102) The present invention can provide a heat shrinkable multilayer film that can prevent layer misalignment at a center seal portion and thereby provide a labelled container having excellent appearance when the film is attached to a container as a heat shrinkable label for dry heat shrinking, and a heat shrinkable label including the heat shrinkable multilayer film as a base film.

REFERENCE SIGNS LIST

(103) 1 front or back layer 2 adhesive layer 3 interlayer 4 adhesive layer 5 front or back layer 6 front or back layer 7 adhesive layer 8 interlayer 9 adhesive layer 10 front or back layer 11 container