JP2000143836A - Heat-shrinkable film and container fitted with same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat-shrinkable film having a small spontaneous shrinkage, excellent heat shrinkability and being capable of being perforated so as to facilitate separation along the lengthwise and crosswise directions by selecting a film containing a polystyrene resin layer and having a specified ratio of the lengthwise tear propagation strength to the crosswise tear propagation strength. SOLUTION: An interlayer containing at least one resin selected from among a polystyrene, a high-impact polystyrene, and a grafted high-impact polystyrene is laminated with an inner or outer layer containing a styrene/butadiene block copolymer having a butadiene content of 10-40 wt.%, the obtained laminate is stretched lengthwise at a ratio of 1-3 by means of rolls and is stretched crosswise at a ratio of 3-8 by means of a tenter, annealed, and cooled to obtain a heat-shrinkable film having a total thickness of 10-150 μm 30-95% of which the interlayer accounts for. This film is printed and perforated to obtain a heat-shrinkable film having a ratio (α/β) of 0.1-1.2 (wherein α is the lengthwise tear propagation strength, and β is the crosswise tear propagation strength).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in perforation cutability, low in natural shrinkage rate, excellent in heat shrinkage property, and used as cap seals and labels for plastic bottles and glass bottles, and other packaging materials. The present invention relates to a suitable heat-shrinkable polystyrene film and its use for a container.

[0002]

2. Description of the Related Art Cap seals and labels attached to plastic bottles, glass bottles and the like by heat shrinking are preliminarily provided with two wires or one wire in order to impart easy-opening properties and to allow easy peeling when recycling bottles and bottles. Main lines are often perforated. On the other hand, polystyrene-based heat-shrinkable films are expected to replace the conventionally used polyvinyl chloride film, but when tearing the film from the end to the other end of the perforation, There was a drawback that it did not tear cleanly (that is, the perforation cutting property was poor).

In order to solve this drawback, Japanese Patent Application Laid-Open No. 62-10 / 1987
No. 9761 proposes a cap seal manufactured by extruding a styrene-butadiene block copolymer from a die and stretching the film only in the transverse direction with respect to the casting direction and making the transverse direction the circumferential direction. Have been.

[0004] However, it is difficult to say that the perforation-cutting property is sufficient even by the above-mentioned proposals, and further proposals have been made in JP-A-6-344440 and JP-A-9-207922. JP 6-344440 discloses the ratio of the length _{L 2} of the film between the maximum length _{L 1} and the hole and the hole of the perforation holes _(L 1 / _{L 2)} is not less than 1.3, and L
₂ is within 0.8 mm. JP-A-9-20
No. 7922 discloses a double line perforation.

[0005]

However, Japanese Patent Application Laid-Open No. 6-344440 has a problem that the perforated hole is long and the interval between the perforated holes is short, so that the appearance is poor. Further, Japanese Patent Application Laid-Open No. 9-207922 has a problem that the appearance is poor because of double line perforations.

[0006] The first problem to be solved by the present invention is:
It does not require any special restrictions on the length of perforation holes, the interval between perforations, or the need for double-line perforations. Another object of the present invention is to provide a heat-shrinkable polystyrene film having excellent perforation cutability.

A second object is to provide a heat-shrinkable polystyrene film having a small natural shrinkage and excellent heat shrinkage characteristics.

A third object is to provide a container equipped with a polystyrene-based heat-shrinkable film having excellent perforation-cutting properties.

[0009]

As a means for solving the above-mentioned problems, the present invention comprises at least one polystyrene resin layer, and has a longitudinal tear propagation strength (α) and a transverse tear propagation strength. (Β) ratio α / β is 0.1 to
A heat-shrinkable film in the range of 1.2.

The natural shrinkage in the horizontal direction is 2.5% or less, the heat shrinkage in the horizontal direction is 20% or more at 80 ° C. × 10 seconds,
45% or more at 90 ° C. × 10 seconds, and the difference is 25%
% Of the heat-shrinkable film.

Further, a container is provided with the perforated heat-shrinkable film.

[0012]

Embodiments of the present invention will be described in detail below.

The polystyrene resin referred to in the present invention refers to polystyrene, impact-resistant polystyrene, graft-type impact-resistant polystyrene, styrene-butadiene block copolymer, and the like.

Polystyrene refers to homopolymers and styrene copolymers composed of styrene derivatives such as styrene, α-methylstyrene and p-methylstyrene, as well as monomers copolymerizable with styrene and styrene derivatives, such as acryl. Acids, methacrylic acid, metal salts thereof (eg, Na, K,
Metal salts such as Li, Ca, Mg, and Zn), and copolymers with aliphatic unsaturated carboxylic acids such as acrylates and methacrylates and derivatives thereof.

The impact-resistant polystyrene is a mixture of a synthetic rubber such as polybutadiene and polyisoprene and the above-mentioned polystyrene, or a polystyrene grafted with a synthetic rubber such as polybutadiene and polyisoprene.

Graft-type impact-resistant polystyrene is defined as particles comprising a rubber-like polymer containing the polystyrene in a continuous phase of the polystyrene and grafting the polystyrene to a rubber component such as polybutadiene and polyisoprene. It is based on a distributed structure.

The styrene-butadiene block copolymer refers to a copolymer comprising a styrene block and a butadiene block in which butadiene is smaller in total weight ratio (preferably, butadiene content is 10 to 40% by weight). BS or (SB) _n
-S (S represents a styrene block, B represents a butadiene block, and n represents an integer of 2 or more). It should be noted that tertiary and quaternary copolymers containing other components in the styrene-butadiene block copolymer are also included in the present invention. As other components, for example, acrylic acid, methacrylic acid, metal salts thereof (for example, metal salts such as Na, K, Li, Mg, Zn, etc.), aliphatic carboxylic acids such as acrylic acid esters and methacrylic acid esters, Derivatives thereof can be exemplified.

Next, perforation processing (cutting property) will be described with reference to FIGS. 1, 2 and 3. FIG. Each figure is a view of a typical example showing a state in which a heat-shrinkable film (that is, a cap seal, a label) pre-perforated has been attached to a container, and FIG. 1 is a longitudinal direction (from the top of the container to the bottom). 2 and 3 (peripheral direction of the container), and FIGS. 2 and 3 are perforated in the vertical direction.

The present inventors have conducted intensive studies in order to impart good perforation cutability to the heat-shrinkable film subjected to such perforation processing. As a result, the heat-shrinkable film was formed into at least one polystyrene resin layer. And the ratio α / of the longitudinal tear propagation strength (α) to the transverse tear propagation strength (β)
The inventors have found that the problem can be solved by using a film in which β is in the range of 0.1 to 1.2, and have accomplished the present invention.

The ratio α / β ranges from 0.1 to 1.2, preferably from 0.1 to 0.9, more preferably from 0.2 to 0.8.
It is. If the ratio is less than 0.1 or exceeds 1.2, the balance between the vertical direction and the horizontal direction is lost, and good perforation cutability cannot be obtained.

The polystyrene-based resin is a resin as described above, and the resin layer may be one layer or more. Further, it may include another resin layer. The one-layer heat-shrinkable film is a film including a layer containing at least one resin selected from the group consisting of polystyrene, impact-resistant polystyrene, graft-type impact-resistant polystyrene, and styrene-butadiene block copolymer.

Preferably, at least one resin selected from the group consisting of polystyrene, impact-resistant polystyrene, and graft-type impact-resistant polystyrene and a butadiene content of 10 to 40% by weight (preferably 15 to 35% by weight,
(Preferably 23 to 30% by weight) of a layer containing a mixture with a styrene-butadiene block copolymer. A film containing at least one resin selected from the group consisting of polystyrene, high-impact polystyrene, and graft-type high-impact polystyrene can easily obtain a film having a small natural shrinkage and a large heat shrinkage. Since heat shrinkage is likely to occur, wrinkles and avatars tend to easily enter the film (cap seal, label, etc.) in the heat shrink finish. For this reason, in order to obtain a film having a large heat shrinkage rate while having a heat shrinkage property, that is, an appropriate heat shrink rate, an appropriate range of manufacturing conditions in a film manufacturing condition described later is narrow. On the other hand, when the styrene-butadiene block copolymer is mixed, rapid thermal shrinkage is suppressed while maintaining a low natural shrinkage rate and a high heat shrinkage rate, and thus there is an advantage that a suitable range of production conditions is widened.

The styrene-butadiene block copolymer is mixed in an amount of 20 to 200 parts by weight, preferably 40 to 150 parts by weight, more preferably 60 to 150 parts by weight, per 100 parts by weight of at least one resin selected from the above group. Department.

More preferably, in addition to the above mixture,
In addition, the resin layer contains an elastomer. The elastomer is not particularly limited, but from the viewpoint of transparency, a conjugated diene content of 45 to 45, such as butadiene and isoprene, is used.
95% by weight (preferably 50 to 90% by weight, more preferably 55 to 65% by weight) of a styrene-conjugated diene block type elastomer is preferred. The mixing amount of the styrene-conjugated diene block type elastomer may be appropriately determined. Usually, 1 to 5 parts per 100 parts by weight of the mixture
0 parts by weight, preferably 2 to 30 parts by weight. Film production conditions for mixing the styrene-conjugated diene block type elastomer to make the ratio α / β between the tear propagation strength in the longitudinal direction (α) and the tear propagation strength in the transverse direction fall within the range of 0.1 to 1.2. There is an advantage that the width is further increased.

As another preferred heat-shrinkable film structure, an intermediate layer (B) containing at least one selected from the group consisting of polystyrene, impact-resistant polystyrene, and graft-type impact-resistant polystyrene, and a butadiene content of 10 to 10% The inner and outer layers (A) and (C) containing 40% by weight (preferably 15 to 35% by weight, more preferably 23 to 30% by weight) of the styrene-butadiene block copolymer are combined with (A) / (B) / (C ) Can be exemplified. The intermediate layer (B) mainly contributes to impart a low natural shrinkage and a high heat shrinkage, and the inner and outer layers (A) and (C) mainly contribute to impart an appropriate heat shrink rate. Lamination method may be any known method such as dry lamination, extrusion lamination,
The co-extrusion method is simple and preferred.

When the intermediate layer (B) is mixed with an elastomer, preferably the above-mentioned styrene-conjugated diene block type elastomer, there are the same advantages as described above. The mixing amount of the styrene-conjugated diene block type elastomer may be appropriately determined. Usually, the amount is 1 to 50 parts by weight, preferably 2 to 30 parts by weight, per 100 parts by weight of the resin of the intermediate layer.
Further, a styrene-butadiene block copolymer may be mixed.

The inner and outer layers (A) and (C) are more preferably
It is to mix polystyrene. The mixing amount is 2 to 100 parts by weight of polystyrene, preferably 7 to 100 parts by weight, based on 100 parts by weight of the styrene-butadiene block copolymer.
50 parts by weight, more preferably 12 to 25 parts by weight.

In the case of cap seals and labels, it is common to form a tube by sealing the center with an organic solvent, but since the styrene-butadiene block copolymer has an appropriate solvent resistance, the resin is used in the inner and outer layers ( A)
When the main component of (C) is used, there is also an advantage that whitening and cracking of the center seal portion do not occur. The inner layer (A) and the outer layer (C) may differ in the MI (melt index) of the styrene-butadiene block copolymer, the butadiene content, the structure, the mixing amount of polystyrene, or the layer thickness. From the viewpoint of the above, it is more preferable that both are the same.

In each layer, a polyolefin resin, a cyclic polyolefin resin, a petroleum resin,
Other resins such as rubbers and various additives, for example, fillers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, nucleating agents, flame retardants, coloring agents, etc. You may. The inner and outer layers (A) and (C) have
Surface treatment may be performed. Although any known surface treatment method may be used, corona discharge treatment, plasma treatment, and flame treatment are simple and more preferred.

The total thickness of the heat-shrinkable film is 10 to
150 μm, usually 20 to 70 μm, and the intermediate layer (B)
Is 30 to 95% of the total thickness, preferably 45
~ 85%.

The layer structure is (A) / (B) / (C),
For example, the number of layers may be further increased, such as (A) / (B) / (A) / (B) / (C). Further, a layer made of a resin other than a polystyrene-based resin such as polyolefin, polyester, or cyclic polyolefin was laminated (via an adhesive layer if necessary) on at least one of the inner and outer layers (A) and (C) outside or inside. It may be something.

Next, an example of a method for producing a heat-shrinkable film will be described. A single extruder is used to melt a polystyrene resin, extrude it from a T-die, take it up with a take-up roll, stretch it 1 to 3 times in the machine direction (1x means not stretched), and after preheating The film is stretched by a tenter in the transverse direction, annealed, cooled, and wound up by a winder to obtain a heat-shrinkable film.
(When extruding into a tube using an annular die instead of a T die, this is cut open to form a flat shape, and a heat-shrinkable film is obtained in the same manner.)

The ratio of the tear propagation strength is determined by the content of the resin constituting the film, the thickness of the film, the extrusion temperature, the draw ratio, the draw temperature, the draw ratio, the draw speed, the preheating temperature, the temperature during drawing, the annealing conditions, And cooling conditions are closely related to each other. The ratio α / β between the longitudinal tear propagation strength (α) and the transverse tear propagation strength (β) of the present invention.
In order to obtain a heat-shrinkable film having a range of 0.1 to 1.2, these conditions may be appropriately selected. Generally speaking, qualitatively speaking, when using a polystyrene resin not containing a styrene-conjugated diene block type elastomer, the take-up temperature is preferably relatively low, and the ratio of transverse stretching ratio / longitudinal stretching ratio is preferred. Is preferably relatively small, and the higher the thermal relaxation rate and the temperature during annealing, the more preferable results are obtained. However, at this time, the heat shrinkage in the horizontal direction is 20% or more at 80 ° C. × 10 seconds,
45% or more at 90 ° C. × 10 seconds, and the difference is 25%
% (Preferably 35% or more at 80 ° C. × 10 seconds, 9%
55% or more at 0 ° C. × 10 seconds, and the difference is 20%
Less than). When the heat shrinkage in the transverse direction is less than 20% at 80 ° C. × 10 seconds and less than 45% at 90 ° C. × 10 seconds, it tends to be impossible to tightly mount the container. On the other hand, if the difference exceeds 25%, thermal shrinkage occurs sharply, so that wrinkles and avatars are generated on the film, and the appearance tends to be poor. (A)
/ (B) / (C) The production of a film having a three-layer structure will be specifically described in Examples below.

The thus obtained film is printed, and in the case of a cap seal or label, the film is sealed at the center with a solvent or ultrasonic waves, and cut into a predetermined length to obtain a cap seal or label. Perforation processing is usually performed using a perforation blade at the time of center sealing processing. The perforation length (hereinafter referred to as cut) and the interval between perforations (hereinafter referred to as bridge) are generally 1 mm or 0.7 mm, respectively, but large PET bottles for aseptic use In some cases, the cut is about 0.7 mm and the bridge is 2.5 to 3.5 mm in terms of drop strength (the film does not break even if the bottle is dropped by mistake). According to the heat-shrinkable film of the present invention, any pattern is excellent in perforation cutability in both the vertical and horizontal directions.

The term "container" as used in the present invention means not only plastic bottles and glass bottles but also various molded articles such as trays and lunch boxes, and all other containers to which the heat-shrinkable film of the present invention can be applied.

[0036]

Next, typical examples of the present invention will be described together with comparative examples.

The measurement of the tear propagation strength is based on JIS P-81.
No.16. The longitudinal direction of the film is the flow direction during the production of the heat-shrinkable film, and in FIGS. 1 to 3, refers to the direction corresponding to the vertical direction of the container. That. (Hereinafter the same)

The measurement of the heat shrinkage is carried out by the following method. That is, a sample was cut out in the vertical direction × horizontal direction = 100 mm × 100 mm and placed in a hot water bath at 80 ° C. (or 90 ° C.).
After immersion for 2 seconds and immediately cooling with cold water, the lateral length L ′ (mm) is measured. This measurement is repeated for 10 samples, and the average value L of L ′ is calculated. And 10
0-L was defined as the heat shrinkage in the lateral direction at 80 ° C (or 90 ° C). (When a heat-shrinkable film is attached to a container, not only a wet heat method but also a dry heat method is adopted. (Dry heat) thermal shrinkage rate was not intentionally adopted.)

The natural shrinkage was defined as the natural shrinkage when the film was allowed to stand naturally at 40 ° C. for 7 days.

The perforation cutability is evaluated by the following method. That is, a cap seal or a label subjected to perforation processing was heat-shrink-fitted to a container, and after cooling, the perforation was evaluated by tearing by hand. ：: Cuts cleanly along the perforation △: Cuts along the perforation, but cuts off the perforation midway ×: Does not cut along the perforation

(Example 1) A styrene homopolymer was added to 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 25% by weight and (SB) _2- S structure to become the inner and outer layers (A) and (C). The resin system mixed with 25 parts by weight is melted by using two extruders, and further, by using another extruder, a graft-type impact-resistant polystyrene serving as an intermediate layer (B) (Asahi Chemical Industry Co., Ltd.) SS-700)
100 parts by weight of styrene-conjugated diene block type elastomer (Tufprene 126 manufactured by Asahi Kasei Corporation)
Is melted and laminated in a 195 ° C. T-die in the order of (A) / (B) / (C), extruded from the T-die, and a take-off roll at 40 ° C. Is drawn at a draw ratio of 102%, and roll stretched 2.0 times in the machine direction at a temperature of 85 ° C. and a stretching speed of 365% / min.
After preheating at 120 ° C. for 6 seconds, the first zone temperature 105
At a second zone temperature of 90 ° C. and a stretching speed of 5330% / min. In a transverse direction by 5.0 times tenter, and relaxed by 1% in the width direction at a temperature of 80 ° C. and a time of 2.5 seconds near the exit of the tenter. While primary cooling with hot air of 75 ° C.
Secondary cooling was performed with a cooling roll at 0 ° C. to obtain a heat-shrinkable film. The thickness of the film is 1 for both the inner and outer layers (A) and (C).
The thickness was 2.5 μm, the thickness of the intermediate layer (B) was 25 μm, and the total thickness was 50 μm. Table 1 shows the tear propagation strength (α) (β), heat shrinkage, and natural shrinkage in the vertical and horizontal directions.

(Example 2) The film obtained in Example 1 was subjected to gravure printing, and a perforation of two lines with a cut of 1 mm, a bridge of 1 mm, and an interval of 10 mm was made in the vertical and horizontal directions using a sewing blade at the time of center sealing. , Cut 0.7mm, bridge 0.7mm, interval 10m
m two perforations in both the vertical and horizontal directions, and a 0.7 mm cut 3.5 mm bridge with a single perforation in the vertical direction only, three types of perforations Was put. The center sealing process is performed using a mixed solvent obtained by mixing 25 parts by weight of tetrahydrofuran and 25 parts by weight of isopropyl alcohol with 100 parts by weight of n-hexane so that the printing surface of each film becomes the inner surface,
Thereafter, the perforations described above were cut and cut to obtain a label (1) having a folded diameter of 100 mm and a length of 100 mm and a cap seal. From a tube product with perforations only in the vertical direction, similarly, folding diameter 100 mm, length 100 m
m (2) was obtained. Next, the label (1) and the cap seal are each put on a plastic bottle having a margin of 5%, and heated at 85 ° C. × 10 seconds or 90 ° C. × by wet heat.
After heat shrink mounting for 10 seconds and cooling, perforation cutability was evaluated. In addition, the label (2) has a margin rate of 6.7% and is 9%.
It was covered with a 00 ml square plastic bottle, and heat shrink-fitted in the same manner to evaluate perforation cutability. Table 2 shows the evaluation results.

(Example 3) A styrene homopolymer was added to 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 25% by weight and (SB) _2- S structure to form the inner and outer layers (A) and (C). The resin system mixed with 25 parts by weight is melted using two extruders, and further polystyrene (SC-008 manufactured by Asahi Kasei Kogyo Co., Ltd.) to be used as the intermediate layer (B) is formed using another extruder. 100 parts by weight of styrene
Butadiene block copolymer (manufactured by Asahi Kasei Corporation)
(Asaflex 830) 67 parts by weight and styrene-conjugated diene block type elastomer (Tafprene 126 manufactured by Asahi Kasei Kogyo Co., Ltd.) 7 parts by weight were mixed, and a resin system was melted. B) / (C)
And then extruded from a T-die.
It is drawn at a draw ratio of 102% using a take-off roll at 0 ° C., stretched 2.0 times in the machine direction at a temperature of 85 ° C. and a draw rate of 365% / min, and preheated at 110 ° C. for 6 seconds.
The first zone temperature is 95 ° C., the second zone temperature is 80 ° C., and the stretching speed is 5330% / min.
In the vicinity of the exit of the tenter, annealing was performed while relaxing 1% in the width direction over a period of 2.5 seconds at a temperature of 80 ° C., cooled primarily with hot air of 75 ° C., and cooled secondarily with a cooling roll of 30 ° C. and thermally contracted. A functional film was obtained. The thickness of the film is the inner and outer layers (A)
Both (C) are 6.3 μm, and the intermediate layer (b) is 37.4 μm.
m, and the total thickness was 50 μm. Table 1 shows the tear propagation strength (α) (β), heat shrinkage, and natural shrinkage in the vertical and horizontal directions. Next, in the same manner as in Example 2, the cap seals and labels prepared using this film were evaluated for perforation cutability. Table 2 shows the evaluation results.

(Comparative Example 1) A styrene homopolymer was added to 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 25% by weight to be the inner and outer layers (A) and (B) and an (SB) _2- S structure. The resin system mixed with 15 parts by weight is melted by using two extruders, and further, by using another extruder, a graft-type impact-resistant polystyrene serving as an intermediate layer (B) (Asahi Chemical Industry Co., Ltd.) SS-700)
100 parts by weight of styrene-conjugated diene block type elastomer (Tufprene 126 manufactured by Asahi Kasei Corporation)
Is melted, melt-stacked in a 195 ° C. T-die in the order of (A) / (B) / (C), extruded from the T-die, and a take-off roll at 40 ° C. At a draw ratio of 102%, and a 2.0-fold roll stretching in the machine direction at a temperature of 85 ° C. and a stretching speed of 365% / min.
After preheating at 15 ° C for 6 seconds, the first zone temperature was 105 ° C,
Tenter stretching in the transverse direction at a stretching temperature of 5330% / min in the second zone at a temperature of 92 ° C. is performed by a factor of 5.0, and annealing is performed near the exit of the tenter while relaxing 1% in the width direction at a temperature of 85 ° C. for 2.5 seconds. Then, the resultant was primarily cooled by hot air of 80 ° C. and secondarily cooled by a cooling roll of 30 ° C. to obtain a heat-shrinkable film. The film thickness of both the inner and outer layers (A) and (B) was 10 μm, the thickness of the intermediate layer (B) was 30 μm, and the total thickness was 50 μm. Vertical and horizontal tear propagation strength (α) (β)
Are shown in Table 1. Next, in the same manner as in Example 2, the cap seals and labels prepared using this film were evaluated for perforation cutability. Table 2 shows the results.

(Comparative Example 2) A styrene homopolymer was added to 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 25% by weight to form the inner and outer layers (A) and (B) and an (SB) _2- S structure. The resin system mixed with 30 parts by weight is melted by using two extruders, and polystyrene (SC-008 manufactured by Asahi Kasei Kogyo Co., Ltd.) to be used as the intermediate layer (B) is further melted by using another extruder. Is melted and laminated in a T die at 190 ° C. in the order of (A) / (B) / (C), extruded from the T die, and with a draw ratio of 102% using a take-off roll at 50 ° C. After taking up and preheating at 110 ° C. for 6 seconds, the first zone temperature was 95 ° C., the second zone temperature was 85 ° C., and the film was stretched 3.0 times in the transverse direction at a stretching speed of 4260% / min. ℃, width over 2.5 seconds While 4% relaxation direction annealed to give a heat-shrinkable film is cooled with a cooling roll of 40 ° C.. The thickness of this film was 20 μm for both the inner and outer layers (A) and (B), 10 μm for the intermediate layer (B), and the total thickness was 50 μm. Table 1 shows the tear propagation strength (α) (β) in the longitudinal direction and the lateral direction. Next, in the same manner as in Example 2, the cap seals and labels prepared using this film were evaluated for perforation cutability. Table 2 shows the results.

[0046]

Since the present invention is a heat-shrinkable film having the above constitution, it has the following effects.

According to the present invention, there is no particular restriction on the length of the perforations, the interval between the perforations, or the necessity of a double-line perforation. By processing, a polystyrene-based heat-shrinkable film having excellent perforation cutability not only in the vertical direction but also in the horizontal direction can be obtained.

Since the natural shrinkage in the horizontal direction is small, there is little dimensional change, and there is no trouble during printing or mounting.

Since the heat shrinkage is large and has an appropriate shrinking speed, the film can be mounted tightly, and no wrinkles or avatars are generated on the film after mounting.

Since the container has excellent perforation cutability and a beautiful film without wrinkles or avatars, it is tightly mounted.
Product value increases.

[Brief description of the drawings]

FIG. 1 is a perspective view of a container equipped with a label having two lines of perforations in a vertical direction and a horizontal direction.

FIG. 2 is a front view of a container equipped with a cap seal having two lines perforated in a vertical direction.

FIG. 3 is a perspective view of a container equipped with a label having a single perforation in a vertical direction.

[Explanation of symbols]

1 container 2 perforation 3 label 4 cap seal

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // B29K 25:00 B29L 7:00 9:00 F term (reference) 3E033 AA01 AA02 AA20 BA22 BB01 BB04 BB05 BB08 CA03 DB01 DB03 DD01 4F071 AA12X AA22 AA22X AA32X AA75 AA77 AH06 BA01 BB06 BB08 BC01 BC10 4F100 AK12A AK12B AK28A AK73A AL04A AL04B AL05A AL05B AL09A BA03 BA06 BA10B DC13 GB16 JA03 J10A01A04 A10A13A

Claims (8)

[Claims] 1. A composition comprising at least one polystyrene resin layer, wherein the ratio α / β of the tear propagation strength (α) in the longitudinal direction to the tear propagation strength (β) in the lateral direction is in the range of 0.1 to 1.2. Heat-shrinkable film. 2. A polystyrene resin layer comprising polystyrene,
The layer comprising a mixture of at least one resin selected from the group consisting of impact-resistant polystyrene and graft-type impact-resistant polystyrene and a styrene-butadiene block copolymer having a butadiene content of 10 to 40% by weight. The heat-shrinkable film according to the above. 3. The heat-shrinkable film according to claim 1, wherein the polystyrene-based resin layer is a resin layer further containing a styrene-conjugated diene block type elastomer having a conjugated diene content of 45 to 95% by weight. 4. An intermediate layer (B) wherein the film comprises at least one member selected from the group consisting of polystyrene, impact-resistant polystyrene and graft-type impact-resistant polystyrene, and styrene having a butadiene content of 10 to 40% by weight. -Inner / outer layer containing butadiene block copolymer (A)
The heat-shrinkable film according to claim 1, wherein (C) is a film laminated in the order of (A) / (B) / (C). 5. The inner and outer layers (A) and (C) each comprise a resin system obtained by mixing 2 to 100 parts by weight of polystyrene with 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 10 to 40% by weight. The heat-shrinkable film according to claim 4, which is A) or (C). 6. The intermediate layer (B) having a conjugated diene content of 45 to 45.
The heat-shrinkable film according to claim 4 or 5, which is an intermediate layer (B) further containing 95% by weight of a styrene-conjugated diene block type elastomer. 7. The natural shrinkage in the transverse direction is 2.5% or less, the thermal shrinkage in the transverse direction is 20% or more at 80 ° C. × 10 seconds, and 90 ° C. ×
The heat-shrinkable film according to any one of claims 1 to 6, wherein the heat-shrinkable film is 45% or more in 10 seconds and the difference is less than 25%. 8. A container equipped with the heat-shrinkable film according to claim 1, which is perforated.