JP2003285369A - Heat-shrinkable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinkable film with good shrinking performance and resistance to natural shrinking properties and excellent mechanical packaging suitability, and a heat-shrinkable multi-layer film. <P>SOLUTION: The heat-shrinkable film is characterized by drawing a block copolymer composition comprising (a) a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene and if necessary, (b) at least one kind of a specified vinyl aromatic hydrocarbon polymer and having a tensile elastic modulus in the drawing direction of lower than 500 MPa. The block copolymer (a) of the vinyl aromatic hydrocarbon and the conjugated diene has a mass ratio of the vinyl aromatic hydrocarbon to the conjugated diene of 50/50-90/10 and a block rate of the vinyl aromatic hydrocarbon of at most 85%. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat-shrinkable film and a heat-shrinkable multilayer film having good shrinkage performance and natural shrinkage resistance.

[0002]

2. Description of the Related Art Conventionally, heat-shrinkable films used as shrink-wrap packaging and shrink-wrap labels for containers have good heat-shrinkability and a good finish after shrinkage, and even when discarded, environmental problems such as polyvinyl chloride can be avoided. A film formed by molding a styrene-butadiene block copolymer is used because it does not exist. In addition, by performing block copolymerization of a vinyl aromatic hydrocarbon and a conjugated diene with an alkyl lithium as an initiator in an organic solvent by living anionic polymerization, the mass ratio of the vinyl aromatic hydrocarbon and the conjugated diene or the addition method may be changed. It is known that the structure of the copolymer can be diversified by the method, and a block copolymer having various physical properties can be obtained, and a heat-shrinkable film using these is known as follows. JP-A-60-49019 discloses a specific styrene-butadiene block copolymer (ratio of styrene to butadiene of 60 to 95/5 to 40, short chain styrene block of 2 to 30 styrene units of 3 to 3).
0%, number average molecular weight (Mn) of 20,000 to 500,000, and styrene block molecular weight of 10,000 to 100,000 are uniaxially or biaxially stretched, and the heat shrinkage rate is 80 ° C. for 5 minutes in the transverse direction of 15% or more, A heat-shrinkable film having a tensile elastic modulus of 5000 kg / cm ² or more in the stretching direction is described. JP-A-60-22452
No. 1 discloses a specific styrene-butadiene block copolymer (ratio of styrene and butadiene of 60 to 95/5).
40, 20 to 8 blocks with styrene content of 90% or more
0%, 10% for blocks with styrene content of 75-90%
As described above, 10% or more of blocks having a styrene content of 75% or less, other styrene-butadiene block copolymers, rubber-like styrene-butadiene block copolymers,
A composition comprising at least one of rubber-modified PS and non-rubber polystyrene-based resin is stretched to have a heat shrinkage rate of 80 ° C.
15% or more in the transverse direction and tensile elastic modulus of 5000 kg / cm ²
The above heat-shrinkable film is described. However, although these heat-shrinkable films have excellent shrinkage performance, because of their high tensile elastic modulus in the stretching direction, those which are not sufficiently satisfactory for mechanical packaging suitability have not been obtained. A well-balanced heat-shrinkable film has been desired.

[0003]

SUMMARY OF THE INVENTION In view of the above situation, the present invention provides a heat-shrinkable film and a heat-shrinkable multilayer having excellent shrinkage performance and natural shrinkage resistance and excellent in machine packaging suitability. The purpose is to provide a film.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a composition mainly composed of a copolymer of a specific vinyl aromatic hydrocarbon and a conjugated diene is used. Stretched and the tensile modulus in the stretching direction is 500 MPa
It was found that a heat-shrinkable film or a heat-shrinkable multilayer film having excellent heat shrinkability and excellent machine packaging suitability can be obtained by setting the amount to be less than the above, and thus the present invention has been completed.

That is, the present invention is characterized in that a block copolymer composition containing the following (a) and, if necessary, (b) is stretched, and the tensile elastic modulus in the stretching direction is less than 500 MPa. Is a heat-shrinkable film. (A) The mass ratio of vinyl aromatic hydrocarbon to conjugated diene is 5
0/50 to 90/10, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene having a vinyl aromatic hydrocarbon block ratio of 85% or less, (b) the following (i) to (i)
at least one vinyl aromatic hydrocarbon polymer selected from v), (i) a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene different from (a) (ii) a vinyl aromatic hydrocarbon polymer (Iii) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid (iv) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid ester (v) Rubber-modified styrene-based polymer (provided that In the above (iii) and (iv), the mass ratio of the vinyl aromatic hydrocarbon and the comonomer copolymerized with the vinyl aromatic hydrocarbon is 5 to 99:95 to 1.) Further, the present invention is at least One layer is a heat-shrinkable multilayer film formed of the above block copolymer composition.

The present invention will be described in detail below. Examples of the (a) vinyl aromatic hydrocarbon used in the block copolymer of the vinyl aromatic hydrocarbon and the conjugated diene used in the present invention include styrene, o-methylstyrene, p-methylstyrene and p-tert-butyl. Styrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene and the like can be mentioned, but styrene is particularly commonly used.

The conjugated diene used in the production of the block copolymer (a) used in the present invention is 1,3-
Butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,
Examples include 3-pentadiene and 1,3-hexadiene, and particularly common examples include 1,3-butadiene and isoprene.

The mass ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 50/50 to 90/10, preferably 55/45 to 85/15. When the mass ratio of vinyl aromatic hydrocarbon is less than 50 mass%, the rigidity of the film is 9
If it exceeds 0% by mass, the stretching temperature during the production of the film will be high, and the heat shrinkability of the film will be poor, so that it cannot be put to practical use.

The structure of the block copolymer used in the present invention and the structure of each block portion are not particularly limited. The structure of the block copolymer includes, for example, a linear or star block copolymer composed of a polymer block mainly containing vinyl aromatic hydrocarbons and a polymer block mainly containing a conjugated diene. In addition, when a copolymer part of vinyl aromatic hydrocarbon and conjugated diene is present in the polymer block mainly composed of vinyl aromatic hydrocarbon or the polymer block mainly composed of conjugated diene, vinyl copolymerized The aromatic hydrocarbon may be distributed uniformly in the polymer block or may be distributed in a taper (gradual decrease) form.

The block ratio of vinyl aromatic hydrocarbon in the block copolymer (a) is 85% or less, particularly preferably 25 to 85%. If the block rate is less than 25% by mass, the rigidity of the film is lowered, and if it exceeds 85% by mass, the heat shrinkability tends to be lowered. The block ratio of vinyl aromatic hydrocarbon is obtained by the following equation. That is, the block rate (%) = (W1 / W0) × 100
Is. Here, W1 represents the mass of the block polymer chain of the vinyl aromatic hydrocarbon in the copolymer, and W0 represents the total mass of the vinyl aromatic hydrocarbon in the block copolymer. Further, W1 in the above formula is a block copolymer obtained by publicly known document “Rubber Chemistry and Technology (Y. TANAKA,
et. al. , RUBBER CHEMISTRY AN
D TECHNOLOGY) " 58 , p. 16 (198)
5) The ozonolysis by the method described in 5), the obtained vinyl aromatic hydrocarbon polymer component is subjected to gel permeation chromatograph (hereinafter abbreviated as GPC) measurement, and the molecular weight corresponding to the chromatogram is determined by standard polystyrene and styrene. It was determined from a calibration curve prepared using an oligomer, and those having a number average molecular weight of more than 3,000 were quantitatively determined from the peak area. An ultraviolet spectroscopic detector whose wavelength was set to 254 nm was used as a detector.

The number average molecular weight of the block copolymer (a) used in the present invention is 40,000 to 500,000.
Particularly preferably, it is 80,000 to 300,000.
When it is less than 40,000, sufficient rigidity and impact resistance of the block copolymer composition cannot be obtained, and when it exceeds 500,000, workability is deteriorated, which is not preferable. The number average molecular weight of the block copolymer in the present invention is determined by gel permeation chromatography (hereinafter referred to as GPC).
Is abbreviated) and determined according to a conventional method.

Next, the production of the block copolymer (a) of the present invention will be described. The block copolymer (a) can be produced by polymerizing a vinyl aromatic hydrocarbon and a conjugated diene monomer in an organic solvent using an organic lithium compound as an initiator. As the organic solvent, butane, pentane, hexane, isopentane, heptane, octane, aliphatic hydrocarbons such as isooctane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, alicyclic hydrocarbons such as ethylcyclohexane, or benzene, toluene Aromatic hydrocarbons such as ethylbenzene and xylene can be used.

The organic lithium compound is a compound in which one or more lithium atoms are bonded in the molecule, and examples thereof include ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium and t.
A monofunctional organolithium compound such as ert-butyllithium, a polyfunctional organolithium compound such as hexamethylenedilithium, butadienyldilithium, and isoprenyldilithium can be used.

As the vinyl aromatic hydrocarbon and the conjugated diene used in the present invention, those mentioned above can be used, and one kind or two or more kinds can be selected and used for the polymerization. Then, in the living anionic polymerization using the organolithium compound as an initiator, almost all of the vinyl aromatic hydrocarbon and the conjugated diene used in the polymerization reaction are converted into a polymer.

In the present invention, the molecular weight of the block copolymer (a) can be controlled by the amount of the initiator added to the total amount of the monomers added.

The block ratio of the vinyl aromatic hydrocarbon in the block copolymer (a) can be controlled by the amount of the randomizing agent added when the vinyl aromatic hydrocarbon and the conjugated diene are copolymerized. Tetrahydrofuran (THF) is mainly used as the randomizing agent, but other ethers, amines, thioethers, phosphoramides, alkylbenzene sulfonates, potassium or sodium alkoxides and the like can also be used.

Suitable ethers for the randomizing agent include dimethyl ether, diethyl ether, diphenyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, etc. in addition to THF. As amines, tertiary amines such as trimethylamine, triethylamine, tetramethylethylenediamine, as well as cyclic amines can be used. In addition, triphenylphosphine, hexamethylphosphoramide, potassium or sodium alkylbenzene sulfonate, potassium or sodium butoxide, etc. can be used as the randomizing agent.

The addition amount of the randomizing agent is preferably 0.001 to 10 parts by mass with respect to 100 parts by mass of all charged monomers. The addition time may be before the start of the polymerization reaction or before the polymerization of the copolymer chain. Further, it can be additionally added if necessary.

In addition, the block ratio can also be obtained by mechanically continuously feeding the vinyl aromatic hydrocarbon and the conjugated diene to the polymerization vessel or by alternately adding the vinyl aromatic hydrocarbon and the conjugated diene to the polymerization vessel in small amounts. You can control.

The block copolymer thus obtained contains a polymerization terminator such as water, alcohol or carbon dioxide,
It is inactivated by adding an amount sufficient to inactivate the active end. As a method of recovering the copolymer from the obtained block copolymer solution, a method of precipitating with a poor solvent such as methanol, a method of evaporating and precipitating the solvent by a heating roll or the like (drum dryer method), a concentrator is used. Any method such as a method of removing the solvent with a vent type extruder after concentrating the solution, a method of dispersing the solution in water and blowing steam to heat and remove the solvent to recover the copolymer (steam stripping method) can be used. The method can be adopted.

The polymer (b) used in the present invention is at least one vinyl aromatic hydrocarbon polymer selected from the following (i) to (v). (I) Block copolymer of vinyl aromatic hydrocarbon and conjugated diene different from (a) (ii) Vinyl aromatic hydrocarbon polymer (iii) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid Copolymer (iv) Copolymer consisting of vinyl aromatic hydrocarbon and (meth) acrylic acid ester (v) Rubber-modified styrene-based polymer (provided that vinyl aromatic hydrocarbon and this vinyl are used in the above (iii) and (iv)) The mass ratio of the comonomer copolymerized with the aromatic hydrocarbon is 5 to 99:95 to 1.)

As the block copolymer of vinyl aromatic hydrocarbon and conjugated diene different from (a) of (i), the block copolymer of vinyl aromatic hydrocarbon and conjugated diene of (a) shown above can be used. Any vinyl aromatic hydrocarbon other than
A conjugated diene block copolymer is used.

As the vinyl aromatic hydrocarbon polymer (ii), a homopolymer or a copolymer of two or more of the above vinyl aromatic hydrocarbons is used. Particularly common is polystyrene.

The copolymer (iii) consisting of vinyl aromatic hydrocarbon and (meth) acrylic acid can be obtained by polymerizing the above vinyl aromatic hydrocarbon and (meth) acrylic acid. Each monomer may be used alone or in combination of two or more. Examples of (meth) acrylic acid include acrylic acid and methacrylic acid.

The copolymer (iv) of vinyl aromatic hydrocarbon and (meth) acrylic acid ester is obtained by polymerizing the above vinyl aromatic hydrocarbon and (meth) acrylic acid ester. Each monomer can be used alone or in combination of two or more.

As the (meth) acrylic acid ester, methyl acrylate, ethyl acrylate, acrylic acid-n-
Butyl, isobutyl acrylate, hexyl acrylate,
Examples thereof include (2-ethyl) hexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, (2-hydroxy) ethyl methacrylate and the like.

The copolymer of (iii) or (iv) has a mass ratio of vinyl aromatic hydrocarbon and (meth) acrylic acid or vinyl aromatic hydrocarbon and (meth) acrylic acid ester of 5 to 99:95. ~ 1, preferably 40-99:
It is obtained by polymerizing a monomer mixture of 60 to 1, more preferably 70 to 99:30.

The rubber modified styrene polymer (v) is obtained by polymerizing a mixture of vinyl aromatic hydrocarbon or a monomer copolymerizable therewith and various elastomers. As the vinyl aromatic hydrocarbon, those described in the production of the block copolymer of the above (a) are used, and as the monomer copolymerizable with this, (meth)
Acrylic acid, (meth) acrylic acid ester and the like are used. Further, as the elastomer, butadiene rubber, styrene-butadiene rubber, styrene-butadiene block copolymer elastomer, chloroprene rubber, natural rubber and the like are used. Particularly preferred rubber-modified styrene-based polymer is impact-resistant rubber-modified styrene resin (HIP
S).

For the MBS resin and MBAS resin, first, polybutadiene or a copolymer rubber latex with styrene containing butadiene as a main component is produced by a known emulsion polymerization method. At this time, a crosslinking agent or a chain transfer agent may be used. Next, the MBS resin is obtained by adding styrene, methyl methacrylate and / or alkyl acrylate to this rubber latex, and the MBAS resin by adding styrene, methyl methacrylate, acrylonitrile and / or alkyl acrylate, and performing graft polymerization.
Examples of the alkyl acrylate used for the MBS resin and the MBAS resin include the alkyl acrylate described in the above-mentioned (iii) vinyl aromatic hydrocarbon and (meth) acrylic acid ester copolymer.

In the present invention, the mass ratio of the block copolymer of (a) to the polymers of (b) (i) to (v) is 20 to 100: 0 to 80, preferably 100 to 100, and preferably 100 to 100. Is 40 to 100: 0 to 60, and particularly preferably 50 to 100: 0 to 50. If the amount of the block copolymer (a) is less than 20 parts by mass, the shrinkability of the heat-shrinkable film will be insufficient.

Various additives may be added to the block copolymer composition of the present invention as required. As additives, various stabilizers, processing aids, light resistance improvers, softeners, plasticizers, antistatic agents, antifogging agents, mineral oils, fillers,
Pigments, flame retardants, lubricants and the like can be mentioned.

As the above-mentioned stabilizer, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-) is used.
5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy-3,5-di-ter
t-pentylphenyl) ethyl] -4,6-di-ter
t-pentylphenyl acrylate, 2,6-di-te
Examples thereof include phenolic antioxidants such as rt-butyl-4-methylphenol, and phosphorus antioxidants such as trisnonylphenyl phosphite. As the processing aid, the light resistance improver, the softening agent, the plasticizer, the antistatic agent, the antifogging agent, the mineral oil, the filler, the pigment, the flame retardant and the like, there can be used general known ones. Examples of the lubricant include methylphenyl polysiloxane, fatty acid, fatty acid glycerin ester, fatty acid amide, hydrocarbon wax and the like.

The composition of the present invention can be obtained by mixing (a) and (b), but the mixing method is not particularly limited, but for example, it is dry blended with a Henschel mixer, a ribbon blender, a V blender or the like. Alternatively, it may be melted by an extruder and pelletized. Alternatively,
It may be added during the production of each polymer, before the initiation of polymerization, during the polymerization reaction, at the stage of post-treatment of the polymer, or the like. When additives are added as needed, for example, the additives may be added to (a) and (b) at a predetermined ratio, and the same mixing method as described above may be used.

The heat-shrinkable film of the present invention is obtained by uniaxially, biaxially or polyaxially stretching a sheet or a film extruded by a known method, for example, a T-die method or a tubular method, using the above composition. can get.

In the heat-shrinkable film of the present invention, it is necessary that at least one layer is formed of the block copolymer composition comprising the above (a) and (b). When the shrinkable film is a heat-shrinkable multilayer film, it is preferable that at least one layer is the above block copolymer composition and the other layer is a layer formed from the following (b ′). (B ') at least one vinyl aromatic hydrocarbon-based polymer selected from the following (i) to (iv), (i) a block copolymer of a vinyl aromatic hydrocarbon different from (a) and a conjugated diene Polymer (ii) Vinyl aromatic hydrocarbon polymer (iii) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid (iv) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid ester (V) The rubber-modified styrene polymer (provided that the mass ratio of the vinyl aromatic hydrocarbon and the comonomer copolymerized with the vinyl aromatic hydrocarbon in the above (iii) and (iv) is 5 to 99:95). It should be noted that (i) in (b ') may be the same as (a) or may be the same as (i) in (b). Also, (b ')
The polymers of (ii) to (v) in (b) are (ii) to
The same as the polymer of (v) is used. Also,
The polymer (b ') may be the same as or different from the polymer (b). The other layer is at least one polymer selected from styrene-butadiene block copolymer, polystyrene, styrene-n-butyl acrylate copolymer, impact-resistant rubber-modified styrene resin (HIPS), MBS resin, and MBAS resin. It is more preferable that the layer is a layer formed of a united component.

The heat-shrinkable multi-layer film of the present invention is obtained by melting the above-mentioned resins for the front and back layers and the intermediate layer with an extruder, respectively, and layering them in a die or a feed block, and then uniaxially or biaxially. Alternatively, it can be obtained by multiaxial stretching. As the die used in the heat-shrinkable film and the heat-shrinkable multilayer film, known ones such as a T-die and a ring die can be used. Examples of uniaxial stretching include a method of stretching an extruded sheet with a tenter in a direction orthogonal to the extrusion direction, a method of stretching an extruded tubular film in the circumferential direction, and the like. Examples of biaxial stretching, after stretching the extruded sheet in the extrusion direction with a roll, a method of stretching in a direction orthogonal to the extrusion direction with a tenter, the extruded tubular film in the extrusion direction and the circumferential direction. Examples include a method of stretching simultaneously or separately. In the multi-layer film, each layer does not have to be one layer, and each layer may have two or more layers.

In the present invention, the stretching temperature is 60 to 120.
C is preferred. At 60 ° C., the film is broken during stretching, and when it exceeds 120 ° C., good shrinkage properties cannot be obtained, which is not preferable. Particularly preferred is the range of Tg + 5 ° C. to Tg + 20 ° C. with respect to the glass transition temperature (Tg) of the composition constituting the film. In the case of a multilayer film, the T of the polymer composition of the layer having the lowest Tg
With respect to g, the range of Tg + 5 ° C. to Tg + 20 ° C. is particularly preferable. The glass transition temperature (Tg) is obtained from the peak temperature of loss modulus. The draw ratio is not particularly limited, but is preferably 1.5 to 8 times. If it is less than 1.5 times, the heat shrinkage tends to be insufficient, and if it exceeds 8 times, stretching is difficult, which is not preferable. When these films are used as heat shrinkable labels or packaging materials, the heat shrinkage rate is preferably 10% or more at 70 ° C. for 10 seconds. If the heat shrinkage ratio is less than 10%, a high temperature is required at the time of shrinkage, which may adversely affect the coated article. A preferable heat shrinkage ratio is 30% or more at the same temperature.
Further, the natural shrinkage ratio is preferably 2.5% or less at 40 ° C. for 7 days. The thickness of the film is 10 to 300.
μm is preferred.

The heat-shrinkable film or the heat-shrinkable multilayer film of the present invention has a tensile elastic modulus in the stretching direction of 500 MPa.
It is necessary to be less than 100 MPa, preferably 100 MPa or more. If the tensile modulus is 500 MPa or more, the suitability for mechanical packaging is poor, which is not preferable. The stretching conditions such as the stretching temperature may be appropriately controlled so that the thermal shrinkage or the natural shrinkage and the tensile elastic modulus as described above can be obtained. Here, the mechanical packaging suitability means that, in the film forming process or the mounting process, for example, a film of a heat shrinkable film is less likely to be broken in a packaging machine, and a finish in a shrink tunnel is finished such as wrinkles, shifts, and tears. It is an important characteristic for practical use, such as excellent properties. The tensile elastic modulus is a value obtained by measuring the tensile elastic modulus of the heat-shrinkable film or the heat-shrinkable multilayer film in the stretching direction under the following conditions. Tensile modulus is JIS at 23 ℃
It measured based on K6871.

The heat-shrinkable film and the heat-shrinkable multilayer film of the present invention are particularly suitable for use as heat-shrinkable labels, heat-shrinkable cap seals, etc., but may also be appropriately used for packaging films and the like. You can The heat-shrinkable label can be produced by a known method, and can be produced, for example, by solvent-sealing the stretched film in the circumferential direction. The container when the heat-shrinkable film or the heat-shrinkable multilayer film of the present invention is used as a heat-shrinkable label is not particularly limited, but polyethylene terephthalate (abbreviated as PET) is used.
A container made of glass, a container made of glass, a container made of aluminum, or the like is preferably used.

[0040]

EXAMPLES The present invention will be further described with reference to examples, but the present invention is not limited to these examples.

Examples 1-5 and Comparative Examples 1-3 Vinyl aromatic hydrocarbon-conjugated diene block copolymer of (a) shown in Table 1 and vinyl aromatic hydrocarbon of (b) shown in Table 2 A block copolymer composition was produced by mixing the system polymers according to the formulations shown in Tables 4 to 5 with a Henschel mixer, and then melting and pelletizing with an extruder. The film is formed by extruding a sheet having a thickness of 0.3 mm at a temperature of 210 ° C., and then uniaxially stretching the sheet at a stretching temperature shown in Tables 4 to 5 by a tenter to form a stretched film. Created.

Tables 4 to 5 show the blending amount (parts by mass) of each component and the physical properties.

Examples 6 to 10 and Comparative Examples 4 to 6 (a) Components for outer layer Component (a): A vinyl aromatic hydrocarbon-conjugated diene block copolymer as shown in Table 1 was used.

[0044]

[Table 1]

Component (b): (i) as shown in Table 2.
Block copolymer of vinyl aromatic hydrocarbon and conjugated diene different from (a), (ii) vinyl aromatic hydrocarbon polymer, (iii) copolymer of vinyl aromatic hydrocarbon and (meth) acrylic acid , (Iv) a copolymer of vinyl aromatic hydrocarbon and (meth) acrylic acid ester,
(V) A rubber-modified styrene polymer was used.

[0046]

[Table 2]

(B) Regarding inner layer components A styrene polymer as shown in Table 3 was used.

[0048]

[Table 3]

(C) Film Production (a) Vinyl aromatic hydrocarbon-conjugated diene block copolymer shown in Table 1 and (b) Vinyl aromatic hydrocarbon-based polymer shown in Table 2 as components for the outer layer. , And (d) the styrene-based polymer shown in Table 3 as the component for the inner layer, the amount of the raw material polymer in each layer shown in Table 6 to Table 7 (part by mass) and the layer ratio (%) A shrinkable multilayer film was prepared. The film is prepared by first melting the polymer or polymer composition corresponding to each layer in a separate extruder to form a multilayer in a T-die,
A sheet having a thickness of 0.3 mm was formed. After that, a tenter was used to draw a stretched film by transversely uniaxially stretching 5 times at the stretching temperatures shown in Tables 6 to 7.

Tables 6 to 7 show the blending amount (parts by mass) of the raw material polymer in each layer and the layer ratio (%) as well as the physical properties.

The physical properties of the film were determined by the following methods. (1) Glass transition temperature (Tg) The glass transition temperature (Tg) of the polymer composition was determined from the peak value by measuring the loss modulus by the dynamic viscoelastic method according to the following procedure. (I) Each polymer pellet was hot-pressed under the condition of 200 to 250 ° C to prepare a sheet having a thickness of 0.1 to 0.5 mm. (Ii) A test piece of an appropriate size was cut out from this sheet and stored in a room at 23 ° C. and 50% RH for 24 hours or more. Then, the loss modulus inherent to the polymer as the test piece was measured using the following apparatus. The measurement was performed while changing the temperature. Device: Rheometrics solid viscoelasticity measuring device R
SA2 (set temperature range: room temperature to 130 ° C., set temperature rising rate: 4 ° C./min, measurement frequency: 1 Hz) (2) Tensile elastic modulus: the stretched film produced above conforms to JIS K6871 -The tensile elastic modulus in the stretching direction was measured at 23 ° C using a Tensilon universal testing machine (RTC-1210A) manufactured by D. (3) Heat shrinkage rate: It was immersed in hot water at 70 ° C. for 10 seconds and calculated from the following formula. Thermal shrinkage (%) = {(L1-L2) / L1} × 100, where L1: length before immersion (stretching direction), L2: 70 ° C.
Length after shrinkage by dipping in warm water for 10 seconds (stretching direction) (4) Natural shrinkage: The natural shrinkage of the film was measured by the following method. A test piece having a MD direction of about 75 mm and a TD direction of about 400 mm was cut out from the stretched film produced under the same conditions as the stretched film whose thermal shrinkage was measured. Marks at intervals of 300.0 mm were attached in the TD direction of this test piece. The stretched film was stored in an environmental tester at 40 ° C. After 7 days of storage, take out the film and remove the distance L between the marked lines.
(Mm) was measured to the unit of 0.1 mm using a caliper. The natural shrinkage ratio was calculated by the following formula 1.

[0052]

[Equation 1]

(5) Mechanical suitability: Solvent sealing was performed in a cylindrical shape with the stretched direction being the circumferential direction. This was attached to a 500 ml PET bottle by a shrink label automatic machine, and further heat-shrinked in the shrink step to be brought into close contact with the PET bottle. The state of the adhered film was observed and the suitability for packaging machine was determined by the following method. ◯: Good adhesion without wrinkles or misalignment. X: Wrinkles, misalignment, or poor adhesion.

From the physical properties shown in Tables 4 to 7, the heat-shrinkable film of the present invention is excellent in heat shrinkability and natural shrinkage resistance, and has a tensile elastic modulus within the range defined by the present invention, thereby being machine-packed. It can be seen that the suitability is excellent.

[0055]

[Table 4]

[0056]

[Table 5]

[0057]

[Table 6]

[0058]

[Table 7]

[0059]

EFFECTS OF THE INVENTION The heat-shrinkable film using the block copolymer composition of the present invention is excellent in heat shrinkability and natural shrinkage resistance, and further excellent in machine packaging. Therefore, these films are subjected to various printings. It can be suitably used as various packaging films such as labels and cap seals.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 7:00 B29L 7:00 C08L 53:02 C08L 53:02 F term (reference) 3E086 AB01 AD30 BA02 BA04 BA15 BB67 CA40 4F071 AA12X AA22X AA75 AF20 AF61 AH04 4F210 AA13E AE01 AG01 RA03 RC02 RG02 RG04 RG43

Claims (8)

[Claims] 1. The following (a) and, if necessary, (b)
A heat-shrinkable film obtained by stretching a block copolymer composition containing: and having a tensile elastic modulus in the stretching direction of less than 500 MPa. (A) The mass ratio of vinyl aromatic hydrocarbon to conjugated diene is 5
0/50 to 90/10, a block copolymer of vinyl aromatic hydrocarbon and a conjugated diene having a vinyl aromatic hydrocarbon block ratio of 85% or less (b) selected from the following (i) to (v) At least one vinyl aromatic hydrocarbon polymer, (i) a block copolymer of a vinyl aromatic hydrocarbon different from (a) and a conjugated diene (ii) a vinyl aromatic hydrocarbon polymer (iii) vinyl aroma Copolymer composed of group hydrocarbon and (meth) acrylic acid (iv) Copolymer composed of vinyl aromatic hydrocarbon and (meth) acrylic acid ester (v) Rubber-modified styrene polymer (provided that (iii) above) In (iv), the mass ratio of the vinyl aromatic hydrocarbon and the comonomer copolymerized with the vinyl aromatic hydrocarbon is 5 to 99:95 to 1.) 2. The heat-shrinkable film according to claim 1, wherein the mass ratio of (a) and (b) is 20 to 100: 0 to 80, with the total composition being 100. 3. (a) and (i) are styrene-butadiene block copolymers, (ii) is polystyrene,
(Iii) is a styrene-methacrylic acid copolymer, (i
v) is at least one copolymer selected from styrene-n-butyl acrylate copolymer, styrene-methyl methacrylate copolymer, and styrene-n-butyl acrylate-methyl methacrylate copolymer, and (v) is The heat-shrinkable film according to claim 1 or 2, which is an impact-resistant rubber-modified styrene resin. 4. A heat-shrinkable multilayer film, wherein at least one layer is formed of the block copolymer composition according to any one of claims 1 to 3. 5. The heat-shrinkable film or heat-shrinkable multilayer film according to claim 1, wherein the heat-shrinkage rate is 10% or more at 70 ° C. for 10 seconds. 6. The heat-shrinkable film or the heat-shrinkable multilayer film according to claim 1, wherein the natural shrinkage rate is 2.5% or less at 40 ° C. for 7 days. 7. A label comprising the heat-shrinkable film or the heat-shrinkable multilayer film according to any one of claims 1 to 6. 8. A container coated with the label according to claim 7.