JP2021147411A - Heat-shrinkable film - Google Patents

Abstract

To provide a heat-shrinkable film, which is excellent in natural shrinkage resistance and exhibits good heat shrinkage and shrinkage finishing property, with a facility and manufacturing cost equivalent to an existing technique.SOLUTION: There are provided a single-layer heat-shrinkable film which contains a block copolymer composition including a structural unit derived from vinyl aromatic hydrocarbon and a structural unit derived from conjugated diene, and a resin composition containing a polyester-based resin, in which a content of the polyester-based resin in the resin composition is 1 mass% or more and 50 mass% or less; and a heat-shrinkable multilayer film having at least one of the single layer.SELECTED DRAWING: None

Description

The present invention relates to a heat-shrinkable film, a heat-shrinkable label using the heat-shrinkable film, and a beverage container.

A heat-shrinkable film using a block copolymer composed of vinyl aromatic hydrocarbons and conjugated diene has excellent heat-shrinkability and finish after shrinkage, and can be applied to various shapes and mounting methods of the packaged material. Widely used for packaging. It is also excellent in that it does not have the problem of environmental pollution unlike polyvinyl chloride when it is disposed of.

However, the heat-shrinkable film using the block copolymer tends to shrink naturally in a high-temperature storage environment, which causes printing misalignment and improper mounting. Therefore, improvement of the natural shrinkage resistance has been an issue.

To solve this problem, as a heat-shrinkable film having excellent natural shrinkage resistance, for example, Patent Document 1 describes a resin composition containing a block copolymer composed of a vinyl aromatic hydrocarbon and a conjugated diene and satisfying a predetermined property. The heat shrinkable films used are described. However, in the conventional technique, the natural shrinkage resistance is still lower than that of the heat-shrinkable film using the polyester resin, and further improvement is required.

On the other hand, Patent Document 2 describes a heat-shrinkable film in which a polyester resin having high natural shrinkage resistance is laminated on a surface layer and a block copolymer composed of vinyl aromatic hydrocarbons and conjugated diene is laminated on an intermediate layer. .. However, in order to laminate these, it is necessary to form a three-kind five-layer structure including an adhesive layer, and there is a problem in terms of equipment and cost.

International Publication No. 2019/074013 Japanese Unexamined Patent Publication No. 2005-131824

Therefore, an object of the present invention is to provide a heat-shrinkable film having excellent natural shrinkage resistance and showing good heat-shrinkability and shrinkage finish at the same equipment and manufacturing cost as existing techniques. ..

As a result of various studies on means for solving the above problems, the present inventors have added a predetermined amount to a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene. The present invention has been completed by finding that the natural shrinkage resistance of a heat-shrinkable film is improved by blending a polyester-based resin.

That is, the gist of the present invention is as follows.
(1) A single-layer heat-shrinkable film containing a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, and a resin composition containing a polyester resin. A single-layer heat-shrinkable film in which the content of the polyester-based resin in the resin composition is 1% by mass or more and 50% by mass or less.
(2) The heat-shrinkable film according to (1) above, wherein the polyester resin is glycol-modified polyethylene terephthalate.
(3) When the total of the structural units derived from vinyl aromatic hydrocarbons and the structural units derived from conjugated diene in the resin composition is 100% by mass, the content of the structural units derived from vinyl aromatic hydrocarbons is The heat-shrinkable film according to (1) or (2) above, wherein the content is 65% by mass or more and 88% by mass or less, and the content of the structural unit derived from the conjugated diene is 12% by mass or more and 35% by mass or less.
(4) In the dynamic viscoelasticity measurement, the main peak of the loss tangent value (tan δ) measured under the conditions of a heating rate of 4 ° C./min and a frequency of 1 Hz according to ISO6721-1 is in the range of 70 ° C. or higher and 110 ° C. or lower. The heat-shrinkable film according to any one of (1) to (3) above, which is present at least one.
(5) A heat-shrinkable multilayer film formed by laminating two or more types of resin compositions, wherein the resin compositions of all layers are structural units derived from vinyl aromatic hydrocarbons and structural units derived from conjugated diene. The content of the polyester-based resin in the resin composition containing the polyester-based resin is 1% by mass or more and 50% by mass, and the resin composition of at least one layer further contains the polyester-based resin. The following heat shrinkable multilayer film.
(6) The heat-shrinkable multilayer film according to (5) above, wherein the polyester resin is glycol-modified polyethylene terephthalate.
(7) When the total of the structural units derived from vinyl aromatic hydrocarbons and the structural units derived from conjugated diene in the resin composition is 100% by mass, the content of the structural units derived from vinyl aromatic hydrocarbons is The heat-shrinkable multilayer film according to (5) or (6) above, wherein the content is 65% by mass or more and 88% by mass or less, and the content of the structural unit derived from the conjugated diene is 12% by mass or more and 35% by mass or less.
(8) In the dynamic viscoelasticity measurement, the main peak of the loss tangent value (tan δ) measured under the conditions of a heating rate of 4 ° C./min and a frequency of 1 Hz according to ISO6721-1 is in the range of 70 ° C. or higher and 110 ° C. or lower. The heat-shrinkable multilayer film according to any one of (5) to (7) above, which is present at least one.
(9) A heat-shrinkable label comprising the heat-shrinkable film or the heat-shrinkable multilayer film according to any one of (1) to (8) above.
(10) A container having the heat-shrinkable label according to (9) above.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a heat-shrinkable film having excellent natural shrinkage resistance and showing good heat-shrinkability and shrinkage finish at the same equipment and manufacturing cost as existing techniques.

Hereinafter, preferred embodiments of the present invention will be described in detail.

In the present invention, the heat shrinkability of a single layer composed of a layer in which a predetermined amount of polyester resin is mixed with a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene. The present invention relates to a film and a heat-shrinkable multilayer film having one or more such layers.

The heat-shrinkable film of the present invention includes a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, and a resin composition containing a polyester-based resin.

The block copolymer composition contains a block copolymer composed of a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene as a main component. The block copolymer used may be one kind, or two or more kinds of block copolymers may be mixed and used at an arbitrary compounding ratio. In the case of a mixture of multiple block copolymers, a predetermined amount of each component may be mixed in a solution state and then the solvent may be removed, or a predetermined amount of each component may be mixed in a solid state and then melt-kneaded by an extruder. preferable.

Examples of vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tertbutylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene and the like. As the vinyl aromatic hydrocarbon, only one of these may be used, or two or more of them may be used. Styrene is particularly preferable as the vinyl aromatic hydrocarbon.

Examples of the conjugated diene include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Can be mentioned. As the conjugated diene, only one of these may be used, or two or more thereof may be used. Particularly preferred as the conjugated diene is at least one of 1,3-butadiene and isoprene, with 1,3-butadiene being more preferred.

In the block copolymer composition, it is preferable that the vinyl aromatic hydrocarbon is styrene and the conjugated diene is 1,3-butadiene.

The block copolymer composition has a content of structural units derived from vinyl aromatic hydrocarbons when the total of structural units derived from vinyl aromatic hydrocarbons and structural units derived from conjugated diene is 100% by mass. It is preferably 65% by mass or more and 88% by mass or less, and the content of the structural unit derived from the conjugated diene is preferably 12% by mass or more and 35% by mass or less, and the content of the structural unit derived from vinyl aromatic hydrocarbon is It is more preferably 70% by mass or more and 84% by mass or less, and the content of the structural unit derived from the conjugated diene is 16% by mass or more and 30% by mass or less. By setting the content of structural units derived from vinyl aromatic hydrocarbons to 88% by mass or less and the content of structural units derived from conjugated diene to 12% by mass or more, the obtained heat-shrinkable film has fracture resistance. Thermal shrinkage obtained by setting the content of structural units derived from vinyl aromatic hydrocarbons to 65% by mass or more and the content of structural units derived from conjugated diene to 35% by mass or less. The rigidity and natural shrinkage resistance of the sex film can be sufficiently increased.

The mass ratio of the content of the structural unit derived from vinyl aromatic hydrocarbon and the structural unit derived from conjugated diene contained in the block copolymer composition is such that the block copolymer composition is anionic polymerized. In general, it can be calculated from the amount (mass) of each monomer charged at the time of producing the polymer.

Further, the mass ratio of the content of the structural unit derived from the conjugated diene can also be measured by using a known halogen addition method. A general measurement procedure for the mass ratio of the content of the structural unit derived from the conjugated diene by the halogen addition method is described below.
That is, after the finely weighed sample is dissolved in an organic solvent capable of completely dissolving to obtain a test solution, an excess amount of iodine monochloride / carbon tetrachloride solution is added to the test solution. React well. Then, the unreacted iodine monochloride remaining in the solution was back-titrated with a sodium thiosulfate / ethanol solution to measure the amount of double bonds in the sample, and the proportion of structural units derived from the conjugated diene was determined. calculate. In general, since a part of the added main raw material may be lost, the mass ratio of the structural unit derived from the conjugated diene is obtained by the halogen addition method, and the other structural units are derived from vinyl aromatic hydrocarbons. It is preferable to use the mass ratio of.

The weight average molecular weight of the block copolymer composition is not particularly limited, but in order to exhibit molding processability and thermal stability in a well-balanced manner, it is preferably 100,000 or more and 400,000 or less, and 100,000 or more. More preferably, it is 250,000 or less.

Examples of the polyester resin include a 1: 1 polycondensate of a polyvalent carboxylic acid and a polyhydric alcohol. Examples of the polyvalent carboxylic acid include terephthalic acid, isophthalic acid, succinic acid, glutaric acid and the like. One kind or two or more kinds of these polyvalent carboxylic acids can be used. Examples of the polyhydric alcohol include ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, polyethylene glycol, tetramethylene glycol and 1,4-cyclohexanedimethanol. Be done. One or more of these polyhydric alcohols can be used. The polyvalent carboxylic acid is preferably terephthalic acid, and the polyhydric alcohol is preferably ethylene glycol, diethylene glycol, or 1,4-cyclohexanedimethanol.

The polyester resin is preferably glycol-modified polyethylene terephthalate. Glycol-modified polyethylene terephthalate is polyethylene terephthalate using terephthalic acid as a polyhydric carboxylic acid and ethylene glycol as a polyhydric alcohol and a polyhydric alcohol other than ethylene glycol, and is compared with polyethylene terephthalate using only ethylene glycol as a polyhydric alcohol. As a result, the crystallinity is low, so that the transparency and the heat shrinkage of the film are good.

Polyester-based resins and block copolymer compositions are incompatible and tend to cause a decrease in transparency when mixed, but by reducing the difference in their refractive indexes, the decrease in transparency of the film is suppressed. be able to. The difference in refractive index between the polyester resin and the block copolymer composition is preferably 0.01 or less, and more preferably 0.005 or less.

Examples of commercially available polyester resins include "Easter Copperister GN001" manufactured by Eastman Chemical Company and "SKYGREEN S2008" manufactured by SK Chemicals. The polyester resin may be a simple substance or a blend of two or more kinds.

The content of the polyester resin in the resin composition is 1% by mass or more and 50% by mass or less. When the content of the polyester resin in the resin composition is 1% by mass or more, the natural shrinkage resistance of the heat-shrinkable film becomes significantly high, and when it is 50% by mass or less, the heat-shrinkage rate and transparency of the film Can be suppressed. The content of the polyester resin in the resin composition is preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less.

The resin composition may contain a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, and a resin other than the polyester resin, if necessary. Examples of such a resin include polystyrene resin and styrene-methyl methacrylate copolymer.

In the dynamic viscoelasticity measurement, the heat-shrinkable film has a main peak of the loss tangent value (tan δ) measured under the conditions of a temperature rise rate of 4 ° C./min and a frequency of 1 Hz according to ISO6721-1 at 70 ° C. or higher and 110 ° C. or lower. It is preferable that at least one is present in the range of 75 ° C. or higher, and more preferably at least one is present in the range of 75 ° C. or higher and 95 ° C. or lower. Here, the main peak is the temperature of the peak when there is one peak, and the temperature of the peak having the highest loss tangent value when there are two or more peaks. By setting the temperature showing the main peak of tan δ to 70 ° C. or higher, the natural shrinkage resistance of the obtained heat-shrinkable film can be sufficiently increased, and the temperature showing the main peak of tan δ should be set to 110 ° C. or lower. Therefore, the heat shrinkage rate of the obtained heat-shrinkable film can be sufficiently increased.

The more detailed conditions for dynamic viscoelasticity measurement are as follows.
(I) A molded product having a thickness of 4 mm and a width of 10 mm is produced by injection molding using a resin composition, a test piece is cut out from this molded product, and stored in a 50% RH room at 23 ° C. for 48 hours for curing. Give.
(Ii) Using a dynamic viscoelasticity measuring device RSA-III (manufactured by TA Instruments), the storage elastic modulus (E') in the temperature range of room temperature to 120 ° C. at a heating rate of 4 ° C./min and a measurement frequency of 1 Hz. And the loss elastic modulus (E ″) are measured, and the loss tangent value (tan δ) is calculated by the following equation.
tan δ = E "/ E'

The heat-shrinkable film may contain various additives, if necessary. Examples of the additive include stabilizers, lubricants, processing aids, blocking inhibitors, antistatic agents, antifog agents, weather resistance improvers, softeners, plasticizers, pigments and the like.

Stabilizers include, for example, 2- [1- (2-hydroxy-3,5-di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenyl acrylate, 2-tert-butyl-6. -(3-tert-Butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,6- Phenol antioxidants such as di-tert-butyl-4-methylphenol, 2,2-methylenebis (4,6-di-tert-butylphenyl) octylphosphite, trisnonylphenylphosphite, bis (2,2) Examples thereof include phosphorus-based antioxidants such as 6-di-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphofite.

Examples of the lubricant include saturated fatty acids such as palmitic acid, stearic acid, and behenic acid; fatty acid esters such as octyl palmitate, octyl stearate, and pentaerythritol fatty acids; Fatty acid amides such as acid amide; higher alcohols such as myristyl alcohol, cetyl alcohol and stearyl alcohol can be used.

As the processing aid, for example, liquid paraffin is generally used, and in addition, an organic acid ester such as an adipate ester can be used.

As the blocking inhibitor, for example, organic fillers such as high impact polystyrene (HIPS) and crosslinked beads of vinyl aromatic hydrocarbon copolymer; silica beads, quartz beads and the like can be used.

As the antistatic agent, for example, surfactants such as nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants can be mainly used.

As the antifogging agent, for example, glycerin fatty acid esters such as glycerin-mono-fatty acid ester and glycerin-di-fatty acid ester; sorbitan fatty acid esters such as sorbitan-mono-palmitic acid ester and sorbitan-mono-stearic acid ester are used. can.

Examples of the weather resistance improver include 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole and 2,4-di-tert-butylphenyl-3'. UV absorbers such as, 5'-di-tert-butyl-4'-hydroxybenzoate, 2-hydroxy-4-n-octoxybenzophenone, and tetrakis (2,2,6,6-tetramethyl-4-piperidyl). ) A hindered amine type weather resistance improver such as -1,2,3,4-butanetetracarboxylate can be used.

When the heat-shrinkable film contains an additive, the content thereof is usually 10% by mass or less, preferably 5% by mass or less, based on the heat-shrinkable film. By setting the blending amount of the additive to 10% by mass or less, it is possible to prevent the additive from being exposed on the surface of the obtained heat-shrinkable film and impairing the appearance.

The present invention is also a heat-shrinkable multilayer film formed by laminating two or more kinds of resin compositions, in which the resin compositions of all layers are derived from structural units derived from vinyl aromatic hydrocarbons and conjugated diene. A block copolymer composition containing a structural unit is contained, at least one layer of the resin composition further contains a polyester resin, and the content of the polyester resin in the resin composition containing the polyester resin is 1% by mass or more 50. It also includes a heat-shrinkable multilayer film having a mass% or less. The number of layers is not particularly limited, but from the viewpoint of productivity, it is preferable that the number of layers is 2 types and 3 layers composed of a surface layer and an intermediate layer.

The content of the polyester-based resin in the resin composition containing the polyester-based resin is 1% by mass or more and 50% by mass or less. By making the film a multi-layer structure, it is possible to suppress a decrease in heat shrinkage rate and transparency as compared with a single-layer film.

The heat-shrinkable multilayer film has a main peak of tangent loss (tan δ) of 70 ° C. or higher and 110 ° C. measured under the conditions of a temperature rise rate of 4 ° C./min and a frequency of 1 Hz in dynamic viscoelasticity measurement. It is preferable that at least one is present in the following range, and more preferably at least one is present in the range of 75 ° C. or higher and 95 ° C. or lower. By setting the temperature showing the main peak of tan δ to 70 ° C. or higher, the natural shrinkage resistance of the obtained heat-shrinkable film can be sufficiently increased, and the temperature showing the main peak of tan δ should be set to 110 ° C. or lower. Therefore, the heat shrinkage rate of the obtained heat-shrinkable film can be sufficiently increased.

As the polyester-based resin, the above-mentioned polyester-based resin can be used for a single-layer heat-shrinkable film, and glycol-modified polyethylene terephthalate is preferable.

The resin composition may contain the above-mentioned resin as a resin other than the block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, and a polyester resin, if necessary. ..

The heat-shrinkable multilayer film may contain various additives as required. As the additive, the above-mentioned additive can be used for a single-layer heat-shrinkable film. When the heat-shrinkable multilayer film contains an additive, the content thereof is usually 10% by mass or less, preferably 5% by mass or less, based on the heat-shrinkable multilayer film.

The thickness of the single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention is not particularly limited, but is preferably 15 μm or more and 100 μm or less.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention have a heat-shrinkability of 15% or more in the stretching direction after being immersed in hot water at 70 ° C. for 10 seconds, and are immersed in hot water at 100 ° C. for 10 seconds. The heat shrinkage in the stretching direction after immersion is preferably 70% or more. By setting the heat shrinkage rate within the above range, it is possible to suppress the occurrence of improper mounting depending on the shape of the packaged body, which is practically preferable.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention have a tensile elastic modulus of 1100 MPa or more and a tensile elongation in the direction orthogonal to the stretching direction of 200% or more and 600% or less as measured by a tensile test. Is preferable. The tensile test can be performed under the conditions described in the examples below. By having these characteristics, a label using a single-layer heat-shrinkable film and a heat-shrinkable multilayer film has sufficient mechanical properties and resistance to an ink solvent during printing.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention preferably have a natural shrinkage rate in the stretching direction of 4% or less when stored at 40 ° C. for 7 days. When the natural shrinkage rate is within the above range, for example, when the film is stored in a high temperature environment where temperature control is not performed, it is possible to suppress the tendency of the film to wavy and other appearance defects, which is practically preferable. ..

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention have a total light transmittance of preferably 85% or more, more preferably 90% or more. The total light transmittance can be measured by the method of JIS K-7361 using a "turbidity meter NDH2000" (manufactured by Nippon Denshoku Industries Co., Ltd.).

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention have a haze of preferably 20% or less, more preferably 15% or less, and particularly preferably 10% or less. The haze can be measured by the method of JIS K-7361 using the same device as the total light transmittance.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention can be produced by a known method. For example, a single-layer heat-shrinkable film can be obtained by forming a resin composition into a film by known melt extrusion molding, calender molding, inflation molding, or the like, and stretching the resin composition in a uniaxial or biaxial direction. The stretching direction is not particularly limited, but the direction (TD) perpendicular to the flow direction (MD) is preferably the highest stretching ratio, and TD will be described below as the stretching direction. Further, the heat-shrinkable multilayer film is preferably produced by stretching a multilayer sheet prepared by multilayer extrusion molding, but a single-layer unstretched sheet is prepared using the resin composition of each layer, and then laminated and stretched. It can also be produced by doing so.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention are stretched in a temperature range of + 5 ° C. or higher and 25 ° C. or lower at which the loss elastic modulus (E ") in the dynamic viscoelasticity measurement shows a main peak. Here, the main peak is the temperature of the peak when there is one peak, and the temperature of the peak having the highest value of the loss elastic modulus when there are two or more peaks. The stretching temperature is When E "is the temperature at which the main peak is shown + 5 ° C. or higher, the natural shrinkage resistance of the obtained heat-shrinkable film can be sufficiently increased, and the stretching temperature is the temperature at which E" shows the main peak + 25 ° C. or lower. Therefore, it is possible to suppress variations in the thickness of the obtained heat-shrinkable film and increase the heat-shrinkage rate.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention are preferably stretched in the stretching direction at a stretching ratio of 3 times or more and 8 times or less in the above temperature range. When the draw ratio is 3 times or more, the heat shrinkage rate of the obtained heat-shrinkable film can be increased, and when the draw ratio is 8 times or less, the natural shrinkage resistance of the obtained heat-shrinkable film can be improved. It can be made sufficiently high and can prevent the film from breaking during stretching.

The single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention have high natural shrinkage resistance, and at the same time have good heat-shrinkability and shrinkage finish. Therefore, the single-layer heat-shrinkable film and the heat-shrinkable multilayer film of the present invention can be suitably used for heat-shrinkable labels such as beverage containers.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the technical scope of the present invention is not limited to these examples.

[Reference example: Production of block copolymer]
A block copolymer was prepared by the following operation.
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in the reaction vessel.
(2) 2000 mL of a 10 mass% cyclohexane solution of n-butyllithium was added thereto as a polymerization initiator solution, and the temperature was maintained at 30 ° C.
(3) 4 kg of styrene was added, and styrene was anionically polymerized. The internal temperature rose to 35 ° C.
(4) After the styrene is completely consumed, the internal temperature of the reaction system is raised to 80 ° C., and while maintaining the internal temperature, a total amount of 144 kg of styrene and a total amount of 12 kg of 1,3-butadiene are added at 144 kg / h, respectively. , 12 kg / h were added simultaneously at a constant addition rate.
(5) After the styrene and 1,3-butadiene are completely consumed, the internal temperature of the reaction system is lowered to 60 ° C., 36 kg of 1,3-butadiene is added all at once, and 1,3-butadiene is anionically polymerized. rice field. The internal temperature rose to 86 ° C.
(6) After 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 70 ° C., 4 kg of styrene was added, and the styrene was anionic polymerized. The internal temperature rose to 73 ° C.
(7) After the styrene is completely consumed, finally all the polymerization active terminals are deactivated with water, and the polymerization contains a polystyrene block, a polybutadiene block, and a block copolymer having a copolymer block of styrene and butadiene. Obtained liquid.
(8) This polymer solution was devolatile and melt-pelled with an extruder to obtain block copolymer A.
In block copolymer A, when the total of the structural units derived from styrene and the structural units derived from 1,3-butadiene in the block copolymer is 100% by mass, the content of the structural units derived from styrene is It was 76.6% by mass, and the content of structural units derived from 1,3-butadiene was 23.4% by mass.

[Example 1-3 and Comparative Example 1-2 Preparation of single-layer heat-shrinkable film]
As a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, the block copolymer described in the reference example is used, and as a polyester resin, manufactured by Eastman Chemicals, Inc. Using "Easter Copolyester GN001", these were mixed so as to have the ratios shown in Table 1, and melt pelletized by an extruder to obtain a resin composition.

Using the obtained resin composition, first, a sheet having a thickness of 0.3 mm was extruded at a temperature of 200 ° C., stretched 1.2 times to MD at 80 ° C. by a longitudinal stretching machine, and then laterally stretched. A single-layer heat-shrinkable film having an average thickness of 50 μm was prepared by stretching 4.5 times on TD at 85 ° C. by a machine.

The heat shrinkage rate, natural shrinkage rate, total light transmittance and haze of the single-layer heat-shrinkable films of Examples 1-3 and Comparative Example 1-2 were measured and subjected to a tensile test.

[Heat shrinkage rate]
The heat shrinkage rate was measured by the following method.
(1) A test piece having an MD width of 100 mm and a TD width of 100 mm was cut out from the heat-shrinkable film.
(2) After completely immersing this test piece in warm water at 70 ° C., 80 ° C., 90 ° C. or 100 ° C. for 10 seconds, take it out, wipe off the water sufficiently, and adjust the length L (mm) of TD. It was measured.
(3) The heat shrinkage rate was calculated by the following formula.
Heat shrinkage rate (%) = {(100-L) / 100} x 100

[Natural shrinkage rate]
The natural shrinkage rate was measured by the following method.
(1) A sample piece having an MD width of 100 mm and a TD width of 350 mm was cut out from the heat-shrinkable film.
(2) A marked line was placed in the center of the test piece so that the TD marked line spacing was 300 mm, stored in an environmental tester at 40 ° C., and the marked line spacing N (mm) was measured after storage for 7 days. ..
(3) The natural shrinkage rate was measured by the following formula.
Natural shrinkage rate (%) = {(300-N) / 300} x 100

[Tensile test]
The tensile test was carried out by the following method.
(1) A strip-shaped sample piece having an MD width of 200 mm and a TD width of 10 mm was cut out from the heat-shrinkable film.
(2) Using a Tensilon universal material tester manufactured by Orientec Co., Ltd., the cut-out sample piece was subjected to tension at a measurement temperature of 23 ° C. and a tensile speed of 200 mm / min, and the tensile elastic modulus and tensile elongation were measured.

[Total light transmittance, Haze, loss tangent value (tan δ)]
Total light transmittance, Haze and loss tangent value (tan δ) were measured by the above method.

Table 1 shows the measurement results of the single-layer heat-shrinkable films of Examples 1-3 and Comparative Example 1-2.

From Table 1, with respect to the single-layer heat-shrinkable films of Examples 1-3 and Comparative Examples 1-2, by adding a polyester-based resin, the physical properties of the film such as the heat-shrinkability and the tensile properties are maintained or improved. The natural shrinkage rate was lowered and the natural shrinkage resistance was significantly improved, but in Comparative Example 2 in which the content of the polyester resin was 75% by mass, the heat shrinkage rate and the transparency were lowered. Therefore, the single-layer heat-shrinkable film of Example 1-3 in which the content of the polyester-based resin is within the range of the present invention has the contents of Comparative Example 1 and the polyester-based resin which do not contain the polyester-based resin. It was shown that both high natural shrinkage resistance and good heat shrinkage can be achieved as compared with Comparative Example 2 which is outside the scope of the present invention.

[Example 4-7 and Comparative Example 3 Preparation of heat-shrinkable multilayer film]
The resin compositions used for the surface layer and the intermediate layer are mixed so as to have the ratios shown in Table 2, and the T die has a feed block so as to have a layer ratio of 10/80/10 (surface layer / intermediate layer / surface layer). A sheet having a thickness of 0.3 mm is extruded and stretched 1.2 times in the MD direction by a longitudinal stretching machine at 80 ° C., and then 4.5 times in the TD direction by a transverse stretching machine at 85 ° C. By stretching, a heat-shrinkable multilayer film having an average thickness of 50 μm was produced.

For the heat-shrinkable multilayer films of Examples 4-7 and Comparative Example 3, the heat-shrinkage rate, natural shrinkage rate, total light transmittance and haze were measured in the same manner as those of the single-layer heat-shrinkable film, and a tensile test was performed. rice field. The measurement results are shown in Table 2.

From Table 2, regarding the heat-shrinkable multilayer films of Examples 4-7 and Comparative Example 3, in Example 4-7, in which at least one of the intermediate layer and the surface layer contains a polyester resin in an amount within a predetermined range. The heat-shrinkable multilayer film was able to achieve both high natural shrinkage resistance and good heat-shrinkability, whereas in Comparative Example 3 in which the content of the polyester-based resin was outside the range of the present invention, heat-shrinkage was achieved. It has been shown that rate and transparency are reduced.

Claims (10)

A single-layer heat-shrinkable film containing a block copolymer composition containing a structural unit derived from a vinyl aromatic hydrocarbon and a structural unit derived from a conjugated diene, and a resin composition containing a polyester-based resin, which is a resin. A single-layer heat-shrinkable film in which the content of the polyester-based resin in the composition is 1% by mass or more and 50% by mass or less. The heat-shrinkable film according to claim 1, wherein the polyester-based resin is glycol-modified polyethylene terephthalate. When the total of the structural units derived from vinyl aromatic hydrocarbons and the structural units derived from conjugated diene in the resin composition is 100% by mass, the content of the structural units derived from vinyl aromatic hydrocarbons is 65% by mass. The heat-shrinkable film according to claim 1 or 2, wherein the content is 88% by mass or less and the content of the structural unit derived from the conjugated diene is 12% by mass or more and 35% by mass or less. In the dynamic viscoelasticity measurement, at least one main peak of the loss tangent value (tan δ) measured under the conditions of a heating rate of 4 ° C./min and a frequency of 1 Hz according to ISO6721-1 is in the range of 70 ° C. or higher and 110 ° C. or lower. The heat-shrinkable film according to any one of claims 1 to 3, which is present. A heat-shrinkable multilayer film formed by laminating two or more types of resin compositions, wherein the resin compositions of all layers contain structural units derived from vinyl aromatic hydrocarbons and structural units derived from conjugated diene. The content of the polyester resin in the resin composition containing the copolymer composition, at least one layer of the resin composition further containing the polyester resin, and the polyester resin is 1% by mass or more and 50% by mass or less. Heat shrinkable multilayer film. The heat-shrinkable multilayer film according to claim 5, wherein the polyester-based resin is glycol-modified polyethylene terephthalate. When the total of the structural units derived from vinyl aromatic hydrocarbons and the structural units derived from conjugated diene in the resin composition is 100% by mass, the content of the structural units derived from vinyl aromatic hydrocarbons is 65% by mass. The heat-shrinkable multilayer film according to claim 5 or 6, wherein the content is 88% by mass or less and the content of the structural unit derived from the conjugated diene is 12% by mass or more and 35% by mass or less. In the dynamic viscoelasticity measurement, at least one main peak of the loss tangent value (tan δ) measured under the conditions of a heating rate of 4 ° C./min and a frequency of 1 Hz according to ISO6721-1 is in the range of 70 ° C. or higher and 110 ° C. or lower. The heat-shrinkable multilayer film according to any one of claims 5 to 7, which is present. A heat-shrinkable label comprising the heat-shrinkable film or heat-shrinkable multilayer film according to any one of claims 1 to 8. A container having the heat shrinkable label according to claim 9.