JPH0767744B2 - Block copolymer uniaxially stretched film, sheet or tube - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a uniaxially stretched film, sheet or tube of a block copolymer which is transparent and has excellent low temperature stretchability and low temperature shrinkability.

[0002]

2. Description of the Related Art Shrink wrapping has recently been proposed because it can cleanly eliminate lumps and wrinkles, which are inevitable with conventional wrapping techniques, and can quickly wrap products closely and irregularly shaped products. Its use is increasing especially for food packaging. Conventionally, vinyl chloride resin has been mainly used as a material for shrink-wrapping films, sheets and the like because it satisfies the required properties such as low-temperature shrinkability, transparency and mechanical strength. However, vinyl chloride resin has been strongly demanded as a substitute for vinyl chloride monomer and plasticizers due to hygienic problems and generation of hydrogen chloride during incineration.

On the other hand, a block copolymer resin composed of a vinyl aromatic hydrocarbon and a conjugated gen does not have the above-mentioned problems and has good transparency and impact resistance, so that it is a raw material for food packaging containers. Is being widely used as. However, conventionally known block copolymers are not suitable as a material for heat-shrinkable packaging because they have a high stretching temperature and a high shrinking temperature.

For example, JP-A-49-102494 and JP-A-49-108177 disclose a block copolymer having a styrene-based hydrocarbon content of 50 to 95% by weight and a styrene-based resin in the block copolymer. Although a packaging film obtained by biaxially stretching a composition containing the above is described, such a film cannot obtain a sufficient shrinkage rate unless the heat shrinkage temperature is about 100 ° C. or higher.

A method for improving the low temperature shrinkage of such a block copolymer is also disclosed in JP-A-50-6673 and JP-B-55.
It is attempted in Japanese Patent No. 5544. The former method is to apply a tubular method to the linear copolymer to expand and stretch it in the temperature range where effective high degree of orientation occurs and perform biaxial orientation at the same time to obtain a film having good low temperature heat shrinkability. It is a manufacturing method. However, in this method, expansion and stretching are started in a temperature range extremely limited according to the amount of butadiene content of the raw material resin, and the film in the stretching zone from the expansion start point to the expansion end point is strictly controlled. A film having the desired low-temperature heat shrinkability cannot be obtained unless a temperature gradient is applied, and thus it is difficult to carry out the film. In the latter method, 10 to 30% by weight of a styrene / butadiene block copolymer having a styrene content of 20 to 50% is blended with a styrene / butadiene block copolymer having a styrene content of 65 to 90% to obtain a low temperature. This is a method for producing a shrinkable biaxially stretched film. However, when the kneading state of both is poor, sufficient low-temperature shrinkability cannot be invented, and this method requires a sophisticated technique and is easily implemented. It has the drawback of being difficult to do.

In view of the above situation, the inventors of the present invention have made earnest studies on a method for easily obtaining a block copolymer film, sheet or the like having excellent low-temperature shrinkability, and as a result, vinyl aromatics constituting the block copolymer have been obtained. It was found that the object can be achieved by stretching a block copolymer having a hydrocarbon-polymerized block having a molecular weight in a specific range at a relatively low temperature, and Japanese Patent Application No. 56-22989 and Japanese Patent Application No. 522989.
Filed No. 6-63325.

[0007]

Then, as a result of further studies on the improvement, the present inventors have found that the vinyl aromatic hydrocarbon polymer block contained in the block copolymer has a molecular weight and a molecular weight within a certain range. When a block copolymer having a distribution was used, it was newly found that it can be stretched at a relatively low temperature and has excellent low-temperature shrinkability, and the present invention has been completed.

That is, according to the present invention, the general structural formula ( AB ) _n (a) A- ( BA ) _n (b) B- (AB) _n (c) [(BA) _n ] M _-2 X (d) [ (AB) _n ] _m-2 X (e) [( BA ) _n- B] _m-2 X (f) [(A-B) _n- A] _m-2 X (G) (In the above formula, A is a vinyl aromatic hydrocarbon polymer block.
B is a polymer block mainly composed of a conjugated diene.
It is ku. The boundary between A block and B block is not always
It need not be clearly distinguished. X is silicon tetrachloride, tetrasalt
Residues of coupling agents such as tin oxide or polyfunctional organic
The residue of an initiator such as a thium compound is shown. n and m are 1 or more
The upper integer, generally 1-5. ) Is represented by any one of, yet the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 20,000 to 50,000
And the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is less than 1.25, and the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60:40 to.
A block copolymer of 95: 5 is stretched at a stretching temperature of 80 to 1
Stretched at 00 ° C. and a draw ratio of 2 to 6 and the heat shrinkage ratio at 80 ° C. in the stretching direction is 40 to 80% .
Stretching at 80 ° C in the orthogonal direction of less than 15%
The present invention relates to a uniaxially stretched film, sheet or tube of a block copolymer having a tensile elastic modulus in the direction of 7,000 Kg / cm ² or more .

According to the present invention, a stretched film, sheet or tube of a block copolymer can be easily obtained, and since the obtained molded product has excellent shrinkability at low temperature, it can be used for a long time at high temperature in the shrink wrapping process. It is suitable for the packaging of articles that may be altered or deformed when heated, for example, packaging of fresh food products and plastic molded products. Hereinafter, the present invention will be described in detail.

In the present invention, the polymer block containing a conjugated diene as a main component has a conjugated diene content of 50% by weight or more, preferably 70% by weight or more, more preferably 9% by weight or more.
It is 0% by weight or more of the polymer block.

When a random copolymer portion of a vinyl aromatic hydrocarbon and a conjugated diene is present in a polymer block containing a conjugated diene as a main component, the vinyl aromatic hydrocarbon copolymerized is present in the polymer portion. It may be distributed uniformly or may be distributed in a taper (gradual decrease) form. The weight ratio of vinyl aromatic hydrocarbon to conjugated diene in the block copolymer is 60:40 to 95: 5, preferably 65:35.
It is 88:12, and more preferably 68:32 to 85:15. When the content of the vinyl aromatic hydrocarbon is less than 60% by weight, the tensile strength and rigidity are poor, and it is unsuitable as a film, a sheet or the like, and when it exceeds 95% by weight, the impact resistance is poor, which is not preferable.

In the block copolymer used in the present invention, the number average molecular weight of the vinyl aromatic hydrocarbon block contained in the block copolymer is 20,000 to 50,000.
It is 0. When the number average molecular weight of the vinyl aromatic hydrocarbon block is less than 20,000, tensile strength and rigidity are poor, and when it exceeds 50,000 , stretching at low temperature cannot be performed and low-temperature shrinkability is poor, which is preferable. Absent.

The ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is less than 1.25, preferably 1.01 to 1.20, more preferably 1.05 to 1.15. Is the range. When the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 1.25 or more, the stretchability at low temperature and the low temperature shrinkability are inferior to those in the range specified by the present invention. There is a tendency.

[0014]

In the present invention, a particularly preferable block copolymer is a block composed of a vinyl aromatic hydrocarbon polymer block, and a polymer block containing a conjugated diene as a main component is substantially composed of a conjugated diene homopolymer. It is a copolymer. Here, the block polymer in which the polymer block mainly composed of conjugated diene is substantially composed of a conjugated diene homopolymer means that the polymer block mainly composed of conjugated diene is randomly copolymerized with the conjugated diene. A block copolymer having a small amount of vinyl aromatic hydrocarbons, in other words, a block copolymer having a small amount of vinyl aromatic hydrocarbons that are not incorporated in the vinyl aromatic hydrocarbon polymer block. Is a block copolymer having an unblocking ratio represented by the following formula of 15% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less.

[0016]

[Equation 1] The weight of the vinyl aromatic hydrocarbon polymer block in the block copolymer and the ratio of the weight average molecular weight to the number average molecular weight are
A method of oxidatively decomposing a copolymer with zetasary butyl hydroperoxide using osmium tetroxide as a catalyst (for example, LM KOLTHOFF, et a.
l. , J, Polym. Sci. 1,429 (194
It can be determined by quantifying it by the method described in 6)) or the like, and measuring the collected vinyl aromatic hydrocarbon polymer block component by gel permeation chromatography.

The block copolymer used in the present invention can basically be produced by a conventionally known method, for example, JP-B-36-
19286, Japanese Patent Publication No. 43-14979, Japanese Patent Publication No. 49-36957, Japanese Patent Publication No. 48-2423, Japanese Patent Publication No. 48-4106, etc., but vinyl aromatic carbonization The production conditions must be set so that the number average molecular weight of the hydrogen polymer block and the ratio of the weight average molecular weight to the number average molecular weight, and the vinyl aromatic hydrocarbon content are within the ranges specified in the present invention.

All of the above-mentioned known methods are methods in which a conjugated gen and a vinyl aromatic hydrocarbon are block-copolymerized using an anionic polymerization initiator such as an organic lithium compound in a hydrocarbon solvent. In the present invention, polymer production is a general formula,

[0019]

[Chemical 1] (In the above formula, A is a polymer block mainly containing vinyl aromatic hydrocarbons and B is a polymer block mainly containing conjugated gen. The boundary between the A block and the B block is not always clearly distinguished. Linear block copolymer represented by the formula (1) is not necessary, and n is an integer of 1 or more.
Or the general formula,

[0020]

[Chemical 2] (In the above formula, A and B are the same as above, and X represents a residue of a coupling agent such as silicon tetrachloride or tin tetrachloride or a residue of an initiator such as a polyfunctional organolithium compound. And n are integers of 1 or more.) A radial block copolymer represented by the formula (1) or an arbitrary mixture of these block copolymers can be used.

In the present invention, a particularly preferred polymer structure of the block copolymer is n in the general formula (a).
= 2 to 10, preferably 3 to 5, more preferably 3 or 4, n = 2-1 in the general formula (b) or (c).
0, preferably 2 to 5, more preferably 2 or 3, in the general formula (d) or (e), n = 2 to 10 and m
= 1 to 10, preferably n = 2 to 5 and m = 1 to 5,
More preferably n = 2 or 3 and m = 1 or 2,
In the general formula (to) or (to), n = 1 to 10 and m
= 1 to 10, preferably n = 1 to 5 and m = 1 to 5,
More preferably n = 1 or 2 and m = 1 or 2.

In the present invention, vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene,
There are vinyl anthracene and the like, but styrene is particularly common. These may be used alone or in combination of two or more. The conjugated gen is diolefin having a pair of conjugated double bonds,
For example, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-
Butadiene, 1,3-pentadiene, 1,3-hexadiene and the like, but particularly common ones are 1,3
-Butadiene and isoprene. These may be used alone or in combination of two or more.

The molecular weight of the polymer block mainly composed of the conjugated gen of the block copolymer used in the present invention is not particularly limited, but generally the number average molecular weight is 500 to 200,0.
00, preferably 1,000 to 100,000.
The number average molecular weight of the block copolymer as a whole is 20,000 to 500,000, preferably 5
It is 30,000 to 300,000.

A particularly preferable block copolymer in the present invention has a vinyl aromatic hydrocarbon content of 73 to 85% by weight and has a melt flow (measured in accordance with JIS K-6870) (200 ° C., 5 kg load) of 0. 0.001-
70, preferably 0.01 to 50, more preferably 0.
It is preferably 1 to 40 g / 10 minutes. The particularly preferable ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 1.05 to 1.15. Such a block copolymer is not only relatively easy to produce, but also has good moldability during film, sheet or tube molding and during stretch molding thereof, and the stretch-molded product obtained also has extremely excellent low temperature shrinkage. It has properties, tensile strength, rigidity and impact resistance. Therefore, the stretched film, sheet or tube of the block copolymer is suitable as a material for a label for heat shrinkage.

The block copolymer used in the present invention is hydrogenated, halogenated, hydrohalogenated, epoxidized or chemically within a range not impairing its basic properties such as low temperature shrinkability and rigidity. Modification such as introduction of a functional group such as a hydroxyl thiol group, a nitrile group, a sulfonic acid group, a carboxyl group and an amino group may be carried out by the reaction.

Various additives may be added to the block copolymer used in the present invention depending on the purpose. Suitable additives include 30 parts by weight or less of polystyrene, coumarone-indene resin, terpene resin, softening agents such as oil, and plasticizers. Further, various stabilizers, pigments, antiblocking agents, antistatic agents, lubricants and the like can be added.
Examples of the antiblocking agent include fatty acid amide, ethylene bisstearate, glycerin fatty acid ester, sorevitan monostearate, saturated fatty acid ester of aliphatic alcohol, pentaerythritol resin acid ester, etc. Handbook "
The compounds described in (Chemical Industry Co., Ltd.) can be used. These are generally 0.01 to 5% by weight, preferably 0.1 to
Used in the range of 2% by weight.

The number average molecular weight of the block copolymer used in the present invention is 20,0 for the purpose of further improving the low temperature shrinkability.
A block copolymer composition containing a low molecular weight vinyl aromatic hydrocarbon polymer or copolymer having a molecular weight of 00 or less, preferably 200 to 10,000, more preferably 300 to 6,000 is used as a base polymer. be able to.
When the number average molecular weight exceeds 20,000, the effect of improving low temperature shrinkability is lost, which is not preferable. Particularly preferred are those having a number average molecular weight of 300 or more and less than 500, and such a low molecular weight polymer or copolymer has a very good effect of improving low temperature shrinkability. The blending amount of the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer is 5 to 100 parts by weight, preferably 10 to 70 parts by weight, and more preferably 15 to 55 parts by weight with respect to 100 parts by weight of the block copolymer.
Parts by weight. If it is less than 5 parts by weight, the effect of improving the low temperature shrinkability is not sufficient, and if it exceeds 100 parts by weight, the impact resistance is unfavorably reduced.

In the present invention, the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer and the number average molecular weight of the block copolymer are 30,000 or more, preferably 5 or more.
10,000 to 1,000,000, more preferably 8
A block copolymer composition containing a vinyl aromatic hydrocarbon polymer or copolymer of 50,000 to 500,000 can be used as a base polymer to improve low-temperature shrinkability and rigidity. Number average molecular weight is 30,000
If it is less than the above range, the effect of improving rigidity is not sufficient, which is not preferable. The blending amount of the vinyl aromatic hydrocarbon polymer or copolymer is 100 parts by weight of the block copolymer,
It is 5 to 80 parts by weight, preferably 10 to 60 parts by weight, and more preferably 15 to 45 parts by weight. If it is less than 5 parts by weight, the effect of improving the rigidity is not sufficient, and if it exceeds 80 parts by weight, the low temperature shrinkability is deteriorated and the impact resistance is also lowered, which is not preferable.

The vinyl aromatic hydrocarbon polymer or copolymer used in the present invention may be a homopolymer or a copolymer of the vinyl aromatic hydrocarbon monomer, or a vinyl aromatic hydrocarbon polymer. Includes copolymers of monomers with other vinyl monomers such as ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylates such as methyl acrylate, methacrylates such as methyl methacrylate, and acrylonitrile. Be done. Particularly preferred are styrene homopolymers, styrene / α-methylstyrene copolymers, and styrene / methyl methacrylate copolymers.

In order to obtain a heat-shrinkable stretched film, sheet or tube from the above block copolymer, it has been conventionally adopted to impart heat-shrinkability to a film, sheet or tube such as vinyl chloride resin. Although the method described above can be basically used, the obtained film, sheet or tube has a heat shrinkage ratio of 40 to 80% at 80 ° C. in the stretching direction. Heat shrinkage at 80 ° C is 40
If it is less than%, the shrinking property at low temperature is poor, so it is necessary to adjust the process uniformly at high temperature in the shrink wrapping process, or to heat for a long time, making it impossible to wrap an article that may be altered or deformed at high temperature. And the shrink wrapping ability is reduced, which is not preferable. In the present invention, the heat shrinkage ratio at 80 ° C. means a uniaxially stretched film, a sheet or a tube.
It is the heat shrinkage ratio in the stretching direction of the molded product when immersed in a heating medium such as hot water at 0 ° C., silicone oil, or glycerin that does not impair the properties of the molded product for 5 minutes.

From the above block copolymers, heat-shrinkable 1
In order to obtain a molded product such as an axially stretched film or sheet, the block copolymer is produced from an ordinary T die or an annular die into a flat shape or a tubular shape at 160 to 250 ° C., preferably 1
It is extrusion-molded at 80 to 220 ° C., and the obtained unstretched product is uniaxially stretched. In the case of uniaxial stretching, in the case of a film or a sheet, it is stretched in the extrusion direction with a calender roll or the like, or in the direction orthogonal to the extrusion direction with a tenter or the like, and in the case of a tube, it is stretched in the extrusion direction or the circumferential direction of the tube. In the present invention, stretching is carried out at a stretching temperature of 80 to 100 ° C. in the machine direction or the transverse direction at a draw ratio of 2 to 6.

When the stretching temperature is less than 80 ° C., breakage occurs during stretching and it is difficult to obtain a desired molded product, and when it exceeds 100 ° C., it is difficult to obtain a product having good low temperature shrinkability. While the draw ratio is selected within the range so as to correspond to the shrinkage that required by the application, if the draw ratio is less than 2 times is not preferable as a heat-shrinkable packaging small thermal shrinkage ratio, also 6
A draw ratio exceeding 2 times is not preferable for stable production in the drawing process. The uniaxially stretched molded product is then cooled, if necessary, immediately at 60 to 100 ° C. for a short time, for example, 3 to
It is also possible to carry out a heat treatment for 60 seconds, preferably 10 to 40 seconds, to implement a means for preventing spontaneous shrinkage at room temperature. The uniaxially stretched stretch-formed product of the present invention has a tensile elastic modulus in the stretching direction of 7,000 Kg / cm ² or more,
It is preferably 10,000 Kg / cm ² or more, more preferably 15,000 Kg / cm ² or more as a heat shrinkable packaging material. Tensile elastic modulus is 7,000 Kg / c
If it is less than m ² , there is a problem that the shrinkage packaging process causes a settling and it is difficult to perform normal packaging.

The uniaxially stretched film, sheet or tube of the present invention is superior in hygiene to the conventional vinyl chloride resin-based ones, and by utilizing its characteristics, various uses,
For example, it can be used for packaging of fresh food, frozen food, confectionery, clothing, stationery, toys, and the like. As a particularly preferred use, after printing characters or designs on the uniaxially stretched film, sheet or tube of the block copolymer of the present invention,
It can be used as a so-called heat-shrinkable label material, which is used by being brought into close contact with the surface of a packaged object such as a plastic molded product, a metal product, or porcelain by heat shrinkage. In particular, since the uniaxially stretch-molded article of the present invention has excellent low-temperature shrinkability, it is suitable as a material for a heat-shrinkable label of a plastic molded article that is deformed when heated to a high temperature.

When the uniaxially stretched molded product of the block copolymer of the present invention is used as a heat shrinkable label material, the shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction is 15%.
Less than 10%, preferably less than 10%, more preferably less than 5%.

[0035]

EXAMPLES In order to describe the present invention in more detail, examples of the present invention will be shown below, but it goes without saying that the contents of the present invention are not limited to these examples. In the following examples, the block copolymer had a melt flow of 1 to 40 g / 10 min.

The ratio of the weight average molecular weight to the number average molecular weight of the polystyrene block of the block copolymer used is the polystyrene block obtained by decomposing the block copolymer or the block copolymer mixture by the above-mentioned oxidative decomposition method. It determined by measuring the component with GPC of Shimadzu LC-1 type.

[0037]

Examples 1 and 2 and Comparative Examples 1 and 2 Styrene having polymer production, styrene content, molecular weight of polystyrene block and ratio of weight average molecular weight to number average molecular weight (hereinafter referred to as Mw / Mn) are shown in Table 1. The butadiene block copolymer was polymerized in n-hexane with n-butyllithium as the initiator.

These copolymers were molded into a sheet using a 40 mmφ extruder, and then uniaxially stretched at a stretching temperature of 4.0 times to prepare a film of about 80 μm. As shown in the examples, the copolymers in which the number average molecular weight and Mw / Mn of the poly (ethylene) block are within the ranges specified in the present invention have a lower stretching temperature than that of the comparative examples and have a stretching temperature of 80 ° C.
It can be seen that since the heat shrinkage ratio is high, it is extremely excellent as a shrink film.

The heat shrinkages of the stretched films of Examples 1 and 2 are the results of the films stretched at 80 ° C. and 90 ° C., but the copolymers of Examples 1 and 2 also have a stretching temperature of 125 ° C.
The heat shrinkage ratio at 80 ° C when the stretched film of
The stretching temperature is 5 to 20%, which is inferior to the films having 80 ° C and 90 ° C. In the uniaxially stretched films of Examples 1 and 2, the heat shrinkage ratio at 80 ° C in the direction orthogonal to the stretching direction was less than 5%. Further, the puncture impact values (kg-cm / cm) of Examples 1 and 2 are 800 and 1.0.
It was 00.

[0040]

[Table 1]

[0041]

Examples 3, 4 and Comparative Examples 3-7 Styrene, Budadiene block copolymers having a polymer structure, styrene content, polystyrene block molecular weight and polystyrene block Mw / Mn as shown in Table 2 were tested. 1
Polymerized in the same manner as. The polystyrene of Comparative Example 8 was polymerized in cyclohexane using n-butyllithium as an initiator. The obtained copolymer was formed into a sheet in the same manner as in Example 1, and uniaxially stretched under the stretching conditions shown in Table 2. The stretching temperature was set to the minimum temperature required for stretching each copolymer.

The physical properties of the stretched film are shown in Table 2. In Examples 3 and 4 of the present invention, the styrene contents were 50 and 1, respectively.
As a result of comparison with Comparative Examples 6 and 7 which are 00% and Comparative Examples 4 and 5 in which the molecular weight of the polystyrene block is 5000 and 85,000, respectively, the copolymer having a styrene content less than the range of the present invention has a tensile strength of It can be seen that those having a small tensile elastic modulus and poor rigidity as a shrink label, and conversely, those having a high styrene content have a small thermal shrinkage and are inappropriate.

Further, the copolymer having a polystyrene block molecular weight below the range of the present invention has a small tensile strength and tensile elastic modulus, and conversely, a polystyrene block having a large molecular weight has a small thermal shrinkage. It can be seen that the block copolymer film according to the present invention has a better balance of film physical properties and heat shrinkability than those of the comparative examples. still,
In the uniaxially stretched films of Examples 3 and 4, the heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction was less than 5%.

Next, in Examples 3 and 4, the polymer structures were

[0045]

[Chemical 3] Except that the polystyrene blocks have the same styrene content and the same number average molecular weight and the same Mw / Mn.
Block copolymers having the polystyrene block were prepared and their stretching properties, physical properties and shrinkage properties were investigated. As a result, the minimum stretchable temperatures of the block copolymers corresponding to Examples 3 and 4 were 85 ° C. and 85 ° C., respectively, and the tensile elastic moduli in the stretching direction were 13,000, respectively.
0 kg / cm ^2, it is a 16,600kg / cm ² 80 ℃
The shrinkage percentages were 62% and 60%, respectively.

[0046]

[Table 2]

[0047]

[0048]

[0049]

[0050]

[0051]

Examples 5, 6 In cyclohexane

[0052]

[Chemical 5] Is polymerized with n-butyllithium as an initiator, and then
A coupling reaction was performed using SiCl ₄ as a coupling agent to produce a radial type styrene-butadiene block copolymer. Example 9 uses Si as a coupling agent.
The radial type and the linear type are mixed by additionally using (CH ₃ ) ₂ Cl.

The stretching conditions are the same as in Example 1. Table 3 shows the measurement results of the physical properties and the heat shrinkage ratio of these stretched films. Even if the polymer structure is a radial type or a blend thereof with a linear type, if the properties of the block copolymer are within the range specified in the present invention, a stretched film excellent in both physical properties and heat shrinkage rate can be obtained. I understand.
In the uniaxially stretched films of Examples 5 and 6 , the heat shrinkage rate at 80 ° C in the direction orthogonal to the stretching direction was less than 5%.

[0054]

Examples 7-9 Polymer structures as shown in Table 3 ,
A styrene-butadiene block copolymer having a styrene content and a polystyrene block was polymerized in the same manner as in Example 1. The stretching conditions are as shown in Table 3 . Table 3 shows the measurement results of the physical properties and the heat shrinkage ratio of these stretched films.

In the uniaxially stretched films of Examples 7 to 9 , the heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction was less than 5%.

[0056]

Example 10 In Example 1, a polymer structure as shown in Table 3 , styrene content, number average molecular weight of polystyrene block, Mw / Mn of polystyrene block and A styrene-butadiene block copolymer mixture having an unblocked rate was polymerized.

The stretching conditions are as shown in Table 3 . Table 3 shows the measurement results of the physical properties and the heat shrinkage ratio of these stretched films. In the uniaxially stretched film of Example 10 , the heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction was 5%.
Was less than.

[0058]

[Table 3]

[0059]

Examples 11 to 13 Block copolymer 10 of Example 2
A block copolymer composition in which 25 parts by weight of low molecular weight polystyrene having a number average molecular weight of 400 was blended with 0 parts by weight (referred to as Example 11 ) and the block copolymer 100 of Example 2
A block copolymer composition (referred to as Example 12 ) in which 30 parts by weight of low molecular weight polystyrene having a number average molecular weight of 400 and 25 parts by weight of polystyrene having a number average molecular weight of 120,000 were mixed in parts by weight was designated as Example 1. It was uniaxially stretched by the same method. The characteristics of the obtained uniaxially stretched film are shown in Table 4 . In Table 4 , the performance of the uniaxially stretched film of the block copolymer of Example 2 is shown as Example 13 .

[0060]

[Table 4]

[0061]

Examples 14 and 15 Using the same polymers as those in Examples 3 and 10 , respectively, and in the same manner, a block copolymer having a styrene content of 75% by weight and an styrene content of 80% by weight and having a thickness of about 40 .mu. Each of the axially stretched films was produced. Next, after printing characters and patterns on these films, a circumferential heat shrinkable label was prepared with the stretched direction being the circumferential direction and the non-stretched direction being the longitudinal direction.
It was covered with a cylindrical cup molded from impact-resistant polystyrene, passed through a shrink tunnel controlled at a temperature of 180 to 200 ° C., and heat-shrinked. As a result, all of these heat-shrinkable labels are in tight contact with the cup surface of the item to be packaged without wobbling or wrinkling,
It didn't come off easily. Moreover, the printed characters and patterns were not locally deformed and had a colorful finish, and the cup of the packaged product was not deformed by heating at all.

Also, the same polymer as in Example 3, Example 3
And the polymer structure in Example 10

[0063]

[Chemical 6] Except that the polymers having the same constitutional requirements are used, and the thickness of 60 μm is measured by the method corresponding to each example.
An axially stretched film was produced. Next, a heat-shrinkable label was produced from these films by the same method as described above, and a cup having a similar appearance was heat-shrinked to obtain a coating having a good appearance.

[0064]

Industrial Applicability According to the present invention, a uniaxially stretched film having excellent low temperature stretchability and low temperature shrinkability can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B29K 105: 02 B29L 7:00 23:00 (56) References JP-A-50-6673 (JP, A) Japanese Unexamined Patent Publication No. 57-25349 (JP, A) Actual Development No. 52-149880 (JP, U) Japanese Patent Publication No. 48-2423 (JP, B1)

Claims (1)

[Claims] 1. A general structural formula ( AB ) _n (a) A- ( BA ) _n (b) B- (AB) _n (c) [(BA) _n ] _m-2. X (d) [ (AB) _n ] _m-2 X (e) [( BA ) _n- B] _m-2 X (f) [( AB ) _n- A] _m-2 X (G) (In the above formula, A is a vinyl aromatic hydrocarbon polymer block.
B is a polymer block mainly composed of a conjugated diene.
It is ku. The boundary between A block and B block is not always
It need not be clearly distinguished. X is silicon tetrachloride, tetrasalt
Residues of coupling agents such as tin oxide or polyfunctional organic
The residue of an initiator such as a thium compound is shown. n and m are 1 or more
The upper integer, generally 1-5. ) , And the vinyl aromatic hydrocarbon polymer block has a number average molecular weight of 20,000 to 50,000.
And the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is less than 1.25, and the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60:40 to.
A block copolymer of 95: 5 is stretched at a stretching temperature of 80 to 1
The film was stretched at 00 ° C. at a draw ratio of 2 to 6 and the heat shrinkage ratio at 80 ° C. in the stretching direction was 40 to 80 %.
Stretching at 80 ° C in the orthogonal direction of less than 15%
A uniaxially stretched film, sheet or tube of a block copolymer having a tensile elastic modulus in the direction of 7,000 Kg / cm ² or more .