JPH05245927A - Block copolymeric uniaxially oriented film, sheet or tube - Google Patents

Abstract

PURPOSE:To obtain a uniaxially oriented film with transparency, excellent low temperature stretching and low temperature contracting properties, and having good mechanical strength by employing block polymer having a specific range of molecular weight and molecular weight distribution as polymer consisting mainly of vinyl aromatic hydrocarbon. CONSTITUTION:In a uniaxially oriented film, sheet or tube suitable for use in contraction wrapping, resin comprising at least polymeric block consisting mainly of one vinyl aromatic hydrocarbon, and polymeric block consisting mainly of one conjugate diene is employed. In this instance, block copolymer is employed wherein a number average molecular weight of the vinyl aromatic hydrocarbon is 10000-70000, and the ratio between the weight average molecular weight of the vinyl aromatic hydrocarbon block and the number average molecular weight is in the range of 1.25-2.5, and the weight ratio between the vinyl aromatic hydrocarbon and the conjugate diene is 60:40--95:5, and which is then subjected to uniaxial orientation, to thereby obtain a uniaxially oriented film or the like which has a thermal contraction of 15% or more at 80 deg.C in the stretching direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniaxially stretched film, sheet or tube of a block copolymer which is transparent, has excellent low temperature stretchability and low temperature shrinkability and has good mechanical strength.

[0002]

2. Description of the Related Art Shrink wrapping has been recently proposed because shrink wrapping can cleanly eliminate lumps and wrinkles, which were inevitable with conventional wrapping techniques, and can quickly wrap a product closely or a strange shape. 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 characteristics such as low-temperature shrinkability, transparency and mechanical strength. However, there is a strong demand for a substitute for the vinyl chloride resin due to hygienic problems of vinyl chloride monomers and plasticizers, hydrogen chloride generation during incineration, and the like.

On the other hand, a block copolymer resin composed of a vinyl aromatic hydrocarbon and a conjugated diene 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 have a high stretching temperature and a high shrinking temperature, and are therefore unsuitable as heat shrink packaging materials.

For example, JP-A-49-102494 and JP-A-49-108177 disclose block copolymers having a styrene-based hydrocarbon content of 50 to 95% by weight and styrene-based resins in the block copolymers. 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 Publication No.-5544. In the former method, a tubular method is applied to a linear copolymer to expand and stretch in a temperature range where effective high degree of orientation occurs and simultaneously perform biaxial orientation, thereby forming a film having good low temperature heat shrinkability. It is a manufacturing method. However, in this method, expansion and stretching are started in an extremely limited temperature range 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 a desired low-temperature heat shrinkability cannot be obtained unless a temperature gradient is applied, and thus it is difficult to carry out the film easily. In the latter method, 10 to 30% by weight of a styrene / butadiene block copolymer having a styrene content of 20 to 50% is added to 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 expressed, and this method requires a sophisticated technique and is easily performed. It has the drawback of being difficult to do.

In view of the above circumstances, the present inventors 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, have found that a vinyl aromatic compound which constitutes the block copolymer. 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 certain range at a relatively low temperature, and Japanese Patent Application No. 56-22989 and Japanese Patent Application No. 56- No. 63325 was filed.

[0007]

Then, as a result of further studies on the improvement, the present inventors have found that the vinyl aromatic hydrocarbon polymer block constituting the block copolymer has a certain range of molecular weight and molecular weight distribution. The present invention has been completed by finding that it is possible to stretch at a relatively low temperature by using the block copolymer having the above-mentioned, and further the impact strength of the stretched film or sheet is improved.

That is, the present invention has a polymer block mainly containing at least one vinyl aromatic hydrocarbon and a polymer block mainly containing at least one conjugated diene, and further, a vinyl aromatic hydrocarbon. The number average molecular weight of the block is 10,000 to 70,000, and the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon block (hereinafter referred to as Mw / Mn) is in the range of 1.25 to 2.5, The weight ratio of vinyl aromatic hydrocarbon to conjugated diene is 60:40.
The present invention relates to a uniaxially stretched film, sheet or tube of a block copolymer, which is obtained by uniaxially stretching a block copolymer of 90: 5 and has a thermal shrinkage rate of 15% or more at 80 ° C in the stretching direction.

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. In addition, since the stretch-molded product has an excellent impact value, it can be suitably used for applications such as labeling of products for the purpose of preventing bottle breakage of soft drinks and the like.

The present invention will be described in detail below. In the present invention, it has at least one, preferably two or more polymer blocks mainly containing vinyl aromatic hydrocarbons and at least one, and preferably two or more polymer blocks mainly containing conjugated dienes. A block copolymer is used. Here, the polymer block mainly containing vinyl aromatic hydrocarbons is a polymer block having a vinyl aromatic hydrocarbon content of more than 50% by weight, preferably 70% by weight or more. Further, the polymer block containing a conjugated diene as a main component is a polymer block having a conjugated diene content of 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more. When a random copolymer part of a vinyl aromatic hydrocarbon and a conjugated diene is present in a polymer block mainly composed of vinyl aromatic hydrocarbon or a polymer block mainly composed of conjugated diene, a vinyl aromatic compound which is copolymerized The group hydrocarbon may be uniformly distributed in the polymer block or may be distributed in a taper (gradual decrease) form. The weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene in the block copolymer is 60:40 to 95: 5, preferably 65:35 to 88:12, more preferably 68:32 to.
It is 85:15. The content of vinyl aromatic hydrocarbon is 6
If it is less than 0% by weight, the film has poor tensile strength and rigidity,
It is unsuitable as a sheet or the like, and if it exceeds 95% by weight, 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 polymer block contained in the block copolymer is 10,000 to 70,
000, preferably 15,000 to 60,000, more preferably 20,000 to 50,000. The vinyl aromatic hydrocarbon polymer block has a number average molecular weight of 10,
If it is less than 000, the tensile strength and rigidity are inferior.
If it exceeds 000, stretching at low temperature cannot be performed and the low temperature shrinkability is poor, which is not preferable.

Incidentally, a block copolymer having two or more vinyl aromatic hydrocarbon polymer blocks, or at least one block copolymer.
In a mixture of two or more block copolymers having one vinyl aromatic hydrocarbon polymer block, the total number average molecular weight of the vinyl aromatic hydrocarbon polymer block in the block copolymer or the mixture and Ratio of the weight average molecular weight and the number average molecular weight as a whole (these are the molecular weights of vinyl aromatic hydrocarbon polymer block components obtained by oxidative decomposition of the block copolymer or the mixture by the method described below). Is obtained within the range specified in the present invention, the block copolymer or the mixture can be used as the block copolymer in the present invention.

The ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 1.25 to 2.
5, preferably 1.3 to 2.0, more preferably 1.4
The range is from to 1.7. The ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block is 1.25.
If less than 2, the impact strength is inferior to that of the present invention, and 2.
When it exceeds 5, it is not preferable because stretching at a low temperature cannot be achieved and the low temperature shrinkability is poor.

The number average molecular weight of the vinyl aromatic hydrocarbon polymer block is determined by measuring the vinyl aromatic hydrocarbon polymer block component obtained by oxidative decomposition of the block copolymer by gel permeation chromatography. You can The Mw / Mn of the vinyl aromatic hydrocarbon polymer block in the block copolymer used is
The polystyrene block component obtained by decomposing the block copolymer by the above-mentioned oxidative decomposition method is measured by gel permeation chromatography and calculated according to the usual method (the method described in "Gel chromatography <Basics>" published by Kodansha). be able to.

In the block copolymer particularly preferred in the present invention, a polymer block mainly composed of vinyl aromatic hydrocarbons is substantially composed of a vinyl aromatic homopolymer, and a polymer block mainly composed of a conjugated diene is used. It is a block copolymer composed essentially of a conjugated diene homopolymer. Here, the polymer block mainly composed of vinyl aromatic hydrocarbon is substantially composed of vinyl aromatic homopolymer,
Moreover, a block copolymer in which a polymer block mainly composed of a conjugated diene is substantially composed of a conjugated diene homopolymer means a polymer block mainly composed of a vinyl aromatic hydrocarbon and a heavy polymer mainly composed of a conjugated diene. A block copolymer containing a small amount of vinyl aromatic hydrocarbons that are randomly copolymerized with the conjugated diene in the united block, in other words, an amount of vinyl aromatic hydrocarbons not incorporated in the vinyl aromatic hydrocarbon polymer block. Is a block copolymer having a low content of 15% by weight or less, preferably 10% by weight or less, 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 determined by oxidizing the copolymer with diethyl butyl hydroperoxide using osmium tetroxide as a catalyst. Decomposition method (for example, LM KOLTHOF
F, et al. J. Polym. Sci. 1,42
9 (1946)) and the like, and also by 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-
The methods described in Japanese Patent Publication No. 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. are mentioned, but vinyl aromatic carbonization is possible. 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 diene 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, the polymer structure has the general formula:

[0020]

[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 dienes. The boundary between the A block and the B block is not always clear. The linear block copolymer represented by the formula (1) or a general formula

[0022]

[Chemical 2]

(In the above formula, A and B are the same as above, and X is 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. (M and n are integers of 1 or more.)
A radial block copolymer represented by or a mixture of any 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 (f) 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, as the vinyl aromatic hydrocarbon, styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, a-methylstyrene, vinylnaphthalene,
There are vinyl anthracene and the like, but styrene is mentioned as a particularly general formula. These may be used alone or in combination of two or more. The conjugated diene is a 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, etc.
Butadiene and isoprene may be mentioned. These may be used alone or in combination of two or more.

The molecular weight of the polymer block mainly composed of the conjugated diene 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 preferred block copolymer in the present invention has a vinyl aromatic hydrocarbon content of 73 to 85% by weight, and has a melt flow (200 ° C., 5 kg load) of 0 measured according to JIS K-6870. 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 from 1.4 to 1.7. 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-formed product obtained also has extremely excellent low-temperature shrinkability, 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. Hydroxyl group, thiol group,
Modification such as introduction of a functional group such as a nitrile group, a sulfonic acid group, a carboxyl group or an amino group may be performed.

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 anti-pricking agent include fatty acid amide, ethylene bis-stearate, sorbitan monostearate, saturated fatty acid ester of aliphatic alcohol, pentaerythritol fatty acid ester and the like, "Plastic and Rubber Additives Handbook" (Chemicals) The compounds described in Kogyo Co., Ltd. can be used. These are generally used in the range of 0.01 to 5% by weight, preferably 0.1 to 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 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. can do.
If the number average molecular weight exceeds 20,000, the effect of improving low temperature shrinkage 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 an extremely 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 lowered, which is not preferable.

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 blended with 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 the 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, 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 copolymer of the vinyl aromatic hydrocarbon type monomer, or the vinyl aromatic hydrocarbon type monomer. 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 homopolymers of styrene, copolymers of styrene and α-methylstyrene, and copolymers of styrene and methyl methacrylate.

In order to obtain a heat-shrinkable stretched film, sheet or tube from the above block copolymer, it has been conventionally used to impart heat-shrinkability to a film, sheet or tube of vinyl chloride resin or the like. However, the heat shrinkage of the obtained film, sheet or tube at 80 ° C. in the stretching direction should be 15% or more, preferably 20 to 90%, more preferably 40 to 80%. I have to. If the heat shrinkage ratio at 80 ° C is less than 15%, the low-temperature shrinkage is poor, so that the shrinking and packaging process is performed at a high temperature and uniformly,
It is necessary to heat for a long period of time, which makes it impossible to wrap an article that may be altered or deformed at a high temperature or reduces the shrink wrapping processing ability, which is not preferable. In the present invention, 80 ° C
The heat shrinkage ratio in the above means the direction in which the uniaxially stretched film, sheet or tube is stretched when the uniaxially stretched film, sheet or tube is immersed in a heating medium such as 80 ° C hot water, silicone oil or glycerin which does not impair the characteristics of the molded product for 5 minutes Is the heat shrinkage rate.

From the above block copolymer, a heat-shrinkable resin
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
The unstretched product obtained by extrusion molding at 80 to 220 ° C. 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 calendar 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,
Stretch in the extrusion or circumferential direction of the tube.

In the present invention, the stretching temperature is 60 to 120.
℃, preferably 70 ~ 110 ℃, more preferably 80 ~
Stretching ratio of 1.5 to 8 in the machine direction or the transverse direction at 100 ° C
It is preferable to stretch the film twice, preferably 2 to 6 times. If the stretching temperature is lower than 60 ° C., breakage occurs during stretching and it is difficult to obtain a desired molded product, and if it exceeds 120 ° C., it is difficult to obtain good low-temperature shrinkability. The stretching ratio is selected within the above range so as to correspond to the required shrinkage ratio depending on the application, but if the stretching ratio is less than 1.5 times, the heat shrinkage ratio is small and not preferable for heat shrinkable packaging. A draw ratio of more than 8 times is not preferable for stable production in the drawing process.

The uniaxially stretched molded product is then cooled, if necessary, immediately after cooling at 60 to 100 ° C. for a short time, for example, 3 to 6.
It is also possible to carry out a heat treatment for 0 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, preferably 10,000 kg / cm ² or more, more preferably 15,000 kg / cm ² or more. Is preferred as the heat shrinkable packaging material. Tensile elastic modulus is 7,000 kg / cm
If it is less than ² , there is a problem that the shrinkage packaging process causes fatigue and it is difficult to perform normal packaging.

The uniaxially stretched film, sheet or tube of the present invention is superior in hygiene compared to the conventional vinyl chloride resin type ones, and by utilizing its characteristics, various applications,
For example, it can be used for packaging of fresh food, frozen food, confectionery, packaging of clothes, 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, the uniaxially stretched molded product of the present invention is excellent in low-temperature shrinkability, and therefore, it is suitable as a material for a heat-shrinkable label of a plastic molded product which 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%.
It is preferably less than 10%, preferably 10% or less, more preferably 5% or less.

[0039]

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 and comparative examples, the melt flow rate of the block copolymer used was in the range of 1 to 40 g / 10 min.

The ratio of the weight average molecular weight to the number average molecular weight of the polystyrene blocks of the block copolymer used is such that the molecular weight of each polystyrene block present in the block copolymer is changed or blocks having polystyrene blocks having different molecular weights are used. It was adjusted by mixing two or more kinds of copolymers or by using these operations together.

[0041]

Examples 1 and 2 and Comparative Examples 1 and 2 Styrene having a polymer structure, a styrene content, a polystyrene block molecular weight and a ratio of the weight average molecular weight to the 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 to prepare a film of about 80 μm. As shown in the examples, the copolymer having the polystyrene block number average molecular weight and Mw / Mn within the ranges specified in the present invention has a lower stretching temperature than that of the comparative example, and has a temperature of 80 ° C.
It can be seen that since the heat shrinkage rate is high, it is extremely excellent as a shrink film.

The heat shrinkage ratios of the stretched films of Examples 1 and 2 are the results of the films stretched at 90 ° C. and 95 ° 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
Each of them is about 5% and the drawing temperature is inferior to the films of 90 ° C and 95 ° C. In the uniaxially stretched films of Examples 1 and 2, 80 ° C. in the direction orthogonal to the stretching direction.
The heat shrinkage rate was less than 5%. The puncture impact values (kg-cm / cm) of Examples 1 and 2 were 3000 and 3700.

[0044]

[Table 1]

[0045]

Examples 3 and 4, Comparative Examples 3 to 8 Examples of styrene-butadiene block copolymers having a polymer structure, styrene content, polystyrene block molecular weight and polystyrene block Mw / Mn as shown in Table 2 were obtained. Polymerized in the same manner as 1. 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 is
The 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 7 and 8 which are 00% and Comparative Examples 5 and 6 in which the molecular weights of the polystyrene blocks are 5000 and 85000, respectively, the copolymers having a styrene content less than the range of the present invention have tensile strength and tensile elasticity. It can be seen that the shrinkage rate is small and the rigidity as a shrink label is poor, and conversely, the one having a high styrene content has a small heat shrinkage rate and is not suitable.

Further, a copolymer having a polystyrene block molecular weight smaller than the range of the present invention has a small tensile strength and a tensile elastic modulus, and conversely, a polystyrene block having a large molecular weight has a small thermal shrinkage ratio. Comparative Example 3 in which the Mw / Mn of the polystyrene block is smaller than the range of the present invention has a low impact resistance, and Comparative Example 4 in which the Mw / Mn is large has a small shrinkage rate and is not preferable. 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.

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 structure was formed.

[0049]

[Chemical 3]

A block copolymer having polystyrene blocks having the same styrene content and the same number average molecular weight and polystyrene blocks having the same Mw / Mn was prepared except that the stretching properties, physical properties and shrinkage properties were examined. It was As a result, the minimum stretchable temperatures of the block copolymers corresponding to Examples 3 and 4 were 95 ° C. and
Was 95 ° C., a tensile modulus in the stretching direction is respectively ^{13500kg / cm 2, 17600kg / cm} 2, respectively puncture impact value 3000 kg-cm
/ Cm, 18000 kg-cm / cm, and the shrinkage rates at 80 ° C were 48% and 47%, respectively.

[0051]

[Table 2]

[0052]

Examples 5 to 8 Examples 5 to 7 are (B'-S) ₃ type copolymers having different non-blocking ratios, and Example 8 is a stretched film of a copolymer having the same structure with a large melt index. Table 3 shows the measurement results of physical properties and thermal shrinkage.
The styrene-butadiene copolymer was polymerized in the same manner as in Example 1 except that cyclohexane was used as a solvent, and the polystyrene block number average molecular weight of the copolymers of Examples 5 to 8 was 15,000 to 40,000. Met. 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 3. The physical properties of the stretched film are shown in Table 3.

When the non-blocking rate becomes smaller as in Examples 6 and 7, the tensile strength and the tensile elastic modulus tend to improve. In the uniaxially stretched films of Examples 5 to 8, the heat shrinkage rate at 80 ° C in the direction orthogonal to the stretching direction was 5%.
Was less than. Next, in Example 5 and Example 6, the polymer structure was formed.

[0054]

[Chemical 4]

Styrene content, melt index, non-blocking rate, polystyrene block molecular weight, and polystyrene block M
Block copolymers having w / Mn were prepared and their stretching properties, physical properties and shrinkage properties were investigated. As a result, the minimum stretching temperatures of the block copolymer corresponding to Example 5 and the block copolymer corresponding to Example 6 were 95 ° C. and
The tensile elastic modulus in the stretching direction is 95 ° C.

[0056]

[Table 3]

[0057]

Examples 9 and 10 In cyclohexane

[0058]

[Chemical 5]

Was polymerized with n-butyllithium as an initiator and then a coupling reaction was carried out with SiCl ₄ as a coupling agent to prepare a radial type styrene-butadiene block copolymer. In Example 9, a radial type and a linear type were mixed by further using Si (CH ₃ ) ₂ Cl as a coupling agent. The stretching conditions are the same as in Example 1. The measurement results of the physical properties of these stretched films and the heat shrinkage ratio are shown in Table 4.

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, the physical properties of the film,
It can be seen that a stretched film having an excellent heat shrinkage rate was obtained. In addition, in the uniaxially stretched films of Examples 9 and 10,
The heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction is 5
It was less than%.

[0061]

Examples 11 to 13 Styrene-butadiene block copolymers having a polymer structure, a styrene content and a polystyrene block as shown in Table 4 were polymerized in the same manner as in Example 1. The stretching conditions are as shown in Table 4. The measurement results of the physical properties of these stretched films and the heat shrinkage ratio are shown in Table 4.

In the uniaxially stretched films of Examples 11 to 13, the heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction was less than 5%.

[0063]

Example 14 In Example 1, by adding a part of the catalyst during the polymerization, the polymer structure as shown in Table 4, the styrene content, the polystyrene block number average molecular weight, and the polystyrene block Mw / Mn. And a styrene-butadiene block copolymer mixture having an unblocked rate was polymerized.

The stretching conditions are as shown in Table 4. The measurement results of the physical properties of these stretched films and the heat shrinkage ratio are shown in Table 4. In the uniaxially stretched film of Example 14, the heat shrinkage ratio at 80 ° C. in the direction orthogonal to the stretching direction was 5%.
Was less than.

[0065]

[Table 4]

[0066]

Examples 15 to 17 Block copolymer 10 of Example 2
A block copolymer composition (referred to as Example 15) in which 0 part by weight of 25 parts by weight of a low molecular weight polystyrene having a number average molecular weight of 400 and the block copolymer 100 of Example 2 were mixed.
A block copolymer composition (referred to as Example 16) 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 5. In Table 5, the performance of the uniaxially stretched film of the block copolymer of Example 2 is shown as Example 17.

[0067]

[Table 5]

[0068]

Examples 18 and 19 Using the same polymers as in Examples 3 and 7, respectively, and in a similar manner, block copolymers having styrene contents of 75% by weight and 80% by weight and having a thickness of about 40 µm were prepared. Each uniaxially stretched film was produced. Next, after printing characters and patterns on these films, a stretched direction is a circumferential direction, and a non-stretched direction is a longitudinal direction to produce a circumferential heat-shrinkable label,
It was put on a cylindrical cup molded from impact-resistant polystyrene and passed through a shrink tunnel controlled at a temperature of 180 to 200 ° C. to be heat-shrinked. As a result, all of these heat-shrinkable labels are in tight contact with the cup surface of the packaged product without fluffiness or wrinkles.
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 7

[0070]

[Chemical 6]

A uniaxially stretched film having a thickness of 60 μm was prepared by a method corresponding to each example, using polymers having the same constitutional elements except for the above. Next, a heat-shrinkable label was prepared from these films by the same method as described above, and a cup having a similar appearance was heat-shrinked by the same method to obtain a coating having a good appearance.

[0072]

Example 20 Using the same block polymer as in Example 3 as the base polymer, a uniaxially stretched film was produced in the same manner as in Example 1. After printing characters and patterns on this uniaxially stretched film, length 26 cm, width (the same direction as the stretching direction)
It was cut into 30 cm, and a heat-shrinkable cylindrical label having a length of 26 cm and a diameter of about 9 cm was prepared using an adhesive. This heat-shrinkable label was placed on a general 1-liter glass bottle having a height of 30 cm, a maximum diameter of 8 cm, and a narrower upper part, and was placed in an oven at 150 ° C. for 1 minute to be heat-shrinked. At that time, the position of the film was set so as to cover the bottom of the container by about 1 cm from the outer circumference toward the center after the heat shrinkage.

As a result, the heat-shrinkable label was in tight contact with the surface of the glass bottle without fluffing or wrinkling,
The printed characters and patterns were not locally deformed. Next, this glass bottle was filled with carbonated drinking water equivalent to 85% of the internal volume and stoppered, then leveled and dropped from a height of 75 cm onto concrete to destroy the glass bottle of the heat shrinkable label. The scattering prevention effect was investigated.
As a result, in the case of a bottle that does not have the heat-shrinkable label attached, 70% or less of the bottle fragments that stay within a radius of 0.5 m from the drop point, whereas the heat-shrinkable label attached It was 96% in the case of the above bottle, and it was confirmed that the heat-shrinkable label prepared from the film of the present invention was excellent in the glass bottle breakage scattering prevention effect.

In Example 3, the polymer structure was changed to

[0075]

[Chemical 7]

A uniaxially stretched film having a thickness of about 80 μm was prepared by a method corresponding to each example, using polymers having the same constitutional elements except for the above. Next, a heat-shrinkable label was prepared from this film by the same method as described above, and a bottle was shrunk by the same method and contracted, and the destruction and scattering prevention effect was examined by the same method as described above. It was confirmed that the bottle fragments remaining within 0.5 m account for 96%, which is excellent in the glass bottle breakage and scattering prevention effect.

[0077]

Examples 21 and 22 According to the orientation treatment shown in Table 6, several block copolymers were mixed to prepare a block copolymer mixture, and a uniaxially stretched film was prepared in the same manner as described above. The performance of each film is shown in Table 6. All films have low-temperature shrinkability, transparency, and suitable for heat-shrinkable labels.
It had rigidity and impact resistance.

Next, a heat-shrinkable label similar to that of Example 20 was prepared from the uniaxially stretched films of Examples 21 and 22, and a glass bottle was coated with the heat-shrinkable label to examine the effect of preventing the glass bottle from breaking and scattering. Also showed the same good result as in Example 20.

[0079]

[Table 6]

[0080]

According to the present invention, a film having excellent low temperature shrinkability and low temperature shrinkability and mechanical strength can be obtained.

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Claims (2)

[Claims] 1. At least one vinyl aromatic hydrocarbon-based polymer block and at least one conjugated diene-based polymer block, wherein the vinyl aromatic hydrocarbon block has a number average molecular weight. Is 10,000
˜70,000, the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon block is in the range of 1.25 to 2.5, and the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60:40 to. The block copolymer of 95: 5 is uniaxially stretched, and the heat shrinkage ratio at 80 ° C. in the stretching direction is 15
% Or more, uniaxially stretched film, sheet, or tube
Boo. 2. The non-blocking rate of the block copolymer is 15
The uniaxially stretched film, sheet or tube according to claim 1, wherein the vinyl aromatic hydrocarbon polymer block has a number average molecular weight of 15,000 to 60,000 in an amount of not more than 5% by weight.