JPH0250856B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-shrinkable block copolymer film that has excellent low-temperature shrinkability, water whitening resistance, and environmental damage resistance. Shrink packaging has been increasingly used in recent years, especially for food packaging, as it can effectively eliminate the bagging and wrinkles that were unavoidable with conventional packaging technology, and it can also quickly wrap products tightly or irregularly shaped items. . Conventionally, vinyl chloride resin has been mainly used as a material for shrink wrapping films, sheets, etc. because it satisfies required properties such as low-temperature shrinkability, transparency, and mechanical strength. However, vinyl chloride resin has hygienic problems due to vinyl chloride monomer and plasticizers.
There is a strong demand for alternatives due to the problem of hydrogen chloride generation during incineration. On the other hand, block copolymer resins made of vinyl aromatic hydrocarbons and conjugated dienes do not have the above problems and have good transparency and impact resistance, so they are widely used as materials for food packaging containers. It is being done. However, conventionally known block copolymers are unsuitable as materials for heat-shrinkable packaging because of their high stretching temperatures and high shrinkage temperatures. For example, JP-A-49-102494 and JP-A-49-
Publication No. 108177 describes a packaging film obtained by biaxially stretching a block copolymer having a styrene hydrocarbon content of 50 to 95% by weight, and a composition in which the block copolymer is blended with a styrene resin. However, such a film cannot achieve sufficient shrinkage unless the heat shrinkage temperature is about 100°C or higher. Methods for improving the low-temperature shrinkability of such block copolymers are also disclosed in JP-A-50-6673 and JP-B-Sho 55-5544.
This is attempted in the Publication No. In the former method, by applying the tubular method to a linear copolymer, simultaneous biaxial orientation is achieved through expansion stretching in a temperature range where effective high degree of orientation occurs, resulting in good low-temperature heat shrinkability. This is a method of manufacturing film. however,
In this method, expansion and stretching is started in a very limited temperature range depending on the butadiene content of the raw resin, and the temperature in the stretching zone from the expansion start point to the expansion end point is strictly controlled. Unless a gradient is provided, a film having the desired low-temperature heat shrinkability cannot be obtained, and therefore it has the disadvantage that it is difficult to implement easily. In the latter method, a styrene-butadiene block copolymer with a styrene content of 20-50% is added to a styrene-butadiene block copolymer with a styrene content of 65-90%.
This method produces a biaxially stretched film with low-temperature shrinkability by blending the two by weight; however, if the kneading conditions of both components are poor, sufficient low-temperature shrinkability cannot be achieved, and the kneading method requires advanced techniques. This method has the disadvantage that it requires a lot of time and is difficult to implement. In view of the current situation, the present inventors have carried out extensive studies on a method for easily obtaining block copolymer films, sheets, etc. with excellent low-temperature shrinkability. A block copolymer whose coalesced block has a molecular weight within a certain range, or a composition in which such a block copolymer is blended with a low molecular weight vinyl aromatic hydrocarbon polymer or a normal high molecular weight vinyl aromatic hydrocarbon polymer. It was discovered that the object could be stretched at a relatively low temperature, and patent application No. 56-22989,
Applications were filed for Japanese Patent Application No. 56-63325 and Japanese Patent Application No. 56-95314. After that, the present inventors further investigated the improvement and found that the vinyl aromatic hydrocarbon polymer block bonded in the block copolymer has a component with a relatively small molecular weight and a component with a relatively large molecular weight. We have newly discovered that by selecting the contents of both components within an appropriate range, it is possible to obtain a heat-shrinkable film that has not only low-temperature shrinkability but also water whitening resistance and environmental damage resistance. The present invention has now been completed. That is, the present invention provides a block copolymer in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene is 60:40 to 90:10, and the polymer structure has the general formula A ₁ -B ₁ -A ₂ B ₁ - A ₁ −B ₂ −A ₂ B ₁ −A ₁ −B ₂ −A ₂ −B ₃ (In the above formula, A ₁ and A ₂ are polymer blocks mainly composed of vinyl aromatic hydrocarbons, and B ₁ ,
B ₂ and B ₃ are polymer blocks mainly composed of conjugated dienes. The boundary between A block and B block does not necessarily need to be clearly distinguished. ), and in the _A1 block and _A2 block, the vinyl aromatic hydrocarbon block is
There is only one polymer block with an average molecular weight of 5000 or more, and that polymer block
In A ₁ block, the average molecular weight is 5000-35000
A′1 is a vinyl aromatic hydrocarbon polymer block _A′1 , and _A′2 is a vinylaromatic hydrocarbon polymer block _A′2 having an average molecular weight of 50,000 or more in the A′2 block, and _A′1 and _A′2 are Weight ratio is 1:2 to 1:
A heat-shrinkable block copolymer film obtained by uniaxially or biaxially stretching the block copolymer of No. 6 and having a heat shrinkage rate of 10% or more at 90°C in the stretching direction, and uniaxially stretching the film. This invention relates to a heat-shrinkable block copolymer film for labels made from molded products. Since the heat-shrinkable film of the present invention has excellent shrinkability at low temperatures, it can be used to package items that may deteriorate or deform if heated at high temperatures for a long period of time during the shrink-wrapping process, such as packaging of perishable foods and plastic molded products. suitable for Furthermore, since the heat-shrinkable block copolymer film of the present invention has excellent water whitening resistance, articles coated with the film may not be exposed to water at room temperature for a long period of time or treated with hot water of 70 to 80°C or higher. water becomes cloudy and loses its transparency (so-called water whitening)
There is no such problem. Therefore, it can be used in fields of application that require exposure to such conditions, such as applications that require sterilization treatment with hot water. Furthermore, the heat-shrinkable film of the present invention has excellent environmental damage resistance,
The article coated with the heat-shrinkable film of the present invention has the feature that it is difficult to break even if it is left in an outdoor environment with severe temperature changes. In particular, when the article to be coated is made of materials such as metal, porcelain, glass, and polyester resin, which have very different properties such as thermal expansion coefficient and absorbency, conventional heat-shrinkable films cannot be used. The heat shrinkable film of the present invention does not have such problems and can be used in the natural environment for a long time. Withstands being left unattended. Therefore, the heat-shrinkable film of the present invention can be particularly suitably used for applications such as labels for containers made of the above-mentioned materials by taking advantage of these advantages. The present invention will be explained in detail below. The block copolymer used in the present invention has a polymer structure as described above. In the present invention, the block copolymer whose polymer structure is represented by the general formula A _{1 -B} 1 -A ₂ -B ₂ is the same as the block copolymer whose polymer structure is represented by the general formula A ₁ -A ₁ -B ₂ -A ₂ . shall be equivalent.
Here, a polymer block mainly composed of vinyl aromatic hydrocarbons is defined as having a content of vinyl aromatic hydrocarbons.
More than 50% by weight, preferably more than 70% by weight of polymer blocks. In addition, a polymer block mainly composed of conjugated diene means that the content of conjugated diene is 50%.
It is a polymer block of at least 70% by weight, preferably at least 70% by weight. In addition, the block copolymer of the present invention has an average molecular weight of conjugated diene-free vinyl aromatic hydrocarbon in its _A1 block.
There is only one vinyl aromatic hydrocarbon polymer block A′ ₁ with a molecular weight of 5,000 to 35,000, and a vinyl aromatic hydrocarbon polymer block A _{′ 2 with} an average molecular weight of 50,000 or more that does not contain a conjugated diene. Polymerize according to the polymerization method described below so that there is only one. In the presence of vinyl aromatic hydrocarbons randomly copolymerized with conjugated dienes in these polymer blocks, even if the vinyl aromatic hydrocarbons are uniformly distributed in the polymer chain, they tend to taper. It may be distributed in a shape. The vinyl aromatic hydrocarbon content of the block copolymer used in the present invention is 60 to 90% by weight, preferably 65 to 85% by weight, and more preferably 68 to 78% by weight. If the vinyl aromatic hydrocarbon content is less than 60% by weight, the film will have poor tensile strength and rigidity, making it unsuitable for use as a heat-shrinkable film. Moreover, if it exceeds 90% by weight, it is not preferable because impact resistance is poor. 1. Characteristics of the block copolymer used in the present invention
One is that the average molecular weight of the vinyl aromatic hydrocarbon polymer block _A'1 present in the _A1 block is 5000~
35,000, preferably 7,000 to 30,000, more preferably
10,000 to 25,000, while the vinyl aromatic hydrocarbon polymer block A′ ₂ present in the A ₂ block
The average molecular weight of is 50,000 or more, preferably 60,000 ~
200000, more preferably 65000 to 150000,
Moreover, the weight ratio of A′ ₁ and A′ ₂ is 1:2 to 1:6, preferably 1:2.5 to 1:5, and more preferably 1:3.
~1:4. In the present invention, the average molecular weight refers to the molecular weight determined from the peak position of a gel permeation chromatogram in GPC (gel permeation chromatography) measurement. The calibration curve for GPC is created using standard polystyrene commercially available for GPC. In addition, the weight ratio of A′ ₁ and A′ ₂ is determined by the gel permeation chromatogram, where the molecular weight is 5000 to 35000.
It is the relative ratio of the peak area in the region with a molecular weight of 50,000 or more. When the average molecular weight of A′ ₁ is smaller than the above range, the impact resistance decreases,
If it exceeds the above range, the low temperature shrinkability will deteriorate, which is not preferable. Furthermore, if the average molecular weight of A' ₂ is smaller than the above range, water whitening resistance and environmental damage resistance will deteriorate, which is not preferable. Furthermore, regarding the weight ratio of A' ₁ and A' ₂ , if the amount of A' ₁ exceeds the above range, water whitening resistance and environmental damage resistance will deteriorate;
On the other hand, if the amount of _A'1 decreases, the low-temperature shrinkability will decrease, which is not preferable. The average molecular weights of vinyl aromatic hydrocarbon polymer blocks A' ₁ and A' ₂ and their quantitative relationship were determined by the method of oxidative decomposition of block copolymers with di-tertiary butyl hydroperoxide using osmium tetroxide as a catalyst ( L.
M.KOLTHOFF, etal., J.Polym.Sci.1, 429
(1946)) vinyl aromatic hydrocarbon polymer blocks A' ₁ and A' ₂
The average molecular weight and their abundance can be determined by measuring with GPC. That is, in the gel permeation chromatogram of the vinyl aromatic hydrocarbon polymer block obtained by decomposing the block copolymer by the above method, the average molecular weight is
From the position of the peak that exists in the region of 5000 to 35000
The average molecular weight of A′ ₁ is determined, and the average molecular weight of A′ ₂ is determined from the position of the peak that exists in the region where the average molecular weight is 50,000 or more. The quantitative relationship between A′ ₁ and A′ ₂ is the area of the vinyl aromatic hydrocarbon polymer blocks present in the region with an average molecular weight of 5,000 to 35,000 and the vinyl aromatic carbonization present in the region with an average molecular weight of 50,000 or more. It is determined by comparing the areas of hydrogen polymer block groups. In addition, if the amount of catalyst, amount of monomer, and polymerization conditions used to produce the block copolymer are known, A′ ₁ can be determined by calculation.
The average molecular weight of A′ ₂ and the quantitative relationship between A′ ₁ and A′ ₂ can be determined. In the block copolymer used in the present invention,
There is no particular restriction on the molecular weight of a polymer block mainly composed of conjugated dienes, but generally the number average molecular weight is
500-200000, preferably 1000-100000.
Further, the number average molecular weight of the block copolymer as a whole is 20,000 to 500,000, preferably 50,000 to 300,000.
It is. A particularly preferred block copolymer in the present invention is one in which the A block constituting the block copolymer is substantially composed of a vinyl aromatic hydrocarbon homopolymer, and the B block is substantially composed of a conjugated diene homopolymer. It is a block copolymer.
Here, a block copolymer in which the A block is substantially composed of a vinyl aromatic hydrocarbon homopolymer and the B block is substantially composed of a conjugated diene homopolymer is defined as It means a block copolymer with a small amount of vinyl aromatic hydrocarbon randomly copolymerized with a diene, and specifically, the overall non-block rate of the block copolymer expressed by the following formula is 15% by weight. below,
Preferably, the amount of the block copolymer is 10% by weight or less, more preferably 5% by weight or less. Non-blocking rate (%) = (Weight of total vinyl aromatic hydrocarbons in block copolymer) - (Block copolymerization/(Weight of total vinyl aromatic hydrocarbons in block copolymer) * * Weight of total vinyl aromatic hydrocarbons in block copolymer) weight of vinyl aromatic hydrocarbon polymer block)/×100 The weight of the vinyl aromatic hydrocarbon polymer block in the block copolymer, that is, the total amount of A′ ₁ and A′ ₂ It is determined by decomposing and quantifying using the oxidative decomposition method. It is preferable to use such a block copolymer because it provides a material with excellent rigidity. In addition, in the present invention, a block copolymer outside the range specified in the present invention may be mixed with the block copolymer specified in the present invention as necessary, but the blending amount is 50% by weight or less, preferably 30
It should be less than 10% by weight, more preferably less than 10% by weight. The block copolymer used in the present invention can basically be produced by conventionally known methods.
Publication No. 19286, Special Publication No. 14989, Publication No. 14989, Special Publication No. 14989
-2423, etc., but the vinyl aromatic hydrocarbon polymer block A′ ₁
The production conditions must be set so that the average molecular weight of and A' ₂ , their quantitative relationship, and the vinyl aromatic hydrocarbon content are within the range specified by the present invention. In the present invention, vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, etc. However, styrene is a particularly common one.
These may be used not only alone, but also as a mixture of two or more. The conjugated diene is a diolefin having a pair of conjugated double bonds, such as 1,
3-butadiene, 2-methyl-1,3-butadiene (isobrene), 2,3-dimethyl-1,3-
Examples include butadiene, 1,3-pentadiene, 1,3-hexadiene, and particularly common ones include 1,3-butadiene and isoprene. These may be used not only alone, but also as a mixture of two or more. The block copolymer used in the present invention has hydroxyl groups,
Modifications such as introduction of functional groups such as thiol groups, nitrile groups, sulfonic acid groups, carboxyl groups, and amino groups may be performed. In the present invention, a block copolymer (component (a)) is combined with a low molecular weight vinyl aromatic hydrocarbon polymer or copolymer (component (b)) for the purpose of improving low-temperature stretchability and low-temperature shrinkability. )) may be blended. In addition, for the purpose of further improving low-temperature stretchability, low-temperature shrinkability, and rigidity, the block copolymer may be combined with component (b) and a relatively high molecular weight vinyl aromatic hydrocarbon polymer or copolymer (with component (c)). ) may also be blended. Furthermore, component (c) alone may be blended into the block copolymer for the purpose of improving rigidity. The vinyl aromatic hydrocarbon polymers or copolymers of components (b) and (c) used in the present invention include the above-mentioned vinyl aromatic hydrocarbon monomers or copolymers as well as the above-mentioned vinyl aromatic hydrocarbon polymers or copolymers. Aromatic hydrocarbon monomers and other vinyl monomers, such as ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylic esters such as methyl acrylate, methacrylic esters such as methyl methacrylate, acrylonitrile, etc. Contains copolymers. Particularly preferred are styrene homopolymers, styrene and α-methylstyrene copolymers, and styrene and methyl methacrylate copolymers. The number average molecular weight of the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer as component (b) used in the present invention is 20,000 or less, preferably 200 to 10,000, more preferably 300 to 5,000. Number average molecular weight is 20000
Exceeding this is not preferable because the effect of improving low-temperature shrinkage is lost. Particularly preferred are those having a number average molecular weight of 300 or more and less than 500, and such low molecular weight polymers or copolymers have an extremely good effect of improving low-temperature shrinkage properties. The amount of the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer of component (b) is 5 to 100 parts by weight, preferably 10 to 70 parts by weight, based on 100 parts by weight of the block copolymer of component (a). weight part,
More preferably, it is 15 to 55 parts by weight. The number average molecular weight of the relatively high molecular weight vinyl aromatic hydrocarbon polymer or copolymer used as component (c) in the present invention is 30,000 or more, preferably 50,000 or more.
~1,000,000, more preferably 80,000~500,000. If the number average molecular weight of component (c) is less than 30,000, it is not preferable because the effect of improving rigidity is not sufficient. The blending amount of the vinyl aromatic hydrocarbon polymer or copolymer of component (c) is the same as that of the block copolymer of component (a).
5 to 80 parts by weight per 100 parts by weight, preferably
The amount is 10 to 60 parts by weight, more preferably 15 to 45 parts by weight. Various additives may be added to the block copolymer used in the present invention or to the block copolymer composition blended with the above vinyl aromatic hydrocarbon polymer or copolymer depending on the purpose. Suitable additives include 30 parts by weight or less of coumaron-indene resins, terpene resins, softeners such as oils, and plasticizers. Further, various stabilizers, pigments, antiblocking agents, antistatic agents, lubricants, etc. can also be added. In addition, examples of antiblocking agents, lubricants, and antistatic agents include fatty acid amide, ethylene bisstearamide, sorbitan monostearate, saturated fatty acid esters of fatty alcohols, and pentaerythritol fatty acid esters, and as ultraviolet absorbers. , pt-butylphenyl salicylate, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-
Chlorobenzotriazole, 2,5-bis-
Compounds described in "Practical Handbook of Additives for Plastics and Rubber" (Kagaku Kogyo Co., Ltd.), such as [5'-t-butylbenzoxazolyl-(2)]thiophene, can be used. These are generally used in a range of 0.01 to 5% by weight, preferably 0.1 to 2% by weight. In the present invention, a block copolymer (formation (a)),
or a block copolymer composition consisting of component (a) and component (b), or a block copolymer composition consisting of component (a), component (b) and component (c), or component (a) and component The block copolymer composition consisting of (c) has a melt flow measured according to JIS K-6970 (200°C, 5 kg load).
is preferably 0.001 to 70, preferably 0.01 to 50, more preferably 0.1 to 30 g/10 min. A block copolymer or block copolymer composition having a melt flow within this range has excellent film formability. In the present invention, component (a), component (a) and component (b), or component (a), component (b) and component (c), or component (a) and component (c),
Alternatively, as for the method of mixing these and other additives, it can be manufactured by any conventionally known compounding method. For example, melt-kneading methods using common mixers such as open rolls, intensive mixers, internal mixers, co-kneaders, continuous kneaders with twin-screw rotors, extruders, etc.; A method of removing the particles by heating is used. To obtain a heat-shrinkable stretched film from the block copolymer or block copolymer composition,
Basically, the methods used to impart heat shrinkability to films made of vinyl chloride resin etc. can basically be used, but the heat shrinkable film obtained can be heated at 90°C.
Thermal shrinkage rate is 10% or more, preferably 15-90
%, more preferably 20-70%. If the heat shrinkage rate at 90℃ is less than 10%, low-temperature shrinkability is poor, so it is necessary to adjust the shrink packaging process to a high temperature and uniformity, or to heat it for a long time, which may cause deterioration or deformation at high temperatures. This is undesirable because it makes it impossible to package such items and reduces shrink-wrapping processing capacity. In addition, in the present invention, 90°C
The heat shrinkage rate refers to the heat shrinkage rate of a uniaxially stretched or biaxially stretched film in a heating medium such as 90°C hot water, silicone oil, or glycerin that does not affect the properties of the molded product.
This is the heat shrinkage rate in each stretching direction of the molded product when immersed for minutes. To obtain a heat-shrinkable uniaxially or biaxially stretched film from the block copolymer or block copolymer composition described above, the block copolymer or block copolymer composition is processed through a conventional T-die or annular die. It is extruded into a flat or tube shape at 150 to 250°C, preferably 170 to 220°C, and the resulting unstretched product is uniaxially or biaxially stretched. For example, in the case of uniaxial stretching, in the case of a film or sheet, it is stretched in the extrusion direction using a calendar roll, etc., or in the direction perpendicular to the extrusion direction using a tenter, etc., and in the case of a tube shape, it is stretched in the extrusion direction of the tube or in the circumferential direction. Stretch. In the case of biaxial stretching, in the case of a film or sheet, the extruded film or sheet is stretched in the longitudinal direction with a metal roll, etc., and then stretched in the transverse direction with a tenter, etc., and in the case of a tube shape, the extruded film or sheet is stretched in the longitudinal direction with a tenter, etc. They are stretched simultaneously or separately in the circumferential direction of the tube, that is, in the direction perpendicular to the tube axis. The heat-shrinkable film of the present invention obtained in this way has a thickness of 5 to 300μ, preferably 10 to 100μ,
More preferably, it is adjusted to be in the range of 30 to 70μ. In the present invention, it is preferable to stretch at a stretching temperature of 60 to 120°C, preferably 80 to 110°C, and a stretching ratio of 1.5 to 8 times, preferably 2 to 6 times, in the machine direction and/or the transverse direction. If the stretching temperature is less than 60°C, breakage occurs during stretching, making it difficult to obtain a desired heat-shrinkable film, and if it exceeds 120°C, it is difficult to obtain a film with good low-temperature shrinkability. The stretching ratio is selected within the above range to correspond to the shrinkage ratio required depending on the application, but if the stretching ratio is less than 1.5 times, the heat shrinkage ratio is low and it is not suitable for heat-shrinkable packaging. A stretching ratio of more than 8 times is not preferable in terms of stable production in the stretching process. In the case of biaxial stretching,
The stretching ratios in the machine direction and the transverse direction may be the same or different. After uniaxial stretching or 2
The heat-shrinkable film after axial stretching is then heated to 60-105°C, preferably 80-95°C, immediately after cooling if necessary.
℃ for a short period of time, e.g. 3-60 seconds, preferably 10-60 seconds.
It is also possible to carry out a heat treatment for 40 seconds to prevent natural shrinkage at room temperature. The uniaxially stretched or biaxially stretched heat-shrinkable film of the present invention has a tensile modulus in the stretching direction of 5000 Kg/cm ² or more, preferably 7000 Kg/cm 2 or more, more preferably 7000 Kg/cm ² or more.
It is preferable for the heat-shrinkable packaging material to be 10,000 Kg/cm ² or more. Tensile modulus in stretching direction is 5000Kg/
When it is ² cm2 or more, it is preferable because normal packaging can be performed without causing sagging during the shrink wrapping process. When the uniaxially stretched or biaxially stretched film of the present invention is used as a heat-shrinkable packaging material, the temperature is 150 to 300°C, preferably 180°C to achieve the desired heat shrinkage rate.
A few seconds to a few minutes at a temperature of ~250℃, preferably 1~
It can be heat-shrinked by heating for 60 seconds, more preferably 2 to 30 seconds. The uniaxially stretched or biaxially stretched film of the present invention is
It is superior in terms of hygiene compared to conventional vinyl chloride resin-based products, and its properties can be used for a variety of purposes.
For example, it can be used for packaging fresh foods, frozen foods, confectionery, clothing, stationery, toys, etc. Particularly preferred applications include printing characters and designs on a uniaxially stretched film of the block copolymer or block copolymer composition defined in the present invention, and then printing the film on plastic molded products, metal products, glass containers, porcelain, etc. Used by heat-shrinking it to the surface of the package.
It can be used as a material for so-called heat-shrinkable labels. In particular, the uniaxially stretched heat-shrinkable block copolymer film of the present invention has excellent low-temperature shrinkability and environmental damage resistance, so it can be used as a heat-shrinkable label material for plastic molded products that deform when heated to high temperatures. Materials whose coefficient of thermal expansion and water absorption are extremely different from those of the heat-shrinkable block copolymer of the present invention, such as metals, porcelain, glass, polyolefin resins such as polyethylene, polypropylene, and polybutene, polymethacrylate resins, and polycarbonates. based resin, polyethylene terephthalate,
It can be suitably used as a heat-shrinkable label material for containers using at least one member selected from polyester resins such as polybutylene terephthalate and polyamide resins. Furthermore, the uniaxially stretched heat-shrinkable block copolymer film of the present invention takes advantage of its excellent water whitening resistance.
It can be used as a material for heat-shrinkable labels for glass bottles, metal containers, plastic containers, etc. containing foods that require sterilization with hot water at 60°C or higher, more generally 75°C or higher. The materials constituting the plastic container in which the heat-shrinkable block copolymer film of the present invention can be used include:
In addition to the above resins, polystyrene, rubber modified high impact polystyrene (HIPS), styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methacrylic acid ester −
Examples include butadiene-styrene copolymer (MBS), polyvinyl chloride resin, polyvinylidene chloride resin, phenol resin, urea resin, melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. These plastic containers may be a mixture of two or more resins or may be a laminate. In addition, when using a heat-shrinkable block copolymer film obtained by uniaxially stretching the block copolymer specified in the present invention as a heat-shrinkable label material, the film is heated at 90°C in the direction orthogonal to the stretching direction. The shrinkage rate is
It is preferably less than 10%, preferably 5% or less, more preferably 3% or less. Examples of the present invention will be shown below to explain the present invention in more detail, but it goes without saying that the content of the present invention is not limited to these Examples. Examples 1 to 7 and Comparative Examples 1 to 5 Block copolymers having the polymer structure, styrene content, etc. shown in Table 1 were produced using n-butyllithium as a catalyst and according to a conventional method.
The block copolymers of Examples 5 to 7 and Comparative Example 4 used n-hexane as a solvent, while the others used cyclohexane as a solvent. These copolymers were formed into a sheet using a 25 mmφ extruder, and then uniaxially stretched 3 times in a tenter to produce a film with a thickness of about 60 μm. At this time, the temperature in the tenter was set to the lowest temperature at which a uniaxially stretched film from each block copolymer could be stably produced without breaking during stretching. Table 1 shows the minimum stretchable temperature of each block copolymer. Next, the tensile modulus of the heat-shrinkable film of each block copolymer in the stretching direction, puncture strength, and heat shrinkage rate at 90°C in the stretching direction were measured. As a result, it was revealed that the heat-shrinkable film of the present invention exhibits good rigidity, impact resistance, and low-temperature shrinkage rate. In addition, these heat-shrinkable films all have a 90%
The heat shrinkage rate at °C was 3% or less. Next, after printing letters and patterns on the heat-shrinkable film of each block copolymer obtained as described above, it is shaped like a cylinder with the stretched direction in the circumferential direction and the non-stretched direction in the longitudinal direction. Make a heat-shrinkable label in the shape of a glass bottle, cover it with a
The material was heat-shrinked by passing through a shrinkage tunnel controlled at a temperature of 250°C. The transit time through the shrink tunnel was controlled to ensure that each heat-shrinkable label was in tight contact with the glass bottle surface;
The lower the heat shrinkage rate at °C, the longer the time required.
In addition, the heat-shrinkable film of Comparative Example 4 had low rigidity;
A good coated product could not be obtained. When the water whitening resistance and environmental damage resistance of the glass bottle coated products of each of the heat-shrinkable films thus obtained were investigated, all of the products coated with the heat-shrinkable block copolymer film of the present invention were found to be good. It had good performance.

【table】

[Table] Examples 8 to 10 According to the formulation method shown in Table 2, a composition in which polystyrene was blended with the same polymer as in Example 5 was prepared, and from this composition, the same composition as in Examples 1 to 7 was prepared. A uniaxially stretched film was produced by the method. (However, the thickness is approx.
It was controlled at 40μ. ) The properties of the obtained heat-shrinkable film are shown in Table 2. By blending low-molecular-weight polystyrene, the low-temperature shrinkability was improved; by blending high-molecular-weight polystyrene, the rigidity was improved; It has become clear that low-temperature shrinkability and rigidity can be improved by blending both polystyrene and high molecular weight polystyrene. Next, from these heat-shrinkable films, Examples 1-
A heat-shrinkable label similar to No. 7 was prepared, and after being heat-shrinked onto a glass bottle, water whitening resistance and environmental damage resistance were examined, and both showed good performance.

【table】

[Table] Example 11 and Comparative Example 6 A heat-shrinkable label made from the same heat-shrinkable film as in Example 5 (referred to as Example 11 here), the number average molecular weight of A′ ₁ and the number average molecular weight of A′ ₂ A heat-shrinkable film of a block copolymer with the same polymer structure and styrene content as in Example 5 except that the number average molecular weight was 40,000 and A' ₁ /A' ₂ = 1/1 (here, a heat-shrinkable film was used for comparison). Example 6) A heat-shrinkable label made from
Three types of cylindrical containers and cylindrical metal cans made of polypropylene, polyester, and polycarbonate were respectively heat-shrinked and coated. Example of investigating the environmental damage resistance of each coated product
No cracks were observed in the samples coated with the film of Comparative Example 6, whereas cracks were observed in all the samples coated with the film of Comparative Example 6. Examples 12-16 Biaxially stretched films were obtained from the same block copolymers or block copolymer compositions as in Examples 1, 5, 8-10 by the inflation method. The stretching temperature was the same as in the case of uniaxial stretching. The properties of the obtained film are shown in Table 3.

【table】

Claims (1)

[Claims] 1. A block copolymer in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene is 60:40 to 90:10, the polymer structure having the general formula A ₁ −B ₁ −A ₂ B ₁ -A ₁ -B ₂ -A ₂ B ₁ -A ₁ -B ₂ -A ₂ -B ₃ (In the above formula, A ₁ and A ₂ are polymer blocks mainly composed of vinyl aromatic hydrocarbons, and B ₁ ,
B ₂ and B ₃ are polymer blocks mainly composed of conjugated dienes. The boundary between A block and B block does not necessarily need to be clearly distinguished. ), and in the _A1 block and _A2 block, the vinyl aromatic hydrocarbon block is
There is only one polymer block with an average molecular weight of 5,000 or more, and in _A1 block, the average molecular weight is 5,000 to 5,000.
35000 vinyl aromatic hydrocarbon polymer block A′ ₁
In _A2 block, the average molecular weight is
50,000 or more vinyl aromatic hydrocarbon polymer block _A'2 , and the weight ratio of _A'1 and _A'2 is 1:
A heat-shrinkable block copolymer film obtained by uniaxially or biaxially stretching a block copolymer having a ratio of 2 to 1:6, and having a heat shrinkage rate of 10% or more at 90°C in the stretching direction. 2 In a block copolymer in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene is 60:40 to 90:10, the polymer structure has the general formula A ₁ -B ₁ -A ₂ B ₁ -A ₁ -B ₂ -A ₂ B ₁ -A ₁ -B ₂ -A ₂ -B ₃ (In the above formula, A ₁ and A ₂ are polymer blocks mainly composed of vinyl aromatic hydrocarbons, and B ₁ ,
B ₂ and B ₃ are polymer blocks mainly composed of conjugated dienes. The boundary between A block and B block does not necessarily need to be clearly distinguished. ), and in the _A1 block and the _A2 block, there is only one vinyl aromatic hydrocarbon block each with an average molecular weight of 5000 or more, and the polymer block Block is
In A ₁ block, the average molecular weight is 5000-35000
The vinyl aromatic hydrocarbon polymer block _A1 has an average molecular weight of 50,000 in the _A2 block.
Vinyl aromatic hydrocarbon polymer block A ₂ or more
Moreover, the weight ratio of A ₁ and A ₂ is 1:2 to 1:
6 is uniaxially stretched,
At least one type selected from metal, porcelain, glass, polyolefin resin, polymethacrylate resin, polycarbonate resin, polyester resin, and polyamide resin, which has a heat shrinkage rate of 10% or more at 90°C in the stretching direction. A heat-shrinkable block copolymer film for labels suitable for labeling containers comprising or as a part thereof.