JP2003049005A - Heat-shrinkable polystyrene resin film, label and container using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a heat-shrinkable polystyrene resin film suitable as a packaging material used for covering, binding and exterior finishing of containers, or the like, and a heat-shrinkable polystyrene resin film having especially a low temperature region of shrinkage appropriate temperature and excellent applicability to aseptic filling and packaging or packaging in a short time and suitable especially when printing, and the like, with a high accuracy are carried out, and to provide a label and a container using the same. SOLUTION: The heat-shrinkable polystyrene resin film is characterized as follows. The heat shrinkage percentage indicated by a change in length after treatment for dipping the film in hot water at 65 deg.C temperature for 10s to the length before treatment in the main shrinkage direction is >=5%. The natural shrinkage percentage indicated by a change in length before and after allowing the film to stand under temperature conditions of 45 deg.C for 1 week is <=10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polystyrene resin film suitable as a packaging material used for covering, binding, and packaging containers, etc. The present invention relates to a heat-shrinkable polystyrene-based resin film, which has excellent applicability to packaging, and is particularly suitable for high-precision printing, and a label and a container using the same.

[0002]

2. Description of the Related Art Since a heat-shrinkable film has a function of shrinkability, it does not use a fixing means such as an adhesive or a fastener,
It can be laminated and integrated with an object by the shrinkage force and shapeability of the film itself. Therefore, it not only has a function of mechanically protecting the object by stacking or coating, but also has a function of binding and sealing. Further, when the heat-shrinkable film itself has a special function, the special function can be added to the object later by laminating. This property is effectively used in the packaging field whose main purpose is to protect objects during storage and distribution, and to impart displayability and design. For example, bottles including glass and plastic bottles, various containers such as cans, and long objects such as pipes, rods, wood, various rod-shaped bodies, or sheet-like bodies for covering, binding, and exterior. It is used as a seal or a seal. In particular,
It is used for covering a part or the whole of the cap, shoulder, and body of a bottle for the purpose of labeling, protection, bundling, and enhancement of commercial value through functionalization. further,
It is also used for the purpose of packing a plurality of items to be packed such as boxes, bottles, plates, rods, notebooks, etc., and for the purpose of bringing a film into close contact with the item to be packed and packaging it with the film (skin package). . At this time, when the film is preliminarily displayed and shaped for the purpose of design, it becomes a product called a label.

Materials for the heat-shrinkable film include polyvinyl chloride, polystyrene, polyester, polyamide,
Aliphatic polyolefins and their derivatives, hydrochloric acid rubber, etc. are used. Usually, a film made of these materials is formed into a tube shape, for example, by covering it with a bottle,
After accumulating pipes, etc., they are heat-shrinked to be packaged and bound. However, conventional heat-shrinkable films have poor heat resistance and cannot withstand boil treatment or retort treatment at high temperatures, and therefore cannot be sterilized at high temperatures when applied to food, hygiene products, and pharmaceutical applications. There are drawbacks. For example, when the retort treatment is performed, the conventional film has a problem that it is easily damaged during the treatment.

In the case of a conventional heat-shrinkable film, a film made of a polyvinyl chloride resin has a very good heat-shrinkage property, but has a poor adhesion to ink during printing such as a label. Since it is easy to form a gel material of the additive to be added when forming a film, pinholes are easily generated on the printed surface. Furthermore, there is a problem that disposal and incineration are difficult from the environmental point of view. A film made of a polyester resin is excellent in heat resistance, dimensional stability, solvent resistance, etc., but it requires precise control of manufacturing conditions in order to achieve desired heat shrinkage characteristics, adhesiveness, etc. There were problems such as cost.

Further, because of the usefulness of the heat-shrinkable film, the heat-shrinkable film has come to be used also in the field where films and labels which are not heat-shrinkable films have been used conventionally. In particular, many labels for beverage containers have been replaced with a heat-shrinkable label from a sticking label made of paper or a film that is not a heat-shrinkable film. In particular,
In the field of labels for plastic bottle containers, the application of heat-shrinkable labels has been active in connection with the problem of recycling, and various forms and methods of packaging design have been implemented. Among them, the low temperature wet heat shrinkage process is the latest clean technology, sterilization technology,
This is a process used for aseptic filling and packaging made possible by a combination of high-speed packaging technology, etc., which allows sterilization of beverages etc. for a short period of time and then completes the packaging in a relatively short time at a relatively low temperature. It is possible to prevent the heat deterioration of the contents and improve the packaging efficiency. The heat-shrinkable film that can be used in the low temperature wet heat shrinkage process needs to have excellent shrinkability in the low temperature range, and the relatively high shrinkage rate is also advantageous from the viewpoint of shortening the process passage time. Conventionally, a heat-shrinkable polyester-based resin film has been used as a film having such characteristics, but when it is necessary to separately collect bottles and labels, it is difficult to separate the heat-shrinkable polystyrene-based polystyrene film. The use of resin films has been sought. However, conventional polystyrene resins have a glass transition temperature of around 100 ° C. and are inferior in low-temperature shrinkability. A method for solving this problem has been attempted. However, there have been problems such as a large natural shrinkage and a decrease in heat resistance after shrinking and mounting.

[0006]

DISCLOSURE OF THE INVENTION The present invention is excellent in low-temperature shrinkability, has a sufficiently high heat shrinkage rate even in the low temperature shrinkage step, does not cause uneven shrinkage of the film during heat shrinkage, and has a beautiful appearance. Furthermore, even if it is exposed to high temperature conditions after shrinkage, its appearance is stably maintained, and it has excellent image formability due to printing, etc. A heat-shrinkable polystyrene resin film most suitable for packaging, a label using this,
And to provide a container.

[0007]

According to the present invention, in the main shrinkage direction, the heat shrinkage ratio shown by the rate of change in length after the process of dipping in hot water at a temperature of 65 ° C. for 10 seconds before the process is 5%.
The heat-shrinkable polystyrene-based resin film having a natural shrinkage of 10% or less, which is the rate of change in length before and after standing for 1 week at a temperature of 45 ° C., was used. Labels and containers.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The constitution of the polystyrene resin constituting the film of the present invention is not particularly limited as long as the shrinkage characteristics described later can be exhibited, but it is preferable to use a polystyrene resin having a syndiotactic structure. It is preferable that the contained polystyrene resin. More preferably,
As the polystyrene resin, it is preferable to use a polystyrene resin having a syndiotactic structure. By using a polystyrene resin having a syndiotactic structure, dimensional stability and heat resistance are improved. By using such a polystyrene-based resin, the density of polystyrene is low, and in addition to being advantageous for separation in the recycling step, it is excellent in heat resistance, particularly heat resistance during heat storage, and after the film formation, Changes in the printing pitch due to contraction are reduced, and high-precision printing can be performed as a label. Further, the durability against the solvent contained in the printing ink is improved, and the printability is excellent.

The polystyrene type resin having the syndiotactic structure is preferably 75 diads (two constitutional units) in the tacticity of quantifying side chain phenyl groups and / or substituted phenyl groups by a nuclear magnetic resonance method. % Or more, more preferably 85% or more, and pentad (5 units) is preferably 30% or more, more preferably 50% or more.

As the polystyrene component constituting the polystyrene resin used in the present invention, polystyrene, poly (p-, m- or o-methylstyrene), poly (2,4-, 2,5-, 3, 4- or 3,5-dimethylstyrene), poly (p-tertiarybutylstyrene), and other poly (alkylstyrene), poly (p-, m)
-Or o-chlorostyrene), poly (p-, m-,
Or poly (halogenated styrene) such as o-bromostyrene), poly (p-, m-, or o-fluorostyrene), poly (o-methyl-p-fluorostyrene), poly (p-, m-, Or poly (halogenated substituted alkylstyrene) such as o-chloromethylstyrene), poly (p
-, M-, or o-methoxystyrene), poly (p
-(M-, or o-ethoxystyrene) or other poly (alkoxystyrene), poly (p-, m-, or o-carboxymethylstyrene) or other poly (carboxyalkylstyrene) poly (p-vinylbenzylpropyl ether) ) Etc., poly (alkyl ether styrene), poly (p
-Trimethylsilylstyrene) and other poly (alkylsilylstyrenes), as well as poly (vinylbenzyldimethoxyphosphide) and the like.

The heat-shrinkable polystyrene resin film of the present invention contains a plasticizer, a compatibilizer, etc. during the polystyrene polymerization or for the purpose of lowering the heat shrinkage initiation temperature and improving impact resistance. It is preferable that it is blended with

In the present invention, it is particularly preferable to add a thermoplastic resin and / or a rubber component to the polystyrene resin. As the thermoplastic resin, polystyrene having an atactic structure, AS resin, ABS
Polystyrene resins such as resins, polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyamide resins such as nylon 6, nylon 66, nylon 12, nylon 4, polyhexamethylene adipamide, polyethylene Polyolefin resins such as polypropylene, polybutene and the like can be mentioned. The rubber component is preferably a rubbery copolymer containing a styrene compound as its constituent component, and examples thereof include random, block or graft copolymers obtained by copolymerizing at least one selected from styrene and the rubber component. . Examples of such a rubber-like copolymer include styrene-butadiene copolymer rubber, styrene-isoprene block copolymer, rubber obtained by hydrogenating a part or all of these butadiene moieties, methyl acrylate-butadiene- Styrene copolymer rubber, acrylonitrile-butadiene-styrene copolymer rubber, acrylonitrile-alkyl acrylate-
Examples thereof include butadiene-styrene copolymer rubber and methyl methacrylate-alkyl acrylate-butadiene-styrene copolymer rubber. The above-mentioned rubbery copolymer containing a styrene compound as its constituent component has a styrene unit and therefore has good dispersibility mainly in polystyrene resin having a syndiotactic structure, and as a result, polystyrene resin Has a great effect of improving physical properties. In particular, as the compatibility modifier, a rubber-like copolymer containing the above-mentioned styrene compound as its constituent component is suitable, and more preferably, for the purpose of reducing the natural shrinkage, a styrene-butadiene block copolymer. It is preferable that the rubber is further graft-copolymerized with one or more components selected from styrene-based monomers, methyl (meth) acrylate, alkyl methacrylate, and derivatives thereof.

Other rubber components include natural rubber, polybutadiene, polyisoprene, polyisobutylene, neoprene, ethylene-propylene copolymer rubber, urethane rubber, silicone rubber, acrylic rubber, polyether-
Ester rubber, polyester-ester rubber and the like can be used.

The weight average molecular weight of the polystyrene resin constituting the film of the present invention is preferably 10,000 or more, more preferably 50,000 or more. When the weight average molecular weight is less than 10,000, the strength / elongation property and heat resistance of the film are likely to decrease. The upper limit of the weight average molecular weight is not particularly limited, but if it is 1,500,000 or more, breakage may occur due to an increase in stretching tension, so that it is preferably less than 1,500,000.

The heat-shrinkable polystyrene resin film of the present invention has a roughened surface, an opaque surface, and a hollowed surface in order to improve electrostatic adhesion, slipperiness, stretchability, processability, impact resistance and the like. , Other resins, plasticizers, compatibility modifiers, inorganic particles, organic particles, colorants, antioxidants, for the purpose of weight reduction,
An antistatic agent or the like can be appropriately added.

As a material constituting the film of the present invention,
By using a polystyrene resin as described above,
Excellent in various heat shrinkage properties, excellent printability such as adhesion to ink when forming a label, and no pinholes are formed on the printed surface of the film. Furthermore, it has excellent disposability and has little impact on the environment when incinerated.

The polystyrene resin constituting the film of the present invention as described above is formed into a film by a method such as an extrusion method or a calender method which has been generally used conventionally. The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. As the stretching method, conventionally used methods such as a roll stretching method, a long gap stretching method, a tenter stretching method and a tubular stretching method can be used. In any of the above methods, stretching may be performed by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. In the above-mentioned biaxial stretching, stretching in the longitudinal and transverse directions may be performed simultaneously, but sequential biaxial stretching in which either one is performed first is effective, and the longitudinal and lateral directions may be performed first. Preferred conditions for producing the heat-shrinkable polystyrene resin film of the present invention are shown below.
The draw ratio is preferably 1.0 to 6.0 times,
The predetermined one direction magnification and the direction orthogonal to the predetermined direction may be the same or different. In the stretching step, the glass transition temperature (Tg) of the resin forming the film
Preheating is preferably performed at a temperature of (Tg + 50) ° C. or less. In heat setting after stretching, after stretching, 30 ° C
It is preferred to pass a heating zone of ~ 150 ° C for about 1 to 30 seconds. Further, after the film is stretched and before or after the heat setting, the relaxation treatment may be performed to an appropriate degree. Further, after the stretching, a step of cooling the film while applying a stress to the film while keeping it in a stretched or tensioned state, or a cooling step after releasing the tensioned state following the treatment may be added.

The thickness of the heat-shrinkable polystyrene resin film of the present invention is not particularly limited, but it is preferably in the range of 6 to 250 μm.

The heat-shrinkable polystyrene resin film of the present invention has a primary shrinkage direction of 1 in hot water of 65.degree.
The heat shrinkage ratio, which is indicated by the rate of change in length after the treatment of dipping for 0 seconds before the treatment, is 5% or more. Preferably, the heat shrinkage is 10% or more, more preferably 20% or more. When the heat shrinkage is less than 5%, the low temperature shrinkability is lowered, and the heat shrinkable polystyrene resin film of the present invention cannot be used for aseptic filling packaging and the like.

As a method for obtaining the desired heat shrinkage rate, the glass transition temperature of the film is lowered by selecting the kind and the blending ratio of the polystyrene resin constituting the heat shrinkable film, and blending the additive components. Further, a decrease in the stretching temperature corresponding to the glass transition temperature and the like can be mentioned. When the resin composition constituting the film is a completely compatible system, the glass transition temperature becomes a weighted average value of each constituent component, so that the use of additional components is increased in order to lower the glass transition temperature to the shrinking process temperature region. , Heat resistance and dimensional stability tend to decrease. When the resin composition that constitutes the film is an incompatible system, it shrinks near the glass transition temperature of the polystyrene resin, which is the main component, but using a modifier for compatibility adjustment, the dispersed state of the components By adjusting
The glass transition temperature of the film can be lowered to the glass transition temperature of the additive component while maintaining the heat resistance of the polystyrene resin.

The heat-shrinkable polystyrene resin film of the present invention is required to have a natural shrinkage rate of 10% or less, which is represented by a rate of change in length before and after being left for 1 week under a temperature condition of 45 ° C. When the natural shrinkage ratio exceeds 10%, the image is deformed due to the natural shrinkage, and the image formability due to printing is deteriorated, so that it is impossible to form a high-definition image. The natural shrinkage is preferably 4% or less, more preferably 1% or less.

As a method of setting the natural shrinkage ratio to 10% or less, for example, the kind and the compounding ratio of the resin constituting the heat-shrinkable film, especially the rubber component is added, and the mixing ratio of the polystyrene resin and the rubber component is adjusted. Adjust, increase the ratio of polystyrene component in polystyrene resin, increase the regularity of polystyrene tacticity, adjust film production conditions, especially increase the film forming temperature or heat setting temperature to increase the crystallinity of the film. And an unnecessary internal stress of the film is relaxed by an annealing treatment after the film is formed.

In the heat-shrinkable polystyrene resin film of the present invention, it is preferable to measure dispersion other than alpha dispersion in the temperature range where alpha dispersion derived from polystyrene is measured in measuring dynamic viscoelasticity of the film. . According to Nakatani, Yamada, et al., Proceedings of the 44th Rheological Symposium (1996) pp. 169-172, a heat-shrinkable polystyrene resin film in which dispersion other than alpha dispersion is measured is alpha dispersion, that is, heat shrinkage. Shrinkage occurs together with relaxation dispersion that causes the phenomenon, and dispersion occurs due to crystallization, generation of gel-like structure, etc. near the end of shrinkage. When dispersion occurs due to crystallization, generation of gel-like structure, etc., heat resistance and dimensional stability after shrinkage are excellent. Dispersions other than alpha dispersion are often found in syndiotactic polystyrene and its copolymers.

In the dynamic viscoelasticity measurement of a film, a heat-shrinkable polystyrene resin film in which dispersion other than alpha dispersion is measured in a temperature range where alpha dispersion derived from polystyrene is measured is, for example, dynamic viscoelasticity. In the above measurement, it is obtained by stretching an unstretched sheet in which the dispersion other than the alpha dispersion is measured in the temperature region where the alpha dispersion derived from polystyrene is measured.

The heat-shrinkable film of the present invention changes its length with respect to the length before the treatment after the treatment of heating for 1 minute at each temperature of 70 ° C. to 100 ° C. at every 10 ° C. in the main shrinking direction. It is preferable that the maximum rate of heat shrinkage, which is the maximum value of the rate, is 40% or more. When the maximum heat shrinkage ratio is less than 40%, the shrinkage is insufficient when used as a label (body label) for a body portion of a bottle that is generally used, and it becomes difficult to adhere the bottle to the bottle. More preferably, the maximum heat shrinkage is 5
It is preferably 0% or more. When the maximum heat shrinkage is 50% or more, the shrinkage is not insufficient even for a PET bottle label that requires high shrinkability. The maximum heat shrinkage is more preferably 60% or more, and particularly preferably 70% or more. When the maximum heat shrinkage ratio is within the above range, insufficient shrinkage does not occur even as a full label for a container having a complicated shape.

As a method of setting the maximum heat shrinkage rate in the above range method, for example, adjustment of the type and blending ratio of the resin constituting the heat shrinkable film, particularly the compatibility state of the materials constituting the heat shrinkable film, Examples of the method include adjusting the production conditions of the film, particularly increasing the stretching ratio, reducing heat setting, and performing crystallization treatment during preheating and then stretching to increase the strain of the polymer chain.

The heat-shrinkable polystyrene resin film of the present invention is preferably used as a packaging material used for covering, binding, and packaging of containers and the like, and a beautiful appearance can be obtained by using the film of the present invention. it can. In particular, the label composed of the film of the present invention has excellent coverage and is suitable for packaging containers. Further, the heat-shrinkable polystyrene-based resin film of the present invention has excellent applicability to a heat storage container, and a container equipped with a label composed of the film of the present invention is exposed to high temperature conditions after shrinkage. Even if it is, the label keeps its appearance stable.
Further, the natural shrinkage rate is low, the image forming property is excellent, and it is suitable for packaging of articles when high-precision printing or the like is performed.
Further, it has excellent low-temperature shrinkability, and has excellent applicability to aseptic filling packaging and short-time packaging.

The present invention will be described in more detail below with reference to test examples and examples, but the present invention is not limited thereto.

Test Example 1. Test Method (1) Heat Shrinkage Ratio The heat shrinkable polystyrene resin films of Examples 1 to 6 and Comparative Examples 1 and 2 have a width of 15 with the main shrinkage direction as the longitudinal direction.
The test piece was cut into pieces each having a length of 200 mm, and marked lines were set at intervals of 200 mm in the longitudinal direction. The test piece was immersed in warm water of a water bath set at a temperature of 65 ° C. for 10 seconds. The distance (X: unit mm) between the marked lines was measured, and the rate of change in length D (unit%) after the treatment with respect to the length before the treatment was calculated using the following formula 1. Also, "main contraction direction"
Was measured in the machine direction and the transverse direction of the film, and the following maximum heat shrinkage was measured, and the direction in which the maximum heat shrinkage was large was taken as the main shrinkage direction. In the films of Examples and Comparative Examples, the lateral direction was the main shrinkage direction. D (%) = {(200−X) / 200} × 100 Formula 1

(2) Natural Shrinkage The heat-shrinkable polystyrene resin films of Examples 1 to 6 and Comparative Examples 1 and 2 have a width of 15 with the main shrinking direction as the longitudinal direction.
The test piece was cut into pieces each having a length of 200 mm, and marked lines were set at intervals of 200 mm in the longitudinal direction. After the test piece was left to stand for 1 week under the temperature condition of 45 ° C., the distance between the marked lines (X ′: unit mm) was measured, and the rate of change in length D ′ with respect to the length before the treatment was measured. The unit (%) was calculated using the following formula 2. D ′ (%) = {(200−X ′) / 200} × 100 Formula 2

(3) Maximum heat shrinkage ratio The heat shrinkable polystyrene resin films of Examples 1 to 6 and Comparative Examples 1 and 2 were each set to have a width of 15 mm with the longitudinal direction and the transverse direction of the film as longitudinal directions. The test piece was cut and marked with marks at 200 mm intervals in the longitudinal direction.
The test piece was placed in the center of the incubator in a hot air circulation type incubator (manufactured by Peng Co., Ltd., FX-1: damper closed, quick heater ON) set to each temperature from 70 ° C to 100 ° C in every 10 ° C. Were allowed to stand and were heated for 1 minute. After the test piece was taken out of the incubator and cooled, the distance (X '': unit mm) between the marked lines was measured, and the rate of change in length D '' (unit:%) after the treatment and before the treatment. ) Was calculated using the following Equation 3. Of this length change rate D '',
The maximum value was defined as the maximum heat shrinkage rate. D ″ (%) = {(200−X ″) / 200} × 100 Formula 3

(4) Dynamic viscoelasticity Each unstretched sheet obtained in the manufacturing process of the heat-shrinkable polystyrene resin film of Examples 1 to 6 and Comparative Examples 1 and 2 was
Width 5 mm, measurement part length 30 with MD direction as longitudinal direction
A test piece was cut to have a size of mm. About the test piece, expansion mode, frequency 50 Hz, -20 to 250 ° C
The dynamic viscoelasticity was measured under the conditions of the temperature range and the heating rate of 2 ° C./min, and the presence or absence of dispersion other than the alpha dispersion was confirmed in the temperature region where the alpha dispersion derived from polystyrene was measured.

(5) Shrinkage unevenness The heat-shrinkable polystyrene-based resin films of Examples 1 to 6 and Comparative Examples 1 and 2 are subjected to metallic back-printing, and the size becomes a square heat-resistant PET bottle label described below (the main shrinkage direction is It has a circular cross section, and the length in the direction perpendicular to the main contraction direction is 1
The label was formed by forming a tube into a cylindrical shape (6 cm).
The label was put on a 350 cc square heat-resistant PET bottle up to the neck and passed through a shrink tunnel. The conditions in the shrink tunnel were such that the first zone was 70 ° C. and the residence time was 4.5 seconds, and the second zone was 80 ° C. and the residence time was 5 seconds. After passing through the shrink tunnel, the print density due to uneven shrinkage of the heat-shrinkable label was visually evaluated according to the following criteria. ⊚: Defects such as unevenness, wrinkles, and looseness are not recognized, and very good ○: Defects such as unevenness, wrinkles, and looseness are hardly recognized, and good Δ: Defects such as unevenness, wrinkles, and looseness are clearly recognized Poor, bad; many defects such as unevenness, wrinkles, looseness, etc.

(6) Heat storage resistance Bottles equipped with a label made of the heat-shrinkable polystyrene resin film of Examples 1 to 6 and Comparative Examples 1 and 2 used for the evaluation of shrinkage unevenness in the above (5) (after heating) ) Was filled with water by removing air as much as possible and sealed with a cap. The bottle was placed sideways on a laboratory hot plate heated to 110 ° C. and left for 24 hours, and then the state of the label was visually evaluated according to the following criteria. ◯: There are not many defects on the label, which is good Δ: Defects are clearly recognized on the label, which is not good ×: There are many defects on the label and they are defective

2. Test results Table 2 shows the results of the above tests (1) to (6).

[0036]

Example 1 Syndiotactic polystyrene (weight average molecular weight 300,000) obtained by copolymerizing 33 mol% of 4-methylstyrene as a constituent was used as a main resin, and styrene was copolymerized as a constituent of 25 wt%. Acrylic acid-n-
A rubber obtained by graft-polymerizing 10 wt% of butyl as a rubber component was mixed as a modifier for 100 parts by weight of a composition which was mixed at a weight ratio of 6 to 4 (main resin / rubber component). High styrene rubber (styrene-butadiene copolymer rubber, 85 wt% styrene as a constituent component)
5 parts by weight), and 0.05 parts by weight of calcium carbonate particles having an average particle diameter of 1.0 μm as a lubricant were melted and kneaded to obtain polymer chips, which were then dried. This was melted at 250 ° C., extruded from a T-die having a lip gap of 800 μm, and brought into close contact with a cooling roll at 40 ° C. by an electrostatic application method to be cooled and solidified to obtain an amorphous sheet. The amorphous sheet was preheated to 115 ° C., stretched in the transverse direction at a stretching temperature of 73 ° C. to a draw ratio of 6.0 times, and then heat-set at 60 ° C. for 20 seconds to obtain a heat-shrinkable film having a thickness of 50 μm. Got An image was formed on the entire surface of one side of the film by halftone printing and used as an example.

Example 2 The main resin was 42-methylstyrene as a constituent.
A heat-shrinkable polystyrene-based resin film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that syndiotactic polystyrene (weight average molecular weight 300,000) obtained by copolymerization in mol% was used.

Example 3 A styrene-butadiene block copolymer obtained by copolymerizing a main resin and styrene as a constituent, which is a rubber component, in an amount of 25 wt% was prepared by adding 1-n-butyl acrylate.
Heat shrinkage with a thickness of 50 μm was carried out in the same manner as in Example 1 except that a composition was used in which the mixing ratio with the 0 wt% graft-polymerized rubber was 7: 3 (main resin / rubber component) by weight. A polystyrene resin film was obtained.

Example 4 A heat-shrinkable polystyrene resin film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the modifier was a hydrogenated product of high styrene rubber.

Example 5 A styrene-grafted polybutadiene obtained by graft-copolymerizing styrene with polybutadiene (grafting rate: 10
A heat-shrinkable polystyrene-based resin film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the content was 0% by weight).

Example 6 A styrene-grafted styrene-butadiene rubber obtained by graft-copolymerizing a modifier with a styrene-butadiene copolymer (styrene content: 25% by weight) (grafting rate: 100).
Except that the weight is 5), the thickness is 5
A 0 μm heat-shrinkable polystyrene resin film was obtained.

Comparative Example 1 Example 5 was repeated except that the main resin was atactic polystyrene and the rubber component was a styrene-butadiene block copolymer obtained by copolymerizing styrene as a constituent component to 25 wt%. Similarly, a heat-shrinkable polystyrene resin film having a thickness of 50 μm was obtained.

Comparative Example 2 The main resin was syndiotactic polystyrene containing no copolymerization component, and the rubber component was styrene-butadiene copolymer rubber obtained by copolymerizing styrene as a constituent component at 25 wt%. A resin and a rubber component are mixed at a weight ratio of 5: 5 (main resin / rubber component), and a modifier is not used.
A heat-shrinkable polystyrene resin film having a thickness of 50 μm was obtained in the same manner as in Example 1.

[0044]

EFFECT OF THE INVENTION The heat-shrinkable polystyrene resin film of the present invention has excellent image formability due to printing and the like, and is unlikely to cause image deformation due to natural shrinkage. In addition, it has a sufficient heat shrinkage ratio in the low temperature shrinking step, and during heat shrinking, it shrinks uniformly without regard to temperature fluctuations or non-uniformity in the shrinking step, and shrinkage unevenness does not occur, giving a beautiful appearance. . Further, even when exposed to high temperature conditions after shrinkage, slack and wrinkles do not occur and the appearance is stably maintained.

[Table 1] Rubber component G1: Styrene (25 wt%)-butadiene block copolymer-n-butyl acrylate (10 wt%) graft copolymer G2: Styrene (25 wt%)-butadiene block copolymer

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 3/04 G09F 3/04 C // B29K 25:00 B29K 25:00 105: 02 105: 02 B29L 7 : 00 B29L 7:00 C08L 25:06 C08L 25:06 (72) Inventor Satoshi Hayakawa 344 Maebata, Kizu character, Inuyama City, Aichi Prefecture Toyobo Co., Ltd. Inuyama factory (72) Inventor Tabota Inuyama, Aichi Prefecture Tokubo Co., Ltd. Inuyama Factory (72) Inventor Shigeru Yoneda 2-8 Dojimahama 2-chome, Kita-ku, Osaka-shi, Osaka Toyobo Co., Ltd. (72) Inventor Katsuhiko Nose Osaka Prefecture 2-8-2 Dojimahama, Kita-ku, Osaka Toyobo Co., Ltd. Main company F-term (reference) 3E067 AA11 AC01 AC03 BA18A BB14A CA01 EE04 FB01 FC01 FC02 3E075 BA83 CA02 DD11 DE23 GA04 3E0 86 AB01 AB03 AD30 BA02 BA15 BB67 CA11 CA34 CA35 4F071 AA22 AF43 AF61 BB06 BB07 BC01 4F210 AA13 AC03 AE01 AG01 AH54 RA03 RC02 RG02 RG04 RG43

Claims (7)

[Claims] 1. In the main shrinkage direction, the heat shrinkage ratio, which is represented by the rate of change in length after the process of dipping in hot water at a temperature of 65 ° C. for 10 seconds before the process, is 5% or more, and under the temperature condition of 45 ° C. A heat-shrinkable polystyrene-based resin film having a natural shrinkage rate of 10% or less, which is represented by a rate of change in length before and after being left for 1 week. 2. In measuring the dynamic viscoelasticity of a film,
In the temperature range where the alpha dispersion derived from polystyrene was measured, dispersions other than alpha dispersion were measured, and in the main shrinkage direction, indicated by the rate of change in length after treatment after immersion in hot water at a temperature of 65 ° C for 10 seconds. 5% heat shrinkage
The heat-shrinkable polystyrene-based resin film having a natural shrinkage rate of 10% or less, which is the rate of change in length before and after standing for 1 week under the temperature condition of 45 ° C. 3. In measuring the dynamic viscoelasticity of a film,
The heat-shrinkable polystyrene-based resin film according to claim 2, which is formed by stretching an unstretched sheet whose dispersion other than alpha dispersion is measured in a temperature range where alpha dispersion derived from polystyrene is measured. 4. 70 ° C. to 10 ° C. in the main shrinkage direction
The maximum heat shrinkage rate, which is the maximum value of the rate of change in length with respect to the length before the treatment, after the treatment of heating for 1 minute at each temperature up to 100 ° C. is 40% or more. Item 5. The heat-shrinkable polystyrene resin film according to any one of items 1 to 3. 5. The heat-shrinkable polystyrene-based resin film according to claim 1, wherein the heat-shrinkable polystyrene-based resin film is made of a polystyrene-based resin containing a polystyrene-based resin having a syndiotactic structure. 6. A label comprising the heat-shrinkable polystyrene resin film according to any one of claims 1 to 5. 7. A container provided with the label according to claim 6.