JPH0732468A - Heat-shrinkable polystyrene film - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a heat-shrinkable polystyrene film suitable as a packaging material used for coating, binding, exterior, and the like. In particular, the present invention relates to a heat-shrinkable polystyrene-based film which has little shrinkage unevenness, gives a shrinkage result excellent in heat resistance, and stably maintains a beautiful finished appearance. [Structure] A polystyrene film, which is made of a resin composition containing a polystyrene polymer having a syndiotactic structure, and is stretched in at least a uniaxial direction, wherein the change rate ΔNz of the refractive index Nz in the thickness direction of the film is as follows. A heat-shrinkable polystyrene film characterized by satisfying the relationship of ΔNz ≤ 0.022 × (100 / Tg) where ΔNz is the difference between Nz of heat-shrinkable polystyrene film and Nz when it is unoriented Tg; Glass transition temperature of film

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 film suitable as a packaging material used for coating, binding, exterior packaging, etc. Particularly, the present invention relates to a heat-shrinkable polystyrene-based film which has little unevenness in shrinkage, gives shrinkage results excellent in heat resistance, and stably retains a beautiful finished appearance.

[0002]

2. Description of the Related Art A heat shrinkable film is used for coating various containers such as bottles (including glass and plastic bottles) and cans, and long objects (pipes, rods, woods, various rods, etc.), and binding. It is used for exterior or exterior use. For example, it is used for covering a part or the whole of the cap portion, shoulder portion, and body portion of a bottle for the purpose of display, protection, bundling, improvement of commercial value and the like. In addition, boxes, bottles, plates, sticks,
It is also used for applications in which a plurality of notebooks and the like are accumulated and packaged, and applications in which a film is brought into close contact with an object to be packaged (skin package). The above applications make use of the shrinkability and shrinkage stress of the film.

Polyvinyl chloride, atactic polystyrene, polyester, polyethylene, rubber hydrochloride and the like are used as the material of the film. Usually, these films are formed into a tube shape, for example, by covering them with a bottle or accumulating pipes and the like, and then heat-shrinking them for packaging or binding. However, since the conventional film has poor heat resistance and cannot withstand boil treatment or retort treatment at high temperature, it cannot be sterilized at high temperature. For example, when a retort process is performed, the conventional film is damaged during the process.

Further, when a conventional film, for example, a polyvinyl chloride film is printed, its adhesion to ink is poor. Furthermore, since polyvinyl chloride easily forms a gel material as an additive, pinholes are easily generated on the printed surface. Also,
Since the conventional film shrinks with time after manufacturing, the printing pitch changes due to the shrinkage, and high-precision printing cannot be performed. In addition, polyvinyl chloride has problems of corrosion due to chlorine gas and acid rain due to hydrogen chloride gas when discarded or incinerated, and thus a heat-shrinkable film that does not cause waste pollution is desired.

In recent years, the amount of plastic bottles used has increased rapidly. When considering the recovery of this bottle, not only when using a different type of film such as polyvinyl chloride or polystyrene, especially when coating a polyester bottle,
Even when the same type of polyester film is used, there is a problem in that the film cannot be directly recovered and reused because it is printed and used. Therefore, it is necessary to separate and remove the coating for reuse, and the method of utilizing the density difference from the polyester bottle is simple and favorable. Therefore, the polystyrene film has a low density and is easily separated, but has poor heat resistance, and when printing is performed, good printing cannot be performed because the polystyrene film is partially dissolved or swelled in the solvent contained in the ink.

[0006]

DISCLOSURE OF THE INVENTION The present invention is to solve the problems of the atactic polystyrene heat shrinkable film among the above-mentioned conventional techniques, and its object is to obtain a sufficiently high heat shrinkage ratio. Provided is a heat-shrinkable polystyrene film that does not cause uneven shrinkage when heat-shrinked, has a beautiful appearance, and stably retains the appearance even under high temperature conditions that will be experienced later. It is in.

[0007]

The present invention relates to a polystyrene film stretched in at least uniaxial direction, which comprises a resin composition containing a polystyrene polymer having a syndiotactic structure, the thickness direction of the film being The variation rate ΔNz of the refractive index Nz of is satisfied by the relationship ΔNz ≦ 0.022 × (100 / Tg), and the shrinkage unevenness is small,
It is intended to provide a heat-shrinkable polystyrene film which gives excellent shrinkage results in heat resistance and stably retains a beautiful finished appearance.

The polystyrene polymer having a stereoregular syndiotactic structure used in the present invention has a tacticity of dyad (constituent unit of which is phenyl group or substituted phenyl group which is a side chain) quantified by a nuclear magnetic resonance method. It is desirable that the syndiotactic structure is 75% or more, preferably 85% or more in two), and 30% or more, preferably 50% or more in pentad (5 units).

Examples of the polystyrene-based polymer include polystyrene, poly (p-, m- or o-methylstyrene), poly (2,4-, 2,5-, 3,4- or 3,5-dimethylstyrene. ), Poly (p-tertiarybutylstyrene) and other poly (alkylstyrenes), poly (p-, m- or o-chlorostyrene), poly (p-, m- or o-bromostyrene), poly (p -, M- or
Poly (halogenated styrene) such as o-fluorostyrene), poly (o-methyl-p-fluorostyrene), poly (p-,
m- or o-chloromethylstyrene) and other poly (halogen-substituted alkylstyrenes), poly (p-, m- or o-methoxystyrene), poly (p-, m- or o-ethoxystyrene), etc. Alkoxystyrene), poly (p-, m- or o-carboxymethylstyrene), etc. Poly (carboxyalkylstyrene) Poly (p-vinylbenzylpropyl ether)
And poly (alkyl ether styrene), poly (p-trimethylsilyl styrene) and other poly (alkyl silyl styrene), and further poly (vinyl benzyl dimethoxy phosphide) and the like.

In the present invention, it is preferable to add a thermoplastic resin or rubber to the polystyrene polymer. Thermoplastic resins include polystyrene-based polymers such as atactic polystyrene, AS resin, ABS resin, etc., and polyester-based polymers such as polyethylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, nylon 6, nylon 66, nylon 1
2. Nylon 4, polyamide polymers such as polyhexamethylene adipamide, polyolefin polymers such as polyethylene, polypropylene and polybutene.
Further, as the rubber component, a rubbery copolymer containing a styrene compound as one component thereof is preferable.
-Part of the butadiene part of the butadiene block copolymer or fully hydrogenated rubber, styrene-butadiene copolymer rubber, styrene-isoprene block copolymer, part of the butadiene part of the styrene-isoprene block copolymer or Fully hydrogenated rubber, methyl acrylate-butadiene-styrene copolymer rubber, acrylonitrile-butadiene-styrene copolymer rubber, acrylonitrile-alkyl acrylate-butadiene-styrene copolymer rubber, methyl methacrylate-alkyl acrylate-butadiene -Styrene copolymer rubber and the like. The rubber-like copolymer containing these styrenic compounds as one component has styrene units,
The dispersibility mainly in the styrene polymer having a syndiotactic structure is good, and as a result, the effect of improving the physical properties is large.

Examples of other rubbers include natural rubber, polybutadiene, polyisoprene, polyisobutylene, neoprene, ethylene-propylene copolymer rubber, urethane rubber, silicone rubber, acrylic rubber, polyether-ester rubber, polyester-ester. Examples thereof include rubber.

The polystyrene polymer used in the present invention has a weight average molecular weight of 10,000 or more, more preferably 50,0.
00 or more. If the weight average molecular weight is less than 10,000, it is not possible to obtain a film having excellent strength and elongation characteristics and heat resistance. The upper limit of the weight average molecular weight is not particularly limited, but if it is 1500,000 or more, breakage may occur due to an increase in stretching tension, which is not preferable.

The polystyrene polymer used in the present invention is used to improve electrostatic adhesion, slipperiness, stretchability, processability, impact resistance, etc., roughening, opacifying, hollowing, and lightweight. For other reasons such as chemical conversion, it is possible to use a mixture of an appropriate amount of other resin, permanent particles, organic particles, plasticizer, compatibilizer, colorant, antioxidant, antistatic agent and the like.

The polystyrene-based composition is formed into a film by a known method (for example, extrusion method or calender method). The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. A usual method is adopted as the stretching method. Examples thereof include roll stretching method, long gap stretching method, tenter stretching method, and tubular stretching method. In any of these methods, the stretching is 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 either first. The draw ratio is arbitrarily set in the range of 1.0 to 6.0, and the predetermined one direction may be the same or different in the direction orthogonal to the predetermined direction.
In the stretching step, preheating is preferably performed at a temperature not lower than the glass transition temperature of the polymer constituting the film, for example, Tg + 50 ° C. or lower. In heat setting after stretching, for example,
After stretching, it is recommended to pass through a heating zone of 30 ° C to 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 a predetermined degree. Furthermore, after the stretching,
A cooling step may be added after cooling the film while applying tension to the film while maintaining the stretched or tensioned state, or after releasing the tensioned state subsequent to the treatment. The thickness of the obtained film is preferably in the range of 6 to 250 μm.

The rate of change of the refractive index in the thickness direction of the heat-shrinkable polystyrene film of the present invention must satisfy the relationship of ΔNz ≦ 0.022 × (100 / Tg). In the syndiotactic polystyrene polymer, the refractive index in the thickness direction of the film increases as the degree of molecular orientation increases. therefore,
In order to increase the amount of shrinkage, it is necessary to increase the degree of orientation. However, as the degree of orientation is increased by stretching, crystallization progresses and good shrinkage characteristics are not exhibited. Further, the glass transition temperature is lowered by adding the rubber component and the like, so that crystallization associated with this orientation does not occur up to a higher orientation state. Therefore, the rate of change ΔNz of the refractive index in the thickness direction of the film needs to be 0.022 × (100 / Tg) or less in order to bring the relationship between the degree of orientation and crystallization into a favorable range. Refractive index change rate ΔNz in the film thickness direction
Is greater than 0.022 × (100 / Tg), good shrinkage behavior is not exhibited. Regarding the glass transition temperature,
In order to obtain the desired shrinkage properties, it is preferably between 60 ° C and 80 ° C.

[0016]

[Function] The heat-shrinkable polystyrene film thus obtained has a smaller shrinkage rate than the conventionally proposed heat-shrinkable film, and when shrinking, uneven shrinkage of the film is less likely to occur and has a beautiful appearance. In addition to being finished, the appearance can be stably maintained even under various high temperature conditions that will be experienced later.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The evaluation method of the film is shown below.

1) Refractive index in the thickness direction (Nz) It was measured using an Abbe refractometer (4-T) manufactured by Atago Co., Ltd.

2) Glass transition temperature (Tg) Using DSC210 manufactured by Seiko Denshi Kogyo Co., Ltd., from room temperature to 20 ° C. /
It was measured at a temperature rising rate of minutes.

3) Heat shrinkage rate The film is cut out so that the direction of shrinkage is the long side and the width is 15 mm. Marks are drawn at intervals of 200 mm in the long side direction. Heat this sample by blowing hot air at 100 ° C for 1 minute,
Measure the amount of change in the distance between the marked lines. The heat shrinkage rate (%) is defined as the percentage of this change amount to the original length.

4) Shrinkage unevenness The film was subjected to metallic printing for shrink labels and formed into a cylindrical tube, which was then covered with a 1.5-liter rectangular PET bottle and passed through a shrink tunnel. The condition of the shrink tunnel is that the first zone is 100 ℃ and the residence time is 4.5.
Seconds, the second zone was 140 ° C. and the residence time was 5 seconds. Visually check the shading of the resulting label due to uneven contraction.
Graded. ⊚: Very good with no defects such as unevenness, wrinkles, or looseness ○: Good with almost no defects such as unevenness, wrinkles, or looseness △: Not very good with defects such as unevenness, wrinkles, or looseness ×; Many defects such as unevenness, wrinkles, and looseness

5) Boil treatment The film is used as a shrink label, covered with a bottle filled with water, and shrinked in hot water at 801 ° C. This was immersed again in hot water at 80 ° C. for 30 minutes, and the state of talumi on the label was visually evaluated in four stages. ⊚: Very good with no defects such as unevenness, wrinkles, or looseness ○: Good with almost no defects such as unevenness, wrinkles, or looseness △: Not very good with defects such as unevenness, wrinkles, or looseness ×; Many defects such as unevenness, wrinkles, and looseness

6) Suitability for Filling with High-Temperature Substance A film is used as a shrink label and shrink-mounted on a bottle by the method used for determining uneven shrinkage. This bottle is filled with hot water of 87 ° C., and after 6 minutes, cooled with water. Then, the state of the talumi on the label was visually determined. ⊚: Very good with no defects such as unevenness, wrinkles, or looseness ○: Good with almost no defects such as unevenness, wrinkles, or looseness △: Not very good with defects such as unevenness, wrinkles, or looseness ×; Many defects such as unevenness, wrinkles, and looseness

Examples 1 to 3 Comparative Example 1 Syndiotactic polystyrene (weight average molecular weight 3000
00) and styrene-butadiene copolymer rubber in a weight ratio of 5
0.05 parts by weight of a mixture of calcium carbonate having a mean particle size of 1.0 μm as a lubricant to 100 parts by weight of the mixture of 5 parts was melted and kneaded to form polymer chips, which were then dried at 310 ° C.
Was melted, extruded from a T-die with a lip gap of 800 μm, adhered to a cooling roll at 40 ° C by an electrostatic loading method, cooled and solidified to obtain an amorphous sheet. The amount of extrusion was changed so that the thickness of the amorphous sheet was 40 μm.

The amorphous sheet was first preheated to 110 ° C. and stretched at a stretching temperature of 100 ° C. while changing the magnification in the transverse direction. The transverse draw ratios were 2.0 (Example 1), 3.0 (Example 2), 4.0 (Example 3) and 5.0 (Comparative Example 1). Then, heat setting treatment was performed at 60 ° C. for 15 seconds. The evaluation results of the obtained film are shown in the table.

[0026]

EFFECT OF THE INVENTION The heat-shrinkable polystyrene film of the present invention has a practically sufficient heat-shrinkage rate, and when it is heat-shrinked and used for coating or binding, temperature fluctuations and nonuniformity in the shrinking process are caused. High temperature conditions that the film experiences after shrinking, such as high temperature sterilization treatment after coating or bundling (eg, retort treatment, boil treatment) or filling of the coated container with high temperature material, giving uniform shrinkage results regardless of It was highly useful in a wide range of packaging material fields with no slack or wrinkles.

[0027]

[Table 1]

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Claims (1)

[Claims] 1. A polystyrene film stretched at least uniaxially, comprising a resin composition containing a polystyrene polymer having a syndiotactic structure, wherein the refractive index Nz change rate ΔNz in the thickness direction of the film. Is a heat-shrinkable polystyrene-based film, characterized in that ΔNz ≦ 0.022 × (100 / Tg) where ΔNz is the difference between Nz of heat-shrinkable polystyrene film and Nz when it is not oriented Tg; Glass transition temperature of film