JPS63315222A - Shrinkable styrene resin film - Google Patents

Abstract

PURPOSE:To eliminate generation of cracks, by a method wherein after stretching of a specified styrene resin film in a longitudinal direction, the same is stretched a little laterally. CONSTITUTION:A film whose mixture ratio of styrene/butadiene/block copolymer resin composed of 60-85wt.% styrene content and 40-15wt.% butadiene content with polyetyrene is styrene/butadiene/block copolymer resin:polystyrene =95:5-50:50 pts.wt. is stretched 2.0-5.0 times in a longitudinal direction, and orientation treatment of the film has been performed 1.05-1. 2 times laterally. When the content of styrene/butadiene/block copolymer is less than the range, it becomes that cracks are apt to occur and when it is much more than the range, stiffness is reduced due to deterioration of the tensile modulus of elasticity and thinning of the film becomes difficult. When a lateral draw ratio is made lower than the range, a prevention effect of the cracks is eliminated and when the same is made higher, the film is apt to generate creases due to shrinkage in a lateral direction at the time when the film is shrinked over a bottle and wrapping height becomes unequal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a styrene resin shrinkable film that prevents cracking.

(Prior Art) Conventionally, heat-shrinkable films mainly made of vinyl chloride resin have been used for labels on cans, glass bottles, etc.
There are many problems, such as the generation of harmful chlorides when the waste is incinerated, and the difficulty of recovering it when labeled on polystyrene containers.

Therefore, in place of vinyl chloride resin, lateral KQ
Stretched styrene-citadiene block copolymer films have come to be widely used as heat-shrinkable films, and many proposals have been made regarding this. However, in order to cover a glass bottle or the like with a film stretched in the transverse direction, the left and right side edges of the film are pasted back together to form a cylindrical film, so the film needs to have some stiffness. If the film thickness is not thick enough, it will not work. Furthermore, since the packaging process includes a film backing process, the packaging machine becomes bulky, which increases costs.

(Problem to be solved by the invention) Therefore, it is proposed to wrap a vertically stretched film around a glass bottle or the like instead of a horizontally stretched film and glue the front and rear edges of the film. has been done.

However, if an unstretched film is simply stretched in the longitudinal direction, cracks will occur if the film is covered with a glass bottle and exposed to sunlight after being sterilized with hot water, but the effect of preventing fragments from scattering in 2-spin cannot be obtained. Yes, the product value will be lost.

In order to solve these problems, the present inventors have conducted intensive studies and found that after stretching a specific styrene resin film in the longitudinal direction, it is then slightly stretched in the transverse direction to prevent cracks. It has been found that it is possible to produce a styrene resin-based shrinkable film that does not cause generation.

(Means for Solving the Problems) The present invention provides that the mixing ratio of a styrene-butadiene block copolymer resin having a styrene content of 60 to 85 weight % and a butadiene content of 40 to 15 weight % and polystyrene is as follows: Styrene-butadiene block copolymer resin:
A styrene resin-based shrinkable film obtained by stretching a film containing 95:5 to 50:50 parts by weight of polystyrene by 2.0 to 5.0 times in the machine direction and 1.05 to 1.2 times in the transverse direction. It is about sex films.

The styrene-butanoene block copolymer resin that can be used in the present invention is a block copolymer composed of a unit consisting of a styrene chain and a unit consisting of a sitadiene chain.
85% by weight, butanoene in the range 40-15% by weight, flow rate, Condition D (ASTMDI 23
8) is preferably 2.0 to 10.0 g/10 minutes.

The polystyrene that can be used in the present invention preferably has a weight average molecular weight in the range of 100,000 to 600,000.

The mixing ratio of the styrene/butadiene block copolymer resin and polystyrene is preferably 95:5 to 50:50 parts by weight of styrene/butadiene block copolymer resin/polystyrene. When the amount of the styrene-butadiene block copolymer is less than the above range, cracks are likely to occur. Furthermore, if the amount of the styrene-butanoene block copolymer resin exceeds the above range, the tensile modulus decreases and the stiffness is lost, making it difficult to form a thin film.

Furthermore, when the film is wound into a roll, a blocking phenomenon occurs in which the films stick to each other, causing whitening and damage of the film, which is undesirable. It is also possible to add an antioxidant to prevent dulling, or to add a lubricant to give the film lubricity. In general, the shrinkability required for styrene resin-based shrinkable films is a shrinkage rate of 20 to 50 inches in the longitudinal direction when heated to 100°C, and a shrinkage rate of 120 inches in the longitudinal direction.
A shrinkage of 40 to 80 inches in the machine direction when heated to 40°C is desired. At the same time, the expansion rate in the lateral direction is desirably less than 15%, preferably less than 5%, in order to prevent wrinkles from forming in the film when it is shrunk in a bottle or the like.

The stretching conditions for imparting the above-mentioned shrinkability and crack-free physical properties to the film include stretching the unstretched film in the longitudinal direction at a stretching ratio of 2 to 5 times at a temperature range of 70°C to 120°C. Stretched to 70 to 1.20 in the transverse direction
℃ temperature range and below the temperature during M stretching, the stretching ratio is 1.0
It is preferable to stretch the film by a factor of 5 to 1.2 times.If the stretching temperature is lower than the above range, the film will break. Moreover, if the stretching temperature is higher than the above range, the shrinkage property will be poor, which is not preferable. If the stretching temperature in the transverse direction is not lower than the stretching temperature in the longitudinal direction, the orientation of the film will be set by heat, and the shrinkability in the longitudinal direction will be significantly reduced.

When the stretching ratio in the transverse direction is lower than the entire above range.

The crack prevention effect is lost. In addition, if the stretching ratio in the lateral direction is higher than the above range, when it is shrunk into a bottle, etc., it will not only tend to wrinkle due to the lateral shrinkage, but also cause the appearance of the wrap to be uneven. becomes worse.

(Examples) Hereinafter, the present invention will be explained in detail according to Examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded.

Examples 1 to 3, Comparative Examples 1 to 3 The raw materials used in the Examples and Comparative Examples were styrene-butadiene block copolymer resin (Philips Nashi Trollium International Co., Ltd., Yataka product name: Resin KR-05).
) and polystyrene (trade name: Estyrene G-32, manufactured by Nippon Steel Chemical Co., Ltd.) in a weight ratio of 85:15, to which 12 parts of glycerin fatty acid ester O was added as a lubricant was used.

These raw materials were first processed into a 50m machine equipped with a coat hanger die.
A non-stretched sheet with a thickness of 0.2 is formed using a φ extruder. Next, using a biaxial stretching device, the film was stretched in the machine direction at a ratio of 2.5 times at a temperature of 110°C, and then stretched in the transverse direction at a temperature of 110°C at a ratio shown in Table 1.

The physical properties of the obtained film were measured according to the evaluation method described below, and the results are shown in Table 1.

Shrinkage rate: Punch out the film into a circle with a diameter of 65m+, draw straight lines in the vertical and horizontal directions, and place these in a constant temperature bath at 100°C and 120°C for 5 minutes. Thereafter, the lengths of straight lines in the vertical and horizontal directions are measured, and the shrinkage rate is calculated according to the following formula.

a: Length after shrinkage) b: Shrinkage rate (%) Packaging property: Process the film into a cylindrical shape (cylindrical length: approx. 122 m, total circumference: outer circumference of bottle + 4 tm), and form a glass bottle (outer diameter 67.5
The wrapper was placed on a cloth and shrunk, and its packaging property was evaluated based on its appearance. Those that could be coated uniformly without loosening were evaluated as good, those that had uneven wrap hide, and those that had wrinkles on the film were evaluated as poor.

Weather resistance: Shrink a film on a glass bottle, then heat it to 90°C assuming hot water sterilization with 74' stripes.
Soak in hot water for 20 minutes. Thereafter, one month after exposure, the appearance of cracks was observed, and those with no cracks were evaluated as good, and those with even a few cracks were evaluated as poor.

As is clear from the above table, Comparative Example 1, which was not stretched in the lateral direction, had many cracks throughout the entire area in the weathering test.
The effect of preventing debris scattering cannot be obtained.

In addition, in Comparative Example 2 where the stretching ratio in the lateral direction was 1.3 times, the shrinkage in the lateral direction was large, resulting in uneven wrapping.
Packaging properties deteriorate. On the other hand, the films of Examples 1 to 3 had good physical properties, and in particular, Example 1 had small shrinkage in the lateral direction and had particularly excellent packaging properties.

(Effect of the invention) The styrene resin-based shrinkable film obtained by the present invention has excellent transparency, less dullness, and has excellent shrinkability. The occurrence of cracks in tests was also significantly suppressed.

Claims (1)

[Claims] Styrene content 60-85% by weight, butadiene content 4
The mixing ratio of styrene/butadiene block copolymer resin and polystyrene is 0 to 15% by weight, styrene/butadiene block copolymer resin: polystyrene =
A film of 95:5 to 50:50 parts by weight is stretched 2.0 to 5.0 times in the machine direction and 1.05 to 1.0 times in the transverse direction.
A styrene resin shrinkable film that has been stretched twice.