JPS6257453A - Polystyrene based heat shrinkable film - Google Patents

Abstract

PURPOSE:A film, obtained by blending block SBR with an impact-resistant polystyrene, capable of mounting on glass bottles with good slipperiness at a high speed, having improved slipperiness and blocking properties in a process of passing through hot water for sterilization in a filling line and suitable for coating drink bottles. CONSTITUTION:A polystyrene based heat shrinkable film obtained by drawing a sheet consisting of (A) 100pts.wt. styrene-butadiene block copolymer (block SBR) with70-80wt% styrene content and 30-20 wt% butadiene content and (B) 3-10pts.wt. impact-resistant polystyrene with 4-10wt% rubber content in one direction and having 60-85% shrinkage in the drawing direction and <=15% shrinkage in the direction perpendicular to the drawing direction on heating at 120 deg.C. The above-mentioned film has>=6000kg/cm<2> tensile modulus in the drawing direction and >=5000kg/cm<2> tensile modulus in the direction perpendicular to the drawing direction. The drawing direction is the winding direction of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polystyrene heat-shrinkable film. More specifically, the present invention relates to a heat-shrinkable film used as a covering material for glass bottles.

[Conventional technology]

Conventionally, vinyl chloride film, which has excellent impact resistance, has been mainly used as a heat-shrinkable film for covering glass bottles, but due to the problem of damaging the walls of garbage incinerators and hygienic issues, this alternative has recently been used. A film of styrene-butadiene rubber lock copolymer (hereinafter abbreviated as block SBR) has been developed as
.

[Problem that the invention seeks to solve]

However, the heat-shrinkable film for block SBR alone has high slip resistance when attached to glass bottles, resulting in a large amount of attachment loss, and furthermore, when the glass bottles attached with this film are sent to the filling line, it is difficult to sterilize them. During the PASTRO process, the bottles come into contact with each other, causing the film to stick, causing the glass bottle to tip over after passing through the PASTRO process, or damaging the film, which only reduces the product value. However, when a glass bottle into which carbon dioxide gas is pressurized is broken, its ability to prevent fragments from scattering is reduced, making it dangerous.

[Means for solving problems]

As a result of intensive research into a heat-shrinkable film that has good mechanical suitability for mounting under such conditions (and has excellent blocking resistance in hot water and good impact resistance), the inventors have developed a block SBR. It was discovered that it is effective to use a mixture of high-impact polystyrene (HIPS), and the present invention was completed.

That is, the present invention is a film obtained by stretching 100 layers of a styrene-butadiene block copolymer having a styrene content of 70 to 80% by weight and a butadiene content of 20 to 30% by weight. The shrinkage rate in the direction is 60-85%, and the shrinkage rate in the perpendicular direction is 15%.
% or less.

The present invention will be explained in detail below.

What is the block SBR used in the present invention? (S-B)n-8, (S-B)n, , B-(S-B)
It has a general structural formula of n (where S: styrene block, B: butadiene block, n: an integer of 2 to 10), styrene content 70 to 80% by weight, butadiene content 30 to 20%. % by weight. If the butadiene content exceeds 30% by weight, the rigidity of the molded film will be insufficient and the sliding resistance against the glass bottle will increase.
There is a lot of loss when attaching it to the bottle. Furthermore, if the butadiene content is less than 20% by weight, the impact resistance of the film will be lowered, so that even if the coated bottle is in contact with the film and flows along the line, cracks will easily occur.

HIPS used in the present invention is a general high-impact polystyrene, and has a rubber content of 4 to 10% by weight.

If the rubber content is less than 4% by weight, the impact strength will decrease and the film will crack if the coated bottle collides with it on the line. 1
If it exceeds 0% by weight, the transparency of the film will be impaired.

The addition ratio of HI PS to 100 parts by weight of block SBR is 3 to 10 parts by weight. Addition amount of HIPS is 3
If the amount is less than part by weight, blocking resistance in hot water will be poor. Furthermore, if HIPS exceeds 10 parts by weight, the impact resistance will be poor, and even if bottles collide with each other on the line and flow, cracks will easily form on the film surface, and the transparency will decrease.

In the present invention, there is no problem in adding colorants, antistatic agents, various stabilizers, etc.

The stretching treatment for obtaining the heat-shrinkable film of the present invention can be carried out by a conventional method for producing a uniaxially stretched film, such as a method in which a sheet extruded from a T-die is stretched in a roll stretching machine, or a film obtained by an inflation method is heated. However, it is sufficient to apply the method of performing stretching treatment by setting a difference in the take-up speed of nip rolls as is, and in consideration of post-processing such as printing and slitting, it is preferable to stretch the film in the take-off (longitudinal) direction.

Preheating conditions in the present invention are preferably in the temperature range of 70 to 120°C, preferably 85 to 110°C, and the stretching ratio is selected to be 3 to 7 times, preferably 4 to 6 times. If the preheating temperature is lower than 70°C, the thickness may become uneven during stretching or the film may be cut, making it difficult to obtain a homogeneous film.
If the temperature exceeds 20°C, the stretching effect will be impaired. If the stretching ratio is less than 3 times, the film will have poor shrinkage properties when heated and will have poor adhesion to the shoulder of the glass bottle. On the other hand, if it exceeds 7 times, it tends to tear in the stretching direction, causing problems in printing, slitting, and other processes.

The shrinkage rate of the film of the present invention is a particularly important physical property,
Measured by the amount of change after 1 minute immersion in a 120°C oil bath,
It is 60 to 85%, preferably 70 to 80% in the stretching direction, and 15% or less, preferably 5% or less in the direction perpendicular to the stretching direction. If the shrinkage rate in the stretching direction is less than 60%, the adhesion of the shoulder of the glass bottle will be poor. Furthermore, if the shrinkage rate in the direction perpendicular to the stretching direction exceeds 15%, the design printed on the film will be deformed, reducing the commercial value of the label.

In addition, the tensile modulus is 6,000 ky/cr1 in the stretching direction.
As mentioned above, 5,000 kg/i or more is required in the direction perpendicular to the stretching direction. Tensile modulus in stretching direction is 6,000 k
If it is less than g/c+d, it will expand and contract during processes that reduce tension, such as printing, slitting, and mounting processes, making it impossible to obtain a homogeneous label. Also, the tensile modulus in the perpendicular direction is s, ooo k
If it is less than g/d, the film may break when attached to a glass bottle, resulting in a lot of loss.

The thickness of the film is not particularly limited, but is usually suitably 20 to 300 μm, and is appropriately determined based on the tensile modulus.

〔Example〕

The present invention will be explained below with reference to Examples.

Examples 1 to 4, Comparative Examples 1 to 7 Using the resins shown in the table as raw materials, a sheet was extruded from a 300n wide T-die attached to a 5011φ extruder, and this sheet was stretched 5 times in the drawing direction to form a sheet with a thickness of 80 μm. A heat-shrinkable film was obtained.

The physical properties of this film and the results of practical tests are listed in the table.

Here, the impact resistance of the film is 10
Visual judgment is made to determine whether or not scratches will occur on the film surface when the barrels collide with each other with a drop of +m. The occurrence of cracks on the film surface means that the film is damaged when the coated glass bottles are passed through the lines.

In addition, blocking resistance was determined by tightening three coated bottles with a force of 1 kg, immersing them in hot water at 85° C. for 20 minutes, and then taking them out and observing their appearance.

The fragment scattering retention rate when the bottle is broken means that 30% of the prescription liquid that generates carbon dioxide gas is placed in a glass bottle (170P) with an internal capacity of 315cc.
0 cc filled, liquid temperature 25℃, internal pressure 4 kg, /+!
Then drop the glass bottle horizontally onto the concrete from a height of 75α to cause it to explode. Measure the weight of the bottle fragments that have accumulated within a radius of 1 m from the point of fall, and add that weight to the sample glass bottle. It is divided by the weight of , and shows the average of 60 pieces. In addition, the glass bottle used was before the anti-blocking test, in which about 90% of the glass bottle weight was covered with a film, and if the scattering retention rate was lower than 90%, it was covered with the film. This indicates that fragments of the film are also scattered, and conversely, a value greater than 90% means that the film has excellent scattering prevention performance.

Comparative Example 8 A film obtained in the same manner as in Example 2 except that the stretching ratio was doubled was used.

The results are shown in the table.

〔Effect of the invention〕

The heat-shrinkable film of the present invention has improved sliding properties with glass bottles and can be installed at high speed, and also has improved sliding properties and blocking properties between the films when passing through the PASTRO process in a filling line. Line stoppages due to bottles overturning have been drastically reduced, and there is no damage to the film, eliminating waste. It also has excellent transparency and impact resistance, and even if a carbonated beverage bottle ruptures under internal pressure, it can coat the bottom of the mouth of the glass bottle to prevent fragments from scattering.

Claims (1)

[Scope of Claims] 1. 100 parts by weight of a styrene-butadiene block copolymer having a styrene content of 70 to 80% by weight and a butadiene content of 30 to 20% by weight, and a rubber content of 4 to 10% by weight.
A film obtained by stretching in one direction a sheet consisting of 3 to 10 parts by weight of impact-resistant polystyrene,
When heated to 0°C, the shrinkage rate in the stretching direction is 60 to 85%,
A heat-shrinkable film having a shrinkage rate of 15% or less in a direction perpendicular to the heat-shrinkable film. 2. Tensile modulus in the stretching direction is 6,000 kg/cm^2
or more, and the tensile modulus in the direction perpendicular to it is 5,000
The heat-shrinkable film according to claim 1, which has a heat shrinkable film of kg/cm^2 or more. 3. The heat-shrinkable film according to claim 1, wherein the stretching direction is the winding direction of the film.