JPS6315134B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a novel heat-shrinkable film with excellent heat-shrinkability. Currently, heat-shrinkable films made from polyvinyl chloride are the mainstream, and there are various methods for producing them. However, it has been pointed out that products made from polyvinyl chloride lack transparency, are weak, and have poor slippage, and have been found to be somewhat inferior in handling during mechanical packaging. . Furthermore, when the waste is incinerated, a new problem arises in that the furnace is corroded, and recently waste treatment organizations have been demanding improvements. Based on these circumstances, the present inventors first developed a material with excellent heat shrinkability, transparency, slipperiness, and
As a heat-shrinkable film that has good mechanical packaging suitability, is strong, and does not corrode incinerators when processing waste, etc., it has a styrene content of 70 to 93.
We proposed a thin film obtained by stretching a thin film made of 0 to 50 parts by weight of polystyrene added to 100 parts by weight of a styrene-butadiene block copolymer having a butadiene content of 30 to 7% by weight. . However, this heat-shrinkable film behaves in a special way during extrusion and stretching, and it is difficult to produce high-quality film using conventional manufacturing methods.
In addition, the cutting ratio of the ears increased, and there were also problems in terms of yield. The inventors of the present invention have made various studies and have put their efforts into finding a method for producing a heat-shrinkable film with excellent quality and good yield, and as a result, they have finally arrived at the present invention. That is, this invention has a styrene content of 70 to 93% by weight and a butadiene content of 30 to 7% by weight.
Styrene-butadiene block copolymer consisting of
When producing a heat-shrinkable film by horizontally tentering a thin film containing 0 to 50 parts by weight of polystyrene per 100 parts by weight, the melting point of the styrene-butadiene block copolymer is lowered from at least 90°C outside the tenter. The gist of this method is to preheat the film to a temperature within a range of 100 to 100°C before stretching. The manufacturing method of the present invention will be described in detail below. The styrene-butadiene block copolymer (hereinafter simply referred to as block copolymer) used in the present invention has a structure in which (S-B)n-S S: styrene block B: butadiene block n: degree of polymerization, where n is 2 or more, preferably 2 to 10,
More preferably, the number is 3 to 5, and styrene blocks are attached on both sides.This copolymer has excellent stretchability and also has exceptional heat shrinkability. It goes without saying that copolymers having different degrees of polymerization may be mixed and used. The block copolymer used in the present invention has the structure described above, and one of the block copolymers commonly used in the past has the structure S-B-S. However, this material has poor stretchability, and therefore it is difficult to stretch at a high magnification, and therefore has poor heat shrinkability, and it is necessary to further improve it before it can be used. Block copolymers are superior. The block copolymer of the present invention has a styrene content of
A composition having a composition of 70 to 93% by weight and a butadiene content of 30 to 7% by weight is used, and if the composition of both components is outside the above range, the desired effect cannot be achieved. Next, the polystyrene used in the present invention is a general polystyrene resin and is not particularly limited. As mentioned above, the heat-shrinkable film of the present invention contains a specific block copolymer and a specific amount of polystyrene as required, and the blending ratio is 0 to 50 parts of polystyrene per 100 parts by weight of the block copolymer.
The amount is preferably about 2 to 40 parts by weight. In this case, if the amount of polystyrene added is less than 2 parts by weight, the stiffness generally tends to decrease, and packaging workability etc. will be reduced, so it cannot be expected to be used in a wide range of applications, but this value is not limited, of course. , the block copolymer alone can also be applied. On the other hand, when it exceeds 50 parts by weight, the influence of polystyrene becomes more apparent.
Favorable results cannot be obtained in terms of impact resistance, etc. The stretching treatment in the present invention is carried out in the transverse direction by a tenter method, and at this time, the stretching temperature can be exemplified at 70°C or higher, preferably about 80 to 95°C. In particular, in the present invention, the preheating temperature before stretching is an important point, and the preheating temperature is particularly preferably in the range of 90°C to a temperature below the melting point of the block copolymer, preferably 90 to 110°C. A tenter is usually used when stretching in the lateral direction, but preheating at 90°C is done outside the tenter.
℃ to a temperature below the melting point of the block copolymer, preferably from 90 to 110℃, and then heated in a tenter from 95℃ to the melting point of the block copolymer,
Preheating preferably in the temperature range of 95-110°C gives good results. In the present invention, by performing a preheating process under specific temperature conditions as described above, the netting phenomenon that occurs during stretching can be prevented, and the edge portion can be stretched smoothly, resulting in an improvement in yield. promised. In addition, in the present invention, after the above-mentioned stretching, annealing, that is, heat treatment is further performed, thereby making it possible to use it as a packaging film.This film has heat shrinkability, and even with the addition of the above-mentioned steps, Of course, it falls within the technical scope of the present invention. The present invention is as described above, and when producing a heat-shrinkable film by stretching a thermoplastic thin film (film) mainly composed of a styrene-butadiene block copolymer having a specific composition in the transverse direction using a tenter method, at least By preheating outside to a specific temperature range, that is, from 90°C to the melting point of the block copolymer, and then stretching.
The cut ratio of the edges has been reduced, making it possible to produce films with good yields. The film obtained by this manufacturing method has excellent heat shrinkability, good transparency, slipperiness, suitability for mechanical packaging, etc., and does not corrode incinerators when processing waste, etc. There are many expectations from various quarters as an alternative to vinyl chloride heat-shrinkable films, which have many problems. Next, examples of the present invention will be shown. <Example 1> Styrene content 85% by weight, butadiene content 15
% by weight of styrene-butadiene block copolymer (this has the structure S-B-S-B-S-B-S, with styrene blocks at both ends and three butadiene blocks in the middle) A raw film was prepared by extrusion. Next, this original film was preheated at 103℃ outside the tenter, then preheated at 106℃ inside the tenter, and then stretched 5 times in the transverse direction at a stretching temperature of 85℃ to create a heat-shrinkable film with a thickness of about 50μ. did. Table 1 shows the heat shrinkability, thickness, yield, tearing, etc. of this film. <Example 2.3> A heat-shrinkable film was obtained using the same material as in Example 1 and setting the stretching ratio as shown in Table 1. <Comparative Examples 1 to 4> Using the same materials as in Example 1, heat-shrinkable films were obtained by setting the stretching ratio, preheating outside the tenter, preheating inside the tenter, and stretching temperature as shown in Table 1. The heat shrinkability, thickness, yield, tear, etc. of these films are summarized in Table 1.

[Table] As described above, the products of the present invention are excellent in both yield and heat shrinkability, and the particularly remarkable effects of the present invention can be seen.

Claims (1)

[Scope of Claims] 1. A thin film containing 0 to 50 parts by weight of polystyrene to 100 parts by weight of a styrene-butadiene block copolymer having a styrene content of 70 to 93% by weight and a butadiene content of 30 to 7% by weight. When producing a heat-shrinkable film by stretching in the transverse direction using a tenter method, the film is preheated at least outside the tenter at a temperature in the range from 90°C to the melting point of the styrene-butadiene block copolymer, and then stretched. A method for producing a horizontally uniaxially stretched heat-shrinkable film. 2. The styrene-butadiene block copolymer has a structure in which (S-B)n-S S...styrene block B...butadiene block n=2-10 both sides are styrene blocks A method for producing a horizontally uniaxially stretched heat-shrinkable film. 3. When stretching in the lateral direction, preheating outside the tenter at a temperature range from 90°C to below the melting point of a styrene-butadiene block copolymer consisting of 70 to 93% by weight styrene content and 30 to 7% by weight butadiene content, 2. The method for producing a transversely uniaxially stretched heat-shrinkable film according to claim 1, wherein the film is then preheated in a tenter at a temperature ranging from 95° C. to a temperature below the melting point of the block copolymer.