JPH0421578B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a shrink film made of a styrene-butadiene block copolymer. (Prior art) Currently, stretched films mainly made of polyvinyl resin are often used as heat-shrinkable films for labels on cans, bottles, etc., cap seals, etc., but they are discarded. Improvements are required due to material handling issues. Recently, as a method to prevent glass containers from scattering,
A method of coating glass containers with a uniaxially stretched film made from a styrene-butane diene block copolymer has been proposed (J.K.I. No. 58-41050,
Jikai Publication No. 59-30850, etc.). (Problems to be Solved by the Invention) However, although the stretched and shrinkable film made from the styrene-butadiene block copolymer has excellent coating properties on glass containers and is effective in preventing glass containers from scattering, weather resistance of the film,
The extrusion appearance, etc., is still not fully satisfactory. (Means for Solving the Problems) Therefore, the inventors of the present invention have conducted intensive studies to further improve these insufficient characteristics, and have arrived at the present invention. That is, the present invention has excellent weather resistance and extruded appearance,
The aim is to provide a shrink film useful for can and bottle labels and cap seals through heat shrink treatment, and its features include styrene-butadiene block copolymer, (A) Adding an ultraviolet absorber selected from benzophenone derivatives and benzotriazole derivatives to significantly improve weather resistance, and also (B) adding a phenolic antioxidant to eliminate the drawbacks such as hard eyes caused by the ultraviolet absorber. As a result, this film has characteristics suitable for use as a shrink wrapping film that may be exposed to sunlight for a long period of time. The present invention will be described in detail below. In the following description, "%" simply means "% by weight", except for "%" which indicates shrinkage rate. In the film of the present invention, the main component resin is styrene-butadiene block copolymer (hereinafter referred to as
(abbreviated as SB copolymer). That is, this S-B copolymer has a weight ratio of styrene and butadiene of 60:40 to 95:5, preferably
70:30-90:10, more preferably 75:25-85:15
It is. Preferably, the number average molecular weight of the styrene block in the S-B copolymer is 10,000 to 200,000.
and more preferably 20,000 to 50,000. And this copolymer has at least one, preferably two or more styrene blocks and at least one
It has several butadiene blocks. Here, butadiene block refers to polybutadiene block or butadiene containing 50% or more, preferably
It is a polymer block containing 70% or more, more preferably 90% or more, and examples of copolymerized monomers that this polymer block may contain include styrene, isoprene, and the like. In addition, the non-blocking rate of this S-B copolymer expressed by the following formula is preferably 15% or less, preferably 10% or less, more preferably 5% or less, and depending on the purpose, it may exceed 15%. Good too. Unblock rate (%) = (Total styrene weight in SB copolymer) - (Styrene weight of styrene block in SB copolymer) / (SB
The total styrene weight in the copolymer) x 100 The above S-B copolymer is, for example,
Structured according to the method described in Publication No. 41050, general formula (a) (S-B)n (n = 3 to 10) (b) S-(B-S)n (n = 2 to 10) (C) B-(S-B)n (n=2-10) (d) [(B-S-)n-]mX (n=1-10, m=1-10) (e) [( S-B-)nS-]mX (n=1-10, m=1-10) (In the above formula, S is a styrene block, B is a butadiene block, and X is a residue of a coupling agent or a polyfunctional organic It is obtained as a linear block copolymer or a radial block copolymer represented by (representing the residue of a polymerization initiator such as a lithium compound) or the like. The melt flow measured according to JIS-K-6870 (200℃, 5Kg load) was 0.1 to 50g/10
minutes is suitable. The number average molecular weight of the butadiene block of this S-B copolymer is not particularly limited, but is between 500 and 100,000.
The number average molecular weight of the S-B copolymer itself is preferably 20,000 to 500,000. Furthermore, functional groups such as hydroxyl groups, thiol groups, sulfonic acid groups, carboxyl groups, and amino groups can be added by hydrogenation, halogenation, halogen hydrogenation, epoxidation, or chemical reactions to the extent that the basic properties of the copolymer are not impaired. It may also be one that introduces Furthermore, a general-purpose styrene resin may be mixed with this copolymer to the extent that the impact strength is not reduced (30% or less). The film of the present invention uses the above-mentioned S-B copolymer as a base material, and contains an ultraviolet absorber and an antioxidant. As UV absorbers, benzophenone derivatives or benzotriazole derivatives are effective, specifically 2-hydroxy-4-octoxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl) -benzotriazole,
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole,
Examples include 2-(2'-hydroxy-3',5'-di-t-amylphenyl)-benzotriazole, 2-(2'-hydroxy-5-t-octylphenyl)-benzotriazole, and others. 2-hydroxy-4-octoxybenzophenone, 2-(2'-
Preferred are hydroxy-5'-methylphenyl)-benzotriazole and 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole. The amount of this ultraviolet absorber added is preferably in the range of 0.05 to 2% based on the S-B copolymer. If the amount is less than this lower limit, the effect of improving weather resistance will be weak, and if the amount exceeds the above upper limit, bleeding may occur. The following phenomenon occurs. This ultraviolet absorber improves weather resistance, and when a film without it is exposed outdoors, it becomes tattered in about 10 to 15 days, but with the film of the present invention, even after 50 days. There are no such inconveniences. However, while the above-mentioned types of ultraviolet absorbers are highly effective in improving weather resistance, it has been found that when added to the S-B copolymer, they cause crosslinking and cause fish eyes. When forming a thin film such as the shrink film of the present invention, if even a small amount of crosslinking occurs, that portion will solidify and become sticky during film formation, which is not only unfavorable in terms of appearance but also problematic in terms of physical properties. As a result of investigating additives that can prevent crosslinking without impairing weather resistance, it has been found that phenolic antioxidants are highly effective in preventing crosslinking of S-B copolymers. Specifically, the phenolic antioxidants include 2-t-butyl-6-(3'-t-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenyl acrylate, 2,2 '-methylene-bis(4-methyl-6-t-butylphenol), 2-
Mention may be made of 6-di-tert-butyl-4-methylphenol, the use of the first being particularly preferred. These antioxidants are 0.1~
It is preferable to use it within a range of 1.5%; if the amount is too small, the effect of preventing crosslinking will be weakened, and if it is too large, it will cause bleeding. Further, if necessary, a lubricant can be added to the above composition to impart a sliding effect to the formed film, but erucic acid amide is particularly preferred since it does not impair printability or solvent sealability. Erucic acid amide may contain a fatty acid amide having less than 20 carbon atoms as an impurity, but as long as this impurity is 20% or less, there is no particular problem and it can be used in the present invention. The amount of erucic acid amide blended is usually 0.05 to the S-B copolymer.
The range of ~1.9% is good; if it is too little, the sliding effect will be insufficient, and if it is too much, bleeding will become large and printability and solvent sealability will deteriorate. The additive can be added to the S-B copolymer at any time from the time of polymerization to the time of melt film formation, but it is preferable to add it before the time of polymerization and production of pellets because it will be uniformly dispersed. . In the present invention, the film needs to have a shrinkage rate of 10 to 80% in at least one direction when heated to 80°C, and a range of 30 to 60% is particularly preferable. If it is less than 10%, it is difficult to tightly shrink coat the article, and if it is more than 80%, it cannot be efficiently produced. Film forming and stretching means are conventionally used T.
A die method, a tubular method, etc. may be used, and stretching may be carried out in a longitudinal direction, a transverse direction, or a biaxial direction depending on the intended use of the film. The stretching temperature is in the range of 2 to 15 degrees Celsius higher than the Vikatsu softening point of the resin.
The stretching ratio may be selected in one direction so as to obtain the above shrinkage ratio in the range of 1.2 to 7.0 times. In addition to the above-mentioned additives, the film of the present invention may also contain colorants and other auxiliary agents. (Effects) The shrink film of the present invention has excellent heat shrinkability,
It not only coats bottles etc. well, but also has good weather resistance, thermal stability and transparency, and has a good appearance, and does not corrode incinerators when disposed of. The film of the present invention can be uniaxially stretched.
Although it is particularly suitable as a heat-shrinkable film for labeling bottles or cap seals, biaxially stretched products can also be used for shrink-wrapping other foods. In addition, especially when used for packaging foods that are sensitive to ultraviolet rays, 2-(2'-hydroxy-3-t-butyl-5-methylphenyl-5-
When chlorobenzotriazole is added in a relatively large amount (0.5 to 2.0%), the wavelength is 380n even with a thickness of about 50μ.
The transmittance of ultraviolet rays of m is 10% or less, making it suitable as a film for blocking ultraviolet rays. In this case, the antioxidant is 2-t
-butyl-6-(3-t-butyl-5-methyl-
2'-Hydroxybenzyl)-4-methylphenylacrylate at 0.7-2.0% or 0.5-1.3% of the antioxidant and 0.2-1.5% of 2-6-di-t-butyl-4-methylphenol. It is preferable to add both % and %. (Example) Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples, and other modifications can be made within the gist of the invention. . Examples 1 to 3, Comparative Examples 1 to 2 In these Examples and Comparative Examples, the weight ratio of styrene and butadiene was 75:25, the number average molecular weight of the styrene block was 40,000, and the Vikato softening point was 93°C. A styrene-butadiene block copolymer was used. The types and amounts of ultraviolet absorbers and antioxidants to be added are shown in the table below. Also, as a lubricant, erucic acid amide 0.2
% was added. This blended composition was extruded into a sheet using a 90 mm extruder, and stretched using a tenter at a temperature of approx.
The film was stretched 5 times in the transverse direction at 100° C. to obtain a film with a thickness of 50 μm. The following physical properties were measured for the obtained film, and the results are shown in the table below. Weather resistance: Using Sunshine Weatherometer - WEL-3-HC type (A-1415) manufactured by Suga Test Instruments Co., Ltd., the film was fixed to it so as not to shrink, and after irradiation, it was Measure the time until the strain elongation reaches 0%. Extrusion appearance: The film after extrusion was evaluated as good if there were no visible marks, and if any marks were observed it was judged as poor. When a film with this fixed eye is printed after being made into a stretched film, ink does not stick to the fixed eye portion. Shrinkage rate: Draw a 10cm straight line in the horizontal direction (film stretching direction) and lengthwise direction on a film cut to 10cm x 10cm, and after immersing it in hot water at 80℃ for 5 minutes, measure the dimension a (cm) of the straight line. The value calculated by the following formula {(10-a)/10}×100 was taken as the shrinkage rate (%) in that direction. Shrinkage appearance: A cylindrical film with the shrinkage direction in the circumferential direction was placed over a glass bottle whose circumference was 5% smaller than the film circumference, and heated for 15 seconds in a Schulik tunnel with a hot air temperature of 200℃. Those that could be covered tightly were evaluated as good, and those that were uneven or loose were evaluated as poor.

[Table] In the above table, the numbers in parentheses below the additives are the amount added (%). As is clear from the above table, Comparative Example 1, which used a UV absorber other than the one according to the invention, had poor weather resistance, and Comparative Example 2, which used an antioxidant other than the one according to the invention, had poor weather resistance. There are many occurrences of this area, and when printing, printing omissions occur in this area. In contrast, the shrink film of the present invention shows good results in all physical properties. The same extruded sheet as in Example 1 was stretched 3 times in the transverse direction using a tenter at a stretching temperature of about 120°C to obtain a film with a thickness of 50μ, and the shrinkage rate in the transverse direction of this film was 7%. It was small and had a poor shrinkage appearance. Example 4 The same styrene-butadiene block copolymer as in Examples 1 to 3 was treated with 2-
(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole at 1.0
%, 2-t-butyl-6-(3't
-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenyl acrylate 0.8%,
2-6-di-t-butyl-4-methylphenol
A composition containing 0.5% of erucic acid amide and 0.2% of erucic acid amide as a lubricant was extruded into a sheet using a 90 mm extruder in the same manner as in Examples 1 to 3, and stretched using a tenter at a temperature of about 100.
The film was stretched 5 times in the transverse direction at ℃ to obtain a film having a thickness of 50μ. The obtained film has weather resistance of 90 hours or more, good extrusion appearance, no blocking, and good shrinkage appearance, and the transmittance of ultraviolet light (wavelength 380 nm) measured with a spectrophotometer is 3. %, it had excellent ultraviolet blocking properties and was transparent in appearance.

Claims (1)

[Claims] 1. The weight ratio of styrene and butadiene is 60:40 or more.
A 95:5 styrene-butadiene block copolymer, (A) an ultraviolet absorber selected from benzophenone derivatives and benzotriazole derivatives, and (B)
A styrene resin shrink film which is made of a composition containing a phenolic antioxidant and has a shrinkage rate of 10 to 80% in at least one direction when heated to 80°C. 2 The UV absorber is 2-(2'-hydroxy-5'-
methylphenyl)-benzotriazole or 2-
The styrenic resin shrink film according to claim 1, which is (2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole. 3 The phenolic antioxidant is 2-t-butyl-
The styrenic resin shrink film according to claim 1, which is 6-(3'-t-butyl-5'methyl-2-hydroxybenzyl)-4methylphenyl acrylate.