JPH0353178B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a glass bottle coated with a film mainly composed of a styrene-butadiene block copolymer, and more specifically, the present invention relates to a glass bottle coated with a film mainly composed of a styrene-butadiene block copolymer. Concerning glass bottles that prevent scratches. Glass bottles are widely used as containers for various liquids, including beer and soft drinks. This glass bottle has excellent transparency, rigidity, heat resistance, and content resistance, making it extremely useful.However, it has poor impact resistance, so it can easily break and scatter due to impact such as being dropped. There is. Therefore, recently, styrene-butadiene block copolymer uniaxially stretched films, polyvinyl chloride uniaxially stretched films, foamed polystyrene uniaxially stretched sheets, etc. are heated and heated in glass bottles called safety sealed bins or pilasty sealed bins. Shrink-coated bottles have been developed that are highly safe. In these covering films or sheets,
The uniaxially stretched film of styrene-butadiene block copolymer not only has excellent transparency, gloss, and mechanical strength, but also has a higher stretching ratio than polyvinyl chloride uniaxially stretched film and foamed polystyrene uniaxially stretched sheet. As a result, it is possible to achieve a high shrinkage rate, and it is considered to be the most suitable film for covering glass bottles by heat shrinkage. However, if a glass bottle coated with a uniaxially stretched film of styrene-butadiene block copolymer is heated and shrunk, if it is left under conditions where the outdoor environmental temperature changes (e.g. temperature difference between day and night), the film A crack occurs, and as a result,
It has the disadvantage that the protective effect on glass bottles is reduced. The cause of this crack is not yet clear, but it does not occur with uncoated film on glass bottles.
It is believed that stress is repeatedly applied to the coating film due to the difference in coefficient of thermal expansion between the glass bottle and the coating film, resulting in stress cracks. The inventors of the present invention have conducted intensive studies on coated films that do not cause stress cracks. As a result, the occurrence of stress cracks is strongly influenced by the stretching conditions of the styrene-butadiene block copolymer and the coating conditions of the film, but ultimately the styrene-butadiene block copolymer coated on the glass bottle is They discovered that the degree of orientation of the stretched film is determined by the degree of orientation represented by the birefringence index, and completed the present invention. It has also been found that this fact holds true even when the styrene-butadiene block copolymer is blended with a resin having excellent affinity with the styrene-butadiene block copolymer, such as polystyrene. That is, the present invention provides a uniaxially stretched film mainly composed of a styrene-butadiene block copolymer.
A glass bottle coated with a heat-shrinkable film, the film having a birefringence index of 1×10 ⁻⁴ or more after heat-shrinking. The resin constituting the stretched film in the present invention is mainly composed of a styrene-butadiene block copolymer, that is, it contains 50% by weight or more of a styrene-butadiene block copolymer. Block copolymers have a styrene content of 60% by weight or more, 95%
% by weight or less, and includes those represented by the general structural formula below. (S-B)n...(A) S(-B-S) _o ...(B) B(-S-B) _o ...(C) (S-B) _-n X...(D) [In the above structural formula, S is a polystyrene block, and B is butadiene alone, a (co)polymer block of a conjugated diene copolymerizable with butadiene, or a random or tapered copolymer block of butadiene and styrene. ,X
is a residue of a coupling agent such as silicon tetrachloride or sug tetrachloride or a residue of a polymerization initiator such as a polyfunctional organolithium compound, n is an integer of 1 to 5, and m is an integer of 2 to 7. . ] If the styrene content is less than 60% by weight, the styrene-butadiene block copolymer becomes elastomer-like, making stretching difficult; if it exceeds 95% by weight, the impact strength of the uniaxially stretched film will decrease. and the protective effect on glass bottles is reduced.
The preferred range of styrene content is 65% to 90% by weight, more preferably 70% to 85% by weight. Melt inflow index (G) of the styrene-butadiene block copolymer used in the present invention
conditions) are 0.1 to 50 g/10 minutes, and the preferred range is 1 to 30 g/10 minutes. The styrene-butadiene block copolymer used in the present invention can be produced by a living anionic polymerization method in a hydrocarbon solvent. In the present invention, styrene-butadiene block copolymers can be used as a blend of two or more types, and polystyrene, high-impact polystyrene, or elastomeric styrene with a styrene content of less than 60% by weight can also be used. The butadiene block copolymer may be blended in an amount up to 50% by weight of the total. It is also possible to add various additives depending on the purpose. Examples of additives include stabilizers, lubricants, anti-blocking agents,
Examples include antistatic agents, dyes, pigments, softeners, plasticizers, and low molecular weight polystyrene. The stretched film used in the present invention is obtained by uniaxially stretching the styrene-butadiene block copolymer or a resin mainly composed of the styrene-butadiene block copolymer by a known method, but it is preferable. As a method of uniaxial stretching,
Examples include a tenter transverse uniaxial stretching method and an inflation method. Conditions for performing uniaxial stretching include the following conditions. Stretching temperature is 60℃~150℃, preferably 80℃
℃ to 120℃, and the stretching ratio is 2 to 8 times, preferably 3 to 6 times. Further, the thickness of the uniaxially stretched film is 20μ to 200μ, preferably 40μ to 100μ. If the film is too thin, it will become stiff and difficult to cover a glass bottle, and if it is too thick, it will be difficult to heat shrink. The uniaxially stretched film used in the present invention preferably has zero orientation in the direction perpendicular to stretching, but it can be used even if it has some orientation. In the present invention, as a means for coating a glass bottle with a uniaxially stretched film mainly composed of a styrene-butadiene block copolymer, the uniaxially stretched film is first formed into a tube by a stretching method at right angles, and then the film is coated onto a glass bottle. A common method is to cover the tube with a tube, heat it from the outside, and then shrink the tube tightly to the glass bottle. At this time, hot air or hot water can be used as the heating medium, and the heating conditions can be controlled by temperature and time. In the present invention, the most important point in order to prevent stress cracks occurring in the coated film is to make the birefringence of the coated film 1×10 ^-4 or higher. Here, the birefringence of the coated film in the present invention means the value in all parts of the entire surface of the film coated on the glass bottle,
According to experiments conducted by the present inventors, it has been found that the part with the greatest amount of shrinkage (generally the neck part) always exhibits the smallest birefringence value among the entire surface of the coated film; The effects of the present invention can be exhibited if the birefringence of the portion with the greatest amount of shrinkage is 1×10 ⁻⁴ or more. In the present invention, the birefringence of the coating film is 1.
If it is less than ×10 ^-4 , just leave the film-covered glass bottle outdoors in a place where the temperature changes, and it will be cured within a month, or within 2 to 3 days if it is short.
Cracks occur on the film. The preferred value of birefringence is 2×10 ^-4 or more, in which case no cracks will be observed even if the film is left for two months or more under the same conditions as above. In the present invention, the birefringence of the coating film is 1.
The coating conditions for coating the glass bottle such that the film is 10 ^-4 or more are the polymer structure of the styrene-butadiene block copolymer, the stretching conditions and film thickness to obtain a uniaxially stretched film, the shape of the glass bottle, Although it is influenced by the maximum shrinkage amount of the film for coating, etc., it can usually be determined by selecting the temperature and heating time of the medium for heating and shrinking the uniaxially stretched film. but,
For example, when using a uniaxially stretched film stretched at an extremely high temperature, no matter how the heat shrinkage conditions for coating the glass bottle are selected, the birefringence of a portion of the coated film will be 1.
It may not be more than ×10 ^-4 , and in this case,
This is not included in the present invention since the coated film would have poor crack characteristics. The shape of the glass bottle that is the object of the present invention is not particularly limited, but generally a glass bottle with a circular cross section or a shape close to it is selected. However, the effects of the present invention can also be achieved with glass bottles whose cross sections are similar to triangles or squares. EXAMPLES In order to explain the present invention in more detail, Examples are shown below, but the present invention is not limited to the following Examples. Note that various characteristics in this example were measured by the following methods. Birefringence: Measured using a polarizing microscope (Beretsu Compensator) manufactured by Olympus Optical Industry Co., Ltd. by cutting small pieces mainly from the neck and some from the body of a film that has been heat-shrinked and coated on a glass bottle. did. Stress crack characteristics: A glass bottle covered with a film was left outdoors in a well-ventilated place protected from direct sunlight and rain, and the occurrence of stress cracks over time was observed. Evaluation,
It is expressed as the number of stress cracks among the number of specimens (5 specimens) tested every 10 days. The glass bottle used in this example had a height of 138 mm, a body outer diameter of 68 mm, and a neck outer diameter of 25 mm. It was coated from the outer circumference to about 10 mm inside. Examples 1 to 3, Comparative Examples 1 and 2 S-B-S-B structure (weight ratio
A styrene-butadiene block copolymer having a melt flow index (G condition) of 10 was polymerized. Here, S is a polystyrene block and B is a polybutadiene block. This styrene-butadiene block copolymer was extruded into a sheet at 180°C using a 40 mmφ extruder, and then stretched using a tenter stretching machine as shown in Table 1.
A transversely uniaxially stretched film was produced under the conditions shown in . The obtained film is heat-sealed,
It was formed into a tube with a length of 130 mm and a fold width of 110 mm, into which a glass bottle was inserted, and then placed in an oven at a constant temperature for a certain period of time to shrink and cover the glass bottle. The shrinkage conditions are also shown in Table 1. Table 1 shows the results of evaluating the birefringence and stress crack properties of this coated film.

[Table] Examples 4 to 6, Comparative Examples 3 and 4 Styrene polymers with a melt flow index (G condition) of 8 having an S-B-S structure using n-butyllithium as a polymerization initiator in a cyclohexane solvent. A butadiene block copolymer was polymerized. Here, S is a polystyrene block of 35 parts by weight each, and B is a styrene-butadiene copolymer block consisting of 10 parts by weight of styrene and 20 parts by weight of butadiene, in which styrene is tapered copolymerized. Then, using the same solvent and polymerization initiator, S-
A styrene-butadiene block copolymer having a B-S-B-S structure and a melt flow index (G condition) of 17 was polymerized. Here, S is each 25 parts by weight polystyrene block and B is each 12.5 parts by weight polybutadiene block. These block copolymers were subjected to sheet extrusion, transverse uniaxial stretching in a tenter, and coating on glass bottles in the same manner as in Example 1 under the conditions shown in Table 2. Table 2 shows the results of evaluating the birefringence and stress crack properties of the obtained coated film.

【table】

[Table] Examples 7 to 10, Comparative Example 5 Four types of styrene-butadiene block copolymers shown in Table 3 were polymerized in a cyclohexane solvent using n-butyllithium as a polymerization initiator.

[Table] These block copolymers or mixtures thereof
0.1 part by weight of erucic acid amide and 2-(2'-hydroxy-5'-methylphenyl) per 100 parts by weight
A composition containing 0.5 parts by weight of benzotriazole was subjected to sheet extrusion, transverse uniaxial stretching with a tenter, and coating on a glass bottle in the same manner as in Example 1 under the conditions shown in Table 4. Table 4 shows the results of evaluating the birefringence and stress crack properties of the obtained coated film.

【table】

[Table] Examples 11 and 12, Comparative Examples 6 and 7 K-Resih 05 (Phillips), a commercially available branched styrene-butadiene block copolymer
Chemical Co., Ltd., styrene content: 75% by weight), sheet extrusion, transverse uniaxial stretching with a tenter, and coating on a glass bottle were performed in the same manner as in Example 1 under the conditions shown in Table 5. Table 5 shows the evaluation results of the birefringence and stress crack properties of the obtained coated film.

[Table] Examples 13 to 15, comparative rows 8 and 9 85 parts by weight of the styrene-butadiene block copolymer used in Example 1, styrene-butadiene thermoplastic elastomer Tuffrene A (manufactured by Asahi Kasei Corporation, Sheet extrusion was carried out in the same manner as in Example 1 under the conditions shown in Table 6 using a composition consisting of 10 parts by weight of styrene (40% by weight) and 5 parts by weight of low molecular weight polystyrene (softening point 75°C). , transverse uniaxial stretching in a tenter, and coating on a glass bottle. However, in Example 15 and Comparative Example 9,
The length of the uniaxially stretched film tube is 125 mm,
The shoulder portion of the glass bottle was coated starting from a portion with an outer diameter of 46 mm (height 110 mm). Table 6 shows the evaluation results of the birefringence and stress crack properties of the obtained coated film.

[Table] As shown above, when a uniaxially stretched film mainly made of styrene-butadiene block copolymer is heat-shrinked and coated on a glass bottle,
It was confirmed that when the birefringence of the coated film is 1×10 ^-4 or more, stress cracks hardly occur in the film, and when it is 2×10 ^-4 or more, no stress cracks occur at all.

Claims (1)

[Claims] 1 A glass bottle coated with a uniaxially stretched film mainly composed of a styrene-butadiene block copolymer, which is heat-shrinked and has a birefringence index of 1×10 ^-4 or more after heat-shrinking. glass bottle.