JPS632777B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a glass container coated with a specific transparent heat-shrinkable film. [Prior art] Conventionally, resinous block copolymers (hereinafter referred to as thermoplastic resins) having an average molecular weight of 40,000 to 300,000 are composed of 60 to 95% by weight of styrene hydrocarbons and 5 to 40% by weight of conjugated diene hydrocarbons. A resin composition containing 0 to 30 parts by weight of polystyrene per 100 parts by weight (100 parts by weight of A transparent film formed by biaxially or multiaxially stretching is disclosed in Japanese Patent Application Laid-open No.
As seen in Publication No. 48-13973, heat shrinkability,
This film has excellent heat sealability and gas permeability, as well as transparency and high gloss, making it suitable for packaging materials such as heat shrink packaging. However, in heat shrink packaging, the stretched film made of this resin composition is exposed to heat shrinkage stress, residual stress due to the shape of the packaged object, and the environment in which the packaged product is stored. In response to changes in the film, thin cracks and cracks often occur in the film (stress cracking phenomenon). These cracks and cracks not only impair the beauty of the Shrink label, but also cause the label to lose its protective effect on the object to be packaged, making it unsuitable as a packaging material. Normally, crack prevention measures include increasing the molecular weight of styrenic hydrocarbons or increasing the content of conjugated diene hydrocarbons in the block structure of resin compositions. [Problems to be Solved by the Invention] However, an increase in the molecular weight reduces the flow of the resin, and an increase in the content of conjugated diene reduces the stiffness of the film and at the same time lowers the temperature at which heat shrinkage starts. Lacks suitability as a heat shrink packaging material.
Therefore, simply adjusting the composition of the resin composition cannot prevent the occurrence of cracks and cracks under severe packaging conditions as described above. An object of the present invention is to provide a film-covered glass container that is free from cracking or cracking on the surface of the covering film after heat-shrink packaging. [Means for Solving the Problems] To summarize the present invention, the present invention relates to a film-coated glass container, which comprises: (A) 60 to 95% by weight of styrenic hydrocarbon and 5 to 5% by weight of conjugated diene hydrocarbon; (B) 10 to 30 parts by weight of polystyrene, and (C) 20 to 50 parts by weight of styrenic hydrocarbon and conjugated diene. A glass container is heat-shrinkable coated with a transparent heat-shrinkable film made by stretching uniaxially, biaxially, or multiaxially a resin composition containing 0.3-10 parts by weight of a rubbery block copolymer consisting of 50-80% by weight of a hydrocarbon. It is characterized by: The styrenic hydrocarbons constituting the thermoplastic resin block copolymer used in the present invention are:
Styrene or α-methylstyrene, etc.
Conjugated diene hydrocarbons include butadiene, isoprene, and the like. To produce a block copolymer from these monomers, an anionic polymerization initiator,
Among them, a method using an organolithium compound and stepwise polymerization of both hydrocarbon monomers, a method of copolymerizing a mixture of both monomers in an inert solvent, or a method of appropriately using these in combination. manufactured by The proportion of styrenic hydrocarbon in the block copolymer is 60 to 95% by weight. Below 60%,
Since the resulting resin resembles a rubber-like elastic body, it is unsuitable for use as a film, and if it exceeds 95%, a film having the above-mentioned properties, which is the object of the present invention, cannot be obtained. The average molecular weight of the block copolymer is in the range of 40,000 to 300,000, preferably 60,000 to 250,000. If it is less than 40,000, the mechanical strength will decrease, and if it exceeds 300,000, the moldability will be poor and it will be difficult to form a film by stretching. The block copolymer has the general structural formula (A-B) _o or (A-B) _o -A
(A is a block of styrenic hydrocarbon polymer,
B is a block of a conjugated diene hydrocarbon polymer, n is a positive integer), and a linear block copolymer represented by the general structural formula: [(A-B) _n ] - _o X However, , A is a polymer block of styrenic hydrocarbon, B is a polymer block of conjugated diene hydrocarbon, X is a residue derived from a polyfunctional compound, m is an integer of 1 or more, n is 3 or 4. be. It is a star-shaped block copolymer represented by As for the structure of the block, even if it is a complete block, it is
As seen in Japanese Patent No. 48546, any so-called tapered block structure containing an AB random copolymer in the transition region between block A and block B may be used. These block copolymers can be classified structurally as follows. (1) A-B (2) A-B-A (3) A-B-A-B (4) A-B-A-B-A (5) A-B-A-B-A-B (6) A-B-A-B-A-B-A (7) [(A-B) _n ] - ₃ X (m and X are as above) (8) [(A-B) _n ] - ₄ X (where m and The block copolymers of structures (2), (7), and (8) lack film-forming processability by stretching and heat shrinkability. On the other hand, the so-called multiblock block copolymers of structures (3), (4), (5), and (6) have good stretching film formability and excellent heat shrinkability.
That is, it is preferable that n is 2 or more, preferably 3 to 5 in the general structural formula (A-B) _o -A. Next, polystyrene is general transparent polystyrene, and any polystyrene with a molecular weight of 100,000 or more that can be molded with a molding machine is sufficient. The amount of polystyrene added is 10
~30 parts by weight. The purpose of adding polystyrene is to improve the stiffness, transparency, and gloss of the film.
If the amount added exceeds 30 parts by weight, the influence of polystyrene will be strong, causing a decrease in impact strength and an unavoidable increase in stretching temperature, which will impair the film's suitability as a packaging material and processability. The rubbery block copolymer (hereinafter referred to as thermoplastic rubber) used in the present invention consists of 20 to 50% by weight of styrene hydrocarbon and 50 to 50% by weight of conjugated diene hydrocarbon.
It is a block copolymer consisting of 80% by weight. Since this block copolymer has a high conjugated diene hydrocarbon content of 50 to 80% by weight, it exhibits rubber elasticity as a solid and can be remelted without a chemical crosslinking agent. If the conjugated diene hydrocarbon content is less than 50% by weight, the film exhibits resin-like properties and oil resistance is reduced, making it undesirable. If it exceeds 80% by weight, the film becomes less transparent and stiff. The resin composition used for the transparent heat-shrinkable film used in the present invention includes 100 parts by weight of thermoplastic resin, 10 to 30 parts by weight of polystyrene, and 0.3 parts by weight of thermoplastic rubber.
~10 parts by weight. That is, 0.3 to 10 parts by weight of thermoplastic rubber is added to 100 parts by weight of thermoplastic resin; if it is less than 0.3 parts by weight, the oil resistance will be poor and the effect of suppressing cracking on the film after heat shrinkage will be small; If the amount exceeds 1 part by weight, the transparency decreases, making it difficult to distinguish the contents after coating the glass container, and furthermore, the stiffness of the film decreases.
Furthermore, 10 to 30 parts by weight of polystyrene is added. Adding 10 parts by weight or more of polystyrene improves transparency, but if it exceeds 30 parts by weight, the oil resistance, that is, the effect of suppressing cracking in the heat-shrinkable film, decreases, and furthermore, the impact strength decreases and the stretching temperature increases. Undesirable. Furthermore, the resin composition may contain a lubricant, if necessary.
Antioxidants, ultraviolet absorbers, colorants, etc. can also be added. In the case of the resin composition used in the present invention, it may be dry-blended using a conventional Henschel mixer, ribbon blender, super mixer, V-blender, etc., and may also be melted and pelletized using an extruder. Preferably, Melt mixing is better. Next, the stretching method used in the present invention may be either the tenter method or the tubular method, and the stretching may be uniaxial, biaxial, or multiaxial in the longitudinal direction or in the transverse direction. The coating of the glass container in the present invention may be carried out by a conventional method, for example, by forming a stretched film into a shape that conforms to the shape of the glass container, covering the glass container, and blowing hot air onto it, or placing it in an oven. The film may be heat-shrinked by heating, etc., and brought into close contact with the glass container. [Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. The method for measuring the physical properties of the film and the crack initiation test method that serves as an indicator of oil resistance and stress cracking resistance when applied to glass containers are as follows. VICAT Softening Point JIS-K-6870 Heat Shrinkage Stress Heat shrinkage stress was measured under the following conditions using a heat shrinkage stress measuring machine manufactured by Toyo Seiki Co., Ltd. Sample shape: Indicated thickness x 20mm (width) x 100mm
(Length) Length direction is stretching direction Measurement temperature: 140℃ (heating medium: silicone oil) Table values are stress (g)/thickness x width (mm ² ) Tensile strength JIS-K-6732 (vertical-stretching direction) Elongation Film Impact Using a film impact tester manufactured by Tester Sangyo Co., Ltd., the strength against impact punching of the film was measured under the following conditions. Shock spherical surface 1", 20℃ Haze ASTM-D-1003 Heat shrinkage rate The film was placed in a constant temperature oven under the following conditions and the heat shrinkage rate was measured. Heat medium: Silicone oil (in a constant temperature oven) Time: 60 seconds Sample shape 10 ×10cm Crack initiation test method Cover the glass container with the film, and heat it at 190℃ while the gear is open.
After cooling by heat shrinking for 60 seconds, apply rapeseed oil evenly to the film surface.
The occurrence of cracks was observed. After coating, the time when a crack of 5 mm or more in length occurred was defined as the crack initiation time. Example 1 Thoroughly dehydrate the reaction vessel with a 100mm jacket.
After charging 80 g of purified benzene and adding a mixture of 9 kg of styrene and 1 kg of butadiene, 0.3 mol of a bifunctional butadiene oligomer dilithium initiator was added as active terminal lithium, and the same contents were added.
Polymerization is completed by raising the temperature to 50°C. Then, a mixture of 8 kg of styrene and 2 kg of butadiene is further added and polymerized. The obtained polymer solution is subjected to steam stripping to recover the polymer. The number average molecular weight of this polymer is 175,000. (Styrene content: 85%, butadiene content: 15%) This polymer is a block copolymer represented by the formula (AB) _o -A (n=3), and was pelletized. For 100 parts by weight of this thermoplastic resin, add polystyrene (Denka Styrene manufactured by Denki Kagaku Kogyo Co., Ltd.) to 100 parts by weight of this thermoplastic resin.
10 parts by weight of GP-1] and 5 parts by weight of thermoplastic rubber [Tuffrene-A manufactured by Asahi Kasei Corporation] were melted and mixed to form pellets. This resin composition is molded using a hot plate press machine at a molding temperature of
A press plate was formed at 170°C to obtain a sheet with a thickness of 225μ12×12cm. This sheet was uniaxially stretched using a Toyo Seiki biaxial stretching machine. Preheating temperature 105℃, preheating time 90 seconds, stretching ratio 4.5
12 x 54 cm at a stretching speed of 1.8 m/min, thickness 48 ~
A 52μ film was obtained. Film characteristics, film forming conditions, etc. are shown in Table 1 below together with other examples. Next, this film was placed on a glass container and heated and shrunk to produce a film-covered glass container. The results of testing its transparency and crack initiation,
It is also shown in Table 1. Both haze and crack generation inhibiting effects were good. Example 2 Thermoplastic resin synthesized by the same method as Example 1
Polystyrene per 100 parts by weight [Denki Kagaku Kogyo
15 parts by weight of Dencastyrol GP-1 manufactured by Co., Ltd.
and thermoplastic rubber [manufactured by Asahi Kasei Corporation - Toughprene]
A] was added in an amount of 8 parts by weight, and the mixture was melted and mixed into pellets. Using these pellets, film formation and crack initiation tests were carried out in the same manner as in Example 1. The results are shown in Table 1 together with the film forming conditions and general physical properties of the film. Both haze and crack generation prevention effects were good. Example 3 Thermoplastic resin synthesized by the same method as Example 1
Polystyrene per 100 parts by weight [Denki Kagaku Kogyo
30 parts by weight of Dencastyrol GP-1 (manufactured by Asahi Kasei Corporation) and thermoplastic rubber (Tuffprene, manufactured by Asahi Kasei Corporation)
A] was added in an amount of 10 parts by weight, and the mixture was melted and mixed into pellets. Using these pellets, film formation and crack initiation tests were carried out in the same manner as in Example 1. The results are shown in Table 1 together with the film forming conditions and general physical properties of the film. Both haze and crack generation inhibiting effects were good. Comparative Example 1 A film was formed and a crack initiation test was conducted in the same manner as in Example 1 using only a thermoplastic resin synthesized in the same manner as in Example 1. This result,
Table 1 shows the film forming conditions and general physical properties of the film. Although the haze was good, the crack prevention effect was poor at 22 minutes. Comparative Example 2 Thermoplastic resin synthesized by the same method as Example 1
To 100 parts by weight, 10 parts by weight of polystyrene (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) was added and melted and mixed to form pellets. Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1.
The results are shown in Table 1 together with the film forming conditions and general physical properties of the film. Although the haze was good, the crack initiation prevention effect was very poor at 80 seconds. Comparative Example 3 Thermoplastic resin synthesized in the same manner as Example 1
To 100 parts by weight, 5 parts by weight of thermoplastic rubber [Tuffrene-A, manufactured by Asahi Kasei Corporation] was added and melted and mixed to form pellets. Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1. The results are shown in Table 1 together with the film forming conditions and general physical properties of the film. Although the effect of inhibiting crack generation is good, the haze is higher than in Example 1. Comparative Example 4 Thermoplastic resin synthesized by the same method as Example 1
To 100 parts by weight, 10 parts by weight of thermoplastic rubber [Tuffrene-A, manufactured by Asahi Kasei Corporation] was added and melted and mixed to form pellets. Using these pellets, film formation and crack initiation tests were carried out in the same manner as in Example 1. The results are shown in Table 1 together with the film forming conditions and general physical properties of the film. Although the effect of inhibiting crack generation is good, the haze is higher than in Example 3. Comparative Example 5 Thermoplastic resin synthesized in the same manner as Example 1
To 100 parts by weight, 15 parts by weight of thermoplastic rubber (Tuffprene-A, manufactured by Asahi Kasei Corporation) was added and melted and mixed to form pellets. Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1. The results are shown in Table 1 along with the film forming conditions and general physical properties of the film. Although the cracking prevention effect is good, the haze is high and the contents cannot be distinguished.

〔Effect of the invention〕

As explained above, the film-coated glass container of the present invention has excellent heat-shrinkability and heat-sealability in addition to transparency, gloss, air permeability, and moisture permeability, which are characteristics of a coated styrenic resin film. Furthermore, due to its favorable physical properties of oil resistance and stress cracking resistance, it has the remarkable effect of being more beautiful and having better durability than conventional products.

Claims (1)

[Scope of Claims] 1 (A) A resinous block copolymer with an average molecular weight of 40,000 to 300,000, consisting of 60 to 95% by weight of a styrene hydrocarbon and 5 to 40% by weight of a conjugated diene hydrocarbon.
100 parts by weight, (B) 10 to 30 parts by weight of polystyrene, and (C) 0.3 to 10% of a rubbery block copolymer consisting of 20 to 50% by weight of a styrene hydrocarbon and 50 to 80% by weight of a conjugated diene hydrocarbon. 1. A film-coated glass container, characterized in that the glass container is heat-shrinkable coated with a transparent heat-shrinkable film obtained by stretching part by weight of a resin composition uniaxially, biaxially, or multiaxially.