JPS6017452B2 - transparent heat shrinkable film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transparent heat-shrinkable film formed by stretching a resin composition comprising a resinous block copolymer, a rubbery block copolymer, and polystyrene.

Traditionally, the average molecular weight is 4, which is composed of 60 to 95% by weight of styrenic hydrocarbon and 5 to 4% by weight of conjugated hydrogen hydrocarbon.
0 to 3 parts of polystyrene per 100 parts by weight of a resinous block copolymer (hereinafter referred to as thermoplastic resin)
A resin composition comprising parts by weight of
Alternatively, use the tubular method at a stretching ratio of 2 to 8 times and a length of 1
Transparent films formed by stretching axially, adjacently uniaxially, biaxially, or multiaxially have excellent heat shrinkability, heat sealability, and gas permeability, as shown in Hakama Sekisho 48-113973, and have excellent transparency. This film has high gloss and is suitable for packaging materials such as heat shrink packaging.

However, in heat-shrink packaging, the stretched film made of this resin composition is subjected to heat shrinkage to the packaging object (various containers, etc.). In response to changes in the storage environment, 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. The occurrence of cracks and cracks depends on the shape and material of the packaged object, and the storage conditions after packaging.

In other words, if the shape of the packaged object is uneven and the material has a high stiffness that alleviates heat shrinkage stress, the heat shrinkage rate tends to be uneven, and the heat shrinkage stress and the shape of the packaged object Cracks and cracks are likely to occur because the residual stress caused by this is difficult to relax. Furthermore, storing such packages in a cool place tends to accelerate the occurrence of cracks and cracks. usually,
As a measure to prevent cracks, methods have been taken to increase the molecular weight of styrenic hydrocarbons or to increase the content of conjugated hydrogen hydrocarbons in the block structure of the resin composition. However, an increase in molecular weight decreases the flow of the resin, and an increase in the content of conjugated gene decreases the stiffness of the film and at the same time lowers the temperature at which heat shrinkage begins.
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. That is, the uses of heat-shrinkable films made from this resin composition are extremely limited depending on the shape and material of the object to be packaged.
Z The purpose of the transparent heat-shrinkable film of the present invention is to be able to package a wide range of ordinary packaging objects, to prevent the occurrence of cracks or cracks after heat-shrink packaging, that is, to have good moldability,
A film that is suitable for use as a packaging material in terms of heat shrinkability, strength, oil resistance, stress cracking resistance, and transparency, and should prevent the occurrence of cracks and breaks after heat shrink packaging from the material resin side. As a result of intensive research, we have arrived at the present invention.
That is, the present invention provides: (1) an average molecular weight of 4 to 30, consisting of 60 to 95% by weight of styrenic hydrocarbon and 5 to 4% by weight of conjugated hydrogen hydrocarbon;
100 parts by weight of a ten thousand resinous block Aoi polymer, 0 to 3 parts by weight of 'B1 polystyrene, and 20 to 5 parts by weight of a styrenic hydrocarbon and 50 to 8 parts by weight of a conjugated hydrogen hydrocarbon.
A rubbery block copolymer consisting of 0.3 to 1% by weight of
0. Parts by weight of the resin composition are stretched monoaxially, biaxially, or multiaxially.

The styrenic hydrocarbon constituting the block copolymer of the thermoplastic resin used in the present invention is styrene, Q-methylstyrene, etc., and the conjugated hydrogen hydrocarbon is butadiene, isoprene, etc.

To produce block copolymers from these monomers,
A method in which both hydrocarbon monomers are polymerized stepwise using an anionic polymerization initiator, especially an organolithium compound, a method in which a mixture of both monomers is copolymerized in an inert solvent, or
It is manufactured by a method in which these methods are used in combination. The proportion of styrenic hydrocarbon in the block copolymer is 60 to 95% by weight. If it is less than 60%, the resulting resin becomes similar to a rubber-like elastic body, making it unsuitable for use as a film, and if it exceeds 95%, a film having the above-mentioned properties, which is the object of this application, cannot be obtained. do not have.

The average molecular weight of the book copolymer is in the range of 40,000 to 300,000, preferably 60,000 to 25,000. If the number of sides is less than 4, the mechanical strength will decrease, and if it is more than 30, 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)n or (A-
B) A linear block copolymer represented by n-A (A is a block of a styrene hydrocarbon polymer, B is a block of a conjugated hydrogen hydrocarbon polymer, and n is a positive integer). , and the general structural formula [(A-B)m-n×, where A is a styrenic hydrocarbon polymer block, B
is a polymer block of conjugated hydrogen-based hydrocarbon, × is a residue derived from a polyfunctional compound, m is an integer of 1 or more, and n is 3 or 4.

It is a star-shaped block copolymer represented by

As for the structure of the block, even a complete block has 48 Tokukan floors.
Block A and Block B as seen in -48546
It may have any so-called tapered block structure containing an AB random copolymer in the transition region. These block copolymers can be classified structurally as follows. {1
} A-B '21A-B-A {3- A-B-A-B '41A-B-A-B-A '51A-B-A-B-A-B ■A-B-A-B -A-B-A '7} [(A-B) m x 3 x (m and x are as above) '8' [(A-B) m x 4 x (however, m and (As mentioned above) The block copolymer of structure '11 cannot be formed into a film due to its low tensile strength at high temperatures.

The block copolymer having the structure '21, {7', t81 lacks film forming processability by stretching and also lacks heat shrinkability.
On the other hand, so-called multi-block block copolymers with structures [31, [41, '5}, '61 are easy to stretch, and have excellent heat shrinkability. . That is, it is preferable to have a general structural formula (AB)n-A in which n is 2 or more, preferably 3 to 5. Next, the 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 0 to 3 parts by weight. The purpose of adding polystyrene is to improve the stiffness, transparency, and gloss of the film, but if the amount added exceeds 3 parts by weight, the influence of polystyrene will be strong, resulting in a decrease in impact strength and an increase in stretching temperature. This may cause damage to the film's suitability as a packaging material and processability, such as loss of quality. Furthermore, when polystyrene is added to the block copolymer, cracks and cracks tend to occur in the film, so a system without the addition is preferable.
The rubbery block copolymer (hereinafter referred to as thermoplastic rubber) used in the present invention is a block copolymer consisting of 20 to 5% by weight of a styrene hydrocarbon and 50 to 8% by weight of a conjugated hydrogen hydrocarbon. It is a polymer.

This block copolymer has a high conjugated hydrocarbon content of 50 to 8% by weight, so there is no chemical crosslinking agent.
It is solid, exhibits rubber elasticity, and can be remelted. If the conjugated hydrogen hydrocarbon is less than 5% by weight, it will exhibit resinous properties and decrease oil resistance, making it undesirable.
Exceeding 20% by weight results in a decrease in film transparency and stiffness. The resin composition used for the transparent heat-shrinkable film of the present invention includes 10 parts by weight of thermoplastic resin and 10 parts by weight of polystyrene.
-3 parts by weight and 0.3 to 12.0 parts by weight of thermoplastic rubber.

That is, 0.3 to 1 part by weight of thermoplastic rubber is added to 10 parts by weight of thermoplastic resin, and 0.3 to 1 part by weight is added to the thermoplastic resin. If it is less than 1 part by weight, the oil resistance will be poor and the effect of suppressing cracking on the film after heat shrinking will be small, and if it exceeds 1 part by weight, the transparency will decrease and it will be difficult to distinguish the contents after coating the container etc. Moreover, this results in a decrease in the temperature at which heat shrinkage starts and in the stiffness of the film. Furthermore, 10 to 3 parts by weight of polystyrene are added. Adding polystyrene at 1 part by weight or more improves transparency, but if it exceeds 3 parts by weight, the oil resistance, that is, the effect of inhibiting cracking in the heat-shrinkable film, decreases, and furthermore, the impact strength decreases and the stretching temperature increases. Yes, it's not good. Furthermore, a paste, an antioxidant, an ultraviolet absorber, a coloring agent, and the like may be added to the resin composition as necessary.

The resin composition used in the present invention can be mixed using a conventional Henschel mixer, ribbon blender, super mixer, or V
They may be dry blended using a blender or the like, or may be melted and pelletized using an extruder, and melt mixing is preferred. Next, the stretching method of the present invention may be either the tenter method or the tubular method, and the stretching can be carried out longitudinally or transversely uniaxially, biaxially, or multiaxially.

The packaging film of the present invention not only has transparency, gloss, air permeability, and moisture permeability, which are characteristics of a styrene resin film, but also has excellent heat shrinkability and heat sealability. It has stress cracking properties and oil resistance, and has appropriate physical properties that can be freely adjusted according to various packaging applications.

The present invention will be explained in detail below using examples.

Example 1100 80 kg of sufficiently dehydrated and purified benzene was charged into the jacketed reaction vessel, and 9 kg of styrene was charged.
After adding a mixture of and butadiene lk9, 0.3 mol of a bifunctional butadiene oligomer dilithium initiator as active terminal lithium was added, and the content was heated to 50:00 to complete polymerization. Then, a mixture of 8k9 styrene and 2 kg of putadiene was added,
Polymerize. 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 was pelletized. For every 10 parts by weight of this thermoplastic resin, 1 part by weight of polystyrene (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) and thermoplastic rubber (Tuffrene-A manufactured by Asahi Kasei Corporation) are added. 5 parts by weight of the mixture were added and melted and mixed to form pellets. This resin composition was press plate molded using a hot plate press machine at a molding temperature of 170 qo to obtain a sheet having a thickness of 225 AI2×12 arcs.

This sheet was uniaxially stretched using a Toyo Seiki biaxial stretching machine. Child heat temperature 105qo, preheating time 90 seconds, stretching ratio 4.5 times,
12 x 54 skin, thickness 48~ at stretching speed 1.8/min
A film with 52 peaks was obtained.

The film properties, film forming conditions, etc. are shown in the table. Both the haze and cracking prevention effects were good.

Example 2 15 parts by weight of polystyrene (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) and thermoplastic rubber (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) were added to 10 parts by weight of thermoplastic resin synthesized in the same manner as in Example 1. 8 parts by weight of Toughprene-A) manufactured by Co., Ltd. was added, and the molten crane was formed into a pellet.

Using this pellet, film formation and crack initiation tests were carried out in the same manner as in Example 1.

The results are shown in the table together with the film forming conditions and general physical properties of the film. Both haze and crack generation prevention effects were good. Example 3 10 parts by weight of thermoplastic resin synthesized in the same manner as in Example 1, 3 parts by weight of polystyrene (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) and 3 parts by weight of thermoplastic rubber (Asahi Kasei Co., Ltd.) Manufactured by Toughprene Co., Ltd.
10 parts by weight of A was added and melted into a pellet.

Using this pellet, in the same manner as in Example 1,
Film deposition and crack initiation tests were conducted.

The results are shown in the table together with the film forming conditions and general physical properties of the film. Both the haze and cracking prevention effects were good. Comparative Example 1 Using a thermoplastic resin synthesized in the same manner as in Example 1,
Film formation and a crack initiation acceleration test were carried out in the same manner as in Example 1.

The results are shown in the table together with the film forming conditions and general physical properties of the film. ．． Bayesian performance was good, but the crack generation prevention effect was poor at 22 minutes. Comparative Example 2 10 parts by weight of polystyrene (Denka Styrol GP-1 manufactured by Denki Kagaku Kogyo Co., Ltd.) was added to 10 parts by weight of thermoplastic resin synthesized in the same manner as in Example 1, and the mixture was melted and mixed into a pellet. did.

Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1.

The results are shown in the table together with the film forming conditions and general physical properties of the film. Although the haze was good, the crack generation prevention effect was very poor at 8% sand. Comparative Example 3 Thermoplastic rubber (Tuffrene-A manufactured by Asahi Kasei Corporation) was added to 100 parts by weight of thermoplastic resin synthesized using the same machine as Example 1.
15 parts by weight of the mixture were added and melted to form a pellet.

Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1.

The results are shown in the table 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 that of Example 1.

Comparative Example 4 To 100 parts by weight of a thermoplastic resin synthesized in the same manner as in Example 1, 10 parts by weight of thermoplastic rubber (Toughprene A manufactured by Asahi Kasei Corporation) was added and melted and mixed into pellets.

Using this pellet, film formation and crack initiation tests were carried out in the same manner as in Example 1.

The results are shown in the table together with the film forming conditions and the 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 To 100 parts by weight of a thermoplastic resin synthesized in the same machine as in Example 1, 15 parts by weight of thermoplastic rubber (Toughbrain A manufactured by Asahi Kasei Corporation) was added and melted and mixed to form a pellet.

Using this pellet, film formation and crack initiation tests were conducted in the same manner as in Example 1.

The results are shown in the table together with the film forming conditions and general physical properties of the film. Although the effect of suppressing crack generation is good, the haze is high and the contents cannot be distinguished.

Corrected table The physical properties of the heat-shrinkable film were measured as follows.

VICAT softening point JIS-K-Ship 70 Heat shrinkage stress Using a heat shrinkage stress measuring machine manufactured by Toyo Seiki Co., Ltd.
Heat shrinkage stress was measured under the following conditions.

Sample shape: Indicated thickness x 2 x 2 (width) x 100 x 100 (length)
Length direction is stretching direction Measurement temperature: 140 ko○ (hot soot: silicone oil) Table value is stress (/thickness x width (unfriendly) tensile strength JIS-K-6732 (vertical stretching direction) stretched film impact tester industry The strength against impact punching of the film was measured under the following conditions using a film impact tester manufactured by the company.

Impact spherical surface 1'', 2000 haze ASTM-D-1003 Heat shrinkage rate The film was placed in a constant temperature bath under the following conditions, and the heat shrinkage rate was measured.

Hot soot: Silicone oil (in a constant temperature bath) Time: 6$eC Sample shape 10 x 10cm Crack initiation test method The film was placed on a glass container and heat-shrinked in a gear oven at 19,000, 6$eC. After cooling, the film Rapeseed oil was applied uniformly to the surface and the occurrence of cracks was observed.

After application, how long does it take for cracks with a length of 5 skins or more to occur? This was taken as the crack occurrence time.

Claims (1)

[Scope of Claims] 1 (A) 100 parts by weight of a resinous block copolymer having an average molecular weight of 40,000 to 300,000 and consisting of 60 to 95% by weight of a styrene hydrocarbon and 5 to 40% by weight of a conjugated diene hydrocarbon; (
B) Resin composition of 10 to 30 parts by weight of polystyrene, and (C) 0.3 to 10 parts by weight of a rubbery block copolymer consisting of 20 to 50% by weight of styrene hydrocarbon and 50 to 80% by weight of conjugated diene hydrocarbon. Objects on 1 axis, 2
A transparent heat-shrinkable film that is axially or multiaxially stretched.