JP3112607B2 - Block copolymer and heat shrinkable film thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a block copolymer comprising a vinyl aromatic hydrocarbon and a conjugated diene having excellent transparency, rigidity, impact resistance, low-temperature stretchability and resistance to natural shrinkage, and a copolymer thereof. And a heat-shrinkable film obtained by stretching the film.

[0002]

2. Description of the Related Art Block copolymerization of vinyl aromatic hydrocarbon and conjugated diene in an organic solvent using alkyllithium as an initiator by living anionic polymerization gives a weight ratio of vinyl aromatic hydrocarbon to conjugated diene and a copolymer. It is known that block copolymers having various physical properties can be obtained depending on the structure. A block copolymer is generally a polymer having excellent impact resistance and transparency. When the content of the conjugated diene in the block copolymer is large, the block copolymer is a thermoplastic elastomer, but the content of the vinyl aromatic hydrocarbon is high. When the content increases, it shows properties as a thermoplastic. Various production methods utilizing these excellent characteristics are disclosed in JP-B-36-192.
No. 86, JP-B-48-4106 and the like. In addition to these excellent properties, it is also used for reinforcement because of its excellent compatibility with various kinds of vinyl aromatic hydrocarbon polymers. For example, Japanese Patent Publication No. 45-19388, Japanese Patent Publication No. 47-43618, Tokiko Sho 51-27
No. 701, for example.

[0003]

However, these block copolymers and polymer compositions are relatively transparent and have good impact resistance, but have poor natural shrinkage resistance. When used as a shrinkable film, the film shrinks greatly during standing (so-called natural shrinkage). Therefore, there is a problem that the label cannot be attached to various bottles, the printing is displaced, and the development of a block copolymer and a heat shrinkable film having improved natural shrink resistance has been desired.

[0004]

[Means to solve the problem] Under these circumstances,
With the aim of improving the disadvantages of the conventional block copolymers, the present inventors have conducted intensive studies on the structure of the block copolymer, particularly on the ratio of a portion where a vinyl aromatic hydrocarbon and a conjugated diene are randomly copolymerized. went. As a result, compared to the block copolymer manufactured by the conventional technology, while maintaining the impact resistance, transparency, rigidity, low-temperature stretchability, block copolymer with significantly improved natural shrinkage resistance and the like, and The inventors have found that the heat-shrinkable film can be obtained, and have reached the present invention.

That is, the present invention provides a vinyl aromatic hydrocarbon polymer block and a block having polymer blocks B1 and B2 comprising a vinyl aromatic hydrocarbon and a conjugated diene (hereinafter, referred to as block B1 and block B2). In the copolymer, at least one terminal is a vinyl aromatic hydrocarbon polymer block, and (1) the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60/40 to 90/10, and the block copolymer Has a number average molecular weight of 40,000 to 500,000, and (2) a block ratio (%) of vinyl aromatic hydrocarbon contained in the block copolymer = (W / W0) × 100 is 25.
(W is the weight of the vinyl aromatic hydrocarbon block in the block copolymer, and W0 is the total weight of the vinyl aromatic hydrocarbon in the block copolymer.) (3) Vinyl In the polymer blocks B1 and B2 composed of an aromatic hydrocarbon and a conjugated diene, the block B1 is a vinyl block.
Weight ratio of aromatic hydrocarbon to conjugated diene is 81/19
~ 92/8, block B2 is co-existed with vinyl aromatic hydrocarbon
The weight ratio with the role diene is 65/35 to 81/19,
And 1.2 ≦ M2 / M1 ≦ 5 (where M2 =
Weight of conjugated diene of polymer block B2 composed of vinyl aromatic hydrocarbon and conjugated diene / weight of vinyl aromatic hydrocarbon of polymer block B2 composed of vinyl aromatic hydrocarbon and conjugated diene, M1 = conjugated with vinyl aromatic hydrocarbon Conjugated diene weight of polymer block B1 composed of diene / polymer block B composed of vinyl aromatic hydrocarbon and conjugated diene
1 is the weight of the vinyl aromatic hydrocarbon. And (b) a heat-shrinkable film obtained by stretching the block copolymer and the above-mentioned block copolymer.

Hereinafter, the present invention will be described in detail. The vinyl aromatic hydrocarbon used in the present invention includes styrene, o-methylstyrene, p-methylstyrene, pt
tert-butylstyrene, 1,3-dimethylstyrene,
There are α-methylstyrene, vinylnaphthalene, vinylanthracene and the like, and styrene is particularly common.

As conjugated dienes, 1,3-butadiene,
2-methyl-1,3-butadiene (isoprene), 2,
Examples thereof include 3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene, and particularly common examples include 1,3-butadiene and isoprene.

The weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is from 60/40 to 90/10, preferably 70/40.
30-85 / 15. If the ratio of the vinyl aromatic hydrocarbon and the conjugated diene is less than 60/40, the transparency and rigidity of the block copolymer exceed 90/10.

The number average molecular weight of the block copolymer is 400
00 to 500,000, preferably 80,000 to 3000
00. If it is less than 40,000, sufficient rigidity and impact resistance of the resin cannot be obtained, and if it exceeds 500,000, workability is deteriorated, which is not preferable.

The vinyl aromatic hydrocarbon polymer block comprises:
It is obtained by polymerizing one or more of the above-mentioned vinyl aromatic hydrocarbons, but a polymer block comprising a single vinyl aromatic hydrocarbon or a copolymer block comprising a plurality of vinyl aromatic hydrocarbons It may be.

The block ratio of vinyl aromatic hydrocarbon is 25.
９０90% by weight, preferably 50-85% by weight. 2
If it is less than 5% by weight, transparency and rigidity are reduced, and if it exceeds 90% by weight, impact resistance is reduced. The block rate of the vinyl aromatic hydrocarbon is as follows: Block rate (%) = (W / W ₀ ) × 100 (where W = weight of vinyl aromatic hydrocarbon block in the block copolymer, W ₀ = block copolymer) The total weight of the vinyl aromatic hydrocarbon in the polymer is shown.)
Here, the total weight of the vinyl aromatic hydrocarbon in the block copolymer is the weight of all the vinyl aromatic hydrocarbons subjected to polymerization, and the weight of the vinyl aromatic hydrocarbon block is obtained by ozonolysis of the block copolymer. [Y. TANAKA, eta
l. , RUBBER CHEMISTRY AND T
The method described in ECHNOLOGY, 58 , 16 (1985)] corresponds to each peak in the GPC measurement of the obtained vinyl aromatic hydrocarbon polymer component (using an ultraviolet spectroscopic detector whose wavelength is set to 254 nm as a detector). The molecular weight was determined from a calibration curve prepared using standard polystyrene and a styrene oligomer, and those having a number average molecular weight exceeding 3,000 were quantified and determined from their peak areas.

Furthermore, a polymer block B ₁ comprising a vinyl aromatic hydrocarbon and a conjugated diene, which is the most important feature of the present invention.
And B ₂ are each obtained by polymerizing one or more of the above-mentioned vinyl aromatic hydrocarbons and conjugated dienes.

In the blocks B1 and B2, the distribution of the vinyl aromatic hydrocarbon and the conjugated diene in each block may be uniform or tapered. Block B
In the formation of No. 1 and B2, the amount of the vinyl aromatic hydrocarbon and the conjugated diene added is such that the block B1 is a vinyl aromatic hydrocarbon.
Weight ratio of element to conjugated diene is 81/19 to 92/8,
Lock B2 is a heavy polymer of vinyl aromatic hydrocarbon and conjugated diene.
The quantitative ratio is selected in the range of 65/35 to 81/19 .

The following equation must be satisfied for the ratio between the block B ₁ and the block B ₂ . _{1.2 ≦ M 2 / M 1 ≦} 5 ( however, the vinyl aromatic hydrocarbon weight M ₂ = block B ₂ conjugated diene weight / block B _2, M ₁ = block B
₁ conjugated diene weight / block B ₁ vinyl aromatic hydrocarbon weight. If the ratio is less than 1.2, the natural shrinkage resistance is inferior. If the ratio exceeds 5, the natural shrinkage resistance is excellent but the impact resistance is poor. As described above, it was completely unexpected from the conventional knowledge that the fact that the proportion of the randomly copolymerized portion was within the specified range was extremely effective for exhibiting the natural shrinkage resistance.

The structure of the block copolymer obtained by the present invention can take any form as long as the above requirements are satisfied. Preferred examples include those having the following general formula. a. AB ₁ -B ₂ b. AB ₁ -B ₂ -A c. _{A-C -B 1 -B 2 d} . _{A-C -B 2 -B 1 e} . _{A-B 2 -C -B 1 f} . AB ₁ -AB ₂ -A g. _{A-C -B 1 -B 2 -A} h. AB ₁ -CB ₂ -A i. _{A-C -B 1 -C -B 2} j. (AB ₁ -B ₂ ) _n -X k. _{(A-C -B 1 -B 2} ) n -X l. _{(A-C -B 2 -B 1} -A) n -X m. _{(A-C -B 2 -C -B} 1) n -X

A in the above structural formula is a vinyl aromatic hydrocarbon polymer block. When there are two or more A's in the structural formula, their molecular weights may be the same or different. In forming the vinyl aromatic hydrocarbon polymer block A, the amount of the vinyl aromatic hydrocarbon to be added is not limited, but is preferably 5 to 40% based on the total amount of the monomers.

B ₁ and B ₂ in the above structural formula are a polymer block comprising a vinyl aromatic hydrocarbon and a conjugated diene as described above.

In the above structural formula, C is a conjugated diene polymer block, which can be obtained by polymerizing the above-mentioned conjugated diene. Even if it is a single conjugated diene polymer, it is a copolymer of a plurality of conjugated dienes. It may be. When there are two or more Cs in the structural formula, their molecular weights may be the same or different. In forming the block C, the amount of the conjugated diene is not limited, but is preferably 1 to 15% based on the total amount of the monomers.

In the above structural formula, X is a residue of a polyfunctional coupling agent or a residue of a polyfunctional organic lithium compound used as an initiator, and n is an integer of 2 to 4. Examples of the polyfunctional coupling agent used in the present invention include silicon tetrachloride, epoxidized soybean oil, and organic carboxylic acid esters. Examples of the polyfunctional organic lithium compound include hexamethylene dilithium, butadienyl dilithium, and isoprenyl dilithium.

Next, the production of the block copolymer of the present invention will be described. The block copolymer of the present invention can be produced by polymerizing a monomer of a vinyl aromatic hydrocarbon and a conjugated diene in an organic solvent using an organolithium compound as an initiator. Examples of the organic solvent include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane, and isooctane; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; or benzene and toluene. And aromatic hydrocarbons such as ethylbenzene and xylene.

The organic lithium compound is a compound in which one or more lithium atoms are bonded in a molecule, and examples thereof include ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, and t-butyl lithium.
Monofunctional organolithium compounds such as tert-butyllithium and the above-mentioned polyfunctional organolithium compounds can be used.

As the vinyl aromatic hydrocarbon and the conjugated diene used in the present invention, those described above can be used, and one or two or more of them can be used for polymerization.

In the present invention, the molecular weight of the block copolymer can be controlled by the amount of the initiator relative to the total amount of the monomers.

The block ratio of the block copolymer can be controlled by the amount of a randomizing agent added when copolymerizing a vinyl aromatic hydrocarbon and a conjugated diene.

As the randomizing agent, tetrahydrofuran (THF) is mainly used, but other ethers, amines, thioethers, phosphoramides, alkylbenzene sulfonates, potassium or sodium alkoxides and the like can also be used. Suitable ethers include, besides THF, dimethyl ether, diethyl ether,
Examples include diphenyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether and the like. As the amines, tertiary amines such as trimethylamine, triethylamine, tetramethylethylenediamine, and cyclic amines can also be used. In addition, triphenylphosphine, hexamethylphosphoramide, potassium or sodium alkylbenzene sulfonate, potassium or sodium butoxide, and the like can be used as a randomizing agent.

The amount of addition is preferably 0.001 to 10 parts by weight based on 100 parts by weight of all charged monomers. It timing addition may be before the start of the polymerization reaction, it may be pre-polymerization of the block B ₁ and block B ₂ parts. Further, it can be added as needed.

In addition, the block rate can also be increased by mechanically continuously feeding the vinyl aromatic hydrocarbon and the conjugated diene to the polymerization vessel, or alternatively by dispensing the vinyl aromatic hydrocarbon and the conjugated diene into the polymerization vessel little by little. Can control.

In order to effectively utilize the block copolymer shown in the present invention in various fields, it is desirable to add various additives as necessary. Examples of the additives include various stabilizers, lubricants, processing aids, antiblocking agents, antistatic agents, antifogging agents, lightfastness improvers, softeners, plasticizers, pigments, and the like.

As the stabilizer, 2,6-di-t-butyl-
Examples include phenolic antioxidants such as 4-methylphenol, and phosphorus-based antioxidants such as trisnonylphenyl phosphite. Antiblocking agent, antistatic agent,
Examples of the lubricant include fatty acid amide, ethylenebisstearamide, sorbitan monostearate, saturated fatty acid ester of aliphatic alcohol, and pentaerythritol fatty acid ester. These additives are preferably used in a range of 5% by weight or less based on the block copolymer.

Other polymers can be blended for modifying the block copolymer shown in the present invention. For example, the vinyl aromatic hydrocarbon polymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene outside the range specified in the present invention, the vinyl aromatic hydrocarbon and another vinyl monomer, for example, And copolymers with ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylates such as methyl acrylate, methacrylates such as methyl methacrylate, and acrylonitrile.

In addition, rubber-modified impact-resistant styrene resin (HIPS), acrylonitrile-butadiene-styrene copolymer (ABS), methyl methacrylate-butadiene-styrene copolymer (MBS), polyphenylene ether resin, polyethylene, polypropylene , Polycarbonate, polysulfone, polyamide, polyester, polyvinyl chloride, polymethacrylate and the like can also be used.

Further, the block copolymer shown in the present invention can be used for modifying other polymers. For example, the above-mentioned vinyl aromatic hydrocarbon polymer, or the above-mentioned vinyl aromatic hydrocarbon and acrylonitrile, acrylic acid ester, methacrylic acid ester, a non-rubber-modified polymer such as a copolymer of maleic anhydride, for example, polystyrene,
By blending the block copolymer of the present invention with a styrene-methyl methacrylate copolymer or the like, the natural shrink resistance of the polymer can be improved.

The heat-shrinkable film of the present invention can be obtained by stretching a sheet or film extruded by the known T-die method or tubular method using the above-mentioned block copolymer into a uniaxial, biaxial or multiaxial film. Can be. Examples of uniaxial stretching include a method of stretching an extruded sheet with a tenter in a direction perpendicular to the direction of extrusion, and a method of stretching an extruded tubular film in a circumferential direction.
As an example of biaxial stretching, after the extruded sheet is stretched in the extrusion direction by a roll, and then stretched in a direction perpendicular to the extrusion direction by a tenter or the like, the extruded tubular film is simultaneously stretched in the extrusion direction and the circumferential direction. Alternatively, there may be mentioned a method of stretching separately.

In the present invention, the stretching temperature is from 60 to 120.
C is preferred. If the temperature is lower than 60 ° C., the sheet or the film is broken at the time of stretching. The stretching ratio is not particularly limited, but is preferably 1.5 to 8 times. 1.
If it is less than 5 times, the heat shrinkage will be insufficient, and if it exceeds 8 times, it is not preferable because stretching is difficult. When these films are used as heat-shrinkable labels or packaging materials, the heat shrinkage must be at least 20% at 80 ° C.
If it is less than 20%, a high temperature is required at the time of shrinkage, which adversely affects the coated article, which is not preferable. The thickness of the film is preferably from 10 to 300 μm.

As the application of the heat-shrinkable film of the present invention, a heat-shrinkable label, a heat-shrinkable cap seal and the like are particularly suitable, but they can also be suitably used for a packaging film and the like.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. However, the present invention is not limited by the following examples.

Examples 1-4 and Comparative Examples 1-6 Styrene and butadiene were polymerized in cyclohexane using n-butyllithium as an initiator and tetrahydrofuran as a randomizing agent to give structural features as shown in Tables 1-3. An A—C B ₁ -B ₂ type block copolymer having the following formula was produced.
The number average molecular weight (Mn) was adjusted by the amount of n-butyllithium added, and the block ratio was adjusted by the amount of tetrahydrofuran added. For example, the copolymer of Example 3 was produced as follows. In a 100 liter polymerization vessel, 65 liters of cyclohexane, 8.5 g of tetrahydrofuran and 3.4
kg of styrene was charged and stirred. Next, 125 cc of n-butyllithium (10% cyclohexane solution) was added at 30 ° C., and then the temperature was raised and polymerization was performed for 40 minutes. Next, 740 g of butadiene was added and polymerized for 40 minutes. Next, 7.26 kg of styrene and 94 of butadiene
0 g was added and polymerized for 40 minutes. Next, styrene 7.
26 kg and 2.81 kg of butadiene were added and polymerized for 40 minutes. Thereafter, an excessive amount of methanol was added to the polymerization solution to terminate the polymerization, the solvent was removed, and the resultant was dried to obtain a target block copolymer.

Tables 1 to 3 also show the physical properties of the injection-molded product of each block copolymer, the minimum temperature at which the film can be stretched during film formation, and the natural shrinkage of the resulting film. The film was prepared by first extruding a sheet having a thickness of 0.2 mm at 210 ° C., and thereafter, using a biaxial stretching device manufactured by Toyo Seiki Seisaku-sho, Ltd., to stretch the film uniaxially four times at 90 ° C. (Thickness: about 50 μm). From the physical properties shown in the table,
It can be seen that the block copolymer of the present invention is excellent in transparency, rigidity, impact resistance, low-temperature stretchability, and natural shrinkage resistance.

The physical properties shown in Tables 1 to 4 were measured by the following methods. (1) Haze: Measured according to ASTM-D-1003 (test piece thickness: 2 mm). (2) Tensile modulus: Measured according to JIS K-6871. (3) Izod impact strength: Measured according to JIS K-6871. (4) Natural shrinkage (%): The stretched film was left at 40 ° C. for 7 days, and was calculated by the following equation. L ₁ : Length before standing (stretching direction) L ₂ : Length after standing (stretching direction)

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043] Examples 5-8 structure of the block copolymer is A-B ₁ -B ₂ (Example 5), A-C-B 1 -C-B 2 ( Example 6), A-C-
B ₁ -B ₂ -A (Example 7) and (A-CB ₁ -B ₂₎
) A block copolymer represented by the general formula of _4- X (Example 8) was produced, and the structural characteristics and physical properties thereof were measured.
It was shown to. In addition, the copolymer of Example 8 is ACB _1-
After completion of the polymerization up to B _2, it was prepared by the addition of 1/4 mole of silicon tetrachloride with respect to n- butyl lithium using to the coupling reaction.

[0044]

[Table 4]

[0045]

The block copolymer of the present invention is excellent in transparency, rigidity, impact resistance, and natural shrinkage resistance. Suitable for heat shrinkable film for labels. Further, since it has excellent low-temperature stretchability, it can be shrunk at a low temperature and short-time at a high temperature, and is suitable for packaging of heat-sensitive fresh food products and plastic molded products. Further, since it has excellent compatibility with other vinyl aromatic hydrocarbon polymers, various molded products can be obtained by blending with other vinyl aromatic hydrocarbon polymers for reinforcement. In addition, injection molding and injection hollow molding are possible, and they can be formed into films / sheets by extrusion molding, inflation molding, or the like, and used for various purposes as they are or by secondary processing such as vacuum pressure molding.

Continuation of front page (56) References JP-A-60-223813 (JP, A) JP-A-58-151218 (JP, A) JP-A-2-49014 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) C08F 293/00-297/08 B29C 61/06 C08J 5/18 CET

Claims (4)

(57) [Claims] 1. A vinyl aromatic hydrocarbon polymer block and a block copolymer having polymer blocks B ₁ and B ₂ comprising a vinyl aromatic hydrocarbon and a conjugated diene, at least one terminal of which is a vinyl aromatic hydrocarbon. A block copolymer, which is a polymer block and satisfies the following (1), (2) and (3). (1) The weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60/40 to 90/10, the number average molecular weight of the block copolymer is 40,000 to 500,000, and (2) the block copolymer contains Of vinyl aromatic hydrocarbon (%) = (W / W0) × 100 = 25
(W is the weight of the vinyl aromatic hydrocarbon block in the block copolymer, and W0 is the total weight of the vinyl aromatic hydrocarbon in the block copolymer.) (3) Vinyl In the polymer blocks B1 and B2 composed of an aromatic hydrocarbon and a conjugated diene, the block B1 is a vinyl block.
Weight ratio of aromatic hydrocarbon to conjugated diene is 81/19
~ 92/8, block B2 is co-existed with vinyl aromatic hydrocarbon
The weight ratio with the role diene is 65/35 to 81/19,
In addition, the relationship of 1.2 ≦ M2 / M1 ≦ 5 is satisfied. (However,
M2 = weight of conjugated diene of polymer block B2 composed of vinyl aromatic hydrocarbon and conjugated diene / weight of vinyl aromatic hydrocarbon of polymer block B2 composed of vinyl aromatic hydrocarbon and conjugated diene, M1 = vinyl aromatic hydrocarbon And the conjugated diene weight of the polymer block B1 composed of
5 shows the weight of the vinyl aromatic hydrocarbon of the polymer block B1 composed of the vinyl aromatic hydrocarbon and the conjugated diene. ) 2. The block copolymer according to claim 1, which has a conjugated diene homopolymer block. 3. The block copolymer according to claim 1, which is obtained by coupling with a polyfunctional coupling agent. 4. A heat-shrinkable film comprising the block copolymer according to claim 1, 2 or 3.