JPH06166772A - Thermoplastic elastomer - Google Patents

Abstract

PURPOSE:To provide the subject elastomer excellent in the balance between its compression set and melt viscosity and excellent in its strength such as tensile strength, etc., by adding a specific amount of a plasticizer to a core-shell type latex rubber. CONSTITUTION:(A) Acore-shell type latex rubber and (B) a plasticizer (e.g. di-n-butyl phthalate, di-2-ethylhexyl adipate) are compounded with each other in a ratio of 100 pts.wt., 10-100 pts.wt. to provide the objective elastomer having a compression set of <=70% and a tensile strength of 30kg/cm<2>. The core material of the component A is preferably a material which is produced from a monomer giving a rubbery polymer having a glass transition temperature of -20 deg.C, such as buthyl acrylate or ethyl acrylate and further which is crosslinked with butylene glycol diacrylate. The shell material of the component A is preferably composed of styrene-acrylonitrile copolymer or polystyrene.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic elastomer comprising a core-shell type latex rubber and a plasticizer.

[0002]

2. Description of the Related Art Conventionally, as a method for improving the load-bearing deformation property of an elastomer, that is, the compression set, a polymer having a double bond in the molecule, for example, butadiene rubber (PB), isoprene rubber (PI), styrene-butadiene rubber. (SB
R), acrylonitrile-butadiene rubber (NBR) and the like have been improved by intramolecularly or intermolecularly crosslinking, but the compression set is improved, but the fluidity, that is, the molding processability is significantly impaired. Therefore, MBS (methyl methacrylate-butadiene-) is used as a so-called core-shell type latex rubber in which the surface of a rubber component cross-linked to have fluidity and material strength is coated with a thermoplastic resin.
Resins such as styrene copolymers) are known. Although the fluidity and the material strength are improved, only a material having poor weather resistance is obtained because it contains a monomer component having a double bond in the polymer chain such as butadiene. Also,
Although the material strength is excellent because of the resin component of the surface layer, there are drawbacks such as lack of flexibility as an elastomer.

On the other hand, in recent years, there has been an increasing demand for easy molding processability required for large-scale injection molding, precision injection molding, etc., particularly a decrease in melt viscosity, and further rubber properties such as compression set and creep resistance. Materials having low compression set and low melt viscosity are desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermoplastic elastomer having an excellent balance between compression set and melt viscosity and excellent general material strength represented by tensile strength and the like.

[0005]

In view of the above-mentioned circumstances, the inventors of the present invention have diligently studied a resin composition prepared by blending a core-shell type latex rubber with a plasticizer, and as a result, the present invention has been achieved. It came to completion.

That is, the present invention is a resin composition containing a core-shell type latex rubber and a plasticizer, which is a thermoplastic elastomer having excellent material strength such as balance between compression set and melt viscosity and tensile strength. It is about. The details of the present invention will be described below.

The structure of the core-shell type latex rubber used in the present invention is mainly composed of butyl acrylate.
A core crosslinked with at least one monomer having a double bond with equal reactivity (crosslinkable monomer), for example, an aromatic divinyl monomer such as divinylbenzene or a compound such as butylene glycol diacrylate. This is a core-shell type latex in which the material portion serves as a rubber component, and the shell portion is constituted by a material whose surface is concentric with the rubber component and which is coated with a thermoplastic resin. The rubber elasticity, that is, the compression set, is expressed in the core material portion, and the thermoplasticity, that is, the fluidity, which is contrary to the rubber elasticity, is expressed in the resin portion of the surface layer,
At the same time, the material strength can be exhibited.

The monomer used for the core material constituting the core-shell type latex rubber is preferably a rubber having a glass transition temperature of -20 ° C., and ethyl acrylate, propyl acrylate, butyl acrylate,
Examples thereof include cyclohexyl acrylate and 2-ethylhexyl acrylate. Further, if necessary, by copolymerizing with styrene, vinyltoluene, styrene monomer such as α-methylstyrene, acrylonitrile, methylmethacrylate, methacrylic acid alkyl ester such as butylmethacrylate, etc. It doesn't matter.

As the crosslinkable monomer, a monomer having two or more double bonds having the same reactivity, for example, an aromatic divinyl monomer such as divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate and butylene. Examples thereof include glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, and the like, butylene glycol diacrylate and hexanediol diacrylate are preferable.

A core-shell type latex composed of the above-mentioned raw materials and containing substantially no double bond, and the core material achieves the purpose if it is crosslinked regardless of the degree of crosslinking. .

The core-shell latex can be prepared to have a uniform average particle diameter of the core material and an average thickness of the shell material by carrying out multistage emulsification and seed polymerization. The average particle diameter of the core material portion is 0.05 to 5 μm, and further, it is 0.
It is preferably 15 to 1 μm. The average particle size is 0.
If it is less than 05 μm, it is difficult to develop sufficient rubber elasticity, that is, compression set, and if it is more than 5 μm, the material strength is impaired.

The shell material of the core-shell type latex rubber used in the present invention is preferably a thermoplastic polymer. For example, as a monomer which is a preferable resin for such a shell material, methyl methacrylate, methacrylic acid esters such as ethyl methacrylate, styrene, styrene-based such as α-methylstyrene, acrylonitrile, vinyl chloride, and the like can be mentioned. To be Among these monomers, a copolymer containing at least two kinds of monomers such as a styrene-acrylonitrile copolymer may be used.

The shell material of the core-shell type latex rubber used in the present invention has a thickness of 5 to 50 nm, preferably 10
~ 30 nm. That is, if the shell thickness is less than 5 nm, the composition is excellent in flexibility as rubber, but the entanglement with the polymers constituting the shell material is not sufficient, and the material strength is impaired. It is possible to improve the material strength and compression set by increasing the thickness of the shell material, but if it is made thicker than necessary, the material strength is excellent but the hardness of the composition becomes extremely high and the molded product becomes resin-like and becomes hot. It impairs flexibility as a plastic elastomer. There is a close relationship between shell thickness and entanglement here,
When the shell thickness is the same, the smaller the molecular weight between entanglement points is, the more easily entangled. For example, the shell material used in the present invention is polymethylmethacrylate (molecular weight between entanglement points 9200, (S. Wu.
J. Polym. Sci. Polym. Phys. 19
89, (27), 723)), styrene-acrylonitrile copolymer (11500), polystyrene (18)
700). Therefore, the molecular weight between entanglement points is preferably 25,000 or less, more preferably 20,000 or less.

The use of the plasticizer in the present invention is not limited. Examples of the plasticizer that can be used in the present invention include di-n-butyl phthalate and di-2 phthalate.
-Ethylhexyl (DOP), di-n-octyl phthalate, diisodecyl phthalate, diisooctyl phthalate,
Phthalic acid plasticizers such as octyldecyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl isophthalate, di-2-ethylhexyl adipate (DOA), di-n-decyl adipate, diisodecyl adipate, sebacic acid Dibutyl, di-2-ethylhexyl sebacate and other aliphatic ester plasticizers, trioctyl trimellitate, pyromellitic acid plasticizers such as tridecyl trimellitate, tributyl phosphate, tri-2-ethylhexyl phosphate, phosphoric acid Examples thereof include phosphoric ester plasticizers such as 2-ethylhexyldiphenyl and tricresyl phosphate, epoxy plasticizers such as epoxy soybean oil, and polyester polymer plasticizers, and one or more of these are used. it can.

The amount of the plasticizer added is 10 to 100 parts by weight, preferably 20 to 80 parts by weight, more preferably 30 to 60 parts by weight, based on 100 parts by weight of the core-shell type latex rubber. That is, when the amount is less than 10 parts by weight, the material strength is excellent, but not only the flexibility as a thermoplastic elastomer is impaired, but also the compression set is poor. On the other hand, if the amount exceeds 100 parts by weight, the flexibility and the low viscosity are excellent, but the material strength is remarkably impaired, and the problem of plasticizer bleeding such as stickiness on the surface occurs.

The core-shell latex resin composition according to the present invention comprises a resin having the same chemical composition as that of the shell material, and two or more kinds of monomers containing the same chemical composition, to the extent that the performance thereof is not extremely deteriorated. It is possible to add a required amount of a copolymer resin obtained by copolymerizing a copolymer resin and a copolymer resin obtained by copolymerizing two or more kinds of monomers including a monomer having excellent compatibility with the shell material.

Further, in the core-shell latex resin composition according to the present invention, an inorganic filler represented by calcium carbonate, talc, etc., which is usually added to the resin composition to the extent that the performance is not extremely deteriorated, Flame retardant typified by antimony oxide and zinc borate, barium stearate,
A heat stabilizer such as zinc stearate and various additives such as an antioxidant and an ultraviolet absorber can be added if necessary.

The kneading method of the compound for obtaining the thermoplastic elastomer of the present invention is not particularly limited, and a general kneading method can be used. That is, the core
The mixture of the shell type latex rubber and the plasticizer can be easily kneaded by heating and melting and mixing under a shearing force with a roll kneading machine, a Banbury type kneading machine, a uniaxial or biaxial extruder and the like. Further, the kneaded product can be easily heat-melt molded by using a usual molding method, that is, a press molding machine, an extrusion molding machine, an injection molding machine or the like.

As an index of the moldability of the thermoplastic elastomer of the present invention, for example, the melt viscosity measured by a capillary rheometer can be mentioned. The melt viscosity is 3500 (poise) or less at a shear rate of 10 ³ (sec ^-1 ) in the rheometer, and more preferably 300.
When it is 0 (poise) or less, molding can be easily performed by using a highly productive molding method such as injection molding.

[0020]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 100 parts by weight of core-shell latex (Staffloid 1413 manufactured by Takeda Pharmaceutical Co., Ltd.) was used as a plasticizer for di-2-ethylhexyl phthalate (DOP) (Vinizer 80K manufactured by Kao Corporation). 40 parts by weight of
Melt kneading was performed at 150 ° C. for 15 minutes using an 8-inch roll.

The obtained mixed sample was press-molded and subjected to each material test. The test results are shown in Table 3.

(Evaluation of compression set) A compression set test was carried out in accordance with JIS K6301. (70 ° C., 22 hours) (Evaluation of tensile strength) A test piece was prepared in the following size, and a tensile strength test was performed using a Tonsilon Tensilon. Test piece: L-shaped dumbbell test piece according to ASTM1822 (distance between marked lines: 0.97 mm, width: 3.18 m)
m, thickness: 2 mm) Tensile speed: 50 mm / min (tensile, tear) (Evaluation of melt viscosity) The melt viscosity is measured by Toyo Seiki Seisakusho Capirograph (die: φ = 1.0 mm, L = 60 m).
m) at 180 ° C. Hereinafter, the melt viscosity means a value when the shear rate measured under the above conditions is 1200 (1 / sec). (Evaluation of Weather Resistance) An L-shaped dumbbell test piece conforming to ASTM1822 was held in a carbon arc type sunshine weatherometer (manufactured by Suga Test Instruments Co., Ltd.), and the weather resistance was evaluated by the residual elongation. Indoor temperature: 63 ° C Total exposure time: 500 hours (repeated rain / rain = 112 minutes / 18 minutes repetition) Elongation residual rate = Elongation after exposure / Elongation before exposure If the residual elongation rate is less than 50% x, 50% or more Was regarded as ○.

Examples 2 to 13 Objectives were obtained under the same conditions as in Example 1 except that the core-shell latex used in Example 1 was replaced by the one shown in Table 1 and the compounding composition shown in Table 2 was used. The composition was obtained and a material test was conducted.

[0025]

[Table 1]

[0026]

[Table 2]

Comparative Example 1 MBS (methyl methacrylate-butadiene-styrene copolymer) (MBS68-K5 manufactured by Nippon Synthetic Rubber Co., Ltd.)
100 parts by weight of di-2-ethylhexyl phthalate (DOP) as a plasticizer (Vinizer 8 manufactured by Kao Corporation)
20 parts by weight of 0 K) were mixed and melt-kneaded at 120 ° C. for 5 minutes using an 8-inch roll.

The obtained mixed sample was press-molded and subjected to each material test. The test results are shown in Table 3.

Comparative Example 2 DO to 100 parts by weight of MBS (MBS68-K5)
The same molding and material tests as in Comparative Example 1 were carried out except that P40 parts by weight was compounded. The test results are shown in Table 3.

[0030]

[Table 3]

[0031]

The composite obtained according to the present invention is a thermoplastic elastomer having an excellent balance between compression set and melt viscosity and excellent material strength.

Claims (3)

[Claims] 1. A composition comprising a core-shell type latex rubber and a plasticizer, wherein the composition of the plasticizer is in the range of 10 to 100 parts by weight relative to 100 parts by weight of the core-shell type latex rubber. Is 70% or less and tensile strength is 3
A thermoplastic elastomer having a value of 0 kg / cm ² or more. 2. The thermoplastic elastomer according to claim 1, wherein the core material of the core-shell type latex rubber has an average particle diameter of 0.05 to 5 μm. 3. A core-shell type latex rubber shell material is composed of a thermoplastic polymer, and the shell material has a thickness of 5: 1.
The thermoplastic elastomer according to claim 1 or 2 having a size of -50 nm.