JP2000169666A - Thermoplastic elastomer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition having preferred performance such as excellent rubber elasticity and oil retentivity, low hardness and permanent compression set, and suitable for such uses as a sealing material, a gasket one, a vibration isolating one, an impact absorbing one, a covering one and a cushioning one. SOLUTION: This thermoplastic elastomer composition comprises (A) 100 pts.wt. hydrogenated block copolymer (having >=60,000 number average molecular weight) obtained by hydrogenating a block copolymer having at least one polymer block mainly from a vinyl aromatic compound and at least one polymer block mainly from a conjugated diene compound, (B) 1-3,000 pts.wt. softener for non-aromatic rubber, having >=100 cSt dynamic viscosity at 40 deg.C and (C) 0-50 pts.wt. polyolefin-based resin including polypropylene as a principal ingredient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermoplastic elastomer composition, and more particularly to a thermoplastic elastomer composition having desired properties such as excellent rubber elasticity, good oil retention, low hardness and small compression set. The present invention relates to a thermoplastic elastomer composition having a sealing material, a gasket material, a vibration damping material, a shock absorbing material, a cover material, a cushioning material, and the like.

[0002]

2. Description of the Related Art In recent years, discs on which information such as a CD-ROM is written have been widely used in electronic devices such as computers, and these are mechanically vulnerable to external and internal vibrations. For this reason, an insulator made of synthetic rubber or the like is mounted for the purpose of vibration isolation. Also, the problem of vibration isolation is becoming important for small and lightweight devices, for example, optical disks such as mini disks and DVDs, and small performance microphones for small videos and micro tape recorders. Conventionally, synthetic rubbers such as silicone rubber, general vulcanized rubbers such as butyl rubber, gels, oil dampers and the like have been used as light-weight vibration damping materials such as small microphones and CD-ROMs. Among these, the rubber material has a hardness of about 20 to 30 ° in JIS A hardness, and even if it is the lowest hardness of about 20 °, the resonance frequency is limited to a high frequency, so that it is intended for light-weight equipment. It is difficult to set the frequency to be the vibration isolation region. In order to achieve low-frequency vibration isolation, it is conceivable to use a more flexible material, for example, a gel, but a material with a low hardness is
It is easily deformed by compression, and the anti-vibration property decreases with time,
There was a concern that low molecular weight components in the material would bleed and adversely affect disks and the like that require vibration isolation.

In recent years, electronic devices such as computers have been improved in performance and miniaturization, and have complicated circuit structures. Even small amounts of dust can cause obstacles. Sex is growing. Conventionally, for the purpose of dust prevention, the hard disk itself was housed in a case and sealed with an elastomer, but since the heat generated by the rotation of the hard disk is accumulated inside the case and failure occurs, in recent years it has been aimed at dust protection. Urethane foams are widely used as gasket materials because of their good set properties and simplicity. However, the urethane foam has a hardness of about 50 ° in JIS-A hardness, has a certain tightening force as a dust-proof gasket material, and has an adhesive tape for attaching to a hard disk storage case. Needed the adhesive means. Increasing the tightening force causes sag of the gasket material, resulting in a reduction in dustproofing. For this reason, there has been a demand for a gasket material that can reduce the tightening force and that can form a packing having low hardness and excellent set characteristics. Furthermore, in recent years, the performance of lamps for automobiles and the like has been improved, the weight thereof has been reduced, and the use of complicated mechanical structures and plastic composite materials has been increasing. Therefore, the need for a gasket that can be easily formed with low hardness and that is excellent in dustproofness and waterproofness is increasing.
Conventionally, gaskets using vulcanized rubber and mechanisms that do not require a gasket have been developed for dust prevention and waterproofing.However, gaskets using vulcanized rubber can provide materials with low hardness. Since it is difficult, the fastening force at the time of installing the gasket has to be increased, and as a result, the plastic member constituting the lamp may be greatly distorted or damaged. Further, even if a gasket is made of a vulcanized rubber of low hardness ignoring manufacturing difficulties, it is extremely difficult to install the gasket on a lamp later. Even in a mechanism that does not require a gasket, the design of the lamp is greatly restricted, and the plastic material that can be used is often limited. For this reason,
There has been a demand for a gasket material having low hardness, which can be integrally formed at the time of molding a lamp, and which is excellent in dustproofness and waterproofness.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoplastic elastomer composition suitable for applications such as a vibration damping material and a gasket material under such circumstances.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the object has been achieved by a thermoplastic elastomer composition containing a specific hydrogenated block copolymer. I found out what could be done. The present invention
It was completed based on such knowledge. That is, the present invention provides (a) hydrogenating a block copolymer consisting of at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound by hydrogenation. 100 parts by weight of the obtained hydrogenated block copolymer having a number average molecular weight of 60,000 or more, and (b) a softener for a non-aromatic rubber having a kinematic viscosity at 40 ° C. of 100 cSt or more. An object of the present invention is to provide a thermoplastic elastomer composition comprising 1 to 3000 parts by weight and (c) 0 to 50 parts by weight of a polyolefin resin containing polypropylene as a main component.

[0006]

DETAILED DESCRIPTION OF THE INVENTION In the thermoplastic elastomer composition of the present invention, at least one of a polymer block mainly composed of a vinyl aromatic compound and a polymer block mainly composed of a conjugated diene compound are used as component (a). A hydrogenated block copolymer obtained by hydrogenating a block copolymer consisting of at least one of the above, wherein the number average molecular weight is 600
A hydrogenated block copolymer of not less than 00 is used. Examples of the hydrogenated block copolymer include, for example, a block copolymer of polybutadiene and polystyrene, and a block copolymer of polyisoprene and polystyrene, or a block copolymer of polybutadiene or an ethylene-butadiene random copolymer and polystyrene. Obtained by hydrogenating the copolymer, for example, a diblock copolymer of crystalline polyethylene and polystyrene, a triblock copolymer of styrene-ethylene / butylene-styrene (SEBS),
Styrene-ethylene / propylene-styrene triblock copolymer (SEPS) and the like, among others, styrene-ethylene / butylene-styrene block copolymer and styrene-ethylene / propylene-styrene block copolymer can be exemplified. As the component (a), a block copolymer having at least two polymer blocks mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound (for example, styrene-butadiene- A hydrogenated block copolymer obtained by hydrogenating a styrene block copolymer or a styrene-isoprene-styrene block copolymer is more preferred. Although the number average molecular weight of these hydrogenated block copolymers is 60,000 or more, this number average molecular weight is 600
If it is less than 00, the bleeding of the softener is remarkable, the compression set is large, and there is a disadvantage that the material cannot be used in actual use. Although the upper limit of this number average molecular weight is not particularly limited,
Usually, it is about 400,000.

The content of the amorphous styrene block in the hydrogenated block copolymer is desirably in the range of 10 to 70% by weight, preferably 15 to 60% by weight. The glass transition temperature (Tg) of the amorphous styrene block portion is 6
Those having a temperature of 0 ° C. or higher, preferably 80 ° C. or higher are desirable. As the polymer of the portion connecting the amorphous styrene blocks at both ends, an amorphous polymer is also preferable, and examples thereof include an ethylene-butylene copolymer, a butadiene polymer, and an isoprene polymer. And a block copolymer or a random copolymer thereof. In addition, these hydrogenated block copolymers are mainly used alone, but two or more kinds may be blended and used.

In the thermoplastic elastomer composition of the present invention, in order to reduce the hardness of the thermoplastic elastomer (a), a non-aromatic component having a kinematic viscosity at 40 ° C. of 100 cSt or more at 40 ° C. is used as the component (b). A softening agent for rubber is compounded. The kinematic viscosity at 40 ° C. of this softener is 100 c.
If it is less than St, the composition loses weight and bleeds significantly due to volatilization, which causes inconvenience that the composition cannot withstand actual use. The kinematic viscosity is 40 ° C. from the practical and manufacturing point of view.
Is preferably 100 to 10,000 cSt, and particularly preferably 200 to 5000 cSt. Further, from the viewpoint of the molecular weight, those having a number average molecular weight of less than 20,000, particularly 10,000 or less, especially 5,000 or less are preferred. As such a softening agent, usually, a liquid or liquid at room temperature is suitably used. Further, both hydrophilic and hydrophobic softeners can be used. The softener having such properties can be appropriately selected from various softeners for non-aromatic rubbers such as mineral oils, vegetable oils, and synthetic oils. Here, mineral oils include process oils such as naphthenic and paraffinic oils, and vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, nagiko oil, peanut oil,
Wood wax, pine oil, olive oil, and the like.
Of these, one or more selected from mineral oil-based paraffinic oils, naphthenic oils, and synthetic polyisobutylene-based oils, and those having a number average molecular weight of 450 to 5,000 are preferred.

These softeners may be used alone or as a mixture of two or more as long as they have good compatibility with each other. The compounding amount of these softeners is 1 to 3000 parts by weight, preferably 50 to 1000 parts by weight, particularly preferably 100 to 300 parts by weight based on 100 parts by weight of the component (a). If the amount is less than 1 part by weight, sufficient hardness reduction cannot be achieved, and the flexibility of the thermoplastic elastomer composition may be insufficient. If the amount exceeds 3,000 parts by weight, the softener tends to bleed, In addition, it causes a decrease in mechanical strength of the thermoplastic elastomer composition. In addition, the compounding amount of this softener is
It is preferable to appropriately select from the above range according to the molecular weight of the hydrogenated block copolymer of the component (a) and the type of other components added to the hydrogenated block copolymer.

[0010] In order to improve the processability and heat resistance of the composition,
As the component (c), a polyolefin-based hydrocarbon resin containing polypropylene as a main component can be added. Examples of the resin include isotactic polypropylene, a copolymer of propylene and a small amount of other α-olefin (for example, propylene-ethylene copolymer, propylene / 4-
Methyl-1-pentene copolymer). When a copolymer of isotactic polypropylene is used as the polyolefin resin, its MFR (J
IS K7210) is from 0.1 to 100 g / 10 min, especially from 0.1 to 100 g / 10 min.
Those having a range of 5 to 50 g / 10 minutes can be suitably used.
The amount of the component (c) is from 0 to 50 parts by weight, preferably from 0 to 30 parts by weight, particularly preferably from 5 to 20 parts by weight, per 100 parts by weight of the component (a). If the amount is more than 50 parts by weight, the resulting thermoplastic elastomer composition has too high a hardness, which is not preferable.

In the thermoplastic elastomer composition of the present invention, a polystyrene resin can be used in combination with the component (c) in order to improve the processability and heat resistance of the composition. As the polystyrene resin, any one obtained by a radical polymerization method or an ionic polymerization method can be suitably used as long as it is obtained by a known production method. The number average molecular weight of the polystyrene resin is preferably 5000 to 5
00000, more preferably 10,000 to 200,000
And the molecular weight distribution [weight average molecular weight (M
The ratio (Mw / Mn) of w) to the number average molecular weight (Mn) is preferably 5 or less. Examples of the polystyrene resin include polystyrene, a styrene-butadiene block copolymer having a styrene unit content of 60% by weight or more, rubber-reinforced polystyrene, poly α-methylstyrene, poly p
-T-butylstyrene and the like, and these may be used alone or in combination of two or more. Further, a copolymer obtained by polymerizing a mixture of monomers constituting these polymers can also be used. In the thermoplastic elastomer composition of the present invention, when a polystyrene resin is used in combination with the component (c), the hardness of the obtained composition tends to be higher than when no polystyrene resin is used. Therefore, the hardness of the obtained thermoplastic elastomer composition can be adjusted by selecting these compounding ratios. In this case, the ratio of polyolefin resin / polystyrene resin is preferably selected from the range of 95/5 to 5/95 (weight ratio).

In the thermoplastic elastomer composition of the present invention, the high-molecular-weight organic material constituting the thermoplastic elastomer composition preferably has a three-dimensional continuous network skeleton structure. The average diameter of the skeleton is 50μ
m, preferably 30 μm or less, the average diameter of the cells (mesh) is 500 μm or less, preferably 300 μm or less, and the volume fraction of the high-molecular organic material is [volume of high-molecular organic material / (volume of high-molecular organic material) (Volume + volume of softener)) × 10
When it is defined as 0 (%), the volume fraction of the high molecular weight organic material is preferably 50% or less, particularly preferably 33% or less.

In order to obtain a thermoplastic elastomer composition containing a large amount of a softening agent and a small amount of a high-molecular-weight organic material, the solubility parameter δ of each of the softening agent and the high-molecular-weight organic material used is δ = (ΔE / V ) ^1/2 (ΔE = molar evaporation energy, V = molar volume) difference of 3.0 or less, preferably
It is preferred to select both materials so that they are less than or equal to 2.5. If this difference exceeds 3.0, from the viewpoint of the compatibility of both materials,
It is not preferable because a large amount of the softening agent is not easily retained, which hinders the lowering of the hardness of the obtained thermoplastic elastomer composition and that bleeding of the softening agent easily occurs.

The thermoplastic elastomer composition of the present invention may optionally contain a polyphenylene ether resin for the purpose of improving the compression set of the composition. The polyphenylene ether resin used here is a homopolymer composed of a repeating unit represented by the following general formula or a copolymer containing the repeating unit.

[0015]

Embedded image

(In the formula, R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a halogen atom or a hydrocarbon group.) As the polyphenylene ether resin, known ones can be used. Specifically, poly (2,6-dimethyl-1,4-phenylene ether), poly (2-methyl-6-ethyl-1,4-phenylene ether), poly (2,6-diphenyl-1, 4-phenylene ether), poly (2-methyl-6-phenyl-1,4-phenylene ether), poly (2,6-dichloro-1,4-
Phenylene ether), and 2,6-
Dimethylphenol and monovalent phenols (for example,
2,3,6-trimethylphenol or 2-methyl-6
A polyphenylene ether copolymer such as a copolymer with (butylphenol) can also be used. Above all, poly (2,6-dimethyl-1,4-phenylene ether)
And a copolymer of 2,6-dimethylphenol and 2,3,6-trimethylphenol, and more preferably poly (2,6-dimethyl-1,4-phenylene ether).

The compounding amount of the polyphenylene ether resin is as follows:
10 per 100 parts by weight of the thermoplastic elastomer composition
It can be suitably selected in the range of up to 250 parts by weight.
If the amount exceeds 250 parts by weight, the hardness of the thermoplastic elastomer composition may increase, and if the amount is less than 10 parts by weight, the effect of improving the compression set obtained by compounding is insufficient. Absent. Further, the thermoplastic elastomer composition of the present invention includes clay, diatomaceous earth,
Silica, talc, barium sulfate, calcium carbonate, magnesium carbonate, metal oxides, flaky inorganic additives such as mica, graphite, aluminum hydroxide, various metal powders, wood chips, glass powders, ceramic powders, granular or powdery It is possible to mix granular or powdered solid fillers such as polymers, other various natural or artificial short fibers and long fibers (eg, straw, hair, glass fiber, metal fiber, other various polymer fibers, etc.). it can.

The weight can be reduced by blending a hollow filler, for example, an inorganic hollow filler such as a glass balloon or a silica balloon, or an organic hollow filler made of polyvinylidene fluoride, a polyvinylidene fluoride copolymer or the like. . Further, in order to improve various physical properties such as weight reduction, it is possible to mix various foaming agents, and it is also possible to mechanically mix gas during mixing or the like.

As other additives, if necessary,
Flame retardants, antibacterial agents, hindered amine light stabilizers, ultraviolet absorbers, antioxidants, coloring agents, silicone oils, silicone polymers, cumarone resins, cumarone-indene resins, phenol terpene resins, petroleum hydrocarbons, rosin derivatives, etc. Various adhesive elastomers such as various tackifiers (Tackifire), Rheostomer B (trade name: manufactured by Riken Vinyl), and High Blur (trade name: manufactured by Kuraray Co., Ltd.) A polystyrene block is connected to both ends of a vinyl-polyisoprene block. Block copolymer) or other thermoplastic elastomers or resins such as Norex (trade name: polynorbornene obtained by ring-opening polymerization of norbornene manufactured by Zeon Corporation).

The above silicone polymer desirably has a weight average molecular weight of 10,000 or more, preferably 100,000 or more. The silicone polymer improves the surface tackiness of a molded article using the thermoplastic elastomer composition. As the silicone polymer, a general-purpose thermoplastic polymer such as polyethylene, polypropylene, or polystyrene, which is blended at a high concentration, can be used in order to improve handleability. In particular, the blended product with polypropylene has good workability and physical properties. As such a material, for example, a commercially available silicone concentrate BY27 series general-purpose type commercially available from Toray Dow Corning Silicone Co., Ltd. may be used. Although the surface condition of the molded article can be improved by blending the silicone polymer, the miscibility of the silicone polymer and the copolymer composed of the vinyl aromatic compound block and the conjugated diene-based compound block is not always required. Not good. This can easily be imagined from the fact that the chemical composition of each polymer is significantly different. Therefore, the silicone polymer may be separated depending on the content of the blend and the molding conditions of the molded article. At this time, the condition can be improved by using a graft polymer obtained by chemically bonding a silicone polymer to a polymer having relatively good miscibility with the component (a), for example, a polyolefin resin. As such a material, for example, a material commercially available as a BY27 series graft type from Toray Dow Corning Silicone Co., Ltd. may be used.

The method for producing the thermoplastic elastomer composition of the present invention is not particularly limited, and a known method can be applied. For example, the above-mentioned components and optional additives are melt-blended using a heating kneader, for example, a single-screw extruder, a twin-screw extruder, a roll, a Banbury mixer, a pravender, a kneader, a high-shear mixer, or the like. Kneading, and further, if desired, adding a crosslinking agent such as an organic peroxide, a crosslinking aid, or the like, or by simultaneously mixing these necessary components, and heat-kneading,
It can be easily manufactured. Further, a thermoplastic elastomer composition obtained by kneading a high-molecular organic material and a softening agent is prepared in advance, and this composition is further added to one or more high-molecular organic materials of the same type or different types used here. It can also be manufactured by mixing. Further, in the thermoplastic elastomer composition of the present invention, crosslinking can be performed by adding a crosslinking agent such as an organic peroxide, a crosslinking aid, or the like.

The crosslinking agent that can be added for partial crosslinking is preferably an organic peroxide. Specifically, for example, 2,5-dimethyl-2,5-di (t
-Butylperoxy) -hexane; 2,5-dimethyl-
2,5-di (benzoylperoxy) -hexane; t-
Butylperoxybenzoate; dicumyl peroxide; t-butylcumyl peroxide; diisopropylbenzohydroperoxide; 1,3-bis- (t-
Butylperoxyisopropyl) -benzene; benzoyl peroxide; 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane and the like, and useful crosslinking aids include, for example, Divinylbenzene, trimethylolpropane triacrylate, ethylene dimethacrylate, diallyl phthalate,
Examples include quinone dioxime, phenylene bismaleimide, polyethylene glycol dimethacrylate, and unsaturated silane compounds. These organic peroxides and cross-linking assistants, when the total amount of the blended materials was 100 parts by weight, were 0.1%
The degree of crosslinking can be adjusted arbitrarily in the range of 1 to 5 parts by weight. These organic peroxides and crosslinking assistants may be used in combination of two or more, if necessary. When an unsaturated silane compound is used as a crosslinking aid, crosslinking can be further advanced by contact with moisture in the presence of a silanol condensation catalyst.

The thermoplastic elastomer composition of the present invention comprises:
Since it contains a thermoplastic elastomer such as SEBS or SEPS, two-color molding is possible, and a molded article having a desired shape can be manufactured at low cost. Also, in the case of conventional thermosetting rubber, it was difficult to mold and vulcanize a member having a desired shape with a material having reduced hardness, but this can be achieved by using the thermoplastic elastomer composition of the present invention. Thus, a molded article having moderate elasticity and excellent mechanical properties can be obtained. Further, in the thermoplastic elastomer composition of the present invention, as the oil component used for lowering the hardness of the thermoplastic elastomer such as SEBS or SEPS, a liquid having a polarity greatly different from the solvent such as paraffin oil is used. In addition, these oils are hardly compatible with the styrene block, which is a cohesive domain of thermoplastic elastomers such as SEBS and SEPS, and have little effect on physical properties such as strength of the elastomer.

[0024]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The evaluation of physical properties in the following Examples and Comparative Examples was performed by the following methods. (1) Hardness Based on JIS K6301 (A type). (2) Oil Retentivity A sheet-like sample of 10 mm × 10 mm and a thickness of 2 mm was sandwiched between graph papers, and a load of 1 kg / cm ² was applied to the sample at 60 ° C.
For 24 hours, and oil seepage was observed.
A sample without oil seepage was indicated by “○”, and a sample with oil seepage was indicated by “×”. (3) Compression set Based on JIS K6301. The number average molecular weight of the copolymer was measured by gel permeation chromatography [apparatus: HLC-8020 (manufactured by TOSO), column: GMHXL-L × 2 + G1000HXL + precolumn (manufactured by TOSO), flow rate: 1.0 ml / min. (Solvent: tetrahydrofuran)], and using a differential refractive index (RI) in terms of polystyrene using monodisperse polystyrene as a standard. The measurement of kinematic viscosity is based on JI
The measurement was performed using a B-type viscometer (manufactured by Tokimec Co., Ltd.) in accordance with SK2283.

Examples 1 and 2 and Comparative Examples 1 to 4 Samples of a thermoplastic elastomer composition were prepared by sufficiently kneading the components having the formulations shown in Table 1 and the physical properties were evaluated. As a result, as is clear from Table 1,
In the thermoplastic elastomer compositions of Examples 1 and 2, oil retention was good, but in the thermoplastic elastomer compositions of Comparative Examples 1 to 4, oil bleeding was observed.

[0026]

[Table 1]

Polymer A: SEPS having a number average molecular weight of 100,000 and a styrene content of 30% by weight Polymer B: SEBS having a number average molecular weight of 50,000 and a styrene content of 30% by weight Oil A: A paraffinic oil having a kinematic viscosity at 40 ° C. of 380 cSt. [Manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW380] (number average molecular weight: 750) Oil B: paraffinic oil having a kinematic viscosity at 40 ° C. of 30 cSt [manufactured by Idemitsu Kosan Co., Ltd., trade name: Diana Process Oil PW32] (number average molecular weight 400) Oil C: a paraffinic oil having a kinematic viscosity at 40 ° C. of 1300 cSt [Mitsui Chemicals Co., Ltd., trade name: Lucant HC100] (number average molecule 1450)

[0028]

The thermoplastic elastomer composition of the present invention has excellent rubber elasticity and good oil retention,
It has properties such as low hardness and small compression set, and is suitable for applications such as seal materials, gasket materials, vibration-proof materials, shock-absorbing materials, cover materials, and cushioning materials.

Continued on the front page F term (reference) 4J002 AE05Y BB12X BB14X BB15X BP01W FD02Y GJ02 GL00 GT00

Claims (1)

[Claims] 1. A method comprising hydrogenating a block copolymer comprising (a) at least one polymer block mainly composed of a vinyl aromatic compound and at least one polymer block mainly composed of a conjugated diene compound. 100 parts by weight of a hydrogenated block copolymer having a number average molecular weight of 60,000 or more, and (b) a softener 1 for a non-aromatic rubber having a kinematic viscosity at 40 ° C. of 100 cSt or more. (C) a thermoplastic elastomer composition comprising (c) 0 to 50 parts by weight of a polyolefin resin containing polypropylene as a main component.