JP2001064474A - Thermoplastic resin composition having high specific gravity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoplastic resin composition having high specific gravity, comparable to lead and excellent in flexibility and processability. SOLUTION: This thermoplastic resin composition having high specific gravity is obtained by including (A) a thermoplastic elastomer of polystyrene- polyisobutylene block copolymer or a mixture of the copolymer with the hydrogenated compound thereof and (B) tungsten powder as a material having high specific gravity and is characterized in that the containing ratio of the thermoplastic elastomer A is 2.5-7.5 wt.% per whole composition and the containing ratio of tungsten powder B is 92.5-97.5 wt.% per whole composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition suitable for use as a lead substitute, and more particularly, to a resin suitable for use requiring high specific gravity and flexibility, such as a balance weight. Composition.

[0002]

2. Description of the Related Art It is desired that a balance weight mounted on a wheel for adjusting a wheel balance of an automobile or the like be as small as possible so as not to impair the appearance of the wheel. It is also desired that it be easily deformed to fit. Therefore, conventionally, the material for forming the balance weight has a high specific gravity,
In addition, lead, which is a metal material having flexibility, has been used.

[0003] However, lead is toxic, and lead that has entered the human body through the skin is difficult to be excreted by being deposited on bones and is accumulated in the body. Therefore, there is no possibility of lead poisoning. Absent. Therefore, in applications where high specific gravity and flexibility are required, such as balance weights,
There is a demand for a material having high specific gravity and having flexibility in place of lead.

[0004]

Heretofore, there has been proposed a thermoplastic resin composition in which tungsten, which is a metal having a high specific gravity, is dispersed in a thermoplastic resin as a lead substitute substance. As such a lead substitute substance, a substance in which a tungsten powder pretreated with a predetermined lubricant is contained in a polyamide resin such as nylon-6 (Japanese Patent Laid-Open No. 60-244888), and a tungsten powder is prepared by using polytetramethylene terephthalate A mixture of a main polymer powder and a specific acrylic rubber-containing graft copolymer (JP-A-2-38448), or a tungsten powder containing nylon, polybutylene terephthalate, polypropylene, ABS Resins and thermoplastic resins such as hard vinyl chloride (Japanese Patent Application Laid-Open No. 2-191476) have been proposed.

Japanese Patent Application Laid-Open No. 7-33905 discloses that a tungsten powder having an average particle diameter of 1 to 30 μm is contained in a thermoplastic resin such as a polyolefin resin, a polyamide resin, a polycarbonate resin, or a PBT resin. A composition for a balance weight is disclosed. The thermoplastic resins disclosed in the above publications have recently been used in recent years because of their ease of processing as compared to metal materials, their excellent corrosion resistance, their relatively low cost, their good insulating properties, and the like.・ It is used in a wide range of fields such as electronic parts, mechanical parts, precision parts, and general industrial parts. In addition, thermoplastic resin is processed in comparison with metal materials that require cutting and sintering processes. In particular, when the injection molding method is employed, there is an advantage that a molded article having a complicated shape can be molded in one step.

[0006] However, the thermoplastic resin compositions disclosed in the above-mentioned publications all achieve high specific gravity comparable to lead and have excellent mechanical strength and impact resistance, but are generally used at room temperature. There was a problem that it was hard and poor in flexibility. In particular, in the thermoplastic resin composition disclosed in JP-A-2-38448, the property of having excellent rigidity, which is opposite to flexibility, is disclosed as an effect of the invention. Therefore, at present, there is no material with high specific gravity and moderate flexibility like lead, and for applications requiring high specific gravity and excellent flexibility, only a material that can use only lead is used. there were.

Accordingly, an object of the present invention is to provide a thermoplastic resin composition having a high specific gravity comparable to lead and having extremely excellent flexibility and processability.

[0008]

Means for Solving the Problems and Effects of the Invention The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, as a resin for dispersing tungsten powder, the above-mentioned thermoplastic resin which has been conventionally used has been used. When a specific thermoplastic elastomer is used in place of the resin, it exhibits excellent flexibility even when the content of the tungsten powder is large, and has a high specific gravity comparable to lead, and excellent workability. ,
In addition, they have found a new fact that a thermoplastic resin composition having excellent heat resistance, aging resistance and weather resistance and suitable for outdoor use can be obtained, and the present invention has been completed.

That is, the high specific gravity thermoplastic resin composition according to the present invention comprises, as a thermoplastic elastomer, (1) a polystyrene-polyisobutylene block copolymer or
(2) a hydrogenated product of a polystyrene-polyisoprene block copolymer, a hydrogenated product of a polystyrene-polybutadiene block copolymer, and a hydrogenated product of a polystyrene-polyisoprene block copolymer having a butadiene unit in the isoprene unit. A mixture of at least one hydrogenated product selected from the group and the polystyrene-polyisobutylene block copolymer, and a tungsten powder as a high specific gravity material, wherein the content of the thermoplastic elastomer is 2. 5 to 7.5% by weight, and the content of the tungsten powder is 92.5 to 97.5% by weight.

The thermoplastic elastomer used in the high specific gravity thermoplastic resin composition according to the present invention includes a rubber component (soft segment) having elasticity in a molecule and a molecule for preventing plastic deformation at around normal temperature. A polymer material that has both a constraining component (hard segment) and the molecular motion of the soft segment is locally constrained by the hard segment. At room temperature, it acts as a rubber elastic body. It shows plastic deformation as it rises.
That is, such a thermoplastic elastomer retains its shape at room temperature, has excellent flexibility to be easily deformed, and can be molded at a high temperature because it is plasticized.

Therefore, according to the high specific gravity thermoplastic resin composition of the present invention using the above thermoplastic elastomer, even when the content of tungsten powder is increased in order to obtain a high specific gravity comparable to lead. Demonstrate excellent flexibility. In addition, since plasticization is performed at a high temperature, it can be applied to injection molding and the like, and has excellent workability. Further, among the thermoplastic elastomers, polystyrene-
The polyisobutylene block copolymer has no double bond in the molecule, and all of the other thermoplastic elastomers are hydrogenated and contain a double bond in the molecule. Since the amount is extremely low, it is excellent in heat resistance, aging resistance and weather resistance, and is suitable as a material of a balance weight mainly used outdoors.

[0012]

Next, the high specific gravity thermoplastic resin composition according to the present invention will be described in detail. (Thermoplastic elastomer) In the high specific gravity thermoplastic resin composition of the present invention, as described above, the thermoplastic elastomer contains (1) a polystyrene-polyisobutylene block copolymer alone, or (2) a polystyrene-polystyrene. Hydrogenated product of isoprene block copolymer, hydrogenated product of polystyrene-polybutadiene block copolymer and polystyrene-
A mixture of the polystyrene-polyisobutylene block copolymer and at least one hydrogenated product selected from the group consisting of hydrogenated products, which contains a butadiene unit in the isoprene unit of the polyisoprene block copolymer, is used.

The polystyrene-polyisobutylene block copolymer described in the above (1) or (2) is a styrene thermoplastic elastomer having a hard segment of polystyrene and a soft segment of polyisobutylene and having no double bond in the molecule. Specific examples thereof include polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS). The hydrogenated product of the polystyrene-polyisoprene block copolymer described in (2) above is a styrene-based thermoplastic elastomer of polyisoprene in which the hard segment is polystyrene and the soft segment is hydrogenated (hydrogenated), Specific examples include polystyrene-poly (ethylene-propylene) -polystyrene triblock copolymer (SEPS), which is a hydrogenated product of polystyrene-polyisoprene-polystyrene triblock copolymer (SIS).

The hydrogenated product of the polystyrene-polybutadiene block copolymer described in (2) above is a styrene-based thermoplastic elastomer in which the hard segment is polystyrene and the soft segment is hydrogenated, and specific examples thereof include: Is a polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer (SEBS), which is a hydrogenated product of polystyrene-polybutadiene-polystyrene triblock copolymer (SBS).
And the like.

The hydrogenated product of the polystyrene-polyisoprene block copolymer described in (2) above, which contains a butadiene unit in the isoprene unit, is obtained by modifying the isoprene unit of the polystyrene-polyisoprene block copolymer. Examples thereof include those in which the isoprene unit is composed of isoprene and butadiene, and those in which a part of the isoprene unit is replaced with a butadiene unit. In all of the hydrogenated block copolymers (3 types) exemplified in the above (2), most (preferably 95% or more) of the double bonds in the molecule are hydrogenated (hydrogenated). Preferably, it is in this way,
By hydrogenating most of the double bonds, a high specific gravity thermoplastic resin composition having excellent heat resistance, aging resistance and weather resistance can be obtained as described later.

The above-mentioned thermoplastic elastomer is SI
A polystyrene-polyisobutylene block copolymer such as BS having no double bond in the molecule;
Other thermoplastic elastomers exemplified in (2) are also excellent because most of the double bonds in the molecule are hydrogenated, and none of them cause a hydrolysis reaction or the like. Heat resistance, aging resistance and weather resistance. Accordingly, the high specific gravity thermoplastic resin composition according to the present invention is used, for example, as a balance weight, mainly in a state of being exposed to the outdoors, or as a wheel of an automobile, etc.
It can be suitably used even when used in an environment where the temperature rises to about 100 ° C.

The physical properties of the above-mentioned thermoplastic elastomer generally vary depending on the content of styrene or the molecular weight and molecular weight distribution of isobutylene, isoprene and butadiene constituting the soft segment. For example, as the styrene content increases, the material becomes harder and loses its flexibility, and as the styrene content decreases, the tackiness increases, making it difficult to produce a thermoplastic resin composition. Also, the strength increases as the molecular weight of isobutylene, isoprene and butadiene constituting the soft segment increases, and the moldability decreases as the molecular weight distribution becomes sharper. In particular, if the molecular weight of the soft segment such as isobutylene or isoprene is large and the molecular weight distribution is sharp, molding becomes extremely difficult.

The styrene content of the above-mentioned exemplified thermoplastic elastomer is generally about 10 to 65%, but in order to impart sufficient flexibility to the high specific gravity thermoplastic resin composition, 13-30 styrene content
%, Preferably about 13 to 20%.
In the present invention, in addition to the above-mentioned thermoplastic elastomers, in addition to the above-mentioned examples, as long as the heat resistance, flexibility, and weather resistance are not insufficient, and within a range that does not change the gist of the present invention. Various known thermoplastic elastomers can be used in combination.

Examples of such thermoplastic elastomers include olefinic thermoplastic elastomers in which the hard segment is polyethylene or polypropylene, the soft segment is ethylene-propylene-diene copolymer (EPDM) or butyl rubber; the hard segment is polyester, and the soft segment is Polyester or aliphatic polyester polyester thermoplastic elastomer; Hard segment is urethane structure, Soft segment is polyether or polyester urethane thermoplastic elastomer; Hard segment is polyamide, Soft segment is polyether or polyester And other thermoplastic elastomers.

A 1,2-polybutadiene-based thermoplastic elastomer in which the hard segment is syndiotactic 1,2-polybutadiene and the soft segment is amorphous polybutadiene;
Polyisoprene, a trans 1,4-polyisoprene-based thermoplastic elastomer whose soft segment is amorphous polyisoprene; an ionomer whose hard segment is a metal carboxylate ion cluster and whose soft segment is amorphous polyethylene; PE / EEA, EVA-based thermoplastic elastomer whose soft segment is ethylene-ethyl acrylate copolymer or ethylene-vinyl acetate copolymer; fluorinated thermoplastic elastomer whose hard segment is fluorinated resin and whose soft segment is fluorinated rubber It is also possible to use them in combination.

Regarding the moldability of the thermoplastic elastomer, the MFR under the condition of 230 ° C. and 2.16 kg was 0.0
5 g / 10 min or more, preferably 0.5 g / 10 min or more,
More preferably, it is 1 g / 10 minutes or more. This is because the blendability of the tungsten powder lowers the moldability as compared with the case where the thermoplastic elastomer is used alone. Further, the thermoplastic elastomer used in the present invention may be in the form of pellets or powder.

The styrene-based thermoplastic elastomer is prepared by using a monofunctional initiator such as alkyl lithium.
A method in which living polymerization is performed in the order of styrene-isoprene-styrene, styrene-butadiene-styrene, a block copolymer is produced (three-step polymerization using a monofunctional initiator), and then hydrogenation is performed, or a similar initiator is used. Similarly, after the living polymerization is carried out, the block copolymer is produced by coupling with an alkyl dihalide (two-step polymerization coupling method) and then hydrogenated.

[Tungsten powder] Tungsten used in the present invention is preferably in a powder form since it is necessary to uniformly blend it with a thermoplastic elastomer.
The particle size is preferably 300 μm or less, more preferably 2 to 100 μm, still more preferably 3 to 30 μm, especially 3 to 27 μm. When the particle size of the tungsten powder increases, when molding by using the injection molding method,
It becomes difficult for the thermoplastic resin composition to pass through the metal gate, and the moldability decreases. Conversely, when the particle size becomes extremely small, the surface area of the tungsten powder increases, and the surface of the tungsten powder cannot be completely covered with a predetermined thermoplastic elastomer.

It is preferable to use a combination of a small particle size and a large particle size because the flowability of the resin composition is improved and the moldability is improved. Therefore, it is preferable to use a mixture of two or more tungsten powders having different particle diameters. For example, it is preferable to use a mixture of 5 μm or less and 27 μm or more. Further, the tungsten powder used in the present invention is preferably subjected to a coupling treatment in order to enhance the affinity with the resin. Examples of the coupling agent include titanate-based, aluminum-based, and silane-based agents. In the present invention, the use of a silane-based coupling agent is optimal from the viewpoint of increasing the affinity with the resin.

[Composition of High Specific Gravity Thermoplastic Resin Composition] In the high specific gravity thermoplastic resin composition of the present invention, the thermoplastic elastomer content is 2.5 to 7.5% by weight, and the tungsten powder content is 92%. 0.5 to 97.5% by weight. If the content of the thermoplastic elastomer is below the above range, molding of the thermoplastic resin composition becomes impossible. Further, even if it can be molded, it is not suitable for practical use due to extremely low moldability.

The lower limit of the content of the thermoplastic elastomer is preferably 2.6% by weight in the above range in order to ensure sufficient moldability (workability) of the thermoplastic resin composition and flexibility of the resin portion. , And more preferably 2.8% by weight. In addition, the upper limit of the content ratio of the thermoplastic elastomer is particularly preferably 5.0% by weight, and more preferably 4.5% by weight in the above range, in order to further increase the content of the tungsten powder. More preferred.

In order to provide the thermoplastic resin composition with such flexibility that it can be easily bent by hand, the content of the thermoplastic elastomer should be not less than 3.0% by weight, preferably 4.0% by weight. What is necessary is just to adjust so that it may become above. On the other hand, when the content ratio of the tungsten powder is less than the above range, the specific gravity of the thermoplastic resin composition cannot be increased, and the specific gravity of the balance weight itself also decreases, so the balance weight may not be suitable for practical use. .

The lower limit of the content ratio of the tungsten powder is set to maintain the specific gravity of the thermoplastic resin composition at a high value.
Among the above ranges, the content is particularly preferably 95.0% by weight, and more preferably 95.5% by weight. Further, the upper limit of the content ratio of the tungsten powder is preferably 97.4% by weight in the above range, in order to secure the necessary minimum content ratio of the thermoplastic elastomer, and 9% by weight.
More preferably, the content is 7.2% by weight.

In the high specific gravity thermoplastic resin composition according to the present invention, if the content ratio of the thermoplastic elastomer and tungsten powder is within the range satisfying the above range, for example, rubber, antioxidant, etc. , Heat stabilizers, ultraviolet absorbers, antistatic agents, crystallization accelerators, coupling agents,
An aggregate, an additive impregnating liquid, a pigment, a dye, a softener, an antioxidant, a crosslinking agent, and the like can be added. However, the above (1)
Polystyrene-polyisobutylene block copolymer, or a hydride of the block copolymer described in (2) above,
As described above, all have no or only a few double bonds in the molecule, and thus are excellent in aging resistance and weather resistance. Therefore, there is basically no need to add an antioxidant, a heat stabilizer, an ultraviolet absorber, an antioxidant, and the like.

The cross-linking agent is used to cross-link the thermoplastic elastomer as necessary, and strengthens the bond between the thermoplastic elastomers, and is more resistant to rubbing and breaking than the uncross-linked one. Work to enhance
Such crosslinking agents include, for example, 2,5-dimethyl-2,
5-t-butylperoxyl-hexyne-3,2,5-
Dimethyl-2,5-di-t-butylperoxyhexane, di (t-butylperoxy) -m-diisopropylbenzene, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, t −
Organic peroxides such as butylperoxycumene are exemplified.

When the high specific gravity thermoplastic resin composition of the present invention is applied to injection molding, a metal salt of a higher carboxylic acid such as zinc stearate is used to improve the releasability in an injection molding machine. It is preferable to mix it as a lubricant. The amount of the lubricant is 0.1 to the high specific gravity thermoplastic resin composition.
It is preferable to set to about 5 parts by weight. [Physical Properties of High Specific Gravity Thermoplastic Resin Composition] (Surface Hardness) The high specific gravity thermoplastic resin composition of the present invention has a J
The durometer hardness HDD of the surface measured by the method specified in IS K 7215 (testing machine type D) is preferably 80 or less, more preferably 60 or less.

If the durometer hardness exceeds 80, sufficient flexibility cannot be obtained, and the high specific gravity thermoplastic resin composition may not be suitable for producing balance weights and the like. The upper limit of the durometer hardness HDD is particularly preferably 50 and more preferably 40 in the above range. In order to adjust the surface hardness of the thermoplastic resin composition to the above range, the content of the thermoplastic elastomer and the tungsten powder is generally set within the above range, although it slightly varies depending on the type of the thermoplastic elastomer used. I just need.

(Specific Gravity) The specific gravity of the thermoplastic resin composition is preferably 8 in order to make the specific gravity of the weight balance sufficient.
It is preferable that this is the case. Among them, it is more preferably 9 or more, and further preferably 10 or more. In order to adjust the specific gravity of the thermoplastic resin composition to the above range, for example, when SIBS (styrene content 30%) having a specific gravity of 0.95 is used alone as the thermoplastic elastomer, the content ratio of the tungsten powder is 92%. It may be adjusted so as to be 0.7% by weight or more (specific gravity 8), 94.1% by weight or more (specific gravity 9), or 95.2% by weight or more (specific gravity 10).

[Preparation method of high specific gravity thermoplastic resin composition]
The method for preparing the high specific gravity thermoplastic resin composition according to the present invention is not particularly limited. For example, a method of melt-kneading the thermoplastic elastomer and tungsten powder using a single-screw or twin-screw extruder, and the like. Various conventionally known methods can be employed. The method of molding the high specific gravity thermoplastic resin composition is not particularly limited, and various known methods such as an injection molding method and a compression molding method can be employed.

As described above, the high specific gravity thermoplastic resin composition according to the present invention can employ various molding methods such as injection molding and compression molding, and is extremely excellent in moldability and workability. I have. Furthermore, the high specific gravity thermoplastic resin composition of the present invention has an advantage that the used composition can be recycled by melting and molding. (Usage field of high specific gravity thermoplastic resin composition) As described above, the high specific gravity thermoplastic resin composition of the present invention is easy to mold, and has a thermoplastic elastomer having flexibility at room temperature and a high specific gravity tungsten powder. Because of the blending configuration, it has a high specific gravity equal to or higher than that of lead, while still maintaining appropriate flexibility.
In particular, it can be used as a substitute for a toxic lead balance weight, and can be used for various uses such as various sports equipment, electric / electronic parts, and mechanical parts.

[0036]

(Silane coupling treatment of tungsten powder)

Reference Example As a silane coupling agent, γ- (2-aminoethyl) aminopropyltrimethoxysilane [SH602
0, manufactured by Dow Corning Toray Silicone Co., Ltd.].

While stirring the tungsten powder in a mixing tank with a high-speed stirring blade (super mixer), 0.3% by weight of the silane coupling agent was dropped, and the temperature in the tank was set to 120%.
Stirring was continued until the temperature reached ℃. Then, it cooled and was used for the following Examples and Comparative Examples as a silane coupling-processed tungsten powder. [Production of high specific gravity thermoplastic resin composition] Example 1 Polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS, styrene content 17% by weight,
(Number average molecular weight Mn = 106000) and the tungsten powder obtained in the above reference example and previously treated with a silane coupling agent, 4.5% by weight: 95.0%.
It was mixed so as to be 5% by weight. Next, this was preliminarily mixed in a mixing tank with a high-speed stirring blade (super mixer), and then melt-kneaded with an extruder to obtain pellets. further,
After heating and drying the pellets, a length of 10
A molded product having a thickness of 0 mm, a width of 25 mm, and a thickness of 2.0 mm was obtained.

The temperature of the injection molding machine was 240 ° C., and the mold temperature was 60 ° C. The density of the molded article thus obtained is 10.
At 3 g / cm ³ , it had flexibility enough to be easily bent by human power at room temperature. In addition, JIS K 7215
According to the provisions of "Durometer hardness test method for plastics", the surface hardness HDD measured by a type D durometer was 22. Example 2 A molded product was obtained in the same manner as in Example 1 except that the mixing ratio of the above-mentioned SIBS and tungsten powder was 3% by weight: 97% by weight.

The density of the molded product was 12.2 g / cm ³ , which was harder than the molded product of Example 1, but still had sufficient flexibility. The surface hardness measured by a type D durometer was 30. Comparative Example 1 A molded product was prepared in the same manner as in Example 1 except that the mixing ratio of the above-mentioned SIBS and tungsten powder was set to 2% by weight: 98% by weight. Was excessive and pellets could not be obtained.

Comparative Example 2 Nylon-6 was used in place of the above SIBS, and the mixing ratio of this nylon-6 to tungsten powder was 5.7.
% By weight: 94.3% by weight, and the temperature of the injection molding machine was 26%.
A molded product was obtained in the same manner as in Example 1 except that the temperature was changed to 0 ° C. The density of the molded product was 10.1 g / cm ³ , and the hardness of the surface measured with a type D durometer was 90, which was not easy to bend with bare hands.

Claims (3)

[Claims] 1. A polystyrene-polyisobutylene block copolymer as a thermoplastic elastomer, or
(2) a hydrogenated product of a polystyrene-polyisoprene block copolymer, a hydrogenated product of a polystyrene-polybutadiene block copolymer, and a hydrogenated product of a polystyrene-polyisoprene block copolymer having a butadiene unit in the isoprene unit. A mixture of at least one hydrogenated product selected from the group and the polystyrene-polyisobutylene block copolymer; and a tungsten powder as a material having a high specific gravity, wherein the content of the thermoplastic elastomer is 2. 5-
A high specific gravity thermoplastic resin composition which is 7.5% by weight and the content of the tungsten powder is 92.5 to 97.5% by weight of the whole. 2. The high specific gravity thermoplastic resin composition according to claim 1, wherein the thermoplastic elastomer has a styrene content of 13 to 30% by weight. 3. The high specific gravity thermoplastic resin composition according to claim 1, wherein the surface has a durometer hardness of 80 or less.