JPH0249049A - Rubber modified styrene-based resin composition having excellent sliding characteristics - Google Patents

Abstract

PURPOSE:To obtain a rubber-modified styrene-based resin having excellent sliding properties, improved dusting phenomena caused by contact wear of long hours and poor appearance in molding by blending a rubber modified styrene-based resin a specific dimethylsilicone oil with a specific polydimethylsiloxane of high degree of polymerization. CONSTITUTION:(A) 100 pts.wt. rubber modified styrene-based resin is blended with (B) 2.2-3.2 pts.wt., preferably 2.5-3 pts.wt. dimethylsilicone oil having 5,000-15,000 centistokes, preferably 10,000-13,000 centistokes viscosity at (25 deg.C) and (C) 0.1-1.5 pt.wt. polydimethylsiloxane of high degree of polymerization having 2X10<5>-8X10<5> number-average molecular weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a rubber-modified styrenic resin composition having excellent sliding properties.

[Conventional technology]

In recent years, technological innovations in the field of home appliances and OAi equipment have been remarkable, and as LSIs become more highly integrated, devices are becoming lighter and smaller. Traditionally, many mechanical parts of such devices have been made of metal, but there is a strong tendency to use plastics, especially for gears, bearings, shakes, etc., to reduce weight.

In such fields, plastics with excellent wear resistance, heat resistance, and creep resistance are required, and currently engineering plastics such as polyacecool and polyester resin are mainly used.

In addition, there is a strong need to reduce weight and size as well as cost reduction, and a shift from engineering plastics to cheaper plastics is progressing.

On the other hand, in response to these industrial needs, there is a known technology to obtain a resin composition with self-lubricating properties by incorporating silicone oil into a styrene resin (for example, "Torre Silico-7J Co., Ltd. [Technical data N
o, FO12J, 1984], and has already been used for several purposes.

[Problem to be solved by the invention]

However, although silicone oil-containing rubber-modified styrene resins obtained by known methods have excellent sliding properties as represented by the coefficient of dynamic friction, they are not suitable for mechanical parts that continuously come into contact with metals and various plastics, such as gears, bearings, and reels. When used, if the contact is continued for a long time, the "flouring phenomenon J" in which the resin is generated as powder due to contact wear is observed on the contact surface.

Such "flour" not only impairs self-lubricating properties but also scatters and adheres, causing various problems such as dropout of recording media.

In order to solve this problem, efforts have been made to apply lubricating oil to the contact portions, but this has not resulted in a fundamental solution and an immediate solution is strongly desired.

[Means to solve the problem]

As a result of intensive research in view of this problem, the present inventors have developed a resin composition in which a rubber-modified styrene resin contains dimethyl silicone oil having a specific viscosity range and highly polymerized polydimethylsiloxane having a specific molecular weight. The inventors have discovered that this problem can be solved by the following methods, and have arrived at the present invention.

That is, in the present invention, 100 parts by weight of a rubber-modified styrene resin is mixed with 2.2 to 3.0 parts of dimethyl silicone oil having a viscosity of 5,000 to 15,000 centistokes at 25°C.
2 parts by weight and a number average molecular weight (Mn) of 2. OXl0S~5
xio' high polymerization degree polydimethylsiloxane 0.1-1
．． This is a rubber-modified styrenic resin composition containing 5 parts by weight and having excellent sliding properties.

The rubber-modified styrenic resin in the present invention is made of a polymer of a rubbery polymer and a styrene monomer.

Examples of styrenic monomers include styrene, side-chain alkyl-substituted styrenes such as α-methylstyrene and α-ethylstyrene, core alkyl-substituted styrenes such as monochlorostyrene, dichlorostyrene, vinyltoluene, and p-methylstyrene; Examples include halogenated styrenes such as bromustyrene and tetrabromostyrene, but styrene and α-methylstyrene are particularly preferred, and at least one of these styrene monomers is used.

Also, if desired, acrylonitrile monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, etc.
Maleimide monomers such as maleimide, N-methylmaleimide, and N-phenylmaleimide, maleic acid monomers such as maleic acid and maleic anhydride, and acrylic acid ester monomers such as methyl acrylate and methyl methacrylate. etc. can also be used in conjunction with the above styrenic monomer.

Examples of the rubbery polymer include polybutadiene, styrene-butadiene copolymer, butadiene-acrylonitrile copolymer, ethylene-propylene-diene copolymer, butadiene-acrylic acid ester copolymer, and the like.

In the present invention, dimethyl silicone oil is used because when dimethyl silicone oil is used, the reduction in the coefficient of dynamic friction is most remarkable. Other modified silicone oils (e.g., phenylmethyl silicone oil, chlorophenyl silicone oil, amino-modified silicone oil, carboxylic acid-modified silicone oil, alcohol-modified silicone oil) have a small effect of reducing the coefficient of dynamic friction, are expensive, and are not practical. do not have.

The content of dimethyl silicone oil is suitably 2.2 to 3.2 parts by weight, most preferably 2.5 to 3.0 parts by weight, per 100 parts by weight of the rubber-modified styrenic resin. If the amount of dimethyl silicone oil is less than 2.2 parts by weight, the development of sliding properties will be insufficient, and if it exceeds 3.2 parts by weight, the dispersion state of the dimethyl silicone oil contained in the rubber-modified styrene resin will deteriorate. It becomes unstable, and dimethyl silicone oil oozes out in the mold during molding and adheres to the mold surface, which is undesirable because it requires wiping at appropriate intervals.

The viscosity of the dimethyl silicone oil is suitably 5,000 to 15,000 centistokes as measured at 25°C. If the viscosity is outside the above range, the dispersion of dimethyl silicone oil in the rubber-modified styrene resin will become unstable, resulting in uneven concentration of dimethyl silicone oil, resulting in a partially high concentration of dimethyl silicone oil. Therefore, appearance defects such as silver and discoloration are likely to occur during molding. The most preferred viscosity of the silicone oil is 10,000 to 13,000 centistokes for the reasons mentioned above.

The molecular weight of the highly polymerized polydimethylsiloxane in the present invention is a number average molecule! (Mn) 2. OX to'〜8
．． OX 10'. This number average molecule it (Mn)
2. If Ox is less than 10', the effect of improving the "powdery flaking" phenomenon, which is one of the objectives of the present invention, will not be sufficient;
If it exceeds ×105, the dispersion of the highly polymerized polydimethylsiloxane becomes unstable, and delamination occurs on the surface of the molded product during molding, which impairs the appearance, which is not preferable.

The content of highly polymerized polydimethylsiloxane is 0.1 to 1.5 parts by weight per 100 parts by weight of the rubber-modified styrene resin.
Parts by weight are appropriate. If the amount added is less than 0.11 parts by weight, the effect of improving the "puffing" phenomenon, which is one of the objectives of the present invention, will not be sufficient, and if it exceeds 1.5 parts by weight, the degree of polymerization will be high. This is not preferable because the dispersion of polydimethylsiloxane becomes unstable and, during molding, layer separation occurs on the surface of the molded product, impairing its appearance.

As a method for producing the rubber-modified styrenic resin composition of the present invention, a rubber-modified styrenic resin, dimethyl silicone oil, and highly polymerized polydimethylsiloxane are melt-blended in a mixer such as a single-screw extruder or a twin-screw extruder. You can do it in any way.

Alternatively, a method may be used in which styrene monomer, dimethyl silicone, and highly polymerized polydimethylsiloxane are mixed during polymerization of the rubber-modified styrenic resin.

Conventional resin additives such as mold release agents such as zinc stearate, antioxidants, pigments, antistatic agents, stabilizers, etc. can be added without departing from the spirit of the present invention.

〔Example〕

Next, the present invention will be specifically explained using Examples and Comparative Examples.

Various tests on the resin composition were conducted by the following methods.

(1) Coefficient of Dynamic Friction A cylinder with an inner diameter of 20 mm, an outer diameter of 26 mm, and a height of 10 mm, with a flange of diameter 40111+1 and thickness of 4 nm+m at the bottom, was injection molded and tested using a thrust wear tester at a sliding speed of 1.2 m/h. win, under the condition of 1.2 kg of load, the upper surface of the molded product and the polystyrene resin “TOBOLEX 860-
01 J (manufactured by Mitsui Toatsu Chemical Co., Ltd.) and the dynamic friction coefficient was measured.

(2) Sliding speed of 1.2 m/min using powder dust thrust wear tester
The sample was rotated for 12 hours under the same conditions as the measurement of the dynamic friction coefficient under the conditions of a load of 1 and 2 kg, and the amount of wear against the polystyrene resin "TOBOLEX 860-01 J" was expressed as the amount of dusting [Channel 3].

(3) Silicone oil adhering to the mold surface 120 cylinder
Using a 150 mm x 12 decoration x 1-thick box mold, molding was repeated 1000 shots at a molding temperature of 220°C. After wiping off the silicone oil adhering to the mold surface, measurements were taken using fluorescent X-rays to determine the molding requirements. It is expressed as the resin amount ratio (pps).

(4) Silver discoloration of the molded product Using the above mold, molding was repeated 1000 shots at a molding temperature of 220°C, and the appearance of the molded product was observed with the naked eye.
It is expressed as the number of molded product shots in which discoloration occurred.

(5) Layer peeling Using the mold described above, molding was repeated 100 times at a molding temperature of 220"C, and the appearance of the molded product was observed with the naked eye. If the highly polymerized polydimethylsiloxane came out in a striped pattern, the layer was peeled off. Peeling was expressed as the incidence rate (%) of laminar peeling.

Example 1 Rubber modified styrenic resin TOBOLEX 860-01 (
(manufactured by Mitsui Toatsu Chemical) 12500 at 25°C to 100 parts by weight
Dimethyl silicone oil with a centistoke viscosity (Toray Silicone rslI-200, 1250)
2.7 parts by weight of 0 [cstl) and a number average molecular weight of 5
0.5 parts by weight of highly polymerized polydimethylsiloxane (BY-16-140 manufactured by Toray Silicone) were blended, melt-mixed using a twin-screw extruder (rAS-30J manufactured by Nakagama), and formed into pellets to be used as samples. did.

The sample was measured for the coefficient of dynamic friction, amount of dusting, amount of silicone oil adhering to the mold surface, silver discoloration of the molded product, and delamination of the molded product using the method described above, and the results are shown in Table 1.

Examples 2 to 9 and Comparative Examples 1 to 8 The content and viscosity of dimethyl silicone oil and the content and number average molecular weight of highly polymerized polydimethylsiloxane were
A lintel composition was obtained and evaluated in the same manner as in Example 1, except for the changes as shown. However, the following dimethyl silicone oils were used for each viscosity.

10,000 centistokes Torre silicone 5H
-20010000 [csL] 3000 centistokes Toray Silicone 5H-
2003000 [cst1 20000 centistokes Torre silicone 5H-
20030000cst and Toray Silicone 5H-20012500cst were mixed at a ratio of 55:45 (weight ratio).

In addition, highly polymerized polydimethylsiloxane was manufactured using Toray Silicone's BY-14-160, which has a number average molecular weight of 500,000 and a dispersion ratio (Mw/Mn) of 2.0, using GPC (gel permeation chromatography). The obtained high polymerization degree polydimethylsiloxanes having different number average molecular weights were used.

The evaluation results are summarized in Table 1.

Comparative Examples 9 to 11 In Comparative Example 9, Toray Silicone 5H-701 was used. In Comparative Example 10, Resilico-7BX-16-860 was used. Comparative Example 1
In the case of Example 1, a resin composition was obtained and evaluated in the same manner as in Example 1 except that Toray Silicone 5F-8418 was used. The results are shown in Table 1.

Comparative Example 12 This is an example of the rubber-modified polystyrene used in Example 1, and is an example that does not contain silicone oil and highly polymerized polydimethylsiloxane.

(Effects of the Invention) As is clear from the results shown in Table 1, the resin composition of the present invention has excellent sliding properties, and is free from the "flouring" phenomenon caused by long-term contact wear and appearance during molding. This solves the defect.

Claims (1)

[Claims] (1) Add 100 parts by weight of rubber-modified styrene resin at 25°C.
2.2 to 3.2 parts by weight of dimethyl silicone oil with a viscosity of 5,000 to 15,000 centistokes, and a number average molecular weight (Mn) of 2.0 x 10^5 to 8.0.
×10^5 high polymerization degree polydimethylsiloxane 0.1~
A rubber-modified styrenic resin composition containing 1.5 parts by weight and having excellent sliding properties.