JPH0368060B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improved rubber-modified styrenic resin compositions, and more particularly, the present invention relates to improved rubber-modified styrenic resin compositions, and more particularly, to rubber-modified styrenic resin compositions in which specific rubber-like substances are dispersed within specific particle size ranges. The present invention relates to a resin composition containing siloxane and having excellent wear resistance and surface activity. Although styrene polymers are one of the thermoplastic resins that have a wide range of uses, their major drawback is that they have poor impact resistance. Therefore, in order to eliminate or improve these drawbacks, attempts have been made to polymerize monovinyl aromatic compounds such as styrene in the presence of rubber-like substances that do not substantially contain crosslinks, thereby achieving high impact strength. It has been known for a long time that styrenic resins reinforced with rubber-like substances can be obtained, and the rubber-reinforced (rubber-modified) styrenic resins obtained in this way have high impact strength. It has come to be widely used in various electrical equipment housings, toys, daily necessities, food containers, lactic acid drink containers, etc. By the way, in recent years there has been remarkable technological innovation in the field of light electrical equipment, including audio and video-related equipment as well as office automation-related equipment. There has been a noticeable trend toward using plastics for bodies, gears, bearings, etc., and in these fields molded products have excellent surface smoothness (surface slipperiness), wear resistance, and impact resistance. At the same time, there is a need for plastics that have cost advantages, and the emergence of such types of plastics is eagerly awaited. On the other hand, it is generally known that surface lubricity can be imparted by adding polyorganosiloxane to the styrene-based resin mentioned above. The reality is that when used as a reel or pivot, there is a limit to its wear-resistant effect and it cannot withstand long-term use, so its uses are limited. As a result of intensive studies to meet various demands under these current circumstances, the present inventors have developed a specific rubber-like material containing 80% by weight or more of high-cis polybutadiene with a content of cis-1,4 bonds of 90% or more by mole. into a rubber-modified monovinyl aromatic compound polymer (hereinafter also referred to as rubber-modified styrenic resin) obtained by dispersing it to a specific average particle size of 1 to 2.5 μm using The present invention was completed by discovering that by blending a specific polyorganosiloxane, a resin composition with dramatically improved target abrasion resistance and surface smoothness can be obtained. That is, the present invention is a rubber-modified styrene obtained by polymerizing a mixture in which 15 to 3% by weight of a rubber-like substance is dissolved in 85 to 97% by weight of a monovinyl aromatic compound (hereinafter also referred to as a styrene monomer). In the resin composition, 80% or more of the rubber-like substance is comprised of high-cis polybutadiene with a content of cis-1,4 bonds of 90 mol% or more, and the average particle size is 1 to 2.5 μm. The use of a specific rubber-like substance and 100 parts by weight of the rubber-modified styrenic resin composition at 25°C.
General formula with a viscosity of 100 to 30,000 centistokes [However, R in the formula represents an alkyl group, a haloalkyl group, an aryl group, or a haloaryl group, R′ and R″ represent a phenyl group or a C ₁ to _{C 6} alkyl group, and m represents the polyorganosiloxane. It is a natural number representing the polysiloxane unit that should be maintained in a liquid state at room temperature. The object of the present invention is to provide a rubber-modified styrenic resin composition with excellent abrasion resistance and surface smoothness.Styrene is preferred as the above-mentioned styrene monomer, but in addition, α
Representative examples include alkylated styrenes such as -methylstyrene or p-methylstyrene, nuclear halogenated styrenes such as 2,4,6-tribromo- or -trichlorostyrene, or various mixtures thereof; is a part of the above styrenic monomer, usually up to about 30% by weight of the styrenic monomer, preferably with other copolymerizable monomers such as methyl methacrylate, (meth)acrylonitrile or vinyl acetate.
It may be used in substitution form up to 10% by weight. Next, in the present invention, at least 80% by weight
As mentioned above, it is necessary to use a specific rubber-like material such as high-cis polybutadiene containing 90 mol% or more of cis-1,4 bonds in order to improve the desired wear resistance. The ratio of the styrene monomer and the rubber-like substance used is such that the rubber-like substance accounts for 3 to 15% by weight, preferably 5 to 12% by weight of the total amount of both components, and It is appropriate that the styrenic monomer accounts for 85 to 97% by weight, preferably 88 to 95% by weight. If the amount of rubber-like substance used is less than 3% by weight, the impact resistance and abrasion resistance will be significantly reduced, while if it exceeds 15% by weight,
Both are unfavorable since not only the abrasion resistance decreases but also the rigidity of the resin is significantly impaired. Moreover, in the present invention, it is necessary that the rubber-like substance is dispersed in the resin matrix so as to have an average particle diameter of 1 to 2.5 μm. If this average particle size is less than 1 μm, the wear-resistant effect and impact resistance cannot be sufficiently exhibited, and if it exceeds 2.5 μm, the wear-resistant effect is similarly insufficient. Therefore, either case is not preferable. Here, the average particle size is defined as the following: dyeing a press-molded resin composition with osmic acid, cutting out an ultrathin section from the dyed material using a microtome, and photographing it using a transmission electron microscope; The particle diameter of all the rubber-like material particles in the same magnification photograph was determined by the following formula. Average particle size ()=Σnd ³ /Σnd ² [] [However, n in the formula represents the number of rubber-like substances having a particle size of d. ] In order to prepare a resin composition containing a rubber-like substance having an average particle diameter within the above-mentioned specific range, it is necessary to appropriately determine the stirring conditions in the prepolymerization step. In general, increasing the stirring rotation speed will reduce the average particle size, and conversely, decreasing the rotation speed will increase the average particle size, so by selecting an appropriate stirring rotation speed, you can achieve the desired average particle size. A resin composition can be obtained. Further, as a method for preparing the rubber-modified styrenic resin, conventionally known and commonly used methods such as continuous bulk polymerization method or bulk-suspension two-stage polymerization method can be applied as is. The polyorganosiloxane used in the present invention is represented by the general formula [] above, and representative examples include polymethylphenylsiloxane, polydimethylsiloxane, and polydiphenylsiloxane. These include various copolymers such as siloxane, trichloropropylmethylsiloxane, trichlorophenylmethylsiloxane, and methylphenyldimethylsiloxane, and these may be used alone or in combination of two or more, but among them, 25 Viscosity at °C is 100
~30000 centistokes, preferably 300~
A range of 20,000 centistokes is suitable. If this viscosity is less than 100 centistokes, it will be difficult to obtain the desired effect of the present invention, and if it exceeds 30,000 centistokes, it will be extremely difficult to uniformly disperse it in the resin. Therefore, neither of these is preferable. The amount of the polyorganosiloxane added is 0.25 to 1.25 parts by weight as silicon content per 100 parts by weight of the rubber-modified styrene resin.
A suitable proportion is preferably 0.4 to 1.0 parts by weight. If the amount added is less than 0.25 parts by weight,
No substantial addition effect can be expected; on the other hand, 1.25
If the amount exceeds 1 part by weight, the whitening of the molded product becomes significant, which tends to impair the appearance, and causes problems during coloring, so neither is preferred. Further, the method of adding the polyorganosiloxane is not particularly limited, but during the process of preparing the rubber-modified styrenic resin, the rubber-like substance dissolved in the styrenic monomer is In order to achieve the anti-wear effect, it is preferable to add the compound while the so-called phase transition phenomenon occurs, in which the continuous phase shifts to the dispersed phase as the polymerization reaction progresses. The thus obtained resin composition of the present invention has extremely excellent abrasion resistance and surface smoothness, and therefore has a wide range of applications, such as reel parts of cassette tapes or VTRs,
Under guide of VTR, key top of PC, rotating stand for PC display, etc.
They range from rails for building materials to gears for toys. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. In the following, all parts and percentages are based on weight unless otherwise specified. Further, various physical property tests on the resin composition were conducted in the following manner. (1) Melt flow index Melt flow index was conducted in accordance with JIS K-6871 at a temperature of 200°C and a load of 5 kg. (2) Abrasion resistance Using a taper abrasion tester, the load was 1 kg and the rotation speed was 15000 mm/min for 60 minutes.
A wear test was conducted using the common material, and the amount of wear (mm ³ ) was expressed. (3) Coefficient of friction Using a Tensilon tensile testing machine, a test piece placed on a sliding surface using a steel plate was tested at a crosshead speed of 800 mm/min and a load of 400 mm/min.
It was measured by pulling it horizontally under the condition of g. (4) Izod impact value Compliant with JIS K-6871. Example 1 "UBEPOL 15HB" [high-cis polybutadiene manufactured by Ube Industries, Ltd.; cis-1,4 bond content =
95 mol%] 4.2 kg (7 parts) styrene 60 kg (100 parts) tert-dodecyl mercaptan 48 g (0.08 parts) were charged and heated to 65° C. for 6 hours with stirring to form a homogeneous solution. Next, the temperature was raised to 110°C and a polymerization reaction was carried out for 7 hours to obtain a prepolymerized product. Thereafter, "SH-710 oil" [polymethylphenylsiloxane manufactured by Toray Silicone Co., Ltd.; 500 centistokes] was added to 100 parts of this prepolymerized material so that the silicon content was 0.75 parts. Mix uniformly, then add this mixture to the internal volume.
It was added to the following aqueous phase prepared in advance in a polymerization tank equipped with a stirrer and dispersed in the form of particles. Water 100 parts Polyvinyl alcohol 0.2 parts Tertiary calcium phosphate 3 parts 2-ethylhexyl sulfate 0.02 parts To this suspension dispersion, 0.1 part of tert-butyl peroxybenzoate and 0.1 part of di-tert-butyl peroxide were added, The polymerization reaction was carried out at 115°C for 3 hours and then at 130°C for 3 hours. The thus obtained composition of the present invention (suspended particles)
was washed with water, dried and then pelletized in an extruder. Thereafter, the pellets were injection molded, and the abrasion resistance (component wear amount), friction coefficient, and Izot impact value were measured on the test pieces obtained. In addition, pellet melt flow index,
The average particle size of the dispersed rubber-like substance was also measured. The results are summarized in Table 1. Comparative Example 1 Changed to use the same amount of "Diene NF-35AS" [low-cis polybutadiene manufactured by Asahi Kasei Corporation; cis-1,4 bond content = 35 mol%] instead of "UBEPOL 15HB" Except for the above, a resin composition was obtained in the same manner as in Example 1, and then pelletized and then injection molded to prepare a test piece and evaluate its physical properties. The results are shown in Table 1. Comparative Example 2 A resin was prepared in the same manner as in Example 1, except that 3.15 kg of "UBEPOL 15HB" and 1.05 kg of "Diene NF-35AS" were used, that is, the usage rate of high-cis polybutadiene was 75%. A composition was obtained, then pelletized, and then injection molded to prepare a test piece, and its physical properties were evaluated. The results are shown in Table 1. Examples 2 to 6 and Comparative Examples 3 to 7 Except for making the changes shown in Table 1, that is, in Example 2 and Comparative Example 3, the amount of high-cis polybutadiene used was the same as in Example 3, In Comparative Examples 4 and 5, the stirring rotation speed was changed so that the average particle diameter of the dispersed rubber-like substance became a predetermined value, and the type of polyorganosiloxane was also changed as in Examples 4 to 6, Comparative Example 6, and 7
In each case, a resin composition was obtained in the same manner as in Example 1, except that the type and amount of polyorganosiloxane used were changed, and then pelletized, and then injection molded to prepare a test piece, and the physical properties were evaluated. I did it. The results are summarized in Table 1.

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Claims (1)

[Claims] 1. 85 to 97% by weight of a monovinyl aromatic compound,
In a rubber-modified resin composition obtained by polymerizing a mixture in which 15 to 3% by weight of a rubber-like substance is dissolved, 80% by weight or more of the rubber-like substance is cis-
It is a high-cis polybutadiene containing 1,4 bonds in a ratio of 90 mol% or more, and the rubber-like substance has an average particle size of 1 to 2.5 μm, and 100 parts by weight of the above rubber-modified resin. For,
General formula with a viscosity of 100 to 30,000 centistokes at 25°C [However, R in the formula is a monovalent organic group selected from the group consisting of an alkyl group, a haloalkyl group, an aryl group, a haloaryl group, and an aralkyl group,
R′ and R″ are each phenyl group or C ₁ to _{C 6}
m is a natural number representing a polysiloxane unit that should allow this polyorganopolysiloxane to maintain a liquid state at room temperature. ] A rubber-modified styrenic resin composition having excellent abrasion resistance and surface smoothness, which contains a polyorganosiloxane represented by the following in a proportion of 0.25 to 1.25 parts by weight as silicon content.