JPH06128339A - Rubber-modified polystyrene resin composition - Google Patents

Abstract

PURPOSE:To obtain the title compsn. excellent in impact resistance and appearance. CONSTITUTION:The compsn. contains soft component particles (A) and copolymer rubber particles (B) both dispersed in the compsn. and satisfies the conditions that particles A have a salami structure and a mean particle size of 0.7-1.7mum, while particles B have a mean particle size of 0.5mum or lower and a core-shell structure comprising a shell consisting mainly of a polymer formed from a styrenic monomer and/or a (meth)acrylic ester monomer and a core consisting mainly of a rubbery polymer formed from a diolefin monomer, and that the wt. proportion of A (Xwt.%) and that of B (Ywt.%) satisfy the relations: 5<=(X+Y)<=30 and 60<=(X/(X+Y))X100<=99.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber-modified polystyrene resin composition. More specifically, the present invention relates to a rubber-modified polystyrene resin composition having improved impact resistance and improved surface appearance.

[0002]

2. Description of the Related Art Generally, as a method for improving the impact resistance of a hard and brittle resin such as polystyrene, a styrene resin as a matrix is obtained by polymerizing a resin monomer in the presence of a rubbery polymer. A method is known in which soft component particles are dispersed in a so-called graft type rubber-modified polystyrene. However, in such a graft type rubber-modified polystyrene, the particle size of the soft component particles containing the rubber-like polymer is closely related to impact resistance and rigidity, and the particle size of the soft component particles is The smaller the particle size, the better the rigidity, but when the particle size falls below a certain limit, the impact resistance sharply decreases, while when the particle size of the soft component is above a certain level, high impact strength can be obtained, but the rigidity tends to decrease. Is known to have. Further, the appearance of the rubber-modified polystyrene as the final product is related to the above particle size, and in order to obtain an excellent appearance,
It is also known that the particle size must be small.

[0003]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a rubber-modified polystyrene resin composition having improved impact resistance and excellent surface appearance.

[0004]

The present inventors have arrived at the present invention as a result of intensive studies to solve the above problems. That is, the present invention is a rubber-modified polystyrene-based resin composition in which soft component particles and rubber-based copolymer particles are dispersed in a styrene-based resin as a matrix, which satisfies the following conditions (a) to (c). And a rubber-modified polystyrene resin composition. (A) The soft component particles have a salami structure, and their average particle size is 0.7 μm or more and less than 1.7 μm. (B) The rubber-based copolymer particles have a core-shell structure,
The shell portion contains a polymer of a styrene monomer and / or a (meth) acrylic acid ester monomer as a main component, the core portion contains a rubber polymer of a diolefin monomer as a main component, and the rubber The average particle size of the copolymer particles is 0.5 μm or less. (C) The weight ratio (X% by weight) of the soft component particles in the rubber-modified polystyrene-based resin composition and the weight ratio of the rubber-based copolymer particles ( Y weight%), the relations of the following formulas (1) and (2) are established: 5 ≦ (X + Y) ≦ 30 (1) 60 ≦ (X / (X + Y)) × 100 ≦ 99 (2)

The details will be described below. The styrene-based resin as a matrix includes, in addition to a resin made of styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dichlorostyrene, 2,5-dichlorostyrene. It also includes resins made of alkyl-substituted styrenes such as styrene.

The soft component particles of the present invention have a so-called salami structure. The salami structure, which is also called a cell structure, refers to a structure in which small particles of a styrene resin are scattered in a rubber-like polymer phase having a particle structure. The structure of the soft component particles can be determined by observation using a transmission electron microscope.

Examples of the rubber-like polymer forming the rubber-like polymer phase in the soft component particles include known middle-cis and high-cis polybutadiene, styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, poly Isoprene, styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated product of the copolymer, and ethylene-propylene rubber are used.

The average particle size of the soft component particles is 0.7 μm or more and less than 1.7 μm. If the particle size is too small, the effect of improving impact resistance is poor, while if the particle size is too large, the surface appearance is poor. Here, the average particle diameter of the soft component particles is determined by the following method. That is, the particle size (d _i ) of soft component particles and the number N _i thereof are obtained by image analysis of a transmission electron micrograph of the rubber-modified polystyrene resin composition, and the average particle size d is obtained according to the following formula. d = Σ (d _i ) ⁴ N _i / Σ (d _i ) ³ N _i

The rubber-based copolymer particles of the present invention have a so-called core-shell structure, and the shell portion is mainly composed of a polymer of a styrene monomer and / or a (meth) acrylic acid ester monomer. The core portion is mainly composed of a rubber polymer of a diolefin monomer, and the rubber copolymer particles have an average particle diameter of 0.5 μm or less.

The core-shell structure, which is also called a single occlusion structure or a capsule structure, refers to a structure composed of a core portion and a shell portion. The structure of the rubber-based copolymer particles can be determined by observation with a transmission electron microscope.

The styrene-based monomer which is a constituent of the shell portion is as described in the styrene-based monomer which constitutes the matrix. The (meth) acrylic acid ester monomer, which is another constituent component of the shell portion, means an acrylic acid ester monomer and / or a methacrylic acid ester monomer, and specifically, methyl methacrylate, methacrylic acid Examples thereof include ethyl acidate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, ethyl acrylate and butyl acrylate. In addition, these may be used individually by 1 type, or may be used in combination of 2 or more type.

The shell portion of the rubber-based copolymer particles of the present invention comprises a homopolymer of the above-mentioned styrene-based monomer, a homopolymer of (meth) acrylic acid ester monomer or a styrene-based monomer ( The main component is a copolymer of (meth) acrylic acid ester monomer.

The core portion of the rubber-based copolymer particles of the present invention is mainly composed of a rubber-based polymer of a diolefin monomer. As the diolefin monomer, propadiene,
1,2-butadiene, 1,3-butadiene, isoprene, chloroprene, 1,3-pentadiene, etc.,
Of these, butadiene and its derivatives are preferred. The core portion contains a polymer of the above diolefin monomer as a main component, but a copolymer of a vinyl monomer copolymerizable with these diolefins can also be used.
The average particle size of the rubber-based copolymer particles is 0.5 μm or less, preferably 0.3 μm or less. If the particle size is too large, the gloss, that is, the surface appearance is poor. Here, the average particle diameter of the rubber-based copolymer particles is determined by the same method as the average particle diameter of the soft component particles.

The rubber-modified polystyrene-based resin composition of the present invention comprises a rubber-modified polystyrene-based resin composition in which the weight ratio of soft component particles (X% by weight) and the weight ratio of rubber-based copolymer particles (Y% by weight). For, the relations of the following equations (1) and (2) are established. 5 ≦ (X + Y) ≦ 30 (1) 60 ≦ (X / (X + Y)) × 100 ≦ 99 (2)

That is, (X + Y) is 5 to 30, preferably 10 to 25. If the value is too small, the impact resistance is poor, while if the value is too large, the appearance is poor. Also, (X
/ (X + Y)) * 100 is 60-99. If the value is too small, the effect of improving impact resistance is insufficient and the object of the present invention cannot be achieved.

For each of X and Y, 5
It is preferably in the range of -30. If these values are too small, the impact resistance may be poor, and if the values are too large, the appearance may be poor.

The weight ratio (X% by weight) of the soft component particles in the rubber-modified polystyrene resin composition is measured by the following method. That is, about 0.5 g of a graft-type rubber-modified polystyrene-based resin composition containing no rubber-based copolymer particles was mixed with 50 ml of a room temperature (23 ° C.) methyl ethyl ketone / methanol mixed solvent (volume ratio = 10/1).
And the dry weight of the insoluble matter at that time is taken as the weight of the soft component particles, and the weight ratio of the weight of the soft component particles to the rubber-modified polystyrene resin composition used is taken as the X value. The weight ratio (Y% by weight) of the rubber-based copolymer particles in the rubber-modified polystyrene-based resin composition is calculated from the weight of the rubber-based copolymer particles used in producing the rubber-modified polystyrene-based resin composition. Desired.
Further, the X value and the Y value can also be determined from the area occupied by each particle by image analysis of a photograph obtained by observing an ultrathin section of the rubber-modified polystyrene-based resin composition with a transmission electron microscope.

The method for producing the rubber-modified polystyrene resin composition of the present invention is, for example, as follows. That is, a graft type rubber-modified polystyrene containing soft component particles is obtained by polymerizing a styrene-based monomer in the presence of a rubber-like polymer. Here, the soft component particle structure, the average particle diameter, and the particle content are controlled by adjusting the polymerization conditions such as the amount of the rubber-like polymer used, the stirring speed, and the polymerization temperature. As the polymerization method, a known bulk polymerization method or a bulk-suspension two-stage polymerization method can be used.

On the other hand, a rubber latex is obtained by a usual method using the above-mentioned diolefin monomer, and the rubber latex is composed of the above-mentioned styrene monomer and / or (meth) acrylic acid ester monomer. The rubber-based copolymer particles having the core-shell structure of the present invention are obtained by grafting the polymer. As the rubber-based copolymer particles,
A commercially available product may be used as the resin modifier. Next, by mixing the above-mentioned graft type rubber-modified polystyrene and the above rubber-based copolymer particles,
The rubber-modified polystyrene resin of the present invention is obtained. Here, in the rubber-modified polystyrene-based resin composition, the rubber-based copolymer particles need to be dispersed in a sufficiently fine state, and for that purpose, it is preferable to melt-knead using a twin-screw extruder. . If the dispersion of the rubber-based copolymer particles is insufficient, the desired physical properties are not sufficiently expressed.

In the rubber-modified polystyrene resin composition of the present invention, a general-purpose polystyrene resin may be mixed and used in combination with the essential components described above within a range not impairing the features of the present invention, and further deteriorated. Auxiliary components such as an inhibitor, a plasticizer release agent and silicone oil may be added.

The rubber-modified polystyrene resin composition of the present invention has improved rigidity while maintaining a high level of rigidity and improved surface appearance, and is used in fields such as office automation equipment, home electric appliances and sheets. Is preferably used in.

[0022]

EXAMPLES Examples will be shown below, but the present invention is not limited to these examples. The data shown in the examples are measured based on the following method. (1) Izod impact strength (impact resistance) Measured according to JIS K7110. However, the standard in which the thickness of the notched sample was 6.4 mm was adopted. (2) Rigidity (flexural modulus) It was measured according to JIS K-7203. (3) Gloss A 150 × 90 × 2 mm flat plate was formed by an injection molding machine, and the 45 ° glossiness of the central part of the flat plate was measured according to JIS K7105.
It was measured according to.

Polybutadiene rubber and / or styrene-
Styrene was polymerized in the presence of butadiene glock copolymer. At this time, a graft type rubber-modified polystyrene (Comparative Examples A1, B1 and C1) having different particle diameters was obtained by adjusting the stirring speed and the polymerization temperature during the polymerization. On the other hand, a general-purpose polystyrene containing no rubber component is used as a rubber-based copolymer particle, and a resin modifier Paraloid KCA-201 (average particle size 0.1
7 μm) was added and mixed to obtain a rubber-modified polystyrene resin shown in D1 of Table 3. The mixing of the copolymer particles was carried out by using a twin screw extruder TEX-44 manufactured by Japan Steel Works at a resin temperature of 220.
It was carried out under the conditions of a temperature of 900 ° C., a rotation speed of 900 rpm, and a pressure of 30 kg / cm ² . Further, the following Examples and Comparative Examples were obtained by mixing each of the above Comparative Examples A1, B1 and C1 with Comparative Example D1 containing no soft component particles. The results are shown in Table 1.
~ 3.

The results show the following. Example A1 and Example A2 are blends of Comparative Example A1 and Comparative Example D1, but it is clear from comparison between Example A1 and Example A2 and Comparative Example A1 that there is almost no reduction in gloss and rigidity. , Impact strength has been improved. On the other hand, Comparative Examples A2 and A3 have X / (X + Y) × 10.
The value of 0 is too small, and the impact strength is lower than that of Comparative Example A1. Comparative example B1 and comparative example B2
The soft component particles have an excessively large particle diameter, and the gloss thereof is considerably inferior to those of Examples A1 and A2. In Comparative Example C1, Comparative Example C2 and Comparative Example C3, the particle size of the soft component particles is too small, and the effect of improving impact strength is hardly seen.

[0025]

[Table 1] −−−−−−−−−−−−−−−−−−−−−−−−−−−−− Practical Example Comparison Comparative Example A1 A2 A1 A2 A3 Soft Component Particle Structure * 1 SSSSS Average particle size μm 1.2 1.2 1.2 1.2 1.2 X wt% 10.8 13.9 15.4 4.6 7.7 Rubber-based copolymer particle structure * 1 CC-CC average particle size 0.17 0.17-0.17 0.17 Y wt% 5.4 1.8 0 12.6 9.0 X + Y wt % 16.2 15.7 15.4 17.2 16.7 (X / (X + Y) × 100) 67.0 88.5 100 26.7 46.1 Ratio A1 / Ratio D1 70/30 90/10 100/0 30/70 50/50 Blend ratio * 2 Evaluation Izod impact strength kg ・ cm / cm 8.2 7.9 7.5 2.8 4.0 Rigidity kg / cm ² 24400 24800 25100 23600 24000 Gloss% 91 92 92 90 91 −−−−−−−−−−−−−−−−−−−−−− −−−−−−

[0026]

[Table 2]

[0027]

Table 3 −−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example Comparative Example Comparative Example C1 C2 C3 D1 Soft Component Particle Structure * 1 CCC-Average Particle size μm 0.2 0.2 0.2-X wt% 20.0 6.0 14.0 0 Rubber-based copolymer particle structure * 1-CCC average particle size-0.17 0.17 0.17 Y wt% 0 12.6 5.4 18.0 X + Y wt% 20.0 18.6 19.4 18.0 (X / (X + Y) × 100) 100 32 72 0 Ratio C1 / Ratio D1 100/0 30/70 70/30 Blend ratio * 4 Evaluation Izod impact strength kg ・ cm / cm 4.5 3.2 4.0 2.4 Rigidity kg / cm ² 21900 23000 22700 23100 Gloss% 104 94 99------------------------------------------

* 1 Structure of soft component particles or rubber-based copolymer particles S: salami structure C: core-shell structure However, in the core-shell structure of Comparative Example C series, the core part is made of polystyrene and the shell part is made of butadiene. It consists of a rubber-based polymer as the main component. In addition, Comparative Example D
The core-shell structured particle of No. 1 satisfied the requirements of the present invention. * 2 Ratio A1 / Ratio D1 Blend Ratio: Comparative Example A1 / Comparative Example D1 Blend Weight Ratio * 3 Ratio B1 / Ratio D1 Blend Ratio: Comparative Example B1 / Comparative Example D1 Blend Weight Ratio * 4 Ratio C1 / Ratio D1 Blend Ratio: Comparative Example C1 / Comparative Example D1 Blend Weight Ratio

[0029]

As described above, according to the present invention, it is possible to provide a rubber-modified polystyrene resin composition having improved impact resistance and excellent surface appearance.

Claims (1)

[Claims] 1. A rubber-modified polystyrene-based resin composition in which soft component particles and rubber-based copolymer particles are dispersed in a styrene-based resin as a matrix, comprising the following (a):
A rubber-modified polystyrene-based resin composition satisfying the conditions (c) to (c). (A) The soft component particles have a salami structure, and their average particle size is 0.7 μm or more and less than 1.7 μm. (B) The rubber-based copolymer particles have a core-shell structure,
The shell portion contains a polymer of a styrene monomer and / or a (meth) acrylic acid ester monomer as a main component, the core portion contains a rubber polymer of a diolefin monomer as a main component, and the rubber The average particle size of the copolymer particles is 0.5 μm or less. (C) The weight ratio (X% by weight) of the soft component particles in the rubber-modified polystyrene-based resin composition and the weight ratio of the rubber-based copolymer particles ( Y weight%), the relationship of the following formulas (1) and (2) is established: 5 ≦ (X + Y) ≦ 30 (1) 60 ≦ (X / (X + Y)) × 100 ≦ 99 (2)