JP3274492B2 - Rubber-modified styrenic resin composition having excellent physical property balance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber-modified styrenic resin composition having a high balance between appearance and impact resistance of a molded article and having high gloss, and a method for producing the same.

[0002]

2. Description of the Related Art ABS resin is a resin having a good balance between the appearance of a molded product and impact strength, and is widely used in household electric appliances, electronic equipment and the like. Recently, the cost reduction trend of these products has increased, the use of rubber-modified styrenic resins in place of ABS resins has increased, and they are also used for large and more complex molded products with thinner walls. It became so. Under such circumstances, a rubber-modified styrene-based resin having good gloss, excellent moldability and high impact strength has been required.

[0003] The rubber-modified styrene-based resin is obtained by dispersing rubber particles in a styrene-based resin, and the particle size of the dispersed rubber particles has an important effect on product performance. The smaller, the better the gloss of the molded article. Usually, the rubber particle diameter (average particle diameter, the same applies hereinafter) in the rubber-modified styrenic resin is about 1.0 to 5.0 μm.
Resins in which rubber particles of m or less are dispersed have also been developed.
However, when the rubber particle diameter of the rubber-modified styrenic resin is 1.0 μm or less, the impact strength is usually significantly reduced, and there is a limit to improving the gloss while maintaining the impact strength of the molded product. In order to solve these problems, a method of blending a rubber-modified styrenic resin in which rubber particles of 1.0 μm or less is dispersed with a rubber-modified styrene resin in which particles of 1.0 μm or more are dispersed is disclosed in
6-41467, JP-A-59-1519, JP-A-63-15
241053 and U.S. Pat. No. 4,146,589. However, these methods have problems such as insufficient gloss and poor balance between impact strength and gloss.

On the other hand, when a styrene monomer in which a styrene-butadiene block copolymer having a high styrene content is dissolved as a rubber component is polymerized, rubber particles having a single occlusion structure of 0.5 μm or less are dispersed in polystyrene. It is well known that they are formed in a state (eg, Angew. Makromol. Chem. 58/59).
P175-198 (1977)). Utilizing this, a method for producing a rubber-modified styrenic resin having extremely excellent gloss and transparency of a molded product is disclosed in JP-B-48-18594, JP-A-61-500977, JP-A-63-48317, and JP-A-63-48317. It is proposed in, for example, Kokai 64-74209. According to these methods, the surface gloss and the transparency of the molded product are certainly remarkably improved as compared with the conventional rubber-modified styrene resin. However, although the impact strength has been improved, it has not been sufficient.

Further, a rubber-modified styrene resin in which rubber particles having a single occlusion structure formed using the above styrene-butadiene copolymer rubber are dispersed, and a normal rubber in which a small amount of rubber particles having a salami structure are dispersed. By blending a rubber-modified styrenic resin and forming the particle size distribution curve of the dispersed rubber particles into a two-peak shape (a distribution curve having two maximum values), the impact resistance is maintained while maintaining the gloss of the molded product at a high level. Attempts to improve U.S. Pat.
2. See, for example, JP-A-63-112646. In these methods, although the impact strength is certainly improved, there are still problems such as insufficient gloss and the need to add polydimethylsiloxane or the like to the resin because the impact strength is insufficient. there were.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rubber-modified styrenic resin which has a significantly improved appearance and a superior impact strength as compared with conventional rubber-modified styrenic resins, and its production. It is to provide a method.

Another object of the present invention is to provide a rubber-modified styrenic resin which is suitable as a resin material for a large, thin and complex-shaped molded product formed by, for example, injection molding.
And a method for manufacturing the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the importance of the above object, and have found that, in a rubber-modified styrenic resin composition, (1) a rubber particle having a salami structure has a small particle size; (2) The rubber particles having a single occlusion structure are made into a dispersed state, the particle size distribution is made into a three-peak shape, and the volume average diameter is set to 0.1.
(3) The particle size distribution is wider than before, and the 5% value of the new 5% value of the volume-based cumulative distribution of rubber-like polymer particles, which is completely different from the conventional knowledge, is 95%. By finding a special index called the value of the ratio of the% value and controlling this, when this rubber-modified styrenic resin is used for a molded product, the appearance of the molded product,
In particular, they have found that the gloss is remarkably improved and the impact strength is also excellent, and the present invention has been completed.

Accordingly, the present invention in styrene monomer homopolymers or copolymers the rubber-like polymer particles rubber-modified styrenic resin composition obtained by dispersing in, (a) the rubber-like polymer particles Salami structure and single occluder
Particles having a salami structure, including particles having a John structure
The volume average diameter of the
The volume average diameter of the particles having a lution structure is 0.1 to
1.0 μm and has a single occlusion structure
The ratio of the number of particles to the total number of particles is 30 to 99%
And the ratio of the number of particles having a salami structure is 70 to 1%.
There, the volume average diameter of (b) the rubber-like polymer particles 0.2-0.8
( c ) the shape of the volume-based particle size distribution curve of the rubber-like polymer particles is composed of three peaks; and ( d ) the cumulative size-based particle size distribution of the rubber-like polymer particles is 5 ( E ) a 5% by weight styrene solution having a viscosity of 20 to 50 centipoise and a styrene-butadiene block having a styrene content of 25 to 50% by weight. A styrene-butadiene block copolymer (II) having a viscosity of 20 to 50 centipoise and a styrene content of 5 to 20% by weight, comprising (I) and (II) Using a rubber-like polymer having a weight ratio of (I) / (II) = 95/5 to 40/60 as a raw material for forming rubber-like polymer particles. It is a resin composition .

The rubber-modified styrenic resin composition according to claim 1, which is obtained by polymerizing a solution obtained by dissolving the rubbery polymers (I) and (II) in a styrenic monomer or a mixture thereof. In the method for producing a rubber-like polymer, the amount of the styrene-based polymer in the reaction vessel for converting the rubber-like polymer into particles is X% by weight, the total amount of the rubber-like polymer is Y% by weight, and the styrene content of the rubber-like polymer (I) is Is defined as Z% by weight, and the conversion of the styrene-based monomer or a mixture thereof is in a range satisfying the following formula (III): 42 ≦ X + 2.33 × Y + (Z−40) ≦ 52 (III) A method for producing a rubber-modified styrenic resin composition having an excellent balance of characteristic properties, wherein an organic peroxide is added to 100 parts by weight of a solution in which a rubber-like polymer is dissolved when granulating a rubber-like polymer. .000
5 to 0.007 parts by weight.

The styrene monomer referred to in the present invention includes styrene, α-methylstyrene, side chain alkyl-substituted styrene such as α-ethylstyrene, vinyltoluene, vinylxylene, ot-butylstyrene, p- Examples thereof include nucleated alkyl-substituted styrenes such as t-butylstyrene and p-methylstyrene, halogenated styrenes such as monochlorostyrene, dichlorostyrene, tribromostyrene, and tetrahydrostyrene, p-hydroxystyrene, and o-methoxystyrene. , Particularly preferably, styrene,
α-methylstyrene and p-methylstyrene.
Styrene monomers can be used alone or in combination of two or more.

The rubber-like polymer particles are prepared by adding a predetermined amount of a rubber-like polymer described later, that is, a styrene-butadiene block copolymer (I) or (II), or the above-mentioned styrene monomer or a monomer of the same. The mixture is polymerized to form a dispersion in the styrene-based polymer.

The styrene-butadiene block copolymer (I) has a styrene content of 25 to 50% by weight,
The 5% by weight styrene solution has a viscosity of 20 to 50 centipoise. The styrene-butadiene block copolymer (II) has a styrene content of 5 to 20% by weight,
The 5% by weight styrene solution has a viscosity of 20 to 50 centipoise.

In the present invention, the rubber-like polymer particles formed as described above have a volume average particle size of 0.2 to 0.1.
It needs to be 8 μm. Here, the volume average particle diameter is measured as follows. That is, an electron micrograph of the resin was taken by an ultra-thin section method, the short diameter and the long diameter of 500 to 700 rubber particles in the photograph were measured, the average was determined as the particle diameter, and the average was obtained by the following equation. is there.

Volume average particle size = ΣnD ⁴ / ΣnD ³ (where n is the number of rubber particles having a particle size of D μm.) When the volume average particle size is less than 0.2 μm, the obtained rubber modified The impact strength of styrene resin is low,
If it exceeds 8 μm, the appearance of the molded product, especially the surface gloss, is undesirably reduced.

In the present invention, the shape of the distribution curve of the rubber-like polymer particles needs to be three peaks.

The fact that the shape of the distribution curve of the rubber-like polymer particles according to the present invention consists of three peaks means that the horizontal axis represents 0.1%.
When plotting the volume-based particle size in μm units and the frequency on the vertical axis, the distribution has five inflection points where the signs (positive and negative) of the tangent slope change.

When the shape of the distribution curve has two peaks, the effect of improving the impact strength is obtained, but the appearance of the molded product is inferior, and the gloss gradient is particularly large. The distribution of the present invention is adjusted by the molecular weight distribution of the rubbery polymer to be used, the ratio of the rubbery polymer to be mixed, and the like. In the present invention, the gloss gradient is defined as a difference in gloss due to a difference in distance from the gate in a molded product of injection molding, a portion where the wall thickness changes or a portion having a corner shape such as a portion where the flow state greatly changes during injection molding and a standard. It indicates the difference in gloss from a typical part.

Further, in the present invention, the number of the rubber-like polymer particles is counted from the larger volume-based particle of the rubber-like polymer particles, and the number is counted, and each of them corresponds to 5% and 95% of the cumulative distribution. Particle size ratio value, ie 5% of cumulative distribution
The value of the ratio of the value to the 95% value (hereinafter referred to as the distribution coefficient) is
45. Preferably in the range of 3.5 to 40,
It is particularly preferably in the range of 4 to 35. If it is less than 3, the effect of improving the impact strength is low, and if it exceeds 45, the appearance of the molded product is inferior, and particularly the gloss gradient becomes large. The amount is adjusted according to the molecular weight distribution of the rubbery polymer to be used, the quantitative ratio of the rubbery polymer to be mixed, the stirring intensity during polymerization, the residence time, and the like.

In the present invention, the ratio of the rubbery polymer (I) to the rubbery polymer (II) is (I) / (II) = 9
It is necessary to be in the range of 5/5 to 40/60. 95/5
If more than 40, the impact strength is low, and if it is less than 40/60, the gloss is low.

The rubber-modified styrenic resin according to the present invention in which the rubbery polymers (I) and (II) are dispersed is, for example, a rubber-modified styrenic resin composition containing the rubbery polymer (I) and a rubber-like styrenic resin composition. A method of separately producing a rubber-modified styrenic resin containing the polymer (II) and blending it with an extruder or the like,
The rubbery polymers (I) and (II) can be obtained by, for example, a method in which the rubbery polymers (I) and (II) are previously mixed in a polymerization reaction tank during the polymerization of the styrenic resin. Is preferred.

The present invention includes a case where the rubber-like polymer particles are particles having a salami structure and a single occlusion structure.

The term "salami structure" as used in the present invention refers to the structure of particles having a plurality of occlusions in one rubber particle when an electron micrograph is taken and observed by an ultra-thin section method of a resin. Further, the single occlusion structure means a structure of particles having only one occlusion in one rubber particle.

In the present invention, among the rubber-like polymer particles, the particles having a salami structure have a volume average diameter of 0.3 to 2.0.
In the range of 0 μm, the volume average diameter of the particles having a single occlusion structure is in the range of 0.1 to 1.0 μm, and the ratio of the particles having the single occlusion structure to the total number of particles is in the range of 30 to 99%. The ratio of the number of particles having a salami structure is preferably in the range of 70 to 1%. In this case, the volume average diameter of the rubbery polymer particles is 0.2
Care must be taken to be in the range 〜0.8 μm.

If the volume average diameter of the particles having a salami structure is larger than 2.0 μm, the appearance of the molded product is inferior, particularly the gloss gradient becomes large, and if it is less than 0.3 μm, the impact strength becomes low. On the other hand, if the volume average diameter of the particles having a single occlusion structure is larger than 1.0 μm, the gloss becomes low,
If it is less than 0.1 μm, the impact strength will be low. When the number of particles having a single occlusion structure is less than 30%,
Gloss decreases or gloss gradient increases. If it is more than 99%, the impact strength decreases.

The ratio of the rubbery polymer to the styrene-based polymer in the rubber-modified styrenic resin composition according to the present invention that satisfies the above conditions is preferably in the range of 3/97 to 25/75.
When the ratio is less than 3/97, the molded article is excellent in gloss, but the impact strength is low. When it exceeds 25/75, the impact strength is improved but the gloss is reduced or the gloss gradient is increased.

As a method for producing the rubber-modified styrenic resin composition of the present invention, the rubbery polymers (I) and (II)
Can be obtained by bulk polymerization or bulk-suspension polymerization by a two-stage polymerization method or the like in which a styrene monomer is dissolved in a styrene-based monomer. Assuming that the amount of the system polymer is X% by weight, the total amount of the rubbery polymer is Y% by weight, and the styrene content of the rubbery polymer (I) is Z% by weight, the value of the following formula (IV) is 42 to 52. It is necessary to adjust the conversion of the styrenic monomer so as to fall within the range described above.

X + 2.33 × Y + (Z−40) (IV) Although particles can be formed outside this range, abnormal particles are generated. When the particle size is less than 42, rubber particles appearing as rods are formed when an electron microscope photograph of the obtained product is observed,
Gloss and impact strength are reduced. On the other hand, when it exceeds 52, giant particles are formed and the gloss is reduced. Making the above formula (IV) a predetermined value specifically means that the amount of the rubber-like polymer in the reaction tank for granulating the rubber-like polymer is large, or that the rubber-like polymer (I) If the styrene content is high, adjust the conversion of the styrene monomer so that the amount of the styrene polymer in the reaction tank for granulating the rubbery polymer increases,
The opposite case means that the conversion of the styrene-based monomer is adjusted so that the amount of the styrene-based polymer in the reaction vessel for converting the rubbery polymer into particles is reduced.

In the present invention, the conversion of the styrene monomer is controlled by a known method, for example, the polymerization temperature, the type and concentration of the polymerization initiator used, the polymerization time, and the residence time in the case of the continuous polymerization method. Is done.

In the present invention, it is not necessary to use a polymerization initiator when granulating the rubber-like polymer. However, as a polymerization initiator, an organic peroxide may be used as a solution 1 in which the rubber-like polymer is dissolved.
It is preferable to use 0.0005 to 0.007 parts by weight with respect to 00 parts by weight. If used in an amount of more than 0.007 parts by weight, some giant particles may be formed, and the gloss may be reduced. The rubber-modified styrenic resin of the present invention may optionally contain a hindered phenolic antioxidant, a phosphorus-based antioxidant, an antioxidant such as a sulfur-based antioxidant, a fluidity improver such as mineral oil, stearic acid. A release agent such as zinc stearate or an organic polysiloxane may be added during the raw material solution or during or after the polymerization.

[0031]

EXAMPLES The present invention will be specifically described below with reference to examples, but these do not limit the scope of the present invention. Evaluation of physical properties (1) Izod impact strength: Measured according to JIS K-6871 (2) Evaluation of practical impact strength: FIG.
(A) A falling weight impact strength test was performed on three portions of the molded article 1 having the shape shown in FIG. 1 (b), that is, the portion (1), the portion (2), and the portion (3). Tip of falling weight R =
It was 6.4 m / m, and the inside diameter of the carrier was 25 m / m. The part (1) is a part where the thickness changes, the part (2) is a part near the corner, and the part (3) is a standard part. (3) Gloss: A molded product having the shape shown in FIGS. 1A and 1B according to JIS 8741 (incident angle 60 °).
The measurement was performed for two sites, site (1), site (2), and site (3). Example 1 A rubber-modified styrene-based resin was produced using a continuous mass polymerization apparatus in which a preheater was connected to the outlets of three reactors each having a stirrer and a vacuum tank was connected. In the first reactor equipped with a stirrer, a styrene content of 40% as a rubbery polymer (I) was added.
4.2% by weight of a styrene-butadiene block copolymer having a viscosity of 35 centipoise in a 35% styrene solution, and a styrene-butadiene block copolymer having a styrene content of 15% and a viscosity of 30 centipoise in a 5% styrene solution as a rubbery polymer (II). 1.8 parts by weight, ethylbenzene 15 parts by weight,
A raw material liquid comprising 79 parts by weight of styrene and 0.005 part by weight of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane as an organic peroxide was continuously supplied. The stirring of the first stirrer was 250 rpm, the reaction temperature was 144 ° C., and the residence time was 1.0 hour. Second
The base is a reaction temperature of 145 ° C, a residence time of 2 hours,
The base was a reaction temperature of 148 ° C. and a residence time of 2.5 hours. The temperature of the preheater was maintained at 210 to 240 ° C., and the degree of vacuum in the vacuum chamber was 40 Torr. The results are shown in Tables 1 and 2. Example 2 Example 2 was performed under the same conditions as in Example 1 except that the first stirring was performed at 180 rpm. Example 3 Example 3 was performed under the same conditions as in Example 1 except that the first stirring was performed at 400 rpm. Comparative Example 1 The same operation as in Example 1 was performed except that the first stirring was performed at 80 rpm. The average particle size of the rubber-like polymer particles in the obtained product was as large as 1.00 μm, and the gloss was low. Comparative Example 2 The same operation as in Example 1 was performed except that the first stirring was performed at 550 rpm. The average particle size of the rubber-like polymer particles in the obtained product was as small as 0.17 μm, and the impact strength was low. Comparative Example 3 In Example 1, the amount of the rubber-like polymer (I) was changed to 6 parts by weight,
The rubbery polymer (II) was not used, and the first stirring was performed for 30 minutes.
Under the same conditions as in Example 1 except that 0 rpm, the reaction temperature was 142 ° C., and the residence time was 1.5 hours, the rubber-like polymer particles had a small particle diameter having a single occlusion structure with an average particle diameter of 0.35 μm. Rubber-modified styrenic resin (A) was produced. Separately, in Example 1, the rubbery polymers (I) and (I)
Instead of I), 6 parts by weight of a 5% styrene solution polybutadiene having a viscosity of 50 centipoise was used, the first stirring was 300 rpm, the reaction temperature was 142 ° C., and the residence time was 1.5.
A rubber-modified styrene resin (B) having a large particle size and a salami structure having an average particle size of 1.15 μm of rubber-like polymer particles was produced under the same conditions as in Example 1 except for the time. The rubber-modified styrenic resins (A) and (B) were mixed at a ratio of 85/15 and melt-kneaded with an extruder to obtain a product. The particle size distribution of the rubbery polymer was two peaks, and the gloss gradient of the molded product was large. Comparative Example 4 The first reaction temperature in Example 1 was set to 148 ° C.
The procedure was performed under the same conditions as in Example 1 except that the residence time was 40 minutes. The obtained product had a large distribution coefficient of 51 and a large gloss gradient of the molded product. Comparative Example 5 In Example 1, the first reaction temperature was 140 ° C.
The procedure was performed under the same conditions as in Example 1 except that the residence time was 3 hours. The obtained product had a small distribution coefficient of 2.7 and low impact strength. Example 4 In Example 1, 5.4 parts by weight of the rubbery polymer (I),
The procedure was performed under the same conditions as in Example 1 except that (II) was changed to 0.6 parts by weight. Example 5 In Example 1, 2.7 parts by weight of the rubber-like polymer (I),
The procedure was performed under the same conditions as in Example 1 except that (II) was changed to 3.3 parts by weight. Comparative Example 6 The rubber-modified styrenic resin (A) produced in Comparative Example 3 was directly molded and evaluated for physical properties. The gloss was high, but the impact strength was low. Comparative Example 7 1.8 parts by weight of the rubbery polymer (I) in Example 1
The procedure was performed under the same conditions as in Example 1 except that (II) was changed to 4.2 parts by weight. The gloss was low. Example 6 Example 6 was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 140 ° C. The conversion of the first styrene monomer was 36.7%. Example 7 Example 7 was carried out under the same conditions as in Example 1 except that the reaction temperature was changed to 150 ° C. The conversion of the first styrene monomer was 45.6%. Example 7 Example 7 was carried out under the same conditions as in Example 1 except that the reaction temperature was 147 ° C and no organic peroxide was used. Comparative Example 8 The procedure was performed under the same conditions as in Example 1 except that the reaction temperature was changed to 136 ° C. The conversion of the first styrene monomer was 33%. When the product was observed with an electron micrograph, rod-like particles were observed, and gloss and impact strength were low. Comparative Example 9 A reaction was performed under the same conditions as in Example 1 except that the reaction temperature was changed to 154 ° C. The conversion of the first styrene monomer was 50.5%. When the product was observed with an electron micrograph, large particles were present and the gloss was low. Comparative Example 10 Example 1 was carried out under the same conditions as in Example 1 except that the reaction temperature was 141 ° C. and 0.01 parts by weight of the organic peroxide was used. The conversion of the first styrene monomer is 43%.
Met. When the product was observed with an electron micrograph, large particles were present and the gloss was low.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

As described above, the rubber-modified styrenic resin obtained by the method of the present invention has an excellent balance of impact strength and appearance, particularly gloss, and is a material for parts of household electric appliances and electronic equipment. The industrial use value is great in the use of the above.

[Brief description of the drawings]

FIG. 1 is a plan view (a) and a sectional view (b) of an injection molded test piece used for evaluation of practical impact strength and gloss.

[Explanation of symbols]

 1 molding

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kozo Ichikawa 1-6-6 Takasago, Takaishi-shi, Osaka Inside Mitsui East Pressure Chemical Co., Ltd. (72) Inventor Akihiko Nakajima 1-6-6 Takasago, Takaishi-shi, Osaka Mitsui East Pressure Within Chemical Co., Ltd. (72) Inventor Masato Takaku 1-6-6 Takasago, Takaishi-shi, Osaka Mitsui East Pressure Chemical Co., Ltd. (56) References JP-A-2-34614 (JP, A) (58) Fields investigated Int.Cl. ⁷ , DB name) C08F 287/00 C08F 279/02 C08L 51/04 C08L 55/02

Claims (3)

(57) [Claims] 1. A rubber-modified styrene resin composition obtained by dispersing rubber-like polymer particles in a homopolymer or copolymer of a styrene-based monomer, wherein (a) the rubber-like polymer particles have a salami structure and Single occluder
Particles having a salami structure, including particles having a John structure
The volume average diameter of the
The volume average diameter of the particles having a lution structure is 0.1 to
1.0 μm and has a single occlusion structure
The ratio of the number of particles to the total number of particles is 30 to 99%
And the ratio of the number of particles having a salami structure is 70 to 1%.
There, the volume average diameter of (b) the rubber-like polymer particles 0.2-0.8
( c ) the shape of the volume-based particle size distribution curve of the rubber-like polymer particles is composed of three peaks, and ( d ) the cumulative distribution of the volume-based particle size of the rubber-like polymer particles is 5 ( E ) a 5% by weight styrene solution having a viscosity of 20 to 50 centipoise and a styrene-butadiene block having a styrene content of 25 to 50% by weight. A styrene-butadiene block copolymer (II) having a viscosity of 20 to 50 centipoise and a styrene content of 5 to 20% by weight, comprising (I) and (II) Using a rubber-like polymer having a weight ratio of (I) / (II) = 95/5 to 40/60 as a raw material for forming rubber-like polymer particles. Resin composition. 2. The rubber-modified styrene-based polymer according to claim 1, wherein a solution obtained by dissolving the rubber-like polymers (I) and (II) according to claim 1 in a styrene-based monomer or a mixture thereof is polymerized. In the method for producing a resin composition, the amount of the styrene-based polymer in the reaction vessel for granulating the rubber-like polymer is X% by weight, the total amount of the rubber-like polymer is Y% by weight, and the amount of the rubber-like polymer (I) is Assuming that the styrene content is Z% by weight, the conversion rate of the styrene monomer or a mixture thereof satisfies the following formula (III): 42 ≦ X + 2.33 × Y + (Z−40) ≦ 52 (III) A method for producing a rubber-modified styrenic resin composition having an excellent balance of physical properties, characterized in that: 3. A rubber according to claim 2, wherein the organic peroxide at the time of the particles the rubbery polymer is added from 0.0005 to 0.007 parts by weight based on 100 parts by weight of the solution prepared by dissolving a rubbery polymer A method for producing a modified styrene resin composition.