JPH0234614A - Rubber-modified styrene resin - Google Patents

Abstract

PURPOSE:To provide the title resin in which the particle diameter of the rubber particle phase and the degree of swelling of a toluene-insoluble portion are each in a specified range and which gives a molding excellent in surface gloss, impact resistance, etc., by polymerizing a styrene monomer in the presence of a butadiene rubber of a specified composition under specified polymerization conditions. CONSTITUTION:A butadiene polymer (A) of a styrene content <25wt.%, a cis-1,4-bond content of 25-45mol.%, a ratio of the weight-average MW to the number-averate MW>=1.7, a solution viscosity of 50-350cP (as determined in a 5wt.% styrene solution), a Mooney viscosity of 25-80 (at 100 deg.C), and a retio of the solution viscosity to the Mooney viscosity >=2 is mixed with a styrene/ butadiene block copolymer (B) of a styrene content of 25-50wt.% in a component A to component B weight ratio of 95/5-45/55. A styrene monomer is polymerized in the presence of the obtained butadiene rubber to produce the title resin in which the weight-mean diameter of the rubber particle phase dispersed in the resin is 0.3-1mum, and the degree of swelling of a toluene insoluble portion in the resin is 7-13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a rubber-modified styrenic resin that has excellent gloss on the surface of a molded product and excellent impact resistance.

[Prior art] Rubber-modified styrenic resins obtained by polymerizing styrenic monomers in the presence of rubbery polymers have a relatively good balance of physical properties and excellent moldability. In addition, it is cheaper than ABS resin, which is a styrene-based resin manufactured using a different manufacturing method, so it is widely used as a general-purpose resin in the fields of light electrical equipment, office equipment, packaging containers, and miscellaneous goods. It is particularly strongly desired to be applied to applications that require appearance such as surface gloss of molded products.

Rubber-modified styrenic resins are generally produced by bulk polymerization or bulk-suspension polymerization of a styrene intermediate solution of butadiene rubber, and the raw material composition, polymerization conditions, etc. are adjusted as appropriate depending on the required physical properties. being done. but,
Conventional rubber-modified styrene resins have had the disadvantage of poor balance between the gloss and impact resistance of the molded product surface.

Rubber-modified styrenic resins exhibit impact resistance due to the dispersed rubber particle phase in the resin, but since these dispersed rubber particles reduce the gloss of the surface of the molded product, the diameter of the dispersed rubber particles can be adjusted as a means to improve the gloss. Conventionally, methods of reducing the size of However, when conventional butadiene-based rubbers are used, for example, with middle cis rubber, if the dispersed rubber particle size is reduced until a satisfactory gloss is obtained, the impact resistance decreases significantly, and with high cis rubber, the impact resistance decreases significantly. Although it is relatively good, there are problems with gloss and appearance, and it has been difficult to obtain a rubber-modified styrenic resin that satisfies the balance between gloss and impact resistance.

In addition, butadiene-based rubbers with lower solution viscosity by lowering the average molecular weight are known as butadiene-based rubbers that can relatively easily reduce the dispersed rubber particle size, but when these are used, impact resistance However, it is difficult to find a satisfactory balance between gloss and impact resistance. It was difficult to obtain a rubber-modified styrenic resin having the following properties.

[Problem to be solved by the invention H The purpose of the present invention is to improve the gloss and appearance of the surface of a molded product while minimizing the drop in impact resistance, thereby creating a rubber with an excellent balance between gloss and impact resistance. An object of the present invention is to provide a modified styrenic resin.

[Means for Solving the Problems] In view of the above problems, the present inventors conducted extensive studies on middle cis-based butadiene rubbers, which tend to have relatively good gloss and appearance compared to other rubbers. The above purpose can be effectively achieved by using a combination of a middle-cis butadiene polymer having a specific structure and a styrene-butadiene block copolymer having a specific structure in a specific ratio, and by having a specific dispersed rubber particle structure. The present inventors have discovered that a rubber-modified styrenic resin with an excellent balance of gloss and impact resistance can be obtained, leading to the present invention.

That is, the present invention provides a rubber-modified styrenic resin obtained by polymerizing a styrene monomer in the presence of a butadiene rubber, comprising: a) the butadiene rubber has a styrene content of less than 25% by weight; The amount of 1,4 bond is 25 to 45 mol%, the ratio of weight average molecular weight to number average molecular weight is 1.7 or more, and the solution viscosity of a 5 wt % styrene solution at 25°C is 50 to 350.
cpsStooo Mooney viscosity at ℃ 25-80,
It consists of a butadiene-based polymer (A) having a ratio of solution viscosity to Mooney viscosity of 2 or more and a styrene-butadiene block copolymer (B) having a styrene content of 25 to 50%, and ( The weight ratio of A) and ([3) is (A)/
(B) -9515 to 45155; b) the weight average particle size of the rubber particle phase dispersed in the resin is 0.3 to 1 μ; and C) the degree of swelling of toluene-insoluble components in the resin is 7 to 13. It relates to a rubber-modified styrenic resin characterized by the following.

The present invention also relates to a rubber-modified styrenic resin containing 0.01 to 0.5% by weight of organic polysiloxane in the rubber-modified styrenic resin.

The butadiene polymer (A) used in the present invention has a styrene content of less than 25% by weight and a cis-1,4 bond amount of 25% by weight.
-45 mol%, the ratio of weight average molecular weight to number average molecular weight is 1.7 or more, and the solution viscosity (SV) of a 5 wt% styrene solution at 25°C is 50 to 350 cps.

Mooney viscosity at 100°C (ML, 100°C
)■+4 is in the range of 25 to 80, and the ratio SV/ML of solution viscosity to Mooney viscosity is required to be 2 or more.

Such a butadiene-based polymer (A) can be obtained by polymerizing 112 polymers containing 1,3-butadiene as a main component using an organic lithium compound catalyst such as ethyllithium, n-butyllithium, or stearyllithium. can. Specific examples of the butadiene polymer (A) include polybutadiene and styrene-butadiene copolymer.

The styrene content of the butadiene polymer (A) is 25-
If it is 5 or more, the impact resistance will be poor, which is not preferable.

If the amount of cis-1,4 alloy 2 is less than 25 mol%, the impact resistance will be poor, while if the amount of cis-1,4 alloy 2 exceeds 45 mol%, the gloss will be poor, which is not preferable.

Moreover, if the ratio of weight average molecular weight to number average molecular weight is less than 1.7, impact resistance will be poor, which is not preferable.

The solution viscosity of a 5% styrene solution at 25°C is 50
If it is less than cps, the impact resistance will be poor, and if it exceeds 350 cps, the gloss will be poor, which is not preferable.

If the Mooney viscosity at 100°C is less than 25, the impact resistance will be poor, and if it exceeds 80, the gloss will be poor, which is not preferred.

When SV/ML is less than 2, the gloss is insufficient and the surface of the resulting rubber-modified styrenic resin molded product may have a poor appearance, which is not preferable.

Moreover, the butadiene-based polymer (A) used in the present invention has 1
, 2 bond amount is preferably 30 mol 96 or less. If the amount of 1,2 alloy exceeds 30 mol%, the impact resistance will be poor, and gelled substances with large particle sizes will easily occur in the resulting rubber-modified styrene resin, resulting in poor appearance on the surface of the molded product. There are some things that I don't like.

The styrene-butadiene block copolymer (B) used in the present invention blocks a conjugated diolefin mainly composed of 1,3-butadiene and a styrene monomer mainly composed of styrene using a lithium-based catalyst. It is a copolymer obtained by copolymerizing, for example - maximum (S-B)
, S (B-S).

n ((S-B) > ), preferably the sequence S-B
Alternatively, it is a block copolymer having a 5-B-5 sequence. Furthermore, the styrene-butadiene block copolymer used in the present invention may partially contain random parts, but
The amount of styrene constituting the styrene block portion needs to be at least 50 mol%, preferably at least 75 mol%, based on the total amount of styrene. If the amount of styrene constituting the styrene block is less than 50 mol%, it is impossible to obtain a rubber-modified styrenic resin that provides good gloss and appearance. In addition, the styrene content in the styrene-butadiene block copolymer is 25 to 50% by weight, 2 parts or 35% by weight.
Two parts at ~45% by weight are required. If the styrene content is less than 25 parts by weight, the gloss improvement effect will be poor, and if the styrene content exceeds 50 parts by weight, the impact resistance will be poor. It is not possible to obtain a rubber-modified styrenic resin with balance.

The butadiene rubber used in the present invention needs to be composed of a butadiene polymer (A) and a styrene-butadiene block copolymer (B), and the weight ratio of (A) and (B) is (A). /(B)-9515 to 45155, preferably (8)/(B)-90/10 to GO/40. If the ratio of (A) exceeds 95 in weight ratio, gloss,
The appearance is unsatisfactory and impact resistance is poor when the proportion of (A) is less than 45 by weight, so in both cases to obtain a rubber-modified styrenic resin with improved gloss and impact resistance. I can't.

Further, the content of butadiene rubber in the rubber-modified styrenic resin of the present invention is not particularly limited, but
In view of the balance of physical properties such as gloss, impact resistance, and rigidity of the resulting rubber-modified styrenic resin, the content is preferably in the range of 3 to 12 fflH%.

The weight average particle size of the rubber particle phase dispersed in the rubber modified styrenic resin of the present invention is 0.3 to 1μ, preferably 0.4μ.
~0.8μ is required. If the weight average particle size of the rubber particle phase exceeds 1μ, the gloss of the rubber-modified styrenic resin obtained will be poor, and if it is less than 0.3μ, the impact resistance will be poor, so a rubber that satisfies both gloss and impact resistance. Modified styrenic resin cannot be obtained.

Further, the degree of swelling of toluene-insoluble components in the rubber-modified styrenic resin of the present invention needs to be 7 to 13, preferably 9 to 12. If the degree of swelling of toluene-insoluble components in the rubber-modified styrenic resin is less than 7, the resulting rubber-modified styrenic resin will have poor impact resistance, and if the swelling degree exceeds 13, the rubber-modified styrenic resin obtained will be poor. It is not preferable because of its poor impact resistance. If the degree of swelling exceeds 13, the gloss of the surface of the molded product will be poor, and problems such as clouding of the surface near the gate, especially in the case of injection molded products, and a significant decrease in the gloss of the flow end surface, are undesirable.

The method for polymerizing the rubber-modified styrenic resin of the present invention includes:
Conventionally known bulk polymerization methods, bulk-suspension polymerization methods, etc. are used. For example, in the case of bulk polymerization, a styrene monomer solution of the butadiene rubber used in the present invention, or a solution prepared by adding toluene, ethylbenzene, etc. as a diluent, is heated with stirring to achieve the desired polymerization. After carrying out preliminary polymerization to a predetermined polymerization rate and carrying out bulk polymerization to a predetermined polymerization rate, unreacted monomers and diluent are removed under heating and reduced pressure conditions to complete the polymerization.

In the case of the bulk-suspension polymerization method, the styrene-based 1112 body solution of the butadiene-based rubber used in the present invention is heated under stirring as a child fi polymerization step to carry out bulk polymerization to a predetermined polymerization rate. This polymerization solution is suspended in water containing a suspending agent, suspension polymerization is carried out in the presence of a polymerization initiator, and the polymerization is completed.

During these polymerizations, additives such as chain transfer agents, polymerization initiators, plasticizers, and antioxidants may be used as appropriate.

The weight average particle size of the dispersed rubber particle phase in the rubber-modified styrenic resin of the present invention is determined by the solution viscosity of the butadiene rubber used,
Changes in the concentration of the rubber solution, the usage ratio of the butadiene polymer (A) and the styrene-butadiene block copolymer (B), the stirring intensity during prepolymerization, the type and amount of the chain transfer agent or polymerization initiator, etc. Adjusted by

In addition, the degree of swelling of toluene-insoluble components in the rubber-modified styrene resin is adjusted by changing the heating and vacuum conditions in the unreacted monomer removal step in the bulk polymerization method, and in the bulk-suspension polymerization method, the degree of swelling of toluene-insoluble components is adjusted by By changing the polymerization temperature and time, the type and amount of the polymerization initiator added, etc., the: A is adjusted.

The weight average particle size of the dispersed rubber particle phase in the rubber-modified styrenic resin of the present invention can be adjusted not only by changing the polymerization conditions but also by blending two or more rubber-modified styrenic resins. can.

In addition, the content of butadiene rubber in the rubber-modified styrenic resin of the present invention can be adjusted not only by changing the amount of butadiene rubber used during polymerization but also by blending it with a styrene resin that does not contain butadiene rubber. be able to.

The styrenic monomer in the present invention refers to styrene, α-
These include methylstyrene, p-methylstyrene, vinylxylene, etc., and these may be used alone or in combination. Further, a part of the styrene monomer can be replaced with a monomer such as acrylonitrile or methyl methacrylate that can be copolymerized with these styrene monomers.

The rubber-modified styrenic resin of the present invention can be mixed with other thermoplastic resins such as polyphenylene ether.

The impact resistance of the rubber-modified styrenic resin of the present invention can be further improved by adding an organic polysiloxane. Here, the organic polysiloxane is a polymer having an organic group and a polysiloxane bond, such as polydimethylsiloxane and polymethylphenylsiloxane. The viscosity of the organic polysiloxane (viscosity at 25°C) is 1
000 to 20000 csL is preferable.

The amount of organic polysiloxane added is 0. OI~0.5% by weight
is preferred. If the amount of organic polysiloxane added is less than 0.01% by weight, the effect of improving impact resistance will not be sufficient, and if the amount of organic polysiloxane added exceeds 0.5% by weight, stickiness may appear on the surface of the molded product. This is not desirable.

Rubber-modified styrenic resin containing organic polysiloxane may be polymerized by adding organic polysiloxane to styrene monomer, or polymerization may be performed by adding rubber-modified styrenic resin and organic polysiloxane using an extruder or the like. It can be manufactured by melt-mixing.

Furthermore, when processing the rubber-modified styrenic resin of the present invention, antioxidants, ultraviolet absorbers, mold release agents, lubricants, fillers, impact modifiers, coloring agents, etc. can be added and mixed as necessary.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Note that the structural analysis of the butadiene rubber in the Examples and Comparative Examples was carried out by the following method.

(1) Cis-1,4 bond amount and 1.2 bond amount Calculated by infrared absorption spectroscopy.

(2) Styrene content Calculated by ultraviolet absorption spectroscopy.

(3) Weight average molecular weight ffl (Mν) and number average molecular weight (M
n) ratio (My/Mn) using GPC (Toyo Soda type, HLC-802UR),
My/@n was measured using a refractometer as a detector and tetrahydrofuran (THF) as a developing solvent.

(4) Solution viscosity (SV) The viscosity of a 5% by weight styrene solution was measured at 25°C using a Cannon-Fenske viscometer.

(5) Mooney viscosity (ML, 100℃) 100℃
Using Mooney viscosity set to , preheating was performed for 1 minute, and the torque value was measured after another 4 minutes.

In addition, physical properties of the rubber-modified styrenic resins in Examples and Comparative Examples were measured by the following method.

(1) A transmission electron micrograph of the rubber particle phase with an average diameter of ff1ffi of 200 to 7
The diameter of 00 rubber particles was measured and calculated using the following formula.

匝ffi Average particle size - ΣN1Di'/ ΣN1Di3 Here, N1 is the number of rubber particles with particle size 1], and particle size D+
is the average value of the long axis and short axis of the rubber particles.

(2) Swelling degree of toluene-insoluble content After dissolving the resin in toluene and leaving it at room temperature for 24 hours,
The toluene-insoluble form W (Ws) in a swollen state was measured by centrifugation and decantation.

Subsequently, drying was performed under reduced pressure, and the weight (Wd) of toluene insoluble matter in the dry state was measured and calculated using the following formula.

Swelling degree of toluene insoluble matter = Ws / Wd (3) A 2-inch thick flat plate was formed by gloss injection molding, and JISK710
5, the 60 degree specular gloss was determined as n1.

(4) Appearance of the surface of the molded product A flat plate with a thickness of 2 mm is molded by injection molding, and those with no abnormalities on the surface appearance are ○, those with slight clouding near the gate are △, and those with scratches, cloudiness, uneven gloss, etc. Those with poor appearance were rated x.

(5) Izot impact value A test piece was molded by injection molding and measured according to JIS K8871.

Example 1 ■, 2 bond amount is 11 mol%, cis-1,4 bond amount is 37 mol%, 1ldv/Mn is 1.8, Mooney viscosity (
ML) is 38, solution viscosity (SV) is 95 cps, SV/
A styrene-butadiene block copolymer rubber having an S (styrene)-B (butadiene) arrangement, which has 6.4 parts by weight of polybutadiene rubber (A) having an ML of 2.5 and a styrene content of 40% by weight. (B)1. A rubber solution in which parts by weight of f3 were dissolved in 99 parts by weight of styrene and 1 part by weight of white mineral oil was charged into an autoclave with an internal volume of 5 g equipped with a stirrer, and at the start of bulk polymerization, 0.02 parts by weight of t-dodecyl mercaptan was added.
Part by weight, 0.05 part by weight of n-dodecylmercaptan was added 2 hours after the start of polymerization, bulk polymerization was carried out at 115° C. for 5 hours with stirring at a stirrer rotation speed of 220 rpm, and then cooled.
A preliminary polymerization solution was obtained. Next, 100 parts by weight of water, 1 part by weight of tertiary calcium phosphate, and 0.0 parts by weight of sodium dodecylbenzenesulfonate were placed in an autoclave with an internal volume of 10j11 equipped with a stirrer.
Next, 100 parts by weight of the prepolymerization solution and 0.001 parts by weight of benzoyl peroxide as a polymerization initiator were added.
2 parts by weight, t-butyl peroxybenzoate 0.35
Parts by weight were added, and suspension polymerization was carried out under stirring at 90°C for 4 hours and at 140°C for 3 hours. Hydrochloric acid was added to the resulting suspension polymerization solution, washed with water, dried, and mixed with 0.1% by weight of 2.8-di-t-butyl-p-cresol and 0.3% by weight of zinc stearate. A rubber-modified styrenic resin was obtained by pelletizing with an extruder. Table 1 shows the physical properties of the obtained resin.

Examples 2 and 3 In Example 1, the polybutadiene rubber (A) had the cis-1,4 bond amount and U7iv/Mn shown in Table 1.

A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the polybutadiene rubbers were changed to ML, SV, and SV/ML, and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. Ta. Table 1 shows the physical properties of the obtained resin.

Example 4 In Example 1, the styrene-butadiene block copolymer rubber (B) was replaced with styrene-butadiene block copolymer rubber (B) having a styrene content of 30% by weight.
A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the butadiene block copolymer rubber (S-B arrangement) was used and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. .

The physical properties of the obtained resin are shown in Table 1.

Comparative Example 1 The same procedure was carried out except that only 7.01 parts of the polybutadiene rubber (^) used in Example 1 was used as the butadiene rubber, and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. A rubber-modified styrenic resin was obtained in the same manner as in Example 1. Table 1 shows the physical properties of the obtained resin.

Comparative Example 2 In Example 1, the ratio of polybutadiene rubber (A) and styrene-butadiene block copolymer rubber (B) was changed to the first
A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the ratio was changed to the one shown in the table and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. Table 1 shows the physical properties of the obtained resin.

Comparative Examples 3 and 4 In Example 1, the polybutadiene rubber (A) had the amount of cis-1,4 bond shown in Table 1, p/l w/M n
.

A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the polybutadiene rubbers were changed to ML, SV, and SV/ML, and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. . Table 1 shows the physical properties of the obtained resin.

Comparative Example 5 In Example 1, the styrene-butadiene block copolymer rubber (B) was changed to a styrene-butadiene block copolymer rubber (S-B arrangement) containing 120% by weight of styrene to adjust the rubber particle size. A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the stirring rotation speed during bulk polymerization was changed.

The physical properties of the obtained resin are shown in Table 1.

Comparative Example 6 In Example 1, the styrene-butadiene block copolymer rubber (B) was mixed with styrene-containing a;
A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that butadiene random copolymer rubber was used and the stirring rotation speed during bulk polymerization was changed to adjust the rubber particle size. Table 1 shows the physical properties of the obtained resin.

Comparative Example 7 In Example 1, the ratio of polybutadiene rubber (A) and styrene-butadiene block copolymer rubber (B) was changed to the first
A rubber-modified styrenic resin was obtained in the same manner as in Example 1, except that the ratios were changed to those shown in the table and the stirring rotation speed during bulk polymerization in Example 1 was lowered. Table 1 shows the physical properties of the obtained resin.

Comparative Example 8 Same as Example 1 except that the amount of polymerization initiator used during suspension polymerization was changed to 0.25 parts by weight of benzoyl peroxide and 0.1 part by weight of t-butyl peroxybenzoate. A rubber-modified styrenic resin was obtained in the same manner. Table 1 shows the physical properties of the obtained resin.

Comparative Example 9 In Example 1, t-
Same as Example 2 except that 0.1 part of butylperoxybenzony) and 0.25 part of di-t-butyl peroxide were used, and the polymerization conditions were changed to 120°C for 3 hours and 145°C for 2 hours. A rubber-modified styrenic resin was obtained in the same manner. Table 1 shows the physical properties of the obtained resin.

(The following is a blank space) As shown in Table 1, the rubber-modified styrenic resins of the present invention in Examples 1 to 4 have an excellent balance of gloss and impact resistance, and the appearance of molded products is also good. When polybutadiene rubber (A) is used alone as in Example 1, or as in Comparative Example 2, the ratio of polybutadiene rubber (A) and styrene-butadiene block copolymer rubber (B) is the same as in the present invention. Cases outside the range or comparative example 3
and 4 when a middle cis polybutadiene rubber (A) having a structure other than the structure of the present invention with SV/ML of less than 2 is used, or a styrene-butadiene block having a structure other than the structure of the present invention as in Comparative Example 5 is used. When polymer rubber (B) is used, or when styrene-butadiene random copolymer rubber is used instead of styrene-butadiene block copolymer rubber (B) as in Comparative Example 6, gloss and durability are improved in both cases. The balance of impact resistance is poor, and Comparative Example 6 also has poor appearance, which is not preferable.

In addition, as in Comparative Examples 7 to 9, even if the butadiene rubber used is within the range of the present invention, the weight average particle diameter of the rubber particle phase or the degree of swelling of toluene-insoluble components in the rubber-modified styrenic resin obtained is outside the scope of the present invention, the balance between gloss and impact resistance is poor, and Comparative Examples 7 and 8
This is not preferable since it also causes poor appearance.

These results show that by using two specific butadiene rubbers in combination within a specific range and controlling the dispersed rubber particle phase to have a specific structure, it is possible to improve the appearance,
It can be seen that a rubber-modified styrenic resin that satisfies both gloss and impact resistance can be obtained.

Example 5 The rubber-modified styrenic resin obtained in Example 1 was heated at 25°C.
A rubber-modified styrenic resin was obtained by kneading and adding 0.1% by weight of polydimethylsiloxane having a viscosity of 1000 cst to an extruder. The gloss of the obtained resin is 1
The Izot impact value was 9.2 kgcm/c+n, indicating good gloss and impact resistance.

[Effects of the Invention] As shown in the above explanation, the rubber-modified styrenic resin according to the present invention has an excellent balance between appearance such as gloss on the surface of molded products and impact resistance, so it is superior to conventional rubber-modified styrene-based resins. It can be applied to applications that require an appearance that is unsatisfactory with resins.

Claims (2)

[Claims] (1) A rubber-modified styrenic resin obtained by polymerizing a styrene monomer in the presence of a butadiene rubber, wherein a) the butadiene rubber has a styrene content of less than 25% by weight, cis-1,4 The amount of bond is 25 to 45 mol%, the ratio of weight average molecular weight to number average molecular weight is 1.7 or more, and the solution viscosity of a 5 weight % styrene solution at 25°C is 50 to 350.
cps, Mooney viscosity at 100°C is 25-80,
Consisting of a butadiene polymer (A) having a ratio of solution viscosity to Mooney viscosity of 2 or more and a styrene-butadiene block copolymer (B) having a styrene content of 25 to 50% by weight,
and the weight ratio of (A) and (B) in the resin is (A)/(B).
)=95/5 to 45/55, b) the weight average particle size of the rubber particle phase dispersed in the resin is 0.3 to 1μ, and c) swelling of toluene-insoluble components in the resin A rubber-modified styrenic resin characterized by having a degree of strength of 7 to 13. (2) The rubber-modified styrenic resin according to claim (1), wherein the rubber-modified styrenic resin contains 0.01 to 0.5% by weight of organic polysiloxane.