The rubber-modified styrene-based resin composition, which is a composite of a styrene-based resin as a continuum of the matrix phase and a diene-based rubbery polymer as a dispersed particulate phase in the matrix, is characterized by the parameters including an average particle diameter of the particles of the rubbery polymer in the range from 0.08 to 1.00 .mu.m, peripheral parameter thereof in the range from 0.1 to 2.5 (.mu.m).sup.-1. (% by weight).sup.-1 and relaxation time T.sub.2 thereof in the range from 300 to 2000 .mu. seconds as the determinant factors of the moldability of the resin composition as well as the impact strength and surface gloss of the shaped articles prepared from the composition.

BACKGROUND OF THE INVENTION 
The present invention relates to a novel styrene-based resin composition. 
More particularly, the invention relates to a rubber-modified 
styrene-based resin composition composed of a styrene-based resin forming 
the matrix phase and a diene-based rubbery polymer as the discrete phase 
dispersed in the matrix and capable of giving a molded article having 
excellent surface gloss and a high impact strength or, in particular, 
planar impact strength to he suitable as a material of parts of 
office-automation instruments and household electric appliances as well as 
sheets and the like. 
It is a widely practiced technology that, with an object to improve the 
impact strength of a styrene-based resin, e.g., polystyrene, that the 
resin is blended with a rubbery polymer or styrene monomer is polymerized 
in the presence of a rubbery polymer so as to effect partial graft 
polymerization of the monomer on to the molecules of the rubbery polymer, 
the remainder of the monomer being polymerized into homopolymeric 
polystyrene, so that the resulting polymeric product is a so-called 
HI-grade polystyrene or a rubber-modified polystyrene-based resin 
composition which is a composite of a polystyrene and a graft copolymer of 
styrene on the molecules of the rubbery polymer. 
The rubbery polymer in such a rubber-modified polystyrene resin composition 
is usually dispersed in the matrix of the styrene-based resin forming the 
dispersed phase. It is well known that the impact strength, rigidity and 
surface gloss of a shaped article prepared from the resin composition is 
greatly influenced by the particle size of the thus dispersed particles. 
For example, a decrease in the particle size of the dispersed rubbery 
polymer results, as a trend, in an improvement in the rigidity and surface 
gloss while the impact strength is rather decreased. Thus, substantially 
no improvement can be obtained in the impact strength of the molded 
articles when the particle size of the rubbery polymer is smaller than a 
certain value. 
Accordingly, the dispersed particles of the rubbery polymer in conventional 
rubber-modified polystyrene resin compositions have a particle diameter of 
at least 1 .mu.m or, usually, in the range from 1 to 10 .mu.m. Such a 
particle diameter is somewhat larger than the optimum particle diameter 
which would give the most remarkable improvement in the rigidity and 
surface gloss of the molded articles so that the resin composition is 
under limitations relative to the fields of application. 
Various attempts and proposals have been recently made with an object to 
obtain a good balance between the impact strength and surface gloss in the 
molded articles of rubber-modified polystyrene resin compositions. For 
example, German Patent Laid-Open Publication No. 3345377 discloses a 
molding material based on a high-impact polystyrene containing particles 
of a rubbery polymer in a controlled particle diameter and structure. 
Further, Japanese Patent Kokai No. 63-199717 and No. 63-207803 disclose 
rubber-modified styrene-based copolymers in which the type of the rubbery 
polymer is specified and the particle diameter of the dispersed particles 
and the grafting ratio on the rubbery polymer are controlled. 
Although these prior art methods are not without improvements in the 
balance of the impact strength and surface gloss of the molded articles of 
the molding materials or copolymers, the improvements thus far obtained 
are far from satisfactory so that it is eagerly desired to develop a 
styrene-based resin composition of high-impact grade capable of giving 
molded articles having well balanced impact strength and surface gloss. 
SUMMARY OF THE INVENTION 
The present invention accordingly has an object to provide a novel and 
improved rubber modified styrene based resin composition of the 
high-impact grade capable of giving molded articles having well balanced 
impact strength and surface gloss by overcoming the problems and 
disadvantages in the conventional high-impact polystyrene resins. The 
invention completed with the above mentioned object is based on the 
unexpected discovery obtained as a result of the extensive investigations 
undertaken by the inventors that the above mentioned object can be well 
achieved by controlling not only the particle diameter but also the 
peripheral parameter and the relaxation time T.sub.2 of the dispersed 
particulate phase of the rubbery polymer. 
Thus, the present invention provides a rubber-modified styrene-based resin 
composition comprising a styrene-based resin as a continuum of the matrix 
phase and a diene-based rubbery polymer as a dispersed particulate phase 
in the matrix, in which the particles of the rubbery polymer have an 
average particle diameter in the range from 0.08 to 1.00 .mu.m, peripheral 
parameter in the range from 0.1 to 2.5 (.mu.m).sup.-1. (% by 
weight).sup.-1 and relaxation time T.sub.2 in the range from 300 to 2000 
.mu. seconds. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The styrene-based resin forming the matrix phase of the inventive resin 
composition is typically a polystyrene but other homopolymers of various 
kinds of aromatic monovinyl monomers and copolymers thereof with other 
types of monomers copolymerizable with styrene or aromatic monovinyl 
monomers also can be the styrene-based resin in the invention. 
Examples of the above mentioned aromatic monovinyl monomers include 
styrene, .alpha.-alkyl-substituted styrenes, e.g., .alpha.-methyl styrene, 
.alpha.-ethyl styrene and .alpha.-methyl-4-methyl styrene, 
nucleus-substituted alkyl styrenes, e.g., 2-methyl styrene, 3-methyl 
styrene, 4-methyl styrene, 2,4-dimethyl styrene, ethyl styrenes, 
2-tert-butyl styrene and 4-tert-butyl styrene, nucleus-substituted 
halogenostyrenes, e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 
4-bromostyrene, dichlorostyrenes, dibromostyrenes, trichlorostyrenes, 
tribromostyrenes, tetrachlorostyrenes, tetrabromostyrenes and 
2-methyl-4-chlorostyrene, 4-hydroxy styrene, 2-methoxy styrene, vinyl 
naphthalenes and the like, of which styrene and .alpha.-methyl styrene are 
preferred. These aromatic monovinyl monomers can be used either singly or 
as a combination of two kinds or more according to need. 
Examples of the preferable monomers copolymerizable with the above named 
aromatic monovinyl monomers include cyano-containing vinyl compounds, 
e.g., acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile and 
.alpha.-chloroacrylonitrile, of which acrylonitrile is more preferable. 
These cyano-containing comonomers can be used either singly or as a 
combination of two kinds or more according to need. It is important and 
advantageous that the copolymerization is performed with a monomer mixture 
in which the amount of the comonomer copolymerized with the styrene 
monomer is such that the resulting copolymer contains at least 55% by 
weight or, preferably, at least 60% by weight of the monomeric moiety 
derived from the styrene monomer. When the weight fraction of the styrene 
moiety in the copolymer is too small, the copolymer would suffer 
undesirable decrease in the thermal stability and flowability in molding. 
It is further optional according to need that the styrene-based copolymer 
contains, besides the moieties derived from the styrene monomer and the 
cyano-containing vinyl monomer, one kind or more of the monomeric moieties 
derived from other types of copolymerizable monomers including, for 
example, anhydrides of unsaturated dibasic carboxylic acids, e.g., maleic 
acid, itaconic acid, hydroxymaleic acid, citraconic acid, phenyl maleic 
acid, aconitic acid, ethyl maleic acid and chloromaleic acid, maleimide 
compounds, e.g., maleimide and N-phenyl maleimide, unsaturated monobasic 
carboxylic acids, e.g., acrylic acid and methacrylic acid, and esters of 
acrylic and methacrylic acids, e.g., methyl acrylate and methyl 
methacrylate, of which the moiety derived from the maleic anhydride is 
particularly preferable in respect of giving certain improvements to the 
copolymer. These comonomeric moieties can be contained in the copolymer 
either singly or as a combination of two kinds or more according to need 
in a weight fraction not to exceed 35% by weight. 
The rubbery polymer forming the particulate dispersed phasse in the 
inventive resin composition is a diene-based rubbery polymer which is not 
particularly limitative. Any of diene-based rubbery polymers 
conventionally used in rubber-modified styrene-based resin compositions 
can be used here. Examples of the suitable rubbery polymers include, for 
example, natural rubber and synthetic rubbers such as polybutadiene 
rubbers, polyisoprene rubbers, block- or random-copolymeric rubbers of 
styrene and butadiene, block- or random-copolymeric rubbers of styrene and 
isoprene and butyl rubbers as well as graft-copolymeric rubbers obtained 
by the graft-copolymerization of styrene on to the above named rubbery 
polymers. These rubbery polymers can be used either singly or as a 
combination of two kinds or more according to need. Preferably, the 
rubbery polymer is a block-copolymeric rubber of styrene and butadiene, 
polybutadiene or a combination thereof in which the weight fraction of the 
styrene moiety is in the range from 20 to 50% by weight. 
The preparation method of the inventive rubber-modified styrene-based resin 
composition is not particularly limitative and can be any of conventional 
methods used in the preparation of rubber-modified styrene-based resin 
compositions. For example, the resin composition can be obtained by 
conducting homopolymerization of the aromatic monovinyl monomer or 
copolymerization thereof with other comonomer or comonomers in the 
presence of the diene-based rubbery polymer. The type of the 
(co)polymerization process is also not particularly limitative and can be 
conventional including emulsion polymerization, bulk polymerization, 
solution polymerization and suspension polymerization in a batch-wise or 
continuous process as well as a multi-stage polymerization method such as 
the bulk-suspension two-step polymerization method, of which the methods 
of continuous bulk or solution polymerization are preferred. 
In the following, an example is described for a preferable preparation 
method of the inventive resin composition by the bulk or solution 
polymerization method in a continuous process. In the first place, the 
aromatic monovinyl monomer, e.g., styrene, or a monomeric mixture thereof 
with other comonomers, e.g., cyano-containing vinyl monomers, is admixed 
with the diene-based rubbery polymer which is dissolved therein at a 
temperature, for example, in the range from 20.degree. to 70.degree. C. 
The solution is introduced into a polymerization reactor equipped with a 
stirrer or, preferably, to the first reactor of a multi-stage series of 
polymerization reactors and polymerization of the monomer or monomers is 
effected therein by heating, usually, at a temperature in the range from 
70.degree. to 150.degree. C. It is preferable that the conversion of the 
monomer or monomers into polymer in the first of the series of the 
reactors is in the range from 0.5 to 3.0 times by weight based on the 
amount of the rubbery polymer dissolved in the monomer mixture. When this 
conversion is lower than 0.5 time, difficulties may be caused in the 
temperature control in the second and subsequent reactors due to an 
increase in the load for the removal of heat of polymerization. When this 
conversion is higher than 3.0 times, on the other hand, the viscosity of 
the polymerization mixture is unduly increased already in the first 
reactor so as to cause coarsening of the rubber particles due to 
incomplete mixing resulting in a resin composition which gives a shaped 
article having a decreased surface gloss. The polymerization mixture 
discharged out of the last in the series of the reactors is subjected to a 
step for the recovery of the solid material from the volatile matters such 
as the unpolymerized monomers, solvents, if used, and the like or the 
so-called devolatilization treatment so that the desired resin composition 
can be obtained. It is desirable that the conversion of the monomer or 
monomers into polymer in the polymerization mixture discharged out of the 
last reactor is at least 65% by weight. When this final conversion is too 
low, the rubber particles have not yet reached stabilization so that the 
particle configuration may be subject to destruction in the subsequent 
devolatilization treatment resulting in a resin composition which gives a 
shaped article having a decreased surface gloss. 
In the above described process, the rubbery polymer is introduced into the 
first of the series of the reactors as being dissolved in the monomer or 
monomer mixture while a portion of the monomer or monomer mixture as well 
as other additives such as the polymerization initiators, chain transfer 
agents or molecular weight-controlling agents and the like used according 
to need can be introduced into the reactor at any stage in the series of 
the reactors. 
The process of devolatilization is performed under a reduced pressure of, 
usually, 50 mmHg of below or, preferably, 30 mmHg or below at a 
temperature in the range, usually, from 200.degree. to 300.degree. C. or, 
preferably, from 230.degree. to 290.degree. C. or, more preferably, from 
240.degree. to 280.degree. C. It was found that the temperature in this 
devolatilization treatment has an influence on the relaxation time 
T.sub.2. 
As is mentioned above, the rubber-modified styrene-based resin composition 
of the invention is prepared preferably by the continuous-process solution 
or bulk polymerization and the diene-based rubbery polymer is dispersed in 
the form of discrete particles in the matrix of the styrene-based resin. 
It should be noted that the resin composition may have no satisfactory 
properties when it is prepared by the so-called grafting emulsion 
copolymerization in which a rubber latex is admixed with the aromatic 
monovinyl monomer or a mixture thereof with other comonomers including the 
cyano-containing vinyl monomers. 
Examples of the above mentioned molecular weight-controlling agent used 
according to need in the above described polymerization process include, 
for example, mercaptans, terpenes and halogenated hydrocarbons such as 
.alpha.-methyl styrene dimer, n-dodecyl mercaptan, tert-dodecyl mercaptan, 
1-phenylbutene-2, fluorene, dipentene, chloroform and the like. 
Further, the polymerization initiator, which is used also according to need 
in the process of polymerization, is selected from organic peroxides 
including peroxy ketal compounds, e.g., 1,1-bis(tert-butylperoxy) 
cyclohexane and 1,1-bis(tert-butylperoxy)-3,3,5-trimethyl cyclohexane, 
dialkyl peroxides, e.g., dicumyl peroxide, di-tert-butyl peroxide and 
2,5-dimethyl-2,5-di(tert-butylperoxy) hexane, diaryl peroxides, e.g., 
benzoyl peroxide and 3-toluoyl peroxide, peroxy dicarbonates, e.g., 
dimyristylperoxy dicarbonate, peroxy ester compounds, e.g., 
tert-butylperoxy isopropyl carbonate, ketone peroxides, e.g., 
cyclohexanone peroxide, hydroperoxides, e.g., p-menthane hydroperoxide, 
and so on. 
It is preferable that the resin composition of the invention consists of 
from 70 to 95% by weight of the styrene-based resin and from 30 to 5% by 
weight of the diene-based rubbery polymer. When the content of the rubbery 
polymer is too low, the impact strength of an article shaped from the 
resin composition cannot be fully improved. When the content thereof is 
too high, on the other hand, the flowability of the resin composition is 
undesirably decreased not to give a shaped article having an increased 
surface gloss. 
It is essential in the resin composition of the invention that the 
particles of the rubbery polymer as the dispersed phase have an average 
particle diameter in the range from 0.08 to 1.00 .mu.m or, preferably, 
from 0.10 to 0.70 .mu.m, a peripheral parameter in the range from 0.1 to 
2.5 (.mu.m).sup.-1. (% by weight).sup.-1 or, preferably, from 0.3 to 2.0 
(.mu.m).sup.-1. (% by weight).sup.-1, and a relaxation time T.sub.2 in the 
range from 300 to 2000 .mu. seconds or, preferably, from 400 to 1800 .mu. 
seconds. The peripheral parameter here implied is a value obtained from a 
transmission-type electron microscopic photograph showing the state of the 
dispersed rubber particles in the matrix of the styrene-based resin. 
Namely, the value is obtained from the total of the peripheral lengths of 
the rubber particles in a unit area given in the unit of (.mu.m).sup.-1 
divided by the content of the rubbery polymer in the composition given in 
the unit of % by weight. The relaxation time T.sub.2 here implied is the 
value of the spin-spin relaxation time of the rubbery constituent in the 
resin composition as determined by the Hahn echo method 
(90.degree.-.pi.-180.degree. pulse method) at 30.degree. C. by using a 
pulse NMR apparatus under the conditions of the measuring frequency of 90 
MHz and 90.degree. pulse width of 1.5 to 2.0 .mu. seconds with hydrogen 
nuclei as the target. 
When the average particle diameter of the dispersed rubber particles is too 
small, the resin composition cannot give a shaped article having a fully 
improved impact strength. When the average particle diameter thereof is 
too large, on the other hand, the surface gloss of the shaped article of 
the resin composition is undesirably low. When the peripheral parameter 
and the relaxation time T.sub.2 are outside the above defined respective 
ranges, the impact strength of the shaped article of the resin composition 
may not be high enough. Each of these three parameters can be controlled 
by appropriately selecting the velocity of agitation in each of the series 
of the reactors and the temperature in the devolatilization treatment of 
the polymerization mixture discharged out of the last reactor in the 
series. 
It is of course optional according to need that the styrene-based resin 
composition of the present invention is processed into a molding compound 
with admixture of various kinds of additives conventionally used in 
styrene-based resin compositions including lubricants, antioxidants, 
plasticizers, flame retardants, photostabilizers, coloring agents and the 
like. It is further optional that a composite molding compound is prepared 
by admixing the inventive resin composition with fillers such as fibrous 
reinforcing fillers, e.g., glass fibers, and inorganic powdery fillers. 
Examples of the above mentioned lubricants include stearic acid, behenic 
acid, stearoamide, methylene bisstearoamide, ethylene bisstearoamide and 
the like. Examples of the above mentioned antioxidants include those of 
the hindered phenol-type such as 2,6-di-tert-butyl-4-methyl phenol, 
stearyl-.beta.-(3,5-di-tert-butyl-4-hydroxy phenyl) propionate, 
triethylene glycol bis-3-(3-tert-butyl-4-hydroxy-5-methyl phenyl) 
propionate and the like and phosphorus-containing ones such as 
tri(2,4-di-tert-butyl phenyl) phosphite, 4,4'-butylidene 
bis(3-methyl-6-tert-butylphenyl-di-tridecyl) phosphite and the like. 
Examples of the plasticizers include mineral oils and polyethylene 
glycols. Examples of the preferable flame retardants include combinations 
of an organic bromine compound, e.g., tetrabromo bisphenol A, decabromo 
diphenyl oxide, brominated polycarbonates and the like, and antimony 
trioxide. 
It is optional that the molding compound of the inventive resin composition 
is compounded with one or more of other polymeric resins such as ABS 
resins, polyvinyl chloride, styrene-acrylonitrile copolymeric resins, 
polycarbonate resins, polybutylene terephthalate, polyethylene 
terephthalate, nylon 6, nylon 11, nylon 12, polyphenylene oxide, 
polyphenylene sulfide and the like. 
In the following, a more detailed description is given by way of examples 
to illustrate the resin composition of the present invention although the 
scope of the invention is never limited thereto. In the examples, each of 
the items for the evaluation of the resin composition was conducted 
according to the method or standard given below. 
(1) Melt index Ml Measurements were made according to ISO R-1133. 
(2) Surface gloss of shaped articles Measurements were made according to 
JIS K 7105. 
(3) Planar impact strength 
a) Test piece: 75 mm.times.75 mm.times.3 mm dimensions prepared by 
injection molding 
b) Testing machine: Drop-weight tester Model RDT 5000 manufactured by 
Rheometrics Co. 
c) Testing conditions: 3.76 kg of overall dart load; 1/2 inch diameter of 
dart point; 2 inches diameter of test piece holder bench; hitting point of 
dart at the center of the test piece; and 1.5 meters/second of hitting 
velocity 
(4) Average diameter of rubber particles 
A transmission-type electron microscope was used to take a photograph 
showing the dispersion of the rubber particles in an ultrathin section of 
the composition having a thickness of 0.1 .mu.m as prepared by using an 
ultramicrotome from the composition stained with osmium tetraoxide. The 
diameters D.sub.i in .mu.m of the image profiles on the photograph of at 
least 1500 rubber particles having a diameter of 0.02 .mu.m or larger were 
determined by using an image analyzer and the area-average particle 
diameter D.sub.s in .mu.m was calculated by using the equation 
EQU D.sub.s, .mu.m=(.SIGMA.n.sub.i D.sub.i.sup.3)/(.SIGMA.n.sub.i 
D.sub.i.sup.2), 
in which n.sub.i is the number of the particles having a diameter of 
D.sub.i .mu.m. The particle diameter here implied is the largest distance 
between any two points on the circumference of the image of a rubber 
particle. 
(5) Peripheral parameter C.sub.i 
An electron microscopic photograph was taken in the same manner as above 
and the overall value L in .mu.m of the peripheral lengths of the images 
of the rubber particles within an area of A .mu.m.sup.2 was determined by 
using an image analyzer to calculate the peripheral density C.sub.d in 
(.mu.m).sup.-1 which is given by C.sub.d, (.mu.m).sup.-1 =L/A. 
Separately, the concentration of the dienic constituent in % by weight in 
the resin composition was determined by the .sup.13 C-NMR spectrometry. 
Thus, a .sup.13 C-NMR spectrum of the sample was obtained by the 
proton-gated decoupling method after elimination of the nuclear Overhauser 
effect (NOE) by using an NMR apparatus at a frequency of 200 MHz under the 
conditions of deuterated chloroform CDCl.sub.3 as the solvent, solute 
concentration of 16% by weight, measuring temperature of 23.degree. C., 
pulse width of 6.9 .mu. seconds (45.degree.) and width of spectrum range 
of 10,000 Hz, from which the concentration of the dienic constituent in % 
by weight in the sample was calculated from the comparison of the 
integrated intensities of the signals in the spectrum inherent in the 
styrene moiety and the diene moiety. The peripheral parameter C.sub.i in 
(.mu.m).sup.-1. (% by weight).sup.-1 is given as the ratio of the 
peripheral density C.sub.d in (.mu.m).sup.-1 ; to the above mentioned 
content of the dienic constituent in % by weight. 
(6) Relaxation time T.sub.2 
The relaxation time T.sub.2 here implied is the value of the spin-spin 
relaxation time of the rubbery constituent in the resin composition as 
determined by the Hahn echo method (90.degree.-.tau.-180.degree. pulse 
method) at 30.degree. C. by using a pulse NMR apparatus under the 
conditions of the measuring frequency of 90 MHz and 90.degree. pulse width 
of 1.5 to 2.0 .mu. seconds with hydrogen nuclei as the target.

EXAMPLE 1 
A polymerization mixture composed of: 
10.0% by weight of a styrene-butadiene copolymer containing 22% by weight 
of the styrene moiety (ZLS-01, a product by Nippon Zeon Co.); 
83.7% by weight of styrene monomer; 
5.0% by weight of ethyl benzene; 
0.01% by weight of n-dodecyl mercaptan; 
0.09% by weight of an antioxidant (Irganox 1076, a product by Ciba Geigy 
Co.): 
1.00% by weight of a mineral oil (a product by Idemitsu Kosan Co.); and 
0.20% by weight of a silicone oil (a product by Toray Silicone Co.) 
was continuously introduced at a constant feed rate of 5.8 liters per hour 
into the first polymerization reactor of a series of reactors having a 
capacity of 7.8 liters and equipped with a stirrer having anchor-type 
blades rotated at 100 rpm. The first reactor was kept at a temperature of 
140.degree. C. so that the conversion of the styrene monomer into polymer 
in the polymerization mixture discharged out of the first reactor was 21%. 
The polymerization mixture coming out of the first polymerization reactor 
was successively introduced into the second and the third in the series of 
reactors, each having a capacity of 11.0 liters and equipped with a 
stirrer having anchor-type blades rotated at 150 rpm and 50 rpm, 
respectively, to continue the polymerization reaction at 145.degree. C. 
and 160.degree. C. in the second and third reactors, respectively. The 
conversion of the styrene monomer into polymer in the polymerization 
mixture discharged out of the third reactor was 72%. The polymerization 
mixture was subjected to the devolatilization treatment in a vacuum vessel 
under a pressure of 10 mmHg at 260.degree. C. to be freed from volatile 
matters followed by pelletization of the rubber-modified styrene-based 
resin composition. Table 1 below shows the results obtained in the 
evaluation tests of the thus obtained resin composition. 
EXAMPLES 2 AND 3 
The experimental procedure in each of Examples 2 and 3 was substantially 
the same as in Example 1 except that the temperature in the 
devolatilization treatment was 280.degree. C. and 245.degree. C., 
respectively. Table 1 below also shows the results obtained in the 
evaluation tests of the thus obtained resin compositions. 
EXAMPLE 4 
The experimental procedure in this example was substantially the same as in 
Example 1 except that the stirrers in the first and second reactors were 
rotated at velocities of 140 rpm and 180 rpm, respectively. Table 1 below 
also shows the results obtained in the evaluation tests of the thus 
obtained resin composition. 
EXAMPLE 5 
The experimental procedure in this example was substantially the same as in 
Example 4 except that the styrene-butadiene copolymer as the rubbery 
polymer in the polymerization mixture was replaced with the same amount of 
a polybutadiene (NF-35AS, a product by Asahi Chemical Industry Co.), the 
polymerization mixture introduced into the first polymerization reactor 
was admixed with 0.03% by weight of 
1,1-bis(tert-butylperoxy)-3,3,5-trimethyl cyclohexane as a polymerization 
initiator and the temperature in the first polymerization reactor was 
115.degree. C. instead of 140.degree. C. The conversion of the styrene 
monomer into polymer in the polymerization mixture discharged out of the 
first and third reactors was 24% and 76%, respectively. Table 1 below also 
shows the results obtained in the evaluation tests of the thus obtained 
resin composition. 
EXAMPLE 6 
The experimental procedure in this example was substantially the same as in 
Example 1 except that the styrene monomer in the polymerization mixture 
was replaced with the same amount of a 75:25 by weight mixture of styrene 
and acrylonitrile, the polymerization mixture introduced into the first 
polymerization reactor was admixed with 0.03% by weight of 
1,1-bis(tert-butylperoxy)-3,3,5-trimethyl cyclohexane as a polymerization 
initiator and the temperature in the first polymerization reactor was 
115.degree. C. instead of 140.degree. C. The conversion of the monomers 
into polymer in the polymerization mixture discharged out of the first and 
third reactors was 28% and 77%, respectively. Table 1 below also shows the 
results obtained in the evaluation tests of the thus obtained resin 
composition. 
COMATIVE EXAMPLES 1 AND 2 
The experimental procedure in each of Comparative Examples 1 and 2 was 
substantially the same as in Example 1 except that the temperature in the 
devolatilization treatment was 295.degree. C. and 225.degree. C. 
respectively. Table 1 below also shows the results obtained in the 
evaluation tests of the thus obtained resin compositions. 
COMATIVE EXAMPLE 3 
The experimental procedure in this comparative example was substantially 
the same as in Example 4 except that the styrene-butadiene copolymer as 
the rubbery polymer in the polymerization mixture was replaced with the 
same amount of a polybutadiene (NF-35AS, a product by Asahi Chemical 
Industry Co.). Table 1 below also shows the results obtained in the 
evaluation tests of the thus obtained resin composition. 
COMATIVE EXAMPLE 4 
The experimental procedure in this comparative example was substantially 
the same as in Example 1 except that the stirrers in the first and second 
reactors were rotated at velocities of 180 rpm and 220 rpm, respectively. 
Table 1 below also shows the results obtained in the evaluation tests of 
the thus obtained resin composition. 
REFERENCE EXAMPLE 1 
The experimental procedure in this reference example was substantially the 
same as in Example 6 except that the monomer mixture was a 50:50 by weight 
mixture of styrene and acrylonitrile instead of the 75:25 by weight 
mixture. Table 1 below also shows the results obtained in the evaluation 
tests of the thus obtained resin composition. 
TABLE 1 
__________________________________________________________________________ 
Rubber particles 
Peripheral Mechanical properties 
Average 
parameter, 
Relaxation Planar *) 
Melt index 
diameter, 
(.mu.m).sup.-1 .multidot. (% 
time, Surface 
impact 
MI, g/10 
.mu.m 
by weight).sup.-1 
.mu. seconds 
gloss 
strength, % 
minutes 
__________________________________________________________________________ 
Example 
1 0.32 0.81 1320 96 100 3.8 
2 0.43 0.86 380 95 90 3.2 
3 0.23 0.75 1860 97 90 3.6 
4 0.10 2.32 1590 99 80 3.5 
5 0.86 0.28 740 93 80 3.3 
6 0.44 1.08 1140 95 100 2.2 
Comparative 
Example 
1 0.40 1.02 270 95 30 3.1 
2 0.48 0.65 2160 94 30 2.2 
3 1.25 0.07 1820 83 0 3.5 
4 0.06 3.47 1710 99 0 3.8 
Reference 
Example 
1 0.36 1.42 440 not moldable due to poor 
flowability 
__________________________________________________________________________ 
*) % of undestroyed among 10 test pieces