Heat-resistant high impact styrene resin, process for production thereof, and resin composition comprising said styrene resin

This invention provides a styrene copolymer resin having heat resistance and impact resistance. The resin is a moldable thermoplastic resin obtained by copolymerizing 3 to 70% by weight of a rubbery polymer and 97 to 30% by weight in total of styrene and methacrylic acid, provided that the proportions of styrene and methacrylic acid are 97 to 65% by weight and 3 to 35% by weight, respectively. The styrene and methacrylic acid are partly grafted to the rubbery polymer.

This invention relates to a novel and useful heat-resistant high impact 
styrene resin, a process for production thereof, and a resin composition 
comprising the styrene resin. 
More specifically, this invention relates to a high impact 
styrene/methacrylic acid copolymer resin having excellent heat resistance 
and surface gloss prepared by copolymerizing a monomeric mixture composed 
essentially of styrene and methacrylic acid in the presence of a rubbery 
polymer to graft part of the monomers to the rubbery polymer, and to a 
process for production thereof. The invention also pertains to a resin 
composition comprising the rubber-modified styrene/methacrylic acid 
copolymer resin and an organopolysiloxane and having high heat resistance 
as well as impact strength while retaining various other properties such 
as surface gloss, moldability, tensile strength and flexural strength in a 
well balanced combination. 
Generally, a polystyrene resin has been widely used as a molding material 
because of its excellent transparency, dimensional stability and 
moldability, but the lack of heat resistance and poor chemical resistance 
have been pointed out as the defects of the polystyrene resin when it is 
compared with various thermoplastic resins. In an attempt to remove these 
defects, a styrene/maleic anhydride copolymer resin (to be sometimes 
referred to as SMA resin hereinafter), and a styrene/acrylonitrile 
copolymer resin (to be sometimes referred to as AS resin hereinafter) have 
been proposed. In the case of the former, since the alternating 
copolymerizability of the two monomers is high, special devices and 
techniques are required in order to copolymerize a small amount of maleic 
anhydride randomly and thus to produce a resin suitable as a molding 
material. There is also a restriction on the production technique in that 
a polymerization method involving using an aqueous medium, for example a 
suspension polymerization method, cannot be employed. The latter has the 
defect of being insufficient in heat resistance and susceptible to 
coloration. 
As a transparent resin which removes these defects of the prior art and has 
a combination of heat resistance and oil resistance, a styrene/methacrylic 
acid copolymer resin (to be sometimes referred to as SMAA resin 
hereinafter), and a resin composition based on the SMAA resin were 
proposed in Japanese Laid-Open Patent Publication No. 96641/1983. The SMAA 
resin can be highly evaluated as a heat-resistant molding material because 
it has a heat-resistant temperature 20.degree. to 30.degree. C. higher 
than the aforesaid polystyrene resin and better transparency. On the other 
hand, it has poor impact strength which restricts its range of 
application. 
If, therefore, impact strength can be imparted to the SMAA resin while it 
retains its inherent properties, its application would evidently extend to 
fields requiring both heat resistance and impact strength, for example as 
automotive parts and accessories such as instrument panels, heater ducts 
and tail lamp housings; household electrical appliances such as air 
conditioner ducts, breaker covers, TV cabinets, hair curlers and 
electrical iron handles; office automation devices and related parts such 
as cassettes for VCR tapes, cassettes for audio tapes, floppy disc casings 
and housings of office automation devices; parts relating to optical and 
image-projecting devices such as camera housings, projector housings, and 
slide magazines; food packages and trays such as those adapted to be 
treated in an electronic range; and various thermal insulating materials 
for use in buildings, heaters and containers. 
So far, no high impact styrene/methacrylic acid copolymer resin has been 
developed which has properties suitable for these various uses. 
On the other hand, in order to improve the impact resistance of styrene 
resins, rubber-modified polystyrene resins containing rubbery polymers as 
dispersed particles have been produced in large quantities, and molded 
articles of such modified polystyrene resins have also been used widely. 
These rubber-modified polystyrene resins, however, have the defect of 
lacking heat resistance among various thermoplastic resins. 
A rubber-modified styrene/maleic acid copolymer resin and a rubber-modified 
styrene/acrylonitrile copolymer resin have been provided to improve the 
heat resistance of rubber-modified polystyrene resin. These resins, 
however, have the same defects as the SMA resin and AS resin mentioned 
above. Specifically, in the case of the former, since the alternating 
copolymerizability of the two monomers is high, special devices and 
techniques are required in order to copolymerize a small amount of maleic 
anhydride randomly and thus to produce a resin suitable as a molding 
material. There is also a restriction on the production technique in that 
an emulsion polymerization method cannot be employed. The latter has the 
defect of being insufficient in heat resistance and susceptible to 
coloration. 
Generally, the following methods are known for improving the moldability of 
a thermoplastic resin. 
(1) A method in which the flowability and consequently the moldability of a 
copolymer resin are improved by lowering its molecular weight. 
(2) A method in which the moldability of a copolymer resin is improved by 
mixing a low-molecular-weight compound as a plasticizing component with 
the copolymer resin. 
(3) A method in which the moldability of a resin is improved by reducing 
the content of a rubbery polymer in the resin. 
These methods, however, cannot be satisfactorily applied to a 
rubber-modified styrene/methacrylic acid copolymer resin. For example, 
according to the method (1), the mechanical strengths such as tensile 
strength of the resin is reduced as its molecular weight is lowered, and 
there is a limit on the degree of lowering the molecular weight. In the 
method (2), the lower softening point of the plasticizing component 
results in a reduction in heat resistance. If the method (3) is used, the 
reduction of the rubbery polymer content leads to a reduction in impact 
resistance which is one characteristics of the copolymer resin in 
question. For the foregoing reason, it is impossible to apply such prior 
art techniques to the rubber-modified styrene/methacrylic acid copolymer 
resin which is the basic component of the composition of the present 
invention. 
If a method or a substance is found which does not reduce impact resistance 
even when the rubbery polymer content of the resin is reduced, the 
moldability of the resin would be improved, and it would be possible to 
expect molded articles of the resin which have improved surface gloss, 
mechanical strengths such as tensile strength and flexural strength, and 
surface hardness. 
We have made extensive investigations in order to remove the various 
defects of the conventional resins described above, and found that a 
copolymer resin or a resin composition comprising the resin, which has a 
specific chemical composition, obtained by graft copolymerizing a vinyl 
monomer mixture composed essentially of styrene and methacrylic acid in 
the presence of a rubbery polymer, or melt-kneading the resulting graft 
copolymer and SMAA resin has strikingly improved impact strength while 
retaining its inherent heat resistance. We have also found that by adding 
a particularly limited amount of an organopolysiloxane to a 
rubber-modified styrene/methacrylic acid copolymer resin having a specific 
chemical composition, a product having markedly improved impact strength 
can be obtained without an adverse effect on its flowability. In other 
words, we have found that if an organopolysiloxane is used in designing a 
resin having a certain degree of impact strength, the amount of a rubbery 
polymer which is one of factors of reducing moldability and is an 
expensive reinforcing material can be reduced, and consequently, a resin 
having heat resistance, impact strength and moldability in a well balanced 
combination can be produced. 
Thus, the present invention provides a moldable thermoplastic styrene 
copolymer resin obtained by copolymerizing a mixture composed of specific 
proportions of a rubbery polymer, styrene and methacrylic acid and as 
required another vinyl monomer copolymerizable with styrene and 
methacrylic acid, and a process for producing the copolymer resin.

More specifically, this invention provides a process for producing a 
styrene copolymer resin, which comprises polymerizing 3 to 70% by weight 
of a rubbery polymer and 97 to 30% by weight in total of styrene and 
methacrylic acid and optionally another vinyl monomer copolymerizable with 
styrene and methacrylic acid, the proportions of styrene and methacrylic 
acid being 97 to 65% by weight and 3 to 35% by weight, respectively, and 
less than 50% by weight of styrene being replaceable with the other vinyl 
monomer, to perform grafting; and separating, washing, dehydrating and 
drying the resulting product. 
The present invention also provides either a resin composition comprising a 
rubber-modified styrene/methacrylic acid copolymer resin containing a 
rubbery polymer as dispersed particles having an average particle diameter 
of 0.1 to 0.8 micrometer and 3 to 35% by weight of methacrylic acid, and 
0.001 to 0.2% by weight, as silicon, of an organopolysiloxane or a mixture 
of a rubber-modified styrene/methacrylic acid copolymer resin containing a 
rubbery polymer as dispersed particles having 0.1 to 0.8 micrometer and a 
styrene/methacrylic acid copolymer resin which mixture contains 1 to 50% 
by weight of the rubbery polymer as dispersed particles and 3 to 35% by 
weight of methacrylic acid, and 0.001 to 0.2% by weight, as silicon, of an 
organopolysiloxane. The composition has high heat resistance and impact 
strength while retaining its various other properties such as moldability, 
surface gloss, tensile strength and flexural srength in a well balanced 
combination. 
What is especially important in regard to the improvement of impact 
strength is firstly that the vinyl monomers consisting of styrene and 
methacrylic acid as essential ingredients are grafted to the rubbery 
polymer, and secondly that when the rubbery polymer is contained as 
dispersed particles having an average particle diameter of 0.1 to 0.8 
micrometer, a small amount of the organopolysioxane is added as an aid for 
improving impact strength. 
The necessity for the aforesaid grafting is evident from the fact that 
when, for example, "RYULEX A-15" (SMAA resin made by Dainippon Ink and 
Chemicals, Inc.) was melt kneaded with various diene-type rubbery 
polymers, an improvement in impact strength was scarcely observed in the 
resulting compositions. Specifically, when polybutadiene (BR), 
styrene/butadiene rubber (SBR) or acrylonitrile/butadiene rubber (NBR) was 
added to the SMAA resin, it only reduced the heat resistance of the resin, 
and an increase in impact strength was only very slight. For example, when 
SBR was added in an amount of 30% by weight to the SMAA resin, the 
resulting composition had an Izod impact strength (determined by ASTM 
D-256, notched, thickness 1/4 inch) of only 3 kg-cm/cm, and lacked 
practical applicability. When attempts were made to melt-knead the SMAA 
resin with various impact-resistant resins such as high impact polystyrene 
resin (HIPS resin), acrylonitrile/butadiene rubber/styrene copolymer resin 
(ABS resin) or methyl methacrylate/butadiene rubber/styrene copolymer 
resin (MBS resin), they were not miscible with each other or had only 
insufficient compatibility, and therefore, a blend having excellent 
mechanical strength could not be obtained. 
The resin of this invention is a graft copolymer obtained by using a 
rubbery polymer, styrene and methacrylic acid as essential materials, and 
particularly using 3 to 70% by weight of the rubbery polymer and 97 to 30% 
by weight in total of styrene and methacrylic acid. Styrene must be used 
in a proportion of 97 to 65% by weight, and methacrylic acid, in a 
proportion of 3 to 35% by weight, based on the sum of styrene and 
methacrylic acid. If required, less than 50% by weight, preferably 1 to 
20% by weight, of the styrene may be replaced by another vinyl monomer 
copolymerizable with the styrene and methacrylic acid. The vinyl monomers 
should be grafted to the rubbery polymer, and the grafting ratio, or the 
percentage of the monomers grafted to the rubbery polymer, is preferably 3 
to 300%. The grafting ratio is analyzed in accordance with the following 
method. 
About one gram of the sample including R % of rubbery polymer is dissolved 
in 100 ml of a mixture of toluene and methanol in a volume ratio of 9:1. 
The insoluble matter is separated by an ultracentrifuge, dried and 
weighed. 
Let the amounts of the sample and the insoluble matter be S grams and D 
grams, respectively, the grafting ratio is calculated from the following 
equation. 
##EQU1## 
The addition of the organopolysiloxane will now be described. 
The heat-resistant high impact copolymer resin in accordance with this 
invention has improved impact strength with an increase in the amount of 
the rubbery polymer added, but it cannot be denied that this tends to 
reduce the flowability and therefore the moldability of the resin. We 
carried out investigations in order to increase the impact strength of the 
heat-resistant high impact styrene copolymer resin of this invention per 
rubbery polymer unit and thus to reduce the amount of the rubbery polymer 
and increase the flowability of the resin. These investigations have led 
to the discovery of the surprising fact that when an organopolysiloxane is 
added to a rubber-modified styrene methacrylic acid copolymer resin 
containing a grafted product of a rubbery polymer having an average 
particle diameter within the range of 0.1 to 0.8 micrometer, the impact 
strength of the resin is markedly improved without substantially changing 
the various properties of the resin such as flowability. 
The effect of adding the organopolysiloxane in designing a resin having a 
fixed level of impact strength is that the amount of the rubbery polymer 
which is one factor of reducing moldability and is itself an expensive 
reinforcing material can be decreased, and consequently, a resin 
composition having a well balanced combination of heat resistance, impact 
strength and moldability can be produced economically. 
By way of example, it has been ascertained that a mixture of 40 parts of a 
rubber-modified styrene/methacrylic acid copolymer resin containing 50% by 
weight of a rubbery polymer having an average particle diameter of 0.35 
micrometer and 13% by weight of methacrylic acid and 60 parts by weight of 
a styrene/methacrylic acid copolymer resin has an Izod impact strength 
(notched; the same hereinafter) of 8.0 kg-cm/cm, but when 0.08% by weight 
(0.03% by weight as silica) of an organopolysiloxane is added to the 
resin, the Izod impact strength increases to 12.0 kg-cm/cm which is about 
1.5 times as large. 
It is not certain why the addition of the organopolysiloxane increases 
impact strength. One possibility is that by the presence of the 
organopolysiloxane, the styrene/methacrylic acid copolymer resin grafted 
to the rubbery polymer gains resistance to breakage during pelletization 
by an extruder or during injection molding. 
This will be more specifically described below. A powdery graft copolymer 
obtained by graft-copolymerizing styrene and methacrylic acid with a 
rubbery polymer (latex) in emulsion, salting out the product, washing it 
and then drying it (namely a rubber-modified styrene/methacrylic acid 
copolymer resin), either as such or as a mixture with a separately 
prepared styrene/methacrylic acid copolymer resin, is kneaded in an 
extruder and pelletized, and the pellets are analyzed. Analysis of the 
pellets shows that the grafting ratio is low when no organopolysiloxane is 
added to the rubber-modified copolymer resin, whereas when the 
organopolysiloxane is added to the rubber-modified copolymer resin, the 
grafting ratio is high. 
When the shapes of the dispersed particles of the rubbery polymer in the 
above two types of pellets are observed from an electron micrograph of 
their ultrathin section, a marked difference is found in the shape of 
rubber particles between the two. Specifically, when the copolymer resin 
does not contain the organopolysiloxane (see FIG. 1), the rubber phase is 
drastically deformed. It is believed that the styrene/methacrylic acid 
copolymer resin grafted to the rubbery polymer (rubber particles) and 
covering the surface of the rubbery polymer is peeled under a high shear 
within the extruder, and the protecting action on the rubber phase by 
grafting is lost. In contrast, when the copolymer contains the 
organopolysiloxane (FIG. 2), the rubber particles in the rubber phase are 
maintained spherical. This is presumably because the styrene/methacrylic 
acid copolymer resin covering the surface of the rubber particles is not 
peeled even under a high shear within the extruder, and the grafting ratio 
at the time of polymerization is retained, with the result that the 
compatibility of the rubber-modified resin with the styrene/methacrylic 
acid copolymer resin as a matrix polymer is good, and the impact strength 
can be improved. 
It is especially important in this invention that the rubbery polymer in 
the form of dispersed particles should have an average particle diameter 
in the range of 0.1 to 0.8 micrometer. If the average particle diameter 
falls outside this range, the effect of adding the organopolysiloxane is 
unexpectedly not produced. 
The fact that the effect of adding the organopolysiloxane can be produced 
only in the case of particle sizes with a relatively narrow range seems to 
be inherent to the rubber-modified styrene/methacrylic acid copolymer 
resin. 
The average particle diameter of the dispersed particles of the rubbery 
polymer is calculated from the following equation after measuring the 
particle diameters of 200 to 500 rubbery polymer particles present in the 
visual field of the electron micrograph of the resin obtained by the 
ultrathin section method. 
EQU Average particle diameter=.SIGMA.n.sub.i D.sub.i.sup.2 /.SIGMA.n.sub.i 
D.sub.i [I] 
wherein D.sub.i is a typical value of the ith class when the measured 
diameters are classed at 0.1 micrometer intervals and is an intermediate 
value between the upper and lower side's values which distinguish that 
class from other classes, and n.sub.i is the sum of rubbery polymer 
dispersed particles of the ith class. 
Typical examples of the rubbery polymer are BR, SBR, NBR and 
ethylene/propylene/polyene rubber (EPDM). The suitable amount of the 
rubbery polymer is 3 to 70 parts by weight, preferably 3 to 50 parts by 
weight, when the total amount of the graft copolymer component is 100 
parts by weight. If it is less than 3 parts by weight, an increase in 
impact strength is not observed virtually. If, on the other hand, it 
exceeds 70 parts by weight, the resulting resin becomes very difficult to 
mold. 
When the average particle diameter of the rubbery polymer is within the 
range of 0.1 to 0.8 micrometer, the impact strength of the resulting 
product is improved effectively by incorporating a small limited amount of 
the organopolysiloxane. Hence, the amount of the rubbery polymer can be 
decreased to 1 to 50 parts by weight. 
The suitable amount of methacrylic acid in the vinyl monomers is 3 to 35% 
by weight. If it is less than 3% by weight, an increase in heat resistance 
is difficult to expect. On the other hand, if it exceeds 35% by weight, 
the melt viscosity of the resulting resin becomes high, and its molding 
becomes difficult. 
The suitable amount of styrene in the vinyl monomers is 97 to 65% by 
weight. Less than 50% by weight, preferably 1 to 20% by weight, of styrene 
may be replaced by another copolymerizable vinyl monomer. 
Since the grafting ratio of the graft copolymer resin is an important 
factor with regard to impact strength, the suitable grafting ratio in this 
invention is 3 to 300% by weight, preferably 3 to 150%. 
Typical examples of the other copolymerizable vinyl monomer include 
alpha-methylstyrene, t-butylstyrene, halogen-substituted styrene, 
vinyltoluene, (meth)acrylonitrile, alpha-chloroacrylonitrile and 
(meth)acrylic esters. 
The organopolysiloxane to be added to increase effects on the impact 
strength of the rubber in the styrene/methacrylic acid copolymer resin in 
accordance with this invention denotes a polymer having structural units 
represented by the following general formula [II] 
##STR1## 
wherein R.sub.1 and R.sub.2 are identical or different and each represents 
an alkyl, aryl or aralkyl group, 
and may be a homopolymer-type organopolysiloxane composed of only one type 
of such a structural unit, or a copolymer-type organopolysiloxane of the 
random, block or graft type. 
The organic groups in the above organopolysiloxane may be partly 
substituted by a hydroxyl group, an alkoxy group, a hydroxyalkyl group or 
a polyhydroxyalkylene group. 
Needless to say, the various organopolysiloxanes above may be used as a 
mixture of two or more. Typical examples of the organopolysiloxane are 
dimethylpolysiloxane, methylphenylpolysiloxane, diphenylpolysiloxane and 
methylbenzylpolysiloxane. Diethylpolysiloxane is preferred. The 
organopolysiloxane used in this invention should have a boiling point of 
at least 120.degree. C., and be thermally and chemically stable at 
temperatures used to mold the resin composition. Suitable 
organopolysiloxanes which meet these requirements are those having a 
viscosity of 10 to 100,000 centistokes, preferably 15 to 50,000 
centistokes, especially preferably 100 to 10,000 centistokes. 
The suitable amount of the organopolysiloxane used is 0.001 to 0.2% by 
weight, preferably 0.002 to 0.08% by weight, especially preferably 0.002 
to 0.05% by weight, as silicon, based on the total amount of the 
rubber-modified styrene/methacrylic acid copolymer resin composition of 
this invention. If it is less than 0.001% by weight, the improving effect 
contemplated by this invention cannot be expected. If, on the other hand, 
it exceeds 0.2% by weight, the improving effect does not increase 
correspondingly, and rather causes a reduction in mechanical strengths 
such as tensile strength. Thus, amounts outside the specified range are 
objectionable. 
The content of the organopolysiloxane as silicon can be determined from the 
amount of the organopolysiloxane added, or by atomic absorption 
spectrochemical analysis of the silicon atoms. 
The organopolysiloxane may be added during the copolymerization of forming 
the rubber-modified styrene/methacrylic acid copolymer, or during 
pelletization in an extruder. When the rubber-modified styrene/methacrylic 
acid copolymer resin is to be blended with another resin, the 
organopolysiloxane may be included in advance in the other resin to be 
blended. Typical other blending resins include, for example, styrene 
resins such as polystyrene, styrene/acrylonitrile copolymer or 
styrene/methyl methacrylate copolymer, and various thermoplastic resins 
such as poly(methyl methacrylate), polycarbonate or polyphenylene oxide. 
To prepare the desired resin by the process of this invention, graft 
polymerization methods for obtaining high impact resins which are 
generally known can be applied. Examples are as follows. 
(1) A bulk polymerization method which comprises dissolving a rubbery 
polymer in vinyl monomers and polymerizing them at 60.degree. to 
150.degree. C. in the presence or absence of an initiator. 
(2) A solution polymerization method which follows the method (1) but in 
which a solvent is used in order to decrease the viscosity of the solution 
and to facilitate its stirring or the conveyance of the liquid polymer and 
the polymerization is carried out in a diluted system. 
(3) A bulk-suspension polymerization method which comprises performing the 
polymerization partially in accordance with the method (1), and thereafter 
completing the polymerization in aqueous suspension. 
(4) An emulsion polymerization method in which a rubber in the form of a 
latex is used as the rubbery polymer and the graft polymerization is 
carried out at 40.degree. to 100.degree. C. in the emulsified state in the 
presence of a peroxide as an initiator. 
In order to obtain a resin having high impact strength and excellent 
quality, it is necessary to use a special version of the emulsion 
polymerization method (4). 
The methods (1) to (4) can be applied to the production of the resin 
contemplated by this invention, but have some inconveniences. 
Specifically, the bulk polymerization method (1) and the solution 
polymerization method (2) are adapted for mass production and are carried 
out on a large scale at high investment costs. Furthermore, with these 
methods, the stirring or conveying of the polymerization mixture or 
product tends to become difficult as the rubber content increases. 
According to the bulk-suspension polymerization method (3), as the rubber 
concentration increases, the viscosity of the polymerization mixture 
increases and this is liable to cause troubles such as the agglomeration 
of the dispersed particles before the suspending step. Hence, the rubber 
content is usually limited to 8 to 10% by weight, and it is sometimes 
difficult to expect an improvement in properties and appearance, 
particularly high impact strength. According to the emulsion 
polymerization method (4), methacrylic acid causes coagulation or breaking 
of the latex, and the system becomes unstable during polymerization and 
may finally be agglomerated (this is due to the deactivation of the 
surface active agent used as an emulsifier in the latex, and this 
phenomenon is frequently observed in an emulsified system containing an 
acid group-containing monomer). 
We have extensively worked in order to overcome these difficulties in the 
prior art, and have found that in the emulsion polymerization method, the 
method of adding methacrylic acid greatly affects the stability of the 
emulsified system and the properties of the resulting copolymer resin. 
Specifically, we have found that by continuously adding a part of 
methacrylic acid in the process of this invention as the polymerization 
proceeds, the agglomeration of the latex during the polymerization can be 
inhibited, and the copolymerization composition can be made uniform, and 
therefore that a resin having higher impact strength than a resin obtained 
by the batch in which the total amount of the monomers are added to the 
reactor before starting the copolymerization process can be obtained. 
Such a special emulsion polymerization method makes it possible to produce 
a copolymer resin which contains as high as 70% by weight of rubber. Thus, 
the resulting resin has strikingly improved impact strength over those 
obtained by other methods and excellent surface gloss as well. 
Furthermore, when the high-impact resin produced by the specific emulsion 
polymerization method in the process of this invention is kneaded with a 
previously prepared SMAA resin, it is easy to adjust the impact strength, 
heat resistance and flowability of the resulting composition. Accordingly, 
this specific method additionally brings about the advantage that products 
can be designed according to the intended usages. 
It will be apparent from the foregoing description that although the 
copolymer resin of this invention can be produced by using the methods (1) 
to (4), the aforesaid special emulsion polymerization method is especially 
suitable in order to obtain resins having excellent quality. By following 
the specific process of this invention, a copolymer resin can be obtained 
which will give molded articles having excellent impact strength, heat 
resistance and surface gloss, and therefore, high-grade molding materials 
comparable to conventional engineering plastics can be provided in the 
fields of electric appliances and precision machinery and appliances as 
well as automotive parts. 
The emulsion polymerization method in this invention will now be described 
in detail. In the following description, a product obtained by graft 
emulsion polymerization of styrene and methacrylic acid in the presence of 
the rubbery polymer latex is referred to as a copolymer resin (A), and a 
styrene/methacrylic acid copolymer resin used to adjust impact strength 
suitably by melt kneading with the resin (A), as a copolymer (B). 
The copolymer resin (A) is produced by emulsion polymerization of 3 to 70% 
by weight (as solids) of the rubbery polymer latex and 97 to 30% by weight 
in total of styrene and methacrylic acid (provided that styrene is used in 
a proportion of 97 to 65% by weight, and methacrylic acid, in a proportion 
of 3 to 35% by weight). But in performing the polymerization, all of the 
rubbery polymer, all of the styrene and 1 to 70% by weight of methacrylic 
acid are first fed into a reactor, and the remaining 99 to 30% by weight 
of methacrylic acid is continuously introduced into the reactor after the 
starting of the copolymerization before the polymerization conversion 
reaches 90%. The emulsion polymerization is carried out with stirring in 
the presence of an emulsifier and an initiator at a temperature of 
40.degree. to 100.degree. C. and for 3 to 12 hours. Then, various 
inorganic salts such as calcium chloride, magnesium chloride, sodium 
chloride or sodium sulfate and/or various acidic substances such as 
hydrochloric acid, sulfuric acid or acetic acid are added to coagulate and 
precipitate the product. The coagulated product is collected by 
filtration, washed with water and dried to give the copolymer resin (A). 
Needless to say, various known initiators, chain transfer agents and 
antioxidants may be used in the above process. 
The type of the surface-active agent (emulsifier) used in the process is 
important to the stability of the emulsified system, and anionic 
surfactants of the sulfate type and sulfonate type are suitable. The use 
of metal salts of higher fatty acids which are usually employed in 
emulsion polymerization is not desirable since they break the emulsion 
system during polymerization. 
As stated hereinabove, typical rubbery polymer latices used in this process 
are polybutadiene latex, SBR latex, NBR latex and EPDM latex. In view of 
the properties of the final product, rubber latices having a high gel 
content are preferred. 
The amount of methacrylic acid in the vinyl monomers is a very important 
factor because it greatly affects the heat resistance of the final 
product. If it is less than 3% by weight, the effect of methacrylic acid 
cannot be produced sufficiently. If it exceeds 35% by weight, the 
emulsified system becomes unstable and coarse particles are liable to form 
by the breakage of the latex. Hence, amounts outside the specified range 
are not desirable. 
In obtaining the copolymer (A), it is recommended to add methacrylic acid 
by a special method which comprises introducing 1 to 70% by weight, 
preferably 1 to 50% by weight, of methacrylic acid at the start of the 
reaction, and continuously adding the remainder (i.e. 99 to 30% by weight, 
preferably 99 to 50% by weight) of methacylic acid with the progress of 
the polymerization before the polymerization conversion reaches 90%. 
When the amount of methacrylic acid to be fed before starting the 
polymerization is less than 1% by weight, a homopolymer of styrene tends 
to form during the early stage of the polymerization, and the properties 
of the final product tend to be deteriorated. If it exceeds 70% by weight, 
the emulsified system becomes undesirably unstable. 
Furthermore, in this specific method, the addition of methacrylic acid is 
preferably effected at a time before the polymerization conversion reaches 
90%. When it is added after the 90% conversion has been reached, 
methacrylic acid can no longer be substantially taken into the resulting 
copolymer resin. 
The graft copolymer resin (A) so obtained is supplied in the form of a 
powder or pellets and used as a molding material. 
The copolymer resin (B) can be obtained by heat polymerizing styrene and 
methacrylic acid in the presence or absence of a polymerization initiator 
as described, for example, in Japanese Laid-Open Patent Publication No. 
96641/1983 cited hereinabove. 
Heat-resistant high impact resins of various grades can be obtained by 
kneading the resulting resin (A) and the resin (B). The resins (A) and (B) 
may be kneaded in desired ratios. The preferred weight ratio of (A) to (B) 
is 20-70:80-30. 
Kneading of the resins (A) and (B) is carried out in a customary manner by 
known conventional devices such as a two-roll mill, a Banbury mixer and an 
extruder. 
Various additives normally used in styrene resins or rubber-nmodified 
styrene resins of the above types, such as plasticizers, heat, light or 
oxygen stabilizers, fire retardants, coloring agents, lubricants, mold 
releasing agents and antistatic agents may be added to the resulting resin 
composition of this invention. 
The heat-resistant high impact styrene/methacrylic acid copolymer resin of 
this invention and the resin composition comprising the copolymer resin 
and the organopolysiloxane in accordance with this invention can be easily 
injection-molded, extruded or compression-molded by ordinary molding 
machines. 
The following Referential Examples, Examples and Comparative Examples 
illustrate the present invention more specifically. All parts and 
percentages are by weight unless otherwise specified. The various 
properties were tested by the following methods. 
Izod impact strength 
Measured in accordance with ASTM D-265 using a 1/4 inch thick notched test 
specimen at 23.degree. C. 
Heat distortion temperature 
Measured in accordance with ASTM D-648 under a maximum fiber stress of 18.6 
kg/cm.sup.2. 
Surface gloss 
In accordance with JIS Z-8741, the specular gloss at an incident angle of 
60 degrees was measured. 
Melt flow rate 
Measured in accordance with ASTM D-1238 under condition I. 
Yield strength 
Measured in accordance with ASTM D-638. 
Flexural strength 
Measured in accordance with ASTM D-790. 
REFERENTIAL EXAMPLE 1 
Preparation of SMAA resin: 
A 5-liter autoclave equipped with a stirrer was charged with 200 parts of 
distilled water, and 0.005 part of sodium dodecylbenzenesulfonate and 0.5 
part of partially saponified polyvinyl alcohol as a suspension stabilizer 
were added and dissolved. Then, the autoclave was successively charged 
with 85 parts of styrene, 15 parts of methacrylic acid, 0.05 part of 
tertiary dodecyl mercaptan, 0.2 part of di-tert.butyl 
peroxyhexahydroterephthalate and 0.1 part of tert.butyl perbenzoate. With 
stirring at a speed of 400 rpm, the temperature was raised to 85.degree. 
C., and the monomers were suspension-polymerized for 10 hours. Then, the 
reaction was further carried out at 120.degree. C. for 3 hours. 
The resulting granular SMAA resin was washed, dehydrated and dried. 
REFERENTIAL EXAMPLE 2 
Preparation of a styrene/methyl methacrylate/methacrylic acid copolymer 
resin: 
The same reactor as used in Referential Example 1 was charged with 200 
parts of distilled water, and 0.005 part of sodium dodecylbenzenesulfonate 
and 1 part of partially saponified polyvinyl alcohol as a suspension 
stabilizer were added and dissolved. Then, the autoclave was successively 
charged with 65 parts of styrene, 20 parts of methyl methacrylate, 15 
parts of methacrylic acid, 0.7 part of benzoyl peroxide, 0.1 part of 
tert.butyl perbenzoate and 0.05 part of tert.dodecyl mercaptan, and with 
stirring at a speed of 400 rpm, the temperature was raised to 80.degree. 
C. The monomers were suspension polymerized for 10 hours at this 
temperature, and the reaction was further carried out at 120.degree. C. 
for 3 hours. 
The resulting granular styrene/methyl methacrylate/methacrylic acid 
copolymer resin was washed, dehydrated and dried. 
EXAMPLE 1 
The same reactor as used in Referential Example 1 was charged with the 
following materials. 
______________________________________ 
Polybutadiene latex 52 parts 
(solid rubber content = 57.4%) 
Styrene 60 parts 
Methacrylic acid 3 parts 
Potassium persulfate 0.3 parts 
tert.Dodecyl mercaptan 0.15 parts 
Sodium dodecylbenzenesulfonate 
2 parts 
Distilled water 200 parts 
______________________________________ 
Nitrogen gas was introduced into the reactor, and with stirring, the 
temperature was raised to 70.degree. C. After this temperature was 
reached, 7 parts of methacrylic acid was continuously added over the 
course of 3 hours. The emulsion polymerization was carried out at this 
temperature for 2 hours. 
To the resulting latex was added a 10% aqueous solution of calcium chloride 
in an amount of 2.5% based on the solids content of the latex, and with 
stirring, the latex was coagulated at a temperature of 90.degree. to 
110.degree. C. The coagulated product was then collected by filtration, 
washed with water, dehydrated, and dried to obtain a powdery graft 
copolymer resin. 
Then, 0.2 part of "Irganox 1076" (an antioxidant made by Ciba-Geigy, West 
Germany) was added to the copolymer resin, and the mixture was pelletized 
by an extruder at a cylinder temperature of 230.degree. C. 
The pellets were then injection-molded and the properties of the molded 
specimen were evaluated. 
The results are summarized in Table 1. 
EXAMPLE 2 
A graft copolymer resin was produced in the same way as in Example 1 except 
that the starting materials were changed as follows: 
______________________________________ 
Polybutadiene latex 52 parts 
(same as in Example 1) 
Styrene 50 parts 
Methacrylic acid (*) 10 parts 
Methyl methacrylate 10 parts 
Potassium persulfate 0.3 parts 
tert.Dodecylmercaptan 0.15 parts 
Sodium dodecylbenzenesulfonate 
2 parts 
Distilled water 200 parts 
______________________________________ 
(*): Three parts of methacrylic acid was charged initially, and the 
remaining 7 parts, added continuously as the polymerization proceeded. 
After charging the reactor with these materials, the same operation as in 
Example 1 was carried out, and the properties of the resulting resin were 
evaluated. 
The results are summarized in Table 1. 
EXAMPLE 3 
The same reactor as used in Referential Example 1 was charged with the 
following materials. 
______________________________________ 
Styrene 82 parts 
Methacrylic acid 10 parts 
Polybutadiene rubber 8 parts 
tert.Dodecylmercaptan 0.08 parts 
______________________________________ 
They were thoroughly dissolved at 60.degree. C., and the inside of the 
reactor was purged with nitrogen gas. With stirring, the monomers were 
polymerized in bulk for 4 hours while the temperature of the inside of the 
reactor was maintained at 110.degree. C. The reaction mixture was cooled 
to 70.degree. C., and 0.2 part of di-tert.butyl 
peroxyhexahydroterephthlate and 0.05 part of tert.butyl perbenzoate were 
added and dissolved. 
Then, an aqueous solution composed of 0.5 part of partially saponified 
polyvinyl alcohol, 0.005 part of sodium dodecylbenzenesulfonate and 100 
parts of distilled water was added to the polymerization system with 
stirring to suspend the bulk polymerization product. The temperature of 
the system was raised to 90.degree. C., and the suspension polymerization 
was carried out for 8 hours. Then the reaction was further carried out at 
120.degree. C. for 3 hours. 
The resulting copolymer resin beads were washed, dehydrated, dried, 
pelletized and injection-molded in the same way as in Example 1, and the 
properties of the molded specimen were evaluated. 
The results are summarized in Table 1. 
EXAMPLE 4 
This Example illustrates a blend of a graft copolymer resin and SMAA resin. 
A graft copolymer was prepared in the same way as in Example 1 except that 
the amounts of the polybutadiene latex and styrene were changed to 87 
parts and 40 parts, respectively. 
Sixty parts of the graft copolymer resin was mixed with 40 parts of SMAA 
resin and 0.2 part of "Irganox 1076", and the mixture was pelletized in an 
extruder at a cylinder temperature of 230.degree. C. The pellets were then 
injection-molded, and the properties of the molded specimen were 
evaluated. The results are summarized in Table 2. 
EXAMPLE 5 
Forty parts of the same graft copolymer resin as obtained in Example 4 and 
60 parts of SMAA resin were used. Otherwise, in the same way as in Example 
4, pelletization and injection molding were carried out, and the 
properties of the molded specimen were evaluated. 
The results are summarized in Table 2. 
EXAMPLE 6 
The amounts of the graft copolymer resin and the SMAA rsin were changed to 
20 parts and 80 parts, respectively. Otherwise, in the same way as in 
Example 4, pelletization and injection molding were carried out, and the 
properties of the molded specimen were evaluated. 
The results are summarized in Table 2. 
COMATIVE EXAMPLE 1 
The same SMAA resin as obtained in Referential Example 1 was used instead 
of the grafted copolymer. Otherwise, in the same way as in Example 1, 
pelletization and injection molding were carried out, and the properties 
of the molded specimen were evaluated. 
The results were summarized in Table 1. 
COMATIVE EXAMPLE 2 
Seventy parts of the same SMAA resin as obtained in Referential Example 1, 
30 parts of "ASAFLEX" (SBR made by Asahi Chemical Industry Co., Ltd.) and 
0.2 part of "Irganox 1076" were mixed, and the mixture was pelletized in 
an extruder at a cylinder temperature of 230.degree. C. 
The pellets were then injection-molded, and the properties of the molded 
specimen were evaluated. 
The results are summarized in Table 2. 
It is particularly noteworthy that the molded specimen had an Izod impact 
strength of 3.0 kg-cm/cm. 
EXAMPLE 7 
The same reactor as used in Referential Example 1 was charged with the 
following materials. 
______________________________________ 
Polybutadiene latex 96.2 parts 
(solid rubber content 52%) 
Styrene 40 parts 
Methacrylic acid 3 parts 
Potassium persulfate 0.2 parts 
tert.Dodecylmercaptan 0.008 parts 
Sodium dodecylbenzenesulfonate 
0.8 parts 
Distilled water 200 parts 
______________________________________ 
Nitrogen gas was introduced into the reactor, and with stirring, the 
temperature was raised to 70.degree. C. When this temperature was reached, 
7 parts of methacrylic acid was continuously added over the course of 3 
hours. Further, the emulsion polymerization was carried out at the same 
temperature for 2 hours. 
To the resulting copolymer latex was added a 10% aqueous solution of 
calcium chloride in an amount corresponding to 2.5% of the solids of the 
latex. With stirring, the latex was coagulated at a temperature in the 
range of 110.degree. to 130.degree. C. The coagulated product was 
collected by filtration, washed with water, dehydrated and dried to obtain 
a powdery graft copolymer resin. 
Forty parts of the graft copolymer resin was mixed with 60 parts of the 
SMAA resin obtained in Referential Example 1 and 0.2 part of "Irganox 
1076", and the mixture was pelletized by an extruder at a cylinder 
temperature of 230.degree. C. 
The pellets were injection-molded, and the properties of the molded 
specimen were evaluated. The results are summarized in Table 3. 
The molded specimen had an Izod impact strength of 8.0 kg-cm/cm. 
The amount of the rubbery polymer in the resulting resin composition was 
20%, and the rubbery polymer had an average particle diameter of 0.35 
micrometer. 
EXAMPLE 8 
A molded specimen was prepared in the same way as in Example 7 except that 
before pelletization in an extruder, 0.08 part of "TORAY SILICONE SH-200" 
(an organopolysiloxane made by Toray Silicone Co., Ltd.) was added to the 
mixture. 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
As shown in Table 3, the resin composition had a silicon content of 0.03%, 
and the molded specimen had an Izod impact strength of 12.7 kg-cm/cm. 
EXAMPLE 9 
SMAA resin was prepared in the same way as in Referential Example 1 except 
that 0.2 part of "TORAY SILICONE SH-200" was added at the time of feeding 
styrene. A molded specimen was prepared in the same way as in Example 8 
except that 60 parts of the SMAA resin and 40 parts of the same graft 
copolymer resin as obtained in Example 7 were mixed without the addition 
of "TORAY SILICONE SH-200". 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
The resulting resin composition had a silicon content of 0.045%, and the 
rubbery polymer in it had an average particle diameter of 0.35 micrometer. 
The Izod impact strength of the molded specimen was 12.1 kg-cm/cm. 
EXAMPLE 10 
A graft copolymer resin was prepared in the same way as in Example 7 except 
that 0.2 part of "TORAY SILICONE SH-200" was added at the time of feeding 
styrene. A molded specimen was prepared in the same way as in Example 8 
except that 40 parts of the resulting graft copolymer resin and 60 parts 
of the same SMAA resin as obtained in Referential Example 1 were mixed 
without the addition of "TORAY SILICONE SH-200". 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
The resulting resin composition had a silicon content of 0.03%, and the 
rubbery polymer in the composition had an average particle diameter of 
0.35 micrometer. 
The Izod impact strength of the molded specimen was 11.9 kg-cm/cm. 
EXAMPLE 11 
A molded specimen was prepared in the same way as in Example 7 except that 
the amounts of the SMAA resin and the graft copolymer resin were changed 
to 40 parts and 60 parts, respectively. 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
As shown in Table 3, the Izod impact strength of the molded specimen was 
12.5 kg-cm/cm. 
EXAMPLE 12 
A powdery graft copolymer resin was prepared in the same way as in Example 
7 except that at the time of feeding styrene, 10 parts of the entire 
styrene (40 parts) was replaced by methyl methacrylate. 
Forty parts of the graft copolymer resin was mixed with 60 parts of the 
styrene/methyl methacrylate/methacrylic acid copolymer resin obtained in 
Referential Example 2, and the mixture was pelletized in an extruder at a 
cylinder temperature of 230.degree. C. 
The pellets were then injection-molded, and the properties of the molded 
specimen were evaluated. The results are summarized in Table 3. 
The rubbery polymer in the resulting resin composition had an average 
particle diameter of 0.35 micrometer, and the molded specimen had an Izod 
impact strength of 8.1 kg-cm/cm. 
EXAMPLE 13 
A molded specimen was prepared in the same way as in Example 12 except that 
before pelletization in the extruder, 0.08 part of "TORAY SILICONE SH-200" 
was added. 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
The resulting resin composition had a silicon content of 0.03%. The Izod 
impact strength of the molded specimen was 15 kg-cm/cm. 
EXAMPLE 14 
A molded specimen was prepared in the same way as in Example 8 except that 
2.0 parts of a mineral oil was added at the time of feeding styrene. 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
COMATIVE EXAMPLE 3 
This example shows that the addition of an organopolysiloxane in an amount 
exceeding 0.2% as silicon does not give a corresponding increase in 
effect. 
A molded specimen as a control was prepared in the same way as in Example 8 
except that before pelletization in the extruder, 0.8 part of "TORAY 
SILICONE SH-200" was added. 
The properties of the molded specimen were evaluated, and the results are 
summarized in Table 3. 
As shown in Table 3, the resulting resin composition had a silicon content 
of 0.3%, and the Izod impact strength of the molded specimen was 12.1 
kg-cm/cm. 
TABLE 1 
______________________________________ 
Example Comparative 
1 2 3 Example 1 
______________________________________ 
Synthesis method 
Emulsion Emulsion Bulk- Suspension 
polymeri- 
polymeri- 
emulsion 
polymeri- 
zation zation polymeri- 
zation 
zation 
Polymer com- 
position (parts) 
Styrene 60 50 82 85 
Methacrylic acid 
10 10 10 15 
Methyl meth- 10 
acrylate 
Rubbery polymer 
30 30 8 -- 
Izod impact 
12.5 13.5 7.4 1.2 
strength 
(kg-cm/cm) 
Heat distortion 
105 103 100 110 
temperature (.degree.C.) 
Surface gloss 
93 89 62 
Grafting ratio (%) 
45 48 150 -- 
______________________________________ 
TABLE 2 
______________________________________ 
Com- 
parative 
Example Example 
4 5 6 2 
______________________________________ 
Blending composition (parts) 
Graft copolymer 20 40 60 -- 
resin 
SMAA resin 80 60 40 70 
"ASAFLEX 810" -- -- -- 30 
Composition of 
the blend (parts) 
Styrene 76 67 58 60 
Methacrylic acid 
14 13 12 10 
Rubbery polymer 10 20 30 30 
Izod impact strength 
5.5 8.0 12.5 
3.0 
(kg-cm/cm) 
Heat distortion temperature 
110 108 105 105 
(.degree.C.) 
Surface gloss 91 88 87 75 
______________________________________ 
TABLE 3 
__________________________________________________________________________ 
Compara- 
tive 
Example Example 
7 8 9 10 11 12 13 14 3 
__________________________________________________________________________ 
Contents of main 
components in the 
composition (%) 
Methacrylic acid 
13 13 13 13 12 13 13 13 13 
Methyl methacrylate 16 16 
Silicon 0.03 
0.045 
0.03 0.03 
0.03 
0.3 
Rubbery polymer 
20 20 20 20 30 20 20 20 20 
Average particle diameter 
0.35 0.35 
of the rubbery polymer 
Properties 
Izod impact strength 
8.0 12.7 
12.1 
11.9 
12.5 
8.1 15 13.5 
12.1 
(kg-cm/cm) 
Melt flow rate 
0.22 
0.21 
0.20 
0.20 
0.03 
0.80 
0.80 
0.22 
0.21 
(g/10 min.) 
Heat distortion 
108 108 108 108 103 101 100 107 108 
temperature (.degree.C.) 
Yield strength 
463 412 440 445 370 420 412 400 400 
(kg/cm.sup.2) 
Flexural strength 
542 512 530 537 385 505 500 500 500 
(kg/cm.sup.2) 
__________________________________________________________________________