Thermoplastic resin composition

A thermoplastic resin composition well balanced among heat resistance, high-impact properties and moldability is provided, which composition comprises 50 to 90 parts by weight of a random copolymer (A) composed mainly of .alpha.-methylstyrene units and acrylonitrile units, 0.2 to 1.0 part by weight based on 100 parts by weight of the random copolymer (A), of an oligomer (B) composed mainly of .alpha.-methylstyrene units and acrylonitrile units and having a molecular weight of 200 to 500 and 10 to 50 parts by weight of a dienic rubber-aromatic vinyl monomer-vinyl cyanide graft copolymer (C).

BACKGROUND OF THE INVENTION 
This invention relates to a thermoplastic resin composition having a good 
moldability and also well balanced between heat resistance and high-impact 
properties. 
It has been well known that .alpha.-methylstyrene-acrylonitrile copolymers 
are generally blended with ABS resins to improve the heat resistance of 
ABS resins (e.g., see Japanese Patent Application laid-open No. Sho 
58-117241/1983). 
However, .alpha.-methylstyrene-acrylonitrile copolymers have a high thermal 
deformation temperature and nevertheless has a high melt viscosity; thus 
thermoplastic resin compositions consisting of such copolymers and ABS 
resins and having good heat resistance have a far lowered moldability as 
compared with that of general ABS resins. For improving the moldability of 
conventional thermoplastic resins hving a good heat resistance, it is 
effective to reduce the molecular weight of 
.alpha.-methylstyrene-acrylonitrile copolymers, but their high-impact 
properties and heat resistance lower exponentially. Further, in the case 
of addition of lubricants, too, their moldability and high impact 
properties are enhanced, but their heat resistance lowers. Thus, in the 
design of thermoplastic resin compositions having a good heat resistance, 
it has been the most important problem to balance the three factors of 
heat stability, moldability and high-impact properties. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a thermoplastic resin 
composition having a good moldability and well balanced between 
high-impact properties and heat resistance. 
The present invention resides in a thermoplastic resin composition 
comprising 50 to 90 parts by weight of a random copolymer (A) composed 
mainly of .alpha.-methylstyrene units and acrylonitrile units, 0.2 to 1.0 
part by weight based on 100 parts by weight of said random copolymer (A), 
of an oligomer (B) composed mainly of .alpha.-methylstyrene units and 
acrylonitrile units and having a molecular weight of 200 to 500 and 10 to 
50 parts by weight of a dienic rubber-aromatic vinyl-vinyl cyanide 
graft-copolymer (C). 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be described more concretely. 
The molecular weight of the .alpha.-methylstyrene-acrylonitrile copolymer 
as the component (A) is preferably in the range of 800 to 1,600 .ANG. in 
terms of number average chain length measured on the basis of polystyrene. 
If the copolymer used has a number average chain length less than 800 
.ANG., its moldability is improved, but its high-impact properties and 
heat resistance lower. On the other hand, if the copolymer used has a 
number average chain length more than 1,600 .ANG., the moldability lowers 
notably and further the residual strain of practically molded product 
becomes greater, which results in lowering the heat resistance of the 
molded product; thus the object of the present invention cannot be 
attained. 
Further, the ratio (A.sub.W /A.sub.N) of the weight average chain length 
(A.sub.W) to the number average chain length of the 
.alpha.-methylstyrene-acrylonitrile copolymer is preferably in the range 
of 1.5 to 3.0. Even if the A.sub.W /A.sub.N is either less than 1.5 or 
more than 3.0, the resulting copolymer cannot have properties which are 
superior in both of heat resistance and moldability. The 
.alpha.-methylstyrene-acrylonitrile copolymer is composed of 65 to 75% by 
weight of .alpha.-methylstyrene and 25 to 35% by weight of acrylonitrile. 
If the quantity of .alpha.-methylstyrene is less than 65% by weight, it is 
difficult to improve the heat resistance, while if the quantity exceeds 
75% by weight in the case of conventional polymerization process, the 
remaining quantity of .alpha.-methylstyrene increases. 
On the other hand, if the quantity of acrylonitrile is less than 25% by 
weight, the copolymerization is difficult so that it is impossible to 
obtain the copolymer with a satisfactory efficiency, while if it exceeds 
35% by weight, notable lowering of heat resistance and degradation of 
color tone result. 
The above .alpha.-methylstyrene-acrylonitrile oligomer as the component (B) 
has a molecular weight in the range of 200 to 500. If the 
.alpha.-methylstyrene-acrylonitrile copolymer has a molecular weight 
greater than 500, it is impossible to improve the moldability of the 
copolymer. The quantity of the lower molecular weight 
.alpha.-methylstyrene-acrylonitrile copolymer is preferably in the range 
of 0.2 to 1.0 part by weight based on 100 parts by weight of the random 
copolymer as the component (A). If it is less than 0.2 part by weight, it 
is difficult to improve the moldability, while if it exceeds 1.0 part by 
weight, the heat resistance lowers although the moldability is improved. 
The above graft copolymer as the component (C) is obtained by 
graft-copolymerizing 25 to 60% by weight of a monomer mixture of an 
aromatic vinyl monomer with a vinyl cyanide in the presence of 40 to 75% 
by weight of a dienic rubber polymer according to known method. The dienic 
synthetic rubber polymer in the component (C) are, for example, 
polybutadiene rubbery polymers, acrylic rubbery copolymers such as those 
of butyl acrylate, ethylene-propylene-diene copolymer rubbery polymers, 
etc. 
Further, examples of the aromatic vinyl monomer are styrene, 
p-methylstyrene, p-tert-butylstyrene, chlorostyrene, etc., and these may 
be used singly or in admixture of two or more kinds thereof. 
Examples of the vinyl cyanide monomer are acrylonitrile, methacrylonitrile, 
etc. 
As to the preferable properties of the aromatic vinyl monomer and the vinyl 
cyanide monomer, that of the aromatic vinyl monomer is 65 to 85% by weight 
and that of the vinyl cyanide monomer is 20 to 35% by weight. 
In the resin composition of the present invention, if the sum of the random 
copolymer (A) and the graft copolymer (C) is rendered 100 parts by weight, 
the proportion of the random copolymer (A) is 50 to 90 parts by weight and 
that of the graft copolymer (C) is 10 to 50 parts by weight. 
The thermoplastic resin composition of the present invention may be 
produced by mixing the .alpha.-methylstyrene-acrylonitrile copolymer as 
the component (A), .alpha.-methylstyrene-acrylonitrile oligomer as the 
component (B) and the graft copolymer as the component (C) by means of a 
general mixer such as Henschel mixer. Further, the thermoplastic resin 
composition may also be produced by simultaneously preparing the 
.alpha.-methylstyrene-acrylonitrile copolymer as the component (A) and 
.alpha.-styrene-acrylonitrile oligomer as the component (B) according to a 
usual polymerization method such as suspension polymerization, followed by 
mixing these copolymers with the graft copolymer as the component (C). 
Still further, the oligomer as the component (B) may be byproduced 
according to the method disclosed in Japanese Patent Publication No. Sho 
45-1825/1970, but since its quantity produced increases, the heat 
resistance of the final composition lowers as shown in Comparative 
Examples. 
Further, additives usually used such as plasticizer, stabilizer, coloring 
agent, etc., may be added to the thermoplastic composition of the present 
invention. 
The present invention will be further described by way of Examples, but it 
should not be construed to be limited thereto and includes various 
modifications and alterations unless these do not surpass the gist of the 
present invention.

EXAMPLE 1 
Preparation of .alpha.-methylstyrene-acrylonitrile copolymer 
Into a 5 l capacity autoclave equipped with a stirrer were added purified 
water (2 kg) and tribasic calcium phosphate (20 g) and the mixture was 
sufficiently agitated while nitrogen gas was blown therein. Thereafter, 
.alpha.-methylstyrene (1.4 kg), acrylonitrile (0.6 kg), potassium 
persulfate (0.2 g) and catalysts indicated in Table 1, followed by purging 
the inside with nitrogen gas, heating the autoclave to raise the contents 
up to temperatures indicated in Table 1, carrying out polymerization 
reaction for 15 hours to complete polymerization, neutralizing the thus 
obtained slurry with 15% hydrochloric acid, dehydrating and drying at 
80.degree. C. to obtain a particulate polymer. 
Measurement of lower molecular weight .alpha.-methylstyrene-acrylonitrile 
copolymer 
The particulate polymer prepared according to the above method was 
dissolved in methyl ethyl ketone, followed by subjecting the solution to 
deposition with methanol, filtering, and vaporizing the methanol filtrate 
to dryness to obtain a pasty substance which was then dissolved in 0.1% by 
weight tetrahydrofuran (THF). The solution was analyzed by GPC (6000A 
manufactured by Waters Co.). GSP-101 manufactured by Nippon Bunko Co. was 
used as the column. The GPC showed peaks of two components. The components 
were separately taken and subjected to measurement of molecular weight by 
FDMS manufactured by Nippon Denki Co. The peak on the higher molecular 
weight side exhibited a molecular weight of 1,120 to 1,260 and the peak on 
the lower molecular weight side exhibited a molecular weight of 224. The 
polymerization conditions and measurement results are shown in Table 1. 
Preparation of graft copolymer 
Into a 5 l capacity autoclave equipped with a stirrer, while nitrogen gas 
being blown therein, were fed a polybutadiene latex having an average 
particle diameter of 0.35.mu. and a concentration of 32% (2.5 kg), 
purified water (1.5 kg) and an aqueous solution (100 g) of a redox 
catalyst consisting of sodium formaldehyde xylate (1.6 g), ferrous sulfate 
(0.027 g) and tetrasodium ehtylenediamine tetraacetate (0.054 g), followed 
by raising the inner temperature to 50.degree. C. with stirring and when 
the temperature reached 50.degree. C., successively or continuously adding 
a monomer mixture of styrene (336 g), acrylonitrile (144 g), 
t-dodecylmercaptane (1.92 g) and diisopropylbenzene hydroperoxide (0.96 g) 
to complete the addition in 5 hours. 
The inner temperature of the autoclave was raised to 70.degree. C. and 
polymerization reaction was continued for 2 hours to complete the 
polymerization. The thus obtained graft polymer latex was coagulated with 
magnesium chloride, followed by washing, dehydrating and drying to obtain 
a white powdery graft copolymer. 
Production and evaluation of thermoplastic resin composition 
.alpha.-methylstyrene-acrylonitrile copolymer (1.4 kg) as the component (A) 
containing lower molecular weight .alpha.-methylstyrene-acrylonitrile 
copolymer as the component (B), the content of the component (B) being 
indicated in Table 1, and graft copolymer (0.6 g) as the component (C), 
were sufficiently mixed by means of Henschel mixer and then melt-kneaded 
by means of an extruder to obtain pellets. 
The thus obtained thermoplastic resin composition was injection-molded to 
prepare sample pieces, which were then subjected to Vicat softening point 
test and Izod impact strength test. Further, the moldability of the 
pellet-form resin composition was evaluated through the spiral flow length 
according to spiral flow test. 
The measurements of Vicat softening point and Izod impact strength was 
carried out according to the following JIS method: 
(1) Vicat softening point: JIS K6870 
(2) Izod impact strength: JIS K6871 
The spiral flow test was carried out under the following conditions: 
(i) Molding machine: Churchill 1040S manufactured by Kawaguchi Tekko Co. 
(ii) Injection pressure: 50 kg/cm.sup.2 G 
(iii) Cylinder temperature: 280.degree. C. 
(iv) Mold temperature: 40.degree. C. 
These results and the resin compositions are shown in Table 3. 
COMATIVE EXAMPLE 1 
Preparation of .alpha.-methylstyrene-acrylonitrile copolymer 
Purified water (3 kg) and sodium dodecylbenzene-sulfonate (225 g) were 
placed in an autoclave equipped with a stirrer and sufficiently agitated 
while nitrogen gas was blown therein, followed by adding 
.alpha.-methylstyrene (1.4 kg), acrylonitrile (0.6 kg), 
t-dodecylmercaptane (14 g) and potassium persulfate (0.9 g), bringing the 
inside of the system into nitrogen atmosphere, heating the autoclave to 
raise the temperature of the contents up to 70.degree. C., and carrying 
out polymerization for 8 hours to complete polymerization. The thus 
obtained .alpha.-methylstyrene-acrylonitrile copolymer latex was 
coagulated with magnesium chloride, washed, dehydrated and dried to obtain 
a white powdery polymer. 
Measurement of lower molecular weight .alpha.-styrene-acrylonitrile 
copolymer, preparation of graft copolymer and production and evaluation of 
thermoplastic resin composition were carried out in the same manner as in 
Example 1. 
COMATIVE EXAMPLE 2 
Example 1 was repeated except that in the preparation of 
.alpha.-methylstyrene-acrylonitrile copolymers, polymerization was carried 
out employing catalysts and conditions indicated in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Initiator Component A Component B 
Amount Polymerization 
Number average Amount 
(% by weight 
temperature 
chain length Molecular 
(% by 
Example Kind*.sup.1 
/monomer) 
(.degree.C.) 
(.ANG.) --A.sub.W /--A.sub.N 
weight 
weight) 
__________________________________________________________________________ 
Example 1 
Run No. 1 
a 0.75 97 1120 2.3 224 0.63 
Example 1 
Run No. 2 
b 0.79 85 1170 2.4 224 0.31 
Example 1 
Run No. 3 
a 0.28 107 1080 2.5 224 0.86 
Compar. ex. 2 
Run No. 1 
c 0.65 115 980 2.4 224 1.32 
Compar. ex. 2 
Run No. 2 
a 2.44 97 770 2.6 224 0.67 
Compar. ex. 2 
Run No. 3 
a 0.16 97 1650 2.5 244 0.61 
Compar. ex. 1 
d 0.06 70 1160 2.3 224 0.05 
Example 1 
Run No. 4 
e 0.80 84 1090 2.3 224 0.28 
__________________________________________________________________________ 
*.sup.1 TABLE 2 
______________________________________ 
Initiator Name 
______________________________________ 
a 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane 
b di-t-butylperoxy-hexahydroterephthalate 
c 2,5-dimethyl-2,5-di(t-butylperoxy)hexane 
d potassium persulfate 
e t-butyperoxy-isobutyrate 
f t-butyperoxy-hexahydroterephthalate 
______________________________________ 
EXAMPLE 2 
.alpha.-methylstyrene-acrylonitrile oligomer 
In the method of Example 1, polymerization was carried out using catalysts 
indicated in Table 3 and at a polymerization temperature at 120.degree. 
for 5 hours. The resulting particulate polymer was dissolved in methyl 
ethyl ketone, followed by subjecting the solution to deposition with 
methanol, filtering, and vaporizing the methanol filtrate to dryness to 
obtain a pasty substance, which was then subjected to liquid 
chromatography to obtain a lower molecular weight polymer having a 
molecular weight of 200 to 500. 
The .alpha.-methylstyrene-acrylonitrile copolymer as the component (A), 
obtained in Comparative Example 1, .alpha.-methylstyrene-acrylonitrile 
oligomer as the component (B), obtained according to the above method and 
the graft copolymer as the component (C), obtained in Example 1 were 
sufficiently mixed by Henschel mixer in composition indicated in Table 4, 
followed by subjecting the mixture to melt-kneading by means of an 
extruder to obtain pellets. The thus obtained thermoplastic resin 
compositions were evaluated in the same manner as in Example 1. The 
results are shown in Table 4. 
TABLE 3 
______________________________________ 
Initiator 
Amount Amount produced 
(% by weight/ 
(% by weight/ 
Kind monomer) monomer) 
______________________________________ 
Run No. 1 
a 2.47 2.03 
Run No. 2 
f 1.82 2.17 
______________________________________ 
TABLE 4 
__________________________________________________________________________ 
Proportions of components in 
Physical properties 
thermoplastic resin composition 
Vicat's Izod impact 
(% by weight) softening point 
strength 
Spiral flow 
Component A 
Component B 
Component C 
(.degree.C.) 
(kg .multidot. cm/cm) 
(cm) 
__________________________________________________________________________ 
Example 1 
Run No. 1 
80 0.50 20 117 5.8 28.2 
Example 1 
Run No. 2 
80 0.25 20 117 5.4 27.1 
Example 1 
Run No. 3 
60 0.52 40 114 21.00 24.6 
Compar. ex. 2 
Run No. 1 
80 1.06 20 112 6.2 29.3 
Compar. ex. 2 
Run No. 2 
80 0.54 20 114 2.0 30.2 
Compar. ex. 2 
Run No. 3 
80 0.48 20 115 6.5 24.8 
Compar. ex. 1 
Run No. 1 
80 0.04 20 117 5.5 24.5 
Compar. ex. 1 
Run No. 2 
60 0.03 40 114 20 20.0 
Example 1 
Run No. 4 
80 0.24 20 117 5.4 27.6 
Example 2 
Run No. 1 
80 0.51 20 117 5.7 28.0 
Example 2 
Run No. 2 
80 0.51 20 117 5.9 28.4 
__________________________________________________________________________