The disclosure relates to a resin composition comprising (A) 75-98 parts by weight of a block copolymer mixture of vinyl aromatic hydrocarbon and conjugated diolefin and (B) 25-2 parts by weight of an impact-resistant styrene resin, characterized in that said copolymer mixture (A) is a mixture of a copolymer (1) and a copolymer (2) (the weight ratio of the copolymer (1) to the copolymer (2) is 1.5 or more), the copolymer (1) being a copolymer which contains 55-85% by weight of vinyl aromatic hydrocarbon, consists of at least one vinyl aromatic hydrocarbon polymer block and at least one conjugated diene polymer block, and has a number average molecular weight of about 10,000 to about 500,000 and the copolymer (2) being a homopolymer of vinyl aromatic hydrocarbon or a copolymer which consists of at least one vinyl aromatic hydrocarbon polymer block and at least one conjugated diene polymer block, the vinyl aromatic hydrocarbon content of said copolymer being 75% by weight or more and at least 5% by weight higher than that of the copolymer (1), said homopolymer or copolymer having a number average molecular weight of about 500 to about 130,000, both of said copolymer (1) and said copolymer (2) being obtained by polymerization in an inert organic solvent with an organolithium compound as a catalyst; and that said impact-resistant styrene resin (B) is a polymer obtained by graft-polymerizing 3-12% by weight of a rubbery conjugated diene polymer and 97-88% by weight of a vinyl aromatic hydrocarbon. The said resin composition is far superior to conventional resin compositions of similar type in balance between impact resistance and transparency.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a resin composition consisting of a block 
copolymer mixture of vinyl aromatic hydrocarbon and conjugated diene and 
an impact-resistant styrene resin, and having an excellent transparency 
and an excellent impact strength. 
2. Description of the Prior Art 
A variety of production processes and compositions have hitherto been 
proposed concerning vinyl aromatic hydrocarbon polymer resins typified by 
styrene resin. Most of the proposals are concerned with improvement in 
impact-resistance of general purpose polystyrene, because it is brittle 
and poor in impact-resistance though it is excellent in transparency, 
surface gloss, beautifulness of appearance, stiffness and tensile 
strength. There have hitherto been attempted incorporation of a special 
rubbery copolymer into the general purpose polystyrene, production of an 
impact-resistant polystyrene resin by graft-polymerization of monomeric 
styrene on rubbery polymer, production of a styrene-butadiene block 
copolymer having a high styrene content, etc. 
As examples of the incorporation of a special rubbery polymer into general 
purpose polystyrene, Japanese Patent Publication No. 7126/69 discloses 
incorporating a linear block copolymer into general purpose polystyrene; 
and Japanese Patent Application Kokai (Laid-Open) No. 25043/74 and U.S. 
Pat. No. 3,853,978 disclose a composition of a general purpose polystyrene 
and a vinyl aromatic hydrocarbon-conjugated diene block copolymer having a 
special block structure and having a relatively high vinyl aromatic 
hydrocarbon content. The impact resistance of these compositions are 
somewhat improved as compared with polystyrene, but cannot be said to be 
sufficient, and the deterioration in stiffness and transparency is 
remarkable. 
The impact-resistant polystyrene resin in which monomeric styrene is 
graft-polymerized on a rubbery polymer can be obtained by dissolving a 
rubbery polymer into monomeric styrene and polymerizing the latter by bulk 
polymerization, suspension polymerization or by combination of bulk and 
suspension polymerizations. This type of impact-resistant polystyrene has 
an excellent resistance to impact. However, it is entirely opaque and poor 
in surface gloss. 
A styrene-butadiene block copolymer having a high styrene content can be 
obtained by living anionic polymerization. It is formed by polymerizing 
styrene and butadiene alternately in an inert solvent with an anionic 
polymerization initiator such as organolithium compound as in Japanese 
Patent Publications Nos. 3252/72 and 2423/73, etc. This type of block 
copolymer having a high styrene content is excellent in transparency and 
superior to general purpose polystyrene in impact-resistance. Though this 
type of block copolymer fulfils our requirements to some extent, it is 
still insufficient in impact-resistance, so that the application field 
thereof is limited. 
As mentioned above, among the impact-resistant polystyrenes so far 
proposed, some are excellent in impact-resistance but are poor in 
transparency, and the others are excellent in transparency but are poor in 
improvement of impact resistance. Thus, there has been discovered no 
impact-resistant polystyrene in which physical properties including impact 
resistance are well balanced with transparency. 
The present inventors previously proposed a styrene resin composition 
having excellent transparency and excellent impact resistance on the basis 
of a conception and a knowledge entirely different from those in the past 
(cf. Japanese Patent Publications Nos. 5,059/78 and 15,958/78 and 
Australian Pat. No. 488,065). This composition is a styrene resin 
composition consisting of: 
(1) a copolymer consisting of at least one vinyl aromatic hydrocarbon 
polymer block and at least one conjugated diene polymer block, and having 
a vinyl aromatic hydrocarbon content of 55-85% by weight, and 
(2) a copolymer consisting of at least one vinyl aromatic hydrocarbon 
polymer block and at least one conjugated diene polymer block, and having 
a vinyl aromatic hydrocarbon content of 75% by weight or more, or a 
homopolymer of vinyl aromatic hydrocarbon, 
both copolymers (1) and (2) being obtained in an inert organic solvent with 
an organolithium compound as a catalyst, characterized in that the weight 
ratio of copolymer (1)/copolymer (2) is not less than 1.5/1 and that at 
least 35% of the polymer chain of copolymer (1) is substantially identical 
in structure with the polymer chain of copolymer (2). Contrary to the 
prior conception that a mixture of polymers having different compositions 
is inferior in transparency to the original polymers, this composition is 
completely transparent and has resistance to impact. 
However, even this block copolymer mixture cannot still be said to be fully 
satisfactory in respect of impact resistance. Although it is comparable or 
superior in impact resistance to the conventional mixture of general 
purpose polystyrene and rubbery polymer or to the conventional block 
copolymers having a high styrene content, a resin having a much more 
excellent impact resistance has been desired. 
For the purpose of improving the impact resistance of a styrene-butadiene 
block copolymer, attempts have been made to incorporate an 
impact-resistant polystyrene resin into such a block copolymer (Japanese 
Patent Publication No. 16,496/77) or to incorporate an impact-resistant 
polystyrene resin and polystyrene into such a block copolymer (Japanese 
Patent Application Kokai (Laid-Open) No. 89,550/76). However, the 
resulting compositions have not necessarily been satisfactory as 
compositions having both excellent transparency and excellent impact 
strength. 
In view of the above problems, the present inventors have conducted 
extensive research to find a new styrene resin composition which is 
excellent in both transparency and impact resistance. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a styrene resin composition 
which is superior to the hitherto known products in both transparency and 
impact resistance. 
Other objects and advantages of this invention will become apparent from 
the following description. 
According to this invention, there is provided a resin composition 
consisting of (A) 75 - 98 parts by weight of a mixture of block copolymers 
of a vinyl aromatic hydrocarbon and a conjugated diene and (B) 25 - 2 
parts by weight of an impact-resistant styrene resin, wherein said 
copolymer mixture (A) is a mixture of copolymer (1) and copolymer (2), the 
weight ratio of copolymer (1) to copolymer (2) being 1.5 or more, 
said copolymer (1) being a copolymer consisting of at least one vinyl 
aromatic hydrocarbon polymer block and at least one conjugated diene 
polymer block, and having a vinyl aromatic hydrocarbon content of 55-85% 
by weight and a number average molecular weight of about 10,000 to about 
500,000, and 
said copolymer (2) being a homopolymer of a vinyl aromatic hydrocarbon or a 
copolymer consisting of at least one vinyl aromatic hydrocarbon polymer 
block and at least one conjugated diene polymer block, and having a vinyl 
aromatic hydrocarbon content of 75% by weight or more, which is at least 
5% higher than that in copolymer (1), said copolymer and homopolymer both 
having a number average molecular weight of about 500 to about 130,000, 
said copolymer (1) and said copolymer (2) being both obtained by 
polymerization in an inert organic solvent with an organolithium compound 
as catalyst; 
and said impact-resistant styrene resin (B) being a polymer obtained by 
graft-polymerizing 97-88% by weight of a vinyl aromatic hydrocarbon on 
3-12% by weight of a rubbery conjugated diene polymer.

DETAILED DESCRIPTION OF THE INVENTION 
In the composition of this invention, the characteristic feature of this 
invention is most plainly exhibited when the weight ratio of the block 
copolymer mixture to the impact-resistant styrene resin is in the range of 
98/2 to 75/25. When the weight ratio is in the range of 98/2 to 90/10, the 
haze (%) of the composition can be kept at about 12 or less, which means 
that the transparency of the block copolymer mixture itself is hardly 
injured. As mentioned above, compositions having a weight ratio of 98/2 to 
90/10 have an excellent transparency and, in addition, the 
impact-resistance thereof is improved as compared with the block copolymer 
mixture per se. On the other hand, compositions having a weight ratio of 
90/10 to 75/25 have a haze exceeding 12%, but are remarkably improved in 
impact-resistance and simultaneously improved in stiffness and heat 
deformation temperature. 
Hitherto, conjugated diene-vinyl aromatic hydrocarbon block copolymers 
having a high vinyl aromatic hydrocarbon content have been considered 
superior in impact resistance to general purpose polystyrene but their 
impact-resistance cannot be said to be satisfactory, so that their use has 
been limited. The composition of this invention wherein the weight ratio 
of the block copolymer mixture to the impact-resistant styrene resin is 
98/2 to 75/25 can be used in a broad range owing to its excellent impact 
resistance. By varying the composition ratio in accordance with the 
balance between impact resistance and transparency which is required for 
the molded product, resin compositions having various characteristic 
properties enough to satisfy the requirement can be provided. 
The composition of this invention can be made into a resin having 
well-balanced characteristics, particularly a resin excellent in both 
impact resistance and transparency, by selecting a composition ratio in 
accordance with the intended characteristic properties. 
The two block copolymers (1) and (2) used in this invention are block 
copolymers obtainable by anion-polymerizing the monomers in an inert 
organic solvent with an organolithium compound as a catalyst. The block 
copolymer (1) is a copolymer consisting of at least one vinyl aromatic 
hydrocarbon polymer block and at least one conjugated diene polymer block, 
and its vinyl aromatic hydrocarbon content is in the range of 55-85% by 
weight. If the vinyl aromatic hydrocarbon content is less than 55%, its 
resinous properties are injured and ultimately the hardness and stiffness 
characteristic of the composition of this invention are injured, which is 
undesirable. If the vinyl aromatic hydrocarbon content exceeds 85% by 
weight, the product cannot have an excellent impact resistance though its 
hardness and stiffness are improved. The preferable copolymers (1) usable 
in the block copolymer mixture are represented by the following general 
formulas: 
EQU A-(B-A).sub.n, (A-B).sub.n, A-B-(B-A).sub.n 
wherein A represents a block composed mainly of vinyl aromatic hydrocarbon; 
B represents a polymer block composed mainly of conjugated diene; and n is 
a number of 1 or more. When n is 5 or more, the procedure of 
polymerization is so complicated that its industrial practice is 
disadvantageous. The block copolymer represented by the aforementioned 
general formulas may be the so-called perfect block copolymer or the 
so-called tapered block copolymer. The concrete process for its production 
may be any process hitherto known. For example, a block copolymer 
represented by A-(B-A).sub.n can be produced by first forming the block A 
with an organolithium compound as catalyst, then forming the block B and 
thereafter forming the block A, namely by the successive addition of 
monomers (Japanese Patent Publication No. 19286/61). It can also be 
produced by a process which comprises mixing the monomers constituting the 
blocks A and B and polymerizing the monomer mixture so as to form a 
tapered block copolymer such as (A-B).sub.n by the utilization of monomer 
reactivity ratio (Japanese Patent Publication No. 17979/68 or British Pat. 
No. 1,130,770). The radial block copolymer represented by the general 
formula A-B-(B-A).sub.n can be obtained by coupling a living block 
copolymer A-B.sup..crclbar. with a polyfunctional coupling agent such as 
polyhalogenides, diester compounds and the like. 
In the block copolymer mixture, copolymer (1) has a number average 
molecular weight of about 10,000 to about 500,000, preferably about 30,000 
to about 300,000, from the viewpoint of excellent mechanical properties of 
the composition obtainable therefrom. 
In the block copolymer mixture, the copolymer (2) is a homopolymer or 
copolymer produced by anionic polymerization with an organolithium 
compound catalyst, said copolymer consisting of at least one vinyl 
aromatic hydrocarbon polymer block and at least one conjugated diene 
polymer block, and having a vinyl aromatic hydrocarbon content of 75% by 
weight or more, which is higher than the vinyl aromatic hydrocarbon 
content in the copolymer (1). If the vinyl aromatic hydrocarbon content is 
less than 75% by weight, the final composition obtainable therefrom loses 
its resinous character and is injured in hardness and tensile strength, 
which is undesirable. The vinyl aromatic hydrocarbon content in the 
copolymer (2) should be at least 5% by weight higher, preferably 10% by 
weight higher, than that in the copolymer (1), from the viewpoint of 
excellent transparency of the composition obtainable therefrom. The block 
structure of the copolymer (2) consisting of at least one vinyl aromatic 
hydrocarbon polymer block and at least one conjugated diene polymer block 
can be represented by the same general formulas as mentioned in respect to 
the copolymer (1), and it may be produced by any hitherto known method. 
In the block copolymer mixture, the copolymer (2) has a number average 
molecular weight of about 500 to about 130,000, preferably about 10,000 to 
about 100,000, more preferably 10,000 to 80,000, from the viewpoint of the 
excellent transparency of the final composition obtainable therefrom. 
In the block copolymer mixture of this invention, the weight ratio of the 
copolymer (1) to the copolymer (2) is 1.5 or more. If the ratio is less 
than 1.5, the transparency of the mixture is injured which in turn reduces 
the transparency of the final composition, which is undesirable. 
In the block copolymer mixture, it is preferable that at least 35% of the 
chain of the copolymer (1) has a substantially identical structure with 
the chain of the copolymer (2), although this invention is not necessarily 
limited thereto. 
The term "substantially identical structure" herein used means that the 
conditions determining a polymer such as molecular weight, molecular 
weight distribution, micro-structure, degree of branching, block structure 
(the style of linkage between vinyl aromatic hydrocarbon and conjugated 
diene), etc. are identical within the controllable range of working 
conditions or the range of analytical error. Diagrammatically, it means 
that in the following diagrams: 
EQU Molecular chain of the copolymer (1) 
EQU Molecular chain of the copolymer (2) 
both the shaded parts are identical in structure. If the shaded part 
occupies only less than 35% of the chain of the copolymer (1), both the 
polymers are poor in compatibility so that transparency of the composition 
is injured. A composition in which at least 35% of the chain of the 
copolymer (1) is substantially identical in structure with the chain of 
the copolymer (2) may be produced by any known process, so far as it can 
give the composition specified above. Concretely speaking, the copolymer 
(2) may be produced by just the same process as employed for producing a 
part of the copolymer (1). That is to say, the block copolymer mixture of 
this invention may be produced by producing the copolymer (2) with the 
same catalyst, solvent and monomer and under the same polymerization 
conditions (temperature, pressure, monomer charging rate, etc.) as in the 
case of the copolymer (1) and then blending the resulting copolymer (2) 
with the copolymer (1) in the state of solution, pellet or the like by the 
conventional procedure. The most recommendable process for the production 
of the block copolymer mixture of this invention comprises first producing 
a part of the copolymer (1) by anionic polymerization followed by 
producing the copolymer (2) in the same polymerization system and under 
the same conditions while continuing the production of the copolymer (1). 
Since the anionic polymerization with an organolithium compound catalyst 
enables the molecular design to be made relatively readily and 
quantitatively, it is suitable for obtaining polymer mixtures having such 
a restricted structure as in the block copolymer mixture used in this 
invention. 
The inert solvent used in the production of the copolymers (1) and (2) 
constituting the block copolymer mixture of this invention may be any 
solvent, so far as it does not inactivate the organolithium compound. 
Preferable examples of said solvent include aromatic hydrocarbons such as 
benzene, ethylbenzene, tolene, xylene and the like; alicyclic hydrocarbons 
such as cyclohexane, methylcyclohexane, ethylcyclohexane and the like; and 
aliphatic hydrocarbons such as hexane, heptane, isopentane and the like. 
It is also permissible to add a small quantity of a polar compound to the 
solvent in order to enhance the polymerization velocity or in order to 
change the monomer reactivity ratio between butadiene and styrene with the 
aim of obtaining a block copolymer having an intended structure. Examples 
of said polar compound include ethers such as tetrahydrofuran, dimethyl 
ether and the like; and tertiary amines such as triethylamine. 
In producing the block copolymers used in this invention, it is preferable 
to employ a solvent composed mainly of aliphatic hydrocarbon as the inert 
solvent. As compared with aromatic and alicyclic hydrocarbons, aliphatic 
hydrocarbons have less toxicity to human body and are less capable of 
causing photochemical smog when distributed in the atmospheric air. When 
the block copolymer mixture used in this invention is produced by 
polymerization in an aliphatic hydrocarbon, it is necessary to effect the 
polymerization in the state that the resulting copolymer is dispersed in 
the form of fine particles in the medium because a copolymer having a high 
vinyl aromatic hydrocarbon content is not dissolved in the aliphatic 
hydrocarbon solvent. Since a dispersion has only a low viscosity, the 
motive power necessary for the agitation of polymerization vessel and for 
the transportation of solution can be saved by the dispersion 
polymerization, which is a merit of this polymerization. 
When the block copolymer mixture used in this invention is produced in an 
aliphatic hydrocarbon solvent, it is preferable to produce the mixture in 
one polymerization system by the two step polymerization method in which 
the organolithium compound is twice supplied. By this technique, the block 
copolymer mixture can be obtained in the form of a stable dispersion. More 
concretely speaking, the polymerization is preferably carried out in the 
following manner. 
In a solvent composed mainly of an aliphatic hydrocarbon, (i) a vinyl 
aromatic hydrocarbon and a conjugated diene are polymerized in a weight 
ratio of 0/100 to 60/40 in an amount of 1 to 80% by weight of the total 
weight of the monomers to be used in all the steps with an organolithium 
compound catalyst to produce: 
(a) an active polymer of the conjugated diene, or 
(b) an active polymer consisting of a random copolymer of the conjugated 
diene and the vinyl aromatic hydrocarbon, or 
(c) an active polymer consisting of at least one vinyl aromatic hydrocarbon 
polymer block and at least one conjugated diene polymer block, 
and (ii) subsequently the residual monomers having a weight ratio of the 
vinyl aromatic hydrocarbon to the conjugated diene of 100/0 to 75/25 and a 
fresh organolithium compound are added to the active polymer obtained in 
(i) and polymerization is effected to produce: 
(d) a homopolymer of the vinyl aromatic hydrocarbon, or 
(e) a copolymer consisting of at least one vinyl aromatic hydrocarbon 
polymer block and at least one conjugated diene polymer block, 
while prolonging the polymer chain of the active polymer obtained in (i). 
The composition comprising the block copolymer mixture produced by 
polymerization in such a hydrocarbon solvent exhibits superiority in 
industrial practice owing to the synergism of the excellent physical 
properties and the excellent effect at the time of the production of the 
block copolymer mixture. 
In the case of obtaining the block copolymer mixture by the above-mentioned 
two-step polymerization method, the vinyl aromatic hydrocarbon content in 
the copolymer (1) can be determined by the following equation if the 
copolymerization is complete: 
##EQU1## 
wherein M.sub.1, B.sub.1 and C.sub.1 are, respectively, the weight of the 
monomers used in the first step polymerization (i), the vinyl aromatic 
hydrocarbon content (% by weight) in the said monomers, and the molar 
amount of the effective organolithium compound, and M.sub.2, B.sub.2 and 
C.sub.2 are those in the second stop polymerization (ii), provided that 
when an organolithium compound containing n active lithium atoms in one 
molecule is used, C.sub.1 and/or C.sub.2 should be multiplied by n. 
On the other hand, the vinyl aromatic hydrocarbon content in the copolymer 
(2) becomes equal to the vinyl aromatic hydrocarbon content in the 
monomers used in the second step polymerization (ii). The weight ratio of 
the copolymer (1) to the copolymer (2) in the block copolymer mixture can 
be determined by the following equation: 
##EQU2## 
Accordingly, the detailed experimental conditions for the above two-step 
polymerization method can be determined by using those equations. 
The organolithium compounds which can be used for producing the copolymers 
(1) and (2) of the block copolymer mixture constituting the composition of 
this invention are organic compounds having at least one lithium atom. 
Examples of said organolithium compound include, for example, 
n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, 
tert-butyllithium, n-pentyllithium, methylcyclohexyllithium, 
benzyllithium, 1,4-dilithio-n-butane, 1,6-dilithio-n-hexane, stilbene 
dilithium, oligoisoprenyl dilithium and the like, among which 
n-butyllithium and sec-butyllithium are most conventional. 
The vinyl aromatic hydrocarbons usable in this invention include styrene, 
o-methylstyrene, p-methylstyrene, m-methylstyrene, .alpha.-methylstyrene, 
p-ethylstyrene, 1,3-dimethylstyrene, vinylnaphthalene, vinylanthracene and 
the like, among which styrene is most conventional. All these vinyl 
aromatic hydrocarbons may be used alone or in admixture of two or more. 
The conjugated dienes usable in this invention are diolefins having 4 to 8 
carbon atoms and one pair of conjugated double bonds. Examples of said 
conjugated diene include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 
2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like, 
among which 1,3-butadiene and isoprene are most conventional. All these 
conjugated dienes may be used alone or in admixture of two or more. 
In the production of the copolymers (1) and (2) of the block copolymer 
mixture constituting the composition of this invention, the temperature of 
polymerization is in the range of -40.degree. C. to +150.degree. C. and 
usually in the range of +40.degree. C. to +120.degree. C. Though the 
period of polymerization time is in the range of 30 minutes to 24 hours, 
it is usually 1 to 10 hours. The atmosphere of the polymerization system 
is preferably substituted by an inert gas such as nitrogen gas. Care must 
be taken of preventing the polymerization system from contamination by 
impurities capable of inactivating the organolithium catalyst or the 
active polymer, such as water, oxygen, carbon dioxide and the like. 
The impact-resistant styrene resin constituting the composition of this 
invention may be any graft-copolymer of a vinyl aromatic hydrocarbon on a 
conjugated diene polymer type rubber. Said impact-resistant styrene resin 
may be any of the known resins such as mentioned in Japanese Patent 
Publications Nos. 26287/63; 18948/64 (or British Pat. No. 963,307); and 
11633/74. It can be produced by dissolving a conjugated diene polymer 
rubber in a vinyl aromatic hydrocarbon monomer and then subjecting the 
resulting solution to bulk polymerization, suspension polymerization or a 
combination of bulk and suspension polymerizations. 
The conjugated diene polymer rubbers usable in the impact-resistant styrene 
resin include, for example, polybutadiene, polyisoprene, butadiene-styrene 
random copolymer, butadiene-styrene block copolymer and the like, as well 
as mixtures thereof. 
Examples of the vinyl aromatic hydrocarbon monomers usable in the 
impact-resistant styrene resin include styrene, o-methylstyrene, 
m-methylstyrene, p-methylstyrene, .alpha.-methylstyrene, dimethylstyrene, 
p-ethylstyrene, vinylnaphthalene, vinylanthracene and the like, among 
which styrene is most conventional. Mixtures of these substances may also 
be used. 
The impact-resistant styrene resin contains said conjugated diene polymer 
rubber and said vinyl aromatic hydrocarbon in amounts of 3-12% by weight 
and 88-97% by weight, respectively. If the content of said conjugated 
diene polymer rubber is less than 3% by weight, the impact resistance of 
the composition is insufficient. If it exceeds 12% by weight, the 
transparency of the composition is injured. 
When it is intended to blend the copolymer mixture (A) with the 
impact-resistant styrene resin to form the composition of this invention, 
they may be blended together by any known procedure. For example, they may 
be blended by means of a roll, screw extruder or the like. Alternatively, 
solutions thereof may first be mixed, followed by evaporating the solvents 
on a hot drum or by means of a steam stripping to recover the resin. 
As mentioned above, the composition of this invention is excellent in 
impact resistance, and the composition ratio can be varied corresponding 
to the required balance of physical properties such as impact resistance, 
transparency, etc. to meet the needs. Therefore, the composition can be 
used as molding elements for various molded products. That is, the 
composition of this invention can be extruded, as it is or after being 
colored, in the same manner as for conventional thermoplastic resins to 
give sheets or films. Also, it can be molded by thermoforming, such as 
vacuum forming, pressure forming and the like, into packages for food 
containers, blister packaging materials, packaging films for vegetables, 
fruits and cakes, and so on. Thus, the composition of this invention can 
be used in a broad packaging material field. Further, the composition can 
also be employed in the production of toys, general merchandise, 
containers, etc. by the technique of injection molding, blow molding and 
the like, in the same manner as usual general purpose resins. 
DESCRIPTION OF PREFERRED EMBODIMENT 
This invention is illustrated by Examples below. It should be understood 
that this invention is not limited to the Examples. 
Example 1 and Comparative Example 1 
By the procedure mentioned below, a B-A-B-A type styrene-butadiene block 
copolymer and an A-B-A type styrene-butadiene block copolymer were 
simultaneously polymerized in toluene with n-butyllithium as a catalyst to 
obtain a homogeneous resin composition: 
A reaction vessel equipped with a stirrer was previously dehydrated, 
deaerated and then purged with nitrogen gas. Then, 30% by weight toluene 
solution of 26 parts by weight of 1,3-butadiene was injected into the 
reaction vessel. Subsequently, a toluene solution of n-butyllithium was 
added in an amount of 0.125 part by weight as the active lithium compound, 
and the monomer was polymerized at 70.degree. C. for 1 hour. After the 
polymerization of the monomer had substantially been completed, 30% by 
weight toluene solution of 74 parts by weight of styrene and a toluene 
solution containing n-butyllithium in an amount of 0.034 part by weight as 
the active lithium compound were added thereto, and the mixture was 
polymerized at 70.degree. C. for 1 hour. After the polymerization of the 
monomer had substantially been completed, 30% by weight toluene solution 
of 26 parts by weight of 1,3-butadiene was added, and the mixture was 
polymerized at 70.degree. C. for one hour. After the polymerization had 
substantially been completed, 30% by weight toluene solution of 74 parts 
by weight of styrene was added, and the mixture was polymerized at 
70.degree. C. for 1 hour. After the polymerization of the monomer had been 
completed, 0.8 part by weight of 4-methyl-2,6-di-tert-butylphenol was 
added to the resulting copolymer solution as a polymerization terminator 
and an antioxidant. The copolymer solution thus obtained was poured into 
an excess of methanol and the resulting precipitates were collected and 
dried under reduced pressure. The composition of the block copolymer 
mixture thus obtained and the results of tests on physical properties are 
indicated in Table 1. 
In this block copolymer mixture, approximately 84% of the chain of 
copolymer (1) had substantially the same structure as the chain of 
copolymer (2). The copolymers (1) and (2) had number average molecular 
weights of about 83,000 and about 70,000, respectively. 
This block copolymer was blended with a commercial impact-resistant 
polystyrene containing about 6% of a conjugated diene rubber, and the 
physical properties of the blended mixture were measured. The results are 
also shown in Table 1. The results evidently demonstrate the superiority 
of the composition of this invention in transparency and impact 
resistance. 
Table 1 
__________________________________________________________________________ 
Example No. 
Properties Comp. Ex. 1 
Example 1 
Comp. Ex. 1 
__________________________________________________________________________ 
Copolymer 
Structure of polymer 
B-A-B-A 
Block (1) Styrene content (% by wt.) 
71 
copolymer 
Copolymer 
Structure of polymer 
A-B-A 
mixture 
(2) Styrene content (% by wt.) 
85 
Copolymer (1)/Copolymer (2) (wt. ratio) 
4.4/1 
Block copolymer mixture/ 
Impact-resistant polystyrene 
(wt. ratio) 100/0 
95/5 
90/10 
80/20 
70/30 
40/60 
0/100 
Melt flow index (g/10 min) 
1) 4.5 4.3 4.0 3.8 3.6 2.9 2.0 
Tensile strength (kg/cm.sup.2) 
2) 210 208 212 210 207 205 220 
Properties 
Tensile elongation at break (%) 
2) 200 180 160 135 120 60 35 
of Izod impact strength (kg-cm/cm) 
2) 3.1 4.0 4.5 6.9 8.5 8.5 7.1 
composi- 
Rockwell hardness (R-scale) 
3) 40 50 57 62 75 96 109 
tion Bending modulus (kg/mm.sup.2) 
4) 110 125 135 155 162 192 215 
Haze (%) 5) 4.5 8.5 12.0 
20.0 
60 White 
White 
__________________________________________________________________________ 
Notes- 
1) Measured according to ASTM D1238-65T, condition 
2) Measured according to JIS K6871- 
3) Measured according to ASTM D785, 
4) Measured according to ASTM D790- 
5) Measured according to JIS K6714 with test pieces having a thickness of 
0.5 mm. 
Comparative Example 2 
Four kinds of block copolymer mixtures were produced by repeating the 
procedure of Example 1, except that the quantities of butadiene, styrene 
and catalyst were varied. The copolymers were blended with the same 
commercial impact-resistant polystyrene as used in Example 1 in a weight 
ratio of block copolymer to impact-resistant polystyrene of 90/10, and the 
physical properties of the blends were measured. The results are indicated 
in Table 2, which evidently demonstrate the superiority of the composition 
of this invention in transparency and impact resistance. 
Example 2 
A block copolymer mixture was produced by repeating the procedure of 
Example 1, except that n-hexane was used as solvent. The solution of block 
copolymer mixture thus obtained was a stable dispersion and had a low 
viscosity. The block copolymer mixture was isolated from the solution, it 
was blended with the same commercial impact-resistant polystyrene as used 
in Example 1 in a weight ratio of 90/10, and physical properties of the 
blend were measured. The results are shown in Table 2, which clearly 
demonstrate the superiority of the composition of this invention in 
balance of physical properties. The data of Example 1 are also shown in 
Table 2 for comparison. 
Table 2 
__________________________________________________________________________ 
Example No. 
Example 
Example 
Properties Comparative Example 2 1 2 
__________________________________________________________________________ 
Co- Structure of polymer 
B-A-B-A 
B-A-B-A B-A-B-A 
B-A-B-A B-A-B-A 
B-A-B-A 
polymer 
Styrene content 
Block (1) (% by wt.) 62.5 65 90 50 71 71 
copolymer 
Co- Structure of polymer 
A-B-A 
A-B-A A-B-A 
A-B-A A-B-A 
A-B-A 
mixture 
polymer 
Styrene content 
(2) (% by wt.) 85 70 95 90 85 85 
Copolymer (1)/copolymer (2) 
(wt. ratio) 1/1 2.5/1 5/1 2/1 4.4/1 
4.4/1 
Block copolymer mixture 
Impact resistant polystyrene (wt. ratio) 
90/10 
90/10 90/10 
90/10 90/10 
90/10 
Melt flow index 
1) 3.5 3.3 4.5 3.8 4.0 4.2 
(g/10 min) 
Tensile strength 
2) 170 140 280 160 212 220 
(kg/cm.sub.2) 
Pro Tensile elongation at 
perties 
break (%) 2) 190 250 5 200 160 155 
of Izod impact strength Unmeasurable Unmeasurable 
composi- 
(kg-cm/cm) 2) 4.2 (no breakage) 
1.2 (no breakage) 
4.5 4.4 
tion Rockwell hardness Unmeasurable Unmeasurable 
(R-scale) 3) 38 (too soft) 
98 (too soft) 
57 59 
Bending modulus Unmeasurable Unmeasurable 
(kg/mm.sup.2) 
4) 115 (too soft) 
214 (too soft) 
135 140 
Haze (%) 5) 26.0 47.3 8.8 51.3 12.0 11.5 
__________________________________________________________________________ 
Notes:- 
1)- 5) are the same as in Table 1. 
Example 3 and Comparative Example 3 
By the procedure mentioned below, a B-A-B-A type styrene-butadiene block 
copolymer and a polystyrene were simultaneously produced in cyclohexane 
with n-butyllithium as a catalyst to obtain a homogeneous resin 
composition: 
A reaction vessel equipped with a stirrer was previously dehydrated, 
deaerated and purged with nitrogen gas. Into the reaction vessel was 
injected 30% by weight cyclohexane solution of 32 parts by weight of 
1,3-butadiene and 32 parts by weight of styrene. Then, a cyclohexane 
solution of n-butyllithium was added in an amount of 0.18 part by weight 
as the active lithium compound, and the mixture was polymerized at 
70.degree. C. for 1 hour with stirring. After the polymerization of the 
monomers had substantially been completed, a cyclohexane solution of 46 
parts by weight of butadiene and 20 parts by weight of styrene was added, 
and the mixture was polymerized at 70.degree. C. for 1 hour. After the 
polymerization of the monomers had substantially been completed, 270 parts 
by weight of styrene and a cyclohexane solution containing n-butyllithium 
in an amount of 0.14 part by weight as the active lithium compound were 
added and the mixture was polymerized at 70.degree. C. for 1.5 hours. 
After the polymerization of the monomer had substantially been completed, 
0.8 part by weight of 4-methyl-2,6-di-tert-butylphenol was added to the 
formed copolymer solution as a polymerization terminator and an 
antioxidant. The copolymer solution thus obtained was poured into an 
excess of methanol, and the resulting precipitates were collected and 
dried under reduced pressure. 
The block copolymer mixture thus obtained had the composition shown in 
Table 3, and approximately 54% of the copolymer (1) chain was 
substantially identical with the copolymer (2) chain in structure. The 
copolymers (1) and (2) had number average molecular weights of about 
100,000 and about 54,000, respectively. 
The block copolymer mixture thus obtained was blended with the same 
commercial impact-resistant polystyrene as used in Example 1 in the 
proportion shown in Table 3, and physical properties of the blend were 
measured. The results are shown in Table 3, which clearly demonstrate the 
superiority of the composition of this invention in balance of physical 
properties. 
Example 4 
A block copolymer mixture was produced by repeating the procedure of 
Example 3, except that n-hexane was used as solvent. The copolymer mixture 
obtained was in the form of a stable dispersion having a low viscosity. 
The copolymer mixture was blended with the same commercial 
impact-resistant polystyrene as used in Example 1 in a weight ratio of 
block copolymer to impact-resistant polystyrene of 90/10, and physical 
properties of the blend were measured. The results are shown in Table 3, 
which demonstrate that a good composition can be obtained from the block 
copolymer mixture polymerized in n-hexane. 
Table 3 
__________________________________________________________________________ 
Example No. 
Comp. 
Properties Ex. 3 
Example 3 Comp. Ex. 3 
Example 
__________________________________________________________________________ 
4 
Copolymer 
Structure of polymer 
B-A-B-A B-A-B-A 
Block (1) Styrene content (% by wt.) 
70 70 
Copolymer 
Copolymer 
Structure of polymer 
A A 
mixture 
(2) Styrene content (% by wt.) 
100 100 
Copolymer (1)/Copolymer (2) (wt. ratio) 
2.4/1 2.4/1 
Block copolymer mixture/ 
Impact resistant polystrene (wt. ratio) 
100/0 
95/5 
90/10 
80/20 
70/30 
30/70 
90/10 
Melt flow (g/10 min) 
1) 
8.5 8.0 7.1 6.0 5.4 3.1 7.2 
Proper- 
Tensile strength (kg/cm.sup.2) 
2) 
285 280 250 242 240 235 250 
ties Tensile elongation at break (%) 
2) 
40 40 38 37 38 37 35 
of Izod impact resistance 
composi- 
(kg-cm/cm) 2) 
2.2 3.0 3.8 5.6 6.8 7.7 4.0 
tion Rockwell hardness (R-scale) 
3) 
82 87 92 95 98 111 91 
Bending modulus (kg/mm.sup.2) 
4) 
175 180 185 193 198 205 183 
Haze (%) 5) 
2.12 
7.0 9.6 20 45 White 
9.0 
__________________________________________________________________________ 
Notes: 
1)- 5) are the same as in Table 1. 
Comparative Example 4 
A styrene-butadiene-styrene block copolymer having a styrene content of 50% 
by weight was produced in cyclohexane with n-butyllithium as a catalyst. 
The formed block copolymer had a melt index of 2.5. 
The block copolymer was blended with a general purpose polystyrene 
(abbreviated to GP-PS) having a number average molecular weight of about 
150,000 and physical properties of the blend were measured. The results 
are shown in Table 4. The results demonstrate that the blend of this 
comparative example is inferior to the composition of this invention in 
balance of impact-resistance, transparency and other characteristics. 
Table 4 
__________________________________________________________________________ 
Comp. Ex. 4 
Block copolymer/Polystyrene (wt. ratio) 
90/10 60/40 
40/60 
30/70 
__________________________________________________________________________ 
Melt flow index (g/10 min) 
1) 
2.4 2.3 2.3 2.2 
Tensile strength (kg/cm.sup.2) 
2) 
150 180 190 210 
Tensile elongation at break (%) 
2) 
400 150 30 15 
Properties 
Izod impact strength (kg-cm/cm) 
2) 
Unmeasurable 
3.5 1.9 1.0 
of (no breakage) 
composi- 
Rockwell hardness (R-scale) 
3) 
Unmeasurable 
30 85 95 
tion (too soft) 
Bending modulus (kg/mm.sup.2) 
4) 
Unmeasurable 
110 150 170 
(too soft) 
Haze (%) 5) 
12.5 28.5 
42.5 
53.5 
__________________________________________________________________________ 
Notes: 1)- 5) are the same as in Table 1. 
Example 5 and Comparative Examples 5 and 6 
By the procedure mentioned below, a B-A-B-A type styrene-butadiene block 
copolymer and a polystyrene were simultaneously produced in cyclohexane 
with n-butyllithium as a catalyst to obtain a homogeneous resin 
composition: 
A reaction vessel equipped with a stirrer was previously dehydrated, 
deaerated and then purged with nitrogen gas. Then, a 20% by weight 
cyclohexane solution of 28 parts by weight of 1,3-butadiene and 40 parts 
by weight of styrene was injected into the reaction vessel. Subsequently, 
a cyclohexane solution of n-butyllithium was added in an amount of 0.227 
part by weight as the active lithium compound, and the mixture was 
polymerized at 70.degree. C. for 1 hour with stirring. After the 
polymerization of the monomers had substantially been completed, 20% by 
weight cyclohexane solution of 52 parts by weight of butadiene was added, 
and the mixture was polymerized at 70.degree. C. for 1 hour. After the 
polymerization of the monomer had substantially been completed, 20% by 
weight cyclohexane solution of 280 parts by weight of styrene and a 
cyclohexane solution containing n-butyllithium in an amount of 0.092 part 
by weight as the active lithium compound were added, and the mixture was 
polymerized at 70.degree. C. for 1.5 hours. After the polymerization of 
the monomer had substantially been completed, a small quantity of methanol 
was added as a polymerization terminator and then 2 parts by weight of 
4-methyl-2,6-di-tert-butylphenol was added as antioxidant. The cyclohexane 
was distilled off from the formed copolymer solution at an elevated 
temperature, to obtain a block copolymer mixture. 
The block copolymer mixture thus obtained had a composition shown in Table 
5, and approximately 60% of the copolymer (1) chain was substantially 
identical with the copolymer (2) chain in structure. Copolymers (1) and 
(2) had number average molecular weights of about 90,000 and about 56,000, 
respectively. 
Next, for comparison, B-A-B-A type styrene-butadiene block copolymers 
having styrene contents of 75% by weight and 80% by weight were produced 
by repeating the procedure adopted in the above-mentioned production of 
block copolymer mixture, except that the n-butyllithium catalyst was at 
once added at the start of polymerization. 
Each of the block copolymer mixture and the block copolymers thus obtained 
was blended with the same commercial impact-resistant polystyrene as used 
in Example 1 in the proportion shown in Table 5, and physical properties 
of the blend were measured. The results are indicated in Table 5, which 
clearly demonstrate the superiority of the composition of this invention 
in impact-resistance, transparency and balance of physical properties. 
Table 5 
__________________________________________________________________________ 
Example No. 
Comp. 
Comp. 
Properties Example 5 
Ex. 5 
Ex. 6 
__________________________________________________________________________ 
Copolymer 
Structure of polymer 
B-A-B-A 
B-A-B-A 
B-A-B-A 
Block (1) Styrene content (% by wt.) 
75 75 80 
copolymer 
Copolymer 
Structure of polymer 
A GP-PS 6) 
-- 
mixture 
(2) Styrene content (% by wt.) 
100 100 -- 
Copolymer (1)/Copolymer (2) (wt. ratio) 
4/1 4/1 -- 
Styrene content of block copolymer mixture (% by wt.) 
80 80 -- 
Block copolymer mixture 
/Impact-resistant polystyrene (wt. ratio) 
85/15 85/15 
85/15 
or block copolymer 
Melt flow index (g/10 min) 1) 
5.3 4.8 5.0 
Tensile strength (kg/cm.sup.2) 
2) 
250 239 255 
Tensile elongation at break (%) 
2) 
33 30 21 
Izod impact strength (kg-cm/cm) 
2) 
4.3 3.3 2.9 
Rockwell hardness (R-scale) 
3) 
93 92 97 
Bending modulus (kg/mm.sup.2) 
4) 
192 185 200 
Haze (%) 5) 
14 20 16 
__________________________________________________________________________ 
Notes:- 
1)- 5) are the same as in Table 1. 
6) A commercial polystyrene having number average molecular weight of ca. 
150,000 was used. 
Example 6 and Comparative Example 7 
A B-A-B-A type styrene-butadiene block copolymer having a styrene content 
of 75% by weight and a number average molecular weight of about 92,000 was 
produced in cyclohexane with n-butyllithium as catalyst. In the same 
manner as above, A-B-A type styrene-butadiene block copolymers having 
styrene contents of 90% by weight, 83% by weight and 77% by weight and 
having a number average molecular weight of about 64,000 were produced in 
cyclohexane with n-butyllithium as a catalyst. The first block copolymer 
was blended with each of the second block copolymers in the proportion of 
2:1 to obtain the three kinds of block copolymer mixtures shown in Table 
6. 
Then, each of these block copolymer mixtures was blended with the same 
commercial impact-resistant polystyrene as used in Example 1, and physical 
properties of the blend were measured. The results are shown in Table 6, 
which clearly demonstrate that the compositions in which the styrene 
contents of the components, constituting the copolymer mixture, fall in 
the ranges specified by this invention are better than the other 
compositions because of the superiority in transparency. 
Table 6 
__________________________________________________________________________ 
Example No. 
Properties Example 6 Comp. Ex. 7 
__________________________________________________________________________ 
Copolymer 
Structure of polymer 
B-A-B-A 
B-A-B-A 
B-A-B-A 
Block (1) Styrene content (% by wt.) 
75 75 75 
copolymer 
Copolymer 
Structure of polymer 
A-B-A 
A-B-A 
A-B-A 
mixture 
(2) Styrene content (% by wt.) 
90 83 77 
Copolymer (1)/Copolymer (2) (wt. ratio) 
2/1 2/1 2/1 
Block copolymer 
/Impact-resistant polystyrene (wt. ratio) 
85/15 
85/15 
85/15 
mixture 
Melt flow index (g/10 min) 1) 
5.1 4.8 4.5 
Tensile strength (kg/cm.sup.2) 
2) 
251 236 225 
Tensile elongation at break (%) 
2) 
31 37 45 
Izod impact strength (kg-cm/cm) 
2) 
4.5 4.8 5.1 
Rockwell hardness (R-scale) 
3) 
91 87 67 
Bending modulus (kg/mm.sup.2) 
4) 
190 181 168 
Haze (%) 5) 
16 20 32 
__________________________________________________________________________ 
Notes:- 
1)- 5) are the same as in Table 1. 
The impact strengths of the compositions obtained in Examples 1-6 and 
Comparative Examples 1-7 were plotted against their hazes on a graph, 
where the impact strength was taken as abscissa and the haze was taken as 
ordinate (logarithmic scale). The relation thus obtained is shown in the 
drawings attached which clearly demonstrate that the compositions of this 
invention are superior to the compositions of the Comparative Examples in 
balance of transparency and impact resistance.