Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-01-09
2003-11-11
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S343000, C524S348000, C524S349000, C524S350000, C524S351000, C524S352000, C524S353000
Reexamination Certificate
active
06646036
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a block copolymer composition excellent in heat stability and color fastness which comprises a block copolymer comprising a specific monoalkenyl aromatic compound and a specific conjugated diene compound and a specific phenolic stabilizer.
BACKGROUND ART
Block copolymers comprising monoalkenyl aromatic compounds and conjugated diene compounds which have not been vulcanized have the similar elasticity to that of vulcanized natural rubbers or synthetic rubbers at room temperature if content of the monoalkenyl aromatic compounds is relatively small and, besides, have the similar processability to that of thermoplastic resins at high temperatures, and, hence, they are widely utilized in the fields of footwear, plastics modification, asphalt, pressure sensitive adhesives, and others.
Furthermore, if content of the monoalkenyl aromatic compounds is relatively large, transparent thermoplastic resins excellent in shock resistance are obtained. Therefore, recently, the block copolymers increase in their usage mainly in the fields of food packaging containers and, moreover, their uses are being diversified into a wide variety of fields.
However, since the block copolymers comprising monoalkenyl aromatic compounds and conjugated diene compounds have carbon—carbon double bonds in the molecules, they suffer from the problems that they are inferior in heat stability and the effects to improve characteristics of the block copolymers per se, for example, elastic characteristics, adhesion and impact resistance cannot be sufficiently exhibited. Accordingly, in order to improve the heat stability of these block copolymers, there have been used phenolic stabilizers, phosphorus stabilizers, sulfur stabilizers, and the like.
For example, BHT (2,6-di-tert-butyl-4-methylphenol) which is most widely used must be used in a large amount because it has a relatively high oxidation inhibition function and a relatively high heat resistance, but is readily volatilized in case the molding temperature is high. Furthermore, when other phenolic stabilizers are used, they must be used in a large amount for obtaining high heat stabilization effect, and, thus, in many cases, there is caused a problem that block copolymer compositions are colored in use at high temperatures or at the time of molding at high temperatures. On the other hand, when phosphorus stabilizers and/or sulfur stabilizers are used in combination with phenolic stabilizers, the heat stabilization effect is improved, but there are problems of hydrolysis in the case of phosphorus stabilizers and odor development in the case of sulfur stabilizers.
In view of the above problems, the applicant proposed in JP-A-4-246454 a technique of improving the heat stability of block copolymers by using, in combination, 0.005-0.05 part by weight of a specific sulfur phenolic stabilizer, 0.1-2.0 parts by weight of other specific phenolic stabilizer, and optionally a phosphorus stabilizer. However, it has been found that even this technique requires use of phosphorus stabilizers in actual use. However, since phosphorus stabilizers have the problem of hydrolysis, there is a limit in heat stabilization effect in actual use, and the technique for improving heat stability of block copolymers without using phosphorus stabilizers is demanded.
As mentioned above, conventional stabilizers, whether they are used singly or in combination of two or more, have a limit in the effect to improve heat stability of block copolymers of monoalkenyl aromatic compounds and conjugated diene compounds, and, for some uses, products having sufficient heat stability cannot be obtained and block copolymer compositions having truly high heat stability performance have long been demanded.
The present invention has been made for meeting the demand, and the object is to solve the problems on heat stability performance in the conventional block copolymer compositions and provide block copolymer compositions which can exhibit excellent heat stability even under being heated at high temperatures, are high in the effect to inhibit production of gel-like materials and excellent in color fastness and have a satisfactory color tone.
DISCLOSURE OF INVENTION
As a result of intensive research conducted by the inventors in an attempt to solve the above problems, it has been found that a block copolymer composition comprising a block copolymer of a specific monoalkenyl aromatic compound and a specific conjugated diene compound and a specific phenolic stabilizer is excellent in heat stability, namely, is not deteriorated in properties even if it is heated at high temperatures, can be inhibited from formation of gel-like materials, is excellent in color fastness and has good color tone. Thus, the present invention has been accomplished.
That is, the present invention relates to a block copolymer composition which comprises (a) a block copolymer comprising a polymer block segment mainly composed of a monoalkenyl aromatic compound and a polymer block segment mainly composed of a conjugated diene compound, content of the monoalkenyl aromatic compound being 5-95% by weight based on the total weight of the copolymer, (b) a phenolic stabilizer represented by the following formula (I):
(wherein R
1
and R
3
are —CH
2
—S—R
5
in which R
5
represents an alkyl group of 1-18 carbon atoms, R
2
represents a hydrogen atom or a methyl group, and R
4
represents an alkyl group of 1-8 carbon atoms or a cycloalkyl group of 5-12 carbon atoms), and (c) at least one phenolic stabilizer selected from the phenolic compounds represented by the following formulas (II)-(V):
(wherein R
6
is represented by the following formula (VI):
R
7
represents an alkyl group of 2-22 carbon atoms, and R
8
-R
12
each represent a hydrogen atom or an alkyl group of 1-6 carbon atoms, with a proviso that two or more of R
8
-R
12
are alkyl groups), content of the phenolic stabilizer (b) being more than 0.05 part by weight and less than 0.6 part by weight and that of the phenolic stabilizer (c) being not less than 0.05 part by weight and not more than 0.8 part by weight based on 100 parts by weight of the block copolymer (a).
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be explained in detail below.
The block copolymer used in the present invention is a block copolymer comprising a polymer block segment mainly composed of a monoalkenyl aromatic compound and a polymer block segment mainly composed of a conjugated diene compound. Furthermore, in the block copolymer of the present invention, content of the monoalkenyl aromatic compound is in the range of 5-95% by weight based on the total weight of the block copolymer. In the present invention, said block copolymer may be used singly or in admixture of two or more.
Here, the polymer block segment which is mainly composed of a monoalkenyl aromatic compound and constitutes the block copolymer of the present invention is a homopolymer of the monoalkenyl aromatic compound or a copolymer of the monoalkenyl aromatic compound and other monomers which contains more than 50% by weight of the monoalkenyl aromatic compound and is substantially mainly composed of the monoalkenyl aromatic compound.
The polymer block segment mainly composed of a conjugated diene compound is a homopolymer of the conjugated diene compound or a copolymer comprising a monoalkenyl aromatic compound and the conjugated diene compound and containing more than 50% by weight of the conjugated diene compound. In such copolymer block, the monoalkenyl aromatic compound may be distributed uniformly or ununiformly (for example, with a taper). Furthermore, in the block, there may coexist a plurality of the portions where the monoalkenyl aromatic compound is distributed uniformly and/or the portions where the monoalkenyl aromatic compound is distributed ununiformly.
In the block copolymer of the present invention, the content of the monoalkenyl aromatic compound must be in the range of 5-95% by weight based on the total weight of the block copolymer. If the content of the mono
Fujiwara Masahiro
Toda Keiichi
Japan Elastomer Co., Ltd.
Szekely Peter
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