Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-07
2003-02-04
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S095000, C525S098000, C525S099000
Reexamination Certificate
active
06515072
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent rubber-modified styrenic resin composition, more particularly to a resin composition which comprises a copolymer matrix and a rubber-particle-dispersed phase formed from rubbery copolymer and which has good chemical resistance, processability, transparency, and impact resistance.
2. Description of the Related Art
Rubber-modified styrenic resin is known to have high toughness and good processability, and is thus widely used in food containers, packaging materials, and housings of household, electrical appliances and office appliances. However, the conventional rubber-modified styrenic resin is generally opaque, and cannot be used to form a transparent article. In the art, it has been suggested that the styrenic resin be blended with a styrene-butadiene block copolymer. However, the resulting styrenic resin composition is not significantly improved in its toughness, and is thus not satisfactory.
Japanese Laid-Open Patent No. 4-180907 discloses a method for polymerizing styrene and methyl methacrylate in the presence of a styrene-butadiene block copolymer. The resulting resin has enhanced transparency and toughness, but it is not satisfactory in processability. Japanese Laid-Open patent No. 8-239532 discloses a resin composition formed from a styrene-butadiene rubber having 1 to 13.8 wt % of 1,2-vinyl unit and styrene-methylmethacrylate copolymer, which have refractive indexes proximate to each other. This resin composition has an average particle size of 0.1 to 2 &mgr;m, with a particle size distribution index of 2 to 5. While this resin composition has improved transparency and impact resistance, its chemical resistance is insufficient.
It has been found by the applicant that by dispersing rubber particles into a copolymer matrix formed from styrenic monomers, (meth)acrylate monomers and vinyl cyanide monomers, and by controlling the specific morphology of rubber particles and specific molecular distribution of the copolymer matrix, a rubber-modified styrenic resin composition of improved transparency and chemical resistance can be obtained.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a transparent rubber-modified styrenic resin composition having good chemical resistance, good processability, high transparency and good impact resistance.
Accordingly, the transparent rubber-modified styrenic resin composition of the present invention comprises:(1) a rubber particle dispersed phase (A) including a rubbery copolymer which is a block copolymer formed from 10 to 50 weight percent of styrenic monomers and 90 to 50 wt % of dienic monomers; wherein said rubbery copolymer contains a polystyrene block in an amount of 5 to 35 wt %, based on total weight of the rubbery copolymer; and (2) a copolymer matrix (B) which is composed of 12 to 70 parts by weight of styrenic unit, 20 to 80 parts by weight of (meth)acrylate unit, 1 to 20 parts by weight of vinyl cyanide unit, and 0 to 40 parts by weight of other copolymerizable monomer units, based on 100 parts by weight of total monomer units. The content of the copolymer matrix (B) having a molecular weight of 3,000~50,000 is in an amount of 15 to 50 wt %, based on the total weight of the copolymer matrix (B). The aforementioned unit means monomers which are polymerized into polymeric form and which are composed of the polymer. For example, a styrenic unit is a polymerized styrenic monomer derivative in the polymer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rubbery copolymer used in the present invention is a block copolymer prepared by anionic polymerization, in which styrenic monomers and dienic monomers are polymerized in the presence of an organic solvent and an organo-lithium compound as the initiator. The rubbery copolymer has a Moony Viscosity (ML
1+4
) of 20 to 80 and a solution viscosity of 3 to 60 cps (5 wt % in SM at 25° C.). The rubbery copolymer contains more than 8 weight percent of 1,2-vinyl structure of the dienic unit. The rubbery copolymer contains 5 to 35 wt % of polystyrene block. The rubbery copolymer may have the following block structures: homopolymer block structure, random copolymer block structure, tapered block structure, linear structure, and branch structure. Representative examples of the aforementioned structures are as follows:
1. Linear Block Copolymer:
(1) (A−B)
n
(2) A(B−A)
n
(3) B(A−B)
n
wherein, polymer block A consists essentially of styrenic unit, polymer block B consists essentially of dienic unit, and n is an integer equal to or greater than 1.
2. Branch Block Copolymer:
(1) [(B−A)
n
]
m+1
X
(2) [(A−B)
n
]
m+1
X
(3) [(B−A)
n
B]
m+1
X
(4) [(A−B)
n
A]
m+1
X
wherein, A and B are as defined above, X is a residue of a coupling agent (such as silicone tetrachloride and tin tetrachloride) or a multi-functional organolithium, and n and m are integers of 1 to 10.
3. Mixtures of the linear block copolymers and the branch block copolymers described in Items 1 and 2, shown above.
Representative examples of the tapered block copolymer are:
D−D/S−S (S−D/S)
n
−S
D−S−D/S−S D/S−(S−D/S)
n
D−S−D/S−S−D X−[(S−D/S)
n
]
m+1
S−D−D/S−S X−[(D/S−S)
n
]
m+1
D/S−S−D−S X−[(S−D/S)
n
−S]
m+1
S−D/S−S X−[(D/S−S)
n
−D/S]
m+1
(S−D/S)
n
D−D/S−S−S−D/S−D
wherein, S is polystyrenic block, D is polydienic block, D/S is adienic/styrenic tapered block copolymer, X is the residue of a multi-functional initiator or a multi-functional coupling agent, and m and n are integers of 1 to 10. In the present invention, the tapered block structure is preferred. Among the above-mentioned examples, D−D/S−S, D−S−D/S−S, and D−D/S−S−S−D/S−D are more preferred.
The rubbery copolymer of the present invention contains the polystyrene block in an amount of 5 to 35 weight percent, preferably 10 to 25 wt %, more preferably 14 to 22 wt %, based on total weight of the rubbery copolymer. When the content of the polystyrene block is less than 5 wt %, the resin composition is poor in transparency. On the other hand, when the content of the polystyrene block is more than 35 wt %, the impact strength of the resin composition would not be satisfactory. The content of 1,2-vinyl structure of the rubbery copolymer used in the present invention is more than 8 wt %, preferably more than 14 wt %. When the content of the 1, 2-vinyl structure is more than 14 wt %, a better balance of good transparency and high impact resistance of the resin composition can be attained.
Examples of the styrenic monomers of the rubbery copolymer of the present invention are styrene, &agr;-methyl styrene, para-methyl styrene, meta-methyl styrene, ortho-methyl styrene, ethyl styrene, 2,4-dimethyl styrene, para-tert-butyl styrene, &agr;-methyl-para-methyl styrene, bromo-styrene, dibromo-styrene, and 2,4,6-tribromo-styrene. The aforementioned styrenic monomers can be used alone or in combination with one another.
Examples of the dienic monomers of the rubbery copolymer of the present invention are 1,3-butadiene, 2-methyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2,3 -dimethyl-1,3-butadiene, isoprene, and 1,3-hexadiene. The aforementioned monomers can be used alone or in combination with one another. Among the aforementioned monomers, 1,3-butadiene and isoprene are preferred.
The organolithium compound used in the preparation of the rubbery copolymer is a compound containing at least one lithium atom. Examples of organolithium initiators are ethyllithium, n-pentyllithium, iso-propyllithium, n-butyllithium, sec-butyllithium, hexyllithium, cyclohexyllithium, phenyllithium, benzyllithium, naphthyllithium, tert-bu
Chi Mei Corporation
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mullis Jeffrey
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