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
2002-08-19
2003-07-15
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C526S065000, C526S228000, C526S342000, C525S233000
Reexamination Certificate
active
06593424
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention relates to a method for preparing a thermoplastic resin having superior heat resistance, and more particularly to a method for preparing a copolymer containing &agr;-methylstyrene and acrylonitrile by continuous bulk polymerization.
(b) Description of the Related Art
Acrylonitrile-butadiene-styrene copolymer resins (hereinafter, called ABS resins) are materials showing good stiffness, impact resistance, surface gloss and chemical resistance, and they are widely used for applications which require these material properties, such as electric and electronic products, and business equipment parts. The ABS resins, however, have low heat resistance and in use, there are constraints in their applications for automobile parts used as interior or exterior materials and the like which require good heat resistance.
Therefore, in order to overcome such limitations, a method of either employing a monomer having good heat resistance or adding inorganic substances to a portion of compositions which constitute the ABS resin may be used.
In general, a method for introducing a monomer having good heat resistance is carried out by adding a maleimide monomer or an &agr;-methylstyrene monomer which have good heat resistance during polymerization, or by mixing a heat resistant copolymer resin which contains heat resistant monomers with ABS resin.
Heat resistant ABS resin prepared by introducing monomers having good heat resistance in some portion should have good properties in impact strength and stiffness as well as heat resistance, and should not raise such problems as decomposition of the resin, thermal discoloration and the like during processing of the resin by extrusion or injection.
Heat resistant copolymer resins as described above are commonly prepared by copolymerizing a maleimide monomer or an &agr;-methylstyrene monomer with vinylcyanide compounds such as acrylonitrile or an aromatic vinyl monomer such as styrene, or by ternary copolymerizing.
Maleimide monomers are characterized by their high reaction rate in polymerization, and thereby arises a problem of controlling the reaction temperature. Further, since &agr;-methylstyrene monomers are characterized by their low depolymerizing temperature (i.e., 61° C.), they not only require prolonged reaction time due to their slow polymerization rate but they also result in polymers which have low molecular weight and which can be easily decomposed by heat.
As these monomers have such properties as described above, methods for producing copolymer resins having good heat resistance are commonly accomplished by emulsion polymerization using batch process which can be carried out at a relatively low temperature and in which the reaction time can be easily controlled.
Various methods are known for the production of copolymer resins having good heat resistance by means of emulsion polymerization. For example, U.S. Pat. No. 3,010,936 discloses a method for producing heat resistant ABS by admixing ABS resin with copolymer or ternary copolymer resin which is prepared by emulsion polymerization of an &agr;-methylstyrene monomer, an acrylonitrile monomer, and a styrene monomer. U.S. Pat. No. 3,367,995 discloses a method for producing heat resistant ABS by emulsion polymerization using rubber latex, styrene, acrylonitrile and &agr;-methylstyrene.
The above referenced methods for producing heat resistant ABS introduce &agr;-methylstyrene to the composition of ABS resin and they have shown to be effective to a certain extent in the improvement of heat resistance.
However, the cited methods have the following problems.
Firstly, emulsion polymerization for producing polymeric resins is typically carried out through a series of processes consisting of polymerization, coagulation, dehydration, and drying, wherein water, emulsifiers, and coagulants are used based on characteristics of the process, with the reaction temperature being lower than that of bulk polymerization.
Secondly, emulsion polymerization can overcome the shortcomings that the resulting resins rarely have high molecular weights due to the low polymerization temperature which is characteristic of &agr;-methylstyrene during the polymerizing process, but on the other hand the slow reaction rate effects extension of the reaction time.
Thirdly, in emulsion polymerization, as the resins have high heat resistance, the coagulation temperature becomes necessarily high, which in turn increases energy consumption during the process as well as making it complicated to set up conditions for the process.
Fourthly, in emulsion polymerization, resins contain a small amount of impurities such as emulsifier and coagulants which are used as supplementary raw materials, and therefore obtained resins are liable to be easily decomposed and discolored by heat when processed through extrusion or injection.
Fifthly, in emulsion polymerization, since acrylonitrile which is more hydrophilic than other monomers undergoes reaction in an aqueous environment, polymers are formed with a higher acrylonitrile content compared with other polymerization processes. Polymers of a high acrylonitrile content are easily discolored by heat and tend to be present as a gel polymer which is insoluble in solvents, eventually remaining as reddish or black impurities and damaging the appearance of the product.
Sixthly, in emulsion polymerization, since there is no recovery process as in the bulk polymerization process by vaporizing unreacted monomers at a high temperature under reduced pressure, a large amount of residual monomers remains within the resin and the residual monomers reduce the heat resistance of the product in proportion to its content.
Because of the problems in the emulsion polymerization process as described above, heat resistant ABS resins produced by use of &agr;-methylstyrene copolymer resins formed by emulsion polymerization have problems of deterioration in external appearance properties, such as lowering of clarity, thermal discoloration and weatherability, as well as odor generation due to decomposition, of the resin, when the ABS resin is processed by extrusion or injection.
As a method for preparing heat resistant ABS resin other than the process using &agr;-methylstyrene copolymer resin, U.S. Pat. No. 4,757,109 and Japanese Patent Publication No. 1983-206657 disclose a method to improve heat resistance of ABS resin by mixing ABS resin with the heat resistant resin produced by emulsion polymerization of maleimide monomer, vinylcyanide monomer and aromatic vinyl compound. These methods are effective to produce resins with high heat resistance in that the more the maleimide monomer content the resin, the higher the heat resistance.
However, as described above, the methods using a maleimide monomer still have problems related to the resins obtained by emulsion polymerization. Moreover, since the reaction proceeds very rapidly and is highly exothermic, there is a limitation in increasing the content of a maleimide monomer within the resin, and in order to overcome such limitation, the polymerization process becomes quite complicated, which is another problem. In addition, the more maleimide is contained within copolymer resins, the poorer the compatibility with ABS resin contained therein, thereby bringing about a problem of reduced impact strength.
On the one hand, U.S. Pat. No. 4,874,829 discloses a method for preparing copolymers or ternary copolymers with &agr;-methylstyrene, acrylonitrile, and maleimide monomers by bulk polymerization. This method employs a large amount of acrylonitrile having a high reactivity in order to overcome the low conversion rate of &agr;-methylstyrene, thereby providing an efficient way to overcome the low conversion rate in the preparation of high heat resistant resins containing &agr;-methylstyrene. However, the reaction mixture of this method includes a high acrylonitrile content, so the resultant resins made by this process tend to be easily discolored and they produce substances like gel which is insoluble in solv
Jang Yun-Chang
Lee Hyung-Sub
LG Chem Ltd.
Teskin Fred
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