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
1999-11-29
2001-06-26
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S226000
Reexamination Certificate
active
06252002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a methyl methacrylate resin composition which exhibits little drawdown in heat molding. This resin composition is suitable for the production of molded articles by extrusion molding, blow molding and expansion molding, especially for the production of large molded articles.
2. Description of Related Art
Methyl methacrylate polymers have sufficient rigidity, excellent transparency and excellent weather resistance. Thus the polymers have been widely used for molded articles by injection molding, such as lamp covers and meter covers of automobiles, spectacle lenses and light guide members, and also for extruded boards by extrusion molding, such as signboards and nameplates.
On the other hand, conventional methyl methacrylate polymers can afford only small molded articles because the tension of the melt oriented resin composition is small in blow molding, and therefore much drawdown is caused. Furthermore, it can be molded by foaming only under limited conditions in temperature, molding pressure and the like. Thus resin compositions with both high flowability and little drawdown have been desired.
With regard to improving processing properties in molding, Japanese Unexamined Patent Publication (Kokai) No. 5-140411 has disclosed a method in which polytetrafluoroethylene is added.
Furthermore, U.S. Pat. No. 5,726,268 has disclosed that methyl methacrylate polymer with a branched structure have high tension in melt orientation with retaining melt flowability.
However, in the method wherein polytetrafluoroethylene is added, the drawdown is improved, but sufficient tension in melt orientation necessary for blow molding in large scale can not be achieved. Therefore, the effect of that method is insufficient. In addition, the transparency, which is one of characteristics of acrylic resin, is also lost because polytetrafluoroethylene has a refractive index different from that of methyl methacrylate polymer.
Although the use of the methyl methacrylate polymer with a branched structure can afford acrylic resin having both higher flowability and higher tension in melt orientation compared with those at the time when a conventional linear methyl methacrylate polymers, such acrylic resin does not have drawdown low enough to make the resin applicable also to blow molding in large scale in which a parison having a length more than 40 cm is used. Thus resin which can exhibit still lower drawdown in melt orientation for producing large scale articles has been demanded.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide methyl methacrylate resin composition having remarkably improved tension in melt orientation, namely having reduced drawdown tendency, with remaining sufficient melt flowability, the resin compositions being able to be applied also to blow molding in large scale and extrusion foaming molding.
The present invention provides a methyl methacrylate resin composition comprising: (A) about 90 to 99% by weight of a methyl methacrylate polymer with a branched structure having a weight average molecular weight of about 80,000 to 400,000 and a molecular weight between branch points, defined by using a z-average molecular weight, of about 30,000 to 500,000; and (B) about 10 to 1% by weight of a high molecular weight methyl methacrylate polymer having a weight average molecular weight of about 1,000,000 to 5,000,000.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The methyl methacrylate polymer with a branched structure will be explained.
The methyl methacrylate polymer with a branched structure is disclosed in U.S.Pat. 5,726,268, and copolymer of monofunctional monomers containing methyl methacrylate as a main component, and polyfunctional monomers copolymerizable with the monofunctional monomers.
The monofunctional monomers comprising methyl methacrylate mean methyl methacrylate itself, or mixtures of about 50% by weight or more, preferably about 70% by weight or more of methyl methacrylate and at least one other monofunctional monomer copolymerizable with methyl methacrylate. The amount of the copolymerizable monofunctional monomer in the copolymer is preferably not less than about 1% by weight, more preferably not less than about 3% by weight, and especially preferably about 3 to 20% by weight.
When the amount of methyl methacrylate is less than about 50% by weight, the copolymer may not have good transparency and mechanical strength which are the characteristics of the methyl methacrylate polymer.
Examples of the copolymerizable, monofunctional monomers include methacrylates such as ethyl methacrylate, propyl methacrylate, butyl methacrylate and benzyl methacrylate; acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and 2-ethylhexyl acrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid; acid anhydrides such as maleic anhydride and itaconic anhydride; esters having a hydroxyl group such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, monoglycerol acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate and monoglycerol methacrylate; amides such as acrylamide, methacrylamide and diacetone acrylamide. In addition, examples of the monomers include nitriles such as acrylonitrile and methacrylonitrile; nitrogen-containing monomers such as dimethylaminoethyl methacrylate; epoxy group-containing monomers such as allyl glycidyl ether, glycidyl acrylate and glycidyl methacrylate; and styrene monomers such as styrene and &agr;-methylstyrene, and the like.
Examples of the copolymerizable polyfunctional monomers include esterified products prepared by esterifying the terminal hydroxyl groups of ethylene glycol or its oligomer with acrylic acid or methacrylic acid, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate and tetraethylene glycol di(meth)acrylate; esterified products prepared by esterifying the hydroxyl groups of dihydric alcohols with acrylic acid or methacrylic acid, such as neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate and butanediol di(meth)acrylate; esterified products prepared by esterifying polyhydric alcohols or their derivatives, such as trimethylolpropane and pentaerythritol, with acrylic acid or methacrylic acid; and aryl compounds having two or more alkenyl groups such as divinylbenzene, and the like.
The methyl methacrylate polymer with a branched structure has the weight average molecular weight (Mw) of about 80,000 to 400,000, preferably about 150,000 to 300,000, and the molecular weight between branch points defined by a Z-average molecular weight (Mzb) of about 30,000 to 500,000, preferably about 50,000 to 200,000.
When the weight average molecular weight (Mw) is less than about 80,000, the methyl methacrylate polymer with a branched structure has insufficient mechanical strength and solvent resistance. Moreover, molded articles obtained from the methyl methacrylate resin composition comprising the methyl methacrylate polymer with a branched structure and the high molecular weight methyl methacrylate polymer become poor in strength and solvent resistance.
When the weight average molecular weight (Mw) is more than about 400,000, the methyl methacrylate polymer with a branched structure has too low melt flowability and thus the resulting resin composition has low moldability.
When the molecular weight between branch points (Mzb) is more than about 500,000, the methyl methacrylate polymer with a branched structure loses
Sakamoto Takashi
Yamada Taiji
Buttner David J.
Pillsbury & Winthrop LLP
Sumitomo Chemical Company Limited
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