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
1999-05-26
2001-09-11
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S084000, C525S085000, C525S902000
Reexamination Certificate
active
06288167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to blends of grafted polyacrylate rubber with other polymers. More specifically it relates to blends of (1) a first grafted rubber polymer wherein the rubber has a core/shell structure where the core is a styrenic polymer and the shell is an acrylate rubber; (2) a second grafted rubber polymer wherein the rubber is selected from the group consisting of diene, ethylene propylene and acrylate rubbers; and (3) a matrix polymer formed from a vinyl aromatic monomer, an unsaturated nitrile monomer and optionally one or more compatible comonomers.
2. Description of Related Art
Polymer blends of grafted rubbers are well known in the prior art. These blends are especially useful as molding and extrusion compositions for indoor and outdoor applications. The blends have good impact and weatherability properties. Blends of various polymers using one or more core/shell type polymers are also known. They are taught in the following patent publications.
EPO Patent Publication 0 534 212 A1 (BASF) teaches a mixture of (1) a graft copolymer having a core of a 50-99.9% by weight of a vinylaromatic monomer with a polyfunctional crosslinker and/or a comonomer with two or more functional groups; and (2) a graft polymer having a rubbery core and a shell having a Tg<25° C.
EPO Patent Publication 0 342 283 (Rohm & Haas) teaches either thermoplastic or thermoset matrix polymers and substantially spherical polymer particles having an average diameter of from 2 to 15 micrometers.
U.S. Pat. No. 4,916,171 to Brown et al teaches core/shell polymers having an alkali-insoluble, emulsion polymer core and an alkali soluble, emulsion polymer shell attached or associated with said core so that upon dissolving said shell with alkali, a portion of said shell remains attached or associated with said core. Also taught are compositions wherein said shell polymer has been neutralized and substantially, but not totally, dissolved so as to form a blend of neutralized core-shell polymer and an aqueous solution of neutralized shell polymer.
U.S. Pat. No. 5,047,474 to Rabinovich et al teaches modifier compositions of acrylic core/shell polymers and alkyl methacrylate-butadiene-styrene core/shell polymers are added to polyvinyl halides to provide materials with improved color depth and impact strength, as well as reduced pearlescence.
U.S. Pat. No. 5,237,004 to Wu et al teaches polymer particles in a size range between 2 and 15 micrometers, and having a refractive index close to, but not identical with, that of a matrix polymer and optionally having one or more enclosing shells, the outer shell being compatible with the matrix polymer, impart light-diffusing properties to the matrix polymer without degrading its physical properties, while the particles having a closer refractive index match to the matrix polymer impart gloss reduction to the surface of the matrix polymer.
U.S. Pat. No. 5,266,610 to Malhotra et al teaches the use of core/shell particulate toughening agents in a composite resin system comprised of thermoplastic and thermoset resins wherein the phase morphology is cocontinuous.
Japanese Patent Publication 62/236,850 to Takeda Chemical Industry teaches a core/shell type structure where the glass transition temperature of the core is higher than that of the shell for use in motor vehicles. The blends of grafted rubbers of the prior art are maybe useful. However they may be difficult to color and lack the balance of properties provided by the blends of the present invention. For example, in the prior art blends of (1) a polybutylacrylate rubber grafted with styrene and acrylonitrile (ASA); and (2) a butadiene rubber grafted with styrene and acrylonitrile (ABS), the polybutylacrylate (PBA) used in the ASA component has a lower refractive index (RI) than the polybutadiene (PBD) used in the ABS which has a lower RI than SAN which is grafted onto the polybutylacrylate and polybutadiene and which is also present in the blends as a free matrix polymer. Thus, the difference in RI between the ASA component and the ABS component causes the ASA/ABS blends to be opaque and more difficult to color than ABS alone.
SUMMARY OF THE INVENTION
The present invention is directed to polymer blends comprising:
(1) from 30 to 50% by weight based on the total weight of the polymer blend of a first grafted rubber component comprising an acrylate rubber which is grafted with a vinyl aromatic monomer and an unsaturated nitrile monomer and wherein the acrylate rubber is a core/shell rubber comprising a core prepared from a vinyl aromatic monomer and one or more optional comonomers and an acrylate rubber shell wherein the average rubber phase particle size (RPPS) of the core/shell rubber is in the range of from 0.08 to 0.5 microns;
(2) from 15 to 30% by weight based on the total weight of the polymer blend of a second grafted rubber component comprising a rubber substrate selected from the group consisting of diene, ethylene propylene and acrylate rubbers which is grafted with a vinyl aromatic rubber and an unsaturated nitrile monomer wherein the average rubber phase particle size of the rubber substrate is in the range of from 0.3 to 8 microns; and
(3) from 20 to 55% by weight based on the total weight of the polymer blend of a matrix polymer formed from a vinyl aromatic monomer, an unsaturated nitrile monomer and optionally one or more compatible comonomers.
DESCRIPTION OF THE INVENTION
In order to improve the colorability of the prior art polymer blends of ASA and ABS, it is necessary to reduce the RI difference between the two phases in order to reduce the contrast ratio (CR) of the blends. One of the methods used to reduce the RI difference is to increase the rubber phase RI to bring it closer to that of the matrix phase. This can be done to the ASA component by preparing a styrene butyl acrylate (SBA) copolymer to be used as the rubber substrate as styrene has a high RI. However, this SBA copolymer has a high glass transition temperature (Tg) that results in loss of low temperature impact.
A better approach that does not affect the rubber phase Tg and preserves low temperature impact is accomplished in the present invention by making a polystyrene core with a polybutylacrylate shell and then grafting this core/shell substrate with SAN.
The core/shell ASA polymer is then blended with a second grafted rubber such as a polyacrylonitrile-butadiene-styrene graft polymer (ABS) and/or a polystyrene-acrylonitrile polymer (SAN) to provide a new molding composition which has better colorability properties, e.g., ease of coloring, increased blackness and/or brightness. In these new compositions less pigment is required to obtain the desired color which results in a cost saving.
A. The Second Grafted Rubber Component
The second grafted rubber component which is blended with the core/shell grafted rubber component are conventional graft polymers which are well known in the art. These are prepared by conventional methods wherein a rubber substrate is grafted with the vinyl aromatic and unsaturated nitrile monomers and optionally one or more additional comonomers. The rubber substrate may be a diene rubber homopolymer or copolymer, an olefin based rubber such as an ethyl propylene (EP) rubber with or without an additional diene monomer (EPDM) and acrylate rubbers. The preferred vinyl aromatic monomers are styrene, alpha methyl styrene and the like. The preferred unsaturated nitrile monomers are acrylonitrile and methacrylonitrile.
One of the preferred second grafted rubber components is poly(acrylonitrile-butadiene-styrene) commonly known as ABS.
The preferred acrylonitrile-butadiene-styrene (ABS) polymer contains from 5 to 30% by weight of a diene rubber based on the total weight of the ABS polymer. The graft and matrix phases of the ABS polymer contain from 5 to 40% by weight of acrylonitrile and from 95 to 60% by weight of styrene based on the total weight of the acrylonitrile and styrene components. The expression ABS is used in the generic sense and includes the know
Chen Chuan-Ju
Peng Fred Ming-sheng
Peng Lily
Bayer Antwerpen S.A./N.V.
Cain Edward J.
Gil Joseph C.
Peng Lily
Preis Aron
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