Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-10-12
2003-12-02
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S523000, C525S055000, C525S065000, C525S066000, C525S069000, C525S403000, C525S404000, C524S504000
Reexamination Certificate
active
06656595
ABSTRACT:
This invention relates to pigment dispersing resins which are conveniently applicable to water-based paint, in particular, water-based automotive finish; and also to water-based pigment dispersions and water-based paint compositions which contain said pigment dispersing resin.
As paint for automotive finish, heretofore those of solvent-based type have been widely used, in which a base resin (base polymer) component such as acrylic resin, polyester resin or alkyd resin having such functional groups as hydroxyl and carboxyl groups; and a curing agent such as amino resin, optionally blocked polyisocyanate compound, epoxy compound and the like are concurrently used.
For the protection of terrestrial environment, paint of low volatile organic matter content (VOC) is demanded in these years. In the field of paint for automotive finish, switching to water-based paint of, in particular, colored base coating paint whose VOC discharge is high has been strongly required, and it is expected that replacement of solvent-based coating with water-based coating will proceed hereafter.
Problems incidental to the switching are, for example: (1) pigment dispersing resin blended in water-based paint is incompatible with the binder component in water-based paint; (2) pigment dispersing resin or dispersant fail to uniformly disperse the pigment and invite flocculation or agglomeration of the pigment; and (3) the pigment dispersing resin or dispersant in the water-based paint composition fail to cure under baking and invite degradation of the coating film performance.
Those pigments used for colored base coating paint generally have hydrophobic surfaces and are difficult to be water-wettable, while pigment dispersing resins conventionally used for solvent-based colored paints have low solubility in water and are inferior in dispersing stability in aqueous media. Hence it is important in designing a pigment dispersing resin for water-based paint, to secure satisfactory levels of both wettability of pigment and dispersing stability of the pigment dispersing resin in an aqueous medium.
Low viscosity and low molecular weight of pigment dispersing resin are considered advantageous for wetting property of pigment; and easy formation of steric repelling layer on the pigment surfaces or good solubility of the pigment dispersing resin in the continuous phase (aqueous medium) are considered advantageous for the dispersing stability. Both the pigment-wetting property and the dispersing stability of the pigment dispersing resin are considered to participate in wetting of the pigment surface with the pigment dispersing resin (a resin having a group capable of forming weak flocculation in aqueous system such as alkyl-group is effective) and in adsorption onto the pigment, which are attributable to the interaction between hydrophobic part on the pigment surface and that of pigment dispersing resin.
Past development of pigment dispersing resins or assistant for water-based paint has been advanced based on the foregoing viewpoints. For instance, Sho 50 (1975)-154328A-JP proposed use of a straight chain anionic polymer containing acidic functional groups, which is obtained through polymerization of a monomer mixture containing as a part of its monomer components an acidic functional group-containing, polymerizable unsaturated monomer such as (meth)acrylic acid, as the pigment dispersing resin. Said polymer, however, exhibits high solubility in aqueous media and hence is unsatisfactory in respect of wetting of pigment. Furthermore, pigment dispersions formed with the use of said polymer show excessively high viscosity and are subject to a drawback of difficult handling.
Hei 1 (1989)-182304A1-JP, Canadian Patent 2149399 and U.S. Pat. No. 5,231,131 disclosed, as the pigment dispersing resin, a graft copolymer obtained through copolymerization of carboxyl-containing macromonomers. Said graft copolymer excels in pigment dispersing stability because its trunk portion is hydrophobic and the branch portion is hydrophilic. Whereas, pigment dispersions formed with the use of said copolymer show high viscosity, and the graft copolymer is far from being satisfactory, in view of the increasing demand for pigment dispersions having high pigment concentration to save cost and to reduce VOC.
On the other hand, top coating paints for automotive finish are required not only high film performance such as durability, acid resistance, washability (scratch resistance) and chipping resistance, but also still better appearance of coated film in sharpness, transparency, color development and the like.
An object of the present invention is to provide pigment dispersing resins which excel in wetting property and dispersing stability even at high pigment concentration and which can provide aqueous pigment dispersions of low viscosity and excellent color developing property.
A further object of the present invention is to provide a water-based pigment dispersion which has low viscosity even at high pigment concentration and which excels in color-developing property.
Another object of the invention is to provide a water-based paint which excels in curability and is capable of forming a painted film of splendid finish appearance in sharpness, transparency, color-developing property and the like.
Still other objects and characteristics of the invention will become apparent from the following descriptions.
We have engaged in concentrative studies with the view to accomplish the above objects and now discovered that copolymers obtained by introducing ionic hydrophilic functional groups and nonionic functional groups into macromonomers which are obtained through copolymerization of specific monomer component such as methacrylic acid ester, styrene or the like in the presence of a metal complex which is a catalytic chain transfer agent or an addition-cleavage type chain transfer agent, and if necessary a radical polymerization initiator, are very favorable as pigment dispersing resin for water-based paint, and thus completed the present invention.
Accordingly, the invention provides a pigment dispersing resin which has a weight-average molecular weight within a range of 3,000-100,000 and which is obtained by copolymerizing a monomeric mixture comprising:
a macromonomer (A) formed through (co)polymerizing, in the presence of a metal complex which is a catalytic chain transfer agent or an addition-cleavage type chain transfer agent and if necessary a radical polymerization initiator, a monomer component comprising at least one polymerizable monomer selected from methacrylic acid esters and styrene, and if necessary methacrylic acid;
a polymerizable, unsaturated monomer (B) containing at least one kind of ionic functional group selected from amino, quaternary ammonium salt and sulfonic acid groups;
a nonionic, polymerizable unsaturated monomer (C) having polyoxyalkylene chain; and
other ethylenically unsaturated monomer (D); in the presence of a radical polymerization initiator (which copolymer is hereafter referred to as “pigment dispersing resin I”).
The invention also provides a pigment dispersing resin (“pigment dispersing resin II”) which has a weight-average molecular weight within a rang of 3,000-100,000 and which is obtained by co-polymerizing a monomeric mixture comprising:
a carboxyl-containing macromonomer (A-1) having a resin acid value of 50-450 mgKOH/g which is obtained through copolymerization of methacrylic acid with at least one copolymerizable monomer selected from methacrylic acid esters and styrene, in the presence of a metal complex which is a catalytic chain transfer agent or an addition-cleavage type chain transfer agent and if necessary a radical polymerization initiator;
a polymerizable unsaturated monomer (B) containing at least one kind of ionic functional group selected from amino, quaternary ammonium salt and sulfonic acid groups;
a nonionic, polymerizable unsaturated compound (C) having polyoxyalkylene chain, and
other ethylenically unsaturated monomer (D); in the presence of a radical polymerization initiator, and reacting t
Kamimori Isao
Nakajima Yoshio
Yukawa Yoshiyuki
Dawson Robert
Feely Michael J
Kansai Paint Co. Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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