Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-12-17
2002-10-29
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S176000, C525S378000
Reexamination Certificate
active
06472463
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polymeric pigment dispersants, more particularly it relates to graft copolymer pigment dispersants having aromatic ester, aromatic amine, and/or quaternary ammonium groups useful for dispersing a wide variety of pigments.
Polymeric materials have been previously known which are effective for dispersing solid pigments in organic solvents and used to form pigment dispersions of uniform color useful in formulating solvent borne paint compositions. Nowadays, such pigment dispersions are widely used, for example, in exterior solvent borne paints for automobiles and trucks.
Much of the past activity concerning polymeric dispersants has been with random copolymers, but these relatively inefficient materials are being replaced by structured pigment dispersants, such as those having graft copolymer (or comb) structures, as for example, as taught in Huybrechts U.S. Pat. No. 5,852,123 issued Dec. 22, 1998. Such graft copolymers are generally composed of a macromonomer grafted onto a polymer backbone and have attached to either the macromonomer or backbone, a polar group known as a pigment anchoring group which is designed to adsorb on the surface of a pigment particle and thereby anchor the polymer to the pigment surface. While the past work indicates that graft copolymers are outstanding dispersants, they also suffer from certain significant drawbacks. For instance, they are not selectively adsorbed by certain pigment types and are oftentimes displaced from pigment surfaces by polar solvents or other polar groups present in the paint system. Ineffective anchoring of the dispersant to a pigment particle surface is highly undesired, since it allows the pigment particles to flocculate or cluster together and results in pigment dispersions and ultimately paints of poor color quality.
Therefore, there is still a need to improve the performance of such pigment dispersants, and in particular to find new graft copolymers that are more effective in dispersing a wider range of pigments.
SUMMARY OF THE INVENTION
The present invention provides a composition suitable for use as a pigment dispersant, which comprises a graft copolymer, preferably polymerized from all acrylic monomers, having a macromonomer grafted onto a polymeric backbone, wherein the graft copolymer has attached to either the backbone or macromonomer, a pigment anchoring group selected from the group consisting of aromatic esters, aromatic amines, and quaternary ammonium cations, or mixtures thereof. The anchoring groups are preferably attached as pendant groups to the graft copolymer by reaction with functional groups on either the backbone or macromonomer. The graft copolymer may also contain other functional groups, such as hydroxyl groups, in either or both the backbone or macromonomer for crosslinking the dispersant into the final thermoset paint composition.
The polymeric backbone comprises about 10 to 90% by weight, preferably about 20 to 80% by weight, of the graft copolymer and the macromonomer comprises about 90 to 10% by weight, preferably about 80 to 20% by weight, of the graft copolymer. The graft copolymer further contains at least about 1% by weight, preferably about 2 to 30% by weight, based on the total weight of the graft copolymer, of pigment anchoring group, and preferably also contains up to about 30% by weight of hydroxyl groups.
The pigment dispersant is produced by a macromonomer approach which involves grafting a macromonomer (which becomes the side chain of the graft copolymer) onto a polymeric backbone. The macromonomer is polymerized first in the presence of cobalt (II) and cobalt (III) complexes as catalytic chain transfer agents to produce macromonomers having only one terminal ethylenically unsaturated group. The macromonomer is then copolymerized with ethylenically unsaturated backbone monomers, which polymerize to form a backbone polymer with macromonomer side chains grafted thereto. The pigment anchoring group is preferably attached in a subsequent reaction through functional groups built into the backbone or macromonomer.
A non-flocculating pigment dispersion is readily formed by combining the pigment dispersant of this invention with any number of commercially available pigments and an appropriate organic liquid carrier. Such dispersions are useful in solvent borne paints where they impart uniform color to the paint and, at the same time, provide improved efficiency of pigment use, lower paint viscosity, and reduced emission of volatile organic solvents.
DETAILED DESCRIPTION OF THE INVENTION
The pigment dispersant of this invention comprises a graft copolymer preferably produced by a macromonomer approach which involves grafting a macromonomer onto a polymer backbone. The macromonomer which contains only one terminal ethylenically unsaturated group becomes the side chain of the graft copolymer and is prepared first. It is then copolymerized with ethylenically unsaturated monomers chosen for the backbone composition to form the graft structure.
To ensure that the macromonomers only have one terminal ethylenically unsaturated group which will polymerize with the backbone monomers, the macromonomers are most conveniently prepared by a free radical polymerization method wherein the macromonomer is polymerized in the presence of a catalytic cobalt chain transfer agent containing a Co
2+
group, a Co
3+
group, or both. Typically, the macromonomer is prepared by polymerizing an acrylic monomer or blend of such monomers, in particular methacrylate based monomers, in the presence of a cobalt chain transfer agent. The macromonomer polymerization is carried out in an organic solvent or solvent blend using conventional polymerization initiators.
Preferred cobalt chain transfer agents that can be used to form the macromonomer are described in U.S. Pat. No. 4,722,984 to Janowicz. Most preferred cobalt chain transfer agents are pentacvano cobaltate (II), diaquabis (borondiflurodimethylglyoximato) cobaltate(II), and diaquabis (borondifluorophenylglyoximato) cobaltate (II). Typically, these chain transfer agents are used at concentrations of about 2-5000 ppm based upon the particular monomers being polymerized and the desired molecular weight. By using such concentrations, macromonomers having a weight average molecular weight (Mw) in the range of about 1,000 to 50,000, preferably about 1,000 to 10,000, can be conveniently prepared.
Typical solvents that can be used to form the macromonomer are alcohols, such as methanol, ethanol, n-propanol, and isopropanol; ketones, such as acetone, butanone, pentanone, hexanone, and methyl ethyl ketone; alkyl esters of acetic, propionic, and butyric acids, such as ethyl acetate, butyl acetate, and amyl acetate; ethers, such as tetrahydrofuran, diethyl ether, and ethylene glycol and polyethylene glycol monoalkyl and dialkyl ethers such as cellosolves and carbitols; and, glycols such as ethylene glycol and propylene glycol; and mixtures thereof.
Any of the commonly used azo or peroxy polymerization initiators can be used for preparation of the macromonomer provided it has solubility in the solution of the solvents and the monomer mixture, and has an appropriate half life at the temperature of polymerization. “Appropriate half life” as used herein is a half life of about 10 minutes to 4 hours. Most preferred are azo type initiators such as 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (methylbutyronitrile), and 1,1′-azobis (cyanocyclohexane). Examples of peroxy based initiators are benzoyl peroxide, lauroyl peroxide, t-butyl peroxypivalate, t-butyl peroctoate which may also be used provided they do not adversely react with the chain transfer agents under the reaction conditions for macromonomers.
The macromonomer contains a single terminal ethylenically unsaturated group, and primarily contains polymerized acrylic monomers and in particular polymerized methacrylic acid or methacrylate monomers. Preferred monomers include methacrylic acid, alkyl methacryl
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Mulcahy Peter D.
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