Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-07-05
2002-09-17
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S303100, C526S307000, C526S307200, C526S317100, C526S318000, C526S318200, C526S319000, C526S320000, C526S321000, C526S328500, C526S329700, C427S393500, C524S005000
Reexamination Certificate
active
06451950
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polymeric pigment dispersants, more particularly, it relates to random copolymer pigment dispersants having multiple pigment anchoring groups. These dispersants are easy to prepare while also being useful for dispersing a wide variety of pigments.
Polymeric pigment dispersants which are effective for dispersing pigments in organic liquids have been previously known and used to form pigment dispersions that are used in a variety of solvent borne coating compositions. Nowadays, such pigment dispersions are widely used, for example, in exterior solvent borne paints for automobiles and trucks.
Structured polymers such as AB block copolymers and graft copolymers are known to be more effective dispersants, in comparison to random copolymers, as for example, as taught by Simms et al U.S. Pat. No. 5,424,364 issued Jun. 13, 1995. However, their synthesis usually involves more complicated chemistries, more demanding reaction conditions, and usually more expensive reagents. This leads to a less robust and oftentimes more costly manufacturing process.
Therefore, there is still a need to improve the performance of random copolymer pigment dispersants, and in particular to find new random copolymers that are more effective in dispersing a wider range of pigments as well as easy to prepare.
Random copolymer dispersants that have been used in the past contain both polar and relatively non-polar segments randomly placed in the polymer dispersant chain. The polar segments known as pigment anchoring segments are designed to attach the copolymer dispersant to the pigment surface, and the non-polar segments known as stabilizing segments are designed to extend into the surrounding solvent medium to provide steric stabilization of the pigment particles, which keeps the pigments dispersed and prevents the pigment particles from coming close enough to one another to cluster together or flocculate.
It is thought that one way to improve the performance of such dispersants is through more effective binding or anchoring of the dispersant to the pigment surfaces. Pigment surfaces are usually heterogeneous having a range of functional groups. This presents the possibilities for enhancing the binding force of a polymeric dispersant to the pigment surfaces through multiple mechanisms such as acid-base, aromatic, dipole-dipole interactions, hydrogen bonding, etc., and potentially leading to a more versatile dispersant, that is selectively adsorbed by a wider range of pigments, and an improved dispersion system. In this fashion, the present invention provides an alternative approach to structured polymers through the use of a random polymer containing multiple pigment anchoring groups, which supply the dispersant with improved dispersing power and versatility.
SUMMARY OF THE INVENTION
The present invention provides a composition suitable for use as a pigment dispersant, comprising a random copolymer, wherein the copolymer has a weight average molecular weight of about 3,000-100,000 and has both pigment anchoring segments and stabilizing segments randomly distributed in the polymer chain, wherein the
(1) the stabilizing segments are non-polar in comparison to the pigment anchoring segments and consist essentially of ethylenically unsaturated monomers that are polymerized into the polymer chain and
(2) the pigment anchoring segments consist essentially of ethylenically unsaturated monomers that are polymerized into the polymer chain and have pigment anchoring groups attached thereto,
wherein the pigment anchoring groups are selected from at least one amide group and one or more additional anchoring groups selected from the group consisting of aromatic esters, aromatic amines, aliphatic amines, and quaternary ammonium groups.
The present invention also provides stable and non-flocculated pigment dispersions formed by combining the pigment dispersant of this invention with any number of commercially available pigments and an appropriate organic liquid carrier. These dispersions are particularly useful in solvent borne coatings, especially automotive 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, in comparison to standard random copolymer dispersants.
DETAILED DESCRIPTION OF THE INVENTION
The pigment dispersant of this invention comprises a random copolymer preferably produced by a conventional free radical polymerization approach which involves copolymerizing the stabilizing monomers in the presence of the anchoring monomers to form the random structure.
The polymerization is carried out in an organic solvent or solvent blend using conventional polymerization initiators. The reaction mixture is typically held at or below reflux temperature until a random copolymer of desired molecular is formed. The random copolymer of the present invention so formed has a weight average molecular weight of about 3,000 to 100,000, preferably about 5,000 to 60,000.
All molecular weights referred herein are determined by GPC (gel permeation chromatography) using a polymethyl methacrylate standard.
Typical solvents that can be used to form the random copolymer 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, ethylene glycol and polyethylene glycol mono- and dialkyl ethers such as cellosolves and carbitols; and glycols such as ethylene glycol and propylene glycol, or any mixtures thereof.
Any of the commonly used azo or peroxy polymerization initiators can be used for preparation of the random copolymer 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.
The stabilizing segment of the random copolymer is soluble in the selected organic liquid carrier and is prepared from ethylenically unsaturated monomer(s) such as alkyl methacrylates and acrylates, cycloaliphatic methacrylates and acrylates and aryl methacrylates and acrylates, as are listed hereinafter. The term “segment” as used herein means one monomer or a cluster of more than 1 monomers.
Typical alkyl methacrylates that can be used have 1-18 carbon atoms in the alkyl group such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethyl hexyl methacrylate, nonyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2-(2-ethoxy ethoxy)ethyl methacrylate, ethoxytriethyleneglycol methacrylate, and the like. Cycloaliphatic methacrylates can be used such as trimethylcyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, and the like. Aryl methacrylates can also be used such as benzyl methacrylate, phenyl methacrylate, and the like.
Typical alkyl acrylates that can be used have 1-18 carbon atoms in the alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethyl hexyl acrylate, nonyl acrylate, lauryl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, and the like. Cycloaliphatic acrylates can be used such as cyclohexylacrylate, trimethylcyclohexylacrylate, t-butyl cyclohexyl acrylate, and the like. Aryl acrylates such a
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Wu David W.
Zalukaeva Tatyana
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