Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-10-07
2001-11-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C523S160000, C523S161000
Reexamination Certificate
active
06316564
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns a pigment dispersant, more particularly, it concerns a pigment dispersant comprising an acrylic block copolymer, prepared by group transfer polymerization, in which one of the blocks is modified with a polar heterocyclic group to facilitate attachment to a pigment surface.
Acrylic block copolymer pigment dispersants prepared by group transfer polymerization (GTP) are known. Typically, such dispersants are of the AB, ABA or BAB types. All have at least one polar segment known as the A segment to facilitate attachment to a pigment surface, and at least one non-polar segment known as the B segment to enhance steric stabilization of the pigment particles in a dispersion and prevent flocculation. In addition, the A block may be modified with pendant polar groups for increased effectiveness, as for example, as taught in Hutchins et al. U.S. Pat. No. 4,656,226, issued Apr. 7, 1987. Such compositions can also be prepared with hydroxyl functional groups in the B segment to allow crosslinking in the final thermoset paint composition so that the dispersant will become part of the network structure; however, the dispersant properties may be negatively influenced.
Continued effort has been directed to improve the performance of pigment dispersants, and in particular to find a new class of acrylic block copolymer dispersants which are well suited for dispersing solid pigments in various liquid media, particularly solvent-borne paint systems.
SUMMARY OF THE INVENTION
The present invention provides a composition suitable for use as a pigment dispersant, comprising an acrylic block copolymer, prepared by GTP polymerization, having at least one relatively polar A segment and at least one relatively non-polar B segment bonded together, each segment having a backbone preferably consisting essentially of polymerized methacrylic monomer units, and said A segment having bonded thereto one or more polar heterocyclic groups selected from the group consisting of mononuclear or dinuclear five and/or six membered rings containing one or more nitrogen atoms as part of the ring and optionally an oxygen and/or sulfur atom wherein the ring contains at least one nitrogen not bonded to a hydrogen atom. The heterocyclic groups are provided as pendant groups either attached directly on the A segment or introduced through urethane and/or urea linkages. The block copolymer preferably also contains hydroxyl functional groups in either or both A and B segment. It is also preferred that the block copolymer be of the AB type.
The present invention is based on the discovery that incorporation of the heterocyclic groups mentioned above on the A segment provide acrylic block copolymers with excellent pigment dispersant characteristics, even in the presence of hydroxyl functional groups on the polymer backbone which are usually needed for crosslinking purposes and to improve the compatibility with the other binder constituents present in the final paint composition.
Preferred heterocyclic groups are triazole, pyrimidine, imidazole, pyridine, morpholine, pyrrolidine, piperazine, piperidine, benzimidazole, benzothiazole and/or triazine. These heterocyclic groups may be unsubstituted or may contain substituents such as, e.g., alkyl, aryl, halogen, and alkoxy groups.
DETAILED DESCRIPTION OF THE INVENTION
GTP techniques can be, and preferably are, used to produce the acrylic block copolymers of the present invention. GTP techniques are known to produce acrylic block copolymers of low molecular weight, generally between 1,300 and 20,000 number average molecular weight (M
n
), with a more precisely controlled molecular weight distribution and compositional distribution. This permits the formation of blocks with low polydispersity and uniform functionality and provides for more efficient dispersing action. GTP techniques are well known and described at length in Hutchins et al. U.S. Pat. No. 4,656,226, issued Apr. 7, 1987, hereby incorporated by reference.
In accordance with that technique, generally an unsaturated monomer is contacted with an initiator and a catalyst system containing silicon, tin or germanium, under which polymerization proceeds in a controlled manner, as opposed to the random manner typical of polymerization reactions, so that a substantially linear polymer can be prepared having polymer chains which are uniform and of the desired molecular weight. Herein, the desired molecular weight for the block copolymer is within the above stated range, although in the present invention, below 13,000 M
n
is particularly preferred.
The acrylic block copolymers of the present invention produced by such techniques preferably have at least one relatively highly polar A segment which functions as an anchoring side on the pigment surface and at least one relatively non-polar B stabilizing segment, usually of higher molecular weight, which preferably contains functional groups for reaction in a thermoset paint composition. The polar A segment is designed to absorb on the surface of a pigment by acid-base interaction, while the B segment provides steric stabilization of the pigment particle against flocculation.
In general, the A segment should be: (1) available for interaction with the pigment surface; and (2) of sufficient size to provide irreversible absorption, but not so large as to completely cover the pigment surface or cause collapse of the B segment (typically M
n
=300-5,000). The B segment should be: (1) of sufficient size to provide steric stabilization (typically M
n
=1,000 or larger); and (2) compatible (sufficiently soluble to prevent phase separation) with the liquid dispersion media (solvent) and matrix binder polymer.
All molecular weights referred herein are determined by GPC (gel permeation chromatography) using a polystyrene standard.
The B segment, as mentioned above, also preferably contains functional groups, such as, e.g., hydroxyl groups, to provide for crosslinking in a final thermoset paint composition to enable the dispersant to become a part of the network structure and for improved compatibility with the other binder components. In order for these groups to be present, the polar anchoring side (A segment) must not be displaced by these other functional groups, since then the pigment dispersion destabilizes.
The present inventors have found not only that introduction of the heterocyclic groups in the acrylic block copolymers of the general type described above improve their performance as pigment dispersants, but also even more unexpectedly that such heterocyclic groups act as efficient anchoring groups even in the presence of hydroxyl groups on the other segment and in the presence of polar solvents which could compete with adsorption on the pigment surface.
In the present invention, it has been found convenient to first form the basic acrylic block copolymer described above by GTP techniques, and then attach the required heterocyclic group directly or indirectly through functional groups positioned on the A anchoring segment using techniques described below.
In the preparation of the basic block copolymer, the blocks can be prepared in any order. That is, either the A segment or the B segment can be prepared first. Furthermore, while AB block copolymers are generally preferred, ABA and BAB triblocks can also be prepared, if desired. In any event, the backbones of each segment consist essentially of at least one polymerized methacrylate or acrylate ester, although methacrylate esters are mostly preferred. In the context of the present invention, the methacrylate and acrylate units are generally referred to herein as methacrylic and acrylic monomer units.
More specifically, the B segment is preferably prepared from an alkyl methacrylate or a blend of alkyl methacrylates such as methyl methacrylate (MMA), butyl methacrylate (BMA), 2-ethyl hexyl methacrylate, and the like. If desired, hydroxyl functional groups can be introduced through hydroxyalkyl methacrylate monomers such as hydroxy ethyl methacrylate (HEMA), hydroxy propyl methacry
Huybrechts Josef
Kraiter Daniel C.
Vervloet Roger
Asinovsky Olga
Benjamin Steven C.
E. I. Du Pont de Nemours and Company
Seidleck James J.
LandOfFree
Acrylic block copolymer pigment dispersants containing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acrylic block copolymer pigment dispersants containing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acrylic block copolymer pigment dispersants containing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2577175