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
1998-08-19
2001-02-13
Yoon, Tae (Department: 1714)
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...
C525S093000, C525S094000
Reexamination Certificate
active
06187854
ABSTRACT:
TECHNICAL FIELD
This invention relates to improved pigment dispersions containing an AB-block polymer dispersant.
BACKGROUND OF THE INVENTION
AB polymer dispersants are known in the art and are used to form pigment dispersions that are used in a variety of coating compositions. U.S. Pat. No. 4,656,226 issued Apr. 7, 1987, to Hutchins et al shows an AB block polymer dispersant having polar groups such as acids or amines that attach to a pigment's surface and the other block of the polymer keeps the pigments stabile in the dispersion or coating composition. U.S. Pat. No. 5,221,334 issued Jun. 22, 1994, to Ma et al also shows AB or BAB block polymers that are used in aqueous printing inks to keep pigments dispersed in the inks.
“Living” free radical polymerization technique, also referred to as group transfer polymerization (GTP) is a well-known technique that is used to form the aforementioned block polymers. In GTP, an initiator splits with one end going to the tail of an acrylic monomer unit and the other to the head. The group at the head transfers to the head of a second monomer unit as that unit is polymerized with the first. Such techniques are described in U.S. Pat. No. 4,417,034 issued Nov. 22, 1983, and U.S. Pat. No. 4,508,880 issued Apr. 2, 1985, to O. W. Webster and U.S. Pat. No. 4,414,372 issued Nov. 8, 1983, and U.S. Pat. No. 4,524,196 issued Jun. 18, 1985 to Farnham et al. The above patents are hereby incorporated by reference.
Conventional truck and automobile finishes comprise a clear coat applied over a pigmented base coat that is applied over a primer layer. The polymer dispersant used in the base coat must not only keep the pigment dispersed but needs to contain a reactive group that will react with the crosslinking agent used in the coating composition which on curing makes the dispersant an integral part of the resulting finish. Polymer dispersants can cause intercoat adhesion failures and usually are used only in limited amounts. Its desirable that the polymer dispersant have reactive groups that will bond with the primer layer to improve intercoat adhesion of the base coat to the primer rather than cause intercoat adhesion problems and cause flaking and chipping of the resulting finish.
SUMMARY OF THE INVENTION
A pigment dispersion useful for forming coating compositions containing dispersed pigment, a carrier liquid and an AB-block polymer dispersant (binder);
the AB block polymer has a number average molecular weight of about 5,000-20,000 and contains 20-80% by weight of a polymeric A segment and correspondingly 80-20% by weight of a polymeric B segment; wherein
the polymeric A segment of the block polymer is of polymerized glycidyl (meth)acrylate monomers reacted with an acid from the group of aromatic carboxylic acids or aliphatic carboxylic acids; and
the B segment is of polymerized alkyl (meth)acrylate monomers having 1-12 carbon atoms in the alkyl group, hydroxy alkyl (meth)acrylate monomers having about 14 carbon atoms in the alkyl group; and
wherein the weight ratio of pigment to binder in the dispersion is about 1/100-200/100;
DETAILED DESCRIPTION OF THE INVENTION
The term (meth)acrylate refers to both the acrylate and methacrylate esters.
The novel pigment dispersion is stable and in general is non-flocculated or agglomerated and is compatible with a variety of polymeric film forming binders that are conventionally used in coating compositions and in particular, compatible with acrylic polymers that are used in coating compositions. The AB block polymer dispersant upon curing of the coating composition into which it has been incorporated, reacts with other film forming components of the coating composition and becomes part of the film and does not cause deterioration of the film upon weathering as may occur if it remained an unreacted component of the film. Also, since the AB block polymer is an excellent dispersant, the ratio of polymer to pigment or polymer being dispersed is less than used with conventional dispersants and a large variety of pigments and polymers can be dispersed thereby enlarging the number and types of pigment dispersions that can be formulated. The AB block polymer has reactive groups that improve adhesion to a primer layer thereby reducing flaking and chipping of the coating composition.
It has been found that improved coating compositions are obtained by using these novel pigment dispersions. These coating compositions also contain a film forming binder usually an acrylic polymer and a curing agent such as a polyisocyanate or an alkylated melamine. Such compositions have the advantage of providing excellent coating properties desirable for automotive finishes. Base coats of conventional base coat/clear coat finishes currently used on automobiles and trucks colored with a carbon black pigment dispersion of this invention have significantly improved black jetness in comparison to base coats colored with conventional carbon black pigment dispersions.
The AB block polymer used to formulate the dispersion of this invention can be prepared by anionic polymerization or by Group Transfer Polymerization techniques. Preferably, the polymer is prepared using GTP techniques as described in the aforementioned GTP patents (U.S. Pat. Nos. 4,417,034, 4,508,880, 4,414,372 and 4,524,196). These polymers have a number average molecular weight of about 5,000-20,000, preferably about 7,500-15,000. The A segment of the polymer comprises about 20-80% by weight of the polymer and correspondingly the B segment of the polymer comprises about 80-20% by weight of the polymer.
All molecular weights referred herein are determined by GPC (gel permeation chromatography) using a polystyrene standard.
The AB block polymer has a relatively highly polar anchoring A segment and a relatively non-polar stabilizing B-segment. The A-segment is designed to absorb on the surface of the pigment and the B-segment provides a steric stabilization of the pigment particle against flocculation. The A-segment must be available for interaction with the pigment surface; (2) of sufficient size to provide irreversible adsorption; and (3) not so large as to completely cover the pigment surface or cause collapse of the B-segment. The B-segment must be: (1) of sufficient size to provide steric stabilization (approximately number average molecular weight of 1500 or larger); and (2) compatible with the dispersion media, typically a solvent, and polymeric film forming material used in a coating composition.
The AB block polymer can be prepared by anionic polymerization using conventional polymerization catalysts and solvents. Usually, the A segment containing polymerized glycidyl (meth)acrylate monomers is prepared first and then the B segment monomers are added and polymerized. It is possible to prepare the B segment initially and then the A segment to form the AB block polymer.
Preferably, the AB block polymer is prepared by using GTP techniques in an inert atmosphere such as nitrogen by charging solvent such as a mixture of tetrahydrofuran and xylene, a catalyst such as tetrabutyl ammonium m-chlorobenzoate and initiator such as 1-methoxy-1-trimethylsiloxy-2-methyl propene into a polymerization vessel and then adding the A segment monomer which is glycidyl (meth)acrylate. When most of the A-segment monomers have reacted typically over 99%, the B-segment monomers are added of alkyl (meth)acrylates, typically methyl methacrylate and butyl methacrylate and the silane blocked hydroxy alkyl (meth)acrylate, typically trimethylsiloxyethyl methacrylate, and polymerization is completed. An aromatic carboxylic acid or an aliphatic carboxylic acid is then added in a sufficient amount to react with all of the glycidyl groups of the polymer and to unblock the silane group of the hydroxy alkyl (meth)acrylate to form the AB block polymer dispersant used in this invention.
Other typical solvents, GTP polymerization catalysts and initiators used to form the AB block polymers are disclosed in the aforementioned GTP patents.
The A-segment of the polymer contains mainly polymerized glycidyl (
Jakubauskas Henry L.
King James G.
McIntyre Patrick F.
Spinelli Harry J.
Benjamin Steven C.
E. I. Du Pont de Nemours and Company
Fricke Hilmar L.
Yoon Tae
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