Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-16
2001-12-04
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S560000, C524S565000, C524S566000, C524S558000
Reexamination Certificate
active
06326420
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pigment dispersions containing pigment, an aqueous carrier, and a pigment dispersant. The pigment dispersant is prepared by controlled radical polymerization in the presence of a monomeric initiator having at least two radically transferable groups. The pigment dispersant contains hydrophilic monomer residues and hydrophobic monomer residues.
BACKGROUND OF THE INVENTION
Pigmented coating compositions are used in a wide variety of applications including, for example, corrosion resistant primers and decorative topcoats in the automotive, industrial and appliance markets. The preparation of pigmented coating compositions generally involves mixing binder resin(s), crosslinker(s), additives, e.g., flow additives, and solvents with a compatible pigment dispersion. Pigment dispersions are typically prepared by mixing dry pigment with a pigment dispersant in the presence of a carrier medium, e.g., an aqueous carrier medium.
Dry pigments are available commercially in the form of agglomerated pigment particles. Pigment agglomerates are more likely to settle out of pigment dispersions and/or pigmented coating compositions, and are accordingly undesirable. To break the pigment agglomerates down into smaller agglomerates and/or individual particles generally requires the use of energy intensive mixing means (commonly referred to as grinding), e.g., sand mills and ball mills. During the grinding process the pigment agglomerates are broken down into smaller agglomerates and/or individual particles the surfaces of which are wetted by the pigment dispersant. The pigment dispersant suspends or disperses the pigment particles in the carrier medium and prevents their re-agglomeration on storage. It is desirable that the pigment dispersion remain substantially stable, e.g., showing minimal pigment settling and viscosity change with time, prior to its use in the preparation of a pigmented coating composition.
Reducing the environmental impact of pigmented coatings compositions, in particular that associated with emissions into the air of volatile organics during their use, has been an area of ongoing investigation and development in recent years. Accordingly, interest in aqueous pigment dispersions has been increasing due, in part, to the inherently low volatile organic content (VOC) of the aqueous pigmented coatings prepared therefrom, which can significantly reduce air emissions during the application process.
Pigment dispersants used in aqueous pigment dispersions are preferably compatible with both the aqueous carrier medium and the hydrophobic surfaces of the pigment particles. Such a combination of disparate properties can be achieved with a pigment dispersant having distinct hydrophobic and hydrophilic polymeric segments or portions, i.e., having well defined polymer chain architecture. A wide variety of radically polymerizable monomers, such as methacrylate and acrylate monomers, are commercially available and can provide a wide range of properties including, for example, hydrophilic and hydrophobic properties. The use of conventional, i.e., non-living or free, radical polymerization methods to synthesize pigment dispersants provides little control over molecular weight, molecular weight distribution and, in particular, polymer chain structure. Aqueous pigment dispersions containing pigment dispersants prepared by conventional non-living radical polymerizations, typically have poor stability, e.g., the pigments re-agglomerate and/or settle out of the dispersion, and are unsuitable for the preparation of aqueous pigmented coatings compositions.
The continued development of aqueous pigment dispersions that are stable and suitable for the preparation of aqueous pigmented coating compositions is desirable. In particular, it would be desirable to develop aqueous pigment dispersions that comprise pigment dispersants having well defined polymer chain architecture in which distinct hydrophilic and hydrophobic polymer segments or portions are present.
U.S. Pat. Nos. 5,807,937, 5,789,487 and 5,763,548, and International Patent Publication No.'s WO 98/40415, WO 98/01480, WO 97/18247 and WO 96/30421 describe a radical polymerization process referred to as atom transfer radical polymerization (ATRP). The ATRP process is described as being a living radical polymerization that results in the formation of (co)polymers having predictable molecular weight and molecular weight distribution. The ATRP process is also described as providing highly uniform products having controlled structure (i.e., controllable topology, composition, etc.). The '937 and '548 patents also describe (co)polymers prepared by ATRP, which are useful in a wide variety of applications including, for example, dispersants and surfactants.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a pigment dispersion comprising:
(a) pigment;
(b) an aqueous carrier selected from water and a mixture of water and at least one organic solvent; and
(c) a pigment dispersant prepared by controlled radical polymerization in the presence of a monomeric initiator having at least two radically transferable groups, and in which said pigment dispersant has a polymer chain structure selected from at least one of the following representative general formulas I and II,
&phgr;-[(G)
p
—(E)
s
—T]
z
I
and
&phgr;-[(E)
s
—(G)
p
—T]
z
II
wherein G is a hydrophobic residue of at least one radically polymerizable ethylenically unsaturated monomer; E is a hydrophilic residue of at least one radically polymerizable ethylenically unsaturated monomer; &phgr; is a residue of or derived from said initiator, and is free of said radically transferable group; T is or is derived from said radically transferable group of said initiator; z is independently for each structure a number from 2 to 10 (e.g., 2, 3, 4, 5, 6, 7, 8, 9 or 10); p and s represent average numbers of residues occurring in a block of residues; p and s are each selected independently for each structure such that said pigment dispersant has a number average molecular weight of at least 500.
Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc, used in the specification and claims are to be understood as modified in all instances by the term “about.”
DETAILED DESCRIPTION OF THE INVENTION
Pigment dispersions according to the present invention comprise a pigment dispersant as represented by general formulas I and II. The polymer chain segments of the pigment dispersant represented by —(G)
p
—(E)
s
—T in general formula I, and —(E)
s
—(G)
p
—T in general formula II may be described as arms that extend out from a residue of or derived from the monomeric initiator. Each arm of the pigment dispersant contains a hydrophobic segment, for example as represented by —(G)
p
—, and a hydrophilic segment, for example as represented by —(E)
s
—. While not intending to be bound by any theory, it is believed that the hydrophilic segments of the arms of the pigment dispersant are associated with the aqueous carrier, while the hydrophobic segments of the arms are associated with the pigment of the pigment dispersion.
As used herein and in the claims, the terms “hydrophobic” and “hydrophilic” are relative to each other. Within an arm of the pigment dispersant, the hydrophobic segment is more hydrophobic than the hydrophilic segment. Correspondingly, within an arm of the pigment dispersant, the hydrophilic segment is more hydrophilic than the hydrophobic segment.
A more quantitative measure of the hydrophobic or hydrophilic nature of a nonionic monomer residue can be obtained by using the following Formula-A: 100×(oxygen weight+nitrogen weight)/(carbon weight). Monomer residues having calculated Formula-A values of greater magnitude are generally considered to be more hydrophilic than monomer residues having calculated Formula-A values of lesser magnitude. For example, the c
Coca Simion
O'Dwyer James B.
Olson Kevin C.
Schimmel Karl F.
Cain Edward J.
Franks James R.
PPG Industries Ohio Inc.
Uhl William J.
Wyrozebski-Lee Katarzyna
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