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
2000-09-27
2003-07-29
Reddick, Judy M. (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...
C524S413000, C524S425000, C524S430000, C524S431000, C524S441000, C524S445000, C524S451000, C524S533000, C524S535000, C524S547000, C524S556000, C524S558000
Reexamination Certificate
active
06599973
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to novel graft copolymers having mixed anionic and nonionic side chains. The invention also relates to their use as pigment dispersants in aqueous dispersions and water borne coating compositions.
Water-dispersible polymers which are effective for dispersing pigment particles in aqueous medium are well known in the art and have been used to form aqueous pigment dispersions useful in formulating water borne coating compositions. Nowadays, such pigment dispersions are widely used, for example in exterior water borne paints for automobiles and trucks.
Aqueous pigment dispersions are generally stabilized and maintained, in a dispersed state, by either a nonionic or ionic technique. When the nonionic technique is used, the pigment particles are stabilized by a dispersant polymer having a nonionic hydrophilic section that extends into the water medium, providing entropic or steric stabilization of the pigment particles against flocculation. While these nonionic polymers provide good dispersing action, the major disadvantage with the nonionic technique is that the final coating film is water sensitive and therefore susceptible to softening and poor adhesion with an overlying water borne clear coat.
In the ionic technique, the pigment particles are stabilized using a polymer of an ion containing monomer, such as neutralized acrylic and methacrylic acid, as for example, as taught in U.S. Pat. No. 5,231,131 to Chu et al issued Jul. 27, 1993. These polymers provide stabilization mainly through a charged double layer mechanism whereby ionic repulsion hinders the particles from flocculation. Since the neutralizing component evaporates upon curing of the coating film, the polymer then becomes no longer water soluble and the final coating film is therefore not water sensitive. Yet, the major disadvantage with the ionic technique is that water borne coatings typically contain organic cosolvents along with water to adjust the physical properties. As the coating cures, the concentration of such solvents increases as water evaporates, which in turn jeopardizes the stability of the pigment dispersion needed to obtain high glamour and color quality demanded by an exterior automotive finish.
To obtain a balance of properties with existing polymeric dispersants has been very difficult. Optimum water sensitivity and dispersion stability has been hard to achieve.
Other problems with waterborne coating compositions are as follows: the pigment dispersion used to form the composition often is not completely compatible with the film forming binder constituents of the composition; the polymeric dispersant does not uniformly disperse the pigments and the pigments flocculate or agglomerate; or the dispersant does not enter into the curing reaction and remains in the film as an unwanted component which may later leach out or cause deterioration of the resulting finish.
A polymeric dispersant is needed that will form an aqueous pigment dispersion that is stable and non-flocculated or agglomerated, will provide optimum dispersibility and water sensitivity, and is compatible with a variety of polymeric film forming binders conventionally used in water borne coating compositions, and will cure with the film to form a finish of automotive quality that does not deteriorate on weathering because of adverse properties caused by the presence of the polymeric dispersant.
SUMMARY OF THE INVENTION
The present invention provides a composition suitable for use as a polymeric pigment dispersant based on an acrylic graft copolymer wherein the graft copolymer has a weight average molecular weight of about 5,000-100,000 and comprises a hydrophobic polymer backbone and discrete anionic and nonionic hydrophilic side chain(s) attached to the backbone wherein
(1) the polymer backbone is hydrophobic in comparison to the side chains and is formed from polymerized hydrophobic (meth)acrylic monomers and contains up to 30% by weight, based on the total weight of the backbone, of polymerized monomers having functional groups that enhance the pigment binding force;
(2) the anionic side chain(s) are anionic hydrophilic (meth)acrylic macromonomers that are attached to the backbone at a single terminal point and are formed from polymerized (meth)acrylic monomers and contain about 2-100% by weight, based on the total weight of the anionic side chain(s), of polymerized acid containing monomers and have a weight average molecular weight of about 1,000-10,000, preferably 2,000-5,000;
(3) the nonionic side chain(s) are nonionic hydrophilic poly(alkylene glycol) (meth)acrylic macromonomers that are attached to the backbone at a single terminal point and are represented by the formula
CH
2
═C(R
1
)C(O)O[—Q—]
n
—R
2
wherein R
1
is H or CH
3
, R
2
is H or an alkyl group of 1 to 4 carbon atoms, Q is —CH
2
CH
2
O—, —CH(CH
3
)CH
2
O—, or a combination thereof, and n is about 10-100 and have a weight average molecular weight of about 500-4,000, preferably about 1,000-2,000; and
wherein the acid groups of the graft copolymer are neutralized with an inorganic base or amine.
The present invention also provides stable and non-flocculating aqueous pigment dispersions containing dispersed pigment, an aqueous carrier medium and the graft copolymer dispersant of this invention. These dispersions are particularly useful in formulating high performance water borne coating compositions and in particular water borne color coat or base coat compositions for clear coat/color coat finishes for automobiles and trucks.
DETAILED DESCRIPTION OF THE INVENTION
The novel graft copolymer of this invention has a hydrophobic backbone that binds to pigment surfaces, and a unique combination of hydrophilic anionic side chain(s) and hydrophilic nonionic side chain(s) that are soluble in the aqueous carrier medium and keep the pigments dispersed. The use of mixed side chains or “arms” provides broader solubility characteristics and utility as a pigment dispersant in high performance water borne coatings.
The graft copolymer of this invention is also compatible with a variety of polymeric film forming binders that are conventionally used in waterborne coating compositions and in particular are compatible with acrylic polymers that are widely used in waterborne coatings. In addition, aqueous pigment dispersions formed from such graft copolymers are stable and in general nonflocculated or agglomerated, even upon curing of the coating formed therefrom. The graft copolymer of this invention also upon curing of the coating, 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 was an unreacted component of the film.
All molecular weights referred herein are determined by GPC (gel permeation chromatography) using a polystyrene standard. The term (meth)acrylic refers to both acrylic and methacrylic compounds. The term (meth)acrylate refers to both methacrylate and acrylate esters.
The graft copolymer of this invention contains about 50-90% by weight of polymeric backbone and correspondingly about 10-50% of side chains. The graft copolymer has a weight average molecular weight of about 5,000-100,000, preferably about 10,000-40,000 and more preferably about 10,000-20,000. The weight ratio of anionic side chain(s) to nonionic side chain(s) contained in the graft copolymer is in the range of about 10:90 to 90:10, preferably 30:70 to 70:30, and typically 50:50.
The backbone portion of the graft copolymer is hydrophobic relative to the side chains and is formed primarily from polymerized ethylenically unsaturated hydrophobic monomers and preferably hydrophobic (meth)acrylic monomers as are listed hereinafter and can, and preferably does, contain up to 30% by weight, preferably 10-20% by weight, based on the weight of the backbone, of polymerized monomers having functional groups, known as pigment anchoring groups, that enhance the pigment binding force.
Preferred hydrophobic monomers that can be used to fo
Mc Intyre Patrick F.
Visscher Karyn B.
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Reddick Judy M.
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