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
2000-12-22
2003-12-02
Cain, Edward J. (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...
C524S601000, C524S612000, C528S272000, C528S288000, C528S297000, C528S308000
Reexamination Certificate
active
06657002
ABSTRACT:
FIELD OF THE INVENTION
The subject invention generally relates to a pigment dispersion utilized in aqueous coating compositions. More specifically, the subject invention relates to a polymeric pigment dispersant for an inorganic pigment and a method of preparing the polymeric pigment dispersant.
BACKGROUND OF THE INVENTION
Aqueous coating compositions typically include a primary binder resin, a crosslinker, a pigment or pigments to improve the aesthetics of the coating composition, and other coating additives such as solvents, flow and appearance control agents, fillers such as extender pigment, and the like.
It is understood in the art that the pigment is incorporated into the aqueous coating compositions via a pigment dispersion. The pigment dispersion is derived from dispersion of the pigment into a grind resin. More specifically, a mill, such as a ball mill, grind mill, or continuous mill, is utilized to incorporate the pigment into the grind resin. The mill integrates the pigment into the grind resin until a desired particle size of the pigment is achieved, and until the pigment is appropriately wetted by the grind resin and uniformly dispersed throughout the grind resin.
The grind resins of the prior art including, but not limited to, polyacrylate-based emulsions, have proven to be inadequate for use as a grind resin for dispersing pigment usable in aqueous coating compositions. The grind resins of the prior art are ineffective because these resins are unable to withstand mechanical forces exerted by the mill when integrating the pigment. These grind resins are also deficient in wetting the pigment and in maintaining the pigment dispersed throughout the grind resin. Instead, with the grind resins of the prior art, such as the polyacrylate-based emulsion grind resin, the pigment tends to coagulate or settle resulting in poor stability and inadequate ‘shelf life’ of the pigment dispersion.
These prior art grind resins also tend to have increased viscosities and, as understood in the art, increased viscosities typically inhibit the amount of pigment that can be incorporated into the grind resin. As a result, pigment dispersions that utilize the grind resins of the prior art cannot attain sufficient pigment-to-binder ratios while maintaining acceptable gloss and appearance in a film of the coating compositions. Also, due to the increased viscosity, these grind resins often require solvent and other additives which increases the overall volatile content of the pigment dispersion—a characteristic that is undesirable throughout the coating industry.
In sum, the prior art grind resins, as detailed above, are characterized by one or more inadequacies. Due to the inadequacies identified in the prior art, it is desirable to provide a polymeric pigment dispersant to be utilized as a grind resin for inorganic pigments and a method of preparing the polymeric pigment dispersant. It is advantageous that the polymeric pigment dispersant according to the subject invention effectively wets pigment, uniformly disperses pigment, and provides increased pigment-to-binder ratios accompanied with acceptable gloss and appearance in the film of the coating composition.
SUMMARY OF THE INVENTION
A polymeric pigment dispersant is disclosed. The polymeric pigment dispersant of the subject invention, a polyester carboxylate, is utilized as a grind resin to incorporate inorganic pigment into a pigment dispersion for aqueous coating compositions. This polymeric pigment dispersant is the reaction product of a first compound having a plurality of hydroxyl groups, a carboxylic acid anhydride, a second compound having at least one epoxy group, and an amine. The preferred polymeric pigment dispersant is the reaction product of pentaerythritol, hexahydrophthalic anhydride, glycidylneodecanoate, and dimethylethanolamine.
A method of preparing the polymeric pigment dispersant is also disclosed. According to this method, the first compound is reacted, or polymerized, with the carboxylic acid anhydride to form an intermediate compound having a plurality of carboxylic acid groups. Once the intermediate compound is formed, the epoxy group of the second compound is reacted with at least one of the carboxylic acid groups of the intermediate compound. The amine is then reacted with the remaining carboxylic acid groups of the intermediate compound in a neutralization step thereby forming the polymeric pigment dispersant of the subject invention.
In the method of preparing the preferred polymeric dispersant, one mole of pentaerythritol is reacted, i.e., polymerized, with four moles of hexahydrophthalic anhydride to form the intermediate compound. With these reactants, the intermediate compound includes four carboxylic acid groups. Next, one mole of glycidylneodecanoate is reacted with one of the four carboxylic acid groups of the intermediate compound, and then three moles of dimethylethanolamine are reacted with the remaining three carboxylic acid groups of the intermediate compound to form the preferred polymeric dispersant.
The general object of the subject invention is to develop a grind resin that effectively wets inorganic pigments used in aqueous coating compositions and that is capable of resisting mechanical forces introduced by the mills that are used to grind and integrate the inorganic pigments into the grind resin. In resisting the mechanical forces exerted by the mills, this grind resin is ideal in that it provides sufficient time for the mill to achieve the ideal particle size of the pigment.
It is a further object of the subject invention to develop a grind resin that has a relatively low molecular weight and a correspondingly low viscosity such that increased pigment-to-binder ratios can be achieved while maintaining a low viscosity for the pigment dispersion. More specifically, as a result of the relatively low viscosity of the grind resin of the subject invention, higher concentrations of pigments can be incorporated into the grind resin to attain the increased pigment-to-binder ratios of the pigment dispersion. Due to the higher concentration of pigment, a solid, into the grind resin, the volatile content of the pigment dispersion, and of the overall coating composition, is decreased. Also, even at the increased pigment-to-binder ratios, this grind resin demonstrates superior dispersion stability through extended shelf life of the pigment dispersion, and this grind resin is able to be completely dispersed into water with little or no co-solvent required to promote dispersibility. This grind resin is also suitable for achieving optimal appearance characteristics, such as distinctiveness and gloss, in a film of the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The polymeric pigment dispersant of the subject invention, a polyester carboxylate, is utilized as a grind resin to incorporate inorganic pigment into a pigment dispersion for aqueous coating compositions. Examples of inorganic pigments that are utilized in aqueous coating compositions include, among other inorganic pigments, titanium dioxide, TiO
2
, and iron oxide, FeO, as well as certain aluminum and mica flake pigments. It is to be understood that the terms polymeric pigment dispersant and grind resin will be used interchangeably throughout the subject application. The polymeric pigment dispersant includes a highly-branched organic structure having various functionalities that promote efficient wetting of the inorganic pigment and optimal stability of the pigment in the grind resin of the pigment dispersion in the aqueous coating composition. These various functionalities will be introduced and discussed below.
The polymeric pigment dispersant is generally the reaction product of a first compound having a plurality of hydroxyl groups, a carboxylic acid anhydride, a second compound having at least one epoxy group, and an amine. The method of preparing the polymeric pigment dispersant includes the steps of reacting by polymerizing the first compound with the carboxylic anhydride to form an intermediate compound having a plurality o
Lanza JoAnn
Ramesh Swaminathan
BASF Corporation
Cain Edward J.
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