Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-12-22
2003-11-04
Harlan, Robert (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S319000, C526S332000, C526S347000, C106S400000, C106S493000, C106S499000, C524S558000
Reexamination Certificate
active
06642338
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 water-based acrylic emulsion dispersants for an inorganic pigment and a method of preparing the acrylic emulsion 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, light-stabilizing additives, 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 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, 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 increase 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 water-based acrylic emulsion dispersants to be utilized as grind resins for inorganic pigments and a method of preparing the water-based acrylic emulsions. It is advantageous that the acrylic emulsion dispersants according to the subject invention effectively wet the pigments, uniformly disperse the pigments, and provide increased pigment-to-binder ratios accompanied with acceptable gloss and appearance in the film of the coating composition.
SUMMARY OF THE INVENTION
A water-based acrylic emulsion dispersant is disclosed. The acrylic emulsion dispersant of the subject invention is utilized as a grind resin, also referred to as a grind emulsion resin, to incorporate inorganic pigment into a pigment dispersion for aqueous coating compositions. This acrylic emulsion dispersant is the reaction product of an ethylenically unsaturated monomer, a vinylaromatic hydrocarbon monomer, a non-functional polyalkylene glycol acrylate or methacrylate monomer, a functional polyalkylene glycol acrylate or methacrylate monomer having a hydroxyl group, and an acid having a first functional acid group reactive with the hydroxyl group, and a second functional acid group capable of providing an acid anion group.
A method of preparing the acrylic emulsion dispersant is also disclosed. According to this method, the ethylenically unsaturated monomer and the vinylaromatic hydrocarbon monomer are combined with water to establish a first reaction blend. A non-functional polyalkylene glycol acrylate or methacrylate monomer and a functional polyalkylene glycol acrylate or methacrylate monomer having the hydroxyl group are combined with water to establish a second reaction blend. Next, the first and second reaction blends are polymerized to form an intermediate emulsion polymer. The intermediate emulsion polymer contains the hydroxyl group which is then reacted with the acid to form the water-based acrylic emulsion dispersant of the subject invention.
More specifically, the second functional acid group of the acid is neutralized with an amine before the first functional acid group of the acid is reacted with the hydroxyl group in the intermediate emulsion polymer. After this neutralization, the first functional acid group reacts with the hydroxyl group in the intermediate emulsion polymer thereby bonding the acid, having the acid anion group, with the intermediate emulsion polymer to form the acrylic emulsion 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 ideal particle sizes of the inorganic pigments.
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 water-based acrylic emulsion dispersant of the subject invention is a ‘primary’ emulsion. By the term primary emulsion, it is to be understood that the subject invention is in a uniform, water-dispersed form with water being the only medium. The acrylic emulsion dispersant 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 acrylic emulsion dispersant and grind resin will be used interchangeably throughout the subject application. The acrylic emulsion dispersant includes both organic and inorganic chemical 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 acrylic emulsion dispersant is generally the reaction product of an ethylenically unsaturated monomer, a vinylaromatic hydrocarbon monomer, a non-functional
Harris Paul J.
Lanza JoAnn
Ramesh Swaminathan
BASF Corporation
Harlan Robert
LandOfFree
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