Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-11-14
2003-06-10
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S427000, C106S443000, C106S462000, C106S503000
Reexamination Certificate
active
06576051
ABSTRACT:
This invention relates to polymer-pigment composite particles. In particular, this invention relates to composite particles containing pigment particles and polymer particles which contain two polymer phases. Further, this invention relates to a process of preparing the composite.
Titanium dioxide is the pigment of choice by most coatings manufacturers, particularly paint manufacturers, to provide whiteness and opacity or “hiding” to the final dried coating. Titanium dioxide is typically the most expensive raw material in a coating formulation. Thus, paint manufacturers have long sought to achieve the desired opacity by using the smallest amount of titanium dioxide possible. A number of techniques have been employed, including:
(1) using titanium dioxide that has an optimal average particle size and particle size distribution for light scattering;
(2) using titanium dioxide that is well dispersed.
The opacifying capability or hiding power of a coating or paint is a function of the spacing of the titanium dioxide particles in the dried coating. The light scattering characteristics of titanium dioxide particles are well known and the average size and size distribution of the titanium dioxide have been optimized by the titanium dioxide manufacturers for maximum scattering. Maximum light scattering occurs when the titanium dioxide pigment particles have a diameter of 200-250 nanometers (nm) and are spaced apart from each other, on the order of a few particle diameters, so that there is minimal interference between the light scattering of neighboring particles.
In an effort to achieve the proper spacing of the pigment particles, titanium dioxide manufacturers have attempted a number of techniques, including encapsulating titanium dioxide particles with a variety of different polymers (either fully in the form of a coating or partially in the form of nodules) or adsorbing a variety of different materials, including polymers (either film forming or non-film forming), to the surface of the titanium dioxide particles. U.S. Pat. No. 5,385,960 discloses an aqueous dispersion of composite particles, the composite particles each including a plurality of selected polymeric latex particles adsorbed to a titanium dioxide particle. The selected polymeric latex particles, which have at least one dihydrogen phosphate functional group, provide spacing between the titanium dioxide particles in films to increase the light scattering of the titanium dioxide particles. U.S. Pat. No. 5,385,960 also discloses that the aqueous dispersion of composite particles must include dibasic phosphate to inhibit a continued increase in the viscosity of the aqueous dispersion. However, the addition of the dibasic phosphate may adversely affect the corrosion resistance of metal coatings containing the composite particles. Further, it is desired that the coatings, which contain the composite particles, have increased levels of scrub resistance, an important property for coatings such as paints.
Coatings containing composites must provide a balance of properties including optical properties such as hiding and gloss, and mechanical properties such as scrub resistance. The composite must have good aqueous stability to allow storage and formulation of the composite, and formulations prepared from the composite. There is a continuing need to improve the scrub resistance of coatings prepared from coating formulations including composites while maintaining the aqueous stability of the composite containing coating formulation. The inventors have found that composites containing polymer particles which are characterized as having two polymer phases, provide a combination of dispersions of composite particles with aqueous stability and coatings with improved scrub resistance.
The present invention provides a composition having composite particles, the composite particles each include at least one two-phase polymer particle adsorbed to a titanium dioxide particle. The two-phase polymer particle contains two polymer phases in which the difference in the glass transition temperatures of the two phases is 10° C. or greater. These two-phase polymer particles are useful for providing titanium dioxide containing composites which are stable as aqueous dispersions and when dried, coatings including the titanium dioxide composites which have improved scrub resistance. The present invention also provides a method of preparing the composite particles.
The first aspect of this invention provides a composition including at least one composite particle; wherein the composite particle comprises a titanium dioxide particle and two-phase polymer particles adsorbed on the surface of the titanium dioxide particle; wherein the composite particle is formed in an aqueous mixture containing at least one titanium dioxide particle, a multiplicity of the two-phase polymer particles, and optionally, dispersant, and the weight ratio of the multiplicity of the two-phase polymer particles to at least one titanium dioxide particle in the aqueous mixture is in the range of 1:20 to 1:2; wherein each of the two-phase polymer particles includes a soft polymer phase with a glass transition temperature less than or equal to 40° C., and a hard polymer phase with a glass transition temperature greater than 40° C.; wherein the difference between the glass transition temperature of the hard polymer phase and the soft polymer phase is at least 10° C.; wherein the average weight ratio of the hard polymer phase to the soft polymer phase is in the range of 10:1 to 1:5; and wherein each of the two-phase polymer particles includes at least one element selected from: at least one phosphorus functional monomer as a polymerized group, at least 5 weight % of at least one carboxylic acid monomer as a polymerized group, based on weight of the two-phase polymer particles, at least one acid macromonomer as a polymerized group, and a water soluble polymer chemically bonded to the two-phase polymer particles wherein the water soluble polymer has a molecular weight of at least 1500 prior to bonding to the two-phase polymer particles and contains at least one moiety adsorbable to the titanium dioxide particle; or the two-phase polymer particles and the titanium dioxide particle have opposite charges.
In the second aspect of this invention, a process is provided for preparing a stable aqueous dispersion of composite particles including the steps of: dispersing titanium dioxide particles in a first aqueous medium; preparing a dispersion or suspension of two-phase polymer particles in a second aqueous medium, wherein the two-phase polymer particles comprise: a soft polymer phase with a glass transition temperature less than or equal to 40° C., and a hard polymer phase with a glass transition temperature greater than 40° C., wherein the difference between the glass transition temperature of the hard polymer phase and the soft polymer phase is at least 10° C., wherein the average weight ratio of the hard polymer phase to the soft polymer phase is in the range of 10:1 to 1:5, and wherein each of the two-phase polymer particles includes at least one element selected from the group consisting of: at least one phosphorus functional monomer as a polymerized group, at least 5 weight % of at least one carboxylic acid monomer as a polymerized group, based on weight of the two-phase polymer particles, at least one acid macromonomer as a polymerized group, and a water soluble polymer chemically bonded to the two-phase polymer particles wherein the water soluble polymer has a molecular weight of at least 1500 prior to bonding to the two-phase polymer particles and contains at least one moiety adsorbable to the titanium dioxide particle; or the two-phase polymer particles and the titanium dioxide particle have opposite charges; preparing a mixture containing the first aqueous medium, the second aqueous medium, and optionally, dispersant, wherein the average weight ratio of the two-phase polymer particles to the titanium dioxide particles is in the range of 1:20 to 1:2; and permitting adsorption of the
Bardman James Keith
Brown Ward Thomas
Donnelly Kenneth Michael
Lieser Bernhard Helmut
Zhang Wei
Greenblatt Gary D.
Koslow C. Melissa
Manlove Shalie
Rohm and Haas Company
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