Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-07-20
2001-04-10
Yoon, Tae (Department: 1714)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C523S205000, C523S334000, C524S497000, C524S847000, C427S385500
Reexamination Certificate
active
06214467
ABSTRACT:
This invention relates to polymer-pigment composites, aqueous dispersions of polymer-pigment composites and paints containing the polymer-pigment composites. More particularly, this invention relates to polymer-pigment composites wherein the polymer is formed from terminally-unsaturated oligomers containing acid functionality.
Titanium dioxide (hereinafter referred to as “TiO
2
”) is the pigment of choice by most coatings manufacturers, particularly paint manufacturers, to provide whiteness and opacity or “hiding” to the final dried coating. TiO
2
is typically the most expensive raw material in a paint formulation. Thus, paint manufacturers have long sought to achieve the desired opacity by using the smallest amount of TiO
2
possible. A number of techniques have been employed, including inter alia:
(1) using TiO
2
that has an optimal average particle size and particle size distribution for light scattering;
(2) using TiO
2
that is well dispersed.
The opacifying capability or hiding power of a coating or paint is a function of the spacing of TiO
2
pigment particles in the dried coating. The light scattering characteristics of TiO
2
particles are well known and the average size and size distribution of the TiO
2
have been optimized by the TiO
2
manufacturers for maximum scattering. Maximum light scattering occurs when the TiO
2
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, TiO
2
manufacturers have attempted a number of techniques, including encapsulating TiO
2
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), onto the surface of the TiO
2
particles. U.S. Pat. No. 5,412,019, for example, discloses the use of preformed polymer particles that are chemically bonded to a polymeric water-soluble compound having a weight-average molecular weight (hereinafter referred to as “Mw”) of at least 1,500, preferably greater than 20,000, prior to chemical bonding and containing moieties that are adsorbable onto the TiO
2
particles.
The polymeric water-soluble compounds described in U.S. Pat. No. 5,412,019 contain moieties that permit adsorption onto the TiO
2
particles through a balance of ionic, steric and van der Waals' forces. One serious drawback of using these water-soluble compounds in the manner described in U.S. Pat. No. 5,412,019 is that the use of high amounts of water-soluble compounds containing the adsorbing moieties (high use levels, high molecular weights or both) compromises the water-resistance properties of the final coating. Furthermore, high molecular weight water-soluble compounds may detrimentally contribute to instability and/or flocculation of a paint composition. Thus, a delicate balance must be struck to achieve a polymer that absorbs onto the TiO
2
particles to give the proper spacing while not detrimentally affecting the properties of the coating formulation and the final dried coating, especially those related to water resistance. Applicants have achieved this balance.
STATEMENT OF THE INVENTION
The invention is directed to a composite, containing:
a. pigment particles; and
b. a plurality of discrete polymer particles adsorbed onto the surface of the pigment particles;
wherein the polymer particles are formed from 0.05% by weight to 20% by weight, based on the weight of the polymer particles, of at least one terminally unsaturated oligomer of the formula:
wherein N is the residue of an ethylenically unsaturated monomer of the formula:
wherein M is the residue of an ethylenically unsaturated acrylic or vinyl monomer other than N;
wherein said N and M residues are randomly arranged in said oligomer;
wherein m is the total number of M residues in said oligomer and is in the range 0 to 35;
wherein n is the total number of N residues in said oligomer and is in the range 1 to 70;
wherein the sum of n and m is in the range from 1 to 70;
wherein X and each Y is independently selected from the group consisting of H, NH
4
, alkali metals and alkaline earth metals;
wherein each Q is independently selected from the group consisting of H and COOX; and
wherein each Z is independently selected from the group consisting of H and CH
3
.
The invention is also directed to a coating composition, particularly a paint, containing these composite particles.
The invention is further directed to a process for preparing an aqueous dispersion of polymer-pigment composite particles, including the steps of:
(1) dispersing pigment particles in a first aqueous medium;
(2) preparing a dispersion or suspension of discrete polymer particles in a second aqueous medium, the polymer particles formed from 0.05% by weight to 20% by weight, based on the weight of the polymer particles, of at least one terminally unsaturated oligomer of the formula:
wherein N is the residue of an ethylenically unsaturated monomer of the formula:
wherein M is the residue of an ethylenically unsaturated acrylic or vinyl monomer other than N;
wherein said N and M residues are randomly arranged in said oligomer;
wherein m is the total number of M residues in said oligomer and is in the range 0 to 35;
wherein n is the total number of N residues in said oligomer and is in the range 1 to 70;
wherein the sum of n and m is in the range from 1 to 70;
wherein X and each Y is independently selected from the group consisting of H, NH
4
, alkali metals and alkaline earth metals;
wherein each Q is independently selected from the group consisting of H and COOX; and
wherein each Z is independently selected from the group consisting of H and CH
3
;
(3) mixing the first aqueous medium and the second aqueous medium;
(4) permitting the polymer particles to adsorb onto the pigment particles to form composite particles; and
(5) optionally, providing dibasic phosphate to the composite particles.
The invention is also directed to a process for preparing an aqueous dispersion of polymer-pigment composite particles, including the steps of:
(1) preparing a dispersion or suspension of polymer particles in an aqueous medium, the polymer particles formed from 0.05% by weight to 20% by weight, based on the weight of the polymer particles, of at least one terminally unsaturated oligomer of the formula:
wherein N is the residue of an ethylenically unsaturated monomer of the formula:
wherein M is the residue of an ethylenically unsaturated acrylic or vinyl monomer other than N;
wherein said N and M residues are randomly arranged in said oligomer;
wherein m is the total number of M residues in said oligomer and is in the range 0 to 35;
wherein n is the total number of N residues in said oligomer and is in the range 1 to 70;
wherein the sum of n and m is in the range from 1 to 70;
wherein X and each Y is independently selected from the group consisting of H, NH
4
, alkali metals and alkaline earth metals;
wherein each Q is independently selected from the group consisting of H and COOX; and
wherein each Z is independently selected from the group consisting of H and CH
3
;
(2) dispersing pigment particles in the aqueous medium;
(3) permitting the polymer particles to adsorb onto the pigment particles to form composite particles; and
(4) optionally, providing dibasic phosphate to the composite particles.
In addition, the invention is directed to a method of improving the opacity of a coating composition, including the steps of:
(1) dispersing pigment particles in a first aqueous medium;
(2) preparing a dispersion or suspension of polymer particles in a second aqueous medium, the polymer particles are formed from 0.05% by weight to 20% by weight, based on the weight of the polymer particles, of at least one terminally unsaturated oligomer of the formula:
wherein N is the residue of an ethylenically unsatu
Edwards Steven Scott
Friel John Michael
Lieser Bernhard Helmut
Maurice Alvin Michael
Nungesser Edwin Hugh
Choi Wendy A.
Rohm and Haas Company
Yoon Tae
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