Coating with improved hiding, compositions prepared therewith, and processes ...

(52) (58)

(56)

Related U.S. Application Data

Provisional application No. 60/377,975, filed on May 7, 2002, provisional application No. 60/337,742, filed on Nov. 9, 2001, provisional application No. 60/325, 382, filed on Sep. 26, 2001, provisional application No. 60/318,734, filed on Sep. 12, 2001, provisional application No. 60/311,207, filed on Aug. 9, 2001, provisional application No. 60/306,929, filed on Jul. 20, 2001, provisional application No. 60/299,701, filed on Jun. 20, 2001.

Int. CI.

C08J 3/00 C08K 3/00 C08K 7/00 C08K 9/00 C08L 43/00 U.S. CI

(2006.01)
(2006.01)
(2006.01)
(2006.01)
(2006.01)

523/200; 523/205; 523/220;

524/401; 524/431; 524/497; 524/547

Field of Classification Search 524/401,

524/431,497,547; 523/205,220,200 See application file for complete search history.

References Cited

U.S. PATENT DOCUMENTS

523/340

FOREIGN PATENT DOCUMENTS

AU

JP

WO

wo wo

592834 60-42466 WO97/20001 WO99/25780 WO01/10946 A2

5/1987 3/1985 6/1997 5/1999 2/2001

OTHER PUBLICATIONS

J. Oil Col. Chem. Assoc. 1968, 51, pp. 875-893.
Proceedings of the Annual Meeting Technical Program of
the FSCT, Oct. 2000, "Phoaphate Monomers as Adhesion
Promoters and Latex Stabilizers", M.J. Chen, J. Kiplinger,
N. Johnson, E. Walsh, H. Adam, pp. 313-326.
Van Herk A. M., "Encapsulation of Inorganic Particles",
Polymeric Dispersions: Principles and Applications, 1997,
pp. 435-450.

Primary Examiner—Patrick D. Niland

(74) Attorney, Agent, or Firm—Kim R. Jessum; Gary D.

Greenblatt

A coating containing pigment particles and a polymer matrix is provided. The coating contains pigment particles that have a scattering coefficient with a linear or quasi-linear relationship to the pigment volume concentration of those pigment particles. The coating has improved hiding and is useful as a protective coating or an aesthetic coating on an underlying substrate. Also provided are compositions useful for preparing the coating, including covalently bonded composite particles and aqueous dispersions containing composite particles. The composite particles each contain a pigment particle with a plurality of polymer particles attached by adsorption on the outer surface of the pigment particle or by covalent bonding to the pigment particle through a coupling agent. Methods to prepare the composite particles and coating compositions containing the composite particles are also provided.

1 Claim, 1 Drawing Sheet

1

COATING WITH IMPROVED HIDING,
COMPOSITIONS PREPARED THEREWITH,
AND PROCESSES FOR THE PREPARATION
THEREOF

5

CROSS REFERENCE TO RELATED PATENT
APPLICATIONS

This is a non-provisional application of prior pending U.S. provisional applications Ser. Nos. 60/299,701 filed Jun. 10 20. 2001; 60/306,929 filed Jul. 20. 2001; 60/311,207 filed Aug. 9, 2001; 60/318,734 filed Sep. 12, 2001; 60/325,382 filed Sep. 26, 2001; 60/337,742 filed Nov. 9. 2001; 60/377, 975 filed May 7, 2002.

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FIELD OF THE INVENTION

This invention relates generally to a coating containing opacifying pigment particles and a polymer matrix. More specifically, the invention relates to such a coating wherein 20 the opacifying pigment particles have a light scattering coefficient with a linear or quasi-linear relationship to the volume concentration of the particles. The invention further relates to a coating wherein the opacifying pigment particles are composite particles, which are inorganic-organic par- 25 tides containing an opacifying pigment particle with at least one polymer particle attached thereto. This invention still further relates to methods of preparing composite particles, and to a method of preparing coating compositions containing composite particles. 30

BACKGROUND OF THE INVENTION

Opacifying pigments provide whiteness, and opacity or "hiding", to opacifying coatings, such as paints. These 35 pigments are present in all coatings that are designed to provide an opaque coating on and concealingly cover an undersurface or substrate surface to which the coating is applied. Opacifying pigments are absent from those coatings that are designed to be clear or transparent. Opacifying 40 pigments are present in opacifying coatings, especially paints. In paints, the opacifying pigment is present irrespective of whether the paint is white or colored. The opacifying pigment of all paints is distinguished from the color specific pigments, also known as tinting agents or colorants, which 45 are additionally present in colored paints. It is the color specific pigments that provide the specific color or tint to non-white paints.

It is desirable that opacifying coatings and paints have a high opacifying capacity so as to enable the coating or paint 50 to completely conceal the undersurface, even if of a sharply contrasting color, while utilizing a minimal application of the coating or paint. It is highly desirable that complete covering of the undersurface is attained with a single application of the coating or paint, having the minimum possible 55 thickness.

Opacifying coating and paint manufacturers have long sought to formulate opacifying coatings and paints having the desired opacity by maximizing the level of hiding for a defined level of opacifying pigment, in an attempt to 60 approach the theoretical maximum hiding capability for a specific opacifying pigment, while minimizing the amount of opacifying pigment actually utilized.

The opacifying capacity or hiding power of an opacifying coating or paint is a measure of the coating's ability to 65 conceal a surface to which the coating is applied. Opacifying capacity is a function of the spacing between the particles of

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opacifying pigment in the dried applied coating. Opacifying capacity of a coating is maximized when the light scattering capability of the opacifying pigment is maximized. Maximum light scattering efficiency occurs when the opacifying pigment particles have a certain diameter and spacing, so that the light scattering capability of each particle does not interfere with the light scattering capability of its neighboring particles. This condition may occur in coatings containing sufficiently low levels of opacifying pigment such that the individual opacifying pigment particles are isolated from each other. Coatings containing such low levels of opacifying pigment, however, do not provide sufficient whiteness and hiding at typical dried coating thicknesses. Achieving the desired levels of hiding and whiteness typically requires higher levels of opacifying pigment. At these higher levels, a statistical distribution of opacifying pigment particles occurs, which results in at least some of the opacifying pigment particles being in such close proximity to one another that there is a loss of light scattering efficiency due to crowding of the opacifying pigment particles.

Increased hiding efficiency is obtained by reducing the crowding of the opacifying pigment particles and minimizing the formation of clusters of opacifying pigment particles. One method uses polymer particles containing select chemical groups which promote adsorption to the opacifying pigment particle.

For example, 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 opacifying pigment particle. The selected polymeric latex particles have dihydrogen phosphate functional groups, which promote adsorption of the selected polymeric latex particles onto the surface of the titanium dioxide particles.

Although these composite particles provide improved hiding, there is still a need to increase the hiding efficiency provided by the opacifying pigment particles, and in particular, to obtain coatings which have hiding values at or near the maximum limit predicted by light scattering theory.

Theoretical hiding efficiency refers to the maximum level of hiding that may be obtained from a defined concentration of pigment particles and is characterized by a linear relationship between the scattering coefficient for the coating and the pigment concentration.

Titanium dioxide (Ti02) is the most common opacifying pigment utilized in opacifying coatings and paints today. Accordingly, the present invention is described hereinafter in the context of the maximum opacifying capacity for titanium dioxide, which occurs at an optimum particle diameter of from about 200 to about 280 nanometers (nm), and when the particles are spaced apart from each other at distances on the order of a few particle diameters. It is to be understood, however, that the scope of the present invention is not limited to titanium dioxide as the opacifying pigment.

Titanium dioxide is the opacifying pigment of choice of most coatings manufacturers, particularly paint manufacturers, to provide whiteness, and opacity or "hiding", to the final dried coating. Titanium dioxide is, however, typically the most expensive raw material in a coating formulation. Heretofore, a number of techniques for minimizing the amount of Ti02, while maximizing the level of hiding provided a certain amount of Ti02 have been employed, including: (1) using titanium dioxide that has an optimal average particle size and particle size distribution for light scattering; and (2) using titanium dioxide that is well dispersed.

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SUMMARY OF THE INVENTION

The present invention provides opacifying coatings having hiding values at or near theoretical hiding efficiency. These coatings are characterized as having opacifying pig- 5 ment particles that have light scattering coefficients with linear or quasi-linear relationships to their pigment volume concentrations. An advantage of the coatings of the present invention is that for a desired level of hiding, these coatings contain lower levels of pigment and/or are applied at lower 10 coat weights than coatings previously known in the art. The use of the coatings of the present invention enables the attainment of increased hiding levels.

According to a first aspect of the present invention, an opacifying coating is provided containing pigment particles 15 having an average particle diameter of up to about 1 micron, a surface, and an index of refraction of at least 1.8; and a polymer matrix for at least partially containing the pigment particles; the pigment particles having a light scattering coefficient, S, described by the equation: 20

S=AV(\-BVe/3)

wherein: V is the pigment volume concentration of the pigment particles and is in the range of about 5 to about 40; 25 ~Vejf is the effective pigment volume concentration of the pigment particles; A is a constant with a value greater than 0; and B is a constant with a value in the range of from 0 to 0.15.

A second aspect of the present invention provides a 30 composite particle including a pigment particle and a plurality of polymer particles, each one of the polymer particles containing at least one reacted complementary functional group forming a covalent bond with the pigment particle.

A third aspect of the present invention provides a com- 35 posite particle including a pigment particle, a first plurality of polymer particles; and a second plurality of reacted coupling agents, such that each one of the reacted coupling agents is covalently bonded to the pigment particle and to a corresponding one of the first plurality of polymer particles. 40

A fourth aspect of the present invention provides a coating composition including a composite particle containing: a pigment particle, a first plurality of polymer particles, and a second plurality of reacted coupling agents, such that each one of the reacted coupling agents is covalently bonded to 45 the pigment particle and to a corresponding one of the first plurality of polymer particles; and a binder.

A fifth aspect of the present invention provides a method for preparing a composite particle, wherein the composite particle contain a pigment particle and a first plurality of 50 polymer particles attached to the pigment particle, the method including the steps of: admixing the pigment particle and a second plurality of molecules of a coupling agent, wherein each molecule of the coupling agent contains a first functional group for reacting with the pigment particle to 55 form a first covalent bond therewith, and a second functional group for reacting with a complementary functional group to form a second covalent bond; forming a modified pigment particle by reacting or allowing to react the pigment particle and at least a portion of the first functional groups of the 60 second plurality of molecules of the coupling agent, such that the modified pigment particle has a third plurality of molecules of the coupling agent with reacted first functional groups, covalently bonded thereto; admixing the modified pigment particle and the first plurality of polymer particles, 65 each of the first plurality of polymer particles containing the complementary functional group; and forming the compos

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ite particle by reacting or allowing to react the second functional group of the third plurality of molecules of the coupling agent and the complementary functional group of the first plurality of polymer particles, forming a covalent bond therebetween, such that at least one of the first plurality of the polymer particles is covalently bonded to one of the third plurality of molecules of the coupling agent.

The second, third, fourth, and fifth aspects of this invention relate, respectively, to covalently bonded composite particles, a coating composition containing the covalently bonded composite particles, and a method of preparing the covalently bonded composite particles.

A sixth aspect of the present invention provides an aqueous polymer dispersion including polymer particles containing polymerized units of phosphorus acid monomer, and having first phosphorus acid groups; and an aqueous medium; such that the aqueous polymer dispersion is substantially free of water soluble polymer having second phosphorus acid groups.

According to a seventh aspect of the present invention, a composite particle dispersion is provided including composite particles, each of which contains a pigment particle having a surface, and a plurality of polymer particles containing polymerized units of phosphorus acid monomer, and having first phosphorus acid groups, wherein the plurality of polymer particles are adsorbed on the surface of the pigment particle; and an aqueous medium; wherein the composite particle dispersion is substantially free of water soluble polymer bearing second phosphorus acid groups and having a molecular weight of at least 40,000.

The aqueous polymer dispersion of the sixth aspect is suitable for preparing the composite particle composition of the seventh aspect.

An eighth aspect of the present invention provides a process for forming the composite particle composition of the seventh aspect of the invention. The process includes the steps of: preparing an aqueous composition including pigment particles and polymer particles having first phosphorus acid groups; wherein the polymer particles contain polymerized units of phosphorus acid monomer; and the aqueous composition is substantially free of water soluble polymer bearing second phosphorus acid groups and having a molecular weight of at least 40,000; and permitting the polymer particles to adsorb onto the pigment particles to form the composite particles.

In a ninth aspect of the present invention, a coating is provided including composite particles; wherein each of the composite particles contains a pigment particle having a surface; and a plurality of polymer particles containing polymerized units of a phosphorus acid monomer and having first phosphorus acid groups, the plurality of polymer particles being adsorbed on the surface of the pigment particle; such that the composite particles are formed by admixing the pigment particles and the plurality of polymer particles in an aqueous medium; wherein the aqueous medium is substantially free of water soluble polymer having second phosphorus acid groups and a molecular weight of at least 40,000.

The sixth and seventh aspects of the present invention relate to compositions having aqueous mediums substantially free of water soluble polymer having second phosphorus acid groups. The eighth aspect of the present invention relates to a process for preparing the composition of the seventh aspect of the present invention. The ninth aspect relates to a coating prepared from the composition of the seventh aspect.