Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-11-21
2003-12-16
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393600
Reexamination Certificate
active
06663917
ABSTRACT:
The present invention relates to an aqueous coating composition providing improved adhesion to friable surfaces such as chalky weathered paint surfaces and masonry surfaces and to a method for producing a coating on a friable surface.
Coatings are frequently desirably applied to surfaces which are both porous and weak, i.e., subject to attrition on abrasion such as, for example, chalky surfaces of coatings which have weathered to an extent that poorly consolidated pigment forms a surface layer on the coating and masonry surfaces, weathered or not, which have a poorly consolidated surface. A substrate to which a coating is applied may have an entirely friable surface or only portions of the surface may be friable. Such substrates present a problem to the applicator in that, without being bound by this mechanism, the aqueous coating composition may not penetrate the weak boundary layer of the friable surface or friable surface areas sufficiently to provide a dry coating with the requisite degree of adhesion to the substrate below the weak surface.
U.S. application Ser. No. 4,771,100 discloses the use of ethoxylated fatty amines in the preparation of single stage latexes containing about 0.1 to 10 weight percent of copolymerized carboxylic acid monomer which have particle sizes between 889 and 1091 Angstroms for use as coatings. No use of these single stage latexes, in combination with ethoxylated fatty amines, to improve adhesion to friable surfaces was disclosed.
U.S. application Ser. No. 5,035,944 discloses a method for treating surfaces, including those of wood, plastic, and cementitious substrates to provide coatings having superior appearance with respect to gloss and hardness. The substrates were treated with aqueous coating compositions including particles of polymer of size 20 to 70 nanometers, having at least two mutually incompatible copolymers in separate phases. The outer portion of the particle was predominately a phase containing a copolymer having a Tg significantly lower than that of copolymer making up the predominate phase of the inner portion (core) of the particle. Preferably, the outer phase copolymer had a low Tg of less than 35° C., while the inner (core) phase copolymer had a high Tg of at least 45° C. The copolymer of the outer phase had a weight average molecular weight (M
w
) of 50,000 to 10,000,000, while the copolymer of the inner (core) phase of the particle had an M
w
of 1,000,000 to 10,000,000. The disclosed particles achieve improved hardness while maintaining good film forming performance by surrounding an inner (core) phase polymer that is hard (i.e., having Tg well above room temperature, and molecular weight of at least 1,000,000) under ambient conditions with an outer phase polymer that is soft and flowable (i.e., having Tg near or below room temperature, and M
w
as low as 50,000). No use of these multi-stage latexes to improve adhesion to friable surfaces was disclosed.
We have now prepared aqueous coating compositions including, dispersed therein, a plurality of polymeric particles having an average particle size of less than 120 nanometers, each polymeric particle including at least one polymer A and at least one polymer B. Polymer A contains, as polymerized units, substantial amounts of acid functional monomers, water soluble monomers, or both. The total amount of acid functional monomers, or water soluble monomers, or both, contained, as polymerized units, in Polymer B is less that the total amount contained in Polymer A. We have, surprisingly, found that these compositions exhibit improved adhesion to chalky weathered surfaces when compared with aqueous coating compositions in which the polymeric particles have been prepared in a single polymerization stage. We have also discovered that the presence of nonionic surfactants further improves the adhesion to chalky weathered surfaces observed for aqueous coating compositions containing the plurality of polymeric particles, each of which includes at least one polymer A and at least on polymer B.
Used herein, these terms, enclosed in quotation marks, are defined as follows:
“friable surface” refers to porous, weak surfaces subject to attrition on abrasion and includes: chalky surfaces of coatings which have weathered to an extent that poorly consolidated pigment forms a surface layer on the coating; masonry surfaces, weathered or fresh, which have a poorly consolidated surface; wall board; weathered uncoated wood; and gypsum.
“polymerization stage” refers to the time interval during which a monomer or a mixture of monomers is polymerized to form polymer;
the “polymeric particles” have an average particle size of less than 120 nanometers, exist in large numbers (i.e., as a “plurality of polymeric particles”) and are prepared by emulsion polymerization accomplished in two or more polymerization stages, at least one polymerization stage of which produces “polymer A”, and at least one polymerization stage of which produces “polymer B”;
“Polymer A” is characterized in that it has either a higher acid number compared to “polymer B”, or that it is prepared from a monomer mixture containing 5-99.5% of at least one water soluble monomer, or both; and
“water soluble” means that the monomer has a water solubility of 8% or more by weight, based on the weight of water, as calculated by the QSAR Method (see Table A below).
“Acid number” is a convenient indicator of the amount of acid functionality contained in a polymer. “Acid number” is defined as the number of milligrams of potassium hydroxide required to neutralize the free acid in one gram of polymer solids.
Acid
Number
=
(
mg
of
KOH
)
(
g
of
polymer
sample
)
The present invention relates to an aqueous coating composition having improved adhesion to friable surfaces including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of −20° C. to 100° C.,
wherein said polymer A is an emulsion polymer consisting essentially of:
(i) at least one copolymerized ethylenically unsaturated nonionic monomer having a water solubility less than 8% by weight, based on the weight of water; and
(ii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 13 to 260; and
(b) at least one polymer B having a glass transition temperature of −20° C. to 100° C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers.
A second aspect of the present invention relates to an aqueous coating composition having improved adhesion to friable surfaces including a plurality of polymeric particles, each of said particles including:
(a) at least one polymer A having a glass transition temperature of −20° C. to 100° C.,
wherein said polymer A is an emulsion polymer including:
(i) 5-99.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated first nonionic monomer having a water solubility of 8% or more by weight, based on the weight of water;
(ii) 0-94.5% by weight, based on said polymer A weight, of at least one copolymerized ethylenically unsaturated second nonionic monomer having a water solubility of less than 8% by weight, based on the weight of water; and
(iii) at least one copolymerized acid monomer, such that the acid number of said polymer A is 3 to 100; and
(b) at least one polymer B having a glass transition temperature of −20° C. to 100° C.,
wherein said polymer B is an emulsion polymer including, as polymerized units, at least one ethylenically unsaturated nonionic monomer,
wherein said particles have an average particle diameter less than 120 nanometers.
A third aspect of the present invention relates to a method for producing a coating on a friable surface including:
(1) applying to said friable surface a layer of an aqueous coat
Gebhart Matthew Stewart
Koziski Kathleen Anne
Cameron Erma
Falk Stephen T.
Hemenway Carl P.
Rohm and Haas Company
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