Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-11-26
2003-09-16
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S507000, C524S457000, C524S588000, C524S591000, C524S839000, C525S100000, C525S102000, C525S123000, C525S455000
Reexamination Certificate
active
06620877
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in waterborne coating compositions of the type that comprise polyisocyanate crosslinking agents and acrylic copolymers having groups that are reactive with isocyanates. In particular, the improvements address the tendency of such coating compositions to develop gaseous inclusions during application of the coating, drying, and/or curing. These gaseous inclusions can cause visible defects that detract from the appearance of the finish of the coated article.
U.S. Pat. No. 5,466,745 to Fiori et al. discloses polyisocyanate crosslinking agents that can be emulsified in water with a surface active material reactive with isocyanates, and the emulsion may be used to form a curable film-forming composition. The emulsified materials are in the form of an oil-in-water emulsion that exhibits good stability even though the polyisocyanate and isocyanate reactive material are highly reactive when applied as a film.
An improvement in the type of composition disclosed by Fiori et al. is the subject of co-pending, commonly owned U.S. Pat. No. 6,005,045. In that patent, a surface active material reactive with isocyanate (e.g., polyol with carboxylate functionality) is used to disperse the polyisocyanate component as in Fiori et al. But improved hardness is attained in the cured coating by avoiding the use of surface active polyols having low T
g
as was required by the Fiori et al. patent. The composition of the 6,005,045 patent is characterized by (a) an aromatic group-containing polyisocyanate crosslinking agent which is non-dispersible in water and which contains at least two reactive isocyanate groups, at least one of which is a tertiary isocyanate group; and (b) a surface active isocyanate-reactive material comprising an active hydrogen-containing acrylic copolymer having a glass transition temperature of at least about 0° C. (preferably greater) prepared from a mixture of polymerizable ethylenically unsaturated monomers comprising about 5 to about 80 (preferably about 10 to about 40) percent by weight, based on the total solid weight of monomers used to prepare the copolymer, of an ethylenically unsaturated aromatic monomer.
Although these improvements in waterborne polyurethane coatings have been advantageous, further improvements are desired toward avoiding gaseous inclusions that cause visible defects. It would be desirable to provide a waterborne film-forming composition containing a polyisocyanate curing agent and an isocyanate reactive material that results in a cured finish having fewer defects originating from gaseous inclusions.
SUMMARY OF THE INVENTION
In accordance with the present invention, an aqueous polymeric dispersion is provided that can be used as a coating composition comprising:
(A) water, having dispersed therein:
(B) the mixture of:
(i) an acrylic polyol having hydrophilic groups;
(ii) a polyol hydrosilylation reaction product of an alkylpolysiloxane and an unsaturated hydroxyalkyl compound; and
(iii) a polyisocyanate component.
Such a composition has been found to have a marked reduction in defects arising from gaseous inclusions. At the same time, the composition possesses a combination of properties typically sought for use as a film-forming composition (i.e., paint for providing a protective and/or decorative coating on a substrate) and can be cured at ambient or elevated temperatures. The aqueous compositions are stable and yet have good reactivity to form a cured coating when applied as a thin layer onto a substrate.
A multi-component composite coating composition is also provided by the present invention. The coating composition comprises a base coat deposited from a pigmented film-forming composition of a variety of known types and a substantially transparent top coat, or “clear coat,” applied over the base coat in which the transparent coat is deposited from the aqueous dispersion of the present invention.
DETAILED DESCRIPTION
Suitable polyisocyanates for use as the polyisocyanate component in the composition of the present invention include liquid or solid polyisocyanate compounds containing at least two reactive (unblocked) isocyanate groups. The advantages of the aforesaid U.S. Pat. No. 6,005,045 can also be attained if the polyisocyanate includes an aromatic group and at least one of the isocyanate groups is a tertiary isocyanate group. By aromatic is meant aryl, alkylaryl, and arylalkyl bound isocyanates. Such polyisocyanates are themselves typically characterized as being substantially hydrophobic and non-dispersible in water. Mixtures of polyisocyanates are also suitable. Examples of appropriate polyisocyanates for a combination of desirable properties include, but are not limited to, meta-&agr;,&agr;,&agr;′,&agr;′-tetramethylxylylenediisocyanate, para-&agr;, &agr;, &agr;′,&agr;′-tetramethylxylylenediisocyanate, as well as biurets and asocyanurates of diisocyantes, wherein at least one of the diisocyanates used to prepare the biuret or isocyanurate contains a tertiary isocyanate group.
In some embodiments the polyisocyanate comprises a urethane adduct of a polyol with a diisocyanate containing at least one tertiary isocyanate group. Suitable polyols include, for example, ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, and the like. Oligomeric and polymeric polyols are also suitable.
The acrylic polyol component of the present invention contains both (i) functionality capable of reacting with isocyanate groups and (ii) hydrophilizing functionality capable of rendering the surface active isocyanate reactive material water dispersible.
In some embodiments the acrylic polyol is an acrylic copolymer having the hydrophilizing groups and isocyanate-reactive functionality incorporated into the polymer via appropriate monomer selection or subsequent modification. Examples of monomers that may be utilized to synthesize the acrylic polyol include carboxyl group-containing ethylenically unsaturated monomers and hydroxyl group-containing ethylenically unsaturated monomers.
The expression “isocyanate-reactive” functionality as utilized herein refers to the presence of functional groups that are reactive with isocyanate groups under conditions suitable for cured coating formation. Such isocyanate-reactive functionality is generally well known to those skilled in the coatings art and includes, most commonly, active hydrogen-containing functionality such as hydroxyl and amino groups. Hydroxyl functionality is typically utilized as the isocyanate-reactive functionality in coatings and is preferred for use in the present invention.
Hydrophilizing functionality is also well known to those skilled in the coatings art and includes, most commonly, anion generating, cation generating and hydrophilic non-ionic functional groups. By anion generating and cation generating are meant functionality such as carboxyl (anion generating) or amino (cation generating) which, when appropriately neutralized, becomes hydrophilic in nature. Hydrophilic non-ionic functionality is, in and of itself, hydrophilic in nature, such as alkylene oxide units. The amount of hydrophilizing functionality present in the acrylic polyol should, upon at least partial neutralization of the anion generating or cation generating groups (if present), be sufficient to render the polyol water-dispersible.
It is preferred, but not necessary, that the acrylic polyol used in the present invention be in accordance with the disclosure in U.S. Pat. No. 6,005,045. There, the active hydrogen-containing acrylic copolymers have a glass transition temperature (T
g
) greater than about 0° C. The T
g
is described in PRINCIPLES OF POLYMER CHEMISTRY, Flory, Cornell University Press, Ithaca, N.Y., 1953, at pages 52-57. The T
g
can be calculated as described by Fox in
Bull. Amer. Physic. Society,
1,3, page 123 (1956). The T
g
can be measured experimentally by using a penetrometer such as a Du Pont 940 Thermomedian Analyzer. The T
g
of the polymers as used herein refers to the calculated value
Klanica Joseph A.
Rearick Brian K.
PPG Industries Ohio Inc.
Sastri Satya
Uhl William J.
Wu David W.
LandOfFree
Combined organic/inorganic polyols in waterborne... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Combined organic/inorganic polyols in waterborne..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Combined organic/inorganic polyols in waterborne... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035364