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
1999-02-22
2002-06-25
Lovering, Richard D. (Department: 1712)
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...
C523S415000, C523S416000, C523S521000, C524S789000, C528S113000, C528S905000
Reexamination Certificate
active
06410635
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a curable coating composition containing an exfoliated silicate material which has been found to enhanced coating properties such as adhesion, appearance, crater resistance, and rheology control.
BACKGROUND OF THE INVENTION
Due to their low cost and commercial availability, the use of clay minerals as rheology modifiers and/or fillers in coating compositions is common. Traditionally these have included such clay minerals as wollastonite, attapulgite, kaolin, talc, mica and calcium carbonate. These materials have been incorporated in both treated and untreated forms, the most common treatment being silanization, to compatibilize the mineral hydrophilic surface with the host polymer. However, a high level of these conventional clays is needed, e.g., 3 to 10 percent by weight base on total solids of the coating composition, to effectuate adequate rheology control in curable coating compositions. At these levels other properties, such as liquid coating properties, for example, working viscosity and storage stability, and cured coating properties, such as appearance and adhesion, can be adversely affected. Minerals such as mica and talc, which are layered silicate materials, i.e., phyllosilicates, have a platy morphology with typical aspect ratios (the ratio of particle width to particle thickness=aspect ratio) of less than 50. These materials are commonly known for use in coatings as rheology modifiers and fillers and, in addition, due to parallel interlamination of the silicate layers, can improve barrier properties.
Also known in the art is the preparation of aqueous dispersions of exfoliated layered silicate materials, such as vermiculite and bentonite clays. Generally, the clay particles are contacted with an ionic solution to effect cation exchange within the interlayer spacing, thereby permitting swelling of the spacing to bring about delamination (or “exfoliation”) upon immersion in aqueous media. These ionic solutions typically contain lithium, alkyl ammonium and/or ammonium carboxylic acid cations. The exfoliated particles are then dispersed under high shear. These dispersions can be used to form or cast films by using drawdown or spraying techniques followed by evaporation of the aqueous phase.
Additionally, it is known to use smectite minerals, particularly montmorillonite clays, in plastic composite materials. These materials are a family of clays having a 2:1 layer structure and, typically, aspect ratios ranging from about 200 to 2,000, which are orders of magnitude greater than for conventional fillers such as mica and talc. The clays are treated with polymers which contain functional groups, e.g., hydroxyl, amine, and amide groups, to enlarge the interlayer spacing such that insertion and ionic attachment of organic molecules to the platelet surfaces can occur (a process known as “intercalation” with the product formed thereby being known as an “intercalate”). During a subsequent polymerization/compounding step in composite formation, individual platelets flake off or exfoliate and are embedded throughout the polymer matrix.
Such polymer-clay composites are described in U.S. Pat. No. 5,853,886 wherein a proton-exchanged layered silicate is intercalated with a basic group-containing polymerizing component. The intercalate is then contacted with a thermoset or a thermoplastic resin system which reacts with the polymerizing component thereby exfoliating the intercalate and forming a hybrid polymer-clay composite.
Although the art teaches the use of the above-described dispersions to form films of exfoliated layered silicate materials, the prior art does not disclose the use of such dispersions in protective or decorative coating compositions. Moreover, although the art teaches the intercalation of layered silicate materials with a polymer containing functional groups, with subsequent exfoliation in the presence of a host polymer to form platelet/polymer composite materials, there is no teaching in the prior art to use layered silicate materials which are exfoliated with functional group-containing polymers in coating compositions, that is, compositions which are deposited on a substrate from a fluid medium, such as a liquid medium, then coalesce on the substrate to form a substantially continuous film.
It has been found that the inclusion in coating compositions of exfoliated silicate materials which are derived from layered silicates, such as montmorillonite clays, and which have been exfoliated with a functional group-containing polymer, provides improved properties such as adhesion, appearance, crater resistance, and rheology control. Moreover, it has been found that these exfoliated silicate materials effectuate these improved properties at levels much lower than those levels needed for more conventional clay materials and, therefore, liquid coating properties, such as storage stability and working viscosity, and cured coating properties, such as adhesion and appearance are not adversely affected.
SUMMARY OF THE INVENTION
In accordance with the present invention, provided is a curable coating composition comprised of the following components:
(a) a polymer containing reactive functional groups;
(b) a curing agent containing functional groups which are reactive with the functional groups of (a); and
(c) an exfoliated silicate material derived from a layered silicate which has been exfoliated with a polymer, the polymer being compatible with the polymer (a) and the curing agent (b). The curable coating compositions are useful as both ambient- and thermally-cured coating compositions which provide enhanced properties such as stability, working viscosity, appearance, adhesion, crater resistance and rheology control.
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used in the specification and claims are to be understood as modified in all instances by the term “about”. As used herein, the term “polymer” is meant to include oligomers.
DETAILED DESCRIPTION OF THE INVENTION
Layered silicate materials suitable for use in component (c) of the curable coating compositions of the invention described immediately above include any clay mineral having a platy morphology which is characterized by a layered lattice structure in which the silicate layer units have a thickness of up to 25 Å, preferably 5 to 15 Å, more preferably 5 to 10 Å, and an interlayer spacing capable of expanding at least 5 Å. Usually, the layers are separated by exchangeable cations metals associated with water molecules. Useful layered silicates include, but are not limited to, phyllosilicates, such as smectite clay minerals, for example montmorillonite, particularly sodium montmorillonite, calcium montmorillonite and/or magnesium montmorillonite; nontronite; biedellite; volkonskonite; hectorite; saponite; sauconite; sobockite; stevensite; svinfordite; vermiculite and the like. Other useful layered materials include micaceous minerals such as illite and mixed layered illite/smectite minerals.
Preferably, the layered silicates employed in the curable compositions of the invention have a cation exchange capacity (a measure of charge density on the surface of the clay particle) of 30 to 200 milliequivalents of cation per 100 grams of layered silicate.
Preferred layered silicate materials are phyllosilicates of the 2:1 type having a negative charge on the layers and a commensurate number of exchangeable cations in the interlayer spaces. More preferably, the layered silicate materials are smectite clay minerals such as montmorillonite; nontronite; biedellite; volkonskonite; hectorite; saponite; sauconite; sobockite; stevensite; and svinfordite. The most preferred of these being montmorillonite materials, preferably those which contain, within the interlayer spacing, exchangeable cations of alkaline or alkaline earth metals, preferably Ca
+
2
and Na
+
, which are associated with water molecules.
As used herein, the term “inter
Karabin Richard F.
Kaylo Alan J.
Lan Tie
Sandala Michael G.
Lovering Richard D.
PPG Industries Ohio Inc.
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