Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-04-05
2004-02-10
Cain, Edward J. (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
Reexamination Certificate
active
06689423
ABSTRACT:
The current invention relates to a coating composition comprising polyacetoacetate and crosslinker for said polyacetoacetate.
BACKGROUND OF THE INVENTION
Coating compositions of this type are generally known from, for example, U.S. Pat. No. 3,668,183, “Polyenamine Coatings: I. Formulation of Coatings and Determination of Film Properties”, K. L. Hoy and C. H. Carder,
Journal of Paint Technology,
Vol. 46, No. 591, April 1974, pages 70-75, and “Polyenamine Coatings: II. Chemical Methods of Improving Film Properties”, C. H. Carder and H. O. Colomb, Jr.,
Journal of Paint Technology,
Vol. 46, No. 591, April 1974, pages 76-78, referred to respectively as “Polyenamine Coatings I” and “Polyenamine Coating II”. Such coating compositions, when properly formulated and applied to a substrate, form a coating having highly desirable properties, such as hardness, flexibility and toughness. There is, however, a continuing difficulty in that such coatings frequently do not adequately adhere to the substrate on which they are applied.
U.S. Pat. No. 3,668,183 generally discloses the production of polyenamine resins by the reaction of polyacetoacetates with blocked polyamines. Also disclosed there is the possible use of a silicone component in the polyacetoacetate end cap to improve acid resistance.
WO-A-94/21738 discloses a crosslinkable liquid carrier-based coating composition comprising organic polymer(s) having acetoacetyl group functionality, a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule and a non-polymeric monoacetoacetyl compound(s) selected from a specific group of such compounds. The ratio of acetoacetyl groups of the acetoacetyl functional polymer(s) to the number of acetoacetyl-reactive amino groups of the polyamine compound(s) is between 0.5/1 and 2/1. The particularly preferred ratio is at or very near to 1.
In EP-A-199087, a coating composition is disclosed comprising a polyacetoacetate and a blocked polyamine crosslinker. The blocked polyamine and the polyacetoacetate are present in an amount such that the ratio of the number equivalents of primary and secondary amino groups of the polyamine to the number of equivalents of acetoacetate of the polacetoacetate is between ½ and 2. The polyacetoacetate has a number average molecular weight (Mn) of 1000-100,000.
In EP-A-417824 a polyacetoacetate with a molecular weight Mn between 200 and 1000 is disclosed. This polyacetoacetate is used as a crosslinker for amine-functional polymers. EP-A-417824 teaches use of an equimolar ratio of polymer and crosslinking agent.
The current invention provides a coating composition of the above-described type which, when cured, has a highly improved adhesion to the substrate. Other advantages include highly desirable cure-to-pot life ratio and corrosion-resistance properties. Further, it is possible to formulate the current compositions with low volatile organic content. Sill further, the coating compositions herein disclosed are especially useful in the production of a multi-layer coating system, in particular for metal substrates, more particularly aluminum substrates, and more particularly, for aluminium for aircraft. In multi-layer coating systems, the coating compositions of the current invention are especially useful as the primer, and particular, primers which are free, or substantially free, of chromate pigment. As used herein, “primer” means any coating layer in direct contact with the substrate, after optional cleaning, conversion coating and/or other pre-treatment of the substrate.
SUMMARY OF THE INVENTION
The coating composition of the instant invention comprises (a) polyacetoacetate having acetoacetate groups and (b) crosslinker for said polyacetoacetate wherein said crosslinker is present in a amount insufficient to crosslink all acetoacetate groups of the polyacetoacetate. Accordingly, generally the ratio of acetoacetate groups to groups capable of crosslinking with acetoacetate groups is >1, preferably about 1.1 to about 2, and most preferably about 1.15 to about 1.5.
In another embodiment the coating composition further comprises an organosilane.
The coating composition of the invention is further characterized in that the organosilane may be of the following general formula
wherein
Z is an amino group, an amino-containing group, an epoxy group, an epoxy-containing group, a mercapto group, a mercapto-containing group, a vinyl group, a vinyl-containing group, an isocyanate group, an isocyanate-containing group, an ureido group, an ureido-containing group, an imidazole group or an imidazole-containing group,
R is an aliphatic, alicylic or aromatic group,
R′ is an alkoxy group or alkoxyalkoxy groups,
R″ is an alkyl group having 1 to about 8 carbon atoms,
x is 0 to about 20,
a is 0 to 3, preferably 0 to 2,
b is 0.1 to 4, preferably 1 to 3,
c is 0 to 3, and preferably 0 to 2, and
the sum of a+b+c is 4.
Preferred organosilanes are aminosilanes, epoxysilanes, mercaptosilanes, vinylsilanes, ureidosilanes, imidazolsilanes and isocyanatosilanes.
DETAILED SUMMARY OF THE INVENTION
Polyacetoacetates are acetoacetate-functional compounds having at least two acetoacetates groups. Polyacetoacetates are well known in the art, for example as demonstrated in the already mentioned U.S. Pat. No. 3,668,183, U.S. Pat. No. 5,021,537, “Polyenamine Coatings I” and “Polyenamine Coatings II”. They can be described as the partial or complete acetoacetylation product of a monomeric polyalcohol having at least two free hydroxyl groups or an oligomeric or polymeric condensation derivative of such polyalcohols. The production of polyacetoacetates, “acetoacetylation”, may be accomplished by various reaction schemes. Some examples are transesterification of alkyl acetoacetates, such as methyl, ethyl or t-butyl acetoacetate with polyols or the reaction of polyol or polythiol with diketene, or the diketene-acetone adduct 2,2,6-trimethyl-1,3-dioxin-4H-one. Such compounds and synthesis mechanisms are well known in the art (see for example U.S. Pat. No. 3,668,183 and “The Acetoacetyl Functionality: A New Approach to Thermoset Coatings”, R. J. Clemens, et al.,
Proceedings: XVI
th
International Conference in Organic Coatings Science and Technology,
Jul. 9-13, 1990, Athens, Greece, page 127 et seq., and “Comparison of Methods for the Preparation of Acetoacetylated Coating Resins”, J. S. Witzeman et al.,
Journal of Coating Technology
62, No. 789, 101 (1990)) and need not be further detailed here.
Preferably, polyacetoacetates used in the current invention are partial or complete acetoacetylation products of (1) monomeric polyalcohols having 2 to 6 hydroxyl groups, (2) partial esters of polyalcohols with monocarboxylic acids (the carboxylic acids having 2 to 22 and preferably 5 to 18 carbon atoms), the partial esters having at least 2 unreacted hydroxyl groups, (3) polymeric condensates having at least 2 hydroxyl groups, suitable polymeric condensates being, for non-limiting example, polyesters, polyethers and/or polyurethanes (see, for example,
The Chemistry of Organic Film Formers,
D. H. Solomon, Robert E. Krieger Publishing Co., 1977) and (4) addition polymers containing at least two (2) hydroxyl groups.
Some examples of monomeric polyalcohols having 2 to 6 hydroxyl groups which can be conveniently converted into polyacetoacetates include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-2-butyl-propanediol, 2-methylpropanediol, 3-methyl-1,5-pentanediol, di-ethylene glycol, triethylene glycol, 1,4-cyclohexyldimethanol, dipropylene glycol, trimethylolethane, trimethylolpropane, glycerol, di-trimethylolpropane, pentaerythritol and the like.
Suitable partial esters of polyalcohols with monocarboxylic acids containing 2 to 22, preferably 5 to 18 carbon atoms, the partial esters having at least 2 unreacted hydroxyl groups, include for example the reaction product of a triol, e.g. trimethylolpropane, with a monocarboxylic acid in a, for example, 1:1 molar ratio. Other su
Schoonderwoerd Nicolaas Antonius Maria
Vandevoorde Paul Marie
Akzo Aerospace Finishes V.o.F.
Cain Edward J.
McGillycuddy Joan M.
Parker Laine E.
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