Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-08-22
2003-04-01
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of metal
C428S413000, C428S458000, C428S460000, C428S461000, C525S016000, C204S499000
Reexamination Certificate
active
06541120
ABSTRACT:
The invention relates to cathodically depositable dipping lacquers (CDL), their production and their use in methods of coating electrically conductive substrates by cathodic dipcoating.
A wide variety of CDL coating compositions are known. The patent literature discloses many examples of ecologically advantageous, lead-free CDL coating compositions containing many different metal compounds, especially tin and/or bismuth compounds, as crosslinking catalysts. For example, there are known from WO 93/24578 CDL coating compositions that contain bismuth salts of aliphatic hydroxycarboxylic acids as catalysts. WO 98/10024 describes CDL coating compositions containing catalytically active mixtures of bismuth and aminocarboxylic acids. EP-A-0 509 437 describes CDL coating compositions that contain dialkyltin dicarboxylates derived from aromatic carboxylic acids as crosslinking catalysts, as well as bismuth or zirconium compounds as further catalysts.
CDL baths are pumped round continuously and are subjected to shear stress. An important criterion for the quality of CDL coating compositions is their shear stability. Shear instability manifests itself in the case of CDL coating compositions as sedimentation. Such sedimentation leads in practice to the inclusion of dirt in the CDL layer, especially during the process of applying CDL coatings to substrate surfaces in the horizontal position. Such sedimentation phenomena can be quantified in the laboratory by determining the sieving residue of CDL baths.
The object of the invention is to provide lead-free cathodically depositable coating compositions having good shear stability.
It has been found that this object can be achieved with aqueous lead-free CDL coating compositions containing binders and, optionally, crosslinking agents, pigments, and/or additives conventionally employed in lacquers, which coating compositions are characterised in that they contain sulfonic acid salts of vanadium, manganese, iron, zinc, zirconium, silver, tin, lanthanum, cerium and/or bismuth and/or sulfonic acid salts of organometallic compounds, preferably of tin, in a total amount of from 0.2 to 2 wt. %, calculated as metal and based on the resin solids (based on binders, any crosslinking agents present and any other resins contained in the CDL coating composition, such as, for example, paste resins).
The lead-free CDL coating compositions according to the invention are aqueous electro-dipping lacquers known per se which can be deposited at the cathode, to which there are added sulfonic acid salts of vanadium, manganese, iron, zinc, zirconium, silver, tin, lanthanum, cerium and/or bismuth and/or organometallic sulfonic acid salts, preferably of tin, for example, as crosslinking catalysts replacing lead catalysts.
The CDL coating compositions according to the invention are aqueous coating compositions having a solids content of, for example, from 10 to 30 wt. %. The solids content consists of the resin solids, of the content of sulfonic acid salts or organometallic sulfonic acid salts that is essential to the invention, any pigments and/or fillers and further additives that may be present. The resin solids consists of conventional CDL binders, which carry cationic substituents or substituents that can be converted into cationic groups as well as groups capable of chemical crosslinking, and any CDL paste resins and crosslinking agents that may be present. The cationic groups may be cationic groups or basic groups that can be converted into cationic groups, for example, amino, ammonium, e.g., quarternary ammonium, phosphonium and/or sulfonium groups. Binders having basic groups are preferred. Basic groups containing nitrogen, such as amino groups, are particularly preferred. Such groups may be present in quaternary form or they are converted into cationic groups in the manner known to the person skilled in the art using a conventional neutralising agent, especially an inorganic or organic acid, such as, for example, a sulfonic acid such as amidosulfonic acid (sulfamic acid) or methanesulfonic acid, lactic acid, formic acid, acetic acid. The degree of neutralisation is, for example, from 20 to 80%.
In addition to the sulfonic acid salts present according to the invention, the CDL coating compositions may contain additives conventionally employed in lacquers, for example conventionally employed in CDL coating compositions, Examples thereof are wetting agents, anticratering agents, flow agents, antifoams, as well as organic solvents customarily used for CDL coating compositions. Examples of such solvents are alcohols, such as, for example, cyclohexanol, 2-ethylhexanol; glycol ethers, such as, for example, methoxypropanol, ethoxypropanol, butoxyethanol, diethylene glycol diethyl ether; ketones, such as for example, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone; hydrocarbons.
The cationic or basic binders may be, for example, resins which contain primary, secondary and/or tertiary amino groups and the amine numbers of which are, for example, from 20 to 250 mg KOH/g. The weight-average molar mass (Mw) of the CDL resins is preferably from 300 to 10,000. The resins that may be used according to the invention are subject to no limitation. It is possible to use the many different self-crosslinking CDL binders and CDL binder/crosslinking agent combinations that crosslink by external means known from the extensive patent literature. Examples of such CDL resins are amino (meth)acrylate resins, aminoepoxy resins, aminoepoxy resins having terminal double bonds, aminoepoxy resins having primary OH groups, aminopolyurethane resins, amino-group-containing polybutadiene resins or modified epoxy resin-carbon dioxide-amine reaction products. Such binders may be self-crosslinking, or they are used in admixture with known crosslinking agents familiar to the person skilled in the art. Examples of such crosslinking agents are aminoplastic resins, blocked polyisocyanates, crosslinking agents having terminal double bonds, polyepoxy compounds, crosslinking agents having cyclic carbonate groups, or crosslinking agents that contain groups capable of transesterification and/or transamidation.
In addition to the CDL binders and any crosslinking agent that may be present, and the content of sulfonic acid salts that is essential to the invention, the CDL coating compositions according to the invention may contain pigments, fillers, and/or additives conventionally employed in lacquers. Suitable pigments and/or fillers are the conventional inorganic and/or organic pigments. Examples are carbon black, titanium dioxide, iron oxide, kaolin, talcum or silicon dioxide, phthalocyanine pigments and quinacridone pigments, as well as anticorrosive pigments, such as zinc phosphate. The nature and amount of the pigments are dependent on the intended use of the CDL coating compositions. If clear coatings are to be obtained, then no pigments or only transparent pigments, such as, for example, micronised titanium dioxide or silicon dioxide, are used. If opacifying coatings are to be applied, then the CDL bath preferably contains colour-giving pigments.
The CDL coating compositions according to the invention contain sulfonic acid salts of vanadium, manganese, iron, zinc, zirconium, silver, tin lanthanum, cerium and/or bismuth and/or organometallic sulfonic acid salts, preferably of the above metals and particularly preferably of tin. Sulfonic acid salts of bismuth and organotin sulfonic acid salts are preferred. The sulfonic acid salts and organometallic sulfonic acid salts, together also referred to hereinbelow as “sulfonic acid salts” for short, are salts derived from one or more mono- or poly-basic, preferably water-soluble sulfonic acids. Examples of sulfonic acid from which the sulfonic acid salts contained in the CDL coating compositions according to the invention may be derived are amidosulfonic acid and/or organic sulfonic acids, such as N-alkylamidosulfonic acids, for example N-C
1
-C
4
-alkylamidosulfonic acids; alkanesulfonic acids, which may be substituted in the alkyl radical, such as m
Klein Klausjörg
Kohhirt Walter
Dawson Robert
E. I. du Pont de Nemours and Company
Keehan Christopher
LandOfFree
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