Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2000-12-27
2002-06-04
Mayekar, Kishor (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S486000, C204S505000, C204S506000, C523S415000
Reexamination Certificate
active
06398934
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a concentrate suitable for the preparation of cathodically depositable coating compositions (i.e., cathodic electrodeposition coating compositions) and to the use thereof for the preparation of cathodic electrodeposition (“CED”) coating compositions.
BACKGROUND OF THE INVENTION
The majority of the CED coating compositions currently employed contain cathodically depositable binders having functional groups comprising active hydrogen, for example hydroxyl groups, primary and/or secondary amino groups, and blocked polyisocyanates as the cross-linking agents. The CED coating compositions are provided as one- or two-component materials, from which cathodic electrodeposition-baths can either be prepared afresh or a compensation of the solids of cathodic electrodeposition-baths in use can be carried out. The one-component materials are water-containing concentrates containing binders and cross-linking agents and, in general, pigments, whereas two-component materials include an aqueous dispersion containing binders and cross-linking agents and a separate aqueous pigment paste.
For reasons of conserving energy, there has been a desire, in particular in the automotive industry, to obtain CED coating compositions that can be stoved at low temperatures.
CED coating compositions that are curable at a low stoving temperature, which contain cathodically depositable binders that are curable with blocked polyisocyanates, and blocked polyisocyanates having isocyanate groups which are bonded to aromatic rings and are blocked with oximes, as the curing agents, are for example known from EP-A-0 199 663, U.S. Pat. Nos. 4,596,744, 4,872,961, 5,096,555 and 5,461,091. The CED materials disclosed therein are chemically unstable. They undergo to a certain extent a decomposition that surprisingly creates no adverse effects in CED coating, but creates problems during transport and storage of the CED materials. During the decomposition, a pressure build-up occurs within the containers containing the CED coating compositions. The speed of the decomposition process depends in particular on the temperature and may lead to an accelerated pressure build-up at high temperatures. The handling of these CED coating compositions in open containers is not allowed under applicable legal restrictions and also for practical reasons. Although the use of pressure containers or pressure compensation containers could be a possible solution for the problem, these CED coating compositions have not been successful, however, in practice because of the requirements involved.
The object of the invention is to provide CED coating compositions which are curable at a low stoving temperature, and which overcome the aforementioned problems.
SUMMARY OF THE INVENTION
The present invention provides a two-component concentrate suitable for the preparation of cathodic electrodeposition coating compositions, comprising, in combination, (a) a binder component comprising an aqueous dispersion of a CED binder having groups comprising active hydrogen that are cross-linkable using blocked polyisocyanate; and (b) a cross-linking component comprising an anhydrous, organic solution of an oxime-blocked isocyanate-functional adduct of an aromatic polyisocyanate and at least one compound comprising at least one group capable of addition towards isocyanate and at least one tertiary amino group.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The concentrate according to the invention contains a binder component and a cross-linking component. The binder component is an aqueous dispersion of a CED binder having functional groups comprising active hydrogen that can be chemically cross-linked by using the oxime-blocked isocyanate groups of the cross-linking component.
CED binders carry cationic groups or groups able to be converted into cationic groups, e.g. alkaline groups, e.g. amino groups, ammonium groups, for example quaternary ammonium, phosphonium and/or sulphonium groups. Preferred are alkaline groups, in particular preferred are nitrogen-containing alkaline groups, such as amino groups. These groups may be present in quaternised form, or they are converted into cationic groups with a conventional neutralising agent, for example lactic acid, formic acid, acetic acid, methanesulfonic acid. The groups able to be converted into cationic groups may be present in completely or partially neutralised form. They are preferably resins containing amino groups, preferably tertiary amino groups, the total amine value of which is 20 to 150, preferably 50 to 100 mg KOH/g. The total amine value consists in this case of 50 to 100, preferably 80 to 100, in particular preferably 100% of tertiary amino groups. The weight average molecular mass (Mw) of these binders is preferably about 300 to 10000.
The CED binders contain functional groups comprising active hydrogen that can be cross-linked with the oxime-blocked polyisocyanate. Examples of such functional groups are primary amino groups, secondary amino groups and in particular hydroxyl groups. Combinations of these groups may be present in the same CED binder, but preferably there are no primary or secondary amino groups apart from the hydroxyl groups. The proportion of the groups comprising active hydrogen in the CED binders corresponds to an active hydrogen value of 50 to 300 mg KOH/g, corresponding to a sum of primary amine value, secondary amine value and hydroxyl value. The hydroxyl value is generally in the range of 50 to 250 mg KOH/g.
CED binders suitable for use in the present invention are known to the person skilled in the art and are conventional amino(meth)acrylic resins, aminopolyurethane resins, amino group-containing polybutadiene resins, epoxy resin-carbon dioxydeamine-reaction products and in particular aminoepoxy resins, for example aminoepoxy resins having primary OH-groups.
An aqueous dispersion of the CED binders is prepared according to methods known to those skilled in the art. For example, the CED binders may be neutralised with acid and diluted with water. Organic solvents that may be present can be removed (or eliminated) by vacuum distillation or other known method. It is also possible to prepare the CED binder in a way to minimize the presence of organic solvents, such as neutralising with acid in the low-solvent state or as a solvent-free melt and then diluting with water to make the dispersion. In addition, the CED binders can also be neutralised with acid as a solution in an olefinically unsaturated monomer capable of radical polymerisation, and then be converted into an aqueous dispersion by diluting with water, followed by a subsequent total polymerisation of the monomer capable of radical polymerisation.
The cross-linking component of the concentrate according to the invention is an anhydrous, organic solution of an oxime-blocked isocyanate-functional reaction product of aromatic polyisocyanate and at least one compound comprising at least one group capable of addition towards isocyanate and at least one tertiary amino group. The reaction products blocked with oxime are designated in short as “cross-linking agents” herein.
The cross-linking agents are prepared by reacting one or more aromatic polyisocyanates with at least one compound comprising at least one group capable of addition towards isocyanate and at least one tertiary amino group and one or more oximes (as the blocking agents). The reaction can take place at temperatures of 20 to 75° C. as a one-step process or in general as a multi-step process. In a multi-step process, for example, at first an isocyanate-functional reaction product is prepared, the free isocyanate groups of which are blocked with oxime in a subsequent step. Alternatively, at first the aromatic polyisocyanate is partially blocked with oxime prior to the reaction with the further components.
Examples of aromatic polyisocyanates suitable for preparing the cross-linking agents are aromatic diisocyanates (diisocyanates having at least one isocyanate group bonded to an aromatic ring) such as phenylene, toluylene, xylyl
Hoenig Helmut
Klein Klausjoerg
Matzer Herbert
Pampouchidis Georg
Valtrovic Manfred
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Mayekar Kishor
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