Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2000-06-12
2002-04-09
Mayekar, K. (Department: 1741)
Stock material or miscellaneous articles
Composite
Of metal
C204S486000, C204S488000, C204S499000, C204S484000
Reexamination Certificate
active
06368719
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing automotive bodies or automotive body parts coated with multiple coating layers.
2. Description of Related Art
It is known from U.S. Pat. No. 5,908,667 to provide automotive bodies and automotive body parts with a multi-layer coating comprising a corrosion protection ectrocoating layer, a second electrocoating layer determining the color shade and an outer protective clear coat layer.
It is known from U.S. Pat. No. 5,882,734 to provide automotive bodies and automotive body parts with a multi-layer coating comprising two successive electrodipcoated layers, a base coat layer determining the color shade and an outer protective clear coat layer.
For reasons of rationalising procedures and saving on materials, in automotive coating there is a need to reduce the number of operations and of coating layers without, however, allowing substantial sacrifices to be made in terms of the conventional overall characteristics of the coatings obtained. Automotive coatings have to fulfil the reqirements of car manufacturers in particular as regards corrosion protection, stone chip resistance and weathering resistance. With respect to corrosion protection, an electrocoating composition must have high throwing power. “Throwing power” is a term of art used to identify the ability of an electrocoating composition to be deposited within voids of a three-dimensional substrate, which is significant for effective corrosion protection. In other words, without high throwing power the electrocoating agent has only low ability to coat recesses, crevices and other internal surfaces of the automotive body and cannot provide adequate corrosion resistance to automotive bodies and body parts. The automotive bodies would be prone to rusting from the internal surface.
SUMMARY OF THE INVENTION
The present invention satisfies the need for a process for preparing automotive coatings which saves on materials and comprises few process steps. The coatings prepared using the process of the present invention also meet the high demands made of automotive coatings, in particular as regards corrosion protection, including corrosion protection of internal surfaces, stone chip resistance and weathering resistance.
Thus the present invention is a process for preparing a multi-layer coating in which a first coating layer of a cathodic electrodeposition coating composition is applied by cathodic electrodeposition to an electrically conductive automotive body or an electrically conductive automotive body part and, as the outer coating layer, a clear coating is applied, in which between the application of the cathodic electrodeposition coating layer and the clear coating a further coating layer can be applied, and in which the cathodic electrodeposition coating composition contains, as the cathodic electrodeposition binder, a seed polymer with an amine value of 30 to 100 mg KOH/g and a hydroxyl value of 50 to 200 mg KOH/g, which can be prepared by radical polymerisation of 70 to 97 wt-% of a monomer mixture comprising hydroxyfunctional olefinically unsaturated monomer (one or more) and amino-functional olefinically unsaturated monomer (one or more) in the presence of 3 to 30 wt-% of an aminoepoxy resin.
A first embodiment of the invention comprises a process for preparing a multi-layer coating in which a coating layer of a cathodic electrodeposition coating composition determining the color shade of the multi-layer coating is cathodically electrodeposited onto an electrically conductive automotive body or an electrically conductive automotive body part and is then baked and thereafter is provided with a clear coating, in which the cathodic electrodeposition coating composition contains, as the cathodic electrodeposition binder, a seed polymer with an amine value of 30 to 100 mg KOH/g and a hydroxyl value of 50 to 200 mg KOH/g, which can be prepared by radical polymerisation of 70 to 97 wt-% of a monomer mixture comprising hydroxy-functional olefinically unsaturated monomer and amino-functional olefinically unsaturated monomer in the presence of 3 to 30 wt-% of an aminoepoxy resin.
A second embodiment of the invention comprises a process for preparing a multi-layer coating in which a first coating layer of a cathodic electrodeposition coating composition is cathodically electrodeposited onto an electrically conductive automotive body or an electrically conductive automotive body part and baked, where, before or after baking the cathodic electrodeposition coating layer, a coating layer of a liquid coating composition determining the color shade of the multi-layer coating is sprayed on and is then provided with a clear coating, in which the cathodic electrodeposition coating composition contains, as the cathodic electrodeposition binder, a seed polymer with an amine value of 30 to 100 mg KOH/g and a hydroxyl value of 50 to 200 mg KOH/g, which can be prepared by radical polymerisation of 70 to 97 wt-% of a monomer mixture comprising hydroxy-functional olefinically unsaturated monomer and amino-functional olefinically unsaturated monomer in the presence of 3 to 30 wt-% of an aminoepoxy resin.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The cathodic electrodeposition coating composition used in the process according to the invention for applying the first coating layer is an aqueous coating composition with a solids content of for example 10 to 30 wt-%. The solid comprises the seed polymer used as the cathodic electrodeposition binder, described below in more detail, and cross-linking agents, pigments and optionally additional binders, paste resin, fillers and non-volatile additives conventionally used in coatings.
The cathodic electrodeposition coating composition used in the process according to the invention contains as the cathodic electrodeposition binder an aminoepoxy/vinyl polymer hybrid binder. This is a seed polymer with an amine value of 30 to 100 mg KOH/g and a hydroxyl value of 50 to 200 mg KOH/g, which can be obtained by radical polymerisation of 70 to 97 wt-% of a monomer mixture comprising hydroxy-functional olefinically unsaturated monomers and amino-functional olefinically unsaturated monomers in the presence of 3 to 30 wt-% of an aminoepoxy resin.
Aminoepoxy resins are known to the person skilled in the art as cathodic electrodeposition binders and are for example described in the patent literature in a vast range of modifications. They are addition products of amine compounds and polyepoxides. Although said addition products are preferred representatives of aminoepoxy resins, the term “aminoepoxy resin” used here is intended to include aminoepoxy resin derivatives such as epoxide/carbon dioxide/amine reaction products. Epoxide/carbon dioxide/amine reaction products are to be understood as addition products of amine compounds and partially or completely carbonated polyepoxides. Partially or completely carbonated polyepoxides are polyepoxides in which some or all epoxy groups have been reacted with carbon dioxide to give 5-membered cyclic carbonate groups, so-called 2-oxo-1,3-dioxolan-4-yl groups. The amino groups can be present as substituents and/or as a component of the polymer backbone in the aminoepoxy resin.
Aminoepoxy resins can for example be prepared by reacting aromatic epoxy resins with primary and/or secondary mono- and/or polyamines. The reaction can be carried out in organic solution or in the melt. If the reaction is performed in organic solution, water-miscible solvents, for example alcohols such as isopropanol, isobutanol, n-butanol; glycol ethers such as methoxypropanol, butoxyethanol; glycol ether esters such as butyl glycol acetate, or water-immiscible solvents such as xylene can be used as solvents or solvent mixtures. Aromatic epoxy resins include epoxy group containing aromatic polyglycidyl ethers. Aromatic polyglycidyl ethers can be obtained for example from reacting polyphenols, preferably diphenols and in particular multi-nuclear diphenols, with epichlorohydrin. To synthesise aminoepoxy resins, it
Doessel Karl-Friedrich
Klein Klausjoerg
Kuehhirt Walter
Siever Ludwig
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Mayekar K.
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