Method for coating metal substrates with a radically polymerizable coating agent and coated substrates
The invention relates to a method and coating agents used in the method which provide good adherence to and good corrosion protection of metal substrates; the coating coating agents are cross-linkable via radical polymerization. Adhesion promoting compounds are present in the conversion layer in a quantity of about 0.01 to 40 weight percent and contain, on average, one reactive unsaturated group and at least one H-active group per molecule.
1. An aqueous coating agent for producing a conversion layer on metal substrates, said coating agent being chromate-free and comprising:
water;
one or more complex fluorides of at least one element selected from Hf, B, Ti, Zr and Si;
at least one ion selected from phosphate, manganate, vanadate, tungstate or molybdate ions
from 0.01 to 40 wt. % of at least one low molecular weight oligomeric or monomeric compound which contains at least one H-active group that is an acidic group and at least one further functional group crosslinkable by radical polymerization,
said oligomeric compound being selected from polyester or polyether oligomers having lateral or terminal (meth)acrylic groups,
said monomeric compound being selected from esters or amides of low molecular weight carboxylic acids, or other monomers which contain activated double bonds;
wherein pH of the aqueous coating agent is below 6; and wherein the low molecular weight compound is present in an amount of 0.5 to 25 wt. % and comprises from 0.1 to 15 wt. % of acidic derivatives of phosphoric acid or phosphoric acid with (meth)acrylates.
2. The aqueous coating agent as claimed in claim 1 , further comprising at least one auxiliary substance selected from reactive silanes, antifoams or wetting agents.
3. The aqueous coating agent as claimed in claim 1 , wherein the radically crosslinkable functional group is an unsaturated carboxylic ester or carboxamide group.
4. The aqueous coating agent as claimed in claim 1 , said coating agent comprising from 0.1 to 25 wt.% of the at least one low molecular weight compound.
5. The aqueous coating agent as claimed in claim 1 , wherein the radically crosslinkable functional group is an acrylic or methacrylic group.
6. The aqueous coating agent as claimed in claim 1 , wherein the low molecular weight compound is selected such that said aqueous coating agent is stable against phase separation or precipitation for more than 3 hours at the pH of the aqueous coating agent.
7. The aqueous coating agent as claimed in claim 1 , wherein said at least one element is present as fluoric acids, or alkali metal and/or ammonium salts.
8. The aqueous coating agent as claimed in claim 1 , wherein said at least one element is present as hexafluorozirconic acid, hexafluorotitanic acid or hexafluorosilicates.
9. An aqueous coating agent for producing a conversion layer on metal substrates, said coating agent being chromate-free and comprising:
water;
phosphoric acid;
hexafluorotitanic acid;
manganese (II);
from 0.01 to 40 wt. % of at least one low molecular weight oligomeric or monomeric compound which contains at least one H-active group and at least one further functional group crosslinkable by radical polymerization, said compound being selected from esters or amides of low molecular weight carboxylic acids, polyester or polyether oligomers having lateral or terminal (meth)acrylic groups, or other monomers which contain activated double bonds; wherein pH of the aqueous coating agent is below 6, wherein said at least one low molecular weight compound comprises a mixture of mono-, di- and tri-esters of the phosphoric acid of 2-hydroxyethyl acrylate.
10. The aqueous coating agent as claimed in claim 9 , further comprising at least one of Zn, Mo and an aminomethyl-substituted polyvinylphenol polymer.
11. The aqueous coating agent as claimed in claim 9 , further comprising a polyvinylphenol polymer.
12. The aqueous coating agent as claimed in claim 9 , wherein no polymerization initiators are present in the aqueous coating agent such that said at least one H-active group and at least one further functional group crosslinkable by radical polymerization remain uncross-linked after deposit on a metal substrate and remain cross-linkable by application of a second coating comprising initiator.