Coating including primer
There is provided a method of coating a substrate comprising applying a first mixture where the first mixture reacts to form covalent bonds to the substrate surface and where the unreacted parts of the first mixture undergo diffusive mixing with a second layer, which is applied on top of the first mixture. This avoids creation of a weak layer, which may otherwise give lower adhesion. The adhesion as well as mechanical properties including the scratch resistance are improved.
1 . A method of coating a substrate (A), said method comprising the steps of
a) providing a substrate (A), said substrate (A) comprising at least a first type of chemical groups, at least a fraction of the first type of chemical groups is at the surface of the substrate (A),
b) applying a layer (B) of a first mixture on the surface of the substrate (A), said first mixture comprising a compound comprising at least a second type of chemical groups, wherein the first type of chemical groups have the ability to react with the second type of chemical groups to form a covalent bond (C),
c) initiating a reaction to form the covalent bond (C) by reaction of the first type of chemical groups and the second type of chemical groups, wherein a reacted layer of a reacted first mixture is formed from the first mixture, wherein the reacted first mixture excludes those molecules of the compound that comprise at least the second type of chemical groups which are covalently bound to the substrate,
d) applying a layer (D) of a second mixture on the reacted layer of the reacted first mixture with the reacted first mixture and the second mixture diffusively mixing so that the concentration calculated by weight of any compound in the reacted layer of the reacted first mixture deviates at most 10% from the concentration of the same compound calculated in both the reacted layer of the reacted first mixture and the layer of the second mixture taken together, within 1 minute after application of the layer (D) of the second mixture at 20° C.,
e) curing the resulting mixture of the reacted first mixture and the second mixture to form a coating.
2 . The method according to claim 1 , wherein the substrate (A) comprises at least one selected from the group consisting of melamine formaldehyde resin, urea formaldehyde resin, poly paraphenylene terephthalamide, polyamide, polyethylene, PMMA, polycarbonate, cyclic olefin copolymers, polyester, polyurethane, acrylonitrile butadiene styrene copolymer (ABS), PVC, polybutadiene, blends of olefins sourced from recycled plastics, a compound comprising at least one abstractable hydrogen atom, and polypropene.
3 . The method according to claim 1 , wherein the first type of chemical groups is a secondary amine and wherein the second type of chemical groups is a carbon-carbon double bond with an electron withdrawing group on at least one side of the carbon-carbon double bond.
4 . The method according to claim 3 , wherein the electron withdrawing group is at least one selected from the group consisting of a triflyl group, a trihalide group, a cyano group, a sulfonate group, a nitro group, an ammonium group, an aldehyde group, a keto group, a carboxylic group, an acyl chloride group, an ester group, an amide group, and ether group, and a halide.
5 . The method according to claim 3 , wherein the compound comprising at least one carbon-carbon double bond is at least one selected from the group consisting of maleic anhydride and maleimide.
6 . The method according to claim 3 , wherein the compound comprising at least one carbon-carbon double bond is at least one selected from the group consisting of a maleate and a fumarate.
7 . The method according to claim 3 , wherein the compound comprising at least one carbon-carbon double bond is at least one selected from the group consisting of an acrylate and a methacrylate.
8 . The method according to claim 1 , wherein the first type of chemical groups is an abstractable hydrogen and wherein the second type of chemical groups is a group with the ability to abstract a hydrogen.
9 . The method according to claim 1 , wherein the reaction in step c) is initiated with actinic radiation.
10 . The method according to claim 1 , wherein the viscosity of the first mixture is 10 Pa*s or lower at the temperature where diffusive mixing occurs.
11 . The method according to claim 1 , wherein the first mixture and the second mixture have different viscosities.
12 . The method according to claim 1 , wherein the first mixture and the second mixture are the same and wherein one of the applied layers is thinner than the other.
13 . The method according to claim 1 , wherein at least one additional layer (G) is added, which additional layer (G) is able to form a solid coating.
14 . The method according to claim 1 , wherein at least one intermediate layer (H) is added after step c) and before step d).
15 . The method according to claim 1 , wherein each molecule of the compound in the first mixture comprises at least two chemical groups of the second type.
16 . The method according to claim 1 , wherein only a fraction of the chemical groups of the second type are reacted in step c).