Coating process with self-crosslinkable composition for electrical steel sheet

1. A coating process for electrical steel sheet using a varnish composition, the coating process comprising the steps of:

a) applying a coating layer of a varnish composition onto a surface of the electrical steel sheet wherein the varnish composition comprises:

(A) about 1 to about 95 wt % of a resin comprising nucleophilic groups selected from the group consisting of OH, NHR and SH, and electrophilic groups that can react with the nucleophilic groups, wherein the resin undergoes transacylation in its main chain and/or side chain(s) by reacting the nucleophilic groups with the electrophilic groups,

(B) about 5 to about 75 wt % of an organic solvent and/or water, wherein the wt % is based on the total weight of the varnish composition and

b) curing the applied at least one coating layer, wherein the curing is performed at curing temperatures in the range of about 200 to about 600° C. and the curing is done in a time period of about 10 seconds to about 1 minute,

wherein the electrophilic groups are carbon atoms bound via double bonds to oxygen atoms in esters.

2. The coating process according to claim 1 wherein the varnish composition comprises

(A) about 5 to about 60 wt % of the resin, wherein the resin undergoes transacylation in its main chain and/or side chain(s),

(B) about 10 to about 70 wt % of the organic solvent and/or water,

(C) 0 to about 20 wt % of a resin different from (A),

(D) about 0.1 to about 10 wt % of a customary additive,

(E) about 0.1 to about 30 wt % of a pigment, filler and/or nano-scaled particle and/or monomeric and/or polymeric element-organic compound,

wherein the wt % is based on the total weight of the varnish composition (A) to (E) and wherein the amount of component (C) is smaller than the amount of component (A).

3. The coating process according to claim 1 wherein the resin of component (A) comprises OH and/or SH as nucleophilic groups.

4. The coating process according to claim 1 wherein the resin of component (A) comprises polyurethanes and/or polyesters comprising the nucleophilic groups and the electrophilic groups wherein the resin undergoes transacylation in its main chain and/or in its side chain(s) by reacting the nucleophilic groups with the electrophilic groups.

5. The coating process according to claim 1 wherein applying comprises applying one coating layer of the varnish composition onto the surface of the electrical steel sheet.

6. The coating process according to claim 1 wherein the curing takes place at temperatures providing a PMT (peak metal temperature) in the range of about 180 to about 260° C.

7. A process for the production of an electrical steel sheet core, the process comprising:

applying a coating layer of a varnish composition onto a surface of the electrical steel sheet wherein the varnish composition comprises:

(A) about 1 to about 95 wt % of a resin comprising nucleophilic groups selected from the group consisting of OH, NHR and SH, and electrophilic groups that can react with the nucleophilic groups, wherein the resin undergoes transacylation in its main chain and/or side chain(s) by reacting the nucleophilic groups with the electrophilic groups,

(B) about 5 to about 75 wt % of an organic solvent and/or water,

wherein the wt % is based on the total weight of the varnish composition and curing the applied at least one coating layer, wherein the curing is performed at curing temperatures in the range of about 200 to about 600° C. and the curing is done in a time period of about 10 seconds to about 1 minute,

wherein the electrophilic groups are carbon atoms bound via double bonds to oxygen atoms in esters,

punching out parts of the coated electrical steel sheet after curing,

stacking and assembling the parts to form a sheet core by technical means chosen from welding, clamping, interlocking, aluminium die casting and riveting.

8. The process according to claim 7 wherein the technical mean comprises welding.

9. An electrical steel sheet coated with a coating process using a varnish composition, the coating process comprising the steps of:

a) applying a coating layer of a varnish composition onto a surface of the electrical steel sheet wherein the varnish composition comprises:

(A) about 1 to about 95 wt % of a resin comprising nucleophilic groups selected from the group consisting of OH, NHR and SH, and electrophilic groups that can react with the nucleophilic groups, wherein the resin undergoes transacylation in its main chain and/or side chain(s) by reacting the nucleophilic groups with the electrophilic groups,

(B) about 5 to about 75 wt % of an organic solvent and/or water, wherein the wt % is based on the total weight of the varnish composition and

b) curing the applied coating layer, wherein the curing is performed at curing temperatures in the range of about 200 to about 600° C. and the curing is done in a time period of about 10 seconds to about 1 minute,

wherein the electrophilic groups are carbon atoms bound via double bonds to oxygen atoms in esters.

10. The process according to claim 1 wherein the varnish composition of step a) additionally comprises

(C) 0 to about 40 wt % of a resin different from (A),

(D) 0 to about 10 wt % of a customary additive,

wherein the wt % is based on the total weight of the varnish composition and wherein the amount of component (C) is smaller than the amount of component (A).

11. The process according to claim 2 wherein the varnish composition of step a) additionally comprises

(E) 0 to about 40 wt % of a pigment, filler and/or nano-scaled particle and/or monomeric and/or polymeric element-organic compound.