Insulating varnish and production method therefor and insulated electric wire using same and production method therefor

1. An insulating varnish, comprising:

a polyamide-imide resin consisting of a repeat unit represented by Formula (1) below derived from a synthesis reaction between a resin component (X) and a diisocyanate component (Y),

wherein the resin component (X) is derived from a synthesis reaction between a diamine component comprising at least one aromatic diamine comprising a divalent aromatic group (R) comprising three or more aromatic rings, and an acid component in the presence of an azeotrope solvent, and

the diisocyanate component (Y) consists of a 2,4′-diphenylmethane diisocyanate (Y 1 ) and a 4,4′-diphenylmethane diisocyanate (Y 2 );

in Formula (1), R denotes the divalent aromatic group comprising three or more aromatic rings, and m and n denote an integer of from 1 to 99,

wherein the molar content of the 2,4′-diphenylmethane diisocyanate (Y 1 ) based on the total diisocyanate component (Y) ranges from 40 to 90 mole %.

2. The insulating varnish according to claim 1 , wherein

the at least one aromatic diamine comprising a divalent aromatic group (R) comprising three or more aromatic rings comprises at least one compound selected from the group consisting of a 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]ether, 9,9-bis(4-aminophenyl)fluorene, 4,4′-bis(4-aminophenoxy)biphenyl, 1,4-bis(4-aminophenoxy)benzene, and isomers thereof.

3. The insulating varnish according to claim 2 , wherein

the azeotrope solvent comprises xylene.

4. The insulating varnish according to claim 1 , wherein the molar content of the 2,4′-diphenylmethane diisocyanate (Y 1 ) based on the total diisocyanate component (Y) ranges from 40 to 80 mole %.

5. An insulating varnish producing method, comprising:

making a synthesis reaction between a diamine component comprising at least one aromatic diamine comprising a divalent aromatic group (R) comprising three or more aromatic rings, and an acid component in the presence of an azeotrope solvent, to produce a resin component (X); and

making a synthesis reaction between the resultant resin component (X), and a diisocyanate component (Y) consisting of a 2,4′-diphenylmethane diisocyanate (Y 1 ) and a 4,4′-diphenylmethane diisocyanate (Y 2 ), to produce an insulating varnish containing a polyamide-imide resin consisting of a repeat unit represented by Formula (1) below;

in Formula (1), R denotes the divalent aromatic group comprising three or more aromatic rings, and m and n denote an integer of from 1 to 99,

wherein the molar content of the 2,4′-diphenylmethane diisocyanate (Y 1 ) based on the total diisocyanate component (Y) ranges from 40 to 90 mole %.

6. The insulating varnish producing method according to claim 5 , wherein

the at least one aromatic diamine comprising a divalent aromatic group (R) comprising three or more aromatic rings comprises at least one compound selected from the group consisting of a 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]ether, 9,9-bis(4-aminophenyl)fluorene, 4,4′-bis(4-aminophenoxy)biphenyl, 1,4-bis(4-aminophenoxy)benzene, and isomers thereof.

7. The insulating varnish producing method according to claim 5 , wherein

the azeotrope solvent comprises xylene.

8. An insulated electric wire, comprising:

a conductor or another insulating coating; and

the insulating varnish according to claim 1 applied thereto and baked to form an insulating coating.

9. The insulated electric wire according to claim 8 , having a substantially rectangular cross section.

10. An insulated electric wire producing method, comprising:

applying the insulating varnish according to claim 1 to a conductor having a circular cross section, and baking it to thereby form an insulating coating; and

rolling the conductor and the insulating coating, to form an insulated electric wire having a substantially rectangular cross section.