Method for forming electrically conductive ultrafine pattern, electrically conductive ultrafine pattern, and electric circuit

A method for forming an electrically conductive ultrafine pattern, the method comprising:

• (1) a step of applying a resin composition (a) to form a receiving layer (A) on a substrate;
• (2) a step of printing an ink (b) containing particles (b1), thereby forming a core pattern (B) made of the ink (b) on the receiving layer (A) by a reverse offset printing method,
• (3) firing or drying the printed core pattern (B) made of the particles (b1) which has been obtained at the step (2) to be a target core pattern for electrolytic plating on the receiving layer (A);
• and
• (4) a step of depositing a metal on the target core pattern formed in the step (3), thereby plating the target core pattern on the receiving layer (A) by an electrolytic plating method,
• wherein the resin composition (a) includes a urethane resin (al) having a weight average molecular weight of 5,000 or more or a vinyl resin (a2), and a medium (a3),
• wherein the urethane resin (a1) has a hydrophilic group and 2,000 to 5,500 mmol/kg of an aliphatic cyclic structure with respect to the total mass,
• wherein the vinyl resin (a2) is a vinylic copolymer containing 10 to 70 percent by mass of methyl methacrylate and 10 to 50 percent by mass of an alkyl (meth)acrylate having an alkyl group with 2 to 12 carbon atoms, and
• wherein the ink (b) contains metal nano particles as the particles (b1) and an organic compound containing a basic nitrogen atom, the metal nano particles being protected by the organic compound and dispersed in the ink (b), and the urethane resin (a1) or the vinyl resin (a2) in the resin composition (a) has a functional group capable of performing a cross-linking reaction with the organic compound which protects the metal nano particles,
• wherein the resin composition (a) includes composite resin particles each composed of a shell layer formed of the urethane resin (a1) and a core layer formed of the vinyl resin (a2).