Process for forming multilayered coating film

Disclosed is a double-layer coating film formation method that includes a step (1) wherein a base coating is applied to a substrate to form an uncured base coating film, a step (2) wherein a clear coating is applied on the uncured base coating film obtained in the aforementioned step (1) to form an uncured clear coating film, and a step (3) wherein the uncured base coating film and uncured clear coating film obtained in the aforementioned step (1) and step (2) are heat cured to form a double-layer coating film. This double-layer coating film formation method is characterized by (a) the L value of the aforementioned uncured base coating film being 70 to 105 in 25° reflection and 20 to 50 in 75° reflection, (b) the value of L, found by subtracting the L value for the aforementioned uncured base coating film from the L value of the aforementioned double-layer coating film at 25° reflection, being -0.3 to 0.15, and (c) the value of L, found by subtracting the L value of the aforementioned uncured base coating film from the L value of the aforementioned double-layer coating film at 75° reflection, being -0.2 to 0.4. Also, the aforementioned clear coating is a clear coating compound that contains: an acrylic resin, which is obtained from a monomer mixture containing 10 to 15% by mass long-chain (meth)acrylic acid ester monomer, in which the ester portion is a straight-chain hydrocarbon group of 9 to 15 carbon atoms, relative to the total quantity of monomer solids, a carboxy group-containing (meth)acrylic monomer, and a hydroxy group-containing (meth)acrylic monomer, the number-average molecular weight of which being 4000 to 6000 and the solids acid number of which being 1 to 5 mg KOH/g; a polyisocyanate compound; and cross-linked resin particles. The double-layer coating film formation method makes possible the formation of a double-layer coating film of superior design, acid resistance, and scratch resistance.