| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a spark plug which exhibits an excellent insulation property by providing the coat layer having a sufficient thickness at a base end side surface of a long leg portion for a relatively long period of time without forming a bridge for coupling a front end of the long leg portion and a ground electrode, and which has a sufficient insulation property even if a coat layer extends across the entire region of the long leg portion, and to provide a method therefor. Ž<P>SOLUTION: The spark plug 1 comprises: an insulator 2; a body metal fitting 3; a center electrode 5; and a ground electrode 27. The insulator 2 has a long leg portion 13 for forming a gap 30 between a front end side inner periphery of the body metal fitting 3 and the long leg portion. A coat layer 41 comprising insulating oil is formed on at least the base end side surface of the surface of the long leg portion 13. In addition, the viscosity of the insulating oil forming the coat layer 41 is 3,000 cs or more. The mass per unit area of the insulating oil with respect to the surface area of the long leg portion 13 is 0.005 mg/mm<SP>2</SP>to 0.05 mg/mm<SP>2</SP>. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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