To enable to prevent corona discharge when a spark plug is wetted with water.
By forming a coating film 33 for electrostatic charging prevention (conductive coating film or resistor coating film) in a range (range shown by arrowhead A) from a part covered by a plug boot 19 out of a surface of an insulator 22 of the spark plug 13 to a part or its vicinity in which a tip side metal packing 30 is arranged, the coating film 33 for electrostatic charging prevention is formed at a part exposed without being covered by a metal housing 21 and the plug boot 19 out of the surface of the insulator 22, and this coating film 33 for electrostatic charging prevention is earth connected to the metal housing 21. By this, at the time of being wetted with water when water is adhered to the part exposed without being covered by the metal housing 21 and the plug boot 19 out of the surface of the insulator 22, electrostatic charging of moisture of the surface of the insulator 22 is prevented by the earth connected coating film 33 for electrostatic charging prevention, and it is prevented that corona discharge is generated between the moisture of the surface of the insulator 22 and the metal housing 21.
| WO/2009/119097 | SPARK PLUG |
| JP5301635 | Spark plug |
| JPH04322092 | SINTERED BODY FOR INSULATOR OF SPARK PLUG |
MAKINO HIROAKI
HASHINASHI KEN
MIWA TETSUYA
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