Abstract: A resistor-containing spark plug 100 has an alumina insulator 2 coated with a glaze layer 2d, the glaze layer 2d has a lead component content of 1 mol % or lower in terms of PbO and containing a silicon component, a boron component, a zinc and/or alkaline earth metal component, and an alkali metal component. The insulator has, in an axially central position thereof, a projection part protruding from the outer circumferential surface thereof and extending in a circumferential direction. That main body of the insulator which is located adjacent to the projection part on the rear side thereof, which is the side opposite to the front side facing the center electrode in the axial direction, has a base portion having a cylindrical outer circumference. The outer circumference of the base portion is covered with the glaze layer which, when examined by the method as provided for in JIS B 0601, gives a surface roughness curve having a maximum height Ry of 10 &mgr;m or smaller.

Abstract: A spark plug retains a resistor and has formed on alumina-based insulator a glaze layer, in which the glaze layer contains Pb component in a content of 1 mol % or less in terms of PbO, contains Si component, B component, Zn component, Al component, Ba component and/or Sr component, and contains F component in a content of 1 mol % or less. In addition, the glaze layer contains one kind or more of alkaline metal components, with Li component being necessary, and further contains one kind or more of phosphate ion, sulfate ion, fluoride ion and chloride ion in a content of 0.5 to 10 mol %. The glaze layer has a Vickers hardness Hv of 100 or more, shows excellent strength, especially impact resistance in spite of a reduced content of Pb component.

Abstract: A glaze layer 2d of the spark plug has the composition comprising 1 mol % or less of a Pb component in terms of PbO; 25 to 45 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % of Ba and/or Sr components in terms of BaO or SrO; 5 to 10 mol % in total of at least one alkaline metal component of of Na, K and Li in terms of Na2O, K2O, and Li2, respectively, where K is essential; and further, 0.5 to 5 mol % in total of one or two kinds or more of Mo, W, Ni, Co, Fe and Mn in terms of MoO3, WO3, Ni3O4, Co3O4, Fe2O3, and MnO2, respectively.

Abstract: A spark plug retains a resistor and has formed on alumina-based insulator a glaze layer, in which the glaze layer contains Pb component in a content of 1 mol % or less in terms of PbO, contains Si component, B component, Zn component, Al component, Ba component and/or Sr component, and contains F component in a content of 1 mol % or less. In addition, the glaze layer contains one kind or more of alkaline metal components, with Li component being necessary, and further contains one kind or more of phosphate ion, sulfate ion, fluoride ion and chloride ion in a content of 0.5 to 10 mol %. The glaze layer has a Vickers hardness Hv of 100 or more, shows excellent strength, especially impact resistance in spite of a reduced content of Pb component.

Abstract: A resistor-containing spark plug 100 has an alumina insulator 2 coated with a glaze layer 2d, the glaze layer 2d has a lead component content of 1 mol % or lower in terms of PbO and containing a silicon component, a boron component, a zinc and/or alkaline earth metal component, and an alkali metal component. The insulator has, in an axially central position thereof, a projection part protruding from the outer circumferential surface thereof and extending in a circumferential direction. That main body of the insulator which is located adjacent to the projection part on the rear side thereof, which is the side opposite to the front side facing the center electrode in the axial direction, has a base portion having a cylindrical outer circumference. The outer circumference of the base portion is covered with the glaze layer which, when examined by the method as provided for in JIS B 0601, gives a surface roughness curve having a maximum height Ry of 10 &mgr;m or smaller.

Abstract: A glaze layer 2d of the spark plug has the composition comprising 1 mol % or less of a Pb component in terms of PbO; 25 to 45 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % of Ba and/or Sr components in terms of BaO or SrO; 5 to 10 mol % in total of at least one alkaline metal component of of Na, K and Li in terms of Na2O, K2O, and Li2, respectively, where K is essential; and further, 0.5 to 5 mol % in total of one or two kinds or more of Mo, W, Ni, Co, Fe and Mn in terms of MoO3, WO3, Ni3O4, Co3O4, Fe2O3, and MnO2, respectively.