JP2007042656A - Spark plug and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug in which Pb content quantity in a glaze can be greatly reduced, thereby complying with the increasing trend of environmental protection. <P>SOLUTION: In the glazing layer 2d of a spark plug 100, the total content of alkaline metal component is contained to 12 wt.% or less (including 0 wt.%), the content of B component is contained to 20-35 wt.% in oxide conversion of B<SB>2</SB>O<SB>3</SB>, and Ti and Zr are blended in the ratio of 2-10 wt.% in oxide conversion weight respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug and a manufacturing method thereof.

  A spark plug used for ignition of an internal combustion engine such as an automobile engine is generally provided with an insulator made of alumina ceramic or the like inside a metal shell to which a ground electrode is attached, and inside the insulator. It has a structure in which a center electrode is arranged. The insulator protrudes in the axial direction from the rear opening of the metal shell, and a terminal metal fitting is arranged inside the protruding portion, and this is a central electrode through a conductive glass seal layer or a resistor formed by the glass sealing process. Connected. Then, by applying a high voltage via the terminal fitting, a spark discharge is generated in the gap formed between the ground electrode and the center electrode.

  However, if the conditions such as the temperature of the plug rises or the ambient humidity rises, the terminal metal fitting and the main metal fitting do not ignite the gap even when a high voltage is applied and wrap around the surface of the insulator protrusion. In some cases, a so-called flashover phenomenon occurs in which discharge occurs between the two. Therefore, in most spark plugs that are generally used, a glaze layer is formed on the insulator surface mainly to prevent this flashover phenomenon. On the other hand, the glaze layer also plays a role of smoothing the surface of the insulator to prevent contamination and increasing chemical or mechanical strength.

Formation of the glaze layer on the insulator is performed by applying a glaze slurry on the surface of the insulator and firing it (referred to as “glazing”). In the case of an alumina insulator for a spark plug, a glaze layer is formed by post-baking at a calcination temperature of 1000 to 1100 ° C. with respect to a baked insulator, so a relatively large amount of PbO is blended in a silicate glass. Conventionally, lead silicate glass-based glazes with a lower softening temperature have been used. However, this has the following drawbacks.
(1) The linear expansion coefficient is small as compared with the alumina-based insulating material used as a base, and the resulting glaze layer is likely to be cracked.
(2) Despite containing a considerable amount of PbO, the smoldering temperature is still as high as 1000 ° C. or higher. In the spark plug manufacturing process, calcination is often performed at the same time as the glass sealing process in order to reduce the number of steps. However, when the calcination temperature is high as described above, there is a problem that oxidation of the terminal fitting and the center electrode is likely to proceed. In order to further reduce the calcination temperature, it is conceivable to blend an alkali metal oxide such as Na ₂ O, but if the content of the alkali metal component in the glaze increases excessively, it causes a decrease in insulation, There is a problem that a flashover is likely to occur.
(3) In recent years, when the interest in environmental protection is increasing on a global scale, glazes containing Pb are gradually shunned. For example, in the automobile industry in which spark plugs are used in large quantities, in consideration of the environmental impact of discarded spark plugs, the use of spark plugs containing Pb-containing glazes is being studied to eliminate them in the future.

  The first of the objects of the present invention is to provide a spark plug in which a glaze layer that can be baked at a low temperature and has a high insulating property as compared with a conventional glaze is formed on an insulator, and a method for producing the same. It is in. The second problem is to provide a spark plug that can greatly reduce the amount of Pb contained in the glaze and that is adapted to the growing trend toward environmental protection.

Means for Solving the Problems and Effects of the Invention

A first configuration (reference invention) of a spark plug of the present invention is a center electrode, a metal shell disposed outside the center electrode, and one end coupled to the metal shell so as to face the center electrode. Between the center electrode and the metal shell, an insulator disposed so as to cover the outside of the center electrode, and a glaze layer formed so as to cover at least a part of the surface of the insulator, Have And in order to solve the said subject, the glaze which comprises this glaze layer is oxidizable element component mainly selected from Si, B, Zn, and Ba and Na, K, and Li, 2 types (henceforth, this 2 It becomes because the) that species of components codoped alkali metal component, 25 a Si component 18 to 35 wt% in weight was oxide converted to SiO _2, with the weight calculated oxide B component _B 2 _{O 3} The co-added alkali metal component contains ˜40% by weight, 10 to 25% by weight in terms of Zn component converted to ZnO, and 7 to 20% by weight in terms of Ba component converted to oxide in BaO. As for Na, Na is contained in Na ₂ O, K is contained in K ₂ O, and Li is contained in Li ₂ O in terms of oxides in an amount of 3 to 9% by weight, respectively.

  The glaze having the notation composition used in the first configuration is obtained when the underlying insulator is made of, for example, an alumina-based insulating material, since the difference in linear expansion coefficient between the insulator is relatively small. Cracks are less likely to occur. Further, since the content of the alkali metal component is set to be relatively high, the softening temperature is lower than that of the conventional lead silicate glass-based glaze, and the calcination temperature can be lowered to 800 to 950 ° C. Therefore, even when smoldering is performed at the same time as the glass sealing step described above, oxidation is unlikely to occur in the center electrode and terminal fittings described later.

  Moreover, although the content of the alkali metal component is high, the insulation is good. In this regard, it is important that one kind of alkali metal component is not added alone, but two kinds selected from Na, K and Li are co-added. That is, according to the inventor's study, when an alkali metal component is blended alone, the conductivity of the glaze increases rapidly with the increase in the content thereof, leading to a significant loss of insulation. Surprisingly, it was found that the electrical conductivity of the glaze does not increase so much even when the total content is considerably increased, and good insulation can be secured. As a result, it is possible to increase the content of alkali metal components without significantly reducing the insulation, and as a result, it is possible to simultaneously achieve the two purposes of ensuring flashover resistance and lowering the calcination temperature. It becomes. In addition, it is also possible to mix | blend other alkali metal components after the 3rd component in the range which does not impair the electroconductivity suppression effect by co-addition of an alkali metal component.

Si component content in the glaze is set to 18-35% by weight at weight was oxide converted to SiO _2. When the underlying insulator is made of an alumina-based insulating material, if the Si component content is less than 18% by weight, the linear expansion coefficient of the glaze becomes too large and defects such as cracks are likely to occur in the glaze layer. Become. On the other hand, if the Si component content exceeds 40% by weight, the linear expansion coefficient of the glaze becomes too small, and defects such as penetration (crazing) tend to occur in the glaze layer. The Si component content is desirably set in the range of 25 to 30% by weight.

Also, B component content _is set in the weight calculated oxide B 2 _{O 3} 25 to 40 wt%. If the B component content is less than 25% by weight, the softening point of the glaze increases, and smoldering at the desired temperature (the above-mentioned 800 to 950 ° C.) may be impossible. On the other hand, if the B component content exceeds 40% by weight, phase separation is likely to occur in the resulting glaze layer, and the glaze layer is devitrified, resulting in problems such as poor insulation or incompatibility with the linear expansion coefficient. May lead to a connection. The B component content is desirably set in the range of 30 to 35% by weight.

  The Zn component content is set in the range of 10 to 25% by weight in terms of oxide converted to ZnO. When the Zn component content is less than 10% by weight, the softening point of the glaze increases, and smoldering at a desired temperature may not be possible. On the other hand, if the Zn component content exceeds 25% by weight, the linear expansion coefficient of the glaze becomes too large, and defects such as cracks may easily occur in the glaze layer. The content of the Zn component is desirably set in the range of 12 to 18% by weight.

  The Ba component content is set in the range of 7 to 20% by weight in terms of oxide converted to BaO. If the Ba component content is less than 7% by weight, the insulating properties of the glaze may be lowered, and the flashover resistance may be impaired. On the other hand, if the Ba component content exceeds 20% by weight, the softening point of the glaze increases, and smoldering at the desired temperature may become impossible. The content of the Ba component is desirably set in the range of 8 to 15% by weight.

Next, regarding the co-added alkali metal component in the glaze, Na is Na ₂ O, K is K ₂ O, Li is an oxide equivalent weight to Li ₂ O, and two of them are 3 to 3, respectively. 9% by weight is contained. If the content of at least one of the components is less than 3% by weight, the softening point of the glaze increases, and smoldering at the desired temperature may not be possible. On the other hand, if the content of at least one of the components exceeds 9% by weight, the linear expansion coefficient of the glaze becomes too large, and defects such as cracks may easily occur in the glaze layer.

  Moreover, the total content of the co-added alkali metal component in the glaze is preferably adjusted in the range of 6 to 14% by weight in terms of oxide. If the total content of the co-added alkali metal components is less than 6% by weight, the softening point of the glaze increases, and sintering at the desired temperature may be impossible. On the other hand, if the total content exceeds 14% by weight, the insulating properties of the glaze may be lowered, and the flashover resistance may be impaired.

Further, of the two components constituting the co-added alkali metal component in the glaze, Na is Na ₂ O, K is K ₂ O, and Li is Li ₂ O, respectively. It is preferable to adjust the value of A1 / A2 in the range of 1.0 to 2.0 when the content is A1 and the molar content of the other is A2. If the value of A1 / A2 deviates from this range to the upper side or lower side, the effect of suppressing the conductivity by co-addition of alkali metal components cannot be achieved sufficiently, and consequently the insulating properties of the glaze are lowered and the flashover resistance is impaired. May be. The value of A1 / A2 is desirably adjusted in the range of 1.5 to 2.0.

In order to suppress the increase in the conductivity of the glaze accompanying the increase in the content of the alkali metal component, it is particularly desirable to use two kinds of Na and K as the co-added alkali metal component. In this case, it is preferable to contain 3 to 9% by weight of the Na component in terms of oxide converted to Na ₂ O and 3 to 9% by weight of the K component in terms of oxide converted to K ₂ O.

  In addition, the total content of the cation component in the glaze, that is, the Si component, the B component, the Zn component, the Ba component, and the co-added alkali metal component, in terms of each oxide, is 95% by weight or more. desirable. When the total content thereof is less than 95% by weight, the softening point of the glaze increases, and smoldering at a desired temperature may be impossible. The total content is desirably 97% by weight or more.

Next, the glaze contains one or more of Al, Ca, Fe, Zr, Ti, Sr, Mg, Bi, Ni, Sn, P and Mn as auxiliary cation components, and Al is Al ₂ O ₃ In addition, Ca is CaO, Fe is Fe ₂ O ₃ , Zr is ZrO ₂ , Ti is TiO ₂ , Sr is SrO, Mg is MgO, Bi is Bi ₂ O ₃ , Ni is NiO, Sn can be contained in SnO ₂ , P can be contained in P ₂ O ₅ , and Mn can be contained in MnO in a total amount of 5% by weight or less in terms of oxide. These components can be positively added according to various purposes, and impurities (or contamination) from raw materials (or clay minerals to be blended when preparing the glaze slurry described later) and refractory materials in the melting process, etc. May be inevitably mixed. In addition, as an Fe component source in the raw material of the glaze, both of Fe (II) ion type (for example, FeO) and Fe (III) ion type (for example, Fe ₂ O ₃ ) can be used. The content of the Fe component in the final glaze layer is displayed as a value converted to Fe ₂ O ₃ regardless of the valence of Fe ions.

  If the total content of the auxiliary cation component exceeds 5% by weight, it becomes impossible to ensure a total content of 95% by weight or more of the main cation component. The total content of auxiliary cation components is desirably 3.0% by weight or less. In the following description, when the main cation component and the auxiliary cation component are collectively referred to, they may be simply referred to as a cation component.

For example, the Al component can be blended in the range of 5% by weight or less to obtain the effect of suppressing the devitrification of glaze. In addition, other components can be appropriately blended in order to adjust the softening temperature of the glaze. In particular, the blending of Bi ₂ O ₃ is effective in lowering the softening temperature of the glaze.

Further, the glaze does not substantially contain the Pb component (excluding those that are inevitably mixed from the glaze raw material), or even if contained, the content is 1.0% by weight or less in terms of PbO Can be. For example, if the Pb component is contained in the glaze in the form of a low valence ion (for example, Pb ²⁺ ), this is oxidized to a high valence ion (for example, Pb ³⁺ ) by corona discharge from the glaze layer surface. In some cases, the insulating property of the glaze layer is lowered and the flashover resistance is impaired. On the other hand, recently, interest in environmental protection is increasing, and lead-free materials are being sought for glazes. In that respect, the glaze used in the spark plug of the present invention is substantially free from Pb except for those containing up to about 1.0% by weight contained as unavoidable impurities, for example, because the cation component does not contain a Pb component. Even if it is reduced to a level that does not contain it, it does not cause any problem, so it can be said that it is advantageous. That is, the second problem of the present invention is solved. The Pb content is desirably 0.1% by weight or less.

Next, the 2nd structure of the spark plug of this invention is the same as that of the above-mentioned 1st structure except the glaze layer. The glaze constituting the glaze layer is mainly a cationic component (hereinafter, mainly referred to the cationic component) Si, B, and Zn, and Ba, it consists of at least one selected from Ti and Zr, the Si component in SiO ₂ 20 to 40 wt% with the weight calculated oxide, 15-25 weight B component _B 2 _{O 3} 20 to 35 wt% with the weight calculated oxide at weight was in terms of oxide of Zn component ZnO %, And Ba component is contained in an amount of 10 to 23% by weight in terms of oxide to BaO, and Ti and Zr are Ti in TiO ₂ and Zr in ZrO ₂ in terms of oxide in total 2 10 wt% and at least one selected from Na, K and Li as an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is Li ₂ O in terms of oxide ,That A total content of 12 wt% or less, further characterized in that the content of Pb was at oxide conversion to form a 0.1% by weight or less PbO.

This second configuration includes the following four inventions. These four inventions can also be implemented in combination of any two or more.
(First invention) The Si component is 20 to 38% by weight in terms of oxide converted to SiO ₂ (can be combined with at least one of the second to fourth inventions).
(Second invention) The ZrO ₂ equivalent weight content of Zr is 3.4% by weight or less (can be combined with at least one of the first, third and fourth inventions).
(Third invention) The TiO ₂ equivalent weight content of Ti is 1.5% by weight or more (can be combined with at least one of the first, second and fourth inventions).
(Fourth invention) The ZrO ₂ equivalent weight content of Zr is WZr, the Ti TiO ₂ equivalent weight content is WTi, and WTi / WZr is 0.2 to 10 (with at least one of the first to third inventions) Can be combined).

The operation and effect of the second configuration of the present invention will be described in detail below, including the operation and effect of the first to fourth inventions. In the glaze layer constituting the main part of the spark plug of the second configuration of the present invention, the total content range of the alkali metal component is limited to 12% by weight or less (including 0% by weight). The content range was limited to 20 to 35% by weight in terms of oxide converted to B ₂ O ₃ , and Ti and Zr were blended at a ratio of 2 to 10% by weight in terms of oxides respectively. There is a feature. By keeping the total content of the alkali metal component and the content of the B component within the above ranges, there is an effect that the glaze layer having a uniform thickness and few defects such as bubbles can be more easily formed.

  The reason why the above effects can be obtained by reducing the contents of the alkali metal component and the B component is considered as follows. That is, in the production method of the present invention to be described later, when the glaze powder is prepared as a glaze slurry, if the blending amount of the alkali metal component and the B component is large, these components are eluted in a slurry solvent such as water, and the slurry May increase the viscosity. When the viscosity of the slurry becomes extremely high (for example, it exceeds 1000 mPa · s), it becomes difficult to obtain a uniform glaze powder coating layer, and the possibility that bubbles and the like are involved is increased. However, by selecting the content range of the alkali metal component and the B component as described above, it becomes possible to easily prepare a glaze slurry having low viscosity and high fluidity, and has a uniform thickness and few defects. It is thought that it becomes easy to obtain a glaze layer.

  If the contents of the alkali metal component and the B component are reduced, the softening temperature of the glaze, that is, the calcination temperature, is increased. As described above, in order to suppress the increase in the softening temperature, the conventional method has been proposed. A large amount of PbO was blended in the glaze. However, in the second configuration, the content of the Pb component can be significantly reduced while suppressing an increase in the softening temperature of the glaze by blending Ti and Zr-based oxide components instead of PbO. Has been successfully reduced to 0.1 wt% or less in terms of PbO. Therefore, the second problem of the present invention described above is solved. In addition, it is further desirable that the Pb component is not substantially contained except for those inevitably mixed from the glaze raw material.

  Further, when the underlying insulator is made of, for example, an alumina-based insulating material, the difference in linear expansion coefficient from this is relatively small, so that the resulting glaze layer is unlikely to crack. And the softening temperature is lower than the conventional lead silicate glass-based glaze, and the calcination temperature can be lowered to 800-950 ° C. Therefore, even when smoldering is performed at the same time as the glass sealing step described above, oxidation is unlikely to occur in the center electrode and terminal fittings described later. Furthermore, since the content of the alkali metal component is reduced, the insulating property (and consequently flashover resistance) of the glaze layer is good. In addition, by blending Ti and Zr-based oxide components, the water resistance or chemical resistance of the resulting glaze layer is improved. For example, even when an alkali metal component in the glaze layer is contained, the elution is prevented. It is suppressed and contributes to the withstand voltage performance improvement of the glaze layer. Regarding the Zr component, the effect of improving the chemical resistance of the glaze layer is more remarkable than that of the Ti component. Here, “good water resistance” means, for example, that the elution of the component from the formed glaze layer to water is unlikely to occur and the elution of the component when the glaze frit is left in the form of an aqueous slurry for a long time. It also means that it becomes difficult to cause a problem that the viscosity of the slurry becomes high.

  In the second configuration, when the total content of the alkali metal components exceeds 12% by weight in terms of oxide, the effect of improving the fluidity of the glaze slurry, and thus the resulting glaze layer thickness or defect reduction The effect peculiar to the second configuration cannot be achieved significantly. Also, in terms of securing the insulating properties of the glaze, it is disadvantageous to add the alkali metal component beyond the above range. On the other hand, since the increase in the softening point is suppressed by blending the glaze layer Ti and the Zr-based oxide component, for the alkali metal component, for example, except for those inevitably mixed from the glaze raw material, etc. It is also possible to reduce to a level not containing. For example, when the content is less than 6% by weight, desirably less than 5% by weight, it can be said that the effect of improving the insulation by reducing the alkali metal component can be achieved more remarkably. In addition, in order to improve the fluidity of the calcination temperature and the molten glaze layer, etc., when a certain amount of alkali metal components must be blended, two or more types of alkali metal components can be used together as in the first configuration described above. Addition is more effective in improving insulation.

  Next, if the total content of Ti and Zr is less than 2% by weight in terms of oxide, the glaze softening point increase inhibiting effect is insufficient, and smoldering at the desired temperature may not be possible. is there. On the other hand, when the total content exceeds 10% by weight, a glaze layer obtained by the calcination is likely to be devitrified. In addition, Ti and Zr oxides, when mixed in appropriate amounts, contribute to lowering the softening temperature of the glaze, for example, by eutectic reaction with other oxide components. If it is an oxide and the total content exceeds 10% by weight, the softening point of the glaze is raised, which may lead to inconvenience that the calcination at the desired temperature becomes impossible. The total content of Ti and Zr in terms of oxide is desirably 3 to 8% by weight.

The Zr component has a slightly larger tendency to increase the viscosity of the molten glaze than the Ti component. Therefore, from the viewpoint of improving the fluidity of the molten glaze and forming a more uniform and excellent appearance glaze layer, the second invention As described above, the content of the Zr component is not more than 3.4% by weight, preferably not more than 3.0% by weight in terms of the weight content in terms of ZrO ₂ .

On the other hand, for the Ti component, since the influence of the increase in the viscosity of the molten glaze is small compared with the Zr component, by making the TiO ₂ equivalent weight content as 1.5% by weight or more as in the third invention, A glaze layer excellent in water resistance or chemical resistance can be formed satisfactorily.

If the Ti component is excessive, the linear expansion coefficient of the glaze layer becomes too low, and if the underlying insulator is made of, for example, an alumina-based insulating material, the difference in the linear expansion coefficient results in the glaze layer. Problems such as penetration (crazing) may occur. Therefore, in order to obtain a glaze layer that is excellent in water resistance or chemical resistance while eliminating such problems, and improving the fluidity of the molten glaze to obtain a uniform and good appearance, a Ti component and a Zr component are added together. It is desirable to do. Specifically, as in the fourth invention described above, the weight content of Zr in terms of ZrO ₂ is WZr, the weight content of Ti in terms of TiO ₂ is WTi, and WTi / WZr is 0.2 to 10. Good. When WTi / WZr is less than 0.2, the content of the Ti component tends to be relatively insufficient, and the content of the Zr component is increased when an effect of improving water resistance or chemical resistance is sufficiently obtained. It must be. As a result, the viscosity of the molten glaze may increase and the glaze layer may have a poor appearance. On the other hand, if WTi / WZr exceeds 10, when the effect of improving the water resistance or chemical resistance is sufficiently obtained, the content of the Ti component must be increased. As a result, the linear expansion coefficient of the glaze layer becomes too low, and crazing or the like may occur easily. The WTi / WZr is preferably 0.5-7.

In the second configuration, Si component content in the glaze is set to 20-40% by weight at weight was oxide converted to SiO _2. When the underlying insulator is made of an alumina-based insulating material, if the Si component content is less than 20% by weight, the linear expansion coefficient of the glaze becomes too large and defects such as cracks are likely to occur in the glaze layer. Become. On the other hand, if the Si component content exceeds 40% by weight, the linear expansion coefficient of the glaze becomes too small, and defects such as penetration (crazing) tend to occur in the glaze layer. It should be noted that, when the Si component content is set to 38% by weight or less as in the first invention, it is possible to further reduce the occurrence of defects such as penetration into the glaze layer. The Si component content is more desirably set in the range of 25 to 35% by weight in terms of SiO ₂ oxide.

Further, in the second configuration, B component content _is set in the weight calculated oxide B 2 _{O 3} 20 to 35 wt%. When the B component content is less than 20% by weight, the softening point of the glaze increases, and smoldering at the desired temperature (the aforementioned 800 to 950 ° C.) becomes impossible. On the other hand, when the B component content exceeds 35% by weight, the fluidity improvement effect of the glaze slurry, and consequently the effect specific to the second configuration such as uniformization of the thickness of the glaze layer or reduction of defects cannot be achieved. . In addition, it also has a disadvantage in that phase separation occurs in the resulting glaze layer, and the glaze layer is devitrified, and problems such as a decrease in insulation or incompatibility with the linear expansion coefficient with the base are likely to occur. The B component content is desirably set in the range of 20 to 28% by weight.

  In addition, from the viewpoint of enhancing the fluidity improving effect of the glaze slurry, the total content of B component and alkali metal component (as oxide) is 42% by weight or less, desirably 35% by weight or less. Further, from the viewpoint of suppressing an excessive increase in the calcination temperature, it is desirable to ensure that the total content of the alkali metal component and the Ti and Zr components (as oxide) is 8% by weight or more.

  Next, in the second configuration, the Zn component content is set in the range of 15 to 25% by weight in terms of oxide converted to ZnO. If the Zn component content is less than 15% by weight, the softening point of the glaze may increase too much, and smoldering at the desired temperature may not be possible. On the other hand, if the Zn component content exceeds 25% by weight, the linear expansion coefficient of the glaze becomes too large, and defects such as cracks may easily occur in the glaze layer. In addition, the content of the Zn component is desirably set in the range of 15 to 20% by weight, and more desirably in the range of 17 to 20% by weight.

  In the second configuration, the Ba component content is set in the range of 10 to 23% by weight in terms of oxide converted to BaO. If the Ba component content is less than 10% by weight, the insulating properties of the glaze may deteriorate and the flashover resistance may be impaired. On the other hand, if the Ba component content exceeds 23% by weight, the softening point of the glaze increases, and smoldering at the desired temperature may become impossible. In addition, the content of the Ba component is desirably set in the range of 12 to 18% by weight.

  In the first configuration and the second configuration of the spark plug of the present invention, the cation component or auxiliary cation component in the glaze is mainly contained in the form of an oxide. Due to factors such as the formation of a glass phase, it is often impossible to directly identify the presence form due to oxides. In this case, if the content of the element component in the glaze layer in terms of the oxide is within the above range, it is regarded as belonging to the scope of the present invention.

  Here, the content of each cation component in the glaze layer formed on the insulator can be identified using a known microanalysis method such as EPMA (electron probe microanalysis) or XPS (X-ray photoelectron spectroscopy). For example, when EPMA is used, either the wavelength dispersion method or the energy dispersion method may be used to measure characteristic X-rays. There is also a method of identifying the composition by peeling the glaze layer from the insulator and subjecting it to chemical analysis or gas analysis.

  Further, the spark plug of the present invention having the glaze layer is a shaft-like member provided integrally with the center electrode or separately from the center electrode with a conductive coupling layer interposed in the through hole of the insulator. It can comprise as a thing provided with the terminal metal part. In this case, the insulation resistance value can be measured by holding the entire spark plug at about 500 ° C. and energizing the terminal metal part and the metal shell through the insulator. In order to ensure insulation durability at high temperatures, it is desirable that the insulation resistance value be 200 MΩ or more in order to prevent the occurrence of flashover or the like.

  FIG. 8 shows an example of the measurement system. That is, a DC constant voltage power source (for example, a power supply voltage of 1000 V) is connected to the terminal fitting 13 side of the spark plug 100 and the metal shell 1 side is grounded, and the spark plug 100 is placed in a heating furnace and heated to 500 ° C. Energize with. For example, considering the case where the energization current value Im is measured using a current measurement resistor (resistance value Rm), the insulation resistance value Rx to be measured is (VS / Im) -Rm, where the energization voltage is VS. (In the figure, the energization current value Im is measured by the output of a differential amplifier that amplifies the voltage difference across the current measurement resistor).

Further, the insulator may be composed of the alumina insulating material containing 85 to 98 wt% in weight was in terms of oxide of Al component to the _Al 2 _{O 3.} In this case, the glaze desirably has an average linear expansion coefficient of the glaze in the temperature range of 20 to 350 ° C. in the range of 50 × 10 ⁻⁷ / ° C. to 85 × 10 ⁻⁷ / ° C. If the linear expansion coefficient is smaller than this lower limit, defects such as penetration (crazing) may easily occur in the glaze layer. On the other hand, if the linear expansion coefficient is larger than this upper limit, defects such as cracks are likely to occur in the glaze layer. The linear expansion coefficient is more preferably in the range of 60 × 10 ⁻⁷ / ° C. to 80 × 10 ⁻⁷ / ° C.

  Here, the linear expansion coefficient of the glaze is obtained by cutting out a sample from a vitreous bulk material obtained by blending and dissolving the raw materials so as to have substantially the same composition as the glaze layer, and using this, by a known dilatometer method, etc. It can be estimated from the measured values. Further, the linear expansion coefficient of the glaze layer on the insulator can be measured using, for example, a laser interferometer or an atomic force microscope.

Next, the first configuration of the spark plug can be manufactured by the first manufacturing method of the present invention described below. That is, the method uses a component source powder as a component source of Si, B, Zn and Ba as cation components and two types (co-added alkali metal components) selected from Na, K and Li, 18 to 35% by weight in terms of oxide converted to SiO ₂ , 25 to 40% by weight in terms of oxide converted to B ₂ O ₃ in the B component, and weight in terms of oxide converted to ZnO as the Zn component 10 to 25% by weight, Ba is 7 to 20% by weight in terms of oxide converted to BaO, and for the co-added alkali metal component, Na is Na ₂ O, K is K ₂ O, Li was mixed in 3 to 9% by weight of Li ₂ O in terms of oxides, mixed and then heated to 1000 to 1500 ° C. to melt, and the melt was quenched, vitrified and ground. Glaze powder using frit A glaze powder preparation process for preparing a powder, a glaze powder deposition process for depositing the glaze powder on the surface of the insulator to form a glaze powder deposition layer, and firing the insulator in a temperature range of 800 to 950 ° C. Thus, the glaze powder deposition layer is baked on the surface of the insulator to form a glaze layer.

The second configuration of the spark plug can be manufactured by the second manufacturing method of the present invention described below. That is, in this method, Si, B, Zn, and Ba as main cation components, and at least one component source powder selected from Ti and Zr, the Si component is converted to SiO ₂ as an oxide. 20 to 40 wt% by weight, 20 to 35 wt% by weight of B component converted to B ₂ O ₃ , 15 to 25 wt% by weight of Zn component converted to oxide by oxide, Ba component 10 to 23% by weight in terms of oxide in terms of BaO, and Ti and Zr are Ti in TiO ₂ and Zr is in terms of oxide in terms of ZrO ₂ in total 2 to 10% by weight. After mixing and mixing so as to contain it, the mixture is heated to 1000-1500 ° C. to melt, and the melt is rapidly cooled, vitrified and crushed to prepare a glaze powder using a frit A glaze powder deposition step of depositing the glaze powder on the surface of the insulator to form a glaze powder deposition layer, and firing the insulator in a temperature range of 800 to 950 ° C. And a glazing step of baking on the surface of the insulator to form a glaze layer.

  In addition, as the component source powder of each component (in addition to the component source powder of the cation component, when the auxiliary cation component is included, the component source powder is also included), oxides of these components (may be complex oxides) In addition, various inorganic material powders such as hydroxides, carbonates, chlorides, sulfates, nitrates, and phosphates can be used. It is necessary to use those inorganic material powders that can be converted into oxides by heating and melting. Moreover, the rapid cooling can employ not only a method in which the melt is poured into water but also a method in which the melt is sprayed onto the surface of the cooling roll to obtain a flake-like rapidly solidified product.

  The glaze powder can be prepared as a glaze slurry in which the frit is dispersed in water or a solvent. In this case, the glaze powder deposition layer can be formed as a coating layer of the glaze slurry by applying the glaze slurry to the insulator surface and drying. As a method of applying the glaze slurry to the insulator surface, a method of spraying the glaze slurry onto the insulator surface from the spray nozzle can easily form a glaze powder deposition layer having a uniform thickness, and its coating thickness. It is easy to adjust the height.

In the glaze slurry, an appropriate amount of clay mineral or organic binder can be blended for the purpose of increasing the shape retention of the formed glaze powder accumulation layer. As the clay mineral, one composed mainly of hydrous aluminosilicate can be used. For example, allophane, imogolite, hisingerite, smectite, kaolinite, halloysite, montmorillonite, illite, vermiculite, dolomite, etc. (or a composite thereof). A seed or mainly two or more kinds can be used. In addition, in terms of the oxide-based component contained, in addition to SiO ₂ and Al ₂ O ₃ , one or two of Fe ₂ O ₃ , TiO ₂ , CaO, MgO, Na ₂ O, K ₂ O, etc. What mainly contains the above can be used.

  In the spark plug of the present invention, a terminal fitting is fixed to one end side of a through hole formed in the axial direction of an insulator, and a center electrode is fixed to the other end side, A sintered conductive material portion (for example, a conductive glass seal layer or a resistor) mainly composed of a mixture of glass and a conductive material for electrically joining them between the terminal fitting and the center electrode in the through hole. Body) is formed. When manufacturing this, a method including the following steps can be adopted. Assembly manufacturing process: With respect to the through hole of the insulator, a terminal metal fitting is arranged on one end side, and a center electrode is arranged on the other end side. An assembly in which a packed layer of sintered conductive material raw material powder mainly composed of glass powder and conductive material powder is formed between the center electrode and the center electrode is manufactured. -Glazing step: An assembly in which a glaze powder deposition layer is formed on the surface of the insulator is heated to a temperature range of 800 to 950 ° C., and the glaze powder deposition layer is baked on the insulator surface to form a glaze layer. The step and the step of softening the glass powder in the packed bed are simultaneously performed. -Pressing process: In the heated assembly, the packing layer is pressed and sintered between the center electrode and the terminal fitting by relatively bringing the center electrode and the terminal fitting within the through hole. The conductive material part.

  In this case, the terminal fitting and the center electrode are electrically joined by the sintered conductive material portion, and the inner surface of the insulator through hole and the terminal fitting and the center electrode are sealed (sealed). Therefore, the smoldering step and the pressing step form a glass sealing step. This method is efficient because the glass sealing step and the calcination step are performed simultaneously. Moreover, since the glaze temperature can be lowered to 800 to 950 ° C. due to the use of the glaze described above, manufacturing defects due to oxidation of the center electrode and terminal fittings are less likely to occur, and the product yield of spark plugs is improved.

  In this case, the softening temperature of the glaze is preferably adjusted in the range of 600 to 700 ° C. When the softening temperature exceeds 700 ° C., a calcination temperature of 950 ° C. or higher is required, and oxidation of the center electrode and the terminal metal fitting is likely to proceed. On the other hand, when the softening temperature is less than 600 ° C., the calcination temperature needs to be set to a low temperature of less than 800 ° C. In this case, the glass used for the sintered conductive material portion must also have a low softening temperature so that a good glass seal state can be obtained. As a result, when the completed spark plug is used for a long time in a relatively high temperature environment, the glass in the sintered conductive material portion is likely to be deteriorated, for example, when the sintered conductive material portion includes a resistor. May lead to performance degradation such as its load life characteristics.

  In addition, the softening temperature of a glaze means what was measured as follows. That is, the glassy glaze bulk obtained by blending and dissolving the raw materials is pulverized to a particle size of about 10 μm to 100 μm. This is subjected to differential thermal analysis while being reheated, and the temperature of the peak appearing next to the first endothermic peak representing the bent point (that is, the second endothermic peak) is defined as the softening temperature. In addition, for the softening temperature of the glaze layer formed on the insulator surface, the content of the cation component and the auxiliary cation component in the glaze layer is analyzed to calculate an oxide-converted composition, which is almost the same as this composition. After mixing and dissolving the oxide raw materials of the respective oxidizable elements so as to be equal, a glass sample is obtained by rapid cooling, and the softening point of the formed glaze layer is estimated from the softening point of the glass sample. .

Next, the insulator on which the glaze layer is to be formed is an insulating material mainly composed of alumina, and contains an Na component in a range of 0.07 to 0.5% by weight in terms of Na ₂ O. Can be composed of materials. In the following description, the term “Na component content” means the content in terms of Na ₂ O unless otherwise specified.

In recent years, in a spark plug used for an internal combustion engine such as an automobile engine, an alumina (Al ₂ O ₃ ) -based material having excellent heat resistance has been used as an insulating material for a long time. As the raw material alumina for the insulating material as described above, one manufactured by the Bayer method (hereinafter also referred to as Bayer alumina) is generally used.

  The Bayer method is a method in which alumina is wet-extracted from bauxite, which is an aluminum ore, and a caustic soda (NaOH) aqueous solution having a relatively high concentration is used as an extraction medium. Therefore, the obtained buyer alumina contains a considerable amount of Na component (for soda), and is used in a form subjected to a soda removal treatment if necessary. And, depending on the degree of soda removal, for example, the sodium component content of 0.05% by weight or less is low soda alumina, the one having about 0.1 to 0.2% by weight is medium soda alumina, Those having a higher Na content, for example, about 0.2% by weight or more, are commonly called soda alumina.

  By the way, since the Na component contained in alumina exhibits high ionic conductivity, if its content is excessive, the insulation resistance value, particularly the insulation resistance value at a high temperature of 500 ° C. or higher is lowered, or at a high temperature. This causes problems such as deteriorating the mechanical strength. Therefore, conventionally, the alumina-based insulating material used for spark plugs should be as low as possible in the Na component, and the Na component content should be set to a low value of 0.05% by weight or less. Has become common sense.

  Here, in order to produce an alumina-based insulator having a low Na component content as described above, it is essential to use a low-soda-based material alumina as a raw material alumina. As described above, low-soda-based alumina is expensive because it requires a soda removal process, and is not necessarily desirable from the viewpoint of raw material costs. However, in recent years, with higher output of automobile engines and the like, higher withstand voltage characteristics and heat resistance have been demanded for spark plug insulators. As a result, the above-mentioned common sense regarding the Na component content in the insulating material is increasingly unwavering, and the current situation is that some high costs due to the use of low soda alumina must be accepted.

  However, the present inventor has conducted intensive studies on the Na component content of the alumina-based insulating material for spark plugs. It has been found that an insulating material having performance comparable to that of a conventional insulating material in which resistance and mechanical strength are not unexpectedly lowered and the Na content is lower than that is obtained. Furthermore, in the present invention, since two layers selected from Na, K, and Li are co-added to the glaze layer, good insulation is ensured. It can be said that it is advantageous when it is composed of a high alumina-based ceramic.

And by setting Na component content in the above ranges, the alumina powder used as a raw material also has a high Na component content of 0.07 to 0.65% by weight in terms of Na ₂ O. (If it exceeds 0.65% by weight, the content of Na component in the obtained insulating material cannot be maintained at 0.5% by weight or less). As a result, instead of the conventional low soda alumina, it is possible to use much cheaper medium soda alumina, ordinary soda alumina, etc., and the insulator for the spark plug, and thus the spark plug using the soda, is dramatically improved. Manufacturing cost reduction is realized.

In order to reduce the Na content in the insulating material to less than 0.07% by weight, alumina powder having a low Na content such as low soda alumina must be used. The above superiority cannot be secured. On the other hand, when the Na component content exceeds 0.5% by weight, the value of the insulation resistance of the material becomes insufficient, and the withstand voltage performance required for the spark plug insulator cannot be satisfied. The Na component content in the insulating material is more preferably 0.07 to 0.25% by weight. Moreover, the alumina powder used as a raw material desirably has a Na component content of 0.07 to 0.3% by weight in terms of Na ₂ O.

  As alumina powder used for manufacture of the said insulating material, what was manufactured by the buyer method can be used. In addition, except for what is contained as an unavoidable impurity, a normal buyer alumina powder hardly contains an alkali metal component other than the Na component (hereinafter referred to as a non-Na alkali metal component). Therefore, when such a buyer alumina powder is used, the total content of non-Na alkali metal components in the resulting insulating material is 0.05 weight in terms of oxide unless they are actively added. % Or less.

  Further, when the present inventor has further intensively studied, the alumina powder obtained by the Bayer method contains Na component also inside the powder particles, but due to the treatment with the caustic soda solution, It was found that the Na component was concentrated in the surface layer portion. And the Na component of the surface layer part of such a powder particle fuse | melts with a sintering auxiliary agent component (after-mentioned additional element component) at the time of baking, and makes a glass phase. The glass phase has a problem that the electrical resistivity decreases due to the solid solution of the Na component, and this acts as a conductive path, resulting in a decrease in the insulation resistance value and insulation withstand voltage of the material.

And as a result of further examination by the present inventors in view of this, the alumina powder to be used has a content of Na component present in the surface layer part of the particle powder of 0.01 to 0.00 in terms of Na ₂ O. It has been found that it is better to use 2% by weight. When the alumina powder in which the content of the Na component in the powder surface layer part exceeds 0.2% by weight, the insulation resistance value and the insulation withstand voltage of the obtained insulating material may be insufficient. In addition, in order to make the content of the Na component present in the surface layer part of the powder particles less than 0.01% by weight, is it necessary to use alumina powder with a low Na component content such as low soda alumina after all? Even when alumina powder having a high Na component content is used, a step of removing the Na component in the surface portion of the powder particle by washing or the like is required, and it becomes impossible to ensure the advantage of the raw material cost over the conventional insulating material. The content of the Na component present in the surface layer part of the particle powder is more preferably 0.01 to 0.1% by weight.

Here, the “content of Na component present in the surface layer portion of the powder particle” means a value measured as follows. First, the total content (unit: wt%) of the Na component in the alumina powder to be measured is measured by ICP analysis, chemical analysis, or the like, and the value is converted to Na ₂ O to be WNa1. Next, 100 g of alumina powder is immersed in 1 liter of distilled water maintained at a temperature of 90 ° C. for 1 hr without stirring. Thereafter, the alumina powder is separated and recovered, and the Na component content (unit: wt%) is measured again, and the value is converted to Na ₂ O to be WNa2. Then, the value WNa1−WNa2 (unit: wt%) obtained by subtracting WNa2 from the previously measured WNa1 is the content of the Na component present in the surface layer portion of the powder particles.

In this case, the structure of the obtained insulating material is mainly composed of alumina matrix phase grains having an alumina content of 99% by weight and a glass phase formed at the grain boundary portion of the alumina matrix phase grains. It will be a thing. Here, the content WGNa of the Na component in the insulating material that is present in the glass phase is preferably 0.4 to ₂ % by weight in terms of Na ₂ O. If the WGNa exceeds 2% by weight, the insulation resistance value and insulation withstand voltage of the insulation material may be insufficient. Moreover, in order to make it less than 0.4 weight%, you have to use the alumina powder with low Na component content, and it becomes impossible to ensure the raw material cost advantage over the conventional insulating material.

In the present specification, a value calculated approximately as follows is used as the WGNa. First, the surface of the material is polished, and this is observed with a scanning electron microscope (SEM) or the like, and the area ratio (corresponding to the volume ratio in the material) of the alumina matrix phase is measured by analyzing the structure image. The value is γA. Next, the weight concentration of the average Na component in the glass phase is determined by using a known fine composition analysis method (for example, EPMA (electron probe microanalysis), EDS (energy dispersive X-ray spectroscopy) or WDS (wavelength dispersive X-ray). Spectra) and the like, and converted to Na ₂ O to obtain NGNa. It is assumed that the material is composed only of the alumina matrix phase and the glass phase, and is almost completely densified by sintering, while the apparent density of the material measured by Archimedes method is ρ0 (unit : G / cm ³ ), and the density of alumina crystal grains is ρ 1 (= 3.97 g / cm ³ ), the weight MG of the glass phase existing per unit volume of material is
MG = ρ0−ρ1 ・ γA (1)
Therefore, WGNa is
WGNa = MG ・ NGNa × 100
= (Ρ0-ρ1, · γA) · NGNa × 100 (wt%) (2)
Can be calculated.

The weight concentration NGNa the average Na component of the glass phase is also the same reason as above, it is preferable that a 0.4 to 2 wt% in terms of Na 2 _O.

Next, in the insulating material of the present invention, the Al component content (hereinafter referred to as WAl) in the weight converted to Al ₂ O ₃ is preferably adjusted in the range of 85 to 98% by weight. If WAl is less than 85% by weight, the high-temperature strength and withstand voltage characteristics of the material may be insufficient. The WAl is desirably 90% by weight or more. However, if WAl exceeds 98% by weight, the amount of the sintering aid component becomes relatively small and it becomes difficult to densify the sintered body, and the sintering temperature rises when trying to sinter densely. As a result, the growth of alumina particles is promoted, and on the contrary, there is a case in which a problem such as deterioration of strength occurs. Therefore, the WAl is preferably adjusted within a range of 98% by weight or less.

In the insulating material of the present invention, one or more additive element components selected from Si, Ca, Mg, Ba, Zn, B and Na are used, Si is SiO ₂ , Ca is CaO, Mg In MgO, Ba in BaO, Zn in ZnO, B in B ₂ O ₃ , Na in Na ₂ O, 0.1 to 15 wt% in total in terms of oxides. it can. As the raw material powder for the production of such an insulating material, to alumina powder 85 to 98 parts by weight, Si, Ca, Mg, Ba, additive element based raw material containing Zn and B, Si in the SiO _2, Ca is CaO, Mg is MgO, Ba is BaO, Zn is ZnO, B is B ₂ O ₃ , and Na is Na ₂ O. What was mix | blended so that it might become ~ 15 weight part is used.

In addition, for example, for each component of Si, Ca, Mg, Ba, and Zn, the additive element-based raw materials are hydroxides, carbonates, chlorides, sulfates in addition to oxides of these components (may be complex oxides). Various inorganic raw material powders such as nitrates and phosphates can be used. These inorganic raw material powders must all be those that can be converted into oxides by firing. As for the B component, in addition to diboron trioxide (B ₂ O ₃ ), various boric acids including orthoboric acid (H ₃ BO ₃ ), Al, Ca, Borates with Mg, Ba, Zn and the like can be used.

  The additive element component melts during firing to form a liquid phase, and functions as a sintering aid that promotes densification. When the total content (hereinafter referred to as W1) of the additive element component in the insulating material in terms of the above oxide is less than 0.1% by weight, it becomes difficult to densify the sintered body. In contrast, the high temperature strength and withstand voltage characteristics at high temperatures are insufficient. On the other hand, if W1 exceeds 15.0% by weight, the high temperature strength of the material is impaired. Therefore, the total content W1 of the additive element components is preferably 0.1 to 15.0% by weight, and more preferably 3.0 to 10.0% by weight.

Among these, the Ba component and the B component also have an effect of remarkably improving the high temperature strength of the insulating material. And Ba component is good to contain 0.02-0.80 weight% in the weight (henceforth WBaO) converted into BaO. When WBaO is less than 0.02% by weight, the effect of improving the high temperature strength due to the BaO blending is not significant. Moreover, when WBaO exceeds 0.80% by weight, the high temperature strength of the material is impaired. WBaO is desirably adjusted in the range of 0.15 to 0.50% by weight. On the other hand, the B component is preferably contained in an amount of 0.01 to 0.75% by weight in terms of B ₂ O ₃ converted weight (hereinafter referred to as WB ₂ O ₃ ). When WB ₂ O ₃ is less than 0.01% by weight, the effect of improving the high-temperature strength by blending WB ₂ O ₃ is not significant. On the other hand, if WB ₂ O ₃ exceeds 0.75% by weight, the high temperature strength of the material is impaired. WB ₂ O ₃ is desirably adjusted in the range of 0.15 to 0.50% by weight.

In order to make the additive element component function more effectively as a sintering aid, a liquid phase with good fluidity can be used at a predetermined sintering temperature lower than that of Al ₂ O ₃ without excess or deficiency. It is important to generate. For this purpose, it is often effective to mix and blend a plurality of components, rather than blending each component alone. For example, when all of the above five types of first additive components are blended in the form of oxide, the material finally obtained is 1.50 to 5.00% by weight in terms of the weight of Si component converted to SiO _2. Containing, 1.20 to 4.00% by weight in terms of Ca component converted to CaO, 0.05 to 0.17% by weight in terms of Mg component converted to MgO, and Ba component to contain 0.15 to 0.50 wt% in weight in terms of BaO, a one containing 0.15 to 0.50 wt% in weight obtained by converting the B component _B 2 _{O 3} desirable.

  Hereinafter, embodiments of the present invention will be described with reference to some examples shown in the drawings. (Embodiment 1) FIGS. 1 and 2 show an embodiment of a spark plug according to the first configuration of the present invention. The spark plug 100 is insulated with a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that the tip 21 protrudes, and an ignition part 31 formed at the tip of the metal shell 1. One end of the center electrode 3 provided on the inner side of the body 2 and the metal shell 1 are joined by welding or the like, and the other end is bent back to the side so that the side surface faces the tip of the center electrode 3. The ground electrode 4 etc. which are arrange | positioned are provided. Further, the ground electrode 4 is formed with an ignition part 32 that faces the ignition part 31, and a gap between the ignition part 31 and the opposing ignition part 32 is a spark discharge gap g.

  The metal shell 1 is formed in a cylindrical shape by a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and a screw portion 7 for attaching the plug 100 to an engine block (not shown) on its outer peripheral surface. Is formed. In addition, 1e is a tool engaging part which engages tools, such as a spanner and a wrench, when attaching the metal shell 1, and has a hexagonal axial cross-sectional shape.

  Next, a through hole 6 is formed in the axial direction of the insulator 2, and the terminal fitting 13 is inserted and fixed from one end side, and the center electrode 3 is also inserted and fixed from the other end side. Has been. A resistor 15 is disposed between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 through the conductive glass seal layers 16 and 17, respectively. The resistor 15 and the conductive glass seal layers 16 and 17 constitute a sintered conductive material portion. The resistor 15 is a resistance obtained by using a mixed powder of glass powder and conductive material powder (and ceramic powder other than glass as required) as a raw material, and heating and pressing the powder in a glass sealing step described later. Consists of body composition. The resistor 15 may be omitted, and the terminal fitting 13 and the center electrode 3 may be integrated by a single conductive glass seal layer.

The insulator 2 has a through hole 6 for fitting the center electrode 3 along its own axial direction inside, and the whole is made of the following insulating material. That is, the insulating material is mainly composed of alumina, and is an alumina-based ceramic sintered body containing 85 to 98% by weight (preferably 90 to 98% by weight) of an Al component in terms of weight converted to Al ₂ O _3. Composed.

The following can be illustrated as a specific composition of components other than Al.
Si component: 1.50 to 5.00% by weight in terms of SiO ₂ ;
Ca component: 1.20 to 4.00% by weight in terms of CaO;
Mg component: 0.05 to 0.17% by weight in terms of MgO;
Ba component: 0.15 to 0.50% by weight in terms of BaO;
Component _B: B 2 _{O 3} 0.15 to 0.50 wt% in terms of weight.

  As shown in FIG. 1, a protruding portion 2 e that protrudes outward in the circumferential direction is formed, for example, in a flange shape in the middle of the insulator 2 in the axial direction. The insulator 2 has a main body 2b in which the side toward the tip of the center electrode 3 (FIG. 1) is the front side, and the rear side of the protrusion 2e is formed with a smaller diameter. On the other hand, on the front side of the protruding portion 2e, a first shaft portion 2g having a smaller diameter and a second shaft portion 2i having a smaller diameter than the first shaft portion 2g are formed in this order. A corrugation 2c is formed at the rear end of the outer peripheral surface of the main body 2b. Further, the outer peripheral surface of the first shaft portion 2g is substantially cylindrical, and the outer peripheral surface of the second shaft portion 2i is substantially conical, with a diameter decreasing toward the tip.

  On the other hand, the axial sectional diameter of the center electrode 3 is set smaller than the axial sectional diameter of the resistor 15. The through-hole 6 of the insulator 2 has a substantially cylindrical first portion 6a through which the center electrode 3 is inserted, and a substantially cylindrical shape having a larger diameter on the rear side (upper side in the drawing) of the first portion 6a. Second portion 6b. As shown in FIG. 1, the terminal fitting 13 and the resistor 15 are accommodated in the second portion 6b, and the center electrode 3 is inserted into the first portion 6a. At the rear end portion of the center electrode 3, an electrode fixing convex portion 3c is formed so as to protrude outward from the outer peripheral surface thereof. And the 1st part 6a and the 2nd part 6b of the said through-hole 6 are mutually connected in the 1st axial part 2g of Fig.4 (a), The electrode for fixing the center electrode 3 is in the connection position. A convex receiving surface 6c for receiving the convex 3c is formed in a tapered surface or a rounded surface.

  Moreover, the outer peripheral surface of the connection part 2h of the 1st axial part 2g and the 2nd axial part 2i is made into the stepped surface, and this is the protruding item | line part 1c as a metal fitting side engaging part formed in the inner surface of the metal fitting 1 Are engaged with each other via a ring-shaped plate packing 63 to prevent axial removal. On the other hand, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is disposed between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, and further On the rear side, a ring-shaped wire packing 60 is disposed via a filling layer 61 such as talc. Then, the insulator 2 is pushed forward toward the metal shell 1, and in this state, the crimping portion 1d is formed by crimping the opening edge of the metal shell 1 toward the packing 60 inward. It is fixed with respect to the insulator 2.

FIG. 4A and FIG. 4B show some examples of the insulator 2. The dimension of each part is illustrated below.
-Total length L1: 30-75 mm.
The length L2 of the first shaft portion 2g: 0 to 30 mm (however, the connection portion 2f with the protruding portion 2e is not included and the connection portion 2h with the second shaft portion 2i is included).
-Length L3 of the second shaft portion 2i: 2 to 27 mm.
-Outer diameter D1 of the main body 2b: 9 to 13 mm.
-Outer diameter D2 of the protruding portion 2e: 11 to 16 mm.
-Outer diameter D3 of the first shaft portion 2g: 5 to 11 mm.
-The base end outer diameter D4 of the second shaft portion 2i: 3 to 8 mm.
The outer diameter D5 of the distal end portion of the second shaft portion 2i (however, when the outer peripheral edge of the distal end surface is rounded or chamfered, in the cross section including the central axis O, at the proximal end position of the rounded portion or chamfered portion Refers to the outer diameter): 2.5-7 mm.
-Inner diameter D6 of the 2nd part 6b of the through-hole 6: 2-5 mm.
The inner diameter D7 of the first portion 6a of the through hole 6 is 1 to 3.5 mm.
-Thickness t1 of the first shaft portion 2g: 0.5 to 4.5 mm.
-Base end portion thickness t2 of second shaft portion 2i (value in a direction orthogonal to central axis O): 0.3 to 3.5 mm.
The tip thickness t3 of the second shaft portion 2i (value in a direction orthogonal to the center axis O; however, when the outer peripheral edge of the tip surface is rounded or chamfered, The thickness at the base end position of the part or chamfered part): 0.2 to 3 mm.
-Average thickness tA ((t2 + t3) / 2) of the second shaft portion 2i: 0.25 to 3.25 mm.

  In FIG. 1, the length LQ of the portion 2k protruding to the rear side of the metal shell 1 of the insulator 2 is 23 to 27 mm (for example, about 25 mm). Furthermore, when taking a longitudinal section including the central axis O of the insulator 2, the insulator on the outer peripheral surface of the protruding portion 2 k of the insulator 2 from the position corresponding to the rear edge of the metal shell 1 through the corrugation 2 c. The length LP measured along the cross-sectional outline until reaching the rear edge of 2 is 26 to 32 mm (for example, about 29 mm).

  The above-mentioned dimensions of the insulator 2 shown in FIG. 4A are, for example, as follows: L1 = about 60 mm, L2 = about 10 mm, L3 = about 14 mm, D1 = about 11 mm, D2 = about 13 mm, D3 = about 7.3 mm, D4 = 5.3 mm, D5 = 4.3 mm, D6 = 3.9 mm, D7 = 2.6 mm, t1 = 3.3 mm, t2 = 1.4 mm, t3 = 0.9 mm, tA = 1.15 mm.

  Further, in the insulator 2 shown in FIG. 4B, the first shaft portion 2g and the second shaft portion 2i each have a slightly larger outer diameter than that shown in FIG. 4A. The dimensions of each part are, for example, as follows: L1 = about 60 mm, L2 = about 10 mm, L3 = about 14 mm, D1 = about 11 mm, D2 = about 13 mm, D3 = about 9.2 mm, D4 = 6.9 mm, D5 = 5.1 mm, D6 = 3.9 mm, D7 = 2.7 mm, t1 = 3.3 mm, t2 = 2.1 mm, t3 = 1.2 mm, tA = 1.65 mm.

  Next, as shown in FIG. 3, the glaze layer 2d is formed on the surface of the insulator 2, specifically, the outer peripheral surface of the main body 2b including the corrugation 2c and the outer peripheral surface of the first shaft 2g. Yes. The formation thickness of the glaze layer 2d is 10 to 150 μm, preferably 20 to 50 μm. As shown in FIG. 1, the glaze layer 2d formed on the main body 2b is formed such that the front side in the axial direction enters a predetermined length inside the metal shell 1, while the rear side is the rear of the main body 2b. It extends to the edge position. On the other hand, the glaze layer 2d formed on the first shaft portion 2g has a connecting portion 2h with which the plate packing 63 abuts, for example, from an axial intermediate position so as to include a contact area with the inner peripheral surface of the metal shell 1. It is formed in the region that reaches.

Next, the glaze layer 2d is mainly cationic component is Si, B, and Zn, and Ba, will from Na, 2 species selected from K, and Li (the co-additive alkali metal components), oxides of Si component in SiO ₂ 18 to 35% by weight in terms of converted weight, 25 to 40% by weight in terms of B component converted to oxide of B ₂ O ₃ , 10 to 25% by weight in terms of Zn component converted to oxide of ZnO, The Ba component is contained in an amount of 7 to 20% by weight in terms of oxide to BaO, and the co-added alkali metal component is Na in Na ₂ O, K in K ₂ O, Li in Li ₂ O in oxide equivalent It is comprised with the glaze which contains 3 to 9 weight% in each weight.

Specifically, glaze is 18 to 35 wt% in weight was in terms of oxide of Si component in SiO _2, 25 to 40 wt% with the weight calculated oxide B component _B 2 _{O 3,} Zn The component is 10 to 25% by weight in terms of oxide converted to ZnO, the Ba component is 7 to 20% by weight in terms of oxide converted to BaO, and the Na component is in terms of oxide converted to Na ₂ O 3 ˜9% by weight, each containing 3 to 9% by weight in terms of oxide of K component converted to K ₂ O, each oxide of Si component, B component, Zn component, Ba component and co-added alkali metal component The total content in the converted value is 95% by weight or more. This glaze does not substantially contain the Pb component, or even if it is contained, its content is 1.0% by weight or less in terms of PbO. The glaze contains one or more of Al, Ca, Fe, Zr, Ti, Sr, Mg, Bi, Ni, Sn, P, and Mn as auxiliary cation components, and Al is Al ₂ O _3. In addition, Ca is CaO, Fe is Fe ₂ O ₃ , Zr is ZrO ₂ , Ti is TiO ₂ , Sr is SrO, Mg is MgO, Bi is Bi ₂ O ₃ , Ni is NiO, Sn may be contained in SnO ₂ , P may be contained in P ₂ O ₅ , and Mn may be contained in MnO in a total amount of 5% by weight or less in terms of oxide.

  Next, the main body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of Ni alloy or the like. A core material 3b made of Cu or Cu alloy is embedded in the main body 3a of the center electrode 3 to promote heat dissipation. On the other hand, the ignition part 31 and the opposing ignition part 32 are mainly composed of a noble metal alloy mainly composed of one or more of Ir, Pt and Rh. As shown in FIG. 2 (b), the main body 3a of the center electrode 3 is reduced in diameter on the tip side and has a flat tip surface, and a disc-like shape made of an alloy composition constituting the ignition portion. The ignition part 31 is formed by stacking the chips and forming a welded part W by laser welding, electron beam welding, resistance welding or the like along the outer edge of the joint surface and fixing the welded part W. Further, the opposing ignition part 32 is formed by aligning the tip with the ground electrode 4 at a position corresponding to the ignition part 31, and similarly forming a welded part W along the outer edge of the joint surface to fix it. It is formed. These chips are formed by, for example, molding and sintering a melting material obtained by blending and melting each alloy component so as to have the indicated composition, or an alloy powder or a single metal component powder blended at a predetermined ratio. It can be comprised by the sintered material obtained. Note that at least one of the ignition part 31 and the opposing ignition part 32 may be omitted.

The spark plug 100 is manufactured, for example, by the following method. First, the insulator 2 is an alumina powder, and each component source powder of Si component, Ca component, Mg component, Ba component, and B component as a raw material powder. And a predetermined amount of a binder (for example, PVA) and water are added and mixed to form a forming base slurry. Each component source powder, for example, the Si component is SiO ₂ powder, Ca components CaCO ₃ powder, Mg components MgO powder, Ba components BaCO ₃ powder, B components can be blended in the form of _H 3 BO ₃ powder. _{Incidentally,} H 3 BO ₃ may be added in the form of a solution.

  The forming substrate slurry is spray-dried by a spray drying method or the like to form a forming substrate granulated product. And the press molding body used as the original form of an insulator is made by carrying out the rubber press molding of the base granule for a shaping | molding. FIG. 9 schematically shows a rubber press molding process. Here, a rubber mold 300 having a cavity 301 penetrating in the axial direction is used, and a lower punch 302 is fitted into the lower opening of the cavity 301. In addition, a press pin 303 that extends in the axial direction in the cavity 301 and defines the shape of the through hole 6 (FIG. 1) of the insulator 2 is integrally projected on the punch surface of the lower punch 302. .

  In this state, the cavity 301 is filled with a predetermined amount of the forming granule PG, and the upper opening of the cavity 301 is closed with the upper punch 304 and sealed. In this state, a hydraulic pressure is applied to the outer peripheral surface of the rubber mold 300, and the granulated product PG in the cavity 301 is compressed through the rubber mold 300, whereby a press-molded body 305 as shown in FIG. In addition, the molding base granulated product PG has a weight of the molding base granulated product PG of 100 parts by weight so that crushing of the granulated product PG into powder particles at the time of pressing is promoted. After ~ 1.3 parts by weight of water is added, the press molding is performed. The outer surface side of the molded body 305 is processed by grinder cutting or the like to be finished into an outer shape corresponding to the insulator 2 in FIG. 1, and then fired at a temperature of 1400 to 1600 ° C. to become the insulator 2.

On the other hand, the glaze slurry is prepared as follows. First, component source powders serving as component sources of Si, B, Zn, Ba, Na, and K (for example, Si component is SiO ₂ powder, B component is H ₃ BO ₃ powder, Zn is ZnO powder, and Ba component is BaCO) ₃ powder, Na is Na ₂ CO ₃ powder, K is K ₂ CO ₃ powder), Si component is 18 to 35% by weight in terms of oxide converted to SiO ₂ , B component is oxide in B ₂ O ₃ Formulated to be 25 to 40% by weight in terms of converted weight, 10 to 25% by weight in terms of the Zn component converted to oxide to ZnO, and 7 to 20% by weight in terms of Ba to oxide converted to BaO. At the same time, the co-added alkali metal component is blended by mixing 3 to 9% by weight of Na in terms of Na ₂ O and K in terms of oxide to K ₂ O, respectively. Next, the mixture is heated to 1000-1500 ° C. to melt, and the melt is poured into water to quench and vitrify, and further pulverized to make a glaze frit. Then, an appropriate amount of clay minerals such as kaolin and glazed clay and an organic binder are blended in the glaze frit, and water is added and mixed to obtain a glaze slurry.

  Then, as shown in FIG. 10, the glaze slurry S is sprayed and applied from the spray nozzle N onto the required surface of the insulator 2 to form a glaze slurry application layer 2d ′ as a glaze powder deposition layer. To dry.

  Next, an outline of the process of assembling the center electrode 3 and the terminal fitting 13 and forming the resistor 15 and the conductive glass sealing layers 16 and 17 to the insulator 2 on which the glaze slurry coating layer 2d ′ is formed. Is as follows. First, as shown in FIG. 11 (a), the central electrode 3 is inserted into the first portion 6a of the through hole 6 of the insulator 2, and then the conductive glass powder H is filled as shown in (b). . Then, as shown in (c), the powder H filled by inserting the pressing rod 28 into the through hole 6 is pre-compressed to form the first conductive glass powder layer 26. Subsequently, the raw material powder of the resistor composition is filled and pre-compressed in the same manner, and further conductive glass powder is filled and pre-compression is performed, so that the center electrode 3 side (lower side) is obtained as shown in FIG. The first conductive glass powder layer 26, the resistor composition powder layer 25, and the second conductive glass powder layer 27 are laminated in the through hole 6 from the side.

  Then, as shown in FIG. 12A, an assembly PA in which the terminal fitting 13 is disposed in the through hole 6 from above is formed. In this state, it is inserted into the furnace and heated to a predetermined temperature of 800 to 950 ° C., which is equal to or higher than the glass softening point, and then the terminal fitting 13 is pressed into the through hole 6 in the axial direction from the side opposite to the center electrode 3. The layers 25 to 27 in the laminated state are pressed in the axial direction. As a result, as shown in FIG. 4B, the layers are compressed and sintered to become the conductive glass seal layer 16, the resistor 15, and the conductive glass seal layer 17, respectively (the glass sealing step).

  Here, the glaze frit contained in the glaze slurry coating layer 2d ′ has a softening temperature of 600 to 700 ° C. by adopting the above-described composition, so that the contents of Na component and K component are relatively high. Since it is set, the softening temperature is lower than that of the conventional lead silicate glass glaze, and the calcination temperature can be lowered to 800 to 950 ° C. Accordingly, as shown in FIG. 12, the glaze slurry coating layer 2d 'is simultaneously glazed by the heating in the glass sealing step to become a glaze layer 2d. In other words, since the heating temperature in the glass sealing process is lowered from the conventional 900 to 1000 ° C. to 800 to 950 ° C., the surface of the center electrode 3 and the terminal fitting 13 is hardly oxidized. . In addition, since the glaze having the above composition has a relatively small difference in linear expansion coefficient from the alumina-based insulating material constituting the insulator 2, the glaze layer 2d is formed during cooling in the glass sealing process also serving as the glaze process. Cracks are less likely to occur.

  The metal shell 1, the ground electrode 4, and the like are assembled to the assembly PA in which the glass sealing process is completed in this way, and the spark plug 100 shown in FIG. 1 is completed. The spark plug 100 is attached to the engine block at the threaded portion 7 and is used as an ignition source for the air-fuel mixture supplied to the combustion chamber. Here, the glaze constituting the glaze layer 2d has a considerably high content of the alkali metal component as described above, but the conductivity is high because two kinds of alkali metal components Na and K are added in combination. It does not increase so much, ensuring good insulation, and excellent flashover resistance.

  The spark plug according to the present invention is not limited to the type shown in FIG. 1, but, for example, as shown in FIG. 5, the tip of the ground electrode 4 is opposed to the side surface of the center electrode 3, and a spark gap g is formed between them. It may be formed. In this case, as shown in FIG. 6 (a), the ground electrode 4 has a total of two, one on each side of the center electrode 3, as shown in FIG. Three or more things can be arranged around. Further, as shown in FIG. 7, the spark plug 100 is configured as a semi-surface discharge type spark plug in which the tip of the insulator 2 is inserted between the side surface of the center electrode 3 and the tip surface of the ground electrode 4. Also good. In this configuration, since spark discharge occurs along the surface of the front end portion of the insulator 2, the fouling resistance is improved as compared with an air discharge type spark plug.

(Example 2)
Examples of the spark plug according to the second configuration of the present invention will be described below. The configuration of the spark plug of Example 2 is exactly the same as that of Example 1 except for the composition of the glaze layer, and the description of the parts other than the glaze layer is detailed with reference to FIGS. Description is omitted. Glaze layer 2d is mainly cationic component is Si, B, and Zn, and Ba, consists of at least one selected from Ti and Zr, 20 to 40 wt% with the weight calculated oxide of Si component in SiO _2, 20 to 35% by weight in terms of oxide of B component converted to B ₂ O ₃ , 15 to 25% by weight in terms of oxide of Zn component to ZnO, and weight of Ba component to oxide in terms of BaO 10 to 23 wt%, Ti and Zr contain Ti in TiO ₂ , Zr contains ₂ to 10 wt% in total in terms of oxides, and Na, K and Li As an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is an oxide converted to Li ₂ O, and its total content is 12 wt% or less, Pb content Are composed of glaze was 0.1 wt% or less in terms of oxide to form a PbO.

Specifically, the composition of the glaze layer can be adjusted to satisfy at least one of the following four aspects. (1) a Si component in weight was oxide converted to SiO ₂ and 20 to 38 wt%. (2) The content of Zr in terms of ZrO ₂ is 3.4% by weight or less. (3) The weight content of Ti in terms of TiO ₂ is 1.5% by weight or more. (4) The weight content of Zr in terms of ZrO ₂ is WZr, the weight content of Ti in terms of TiO ₂ is WTi, and WTi / WZr is 0.2 to 10.

The manufacturing method of the spark plug 100 having the glaze layer 2d is substantially the same as that of the first embodiment except that the raw material blending composition of the glaze slurry to be used is different. Preparation of the glaze slurry is a component source powder serving as at least one component source selected from Si, B, Zn and Ba, and Ti and Zr (for example, Si component is SiO ₂ powder, B component is H ₃ BO ₃ Powder, Zn is ZnO powder, Ba component is BaCO ₃ powder, Ti is TiO ₂ powder, Zr is ZrO ₂ powder), and Si component is converted to SiO ₂ in an oxide conversion weight of 20 to 40% by weight, B component _{20 to} 35% by weight in terms of oxide in terms of B ₂ O ₃ , 15 to 25% by weight in terms of oxide in terms of Zn to ZnO, and 10 to 10% in terms of oxide in terms of Ba component to BaO. In addition to containing 23 wt%, Ti and Zr are mixed and mixed so that Ti contains TiO ₂ and Zr contains ₂ to 10 wt% in total in terms of oxides, respectively. . In the case where at least one selected from Na, K and Li is blended as an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is Li ₂ O in terms of oxide, The component source powder is blended so that the total content is 12% by weight or less. Next, the mixture is heated to 1000-1500 ° C. to melt, and the melt is poured into water to quench and vitrify, and further pulverized to make a glaze frit. Then, an appropriate amount of clay minerals such as kaolin and glazed clay and an organic binder are blended in the glaze frit, and water is added and mixed to obtain a glaze slurry.

  By selecting the content range of the alkali metal component and the B component as described above, it becomes possible to easily prepare a glaze slurry having a low viscosity and a high fluidity. As shown in FIG. 10, this glaze slurry S is sprayed and applied from the spray nozzle N onto the required surface of the insulator 2 to thereby have a uniform thickness and less entrainment of the glaze slurry 2d. Can form. Hereinafter, since the process of obtaining a spark plug through drying and calcination is substantially the same as in Example 1, detailed description thereof is omitted. The glaze layer 2d having a uniform thickness and few defects can be obtained by calcination. Moreover, since the glaze softening temperature is as low as 600-700 degreeC similarly to Example 1, as a result, the heating temperature of a glass sealing process is low-temperatured from the conventional 900-1000 degreeC to 800-950 degreeC, A center electrode 3 and the surface of the terminal fitting 13 are less likely to be oxidized. Further, since the glaze having the above composition has a relatively small difference in linear expansion coefficient from the alumina-based insulating material constituting the insulator 2, the glaze layer 2d is formed in the glaze layer 2d during cooling in the glass sealing process which also serves as the glaze process. Cracks are less likely to occur. On the other hand, since the glaze constituting the glaze layer 2d has a small content of the alkali metal component, good insulation is ensured and the flashover resistance is excellent.

  In addition, the spark plugs of Example 1 and Example 2 may have the same glaze layer 2d depending on how the composition is selected. In this case, the effect in the first configuration and the effect in the second configuration can be achieved simultaneously.

Experimental example

In order to confirm the effect of the present invention, the following experiment was conducted.
(Experimental example 1)
The insulator 2 was produced as follows. First, as a raw material powder, SiO ₂ (purity 99.5%, average) with respect to alumina powder (alumina 95 wt%, Na content (Na ₂ O conversion value) 0.1 wt%, average particle size 3.0 μm). Particle size 1.5 μm), CaCO ₃ (purity 99.9%, average particle size 2.0 μm), MgO (purity 99.5%, average particle size 2 μm), BaCO ₃ (purity 99.5%, average particle size) 1.5 μm), H ₃ BO ₃ (purity 99.0%, average particle size 1.5 μm), ZnO (purity 99.5%, average particle size 2.0 μm) in a predetermined ratio, and this combination Based on 100 parts by weight of the total powder, 3 parts by weight of PVA as a hydrophilic binder and 103 parts by weight of water were added and wet-mixed to prepare a molding base slurry.

Subsequently, the slurry having different compositions was dried by a spray drying method to prepare a spherical molding base granulated product. In addition, the granulated product is sized by a sieve to a particle size of 50 to 100 μm. And this granulated material is shape | molded by the pressure of 50 Mpa by the rubber press method demonstrated using FIG. 9, and it grinds the outer peripheral surface of the molded object, processes it to a predetermined insulator shape, and temperature 1550 degreeC. Insulator 2 was obtained by baking. Note that, by fluorescent X-ray analysis, the insulator 2 was found to have the following composition:
Al component: 94.9% by weight in terms of Al ₂ O ₃ ;
Si component: 2.4% by weight in terms of SiO ₂ ;
Ca component: 1.9% by weight in terms of CaO;
Mg component: 0.1% by weight in terms of MgO;
Ba component: 0.4% by weight in terms of BaO;
Component _B: B 2 _{O 3} in terms of 0.3% by weight.

  The dimensions of each part of the insulator 2 shown with reference to FIG. 4A are as follows: L1 = about 60 mm, L2 = about 8 mm, L3 = about 14 mm, D1 = about 10 mm, D2 = about 13 mm, D3 = about 7 mm, D4 = 5.5 mm, D5 = 4.5 mm, D6 = 4 mm, D7 = 2.6 mm, t1 = 1.5 mm, t2 = 1.45 mm, t3 = 1.25 mm, tA = 1.35 mm . Further, referring to FIG. 1, the length LQ of the portion 2 k protruding to the rear side of the metal shell 1 of the insulator 2 is 25 mm, and a longitudinal section including the central axis O of the insulator 2 is taken. Sometimes, on the outer peripheral surface of the protruding portion 2k of the insulator 2, the stepped outline from the position corresponding to the rear end edge of the metal shell 1 through the corrugation 2c to the rear end edge of the insulator 2 The length LP measured along the line is 29 mm.

Next, the glaze slurry was prepared as follows. First, SiO ₂ (purity 99.5%), H ₃ BO ₃ powder (purity 98.5%), ZnO powder (purity 99.5%), BaCO ₃ powder (purity 99.5%), Na ₂ as raw materials. CO ₃ powder (purity 99.5%), K ₂ CO ₃ powder (purity 99%), Al ₂ O ₃ powder (purity 99.5%), Fe ₂ O ₃ powder (purity 99.0%), CaCO ₃ Powder (purity 99.8%), TiO ₂ powder (purity 99.5%), SrCO ₃ powder (purity 99%), SnO ₂ powder (purity 99%), FeO powder (purity 99%) in various ratios Then, the mixture was heated to 1000 to 1500 ° C. to melt, and the melt was poured into water to quench and vitrify, and further pulverized to a particle size of 50 μm or less with an alumina pot mill to prepare a glaze frit. Then, 3 parts by weight of New Zealand kaolin as a clay mineral and 2 parts by weight of PVA as an organic binder are blended with 100 parts by weight of the glaze frit, and 100 parts by weight of water is added and mixed to obtain a glaze slurry. It was.

The glaze slurry was sprayed on the surface of the insulator 2 from the spray nozzle as shown in FIG. 10 and then dried to form a glaze slurry coating layer 2d ′. The coating thickness of the glaze after drying is about 80 μm. Using this insulator 2, various spark plugs 100 shown in FIG. 1 were prepared by the method already described with reference to FIGS. However, the outer diameter of the threaded portion 7 was 14 mm. Further, as the raw material powder of the resistor 15, B ₂ O ₃ —SiO ₂ —BaO—Li ₂ O-based glass, ZrO ₂ powder, carbon black powder, TiO ₂ powder, metal Al powder, conductive glass seal layer 16, As the raw material powder of No. 17, B ₂ O ₃ —SiO ₂ —Na ₂ O glass, Cu powder, Fe powder, and Fe—B powder were used, respectively, and the heating temperature at the time of glass sealing, that is, the calcination temperature was 900 ° C. went. Note that the thickness of the glaze layer 2d formed on the surface of each insulator 2 was approximately 50 μm.

On the other hand, a glaze sample coagulated in a lump without being crushed was also prepared. In addition, it was confirmed that this bulk glaze sample was vitrified (amorphized) by X-ray diffraction. The following experiment was conducted using this. Chemical composition analysis: by fluorescent X-ray analysis. Tables 1 and 3 show the analysis values for each sample (according to oxide conversion values). In addition, although each composition of the glaze layer 2d formed on the surface of the insulator 2 was measured by the EPMA method, it was confirmed that it almost coincided with the analysis value measured using the lump sample. Thermal expansion coefficient: A measurement sample having a size of 5 mm × 5 mm × 10 mm was cut out from a block sample and measured as an average value from 20 ° C. to 350 ° C. by a known dilatometer method. Moreover, when the measurement sample of the said dimension was cut out also from the insulator 2 and the same measurement was performed, the value was 73 * 10 < ^-7 > / ^degreeC . Softening temperature: Differential thermal analysis was performed while heating 50 mg of the powder sample, measurement was started from room temperature, and the temperature at which the second endothermic peak was reached was measured as the softening temperature.

  Moreover, about each spark plug, the insulation resistance measurement in 500 degreeC was performed with the energizing voltage 1000V by the method already demonstrated using FIG. Moreover, the formation state of the glaze layer 2d with respect to the insulator 2 was observed visually. The above results are shown in Tables 1 to 4.

  That is, for the spark plug in which the glaze layer that satisfies the requirements of the first configuration of the present invention is formed, the glaze layer is free from cracks and other defects, and is good even at a low calcination temperature of 800 to 950 ° C. It can be seen that a neat glaze layer is obtained. Moreover, although the content of the alkali metal component is large, the insulation resistance at 500 ° C. is as high as 200 MΩ or more, suggesting that it has good flashover resistance.

(Experimental example 2)
An insulator 2 having the same shape and material as in Experimental Example 1 was prepared. Moreover, the glaze slurry was prepared as follows. First, SiO ₂ (purity 99.5%), H ₃ BO ₃ powder (purity 98.5%), ZnO powder (purity 99.5%), BaCO ₃ powder (purity 99.5%), Na ₂ as raw materials. CO ₃ powder (purity 99.5%), K ₂ CO ₃ powder (purity 99%), Li ₂ CO ₃ powder (purity 99%), Al ₂ O ₃ powder (purity 99.5%), CaCO ₃ powder ( Purity 99.8%), TiO ₂ powder (purity 99.5%), ZrO ₂ powder (purity 98%) were blended in various ratios, and the mixture was heated to 1000-1500 ° C. to melt, and the melt Was poured into water, quenched and vitrified, and further pulverized with an alumina pot mill to an average particle size of 9 to 10 μm to prepare a glaze frit. Then, a glaze slurry is obtained by blending and mixing 10% by weight of kaolin (kaolin in the UK) as clay mineral, 1% by weight of acrylic organic binder, 35% by weight of water, and the balance as the glaze frit. It was.

  Each obtained slurry was allowed to stand in a constant temperature bath at 40 ° C. for 10 days in order to stabilize the elution state of the B component and the alkali metal component from the glaze frit. , Manufactured by Tokyo Keiki Co., Ltd., model number BH).

  Except for the use of the glaze slurry, various spark plugs 100 shown in FIG. 1 were prepared under the same conditions as in Experimental Example 1 (1000 for each glaze composition). Note that the thickness of the glaze layer 2d formed on the surface of each insulator 2 was approximately 50 μm. Each spark plug thus obtained was measured for insulation resistance at 500 ° C. in the same manner as in Example 1. Moreover, the formation state of the glaze layer 2d with respect to the insulator 2 was observed visually.

On the other hand, a glaze sample coagulated in a lump without being crushed was also prepared. In addition, it was confirmed that this bulk glaze sample was vitrified (amorphized) by X-ray diffraction. The following experiment was conducted using this.
(1) Chemical composition analysis: by fluorescent X-ray analysis. Table 5 shows the analysis values for each sample (according to oxide conversion values). In addition, although each composition of the glaze layer 2d formed on the surface of the insulator 2 was measured by the EPMA method, it was confirmed that it almost coincided with the analysis value measured using the lump sample.
(2) Softening temperature: A differential thermal analysis was performed while heating 50 mg of the powder sample, measurement was started from room temperature, and the temperature at which the second endothermic peak was reached was measured as the softening temperature. The results are shown in Table 6.
(3) Whether or not cracking or crazing had occurred in the glaze layer obtained by glazing was visually determined, and the number of generations in 1000 was determined. The results are shown in Table 6.

  That is, it can be seen that the spark plug in which the glaze layer that satisfies the requirements of the second configuration of the present invention is formed has a good melting state of the glaze layer and the occurrence frequency of cracks and crazing is low. In particular, a good glaze layer is obtained even at a low calcination temperature of 800 to 950 ° C. Further, the insulation resistance at 500 ° C. is as high as 200 MΩ or more, suggesting that it has good flashover resistance. Moreover, it turns out that the glaze slurry used for glaze layer formation has contributed to glaze layer formation with a comparatively small viscosity, a homogeneous, few defect.

The whole front sectional view showing an example of the spark plug of the present invention. The front fragmentary sectional view of the principal part of FIG. 1, and sectional drawing which expands and shows the vicinity of the ignition part further. The front view which shows the external appearance of an insulator with a glaze layer. The longitudinal section showing some examples of an insulator. The whole front view which shows another example of the spark plug of this invention. The top view of the ignition part vicinity of FIG. 5 and the top view of the modification. The whole front view which shows another example of the spark plug of this invention. Explanatory drawing which shows the measuring method of the insulation resistance value of a spark plug. Explanatory drawing of the rubber press method. Explanatory drawing of the formation process of a glaze slurry application layer. Explanatory drawing of a glass sealing process. Explanatory drawing following FIG.

Explanation of symbols

1 metal shell 2 insulator 2d glaze layer 2d 'glaze slurry application layer (glaze powder accumulation layer)
3 Center electrode 4 Ground electrode 13 Terminal fitting 15 Resistor (sintered conductive material part)
16, 17 Conductive glass seal layer (sintered conductive material part)
S glaze slurry

Claims (10)

A center electrode, a metal shell disposed outside the center electrode, a ground electrode disposed so that one end of the metal shell is coupled to face the center electrode, and the center electrode and the metal shell In the meantime, it has an insulator arranged so as to cover the outside of the central electrode, and a glaze layer formed in a form covering at least a part of the surface of the insulator, and the glaze constituting the glaze layer is , Consisting mainly of a cation component (hereinafter referred to as a main cation component) Si, B, Zn and Ba and at least one selected from Ti and Zr, and the Si component is converted into SiO ₂ by weight in terms of oxides of 20 to 20 38% by weight, 20 to 35% by weight in terms of B component converted to oxide of B ₂ O ₃ , 15 to 25% by weight in terms of Zn component converted to oxide in ZnO, Ba component to oxide in BaO 1 in converted weight 0 to 23% by weight, Ti and Zr contain Ti in TiO ₂ and Zr in ₂ to 10% by weight in terms of oxides, respectively, and from Na, K and Li. At least one selected as an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is an oxide converted weight to Li ₂ O, and the total content is 12 wt% or less, and Pb The spark plug is characterized in that its content is 0.1% by weight or less in the form of oxide converted to PbO. A center electrode, a metal shell disposed outside the center electrode, a ground electrode disposed so that one end of the metal shell is coupled to face the center electrode, and the center electrode and the metal shell In the meantime, it has an insulator arranged so as to cover the outside of the central electrode, and a glaze layer formed in a form covering at least a part of the surface of the insulator, and the glaze constituting the glaze layer is , Consisting mainly of a cation component (hereinafter referred to as a main cation component) Si, B, Zn and Ba and at least one selected from Ti and Zr, and the Si component is converted into SiO ₂ by weight in terms of oxides of 20 to 20 40% by weight, 20 to 35% by weight in terms of B component converted to oxide of B ₂ O ₃ , 15 to 25% by weight in terms of Zn component converted to oxide in ZnO, Ba component to oxide in BaO 1 in converted weight In addition to 0 to 23% by weight, Ti and Zr contain Ti in TiO ₂ and Zr in ₂ to 10% by weight in terms of oxides in terms of oxide, and the weight of Zr in terms of ZrO ₂ When the content is 3.4% by weight or less and at least one selected from Na, K and Li is an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is Li ₂ O The spark plug is characterized in that the total content is 12% by weight or less in terms of oxide converted weight, and the Pb content is 0.1% by weight or less in terms of oxide converted to PbO. . A center electrode, a metal shell disposed outside the center electrode, a ground electrode disposed so that one end of the metal shell is coupled to face the center electrode, and the center electrode and the metal shell In the meantime, it has an insulator arranged so as to cover the outside of the central electrode, and a glaze layer formed in a form covering at least a part of the surface of the insulator, and the glaze constituting the glaze layer is , Consisting mainly of a cation component (hereinafter referred to as a main cation component) Si, B, Zn and Ba and at least one selected from Ti and Zr, and the Si component is converted into SiO ₂ by weight in terms of oxides of 20 to 20 40% by weight, 20 to 35% by weight in terms of B component converted to oxide of B ₂ O ₃ , 15 to 25% by weight in terms of Zn component converted to oxide in ZnO, Ba component to oxide in BaO 1 in converted weight Together containing 0-23 wt%, Ti and Zr, Ti in TiO _2, Zr is contained 2-10 wt% in total at the weight calculated respectively oxide ZrO _2, and TiO ₂ conversion weight of Ti When the content is 1.5% by weight or more and at least one selected from Na, K and Li is an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is Li ₂ O The spark plug is characterized in that the total content is 12% by weight or less in terms of oxide converted weight, and the Pb content is 0.1% by weight or less in terms of oxide converted to PbO. . A center electrode, a metal shell disposed outside the center electrode, a ground electrode disposed so that one end of the metal shell is coupled to face the center electrode, and the center electrode and the metal shell In the meantime, it has an insulator arranged so as to cover the outside of the central electrode, and a glaze layer formed in a form covering at least a part of the surface of the insulator, and the glaze constituting the glaze layer is , Consisting mainly of a cation component (hereinafter referred to as a main cation component) Si, B, Zn and Ba and at least one selected from Ti and Zr, and the Si component is converted into SiO ₂ by weight in terms of oxides of 20 to 20 40% by weight, 20 to 35% by weight in terms of B component converted to oxide of B ₂ O ₃ , 15 to 25% by weight in terms of Zn component converted to oxide in ZnO, Ba component to oxide in BaO 1 in converted weight In addition to 0 to 23% by weight, Ti and Zr contain Ti in TiO ₂ and Zr in ₂ to 10% by weight in terms of oxides in terms of oxide, and the weight of Zr in terms of ZrO ₂ The content rate is WZr, the TiO ₂ equivalent weight content rate of Ti is WTi, WTi / WZr is 0.2 to 10, and at least one selected from Na, K and Li is an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is Li ₂ O in terms of oxide, the total content is 12% by weight or less, and the Pb content is converted to PbO in oxide form A spark plug characterized by being 0.1% by weight or less.   The spark plug according to any one of claims 1 to 4, wherein the glaze has a total content of at least one selected from Ti and Zr and the alkali metal component of 8% by weight or more.   The spark plug includes a shaft-shaped terminal fitting provided integrally with the center electrode or separately from the center electrode with a conductive coupling layer interposed therebetween in the through-hole of the insulator, The insulation resistance value measured by holding the entire spark plug at about 500 ° C. and energizing the terminal metal part and the metal shell through the insulator is 200 MΩ or more. The spark plug according to any one of 5. The insulator is made of an alumina-based insulating material containing 85 to 98% by weight of an Al component in terms of oxide converted to Al ₂ O ₃ , and the glaze is the temperature in a temperature range of 20 to 350 ° C. The spark plug according to any one of claims 1 to 6, wherein the average linear expansion coefficient of the glaze is 50 x ^10-7 / C to 85 x ^10-7 / C.   The spark plug according to any one of claims 1 to 7, wherein a softening temperature of the glaze is 600 to 700 ° C. It is a manufacturing method of the spark plug in any one of Claim 1 thru | or 8, Comprising: Each component source of Si, B, Zn, and Ba as said main cation component, and at least 1 sort (s) chosen from Ti and Zr; the component source powder comprising 20 to 40 wt% in weight was in terms of oxide of Si component in SiO _2, 20 to 35 wt% with the weight calculated oxide B component _B 2 _{O 3,} ZnO and Zn components 15 to 25% by weight in terms of oxide, and 10 to 23% by weight in terms of Ba component in terms of oxide to BaO, Ti and Zr are Ti in TiO ₂ and Zr in ZrO ₂ After mixing and mixing so as to contain a total of 2 to 10% by weight in terms of oxides, the mixture is heated to 1000 to 1500 ° C. to melt, and the melt is rapidly cooled to glass Powder A glaze powder preparation step of preparing a glaze powder using the frit thus formed, a glaze powder deposition step of depositing the glaze powder on the surface of the insulator to form a glaze powder deposition layer, and the insulator at 800 to 950 ° C. And a glaze firing step in which the glaze powder deposition layer is baked onto the surface of the insulator to form the glaze layer by firing in a temperature range of.   A terminal fitting is fixed to one end side of the through hole formed in the axial direction of the insulator, and a center electrode is fixed to the other end side, and the terminal is fixed in the through hole. In order to manufacture a spark plug in which a sintered conductive material portion mainly composed of a mixture of glass and a conductive material is formed between the metal fitting and the center electrode to electrically join them. A terminal fitting is disposed on one end side of the through hole of the insulator, and a center electrode is disposed on the other end side. The terminal fitting and the center electrode are disposed in the through hole. An assembly manufacturing process for manufacturing an assembly in which a packed layer of sintered conductive material raw material powder mainly composed of glass powder and conductive material powder is formed, and in the heated assembly, In the center electrode and the terminal gold The filler layer is pressed between the center electrode and the terminal fitting to form the sintered conductive material portion, and the glaze powder deposition layer is formed on the surface of the insulator. Heating the formed assembly to a temperature range of 800 to 950 ° C. to bake the glaze powder deposition layer on the insulator surface to form the glaze layer; and the glass in the filling layer The method for producing a spark plug according to claim 9, further comprising the calcination step of simultaneously performing a step of softening the powder.

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