JP2006196474A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug that has a glaze layer containing a Pb component in a low proportion, capable of being baked at relatively low temperatures, having an excellent insulating property, easy to obtain smooth baked surfaces, and capable of improving the mechanical strength of an insulator having the glaze layer. <P>SOLUTION: The glaze layer 2d of the spark plug 100 has a composition that contains: an Si component in a proportion of 15 to 60 mol% in terms of SiO<SB>2</SB>; a B component in a proportion of 22 to 50 mol% in terms of B<SB>2</SB>O<SB>3</SB>; a Zn component in a proportion of 10 to 30 mol% in terms of ZnO; at least one of a Ba component and an Sr component in a proportion of 0.5 to 35 mol% in total in terms of BaO and SrO, respectively; an F component in a proportion of 1 mol% or less; an Al component in a proportion of 0.1 to 5 mol% in terms of Al<SB>2</SB>O<SB>3</SB>; and an alkaline metal component consisting of at least one of Na, K and Li in a proportion of 1.1 to 10 mol% in total in terms of Na<SB>2</SB>O, K<SB>2</SB>O and Li<SB>2</SB>O, respectively, wherein Li is essential, and wherein the proportion of the Li component is 1.1 to 6 mol% in terms of Li<SB>2</SB>O. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

      The present invention relates to a spark plug.

  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.

  In the case of alumina-based insulators for spark plugs, lead silicate glass glazes that have a relatively low softening point by blending a relatively large amount of PbO with silicate glass have been used. In recent years, there has been an increasing interest in glazing, and glazes containing Pb are increasingly 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.

  However, borosilicate glass and alkali borosilicate glass-based lead-free glazes that are being considered as substitutes for such Pb-containing glazes avoid problems such as high glass transition points or insufficient insulation resistance. I wanted to. In order to solve this problem, Japanese Patent Application Laid-Open No. 11-43351 discloses a composition of a lead-free glaze that achieves glass stabilization without reducing fluidity during sintering by adjusting the composition of the Zn component, etc. JP-A-11-106234 discloses a composition of a lead-free glaze in which the insulation resistance is improved by the co-addition effect of an alkali component.

  By the way, the glaze layer for spark plugs prevents dirt from adhering to the surface of the insulator, improves creeping discharge withstand voltage to prevent flashover, and eliminates defects on the surface of the insulator that are prone to breakage. It also fulfills the function of filling and improving strength. However, in a recent internal combustion engine whose output is particularly high, vibrations and impacts received by the spark plug during operation are considerably large, and even if a glaze layer is formed, breakage of the insulator may become a problem. In addition, if an excessive tightening torque is applied when the spark plug is attached to the cylinder head (particularly when assembling using a power tool such as an impact wrench), the insulator may still be broken. In addition, since the voltage applied to the spark plug has been increased along with the enhancement of the engine performance, there is a demand for insulation performance that can withstand glazes even in a more severe environment. In the glaze composition disclosed in Japanese Patent No. 106234 and Japanese Patent Laid-Open No. 11-106234, there is a problem that the glaze composition for achieving both insulating performance and mechanical properties is not always sufficiently studied.

  The problem of the present invention is that the content of the Pb component is small, it can be fired at a relatively low temperature, has excellent insulating properties, and it is easy to obtain a smooth fired surface, and the mechanical strength of the insulator with a glaze layer is also high. It is an object to provide a spark plug having a glaze layer that can be improved.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, a spark plug of the present invention is a spark plug in which an insulator made of an alumina-based ceramic is disposed between a center electrode and a metal shell, and covers at least a part of the surface of the insulator. An oxide-based glaze layer is formed, and the glaze layer is
The content of the Pb component is 1 mol% or less in terms of PbO,
The Si component is converted to SiO ₂ in an oxide conversion value of 15 to 60 mol%, the B component is converted into an oxide conversion value into B ₂ O ₃ , and the Zn component is converted into an oxide conversion value into ZnO. 10 to 30 mol%, Ba and / or Sr components are contained in a total of 0.5 to 35 mol% in terms of oxide conversion to BaO or SrO,
The content of the F component is 1 mol% or less,
The Al component contained 0.1 to 5 mol% in terms of oxide values to _Al 2 _{O 3,}
As an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is a value in terms of oxide converted to Li ₂ O, and a total of 1.1 to 10 mol of one or two or more essential components of Li. % In the range,
And, wherein the range of content of Li component is a 1.1～6Mol% in terms of oxide value to Li ₂ O.

In the spark plug of the above basic invention, in order to achieve compatibility with the above-mentioned environmental problems, the glaze used is premised on the content of the Pb component being 1.0 mol% or less in terms of PbO (hereinafter referred to as “PbO”). The glaze whose Pb component content is reduced to this level is referred to as a lead-free glaze). Further, if the Pb component is contained in the glaze layer in the form of ions with a low valence (for example, Pb ²⁺ ), this is oxidized to ions with a high valence (for example, Pb ³⁺ ) by corona discharge, etc. Since the insulating properties may be reduced and the flashover resistance may be impaired, it is advantageous in this respect to reduce the Pb content as described above. The Pb content is desirably 0.1 mol% or less, and more desirably substantially not contained (excluding those inevitably mixed from glaze raw materials).

  However, as a result of studies by the present inventors, it has been found that when the content of the Pb component in the glaze layer decreases, the mechanical strength, particularly impact resistance, of the glaze layer tends to be relatively lowered. Therefore, it can be sintered at a relatively low temperature by containing an Si component, a B component, a Zn component, a Ba and / or Sr component, an Al component, and an alkali metal component essential for the Li component in the above range. Thus, the inventors have found that the mechanical strength, in particular, the impact resistance of the insulator with a glaze layer can be greatly improved because it is easy to obtain a smooth glazed surface with excellent insulation, and the present invention has been completed. As a result, even when mounted on a high-power internal combustion engine, the spark plug insulation breaks during operation, or when the spark plug is mounted on the cylinder head (especially, a power tool such as an impact wrench is used). Even when a slightly excessive tightening torque is applied during the assembly), the insulator is less likely to break.

  Hereinafter, the critical meaning of the content range of each component of the glaze layer in the configuration of the spark plug will be described. The Si component is a skeleton forming component of the vitreous glaze layer, and is also an indispensable component for ensuring the insulating properties of the glaze layer. If the content is less than 15 mol%, it may be difficult to ensure sufficient insulation performance. Moreover, when Si component exceeds 60 mol%, sinter firing may become difficult. The Si component content is more desirably set in the range of 25 to 40 mol%.

  In addition, the B component is the main component of the skeleton forming component of the vitreous glaze layer together with the Si component, and when combined with the Si component, the glaze softening point is lowered and the flowability during calcination is improved. It also makes it easy to obtain a smooth glazed surface. However, when the B component content is less than 22 mol%, the softening point of the glaze increases, and smoldering may become difficult. On the other hand, when the B component content exceeds 55 mol%, appearance defects such as wrinkles tend to be caused. Or the water resistance of the glaze slurry may be impaired. Further, depending on the content of other components, there may be a concern about problems such as devitrification of the glaze layer, deterioration of insulating properties, or incompatibility with the thermal expansion coefficient with the base. The B component content is desirably set in the range of 25 to 35 mol%.

  The Zn component content increases the fluidity at the time of calcination instead of the Pb component, and makes it easy to obtain a smooth glazed surface. In addition, by blending more than a certain amount, the difference in thermal expansion coefficient between the insulator base made of alumina ceramic and the glaze layer is reduced, the occurrence of defects in the glaze layer is prevented, and the residual level of tensile residual stress Suppresses the strength of the insulator with the glaze layer, and in particular increases the impact resistance. However, when the content is less than 10 mol%, the thermal expansion coefficient of the glaze layer becomes too large, and defects such as penetration may easily occur in the glaze layer. Moreover, if the Zn component is insufficient, smoldering may be difficult. On the other hand, when the content of the Zn component exceeds 30 mol%, white turbidity or the like tends to occur in the glaze layer due to devitrification. The content of the Zn component is more desirably adjusted in the range of 10 to 20 mol%.

  The Ba component or Sr component contributes to the improvement of the insulating properties of the glaze layer and is also effective in improving the strength. If the total content is less than 0.5 mol%, the insulating properties of the glaze may be reduced, leading to a loss of flashover resistance. On the other hand, if the total content exceeds 31 mol%, the thermal expansion coefficient of the glaze layer becomes too high, and defects such as penetration occur in the glaze layer, and tensile stress tends to remain in the glaze layer when cooled from a high temperature. Thus, the strength of the insulator with the glaze layer, such as impact resistance, is likely to be impaired. Further, the glaze layer is devitrified and white turbidity is likely to occur. The total content of the Ba and Sr components is preferably set in the range of 0.5 to 20 mol% from the viewpoint of improving the insulation and adjusting the thermal expansion coefficient. In particular, the range of the above-mentioned Si component is 25 to 40 mol. The effect is large when% is used. In addition, Ba component and Sr component may contain any one individually, and may mix and contain both. However, in terms of raw material cost, it is advantageous to use a cheaper Ba component.

Note that the Ba component and the Sr component may exist in a form other than the oxide in the glaze depending on the raw materials used. For example, when BaSO ₄ is used as the Ba component source, the S component may remain in the glaze layer. This sulfur component may be concentrated near the surface of the glaze layer during glazing, thereby reducing the surface tension of the molten glaze and improving the smoothness of the resulting glaze layer.

Next, the F component is made 1 mol% or less when the flux component containing more than 1 mol% in the glaze (for example, a medium flux containing F component such as CaF ₂ (fluorite) is added to the glaze. Is contained inevitably), bubbles tend to become a starting point of breakage in the glaze at the time of glazing, and the strength of the insulator with the glaze layer, such as impact resistance, is impaired. Because. Moreover, the gas which contains F component at the time of a sinter is generated, and it reacts with the refractory which comprises a furnace wall etc., and the malfunction which shortens a furnace wall lifetime tends to be caused. It is more desirable that the F component is not contained in the glaze layer as much as possible. For that purpose, it is better not to use a medium flux containing an F component such as the above-mentioned CaF ₂ as much as possible.

  Next, the Al component expands the temperature range that can be sintered, stabilizes the fluidity of the glaze during calcination, increases the strength of the glaze layer, and significantly increases the impact resistance of the insulator with the glaze layer. Eggplant. However, if the content is less than 0.1 mol% in terms of the above-mentioned oxide, the effect is poor, and if it exceeds 5 mol%, the resulting glaze layer becomes an opaque matte state (so-called mat shape), and the appearance of the spark plug is impaired. In addition to this, the markings formed on the base cannot be read. The content of the Al component is desirably 1 to 3 mol%.

  Next, the alkali metal component in the glaze layer is used mainly for the purpose of lowering the softening point of the glaze layer and increasing the fluidity at the time of calcination. The total content is 1.1 to 10 mol%. If it is less than 1.1 mol%, the softening point of the glaze will increase, and smoldering may become impossible. Moreover, when it exceeds 10 mol%, the insulation of a glaze layer falls and flashover resistance may be impaired. The content of the alkali metal component is desirably 5 to 8 mol%. In addition, with respect to the alkali metal component, it is more effective for coexisting two or more kinds selected from Na, K, and Li to suppress the lowering of the insulating properties of the glaze layer, instead of adding one kind of alkali metal component alone. . As a result, it is possible to increase the content of alkali metal components without degrading insulation, and as a result, it is possible to simultaneously achieve the two purposes of ensuring fluidity and ensuring flashover resistance during smoldering. (So-called alkali co-addition effect).

  Of the alkali metal components, the Li component has a particularly high fluidity improving effect during calcination, and is effective not only in obtaining a smooth and few defect glazed surface, but also a thermal expansion coefficient of the glaze layer. It has a remarkable effect on the suppression of the rise of the tensile strength, and consequently, the residual tensile stress generated in the glaze layer is remarkably suppressed. All of these have the effect of improving the strength of the insulator with the glaze layer, for example, impact resistance. However, if the content of the Li component in terms of the oxide is less than 1.1 mol%, the effect is poor, and if it exceeds 6 mol%, the insulating properties of the glaze layer are not sufficiently ensured. The content of the Li component is more desirably 2 to 4 mol%.

Hereinafter, a more desirable composition of the glaze layer will be described.
In the glaze layer, the ZnO content in terms of ZnO is NZnO (mol%), the Ba content in terms of BaO is NBaO (mol%), and the Sr component content in terms of SrO is NSrO (mol%). The total content NZnO + NBaO + NSrO is desirably 15 to 45 mol%. If the total content thereof exceeds 45 mol%, the glaze layer may be devitrified to cause white turbidity. For example, on the outer surface of the insulator, visual information such as characters, figures, or product numbers for specifying the manufacturer etc. is printed and printed using a color sticker, etc. It may be difficult to read the visual information. Moreover, if it is less than 15 mol%, the softening point of a glaze will rise too much and it will become difficult to smolder and it may also cause the appearance defect. The total content is desirably 15 to 25 mol%.

  Further, the glaze layer is preferably NZnO> NBaO + NSrO. By doing so, the thermal expansion coefficient of the glaze layer is further reduced, and the difference in thermal expansion coefficient with the alumina-based ceramic that is the base is further reduced, so that the tensile stress level remaining in the glaze layer after calcination is reduced. It is also possible to make it smaller, and further to make the residual stress into a compressive stress state. As a result, the impact resistance of the insulator with a glaze layer can be further improved.

  The Li component is preferably set in the range of 0.2 ≦ Li / (Na + K + Li) ≦ 0.5 in terms of the molar content in terms of oxide as described above. If the proportion of Li is less than 0.2, the coefficient of thermal expansion becomes too large compared to the underlying alumina, and as a result, defects such as penetration (crazing) are likely to occur, and the finish of the fired surface becomes insufficient. There is a case. On the other hand, when the ratio of Li is greater than 0.5, Li ions have a relatively high mobility among alkali metal ions, and thus may adversely affect the insulating performance of the glaze layer. The value of Li / (Na + K + Li) is more preferably adjusted in the range of 0.3 to 0.45. In addition, in order to further enhance the insulation improvement effect due to the co-addition effect of the alkali metal component, in the range where the total content of the alkali metal component is excessive and the conductivity is not impaired, the K, Na, etc. It is also possible to mix other alkali metal components after the third component, and it is particularly desirable to contain all three components of Na, K and Li.

  The glaze layer preferably has NB2O3 / (NZnO + NBaO + NSrO) of 0.5 to 2.0. If the value is less than 0.5, the glaze layer tends to be devitrified, and if it exceeds 2.0, the softening point of the glaze layer may be increased, and calcination may be difficult.

Next, the glaze layer contains one or more components of Ti, Zr and Hf, Zr is ZrO ₂ , Ti is TiO ₂ and Hf is HfO ₂ in terms of oxides in total. It can contain in the range of 0.5-5 mol%. By including one or more components of Ti, Zr and Hf, water resistance is improved. Regarding the Zr component or the Hf component, the water resistance improving effect of the glaze slurry is more remarkable than the Ti component. Note that “good water resistance” means that, for example, when a powdery glaze raw material is mixed with a solvent such as water and left for a long time in the form of a glaze slurry, the viscosity of the glaze slurry due to component elution increases. It means that it becomes difficult to occur. As a result, when applying the glaze slurry to the insulator, it becomes easy to optimize the coating thickness, and the variation in thickness is reduced. As a result, it is possible to effectively optimize the thickness of the glaze layer formed by the calcination and reduce variations. In addition, if the total content of the above components is less than 0.5 mol%, the effect is poor, and if it exceeds 5 mol%, the glaze layer tends to devitrify.

Further, the glaze layer contains one or more components of Mo, W, Ni, Co, Fe and Mn (hereinafter referred to as fluidity-improving transition metal components), Mo is MoO ₃ , W is WO ₃ , Ni is Ni ₃ O ₄ , Co is Co ₃ O ₄ , Fe is Fe ₂ O ₃ , and Mn is MnO ₂ in terms of oxides, and the total content is 0.5 to 5 mol%. it can. By adding one or more components of Mo, W, Ni, Co, Fe and Mn within the above-mentioned content range, the fluidity at the time of calcination can be secured, and as a result Since a glaze layer that can be baked and has excellent insulating properties and has a smooth glazed surface is obtained, the impact resistance of the insulator with a glaze layer can be further enhanced.

  If the total content in terms of oxide is less than 0.5 mol%, the effect of improving the fluidity at the time of calcination and making it easy to obtain a smooth glaze layer may not always be sufficiently achieved. On the other hand, if it exceeds 5 mol%, smoldering may be difficult or impossible due to an excessive increase in the softening point of the glaze.

  Moreover, as a problem when the content of the fluidity-improving transition metal component becomes excessive, there is a case where unintentional coloring may occur in the glaze layer. For example, on the outer surface of the insulator, visual information such as characters, figures, or product numbers for specifying the manufacturer or the like is printed using a color glaze, but the glaze layer is colored so strongly. If it becomes too much, it may be difficult to read the printed visual information. Another realistic problem is that the color change resulting from the change in the glaze composition is reflected on the buyer side as “a change without the reason for the familiar appearance color”, and the product does not always accept smoothly due to its resistance. Such a problem may occur.

  The insulator forming the base of the glaze layer is composed of white alumina-based ceramic in the present invention. However, in terms of preventing or suppressing coloring, the insulator is formed on the insulator. It is desirable to adjust the composition so that the observed appearance color tone of the glaze layer is 0 to 6 in saturation Cs and 7.5 to 10 in brightness Vs, for example, adjusting the content of the transition metal component. When the saturation exceeds 6, hue discrimination with the naked eye becomes remarkable, and when the lightness is less than 7.5, a gray or blackish tone is easily identified. In either case, there is a problem that the appearance of “clearly colored” cannot be wiped out. The saturation Cs is desirably 0 to 2, more desirably 0 to 1, and the saturation Vs is desirably 8 to 10 and more desirably 9 to 10. In this specification, the measurement method of lightness VS and saturation CS is defined in JIS-Z8722 “Measurement method of color” in “4.3 Spectral measurement method” and “4.3 Reflection object measurement method”. It is assumed that the method described above is used. However, as a simple method, it is also possible to know the brightness and saturation by visual comparison with a standard color chart created in accordance with JIS-Z8721.

  Mo, Fe, and then W are particularly prominent in the fluidity improvement effect at the time of smoldering. For example, all of the essential transition metal components can be Mo, Fe, or W. Further, in order to further enhance the fluidity improvement effect during smoldering, it is desirable that 50 mol% or more of the fluidity improvement transition metal component is Mo.

  In addition, the glaze layer has 1 to 10 mol% of Ca component in terms of oxide converted to CaO, and one or two of Mg component of 0.1 to 10 mol% in terms of oxide converted to MgO. A total of 1-12 mol% of seeds or more can be contained. These components contribute to the improvement of the insulating properties of the glaze layer. In particular, the Ca component is effective next to the Ba component or the Zn component in improving the insulating properties of the glaze layer. If the addition amount is less than the above lower limit values, the effect is poor, and if the upper limit value of each component or the upper limit value of the total content is exceeded, smoldering is difficult or impossible due to excessive increase in the softening point. There is a case.

The glaze layer contains one or more auxiliary components of Bi, Sn, Sb, P, Cu, Ce and Cr, Bi is Bi ₂ O ₃ , Sn is SnO ₂ , and Sb is Sb ₂ O ₅ , P in P ₂ O ₅ , Cu in CuO, Ce in CeO ₂ , and Cr in Cr ₂ O ₃ should be contained in a total amount of 5 mol% or less in terms of oxides. it can. These components can be positively added according to various purposes, or a refractory material in a melting process for producing a glaze raw material (or a clay mineral to be blended when preparing a glaze slurry described later) or a glaze frit. In some cases, impurities (or contaminants) are inevitably mixed. Both of them have the effect of increasing the fluidity during the calcination and suppressing the formation of bubbles in the glaze layer, or preventing the deposits on the glazed surface from being encased during the flow and becoming abnormal protrusions. Bi and Sb are particularly effective (Bi may be designated as a restricted substance in the future). Also, rare earth elements RE other than Ce (however, selected from the group consisting of Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), It can be used as an auxiliary component and, together with Ce, is effective in improving the fluidity at the time of smoldering following Bi and Sb. In this case, Pr is converted to Pr ₇ O ₁₁ , and the others are converted to oxides of RE ₂ O ₃ .

  In the configuration of the spark plug of the present invention, each component in the glaze is often contained in the form of an oxide, but due to factors such as the formation of an amorphous glass phase, it is oxidized. In many cases, it is not possible to directly identify the existence form of an object. 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 component of 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.

By adopting the above composition as the glaze layer composition, the insulator that protrudes from the metal shell with respect to the test fixture fixing base with the direction away from the spark discharge gap in the axial direction of the insulator as the backward direction While the rear part is fixed vertically upward, a steel hammer of 1.13 kg is attached to the tip of the shaft fulcrum located on the central axis of the insulator further above the insulator rear part. Attach a 330 mm long arm so that it can pivot, and determine the position of the shaft fulcrum so that the hammer position when lowered to the rear part of the insulator is 1 mm as the vertical distance from the rear end surface of the insulator,
The operation of lifting the hammer so that the turning angle of the arm from the central axis becomes a predetermined value and lowering the hammer toward the rear part of the insulator by free fall is repeated while increasing stepwise at intervals of 2 °. In this case, the impact endurance angle value required as the limit angle when the insulator is cracked can be ensured to be 35 ° or more. As a result, when the spark plug is attached to a high-power internal combustion engine, it receives vibration / impact, or when the spark plug is attached to the cylinder head (especially when assembling with a power tool such as an impact wrench). Even when a somewhat excessive tightening torque is applied, it is possible to effectively prevent or suppress a problem that the insulator breaks.

  In addition, the insulator is formed with a circumferential protrusion on the outer peripheral surface at an axially intermediate position, and the insulator is adjacent to the protrusion on the rear side with the side toward the tip of the center electrode in the axial direction as the front side. A configuration in which the outer peripheral surface of the base end portion of the main body is formed in a cylindrical shape, and the glaze layer is formed in a thickness range of 7 to 50 μm so as to cover the outer peripheral surface of the base end portion can be adopted.

  In automobile engines and the like, a method of attaching a spark plug to an engine electrical system using a rubber cap is generally widely used. However, in order to improve flashover resistance, the adhesion between the insulator and the inner surface of the rubber cap is required. is important. As a result of intensive studies by the present inventors, it was found that in lead-free glazes of borosilicate glass or alkali borosilicate glass, it is important to adjust the thickness of the glaze layer in order to obtain a smooth glazed surface. . And, since the outer peripheral surface of the base end portion of the insulator main body is particularly required to adhere to a rubber cap, the flashover resistance and the like cannot be sufficiently ensured unless the film thickness is adjusted properly. There was found. Therefore, in the spark plug of the third invention, in the insulator having the lead-free glaze layer of the above composition, the glaze layer is set by setting the film thickness of the glaze layer covering the outer peripheral surface of the base end portion of the main body portion within the above numerical range. The adhesion between the baked surface and the rubber cap can be improved without lowering the insulating property, and the flashover resistance can be improved.

  Moreover, the impact resistance of the insulator with a glaze layer can be further improved by adjusting the thickness of the glaze layer as described above. If the thickness of the glaze layer at the relevant part of the insulator is less than 7 μm, the glaze layer becomes too thin and the absolute strength or the effect of defect covering on the insulator surface is not good. It may be sufficient and impact resistance may be insufficient. On the other hand, if the thickness of the glaze layer exceeds 50 μm, it is difficult to ensure insulation in the lead-free glaze layer having the above composition, which leads to a decrease in flashover resistance as well as the balance between the thermal expansion coefficient and the thickness of the glaze layer. The residual stress amount after calcination determined by is too large, and the impact resistance may be insufficient. The thickness of the glaze layer is more preferably 10 to 30 μm.

  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. 4 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 configured to Al component in the alumina insulating material containing 85～98Mol% in terms of oxide values to _Al 2 _{O 3.} In addition, the glaze layer preferably has an average thermal expansion coefficient of the glaze layer in the temperature range of 20 to 350 ° C. in the range of 50 × 10 ⁻⁷ / ° C. to 85 × 10 ⁻⁷ / ° C. . If the thermal expansion coefficient is smaller than this lower limit value, defects such as cracks and splattering may easily occur in the glaze layer. On the other hand, if the thermal expansion coefficient is larger than this upper limit value, defects such as a glaze layer tend to occur. The thermal expansion coefficient is more preferably in the range of 60 × 10 ⁻⁷ / ° C. to 80 × 10 ⁻⁷ / ° C.

  The thermal expansion coefficient of the glaze layer was measured by a known dilatometer method using a sample cut out of a glassy bulk material obtained by blending and dissolving the raw materials so as to have substantially the same composition as the glaze layer. It can be estimated by value. The thermal 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 spark plug of the present invention can be manufactured by the following manufacturing method. That is, in this method, after mixing and mixing the component source powders that are the respective component sources of the glaze so as to obtain the desired composition, the mixture is heated to 1000 to 1500 ° C. to melt it, A glaze powder preparation process for preparing a rapidly-cooled, vitrified and crushed glaze powder;
A glaze powder deposition step of depositing the glaze powder on the surface of the insulator to form a glaze powder deposition layer;
A glaze firing step in which the glaze powder deposition layer is baked onto the insulator surface by heating the insulator to form a glaze layer;
including.

  In addition, as the component source powder of each component, various inorganic materials such as hydroxides, carbonates, chlorides, sulfates, nitrates, phosphates, etc. in addition to oxides of these components (may be complex oxides) Powder 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 used as a glaze slurry by dispersing it in water or a solvent. For example, a glaze powder deposition layer is formed as a coating layer of the glaze slurry by applying the glaze slurry to an insulator surface and drying it. it can. 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.

An appropriate amount of clay mineral or organic binder can be blended in the glaze slurry 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 forms 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. However, it is also possible to perform the calcination process first and then perform the glass sealing process.

  The softening point of the glaze layer is preferably adjusted in the range of 520 to 700 ° C., for example. When the softening point exceeds 700 ° C., a calcination temperature of 950 ° C. or higher is required when the glass sealing process is also used as a calcination process, and oxidation of the center electrode and terminal fittings is likely to proceed. On the other hand, when the softening point is less than 520 ° C., it is necessary to set the calcination temperature 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 point 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, the sintered conductive material portion includes a resistor. May lead to degradation of performance such as load life characteristics. The softening point of the glaze layer is desirably adjusted in the range of 600 to 700 ° C.

  The softening point of the glaze layer is, for example, the peak that appears next to the first endothermic peak representing the bent point (that is, the second occurrence) by performing differential thermal analysis while peeling the glaze layer from the insulator and heating it. The temperature of the endothermic peak is defined as the softening point. In addition, for the softening point of the glaze layer formed on the insulator surface, the content of each component in the glaze layer is analyzed to calculate the oxide-converted composition, and each composition is almost equal to this composition. It is also possible to estimate the softening point of the formed glaze layer based on the softening point of the glass sample by mixing and dissolving the oxide raw material of the element to be oxidized and then rapidly cooling to obtain a glass sample.

  Hereinafter, embodiments of the present invention will be described with reference to some examples shown in the drawings. FIG. 1 shows 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.

  A through hole 6 is formed in the axial direction of the insulator 2, a terminal fitting 13 is fixed to one end portion thereof, and the center electrode 3 is fixed to the other end portion. 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, the Al component, 85～98Mol% in terms of value to the _Al 2 _{O 3} (preferably 90~98mol%) is constructed as an alumina based ceramic sintered body containing The

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

  In the middle of the insulator 2 in the axial direction, a protruding portion 2e protruding outward in the circumferential direction is formed in a flange shape, for example. 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. 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.3 (a), and it is for the electrode fixing of the center electrode 3 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. 3A and FIG. 3B 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 wall 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-described dimensions of the insulator 2 shown in FIG. 3A 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. 3B, the first shaft portion 2g and the second shaft portion 2i each have a slightly larger outer diameter than that shown in FIG. 3A. 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. 2, 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. The thickness of the glaze layer 2d is 7 to 150 μm, preferably 10 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.

  Next, the glaze layer 2d has at least one of the compositions of the present invention described in the section for solving the problem and the action / effect. The critical meaning of the composition range of each component has already been described in detail and will not be repeated here. Further, the thickness of the glaze layer 2d at the outer peripheral surface of the base end portion of the insulator main body portion 2b (the portion that protrudes rearward from the metal shell 1 and presents the cylindrical outer peripheral surface to which the corrugation portion 2c is not provided) t1 (average value) is 7 to 50 μm. The corrugation portion 2c can be omitted. In this case, the thickness (average) of the glaze layer 2d on the outer peripheral surface of the portion up to 50% of the protruding length LQ of the main body portion 1b with the rear end edge of the metal shell 1 as a base point Value) is taken to be t1.

  Next, the main body 3a of the ground electrode 4 and the center electrode 3 is 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. The main body 3a of the center electrode 3 is reduced in diameter on the front end side and has a flat front end surface, on which a disk-shaped chip made of an alloy composition constituting the ignition portion is overlapped, and the outer edge of the joint surface The ignition part 31 is formed by forming the welded part W along the part by laser welding, electron beam welding, resistance welding or the like and fixing it. 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. For example, each component source powder is composed of SiO ₂ powder for Si component, CaCO ₃ powder for Ca component, MgO powder for Mg component, BaCO ₃ or BaSO _{4 for} Ba component, and H ₃ BO ₃ powder for B component. it can. _{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. The molded body is further processed by grinder cutting or the like on the outer surface side to finish the 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 such as Si, B, Zn, Ba, and alkali metal components (Na, K, Li) (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 or BaSO ₄ powder, Na is Na ₂ CO ₃ powder, K is K ₂ CO ₃ powder, Li is Li ₂ CO ₃ powder) so as to obtain a predetermined composition And mix. Next, the mixture is heated to 1000 to 1500 ° C. to melt, and the melt is poured into water to quench and vitrify, and further pulverized to make a glaze powder. And a glaze slurry is obtained by mix | blending an appropriate quantity with clay minerals, such as a kaolin and a clam clay, and an organic binder, and adding water and mixing with this glaze powder.

  Then, as shown in FIG. 5, 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 to Fig.6 (a), after inserting the center electrode 3 in the 1st part 6a with respect to the through-hole 6 of the insulator 2, it fills with the conductive glass powder H as shown to (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 preliminarily compressed in the same manner, and further, the conductive glass powder is filled and preliminarily compressed, so that 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. 7A, 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 a heating 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, if the softening point of the glaze powder contained in the glaze slurry coating layer 2d ′ is set to 600 to 700 ° C., the glaze slurry coating layer 2d ′ is simultaneously melted by heating in the glass sealing step as shown in FIG. The glaze layer 2d can be baked. In addition, by adopting a relatively low temperature of 800 to 950 ° C. as the heating temperature in the glass sealing process, oxidation to the surface of the center electrode 3 and the terminal fitting 13 is less likely to occur.

  When a burner type gas furnace is used as a heating furnace (also serving as a smoldering furnace), the heating atmosphere contains a relatively large amount of water vapor as a combustion product. At this time, by using a glaze composition in which the content of the B component is kept at 40 mol% or less, the fluidity at the time of calcination can be secured even in an atmosphere where a lot of water vapor exists. It is possible to form a glaze layer that is smooth and homogeneous and also has good insulating properties.

  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 attachment of the high-voltage cable or the ignition coil to the spark plug 100 is constituted by a rubber cap (for example, silicon rubber or the like) that covers the outer peripheral surface of the main body 2b of the insulator 2 as shown by a virtual line in FIG. ) Performed using RC. The rubber cap RC has a hole diameter smaller by 0.5 to 1.0 mm than the outer diameter D1 (FIG. 3) of the main body 2b. The main body 2b is pushed into the hole so as to be covered up to the base end while elastically expanding the hole. As a result, the rubber cap RC is in close contact with the outer peripheral surface of the base end portion of the main body 2b on the inner surface of the hole, and functions as an insulating coating for preventing flashover and the like.

  Note that the spark plug of the present invention is not limited to the type shown in FIG. 1, and may be one in which the tip of the ground electrode is opposed to the side surface of the center electrode and a spark gap is formed therebetween. Further, the spark plug may be configured as a semi-surface discharge type spark plug in which the tip of the insulator is inserted between the side surface of the center electrode and the tip surface of the ground electrode.

In order to confirm the effect of the present invention, the following experiment was conducted.
The insulator 2 was produced as follows. First, as a raw material powder, SiO ₂ (purity 99.5%, average particle diameter) with respect to alumina powder (alumina 95 mol%, Na content (Na ₂ O conversion value) 0.1 mol%, average particle diameter 3.0 μm). 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 mixed powder A molding base slurry was prepared by adding 3 parts by mass of PVA as a hydrophilic binder and 103 parts by mass of water, with the total amount being 100 parts by mass, and wet mixing.

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. Then, this granulated product is molded at a pressure of 50 MPa by a known rubber press method, and the outer peripheral surface of the molded product is processed into a predetermined insulator shape by grinding, and fired at a temperature of 1550 ° C. Thus, an insulator 2 was obtained. In addition, it was found by fluorescent X-ray analysis that the insulator 2 has the following composition: Al component: 94.9 mol% in terms of Al ₂ O ₃ ; Si component: _{2. in} terms of SiO 2. 4 mol%; Ca component: 1.9 mol% in terms of CaO value; Mg component: 0.1 mol% in terms of value to MgO; Ba component: 0.4 mol% in terms of value to BaO; B _component: B 2 _{O 3} in terms of value 0.3 mol%.

  Further, the dimensions of each part of the insulator 2 shown with the aid of FIG. 3A 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%), Al ₂ O ₃ powder (purity 99.5%), H ₃ BO ₃ powder (purity 98.5%), Na ₂ CO ₃ powder (purity 99.5) as raw materials. _%), K 2 CO ₃ powder (purity 99%), _Li 2 CO ₃ powder (purity 99%), SrCO ₃ powder (purity 99%), BaSO ₄ powder (purity 99.5%), ZnO powder (purity: 99 0.5%), MoO ₃ powder (purity 99%), Fe ₂ O ₃ powder (purity 99%), WO ₃ powder (purity 99%), Ni ₃ O ₄ powder (purity 99%), MnO ₂ powder (purity) 99%), CaO powder (purity 99.5%), ZrO ₂ powder (purity 99.5%), TiO ₂ powder (purity 99.5%), HfO ₂ powder (purity 99%), MgO powder (purity 99 .5%), _Bi 2 _{O 3} powder (purity 99%), SnO ₂ powder (pure 99.5%), _Sb 2 _{O 5} powder (purity _99%), P 2 _{O 5} powder (purity 99%), CuO powder (purity 99%), CeO ₂ powder (purity 99%), _Cr 2 _{O 3} powder (Purity 99.5%), Sb ₂ O ₅ powder (Purity 99%) are blended in various ratios, the mixture is heated to 1000-1500 ° C. to melt, and the melt is poured into water to quench and cool. Furthermore, the glaze powder was produced by grinding | pulverizing to a particle size of 50 micrometers or less with an alumina pot mill. Then, 3 parts by mass of New Zealand kaolin as a clay mineral and 2 parts by mass of PVA as an organic binder are blended with 100 parts by mass of this glaze powder, and further 100 parts by mass 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. 5 and then dried to form a glaze slurry coating layer 2d ′. The coating thickness of the glaze after drying is about 100 μm. Using this insulator 2, various spark plugs 100 shown in FIG. 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.

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. Tables 1 to 5 show the analysis values (according to oxide-converted values) of the respective samples. 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] 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 .
[3] Softening point: 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 obtained was measured as the softening point. This temperature corresponds to a temperature at which the viscosity of the glaze reaches 4.5 × 10 ⁷ poise.

  Moreover, about each spark plug, the insulation resistance measurement in 500 degreeC was performed by the energizing voltage 1000V by the method already demonstrated using FIG. Further, the formation state of the glaze layer 2d on the insulator 2 was visually observed, and the thickness of the glaze layer at the outer peripheral surface position of the base end portion of the insulator was measured by SEM observation of the cross section.

  Further, the following impact test was performed on each test product. That is, as shown in FIG. 8, the mounting screw portion 7 of each spark plug 100 is screwed into the screw hole 203a of the test article fixing base 203 and fixed so that the main body portion 2b of the insulator 2 protrudes upward. Then, an arm 201 having a steel hammer 200 attached to the tip is pivotably attached to a shaft fulcrum 202 located on the central axis O of the insulator 2 further above the main body 2b. In addition, the length of the arm 201 is 330 mm, the weight of the hammer 200 is 1.13 kg, and the hammer position when lowered to the rear side main body portion 2 b of the insulator 2 is a vertical direction from the rear end surface of the insulator 2. The position of the shaft fulcrum 202 is determined to be 1 mm in distance (so as to correspond to the first peak position of the corrugation 2c). Then, the operation of lifting the hammer 200 so that the turning angle from the central axis O of the arm 201 becomes a predetermined value and lowering the hammer 200 toward the rear side main body portion 2b by free fall is gradually increased at an angular interval of 2 °. While being repeated, the impact durability angle value θ at which the insulator was cracked was determined. The above results are shown in Tables 1-5.

  According to this result, by selecting the glaze composition according to the present invention described above, it is possible to sinter at a relatively low temperature despite the fact that Pb is hardly contained, and sufficient insulation performance is ensured. I understand that. In addition, the appearance of the glazed surface is generally good. Furthermore, it can be seen that the impact durability angle value can be secured to a good value of 35 ° or more, and the impact resistance of the insulator with the glaze layer can be improved.

The whole front sectional view showing an example of the spark plug of the present invention. The front view which shows the external appearance of an insulator with a glaze layer. The longitudinal section showing some examples of an insulator. Explanatory drawing which shows the measuring method of the insulation resistance value of a spark plug. Explanatory drawing of the formation process of a glaze slurry application layer. Explanatory drawing of a glass sealing process. Explanatory drawing following FIG. The figure which shows the measuring method of an impact durability angle value.

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 S Glaze slurry

Claims (14)

In the spark plug in which an insulator made of alumina ceramic is disposed between the center electrode and the metal shell, an oxide-based glaze layer is formed so as to cover at least part of the surface of the insulator, and the glaze layer is ,
The content of the Pb component is 1 mol% or less in terms of PbO,
The Si component is converted to SiO ₂ in an oxide conversion value of 15 to 60 mol%, the B component is converted into an oxide conversion value into B ₂ O ₃ , and the Zn component is converted into an oxide conversion value into ZnO. 10 to 30 mol%, Ba and / or Sr components are contained in a total of 0.5 to 35 mol% in terms of oxide conversion to BaO or SrO,
The content of the F component is 1 mol% or less,
The Al component contained 0.1 to 5 mol% in terms of oxide values to _Al 2 _{O 3,}
As an alkali metal component, Na is Na ₂ O, K is K ₂ O, Li is a value in terms of oxide converted to Li ₂ O, and a total of 1.1 to 10 mol of one or two or more essential components of Li. % In the range,
And a spark plug, characterized in that the range of content of Li component is a 1.1～6Mol% in terms of oxide value to Li ₂ O. The glaze layer is 0.5 to Si component contained 25～40Mol% in terms of oxide value in SiO _2, Ba and / or Sr components, to no BaO in total at oxide conversion value to SrO The spark plug according to claim 1, containing 20 mol%.   In the glaze layer, the ZnO content in terms of ZnO is NZnO (mol%), the Ba content in terms of BaO is NBaO (mol%), and the Sr component content in terms of SrO is NSrO (mol%). The spark plug according to claim 1 or 2, wherein NZnO + NBaO + NSrO is 15 to 45 mol%.   In the glaze layer, the ZnO content in terms of ZnO is NZnO (mol%), the Ba content in terms of BaO is NBaO (mol%), and the Sr component content in terms of SrO is NSrO (mol%). The spark plug according to any one of claims 1 to 3, wherein NZnO> NBaO + NSrO. The glaze layer comprises B ₂ O ₃ converted B component content NB ₂ O ₃ (mol%), ZnO converted Zn component content NZnO (mol%), BaO converted Ba component content N BaO (mol%). The spark plug according to any one of claims 1 to 4, wherein the content of Sr component in terms of SrO is NSrO (mol%), and NB2O3 / (NZnO + NBoO + NSrO) is 0.5 to 2.0. The glaze layer contains one or more components of Ti, Zr and Hf, Zr is ZrO ₂ , Ti is TiO ₂ , and Hf is HfO ₂ in terms of oxides in total. The spark plug according to any one of claims 1 to 5, which is contained in a range of 5 to 5 mol%. The glaze layer contains one or more of Mo, Fe, W, Ni, Co and Mn, Mo is MoO ₃ , Fe is Fe ₂ O ₃ , W is WO ₃ , and Ni is Ni ₃ O _4. The spark plug according to any one of claims 1 to 6, wherein Co is Co ₃ O ₄ , and Mn is MnO ₂ in terms of oxides in a total amount of 0.5 to 5 mol%. .   The glaze layer is one or more of 0.5 to 10 mol% Ca component in terms of oxide converted to CaO and 0.5 to 10 mol% Mg component in terms of oxide converted to MgO. The spark plug according to any one of claims 1 to 7, comprising a total of 0.5 to 12 mol%. The glaze layer is composed of one or more of Bi, Sn, Sb, P, Cu, Ce and Cr. Bi is Bi ₂ O ₃ , Sn is SnO ₂ and Sb is Sb ₂ O ₅ , P in P ₂ O ₅ , Cu in CuO, Ce in CeO ₂ , and Cr in Cr ₂ O ₃ in terms of oxides, respectively, in a total amount of 5 mol% or less. The spark plug according to any one of the above. In the insulator, a circumferential protrusion is formed on the outer peripheral surface at an axially intermediate position,
In the axial direction, the side toward the tip of the center electrode is the front side, and the outer peripheral surface of the base end portion of the insulator main body adjacent to the rear side with respect to the protruding portion is formed in a cylindrical shape,
The spark plug according to any one of claims 1 to 9, wherein the glaze layer is formed in a thickness range of 7 to 50 µm so as to cover an outer peripheral surface of the base end portion. While the direction away from the spark discharge gap in the axial direction of the insulator is the rear direction, the metal shell is fixed to the test article fixing base so that the insulator rear portion protruding from the metal shell is vertically upward, Further above the insulator rear part, a 330 mm long arm having a 1.13 kg steel hammer attached to the tip is pivotably attached to a shaft fulcrum located on the central axis of the insulator. The position of the shaft fulcrum is determined so that the hammer position when lowered to the rear part of the insulator is 1 mm as a vertical distance from the rear end surface of the insulator,
The operation of lifting the hammer so that the turning angle of the arm from the central axis becomes a predetermined value and lowering the hammer toward the rear part of the insulator by free fall is repeated while increasing stepwise at intervals of 2 °. The spark plug according to any one of claims 1 to 10, wherein an impact durability angle value obtained as a limit angle when a crack occurs in the insulator is 35 ° or more. In the through hole of the insulator, the spark plug is
An axial terminal fitting provided integrally with the center electrode or separately from the center electrode with a conductive coupling layer interposed therebetween,
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. 11. The spark plug according to any one of 11 above. The insulator is constituted by alumina insulating material containing 85～98Mol% by weight was in terms of oxide of Al component to the _Al 2 _{O 3,}
The glaze layer has an average thermal expansion coefficient of 50 × 10 ⁻⁷ / ° C. to 85 × 10 ⁻⁷ / ° C. in the temperature range of 20 to 350 ° C. 13. The spark plug according to item. The spark plug according to any one of claims 1 to 13, wherein a softening point of the glaze layer is 600 to 700 ° C.

Images