JP2002246144A - Insulator for spark plug and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulator for a spark plug, capable of having higher performance in durability to a dielectric breakdown, and being manufactured at a low cost. SOLUTION: The insulator for a spark plug 2 includes a first part 2p and a second part 2s respectively formed of insulating ceramic, for example, alumina ceramic mainly consisting of alumina. Each of the parts are formed of insulating ceramic having different composition, so that the first part 2p on a side of a spark discharge gap g which is likely to create the problem of, such as the dielectric breakdown resulting from applying a high voltage has a insulation property higher than the second part 2s, which is relatively not likely to create the problem of, such as dielectric breakdown. A composition grading region which a content of one or more than two components (a component relative to the insulation property), relating to a degree of the insulation property sequentially changes, is formed in an adjacent direction of the first part 2p and the second part 2s, in at least a boundary part of the first part 2p and the second part 2s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug insulator and a spark plug using the same.

[0002]

2. Description of the Related Art In recent years, the area occupied by intake and exhaust valves in a combustion chamber has been increasing with the increase in the output of internal combustion engines used in automobiles and the like. Therefore, the spark plug for igniting the air-fuel mixture is required to be downsized, and a supercharger such as a turbocharger is used.
Since the temperature in the combustion chamber also tends to increase, an insulator made of an alumina-based insulating material having excellent heat resistance is generally used. Another important reason why an insulator made of alumina is used as an insulator for a spark plug is that alumina has excellent withstand voltage characteristics at high temperatures. However, in recent years, as the size of the spark plug has been reduced, the thickness of the insulator has also tended to be reduced, and an insulator having excellent withstand voltage characteristics has been demanded.

For example, alumina ceramics using a ternary sintering aid of SiO ₂ —CaO—MgO have been widely used as a material for an insulator for a spark plug. However, since this kind of sintering aid forms a low-melting glassy grain boundary phase in the ceramic, there is a problem that dielectric breakdown easily occurs when a high voltage is applied at a high temperature. Also, in the alumina raw material manufactured by the Bayer method or the like, a considerable amount of Na component is inevitably mixed for reasons of the manufacturing method, but this Na component dissolves in the grain boundary phase and lowers the withstand voltage. It also causes.

Therefore, an insulator in which the content of alumina is increased to 95 to 98% by mass to improve the withstand voltage characteristic, an insulator in which the Na content is reduced by using low soda alumina, and Y ₂ O ₃ or La ₂ O
By blending rare earth components ₃ such as to produce a high-melting-point grain boundary phase, an insulator having improved withstand voltage characteristics (for example, JP-63-
No. 190753).

[0005]

However, the cost of the production method or the raw material is higher than that of general alumina ceramics, and the price of the final spark plug rises in exchange for the improvement of performance. Inevitable.

An object of the present invention is to provide an insulator for a spark plug which has higher performance in terms of durability against dielectric breakdown and the like and can be manufactured at a low cost, and a spark plug using the same. is there.

[0007]

The first structure of the insulator for a spark plug according to the present invention has an axial shape and the spark plug gap of the spark plug is located in the axial direction. With the side as the tip side, the first portion forming the tip side, and the second portion adjacent to the first portion in the axial rear side, the first portion has higher insulation than the second portion, so that At least at the boundary between the first portion and the second portion, at least at the boundary between the first portion and the second portion, one or more of the insulating ceramics involved in the magnitude of the insulating property in the direction adjacent to the first portion and the second portion. A composition gradient region in which the content of the component (insulation-related component) continuously changes is formed. In the spark plug according to the present invention, the insulator is arranged between the metal shell and the center electrode, and at the distal end side of the insulator, a ground electrode and a center electrode whose base ends are coupled to the metal shell. A spark discharge gap is formed between them (the same applies to a second configuration described later).

According to the above configuration, the first portion on the side of the spark discharge gap, which tends to cause a problem such as dielectric breakdown due to the application of a high voltage, has improved insulation properties compared with the second portion where the problem such as dielectric breakdown is relatively unlikely to occur. Since the first portion is made of ceramic, the withstand voltage characteristic of the first portion that is easily affected by the application of a high voltage during spark discharge can be improved. In general, ceramics with improved insulating properties are often expensive in terms of cost, but in the present invention, such ceramics may be selectively applied only to the first portion, so that the entire insulator may be used. It is possible to improve the durability against dielectric breakdown and the like while suppressing the cost increase. Further, the first portion and the second portion are configured as having different materials or compositions so as to cause a difference in insulation, but at least a boundary portion between the first portion and the second portion has an adjacent direction. Since the composition gradient region of the insulating participation component is formed in the above, for example, the bonding strength between the first portion and the second portion is improved. In addition, since it is difficult for a steep discontinuity in the coefficient of thermal expansion to occur between the first part and the second part, when the cycle of heating / cooling is repeated in the combustion chamber, the first part and the second part are separated. It is difficult for thermal stress to concentrate on the boundary, and the thermal shock resistance is improved.

The first portion and the second portion of the insulator are made of alumina ceramic mainly composed of alumina, which is particularly excellent in insulation and relatively inexpensive when a sintered ceramic material is used. It is effective to do. Alternatively, another type of ceramic such as aluminum nitride may be used. Further, the first portion and the second portion can be made of ceramics whose main components are different from each other.

Next, a second structure of the insulator for a spark plug according to the present invention is constituted by an insulating ceramic so as to have a shaft shape, and is related to the magnitude of the insulating property of the insulating ceramic.
The composition gradient region in which the content of one or more components (insulation-related components) changes continuously from the insulator surface side toward the inside so that the surface layer has higher insulation than the inner layer. It is characterized by being formed.

[0011] According to the above structure, the insulation of the surface portion of the insulator, which is likely to cause a starting point such as dielectric breakdown due to the application of a high voltage, is more improved than the inner layer portion in which the problem of the dielectric breakdown is relatively unlikely to occur. Since the distribution of the insulation-related components is adjusted, the withstand voltage characteristics of the insulator surface layer that is easily affected by the application of a high voltage during spark discharge can be improved. In general, ceramics with improved insulating properties are often expensive in terms of cost, but in the present invention, such ceramics may be selectively applied only to the surface layer portion, so that the entire insulator It is possible to improve the durability against dielectric breakdown and the like while suppressing the cost increase. Further, the insulator surface layer portion and the inner layer portion are configured as having different contents of the insulating participating components so as to cause a difference in the insulating properties. Is formed, the bonding strength between the inner layer portion and the outer layer portion is improved, for example. In addition, since it is difficult to generate a steep discontinuity in the coefficient of thermal expansion between the inner layer portion and the outer layer portion, when the heating / cooling cycle is repeated in the combustion chamber, the thermal stress is less likely to be locally concentrated, Thermal shock resistance is improved.

Also in the second configuration, the insulating ceramic can be made of an alumina ceramic containing alumina as a main component, aluminum nitride, or the like.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 as an example of the present invention shown in FIGS. 1 and 2 is formed on a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a distal end portion 21 protrudes, and a distal end. One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like while the ignition portion 31 is protruded, and the other end is bent back to the side. Includes a ground electrode 4 and the like arranged so as to face the tip of the center electrode 3. Further, the ground electrode 4 is provided with a firing portion 32 facing the firing portion 31.
The gap between the opposing firing part 32 is the spark discharge gap g.
It has been.

The insulator 2 has a shaft-like shape and, when assembled to the spark plug 100, forms a tip portion in the direction of the axis O located on the side of the spark discharge gap g.
And a second portion 2s adjacent to the first portion 2p on the rear side in the direction of the axis O are each made of alumina ceramic mainly composed of alumina. The second portion 2s can be made of, for example, alumina ceramics of the same material as the conventional insulator for a spark plug. Also, the first part 2p
Between the first part 2p and the second part 2s.
A composition gradient region 2y having a composition intermediate with s is formed.

The material of the first part 2p is the second part 2p.
It is configured as having better insulation than s. Specifically, it is configured as a ceramic satisfying at least one of the following requirements. Those having a structure in which the content of the grain boundary phase (or the area ratio in the structure cross section) is smaller than that of the second portion 2s. As shown in FIG. 2B, using the grain boundary phase as an insulating-related component, the content of the grain boundary phase between the first portion 2p and the second portion 2s increases toward the first portion 2p. A continuously decreasing composition gradient region is formed. In order to reduce the content of the grain boundary phase, it is necessary to reduce the amount of the sintering aid component. In this case, the sintering aid component is added to the alumina powder, and the alumina powder and the sintering aid are mixed. It is effective to set the blending amount to about 0.3 to 5% by mass based on the total amount of the components.

One having a structure in which the content of the crystal phase in the grain boundary phase (or the crystallization rate of the grain boundary phase) is larger than that of the second portion 2s. A composition in which the content (or crystallization ratio) of the crystal phase continuously increases toward the first portion 2p between the first portion 2p and the second portion 2s using the crystal phase as an insulating-related component. An inclined region is formed. Examples of the crystal phase that contributes to the improvement of the insulating property include rare earth-containing compounds (for example, a composite oxide of a rare earth element and silicon) described later, and CaAl ₁₂ O ₁₉ and BaAl as phases that do not contain a rare earth.
There are crystal phases such as ₁₂ O ₁₉ , MgAl ₂ O ₄ , and Al ₆ Si ₂ O ₁₃ (mullite).

The one having an alumina content higher than that of the second portion 2s. Then, using the alumina content as an insulating-related component, as shown in FIG. 2C, between the first portion 2p and the second portion 2s, the alumina content is the first portion 2p.
A composition gradient region that continuously increases toward the side is formed. By increasing the alumina content of the first portion 2p more than the second portion 2s, it is possible to improve the withstand voltage characteristics of the first portion 2p, which is easily affected by the application of a high voltage during spark discharge. Specifically, a higher alumina content means that the amount of the sintering aid added can be kept low, so that the content of the grain boundary phase formed or the average thickness of the grain boundary phase decreases. Is considered to be a factor to improve the withstand voltage characteristics. In addition, it is only necessary to apply a high alumina ceramic which is expensive in cost to only the first portion 2p, and the second portion 2s
Can be made of less expensive ceramics having a lower alumina content, so that it is possible to improve the durability against dielectric breakdown and the like while suppressing an increase in the manufacturing cost of the entire insulator 2.

The specific content of the alumina component in the first portion 2p is 95 to 1 in terms of mass in terms of Al ₂ O _3.
It can be selected in the range of 00% by mass. In this case, for example, Si, Ca, Mg, Ba and B components functioning as sintering aids, Si is SiO ₂ , Ca is CaO, Mg is MgO
In addition, Ba is contained in BaO and B is contained in B ₂ O ₃ in a total amount of up to 5% by mass in terms of oxide. Can be promoted. Further, as a sintering aid, it is of course possible to employ a rare earth element component described below. On the other hand, when high-temperature and high-pressure sintering such as hot isostatic pressing is possible, a dense sintered body can be obtained even with the sintering agent almost eliminated. The first part 2p
Is preferably 95% or more, and more preferably 98% or more, from the viewpoint of improving the withstand voltage characteristics particularly at high temperatures.

When the content of the rare earth element R is the second part 2
higher than s. Then, as shown in FIG. 2 (d), the content of the rare earth element component R is between the first portion 2p and the second portion 2s using the content of the rare earth element component R as an insulating-related component. A composition gradient region that continuously increases toward a part 2p side is formed. Rare earth element component R
Are Sc, Y, La, Ce, Pr, Nd, Sm, Eu,
One or more of Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which are added as a sintering aid, for example, in the form of an oxide. Since the rare earth element component mainly forms a high melting point compound phase in the grain boundary phase, increasing the content of the rare earth element component in the first portion 2p more than that in the second portion 2s reduces the effect of high voltage application during spark discharge. The withstand voltage characteristics of the first portion 2p that is easily affected can be improved. The factor is that the crystallization of the grain boundary phase is promoted. Further, a mechanism in which a fine rare earth-containing compound precipitated as a crystal phase in the grain boundary phase divides or bypasses the conductive path to improve the withstand voltage of dielectric breakdown can be considered. On the other hand, the increase in the added amount of the rare earth element component is relatively expensive, but since it is sufficient to add a large amount of the rare earth element component only in the first portion 2p, it is possible to suppress the increase in the manufacturing cost of the insulator 2 as a whole. It is possible to improve durability against breakage and the like.

The specific content of the rare earth element component in the first portion 2p is as follows: when R is Ce, RO ₂ , Pr
In the case of the above, R ₆ O ₁₁ , and in other cases, R ₂ O ₃ can be selected in the range of 0.01 to 18% by mass in terms of oxide. These rare earth element components can be blended, for example, in the form of an oxide powder as a sintering aid. It is more effective to use one or more of Pr, Nd, and Dy among the above rare earth element components from the viewpoint of improving the withstand voltage characteristics at high temperatures. Note that N
If a form in which the d component and the Pr component are added in combination is adopted,
For example, a non-separable rare earth oxide of dymium mainly composed of Nd and Pr can be used, which is effective in reducing the raw material cost.

It is of course possible to mix other sintering aid components together with the rare earth element component R. For example, one or more of Si, Mg, Ca, Ba and B may be co-added. It can be blended as a binder component. In particular, Si
A high melting point composite oxide can be easily formed with the rare earth element component, and the effect of improving the withstand voltage characteristics at high temperatures can be further enhanced.

The content of the alkali metal component in the second part 2
lower than s. Then, as shown in FIG. 2 (e), the content of the alkali metal component is the content of the alkali metal component between the first portion 2p and the second portion 2s. A composition gradient region that continuously decreases toward the side is formed. The alkali metal component is, for example, one or more of Li, Na, and K, all of which have high ionic conductivity and, when they become a grain boundary phase forming component, the content thereof is excessive. This leads to a decrease in withstand voltage characteristics. Therefore, the first part 2
By making the content of the alkali metal component of p lower than that of the second portion 2s, the withstand voltage characteristics of the first portion 2p that is easily affected by the application of a high voltage during spark discharge can be improved. On the other hand, an alkali metal element is often inevitably contained in an alumina raw material such as Na, for example, due to a factor in the production method. An alumina raw material whose content is reduced (for example, low soda alumina) is used as a normal alumina raw material ( For example, it is more expensive than medium soda alumina or ordinary soda alumina). However, in the above configuration, such an alumina-based ceramic having a low alkali metal component content may be applied only to the first portion 2p, and the material of the second portion 2s may have a lower alkali metal component content. Since the insulator 2 can be made of a high-priced and inexpensive ceramic, it is possible to improve the durability against dielectric breakdown and the like while suppressing an increase in the manufacturing cost of the entire insulator 2. For example, when low-soda alumina powder is used as a raw material and an alkali metal component other than Na is not actively added, the content of the alkali metal component can be kept to 0.05% by mass or less in terms of oxide. It is.

On the other hand, as a specific material of the second portion 2s, for example, the content of the sintering aid component is 5 to 5 in terms of oxide.
15% by mass, and 0.07 to 0.5% by mass in terms of Na ₂ O, for example, as an alkali metal component.
Can be employed. With such a Na content, medium soda alumina or ordinary soda alumina can be used as a raw material without any problem.

Next, details of the overall shape of the insulator 2 will be described. First, a through-hole 6 is formed in the insulator 2 in the axial direction, and a terminal fitting 13 is inserted and fixed from one end thereof, and the center electrode 3 is inserted and fixed from the other end thereof. ing. Further, a resistor 15 is arranged between the terminal fitting 13 and the center electrode 2 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively. The resistor 15 is formed of a resistor composition obtained by mixing glass powder and conductive material powder (and ceramic powder other than glass as required) and sintering the mixture by hot pressing or the like. The conductive glass seal layers 16 and 17 are made of Cu, Sn,
It is made of glass mixed with a metal powder mainly composed of one or more metal components such as Fe. Note that 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.

As shown in FIG. 1, a protrusion 2e projecting outward in the circumferential direction is formed, for example, in the form of a flange at the middle of the insulator 2 in the axial direction. The protruding portion 2e is formed on the insulator 2 with the side facing the tip of the center electrode 3 as the front side.
The main body 2b whose rear side is formed to have a smaller diameter than this.
It has been. On the other hand, on the front side of the protrusion 2e, a first shaft 2g having a smaller diameter than the first shaft 2g and a second shaft 2i having a smaller diameter than the first shaft 2g are formed in this order. A glaze 2d is applied to the outer peripheral surface of the main body 2b, and a corrugation 2c is formed at the rear end of the outer peripheral surface. The outer peripheral surface of the first shaft portion 2g has a substantially cylindrical shape, and the outer peripheral surface of the second shaft portion 2i has a substantially conical surface shape whose diameter decreases toward the distal end.

The axial sectional diameter of the center electrode 3 is
Is set to be smaller than the shaft cross-sectional diameter. 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 portion formed on the rear side (upper side in the drawing) of the first portion 6a with a diameter larger than this. And a second portion 6b. As shown in FIG.
The resistor 3 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 of the center electrode 3, an electrode fixing projection 3c is formed to protrude outward from the outer peripheral surface thereof. The first portion 6a and the second portion 6b of the through hole 6 are connected to each other in the first shaft portion 2g, and the connection position receives the electrode fixing convex portion 3c of the center electrode 3. Is formed in a tapered surface or a round surface.

Further, the outer peripheral surface of the connecting portion 2h between the first shaft portion 2g and the second shaft portion 2i is a stepped surface, and this is a stepped surface.
Ridge 1 as a metal shell side engaging portion formed on the inner surface of
By engaging with c via a ring-shaped plate packing 63, axial removal is prevented. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2,
A ring-shaped packing 62 that engages with the rear side peripheral edge of the flange-shaped protrusion 2e is arranged, and further on the rear side, a ring-shaped packing 60 is arranged 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 opening edge of the metal shell 1 is swaged inward toward the packing 60 to form a swaged portion 1d. It is fixed to the insulator 2.

The metal shell 1 is formed of a metal such as low-carbon steel into a cylindrical shape, constitutes a housing of the spark plug 100, and has a plug 10 on its outer peripheral surface.
There is formed a screw portion 7 for attaching 0 to an engine block (not shown). The outer diameter of this thread 7 is 18 m
m or less (for example, 18 mm, 14 mm, 12 mm, 10 mm
mm etc.). Reference numeral 1e denotes a tool engagement portion that engages a tool such as a wrench or a wrench when the metal shell 1 is attached, and has a hexagonal axial cross-sectional shape.

Next, the body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of a Ni alloy or the like such as Inconel (trade name). Further, a core material 3b made of Cu or Cu alloy or the like is embedded in the center electrode 3 to promote heat radiation. On the other hand, the ignition part 3
1 and the opposing firing part 32 are Ir, Pt and Rh of 1
It is mainly composed of a noble metal alloy containing at least one kind or two or more kinds. The main body 3a of the center electrode 3 has a reduced diameter on the tip end side and a flat tip end face. A disk-shaped chip made of an alloy composition constituting the ignition portion is superimposed on the tip end, and the outer edge of the joining surface is further joined. Laser welding along the part,
The ignition portion 31 is formed by forming a welded portion by electron beam welding, resistance welding, or the like and fixing the welded portion. The opposing firing portion 32 is formed by aligning the tip with the ground electrode 4 at a position corresponding to the firing portion 31, forming a weld along the outer edge of the joint surface, and fixing the same. Is done. In addition, these chips are obtained by molding and sintering, for example, a molten material obtained by blending and melting each alloy component so as to have the indicated composition, or an alloy powder or a metal single component powder blended in a predetermined ratio. It can be constituted by the obtained sintered material. Note that at least one of the firing part 31 and the opposing firing part 32 may be omitted.

The insulator 2 can be manufactured, for example, by the following method. First, as a raw material powder, an alumina powder and a sintering aid powder are blended so as to have a composition determined for each of the first portion 2p and the second portion 2s, and a hydrophilic binder (for example, PVA) and water are mixed. Add and mix to make a molding base slurry.

The forming base slurry is spray-dried by a spray drying method or the like to form a forming base granule PG1 (for the first portion 2p) and a forming base granule PG2 (for the second portion 2p).
s). These molding base granules PG1 and P
G2 is subjected to rubber press molding to produce a press molded body serving as a prototype of the insulator. FIG. 3 schematically shows a process of rubber press molding. Here, a rubber mold 300 having a cavity 301 penetrating therethrough in the axial direction is used, and an upper punch 304 is fitted into an upper opening of the cavity 301. Further, on the punch surface of the lower punch 302, a press pin 303 that extends in the axial direction within the cavity 301 and that defines the shape of the through hole 6 (FIG. 1) of the insulator 2 is integrally formed. .

In this state, the cavity 301 is filled with a predetermined amount of the base granules PG1 and PG2 for molding, and the upper opening of the cavity 301 is closed with an upper punch 304 to be sealed. At this time, one of the green body granules for molding PG1 and PG2 is first filled on the lower side in the axial direction of the press pin 303, and then the other is filled on the upper side. Thereby, the granulated material PG1 for the first portion 2p and the granulated material PG2 for the second portion 2s are separated by 2 in the axial direction in the cavity 301.
Filled in layers.

In this state, a liquid pressure is applied to the outer peripheral surface of the rubber mold 300, and the granules PG1 and PG2 of the cavity 301 are removed.
By compressing through the rubber mold 300, FIG.
As shown in (a), a pressed compact 202 is obtained in which powder compacts 202p and 202s of the granules PG1 and PG2 are joined in the axial direction. The outer surface of the press-formed body 202 is processed by grinder cutting or the like to finish the outer shape corresponding to the insulator 2 in FIG.
As shown in (b), the molded body to be fired 152 having a powder molded portion 152p having a shape corresponding to the first portion 2p and a powder molded portion 152s having a shape also corresponding to the second portion 2s.
Is obtained. The molded body to be fired 152 is fired at a predetermined temperature.

At the time of this firing, the components of the two powder molded parts 152s and 152p are mutually diffused between the powder molded parts 152s and 152p via the boundary surface 152b,
FIG. 2 shows a length determined according to the firing temperature and the firing time.
A composition gradient region 2y as shown in FIG. For example,
2B if the content of the sintering aid component (content of the grain boundary phase) is low, and FIG. 2B if the powder molding portion 152p has a higher alumina content than the powder molding portion 152s. 2 (c), a composition as shown in FIG. 2 (d) if the content of the rare earth element component is higher, and a composition as shown in FIG. 2 (e) if the content of the alkali metal component is lower. Each of the inclined regions can be formed. Needless to say, two or more of these insulating-related components may simultaneously form a composition gradient region in which the components are inclined. For example, if the composition of both powder molding parts 152s and 152p is adjusted so that the alumina content is high and the rare earth element component content is high in the powder molding part 152p, FIG. 2C and FIG. Is formed at the same time. On the other hand, in FIG. 4B, since the influence of component diffusion is unlikely to extend to a region far away from the boundary surface 152b, the powder molded portions 152s and 152p have a substantially uniform composition with respect to the insulating-related components of interest. As far as possible, in the obtained first portion 2p and second portion 2s, regions in which the content of the insulating participating component is substantially constant are formed adjacent to the composition gradient regions.

When the above firing is completed, the insulator 2 shown in FIG. 1 is completed by applying a glaze to finish firing.

As shown in FIG. 5, the insulator 2 is made up of the above-mentioned respective insulating-related components (alumina component, grain boundary phase (sintering aid component), rare earth element component, and alkali (not shown). One or more selected from the metal components) is stepwise ((b), (c),
(D)) or continuous ((e): an example of the alumina component here, but of course, other components related to insulation may be used). This is, for example, as shown in FIG.
A plurality of types of green body granules for molding PG1 to PG5 having different contents of the powder as the source of the insulation-related component are formed in a molding die 30 in the order of the content corresponding to the inclination direction of the insulation-related component.
Then, the filling granules PG <b> 1 to PG <b> 5 are charged into the cavity 301 in order to form a filling layer PG that is stacked and filled so as to minimize mixing.

Then, the filling layer PG is subjected to rubber press molding as shown in FIG. 6 to obtain a press molded body 202 shown in FIG. 7A. This press-formed body 202 has powder-formed parts 202s, 202 having different contents of the insulating-related components.
d, 202c, 202b, and 202a are formed corresponding to the filling order of the forming base granules PG1 to PG5.
If this is processed in the same manner as in FIG. 4, as shown in FIG. 7 (b), the powder molding parts 152a, 152b, 152c, 152
The fired molded body 152 having d and 152s is obtained,
By firing this, the insulator 2 of FIG. 5A can be manufactured.

5 (b) to 5 (d), regions where the content of the insulating-related component is substantially constant are formed corresponding to the forming granules PG1 to PG5, and the adjacent regions are formed. The composition gradient regions are formed in between, and the entire composition change profile is in a step shape.For example, the content of the powder as a source of the insulating-related component is more finely changed. If a set is used, or if the baking time is lengthened and the component diffusion is sufficiently advanced, FIG.
As shown in (e), it is possible to form a composition gradient region in which the composition is continuously changed over the entire length of the first portion 2p.

Next, as shown in FIG.
In the radial direction with respect to the central axis O, the insulating property is higher than that of the inner circumferential surface side where the outer circumferential surface side is the through hole 6 side so that the surface layer portion has higher insulating property than the inner layer portion. In this manner, the composition gradient region 2u in which the content of the insulating participating component continuously changes from the insulator surface side toward the inside may be formed. Again, the insulating-related component is an alumina component (FIG. 8 (c): increased on the outer peripheral surface side), a grain boundary phase (sintering aid component) (FIG. 8 (b):
(Lower on the outer peripheral surface side), rare earth element components (FIG. 8 (d):
The height is increased on the outer peripheral surface side) and the alkali metal component (FIG. 8)
(E): lower on the outer peripheral surface side). In the present embodiment, the insulator 2 is selectively formed only at the distal end portion (the second shaft portion 2i in FIG. 8), which requires particularly high insulation properties. Note that the composition gradient region 2u in the present embodiment is formed in a section from the outer peripheral surface of the insulator 2 to an intermediate position in the radius r direction, or as shown in FIGS.
As shown by a broken line in (e), it may be formed over the entire section up to the inner peripheral surface.

The composition gradient region 2u as described above can be formed, for example, as follows. First, a molded body 152 as shown in FIG. 9A is produced by a method substantially similar to that shown in FIGS. 3 and 4 except that a molding-use base granule having a single composition is used. The molded body 152 has a substantially uniform reference composition as a whole with respect to the insulating-related components. On the other hand, a slurry S in which a component source powder of an insulating participating component is suspended is separately prepared. The slurry S is applied to a portion 152i of the molded body 152 where the composition gradient region 2u is to be formed, and dried to form a powder coating layer AP as shown in FIG. 9B. For example, when it is desired to increase the content of the insulating participating component on the insulator surface side, the powder coating layer AP in which the content of the component source powder of the insulating participating component is higher than that of the molded body 152 is formed. Next, the suspension amount of the component source powder in the slurry S to be used is adjusted.

For example, when it is desired to increase the content of the rare earth element component in the surface layer of the insulator, a rare earth powder is used as the component source powder, and the content of the rare earth powder in the powder application layer AP is made higher than that of the compact 152. . The powder coating layer AP can be formed entirely of rare earth powder, for example. When the compact 152 on which the powder coating layer AP is formed in this manner is fired, the rare earth element component in the powder coating layer AP diffuses toward the insulator 2 as shown in FIG. d)
As shown in (2), the composition gradient region 2u is formed on the surface layer side of the insulator 2 such that the content of the rare earth element component is high.

On the other hand, when it is desired that the content of the insulating-related component is lower on the insulator surface side, the powder coating layer AP in which the content of the component source powder of the insulating-related component is lower than that of the molded body 152 is formed. The suspension amount of the component source powder in the slurry S to be used is adjusted so as to be formed. For example, when it is desired to lower the alkali metal component in the surface layer portion of the insulator, the content of the alkali metal component in the powder coating layer AP is determined by the molding 152
And the content of the alumina powder may be increased instead. Thereby, the composition gradient region 2u is formed so that the content of the alkali metal component becomes low (in other words, the content of the alumina component becomes high) on the surface layer side of the insulator 2.

The firing is performed in a reducing atmosphere in which CO, hydrogen, or the like is circulated, or the molded body 152 is embedded in a reducing atmosphere forming powder mainly composed of carbon and fired to obtain an alumina insulating material. In the surface layer, a composition gradient region using the grain boundary phase as an insulating-related component can be formed such that the formation amount of the grain boundary phase based on the sintering aid component is reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a spark plug using an insulator according to a first configuration of the present invention.

FIG. 2 is an explanatory view exemplifying some forms of forming the composition gradient region.

FIG. 3 is an explanatory view showing one example of an insulator manufacturing process for forming the composition gradient region of FIG. 2;

FIG. 4 is a process explanatory view following FIG. 3;

FIG. 5 is an explanatory view exemplifying some modified examples of the formation form of the composition gradient region.

FIG. 6 is an explanatory view showing one example of an insulator manufacturing process for forming the composition gradient region of FIG. 5;

FIG. 7 is a process explanatory view following FIG. 7;

FIG. 8 is an explanatory view exemplifying several forms of forming a composition gradient region of a spark plug using an insulator according to a second configuration of the present invention.

FIG. 9 is an explanatory view showing an example of an insulator manufacturing process for forming the composition gradient region in FIG. 9;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal shell 2 insulator 2 p first part 2 s second part 2 u, 2 y composition gradient region 3 center electrode 4 ground electrode g spark discharge gap

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Katsura Matsubara 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Nihon Toku Toki Co., Ltd. No. 18 Japan Special Ceramics Co., Ltd. (72) Inventor Hiroto Ito 14-18 Takatsujicho, Mizuho-ku, Nagoya City, Aichi Prefecture Inside Japan Special Ceramics Co., Ltd. (72) Inventor Kenji Nunome Mizuho-ku, Nagoya City, Aichi Prefecture 14-18, Takatsuji-cho F-term in Japan Special Ceramics Co., Ltd. (reference) 4G030 AA11 AA36 BA12 CA05 CA07 5G059 AA05 AA08 CC02 FF01 FF02 FF10 FF14

Claims (15)

[Claims] 1. A first portion forming an end of a spark plug in which the spark discharge gap is located in the axial direction, and a first portion forming the end, and an axially rear side of the first portion in the axial direction. A second portion adjacent to the first portion is made of insulating ceramics having different compositions from each other so that the first portion has higher insulation than the second portion, and the first portion and the second portion At least at the boundary, the content of one or more components (hereinafter referred to as insulating-related components) that contribute to the magnitude of the insulating property continuously changes in the direction adjacent to the first portion and the second portion. An insulator for a spark plug, wherein a composition gradient region is formed. 2. The first portion and the second portion each have a structure in which main phase particles which are main components of an insulating ceramic are bonded by a grain boundary phase having a lower melting point than the main phase particles. In the first portion, the content of the grain boundary phase is smaller than that of the second portion, and in the composition gradient region, the content of the grain boundary phase as the insulating participating component is the first portion. The insulator for a spark plug according to claim 1, wherein the insulator continuously decreases toward the side. 3. The first portion and the second portion each have a structure in which main phase particles that are the main components of the insulating ceramic are bonded by a grain boundary phase having a lower melting point than the main phase particles. In the first portion, the crystallization rate of the grain boundary phase is higher than that of the second portion, and in the composition gradient region, the crystallization rate of the grain boundary phase as the insulating-related component is higher than the second portion. The insulator for a spark plug according to claim 1 or 2, wherein the insulator continuously increases toward one component side. 4. The insulator for a spark plug according to claim 1, wherein each of said first portion and said second portion is made of alumina ceramic containing alumina as a main component. 5. The alumina content of each alumina ceramic is higher in the first portion than in the second portion, and the alumina content as the insulating-related component in the composition gradient region is closer to the first portion. The insulator for a spark plug according to claim 4, wherein the insulator continuously increases. 6. The rare earth element content of each alumina ceramic is higher in the first portion than in the second portion, and in the composition gradient region, the rare earth element content as the insulating participating component is higher than the first portion. The insulator for a spark plug according to claim 4 or 5, wherein the insulator continuously increases toward the side. 7. The content of the alkali metal component of each alumina ceramic is lower in the first portion than in the second portion, and in the composition gradient region, the content of the alkali metal component as the insulating-related component is lower than the second content. The insulator for a spark plug according to any one of claims 4 to 6, wherein the insulator continuously decreases toward a partial side. 8. The insulating layer according to claim 1, wherein said insulating ceramic has one or more components (hereinafter, referred to as insulating-related components) that contribute to the magnitude of the insulating property of said insulating ceramic. An insulator for a spark plug, wherein a composition gradient region that continuously changes from the insulator surface side toward the inside is formed so that the portion has a higher insulating property than the inner layer portion. 9. The insulating ceramic has a structure in which main phase particles, which are main components of the insulating ceramic, are bonded in a grain boundary phase having a lower melting point than the main phase particles. 9. The insulator for a spark plug according to claim 8, wherein the content of the grain boundary phase as a sex-related component continuously decreases from the inside of the insulator toward the surface side. 10. The insulating ceramic has a structure in which main phase particles, which are main components of the insulating ceramic, are bonded in a grain boundary phase having a lower melting point than the main phase particles. The insulator for a spark plug according to claim 8 or 9, wherein the crystallization ratio of the grain boundary phase as a sex-related component continuously increases from the inside of the insulator toward the surface side. 11. The insulator for a spark plug according to claim 9, wherein the insulating ceramic is made of an alumina ceramic containing alumina as a main component. 12. The insulator for a spark plug according to claim 11, wherein the content of alumina as the insulating-related component continuously increases from the inside of the insulator toward the surface. 13. The insulator for a spark plug according to claim 11, wherein the content of the rare earth element as the insulating-related component continuously increases from the inside of the insulator toward the surface side. 14. The spark plug according to claim 11, wherein the content of the alkali metal component as the insulating-related component continuously decreases from the inside of the insulator toward the surface. Insulator. 15. The semiconductor device according to claim 1, wherein the metal shell is provided between the metal shell and the center electrode.
15. The insulator according to any one of claims 14 to 14, wherein a spark discharge gap is formed between the ground electrode and the center electrode whose base end is coupled to the metal shell at the distal end side of the insulator. Spark plug characterized by the following.