JP5688880B2 - Glass composition for forming a resistor for a spark plug - Google Patents

Description

TECHNICAL FIELD The present invention relates to a glass composition for forming a resistor for a spark plug , and particularly to a glass composition for forming a resistor for a spark plug suitable for forming a resistor for a spark plug .

  2. Description of the Related Art Resistor-containing spark plugs are widely used as spark plugs for engines such as automobiles. As shown in FIG. 1, the spark plug with a resistor is provided between a conductive glass body 2 a in contact with the terminal electrode 1 and a conductive glass body 2 b in contact with the center electrode 3 in an inner hole of an insulator (not shown). The resistor 4 is interposed. If a resistor is introduced into the spark plug, leakage of high-frequency noise radio waves generated when the spark plug is ignited can be suppressed.

  Generally, a spark plug with a resistor is manufactured as follows. After inserting the center electrode 3 into the lower end of the inner hole of the insulator and filling the inner hole of the insulator with a predetermined amount of the conductive glass body material, press pressure is applied to the conductive glass body material to Make it flat. Next, after filling a predetermined amount of resistor material on the conductive glass body material, a pressing pressure is applied to the resistor material to flatten the surface of the resistor material. Thereafter, a predetermined amount of conductive glass body material is filled on the resistor material. Here, the conductive glass body material and the resistor material are processed into granules in order to easily fill the inner holes of the insulator. Next, after inserting the terminal electrode 1 into the upper end of the inner hole of the insulator, the conductive glass body material and the resistor material are sintered by a so-called hot pressing process in which a load is applied to the terminal electrode 1 while heating at about 900 ° C. Then, the conductive glass bodies 2a, 2b and the resistor 4 are formed, the tip of the terminal electrode 1 is press-fitted into the conductive glass body 2a, and the tip of the center electrode 3 is press-fitted into the conductive glass body 2b. Finally, an insulator is fixed to a housing provided with a ground electrode to form a spark plug.

  In general, a resistor material obtained by granulating a resistor material made of coarse glass powder, fine glass powder, ceramic powder, conductive powder or the like is used. The resistor produced using this resistor material has a state in which a coarse glass powder or a ceramic powder retains its original shape, and a bonded glass phase in which the fine glass powder is melted and solidified exists in the gap between these particles. Become. In addition, conductive powder is dispersed in the binder glass phase, and the coarse glass powder functions as block particles that bend (detour) the conductive path (see, for example, Patent Documents 1 and 2). It is known that when the conductive path is bent, the resistance of the resistor to absorb high-frequency noise radio waves increases.

JP 9-306636 A JP 2005-340171 A JP 2007-122879 A

  In recent years, engines tend to be miniaturized, and spark plugs also tend to be miniaturized. However, when the spark plug is reduced in size, it is necessary to reduce the content of the resistor formed in the inner hole of the insulator. In other words, coarse glass that absorbs high-frequency noise radio waves inside the spark plug Since it is necessary to reduce the content (glass layer) of the powder or the like, it is difficult for the resistor to suppress leakage of radio frequency noise radio waves due to this. Note that, when the spark plug is ignited, high-frequency noise radio waves are generated. If a large amount of this high-frequency noise radio waves leaks, there is a risk that the vehicle-mounted TV, radio, radio, etc. will be disturbed.

  In view of such circumstances, in paragraphs [0011] to [0013] of the specification of Patent Document 3, “the spark plug of the present invention has a through hole extending in the axial direction, and the through hole is the first through hole. An insulator serving as a second through hole having a hole diameter larger than that of the first through hole on the rear end side of the hole and the first through hole; and a center electrode disposed in the first through hole of the insulator; A spark plug comprising a terminal fitting disposed in the second through hole of the insulator, and formed of a conductive ceramic sintered body in the second through hole, and the center electrode and the A ceramic sintered body resistor that is electrically connected to the terminal fitting is disposed, and an axial length of the ceramic sintered body resistor is 40% or more of an axial length of the second through hole. In the present invention, it is preliminarily sintered as such a resistor. By inserting the ceramic sintered body resistor into the second through-hole of the insulator, the length of the ceramic sintered body resistor is sufficiently long without being restricted by the length of manufacturing as in the prior art. As a result, the effective dielectric constant between the center electrode and the terminal electrode can be reduced, the capacitive discharge current generated during ignition can be reduced, and the noise prevention effect can be increased. By setting the length (LR) of the combined resistor to 40% or more of the length (LH) of the second through hole ((LR / LH) × 100 ≧ 40), the distance between the center electrode and the terminal electrode is increased. It is possible to reduce the effective dielectric constant, reduce the capacity discharge current generated at the time of ignition, and obtain a sufficient noise prevention effect.The length (LR) of the ceramic sintered body resistor is the second through hole. When the length (LH) is less than 40%, sufficient effect is obtained. Furthermore, the more preferable length (LR) of the ceramic sintered body resistor is 50% or more of the length (LH) of the second through hole ((LR / LH) × 100 ≧ 50). It is shown that by optimizing the structure of the spark plug, the effective dielectric constant between the terminal electrode and the center electrode is reduced to prevent the generation of high-frequency noise radio waves. However, even if such optimization is performed, leakage of high-frequency noise radio waves cannot be sufficiently suppressed.

  In addition, when the spark plug is downsized, the mechanical strength of the resistor decreases, or the frictional resistance at the time of press-fitting the terminal electrode increases, so that it becomes difficult to press-fit the terminal electrode, and the resistance value of the resistor varies. It becomes easy. In addition, it is considered that it is easily affected by fluctuations in the hot press temperature, and the resistance values of the resistors are likely to vary. In the spark plug manufacturing process, it is difficult to strictly regulate the hot press temperature, and the hot press temperature must be managed with a certain fluctuation range.

  In view of this, the present invention creates a resistor-forming glass composition having a high ability to absorb high-frequency noise radio waves in order to form a resistor that efficiently absorbs high-frequency noise radio waves. The technical challenge is to improve productivity.

As a result of diligent efforts, the inventors have reduced the dielectric constant of the glass while maintaining the softening properties of the glass, specifically, by introducing either MgO or SrO into the glass composition. It is found that the technical problem can be solved, and is proposed as the present invention. That is, the glass composition for forming a resistor for a spark plug of the present invention has, as a glass composition, 40% by mass, SiO ₂ 40-60%, B ₂ O ₃ 28-43%, Li ₂ O + Na ₂ O + K ₂ O (Li ₂ the total amount of O and Na ₂ O and _{K 2 O) 2.0~6.0%, Li} 2 O 1.5~5.9%, MgO + SrO ( total amount of MgO and SrO) 4.4 to 17. 5 %, dielectric constant at 25 ° C. and 1 MHz is 5.5 or less, dielectric loss tangent at 25 ° C. and 1 MHz is greater than 0.0018, glass transition point is 490 to 590 ° C., yield point is 530 It is -700 degreeC, and a thermal expansion coefficient is 40-60 * 10 < ^-7 > / degreeC , It is characterized by the above-mentioned.

The glass composition for forming a resistor for a spark plug of the present invention regulates the glass composition range as described above. In this way, since the dielectric constant of the glass can be reduced, the ability of the glass to absorb high-frequency noise radio waves can be significantly increased, and as a result, the spark plug can be easily downsized. In this way, the thermal expansion coefficient of the glass can be lowered while improving the thermal stability of the glass without unduly increasing the yield point of the glass.

Spark plug resistor forming a glass composition of the present invention, Ru der 25 ° C., the dielectric constant at 1 MHz 5.5 or less. In this way, the ability of glass to absorb high-frequency noise radio waves is significantly improved, and even if the glass content in the resistor is small, high-frequency noise radio waves can be sufficiently absorbed, making it easier to reduce the size of the spark plug. . Here, the “dielectric constant at 25 ° C. and 1 MHz” is a glass substrate of 50 × 50 × 3 mm (a glass powder densely sintered) or a glass ingot of 50 × 50 × 3 mm as a measurement sample. It refers to a value measured by attaching electrodes of 30 mmφ to the front and back surfaces of an optically polished glass substrate and applying a voltage between the electrodes.

  The inventors of the present invention focused on the fact that the dielectric constant of the resistor can be reduced by reducing the dielectric constant of the glass, and for this purpose, the inventors have found that the glass composition range should be regulated as described above. . As a result, the effective dielectric constant between the center electrode and the terminal electrode is reduced, the capacity discharge current generated when the ignition plug is ignited can be reduced, and as a result, the ability to absorb high-frequency noise radio waves can be improved.

Spark plug resistor forming a glass composition of the present invention, 25 ° C., have greater than a dielectric loss tangent 0.0018 at 1 MHz. In this way, the ability of glass to absorb high-frequency noise radio waves can be improved, and the spark plug can be easily downsized. Here, “dielectric loss tangent at 25 ° C., 1 MHz” is a glass substrate of 50 × 50 × 3 mm (a glass powder densely sintered) or a glass ingot of 50 × 50 × 3 mm as a measurement sample. It refers to a value measured by attaching electrodes of 30 mmφ to the front and back surfaces of an optically polished glass substrate and applying a voltage between the electrodes.

  Through detailed investigations by the present inventors, it has been found that increasing the dielectric loss tangent of glass increases the ability of glass to absorb high frequency noise. Although the details of this mechanism are not clear and are currently under intensive investigation, the present inventors have found that when the dielectric loss tangent of the glass is large, when the spark plug is ignited, a high frequency is generated at the interface of the coarse glass of the resistor. It is estimated that the noise radio wave energy is easily converted into thermal energy, and the high frequency noise radio wave is attenuated.

Spark plug resistor forming a glass composition of the present invention, the glass transition point Ru der 490 to 590 ° C.. Here, the “glass transition point” refers to a value measured by a push rod type thermal expansion coefficient measurement (TMA) apparatus.

Spark plug resistor forming a glass composition of the present invention, the yield point is Ru der 530-700 ° C.. Here, the “bend point” refers to a value measured with a TMA apparatus.

Spark plug resistor forming a glass composition of the present invention, the thermal expansion coefficient of Ru 40~60 × ^{10 -7} / ℃ der. Here, the “thermal expansion coefficient” refers to a value measured with a TMA apparatus, and refers to a value measured within a temperature range of 30 to 380 ° C.

It is preferable that the glass composition for forming a resistor for a spark plug of the present invention does not substantially contain PbO. In this way, environmental demands in recent years can be satisfied. Here, “substantially does not contain PbO” refers to a case where the content of PbO in the glass composition is 1000 ppm or less.

Spark plug resistor forming a glass composition of the present invention, Ru used for the spark plug.

The glass powder for forming a resistor for a spark plug of the present invention preferably contains a glass powder made of the above-described glass composition for forming a resistor.

The glass powder for forming a resistor for a spark plug of the present invention preferably has phase separation characteristics. Here, “having phase separation characteristics” refers to a case where glass undergoes phase separation when heat treatment is performed at any temperature of 600 to 900 ° C. for 10 minutes, for example, by TEM (Transmission Electron Microscope) or the like. If observed, it can be determined whether the glass is phase-separated. In addition, when the glass powder for forming a resistor is already phase-divided before the heat treatment is performed, it is determined that it has “phase-separation characteristics”.

In general, the phase separation refers to a state in which the glass component is separated into a high-viscosity silica-rich phase mainly composed of SiO ₂ and a low-viscosity glass phase composed of other components. Usually, the silica-rich phase has a skeleton, and a low-viscosity glass phase exists in the gap. When the resistor forming glass powder has phase separation characteristics, the coarse glass powder hardly dissolves conductive powder such as carbon black, titanium carbide, titanium nitride, and silicon carbide in the glass in the hot pressing step. On the other hand, the fine glass powder dissolves the conductive powder in the glass in a hot pressing process. As a result, a conductive path made of conductive powder can be formed in the vicinity of the coarse glass powder. The reason why the coarse glass powder does not take in the conductive powder in the hot pressing process is thought to be due to the phase separation of the glass, but the detailed mechanism is unknown and is currently under intensive investigation. In addition, when the resistor forming glass powder has phase separation characteristics, the coarse glass powder undergoes plastic deformation due to the softening flow of the low-viscosity glass phase in the hot pressing process. The shape can be maintained and it can function as a block particle.

The glass powder for forming a resistor for a spark plug of the present invention preferably has a glass powder particle size of 150 to 450 μm.

It is explanatory drawing which shows the principal part of a spark plug with a resistor.

The reason for limiting the glass composition range as described above in the glass composition for forming a resistor for a spark plug of the present invention will be described below.

SiO ₂ is a component that forms a skeleton of the glass, is a component that thermally stabilizes the glass and lowers the thermal expansion coefficient of the glass, and its content is 40 to 60%, preferably 45 to 55%. More preferably, it is 48 to 52%. When the content of SiO ₂ is less than 40%, the glass becomes thermally unstable, and it becomes difficult to stably produce the glass. In addition, the thermal expansion coefficient of the glass increases too much, and the resistor and the conductive glass. Peeling or cracking is likely to occur at the interface of the body or insulator. On the other hand, when the content of SiO ₂ is more than 60%, the yield point of the glass is unreasonably raised, and the glass is difficult to be deformed in the hot press process, and problems such as terminal floating are likely to occur.

B ₂ O ₃ is a component that forms the skeleton of the glass, is a component that thermally stabilizes the glass and lowers the yield point of the glass, and further is a component that causes phase separation of the glass. The content is 28 to 43%, preferably 32 to 39%, more preferably 33 to 38%. If the content of B ₂ O ₃ is less than 28%, the glass becomes thermally unstable and it becomes difficult to stably produce the glass, and the yield point of the glass is unreasonably raised, Glass becomes difficult to be deformed, and problems such as terminal floating are likely to occur. On the other hand, when the content of B ₂ O ₃ is more than 43%, the thermal expansion coefficient of the glass is excessively increased, and peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

_{Li 2 O + Na 2 O +} K 2 O , as well as reducing the yield point of the glass, a component to promote phase separation of the glass, the content thereof is 2.0 to 6.0%. _{Li 2 O + Na 2 O +} K 2 _O content polytene, the thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

Li ₂ O is a component for reducing the yield point of glass and promoting phase separation of glass, and its content is 1.5 to 5.9% . Li 2 _O content polytene, the thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator. From the viewpoint of promoting phase separation of glass, Li 2 _O in the glass composition in an essential component, good Mashiku is preferably contained more than 3%.

Na 2 _O, as well lowers the yield point of the glass, a component to promote phase separation of the glass, the content thereof, good Mashiku is 0-2%. Na 2 _O content polytene, the thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

K 2 _O is, with decreasing the deformation point of the glass, a component to promote phase separation of the glass, the content thereof, good Mashiku is 0-2%. K 2 _O content polytene, the thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

MgO + SrO is a component that lowers the dielectric constant of the glass and lowers the yield point of the glass. Further, when the hot press temperature fluctuates, it is a component that prevents a problem that the resistance value of the spark plug varies. is 4.4 to 17.5%, good Mashiku is 4.4 to 14%. The Most multi content of MgO + SrO, thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator. On the other hand, when the content of MgO + SrO is not less, it reduces the absorption capacity of the high-frequency noise waves glass, resulting in difficult to miniaturize the spark plug. If the content of MgO + SrO is not less, rises unduly sag of the glass, the glass is difficult to deform by hot pressing step, problems such as pin lifting is likely to occur.

MgO, together significantly reduces the dielectric constant of the glass is a component to lower the yield point of the glass, also a component to promote phase separation of the glass, the content thereof is good Mashiku 0 15%, more preferably 1-8%. The Most multi content of MgO, in addition to the thermal stability of the glass tends to decrease, too increase the thermal expansion coefficient of the glass, the interface at a peel or crack resistor and the conductive glass body or the insulator Is likely to occur. In addition, it is preferable to contain 1% or more of MgO as an essential component in the glass composition from the viewpoint of enhancing the ability of glass to absorb high-frequency noise radio waves.

SrO is a main component that lowers the dielectric constant of glass and a component that lowers the yield point of glass. Also, SrO, when hot pressing temperature is varied, a component to prevent a problem that the resistance value of the ignition plug varies, its content, good Mashiku 3 to 15%, more preferably from 4 to 13% . The content of SrO is polytene, the thermal expansion coefficient of the glass is too increased, peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator. In addition, from the viewpoint of enhancing the ability of glass to absorb high frequency noise and radio waves, it is preferable to contain SrO as an essential component in the glass composition at 1% or more, preferably 3% or more.

In addition to the above components, the glass composition for forming a resistor for a spark plug of the present invention can contain, for example, the following components in addition to the above components.

Al ₂ O ₃ is a component that lowers the thermal expansion coefficient of glass together with a component that improves the water resistance of glass, and its content is 0 to 10%, preferably 0 to 5%. When the content of Al ₂ O ₃ is more than 10%, the yield point of the glass is unreasonably raised, the glass is hardly deformed in the hot pressing process, and problems such as terminal floating are likely to occur.

  CaO is a component that significantly lowers the dielectric constant of glass and lowers the yield point of glass, and its content is 0 to 20%, preferably 0 to 15%, more preferably 0 to 10%. . When the content of CaO is more than 20%, the thermal expansion coefficient of the glass is excessively increased, and peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

  BaO is a component that lowers the yield point of the glass, and also prevents a variation in the resistance value of the spark plug when the hot press temperature fluctuates, and its content is 0 to 25%, preferably 0 to 0%. 20%, more preferably 0 to 15%. When the content of BaO is more than 25%, the dielectric constant of the glass increases, and the glass's ability to absorb high-frequency noise waves decreases. On the other hand, when the content of BaO is more than 25%, the thermal expansion coefficient of the glass is excessively increased, and peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator. From the viewpoint of reliably reducing the dielectric constant of the glass, it is preferable that the content of BaO is 15% or less, desirably 10% or less, and more desirably substantially not contained as the glass composition. Here, “substantially does not contain BaO” refers to a case where the content of BaO in the glass composition is 3000 ppm or less.

  Alkaline earth metal oxides (MgO, CaO, SrO, BaO) are components for promoting the phase separation of glass and at the same time, components that affect the dielectric constant of glass. The smaller the ionic radius of the alkaline earth metal oxide, the easier the glass is phase-separated. Specifically, the glass is more likely to phase-separate in the order of MgO, CaO, SrO, BaO. When the phase separation tendency of glass becomes high, the phase separation state easily fluctuates even with a small change in the heat treatment temperature. As a result, when the hot press temperature fluctuates, the resistance value of the spark plug varies. It becomes easy. On the other hand, the smaller the molecular weight of the alkaline earth metal oxide, the smaller the dielectric constant of the glass. Specifically, the dielectric constant of the glass decreases in the order of MgO, CaO, SrO, BaO. Considering characteristics such as dielectric constant, phase separation, yield point, etc., as described in paragraph [0033] of the present specification, the content of MgO + SrO in the glass composition is 1 to 25%, preferably 3 to 20 %, More preferably 4-14%. In this way, the ability to absorb high-frequency noise radio waves can be dramatically increased, and further, it is possible to prevent a problem that the resistance value of the spark plug varies. As a result, the reliability and productivity of the spark plug are improved. Can be improved.

Further, the glass composition for forming a resistor for a spark plug of the present invention can further contain various components up to 10% as a glass composition. For _{example, TiO 2, ZrO 2, Bi} 2 O 3, Cs 2 O, La 2 O 3, Gd 2 O 3, V 2 O 5, WO 3, Sb 2 O 3, SnO 2, Nb 2 O 5, Y 2 O ₃ , CeO ₂ , P ₂ O _{5 and the} like can be added up to 20%, preferably up to 10%. In addition, although the glass composition for resistor formation for spark plugs of this invention does not completely exclude inclusion of PbO, it is preferable not to contain PbO substantially from an environmental viewpoint as already stated.

In the spark plug resistor forming a glass composition of the present invention, the dielectric constant at 25 ° C., 1 MHz is 5.5 or less, 5.4 or less favorable preferred, more preferably 5.3 or less. If the dielectric constant at 25 ° C. and 1 MHz is greater than 5.5, the glass's ability to absorb high-frequency noise radio waves will be low, and if the spark plug is downsized, it will be difficult to absorb high-frequency noise radio waves. May interfere with radio, radio, etc.

In the spark plug resistor forming a glass composition of the present invention, 25 ° C., a dielectric loss tangent at 1MHz is greatly than 0.018, 0.0020 or good preferred, more preferably 0.0025 or more. If the dielectric loss tangent at 25 ° C. and 1 MHz is less than 0.0018, it will be difficult to increase the high frequency noise absorption capability of the glass, and if the spark plug is downsized, it will be difficult to sufficiently absorb the high frequency noise radio waves. May interfere with TV, radio, radio, etc.

In the spark plug resistor forming a glass composition of the present invention, the density is preferably less than 2.55 g / cm ^3, more preferably 2.50 g / cm ³ or less, more preferably 2.45 g / cm ³ or less. The smaller the density, the lighter the glass and, as a result, the lighter the spark plug.

In the spark plug resistor forming a glass composition of the present invention, the glass transition point is 490-590 ° C., 500-550 ° C. virtuous preferred, more preferably five hundred and five to five hundred and forty ° C.. When the glass transition point is lower than 490 ° C., the coarse glass powder easily dissolves the conductive powder in the hot pressing process, so that the coarse glass powder hardly functions as a block particle that bypasses the conductive path, and the high frequency of the resistor Noise absorption capacity is likely to decrease. On the other hand, when the glass transition point is higher than 590 ° C., it is difficult for the glass to be deformed in the hot pressing process, and problems such as terminal floating are likely to occur.

In the spark plug resistor forming a glass composition of the present invention, the yield point is 530~700 ℃, 540~650 ℃ virtuous preferred, more preferably 550 to 600 ° C.. When the yield point is lower than 530 ° C., the coarse glass powder easily dissolves the conductive powder in the hot pressing process, so that the coarse glass powder hardly functions as a block particle that bypasses the conductive path, and the high-frequency noise of the resistor The ability to absorb radio waves tends to decrease. On the other hand, if the yield point is higher than 700 ° C., the glass is not easily deformed in the hot pressing process, and problems such as floating of the terminal are likely to occur.

In the spark plug resistor forming a glass composition of the present invention, the thermal expansion coefficient is ^{40~60 × 10 -7 / ℃, 45~58} × 10 -7 / ℃ virtuous Mashiku, 53 to 58 × 10 ^-7 / ° C is more preferable. In order to make the thermal expansion coefficient lower than 40 × 10 ⁻⁷ / ° C., it is necessary to increase the content of SiO ₂ or the like in the glass composition. In such a case, the yield point of the glass becomes high. As a result, the glass becomes difficult to be deformed in the hot pressing process, and problems such as terminal floating easily occur. On the other hand, if the thermal expansion coefficient is higher than 60 × 10 ⁻⁷ / ° C., peeling or cracking is likely to occur at the interface between the resistor and the conductive glass body or the insulator.

The glass powder made of the above-described glass composition for forming a resistor for a spark plug is used as the glass powder for forming a resistor for a spark plug of the present invention. If it is processed into glass powder, the glass is easily deformed in the hot press process, and if it is processed into granules, it becomes easier to fill the inner hole of the insulator with the resistor material.

The glass powder for forming a resistor for a spark plug of the present invention preferably has phase separation characteristics. Since the preferable reason has already been described, the description thereof is omitted here for convenience.

In the glass powder for forming a resistor for a spark plug of the present invention, the particle size of the glass powder is preferably 150 to 450 μm, and more preferably 200 to 350 μm. If the particle size of the glass powder is 150 to 450 μm, it can function properly as block particles. If the particle size of the glass powder is smaller than 150 μm, the glass powder dissolves the conductive powder in the hot pressing process, and the coarse glass powder becomes difficult to function as block particles that bypass the conductive path, and the resistor absorbs high frequency noise waves. Tends to decrease. On the other hand, when the particle size of the glass powder is larger than 450 μm, it becomes difficult to process into a granule, and it becomes difficult to fill the glass powder into the inner hole of the insulator, and in addition, the glass powder is difficult to be deformed in the hot press process. Problems such as floating easily occur. Here, “150-450 μm particle size” means passing through a sieve having an opening of 450 μm and not passing through a sieve having an opening of 150 μm.

In the glass powder for the resistor forming a spark plug of the present invention, the average particle diameter _{D 50} of the glass powder is preferably 150~450μm, 200~350μm is more preferable. If the average particle diameter _{D 50} of the glass powder 150～450Myuemu, can function properly as a block particles. And 150μm smaller than the average particle diameter D ₅₀ of the glass powder, the glass powder is dissolved conductive powder by hot pressing step, coarse glass powder becomes difficult to function as a block particles divert conductive path, high frequency noise of the resistor The ability to absorb radio waves tends to decrease. On the other hand, a 450μm larger average particle diameter D ₅₀ of the glass powder, hardly processed into granules, in addition to being difficult to fill the glass powder in the inner hole of the insulator, the glass powder is deformed by hot pressing step This makes it difficult to cause problems such as terminal floating. Here, the “average particle diameter D ₅₀ ” refers to a value measured by the laser diffraction method. In the volume-based cumulative particle size distribution curve measured by the laser diffraction method, the cumulative amount is accumulated from the smaller particle. The particle diameter is 50%.

The glass powder for forming a resistor for a spark plug of the present invention can also be used as a fine glass powder for forming a resistor. In that case, the average particle diameter _{D 50} of the glass powder is preferably less than 150 [mu] m, more preferably at most 100 [mu] m. If the average of the glass powder the particle diameter D ₅₀ is at 150μm or more, hardly glass powder melted in the hot pressing process, defects such as pin lifting is likely to occur. Note that if the coarse glass powder and the fine glass powder have the same glass composition, the two are firmly bonded in the hot pressing step, so that the mechanical strength of the resistor can be increased.

In the glass powder for forming a resistor for a spark plug of the present invention, the maximum particle diameter _Dmax of the glass powder is preferably 450 μm or less, and more preferably 400 μm or less. When the average particle diameter _Dmax of the glass powder is larger than 450 μm, it becomes difficult to fill the glass powder into the inner hole of the insulator when the inner hole of the insulator is reduced in diameter. Here, the “maximum particle diameter D _max ” refers to a value measured by the laser diffraction method. In the volume-based cumulative particle size distribution curve measured by the laser diffraction method, the accumulated amount is accumulated from the smaller particle. The particle diameter is 99%.

The glass powder for forming a resistor for a spark plug of the present invention is preferably used for a spark plug. Since the glass powder for forming a resistor for a spark plug of the present invention can sufficiently absorb high-frequency noise radio waves even if the filling amount of the glass powder is reduced, it is advantageous when the spark plug is downsized.

Hereinafter, based on an Example, this invention is demonstrated in detail. Tables 1-3 show sample No. 1-18 are shown. Sample No. 18 is a conventional resistor-forming glass powder.

  First, a glass batch in which raw materials such as various oxides and carbonates were prepared so as to have the glass composition in the table was prepared, and this was put in a platinum crucible and melted at 1300 ° C. for 2 hours. Next, a part of the molten glass was poured out into a carbon mold to obtain a plate-like glass sample. Moreover, after shape | molding a part of molten glass into a thin piece shape with a water-cooling roller, after pulverizing with a ball mill, it classified with the test sieve and obtained each glass powder.

  Sample No. For 1 to 18, the glass transition point, yield point, thermal expansion coefficient, dielectric constant, dielectric loss tangent, volume resistivity, function as block particles, sinterability, and phase separation were evaluated.

  The glass transition point and yield point were measured with a TMA apparatus. In addition, the measurement sample of TMA used what sintered the glass powder.

  The thermal expansion coefficient was measured in a temperature range of 30 to 380 ° C. using a TMA apparatus. In addition, the measurement sample of TMA used what sintered the glass powder.

  The dielectric constant and dielectric loss tangent were measured by using a glass substrate of 50 mm × 50 mm × 3 mm thickness (glass powder densely sintered) as a measurement sample, and attaching 30 mmφ electrodes on the front and back surfaces of the glass substrate. A voltage was applied and measured. The measurement conditions were 25 ° C. and 1 MHz, and the front and back surfaces of the glass substrate were optically polished.

  The volume resistivity was measured by a method based on ASTM C657-78. A 50 mm × 50 mm × 0.7 mm thick glass substrate (glass powder densely sintered, front and back surfaces optically polished) was used as a measurement sample. A metal Al film was formed on the front and back surfaces of this glass substrate by vapor deposition to form an electrode having a thickness of about 2000 nm. The main electrode was a circle with a diameter of 29 mm, the guard electrode was a ring with an outer diameter of 44 mm and an inner diameter of 31 mm, and the bottom electrode was a circle with a diameter of 44 mm. Next, the volume resistivity at each temperature in the table was measured. The volume resistivity is shown for reference and is a value that can serve as an index indicating the conductivity of glass.

The function as a block particle was measured as follows. First, a sample in which 5% by mass of carbon black was added to each glass powder having a mass corresponding to the density of glass (particle size: 150 to 450 μm, average particle size D ₅₀ = 300 μm) was pressed into a button shape having an outer diameter of 20 mm using a mold. Subsequently, after the obtained button sample was sandwiched between alumina substrates, it was put into an electric furnace maintained at 900 ° C., heated at a press pressure of 100 kg / cm ² for 10 minutes, and then the button sample was removed from the electric furnace. The button sample was taken out and evaluated by observing the appearance of the obtained button sample. The glass powder is slightly deformed, but it is not completely melted and the carbon black is not dissolved in the glass is marked with “O”, the glass powder is completely melted, or the carbon black is not in the glass. What was melt | dissolved was evaluated as "x".

For sinterability, glass powder having a mass corresponding to the density of glass (average particle diameter D ₅₀ = 50 μm) was pressed into a button shape having an outer diameter of 20 mm using a mold, and the obtained button sample was placed on an alumina substrate. After mounting, the temperature was raised at 20 ° C./min in an electric furnace, held at 900 ° C. for 10 minutes, lowered at a rate of 20 ° C./min, and evaluated by observing the appearance of the obtained button sample. did. Button and the sample has a gloss, a diameter of the button sample is less than 17.8mm and "○", no glossy button sample, or the diameter of the button sample that potato size from 17.8mm "× ".

  The phase separation was evaluated by observing with a TEM a sample obtained by processing the button sample into a predetermined shape. The glass was phase-separated as “◯”, and the glass not phase-separated as “x”.

  As is apparent from Tables 1 to 3, sample No. Nos. 1 to 17 were excellent in evaluation of glass transition point, yield point, thermal expansion coefficient, dielectric constant, dielectric loss tangent, function as block particles, sinterability and phase separation. In particular, sample no. 1 to 17 can reduce the effective dielectric constant between the terminal electrode and the center electrode because the dielectric constant is low, and as a result, even if the spark plug is downsized, high-frequency noise radio waves can be accurately absorbed. it is conceivable that. On the other hand, sample No. No. 18 does not contain MgO + SrO in the glass composition, and thus has a high dielectric constant. If the spark plug is downsized, it is considered that high-frequency noise radio waves leak.

As apparent from the above description, the glass composition for forming a resistor for a spark plug of the present invention is a coarse glass powder or a fine glass powder for forming a resistor in the inner hole of an insulator of a spark plug. Is preferred.

DESCRIPTION OF SYMBOLS 1 Terminal electrode 2a, 2b Conductive glass body 3 Center electrode 4 Resistor

Claims (6)

As a glass composition, in _{mass%, SiO 2 40~60%, B} 2 O 3 28~43%, Li 2 O + Na 2 O + K 2 O 2.0~6.0%, Li 2 O 1.5~5.9 %, MgO + SrO 4.4 to 17.5 %, dielectric constant at 25 ° C. and 1 MHz is 5.5 or less, dielectric loss tangent at 25 ° C. and 1 MHz is larger than 0.0018, and glass transition point is 490 to A glass composition for forming a resistor for a spark plug , characterized by having a temperature of 590 ° C., a yield point of 530-700 ° C., and a thermal expansion coefficient of 40-60 × 10 ⁻⁷ / ° C. 2. The glass composition for forming a resistor for a spark plug according to claim 1 , which is substantially free of PbO. Density claim 1 or spark plug resistor forming glass composition according to any one of 2 and less than 2.55 g / cm ^3. A glass powder for forming a resistor for a spark plug, comprising the glass powder made of the glass composition for forming a resistor according to any one of claims 1 to 3. The glass powder for forming a resistor for a spark plug according to claim 4 , wherein the glass powder has a phase separation characteristic. The glass powder for forming a spark plug resistor according to claim 4 or 5 , wherein the glass powder has a particle size of 150 to 450 µm.