JP2013114810A - Film-forming composition and spark plug provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film-forming composition which has electrical conductivity and is excellent in adhesion to an object to be bonded, and to provide a spark plug provided with the same.SOLUTION: The film-forming composition of the present invention contains, as a main component, a perovskite oxide containing lanthanum and contains a manganese oxide and a silicon oxide. The film-forming composition has electrical conductivity by containing, as a main component, the perovskite oxide containing lanthanum. Since the manganese oxide and the silicon oxide form a glass phase, the film-forming composition is excellent in adhesion to an object to be bonded.

Description

  The present invention relates to a film forming composition and a spark plug using the same.

  Generally, a spark plug used for ignition of an internal combustion engine such as an automobile engine has a tubular insulator disposed inside a metal shell to which a ground electrode is attached, and a center electrode is disposed inside the insulator.

  This insulator extends in the axial direction from the opening on the rear side of the metal shell, and a terminal metal fitting is arranged inside the extended insulator, and this terminal metal fitting is centered through a conductive glass seal layer, a resistor, etc. Connected with electrodes.

  Then, by applying a high voltage through the terminal fitting, a spark discharge is generated in the discharge gap formed between the ground electrode and the center electrode, and the air-fuel mixture in the combustion chamber of the internal combustion engine burns. Has been.

By the way, since spark discharge is accompanied by instantaneous current change, it is known that radio current noise is generated by this current change. If this radio noise is large, an ECU (e.g., ECU for controlling a vehicle equipped with a spark plug) In addition to affecting electronic equipment such as the Engine Control Unit), it may also cause radio interference to the outside world.

Therefore, for the purpose of reducing this radio noise, for example, in Patent Document 1, an ABO ₃ type perovskite oxide (A) is used as a coating layer covering the outer surface of the insulator held inside the metal shell. A high dielectric constant having a dielectric constant higher than that of alumina, wherein the site contains at least one of Ca, Sr, Ba, Pb, and La, and the B site contains at least one of Zr, Ti, Ce, and Al). Spark plugs using members have been proposed.

International Publication No. 2009/133683 Pamphlet

  By the way, for the purpose of reducing radio noise, a coating layer covering the outer surface of an object to be bonded such as an insulator constituting a spark plug is required to have conductivity and adhesion to the object to be bonded. It is done. Therefore, there has been a demand for a film-forming composition that is excellent in conductivity and excellent in adhesion to an object to be bonded and a spark plug including the same.

  In view of such problems, the present invention provides a film-forming composition having conductivity and high adhesion to an object to be bonded, and a spark plug including the composition.

  The film-forming composition of the present invention is characterized by containing a perovskite oxide containing lanthanum as a main component and containing manganese oxide and silicon oxide.

The spark plug of the present invention includes a center electrode, a metal shell, and a tubular insulator disposed between the center electrode and the metal shell, and at least a part of the surface of the insulator is formed. It is characterized by being coated with the film forming composition.

  The film-forming composition of the present invention is mainly composed of a perovskite oxide containing lanthanum and contains manganese oxide and silicon oxide. Therefore, the film-forming composition has conductivity and manganese oxide and silicon oxide form a glass phase. Thereby, it can be set as the film forming composition excellent in adhesiveness with a to-be-joined object.

  The spark plug of the present invention includes a center electrode, a metal shell, and a tubular insulator disposed between the center electrode and the metal shell, and at least a part of the surface of the insulator is formed. Since it is covered with the film forming composition, it is possible to reduce radio noise and to make a spark plug excellent in long-term reliability.

The left side from a center line is a front view and the right side from a center line is a sectional view showing an example of a spark plug coated with the film forming composition of this embodiment.

  The film-forming composition of the present embodiment is mainly composed of a perovskite oxide containing lanthanum (hereinafter, the perovskite oxide containing lanthanum is referred to as a lanthanum-containing perovskite oxide), and manganese oxide and silicon oxide. It is important to include

  The lanthanum-containing perovskite oxide has high electron conductivity, so that the conductivity of the film-forming composition is increased, and manganese oxide and silicon oxide form a glass phase to form crystalline particles of the lanthanum-containing perovskite oxide. And the crystal grains constituting the joined body are strongly bound, so that the adhesion to the joined body is increased.

  Here, examples of the lanthanum-containing perovskite oxide include lanthanum chromite, lanthanum strontium manganite, lanthanum strontium iron cobaltite, lanthanum strontium ferrite, lanthanum strontium cobalt ferrite, lanthanum nickel ferrite, or lanthanum cobaltite The perovskite oxide can be used. Moreover, the main component in this embodiment means the component which occupies 60 mass% or more among the components which comprise the composition for film formation.

  Of the lanthanum-containing perovskite oxides, lanthanum chromite oxides (hereinafter referred to as lanthanum chromite oxides) are particularly preferable. When the perovskite oxide is lanthanum chromite, the density can be sufficiently increased, so that the adhesion to the object can be improved and the electron conductivity can be further increased.

When the lanthanum-containing perovskite oxide is lanthanum chromite, at least one of magnesium, titanium, vanadium, manganese, iron, and cobalt is used.
The seed may be dissolved in lanthanum chromite.

Further, the lanthanum chromite includes at least lanthanum magnesium chromite in which a part of chromium ions (Cr ³⁺ ) constituting the lanthanum chromite is replaced with magnesium ions (Mg ²⁺ ) and lanthanum calcium chromite substituted with calcium ions (Ca ²⁺ ). Any one of them is preferred. In such a case, since many holes (holes) are generated, the electrons easily move through these holes, and high electron conductivity can be obtained.

Lanthanum chromite, composition formula, for _{example, La (Cr 1- (x +} y) M x N y) z O 3 (M is at least any one of magnesium and calcium, N is the titanium, vanadium, manganese, iron And x and y are both greater than 0 and less than or equal to 0.3, and z is greater than or equal to 0.9 and less than or equal to 1).

  The lanthanum-containing perovskite oxide can be determined for its stoichiometric composition and content using a transmission electron microscope equipped with an energy dispersive X-ray spectrometer.

  On the other hand, the film forming composition of the present embodiment contains manganese oxide and silicon oxide. For example, when the film-forming composition of the present embodiment is used to form a film that covers an object to be bonded, manganese oxide and silicon oxide form a glass phase. Accordingly, the crystal particles of the lanthanum-containing perovskite oxide enter between the crystal particles constituting the object to be bonded, and the crystal particles can be strongly bonded to each other. Thereby, the adhesiveness of a film and a to-be-joined object can be improved.

  Manganese oxide and silicon oxide can be identified using an X-ray diffraction method. In addition, each content of manganese oxide and silicon oxide is obtained by calculating each content of manganese and silicon by fluorescent X-ray analysis or ICP (Inductively Coupled Plasma) emission spectroscopy, and converted to manganese oxide and silicon oxide, respectively. It can ask for.

In particular, the film-forming composition of this embodiment has a lanthanum-containing perovskite-type oxide content and a total content of manganese oxide and silicon oxide of 80% by mass or more and 96% by mass or 4% by mass or more, respectively. It is preferable that the mass ratio of manganese oxide to silicon oxide (MnO ₂ : SiO ₂ ) is 3:12 or more and 12: 3 or less, and the range of these oxides is within this range. If it exists, while being able to ensure electrical conductivity fully, the adhesiveness with respect to a to-be-joined object can be made still higher.

  FIG. 1 is a front view on the left side of the center line and a cross-sectional view on the right side of the center line, showing an example of a spark plug including a film made of the film forming composition of the present embodiment.

  The spark plug 3 in the example shown in FIG. 1 includes a tubular insulator 32 between the center electrode 33 and the metal shell 31.

A ground electrode 35 that is opposed to the central electrode 33 with a discharge gap 38 therebetween is fixed to the metal shell 31. A stepped portion 32 b is formed on the outer peripheral portion of the insulator 32. A support portion 313 is formed on one end side of the metal shell 31 so as to project radially inward toward the insulator 32. The stepped portion 32b of the insulator 32 is formed by the support portion 313 of the metal shell 31. It is supported.

  On the other end side of the insulator 32, a stepped portion 32a is formed. The stepped portion 32 a of the insulator 32 is supported by the support portion 314 on the other end side of the metal shell 31.

  One end 3 b side of such a spark plug 3 is inserted into a combustion chamber (not shown) of the internal combustion engine, and a high discharge voltage (about −10 kV to −35 kV) is applied between the center electrode 33 and the ground electrode 35. As a result, spark discharge occurs in the discharge gap 38, and the air-fuel mixture in the combustion chamber burns. Further, in the vicinity of the discharge gap 38, ions are generated with the combustion, so that an ionic current flows between the center electrode 33 and the ground electrode 35.

A thread 31a is formed on the outer peripheral portion of the metal shell 31, and the engine block (
The spark plug 3 is detachably attached to the unillustrated).

  The insulator 32 is held inside the metal shell 31, and both end portions of the insulator 32 extend from the metal shell 31, respectively. Further, a center electrode 33 and a stem portion 34 are held inside the insulator 32.

  One end portion of the center electrode 33 extends from one end portion of the insulator 32, and one end of the stem portion 34 extends from the other end portion of the insulator 32, and the other end portion of the center electrode 33 and the stem portion 34 The other end is electrically connected.

The stepped portion 32a of the insulator 32 and the support portion 314 of the metal shell 31 are sealed with a packing 36 made of a material having excellent heat resistance, for example, iron or copper. Similarly, the stepped portion 32b of the insulator 32 and the support portion 313 of the metal shell 31 are sealed with a packing 37 made of a material having excellent heat resistance, for example, iron or copper. That is, the support portions 314 and 313 support the stepped portions 32a and 32b via the packings 36 and 37, respectively.

  After the packing 37 is disposed on the stepped portion 32b, the insulator 32 is inserted into the metal shell 31 from the other end of the metal shell 31, and then the packing 36 is disposed on the stepped portion 32a. Then, by crimping the other end portion of the metal shell 31 so as to be bent inward, the packings 36 and 37 are pressed and deformed between the stepped portions 32a and 32b and the support portions 314 and 313. By this deformation, the packings 36 and 37 are in close contact with the stepped portions 32a and 32b and the support portions 314 and 313.

Then, at least a part of the surface of the insulator 32, for example, a portion located in the vicinity of the support portion 314 of the metal shell 31 of the insulator 32 is covered with the coating 39 made of the film forming composition of the present embodiment. Yes.

  This portion includes the entire circumference of the stepped portion 32a, the entire circumference of the extending portion 32c extending from the stepped portion 32a to the gap C side (the other end portion side of the insulator 32) by a predetermined dimension (for example, 6 mm), Of the outer peripheral portion of the body 32, the entire periphery of the extending portion 32d extending from the stepped portion 32a to the opposite side of the gap C (one end portion side of the insulator 32) by a predetermined dimension (for example, 1 mm).

The extending portion 32c includes a facing portion facing the support portion 314 and a gap C side (stepped portion 32a from the facing portion).
And an extending portion extending to the opposite side. In addition, the dimension L in the radial direction of the gap C is, for example, 0.4 m
m.

  The coating 39 is formed on the entire circumference of the first portion 39a formed on the entire circumference of the stepped portion 32a, the second portion 39c formed on the entire circumference of the extended portion 32c, and on the entire circumference of the extended portion 32d. It consists of three parts 39d.

  The first portion 39a of the coating 39 is electrically connected to the metal shell 31 through the packing 36 over the entire circumference, and the third site 39d of the coating 39 is electrically connected to the metal shell 31 over the entire circumference. .

  Here, since the coating 39 made of the film forming composition of the present embodiment, which is coated on the outer surface of the metallic shell 31, has conductivity, the positive charge dispersed in the coating 39 is the metallic shell 31. A small amount will always be released to the side. Thereby, local accumulation of positive charges at the outer peripheral portion of the insulator 32 can be suppressed, and radio noise can be reduced.

In the present embodiment, it is preferable that the coating 39 further contains the same component as the main component of the tubular insulator 32. For example, as the composition of the coating 39, when the same component as the main component of the insulator 32 is contained, a glass phase is formed with the main component, manganese oxide, and silicon oxide. The sex becomes even higher.

Therefore, when the main component of the insulator 32 is aluminum oxide, the film-forming composition preferably contains aluminum oxide. In this case, for example, the content of the lanthanum-containing perovskite oxide is The total content of manganese oxide, silicon oxide and aluminum oxide is 4% by mass or more and 20% by mass. Further, it is preferable that the mass ratio of manganese oxide to silicon oxide (MnO ₂ : SiO ₂ ) is 3:12 or more and 12: 3 or less, and the balance is aluminum oxide.

  In the above-described example, an example in which the composition constituting the coating 39 contains the same component as the main component of the insulator 32 has been described. For example, a part of the main component of the insulator 32 diffuses into the coating 39. As a result, the composition that eventually forms the coating 39 may contain the same component as the main component of the insulator 32.

  Here, aluminum oxide can be identified using an X-ray diffraction method. The content of aluminum oxide can be determined by obtaining the aluminum content by fluorescent X-ray analysis or ICP (Inductively Coupled Plasma) emission spectroscopy and converting it to aluminum oxide.

  The film 39 is preferably 30 μm or more and 55 μm or less in thickness. When the thickness of the coating 39 is in this range, the coating 39 can be efficiently produced, and ion current detection used for detecting the combustion state of the air-fuel mixture and the occurrence of knocking in the combustion chamber of the internal combustion engine It becomes easy to suppress spike noise that causes erroneous detection of means (not shown).

  In addition, it is preferable that an insulating coating made of, for example, a glass-based material is formed on substantially the entire circumference of the side surface on the other end side protruding from the metal shell 31 in the outer peripheral portion of the insulator 32. .

  Next, the film forming composition and the spark plug manufacturing method of this embodiment will be described.

First, the lanthanum-containing perovskite oxide powder is, for example, 80% by mass to 96% by mass, and the manganese oxide powder and the silicon oxide powder are, for example, 4% by mass to 20% by mass and oxidized. Preparation is made so that the mass ratio of manganese to silicon oxide (MnO ₂ : SiO ₂ ) is 3:12 or more and 12: 3 or less, and these powders are mixed together with an organic solvent such as terpineol using a mortar, pot mill, or the like. As a result, the film-forming composition of the present embodiment in the form of a paste can be obtained.

  Further, when the insulator 32 is mainly composed of aluminum oxide, the film-forming composition is a lanthanum-containing perovskite oxide powder, for example, 80 mass% to 96 mass%, manganese oxide powder, Silicon oxide powder and aluminum oxide powder, for example, 1% by mass to 10% by mass, 1% by mass to 10% by mass, and 0% by mass to 10% by mass, respectively. By mixing with an organic solvent using a mortar, pot mill, or the like, a paste-like film forming composition of the present embodiment can be obtained.

  This paste-like film-forming composition is applied to the entire circumference of the stepped portion 32a, the extended portion 32c, and the extended portion 32d of the insulator 32 using a screen printing method, and the temperature and holding time are 1350 ° C. The coating 39 can be obtained by heat treatment at 1 ° C. for 4 hours or less at 1 ° C., and the insulator 32 coated with the coating 39 is attached to the metal shell 31 so that the spark plug of the embodiment shown in FIG. 3 can be obtained.

3: Spark plug
31: Metal fitting
32: Insulator
33: Center electrode
35: Ground electrode
38: Discharge gap
39: coating

Claims (4)

  A film-forming composition comprising a perovskite oxide containing lanthanum as a main component and containing manganese oxide and silicon oxide.   2. The film forming composition according to claim 1, wherein the perovskite oxide is a lanthanum chromite oxide.   The center electrode, a metal shell, and a tubular insulator disposed between the center electrode and the metal shell, wherein at least a part of the surface of the insulator is according to claim 1 or 2. A spark plug which is covered with a film forming composition.   The spark plug according to claim 3, wherein the film-forming composition further contains the same component as the main component of the tubular insulator.

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