JP4500335B2 - Spark plug gasket, spark plug, and spark plug gasket manufacturing method - Google Patents

Description

  The present invention relates to a spark plug gasket for an internal combustion engine, a spark plug, and a spark plug gasket manufacturing method.

JP-A-6-338379

  Spark plugs used to ignite internal combustion engines, such as gasoline engines for automobiles, etc., have an insulator outside the center electrode and a metal shell on the outside, forming a spark discharge gap with the center electrode. The ground electrode is attached to the metal shell. And it attaches and uses to the cylinder head of an engine with the attaching screw part formed in the outer peripheral surface of a metal shell. Further, a gasket is fitted into the base end portion of the mounting screw portion formed on the outer peripheral surface of the metal shell.

  The metal shell and gasket are generally made of an iron-based material such as carbon steel, and the surface thereof is often galvanized for corrosion protection (Patent Document 1). Although the galvanized layer has an excellent anticorrosive effect against iron, as is well known, the galvanized layer on iron is easily consumed by sacrificial corrosion, and the appearance is changed to white due to the generated zinc oxide. There are also disadvantages that are easily damaged. Therefore, in many spark plugs, the surface of the galvanized layer is further covered with a chromate film to prevent corrosion of the plated layer.

  By the way, a so-called yellow chromate film has been used as a chromate film applied to the metal shell or gasket of the spark plug. Since this yellow chromate film has good anticorrosion performance, it has been widely used in fields other than spark plugs, such as canned inner surface coating. However, in recent years when interest in environmental protection has been increasing on a global scale due to the fact that a part of the chromium component is contained in the form of hexavalent chromium, it has been gradually shunned. For example, in the automobile industry in which spark plugs are used in large quantities, in view of the environmental impact of waste spark plugs, the use of chromate coatings containing hexavalent chromium has been studied to be eliminated in the future. In addition, since the treatment bath for the yellow chromate film treatment contains a relatively high concentration of hexavalent chromium, there is a problem that the waste liquid treatment is very expensive.

  In response to this trend, the development of a chromate film that does not contain hexavalent chromium, that is, a film in which substantially all of the chromium component is contained in the form of trivalent chromium has been underway relatively early. The treatment bath generally has a low hexavalent chromium concentration, and a bath containing no hexavalent chromium has been developed, and the problem of waste liquid treatment has been reduced. However, the trivalent chromium-based chromate film has a major drawback in that the anticorrosion performance is inferior to that of the yellow chromate film, and has not been widely used as a coating film for the metal shell of the spark plug.

  In addition, the chromate film, including the yellow chromate film, has a common drawback that it has poor heat resistance. In an automobile engine or the like, since the cylinder head to which the spark plug is attached is water-cooled, the spark plug is unlikely to become extremely hot. However, if the engine operation is continued under conditions where a large heat load is applied, or if the spark plug is mounted at a position that is relatively close to the exhaust manifold, the temperature of the metal shell sometimes becomes about 200-300 ° C. May rise to. Under such circumstances, there is a problem that the deterioration of the chromate film is likely to proceed and the anticorrosion performance is drastically lowered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug gasket that has a low hexavalent chromium content in the chromate coating covering the gasket surface and is superior in corrosion resistance and heat resistance compared to conventional chromate coatings, and a spark using the same. It is to provide a method for manufacturing a plug and a gasket for a spark plug.

Means and actions / effects for solving the problems

In order to solve the above problems, the first configuration of the gasket for a spark plug of the present invention is:
It is used by being fitted into the base end portion of the mounting screw portion formed on the outer peripheral surface of the spark plug metal shell, and at least a part of its surface contains a chromium component and a phosphorus component as cationic components, and 90% by weight or more of the chromium component is trivalent chromium, and the phosphorus component is covered with a composite chromate film containing 1 to 15% by weight in terms of PO ₄ ,
The composite chromate film has a phosphorus component-dispersed chromate layer in which the phosphorus component is dispersed in the trivalent chromium-based compound and the content of the phosphorus component is 2 to 15% by weight in terms of PO _4. Features.

  The “cationic component” means an ion valence at the binding energy peak of the component (element or atom) of interest in the photoelectron spectrum obtained when the film is analyzed by X-ray photoelectron spectroscopy (XPS or ESCA). This refers to a component that has a chemical shift in a direction in which the number is positive.

In the above-described structure, what is formed on the surface of the metal shell contains a chromium component and a phosphorus component as cation components, 90% by weight or more of the chromium component is trivalent chromium, and the phosphorus component is converted to PO ₄ The composite chromate film is contained in an amount of 1 to 15% by weight. That is, in the normal yellow chromate film, about 25 to 35% by weight of the chromium component is hexavalent chromium, whereas in the film of the present invention, the content of hexavalent chromium with respect to the chromium component is as low as 10% by weight or less. Therefore, it is possible to enhance the effect on environmental measures to reduce hexavalent chromium. Also, the chromate treatment liquid used does not contain any hexavalent chromium component, or even if it contains it, the amount can be greatly reduced compared to the treatment liquid such as yellow chromate coating, so there is a problem with the drainage treatment. Is less likely to occur.

  The composite chromate film used in the first configuration of the spark plug gasket of the present invention is characterized in that it contains a phosphorus component as a cation component. By including a phosphorus component in the composite chromate film, the anti-corrosion performance is greatly improved as compared with the usual trivalent chromium-based chromate film, and the metal shell can be sufficiently given durability against corrosion. Become.

If the content of the phosphorus component in the composite chromate film is less than 1% by weight, the anticorrosion performance is insufficient. In addition, a phosphorus component content exceeding 15% by weight is very difficult to form because there is a limit to the concentration of the phosphorus component in the processing solution used. The content of the phosphorus component in the composite chromate film is more preferably 5 to 10% by weight. Further, it is desirable that the phosphorus component is mainly contained in the form of phosphate ions (PO ₄ ³⁻ ) in order to improve the anticorrosion performance of the composite chromate film.

The composite chromate film includes a phosphorus component-dispersed chromate layer in which a phosphorus component is dispersed in a trivalent chromium-based compound and the content of the phosphorus component is 2 to 15% by weight in terms of PO ₄ . Such a phosphorus component-dispersed chromate layer can be easily formed by immersing the metal shell in a chromate treatment bath containing phosphoric acid or phosphate, and the trivalent chromium-based compound and the phosphorus component are By forming the dispersed state, the anticorrosion performance of the composite chromate film can be further improved. In this case, the phosphorus component is derived from phosphoric acid or phosphate contained in the chromate treatment bath.

The phosphorus component concentration of the phosphorus component-dispersed chromate layer as described above is desirably 2% by weight or more in terms of PO ₄ from the viewpoint of ensuring anticorrosion performance. On the other hand, since there is a limit to the phosphorus component concentration in the chromate treatment solution to be used, it is very difficult to form a phosphorus component-dispersed chromate layer having a phosphorus component concentration exceeding 15% by weight in terms of PO ₄ . The thickness of the phosphor component-dispersed chromate layer is 0.2 to 0.4 μm. When the thickness is less than 0.2 μm, the anticorrosion performance of the phosphor component-dispersed chromate layer becomes insufficient. Moreover, it is difficult to realize a thick chromate layer exceeding 0.4 μm by trivalent chromium-based chromate treatment.

Next, the second configuration of the spark plug gasket of the present invention is used by being fitted into the base end portion of the mounting screw portion formed on the outer peripheral surface of the spark plug metal shell, and at least one of its surfaces. Part contains a chromium component and a silicon component as a cation component, 90% by weight or more of the chromium component contained is trivalent chromium, and the silicon component is contained in an amount of 5 to 75% by weight in terms of SiO _2. It is covered with a composite chromate film,
The composite chromate film has a silicon component-dispersed chromate layer in which the silicon component is dispersed in the trivalent chromium-based compound and the content of the silicon component is 10 to 40% by weight in terms of SiO _2. Features.

  The composite chromate film also used in the above configuration has a low hexavalent chromium content of 10% by weight or less with respect to the chromium component, so that the effect on environmental measures to reduce hexavalent chromium can be enhanced. The problem of drainage treatment is also less likely to occur. In addition, by including a silicon component as a cation component, the anticorrosion performance and heat resistance are greatly improved as compared to a normal trivalent chromium-based chromate coating, and the durability against corrosion of the metal shell can be greatly improved. become.

  When the content of the silicon component in the composite chromate film is less than 5% by weight, it is difficult to ensure anticorrosion performance and heat resistance. Moreover, when it exceeds 75 weight%, the content rate of a chromate compound will fall relatively, and it will lead to corrosion protection performance being impaired on the contrary. The content of the silicon component in the composite chromate film is more preferably 15 to 40% by weight.

The composite chromate film is a silicon component-dispersed chromate layer in which a silicon component is dispersed in a trivalent chromium-based compound and the content of the silicon component is 10 to 40% by weight in terms of SiO ₂ . Such a silicon component-dispersed chromate layer can be easily formed by immersing the metal shell in a chromate treatment bath containing an alkali silicate, and the trivalent chromium compound and the silicon component are dispersed. By forming, the anticorrosion performance and heat resistance of the composite chromate film can be further improved. In this case, the silicon component is derived from the alkali silicate contained in the chromate treatment bath.

The silicon component concentration in the silicon component-dispersed chromate layer as described above is desirably 10% by weight or more in terms of SiO ₂ from the viewpoint of ensuring corrosion resistance and heat resistance. In addition, since there is a limit to the alkali silicate concentration in the chromate treatment liquid to be used, it is very difficult to form a silicon component dispersed chromate layer having a silicon component concentration exceeding 40% by weight in terms of SiO _2. .

  The spark plug of the present invention is characterized in that the gasket for a spark plug of the present invention is fitted into a base end portion of a mounting screw portion formed on the outer peripheral surface of the metal shell. In the spark plug, the gasket is formed by screwing the threaded portion of the metal shell into the threaded hole on the cylinder head side, so that the flange-shaped gas seal portion formed on the proximal end side of the threaded portion and the opening periphery of the threaded hole It compresses and deforms so as to be crushed, and serves to seal between the screw hole and the gas seal portion.

  In addition, the structure of the phosphorus component dispersed chromate layer and the structure of the silicon component dispersed chromate layer are combined with each other (for example, when viewed from the viewpoint of the phosphorus component dispersed chromate layer, the silicon component is in the range of 10 to 40% by weight. It is also possible to be contained. As a result, the effect of improving the anticorrosion performance by dispersing the phosphorus component and the effect of improving the anticorrosion performance and heat resistance by dispersing the silicon component are combined to realize a composite chromate film with even better performance.

In addition, it is desirable that the phosphorus component in the phosphorus component-dispersed chromate layer is mainly contained in the form of phosphate ions (PO ₄ ³⁻ ) in order to improve the anticorrosion performance of the composite chromate film. Further, it is desirable that the silicon component is mainly contained in the form of silicon oxide (for example, silicon dioxide (SiO ₂ )) in order to improve the anticorrosion performance and heat resistance performance of the composite chromate film. In the present specification, if the peak of phosphorus having a valence of +5 or close thereto and the peak of oxygen having a valence of −2 or close thereto are detected simultaneously in the above-mentioned XPS photoelectron spectrum, the phosphorus component is oxygen. It is thought that it is contained in a combined form. Further, if a silicon peak having a valence of +4 or close to this and a peak of oxygen having a valence of -2 or close thereto are detected simultaneously, the silicon component is contained in a form bonded to oxygen. Think.

  The chromate film is formed by the reaction between the base metal and a solution containing chromate ions. In this film formation reaction, trivalent chromium forms a polymer-like complex by a bridge of hydroxyl and oxygen. Therefore, it is said that the main mechanism is to precipitate and deposit in the form of gel on the surface of the underlying metal. When a hydroxyl group is bonded to trivalent chromium, the valence of chromium is apparently shifted to +4 due to the influence of protons contained in the hydroxyl group. In the present specification, if a peak component chemically shifted from a trivalent chromium peak position to a position corresponding to a valence of approximately +4 is observed in the XPS photoelectron spectrum, the chromium component is regarded as a component of the chromate film. I think that it has become.

  The chromate treatment is a kind of chemical conversion treatment in which the chromium component is replaced and deposited while the base metal is oxidized and eluted. Therefore, in the electroless chromate treatment in which power is not supplied from the outside, the base metal needs to be a metal that can be eluted in the chromate treatment bath. In spark plugs, the metal shell or gasket is generally composed of an iron-based material such as carbon steel, and a zinc-based plating layer consisting mainly of zinc is formed on the surface of the metal for corrosion protection. can do. In this sense, this zinc-based plating layer is convenient as a base metal for forming a chromate film. In this case, the eluted zinc component is often taken into the chromate film. The zinc-based plating layer can be formed by known electrolytic galvanization or hot dip galvanization.

  On the other hand, if the electrolytic chromate treatment method is employed, a chromate film can be formed even if the metal component is mainly a nickel-based plating layer made of nickel.

  In the phosphorus component-dispersed chromate layer or silicon component-dispersed chromate layer, the total weight of the chromium component is 50% by weight or more in the remaining portion excluding the weight of the phosphorus component or silicon component from the total weight of the cation component. It is desirable to ensure anticorrosion performance. In this case, other cation components other than the chromium component may be components such as zinc and nickel.

  A silica-based layer mainly composed of silicon oxide can be formed on the surface layer portion of the composite chromate film. Thereby, the anticorrosion performance and heat resistance of a composite chromate film can be further improved. In this case, the silica-based layer similarly needs to have a total weight of the silicon component of 50% by weight or more with respect to the total weight of the cation component, and the balance is other cation components such as chromium, zinc, nickel, etc. It may be a component of.

  The silica-based layer is formed by using a base trivalent chromium-based chromate layer (for example, phosphorus component-dispersed chromate layer or silicon component-dispersed chromate layer: phosphorus component or silicon component, phosphorus component-dispersed chromate layer or silicon component-dispersed chromate). (It may be a chromate layer that does not contain at a content exceeding the lower limit of the layer. In this case, the silicon component content of the entire composite chromate layer including the silica-based layer may be 5 to 75% by weight) After applying a silicate solution in which an alkali silicate is dissolved in a predetermined solvent to the metal shell in which is formed, the solvent can be evaporated. In this case, the silica-based layer is mainly composed of an oxide mainly composed of an alkali metal element and silicon.

  In addition, for the formation of the silica-based layer, a vapor phase film forming method such as high-frequency sputtering, reactive sputtering, ion plating, or chemical vapor deposition (CVD) may be used. However, according to the above method by application of the silicate solution, the metal shell (or gasket) after the chromate treatment is immersed in the silicate solution, or after the silicate solution is applied by spraying or the like, A silica-based layer can be easily formed simply by drying the coating film.

  In addition, a trivalent chromium-silicon dispersion layer in which the trivalent chromium component and the silicon component are dispersed between the base trivalent chromium-based chromate layer and the silica-based layer at an intermediate content ratio between the two layers is formed. May be. Thereby, the anticorrosion performance or heat resistance of the composite chromate film may be further improved. For example, the formation of the trivalent chromium-silicon dispersion layer as described above means that a kind of composition gradient structure is formed between the trivalent chromium-based chromate layer and the silica-based layer. Due to the effects of improving the adhesion between the trivalent chromium-based chromate layer and the silica-based layer and reducing the stress based on the difference in shrinkage between the trivalent chromium-based chromate layer and the silica-based layer during heating, Performance improvement can be achieved.

  It is said that the anti-corrosion performance of yellow chromate coatings, etc., is due to the fact that the trivalent chromium network is restored by the action of the hexavalent chromium contained even when the coating is destroyed in a corrosive environment. ing. However, in the trivalent chromium-based chromate layer, since such a repair effect due to hexavalent chromium cannot be expected, if defects such as pinholes occur in the coating, the influence of corrosion directly affects the base such as the zinc-based plating layer, It is thought that corrosion progresses rapidly. However, in the composite chromate film with the above structure, the trivalent chromium-based chromate layer is overcoated with a silica-based layer, and the influence of corrosion is difficult to reach the surface of the trivalent chromium-based chromate layer and thus the underlayer, thereby preventing corrosion. It is estimated that the performance will be improved.

  On the other hand, it is considered that the conventional chromate film is inferior in heat resistance because the chromate film is contracted by heating and defects such as cracks are likely to occur. However, in the above configuration, even if the above-described defects occur in the trivalent chromium-based chromate layer, the anticorrosion performance deteriorates because the surface is overcoated with a silica-based layer having good heat resistance. Presumed to be difficult.

  In order to form a uniform silica-based layer, it is also important to improve the wettability between the silicate solution and the base trivalent chromium-based chromate layer. For example, if defects such as pinholes or cracks (including those that inherit defects in the ground due to scratches or adhesion of foreign matter) are formed in the ground trivalent chromium-based chromate layer, the wettability is good. When no silicate solution is used, bubbles and the like are likely to remain in the defect. In this case, it is also effective to mix an appropriate amount of a surfactant in the aqueous silicate solution.

  On the other hand, after completion of the chromate treatment step, there is also a method of performing a silica-based layer forming step by immersing the surface of the metal shell in a silicate solution in an undried or semi-dried state. That is, after completion of the chromate treatment, a base trivalent chromium-based chromate layer is formed on the surface of the metal shell in an undried or semi-dried state with a slight moisture content, and the silicate aqueous solution to be subsequently applied is formed. Familiarity with is also good. As a result, even if defects are formed in the underlying trivalent chromium-based chromate layer, the silicate aqueous solution sufficiently penetrates into the defects, making it difficult for bubbles and the like to remain, resulting in good anticorrosion performance of the coating It can be. Further, as another effect, the chromate treatment liquid remaining in the surface layer portion of the formed base trivalent chromium chromate layer is mixed with a part of the applied aqueous silicate solution, and the trivalent chromium-silicon described above is mixed. There is an advantage that a dispersed layer is easily formed. The effect of forming the trivalent chromium-silicon dispersion layer has already been described.

  When the base metal layer is a galvanized layer and the above-described composite chromate film is formed thereon, the “5. neutral salt spray test” in the plating corrosion resistance test method defined in JISH8502 is performed. Further, it is possible to secure a durability time of 40 hours or more until white rust derived from corrosion of the galvanized layer appears about 20% or more of the entire surface. This is a sufficient level of corrosion resistance that the spark plug metal shell should have.

  Also, as a problem unique to spark plugs, if the engine continues to run under conditions where a large heat load is applied, or if the spark plug is mounted in a position relatively close to the exhaust manifold, sometimes the The temperature may rise to about 200-300 ° C. However, when the base metal layer is a galvanized layer and the above-described composite chromate film is formed, good durability performance can be obtained even in the following test assuming such a situation. That is, after heating in the atmosphere at 200 ° C. for 0.5 hour, when the “5. Neutral salt spray test method” in the plating corrosion resistance test method stipulated in JISH8502 is performed, corrosion of the galvanized layer is caused. Durability time until white rust derived from the surface appears about 20% or more can be secured for 40 hours or more.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, some embodiments of the present invention will be described with reference to the drawings.
A spark plug 100 with a resistor as an example of an application target of the present invention shown in FIG. 1 includes a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that the tip portion protrudes, and a tip portion. A center electrode 3 provided on the inner side of the insulator 2 in a protruding state, and a ground electrode 4 and the like that are disposed so that one end is coupled to the metal shell 1 and the other end faces the tip of the center electrode 3. ing. A spark discharge gap g is formed between the ground electrode 4 and the center electrode 3.

  The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through-hole 6 for fitting the center electrode 3 along its own axial direction. A terminal fitting 13 is inserted and fixed on one end side of the through hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 13 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively.

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

  On the other hand, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is disposed between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, and further On the rear side, a ring-shaped 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 crimping portion 1d is formed by crimping the opening edge of the metal shell 1 toward the packing 60 inward. It is fixed with respect to the insulator 2.

  Further, a spark plug gasket (hereinafter also simply referred to as a gasket) 30 of the present invention is fitted into the proximal end portion of the threaded portion 7 of the metal shell 1. The gasket 30 is a ring-shaped part formed by bending a metal plate material such as carbon steel. By screwing the screw portion 7 into the screw hole on the cylinder head side, the flange-shaped gas seal portion 1f on the metal shell 1 side. Between the screw hole and the periphery of the opening of the screw hole, it is deformed so as to be compressed and crushed in the axial direction, and serves to seal the gap between the screw hole and the screw part 7.

  Next, a zinc plating layer 41 (zinc-based plating layer) for corrosion prevention is formed on the entire outer surface of the base layer (for example, carbon steel) 40 of the metal shell 1, and the outer side thereof is covered with the composite chromate film 42. . Similarly, a galvanized layer 45 and a composite chromate film 46 are also formed on the outer surface of the gasket 30. The galvanized layer and the composite chromate film are both formed by the same method, and will be described below representatively on the metal shell 1 side.

  The galvanized layer 41 is formed by a known electrolytic galvanizing method, and has a thickness of about 3 to 10 μm, for example. If the thickness is less than 3 μm, sufficient corrosion resistance may not be ensured. Conversely, a film thickness exceeding 10 μm is excessive in terms of ensuring corrosion resistance, leading to an increase in cost. Further, when the ground electrode 4 is bent or when the caulking portion 1d is formed, the plating layer is easily cracked.

On the other hand, the composite chromate film 42 is a trivalent chromium-based chromate layer in which the main component of the cation component is a chromium component and 90% by weight or more of the chromium component is composed of trivalent chromium, and is formed as one of the following. Yes.
(1) Phosphorus component-dispersed chromate layer: The phosphorous component is dispersed in the trivalent chromium compound, and the content of the phosphorous component is 2 to 15% by weight in terms of PO ₄ . The phosphorus component is preferably contained mainly as phosphate ions.
(2) Silicon component-dispersed chromate layer: The silicon component is dispersed in the trivalent chromium compound, and the content of the silicon component is 10 to 40% by weight in terms of SiO ₂ . The silicon component is preferably contained mainly as silicon oxide. Further, the phosphorus component may be contained in the range of 1 to 15% by weight in terms of PO ₄ , and the anticorrosion performance of the composite chromate film 42 can be further improved. It should be noted that as much of the chromium component as possible should be a trivalent chromium component, and desirably substantially all of the chromium component should be a trivalent chromium component.

  The thickness of the composite chromate film 42 is preferably 0.2 to 0.4 μm. If the thickness is less than 0.2 μm, the anticorrosion performance of the composite chromate film 42 may be insufficient. Moreover, it is difficult to realize a thick chromate layer exceeding 0.4 μm by trivalent chromium-based chromate treatment.

The composite chromate film 42 as described above can be formed by immersing a metal shell in which a zinc plating layer having a predetermined film thickness is formed by a known electrolytic galvanization method or the like in a chromate treatment solution. Examples of usable chromate treatment liquid include those containing the following components (so-called colorless or blue chromate treatment liquid).
Chromic anhydride: 0.1 to 2 g / l Sulfuric acid: 0.3 to 5 g / l Nitric acid: 0.5 to 10 g / l Phosphoric acid: Add to about 2 g / l as needed Fluoric acid: As needed In this treatment liquid added to about 2 g / liter, the amount of chromic anhydride, which is a hexavalent chromium source, is reduced to less than half that of 4-10 g / liter of the so-called yellow chromate treatment liquid. Yes. Sulfuric acid functions as a reaction accelerator, and nitric acid functions as an oxidizing agent for elution of the base metal. On the other hand, phosphoric acid has the role of improving the adhesion of the chromate film to the underlying metal, and hydrofluoric acid is incorporated into the film as an anion, strengthening the bridge bond in the polymer complex structure, and improving the film strength and thus the anticorrosion performance. Play a role to improve.

In addition, it is also possible to use the following liquid that does not use a solute serving as a hexavalent chromium source (so-called chromium (III) chromate treatment liquid).
Chromium potassium sulfate (so-called chromium alum): 2.5 to 3.5 g / liter Nitric acid: 3.5 to 4.5 g / liter Hydrofluoric acid: 1.5 to 2.5 g / liter

On the other hand, by using a compound containing a trivalent chromium salt and a complexing agent for trivalent chromium, it is possible to form a dense and thick trivalent chromium-based chromate layer, which is difficult with a general chromate treatment method. It becomes possible. Details of such a chromate treatment liquid are disclosed in German Published Patent Publication DE19638176A1, so only an example of the liquid composition is shown below.
Chromium chloride _{(III) (CrCl 3 · 6H} 2 O): 50g / l of cobalt nitrate _{(II) (Co (NO 3} ) 2): 3g / liter sodium nitrate _(NaNO 3): 100g / l malonic acid: 31.2 g /liter

  Note that the chromate treatment liquid is not limited to the above as long as the content ratio of trivalent chromium to the chromium component in the chromate film can be 90% by weight or more.

In the chromate treatment liquid, phosphoric acid is 0.1 to 2 g / liter as a phosphorus component source, and alkali silicate (for example, sodium silicate) is 1.0 to 4.0 g / liter as a silicon component source. It is blended with. As the silicate, a so-called aqueous solution of water glass can be used. The general formula of water glass is represented by M ₂ O · nSiO ₂ (where M is an alkali metal element such as sodium or potassium).

  As water glass, n is about 2-4. When n is 2 or less, gelation hardly occurs and the water-soluble one is obtained, so that a stable film cannot be obtained. On the other hand, when n exceeds 4, hydrolysis of the alkali silicate proceeds excessively in the chromate treatment solution, and silicon dioxide gel precipitates and precipitates, making it impossible to stably carry out the chromate treatment step. Note that n is more preferably in the range of 3-4.

  The reaction during the chromate treatment is considered to be as follows. That is, when the metal shell with the galvanized layer is immersed in the liquid, the zinc ions dissolve and the chromium ions in the liquid are replaced by this, and precipitate as a gel-like film mainly composed of chromium (III) hydroxide. At the same time, phosphate ions or alkali silicate components forming the phosphorus component are taken into the film and dispersed therein. For example, in the case of a silicon component-dispersed chromate layer, as shown in FIG. 2A, a gel-like cured product 42e mainly composed of alkali silicate and silicon dioxide is contained in a polymer complex substrate 42d of trivalent chromium. It is thought to have a distributed structure.

  A part of the dissolved zinc is also taken into the film in the form of, for example, zinc chromate. On the other hand, the structure of the chromate film to be formed is presumed to have, for example, a shape as shown in FIG. 2B (however, no phosphorus component or silicon component is drawn). That is, a polymer complex of trivalent chromium formed in a network by a hydroxyl group or oxygen bridge is formed, and a part of the network is an anion such as chromate, dichromate, sulfuric acid, chloride or fluoride (type of anion). Are different depending on the composition of the chromate treatment solution to be used). The formation thickness of the chromate layer can be adjusted, for example, by adjusting the immersion time, liquid temperature, and liquid pH of the metal shell in the chromate treatment liquid.

  The metal shell 1 or gasket 30 treated in this way has a composite chromate coating 42 formed on its galvanized layer, which is significantly higher in corrosion protection than conventional trivalent chromium-based chromate coatings and further yellow chromate coatings. It has performance or heat resistance, and can sufficiently impart durability against corrosion to the galvanized layer.

  Next, as shown in FIG. 3 (a), a base trivalent chromium-based chromate layer (hereinafter referred to as a chromate (hereinafter referred to as chromate)) in which the main component of the cation component is a chromium component and 90% by weight or more of the chromium component is composed of trivalent chromium. The surface of 42a (also referred to as III) layer) can be covered with a silica-based layer 42c composed mainly of silicon oxide. When the silica-based layer 42c is formed, the whole is regarded as the composite chromate film 142 together with the base trivalent chromium-based chromate layer 42a. In this case, the silicon content in the entire composite chromate film 142 is 5 to 75% by weight. A trivalent chromium-silicon dispersion layer 42b in which a trivalent chromium component and a silicon component are dispersed at an intermediate content ratio between the two layers 42a and 42c is formed.

  The chromate (III) layer 42a may be an ordinary trivalent chromium-based chromate film that does not contain a phosphorus component or silicon component. However, by using a phosphor component-dispersed chromate layer or a silicon component-dispersed chromate layer as described above, anticorrosion performance is achieved. Alternatively, the heat resistance can be further improved. In particular, the phosphor component-dispersed chromate layer has better anti-corrosion properties than the silicon component-dispersed chromate layer and is slightly inferior in heat resistance, but the formation of a silica-based layer greatly compensates for the heat resistance, and the balance between anti-corrosion and heat resistance. A more excellent composite chromate layer can be realized.

  The total thickness of the composite chromate film 142 is, for example, 0.8 to 1.5 μm. When the total thickness is less than 0.8 μm, the anticorrosion performance and heat resistance imparting effect on the galvanized layer 41 may be insufficient. On the other hand, a film thickness exceeding 1.5 μm is excessive in terms of ensuring corrosion resistance, leading to an increase in cost. In addition, the composite chromate film 142 may be easily peeled off.

  The thickness of the chromate (III) layer 42a is preferably 0.2 to 0.4 μm. When the thickness is less than 0.2 μm, the anticorrosion performance of the composite chromate film 142 may be insufficient. On the other hand, if the film thickness exceeds 0.4 μm, hexavalent chromium tends to remain in the film, and the chromate (III) layer 42a having the desired composition may not be obtained. On the other hand, the thickness of the silica-based layer 42c is preferably 0.2 to 0.8 μm. When the thickness is less than 0.2 μm, the anti-corrosion performance and heat resistance of the composite chromate film 142 may be insufficient. On the other hand, a film thickness exceeding 0.8 μm is an excessive specification, which not only leads to an increase in cost, but also the film may be easily peeled off.

  FIG. 4 schematically shows an example of a method for forming the composite chromate film 142. First, the metal shell 1 on which a galvanized layer having a predetermined film thickness is formed by a known electrolytic galvanizing method or the like is immersed in the chromate treatment solution 50. As a result, as shown in FIG. 5A, a chromate (III) layer 42 a is formed on the surface of the galvanized layer 41 of the metal shell 1. The composition of the chromate treatment solution 50 is as described above. However, if phosphoric acid or silicate is not blended, an ordinary trivalent chromium-based chromate film is obtained.

  Next, as shown in FIG. 3 (b), the metal shell 1 after the formation of the chromate (III) layer 42a is in an undried or semi-dried state in an aqueous silicate solution 51 (silicate solution). By dipping and then drying, a trivalent chromium-silicon dispersion layer 42b and a silica-based layer 42c are formed as shown in FIG. 5 (c).

As the silicate aqueous solution 51, an aqueous solution of water glass can be used. Here, as the water glass, those having n of about 2 to 4 are used. If the content of alkali metal M converted to M ₂ O in the entire composite chromate film 42 is μ1, and the content of silicon component converted to SiO ₂ is μ2, then the value of μ2 / μ1 is 2 It is desirable to adjust in the range of -4, preferably 3-4.

  In order to form the silica-based layer 42c as uniformly as possible on the chromate (III) layer 42a, the silicate aqueous solution 51 is desirably adjusted to a concentration of alkali silicate of 30 to 200 g / liter. When the concentration is less than 30 g / liter, the formation thickness of the silica-based layer 42c becomes insufficient, and the anticorrosion performance or heat resistance performance of the composite chromate film 142 may not be ensured. On the other hand, when the concentration exceeds 200 g / liter, the viscosity of the aqueous silicic acid solution 51 becomes too high, and it becomes difficult to form a uniform silica-based layer due to the occurrence of coating unevenness and the like.

  As shown in FIG. 5 (a), the chromate treatment liquid 50 remains on the surface portion of the chromate (III) layer 42 a immediately after being pulled up from the chromate treatment liquid 50, and is immersed in the silicate aqueous solution 51. As shown in FIG. 5B, for example, a mixed layer 42b ′ is formed by mixing with a part of the applied aqueous silicate solution 51. When this is dried, as shown in FIG. 5 (c), a trivalent chromium-silicon dispersion layer 42b derived from the mixed layer 42b ′ is formed between the chromate (III) layer 42a and the silica-based layer 42c. It is formed. The trivalent chromium-silicon dispersion layer 42b is formed by mixing the chromate treatment solution 50 and the silicate aqueous solution 51 (or the penetration of the silicate aqueous solution 51 into the chromate (III) layer 42a). The trivalent chromium component and the silicon component are dispersed at an intermediate content ratio between 42a and 42c. This means that a kind of composition gradient structure is formed between the chromate (III) layer 42a and the silica-based layer 42c via the trivalent chromium-silicon dispersion layer 42b. Effects such as improved adhesion and stress reduction based on the difference in thermal shrinkage can be achieved. In addition, the trivalent chromium-silicon dispersion layer 42b may reach the surface of the composite chromate film 142, and a clear silica-based layer may not be formed. In addition, the trivalent chromium-silicon dispersion layer 42b may extend to the zinc plating layer 41 side, and the presence of the chromate (III) layer 42a in which silicon is not dispersed may be unclear. In an extreme case, the entire composite chromate film 142 is occupied by a single trivalent chromium-silicon dispersion layer 42b. In this case as well, the distribution of the silicon component is on the surface side of the composite chromate film 142. A kind of composition gradient structure which is large and small on the galvanized layer 41 side is formed.

  After completion of the chromate treatment, the surface of the metal shell 1 ′ in an undried or semi-dried state is formed with the chromate (III) layer 42 a in a wet state, and the familiarity with the silicate aqueous solution 51 is improved. Accordingly, as shown in FIG. 6A, even if a defect def such as a pinhole is formed in the chromate (III) layer 42a, the silicate aqueous solution 51 is sufficiently easily permeated here and the formed silica. It is possible to make it difficult for bubbles and the like to remain in the system layer 42c (FIG. 6B).

  After the chromate treatment, the surface of the metallic shell 1 ′ may be dried and immersed in the silicate aqueous solution 51. In this case, since the chromate (III) layer 42a is once dried, the mixed layer 42b 'of the chromate treatment solution 50 and the silicate aqueous solution 51 is hardly formed. Therefore, as shown in FIG. 3B, a clear trivalent chromium-silicon dispersion layer 42b may not be formed between the chromate (III) layer 42a and the silica-based layer 42c.

Example 1
Using the cold forging carbon steel wire SWCH8A defined in JIS G3539 as a material, the metal shell 1 having the shape shown in FIG. 1 was manufactured by cold forging. The nominal diameter of the threaded portion 7 of the metal shell 1 was 14 mm, and the axial length was about 19 mm. Next, an electrolytic galvanizing treatment using a known alkali cyanide bath was performed on the galvanized layer to give a galvanized layer having a thickness of about 6 μm.

Next, the chromate treatment solution 50 shown in FIG. 4 is dissolved in deionized water at a rate of 3 g / liter of potassium potassium sulfate, 4 g / liter of nitric acid, 2 g / liter of hydrofluoric acid, and phosphoric acid is 0.1 to 1. Prepare a mixture of sodium silicate (water glass) having a composition of 0 g / liter, Na ₂ O.3.5SiO ₂ at various ratios of 1.0 to 3.5 g / liter, and keep the liquid temperature at 20 ° C. did. On the other hand, sodium silicate (water glass) having a composition of Na ₂ O.3.5SiO ₂ was dissolved in deionized water at a concentration of 100 g / liter to prepare an aqueous silicate solution 51.

  Then, the galvanized metal shell was immersed in the chromate treatment solution 50 for 15 seconds, then drained only, and dried with warm air at 80 ° C. to form various composite chromate films (Table 1: Sample numbers). 2-11). For sample numbers 5 and 10, the chromate film was dried, immersed in the silicate aqueous solution 51, and dried with hot air at 80 ° C. to form a silica-based layer. For comparison, a test product (No. 1) using a chromate treatment liquid not containing phosphoric acid or water glass and a test product (No. 12) in which only a silica-based layer was formed without forming a chromate film were also prepared. . Further, it is immersed in the same chromate treatment solution 50 as that of No. 5 for 15 seconds, then only drained and immediately dried in a silicate aqueous solution 51 without drying, and further dried with hot air at 80 ° C. A test product was also prepared (No. 13).

When the XPS photoelectron spectrum was measured while etching the composite chromate film of No. 5 in the thickness direction, the main component of the cation component was chromium, and then a large amount of zinc was detected. Further, as a result of examining the peak of the chromium (2p2 / 3) in more detail, 99% by weight or more of the chromium component was trivalent chromium. About each test article (numbers 1-4, 6-9, 11) which does not form a silica system coat, in addition to the above-mentioned XPS measurement, when the composition analysis of the composite chromate coat was performed using fluorescent X-ray analysis together, It was found to have the phosphorus component and silicon component concentrations shown in Table 1. In addition, since chemical shifts in the positive valence direction were observed in the phosphorus and silicon peaks in the XPS spectrum, and oxygen was detected simultaneously, both components were in the form of phosphate ions and silicon oxide (probably SiO ₂ ). Was presumed to exist. When the film thickness of the composite chromate film was measured by actual measurement from a cross section by SEM, it was about 0.25 to 0.30 μm.

Further, the silica-based layer the formed specimen for (number 5 and 10), by measuring the X-ray fluorescence analysis of XPS photoelectron spectrum while etching in the thickness direction, the silica-based layer was SiO ₂ in terms of silicon It was found that the oxide-based film contained 77 wt% in terms of value and 22 wt% in terms of sodium converted to Na ₂ O. Moreover, when the film thickness of the silica-type layer was measured by actual measurement from the cross section by SEM, it turned out that it is about 0.7 micrometer.

Next, FIG. 7 shows the result of measuring the XPS photoelectron spectrum of the sample No. 13 while etching the composite chromate film in the thickness direction. From the spectral peak intensity of each component at each etching depth, formation of a chromate layer having a composition gradient structure in which the silicon component gradually decreases in the depth direction from the surface was observed. Further, when the contents of the phosphorus component and silicon component in the entire composite chromate film were measured in the same manner as described above, the phosphorus component was 8% by weight in terms of PO ₄ and the silicon component was 14% by weight in terms of SiO _2. I found out.

  The above test product is subjected to a salt spray test specified in JISZ2371, and white rust derived from corrosion of the galvanized layer appears about 20% or more of the entire surface, or red rust derived from corrosion of the underlying iron layer. Durability evaluation was carried out according to the time until a slight visual check was made. The results are shown in Table 1.

  It can be seen that the test article on which the composite chromate film was formed showed an overwhelmingly superior durability than the test article of the comparative example. Next, Table 1 shows the results of the same salt spray test after heat-treating a test product similar to the above at 200 ° C. for 30 minutes in the air. The test products of the present invention, in particular, the test products of Nos. 6 to 9 and 11 in which a silicon component is dispersed, and the test products of Nos. 5, 10 and 13 in which a silica-based film is formed have extremely good durability. You can see that

(Example 2)
Using the cold forging carbon steel wire SWCH8A defined in JIS G3539 as a material, the metal shell 1 having the shape shown in FIG. 1 was manufactured by cold forging. The nominal diameter of the threaded portion 7 of the metal shell 1 was 14 mm, and the axial length was about 19 mm. Next, an electrolytic galvanizing treatment using a known alkali cyanide bath was performed on the galvanized layer to give a galvanized layer having a thickness of about 6 μm.

Next, as the chromate treatment solution 50 shown in FIG. 4, a solution prepared by dissolving 3 g / liter of potassium chromium sulfate, 4 g / liter of nitric acid, and 2 g / liter of hydrofluoric acid in deionized water is prepared, and the liquid temperature is set to 20 ° C. Retained. On the other hand, sodium silicate (water glass) having a composition of Na ₂ O.3.5SiO ₂ was dissolved in deionized water at a concentration of 100 g / liter to prepare an aqueous silicate solution 51. Then, the galvanized metal shell is immersed in the chromate treatment solution 15 for 15 seconds, and then is immediately immersed in the silicate aqueous solution 51 in a state where only the liquid is removed and drying is not performed. A composite chromate film was formed by drying with warm air (test product (3): product of the present invention).

FIG. 8 shows the result of measuring the photoelectron spectrum of XPS while etching this composite chromate film in the thickness direction. From the spectral peak intensity of each component at each etching depth, up to about 0.4 μm from the surface, the peak of chromium (2p2 / 3) is hardly observed, and a silica-based layer mainly composed of silicon oxide is obtained. You can see that Further, when examined in more detail by fluorescent X-ray analysis, the silica-based layer contains about 77% by weight of silicon in terms of SiO ₂ and about 22% by weight of sodium in terms of Na ₂ O. I found out.

  On the other hand, although a slight silicon peak was observed at a depth of 0.7 to 1 μm from the surface, the cation component was mainly chromium and then a large amount of zinc was detected. Further, as a result of examining the peak of the chromium (2p2 / 3) in more detail, 99% by weight or more of the chromium component was trivalent chromium. That is, it was found that the approximately 0.3 μm portion in the depth range was a trivalent chromium-based chromate layer.

  Then, the portion having a thickness of about 0.3 μm located in the middle of the two layers is a trivalent chromium containing a chromium component and a silicon component in an intermediate composition of both layers from the spectral peak intensity of each component of XPS. It was found that it was a silicon dispersion layer. Further, from the XPS depth profile, it was found that the content of the silicon component in the entire composite chromate film was 8% by weight.

In addition, after being immersed in the chromate treatment liquid 50 for 15 seconds, not immersed in the silicate aqueous solution 51 but dried as it is (test product (2): comparative example), conversely, not immersed in the chromate treatment liquid 50, What was immersed and dried only in the silicate aqueous solution 51 (test product (4): comparative example) was also prepared. When the formed films of the test products (2) and (4) were analyzed by XPS and X-ray fluorescence analysis, the former had a thickness content of about 0% with a trivalent chromium content in the chromium component of approximately 99% or more. The latter is an oxide film containing 77% by weight of silicon in terms of SiO ₂ and 22% by weight of sodium in terms of Na ₂ O. all right.

  On the other hand, a yellow chromate treatment solution prepared by dissolving chromic anhydride at a rate of 7 g / liter, sulfuric acid 3 g / liter, and nitric acid 3 g / liter in deionized water was prepared and kept at a liquid temperature of 20 ° C. Then, the metal shell was dipped in this for about 15 seconds, pulled up, and dried to prepare a comparative example (test product (1)). When the formed film was analyzed by XPS, it was found that the chromate film had a thickness of about 0.5 μm, in which about 30% by weight of the chromium component was hexavalent chromium and the balance was trivalent chromium.

  A salt spray test specified in JISZ2371 is performed on the test items (1) to (4) above, until white rust derived from corrosion of the galvanized layer appears about 20% or more of the entire surface, or the underlying iron Durability evaluation was performed based on the time until red rust derived from the corrosion of the layer was visually confirmed. The result is shown in FIG. That is, the test product (3) which is the product of the present invention in which the composite chromate film is formed exhibits overwhelmingly superior durability than the test product of any comparative example, including the test product (1) treated with yellow chromate. You can see that Further, from the results of the test products (2) and (4), it is understood that when the trivalent chromium-based chromate layer or the silica-based layer is formed alone, good durability is not obtained.

  Next, the test results (1) to (4) above were heat-treated at 200 ° C. for 30 minutes in the air, and then the results of the salt spray test were similarly shown in FIG. The test product (1) subjected to the yellow chromate treatment has a significantly reduced durability due to heat treatment, whereas the test product (3) according to the present invention exhibits extremely good durability. I understand.

The longitudinal half sectional view which shows the spark plug which is an example of the application object of this invention. The conceptual diagram which shows the structure of a composite chromate film. The conceptual diagram which shows the structure of the composite chromate film which has a silica type layer. Explanatory drawing of a chromate treatment process and a silica type layer formation process. The figure explaining the formation process of the composite chromate film in the process of FIG. 4, and the presumed structure of a chromate layer. The figure explaining the effect of the method of forming a silica type layer in an undried state after chromate treatment. The figure which shows the analysis result by XPS of the composite chromate film formed in the test article 13 of Example 1. FIG. The figure which shows the analysis result by XPS of the composite chromate film | membrane formed in the test article (3) of Example 2. FIG. The graph which shows the result of the salt spray test with respect to the test article of an Example (no heat processing). The graph which shows the result of the salt spray test with respect to the test article of an Example (after heat processing).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main metal fitting 2 Insulator 3 Center electrode 4 Ground electrode 30 Spark plug gasket 41, 45 Zinc plating layer 42, 46, 142 Composite chromate coating 42a Trivalent chromium system chromate layer 42b Trivalent chromium-silicon dispersion layer 42c Silica system layer 100 spark plug

Claims (9)

It is used by being fitted into the base end portion of the mounting screw portion formed on the outer peripheral surface of the spark plug metal shell, and at least a part of its surface contains a chromium component and a phosphorus component as cationic components, and 90% by weight or more of the chromium component is trivalent chromium, and the phosphorus component is covered with a composite chromate film containing 1 to 15% by weight in terms of PO ₄ ,
The composite chromate film has a phosphorus component-dispersed chromate layer in which a phosphorus component is dispersed in a trivalent chromium compound and the content of the phosphorus component is 2 to 15% by weight in terms of PO _4. A gasket for spark plugs. It is used by being fitted into the base end of the mounting screw part formed on the outer peripheral surface of the spark plug metal shell, and at least a part of the surface contains a chromium component and a silicon component as a cation component. 90% by weight or more of the chromium component to be formed is covered with a composite chromate film containing trivalent chromium and containing 5 to 75% by weight of silicon component in terms of SiO ₂ .
The composite chromate film has a silicon component-dispersed chromate layer in which a silicon component is dispersed in a trivalent chromium compound and the content of the silicon component is 10 to 40% by weight in terms of SiO _2. A gasket for spark plugs. The spark plug gasket according to claim 2, wherein the silicon component-dispersed chromate layer contains a phosphorus component in a range of 1 to 15% by weight in terms of PO ₄ .   Durability time until white rust derived from corrosion of galvanized coating appears about 20% or more of the entire surface when performing “5. Neutral salt spray test method” in the corrosion resistance test method of plating specified in JISH8502 The spark plug gasket according to any one of claims 1 to 3, wherein is at least 40 hours.   After heating at 200 ° C. for 30 minutes in the air, white rust derived from corrosion of the galvanized film when the “5. Neutral salt spray test method” in the plating corrosion resistance test method prescribed in JISH8502 is performed. The gasket for a spark plug according to any one of claims 1 to 4, wherein a durability time until approximately 20% or more of the entire surface appears is 40 hours or more.   6. A spark plug, wherein the spark plug gasket according to claim 1 is fitted into a base end portion of a mounting screw portion formed on an outer peripheral surface of the metal shell. It is a manufacturing method of the gasket for spark plugs of Claim 1,
By immersing the gasket in a chromate treatment bath containing phosphoric acid or phosphate, 90% by weight or more of the chromium component contained on the surface of the gasket is trivalent chromium, and the phosphoric acid or A method for producing a gasket for a spark plug, comprising a chromate treatment step of forming a phosphorous component-dispersed chromate film containing a phosphorous component derived from a phosphate in an amount of 2 to 15% by weight in terms of PO ₄ . A method for producing a gasket for a spark plug according to claim 2,
By immersing the gasket in a chromate treatment bath containing alkali silicate, 90% by weight or more of the chromium component contained on the surface of the gasket is trivalent chromium, and the alkali silicate A method for producing a gasket for a spark plug, comprising a chromate treatment step of forming a silicon component-dispersed chromate film containing 10 to 40% by weight of a silicon component derived from SiO ₂ . The chromate treatment bath contains phosphoric acid or phosphate, and the silicon component-dispersed chromate film contains 1 to 15% by weight of the phosphoric acid or phosphate component derived from phosphate in terms of PO _4. The method for producing a spark plug gasket according to claim 8.

Images