JP3344960B2 - Spark plug and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A spark plug used for ignition of an internal combustion engine, for example, a gasoline engine for an automobile or the like, is provided with an insulator outside a center electrode and a metal shell outside the center electrode. It has a structure in which a ground electrode forming a spark discharge gap is attached to the metal shell.
The metal shell is mounted on the cylinder head of the engine by a mounting screw formed on the outer peripheral surface of the metal shell.

The metallic shell is generally made of an iron-based material such as carbon steel, and its surface is often plated with zinc for corrosion protection. The galvanized layer has an excellent anticorrosion effect on iron, but as is well known, the galvanized layer on iron is easily consumed by sacrificial corrosion,
There is a disadvantage that the generated zinc oxide discolors white and the appearance is easily impaired. 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.

A so-called yellow chromate film has been used as a chromate film applied to a metal shell of a spark plug. This yellow chromate coating is
Because of its good anticorrosion performance, it has been widely used in fields other than spark plugs, such as, for example, for coating inner surfaces of cans. However, the concern that some of the chromium components are contained in the form of hexavalent chromium has led to a growing concern on environmental protection in recent years that has been increasingly avoided. For example, in the automotive industry where spark plugs are used in large quantities,
Considering the environmental impact of waste spark plugs, studies are underway to eliminate the use of hexavalent chromium-containing chromate coatings in the future. Further, since a treatment bath containing a relatively high concentration of hexavalent chromium is used as a treatment bath for the yellow chromate film treatment, there is a problem that a large cost is required for waste liquid treatment.

[0005]

In response to this trend, the development of chromate coatings that do not contain hexavalent chromium, ie, coatings in which substantially all of the chromium component is contained in the form of trivalent chromium, has been relatively developed. It has been advanced from an early stage.
The treatment bath generally has a low hexavalent chromium concentration, and some baths containing no hexavalent chromium have been developed, and the problem of waste liquid treatment has been reduced. However, the trivalent chromium-based chromate coating has a major drawback in that the anti-corrosion performance is inferior to the yellow chromate coating, and has not been widely used for coating a metal shell of a spark plug.

[0006] Further, the chromate coatings used so far, including the yellow chromate coating, have a common drawback of 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 rarely becomes extremely hot. However, if the operation of the engine is continued under the condition that the heat load is large, or if the spark plug is mounted at a position relatively close to the exhaust manifold, sometimes the temperature of the metal shell is about 200 to 300 ° C. May rise to Under such circumstances, the deterioration of the chromate film tends to progress,
There is a problem that the anticorrosion performance is rapidly reduced. In addition, conventional chromate coatings include acid rain, carbon dioxide or nitrogen oxides or sulfur oxides contained in exhaust gas, and in the case of gas engines and the like, acid water generated from the engine.
There is a problem that the performance is liable to be further deteriorated when the acidic component is attacked.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug which has a low hexavalent chromium content in a chromate film covering the surface of a metal shell, and is superior in anticorrosion performance and heat resistance as compared with a conventional chromate film, and a method of manufacturing the same. Is to provide.

[0008]

In order to solve the above-mentioned problems, a spark plug according to the present invention comprises a center electrode, an insulator provided outside the center electrode, and an insulator provided outside the insulator. A metal electrode provided, and a ground electrode disposed so as to face a spark discharge gap between the central electrode and the center electrode. Further, 95% by weight or more of the chromium component contained is provided. By a chromate film of trivalent chromium and having a thickness of 0.2 to 0.5 μm,
The surface of the metal shell is covered.

[0009] In the above construction, trivalent chromium forms 95% by weight or more of the chromium component contained on the surface of the metal shell and has a thickness of 0.2 to 0.5 µm.
m is a chromate film. That is, in the ordinary yellow chromate coating, hexavalent chromium accounts for about 25 to 35% by weight of the chromium component, whereas in the coating of the present invention, the content of hexavalent chromium with respect to the chromium component is as low as 5% by weight or less. Therefore, the effect on environmental measures for reducing hexavalent chromium can be enhanced. In addition, the chromate treatment solution used does not contain any hexavalent chromium component as described later, or even if it does, the amount can be significantly reduced as compared with a treatment solution such as a yellow chromate film. Processing problems are less likely to occur.

In the case of a conventional trivalent chromium-based chromate film such as a gloss chromate film commonly referred to as Unichrome or a blue chromate film, the inventors of the present invention have a maximum thickness of about 0.1 μm. And thin,
We thought that sufficient corrosion resistance and heat resistance could not be secured for the metal shell in the main usage environment of the spark plug, and as a result of intensive studies on the film thickness, we found a film thickness range particularly suitable for spark plugs. The invention was completed. That is, by ensuring that the thickness of the chromate film is 0.2 μm or more, the anticorrosion performance of the chromate film mainly composed of trivalent chromium is significantly improved, and the metal shell can be sufficiently imparted with corrosion resistance. Become like Further, the corrosion resistance of the metal shell can be sufficiently maintained even in an environment peculiar to a spark plug in which the temperature easily rises and is easily susceptible to acid attack or the like.

Some spark plugs have a ring-shaped gasket to be fitted to the base end of a mounting screw formed on the outer peripheral surface of a metallic shell. In this gasket, the screw portion of the metal shell is screwed into the screw hole on the cylinder head side, so that the gasket is crushed between the flange-shaped gas seal portion formed on the base end side of the screw portion and the peripheral edge of the opening of the screw hole. And serves to seal between the screw hole and the gas seal portion. In this case, at least a part of the surface of the gasket can be covered with the chromate film. This makes it possible to sufficiently impart corrosion resistance and heat resistance to the gasket as well as the metal shell.

The chromate film has a thickness of 0.2 μm.
If it is less than 1, the anticorrosion performance and heat resistance cannot be sufficiently secured. On the other hand, if the thickness exceeds 0.5 μm, cracks may occur in the coating (for example, during processing in assembling or the like) or the coating may easily fall off, leading to impairment of the anticorrosion performance. The thickness of the chromate film is desirably 0.3 to 0.5 μm. In addition, it is desirable that the chromate film does not substantially contain hexavalent chromium.

[0013] The chromate treatment is a kind of chemical conversion treatment in which a chromium component is replacedly deposited while oxidizing and eluting a base metal. Therefore, in an electroless chromate treatment in which power is not supplied from the outside, the base metal needs to be a metal that can be eluted into the chromate treatment bath. In a spark plug, the metal shell or gasket is generally made of an iron-based material such as carbon steel, and a zinc-based plating layer mainly made of zinc is formed on the surface of the metal shell to prevent corrosion. can do. This zinc-based plating layer is advantageous as a base metal for forming a chromate film in the above sense. 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 zinc plating or hot-dip galvanizing.
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.

By forming a zinc plating layer on the base metal layer and forming a chromate film in the above-mentioned thickness range on the zinc plating layer, "5. Neutral salt spray test" in the corrosion resistance test method for plating specified in JIS 8502. when the conducted "white rust resulting from corrosion of the zinc plating layer endurance time until appearing more than 20 percent of the total surface, it is possible to secure more than 40 hours. This is a sufficient level of corrosion resistance that the metal shell of the spark plug should have.

Further, as a problem peculiar to the spark plug,
If the engine continues to operate under conditions where the heat load is high, or if the spark plug is installed at a position relatively close to the exhaust manifold, the temperature of the metal shell sometimes rises to about 200 to 300 ° C. May be. However, by forming the underlayer metal layer as a galvanized layer and forming a chromate film having the above-described thickness, good durability performance can be obtained even in the following test assuming such a situation. That is, after heating in air at 200 ° C. for 0.5 hour, JI
When performing the "5. Neutral Salt Spray Test Method" in the prescribed plating corrosion resistance testing method SH8502, white rust resulting from corrosion of the zinc plating layer is endurance time until appearing more than 20 percent of the total surface , 40 hours or more.

[0016] The metal shell and gasket of the spark plug are easily attacked by acidic components such as carbon dioxide, nitrogen oxides and sulfur oxides contained in exhaust gas and the like. However, by forming the undercoat metal layer as a galvanized layer and forming a chromate film having the above-described thickness, good durability performance can be obtained even in the following test assuming such a situation. That is, when performing a "7 CASS test method" at a defined plated corrosion resistance test method JISH8502, white rust resulting from corrosion of the zinc plating layer is endurance time until appearing more than 20 percent of the total surface, 20 hours or more.

Next, the method for producing a spark plug according to the present invention comprises immersing a metal shell (or gasket) in a chromate treatment bath containing a trivalent chromium salt and a complexing agent for trivalent chromium. A chromate film as described above is formed on the surface of a metal shell (or gasket).

By using, as a chromate treatment bath, a mixture of a trivalent chromium salt and a complexing agent for trivalent chromium, a dense and thick trivalent chromium-based chromate film, which is difficult with a general chromate treatment method, is obtained. This makes it possible to easily form a trivalent chromium-based chromate coating of 0.2 to 0.5 μm, which is the gist of the spark plug of the present invention. The method for forming such a chromate film is disclosed in detail in DE 19638176 A1. The outline will be described below.

As described above, in the process of forming a chromate film, oxidation and elution of an underlying metal (eg, zinc) first occur in a treatment bath, and the eluted underlying metal component reacts with a solution containing chromate ions. It has been theorized that the main mechanism is that trivalent chromium forms a polymer complex by a hydroxyl group or an oxygen bridge and precipitates and deposits on the surface of the underlying metal in a gel state. In this case, in order for the chromate film to grow, the elution of the base metal and the reaction and deposition of the eluted base metal with the chromate ions in the bath must proceed in parallel. However, when the chromate film is deposited to some extent, the elution reaction of the underlying metal layer, which is a heterogeneous reaction via the interface with the bath solution, is prevented, and the film growth stagnates.

According to the disclosure of the above-mentioned German published patent application, in order to increase the thickness of the coating, dissolution of the base metal and
It is important that the rate of reverse dissolution of the deposited chromate film be as small as possible while increasing the rate of film deposition by the reaction between the dissolved base metal component and trivalent chromium. Then, in the above method, it is considered that by adding an appropriate complexing agent to the bath and complexing trivalent chromium, the precipitation of the film is promoted and the film can be made thicker.

As complexing agents, various chelating agents (dicarboxylic acid, tricarboxylic acid, oxyacid (hydroxyl dicarboxylic acid or hydroxylic tricarboxylic acid, etc. )) : for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimerine Acid, coric acid, aseleic acid, sebacic acid, maleic acid, phthalic acid, terephthalic acid, tartaric acid, citric acid,
It is effective to use malic acid, ascorbic acid, etc.) . The complexing agents that can be used are as described in the aforementioned German patent publication.

In order to increase the thickness of the coating, it is effective to raise the temperature of the chromate treatment bath to about 20 to 80 ° C. If the bath temperature is lower than 20 ° C., the effect of increasing the coating thickness by increasing the temperature can hardly be expected, and if the bath temperature is 80 ° C. or higher, control of bath conditions becomes difficult due to severe evaporation of water from the bath. Further, the immersion time of the object to be treated (metal shell, gasket, etc.) in the chromate bath is preferably set to 20 to 80 seconds. If the immersion time is less than 20 seconds, the thickness of the formed chromate film may not be sufficiently secured. On the other hand, if the immersion time exceeds 80 seconds, the formed chromate film becomes too thick, causing cracks in the film (for example, at the time of processing in assembling or the like) or easily falling off of the film, and on the contrary, the anticorrosion performance May be impaired.

On the other hand, in order to promote the dissolution of the base metal, a range in which the re-dissolution of the deposited film does not become intense,
It is effective to lower the pH of the chromate treatment solution. A desirable pH range is, for example, about 1.5 to 3. Further, in order to suppress the re-dissolution of the deposited film, it is effective to incorporate a hardly re-dissolved hydroxide such as nickel, cobalt or copper into the film. For this purpose, the above metal compound can be dissolved and blended in the chromate treatment bath.

Next, as a result of further studies by the present inventors, a predetermined amount of a sodium salt (for example, sodium nitrate, etc.) is adjusted so that the content of the sodium component in the chromate-treated film is 2 to 7% by weight. ) Was found to be more easily formed into a thick chromate film by adding it to the chromate treatment bath. Although the detailed mechanism is unknown, it is presumed that if sodium ions are taken into the chromate film, the chromate film is less likely to be redissolved in the treatment bath. If the content of the sodium component in the chromate-treated film is out of the range of 2 to 7% by weight, it may be difficult to secure a thick film of the chromate film to 0.2 μm or more. The content of the sodium component in the chromate-treated film is more desirably 2 to 6% by weight.

When a film is formed on the gasket , it goes without saying that the same method can be applied by replacing the metal shell with the gasket in the above process.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 including a resistor as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion protrudes, and a tip portion protruding. Insulator 2 in state
And a ground electrode 4 and the like, one end of which is coupled to the metal shell 1 and the other end of which is arranged to face the center electrode 3. 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. . The terminal fitting 13 is inserted and fixed to one end of the through hole 6, and the center electrode 3 is inserted and fixed to the other end of the through hole 6. A resistor 15 is arranged 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 of a metal such as carbon steel into a cylindrical shape, and forms a housing of the spark plug 100 and has a plug 100 on its outer peripheral surface.
Is formed on the engine block (not shown). Reference numeral 1e denotes a tool engagement portion that engages a tool such as a wrench or a wrench when the metal shell 1 is attached, and has a hexagonal axial cross-sectional shape. On the other hand, between the inner surface of the rear opening of the metal shell 1 and the outer surface of the insulator 2, a ring-shaped wire packing 62 that engages with the rear peripheral edge of the flange-shaped protrusion 2e is arranged. On the rear side, a ring-shaped packing 60 is arranged via a filling layer 61 such as talc. Then, the insulator 2 is pushed forward toward the metal shell 1 and, in this state, the opening edge of the metal shell 1 is swaged inward toward the packing 60 to form a swaged portion 1d. It is fixed to the insulator 2.

A gasket 30 is fitted into the base end of the screw 7 of the metal shell 1. The gasket 30 is a ring-shaped part obtained by bending a metal plate material such as carbon steel, and the screw portion 7 is screwed into a screw hole on the cylinder head side to form a flange-shaped gas seal portion 1f on the metal shell 1 side. Between the screw hole and the opening peripheral portion of the screw hole, it is compressed in the axial direction and deformed so as to be crushed, and serves to seal a gap between the screw hole and the screw portion 7.

Next, a zinc plating layer 41 for corrosion protection is formed on the entire outer surface of the underlayer (for example, carbon steel) 40 of the metal shell 1.
(A zinc-based plating layer) is formed, and further outside thereof is covered with a chromate film 42. Gasket 30
Similarly, a galvanized layer 45 and a chromate film 46 are formed on the outer surface of the. These galvanized layers and chromate coatings are both formed by the same method, and will be described below on behalf of the metal shell 1 as an example.

The galvanized layer 41 is formed by a known electrolytic galvanizing method.
It is about 10 μm. If the thickness is less than 3 μm, it may not be possible to secure sufficient corrosion resistance.
If the film thickness exceeds the above range, the specification is excessive in terms of securing the corrosion resistance, and the plating time is prolonged and the production efficiency is reduced, leading to an increase in cost.

On the other hand, in the chromate film 42, 95% by weight or more of the chromium component contained is trivalent chromium, and the thickness thereof is 0.2 to 0.5 μm. Incidentally, chromium component may that as many parts has become a trivalent chromium component, desirably between all the chromium component is in the trivalent chromium component.

FIG. 2 schematically shows an example of a method of forming the chromate film 42. That is, the metal shell 1 on which a galvanized layer having a predetermined thickness is formed by a known electrolytic galvanizing method or the like is immersed in the chromate treatment bath 50. The type of the chromate treatment bath 50 to be used has already been described. As a result, FIG.
As shown in (a), the zinc plating layer 41 of the metallic shell 1 "
A chromate film 42 is formed on the surface of the substrate. In addition,
FIG. 2 is an explanatory view showing a conceptual process, in which the metal shell 1 is simply immersed in the chromate treatment bath 50. However, in order to improve the treatment efficiency, a known barrel treatment method (liquid permeation) is used. (A process in which metal shells are piled up and inserted in a non-conductive container, and the container is rotated in the processing bath 50).

The metal shell 1 after the chromate treatment is washed and dried, then incorporated in the spark plug 100 shown in FIG. The metal shell 1 or the gasket 30 has a chromate coating formed on its galvanized layer, which has significantly higher anticorrosion performance and heat resistance than a conventional trivalent chromium-based chromate coating and furthermore a yellow chromate coating. It becomes possible to sufficiently impart corrosion resistance to the plating layer. Hereinafter, results of an experiment performed to confirm the effect will be described.

[0035]

(Example 1) A metal shell 1 having the shape shown in FIG. 1 was manufactured by cold forging using a carbon steel wire SWCH8A for cold heading specified in JIS G3539 as a raw material.
The nominal size of the threaded portion 7 of the metal shell 1 is 14 mm,
The axial length was about 19 mm. Next, a zinc plating layer having a film thickness of about 6 μm was formed by subjecting this to electrolytic zinc plating using a known alkaline cyanide bath.

Next, a chromate treatment bath 50 shown in FIG.
With chromium chloride (II
_{I) (CrCl 3 · 6H 2} O) of 50 g, cobalt nitrate (I
I) 3 g of (Co (NO ₃ ) ₂ ), sodium nitrate (Na
A bath was prepared by dissolving 100 g of NO ₃ ) and 31.2 g of malonic acid, and the temperature of the bath was maintained at 60 ° C. by a heater, and the pH of the bath was adjusted to 2.0 by adding an aqueous solution of caustic soda. Then, the zinc-plated metal shell was immersed in the chromate treatment solution 50 for 60 seconds, washed with water, dried, and dried with warm air at 80 ° C. to form a chromate film (test sample: Example).

On the other hand, as a yellow chromate treatment bath, 7 g / liter of chromic anhydride and 3 g of sulfuric acid with respect to deionized water.
Per liter and nitric acid at a rate of 3 g / liter were prepared and maintained at a liquid temperature of 20 ° C. Then, a metal shell was immersed in this for about 15 seconds, pulled up, and dried to produce a test piece (test product: comparative example). As a luster chromate treatment bath, chromium potassium sulfate 3 against deionized water is used.
g / L, 4 g / L nitric acid and 2 g / L hydrofluoric acid were prepared and maintained at a liquid temperature of 20 ° C. Then, a metal shell was immersed in this for about 15 seconds, pulled up, and dried to produce a test piece (test product: comparative example).
When the thickness of the chromate film of each of the above test products was measured by actual measurement from a cross section by SEM, the test products were 0.33 μm, 0.31 μm, and 0.07 μm. The cross-sectional SEM image used for the film thickness measurement is shown in FIG.
3 is shown. (A) of the test product, (b) of the test product,
(C) is each SEM image of a test article. In order to facilitate observation of the chromate film, an Au thin film is formed on the surface of the film by a sputtering method. In the SEM image, the underlying zinc plating layer having high conductivity and the Au coating layer
Since the chromate film layer having a low conductivity appears dark, the image of the chromate film can be easily confirmed from the contrast. In each SEM image, a white line is displayed at a position corresponding to each boundary between the chromate coating layer confirmed from the contrast, the galvanized layer, and the Au coating layer, and the film is determined from the distance between the white lines. Identify the thickness.

On the other hand, the presence of chromium in each of the formed chromate films was examined by X-ray photoelectron spectroscopy (XPS). FIG. 3 shows a peak portion of chromium (2p _2/3 ) in a photoelectron spectrum with the test sample. In the test sample (solid line), no peak appears at the position corresponding to hexavalent chromium, and it can be confirmed that almost all of the chromium component is trivalent chromium. On the other hand, in the test sample, the peak of trivalent chromium overlaps with the peak of hexavalent chromium, and a bump-like bulge appears on the shoulder on the high energy side of the peak.

FIG. 4 shows the shape of each peak assuming that the intensity of the photoelectron X-ray is I (vertical axis in the figure: cps) and the binding energy value is x (horizontal axis in the figure: eV). -(X-μ) ² / 2σ ² ｝ ‥‥ (1) (where μ represents the x-coordinate of the peak and σ represents the half-width of the peak curve), and the result of the peak separation analysis. It is. According to this, the peak height of trivalent chromium is defined as I1, and the peak height of hexavalent chromium is defined as I2.
/ (I1 + I2) is about 0.2 (in terms of hexavalent chromium reduction, I2 / (I1 + I2) is desirably 0.05 or less). A calibration curve was prepared using a standard sample of dichromium trioxide, and the weight content of hexavalent chromium in the total amount of chromium components was calculated based on the calibration curve. About 15% by weight was hexavalent chromium and the balance was trivalent chromium. It turned out to be chrome. The same analysis was performed on the sample and the sample, but substantially all of the chromium component was trivalent chromium.

With respect to the above test items, JIS85
Perform the “5. Neutral salt spray test method” in the corrosion resistance test method of plating specified in No. 02, and evaluate the durability by the time until white rust resulting from corrosion of the galvanized coating appears about 20% or more of the entire surface. went. In this specification, the metal shell is used as a sample as it is, and one surface of the tool engaging portion (hexagonal portion) is used as a sample surface. FIG. 5 shows the results. In other words, the metal shell satisfying the requirements of the spark plug of the present invention showed a very good durability time of 240 hours. This is substantially the same as the test product using the yellow chromate treatment, and is about eight times as large as the test product using the conventional thin glossy chromate film.

Further, for a test specimen prepared in the same manner as described above, the “7. Cas test method” in the plating corrosion resistance test method specified in JIS H8502 was performed.
The evaluation was made based on the durability time until white rust resulting from corrosion of the galvanized coating appeared on about 20% or more of the entire surface. Further, a durability test using sulfuric acid and nitric acid was performed as follows. First, a sulfuric acid solution or a nitric acid solution having a pH of 2 is placed in a desiccator, and the test article is sealed in the desiccator so that the test article and the acid solution do not come into direct contact with each other but can come into contact with the solution vapor. Then, the desiccator was held in a thermostat at a temperature of 90 ° C., and evaluated according to the same criteria as in the above-mentioned Cass test. The above results are shown in FIG.
And FIG. In each of the tests, the test specimens using the yellow chromate treatment or the gloss chromate treatment showed only a short durability time, whereas the test specimens according to the examples of the present invention showed good durability results. It turns out that it shows.

Next, a spark plug as shown in FIG. 1 was prepared using the metal shell described above, and was attached to a 6-cylinder, 2000 cc gasoline engine.
A mounting test was performed by operating continuously for 10 hours at pm and with the throttle fully open. The temperature of the metal shell during operation was about 200 ° C. FIG. 8 shows the results of the same neutral salt spray test as described above for each test product after the mounting test. While the test product using the yellow chromate treatment or using the gloss chromate treatment showed only a short durability time of about 20 hours, the test product according to the embodiment of the present invention has the durability even after mounting the engine. The time was 180 hours, which was a good result.

The specimen was heated to 200 ° C. in the air using a thermostat, kept for 30 minutes, and then subjected to the same neutral salt spray test. While the test article using the chromate treatment showed only a short durability time of about 20 hours, the test article according to the example of the present invention showed a good result of 200 hours.

(Embodiment 2) A metal shell similar to that of Embodiment 1
Was manufactured under the same conditions until the zinc plating treatment. Next
Then, as a chromate treatment bath, add 1 l to deionized water.
Chromium (III) chloride (CrCl₃・ 6H
₂O) and 50 g of cobalt (II) nitrate (Co (N
O ₃)₂) And sodium nitrate (NaNO₃) To 5
0-150 g, dissolve in the ratio of malonic acid 31.2 g
The bath temperature is kept at 60 ° C by the heater.
At the same time, the pH of the bath is adjusted by adding an aqueous solution of caustic soda.
Adjusted to 2.0. And the metal shell after galvanizing
Immerse in the above chromate treatment liquid 50 for 60 seconds, then wash with water
・ After drying, dry with warm air at 80 ° C to
A chromate film was formed. And the obtained chromate
The thickness of the film was determined by observing the cross section of the SEM as in Example 1.
Measure and determine the Na content by X-ray photoelectron spectroscopy (XPS)
Investigated by Was measured by The above results are shown in FIG.
You. That is, the Na content in the coating is 2 to 7% by weight,
Large film thickness in a relatively short time when 2-6% by weight
It can be seen that a chromate film of No. was obtained.

(Embodiment 3) A metal shell similar to that of Embodiment 1
Was manufactured under the same conditions until the zinc plating treatment. Next
Then, as a chromate treatment bath, add 1 l to deionized water.
Chromium (III) chloride (CrCl₃・ 6H
₂O) and 50 g of cobalt (II) nitrate (Co (N
O ₃)₂) And sodium nitrate (NaNO₃) To 5
0-150 g, dissolve in the ratio of malonic acid 31.2 g
The bath temperature is kept at 60 ° C by the heater.
At the same time, the pH of the bath is adjusted by adding an aqueous solution of caustic soda.
Adjusted to 2.0. And the metal shell after galvanizing
Immerse in the above chromate treatment solution for 40-80 seconds, and then
After washing and drying, dry with warm air at 80 ° C
A chromate film was formed. Each after chromate film formation
Neutral salt spray test similar to Example 1 was performed on the metal shell.
Was evaluated. The results are shown in FIG. Coating thickness
Is 0.2 to 0.5 μm, especially 0.3 to 0.5 μm
It can be seen that good durability results have been obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal half sectional view showing a spark plug according to an embodiment of the present invention.

FIG. 2 is an explanatory view of a chromate treatment step.

FIG. 3 is a view showing the results of X-ray photoelectron spectroscopy analysis of the chromate films of the test samples of Example 1 and (the peak portion of chromium (2p _2/3 ) in the photoelectron spectrum).

FIG. 4 is a view showing a result of performing peak separation analysis on a chromium (2p _2/3 ) peak portion of a photoelectron spectrum of the same test sample.

FIG. 5 is a graph showing the results of a neutral salt spray test performed on each test sample of Example 1.

FIG. 6 is a graph showing the results of the same Cass test.

FIG. 7 is a graph showing the results of the same acid durability test.

FIG. 8 is a graph showing the results of a neutral salt spray test after mounting the engine.

FIG. 9 shows Na in the chromate film of the test sample of Example 2.
5 is a graph showing the relationship between the amount and the coating thickness.

FIG. 10 is a graph showing the relationship between the thickness of a chromate film and the durability time of salt water spray of the test article of Example 3.

FIG. 11 is a cross-sectional SEM of each test sample used in Example 1.
image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode 30 Gasket 50 Chromate treatment bath 41, 45 Galvanized layer 42, 46 Chromate coating 100 Spark plug

Continuation of the front page (56) References JP-A-1-92092 (JP, U) JP-B6-84547 (JP, B2) JP-B-59-953 (JP, B2) JP-B-56-15791 (JP) , B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01T 13/00-21/06 C23C 22/30-22/53

Claims (12)

(57) [Claims] A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. And a ground electrode disposed in opposition to the chromate coating, wherein 95% by weight or more of the chromium component contained is trivalent chromium, and the thickness thereof is 0.2 to 0.5 μm. A spark plug, wherein a surface of the metal shell is covered with the metal plug. Wherein said chromate film is a spark plug according to claim 1, containing no hexavalent chromium component. 3. A gasket having a ring shape to be fitted to a base end portion of a mounting screw portion formed on an outer peripheral surface of the metal shell, at least a part of a surface of the gasket is covered with the chromate film. The spark plug according to claim 1. 4. A spark plug according to any one of 3 to the content of sodium components in the chromate coating claims 1 to 2 to 7 wt%. Wherein said metal shell, a spark plug according to any one of the claims 1 zinc plating film is formed as a base metal layer of the chromate coating 4. Appears when performing the "5. Neutral Salt Spray Test Method" white rust resulting from corrosion of the zinc plating film is more than 20% of the total surface of 6. JISH8502 defined plated corrosion resistance test method Endurance time until
The spark plug according to claim 5, which is for 40 hours or more. 7. After heating at 200 ° C. for 30 minutes in the atmosphere, when performing “5. Neutral salt spray test method” in the corrosion resistance test method for plating specified in JIS H8502, corrosion of the galvanized coating film occurs. 7. The spark plug according to claim 5, wherein a durability time required for white rust derived from the surface to appear by 20% or more of the entire surface is 40 hours or more. When 8. was "7 CASS test method" at a defined plated corrosion resistance test method JISH8502, durability until white rust resulting from corrosion of the zinc plating film occurs more than 20% of the total surface time, spark plug according to any one of claims 5 to 7 is more than 20 hours. 9. A spark discharge gap is formed between a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the center electrode. A method for manufacturing a spark plug comprising a ground electrode disposed opposite to the spark plug, wherein a trivalent chromium salt and a complexing agent comprising a chelating agent for trivalent chromium are mixed in a chromate treatment bath. By immersion in the surface of the metal shell, the chromium component 9
5% by weight or more is trivalent chromium, and the film thickness is 0.1%.
A method for producing a spark plug, comprising forming a chromate film having a thickness of 2 to 0.5 μm. 10. The chromate treatment bath may be 20 to 8
The method for producing a spark plug according to claim 9, wherein the spark plug is used in a state where the bath temperature is adjusted to 0 ° C. 11. The immersion time of the metal shell in the chromate treatment bath is set to 20 to 80 seconds.
2. The method for manufacturing a spark plug according to item 1. 12. In the chromate treatment bath, the content of the sodium component in the obtained chromate film is 2 to 12.
So that 7 wt%, spar <br/> Kupuragu method according to any one of claims 9 to 11 a predetermined amount of sodium salt of is blended.