Electric lamp and discharge devices – Spark plugs
Reexamination Certificate
2001-06-28
2004-12-14
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Spark plugs
C313S123000, C313S130000, C313S137000, C313S141000, C313S143000, C445S007000, C106S286400, C106S286600, C428S522000, C428S336000, C501S014000
Reexamination Certificate
active
06831396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a spark plug.
2. Description of the Related Art
A spark plug used for ignition of an internal engine of such as automobiles generally comprises a metal shell to which a ground electrode is fixed, an insulator made of alumina ceramics, and a center electrode which is disposed inside the insulator. The insulator projects from the rear opening of the metal shell in the axial direction. A terminal metal fixture is inserted into the projecting part of the insulator and is connected to the center electrode via a conductive glass seal layer which is formed by a glass sealing procedure or a resistor. A high voltage is applied to the terminal metal fixture to cause a spark over the gap between the ground electrode and the center electrode.
Under some combined conditions, for example, at an increased spark plug temperature and an increased environmental humidity, it may happen that high voltage application fails to cause a spark over the gap but, instead, a discharge called as a flashover occurs between the terminal metal fixture and the metal shell, going around the projecting insulator. Primarily for the purpose of avoiding flashover, most of commonly used spark plugs have a glaze layer on the surface of the insulator. The glaze layer also serves to smoothen the insulator surface thereby preventing contamination and to enhance the chemical or mechanical strength of the insulator.
In the case of the alumina insulator for the spark plug, such a glaze of lead silicate glass has conventionally been used where silicate glass is mixed with a relatively large amount of PbO to lower a softening point. In recent years, however, with a globally increasing concern about environmental conservation, glazes containing Pb have been losing acceptance. In the automobile industry, for instance, where spark plugs find a huge demand, it has been a subject of study to phase out Pb glazes in a future, taking into consideration the adverse influences of waste spark plugs on the environment. As a substitute for the conventional Pb glazes, for example, boro-silicate glass or alkali borosilicate glass based glazes have been proposed in JP-A-11-43351 or JP-A-11-106234.
On the surface of the insulator of the spark plug, there are formed markings composed of letters, signs or other images such as manufacturer names, log marks or products numbers. The markings are printed with an ink mixed with a pigment on the insulator surface on which a glaze layer is not formed, followed by coating a glaze on the markings and baking it. In this case, the marking layer is seen through the glaze layer that is made transparent. For distinguishing kinds or forms of the spark plugs easily, the marking layer is often formed by changing a color per each of the kinds or forms.
When the marking layer is formed under the glaze layer, a coloring metallic oxide composing a pigment in the marking layer inevitably causes reaction to a certain degree with components in the glaze layer while baking the glaze. If an existing Pb containing type is employed as the glaze layer, a tint inherent in the coloring metallic oxide is easily maintained, and desired colors can be constantly obtained. However, according to an inventor's studies, it has been found that if using a glaze where the amount of Pb component in the glaze was controlled to be small like a leadless glaze, it was difficult to adjust the color in the marking layer to be desired tints.
SUMMARY OF THE INVENTION
Accordingly it is an object of the invention to offer a spark plug enabling to stably color the marking layer, which is formed under the glaze layer, even if the Pb amount is decreased in the glaze layer.
For accomplishing the above object, a first structure of the spark plug of the invention has marking layer formed on a surface of an insulator and a glaze layer covering the marking layer so that the marking layer can be seen through the glaze layer, and is characterized in that the glaze layer contains 5 mol % or less Pb component in terms of PbO, and kinds and amounts of metallic element components contained in the marking layer are adjusted in such manners that tint of the marking layer seen through the glaze layer is 3 or less in the brightness specified by JIS:Z872 , and 3 or less in the chroma specified by JIS:Z872, otherwise 4 or less in the brightness as well as 2 or less in the chroma.
Desiring the marking layer in particular to color in black, it is important that when observing the marking layer through a reflected white light, the marking layer evenly absorbs the light in each wavelength range of visible spectra such that no outstanding reflection arises by lights of specified wavelength areas, and the level of the whole reflected light is lowered. However, if the Pb amount in the black glaze layer is 5 mol % or lower in terms of PbO, other components than Pb in the glaze layer react with metallic oxides in the marking layer, and the level of light absorption of the specific wavelength by the metallic oxide generating said reaction is changed, otherwise the wavelength of the light absorption is shifted, whereby a balance of the light absorption for coloring the black is lost, and as a result, the marking layer deviates from the black and are easy to color an unwelcome tint. Under such conditions, when distinguishing kinds or types of the sparkplugs by, e.g., colors of markings, the distinguishing will be often difficult. As another realistic problem, there is a case that tint changing in the marking layer is seen to purchasers as “unreasonable alternation in familiar colors in external appearance”, so that an inconvenience occurs that products could not always be quickly accepted because of a resistant feeling thereto.
Therefore, in the invention, if kinds and amounts of metallic element components contained in the marking layer are adjusted in such manners that the tint of the marking layer seen through the glaze layer of the Pb amount being 5 mol % or smaller is 3 or less in the brightness specified by JIS:Z8721 (1993) and 3 or less in the chroma, otherwise 4 or less in the brightness as well as 2 or less in the chroma, and even if the glaze layer of the low Pb amount is as mentioned above, externally appearing colors of the marking layer formed under the glaze layer can be constantly recognized as the black.
In the present specification, a measuring method of measuring the brightness and the chroma adopts the method specified in “4.3 A Measuring Method of Reflected Objects” of “4. Spectral Colorimetry” in the “A Measuring Method of Colors” of JIS-Z8722 (1994). The brightness and the chroma can be known comparing the result of measuring the brightness and the chroma by the above method with those of standard color chart prepared according to JIS-Z8721.
As a simple method, the brightness and the chroma can be known through visual comparisons with standard color chart prepared according to JIS-Z8721.
The adjustment of the kind or the amount of the metallic element components contained an the marking layer may be performed in accordance with, for example, the following technical concept. What contributes to coloring in the marking layer is mainly several kinds of transition metallic cations (called as “coloring metallic component” hereafter) ready for causing light absorption by electron transition, and it is assumed that a final coloring of the marking layer is roughly reflected spectra observed as overlapping of light absorption derived from each of metallic cations, in other words, is recognized as mixed condition of colors derived from each of the contained coloring metallic components. It has been found that when the amount of Pb component in the glaze layer goes down, as a result of the inventor's investigation, specific coloring metallic components such as Cr are easy to make changes in appearing colors (called as “ready discoloring metallic component” hereafter) owing to reaction with the glaze layer reducing the Fb amount. In this case, if the ready discoloring metallic
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
Patel Nimeshkumar D.
Roy Sikha
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