Coating processes – Electrical product produced – Metal coating
Reexamination Certificate
1999-11-05
2001-03-06
Beck, Shrive (Department: 1762)
Coating processes
Electrical product produced
Metal coating
C427S123000, C427S376700, C427S383100, C106S001230, C106S001250, C106S001260, C106S001270, C106S001280, C106S001290
Reexamination Certificate
active
06197366
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a metal paste and a production process of a metal film. More particularly, the present invention relates to a metal paste that is able to form a metal film by low-temperature baking, and a production process of a metal film that uses said paste. The metal paste of the present invention is useful as the raw material of a metal film used for the surface treatment, coating, demagnetizing and decoration of electronic materials, electronic devices and mechanical materials, etc., and in catalysis and sterilization. Moreover, it is also useful as the raw material of a metal film used in the fields of pharmaceuticals and agricultural chemicals, etc.
In addition, if there was a process for easily producing a desired metal film even when metals are used directly as the base metal at present, there are many cases in which their use after forming into a metal film would be easier to handle and more economical. However, since baking at high temperatures is required to form a metal film, the substrate is limited to materials having a high melting point. Therefore, if the baking temperature for forming a metal film can be made lower, applications could be expanded to include general-purpose, inexpensive substrates having a low softening point (such as glass or plastic etc.). The present invention relates to a metal paste for low-temperature baking that allows this wide range of applications.
BACKGROUND ART
Metals have useful properties that are unique to each type of metal. Each of these types of metals are used either alone or in the form of an alloy for surface treatment, coating, demagnetizing and decorating of electronic materials, electronic devices, mechanical materials and so forth, as well as catalysis, sterilization, and even in the fields of pharmaceuticals and agricultural chemicals etc. by utilizing their respective characteristic performance (such as electrical conductivity, resistance, semi-conductivity, transparency, ionicity, corrosion resistivity, friction, light blocking, coloring and/or metallic luster) after forming into a film by various means on a substrate such as ceramics and so forth.
The following lists examples of technologies of the prior art used to produce metal films: (1) methods that require a high vacuum such as sputtering; and, (2) methods in which metallic ink is applied and baked such as the thick film paste method. The sputtering method of (1) requires an expensive, high-vacuum and large apparatus, has poor mass-productivity due to batch production, and has high production costs. Consequently, the paste method of (2) is used because of its low equipment cost and high productivity. In this method, various types of metal paste are coated onto a substrate and baked, allowing metal films to be produced continuously and inexpensively using a simple process and apparatus.
The paste used in this thick film paste method is a heterogeneous viscous liquid simply comprising forming various types of metal into fine particles and dispersing in a solvent. Coating and baking this viscous liquid results in a metal film in which the metal particles simply make contact, thereby preventing the formation of a uniform film. Consequently, in the case of silver-palladium alloy that is most frequently used in the electronics industry, even if formed with the thick film paste method, it is necessary to bake by heating to a high temperature of about 950° C. and physically melt the metal particles to obtain a uniform thin film. Consequently, only ceramic substrates, metal substrates or other substrates having a high melting point could be used for the substrate on which the metal film is formed. In addition, a large baking oven and peripheral facilities able to withstand high temperatures, and an energy source and so forth for high-temperature baking are required to perform baking at high temperatures.
Consequently, if the paste baking temperature could be lowered further, equipment costs could be reduced, energy could be saved, and costs could be lowered. In addition, since it desirable to form a metal film on a general-purpose, inexpensive substrate having a low softening point (such as glass or plastic etc.), it is preferable to further lower the baking temperature at which metal film is formed to allow use of those substrates.
In order to overcome this shortcoming, a method has been proposed (organometallic (MO) method) in which inorganic metal particles are first converted to an organometallic compound, coated after uniformly dissolving in a solvent, and then baked to obtain a thin, uniform metal film. For example, in the case of gold, a paste method using an organometallic compound containing sulfur allows the formation of a uniform gold film demonstrating equal performance while requiring approximately only {fraction (1/7)} the amount of gold as compared with the thick film paste method in which fine particles of gold are kneaded into a paste. Consequently, in fields that use gold, production is switching over to the MO method from the conventional thick film paste method.
A synthesis method in which an organic substance is bonded directly to a metal to transform into an organometallic compound is typically used as a method for producing the above-mentioned organometallic compound. In this synthesis method, a special production method is required to convert inorganic metal into an organometallic compound. In addition, since it is difficult to convert at a yield of 100% at that time, this method is more expensive than methods using metal and solvent. Thus, although this method can be used practically in the case the base metal itself is an expensive metal like gold, in the case of other metals, the use of this method results in the cost required for the process of converting to an organometallic compound being higher than the price of the metal itself. Consequently, there is a need in industry for a metal paste that allows metal films to be produced both inexpensively and easily.
DISCLOSURE OF THE INVENTION
In consideration of the above-mentioned problems, the inventors of the present invention found that when a general-purpose, inexpensive solid organo- or inorganometallic compound, and not a special, expensive organometallic compound, is mixed with a general-purpose, inexpensive amino compound, it unexpectedly changes into a liquid or mud to allow the obtaining of a coatable, viscous metal paste, thereby leading to completion of the present invention.
A production process in which an organo- or inorganometallic compound can be directly formed into a paste in the form of a metalloorganic (MO) ink by adding an amino compound to a solid organo- or inorganometallic compound followed by a simple means of manipulation in the form of stirring is not known in the literature.
According to the present invention, a metal paste is provided which demonstrates coatable viscosity and is composed of an organo- or inorganometallic compound of a metal that is a solid at normal temperature and belongs to groups 3 through 15 of the periodic table, and an amino compound as medium.
Although organometallic compounds are typically unstable, the compound is stabilized by the addition of organic acid and organic alcohol to the above-mentioned metal paste, thereby providing a metal paste which is characterized by improving solubility and printability.
Moreover, according to the present invention, a production process of a metal film is provided characterized in that the above-mentioned metal paste is coated onto a substrate and baked at a low temperature of 90° C.-550° C. to form a metal film.
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Barr Michael
Beck Shrive
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Hazzard Lisa Swiszcz
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