Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-09-14
2002-09-17
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S433000, C428S446000, C428S697000, C252S514000, C252S520300, C106S001230, C106S001240, C106S001280
Reexamination Certificate
active
06451433
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fine metal particle-dispersion solution including metals such as noble metal and copper (a metal colloid) and a method for producing the solution; a coating solution for forming electrically conductive films; a conductive film using the solution and a method for forming the film. The fine metal particle-dispersion solution of the present invention is useful for various purposes and particularly useful for transparent films, more particularly for a transparent film for providing a Braun tube and/or a CRT of a TV and/or a computer with an antistatic property for static electricity, a sealing property for electromagnetic waves including ultraviolet rays and infrared rays and an anti-glaring property, which requires a low temperature baking.
2. Description of the Related Art
Since fine metal particles having a mean primary particle size of from several nm to several tens of nms (a metal colloid) can pass rays therethrough, a transparent film can be formed by combining the particles with a binder. Particularly silver fine particles are widely used for the above-mentioned use.
In relation to a transparent film for a Braun tube and a CRT of a TV and/or a computer, it is known that the Braun tube of a TV and a CRT of a computer can be provide with an antistatic property for static electricity and anti-glaring property (protection from the projection of an outer light) by a two layer film formed by an upperlayer of a transparent film having a low refractive index (for example, a film composed of a silica type material) on an underlayer of a transparent film having a high refractive index. The transparent film having the above-mentioned two layers composed of semiconductor fine particles such as ITO (indium oxide doped by tin) and ATO (tin oxide doped by antimony) is disclosed in JP-A 5-290634 and JP-A 6-12920.
Recently, there have developed concerns over bad influences on the human body produced by electromagnetic waves released from Braun tubes and CRTs and error functioning of computers caused by electromagnetic waves from outside thereof, and there have been set in various countries new standards for the emission of electromagnetic waves of low frequency. Consequently an electromagnetic wave-sealing property has been required for Braun tubes and CRTS. For providing the electromagnetic wave-sealing property, it is necessary to form a conductive film having a low resistance of from 10
2
to 10
3
&OHgr;/□ in terms of surface resistance on the surface of the Braun tube or CRT which is a base. As the underlayers of the transparent film according to the above-mentioned two layers have a low conductivity, it is difficult to obtain the low resistance as mentioned-above.
Accordingly, trials were carried out to satisfy all of the electromagnetic wave-sealing property, antistatic property and anti-glare property by forming the underlayer of transparent film of the two layers using metal particles having a mean primary particle size of up to 0.2 &mgr;m (200 nm), in some case, up to 0.05 &mgr;m (50 nm) to provide a low resistance. For examples, JP-A 8-77832, JP-A 9-115438, JP-A 9-331183, JP-A 10-74772, JP-A 10-154473 disclose the above-mentioned trials. The fine particles of noble metal are mainly used and the fine particles of Ag are most frequently used as fine metal particles from the standpoint of conductivity.
A particle size having a mean primary particle size of up to 200 nm are within a colloid area. That is, a dispersion solution including metal particles having the mean primary particle size of such a small size is a metal colloid. The metal colloid is hydrophobic. As the fine metal particles as a dispersion have an inferior affinity for water as a dispersion medium, the metal colloid is thermodynamically unstable with the result that aggregation easily arises when an electrolyte exists. Accordingly, it is necessary to add a large amount of a protective colloid (a hydrophilic colloid such as a water-soluble polymer) having a function to stabilize the hydrophobic colloid such that the metal colloid can be stable.
In case of a metal colloid containing a large amount of the protective colloid, the protective colloid which is typically an organic material having no conductivity impedes conductivity when used for forming a conductive film. For that reason, a sufficient conductivity is unavailable without raising the baking temperature for forming the transparent film up to a high temperature which makes it possible completely to dissolve and purge the organic material (for example, higher than 350° C.). However such a high baking temperature causes the drop of a phosphor included in the Braun tube, the inferiority of measurement accuracy, the change of vacuum balance due to a gas generation and the corrosion of a electron gun in case of forming a transparent film on a Braun tube or a CRT of a TV and/or computer.
It is known from more than 100 years ago that an aqueous solution of metal salt is reacted with a reduction agent to produce a metal colloid. However, any methods use a large amount of a protective colloid to stabilize the metal colloid except for the method disclosed by Carey Lea in 1889 (M. Carey Lea, American Journal of Science, 37:491, 1989).
According to the Carey method, an aqueous solution of sodium citrate and an aqueous solution of ferrous sulfate are mixed, thereby adjusting the aqueous solution of reduction agent including citrate ion and ferrous ion (that is, aqueous solution of ferrous sulfate), and then the adjusted aqueous solution of reduction agent is mixed with an aqueous solution of silver nitrate to reduce silver nitrate with the result of obtaining a silver colloid. Citrate ions stabilize the colloid adsorbed to fine silver particles such that the silver colloid can be stabilized without adding a polymer protective colloid.
In principle, this method can be used for producing any other noble metal colloid by replacing the aqueous solution of silver nitrate with an aqueous solution of another noble metal salt.
JP-A 10-66861 discloses a silver colloid solution and the method for producing the same, based on the Carey Lea method. According to the method, the aqueous solution of the reduction agent and the aqueous solution of silver nitrate are mixed while stirring at from 1,000 to 10,000 rpm, preferably changing the temperature or stirring speed during the process, thereby to precipitate fine silver particles having various sizes. The precipitated fine silver particles are recovered by centrifugation and the recovered fine particles are dispersed in water such that a solid content of silver is from 1 to 80 wt. % for use as a coating material for forming a transparent conductive film.
According to the Carey Lea method and the method disclosed in JP-A 10-66861, the stabilized colloid can be obtained in case of a silver colloid and some noble metal colloid.
However, the stabilized colloid can not be necessarily obtained by the above-mentioned methods in case of another noble metal and other metals such as Cu. Furthermore, serious problems have been found when a metal colloid is produced using two or more kinds of metals (for example, silver and palladium). That is, according to the above-mentioned methods, different kinds of metals precipitate individually (for example, silver and palladium individually) to form the metal colloid. Accordingly, when the metal colloid is used for a coating material, fine metals particles move during forming a film or baking the film and the fine particles of the same kind of metal is easy to gather each other with the result that there is a tendency to form a film having a nonuniform distribution of different kinds of metals therein. Therefor, a film property differentiates according to part by part of the film with the result that a transparent conductive film having a stable quality can not be obtained.
In addition, when the above-mentioned two layer film is formed using the silver colloid produced by the Carey Lea method and the method dis
Hayashi Toshiharu
Oka Tomoko
Shibuta Daisuke
Jones Deborah
McNeil Jennifer
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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