Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-08-23
2002-04-16
Dawson, Robert (Department: 1713)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C523S215000, C523S468000
Reexamination Certificate
active
06372349
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a high-resistivity carbon black and a color filter using it. The high-resistivity carbon black according to the present invention is suited for use as carbon black for insulating black matrices and spacers of optical color filters used in color TV, liquid crystal color TV, cameras, etc.
In the liquid crystal displays, a liquid crystal material is filled in the spaces of about 1 to 10 &mgr;m formed in a transparent substrate such as glass substrate provided with the transparent electrodes, and the liquid crystal is oriented in a fixed direction by a voltage applied across the electrodes to form a transparent portion and an opaque portion to thereby display an image. In the color liquid crystal displays, the color filters for the three colors, viz. red (R), green (G) and blue (B) corresponding to the three primary colors of light are provided on a transparent substrate, and light transmission through the liquid crystal is controlled by adjusting the voltage applied to the transparent electrodes, whereby to control the amount of light passing through the R, G and B three color filters to make color display by color development caused by the addition of the three primary colors.
Various methods are available for forming the R, G and B color layers. For instance, a method can be used in which such layers are formed on a substrate provided with the black matrix films partitioning the respective colors, or the black matrix films are provided after forming the three colors of R, G and B. In either case, the role of the black matrix is to demarcate the three primary colors R, G and B from each other and to screen the light from the liquid crystal driving electrodes or TFT (thin-film transistors) provided on the substrate in opposition to the color filters.
As an example of black matrices of color filters used for the above purpose, there is known the type in which the resist film having carbon black dispersed therein as black coloring material is patterned. Carbon black is essentially a conductive material, so that the resist film having such a material dispersed therein necessarily exhibits conductivity or semiconductivity. So, development of a carbon black having increased resistivity (insulating performance) while maintaining its light screening activity has been strongly desired.
The present applicant have made various studies on carbon black coated with a resin, such as polyfunctional epoxy resin, to be used as high-resistivity carbon black for black matrices of color filters, and on the method of producing such carbon black (Japanese Patent Application Laid-Open (KOKAI) Nos. 9-26571, 9-71733, 9-95625, 9-124969, 9-304760, 10-60169, 10-330643, 10-60988, 10-60989, 11-80583, 11-80854, etc.), and also proposed a high-resistivity carbon black which has been subjected to a specific oxidation treatment on the surface (Japanese Patent Application Laid-Open (KOKAI) Nos. 11-181324, 11-181326, etc.). However, by using the above-mentioned conventional techniques, volume resistivity of any obtained carbon black has been limited to the order of 5 to 50 &OHgr;·cm at the highest.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high-resistivity carbon black having a high light screening performance and a low surface reflectance and also capable of providing a thin-film black matrix.
Another object of the present invention is to provide a color filter using the said carbon black for the black matrix.
To attain the above aim, in the first aspect of the present invention, there is provided a high-resistivity carbon black coated with a resin on the surface and having a volume resistivity of not less than 100 &OHgr;·cm.
In the second aspect of the present invention, there is provided a process for producing the high-resistivity carbon black as defined in the first aspect, which comprises adding and mixing a resin-containing solution in a carbon black dispersion to coat the carbon black particle surfaces with the resin, and then curing the resin to obtain resin-coated carbon black having a volume resistivity of not less than 100 &OHgr;·cm.
In the third aspect of the present invention, there is provided a carbon black dispersion for black matrix forming resist, comprising (a) a high-resistivity carbon black coated with a resin on the surface and having a volume resistivity of not less than 100 &OHgr;·cm, (b) a dispersant having an electron donative group, and (c) a dispersing medium.
In the fourth aspect of the present invention, there is provided a color filter having a black matrix obtained by patterning a resist film having a black coloring material dispersed therein, wherein a high-resistivity carbon black coated with a resin on the surface and having a volume resistivity of not less than 100 &OHgr;·cm is used as the black coloring material.
The said high-performance carbon black can be used advantageously as a black coloring material for color filters.
DETAILED DESCRIPTION OF THE INVENTION
The high-resistivity carbon black according to the present invention is coated with a resin on the surface. The starting carbon black used in the present invention is not specifically defined, but it is preferable to use the type in which the value obtained from dividing volatile content by specific surface area (amount of volatiles based on unit specific surface area) is not less than 0.01%·g/m
2
, preferably not less than 0.02%·g/m
2
, more preferably not less than 0.03%·g/m
2
. Specific reference to the above attribute (concerning the amount of volatiles based on unit specific surface area) of the present carbon black is for the reason that the more the specific surface area of carbon black, the more amount of volatiles adhere on the (carbon black particle) surfaces, but the volume resistivity mentioned later does not represent the absolute amount of volatiles but is interrelated with the amount of volatiles adhering on the unit surface area.
The volatile content of carbon black can be increased by an oxidation treatment of carbon black with ozone and/or hydrogen peroxide. Generally, as the oxidizing agent of carbon black, there are used, beside those mentioned above, nitric acid, NO gas, NO
2
gas, air, SO
3
gas, fluorine gas and the like, but the improvement of volume resistivity with a relatively small amount of volatiles based on unit specific surface area is achieved especially when ozone and/or hydrogen peroxide are used as the essential oxidizing agent in combination with the said other oxidizing agents such as nitric acid and NO
2
gas.
Volatile content was determined by a method in which carbon black is heated at 950° C. for 7 minutes and percent loss in weight is calculated according to JIS K 6221. Specific surface area can be determined by the nitrogen adsorption method using the BET formula. That is, nitrogen adsorption of carbon black is measured by the low-temperature nitrogen adsorption method using a low-temperature nitrogen adsorbing device (Sorptomatic, 1800 mfd. by, Carlo Elba Co., Ltd. Italy), and based on the thus measured nitrogen adsorption, the specific surface area is calculated by the multiple point method using the BET formula.
The starting carbon black used in the present invention is preferably the one which has an ash content of not more than 1.0% by weight, especially not more than 0.5% by weight. Main components of ash are alkaline metals or alkaline earth metals such as Na, K, Ca, etc., and carbon black with high contents of these ash components has difficulties in improving its volume resistivity. Reduction of such ionic conductive materials can be achieved by proper selection of stock oil, gas and additives used in the production of carbon black. It can also be attained by washing with water or pickling of carbon black just out of the kiln. Ash content can be calculated from the amount of ash that remains after 5- to 6-hour combustion of carbon black in the air at 750° C.
It is also preferable that the dispersed particle diameter of carbon black in the dispersion is as small as possible.
Arata Satoru
Hisashi Hideyuki
Sekine Yuuichi
Conlin David G.
Dawson Robert
Edwards & Angell LLP
Mitsubishi Chemical Corporation
O'Day Christine C.
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