Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
1999-10-01
2001-06-26
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
Reexamination Certificate
active
06251548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition for forming a light-shielding layer that has excellent light-shielding properties and that is useful in the field where non-conductivity is required. More specifically, the present invention relates to a composition for forming a non-conductive light-shielding layer, useful for making the light-shielding layer (black matrix) of a color filter to be used for liquid crystal displays or the like, to a non-conductive light-shielding layer made from the composition, and to a color filter comprising the light-shielding layer.
2. Background Art
It has conventionally been known that either a light-shielding layer comprising a thin film of a metal such as chromium, nickel or aluminum, or a light-shielding layer comprising a binder resin and a pigment such as carbon black or titanium oxide dispersed in the binder resin is provided on the non-picture-element area of a color filter useful for liquid crystal displays or the like in order to increase the contrast of images displayed.
However, the above-described conventional light-shielding layers are electrically conductive, so that they have the following problems: it is necessary to separately provide an insulating layer when either one of the light-shielding layers is provided between transparent electrode layers; the light-shielding layers tend to cause short circuiting between electrode layers; and cross talk between electrode layers which are adjacent to each other through the conductive light-shielding layer is increased. Further, in the case where a non-conductive light-shielding layer is provided by dispersing a non-conductive inorganic pigment such as titanium oxide in a binder resin, there exists such a problem that the pigment cannot be easily dispersed in the binder resin because the particle diameter of the pigment is large. In addition, the resulting light-shielding layer (coating layer) is insufficient in blackness.
An object of the present invention is therefore to provide a composition suitable for forming a light-shielding layer that is excellent in both light-shielding properties and blackness and that is not electrically conductive, and a non-conductive light-shielding layer formed from the composition.
SUMMARY OF THE INVENTION
The above object can be attained by a composition for forming an non-conductive light-shielding layer of the present invention, comprising an alkali-soluble binder, a pigment, a photopolymerizable monomer, a photopolymerization initiator and a solvent, wherein the pigment comprises fine particles of a double oxide selected from CuMn
2
O
4
, and CuMn
2
O
4
in which a part of Mn is substituted with Fe, Co and/or Ni.
By the use of the composition of the present invention, it is possible to obtain a light-shielding layer excellent in light-shielding properties and blackness, having no conductivity.
DETAILED DESCRIPTION OF THE INVENTION
As the alkali-soluble binder for use in the composition for forming a non-conductive light-shielding layer of the present invention, a preferable binder is one that can contribute to the dispersibility of the pigment, which is highly compatible with the photopolymerizable monomer and the photopolymerization initiator, which is highly soluble in an alkaline developer and also in the organic solvent, which can show high adhesion to a substrate even when exposed especially to an alkaline developer or a cleaning fluid for many hours during the pattern-forming process including exposure and development, and whose strength, softening temperature and the like are suitable as a component of a color filter. Such a preferable binder can be selected from a wide variety of polymer materials which will be described below.
Specific examples of the polymer materials include copolymers containing a monomer having an acid radical such as a carboxyl group, for example, methacrylic, acrylic, itaconic, crotonic, maleic or partially-esterified maleic acid copolymers, and cellulose derivatives having a carboxyl group as a side chain. Further, a carboxyl-modified polymer obtained by adding a cyclic acid anhydride to a polymer having a hydroxyl group or the like serving as a site of modification can also be preferably used. In addition to these polymer materials, there can be mentioned water-soluble polymers such as polyvinyl pyrrolidone, polyethylene oxide and polyvinyl alcohol. Furthermore, there can be mentioned copolymers of an unsaturated organic acid and an unsaturated organic acid ester such as methyl acrylate, ethyl methacrylate, benzyl methacrylate or glycidyl methacrylate, and polymers obtained by addition-polymerizing other unsaturated organic acid esters in a predetermined amount to these copolymers can also be used.
In the present invention, the most preferable alkali-soluble binder is an epoxy resin, and examples thereof include a resin having reactive double bond groups which have been introduced by adding glycidyl methacrylate or the like to two or more epoxy groups in one molecule of the epoxy resin, and a modified epoxy resin which is obtained by introducing a carboxyl group by the addition of a cyclic acid anhydride to the above-described epoxy resin so as to impart thereto polymerization-initiating properties and alkali-developability. In particular, a bisphenol A-type vinyl ester whose basic skeleton is a condensation product between bisphenol A-type and epichlorohyrin is preferred as the epoxy resin. The modified epoxy resins are very excellent in pigment-dispersing properties, resistance to alkalis and adhesion to a substrate, and can impart high film strength to light-shielding layers.
Further, a light-shielding layer improved in various types of strength can be obtained by the use of the above-described epoxy resin binder which has been rendered polymerizable by introducing reactive double bond groups to at least a part of the epoxy resin binder. The average number of the reactive double bond groups to be introduced is preferably 0.1 to 20 per one molecule of the binder.
Furthermore, in order to impart suitable resistance to an alkaline developer in the light-shielding layer, it is preferable that the acid value of the epoxy resin binder be in the range of approximately 70 to 250 mg KOH/g. When the acid value of the binder is in excess of this range, although pattern resolution can be attained by subjecting the light-shielding layer to exposure and development, the resulting patterned surface tends to have small cracks because the light-shielding layer is insufficient in resistance to alkaline developer. There is therefore such a possibility that an alkaline developer rapidly penetrates into the light-shielding layer from these cracks to finally cause separation of the resist from the substrate. On the other hand, when the acid value of the binder is smaller than the above-described range, the light-shielding layer formed has decreased solubility in alkalis, so that there may be case where even the non-exposed area of the light-shielding layer cannot be dissolved in the developer. Thus, a pattern cannot be properly formed on the light-shielding layer.
It is preferable that the molecular weight of the epoxy resin binder be in the range of 2,000 to 20,000. When the epoxy resin has a molecular weight of less than 2,000, it cannot fully function as a binder. On the other hand, when the epoxy resin has a molecular weight of more than 20,000, it tends to coagulate pigment particles and thus deteriorate the storage stability of the composition. Moreover, a light-shielding layer formed by using such an epoxy resin is poor in adhesion to a substrate, pattern-forming properties and smoothness.
The content of the epoxy resin binder is preferably 5 to 80% by weight of the total solids of the liquid composition.
Specific examples of the aforementioned epoxy resin binders include bisphenol A-type epoxy acrylates (trade name:
“VR-60”, “VR-90”) manufactured by Showa Highpolymer Co., Ltd., Japan; bisphenol A-type epoxy acrylates (trade name: “EB600”, “EB3701”) manufactured by DAICEL
Kogo Kyoko
Nagashima Junzo
Sega Syunsuke
Yoshihara Toshio
Dai Nippon Printing Co. Ltd.
McPherson John A.
Parkhurst & Wendel L.L.P.
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