Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
2000-02-28
2002-09-24
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
06455207
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-sensitivity photopolymerization initiator for producing a color filter; to a high-quality photosensitive coloring composition for producing a color filter, which can be developed with a solvent or an aqueous alkaline solution after irradiation with UV light; to a color filter which is used in devices such as a solid state pick-up device and a liquid crystal display device; and to a method for producing the color filter.
BACKGROUND OF THE INVENTION
In recent years, demand has arisen for a color filter used in a device such as a liquid crystal display device, where the filter is thin and defect-free; has properties such as heat and light resistance; and has optical properties such as high transparency and high contrast in accordance with the trend toward reducing the thickness and increasing the width of the device. In addition, increase of the yield of a production step and reduction in the number of production steps are more and more required, along with a demand for reducing production cost of a color filter. A color filter per se comprises a transparent substrate such as a glass plate on which fine stripes of two or more hues are disposed in a parallel or crossing manner or fine pixels are disposed in lateral and longitudinal directions in a predetermined pattern. Each pixel has a fine shape and a dimension of some 10 &mgr;m to some 100 &mgr;m, and the pixels for each hue must be arrayed according to a predetermined order. Thus, a variety of methods for producing a color filter have been proposed. Of these, from many viewpoints, such as the precision of the produced filter and production cost, a pigment-dispersion method employing a photosensitive coloring composition in which a pigment is dispersed has gained wide acceptance.
The pigment-dispersion method comprises applying, on a substrate, a photosensitive coloring composition containing a pigment, a resin serving as a matrix, and a cross-linking agent; and forming each coloring layer in a predetermined pattern through photolithography. More specifically, a color filter is produced through the following steps: applying the aforementioned photosensitive coloring composition for achieving one filter color on a transparent substrate such as a glass plate; exposing patternwise; developing the unexposed portion with a solvent or an aqueous alkaline solution to thereby form a pattern of a first color; and sequentially repeating the procedure for another filter color. A negative-type photosensitive coloring composition is predominantly employed as the above described coloring composition, in view of properties of the produced color filter and a wide range of usable materials. Currently, during development, a solvent is used very seldom, from the viewpoints of environmental problems; instead, an aqueous alkaline solution is predominantly used. Exposure is typically carried out by use of UV light. In the above production steps, only a predetermined portion is irradiated with light such as UV light, to thereby cause a chemical reaction; i.e., radical polymerization, exclusively in the exposed portion.
Since a negative-type photosensitive composition predominantly undergoes radical polymerization, the sensitivity of the composition may be reduced through inhibition of polymerization caused by oxygen in the air. In order to solve this problem, for example, the applied photosensitive composition is irradiated with light after an oxygen-shielding film such as a poly(vinyl alcohol) film is formed on the composition. However, recently, demand has arisen for a photopolymerization initiator for producing a color filter, where the initiator has such high sensitivity that additional treatment such as the provision of an oxygen-shielding film can be eliminated.
In this connection, Japanese Patent Application (kokai) No. 6-201913 discloses a photopolymerization initiator comprising solely a triazine compound, and a photopolymerization initiator comprising a triazine compound and an imidazole compound in combination. Japanese Patent Application (kokai) No. 10-253813 discloses a photopolymerization initiator comprising a polyfunctional thiol compound and at least one compound selected from a biimidazole compound, a titanocene compound, a triazine compound, and an oxadiazole compound. Photopolymerizable compositions containing these photopolymerization initiators for achieving red, green, and blue colors have a certain degree of sensitivity. However, a photopolymerizable composition for achieving a black color, particularly a photopolymerizable composition containing a black pigment, has drawbacks, such as a considerable reduction in sensitivity due to a shielding effect of the black pigment during exposure, increase of exposure time, and insufficient curing, even when the composition contains the above-described polymerization initiator.
SUMMARY OF THE INVENTION
The present inventors have found that a photopolymerization initiator comprising a sensitizer (A) which absorbs light having a wavelength of 300-500 nm, an organic boron complex (B), and a thiol-group-containing compound (C) is suitable for producing a color filter, and that the above problems are solved by use of the initiator. The present invention has been accomplished on the basis of this finding.
In view of the foregoing, an object of the present invention is to provide a high-sensitivity photopolymerization initiator for producing a color filter.
Another object of the present invention is to provide a photosensitive coloring composition containing the initiator.
Another object of the present invention is to provide a color filter exhibiting excellent resistance to a variety of phenomena.
Another object of the present invention is to provide a method for producing the color filter.
Accordingly, the present invention provides a photopolymerization initiator for producing a color filter comprising a sensitizer (A) which absorbs light having a wavelength of 300 to 500 nm; an organic boron complex (B) represented by formula (1):
wherein each of R
1
, R
2
, R
3
, and R
4
represents an alkyl group, an aryl group, an aralkyl group, an alkenyl group, a heterocyclic group, or an alicyclic group; and Z
+
represents an ammonium cation, a sulfonium cation, an oxosulfonium cation, a pyridinium cation, a phosphonium cation, an oxonium cation, or an iodonium cation; and a thiol-group-containing compound (C).
Preferably, the thiol-group-containing compound (C) is at least one species selected from 2-mercaptobenzothiazole, trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), and pentaerythritol tetrakis(3-mercaptopropionate).
Preferably, the sensitizer (A) contains a benzophenone compound and/or a biimidazole compound.
The present invention also provides a photosensitive coloring composition for producing a color filter, which comprises a transparent polymer (D) soluble in a solvent or an aqueous alkaline solution, a compound having an ethylenic unsaturated bond (E), a pigment (F), and the above-described photopolymerization initiator.
The present invention also provides a color filter having pixels fon-ned on a transparent substrate by use of the photosensitive coloring composition.
The present invention also provides a method for producing a color filter comprising forming a layer of the photosensitive coloring composition on a transparent substrate and photocuring exposed portions of the layer of the composition through exposure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will next be described in more detail. When R
1
, R
2
, R
3
, and R
4
in formula (1) represent alkyl groups, and the alkyl groups may have substituents. Specifically, a C
1
-C
12
linear or branched alkyl group which may have a substituent is preferred. Examples of suitable alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group,
Katoh Tsuyoshi
Ogata Tomonari
Showa Denko Kabushiki Kaisha
Sughrue & Mion, PLLC
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