Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
2002-02-25
2004-05-18
Berman, Susan (Department: 1711)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
C430S270100, C522S035000, C522S904000, C522S905000, C522S152000
Reexamination Certificate
active
06737203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with new polymers, compositions comprising these polymers, and methods of using these compositions to form a color filter for use in a liquid crystal display. More particularly, the polymers comprise recurring monomers of styrene and maleic anhydride with amino functional groups (e.g., 4-aminoacetophenone, 2-aminophenol, 4-aminobenzoic acid) bonded to at least some of the maleic anhydride monomers.
2. Description of the Prior Art
Color filters are commonly used in liquid crystal display panels, imaging devices, and similar items, and are generally comprise a mosaic of pixels or as a striped pattern. A liquid crystal display is usually produced by forming a multicolor image layer on a transparent glass substrate. The multicolor image layer typically contains red, green, and blue picture elements and, in some cases, also includes a black-colored or black-shaded matrix. A protective layer is then formed on the multicolored image layer, and a transparent conductive layer is subsequently formed on the protective layer, usually by sputtering of indium-tin-oxide (ITO). In the case of a super twisted nematic (STN)-type or a ferroelectric liquid crystal-type panel, the transparent conductive layer is further processed through photolithography to yield a color filter equipped with a transparent electrode, after which an oriented film is formed on the transparent electrode. That substrate and another similarly-formed substrate are sealed together with a gap therebetween, with liquid crystals being poured between the two substrates to yield the display panel.
In the past, the protective layer has been formed on the multicolor image layer for a variety of reasons. For example, the protective layer protects the multicolor image layer from various chemicals (e.g., solvents for the photoresist, acidic etching solutions, basic resist release solutions, solvents for the oriented film coating) used in the photolithographic process carried out to produce the transparent conductive layer. Furthermore, the protective layer gives flatness to the multicolor image layer and assists in maintaining the gap between the two substrates into which the liquid crystals are poured. It is important that the protective layer is transparent (without cloudiness or turbidness) in the visible light region, and that the layer is strongly adhered to both the multicolor image layer and to the substrate.
Recently, there has been a demand to remove the protective layer in order to insure sealing in the non-image portions. As a result, the color layer must be formulated to function in the same manner as the protective layer. Photosensitive resin-type binders are generally used as binders for the color layer in order to enable the layer to meet the above-described requirements. The most popular of these binder resins are those which can be crosslinked by a photo-induced reaction when exposed to UV light. The unexposed portions can then be developed in aqueous alkali solutions which are safe and are the environmentally preferred solutions. The resin is thereafter further cured by heating to give increased chemical resistance.
Color filters containing such a photosensitive resin are prepared by dispersing pigments in the resin. The resin/pigment system also includes dispersing agents which stabilize the pigment dispersion, surfactants which improve the coating smoothness, an addition-polymerizable monomer having an ethylenically unsaturated double bond which improves photo-crosslinking density, and photoinitators for catalyzing the photo-crosslinking reaction.
The color filters must have several other properties in addition to the properties discussed above with respect to the protective layer. For example, the color filter must be able to define a clear pattern of pixels or stripes at small dimensions (e.g., pixel sizes as small as 5 &mgr;m). To produce a distinct image without blurriness or fuzziness, the pixels must also be of uniform size and thickness and have straight, clean edges without roughness or pigment residue. Furthermore, the pigments in the composition used in forming the color filter must remain dispersed in the composition over long periods of time, and the composition must also maintain color purity even after prolonged exposure to light. That is, there should be little or no yellowing or discoloration of either the photosensitive resin or the pigments of the composition. Finally, the resulting color filter must be readily processible by standard photolithographic techniques (e.g., the color filter should not require a broadband UV exposure of over 600 millijoules).
Examples of known photosensitive resins for color filters are described in U.S. Pat. No. 5,445,919 to Wakata et al., U.S. Pat. No. 5,514,502 to Wakata et al., and U.S. Pat. No. 5,650,263 to Wakata et al. These patents describe photopolymerizable compositions which comprise a photopolymerization initiator or a photopolymerization initiator system, an addition-polymerizable monomer having at least one ethylenically unsaturated double bond, and a resin obtained by reaction of an anhydride-containing copolymer having a number average molecular weight of 500 to 30,000. This resin has primary amines in a ratio to the copolymer at 0.1 to 1.0 equivalent per equivalent of the anhydride in the copolymer.
Another resin of this type is disclosed in U.S. Pat. No. 5,641,594 to Kudo et al. This composition includes: a polymer having alcoholic or phenolic hydroxyl groups; a compound capable of producing a nitrene when irradiated with an actinic radiation; a pigment; and a solvent. The composition can further contain a heat crosslinking agent and/or a compound having a polymerizable double bond in addition to the above ingredients.
The compositions described in the '919, '502, '263, and '594 are inadequate for developing color filters with sufficient resolution and small pixel size required in modern high-resolution devices. While these compositions may satisfy some of the requirements described above, none of these resins can meet all color filter needs, especially at 2-4 &mgr;m resolution. Furthermore, these compositions require the use of a thermal-crosslinking agent such as tris(acryloloxyethyl) isocyanurate, diisocyanates, or methacrylate melamine compounds. While such additives can improve film hardness and chemical resistance, they are difficult to use and environmentally unfriendly. Isocanates in particular are known carcinogens.
U.S. Pat. No. 5,998,091 to Suzuki describes the synthesis of various monomers, that may be useful for the synthesis of a photosensitive resin which can be used to manufacture color filter materials. While this patent discloses various monomer structures which aid in adhesion to the substrate, alkaline solubility, and pigment dispersion stability, it does not disclose a final polymer composition which can meet the needs described above. In particular, this patent does not disclose a composition which has high photosensitivity, film hardness, and chemical resistance required for color filter materials.
European Patent Application No. 780,731 describes a photosensitive resin which incorporates a phosphoric methacrylate resin, in addition to the photosensitive resin to improve solubility in alkali developer. However, this system discloses nonhomogenous intermixing of the two binder resins which can result in uneven develop characteristics across the entire color filter panel. This is especially true at 2-4 &mgr;m pixel sizes, where uniform development is very critical.
U.S. Pat. No. 6,007,966 to Lin describes an alkali-developable, negative acting photosensitive composition which comprises a polymer binder, a photoinitiator, and an unsaturated photomonomer. The polymer binder is prepared from a reaction among a styrene-maleic anhydride resin containing repeating units of styrene and anhydride groups, an unsaturated compound containing at least one hydroxy group and at least three acrylic groups, and a saturated alco
Brewer Dan W.
Fowler Shelly
Limmer Timothy
Mayo Jonathon
Stroder Mike
Berman Susan
Brewer Science Inc.
Hovey & Williams, LLP
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