1. Technical Field
The present invention relates to a curable composition favorable for forming a color filter for use in liquid crystal display elements (LCD) and solid-state image pickup elements (such as CCD and CMOS), a color filter, and a method for manufacturing the color filter.
Further, the present invention relates to a curable composition which can be utilized in: three-dimensional photofabrication and holography; image forming material such as color filters, photoresists, planographic printing plate materials and color proofs; and photocurable materials such as inks, paints, and adhesives, coating agents, and dental materials. The invention also relates to a color filter using the curable composition, and a manufacturing method thereof.
2. Related Art
A color filter is an essential constituent of liquid crystal displays and solid-state image pickup elements.
Since liquid crystal displays are compact and provide equivalent or greater performance as display devices when compared with CRTs, therefore they are replacing CRTs as television screens, personal computer screens, or other display device. In recent years, the trend in development of liquid crystal displays from conventional monitor applications in which screens are of a relatively small size towards TV applications requiring a large scale screens and high image quality.
In applications of color filter for liquid crystal displays (LCD), the substrate size is being extended due to large size TV production, and curing at a low energy is desired in order to improve productivity when large substrates are used. In addition, in liquid crystal displays in TV applications, higher image quality is required as compared with the previous monitor applications. That is, an improvement in contrast and in color purity is required. For improving the contrast, regarding curable compositions used in manufacturing the color filters, a smaller particle size of coloring agents (organic pigments etc.) used is required (e.g. see Japanese Patent Application Laid-Open (JP-A) No. 2006-30541). Accompanying this, there is a tendency that the addition amount of dispersants for dispersing pigments is increased. In addition, for improving the color purity, content of the coloring agent (organic pigment) within the solid content of the curable composition is required to be higher. Therefore, there is a tendency that the content of photopolymerization initiators and photopolymerizable monomers within the solid content in the curable composition is decreased.
On the other hand, curing at a low energy is also desired in applications of color filters for solid-state image pickup elements. In addition, film patterns are getting thinner and, accompanying this, the concentration of pigments in such compositions is rising. Furthermore, in a pigment-based color filter, there is a tendency that the proportion of pigment dispersant in the composition increases as the pigments get finer. Due to these factors, in both liquid crystal display applications and in solid-state image pickup element applications, since the content of photopolymerization initiator and photopolymerizable monomers, which are necessary components for curing the curable composition, is restricted and as the concentration of the coloring agents is increased, there arises a problem that sensitivity is low, and sufficient curing is not obtained. This means that adhesion to the substrate is insufficient, and there are significant difficulties in forming the desired pattern. As a countermeasure to this problem, the technique of introducing a silane coupling agent for improving substrate adhesion (e.g. see JP-A No. 2006-30541 and JP-A No. H11-38226), and the technique of using a photopolymerization initiator having a particular functional group (e.g. see JP-A No. 2005-99488) are proposed, however in practice further improvement is desired.
In addition, since a curable composition containing a polyfunctional acrylate compound can be cured in a very short time with irradiation of rays of actinic energy such as ultraviolet rays, and is excellent in productivity, it has been conventionally used widely in three-dimensional photofabrication and holography, or as an image forming material in color filters, photoresists, and planographic printing plate materials and color proofs, in inks, paints, adhesives, coating agents and dental materials.
Examples of such the polyfunctional acrylate compound include polyfunctional acrylates such as polyethylene glycol diacrylate, trimethylolethane triacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, hexanediol acrylate, trimethylolpropane tri(acryloyloxypropyl) ether, tri(acryloyloxyethyl) isocyanurate; compounds obtained by adding ethylene oxide or propylene oxide to polyfunctional alcohols such as glycerin and trimethylolethane, followed by acrylation; urethane group-containing acrylates (e.g. see JP-A No. 5-170705, JP-A No. 11-193325, JP-A No. 2000-239332 and JP-A No. 2005-104842), polyester acrylates (e.g. see JP-A No. S48-64183, Japanese Patent Application Publication (JP-B) No. S49-43191, and JP-B No. S52-30490), polyfunctional acrylates such as epoxy acrylates which are reaction products of an epoxy resin and acrylic acid, and mixtures thereof.
In recent years, demand for such curable compositions is increasing further enhanced in the aforementioned applications, and compositions which are cured at lower energy, compositions which are cured faster, and compositions which form a finer image are required. Among these, since curable compositions for color filters, inks and paints contain coloring matter which absorbs rays of actinic energy such as ultraviolet rays, there is the problem that while the surface is cured, the inside is not sufficiently cured.
In applications of color filters for solid-state image pickup elements (CCD, CMOS, etc.), since a still higher resolution pattern is desired, and a film thickness of 1.2 μm or less is required, a large amount of coloring matter must be added to the curable composition, and there is a tendency that the proportion of polyfunctional acrylate is reduced. In addition, in applications of color filters for liquid crystal displays (LCD), the substrate size is increasing due to the production of large size TVs, and curing at a low energy is desired in order to improve productivity a large substrate is used. In addition, there is a tendency that with pigment getting finer in order to improve the contrast, the proportion of pigment dispersant in the composition is increased, and the proportion of polyfunctional acrylate is reduced. Due to this there is a problem that, in both solid-state image pickup element applications and LCD applications, sensitivity is low, and sufficient curing is not obtained. This means that adhesion to the substrate is insufficient, and fading occurs even at light-exposed portions, and there are significant difficulties in forming a desired pattern.