1. Technical Field
The present invention relates to a color filter ink set, a color filter, an image display device, and an electronic device.
2. Related Art
Color filters are generally used in liquid crystal display devices (LCD) and the like that display color. A color filter is generally provided with three colors of colored portions that correspond to the three primary colors of light, which are red, green and blue, and in a liquid crystal display device provided with the color filter, color display is performed by adjusting the transmittance of light in the three colors of colored portions.
Color filters have conventionally been manufactured using a so-called photolithography method in which a coating film composed of a material (color layer formation composition) that includes a colorant, a photosensitive resin, a functional monomer, a polymerization initiator, and other components is formed on a substrate, and then photosensitive processing for radiating light via a photomask, development processing, and the like are performed. In such a method, the color filters are usually manufactured by repeating a process in which a coating film corresponding to each color is formed on substantially the entire surface of the substrate, only a portion of the coating film is cured, and most of the film other than the cured portion is removed, so that there is no color overlap. Therefore, only a portion of the coating film formed in color filter manufacturing remains as a color layer in the finished color filter, and most of the coating film is removed in the manufacturing process. Therefore, not only does the manufacturing cost of the color filter increase, but the process is also undesirable from the perspective of resource saving.
Methods have recently been proposed for forming the color layer of a color filter through the use of an inkjet head (droplet discharge head) (see Japanese Laid-Open Patent Application No. 2002-372613, for example). In such a method, because the discharge position and the like of droplets of the material (color layer formation composition) used to form the color layer are easily controlled, and waste of the color layer formation composition can be reduced, the environmental impact can be reduced, and manufacturing cost can also be minimized. The same composition of liquid medium is generally used in each color of ink in an ink set for a color filter.
The colored portions of each color in a color filter include the corresponding color of pigment. C. I. Pigment Green 36 is generally used as the pigment in green-colored ink (green ink) for forming a green colored portion. C. I. Pigment Green 36 (green pigment) and a yellow pigment such as C. I. Pigment Yellow 150 are used in the green ink for hue adjustment and other purposes. Through the use of C. I. Pigment Yellow 150 (yellow pigment), effects can be anticipated whereby the transmittance of light is enhanced (a bright panel is obtained) while the content ratio of C. I. Pigment Green 36 (green pigment) is relatively reduced, and the color reproduction range is maintained. In order for the effects of using C. I. Pigment Yellow 150 (yellow pigment) to be adequately demonstrated, C. I. Pigment Yellow 150 (yellow pigment) must be included at a relatively high concentration (e.g., 2.0 to 5.0 wt %) in the green ink. There is relatively little effect on the viscosity of the ink when the content ratio of C. I. Pigment Yellow 150 (yellow pigment) in the ink is relatively low, but when the content ratio is relatively high, the viscosity of the ink abruptly increases. As a result, when the green ink includes a relatively high concentration of C. I. Pigment Yellow 150 (yellow pigment), the viscosity of the green ink is high relative to the viscosities of the other colors of ink, and problems occur in that there is a large difference between the discharge quantities of each color of ink. Since the discharge quantity easily becomes unstable in the green ink, unevenness of color easily occurs between regions of the color filter. Since the droplet discharge device (industrial) used for color filter manufacturing is entirely different from what is used for a printer (consumer-level), and the droplet discharge device is used for mass production and droplet discharge onto large-scale workpieces (substrates), for example, there is a need to discharge large quantities of droplets for long periods of time. Because the droplet discharge device is used under such harsh conditions, variation of the droplet discharge quantity occurs more readily than in a consumer-level printer, but when such variation of the discharge quantity occurs, fluctuations in characteristics occur among numerous manufactured color filters, fluctuation of color saturation occurs between regions of a color filter, and the reliability of the color filter as a product is significantly reduced.
There has recently been a tendency towards using color filter inks having a high colorant content in order to maintain a wider color reproduction range in a color filter, but such problems as those described above become more severe as the content ratio of the colorant is increased.
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