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Patent Issued for Color Filter Manufacturing Method, Patterned Substrate Manufacturing Method, and Small Photomask

September 12, 2014



By a News Reporter-Staff News Editor at Entertainment Newsweekly -- A patent by the inventors Ikeda, Takeshi (Tokyo, JP); Aoki, Eishi (Tokyo, JP); Harada, Genki (Tokyo, JP), filed on November 17, 2010, was published online on August 26, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8815477 is assigned to Toppan Printing Co., Ltd. (Tokyo, JP).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to methods of manufacturing a color filter and patterned substrate for use in, e.g., a field emission display device, fluorescent display device, plasma display (PDP), and liquid crystal display device. The present invention particularly relates to a color filter manufacturing method using a plurality of small photomasks, a patterned substrate manufacturing method, and the small photomask.

"A color filter for use in a color liquid crystal display device or the like is an essential member of the color liquid crystal display device or the like, and has functions of improving the image quality of the liquid crystal display device and giving each pixel a corresponding primary color. A filter segment or black matrix forming this color filter is manufactured as follows. That is, after a glass substrate or the like is coated with a photosensitive material, the excess solvent is removed by drying. Subsequently, the photosensitive material is irradiated with an active energy line via a photomask for pixel formation by, e.g., proximity exposure using an ultra-high-pressure mercury lamp. Consequently, the portion irradiated with the energy is cured (negative type) or the alkali solubility is increased (positive type), thereby removing a portion to be dissolved by an alkali solution or the like. A color filter is manufactured by repeating this process for each color.

"Recently, the color liquid crystal display devices have formed a large market of liquid crystal color television displays, car navigation displays, and notebook PCs integrated with liquid crystal displays. The color liquid crystal display devices are also widely used as desktop PC monitors and television monitors that offer energy- and space-saving features. With the spread of the color liquid crystal display devices in general markets, demands for improving the color reproduction characteristics are increasing.

"Also, to increase the contrast, a black matrix is generally formed between filter segments of the individual colors of the color filter. Recently, to solve the environmental problems, decrease the reflection, and reduce the cost, a resin black matrix formed by dispersing a light-shielding dyestuff in a resin is attracting more attention than a chromium metal black matrix. However, the resin black matrix has the problem that the light-shielding performance (optical density) is lower than that of the chromium metal black matrix.

"To improve the color reproduction characteristics of the color filter and the light-shielding performance of the black matrix, it is necessary to increase the content of a dyestuff in a photosensitive coloring composition or increase the film thickness. However, if the content of a dyestuff is increased in a conventional method such as proximity exposure by which ultraviolet light or the like from an ultra-high-pressure mercury lamp is used as an active energy source as a light source, the problems such as the decrease in sensitivity and the deterioration of the development properties and resolution arise. Also, if the film thickness is increased, the exposure light does not reach the bottom of the film, and this poses the problems that, e.g., the linearity and sectional shape of the filter segments and black matrix deteriorate. Note that in the description of the present invention, the filter segments refer to individual coloring pixels of red, green, and blue, and the black matrix refers to a light-shielding black thin-line pattern for dividing these filter segments. Note also that light (a laser beam) from a laser as an exposure light source will simply be referred to as a laser hereinafter.

"On the other hand, with the spread of the color liquid crystal display devices, demands for reducing the cost of the color filter are increasing. In the above-mentioned proximity exposure method, an ultra-high-pressure mercury lamp is generally used as a light source, and illuminating light whose illumination unevenness is eliminated by a fly-eye lens or microlens is converted into parallel light by a collimator lens. A photomask and a substrate on which a photosensitive resin layer such as a color resist is formed are arranged with a spacing of a few ten .mu.m to a few hundred .mu.m. The parallel light is emitted from above the photomask, thereby transferring the pattern of the photomask onto the substrate.

"As described above, the proximity exposure method using an ultra-high-pressure mercury lamp requires no projecting exposure system. Since the apparatus configuration is very simple, the apparatus cost is low. Also, the same substrate area as the photomask can be exposed by one shot. Therefore, the method has the advantage that the tact is short when using a large photomask having almost the same size as that of the substrate. However, as the screen size of a product using the color filter increases, or to attach a number of large screens to one large-sized transparent substrate, the size of the photomask must further be increased. Since upsizing the photomask increases the manufacturing cost, it is important to reduce the cost of the photomask.

"As a method of reducing the manufacturing cost of the photomask, patent reference 1 has disclosed a maskless exposure method that uses a laser as a light source and forms a two-dimensional image by relative scanning while modulating the light based on image data. Patent reference 2 has disclosed a laser exposure apparatus to be used to form the black matrix of the color filter. Since the laser exposure method can form pixels without using any expensive photomask, a large cost down can be expected. However, the laser exposure method using no photomask makes it difficult to develop a spatial modulation element to be used in exposure and a photosensitive resin composition suitable for the laser. In addition, fine patterns having good shapes are difficult to form. Furthermore, in the method described in patent reference 1, the exposure sensitivity must be increased by forming an oxygen-blocking film.

"Patent reference 3 has disclosed an inkjet method capable of simultaneously printing three colors, i.e., R, G, and B by using coloring resin compositions of these colors as inks. Since the three colors can be printed at the same time, wastage of the materials is little. In addition, a reduction in environmental load and a large cost down can be expected because the pixel formation process is shortened. However, the inkjet method has the problem that a coloring layer printed by an ink ejector has not a flat shape but a projecting shape."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Problems to be Solved by Invention

"The present invention has been made to solve the above-mentioned problems, and has as its object to provide a color filter manufacturing method capable of forming filter segments and a black matrix superior in linearity and sectional shape and having a sufficient film thickness as a color filter, capable of downsizing an expensive photomask in order to reduce the cost of the photomask, and also capable of suppressing the decrease in productivity, and provide a patterned substrate manufacturing method and a small photomask.

"The present invention also proposes a technique capable of setting an arbitrary exposure amount, thereby solving the problem that a photosensitive resin layer is insufficiently photocured owing to the wavelength of an exposure light source used or the sensitivity characteristics of the photosensitive resin layer and wrinkled by annealing in a post-process, and the problem that it is difficult to form structures having different heights as liquid crystal spacers by performing pattern exposure once.

"Means for Solving the Problems

"According to the extensive studies made by the present inventor, a photomask can be downsized by performing proximity exposure via a photomask for pixel formation by using a laser as a light source. It is also possible to suppress the decomposition of a photosensitive resin coating film caused by the abrasion phenomenon and form filter segments having a sufficient film thickness, by performing exposure such that the cumulative exposure amount is 1 to 150 mJ/cm.sup.2. The present invention has been made based on these findings.

"A first aspect of the present invention is a color filter manufacturing method for forming a filter segment and a black matrix by repeating at least: (a) a coating step of coating a substrate with a photosensitive resin layer made of a photosensitive resin composition; (b) a pattern exposure step of curing the photosensitive resin layer on the substrate by pattern exposure; © a developing step of removing an unexposed (uncured) portion of the photosensitive resin layer by developing the exposed photosensitive resin layer; and (d) a sintering step of thermosetting the developed photosensitive resin layer, in this order a plurality of number of times, characterized in that in the exposure step (b), a laser is used as a light source, a plurality of photomasks each having a pattern region smaller than a whole exposure region on the substrate are used as photomasks for pixel formation, and proximity exposure is performed by repetitively emitting the laser a plurality of number of times via the photomasks such that a cumulative exposure amount is 1 to 150 mJ/cm.sup.2.

"According to the second aspect of the present invention, in the color filter manufacturing method according to the first aspect mentioned above, a frequency of the laser is 1 to 500 Hz.

"According to a third aspect of the present invention, in the color filter manufacturing method according to the first aspect mentioned above an energy density per pulse of the laser is 0.1 to 1,000 mJ/cm.sup.2, and a pulse width is 0.1 to 3,000 nsec.

"According to a fourth aspect of the present invention, in the color filter manufacturing method according to the first aspect mentioned above in the exposure step (b), the photosensitive resin layer is photocured by emitting the laser such that the cumulative exposure amount is 1 to 50 mJ/cm.sup.2.

"According to a fifth aspect of the present invention, in the color filter manufacturing method according to the first aspect mentioned above a molar absorption coefficient (.epsilon.308) at 308 nm of a photopolymerization initiator used in the photosensitive resin composition is larger than a molar absorption coefficient (.epsilon.365) at 365 nm.

"According to a sixth aspect of the present invention, in the color filter manufacturing method according to the first aspect mentioned above a ratio (I/M) of a mass (I) of a photopolymerization initiator to a mass (M) of a monomer used in the photosensitive resin composition is 0.01 to 0.45.

"A seventh aspect of the present invention is a patterned substrate manufacturing method comprising: (a) a coating step of coating a rectangular substrate with a photosensitive resin layer made of a photosensitive resin composition; and (b) a pattern exposure step of exposing the photosensitive resin layer on the substrate by pattern exposure while moving the substrate in a longitudinal direction, characterized in that in the exposure step (b), a laser is used as an exposure light source, a plurality of small photomasks for pattern formation are arranged in a widthwise direction of the substrate, and proximity exposure by which the same pattern is repetitively irradiated with the laser is performed.

"According to an eighth aspect of the present invention, in the patterned substrate manufacturing method according to the seventh aspect mentioned above, the plurality of small photomasks arranged in the widthwise direction comprise two rows of the small photomasks arranged in a moving direction of the substrate.

"According to a ninth aspect of the present invention, in the patterned substrate manufacturing method according to the seventh aspect mentioned above, the small photomask is obtained by forming not less than two different types of patterns in the same mask plane in a moving direction of the substrate, and one of the patterns is selectively exposed in accordance with the type.

"Another aspect of the present invention is the patterned substrate manufacturing method according to the seventh aspect mentioned above, characterized in that the pattern exposure is performed by changing an exposure amount by changing the number of shots of exposure from the laser.

"Another aspect of the present invention is a small photomask for use in a color filter manufacturing method according to the first aspect mentioned above, characterized in that not less than two different types of patterns are formed in the same mask plane.

"Effects of Invention

"In the present invention, a photosensitive resin composition is cured or exposed within a very short time by emitting a laser having a specific wavelength at a low output for a short time period. Therefore, filter segments and a black matrix superior in shape can be formed at a low cost by using a small photomask. Also, since a plurality of small photomasks are used together, patterns can be formed with high accuracy without decreasing the productivity. In particular, efficient laser exposure can be performed without decreasing the throughput by arranging a plurality of small photomasks along the widthwise direction of a large-sized rectangular transparent substrate (a substrate coated with a photosensitive resin). Furthermore, the technique of the present invention can largely reduce the cost of the photomask. Since small photomasks are arranged in the widthwise direction of the rectangular substrate, the number of small photomasks can be made smaller than that when arranging them in the longitudinal direction of the rectangular substrate.

"In addition, since proximity exposure is performed such that the cumulative exposure amount is 1 to 150 mJ/cm.sup.2, it is possible to suppress the decomposition and evaporation of a photosensitive resin layer caused by the abrasion phenomenon, and manufacture filter segments and a black matrix having a sufficient film thickness, or a patterned substrate including, e.g., TFTs. The techniques described in the present invention are applicable not only to the manufacture of a liquid crystal display substrate, but also to the manufacture of patterned substrates for, e.g., a plasma display, organic EL display substrate, printed circuit board, and solar cell.

"Furthermore, when forming filter segments by using a photosensitive resin layer or forming a structure or the like on a color filter or on a substrate including TFT elements, the present invention has a large effect of forming the target filter segments or structure with a high degree of freedom by performing pattern exposure with different exposure amounts by changing the number of shots from a laser source. By performing divisional exposure by using a photo-alignable organic material, a liquid crystal alignment film pattern having a plurality of alignment regions can be formed. Alternatively, phase-difference patterns in which the retardation is controlled for each color can be formed by using a liquid crystal polymer whose retardation is adjustable by laser exposure. In the pattern exposure of a photosensitive resin layer containing a blue pigment as a coloring material, the problem of the formation of wrinkles caused by insufficient curing can be eliminated by increasing the number of shots of exposure from the laser source in a peripheral portion of the effective screen or on the end face of the substrate. Similarly, spacers having different heights for adjusting the gap between liquid crystal cells can be formed by adjusting the number of shots of exposure from the laser source."

URL and more information on this patent, see: Ikeda, Takeshi; Aoki, Eishi; Harada, Genki. Color Filter Manufacturing Method, Patterned Substrate Manufacturing Method, and Small Photomask. U.S. Patent Number 8815477, filed November 17, 2010, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8815477.PN.&OS=PN/8815477RS=PN/8815477

Keywords for this news article include: Television, Toppan Printing Co., Toppan Printing Co. Ltd.

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Source: Entertainment Newsweekly


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