Method of making liquid crystal display

Abstract: A method of making a liquid crystal display comprises the steps of injecting a liquid crystal into a liquid crystal container (3) through a liquid crystal inlet (4) provided on the liquid crystal container, and sealing the liquid crystal inlet with a sealant containing particles having a diameter which is 0.8 to 1.5 times the thickness of a liquid crystal layer in the liquid crystal container.

Description: This invention relates to a method of making a liquid crystal display, and in particular, to a method for sealing a liquid crystal inlet through which liquid crystal is injected into a liquid crystal container. In recent years, liquid crystal displays have been increasingly used in various types of electronic equipment. A liquid crystal display is, for example, composed of a liquid crystal container, in which a liquid crystal is injected. The liquid crystal container comprises two transparent electrode substrates, each having a transparent electrode formed on one surface thereof, facing each other with a small distance between them, which are sealed around the circumference. In such a liquid crystal display, the uniformity of the liquid crystal display screen is a critical factor for display performance. In a TN-type liquid crystal display, for example, a difference in the thickness of the liquid crystal container will cause color irregularity to occur when no electric field is applied in a normally black mode, and will also cause differences in electro-optic properties to occur, resulting in unsatisfactory display quality. Therefore, the unevenness in the thickness of the liquid crystal chamber should be within ± 0.2 micrometres. Although conventional liquid crystal chambers use spherical spacers of glass or plastic between the two transparent electrode substrates facing each other to keep the thickness of the liquid crystal cell uniform, the transparent electrode substrates may be deformed during the baking of the sealant used around the circumference of the liquid crystal container, and also by the entrance of foreign matter into the container. It was difficult to obtain liquid crystal containers of a uniform thickness. This disadvantage becomes more significant with increases in the chamber size, and particularly, the thickness of the liquid crystal container tends to be larger than the diameter of the spacers at the central portion. To solve such a problem, a method has been adopted to assure uniform thickness of the liquid crystal container by pressurizing the liquid crystal container after injecting the liquid crystal, in the direction in which the transparent electrode substrates are stacked, under a pressure of about 150g/cm2 for about one hour, and by sealing the liquid crystal inlet with a sealant such as an ultraviolet curing resin. By the above described method, however, although the thickness of the liquid crystal container may be made uniform throughout, the sealant may permeate into the display area of the liquid crystal container or to the vicinity thereof in 10 to 20 seconds after sealing the liquid crystal inlet, resulting in low yields. This problem was difficult to solve even if a sealant with high viscosity is used. This invention intends to solve the above described problem, and it is the object of this invention to prevent the sealant from permeating into the display area of the liquid crystal container or the vicinity thereof when the liquid crystal inlet of the liquid crystal container is sealed, and to provide a method of making a liquid crystal display which can effectively achieve a high yield. The present invention is disclosed in the attached claims. The method of making a liquid crystal display according to this invention is characterized by the steps of injecting a liquid crystal through a liquid crystal inlet provided on a liquid crystal container comprising two parallel substrates, and sealing said liquid crystal inlet using a sealant containing particles having a diameter which is 0.8 to 1.5 times the thickness of the liquid crystal layer defined by said substrates. According to the method of making a liquid crystal of this invention, the liquid crystal inlet is sealed with the sealant containing particles having a diameter which is 0.8 to 1.5 times the thickness of the liquid crystal layer in the liquid crystal container, and spherical matters function to prevent the sealant from entering into a display area of the liquid crystal chamber or the vicinity thereof when the liquid crystal inlet is sealed. Therefore, there are extremely few opportunities for the sealant to enter in the display area of the liquid crystal container or its vicinity, and the yield of the product is effectively improved. The effectiveness of this invention is especially high when an ultraviolet curing resin and the like is used as the sealant, because such a sealant has high tendency to permeate into the display area of the liquid crystal container. If the diameter of particles mixed in the sealant exceeds 1.5 times the thickness of the liquid crystal layer, it is difficult for the particles to enter into the liquid crystal container through the inlet; and if the diameter is smaller than 0.8 times the thickness of the liquid crystal layer, the sealant permeates easily into the display area of the liquid crystal container. An embodiment of the invention will now be described with reference to the accompanying drawings wherein: Fig. 1 is a perspective view illustrating one embodiment of a method of making a liquid crystal display according to this invention. Fig. 2 is a cross-sectional view of the liquid crystal display shown in Fig 1. Fig. 3 is a cross-sectional view of the liquid crystal inlet when it is being sealed in accordance with the making method of this invention. Fig. 4 if a front view of the liquid crystal inlet shown in Fig. 3. Fig. 1 through Fig. 4 illustrate one embodiment of a method of making a liquid crystal display according to this invention. In this embodiment, a liquid crystal 5 is injected through a liquid crystal inlet 4 into a liquid crystal container 3, which is composed of two transparent electrode substrates 1a and 1b spaced at a distance of 10 microns from each other, which is to be the thickness of a liquid crystal layer, and sealed with a sealant 2 around the circumference. The liquid crystal container 3 is then pressurized for about one hour under a pressure of about 150g/cm2 from the direction in which the transparent electrode substrates 1a and 1b are stacked. Then, the liquid crystal inlet 4 is sealed. As the sealant, an ultraviolet curing resin UV-1000 (Sony Chemical Co. Ltd.) containing Micropearl (Sekisui Fine Chemicals Co., Ltd.) which are the particles 6 having a diameter of 11 micrometres was used. The ratio of the ultraviolet curing resin to Micropearl was 1:0.05 by weight. After sealing the liquid crystal inlet 4, ultraviolet ray is irradiated onto the sealant for about 30 seconds to cure it. The liquid display thus produced was checked and no sealant permeation was observed in the display area or its vicinity. As the reliability test, a heat cycle test from -40°C to +100°C was performed for 100 hours, and no abnormality such as the flowout of the sealant was observed. Furthermore, Micropearl with a particle diameter of 9.5 micrometres was used to mix with the sealant under the same conditions, and the same results were obtained. This invention in not limited to the embodiment described above, but various modifications may be performed within the scope of this invention as defined by the appended claims. In the above embodiment, for example, glass fibers may be used in place of Micropearl to obtain the same results. Although an ultraviolet curing resin was used in the above embodiment, this invention is not limited thereto, and the same effect will be achieved for example by a silicone-based sealant (normal temperature curing). Moreover, this invention is not limited to the thickness of the liquid crystal layer in the liquid crystal container of the embodiment described above, or to the materials of the liquid crystals. As described above, according to the method of making a liquid display of this invention, the use of a sealant containing particles having diameters 0.8 to 1.5 times the thickness of the liquid crystal layer in a liquid crystal container effectively stops the permeation of the sealant into a display area of the liquid crystal container or its vicinity on sealing the liquid crystal inlet of the liquid crystal container. Therefore, the opportunity for the sealant to permeate into the display area of the liquid crystal container and its vicinity is greatly reduced, and the yield of the product is effectively improved.

Claims: A method of making a liquid crystal display, comprising the steps of injecting a liquid crystal into a liquid crystal container (3) comprising two parallel substrates (1a,1b) through a liquid crystal inlet (4) provided on said liquid crystal container, and sealing said liquid crystal inlet with a sealant containing particles (6) having a diameter which is 0.8 to 1.5 times the thickness of the liquid crystal layer (5) defined by said substrates. A method according to claim 1, wherein the sealant comprises ultraviolet curing resin. A method according to claim 2, wherein the ratio of resin to particles is 1:0,05 by weight. A method according to claim 1, wherein the sealant comprises a silicone based sealant. A method according to any of the preceding claims, wherein the diameter of the particles is between 9,5 to 11 micrometres and the thickness of the crystal layer is 10 micrometres. A method according to any of the preceding claims, wherein the particles comprise glass fibers.

Inventors: NAKANO TETSUYA, SUZUKI SHUNJI, TERADA KENJI, TOMII HITOSHI, NAKANO, TETSUYA, SUZUKI, SHUNJI, TERADA, KENJI, TOMII, HITOSHI
Applicants: IBM, TOSHIBA KK, INTERNATIONAL BUSINESS MACHINES CORPORATION, KABUSHIKI KAISHA TOSHIBA
Application year: 1990
Main classification: G02F1
IPC codes: G09F9, G02F1