Abstract: The object of the present invention is to provide a plastic image fiber having a small optical transmission loss. The plastic image fiber comprises N (where N is an integer equal to or greater than 2) number of cores which are disposed within a cladding. The each of the cores has an index of reflection that continuously changes at a peripheral part of the core. The index of reflection at the peripheral part on a center side of the core is greater than an index of reflection at the peripheral part on a cladding side.

Abstract: The object of the present invention is to provide a plastic image fiber having a small optical transmission loss. The plastic image fiber comprises N (where N is an integer equal to or greater than 2) number of cores which are disposed within a cladding. The each of the cores has an index of reflection that continuously changes at a peripheral part of the core. The index of reflection at the peripheral part on a center side of the core is greater than an index of reflection at the peripheral part on a cladding side.

Abstract: Disclosed is a composite optical fiber which has high flexibility and is hard to break. The composite optical fiber comprises a larger-diameter optical fiber and smaller-diameter optical fibers each having a smaller diameter than that of the larger-diameter optical fiber, wherein the larger-diameter fiber and the smaller-diameter optical fibers are so arranged that the larger-diameter fiber is surrounded by the smaller-diameter optical fibers, and the smaller-diameter optical fibers that surround the larger-diameter optical fiber are made from a plastic material.

Abstract: Disclosed is a composite optical fiber which has high flexibility and is hard to break. The composite optical fiber comprises a larger-diameter optical fiber and smaller-diameter optical fibers each having a smaller diameter than that of the larger-diameter optical fiber, wherein the larger-diameter fiber and the smaller-diameter optical fibers are so arranged that the larger-diameter fiber is surrounded by the smaller-diameter optical fibers, and the smaller-diameter optical fibers that surround the larger-diameter optical fiber are made from a plastic material.

Abstract: In a transmission type screen and other optical devices formed by combining optical sheets such as a Fresnel lens sheet and a lenticular lens sheet, the generation of stray light and defective appearance caused by a friction-reducing agent are prevented. In the optical devices such as a transmission type screen 3 formed by combining a plurality of optical sheets such as a Fresnel lens sheet 1 and a lenticular lens sheet 2, a friction-reducing agent 20 is provided on a surface of at least one of the optical sheets at a thickness of 0.3 nm or more to 10 nm or less. A coating applicator 30 for the friction-reducing agent 20 includes: a transfer roller 31; coating liquid-supplying means 32 for supplying the coating liquid 20 to the transfer roller 31; and scraping means 35 for adjusting the thickness of the coating liquid 20 adhering to the transfer roller 31. In the coating liquid 30, the surface roughness Ra (JIS B 0601-1982) of the transfer roller 31 is set to 0.01 to 1 ?m.

Abstract: In a transmission type screen and other optical devices formed by combining optical sheets such as a Fresnel lens sheet and a lenticular lens sheet, the generation of stray light and defective appearance caused by a friction-reducing agent are prevented. In the optical devices such as a transmission type screen 3 formed by combining a plurality of optical sheets such as a Fresnel lens sheet 1 and a lenticular lens sheet 2, a friction-reducing agent 20 is provided on a surface of at least one of the optical sheets at a thickness of 0.3 nm or more to 10 nm or less. A coating applicator 30 for the friction-reducing agent 20 includes: a transfer roller 31; coating liquid-supplying means 32 for supplying the coating liquid 20 to the transfer roller 31; and scraping means 35 for adjusting the thickness of the coating liquid 20 adhering to the transfer roller 31. In the coating liquid 30, the surface roughness Ra (JIS B 0601-1982) of the transfer roller 31 is set to 0.01 to 1 ?m.

Abstract: In a method of manufacturing a plastic optical fiber by heating and drawing either one end portion of a transparent plastic rod, a plastic optical fiber having a cross sectional form approximately similar to the cross sectional form of the transparent plastic rod, the transparent plastic rod is heated by exposing near infrared ray which is radiated from a near infrared ray source. This can prevent the plastic optical fiber from causing to blow many bubbles on the surface and heat degradation to allow the plastic optical fiber to be obtained with a high quality.

Abstract: In a method of manufacturing a plastic optical fiber by heating and drawing either one end portion of a transparent plastic rod, a plastic optical fiber having a cross sectional form approximately similar to the cross sectional form of the transparent plastic rod, the transparent plastic rod is heated by exposing near infrared ray which is radiated from a near infrared ray source. This can prevent the plastic optical fiber from causing to blow many bubbles on the surface and heat degradation to allow the plastic optical fiber to be obtained with a high quality.

Abstract: In a type of continuous casting of steel in which a straight mold is employed and a cast strand is guided while being bent, molten steel is continuously teemed into said straight mold; an unsolidified cast strand with a solidified shell formed on it is guided substantially vertically downward within a range from 3 to 7m from the meniscus of molten steel in said straight mold; then, said unsolidified cast strand being in the vertical position is guided within a range from 1 to 4m while being bent at multiple points by gradually decreasing the radius of curvature of said cast strand for each of successively arranged pairs of bending rollers; then the solidification of said unsolidified cast strand thus bent at multiple points is completed before a spot-straightening point while further guiding said cast strand along a constant curvature, the track length of said constant curvature guide being within a range from 35 to 85% of the length from said meniscus of molten steel in said straight mold up to said spot-str

Abstract: This invention relates to an improved mold for continuous casting process, wherein a metallic material having cooling capacity of 0.1 to 0.7 [cal/(cm.sup.2 ..degree. C .sup.. .sqroot. sec)] and thermal conductivity (.lambda.) of 0.3 to 0.7 [cal/(cm.sup.. sec.sup...degree. C)] is used as a mold whereby surface checkings such as tortoise shell patterns or cracks are prevented from occuring.