Abstract: A transmission type screen having a screen body constituted by at least one plastic sheet formed of a multiplicity of transparent plastic strands arranged in the shape of a sheet, each the strands being welded together at outer surfaces thereof. Each of the transparent strand may have a main portion and another portion different from the main portion in terms of optical effects. This transmission type screen is manufactured by spinning off the transparent strands from a spinning nozzle while aligning the strands; welding each adjacent over of the strands to form a sheet; and forming a screen body from at least one sheet obtained in this manner.

Abstract: A projection screen is comprised of a sheet formed by a multiplicity of light-transmitting plastic strands which strands are arranged and welded in parallel with one another. The width W (mm) of the screen and the pitch p (mm) of the strands meet the following condition (1):0.03.ltoreq.p.ltoreq.W/1000 (1)The radius of curvature R.sub.1 (mm) of the strand at a first side of the screen is determined by the following condition (2)0.5.times.p.ltoreq.R.sub.1 .ltoreq.p (2)The radius of curvature R.sub.2 (mm) of the strand at a second side of the screen meets the following condition(3):R.sub.2 .ltoreq.R.sub.1 (3).

Abstract: A transmission type screen having a screen body constituted by at least one plastic sheet formed of a multiplicity of transparent plastic strands arranged in the shape of a sheet, each the strands being welded together at outer surfaces thereof. Each of the transparent strand may have a main portion and another portion different from the main portion in terms of optical effects. This transmission type screen is manfactured by spinning off the transparent strands from a spinning nozzle while aligning the strands; welding each adjacent over of the strands to form a sheet; and forming a screen body from at least one sheet obtained in this manner.

Abstract: A multifilament type plastic optical fiber having a substantially rectangular cross-section and an islands-in-the-sea structure in which 100 to 10,000 islands are arranged in the sea, wherein the respective islands have a substantially circular cross-section and a core-sheath structure, the islands are arranged in a zigzag-stacked structure, the core occupaney ratio in the multifilament type optical fiber cores section is at least 50% and the brightness index value I which is defined by the following (1), is at least 4.5.times.10.sup.-2 : ##EQU1## wherein S stands for the core occupancy ratio in the multifilament type optical fiber, .alpha. stands for the transmission loss (dB/m) per meter of the multifilament type optical fiber, NA stands for the numeral apertures, and L stands for the length (m) of the used optical fiber.

Abstract: An endoscope comprising as an image-transmitting member a multifilament type plastic optical fiber, an object lens arranged on one end of the optical fiber and a device for guiding an image of an object transmitted to the other end of the optical fiber to an image-receiving portion, wherein the multifilament type plastic optical fiber has an islands-in-sea structure in which 50 to 10,000 light-transmitting core-sheath structure islands having a diameter of 5 to 200 .mu. are arranged in the sea so that the same positional relationship of the islands is maintained on both ends of the optical fiber, and the core occupancy ratio in the total cross-section of the optical fiber is at least 50%.

Abstract: A multifilament type plastic optical fiber having a substantially rectangular cross-section and an islands-in-the-sea structure in which 100 to 10,000 islands are arranged in the sea, wherein the respective islands have a substantially circular cross-section and a core-sheath structure, the islands are arranged in a sigzag-stacked structure, the core occupancy ratio in the multifilament type optical fiber cores section is at least 50% and the brightness index value I which is defined by the following (1), is at least 4.5.times.10.sup.-2 :I=S.multidot.NA.sup.2 .multidot.10.sup.-(.alpha.L/10) (1)wherein S stands for the core occupancy ratio in the multifilament type optical fiber, .alpha. stands for the transmission loss (db/m) per meter of the multifilament type optical fiber, NA stands for the numeral apertures, and L stands for the length (m) of the used optical fiber.

Abstract: An optical fiber array comprising a great number of multifilament type plastic optical fibers having a substantially rectangular peripheral sectional shape and including 10 to 10000 light-transmitting islands having a diameter of 5 to 200 .mu.m, which are densely arranged in the sea, wherein one ends of the multifilament type plastic optical fibers are arranged in one line or a plurality of lines and the other ends thereof are integrated in a substantially rectangular or substantially circular shape.

Abstract: A plastic optical fiber which is superior in the light transmission characteristics, particularly in those within a visible light region and also superior in heat resistance, and a process for producing the same are provided, which plastic optical fiber comprises a polycarbonate as its core material and a polymer as its cladding material having a refractive index lower than that of the core material, wherein the relationship between the light transmission loss L.sub.500 (dB/km) of the fiber as measured at a wavelength of 500 nm and that as measured at 660 nm being expressed by the following inequality:L.sub.500 <L.sub.660 +4,000.

Abstract: A multifilament type plastic optical fiber having a substantially uniform cross-section and an islands-in-sea structure, in which 10 to 10,000 islands are arranged in the sea, the respective islands have a substantially uniform cross-section having a diameter of 10 to 200.mu.

Abstract: There is provided a plastic optical fiber capable of exhibiting good light transmitting characteristics even at high temperatures, which comprises a core layer, a cladding layer, and a protective layer as basic consititutional units, wherein the protective layer has a heat distortion temperature [HDT] of at least 120.degree. C., a thickness of at least 10 .mu.m, and a cross-sectional area of at least 0.07 times the sum of cross-sectional areas of the core and cladding layers. There is also provided such a plastic optical fiber good in high-temperature light transmitting characteristics, which comprises a core layer, a cladding layer, and a protective layer as basic constitutional units and has a plastic coating layer having a silane-crosslinked structure provided as an outer layer thereof, wherein the protective layer has a heat distortion temperature [HDT] of at least 120.degree. C., a thickness of at least 10 .mu.m, and a cross-sectional area of at least 0.

Abstract: A process for the preparation of a multifilament optical fiber having 1,000 to 10,000 islands as optical filaments, which comprises using a composite spinning spinneret for the preparation of an islands-in-a-sea type multifilament fiber, which comprises at least three piled orifice plates including an orifice plate having many island-forming nozzle holes, an orifice plate having a sea-forming nozzle hole and an orifice plate having a filament-gathering nozzle hole, the nozzle hole of the orifice plate arranged just above the lowermost orifice plate having a trumpet-shaped opening extending toward the lower end face thereof and a sea component flow passage being formed between two orifice plates arranged just above the lowermost orifice plate, and supplying a thermoplastic polymer for forming cores of optical filaments from the island-forming nozzle holes and a sea-forming thermoplastic polymer from the sea-forming nozzle hole to effect composite spinning and gathering many filaments in the gathering nozzle ho

Abstract: An optical fiber assembly comprising at least two plastic optical fibers and an embedding material, said plastic optical fibers being arranged substantially in parallel to each other and embedded in said embedding material, wherein each plastic optical fiber comprises a core of polymer having a refractive index, n.sub.1, and a cladding of a polymer having a refractive index, n.sub.2, wherein the refractive indices n.sub.1 and n.sub.2 satisfy the following relationship [I]n.sub.1 -n.sub.2 >0.01 [I]The optical fiber assembly is prepared by extruding from a spinneret a plurality of optical fibers having a core-cladding structure and an embedding material of a polymer in three layers of core, cladding and embedding material, according to a melt-spinning method; arranging the optical fibers in parallel to each other before solidification thereof; and bonding the optical fibers together through the embedding material.

Abstract: Method for producing a crimped yarn in which a thermoplastic yarn is false twisted at a speed exceeding 300 m/min. by using a twisting tube comprising a friction twisting surface of wear-resistant material having a high frictional coefficient, the false twisting being performed under a particular relationship among the yarn speed, surface speed of the twisting tube, denier of the yarn, and the yarn tension at the inlet and outlet sides of the twisting tube.

Abstract: There is provided a filament of improved light transmission having a sheath-core composite structure formed of a methyl methacrylate polymer core material and a fluorine-containing polymer sheath material. The light transmitting filament is characterized in that the methyl methacrylate polymer core material is prepared by the specific procedure of continuous bulk polymerization and subsequent removal of volatile contents, wherein the polymerization is performed in a continuously and thoroughly stirred reaction vessel at a low catalyst concentration and a relatively high temperature and with improved conversion. The light transmitting filament possesses an absorption coefficient (k) of no greater than 6 .times. 10.sup.-.sup.3 cm.sup.-.sup.1.