INK RIBBON SUBSTRATE

Abstract: A substrate of an ink ribbon to be used in an impart printer wherein the fused part of the ribbon has excellent durability. The substrate is characterized in that at least either the warp or the weft is a core/sheath type composite yarn composed of a core made from a polyamide and a sheath made from another polyamide having a melting point lower than that of the former.

Description: The present invention relates to a base fabric for an ink ribbon which provides an ink ribbon used for an impact-type printer and exhibits excellent durability on the welded part. Recently, as an ink ribbon used for an impact-type printer, the conventional spool types have been decreasing and products wherein a long tape-like ink ribbon is folded and stored in a cassette have been increasing. However, in such ink ribbons, both ends are welded (adhered) by means of an ultrasonic welder to be made into an endless-type product and the life of the welded part exerts an influence upon the life of the ink ribbon. Namely, as the ink ribbon receives an impact by a head pin of a printer during printing and is grandually destroyed, the welded part exhibits lower durability than that for the ordinary part of a base fabric. Especially these days, with remarkable increase in speeding up and impacting up of printers, remarkable improvement on durability of the welded part of the ink ribbon has been earnestly desired. As a means for improving durability of the welded part, a technique wherein a thermoplastic synthetic resin layer with a melting point lower than that of the base fabric was placed between two ink ribbons and was welded, was proposed in Japanese Patent Publication No. 13,431/1982. However, problems still existed in that the degree of improvement in durability of the welded part was not practically sufficient even by this method and effecting the welding was not easy either; namely it is the present position that sufficient improvement in durability of the welded part in order to cope with speeding up and impacting of a printer has not been realized. The present invention provides a base fabric for an ink ribbon with good durability of the welded part. The present invention uses the following means for realizing such a purpose. Namely, the base fabric for an ink ribbon of the present invention is characterized by a constitution wherein at least one yarn of the warp and weft constituting the base fabric is constituted of core/sheath-type composite fibers wherein the sheath component consists of a polymer with a melting point lower than that of the core component. An example of favorable embodiments is the case wherein the core component of said core/ sheath-type composite fiber is a polyamide polymer and the sheath component is a polyamide polymer with a melting point lower than that of said polyamide polymer. Thus, the present invention has a base fabric for an ink ribbon which is formed with a fiber having weldability as a single fiber unit. Namely, a base fabric woven by using a core/sheath composite fiber wherein the inner layer (the core) of the single fiber is constituted of a high melting point polymer and the surface layer part (the sheath) is constituted of a low melting point polymer as at least one of the warp and the weft yarns, exhibits extremely high adhesive force by welding and no extreme decrease in strength by welding and durability of the welded part is remarkably improved. As the polymer used for the core of the present invention, polyamides and polyesters are representative and especially, as the polyamides, nylon 46, nylon 66, nylon 610, nylon 11 etc., are cited and as polyamides used for the sheath, such a nylon that has a melting point lower than that of the core polymer, preferably 10-120°C lower and more preferably 20-100°C lower among these nylons, for example, a copolymer wherein an amide raw material for tha above described nylon is copolymerized with one or more different kinds of amide raw materials can be used. As the polyesters, polyethylene terephthalate, polybutylene terephthalate or copolymers thereof are used as the core or the sheath components. The composite ratio of the sheath in the core/sheath composite fiber is preferably 10-90% by weight of the composite fiber from the viewpoint of improvement of durability of the welded part and more preferably, 20-80%. Beyond the range of 10-90% the effect for improving durability of the welded part decreases. The melting point of the sheath compmnent is preferably 10-120°C lower than that of the core compmnent from the viewpoint of durability of the welded part and more preferably 20-100°C lower. When the difference in melting point is less than 10°C, the effect of durability of the welded part decreases and when the difference exceeds 120, spinnability of the core/sheath composite fiber decreases. The relative viscosity measured in sulfuric acid of the polymer constituting the core or the sheath component is preferably 2.4-3.8 from the viewpoint of durability of the welded part. In addition, the content of titanium oxide incorporated in the fiber is preferably 0.15% or less but it is not restricted by this limitation. On the other hand, the denier of the warp or weft is preferably 5-150 denier. In addition, the denier of a monofilament constituting such a yarn is preferably 0.6-3.0 denier being generally used for forming a thin base fabric. When the denier of the monofilament is less than 0.6 denier, there exists a tendency that durability of the base fabric part decreases and when the denier of a monofilament exceeds 3.0 denier, clarity of printing tends to become worse. Both the warp and weft may be non-twisted but additional twisting in the range of 150-700 T/m is preferable and in the range of 200-600 T/m is more preferable from the viewpoint of weaving characteristics. As a fabric texture for such a base fabric an ink ribbon, plane weave, inductive plane weave, twill weave, satin weave etc., are used but it is not specifically restricted by them. As the weaving density of such a fabric, the warps are preferably 5.12 - 23.6 yarns/mm (130-600 yarns/in), more preferably 5.51 - 21.7 yarns/mm (140-550 yarns/in) and the wefts are preferably 8.94 - 15.7 yarns/mm (100-400 yarns/in), more preferably 4.33 - 13.8 yarns/mm (110-350 yarns/in). The base fabric for an ink ribbon thus obtained is usually performed by scouring and setting as a finishing operation after weaving. Preferably, it is scoured by liquid flow and is set for finishing in the range of 160-240°C by means of a pin tenter. Thereafter, the base fabric is adhered (impregnated) with an appropriate amount of an ink material such as a conventional ink and is welded to form an endless ink ribbon. Welding is usually performed by welding both ends of a base fabric for an ink ribbon by means of an ultrasonic welder. On the base fabric for an ink ribbon of the present invention, a stable welding can be accomplished in spite of the existence of an oil ink even if welding is performed under a condition wherein the fabric is impregnated with the oil ink as described above. On the contrary, in a method wherein welding is performed by placing low melting point sheet between the welding parts as the conventional technology, there exists a limitation on improvement of durability of the welded part probably because the welded area is not made large enough. It is a matter of course that the base fabric for an ink ribbon of the present invention can be a product which is treated with an appropriate after-treatment such as high pressure fluid treatment, plasma treatment, surface active agent treatment and resin processing. Best embodiments of the invention will now be explained in more detail hereinbelow with reference to the following. (1) The method for evaluation of durability of the welded part of the base fabric in Examples was performed by the following method. A prepared base fabric for an ink ribbon was cut by fusing into a width of 13 mm and was cut once by scissors into a whole length of 13 m and then, these fabrics were coated with 22 wt.% oil ink (CBK-14 manufactured by Sakata Inks Co., Ltd.) based on the weight of the base fabric and then, were welded by means of an ultrasonic welder (M-8400 manufactured by Branson Co., Ltd.). Seven welded parts were provided in an approximately equal distance in the ink ribbon to prepare an endless ink ribbon. This ink ribbon was stored in a cassette for 24 pin dot printer (UP-130K manufactured by Espon Co., Ltd.) and this cassette was set in the above described printer and English letters and numerals were printed and the number of printed letters in which a pinhole occurred on the welded part was counted and the mean value was taken as the durability of the welded part of the base fabric. o ○ : 1.11 million letters or more o : 0.91-1.10 million letters ▵ : 0.71-0.90 million letters x : 0.70 million letters or less Examples 1-12 and Comparative Example 1 Nylon filament yarn each having a melting point shown in Table 1, namely, for a core/sheath-type composite fiber wherein a nylon 66 polymer with a relative viscosity measured in sulfuric acid of 2.85 was used as the core and a nylon 6 polymer with a relative viscosity measured in sulfuric acid of 2.80 was used as the sheath, multifilament yarns each with a polymer weight ratio of the core to the sheath of 9.5/0.5, 9/1, 8/2, 7/3, 6/4, 5/5, 4/6, 3/7, 2/8, or 1/9 and with 44dtex (40 denier) 34 filaments were prepared (Examples 1-10). In addition, based on a core/sheath-type composite fiber wherein a nylon 66 polymer with a relative viscosity measured in sulfuric acid of 2.85 was used as the core and a nylon 6 polymer with a relative viscosity measured in sulfuric acid of 2.80 was used as the sheath, a multifilament yarn with a polymer weight ratio of the core to the sheath of 50/50 and with 44dtex (40 denier) 24 filaments was prepared (Example 11). In addition, a multifilament yarn with 44dtex (40 denier) 34 filaments which consists of core/sheath-type composite fibers (the weight ratio of the core/the sheath: 50/50) wherein a nylon 66 polymer with a relative viscosity measured in sulfuric acid of 2.85 was used as the core and a copolymer of nylon 6 and nylon 66 with a relative viscosity measured in sulfuric acid of 2.80 (the weight ratio of nylon 6 to nylon 66: 85:15 and the melting point: 190°C) was used as the sheath, was prepared (Example 12). On the other hand, an ordinary multifilament with 44dtex 40 denier 34 filaments consisting of only a generally used nylon 66 was prepared (Comparative Example 1). On these yarns, additional twisting of 280 T/m was performed on each of yarns used for warps of fabrics and yarns with no additional twisting were used as wefts. Fabrics consisting of a plane texture were prepared by using the warps and the wefts respectively prepared and scouring and finishing set were performed by a conventional method to prepare base fabrics for an ink ribbon shown in Table 1. Using these fabrics for an ink ribbon, ink ribbons were prepared based on the above described testing method and durabilities of the welded parts were measured and the results were shown in Table 1. As clearly seen in Table 1, the samples for Examples 1-12 exhibited good durabilities of the welded parts of the base fabrics. On the contrary, in Comparative Example 1, durability of the welded part of the base fabric was bad and was not fit for practical use. As the base fabric for an ink ribbon of the present invention exhibits good durability of the welded part of the base fabric, it can be used as an endless ink ribbon having a welded part among ink ribbons used for various impact printers such as line printers and serial printers. Not only demands for ink ribbons for general impact printers such as these can be expected but also a large demand can be expected especially in high speed-type printers, high duty copying-type printers etc., with strong impact.

Claims: A base fabric for an ink ribbon characterised in that at least one yarn of the warp and weft of the base fabric is constituted of core/sheath-type composite fibers wherein the sheath component is a polymer with a melting point lower than that of the core component. A base fabric according to claim 1, wherein the core component of said core/sheath-type composite fiber is a polyamide and the sheath component is a polyamide with a melting point lower than that of said polyamide of the core component. A base fabric according to claim 1 or 2, wherein the melting point of said sheath component is 10-120°C lower than the melting point of said core component. A base fabric according to claim 3, wherein the melting point of said sheath component is 20-100°C lower than the melting point of said core component. A base fabric according to any preceding claim, wherein the composite ratio (weight ratio) of core/sheath is 80/20-10/90. A base fabric according to any preceding claim, wherein the sheath is a copolymer of nylon 66 and nylon 6 and the core component is nylon 66. A base fabric according to any one of claims 1 to 5, wherein the sheath component is nylon 6 and the core component is nylon 66. A base fabric according to any preceding claim, wherein the ink ribbon is an endless type ink ribbon having a welded part.

Inventors: HIROE NOBUTAKE, KATO TETSUYA, HIROE, NOBUTAKE, KATO, TETSUYA
Applicants: TORAY INDUSTRIES, TORAY INDUSTRIES, INC.
Application year: 1993
Main classification: B41J31
IPC codes: B41J31