As multi-color ink ribbons for use with a typewriter or the impact type printers of word processors, computers and other devices, there are known a two-color ink ribbon comprising a textile substrate saturated with black and red liquid inks on both sides of an ink-resistant borderline and a four-color or other multi-color ink ribbon comprising a substrate fabric similarly saturated with, for example, black, cyan, magenta and yellow liquid inks.
This type of multi-color ink ribbon has the drawback of "migration", an intermingling of the inks of different colors from the adjacent ink-saturated lanes during storage, distribution or use and a variety of preventive countermeasures have been proposed.
For example, the Japanese Official Gazette of Utility Model Laid-open Application No. 65012/1976 discloses the art of forming such a borderline between ink-saturated lanes by a hot melting technique or by impregnation with a plastic composition.
The Japanese Official Gazette of Patent Laid-open Application 128412/1978 discloses the art of forming such a borderline by causing the substrate fabric to contact a thermal means such as a hot roller or the like.
The Japanese Official Gazette of Utility Model Laid-open Application No. 134516/1979 teaches the technique of forming a borderline wherein the substrate fabric is melted under pressure by means of the pressure tip of an ultrasonic welder.
The Japanese Official Gazette of Patent Laid-open Application 140285/1983 teaches the technique of forming a borderline by coating the substrate fabric with a water repellent agent such as silicone oil, paraffin, wax, a fluorine-containing resin, or the like.
However, the method in which the borderline is formed by coating the substrate fabric with a plastic material or a water repellent agent is disadvantageous in that if one tries to assure a sufficient penetration of the coating agent into the substrate fabric to prevent formation of pinholes, the coating agent will diffuse too much into the substrate so that a broad ink-resistant zone is formed in the substrate fabric. As a result, the ribbon must have a fairly large width and this, in turn, makes it essential to scale up both the ribbon feed mechanism and the shifting mechanism for color change. Furthermore, it is technically difficult to accurately construct a borderline of uniform width by any of such coating techniques.
The method of forming a borderline by melting the substrate fabric with a heating means such as the hot roller or pressure tip of a high frequency welding machine is disadvantageous in that the heating means picks up the molten masses of the substrate to cause an irregular travel of the fabric and a variation in heating temperature. Such troubles result in a local under-melting or over-melting at the points of contact so that pinholes are formed in the borderline to cause a migration of inks from the adjacent ink-saturated lanes.
In addition, as shown in FIG. 4 which is a partially expanded view (a schematic tracing of a micrograph) showing the borderline formed by the above method employing a heating means, a portion of the melted fiber collects and is solidified to form resin build-ups 5a along both edges of the borderline (5) and these resin build-ups 5a tend to interfere with the operation of the ribbon shift guide during the use of the ink ribbon or cause an instability of the direction of travel; the result is irregular traveling. In FIG. 4, the numeral 3 denotes the substrate fabric, 3a the warp fiber of the same, 3b the weft fiber of the same, and 5 the borderline.
It is an object of this invention to provide a multi-color ink ribbon free of the above-mentioned disadvantages. It is another object of this invention to provide a method for manufacturing such a multi-color ink ribbon.