EP0404064A2

EP0404064A2 - Ink ribbon

Info

Publication number: EP0404064A2
Application number: EP90111567A
Authority: EP
Inventors: Hirokazu Oki Electric Industry Co. Ltd. Andou; Katsuya Oki Electric Industry Co. Ltd. Kamimura; Iwao Oki Electric Industry Co. Ltd. Hashimoto; Kiyoshi Oki Electric Industry Co. Ltd. Ikeda
Original assignee: Oki Electric Industry Co Ltd
Current assignee: Oki Electric Industry Co Ltd
Priority date: 1989-06-19
Filing date: 1990-06-19
Publication date: 1990-12-27
Also published as: EP0404064A3; JPH0319882A

Abstract

In an ink ribbon (1) impregnated with ink for printing on a print medium (2) on a platen (4) by driving print wires (3) so as to strike the platen (4), the fabric of the ink ribbon (1) is formed by interweaving vertical and horizontal strands, and the ratio of densities of said vertical and horizontal strands lies in the range 0.70 - 1.43.

Description

BACKGROUND OF THE INVENTION

This invention concerns an ink ribbon for use in an impact printer.
Conventionally, ink ribbons consisted of tapes impregnated with ink which were interposed between a print medium and a print head in a printer, and especially a dot impact printer, for printing. The material of the ribbon was often nylon.
Fig. 6A and Fig. 6B show the arrangement of the print medium and ink ribbon. Fig. 6A shows their positions when printing is not being carried out, and Fig. 6B shows their positions during printing.
As shown in the figures, ink ribbon 1 is positioned over print medium 2. Dot matrix printing is carried out when print wire 3 of the print head strikes platen 4 via ink ribbon 1 and print medium 2 so as to transfer the ink with which ink ribbon 1 is impregnated onto print medium 2.
The properties required of the fabric of said ink ribbon 1 are as follows:

(1) It can be thoroughly impregnated with ink.
(2) It does not catch on print wire 3.
(3) It is thin.
(4) It has strength to withstand striking by a print wire

The second of the above properties, i.e. that of catching on the print wires will first be explained.
Modern printers are able to print Chinese characters, and so that these can be printed with high quality, manufacturers are tending to increase the number of pins in the print head and to make the print wires thinner. At the same time, as shown in Fig. 9 (which is an electron micrograph, in which the distance between the inner ends of short bars "- -" at the bottom margin is 100 µ m), high density ink ribbons 1 are being used so that they do not catch on the print wire.

The fabric of a conventional ink ribbon is formed by interweaving vertical and horizontal strands, and it may typically have the following specification:

Strand thickness:	40 denier (= 4.444·10⁻⁶kg/m)
Number of filaments per strand:	34
Vertical strand density (Vertical spatial frequency):	214/inch (= 8.425/mm)
Horizontal strand density (Horizontal spatial frquency):	126/inch (=4.961/mm)
Thickness:	0.12 mm

The third of the above properties, i.e. the thickness of the fabric, will now be discussed.
In Fig. 6A, ink ribbon 1 is adjacent to print wire 3, and a space is provided between ink ribbon 1 and print medium 2 so that ink is not transferred to print medium 2 when printing is not being carried out.
The gap between the tip of print wire 3 and the surface of platen 4 (referred to hereafter as the "platen-wire gap" (P-W gap), as shown in Fig. 7, is closely related to the time of travel and return of print wire 3. For instance, when the P-W gap is relatively small, the time taken for the print wire to move forward and return to the original position is t1, while when the P-W gap is relatively large, the time taken is t2, which is Δ t longer than t1. Thus, the smaller is the P-W gap, the higher is the speed at which printing can be carried out.
As shown in Fig. 6B, in the instant when one print wire prints, ink ribbon 1 is compressed to approx. 1/3 of its thickness, and print medium 2 is compressed to approx. 75% of its thickness. The distance over which print wire 3 operates therefore increases by the amount by which ink ribbon 1 is compressed.
The thinner is ink ribbon 1, the smaller the platen-wire gap can be made, and the less the amount of compression that occurs in printing. As a result, the distance over which print wire 3 operates is smaller, and printing can be speeded up.
The fourth of the above properties, i.e. that of strength, will now be described.
Fig. 8A and Fig. 8B show the ink ribbon when it is installed.
Ink ribbon 1 is a tape of width about 5 mm - 30 mm and length about several m - 100 m. It may be in the form of a loop housed in a cassette 6 as shown in Fig. 8A, or in the form of a reel 7 as shown in Fig. 8B, and by passing the ribbon back and forth between the print head 5 and print medium 2, printing may be carried out for long periods.
The ribbon must therefore have sufficient strength to withstand long periods of use.
The conventional ink ribbons are subject to a force of 10 - 20 kg/mm² by each print wire when it strikes the ribbon 1. Consequently, if printing is carried out repeatedly over long periods, the strength of ink ribbon declines and the ribbon tears. This decides the useful life of ink ribbon 1.
Further, if the ribbon tears, it may also catch on print wire 3 and damage the wire.
The life of ink ribbon 1 will now be discussed.
The life of the ink ribbon is deemed to have been attained when the ink with which the ribbon 1 is impregnated decreases, and the characters printed by it can no longer be distinguished; or when the strength of the ribbon fabric decreases, and the ribbon feed no longer operates correctly; or when the strength of the ribbon decreases so much that the ribbon tears.
Normally, the life of the ribbon is deemed to have been reached when the ink with which the ribbon is impregnated has decreased. If the ribbon is impregnated with 20% ink with respect to the weight of ribbon fabric, about 30,000 Chinese characters can be printed per 1 m of ink ribbon, which corresponds to about 200,000 strikes per print wire.
The fabric of the ink ribbon must therefore retain sufficient strength even when the printed characters have become too faint to read.
This invention aims to provide an ink ribbon which retains sufficient strength even when it is no longer possible to read the characters printed by it, which does not catch on the print wires, and which does not present any risk of damaging the print wires.

SUMMARY OF THE INVENTION

In the ink ribbon of this invention, which is used in printers where print wires are driven to strike a platen and print a print medium on the platen, the fabric of the ribbon is formed by interweaving vertical and horizontal strands wherein the ratio of densities (spatial frequencies) of said vertical and horizontal strands lies in the range 0.70 - 1.43.
According to this invention, the fabric of the ribbon is formed by interweaving vertical and horizontal strands wherein the ratio of the densities of said vertical and horizontal strands lies in the range 0.70 - 1.43. It is thus possible to make the ribbon fabric thinner, and ensure that the fabric retains sufficient strength even when the printed characters can no longer be read.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an electron micrograph showing the strand structure of the ink ribbon of Embodiment 1 of this invention.
Fig. 2 is a chart comparing the specifications of the ink ribbons of this invention and a conventional ink ribbon.
Fig. 3 is a drawing showing the relation between vertical strand density, horizontal strand density and density ratio on the horizontal axis, and the thickness and tensile strength of the ink ribbon fabric on the vertical axis.
Fig. 4 is a drawing showing the relation between the number of dots actually printed by the ribbons and their tensile strength.
Fig. 5 is a drawing showing the relation between tensile strength and density ratio.
Fig. 6A and Fig. 6B are drawings showing the position of the print medium and an ink ribbon in a printer.
Fig. 7 is a drawing showing the displacement of the print wires.
Fig. 8A and Fig. 8B are drawings showing an ink ribbon when installed.
Fig. 9 is an electron micrograph showing the strand structure of a conventional ink ribbon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention will now be described in more detail with reference to the drawings.
Fig. 1 is an electron micrograph showing the strand structure of the ink ribbon in Embodiment 1 of this invention. In Fig. 1, the distance between the inner ends of short bars "- -" at the bottom margin is 100 µ m). Fig. 2 is a comparison of the specifications of the ink ribbon of this invention and a conventional ink ribbon.
As seen from the figures, in contrast to conventional ink ribbons, the vertical and horizontal strand densities in this example are arranged to be substantially equal.
In Embodiment 1, the vertical strand density is 170 strands/inch, and the horizontal strand density is also 170 strands/inch. The thickness of the ink ribbon fabric then becomes 0.098 mm, which is 0.022 mm less than in conventional ribbons.
In Embodiment 2 of this invention, the, vertical strand density is 190 strands/inch, and the horizontal strand density is 150 strands/inch. The thickness of the ink ribbon fabric then becomes 0.106 mm, which is 0.014 mm less than in conventional ribbons.
In Embodiment 3 of this invention, the vertical strand density is 150 strands/inch, and the horizontal strand density is 190 strands/inch. The thickness of the ink ribbon fabric then becomes 0.105 mm, which is 0.015 mm less than in conventional ribbons.
In Fig. 2, other cases are given in Comparative Examples 1 - 3. In comparison to the ribbons of Embodiments 1 - 3, there is less decrease in fabric thickness.
In Fig. 3, vertical strand density, horizontal strand density and density ratio are marked on the horizontal axis, while the thickness and tensile strength of the ink ribbon fabric are marked on the vertical axis.
As shown in the figure, in the case of Embodiment 1 where vertical and horizontal strand densities are equal, the fabric is at its thinnest and the tensile strengths of vertical and horizontal strands are well-balanced.
In the case of Embodiments 2 and 3, the thickness of the fabric is small, but the balance between vertical and horizontal tensile strength is upset.
Fig. 4 shows the relation between the number of dots printed and tensile strength when the ink ribbons of this invention and a conventional ink ribbon were actually used.
In the experiment, ink ribbons of length 100 m were employed. The horizontal axis shows the number of operations by 1 print wire per 1 m of ribbon, while the vertical axis shows the tensile strength of 1 inch of ribbon.
*) (= 1.967 kg/mm)
Experiences show that when the tensile strength decreased below 5 kg/inch,* the ink ribbon could no longer be used and its useful life expired. If the ribbon is used beyond this point, it might break the print wires or cause other damage.
As shown in the figure, the life of a conventional ink ribbon is approx. 160,000 strikes/m, after which the ribbon tears completely.
On the other hand, in the ink ribbons of Embodiments 1 - 3 of this invention, the ribbons retain a considerable tensile strength even after approx. 200,000 strikes/m.
Fig. 5 shows the relation between tensile strength and density ratio after carrying out a printing test of 200,000 strikes/m on the ink ribbons of Embodiments 1 - 3, and Comparative Examples 1 - 3.
It is seen that in both Embodiment 2 and Embodiment 3, tensile strength was higher and better results were obtained than with conventional ribbons. In Comparative Examples 1 - 3, however, the tensile strength after 200,000 strikes/m was insufficient.
This invention is not limited to the above embodiments, and it shall be understood that various modifications which are possible within the spirit of the invention shall not be excluded from it.
In the above embodiments, for instance, the thickness of a strand was said to be 40 denier, but a similar effect is obtained with strands of other thicknesses.
Further, in the above embodiments, the sum of the densities of vertical and horizontal strands is constant, but a similar effect is obtained in other cases.
As described above in detail, according to this invention, the fabric of the ink ribbon is formed by interweaving vertical and horizontal strands, and the ratio of densities of said vertical and horizontal strands is in the range 0.70 - 1.43. This makes it possible to reduce the thickness of the ink ribbon fabric without decreasing its tensile strength.
The platen-wire gap can thus be made small, and the printing speed of a printer, especially a wire dot impact printer, can be increased.
Further, the strengths of the vertical and horizontal strands are well balanced, an ink ribbon with high impact resistance during printing can be obtained, the life of the ribbon is extended, the ribbon is more economical, and there is less risk of print wires breaking due to tears in the ribbon.
*) (= 7.48/mm)
**) (= 5.91/mm)

Claims

1. An ink ribbon impregnated with ink for printing on a print medium on a platen by driving print wires so as to strike the platen, wherein:

(a) the fabric of the ink ribbon is formed by interweaving vertical and horizontal strands, and

(b) the density ratio between said vertical and horizontal strands lies in the range 0.70 - 1.43.

2. An ink ribbon according to claim 1, wherein the vertical strand density is within the range of about 150 to about 190 strands/inch,* and the horizontal strand density is also about 190 to about 150 strands/inch.**

3. An ink ribbon according to claim 2, wherein the thickness of the ink ribbon fabric is 0.098 to 0.106 mm.

4. An ink ribbon according to claim 1, wherein the thickness ofthe strand is about 40 denier and the number of filaments per strand is about 34.

5. An ink ribbon according to claim 1, wherein the material for ink ribbon is nylon.

6. An ink ribbon according to claim 1, wherein the horizontal and vertical strand densities are substantially equal to each other.