Ink transfer ribbon

Details Ink transfer ribbon Ink transfer ribbon

1998-07-13

2001-08-21

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S409000, C428S484100

Reexamination Certificate

active

06277475

ABSTRACT:

The present invention concerns a color transfer ribbon, which has (a) a flexible micro-porous carrier, (b) one or several intermediate layers and (c) one or several layers of a transfer color. Such color ribbons are used in key stroke printers and key stroke typewriters.
Transfer color ribbons which are employed in typewriters or similar printers, usually have a micro-porous carrier of plastic material, which is coated with a layer of a transfer color, which may, among others, contain oil and material which is transferred to paper during the printing action. The micro-porosity of the carrier is an important pre-requisite for sufficient anchoring of the color layer(s) on the carrier. With the aid of the transfer color ribbon, symbols are printed onto substrates, whereby the transferred symbols adhere either permanently to the substrate or can be removed with aid of an adhesive strip, which allows corrections. Such color ribbons are usually wound on spools fitted in color tape cassettes installed in key stroke typewriters or printers. The color ribbon cassettes permit simple installation of color ribbons in the machine.
Application of a transfer color layer on the carrier is usually done from a melt or from a solution in a solvent. U.S. Pat. No. 3,825,470 describes a correctable transfer color ribbon. U.S. Pat. No. 3,496,015 describes a so-called MICR ribbon (MICR=magnetic ink character recognition). The layer of the transfer color may have a spongy structure, whereby during key stroke, a small amount of color is extruded and transferred to the substrate. The layer of the transfer color can, alternatively, also be pictorially detached and holohedrally transferred.
The layer of the transfer color contains in general oils or oil-like modification substances, such as for example, fatty acid alkyl esters, which can migrate after application into the micro-porous carrier. This may lead to problems with respect to transfer color ribbons—specifically those of small width, during transport through the printer mechanism. If, for example, oil exits from the color ribbon to the transport mechanism, the presence of oil during the ribbon transport may result in higher traction resistance and even in sticking, so that the ribbon is no longer moved by the transport mechanism. Furthermore, the oil, when it gets on the drive wheel, can act as a lubricating agent and cause the ribbon to slip, so that the ribbon ceases to move.
As a further problem, the oil can accumulate in such volume on the drive wheel, that the transfer color ribbon will stick to it because of adhesion. In a rolled-up state on the supply spool, the front side of the ribbon comes, furthermore, in contact with the reverse side of the next loop and minor oil quantities may result in the sticking together of loops and increased unwind resistance. These problems are further intensified by the effect of heat.
Additional problems arise due to static electricity. In the color ribbon cassette and in the transport mechanism of the printer, the color ribbon is passed along stationary surfaces. Due to the build-up of friction electricity, the color ribbon may stick to these stationary surfaces, which leads to added stress on the printer motor. In traditional color ribbons, this problem is being faced in that the thermo-transfer color has a certain electrical conductivity in order to thus avoid the generation of static electricity. Naturally, this will restrict, to a significant extent, freedom in the formulation of the transfer color.
EP-A- 0 167 932 proposes a reverse-side layer, in order to combat the problems caused by oil migration through the carrier foil. The said reverse-side layer guarantees a clean friction surface and good contact with the drive device. The reverse-side layer may contain a polyester, a vinyl chloride resin or a polyurethane resin and also a silicic acid-holding filler. It is evident from disclosure of EP-A-0 167 932, that this reverse-side layer acts as barrier coating for the oil migration. An increase in the surface roughness is not addressed. Nor does the EP-A-0 167 932 deal with the problems relating to electrostatic electricity. Moreover, it is a drawback that a separate reverse-side layer must be applied onto the reverse side of the carrier in a separate production step.
U.S. Pat. No. 4 675 233 describes an ink transfer material for printers which has a bi-axially oriented polyester foil and a transfer ink layer, whereby the bi-axially oriented polyester foil has a thickness from 1 to 15 &mgr;m and the rough surface an average roughness value from 0.02 to 1 &mgr;m and a maximum height from 0.2 to 10 &mgr;m. Polyester foils, however, are not micro-porous and constitute a barrier coating or the oil migration. Therefore, polyester foils are unsuitable for use as carrier materials for color ribbons in key stroke printers and key-stroke typewriters.
Consequently, it was the object of the present invention to eliminate the described problems in connection with oil migration and static electricity in simple and economic fashion.
According to the invention, this object is solved by a color transfer ribbon which is characterized in that the reverse side of the carrier has a surface roughness with roughness depth R
1
of at least approximately 400 nm and a mean roughness value R
a
of at least approximately 40 nm.
The term “Roughness Depth R
1
” signifies the distance from the basic or reference profile of a surface profiled, in other words the maximum “hill-valley distance” between reference profile and actual profile, which is also called CLA (center line average), i.e., the arithmetical mean of the deviations of the profile from a center line.
The “hills” on the reverse side of the carrier prevent formation of a cohesive oil film which demonstrates unwelcome adhesive tendency vis-a-vis the adjacent loop or other surfaces. The “hills” act, moreover, as distance keepers and prevent full plane contact of the reverse side of the ribbon with other surfaces, which clearly reduces the friction resistance and wind-down resistance.
Traditional carrier foil for printer color ribbons are usually produced by means of extrusion of melt flow, whereby a slot nozzle serves as extruder, from which the melt drops onto a cooled extrusion base (drum or ribbon), or by extrusion into a water bath.
The foil properties, such as porosity, tensile strength and surface roughness greatly depend upon the crystallinity, the molecular weight distribution and the manufacturing conditions, and that is why selection of employable raw materials is highly restricted at the present time. Two suitable HDPE grades for carrier foils are for example M5395/1 by Lyondell and 6340/3 by Dupont. Surface roughness of these traditional carrier foils varies considerably, depending upon charge, the values for R
t
and R
a
however lie always clearly below 400 or 40 nm.
In preferred specific embodiments, R
t
ranges approximately from 400 to 5,000 nm and R
a
approximately 40 to 500 nm, specifically R
t
ranges approximately from 600 to 2,500 nm and R
a
approximately 70 to 250 nm. Most specifically preferred is R
t
of at least approximately 650 nm and R
a
of at least approximately 80 nm. The effect of differing roughness depths or of a differing mean roughness value of the carrier upon the drive torque of a color ribbon cassette is represented in the attached
FIGS. 1 and 2
. R
t
and R
a
were altered via variation of particle size and concentration of the filler of a color ribbon carrier, the manufacture of which is described below. It is clearly apparent that the required torque declines with rising R
t
or R
a
.
For purposes of the invention R
t
or R
a
were ascertained by means of a Form-TALYSURF Series 2 Laser Instrument (from RANK TAYLOR HOBSON). Determination of roughness was done according to BS 1134.
The necessary surface roughness of the micro-porous carrier is preferably produced by employing a particle shaped filler substance, which is for example incorporated into the carrier foil during extrusion of the thermoplastic synthetic material

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