WO1990001524A1

WO1990001524A1 - Machine-readable ink

Info

Publication number: WO1990001524A1
Application number: PCT/DE1989/000340
Authority: WO
Inventors: Lutz VITÉ
Original assignee: Siemens Aktiengesellschaft
Priority date: 1988-08-05
Filing date: 1989-05-30
Publication date: 1990-02-22
Also published as: DE3826734A1

Abstract

An ink for ink jet printers contains, in addition to the solvent, the pigment and possibly other additives, organic additives whose absorption of electromagnetic radiation in the infrared range (approximately 700 to 1000 nm) can be readily measured by silicon-based detectors. Known organic compounds suitable as additives are chosen, for example, from the group containing nigrosines, azo dyes, cyanins or the photographic dyes. All known inks, in particular black inks, become machine readable when mixed with the additives.

Description

Machine readable ink.

The invention relates to an ink, in particular for inkjet printers, which contains at least one solvent, at least one soluble dye and optionally further soluble auxiliaries.

In the case of inkjet printers, the ink is transferred from the print head to the medium to be printed on by ejecting an ink droplet from the print head onto the medium, in particular on paper. Such a printhead has various fine nozzle openings, into which equally fine ink channels open. These ink droplets can be thrown off, for example, by the sudden supply of a certain amount of thermal energy, as a result of which part of an ink component evaporates and thereby generates kinetic energy (bubble jet method).

Such and other inkjet printers therefore also require special inks which, for example, may no longer contain any solids. The inks, which consist of one or more aqueous or organic-based solvents, at least one organic dye and optionally other auxiliaries, have an absorption spectrum for visible light which corresponds to that of the added dyes. Most organic dyes show a strongly decreasing absorption in the range between 600 and 650 nm, which is then negligibly low between 700 and 900 nm. A renewed absorption of energy (radiation) only begins again at around 900 nm. With the new media of modern communication technology, not only the fast and secure transmission of data or images is required, but increasingly also the fast and reliable detection of the same data, in digital or analog form, on printed or written data carriers is scanned and read, for example, with light-sensitive detectors. Representatives of such machine tools are, for example, image sensor lines or bar code readers. Such detectors usually contain photodiodes based on silicon as a light-sensitive element. However, these have the disadvantage that their maximum sensitivity is between 700 and 900 nm and that they are therefore difficult or impossible to recognize characters which are printed with an ink containing only conventional organic dyes. In the case of ribbons or other printing processes, this problem is avoided by adding an additive which absorbs in the range between 700 and 1000 nm. Materials used for this purpose and absorbing in the ultraviolet wavelength range are, for example, carbon black, aluminum powder, cobalt or copper compounds or other pigments. Such solids may not be contained in solvent inks for inkjet printing because of their insolubility.

The object of the present invention is therefore to provide a black ink, in particular, which is suitable for an inkjet printing process and which can be detected by machine readers.

This object is achieved according to the invention by an ink of the type mentioned at the outset in that it contains organic additives which are soluble in the at least one solvent and which have an absorption which is readily measurable with detectors based on silicon for electromagnetic radiation in the ultraviolet wavelength range.

Further refinements of the invention can be found in the subclaims.

The basic idea of the invention is to add, in addition to the optically recognizable dye, a further dye which absorbs in the sensitivity range of the photodetectors. Such "machine-readable" dyes or additives are said in Be absorb between 700 and 1000 nm. Dyes with these absorption areas are known from several types of dyes. This makes it possible to add such an additive to known ink mixtures in order to achieve good machine readability. The additives to be used in terms of quantity, roughly in the order of magnitude of the dye concentration, hardly influence the other ink properties. Because of the diverse selection, it is possible to find a suitable and well-tolerated additive for every ink mixture. The present invention provides a machine readable ink for ink jet printers for the first time.

Suitable ultraviolet absorbing additives are, for example, the nigrosines. These derivatives of the phenazine themselves are dyes and are water-soluble through multiple sulfonation. They can therefore also be mixed with inks which have an aqueous solvent system.

From the group of azo dyes, compounds have recently been known which have an absorption maximum in the ultraviolet wavelength range or show a sufficiently high absorption in this range. Some such representatives are, for example, in the article by K. A. Bello and J. Griffiths in

Journal of the Chemical Society, Chemical Communication, 1986, page 1639 ff. These are compounds of the general formula

where X is a divalent radical with at least one exo-hetero double bond, Hai is chlorine or bromine and R is a para-aminophenyl radical which can also carry an acetamide group in the ortho position to the azo group.

The para group in the amino group can still be mono- or dialkylated and the phenyl radical can carry further electron-donating substituents. With a selected compound that obeys this structural formula, an absorption maximum at 806 nm is measured in dimethyl sulfoxide. This is therefore in the maximum sensitivity range of the photodetectors used for machine readers on a silicon basis. Therefore, inks containing such an additive can be "read" very well by silicon photodetectors.

Other suitable additives are selected from the group of cyanines. This of the general structural formula

By varying the chain length (over n) or by a suitable choice of the end heterocyclic ring systems and the radicals R, obeying compounds enable the representation of correspondingly longwave or. in the ultra-red wavelength absorbing species. Five- and six-membered heterocycles, which can also be part of multinuclear aromatics, are particularly suitable for the terminal ring systems. Examples include quinoline, thiazole, pyrrole, imidazole and oxazole. Suitable long-wave absorbing representatives of this dye group are generally known and can be found in the standard works of dye chemistry.

A last group of compounds which are suitable as additives according to the invention are ultraviolet-sensitive photo dyes. These dyes are used, for example, for infrared-sensitive films, and are therefore also commercially available. A black dye is expediently used for a machine-readable ink, since there is an undefined color overlay with the additive in the case of other dyes which absorb in the visible range of the light spectrum. In addition to direct dyes such as direct black 171, direct black 168 or direct black 154, solvent, reactive or food dyes can also be used as black dyes. As an example of the last two dye groups, only reactive black 31 and food black 2 are mentioned. A mixture of dye and ultra-sensitive additive that is well suited for inks is, for example, a 1: 1 mixture (by weight) of nigrosine and direct black 171. The solvent system can be selected for ink jet printers, as in known ink compositions.

In a further embodiment of the invention, nigrosine represents the actual dye as an organic additive according to the invention, to which, however, other dyes may not necessarily be added in a small proportion in order to achieve a more visually pleasing color.

9 claims

Claims

1. Ink, in particular for inkjet printers, containing at least one solvent, at least one soluble dye and, if appropriate, further soluble auxiliaries, characterized in that the ink contains organic additives which are soluble in the at least one solvent and which have a detector with silicon-based detectors for electromagnetic radiation of the ultraviolet wavelength range have readily measurable absorption.

2. Ink according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the additives for the wavelength range from 700 to 1000 nm have sufficient absorption.

3. Ink according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the additives are selected from the group of sulfonated nigrosines.

4. Ink according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e-t that the additives are selected from the group of azo dyes.

5. Ink according to claim 4, d a d u r c h g e k e n n z e i c h n e t that the additives of the general formula

correspond, where X is a divalent radical with at least one exo-permanent heterodoplic bond of the type C = 0,

C = S or S = 0, Hai represents chlorine or bromine and R is a para-aminophenyl radical which may have an acetamide group in the ortho position and where the para-amino group may be mono- or dialkylated.

6. Ink according to claim 1 or 2, characterized in that the additives from the group of cyanines are selected.

7. Ink according to at least one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that the additives are selected from the group of ultra-sensitive photo dyes.

8. Ink according to at least one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that direct black 171 as a dye and nigrosine as an additive are contained.

9. Ink according to at least one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that the dye nigrosine is included as an organic additive, nigrosine representing the at least predominant proportion of the total dye content of the ink or the only dye contained.