WO2013083962A1

WO2013083962A1 - Mixtures of magenta dyes and inks for use in ink-jet printing

Info

Publication number: WO2013083962A1
Application number: PCT/GB2012/052986
Authority: WO
Inventors: Clive Foster
Original assignee: Fujifilm Imaging Colorants Ltd
Current assignee: Fujifilm Imaging Colorants Ltd
Priority date: 2011-12-08
Filing date: 2012-12-03
Publication date: 2013-06-13
Anticipated expiration: 2014-06-08
Also published as: GB201121114D0

Abstract

A magenta dye mixture for ink-jet three printing comprising three defined dyes.

Description

MIXTURES OF MAGENTA DYES AND INKS FOR USE IN INK-JET PRINTING

This invention relates to dyes mixtures, to compositions and inks for ink-jet printers, to printing processes, to printed substrates and to ink-jet printer cartridges.

Ink-jet printing is a non-impact printing technique in which droplets of ink are ejected through a fine nozzle onto a substrate without bringing the nozzle into contact with the substrate. The set of inks used in this technique typically comprise yellow, magenta, cyan and black inks.

With the advent of high-resolution digital cameras it is becoming increasingly common to print photographs using an ink-jet printer.

While ink-jet printers have many advantages over other forms of printing and image development there are many technical challenges to be addressed. For example, there are the contradictory requirements of providing ink colorants that are soluble in the ink medium and yet display excellent water-fastness (i.e. prints do not run or smudge when printed). The inks also need to dry quickly to avoid sheets sticking together after they have been printed, but they should not form a crust over the nozzles in the printer head. Storage stability is also important to avoid particle formation, in the ink cartridge, which could block the tiny print head nozzles. This is important since consumers can keep an ink-jet ink cartridge for several months. Furthermore, and especially important with photographic quality reproductions, the resultant images should not bronze or fade rapidly on exposure to light or common oxidising gases such as ozone.

For high quality photorealistic ink-jet printing it is particularly important that the shade and chroma of each colorant is exactly right so that any image may be optimally reproduced. To achieve this more than one colorant may be used in the ink.

Selecting which colorants to use in an ink is an art in itself since the chemist has to identify which mixture of colorants will yield a print with the required optical properties on a variety of diverse substrates. The chemist must also ensure that the selected mixture of colorants yield an ink which meets the demanding performance criteria as set out above. They also have to minimise the cost of the colorant(s), the most expensive component of the ink, without adversely effecting the inks performance.

The present invention provides a mixture of dyes and salts thereof comprising:

(a) a dye of Formula (1 ) and salts thereof:

Formula (1 )

wherein:

R¹ and R² are independently H or optionally substituted C_1-4alkyl;

R³ is optionally substituted alkyl; and

n is greater than 0:

(b) a xanthene dye and salts thereof; and

(c) a dye of Formula (2) and salts thereof:

Formula (2)

wherein:

A is optionally substituted aryl;

R⁴ and R⁵ are independently H or optionally substituted C_1-4alkyl: and

R⁶ is either optionally substituted phenyl carrying up to 4 optional substituents selected from the group consisting of -OH, -COOH, -SO₃H and optionally substituted Ci_-4alkyl or R⁵ and R⁶ together with the nitrogen atom to which they are attached represent an optionally substituted aliphatic or optionally substituted aromatic ring system:

wherein the ratio of the components (a) to (b) to (c) is in the range of from 90:5:5 to 5:90:5 to 5:5:90 parts by weight.

Preferably in dyes of Formula (1 ) R¹ is methyl or ethyl.

Preferably in dyes of Formula (1 ) R² is methyl. Preferably in dyes of Formula (1 ) R³ is Ci_-8alky,l more preferably R³ is t- butyl.

Preferably in dyes of Formula (1 ) R¹ is methyl or ethyl, R² is methyl and R³ is t-butyl.

Preferably in dyes of Formula (1 ) n is in the range of from 3 to 6. More preferably n is in the range of from 3 to 5.

The sulfonic acid groups, represented by n, may be present as substituents on any suitable site on compounds of Formula (1 ).

Preferably when R³ is t-butyl then n is 4 with one sulfonic acid on each of the component aniline and benzothiazole ring systems.

A preferred compound of Formula (1 )is of Formula (3) and salts thereof:

Formula (3)

wherein R¹ is methyl or ethyl.

Preferably the xanthene dye is selected from the group consisting of C. I.

Acid Red 50 and salts thereof, C. I. Acid Red 52 and salts thereof, C. I. Acid Red 94 and salts thereof and C. I. Acid Red 289 and salts thereof. More preferably the xanthene dye is C. I. Acid Red 52 and salts thereof.

Preferably the xanthene dye and salts thereof is a single dye. However in some embodiments it is preferable to use a mixture of two or more xanthene dyes and salts thereof.

C. I. Acid Red 52 has the following structure:

C. I. Acid Red 52 and salts thereof, C. I. Acid Red 94 and salts thereof and C. I. Acid Red 289 and salts thereof are commercially available from a number of suppliers. Preferably prior to use C. I. Acid Red 52 and salts thereof, C. I. Acid Red 94 and salts thereof and C. I. Acid Red 289 and salts thereof are purified so as to convert them to a form suitable for ink-jet printing. Preferred purification steps include reverse osmosis to remove inorganic impurities and screening to remove particulate matter.

Preferably in the dyes of Formula (2) and salts thereof A is optionally substituted naphthyl or optionally substituted phenyl. More preferably in the dyes of Formula (2) A is naphthyl substituted with 1 to 3 substituents selected from the group consisting of -OH, -COOH, -SO₃H and optionally substituted Ci_-4alkyl (especially unsubstituted Ci_-4alkyl and more especially methyl) or phenyl substituted with 1 to 3 substituents selected from the group consisting of -OH, - COOH, -SO₃H and optionally substituted Ci_-4alkyl (especially unsubstituted Ci- ₄alkyl and more especially methyl). In one preferred embodiment A is naphthyl carrying a single -SO₃H. In a second preferred embodiment A is phenyl carrying a single -COOH.

In the dyes of Formula (2) when R⁶ is optionally substituted phenyl it preferably carries 1 to 3 substituents selected from the group consisting of -OH, - COOH, -SO₃H and optionally substituted Ci_-4alkyl (preferably unsubstituted Ci- ₄alkyl and more preferably methyl). Preferably when R⁶ is optionally substituted phenyl it has 2 methyl substituents and 1 -SO₃H substituent.

In the dyes of Formula (2) when R⁶ is phenyl preferably R⁴ and R⁵ are independently H or methyl. More preferably R⁴ and R⁵ are both H.

In the dyes of Formula (2) when R⁵ and R⁶ together with the nitrogen atom to which they are attached represent an optionally substituted aliphatic or optionally substituted aromatic ring system then preferably they are an optionally substituted morpholinyl ring and more preferably an unsubstituted morpholinyl ring.

Particularly preferred dyes of Formula (2) are of Formula (4) and (5) and salts thereof:

Formula (5)

Preferably component (a) is present in the range of from 40 to 80 parts by weight, more preferably in the range of from 50 to 75 parts by weight and especially in the range of from 55 to 70 parts by weight.

Preferably component (b) is present in the range of from 5 to 40 parts by weight and more preferably in the range of from 10 to 30 parts by weight.

Preferably component (c) is present in the range of from 5 to 40 parts by weight, more preferably in the range of from 10 to 30 parts by weight and especially in the range of from 15 to 20 parts by weight.

The mixture of dyes according to the present invention may be used in the preparation of magenta inks for use in ink-jet printing. They may also be used to shade other coloured inks.

The dyes of Formula (1 ) are among the most effective of all magenta ink-jet dyes. However, they are extremely expensive to make. The applicants have found that by mixing the dyes of Formula (1 ) with other specific cheaper dyes it is possible to obtain a dye mixture which shows a technical performance close to that seen with the dyes of Formula (1 ) alone and which matches the exact optical properties required in a magenta ink for use in ink-jet printing.

Acid and basic groups on the dyes shown herein, particularly acid groups, are preferably in the form of a salt. Thus, the Formulae shown herein include the compounds in free acid and in salt form.

Preferred salts are alkali metal salts, especially lithium, sodium and potassium, ammonium and substituted ammonium salts (including quaternary amines such as ((CH₃)₄N⁺) and mixtures thereof. Especially preferred are salts with sodium, lithium and ammonium.

The dyes disclosed herein may be converted into a salt using known techniques.

The dyes disclosed herein may exist in tautomeric forms other than those shown in this specification. These tautomers are included within the scope of the present invention.

The dyes of Formula (1 ) may be prepared using those processes described in US 7,201 ,477 which is incorporated herein by reference. The dyes of Formula (2) may be prepared using those processes described in US 6,344,076 and US 6,635,747 which are incorporated herein by reference

According to a second aspect of the present invention there is provided a composition comprising a mixture of dyes and salts thereof, as described in the first aspect of the invention, and a liquid medium.

Preferred compositions according to the second aspect of the invention comprise:

(a) from 0.01 to 30 parts of a mixture of dyes and salts thereof according to the first aspect of the invention; and

(b) from 70 to 99.99 parts of a liquid medium;

wherein all parts are by weight.

Preferably the number of parts of (a)+(b)=100.

The number of parts of component (a) is preferably from 0.1 to 20, more preferably from 0.5 to 15, especially from 1 to 6, more especially from 3 to 6 and particularly from 4 to 6 parts by weight.

The number of parts of component (b) is preferably from 80 to 99.9, more preferably from 85 to 99.5, especially from 94 to 99, more especially from 94 to 97 and particularly from 94 to 96 parts by weight.

Preferably component (a) is completely dissolved in component (b). Preferably component (a) has a solubility in component (b) at 20°C of at least 10%. This allows the preparation of liquid dye concentrates that may be used to prepare more dilute inks and reduces the chance of the dye precipitating if evaporation of the liquid medium occurs during storage.

Preferred liquid media include water, a mixture of water and organic solvent and organic solvent free from water. Preferably the liquid medium comprises a mixture of water and organic solvent or organic solvent free from water.

When the liquid medium (b) comprises a mixture of water and organic solvent, the weight ratio of water to organic solvent is preferably from 99: 1 to 1 :99, more preferably from 99: 1 to 50:50 and especially from 95:5 to 80:20.

It is preferred that the organic solvent present in the mixture of water and organic solvent is a water-miscible organic solvent or a mixture of such solvents. Preferred water-miscible organic solvents include Ci_-6-alkanols, preferably methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol; linear amides, preferably dimethylformamide or dimethylacetamide; ketones and ketone-alcohols, preferably acetone, methyl ether ketone, cyclohexanone and diacetone alcohol; water-miscible ethers, preferably tetrahydrofuran and dioxane; diols, preferably diols having from 2 to 12 carbon atoms, for example ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol and thiodiglycol and oligo- and poly-alkyleneglycols, preferably diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol; triols, preferably glycerol and 1 ,2,6-hexanetriol; mono-Ci_-4-alkyl ethers of diols, preferably mono-Ci_-4-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxyethanol, 2-(2- methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol, 2-[2-(2- methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether; cyclic amides, preferably 2-pyrrolidone, N-methyl- 2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and 1 ,3-dimethylimidazolidone; cyclic esters, preferably caprolactone; sulfoxides, preferably dimethyl sulfoxide; and sulfones, preferably sulfolane. Preferably the liquid medium comprises water and 2 or more, especially from 2 to 8, water-miscible organic solvents.

Especially preferred water-miscible organic solvents are cyclic amides, especially 2-pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrrolidone; diols, especially 1 ,5-pentane diol, ethyleneglycol, thiodiglycol, diethyleneglycol and triethyleneglycol; and mono-Ci_-4-alkyl and Ci_-4-alkyl ethers of diols, more preferably mono- Ci_-4-alkyl ethers of diols having 2 to 12 carbon atoms, especially 2-methoxy-2-ethoxy-2-ethoxyethanol.

When the liquid medium comprises organic solvent free from water, (i.e. less than 1 % water by weight) the solvent preferably has a boiling point of from 30 to 200°C, more preferably of from 40 to 150°C, especially from 50 to 125°C. The organic solvent may be water-immiscible, water-miscible or a mixture of such solvents. Preferred water-miscible organic solvents are any of the hereinbefore- described water-miscible organic solvents and mixtures thereof. Preferred water- immiscible solvents include, for example, aliphatic hydrocarbons; esters, preferably ethyl acetate; chlorinated hydrocarbons, preferably CH₂CI₂; and ethers, preferably diethyl ether; and mixtures thereof.

When the liquid medium comprises a water-immiscible organic solvent, preferably a polar solvent is also included since this may enhance the solubility of the dyes in the organic liquid medium. Examples of suitable polar solvents include Ci_-4-alcohols.

In view of the foregoing preferences it is especially preferred that where the liquid medium is organic solvent free from water it comprises a ketone (especially methyl ethyl ketone) and/or an alcohol (especially a Ci_-4-alkanol, more especially ethanol or propanol).

The organic solvent free from water may be a single organic solvent or a mixture of two or more organic solvents. It is preferred that when the liquid medium is organic solvent free from water it is a mixture of 2 to 5 different organic solvents. This allows a liquid medium to be selected that gives good control over the drying characteristics and storage stability of the ink.

Liquid media comprising organic solvent free from water are particularly useful where fast drying times are required and particularly when printing onto hydrophobic and non-absorbent substrates, for example plastics, metal and glass.

The liquid media may of course contain additional components conventionally used in ink-jet printing inks, for example viscosity and surface tension modifiers, corrosion inhibitors, biocides, kogation reducing additives and surfactants which may be ionic or non-ionic.

Although not usually necessary, further colorants may be added to the ink to modify the shade and performance properties.

It is preferred that the composition according to the invention is ink suitable for use in an ink-jet printer. Ink suitable for use in an ink-jet printer is ink which is able to repeatedly fire through an ink-jet printing head without causing blockage of the fine nozzles. To do this the ink must be particle free, stable (i.e. not precipitate on storage), free from corrosive elements (e.g. chloride) and have a viscosity which allows for good droplet formation at the print head.

Ink suitable for use in an ink-jet printer preferably has a viscosity of less than 20 cP, more preferably less than 10 cP, especially less than 5 cP, at 25°C.

Ink suitable for use in an ink-jet printer preferably contains less than

500ppm, more preferably less than 250ppm, especially less than 100ppm, more especially less than 10ppm in total of divalent and trivalent metal ions (other than any divalent and trivalent metal ions bound to a colorant of Formula (1 ) or any other colorant or additive incorporated in the ink).

Preferably ink suitable for use in an ink-jet printer has been filtered through a filter having a mean pore size below Ι Ομηι, more preferably below 3μΓη, especially below 2μΓη, more especially below 1 μΓη. This filtration removes particulate matter that could otherwise block the fine nozzles found in many ink-jet printers.

Preferably ink suitable for use in an ink-jet printer contains less than

500ppm, more preferably less than 250ppm, especially less than 100ppm, more especially less than 10ppm in total of halide ions, particularly chloride ions.

The inks may be incorporated in an ink-jet printer as a high concentration magenta ink, a low concentration magenta ink or both a high concentration and a low concentration ink. In the latter case this can lead to improvements in the resolution and quality of printed images. Thus the present invention also provides a composition (preferably an ink) where component (a) is present in an amount of 2.5 to 7 parts, more preferably 2.5 to 5 parts (a high concentration ink) or component (a) is present in an amount of 0.5 to 2.4 parts, more preferably 0.5 to 1 .5 parts (a low concentration ink).

A third aspect of the invention provides a process for forming an image on a substrate comprising applying a composition, preferably ink suitable for use in an ink-jet printer, according to the second aspect of the invention, thereto by means of an ink-jet printer.

The ink-jet printer preferably applies the ink to the substrate in the form of droplets that are ejected through a small orifice onto the substrate. Preferred ink- jet printers are piezoelectric ink-jet printers and thermal ink-jet printers. In thermal ink-jet printers, programmed pulses of heat are applied to the ink in a reservoir by means of a resistor adjacent to the orifice, thereby causing the ink to be ejected from the orifice in the form of small droplets directed towards the substrate during relative movement between the substrate and the orifice. In piezoelectric ink-jet printers the oscillation of a small crystal causes ejection of the ink from the orifice.

The substrate is preferably paper, plastic, a textile, metal or glass, more preferably paper, an overhead projector slide or a textile material, especially paper.

Preferred papers are plain or treated papers which may have an acid, alkaline or neutral character. Photographic quality papers are especially preferred. Photographic quality paper give a print with a finish which is similar in quality to that typically seen with silver halide photo printing.

A fourth aspect of the present invention provides a material preferably paper, plastic, a textile, metal or glass, more preferably paper, an overhead projector slide or a textile material, especially paper more especially plain, coated or treated papers printed with a mixture of dyes and salts there of as described in the first aspect of the invention, a composition according to the second aspect of the invention or by means of a process according to the third aspect of the invention.

It is especially preferred that the printed material of the fourth aspect of the invention is a print on a photographic quality paper printed using a process according to the third aspect of the invention.

A fifth aspect of the present invention provides an ink-jet printer cartridge comprising a chamber and a composition, preferably ink suitable for use in an ink- jet printer, wherein the composition, preferably the ink, is in the chamber and the composition is as defined and preferred in the second aspect of the present invention. The cartridge may contain a high concentration ink and a low concentration ink, as described in the second aspect of the invention, in different chambers. The invention is further illustrated by the following Examples in which all parts and percentages are by weight unless otherwise stated.

Examples

An example of the invention will now be described by reference to the accompanying drawing:

Figure 1 shows a comparison of the reflection spectra of an ink containing the dye of the Comparative Example and Example Ink 14.

Dye Examples 1 and 2

The following dyes, which are Examples of component A, were prepared using those processes as described in US 7,201 ,477 which processes are incorporated herein by reference:

Dye Examples 3 and 4

Dye Examples 3 and 4 which are Examples of component (c), were prepared using those processes as described in US 6,344,076 and US 6,635,747.

Dye Example 3

Dye Example 4

Comparative Example

The comparative Example is Example 1 in of US 7,270,406, which is incorporated herein by reference, a magenta ink-jet dye which displays outstanding characteristics

Example 5

Preparation of Inks

Inks were prepared by dissolving the total parts by weight of dyes according to Table 1 in sufficient liquid medium, by weight to bring the total parts of the ink, by weight, to 100 and adjusting the pH of the ink to between 8 to 8.5 using sodium hydroxide.

The liquid medium comprises % by weight

Diethylene glycol 7%

Ethylene glycol 7%

2-Pyrollidone 7%

Surfynol^R™ 465 1 %

Tris buffer 0.2%

Water 77.8%

Surfynol 465 is a surfactant from Air Products.

The comparative ink was prepared by dissolving 5 parts by weight of the Comparative Example dye in 95 parts of the above liquid medium.

Table 1

In Table 1 :

Component (a) is the dye of Dye Example 1

Component (b) is C. I. Acid Red 52

Component (c) is the dye of Dye Example 3

Ink-jet Printing

Inks prepared as described above were filtered through a 0.45 micron nylon filter and then incorporated into empty print cartridges using a syringe.

These inks were then ink-jet printed on to the following ink-jet media:

HP Advanced Plain Paper; and

HP Advanced Photo Paper (HPP).

The prints were tested for ozone fastness by exposure to 1 ppm ozone at 40°C, 50% relative humidity for 24 hours in a Hampden 903 Ozone cabinet. Fastness of the printed ink to ozone can be judged by the difference in the optical density before and after exposure to ozone.

Optical density measurements were performed using a Gretag^R™ spectrolino spectrophotometer set to the following parameters :

Measuring Geometry 0°/45°

Spectral Range 380-730nm

Spectral Interval 10nm

llluminant D65 Observer 2° (CIE 1931 )

Density Ansi A

External Filler None

Ozone fastness is assessed by the percentage change in the optical density of the print, where a lower figure indicates higher fastness.

The results are shown below in Tables 1 and 2 and in Figure 1 .

Table 2

Table 2 below shows the results of the CIE colour co-ordinates (L, a, b) and ozone fastness of the print on HP Advanced Plain Paper at 80% print depth.

Ink Example L a b

Comparison 47 62 -14

1 47 64 -14

2 47 64 -12

3 48 64 -14

4 48 64 -13

5 48 64 -1 1

6 49 63 -9

7 49 65 -7

8 50 65 -5

9 46 64 -13

10 47 64 -12

1 1 47 64 -13

12 47 64 -1 1

13 47 64 -8

14 47 64 -7

15 48 64 -5

16 48 64 -4

Table 3

Table 3 below shows the results of the CIE colour co-ordinates (L, a, b) and ozone fastness of the print on HP Advanced Photo Paper at 80% print depth.

Clearly from Tables 1 and 2 the dye mixtures of the present invention are able to accurately reproduce the spectral properties of a leading magenta ink-jet dye at a lower unit cost and with improved fastness properties. Further Inks

The inks described in Tables A and B may be prepared using the same dye mixture as in Example Ink 14. The dye mixture indicated in the first column is dissolved in 100 parts of the ink as specified in the second column on. Numbers quoted in the second column onwards refer to the number of parts of the relevant ink ingredient and all parts are by weight. The pH of the ink may be adjusted using a suitable acid or base. The inks may be applied to a substrate by ink-jet printing.

The following abbreviations are used in Tables A and B:

PG = propylene glycol

DEG = diethylene glycol

NMP = N-methyl pyrrolidone DMK = dimethylketone IPA = isopropanol

2P = 2-pyrrolidone

MIBK = methylisobutyl ketone P12 = propane-1 ,2-diol

BDL = butane-2,3-diol TBT = tertiary butanol

TABLE A

Dye Water PG DEG NMP DMK I PA 2P MIBK

2.0 80 5 6 4 5

3.0 90 5 5

10.0 85 3 3 3 6

2.1 91 8 1

3.1 86 5 4 5

1 .1 81 9 10

2.5 60 4 15 3 3 6 5 4

5 65 20 10 5

2.4 75 5 10 5 5

4.1 80 3 5 2 10

3.2 65 5 4 6 5 10 5

5.1 96 4

10.8 90 5 5

10.0 80 2 6 2 5 1 4

1 .8 80 5 15

2.6 84 1 1 5

3.3 80 4 10 6

12.0 90 7 3

5.4 69 2 20 2 1 3 3

6.0 91 4 5

TABLE B

Claims

A mixture of dyes and salts thereof comprising:

a dye of Formula (1 ) and salts thereof:

Formula (1 )

wherein:

R¹ and R² are independently H or optionally substituted C_1-4alkyl;

R³ is optionally substituted alkyl; and

n is greater than 0:

(b) a xanthene dye and salts thereof; and

(c) a dye of Formula (2) and salts thereof:

Formula (2)

wherein:

A is optionally substituted aryl;

R⁴ and R⁵ are independently H or optionally substituted Ci_-4alkyl: and R⁶ is either optionally substituted phenyl carrying up to 4 optional substituents selected from the group consisting of -OH, -COOH, -SO₃H and optionally substituted Ci_-4alkyl or R⁵ and R⁶ together with the nitrogen atom to which they are attached represent an optionally substituted aliphatic or optionally substituted aromatic ring system: wherein the ratio of the components (a) to (b) to (c) is in the range of from 90:5:5 to 5:90:5 to 5:5:90 parts by weight.

2. A mixture of dyes and salts thereof as claimed in claim 1 wherein in dyes of Formula (1 ) R¹ is methyl or ethyl, R² is methyl and R³ is t-butyl.

3. A mixture of dyes and salts thereof as claimed in either claim 1 or claim 2 wherein in dyes of Formula (1 ) n is in the range of from 3 to 5.

4. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein the dye of Formula (1 ) is of Formula (3) and salts thereof:

Formula (3)

wherein R is methyl or ethyl.

5. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein the xanthene dye is selected from the group consisting of C. I. Acid Red 50 and salts thereof, C. I. Acid Red 52 and salts thereof, C. I. Acid Red 94 and salts thereof and C. I. Acid Red 289 and salts thereof.

6. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein the xanthene dye is C. I. Acid Red 52 and salts thereof.

7. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein in the dyes of Formula (2) A is naphthyl substituted with 1 to 3 substituents selected from the group consisting of -OH, -COOH, -SO₃H and optionally substituted Ci_-4alkyl or phenyl substituted with 1 to 3 substituents selected from the group consisting of -OH, -COOH, -SO₃H and optionally substituted C_1-4alkyl.

8. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein in the dyes of Formula (2) when R⁶ is optionally substituted phenyl carrying 1 to 3 substituents selected from the group consisting of -OH, -COOH, - SO₃H and optionally substituted C_1-4alkyl.

9. A mixture of dyes and salts thereof as claimed in any one of claims 1 to 7 wherein In the dyes of Formula (2) when R⁵ and R⁶ together with the nitrogen atom to which they are attached represent an optionally substituted aliphatic or optionally substituted aromatic ring system then they are an optionally substituted morpholinyl ring.

10. A mixture of dyes and salts thereof as claimed in any one of the preceding claims wherein the dyes of Formula (2) are of Formula (4) and (5) and salts thereof:

Formula (5)

1 1 . A composition comprising a mixture of dyes and salts thereof, as described in any one of claims 1 to 10, and a liquid medium.

12. A composition as claimed in claim 10 which is ink suitable for use in an ink- jet printer.

13. A process for forming an image on a substrate comprising applying ink suitable for use in an ink-jet printer, according to claim 12, thereto by means of an ink-jet printer.

14. A material printed with a mixture of dyes and salts thereof as described in any one of claims 1 to 10.

15. An ink-jet printer cartridge comprising a chamber and ink suitable for use in an ink-jet printer, according to claim 12, wherein the ink is in the chamber.