METHOD FOR PREPARING A COLORANT FOR USE IN A HOT MELT INK

Abstract

A method for preparing a colorant for use in an ink composition including a substantially non-aqueous carrier composition includes providing a chromophore precursor including one or multiple functional groups which may be subjected to a chemical reaction to form a salt with a preselected counter ion; providing a salt including the preselected counter ion; and providing an organic solvent that is not miscible with water and wherein the reaction product of the chromophore precursor and the salt including the preselected counter ion is soluble; preparing a chromophore precursor solution in water by dissolving a quantity of the chromophore precursor in water adding a quantity of the organic solvent while stirring; adding the salt including the preselected counter ion while stirring to form a resalted chromophore; separating the resalted chromophore from the reaction mixture. The addition of the salt including the preselected counter ion is performed until a molar excess of counter ion has been added with respect to the molar amount of functional groups comprised in the chromophore precursor; A colorant is obtainable and an ink composition includes such a colorant.

Claims

1. A method for preparing a colorant for use in an ink composition comprising a substantially non-aqueous carrier composition, the method comprising the steps of: a. providing a chromophore precursor comprising one or multiple functional groups which may be subjected to a chemical reaction to form a salt with a preselected counter ion; a salt comprising the preselected counter ion; and an organic solvent that is not miscible with water and wherein the reaction product of the chromophore precursor and the salt comprising the preselected counter ion is soluble; b. preparing a chromophore precursor solution in water by dissolving a quantity of the chromophore precursor in water; c. adding a quantity of the organic solvent while stirring; d. adding the salt comprising the preselected counter ion while stirring to form a resalted chromophore; e. optionally filtering the mixture obtained in step d; f. separating the resalted chromophore from the mixture obtained in step d or optionally in step e; wherein step d is performed until a molar excess of counter ion has been added with respect to the molar amount of functional groups comprised in the chromophore precursor;

2. The method according to claim 1, wherein the molar excess of counter ion is expressed as the ratio of the molar amount of counter ion and the molar amount of functional groups comprised in the chromophore precursor which ratio ranges from 1.01:1 to 2.5:1.

3. The method according to claim 1, wherein the separating step f comprises the sub-steps: f1. allowing the mixture obtained in step d or optionally in step e to separate into an aqueous phase and an organic phase by allowing the mixture to rest; f2. removing the aqueous phase; f3. optionally rinsing the organic phase multiple times, each time with more or less a similar amount of water; f4. optionally filtering the organic phase; and f5. concentrating the organic phase by evaporation of the organic solvent.

4. The method according to claim 3, wherein step f3 comprises multiple rinsing steps which are performed with decreasing amounts (mass) of water in each subsequent step.

5. The method according to claim 3, wherein the initial rinsing step is performed with an amount (mass) of water that is larger than the amount (mass) of the organic phase, preferably in a mass ratio water:organic phase of between 1.1:1 and 2.5:1.

6. The method according to claim 1, wherein the chromophore precursor comprises a colorant from the anthrapyridone series.

7. The method according to claim 6, wherein the chromophore precursor comprises at least one sulphonic acid group and/or a derivate thereof as functional group(s).

8. The method according to claim 1, wherein the salt comprises a counter ion selected from the group consisting of phosphonium groups and ammonium groups.

9. The method according to claim 1, wherein the salt is a chloride salt.

10. A colorant obtained by the method according to claim 1.

11. The colorant according to claim 10, wherein the counter ion is tetra butyl phosphonium or tetra butyl ammonium.

12. An ink composition comprising a colorant according to claim 10.

13. The ink composition according to claim 12, wherein the ink composition is a hot melt ink composition, which is solid at room temperature and liquid at a higher temperature and comprising a substantially non aqueous carrier composition.

14. The ink composition according to claim 13, wherein the non aqueous carrier composition comprises an amorphous binder and a crystalline component.

15. The colorant obtained by the method according to claim 2.

16. The colorant obtained by the method according to claim 3.

17. The colorant obtained by the method according to claim 4.

18. The colorant obtained by the method according to claim 5.

19. The colorant obtained by the method according to claim 6.

20. The colorant obtained by the method according to claim 7.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0065] FIG. 1. Results preparation of colorants in accordance with Comparative Example A (left) and Example 1 (right), comprising methyltriphenylphosphonium as counter ion.

[0066] FIG. 2. Results preparation of colorants in accordance with Comparative Example B (left) and Example 2 (right), comprising tetrabutylammnonium as counter ion.

[0067] FIG. 3. Results preparation of colorants in accordance with Comparative Example C (left) and Example 3 (right), comprising tetrabutylphosphonium as counter ion.

[0068] FIG. 4 Results preparation of colorants with a range of molar ratios between the counterion (tetrabutylammnonium) and the functional (reactive) groups in the anthrapyridone chromophore (Acid Red 143) precursor.

[0069] FIG. 5 Results of migration tests of magenta colorants (prepared) according to the present invention in comparison with a reference magenta colorant.

[0070] FIGS. 6A-6C Result of solubility tests of A) AR143/MTP; B) AR143/TBP; and C) AR143/TBN

DETAILED DESCRIPTION

Materials

[0071] The chromophores, in particular Acid Red 143 are obtained from Archroma Management LLC.

[0072] Cyclohexane and toluene are obtained from Merck.

[0073] All other components are obtained from Sigma Aldrich (unless stated otherwise).

Methods

Migration Test

[0074] A chromatography test is performed to provide an (comparative) indication of migration of a colorant on a print substrate. For this, solutions of the colorants to be tested, in dichloromethane are prepared. The prepared solutions contain substantially equal concentrations of colorant. For the purpose of the present invention, the eluent solution consists of a cyclohexane/toluene mixture (50 wt %/50 wt %). A sheet of Wattmann 1-CHR paper is used as a substrate. At about 1 cm from the bottom edge of the paper sheet dots of equal size of the colorant solutions are made (by using a pipette). Each dot is positioned at substantially the same distance from the bottom edge of the paper sheet. Then the sheet is left to dry. A beaker is filled with eluent solution such that the level of eluent solution is less than 1 cm. The dried test sample (paper sheet provided with colorant dots) is placed in the beaker such that the lower edge of the paper sheet touches the bottom of the beaker. Due to capillary flow the eluent solution will flow upward in the paper sheet. This set up is left to stand until the wetted height of paper sheet is at least 1.5 times the height to which the most soluble colorant rises. The results are judged qualitatively. If the colorant dot remains at the starting position, migration is not likely to occur. If the colorant is transported with the eluent solution and forms a streak, that particular colorant is likely to migrate on the substrate.

Solubility Test

[0075] 5 phr (parts per hundred resin (mass)) is added to 50 grams of carrier composition (composition see Examples) at a temperature of 130 C. The carrier composition is filtered beforehand over a 200 nm nylon filter (Pall Ultipor N66). After 4 hours of stirring under nitrogen environment the ink is directly filtered (at a filter pressure p of 1 bar) over a 450 nm glass filter (Pall Ultipor GF) with a circular filtration area with a diameter d of 5 mm. Images of the filters are used to qualitatively judge the solubility of the tested colorant, in particular with reference to one another. In general, the smaller the residue present on the filter (when tested under similar conditions), the better the solubility of the tested colorant in the used carrier composition is. Light microscopy can be used to judge if the residue on the filter is dye related.

EXAMPLES

Comparative Examples (CEx) A-C and Examples (Ex) 1-3: Preparation of Colorants According to the Prior Art and According to the Present Invention

[0076] As starting material 5 grams of a 10.5 w % solution of anthrapyridone chromophore (acid dye), Acid Red 143 (AR143), obtained from Achroma was used [solution with pH of 7]. This chromophore precursor comprises one or multiple (in this example: two) functional groups which are subjected to a chemical reaction to form a salt. Molar quantities counter ion with regard to the number and nature of functional groups were calculated. Molar ratios of the chromophore with respect to the counter ion of 1:0.85 (Comparative Examples A-C) and 1:1.1 (Examples 1-3) were applied, see Table 1. The ratio 1:0.85 is also used in the prior art. The counter ions methyltriphenylphosphonium, tetrabutylammonium and tetrabutylphosphonium were used to resalt the acid dye. 3.6 grams of isoamyl alcohol (ratio between isoamylalcohol and Acid Red solution 0.72:1) was added after which was stirred for 30 minutes. While stirring the calculated amount of counter ion was added.

TABLE-US-00001 TABLE 1 amount of salts used in comparative examples A-C and examples 1-3 Counter ion salt Ratio 1:0.85 [g] Ratio 1:1.1 [g] Methyltriphenylphosphonium-bromide CEx A 0.366 Ex 1 0.473 Tetrabutylammnonium-bromide CEx B 0.330 Ex 2 0.427 Tetrabutylphosphonium-bromide CEx C 0.347 Ex 3 0.450

[0077] The mixture was stirred for two hours and which after the mixture was allowed to separate into different phases by allowing the mixture to rest for at least two hours. The results are shown in FIGS. 1 (CEx A and Ex 1), 2 (CEx B and Ex 2) and 3 (CEx C and Ex 3). In the pictures the lower layer is the aqueous layer (indicated with 10, 10, 10 and 11, 11, 11 respectively), due to the solubility of the solvent (isomyl alcohol) in this aqueous layer, the aqueous layer will always be slightly coloured, because the colorant is soluble in the isomyl alcohol to some extent).

[0078] From these Figures it can be clearly seen that using a molar deficit amount of salt containing the counterions compared to the number of functional (reactive) groups in the chromophore (i.e. CEx A-C), the aqueous phase contains a larger concentration (darker colour) of colorant than when an excess amount of salt is used (i.e. Ex 1-3).

[0079] It can therefore be concluded that the reaction to form a salt of the chromophore precursor and the counterion is incomplete and results in colorant that is still (partly) soluble in the aqueous phase. Consequently the incompletely converted chromophore precursor will not be soluble in a non-aqueous hot melt ink composition.

[0080] In accordance with the present invention, a molar excess of the counter ion is used with reference to the molar amount of functional groups comprised in the chromophore precursor in order to bring the reaction to completion (Ex. 1-3).

[0081] In FIG. 4 the results of preparations of colorants with a range of molar ratios between the counterion (tetrabutylammnonium) and the functional (reactive) groups in the anthrapyridone chromophore (Acid Red 143) precursor is shown. The used relative molar amount of counterion with respect to the molar amount of functional (reactive) groups present in the chromophore precursor is denoted below the respective bottle. From this Figure it can be derived that at an excess ratio 1.1:1 (fourth bottle from the left) indeed decreases the solubility in the aqueous phase.

Example 4: Preparation of a Colorant Using a Method According to the First Aspect of the Present Invention

[0082] As starting material 1400 grams of a 10.5 w % solution of anthrapyridone chromophore (acid dye), Acid Red 143 (AR143), obtained from Achroma was used [solution with pH of 7]. This chromophore precursor comprises one or multiple (in this example: two) functional groups which are subjected to a chemical reaction to form a salt. The required molar quantity counter ion with regard to the number and nature of functional groups was calculated. A molar ratio of the chromophore with respect to the counter ion of 1:1.1 was applied. 1008 grams of isoamylalcohol (ratio between isoamylalcohol and Acid Red solution 0.72:1) was added after which was stirred for 30 minutes. While stirring 122 grams of the counter ion tetrabutylammonium-bromide (TBN-Br) was added. The mixture was stirred for two hours which after the mixture was filtered first over a 1 m filter (Pall, SealKleen IJF-X9860). The mixture was allowed to separate into different phases by allowing the mixture to rest for at least two hours. The aqueous phase was separated from the mixture by using a separatory funnel. The organic (isoamylalcohol) phase (containing the resalted chromophore) was rinsed with water for several times until the organic phase was within specification (i.e. containing 2 ppm or less bromide). Several rinsing schemes were used as shown in the table below.

TABLE-US-00002 number of rinsing rinsing steps till bromide scheme organic phase:rinsing water <2 ppm A 1 rinse 1:1 and 9 rinses 1:0.5 9 B 2 rinses 1:1.5 and 5 rinses 1:0.5 7 C 2 rinses 1:1.5 and 4 rinses 1:1 6

[0083] For example scheme B is performed as follows: the first two times the amount of water that was used to rinsing the isoamylalcohol phase was 1750 grams (ratio between rinsing water and Acid Red solvent solution (i.e. the organic phase) 1.5:1). This was followed by five times the amount of water that was used to rinsing further the isoamylalcohol phase was 583.3 grams (ratio between rinsing water and Acid Red solution 0.5:1). It is concluded that by starting the rinsing sequence with rinsing steps with an amount (mass) that is larger than the amount (mass) of the organic phase, less rinsing steps are required, while using the same total amount of water (compare schemes A and B: in both cases the total amount (mass) of water used is 5.5 times the amount (mass) of the organic phase, while in scheme B 7 rinsing steps are required, while in scheme A 9 rinsing steps are required). If the amount of water used in the subsequent steps is further increased (compare schemes B and C), the rinsing efficiency can be further improved.

[0084] After rinsing the isoamylalcohol phase was concentrated by evaporation. The remaining product is the salt of the chromophore (AR143 in the present example) and the counter ion. For the present example MTP, TBP and TBN respectively.

Example 5 Preparation of an Ink Carrier Composition

[0085] A carrier composition containing 70% by weight of the bis-ester formed from the reaction of hexanediol and 2 mol-equivalents of p-methoxy benzoic acid. This compound is known as 1,6-bis(methoxybenzoyloxy)hexane (1,6-4A) and is disclosed in U.S. Pat. No. 6,682,587 (Table 3, compound 8). In addition, the carrier composition contains 30% by weight of an amorphous component which is a mixture of different compounds. This amorphous component can be obtained by reacting di-isopropanolamine, benzoic acid and succinic acid anhydride as explained in example 3 of U.S. Pat. No. 6,936,096. These components are melt mixed as to form a carrier composition.

[0086] Inks that can be formed with the carrier composition according to Example 5 and a colorant according to Example 4 appear to have a sparkling magenta color that will hardly show any visible migration of the coloring material when transferred to a plain paper receiving material. Even in case the receiving material is subsequently laminated with another layer, e.g. a transparent foil, the transferred image will substantially retain its sharpness and image quality.

Example 6 Migration Test

[0087] The colorants prepared in Example 4 and a reference colorant (Solvent Red 149, SR149) were subjected to the migration test as described above. The results are shown in FIG. 5. The following colorants are shown: AR143/TBP (1); AR143/TBN (2); AR143/MTP (3) and a reference colorant SR149 (4). It can be concluded that in view of the reference colorant, the resalted colorants prepared in Example 4 show no migration, while the reference colorant shows significant migration.

Example 7 Solubility Test

[0088] The colorants prepared in Example 4 and the carrier composition prepared in Example 5 are used to perform the above described solubility test. The results are shown in FIG. 6. The darkness of the spot in the middle of the filter is an indication for the amount of residue present on the filter. In FIG. 6 it can be clearly seen that the filter used for AR143/MTP (FIG. 6A) shows the darkest spot, followed by the filter used for AR143/TBP (FIG. 6B) which has a spot that has a similar color than the surroundings and finally the lightest spot is observed on the filter used for AR143/TBN (FIG. 6C). Therefore, it is shown that AR143/TBP and AR143/TBN have improved solubility in the carrier composition compared to AR143/MTP, and AR143/TBN shows the highest solubility in the used carrier composition.

[0089] Without wanting to be bound to any theory it is believed that solubility of the colorants in the carrier composition may be improved by using a counter ion having a branched structure in order to provide significant steric hindrance, which may prevent crystallization of the colorant in the carrier composition. In view of solubility in the in carrier composition, the counter ion must have sufficient affinity with the components in the ink carrier composition. Inventors have found that branched counter ions indeed show improved solubility with reference to standard C.I. Solvent Red 149 colorant. Furthermore, inventors have found that the tetra butyl substituted counter ions show superior solubility in the carrier composition of the ink compared to counter ion methyl-triphenyl phosphonium. Of these the ammonium variant (i.e. tetrabutylammonium, TBN) shows the best solubility.

[0090] It is further believed that due to the high(er) electronegativity resulting in a stronger bond between the chromophore and the ammonium counter ion, such colorants shows less sensitivity towards formation of alkali and earth alkali salts of the chromophore deposits that may cause print head defects. Printer engine tests prove this hypothesis.

[0091] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually and appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any combination of such claims are herewith disclosed. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).