A Pigment Precursor for Inkjet Inks
Ohya, Hidenobu ＊Kida, Shuji ＊Abe, Takao ＊There are two general categories of water-based inkjet inks: dye-based inks and pigment-based inks. Pigment-based inks provide images with comparatively greater stability when subjected to light or to chemicallyreactive materials such as oxidizing gases. However, pigment-based inks typically fail to provide image gloss
and resistance to abrasion. In response, we have developed a novel inkjet ink that employs a new watersoluble pigment precursor. During printing, this pigment precursor ink behaves much like a dye-based ink. But
once this ink has been applied to the print medium, a simple treatment triggers the provision of pigment
particles. The result is an image that possesses not only high image stability but also high gloss and highresistance to abrasion.

１

3. The post-printing treatment of the medium to re-Introduction

lease the pigment from the pigment precursor, andRecent years have seen marked technical advances in

4. The evaluation of the terminal image.

inkjet printing, with the image quality and the image
stability of inkjet prints approaching those of photographic

２．１

Design and synthesis of pigment precursor

We selected a quinacridone pigment（CI Pigment Redprints.
Many efforts that have borne on bringing high image122）as our color material because magenta presents thequality and high image stability together have been made.

greatest challenge to simultaneously achieving optical

Bauer, Baumgart, and Zoller surveyed a number of wa-brightness and high image stability.

ter-soluble magenta dyes.

１）

Bugner and Burmel studied

the effect of particle size in pigment inks on such characteristics as printing reliability, image quality, and durability. ２） Tsutsumi, Sawada, and Nakano developed anemulsion colorant involving a water-based polymer emulsion that contained a water-insoluble dye or pigment. ３）
Zhimin and Abul developed a solvent-soluble pigment
precursor（latent pigments）.４） And Parazak examined
the application of latent pigments to inkjet printing ５） .
We join these efforts with a method in which a watersoluble pigment precursor penetrates the surface of theprinting medium and then releases a pigment. This combines the high gloss and resistance to abrasion of a dye-Fig.1 Pigment precursor

based ink with the superior light stability of a conventional pigment-based ink.

In the pigment precursor that we designed and synthesized（Fig. １）, the nitrogen atoms（A）are protected

２by groups（B）to increase water solubility, which is ac-

Experimental

complished by preventing the aggregation of molecules.

Our work may be viewed in four segments:

The groups contain a water-soluble radical（C）. The

1. The design and synthesis of a new water-solublecomposition of the groups（B）is designed to afford easeof synthesis and stability in water. Compared to an m-pigment precursor,
2. The preparation of an ink containing that water-

sulfonic acid salt type, this o-sulfonic acid salt type pre-soluble pigment precursor, and printing an interim

cursor is easy to synthesize and provides good stability;

image with that ink,

in this, the steric effect of the o-sulfonic acid salt is likelyinvolved.

Ink Jet Technology DivisionCorporate Technology Center

The pigment precursor was synthesized from CI Pig-

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ment Red 122 and o-sulfobenzoic anhydride, using NaH

pound obtained was identified as the target compoundin HMPA or N-methylpyrolidone（Fig. ２）. The com-through NMR and mass spectra.

Fig.2 Synthesizing the pigment precursor

The pigment precursor was dissolved in water to approximately a 10% solution, the solution was colored yel-２．２

Ink preparation and printing

We prepared an ink containing the pigment precur-

low, and the stability of the pigment precursor was thensor, consisting of the following:studied at various pH values. The pigment precursor

Pigment precursor（6%）

was stable in alkali （Fig. ３） and neutral conditions,

Diethylene glycol（10%）

while in acidic conditions（in a pH 1.68 buffer）, the pre-Glycerol（10%）

cursor was slowly hydrolyzed at room temperature, andTriethylene glycol mono-n-butyl ether (10%)

a red precipitate appeared.

Nonionic surfactant（0.1%）
Deionized water（63.9%）
With this ink, we printed on a porous medium（Konica
Inkjet Paper Photolike QP）with a commercial inkjet printer（Piezo type）and obtained a yellow image（Fig. ５）.
２．３

Post-printing treatment

Prints were sprayed with diluted sulfuric acid or ptoluene sulfonic acid aqueous solution, and heated to 90130℃ for several seconds with a commercial laminator.
This post-printing treatment caused the pigment precursors to be hydrolyzed and thus to release the pigment particles（Fig. ４）. Consequently, from the yelFig.3 Stability of the pigment precursor（pH10.0）

lowish, interim image, the reddish, terminal image
emerged.

Fig.4 Synthesizing the pigment precursor

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２．４

Evaluation the image

Pigments naturally provide high light stability. How-We measured the reflection spectra of the terminal

ever, with a conventional pigment image（Fig. ７ A）,

image and compared it with that of an image printed

the pigment lies chiefly on the surface of the medium.

with conventional CI Pigment Red 122 water-based ink

Because the average size of the pigment particle is（Fig. ５）. The two spectra were nearly identical.

roughly 100-150nm, the pigment particle is prevented
from penetrating the surface. The result is a surface
roughness that both limits gloss and leaves the image
susceptible to abrasion.
In contrast, dye images（Fig. ７ B）, by their nature,
do not provide sufficient light stability. However, because
dye images penetrate the surface of the medium, they
do allow high gloss and high resistance to abrasion.
In the pigment precursor image（Fig. ７ C）, the pigment precursor deposits the pigment well below the surface of the medium; thus, just as with dyes, gloss andresistance to abrasion are high. But at the same time, byvirtue of being true pigments, light stability is also high.
It should be observed that the light stability of ourexperimental pigment precursor images, while exhibiting the characteristically superior light stability of a pigment image, does not yet match the performance of aconventional pigment-based ink（Fig. ６）. As we address this challenge, we note that the light stability of a

Fig.5 Reflection spectra

pigment image generally increases with the size of theExtending our comparison to encompass an appropri-pigment particles.

ate dye image, we evaluated the gloss, light stability, andresistance to abrasion resultant from the three types ofinks（Table １）. The pigment precursor image exhibited the high gloss and resistance to abrasion of the dyeimage while it approached the light stability of the conventional pigment image.
Table1 Image evaluations

To determine how the pigment precursor image managed to simultaneously avoid the low gloss and resistanceto abrasion of the conventional pigment image and thelow light stability of the dye image, we examined micro-Fig.6 Light stability

scopic, cross-sectional views of each image（Fig. ７）.

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Fig.7 Cross-sectional views of images

３Conclusion

We synthesized a quinacridone type water-soluble pigment precursor and evaluated its performance. Our results indicate that inkjet inks using pigment precursors
promise to combine the high gloss and resistance to abrasion of dye-based inks with the high light stability ofconventional pigment inks.

References
１）Wolfgang Bauer, Dieter Baumgart, and Walter Zoller, IS&T's
NIP12: International Conference on Digital Printing Technologies, Proceedings, pp.59-65 (1996)
２）D.E. Bugner and A.D. Bermel, IS&T's NIP13: International Conference on Digital Printing Technologies, Proceedings, pp.667669 (1997)３）T. Tsutsumi, M. Sawada, and Y. Nakano, IS&T's NIP15: International Conference on Digital Printing Technologies, Proceedings, pp.133-136 (1999 )４）Hao Zhimin and Iqbal Abuul, United States Patent No.5591865,5616725, 5646299, and 5650520
５）Dennis P. Parazak, Japanese Patent Publication Open to Public
Inspection No. 11-246809

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