WO1991010710A1

WO1991010710A1 - Black ink for ink jet systems

Info

Publication number: WO1991010710A1
Application number: PCT/US1991/000402
Authority: WO
Inventors: Linda T. Creagh; Steven J. Fulton; Lawrence R. Young
Original assignee: Spectra, Inc.
Priority date: 1990-01-22
Filing date: 1991-01-22
Publication date: 1991-07-25

Abstract

In the particular embodiments described in the specification, a black ink for an ink jet system contains a vehicle which is solid at room temperature and may be liquefied at elevated temperature together with 1 % to 10 % black pigment and 0.1 % to 3.0 % of a dye which, together with the color of the ink vehicule, produces a black appearance.

Description

Black Ink for Ink Jet Systems

Technical Field

This invention relates to black inks for use in ink jet systems and, more particularly, to a new and improved black ink for ink jet systems.

Background Art

Many ink jet systems utilize black inks contain¬ ing a dye which is soluble in the ink vehicle. Such dyes, however, which are usually based on organic compounds, tend to lack long-term stability and may be degraded by extensive exposure to heat and light. Moreover, such dyes, when used in hot melt ink sys¬ tems, tend to produce perceptible offset from a printed page onto the hand of a user, for example.

To overcome such problems, black inks for ink jet systems have been formulated with a finely dispersed pigment such as carbon black which does not degrade in response to environmental conditions or tend to pro- duce offset. It has recently been found, however, that, when hot melt ink drops are caused to spread after application by maintaining them above the melt¬ ing point to reduce the contact angle, as described, for example, in the Fulton et al. Patent No. 4,873,134, the concentration of black pigment in the periphery of the drop is decreased so that a projected image of the drop takes on the color of the ink ve¬ hicle which may be brown, rather than appearing black.

Disclosure of Invention Accordingly, it is an object of the present in¬ vention to provide a new and improved black ink for ink jet systems which overcomes the above-mentioned disadvantages of the prior art. Another object of the invention is to provide a black ink for ink jet systems in which the thin edges of a drop which has been spread upon a substrate are projected as substantially black. These and other objects of the invention are attained by providing a hot melt ink comprising a vehicle which is solid at room temperature and may be liquefied by heating for projection in drop form onto a substrate, a black pigment uniformly dispersed in the vehicle, and a dye which is soluble in the vehicle and causes the thin layers of the vehicle to be pro¬ jected as black.

Further objects and advantages of the invention will be apparent from a reading of the following de- scription of preferred embodiments.

Best Mode for Carrying Out the Invention

During the application of hot melt ink to a transparent substrate, as described in the Fulton et al. Patent No. 4,873,134, the ink drops tend to solid- ify with a hemispherical shape which refracts light from a projection system, preventing good color rendi¬ tion in the projected image. As described in the Fulton et al. patent, this problem can be overcome by maintaining the ink at a temperature above its melting point until the drops have spread to provide a reduced contact angle with the surface of the transparent sub¬ strate. Surprisingly, however, the ink vehicle spreads during such spreading at a rate which is more rapid than the rate of diffusion of a pigment such as carbon black into the periphery of the drop. As a result, when the enlarged drop is solidified, the peripheral region is significantly depleted of black pigment, whereas the central portion retains black pigment to appear opaque in transmission. As a re- suit, the projected enlarged drops have an opaque central region with a peripheral region which projects essentially the inherent color of the ink vehicle rather than that of the black pigment.

In order to overcome this problem in accordance with the invention, a pigmented black ink is provided which includes from about 0.1% to about 3.0%, and preferably from about 1% to about 2% by weight, of a dye which is soluble in the ink vehicle. Preferably, the dye is a conventional black dye such as Calco nigrosine, but it may also be a colored dye which, in combination with the inherent color of the ink ve¬ hicle, absorbs all colors uniformly so as to appear substantially black.

The hot melt ink includes a transparent carrier of any conventional type, such as a wax or wax-based system, and 1% to 10%, and preferably 3% to 5%, of finely divided black pigment such as carbon black dispersed therein, along with 0.1% to 3.0%, and pref¬ erably 1% to 2%, of a black dye, such as Calco nigro¬ sine black, which is soluble in the ink vehicle. In a preferred embodiment, the ink vehicle con¬ tains about 4% carbon black and about 1% Calco nigro¬ sine black.

If the ink vehicle is yellow or brown in tone, a blue dye, such as Neozapon blue-807, Orient oil blue- 603 or Shimado oil blue SB, may be used. If the ink vehicle is gray or blue in tone, a red or magenta dye such as oil scarlet may be used.

With a black ink prepared in accordance with the invention, ink drops can be caused to spread on a substrate by maintaining them above the melting point of the ink for a selected time to reduce the contact angle of the drop without resulting in a loss of opacity or color change in the peripheral regions of the drop. Although the invention has been described herein with reference to specific embodiments, many modifica¬ tions and variations therein will readily occur to those skilled in the art. Accordingly, all such vari- ations and modifications are included within the in¬ tended scope of the invention.

Claims

1. A black ink for an ink jet system comprising a vehicle which is solid at room temperature and may be liquefied at elevated temperature, from about 1% to about 10% by weight of a black pig¬ ment dispersed in the vehicle, and from about 0.1% to about 3.0% of a dye which is soluble in the vehicle and which, together with any color in the vehicle, produces a black appearance.

2. A black ink in accordance with Claim 1 containing from about 3% to about 5% black pigment.

3. A black ink in accordance with Claim 1 containing from about 1% to about 2% soluble dye.