Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-11-23
2002-04-09
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860, C106S031900
Reexamination Certificate
active
06368397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a new ink for ink jet printing, a combination of the ink and a liquid, and a method for ink jet printing with those.
2. Description of the Related Arts
Among many printing methods is the so-called ink jet printing, which causes a liquid ink or a molten solid ink to jet from a nozzle, slit, or porous film, thereby making records on paper, cloth, film, and the like. The printer for ink jet printing has the advantage of being small in size, low in price, and quiet in operation. It is commercially available as a black (monochromatic) printer which achieves high-quality printing on plain paper (such as report paper and copying paper). With the wide diffusion of ink jet printers, attempts have been made to improve ink for ink jet printing.
Ink for ink jet printing should (1) give uniform images with high resolution and high density without color mixing (intercolor bleed), (2) discharge itself accurately and stably without nozzle clogging due to drying, (3) dry rapidly on paper, (4) give images with good fastness, and (5) have good long-term stability. Many attempts have been made to meet these requirements.
Ink for ink jet printing has been dominated by ink of water-based dye. It poses a problem of waterfastness and light fastness arising from the water-soluble dye. It is not necessarily satisfactory in image storage stability. On the other hand, many kinds of ink containing pigment as a colorant have been proposed for improvement on waterfastness and light fastness. Having achieved the purpose and being preference, some of them have been put to practical use. For example, U.S. Pat. No. 5,085,698 discloses an ink containing an AB or BAB block copolymer as a dispersant, and U.S. Pat. No. 5,172,133 discloses an ink containing a specific pigment, water-soluble polymer, and solvent.
A pigment ink is good in waterfastness but is liable to flocculate during storage for a long time or at a high temperature, or it poses a problem of storage stability. Optical density and dispersion stability are mutually contracting properties. A pigment with a high flocculation force flocculates on paper after printing, thereby giving a high optical density; however, it is poor in dispersion stability because of its high flocculation force.
There are several ways of increasing the optical density by (1) increasing the concentration of pigment in ink, (2) using a more hydrophobic dispersant, (3) decreasing the amount of dispersant, and (4) using a pigment with higher oil absorption. The first results in poor storage stability and head clogging due to pigment flocculation. The second to fourth also result in poor storage stability, particularly at a high temperature. Improvement in dispersion stability needs some means contrary to the foregoing. High optical density is still incompatible with good dispersion stability.
Japanese Patent Application Laid-open Nos. 8-193175 and 9-207424 disclose a method of increasing optical density by causing the pigment to react with a treating solution for flocculation immediately after printing with a pigment ink. This method achieves independently the object of increasing optical density and the object of improving dispersion stability. However, this method has the disadvantage of requiring a treating solution in addition to ink. This treating solution increases the total amount of liquid on paper, presenting problems such as longer drying time and paper wrinkling and curling.
SUMMARY OF THE INVENTION
The present invention was completed to solve the above-mentioned problems involved in the prior art technology. The present invention provides an ink for ink jet printing which is of pigment dispersion type and is characterized by both good storage stability and high optical density at time of printing.
The present invention also provides an ink for ink jet printing which invariably produces clear images on plain paper. The present invention also provides a recording material of an ink and a liquid which prevents an ink of pigment dispersion type from mixing with another ink of different color, thereby giving clear images, at the time of ink jet printing on plain paper.
The present invention also provides a method for performing ink jet printing with the ink for ink jet printing.
The inventors of the present invention carried out extensive studies on an ink for ink jet printing of pigment dispersion type which comprising pigment, aqueous polymer, water-soluble organic solvent, and water. It was found that if the ink is to give a high optical density, the ink should be able to produce particles of adequate size on paper and hence the ink should contain particles having a particle diameter larger than 0.5 &mgr;m. Such coarse particles, however, are liable to clog the passage from the ink reservoir to the head and to flocculate and precipitate during long-term storage. It was also found that an ink gives a high optical density at the time of printing if it contains particles such that the number of particles, having a particle diameter larger than 0.5 &mgr;m, is less than 6×10
4
/&mgr;l before ink jetting and the number of particles, having a particle diameter larger than 5 &mgr;m, is less than 50/&mgr;l before ink jetting and the number of particles, having a particle diameter larger than 0.5 &mgr;m, increases to 6×10
4
/&mgr;l to 6×10
5
/&mgr;l after ink jetting. The present invention is based on this finding.
The present invention covers an ink for ink jet printing which contains a pigment, a water-soluble organic solvent, and water. In the ink, the number-average particle diameter is from 10 to 150 nm after ink jetting, the number of particles having a particle diameter larger than 0.5 &mgr;m is 6×10
4
to 6×10
5
/&mgr;l after ink jetting, and the number of particles having a particle diameter larger than 5 &mgr;m is less than 50/&mgr;l after ink jetting.
In the ink, the number-average particle diameter may be 10 to 150 nm before ink jetting, the number of particles having a particle diameter larger than 0.5 &mgr;m may be less than 6×104 before ink jetting, the rate of change of the number-average particle diameter may be from 0 to 50%, and the number of particles having a particle diameter larger than 0.5 &mgr;m is 6×10
4
/&mgr;l to 6×10
5
/&mgr;l after ink jetting.
In the ink, the number of particles having a particle diameter larger than 0.5 &mgr;m may increase threefold or more after ink jetting.
The ink may contain an aqueous polymer having an HLB of 11 to 15.
In the ink, the aqueous polymer may be a dispersant and the water-soluble organic solvent may have a solubility parameter equal to or larger than 11.
In the ink, the water-soluble organic solvent having a solubility parameter equal to or larger than 11 and smaller than 15 may be less than 5 wt % of the total amount (by weight) of the ink, and the water-soluble organic solvent having a solubility parameter of 15 and above may be 1 to 50 wt % of the total amount (by weight) of the ink.
In the ink, the dispersant may have a weight-average molecular weight of 3000 to 20000.
In the ink, the pigment may be carbon black having a primary aggregate particle diameter of 10 to 30 nm.
The method of ink jet printing according to the present invention uses the above ink for ink jet printing.
The method of ink jet printing may employ the thermal ink jet system.
The recording material according to the present invention contains the above ink and a second liquid containing a water-soluble organic solvent with a solubility parameter of 9 to 11 and/or a surfactant and water.
In the recording material, the ink may have a surface tension of 35 to 55 mN/m and the second liquid may have a surface tension of 20 to 40 mN/m.
In the recording material, the second liquid may contain a multivalent metal salt and/or a cationic compound.
In the recording material, the second liquid may or may not contain a colorant.
The above method of ink jet printing may use the above recording material.
In the method of ink
Hashimoto Ken
Horinouchi Kyoko
Ichizawa Nobuyuki
Yui Toshitake
Faison Veronica F.
Fuji 'Xerox Co., Ltd.
Koslow C. Melissa
Morgan & Lewis & Bockius, LLP
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