Ink jet printing process

Details Ink jet printing process Ink jet printing process

1998-12-18

2001-03-27

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Medium and processing means

C347S105000

Reexamination Certificate

active

06206517

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an ink jet printing process for improving the light stability of an ink jet image formed from an aqueous ink containing a certain cationic dye.
BACKGROUND OF THE INVENTION
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is molecularly dispersed or solvated by a carrier medium. The carrier medium can be a liquid or a solid at room temperature. A commonly used carrier medium is water or a mixture of water and organic co-solvents. Each individual dye molecule is surrounded by molecules of the carrier medium. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier medium, such inks also generally suffer from poor water-fastness.
DESCRIPTION OF RELATED ART
JP 10-219157 relates to an ink jet ink comprising an aqueous medium, a colorant and a very small amount of glutaraldehyde as a biocide.
There is a problem with using this ink, however, in that when it is printed on an image-recording element, the resultant image fades when exposed to light over a period of time, i.e., has poor light stability.
It is an object of this invention to provide an ink jet printing process for improving the light stability of an ink jet image formed from an aqueous ink containing a deprotonated cationic dye. It is another object of the invention to provide an ink jet printing process where the laydown of the hardener applied can be precisely controlled independently of ink laydown and can be applied non-imagewise to the entire element.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the present invention which comprises an ink jet printing process for improving the light stability of an ink jet image comprising:
a) providing an ink jet recording element comprising a support having thereon an image-recording layer comprising a cross-linkable polymer of gelatin or acetoacetylated poly(vinyl alcohol) and a mordant;
b) applying liquid ink droplets of a dye on the image-recording layer in an image-wise manner, the dye being a water-soluble deprotonated cationic dye which is capable of being reprotonated to a cationic dye having a N—H group which is part of a conjugated system; and
c) applying an aqueous solution of a multivalent inorganic salt to the image to cross-link the polymer.
It was found that when an aqueous solution containing a hardener is applied to a cationic dye-based ink image where the image-receiving layer has a cross-linkable polymer and a mordant, that the light stability of the image is improved.
DETAILED DESCRIPTION OF THE INVENTION
This process offers an advantage over incorporating a hardener in an ink since the hardener can be applied in both imaged and non-imaged areas, and the laydown can be precisely controlled independent of ink laydown.
The hardeners employed in the invention may be used at concentrations ranging from 0.10 to 5.0 weight percent of active ingredient in the aqueous solution, preferably 0.25 to 2.0 weight percent.
The aqueous hardener solution may also contain, if desired, cosolvents, humectants, surfactants, and other ingredients commonly added to ink jet inks.
The multivalent inorganic salt hardener that can be employed in the invention include the following (including mixtures thereof): sulfates of a trivalent metal such as aluminum sulfate, iron sulfate, boron sulfate, gallium sulfate, indium sulfate, titanium sulfate, etc., nitrates of iron, aluminum, zinc, etc.
Specific examples of multivalent inorganic salt hardener s useful in the invention include the following:
Hardener 1 ferric nitrate
Hardener 2 aluminum nitrate
Hardener 3 zinc nitrate
Hardener 4 zinc sulfate
Hardener 5 aluminum sulfate
In a preferred embodiment, the hardener employed in the invention is aluminum sulfate.
The aqueous hardener solution may be applied to the ink jet image in accordance with the invention in a non-imagewise manner either through a separate thermal or piezoelectric printhead, or by any other method which would apply the hardener solution evenly to the image, such as a spray bar or immersing the element in a bath of hardener. Methods of applying a hardener solution are disclosed in commonly-owned U.S. patent application Ser. No. 09/083,673 filed May 22, 1998, entitled “Printing Apparatus With Spray Bar For Improved Durability” of Wen et al. and U.S. patent application Ser. No. 09/083,876, filed May 22, 1998, entitled “Ink Jet Printing Apparatus With Print Head For Improved Image Quality” of Wen et al., the disclosures of which are incorporated herein by reference.
Deprotonated cationic dyes useful in the invention which are capable of being reprotonated to a cationic dye having a N—H group which is part of a conjugated system are described in U.S. Pat. No. 5,523,274, the disclosure of which is hereby incorporated by reference.
In a preferred embodiment of the invention, the deprotonated cationic dye employed in the invention and the corresponding cationic dye having a N—H group which is part of a conjugated system have the following structures:
wherein:
X, Y and Z form a conjugated link between nitrogen atoms selected from CH, C-alkyl, N, or a combination thereof, the conjugated link optionally forming part of an aromatic or heterocyclic ring;
R represents a substituted or unsubstituted alkyl group from about 1 to about 10 carbon atoms;
R
1
and R
2
each individually represents a substituted or unsubstituted phenyl or naphthyl group or a substituted or unsubstituted alkyl group from about 1 to about 10 carbon atoms; and
n is an integer of from 0 to 11.
The deprotonated cationic dyes according to the above formula are disclosed in U.S. Pat. Nos. 4,880,769, 4,137,042 and 5,559,076, and in K. Venkataraman ed.,
The Chemistry of Synthetic Dyes
, Vol. IV, p. 161, Academic Press, 1971, the disclosures of which are hereby incorporated by reference. Specific examples of such dyes include the following (the &lgr; max values and color descriptions in parentheses refer to the dye in its protonated form):
The dyes described above may be employed in any amount effective for the intended purpose. In general, good results have been obtained when the dye is present in an amount of from about 0.05 to about 1.0 g/m
2
, preferably from about 0.1 to about 0.5 g/m
2
. Dye mixtures may also be used.
A mordant can be used in the image-recording element used in the invention to fix the deprotonated cationic dye. For example, there may be used an anionic polymer such as sulfonated and carboxylated polyesters, sulfonated and carboxylated acrylates, poly(vinyl sulfonic acid), poly(vinyl styrene sulfonate sodium salt), sulfonated and carboxylated polyurethanes, sulfonated polyamides, polyolefinic emulsions, carboxylated butadiene, or derivitized anionic gelatin. In a preferred embo

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