Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-01-26
2003-04-29
Hess, Bruce H. (Department: 1774)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C428S195100
Reexamination Certificate
active
06554418
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an inkjet printing process for improving the smear, light stability and density of a printed image containing an ink jet ink containing a water-soluble anionic dye and a cationic receiver.
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 inkjet, 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. Inkjet 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 inkjet 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.
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer. The ink-receiving layer may be a polymer layer which swells to absorb the ink or a porous layer which imbibes the ink via capillary action.
Ink jet prints, prepared by printing onto ink jet recording elements, are subject to environmental degradation. They are especially vulnerable to water smearing, dye bleeding, coalescence and light fade. For example, since ink jet dyes are water-soluble, they can migrate from their location in the image layer when water comes in contact with the receiver after imaging. Highly swellable hydrophilic layers can take an undesirably long time to dry, slowing printing speed, and will dissolve when left in contact with water, destroying printed images. Porous layers speed the absorption of the ink vehicle, but often suffer from insufficient gloss and severe light fade. There is a need to provide an ink jet recording element which overcomes the above deficiencies.
EP A 1 022 383 A1 discloses a treating agent for a sheet surface to be used in ink jet printing. The treating agent is described as being a graft copolymer composed of a backbone polymer and a branch polymer, either of which is a polymer having vinyl alcohol units, and the other of which is a polymer having cationic groups. However, there is a problem with this graft copolymer in that images printed on an image-receiving layer containing this graft copolymer have undesirable smearing when subjected to high humidity conditions.
It is an object of this invention to provide an ink jet printing method using anionic dyes suitable for use in aqueous inks for ink jet printing that will provide images with better smear, light stability and density using certain receiver elements.
SUMMARY OF THE INVENTION
This and other objects are achieved in accordance with this invention which relates to an inkjet printing method, comprising the steps of:
A) providing an ink jet printer that is responsive to digital data signals;
B) loading the printer with ink-receptive elements comprising a support having thereon an image-receiving layer comprising a graft copolymer comprising a backbone copolymer and at least one branch copolymer, the backbone copolymer comprising structural units capable of being oxidized by a transition metal catalyst and the branch copolymer comprising cationic units and neutral hydrophilic units;
C) loading the printer with an ink jet ink composition comprising water, a humectant, and a water-soluble anionic dye; and
D) printing on the image-receiving layer using the ink jet ink in response to the digital data signals.
It has been found that use of the above dyes and image-receiving layer provides excellent smear, light stability and density.
DETAILED DESCRIPTION OF THE INVENTION
Any anionic, water-soluble dye may be used in a composition employed in the method of the invention such as a dye having an anionic group, e.g., a sulfo group or a carboxylic group. The anionic, water-soluble dye may be any acid dye, direct dye or reactive dye listed in the COLOR INDEX but is not limited thereto. Metallized and non-metallized azo dyes may also be used as disclosed in U.S. Pat. No. 5,482,545, the disclosure of which is incorporated herein by reference. Other dyes which may be used are found in EP 802246-A1 and JP 09/202043, the disclosures of which are incorporated herein by reference. In a preferred embodiment, the anionic, water-soluble dye which may be used in the composition employed in the method of the invention is a metallized azo dye, a non-metallized azo dye, a xanthene dye, a metallophthalocyanine dye or a sulfur dye. Mixtures of these dyes may also be used. An example of an anionic dye which may be used in the invention is as follows:
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 0.2 to about 5% by weight of the ink jet ink composition, preferably from about 0.3 to about 3% by weight. Dye mixtures may also be used.
As noted above, the graft copolymer useful in the invention comprises a graft copolymer comprising a backbone copolymer and at least one branch copolymer, the backbone polymer comprising structural units capable of being oxidized by a transition metal catalyst and the branch copolymer comprising cationic units and neutral hydrophilic units.
Examples of backbone polymers comprising structural units capable of being oxidized by a transition metal catalyst include substituted or unsubstituted vinyl polymers or cellulosics, preferably poly(vinyl alcohols), poly(N-vinylpyrrolidones), polyamides, or substituted celluloses such as alkyl celluloses, hydroxyalkyl celluloses, etc. The backbone polymer can be a homopolymer or a copolymer. On being oxidized, the backbone polymer presumably forms a free radical site on the backbone that can attack ethylenically unsaturated branching monomers, thus leading to the formation of a grafted copolymer. A preferred transition metal catalyst is a Ce
IV
salt. Particularly preferred backbone polymers useful in the invention are poly(vinyl alcohols), such as those having from about 60 mol % to about 100 mol % hydrolyzed.
The branch copolymer that is grafted onto the backbone polymer comprises both cationic units as well as neutral, hydrophilic units. Monomers used to introduce cationic units into the branch copolymer include those with the following general structure:
where R is each independently H or a substituted or unsubstituted alkyl group of 1 to about 4 carbon atoms, M is a group containing cationic charge, and X is an anion or a mixture of anions.
Preferred examples of M are:
where A is either 0 or NH, each R
1
, independently represents an alkyl, cyclic alkyl, or aryl group having from 1 to about 20 carbon atoms, and n is an integer from 2 to about 12.
Another preferred example of M is:
where R
1
is defined as
Chen Tien-Teh
Kung Teh-Ming
Lawrence Kristine B.
Teegarden David M.
Cole Harold E.
Eastman Kodak Company
Grendzynski Michael E.
Hess Bruce H.
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