Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-02-19
2001-02-13
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031280, C523S201000
Reexamination Certificate
active
06187086
ABSTRACT:
TECHNICAL FIELD
The present invention relates to generally to ink-jet inks, and, more particularly, to ink-jet inks with improved bleed control.
BACKGROUND ART
In ink development work with a new technology, one of the most important parameters to be considered is the bleed control between black and color inks, often referred to as “K/C control” or “K/C bleed”. Using self-dispersed pigments as the colorant tends to result in relatively poor bleed control, compared to pigments that use a separate dispersant molecule. In these inks, the black ink contains the pigment, while the color inks contain one or more appropriate water-soluble dyes (cyan, yellow, magenta).
One might ask why it is so difficult to control bleed with self-dispersed pigments even though they have a negative charge and the color ink is low pH. The answer to this question is crucial in inventing a solvent system that can reduce bleed. Self-dispersed pigments, such as available from Cabot Corp., have negatively-charged groups that are covalently-bonded to the pigment surface. Theoretically, either a positive charge from cations, or a proton from a low pH color ink in the vicinity of two negatively-charged black, self-dispersed pigment particles should lower their electrostatic potential and allow the pigments to come closer and agglomerate. This apparently does not happen to the desired extent with the self-dispersed pigment and they don't crash with the same intensity on the paper. Without subscribing to any particular theory, it appears that their mutual collisions do not lead to agglomeration; in other words, their collisions are elastic in nature in that the two colliding particles bounce back away from each other. This is in contrast to a pigment-based ink using a separate dispersant, such as disclosed in U.S. Pat. No. 5,500,082, issued to H. Matrick et al. Such dispersant molecules with large “tentacles” (long chain carbons) sticking out and which have a more chance to “stick together” in the event of a collision.
Thus, there is a need to provide an ink containing a self-dispersing pigment that evidences improved bleed control.
DISCLOSURE OF INVENTION
In accordance with the present invention, two classes of solvents that help to reduce bleed are used in formulating inks that contain self-dispersed pigments. The two classes are organic esters and certain diols and triols.
The solvents disclosed herein help self-dispersed pigments to agglomerate by producing successful mutual collisions when the electrostatic potential is reduced with positively charged color inks. The details of this mechanism are not understood clearly yet. These solvents could be changing the dielectric constant of the ink, thereby reducing the repulsion potential of the pigment particles themselves.
BEST MODES FOR CARRYING OUT THE INVENTION
In accordance with the present invention, bleed control between black (K) inks containing self-dispersed pigments and color (CYM—cyan, yellow, magenta) inks containing water-soluble dyes is improved by incorporating either an organic ester or a diol in the black ink formulation.
1. Organic Esters
Non-surfactant organic esters having the formula R—COOR′ may be suitably employed in the practice of the present invention, where R and R′ are independently hydrogen, alkanes, alkenes, alkynes, alkoxies, carboxylates, and mixtures thereof, including both straight chain and branched chain structures and further including all stereoisomers. Examples of the ester group (—COOR′) include citrate, succinate, lactate, formate, gluconate, tartrate, malonate, fumarate, malate, sebacate, laurate, glutarate, acetate, oxylate, adipicate, pimelicate, subericate, azelaicate and mixtures thereof The number of carbon atoms in the R and R′ groups ranges from 1 to 5. The organic esters that are useful in the practice of the present invention are those that are solvents, not surfactants.
Examples of such non-surfactant organic esters include triethyl citrate, trimethyl citrate, and acetyl trimethyl citrate, and acetyl triethyl citrate; these esters are available under the tradenames Citroflex 2, Citroflex 1, Citroflex A1, Citroflex A2, respectively, all from Morflex Inc.
The concentration of the organic esters employed in the practice of the present invention is within the range of about 0.5 to 7 wt %, preferably about 2 to 4 wt %, and most preferably about 3 wt%, of the ink composition.
2. Diols and Triols
Several diols and triols were tested and showed substantial improvement in black/color bleed. These diols are 2-methyl-2,4-pentanediol (hexylene glycol), 1,2-octanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,5-dimethyl-2,5-hexanediol, and 1,2-hexanediol. The triol is 3-methyl-1,3,5-pentanetriol.
The concentration range of the diols/triols, other than 1,2-octanediol, employed in the practice of the present invention is within the range of about 0.1 to 10 wt %, preferably about 1 to 7 wt %, and most preferably about 2 to 5 wt %, of the ink composition. The concentration range of 1,2-octanediol is within the range of about 0.25 to 1 wt %, preferably about 0.5 wt %, of the ink composition.
Not all diols are useful in reducing bleed between black and color inks. Examples of such diols include 3-hexyne-2,5-diol, and 2,5-dimethyl-3-hexyne-2,5-diol.
3. Ink Compositions—Black Inks
The black inks of the invention comprise a pigment and a vehicle. Specifically, the black inks of the present invention comprise about 5 to 50 wt %, preferably about 10 to 25 wt %, water-miscible organic co-solvent, about 0.05 to 10 wt %, preferably about 0.5 to 10 wt %, pigment, about 0.005 to 50 wt %, preferably about 0.1 to 10 wt %, more preferably about 0.5 to 5 wt %, durable latex polymer, about 0.005 to 50 wt %, preferably about 0.1 to 10 wt %, more preferably about 0.5 to 5 wt %, primer latex polymer, and water, in addition to the ester or diol/triol additive discussed above. Other components and additives to the ink may also be present, as discussed below.
3A. Self-Dispersed Pigments
In one embodiment, the colorant employed in the ink is a self-dispersing pigment. Such pigments suitable for use in the practice of the present invention include all chemically-modified, water-dispersible pigments known for use in ink-jet printing. These chemical modifications impart water-dispersibility to the pigment precursors that encompass all organic pigments.
For self-dispersibility or water solubility, the pigments herein are modified by the addition of one or more organic groups comprising at least one aromatic group or a C
1
-C
12
alkyl group and at least one ionic or ionizable group. The ionizable group is one that forms its ionic groups in the aqueous medium. The ionic group may be anionic or cationic. The aromatic groups may be further substituted or unsubstituted. Examples include phenyl or naphthyl groups and the ionic group is sulfonic acid, sulfinic acid, phosphonic acid, carboxylic acid, ammonium, quaternary ammonium, or phosphonium group.
Depending on the process selected, the pigment can either be anionic or cationic in character. As commercially available, the anionic chromophores are usually associated with sodium or potassium cations, and the cationic chromophores are usually associated with chloride or sulfate anions.
For modification, one preferred method is treatment of a carbon black pigment with aryl diazonium salts containing at least one acidic functional group. Examples of aryl diazonium salts include those prepared from sulfinic acid, 4-aminobenzoic acid, 4-aminosalicylic acid, 7-amino-4-hydroxy-2-naphthylenesulfonic acid, aminophenyl-boronic acid, aminophenylphosphonic acid, and metalinic acid.
Ammonium, quaternary ammonium groups, quaternary phosphonium groups, and protonated amine groups represent examples of cationic groups that can be attached to the same organic groups discussed above.
Reference is made to U.S. Pat. Nos. 5,707,432; 5,630,868; 5,571,311; and 5,554,739 for a discussion of modified carbon black pigments and methods of attaching the functionalized groups.
The following water
Bell Mark L.
Faison Veronica F.
Hewlett--Packard Company
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