Aqueous ink compositions

Details Aqueous ink compositions Aqueous ink compositions

1999-03-18

2002-02-05

Jagannathan, Vasu (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S601000, C524S609000

Reexamination Certificate

active

06344497

ABSTRACT:

This invention relates to an ink jet printing process and to inks.
Inks containing water-soluble dyes, water and organic solvents are well known. For example Zeneca's British Patent application No. 2,275,479 describes such inks and their utility in ink jet printing (“IJP”).
Inks containing a water-insoluble acrylic polymer and an oil soluble dye are described in U.S. Pat. No. 4,680,332. These inks are suitable for piezoelectric IJP but when they are used in thermal IJP they tend to block printer nozzles giving poor quality images which have a “quilted” appearance.
WO91/06608 describes aqueous inks containing a polyester, water, a pigment and a wax. Whilst these inks are useful in printing presses, the pigments they contain require intensive and expensive milling to make them fine enough to pass through ink jet printer heads and the pigments have a tendency to settle out from the ink on standing for long periods. Furthermore, images formed from inks containing insoluble pigments are generally opaque and this limits their usefulness on overhead projector slides.
WO95/34024 describes a process for preparing an optical filter comprising a coloured cross-linked polymeric coating on a transparent substrate.
There is a need for inks which are suitable for thermal IJP, have high colour strength and give clear, high water-fast images with high light fastness when printed on a substrate.
According to the present invention there is provided an ink composition comprising water, a water-dissipatable polyester, a disperse dye or a solvent soluble dye or a mixture of such dyes, a water-immiscible organic solvent and a water miscible organic solvent.
The Water-Dissipatable Polyester
The water-dissipatable polyester may be prepared using conventional polymerisation procedures known to be effective for polyester synthesis. Thus, it is well known that polyesters contain carbonyloxy (i.e. —C(═O)—O—) linking groups and may be prepared by a condensation polymerisation process in which an acid component (including ester-forming derivatives thereof) is reacted with a hydroxyl component. The acid component may be selected from one or more polybasic carboxylic acids, e.g. di- and tri-carboxylic acids or ester-forming derivatives thereof, for example acid halides, anhydrides or esters. The hydroxyl component may be one or more polyhydric alcohols or phenols (polyols), for example, diols, triols, etc. (It is to be understood, however, that the polyester may contain, if desired, a proportion of carbonylamino linking groups —C(═O)—NH— (i.e. amide linking groups) by including an appropriate amino functional reactant as part of the “hydroxyl component”; such as amide linkages). The reaction to form a polyester may be conducted in one or more stages. It is also possible to introduce in-chain unsaturation into the polyester by, for example, employing as part of the acid component an olefinically unsaturated dicarboxylic acid or anhydride.
Polyesters bearing ionised sulphonate groups may be prepared by using at least one monomer having two or more functional groups which will readily undergo an ester condensation reaction (e.g. carboxyl groups, hydroxyl groups or esterifiable derivatives thereof) and one or more sulphonic acid groups (for subsequent neutralisation after polyester formation) or ionised sulphonate groups (i.e. neutralisation of the sulphonic acid groups already having been effected in the monomer) in the synthesis of the polyester. In some cases it is not necessary to neutralise sulphonic acid groups since they may be sufficiently strong acid groups as to be considerably ionised in water even without the addition of base. Often, the sulphonic acid or ionised sulphonate containing monomer is a dicarboxylic acid monomer having at least one ionised sulphonate substituent (thereby avoiding any need to effect neutralisation subsequent to polyester formation). (Alternatively, alkyl carboxylic acid ester groups may be used in place of the carboxylic acid groups as ester-forming groups). Such a monomer will therefore be part of the acid component used in the polyester synthesis.
Preferred polybasic carboxylic acids which can be used to form the polyester have two or three carboxylic acid groups. For example, one can use C
4
to C
20
aliphatic, alicyclic and aromatic compounds having two or more carboxy groups and their ester forming derivatives (e.g. esters, anhydrides and acid chlorides), and dimer acids such as C36 dimer acids. Specific examples include adipic acid, fumaric acid, maleic acid, succinic acid, itaconic acid, sebacic acid, nonanedioic acid, decanedioic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid and tetrahydrophthalic acid and their acid chlorides. Anhydrides include succinic, maleic, phthalic and hexahydrophthalic anhydrides.
Preferred polyols which can be used to form the polyester include those having from 2 to 6, more preferably 2 to 4 and especially 2 hydroxyl groups per molecule. Suitable polyols having two hydroxy groups per molecule include diols such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), the 1,2-, 1,3- and 1,4-cyclohexanediols and the corresponding cyclohexane dimethanols, diethylene glycol, dipropylene glycol, and diols such as alkoxylated bisphenol A products, e.g. ethoxylated or propoxylated bisphenol A. Suitable polyols having three hydroxy groups per molecule include triols such as trimethylolpropane (1,1,1-tris (hydroxymethyl)ethane). Suitable polyols having four or more hydroxy groups per molecule include pentaerythritol (2,2-bis(hydroxymethyl)-1,3-propanediol) and sorbitol (1,2,3,4,5,6-hexahydroxyhexane).
Compounds having two or more groups which readily undergo an ester condensation reaction and have one or more sulphonate groups are dicarboxylic acid monomers having at least one ionised sulphonate group. Examples of such compounds are aromatic dicarboxylic acids having an ionised sulphonate group, for example those of the formula:
wherein M is a cation (preferably sodium, lithium or potassium); and each R
c
independently is H, a cation or C
1-4
-alkyl (preferably methyl or ethyl). Preferred compounds of the above formula are of formula:
wherein M and R
c
are as defined above. Particularly preferred is the mono sodium salt (one R
c
is H, the other is Na), this material being known as sodio-5-sulphoisophthalic acid (SSIPA).
Other useful compounds which have two or more groups which readily undergo an ester condensation reaction and have one or more sulphonate groups are dihydroxy monomers having at least one sulphonate group, especially those of the formula:
wherein M is as hereinbefore defined above and each R
d
independently is alkylene, preferably C
2-4
-alkylene. Preferred compounds of the above formula are:
wherein M is as hereinbefore defined.
Polyesters bearing ionised carboxy groups can be prepared by various means. For example, if the hydroxyl component of the reactants is stoichiometrically in excess of the acid component, a hydroxyl-terminated polyester can be formed, which may be subsequently converted to a carboxy terminated polyester by wholly or partially reacting the hydroxyl groups with an appropriate reagent (e.g. an acid anhydride or a dicarboxylic acid). Alternatively, terminal carboxy functionality may be directly introduced by employing an appropriate stoichiometric excess of the acid component reactants. In another alternative, chain-pendant carboxy groups may be introduced by using reagents such as dimethylol propionic acid (DMPA) since if appropriate reaction condition are employed (e.g. polymerisation temperature below 150° C.) the hindered carboxy group thereof does not take part to any significant extent in the ester-forming reactions during the polyester synthesis and the DMPA effectively behaves as a simple diol. Chain-pendant and/or terminal carboxy groups could also be introduced by employing a tri- or higher functionality car

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