Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-08-23
2004-09-21
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S507000, C524S522000, C524S523000, C524S513000, C524S504000, C524S505000
Reexamination Certificate
active
06794425
ABSTRACT:
The invention relates to compositions containing pigments and to their use in inks for ink-jet printing.
Ink-jet printing involves printing an image onto a substrate using ink droplets ejected through a fine nozzle onto a substrate without bringing the fine nozzle into contact with the substrate.
There are many demanding performance requirements for colorants and inks used in ink-jet printing. For example they desirably provide sharp, non-feathered images having good water-fastness, light-fastness and optical density. The inks are often required to dry quickly when applied to a substrate to prevent smudging, but they should not form a crust which would block the tip of the fine nozzle. The inks should also be stable to storage over time without decomposing or forming a precipitate which could also block the fine nozzle.
Thermal and piezoelectric ink-jet printers are widely used, thus there is a need for inks, suitable for use in both types of printers, having high colour strength and giving images having a high light-fastness and water-fastness when printed on a typical substrate, especially plain paper.
It is known to include aqueous resins emulsions in ink formulations to improve water-fastness of resultant prints. For example EP 0882 771 discloses an aqueous ink-jet recording liquid containing a pigment and a solubilised resin emulsion, and EP 796 901 discloses an aqueous pigment ink jet-recording liquid containing an aqueous dispersion resin consisting of a core/shell acrylic polymer.
It has now been found that combinations of a pigment with a low molecular weight hydrophilic polymer and a high molecular weight hydrophobic polymer in a liquid medium results in a composition which is suitable as an ink for use in thermal and piezo ink-jet printers, shows stability over a range of conditions and the resultant prints show improved water-fastness, light-fastness, optical density and smear resistance over the use of a single resin component.
Thus, according to the present invention there is provided a composition comprising the components:
(a) a hydrophilic polymer having a number average molecular weight less than 30,000;
(b) a hydrophobic polymer having a number average molecular weight more than 40,000;
(c) pigment; and
(d) liquid medium.
The number average molecular weight (Mn) for components (a) and (b) may be measured by any of the well known techniques, preferably by gel permeation chromatography (“gpc”). The gpc method used for determining Mn preferably comprises applying the polymer to a chromatography column packed with cross-linked polystyrene/divinyl benzene, eluting the column with tetrahydrofuran at a temperature of 400° C. and assessing the Mn of the polymer compared to a number of a polystyrene standards of a known Mn. Suitable cross-linked polystyrene/divinyl benzene chromatography columns are commercially available from Polymer Laboratories.
As an alternative to the gpc method for determining Mn one may use other methods, for example multi-angle light scattering.
Preferably the Mn of component (a) is less than 20,000, more preferably less than 12,500 and especially less than 10,000. Preferably the Mn of component (a) is more than 500. Preferably the Mn of component (b) is more than 60,000 more preferably more than 70,000. Preferably the Mn of component (b) is less than 10 million, more preferably less than 2 million.
The hydrophilic and hydrophobic polymers may each independently be homopolymers or copolymers. Preferably the hydrophilic and hydrophobic polymers are copolymers.
Component (a) is preferably hydrophilic by virtue of the presence of ionic and/or non-ionic water dispersing groups in the hydrophilic polymer. The hydrophilic polymer is preferably prepared by polymerising one or more monomers having water-dispersing groups, optionally with one or more monomers which are free from water-dispersing groups. The nature and level of water-dispersing groups in the polymer influences whether a solution, dispersion, emulsion or suspension is formed on dissipation of the hydrophilic polymer in aqueous media. Preferably the level of monomers having water-dispersing groups is from 5 to 80% by weight of the hydrophilic polymer. Preferably the level of monomers having water-dispersing groups is at least 5% by weight greater in the hydrophilic polymer than the level of monomers having water-dispersing groups in the hydrophobic polymer. For example, if the level of monomers having water-dispersing groups is 5% by weight of the hydrophobic polymer then the level of monomers having water-dispersing groups in the hydrophilic polymer is preferably at least 10% by weight of the hydrophilic polymer. More preferably the level of monomers having water-dispersing groups is at least 10% by weight greater in the hydrophilic polymer than the level of monomers having water-dispersing groups in the hydrophobic polymer. Preferably a solution is formed on dissipation of the hydrophilic polymer in water, although a minor amount of the hydrophilic polymer may be insoluble in water and exist as dissipated particles when mixed with aqueous media or water.
Water-dispersing groups are preferably pendant to the main polymer backbone. Preferred ionic water-dispersing groups are anionic water-dispersing groups, especially carboxylic, phosphonic and or sulphonic acid groups. Preferred non-ionic water-dispersing groups are polyoxyalkylene groups, more preferably polyoxyethylene groups.
A small segment of the polyoxyethylene group can be replaced by a oxypropylene segment and/or oxybutylene segment, however the polyoxyethylene group should still contain oxyethylene as a major component. When the water-dispersing groups in the hydrophilic polymer are predominantly polyoxyethylene groups, the polyoxyethylene group content preferably does not exceed 25% by weight, more preferably does not exceed 15% by weight, based on the total weight of the hydrophilic polymer.
The anionic water-dispersing groups are preferably fully or partially in the form of a salt. Conversion to the salt form is optionally effected by neutralisation of the polymer with a base, preferably during the preparation of the hydrophilic polymer and/or during the preparation of the composition of the present invention. If anionic water-dispersing groups are used in combination with a non-ionic water-dispersing group, neutralisation may not be required.
Preferably the base used to neutralise any anionic water-dispersing groups is ammonia, an amine or an inorganic base. Suitable amines include tertiary amines, for example triethylamine or triethanolamine. Suitable inorganic bases include alkaline hydroxides and carbonates, for example lithium hydroxide, sodium hydroxide, or potassium hydroxide. A quaternary ammonium hydroxide, for example N
+
(CH
3
)
4
OH
−
, can also be used. Generally a base is used which gives the required counter ion desired for the composition. For example, preferred counter ions include Li
+
, Na
+
, K
+
, NH
4
+
and substituted ammonium salts.
Component (a) is preferably a hydrophilic acrylic, polyurethane or polyester polymer, more preferably a hydrophilic acrylic or polyurethane polymer, especially a hydrophilic polyurethane polymer.
When component (a) is a hydrophilic acrylic polymer it preferably has a glass transition temperature (Tg) greater than −10° C. and more preferably from 20° C. to 120° C. Tg is the temperature at which the polymer changes from a glassy, brittle state to a plastic, rubbery state, and may be measured by differential scanning calorimetry.
When component (a) is a hydrophilic acrylic polymer it preferably has an acid value from 30 to 200 mgKOH/g, more preferably from 30 to 150 mgKOH/g and especially from 40 to 100 mgKOH/g.
The hydrophilic acrylic polymer has preferably been obtained from the polymerisation of one or more olefinically unsaturated monomers having ionic and/or non-ionic water-dispersing groups, optionally in the presence of one or more olefinically unsaturated monomers which are free from ionic and non-ionic water-dispersing groups.
P
Annable Tom
Ellis Gordon Lee
Mahon Paul Francis
Richards Stuart Nicholas
Yeates Stephen George
Avecia Limited
Shosho Callie
LandOfFree
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