Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-09-29
2003-10-14
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...
C524S590000, C524S871000
Reexamination Certificate
active
06632858
ABSTRACT:
This invention relates to polyurethanes, to inks comprising polyurethanes and to their use in ink jet printing.
Ink jet printing involves printing an image onto a substrate by ejecting ink droplets through a fine nozzle onto the 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 light fastness when printed on a typical substrate, especially plain paper.
EP 0769 509 describes a high molecular weight chain extended polyurethane, formed from a colored isocyanate-terminated polyurethane prepolymer, for use in ink jet printers with piezo heads. However this composition is not ideal for use in ink jet printers with thermal heads because the use of heat can result in nozzle blockage and other operability problems.
According to a first aspect of the present invention there is provided a non-isocyanate terminated, colored, water-dissipatable polyurethane having a weight average molecular weight less than 30,000 obtainable from the reaction of a mixture comprising the components:
i) at least one organic polyisocyanate;
ii) at least one isocyanate-reactive compound providing water-dispersing groups; and
iii) at least one colorant having at least two functional groups selected from isocyanate groups and isocyanate-reactive groups.
The colored water-dissipatable polyurethane preferably has a weight average molecular weight (Mw) less than 30,000 because this Mw leads to an improved performance of inks containing the polyurethane, especially for use in thermal ink jet printers. The Mw of the polyurethane is preferably less than 25,000, more preferably from 1000 to 25,000, more preferably from 1000 to 20,000, most preferably from 1000 to 15000 and especially from 1000 to 10,000. Mw may be measured by gel permeation chromatography.
The gel permeation chromatography method used for determining Mw preferably comprises applying the polyurethane to a chromatography column packed with cross-linked polystyrene/divinyl benzene, eluting the column with tetrahydrofuran at a temperature of 40° C. and assessing the Mw of the polyurethane compared to a number of a polystyrene standards of a known Mw. Suitable chromatography columns packed with cross-linked polystyreneldivinyl benzene are commercially available from Polymer Laboratories.
As an alternative to the gpc method for determining Mw, one may use other methods, for example multi-angle light scattering.
Component i) may be any organic polyisocyanate known in the art, preferably having two isocyanate groups, and include aliphatic, cycloaliphatic, aromatic or araliphatic isocyanate. Examples of suitable organic polyisocyanates include ethylene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenyl-methane diisocyanate and its hydrogenated derivative, 2,4′-diphenylmethane diisocyanate and its hydrogenated derivative, and 1,5-naphthylene diisocyanate. Mixtures of the polyisocyanates can be used, particularly isomeric mixtures of the toluene diisocyanates or isomeric mixtures of the diphenylmethane diisocyanates (or their hydrogenated derivatives), and also organic polyisocyanates which have been modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues.
Preferred organic polyisocyanates include cycloaliphatic polyisocyanates, especially isophorone diisocyanate, and aliphatic isocyanates, especially 1,6-hexamethylene diisocyanate or hydrogenated 4,4-diphenyl methyl diisocyanate. A small quantity of triisocyanates may be included as part of component i) but this amount preferably does not exceed 5% by weight relative to the total weight of component i). In a preferred embodiment component i) consists of a mixture of diisocyanate and from 0 to 5% of triisocyanate by weight relative to the diisocyanate.
Component ii) providing water-dispersing groups preferably has at least one, and preferably two, isocyanate-reactive groups. Preferred isocyanate-reactive groups are selected from —OH, —NH
2
, —NH—and —SH. Isocyanate-reactive compounds having three isocyanate-reactive groups may be present, preferably in low levels not exceeding 5% by weight relative to the total weight of component ii). These isocyanate-reactive groups are capable of reacting with an isocyanate (—NCO) group in component i) or component iii).
The water-dispersing groups are preferably present in the polyurethane as in-chain, pendant or terminal groups. Further water-dispersing groups may be introduced into the polyurethane by means of a capping reagent having one isocyanate or isocyanate-reactive group and a water-dispersing group.
The nature and level of water-dispersing groups in the polyurethane influences whether a solution, dispersion, emulsion or suspension is formed on dissipation of the polyurethane.
The water-dispersing group content of the polyurethane may vary within wide limits but is usually selected to be sufficient to ensure the polyurethane forms stable ink-jet printing inks in water and aqueous media. The polyurethane is preferably soluble in water, although minor amount of the polyurethane may be insoluble in water and exist as dispersed particles when mixed with aqueous media or water.
Preferably the proportion of insoluble polyurethane is less than 50%, preferably less than 40% and most preferably less than 30% by weight relative to the total weight of the polyurethane. This allows the preparation of concentrates which may be used to prepare more dilute inks and reduces the chance of the polyurethane precipitating if evaporation of the aqueous media occurs during storage. The size of insoluble polyurethane particulates when dissipated in an ink is preferably less than 100nm, and more preferably less than 60nm.
The water-dispersing groups may be ionic, non-ionic or a mixture of ionic and non-ionic water-dispersing groups. Preferred ionic water-dispersing groups include cationic quaternary ammonium groups and anionic phosphonic acid groups, sulphonic acid groups and carboxylic acid groups. More preferred ionic water-dispersing groups are sulphonic acid groups and carboxylic acid groups.
The ionic water-dispersing groups may be incorporated into the polyurethane in the form of a low molecular weight monomers, polyol or polyamine bearing the appropriate ionic water-dispersing groups where polyol excludes polyesters bearing sulphonic acid groups. Preferred isocyanate-reactive compounds providing water-dispersing groups are diols having one or more carboxylic acid groups or sulphonic acid groups, where examples include bis(2-hydroxyethyl)-5-sodiosulphoisophthalate and dihydroxy alkanoic acids, especially 2,2-dimethylol propionic acid and/or mixtures thereof.
The carboxylic and sulphonic acid groups may be subsequently fully or partially neutralised with a base containing a cationic charge to give a salt. If the carboxylic or sulphonic acid groups are used in combination with a non-ionic water-dispersing group, neutralisation may not be required. The conversion of any free acid groups into the corresponding salt may be effected during the preparation of the-polyurethane and/or during the preparation of an ink from the polyurethane.
Preferably the base used to neutralise any acid water-dispersing groups is ammonia, an amine or an inor
Gregory Peter
James Mark Robert
Padget John Christopher
Pears David Alan
Avecia Limited
Pillsbury & Winthrop LLP
Shosho Callie
LandOfFree
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