GB2314561A

GB2314561A - Jet inks

Info

Publication number: GB2314561A
Application number: GB9613244A
Authority: GB
Inventors: Nicholas Alexander Walker; Michael Walker Pitcher
Original assignee: Ilford Ltd
Current assignee: Ilford Imaging UK Ltd
Priority date: 1996-06-25
Filing date: 1996-06-25
Publication date: 1998-01-07
Anticipated expiration: 2016-06-25
Also published as: GB2314561B; GB9613244D0

Abstract

A aqueous jet ink comprises essentially: a) an aqueous carrier medium, b) a pigment and c) a hydrogenated castor oil poly(ethylene)oxide condensate Preferably an organic cosolvent is also present.

Description

Field of the Invention This invention relates to aqueous inks for ink jet printers, and, more particularly to aqueous, pigmented inks which contain a hydrogenated castor oil poly(ethylene oxide) condensate.

Background of the Invention Ink jet printing is a non-impact method that in response to a digital signal produces droplets of ink that are deposited on a substrate such as paper or transparent film. Ink jet printers, especially thermal or bubble jet drop-on-demand printers have found broad application as output for personal computers in the office and the home.

A major concern with all ink jet printing devices is pluggage of nozzles during peration-and between operations. A critical measured property for an ink jet ink is the "decap time" which is the length of time over which an ink remains fluid in a pen opening when exposed to air and therefore capable of firing a drop of ink at its intended target. "Decap" means the pen is uncovered or "decapped". The major cause of decap failure is due to evaporation of the aqueous carrier medium, i.e., either cosolvent or water. Initial evaporation generally causes an increase in viscosity which affects the ability of the nozzle to fire a drop since ink jet pens are designed to operate within specific viscosity ranges. Initial failure may be a displacement from the intended target position caused by deflection of the drop or creation of an altered trajectory. Continued evaporation may result in a solid component being precipitated or crystallised in the nozzle which in turn could result in an undesirable satellite spray occurring or a single line of print diverging into a double line. Finally, the nozzle may form a solid skin and totally fail by no longer ejecting ink.

Inks for ink-jet use commonly use dyes as colorants. For such inks, it is known that nozzle pluggage can be reduced or eliminated by an addition of a proportion of between 5 and 50%, commonly around 10%, of a relatively involatile organic cosolvent to an aqueous ink.

Various simple aliphatic polyols, such as glycerol, ethylene glycol, propylene glycol, and diethylene glycol are known to be useful for this purpose. In addition, United States Patent 5,169,438 states that cycloaliphatic diols are useful pluggage inhibitors, US Patent 5,173,112 states that various water soluble amides are useful, US Patent 5,205,861 describes the use of heterocyclic diols, and US Patent 5,268,027 describes the use of alkyl bis polyol ethers.

There is interest in using pigments as the colorants for inkjet use, mainly because of the better fastness of prints from such inks towards light and washing. The situation becomes more complicated with such inks, due to the possibility of pigment aggregation or flocculation, and it is not easy, even with the addition of organic cosolvents, to inhibit pluggage efficiently without introducing other disadvantages.

A need therefore exists for a method of inhibiting pluggage for aqueous pigmented inks which does not introduce other disadvantages. We have found that certain poly(ethylene oxide) condensates of hydrogenated castor oil are useful additives for pigmented ink jet inks, which give stable ink formulations with inhibited pluggage.

Summarv of the Invention The invention relates to an aqueous inkjet ink composition comprising: (a) an aqueous carrier medium, (b) a pigment (c) a hydrogenated castor oil poly(ethylene oxide) condensate The inks of this invention have superior decap performance, are extremely stable, are rapid drying, have low viscosity, exhibit excellent print quality, and provide excellent water resistance after drying. They may be used with a variety of ink jet printers such as continuous, piezoelectric, drop-on-demand and thermal or bubble jet drop-onaemand, and are particularly adapted for use in thermal inkjet printers.

The inks of this invention are useful for printing on any of the substrates commonly used for ink-jet printing, for example so-called plain paper, coated paper, and transparent film materials.

Detailed Description of the Invention The invention relates to pigmented ink jet ink compositions which are particularly suited for use in ink jet printers in general, and thermal ink jet printers in particular. The pigmented inks comprise an aqueous carrier medium, a pigment, a poly(ethylene oxide) condensate of hydrogenated castor oil, together with optionally an organic polyol cosolvent together with other components which are advantageously added to aqueous inks, such as surfactants, viscosity modifiers, and biocides. In addition, sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities. Ethoxylated hydrogenated castor oils are well known surfactants. They may be prepared by reduction of castor oil, which is a natural product, and reaction with ethylene oxide. The number in brackets refers to the approximate number of ethylene glycol repeat units per castor oil molecule. Preferably the ethoxylated hydrogenated castor oil comprises appr4ely 40 ethylene glycol repeat units per castor oil molecule.

The term pigment describes a colorant which is essentially insoluble in the aqueous ink medium. Suitable pigments include almost any compound of the types classified as a pigment by the Colour Index, together with certain compounds classified by the Colour Index as vat or disperse dyes. Numerous other insoluble coloured compounds which are not included in the Colour Index are also suitable. Commercially pigments are often supplied as a pigment dispersion, and this invention is useful for pigments supplied as such dispersions, which commonly include dispersants and other cosolvents as well as water.

Preferred specific examples of pigments for a black ink include carbon black (C.I. Pigment Black 7), such as furnace black, lamp black, acetylene black, and channel black, and o-nitroaniline black (C.I. Pigment Black 1). Preferred specific examples of the pigment for a coloured ink include C.I.Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 53, 55, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138 and 153, C.I. Pigment Orange 5, 13, 16, 17, 36, 43 and 51, C.I. Pigment Red 1, 2, 3, 9, 17, 22, 23, 31, 38, 48:1, 48:2, 48:3, 48:4, 49:1, 52:2, 53:1 and 57:1, 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 104, 105, 106, 112, 114, 122, 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 188, 190, 193, 209, 219, C.I. Pigment Violet 1, 3, 5:1, 16, 19, 23, 38, C.I. Pigment Blue 1,2, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17:1, 56, 60, 63, and C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36. It is also possible to use, besides the above-described pigments, processed pigments such as graft carbon having a surface treated with a resin or the like. It is also possible to mix more than one pigment in the inks of the invention.

The ink may be prepared by dispersing the pigment or predispersed pigment with the hydrogenated castor oil poly(ethylene oxide) condensate and other components in water-wi+ an optional cosolvent.

The dispersing step may be accomplished in a horizontal mini mill, a ball mill, an attritor, or by passing the mixture through a plurality of noales within a liquid jet interaction chamber at a liquid pressure of at least 1000 psi to produce a uniform dispersion of the pigment particles in the aqueous carrier medium.

It is sometimes desirable to make the pigmented ink jet ink in concentrated form, which is subsequently diluted to the appropriate concentration for use in the ink jet printing system.

This technique permits preparation of a greater quantity of pigmented ink from the equipment. If the pigment dispersion is made in a solvent, it is diluted with water and optionally other solvents to obtain the appropriate concentration. If the pigment dispersion is made in water, it is diluted with either additional water or water soluble solvents to make a pigment dispersion of the desired concentration. By dilution, the ink is adjusted to the desired viscosity, colour, hue, saturation density, and print area coverage for the particular application.

The ink may contain up to approximately 30% pigment by weight, but will generally be in the range of approximately 0.1 to 15%, preferably approximately 0.1 to 8%, by weight of the total ink composition for most thermal ink jet printing applications.

The particle diameter of the pigment is preferably 101lm or less, particularly preferably lym or less.

The ink may contain up to 25% of the hydrogenated castor oil poly(ethylene oxide) condensate by weight, but preferably between 3% and 15% by weight, depending on the pigment used and other properties desired of the ink.

The aqueous carrier medium is water or a mixture of water and at least one water soluble organic solvent.

Deionized water is commonly used. Selection of a suitable mixture of water and water soluble organic solvent, depends on the requirements of the specific application, such as the desired surface tension and viscosity, the selected pigment, the drying time of the pigmented ink jet ink, and the type of substrate onto which the ink will be printed.

Representative examples of water-soluble organic solvents that may be selected -include (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol: (2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; (3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such as ethyl lactate, (5) polyhydric alcohols, such as ethylene glycol, diethylenelglycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2, 4-pentanediol, 1,2,6-hexanetriol and thiodiglycol; (6) lower alkyl mono-or di-ethers derived from alkylene glycols, such as ethylene glycol monomethyl (or -ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, triethylene glycol mono-methyl (or -ethyl) ether and diethylene glycol di-methyl (or -ethyl) ether; (7) nitrogen containing organic compounds such as urea, pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and (8) sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone.

A mixture of water and a water soluble organic solvent having at least 2 hydroxyl groups such as diethylene glycol is preferred as the aqueous carrier medium. It is also possible to use a mixture of water and more than one water soluble organic solvent.

The aqueous composition may contain up to 50% of the organic cosolvent, but preferably up to 10% of each of the organic cosolvents, and most preferably between about 5% and about 10% of the organic cosolvent.

The following examples will serve to illustrate the invention: Example 1 A commercially available fmely dispersed form of Copper Phthalocyanine (C.I. Pigment blue 15:3) was used. This consists of about 40% raw pigment, and contains a p-n-aikyl phenol ethoxylate as dispersant as well as some propylene glycol. An ink was prepared using the following formulation: Pigment dispersion 12.5g Diethylene glycol 5.0g PEG (40) Hydrogenated Castor Oil 9.0g Water to make 100g The mean particle size was 0.45nm measured on a Coulter LS 130.

An HP51626A ink-jet cartridge was filled with this ink and loaded into an HP560 printer.

On jetting, a good quality cyan print was produced. The cartridge was then left overnight.

On jetting, a good quality print was produced immediately, with no evidence of pluggage.

The ink was prepared as follows: To distilled water, 9g of PEG (40) Hydrogenated castor oil was added, this was stirred magnetically for 10 minutes. To the resultant mixture 5g of Diethylene glycol was added, and stirred for a further five minutes. This fmal mixture was then added to 12.5g of the pigment dispersion and stirred for another 10 minutes.

Example 2 A commercially available finely dispersed form of CI Pigment Red 184 was used, which again contains about 40% raw pigment, alkyl phenol ethoxylate as a dispersant, and propylene glycol. Inks were prepared using the following formulation: Pigment dispersion 12.5g Additive 5.0g Diethylene Glycol l0.0g Water to make 100g Different inks were prepared using the following additives: (Only the ink of the invention comprised the PEG hydrogenated castor oil) a) PEG (40) Hydrogenated castor oil invention b) Polyethylene glycol (PEG 2000) - comparison c) Fatty alcohol ethoxylate - comparison d) PEG (150) lanolin - comparison e) Cis -1, 5 - cyclooctane diol - comparison, see USP 5,159,43Q f) 1,4 - cyclohexane diol - comparison, see USP 5,169,438 g) (no additive) - control The average particle size of all of these inks measured on the LS130 was 0.20nm. Inks A-G were all individually filled into HP51626A ink-jet cartridges, loaded into'an HP560 printer, and jetted according to a program to give a print of solid colour. All the inks.gavle.a.good colour density, and jetted satisfactorily.

The cartridges were then left overnight. The following day they were again jetted using the same program. In this case, the number of traverses of the print head needed to give an even coverage was counted. For a good ink, this should be zero, or a low number, implying that all the individual jets in the cartridge print immediately with no pluggage. For a bad ink, showing evidence of pluggage, this will be a high number, with a maximum of 58 showing that not all the jets are firing properly even after a full sheet has been printed. The results are given below, showing the advantage of the inventive ink.

Ink Lines for all jets to fire A - invention 0 B - comparison 17 C comparison > 58 D - comparison > 58 E USP 5,169,438 > 58 F USP 5,169,438 > 58 G - control > 58 This example shows the advantage of the inventive ink, particularly when compared with inks C-G, which effectively blocked all the nozzles of the cartridge on standing.

Example 3 A set of coloured inks was prepared as in example 1, using PEG (40) hydrogenated castor oil as in example 2a. The inks were charged into cartridges and left overnight as in example 2; and the number of lines to give a full print was counted as in example 2. The ink formulation and results are given in the table.

Colour CI Pigments % Diethylene % No. Average Particle Additive Glycol t Pigment lines Size ( m) Cyan Blue 15:3 9 5 3 0 0.4511m Yellow Yellow 13 3 15 3 1 0.12 m Magenta Red 184 9 15 3 1 0.201lm Black Black7 3 5 3 O 0.12m

Claims

Claims:1. An aqueous ink jet composition which comprises essentially: a) an aqueous carrier medium, b) a pigment and

c) a hydrogenated castor oil poly(ethylene)oxide condensate
2. An aqueous ink jet composition wherein according to claims the hydrogenated castor oil poly(ethylene) oxide condensate comprises approximately forty ethylene glycol repeat units per castor oil molecule.
3. An aqueous ink jet composition according to claim 1 which comprises at least one organic cosolvent.
4. An aqueous ink jet composition according to claim 3 wherein the organic cosolvent is diethylene glycol.
5. An aqueous ink jet composition according to claim 1 wherein the hydrogenated castor oil poly(ethylene)oxide condensate is present in the composition to the extent of 3 to 15% by weight.
6. An aqueous ink jet composition according to claim 3 wherein the amount of organic cosolvent present in the aqueous composition is from 5 to 10% by weight.
7. An aqueous ink jet composition according to claim 3 which comprises at least one further additive selected from a surfactant, a solution viscosity modifier and a biocide.