GB2401872A - Ink jet ink and recording process - Google Patents

Abstract

There is provided an ink jet ink composition which comprises:- <SL> <LI>(a) at least one pigment; <LI>(b) dipropylene glycol propyl ether; <LI>(c) at least one emulsion resin; and <LI>(d) an aqueous carrier medium. </SL> Preferably the ink jet ink also comprises a solution resin, a dispersant for the pigment and a surfactant. There is also provided an ink jet printing process using the ink of the invention in a piezo drop-on-demand ink jet printer to print on a poly vinyl chloride printable medium and drying the print using infra-red radiation.

Description

Ink Jet Ink and Recording Process

Field of the Invention

This invention relates to improved inks for ink jet printers, and in particular to an ink jet ink and method for printing on hydrophobic polymeric substrates.

Backpround 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 have found broad application as output for personal computers in the office and the home, primarily due to its relatively low cost, speed and quiet operation. There are several classes of ink jet printer, for instance thermal drop-on-demand printers, piezo drop-on-demand printers, and continuous ink jet printers.

In recent years the ready availability of ink jet printing systems means that there has been increased interest in using such systems as an alternative to traditional analogue printing methods. In particular, there is interest in employing ink jet printing methods in large and very large format applications for uses such as banners, signage, displays, posters and billboards.

The use of ink jet printing brings important advantages in such applications, in particular the ease and cheapness of setting up small production runs when compared with conventional printing methods. Yet, there are also disadvantages. For example, the types of final products produced for these applications may be far more exposed to the elements in outdoor usage and to handling, and thus need to be far more lightfast, waterfast, and abrasion resistant than typically required for office or home printing applications. Further, there is particular interest in printing on vinyl (PVC) and other hydrophobic, durable substrates that are commonly used in large format printing applications, but the aqueous inks generally preferred in ink jet do not print well (or at all) on such substrates, either because the ink does not adequately wet the substrate during printing resulting in a poor quality print, or because the ink does not adhere well and is insufficiently robust to handling damage. Thus, it is normally required either that such substrates he pre-treated to improve adhesion and wetting of the ink when printed, such as by corona discharge as disclosed in United States Patent 5,780,118; that such substrates be coated with an ink-receiving coating or coatings in order to accept an aqueous ink; or that non-aqueous inks are used. Non- aqueous inks are disliked lor well-known environmental reasons, whereas pre-treatment or coating of the substrate adds considerably to the cost.

Consequently there is considerable interest in developing a system to allow printing with aqueous ink jet inks onto untreated hydrophobic substrates such as vinyl whereby robust lightfast images may easily be produced.

There is particular interest in developing such a system using a piezo drop-on-demand ink jet printing method, as such ink jet printers are more common in a number of large format printing applications.

European Patent Application 0 882 770 A discloses a surfactant system for ink jet inks for printing on hydrophobic surfaces wherein the ink comprises an aqueous carrier medium; a colorant; and a mixture of at least one siloxane surfactant; and at least one fluorinated surfactant and exhibits excellent wetting on hydrophobic surfaces.

Further, United States Patent 6,087,416 discloses aqueous pigmented ink jet inks for printing on vinyl substrates in which the ink comprises an aqueous vehicle containing at least water and a water-miscible glycol or glycol ether, wherein water constitutes no more than 80% by weight based on the total weight of the vehicle; an insoluble colorant (preferably a pigment); a polymeric dispersant; a silicon or fluorinated surfactant; and, optionally but preferably, a graft copolymer binder having a hydrophobic backbone and non-ionic, hydrophilic side chains, which binder is soluble in the aqueous vehicle but insoluble in water.

However there is interest in using inks with a lower content of organic cosolvent and in avoiding the specialist silicon and fluorinated surfactants.

Furthermore, it is also known that vigorous drying conditions are useful for improving printing and image quality on hydrophobic substrates. In particular United States Patents 6,425,663 and 6,508,550 disclose microwave drying methods for use with ink jet printers.

We have developed ink formulations and a printing method particularly useful for piczo drop-on-demand ink jet printers which is capable of providing durable, waterfast, lightfast images directly on vinyl substrates without any need for pre-treatment or coating of the substrate.

Summary of the Invention

According to this invention there is provided an ink jet ink composition comprising: (a) at least one pigment; (b) dipropylene glycol propyl ether; (c) at least one emulsion resin; and (d) an aqueous carrier medium.

I'he term pigment describes a colorant which is essentially insoluble in the aqueous ink medium. Many pigments are listed in the Pigments and Solvent Dyes section of the Colour Index international, published by the Society of Dyers and Colourists in 1997. Suitable pigments for the invention include those classified by the Colour Index as C.I. Pigment Black 1; C.I. Pigment Black 7; C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 55, 74, 81, 83, 87,95,97,98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 151, 154, 155, 180,and213; C.I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, 71, and 73; 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, 57:1, 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 112, 114, 122, 123, 146, 149, 166, 168, 170, 175, 176, 178, 179, 184, 185, 188, 190, 202, 207, 209, and 222; C.I. Pigment Violet 1, 3, 5:1, 19, 23, 35, and 37; C.I. Pigment Blue 1, 2, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 56, 60, 76, 79, and 80; and C.I. Pigment Green 1, 4, 7, 8, 10, and 36. However almost any suitable insoluble coloured compound may be used in the inks of the invention. It is also possible to mix more than one pigment in the inks of the invention.

Many of the above pigments are available commercially in finely divided forms which are specifically aimed at ink jet use. It is preferred to use such available forms in the inks ol'this invention.

Preferred pigments include Carbon black which is listed by the Colour Index as Pigment Black 7. Examples include furnace black, lamp black, acetylene black, and channel black; further it is also possible to use processed pigments having a surface treatment of the particles such as socalled self dispersing carbon black and graft carbon black. By a surface modified carbon black is meant a carbon black pigment, the particles of which have been modified by incorporation of organic groups at the surface such as, for example, carboxylic or sulphonic acid groups. Such modified carbon black pigments are known and commercially available from suppliers such as Cabot Corporation and Orient Corporation.

Preferred cyan pigments include Phthalocyanine pigments, for example C.I. Pigment Blue 15:1, 15:2, 15:3, 15:4, ]5:6, 16, 75, 76, and 79, and most preferably the Phthalocyanine pigment is p-copper phthalocyanine, C.I. Pigment Blue 15:3 or 15:4. Preferred magenta pigments include Quinacridone pigments, for example Pigment Red 122, 207, and 209 or Pigment Violet 19, of which Pigment Red 122 is especially preferred. Preferred yellow pigments include, for example C.l. Pigment Yellow 74, 128, 155, and 180.

The pigment may be used in the form of a dry powder. However organic pigments are often supplied commercially as a concentrated aqueous pigment dispersion, and this invention is also useful for pigments supplied as such dispersions, which commonly include dispersants and other cosolvents as well as water. Alternatively the pigment may be supplied in the form of a water wet presscake. In presscake form, the pigment is not aggregated to the extent that it is in dry form and thus the pigment does not require as much deaggregation in the process of preparing the inks from dry pigments.

The total pigment concentration of the ink may be up to approximately 30% by weight, but will generally be between about 1% and about 15%, preferably approximately 3 to 8%, by weight of the total ink composition. The concentration depends on the particular pigment used and the printer.

Dipropylcne glycol propyl ether is commercially available. It is hereinafter referred to as DPnP. 'l'he content of DPnP in the ink may be up to 10%, preferably between approximately 1 % and approximately 8%.

The term emulsion resin used herein refers to an aqueous dispersion comprising water or an aqueous solvent as a continuous phase and small particles of an organic polymer as dispersed particles; such may also be called a latex, an aqueous emulsion, or a polymer emulsion. Preferably the small particles of the emulsion resin are characterised by an average particle size below approximately 200 nm, more preferably below approximately nm. Such emulsion resins may generally be prepared by emulsion polymerization.

Preterably, in order to avoid blockage of the nozzles of the printer the organic polymer of the emulsion resin has a glass transition point (Tg) above room temperature, for instance 30 C or above, preferably 40 C or above. Further, the polymer of the emulsion resin preferably has a minimum film-forming temperature 30 C or above, especially 40 C or above. It is especially preferred that the insoluble polymer of the emulsion resin particles should have a coalescing property in the presence of the organic solvent components of the ink. The term coalescing property means that the polymer of the emulsion resin will form a non-tacky resin film in the presence of the organic components of the ink after evaporation of the aqueous component. This resin film functions to bind the pigment particles contained in the ink composition together after printing and fix them onto the surface of recording medium. It is considered that this can provide images having excellent rubbing/scratch resistance and waterfastness.

Suitable emulsion resins are known and are commercially available. Specific examples of the polymer component constituting the small polymeric particles include acrylate polymers, vinyl acetate polymers, styrene/butadiene polymers, styrene/acrylate polymers, butadiene polymers, epoxy polymers, urethane polymers, copolymers of such types, and the like. Copolymers may be present in the form of a block copolymer or a random copolymer. Preferably the emulsion resin comprises an acrylate polymer characterized by an acid number below approximately 100. The acid number of such a polymer is a well known property and is defined as the number of milligrams of potassium hydroxide required to neutralise 1 gram of the material. A particularly suitable commercially available emulsion resin is an acrylate polymer having an acid number of 70 and an average particle size of 84.7 nm, further characterized by a glass transition temperature (Tg) of 64 C, and a molecular weight of >200,000.

The concentration of the emulsion resin in the ink may be up to approximately 10%, preferably between approximately 1% and 8%, dry solid content by weight of the total ink composition. The concentration depends on the particular resin used and the properties desired of the ink.

Preferably the ink composition also comprises at least one solution resin. By solution resin is meant an organic resin polymer which is soluble in the aqueous ink formulation. Suitable solution resins include in particular acrylate polymers comprising solubilising monomers such as acrylic, methacrylic, and maleic acids, generally in combination with one or more additional vinylically unsaturated monomers such as styrene, acrylate esters, and the like.

The polymer may be present in the form of a block copolymer or a random copolymer.

Many such acrylate polymers and copolymers are well known and commercially available.

Preferably the solution resin is characterized by an acid number greater than approximately 100, preferably within the range of approximately l 50 to 250.

Such resins may be supplied commercially in the form of concentrated aqueous solutions, or as solids or emulsions which are to be dissolved in water in the presence of a base.

Suitable bases for dissolving such resins include sodium or potassium hydroxide, ammonia, or an organic amine base such as ethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, I-(dimethylamino)-2-propanol, or 2- amino-2- methyl-l-propanol. It is also possible to use mixtures of such bases to dissolve the copolymer resin.

The concentration of solution resin in the ink may be up to approximately 10%, preferably between approximately 0.5% and 5%, especially between approximately 0.5% and 2%, dry solid content by weight of the total ink composition. The concentration depends on the particular resin used and the properties desired of the ink.

By an aqueous carrier medium is meant a medium which is water or is predominantly water. Deionised water is commonly used. Optionally and preferably the ink composition may additionally comprise at least one water-miscible organic cosolvent. The additional water-miscible organic cosolvent is not particularly limited and may be any organic solvent which has sufficient solubility in water. Preferred examples of water- miscible organic solvents that may be selected include hydroxylic organic solvents, especially solvents having at least 2 hydroxyl groups; for example ethylene glycol, thiodiglycol, glycerol, 1,2-hexanediol, and 1,5-pentanediol; ethylene glycol condensates such as diethylene glycol, triethylene glycol, polyethylene glycol, and ethoxylated glycerol; nitrogen containing organic compounds such as 1,3- dimethyl imidazolidinone, urea, pyrrolidone, and N-methyl-2-pyrrolidone; and mixtures comprising these solvents.

The ink may comprise up to a total of approximately 50% of the additional organic solvent or solvents, but preferably the ink comprises less than 20% additional organic cosolvent, most preferably between approximately 5% and 15% additional organic cosolvent.

Preferably the inks of the invention also comprise at least one surfactant. The surfactant used is not particularly limited. Examples of suitable surfactants include nonionic surface active agents such as alkylene oxide derivatives, for example polyethylene glycol alkyl or alkylaryl ethers, polyethylene glycol esters, polyethylene glycol ethers of acetylene dials, or polyethylene glycol / polypropylene glycol condensates; glycidol derivatives such as alkylphenol polyglycerides; aliphatic esters of polyhydric alcohols or sucrose; anionic surfactants such as dialkyl sulphosuccinates, N-acyl-N-alkyltaurines, Nacylsarcosinates, alkylsulphonates, alkylbenzenesulphonates, alkylnaphthalenesulphonates, and surfactants comprising a sulphuric acid ester group or a phosphoric acid ester group, such as alkyl sulphuric acid esters, alkyl phosphoric acid esters and sulphated or phosphated polyethylene glycol alkyl or alkylaryl ethers. Many suitable surfactants are well known and commercially available. A particularly suitable surfactant is sodium dioctyl sulphosuccinate.

Further, fluorinated or perfluorinated surfactants or silicone surfactants may also be used, but this is not preferred, and one of the advantages of the invention is that good properties of the inks and prints may be attained without use of such surfactants..

The surface tension may be adjusted by appropriate addition of surfactant to be below 40 dyne/cm, preferably between approximately 25 dyne/cm and approximately 35 dyne/cm.

Optionally and preferably the ink may also comprise at least one dispersant for the pigment. The purpose of the dispersant is to stabilise the particles and prevent flocculation, aggregation, and settling of the ink. Suitable dispersants Nor pigmented ink jet inks are well known in the art, and include polymeric dispersants as well as some non-polymeric compounds of the surfactant type. Suitable dispersants for the inks of this invention include macromolecular polyionic dispersants, for example copolymers of styrene with acrylic, methacrylic, or maleic acids; various types of poly(ethylene oxide) condensates such as alkyl polyethylene oxide ethers and sulphate or phosphate esters thereof; and suri'actants such as sarcosinate compounds. A preferred dispersant for the inks of the invention is a styrene/acrylate copolymer, by which is meant a copolymer comprising styrene or a substituted styrene; acrylic, methacrylic, or maleic acids; and optionally with additional vinylically unsaturated comonomers such as acrylate esters. Preferably this dispersant is characterized by an acid number of between about 150 and about 250, a glass transition temperature between approximately 70 and approximately 150 , and a molecular weight of between approximately 2000 and approximately 25000, and most preferably the molecular weight is approximately 5000 - 15000.

Many suitable styrene acrylate dispersants are commercially available. Such styrene acrylate copolymer dispersants may be supplied commercially in the form of concentrated solutions in aqueous base, or as solids which are to be dissolved in water in the presence of a base. Suitable bases Nor dissolving such dispersants include sodium or potassium hydroxide, ammonia, or an organic amine base such as ethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, I-(dimethylamino)-2-propanol, or 2amino-2- methyl-l-propanol. It is also possible to use mixtures of such bases to dissolve the styrene acrylatc copolymer. The dispersant may be the same as the solution resin.

There may be present up to 400% of the dispersant by weight on the pigment, but preferably between about 10% and about 100% by weight on the pigment, and most preferably approximately 20 to 50% by weight on the pigment, depending on the pigment and dispersant used and other properties desired of the ink.

Thus according to a particularly preferred aspect of this invention there is provided an ink jet ink composition comprising: (a) at least one pigment; (b) a dispersant for the pigment; t (c) dipropylene glycol propyl ether; (d) at least one emulsion resin; (e) at least one solution resin; (f) at least one surfactant; (g) at least one additional water-miscible organic solvent; and (h) an aqueous carrier medium, wherein the pigment, dispersant, emulsion resin, solution resin, surfactant, additional water-miscible organic solvent, and aqueous carrier medium are as hereinbefore defined.

further, the pigmented inks of the invention may also comprise other components which are advantageously added to aqueous ink jet inks, for example viscosity modifiers, biocides, and sequestering agents such as EDTA.

The pl I ol the ink may be controlled by the quantity of base added to the solution resin or dispersant, or by appropriate addition of acid or base to the final ink. Generally the pH of the ink is between about 7 and about 10, preferably between approximately 8 and 10.

The preferred viscosity of the inks depends on the specific printer in use and on the I application. One of the advantages of the invention is that a desirably low viscosity of the inks may readily be achieved, typically between approximately 2.5 cP and approximately 4.5 cP. However if necessary the viscosity may be increased by changing the concentration of the components, in particular the solution resin and organic cosolvent, by appropriate selection of these components, or by adding thickeners. Suitable thickeners include acrylic I polymers, urethane polymers, and polyethers, of which acrylate polymers are preferred.

Suitable acrylate polymers include the same classes of materials used as the solution resin.

It is generally desirable to prepare a concentrated dispersion by dispersing the pigment in water in the presence of one or more dispersants, and then to dilute this dispersion with additional water together with the DPnP, resins, and any other additives to form the ink.

This technique permits preparation of a greater quantity of pigmented ink from the equipment. By dilution, the ink is adjusted to provide the desired concentration, colour strength, and other properties for the particular application. Thus another preferable aspect of the invention provides a method for preparing an ink jet ink comprising:- t (a) dispersing at least one pigment and a dispersant for the pigment in an aqueous carrier medium; and i (b) diluting the dispersion thus produced with dipropylene glycol propyl ether, together: with at least one emulsion resin, at least one solution resin, at least one additional water-miscible organic solvent, and water; to produce an ink.

The dispersing step may be accomplished by many well known methods, for example in a horizontal mini mill, a ball mill, a roll mill, an attritor, a homogeniser or by passing the mixture through a plurality of nozzles within a liquid jet interaction chamber at a liquid pressure of at least 1000 psi (6 89 MPa) as described in United States Patent Specification 5,026,427 to produce a uniform dispersion of the pigment particles in the aqueous carrier medium.

A suitable average particle size of the pigment is 10,um or less, preferably I Em or less, most preferably 200 nm or less, especially from 50 rim to 200 nm.

In another embodiment of the present invention there is provided an ink set comprising two I or more inks according to the invention. In particular, there is provided a set of four inks comprising the three subtractive primary colours cyan, magenta, and yellow, together with a black ink (commonly referred to as CMYK). Using this ink set, the number per unit area and diameter of the ink dots formed on the recording medium may be controlled for colour mixing according to the densities of three primary colour components in the original I images to be recorded, thus reproducing the original colour.

In yet another aspect of the present invention, there is provided an ink jet printing process using the ink of the invention as hereinbefore defined comprising: t À Taking an ink jet printer; À loading the printer with an ink comprising: i (a) at least one pigment; (b) a dispersant for the pigment; (c) dipropylene glycol propyl ether; (d) at least one emulsion resin; (e) at least one solution resin; (f) atleast one surfactant (g) at least one additional water-miscible organic solvent; and (h) an aqueous carrier medium.

À printing the ink on to an ink jet printable medium; and À drying the print using infra-red radiation.

Any suitable ink jet printer may be used, but a piezo drop-on-demand printer is especially preferred.

The ink jet printable medium may be any suitable sheet like medium as commonly used for I ink-jet printing able to accept the ink formulation, for example paper, coated paper, and I polymeric substrates such as cellulose acetates, polyethylene, polypropylene, poly vinyl chloride, and polyesters including poly ethylene terephthalate and poly ethylene naphthalate. However, the inks of the invention are particularly suitable for printing on hydrophobic substrates. Thus according to this preferred embodiment of the invention the printable medium is a hydrophobic polymeric medium such as polyvinyl chloride, I polyester, polyethylene, or polypropylene, and most preferably is untreated polyvinyl chloride.

Use of infra-red radiation for drying an ink jet print is known according to British Patent application GB 2 370 834 A and elsewhere. There is no particular restriction on the infra red heating unit used for drying the print, which may be any of those known in the art. The emitted infra red radiation may be so-called short wave, of wavelength between about 0.5 rim and 2 m, medium wave emitting between about 2,um and about 3.5 sum, or long wave emitting above 3.5 1lm. Preferably medium wavelength radiation is used. Suitable infra red radiation sources and units are well known, and commercially available from companies such as Ircon Drying Systems AB of Vanersborg, Sweden; Krelus AG of Hirschthal, Switzerland; Heraeus Noblelight GmbH of Kleinostheim, Germany; and Compact Engineering Limited of Thirsk, England.

Preferably the print is dried using int'ra-red radiation in the presence of an ample flow of air, which not only serves to cool the infra-red source but may be directed towards the print surface to disturb the boundary layer and aid evaporation.

The inks, ink set, and printing method of the invention produce pleasing high quality images of good image tone and high maximum density. Furthermore the prints exhibit excellent lightfastness suitable for applications such as banners, signage, displays, posters, I billboards, and the like.

The following examples will serve to illustrate the invention:

Example I

In this example, an inventive ink comprising the solvent Dipropylene glycol propyl ether (OPnP) is prepared and compared with five comparison inks with various alternative solvents.

Preparation of Pigment Dispersions A magenta dispersion was prepared according to the formulation shown in Table 1, where all parts are by weight, using a Microfluidiser model M210C at 30000 psi (200 MPa). The dispersion was then centrifuged to remove oversized particles. The magenta pigment was a commercial sample of Pigment Red 122 available under the trade name Hostaperm Pink E from Clari ant. The di spersant was a commercially available styrene acryl ate copolymer having an acid number of 214, a Tg of 128 C, and a molecular weight of 17000 neutralised with potassium hydroxide. The average particle size of the pigment dispersion was less than 200nm.

Table 1.

Component % by Weight Pigment Red 122 10 Dspersant 2 Deionised water to make 100 Preparation of Inks luks were prepared according to the formulations shown in Table 2 using samples of the dispersion prepared above. In this table all parts are measured by weight. The surfactant used was sodium dioctyl sulphosuccinate. The emulsion resin used was a commercially available acrylate polymer emulsion having a solid content of 46% and an average particle size of 84.7 nm; the polymer has an acid number of 70, a minimum film-forming temperature oi 60 C, a Tg of 64 C, and a molecular weight >200,000. The solution resin is a 20% aqueous solution of the same styrene acrylate polymer used as dispersant. EG1 is an ethoxylated glycerol with a degree of ethoxylation approximately 26. The comparison solvent DPM is dipropylene glycol methyl ether and the comparison solvent NMP is N-methyl pyrrolidone.

The pH of the inks was adjusted to >8 when necessary by appropriate additions of potassium hydroxide.

Table 2

Component TO by weight Ink 1 Ink 2 1 Ink 3 1 Ink 4 1 Ink 5 1Ink 6 Invention Comparison inks Pigment Dispersion 35 35 1 35 | 35 35 35 Diethylene Glycol 6 6 l 6 6 6 EG1 4 4 4 1 4 4 4 Solution Resin 4.6 4. 6 1 4.6 1 4.6 14.6 4.6 Emulsion Resin 11.8 1 11.8 11.8 1 11.8 111.8 11.8 Surfactant 0.5 0.5 0.5 0.5 0.5 0 5 DPnP 5 DPM 5 1 1 2.5 NMP l 5 | Butanol l l 2.5 1 1,2-hexane diol 5 1,3-propane diol l l l 5 Deionised water to 100 100 | 100 | 100 100 100 Print Test The inks were loaded into cartridges and test charts printed using an Epson 1160 piezo drop-on-demand printer on standard commercial uncoated untreated matt vinyl (MPI3021) from Avery Dennison. The inks were in-line dried using a lIeraeus Noblelight I Kw medium wave carbon IR drier in combination with high air flow.

The prints were assessed visually for print quality. Further, adhesion of the ink to the substrate was tested as follows: A sticky tab was adhered to the sample and then pulled off at an angle of 180 using a quick, smooth motion. Adhesion of the ink to the substrate was assessed visually by looking at the area where the tab had been pulled off the print for any surface damage or loss of ink. If no ink had been removed adhesion was assessed as excellent, but if the surface of the ink film has been marked or damaged or if a lot of ink had been removed then adhesion was poor. The print quality of the inventive ink was excellent and similar in

quality to that expected when using a vinyl substrate treated with an inkjet receiving coating. The inventive ink had very good adhesion to the vinyl. The comparison inks gave poor print quality.

Example 2

In this example, five additional inventive magenta inks are prepared with various pigments and dispersant levels and compared with the inventive ink above.

Preparation of Pigment Dispersions Three magenta dispersions were prepared using a Microfluidiser Model Ml IOL at 12000 psi (82 7 MPa) according to the formulations shown in Table 3, where all parts are by weight.

Table 3

Component % by Weight Dispersion ADispersion B Dispersion C Pigment Red 122 10l 10 10 Dispersant 43 2 Deionised water to 100100 100 The dispersions were centrifuged to remove oversized particles. The magenta pigment was a commercial sample of Pigment Red 122 available under the trade name Cromophtal Pink PT from Ciba. The dispersant was the same as in Example 1. The average particle size of the dispersions was less than 200nm.

Two additional magenta dispersions were prepared according to the formulations shown in Table 4, where all parts are by weight, using a Microfluidiser model M1101, at 12000 psi (82 7 MPa).

Table 4 _._

Component % by Weight Dispersion D Dispersion E Pigment Red 122 10 10 Dispersant | 2 Deionised water to make l 100 100 l The dispersions were centrifuged to remove oversized particles. The ma yenta pigment in Dispersion D was a commercial sample of Pigment Red 122 available under the trade name Inkjet Magenta EO2 from Clariant, the magenta pigment in Dispersion E was a commercial sample of Pigment Red 122 available under the trade name Toner Magenta EB from Clariant. The dispersant was as in Example 1. The average particle size of the dispersions was less than 200nm.

Preparation of Inks Inventive inks 7 - 11 were prepared according to the formulations shown in Table 5 from the five dispersions (A-E) prepared above. All parts are measured by weight. The surlactant, solution resin, emulsion resin, and ethoxylated glycerol were the same as in Example l. The pH of the inks was adjusted by appropriate additions of potassium hydroxide to >8 when necessary. ]6

Table 5 _.

Component Amount by Weight Ink 7 Ink 8 l Ink 9 l Ink 10 l Ink 11 l Invention Invention Invention Invention Invention Dispersion A 35 Dispersion B 35 Dispersion C 35 l Dispersion D 35 l Dispersion 12 35 Diethylene Glycol 66 _6 6 EGI 44 4 4 4 Solution Resin 4.64.6 4.6 4.6 4. 6 l Emulsion Resin 11.811.8 11.8] 1.8 11.8 Surfactant 0.50.5 0.5 10.5 0.5 DPnP 55 5 5 5 1 Deionised water to 100100 100 100 100 | Print T est All five inks were printed and tested as in Example 1. The print quality of the inventive inks 7 - 11 was assessed as good, and the adhesion of the inks to the vinyl substrate was assessed as very good.

Example 3.

In this example, five inventive cyan inks are prepared with various pigments and dispersant levels and compared to the inventive ink 1 above.

Preparation oi Pigment Dispersions Four cyan dispersions were prepared using a Microfluidiser model Ml IOL at 12000 psi (82 7 MPa) according to the formulations shown in Table 6, where all parts are by weight.

Table 6.

Component % by 7Veight Dispersion F Dispersion G Dispersion H Dispersion I Pigment Blue 15:3 7 10 l Dispersant l Deionised water to 100 100 100 l 100 The dispersions were centrifuged to remove oversized particles. The cyan pigment was a commercial sample of Pigment Blue 15:3 available under the trade name Toner Cyan BG from Clariant. The dispersant was the same as in Example 1. The average particle size of the dispersions was less than 200nm.

One further cyan dispersion was prepared using a Microfluidiser model M1 10L at 12000 psi (82 7 MPa) according to the formulation shown in Table 7, where all parts are by weight.

Table 7

| Component I W/eibght I Dispersion J Pigment Blue 15:3 10 Dispersant Deionised water to 100 The dispersion was centrifuged to remove oversized particles. The cyan pigment was a commercial sample of Pigment Blue 15:3 available under the trade name Hostaperm Blue B2G02 from Clariant. The dispersant was the same as in Example 1. The average particle size of the dispersion was less than 200nm.

Preparation of Inks IS Inventive inks 12 - 16 were prepared according to the formulations shown in Table 8 from the five dispersions F - J prepared above. All parts are measured by weight. The surfactant, emulsion resin, solution resin, and ethoxylated glycerol were as in Example 1. The pH of the inks was adjusted by appropriate additions of potassium hydroxide to >8 when necessary.

Table 8

Component l Amount by Weight Ink 12 iTnk 13 | leak 14 | Ink 15 Ink 16 Invention Invention Invention Invention Invention Dispersion F 35.7 Dispersion G 31.3 l l Dispersion H | 27.8 | Dispersion I l 25 Dispersion J l 13 Diethylene Glycol 6 l F,GI l 4 4 1 4 144 Solution Resin l 4.6 4. 6 l 4.6 |4.64.6 Emulsion Resin 11.8 11.8 11.8 l11.811.8 Surfactant 0.5 0. 5 0.5 l0.50.5 DPnP 5 5 5 55 Deionised water to l 100 100 l 100 100100 Print Test All five inks were printed and tested as in example 1. The print quality of the inventive inks 12 -16 was as good as that of ink 1 and all the inventive inks 12 -16 had very good adhesion to the vinyl.

Example 4

in this example, an inventive black ink is prepared and compared with the inventive ink I disclosed in example 1.

Preparation of Pigment Dispersion A black dispersion was prepared according to the formulation shown in 'Table 9, where all parts are by weight, using a Microfluidiser model M11 OL at 12000 psi (82 7 MPa).

Table 9

| Component | W/ eibght Dispersion K l Pigment Black 7 l Dispersant Deionised water to l 100 The dispersion was centrifuged to remove oversized particles. The black pigment was a commercial sample of Pigment Black 7 available under the trade name S170 from Degussa. T he dispersant was the same as in Example l. The average particle size of the dispersions was less than 200nm.

Preparation of Inks An ink was prepared using the dispersion prepared above and by diluting according to the formulations shown in Table 10.

Table 10

Component Amount by Weight Ink 17 Invention Dispersion K 38.9 Diethylene Glycol EG1 4 Solution Resin 4.6 Emulsion Resin 11.8 Surfactant 0.5 DPnP 5 Deionised water to 100 All parts are measured by weight. The surfactant, emulsion resin, solution resin, and ethoxylated glycerol were the same as in Example 1. The pH of the ink was adjusted by appropriate additions of potassium hydroxide to >8 when necessary.

Print T est The ink was printed and tested as in Example l. The printability of the inventive ink 17 l 5 was as good as that of inventive ink 1, and inventive ink 17 had very good adhesion to the vinyl.

Example 5

in this example, two inventive yellow inks are prepared and compared with the inventive ink l disclosed above.

Preparation of Pigment Dispersions Two yellow dispersions were prepared using a Microfluidiser model M1 IOL at 12000 psi (82 7 MPa) according to the formulations shown in Table 11, where all parts are by weight.

Table 11

Component % by Weight Dispersion I, Dispersion M Pigment Yellow 155 10 9 Dispersant 2 2 Deioinised water to make 100 100 l The dispersions were centrifuged to remove oversized particles. The yellow pigment in dispersion L was a commercial sample of Pigment Yellow 155 available under the trade; name Novoperm Yellow 4G from Clariant. The yellow pigment in dispersion M was a commercial sample of Pigment Yellow 155 available under the trade name Inkjet Yellow 4G from Clariant. The dispersant was the same as in Example 1. The average particle size of the dispersions was less than 200nm.

Preparation of Inks Inks were prepared using the two dispersions prepared above and by diluting according to the formulations shown in Table 12. All parts are measured by weight. The surfactant, emulsion resin, solution resin, and ethoxylated glycerol were the same as in Example 1.

The pH of the inks was adjusted to >8 when necessary by appropriate additions of potassium hydroxide.

Table 12

Component Amount by Weight

_ _ _

Ink 18 Ink 19 Invention Invention Dispersion L 35 Dispersion M 38.9 Diethylene Glycol 6 F,G1 4 4 Solution Resin 4.6 4.6 Emulsion Resin 11. 8 11.8 Surfactant 0.5 0.5 DPnP 5 5 Deionised water to 100 100 Print Tests Both inks were printed and tested as in Example 1. The print quality of the inventive inks 18 and 19 was as good as inventive ink l and the inventive inks had very good adhesion to the vinyl.

Example 6

An inkset incorporating inventive inks 2 (Magenta), 15 (Cyan), 19 (Yellow) and 17 (Black) was loaded into an Epson 1160 printer. A four colour test pattern incorporating cyan, magenta, yellow, black, red, green, blue and three colour density wedges and other elements was printed on uncoated untreated matt vinyl (MPI3021) from Avery Dennison.

l O The inks were in-line dried using a Heraeus Noblelight medium wave IR drier in combination with high air flow. The print quality of the inventive inkset was assessed as excellent with smooth solid colour fills and little intercolour bleed. The quality was similar to that expected when using an inkjet coated coated vinyl, showing the usefulness of the inventive inks and ink set.

Claims (13)

1. Claims:- I. An ink jet ink composition which comprises: (a) at least one

   pigment; (b) dipropyleneglycolpropyl ether; (c) at least one emulsion resin; and (d) an aqueous carrier medium.
2. 2. An ink jet ink composition according to claim I which additionally comprises at least one solution resin.
3. 3. An ink jet ink composition comprising: (a) at least one pigment; (b) a dispersant for the pigment; (c) dipropylene glycol propyl ether; (d) at least one emulsion resin; (e) at least one solution resin; (I) at least one surfactant; (g) at least one additional water-miscible organic solvent; and (h) an aqueous carrier medium.
4. 4. An aqueous ink jet ink composition according to any of claims I - 3 wherein the emulsion resin is an acrylate polymer characterized by an acid number below 100 and an average particle size below 200nm.
5. 5. An aqueous ink jet ink composition according to any of claims 2 - 4 wherein the solution resin is a styrene/acrylate polymer characterized by an acid number within the range of 150 to 250.
6. 6. An aqueous ink jet ink composition according to claim 3 wherein the surfactant is dioctyl sulphosuccinate or salt thereof.
7. 7. An aqueous ink jet ink composition according to claim 3 wherein the dispersant is a styrene/acrylate copolymer.
8. 8. A method tor preparing an ink jet ink comprising: (a) dispersing at least one pigment and a dispersant for the pigment in an aqueous carrier medium; and (b) diluting the dispersion thus produced with dipropylene glycol propyl ether, together with at least one emulsion resin, at least one solution resin, at least one additional water-miscible organic solvent, and water; to produce an ink.
9. 9. An ink set comprising two or more inks wherein at least one of the inks is formulated according to any of claims 1 - 7.
10. 10. An ink set according to claim 9 which comprises cyan, magenta, yellow, and black inks.
11. I I. An ink jet printing process comprising: i. taking an ink jet printer; ii. loading the printer with at least one ink according to any of claims I - 7; iii. printing the ink on to an ink jet printable medium; and iv. drying the print using infra-red radiation.
12. 12. An ink jet printing process according to claim 11 wherein the ink jet printer is a piezo drop-on-demand ink jet printer.
13. 13. An ink jet printing process according to claim 11 or 12 wherein the ink jet printable medium is poly vinyl chloride.