GB2507727A - Inkjet ink - Google Patents

Abstract

An inkjet ink comprises at least one volatile organic solvent, at least one colorant, at least one humectant, and a terpene-phenolic resin. The terpene-phenolic resin may comprise a copolymer of pinene with phenol or bisphenol and may have a molecular weight of 500-1000. The humectant may be selected from polyol, glycol ether, glycol ether acetate, diacetone alcohol, 2-pyrrolidinone, N-methylpyrrolidinone, ethyl lactate, butyl lactate, propylene carbonate, 1,3-dimethyl-2-imidazolidindione and/or alkyl ester, although it is preferably propylene glycol monomethyl ether. The ink may further comprise one or more binders or surfactants. Typically, the ink comprises up to 50 wt.% organic solvent (such as ethanol), 0.5-15 wt.% colorant, at least 35 wt.% humectant, up to 30 wt.% terpene-phenolic resin, up to 30 wt.% binder (such as an acrylic binder), and up to 1 wt.% surfactant (such as a polyether-modified polydimethylsiloxane). The ink is intended to be compatible with a thermal inkjet printer.

Description

INIJETINK COMPOSITION

Field of the Invention

This invention relates to inkjet ink compositions and in particular, though not necessarily solely, to compositions fbr thermal inkjet (lii) printing.

Background of the Invention

In the field of industrial coding and marking codes, dating, and traceability information are applied directly onto products and/or product packaging. To achieve high quality images on a consistent basis in industrial environments, it is advantageous thr the inkjet ink to have a long decap time.

Decap time is defined as the period of time that aprinthead can be left uncapped at idle and still produce a high quality code when printing is restarted. Some inlcjet inks suffer from the ink drying out around the nozzles resulting in poor decap behaviour and therefore a loss of print quality. Poor decap behaviour is often caused by the solvcnt in the ink cvaporating and lcaving bchind non-volatile matcrials which at lcast partially obstruct the nozzles and are thereibre detrimental to jetting perfbrmance.

A common method of improving the decap performance of an inkjet ink is to add non-volatile humectants to the ink to reduce the likelihood of the ink drying in the nozzles. However this can have a detrimental effect on the drying time of the ink.

Thermal inkjet (TIJ) printing is a desirable coding and marking technology as it offers significantly higher print resolutions than competing technologies in the field, such as continuous inkjet However, with the increasing trend to use flexible plastic materials for food packaging, there is a requirement for inks to dry quickly and adhere well to these semi-porous and non-porous substrates. The majority of commercially available thermal inkjct inks arc water based and, as a rcsult, suffer from rclativcly long drying times and poor adhesion on semi-porous or non-porous substrates. Thus there is a need for TIJ inks containing volatile organic solvents.

The art published to date reveals the use of various additives to improve the decap behaviour of inkjet inks, including TIJ inks, containing solvents, colorants, binders and humcctants.

International (PCT) Patent Application W0201 1/04 1364, discloses a thermal inkjet ink composition including a volatile organic solvent, a binder resin, a dye, up to 40% of a humectant to keep the drying time low, and an additive for extending the decap time. The additive is selected form plastieisers, surfaetants, aliphatic hydrocarbons, drying oils and mixtures thereoL the resulting inks exhibiting a maximum decap time of 10 minutes.

International (PCT) Patent Application W02010/042105 discloses the use of a decap controlling additive which has a vapour pressure from 1-5mm Hg at 25°C, has a boiling point greater than the base solvent of the ink and is selected from the group consisting of 1-methoxy-2-propanol, ethyl lactate, tert-butanol, tert-butyl acetate, 1-butanol and combinations thcrcof Thc inks cxcmplificd in this application cxhibit a maximum decap time of 5 minutes.

US Patent 8182597 discloses a solvent based inkjet ink composition comprising at least 50 weight % volatile organic solvent, a colorant, a humectant, from 0.3 weight % to 8 weight % of a binder resin and not more than 5 weight % water, where the ink composition is suitable for use in a thermal ink jet printer and has a decap time of at least 60 seconds. Again the maximum decap time illustrated in this patent is 5 minutes.

US Patent 8142559 discloses a thermal ink jet ink comprising one or more volatile organic solvents selected from C1-C4 alcohols, C-C5 ketoncs and mixturcs thercof n j one or more humectants wherein the humectants are present in an amount not more than 30 weight %, one or more binder resins and one or more dyes, where the ink composition is suitable for use in a thermal ink jet printer and has a decap time of at least 15 seconds. In the examples given in the patent, maximum useful decap time is limited to 60 seconds.

European Patent No 0 501 406 discloses an ink for an inkjet printer containing an oil soluble dye, a synthetic resin and an organic solvent where the synthetic resin contains a terpene-phenol copolymer resin and a styrene-acrylic eopolymer resin.

The terpene-phenol eopolymer resin and styrene-acrylie eopolymer resins are included to provide excellent jetting stability, excellent abrasion resistance, adhesion to various recording materials and, in particular, excellent spreading of the ink dots and adhesion to a recording material attached with a wax, and a recording material coated with a coating composition containing a wax. The ink described is suitable for use in a continuous inkjet printer, an environment in which dc-cap performance is not generally an issue because ink is circulated continuously and, at the end of printing, the print head is generally flushed to ensure ink does not remain in the nozzle. Not surprisingly, there is no mention of humectants in EP 0 501 406 and this patent is also silent as to decap performance.

It is an object of this invention to provide a thermal ink jet ink composition for a thermal inkjet printer that will not only exhibit drying times in the order of less than 5 seconds on non-porous substrates but which is also capable of exhibiting decap times of at least 1 hour.

Summary of the Invention

Accordingly, in one aspect, the invention provides an inkjet ink composition including one or more volatile organic solvents and one or more colorants, said ink being characterised in that it includes one or more humectants and a teipene phenolic Preferably said ink includes one or more binders.

Prefcrably said one or more binders are selected from polyamide resins, polyurethane rcsins, rosin cstcr resins, acrylic resins, polyvinyl butyral resins, polycstcn, phcnolic resins, vinyl resins, polystyrene/polyacrylate copolymers, cellulose ethers, cellulose nilrate resins, polymaleic anhydrides, acetal polymers, polystyrene/polybutadiene copolymers, polystymne/polymethactylate copolymers, sulfbnated polyesters, aldchyde resins, polyhydroxystyrenc resins and polyketonc resins and mixtures of two or more thereof.

Preferably said one or more binders are present in an amount up to 30% by weight More preferably said one or more binders are present in an amount up to 10% by weight.

Prcfcrably said onc or more volatile organic solvents arc present in an amount less than 50 weight %.

More preferably said one or more volatile organic solvents are present in an amount of 5% to 40% by weight.

Preferably said one or more volatile organic solvents are selected from alcohols, ketones, esters and ethers and mixtures thereof More preferably said one or more volatile organic solvents are selected from C 1-C4 alcohols.

Yet more prcfcrably said volatile organic solvent compriscs ethanol.

Preferably said one or more colourants are present in an amount of from 0.1% to 15% by weight. More preferably said one or more colourants are present in an amount of from 0.5% to 10% by weight based on the total weight of the composition.

Preferably said one or more colourants comprise any suitable dye and/or pigment.

Prefcrably said one or more humectants are present in an amount greater than 35 weight %.

Preferably, said one or more humectants are selected from the group consisting of polyol, glycol ether, glycol ether acetates, diacetone alcohol, 2-pyrrolidinone, N- methylpyrrolidinone, ethyl lactate, butyllactate, propylene carbonate, 1,3-dimethyl-2-imidazolidindione, and alkyl esters, and any combination thereof Preferably said polyol is selected from the group consisting of polyethylene glycol, polypropylene glycol, poly(ethylene-co-propylene glycol), trimethylol propane, ethylene glycol, glycerin, diethylene glycol, triethylene glycol, tripropyleneglycol, tetraethylene glycol, pentaethylene glycol, 1,2-propylene glycol, I,3-propanediol, butylcnc glycol, tricthylcnc glycol, 1,2,6-hcxanctriol, thiodiglycol, hcxylcnc glycol, bis-2-hydroxyethyl ether, 1,4-butanediol, 1,2-butenediol, 1,4-butenediol,1,3- butenediol, 1,5-pentanediol, 2,4-pentanediol, 2,4-heptanediol, 1,8-octanediol, 1,10-decanediol, 1,1 2-dodecanediol, I,4-cyclohexanediol, I,4-cyclohexanedimethanol, 1,2-bis(hydroxymethyl)eyclohexane, 1,2-bis(hydroxyethyl)-eyclohexane,3-methyl- 1,5 pentanediol, 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol, pentaerythritol, sorbitol, matmitol, and any combination thereof Preferably said glycol ether is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol n-propyl ether, propylene glycol t-butyl ether, propylene glycol n-butyl ether, dipropylene glycol methyl ether, dipropylene glycoln-propyl ether, dipropylene glyeol t-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-propyl ether, tripropylene glycol t-butyl ether, tripropylene glycol n-butyl ether, ethyl cellosolve, methyl cellosolve, polyethylene glycolmonomethyl ether, polypropylene glyeol monomethyl ether, methoxytriglycol, ethoxytriglycol, butoxytriglyeol, 1-butoxyethoxy-2-propanol, and any combination thereof Preferably, the glycol ether is selected from the group consisting of ethylene glyeolmonomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, tripropylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, and any combination thereof A particularly preferred humectant is propylene glycol monomethyl ether.

Preferably said terpene phenolie resin comprises a copolymer of a pinene and a phenol such as phenol or bisphenol.

Preferably said terpene phenolic resin is selected to have a molecular weight in the range 500 to 1000.

Preferably said terpene phenolic resin comprises a copolymer of a pinene and a phenol such as that sold under the trade mark Dertophene T. Preferably said terpene phenolie resin is present in an amount of 30% by weight.

More preferably said terpene phenolic resin is present in an amount up to 20% by weight and even more preferably up to 10% by weight.

Preferably said ink further includes a surfaetant.

Preferably said surfactants is selected from modified polysiloxanes, alkyl modified polyoxyalkyleneamines, alkyl modified propoxylated (poly(oxypropylene)) diamines, alkyl ether amines, nonyl phenol ethoxylates, ethoxylated fatty amines, fluorinated organic acid diethanolamine salts, alkoxylated ethylenediamines, alkyl modified polyethylene oxides, alkyl modified polyallcyleneoxides, alkyl phosphate ethoxylate mixtures, polyoxyalkylene derivatives of propylene glycol and polyoxyethylated fatty alcohols.

More preferably said surfactant comprises a polyethcr modified polydimethylsiloxane.

Preferably said surfactant is present in an amount up to 1 % by weight.

More preferably said surfactant is present in an amount from 0.0 1% to 0.5% by weight.

Preferably said ink is compatible with the components of a thermal inkjet printer.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future.

Detailed Description of Method

This invention provides a thermal inkjet ink composition comprising one or more volatile organic solvents and one or more colorants. The characteristic of the ink is that it further includes one or more humectants, a terpene phenolic resin and, optionally, one or more binders. The resulting ink is suitable for being applied directly onto products and/or product packaging to achieve high quality images.

To achieve high quality codes, it is important that the ink can provide a long decap time so that high quality codes can be printed after periods of printer inactivity. In addition, thermal inkjet compositions for industrial marking and coding should exhibit short drying times on semi-porous or non-porous substrates, good adhesion on semi-porous or non-porous substrates and compatibility with the components of a thermal inkj et printer cartridge.

To improve adhesion onto non-porous substrates, it is known to add binders to the inkjet ink composition. However it is well known that the addition of binders can substantially reduce decap time. Terpene phenolie resins are known in the art to act as tackifiers to improve adhesion on to non-porous substrates. However intuitively one would also expect the addition of terpene phenolic resins to adversely affect decap time. It was therefore a surprise to the inventors to find that although a minor improvement in adhesion was achieved on addition of the terpene phenolic resin, a substantial improvement in deeap time was observed.

The term "decap control," as referred to herein, means the ability of the inkjet ink to readily eject from the print head, upon prolonged exposure to air. The ink deeap time is measured as the amount of time that an inkjet printhead may be left uneapped before the printer nozzles no longer fire properly, potentially because of clogging or plugging. Generally, nozzle(s) may become clogged (i.e. impeded, slowed) or plugged (i.e. obstmcted, substantially or completely closed) by a viscous plug that forms in the nozzle(s) as a result of water/solvent loss, crusting of the ink, and/or crystallization of the dye in and/or around any of the nozzles. If a nozzle has become clogged, ink droplets ejected through the nozzle's orifice may be misdirected, which may adversely affect print quality. When an orifice is plugged, it becomes substantially or completely blocked. As a result of the nozzle being plugged, the ink droplets may not pass through the affected nozzle. Thus, the criteria for measuring failure to fire by a nozzle is that there is a misdirection of ink through the nozzle's orifice to a lesser or greater degree, or a complete blockage, which can be precisely indicated in a printed image on media printed by the nozzle. The clogging and plugging effect on nozzles and their ink printing performance can be tested by various methods. In its simplest form, one method involves printing a given test pattern with the printhead nozzles to verify their working condition. This is followed by exposing the nozzles to the air for predetermined increasing periods of time without printing or spitting the nozzles. Then, all of the nozzles are printed again in the given test pattern for the second time. The test patterns are then compared to determine the number of weak or misdirected nozzles. The longest period of time that the printhead may be left uncapped, yet still produce a high quality code with minimal missing nozzles when printing resumes, is taken as the decap time of the ink composition.

In the worst case, such nozzle clogging or plugging results in a complete failure to fire by the nozzle.

To assess the quality of the test pattern, 2D datamatrix codes were used and were analyzed using an LYS Integra 9505 bar code verifier. A grade of A-C is taken as acceptable while a 13, F or not valid' indicates a poor quality code.

Drying time is defined as the time taken for a printed code to dry on a chosen substrate. This is assessed by printing range of characters (usually an X) on the substrate at the chosen resolution and at one second intervals, successive characters being wiped with a gloved finger until the print ceases to smear.

Adhesion is assessed by preparing a i2m draw-down of the ink onto the substrate of choice which is then allowed to dry thoroughly overnight. The surface of the ink draw-down is then scored with a Sheen Cross Hatch Cutting Wheel and a piece of3M SCOTCH® tape grade 810 is adhered firmly over the top of the cross hatched area.

The tape is then removed and adhered to a piece of white card. Image analysis software is then used to assess how dark the section of tape is that was adhered to the ink draw-down giving an indication of how much ink was removed with the tape. A scale of 0-246 is used where 0 indicates the tape is black and all of the ink has been removed with the tape as a result of poor adhesion, and 246 indicates that no ink has been removed due to excellent adhesion of the ink on the substrate.

Compatibility of the ink with the components of the thermal inkjet printer cartridge may be assessed according to two methods. One method involves filling the printer cartridge with the ink and storing it at high (40°C) and low (5°C) temperatures for up to a year and, at predetermined time frames, carrying out printing tests to assess image quality. If there is any incompatibility between the ink and the cartridge components a loss of image quality is seen. The second method involves carrying out soak tests where critical components of the cartridge arc soaked in the ink for 4 weeks at 40°C after which any changes in mass or shape / size are assessed.

Incompatibilities show up as changes in mass or shape / size.

In an effort to achieve a solvent based ink with the features discussed above an ink formulation is disclosed comprising one or more volatile organic solvents, one or more colorants, one or more humeetants, a terpene phenolie resin and optionally other ingredients such as binders, surfactants and bioeides. The term ink colorant refers to any species that may provide colour to the ink.

The inkjet ink composition disclosed herein is particularly intended for drop-on demand printing, such as a thermal inkjet printing or Piezo inkjet printing. More particularly, the inkjet ink composition as described herein is intended for thermal inkjet (TIJ) printing.

The one or more volatile organic solvents are selected from alcohols, ketones, esters and ethers and mixtures thereof and are preferably selected from Ci-C4 alcohols, examples of which are ethanol, 1-propanol and 2-propanol. The organic solvent is included in the formulation to evaporate quickly to give short drying times and to penetrate the semi-porous or non-porous substrates to help improve the adhesion.

The preferred organic solvent is ethanol and may be present at a level of up to 50% by weight, prcfcrably 5 to 40% by wcight.

Any suitable colourant may be used in the present invention. The colorant may comprise any suitable dye and/or pigment. The colorant refers to any species that may provide colour to the ink -Any dye that is soluble in the organic solvent may be used and chosen from the dyes commonly used in ink compositions, especially inkjet ink formulations such as, but not necessarily restricted to, direct dyes, acid dyes, basic dyes, food grade dyes, basic dyes, reactive dyes, disperse dyes and mixtures thereof Inorganic and organic pigments may be used as the pigment without particular limitation. Inorganic pigments usable herein include, in addition to titanium oxide and iron oxide, carbon blacks produced by known processes, such as contact, furnace, and thermal processes. Organic pigments usable herein include (but are not confined to) azo pigments (including azo lake, insoluble azo pigment, condensed azo pigment, and chelate azo pigment), polycyclic pigments (for example, phthalocyanine, perylene, perinone, anthraquinone, quinaeridone, dioxazine, thioindigo, isoindolinone, and quinophthalone pigments), dye-type chelate pigment (for example, basic dye-type chelate pigments and acid dye-type chelate pigment), nitro pigments, nitroso pigments, and aniline black.

Preferably the colourant, which may be a pigment or a dye, is present in an amount of from 0.1% to 15% by weight based on the total weight of the composition. More preferably, the inkjet ink composition comprises from 0.5% to 10% by weight of colorant based on the total weight of the composition.

1-lumectants are additives which maintain a wet environment in the vicinky of the ink jet nozzle during the cvaporation process, thus extending the decap time. However high levels of humectant can also adversely affect drying time.

Preferably, humectants have a boiling point greater than 150°C, greater than 200°C, or greater than 250°C, and/or a relative evaporation rate less than 1.0, less than 0.9, less than 0.7, less than 0.4, less than 0.1, or less than 0.01. The humeetants typically are solvents having one or more polar functional groups such as hydroxyl, ether, amide, ester, ketone, and carbonate, for example, two functional groups, which may be the same or different, such as two hydroxyl groups or one hydroxyl group and one ether group. Preferably, the one or more humectants are selected from the group consisting of polyol, glycol ether, glycol ether acetates, diacetone alcohol, 2-pyrrolidinone, N-methylpyrrolidinonc, ethyl lactate, butyllactate, propylene carbonate, 1,3-dimethyl-2-imidazolidindione, and alkyl esters, and any combination thereof For example, the polyol is selected from the group consisting of polyethylene glycol, polypropylene glycol, poly(cthylcnc-co-propylcnc glycol), trimethylol propane, ethylene glycol, glycerin, diethylene glycol, triethylene glycol, tripropyleneglycol, tetraethylene glycol, pentaethylene glycol, 1,2-propylene glycol, 1,3-propanediol, butylene glycol, triethylene glycol, I,2,6-hexanetriol, thiodiglycol, hexylenc glycol, bis-2-hydroxyethyl ether, I,4-butanediol, 1,2-butenediol, I,4-butenediol, 1,3- butenediol, 1,5-pentanediol, 2,4-pentanediol, 2,4-heptanediol, 1,8-octanediol, 1,10-decanediol, 1,1 2-dodecanediol, 1,4-cyelohexanediol, 1,4-eyelohexanedimethanol, I,2-bis(hydroxymethyl)cyclohexane, I,2-bis(hydroxyethyl)-cyclohexane,3-methyl- 1,5 pentanediol, 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol, pentaerytbritol, sorbitol, matmitol, and any combination thereof A preferred humectant is glycol ether, for example, a glycol ether selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glyeol monomethyl ether, tripropylene glyeol mononiethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomcthyl ether, diethylenc glycol monoethyl ether, propylene glycol n-propyl ether, propylene glycol t-butyl ether, propylene glycol n-butyl ether, dipropylene glycol methyl ether, dipropylene glyeoln-propyl ether, dipropylene glycol t-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-propyl ether, tripropylene glyeol t-butyl ether, tripropylene glycol n-butyl ether, ethyl cellosolve, methyl cellosolve, polyethylene glycolmonomethyl ether, polypropylene glycol monomethyl ether, methoxytriglycol, ethoxytriglyeol, butoxytriglycol, 1-butoxyethoxy-2-propanol, and any combination thereof, and preferably, the glycol ether is selected from the group consisting of ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, tripropylene glycol monomethyl ether, ethylene glyeol monobutyl ether, diethylene glycol monomethyl ethcr, diethylene glycolmonoethyl ether, and any combination thereof A prefencd humectant is propylene glycol monomethyl ether.

Humectants are known in the art to increase decap times of inkjet inks; however, excessive amounts of humectants are known to increase the drying time of the ink jet ink composition. For this reason humeetants are typically used in an amount of 30 weight % or less. In the thermal inkjet ink composition of this invention it has been found, surprisingly, that the one or more humectants can be present in an amount greater than 35 weight % and preferably greater than 40 weight % whilst still achieving low drying times.

The terpene phenolic resin for use in this invention is preferably a copolymer of a terpene such as a-pinene, 3-pinene etc and a phenol such as phenol, bisphenol etc. The molecular weight of the terpene phenolie resin is preferably from 500 to 1000. A suitable commercially available terpene phenolic resin is Dertophene T, available from Les Dérivés Résiniques & Terpéniques, although the terpene phenolic resin for use in this invention is not limited to this example. The terpene phenolic resin may be present in an amount up to 30% by weight but preferably up to 20% by weight and more preferably up to 10% by weight.

Suitable binders include polyamide resins, polyurethane resins, rosin ester resins, acrylic resins, polyvinyl butyral resins, polyesters, phenolic resins, vinyl resins, polystyrene/polyacrylate copolymers, cellulose ethers, cellulose nitrate resins, polymaleic anhydrides, aeetal polymers, polystyrene/polybutadiene eopolymers, polystyrene/polymethacrylate copolymers, sulfonated polyesters, aldehyde resins, polyhydroxystyrene resins and polyketone resins and mixtures of two or more thereof The inkjet ink composition may comprise up to 30% by weight of binders based on the total weight of the composition. More preferably, the inkjet ink composition comprises up to 10% by weight of binders based on the total weight of the composition.

Optionally the ink jet ink composition may contain other ingredients such as surfactants. Suitable surfactants include modified polysiloxanes, alkyl modified polyoxyalkyleneamines, alkyl modified propoxylated (poly(oxypropylene)) diamines, alkyl ether amines, nonyl phenol ethoxylates, ethoxylated fatty amines, fluorinated organic acid diethanolamine salts, alkoxylated ethylenediamines, alkyl modifiedpolyethylene oxides, alkyl modified polyalkyleneoxides, alkyl phosphate ethoxylate mixtures, polyoxyalkylene derivatives of propylene glycol and polyoxyethylated fatty alcohols. A preferred surfactant is a polyether modified polydimethylsiloxane. The surfaetant may be present in the inkjet ink composition in an amount up to I weight %, preferably in the range from 0.01 to 0.5 weight %.

Typically the thermal ink jet ink composition disclosed herein has a viscosity of less than about 10 mPa.s, preferably less than about 5 mPa.s, more preferably less than about 3 mPa.s, and most preferably less than about 2 mPa.s, for example, a viscosity from about ito 4 or from about ito about 3 mPa.s at 25°C.

Typically the thermal ink jet ink composition has a surface tension from about 20 to about 50 mN/m preferably from about 21 to about 35 mN!m at 25°C.

The thermal ink jet ink composition described herein provides a long decap time so that high quality codes can be printed after significant periods of printer inactivity.

For example the ink has a dccap time of at least i hour, preferably at least 2 hours, at least 4 hours, at least hours and most preferably at least 16 hours at 25°C.

In addition, the ink has one of more of the following features: short unassisted drying time on semi-porous or non-porous substrates, good adhesion on semi-porous or non-porous substrates and compatibility with the components of a thermal inkjet printer cartridge. For example the thermal ink jet ink composition has an unassisted drying time on a non-porous substrate such as polypropylene of less than 10 seconds, 5 seconds or less or 2 seconds or less depending on the printing resolution. On porous substrates such as carton board, shorter unassisted drying times are achieved, for example less than 1 second.

In a preferred embodiment, the thermal ink jet ink composition has a dccap time of at least 1 hour, good adhesion and a drying time of less than 5 seconds on non-porous substrates when used in a thermal ink jet print head.

Example

A set of Thermal inkjet inks suitable for printing onto semi-porous and non-porous substrates were prepared using the formulations shown in Table 1.

Component InkI Ink 2 Ink 3 Ink 4 (Control) Ethanol / % 34.0 33.5 32.5 32.0 Propyl enegi yco I 49.5 49.5 49.5 49.5 monomethyl ether / % 1,1,2,2-Tetramethoxyethane / 11.4 11.4 11.4 11.4 Surfactant/% 0.1 0.1 0.1 0.1 Acrylic binder / % -0.5 -0.5 DertopheneT/% --1.5 1.5 Dye/% 5.0 5.0 5.0 5.0

TABLE 1

To assess the decap performance thermal inkjct cartridges were filled with each ink and 2D datamatrix codes were printed at 600x200dpi. Each cartridge was then left with the nozzles exposed to the air for predetermined periods of time without printing or spitting the nozzles. After each time period, the same 2D datamnix code was printed again. After each test point, the 2D datamatrix codes were graded using an LVS Integra 9505 bar code verifier. A grade of A-C is taken as acceptable while aD, F or not valid' indicates a poor quality code. Table 2 shows the results for each ink.

Ink 2D Datamatrix Grade After Decap Period seconds 3 minutes 3 hours 16 hours 1 (control) B Not valid Not valid Not valid 2 D Not valid Not valid Not valid 3 B B B C 4 C B B C

TABLE 2

The data in Table 2 show that addition of the acrylic binder to the ink composition (ink 2) resuhs in a worse decap behavior compared to the control ink. However when the terpenc phcnolie resin (in this case Dcrtophene T) was added (ink 3), a substantial improvement in decap time was seen where good quality codes were still produced cvcn after the nozzles had been idle and exposed to the air for 16 hours. The extended deeap time was also seen when both the acrylic binder and the terpene phenolic resin were included in the ink composition (ink 4).

To test for the effect of the acrylic binder and terpene phenolic resin on adhesion, l2jim draw-down of the inks were prepared on polypropylene substrates and allowed to dry thoroughly overnight. The tape adhesion test was then carried out, the results of which can be seen in Figure 1 appended hereto. A visual assessment of the adhesion was made and in addition, the samples were assessed using image analysis software where a scale of 0-246 is used. 0 indicates the tape is black and all of the ink has been removed with the tape as a result of poor adhesion and 246 indicates that no ink has been removed due to excellent adhesion of the ink on the substrate.

Ink Visual Assessment of Adhesion Image Analysis Assessment of Adhesion Ink 1 (control) No adhesion -all ink removed 0 Ink 2 No adhesion -all ink removed 0 InIc 3 Some adhesion -approx 50% ink 29 removed Ink 4 Good adhesion 106

TABLE 3

The data in Table 3 and images in Figure 1 indicate that poor adhesion was achieved when either the acrylic binder or the terpene phenolic resin was used alone, but when combined a significant improvement in adhesion onto non porous substrates such as polypropylene was achieved.

The data in Table 4 show the drying time results for both inks when printed at two different resolutions onto a non-porous substrate such as polypropylene.

Ink Drying Time at 300x200dpi Drying Time at 600x200dpi on Polypropylene on Polypropylene Ink 1 (control) 1-2 seconds 2-3 seconds Ink 2 1-2 seconds 2-3 seconds Ink 3 1-2 seconds 2-3 seconds Ink 4 1-2 seconds 2-3 seconds

TABLE 4

The data in Table 4 show that although the inkjet ink composition contains greater than 30% humectant (the maximum level typically used in inkjet inks to prevent an increase in drying time), short unassisted drying times are still achieved.

While a specific embodiment has been described in detail above, it will be apparent to those skilled in the art that the disclosed embodiment may be modified using different ink formulations in alternative Thermal lnkjet printing heads.

Claims (30)

1. Cia mis 1. An ii*jet ink composition including one or more volatile organic solvents and one or more colorants, said ink being characterised in that it includes one or more humectants and a terpene phenolic resin.
2. 2. An inlcjet ink as claimed in claim I further including one or more binders.
3. 3. An inkjet ink as claimed in claim 2 wherein said one or more binders are selected from polyamide resins, polyurethane resins, rosin ester resins, acrylic resins, polyvinyl butyral resins, polyesters, phenolic resins, vinyl resins, polystyrene/polyacrylate copolymers, cellulose ethers, cellulose nitrate resins, polymaleic anhydrides, acetal polymers, polystyrene/polybutadiene copolymers, polystyrene/polymethactylate copolymers, sulfonated polyesters, aldehyde resins, polyhydroxystyrene resins and polyketone resins and mixtures of two or more thereof
4. 4. An inkjet ink as claimed in claim 2 or claim 3 wherein said one or more binders are present in an amount up to 30% by weight.
5. 5. An inkjet ink as claimed in claim 4 wherein said one or more binders are present in an amount up to 10% by weight.
6. 6. An inkjet ink as claimed in any one of claims 1 to 5 wherein said one or more volatile organic solvents are present in an amount less than 50 weight %.
7. 7. An inkjet ink as claimed in claim 6 wherein said one or more volatile organic solvents are present in an amount of 5% to 40% by weight.
8. 8. An inkjet ink as claimed in any one of claims 1 to 7 wherein said one or more volatile organic solvents are selected from alcohols, ketones, esters and ethers and mixtures thereof
9. 9. An inkjet ink as claimed in claim 8 wherein said one or more volatile organic solvents are selected from C1-C4 alcohols.
10. 10. An inkjet ink as claimed in claim 9 wherein said volatile organic solvent comprises ethanol.
11. 11. An ii*jet ink as claimed in any one of claims 1 to 10 wherein said one or more colourants are present in an amount of from 0.1% to 15% by weight.
12. 12. An inkjet ink as claimed in claim 11 wherein said one or more colourants are present in an amount of from 0.5% to 10% by weight based on the total weight of the composition.
13. 13. An inkjet ink as claimed in any one of the preceding claims wherein said one or more eolourants comprise any suitable dye and/or pigment.
14. 14. An inkjet ink as claimed in any one of the preceding claims wherein said one or more humectants are present in an amount greater than 35 weight %.
15. 15. An inkjet ink as claimed in any one of the preceding claims wherein said one or more humectants are selected from the group consisting of polyol, glycol ether, glycol ether acetates, diacetone alcohol, 2-pyrrolidinone, N- methylpyrrolidinone, ethyl lactate, butyllactate, propylene carbonate, 1,3-dimethyl-2-imidazolidindione, and alkyl esters, and any combination thereof
16. 16. An inkjet ink as claimed in claim 15 wherein said polyol is selected from the group consisting of polyethylene glycol, polypropylene glycol, poly(ethylene-co-propylene glycol), trimethylol propane, ethylene glycol, glycerin, diethylene glycol, triethylene glyeol, tripropyleneglycol, tetraethylene glyeol, pentaethylene glycol, 1,2-propylene glycol, I,3-propanediol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, bis-2- hydroxyethyl ether, 1,4-butanediol, 1,2-butenediol, I,4-butenediol, 1,3-butenediol, I,5-pentanediol, 2,4-pentanediol, 2,4-heptanediol, I,8-octanediol, 1, 10-decanediol, 1, 12-dodecanediol, 1,4-cyclohexanediol, 1,4- cyclohexanedimethanol, 1,2-bis(hydroxymethyl)cyclohexane, 1,2- bis(hydroxyethyl)-cyclohexane,3 -methyl-1,5 pentanediol, 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol, pentaerythritol, sorbitol, mannitol, and any combination thereof
17. 17. An inkjet ink as claimed in claim 15 wherein said glycol ether is selected from the group consisting of ethylene glyeol monomethyl ether, ethylene glycol monoethyl ether, propylene glyeol monomethyl ether, tripropylene glycol monomethyl ether,ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glyeol monoethyl ether, propylene glyeol n-propyl ether, propylene glyeol t-butyl ether, propylene glycol n-butyl ether, dipropylene glycol methyl ether, dipropylene glycoln-propyl ether, dipropylene glycol t-butyl ether, dipropylene glycol n-butyl ether, tripropylene glyeol n-propyl ether, tripropylene glycol t-butyl ether, tripropylene glycol n-butyl ether, ethyl eel losolve, methyl eel losolve, polyethylene glyeolmonomethyl ether, polypropylene glyeol monomethyl ether, methoxytriglyeol, ethoxytriglycol, bntoxytriglyeol, 1 -butoxyethoxy-2-propanol, and any combination thereof.
18. 18. An inkjet ink as claimed in claim 15 wherein the glycol ether is selected from the group consisting of ethylene glycolmonomethyl ether, ethylene glyeol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, tripropylene glyeol monomethyl ether, ethylene glyeol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, and any combination thereof
19. 19. An inkjet ink as claimed in any one of the preceding claims wherein said one or more humectants is propylene glycol monomethyl ether.
20. 20. An inkjet ink as claimed in any one of the preceding claims wherein said terpene phenolic resin comprises a copolymer of a pinene, and a phenol such as phenol or bisphenol.
21. 21. An inkjet ink as claimed in any one of the preceding claims wherein said terpene phenolic resin is selected to have a molecular weight in the range 500 to 1000.
22. 22. An inkjet ink as claimed in any one of the preceding claims wherein said terpene phenolic resin comprises that sold under the trade mark Dertophene T.
23. 23. An inkjet ink as claimed in any one of the preceding claims wherein said terpene phcnolic resin is present in an amount of up to 30% by weight.
24. 24. An inkjet ink as claimed in claim 23 wherein said terpene phenolie resin is present in an amount up to 20% by weight and, preferably, up to 10% by weight.
25. 25. An inkjet ink as claimed in any one of the preceding claims further including a surfaetant.
26. 26. An inkjet ink as claimed in claim 25 wherein said surfactant is selected from modified polysiloxanes, alkyl modified polyoxyalkyleneamines, allyl modified propoxylated (poly(oxypropylene)) diamines, alkyl ether amines, nonyl phenol ethoxylates, ethoxylated fatty amines, fluorinated organic acid diethanolamine salts, allwxylated ethylenediamines, alkyl modified polyethylene oxides, alkyl modified polyalkyleneoxides, alkyl phosphate ethoxylate mixtures, polyoxyalkylene derivatives of propylene glycol and polyoxyethylated fatty alcohols.
27. 27. An inkjet ink as claimed in claim 26 wherein said surfactant comprises a polyether modified polydimethylsiloxane.
28. 28. An inkjet ink as claimed in any one of claims 25 to 27 wherein said surfactant is present in an amount up to 1 % by weight.
29. 29. An inkjet ink as claimed in claim 28 wherein said surfactant is present in an amount from 0.01% to 0.5% by weight.
30. 30. An inkjet mk as claimed in any one of the preceding claims when compatible with the components of a thermal inkjet pnnter.