GB2517592A

GB2517592A - Method for designing inks

Info

Publication number: GB2517592A
Application number: GB1413609.7A
Authority: GB
Inventors: Angelique Runacre; Mark Pemble; Gemma Osborne
Original assignee: Sericol Ltd
Current assignee: Sericol Ltd
Priority date: 2013-08-05
Filing date: 2014-07-31
Publication date: 2015-02-25
Also published as: GB201313929D0; GB201413609D0

Abstract

A method for designing or preparing an ink for an ink jet printer having a printhead with a nozzle plate and a piezoelectric actuator comprises: (i) mixing together components to form an ink; wherein: F is the frequency (KHz) at which the piezoelectric actuator operates when printing and D is the average ink droplet volume (picolitres) created by the piezoelectric actuator at frequency (F); and (iii) if Equation 1 is not satisfied, adding one or more components to the ink in order to satisfy Equation 1. Typically, the ink components comprise (a) compound having one ethylenically-unsaturated group (preferably N-vinylcaprolactam with 2-phenoxy ethyl acetate), (b) compound having more than one ethylenically-unsaturated group (preferably urethane diacrylate oligomer optionally combined with ethoxylated trimethylolpropane triacrylate and propoxylated neopentylglycol diacrylate), and (c) a colorant.

Description

METHOD FOR DESIGNING INKS

This invention relates to method for designing and/or preparing inks suitable for use in ink jet printing.

Ink jet printing is a commonly used technique for printing substrates.

Water-based, solvent-based and radiation-curable ink jet printing inks are commercially available.

Many ink jet printers contain a printhead comprising a piezoelectric actuator and a nozzle plate. The nozzle plate comprises numerous holes or nozzles. The piezoelectric actuator vibrates, creating pressure waves which eject ink droplets through the nozzles or holes and onto the substrate. By controlling the position of the printhead relative to a substrate, and controlling which nozzles are firing at any point in time, one can use the printer to form a desired pattern of ink on the substrate which corresponds to desired text, images etc. To achieve good print quality, it is often important that a uniform, thin film of ink is formed across the surface of the nozzle plate. If the printhead nozzle plate is incorrectly wetted, print quality defects may occur as a result of an irregular build-up of ink on the nozzle plate and from nozzle blockage, obstruction causing jet deviation, ink dripping, drop starvation or mis-firing. When using radiation-curable inks, the mis-firing and irregular wetting of the nozzle plate can result in cured or partially cured ink blocking or otherwise obstructing the nozzles. This can permanently damaging the printhead or require a greater level of printhead maintenance to keep the head functioning correctly.

We have now found that when designing inks intended to provide good quality ink jet prints, there are relationships between the surface tension and polarity of an ink and the printhead properties which can be used to influence the ultimate performance of the ink. Knowledge of these relationships can be used to design and/or prepare inks which are highly compatible with the printhead through which they will pass and one can thereby obtain high quality prints.

According to a first aspect of the present invention there is provided a method for designing and/or preparing an ink for an ink jet printer comprising a printhead having a nozzle plate and a piezoelectric actuator, said method comprising the steps of: (i) selecting components for the ink and mixing said components together to form an ink (ink 1); (ii) determining the surface tension in mN/rn (ST) and polarity (P) of ink 1 at 25°C and determining whether Equation 1 is satisfied: ( x! -zo) +I+(sT/5) ] Equation 1 wherein: F is the frequency in KHz at which the piezoelectric actuator operates when printing the ink; D is the average ink droplet volume in picolitres created by the piezoelectric actuator at frequency (F); and P and ST are as hereinbefore defined; and (iii) if Equation 1 is not satisfied, adding one or more components to Ink 1 in order to satisfy Equation 1.

In this specification (including its claims), the verbs "comprise" and "contain" and their conjugations are used in their non-limiting sense to mean that items following the words are included, but items not specifically mentioned are not excluded. In addition, reference to a feature by the indefinite article "a" or "an" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.

For example "having one" means having one and only one (not including two or more). The indefinite article "a" or "an" thus usually means "at least one".

Preferably the method of the present invention further comprises the step of determining whether the ink 1 satisfies Equation 2 and if Equation 2 is not satisfied, adding one or more components to Ink 1 in order to satisfy Equation 2: ST < (SE-3) Equation 2 wherein SE is the surface energy of the nozzle plate in dynes/cm (when measured at 20°C) and ST is as hereinbefore defined.

The ink may be any kind of ink, although it is preferably a non-aqueous (e.g. solvent-based) ink or a radiation-curable ink, especially a radiation-curable ink comprising less than 5wt% organic solvent. Preferred radiation-curable inks are non-aqueous radiation-curable inks, especially non-aqueous UV-curable inks.

The components used to prepare non-aqueous (e.g. solvent-based) inks include organic solvents and colorants (to provide the ink with colour). Additionally aqueous inks comprise water and the organic solvents are usually then chosen to be water-miscible.

Inks have been in existence for many years and numerous components suitable for making such inks are commercially available.

The components used to prepare radiation-curable inks typically comprise compounds comprising one or more ethylenically unsaturated group (such compounds cure when irradiated) and colorants (to provide the ink with colour).

Additional optional components include photoinitiators (to help cure the ink when irradiated, especially when the irradiation is with UV light), organic solvents (to adjust the polarity and/or surface tension of the ink), stabilisers, charged compounds for continuous ink jet printers and surfactants (ionic and non-ionic, to adjust the surface tension and/or viscosity of the ink).

In order to satisfy equation 1, one may choose low values of F, D and/or choose components that will result in a low ST. A low value of ST also helps to satisfy Equation 2.

Preferably the components are selected in step (i) to provide an ink comprising: a) a compound having one ethylenically unsaturated group; b) a compound having more than one ethylenically unsaturated group; c) optionally an organic solvent (preferably less than Swt% relative to the total weight of ink); and d) a colorant.

One may ensure that the ink has a high polarity by including polar components within the ink and avoiding non-polar (or hydrophobic) components or keeping the content of such non-polar (or hydrophobic) components low. For example, polar components such as propylene carbonate, glycerol, phenoxyethyl (meth)acrylate and trimethylolpropane tri(meth)acrylate will generally increase the polarity of the ink. Non-polar or hydrophobic components such as isobornyl (meth)acrylate, octyl (meth)acrylate and decyl (meth)acrylate will generally decrease the polarity of the ink.

One may ensure that the ink has a low surface tension by including within it components which have a low surface tension and/or one or more surfactants.

Components having low surface tension include lower alcohols (e.g. methanol, ethanol and isopropanol) and toluene. Numerous surfactants are commercially available and include ionic surfactants and non-ionic surfactants (e.g. SurfynolTM surfactants).

The compounds having one or more than one ethylenically unsaturated group are optionally monomeric, oligomeric or polymeric, with monomeric compounds being preferred.

Preferred ethylenically unsaturated groups are vinyl groups, (meth)acrylic groups, especially (meth)acrylate and (meth)acrylamide groups. Examples of ethylenically unsaturated groups include acrylamide (H2C=CHCON<) groups, methacrylamide (H2C=C(CH3)CON<) groups, acrylate H2C=CHCO2 groups and methacrylate (H2C=C(CH3)C02-) groups.

As examples of compounds having one (i.e. only one) ethylenically unsaturated group there may be mentioned (meth)acrylamide, (meth)acryloylmorpholine, isobutoxymethyl(meth)acrylam ide, isobornyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyldiethylene glycol (meth)acrylate, t-octyl (meth)acrylam ide, diacetone (meth)acrylam ide, lauryl (meth)acrylate, dicyclopentadiene (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, N5N- dimethyl(meth)acrylam ide, tetrachlorophenyl (meth)acrylate, 2-tetrachlorophenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, tetrabromophenyl (meth)acrylate, 2-tetrabromophenoxyethyl (meth)acrylate, 2- trichlorophenoxyethyl (meth)acrylate, tribromophenyl (meth)acrylate, 2- tribromophenoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, N-vinylcaprolactam, N-vinylpyrrolidone, phenoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, pentachlorophenyl (meth)acrylate, bornyl (meth)acrylate and methyltriethylene diglycol (meth)acrylate and mixtures comprising two or more thereof.

Commercially available compounds having one ethylenically unsaturated group include: SR256 (2(2-ethoxyethoxy ethyl acrylate), SR339c (2-phenoxy ethyl acrylate), SR395 (isodecyl acrylate), SR4S9D (tridecyl acrylate), SR531 (cyclic trimethylolpropane formal acrylate), SR49SB (caprolactone acrylate), SR535 (dicyclopentadienyl methacrylate), SR 506D (isobornyl acrylate), 5R423 (isobornyl methacrylate), SR 313A, 313B and 313D (C12-C14 alkyl (meth)acrylates), all available from Sartomer Co. Inc. and Ciba Ageflex FM6 (n-hexyl (meth)acrylate available from Ciba Specialty Chemicals).

In view of the above requirement for polarity (P) in Equation 1, it is preferred for the ink not to contain large amounts of non-polar, ethylenically unsaturated compounds (e.g. SR 5060, SR423, SR395 and 5R498D). However such non-polar, ethylenically unsaturated compounds may still be included in the ink and may in fact confer desirable properties on the ink, provided that the ink satisfies the requirements of feature (H) defined above.

Preferably component a) comprises an N-vinyl amide or N-acryloyl amine (e.g. N-vinyl caprolactam, N-vinyl piperidine or N-acryloyl morpholine) and a monofunctional methacrylate (e.g. 2-phenoxy ethyl acrylate).

Preferably the ink comprises 1 to 90 parts, more preferably 40 to 80 pads, especially 50 to 75 parts by weight of compounds having one ethylenically unsaturated group.

Compounds having more than one ethylenically unsaturated group include compounds having two ethylenically unsaturated groups, compounds having three or more ethylenically unsaturated groups and mixtures comprising two or more thereof.

As examples of compounds having more than one ethylenically unsaturated group there may be mentioned ethylene glycol di(meth)acrylate, 1,10-decanediol diacrylate, dicyclopentenyl di(meth)acrylate, dipropylene glycol di(meth)acrylate, 3-methyl pentanediol diacrylate, divinyl ethers (e.g. DVE-3), triethylene glycol diacrylate, tetraethylene glycol di(meth)acrylate, tricyclodecanediyldimethylene di(meth)acrylate, tris(2-hydroxyethyisocyanurate di(meth)acrylate, tris(2- hydroxyethyisocyanurate tri(meth)acrylate, caprolactone-modified tris(2-hydroxyethyisocyanurate tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, E0-modified trimethylolpropane tri(meth)acrylate, P0-modified trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1 4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, polyester di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate E0-modified bisphenol A di(meth)acrylate, P0-modified bisphenol A di(meth)acrylate, E0-modified hydrogenated bisphenol A di(meth)acrylate, P0-modified hydrogenated bisphenol A di(meth)acrylate, E0-modified bisphenol F di(meth)acrylate and mixtures comprising two or more thereof.

Commercially available compounds having more than one ethylenically unsaturated group include: SR 295 (pentaerythritol tetracrylate); SR 350 (trimethylolpropane trimethacrylate); SR 351 (trimethylolpropane triacrylate); SR 367 (tetramethylolmethane tetramethacrylate); SR 368 (tris(2-acryloxy ethyl) isocyanurate triacrylate); SR 399 (dipentaerythritol pentaacrylate); SR 444 (pentaerythritol triacrylate); SR 454 (ethoxylated (3) trimethylolpropane triacrylate); SR 833S (tricyclodecane dimethanol diacrylate), SR 833S (a diacrylate) and SR 9041 (dipentaerythritol pentaacrylate ester).

Preferably the ink comprises 0 or 1 to 70 parts, more preferably 1 to 20 parts, especially 5 to 11 pads by weight of compounds having two (i.e. only two) ethylenically unsaturated groups.

Preferably the ink comprises 1 to 20 pads, especially 3 to 9 parts by weight of compounds having three or more ethylenically unsaturated groups.

The ink optionally comprises one or more oligomers having more than one ethylenically unsaturated group, e.g. urethanes and/or polyesters having more than one ethylenically unsaturated group.

The ink optionally comprises a urethane acrylate oligomer. Where such a monomer contains one or more than one ethylenically unsaturated groups it is part of component a) or b) respectively. The urethane acrylate oligomer is preferably an aliphatic urethane acrylate oligomer Examples of commercially available aliphatic urethane acrylate oligomers include: CN 934 ON 934X50, ON 944B85, ON 945A60, CN 945385, ON 953370, ON 961 E75, CN 961 H81, ON 962, ON 963A80, ON 963B80, CN 963E75, ON 963E80, ON 963J85, CN 964, CN 964A85, ON 964385, CN 964H90, ON 964E75, ON 965, ON 965A80, ON 966A80, ON 966B85, ON 966H90, ON 966180, ON 966J75, CN 966R60, CN 968, ON 982E75, ON 982P90, ON 983, CN 983388, CN 984 and ON 985B88, all available from Sartomer, and mixtures comprising two or more thereof.

Examples of commercially available aromatic urethane acrylate oligomers include ON 970A60, ON 970E60, CN 970H75, ON 971 A80, ON 972, ON 973A80, CN 973H85, CN 973J75, CN 975, CN 977C70, ON 978, CN 980, CN 980M50, ON 981, ON 981 A75, CN 981 BBS, ON 982A75 and CN 982B88, all from Sartomer, and mixtures comprising two or more thereof.

Preferably component b) comprises a urethane di-acrylate oligomer.

When a urethane acrylate oligomer is included in the ink the amount is typically 0.25 to 10 pads, especially 1 to 6 pads by weight.

The ink preferably comprises 0 to 4.9 parts, more preferably 0.1 to 4.5 pads, especially 0.5 to 4.5 pads of organic solvent.

In one embodiment all of the organic solvents present in the ink have a boiling point of 140 to 250G.

The organic solvent preferably has a higher polarity and optionally a lower surface tension than all of the radiation-curable components of the ink, e.g. components a) and b) (including bi) and b2) mentioned below).

The most preferred organic solvents are selected from glycol ethers, cyclic lactones, organic carbonates, dibasic esters, bio-solvents and mixtures comprising two or more thereof.

Preferred glycol ethers include diethylene glycol diethyl ether, DowanolTM DPM, ethoxy propanol, propoxy propanol and butoxy propanol.

Preferred organic carbonates include propylene carbonate.

Preferred cyclic lactones include y-butyrolactone, y-valerolactone and 5-va lero I actone.

The preferred organic solvent comprises an organic carbonate (especially propylene carbonate) and/or a glycol ether (especially diethylene glycol diethyl ether).

Organic solvents comprising y-butyrolactone and one or more glycol ethers and/or propylene carbonate are also preferred.

Dibasic esters typically comprise a di(C14 alkyl) ester of a saturated aliphatic dicarboxylic acid having 3 to 8 carbon atoms, e.g. of the following formula: 0 0

-N N

N. N. PD' DRt wherein: A represents (CH2)l.a; and R1 and R2 are the same or different and represent C1.4 -alkyl, preferably methyl or ethyl, and most preferably methyl.

Organic solvents do not cure when they are irradiated, i.e. they are inert.

Therefore organic solvents are free from ethylenically unsaturated groups.

The colorant is preferably a pigment, or a dye, e.g. an oil-soluble dye (also called a water-insoluble dye). The pigment which can be used as colorant is not particularly limited, for example it can be an organic or inorganic pigment or a mixture thereof. Numerous commercially available pigments are listed in the Colour Index International.

Examples of red or magenta pigments include Cl. Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 208, 216, 226 and 257; Cl. Pigment Violet 3, 19, 23, 29, 30, 37, 50 and 88; and Cl. Pigment Orange 13, 16, 20 and 36.

Examples of blue or cyan pigments include Cl. Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36 and 60.

Examples of green pigments include Cl. Pigment Green 7, 26, 36 and 50.

Examples of yellow pigments include Cl. Pigment Yellow 1, 3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110, 137, 138, 139, 153, 154, 155, 157,166, 167, 168, 180, 185 and 193.

Examples of black pigments include carbon blacks and Cl. Pigment Black 7, 28 and 26.

Examples of white pigments include titanium dioxide and Cl. Pigment White 6, 18 and 21.

The oil-soluble dye is preferably substantially insoluble in water (e.g. a water-solubility of below lwt% at 25°C) and soluble in the remaining components of the ink (solubility above lwt% at 25°C).

Examples of preferred oil-soluble dyes include: the Cl. Solvent dyes mentioned below: Cl. Solvent: Black 3, 7, 27, 29 and 34; Yellow 14, 16, 19, 29 30, 56 82, 93 and 162; Red 1, 3, 8, 18, 24, 27, 43, 49, 51, 72, 73, 109, 122, 132 and 218; Violet 3; Blue 2, 11, 25, 35, 38, 67 and 70; Green 3 and 7; and Orange 2; and the C.l disperse dyes mentioned below: Cl. Disperse: Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184:1, 186, 198, 199, 201, 204, 224 and 237; Orange 13, 29, 31:1, 33, 49, 54, 55, 66, 73, 118, 119 and 163; Red 54, 60, 72, 73, 86, 88, 91, 92, 93, 11.1, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167:1, 177, 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356 and 362; Violet 33; Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165:1, 165:2, 176, 183, 185, 197, 198, 201, 214, 224, 225, 257, 266, 267, 287, 354, 358, 365 and 368; and Green 6:1 and 9.

Typically when the colorant is insoluble in the other ink ingredients, it is dispersed with the other ink ingredients using a dispersing device, for example, a ball mill, bead mill, sand mill, attritor, roll mill, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet type jet mill, paint shaker or the like.

It is also possible to include a dispersant in the ink, especially when the colorant comprises a pigment. Although the type of dispersant is not particularly limited, it is preferred to use a high-molecular weight dispersant. Examples of the high-molecular weight dispersant include the SolsperseTM hyperdispersants. It is also possible to use a synergist with the dispersant. In the present invention, the dispersant (when included) is preferably added in an amount of from 1 to 50 parts by weight per 100 parts by weight of colorant.

The colorant may be a single component or a combination of two or more components (e.g. 2 or more pigments).

When the colorant comprises a pigment it preferably has an average particle size below 0.5 pm, more preferably below 0.3 pm, especially below 0.2 pm. This is for storage stability advantages, and also because larger particles could block the fine nozzles of an ink jet printer if the ink is used in such a printer.

When calculating the number of parts of component d), the weight of any additional ingredients (e.g. dispersant, diluent, liquid vehicle etc.) are not included.

The ink preferably comprises 0.1 to 15 parts, more preferably 0.5 to 10 parts, especially 0.75 to 8 pads of colorant.

Preferably the total number of parts by weight of components a) to d) (and e) when present) adds up to 100. When the total number of parts by weight of components a) to d) adds up to 100 this does not rule out the presence of further components, it merely further defines the total amount of components a) to d).

When UV light is used to cure the printed ink, the ink preferably contains one or more photoinitiators (component e)). Whilst any commercially available photoinitiator can be used which matches the radiation, those with a low tendency for yellowing are preferred. Examples of suitable photoinitiators include alpha- hydroxyalkylphenones, such as 2-hydroxy-2-methyl-1 -phenyl propan-1 -one, 2- hydroxy-2-methyl-1 -(4-tert-butyl-) phenylpropan-1 -one, 2-hydroxy-[4 -(2- hydroxypropoxy)phenyl]-2-methylpropan-1 -one, 2-hydroxy-1 -[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1 -one, 1 -hydroxycyclohexylphenylketone and oligo[2-hydroxy-2-methyl-1 -{4-( 1 -methylvinyphenyl}propanone], alpha-aminoalkylphenones, alpha-sulfonylalkylphenones and acylphosphine oxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (e.g. LucirinTM TPO), ethyl- 2,4,6-trimethylbenzoylphenylphosphinate and bis(2,4,6-trimethylbenzoy- phenylphosphine oxide (e.g. LucirinTM BAPO), benzophenone, 1- hydroxycyclohexyl phenyl ketone, benzil dimethylketal, bis(2,6-dimethylbenzoy- 2,4,4-trimethylpentylphosphine oxide and mixtures comprising two or more thereof. Such photoinitiators are known and are commercially available, for example under the trade names lrgacureTM, DarocurlM and LucerinTM (from BASE). An especially preferred photoinitiator is lrgacureTM 2959.

Preferably the ink comprises 0.1 to 15 parts by weight, more preferably 0.5 to 12 parts by weight of photoinitiator(s).

Optionally the ink further comprises an anti-oxidant. When the ink contains an antioxidant, the preferred antioxidant is a sterically hindered tertiary or secondary amine. Examples of such amines include N,N-diphenylamine, N-nitroso-diphenylamine, nitrosodiethylaniline, p-phenylenediamine, an N,N'-di(Ci.4) alkyl-p-phenylenediamine such as N,N'-di-isobutyl-p-phenylenediamine, or N,N'-di-isopropyl-p-phenylenediam in lrganoxTM 5057 (produced by Firma Ciba Spezialitaetenchemie), N-phenyl-p-phenylenediamine, N, N'-diphenyl-p- phenylenediam i, N-isopropyl-N-phenyl-p-phenylenediam me, N, N'-di-s-butyl-p- phenylenediamine (KerobitTM BPD produced by BASF Aktiengesellschaft), N-phenyl-N'-isopropyl-p-phenylenediam me (VulkanoxTM 4010 produced by Bayer A G), N-(1,3-dimethylbuty-N'-phenyl-p-phenylenediamine, N-phenyl-2-naphthylamine, iminodibenzyl, N,N'-diphenylbenzidine, N-phenyltetraaniline, acridone, 3-hydroxydiphenylamine, 4-hydroxydiphenylamine, hydroquinone monomethyl ether, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1 -oxyl and mixtures comprising two or more thereof.

When an antioxidant is included in the ink the amount is typically 0.01 to 0.25 pads by weight.

In one embodiment the ink is free from surfactants.

Curing rates may be increased by including an amine synergist in the ink.

Suitable amine synergists include, for example, free alkyl amines, e.g. triethylamine or triethanol amine; aromatic amines, e.g. 2-ethylhexyl-4-dimethylam inobenzoate, ethyl-4-dimethylaminobenzoate and also polymeric amines as polyallylamine and its derivatives. Curable amine synergists such as ethylenically unsaturated amines (e.g. acrylated amines) are preferable since their use provide inks having less odour due to their ability to be incorporated into the cured ink. When used, the amount of amine synergists is preferably from 0.1 to 1 Owt.% based on the total weight of the ink, more preferably from 0.3 to 3wt%.

UV stabilizers may be included in radiation-curable inks to reduce or prevent premature polymerization during the manufacture and storage of the ink.

Examples of suitable stabilisers include AdditolTM sioo, silo and S120 from Cytec, FlorstabTM UV1, UV5, UV8, UV11 and UV12 from Kromachem; and TinuvinTM 328, 384, 1130, 400, 123, 292 and 5151 from Ciba.

When the ink contains a UV stabiliser, the amount present is selected so as not to unduly interfere with the process for radiation curing the ink in normal use.

Typically 0.1 to lwt% of the UV stabiliser (e.g. an aluminium salt) is used, relative to the total weight of components a) to e).

When a surfactant is included in the ink the amount is typically 0.1 to 2.Swt% surfactant, relative to the total weight of components a) to e).

Preferably the ink has a viscosity of from 5 to 40 cP, more preferably 15 to cP, especially 18 to 27 cP, when measured at 25°C.

Preferably the ink has a surface tension of 20 to 50 mNIm, more preferably 28 to 40 mN/m, when measured at 25°C.

Preferably the ink is curable using ultra violet light, especially using a light emitting diode which emits ultraviolet light (UV-LED) or a medium pressure mercury lamp.

In a particularly preferred embodiment, the ink comprises the following components: a) 40 to 80 parts of a compound having one ethylenically unsaturated group; bi) 1 to 20 parts of a curable compound having two ethylenically unsaturated groups; b2) 1 to 20 pads of a curable compound having three or more ethylenically unsaturated groups; c) 0 to 4.9 parts of organic solvent (preferably having a higher polarity and/or a lower surface tension than components a), bi) and b2)); d) 0.1 to 15 parts of colorant; and e) 0.1 to 15 parts of photoinitiator; wherein all parts are by weight.

One may determine the surface tension (ST) of the ink at 25°C using a KSV Sigma tensiometer fitted with a platinum DuNouy ring or by using a similar device, e.g. as described below in the Examples section.

The polarity of the ink may be determined from the surface tension (ST) and the interfacial tension (lET) of the ink using the software provided with the DataPhysics OCA 20 equipment, e.g. as described below in the Examples section.

One may determine the lET of the ink using a KSV Sigma tensiometer, e.g. as described below in the Examples section.

Thus for a particular ink jet printer one will know the nozzle plate surface energy, droplet volume and frequency at which the piezoelectric actuator will be operated. In order to design a suitable ink which satisfies Equation 1 and optionally Equation 2, one may select ink ingredients which, when mixed, will provide an ink having the surface tension and polarity to ensure that Equation 1 is satisfied. The polarity and surface tension of ink ingredients are widely published and one may use the published data in order to design a suitable ink.

If Equation 1 and optionally 2 are not satisfied, one may add one or more components to Ink 1 in order to satisfy Equation 1 and also Equation 2 if desired.

For example, one may add one or more polar components to the ink in order to increase the value of P or one may add one or more non-polar components to the ink in order to decrease the value of P. One may also add one or more surface tension-reducing components in order to reduce the value of ST or one may add one or more components having high surface tension to the ink in order to increase the value of ST. One may perform step (iii) as many times (e.g. zero times or 1 or more times) as necessary until an ink is obtained which satisfies Equation 1 and optionally also Equation 2.

Examples of polar components which may be added to the ink in step (iH) in order to increase the value of P are as hereinbefore described. Alternatively, one may reduce the amount of such polar components in the ink order to reduce the value of P. Examples of surface tension-reducing components which may be to the ink in step (iii) in order to decrease the value of ST are as hereinbefore described.

Alternatively, one may reduce the amount of such tension-reducing components in the ink order to increase the value of ST.

The method of the present invention optionally comprises one or more of the following steps (a) to (c), e.g. before step (0: (a) determining the surface energy of the nozzle plate (SE) in dyneslcm; (b) determining the frequency in KHz at which the piezoelectric actuator will operate (F) when printing the ink; and (c) determining the average droplet volume in picolitres (D) created by the piezoelectric actuator at frequency (F).

One may determine the surface energy of the nozzle plate in dynes/cm (SE) from literature, consultation or by analysis. For example, literature accompanying the ink jet printer comprising the nozzle plate and/or patents describing the printer will sometimes describe the SE of the nozzle plate.

Alternatively, one may consult (i.e. ask) the supplier or manufacturer of the ink jet printer what the SE is of the nozzle plate.

Furthermore, one may determine SE by analysis using, for example, contact angle methodologies, e.g. using commercially available apparatus such as the DataPhysics OCA 20. A preferred contact angle methodology employs three liquids, e.g. ethylene glycol (5pl), diiodomethane (2pl) and water (lOpI). Using commercially available apparatus, the static contact angle at 20°C may be measured three times for each liquid, allowing a drop of each liquid to fall onto the nozzle plate surface. The resultant values for the static contact angles may then be inputted to the SE analysis tool provided with the apparatus, and the surface energies may be determined using the Owens, Wendt, Rabel & Kaelble (OWRK) method.

Preferably the nozzle plate has a surface energy > 30 dynes/cm, more preferably> 35 dynes/cm. Printheads comprising nozzle plates having the desired surface energy are commercially available from FUJIFILM Dimatix.

In a preferred embodiment, the nozzle plate is constructed from silicon or a silicon compound or carries a coating made from silicon or a silicon compound.

Such nozzle plates are particularly robust and resistant to caustic or aggressive inks. Printheads comprising nozzle plates having the desired surface energy and constructed from silicon or a silicon compound are available from FUJIFILM Dimatix under the trade name "0-Class".

The frequency in KHz at which the piezoelectric actuator will operate (F) may often be selected by the user of the ink jet printer, e.g. using software provided with the printer. Literature and/or software accompanying the ink jet printer will often state the frequency or frequencies at which the actuator operates.

Alternatively, one may consult (i.e. ask) the supplier or manufacturer of the ink jet printer what the value of F is.

For greyscale printing, it is possible to apply multiple pulses of electricity (typically 2, 3 or 4 pulses of electricity) to the piezoelectric actuator per Hz and thereby increase the effective frequency (F) of the piezoelectric actuator. For example, if three pulses of electricity are applied per Hz to a 20 KHz piezoelectric actuator, the effective frequency is 60 KHz and the value of F to be used in Equation 1 is 60. Similarly, if two pulses of electricity are applied per Hz to a 12 KHz piezoelectric actuator, the effective frequency is 24 KHz and the value of F to be used in Equation 1 is 24. Often an approximate knowledge or estimate of the likely frequency in KHz at which the piezoelectric actuator will operate is sufficient to design or prepare the ink by the method of the present invention. For example, if it is known that an inkjet printer will be used in a particular market segment where the frequency (F) is likely to be between X and Y Khz (where X and Y are numbers, e.g. 20 and 50 respectively), one may use the present method to design an ink which satisfies Equation 1 and optionally Equation 2 above across the entire frequency range X to Y, without even knowing the exact value of F which will be used in practice. Thus the determination of the frequency F need only be approximate for the ink designer to create an ink which will provide good quality prints to a wide range of users even if they use slightly different frequencies and drop sizes to each other.

Preferably the piezoelectric actuator operates at a frequency of at least 25 KHz, more preferably at least 30 KHz, especially at least 40 KHz. Preferably the piezoelectric actuator operates at a frequency of less than 100 KHz. In some ink jet printers it is possible to adjust the frequency (F) at which the piezoelectric actuator operates using software provided with the ink jet printer. Often the pre-set operational print modes of a printing machine will adjust frequency automatically depending on parameters such as number of print passes used to build the image, or number of heads selected.

The average volume of the droplets (D) in pL (picolitres) for a particular frequency is usually specified by the manufacturer of the printhead comprising the nozzle plate and may in some cases be selected by the user from a number of options, using software provided with the ink jet printer. For example, the Q-class printhead from FUJIFILM Dimatix is available as 0256/10 and 0256/30 models.

With the 0256/10 model one may select drop sizes of lOpL, 2OpL or 3OpL. With the 0256/30 model one may select drop sizes of 2SpL, 5OpL or 8OpL. The actual dropsize D for a given printhead may change a little from that selected depending on the frequency F. D is the volume of the droplets being created by the piezoelectric actuator, before any droplet merging which may take place at the nozzle plate. In greyscale multidrop printing it is possible for several droplets (e.g. three droplets, being for example 10 pL, 9 pL and 11 pL) to merge at the nozzle plate to create a single droplet (e.g. a single 30 pL droplet) and in this case D has a value of 10 (not 30).

However where such information is not provided, or where one wishes to determine the value of D at an alternative frequency F, one may determine the value of D by ejecting a known number of droplets (e.g. a total of 128 million droplets) from all nozzles present on the nozzle plate into a pre-weighed receptacle, weighing the receptacle containing the droplets, calculating the average mass per droplet and dividing this mass by the density of the ink. Where droplets merge at the nozzle plate, e.g. in greyscale printing where typically three droplets merge into one at the nozzle plate, the merging should also be taken into account when calculating D (e.g. by dividing the value by 3 when 3 droplets merge at the nozzle plate to calculate the value of D per pre-merged droplet).

The method of the present invention can be used to design inks for particular printheads having a nozzle plate of known surface energy. Once an ink has been designed in this way, it is not generally necessary to perform the method again when making subsequent batches of the same ink for the same printhead.

One may simply use the ink formulation previously designed by the present method. Thus a second aspect of the present invention also provides a method for preparing an ink comprising mixing components together in accordance with a recipe designed by the method according to the first aspect of the present invention.

The invention in further illustrated by the following examples in which all parts and percentages are by weight unless otherwise stated.

Examples

An Apollo II ink evaluation rig was obtained from FUJIFILM Dimatix which comprised a QS256110 printhead.

The surface energy (SE) of the nozzle plate in the QS256110 printhead was measured using DataPhysics OCA 20 equipment employing three liquids: ethylene glycol (5pl), diiodoniethane (2pl) and water (lOpI). Using this equipment, the static contact angle at 25°C was measure three times for each liquid, allowing a drop of each liquid to fall onto the nozzle plate surface. The resultant values for the static contact angles were inputted to the SE analysis too, and the surface energy of the nozzle plate was determined using the Owens, Wendt, Rabel & Kaelble (OWRK) method. The nozzle plate was found to have a surface energy of 48 dynes/cm.

The frequency in KHz at which the piezoelectric actuator will operate (F) when printing the ink (20KHz or 40KHz) was selected using the software provided with the printer.

The average droplet volume in picolitres (D) at each frequency (F) was determined by ejecting a known number of droplets from all nozzles into a pre-weighed receptacle, weighing the receptacle containing the droplets, calculating the average mass per droplet and dividing this mass by the density of the ink. In the Examples we used binary mode and hence there was no merging of droplets at the nozzle plate.

The following components were used in the Examples to make inks: SR339c is 2-phenoxy ethyl acrylate, obtained as SartomerTM SR339c.

NVC is N-vinyl caprolactam.

SR454 is ethoxylated (3) trimethylolpropane triacrylate, obtained as SartomerTM SR454.

LJV12 is a 3Owt% suspension of an aluminium tris (N-hydroxy-N-nitroso phenylaminato-O-O' salt in phenoxy ethyl acrylate, obtained as Florstab UV12.

SR9003 is propoxylated neopentylglycol diacrylate, obtained as SartomerTM SR9003.

CN964 is an aliphatic polyester based urethane diacrylate oligomer, obtained from Sartomer as CraynorTM CN964.

Cyan PD is a cyan dispersion comprising 30%wt% of Cl. Pigment Blue 15:4 (i.e. a colorant) and the remainder (70%) consisted of n-propylene glycol diacrylate (59wt%), UV12 (lwt%) and a dispersant (lOwt%).

TPO is 2,4,6-trimethylbenzoyldiphenylphosphine oxide, a photoinitiator obtained from BASF under the name LucirinTM TPO.

lrg 184 is 1 -hydroxy-cyclohexyl-phenyl-ketone, a photoinitiator obtained from Ciba under the name lrgacureTM 184.

JPC is propylene carbonate obtained from Agfa chemicals.

IBOA is isobornyl acrylate, obtained from Sartomer as SartomerTM 5R506.

Red 355 is Cl. Solvent Red 119, a dye obtained from BASF as Neozapan Red 335.

CN964A85F is a urethane acrylate resin comprising lSwt% of n-propylene glycol diacrylate, obtained from Sartomer as CraynorTM C N 964A85 F. The components indicated in Table 1 below were mixed to give inks A to D. The surface tension (ST) of the inks at 25°C was determined in using a KSV Sigma tensiometer fitted with a platinum DuNouy ring. The tensiometer was set in Surface Tension Ring Mode, density measurement was obtained using method 2 provided with the equipment. The ST of each ink was measured 3 times and the average figure was used.

The interlacial tension (IFT) of the inks was determined in using a KSV Sigma tensiometer fitted with a platinum DuNouy ring and weight accessory, using a 2-phase sample and a temperature of 25°C. The low density phase was FC-72 perfluoro compound and the ink was the high density phase. The Interfacial Tension Ring Mode was selected. The density difference between the two phases was inputted into hardware and method 2 selected. The FC-72 pertluoro compound had a density of 1.68 g/cm3. The tensiometer was operated in push mode and the lET was measured 3 times using Huh-Mason correction and the average figure was calculated.

The polarity of the inks was calculated from their ST and lET using the software provided with the DataPhysics OCA 20 equipment mentioned above.

Using this software, the high density phase from method 4 (perfluorohexane) was selected. The ST and lET of the ink were inputted and the polarity was calculated by the software using the WORK method according to the Owens-Wendt method.

The ST and polarity of the inks, determined as described above, are also

shown in Table 1:

Table 1

Component InkA InkS lnkC lnkD Component a) SR339c 0 38.47 38.47 0 NVC 24.59 24.59 24.59 0 1 ethylenically unsaturated IBOA 38.47 0 0 84.0 group _____________ ____________ ___________ ____________ ____________ Component b) SR454 7.49 7.49 7.49 o SR9003 4.0 4.0 1.0 0 >1 ethylenically CN964 0 4.00 4.00 0 unsaturated CN964A85F 4.0 0 0 15.0 group _____________ ____________ ___________ ____________ ____________ Component c) JPC 0 0 3 0 organic solvent Component d) Cyan PD 8.65 8.65 8.65 0 colorant Red 355 0 0 0 1.0 Other UV12 0.3 0.3 0.3 0 components TPO 9.5 9.5 9.5 0 ___________ lrg 184 3.0 3.0 3.0 0 Total number of parts 100 100 100 100 ST (dyne/cm) 32.0 36.5 34.8 30.8 Polarity 6.59 9.30 11.90 3.64 Notes: 1) The colorant Cyan PD is a 30 wt% dispersion of Cl. Pigment Blue 15:4 in a liquid vehicle comprising a dispersant. Thus for the inks containing Cyan PD, the amount of colorant present was 30% of the amount indicated in Table 1.

2) All amounts in Table 1 are in parts by weight.

Printing The inks described in Table 1 were printed onto paper and self-adhesive vinyl using the abovementioned Apollo II ink evaluation rig and cured using UV light by passing the printed substrate through a UV belt drier. The printhead in the rig comprised a variable frequency piezoelectric actuator, operating at the frequency 20KHz or 40KHz, as indicated in Table 2 and Table 3 respectively.

Table 2 -Printing at 20KHz Comparative Example 1 Example 2 Comparative Example 1 ____________ ___________ Example 2 InkA lnkB lnkC lnkD ST (dyne/cm) 32.0 36.5 34.8 30.8 Polarity (P) 6.59 9.30 11.90 3.64 Is Equation 1 No -7.6 is Yes -8.5 is Yes -8.2 No -7.5 is >P satisfied? <P <P Is Equation 2 Yes -32.0 Yes -36.5 Yes -34.8 Yes -30.8 satisfied? is < (48-3) is < (48-3) is < (48-3) is < (48-3) Averagedroplet 11 11 11 11 volume in pL ______________ _____________ ____________ _____________ Predicted print quality at Poor Good Good Poor F=2OKHz ______________ _____________ ____________ _____________ Table 3 -Printing at 40KHz Comparative Comparative Example 3 Comparative Example 3 Example 4 ___________ Example 5 InkA lnkB lnkC lnkD ST (dyne/cm) 32.0 36.5 34.8 30.8 Polarity (P) 6.59 9.30 11.90 3.64 Is Equation 1. No -10.3 is Yes -9.96 No -9.16 is No-9Ais>P satisfied? >r IS <r > Is Equation 2 Yes -32.0 Yes -36.5 Yes -34.8 Yes -30.8 satisfied? is < (48-3) is < (48-3) is < (48-3) is < (48-3) Average droplet 10 10 10 10 volume in pL ______________ _____________ ____________ _____________ Predicted print quality at Poor Poor Good Poor F=4OKHz _____________ ____________ ___________ ____________ Note: the wetting of the nozzle plate with ink in the Apollo II rig (determined visually) was used as an indication of print quality that would arise had a commercial ink jet printer been used. "Predicted print quality" is therefore inferred from the visual examination of the nozzle plate flooding.

Tables 2 and 3 show that when the method of the present invention was performed such that the components were mixed to give an ink satisfying Equation 1, the predicted print quality was better than when Equation 1 was not satisfied.

Claims

CLAIMS1. A method for designing and/or preparing an ink for an ink jet printer comprising a printhead having a nozzle plate and a piezoelectric actuator, said method comprising the steps of: (ii) selecting components for the ink and mixing said components together to form an ink (ink 1); (ii) determining the surface tension in mN/m (ST) and polarity (F) of ink 1 at 25°C and determining whether Equation 1 is satisfied: xt) ] Equation 1 wherein: F is the frequency in KHz at which the piezoelectric actuator operates when printing the ink; D is the average ink droplet volume in picolitres created by the piezoelectric actuator at frequency (F); and P and ST are as hereinbefore defined; and (iii) if Equation 1 is not satisfied, adding one or more components to Ink 1 in order to satisfy Equation.
2. A method according to claim 1 which further comprises the step of determining whether the ink 1 satisfies Equation 2 and if Equation 2 is not satisfied, adding one or more components to Ink 1 in order to satisfy Equation 2: ST < (SE-3) Equation 2 wherein SE is the surface energy of the nozzle plate in dynes/cm and ST is as defined in claim 1.
3. A method according to claim 1 or 2 wherein the ink is a radiation-curable ink.
4. A method according to any one of the preceding claims wherein the pinthead comprises a piezoelectric actuator capable of operating at a frequency frequency (F) of at least 20KHz.
5. A method according to any one of the preceding claims wherein the printhead comprises a nozzle plate having a surface energy of >35 dynes/cm.
6. A method according to any one of the preceding claims wherein the components are selected to provide an ink comprising: a) a compound having one ethylenically unsaturated group; b) a compound having more than one ethylenically unsaturated group; c) a colorant; and optionally d) an organic solvent.
7. A method according to claim 6 wherein the organic solvent d) has a lower surface tension than components a) and b).
8. A method according to any one of the preceding claims wherein the components comprise a photoinitiator.
9. A method according to any one of the preceding claims wherein the ink comprises the following components: a) 40 to 80 parts of a compound having one ethylenically unsaturated group; bi) 1 to 20 parts of a curable compound having two ethylenically unsaturated groups; b2) 1 to 20 pads of a curable compound having three or more ethylenically unsaturated groups; c) 0 to 4.9 parts of organic solvent; d) 0.1 to 15 pads of colorant; and e) 0.1 to 15 parts of photoinitiator; wherein all parts are by weight.
10. A method according to any one of claims 6 to 9 wherein component a) comprises N-vinyl caprolactam and 2-phenoxy ethyl acrylate.
11. A method according to any one of claims 6 to 10 wherein component b) comprises a urethane di-acrylate oligomer.
12. A method according to any one of the preceding claims wherein step (iii) comprises adding one or more polar components to the ink in order to increase the value of P and/or adding one or more non-polar components to the ink in order to decrease the value of P.
13. A method according to any one of the preceding claims wherein step (iii) comprises adding one or more surface tension-reducing components in order to reduce the value of ST and/or adding one or more components having high surface tension to the ink in order to increase the value of ST.
14. A method according to any one of the preceding claims wherein the resultant ink comprises an organic solvent and one or more radiation-curable monomers, wherein the organic solvent has a higher polarity and optionally a lower surface tension than said radiation-curable monomers.
15. A method for preparing an ink comprising mixing components together in accordance with a recipe designed by a method according to any one of the preceding claims.