Patent Description:
There is growing concern over sustainability and the environmental impact of petroleum based mineral oils which are used as solvents within printing inks to adjust rheological properties and ink setting speeds and drying times. Mineral oil is widely known and may be understood to refer to refined petroleum-based hydrocarbons. A typical intaglio ink will contain up to <NUM>% of mineral oil distillate such as Exxsol D60 (de-aromatised, low aromatic hydrocarbon solvent, distillation range <NUM>-<NUM>). This has created the need for printing inks, especially intaglio ink compositions, which contain reduced amounts of mineral oil and more preferably are free of mineral oil and not classified as VOC under <NUM>/<NUM>/EC directive and contain less than <NUM>% VOC under <NUM>/<NUM>/EC directive, and are especially suited for the intaglio printing of security documents such as banknotes, passports and the like.

Modern intaglio ink formulations need to fulfil a complex range of requirements, which are significantly different to those for other paste inks used in offset and letterpress printing.

In the intaglio printing process, a rotating engraved steel cylinder, carrying a pattern or image to be printed, and heated to a temperature of the order of <NUM>, is supplied with ink by one or more schablones. Subsequent to the inking, any excess of ink on the plain surface of the printing cylinder is wiped off by a rotating wiping cylinder. The remaining ink in the engraving of the printing cylinder is transferred under pressure onto the substrate to be printed, which may be a paper, polymeric or hybrid material in sheet or reel form, while the wiping cylinder is cleaned by a wiping solution, which is alkaline in nature and composed of mainly demineralised water normally containing between <NUM> to <NUM>% sodium hydroxide (caustic soda) and approximately <NUM>% of sulphonated castor oil.

One of the distinguishing features of the intaglio printing process is that the film thickness of the ink transferred to the substrate can be varied from a few micrometers to several tens of micrometers by a correspondingly engraved printing plate. This ability to vary the film thickness is a most desirable feature of the intaglio printing process and the tactile feel of these relief effects is a strong security feature.

The pronounced relief of the intaglio printing accentuates the problem of ink drying and "set-off", which is the unwanted transfer of ink from one printed sheet to the reverse side of the sheet lying on top of it in a stack. In cases of severe "set-off", the sheets can stick together. The sticking together of paper sheets due to ink set-off is called "blocking". Separation of blocked sheets can result in severe damage to one or both. Hence, solvents which are advertised as being suitable for generic "inks" may not be suitable for intaglio inks in particular, due to the specific technical requirements for intaglio inks.

Intaglio ink formulations need to be able to print cleanly at high film thicknesses on intaglio presses, particularly on high speed sheetfed intaglio printing presses without causing "set off" in the sheet stack.

The factors influencing ink drying and "set-off" are determined by the printing ink formulation, the engraving depth and evenness, the printing conditions, the printing substrate, the number of stacked sheets per pile, the time between printing and handling of the piles and the way that the printed piles of paper are handled after printing.

The problem of improving drying and reducing set-off in oxidatively curing intaglio inks has been addressed historically in the art in several ways but mainly include the use of mineral oil solvents with relatively low boiling points that readily evaporate on the printing plate and from the ink film after printing.

Intaglio ink formulations require good solubility in intaglio wiping solutions which are used in the water wipe intaglio printing process to ensure effective wiping of chrome plated nickel printing plates with PVC plastisol wiping rollers. Hence, water wipe intaglio inks may be understood to mean inks which are suitable for use in intaglio printing processes that use alkaline wiping solutions. For example, a water wipe intaglio ink may be graded with a score of at least <NUM>, preferably at least <NUM>, when testing according to the Wiping Solution Solubility test using Wiping Solution A defined in the examples.

Intaglio ink formulations preferably have excellent durability and pass stringent chemical and physical resistance tests. They would preferably have a long shelf-life and be suitable for drying with siccative driers. These properties are achieved by using varnish systems which are highly tailored for the application and utilize polymeric materials with a wide range of molecular weight and functionality. Intaglio printing inks for security printing are normally composed of an oxidatively curable material, such as an alkyd resin or a modified alkyd resin, a high acid value phenolic resin, pigment, inorganic fillers, rheology modifiers, waxes, emulsifying agent (if required), siccative driers and low boiling point mineral oil distillate to produce a finished product that will adequately solubilise in the alkaline wiping solution on press, exhibit good drying and anti-setoff properties and possess the required chemical resistance specified for that particular document or banknote by the end user.

Intaglio ink formulations are traditionally characterized by tack, viscosity and drying time measurements which are well known to those skilled in the art. It is preferred that any change made to one component of the varnish system does not adversely affect these parameters.

Citation or identification of any document in this application is not an admission that such represents prior art to the present invention.

A number of different approaches can be found in the prior art where renewable alternatives have been used in printing inks for the offset printing process. However, these are based on bio-renewable solvents in the form of fatty acid esters of vegetable oils such as rapeseed oil (see <CIT>). <CIT> refers to fatty acid esters of isosorbide as solvents for offset inks. These fatty acid ester solvents used in the formulation of offset inks are high solvency, non-toxic liquids which are virtually non-volatile when compared to their traditional printing ink distillate counterparts. This renders them unsuitable for use in intaglio inks as the high solvency power results in an unacceptable reduction in viscosity and printability and the slow evaporation rate means that the inks do not set or dry quickly, resulting in unacceptable levels of "set-off".

There have been attempts to produce more environmentally sustainable intaglio inks by reducing the amount of environmentally damaging mineral oil solvents required in the formulations. For example, <CIT> refers to a water-based intaglio printing ink having a) an epoxy resin ester reacted with an unsaturated monobasic acid and a reactive monomer, b) a glycol and/or glycol ether c) a pigment, d) a monoalkanolamine, e) a drier and f) water. However, these efforts to reduce the VOC content of the intaglio inks, or increase the water tolerance of such inks, have failed to be widely commercially adopted due to reduced performance compared with conventional intaglio inks.

Other approaches have been used to increase the environmental sustainability of intaglio inks which are based on the use of vegetable oils such as linseed oil, tung oil, dehydrated castor oil, soybean oil or esterified soya bean oils. In <CIT> the use of vegetable oils, varnishes and high boiling point solvents preferably with a boiling point higher than <NUM>, in a water wipeable, non-smearing intaglio ink composition are mentioned.

<CIT>, refers to replacing the mineral oil solvent with soya bean oil which is reacted with other materials at a temperature of <NUM>-<NUM> to form into ink varnishes. A small amount of free soya bean oil may be used at the end of the production process to adjust the final viscosity.

<CIT> refers to a soybean oil-based intaglio ink comprising alkyds synthesised at least in part from soybean oil and tung oil, and/or linseed oil. The soybean oil is reacted with other materials to form an alkyd, so it is not present as a free material. The intaglio ink also contains <NUM> to <NUM> % of mineral oil.

<CIT> relates to an intaglio ink comprising a varnish comprising an alkydmodified soybean oil and method for producing the same.

<CIT> relates to a renewable solvent composition having a high i-paraffin content of at least <NUM> wt. % and a boiling point in a range of from <NUM> to <NUM>.

<CIT> relates to a pressure-sensitive, carbonless copying system and to a process for the production of pressure-sensitive, carbonless copying system.

<CIT> relates to a water-wiping intaglio ink and manufacturing method thereof.

<CIT> relates to a gravure ink and a binder thereof, in particular to a soybean oil-based gravure ink and a binder thereof.

<CIT> relates to an infrared absorptive intaglio printing ink, and more particularly to an infrared absorbing intaglio printink ink for preventing forgery.

It is an object of the present invention to overcome the shortcomings of the prior art, in particular by disclosing intaglio ink compositions which do not require the use of environmentally damaging high boiling point petroleum based hydrocarbons within the formulation, while still being in the required viscosity range required by the intaglio printing process, and showing effective drying and setting properties to avoiding significant set off between sheets when stacked in a printing press delivery pile.

It is a further object of the invention to provide preferred embodiments which exhibit equivalent or improved chemical resistance properties when compared to the low boiling point mineral oil distillate ink formulations currently being used.

Another object of the invention is to provide preferred embodiments which exhibit equivalent or improved solubility characteristics in a wide range of sodium hydroxide containing wiping solutions when compared to the low boiling point mineral oil distillate ink formulations currently being used.

The invention provides a varnish which is suitable for formulating intaglio inks, comprising a bio-renewable iso-alkane vegetable oil-based solvent, oxidatively curable materials, and high acid value resins having an acid number of <NUM>-<NUM> mgKOH/g, wherein the varnish is mineral oil-free; wherein the oxidatively curable materials comprise an epoxy ester and/or a urethane modified alkyd.

The invention also provides a water wipe security intaglio printing ink composition comprising a bio-renewable iso-alkane vegetable oil-based solvent, as oxidatively curable material an epoxy ester and/or a urethane modified alkyd, and a high acid value resin having an acid number of <NUM>-<NUM> mgKOH/g; wherein the ink is mineral oil-free.

The invention also provides a method of intaglio printing security documents such as banknotes and passports on paper, polymeric or hybrid substrate using an ink of the invention.

The invention also provides an intaglio ink comprising a varnish of the invention, optionally further comprising additional bio renewable solvent.

The invention also provides a printed article obtained from printing an ink of the invention, optionally wherein the article is a security document.

The invention also provides a method of making a varnish which is suitable for formulating intaglio inks, the method comprising obtaining a bio-renewable iso-alkane vegetable oil-based solvent from <NUM>% certified vegetable oil feedstocks, and forming a varnish comprising the bio-renewable iso-alkane vegetable oil-based solvent, oxidatively curable materials, and high acid value resins having an acid number of <NUM>-<NUM> mgKOH/g, wherein the varnish is mineral oil-free;
wherein the oxidatively curable materials comprise an epoxy ester and/or a urethane modified alkyd; optionally wherein the method further comprises:.

The invention also provides a method of making a mineral oil-free intaglio ink, the method comprising making a varnish by following either of the above-mentioned methods, and making an intaglio ink comprising the varnish.

We have found that iso-alkane type of vegetable oils can be used to replace petroleum-based solvents within intaglio formulations despite having a lower solvency power and higher boiling point when compared to the traditional mineral oil distillates used in the formulation of these types of printing inks. An iso-alkane may be understood as any branched-chain alkane, but especially one having a methyl group attached to the penultimate carbon atom of the main chain. The iso-alkanes are obtained from <NUM>% certified vegetable origin feedstocks, which can be understood to mean they are bio-renewable, but which are then hydrogenated and distilled to give products with a narrow cut of carbon chain lengths and narrow boiling ranges. The carbon chain length of the iso-alkane may be C10-C20, preferably C13-C18. The iso-alkane may have an initial boiling point of <NUM>-<NUM>, <NUM>-<NUM>, or <NUM>-<NUM>. The iso-alkane may have a final boiling point of <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, or <NUM>-<NUM>. The difference between the initial and final boiling point of the iso-alkane may be less than <NUM>, less than <NUM>, or preferably less than <NUM>. Boiling points are typically reported by commercial suppliers. Boiling points may be measured according to ASTM D86-<NUM>, e.g. at <NUM>. Iso-alkane vegetable oil-based solvents are available from commercial suppliers.

In a preferred embodiment of the invention, the combination of bio renewable iso-alkanes of vegetable oil with a carbon chain length of C13-C18 with a naturally occurring drying oil such as refined soya bean oil, refined linseed oil or tung oil enables the formulation of mineral oil-free intaglio inks which are not classified as containing VOC under European Regulation with the correct viscosity and tack, which are suitable for security printing on various substrates, especially banknote substrates. Another advantage of these formulations is that they can perform well in press wiping solutions with lower NaOH concentrations without affecting the quality of print or causing any increase in intaglio plate wear on the press. An alkaline wiping solution based on sodium hydroxide and a surfactant/detergent in demineralized water is used in the intaglio printing process to remove/wipe any excess ink from the engraved printing cylinder during printing. Once in the wiping solution, the waste ink can be treated in the press waste treatment facility. The press wiping solution, which has a direct impact on the environment, can contain <NUM>% or more of sodium hydroxide, therefore reducing the amount used will be environmentally more advantageous and desirable.

The varnishes and inks may be substantially free of water, for example comprising less than <NUM> wt% water, or are free from water.

The varnishes and inks are preferably not classified as VOC under <NUM>/<NUM>/EC directive. Alternatively or in addition, the varnishes and inks preferably contain less than <NUM>% VOC under <NUM>/<NUM>/EC directive, for example less than <NUM>/l VOC.

The ink may have a viscosity at <NUM> of <NUM>-<NUM> Pa·s, preferably <NUM>-<NUM> Pa·s. The varnish may have a viscosity at <NUM> of <NUM>-<NUM> Pa·s, preferably <NUM>-<NUM> Pa·s. Viscosity ma be measured according to ASTM D4287-<NUM>. For example, viscosity may be measured with a viscometer, such as a CAP <NUM>+ Viscometer available from Brookfield Engineering, using a <NUM> of sample of product, where the equipment setting is Spindle <NUM> at a speed of 50rpm at <NUM> for a varnish and <NUM> for an ink.

The invention includes a method of making a mineral oil-free varnish suitable for formulating intaglio inks, the method comprising:.

The inert conditions are typically under an inert atmosphere such as nitrogen, argon, or carbon dioxide. In this way, the mixture is prevented from reacting with oxygen in the air.

The heating in step (a) may be to <NUM>-<NUM> or <NUM>-<NUM>. Typically the heating results in the high acid value resins (which are often obtained in solid form) dissolving in the oxidatively curable materials. Thus, step (a) may include agitating the oxidatively curable materials and the high acid value resins, optionally for at least <NUM> minute, such as from <NUM> minutes to <NUM> hour.

The materials heated in step (a) may be free from vegetable-based solvents, and may consist of oxidatively curable materials and high acid value resins. Advantageously, it has been found that the use of vegetable oil-based bio-renewable iso-alkane as the solvent in step (b) avoids the need to include solvents in the heating step (a). This leads to a safer process since it avoids the need to add a solvent, which may be volatile, to a reaction vessel at high temperature.

The mixture may be cooled before step (b) is performed, optionally by at least <NUM> and/or to <NUM> or less. In this way, the risk of the solvent vapor igniting is minimized. Step (b) may be performed under inert conditions, again minimizing the risk of the solvent vapor igniting.

To facilitate the formation of the varnish step (b) may include agitating the mixture comprising the bio-renewable iso-alkane vegetable oil-based solvent.

After step (b) the mixture comprising the bio-renewable iso-alkane vegetable oil-based solvent is typically cooled to ambient temperature, when it may then be incorporated into an intaglio ink.

The invention provides a method of making a mineral oil-free intaglio ink, the method comprising making a varnish by following the method of making a varnish recited above, and making an intaglio ink comprising the varnish. Making the intaglio ink is typically performed at ambient temperature, typically under ambient atmosphere.

Making the intaglio ink typically comprises mixing into the varnish one or more of oxidatively curable materials, high acid value resins, colorants, fillers, rheology modifiers, waxes, emulsifying agents, and siccative driers. The mixing may include triple-roll milling, optionally a pre-mixing step followed by triple-roll milling.

Intaglio printing inks for security printing are normally composed of oxidatively curable material, a high acid value resin, colorants, fillers, rheology modifiers, waxes, emulsifying agents, siccative driers and solvents. Details of these components are provided below. It will be understood that these details are relevant to the varnishes, inks, and methods provided by the present invention.

The oxidatively curable materials may include linseed or soybean based alkyd of long oil length, medium-oil-length, or short oil length where the acid used may be acid anhydride, phthalic acid, isophthalic acid, diolefinic acid or vinylformic acid and a polyvalent alcohol such as glycerol, pentaerythritol, ethylene glycol, trimethylolpropane or tetramethylolmethane; urethane modified alkyd such as urethane modified soya or linseed oil alkyd; modified soya or linseed oil alkyd; epoxy ester; high acid value alkyd; long chain unsaturated polyacid such as fumaric acid modified vegetable oil and/or drying oils such as tung oil and/or linseed oil. Preferably the oxidatively curable materials are selected from the group consisting of linseed and soybean-based alkyds of long oil length, medium-oil-length, and short oil length and combinations thereof.

Long, medium, and short oil length alkyds are widely used terms which may indicate the fatty acid content of the alkyd. For instance, long oil alkyds may contain more than <NUM> wt% fatty acids, medium oil alkyds may contain <NUM>-<NUM> wt% fatty acids, and short oil alkyds may contain less than <NUM> wt% fatty acids.

In the varnish, the oxidatively curable materials may be present in an amount of <NUM>-<NUM> wt% or <NUM>-<NUM> wt%. The ink may comprise <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt% oxidatively curable material.

In the invention, the oxidatively curable materials comprise an epoxy ester and/or a urethane modified alkyd. The epoxy ester may be a reaction product of a vegetable oil fatty acid and an epoxy resin. The urethane modified alkyd may be a reaction product of the residual OH groups of a vegetable based liquid alkyd resin and the NCO groups from an isocyanate such as TDI (toluene diisocyanate).

The epoxy ester and/or urethane modified alkyd may be present in the varnish in an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%. The epoxy ester and/or urethane modified alkyd may be present in the ink in an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%.

The epoxy ester may be present in the varnish an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%. The epoxy ester may be present in the ink in an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%.

The urethane modified alkyd may be present in the varnish an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%. The urethane modified alkyd may be present in the ink in an amount of <NUM>-<NUM> wt%, <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%.

The High Acid Value Resins may include high acid value rosin modified phenolic resin based on gum rosin, paraformaldehyde and/or fumaric acid and/or maleic anhydride and/or pentaerythritol and/or nonylphenol and/or octyl phenol. The acid value of the high acid value resin, for example the described high acid value rosin modified phenolic resin, is <NUM>-<NUM> mgKOH/g, more preferably <NUM>-<NUM> mgKOH/g.

In the varnish, the high acid value resin may be present in an amount of <NUM>-<NUM> wt% or <NUM>-<NUM> wt%. The ink may comprise <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%, or <NUM>-<NUM> wt% high acid value resin.

Acid Value may be determined by titration with <NUM> potassium hydroxide solution using phenolphthalein solution indicator, as is widely known. For example, acid value may be determined by weighing approximately <NUM> of sample accurately (to <NUM> decimal places) into a clean, dry conical flask and recording the amount used. Approximately <NUM> of a <NUM>:<NUM> mixture of toluene and industrial methylated spirit is then added to the conical flask to dissolve the varnish sample along with <NUM>-<NUM> drops of phenolphthalein solution indicator. Standardized <NUM> potassium hydroxide in methanol is then titrated into the conical flask solution with mixing until a pink color develops and persists for <NUM> seconds. The Acid Value of the varnish is determined by using the calculation below. <MAT> Weight of sample used.

The Acid Value result is recorded as milligrams of potassium hydroxide per gram of sample or mg KOH/g.

Fillers may include organoclays, fumed silica, aluminum silicate, aluminum hydrosilicate, ground natural calcium carbonate, barium sulphate or fine china clay.

The ink may comprise <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%, or <NUM>-<NUM> wt% filler.

The colorant may be any pigment that can be employed in printing inks. It may be organic or inorganic and may be a dye or pigment. Typical examples of useable colorants include, but are not limited to, inorganic pigments, such as Pigment White <NUM> (Titanium Dioxide), Pigment Black <NUM> (carbon black), Pigment Black <NUM> (Black Iron Oxide), Pigment Red <NUM> (Red Iron Oxide) and Pigment Yellow <NUM> (Yellow Iron Oxide), and organic pigments such as Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment 26Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Yellow <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Orange <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Red <NUM>, Pigment Blue <NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Blue <NUM>:<NUM>, Pigment Green <NUM>, Pigment Green <NUM>, Pigment Violet <NUM> and the like.

Suitable inorganic pigments include, but are not limited to, carbon black and titania (TiO<NUM>), while suitable organic pigments include, but are not limited to, phthalocyanines, anthraquinones, perylenes, carbozoles, monoazo- and disazobenzimidazolones, isoindolinones, monoazonaphthols, diarylidepyrazolones, rhodamines, indigoids, quinacridones, diazopyranthrones, dinitranilines, pyrazolones, dianisidines, pyranthrones, tetrachloroisoindolinones, dioxazines, monoazoacrylides, and anthrapyrimidines. It will be recognized by those skilled in the art that organic pigments are differently shaded, or even have different colors, depending on the functional groups attached to the main molecule.

The dyes include but are not limited to azo dyes, anthraquinone dyes, xanthene dyes, azine dyes, combinations thereof and the like.

The ink may comprise <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%, or <NUM>-<NUM> wt% colorant.

As with most ink and coating compositions, additives may be incorporated to enhance various properties. A partial list of such additives includes but is not limited to adhesion promoters, silicones, light stabilizers, optical brighteners, de-gassing additives, ammonia, flow promoters, defoamers, antioxidants, stabilizers, surfactants, dispersants, plasticizers, rheological additives, waxes, silicones, etc..

Solvents for security inks may include vegetable oil (e.g. soya bean oil, castor oil, rapeseed oil, linseed oil, tung oil), mineral oil, aliphatic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, ketones, aldehydes, alcohols, ethers, esters. Drying oils such as linseed oil and tung oil may act as both solvents and as oxidatively curable materials.

The invention utilizes bio-renewable iso-alkane vegetable oil-based solvents. The varnish may comprise <NUM>-<NUM> wt% or <NUM>-<NUM> wt% bio-renewable iso-alkane vegetable oil-based solvent. The ink may comprise <NUM>-<NUM> wt%, or <NUM>-<NUM> wt%, or <NUM>-<NUM> wt% bio-renewable iso-alkane vegetable oil-based solvent.

Co-solvents, which are preferably bio-renewable, many include refined soya bean oil, rapeseed oil, castor oil, refined linseed oil and tung oil.

The varnish may comprise <NUM>-15wt% or <NUM>-10wt% of a bio-renewable co-solvent. The ink may comprise <NUM>-<NUM> wt% or <NUM>-<NUM> wt% of a bio-renewable co-solvent.

The present invention has been described in detail, including the preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and/or improvements on this invention that fall within the scope the invention, as defined in the claims.

The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention.

The varnishes are prepared by mixing the oxidatively curable materials (e.g. alkyd components, long chain polyacid and epoxy ester) together in accordance with the formulations in the examples and heating to <NUM> under inert gas. The resin (e.g. modified phenol formaldehyde resin) is added and the mixture is stirred until the resin is completely dissolved. The mixture is cooled to <NUM> and the requisite solvents in the formulations are added. The mixture is allowed to cool to room temperature before incorporating into an intaglio ink.

Viscosity, tack and solids content was measured for the above varnish examples using the following test methods:.

VISCOSITY: Measured with a CAP <NUM>+ Viscometer using a <NUM> of sample of product. The equipment setting was Spindle <NUM> at a speed of 50rpm at <NUM>.

TACK: Measured using the Protack Tack Meter. Varnishes were tested using <NUM> of sample with the machine set to Program <NUM> @ <NUM>.

SOLIDS CONTENT OF VARNISHES: The solids content was determined using a Sartorius MA35 Solids Content Testing Unit. <NUM> of varnish sample was accurately weighed onto a foil square on the Sartorius MA35 unit which had been set at a temperature setting of <NUM> for a duration of <NUM> minutes. The lid is then closed to start the test and the solids content of the varnish sample automatically indicated after the test is completed on a digital readout.

Table <NUM> exhibits the fitness for use for all of the inventive examples (Examples <NUM>-<NUM> and <NUM>) in terms of tack. As is known to those skilled in the art; viscosity and solids content can be further adjusted by suitable solvent additions, so all the inventive examples were suitable for incorporation into intaglio printing inks.

The varnish examples in Table <NUM> were incorporated into a standard intaglio ink formulation detailed in the examples below. Approximately <NUM> sized batches of inks were produced by premixing all materials on a laboratory tri-foil mixer for approximately <NUM> minutes until a smooth paste had been achieved. The pre-mix was then given two passes through a small production triple roll mill at medium setting conditions (15psi, front and back roller settings). Particle size was checked on a <NUM> Sheen grinding gauge. If there was scratching above <NUM> further milling would be required. In the comparative ink formulations based on refined linseed oil (Example <NUM> and Example <NUM>), additional refined linseed oil was required to achieve suitable viscosity and tack for testing purposes.

Viscosity, tack, drying time and solubility in wiping solution was measured for the above intaglio ink examples using the following test methods:
VISCOSITY: Measured viscosity on a CAP <NUM>+ Viscometer using a <NUM> of sample of product. The equipment setting was Spindle <NUM> at a speed of 50rpm. Intaglio inks are tested at <NUM>.

TACK: Tack is measured using the Protack Tack Meter. Intaglio inks are tested using a <NUM> sample with the machine set to Program <NUM> at <NUM>.

INK DRYING TIME: The drying times of the Intaglio Permanent Carmine Ink preparations were tested on the TQC Sheen Drying Recorder. A 25µ film of ink was applied to a large glass slide using a film applicator, the machine set to zero, the needle applied to the ink surface and the recorder switched on. The ink drying time is recorded as being the point where the needle no longer makes a mark in the ink film on the glass slide.

INK SETTING SPEED: <NUM>-inch-wide prints of all the Intaglio Permanent Carmine Inks preparations were prepared on banknote paper using the Peach Print Proofer using <NUM> of ink sample. Immediately after printing, another sheet of banknote paper was placed on top and both sheets fixed back in the printer on the printing platform with a fresh roller in contact. The roller mechanism was then moved forward at timed intervals (<NUM>. etc.) and the intensity of ink transfer onto the second sheet for each sample obtained. Each of the inks' setting speed was graded against the standard using the following nomenclature: = standard; ↑ standard (faster than standard); ↓ standard (slower than standard).

Wiping Solution is placed into a <NUM> glass beaker, a magnetic stirrer bar added and the contents heated under stirring on a hot plate mixer to <NUM>. Approximately <NUM> of each of the ink samples is applied to the inside of a <NUM> glass measuring cylinder, near the top, and the <NUM> wiping solution poured into the measuring cylinder to the top. The time when the ink first started to precipitate in the wiping solution (in seconds) is recorded along with the ability for the ink to precipitate in the solution graded from <NUM> to <NUM> using the following criteria:.

Table <NUM> exhibits the fitness for use as printing inks of the inventive examples (Examples <NUM>-<NUM>, <NUM> and <NUM>) in terms of setting properties, viscosity, tack and wiping solution solubility. In particular they show satisfactory drying, setting characteristics and solubility in press wiping solutions with lower NaOH concentrations. This means that the inks are suitable for printing on commercial intaglio printing presses and will give good quality prints without set-off defects.

The raw materials in Examples <NUM> and <NUM> were manipulated to achieve the required setting and drying properties in the intaglio ink formulation. Manipulation of the raw materials in a varnish formulation means that the percentages of each component are adjusted to obtain the required rheology, setting and drying properties in the final ink.

Notably, the examples using iso-alkane vegetable-based solvent (Examples <NUM>-<NUM>, and <NUM>) were found to have improved properties for use as intaglio inks compared to the comparative examples using the vegetable-based solvents Fatty Acid Ester of Vegetable Oil and Refined Linseed Oil (Examples <NUM>, <NUM>, and <NUM>), in particular improved drying time and setting speed. This demonstrates the improvement provided by the invention in comparison to other mineral oil-free formulations utilizing vegetable-based solvents.

<NUM>-inch-wide prints of all the laboratory produced Permanent Carmine Intaglio Inks were prepared on banknote paper using the Peach Print Proofer using <NUM> of ink sample. Physical resistance was measured on prints which had been left to dry for <NUM> hours at ambient temperature and humidity. Rub resistance was tested using the THI rub tester using a 4lb weight for <NUM> rubs and the transfer of color on the back of the facing sheet of paper/poly stock graded for scuff/rub intensity. The prints were allowed to dry at ambient temperature and humidity for at least <NUM> days prior to testing for chemical resistance. The prints were cut into strips and the chemical resistance tests carried out on each of the dried inks as detailed in Table <NUM> below.

All solutions require thorough mixing until fully homogeneous prior to use.

Claim 1:
A varnish which is suitable for formulating intaglio inks, comprising a bio-renewable iso-alkane vegetable oil-based solvent, oxidatively curable materials, and high acid value resins having an acid number of <NUM>-<NUM> mgKOH/g, wherein the varnish is mineral oil-free;
wherein the oxidatively curable materials comprise an epoxy ester and/or a urethane modified alkyd.