One particular area of printing that has achieved significant growth in recent years has been the field of inkjet printing where several print systems are possible. Continuous inkjet is known as CIJ and finds widespread use in the coding of many articles in everyday use. One particular example is the date coding of foodstuffs having a specific shelf life. The CIJ system produces a continuous stream of ink droplets which are projected towards the substrate. In one embodiment of the system, the ink droplets that are not required for image formation are deflected by an electric field into a gutter and recycled to the ink reservoir.

In another inkjet system, the ink in the ink head may be heated to produce a bubble which then causes a droplet to be emitted from the print head onto the substrate as required. This system is known as thermal drop-on-demand (DOD) or bubble jet.

A further inkjet system is known as piezo DOD whereby the emission of the ink droplet is caused by an electromechanical deformation in the print head. There are many and varied types of inkjet printing systems in use for home, office or industrial applications. In all these such cases, the composition of the ink plays a vital role in achieving optimum performance for the inkjet system used.

One of the problems of ink makers and printers in recent years has been the increasing concern over pollution of the environment. Many ink formulations have been based on volatile organic solvents which are deemed to be harmful to health and the environment. Some such inks are still used by the printing industry, for example in flexography and gravure printing, as well as in some inkjet print systems. Thus, there is a trend and need to change to more environmentally acceptable systems such as water based inks which do not suffer from the same environmental problems caused by volatile organic solvents.

Aqueous ink formulations contain colourants of various types.

These may be based, for example, on carbon blacks, coloured pigments and dispersions or they may be solutions of soluble dyes. Various additives are made to these formulations to confer various properties that are deemed to be advantageous. Thus, wetting agents may be added to improve spreadability, antifoam agents to control foaming, and biocides to limit bacterial activity and so on. Also, polymers may be added in some applications. These may confer some stability to colourant dispersions to prevent coalescence or aggregation or to prevent settling out on storage of the inks. It is known, for example, to use proteins such as gelatin as dispersants in inkjet inks (US 5702510, US 5736606).

Whilst it is possible in this way to provide stable dispersions for use as inkjet inks, these inks can suffer from various limitations in use. Thus, the inks can variously show low ease of prime, and problems of satellite formation and poor dot roundness at moderate throw distances. We have investigated these problems and have found that they can be reduced or overcome by improving the rheological properties of the inkjet inks. In principle, this could be achieved by increasing the amount of protein, e. g. gelatin, in the ink but in practice this is unsatisfactory because, at the amount of protein needed for the desired rheological effects, the viscosity of the ink would be too high and may even gel Thus, if an ink with normal viscosity for inkjet application is to be produced using standard gelatins, the concentration of the gelatin must be reduced to such low levels that there is no benefit as a rheological control additive.

We have now found, however, that aqueous inkjet inks of excellent stability and performance can be obtained, with good control of rheological properties (allowing good throw distances with low formation of satellite drops, for example) by using a hydrolysed protein or chemically-modified, hydrolysed protein or hydrolysed chemically-modified protein.

Thus, in one aspect, the invention provides an aqueous inkjet ink which comprises an aqueous medium, an ink component, and a hydrolysed protein or chemically modified hydrolysed protein or hydrolysed chemically-modified protein.

In another aspect, the invention provides a method of printing using an inkjet printer, wherein there is used an aqueous inkjet ink comprising an aqueous medium, an ink component, and a hydrolysed protein or chemically- modified hydrolysed protein or hydrolysed chemically-modified protein.

By"hydrolysed protein"or"hydrolysed chemically modified protein", we mean a protein or chemically-modified protein which has been hydrolysed to a weight-average molecular weight typically from 2 to 100 kD, and preferably from 7 to 50 kD. The optimum molecular weight may vary for different protein sources. Hydrolysed gelatins are often described as"zero Bloom"gelatins since, unlike conventional gelatins, under the standard test conditions of 6 2/3%, 1 Q°C used for gelatin testing (BS757 : 1975), the Bloom gel strength is zero.

Hydrolysis may be achieved by heat. catalysed by acid or alkali, but more selective hydrolysis is achieved by using proteolytic enzymes at comparatively low temperatures which also minimises development of colour and odour. The enzyme may finally be deactivated such as by heating. Hydrolysed gelatins are characterised by a very much reduced ability to gel and consequently are soluble in cold water ; the higher molecular weight types exhibit weak gelling properties at high concentrations (above 20%) and at low temperatures (below 15°C). They are normally supplied commercially as spray-dried powders or as concentrated solutions. Despite their lower molecular weight, these hydrolysed gelatins retain many of the valuable properties associated with gelatin, such as protective colloid action, emulsion stabilisation, film-forming ability and ampholytic (acidic and basic) behaviour.

Some properties of some commercially available hydrolysed gelatins are shown in the table. Property Crotein C Crotein A Crotein O Physical form spray-dried powder spray-dried powder spray-dried powder Moisture % 7. 0 max 7. 0 max 7. 0 max Ash % 2. 0 max 2. 0 max 2. 0 max x Nitrogen % 16-18 16-18 16-18 Viscosity 10% 2S°C 35-45 20-25 17-19 mps pH 10% 25°C 5. 5-6. 5 5. 5-6. 5 5. 5-6. 5 Weight-average 50kD 30kD 15kD molecular weight (approx) A practical example for the enzyme hydrolysis of gelatin using trypsin is given in GB 1177185 (Kodak). Another example using acid hydrolysis is given in US 3, 763, 138 (DuPont) and another using alkaline hydrolysis is given in GB 1475364 (Hausmann).

By"chemically modified protein"or"chemically modified hydrolysed protein", we mean a protein or hydrolysed protein which has been reacted with a reactive species which can chemically bond with some of the amino acid residues present in the protein chains such as the amino group of lysine or terminal amino groups the carboxyl group of aspartic and glutamic acids or terminal carboxyl groups : the hydroxyl groups of serine and threonine or the thiol group of cysteine. Examples include the reaction of hydrolysed gelatin with dibasic acid anhydrides such as succinic anhydride which is understood to react with the amino group of the lysine side chain and terminal amino groups to produce a product known as succinylated (hydrolysed) gelatin (see patent GB 1475364 Hausmann). By"chemically modified protein"or"chemically modified hydrolysed protein"we mean also a protein or hydrolysed protein which has been modified through enzymic reaction. One example is the use of a protein crosslinking enzyme such as transglutaminase. Another type of reaction by which a protein or hydrolysed protein can be chemically modified is that which uses a free radical mechanism which results in a reaction known as a grafting reaction between, for example, unsaturated monomers and the protein. Thus, in one example, hydrolysed gelatin and methacrylic acid may undergo a free radical copolymerisation reaction in the presence of an initiator to yield a product known as methacrylated (hydrolysed) gelatin (some similar preparations are described in EP-A-089312 (Ciba-Geigy)). A further reaction type is where the protein or hydrolysed protein undergoes a chemical change without the addition of substituents. Examples include the racemisation of the amino acids from 1 to d form under alkaline conditions, oxidation of the amino acid side chains of methionin and cysteine, and the deamination of the amino side chain of lysine (the racemisation of the amino acids is described in GB 1475364 (Hausmann) and the controlled oxidation of methionine is described in US patent no. 5, 412, 075 (Eastman Kodak)).

The chemical modification of proteins and hydrolysed proteins alters their properties. For example, in some cases the charge distribution is altered by increasing or lowering the isoionic pH. Increasing the isoionic point can lead to enhanced stabilisation of ink colourants such as anionic dyes. Also, the hydrophilic/hydrophobic balance may be changed or the surface activity increased.

In this way, chemically modified proteins and hydrolysed proteins can be made which provide useful and advantageous effects in inkjet inks in accordance with the invention.

Chemical modification of gelatin (which is a protein derived from the natural protein collagen) is described in the chapter on"The Chemical Reactivity of Gelatin"by R. C. Clarke and A. Courts in the book"The Science and Technology of Gelatin"edited by A. G. Ward and A. Courts, published by Academic Press in 1977. Further discussion of the chemical modification of proteins may be found in the book"Modification of Proteins"edited by RE. Feeney and J. R. Whitaker, published by American Chemical Society in 1982 as No. 198 in the Advances in Chemistry Series. Another reference text is "Chemical Modification of Proteins"by G. E. Means and R. E. Feeney published by Holden-Day Inc. in 1971.

It is to be understood that there is a wide and varied range of chemical modifications that can be made with proteins and hydrolysed proteins and many of these modifications are described in the publications cited above.

Among such chemically modified proteins and hydrolysed proteins are those with the following substituent groups : acetyl, succinyl, phthalyl, maleyl, phenyl carbamyl, carbamyl, dodecenylsuccinyl, hydroxyethyl cellulose silane terpolymer, hydroxypropyltrimethyl, hydroxypropyllauryl dimethyl, hydroxypropylcocodimethyl, silanol hydroxypropyl, methacrylylhydroxypropyl and copolymers with acrylic acid, methacrylic acid, acrylamide, methacrylamide, methyl methacrylate, vinyl sulphonate, styrene sulphonate, urethane, vinyl pyrrolidone.

Examples of commercially available chemically modified hydrolysed proteins useful in this invention are : Crotein Q A modified hydrolysed gelatin having a trimethyl quaternary substituent at amino groups.

Croquat L A modified hydrolysed gelatin having a lauryl dimethyl quaternary substituent at amino groups.

Croquat M A modified hydrolysed gelatin having coconyl dimethyl quaternary substituent at amino groups.

Succinyl gelatin A modified hydrolysed gelatin having a succinyl substituent at amino groups.

Crodasone C A modified hydrolysed gelatin having a silanol substituent at amino groups.

The"hydrolysed, chemically-modified proteins"used in the invention are protein materials that have undergone a chemical change as a first stage to produce a"chemically-modified protein"before introducing a subsequent stage of reducing the molecular size through a hydrolysis reaction to produce the "hydrolysed, chemically-modified protein". Thus, for example, a protein material such as gelatin may be reacted with a reactive quaternary reagent to form a gelatin where some or all of the lysine amino groups, for example, may contain substituent quaternary groups to form a gelatin derivative. Such gelatin derivative may then be hydrolysed by various techniques such as the use of enzyme or acid hydrolysis to give a product with lower average molecular weight which may then be described as a hydrolysed, quaternary-modified gelatin.

Proteins which can be hydrolysed, or hydrolysed and chemically modified, or chemically modified and hydrolysed, for use in the present invention can be obtained from plant sources such as soya, maize, and wheat and from animal sources such as collagen, silk, keratin, elastin, casein, and reticulin though this is not a complete listing of such proteins. Collagen proteins can be obtained from various animal species including cattle, pig, sheep, poultry and fish where the collagen may be converted into gelatin from collagen containing tissues such as skin and bone. The manufacture of such gelatins can be carried out using various processes such as alkaline, acid, or enzyme treatments as is well known in the art and described in various patents and texts. A useful reference textbook is"The Science and Technology of Gelatin"edited by A. G. Ward and A. Courts, published by Academic Press in 1977. The proteins employed in this invention may be used to advantage in ink systems designed for packaging or labelling of edible or pharmaceutical products. Thus, an edible or pharmaceutical grade of hydrolysed protein could be used in conjunction with approved colourants in such ink formulations.

Generally, inkjet inks are fluids which, when applied to a paper or other receiving material, form an image or pattern of droplets that can be detected by the human eye. Examples of this are found in standard home and office print systems using printers such as those supplied by companies such as Hewlett Packard, Epson, Lexmark combined with receiver sheets of white paper, for example.

The inks of the present application, however, include any fluid that can be detected by any means when such fluid is ejected as droplets onto a receiving body. Visible inks containing carbon black dispersions, dispersions of coloured pigments or solutions of coloured dyes can form droplet images which may be readily recognised by the human eye when applied to suitable receiver sheets such as white paper. However, for other applications such as for security marking, it may be preferable to use inks that produce images that are not directly visible to the human eye. Such inks may have absorbance in the ultraviolet region or infrared which can be detected using appropriate devices. Inks suitable for machine-readable systems may contain components having other properties such as magnetic properties or various electrical or optical properties that enable images produced using these. inks to be detected in machine-readable systems. In other examples, the inks may contain one or more colourless components that become visible when irradiated such as by W light or become visible by other means such as by heating or by further chemical interaction. These inks may be described as invisible inks.

Furthermore, the inks of the present invention also include fluids where the deposition of droplets is not intended to be used for reading or detection by human or machine devices but the droplets may be used to confer other functionality to the receiving medium. Examples of this would be the jetting of droplets which are capable of conducting electricity such as might be useful in micro-electronic devices or capable of magnetic or other such properties which might be useful in various applications including those such as microfabrications.

Other inks could contain reactive species such as those capable of forming crosslinked polymeric images as disclosed in EP-A-883, 025 and EP-A-883, 206 and which could find application in areas such as silk-screen printing.

Thus, the"ink component"present in the inkjet inks of the present invention can be an image-forming component such as a pigment or colourant, or an"invisible"ink component, or it can have a function other than visibility, eg to provide an electrically conductive image etc. These are examples only of what is intended to be encompassed by the inkjet inks of the invention.

The inkjet inks of the invention may comprise, in addition to an ink, other components such as, for example, co-solvents, humectants, drying agents, wetting agents which may be anionic, cationic or non-ionic, anti-foam agents, biocides, chelating agents, conductivity enhancing agents, corrosion inhibiters and anti-kogation agents. The amounts and nature of these components will be well understood by those skilled in the art and no further description will be given herein.

The amount of hydrolysed or chemically modified hydrolysed or hydrolysed chemically modified protein to be included in the inks of the invention will depend on the inkjet printing system being used. For example, for thermal inkjet, the amount to be included will normally be from 0. 1 to 40%, preferably from 1 to 10% and most preferably from 1 to 5%. For continuous inkjet systems, the amount to be included will normally be from 0. 1 to 40%, preferably from 2 to 20% and most preferably from 5 to 20%.

In accordance with a feature of the invention, the aqueous inkjet inks may have a proportion of the water replaced with other solvents. Such water and non-aqueous solvent mixtures can assist, for example, the flow characteristics of the ink and the spreadability as well as modifying the drying rates. The compatibility of some hydrolysed or chemically modified hydrolysed proteins with some aqueous solvent mixtures was determined over the range from 0-80% of the non-aqueous solvent. Solutions were prepared in water, the pH adjusted with sodium hydroxide to pH 8. 0-8. 5 before adding the cosolvent. The protein concentration in the final solution was 5%. The compatibility range is the percentage of non-aqueous solvent in the solution where there is no turbidity, phase separation or precipitation apparent.

Table of compatibility range of cosolvent (%) with water at 20°C for various protein samples. Ethanol iso propanol ethyl lactate glycerol Crotein O 0-40 0-40 0-60 0-80 Crotein C 0-40 0-40 0-40 0-80 Crotein Q 0-40 0-40 0-40 0-80 Croquat L 0-60 0-40 0-60 0-60 Succinyl hydrolysed 0-40 0-20 0-40 0-80 gelatin Crodasone C 0-40 0-40 0-40 0-80 This Table shows that a range of different hydrolysed and chemically modified proteins is compatible with various solvent mixtures.

Colorant compatibility-pigmented systems The compatibility of hydrolysed protein and hydrolysed protein derivatives with various pigment colorant systems was demonstrated. The following pigment ink bases were used : Forthsperse Black PC1 Pigment Black 7, Carbon Black 30% solids ; stabiliser 10-15% ; anionic surfactant ; bactericide ; pH 8. 0-8. 5 Forthsperse Black K2 Pigment Black 7, Carbon Black 50% solids ; stabiliser 10-15% ; non-ionic surfactant 2-7% ; bactericide ; pH 8. 0-8. 5 Forthsperse Red BRS Pigment Red 4 Forthsperse Blue C Beta Pigment Blue 15 : 3 Forthsperse Yellow GG Pigment Yellow 1 A series of model inks was produced using 5 parts of the above pigment dispersions and 10 parts of 12% solutions of various proteins at pH 8. 4- 8. 8 to give inks containing 8% protein. After mixing, the inks were examined for signs of incompatibility such as separation or precipitation of pigment. The Table below shows that in the majority of examples the pigment ink formulation appears to be stable with no incompatibility apparent. Pigment Appearance added Crotein O BlackPC opaque-no incompatibility detected Black K2 2 layers-incompatible Red opaque-no incompatibility detected Blue opaque-no incompatibility detected Crotein Q BlackPC opaque-no incompatibility detected Black K2 2 layers-incompatible Red opaque-no incompatibility detected Blue opaque-no incompatibility detected Croquat L BlackPC opaque-no incompatibility detected Black K2 2 layers-incompatible Red opaque-no incompatibility detected Blue opaque-no incompatibility detected Croquat M BlackPC opaque-no incompatibility detected Black K2 2 layers-incompatible Red opaque-no incompatibility detected Blue opaque-no incompatibility detected Succinyl hydrolysed BlackPC opaque-no incompatibility detected gelatin Black K2 clear upper layer-not compatible Red clear upper layer-not compatible Blue clear upper layer-not compatible Crodasone C BlackPC not compatible Black K2 not compatible Red not compatible Blue not compatible Colorant compatibility-soluble dye systems The compatibility of hydrolysed protein and hydrolysed protein derivatives with various soluble dye colorant systems was demonstrated. The following water-soluble acid dyes were dissolved to give 6% solutions at pH about pH 8. 5 : Nigrosine, water soluble (acid black 2) Coomassie Brilliant Blue R250 Bromophenol blue Chlorophenol red Erythrosine, water-soluble (not fully dissolved) The following protein solutions were prepared at 12% concentration with pH around pH 8. 5 Crotein O Crotein Q Croquat L Croquat M Succinyl hydrolysed gelatin Crodasone C The protein and dye solutions were mixed in equal proportions and the solutions examined for signs of incompatibility. No indication of any incompatibility was apparent.

This shows that proteins can be used to form stable ink formulations.

Improved gloss Some model ink formulations were prepared using the pigment Forthsperse Black PC1 and various proteins.

As a control, a dispersion was made using the following acrylic resin ink base DI water 3200g Joncryl 678 acrylic resin 800g 20% solids (supplied by S C Johnson Polymer bv) Ammonia 180g to pH8. 5+0. 3 The polymer and protein solutions were prepared and the pH adjusted to pH 8. 5 with sodium hydroxide. Solvent and pigment were added to produce an ink formulation having polymer/protein 10%, solvent (digol 10% or ethanol 20%) and pigment 5% (dry basis). A writing test and a draw down test using a K bar with 36 turns per inch (14 per cm) were carried out on plain copy paper (International Paper DuoCopy 80g) and on gelatin coated glossy paper. The digol coatings were slow to dry but were found to be dry after leaving at ambient temperature for 7 days. Reflection densities were measured (using an X-rite reflection densitometer) on the dry samples. All of the sample inks showed good flow characteristics in the writing test. Cosolvent Reflection Reflection Observations density density plain paper glossy paper Aqueous ink Digol 1. 36 1. 46 base Crotein O Digol 1. 49 1. 55 Crotein Q Digol 1. 66 1. 69 Aqueous ink ethanol 0. 7 1. 44 bleed through base plain paper Crotein O ethanol 1. 04 1. 55 bleed through plain paper Crotein ethanol 0. 95 1. 56 bleed through plain paper It can be seen that the model formulations containing the proteins show superior reflection densities.

Inkjet printing systems To illustrate the benefits of using proteins in ink formulations for inkjet printing, we have evaluated a simple hydrolysed protein, Crotein O, and a modified hydrolysed protein, Crotein Q, in a range of inkjet printing systems.

Inkjet printing systems-continuous inkjet The two proteins Crotein O and Crotein Q were formulated into common Continuous Inkjet (CIJ) water based inks. The performance of the inks were then evaluated in a Domino CB1 continuous inkjet printer.

These inks were taken through a printer assessment of 5 hours continuous printing. Formulation (%) PIF 5 PIF 8 Crotein O 13. 6 Crotein Q 8. 77 Bayscript Black SP Liquid 17. 6 Projet Fast Black 2 39. 5 Diethylene Glycol 0. 88 0. 9 Surfynol 104E 0. 26 0. 27 Surfynol 75D 0. 26 0. 27 Water 72. 3 45. 5 Comments Filtered 2. 7 then 1y Filtered 2. 7µ then 1µ The manufacturing method was as follows : The protein was added to the water and mixed on a Silverson air driven mixer for 10 minutes, then left for 10 minutes or longer to allow the solution to clear. Dye was added and mixed for a further 10 minutes. The rest of the ingredients then added together and mixed for a further 5 minutes. The ink was then filtered through a 2. 7 glass fibre filter then through a 1 glass fibre filter.

Physical properties testing was then performed on the ink.

Physical Properties Physical Property Crotein Q Crotein O PIF 5 PIF 8 Conductivity (pS/cm) 9190 4900 Filtration (sec) 4. 9 17 Filter Paper condition Clean Clean Surface Tension (dynes/cm) 31. 52 32. 5 Viscosityg25°Cg60rpm (cP) 4. 91 3. 7 pH 7. 6 7. 1 Both PIF 5 and PIF 8 exhibited typical physical properties required for a CIJ ink.

A printer assessment of these two inks was performed using a Domino Codebox printer. The printer was configured with a 75pm nozzle ; a 5um inline feed filter and single line (7x5 dot matrix) print software. Each ink was run in the printer for a five-hour continuous print cycle. During the printer assessment the following key characteristics were monitored : * Gutter performance * Ink Feed pump performance * Jet wander * Jet break up Foaming 'Print Quality Jet Break up : Using a piezoelectric crystal in contact with the fluid to apply a disturbance in the fluid accurately controls the break up of a continuous inkjet ink to produce discrete drops. For single nozzle, continuous inkjet technology, the piezoelectric crystal oscillates at 64KHz producing 64, 000 drops per second. When a voltage is applied to the piezoelectric crystal, it will flex and the degree of flex will depend on the magnitude of the voltage applied. This applied voltage is known as the modulation voltage. The value of the modulation voltage is critical to producing good drop formation. The level of modulation can also affect the shape and position at which the drops break up in the charge electrode which is where the charge is applied to the drops. A variation of the modulation voltage can also create smaller satellite drops. The modulation voltage is dependent on the chemical and physical characteristics of the ink. Drop break up is dependent on- Modulation voltage * Pressure * Viscosity * Temperature of ink * Density of ink Phasing : Phasing refers to the synchronisation of the charge voltage and drop break up position within the charge electrode. The phasing process is a feedback loop to ensure that the charge is always applied to the drop at the exact time that that the drop is formed. Incorrect charging of the drop before or after it has formed will lead to unreliable printer performance and poor print quality Modulation Window : The modulation window describes the range of modulation voltages that can be applied to an ink to produce reliable break up within the charge electrode and good print quality. The larger the modulation window of an ink, the more robust the system becomes, as the tolerance to performance variations in print head components and changes in ink viscosity increases.

Pressure Window : The pressure window of an ink describes the range of operating pressure over which a particular ink will give good modulation and correspondingly good print quality. A large pressure window means that an ink will be less sensitive to viscosity fluctuations during normal operation.

Jet Wander : The stability of the jet over extended periods of time is important to maintain reliable print quality. The degree of instability is known as jet wander and is often described as the degree of deviation of the jet from its starting position.

Gutter Performance : The gutter collects and returns to the main ink reservoir unprinted ink drops. Ink flow in the gutter is a major factor in determining printer reliability.

The flow of ink into the gutter and any potential build up of ink around the gutter is inspected visually.

Pump Performance : The performance of the pressure feed pump and vacuum gutter pump are highly dependent on the properties and stability of the ink. The pumps are carefully inspected throughout a printer trial for any sign of wear or poor performance.

High Voltage Plates : The high voltage plates are visually inspected throughout a printer trial. An ink with poor modulation (generating satellites) or one that has excessive jet wander can cause ink to be deposited onto the high voltage plates. Over a period of time the ink can build up onto the plates and cause"furring."This will eventually lead to poor print quality or the printer will stop running as a result of charge or high voltage faults.

The following protocol was used to prepare the printer before each ink test- * The printer was flushed using deionised water to ensure the ink system was cleaned of any contamination * The nozzle plate was cleaned Jet break up images for the inks were taken. Images were captured to computer using a 64kHz strobe and CCD camera.

Table 5 hours continuous printing Ink Crotein 0Crotein Q PIF 8 PIF 5 Start End Start End Modulation Data (volts) Vmin 10 10 10 10 Vmax >150 >150 >150 120 Vpeak 40 35 57 50 Vset 35 30 50 50 Pressure (psi) Pmin 38 38 44 42 Pmax 54 58 >60 60 Pset 46 46 51 51 Observations Jet Wander None None None None Gutter Vacuum Good Good Good Good HV plates Clean Clean Clean Clean Foaming Some Some None None Jet Break up Good Good Good (low in Good (low in CE) CE) Print Quality Good Good Good Good Print Failures None None None None For both these protein inks, a wide modulation window is observed, a good predictor of reliable printer operation. The pressure window is also wide enough for reliable operation and remained stable throughout testing. The jet was stable throughout the trial and exhibited good print quality. Good jet break up performance with reliable, stable drop formation was seen throughout the testing.

Good print quality was seen throughout the trial. Overnight stop start was also good.

Print samples on several different substrates were taken during the printer performance testing.

Print Quality General observation of the quality of the print on the substrate Substrate Crotein Q Crotein 0 PIF 5 PIF 8 Glass Good Slight Spread Aluminium Sheet Good Good Cardboard Good Good Copy Paper Good Good Inkjet Paper Good Good Aluminium Foil (shiny) Slight Spread Good Aluminium Foil (matt) Slight Spread Good Melinex (White) Good Good Scratch resistance Attempt to remove the print by scratching with the fingernail Substrate Crotein Q Crotein O PIF 5 LPIF 8 Glass Comes off Comes of with difficulty Aluminium Sheet Comes off easily Comes off easily Cardboard Good Good Copy Paper Good Good Inkjet Paper Good Good Aluminium Foil (shiny) Good Good Aluminium Foil (matt) Good Good Melinex (white) Comes off Good Rub resistance Attempt to remove the print by rubbing with the finger. Substrate Crotein Q Crotein O PIF 5 PIF 8 Glass Good Good Aluminium Sheet Good Good Cardboard Good Good Copy Paper Good Good Inkjet Paper Good Good Aluminium Foil (shiny) Good Good Aluminium Foil (matt) Good Good Melinex (white) Good Good These results show that Crotein O and Crotein Q can be used successfully in water based inkjet formulations. There is good jet break up and jet performance ; the print quality is good with good end user performance on the substrates tested.

Inkjet printing systems-thermal inkjet printing The Crotein proteins were used to formulate some thermal inkjet printer inks. A Lexmark 6000 printer was selected for this work as being representative of a typical SOHO thermal printer. The black cartridge (Type 12A1970) was used as the test print head.

The following inks were formulated : Table 6 Formulation PIF 7c PIF 60 Crotein O 3. 5 Crotein Q 3. 0 Projet Fast Black 2 42. 6 36. 4 Diethylene glycol 5. 7 4. 9 Surfynol 104E 0. 1 0. 1 Surfynol 75D 0. 1 0. 1 Water 45. 4 53. 4 2-pyrrolidone 1. 4 1. 2 Ures0350. 3 Glycerol 0. 75 0. 6 The inks were filtered using a 1-micron filter paper before use. To charge the Lexmark black cartridge it was first emptied by a combination of suction withdrawal through the top air hole using a syringe and hypodermic needle and by printing full black pages until no further colour was produced. The cartridge was then charged with lOg of 1 micron filtered deionised water and printing continued. This was repeated 2 to 3 times until an almost colourless print was obtained. The cartridge was then charged with lOg of the test ink and prints made after checking for the number of nozzles firing using the Lexmark printer driver software. A fresh cartridge was used for each ink Using the ink PIF 7c (Crotein O) it was possible to charge the cartridge and obtain 90% success in firing all the nozzles as shown on the test chart. Various test prints were then taken using inkjet and photoquality media.

The quality of print was acceptable. Using the ink PIF 60 (Crotein Q) better quality printing was obtained. The ink tended to dry on standing but could be recovered by printing black blocks or performing a nozzle clean routine. It was possible to obtain-95% success in firing the nozzles. On standing for 60 hours on the Lexmark print head station even better prints were obtained. The number of nozzles firing was >99% and was capable of printing text pages in excess of 20 times continuously.

Inclusion of Crotein O and Crotein Q at significant concentrations into thermal inkjet formulations has proved to be possible. The lifetime of the heads seems to be long especially as demonstrated with by continuous printing with the Crotein Q containing ink. Development of an optimised ink formulation would eliminate any drying of ink in the nozzles It is a significant invention to show that it is possible to use materials such as proteins in a thermal inkjet print head since most thermal inkjet inks contain little if any materials in the way of polymeric binders.

Some work has been published by HP (US patent 5, 814, 683 Hewlett- Packard and Meyer, Bazilevsky, Rozhkov, Effects of polymeric additives on TIJ inks, IS&T NIP 13 1997 Proceedings, page 675ff) on the use of polyacrylamides at ppm levels to reduce the amount of satellite formation by reducing ligament fracture, the disadvantage of these materials is that they significantly reduce the velocity of the drop and hence useable throw distance. The results obtained with the industrial piezo printhead (described below) show that these gelatin derivatives have a beneficial effect on dot shape without reducing drop velocity significantly.

Inkiet printing systems-SOHO piezo DOD The proteins were formulated into inks suitable for piezo DOD printers as found in the SOHO market. The evaluation was carried out in an Epson 440 printer typical of those found attached to home personal computers, this printer uses what is known as a the MACH technology whereby a piezo chip, when activated, flexes onto an ink chamber to produce a droplet.

Three series of inks were formulated : 1. A YMCK set with no Crotein O or Crotein Q present (Inks PIF 38-41) 2. A YMCK set with Crotein Q present (Inks PIF 46-49) 3. A YMCK set with Crotein O present (Inks PIF 50-53) The formulations and their physical properties are given in the Table.

These were then introduced into an Epson 440 printer.

Table Ink Formulations for SOHO Piezo DOD Printer Formulation PIF PIF PIF PIF PIF PIF PIF PIF PIF PIF PIF PIF 38 39 40 41 46 47 48 49 50 51 52 53 1 Crotein 0 1. 5 1. 6 2 0. 7 2 CroteinQ 1. 5 1. 6 2 0. 7 1 3 Bayscript 19. 6 19. 6 Black SP Liquid 4 Projet Fast 65 Black 2 5 Diethylene 6 6 6 6 5. 5 5. 7 5. 7 2. 4 5. 5 5. 7 5. 7 2. 4 Glycol 6 Surfynol 104E 0. 15 0. 15 0. 15 0. 1 0. 1 0. 1 0. 03 0. 1 0. 1 0. 1 0. 1 7 Surfynol 75D 0. 15 0. 15 0. 15 0. 1 0. 1 0. 1 0. 03 0. 1 0. 1 0. 1 0. 1 8 Water 39. 7 39. 7 87. 7 24. 7 47. 5 45. 4 89. 7 77. 3 47. 5 45. 4 89. 7 77. 3 9 2-Pyrolidinone 2 2 2 2 10 Urea 0.5 0.5 0.5 0.5 11 Glycerol 1. 5 1. 5 1. 5 1. 5 12 Projet fast 50 47. 1 47. 1 Magenta 2 13 Project Fast 50 45. 3 45. 3 cyan 2 14 Duasyn Acid 2 2. 4 2. 4 Yellow Filter Paper clean red clean clean clean clean clean clean clean clean clean clean condition ppt Surface Tension 33 33. 5 33 34. 5 34. 5 33. 5 32. 5 33. 5 34 33. 5 33. 5 33. 5 (dynes/cm) Viscosity@25°C 1. 53 1. 55 1. 43 1. 44 1. 58 1. 57 1. 55 1. 55 1. 55 1. 56 1. 5 1. 51 @60rpm (cP) pH 8.95 7.93 7.75 8.35 8.79 7.9 7.78 9.03 8.83 7.85 7.27 9.06 The inclusion of the test materials was found to give a more robust system over the inks without the proteins. The prime was held better and there was greater latitude in relative height difference between the ink reservoir and the print head. Comparing the inks with Crotein O and the inks with Crotein Q, the Crotein Q based inks were found to be better for continuous printing, ease of prime and overall print quality.

Inkjet printing systems-industrial DOD The protein samples were examined in inks suitable for printing with an industrial DOD printhead. A Trident Microcodelm was chosen as the print head, this uses small rods of a piezo material, which contract on application of an electric field and are then allowed to rapidly relax firing a drop through a nozzle.

The formulations, using Crotein O and Crotein Q, were prepared by first dissolving the gelatin in the solvent, then adding the dye and sonicating the solution. The inks were then filtered through Whatman 1 . m glass-fibre filters, after which, surfactants and biocides were added. Before being loaded into a Trident Microcoder print head the inks were degassed by having helium bubbled through them for twenty minutes. The head was primed using a combination of pressure and gentle wiping with lint free cloth.

Table PIF 54 PIF PIF 56 PIF 57 55 Crotein O 23 18. 6 Crotein Q - 19 - 14. 05 Pro-jet Black OA-PZ 12 12 13. 9 12. 9 Surfynol 104-E 0. 5 0. 4 0. 3 0. 2 Surfynol DF-75 0. 15 0. 15 0. 15 0. 15 Proxel 0. 2 0. 2 Water 64. 15 68. 25 80 : 20 Water : IMS 67. 05 72. 7 Surface Tension 33. 5 33. 5 32. 5 32. 5 Viscosity @ 25°C/cP 8. 48 10. 6 9. 23 9. 37 Viscosity @ 35°C/cps 5. 95 7. 66 Drying time on glass was around 25 seconds for the purely aqueous ink containing Crotein Q, and around 20 seconds for the others. Continuous printing was of a much higher quality for the alcohol containing inks. Throw distances were investigated by taking print samples at 2mm, 5mm, 7mm and 10mm distances from the print head. These were then analysed using the ImageXpert equipment to measure the number of satellite drops, and the roundness of dots formed.

The throw distances themselves were quite high-in every case the print was easily legible at 10mm, if quite poor quality, and no shadow image was seen.

Figure 1 of the accompanying drawings is a plot of satellite formation against throw distance for the four inks PIF 54-57. As is shown in Figure 1, satellite formation was considerably lower for the inks made with 20% alcohol than the purely aqueous ones. Also it seems that inks containing Crotein Q are less likely to form satellites than those containing Crotein O. As would be expected, satellite formation increases with throw distance, although apparently to a lesser degree with PIF 56 and PIF 57.

The satellites that are formed by the purely aqueous ink tend to be smaller and this is also true of the actual dots-in other words the droplets of alcohol containing ink spread out more on the paper.

Figure 2 of the accompanying drawings is a plot of dot roundness against throw distance for the two purely aqueous inks PIF 54 and PIF 55. Dot roundness does not vary much with throw distance, but does seem to be better for inks containing Crotein Q. However, the tendency of dots from the alcohol containing ink to bleed together means that dot roundness is hard to quantify for these since they are not single dots. Figure 2 shows the superior printing of the Crotein Q based ink over that which contains Crotein O.

Simply from looking at the print samples, and magnifications of them, it is clear that Crotein Q leads to a better print quality than Crotein O, possibly because its higher molecular weight leads to better drop formation : The samples containing alcohol were much easier to print, probably because they took longer to dry in the head, and in general their print quality was superior to the purely aqueous inks.

It can be concluded that these proteins may be used in formulations suitable for industrial DOD print heads, the formulations can be water or water/alcohol based. Superior results were observed with those inks made containing Crotein Q. Overall, the performance of the protein inks can be modified by chemical derivatisation as illustrated by the behaviour of Crotein Q compared with Crotein O.