some ink recipes.docx

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Some Ink RecipesComplied and written by Claes G Lindblad on May 21, 1998.

I became interested in inks more than 20 years ago, when trying to tame a dip steel

pen to behave nicely. All inks available locally were intended for fountain pen use,meaning they were too runny and too thin for proper scribal use.

The Persian Recipe - my First Ink Attempt

Then I came across an old recipe, once upon a time used by Hassan, a Persian Scribe.It told me to find:

Ingredients

500 g water

5 g salt 250 g gum arabic (see note below)

30 g gall apples, grilled andpowderized

40 g iron sulphate (a.k.a. copperasor vitriol)

30 g honey

20 g soot for stage 3 (see table atright)

Directions

1. Mix the six first ingredients.2. Leave them on a slow fire for two hours and stir

now and then.3. Then add 20 g soot.4. Heat it for another hour.5. Filter and pour into bottles.

It sounded thrilling as well as an easy task. Since I was a newbie, I did not knowwhere to find all strange ingredients, in fact, it took me three weeks to scout themdown. I started, late one evening. Three hours later the moment of truth arrived - butmy concoction did not have the slightest resemblance with ink. Well, it was black, allright, but it behaved much more like a heap of butter, just out from the fridge. Therewas not a chance in the world to 'filter' it through anything, I had to scoop it up with aknife to transport it to a wide-mouthed container with a close-fitting lid.

What did I do Wrong?

Well, the recipe was printed in French, so I had missed the 'slow fire' bit, and hadboiled it for three hours... For this reason, I gave it the name of 'Blusch' (which is anon-existing word, composed of the Swedish words 'Blck' and 'Tusch' = 'Ink' and'Chinese/Indian Ink').


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There is a strange thing in the recipe above, viz. the amount of gum arabic. 250grammes? One tenth of it sounds more reasonable -- but who am I to fight Hassan, thePersian Scribe?

Oh - there is one thing missing in the instructions above, a task which is as boring as

time-consuming: it took me one full hour to clean the pan afterwards... In short, do notstart your alchemistic era with the recipe above. Instead, I recommend a more normal,ferrogallic ink.

Basic Ink Formula

The basic ferrogallic ink formula is very simple: 1-2-3-30 (parts per weight).

Ingredients

1 part gum arabic

2 parts copperas (=vitriol)

3 parts gall apples

30 parts of water

Directions

1. Crush the galls finely.2. Add water.3. Stir. Let stand for 1-2 days in the sun.4. Add copperas.5. Stir. Let stand for 1-2 days in the sun.6. Add gum arabic.7. Stir, sieve and bottle.8. Ready!

An Ink for Hectic Types.

In case you are the hectic type, take a cheap red wine, rich in tannin, instead of water -- and pure tannin instead of galls. Good galls contain about 60 % of tannin (which isthe active ingredient we are after), so use 1.8 parts of pure tannin instead of galls inthe recipe above.

Ingredients

1 part gum arabic

2 parts copperas (=vitriol)

1.8 parts pure tannin 30 parts of red wine

Swift directions:

1. Heat the wine to about 50-60 degrees Centigrade.2. Add tannin, stir.3. Add copperas, stir.4. Add gum arabic, stir.

You will be able to make it in about 15 minutes.


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Regulating the Viscosity

Now, the ingredient which governs the viscosity (the flow) of the ink is gum arabic. Incase you like pointed pens, about *half* the amount of gum arabic would suffice, Ipresume. It is quite OK to make the batch with less gum arabic and then add more

later on, if called for. But it is impossible to decrease the amount afterwards -- and ifyou dilute your ink with water or wine, you will also lose some of its blackness andcovering power.

Where to Find the Ingredients?

GumArabic

is probably the easiest ingredient to find, since it is used in enormous quantities bycandy factories. Certain products contain up to 99 per cent gum arabic - the minuterest is flavourings...

Copperas (iron sulphate, vitriol) is also used by gardeners to kill weed, i.e. a garden centermay be able to help you.

Gallapples

can sometimes be found in stores specialized in items for do-it-yourself yarn dyers.They may also have copperas.

Tanninin its pure form, tannin is probably only found in stores selling lab and chemistrysupplies.

Good luck with your experiments!

Back to Table of Contents.
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From the desk of Rick Bullock Mister Inkjet Pty. Ltd. Australia [email protected]

Technical ReportWater-Based Ink Jet Inks:

A Quick Study

Everyone who works with inks for the office/desk top printer cartridge market realises that theyare water-based, meaning the primary solvent is water. Everyone knows that there are manyother ingredients that add significantly to the performance. What may not be known is how theseingredients are used and how they can affect the overall functionality of the product.The more you know about inks, their raw materials and the processes used to qualify them, thebetter you are able to understand how they work. This knowledge provides the foundation on

which to question your supplier's ink formulation and quality control processes. Knowing thebasics of the technology can assure that you receive the highest quality inks available.Any good ink manufacturer will have implemented a raw materials quality control program,which should be continually monitored and administered. This article covers most of these majorink components, discusses the characteristics each one brings to the formula and the methodsused to test them. While all of them are not used in every ink formula every time, they are thebuilding blocks of the majority of inks in use today. Similarly, there can be more than oneingredient of each type in some of these categories (multiple dyes, multiple humectants ... )

"Major" Components

WaterWater is the major component of ink. Water is the foundation on which everything else depends.So, to build a stable system and limit any outside contaminants, you must first ensure that thewater used is as pure as possible. The use of a water softener or deionising columns alone to treatwater is common with some ink manufacturers. However, such a simplified system can lead toconcerns in several areas including longer-term ink storage. A multi-step purification process ispreferred. These steps may include charcoal filtering, reverse osmosis and UV light purificationto produce water with very minimal contaminants. Checking the water for conductivity is a goodway to test purity. A reading of "O" for conductivity is a good standard to base acceptance.Testing for the contaminants in parts per million is another well-accepted method of determiningwater purity. Testing for purity must be done on an ongoing basis, preferably before each time

the water is used to make ink.

ColourantInk colourants are either dye or pigment. They come in various styles and qualities from a widerange of suppliers. Much of the research for inks centres on the colourant itself and thefunctional characteristics it brings to the ink. Specific dyes and dye combinations requirechanges in other components of the ink to control performance.


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As with anything, selection of a colourant must be based on more than price. Inexpensive dyescan sometimes lead to more work and greater cost in the long run than a pricier purified version.Purified dyes can be pH balanced, filtered, treated by reverse osmosis and/or contain varioustypes of biocides or fungicides that prolong shelf life. Incoming tests on dyes should evaluate, ata minimum, viscosity, pH, surface tension, colour matching and quantitative and qualitative

analysis by UV Vis Spectrophotometry. UV Vis analysis should include a minimum absorbanceat a given dilution and a test for (or the wavelength of light that has the maximumabsorbance). A good additional step includes making specified ink with the new dye and printtesting it against a standard. These steps allow the manufacturer to make a determination on theoverall useability of the material.

Co-Solvent/HumectantCo-solvents and humectants usually, including alcohols and glycols, are added to the ink as anadditional vehicle or carrier for the colourant. They may also be used to control or limitevaporation of the ink. Most glycols are hygroscopic, which means they can remove moisturefrom the air. When added to ink, glycols reduce evaporative tendencies. Since the cartridges and

print heads used in the office/desk top printers are designed to be drop-on-demand, the inks areexposed at the open orifices to the atmosphere.Even when the cartridge is in the "parked" position while the printer is not in use, someevaporation of water from the ink can occur through these orifices. Because of this evaporation,the ink's characteristics can change slightly, including its viscosity or the level of concentrationof materials (less water, more dye, more surfactants ... ).The shift in ink characteristics can cause some of the orifices to become partially or completelyplugged and result in a line print defect until the cartridge is cleaned. Humectants reduce theevaporation at the orifices and thereby reduce clogged print heads resulting from evaporation.Humectants are usually tested for viscosity, surface tension and specific gravity. If there arequestions concerning the test data received on a humectant, an ink can be formulated and printtested to confirm the acceptance of the material.

"Other" Components

Fixative/PenetrantThe fixative/penetrant component can be a number of materials all designed to facilitate the inktravelling to the paper. Once the ink is in the substrate, these materials can also fix or hold theink and can reduce feathering or wicking tendencies to a certain degree. Fixative/penetrantmaterials must be added in a controlled amount to be sure the ink does not permeate the substratetoo quickly, causing the colour to be seen on the back of the page.

SurfactantsSurfactants are added to adjust the surface tension of the resultant ink. If the surface tension of anink is too high, the ink may not wet (or travel) through the cartridge correctly. Sporadic printingmay occur under some high use conditions. A high surface tension also may cause the ink to notwet ' out (or penetrate) the substrate effectively, resulting in uneven prints and longer dry times.If the surface tension of an ink is too low, it could drip out of the cartridge and cause flooding ofthe print head at the orifices during use. Low surface tension can also cause the print to wick orfeather excessively on certain substrates and as a result the character will be fuzzy. So, thesurfactant must work in combination with the penetrant or fixative. The ink must travel out of the


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cartridge effectively and print evenly. Once on the substrate, it must be absorbed into thematerial quickly to adhere and reduce dry time but not so fast that it goes through the paper orfeathers excessively.

Resin

Resins are added to give a specific durability to the printed character. Once the ink dries on thesubstrate, a resin can give it additional abrasion resistance. This effect is not always needed but isavailable. Care must be taken when resins are used because they can cause additional plugging ofthe orifices. If there is some evaporation at the orifices, the resin could cause a "film" to formand result in line defects in the print.

Biocides/FungicidesSince inks are water-based and can be stored for long periods of time, biocides and fungicidesare added to eliminate growth of bacteria and fungus in the materials. When these are added, caremust be taken that other attributes of the ink, like pH and surface tension, are not adverselyaffected and the overall performance remains the same.

Buffering Agents/OtherThese materials are used to add or control specific characteristics to the ink. For example, somedyes require pH control for longer-term storage so a buffering agent is needed to maintain therange required. Other characteristics include corrosion resistance and ink flow rate.As you can see, your ink manufacturer needs to understand the "balance" required to make andmaintain a high quality product. Having a working familiarity yourself can only enhancethe dependability of the product you sell to your customers.

Water-Based Ink Jet InkIngredients Amount FunctionWater 50%-90% Ink Solvent

Colourant 1%-15% Colour SourceCo-Solvent/Humectant 2%-20% Ink vehicle, prevents evaporationFixative/Penetrant 0%-10% Assist fixing the ink to the substrateSurfactant 0.1%-6% Surface tension and wettingResin 0.2%-10% Durability and adhesionBiocide 0.02%-0.4% Prevents bacterial growthFungicide 0.01%-0.4% Prevents fungal growthBuffering Agent 0.05%-1% Control ink pH levelOther 0.01%-1% Controls ink specific characteristics

Australian Universal Inkjet Specifications

Equipment used in conducting the following test:


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Surface tension Tensiometer with 6 cm ringViscosity Brookfield Model LVT with UL

Adapter 72 degree temperature.pH PHEP #3 ATC MeterColour Draw Downs Leneta #806 draw down meter

CYANpH 7.0 - 8.0Surface Tension 34/40 DynesViscosity 1.7 - 2.0

MAGENTApH 7.0 - 8.0Surface Tension 34/40 DynesViscosity 1.7 - 2.0

YELLOWpH 7.0 - 8.0

Surface Tension 34/40 DynesViscosity 1.7 - 2.0

BLACKpH 7.0 - 8.0Surface Tension 34/40 DynesViscosity 1.7 - 2.0

LIGHT CYANpH 7.0 - 8.0Surface Tension 34/40 DynesViscosity 1.7 - 2.0

LIGHT MAGENTA

pH 7.0 - 8.0Surface Tension 34/40 DynesViscosity 1.7 - 2.0

The reality is that most inkjet cartridge manufacturers make inkthat falls in these ranges. Some, about 10%, fall out side ofthese specifications however, when mixed with our ink the resultis to normalize the pH.Viscosity and surface tension are the same foreveryone. HOMELINKS
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The relatively direct use of ink in an inkjet looks like a huge advantage for all sorts ofprinting tasks. In principle a thin bar of printhead fed with ink could produce anythingfrom a school essay to wallpaper with each individual dot placed as it has been told bya computer. There is a lot of potential, for instance:

Books could be printed on demand - something happening on a limited scale now, butwith low cost inkjet machines this could be done on bookshop or print-works scale.

Newspapers and magazines could be written for the reader - addressing their specificinterest areas - and obviously with much better targeted advertising.

Personalisation can be applied to any surface - not just wallpaper but clothing and carbodies. Personalised number plates would seem a bit naf if the whole paint job couldbe unique.

Commercial printing is moving in this direction. Scitex have high speed colourprinters. Heidelberg can add an inkjet personalisation unit onto their presses. In 2006the majority of printing is still done with conventional presses but the market isswitching around to digital methods. Big commercial printers can be based on inkjetor laser methods. Inkjets have the advantage that they use straight forward directmethods and "digital inks" are a thinner version of conventional printers ink. Laserprinter processes need several stages.

Low cost home computer printers are opening up all sorts of new possibilities. Homeprinters are commonly aimed at photography; business printers at letterheaded

correspondence, personalised mailings from databases and catalogue production.

Perhaps one of the problems with inkjets is that people expect one kind of cartridge todo too many things. A cartridge good for colour photography is not ideal for printingout low cost text. Neither will be very good for labelling CDs or pickle jars. There is agrowing market for specialised cartridges but perhaps printer makers aren't helpingthe market as much as they might. If you need a special cartridge where do you keep itwhen not in use? The foil pack it came in has been opened - perhaps it would be betterif manufacturers shipped them in tins?. A part used cartridge should probably be keptcool - would putting it in the fridge help? Inkjets would be less troublesome if people

knew what was going on.

A limit at present is that highly coloured fluids that might go through an inkjet headall have a tendency to clog. At the moment human ingenuity stumbles just trying toget an inkjet fax machine cartridge to last a week without streaking.

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adopted brushes rather than pens. The brush can hold a much thicker material thatholds its colour better - paint is pigment in varnish. Brushes were good for Chinesecalligraphy as well - relatively complex characters holding a lot of meaning. Latinalphabets work better with small characters and suited pen and ink.

For printing with presses new inks were needed. Soot, turpentine and walnut oil madea greasy ink paste that worked quite well.

Inkjets really only became practical in the 1970s. Drop on demand inkjet printing

relies on computer intelligence continually generating the pattern to be used. Inkjet isa new application method, so it may take a while to develop the best possible inks.

Scientific Colours.

Old formulations for inks, dyes and paints were largely serendipitous discoveries byalchemists. German chemists in the later half of the 19th century began to besuccessful with long-lasting colour dyes.

Ink and dye are clearly related - things which will dye a cloth might be used as an ink.However the process to dye clothing can use strong alkali, acid or high temperature.The cloth can be treated with alum mordant. Any treatment is acceptable as long asthe colour persists but the cloth is left wearable. Ink usually has to applied withoutextreme force, heat or chemical reaction - although laser and thermal printers do use acertain amount of heat, pressure and chemistry .

Parker "Quink" - quick drying ink - is often considered a breakthrough. To get thequick drying properties Parker used a solution including isopropyl alcohol and water.

The rapid evaporation of the isopropyl part reduced or eliminated the need for blottingpaper. Quink did, however, need a new design of pen because the isopropyl damagedthe plastics of most other pens. Parker made more money from the ink than the pen - arelationship inkjet manufacturers have carried on.
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Modern Inks.

Inks for modern digital printers come in several forms. Just as inks, dyes and paints

are inter-related so are printer materials.

Laser printers use solid powders. The carrier is a plastic such as styrene, acrylateor polyester resin mixed with colourant and materials to give the right electrostaticproperties.

Thermal printers use waxes or resins mixed with the colourant. The printheadlocally melts material to transfer it to paper.

Impact printers use a greasy ink held in a ribbon. Impact printer ink is often mostlike traditional printers formulations.

Liquid inkis a dye or pigment mixed in some kind of liquid carrier. The liquid inksused in most inkjet printers owe more to modern industrial chemistry than to alchemy- but there is still a bit of both. The primary aim is to colour the paper, doing thisneatly, reliably and repeatedly using a printhead with hundreds of tiny chambers firingthousands of times per second is difficult.

An ink can have several components matching it to the mechanism that will beapplying it. They include:

Colourant - is what the rest of the ink is there to deliver. It can be a dye or apigment.

Carrier - or "base" is the liquid that transports the colourant to its point of use.Usually the ink is mainly carrier and the carrier is mainly water.

Other Things - Surfactants, Buffer, Biocide, Chelating Agent, Defoamer,Solublizer.

Modern inks are quite intriguing but unfortunately the actual formulations are often

the basis of some industrial fortune - so they aren't made public. Hewlett Packard'sformulation is just as secret as that for Coca Cola - and possibly even more widelyimitated.

Amateur sleuths can take a drop of ink and some damp filter paper and attempt tofigure out the formulation using liquid chromatography - dye based inks develop all
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sorts of coloured rings. The major inkjet makers maintain labs to reverse engineer oneanother's products - although they get annoyed when people crack their own secrets.

Colourant.

Light is electromagnetic radiation visible to the human eye. Colours are wavelengthsor frequencies of electromagnetic energy often characterised in particle form as"photons". Photons hitting the atomic structure of an object can be:

absorbed -raising its temperature so the energy is re-emitted at a much lowerfrequency.

reflected - bouncing off (which involves creating a localised electromagnetic field).

absorbed and immediately re-emitted at a different frequency - as with fluorescence.

These effects happen at the level of the "wavelength" - about 380 nanometres forviolet and 740 nm for red light. The nature of the material influences what happens,which is what makes sight such a useful sense. Sight is a way of remote-sensing thenature of things.

Film, TV, painting and printing are ways of misleading the eye about the nature of

things.

Film and TV add light sources together - usually red, green and blue.

Painting and printing subtract and absorb light from what will be reflected. Forinstance, magenta ink (which looks and is red-blue) absorbs the green and reflects theother two colours.

Colourants are often classed as dyes or pigments. The distinction between dye andpigment is rarely clear to the end user, but often made in discussion about materials.
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Dye - a coloured liquid. The colouration comes from molecules of somesubstance(s) dissolved in the liquid. Because the dye is a pure liquid itshouldn't clog even the smallest channels of a printhead - which is a veryhelpful property.

A simple test for a dye is that it passes through filter paper unchanged. Ifthere is a deposit left on the paper that isn't just staining with the dye andwon't wash through then there are other components - gels perhaps orpigments.

Dye carrier diffuses into paper, dries andleaves the dissolved material behind.

A dye will soak into the paper which should help give a zone of colour that is noteasily removed. Because the dye sinks in a lot of dye may be used in printing. If theabsorbency of the material is not what was expected the image may feather or bleed atthe edges.

Dye on paper that sinks into the fibre is lost to view and makes less contribution to thereturned light. The liquid component will first be absorbed, then it will evaporateleaving small dry crystals of material behind. The cover and distribution of thecrystals gives the strength of colour seen. Because the material is deposited so finely itshould look even.

The colour of the dye is generated at a molecular scale. Exposure to ultraviolet lighttends to break the molecules and hence the colour down. If the dye reacts with aningredient in the paper it may also change colour. Ozone, O3 which is a small butnatural component of air will also react with dye components - probably turning themto grey oxides.

Paper designed to take up dye well needs a certain amount of filler to trapthe dye material close to the surface where it will be seen. Dye that sinks

below the fibres is lost to sight. The small crystals and infilling in cracksin fibres should mean that a dye adheres to the paper fairly well, but itmay not colour it all that intensely and may fade quite quickly.

The latest generation of inkjet dye based inks intended for photography claim verylong stable lives - HP says 108 years.


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The liquid nature of a dye is obviously a good thing in an inkjet since it shouldn'tblock the nozzles.

Pigments - are particles with the required colour. In an ink its asuspension of particles in a liquid.

The particles are not dissolved. Small particles will stay in suspension easily due toBrownian motion but very small and regular particles may not be easy to make.

Pigment particles are often a fine powder - the product of grinding a mineral forinstance.Emulsification can also be used - chemical compositions precipitates out of solution.

Carbon black is the most common pigment - used in inkjet ink, laser toner and manyother black things like vehicles tyres. The production process is basically smokycombustion of oil.

To prevent particles being inclined to separate out they need to be reduced to a scalewhere they are just several microns across. This suits inkjet heads as well, the nozzlesin a head may be 10 microns across. A possibility with fine powders is that they maybe uneven and block a nozzle or may flocculate.

Most of a pigment settles on top of the paper, which means comparatively little needbe used to give colour. A further advantage is that the pigment material is usuallychemically inert and less vulnerable to ultraviolet. Something in the liquid may beneeded to bind the pigment to the paper.

Pigment carrier diffuses into paper. Particles ofmaterial are left on the surface.

Pigments are usually divided into two groups - inorganic and organic

Inorganic pigments are minerals. Iron gives red and green colours. Cobalt andtitanium salts are used for other colours. Chrome salts are popular - they give a widecolour range. Lead became unpopular because white lead in paint and tetraethyl lead
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in petrol created political storms. Some lead salts are insoluble and biologically inertso they could be used but are banned.

Organic pigments are derived from chemical reactions, normally using an oilfeedstock.

A potential disadvantage with pigments is that some change the texture of the paper -the collection of crystals on the surface can be visible giving the paper an odd mattfinish.

Paper designed for a pigment might ideally have a bit more texture to actas traps and filters for the particles.

At the moment most inkjet inks use a pigment black (carbon black) but dye basedcolours. Epson is using pigment based colours in the Ultrachrome ink for the StylusC66 and Stylus Photo R800 and claiming a stable life of 80 years for them.

Colours.

People have colour vision so they ideally want something more flexible than a blackcolourant. The human eye has three types of colour sensor and can be "fooled" intoseeing colours by changing the mix of wavelength that each receives. There are twoways to do this:

Additive colour builds the colour wanted using Red, Green and Blue lights on a darkbackground. This gives the RGB method used by screens.

Subtractive colour removes the unwanted colours from white light reflected from apage. Subtractive colour uses Cyan, Magenta and Yellow colourants so this is calledthe CMY process. As it happens people do use blacKfor a lot of purposes, so mostprinters also have a straight, simple black ink. Most colour printers use a CMYKprocess.

Nature does provide a reasonable source of black pigment - carbon black which isessentially a specially produced soot - so ink still has some of its traditionalingredients.
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Cyan, Magenta and Yellow are more difficult. The chemicals and processes usedoften appear to be proprietary secrets.

Liquid Carrier.

Inks use a liquid carrier that evaporates or is absorbed and a colour that remainsbehind. The flow characteristics of the liquid - its viscosity, surface tension andcapillary action are important in transporting the colour. Once the colour has arrivedthe liquid should disappear.

Inkjet inks seem to use quite a large volume of carrier, which acts as their propellant.

Water is the obvious liquid. Water will dissolve the widest range of materials, isodourless, is absorbed quite readily by most materials and evaporates quite slowly.

Disadvantages are that water reacts with metallic components in any inkingmechanism. Water evaporates so slowly it can break up the fibrous mat of the paper ifa lot of ink is used. Most inks are 60 to 90% water.

Alcohols will dissolve waxes and other organic materials and will carry pigments.The advantage of alcohols is that there are several types and most evaporate quitequickly. Isopropyl alcohol was a component in "Quink" and remains popular in inks.Isopropyl does react with some plastics.

Oils will also dissolve waxes and organic materials and carry pigments. Oils generally

don't react with metallic components - but do with some plastics, like organicpigments.

Water and alcohol in solution have some of the properties of each in proportion tothe mixture. Water and alcohol also have different surface tensions so mixture canvary the energy input needed to eject ink. Most inkjet inks are mainly water basedwith some isopropyl alcohol, ethylene glycol and other volatile organic solvents suchas ketones.

The carrier is an essential part of all inks - they need the right characteristics of

viscosity and surface tension. Thermal inkjets additionally need the ink to vaporiseand condense in the right manner.

Other Ink Components.
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Water, alcohol and a pigment colourant may not mix, or if they do so the pigment maynot easily flow, may flocculate and turn into a gel, or settle out. Ink has various minorcomponents to make it workable.

Surfactants are usually the main additional component

Buffer, Biocide, Chelating Agent, Defoamer, Solublizer.

New Scientist 20th Feb 1999 has an article outlining the problem of manufacturingreliable polymers from the dozen or so groups of monomers and a new "VladimirInitiator" which improves the process. The discovery has immediate application inphotolithography where the erratic length of ordinary photoresist polymers has tendedto spoil sharp features. Another application is in block copolymers used in inkjetprinters. Inks contain polymers which are soluble at one end, insoluble at the other.The insoluble end of the polymer attaches to a carbon black, the soluble portion forms

a shell around the pigment so it can be suspended in water. The new Vladimir initiatorwould produce better polymers more cheaply.

The article doesn't seem directly accessible, but use this link to New Scientist andsearch for "vladimir initiator"

Inkjet Inks.

When Frank Cloutier and his team at HP were developing their first inkjet printer itseems that they weren't initially all that interested in the ink itself. The initial focuswas on the novel delivery mechanism. They wanted the ink in a cartridge so userscould keep their hands clean, but initially thought ordinary fountain-pen ink would do.

In fact the main benefit of the inkjet printer is the cheap basic mechanism and the wayit can handle colour easily.

Problems are outlined in the following list:

Thermal inkjets need to vapourise the ink violently. The temperature reached seems tobe of the order 300 centigrade. This creates sufficient pressure to overcome viscosityand surface tension. Ink carrier is acting as a propellant.

Piezoelectic inkjets pump ink mechanically so ink composition isn't a major issue - the
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two office printer types are the Epson series which uses aqueous ink and the XeroxPhaser which uses molten wax. Air locks are a problem.

Viscosity and surface tension have to be right to flow through the manifolds, chambersand - under pressure - the nozzles. Ink should not flow through the pads and pressurerelief holes

Ordinary inks in a thermal head produce "kogation" - a build-up of scale on the heater-resistors in thermal cartridges.

The chemical composition of the ink attacks adhesives such as the silicone sealantinitially used to glue the cartridges together.

Ink attacks metal and plastic components. It also proved possible for inks to dry outthrough the plastic body.

Ink particle size becomes very important as nozzle size is reduced. At 1200 dpi the dotson the page are 20 microns across and the nozzles of the printer are probably less than10 microns. A fragment of dust in the ink would completely block a nozzle.

Air bubbles will break the capillary action that maintains ink flow in the head. Bubblemight migrate into the channels if a cartridge is inverted. Dissolved gasses or air in theink is highly likely to separate out with the pressure waves near the printhead nozzles.

Colour stability on the page is important and until recently inkjet inks have notdelivered it.

So whilst "Quink" might work in an inkjet it usually isn't ideal.

Merits

Inkjets are in some ways a very favourable environment for ink handling. Thematerial is normally delivered in a carefully designed tank or cartridge that remainssealed until it is about to be used. The tank isn't usually very large, partly because ithas to be mounted on the carriage and would make it heavy, but also becauseprintheads don't last terribly long. Manufacturers may also have an eye to profits. Inprinciple if the ink needs ultrasound or heat to activate it that can be supplied - thoughso far these potentialities haven't been much used.

The ink will be delivered in droplets measured in picolitres from tubes less than 100th

of a millimetre across (at 2500 dpi). The ink mustn't settle out or dry in the tubes.Most importantly, if it is used in a thermal printhead, the liquid component needs tovapourise easily when a heater turns on then condense rapidly when it turns off.

Besides a strong colour there are two premier properties required in inkjetformulations: mobility in the head and immobility on the paper. Whilst the ink is inthe printhead it should be very mobile and not adhere to or react with any of theworking parts. In a thermal printhead the ink must also contain a component that will


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evaporate suddenly when the element heater is tuned on so the ink ejects. When theink hits the paper it should ideally turn to stone, any flow within the paper beyond thatneeded to make it adhere is undesirable. Xerox "Phaser" solid inks match this needrather well.

Printer manufacturers generally rely on absorption into the paper and evaporation todry the ink. Absorption is the main initial route. If the paper is not absorbent, thecarrier evaporates slowly or the dye is a solution when the printer design called for apigment then the ink will smudge in the paper. Material in suspension will settle outmore quickly and not disperse through the paper. If ink diffusing into paper is a realproblem then heating the paper will help the HP1200C uses a halogen lamp to drivewetness out of the paper just after printing.

Target properties include:

Precisely reproducible colour and colour density Correct spreading qualities (viscosity, surface tension and electrostatic) Mixable with other colours Chemical inertness especially to other inks and to common paper ingredients Insolubility once used, Colour stability in ultraviolet,

This combination of properties is a tall order, but unless ink matches these criteriareasonably well a printer will perform badly. Mixing cyan and yellow inks shouldgive greenan ink composition that gives brown streaks due to a chemical reaction

would not be acceptable. Paper components could also react with a dye and this wouldbe equally undesirable. Equally unacceptable are inks that fade, are eaten by microbesor bleed into the paper.

Older generations of inkjet ink weren't stable, particularly if they were used unframedas pictures in a sunlit place. Recent inks like Epson's UltraChrome and HPs 343/344ink are extremely stable when used with the right paper.

--

Graham Huskinson 2010

This page is like all those in the "book" section in being under development.

If you think this page is wrong in some respect or have better information on howthings are done let us know. Clickhere.
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