Ink

Ink for the writing

They are liquid substances resulting from the setting in organic solution of dyes of origins , Végétal E, Minéral E or Chimique, in a Solvant.

the invisible Ink or invisible ink is a substance becoming visible only by one later action on the support of writing (heating or vaporization of chemicals).

Inks for the drawing

An ink of quality is measured by its fluidity and its fixity. Also, it must mark paper, either while being impregnated there, or by leaving there a trace which dries quickly on the surface. What attracts the draftsman towards a black ink is his chromatic power.

the ink of nut gall appears at the 12th century; it was initially employed in writing. It is an ink of an excellent quality and manufactured in great quantity.
the Indian ink offers an optimal quality in the field of the durability and the glare of its color. The true Indian ink is of a pure black and brilliance. It is introduced in Europe as of the Middle Ages, and is sometimes used in the manuscripts former to the 13th century. It is a rare and very expensive ink; It is obtained by the dispersion of Carbon black in an aqueous solution added with Gélatine.
the bistre is recommended to the miniaturists who seek to create effects of transparency. Because of its less intense coloring, it does not return the depth with conviction and does not authorize features of a great strength of character.
the inks of color are used in the illustration of books or the decorative drawing. But one should not confuse inks of color with the colors of the watercolour.

Ink for printing works

Presentation

Inks for printing works, although homogeneous, are in fact a mixture of components. Certain formulas of ink can contain up to 20 different components. However, whatever the process of impression, one can divide these components as follows:

dye (from 5 to 25% of the weight according to the type of ink): one generally uses Pigment S very finely divided and maintained into suspension in the vehicle. It also sometimes happens to use dye S which have the best returned color (Gamut) but which is degraded more quickly with the light;
the vehicle (approximately 70%): it is the liquid phase of ink. It consists of a mixture of Polymère S, thinners and/or of Solvant S. Its role is multiple: to transport the pigment/coloring on the support and to fix it at this one. The choice of the vehicle determines not only the mode of drying but also the main features of film of ink (resistance, adhesion…) ;
the additives (approximately 10%): they make it possible to optimize the characteristics of ink during and after the impression. They are also used to facilitate the implementation of ink (agents dispersing, antifoaming, etc)

According to the process of impression, ink can have a very different aspect. For example the offset requires a viscous ink (or pasty) whereas the Héliogravure, the Flexographie, the Sérigraphie and the Jet of ink require an ink definitely more liquid.

Various types of drying

The principle of the impression is to deposit a fine layer of ink on the support (that it is Papier, plastic film or other). This layer of ink must have a good cohesion and a good adhesion with the support.

One can consider two types of dryings: physical drying and chemical drying, but the two types of drying can be used simultaneously, the goal being of course to reduce the time of drying and the consumption of energy.

Physical drying (or coldset )

Here, the vehicle of ink or at least part of this vehicle, generally the species of low molecular weight like solvents, water in the case of aqueous inks, will penetrate by Capillarité in the support. The Pigment S and some other components of the formula remain on the surface. Ink does not dry strictly speaking, but its viscosity increases at such a point that it can apparaîte dry with the touch.

This drying, known as coldset (cold drying), is mainly used on the rotary presses of press (Papier S newspapers) and always with porous supports. For this reason one can have ink on the fingers by rubbing a newspaper.

Chemical drying

Ink, in contact with the air undergoes a Oxydo-polymerization which leads to a dry film of ink.

The elements likely to polymerize are plant oils (flax, Colza, Tung…) and of many derivatives of these plant oils like the alkydes (polyesters modified with plant oils). These species in common have the presence of double unsaturated connections carbon-carbon likely to react with oxygen in air, in the presence of Catalyseur S metal (salts of Cobalt or Manganèse for example). The Polymérisation can be very long (8 to 12 midnight, sometimes more) and one can possibly accelerate it using driers with Infra-rouge S (contribution of heat).

The products given off by the Oxydo-polymerization (Aldehyde S, Ketone S and carboxylic acid, inter alia) often cause unpleasant odors and prevent the use of chemical drying for food packing.

Mixed drying (or quickset )

It associates physical drying (by penetration) and chemical drying (by Oxydo-polymerization).

Part of the vehicle, primarily the solvents, is initially absorbed by the porous substrate, which leaves a film of fresh ink on the surface. This one goes, in the second time, to dry by Oxydo-polymerization, in a few hours generally.

The addition of driers with Infra-rouge accelerates the reaction but causes a rather strong consumption of energy.

A hybrid drying of the same type associates the evaporation of solvent (drying heat-set) and Oxydo-polymerization.

Thermal drying (or heatset )

It combines at the same time drying by Infiltration and drying by evaporation. Part of the vehicle of ink is absorbed by the support (10 to 20%) and the other part evaporated in furnaces heated between 100 and 200 °C. The furnaces are supplied by Gaz (Butane, Propane, LPG…) or Fuel.

The evaporated products must then be recovered not to be rejected into the atmosphere.

Drying by Ultraviolet radiation (UV) or Electron Beam (EB) electron beams

The polymerization of inks with drying UV is initiated by the light UV which cleaves a Photo-initiator thus giving rise to very reactive species (electrons or cations). Those immediately induce a reaction of polymerization of the Monomère S and Oligomère S reagents contained in ink. Polymerization generally takes place by ridicalizing way and more rarely by cation way.

The polymerization of inks with drying EB is initiated by a beam of electron S. Of share concerned energy, ink with drying EB can be formulated without Photo-initiator. Apart from this compound, the formula is rather similar to that of an ink with ridicalizing drying UV. Drying EB requires an inertization (use of nitrogen) to avoid the inhibition of the reaction of polymerization by oxygen in ambient air.

The advantage of these systems is that one can obtain an ink dries quasi instantaneously and without spending much of energy. Moreover, the film of ink is very resistant to abrasion, ageing, all kinds of chemical agents like to moisture…

N the other hand, systems UV or EB are less changeable (they are not compatible with all the pigments), they are less stable with storage, they often contain irritating ingredients, which requires additional precautions during the handling of inks and can pose problems with de-inking.

These inks are very much used in packing and allow the impression on not very porous supports (PVC, art paper…)

offset

In offset: ink is fatty because the process rests on antagonism water-ink. It is very viscous (does not run). The various modes of drying of ink will influence its composition: Drying UV, Hot-melt… They has a Viscosité consequently: 2 to 40 Pa.s

Composition

The Pigment S

The process offset allows the deposit of a very fine film of ink. So the pigments must have a very good coloring capacity. Moreover, they must be compatible with the solution of damping which makes it possible to create a emulsion between water and the ink .

The nature of the printed paper form, from its use, can also influence the choice of the pigments (transparency or opacity, behavior with the light, moisture, resistance to chemical agents, constraints toxicological

The vehicle

It is about the heart of ink, it is what will bind the pigments between them and also with the support. Generally, one uses a mixture made up of one or more hard resins and more fluid materials commes of plant oils or oil distillates (the latter tend to being reduced for obvious environmental reasons).

plant oils are the historical components of inks, Peinture S or varnished.

the Linseed oil is the most used plant oil. It is extracted mechanically or by action from a solvent. It is produced with the E. - U., in Russia, Argentine and India. According to its source, it has different properties. It is necessary to purify it before its use because it contains impurities (tannins…) who can harm ink.
the oil of Tung is extracted from almonds of the fruits of the wood of Tung. It with the property to be appropriate well for inks for fast drying.
the oil of Soja is, with the linseed oil, the oil most used in the field of the Imprimerie. It is obtained starting from seeds. It is the oil most abundantly produced with the E. - U.. It can be used without purification and is appreciated for the improvement that it brings to damping pigments.
the oil of Tournesol is mainly used to prepare resins alkydes.
the oil of Colza is manufactured with genetically modified seedlings.
the tall oil is under product of the delignification of the Résineux. During the manufacture of paper the Pulp kraft or bisulfite, the resins and greasy substances contents in wood form resinic fatty-acids and salts. After treatment, it can be used in the manufacture of inks.

the oil distillates made great great strides as from the Second world war and are largely used because of their low costs. One finds them in particular in the impression of the newspapers. However the oil crisis of 1973 and the strong ecological pressures reveal new products containing plant oils. Although always used, these inks are subjected to a severe regulation.

Additives

The simple combination of a vehicle and pigments gives only inks of poor quality. To improve those, one has recourse to the additives (less than 5% of the mass). Those have various roles: acceleration of drying, improvement of the brilliance, better resistance of film of ink…

One finds among these additives:

the waxes (animal, vegetable or mineral) which in the beginning were incorporated in inks to reduce the Tack of it. Currently, the purpose of the synthetic waxes dominate the market and are to improve the surface quality of inks (abrasive resistant, coefficient of friction of film of ink…).
siccative the is Catalyseur S of the oxydopolymerisation of inks. They make it possible to largely improve time of drying of inks of the type quick set . They are generally metal salts such as the Cobalt and the Manganèse.
the antioxydants make it possible to control the oxydopolymerisation of inks offset. They tend to reduce the formation of skin to the surface of ink without however obstructing the drying of this one.
the anti-mackling compounds are particles of Silice or Amidon of which the thickness is slightly higher than that of film of ink. Their use makes it possible to reduce mackling (wet carryforward of ink of the back on the recto of the following page).

Inks with solvents: Photogravure and Flexographie

In the Photogravure, an ink with weak Viscosity (5 to 50 mPa.s) and with very fast drying is necessary. The evaporation of one or more rather volatile solvents is thus the method of the fastest drying and most economic currently. However, the use of these solvents is not without risk: they are generally very flammable and sometimes poisons. Their use requires great precautions, and they are covered by a very severe regulation. Research to develop inks with water is in hand, but the results are not yet satisfactory.

The Flexographie is a process in relief on which the printing form is a flexible photopolymère. The size of the relief is about the millimetre. The flexography is mainly used in packing, specification coming from the advantages which a process of impression can have whose printing form is flexible (corrugated cardboard, plastic bags…). It is also used for the impression of the daily newspapers (in Italy for example). Contrary to the Photogravure, the flexography succeeded in adopting inks with water.

Mode of drying

The drying of inks photogravure or flexography is done by evaporation forced of or solvents at the time of the passage of printed in a furnace with hot air. The furnace must be dimensioned according to ink (temperature of evaporation of the liquid, its saturating steam pressure, its latent heat of vaporization…) and of the machine (Width, speed…).

In practice, one accelerates evaporation by the average following:

By Conduction: the reel passes on heated cylinders,
By Convection: the reel passes through driers to hot air,
By radiation: infra-red radiation or Microwave. There is then caloric intake; not to confuse with Ultraviolet drying which, implies chemical changes of ink to him.

Physical drying (by absorption of ink by the support) requires a porous support (Papier or paperboard) and cannot be used on other supports.

Solvents used

The solvents contained in these inks are only temporary because they are eliminated by evaporation and/or infiltration during drying of the printed paper form. So they do not take part theoretically in the final properties of film of ink. However, it happens that residual solvent is prisoner and he results from it from the problems of odor, of toxicity…

the solvents most used in photogravure packing are:

alcohols
Acetone
Acetate S
ethers of aliphatic Glycol
Hydrocarbon S

In photogravure edition , one uses almost exclusively Toluène

In flexography , one uses:

alcohols
Acetate S
ethers of Glycol

Polymers used

The addition of Polymère S makes it possible to improve the properties of film of ink, in particular its adherence with the support, its solubility with solvent chosen, its brilliance, its resistance and its damping of the pigments.

One uses amongst other things:

Nitrocellulose
Ethyl cellulose

Additives

the waxes change the surface quality of film of ink. They in particular make it possible to increase the friction resistance, to improve slipping it…
the mineral loads to correct viscosity
the plasticizers to give flexibility to film of ink.
the surfactants increase the damping of the Pigment S

Jet of ink

The process Jet of ink can be divided into two categories: the continuous jet (Continuous Ink Jet CIJ) or the drop with the request (Drop One Demand). Those having also various methods of ejection (see Jet of ink). Of this fact inks must be different.

CIJ requires very a good quality of ink, with the risk of stopping the tubes of ejection. It is generally necessary to find a compromise between the performances of the printer and the quality of impression. An ink always consists of Solvant, dye, a binder and additives.

The solvent , also called vehicle is used to transport the ink of the tank until the media. It contributes also largely to drying. The Volatilité of solvent is determining in the drying of ink: a not very volatile solvent can involve problems of drying and too volatile is likely to create a skin on the surface of the drop what will limit in-depth drying. In order to determine the time of drying well, one generally uses Méthyléthylcétone (MEK), Acétate S, ether glycol and alcohol S. the use of these solvents poses obvious environmental problems. Research currently develops inks containing water or of Encre UV.

The dye is the substance or the particles which give the color of an ink. At the beginning one used mainly dyes which were to be very soluble in solvent in order to avoid any drying inside the capillary. They must have a good behavior with the light and not use a Heavy metals. The new tendency is to use very fine Pigment S (<1µm). But those pose problems because they arrive at stopping the tubes.

The purpose of the binder is to ensure the cohesion of ink and to control its Viscosité. It ensures the adhesion of the dye the support. It is about one of the components most difficult to proportion in the formulation. Phenolic resins formerly were used but those Ci did not age well and stopped the print heads. Currently one moves more towards the use of Copolymère S.

The additive are also determining in the quality of ink. They are however in negligible quantity (less than 1%). They seek to improve the Fluidité, the Adhésion, the Rhéologie of the binder or the Conductivité of ink. Conductivity is a crucial factor in the Jet of ink CIJ. It is then necessary to control this parameter well.

Inks with water

The legislative and environmental pressures pushed to develop inks containing water and either containing solvent. Indeed inks containing water offer a good means of meeting the legal requirements and improve the work conditions. Moreover they make it possible to reduce the costs of the reprocessing of solvents.

They first of all were largely spread in Flexographie and start to develop in Héliogravure. The supports first of all were of the porous supports such as the Papier and the paperboard and they were thus limited to packing and the daily press. But today, these inks make it possible to print on supports varied such as the polyester films.

Note:: Of the hybrid systems starts to appear which combine inks with water and inks UV (see further) . They have then the advantage of inks UV while being nettoyables with water. These inks are applicable in fine layers for the Flexographie and the Héliogravure or in thick layer as for the Sérigraphie.

Characteristics

*Composition:

Water: 45 to 75%
Pigment: 10 to 20%
Resin: 10 to 15%
Additive: 1 to 7%
Solvent: 0 to 10%

Polymeric: two types of polymers are present in these types of ink; the water-soluble ones which improves the properties of printing quality of ink and of the polymers in emulsion which improve the properties of film of ink on the printed paper form.
Pigments: they depend on the type of vehicle, of pH of ink… They are generally basic organics.
Additive:

Waxes: change the surface quality of film of ink. They in particular make it possible to increase the friction resistance, to improve slipping it…
Antimousse: prevent the foam formation and thus improves the impression.

Inks UV and EB

The environmental constraints on the solvent emission are increasingly strong. Moreover, drying must always be faster to answer the always increasing requirements of production. It was thus necessary for the manufacturers of ink to develop a new technology.

Inks UV (Ultraviolet) and EB (Electron-beam = bombardment of electrons ) are these new inks. The vehicle of these inks, although near to traditional inks has a quite different composition: they contain Prépolymère S, Monomère S and a Photoamorceur. The photoamorceurs are exities by UV and start a reaction of polymerization in chain of the prépolymères and monomers. The reaction is complete and quasi-instantaneous. The film of ink is then, normally, without any residual odor, which is very appreciable in food packing for example. The film of ink is of an excellent solidity, which with the disadvantage of posing problems with the Désencrage. Moreover inks UV remain more expensive than their big sisters.

The process is the same one for inks EB, only the photoamorceurs change.

Electrophotography and Xerography

Ink is stored in a Toner liquid or solid. In the beginning, ink was solid (in the form of powder) but the use Toner liquid tends to extend because they allow a better quality.

Inks Thermochromiques

They have the characteristic to have a variable color. This one varies in a reversible or irreversible way according to the temperature. these inks pass from the state coloured to colorless when the temperature rises.

The development of these inks started in the years 1970. At the beginning these inks were formulated only for serigraphy, this process offering a more intense contrast of colors. About the years 1980-1985 their formulation extended to the system flexographic. With the new applications the market increased and one now uses these inks in conventional offset and UV, like jet impression of ink.

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Substance of animal origin

Ink is also a substance, also called Sépia , produced by the Céphalopode S, the cuttlefish, the Calamar, the Poulpe…, which they project in water in the form of a cloud to mask their escape in the event of aggression.

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The disease of ink

The ink is also a very serious disease of the Châtaignier caused by a Champignon, named thus because of the black coloring which the root S. take.

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Direction of the word ink

The expression “to make spot of ink” means to clash, disfigure, like a spot of ink ruins a differently impeccable duty: “(...) with the degraded sites, the urbanization in spot of ink, the sick structures (...)”

Simple: Ink

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