PRINTING INKS

 

PRINTING INKS 

 

CONSTITUENTS, PURPOSEN OR FUNCTION 

CONSITTUENTS 

1.     Pigments / 

Dyes(used in liquid ink)

2.     Vehicle /  solvent(used in liquid ink)

3.     Dryers

4.     Anti-Oxidant 

5.     Additives –Plasticizer

INORGANIC PIGMENTS- inorganic pigments produced by precipitation(from yellow , cadmium red , bronze, trussing  blue ) are in termination use.

 

ORGANIC PIGMENTS– Organic pigment are mostly derived organic chemicals which are now mostly petroleum waste and most use at the visual spectrum can be match by  this pigment .

 

PIGMENTS 

1.     Carbon black 

2.     Transparent black 

3.     Opack white 

4.     Cadmium selenide 

5.     Iron oxides 

2.     Orange & yellow 

 

VEHICLE- A vehicle is to carry the pigments to the paper surface and protect the images during life spine of the print, in addition to adhesion to the paper surface. Whether a printing ink is applied in liquid or produce from the resulting dry ink film it must have the hardness, addition an flexibility during its lifetime. This property are achieved by surrounding the pigment particles with are resinous polymeric material of high molecular weight 

Resins may be blended with or chemically combined with natural drying in order to improve their performance.

CHARACTERSTIC OF VEHICLE 

1.     It is the liquid portion of the ink.

2.     It will carry dispersed pigment. 

3.     It will protect the printing.

4.     It also provide the work ability and drying properties.

5.     It will adhere the pigments on substance.

6.     It is transfer the dispersed pigments from the press ink duck through the roller, printing plate, and blanket.z

 

Some of important vehicles are oils may be from animal, vegetable or minerals. Vegetable oils are linseed oil olive or oil and mineral oil obtain from petroleum. The mostly used is linseed oil which is extracted from the seed of flex plants and some are extracted from other. This oils absorb atmospheric oxygen and get polymerized to become solidify. Non-drying oil include the mineral oil which are huger boiling extracting of petroleum.  

 

DRYER -The dryer is used to accelerate the printing ink, after it is transferred on the substrate. It assists oxidation if the small amount of dryer with the ink acts as a catalyst. Acceleration chemical change without altering itself in initial stage of drying the drying the dryer act as a carrier of oxygen to the vehicle. In the letter press of drying help in the vehicle. In the letter press of drying the dryer help in the polymerization of ink fill result in solidification.

 

PLASTISIZER- This may be considered as high boiling that low volatility solvents whose main purpose is to be brittle and it formation also prompts addition to the substance to be affective the molecules of plastisiszer must penetrate  between the long chain molecules of the resin blinder. Plasticizer are incorporated in gravure and flexographic inks and in most surface coating drying by solvent evaporation.

 

PIGMENTS:

•        Colowing matter used in printing are generally pigments.

•        Pigments are insoluble in vehicle.

•        Dispersed in vehicle rather than dissolved. 

•        Importance properties of ink should have good colour strength, reasonable stability to light and chemical, flow proportion .

 

Pigments- Coloring matter used in printing is generally pigments.

•  Pigments are insoluble in vehicle. 

•  Dispersed in vehicle rather than dissolved

•  Important properties for ink should have good strength, reasonable stability to light and chemical, flow properties.

Vehicle- A vehicle is to carry the pigments to the paper surface and protect the image during life span of the print, in addition to adhesion to the paper surface. When printing ink is applied on substrate the dry ink film must have the hardness, adhesion and flexibility during its lifetimes. This property is achieved by surrounding the pigments particles with resinous polymeric material of high molecular weight. 

 

 

SOLVENT - Solvent are liquid capable of dissolving other substance and those used on printing ink are able to dissolved resin or oils. Some of the common printing ink to dissolved resin or oils. Some of the common printing solvent are – Petroleum distillates, methylated spirit, Acetone, Ethyal acetate etc.

 

In practices once does find substance tend to dissolved best in solvents having similar polarity. Since the solvent is usually required to leave the ink film immediately after printing, its rate of evaporation it is often necessary to use a mixture of solvent. Other solvent properties which have to be considered are there flash point, toxicity, odor and there tendency to have a trace of solvent trapped in dry film.              Solvent of resins are often diluted with   a second liquid which through miscible with the solvent, has no solvent power for the resin. Such a liquid is called a diluents and it may be added in order to adjust the viscosity, evaporation rate, cost and some other property of the mixture.

 

Other additives in printing ink:Natural or synthetic waxes are sometimes include to impact rub-resistances, improved slip and water repellent properties. Wax compounds may also be added to letterpress and litho inks to reduce their tack without appreciably affecting there flow properties. Antioxidants are organic additives designed to improve the press- life of printing ink delaying the oxidation drying.

 

Ink – types of ink  

Early varieties of ink include Indian ink, various natural dyes made from metals, the husk or outer covering of nuts or seeds, and sea creatures like the squid (known as sepia). India ink is black and originated in Asia. Walnut ink and iron- gall nuts ink were made and used by many of the early masters to obtain the golden brown ink used for drawing. Ink – pigmented inks 

Pigmented inks contain other agents that ensure adhesion of the surface and prevent it from remove by mechanical abrasion. These material are typically referred to as resins (in solvent-based ink)Or binding agents (in water – based ink).

 

Ink – Dyes in inks  

Dyes, however, are generally much stronger and can produce more colour of a given density per unit of mass. However, because dyes are dissolved in the liquid phase, they have a tendency to soakintopaper, thus making the ink less efficient and also potentially allowing for the ink to bleed at the edges, producing poor quality printing.

 

To circumvent this problem , dyes based ink are made with solvents that dry rapidly or are used with quick – drying methods of printing , such as blowing hot air on the fresh print, other methods to resolve this include harder paper sizing and more specialized paper coating . The latter is particularly suited to inks that are used in non-industrial setting 

(And thus must conform to tighter toxicity and emission controls), such as inkjet printer inks, include coating the paper with a charged coating. if the dyes has the opposite charge, then it is attracted to and retained by this coating , while the solvent soaks into the paper . Cellulose, the material that paper is made of, is also naturally charged, and so a compound that complexes with boat the dyes and the paper surface aids retention at the surface. Such a compound in common use ink-jet printing inks is polyvinyl pyrrolidone.

 

An additional advantages of dye-based ink system is that the dyes molecules interact chemically with other inks ingredients. This means that they can benefits more than pigmented ink from optical brighteners and colour-enhancing agents designed to increase the intensity and appearance of dyes. Because dyes get their colour from the interaction of electrons in there molecules, the way in which the electrons can move is determined by the charged and extent of electron delocalisation in the other ink ingredients. The colour emerges as function of the light energy that fall on the dye. Thus, if an optical brightener or colour enhancer absorbs light energy and emits it through or with the dyes, the appearance change, as the spectrum of light re-emitted to the observer changes.

 

A disadvantages of dyes based inks is that they can be more susceptible to fading, especially when exposed to ultraviolet radiation as in sunlight.

Pigments contain the different colours

 

 

PIGMENTS

The same basic pigments are used to produce all inks for the various printing processes. To some degree the pigments type determines whether the inks will be transparent or opaque. It also determines image permanency when exposed to various solvent such as water, oil, alcohol, and acid. Pigments are divided into four groups: black, white, organic or inorganic colour pigments. Name of the some pigments are:-

1)     Black pigments: - black pigments are produce by burning nature gas and oil onto a collecting device. The by-products from the burning process are called thermal black and furnace black. Furnace black, the most popular pigment, is made from oil in a continuous furnace black, which is made from natural gas. Each type of black pigments has unique properties. The pigments are used individually or mixed to produce the best pigment for the specified printing process.

 

2)     White pigments: - white pigment are sub-division in two groups: opaque pigments and transparent pigments. White ink containing “opaque” pigments 

(Through which light cannot pass) is used when transferring an image to cover a substrate or when overprinting another colour. Opaque whites are also used for mixing white other inks to lighten the colour or hue. “Transparent” white pigments (through which light can pass) are used to allow the background material or ink, to produce a tine of another colour, and to extend or add to some of the more costly material in the inks formula.

Transparent pigments are often referred to as “extenders “or extender base.”

 

3)     Red for opaque full strength reds, one has to rely on the inorganic colours which are fast to light but heavy. It fairly light fast although it darkens on prolonged exposure and is decomposed by alkalis.

 

4)     Cadmium selenide: provide a range of very fast reds for flesh tints.

 

5)     Iron oxides: are available in special chemically prepared grades for making brownish reds of great performance reds of great performance. Red dyes both such as, rhodamine and magenta and acid such as cosine and phloxine are used in alcoholic solution for flexographic inks and basic dyes are commonly pigments for all types of inks.

 

6)     Orange & yellows: All shades of yellow from primrose to orange can be obtained by using various grades of lead chromate

The shade of all the chrorne yellow can be matched in transported colours, very strong, fast to light and alkalis by the use of the pigments dyestuffs known as hansa yellow.

7)     Brown: synthetic iron oxides are used for cheaper light fast inks but for liner work, mixture of other colour are employed. Nature occurring iron oxide have poor working and various drying and general pigment from phthalocyanine pigments.

8)     Blue: the iron blues (Bronze blue, Prussian blue etc.) are universally useful in all sorts of inks. This groups of pigments has moderate colour strength, good fastness to light and excellent drying and general pigments properties. Four colour process blues are now prepaid from phthalocyanine pigments.

9)     Green: The very poisonous sehweinfurth green having eliminated from inks for most inorganic green are made bymixing lead chromes and iron blues giving the chrome. Hydrated chromium oxide is also occasionally used from plate tint very fast to light.

10) Violet: various grades of methyl violet are in common used as basic as dyes and derived fast lakes which are largely used as toners for black inks.

 

 

Organic pigments: - they are derived from living organism. All pigments contain carbon and hydrogen and most are made from petroleum, however coalwood, animal fat, and vegetable oil the major advantages of organic pigments, provide a wider selection of colour, brighter, more transparent and purer than inorganic pigments. These qualities are most important for four colour printing process.

 

Inorganic pigments: - inorganic pigments are produced by are precipitation (from yellow, cadmium, grey, brown, trussion blue)

 

Vehicles: - the printing process and drying system determine the vehicle used in the manufacturing process. The vehicles of an ink is liquid portation that holds and carries the pigments. It also provides work ability and drying properties and blinds the pigments to the substance after the ink has dried.

 

Each vehicle used in the manufactures of inks has a slightly different composition. Non-drying vehicle used in newspaper and comics book production are made from penetrating oil base to control track and flow.

Most letter press and offset inks dry by oxidation. Linseed oil and litho varnish are the most widely used drying vehicles for these inks. The way in which the oils and varnish are “cooked” or prepaid determine the viscosity of the viscosity of the final ink.

 

The drying properties of linseed oil and similar oils depends on the unsaturated portion of the fatty acid chains the double bond –CH=CH- providing points for attack by atmospheric oxygen.

 

it include the mineral oil. Mineral oils are the basic liquid component in news ink and they are also used as colvents and diluents in many ink drying primarily by oxidation 

 

The drying properties of linseed oil

 

                         

 CHARACTERSTICS OF VEHICLE

1.               It is the liquid portion of the ink. 

2.               It will carry dispersed pigment.

3.               It will adhere the pigment on substrate.

4.               It will protect the printing.

5.               It also provides the work ability and drying properties.

6.               It is to transfer the dispersed pigments from the press ink duck through the roller, printing plate, and blanket.

 

Some of the important vehicles are oils may be from animals, vegetables and minerals. Vegetables oils linseed oil or olive oil and mineral which are extracted from the seeds of flex plants and some are extracted from other. These oils absorb atmospheric oxygen and get polymerized to be solidity.

                       Nondrying oil include the mineral oil which are high boiling extraction of petroleum.

DRIER- The drier is used to accelerate the printing ink after it is transferred on the substrate. It assists oxygen if the small amount of dryer within the ink acts as a catalyst. Accelerating chemical change without altering it- self in initial stage of drying the dryer act as a carrier of oxygen t the vehicle. In the letter press the drier help in the polymerization of ink film result in solidification. Printing ink most dryer are compound of salt of manganese and lead. Manganese has much slower drying action. Lead is general purpose drier and gives through drying in the ink tracks. Drier action increased with increasing temperature thus in dryer faster in the hot than in cold weather.

 

PLASTISIZER-This may be consider as high boiling that is low volatility solvents whose main purpose is impart flexibility otherwise the ink will be brittle formation and it also prompts adhesive to the substrate. To be effective the molecules of plasticizer must penetrated in gravure and flexographic inks and is most surface coating drying by solvent evaporation. 

 

SOLVENTS- Solvents are liquid capable of dissolving other substance and those used in printing ink are able to dissolve resin or oils. Some of the common printing solvents are- Petroleum distillates, Ethylated spirit, Acetone, Ethyl acetate etc.

 In practice one does find the substrate tend to dissolve best in solvents having similar polarity. Since the solvent is usually required to leave the ink film immediately after printing , its rate of evaporation is obviously very important. In order to obtain the correct rate of evaporation which have to be considered are their flash point, toxicity, odor and their tendency to have a trace of solvent trapped in the dry film.

 Solutions of resins are often diluted with a second liquid which though miscible with the solvent, has no solvent power for the resin. Such a liquid is called a diluents and it may be added in order to adjust the viscosity, evaporation rate , cost and some other property of the mixture. 

 

OTHER ADDITIVES IN PRINTING INK-

 

 Natural or synthetic waxes are sometimes included to impact rub- resistance slip and water repellent properties. Wax compounds may also be added to letterpress and litho inks to reduce their tack without appreciably affecting their flow properties. Antioxidants are organic additives designed to improve the press- life of printing ink by delaying the onset oxidation drying. 

 

ORGANIC PIGMENTS- 

Account for the colored inks. 

Inorganic colored pigments are very rarely used nowadays, as they usually contain toxic heavy metals (chromium, cadmium, lead, etc.).

For red and yellow inks, azo pigments are most frequently used. Their formula contains the azo group, -N=N-.

The human body is able to cleave the azo group into the compounds which it is made of, thus producing aromatic amines, some of which are carcinogenic.

Hence, under EC legislation, azo dyestuffs are to be regarded as carcinogenic, too, if the underlying amine is. With pigments, the risk is considered very small; whether it is nil remains to be seen. Molecules absorb light in the visible range if there is a conjugated system of double bonds in the molecules, that is, if single and double bonds alternate. 

 

BINDERS-Binders, i.e. that part of the vehicle which remains on the printing stock, may be 

•                  Just dissolved in some suitable solvents, which is removed after printing (suitable substances usually are called resins),

•                  Formed from the vehicle or parts of it by means of a chemical reaction, or  •     A mixture of both.

In case of 2 or 3, the formation of the binder may, in part, be performed in the manufacture of the varnish. 

 

RESIN-Resin is the comprehensive expression for a broad selection of naturally occurring, semi synthetic or synthetic materials which are employed as (e.g.) binders for printing inks.

Chemically, they are polymers. They are solids or rather viscous liquids. Most of them are of a non- crystalline structure. *Resins may be blended with or chemically combined with natural drying oil in order to improve their performance.   

 

Natural resins include

•                  Resin from pine trees, which can be separated into turpentine oil and colophony. Colophony is amber, hard and brittle substance. Its main constituent is a biotic acid. It cannot be used as such, but must be chemically modified, e.g. esterifies with glycerol or reacted with malefic or furmeric acid anhydrides.

•                  Asphalts, which is the residue when crude oil or coal tar distilled. They are very dark and hence can only be used for black inks. There are naturally occurring materials of a similar composition.

•                  Shellac is made from the secretion of an insert. Its special property is its solubility in ethylated spirit and, after saponification, in water. Its importance has decline. 

Semi- synthetic resins include

•                  Alkyd Estes. These are polyesters made of ( e.g.) phthalic acid esters and glycerol, which are modified with some fatty acid. Depending on the fatty acid employed, the alkyd may be “drying” or

“non- drying”. 

•                  Chemically modified cellulose, such as o      Nitrated cellulose o Ethyl cellulose o         Sodium carboxymethyl cellos o         Etc.

 

Semi- synthetic resins are virtually innumerable.

Important examples include

•                  Acrylic resins

•                  Polyvinyl acetate

•                  Polyvinyl alcohol

•                  Polyamide resins

•                  Polyurethane resins

•                  Epoxy resins