BASIC COURSE IN PRINTING TECHNOLOGY

The main Printing process Letter press Offset Lithography Gravure Flexography Screen Printing Other Reprographic process

Letter Press Letter Press is a relief process The image is reversed and it is non readable The process uses metal type which is hand set or machine set Pictures are made from blocks made of photo engraving. Inks are tacky and drying by absorption, oxidation Used for printing bill books, wedding cards of smaller number say upto 1000 impressions

Offset Lithography It is a plano graphic process Uses the principle of oil and water do not mix The image and the non image are in the same plane. There are three basic cylinders Plate cylinder (Image carrier – readable) Blanket cylinder (carries the image) Impression cylinder (transfers Printing) The inks are tacky and it is Thixotrophic in nature Can Print on relatively rougher surfaces The inks dry by absorption and by oxidation and polymerisation

Offset Lithography Most commonly used press where the number of impressions are any thing from 1000 – 50 ,000 copies. Sheet fed - cartons, folders, magazine covers Web offset – magazines , news papers etc Low preparatory costs when compared to other process Operation skill required is very high

Gravure Intaglio process – the image area is recessed The gravure cylinder where the image is etched ( image carrier) is immersed in a pool of liquid inks The inks are carried by the cylinder and the excess ink is wiped by the doctor blade The impression from a rubber roll makes the ink to transfer to the substrate through capillary action The image is non readable Mostly economical where the run length is very high

Gravure Most common application are cigarette, flexible laminates, currency notes etc. The initial cylinder costs are very high which is justified only if the run length is high Requires very smooth surface as the image is direct contact with the substrate Also good compressibility ensures better printing Produces a continuous tone effect in the image

Flexography A form of relief Printing uses rubber or resilient plastic plates ( photo polymer plates) The inking system uses a special annilox roller immersed in liquid inks Inks dry by evaporation Uses water based inks and is most friendly for food packing applications For large runs of liquid packaging, getting popularity in publishing abroad

Screen printing It is a stencil process Can print on any surface Uses high tack paste inks Used for very short run job as the initial cost is less Used for printing visiting cards, textile printing etc.

Printing a job The ad agency or the customer prepares a rough layout or dummy The customer gives the copy for reproduction which can be text matter, line drawings, photographs etc The customer prepares a mechanical layouts which shows the position and others which is called art work The type setting is done

Photographic Originals Quality and Productivity Litho – Offset Print Production Photographic Originals

Quality and Productivity Litho – Offset Print Production Artists’ Originals

Quality and Productivity Litho – Offset Print Production Graphic Originals

Quality and Productivity Litho – Offset Print Production Text ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 1234567890 `~!@#$%^&*()-_=+;:’”,<.>/?

Quality and Productivity Litho – Offset Print Production Digital Originals

Printing a job … contd The photographs, pictures which are continuous are scanned. The text and pictures are combined as per the art work After these they are assembled to make a negative Depending on the plates, negative or positive is exposed with the plate to give the Plate for printing

Printing a job … contd The plate is developed after exposure and is mounted on the printing machine The printing takes place with the help of the ink and the image from the plates After printing post printing operations like cutting , varnishing, punching are done

Colour theory Additive primaries – Blue , green, red – The combination these three coloured lights give white light. The principle used in TVs, computer monitors etc Subtractive primaries – Maganta, cyan, yellow –The combination othese three pigments/dyes give black – Used in printing, painting etc

Colour Measurement Human Vision

Additive Colours

Colour Measurement Colour Monitors RGB RGB RG GB G RB R B K

Colour theory 4 Colour printing – A picture is scanned and four positives of cyan , yellow , maganta , black are taken Cyan – Red filter Maganta – Green filter Yellow – Blue filter Black printer – Under colour removal

The process of printing The printing process is done through dots. The tonal gradation is achieved through varying the size of the dots but the number of dots remain same. The number of dots in a square area determine the resolution of the picture The half tone process is done through screens in printing.

Paper Properties and their relation to Printing Caliper/Bulk/Density Determines the pressure required to get good Print Uniformity in caliper to minimise variation across the sheet Bulk/density determines the print reproduction in direct contact process Creasing and folding property

Paper Properties and their relation to Printing Smoothness/Roughness Determines the ink transfer and dot reproduction on the surface Final Print gloss and Varnish Gloss Dot Gain

Impact of smoothness and Coating newsprint coldset art paper glossy inks

Quality and Productivity Litho – Offset Print Production Dot Gain Dot size on scanners display Dot size on print Dot gain

Paper Properties Colour Expressed as Whiteness, Brightness and L, a, b values. Print colour reproduction (shade Matching)

Paper Properties Moisture and Dimensional Stability Runnability in web feed process Blistering in Heat set web offset Register control in sheet fed offset Folding and Creasing

Paper properties Tensile Strength Pick strength Runnability in web feed process Pack formation in flexible laminates Pick strength Ability to take high tack inks Ability to run at faster speeds

Paper Properties Water Absorbency Ink Absorbency Ink drying Dimensional stability Ink Absorbency Post Print gloss Pick strength

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