Upload
emilia-christmas
View
256
Download
10
Tags:
Embed Size (px)
Citation preview
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
Artists’ Originals
Quality and Productivity
Litho – Offset Print Production
Graphic Originals
050
100
1stQtr
3rdQtr
Quality and Productivity
Litho – Offset Print Production
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
1234567890`~!@#$%^&*()-_=+;:’”,<.>/?
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
1234567890`~!@#$%^&*()-_=+;:’”,<.>/?
Text
Quality and Productivity
Litho – Offset Print Production
Digital Originals
Quality and Productivity
Litho – Offset Print Production
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
Human Vision
Colour Measurement
Additive Colours
RGB RG GB G RB R B
Colour MonitorsRGB
K
Colour Measurement
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
art paper
glossy inks
newsprint
coldset
Dot gain
Dot sizeon print
Dot size onscanners display
Dot Gain
Quality and Productivity
Litho – Offset Print Production
ideal
art paperglossy inks
newsprint
dirty base
density of original
printdensity
white base
limit
Tone Reproduction(Print Density)
Quality and Productivity
Litho – Offset Print Production
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– 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 drying– Dimensional stability
• Ink Absorbency– Post Print gloss– Pick strength– Ink drying
Thank you