BASIC COURSE IN PRINTING TECHNOLOGY

Report
The main Printing process
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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
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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
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
100
50
0
1st 3rd
Qtr Qtr
Quality and Productivity
Litho – Offset Print Production
Text
ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz
1234567890
`~!@#$%^&*()-_=+;:’”,<.>/?
ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz
1234567890
`~!@#$%^&*()-_=+;:’”,<.>/?
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
art paper
newsprint
glossy inks
coldset
Quality and Productivity
Litho – Offset Print Production
Dot Gain
Dot size on
scanners display
Dot size
on print
Dot gain
Quality and Productivity
Litho – Offset Print Production
Tone Reproduction
(Print Density)
print
density
ideal
limit
art paper
glossy inks
newsprint
dirty base
white base
density of original
Paper Properties
• Colour
– Expressed as Whiteness, Brightness and L, a, b
values.
– Print colour reproduction (shade Matching)
Paper Properties
• Moisture and Dimensional Stability
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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

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