printing process as graphics. offset lithography
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Printing Process
AS Graphics
Offset Lithography
Offset Lithography
• Description– the paper does not come into direct contact with
the printing plate. Instead, the image is transferred to a rubber roller.
– Very fast, high quality process
Offset Lithography
• Materials– Paper– thin card
– magazines, posters, flyers, packaging and books.
Offset Lithography
• Keywords– Aluminium plates– Photopolymer resin– Rubber transfer– Gum arabic– Laser hardening– Offset– CMYK– Colour separation
Offset Lithography• Stages
– Digital Artwork• Produce in Adobe Photoshop• Layout• Colour Separation
– Produce plates• Photopolymer resin coated aluminium plate• Exposed to a laser• Hardens exposed areas• Unexposed parts washed off• Plate coated in gum arabic to protect against surface oxidisation
– Print• Solvent based ink• based on the repulsion of oil and water• non-printing area attracts a water-based film, keeping the non-printing
areas ink-free
– Trim
Offset LithographyAdvantages• Consistent high image quality. (1),• Offset printing produces sharp and clean
images and type. (1), • Rubber blanket conforms to the texture of
the printing surface. (1),• Quick and easy production of printing plates.
(1)• Aluminium printing plates have lower costs
(1), • Longer printing plate life than on direct litho
presses because there is no direct contact between the plate and the printing surface. (1),
• Can exceed run lengths of a million impressions. (1),
• Economical method to produce high quality printing in commercial printing quantities. (1),
• More suitable than Gravure for batch production (1)
Disadvantages• Expensive to set up, Slightly inferior
image quality compared to rotogravure or photogravure printing. (1),
• Anodized aluminium printing plates can become sensitive. (1),
• Printing deteriorates and prints in non-image/background areas when developed plates are not cared for properly. (1),
• Takes time to produce plates and printing press setup. (1),
• Not suitable for small quantity printing jobs. (1)
Gravure
Gravure
• Description– In gravure printing, the image is made up of small
holes sunk in the surface of the printing plate. The holes are filled with ink and any excess is removed. Paper comes into contact with the ink in the holes when it is pressed against the plate.
Gravure
• Materials– Paper, card
– magazines, mail-order catalogues, packaging, and printing onto fabric and wallpaper. It is also used for printing postage stamps and decorative plastic laminates, such as kitchen worktops.
Gravure
• Keywords– Copper plate– Image negative– Etching (laser / chemical)– Chromium layer– CMYK– Colour separation– Doctor blade– Sunken holes
Gravure• Stages
– Digital Artwork• Produce in Adobe Photoshop• Layout• Colour Separation
– Produce plates• Copper plate• Chemical etching or laser engraving (laser most used)• Both very precise• Coated in thin chromium layer to durability and longevity of life• 4 plates produced (one for each colour, CMYK)
– Print• See image (roller names, doctor blade)• Ink falls into gaps on cylinder• Doctor blade wipes off excess• Solvent or water based inks• Dryer between colours (water takes longer to dry and higher temperatures)
– Trim
GravureAdvantages
– It gives consistent colour (1) helped by the ink drying on evaporation (1),
– Allows high speed printing (1) and is good for long print runs (1),
– Good results on cheap paper (1) and gives / cost effective high quality print (1),
– A range of colours can be used (1) using different plates (1),
– Can print on wide rollers (1) for specialised applications e.g. vinyl flooring (1),
– Gravure cylinders last longer than other methods. (1), Inks dry immediately. (1)
Disadvantages– Printing plates are more
expensive. (1), – Registration not as
good as offset process. (1),
– Solvent inks give off much higher VOC’s. (1),
– Water based inks do not print as well as solvent based inks. (1)
Flexography
Flexography
• Description– Flexography uses a relief image on thin, flexible
printing plates made of rubber.– Good for none flat surface sheet materials
Flexography
• Materials– cellophane– Polythene– metallic films– Corrugated card– Other card and paper
– shopping bags, newspapers, cardboard boxes, cornflake packets, crisp packets, yoghurt pot tops and wallpaper and paperback books.
Flexography
• Keywords– Flexible Photo polymer sheet– UV lamps– Film negative– Anilox roller– Impression cylinder– Plate cylinder– Ink roller– Dryer– Block colour
Flexography• Stages
– Digital Artwork• Produce in Adobe Photoshop• Layout• Colour Separation
– Produce plates• Produce image negatives (inverse)• Photo polymer sheet• Expose to UV lamps (hardens back)• Expose front to UV (using film negative) - this hardens the exposed areas• None exposed parts washed away in processing tank (with brushes)• Dried in oven• Trimmed to size• Photopolymer sheet attached to plates• Plate produced for each colour (CMYK????)
– Print• See image (roller names)• Solvent based ink• Dryer between colours
– Trim
FlexographyAdvantages• Can be used to print on uneven
surfaces (1) as Printing plates are flexible with raised ink pattern. (1)
• Use of fast drying water based inks (1) so corrugated card doesn’t absorb excess moisture so card doesn’t warp. (1)
• Low viscosity inks used (1) so flow into rippled surfaces (1)
• Least expensive and simplest printing (1) so doesn’t add to cost of product. (1)
• Low pressure from rollers (1) so printing doesn’t bend/ crush the product. (1)
Disadvantages• The text/image must be
reversed, so flexography is not suitable for detailed images like photos (1),
• Flexography produces poor shadows (1),
• The number of impressions per plate are more limited than offset (1),
• There is a problem with bleeding (1),
• Overall, flexographic printing quality lacks fine colour detail and vibrance (1)
Screen Printing
Screen Printing
• Description– The screen is made from a fine mesh material. A
stencil is placed under the screen and ink forced through the stencil onto the material below.
– Screen printing with stencils is best for blocks of colour.
Screen Printing
• Materials– Card, board, plastics and metals
– posters, display boards, fabrics, wallpaper and control panels of electronic products.
Screen Printing
• Keywords– Nylon screen– UV light– Water jet– Film positives– Stencil
Screen Printing• Stages
– Digital Artwork• Produce in Adobe Photoshop / other software • [Colour Separation]
– Produce screen(s)• Film positives produced of artwork (for that colour)• Nylon coated with photo sensitive emulsion• Screen exposed to UV light• Exposed areas hardened• Water jets wash away unhardened areas• Self adhesive metal foil applied to screen• [One screen produced for each colour]
– Print• See image (part names)• Ink passes through holes that were not hardened• Solvent based ink• [Dryer between colours]• CMYK or block colour
– Trim
Hand screens:• Stencil design cut• Stencil placed under
frame but above paper
• Line of ink placed at one end of screen
• Use squeegee to draw ink across screen, pressing firmly
• Carefully lift screen• Evaluate and repeat
Screen PrintingAdvantages• block colours, • low setup cost, • very large range of materials including
fabric, • can be used to print directly on any
surface/material,• economical for short runs, • can be used for a range of production
methods, • relatively easy to do,• stencils can be hand cut or photo-
emulsion, can be fully automated production printing,
• produces identical/replica images, • stencils can be easy to
produce/reusable, • can be used to print on flat/curved
surfaces
Disadvantages• difficult to achieve details
(1),• printing ink can take long
periods to dry (1), • time consuming process (1), • adds to product unit cost
(1),• expensive on long runs (1),• specialist process (UV)
needed to dry ink fast (1)
Die Cutting
• Automated / machine process • Cutter for nets and ‘odd’ shapes Cutting and
scoring achieved at the same time Multiple/identical sheets can be cut at the same time Accuracy/cuts cleanly/better quality finish Allows lay planning/tessellation Removes the human error when cutting Cost effective on large runs Die can be reused on another production runHigh speed process
Die CuttingAdvantages• Data feed back to a computer (1)
which aligns the die with the crop marks. (1)
• Multiple/ Identical nets can be cut (1) at speed/ Dies can be reused (1)
• Unskilled labour can be used (1) as operating system very simple/reduced labour cost. (1)
• Automated/ Much quicker process (1) reduces lead times/increase rate of production/ allows continuous production. (1)
• Process is more accurate (1) removing human error (1)
• Allows for tessellation of nets (1) reducing wastage (1)
• Can cut and score. Crease at the same time (1) saving time (1)
Disadvantages• Expensive set up cost /
machinery• Wear of tools
Safety Features of all these processes
• Full guards (1) protecting cutting blades / moving parts (1)
• Light beam (1) which stops operation if the beam is broken (1)
• Emergency stop button (1) to isolate power/stop machine quickly (1)