Printing Process AS Graphics

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 Lithography Advantages 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

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

Gravure Advantages – 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

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

Flexography Advantages 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

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 Printing Advantages 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 run High speed process

Die Cutting Advantages 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)