WHAT IS PRINTING ? A printing process describes the method adopted by a system to transfer the image on to a substrate (material). This also means that a printing system will have a medium that carries the image in the first place before it enables the process of reproduction. Getting this printing surface prepared is dependent on the printing process. Over the years, many different ways of putting ink on paper developed and these evolved to be the printing processes. The mechanics adopted under different systems are so different that they cater to specific applications in the market. Printing is a process for reproducing text and images using a master form or template. The earliest examples include Cylinder seals and other objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The earliest known form of woodblock printing came from China dating to before 220 A.D. Later developments in printing include the movable type, first developed by Bi Sheng in China. Johannes Gutenberg introduced mechanical movable type printing to Europe in the 15th century, his printing press key role in the development of the Renaissance,
Reformation, the Age of Enlightenment, and the scientific revolution and laid the material basis for the modern knowledgebased economy and the spread of learning to the masses. Modern large-scale printing is typically done using a printing press, while smallscale printing is done free-form with a digital printer. Though paper is the most common material, it is also frequently done on metals, plastics, cloth and composite materials. On paper it is often carried out as a large-scale industrial process and is an essential part of publishing and transaction printing.
Relief Printing
/ letterpress/exography printing
Planographic Printing / offset printing
Recess Printing
/ Intaglio/gravure printing
Stencil Printing / screen printing
Digital Printing / toner and inkjet
Woodblock printing 200 Movable type 1040 Printing press c. 1440 Etching c. 1515 Mezzotint 1642 Aquatint 1772 Lithography 1796 Chromolithography 1837 Rotary press 1843 Hectograph 1869 Offset printing 1875 Hot metal typesetting 1884 Mimeograph 1886 Photostat and Rectigraph 1907 Screen printing 1910 Spirit duplicator 1923 Xerography 1938 Phototypesetting 1949 Inkjet printing 1951 Dye-sublimation 1957 Dot matrix printing 1968 Laser printing 1969 Thermal printing c. 1972 3D printing 1984 Digital printing 1991
EVOLUTION OF PRINTING
LETTER PRESS As the name of the process says, the image areas are in relief and the non-image areas are in recess. On application of ink, the relief areas are coated with a film of ink and the non-image areas are not. With pressure over the substrate to bring it in contact with the image area, the image is then transferred to the substrate. If you can picture how a rubber stamp transfers ink to paper, then you understand the principle of letterpress and flexography. Relief printing was the earliest form of printing and remained dominant for a very long time. The movable type of the hot metal era were all used with letterpress. This printing process takes its name from the manner in which the process was employed, primarily for type, and later engravings.
FLEXOGRAPHY A letterpress printed product can be identified by the indentation that it creates in the paper. This is due to the mechanical pressure applied to the paper. In spite of this, letterpress produces images that are sharp and clean. It is a direct printing process, which means that ink is transferred directly from the printing surface to the substrate. Letterpress is still used to some extent for embossing, imprinting, and special-purpose reproduction.
COMPOSING
[
Platen press - Flat to flat Cylinder press - Flat to cylinder surface Rotary press - Cylinder to cylinder surface
]
This process adopts the same principle of relief printing and is therefore similar to letterpress. The printing surface is made of rubber instead of metal. The plate (the printing surface) is imaged from film or laser. Rubber plates were replaced by photopolymer plates during the 1970s as was the case with letterpress printing. Flexography is largely used in the packaging industry, where the substrates used are plastic, aluminum, foil, etc., for which the rubber plates are more suitable, due to their being soft. Usually flexography prints rolls of paper or foil instead of cut sheets. Flexography features: • Printing from wrong-reading raised image, flexible plate direct to substrate • Principal applications: almost any substrate which can go through a web press – tissue, plastic film, corrugated board, metal foil, milk crates, gift wrap, folding cartons, labels, etc.
[
Relatively expensive High printing speed Web and sheet fed presses
]
• Recognition characteristics: as a relief printing method, has recognizable, but slight, ink halo effect around letters and solid color areas the length of the web substrate makes flexography very suitable for products such as wallpaper and wrapping paper. The continuous, repeated imaging capability, along the length of the web substrate makes flexography very suitable for products such as wallpaper and wrapping paper.
FLEXIBLE RUBBER PLATE
LITHOGRAPHY Offset printing is a widely used printing technique. Offset printing is where the inked image is transferred (or "offset") from a plate to a rubber blanket. An offset transfer moves the image to the printing surface. When used in combination with the lithographic process, a process based on the repulsion of oil and water; the offset technique employs a flat (planographic) image carrier. So, the image to be printed obtains ink from ink rollers, while the non-printing area attracts a film of water, keeping the non-printing areas ink-free. The modern “web” process feeds a large reel of paper through a large press machine in several parts, typically for several metres, which then prints continuously as the paper is fed through. Currently, most books and newspapers are printed using the technique of offset lithography. Development of the offset press came in two versions: in 1875 by Robert Barclay of England for printing on tin, and in 1904 by Ira Washington Rubel of the United States for printing on paper.
Printing and non printing areas in the same height, differentiated by chemical and physical surface properties. Chemical property that water and oil don’t mix. Called offset because that the image isn’t printed directly to the paper from the plates, but is offset or transferred to another surface and then it will transfer to the paper.
DRY OFFSET PRINTING
WATER & OIL~ DON'T MIX
Advantages Relatively inexpensive and high quality Variety of materials can be printed onto. Blankets save wear and tear Double side printing in single pass Disadvantages Costly for small quantity How to identify offset printed material ? Impression even in half tones Clear outline Sharp and crisp Better text reproduction than in gravure
• Relief printing plate that transfers multiple colors to a rubber pad or blanket. The blanket then transfers as inked image to a substrate. • No water involved and hence no oil based ink repelling scenario. • Ink cured onto the substrate using high intensity UV light • Used in plastic bags, containers plastic lids, cosmetic tubes, aluminium cans, etc. • Low-cost, high speed process. • Printing round objects like container with diameter up to 12 inches
no oil based ink repelling
GRAVURE Gravure feature: • Three major segments: publications, packaging, and specialty product printing. • Principal applications: packaging, longrun magazines and newspaper inserts, catalogs, wallpaper, postage stamps, plastic laminates, vinyl flooring. • Cylinders last forever, making repeat runs • Cost of making cylinders remains high, making gravure expensive for jobs that are not repeated or not extremely long.
opposite of
letterpress
Recess printing— Gravure is another direct printing process, like letterpress with, however some major differences. The image is directly transferred from the image carrier, which is usually a cylinder, onto the substrate. Gravure is called intaglio because the image areas are in a sunken area and the nonimage areas are in relief. This must sound like an exact opposite of the letterpress process. In a way, that is true.
SCREEN PRINT This is a process that is used by many artisans for short-run jobs. It is such a less expensive process that many screen printing units are operated out of garages. But that does not mean that screen printing cannot offer good quality printing. It is a pretty simple process to understand and operate. The image that needs to be printed is first captured on a photographic material, a positive usually. A silk screen is stretched tightly by hinging around a wooden frame. The process derives its name from this silk screen, which was used as the image carrier. The positive image is then transferred to the screen and developed. The image that has been transferred to the silk screen is on the porous area of the screen. The non-image areas are blocked out during the stage of image creation itself. Screen printing features: • Printing by forcing ink through a stenciled screen mesh image directly onto substrate • Principal applications: can print on any substrate; point-ofpurchase displays, billboards, decals, fabric, electronic circuit boards, glasses, etc. • Ink formulation, screen mesh count, and image type are major quality factors • Recognition characteristics: heavy, durable, brilliant layer of ink.
VERSATILE
OTHER PROCESSES Electro Photography Artwork is placed face down on a glass plate and is illuminated by ourescent light which travels length of the image. Reected image is directed through the lenses in to a electrically charged drum. This charge leaks away where light from the image falls on the drum. A resin based powder (Toner) attracted to the image areas. This pattern of toner is transferred to the paper, where its xed and fused by heat. Laser copier works like combined scanners and image setters by scanning the image digitally and using a laser to write the image onto electrostatic drum.
Callotype (Photo Gelatin) Collotype Printing is a screen less Plano graphic technique for high quality reproduction. Invented in the 19th century, is little known today. Finest technique for reproduction of paintings. Screenless planographic technique. The only method where the greytone can be printed without using dots. Glass plate is first coated with light sensitive gelatin solution. Then exposed to continuous tone negatives. This is soaked in glycerin which is absorbed in the non harden areas.
Pad Printingt Pad Printing is contact-based printing process in which a silicone pad is used to li the color from a plate and then transfer it on to the surface of the item to be printed. It is also called Tampon printing as the silicon pad was traditionally known as tampon. When the print area is small and not flat Silicon ball is used to lift the color from a plate and then transfer it on the surface of the item to be printed. Eg golf ball
Thermography Not appropriate for halftones. Print finishing process that produces glossy raised lettering by funding thermographic powder to the print. The text is first printed and then is coated with fusible resin powder. When passed under the IR, resin pigment is fused to give hard raised image. Edges of the text is not sharp and clear.
PAGING AND IMPOSITION Documents of more than one page, whether they are bound or not, often ,must be printed with the pages arranged differently. Eg: 8 page newsletter Factors: • Design of printed piece • Multicolor, process color or single color ? • Whether one sided or both sided • Type of finishing such as folding trimming and binding • Type and size of paper used • Whether image position in relation to grain direction will affect folding operations Types One side: One printing plate is used to print on one side as it passed through the press. Common in small, offset print operations. Sheetwise imposition: Two printing plates are used. One plate per side. After one side is done, sheets are turned over and other side is done.
Ganged imposition: When one job on each press sheet would be a very inefficient use of the equipment, more than one job is run on the same sheet. Eg: It would be impossible to print 2x31/2 in business cards on 11x17 in press. To overcome this, several jobs are ganged together, reproduced on a large sheet and then cut to final sizes.
Signature imposition: Large single sheet is frequently passed through a printing press and then folded and trimmed to form a portion of a book or magazine.