Offset lithography

The image areas of a modem offset plate accept ink and are hydrophobic, while the nonimage areas accept water and are hydrophilic. While this basic principle is common to all forms of offset lithography, there are many differences between offset plates and the method they use to separate the image from the nonimage areas.  

The ink used in offset lithography has similar properties to those used in a letterpress in that both inks are very viscous. The water solution, called a fountain solution, is used to keep the ink from adhering to the nonimage areas of the 

3 The Printed Circuit Board and the Deveiopment of the Eiectronics industry 

The roots of circuit boards stretch all the way back to 1925, when Ducas was granted a patent for a method of forming electroplated conductor patterns in copper, gold, or silver on a nonconductive base material. Although he formed the conductor patterns by stenciling rather than photoetching, these patterns are of interest because of their remarkable resemblance to modern-day circuit patterns. He stenciled a conductive paste on a plastic base and electroplated it with the aforementioned metals. 

Ducas designed these conductors to interconnect circuit elements in place of wires, while using the base as an insulator, in a method he described in one of the claims of the invention for constructing electrical circuits arranged. .. upon the panel surfaces. .. for interconnecting terminals of electrical instruments secured to [the] surfaces. Remarkably, there exists no evidence that extensive commercial use was made of this invention, nor of any subsequent circuit board invention, until World War II.  

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Most metals receive a base coat of enamel (or occasionally paint), which is baked on. Printing then takes place on the enamel coating by offset lithography, dry offset letterpress, and occasionally other processes. 

Letterpress and Offset Letterpress (Dry Offset) Lithography Rotogravure Printing Rapid Prototyping UV Powder Coatings... 

Offset lithography is the most common process used for printing on paper. It is used for folding carton stock and for can and bottle labels. Most lithographic presses are sheet fed, although there are some web-fed presses. A particular application of offset lithography is the printing of flat metal sheets that are then... 

Offset Lithography High throughput. Limited in thickness Not expected to be a major... 

The commercial printing industry embraces a wide variety of processes for putting ink on paper. This review will be concerned with letterpress and offset lithography in their conventional forms. 

In the case of offset lithography the wetting of the surface of paper and subsequent sorption of fountain solution is Important for the avoidance of printing problems such as Ink refusal in multicolor printing, llntlng and picking, and Interference with ink drying mechanisms when residual acid In paper is solubilized. 

Their main disadvantage is that the heat of vaporization of water is greater than that of the organic solvents usually used, e.g., 1043 BTU/ lb as compared with about 180 BTU/lb for toluene, methyl ethyl ketone, and ethyl acetate. Also, the utility of these inks is limited they cannot be used in letterpress printing because they dry too rapidly on open roller systems, and they cannot be used in web-offset lithography because they are miscible with the aqueous fountain solution. Moreover, the water may swell the paper substrate and give poor register, and paper printed with some water-based inks cannot be recycled in the presently-used processes. 

Flexography and gravure (offset lithography may eventually come on stream). 

The vast majority of metal containers built-up from sheet materials are decorated in the flat prior to fabrication. The process most used (offset lithography) was used for printing on metal long before it was adapted for printing paperboard. A process which is basically dry offset lithography is also being increasingly used. 

Metal containers produced by impact extrusion must be decorated as the last stage rather than the first stage. The process normally used is rotary dry offset letterpress. Drawn containers may be decorated either before fabrication (by offset lithography) or after fabrication (by dry offset letterpress). The choice depends on the depth of draw and the amount of distortion which can be tolerated. Deep drawn components are invariably decorated after forming. 

Offset lithography is a planographic process and depends on the chemical modification of the surface of the printing plate so that only the image areas accept ink and the nonimage areas accept water. 

Offset lithography is used to decorate metal sheet for shallow drawn containers and lids since the resultant distortion is inherently small. When deeper one-piece containers, e.g. drawn and wall ironed aerosol cans, are printed most of the decoration is normally on the sidewall. One technique used is known as distortion printing. The original design is printed in the flat in a condensed or distorted fashion which is calculated geometrically so that when the three-dimensional can is formed... 

The decorative effects which can be achieved by offset letterpress printing are much more limited than those available by offset lithography on sheet materials. The design is limited to a maximum of six colours and a second pass is not possible. 

Planographic—print area and non-print area are in the same plane—offset lithography, dry offset lithography. 

Offset lithography uses thinner inks than letterpress and originally oxidation (linseed oil), but now quick-setting inks are more widely used. On metal containers, oxidation was accelerated by heat but synthetic resins are now employed, thus giving a combination of polymerisation and oxidation. Heat also permits some evaporation, giving more rapid drying with a harder finish. 

Plates may be either line or half tone. The inked image is offset onto a rubber blanket and then printed from this blanket onto the item being printed. It is used to print paper and board, metal in the flat sheet (tin plate) and occasionally plastic or foil. Offset lithography applies a relatively thin film of ink. 

FIRST PHOTOGRAPH FROM NATURE (1903) OFFSET LITHOGRAPHY (1840) AMMONIUM DICHROMATE IN STARCH ... 

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