Print Process

Print Processes

Print Processes.

Rotary Printing

A rotary printing press is a printing press in which the images to be printed are curved around a cylinder. Printing can be done on large number of substrates, including paper, cardboard, and plastic. Substrates can be sheet feed or unwound on a continuous roll through the press to be printed and further modified if required (e.g. die cut, overprint varnished, embossed). Printing presses that use continuous rolls are sometimes referred to as "web presses". Today, there are three main types of rotary presses; offset including web offset, rotogravure, and flexo (short for flexography). While the three types use cylinders to print, they vary in their method.

Rotogravure
Rotogravure (Roto or Gravure for short) is a type of intaglio printing process; that is, it involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press. Once a staple of newspaper photo features, the rotogravure process is still used for commercial printing of magazines, postcards, and corrugated (cardboard) product packaging.

Flexography
flexography,  form of rotary printing in which ink is applied to various surfaces by means of flexible rubber (or other elastomeric) printing plates. The inks used in flexography dry quickly by evaporation and are safe for use on wrappers that come directly in contact with foods. In flexography, the desired imagery or lettering is engraved in the form of tiny indentations, or cells, onto a flexible rubber plate by means of plastic-molding techniques. Liquid ink is flooded onto a rotating ink-metering roller while a blade inclined at a reverse angle to the direction of rotation shaves any surplus ink from the ink-metering roller. The remaining ink is rolled onto the rubber printing plate, which is affixed to a rotary letterpress cylinder, and the plate’s tiny indentations receive and hold the ink. The inked plate then transfers the image or type to paper (or some other material) that is held on an impression cylinder.

Offset Lithography

Lithography  is a method for printing using a stone or a metal plate with a completely smooth surface. Invented in 1796 by German author and actor Alois Senefelder as a cheap method of publishing theatrical works, lithography can be used to print text or artwork onto paper or other suitable material.

Lithography originally used an image drawn (etched) into a coating of wax or an oily substance applied to a plate of lithographic stone as the medium to transfer ink to a blank paper sheet, and so produce a printed page. In modern lithography, the image is made of a polymer coating applied to a flexible aluminum plate. To print an image lithographically, the flat surface of the stone plate is roughened slightly—etched—and divided into hydrophilic regions that accept a film of water, and thereby repel the greasy ink; and hydrophobic regions that repel water and accept ink because thesurface tension is greater on the greasy image area, which remains dry. The image can be printed directly from the stone plate (the orientation of the image is reversed), or it can be offset, by transferring the image onto a flexible sheet (rubber) for printing and publication.

Offset Printing 

Offset printing is a commonly used printing technique in which the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called "fountain solution"), keeping the non-printing areas ink-free.

Development of the offset press came in two versions: In 1875 by Robert Barclay of England for printing on tin, and in 1903 by Ira Washington Rubel of the United States for printing on paper.

Pad Printing

Pad printing is a printing process that can transfer a 2-D image onto a 3-D object. This is accomplished using an indirect offset (gravure) printing process that involves an image being transferred from the cliché via a silicone pad onto a substrate. Pad printing is used for printing on otherwise impossible products in many industries including medical, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment and toys. It can also be used to deposit functional materials such as conductive inks, adhesives, dyes and lubricants. Physical changes within the ink film both on the cliché and on the pad allow it to leave the etched image area in favor of adhering to the pad, and to subsequently release from the pad in favor of adhering to the substrate. The unique properties of the silicone pad enable it to pick the image up from a flat plane and transfer it to a variety of surfaces, such as flat, cylindrical, spherical, compound angles, textures, concave, or convex surfaces.

Digital Printing 

Digital printing refers to methods of printing from a digital based image directly to a variety of media. It usually refers to professional printing where small run jobs from desktop publishing and other digital sources are printed using large format and/or high volume laser or inkjet printers. Digital printing has a higher cost per page than more traditional offset printing methods but this price is usually offset by the cost saving in avoiding all the technical steps in between needed to make printing plates. It also allows for on demand printing, short turn around, and even a modification of the image (variable data) with each impression. The savings in labor and ever increasing capability of digital presses means digital printing is reaching a point where it could match or supersede offset printing technology's ability to produce larger print runs of several thousand sheets at a low price. The main differences between digital printing and traditional methods such as lithography, flexography, gravure, or letterpress are that no need to replace printing plates in digital whereas in analog printing plates are continuously replaced, resulting in a quicker and less expensive turn around time, and typically a loss of some fine-image detail by most commercial digital printing processes. The most popular methods include inkjet or laser printers that deposit pigment or toner onto a wide variety of substrates including paper, photo paper, canvas, glass, metal, marble and other substances.

Screen Printing
Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink into the mesh openings for transfer by capillary action during the squeegee stroke. Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced into the mesh openings of the mesh by the fill blade or squeegee and onto the printing surface during the squeegee stroke. It is also known as silkscreen, serigraphy, and serigraph printing. A number of screens can be used to produce a multicoloured image.

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