Graphic Communication Chapter 20 Printing: Graphic Communication

The process of printing rakes written words and places their image on a material. Printing is applied to a material called the substrate. Originally, almost all printing was done on paper. Today, printing is done on a variety of substances including: paper, glass, plastic, cloth, ceramics, metal, and wood. The result of this mixture is a broad range of printed products. These products include: newspapers, magazines, books, brochures, pamphlets, labels, stickers, clothing designs and signs.

Printing Methods Today, there are six major printing processes: Relief Lithography Gravure Screen Electrostatic Ink jet

Relief Printing Relief printing the oldest of all printing processes, uses an image that is on a raised surface and it is pressed against the substrate. Pressure forces the ink to adhere to the substrate, producing the printed message. Relief printing requires that the image be reversed or “wrong reading,” on the printing block, or image carrier.

The two main types of relief printing are relief printing are letterpress and flexography. Letterpress uses metal plates or metal type as the image carrier. Accounts for less than 5 percent of all printing.

Lithographic Printing Lithographic printing, or offset lithography, is the most widely used method of printing today. Prints from a flat surface. Offset lithography, based on the principle that oil and water do not mix. Discovered by Alois Senefelder.

Fig. 20-4

A “light reading” image is produced on a image carrier called an offset plate. The linked image on the plate is first transferred to a special rubber roller called an offset blanket. This reverses the image. The image becomes “right reading” again when it is transferred to paper as it is fed through the press. Because the original image is first offset to the blanket, the process is called offset lithography. Modern offset presses can produce more than 500,000 copies from a single offset printing rate.

Gavure Printing Finely detailed items, like paper money and postage stamps, are usually printed using the gravure or intaglio process. Is the opposite of relief printing. The message is chemically etched or scribed into the surface of the image carrier. Carrier is then coated with ink. Next, the surface ink is scraped off with a doctor blade. This leaves ink only in the recessed areas of the carrier.

Fig. 20-6

When paper is pressed very tightly against the carrier, it picks up the ink in the cavities. Gavure is an expensive process. It is economical for very long production runs because one gravure plate can withstand several million impressions. In addition to money and stamps, some magazines are printed with this process.

Screen Printing Screen printing is a very old printing process, dating back more than 1000 years. Uses a stencil with openings that are the shape of the message; The stencil is mounted on a synthetic fabric screen. Paper is then placed beneath the screen, and ink is applied to the screen’s upper surface. ‘finally, a squeegee is pulled across the stencil. This forces ink through the openings of the stencil to produce the printed product.

Fig. 20-6

Screen printing is used too print on fabrics, T-shirt, drinking glasses, PC (printed circuit) boards, and many other products. Also used to print small quantities of very large products, such as posters or billboards.