Flexographic, Gravure and Sheet Fed Offset Printing from buzai232's blog

Flexographic, Gravure and Sheet Fed Offset Printing

Flexography (Flexo) printing uses a raised-image printing plate. Photopolymer, or rubber, plates are used to transfer the print image. Conventional liquid or sheet photopolymer plates are used for line art. Laser-imaged, direct-to-plates (DTP) are used for all four-color process, all duotone, and most halftone images. As the plate cylinder rotates, it comes in contact with an anilox, or ink roller, which inks the raised portion of the printing plate. The plate then transfers the ink to the web, or paper. The anilox roll is laser-engraved with thousands of recessed cells that fill up with ink. The doctor blade controls the ink transfer to the plate. The doctor blade wipes off all ink except what is in the cells of the anilox roll. Compared to offset printing, this method offers significantly more ink transfer. (Refer to diagram below)Get more news about Flexographic Flat Printer,you can vist our website!

There is "gain," or growth, of Flexo images. For example, if the image area is a process/halftone with a 2% dot in the art/plate (typically the minimum for Flexo), it will print between 9-12% dot on coated papers and 12-15% dot on uncoated papers. This gain occurs for several reasons: As mentioned, the amount of ink transferred increases the image dot size. The contact pressure to transfer from anilox to plate to paper also increases the image dot size.

The substrates needed to ensure efficient machineability of roll paper into bags are not as smooth as those in offset printing. A rougher sheet can increase the size of the image dot because it requires more plate pressure to print. In addition, more ink is absorbed in a rougher paper. There also is more inherent machine movement in Flexo than in offset printing, so registration is not as tight and larger traps between colors are required.

Flexo can maintain resolution levels of 65-110 line on uncoated papers (such as Kraft and white) and 110-133 line on coated papers (claycoat).Gravure prints from a "cut-in," or recessed, surface. An engraved metal printing cylinder is used to transfer the printed image to the paper. As the gravure image cylinder rotates in the ink pan, the engraved cells of the image are filled with ink. The doctor blade controls and meters the ink by wiping the excess from cylinder surface, leaving ink only within engraved cells. The gravure cylinder then comes in contact with the paper substrate, transferring the printed image with the help of the rubber impression cylinder, which pulls the ink from the engraved cells. (Refer to the diagram below.)

There is "gain," or growth, in gravure printing. For example, if the image area is a process/halftone with a 3% dot in the art/cylinder (typically the minimum for gravure), it will print between 5-7% dot. Gravure is excellent for printing strong metallic inks.

Gravure prints on rolls of the same claycoat paper as Flexo and therefore has many of the same characteristics. However, gravure offers tighter registration that requires minimal traps and can maintain resolution levels of 150-175 line.