Printing Secrets from Online Printing Services

 

Flexographic Printing

 

Flexo Printing: The undisputed king of
printed flexible packaging

Wilipedia entry for flexographic printing.

Applications:

The most common process used to print packaging materials is Flexography.

Some of the products manufactured by this process include –

 

The Flexographic printing (or flexo printing) method can produce fairly good quality on many different stocks and is the most cost effective and less complicated of the printing processes used for packaging printing.

The use of flexographic printing presses is on the increase. There are two primary reasons for this –

The widespread use of water-based inks in flexo printing means a large reduction in VOC emission compared to the heatset web or gravure printing processes.

Publication flexography is used mainly in the production of newspaper, comics, directories, newspaper inserts, and catalogues. Packaging flexography is used for the production of folding cartons, labels, and packaging materials. Large quantities of inks are used during normal runs on flexographic presses; however, some printers are able to recycle a majority of their spent inks and wash waters.

Major chemicals used in flexography include platemaking solution, water and solvent based inks, and blanket/roller cleaning solvents.

Flexography is a form of rotary web letterpress, combining features of both letterpress and rotogravure printing, using relief plates comprised of flexible rubber or photopolymer plates and fast drying, low viscosity solvent, water-based or UV curable inks fed from an "anilox" or two roller inking system.

The flexible (rubber or photopolymer) plates are mounted onto the printing cylinder with double sided adhesive tape. Plates are sometimes backed with thin metal sheets and attached to the cylinder with fastening straps for close register or ink alignment.

This adds additional cost to the plate and requires more makeready time, but when quality printing is critical this type of plate can make the difference.

 

Flexo Process Overview

In the typical flexo printing sequence, the stock is fed into the press off a roll. The image is printed as stock is pulled through a series of print units. Each print unit is printing a single colour. As with Gravure and Lithographic printing, the various tones and shading are achieved by overlaying the 4 basic shades of ink.

These are magenta, cyan, yellow and black. Magenta being the red tones and cyan being the blue. 

The process of printing each colour on a flexo press consists of a series of four rollers:

 

The first roller transfers the ink from an ink pan to the meter roller or Anilox Roll, which is the second roller. The Anilox roller meters the ink to a uniform thickness onto the plate cylinder.

The stock then moves between the plate cylinder and the impression cylinder, which is the fourth roller.

The impression cylinder applies pressure to the plate cylinder, thereby transferring the image onto the stock. The web, which by now has been printed, is fed into the overhead dryer so the ink is dry before it goes to the next print unit.

After the stock has been printed with all colours the web MAY be fed through an additional overhead tunnel dryer to remove most of the residual solvents or water. The finished product is then rewound onto a roll or is fed through the cutter.

The major unit operations in a flexographic printing operation are:

 

Image Preparation

Image preparation begins with camera-ready (mechanical) art/copy or electronically produced art supplied by the customer. Images are captured for printing by camera, scanner or computer.

Components of the image are manually assembled and positioned in a printing flat when a camera is used. This process is called stripping. When art/copy is scanned or digitally captured the image is assembled by the computer with special software.

A simple proof is prepared to check for position and accuracy. When colour is involved, a colour proof is submitted to the customer for approval.

Flexo Plate Making

Flexographic and letterpress plates are made using the same basic technologies utilizing a relief type plate. Both technologies employ plates with raised images (relief) and only the raised images come in contact with the stock during printing.

A Flexo plate ismade of a flexible material, such as plastic, rubber or UV sensitive polymer (photopolymer), so that it can be attached to a roller or cylinder for ink application. There are three primary methods of making flexographic plates; photomechanical, photochemical and laser engraved plates.

 

Flexo Printing Presses

 

The five types of printing presses used for flexographic printing are the stack type, central impression cylinder (CIC), in-line, newspaper unit, and dedicated 4, 5, or 6 colour unit commercial publication flexographic presses.

All five types employ a plate cylinder, a metering cylinder known as the anilox roll that applies ink to the plate, and an ink pan. Some presses use a third roller as a fountain roller and, in some cases, a doctor blade for improved ink distribution. 

Flexo Inks

Flexo inks are very similar to packaging gravure printing inks in that they are fast drying and have a low viscosity. The inks are formulated to lie on the surface of non-absorbent stocks and solidify when solvents are removed. Solvents are removed with heat, unless U.V. curable inks are used.

 

Finishing

After printing, the stock may run through a number of operations to be "finished" and ready for shipment to the customer. Finishing may include operations such as coating, cutting, folding and binding.

 

 

Printed packaging or business stationery, find out

how you can slash your costs by up to 32%.

 

Check our

FREE Printing Perth Guide

 

Available FREE to download by everyone.

 

It's already been downloaded by

more than 1,820 Perth businesses!!

 

 

          "Thankyou for making my life

                a lot easier"

                                                  Christine Steel

                                         Executive Secretary

                                   Centurion Garage Doors

 

 

---