10. Match the term with the definition:

1.benzene	a) a stiff usually brownish or grayish material like thick paper, used for making boxes, back of books, etc.
2. flexible	b) to force (a substance) into less space; press together
3. cardboard	c) a colourless liquid obtained chiefly from coal that burns quickly and is used to make certain types of engine run, and in making various chemical products.
4. packaging	d) that can bend or be bent easily.
5.to compress	e) material used for packing products

11. Complete the following sentences:

1. Flexography is the printing process using………………………

2. The term “flexography” means………………………………….

3. Printing plates are produced from……………………………….

4. Flexographic printing can be done on…………………………...

5. Printing units usually consist of………………………………..

6. The principle of sleeve technology consists of………………….

7. The quality of flexographic printing is now…………………….

8. The inks used in flexography can be……………………….

Unit SIX

TEXT

Screen printing

Screen printing is one of the most versatile processes for transferring ink and technical coatings. Its application ranges from artistic applications to the large-scale industrial sector, from single-item production to long print runs. Printing can be done on paper, textiles, ceramics, and plastics, in the form of endless webs and single sheets, and also on objects of the most varying nature and shape, such as glasses, mugs, and control panels.

The range of inks is correspondingly varied. Very often special inks are involved that are adapted to the relevant applications. The four-color process typical of publication printing is also used. The appliances, machinery, and systems utilized for screen printing range from the simplest of devices and machines for crafts work to large-scale plants on an industrial production scale.

Screen printing is a push-through process, a special type of stencil printing, which means that during the printing process the ink passes through the screen and onto the substrate.

The stencil printing process is one of the oldest printing processes. Lettered stencils, stencils for applying embroidered artwork for monograms on laundered items, or for applying text and markers to all types of mailroom packaging have been in common use for a long time and are still in use today. The use of stencils enables a fast application of information in the form of texts, symbols, and pictograms on the most diverse of substrates. The stencil is fastened onto the surface on which printing is to be done, and the ink reaches the desired position through the stencil apertures. The ink can be painted on with a brush or a squeegee, or sprayed on with a spray gun or an airbrush.

Stencil printing has one general disadvantage that restricts its use, namely that all parts of the stencil must be connected to each other. This means that with most letters, for example, stabilization gutters are needed to link the inner parts or those parts that might easily snap off to the surrounding material. This disadvantage does not occur with screen printing, where the screen/silk fabric takes on the function of the gutters and thereby places no restrictions on the motif’s design. The ink surrounds the screen mesh and forms closed surfaces between the masking parts of the stencil. The stencil is placed on or within the screen, glued to it, and held in position in that way. Thus the screen is merely a carrier for the stencil. The stencil is the carrier of the printed information. The printing plate is the combination of screen and stencil. This allows virtually complete freedom for designing the motif, right up to halftone printing. It must only be ensured both that the smallest masking reference surfaces of the stencil are still held in the screen fabric and that the smallest openings of the stencil are not closed by screen threads or threads crossing, which would result in the ink transfer being partially prevented or at least impaired. This limits the potential screen definition and range of tone values.

The carrier of the printed information, the stencil, is produced in a different way. Production methods vary from extremely simple manual work to the high-tech methods of “computer to screen”. The most commonly used method of plate making for screen printing is currently the application of photomechanical stencil material based on diazo (photopolymer).

Printing process

The ink is first spread over the plate by a squeegee as evenly as possible and with virtually no pressure. This takes place without contact between screen and substrate. This “flooding” produces a cleaning of the ink residues remaining in and on the plate from the preceding printing processes. The ink is then pressed through the plate and onto the substrate with a higher squeegee pressure. The wetting connection between ink and the surface to be printed is produced by this process, which is followed by the separation of plate and substrate. During this separation the ink is really drawn out of the screen mesh (in a comparable way to the emptying of the gravure printing cells). This process is particularly well-supported by the fact that the screen is not placed directly on the substrate, but rather at a certain distance above it and only comes into contact with the surface to be printed as a result of the squeegee. The screen tension built up in this way leads to the screen withdrawing from the ink adhering to the surface immediately downstream of the squeegee area.

Рис.5

Flat-bed Screen Printing (Screen Printing with a Flat Printing Plate)

The printing plate, which is typically the screen tensioned on a frame with the stencil fitted on it, and the substrate are on planes parallel to each other.

Rotary Screen Printing

Development of the rotary screen enabled repeat “flatbed printing” of endless webs for textile, wallpaper, and decorative printing to be replaced by a continuous rotary printing process that is able to print without seams using a corresponding plate. The rotary screen printing plate is open at the ends. The openings in the cylinder enable the insertion of the squeegee and guide it over the printing nip. The ink is pumped into the screen by a tube system on the squeegee holder.

Drying

Since very thick films of ink are applied in screen printing, the drying process of the most commonly used solvent-based inks requires a relatively long time. Products lying flat, such as posters or clothing, are dried in drying racks and by blowers. Continuous ovens with different hot air blowers and/or radiation sources (with UV light for UV inks) are also used.

The potential uses of screen printing are very complex:

• Large-format posters in fairly small print runs. The quite thick ink film produces coloring that is very brilliant and resistant even with halftone color impressions.

• Large printing surfaces for high resistance inks are found with traffic signs and routing systems.

• Vehicle fittings.

• Circuit boards for electronic circuits.

• Photo resistors and solar cells, which serve as the contact points for current transfer.

• Printing on CDs.

• Clothing, canvas shopping bags, webs of material, and so on, can be printed in both flatbed and rotary screen printing.

• Transfer images for ceramic decoration. A recognizable feature of these ceramic products is the thick layer of ink. The images can be placed above or below the glazing.

Seamless decorations such as textile webs, wallpaper, and other decorative products, as well as labels often require rotary printing combined with reel material. Special machines are designed for this. Rotary screen printing with sheet material is used primarily for higher print runs.