Serigraphy is a Technique of impression.

History

Serigraphy (of Latin sericum the Silk and of the Greek graphein the writing) is a technique of Imprimerie which uses silk screens interposed between ink and the support. The supports used can be varied and not necessarily plane (paper, paperboard, textile, metal, glass, wood, etc.). It was used amongst other things by the Japan board to print the Blason S on the Kimono S.

Specificities

Avantages

• It authorizes a strong deposit of Encre which guarantees not only a intense Couleur which lasts in time but also a good opacity;
• It is interesting economically even for courts pulling S (but the numerical impression raises the break-even point);
• It authorizes the impression of supports of all nature and not necessarily plane (metal bottles, quills, machines).

Inconvénients

• It did not authorize the impression of too fine details in inks with solvents, but this light problem was solved at the time of discovered ink UV (which does not dry in the mesh but only under lamp with rays ultra-violet);
• It is not as fast as the impression offset (order of magnitude from 1 to 30);
• It is not very precise for the location (less than can the being the offset printing).

How to recognize it…

• With a simple magnifying glass (Thread-counter): no screen is visible, the color is laid out in " aplats" , it is possible to detect an impression carried out screen prints some by observing the edge of a printed feature, if one observes light hatchings in zigzag then one is doubtless in front of a serigraphy. The defect observed is the tooth of saw , imperfection caused by the Maille S of fabric during the impression.

Scopes of application

Used for the objects in volume, or of the supports not flexible device. It makes it possible to print reasons in a repetitive way with an almost unperceivable deformation on many matters such as:

• Paper

• plastic paperboard
• Wood
• S (PVC, polyethylene, polypropylene, polystyrene, ABS…)
• Textile Metal
• Glass
• S (cotton, nylon, polyester…)
• and well of others still insofar as specific ink exists for the matter in question
• it is also possible to make serigraphy on food (pastry making) and in this case one uses edible sugar or dyes

Serigraphy is a process used mainly in the field of graphic industries:

• the Descriptive (road panels, instrument panels, stickers…)

• the Publicity (posters, objects, totems…)
• the textile (sporting tee-shirts, caps, shirts…)
• the electronic (Printed circuit)
• nonexhaustive list

It is also used in the field of visual arts.

The technique consists in making pass an ink through a screen (kind of Pochoir). Ink settles thus on the support by reproducing the open shapes of the screen.

Screen

It is the printing form of the serigraphic process of impression. It consists of a tended fabric (in the past out of silk, replaced by polyamide mainly) and fixed on a framework (in the past out of wood, today out of aluminum) using special adhesives fabrics + hardener. The virgin fabric is uniformly porous. It must be prepared so that the impression of a reason is possible, it is the clichage.
The mesh of the screen will determine the quantity of ink deposited. It is expressed of many wire to cm: 9,15,21,31,43,77 (textile in general) and 90,120,150,180 (other applications), follows the diameter of the wire then (in microns). EX: 90.040 = 90 fils/cm; diam. wire of 40 microns. The higher the number of wire is, the less important the deposit is and the higher the smoothness is. One will use meshs raised to print details (from 120/140), of the fine texts,….
The less high the number of wire is (Mesh 90 for example) and the more important the deposit will be. One will use meshs weak in the case of impressions of flat tints, when an important opacity is wished.

Stereotyping

The virgin fabric is initially entirely stopped with a photosensitive emulsion, it is the enduction.
Once dries, a photosensitive emulsion hardens when it is exposed to a radiation Ultraviolet, it is the insolation.

Elementary principle

The emulsion exposed to the ultra-violets hardens, it stops fabric and ink does not pass pas.
The emulsion protected from the ultra-violets does not harden, one removes it with water, it does not stop fabric and ink passes, it is the principle of the " pochoir".

The colors of the reasons to be printed separate on transparent films and are thus represented in opaque black or red inactinic (which blocks the ultraviolet rays). There is a film distinct for each color from the reason to reproduce. This film (also called Offset film) is positioned on the screen coated during the insolation and makes it possible to block the ultraviolet rays where it is wished that ink be able to cross the meshs of the tissu.

Technical principle

The process of hardening is in fact based on the principle of oxydoreduction. In an initial state the emulsion is rich in electrons and water soluble. In the presence of salts of heavy metals like bichromate, and under the action of the actinic light (ultra-violet for serigraphy), there will be a transfer of the electrons of the emulsion towards bichromate. The emulsion changes property and becomes thus insoluble in water. Other molecules as the fish glue and certain polymers of synthesis can give this reaction. Certain authors say that the bichromate is in fact a peroxide which, under the action of the light, will be divided into two (ridicalizing mechanism). The model of the reaction is presented on the diagram of Ci-contre.

When the insolation is finished, the screen is rinsed with water. The not hardened emulsion is driven out fabric, it is the dépouillement.
After final improvement and correction of possible the small defects, the screen is ready for pulling.

Pulling

Two great fields are distinguished, industrial serigraphy (flat or Rotative) and textile serigraphy.

Industrial serigraphy flat

The screener puts in Repérage the screen and the matter to print so as to position the impression at the desired place. It must show anticipation because the colors are generally printed the ones following the others with intermediate dryings (with the free air, out of drying oven or tunnel UV according to ink used).

The support to be printed is maintained in place against three blocks (holds to always position the supports at the same place) or against a " calage" realized to measure on a suction table allowing the support to be stable in car or biciclette.

Once the screen fixed in the machine of impression, the screener must regulate the " except contact" (distance between the screen and the support which makes it possible to avoid " baver" during the impression or to stick screen/support). Then, ink is deposited on fabric of the screen. A scraper of impression having a flexible plastic side (polyurethane for example) makes it possible to apply ink to the support through the open meshs of fabric of the screen. The screener or the machine exerts a pressure on the scraper in " tirant" towards him of a displacement to traverse the entirety of the reason, it is what gives the expression of " tirage" (or scraping). The operation is carried out as much once than there are supports and colors with imprimer.

Remark
There exist today very powerful machines which allow the impression of all the colors in only once. These machines are in fact of the assemblies of traditional machines monochromic and of the automated systems the circulation and the location of the supports to print ensure images for children.

Screen print " rotative"

The process remains the same one as that quoted above, only the machine (Cylindrique) and the chock differ. One uses this technique to print any cylindrical object (glasses with the, with mustard, special penholders… and other objects).

Screen print Textile

The Textile is not a rigid but flexible matter. It is consequently not possible to print the first color, to withdraw the textile, to dry ink then to reposition the textile at the same place without deformation to print the following color. In the Textile field, the screener is obliged to print all the colors in only once, i.e. without moving the support to be printed. One then uses a carousel on which one fixes all the screens. The textile being often a pullover (but one can as well print any fabrics to leather in Quadrichromie), it is threaded on a Jeannette (gauge of wood who represents a flat bust) on which one vaporized adhesive beforehand. The impression is carried out while following the same process as for industrial serigraphy flat.

Remark
The management of the location of the colors between them is more complex in the textile field because one locates the colors with stolen the and not the ones after the others.

Today, for reasons of quality and technical simplification, one uses the " more and more; hot transfer " which consists in plating a plastic film (beforehand printed and coated of adhesive) under a press (imitating the domestic iron) which will guarantee the Transfert impression on the support.

Scouring

The screener can re-use a screen for another work. Using chemicals the screener softens the emulsion which resisted water and fabric with a cleaner high pressure drives out. When the screen is clean, it can be re-used for another work. When small traces of ink or emulsion remain in fabric after the scouring, one speaks about a phantom image . If one carries out a work by using a screen which has a phantom image, one exposes oneself to the reminiscence of the old reason in the new printed reason! Therefore, when the screener notes a phantom image, it carries out a specific treatment to eliminate it.

Environment

The companies of serigraphy consume large quantities of water for their process of manufacture (in particular for stereotyping, the scouring and the anti-phantoms treatments). Much of them chooses today to reprocess their waste water for less polluting and to save (re-use of the water treated for the processes). Waste inks, the solvents of cleaning, old inks is them also eliminated more and more properly near specialized companies bus from the organizations of environmental protection like the DRIRE veillent.

Site of the DRIRE

Use in art

The technique was also employed in the Art, in particular by the movement Pop art, and its emblem Andy Warhol, for the impression on fabrics. Its coloured reproductions of Marilyn Monroe tend to want to show to the Marchandisation artists in the Consumer society of its time.

The first serigraphic demonstrations in the impression on paper are about the years 1920. It is with Berlin that Kodloff and Biegeleisen made the first demonstration of it, by naming the process “Siebdruck”. Starting from 1938, the Estampe seized serigraphy, especially after the exposure of the “serigraphs” of Guy MacCoy to the the United States of America.

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