Tuesday, July 12, 2011

HISTORY OF SCREEN PRINTING

HISTORICAL DEVELOPMENT OF SCREEN PRINTING
Screen printing is very familiar terms in textile printing sector. Innumerable kids developed with simple stencils by cutting out shapes from card, and brushing or spraying paint or ink through the holes on to cloth beneath. Industrial stencil sets for lettering are made of waxed card or metal, and incorporate ties to hold the solid areas together and to prevent the centers of letters such as O or P from falling out. The ties produce unsightly lines across the stenciled letters.

History of screen printing in centuries ago, when the Japanese developed the stenciling technique for textile screen printing and brought it to a fine art, they overcame this problem by using human hair or silk threads as ties. These were so fine that the colour spread underneath them, disguising their presence. By the 19th century, the use of this method for printing fabric had spread far beyond history of Japans screen printing and was used worldwide.

History of screen printing in the mid-19th century, French printers introduced the use of a woven silk fabric to provide a continuous support for the paper stencil. For the absolute results the support cloth was stretched across a frame, and the combination became known as a screen. The development was important because in this way not only were ties automatically provided, but the amount of colour paste applied could also be controlled. Soon after, the paper stencil was replaced by a durable paint on the screen fabric.

From this time onwards the advantages of screen printing became increasingly appreciated, especially in fashion houses. Designs are relatively easy to transfer to screens and the frame size can be readily varied. The designer, freed from the restrictions of copper rollers, thus had far greater freedom to choose repeat sizes. In addition, the pressure applied in screen printing is much lower than in roller printing with the result that surface prints with an improved ‘bloom’ or colour strength are obtained, and textured surfaces are not crushed.

The development of screen printing to its modern, highly productive form ran parallel with improvements in the printing screens themselves. Accurate printing of multicolored designs requires stable screens. Screen fabrics made from hydrophilic yarns, such as silk, cotton, viscose rayon or cellulose diacetate, are apt to sag when in contact with water-based print pastes. The introduction of hydrophobic synthetic fibres such as nylon and polyester, especially the latter, made it possible to manufacture stable screens that maintained tension when wet. Their high tensile strength also allowed the fabric to be stretched more tightly over the screen frame, thus improving the accuracy that could be attained. Further improvement came with the introduction of metal screen frames to replace the wooden ones used hitherto, which tended to warp when subjected to a regime of continually alternating wetting and drying.

Strong, stable screens enabled the hand screen-printing process to be mechanised. The first development was the introduction of a movable carriage, in which the screens are mounted one at a time. The squeegee (a flexible rubber blade used to spread the printing paste across the screen and force it through the open areas) was driven across the screen by a motor attached to the carriage. In this method, which is still in use, the fabric being printed is stuck down on long tables and one colour is printed at a time, just as in hand-screen printing.

The 1950s saw the advent of fully automatic, flat-screen printing, the Buser, Stork and Johannes Zimmer machines being prominent. These machines print all the colours in a design simultaneously along the top of an endless conveyor belt (blanket). The blanket and fabric are stationary while the printing operation takes place and then move on when the screens are raised; hence the fabric movement is intermittent.

Fully continuous printing is best achieved using cylindrical (rotary) screens and many attempts were made to form flat wire mesh screens into cylinders, despite the necessity of a soldered seam. When printing through a cylindrical screen with a seam, a line will show across the fabric once every cylinder circumference, unless the seam can be hidden within the design. This was the approach used in the screens manufactured by A J C de O Barros for the Aljaba machine, first introduced in 1954. Barros has written an interesting description of the Aljaba screens and machines.

Wire-mesh screens are too open for printing purposes, and on the early Aljaba screens electrodeposited copper partially filled the holes. This process was later discarded, to be replaced by the use of an outer seamless woven nylon sleeve. Later still, in fact after the closure of the Aljaba company, W Sword introduced a new version of the wire-mesh screen, the Durascreen, in which the holes in the mesh were partially filled with a flexible polymer by electrophoretic coating. The same process can also be used on electroformed nickel screens, extending their life considerably, since the flexible polymer coating reduces the risk of creasing.

An important innovation of the Aljaba company was the duplex machine used by some printers to print both faces of curtain fabrics. The fabric ran vertically upwards between pairs of screens, print paste being forced through the screens by metal roller squeegees.

The invention of seamless screens of electrodeposited nickel was the really significant step which heralded the rapid expansion of rotary-screen printing. Peter Zimmer (Austria) introduced the galvano screen in 1961, and Stork (Holland) the lacquer screen in 1963. These screens soon proved to be superior, in many respects, to Aljaba screens. When Stork introduced their machine, based on the lacquer screen, at the 1963 ITMA Textile Machinery Show at Hannover it was an immediate success, so much so that Stork decided to stop manufacturing fully automatic flat-screen machines. Between 1964 and the end of 1972 Stork sold 600 rotary machines throughout the world.

Machines using rod or roller squeegees, such as those manufactured by Peter Zimmer and Mitter, have been very successful in printing wider substrates, such as carpets. Rotary-screen machines have also been used to print paper for the transfer printing process. Currently rotary-screen printing is the predominant printing method worldwide, having substantially replaced copper-roller (intaglio) printing.