Printing Processes:There are five main methods of printing a fabric, these being the block, roller, screen, heat transfer and ink-jet methods. The heat transfer method differs from the others in that it involves the transfer of color from the design printed on paper through the vapour phase into the fibres of the fabric. With the other methods the dye or pigment is applied to the fabric surface through a print paste medium. The ink jet printing process however is a comparatively recent innovation and is referred to as a 'non-impact' method, because the print paste is fired on to the textile from a jet which is not actually in contact with the fabric.
DIFFERENT TYPES OF PRINTING METHOD
Block Printing :
The blocks are usually made of wood and the design is hand carved, so that it stands out in relief against the background surface. The print paste is applied to the design surface on the block and the block then pressed against the fabric. The process is repeated with different designs and colours until the pattern is complete.
Block printing is a slow, laborious process and is not suitable for high volume commercial use. It is a method still practised in the oriental countries where markets exist for the types of printed fabrics produced.
Roller printing has traditionally been preferred for long production runs because of the very high speeds possible. It is also a versatile technique since up to a dozen different colours can be printed simultaneously. The basic roller printing equipment, shown in Fig. 7.1, consists of a number of copper faced rollers in which the design is etched. There is a separate printing roller for each colour being printed. Each of the rollers rotates over the fabric under pressure against an iron pressure roller. A blanket and backing cloth rotate over the pressure roller under the fabric and provide a flexible support for the fabric being printed. A colour doctor blade removes paste or fibres adhering to the roller after contact with the fabric. After the impression stage the fabric passes to the drying and steaming stages.
Screen Printing :
This type of printing has increased enormously in its use in recent years because of its versatility and the development of rotary screen printing machines which are capable of very high rates of production. An additional significant advantage is that heavy depths of shade can be produced by screen printing, a feature which has always been a limitation of roller printing because of the restriction to the amount of print paste which can be held in the shallow depth of the engraving on the print roller. Worldwide, some 61% of all printed textile fabric is produced by the rotary screen method and 23% by flat screen printing.
There are two basic types of screen printing process, the flat screen and the rotary screen methods.
Heat Transfer Printing :
Transfer printing techniques involve the transfer of a design from one medium to another. The most common form used is heat transfer printing in which the design is printed initially on to a special paper, using conventional printing machinery. The paper is then placed in close contact with the fabric and heated, when the dyes sublime and transfer to the fabric through the vapor phase.
Ink-Jet Printing :
There has been considerable interest in the technology surrounding non-impact printing, mainly for the graphic market, but the potential benefits of reductions in the time scale from original design to final production has led to much activity in developing this technology for textile and carpet printing processes. The types of machines developed fall into two classes, drop-on-demand (DOD) and continuous stream (CS).
Carpet Printing :
The printing of carpets only really achieved importance after the introduction of tufted carpets in the late 1950s. Until then the market was dominated by the woven Wilton carpets and Axminster designs were well established, but by the 1980s tufted carpet production accounted for some 80% (by area) of UK production. Much of this carpet production was printed because the range of patterns possible to produce using tufting machines was limited and there was a desire to produce a greater flexibility of design for these types of carpet
The printing of a design on the sheet of warp yarns before weaving. The fillingis either white or a neutral color, and a grayed effect is produced in the areas of the design.
A printing method in which the design can be produced: (1) by applying a resistagent in the desired
design, then dyeing the fabric, in which case, the design remains whitealthough the rest of the fabric is dyed; or (2) by including a resist agent and a dye in the pastewhich is applied for the design, in which case, the color of the design is not affected bysubsequent dyeing of the fabric background.
A method of printing from photoengraved rollers. The resultant designlooks like a photograph. The designs may also be photographed on a silk screen which is used inscreen printing.
Printing by the use of pigments instead of dyes. The pigments do notpenetrate the fiber but are affixed to the surface of the fabric by means of synthetic resins whichare cured after application to make them insoluble. The pigments are insoluble, and application isin the form of water-in-oil or oil-in-water emulsions of pigment pastes and resins. The colorsproduced are bright and generally fat except to crocking.
A process wherein the background color of a design is printed rather than dyed.
A method of printing to obtain a raised design on a sheer ground. Thedesign is applied with a special chemical onto a fabric woven of pairs of threads of differentfibers. One of the fibers is then destroyed locally by chemical action. Burn-out printing is oftenused on velvet. The product of this operation is known as a burnt-out print.
A process wherein the colors for the desired designs are applied directly to thewhite or dyed cloth, as distinguished from discharge printing and resist printing.
In “white” discharge printing, the fabric is piece dyed, then printed with apaste containing a chemical that reduces the dye and hence removes the color where the whitedesigns are desired. In “colored” discharge printing, a color is added to the discharge paste inorder to replace the discharged color with another shade.
A method of printing a pattern on the face and the back of a fabric with equalclarity.