When colored patterns and designs are applied to a finished fabric for its decoration, it is called 'Printing'. In printing, the color is firmly affixed to the fiber so that it may not be affected by washing and friction. Textile printing is related to dyeing in the sense that in both the processes color is applied to the fabric. The difference lies in the fact that in dyeing, the color is applied uniformly to the whole fabric whereas in printing one or more colors are applied to it in selected parts only, and in sharply defined patterns.
The Dyes used for printing mostly include vat, reactive, naphthol and disperse colors which have good fastness properties. Pigments are also used extensively for printing. These colors are fixed to the fiber through resins that are very resistant to laundering or dry cleaning. Improved resins, better pigments or more effective anticrock agents are used to counter the problem of croaking colors on a printed fabric. Some prints are made from basic colors mixed with tartar emetic and tannic acid but they are not very acceptable in todays market.
For cotton printing vat and reactive dyes are generally used. Silk is usually printed with acid colors. Wool is printed with acid or chrome dyes but before printing it is treated with chlorine to make it more receptive to colors. Manmade fibers are generally printed with disperse and cationic dyes.
Methods of Printing
For printing color on a fabric, mostly three techniques are applied: Direct Printing, Discharge Printing and Resist Printing.
Direct Printing It is the most common approach to apply a color pattern onto a fabric. If done on colored fabric, it is known as overprinting. The desired pattern is produced by pressing dye on the fabric in a paste form. To prepare the print paste, a thickening agent is added to a limited amount of water and dye is dissolved in it. Earlier starch was preferred as a thickening agent for printing. Nowadays gums or alginates derived from seaweed are preferred as they allow better penetration of color and are easier to wash out. Most pigment printing is done without thickeners because the mixing up of resins, solvents and water produces thickening anyway.
Discharge Printing In this technique, the fabric is dyed in piece and then it is printed with a bleaching agent that destroys the color in the designated areas. Sometimes, the base color is removed and other color is printed in its place. The printed fabric is steamed and then thoroughly washed.
Resist Printing In this technique, a resist paste is fixed onto the fabric and then it is dyed. The dye affects only those parts that are not covered by the resist paste. After dyeing, the resist paste is removed leaving a pattern on the background of the fabric.
There are various methods of printing in which one of the above three techniques is used - Block Printing, Roller Printing, Duplex Printing, Stencil Printing, Screen Printing, Transfer Printing, Jet Spray Printing, Electrostatic Printing, Photo Printing, Batik Dyeing, Tie Dyeing, Airbrush (Spray) Painting and Digital printing
Block Printing The designs are carved on a wooden or metal block and the dyestuff in paste form is applied to the design on the face of the block. The block is pressed down firmly by hand on the surface of the fabric.
Roller Printing In this method which can be called a machine counterpart of block printing, engraved copper cylinders or rollers are used in place of hand carved blocks. When the rollers move, a repeat of the design is printed on the fabric. The printed cloth is passed into a drying chamber and then in a steam chamber where the moisture and heat sets the dye.
Duplex Printing Printing is done on both sides of the fabric either through roller printing machine in two operations or a duplex printing machine in a single operation.
Screen Printing It is done either with flat or cylindrical screens made of silk threads, nylon, polyester, or metal. The printing paste or dye is poured on the screen and forced through its unblocked areas onto the fabric. Based on the type of the screen used, it is known as 'Flat Screen Printing' or 'Rotary Screen Printing'.
Stencil Printing The design is first cut in cardboard, wood or metal. The stencils may have fine delicate designs or large spaces through which color is applied on the fabric. This method is very expensive and thus its use is limited.
Transfer Printing In this method, The design on a paper is transferred to a fabric by vaporization. There are two main processes for this- Dry Heat Transfer Printing and Wet Heat Transfer Printing. Various types of cylinders such as electrically heated cylinder, perforated cylinder etc. are used for pressing a fabric against a printed paper which transfers the pattern to the fabric
Airbrush (Spray) Painting
Airbrush (Spray) Painting In this method, the dye is applied with a mechanized airbrush which blows or sprays color on the fabric.
Electrostatic Printing A dye- resin mixture is spread on a screen bearing the design and the fabric is passed into an electrostatic field under the screen. The dye- resin mixture is pulled by the electrostatic field through the pattern area onto the fabric.
Photo Printing The fabric is coated with a chemical that is sensitive to light and then any photograph may be printed on it.
Jet Spray Printing
Jet Spray Printing Designs are imparted to fabrics by spraying colors in a controlled manner through nozzles.
Tie Dyeing Firm knots are tied in the cloth before it is immersed in a dye. The outside portion of the immersed fabric is dyed but the color does not penetrates the inside portions of the tied knots. There are various forms of Tie dyeing like Ikat Dyeing where bundles of warp and/ or weft yarns are tie dyed prior to their weaving. In Plangi Dyeing the gathered, folded or rolled fabric is usually held with stitching to form specific patterns.
Batik Dyeing It is a resist dyeing process. Designs are made with wax on a fabric which is then immersed in a dye. The portion not having wax absorbs the color.
Digital printing In this form of printing micro-sized droplets of dye are placed onto the fabric through an inkjet printhead. The print system software interprets the data supplied by a cademic_Textile digital image file. The digital image file has the data to control the droplet output so that the image quality and color control may be achieved. This is the latest development in textile printing and is expanding very fast.
Flocking is the technique of depositing many small fiber particles, called "flock" onto a surface of a fabric to produce design. Instead of dyes, an adhesive is used to affix the flocks on the fabric. Then, roller printing produces design on its surface. Nowadays, this is done by the application of high-voltage electric field too. Flocks of cotton, wool, rayon, nylon and acrylic are all used for the purpose.