Textile Printing Textile Printing Defined as Localised form

Textile Printing

Textile Printing • Defined as “Localised form of a coloration onto a substrate to develop a specific pattern or design”. • Viscous pastes are used for printing to achieve the proper design sharpness. • Printing uses the same dyes or pigments applied to produce a dyed fabric

Classification of Printing Methods of Printing • Following are the methods: • Block Printing • Roller Printing • Screen Printing • Flat Bed Printing • Rotary Screen Printing • Heat Transfer Printing • Inkjet Printing Styles of Printing • • • Following are the Styles: Direct Printing Flock Printing Discharge Printing Resist Printing

Block Printing • The blocks are usually made of wood and the design is hand fixed, so that it stands out relaxed 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.

Block Printing

Printing Techniques: Roller Printing • Color is transferred to fabric with an engraved roller. • Rollers are hollow metal cylinders coated with copper with designed grooves on it. • The roller collects the color from a furnishing roller which is dipped partially into the print paste. • The paste is trapped into engravings. • Excess paste is removed by a ‘doctor blade’

Roller Printing Process

Printing Techniques: Roller Printing • Fabric comes in contact with the engraved roller and the areas in contact with the grooves (having the paste) collect the color. • Print design repeat depends on circumference. • Fabric is dried after printing. • Limitation • Change of design takes too much time • Reduced color yield because of high printing pressure

Roller Printing Machine

Printing Techniques: Screen Printing • Screen consists of a perforated mesh (fabric or metal) stretched in planer or cylindrical shape • Non printing area is blocked with suitable materials • Print paste is forced to penetrate (using a squeegee) through the unblocked holes (printing area) to the fabric stretched beneath it • Hand Screen Printing

Printing Techniques: Screen Printing • Flat Bed Screen Printing • Fabric is in continuous length • Fabric supported by a conveyor belt • Belt moves intermittently • When the belt stops the screen lowers and come in contact with the fabric • Pressure is applied on print paste with the help of squeegee and it penetrates through the printable area to form a design in a single color • Each color follow a pattern but with a separate screen • Squeegee • Blade • Roller • Limitation • Low Productivity

Flat Bed Printing Machine

Application of Paste on Flat Bed Printing Machine

Printing Techniques: Screen Printing • Rotary Screen Printing Screen is made of metal mesh in cylindrical shape End rings keep it in stretched form The fabric is sticked to a conveyor belt that supports the screens The fabric passes under the screen which is rotated (by a motor at one end) as the fabric moves • Each screen prints a single colour • •

Printing Techniques: Screen Printing • A squeegee inside the screen presses the paste to move out of the unblocked mesh • Squeegee remains at lower area that contacts the fabric • Squeegee • Blade type • Rod Type • Correct design registration depends on screen positioning • Advantages: • Printing of intricate patterns • High production rates

Rotary Screen Printing

Rotary Screen Printing

Printing Techniques: Transfer Printing • Uses special “Transferable dyes” that sublimate on heating • When heat is applied to the material having the printed dyes it transfers on to the fabric which is in contact with it • The dyes are first printed on a cellulosic paper • The paper in along with fabric passes under the heating arrangement • Temperature of heating calendar or belt may be up to 180 C • No after treatment is usually required • Disadvantages • Vapor phase printing is limited to synthetics only so not used extensively on bulk scale

Transfer Printing Machines

Direct Printing • In this style, every component part of the design is “Saved for”, i. e. colours do not overlap and each has its own specific place on the fabric. • In other words each colour has a place saved for it on the fabric and the printing operation will ensure that the right colours are placed in the right “ saved for” locations.

Over Printing • This is the term used for designs in which one or more colours are made to print on top of colours.

Discharge Printing • The fabric is first pre-dyed on the dyeing equipment. The dry fabric is then over printed with print paste containing a chemical which will destroy the color of the dyed ground shade within the printed areas.

Resist Printing • The printing process takes place first, and the ground shade is is pad dyed or printed on the final screen. • Again the printed head colors contain a chemical which does not allow the fixation but will resist the ground color from mixing in the printed area. • The chemical used in to discharge or resist the ground color could be a reducing agent or even an alkali depending upon the dyes being used.

Printing Paste Formulations • Pastes for reactive Printing • Stock • Thickener • Oxidizing Agent • Urea • Print Paste • Dye • Alkali • Pastes for Pigment Printing – Stock • Thickener • Liqour Ammonia – Print Paste • Pigment • Binder

Functions of Printing Ingredients • Thickener: It converts the liquid printing ingredients into paste. It simply polymerizes and increases the Viscosity of liquid to produce thick paste. • Oxidizing Agent: To prevent the dye to be reduced in steaming environment. • Urea: it does Endothermic reaction thus converts the steam into water vapors in order to let the dye penetrate inside the polymer system of Fiber. • Acid / Alkali: It brings the necessary p. H for the crosslinking / Covalent bond forming reaction to take place. • Liqour Ammonia: It swells the pigment paste and keeps the p. H alkaline to prevent pre-crosslinking. • Binder: It makes cross links in between the fiber and pigment particle.

Post Print Process • Drying, • AT 110 -120 C for 1 to 2 minutes. • Fixation • Curing by dry heat. At 150 -170 C for 5 minutes. • Usually for pigment printing • Dry heat is applied to cross link the binder thus entrapping the pigment particles into it

Post Print Process • Ageing (Steaming) • Usually for dyes as they need to penetrate into the fiber • Time depends on temperature and fiber type • For reactive printing applied at 100 C for 5 -15 min, however times reduces as temperature of steam increases • Steam provides the required moisture for dye penetration by condensing onto fabric and forming a localized dyebath • Hygroscopic agents, as Urea, help to attain this moisture on fabric surface • Washing • To remove unfixed dye • Usually for dyes only

References • http: //textilelearner. blogspot. com/2011/07/printing-method-of-printing_5617. html#ixzz 2 r. Bw. C 8 yg. K Eurotex