Devanu n ishan


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Devanu n ishan

  1. 1. Devanu Roy Choudhury (Roll No. 6) Ishan Rastogi (Roll No. 7) B.F.T. (V)
  2. 2.  Most common approach of printing  Can be done on a white or coloured fabric  If done on coloured fabric, it is known as overprinting.  The desired pattern is produced by imprinting 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 pigment is dissolved in it. ◦ gums or alginates derived from seaweed are used as thickening because they are easier to wash out, do not themselves absorb any colour and allow better penetration of colour. ◦ Most pigment printing is done without thickeners as the mixing up of resins, solvents and water itself produces thickening.
  3. 3.  In this approach, the fabric is dyed in piece and then it is printed with a chemical that destroys the colour in the designed areas.  Sometimes, the base colour is removed and another colour is printed in its place.  The printed fabric is steamed and then thoroughly washed.  This approach is on decline these days.
  4. 4.  A resist paste is imprinted on 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 a dark background.
  5. 5. There are various methods of printing in which one of the three techniques - direct, discharge or resist is used.
  6. 6.  The designs are carved on a wooden or metal block and the size paste 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.
  7. 7.  In this machine counterpart of block printing, engraved copper cylinders or rollers are used in place of hand carved blocks.  With each revolution of the roller, a repeat of the design is printed.  The printed cloth is passed into a drying and then a steam chamber where the moisture and heat sets the pigment.
  8. 8.  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.
  9. 9.  It is done either with flat or cylindrical screens made of silk threads, nylon, polyester, vinyon or metal.  The size paste 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 ◦ Rotary Screen Printing
  10. 10.  The design is first cut in cardboard, wood or metal. The stencils may have fine delicate designs or large spaces through which colour is applied on the fabric.  Its use is limited due to high costs involved.
  11. 11.  In this form of printing micro-sized droplets of pigments are placed onto the fabric through an inkjet print head.  The print system software interprets the data supplied by a cademic_Textiledigital 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.
  12. 12.  Firm knots are tied in the cloth before it is immersed in a dye bath.  The outside of the immersed portion is dyed but the inside is not penetrated.  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. ◦ Plangi Dyeing - the gathered, folded or rolled fabric is usually held with stitching to form specific patterns.
  13. 13.  It is a resist printing process.  Designs are made with wax on a fabric which is then immersed in a dye. The unwaxed portion absorbs the colour.
  14. 14.  The design on a paper is transferred to a fabric by vaporization. There are two main processes for this- ◦ Dry Heat Transfer Printing In Conventional Heat Transfer Printing, an electrically heated cylinder is used that presses a fabric against a printed paper placed on a heat resistant blanket. In Infrared Heat Vacuum Transfer Printing, the transfer paper and fabric are passed between infrared heaters and a perforated cylinder which are protected from excessive heat by a shield. ◦ Wet Heat Transfer Printing The Wet Heat Transfer Printing uses heat in a wet atmosphere for vaporizing the print pattern from paper to fabric.
  15. 15.  It is a direct printing technique where the background colour and the design are both printed onto a white fabric usually in a one operation.  Any of the methods like block, roller or screen may be used.
  16. 16.  The fabric is coated with a chemical that is sensitive to light and then any photograph may be printed on it.
  17. 17.  Designs are imparted to fabrics by spraying colours in a controlled manner through nozzles.
  18. 18.  A pigment- resin mixture is spread on a screen bearing the design and the fabric is passed into an electrostatic field under the screen.  The pigment- resin mixture is pulled by the electrostatic field through the pattern area onto the fabric.
  19. 19.  It is roller printing applied to warp yarns before they are woven into fabric.
  20. 20.  A misfit is a print defect caused by improper alignment of the screens. Also known as “out of registration,” misfits leave unprinted areas in the design. For example, a green leaf may overlap its black outline or print over another color. Up to 10 % of printed goods designated as first quality contain some level of misfit.
  21. 21.  A stick-in occurs when a small fiber or piece of lint gets stuck in the screen opening. The result is a small pen tip sized unprinted circle in the design. A stick-in is very difficult to see and often goes unnoticed during a long run.
  22. 22.  A scrimp defect occurs when the fabric creases underneath one of the screens during the printing process. The pattern is then printed on top of the crease, leaving a large unprinted area when the fabric returns to its relaxed state.
  23. 23.  Wicking, also known as flushing, occurs when the printed area bleeds out into the unprinted area. The result is a “haloing” or shadowing effect around the outline of the pattern design. Residual salts left in the fabric during resin finishing and / or poor fabric preparation often cause wicking.
  24. 24.  After printing some spots occur on printed fabric
  25. 25.  Can occur due to uneven roller or squeegee pressure while printing paste is applied
  26. 26.  defect created by the print head’s movement over the substrate.  If the head is not properly aligned, or if the substrate advances unevenly, the result is a slight horizontal “band” or line of unprinted area.  Banding can be reduced or prevented :- ◦ with nozzle redundancy and multiple passes by the scanning print head. ◦ In addition, banding is naturally reduced by most fabric substrates.
  27. 27.  occurs when the inkjet nozzle fails to send a drop of ink onto the fabric. Similar to a stick- in, the result is a small, unprinted area. In addition to misfires, nozzle clogging also plays a big role in digital defects.  When an inkjet nozzle clogs, the pattern may lose some or all of one colour. Fortunately, the inkjet drop is tiny, and most misfires and clogs are not seen if the printer has been designed with nozzle redundancy.
  28. 28.  Fabric handling also plays a role in the creation of defects with digital printing. Because most digital printers use a scanning head to print across the width of the fabric, the fabric must remain perfectly still or the image can be distorted.  One of the biggest fabric handling related defects occurs when the fabric buckles or gets wrinkled, causing the scanning inkjet head to come in contact with the fabric. The result is a nasty ink smear and possibly a damaged print head.
  29. 29.  In woven fabrics, a horizontal band off- shaded yarns extending from selvedge to selvedge caused by differences in filling yarn size or difference in tension of warp or filing yarns
  30. 30.  colour in a dyed fabric which rubs off rather easily onto other fabric surfaces. May be caused by inadequate soaping at the completion of dyeing cycle  Most frequently occurring imperfections – result from dyeing processes  Due to faulty or improper dyeing procedures, OR preparation of the fabric prior to dyeing, OR imperfections in the fabric itself.
  31. 31.  loss of color from a dyed fabric when immersed in a liquid. Liquid subsequently becomes colored
  32. 32.  an expression referring to the fact the color of the dyed fabric does not match the std. color or referenced sample.
  33. 33.  shade change in fabric which appears as a horizontal selvedge-to selvedge change. Caused by a filling change (new filling bobbin) or loom stop and subsequent start up
  34. 34.  A discolored area on the cloth. Caused by foreign matter such as dirt, grease, oil or residues of sizing on the fabric being dyed.
  35. 35.  differences in the shade of a fabric from edge to edge or one end of a fabric to the other Called selvedge-to-selvedge (or selvedge to center) shading or end-to-end shading respectively.
  36. 36.  Places in the fabric which have been excessively weakened, usually by exposure to processing chemicals. When the entire fabric is weakened, it is referred to as Tender goods. Also occurs in printing and finishing procedures.