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Roller printing.

  2.  Printing can also be defined as localized dyeing.  Roller printing, also called cylinder printing or machine printing, on fabrics is a textile printing process.  Invented by : Thomas Bell of Scotland in 1783.  It is a modern continuous printing technique.  This was introduced in an attempt to reduce the cost of the earlier copperplate printing.
  3.  In this machine counterpart of block printing, engraved Cu cylinders or rollers are used in place of hand carved blocks.  In this method, a heavy copper cylinder (roller) is engraved with the print design by carving the design into the copper.  Copper is soft, so once the design is engraved, the roller is electroplated with chrome for durability.
  4. Roller-printed cotton cushion cover panel , 1904
  5. ENGRAVED COPPERPLATE PRINTING The printing of textiles from engraved copperplates was first practiced by Bell in 1770. It was entirely obsolete. The presses first used were of the ordinary letterpress type, the engraved plate being fixed in the place of the type. In later improvements the well-known cylinder press was employed; the plate was inked mechanically and cleaned off by passing under a sharp blade of steel; and the cloth, instead of being laid on the plate, was passed round the pressure cylinder.
  6. The plate was raised into frictional contact with the cylinder and in passing under it transferred its ink to the cloth. The great difficulty in plate printing was to make the various impressions join up exactly; and, as this could never be done with any certainty, the process was eventually confined to patterns complete in one repeat, such as handkerchiefs, or those made up of widely separated objects in which no repeat is visible, like, for instance, patterns composed of little sprays, spots
  7. It gives higher production without rotary screen printing machine.14 colors can be used for printing. Even Medium designs can be produced. It can be used for printing any style.  Any color is used for printing without higher alkali or conc. acid. Higher production by using single color. Complex design is possible.
  8. OPERATION  This machine has a main cylinder that is fitted with a large gear. In this printing, the print paste is supplied from reservoirs to rotating copper rollers, which are engraved with the desired design.  These rollers contact a main cylinder roller that transports the fabric. By contacting the rollers and the fabric, the design is transferred to the fabric.
  9.  ENGRAVED ROLLERS  Solid and shell engraved rollers are available which varies in length.  When the copper engraved rollers are chromium or nickel plated their lives can be considerably lengthened.
  10.  As many as 16 rollers can be available per print machine, each roller imprints one repeat of the design.  As the roller spins, a doctor blade in continuous mode scrapes the excess of paste back to the color trough.
  11.  DOCTOR BLADES : Color doctor :- color doctor is made of steel.  It consists of a sharp steel blade and has a razor like edge, which rests on the engraved roller.  The other edge is clamped between two brass plates and screwed together.  The doctor blade is given a to and fro motion parallel to the direction of the roller axis to prevent unequal wear and tear of the blade edge which is done by the transverse motion.
  12.  At the end of each batch the paste reservoirs are manually emptied into appropriate printing paste batch containers and squeezed out.  The belt and the printing gear (roller brushes or doctor blades, squeegees and ladles) are cleaned up with water.
  13. LINT DOCTOR:  The lint doctor is made of brass  No transverse motion is imparted to it.  It’s purpose is to pick up loose cotton fibers attached to the engraved roller, which otherwise would find their way into the printing paste in the color box.  LAPPING:  This is covering of the central pressure bowl and is made up of a special fabric of linen warp and worsted weft.  Eight to twelve layers of the fabric are wound on the bowl to free from creases.
  14. BLANKET:  It is a thick woollen cloth tightly woven and felted.  It is of uniform texture , elasticity and of equal thickness.  This increases the elasticity of the lapping and it circulates continuously round the pressure bowl between the lapping and cloth to be printed.  After continuous use the blanket becomes hard and soiled by the paste penetrating into it and must be either turned or replaced.
  15. BACK GREY:  When the woolen blanket is used unbleached cotton cloth is run between the blanket and the cloth to be printed protects the blanket from the paste passing through the cloth.  It is not necessary when the washing blanket is employed .  It is wound on a roller and after printing it leaves the machine and is wound again on another roller.  After use it is taken for bleaching and may be used for printing.
  16. DEFECTS SCRATCHES : When grit particles in the printing paste cut the smooth surface of the roller, the scratches produced will also transfer the paste to the cloth. By burnishing ( polishing) the roller as well as by staining ( filtering) the printing paste , the fault can be removed.
  17. SNAPPERS : Loose threads from the cloth escaping under the lint doctor , bits of the dried up paste and other hard particles cause snappers, which are large doubled stripes of color running along the length of the cloth. A larger amount of paste is transferred to the fabric . This defect can be prevented by washing and cleaning the doctor blade , roller and by staining the paste.
  18. LITTS : Very minute snappers called litts are produced at regular intervals on the cloth. These are caused by hard particles like a metal piece getting embedded in the engraving of the roller and protruding from it , there by lifting the doctor blade temporarily. STREAKS: Streaks are very fine lines or series of lines running along the piece and parallel to selvedges.These may be due to scratches on the engraved roller or a cut in the doctor blade edge.Polishing the roller and sharpening the doctor blade edge are the remedial measures to be taken.
  19. SCUMMING: Spoiling of the by one or more colours due to insufficient scrapping of the print paste from the engraved portion . It can be due to: * Rough Doctor Blade Edge * Badly Adjusted Engraved Roller * Defective Printing Paste SCRIMP: Creases , which are remaining in the cloth while printing give rise to the defect of non printing underneath the fold.
  20. UNEVEN PRINTING: Uneven pressure due to faulty lapping or improper feed of the print paste ,too much polishing of certain parts to eliminate scratches ,give uneven impressions LOBBYING: This is an uneven printing due to slippage of a roller round its mandrel, due to improper fitting . BACK-GREY CREASE: This defect is caused due to improper feeding of fresh back-grey, inefficient washing and improper drying of used back grey .
  21. BACK-GREY STITCH IMPRESSIONS : Although this is an inevitable defect because of the stitch impressions, it can be minimized by using the suitable sewing thread.
  22. ADVANTAGES.  Higher production without rotary screen printing machine.  14 colors can be used for printing.  Medium design can be produced.  Can be used for printing any style.  Any color is used for printing without higher alkali or conc. acid.  Higher production by using single color.  Complex design is possible.
  23. DISADVANTAGES.  Large design is not possible.  Higher coloring effect is not possible as like block printing.  Lower production by using more than one color.  Changing time is high.  Engraving the printing roller is expensive Operation.