In roller printing, the design is put on to the fabric by copper engraved rollers.(copper engraved cylinders).
The main distinguishing feature of roller printing is that it is a mechanized process i.e, the patterned effect is produced with the help of machine with engraved rollers.
The roller engravings match exactly the artistic designer’s creative sketch.
A separate engraved cylinder is required for each colour in the print.
The size of the engraved cylinders is governed by the printing machine and the design.
Rollers are engraved either by hand, machine or by panthographs or photographic engraving.
Hand engraving is rarely used today. In machine engraving the design is stamped on to copper roller surface by means of previous mill (soft steel cylinders) with design, applying pressure.
Roller Printing Machine:
The essential part of the machine consists of a large central cylinder. The central cylinder is made of steel or cast iron. It rotates with the moving fabric.
This central cylinder is wrapped with 8-12 layers of cloth called lapping which is a mixed cloth with linen warp and worsted weft.
It resists the pressure to which it is subjected during printing.
Since the central cylinder is made of cast iron, it is therefore, covered with an endless woolen felt cloth or blanket to give elasticity to the fabric being printed.
A cheap grey cotton fabric called backgrey is run between the blanket and the fabric being printed.
Each roller is polished after engraving for uniform smoothness so that the dye will spread evenly on the raised areas.
They are then locked in to precise portions on the machine for proper registrations.
The number of rollers used depends on the number of colours in the design.
As many as 16 colours (rollers) can be employed. But usually not more than 4-6 rollers are used.
Method of Application:
The fabric which is to be printed is fed in to the machine as the driving motor is switched on, it moves forward around the central cylinder which also starts rotating.
Each of the engraved rollers first comes in contact with a companion roller that has been submerged in the dye paste. As the engraved rollers rollers come in contact with the dye fabric and are pressed against it, the colour is transferred and the particular part of the design is impressed on the cloth.
The doctor blade scrapes off excess colour paste.
The lint doctor removes any lint, loose fibre etc from the cloth being printed.
As the fabric is passed between the engraved rollers and the smooth cylinder rollers, the dye from the shallow areas is pressed on it.
The backgrey absorbs the excess print paste and prevents it from striking through and staining the smooth rollers.
When the cloth is fully printed, it moves forward and leaves the cylinder. It is then drying chamber and then in to the steam chamber where the dye is set by the moisture and heat.
The backgrey is eventually washed out and reused.
Suitability:
Characteristics of prints:
Large quantities of cloth can be printed economically by this method.
Faulty joints at the repeats never occur and joint marks are totally absent in this method.
Fine sharp out lines and subtle graduations of tint and stipple can be produced by these methods, which are impossible by block printing techniques.
Half-tone effects can be produced by this method.
The repeat of the design in roller printing is limited to the size of the roller.
Identification:
Usually traditional patterns like stripes, checks, spots are done in this method.
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