Roller Printing Roller Printing Defects

 Roller Printing Defects and Their Remedies: 

1. Misfitting of Pattern :

This defect occurs when there are two or more colors in a pattern and is caused due to carelessness. t has to be rectified by proper adjustment of the rollers.

2. Scratches:

These are caused on the rollers due to gritty particles (of sand or metal, in the color of the paste which cut into the surface of the rollers and show up on the cloth when it is fully developed.

The defect can be remedied by burnishing the roller and straining the paste through a fine mesh filter,

3. Snappers:

These appear as large double stripes of color caused by some foreign matter getting embedded under the doctor's edge and lifting the roller now and then thus producing a smudgy stripe on the cloth.

The most common cause of snappers is loose threads from the cloth escaping under the lint doctor and being carried up to the cleaning doctor which they lift.

Snappers also appear due to the presence of solid particles in the paste. The remedy is to clean the doctor and roller by washing and getting the paste strained again

4. Lifts:

These appear like small snappers but they occur at regular intervals on cloth. They are caused by the minute due to particles of grit under the doctor blade o the particle of steel that has become embedded in the roller and which by projecting a little into the doctor every time passes under it leaving some color on under the graved surface of the roller which is transferred to the cloth. The remedy is to clean the doctor and roller and get the paste started.

5. Streaks:

These appear as a series of line lines running along that cloth parallel to its selvages; they are caused by a scratch on the roller or a snip In doctor edge.

The lines become wavy due to the transverse motion of the doctor's blade. The monody is to polish the roller and resharpen the cleaning doctor,

Streaks may appear due to the presence of solid particles in the paste In thick case, the remedy is to strain the pasted property.

6. Scumming:

This defect is produced by insufficient cleaning of the unengaged surface of the printing roller whereby the whole cloth is spoiled by a film of one or more colors.

It may arise from a rough doctor's edge a badly adjusted doctor a badly faced roller or a deflective color paste.

The remedy is to sharpen the director edge or adjust the doctor: polish the roller or prepare the color paste properly depending upon the

7. Strimps:

This defect is caused by causes in the cloth which passes through the machine and appears as white places.

The remedy is to remove the creases by moans of good scrimp rails or wet out the cloth and dry it before printing

8. Uneven printing

Uneven printing is caused by various factors as under

A.  When the pressure of the roller against the cylinder is uneven, one odor of the cloth appears darker than the other. The remedy is to adjust that pressure property.

B.  When' the lapping is not uniform, a dark band appears in the middle of that cloth; the remedy is to remove the inequality in lapping.

C. If the fresh color is fed into the color box at one point only instead of distributing it evenly from end to end, uneven effects are produced.

The remedy is to replenish the box as evenly as possible to keep the paste of the same composition, strength, and tone throughout.

D. When the colors are badly mixed or if they separate out in the course of working, unevenness is produced; heavy precipitates of pigment colors are very apt to settle down especially if the Pasto is thin; in mixtures, one constituent may settle more rapidly than others with the result that the color is weakened and altered at the same time.

If the Pasto is too thin, the color goes beyond the boundaries of the casing. The remedy is to stir the color paste from time to time to prevent it from settling down either in the color box of the machine or in the tub that contains the supply.

Lighter prints are produced if the color paste is too thick because it is too solid to be accorded freely; in such a case the consistency of the paste has to be Avoid pinkie It a roller has been polished a good deal in one part to remove scratches, the engraving gets reduced in-depth with the result that the reduced part gives a weaker imoraseinn

Advantages of Roller printing

1. Being a mechanized process, large quantities of cloth can be printed economically by this method;

2. Faulty joints at the repeats never occur and joint marks are totally absent in this method;

3. Fine sharp outlines and subtle gradations of tint and stipple can be produced by this method which is impossible to obtain by block printing of any kind; the halftone effect can be best produced by this method.

 Disadvantages of Roller Printing:

1. The method is not economical for short runs of the fabric;

2.  is difficult to produce blotch designs by this method unless printing is carried out by the discharge style.

3. The number of colors used for printing a pattern is ( usually limited to 4 or 6 because even though 16 engraved rollers can be used, in practice, it is difficult to use more than 4 engraved rollers because of the difficulty of alignment of the design and carry-over of the Color paste.

4. The repeat of design in roller printing is limited to the size of the roller i.e. up to 46 cm. maximum whereas in screen printing, the screen size can Be 1 meter 30 a repeat of 90 cm, that is, nearly double that of roller print is possible,