Tips About Powder in Offset Printing Machines

Powder is used to prevent backlash and for better drying of printed works through oxidation and creates a gap between the printed sheets.

Powder does not cause drying. At the same time, powder can improve the sliding behavior of printed sheets in the machine and in the finishing steps after printing. 

Various printing devices and systems have a powder spraying system. Their common goal is to spread a small amount of powder evenly throughout the sheet.

Classification of drying powder

Powder is made of different materials and in different sizes from 10 to 80 microns.

The most important factor of powder quality is the homogeneous sorting of powder size.

Odoo • A picture with a caption
Add a caption to enhance the meaning of this image.

There are three main types of powder:

•Powder made of calcium carbonate (a product of inorganic and mineral materials)

• Powder made from natural starch (vegetable product)

•Powder with sugar base

powder with calcium carbonate base

Calcium carbonate drying powder is heavier, creates little dust (much less than starch and powdered sugar) and can be used in smaller quantities.

The crystal structure of calcium carbonate can lead to the roughness and sanding of the printed work and it damages the plate and parts of the machine.

Starch-based spray powder:
This powder has a soft and round grain. It is insoluble in water and alcohol.
Natural starch powder is hydrophilic and absorbs moisture without dissolving.
Starch powder it is gentle on the plate and the printing machine, and it can be easily used by all powder sprayers.
Unrefined starch powder is suitable for additional coatings (offline) and lamination without stains.
Starch-based powder is ideal for use with water-based varnishes and greatly aids in creating an even palette and smooth delivery.
Note: Starch powder must be used in electrostatic powder sprayers (Oxydry), because other powders do not work in this system.
Starch powder for water-based varnish:
You may also come across other names like silicon powder, but they still mean starch powder.
Processed starch powder for water-based varnish should only be used if there are no multiple prints. Not suitable for subsequent finishing processes such as coating, lamination or hot foiling.
The use of starch powders has increased significantly.
Sugar base powder:
These powders are soluble in water and create minimal build-up on tires, which makes them suitable for multiple printings.
Sugar-based powder reacts strongly to heat and should not be used in combination with a dryer, as it blocks the powder path of the sprayer.
Sugar-based powder should not be used in combination with water-based varnish.
Powder selection criteria:
Choose approved powders. The trade association has approved the powders and published the relevant instructions.
For packaging printers, there are new guidelines on the purity of starch powder made from genetically engineered corn and potato starch.
In general, uncoated papers are more absorbent than coated papers and require less powder.
The rougher the printing paper, the larger the powder grain should be.
In case of double-sided printing, the unevenness of the paper is important and determines the powder grain size
If this reduces the amount of powder needed, it is recommended using larger grains.
The type of powder must match the finishing operations (coating, lamination, hot foil).
Heavy powders (calcium carbonate) - especially at high printing speeds - can be applied to the sheet more accurately than lighter powders (starch).
Problems that arise during the use of powder and points that should be paid attention to.
When printing at a speed of 15,000 sheets per hour, approximately 4 sheets are passed through the spray powder every second.
If you use poorly sorted powder, a lot of powder is circulated and only the larger particles have a chance to reach the paper. Small particles (probably) just fly around and make the car dirty.
Heavy powder works more accurately on paper. Calcium carbonate is significantly heavier than other types of powder (starch powder and sugar powder).
To reduce the wear of machine parts, calcium carbonate powder is coated and the grains are rounded in a special operation.
If you use poorly sorted powder, a lot of powder is circulated and only the larger particles have a chance to reach the paper. Small particles (probably) just fly around and make the car dirty.
Odoo • A picture with a caption
Add a caption to enhance the meaning of this image.

Common problems associated with drying powder

Uneven powder distribution.

Powder nozzles or path tubes are blocked or disabled.

The air of the blowers (wind on the job) is very strong in delivery.

The air suction is very strong.

Testing the performance of powder spray nozzles

Check the application of the powder in the machine with a black sheet (printed paper or by printing zinc).

You can also use an old blanket.