Registered in England No. 1725990 © Pomeroy Pressroom Products Ltd 2010 Website design by: AH Designs Anti-Set-Off Spray Powders Q & A / Advice - Anti-Set-Off Spray Powders: Anti-set-off spray powders are looked upon as a necessary evil (especially as print speeds increase), as they remain the only practical method of ensuring that the printed sheets in your delivery pile do not stick together as a result of wet ink transferring from one printed sheet to another. Anti-set-off powders achieve this by creating an air gap (spacer) between printed sheets, thus preventing ink from one printed sheet contacting another and thus allowing the printing ink to dry naturally. There are different grades of anti-set-off spray powders, to cater for different types of substrate and differing absorption rates of the printing inks being used. Anti-set-off spray powders are not required for the following applications: - Printers using UV cured inks. - Rotary Presses (including rotary letterpress). - Web offset (i.e. Magazine printing). - Flexographic (i.e. flexible packaging). - Gravure (i.e. Catalogues). - Silk screen printing. - Digital printing (inkjet or toner). Is Particle Size Important? Uniform particle size is the key to producing a consistent, high performance anti-set-off powder. Most traditional anti-set-off spray powders have a spread of different particle sizes in the prescribed range of the powder which leads to a percentage of small particles that never reach the printed sheet. This means more spray powder is required to ensure the right amount of the correct size particles reach the printed sheet. Pomeroy SureSpray Anti-Set-Off Spray Powders have a more uniform range of particles with fewer “fines” which create dust and wasted powder. For those printers using a new model of printing press, ultra low-dust grades are recommended, as these can allow you to reduce the amount of spray powder used by up to 55% (when compared to conventional powders). This is primarily due to the spray heads on new presses being very accurately adjusted to the target sheet. By reducing the amount of powder being sprayed, you also reduce the amount of ‘waste’ dust being created in the pressroom, meaning less cleaning and more printing. Using the wrong grade of spray powder: By using the incorrect grade of spray powder and therefore particle size, can result in you wasting upto 80% of your spray powder. In addition using the incorrect grade will cause housekeeping issues and eventually cause accelerated wear on the delivery chains and gripper bars. If you use a grade with too large a particle size, this can result in problems causing a ‘sandpaper’ feel on the substrate which can give rise to problems in lamination and varnishing. Storage Conditions: Anti-Set-Off Spray Powders should be stored at room temperature in dry conditions. Containers should be fully sealed after use to prevent the spray powder becoming damp or contaminated. Troubleshooting: Clogging: Possible causes include: ▪ Moisture. ▪ Using old spray powder (2 years+). ▪ Shards / Debris in the spray powder. ▪ Low quality product (using cheap Raw Materials). Excessive Dust: Possible causes include: ▪ Incorrect spray powder being used. ▪ Settings too high to compensate for blocked nozzles. ▪ “Fines” from low quality raw materials. Setting-Off: Possible causes include: ▪ Poor machine/applicator settings. ▪ Blocked spray nozzles. ▪ Powder compaction in the reservoir. ▪ Powder flow due to compaction. ▪ Incorrect grade of spray powder for application and/or substrate. ▪ Faulty spray unit (usually with the vibration cone or agitator). ▪ Poor machine settings. Localised Setting-Off: Possible causes include: ▪ Individually blocked spray nozzles (therefore an uneven spray across the printed sheet). Compaction / Poor Flow: Possible causes include: ▪ Reservoir too full: Do not overfill the spray powder reservoir, as the powder will compact and not flow. We recommend only filling the reservoir half-way, thus allowing the spray powder room to circulate and flow.