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Target Market: Coatings
Application Description
High quality inks are used in a number of applications including newspapers, magazines, computer printers, candy wrappers and beer cans. These inks must be filtered to provide clear, concise print graphics. Higher resolution and print quality have increased the need for better inks and print nozzle capability. The creation of offset press rolls using photolithography is one example where filtration is playing an increasing role.
Material
Porous Polyethylene
Types of Filters Used
Historically, the most common filter used on low quality ink applications is needle felt bags. In recent years, meltblown bags and cartridges have been introduced at the point of application on higher quality inks. The cartridges can be either cylindrical depth filters or pleated cartridges.
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Purpose of Filtration
The primary purpose of filtration is to remove particles caused by agglomerated pigment, resin or dirt. This particulate contamination can cause print defects such as stars, lumps, rough areas, splatters and spits. These defects cause poor print quality and rejected graphics. Throughout its life, a filter should effectively remove all particles big enough to cause print defects or nozzle clogging, but not be so tight as to remove the desired pigments and resins. Many filters become more efficient during their life due to the accumulation of particulate. This can be detrimental to ink applications. Some filters remove a broad range of particles above and below their respective ratings. Filters that effectively only remove particles at and above their rating while allowing the smaller particles to pass through are called classifying filters. Ideal for this type of application, classifying filters are particularly effective if they maintain their efficiency over a significant portion of their life.
Common Filtration-Related Problems
- Fish Eyes - Defects caused by lubricating oils (silicone) sometimes found on filters to assist in the manufacturing process
- High Filter and Ink Usage - Premature plugging caused by contaminated paint, tight and/or low surface area filters resulting in high filter usage and lost paint (filter change outs can result in $10,000 in lost ink)
- Stars and Rough Surfaces - Surface defects caused by particles passing through the filter due to improper sealing, migration or too large a pore size
- Spits, Splats, Uneven Coatings, Nozzle Plugging - Plugged spray nozzle caused by particles passing through or around the filter
- Uneven or Lack of Coating - Plugged filter caused by lack of sufficient ink pressure to operate the spray nozzle
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