The air-laid technology is a process for dispersing and forming fibers by aerodynamic principle. Its most prominent feature is adapt to processing fibers fineness less than 5.5 deniers, such as wood pulp fibers, natural fibers, rayon fibers, synthetic fibers, inorganic and recycled shorter fibers.
The critical technology of dry air-laid to make the fibers randomly and evenly distributed after formation. The two necessary conditions: separate the fibers into individual completely and make the fibers forming a sheet evenly.
Factors affecting fiber separation
- The pulpboard has to be a fluffy treatment to make the pulp soft, fluffy and easy to be separated.
- Moderate pulpboard humidity: Generally between 8% to 10%. Lower moisture will generate static electricity during the fiber separation process, make the fibers into a mass. Meanwhile, higher humidity goes against fiber separation, and many fiber bundles remain in the sheet to affect the appearance and quality.
- Equipment requirements: strong crushing capacity, no agglomeration, uniform pulp fiber.
Factors affecting the uniform fiber-forming
The uniformity of the fiber sheet refers to the even degree of the fiber arrangement in the sheet. Its structure should be uniformly distributed in a three-dimensional space and compact after forming.
- Process conditions
- Balance vacuum degree: The fiber stream stirred and crashed into single fibers by the airflow and the toothed roller in a forming head, then passed through the sieve into the sedimentation chamber.
In the sedimentation chamber, The pulp and the air should in a rated balance, which effected by the in-air fan and the adjustable vacuum pump. For different quantitative fibers, adjust the air volume and speed by the vacuum pulp to keep the vacuum to maintain the balance between the pulp and the air.
The air will get swirl and the fibers will flocculate into a mass under improperly vacuum degree.
- Moderate temperature and humidity: The primary purpose of moderate temperature and humidity is to make the fibers easy to disperse and less the static electricity. Typically, humidity-controlled at 90%.
- Cleanliness of the forming mesh belt: A conductive mesh belt is required in the forming process to avoid the small fiber adhesive on the belt and block it, that will cause no or less fiber laid at this area, which will form thinner point blemish or holes in the final product. Therefore, the conductive property and cleaning process of the forming mesh belt is very important.
- Equipment that decides the fiber formation uniformity
Two perforated sieve cylinders are fixed in the forming head, the material distribution system delivers the fiber mass to each end of the sieve drum to ensure uniform fiber distribution.
In the sieve cylinder, there are dispersing toothed roller with tooth rotate in opposite direction to the cylinder, this makes the roller dispersing the fibers sufficiently. Usually, the distance between the toothed roller and the cylinder, and the diameter of the hole perforated on the sieve cylinder are determined by the fiber size.
Other factors affecting air-laid forming
- Anti-static in the forming process
In the dry-laid papermaking process, the transportation and forming of fibers rely on air, which is easy to generate static electricity due to friction, etc. The static not only affects product quality but also has the risk of fire.
There are two methods to eliminate the static during the forming process:
- accelerate the static electricity run-off:
- Increasing the temperature and humidity to reduce the fiber surface resistance, could enhance the fiber conductivity significantly;
- Use the conductive anti-static process mesh belt, and apply antistatic smooth tape on the inwall of the sedimentation chamber.
- Neutralize static electricity to reduce static electricity. Add the antistatic agent to the pulpboard before it is pulverized to prevent static electricity generated.
- Main points for choosing a conductive forming mesh belts
- Temperature resistance of the process mesh belt
- The anti-static property, help to reduce and eliminate the static charge
- Air permeability, lower air permeability will reduce the tiny fiber loosing to get a tight sheet, and in the opposite, higher ventilation will get a loose sheet
- Weave pattern and constructure, a well-designed constructure will make the mesh belt enable to grasp the fiber in conveying and release easily at the end
- Material, PET is the most widely used for its high strength, excellent temperature & chemical resistance, smooth running and dimensional stability.
For more information about the conductive anti-static process mesh belt, contact us right now!