The application of Alkyl Ketene Dimer (AKD) sizing agents in paper mills, while highly beneficial, can sometimes present operational challenges. Recognizing and effectively troubleshooting these issues is crucial for maintaining product quality and process efficiency. NINGBO INNO PHARMCHEM CO.,LTD. offers guidance on common AKD sizing problems and their solutions.

1. Inadequate Sizing (Low Water Resistance)

This is perhaps the most frequent issue, characterized by paper that absorbs liquids too readily, leading to poor printability and reduced functionality. Common causes include insufficient AKD dosage, improper pH levels (too acidic), poor retention of AKD on the fibers, or incomplete curing. To troubleshoot:

  • Adjust Dosage: Ensure the AKD dosage is within the recommended range.
  • Monitor pH: Verify that the system pH is maintained between 7-9 for optimal AKD reactivity.
  • Enhance Retention: Review the use and type of retention aids, as these are critical for keeping AKD on the fibers.
  • Optimize Curing: Ensure sufficient drying temperature and time in the paper machine's drying section to facilitate proper AKD curing.

2. Poor Emulsion Stability

An unstable AKD emulsion can lead to uneven sizing, streaks, and deposits on machinery. This can stem from improper emulsion preparation, incorrect storage temperatures, or issues with emulsifying agents. Solutions include:

  • Review Preparation: Ensure the AKD emulsion is prepared according to strict specifications, with correct temperature and mixing.
  • Proper Storage: Store AKD emulsions under recommended conditions to prevent degradation.
  • Emulsifier Check: Verify the quality and dosage of emulsifiers used.

3. Deposits on Paper Machine Equipment

The formation of deposits on rollers, felts, and other machine parts can disrupt operations and affect paper quality. This can be caused by over-application of AKD, interactions with other chemicals, or poor retention leading to excessive free AKD. Troubleshooting steps include:

  • Optimize Dosage: Reduce AKD dosage if it exceeds requirements.
  • Improve Retention: Implement or optimize retention aids to bind more AKD to the fibers.
  • Chemical Compatibility: Assess compatibility with other chemicals in the furnish; some combinations might exacerbate deposit formation.
  • Regular Cleaning: Maintain a rigorous cleaning schedule for all processing equipment.

4. Delayed Sizing Effect (Hysteresis)

AKD sizing can exhibit a 'ripening' period, meaning the full sizing effect develops over time after the paper leaves the machine. If this delay is too long or inconsistent, it can pose challenges for quality control. While some aging is normal, understanding AKD sizing mechanism paper helps explain this. Ensuring proper curing conditions during drying can help accelerate the initial sizing development.

NINGBO INNO PHARMCHEM CO.,LTD. advises that consistent quality control testing, such as Cobb tests, is essential for monitoring sizing performance and identifying issues early. By understanding these common AKD sizing issues and applying these troubleshooting techniques, paper mills can ensure efficient and effective use of AKD sizing agents, leading to consistently high-quality paper products.