How to convert from acid sizing to neutral sizing

Detailed Conversion Steps

Step 1: Preliminary Assessment and Preparation
Clearly define your goals: Why are you converting? Is it to improve paper strength and brightness? To use cheaper calcium carbonate fillers? Or to produce durable paper? Having a clear goal helps set reasonable expectations and evaluation criteria.

System Cleaning: This is the most critical first step. The entire paper machine system must be thoroughly cleaned, including:
Slurry System: Stock chest, flushing pump, and piping.
Wet End System: Headbox, white water circulation system.
Dry End System: Wire section, press section, dryer section (especially the dryer surface), size press (if surface sizing was previously used), and calender.
Purpose: Remove residual alumina, rosin size, and acidic deposits from the old system. Any residual acid will significantly interfere with the AKD sizing efficiency.

Chemical Evaluation and Selection:
AKD Emulsion: Determine the initial addition level based on the paper grade and target (typically 0.05% to 0.15% for bone dry pulp). Retention and Drainage Aids: AKD retention is critically dependent on a good retention aid system. This typically requires switching from a single cationic polyacrylamide (CPAM) or a dual/multi-component retention aid system (such as a CPAM/bentonite system).
Fillers: Calcium carbonate (GCC/PCC) is acceptable and recommended. This is one of the main economic benefits of switching to alkaline sizing. Kaolin (commonly used in acidic conditions) should be discontinued.
Aluminum sulfate (alumina): Its use must be discontinued or significantly reduced. Alumina is a natural enemy of AKD, destabilizing the AKD emulsion and rendering it ineffective.
Dyes and Other Additives: Check the compatibility of all existing dyes and chemicals to ensure they are suitable for neutral/alkaline environments.