(Detailed guide on wet end chemicals used in multilayer board machines, including uses, advantages, disadvantages, and suppliers in India.)
Introduction
In a multilayer board machine, the wet end section plays a critical role for sheet formation, strength, drainage, runnability, and final board quality. With increasing use of recycled fiber, high ash loading, and higher machine speeds, correct selection and control of wet end chemicals has become more important than ever.
What is the Wet End of a Multilayer Board Machine?
The wet end includes all process areas from pulping to sheet formation on the wire. In a multilayer board machine, each layer (top, middle, back) may have different furnish compositions, but the wet end chemistry philosophy remains common:
- Control fiber bonding
- Improve drainage
- Maximize retention of fibers and fillers
- Ensure stable machine operation
- Achieve target board properties at lowest cost
1. Retention and Drainage Aids
Description & Specification:
Retention and drainage aids are mainly polymer-based chemicals, such as:
- Cationic Polyacrylamide (CPAM)
- Anionic Polyacrylamide (APAM)
- Polyethyleneimine (PEI)
- Microparticle systems (colloidal silica, bentonite)
Role of Retention Aid in Wet End:
Retention Aid Chemicals supplied as liquid emulsions or powders, having different molecular weights and charge densities.
- Retention aid Improve retention of fibers, fines, and fillers at the time of sheet forming, Increase drainage rate on wire Table and Reduce solids load in white water
- It Reduces raw material loss (fiber loss), Allows to increase machine speed machine speed and also improves sheet formation and uniformity.
Advantages:
- Higher productivity
- Lower chemical and fiber losses
- Cleaner wet end system
Disadvantages:
- Overdosing causes flocculation and poor formation
- Requires precise charge balance control
Major Suppliers of RDA Chemicals: Nalco, Solenis Chemicals, Tanisha Resins, Kemira Chemicals, and Haber chemicals.
2. Internal Sizing Chemicals
Description & Specification:
- Rosin-based sizing agents
- Alkyl Ketene Dimer (AKD)
- Alkenyl Succinic Anhydride (ASA)
Role of Internal Sizing Chemicals:
Sizing chemicals are usually supplied as emulsions or dispersions compatible with acidic, neutral and alkaline papermaking systems. PAC and Alum are used to maintain the system pH and also required for reaction with Rosin in acidic and neutral sizing process.
- Sizing Chemicals Provide resistance to water and moisture penetration in paper and paper board and also improve strength and printability of board.
- Internal sizing is Essential for all types of paper, packaging board, carton board, and food packaging paper and board.
Advantages:
- Improves end-use performance of paper and paper board
- Allows use of higher recycled fiber
Disadvantages:
- ASA is sensitive to hydrolysis
- Rosin requires strict pH control and alum or PAC addition.
Major Suppliers of Internal Sizing Chemicals: Ivax Chemicals, Kemira Chemicals, Haber Chemicals, Jaiaravali Industries, Rishab Chemicals
3. Dry Strength Chemicals
Description & Specification:
- Cationic starch
- Polyacrylamide (PAM) dry strength resins
- Spray Starch
Role of Dry Strength Chemicals:
- Dry Strength chemicals improve tensile strength, burst, stiffness and internal bonding (Ply Bond) and these chemicals compensate for strength loss due to recycled fibers
- Dry Strength chemicals enables cost reduction by using lower-quality fiber and improves board converting performance.
Advantages:
- Cost-effective strength improvement
- Better runnability in corrugation and printing
Disadvantages:
- Overuse can reduce drainage
- Requires proper cooking and dilution (for starch)
Major Suppliers of Dry Strength Chemicals:
Indian Supplier-Vijaynagar Biotech, Santosh Starch, Roquette starch, Paramesu Biotech, Bharat Starch, SPAC Starch.
International Supplier – General Starch, SMS (Siam Modified starch) starch, Ingredion Starch product,
4. Wet Strength Resins
Description & Specification:
- Polyamide Epichlorohydrin (PAE)
- Melamine Formaldehyde (MF)
- Urea Formaldehyde (UF)
Role of Wet Strength Chemicals:
- Wet strength chemicals maintain sheet strength under wet or humid conditions.
- Wet strength paper and board are used for specialty packaging boards
Advantages:
- Improves moisture resistance
- Enhances board durability
Disadvantages:
- Higher cost
- Environmental and regulatory concerns for formaldehyde-based resins
5. Defoamers and Antifoams
Description & Specification:
Defoamers control air entrainment and foam generation in the wet end. Common types include:
- Silicone-based defoamers
- Mineral oil-based defoamers
Role of Defoamers and Antifoams:
- Defoamers Prevent foam-related sheet defects
- Defoamers Improve drainage and formation
Advantages:
- Stable machine operation
- Reduced sheet breaks
Disadvantages:
- Excess dosing can reduce sizing and bonding efficiency
Major Suppliers of Dry Strength Chemicals: Nalco chemicals, Ivax Chemicals, Solenis Chemicals, Haber Chemicals.
6. Biocides and Deposit Control Chemicals
Description & Specification:
- Oxidizing and non-oxidizing biocides
- Pitch and stickies control agents
Role of Biocides:
- Biocides Control slime and microbial growth in system of paper board machine. It also Prevent deposit formation on wires and felts of paper machines.
- Biocides are essential when using recycled fibers
Advantages:
- Improved cleanliness
- Reduced downtime and sheet defects
Disadvantages:
- Environmental handling requirements
- Resistance may develop if poorly managed
Major Suppliers of Dry Strength Chemicals: Solenis Chemicals, Haber Chemicals, Buckman Chemicals, Proclin chemicals, Amazon Chemicals.
Layer-wise Chemical Strategy in Multilayer Board Machine
Top Layer
- Focus on formation, sizing, and surface quality
- Lower defoamer carryover
Middle Layer
- Focus on drainage and cost optimization
- Higher tolerance for recycled fiber
Back Layer
- Higher dry strength requirement
- Strong stickies and pitch control needed
Conclusion
Efficient wet end chemical management is the backbone of stable operation in a multilayer board machine. Correct selection, dosing, and monitoring of wet end chemicals not only improve board quality and strength, but also significantly reduce production cost and downtime.
A systematic approach combining retention optimization, proper sizing, strength enhancement, and deposit control ensures consistent performance even with high recycled fiber usage.