Background and Task

Paper and board are primarily composed of cellulose fibers. Due to the abundance of hydroxyl groups, cellulose is naturally highly hydrophilic and therefore exhibits a strong tendency to absorb water.

Direct contact with water can lead to fiber swelling, structural changes, loss of strength, and reduced printability and processability.

To specifically control these properties, sizing agents are added during paper manufacturing. The most widely used sizing agents are Alkyl Ketene Dimer (AKD) and Alkenyl Succinic Anhydride (ASA).

These sizing agents render cellulose fibers hydrophobic and thereby:

• reduce water absorption,
• improve dimensional stability,
• increase surface strength, and
• optimize printing and converting performance.

Due to its rapid reactivity and high efficiency, ASA has become one of the most important sizing agents for modern high-speed paper machines.

Before being introduced into the stock preparation system, ASA must be finely dispersed and encapsulated within a protective colloid, typically cationic starch, to form a stable emulsion.

This emulsification process fulfills several critical functions:

• protecting reactive ASA from premature hydrolysis,
• ensuring uniform distribution throughout the stock system,
• promoting targeted adsorption onto cellulose fibers, and
• enabling efficient hydrophobization of the final product.

A high-quality ASA emulsion not only improves the water resistance of paper and board but also contributes significantly to:

• improved printability,
• controlled absorbency,
• reduced dusting,
• greater process stability, and
• higher paper machine productivity.

As a result, emulsion quality has a direct impact on both paper quality and the overall economic performance of the production process.

The Challenges

Alkenyl Succinic Anhydride (ASA) is the most widely used reactive sizing agent in paper and board production.

ASA is a hydrophobic, oil-like liquid that is insoluble in water and highly sensitive to hydrolysis. Even brief contact with water can initiate chemical reactions that significantly reduce its effectiveness.

To ensure efficient sizing performance, ASA must therefore be emulsified immediately before use as extremely fine droplets within a protective colloid, typically cationic starch.

Producing a stable ASA emulsion places high demands on process engineering and emulsification technology.

The Delicate Balance of Shear Forces

Successful emulsification requires precise control of shear forces.

Excessive shear can damage the protective starch layer surrounding the droplets, causing droplet coalescence and reducing emulsion stability.

Insufficient shear, on the other hand, produces droplets that are too large. These droplets:

• are not fully encapsulated,
• hydrolyze more rapidly, and
• result in uneven sizing performance.

Incomplete Encapsulation

Complete encapsulation of every ASA droplet is essential for long-term emulsion stability.

Insufficiently coated droplets react prematurely with water, resulting in reduced sizing efficiency and increased chemical losses.

Unstable Emulsions

Non-uniform droplet size distributions and inadequate dispersion can lead to:

• phase separation,
• sedimentation,
• deposit formation, and
• unstable operating conditions.

High Energy and Time Consumption

Conventional agitator-based systems often require long mixing times and large process tanks to adequately combine hydrophobic and hydrophilic components.

Quality Problems in Paper Production

Even minor deviations in emulsion quality can negatively affect:

• sizing performance,
• printability,
• surface quality,
• deposit formation, and
• machine runnability.

Typical consequences include:

• increased deposit formation,
• uneven hydrophobization,
• blue spot defects, and
• reduced production efficiency.

The Solution

Cavitron supplies emulsification machines specifically developed for the production of highly stable ASA emulsions in starch paste.

The core of the technology is a specially optimized rotor/stator system featuring:

• slotted and perforated rotor and stator rings,
• extremely narrow gap tolerances, and
• optimized product flow guidance.

This design generates precisely controlled shear forces, enabling the reproducible production of extremely fine and stable ASA emulsions.

During continuous processing, ASA is introduced directly into the starch phase and dispersed immediately. This produces exceptionally fine droplets while simultaneously ensuring complete encapsulation by the starch.

With a Cavitron ASA emulsification system:

Optimized Droplet Size Distribution

Precisely controlled shear forces generate a uniform and application-specific droplet size distribution, ensuring reliable encapsulation and high emulsion stability.

Homogeneous Distribution

The unique rotor/stator geometry prevents the formation of ASA agglomerates and ensures uniform distribution throughout the starch phase.

Improved Emulsion Stability

Controlled droplet sizes and complete encapsulation significantly reduce hydrolysis and improve long-term emulsion stability.

Shorter Process Times

Continuous high-intensity mixing substantially accelerates the emulsification process compared to conventional batch systems.

Reduced ASA Consumption

Depending on the application, optimized emulsification can reduce ASA consumption by up to 20% while maintaining the required sizing performance.

Improved Product Quality

The resulting emulsions offer:

• reduced deposit formation,
• high process stability, and
• significantly fewer blue spot defects.

Customer Benefits

High Product Quality

The rotor/stator system specifically developed for ASA applications delivers rapid and highly uniform emulsification with excellent emulsion stability.

Reproducible Process Performance

Continuous operation within a closed system ensures:

• consistent operating conditions,
• reproducible emulsion properties, and
• uniform product quality.

Precisely Adjustable Energy Input

Shear intensity can be accurately controlled through rotor speed and adapted to individual formulations and operating requirements.

Reduced ASA Consumption

Efficient emulsification allows significant reductions in ASA usage without sacrificing sizing performance.

Improved Paper and Board Quality

Stable and homogeneous emulsions improve:

• hydrophobicity,
• printability,
• surface quality, and
• process stability.

Compact and Clean Production

Compared with conventional batch systems, the continuous Cavitron process requires considerably less floor space. Forced product conveyance minimizes:

• deposits,
• vessel contamination, and
• cleaning requirements.

Environmentally Friendly and Safe Operation

The entire emulsification process takes place within a closed system, minimizing:

• emissions,
• product contamination, and
• operator exposure to process media.

Robust and Energy Efficient

Cavitron systems are characterized by:

• low energy consumption,
• high operational reliability,
• simple maintenance, and
• excellent tolerance to viscosity fluctuations.

Customized Solutions

Each system can be tailored to specific customer requirements through:

• different rotor/stator configurations,
• various drive concepts,
• heating and cooling jackets,
• multi-component feeding systems,
• special shaft sealing systems, and
• advanced automation solutions.

Complete Systems from a Single Source

In addition to stand-alone machines, Cavitron supplies complete ASA emulsification plants including:

• tank systems,
• dosing equipment,
• conveying technology, and
• automation and control systems.

Conclusion

The quality of the ASA emulsion has a decisive influence on the efficiency and profitability of modern paper and board production.

Controlled droplet size, complete encapsulation, and high emulsion stability are essential prerequisites for optimal sizing performance.

Thanks to their specially developed rotor/stator technology, Cavitron emulsification systems enable the reproducible, energy-efficient, and highly stable emulsification of ASA in starch-based sizing formulations.

Paper and board manufacturers benefit from:

• improved product quality,
• greater process stability,
• reduced chemical consumption,
• lower deposit formation, and
• increased production efficiency.

With decades of expertise in emulsification and process engineering, Cavitron is a trusted partner for both the development of modern ASA emulsification systems and the optimization of existing production processes.

Overview of Customer Benefits

General Technical Specifications

Static Seals:
Viton®, PTFE (Teflon®), Kalrez®, and other elastomer materials.

Operating Pressure:
Application-specific, up to 100 bar; standard design up to 10 bar.

Operating Temperature:
Application-specific, up to 250°C; standard design up to 150°C.

Power Ratings and Energy Consumption:
See machine specifications overview:
Download Datasheet.

Drive Systems and Power Transmission:
Three-phase electric motors, high-frequency motors, mechanical gearboxes, variable-speed drives, continuously adjustable electronically controlled drive systems, V-belt drives, and Poly-V belt drives.

Processing Intensity Levels:
Application-specific, ranging from coarse mixing and homogenization to ultra-fine dispersion in the angstrom range.

Bearing Systems:
Tapered roller bearings and double angular contact ball bearings.