Paper two-sidedness is a complex quality issue involving the distribution of fibers, fines and fillers through the thickness of the sheet, as well as the way the wet web is formed, dewatered, dried and finished.

Because two-sidedness is closely related to wet forming, an effective improvement program should begin before the sheet reaches the press or calender section.

The source material identifies several important approaches: improving wet-end retention, optimizing refining and fiber furnish, using multi-layer headbox technology, managing fillers more precisely, balancing dewatering and coordinating machine speed with the drying profile.

1. Optimize Stock and Wet-End Chemistry

Wet-end chemistry provides an important opportunity to improve the structural uniformity of the paper sheet.

The objective is to increase the retention of fines and fillers while promoting a more uniform distribution of these components through the Z-direction, or thickness direction, of the sheet.

Improve Fines and Filler Retention

Chemical retention aids can reduce the amount of fines and fillers lost through the forming fabric.

Improved retention can contribute to:

• Higher overall fines retention
• Higher filler retention
• Reduced loss through the wire
• More uniform Z-direction distribution
• Reduced differences between the two paper surfaces

The original material specifically identifies the dual-component microparticle retention system as more effective than a single-polymer retention system for this purpose.

Under the conditions referenced in the source material, filler retention can be increased by nearly 20%, while filler distribution becomes more uniform.

2. Optimize Refining and Fiber Furnish

The condition of the fibers also influences sheet uniformity.

Improve Fiber Fibrillation

Appropriate refining promotes fiber fibrillation and increases the available bonding area between fibers.

Better fibrillation can contribute to:

• Improved sheet formation
• Increased fiber-to-fiber bonding
• Better structural uniformity
• Improved paper strength

Refining should therefore be considered together with fiber furnish when attempting to improve paper two-sidedness.

3. Use Multi-Layer Headbox Technology

A Multi-Layer Headbox provides another approach to controlling the structure of the paper sheet.

Instead of treating the sheet as one uniform fiber layer, the headbox can establish a multi-layer structure in which different fiber characteristics are assigned to different layers.

For example, the furnish of a selected surface layer can contain a greater proportion of fine fibers.

By optimizing the fiber composition of individual layers, differences in properties between the two sides can be compensated through the sheet structure itself.

This makes multi-layer headbox technology a structural approach to reducing two-sidedness rather than relying entirely on downstream correction.

4. Improve Filler Management

Filler management should consider more than total filler dosage.

According to the source material, the type and particle size of the filler should also be controlled.

The document gives small-particle, spindle-shaped Precipitated Calcium Carbonate (PCC) as an example.

A suitable filler morphology and particle size can promote more uniform distribution within the paper sheet.

Improved filler distribution can, in turn, help reduce differences between the two surfaces.

5. Balance Paper Machine Speed and the Drying Curve

Paper two-sidedness can also be intensified during drying.

Machine speed and drying capacity should therefore be properly matched.

The dryer-cylinder temperature profile should be optimized to avoid excessive differences in drying rate.

If the two surfaces or different portions of the sheet experience substantially different drying conditions, existing structural differences may become more pronounced.

Controlling the relationship between:

Machine Speed + Drying Capacity + Dryer Temperature Profile

is therefore an important part of maintaining stable paper quality.

6. Key Technologies for Reducing Paper Two-Sidedness

The source material identifies six main technical approaches.

6.1 Gap Former

Application: Forming Section

A Gap Former enables simultaneous drainage from both sides of the wet web.

The principle is to reduce the structural difference created by predominantly one-sided dewatering and address paper two-sidedness closer to its source.

Main objective:
Create more balanced two-sided dewatering and reduce the fundamental difference between the two surfaces.

6.2 Top-Wire Former

Application: Forming Section

A Top-Wire Former introduces an additional drainage direction above the existing forming section.

This allows the wet web to experience two-sided drainage rather than relying primarily on downward drainage through the original forming fabric.

Main objective:

• Improve sheet formation
• Introduce more balanced dewatering
• Reduce structural two-sidedness

For existing Fourdrinier machines, this can be an important forming-section upgrade option.

6.3 Hot-Roll Calendering and Steam Box

Application: Calender / Dryer Section

Hot-roll calendering and steam treatment act later in the production process.

Their role is to adjust stress differences between the two surfaces and improve the balance of surface properties.

Main objective:

• Improve paper smoothness
• Balance surface properties
• Reduce remaining surface two-sidedness

These technologies are more appropriately considered downstream corrective measures rather than substitutes for proper sheet formation.

6.4 Dual-Component Microparticle Retention System

Application: Wet-End Chemistry

This retention strategy focuses on improving the distribution of fillers and fines through the thickness of the sheet.

Better Z-direction uniformity helps reduce composition differences between the two surfaces.

Main objective:

• Improve fines and filler retention
• Improve component distribution
• Reduce dusting and linting

6.5 Multi-Layer Headbox

Application: Stock Delivery / Forming System

A Multi-Layer Headbox establishes different fiber layers and allows the fiber furnish of each layer to be optimized separately.

This makes it possible to compensate for property differences through structural design.

Main objective:
Reduce two-sidedness by balancing the characteristics of different sheet layers.

6.6 Dandy Roll

Application: Forming Section

A Dandy Roll uses mechanical action on the developing wet web to influence sheet formation.

Its application can promote more uniform distribution of fibers and fillers.

Main objective:

• Improve formation
• Improve fiber distribution
• Improve filler distribution

7. Prevention During Forming Should Come First

The causes of paper two-sidedness are complex, but the source material emphasizes that it is fundamentally associated with the wet-forming process.

For this reason, the preferred strategy is:

Prevent the difference during sheet formation first, then use downstream measures for further correction.

From a long-term equipment perspective, forming technologies capable of providing balanced two-sided drainage—particularly Gap Formers and Top-Wire Formers—can address the problem closer to its origin.

However, equipment modification alone is not the complete answer.

8. Combine Mechanical and Chemical Solutions

Producing paper with highly uniform properties on both surfaces requires several measures to work together.

A practical optimization route can be expressed as:

Fiber Furnish → Refining → Wet-End Retention → Headbox → Forming → Two-Sided Dewatering → Drying → Calendering

The source material recommends combining:

• Chemical retention
• Stock optimization
• Balanced forming and dewatering
• Press and calender optimization
• Drying control

This integrated approach can improve the uniformity of the sheet structure and help meet higher paper quality requirements.

Huatao Group – Paper Machine Solutions for Improving Two-Sidedness

For paper mills looking to improve paper two-sidedness, sheet formation and dewatering performance, Huatao Group provides equipment and components for paper machine forming, pressing and finishing applications.

Relevant products include:

• Gap Former
• Top-Wire Former
• Dandy Roll
• Dewatering Elements
• Suction Press Roll
• Blind-Drilled Press Roll
• Press Roll
• Jumbo Press Roll
• Calender Roll
• Bow Roll

For further assistance with paper two-sidedness or paper machine equipment selection, please contact Huatao Group.

Contact Huatao Group

Website: www.huataolover.com
Email: service@huataogroup.com
WhatsApp / WeChat: +86 151 03371897   

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