In the packaging industry, duplex boards play a vital role. Used widely in carton manufacturing, their quality directly impacts customer perception through factors like print fidelity and overall appearance. This underscores the importance of rigorous quality control throughout the entire production process, from the board mill to the printer-converter stage. Such measures are essential to guarantee the desired quality and visual appeal of the final product, the carton.

In the previous article, we explored the importance of maintaining optimal duplex board quality throughout production. We established that even unconventional materials can yield high-quality boards when proper control measures are implemented.

Building upon this foundation, this, "Part 2" of our three-part series, delves deeper about the common defects encountered in duplex boards. We will identify these defects and explore various strategies to minimize their occurrence, ensuring the production of consistent, high-quality boards.

Stay tuned for the part 3, where we'll explore the remaining defects and their preventive measures.

List of Common Defects in Duplex Board

Curl and waviness
Variation in Caliper and G.S.M
Poor stiffness
Poor creasing quality
Poor smoothness and gloss
Burn mark and streaks
High or low bulk density
Fluff
High or low ink absorbency
Low brightness
Delamination
Shade variation
Poor Physical strength properties
Poor Glueability
Poor vamishability
Colour reversion
Poor waxing anG high wax absorbency
Poor dimension and stability

This article, the second in the three-part series, explores the listed subsequent six (from 7 - 12) commonly encountered defects in duplex board production, delving into their causes and potential solutions. These are :- High or low bulk density, Fluff, High or low ink absorbency, Low brightness, Delamination and Shade variation.

7) High and Low bulk

Controlling bulk in duplex board is crucial for achieving the desired thickness, stiffness, and printability. Both high and low bulk can negatively impact the board's performance and aesthetics. Here's how to prevent and address these issues:-

Furnish selection:

Use a balanced furnish with a mix of dense and bulking fibers. Explore options like refined wood pulp and specific recycled paper grades with varying bulk characteristics.
Minimize the use of fillers that contribute to bulk without adding significant strength.

Pressing optimization:

Optimize nip pressures at various wet pressing stages to achieve the desired board thickness without over-compressing (high bulk) or under-compressing (low bulk) the fibers.

Calendering control:

Fine-tune calendering pressure and temperature to achieve desired smoothness without excessively compacting the board (high bulk) or minimizing its natural bulk (low bulk).

8) FLUFF

Fluff refers to fibers loosely attached to the surface of your duplex board, appearing as a fuzzy or hairy texture. This defect can affect printability, adhesion, and overall aesthetic quality. Here are ways to prevent and minimize fluffing of the duplex board:

Furnish control:
- Use well-beaten pulp in the furnish mix. Proper beating helps disperse fibers evenly and promotes bonding, reducing loose fibers on the surface.
- Optimize fiber length distribution. Try to minimize the presence of short fibers, as they can contribute to fluffing.

Beater additives:

Explore wet-end additives like retention aids or fiber bonding agents. These can improve fiber-to-fiber bonding and minimize surface fiber detachment.
Adjust the dosage of chemicals to achieve the desired fiber characteristics.

Surface sizing:

Apply a smooth and uniform surface size to the board. This creates a barrier between the fibers and external forces, reducing the likelihood of fiber detachment. Choose size formulations compatible with your printing or finishing processes.

Calendering optimization:

Minimize calendering pressure and temperature. Excessive calendering can damage fibers and promote surface fuzzing.

9) High or Low ink absorbency

Ink absorbency plays a crucial role in achieving desired print quality and performance on duplex board. Both high and low absorbency can lead to issues like inconsistent ink distribution, poor color saturation, and even surface degradation. Here's how to prevent and address these concerns:-

Furnish selection:

Use a balanced furnish with a mix of fibers with varying ink absorption characteristics. Explore options like:

Highly refined wood pulp for good ink holdout (resists excessive absorption).
Specific recycled paper grades with moderate absorbency for smooth ink laydown.

Minimize the use of highly absorbent fillers that can lead to uneven ink absorption and blotchiness.
It has been observed that if the boards are made more compact, their ink absorption property is lowered

Surface sizing:

Apply a uniform and appropriate surface size. Sizing acts as a barrier, controlling ink penetration and ensuring consistent ink laydown on the surface. Choose sizing formulations compatible with your chosen inks and printing process.
Addition of certain chemicals to the stock and surface sizing can be used to control high or low ink absorbency problems.

Calendering control:

Optimize calendering pressure and temperature. Excessive calendering can close pores and reduce ink absorbency, while insufficient calendering can lead to higher, uneven absorption.

10) Low Brightness

Brightness is a crucial visual attribute of duplex board, impacting its aesthetic appeal and suitability for various applications. Here are ways to prevent and minimize low brightness issues in duplex board:-

Raw Material Selection:

Choosing high-quality pulp and other raw materials with good brightness characteristics is the most important method in avoiding low brigthness issue.

Furnish selection:
- Use bleached chemical pulp in the furnish mix. Bleaching helps remove lignin, a natural wood component that contributes to a brownish hue.
- Minimize the use of recycled paper with a high content of unbleached fibers, as these can significantly reduce overall brightness.
- Consider using brightening agents like optical brightening agents (OBAs) during pulp processing. OBAs absorb UV light and re-emit it as visible blue light, enhancing perceived brightness.

Drying Control:

overdrying should be avoided which reduces tile brightness of the board.

Coating considerations:

Apply a white or light-colored coating to the surface of the board. This can significantly improve the overall brightness, especially for boards with a darker base material.
Choose coating formulations with minimal yellowing index (YI) to ensure they don't diminish board brightness over time.

11) Delamination

Delamination is the separation of the individual plies in the duplex board. It can significantly compromise the strength, functionality, and aesthetics of the duplex board. Here are some strategies to **prevent and minimize delamination**:-

Furnish selection:
- Use compatible fiber types in each ply. Choose fibers with similar water absorption characteristics and shrinkage rates to minimize stress during drying.
- Consider using long-fibered pulp in the core ply, as it provides better internal bonding and reduces delamination risk.
Moisture Control:
- Maintaining appropriate moisture levels in the wet sheet is crucial when it joins with other wet sheets. It is also essential to make sure no air gets trapped between two sheets.
- The moisture content should be uniform throughout both machine-direction and cross-direction.

Beating optimization:

Optimize beating intensity for each ply based on its fiber composition. Proper beating promotes fiber development and inter-fiber bonding, crucial for preventing delamination.

Adhesive selection and application:

Choose a strong and compatible adhesive, considering factors like the type of fibers used, intended application, and drying conditions.
Ensure uniform and consistent adhesive application throughout the board. This can be achieved through proper equipment maintenance and process control.

Drying control:

Maintain consistent drying conditions throughout the process, including temperature, humidity, and air circulation. Uneven drying can cause differential shrinkage and lead to delamination.

Pressing optimization:

Apply adequate pressure during pressing to ensure good bonding between the plies. However, excessive pressure can damage the fibers and also contribute to delamination.

12) Poor physical strength properties

Physical strength is crucial for the functionality and durability of duplex board. Here's how to prevent and minimize issues like low tensile strength, poor tear resistance, and weak stiffness:-

Furnish selection:
- Use strong and well-bonded fibers in the furnish mix. Explore options like:
- Minimize the use of fillers that contribute to bulk without adding significant strength.

Beating optimization:

Optimize beating intensity and refining for each ply based on fiber composition. Proper beating promotes fiber development, inter-fiber bonding, and network formation, leading to improved strength.

Pressing optimization:
**Apply adequate pressure and dwell time** during pressing to ensure optimal bonding between the plies. **Insufficient pressure** can lead to weak bonds and reduced strength.

Adhesive selection and application:
- Choose a strong and compatible adhesive, considering factors like the type of fibers used and intended application.
- Ensure uniform and consistent adhesive application throughout the board. This can be achieved through proper equipment maintenance and process control.

Conclusion

At Paxert LLP, we offer not just a diverse range of pulp and paper products, but also free consultations and assistance in identifying and solving any defects encountered in duplex boards and other paper products. and the guarantee of quick, efficient service tailored to your specific needs.

For a free consultation and personalized solutions to your duplex board and paper product defects, contact us today.

Common defects in Duplex board and their Solutions - Part 2