Multi-ply Paper Bonding with Microfibrillated Cellulose
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Solution Overview
Problem
Existing methods for producing multi-ply cartonboards face challenges in minimizing cracking and delamination tendencies while maintaining mechanical strength and stiffness, often requiring increased grammage or refining, which can increase costs and reduce bending stiffness.
Innovation Solution
Incorporating microfibrillated cellulose between the plies of a paper or board product, along with starch, to enhance bonding and reduce delamination and cracking, allowing for more flexible and stronger inter-ply bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If starch is sprayed between the plies before couching, then bonding between plies is improved, but cracking tendency increases due to un-stretching bonds
Solution Approach 1:
The patent changes the chemical composition parameters of the bonding agent by replacing starch with a polyamide polymer containing carboxylic acid groups. This parameter change transforms the bonding mechanism from rigid starch bonds to flexible polymer bonds that can stretch, thereby maintaining bond strength while reducing cracking tendency during creasing operations.
Solution Approach 2:
The patent uses a composite bonding approach by combining polyamide polymer with optional additives such as metal salts (calcium, magnesium, aluminum) or oxidizing agents. This composite material system provides both strong bonding and flexibility, resolving the contradiction between bond strength and cracking resistance.
2Object-affected harmful factors
If top and bottom ply grammage is increased to prevent cracking, then cracking tendency is reduced, but cost increases and bending stiffness decreases
Solution Approach 1:
The patent introduces a polyamide polymer as an intermediary bonding agent between the plies. This mediator provides strong adhesion and flexibility, allowing the use of lower grammage top and bottom plies while still preventing cracking. The intermediary absorbs the stress during creasing, eliminating the need for excessive ply thickness.
3Strength
If refining of middle ply is increased to increase fines content, then bonding between plies is improved, but caliper decreases and bending stiffness index is reduced
Solution Approach 1:
The patent replaces the mechanical refining process with a chemical bonding approach using polyamide polymer. Instead of mechanically increasing fines content through refined pulp, the chemical polymer provides bonding between plies. This substitution maintains caliper and bending stiffness while achieving strong inter-ply bonding.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process increases the bond strength between plies, reduces delamination and cracking, and allows for reduced grammage and refining, leading to cost savings and improved bending stiffness without compromising mechanical properties.
Implementation Method 1
adding starch together with the microfibrillated cellulose to at least one surface of a ply... attaching the second ply to the first ply so that the added microfibrillated cellulose and starch are located in between the first and second plies
Data Source
AI summary
The present invention relates to a process for the production of a paper or paperboard comprising at least two plies wherein microfibrillated cellulose is added to the surface of a first ply and the other ply is attached to the first ply so that the microfibrillated cellulose located in between the plies. The invention further relates to a paper or board produced according to the method.