Surface Sizing Dense Microfibrillated Cellulose Films
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Solution Overview
Problem
Surface sizing of dense films or webs made of microfibrillated cellulose is challenging due to their closed surface, which prevents absorption of sizing chemicals, and existing methods often lead to web breaks or uneven coating, especially at high speeds and on wide paper machines.
Innovation Solution
A method involving the formation of a web with a high microfibrillated cellulose content, surface sizing while the web is still wet, and drying it to a low moisture content to enhance chemical penetration and adhesion, allowing for efficient impregnation and production of dense, thin films with improved properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If surface sizing is applied to dense films at high speeds, then productivity is improved, but the contact time between coating and drying is too short to achieve proper impregnation and penetration of sizing chemicals
Solution Approach 1:
The web is sized in a wet state before complete drying occurs. The sizing chemicals are applied to the web while it still contains moisture, allowing the chemicals to penetrate and impregnate the dense film structure more effectively. This preliminary action of sizing before full drying enables proper chemical absorption without requiring extended contact times at high production speeds
2Manufacturing precision
If the impregnation nip is extended and contact time is increased to facilitate chemical penetration, then impregnation quality is improved, but the web may break due to weakened inter-fibrillar interactions
Solution Approach 1:
The key parameter changed is the moisture content of the web during the sizing process. By maintaining the web in a wet state (higher moisture content) during sizing chemical application, the film structure becomes more accessible to chemicals without requiring prolonged mechanical processing. This parameter change enables effective impregnation while preserving web integrity, as the wet state allows chemical penetration without the need for extended nip pressure that would weaken inter-fibrillar bonds
3Ease of manufacture
If impact coating processes are used on dense substrates, then coating application is simplified, but the substrate becomes structured with clear differences between top, middle and back layers
Solution Approach 1:
The web is sized while still wet, before the drying process creates a structured, layered configuration. By performing the sizing action preliminarily, while the web structure is still uniform and accessible, the sizing chemicals can penetrate throughout the web cross-section evenly. This prevents the formation of a structured substrate with distinct layers, as the chemicals are already impregnated before the drying-induced layering occurs
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
This method enables efficient penetration and interaction of sizing chemicals with cellulose, resulting in a more homogeneous film structure, reduced curl, and enhanced barrier properties, while maintaining web strength and preventing breaks, even on wide paper machines.
Implementation Method 1
an extended impregnation nip and longer contact times will probable facilitate the film swelling, diffusion and penetration of both water and the applied chemicals
Implementation Method 2
an extended impregnation nip and longer contact times will probable facilitate the film swelling, diffusion and penetration of both water and the applied chemicals
Implementation Method 3
when surface sizing a web comprising microfibrillated cellulose (MFC), while the film is still wet, i.e. has a relatively high moisture content, the absorption and fixation of the sizing chemicals in the film is enhanced
Data Source
AI summary
A method for manufacturing a film, wherein said film has a basis weight of less than 50 g/m2 and wherein the density of the film is higher than 750 kg/m3 comprising the steps of: providing a suspension comprising microfibri Hated cellulose (MFC); forming a web of said suspension on a porous wire, microfibrillated cellulose (MFC); surface sizing said web, wherein the web, at the beginning of the surface sizing step, has a moisture content in the range of from 10 to 50 wt-%; drying said surface sized web to a final moisture content of between 0.1- 20 wt-% to form said film.