Cellulose Barrier Substrate Coating With Heated Roll Drying
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Solution Overview
Problem
Existing methods for producing thin cellulose-based barrier substrates coated with aqueous-based barrier coatings face challenges such as web weakening, dimensional instability, and difficulty in handling due to water penetration and swelling, which affect tensile strength and barrier properties, especially at high humidity.
Innovation Solution
A method involving application of an aqueous-based composition on a thin web comprising highly refined cellulose fibers and/or MFC while the web is in contact with a heated roll or belt, allowing for immediate evaporation of water and reducing penetration, thereby maintaining tensile strength and dimensional stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aqueous-based barrier coatings are applied on thin cellulose-based substrates comprising highly refined fibers or MFC, then barrier properties towards oxygen, air, water vapour and aromas are improved, but the web breaks or dimensional stability problems occur due to wetting and water sorption
Solution Approach 1:
The web is pre-heated by contact with a heated roll or belt before the aqueous-based coating is applied. This preliminary heating action reduces water sorption and wetting of the web during subsequent coating, preventing web breaking and dimensional instability while still allowing the coating to provide improved barrier properties
Solution Approach 2:
The temperature parameter of the web is changed by heating it before coating application. This parameter change reduces the web's affinity for water, allowing aqueous-based coatings to be applied without causing excessive water sorption, web swelling, or loss of tensile strength
2Object-affected harmful factors
If solids of the applied solutions or dispersions are increased to reduce wetting of the web, then water sorption is reduced, but higher coat weight and higher viscosity are generated
Solution Approach 1:
Instead of changing the composition parameter (solids content) of the coating solution, the temperature parameter of the web is changed before coating application. This reduces water sorption and allows lower solids content coatings to be applied without excessive wetting, thereby reducing coat weight
3Strength
If basis weight of the cellulose-based web is increased to reduce water sensitivity, then strength is improved, but cost increases and drying capacity requirements increase
Solution Approach 1:
The temperature parameter of the web is changed before coating application, which reduces water sorption and improves dimensional stability. This allows thin, low basis weight webs to be used without sacrificing strength or water sensitivity resistance, thereby reducing manufacturing cost
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 method produces a barrier substrate with high barrier properties and strength, while being repulpable, without the need for high coat weights or excessive hydrophobizing agents, ensuring effective moisture resistance and recyclability.
Implementation Method 1
applying, in a first coating step, at least one first composition comprising a polymer dispersed or dissolved in an aqueous medium on the first side of the web while the second side of the web is in contact with the heated roll or belt so that water applied with the aqueous composition on the web is evaporated
Data Source
AI summary
The present invention relates to a process for manufacturing a barrier substrate, comprising the steps of: —providing a web comprising at least one first layer, which first layer comprises at least 30 weight-% highly refined cellulose fibers having a Schopper Riegler value of 60-95 SR # and/or at least 30 weight-% microfibrillated cellulose (MFC), as calculated on the total dry weight of said first layer, which web has a first side and a second side and which web exhibits an air resistance (Gurley) of at least 1000 s/100 ml, preferably at least 2000 s/100 ml, as measured according to ISO 5636-5, —providing a heated roll or a heated belt, —applying at least one first composition comprising a polymer dispersed or dissolved in an aqueous medium on the first side of the web while the web is in contact with the heated roll or belt, in a first coating step, thereby providing the web with a first barrier layer forming a barrier coated web, —optionally drying said web provided with the first barrier layer in a drying step. 20 The invention relates also to a barrier substrate, a barrier substrate laminate with a polymer layer and a packaging material comprising the barrier substrate.