Packaging Paper with Controlled Elongation and Roughness
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Solution Overview
Problem
Conventional packaging papers face challenges in balancing mechanical strength, printability, and surface smoothness, often compromising one property for another, such as increased elongation at break leading to poor printability or higher basis weight reducing air permeability.
Innovation Solution
A packaging paper made from at least 90% primary pulp with specific fiber length and filler content, combined with cationic starch, and optionally coated with polyolefins or polylactic acid, to achieve high tear resistance, flexibility, and smoothness, while maintaining air permeability and printability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the breaking elongation of packaging paper is increased through (micro)creping in a Clupak system, then the paper can withstand high mechanical loads and drops, but the printability deteriorates due to increased surface roughness
Solution Approach 1:
The patent applies local quality by differentiating the surface characteristics of the paper. The (micro)creping process creates a rougher surface structure that provides mechanical strength and elongation, while controlled calendering creates smoother localized areas that maintain printability. This allows different regions of the paper to have optimized properties for their specific functions.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the calendering pressure and temperature parameters to optimize the surface smoothness without significantly affecting the bulk mechanical properties. By carefully controlling these parameters, the paper achieves both high breaking elongation through (micro)creping and adequate printability through controlled surface smoothing.
2Strength
If the basis weight of packaging paper is increased to improve strength, then the paper becomes more durable, but air permeability decreases
Solution Approach 1:
The patent employs composite materials by combining kraft paper with specific additives and coatings that enhance strength properties without significantly increasing basis weight. The use of cationic starch and other processing aids creates a composite structure that maintains porosity and air permeability while improving mechanical strength and durability.
Solution Approach 2:
The patent applies local quality by concentrating strengthening agents and additives at specific locations within the paper structure, particularly at fiber junctions and surface regions, rather than uniformly increasing basis weight throughout. This localized reinforcement maintains air permeability while improving overall durability.
3Manufacturing precision
If excessive calendering is applied to create a smooth surface for printability, then the paper becomes easier to print on, but the elongation at break and mechanical properties deteriorate
Solution Approach 1:
The patent applies partial action by using moderate calendering rather than excessive calendering. This controlled approach provides sufficient surface smoothness for printability while avoiding the over-compression that would damage fiber bonds and reduce elongation at break. The calendering is optimized to achieve the minimum necessary smoothness without compromising mechanical properties.
Solution Approach 2:
The patent utilizes parameter changes by optimizing calendering temperature, pressure, and roll speed parameters to achieve surface smoothness with minimal impact on mechanical properties. By carefully controlling these parameters, the paper maintains both printability and elongation at break.
Data Source
AI summary
Packaging paper consisting of an unbleached kraft paper with a kappa value according to ISO 302:2015 between 38 and 60, preferably between 40 and 58, as the base paper, which is optionally coated on at least one side, wherein the kraft paper is made from at least 90% virgin pulp, has a basis weight according to ISO 536:2019 between 60 g/m² and 150 g/m² and an air resistance according to ISO 5636-5:2013 (Gurley) between 5 and 30 seconds, characterized in that the base paper has an elongation at break in the machine direction according to ISO 1924-3:2005 between 2.5% and 8.5% and a Bendtsen roughness according to ISO 8791-2:2013 between 70 ml/min and 600 ml/min, preferably between 150 ml/min and 550 ml/min, particularly preferably 200 ml/min to 500 ml/min ' and methods for its manufacture.