Creped Tissue with Machine-Direction Pattern for Bulk and Softness
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Solution Overview
Problem
Conventional through-air drying processes for tissue manufacturing are energy-intensive and struggle to produce tissue products with three-dimensional surface patterns, especially when using furnishes with non-uniform permeability, such as recycled fibers.
Innovation Solution
The use of a patterned structuring belt with discrete depressions arranged to form machine-direction oriented line elements during the wet pressing process imparts a three-dimensional pattern to the tissue web, enhancing caliper, bulk, and handfeel, while maintaining energy efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If through-air drying processes are used to produce tissue products with three-dimensional surface patterns, then enhanced bulk and softness are achieved, but energy consumption increases significantly
Solution Approach 1:
The fabric is pre-patterned with three-dimensional structures (protrusions and recesses) before the tissue web is formed. This preliminary structuring allows the web to be molded into the desired pattern during the wet pressing stage, eliminating the need for energy-intensive through-air drying to create the pattern later.
Solution Approach 2:
The invention replaces the thermal field (hot air drying) with a mechanical field (wet pressing against a patterned fabric). The mechanical pressure during wet pressing imprints the three-dimensional pattern directly onto the web, substituting the thermal energy-based through-air drying process with a mechanical molding process that occurs at lower energy cost.
2Use of energy by moving object
If conventional wet pressing is used to mechanically dewater webs, then energy efficiency is improved, but three-dimensional surface patterns cannot be effectively produced due to insufficient hydrogen bonding at low consistencies
Solution Approach 1:
The fabric is pre-patterned with three-dimensional structures before the web is formed. This preliminary structuring allows the web to be molded into the desired pattern during wet pressing, even at low consistencies where hydrogen bonding is insufficient, because the pattern is imposed mechanically rather than relying on fiber bonding alone.
Solution Approach 2:
The invention changes the consistency parameter at which patterning occurs. Instead of requiring high consistency (30% or more) for effective hydrogen bonding and pattern retention, the process enables pattern formation at lower consistencies (below 30%) by using the patterned fabric as a mechanical mold during wet pressing, before the web is fully dewatered.
3Shape
If through-air drying is used with recycled fiber furnishes having non-uniform permeability, then three-dimensional patterns may be produced, but the process becomes even more energy intensive and less reliable
Solution Approach 1:
The invention replaces the thermal field (hot air drying) with a mechanical field (wet pressing against a patterned fabric). This mechanical approach to pattern formation is less sensitive to variations in web permeability caused by recycled fiber composition, improving reliability across different furnish types.
Solution Approach 2:
The invention changes the operating conditions from high-temperature thermal drying to lower-temperature wet pressing. This parameter change makes the process more suitable for recycled fiber furnishes with non-uniform permeability, as the wet pressing mechanism does not rely as heavily on uniform air flow through the web.
4Strength
If the nascent web is pressed against a Yankee dryer at consistencies of 30 percent or so, then firm adhesion is achieved, but it becomes difficult to retain molded patterns due to insufficient hydrogen bonding
Solution Approach 1:
The fabric is pre-patterned with three-dimensional structures before the web is formed and pressed. This preliminary structuring ensures that the pattern is mechanically imposed on the web during wet pressing, and the subsequent adhesion to the Yankee dryer preserves this pre-established pattern rather than requiring hydrogen bonding to create it during drying.
Solution Approach 2:
Instead of relying on hydrogen bonding to create and retain the pattern during drying (the conventional approach), the invention inverts the sequence: the pattern is mechanically imposed first during wet pressing, then adhesion to the dryer is used to retain the already-formed pattern. This inversion decouples pattern formation from the adhesion process.
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 creped, wet pressed tissue products with improved sheet bulk, lower stiffness, and enhanced handfeel, achieving a Stiffness Index of 10.0 or less and a basis weight of 30 to 60 gsm, while being energy efficient and suitable for use with recycled fibers.
Implementation Method 1
conventional wet pressing (CWP) processes have certain advantages over conventional through-air drying (TAD) processes including lower energy costs associated with the mechanical removal of water
Implementation Method 2
The use of a patterned structuring belt that supports the nascent web in the press section of a tissue machine produces a tissue product having improved caliper, improved sheet bulk, lower stiffness and improved handfeel
Implementation Method 3
pressing the partially dewatered tissue web onto a cylindrical dryer to dry the tissue web
Implementation Method 4
creping the dried tissue web from the surface of the cylindrical dryer
Data Source
AI summary
Disclosed are tissue products, particularly creped, wet-pressed tissue products, having improved physical properties such as a high caliper and a low degree of stiffness. The products are manufactured by molding the nascent tissue web to the structuring belt such that the pattern disposed on the fabric is imparted to the web and can be seen by the consumer in the finished product. Preferably the molding step occurs immediately prior to creping such that the molded, nascent, web is transferred from the structuring belt to a cylindrical dryer and then subsequently removed by creping. The structuring belt imparts the tissue web with a plurality of discrete molded elements arranged to form continuous, substantially machine direction (MD) oriented, line elements that not only provide the products with an aesthetically pleasing appearance but also improves certain physical properties of the finished product.