Patterned Calender Roll for Smooth Tissue With Preserved Bulk
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Solution Overview
Problem
Conventional calendering processes result in significant loss of Sheet Bulk and surface stiffness when producing spirally wound tissue products, leading to a decrease in Roll Bulk and undesirable firmness.
Innovation Solution
The use of a patterned calender roll with male elements covering 60 to 95% of the surface area, which reduces Z-direction variability and maintains web bulk while improving surface smoothness, is employed to produce a tissue product with enhanced Roll Bulk and firmness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional calendering with smooth unpatterned rolls is used, then surface smoothness is improved, but Sheet Bulk is significantly lost
Solution Approach 1:
The calender roll surface is designed with localized male elements (protrusions) rather than a uniformly smooth surface. These male elements are distributed across the roll surface at specific locations, providing localized smoothing action only where needed, while leaving the overall bulk of the web preserved. This resolves the contradiction by applying smoothness-enhancing pressure only in specific local areas rather than uniformly across the entire surface.
Solution Approach 2:
The calender roll surface is segmented into discrete male elements rather than being a continuous smooth surface. Each male element acts as an independent smoothing zone, allowing the web to maintain bulk in areas between the elements while receiving smoothing treatment at the element locations. This segmentation enables selective application of compressive force to improve smoothness without uniformly reducing bulk.
2Shape
If conventional calendering is used to smooth the tissue surface, then surface smoothness is improved, but the tissue becomes stiffer
Solution Approach 1:
The male elements on the calender roll provide localized smoothing pressure only at specific points on the web surface, rather than applying uniform compression across the entire surface. This localized approach smooths the surface irregularities that cause stiffness while preserving the overall compressibility and softness of the bulk tissue structure in areas not directly contacted by the male elements.
Solution Approach 2:
The calendering action is applied partially through discrete male elements rather than full-surface contact. This partial action provides sufficient smoothing effect to reduce stiffness caused by surface irregularities, while avoiding excessive compression that would uniformly increase overall tissue stiffness. The male elements deliver concentrated smoothing pressure only where needed.
3Shape
If conventional calendering is used, then surface smoothness is improved, but Roll Bulk decreases
Solution Approach 1:
The male elements on the calender roll apply smoothing pressure locally at discrete positions on the web, rather than uniformly across the entire surface. This localized compression improves surface smoothness while minimizing the overall volume reduction of the rolled product, as the majority of the web bulk is not subjected to intense compressive forces.
Solution Approach 2:
The calender roll surface is segmented into discrete male elements that independently contact the web at separate locations. This segmentation allows the web to maintain its bulk structure in regions between the male elements, while still achieving smoothness improvement at the contact points. The segmented approach prevents uniform compression that would reduce Roll Bulk.
4Shape
If conventional calendering is used, then surface smoothness is improved, but Z-direction variability increases
Solution Approach 1:
The male elements on the calender roll provide localized smoothing pressure at specific positions on the web surface. This localized action addresses surface irregularities that cause Z-direction variability (thickness variation) at contact points, while the distribution of male elements across the roll surface ensures uniform smoothing coverage, thereby reducing overall Z-direction variability rather than increasing it.
Solution Approach 2:
The male elements on the calender roll are arranged in patterns that replicate across the roll surface, creating a consistent copying effect as the roll rotates. This repetitive pattern of localized smoothing actions uniformly reduces Z-direction variability across the entire web width and length, rather than creating additional variability through irregular or asymmetric compression zones.
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 approach results in tissue products with improved Sheet Bulk, Surface Smoothness, and Roll Structure, maintaining a greater percentage of caliper and bulk compared to conventional calendering methods, while avoiding excessive compression and pattern imprinting.
Implementation Method 1
The male elements, which may generally be any shape, have a surface area greater than about 300 mm2... and cover from about 60 to about 98 percent of the surface of the roll... creating a calender nip there between, and passing the tissue web through the calender nip
Data Source
AI summary
The novel tissue products of the present invention are generally produced by calendering a tissue basesheet using at least one patterned roll. In one embodiment the patterned roll replaces the flat steel roll commonly used in calendering. The elements on the patterned roll provide a means of providing a nip having variable loading such that Z-direction variability in the web is reduced, yielding a smoother web, but without subjecting the web to excessive compression forces and preventing excessive caliper loss. Thus, webs converted according to the present invention tend to retain a greater percentage of their caliper and bulk when converted compared to webs converted using conventional calendering means.