Perfluoropolyether-Modified Roll Covering for Press Section Dewatering
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Solution Overview
Problem
Press roll coverings and suction press roll coverings in paper machines become contaminated over time, leading to reduced dewatering efficiency and instability due to filler, fiber agglomerate, and resin impurities, causing hydraulic or mechanical marks and fluctuations in the cross-sectional moisture profile.
Innovation Solution
A roll covering formed from a polymer mixture including a prepolymer, curing agent, and perfluoropolyether additive, which lowers surface energy, preventing water and dirt adhesion and improving hydrolysis resistance, chemical resistance, and mechanical properties, thereby enhancing dewatering efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If press roll coverings are used with conventional polyurethane coatings, then initial dewatering performance is achieved, but contamination accumulates over time causing reduced dewatering efficiency and hydraulic marks
Solution Approach 1:
The invention changes the chemical composition parameters of the polyurethane coating by incorporating specific additives (silane-modified polyesters, perfluorinated compounds, or waxes) into the polymer mixture. This modifies the surface properties of the roll covering to reduce contamination adhesion and improve resistance to hydraulic marks while maintaining dewatering efficiency throughout extended service periods
Solution Approach 2:
The invention creates a composite polyurethane material system combining base polyurethane polymers with functional additives (silane-modified polyesters, perfluorinated compounds, or waxes). This composite structure provides both the mechanical properties needed for roll operation and the surface characteristics that prevent contamination buildup, resolving the contradiction between initial performance and long-term reliability
2Ease of operation
If mechanical cleaning devices are used to clean roll coverings, then some surface contamination is removed, but holes and grooves remain clogged and cleaning effectiveness is inadequate
Solution Approach 1:
The invention replaces reliance on mechanical cleaning systems with a chemically active surface coating that inherently resists contamination adhesion. The modified polyurethane surface properties prevent fillers, fiber agglomerates, and resin impurities from firmly attaching to the roll covering, making mechanical cleaning supplementary rather than essential and significantly improving overall cleaning effectiveness
3Ease of operation
If wash solutions are used to treat roll coverings, then contamination is removed, but unwanted substances enter the fibrous web and web rewetting occurs
Solution Approach 1:
The invention applies a preliminary protective action by incorporating contamination-resistant additives into the polyurethane coating formulation before the roll is put into service. This pre-established surface property prevents contamination from firmly attaching in the first place, eliminating the need for subsequent wash solution treatments that could cause web contamination or rewetting
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 solution effectively prevents contamination, maintains dewatering efficiency, and stabilizes the cross-sectional moisture profile, improving the quality of the end product by rapidly removing water and dirt from the roll surface.
Implementation Method 1
The functional layer is formed of a polymer which is a mixture of at least one prepolymer, at least one curing agent and/or at least one crosslinking agent, and at least one additive. The additive is selected from the following group: perfluoropolyether, bifunctional perfluoropolyether and mixtures thereof.
Implementation Method 2
The press rolls or suction press rolls used are often coated with polyurethane. The dewatering capacity of the press roll covering or suction press roll covering in that case is dependent primarily on the surface structure of the roll covering.
Implementation Method 3
In the case of suction press rolls, there are commonly additionally suction holes present as well, which pass through the roll shell. Water is drawn from the fibrous web through the suction holes by using, for example, a suction box located in an inside volume of the roll.
Data Source
AI summary
A roll for a press section of a machine for making and/or finishing a fibrous web, such as a paper, board, or tissue machine, includes a roll body or roll shell and, disposed on the roll body or roll shell, a roll covering which has at least one functional layer which is suitable for entering into contact with the fibrous web or with a paper machine fabric. The functional layer is formed of a polymer which is a mixture of at least one prepolymer, a curing agent, a crosslinking agent, and an additive. The additive is selected from the following: perfluoropolyethers, bifunctional perfluoropolyether, or mixtures thereof.