Air-Supported Backup Roll for Uniform Thin Die Coating
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Solution Overview
Problem
Existing slot die coating technologies face challenges in achieving uniformity and precision when applying thin coatings (less than 50 micrometers) on a moving web, particularly due to limitations in gap control between the coating die and the back-up roll, leading to coating defects and impractical precision requirements.
Innovation Solution
A coating apparatus with a back-up roll having a shell rotatably supported by a pressurized air layer, allowing the shell to deform and translate, which balances forces from the air layer and the coating bead, enabling uniform application of low-viscosity liquids with adjustable air flow rates to maintain coating uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gap between coating die and back-up roll is reduced to achieve thinner coatings, then coating thickness decreases, but manufacturing precision requirements become impractically high
Solution Approach 1:
The back-up roll is replaced with a compliant roller that can dynamically adjust its surface position in response to coating bead pressure variations. This dynamic compliance allows the roller to automatically compensate for gap variations, enabling thin coating application without requiring impractically high static gap control precision
Solution Approach 2:
The mechanical properties of the back-up roll are changed from rigid to compliant by using a flexible or air-supported structure. This parameter change allows the roller surface to deform and adapt to pressure changes in the coating bead, maintaining uniform gap conditions even when applying thin coatings
2Manufacturing precision
If the gap between coating die and back-up roll is made uniform to improve coating uniformity, then coating uniformity improves, but device complexity increases
Solution Approach 1:
The compliant back-up roll structure enables self-compensation of gap variations through its inherent flexibility. The roller automatically adjusts its surface position in response to local pressure changes in the coating bead, eliminating the need for complex external control systems to maintain gap uniformity
Solution Approach 2:
A flexible shell or thin film structure is used for the back-up roll, allowing the surface to conform and adapt to pressure variations in the coating process. This flexibility inherently maintains uniform gap conditions without requiring complex mechanical control mechanisms
3Manufacturing precision
If pressurized air layer is used to support the shell, then coating uniformity improves through dynamic gap adjustment, but energy consumption increases
Solution Approach 1:
A pressurized air layer is introduced between the back-up roll shell and its support structure, creating a compliant, floating support system. This pneumatic cushion allows the shell to dynamically adjust its position in response to coating pressures, improving coating uniformity while using relatively low energy to maintain the air pressure
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 solution enhances coating uniformity and reduces coating defects by dynamically adjusting the effective gap between the die and the roll, allowing for precise control of coating thickness and viscosity, even at low coat weights, thereby overcoming the limitations of traditional slot die coating systems.
Implementation Method 1
providing a roll comprising a shell rotatably supported by at least one pressurized air layer between the shell and a core
Implementation Method 2
providing a roll comprising a shell rotatably supported by at least one pressurized air layer between the shell and a core
Implementation Method 3
Fluid pressure can be generated in the coating bead due to the confinement of the fluid and the motion of the web. An air flow rate supplied to the core to form the at least one pressurized air layer can be adjusted such that the shell can deform and/or translate in space to balance forces from the pressurized air layer and the coating bead
Data Source
Figure 1
Figure 2
Figure 2A'
AI summary
Methods and apparatuses for applying coatings on a moving web are provided. A coating die and a back-up roll engage with each other. The back-up roll includes a shell rotatably supported by a pressurized air layer. When a coating material is dispensed from the coating die onto the web to form a liquid coating, the pressure of the air layer is controlled such that the shell translates in space to balance forces from the air layer and the coating bead, while the web is being translated to drive the shell.