Slit Die Flow Path Angles Suppress Liquid Layer Undulation
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Solution Overview
Problem
Conventional liquid application apparatuses often result in an undulating interface between the upper and lower layers, leading to nonuniform thickness of the lower layer, particularly when it is thin (5 μm or less).
Innovation Solution
A liquid application apparatus with a slit die having two flow paths that join at an opening, where specific angles (α = 0.5 to 25°, β = 0 to 70°) and distances (γ = 0.05 to 2.8 mm) are maintained, along with a preferred width ratio of the flow paths (3:2 to 3:1), and a liquid application method using a high solid concentration (20 to 30 wt %) for the lower layer to suppress undulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional liquid application apparatuses are used, then liquid layers can be applied to the sheet, but undulation occurs at the interface between the upper layer and lower layer, resulting in nonuniform thickness
Solution Approach 1:
The liquid application system is divided into two separate flow paths (upper layer flow path and lower layer flow path) that are spatially segmented and then joined at a specific angle. This segmentation allows independent control of each layer's liquid flow, enabling precise adjustment of flow dynamics to suppress interface undulation while maintaining manufacturing precision.
Solution Approach 2:
The invention changes critical geometric parameters of the flow path configuration, specifically setting the joining angle α between 0.5 to 25 degrees and the angle β between 0 to 70 degrees. These parameter changes optimize the flow dynamics at the interface, reducing turbulence and preventing undulation, thereby improving interface flatness without excessive device complexity.
2Manufacturing precision
If the lower layer is made relatively thin (5 μm or less), then coating precision is improved, but undulation at the interface becomes significantly more severe
Solution Approach 1:
The flow path configuration is designed in advance to counteract the harmful effect of interface undulation before it occurs. By pre-setting the joining angle α and angle β within specific ranges, the liquid flows are conditioned to merge smoothly, preventing the formation of undulations that would otherwise occur when applying thin lower layers, thus maintaining thickness uniformity without severe interface defects.
3Manufacturing precision
If high solid concentration liquid (20 to 30 wt %) is used for the lower layer, then coating quality is improved, but undulation at the interface becomes severe and the lower layer often disappears in part
Solution Approach 1:
The invention changes the geometric parameters of the flow path configuration (joining angle α and angle β) to accommodate high solid concentration liquids. These parameter changes create a flow environment that prevents premature solidification and interface instability, allowing high solid concentration liquids to be applied uniformly without causing severe undulation or layer disappearance.
Data Source
AI summary
A liquid application apparatus includes a guide roll for guiding a sheet for application, and a slit die for applying a liquid to a surface of the sheet for application from an opening. The slit die has an upper layer flow path and a lower layer flow path spaced in the rotational direction of the guide roll and joining at the opening. In a cross section perpendicular to the axis of the guide roll, an angle α formed by the center line of the upper layer flow path and the center line of the lower layer flow path is 0.5 to 25°, an angle β formed by a line connecting the intersection point of the center line of the upper layer flow path and the center line of the lower layer flow path with the axis of the guide roll and by the center line of the upper layer flow path is 0 to 70° as measured from this connecting line toward the center line of the upper layer flow path in the direction opposite to the rotational direction of the guide roll, and the distance γ between a point where the two flow paths and join and the opening is 0.05 to 2.8 mm.