Shear-Sensitive Coating Dosing via Vertical Nip Injection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing coating processes for shear-sensitive coating compounds result in unacceptably high shear rates, leading to agglomeration of the coating compound, which is undesirable for achieving smooth, defect-free layers.
Innovation Solution
A device with a forced conveying system that doses the coating compound into the coating nip via a lower nip opening, minimizing shear rates and avoiding long residence times, while a seal-free chamber system ensures homogeneous distribution and prevents high pressure exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the outlet nozzle is positioned close to the transfer roller to enable dosing of the coating compound, then the coating compound can be effectively applied, but very small gaps are created leading to unacceptably high shear rates and agglomeration of the coating compound
Solution Approach 1:
The outlet nozzle is positioned at a distance from the transfer roller in the vertical dimension, creating a larger gap that reduces shear rates. The coating compound is dosed from above rather than from the side, changing the spatial dimension of dosing to avoid high shear stress in the narrow gap between the nozzle and roller surface.
2Reliability
If side limiters or doctor blades are used to seal the coating area, then the coating compound can be contained and distributed, but very small gaps are created leading to high shear rates and agglomeration
Solution Approach 1:
The harmful side limiters and doctor blades that create high shear rates are removed from the system. Instead, the coating area is contained through the geometric configuration of the dosing chamber and the natural flow of the coating compound under gravity, eliminating the need for sealing elements that would create small gaps and high shear stress.
3Productivity
If the coating compound is subjected to high pressure in the coating nip area, then the coating compound can be forced through the nip, but agglomeration of the coating compound occurs
Solution Approach 1:
The dosing chamber is designed to be substantially pressure equalized with the environment, eliminating pressure differences that would force the coating compound through the nip at high pressure. The coating compound flows into the nip under gravity and its own weight, maintaining low pressure throughout the process to prevent agglomeration.
4Productivity
If the outlet nozzle is positioned close to the transfer roller, then dosing can be effective, but long residence times of the coating compound in the coating machine occur
Solution Approach 1:
The coating compound is dosed directly from the outlet nozzle into the coating nip in a single, rapid motion, skipping the intermediate step of flowing through long channels or waiting in reservoirs. This direct dosing path minimizes residence time while maintaining effective coating application.
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 the formation of agglomerates, ensuring smooth, defect-free coatings by maintaining low shear rates and uniform residence times of the coating compound within the coating nip.
Implementation Method 1
the storage and in some cases also the pre-dosing of the coating compound is realized in areas of the device with very small distances between two walls of the device, for example in the area of the outlet nozzle, which leads to a considerable shear stress of the dispersions
Implementation Method 2
A gap formed between the spraying device and the transfer roller can be dimensioned so that excess coating compound can flow out of the coating nip via the gap between the spraying device and the transfer roller due to a geodetic pressure difference
Data Source
AI summary
The invention relates to a device for processing shear-sensitive coating compounds, with a transfer roller and a doctor blade, in particular a comma doctor blade, which are spaced apart from one another to form a coating nip, the device further having an outlet nozzle for dosing a coating compound, the outlet nozzle facing a lower nip opening of the coating nip with its nozzle opening, wherein the device comprises a forced conveying system via which a coating compound is dosed into the coating nip, the transfer roller and the doctor blade being arranged next to each other, so that the coating nip is permeable in the vertical direction (z), wherein the coating nip is between 30 and 400 μm and the outlet nozzle is an outlet of a rinsing chamber arranged below the coating nip. A corresponding method is also described.