Inkjet Head Shear-Rate Control for Uniform Thixotropic Ink Ejection
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Solution Overview
Problem
Highly thixotropic inks exhibit unstable ejection due to rapid viscosity changes during shear, leading to non-uniform ejection speeds among nozzles and deteriorated image quality in inkjet heads, particularly when circulation flow paths are misaligned with ejection directions.
Innovation Solution
Control the average shear rate in ink flow paths communicating with nozzles to be 100 [1/s] or more, using an inkjet recording apparatus with specific ink viscosity relationships and an ink circulation device to maintain uniform ejection speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solid content concentration of ink is increased to achieve high pinning properties, then the ink exhibits thixotropic properties and viscosity increases after ejection, but the ink viscosity changes rapidly during ejection causing unstable ejection
Solution Approach 1:
The invention changes the thixotropic properties parameter of the ink by specifying precise viscosity ratios at different shear rates (A100/A1 > 0.05 and A1000/A100 < 0.5). This parameter optimization allows the ink to maintain stability during ejection while achieving high pinning properties after deposition.
2Speed
If a highly thixotropic ink is used to achieve rapid viscosity decrease during ejection, then the ink flow velocity increases rapidly, but it becomes difficult to make flow velocities inside multiple pressure chambers uniform resulting in non-uniform ejection speeds
Solution Approach 1:
The invention optimizes the thixotropic properties parameters (A1, A100, A1000 viscosity values and their ratios) to achieve a balance between ejection speed and uniformity. The specific viscosity ratio constraints ensure that the ink responds appropriately to shear rate changes while maintaining consistent flow across multiple nozzles.
3Stability of the object's composition
If the circulation flow velocity is increased to suppress viscosity changes during ejection, then the ejection speeds among nozzles become uniform, but liquid droplets bend to the direction of circulation when circulation and ejection directions are perpendicular
Solution Approach 1:
The invention changes the viscosity parameters of the ink through controlled thixotropic properties, allowing uniform ejection speeds to be achieved at lower circulation flow velocities. This prevents excessive circulation forces that would cause droplet bending, while still maintaining viscosity uniformity across nozzles.
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
Suppresses viscosity changes during ejection, ensuring uniform ejection speeds among nozzles and improves image quality by stabilizing ink ejection.
Implementation Method 1
the ink exhibits thixotropic properties, the ink viscosity changes according to the shear force
Implementation Method 2
A highly thixotropic ink is such that during ejection, the ink flow velocity rapidly increases, and at the same time, the ink viscosity is also rapidly decreased
Data Source
Figure 1~2
Figure 3A~3B
Figure 4
AI summary
An image formation method of the present invention is an image formation method that uses an inkjet recording apparatus having an inkjet head including a pressure chamber, nozzles, and a plurality of ink discharging flow paths, in which the plurality of ink discharging flow paths are arranged such that two or more of the ink discharging flow paths are provided to the ejection opening of the nozzle, the inkjet recording apparatus includes an ink circulation device that circulates the ink to the ink discharging flow paths through the ink supply path, the relationships of the following Formula (I) and Formula (II) are satisfied when a viscosity at 25°C of the ink at a shear rate of 1 [1/s] is designated as A1, and the viscosity at a shear rate of 100 [1/s] is designated as A100, and the viscosity at a shear rate of 1000 [1/s] is designated as A1000, and the ink circulation device controls the average shear rate in the flow paths communicating with the nozzles in the pressure chamber to be 100 [1/s] or more: A1000<A100<A1 A100−A1000<A1−A100.