Inkjet Nozzle Recirculation Paths for Ink Quality
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Solution Overview
Problem
Ink characteristics can change over time in inkjet nozzles between print jobs, leading to variations in ink drop quality, and existing recirculation methods face challenges in maintaining ink freshness and preventing settling or drying of inks with volatile solvents, which can affect printing quality and require complex recirculation paths that may reduce jetting efficiency.
Innovation Solution
The implementation of recirculation flow paths with specific fluidic resistances and pressures to maintain ink freshness and quality, including a nominal negative pressure system that recirculates ink through nozzle and refill chambers, ensuring consistent ink characteristics and reducing the risk of ink drying or settling, while minimizing the impact on jetting efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If recirculation flow paths are implemented to maintain ink freshness, then ink quality consistency is improved, but device complexity increases
Solution Approach 1:
The patent combines the recirculation function with the existing ink supply system by integrating recirculation flow paths into the nozzle plate structure. The recirculation channels are formed within the same plate that contains the nozzle openings, merging two functions (ink delivery and ink recirculation) into a single integrated component, thereby reducing overall device complexity while maintaining ink freshness.
Solution Approach 2:
The recirculation system operates passively using pressure differentials created during normal inkjet operation. The ejection of ink drops generates negative pressure that automatically draws ink through the recirculation paths, eliminating the need for external pumps or active control mechanisms. This self-service approach maintains ink quality without adding complex active components.
2Reliability
If recirculation pressure is increased to improve ink recirculation flow rate, then ink freshness is maintained better, but jetting efficiency decreases
Solution Approach 1:
The patent optimizes the recirculation flow rate to a specific parameter range (10-100 nL/min) that balances ink freshness maintenance with jetting efficiency. This parameter change ensures sufficient recirculation to prevent ink degradation while keeping the recirculation pressure low enough (10-40 inwg) to avoid interfering with the ink ejection process. The fluidic resistance of recirculation channels is specifically designed to achieve this optimal flow rate.
3Reliability
If fluidic resistance in recirculation paths is decreased to increase recirculation flow, then ink circulation is improved, but pressure stability at nozzle changes
Solution Approach 1:
The patent creates different local flow conditions within the nozzle plate structure. The recirculation channels have specific dimensions and configurations that provide appropriate fluidic resistance locally, while the main ink delivery paths remain unaffected. This local quality differentiation allows effective ink circulation through recirculation paths while maintaining stable pressure at the nozzle openings for consistent jetting performance.
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 ensures that ink drops ejected after a period of non-use have the same quality as those jetted before and after, maintaining consistent printing performance and preventing issues like bubble formation due to air absorption, thereby enhancing the reliability and quality of inkjet printing.
Implementation Method 1
Ink is held under a nominal negative pressure associated with a characteristic of a meniscus of the ink in the nozzle when ejection of ink from the nozzle is not occurring
Implementation Method 2
another location spaced from the nozzle end that is to be subjected to a recirculation pressure lower than the nominal negative pressure so that ink is recirculated from the nozzle through the flow path at a recirculation flow rate
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An apparatus includes an inkjet assembly having inkjet nozzles through each of which ink flows at a nominal flow rate as it is ejected from the nozzle onto a substrate. Ink is held under a nominal negative pressure associated with a characteristic of a meniscus of the ink in the nozzle when ejection of ink from the nozzle is not occurring. The apparatus includes recirculation flow paths, each flow path having a nozzle end at which it opens into one of the nozzles and another location spaced from the nozzle end that is to be subjected to a recirculation pressure lower than the nominal negative pressure so that ink is recirculated from the nozzle through the flow path at a recirculation flow rate. Each recirculation flow path has a fluidic resistance between the nozzle end and the other location such that a recirculation pressure at the nozzle end of the flow path that results from the recirculation pressure applied at the other location of the flow path is small enough so that any reduction in flow rate below the nominal flow rate when ink is being ejected is less than a threshold, or a change in the nominal negative pressure when ink is not being ejected is less than a threshold, or both.