Thermal Ink-Jet Head Protective Layer Stability
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Solution Overview
Problem
Thermal ink-jet heads with insulating protective layers made of silicon nitride, silicon oxide, or silicon carbide experience dissolution during long-term storage, leading to reduced protective layer thickness and increased foaming energy, causing image deterioration and ejection failures due to abnormal foaming and temperature increases.
Innovation Solution
Incorporating a polyvalent carboxylic acid or its salt in the ink at specific concentrations (0.001 mmol/l to 0.5 mmol/l) to suppress the dissolution of the protective layer and prevent ejection failures, while maintaining thermal efficiency and printing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is formed on the heat generating portion to protect from cavitation damage and chemical reaction, then reliability is improved, but thermal efficiency deteriorates due to increased thickness required for protection
Solution Approach 1:
The patent uses a composite protective layer structure consisting of a Ta (tantalum) layer and an insulating layer (SiN, SiO, or SiC). The Ta layer provides cavitation resistance and chemical stability, while the insulating layer provides electrical insulation and additional protection. This composite structure allows each layer to be optimized for its specific function, achieving both high reliability and thermal efficiency by distributing the protective functions across multiple specialized layers rather than requiring a single thick layer.
2Reliability
If the protective layer thickness is increased to protect wiring from ink, then reliability is improved, but thermal efficiency deteriorates due to heat insulation
Solution Approach 1:
The protective layer is segmented into distinct functional layers: a Ta layer for cavitation and chemical protection, and a separate insulating layer (SiN, SiO, or SiC) for electrical insulation and wiring protection. This segmentation allows each layer to be optimized for its specific protective function without requiring excessive total thickness, thereby maintaining thermal efficiency while achieving comprehensive protection.
Solution Approach 2:
The combination of Ta layer and insulating layer creates a composite protective structure where the Ta layer handles mechanical and chemical challenges, while the insulating layer handles electrical protection. This composite approach achieves wiring protection with minimal thickness, preventing heat insulation issues.
3Reliability
If a Ta layer is formed as the upper layer for cavitation resistance, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs a composite structure with a Ta layer formed by sputtering followed by an insulating layer formed by CVD or PECVD. By utilizing existing semiconductor manufacturing equipment and processes for both layers, the patent achieves reliable cavitation resistance without significantly increasing manufacturing complexity. The insulating layer can be formed using standard CVD or PECVD equipment already present in semiconductor fabrication facilities.
4Use of energy by moving object
If the protective layer is made thinner to improve thermal efficiency, then energy consumption is reduced, but protection capability deteriorates
Solution Approach 1:
The composite structure of Ta layer and insulating layer enables each layer to be made thin while collectively providing comprehensive protection. The Ta layer, though thin, provides excellent cavitation and chemical resistance, while the insulating layer provides electrical protection. Together, they achieve adequate protection with minimal total thickness, maintaining thermal efficiency.
Solution Approach 2:
Each layer in the composite structure is optimized for its specific local function: the Ta layer is optimized for cavitation and chemical resistance, while the insulating layer is optimized for electrical insulation. This local quality optimization allows each thin layer to perform its specific protective function effectively, achieving overall reliability without requiring excessive thickness.
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 ensures stable ejection properties and image quality even after long-term storage, with minimal changes in driving pulse and temperature, by balancing kogation formation and protective layer stability.
Implementation Method 1
a heat generating portion that generates thermal energy for ejecting the ink from an ejection opening
Implementation Method 2
a protective layer containing at least one selected from the group consisting of a silicon oxide, a silicon nitride, and a silicon carbide
Data Source
AI summary
There is provided an ink cartridge including: a thermal ink-jet head provided with a heat generating portion that generates thermal energy for ejecting ink from an ejection opening, and contains the ink. In the ink cartridge, the heat generating portion has, at its surface in contact with the ink, a protective layer containing at least one selected from the group consisting of a silicon oxide, a silicon nitride, and a silicon carbide; and the ink contains at least one of a polyvalent carboxylic acid and a salt thereof, and the total content of the polyvalent carboxylic acid and the salt thereof is in the range of from 0.001 mmol/l or more to 0.5 mmol/l or less. The ink cartridge shows a small change in driving pulse and a small change in image to be outputted, and provides sufficient ejection property and sufficient printing durability.