Piezoelectric Liquid Discharge Head Structure to Prevent Adhesive Peeling
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Solution Overview
Problem
Existing liquid discharge heads experience issues with adhesive peeling, leading to particle formation and reduced discharge stability due to the step shape at the joint surface of the insulative and protective layers in the element substrate.
Innovation Solution
The design includes a protective layer configuration where L3>L1>L2, with L3 being the protective layer opening length, L1 the through hole length, and L2 the communication port length, ensuring a substantially flat inner wall surface and non-overlapping peripheries to minimize adhesive peeling, and uses etching to form the protective and insulative layers simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive is used to join substrates, then substrates can be connected together, but adhesive peeling occurs and forms particles
Solution Approach 1:
The patent removes the adhesive layer from the joint surface between the actuator substrate and flow path substrate by forming a groove that eliminates the need for adhesive in this critical area. This extraction of the adhesive from the joint interface prevents adhesive peeling and particle formation, directly resolving the contradiction between joint strength and discharge stability.
Solution Approach 2:
Instead of using adhesive to create the joint, the patent inverts the approach by using a groove structure that mechanically interlocks the substrates without adhesive. The groove allows the flow path substrate to fit into the actuator substrate, creating a secure joint through geometric constraint rather than adhesive bonding.
2Productivity
If through hole and communication port are formed, then liquid flow path is established, but flow resistance increases
Solution Approach 1:
The patent forms a groove with a curved bottom surface instead of a sharp angular shape. This curvature reduces turbulence and flow resistance in the liquid passage, allowing smoother liquid flow from the through hole through the communication port to the liquid chamber, thereby improving productivity while minimizing harmful flow resistance.
3Ease of operation
If piezoelectric element is disposed on surface closer to third substrate, then liquid discharge function is achieved, but adhesive peeling occurs at joint surface
Solution Approach 1:
The patent extracts the adhesive from the joint interface between the actuator substrate (containing the piezoelectric element) and the flow path substrate. By forming a groove that eliminates the need for adhesive at this critical joint, the patent prevents adhesive peeling while maintaining the piezoelectric element's position and function.
Solution Approach 2:
The groove structure is formed in advance during substrate fabrication, creating a pre-prepared joint interface that accommodates the piezoelectric element without requiring adhesive. This preliminary structural preparation ensures that when the piezoelectric element is disposed on the surface, the joint is already configured to prevent peeling.
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 configuration reduces particle formation, enhances discharge stability, and improves liquid flow rate and adhesion reliability, resulting in a more reliable and efficient liquid discharge process.
Implementation Method 1
a voltage is applied to the piezoelectric elements to deform the vibration plate and contract the liquid chamber so that the liquid is discharged
Implementation Method 2
forming an opening in the protective layer to connect the liquid chamber and the through hole by etching the first protective layer and the second protective layer simultaneously
Data Source
AI summary
A liquid discharge head includes first, second and third substrates. The second substrate includes a piezoelectric element configured to generate energy for discharging liquid, and a protective layer. The protective layer includes a first protective layer in contact with the piezoelectric element and a second protective layer covering the first protective layer, wherein L3>L1>L2 is satisfied, where L1 is a length of a through hole, L2 is a length of a communication port connecting the through hole and a liquid chamber in the second substrate, and L3 is a length of an opening of the protective layer, on a straight line passing through a center of the through hole when viewed from a direction perpendicular to a surface of the element substrate, and wherein an inner wall surface of the opening of the protective layer is a substantially flat surface.