Thermal Head Crack Suppression via Protection Film
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Solution Overview
Problem
Thermal storage layers in thermal heads can crack, leading to potential chip formation and deterioration of electrodes and heat-generating resistors, especially when the thermal head is driven, causing cracks to extend and penetrate through the layers.
Innovation Solution
A thermal head design featuring a heatsink, a head base with a substrate and heat-generating portions, a thermal storage layer made of glass with a first and second covering layer, and protection films positioned to reduce the likelihood of crack extension, including a first protection film not disposed above the substrate's edge to prevent external contact and a second protection film with a convex portion for smooth ink ribbon separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the thermal storage layer is made of glass to provide thermal storage function, then thermal storage capability is improved, but the layer becomes prone to cracking and chip formation during operation
Solution Approach 1:
The patent applies beforehand cushioning by providing a protection film that extends beyond the edge of the substrate before cracks can form and propagate. This protection film acts as a preventive measure that absorbs and distributes stress, preventing cracks from initiating and extending in the thermal storage layer during thermal cycling operations.
Solution Approach 2:
The patent uses an intermediary approach by introducing a protection film as a mediator between the thermal storage layer and the external environment. This protection film serves as a buffer that protects the fragile thermal storage layer from mechanical stress and thermal shock, allowing the glass layer to maintain its thermal storage function without suffering from crack propagation.
2Reliability
If the protection film extends to the edge of the substrate to maximize protection, then crack prevention is improved, but manufacturing complexity increases due to alignment requirements
Solution Approach 1:
The patent applies local quality by making the protection film extend locally beyond the substrate edge in the longitudinal direction, rather than requiring uniform extension in all directions. This localized extension provides adequate crack prevention where it is most needed (at the edges where cracks typically initiate) while avoiding the manufacturing complexity of extending the film equally in all directions with perfect alignment.
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 design effectively reduces the possibility of crack extension in the thermal storage layer and improves the thermal head's durability and printing performance by preventing chip formation and deterioration of heat-generating components.
Implementation Method 1
a thermal storage layer (13) disposed on one main surface of the substrate (7) so as to extend to an edge (7a) of the substrate (7)
Implementation Method 2
heat-generating portions (9) disposed above the substrate (7)
Data Source
Figure 1
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Figure 4
AI summary
Extension of a crack occurring in a thermal storage layer and a protection film is suppressed. A thermal head (X1) of the invention includes a substrate (7), a thermal storage layer (13) disposed on one main surface of the substrate (7) so as to extend to an edge (7a) of the substrate (7), the thermal storage layer (13) being formed of glass; electrodes disposed on or above the thermal storage layer (13) apart from the edge (7a) of the substrate (7); heat-generating resistors (9) disposed above the thermal storage layer (13) apart from the edge (7a) of the substrate (7), the heat-generating resistors (9) being connected to the electrodes; a first covering layer (24) disposed on or above the electrodes and the heat-generating resistors (9); and a protection film (25) disposed on or above the first covering layer (24). The first covering layer (24) extends from atop the electrodes and the heat-generating resistors (9) toward atop the thermal storage layer (13) on the edge (7a) of the substrate (7), and the protection film (25) is disposed on or above the first covering layer (24) disposed on or above the electrodes and the heat-generating resistors (9) and an edge (25a) of the protection film (25) is not disposed above the edge (7a) of the substrate (7).