Heater Substrate Cracking Prevention via Heat Conduction Layer
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Solution Overview
Problem
Existing image heating apparatuses are prone to heater substrate cracking due to abnormal temperature increases caused by malfunctioning power supply circuits, leading to thermal and mechanical stress, which conventional solutions like thermal fuses and switches often fail to adequately mitigate, especially when improperly attached or with inadequate thermal management.
Innovation Solution
The image heating apparatus incorporates a heat conduction layer on the back surface of the heater substrate, combined with a thermal fuse and thermistor, to distribute heat evenly and provide a larger contact area for heat dissipation, reducing thermal stress and mechanical strain on the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal fuse or thermal switch is attached directly to the heater substrate to interrupt primary current before substrate cracking, then the substrate can be protected from thermal stress, but the substrate becomes subject to mechanical stress from the current interrupting member which may cause cracking
Solution Approach 1:
A heat conduction layer is introduced as an intermediary between the thermal fuse and the heater substrate. This layer has higher thermal conductivity than the substrate, allowing it to effectively conduct heat away from the substrate while distributing the mechanical contact stress over a larger area, thus preventing both thermal and mechanical damage to the substrate
Solution Approach 2:
The heat conduction layer is applied specifically at the location where the thermal fuse contacts the substrate, creating a localized region with enhanced thermal conductivity and stress distribution properties. This targeted approach protects the critical contact area without requiring modification of the entire substrate structure
2Duration of action of stationary object
If a heat radiating member is attached to the back surface of the heater substrate to maintain uniform temperature, then the substrate can withstand thermal stress longer, but the device complexity increases
Solution Approach 1:
The heat conduction layer serves multiple functions simultaneously: it acts as a thermal management component to maintain uniform substrate temperature, a mechanical interface to distribute contact stress, and a protective layer between the thermal fuse and substrate. This multi-functionality achieves extended substrate durability without adding significant structural complexity
3Speed
If the current interrupting member is made with larger thermal capacity to respond faster to abnormal temperature, then the substrate is protected more quickly, but the substrate temperature becomes nonuniform causing thermal stress
Solution Approach 1:
The heat conduction layer has higher thermal conductivity than the substrate material, which changes the thermal parameter profile at the contact region. This allows the thermal fuse to respond quickly to temperature abnormalities while the high-conductivity layer rapidly distributes heat laterally, preventing localized temperature drops and maintaining overall substrate temperature uniformity
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 significantly extends the time before the heater substrate cracks, providing a margin for the thermal fuse to interrupt the power supply before substrate failure, thus preventing cracking and ensuring reliable operation under abnormal conditions.
Implementation Method 1
a heat conduction layer on the back surface of the heater substrate
Implementation Method 2
thermal fuse...interrupts the primary current before the heater substrate is made to crack by the thermal and/or mechanical stress
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An image heating apparatus for heating a toner image formed on a recording material, the image heating apparatus includes a heater (203) including a substrate (203a) and a heat generating resistor (203b) thereon for generating heat for heating the toner image, by electric power supply; an electric power shut-off member (206) operable in response to an abnormality temperature rise of the heater to shut off the electric power supply; and a heat conduction member (207, 208) having a thermal conductivity, in a direction of a thickness of the substrate, higher than that of the substrate, wherein a contact area between the heat conduction member and the substrate is larger than a contact area between the heat conduction member and the electric power shut-off member.