Analysis of PI heating element and silicone heating element technology

The fundamental heating elements of modern industrial and consumer sectors are flexible electric heating films, which typically consist of an insulating film, a metal heating element, a thermistor, and positive and negative leads. A composite structure is created by utilising an alloy sheet as the heating core, an outer insulator of polyimide film (PI film) or silicone, and an interior conductor of metal foil/wire through a high-temperature, high-pressure heat-sealing process. Hongli Electric Heating is committed to being at the forefront of the industry, and its electric heating film products primarily employ PI film and silicone as key insulating materials. This approach has been shown to offer distinctive technological advantages in a variety of application scenarios.

I. Technical Characteristics of PI Heating Elements

(I) Manufacturing Process and Structural Design
Precision etching technology is employed by PI heating elements to create customised heating circuits from metal substrates such as stainless steel, copper, or iron-chromium-aluminum alloys. The double-sided insulating covering layer is a high-purity polyimide film. A controllable thickness integrated structure is achieved by means of a high-temperature hot-press curing process (200-350℃, 5-15MPa). The finished product's total thickness ranges from 0.13 to 0.21mm, with the standard thicknesses of the PI film being 0.05mm and 0.08mm. This results in ultra-thin and highly integrated designs.

Core Performance Indicators (II)

PI material possesses exceptional dielectric properties, with a dielectric constant as low as 2.5 and a dielectric strength of 100-300kV/mm, demonstrating outstanding electrical insulation and temperature resistance. It meets the reliable operation requirements of high and low temperature environments by maintaining stable dielectric properties in extreme temperature ranges from -269℃ to 400℃.

Mechanical Properties: The material exhibits exceptional mechanical properties. In its unfilled state, the tensile strength is ≥100MPa, with pyromellitic PI films reaching 250MPa and biphenyl Upilex films exceeding 530MPa. The structural stability is guarantyd by the elastic modulus's persistence at 3-4GPa in the presence of intricate operating conditions.

Chemical and Irradiation Stability: PI material is highly chemically inert, ensuring that it remains stable in the presence of most organic solvents and dilute acid environments. Some models are suitable for radiation environment applications due to their ability to retain up to 90% of their film strength even after 5×10⁹rad rapid electron irradiation.

(III) Product Structural Characteristics
The structure of the PI heating film is sandwich-like. The outermost layer is a yellow, flexible PI insulating layer that provides mechanical protection and electrical isolation. The middle layer is a precision-etched metal heating resistance wire that facilitates efficient heating. The bottom PI film further improves insulation performance, ensuring safety during use.

(IV) Technological Advantages and Application Areas
PI heating elements are extensively employed in high-precision temperature control scenarios due to their high thermal conductivity (thermal conduction rate > 2W/(m・K)), flexibility, and ultra-thinness. They are employed in the industrial sector to freeze-proof preheat electronic components in extremely cold environments, provide low-temperature start-up protection for lithium battery packs in the new energy vehicle field, enable rapid heating functions in portable devices in the consumer electronics industry, and achieve precise body temperature maintenance in medical equipment.

II. Silicone Heating Surfaces' Technical Properties

(I) Material Selection and Structural Design
The insulating substrate for the silicone heating surface is high-temperature pressed silicone fibreglass textile. The heating layer can be created through the use of resistance wire winding or metal etching. Resistance wire winding is less costly; however, it is characterised by a lack of surface smoothness and an uneven heating density (roughness Ra 3.2 - 6.3 μm). In contrast, metal etching employs precision photolithography to establish a uniform heating line design with a line width of 0.1 - 0.3 mm, thereby enhancing temperature uniformity by approximately ±2℃. However, this process results in a 30-50% increase in manufacturing costs.

Core Performance Indicators (II)
Physical and Mechanical Properties: Silicone material is capable of closely conforming to intricate curved surfaces and ensuring efficient heat transfer due to its high mechanical strength and flexibility. It has a Shore hardness of 40-60A and a tensile strength of ≥5MPa.

Thermal Performance: The product thickness is adjustable between 0.5 and 3 mm. It is capable of meeting the requirements of rapid heating due to its fast response speed, low heat capacity, and a surface heating power density of up to 4 W/cm².

Environmental Adaptability: Silicone material exhibits exceptional weather resistance, ensuring consistent performance across a temperature range of -60℃ to 200℃. It is capable of withstanding UV ageing for more than 1000 hours and possesses excellent hydrophobicity and chemical resistance, which enables it to be used for an extended period in corrosive gas and high humidity environments.

(III) Product Application Scenarios: Silicone heating elements are crucial in the industrial sector due to their exceptional strength, corrosion resistance, and high temperature resistance. They are employed in outdoor communication base stations to prevent condensation, in chemical equipment to sustain reaction temperatures, for oil pipeline antifreeze insulation, and for winter defrosting of solar equipment. Uniform heating across the entire surface is achieved through customised designs.

The variegated application system for electrothermal film products is jointly constructed by PI heating elements and silicone heating elements, which possess distinct material properties and technological advantages. Users have the ability to choose an appropriate electric heating solution by considering the specific operating temperature range, environmental conditions, mechanical requirements, and cost budget. For additional information regarding product selection or customisation requirements, please reach out to our technical team for expert assistance.