Flexible Heater Manufacturers: Silicone Rubber vs Kapton

Silicone Rubber and Kapton are the two major materials in the market of flexible heating. Even though the basic feature of the two is that of being flexible, their chemical structure, thermal boundaries and physical features qualify them to be in vastly different environments.

This paper gives a technical comparison in detail so that the engineers and procurement professionals will know which flexible heater manufacturer is the best in their particular application.

Understanding the Base Materials

It is imperative to know what these performance metrics comprise before comparing their performance metrics.

The manufacturers of the Silicone Rubber Heaters make it by placing an element of resistive etching into the fibreglass-reinforced silicone rubber between layers of the substance. The silicone is vulcanised to make a waterproof, shockproof and a flexible composite. They are also characterised by high strength and ability to seal the environment.

Polyimide heaters or Kapton heaters are heating devices that are based on a fine layer of Kaplon as the insulator. The resistive circuit is usually etched on a thin foil of either copper or Inconnel followed by lamination between two very thin layers of Kaplon film. This makes the flexible heating element much thinner and lighter than the silicone variant.

Temperature Range: The Defining Factor:

The greatest distinction between these two flexible heating solutions is the thermal operating range.

• Silicone Rubber: Heaters made of standard silicone rubber are normally rated to continuous operation at 230-Degree Celsius. High temperature silicone speciality formulations are able to operate the limit marginally higher, but in most cases are not exceeding the 260degC threshold. Beyond this temperature, the silicone polymer chain starts to degrade causing brittle nature and the loss of dielectric strength.
• Kapton: Polyimide is a film that is highly thermally stable. Kapton heaters can be used continuously at temperatures of up to 260degC and can be exposed intermittently to temperatures of up to 400degC without melting or degrading. This renders Kapton as the default to use in ultra-high-temperature applications.

To be on the safe side, make sure the flexible heater manufacturer is able to deliver in this respect.

Physical Profile: Thickness and Compactability

Physical dimensions of heater are critical in case space is of any issue.

• Silicone Rubber: Silicone heaters have a natural increased thickness. The fibreglass reinforcement weaving and the process of vulcanisation achieved lead to an average thickness of between 1.5 mm and 3.0 mm. Though they are flexible heating solutions, they consist of a thickness that is of a rubbery nature and therefore may not fit in very narrow crevices.
• Kapton: Kapton heaters are very thin. The typical construction typically makes it only 0.1 mm to 0.3 mm thick. Their ultra-low profile makes them applicable to the use in designs where space is in microns (e.g. hard disc drives or miniature battery packs). Their slimness also ensures that the thermal mass of the heater itself is minimised to enable exceptionally fast response times.

Chemical Resistance and Outgassing

Chemical compatibility will be determined by the environment that the heater is operating in.

• Silicone Rubber: Silicone is typically inert, water resistant, oxygen resistant and ozone resistant. It works very well in the outdoor or damp conditions. But silicone rubber is porous and may take up some oils and solvents and therefore swell and degrade. Moreover, the standard silicone is not applicable in the vacuum. It is aggressive outgassing and volatile compounds are given off on exposure to low pressures potentially contaminating delicate optics or semiconductor wafers.
• Kapton: Polyimide surface is made of better resistance to a broader scope of chemicals and solvents. The most vital thing about Kapton is that the outgassing rates are very low and it is within the NASA standards of ASTM E595 regarding space applications. This necessitates Kapton heaters in applications where semiconductor fabrication equipment, vacuum chambers and aerospace where contamination is not acceptable.

This is a very important consideration during the selection of the appropriate flexible heating solution, especially where lives may be at stake.

Mechanical Durability and Abrasion

• Silicone Rubber: Silicone heaters are very tough. The elastic nature offers a good shock absorbing and vibration suppressing ability. It is very tear and abrasion-resistant. Silicone is more secure in this situation, when you need to wrap a heater around a pipe in an industrial plant and it may be hit by tools or operatives. It is also self-extinguishing which provides extra fire security.
• Kapton: Kapton film is tough regarding its thickness but is prone to tearing and puncturing. When the thin layer of polyimide is creased sharply during installation or when used under abrasion, it may rip apart, resulting in electrical breakage. Kaplon heaters are hard to fix after breaking, whereas silicone heaters can frequently be fixed in the field using high temperature RTV silicone.

It is essential that flexible heater manufacturers in India know the extent of the material to make sure the reliability of the device in every conceivable circumstance.

WATT Density and Heat Distribution

• Silicone Rubber: The application of silicone heaters can be made even on the surface since its construction is thicker, thereby enabling even distribution of heat over the surface. They do not usually attain densities of active cooling down to the watt. The heat mass of the silicone aids in the dispersion of the heat minimising hot spots.
• Kapton: Kapton is very thin and therefore the resistive circuit is directly adjacent to a heated surface. This gives a high efficiency in terms of heat transfer. The ability of the heaters to attain very high watt densities is due to the fact that the heat is immediately captured in the target surface instead of being trapped in the insulator. But, unless well regulated, this proximity must be a source of hot spots in the event the heater is not in even contact with the heat sink.

Cost and Economic Considerations

• Silicone Rubber: Silicone heaters tend to be economical, particularly when the surface size is large. The manufacturing processes and materials are cheaper as compared to precision chemical etching. Silicone is the most cost effective when the application needs no ultra-thin profiles and the ability to endure extreme temperatures.
• Kapton: Kapton The production of Kapton heaters includes photochemical etching which is a costly and more complicated process. Also, the unprocessed polyimide film is more expensive than silicone rubber. This means that Kaplon heaters will have a premium price tag but only their performance in harsh conditions would justify it.

Although cost is a critical element that needs to be taken into consideration by flexible heater manufacturers, performance, safety and other performance parameters must not be compromised.

Regulatory Compliance: Food and Medical

• Silicone: Silicone rubber is naturally tasteless, odourless and non-toxic. It is in common form in FDA-approved direct food contact grades. It is also biocompatible and may withstand high temperatures of autoclave sterilisation and this makes it suitable in the medical equipment that may have to undergo repeated cycles of sterilisation.
• Kapton: Kapton is also a chemically inert material with a tendency to be utilised in medical equipment. Nonetheless, it has not found widespread application as a direct food contact substance as silicone. The main medical benefit of Kapton is that it can be applied in surgical instruments or other diagnostic equipment requiring a thin precise heat source but sterilisation is accomplished by gamma radiation or ethylene oxide instead of steam autoclaving.

Applications Scenarios: A Quick Reference Guide

In order to select the most appropriate flexible heating solutions, take into consideration the following applications of each material:

Choose Silicone Rubber If:

• The Environment is Rough Industrial machinery, construction equipment or out-of-doors enclosures.
• Food Service Involved: Food warmers, heat serving trays or beverage dispensers.
• You Need a Weather Seal: Silicone is good in moisture and UV resistance.
• Cost: This is a Main Factor: You require a high area of heating at a cost.

Choose Kapton If:

• Space is Minimal: You are creating a small gadget such as a laptop battery heater or a 3D printer print bed.
• Vacuum is necessary: You are being in a semiconductor process chamber or aerospace satellite component.
• Response Time is Important: At least the heater must reach the target temperature within a few milliseconds.
• Temperatures Above 250degC: You are in high-temperature material testing or in de-icing of aerospace.

Conclusion

No one installation exists that can be considered the best flexible heating element, and the correct selection is all a matter of the environmental and physical constraints of the application.

Silicone Rubber is the workhorse of the industry. The industrial flexible heaters are a rough-and-tough product that is suitable in an environment employing sealing, mechanical endurance, and price the most relevant factors. It is easy to deal with moisture, shock and bend.

Kapton is the specialist. This flexible heating system is the material used in cutting-edge technology industries. When temperatures are to be pushed into an extreme, when small spaces need to be squeezed into, when the highest level of purity in a vacuum is required, the high price of Kaplon is compensated by the unmatched performance level.

Through comparing the thermal needs with the physical space as well as the chemical environment, an engineer can be assured to make the right choice of material which can offer the best performance and the life of his or her particular thermal system.