Cooling Rate Effects on PTFE Tape

As an original manufacturer of PTFE high-temperature tapes, Jiangsu Aokai New Materials hereby elaborates the impacts of cooling methods and cooling rates on the performance of cured PTFE high-temperature tapes.

I. Essence of PTFE Crystallization Characteristics and Cooling Rate Regulation

The PTFE substrate of cured high-temperature tape belongs to semi-crystalline polymer, which undergoes rapid crystallization during cooling after sintering. Essentially, cooling rate is the core process parameter to control the crystallinity of PTFE high-temperature tape: slower cooling leads to higher crystallinity, while faster cooling results in lower crystallinity.

II. Effects of Slow Cooling on PTFE High-temperature Tapes

Influence on Internal Stress Slow cooling can effectively reduce residual thermal stress inside the tape. When the tape is cooled naturally inside the furnace, the PTFE matrix and glass fiber skeleton have sufficient time to adjust shrinkage differences through molecular chain relaxation, avoiding local stress concentration.

The widely adopted process is to cool the tape naturally in the furnace to 150–200℃ before taking it out for air cooling. This slow cooling process cuts down internal stress effectively and prevents coating delamination and cracking.

Influence on Dimensional Stability Slow cooling greatly improves dimensional stability. During slow cooling, PTFE molecular chains arrange into regular crystal lattices sufficiently, forming high crystallinity and well-developed crystal grains, which ensures stable final dimensions.

Slight thermal shrinkage will occur under high temperature in actual use, so it is recommended to reserve 1%–2% margin during application. Slow cooling enables steady shrinkage with minimal residual deformation.

Influence on Adhesive Performance Slow cooling exerts dual effects on adhesion property. On one hand, it allows the adhesive layer to complete cross-linking and stress relaxation fully, maintaining stable bonding strength. On the other hand, higher crystallinity increases surface rigidity of PTFE substrate, causing concentrated stress on bonding interface under peeling force.

III. Effects of Rapid Cooling on PTFE High-temperature Tapes

     Influence on Internal Stress Rapid cooling is the main cause of excessive internal stress. Direct quenching after           sintering creates huge temperature difference between PTFE matrix and glass fiber framework, generating instant         shrinkage stress and easily forming fine cracks.

The surface layer shrinks and hardens rapidly while the inner layer remains expanded, forming a thermal stress state of outer tension and inner compression, which directly causes tape cracking.

Influence on Dimensional Stability Rapid cooling shifts the crystallization peak to lower temperature and reduces crystallinity with incomplete crystal structure. The tape stays in an unbalanced frozen state after quenching. Secondary crystallization and post-shrinkage may happen under subsequent temperature changes, leading to gradual dimensional deviation.

Influence on Adhesive Performance Fast cooling inhibits full cross-linking of adhesive layers. The adhesive is frozen before forming complete cross-linked network, resulting in decreased bonding strength and temperature resistance.

Under repeated cold and hot cycling, thermal expansion difference between PTFE substrate and adhesive layer produces interfacial stress, accelerating adhesive aging and debonding, and greatly weakening viscosity durability.

IV. Comparison of Different Cooling Methods

In general, slow and uniform cooling is the fundamental principle for post-curing treatment of PTFE high-temperature tapes. It is recommended to adopt in-furnace natural cooling after sintering, and take out the tapes for air cooling to room temperature after the temperature drops below 150–200℃. Uneven cooling during production will cause slackness and ultimately damage product quality.

The above content is provided by Jiangsu Aokai New Materials Technology Co., Ltd.

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