What about Rubber?

Good properties, but difficult to handle.

Rubber is the most widely used material for these purposes and does have some advantages. Namely, they seal very well. The typical compression set for nitrile rubber at standard conditions of 100 °C/24h is 20–30%. In addition, these rubbers are a well-established option, on top of being thermally, chemically, and mechanically robust, with low material costs. However, one glaring disadvantage is that they are especially difficult to integrate into production settings.

If a round sealing geometry is required, then rubber O-rings are still the most economical solution. In the case of sealing cords or tapes, such as those used for housings, efficient production is more complicated. They require an additional manual bonding step at the connecting point where the two ends meet, making the process more time-consuming.

More complex rubber geometries can be produced by punching or vulcanizing. While this allows for simple production processes, its benefits can only be leveraged in high production volumes. Simpler assembly processes exist. Furthermore, molds for these gaskets are particularly expensive.

Sealing the Gap with Thermoplastic Elastomers

An alternative with limited temperature application range.

Seals made of thermoplastic elastomers (TPE) offer an alternative. They are applied directly to the component via injection molding. They are robust, abrasion-resistant, and adhere well to technical plastics such as PA, PC, or PBT, making the seal resistant to leakage. At room temperature, TPE behave like classic elastomers, but its thermoplastic component limits the temperature application range to 80–100 °C, with the compression set increasing at higher temperatures. For TPU, the compression set is about 80% (100 °C/24 h), while other TPE types are able to achieve values of 50 %.

The injection molding process is less complex than vulcanizing. However, TPUs’ moderate processing properties and tool requirements for each geometry keep it from being too simple. In addition, a multi-component injection molding machine is required to avoid reinserting the component in an additional process step.

First It’s Liquid, Then It’s Tight

Cheaper, More Flexible, and Better Results: Liquid Gaskets.

With liquid gaskets, such investment costs can be avoided. These gasket types are flow-resistant, highly viscous, adhesive-based products which are dispensed according to the desired height and shape, then cured in their application position. Their application flexibility makes them suitable for complex component geometries, even three-dimensional ones. Another advantage of liquid gaskets compared to solid gaskets is that they mold and adhere, not just rest on uneven surfaces, thus better sealing them while allowing for higher manufacturing tolerances.

The FIPG process (Form-In-Place Gasket)

This method of using liquid gaskets is what is known as the FIPG process (Form-In-Place Gasket). So far, silicone- or polyurethane-based products have often been used for liquid gaskets. They involve fewer process steps than rubber or TPU seals, reduce machine setup times, and produce less rejects than cutting dies. Production processes can bee asily automated, with only one system needed for all components to be produced. Potential dispensing errors in sealant beads are detected by fluorescence for optical in-line quality control. Since it is no longer necessary to keep a large number of seals in stock, storage costs are not an issue.

While their seal is effective, these two-component systems cure slowly and are therefore better suited for large components or small series. In the latter case, the uncomplicated and flexible process liquid gaskets enable has often not been able to compensate for its slower speed compared to rubber or TPU seals.

The CIPG process (Cure-In-Place-Gasket)

However, light-curing one-component acrylates have been on the market for some time now, demonstrating their strengths in large-series production by enabling quick CIPG processes (Cure-In-Place-Gasket). High-energy UV light ensures that the adhesive reaches its final strength within seconds, thus allowing for short cycle times and direct component processing, all important aspects to achieve a high production volume.

Their good shape recovery properties ensure a reliable seal after joining; A low compression set of up to 10 % (85 °C, 24 h) allows them to restore their original geometries when there is no more pressure. Numerous surface-dry versions allow repeated disassembly. In addition, acrylate-based CIPGs meet IP67 requirements, thanks to their water-repellent properties. They are PWIS- and solvent-frees, featuring a service temperature range from -40 to 120 °C.

Know the difference between FIPG and CIPG processes

DELO's Versatile Liquid Sealant for CIPG Processes

An excellent liquid sealant for these processes is DELO PHOTOBOND SL4165, which has a compression set of 15%, thus demonstrating good elastic recovery. These properties ensure a reliable seal and help manufacturers meet the tightness requirements according to IP67, the IP rating used for smartphone classification.

DELO PHOTOBOND SL4165 cures by either UV or visible light in a matter of seconds without thermal influence, and thus enables the aforementioned CIPG process. It is comprised of one component and is free of solvents and paint-wetting impairment substances.

Its range of applications includes the sealing of housings in consumer electronics such as white goods or landline and mobile phones. Using this CIPG material in the field of power electronics in cars, such as in high-voltage accumulators or electronic transmission control components, is also feasible. This is only one of several CIPG materials DELO has on offer, each with its own properties that best cater to any sealing use case.

Take 2: Sealing and Bonding in One Go

A permanent solution with sealing effects

Seal bonding is another alternative and the ideal solution if a seal is explicitly meant to be nondetachable. Here again, it is possible to create any geometry and to use fluorescence for in-line quality control. An additional advantage is its power transmission, where adhesives not only seal components but join them permanently. This translates to reduced space requirements. Screws are no longer required, allowing for smaller housings, miniaturization of assemblies, and fewer production steps.

For high-volume applications, light-curing acrylates and epoxy resins are particularly suitable, depending on the thermal and chemical requirements. While epoxy resins are slightly more stable in temperature, acrylates provide greater flexibility and faster curing. In addition, dual-curing versions exist for both product families. Curing in ovens or by contact with air humidity, these adhesive types ensure full crosslinking even in shadowed areas.

Conclusion

Seals are not just rubber rings; they have become more diverse than ever. Bonding technology, with its light-curing liquid gaskets and seal bonding solutions, provides users with new options to optimize their design and achieve both efficient and flexible production processes.