What are crosslinkable resins? Their functions, applications, and optimal material selection.

Crosslinkable resins, in which polymer chains form a three-dimensional network structure, dramatically improve properties such as heat resistance, creep resistance, and rubber elasticity. This article provides a comprehensive overview, from the basics of crosslinkable resins to applications requiring crosslinking, and the diverse range of crosslinkable compound solutions offered by Mitsubishi Chemical.

What are crosslinkable resins?

Crosslinkable resins are resins that have a three-dimensional network structure by forming crosslinking points between polymer molecular chains. Through the crosslinking reaction, they are given heat resistance, creep resistance, chemical resistance, and excellent rubber elasticity (compression set characteristics) that cannot be obtained with ordinary thermoplastic resins. Crosslinking methods include electron beam crosslinking, peroxide crosslinking, phenol resin crosslinking, and silane crosslinking, and the optimal application and balance of properties differ depending on the method.

Application examples of crosslinkable resins

The automotive industry demands both lightweight construction and heat resistance. Dynamically crosslinked thermoplastic elastomers are not only lighter than vulcanized rubber, but unlike vulcanized rubber, they can be molded like ordinary thermoplastic resins, making them suitable for two-color molding with resin parts such as polypropylene, and composite molding with metal parts.

Examples of applications: Vibration damping rubber, hose clips, seals and gaskets, heat-resistant ducts, engine compartment components.

The role of crosslinkable resins as wire insulation materials is to provide long-term durability of heat resistance. In particular, for cables used in solar power generation systems and automobiles, both heat resistance and long-term durability are required, so crosslinking is necessary to achieve high heat resistance and durability. Silane crosslinking types are easy to industrialize because crosslinking proceeds with a simple water crosslinking treatment after molding.

Examples of applications: automotive harnesses, solar power generation cables, low-smoke cables, railway vehicle cables

For water supply and hot water piping, heat resistance and long-term dimensional stability are of paramount importance. Silane cross-linked resins minimize resin creep even in environments where high-temperature hot water flows, preventing pipe damage. Similarly, cross-linking is an essential technology for underfloor heating piping, as it is unaffected by creep caused by high-temperature circulation.

Examples of applications: Water supply and hot water piping, underfloor heating pipes and tubes

Seal components require excellent compression set characteristics. Crosslinking, which bonds molecular chains, dramatically improves the recovery force after being subjected to compressive force, allowing the sealing function to be maintained over a long period of time.

Examples of applications: seals and gaskets, vibration damping rubber, cushioning materials

Introducing Mitsubishi Chemical's crosslinkable compounds and application examples.

Trexprene™ is a dynamically crosslinked thermoplastic elastomer (TPV) made by blending an olefin resin matrix with crosslinked olefin rubber, and is a type of thermoplastic elastomer (TPE). Its greatest advantage is that it has performance comparable to vulcanized rubber (EPDM), but does not require a crosslinking process at the customer's site and can be molded in the same way as conventional thermoplastic resins. Because it is recyclable, it is used as a substitute for vulcanized rubber, contributing to a reduction in production time, production costs, and environmental impact.

① Treexprene™ (fully cross-linked type)

The fully cross-linked type offers a wide range of hardness levels, from approximately Duro hardness A40 to D55, achieving performance comparable to vulcanized rubber through thermoplastic processing.

Main features

• Excellent compression set characteristics (20% or more) provide superior sealing performance.

• Can be used in environments with a heat resistance of 110-120°C.

• Excellent oil resistance, making it suitable for parts that come into contact with oils and greases.

Molding method

Molding of general polyolefins using extrusion molding machines, injection molding machines, and blow molding machines.

Applicable use

• Automotive heat-resistant components (engine compartment parts, etc.)

• Vibration-damping rubber

• Seals and gaskets

② Treexprene™ (partially cross-linked type)

The partially cross-linked type has a hardness range of approximately Duro hardness A50 to A90. While its compression set is slightly inferior to the fully cross-linked type in the same hardness range, it excels in low specific gravity, moldability, and color.

Main features

• Low specific gravity (0.88–0.89 g/cm³) contributes to product weight reduction.

• Excellent molded appearance allows for products with high aesthetic appeal.

• Excellent color reproduction, enabling the creation of products with vibrant colors.

Molding method

Molding using general polyolefin extrusion molding machines, injection molding machines, and blow molding machines.

Applicable use

• Automotive exterior and interior components, lip moldings

• Various types of grips

Linklon™ is a silane-crosslinkable polyolefin resin. Based on polyethylene (PE) or polypropylene (PP), it undergoes crosslinking in a water-contact environment at the customer's site.

Main features

• Excellent moldability; can be processed under molding conditions equivalent to those for polyolefins.

• Crosslinking proceeds in hot water or a high-temperature, high-humidity atmosphere, making the crosslinking process easy.

• Excellent heat resistance, creep resistance, and shape memory properties.

Molding method

During molding using general polyolefin extrusion and injection molding machines, a catalyst masterbatch is added, and after molding, a crosslinking treatment is performed in hot water or in a high-temperature, high-humidity environment.

Applicable use

• Water supply and hot water pipes, underfloor heating pipes

• Wire insulation material (insulating material)

• Solar cell encapsulant

Olefista™ is the name of Mitsubishi Chemical's flame-retardant resin compound. While flame retardancy is imparted to various resins, the QX series features flame retardancy imparted to silane-crosslinked polyolefins. It is a flame-retardant crosslinked resin compound with excellent heat resistance, oil resistance, and chemical resistance.

Main features

• Offers a lineup of non-halogen and halogen grades, with high flame retardancy.

• Complies with UL rated temperature range of 105°C to 150°C, enabling stable use in high-temperature environments.

• Cross-linking improves heat resistance, oil resistance, and chemical resistance.

Molding method

During molding using general polyolefin extrusion and injection molding machines, a catalyst masterbatch is added, and after molding, a crosslinking treatment is performed in hot water or in a high-temperature, high-humidity environment.

Applicable use

• Wire insulation materials (automotive cables, solar power generation system cables, etc.)

• Electrical equipment

• Spattered tube

If you are looking for a crosslinkable resin

Mitsubishi Chemical offers a wide range of crosslinkable resin compounds with diverse crosslinking methods and functionalities. We propose the optimal crosslinkable resin to suit your application and required properties, such as heat resistance, creep resistance, and rubber elasticity. Please feel free to contact us if you have any questions or need advice regarding crosslinkable resin material selection.