Thermal crosslinkers are compounds that, upon heating, chemically react with active groups on polymer molecular chains to form a three-dimensional crosslinked network structure. If initiators are the "switch" that "starts polymerization," then crosslinkers are the "link" that "builds the network"-they connect linear or slightly branched macromolecular chains through chemical bonds, transforming thermoplastic materials into thermosetting materials, thereby significantly enhancing the mechanical strength, heat resistance, solvent resistance, and dimensional stability of finished products.
Common types of thermal crosslinkers include isocyanates (reacting with hydroxyl/amino groups), epoxy resins (reacting with amines/anhydrides/phenolic hydroxyls), amino resins (reacting with hydroxyls), peroxides (free-radical crosslinking), etc. They are widely used in rubber vulcanization, thermosetting plastic molding, baking curing of coatings, and thermal curing of adhesives.
In the field of crosslinkers, our company highlights three major product series: blocked imidazole curing agents, Thiol-series polythiol curing agents, and blocked isocyanates. In parallel, to address stability issues during storage and use of formulation systems, we offer the complementary EAP series of stabilizers, providing customers with a complete solution spanning from crosslinking curing to long-term storage.
3.2 Blocked Imidazole Curing Agents
Imidazole compounds (e.g., 2-methylimidazole, 2-ethyl-4-methylimidazole) are commonly used catalytic curing agents for epoxy resins, offering high reactivity, moderate curing temperatures, and good heat resistance of cured products. However, conventional imidazoles undergo slow reactions with epoxy resins even at room temperature, resulting in extremely short pot life for one-component formulations (typically only days to weeks), with continuous viscosity increase that causes significant inconvenience in production and use.
Our blocked imidazole curing agents employ chemical blocking technology to reversibly "protect" the active nitrogen atoms on the imidazole ring, keeping the imidazole in a "dormant" state at ambient temperature. Upon heating to the set temperature, the blocking groups are removed, releasing active imidazole to rapidly catalyze the epoxy curing reaction. This design delivers the following core values:
Extended room-temperature storage: One-component epoxy formulations remain stable for over 6 months at room temperature with minimal viscosity change, eliminating the need for cold-chain transportation and storage.
Controllable curing temperature: Depending on the blocking group design, the deblocking temperature can be adjusted within 80–150°C to suit different processing requirements.
High curing efficiency: Once deblocked, the curing reaction proceeds rapidly with full crosslinking, yielding cured products with high Tg and good heat and humidity resistance.
This product is particularly suitable for one-component epoxy structural adhesives, epoxy encapsulants, epoxy SMC/BMC molding compounds, and other applications requiring long-term storage stability and rapid heat-induced curing.
3.3 Thiol-Series Polythiol Curing Agents
3.3.1 Product Features and Technical Advantages
Our Thiol series are secondary-distillation polythiol mercaptan compounds. Compared to conventional polythiol products, their most outstanding advantages are:
Extremely low odor: Through distillation purification technology, low-boiling sulfur-containing impurities are effectively removed, resulting in significantly lower odor than commercially available counterparts. This improves the production environment and makes them especially suitable for odor-sensitive applications such as cosmetic packaging, food-contact materials, and indoor uses.
High purity and high activity: The mercaptan (–SH) functionality is precisely defined, with consistent reactivity and excellent batch-to-batch stability.
3.3.2 Improving Oxygen Inhibition in UV-Curable Systems
In free-radical photopolymerization systems, oxygen inhibition is a primary obstacle to surface curing. Oxygen in the air readily adds to free radicals in the system, forming less reactive peroxy radicals, which slow down or terminate surface polymerization and result in tacky film surfaces.
Our Thiol polythiols demonstrate a unique "oxygen-scavenging" effect in this regard:
The active hydrogen (–SH) in thiols reacts rapidly with peroxy radicals (ROO•), reducing them to peroxides while the thiol is dehydrogenated to form thiyl radicals (RS•). These thiyl radicals are sufficiently active to continue participating in the addition reaction with acrylate monomers, thereby converting oxygen-which normally "consumes" radicals-into thiyl radicals that can participate in chain growth, fundamentally mitigating oxygen inhibition.
Practical results include:
Achieving tack-free, dry surface finishes even under low-energy curing conditions (e.g., low-power LED, high-speed printing).
Significantly improved double-bond conversion and overall crosslink density of the film.
Enhanced adhesion to metals, glass, and polymeric substrates, improving coating toughness.
3.3.3 Application in Epoxy Curing Systems
When Thiol polythiols are used in combination with tertiary amine accelerators, they enable low-temperature rapid curing of epoxy resins. The thiol-epoxy ring-opening addition reaction, catalyzed by tertiary amines, proceeds quickly with moderate exothermic behavior. The cured products exhibit excellent adhesive strength, tensile strength, and improved heat and humidity resistance, making them suitable for epoxy adhesives and composite materials requiring high reliability and weatherability.
3.3.4 Application in UV-Curable Inks
In UV offset, gravure, roller-coating, and other low-film-thickness, low-energy, high-speed printing processes, adding Thiol polythiols significantly increases curing speed, yielding dry, non-blocking surfaces without residual tacky monomers. Additionally, since the thiol structure contains no aromatic rings, it is less prone to oxidative yellowing, contributing to improved anti-yellowing performance of printed matter, especially in white and light-colored ink systems.
3.3.5 Application in UV-Curable Adhesives and 3D Printing
For applications requiring thick-film rapid curing-such as UV-curable nail gels, photoresists, and 3D printing photopolymer resins-the thiol-ene UV curing system offers a unique advantage: it is not limited by oxygen inhibition and enables deep-layer curing in thick sections. Our Thiol series performs excellently under 365 nm and 415 nm LED cold-light sources, high-pressure mercury lamps, lasers, and other conditions. They show good compatibility with base resins and, after curing, yield transparent, colorless products with virtually no residual odor, meeting high sensory quality standards in cosmetics, medical, electronics, and other industries.
3.4 Blocked Isocyanates
Blocked isocyanates are a class of "deblocking-type" curing agents developed to address the pain points associated with the storage and use of conventional isocyanate crosslinkers.
Traditional isocyanates (e.g., TDI, HDI trimers, etc.) are highly reactive and readily react with resins containing active hydrogens (e.g., polyols, amines) at room temperature. While this facilitates rapid crosslinking, it also brings a series of challenges:
Extremely short pot life for one-component formulations, often requiring strict nitrogen protection and low-temperature storage.
High toxicity and volatility of isocyanate monomers, posing health and environmental risks to operators.
High sensitivity to moisture, leading to foaming and thickening.
Our blocked isocyanates "lock" the isocyanate groups (–NCO) using chemical blocking agents (such as caprolactam, butanone oxime, phenols, etc.) to form stable urethane derivatives:
"Lock the reactivity with a chemical lock; heating unlocks the reaction."
At room temperature: Blocked isocyanates show almost no reaction when mixed with resins, allowing one-component coatings or adhesives to maintain storage stability for several months, while greatly reducing toxic exposure risks during handling.
Upon heating: When the temperature reaches the deblocking temperature (typically 120–160°C), the blocking agent is removed, regenerating highly reactive isocyanate groups that rapidly crosslink with hydroxyl, amino, and other groups in the resin.
This product is widely used in one-component polyurethane baking coatings, high-temperature curing adhesives, and elastomers, significantly improving process convenience and safety without compromising final crosslinking performance.
3.5 EAP Series Stabilizers-"Safeguarding" Formulation Systems
Stabilizers are the indispensable "invisible guardians" in formulation systems. While they do not directly participate in chemical reactions like initiators or crosslinkers, their role is critical to the entire product lifecycle from manufacturing to end-use. Our EAP series stabilizers provide targeted solutions for the thermal stability, storage stability, and light stability requirements of different systems.
3.5.1 EAP-45-Storage Thermal Stabilizer for Free-Radical Polymerization Systems
EAP-45 is a compounded hindered phenol inhibitor specifically designed for free-radical polymerization systems such as UV inks, UV coatings, and UV adhesives. Its core function is to ensure thermal stability during production, transportation, and warehousing while minimally affecting the final UV curing speed.
Mechanism: The hindered phenol structure traps trace free radicals generated spontaneously by heat during storage, preventing premature polymerization before exposure to light, thereby maintaining viscosity stability and preventing gelation.
Key advantages: In high-reactivity clear varnishes or deeply pigmented inks containing high concentrations of long-wavelength photoinitiators, EAP-45 is particularly critical-it achieves a precise balance of "inhibition vs. initiation" at very low addition levels: no curing during storage, but normal curing upon light exposure.
Performance: It causes no yellowing, no off-odor during curing, and contains no heavy metals, fully complying with environmental and safety regulations in packaging, medical, electronics, cosmetics, and other industries.
3.5.2 EAP-55-Specific Inhibitor for Amine/Imidazole-Cured Epoxy Systems
EAP-55 is a specially developed inhibitor for amine- and imidazole-based blocked epoxy curing systems, suitable for one-component epoxy adhesives, encapsulants, prepregs, and similar products.
During storage and transportation, EAP-55 effectively suppresses the slow addition polymerization between amine or imidazole curing agents and epoxy resins, significantly improving thermal storage stability and preventing viscosity rise and gel failure.
It has minimal impact on crosslinking speed-after deblocking, curing proceeds normally, with no yellowing, no dulling of the cured film, and no adverse effects on glass transition temperature (Tg) or heat/humidity resistance of the finished product.
It is compatible with various epoxy resins and modified epoxies. It is recommended to pre-dilute the inhibitor before adding to the resin system for thorough dispersion, with a recommended addition level of 0.5%–3% of the total formulation weight.
3.5.3 EAP-65-Thermal Blocking Agent for Cationic Thermal Initiator Systems
EAP-65 is a thermal blocking agent specifically designed for cationic thermal initiator systems, addressing the pain point of slow acid generation at ambient temperature that causes premature aging of formulations.
Without a thermal blocking agent, one-component adhesives containing cationic thermal initiators typically have a shelf life of only 2–7 days at room temperature (depending on base resin activity), with viscosity rising sharply or even complete gelation-often requiring full cold-chain logistics at high cost and risk.
With EAP-65, thanks to its excellent compatibility and low addition level, a dramatic change is achieved:
Extended room-temperature storage: With EAP-65 added, systems can be stably stored for 3–6 months at temperatures not exceeding 40°C, with viscosity increase controlled within 10%.
Slightly elevated deblocking temperature: When used in combination with our CTI-100 cationic thermal initiator, the thermal deblocking temperature only modestly rises from the original 80°C to about 90°C, still allowing rapid curing under conventional baking conditions, with no negative impact on the physical or chemical properties of the final cured product.
This breakthrough product makes commercial large-scale application of one-component cationic thermal-curing formulations practically feasible, greatly lowering customers' storage and transportation barriers.
3.6 Summary
From the "driving forces" of heat-activated curing-blocked imidazoles and blocked isocyanates-to the Thiol polythiols that combine UV-curing synergy with low-temperature epoxy curing, and to the EAP series stabilizers that safeguard the "healthy lifecycle" of formulations, we are committed to providing customers with finely tailored product support across the entire crosslinking and curing process. Whether your priority is storage stability, curing efficiency, environmental safety, or high transparency and low odor, our solutions respond precisely to create long-term, stable, and reliable value for your formulation systems.