| HS Code | 622952 |
| Chemical Composition | Bisphenol AF and quaternary phosphonium salt blend |
| Function | Crosslinking/vulcanizing agent for FKM fluoroelastomers |
| Physical Form | White to off-white powder |
| Specific Gravity | Approximately 1.3 - 1.5 at 25°C |
| Melting Range | Approximately 120 - 160°C |
| Solubility | Soluble in ketones, esters, and low alcohols; insoluble in water |
| Recommended Dosage | 1.5 - 3.0 phr, depending on FKM grade and required crosslink density |
| Curing Temperature | Efficient cure at 170 - 190°C; press cure plus post-cure recommended |
| Storage Shelf Life | At least 12 months when stored in a cool, dry, tightly sealed container |
| Safety Hazard | May cause skin and eye irritation; avoid dust inhalation and use with proper ventilation |
As an accredited FKM Curative V5 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | FKM Curative V5 is supplied in sealed 25 kg fiber drums with polyethylene liners, ensuring safe handling, stability, and contamination-free storage. |
| Container Loading (20′ FCL) | FKM Curative V5 is loaded in a 20′ FCL, securely packed on pallets, protected from moisture, and sealed for safe transport. |
| Shipping | FKM Curative V5 is shipped in sealed, corrosion-resistant containers, often with desiccant, to prevent moisture exposure. Transport must comply with applicable dangerous goods regulations, including proper labeling, SDS availability, and spill containment. Keep upright, dry, and away from oxidizers or high temperatures. |
| Storage | Store FKM Curative V5 in its original, tightly sealed container in a cool, dry, well-ventilated area away from direct sunlight, heat sources, and ignition sources. Keep container upright and protected from moisture and contamination. Avoid prolonged exposure to high temperatures. Follow manufacturer guidelines and shelf-life recommendations for optimal performance and safety. |
| Shelf Life | Shelf life is typically 12 months when stored in original, tightly sealed containers in a cool, dry place. |
Fuel injector seals are typically injection molded from a medium-viscosity bisphenol-curable FKM gum charging 2.0 phr to 2.4 phr of FKM Curative V5 on a 250 kN clamp force electric injection molding machine with a 36 mm plasticizing screw and a 16-cavity cold-runner block. The compound is classified under ASTM D1418 as FKM and the press cure at 177°C is held for the moving-die rheometer t90 plus 2 min; typical ODR t90 for this dosage range in medium-viscosity FKM is 4.0–6.0 min. Compression molded sections thicker than 6.0 mm are cured at 170°C with extended dwell to avoid center porosity. Post-curing in an air-circulating oven at 232°C for 16 h completes the bisphenol AF/phosphonium ether crosslink network and removes volatile cure by-products. Fluid resistance is tested under ASTM D471-16a in Fuel C at 23°C for 70 h and 168 h; volume swell for a 70 Shore A system containing 15 phr medium thermal carbon black is typically below 5.0%. E10 and E85 protocols modify the test fluid with ethanol and shift swell values upward; ethanol tolerance is governed by FKM fluorine content and V5 crosslink density. The injection gate diameter is maintained below 0.8 mm to prevent premature cold-runner loss from scorch. Fuel pump O-ring cavities are vented to 0.02 mm because cavity fill time exceeding 4.0 s can generate back-rinding at the parting line. Under-cured seals showing residual extractable bisphenol are rejected by a 2 h acetone extraction check against a 3.0% maximum mass loss.
Downhole packer elements for sour service are compounded from high-viscosity bisphenol-curable FKM with 2.5 phr V5, 30 phr medium thermal carbon black N990, 6 phr calcium hydroxide, and 3 phr magnesium oxide. Press cure takes place in a 450 t vacuum compression press at 173°C for 30–45 min, and the parts are post-cured at 232°C for 24 h in a forced-air oven. The bisphenol AF/phosphonium system produces aromatic ether crosslinks that give lower long-term compression set than amine-cured FKM; this is measured by ISO 815-1:2019 method B under 25% constant deflection at 200°C for 70 h and is typically below 20% for 90 Shore A compounds. Explosive decompression resistance is evaluated according to NORSOK M-710 Annex B and ISO 23936-2:2011, with the seal shocked from high-pressure methane/carbon dioxide mixtures at 100°C and 150°C across controlled depressurization cycles. The V5-cured system allows a high crosslink density that resists gas bubble nucleation, but underdosing creates unreacted bisphenol domains that act as gas nucleation sites. A batch-to-batch compression set variation of ±4 points has been observed when the post-cure oven load exceeds 3.0 kg/L and air exchange falls below 50 changes/h; the same load condition leaves surface tack caused by incomplete devolatilization. FKM compounds cured with V5 should not be placed in contact with amine-based corrosion inhibitors at high pH, because amine attack at the polymer backbone accelerates surface hardening and increases retained compressed set.
For aerospace hydraulic O-rings manufactured to AS568 sizes 006–154 from a 75 Shore A V5-cured FKM compound, the cure is commonly run in a 150 t vacuum press at 177°C for 15 min, followed by a 232°C post-cure for 16 h. The procured material is tested to ASTM D412-16 for tensile strength and elongation, ASTM D2240-15e1 for hardness, and ASTM D395-16e1 method B for compression set. Fluid compatibility is assessed with MIL-PRF-83282 hydraulic fluid at 135°C for 70 h and with MIL-PRF-87257 at 200°C for 70 h; after MIL-PRF-83282 exposure, volume swell and hardness change are generally specified to remain below 12% and ±5 Shore A. The use of V5 at 1.8–2.2 phr balances compression set and extraction resistance, but thin cross sections below 1.78 mm exhibit dimensional instability during cryogenic deflashing at -196°C; production lines therefore use tumbling deflashing at 5°C to avoid microcracking. Phosphate ester hydraulic fluids such as Skydrol are outside the compatibility envelope for FKM, and bisphenol-cured FKM parts should not be installed in that fluid; ethylene-propylene or TFE/P materials are required. Standard FKM grades are rarely used below -18°C, while low-temperature FKM compounds extend sealing to approximately -40°C.
Short-term heat excursions in turbocharger compressor outlet O-rings and charge air seals expose V5-cured FKM to 210–230°C. Hot air aging is performed under ASTM D573-04 in a single-zone air oven at 200°C and 230°C for 168 h. A 75 Shore A compound containing 2.0 phr V5 and 30 phr carbon black N990 typically retains 6–10 MPa tensile strength and 80–120% elongation after 168 h at 230°C, but only if the post-cure is completed at 232°C for 24 h. The pass or fail criterion is often retention of 50% of initial elongation; undercured parts fail within 72 h because residual V5 curative fragments accelerate oxidative chain scission. The critical processing threshold is the oven temperature ramp between 150°C and 230°C, which should not exceed 2°C/min; faster ramp rates produce surface hardness gradients. Injection molding of charge air seals on a 300 kN press with a 28 mm screw requires a melt temperature below 180°C and a mold temperature of 180–190°C. At mold temperatures above 200°C, the V5 accelerator generates phosphonium decomposition by-products that leave a brown exudate on the part surface. The O-ring cross section is limited to a 2.65 mm minimum to prevent flow weld lines during fast cavity filling. Compression set data under ISO 815-1:2019 method B at 200°C for 70 h typically increase from 12% to 18% after heat aging; this shift is used as the batch acceptance limit.
| Application segment | Standard | Condition | Measured property |
|---|---|---|---|
| Fuel injector O-rings | ASTM D471-16a | Fuel C, 23°C, 70 h | Volume swell |
| Oilfield packers | NORSOK M-710 | CH4/CO2, 100°C and 150°C | Explosive decompression rating |
| Aerospace hydraulic O-rings | MIL-PRF-83282 | 135°C, 70 h | Volume swell, hardness change |
| Turbocharger O-rings | ASTM D573-04 | 230°C, 168 h | Tensile/elongation retention |
| Acid diaphragm | ISO 1817:2015 | 80% H2SO4, 80°C, 168 h | Volume swell, hardness change |
| Heat exchanger gaskets | ISO 1817:2015 | Water/steam, 150°C, 168 h | Volume swell, tensile loss |
In hot concentrated sulfuric acid and phosphoric acid service, V5-cured FKM diaphragms and valve seats are compression molded in a 300 t vacuum press at 165°C for 25 min, then post-cured in a nitrogen-purged oven at 232°C for 24 h. The nitrogen purge reduces oxidative surface hardening and lowers volatile organic residue. Immersion testing follows ISO 1817:2015 in 80% sulfuric acid at 80°C for 168 h; typical volume swell is below 5% and hardness change is within ±5 Shore A. For 40% phosphoric acid at 100°C for 168 h, the bisphenol-cured network remains stable when the compound uses 6 phr calcium hydroxide as acid acceptor. FKM is not compatible with low molecular weight amines, ketones, or some polar solvents; in diaphragm valve bodies where an amine-based process buffer is used, a TFE/P or EPDM diaphragm is substituted. The V5 dosage is set at 2.4 phr for acid service because higher loadings create a tighter network but reduce elongation and flex fatigue resistance. Processing of large-diameter diaphragms above 300 mm requires a multi-stage press cure profile from 150°C to 165°C at 1°C/min to avoid trapped air and surface blistering. The finished diaphragm is inspected by ASTM D412-16 tensile testing on die-cut dumbbells and by a leak test at 1.1× rated pressure.
Steam and condensate attack heat exchanger gaskets through hydrolysis of the polymer backbone and extraction of metal oxide acid acceptors. A V5-cured FKM gasket formulated with 2.0 phr V5, 25 phr carbon black, and low Ca(OH)2 content is press cured at 177°C for 12 min and post-cured at 232°C for 16 h. The cured network is tested by ISO 1817:2015 in deionized water and low-pressure steam at 150°C for 168 h; standard FKM typically shows volume swell below 3% and tensile loss below 15%, but exposure to wet steam above 180°C causes marked reversion in bisphenol-cured FKM within 500 h. Heat exchanger gaskets are therefore limited to saturated steam environments below 170°C. The gasket mating surface is molded with 0.5 mm sealing beads, and the mold is closed at 0.5 mm/s to prevent bead tearing. Batch release includes ASTM D2240-15e1 hardness at 70±5 Shore A and compression set per ISO 815-1:2019 method B at 200°C for 70 h of less than 18%. V5-cured FKM is suitable for steam condensate containing traces of hydrocarbons but is not resistant to steam containing ammonia or morpholine pH-boosting additives; those chemicals attack the FKM backbone and lead to surface erosion.
Semiconductor wet bench seals manufactured from V5-cured FKM are usually injection molded in an ISO Class 7 cleanroom using a 100 kN electric press with a 25 mm screw and polished mold plates. The compound is prepared with 2.0 phr V5 and reduced metal oxide loadings, because extractable cations interfere with wafer-level trace metal analysis. Post-curing is performed at 232°C for 24 h in a Class 100 oven, followed by an ultrapure water rinse at 60°C for 4 h to remove surface ions. Leachate testing is performed under SEMI F57 protocols for ultrapure water and dilute acid/oxidizer blends; published data for specific V5-cured FKM configurations is limited, so each molding lot is validated by inductively coupled plasma mass spectrometry for Fe, Na, and K at part-per-billion levels. The seals are used in wet bench quick-disconnect couplings and valve glands exposed to 60–100°C dilute sulfuric acid and hydrogen peroxide mixtures, where compression set after 168 h at 100°C must remain below 20%. Bisphenol-cured FKM is not suitable for downstream dry-etch or oxygen plasma chambers; there the seal material is perfluoroelastomer. The V5 accelerator decomposition products must be fully volatilized during post-cure, because residual phosphonium species can nucleate particles in high-purity deionized water. The production mold is fitted with vacuum degassing channels at 0.02 mm depth; without these, trapped gas causes black specks on the seal surface.
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For fluoroelastomer compounds based on vinylidene fluoride–hexafluoropropylene dipolymers and vinylidene fluoride–hexafluoropropylene–tetrafluoroethylene terpolymers, vulcanization is typically performed with a bisphenol AF/onium accelerator package or with a peroxide/coagent system. FKM Curative V5 is a bisphenol-type incorporated curative supplied as a pre-dispersed masterbatch for these elastomer grades. The designation V5 is a manufacturer model code rather than a chemical description; it identifies a controlled ratio of bisphenol AF-type curative and onium accelerator carried on an elastomer-compatible carrier. The product is used in injection-molded O-rings, compression-molded gaskets, transfer-molded seals, extruded profiles, and custom parts for dry-heat service, fuel sealing, oil and gas sealing, and chemical processing environments where low compression set after long thermal exposure is required.
The curative is normally introduced after fillers and acid acceptors have been incorporated, because the masterbatch is reactive at elevated dump temperatures. In a two-pass mixing sequence, the first pass disperses polymer, magnesium oxide, calcium hydroxide, and carbon black or mineral fillers; the second pass incorporates the FKM Curative V5 masterbatch at reduced rotor speed and a dump temperature below 110 °C. This sequence prevents scorch during storage and shaping. Typical loading of the V5 masterbatch in a 100 phr FKM base polymer formulation is 1.0–3.5 phr, depending on crosslink-density target, polymer fluorine content, and acid acceptor package. Over-addition beyond 4.0 phr can produce excessive crosslink density, lower elongation, and increased mold fouling; under-addition below 1.0 phr can result in poor compression set and reduced heat stability.
Under ASTM D5289-19a at 177 °C and a 0.5 ° arc, class-typical bisphenol-cured FKM compounds exhibit minimum torque of 1.5–2.5 dN·m, maximum torque of 15–25 dN·m, scorch time ts2 of 1.2–2.0 min, and t90 of 3.5–6.0 min. For V5 specifically, published data for this specific configuration is limited; the user should establish lot-specific MDR curves on the production compound because polymer fluorine content, filler structure, and metal oxide ratio alter torque values. The cure rate increases significantly with mold temperature; a 10 °C rise between 170 °C and 190 °C typically reduces t90 by roughly 40–50%. This sensitivity requires tight mold-surface temperature control, generally within ±3 °C, for transfer and injection molding of precision seals.
Post-cure is mandatory after press cure. A standard oven post-cure of 230 °C for 16–24 h completes the bisphenol crosslinking elimination reaction and volatilizes residual cure by-products. Compounds demolded without post-cure often show higher compression set, lower modulus stability, and outgassing in service. The post-cure chamber should maintain forced air or vacuum and temperature uniformity of ±5 °C; thick sections may require stepwise heating to avoid fissuring and internal porosity.
Mixing line observations indicate that the curative is introduced on a two-roll mill or in an internal mixer. On a 45 L intermeshing internal mixer operating at 30 rpm, a two-pass sequence using a first-pass dump temperature of 120 °C and a second-pass dump temperature of 95–105 °C avoids visible scorch. Process records from similar incorporated bisphenol curatives indicate that stock temperatures above 120 °C in the second pass produce hard agglomerates and increased reject rates at the injection stage. The masterbatch should be pre-blended with a small amount of filler or polymer before addition to reduce localized curative concentration and accelerator-rich domains that can cause premature crosslinking. Continuous mixing trials on a 25 mm co-rotating twin-screw extruder with L/D 40:1 require barrel zones of 70–90 °C and screw speeds below 200 rpm; higher adiabatic heating can initiate crosslinking before the strand die.
Storage of the V5 masterbatch is recommended below 30 °C and 50% RH. If the material has been exposed to ambient humidity above 60% RH for more than 24 h, pre-drying at 40–50 °C for 2–4 h is required before use. Moisture absorbed on the carrier can generate porosity in thick cross-sections and lower effective cure density at the center of compression-molded parts.
| Parameter | Typical range | Test method |
|---|---|---|
| Appearance | Off-white to light tan slab or pellet | Visual |
| Volatile matter | <0.5 wt% | ASTM D5668-21 |
| Ash residue | 0.1–0.5 wt% | ASTM D297-15 |
| Mooney viscosity ML 1+4 at 100 °C | 30–70 MU | ASTM D1646-19 |
| Active curative content | Supplier-controlled; no public limit | Supplier HPLC or equivalent |
Quality control laboratories should include MDR curve comparison, Mooney scorch, and physical property testing on a standard reference compound before production release. A reference compound is necessary because curative masterbatches can shift cure rate when polymer fluorine content changes. For a 66% fluorine dipolymer, a reference black compound at 30 phr N990 carbon black, 3 phr magnesium oxide, and 6 phr calcium hydroxide may be used; the MDR t90 at 177 °C should fall within the control limit. Published data for this specific configuration is limited, so control limits should be generated from 10–15 production lots. Mooney scorch is run at 121 °C per ASTM D1646-19; the acceptance limit depends on the molding process.
The primary difference is crosslink architecture. Diamine-based cure systems form amine-derived networks that are historically prone to reversion and higher compression set after long-term heat exposure. Bisphenol-cured FKM, including V5-type packages, is characterized by aromatic ether crosslinks after post-cure, giving improved compression set and heat resistance. In a comparative evaluation using ASTM D395-18 Method B after 70 h at 200 °C, class-typical compression set values for bisphenol-cured FKM are 15–25%, while diamine-cured equivalents are often 30–45%. Tensile strength per ASTM D412-16 is generally 10–16 MPa for bisphenol-cured black FKM compounds, with elongation at break of 150–250%. Diamine-cured equivalents may show 8–13 MPa tensile strength and lower retention of elongation after aging.
Compared with peroxide/coagent systems, the V5 bisphenol package does not require a free-radical initiator and does not generate the same acidic decomposition by-products during press cure. Peroxide-cured FKM may be preferred for hot-water, steam, acid, coolant, and biofuel exposure; bisphenol-cured FKM is often preferred for dry-heat sealing applications where compression set resistance is dominant. Selection cannot be made on curative type alone because polymer composition, fluorine content, filler type, and acid acceptor package govern final performance.
| Property after 70 h at 200 °C | Bisphenol V5-type | Diamine-cured | Peroxide-cured |
|---|---|---|---|
| Compression set, % | 15–25 | 30–45 | 20–35 |
| Tensile strength, MPa | 10–16 | 8–13 | 10–18 |
| Elongation at break, % | 150–250 | 120–220 | 150–300 |
| Hot water/steam resistance | Fair; formulation-dependent | Moderate | Superior |
At seal manufacturing plants, FKM Curative V5 is used in compounds that must balance scorch safety at injection-molding temperatures with rapid cure. A typical injection-molding setup for a bisphenol-cured FKM compound uses barrel zones of 70–90 °C, screw speed of 40–80 rpm, back pressure of 0.2–0.5 MPa, and mold temperature of 180–200 °C. Injection pressure is often 30–80 MPa depending on cavity count and runner geometry. The material should not remain in the barrel at temperature for more than 6–10 min to avoid scorch; shot size should be adjusted so that residence time is kept below the MDR ts2 at the maximum barrel temperature.
For compression molding, preforms are usually cut or extruded and placed in a mold at 170–185 °C under pressure. Cure time is set by the thickest cross-section; a starting point is 5–10 min for a 2 mm cross-section, with additional time for thicker sections. Oven post-cure at 230 °C for 24 h is typical for O-rings and gaskets requiring low compression set. After post-cure, parts are usually washed or baked further to remove surface residues.
In transfer molding of 70 Shore A FKM O-rings using a 200 tonne press and a 16-cavity tool, mold fouling is a primary process cost. Bisphenol-cured FKM compounds can deposit a low-molecular-weight residue on mold surfaces during repeated cycles. The V5 masterbatch design influences the type and amount of residue through the carrier and accelerator ratio. Process records from similar incorporated bisphenol curatives indicate that a mold temperature of 190 °C combined with a stock residence time above 8 min increases the rate of visible deposit formation. Demolding force is lower when the mold is kept at 180–185 °C and when a semi-permanent release agent is applied at intervals of 50–100 cycles. Published data for V5-specific fouling rates in this configuration is limited; users should log demolding force and mold deposit thickness during initial production runs.
Premature scorch in the transfer pot is a common failure mode when pot temperature exceeds 100 °C or when the compound is held in the pot for more than 5 min. The result is inhomogeneous flow lines, incomplete cavity filling, and high reject rates. In-mold pressure transducers or ejection-pin load cells can be used to measure demolding force because no single ASTM method covers all tool geometries.
Because the curative package contains an onium accelerator, the material is incompatible with amine-containing process aids, amine-based mold release agents, and basic amine antioxidants. These additives can protonate the bisphenol/onium complex and retard cure or produce surface tack. Acid acceptors such as magnesium oxide and calcium hydroxide are required. Zinc oxide is generally not sufficient as the sole acid acceptor because it can interfere with the cure complex. The bisphenol cure package should not be used as a drop-in replacement for peroxide-cure compounds without reformulation, because the acid acceptor balance, filler surface chemistry, and post-cure schedule must be re-optimized.
Regulatory status must be confirmed on the finished compound. FKM Curative V5 is an industrial rubber compounding ingredient; it is not itself a food-contact material. Final articles may be evaluated under FDA 21 CFR 177.2600 for rubber articles in contact with food only after extraction testing on the finished part. Compounds may also be tested to ASTM D471-16 for fluid resistance and ISO 23936-1:2022 for oil and gas service. REACH registration and SVHC content should be confirmed from the supplier safety data sheet. RoHS 2011/65/EU compliance is an article-level requirement and is not automatically conferred by the curative choice.
Because public literature does not yet contain full V5-specific engineering data, compound development should not rely on class-typical values for critical dimensions or safety factors. A design of experiments varying curative loading, acid acceptor ratio, and post-cure time is required. The MDR curve, physical properties after ASTM D412-16, compression set after ASTM D395-18, and fluid aging after ASTM D471-16 should be generated for each production lot. Published data for this specific configuration is limited, and no decision should be drawn from generic FKM cure comparisons without laboratory confirmation.
