E57-81H Class H Solvent-Free Insulating Varnish
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Short Product Description：
E57-81H is a single-component, solvent-free insulating varnish based on heat-resistant modified unsaturated polyester resin and a high-purity reactive diluent. Designed for vacuum and atmospheric impregnation of transformers, motors, and reactors, it combines Class H heat resistance with strong adhesion, good penetration, and electrical performance after water exposure.
- Description
- Technical Data
- FAQ
Description
Product Overview：
E57-81H is a heat-curing electrical insulating varnish formulated with modified unsaturated polyester resin, a high-purity reactive diluent, stabilizers, and additives. The TDS specifies X-88 as the reactive diluent for this grade.
Developed for winding impregnation, E57-81H penetrates assemblies and forms a bonded insulating structure after curing. Strong adhesion between winding and insulation components helps reduce electromagnetic vibration and associated noise, while cured-film flexibility helps accommodate differential thermal expansion between metal and insulating materials.
This polyester insulating varnish also offers moisture resistance, mold resistance, refrigerant resistance, and resistance to thermal shock. Its single-component formulation simplifies preparation for vacuum and atmospheric impregnation processes used in electrical equipment manufacturing.
The manufacturer identifies E57-81H as a Class H insulation resin. Suitability for a specific operating temperature should be verified using the complete insulation system and finished equipment.
Key Features and Benefits：
· Class H Heat Resistance: Designed for winding insulation applications requiring elevated-temperature performance.
· Single-Component Formulation: Simplifies preparation without a separate two-component resin and hardener mixing step.
· High-Purity Reactive Diluent: The TDS specifies X-88 for this grade, providing a defined material for supplier-approved viscosity adjustment.
· Strong Adhesion and Mechanical Reinforcement: Helps secure winding components and reduce electromagnetic vibration and associated noise.
· Good Impregnation Performance: Supports penetration into winding assemblies through vacuum and atmospheric impregnation.
· Electrical Performance After Water Exposure: Specified dielectric strength is ≥22 MV/m under normal conditions and ≥20 MV/m after 24 hours of water immersion.
· Moisture and Mold Resistance: Supports applications where resistance to humidity and mold is an important insulation requirement.
· Thermal Shock Resistance: A degree of cured-film flexibility helps accommodate movement caused by temperature changes and differences in material expansion.
· Refrigerant Resistance: Rated “Excellent” after a 96-hour refrigerant resistance test in the TDS. Compatibility should be confirmed with the intended refrigerant.
· Heat-Activated Curing: A specified gel time of 6 ± 3 minutes at 140 ± 2°C supports process characterization. Full curing requires the appropriate baking cycle.
Typical Applications：
E57-81H insulating varnish is intended for vacuum and atmospheric impregnation of:
· Dry-Type Power Transformers: Winding insulation and bonding of transformer components.
· Electrical Reactors: Coil impregnation requiring electrical insulation and mechanical support.
· Electric Vehicle Motors: Insulation treatment of motor windings used in new energy vehicles.
· Large Generators: Impregnation of generator winding assemblies.
· Hoisting and Crane Motors: Winding insulation for motors used in lifting equipment.
· Inverter-Duty Motors: Impregnation of windings in variable-frequency motor systems.
· Refrigerant-Resistant Motors and Electrical Equipment: Applications requiring compatibility with the intended refrigerant environment.
Validate compatibility with wire enamel, insulation materials, and other assembly components before production use.
Physical Properties：
The following physical, processing, and electrical properties are reported in the E57-81H TDS, with test methods referenced to GB/T 15022.2-2017.
| Test Item | Specification |
| Appearance: | Pale yellow to light brown transparent liquid, free of mechanical impurities |
| Viscosity: Ford Cup No.4 viscometer, 23±2℃ (s) | 45±15 |
| Density: (g/cm³) at 25℃ | 1.05±0.03 |
| Gel time: Test tube method, 140±2℃ (min) | 6±3 |
| Thick-layer curing capability: 140±5℃, ≥2h | S₁, U₁, I₂.₁ |
| Dielectric strength: (MV/m)Normal state: After 24h water immersion: |
≥ 22 ≥ 20 |
| Volume resistivity: (Ω·m)Normal state: After 24h water immersion: |
≥ 1×10¹³ ≥ 1×10¹² |
| Refrigerant resistance: 96h | Excellent |
| Storage stability: (Closed cup method) 75±2℃, 24h (no gelation) | Pass |
| (1) The storage life of this product is 6 months. (2) Curing conditions for items 6 and 7: 140±5℃ for 6h. (3) High-purity eco-friendly reactive diluent: X-88. | |
Technical Notes:
· Specimens for dielectric strength and volume resistivity testing were cured at 140 ± 5°C for 6 hours.
· Viscosity is expressed as cup flow time in seconds, not dynamic viscosity in mPa·s.
· Volume resistivity is reported in Ω·m.
Application Guidance：
· Working Viscosity
Select the working viscosity according to component size, winding structure, and impregnation requirements. The TDS provides the following reference ranges:
| Application Category | Reference Working Viscosity |
|---|---|
| General applications | 20–40 s |
| Applications with higher performance requirements | 45 ± 15 s |
| Small electrical components | 12–18 s |
Confirm the measurement conditions and adjustment procedure with the supplier. Use the specified X-88 reactive diluent according to the supplier’s instructions.
· Reference Impregnation and Curing Process
| Process Step | Reference Temperature | Reference Time |
|---|---|---|
| Workpiece preheating | 110–120°C | 2–4 h |
| Impregnation | 40–50°C | 15–30 min |
| Draining | Not specified | 20–40 min |
| Oven curing | 145–150°C | 4–8 h |
For applications with higher performance requirements, the TDS recommends extending the baking time by 2–10 hours or using an alternative schedule of 160°C for 8 hours.
These parameters are starting points for process development. Validate the cycle using the actual component geometry, thermal mass, impregnation equipment, and required insulation performance.
Laboratory gel time must not be used as the full curing time. Confirm complete curing throughout the winding assembly before electrical testing or service.
· Impregnation Bath Maintenance
For continuous operation, the TDS recommends adding more than 10% fresh insulating resin approximately monthly, with the interval adjusted to actual use. Confirm the replenishment basis with the supplier.
Filter the resin regularly during prolonged use and monitor its condition to maintain a consistent impregnation process.
Precautions：
· Determine the dilution ratio, baking temperature, and baking time experimentally based on product shape, size, and specific requirements.
· The product may absorb moisture and turn whitish under high humidity; performance remains unaffected after baking.
· This product is flammable; keep away from fire and heat sources.
Packaging, Storage/Transport & Shelf Life：
· Packaging: metal pails, 18 KG/pail
· Storage & transport: flammable chemical — keep away from fire and heat; handle per regulations; store cool (RT), dark and dry.
· Shelf life: stored sealed, 6 months at 5-25℃.
Frequently Asked Questions About E57-81H Insulating Varnish
1. What is E57-81H insulating varnish used for?
E57-81H is a single-component, heat-curing modified unsaturated polyester insulating varnish designed for winding impregnation. Typical applications include dry-type power transformers, electrical reactors, electric vehicle motors, large generators, crane motors, and inverter-duty motors.
After curing, it provides electrical insulation and mechanical reinforcement. Validate compatibility with wire enamel, insulation materials, and other assembly components before production use.
2. What is the thermal class of E57-81H?
The manufacturer identifies E57-81H as a Class H insulation resin. It is intended for winding applications requiring elevated-temperature insulation performance.
The finished equipment’s operating-temperature rating depends on the complete insulation system and service conditions. Thermal classification is separate from the baking temperature used to cure the resin.
3. Does E57-81H require a separate hardener?
No. E57-81H is supplied as a single-component formulation and does not require a separate two-component resin and hardener mixing step.
It cures through heating under a validated baking cycle. When viscosity adjustment is required, use the specified X-88 reactive diluent according to the supplier’s instructions.
4. Which reactive diluent should be used with E57-81H?
The E57-81H TDS specifies X-88 high-purity reactive diluent. Confirm the addition ratio and adjustment procedure with the supplier before preparing production material.
Do not assume that diluents specified for other insulating varnish grades are interchangeable. Validate the adjusted formulation for penetration, resin pickup, curing, and electrical performance.
5. What working viscosity is recommended for E57-81H?
The supplied varnish has a specified flow time of 45 ± 15 seconds, measured with a Ford No. 4 cup at 23 ± 2°C.
The TDS provides working-viscosity references of 20–40 seconds for general applications, 45 ± 15 seconds for higher performance requirements, and 12–18 seconds for small electrical components. Confirm the measurement conditions for these ranges and select the working viscosity through trials on the actual winding.
6. Can E57-81H be used for vacuum and atmospheric impregnation?
Yes. E57-81H supports both vacuum and atmospheric impregnation of suitable winding assemblies.
The reference process specifies workpiece preheating at 110–120°C for two to four hours, impregnation at 40–50°C for 15–30 minutes, and draining for 20–40 minutes. Confirm the temperature measurement points and equipment settings with the supplier. The supplied data does not define a numerical vacuum setpoint.
7. What curing temperature and time are recommended for E57-81H?
The reference production schedule specifies oven curing at 145–150°C for four to eight hours.
For higher performance requirements, the TDS recommends extending baking by two to ten hours or using an alternative schedule of 160°C for eight hours. Validate the selected cycle according to component geometry, thermal mass, oven loading, and the temperature limits of all assembly materials.
8. Does E57-81H fully cure in six minutes?
No. The specified gel time of 6 ± 3 minutes at 140 ± 2°C describes gel formation under laboratory conditions, not complete curing of an impregnated winding.
The thick-layer curing test is also a separate material test. Use a validated production baking cycle and confirm complete curing throughout the assembly before electrical testing or service.
9. How does E57-81H help reduce winding vibration and noise?
E57-81H bonds winding and insulation components after curing, helping limit movement associated with electromagnetic vibration and noise.
Its cured-film flexibility also helps accommodate differences in thermal expansion between metal and insulating materials. Actual performance depends on assembly design, varnish penetration, material compatibility, and curing quality.
10. What electrical insulation performance does E57-81H provide?
E57-81H has specified dielectric strength of at least 22 MV/m under normal conditions and at least 20 MV/m after 24 hours of water immersion. These values are equivalent to 22 kV/mm and 20 kV/mm.
Specified volume resistivity is at least 1 × 10¹³ Ω·m under normal conditions and at least 1 × 10¹² Ω·m after immersion. The electrical test specimens were cured at 140 ± 5°C for six hours.
11. Is E57-81H suitable for humid or refrigerant-exposed environments?
The manufacturer describes E57-81H as moisture- and mold-resistant. Its electrical properties after the stated water-immersion test provide reference data for moisture-exposed applications.
12. How should an E57-81H impregnation bath be maintained?
Filter the resin regularly during prolonged use and monitor its condition to maintain consistent processing.
For continuous operation, the TDS recommends adding more than 10% fresh resin approximately monthly, with the interval adjusted to actual use. Confirm the percentage basis and replenishment procedure with the supplier before implementing this routine.
13. What safety and compliance documents are available for E57-81H?
The Insulating Varnish downloads section lists an MSDS, RoHS documentation, and a VOC content test report. Specify E57-81H when requesting documents so the applicable report or declaration and its product coverage can be confirmed.
The Thinners section separately lists RoHS documentation and a halogen content test report.
14. How is E57-81H packaged, and what is its shelf life?
E57-81H is supplied in 18 kg metal pails. Its stated shelf life is six months when stored sealed at 5–25°C.
Store it in a cool, dark, dry location away from fire and heat sources, following the current MSDS. The accelerated storage-stability test at 75 ± 2°C for 24 hours is a laboratory test, not a recommended storage condition.
15. What information should I provide when requesting an E57-81H quotation?
Include your equipment type, winding materials, required thermal class, impregnation method, and available curing conditions. For refrigerant-exposed equipment, specify the refrigerant, lubricant, and service conditions.
For pricing and delivery, provide the required quantity, destination, target delivery date, and any requirements for X-88 reactive diluent, trial material, or supporting documents.