Insulated laminated copper foil is an important functional material in transformer manufacturing. It is made by coating insulating coating or laminating composite insulating film on the surface of high-quality copper foil substrate. This material changes the traditional process of separate winding insulation layer for transformer windings, integrating conductive and insulating functions into a single material. Compared with traditional wrapping insulation methods, insulated laminated copper foil has significant advantages such as stable and reliable insulation performance, high dimensional accuracy, convenient for automated winding, and space-saving in winding design. It is widely used in oil-immersed transformers, dry-type transformers, epoxy cast transformers, furnace transformers, rectifier transformers, and special reactors.
I. Technical Characteristics and Advantages of Insulated Laminated Copper Foil
1.1 Definition and Classification
Insulated laminated copper foil can be divided into the following main types according to its structure and manufacturing process:
- Coated insulated copper foil is formed by evenly coating insulating resin or insulating varnish on the copper foil surface through dip coating, roll coating, or spray coating, followed by baking and curing. This type has relatively thin insulation layer, usually used for low voltage transformer windings, with advantages of relatively low cost and high production efficiency.
- Laminated insulated copper foil is composed by hot pressing copper foil with polyester film, polyimide film, PTFE film, or NOMEX paper. This type has uniform and stable insulation layer thickness, high breakdown voltage, and excellent insulation performance, especially suitable for medium and high voltage transformer applications requiring high insulation requirements.
- Impregnated insulated copper foil is formed by immersing copper foil into insulating varnish or resin solution, impregnating insulating medium into surface micro-pores of copper foil under vacuum, then curing. This process results in uniform insulation performance but relatively thin insulation layer, mainly used for special application scenarios.
1.2 Core Advantages
- Excellent insulation performance: High breakdown voltage, large insulation resistance, uniform and continuous insulation layer without bubbles or impurities, effectively preventing partial discharge.
- High dimensional accuracy: Thickness tolerance within ±0.01mm, width tolerance within ±0.2mm, beneficial for automated winding.
- Convenient for automated winding: Smooth surface with moderate friction coefficient, suitable for high-speed winding on automatic winding machines.
- Space-saving: Thin insulation layer improves copper conductor fill factor, achieving higher capacity or reducing transformer size.
- Optional temperature resistance grades: B class (130°C), F class (155°C), H class (180°C) available.
1.3 Main Application Areas
- Oil-immersed transformers (distribution transformers, power transformers)
- Dry-type transformers (epoxy cast transformers, encapsulated winding transformers)
- Special transformers (furnace transformers, rectifier transformers, rail transit transformers)
- Reactors (series reactors, shunt reactors)
II. Technical Specifications
2.1 Copper Foil Substrate Requirements
| Parameter | Requirement |
|---|---|
| Copper Foil Grades | C11000 (≥99.90% Cu), C10100 (≥99.99% Cu), C10200 (≥99.95% Cu) |
| Conductivity | ≥101% IACS (annealed) |
| Thickness Range | 0.1-0.5mm |
| Thickness Tolerance | ±0.02mm (standard), ±0.01mm (precision) |
| Width Range | 5-200mm |
| Width Tolerance | ±0.2mm |
| Tensile Strength | 200-280 MPa (annealed) |
| Elongation | ≥15-25% |
2.2 Insulation Layer Materials
| Material | Temperature Grade | Thickness | Breakdown Voltage | Typical Application |
|---|---|---|---|---|
| PET Polyester Film | B Class (130°C) | 0.025-0.05mm | ≥3kV/mm | Oil-immersed transformers |
| PI Polyimide Film | H Class (180°C) | 0.025-0.075mm | ≥5kV/mm | High temp, special transformers |
| PTFE Film | F/H Class (155-180°C) | 0.025-0.05mm | ≥4kV/mm | High frequency applications |
| NOMEX Paper | H Class (180°C) | 0.05-0.18mm | ≥4kV/mm | High mechanical strength |
| Epoxy Coating | F/B Class (130-155°C) | 0.02-0.05mm | ≥3kV/mm | Epoxy cast transformers |
2.3 Insulation Performance Parameters
| Test Item | Requirement | Standard |
|---|---|---|
| Breakdown Voltage | ≥3kV/mm (single-side) | IEC 60243 |
| Insulation Resistance | ≥10¹² Ω·cm | IEC 60093 |
| Peel Strength | ≥1.0 N/mm | GB/T 2790 |
III. Manufacturing Process
3.1 Coating Type Process
Copper foil substrate → Surface pretreatment → Insulation coating → Baking and curing → Winding and inspection
Key parameters: Surface tension ≥38 mN/m, coating thickness precisely controlled, curing at 150-250°C for 30-120 minutes.
3.2 Lamination Type Process
Copper foil substrate → Insulation film → Hot pressing lamination → Cooling and shaping → Winding and inspection
Key parameters: Lamination pressure 1-5 MPa, lamination temperature 150-200°C, insulation film tension uniformly controlled.
3.3 Quality Control Points
| Stage | Control Item | Standard |
|---|---|---|
| Incoming inspection | Copper foil thickness, conductivity | Per specification |
| Surface treatment | Surface tension | ≥38 mN/m |
| Coating/Lamination | Insulation layer thickness | ±0.005mm |
| Curing/Hot pressing | Temperature, time, pressure | Per process doc |
| Finished product | Breakdown voltage, peel strength | Per technical requirements |
IV. Selection Guidelines
4.1 By Temperature Resistance Grade
| Grade | Application | Recommended Material |
|---|---|---|
| B Class (130°C) | Oil-immersed transformers | PET polyester film |
| F Class (155°C) | Dry-type transformers | PET + epoxy / PTFE |
| H Class (180°C) | High temp, special transformers | PI / NOMEX |
4.2 By Voltage Level
| Voltage Level | Insulation Thickness |
|---|---|
| ≤690V | Single-side 0.025-0.05mm |
| 690-3300V | Single-side 0.05-0.075mm |
| 3300-11000V | Double-side or thickened |
| >11000V | Customized per design |
4.3 By Winding Process
- Automatic winding: Laminated type recommended (uniform thickness, flat surface)
- Manual winding: Coated type acceptable (better flexibility)
- Stamping process: High peel strength grade required
V. Industry Standards and Certifications
5.1 Applicable Standards
| Standard System | Standard Number | Scope |
|---|---|---|
| IEC | IEC 60325, 60243, 60296, 60093 | International |
| GB | GB/T 5231, 1981, 2790 | China |
| ASTM | ASTM B372, D149 | USA |
| JIS | JIS H3100 | Japan |
5.2 Certifications
RoHS, REACH, UL 1446 – Product safety and environmental compliance certifications.
VI. Quality Inspection
6.1 Incoming Inspection
| Test Item | Method |
|---|---|
| Copper foil thickness | Precision thickness gauge |
| Conductivity | Eddy current conductivity meter |
| Insulation layer thickness | Microscopy |
| Breakdown voltage | Voltage tester |
| Peel strength | Peel testing machine |
6.2 Shipping Standards
AQL: Appearance 0.65, Dimensional 1.0, Electrical 0.65
6.3 Storage Requirements
Room temperature, humidity ≤60%RH, avoid direct sunlight. Shelf life: 12-24 months depending on insulation material type.
VII. Supplier Selection
7.1 Core Capabilities
- Integrated copper foil + insulation lamination production
- Multiple insulation material options (PET, PI, PTFE, NOMEX)
- Insulation layer thickness tolerance ±0.005mm
- Customization capability for special specifications
7.2 Technical Services
- Insulated system overall solutions
- Temperature/voltage grade selection guidance
- Third-party testing support
- Small batch samples (10-50kg)
VIII. Product Specifications (Reference)
| Copper Base | Insulation | Grade | Thickness Range | Width |
|---|---|---|---|---|
| C11000 | PET Film | B Class | 0.1+0.025mm | 5-200mm |
| C11000 | PI Film | H Class | 0.1+0.025mm | 5-200mm |
| C10100 | PTFE Film | F/H Class | 0.1+0.025mm | 5-200mm |
| C11000 | NOMEX | H Class | 0.1+0.05mm | 5-200mm |
| C11000 | Epoxy | F/B Class | 0.1+0.02mm | 5-200mm |
Conclusion
Insulated laminated copper foil is a key functional material in transformer manufacturing. Its technical performance and product quality are directly related to the safe operation and service life of transformers. Selection should consider temperature resistance grade, voltage level, capacity specifications, and winding process.
Our company has focused on exporting electrical wire and metal foil for 30 years, and is a professional insulated laminated copper foil manufacturer. We can provide C11000/C10100/C10200 series products with PET, PI, PTFE, NOMEX insulation materials, supporting B/F/H class temperature resistance requirements. Samples can be shipped globally.
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