The following content focuses specifically on GB/T 1303 3021 grade insulating materials. From the perspective of resin preparation (“resin kitchen”) and impregnation/lamination processes, it provides a systematic description covering raw materials, resin (adhesive) system, process route, equipment configuration, and performance limitations. This text is suitable for technical selection, factory planning of Equipment Choice, and formal external technical documentation.
I. Industry Positioning and Standard Attributes of 3021
3021 belongs to Phenolic Resin Impregnated Paper-based laminated insulating sheet.
Common English Expressions include: Phenolic Paper Laminated sheet, Phenolic Paper-based Insulating sheet.
Applicable standards: GB/T 1303 ( aligned with IEC 60893 system, PFCP category.
Industry Common name: General-purpose paper-based phenolic laminate.
II. Composition of 3021: “Raw Materials + Resin System” (Core)
2.1 Substrate type: Electrical insulating paper, kraft paper/bleached pulp paper.
Key indicators:
Basis weight: 120~200g/m²
low ash content
high impregnation uniformity
Relatively low requirement of MD/TD strength consistency (compared with fiberblass)
3021 upper performance limit is primarily determined by the paper itself, rather than by downstream processing.
2.2 Resin System (Defines the nature of 3021)
Resin Type: Thermosetting phenolic resin
mainly alkaline or neutral systems
Typical resin preparation composition
Phenol
Formaldehyde
catalyst (e.g., NaOH/Organic amines)
Diluent/solvent (e.g., Ethnaol/methanol)
Minor modifier (to improve flexibility or reduce brittleness)
Typical resin characteristics
solids content: 45~55%
viscosity: medium-to-low (suitable for full paper impregnation )
Reaction mechanism: condensation polymerization with water generation
2.3 Why 3021 uses phenolic resin only?
from an engineering perspective:
The heat resistance of paper-based substrates is inherently limited
Phenolic resin provides:
low curing temperature
Good flowability
lowest overall cost
best compatibility with cellulose
This is also a fundamental reason why 3021 cannot be upgraded to a high thermal class.
III. Performance Boundaries of 3021 (Engineering View)
| Item | Typical Level of 3021 |
| Thermal class | Class-B 120°C |
| Dielectric strength | Medium |
| Water Absorption | Relatively high |
| Mechanical Strength | low to medium |
| Dimensional stability | average |
| Machinability | Excellent (sawing, turning, milling) |
| Cost | very low |
The advantage of 3021 is not peak performance, but cost-effectiveness and ease of machining.
IV. Complete Manufacturing Process Route for 3021
4.1 Process overview
Phenolic Resin Preparation --- Paper impregnation --- Dying to B-stage ---Cutting/Stacking --- Hot-press Lamination --- Post Curing --- cut-to-size machining
NTRY applies the full process equipment of a resin kitchen, impregnation line, lamination press, cutting, etc., to all equipment and facilities.
V. Process Breakdown by Section + Associated Equipment
5.1 Resin Preparation Section (Resin kitchen)
Process characteristics
- single-kettle or dual-kettle operation
- wide reaction/process window
- Relatively low precision requirement
Key equipment
- Phenolic resin reactor (kettle)
- condenser and reflux system
- solvent metering system
- resin storage tanks
Compared with FR-4 system, resin preparation for 3021 is a lower-barrier process.
5.2 NTRY paper impregnation line (critical but not complex)
Process charateristics
- Single bath impregnation
- Resin pickup controlled by doctor rollers.
- low web tension requirement
NTRY impregnation configuration
- unwinder
- impregnation unit
- metering/doctor/squeeze roller
- multi-zone hot-air oven (120°C~160°C)
- cut to sheets
Process objectives
- full impregnation of paper fibers
- surface dry and non-tacky
- internal resin remains capable of secondary flow during lamination
5.3 B-stage impregnated paper
- required condition
- dry surface
- stackable
- re-softens and flows again upon heating
Key Control points:
- over-dried: poor interlayer bonding during lamination
- over-wet: bubbles /delamination
5.4 Hot-press lamination press
- hot-press method
- atmospheric pressure or slight vacuum
Typical parameters
Temperature: 140°C~160°C;
Pressure: 2-4MPa
Cycle: 30~60minutes
Equipment;
- NTRY multi-opening hot press
- press plate tooling system (caul plates/templates as applicable)
- basic programmable pressure cycle control
5.5 Post-Curing and Finishing
Post-curing
- 140°C~150°C;
- 8-24hours
- improves dimensional and electrical stability
Machining /finishing ( 3rd parities facility)
- sawing
- punching
- CNC machining
VI. Engineering Differences vs. Adjacent Grades (Common Confusions)
| Item | Typical Level of 3021 |
| 3020 | Lower-grade paper and resin system |
| 3021 | | Standard general industrial grade |
| 3025 | Cotton fabric reinforcement; higher mechanical strength |
| G10/G11 | Fiberglass + epoxy; fundamentally different system |
VII. Engineering Conclusions (For Equipment/Process Teams)
1, 3021 is the insulating sheet with the highest process tolerance
2. Only three key control points are critical
- Resin solids content
- Paper impregnation degree
- Hot-press deaeration/venting
3. Any attempt to "significantly improve 3021 performance " will ultimately be limited by the paper substrate's intrinsic ceiling.
4. The core value of 3021 lines in:
- low cost
- Easy machining
- Stable large-volume supply
