DDP Insulation Paper: Production Process, Specifications

Time: 10-24 2025 Auther: Xujue Electrical

1. Introduction to DDP Insulation Material DDP (Diamond Dotted Paper) is an electrical insulation material made by c...

1. Introduction to DDP Insulation Material

DDP (Diamond Dotted Paper) is an electrical insulation material made by coating an electrical insulating paper with epoxy resin in a diamond-shaped dotted pattern. After drying and semi-curing (B-stage), the resin becomes tack-free but can be reactivated by heat.
When the coils are later heated (e.g., during transformer vacuum drying or coil curing), the resin melts and bonds adjacent layers together, significantly improving mechanical strength and insulation integrity.

ddp insulation paper

2. Production Process

1) Raw Material Preparation

Base Paper: High-density electrical insulation paper (e.g., DuPont Nomex paper or high-grade kraft insulation paper).

Coating Resin: Epoxy resin mixed with curing agents, leveling agents, and anti-settling additives.

2) Formulation and Mixing

Epoxy resin, curing agent, and additives are mixed in precise ratios to adjust viscosity and control the curing rate.

3) Coating Process

The resin is applied to the paper surface in a diamond-dot pattern using one of the following coating methods:

Gravure coating

Screen coating

Laser-dot coating

ddp insulation paper product workshop

4) Drying and Semi-Curing (B-stage)

Under controlled temperature (typically 90–120°C), the coated paper is partially cured to achieve a semi-solid (B-stage) condition:

Non-sticky surface

Flexible and rollable

Can re-melt and fully cure upon later heating

5) Rewinding and Cutting

After inspection (dot spacing, coating uniformity, surface quality), the semi-cured paper is wound into rolls and cut into specified widths (e.g., 1000mm, 1200mm, etc.).

3. Main Specifications of DDP Insulation Paper

Item	Unit	Typical Value / Range	Notes
Base paper thickness	mm	0.08 / 0.13 / 0.17 / 0.20 / 0.25 / 0.30	Common grades
Dot pattern	–	Diamond / Square / Grid	Diamond is standard
Dot spacing	mm	3.0×3.0 / 4.0×4.0 / 5.0×5.0	Customizable
Resin coverage	%	25–45	Surface coverage
Resin content	%	10–20	By mass
Dielectric strength	kV/mm	≥8	At room temperature
Tensile strength (MD)	N/10mm	≥50	Varies with base paper
Thermal curing temperature	°C	130–160	For final curing
Curing time	min	10–30	Depends on process
Standard width	mm	1000 / 1200 / 1500	Custom available
Standard roll length	m	50 / 100 / 500	Depends on thickness

4. Properties and Applications

Key Features:

Excellent dielectric strength

Strong interlayer adhesion after curing

High mechanical strength and heat resistance (Class B–F)

Stable structure under oil or dry-type environments

Typical Applications:

Inter-turn insulation for oil-immersed transformers

Layer insulation for dry-type transformer windings

Insulation for motor stator windings

Layered insulation in reactors, inductors, and instrument transformers

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