Graphite Paper Manufacturing Process: From Natural Graphite to Flexible Sheets

The starting point is not "graphite powder", but natural flake graphite.

• Carbon content: Industrial grade ≥ 90%, commonly used for sealing/heat dissipation grade at 99%/99.5%
• Particle size: 80-100 mesh, common
• The larger the scales → the longer the "worm" after expansion → the better the strength after rolling
• Ash content, sulfur content, and chlorine content directly determine whether it can be made into nuclear/semiconductor grade later on

The natural graphite layers were originally adhered to each other by van der Waals forces.
This step involves treating with concentrated sulfuric acid and oxidants (nitric acid/hydrogen peroxide/potassium permanganate) to allow acid molecules to penetrate the interlayer and generate graphite interlayer compounds (GIC, expandable graphite).
Key points:

• Slow reaction at a temperature of 30-50 ℃
• Acid concentration, oxidant dosage, and reaction time determine the degree of intercalation
• Insertion too light → No expansion at high temperatures → Paper brittleness
• Excessive intercalation → high sulfur residue → galvanic corrosion of stainless steel flange

After inserting, it's not about burning it directly, but about "taking a shower" first:

• Filter press/centrifuge to recover concentrated acid (reusable)
• Repeatedly wash with water until pH is neutral
• Low temperature drying (<100 ℃), cannot expand in advance

Export level indicators usually include:

• Sulfur ≤ 800 ppm (good factory ≤ 300 ppm)
• Chlorine ≤ 50 ppm
• Ash content ≤ 1.0% (nuclear grade ≤ 0.2% or even ppm level)

Dry expandable graphite is fed into an expansion furnace (800-1000 ℃, in a few seconds).

The interlayer acidic agent vaporizes, causing the graphene layer to "pop" open and expand by 100-800 times, resulting in a pile of black, fluffy, worm like expanded graphite worms.

At this moment:

• The loose density may only be 0.002-0.01 g/cm ³
• Cannot be used directly
• But the layers have already been 'opened', and only when they are pressed out later will there be flexibility

1. Continuous rolling method (mainstream for making rolls/graphite paper)

• No ink or glue added
• Worm flattened, oriented, and interlocked by rollers
• Thickness of 0.15/0.25/0.35/0.5/1.0 mm is acceptable
• Width can be 500/1000/1500 mm

2. Compression molding method (for making thick plates/irregular blanks)

• Worm enters the mold cavity → hydraulic pressure holding → thick plate output
• 35mm thick, 0.1 g/cm ³ "fluffy large board" with more uniform molding
• But the surface is not rolled smooth, and the thickness tolerance is not so beautiful

3. Precision rolling (electronic heat dissipation grade)

• Four roll/multi roll precision pressing
• The thickness tolerance can be within ± 0.005 to ± 0.05 mm
• The in-plane thermal conductivity is achieved by arranging the layers along the X-Y direction

At least look at these inside the factory:

• Carbon content: 98%/99%/99.5%/99.9%
• Density: 0.7/1.0/1.2/1.4 g/cm ³
• Thickness tolerance: ± 0.03mm for ≤ 1.5mm, ± 0.05mm for thick plates
• Tensile strength: Industrial grade ≥ 4.0 MPa, premium grade ≥ 5.0 MPa
• Compression rate 35-55%, rebound rate ≥ 10-12%
• Sulfur, chlorine, ash content, thermogravimetric analysis
• In plane thermal conductivity: natural graphite paper 100-600 W/m · K, with high orientation up to 1500+

• Natural graphite paper: flakes → intercalation → expansion → rolling, thickness starting from 0.15mm, partial sealing/industrial heat dissipation
• Synthetic graphite film: PI film carbon graphitization, 0.012-0.05mm, suitable for hot use on mobile phones
• The former is "soft, thick, and well sealed"; The latter is "thin, brittle, and thermally conductive and explosive within the surface"