Automotive filter paper is a specialised, impregnated filter substrate designed for the purification of fluids and gases in internal combustion engines and new energy vehicles. Unlike ordinary paper, it is manufactured from wood pulp, synthetic fibres and glass fibres, formed on an inclined wire paper machine and subsequently cured and modified with resin; It is used in the three main types of filters-air, engine oil and fuel-and its core function is to trap dust, metal particles, gum, moisture and PM2.5, thereby protecting the engine and the passenger compartment.

Main Production Processes (Wet-process papermaking + Functional post-treatment)

1. Raw Material Blending and Pulping (determines the basic filtration structure)
Base materials are categorised into three types and blended as required:
Standard Version: Long-fibre coniferous wood pulp (85%–90%), ensuring rigidity and porosity; a small amount of cotton pulp to enhance toughness
Oil- and High-Temperature-Resistant Version: Addition of polyester/aramid fibres (3%–8%), resistant to engine oil temperatures of 160–190°C
High-precision variant: Composite of glass fibre and PP melt-blown nanofibres, capturing ultra-fine particles as small as 0.3 μm. Additives: Dispersants, wet-strength agents, pore-size-controlling powders (kaolin / silica powder); mixing, grading and removal of short fibres to ensure fibre uniformity.
2. Wet-forming into a web (forming three-dimensional gradient pore channels)
Formed on an inclined wire paper machine to ensure stable, interlaced fibre pores and avoid excessive variations in pore size.

3. Pre-drying
Dried by hot air penetration, reducing moisture content to 10%–15% in preparation for resin impregnation, thereby preventing moisture from diluting the resin.
4. Resin Impregnation and Curing
Hydrophobic and oleophobic coating: for fuel and engine oil filter paper, resisting wetting by oil and water and preventing filter pore blockage
5. Slitting, Rewinding and Corrugation
Corrugation: forming 30–45° wave-like creases, tripling the filtration area, significantly increasing dust-holding capacity and extending service life
6. Final Product Inspection
Tests are conducted for air permeability, filtration efficiency, burst strength, temperature resistance, oil resistance, dust-holding capacity and pressure drop. Products may only be released from the factory once they comply with the ISO 4548 and ISO 16889 automotive filter media standards.

Product Characteristics of the Three Major Categories

Product Categories	Operating Medium	Key Parameters	Product Features	Product Classification
Air filter paper	Ambient air, -40–120 °C	Pore size 8–25 μm; filtration efficiency for 0.3 μm particles 98%–99.5%; high dust-holding capacity ≥35 g/m²	High breathability, low air intake resistance; high rigidity, retains shape when folded, resistant to wind, sand and dampness; commonly used as the first line of defence for air intake	Standard semi-coated, long-life fully-coated, and electrostatic high-efficiency variants
Engine oil filter paper	High-temperature lubricating oil, continuous 120–160 °C, instantaneous 190 °C	Pore size: 5–15 μm; pressure resistance: 600 kPa	Fully phenolic resin-impregnated, resistant to engine oil corrosion and high pressure; extremely high wet strength, does not powderise or perforate even after prolonged immersion; resistant to cyclic oil pressure shocks; gradient multi-layer structure balancing flow rate and precision filtration, capable of intercepting metal swarf, carbon deposits and sludge	-
Fuel filter paper	Petrol / diesel; resistant to solvents; separates trace moisture	Ultra-fine pore size: 3–10 μm	Hydrophobic surface modification ensures high oil–water separation efficiency, protecting the precision components of fuel injectors; resistant to swelling caused by alcohol-blended petrol and biodiesel; no resin leaching to block fuel lines; captures rust-related impurities, gum and free water	-

Full-Scene Applications (Petrol/Diesel Vehicles + Commercial Vehicles + New Energy Vehicles)

Air filters, oil filters, fuel filters (petrol/diesel), new applications for new energy vehicles, and applications in construction machinery (heavy goods vehicles, coaches, loaders, excavators).

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