The filtration performance of nonwoven filter media is affected by many factors. External factors include particle size and distribution of dust source, flow rate of filtered gas, etc. Internal factors include pore structure, thickness, etc. The pore structure of nonwoven materials includes pore size and its distribution, porosity and so on. There are three factors that affect the filtration efficiency:

1. Average pore size of filter material

Within a certain range, the filtration efficiency is inversely proportional to the average pore size of the filter material, and the smaller the average pore size of the filter material, the higher the filtration efficiency. The average pore size of the non-woven filter material is mainly affected by the fiber diameter and thickness. The finer the fiber, the smaller the average pore size; the thicker the non-woven filter material with the same fiber specification, the smaller the average pore size.

2. Porosity of filter material

The unique fiber network structure of non-woven fabrics forms pores with relatively uniform distribution and small pore size, so that when the filter carrier phase passes through the tortuous diameter of the filter fiber, the dispersion effect is enhanced, and the particles to be separated in the carrier have more opportunities to collide with the fibers. Or stick. Therefore, porosity is an important factor affecting the performance of the filter material.

The porosity of the filter material refers to the ratio of its pore volume to the total volume. The lower the porosity of the filter material, the greater the fiber filling rate, the stronger the interference effect on the particles, the higher the collection efficiency, and the higher the filtration efficiency. As the porosity of the filter material increases, the ability to separate and capture particles in the gas is weakened, so the filtration efficiency decreases.

The relationship between filtration efficiency, filtration resistance and porosity, fiber diameter and thickness of filter material was simulated by computer. It was found that the filtration efficiency of the filter material increased with the decrease of the porosity and fiber diameter of the filter material, and there was a nonlinear relationship.

3. Thickness of filter material

By establishing a filtration model to predict the filtration efficiency and filtration capacity of the filter material for particulate matter. The influence of different filter material thicknesses and different filter areas on the filter efficiency was analyzed.

The actual test found that the predicted value of the filtering model was in good agreement with the measured value. This also provides a reliable reference for designing the thickness of the filter material and the maximum effective pore size to achieve a specific filtration efficiency and filtration capacity.

At the same time, we use the filtration accuracy data of melt-blown non-woven fabrics as the main material structure in medical mask products as a reference:

1. BFE95 (weight: 18-30g)

Tested at a flow rate of 32 liters, the filtration effect of 3 micron bacterial particles reaches 95%.

2. BFE99 (weight: 20-30g)

Tested at a flow rate of 32 liters, the filtration effect of 3 micron bacterial particles reached 99%.

3. VFE99 (weight: 25-30g)

Tested at a flow rate of 32 liters, the filtration effect of 3 micron virus particles reached 99%.

4. PFE99 (weight: 24-30g)

Tested at a flow rate of 32 liters, the filtration effect of 0.1 micron particles reaches 99%.

5. KN90 (weight: 30-50g)

Tested at a flow rate of 55 liters, the filtration effect of 0.3 micron solid particles reaches 90%.

6. N95 (gram weight: double layer 50g)

Tested at a flow rate of 85 liters, the filtration effect of 0.3 micron solid particles reaches 95%.

7. N99 (gram weight: double layer 80g)

Tested at a flow rate of 85 liters, the filtration effect of 0.3 micron solid particles reaches 99%.

8. FFP1 (weight: 50g)

Equivalent to the N90 standard.

9. FFP2 (weight: 50g)

Equivalent to the N95 standard.

It can be seen that the filtration level and precision of meltblown nonwovens are quite excellent. Melt-blown non-woven fabric has a film of many criss-cross fibers stacked in random directions. The fiber diameter ranges from 0.5 to 10 microns, and its fiber diameter is about one-thirtieth of that of a hair. However, the fiber diameter range of spunlace non-woven fabrics is usually 1~1.7dtex (about 10~17 microns). Only entanglement) There are still relatively large gaps between fibers under macroscopic conditions. Therefore, spunlace non-woven fabrics are not suitable for the manufacture of materials with filtration or protection requirements such as masks or protective clothing.