A Brief Analysis of Filter Paper

There are two main aspects of filter paper analysis: the filter characteristics of filter paper and the physical properties. Mainly carry out the relationship between the physical properties of their filter paper and the performance of the filter, the relationship between the filter characteristics of the filter paper and the performance of the filter. The interaction between the various indicators of the filter paper is related to each other, and several parameters of the filter paper determine the filtration and performance together.

Hawach has both qualitative filter paper and quantitative filter paper: The difference between quantitative filter paper and qualitative filter paper is mainly the impurity content. Qualitative filter paper is used for qualitative chemical analysis and corresponding filtration separation; quantitative filter paper is for quantitative chemical analysis in gravimetric analysis tests and corresponding analytical tests.

Qualitative filter paper
Standard grade and wet strength grade: The reinforced qualitative filter paper added a small amount of chemical stabilizer to increase the bursting resistance of the filter paper. However, because the stabilizer contains nitrogen, the qualitative filter paper is not recommended for the Kay nitrogen test, which is a method for determining the amount of total nitrogen in a compound or mixture.

Quantitative filter paper
Ashless grade hardened low ash grade, hardened ashless grade: The essential difference is the impurity content and hardness.
Hardened low ash grade and hardened ashless grade mean the surface acid pickling on the basis of quantitative filter paper to increase the surface bursting strength of filter paper. After use and sample filtration, it is necessary to scrape the retentate for quantitative analysis. The ashless grade has a lower ash content than the low ash grade.

Filter paper material

The filter paper can be made of natural fiber, chemical fiber, and glass fiber. The natural fiber includes softwood pulp, hardwood pulp, and beech grass pulp; filter papers generally use mixed pulp and add a little cotton pulp.

Filter paper structure

The filter paper has directionality, the fiber of the front side is looser; the back side has tight fibers; the front side pores are in the shape of a bell mouth; the pores become smaller along the thickness direction of the filter paper; the thickness of filter paper is about 0.35~0.5mm, and the dust particles size is from a few microns to tens of micrometers. The filtration of the filter paper is more than the screening function, also with the function of deep filtration; its side enlargement shows that the filter paper is a multi-layer structure. The front side should face the airflow direction and the back should be the air outflow direction. On the backside, draw a color line to facilitate the user’s identification to prevent mistakes.

Technical indicators

The technical specifications of the filter paper can be mainly divided into two aspects, one is the filter characteristics of the filter paper, and the other is the physical characteristics. Filtration characteristics include gas permeability, maximum pore size, and average pore size. Physical properties include basis weight, thickness, stiffness, burst strength, resin content, and the like.

Fluffy: being fluffy to the breathable, density of 0.15 ~ 0.35g / cm3, high alpha fiber.

Micropores: small pore size, a large number of perforations, filtering out fine particles, and the airflow is unobstructed; the size of the pores is normally distributed, expressed by the following parameters–maximum aperture and average aperture.

Strength: expressed in terms of bursting strength, stiffness, tensile strength, and physical strength of tear;

Quantitative: quality of filter paper per square meter, unit: g / m2.
Refers to the thickness of the filter paper, excluding the corrugation depth. Unit: mm.

Air resistance: the resistance of the filter paper to airflow. The value of the pressure drop obtained by passing 100 cm of filter paper through 85 liters of air in one minute is indicated. The unit is mbar. or water column height.

Corrugation depth: the depth of the groove pressed to enhance the longitudinal stiffness of the filter paper, in mm. In general, its value is 0.2mm.

Air permeability: the amount of air passing through the filter paper per unit of time under a certain area and a certain degree of vacuum. The unit is l/m2•s.

Maximum aperture: the diameter of the largest sphere that can pass through the filter paper. Unit: μm.

Average Aperture: the pore size derived from the “burst” bubbling pressure is called the average pore size. The unit is μm.

Burst resistance: the maximum pressure that can be applied to the unit area of the filter paper. Unit: Kpa

Filter paper glue dipping

If the filter paper is made only from the filter material, it is still too weak to withstand the violent processing of the filter production line, the filter membrane is easily broken during use;
Solution: filter paper glue dipping- usually impregnated with resin; resin content 10-30%, physical strength increased by 300%. The resin content is insufficient, the strength of the filter paper is low; the resin content is too high, and the filter paper becomes brittle and easily damaged. The resin can be a phenolic resin, Phenolic varnish, alcohol fibrin, and water-soluble resin.

Cured and non-cured filter paper

The cured filter paper must be heated for 10-15 minutes to cure the resin and increase the stiffness of the filter paper. But it will release harmful air, formaldehyde, free benzene, phenol derivatives, and amines;
Non-cured filter paper adopts immersion technology with thermoplastic resin. During the processing of non-curing resin, only a little heat or no heating is needed, which has certain flexibility at room temperature, suitable for manufacturing air filter elements with air as the medium.