vol.61-3 (2023/9/30)

Glass fiber filter media

Glass fiber filter media for air filters, consisting of wet-laid nonwoven fabrics made by papermaking technology, have filtration performance ranging from medium efficiency to HEPA/ULPA and are used in a wide range of applications. The reasons why glass fiber is suitable as a filtering material are as follows.
(1) A wide variety of fiber diameters is available, which can be combined to obtain filter media with a wide range of performance. (2) Compared to other materials, fine fibers of 1 μm or less can be produced at a low cost, making the price of filter media relatively low. (3) Because the glass fiber is noncombustible, the resulting filter media is flame retardant. (4) The stiffness of the fiber is high, and the resulting filter media has high stiffness. Therefore, the filter media is less likely to deform during ventilation. Furthermore, the high porosity of the glass fiber fabrics results in the filter media with low pressure drop and high collection efficiency.
In this article, the materials, manufacturing methods, and properties of glass fiber filter media are outlined. Future topics include composites with other fibers and PFAS-free filter media.

Synthetic fiber filter media

In recent years, there has been a demand for improved air quality in living spaces, and this trend has become even stronger due to the current COVID-19 pandemic. Synthetic fiber filter media is one of the best ways to protect people from pathogen aerosols. Electret processing is effective in improving the performance of synthetic fiber filter media. Furthermore, we have succeeded in improving the durability and imparting antibacterial and antiviral properties of electret filter.

Activated carbon filter media

Activated carbon filter media has a very porous structure and is used as filter media in a wide range of fields, including the semiconductor and automotive industries. Although activated carbon is a material with a long history, it is widely used in cutting-edge fields and is a material that is expected to find increasingly new applications in the future.

Media structure and application of pre-filter

The air filter media made of the synthetic fibers have been broadly used in various application since the filter media can be designed flexibly for customer’s requirement. The synthetic fibers are selected depend on the application according to those chemical and physical characteristics. Production process can give fiber the optimum structure of filter media and various function by chemical agents. Filter media are designed as filter unit to achieve low pressure drop, long life and high efficiency.
This paper introduces the technologies of materials, process, test methods, structures, applications and recent trends especially for pre-filter (coarse filter) media of non-woven fabrics.

Antibacterial enzyme filter media

Air filter catches microorganisms as well as airborne dust particles, however, there is a risk of secondary contamination*. Enzyme filter functions as anti-propagation of gram-positive bacteria, dissolving fungal hyphae and inactivating envelope type viruses. Enzyme is a safety material to humans and keeps its lytic function long time by being immobilized on the OH substrate of the filter fibers. As known as natural catalyst, enzyme repeats lytic action.
Enzyme can be immobilized on glass fibers and non-woven materials from which HEPA, middle grade filters and pre-filters can be made. They are used in food and beverage industry, hospitals, pharmaceutical companies, laboratories, commercial buildings, and so on.
*Secondary contamination is increase of captured bacteria or fungi in a filter propagate by taking nutrient from the dust, and then the cell-divided microorganisms are pushed to the downstream by air-flow.

Filter media for the bag filter

The filter bag is a surface filter method which uses the layer of the particles which first adhere to the surface as a temporary filter layer for separating and collecting minute particles. If the dust of a certain particle diameter distribution passes through the filter bag, the larger particles adhere to the threads by inertial impaction. Then smaller particles adhere to the threads by diffusion or obstruction, forming bridges of particles between the threads.
The primary layer of adhered particles contains numerous minute hole. These minute holes collect minute particles.
For this reason, the filter bags have a higher collecting performance than other dust collectors. When the pressure loss of the bag filter increases, the dust is shaken off.

Determination of Aldehydes in Indoor Air by High Performance Liquid Chromatography with O-(2,3,4,5,6-Pentafluorobenzyl) hydroxylamine derivatization-Focusing on Acrolein-

There are various sources of harmful aldehydes in the indoor environment. For example, formaldehyde is used in building materials and household products, acetaldehyde is used in wood and solvents, acrolein is produced when smoking or using mosquito coils. In addition, hexanal, heptanal, octanal, nonanal, and so on, are generated from human exhalation, and there is concern about indoor air pollution in crowed buildings. Currently, the 2,4-dinitrophenylhydrazine high-performance liquid chromatography (DNPH-HPLC) method is used worldwide for measuring aldehydes in the air.
However, it cannot be used for acrolein measurement as the derivative decomposes during the process. To address this issue, we prepared a scavenger using pentafluorobenzylhydroxylamine (PFBHA) as a reactive reagent. Additionally, sodium ethylenediaminetetraacetate was added to the scavenger as an antioxidant. In this study, primary criteria such as storage stability of acrolein derivatives in scavengers, process measurement accuracy, reagent storage stability, and comparison with standard method, were investigated, and a method for measuring acrolein using HPLC was established.

Principles and features of local air purifying devices utilized airflow control technology

This paper addresses the principle and features of two kinds of local air cleaning system utilizing controlled uniform airflow. Push-pull ventilation systems are a local ventilator that protects workers by efficiently removing hazardous substances using uniform airflow where contaminated air is in the workplace. Open-clean systems developed by Koken create extremely high cleanliness levels of zone in the open air using uniform airflow.

Nanoparticle collection using water condensation capture

Particle contamination in semiconductor process fluids such as ultrapure water (UPW) and air can cause defects on wafer surfaces. Traditionally, laser particle counters have been used to monitor particle contamination in UPW, but it is difficult to detect particles smaller than 20 nm while the size of killer particle is now as small as 7 nm. The Spot Sampler, an aerosol particle collector that uses the laminar-flow condensation growth capture technology, can collect particles in liquid coupled with a proper nebulizing system. With this sampler, aerosol particles as small as 5 nm can be enlarged by condensation of super-saturated water vapor which transports by diffusion from the warmed wet wall of porous tube (wick) toward the center of laminar aerosol flow. Finally, the original nanoparticles are grown into large droplets and then collected by gentle impaction with high efficiency into 1-mm spot on a substrate such as a silicon wafer. The morphology and chemical composition of collected particle sample can be analyzed using SEM or EDX to help identify the contamination sources.