Microfiltration is a type of filtration process in which membrane filter, with pore sizes that vary from 0.1μm to 10μm, is used to trap fine particles or microorganisms.
Fujifilm and "filtration technology" may sound somewhat unrelated, but Fujifilm’s research into filtration technology can be traced back to nearly half a century ago. Based on the technology of photographic films, Fujifilm came up with the idea of making microscopic holes in film to optimize the film material. Completed in this way, through trial and error, was "AstroPore", a micro filter having numerous micro pores. With improvements from time to time since its launch in 1969, AstroPore has been in production for more than 40 years. Its superior quality has received high recognition from many customers, firmly supporting Fujifilm’s growth until today.
Now, let's see the features of micro filters. Generally, micro filters can be classified into two types depending on their trapping mechanism and structure.
1. Nominal (filtration) type
2. Absolute (filtration) type
The "nominal type" has a structure in which fibers are randomly tangled with each other. On the other hand, the "absolute type" typically has numerous micro-sized pores inside a synthetic resin film or membrane, which enables particles larger than a defined size to be trapped.
Today, our micro filters are used at manufacturing sites of a wide variety of industries. Listed below are just few examples of how they are used…
- Removing yeast and bacteria from brewery processes (beer, wine and Japanese sake)
- Removing any harmful organisms in bottled water
- Removing contaminants from cleaning liquids used in washing processes for liquid crystal panels and semiconductors
Our membrane filter has a unique characteristic where the structure is asymmetric. The pore diameter in the film is rather large on the inlet side but gradually becomes smaller towards the outlet side (see "PSE membrane structure" on the right). Coarse particles are first trapped near the inlet side, while finer particles are trapped by finer pores that are situated further, towards the outlet side of the membrane. The pictures on the right show the cross section of the membrane. Filtered material flows from the top (inlet side) to bottom (outlet side). As you can see, the pore size gradually becomes smaller towards the outlet side.
Due to this asymmetric structure, you can see the difference in the thickness of the dense layer. In normal symmetric membranes, structure that could be seen in other competitor’s filters, pore size remains the same throughout the membrane. On the other hand, Fujifilm’s filter contains various pore sizes that gradually become smaller towards the outlet side. Due to this, Fujifilm filter is able to make the dense layer thin, but retaining the same filtration quality.
Fujifilm filters meet the demands of customers and are highly recognized for these three strengths.
Conventional filters contain unified pore size throughout the membrane so the filtration is concentrated towards the inlet side. However, our membrane makes use of its entire body, coarse particles being trapped first and finer particles are trapped deeper. Our filter takes advantage of its asymmetric structure, leading to a longer service life (see "Trapping of latex mixture" below).
Imagine an hourglass with the bottom glass bulb being cut in the middle. The larger pores on the inlet side ensure a low initial pressure loss. The pore size gradually decreases, however, becomes larger again on the outlet side. Also, the dense layer where pressure loss occurs usually is thin compared to other membranes. These two features provide low initial pressure loss and high flow rate.
The pore diameter can be as small as 0.03 μm, depending on the product grade. Sharp pore size distribution curves (see charts below) assure reliable removal of fine particles and microorganisms.
![[photo] AstroPore FP-20N microfilter cartridge housing](https://asset.fujifilm.com/www/ar/files/2023-06/0f57f12c0ca3a6798403640cba9b0634/MicroFilter-CartridgeHousing.jpg)