Sometimes what appears logical is, in fact, incorrect when it comes to cleanroom markets and technologies
By Robert McIlvaine and Betty Tessien of The McIlvaine Company
The common wisdom relative to cleanroom markets and technology is not necessarily always right. One of the most important misconceptions has to do with filtration efficiency.
Filter efficiency on nanoparticles is low
HEPA filters are thought to be more efficient for particles above and below 0.3 microns. In other words, the lowest efficiency is achieved on particles 0.3 microns in diameter. That’s because Brownian movement causes the 0.2 micron particles to more easily collide with the filter surface.
Now we are very concerned about providing cleanrooms for nanotechnology operations. It is possible that there will be large generation of particles only a few nanometers in diameter-the 0.2 micron particle is one with a diameter of 200 nanometers. In determining the cleanliness of cleanrooms, we are only counting particles of 0.1 microns, or 100 nanometers, in diameter and larger. So, we could have a Class 1 cleanroom filled with 90 nanometer particles.
Logic tells us that as the diameter approaches 0, the particle will act as a gas and pass through the filter media. But there is apparently little research on the performance of HEPA or ULPA filters on the small nanoparticles. The problem in determining this filter efficiency will be finding an accurate way to make the measurement. At least some progress on this front has been made on chemical speciation. A method has been found to break the particles down to the atomic level, at which point they (in the aggregate) present enough surface area to be measured by a mass spectrometer.
Table 1: Analysis of the cleanroom industry in all of the Americas.
The capture of these very fine nanoparticles will be critical to the whole future of the nanotechnology industry. One option will be the use of nanofibers in the filtration media. Another possibility is activated carbon.
A fertile field for investigation will be electrostatic enhancement. A pre-charger can be placed ahead of the ULPA filter. There are versions of this technology widely used in air-pollution control. The difference is that these systems are designed for removal of larger particles, so modifications would be needed to adapt this concept to nanoparticle capture.
Equally promising is a radically different concept called “liquid encapsulation.” The recirculating air passes through a screen, which is similar to the wand used in bubble-making toys. A film of liquid with surfactant to lower-surface tension passes over the screen. On the downside of the screen, the air and liquid have been converted to dense foam made up of tiny bubbles. Brownian movement of the tiny nanoparticles will ensure their impingement on the inside of the bubbles. A mechanical foam breaker then separates the air and the liquid. To provide the right relative humidity, the liquid can be a non-aqueous solution.
This liquid encapsulation technology holds great promise for destruction of microorganisms, as well. If the liquid contains a disinfectant, the impinged virus or other contaminant would be killed.
US cleanroom manufacturing growing, not shrinking
The average American will tell you that we have become a service economy and that all the manufacturing jobs are moving to Asia. The truth is that manufacturing revenues and profits have continued to grow in the US. In fact they represent the same percentage of GDP as they did some years ago.
What has changed, though, is the productivity of the work force. We now manufacture more with fewer people. So, this shrinkage of manufacturing jobs is a positive long-term development. Within this greater picture are some industries that are growing and others that are not. Table 1 shows an analysis for the cleanroom industry in all of the Americas, from Canada to Argentina.
The cleanroom industry in the Americas reached a low point in 2002, and then started to rebound. Space in use grew 4 percent in 2003, followed by a 5 percent gain in 2004, and 6 percent last year. This year, a 6 percent growth of space in use is projected. Some geographical areas are experiencing greater cleanroom growth than others. Puerto Rico is at the top of the list-Amgen, a biotechnology company, is building a new $1 billion facility there. Also, many major pharmaceutical and biotech companies have located major manufacturing plants on the island.
Chinese growth not a negative for US suppliers
The conventional wisdom is that the imports of gloves and certain other cleanroom consumables from China are harming US cleanroom suppliers and this situation more than offsets the exports to China by US manufacturers and suppliers. While it is true that there is a negative trade balance with a certain number of the low-tech consumables, there indeed is a positive balance on high-tech consumables and hardware. In fact, some of the biggest impacts on the US economy are negative because of high Chinese imports rather than exports.
Stainless steel-which is used in mini-environments and many other cleanroom products-is much more costly now than it was a few years ago. One of the main reasons is the very large imports by China. The high energy costs experienced by cleanroom operators is due in part to the fact that China has become the second largest importer of oil behind the US.
Even more important to the US economy is the fact that US companies are setting up manufacturing facilities in China and are finding success in selling cleanroom products there. Hollingsworth & Vose, as well as a number of other filter media suppliers, have successfully started manufacturing operations in China. Several years ago, laws were changed, thereby essentially ensuring long-term leases of property and the ability of foreign manufacturers to own their Chinese operations.
Robert McIlvaine is president and founder of the McIlvaine Company in Northfield, IL. The company first published “Cleanrooms: World Markets” in 1984 and has since continued to publish market and technical information for the cleanroom industry.
Betty Tessien is the cleanroom publications editor for the McIlvaine Company.