Textiles are a vital component for maintaining and functioning in cleanroom environments.
Textiles play a variety of roles in protecting cleanrooms from contamination, and although many components and processes have remained the same over the years, advances are also being made. Among changes are: a new textile laundering option, increased comfort levels of cleanroom clothing, and ways to control and bring down the costs associated with cleanrooms.
According to Merriam-Webster, a clean room is “a room for the manufacture or assembly of objects (as precision parts) that is maintained at a high level of cleanliness by special means.” Those means include controlling the air quality, lighting, flooring, walls and any element that is in the room—including the products produced and production equipment.
“All of the considerations have the same main goal: eliminating and/or minimizing contamination,” says Steve Glosson, market manager for Integrity® Protective Fabrics, Precision Fabrics Group Inc. (PFG), a Greensboro, N.C.-based manufacturer of woven and nonwoven fabrics for high-performance industries.
Airflow rates, direction of airflow, temperature and humidity are controlled using highly specialized HVAC systems equipped with ultraefficient HEPA filters. “HEPA filters are normally arranged in the suspended ceiling to provide the appropriate airflow of the textiles (and workers) below. The airflow forces residual particles through carefully designed and placed air vents or grates,” says Richard Kinsman, president and CEO of CO2Nexus Inc. in Littleton, Colo., a company that develops equipment, processes and consumables that utilize liquid carbon dioxide as a solvent for processing textiles.
Cleanrooms are used in the production of pharmaceuticals, biopharmaceuticals, medical devices and semi-conductor electronics and are classified by the number of particles measured in the laboratory’s air as measured by ISO Standard 14644-1 “Classification of Air Cleanliness.” Classifications range from 1 to 9, with 1 being the “cleanest.”
“For example, cleanrooms used for semi-conductor/electronics manufacture are typically ISO Class 3-rated,” Glosson says. “That means that only 1 particle of 0.5 microns or greater is allowed per cubic foot of air. Sterile pharmaceutical manufacture typically uses ISO Class 4 cleanroom standards, which still allow only 10 particles of 0.5 microns or greater in size per cubic foot of air.” (A human hair is approximately 75-100 microns in diameter.)
The power of conductive fibers
Cleanroom contamination can come from a variety of sources, including from cleanroom workers’ skin cells and skin oils, cosmetics and colognes, and hair and lint from clothing. PFG is one company that manufactures fabric used in clothing to prevent contamination caused by humans inside the cleanroom. Clothing made from the fabric includes coveralls, hoods, boots and undergarments sewn with textiles made from continuous filament yarns.
“The two main applications using PFG fabrics are pharmaceutical and semi-conductor/electronics,” Glosson says. “Our Integrity® 2000 fabric has the smallest pore size (distance between yarns) of the Integrity product line. It is used in some of the most demanding cleanroom environments, such as those used for semi-conductor/electronics manufacture, which are typically ISO Class 3-rated. And our Integrity 1800 is manufactured for pharmaceutical applications, which are typically ISO Class 4-rated.
For static dissipation, conductive fibers are used in the production of cleanroom textiles. In addition to the tightly woven fabric construction, PFG’s Integrity products also contain conductive fibers—carbon yarns in stripe or grid patterns to act as electrostatic dissipaters to prevent static charges that can permanently damage electronic components, as well as deal with nuisance static (e.g. static cling of the garment to the wearer). To reduce bio-burden in the cleanroom environment, permanent topical antimicrobial treatments are also applied.
It’s not only the fabric used to make the body of the garments that needs to be considered; knits used for cuffs and neck trims need to meet the same performance requirements. St. Croix Falls, Wis.-based Straus Knitting Mills Inc., which specializes in manufacturing custom-knit trim and fabric, offers four types of conductive fibers: X-Static, Beltron, Resistat and Nega-Stat. “The most commonly used of the four is X-Static yarn, which is a silver-coated nylon or silver-coated polyester,” says Doug Hager, vice president of sales for Straus Knitting. “But the more durable product is often a carbon-based conductive fiber, such as Resistat, Beltron and Nega-Stat because the carbon-based fibers are inherently conductive, whereas the silver, which is a coating, is more susceptible to flaking.”
Cleaning cleanroom textiles
“One of the major complications for our products—primarily the cuffs and somewhat lesser fabrics—is the type of laundering to which they are subjected,” Hager says. “Particularly problematic is autoclaving, which is done in several end-use applications, such as those for military labs where both static discharge and contamination are issues.”
The best type of substrate to use for silver coating depends to some degree on how high the laundering temperatures will be. Autoclave temperatures for cleanroom textiles can reach 250 F. During some of the drying treatments after autoclaving at those high temperatures, nylon approaches a gel point, Hager says.
“We work with our customer to determine what the anticipated laundering practices will be before we decide on the best fabric for the trim,” he says. “We also make a point of letting the customer know that our products aren’t necessarily launderable under the umbrella of the garment’s body fabric because in many cases, if not most cases, we don’t know the other component parts of the garment and what their limitations might be.”
Although water-based textile processing is the dominant method to clean textiles, CO2Nexus developed a cleaning process using carbon dioxide as a primary cleaning solvent instead of water. “CO2Nexus has introduced a significant paradigm shift to the market that virtually eliminates the use of washing water, eliminates all dryers, reduces facility footprint, headcount, wear on the textiles and much of the maintenance requirements typical of today’s infrastructures,” Kinsman says.
Advancements in textiles used in clean room clothing have to do with increased comfort, Glosson says. “Most fabrics traditionally used in clean room garments in the U.S. are constructed with a very tight weave to restrict pore size in the fabric, which makes the material an effective barrier, but also can restrict the garment’s breathability. For example, PFG’s Integrity 1900 and 1950 are woven with finer yarns than those used previously, Glosson says. “That enables us to weave these fabrics with more pores per square inch to improve breathability. Since the resultant pore size is even smaller than that of conventional clean room fabrics, filtration efficiency isn’t sacrificed.”
For cleaning parts or goods processed in cleanrooms, such as medical devices or optics, woven polyester or nylon wipers are used. “There are a variety of levels of wipers, much like with cleanrooms,” says Craig Heiser, president of Newnan, Ga.-based Scientific Textiles, a manufacturer and distributor of a variety of cleanroom textiles. “The wipers are processed to remove as much lint as possible depending on which class of cleanroom they will be used in, ranging from 10 to 100. Class 10 has the least lint and is used for bio or pharmaceuticals and 100 is used for general purpose cleanroom applications.”
The wipers also vary in weight—light weight, medium weight and heavy weight, depending on how much solvent or fluid the customer needs to put on the wiper to wipe down the product. The most common wiper used in the industry is a polyester medium weight, class 100, Heiser says. Whether the wipers are laser cut or knife cut also depends on the end use. A knife cut introduces the possibility of frayed edges; a laser cut is more expensive, but the edges are fused.
Some innovations in the cleanroom market are driven by cost. “People are looking for less costly alternatives without losing performance,” Hager says. In the semi-conductor/electronic market, the use of benchtop, self-contained isolation cabinets are a money-saving option for manufacturing certain components. The cabinets contain the proper cleanroom environment for what is being manufactured and gloves are incorporated into the cabinets to allow human interaction with the product.
“This is a much smaller environment, easier-to-maintain cleanroom conditions and relatively inexpensive considering the cost of a huge, highly-filtered manufacturing space,” Glosson says. “The use of isolation cabinets can also allow the manufacturer to use less expensive cleanroom clothing for the surrounding environment, further reducing costs.”
The cost of water is becoming more of a factor for water-based textile processing, according to Kinsman. “Water-based infrastructure is expensive to buy, install and maintain but [it] is still the standard,” he says. However, textile processing systems using CO2 is gaining. It introduces gaseous CO2 into the main chamber and it is pressurized into liquid form (about 700 psi and 60 F). The garments go through a processing cycle, after which the chamber is depressurized, thereby returning the CO2 to a gaseous form and leaving the garments dry and cool to the touch.
“By replacing water-based methods with liquid carbon dioxide (CO2)-based cleaning methods, operational costs, capital infrastructure and sustainability impact can all be significantly reduced—all while maintaining superior cleaning and disinfection standards,” Kinsman says.