By Robert McIlvaine and Betty Tessien of The McIlvaine Company
Last month, this column focused on the use of reusable cleanroom garments as an alternative to disposable garments. In particular, it addressed the issues of particulate contamination, sterility, static-control issues, fabric testing, comfort, and fabric construction and durability. This month, the topic of reusable garments continues with the examination of various materials and fabrics, and a look at suppliers and processors.
Some of the first attempts to curtail the particle-penetration problem were done by hot-pressing, or calendaring, the woven fabric in order to close the rectangular pores. This indeed was successful, but it also created a nonbreathing, uncomfortable garment that generated high levels of particulates caused by stress raised in the now-compressed filaments. Another approach was to use a finer denier thread, which was more tightly woven. This improved filtration efficiency but resulted in a very lightweight material that lacked durability during wear, resulting in snags and high abrasion areas from cleaning, with breakdown due to machine flexing.
Without question, providing properties of stain release, softening, antistats, and antimicrobials as finishes are a serious challenge for cleanroom garments. Any finishes added cannot be part of the problem. Moreover, finishes do not just need to be functional; they need to be durable. Chemical sluffage, leaching, or volatilization can add unwanted pollutants to the cleanroom, the wearer, and the products being produced.
Materials and fabrics
Curt White, director of R&D at Ægis Environments, reports that the company’s ÆGIS Microbe Shield® Antimicrobial Treatment has experienced a growing demand for its use on cleanroom outergarments and undergarments. Microorganisms sourced from the operators (skin, hair, respiratory system, and digestive system), the workplace environment (walls, ceilings, floors, and air-handling systems), or the work products (metals, electronics, pharmaceuticals, foods, etc.) are significant pollutants in the cleanroom.
These organisms are particulate pollutants (spores and body parts) and chemical pollutants (metabolic products and wastes such as organic acids, enzymes, myco or other exotoxins, etc.) and can cause disease and staining, deterioration, and odors. These activities of microorganisms destroy products, contaminate, and adulterate products, and place operators or laundry personnel at risk of disease or discomfort.
According to John Smith of Precision Fabrics Group (PFG), in the US market, most of the fabrics sold are plain weaves, whereas in Europe, a much higher percentage of the fabrics are twill weaves. “Since the fabrics have to perform the same function of particle filtration, it seems that both can do so if they are properly constructed,” he says. “With plain weaves, the fabrics are woven tightly of fine denier yarns, creating a low mean pore size. Controlling the various manufacturing steps reduces the pore size further. By reducing the pore size, though, the filtration efficiency is improved and, just as in a filter, the filtration gets better as the pores fill.
Smith continues, “With twill weaves, the filtration can also be quite good, but by a different mechanism: creation of a tortuous path to trap particles in the fabric thickness. The advantage that the twill weaves have is that the hand is more supple than a plain weave, although the plain weaves become more supple after laundering. The disadvantage is the higher fabric weight and, therefore, garment weight, and potential latent release of particles if the laundering is not done properly. The good news here is that laundries in both the US and Europe are very knowledgeable in decontamination procedures and quality control.”
According to Adam Vesely, director of operations for the cleanroom division at G&K Services, there has been a significant reduction in the overall costs for reusable cleanroom garment programs during the past five years. He cites three main factors driving that reduction:
- Consolidation of the specialist cleanroom laundry service providers within the North American market has led to increased economies of scale among the large national providers.
- A reduction in demand within the US due to microelectronic manufacturing migration overseas. This has led to an excess laundering capacity within the microelectronic market centers, resulting in aggressive price competition.
- An increasingly knowledgeable client base that, with the assistance and expertise of the more reputable laundry providers, has improved the administration and management of their reusable cleanroom garment programs among their end users.
Suppliers and processors
In the reusable segment, Burlington Fabrics, Precision, and Stern & Stern Industries are some of the largest US suppliers. However garment sewers also purchase special items, such as zippers, snaps, and elastic, in addition to rolled goods. For example, Strauss Knitting supplies ESD knitted cuffs, which are manufactured differently than the rolled goods for the garments. Meanwhile, Seiren and other Japanese suppliers are supplying fabrics not only to the Asian market, but also to the US and Europe, as well.
The idea of the best type of weave, finish, and static dissipative measures is unique to each manufacturer. John Smith of PFG Fabrics says the durability and effectiveness of the ÆGIS Microbe Shield Treatment provides a feature that satisfies the cleanroom garment users’ demand for antimicrobial protection. It is a complement to the increasing technical properties of the firm’s fabrics for the cleanroom and laundry industries. PFG and other fabric manufacturers are challenged to balance properties-such as stain release, other cleanability factors, softness and drape, and antimicrobial-with the physical stability needed for the use and abuse, and the laundering protocols required by the cleanroom garment customers and the laundries. In the case of undergarments, the need for antimicrobial properties is magnified, and wickability and comfort control become very important to the end user.
According to Burlington’s Lisa Brown, the company’s fabrics are made in North Carolina, Virginia, or Asia, and then shipped all over the world. Usually the firm sells its fabrics to the garment manufacturers, which then sell the garments to laundry services. The laundry services, in turn, rent or sell the garments. Specifying what is needed in fabric qualities, the laundries often work with the fabric manufacturers because the manufacturers have the technology and testing facilities for different garment fabrics. In fact, Burlington has its own microbiology lab and its own cleanroom for testing, states Brown. She adds that the use of sterilized garments is increasing as the demand for cleanliness increases.
Because processing-especially steriliza-tion and gamma processing-degrades the fabrics of the garments, Burlington as well as other manufacturers are constantly working on improving the technology and yarns in fabric materials to create garments with a longer life. As such, Burlington buys raw material from fiber suppliers, and then processes the yarns in proprietary ways to created rolled goods. Polyester is most often used because it has a nonlinting filament base.
Silver microfilaments that act as antimicrobial agents have been added to some fabrics. However they may degrade at high temperatures in cleanroom laundry systems, thereby resulting in particle release. This may be acceptable in a hospital setting where particle minimization is not critical, but in a semiconductor fab, the potential of loose silver microfilaments is unacceptable. Ægis provides another patented Microbe Shield product that the company claims is compatible with virtually all substrates, including natural and synthetic fibers. It is applied at the mill and incorporated into the wet-finish process.
The product is a solid molecular micropolymer designed to physically kill microbes by attracting the microbe with their positive charge, rupturing their cell membrane on contact with their long molecular chain, followed by a shock from the antimicrobial’s positive charge. According to the company, the antimicrobial is not consumed, does not dissipate, and uses no arsenic, tin or heavy metals, or polychlorinated phenols. To this end, the company says Microbe Shield does not lead to an environment that promotes adaptive microorganisms, and claims it is fully effective as long as the surface remains intact.
According Smith, it’s also possible to create another barrier: fluid resistance. “Integrity 2000 uses small pore size, Microbe Shield antimicrobial, and a treatment for fluid resistance,” he says. “This inhibits the penetration of bioactive particles from being transported through the fabric and into sterile environments, and reduces the chance a fluid penetrating the garment to the skin of the wearer.”
Although White Knight sold off the consumable line of its business, the reusable cleanroom garments division still has a robust market share. White Knight Engineered Products, Inc. focuses on woven fabrics and reusable protective apparel. Marketing Director Angel Trimble says that White Knight’s extensive experience, combined with a commitment to innovation and strict quality requirements, allows the company to offer a full line of in-stock standard designs that meet the needs of various industries. Moreover, White Knight has a product development team that allows customers to bring their issues before the group, and White Knight will work to design a product that meets customer-specific needs.
Table 1: Use patterns
Although White Knight is frequently the first point of contact for end users, about 98 percent of its business comes from the laundries of cleanroom garments. Its stocking program, with tried-and-true products on hand, also allows changes in fabrics and designs as needed. The firm offers a variety of wrist closure options, including knit cuffs, elastic, snap adjustments, and thump loops, according to Trimble.
Worker safety in the area of fire protection and arc-flash resistance also is a growing direction for garments. White Knight offers garments that are flame-resistant, to meet new standards of the National Fire Protection Association (NFPA) 70E Electrical Safety Regulations. These mandate specific requirements for the level of protection based on the worker’s job function. For this, White Knight offers a coverall that meets the NFPA 70E Category 1 standard of 5.0 cal/cm2. The company also offers a double-layer garment to meet the 8.0 cal/cm2 standard for Category 2 protection.
Filament Nomex®, a trademarked and patented material developed by DuPont, is being incorporated into garments because it features properties that immediately extinguish arc-flash fabric fires. When polyester ignites, it melts onto the skin, which may result in a third-degree burn.
Marketed by Terra Universal and others, ChemStat 909A is an antistatic cleanroom fabric developed by Stern & Stern Industries, following years of research requested by NASA for the Space Shuttle program. This fabric is reported to offer state-of-the-art solutions to the three most typical problems associated with synthetic cleanroom apparel: electrostatic interference, worker discomfort, and environmental degradation. It is designed for use in Class 10 (ISO Class 4) cleanrooms.
The 100 percent polyester high-performance fabric comes with a patented raised grid of conductive carbon/polyester yarns. The raised grid draws static electricity out of the fabric, and then dissipates it into the air. According to the company, the twill weave provides more than three times the tear strength of conventional plain-weave fabrics, while the ChemStat 909A conductive yarn is an extruded copolymer impervious to over 300 industrial launderings.
Table 2: Reusable cleanroom clothing
According to Michele McSwain of TW CLEAN, the company has developed a garment system that provides a safe path to ground for the garment and the wearer, for the fastest and most reliable elimination of static charges. “TW CLEAN’s GROUND ZERO product series, including lab coats, coveralls, hoods, and conductive booties, has been designed specifically to control static charges generated by the garments and personnel in a cleanroom environment, thus eliminating the need for wrist straps and heel grounders. They also can be continuously grounded and monitored,” she says. “The ability to manage the static charges inherent to cleanroom garments is the only real advancement in cleanroom garment technology in more than a decade, and it becomes more significant with the release of each new and smaller electronic device.”
The membrane garments are among the most recent entries into the cleanroom garment market, though GORE-TEX® Cleanroom Garments have been produced for nearly 20 years. Membrane garments have higher filtration performance, thus providing increased particle-capture efficiency. According to Sean Doyle with WL Gore & Associates, Inc., GORE-TEX Cleanroom Garments made with GORE-TEX high-performance, non-shedding, durable, antistatic cleanroom laminate fabric have a filtration efficiency of 99.9999 percent at 0.12 microns when properly maintained.
“These garments can be used in ultra-clean (nonsterile) Class 1 (ISO Class 3) to Class 100 (ISO Class 5) environments. In addition, the moisture vapor transmission rate (MVTR) of the GORE-TEX Cleanroom Garment is greater than 25,000 grams of water/square meters/24 hours, which results in a drier, more comfortable garment,” says Doyle. “With the potential for sealed seam designs-which eliminate particle transmission through needle holes-membrane garments give the most complete particle barrier. Finally, GORE-TEX Cleanroom Garments have the unique ability to have small tears repaired, thus restoring the garment to full particle-capture efficiency. However, with all these benefits comes increased cost. Businesses have to evaluate whether or not the benefits of a high-purity reusable membrane garment have a value in their manufacturing process.”
Another company, ARAMARK Uniform Services (AUS), has developed a complete line of cleanroom garments that meets the requirements of all segments of the industry, including custom garments developed for specific applications, claims Mike Rataj, director of quality control with the company. These custom garments range from coldroom cleanrooms (less than 50°F) to custom over-the-head garments for the tissue-culture industry.
Table 3: Reusable clothing in China
Suppliers and processors of cleanroom reusable garments offer their customers various competitive options. As an example of how cleanroom garment suppliers operate, with more than 25 years of experience in the industry, AUS states that it currently provides cleanroom garments to 19 of the top 21 pharmaceutical companies in North America. Says Rataj, “Features and benefits of AUS stock garments include those designed with specific features to enhance their performance in the cleanroom. Examples include AUS’s use of gamma-compatible coil zippers to reduce the amount of contamination that passes through the zipper, and thumb loops on the sleeves to prevent skin exposure at the wrist, and conductive cuffs on ESD garments to provide the most effective electrical connections.”
According to Rataj, every ARAMARK garment is bar-coded. Each bar code is scanned whenever a garment is processed, providing a comprehensive tracking system. Whenever a garment has undergone a predetermined number of laundry cycles, the item is removed from service and replaced with an identical garment.
Another example of competitive options comes from Cintas Cleanroom Resources, which claims to be the “first national cleanroom garment laundry to establish an ISO-based quality-management system and achieve ISO 9000 registration,” says Jan Eudy.
Meanwhile, Vesely notes that G&K Services’ Cleanroom Division is the largest cleanroom laundry service provider within the North American market. It operates a network of seven dedicated cleanroom laundry-processing facilities throughout the US and Canada. This network of facilities, when coupled with the company’s Copy Exact Operating Procedures, provides customers with unparalleled service response times and business continuity/disaster recovery capability.
Robert McIlvaine is president and founder of the McIlvaine Company, 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.