Evaluation Methods for Cleanroom Garments
A qualified cleanroom garment (hereinafter referred to as a cleanroom garment) plays a crucial role in maintaining the cleanroom environment. Therefore, researching evaluation methods for cleanroom garments and providing guidance for their production, design, and selection is of considerable significance.
The human body is the largest source of contamination in a cleanroom. Therefore, researching evaluation methods for cleanroom garments and providing guidance for their production, design, and selection is of considerable significance.
Regardless of the cleanroom level, cleanroom garments must possess four basic elements: cleanliness performance, electrostatic performance, durability, and comfort. Table 1 explains the meaning and function of these four elements.
Evaluating the cleanliness performance of cleanroom garments requires considering both dust-free and dust-filtering aspects. Equating dust-free with cleanliness is inappropriate.
1. Dust-Free
Dust-free refers to the garment itself not generating dust. This requires selecting dust-free fabrics and accessories during the production and design process of cleanroom garments, and minimizing the possibility of dust generation and accumulation during cutting, sewing, and style design. Using simple tools, you can determine whether cleanroom garments possess dust-free properties in the following ways:
Observe the fabric under a microscope to see if it is woven with long-filament fibers.
Natural fibers such as cotton and linen are short fibers, which easily generate particulate matter at the fiber ends, and therefore cannot be used in cleanrooms. Therefore, cleanroom garments must be woven with chemically synthesized long-filament fibers. Furthermore, fibers spun from recycled chips contain a certain proportion of recycled materials, which contain more impurities and increase fabric dust generation, so they cannot be used in cleanrooms either. This can be easily distinguished using a microscope or a high-powered magnifying glass.
Observe under a microscope whether the antistatic fibers added to the fabric will become a source of dust generation.
Cleanroom garments must use antistatic fibers; choosing the wrong antistatic fiber may cause contamination. Currently, there are two common types of antistatic fibers-surface-carburized antistatic fibers and composite-spun antistatic fibers. Surface-carburized antistatic fibers, because their conductive components are coated on the base surface, are easily peeled off in large quantities by washing and friction, increasing the amount of dust generated by the fabric, and therefore cannot be used in cleanroom environments. Composite spun antistatic fibers are produced by thoroughly mixing conductive components with a molten matrix material, then combining them with the matrix material through special spinnerets to form fibers. Therefore, they are wear-resistant, washable, and do not easily generate dust.
Under a microscope, if the surface of the antistatic fiber is rough and has translucent spots, it can be identified as a surface-carburized antistatic fiber, which cannot be used to make cleanroom garments (Figure 2).
Checking the Dust-Generating Properties of Garment Accessories
The following accessories can potentially contaminate the cleanroom environment: sewing thread containing short fibers, care labels, ear loops, cuff ribbing, leg ribbing, dust-generating hook and loop fasteners, zippers with peeling plating, and garment labels with easily flaking printed ink. This is also an important factor in evaluating the quality of a cleanroom garment. All accessories for cleanroom garments must be made of dust-free materials. Check if the cutting and sewing of cleanroom garments meet the standards.
Improper cutting and sewing increases the amount of dust generated by cleanroom garments because the edges of the garment pieces can emit particles. Therefore, cleanroom garments require the use of hemming techniques such as rolled edges, three-fold hems, rolled edges, or four-fold hems to treat the connections between the garment pieces. Furthermore, exposed raw edges must be heat-fused. Some high-level cleanroom garments also require laser cutting of the fabric to reduce dust generation.
Check if the garment style is appropriate.
Cleanroom garments should be designed to minimize dust accumulation, including: reducing wrinkles; pen holders should not have closed bottoms; and reducing unnecessary accessories (such as pockets). Additionally, the garment design should not be too loose to reduce friction and control dust generation. These requirements should also be considered when evaluating a cleanroom garment.
Helmke Roller Test
In addition to the above simple evaluation methods, IEST-RP-CC003.3 specifies the Helmke roller test method to scientifically and quantitatively evaluate the dust generation indicators of cleanroom garments and fabrics. The testing method involves tumbling clothing or consumables in a stainless steel drum and using an air particle counter to measure the number of particles of various specified sizes per cubic foot.
2. Dust Filtration
Another important indicator of the cleanliness performance of cleanroom garments is the dust filtration rate, also known as the dust capture rate in Japan. This refers to the effectiveness of cleanroom garments in preventing the diffusion of particles from the human body. The dust filtration performance of cleanroom garments can be assessed from the following aspects:
* **Examine the warp and weft density of the garment fabric**
Warp and weft density is an indicator of the tightness of the fabric. The higher the warp and weft density, the smaller the gaps in the fabric, and the better the dust filtration rate. The warp and weft density of the garment fabric can be easily judged using a commercially available warp and weft density microscope.
* **Examine the linear density (D number) of the fibers used in the garment fabric**
Generally, the finer the individual fiber (lower the linear density), the more fibers are arranged in the same area, the better the filling effect, the denser the woven fabric, and the better the particle blocking effect. Therefore, high-level cleanrooms generally use fabrics spun from long-filament fibers with lower linear density to make cleanroom garments.
However, an increase in the total number of fibers leads to an increase in the total surface area of the fibers, thereby increasing [the fiber's surface area].