Fabrics Utilized In Cleanroom
Garments
DuPont's Tyvek is well known in the
cleanroom industry as a fabric used for manufacturing disposable protective
clothing. Tyvek is fabricated from millions of very fine continuous polyethylene
fibers overlapping to form a dense sheet structure that functions as a
protective shield. The process used to manufacture these fibers is known as
spunbonding.
Tyvek was originally tried in cleanrooms
in the early 1960s. It favorably passed a test set up to compare it with woven
fabrics and rate it for comfort. This nonwoven has been upgraded over the years
and has proven to be a good performer for Class 100 to Class 100,000. Its
disadvantages include free fiber generation at wear points. It is antistatic
close up but not static shielding. It has a 3 micron to 10 micron filtering
efficiency. Average use is two to three days, except in sterile areas where
three of four garments are used each day. Recleaning is practical but shedding
increases with each laundering or dry cleaning.
Tyvek is essentially chemically and
biologically inert. Its physical properties are unaffected by most organic and
inorganic chemicals, including acids, bases and salts. The fabric can absorb
certain organic solvents. This can cause slight swelling of the Tyvek before the
solvent evaporates.
Tyvek has high tensile-tear strength in
all directions, wet or dry. Water has no effect on its strength, and it retains
its toughness and flexibility down to -100°F. Because the fabric is a synthetic
non-woven, the flammability characteristics are similar to most synthetic
fibers. If exposed to a flame, Tyvek will shrink away quickly.
Most reusable cleanroom garments are made
of woven polyester. These inherently anti-static fabrics may be woven using any
of the three basic weaves. The most commonly used is a twill weave. The twill is
readily identified by the diagonal lines that the weave creates on the surface
of the fabric. The yarns in the twill fabric are usually spaced closely
together, packed tightly and held firmly in place, thereby exhibiting greater
strength and durability, resulting in good resistance to abrasion and superior
soil- shedding properties.
Each manufacturer has his own idea of the
best type of weave and static dissipative measures.
Some of the first attempts to curtail the
penetration problem were by hot-pressing the woven fabric to close the
rectangular pores. This succeeded, but created a non-breathing, uncomfortable
garment that also generated high levels of particulates caused by stress raises
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 in wearing,
resulting in snags and high abrasion areas and in cleaning with breakdown due to
machine flexing.
The membrane garments are the most recent
entries into the cleanroom garment market. These garments give the most complete
particle barrier, but also are the most expensive.