Note: Descriptions are shown in the official language in which they were submitted.
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Clean room suit with adsorbent properties
The man skilled in the art is aware of the fact that, in the process of
manufacturing
electronic components, especially high-quality microchips, the reject rate is
increased not only by particles, but also by gases s~ueh as ammonia, volatile
organic
acids and siloxanes, even if these are only present in the ppb range. While
these
gases can be Fltered out by special adsorption filters in the air supply, this
does not
take man into account as a source of enussions. The clean room suits in use
today
merely prevent the emergence of particles, especiatly skin particles, but not
the
cmergertce of gases. Man releases gases, including ammonia, which is harmful,
and
orbanic acids, via his skin (sweat), digestive system and respiration. Also,
siloxanes,
which are believed to originatE from skin and hair sp~~ays, deodorants and
certain
cosmetics, lead to faulty batches in production in ultra-clean rooms.
It is thus the object of the present invention to provide a clean room suit
which is
effective not only against particles, but also against gases enutted by the
wearer.
The solution to this problem is a clean room swit comprising a particle filter
layer
with good breathing properties and, on the side facing the wearer, an
adsorption
layer of activated charcoal. Clean room suits are known in the art. They may
be
disposable or reusable articles. Among the former .is a dense spun-bonded
fabric
made from very thin polyethylene fibres (Tyvek~. Reusable, i.e. washable,
clean
room suits are as a rule woven or knitted fabrics made from synthetic fibres
such as
polyesters, nylon, polypropylene, polyethylene, aramides and acrylic fibres.
In
addition, non-woven fabrics are also produced from very Ftne endless fibres
made
from these materials.
Features which clean room suits have in conuz~on are the fact that they retain
all the
particles and aerosols emitted by the body, and that the clean room suit
itself must
likewise not release any particles or decomposition products; it must be light
in
weight, wear and tear resistant and pleasant to wear. Known materials for the
production of clean room suits are UCX, SCX, 1-II;PA and U1.PA clotlu and dle
PURITA materials_ Even though particles of 0,1 pm and more need to be retained
completely, sufficiently good breathing properties must be preserved.
polyester
particle filter woven or knitted fabrics of this kind have a rri<~ss per unit
area of 50 to
200 g/m2, and especially 100 to 7 50 g/mZ.
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Protective suits are known from the military sector wlueh are intended to
protect
the wearer against skin poisons. A blanket filter which is particularly
suitable for this
purpose is described in the German patent 33 04 349. The skin poisons referred
to
are sparingly volatile substances which arc easy to adsorb. It could not
therefore be
expected that a protective suit which protects the skin against chemical
toxins and
warfare agents would also prevent the escape of readily volatile substances
emitted
by the skin anal would enable the adsorption of gases such as ammonia even in
the
ppb range.
lU For the purposes of the present invention, the adsorption layer of
activated charcoal
can be attached to a very air-permeable area-measured textile material or
directly to
the inside of the material of the clean room suit. In accordance with Dlr C 33
04
349, the activated charcoal of the adsorption layer can, for example, take the
form
of grains of activated charcoal, and especially fine-pored spheroidal charcoal
with
diameters of 0,3 to 1 mm and an internal surface area of more than 500 mz/g,
which
are attached to a very air-permeable textile substrate by means of an adhesive
applied discontinuously or intermittently_ The substrate can be laminated to
the
inside of the particle filter layer and additionally covered with a light
fabric or can
even be worn as an undergarment beneath the particle filter layer. A
protective
material of this kind is described in the German utility model G 89 16 25~_
The grains of activated charcoal c:an also be fixed directly to the inside of
the
particle filter in accordance with the process of DE G 33 04 349 by means of
an
adhesive applied discontinuously.
A different means of Forming the adsorption layer of activated charcoal, which
is
l~~nown per sc, is the process of "charcoal printing", which is known from DE
C 32
11 322, in which the air-permeable substrate is printed with a paste
consisting of
tine activated charcoal and a binder. 'This is also a good possibility for
clean room
suits which are only used as disposable suits and which consist, for example,
of
calendered thin polyoleFn non-woven fabrica and whiclx can then be printed on
the
islside, in accordance with the invention, with a large number of small heaps
of
charcoal between 0,2 and 0,8 mm in diameter.
Finally, the layer of activated charcoal on the inside of the clean room suit
with the
particle filter layer with good breathing properties can also consist of a
th.i n, and in
partiwlar reticulated, foam impregnated with a suspension of activated
charcoal
powder and binder and coated with the powdered charcoal in this way.
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The ideal solution is to have an adsorption layer comprising an activated
charcoal
non-woven fabric or area-measured textile material of activated charcoal
covered ora
both sides with fabric, since these materials have a huge external surface
area,
where the adsorption bebins, compared to granular activated charcoal, so that
the
probability of a collision with the charcoal is extremely great. In the case
of area-
measured textile materials of activated charcoal, the greater part of the pore
system
consists of very narrow micro-pores with diameters of less than 2 nm, and in
particular less than 1 nm. Since no great capacity is required, an internal
BET
surface area of less than 1200 m2/g is sufFcient, especially since the
mechanical
load-bearing capacity declines as the activation increases.
A product -whicl-t .is particularly suitable for the presem invemion is Activ-
ated Char-
coal Cloth (ACC) from Charcoal Cloth Ltd. (sec Filtration and Separation 1986,
pp.
I C~~ ~65~.
While the layer of activated charcoal in the various designs is very effective
for the
majority of volatile products released by human beings, ammonia is
nevertheless
not adsorbed particularly well. In a preferred embodiment of the invention, it
is
therefore provided for the particle Flter layer of the clean room suit with,
good
breathing properties to be impregnated with a physiologically compatible, non-
volatile organic acid. The same can also be done with the activated charcoal
adsorption layer of the clean room suit.
Suitable for the reaction with the ammonia and, where applicable, with lower
amines are organic acids with high boiling paints or those which are solid at
room
temperature with a pH of less than 5, and especially less than ~, and which
are
physiologically harmless if they should come into contact with the skin. These
acids
need tv be capable of binding ammonia in the form of the corresponding
ammonium salts. If the whole clean room suit or only the particle filter layer
impregnated with; the acids is washed for the purpose of regeneration, these
ammonium salts are easily washed out, and the clean room suit can subsequently
be impregnated with the acid again.
Examples of suitable acids are citric acid, tartaric acid, malic acid, lactic
acid,
mandelic acid, phthalic acid, isophthalie acid, terephthalic acid, suberic
acid,
malonic acid, ascorbic acid, aspartic acid, benzoic acid and glutamic acid.
Citric acid
3S is preferred, and this aspect of the invention is also explained below with
reference
to citric acid by way of example.
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It has been found that aetiv~ated charcoal impregnated with citric acid is
particularly
suitable for adsorbing ammonia and volatile amines. 1t can be presumed that
moisture adsorbed in the process plays an important part. The advantages of
citric
acid impregnation are. it is unproblematic when worn close to the skin,
Fabrics not
damaged, and there is the possibility of re-impregnation during the rinsing
step after
washing. For the initial impregnation or - in the case of reusable clean room
suits -
for the re-impregnation after washing, it is advisable to use a 0,5 to 20, and
especially 1 to I0, per cent by weight solution of citric acid. 'The same
applies,
mutatis mutandis, to the other organic acids mentioned.
It was not found that any c.itrie acid adhering to the outer particle filter
layer
became detached in the form of ultra-fine crystals which contaminated the
ultra-
clean air. ~otheravise, only the adsorption layer should be impregnated, which
would in turn make it necessary to have a two-part clean room suit, with the
particle and adsorption filter layer separated.
Citric acid impregnation of the particle filter Iayer is sufficient to
prevent, more or
less completely, the emission of ammonia and amines escaping from the skin.
This
finding makes it possible to design a two-part clean room suit consisting, on
the
one hand, of a polyester suit impregnated with citric acid to prevent Lhe
emission c.>F
particles and, on the other hand, with the <non-impregnated) adsorption layer
beneath it to bind the other vohZtile body emissions. Since impregnating the
activated charcoal tends in general to impair the adsorptive properties, this
alternative should be regarded as a positive feature. As it can be assumed
that the
particle filter layer worn on the outside will be washed more frequently than
the
adsorption layer and that only the particle filter layer needs to be re-
impregnated,
the separation into a particle and ammonia filter layer and an adsorption
filter layer
makes sense.
The man skilled in the art has various possible methods at his disposal for
covering
the activated charcoal layer on both sides. Merely by way of example, one
might
mention the possibility of providing the fabric cover with melt adhesive
points
printed on and then performing thermal lamination. It is also possible to use
the
particle filter layer itself as the cover For the activated charcoal layer. In
this case,
however, the advantages of separate washing are lost.
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Finally, it should also be mentioned that attention muse be paid, when washing
the
adsorption layer, to ensuring that the pore structure is not excessively
burdened by
surfactants. The purpose of washing is not so much to achieve a visual effect
as to
remove body grease, sweat components and other body discharges. In view of the
large range of detergents and surfactants available, the man skilled in the
art needs
to make his own Choice by means of experiments. As far as possible, pure
surfactants, such as lauryl sulphate, should be used. Good results were
obtained
with mixtures of ethanol and water.
A polyester-based fabric suitable for clean room suits (mass per unit area
approx.
100 g/m~ was printed internuttcntly, in accordance with DE C 33 04 349, with
an
adhesive substance based on Impranil I-IS 62 and imprafix HISC, both products
available from Bayer AG, using a 25-mesh template (application weight approx.
25 glmz, coverage approx. 30 %). A fine-pored, very abrasion-resistant
spheroidal
charcoal on the basis of pitch, with an internal surface area of approx. 1,200
rrr2/g
and a diameter of 0,3 to 0,5 mm, was scattered over the sticky heaps and
subsequently cured, The application weight of the spheroidal charcoal was
170 g/m2. The spheroidal charcoal is described in US A 1 468 y82, inter alia.
In the same way, a spheroidal charcoal was used which was manufactured in
conformity with DE 43 28 21.9 AX and had micro-pore diameters of around 0,5
nm.
The internal surface area ought to be at least 500 n'rz/g, preferably at least
900 nzZ/g,
while sphere diameters of 0,3 to 1,0 mm arc convenient.
Glean room suits were produced from the material charged with activated
charcoal
and compared In practice with normal clean room suits made from the same
material but not charged with activated charcoal- ~tll~ereas in the latter
ease, an
emission of alkaline (NHS and acidic volatile substances produced by the
wearer
was Found-in the ppb range, these substances were absent when tl-rc: suit
according
to tie invention was worn. 1'he experiment was conducted ever a period of
4 weeks, with the suits being washed a total of 4 times with lauryl sulphate
added.
The suit according to the invention was subsequently impregnated with a 1 %
citric
acid solution. In this suit, no emissions of NH3 at alI could be found any
longer. The
suit was washed, re-impregnated with 1 % citric acid during the rinsing stage
and
dried. Here too, no measurable emission of any kind whatsoever could be found.
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In addition, a clean room suit was taitored which, beneath the particle filter
layer,
contained an adsorption layer of a 40 g/mz activated charcoal non-woven
material
covered by a 30 g/m2 polyester knitted material. When worn experimentally, an
NH3
emission was detected which it was no longer possible to measure in practice,
and
which was completely suppressed after impre~mation with. citric acid as
described in
the previous example.
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