The invention provides a desiccant composition comprising an alcohol
and a fluorinated aliphatic hydrocarbon compound of the general
formula wherein m and n each is a positive integer satisfying the
relations: 4.ltoreq.n.ltoreq.6 and 2n-2.ltoreq.m<2n+2 and a
method of desiccating an article with said desiccant composition.
2. The desiccating method of claim 1 which comprises dipping said
article in said desiccant
3. The desiccating method of claim 1 which comprises spraying said
article with said desiccant composition at a temperature of about
40.degree. C. to the boiling temperature of the composition.
4. The desiccating method of claim 1 which comprises contacting
said article with the vapor of said desiccant composition.
5. The desiccating method of claim 1 which comprises dipping said
article in said desiccant composition maintained at a temperature
between 40.degree. C. and the boiling temperature of the composition
and, then, contacting the same article with the vapor of said desiccant
6. The desiccating method of claim 1 which comprises spraying said
article with said desiccant composition at a temperature of about
40.degree. C. to the boiling temperature of the composition and,
then, contacting the same article with the vapor of said desiccant
7. The desiccating method of claim 1 wherein said alcohol is present
in an amount of from 3 to 15% by weight of the composition.
The present invention relates to a desiccant composition and a
method of desiccating articles with the desiccant composition.
Throughout this specification and appended claims, % stands for
percent by weight and the term `desiccation`, inclusive of its derivative
terms, means removal of surface water from any article and is synonymous
with drying and dehydration.
Wafers for the fabrication of semiconductor devices such as IC
and LSI, plated articles, optical lenses, photolithographic masks,
liquid display device components, electronic parts and various other
parts made of metal, plastic, glass or/and ceramic materials (all
referred to collectively as an article) are rinsed and, then, dehydrated
in various intermediate stages of fabrication or at the final stage
in the production process. Typically an article is rinsed with an
aqueous detergent solution and demineralized water and, then, dehydrated.
The residual water on the surface of an article can be a source
of stain or rust and, as such, is an important parameter determinant
of the field performance of the article.
For the effective dehydration of an article, it is common practice
to use an alcohol, e.g. isopropyl alcohol or ethanol, a chlorofluorocarbon
(CFC), e.g. trichlorotrifluoromethane, or a composition comprising
such a chlorofluorocarbon (CFC), an alcohol and a surfactant.
However, isopropyl alcohol and ethanol are not satisfactory from
workability points of view because they are highly inflammable to
cause hazards. CFCs, mentioned above, destroy the ozone layer of
the stratosphere so that, as frequently pointed out, they may exert
serious adverse effects on the ecology of the earth, involving humans
as well. Therefore, as far as the CFCs with a high risk of destroying
the ozonosphere are concerned, both use and production have been
restricted by international agreements.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel desiccant
composition and a method of desiccating an article with the desiccant
The inventor of the present invention explored this realm of technology
against the foregoing background and found that a composition comprising
a defined fluorinated aliphatic hydrocarbon compound and a defined
alcohol exhibits excellent performance characteristics in the elimination
of water from the surface of an article.
Therefore, the present invention provides
a desiccant composition comprising an alcohol containing 1 to 4
carbon atoms and a fluorinated aliphatic hydrocarbon compound of
the general formula
wherein m and n each represents a positive integer satisfying the
relations: 4.ltoreq.n.ltoreq.6 and 2n-2.ltoreq.m<2n+2 and
a method of desiccating an article which comprises contacting the
article with the above desiccant composition to thereby remove surface
water from the article.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing a typical desiccating device
for use in practicing the method of the invention. As illustrated,
a first dip tank is indicated at 1 a second dip tank at 2 a water
separator at 3 a vapor zone at 4 a heater unit at 5 a vapor tank
at 6 a cooling pipe at 7 and a condensate tank at 8.
The alcohol containing 1 to 4 carbon atoms, which is used in admixture
with the above-mentioned fluorinated aliphatic hydrocarbon compound,
includes methanol, ethanol, i-propanol, n-propanol, i-butanol, sec-butanol
and tert-butanol, among others. In addition, such fluorinated alcohols
as 222-trifluoroethanol, 2233-tetrafluoropropanol, 22333-pentafluoropropanol,
etc. can also be employed. Among these alcohols, methanol, ethanol,
i-propanol, n-propanol and pentafluoropropanol are preferred, and
methanol, ethanol, i-propanol and n-propanol are more preferred.
These alcohols can be used alone or as a mixture of two or more
The preferred desiccant composition of the invention meets the
(1) To be hardly inflammable or nonflammable to insure working
(2) Boiling at a temperature within the range of 40.degree. to
80.degree. C. This is preferred from performance points of view;
(3) Water solubility being within the range of 0.1 to 3%, preferably
0.1 to 2%. If the solubility is less than 0.1%, the efficiency of
dehydration will be insufficient. Conversely if the solubility exceeds
3%, the dissolution of water-soluble contaminants will increase
to leave stains after removal of water.
To meet the above criteria, the proportions of a fluorinated aliphatic
hydrocarbon compound to alcohol, which are of course dependent on
the water solubilities of the two components employed, are generally
such that the composition contains about 25% or less, preferably
3 to 15%, of the alcohol and is more preferably such that the two
components form an azeotropic mixture or an azeotrope-like mixture
(a mixture which is not an azeotropic mixture in the strict sense
but a mixture showing a constant boiling temperature and a constant
composition). If the proportion of the alcohol exceeds about 25%,
the amount of water that can be dissolved in the composition will
exceed about 3% and this means that the dissolution of water-soluble
contaminants is assisted to increase the incidence of stain and,
at the same time, the composition will become easily inflammable.
Conversely, if the proportion of the alcohol is less than 3%, the
solubility of water in the desiccant composition will not be more
than 0.1%, with the result that the affinity of the composition
for the surface water of an article is decreased to compromise the
dehydrating performance of the composition.
Where necessary, the desiccant composition of the invention may
contain any known additives that are commonly incorporated in compositions
of this type for various purposes. Among such additives are auxiliary
dehydrating agents such as surfactants, stabilizers, hydrogen-containing
chlorofluorinated hydrocarbons with low potentials to destroy the
ozonosphere, and hydro-carbons which do not destroy the ozonosphere.
The specific procedure of removing surface water from an article
with the above desiccant composition comprises contacting the article
with the desiccant composition. Such contact can be achieved by
various techniques, e.g. by dipping the article in the desiccant
composition, by spraying the article with the desiccant composition,
by contacting the article with the vapor of the desiccant composition,
by dipping the article in the desiccant composition and then contacting
it with the vapor of the composition, and by spraying the article
with the desiccant composition and further contacting it with the
vapor of the composition. It is generally recommended that the desiccant
composition of the invention should be used at an elevated temperature
of about 40.degree. C. to its boiling temperature and preferably
about 40.degree. C. to a temperature about 5.degree. C. lower than
the boiling temperature. The dehydrating power of the composition
is decreased at temperatures below 40.degree. C. For improving the
dehydrating effect of the procedure comprising contacting the article
bearing surface water with the desiccant composition, certain adjunct
means such as tumbling, ultrasonication, etc. can be employed.
For the removal of surface water from an article with the desiccant
composition of the invention, the same equipment and the same procedure
can be employed as those used for the conventional chlorofluorocarbon
type or other desiccant composition. While there is, thus, no limitation
on the equipment and procedure, the system illustrated by way of
example in FIG. 1 may be employed with advantage.
Referring to FIG. 1 which is a schematic sectional view showing
an exemplary desiccating device for use in the desiccating method
of the invention, an article bearing surface water (not shown) is
first dipped in the desiccant composition of the invention in a
first dip tank 1 equipped with a heater unit, where a substitution
of the composition for water takes place. The water thus leaving
the article floats up on the surface of the desiccant composition
due to a difference in specific gravity.
When the article demands a sophisticated degree of dehydration,
the article which has been dipped in the first dip tank 1 is transferred
to a second dip tank 2 provided with heater means, where it is dipped
in the desiccant composition of the invention again, whereby the
desired high degree of dehydration can be accomplished. The desiccant
composition overflowing the first dip tank 1 and having been substantially
deprived of water by a water separator 3 and the desiccant composition
reclaimed by condensation of the ascending vapor of the composition
in a vapor tank 6 and substantially capable of dehydration are recycled
to said second dip tank 2.
When a still higher degree of dehydration is necessary, the article
which has passed through a dipping process in the second dip tank
2 is transferred to a vapor zone 4 disposed overhead said vapor
tank 6 equipped with heater unit 5. In this zone 4 the article is
contacted with the vapor of the desiccant composition for further
removal of water. Disposed above the vapor zone 4 is a cooling pipe
7 where the ascending vapor of the desiccant composition is condensed
and the resulting condensate which is substantially capable of dehydration
drips down into a condensate tank 8.
There is no limitation of the type of said water separator 3 and
the process of dehydration involved but any device and procedure
that are capable of separating water can be employed. For example,
the method comprising cooling the desiccant composition to separate
water, the method for separating water from the desiccant composition
by distillation and the method of separating water by means of an
pervaporation membrane and the corresponding devices for practicing
these methods can be employed.
Shown in FIG. 1 is a dehydrating system in which an article is
dehydrated with an equipment having two dip tanks and one vapor
tank. However, any other systems can likewise be employed. For example,
according to the amount of surface water, the required degree of
dehydration, and the ease of separation of water from the article,
the equipment may simply comprise one dip tank or one vapor tank,
or one dip tank and one vapor tank. Dehydration by a spray device
is also feasible.
The desiccant composition of the invention will not cause environmental
problems such as destruction of the ozonosphere.
Furthermore, the desiccant composition of the invention is quite
outstanding in the elimination of surface water from an article.
Moreover, the desiccant composition is hardly inflammable or nonflammable
and, therefore, advantageous in handling.
Unlike i-propanel and ethanol, the desiccant composition can be
easily separated from water by reducing its temperature.
The desiccant composition has an ability to readily separate the
water contained therein so that the water can be easily removed
from the desiccant composition and the loss of the composition is
reduced. The desiccant composition is not liable to adversely affect
Furthermore, the desiccant composition consisting in an azeotropic
mixture or a an azeotrope-like mixture is easy in management. Needless
to say, repeated evaporation and condensation for recovery and reuse
does not substantially alter the proportions of the components.
The following example is intended to illustrate the invention in
A glass sheet (50 mm.times.50 mm.times.1 mm) previously cleaned
and bearing surface water was subjected to desiccation treatment
as shown in Table 1. The desiccant compositions used are shown in
The dehydrated glass sheet was then dipped in a predetermined quantity
of dry methanol and the gain in the water content of the methanol
after dipping was measured by the Karl-Fischer method. The amount
of water thus determined was expressed as "W.sub.1 ".
On the other hand, a glass sheet (50 mm.times.50 mm.times.1 mm)
cleaned and bearing surface water was not subjected to dehydration
treatment with the desiccant composition but directly to dipping
treatment in a predetermined quantity of dry methanol and the gain
in water content of the methanol after dipping was measured by the
Karl-Fischer method. The amount of water thus determined was expressed
Then, the percent dehydration H (%) was calculated by means of
the following equation.