Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
STABILIZED AZEOTROPE-LIKE COMPOSITIONS
OF 1,1-DICHLORO-2,2,2-TRIFLUOROETHANE AND
1.1-DICHLORO-1-FLUOROETHANE
In pending patent application Serial No.
07/297,366, filed February 15, 1989, constant-boiling,
azeotrope-like compositions comprising
1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and
1, l-di chloro-1-fluoroethane (HCFC-141b) with methanol and
ethanol were disclosed as effective cleaning solvent
compositions, particularly with regard to the cleaning of
electronic circuit boards.
As described in the aforementioned application,
current industrial processes for soldering electronic
components to circuit boards involve coating the entire
circuit board with a flux composition and, thereafter,
passing the coated side of the board over preheaters and
then through molten solder. The flux composition cleans
the conductive metal parts and promotes solder adhesion.
; Commonly used fluxes consist, for the most part, of rosin
used alone or rosin with activating additives, such as
~- 25 amine hydrochlorides or oxalic acid derivatives.
~ ; ~ After soldering, which thermally degrades part of
;~ ~ the rosin, flux and flux residues are often removed from
the board with an organic solvent composition. Since
requirements for the removal of contaminants from circuit
boards are very stringent, most current industrial circuit
board cleaning processes involve the use of vapor defluxing
techniques. In the conventional operation of a vapor
defluxer, the soldered circuit board is passed through a
sump of boiling organic solvent, which removes the bulk of
the rosin---including thermally degraded rosin ---and
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thereafter, through a sump which contains freshly distilled
solvent and finally through solvent vapor above the boiling
sump, which condenses on the circuit board to provide a ,
final rinse with a clean, distilled solvent. Additionally,
the circuit board could also be sprayed with distilled
solvent, if required, before the final rinse.
While constant-boiling, azeotrope-like
compositions of 1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, as described in pending U.S.
Patent Application Serial No. 07/335,940, filed April 10,
1989, are excellent solvent systems for cleaning circuit
boards, for practical industrial use these solvent systems,
as is the case with many solvent systems, should be
stabilized against compositional changes during both use
and long term storage. Changes, such as oxidation,
polymerization, component interactions, and the like, may
generate products which adversely affect the circuit boards
being cleaned or the solvent compositions themselves.
It is therefore an object of the present invention
to provide constant-boiling, azeotrope-like compositions o~
1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, which are compositionally
stable dur~ng use and long term storage and which minimize
the formation of undesirable reaction products, which may
adversely affeGt electronic circuit board cleaning.
INVENTION SUMMARY
What has been discovered is a stabil~zed
azeotrope-like composition comprising an azeotrope-like
composition consisting of effective amounts of
1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, such azeotrope-like ~ ;
composition having a boil~ng point of about 31C at
substantially atmospheric pressure and a stabilizer package
comprising one or more of effective stabilizing amounts of
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nitromethane, diisopropylamine, 1,2-butylene oxide and/or
4-methoxyphenol. The stabilizer package may also comprise
effective stabilizing amounts of 1,2-propylene oxide and
nitromethane with or without one or more of
diisopropylamine, 1,2-butylene oxide and/or
4-methoxyphenol.
DETAILE~ DESCRIPTION OF THE INVENTION
By effective amounts is meant the amounts of
1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and
1,1-dichloro-1-fluoroethane (HCFC-141b), which, when
combined, result in the formation of the azeotrope-like
compositions of the instant invention as disclosed in U.S.
Patent Application Serial No. 07/335,940, filed April 10,
1989, incorporated herein by reference.
By effective stabilizing amounts is meant at least
some of one or more of nitromethane, diisopropylamine,
1,2-butylene oxide and/or 4-methoxyphenol. Also, by
effective stabilizing amounts is meant at least some of
1,2-propylene oxide and nitromethane with or without one or
more of diisopropylamine, 1,2-butylene oxide and/or
4-methoxyphenol. When the effective stabilizing amounts of
the disclosed compounds are combined with the
azeotrope-like composition of
1,1-dichloro-2,2,2-trifluoroethane (CHCl2CF3) and
1,1-dichloro-1-fluoroethane (CCl2FCH3), they allow such
azeotrope-like composition to be used and stored
commercially, i.e., provide commercially acceptable
appearance, corrosivity and resistance to loss of integrity
of the azeotrope-like composition.
Commercially available HCFC-123 may contain minor
amounts of 1,2-dichloro-1,1,2-trifluoroethane, e.g., as
much as about 20.0 weight percent
1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a) which
mixture is intended to be covered by the language
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1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) as well as
the inclusion of minor amounts of other materials which do
not significantly alter the azeotrope-like character of the,
cleaning solvent compositions.
The stabilized compositions of the present
invention may comprise admixtures of effective amounts of
1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, which compositions form
azeotrope-like compositions which may ccntain one or more
of about 0.1 to 0.8 weight percent of nitromethane, about
0.05 to 0.4 weight percent 1,2-propylene oxide, about 0.025
to 0.2 weight percent diisopropylamine and about 0.002 to
0.016 weight percent 4-methoxyphenol, said stabilizer
weight percentages are based on the weight of the
azeotrope-like compositions.
The present azeotrope-like compositions comprise
admixtures of 1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, more specifically, the present
compositions comprise mixtures of about 1-99 weight percent
1,1-dichloro-2,2,2-trifluoroethane and about 99-1 weight
percent 1,1-dichloro-1-fluoroethane.
The present azeotrope-like compositions may also :
comprise admixtures of about 20-80 weight percent
1,1-dichloro-2,2,2-trifluoroethane and about 80-20 weight
percent 1,1-dichloro-1-fluoroethane which boil at about
31C, at substantially atmospheric pressure.
It has been found that azeotrope-like compositions
:of the instant invention which contain a minimum of about
35 weight percent 1,1-dichloro-2,2,2-trifluoroethane are
30 nonflammable, as determined by a flammability test similar :
to ASTM E9I8.
A preferred azeotrope-like composition of the
instant invention has the following composition: about 65
weight percent 1,1-dichloro-2,2,2-trifluoroethane and about
35 weight percent 1,1-dichloro-1-fluoroethane. The
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azeotrope-like composition boils at about 31C, at
substantially atmospheric pressure.
The above azeotrope-like compositions are
effective solvents for cleaning electronic circuit boards.
Such solvent compositions are characterized by desirable
properties of relatively low boiling points,
non-flammability, relatively low toxicity and high solvency
for flux and flux residues. The components also permit
easy recovery and reuse without loss of their desirable
characteristics because of their azeotrope-like natures and
relatively low boiling points.
While the azeotrope-like compositions of
1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane perform well in printed circuit
board vapor defluxing-degreasing applications, it is
recognized that in order to take practical advantage of the
unique properties of these solvent compositions, certain
other desirable properties should be imparted to the
compositions, particularly, when the solvent systems are to
be used commercially.
One such desirable property is storage stability.
It is recognized that any material which is to be used
commercially must usually be inventoried. Such storage can
be for short intervals or for longer periods of months or
even years. Thus, for solvent compositions to be useful,
they should be stabilized against any significant
deleterious changes which may be brought about by
oxidation, polymerization or component interaction during
storage or use. Such changes may result in solvent
discoloration, the formation of undesirable by-products,
such as chloride ions and acids and/or the formation of
insoluble polymeric materials. It has been found that the
addition of an one or more of the compounds listed above,
in the aforementioned concentration ranges, perform as
effective storage stabilizers.
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Another commercially desirable characteristic to
be imparted to the solvent system is in-use stability. For
example, as described above, in the vapor defluxing
cleaning procedure, the circuit board to be cleaned is
first passed through a sump which contains boiling solvent~
for removal of bulk rosin, including thermally degraded
rosin. In this sump, the organic solvent is in contact
with a heat soùrce for a prolonged time. After passage
through the first sump, the circuit board is passed through
a sump which contains freshly distilled solvent and finally
through solvent vapor over a boiling sump, which provides a
- final rinse with a clean solvent which condenses on the
circuit board. Thus, in use, the organic solvent is
subjected to constant heating either in maintaining boiling
sumps or in vaporizing the solvent to provide freshly
distilled solvent or vapor to condense on the circuit board
for the final rinse. It is, therefore, highly desirable to
minimize any change in the solvent system which can
adversely affect the cleaning process or degrade the
integrity of the solvent. As mentioned earlier, such
changes may be due to oxidation, polymerization or
interaction between the solvent system components.
For example, one such interaction which should be
minimized is the interaction between the
hydrochlorofluorocarbons and metals, at elevated
temperatures, which may generate acidic by-products and
chloride ions. Reactive metals such as zinc and aluminum
as well as certain aluminum alloys, which are often used as
materials of circuit board construction, are particularly
susceptible to such interaction. It has been found that
nitromethane may be incorporated in the present solvent -~
system in concentrations of about 0.1 to 0.8 weight percent
and effectively retard this type of attack and, in
addition, prevent the formation of gel.
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The stabilizer package comprising
diisopropylamine, in a concentration of about 0.025 to 0.2
weight percent, 4-methoxyphenol, in a concentration of
about 0.002 to 0.016 weight percent, 1,2-propylene oxide,
in a concentration of about 0.05 to 0.4 weight percent, and
nitromethane, in a concentration of about 0.05 to 0.8
weight percent, enhances the stability of the present
solvent system. All weight percentages are based on the
weight of the of the 1,1-dichloro-2,2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane azeotrope-like composition.
As shown in the examples, the stabilizers when
used together in the present solvent system
(4-methoxyphenol, 1,2-propylene oxide, diisopropylamine and
nitromethane) appear to enhance the stability of the
solvent system. The ranges of acceptable performance for
stabilizer concentrations when used together is the same as
disclosed herein for when they are used separately. It
should be noted that stabilizer concentrations higher than
those specified can be employed; under normal
circumstances, however, higher stabilizer concentrations do
not generally provide additional inhibition advantage.
Other acceptable inhibitor-stabilizer systems,
which provide storage and use stability to the
aforedescribed azeotrope-like compositions are:
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Inhibitor~s) Wei~ht Percentaae~s)
Nitromethane 0.2
Diisopropylamine 0.05
1,2-Butylene oxide 0.05
4-Methoxyphenol 0.004
Nitromethane + 1,2-propylene oxide 0.2 + 0.05
Nitromethane + 1,2-butylene oxide 0.2 + 0.05
Nitromethane ~ 1,2-prspylene oxide +
diisopropylamine 0.2 + 0.05 ~ 0.05
Nitromethane + 1,2-butylene oxide ~ -
diisopropylamine 0.2 + 0.05 + 0.05
Nitromethane + 1,2-propylene oxide
1,2-butylene oxide 0.2 + 0.05 + 0.05 -
15 Nitromethane + 1,2-propylene oxide +
4-methoxyphenol 0.2 + 0.05 ~ 0.004
The preferred stabilized, constant-boiling,
azeotrope-like composition of the present invention
contains about 65 weight percent of
1,1-dichloro-2,2,2-trifluoroethane, about 35 weight percent
1,1-dichloro-1-fluoroethane, about 0.1 to 0.8 weight
percent of nitromethane, about 0.05 to 0.4 weight percent
1,2-propylene oxide, and about 0.025 to 0.2 weight percent
percent diisopropylamine and about 0.002 to 0.016 weight
percent 4-methoxyphenol. -
A more preferred, stabilized, azeotrope-like
composition of the present invention contains about 65
weight percent 1,1-dichloro-2,2,2-trifluoroethane, and
about 35 weight percent 1,1-dichloro-1-fluoroethane, about
0.2 weight percent nitromethane, about 0.05 weight percent
1,2-propylene oxide, about 0.05 weight percent
diisopropylamine and about 0.004 weight percent
4-methoxyphenol.
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The present invention thus provides stabilized,
azeotrope-like compositions of
1,1-dichloro-2/2,2-trifluoroethane and
1,1-dichloro-1-fluoroethane, which can be stored for long
periods periods of time, which will undergo little or no
change during either prolonged storage or commercial use
and which minimize both aluminum corrosion and gel
formation.
The methods of combining the inhibitors with the
azeotrope-like compositions of this invention are
well-known in the art. They can be prepared by any
convenient method including mixing or combining the desired
component amounts in suitable containers. A preferred
method is to weigh the desired component amounts and
thereafter combine them in an appropriate container.
The aforestated stabilized, azeotrope-like
compositions have low ozone depletion potentials and are
expected to decompose almost completely prior to reaching
the stratosphere.
The stabilized, azeotrope-like compositions of the
present invention permit easy recovery and reuse of the
solvent from vapor defluxing and degreasing operations
because of their azeotrope-like natures. As an example,
the azeotrope-like mixture of this invention can be used in
cleaning processes such as described in U.S. Patent No.
3,881,949, which is incorporated herein by reference.
EX~MPLES
Comparative seven day stability tests of solvent
system combinations of about 65 weight percent
dichloro-2,2,2-trifluoroethane and about 35 weight
percent l,l-dichloro-1-fluoroethane with various inhibitor
combinations were carried out by refluxing 150 ml of the
solvent combination in a series of 500 ml Pyrex flasks
using 90 percent, at 25C, water-saturated solvents. The
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flasks were connected to water-cooled condensers, on top of
which were affixed Drierite~ desiccant tubes to exclude
atmospheric moisture from the test systems. Additionally, ,
stainless steel (SS-304) specimens were located at the
refluxing solvent vapor/air interfaces in the condensers
and coupled stainless steel (SS-304)/aluminum alloy
(AL-7075) specimens were located in the boiling liquids.
The 1,1-dichloro-1-fluoroethane used in these
tests contained about 500 parts per million by weight of
vinylidene chloride, an impurity normally found in the
crude product; however, no vinylidene chloride was used in -
test number 1 below. The solvent inhibitor systems tested
are described in the Table.
The following tests were performed on each
individual test system subsequent to test exposures~
1. Chloride ion concentration was measured at
the end of the test by extracting the solvent with an equal
volume of deionized water and analyzing the water for
chloride ion concentration. The original, uninhibited,
solvent contained less than 0.2 ppm chloride ion. Chloride
ion increase generally represents loss of solvent system
component stability. Stability loss is generally
accompanied by increased acidity.
2. The pH changes of the solvent (final minus
original) were determined by extracting the acid from the
solvents with equal volumes of pH neutral (pH = 7),
deionized water and checking the pH of the water.
3. Corrosion rates were measured by rubbing the
metal surfaces with ink and pencil erasers, brushing the
surfaces, rinsing the specimens sequentially with
1,1,2-trichlorotrifluoroethane, deionized water and
acetone, drying for 24 hours over Drierite~ desiccant and
weighing the sample to 0.0001 gram. Metal specimen weight
loss is expressed in mils/year. An aluminum (Al-7075)
corrosion rate of 4 mils/year is considered acceptable.
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4. Appearance of the solvent and the aluminum
specimens (Al-7075) were rated visually using the following
rating criteria:
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APPEARANCES
RATINGS ACCEPTABLE LIQUID ALUMINUM-7075 (*)
0 Yes N0 CHANGE OR TRACE CHANGE
Clear, colorless. Bright and shiny.
No gel drops.
1 Yes VERY. VERY SLIGHT BUT ACCEPTABLE CHANGES
~ery slight, clear, Very, very slight
colorless gel drops corrosion on ca.
formed. 1% of surface.
2 Borderline VERY SLlGHT BORDERLINE CHANGES NOTED.
MAY OR~Y~Y NOT BE ACCEPTABLE FOR
INTENDED END USE.
Clear. Slight Very slight
gel drops corrosion
formed or black spot
deposits on ca.
10-20% of surface.
3 No SLIGHT. UNACCEPTABLE CHANGES NOTED
Moderate amount of Slight spotting
gel drops in the and corrosion on
liquid. ca. 50X of surface.
; 4 No Severe amount of
gel in the liquid.
(*) All reactivity occurred on the Al-7075 surface
which interfaced with the SS-304 in the liquid. The SS-304
specimens were essentially unchanged throughout the tests
except in test 13.
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_ TABLE
075
CORROS. APPEARANCE
TEST STABILIZERS SOLVENT RATE, RATINGS
NO. WT. % ~ ~H Cl- MILS/YR LIOU~D(X) Al-7~75(~)
1NONE O 0.0 0.8 0.9 0
2NONE O 0.5 0~9 0.9 4 0+
3 NM 0.2 0.1 0.7 0.3 0 0+
4DIPA 0.05 0.1 1.1 1.0 0
1,2-P0 0.05 -0.4 0.5 0.8 4
6 1,2-B0 0.05 0.1 0.4 1.1 0 0
7 4-MP 0.004 0.2 0.4 0.8 0 0+
0 8 NM 0.2 0.2 0.4 0.9 0 0+
1 1,2-P0 0 05
9 NM 0 2 0.0 0.3 1.2 0
1,2-B0 0.05
NM 0.2 0.0 0.8 0.9 0
1,2-P0 0.05
DIPA 0.05
11 NM 0.2 -0.1 0.7 1.1 0 0
1,2-B0 0.05
DIPA 0.05
12 NM 0.2 0.0 0.8 0.9 0 0
1,2-P0 0.05
DIPA 0.05
4-MP O 004
13 DIPA 0 05 0.0 2.5 2.5 0 0
1,2-P0 0.05 (1)*
*On SS-304 surface in air space dbove condensing vapor.
(X) All ratings are based on gel formation in the
liquid phase.
25(Y) Relation of metal ratings to appearance changes.
All ratings are based on the appearance of the Al-7075
surface in the liquid phase except as noted.
AL-7075 ~ 1~ very, very, sl~ght corroslon on about 1%
of surface
30SS-304 z 1 - very, very slight haze on about 20% of the
metal surface.
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The abbreviations used in the Table are:
1,2-B0 = 1,2-butylene oxide 1,2-P0 = 1,2-propylene oxide
NM = nitromethane 4-M ~ 4-methoxyphenol
DIPA = diisopropylamine
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