Azeotrope-like compositions comprising of trichlorotrifluoroethane, methanol, nitromethane, acetone, and methyl acetate which are stable and have utility as vapor degreasing agents and as solvents in a variety of industrial cleaning applications including the defluxing of printed circuit boards.

FIELD OF THE INVENTION 
This invention relates to azeotrope-like mixtures of 
trichlorotrifluoroethane, methanol, nitromethane, acetone, and methyl 
acetate. These mixtures are useful as vapor degreasing agents and as 
solvents to remove rosin fluxes from printed circuit boards. 
BACKGROUND OF THE INVENTION 
Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained 
widespread use in recent years as effective, nontoxic, and nonflammable 
agents useful in degreasing applications. Trichlorotrifluoroethane in 
particular has been found to have satisfactory solvent power for greases, 
oils, waxes and the like. Trichlorotrifluoroethane also finds wide use in 
removing solder fluxes from printed wiring boards and printed wiring 
assemblies in the electronics industry. Such circuit boards normally 
consist of a glass fiber reinforced plate of electrically resistant 
plastic having electrical circuit traces on one or both sides thereof. The 
circuit traces are thin flat strips of conductive metal, usually copper, 
which serve to interconnect the electronic components attached to the 
printed wiring board. The electrical integrity of the contacts between the 
circuit traces and the components is assured by soldering. 
Current industrial processes of soldering circuit boards involve coating 
the entire circuit side of the board with a flux and thereafter passing 
the coated side of the board through molten solder. The flux cleans the 
conductive metal parts and promotes a reliable intermetallic bond between 
component leads and circuit traces and lands on the printed wiring board. 
The preferred fluxes consist, for the most part, of rosin used alone or 
with activating additives such as dimethylamine hydrochloride, 
trimethylamine hydrochloride, or an oxalic acid derivative. 
After soldering, which thermally degrades part of the rosin, the flux is 
removed from the board by means of an organic solvent. 
Trichlorotrifluoroethane, being non-polar, adequately cleans rosin fluxes; 
however, it does not easily remove polar contaminants such as the 
activating additives. 
To overcome this deficiency, trichlorotrifluoroethane has been mixed with 
polar components such as aliphatic alcohols or chlorocarbons such as 
methylene chloride. As example, U.S. Pat. No. 2,999,816 discloses the use 
of mixtures of 1,1,2-trichloro-1,2,2-trifluoroethane and methanol as 
defluxing solvents. 
The art has looked, in particular, towards azeotropic compositions 
including the desired fluorocarbon components such as 
trichlorotrifluoroethane and other components which contribute 
additionally desired characteristics, such as polar functionality, 
hydrogen bonding strength, increased solvency power, and stability. 
Azeotropic compositions are desired because they exhibit a minimum boiling 
point and do not fractionate upon boiling. This is desirable because in 
vapor degreasing equipment with which these solvents are employed, 
redistilled material is generated for final rinse-cleaning. Thus, the 
vapor degreasing system acts as a still. Unless the solvent composition 
exhibits a constant boiling point, i.e., is an azeotrope or is 
azeotrope-like, fractionation will occur and undesirable solvent 
distribution may act to upset the cleaning and safety of processing. 
Preferential evaporation of the more volatile components of the solvent 
mixtures, which would be the case if they were not azeotropic or 
azeotrope-like, would result in mixtures with changed compositions which 
may have less desirable properties, such as lower solvency for rosin 
fluxes, less inertness towards the electrical components soldered on the 
printed circuit board, and increased flammability. 
A number of trichlorotrifluoroethane based azeotrope compositions have been 
discovered which have been tested and in some cases employed as solvents 
for miscellaneous vapor degreasing and defluxing applications. For 
example, U.S. Pat. No. 3,573,213 discloses the azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane and nitromethane; U.S. Pat. No. 
2,999,816 discloses an azeotropic composition of 
1,1,2-trichloro-1,2,2-trifluoroethane and methanol; U.S. Pat. No. 
3,960,746 discloses azeotrope-like compositions of 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol, and nitromethane; U.S. 
Pat. No. 4,268,407 discloses an azeotropic composition comprising of 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol, methyl acetate, and 
nitromethane; U.S. Pat. No. 4,045,366 discloses the ternary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane, nitromethane and acetone, and 
Japanese Pat. No. 73-33878 discloses the ternary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol, and acetone. 
The art is continually seeking new fluorocarbon based azeotropic mixtures 
or azeotrope-like mixtures which offer alternatives for new and special 
applications for vapor degreasing and other cleaning applications. 
It is accordingly an object of this invention to provide novel 
azeotrope-like compositions based on 1,1,2-trichloro-1,2,2-trifluoroethane 
which have good solvency power and other desirable properties for vapor 
degreasing applications and for the removal of solder fluxes from printed 
circuit boards. 
Another object of the invention is to provide novel constant boiling or 
essentially constant boiling solvents which are liquid at room 
temperature, will not fractionate under conditions of use and also have 
the foregoing advantages. 
A further object is to provide azeotrope-like compositions which are 
relatively nontoxic and nonflammable both in the liquid phase and the 
vapor phase. These and other objects and features of the invention will 
become more evident from the description which follows. 
DESCRIPTION OF THE INVENTION 
In accordance with the invention, novel azeotrope-like compositions have 
been discovered comprising trichlorotrifluoroethane, methanol, 
nitromethane, acetone and methyl acetate, with 
1,1,2-trichloro-1,2,2-trifluoroethane being the trichlorotrifluoroethane 
of choice. 
In one embodiment of the invention, the azeotrope-like compositions 
comprise from about 83.5 to about 93.8 weight percent of 
1,1,2-trichloro-1,2,2-trifluoroethane, from about 5.1 to about 6.4 weight 
percent of methanol, from about 0.01 to about 1.0 weight percent of 
nitromethane, from about 0.3 to about 5.1 weight percent of acetone, and 
from about 0.1 to about 6.0 weight percent of methyl acetate. 
In a preferred embodiment of the invention, the azeotrope-like compositions 
comprise from about 90.5 to about 93.5 weight percent of 
1,1,2-trichloro-1,2,2-trifluoroethane, from about 5.7 to about 6.1 weight 
percent of methanol, from about 0.05 to about 0.2 weight percent of 
nitromethane, from about 0.4 to about 2.0 weight percent acetone, and from 
about 0.2 to about 1.7 weight percent methyl acetate. 
In the most preferred embodiment of the invention, the azeotrope-like 
compositions comprise from about 91.4 to about 93.5 weight percent of 
1,1,2-trichloro-1,2,2-trifluoroethane, from about 5.8 to about 6.0 weight 
percent of methanol, from about 0.03 to about 0.1 weight percent of 
nitromethane, from about 0.6 to about 1.2 weight percent acetone, and from 
about 0.4 to 1.2 weight percent methyl acetate. All of the above-described 
compositions possess constant or essentially constant boiling points of 
about 39.7.degree. C..+-.0.2.degree. C. at 760 mm Hg pressure. The precise 
azeotropic composition has not been determined but has been ascertained to 
be within the above ranges. 
All compositions within the above-indicated ranges, as well as certain 
compositions outside the indicated ranges, are azeotrope-like, as defined 
more particularly below. 
It has been found that these azeotrope-like compositions are stable, 
reasonably safe to use and that the preferred compositions of the 
invention are nonflammable (exhibit no flash point when tested by the Tag 
Open Cup test method--ASTM D1310-80) and exhibit excellent solvency power. 
These compositions have been found to be particularly effective when 
employed in conventional degreasing units for the dissolution of rosin 
fluxes and the cleaning of such fluxes from printed circuit boards. 
For the purpose of this discussion, by azeotrope-like composition is 
intended to mean that the composition behaves like a true azeotrope in 
terms of its constant boiling characteristics or tendency not to 
fractionate upon boiling or evaporation. Such composition may or may not 
be a true azeotrope. Thus, in such compositions, the composition of the 
vapor formed during boiling or evaporation is identical or substantially 
identical to the original liquid composition. Hence, during boiling or 
evaporation, the liquid composition, if it changes at all, changes only to 
a minimal or negligible extent. This is to be contrasted to 
non-azeotrope-like compositions in which during boiling or evaporation, 
the liquid composition changes to a substantial degree. 
As is well known in this art, another characteristic of azeotrope-like 
compositions is that there is a range of compositions containing the same 
components in varying proportions which are azeotrope-like. All such 
compositions are intended to be covered by the term azeotrope-like as used 
herein. As an example, it is well known that at differing pressures, the 
composition of a given azeotrope will vary at least slightly and changes 
in distillation pressures also change, at least slightly, the distillation 
temperatures. Thus, an azeotrope of A and B represents a unique type of 
relationship but with a variable composition depending on temperature 
and/or pressure. 
The 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, nitromethane, acetone, 
and methyl acetate components of the novel solvent azeotrope-like 
compositions of the invention are all commercially available. A suitable 
grade of 1,1,2-trichloro-1,2,2-trifluoroethane, for example, is sold by 
Allied Corporation under the trade name "GENESOLV.RTM. D".

EXAMPLES 1-5 
The azeotrope-like compositions of the invention were determined through 
the use of distillation techniques designed to provide higher 
rectification of the distillate than found in most vapor degreaser 
systems. For this purpose a five plate Oldershaw distillation column was 
used with a cold water condensed, timer controlled magnetically activated 
liquid dividing head. Typically, approximately 350 cc of liquid were 
charged to the distillation pot. The liquid was a mixture comprised of 
various combinations of 1,1,2-trichloro-1,2,2-trifluoroethane, methanol, 
nitromethane, acetone, and methyl acetate. The mixture was heated at total 
reflux for about one hour to ensure equilibration. For most of the runs, 
the distillate was obtained using a 5:1 reflux ratio which increases 
rectification and at a boil-up rate of 250-300 grams per hr. Approximately 
150 cc of product were distilled and 5 approximately equivalent sized 
overhead cuts were collected. The vapor temperature (of the distillate), 
pot temperature, and barometric pressure were monitored, A constant 
boiling fraction was collected and analyzed by gas chromatography to 
determine the weight percentages of its components. 
To normalize observed boiling points during different days to 760 mm of 
mercury pressure, the approximate normal boiling points of 
1,1,2-trichloro-1,2,2-trifluoroethane rich mixtures were estimated by 
applying a barometic correction factor of about 26 mm Hg/.degree.C., to 
the observed values. However, it is to be noted that this corrected 
boiling point is generally accurate up to .+-.0.4.degree. C. and serves 
only as a rough comparison of boiling points determined on different days. 
By the above-described method, it was discovered that a constant boiling 
mixture boiling at 39.7.degree..+-.0.2.degree. C. at 760 mm Hg was formed 
for compositions comprising about 90.5 to about 93.5 weight percent 
1,1,2-trichloro-1,2,2-trifluoroethane (FC-113), about 5.8 to about 5.9 
weight percent methanol (MeOH), about 0.01 to about 0.1 weight percent 
nitromethane, about 0.3 to about 2.0 weight percent acetone, and about 0.2 
to 1.7 weight percent methyl acetate. Supporting distillation data for the 
mixtures studied are shown in Table I. 
TABLE I 
______________________________________ 
Starting Material (wt. %) 
Methyl 
Example FC-113 MeOH MeN0.sub.2 
Acetone Acetate 
______________________________________ 
Distil- 
lation 
(5 plate) 
1 83.5 5.1 0.3 5.1 6.0 
2 91.5 6.0 0.1 1.2 1.2 
3 92.8 5.9 0.3 0.6 0.4 
4 92.5 5.8 0.2 0.9 0.6 
5 91.3 5.9 0.3 1.8 0.6 
______________________________________ 
Constant Boiling Fraction (wt. %) 
Methyl 
Example FC-113 MeoH MeNO.sub.2 
Acetone Acetate 
______________________________________ 
1 90.5 5.8 0.01 2.0 1.7 
2 93.2 5.8 0.03 0.6 0.4 
3 93.5 5.9 0.1 0.3 0.2 
4 93.5 5.8 0.06 0.5 0.2 
5 93.1 5.8 0.05 0.8 0.2 
______________________________________ 
Barometic 
Vapor Pressure Corrected Boiling 
Example Temp (.degree.C.) 
(mm Hg) Point to 760 mm Hg 
______________________________________ 
1 39.5 747.3 40.0 
2 39.2 747.8 39.7 
3 38.8 743.5 39.5 
4 39.0 743.5 39.7 
5 39.3 751.0 39.7 
39.7.degree. c. .+-. 0.2.degree. C. 
______________________________________ 
From the above examples, it is readily apparent that additional constant 
boiling or essentially constant boiling mixtures of the same components 
can readily be identified by anyone of ordinary skill in this art by the 
method described. No attempt was made to fully characterize and define the 
true azeotrope in the system comprising 
1,1,2-trichloro-1,2,2-trifluoroethane, methanol, nitromethane, acetone, 
and methyl acetate, nor the outer limits of its compositional ranges which 
are constant boiling or essentially constant boiling. As indicated, anyone 
of ordinary skill in the art can readily ascertain other constant boiling 
or essentially constant boiling mixtures, it being kept in mind that 
"constant boiling" or "essentially constant boiling" for the purposes of 
this invention means constant boiling or essentially constant boiling in 
the environment of a vapor degreaser system such as utilized in the art. 
All such mixtures in accordance with the invention which are constant 
boiling or essentially constant boiling are "azeotrope-like" within the 
meaning of this invention. 
EXAMPLE 6 
To illustrate the azeotrope-like nature of the mixtures of this invention 
under conditions of actual use in vapor phase degreasing operation, a 
vapor phase degreasing machine was charged with a preferred azeotrope-like 
mixture in accordance with the invention, comprising about 92.1 weight 
percent 1,1,2-trichloro-1,2,2-trifluoroethane (FC-113), about 5.8 weight 
percent methanol, about 0.1 weight percent nitromethane, about 1.2 weight 
percent acetone, and about 0.8 weight percent methyl acetate. The mixture 
was evaluated for its constant boiling or non-segregating characteristics. 
The vapor phase degreasing machine utilized was a small water-cooled, 
three-sump vapor phase degreaser with an attached still, which represents 
a type of system configuration comparable to machine types in the field 
today which would present the most rigorous test of solvent segregating 
behavior. Specifically, the degreaser employed to demonstrate the 
invention contains two overflowing rinse-sumps and a boil-sump. The sump 
adjacent to the boil-sump is referred to as the work sump. The boil-sump 
and the still are electrically heated, and each contains a low-level 
shut-off switch. Solvent vapors in both the degreaser and the still are 
condensed on water-cooled stainless-steel coils. The still is fed by 
gravity from the boil-sump. Condensate from the still is returned to the 
first rinse-sump, also by gravity. The capacity of the unit is 
approximately 3.5 gallons. This degreaser is very similar to Baron 
Blakeslee 2 LLV 3-sump degreasers with an attached still which are quite 
commonly used in commercial establishments. 
The solvent charge was brought to reflux and the compositions in the rinse 
sump containing the clear condensate from the still, the work sump 
containing the overflow from the rinse sump, the boil sump where the 
overflow from the work sump is brought to the mixture boiling point, and 
the still were determined with a Perkin Elmer Sigma 3 gas chromatograph. 
The temperature of the liquid in the boil sump and still was monitored 
with a thermocouple temperature sensing device accurate to .+-.0.2.degree. 
C. Refluxing was continued for 48 hours and sump compositions were 
monitored throughout this time. A mixture was considered constant boiling 
or non-segregating if the maximum concentration difference between sumps 
for any mixture component was .+-.2 sigma around the mean value. Sigma is 
a standard deviation unit and it is our experience from many observations 
of vapor degreaser performance that commercial "azeotrope-like" vapor 
phase degreasing solvents exhibit less than a .+-.2 sigma variation in 
composition with time and yet produce very satisfactory non-segregating 
cleaning behavior. 
If the mixture were not azeotrope-like, the high boiling components would 
very quickly concentrate in the still and be depleted in the rinse sump. 
This did not happen. Also, the concentration of each component in the 
sumps stayed well within .+-.2 sigma. These results indicate that the 
compositions of this invention will not segregate in any types of 
large-scale commercial vapor degreasers, thereby avoiding potential 
safety, performance, and handling problems. The preferred composition 
tested was also found not to have a flash point according to recommended 
procedures ASTM D 56-79 (Tag Closed Cup) and ASTM D 1310-80 (Tag Open 
Cup). 
EXAMPLE 7 
This example illustrates the use of the preferred azeotrope-like 
composition of the invention to clean (deflux) printed wiring boards and 
printed wiring assemblies. 
Three commercial rosin-based fluxes were used in this test. The fluxes were 
Alpha 611F (manufactured by Alpha Metals Inc.), Kester 1585-MIL 
(manufactured by Kester Solder), and Kenco 885 (manufactured by Kenco 
Industries Inc.). Predesigned printed wiring boards were fluxed in a 
Hollis 10-inch TDL wave solder machine. For Alpha 611F and Kester 1585-MIL 
fluxes, altogether twelve such test boards were prepared for defluxing. Of 
these, six contained some electronic components soldered to the board and 
the other six did not have any components on the board. For Kenco 885, 
eight boards were run; four with components and the other four without any 
components. 
The printed wiring assemblies with electronic components (used in this 
test) were high density boards each having a one sided surface area of 
18.97 square inches and containing two 36 pin dual in line packages (DIP), 
two 24 pin DIP's, five 16 pin DIP's and forty-one discrete components 
(resistors and capacitors). 
Prior to fluxing and soldering, all specimens were pre-cleaned following a 
vigorous pre-cleaning schedule to ensure very low levels of contamination 
before fluxing. In our experiments, the determination of the ionic 
contaminants on printed wiring board surfaces was made with a Kenco.RTM. 
Omega-meter, which is a standard industry test method for cleanliness. The 
Kenco Omega-meter employs a 75/25 volume % mixture of isopropyl 
alcohol/water to rinse the printed wiring boards, and the changes in 
specific resistivity of the solution are monitored up to 30 minutes. Three 
resistivity readings were taken for each run: (i) the initial resistivity 
at time zero, (ii) the resistivity after 15 minutes, and (iii) the 
resistivity at 30 minutes. The raw data were converted to micrograms (mg) 
per square inch of ionic contaminants, which is expressed in the standard 
way in terms of equivalents of sodium chloride (NaCl). 
Utilizing this technique, it was determined that all specimens used for our 
experiments would be precleaned to 0.05 mg or less of sodium chloride 
equivalent per square inch. 
Cleaning (defluxing) was performed in a Branson B400R two-sump vapor 
degreaser. The first sump is used as the working sump and holds boiling 
solvent, and the second sump is used as the rinse sump. Refrigerated 
cooling coils line the upper wall of the apparatus to maintain a vapor 
blanket. 
The cleaning schedule employed to demonstrate the usefulness of this 
invention was as follows: (i) two (2) minute exposure to the vapors over 
the boil sump, (ii) half a minute full immersion in the cold sump, (iii) 
half a minute re-exposure to the vapors over the boil sump. 
After defluxing two replicate analyses of boards with no components and two 
replicate analyses of boards with components were made in the Kenco 
Omega-meter. In the case of Alpha 611F and Kester 1585-MIL, each replicate 
analysis consisted of testing three boards together at the same time in 
the Omega meter test tank and in the case of Kenco 885 each replicate 
analysis consisted of testing two boards together at the same time in the 
Omega meter test tank. 
The azeotrope-like composition used to illustrate the usefulness of the 
invention to deflux printed wiring boards was comprised of about 90.7 
weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, about 5.7 weight 
percent of methanol, about 0.1 weight percent of nitromethane, about 1.9 
weight percent of acetone, and about 1.6 weight percent of methyl acetate. 
The cleaning performance of the azeotrope-like composition of this 
invention was also compared to that of two commercial defluxing solvents, 
Genesolv.RTM. DMS and Freon.RTM. TMS, where both commercial solvents 
consist of azeotrope-like compositions of trichlorotrifluoroethane, 
primary alcohol(s), and nitromethane. Genesolv.RTM. DMS is a blend of 92.0 
weight percent trichlorotrifluoroethane, 4.0 weight percent of methanol, 
2.0 weight percent of ethanol, 1.0 weight percent of isopropyl alcohol, 
and 1.0 weight percent of nitromethane. Freon.RTM. TMS is a blend of 94.05 
weight percent of trichlorotrifluoroethane, 5.7 weight percent of 
methanol, and 0.25 weight percent of nitromethane. The following table 
summarizes the residual ionic contamination left on fluxed printed circuit 
boards cleaned by the above azeotrope-like composition of this invention, 
Genesolv.RTM. DMS and Freon.RTM. TMS. 
TABLE II 
______________________________________ 
Performance Testing 
Residual Ionic Contamination 
(average of all runs) 
(mg NaCl/in.sup.2) 
Boards with Boards with 
Azeotrope-Like 
Solder No Components 
Components 
Solvent Flux 15 min. 30 min. 
15 min. 
30 min. 
______________________________________ 
This invention 
AlPHA 1.25 1.49 2.88 3.33 
611 
Genesolv .RTM. DMS 
ALPHA 1.68 2.07 3.79 4.40 
611 
Freon .RTM. TMS 
ALPHA 1.76 2.15 4.20 4.91 
611 
This invention 
Kester 
1585-MIL 3.50 4.16 7.00 8.06 
Genesolv .RTM. DMS 
Kester 
1585-MIL 5.96 6.92 12.38 14.29 
Freon .RTM. TMS 
Kester 
1585-MIL 8.64 9.75 19.38 21.37 
This invention 
Kenco 885 7.26 9.02 15.28 18.27 
Genesolv .RTM. DMS 
Kenco 885 14.95 17.61 30.93 35.95 
Freon .RTM. TMS 
Kenco 885 9.67 11.24 27.72 31.51 
______________________________________ 
As stated earlier, the industry has recognized that admixtures of 
trichlorotrifluoroethane with strongly hydrogen bonding components such as 
aliphatic alcohols, especially methanol, greatly enhance the ability of 
trichlorotrifluoroethane alone to remove the ionic activator components of 
rosin fluxes from printed wiring boards. Unexpectedly, we found that 
adding other solvents such as acetone and methyl acetate (which are not as 
strongly hydrogen bonding as methanol) to a mixture of 
trichlorotrifluoroethane, alcohol(s), and nitromethane produces an 
apparent synergistic effect which improves the cleaning ability of the 
blend. As the above example shows, particularly in the case of boards 
fluxed with highly activated rosin fluxes such as Kester 1585-MIL and 
Kenco 885, there is a statistically significant improvement in cleaning 
ability for the solvent of this invention over the two commercial 
defluxing solvents.