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Description  |
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FIELD OF THE INVENTION
This invention relates to azeotropic compositions of
chlorofluorohydrocarbons with alcohols, ethers, or ketones. In a further
aspect, the invention relates to new solvent compositions. In another
aspect, the invention relates to methods of removing excess solder flux
from circuit boards.
BACKGROUND OF THE INVENTION
Azeotropic mixtures are liquid mixtures of two or more substances which
mixtures behave like single substances in that the vapor produced by
partial evaporation of the azeotropic liquid has the same composition as
does the liquid. Azeotropic compositions exhibit either a maximum or
minimum boiling point as compared with that of other but non-azeotropic
mixtures of the same substances or components.
Chlorofluorohydrocarbons have found usage for a variety of purposes. For
some solvent purposes, however, the chlorofluorohydrocarbons in themselves
have not exhibited adequate abilities. Particularly deficient have been
the chlorofluorohydrocarbons in dissolving excess solder flux from printed
circuits. Printed circuits are formed from a soft metal on a solid
non-conducting surface such as a reinforced phenolic resin. During the
manufacturing processes, the solid surface or support is coated with the
soft metal. The particular desired portion or configuration of metal is
coated with an acid-impervious protective coating, and the excess
unprotected metal is removed by an acid etching process.
The protective coating subsequently must be removed since solder joints
must ultimately be made onto the printed circuit. After the impervious
coating is removed, the circuits are coated with a rosin flux to permit
the joints to be soldered, and after soldering the rosin flux itself must
be removed. For removal of such coatings and fluxes, highly efficient
uniform composition solvents are desirable.
OBJECTS OF THE INVENTION
It is an object of this invention to provide novel azeotropic compositions.
It is a further purpose of this invention to provide new compositions of
matter useful for dissolving solder flux.
Other aspects, objects, and the several advantages of my invention will be
readily apparent to one skilled in the art to which the invention most
nearly pertains from the reading of my description and consideration of my
appended claims.
DESCRIPTION OF THE INVENTION
I have discovered useful azeotropes of 1,2-dichloro-1-fluoroethane with
each of the tetrahydrofuran, methyl ethyl ketone, methanol, ethanol,
isopropanol; and of 1,2-dichloro-1,2-difluoroethane with each of
tetrahydrofuran, methyl ethyl ketone, acetone, ethanol, and isopropanol.
An azeotrope may be defined as a constant boiling mixture which distills
without change in composition. Yet, at a differing pressure, the
composition indeed may vary, at least slightly, with the change in
distillation pressure, which also changes, at least slightly, the
distillation temperature. An azeotrope of A and B may represent a unique
type of relationship with a variable composition.
Thus, it should be possible to fingerprint the azeotrope, which may appear
under varying guises depending upon the conditions chosen, by any of
several criteria: The composition may be defined as an azeotrope of A and
B, since the very term azeotrope is at once definitive and limitative,
requiring that A and B indeed form this unique composition of matter which
is a constant boiling admixture. Or, the composition may be defined as a
particular azeotrope of a weight per cent relationship or mole per cent
relationship of A:B, but recognizing that such values point out only one
such relationship, whereas a series of relationships of A:B may exist for
the azeotrope, varied by influence of temperature and pressure. Or,
recognizing that broadly speaking an azeotrope of A:B actually represents
a series of relationships, the azeotropic series represented by A:B may in
effect be fingerprinted or characterized by defining the composition as an
azeotrope further characterized by a particular boiling point at a given
pressure, thus giving identifying characteristics without unduly limiting
the scope of the invention.
EXAMPLES
The following data are presented in order to assist in disclosing and
describing my invention, and, therefore, are not intended to be limitative
of the reasonable scope thereof.
The azeotropes of my invention were prepared by distilling mixtures of the
chlorofluorohydrocarbon and the other component until the overhead
temperature reached a constant value and the composition of the distillate
remained unchanged as verified by GLC analysis, thereby establishing the
existence of a minimum boiling azeotrope in each case.
The azeotropes were tested as solvents for solder flux on printed circuits.
EXAMPLE I
Azeotropic compositions were prepared and characterized by the properties
tabulated below.
TABLE I
__________________________________________________________________________
Composition
of Azeotrope
Azeotrope.sup.(a)
Chlorofluoro- Chlorofluoro-
B.P. (Pressure)
hydrocarbon
Alcohol
hydrocarbon/Alcohol
__________________________________________________________________________
56.degree.C
(742 mm)
141.sup.(b)
Methanol
(73.5/26.5 wt.%
(64.4/35.6 area %
65.degree.C
(749 mm)
141 Ethanol
81.2/18.8 wt.%
68.degree.C
(740 mm)
141 Isopropanol
81.3/16.6.sup.(d) wt.%
52.degree.C
(741 mm)
132.sup.(c)
Methanol
90.4/9.6 wt.%
56-57.degree.C
(748 mm)
132 Ethanol
94.9-95/5-5.1 wt.%
47.degree.C
(744 mm)
132 Isopropanol
98.7/1.3 wt.%
__________________________________________________________________________
.sup.(a) B.P. is the boiling point for the azeotropic composition at
substantially atmospheric in each case. The pressure showing was the
atmospheric barometric pressure taken from daily laboratory readings.
.sup.(b) 141 represents 1,2-dichloro-1-fluoroethane
.sup.(c) 132 represents 1,2-dichloro-1,2-difluoroethane
.sup.(d) Remaining 2.1 weight per cent not identified.
The azeotropes were tested as solvents for removal of solder flux from
commercial circuit boards, with results as shown below, along with
comparative runs:
TABLE II
______________________________________
Wt.% of Flux
Runs Solvent Systems Dissolved
______________________________________
1 141/methanol 97.0
2 141/ethanol 91.5
3 141/isopropanol 95.7
4 132/methanol 98.7
5 132/ethanol 94.0
6 132/isopropanol 98.0
7 113 .sup.(e) 28.4
8 1,1,1-trichloroethane 82.6
9 113/ethanol azeotrope 66.5
10 113/ethanol/acetone azeotrope
57.0
11 113/isopropanol azeotrope
69.5
12 141 51.3
13 132 74.2
______________________________________
.sup.(e) 113 represents 1,1,2-trichloro-1,2,2-trifluoroethane.
The data in Table II show that the novel azeotropic compositions of this
invention were more effective than several commercially available solvents
or of 141 or 132 alone in removing solder flux from printed circuit
boards.
EXAMPLE II
Azeotropic compositions were prepared and characterized by the properties
tabulated below:
TABLE III
______________________________________
Approximate
Weight Percent
Composition
of Azeotrope
Azeotrope Chlorofluoro- Chlorofluorohy-
B.P. (Pressure)
hydrocarbon Ether drocarbon/Ether
______________________________________
74.degree.C
(739 mm) 141 THF.sup.(f)
61.8/38.2
70.degree.C
(739 mm) 132 THF 45.9/54.1
______________________________________
.sup.(f) THF represents tetrahydrofuran.
The azeotropes were tested as solvents for removal of solder flux from
commercial circuit boards, with results as shown below, along with
comparative runs with other similar materials.
TABLE IV
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Runs Solvent Systems Wt.% of Flux Dissolved
______________________________________
14 141/THF 100
15 132/THF 100
16 1,1,1-Trichloroethane
82.6
17 113/ethanol azeotrope
66.5
18 141 51.3
19 132 74.2
______________________________________
The data in Table IV above show that the novel azeotropic compositions of
this invention were more effective in removing solder flux from printed
circuit boards than several commercially available solvents or 141 or 132
alone.
EXAMPLE III
Azeotropic compositions were prepared and characterized by the properties
tabulated below:
TABLE V
______________________________________
Approximate Wt.%
Composition
of Azeotrope
Azeotrope Chlorofluoro- Chlorofluorohy-
B.P. (Pressure) hydrocarbon
Ketone drocarbon/Ketone
______________________________________
80.degree.C
(atmospheric)
141 MEK.sup.(g)
54.1/45.9
80.degree.C
(743 mm) 132 MEK 39.8/60.2
66.degree.C
(736 mm) 132 Acetone
72.3/27.7
______________________________________
.sup.(g) MEK represents methyl ethyl ketone.
The azeotropes were tested as solvents for removal of excess solder flux
from commercial circuit boards, with the results as shown below, along
with comparative runs with other materials.
TABLE VI
______________________________________
Wt.% of
Runs Solvent Systems Flux Dissolved
______________________________________
20 141/MEK 100
21 132/MEK 98
22 1,1,1-Trichloroethane
82.6
23 113/ethanol azeotrope
66.5
24 113/ethanol/acetone azeotrope
57.0
25 141 51.3
26 132 74.2
______________________________________
The data in Table VI above show that the novel azeotropic compositions of
this invention were more effective in removing solder flux from printed
circuit boards than several commercially available solvents or 141 or 132
alone.
EXAMPLE IV
Flash point data were obtained for azeotropic compositions of my discovery:
TABLE VII
__________________________________________________________________________
Flash Point of
alcohol, ether
Run Azeotrope or ketone.sup.(i)
No. Azeotrope Flash Point, .degree.F.sup.(h)
Component Alone
__________________________________________________________________________
27 141/methanol
46.degree.F
51.degree.F
28 141/ethanol
75.degree.F.sup.(j)
56.degree.F
29 141/isopropanol
-- 53.degree.F
30 132/methanol
46.degree.F
51.degree.F
31 132/ethanol
75.degree.F.sup.(k)
56.degree.F
32 132/isopropanol
75.degree.F.sup.(l)
53.degree.F
33 141/THF 40.degree.F
6.degree.F
34 132/THF 36.degree.F
6.degree.F
35 141/MEK -- 23.degree.F
36 132/MEK 42.degree.F
23.degree.F
37 132/Acetone
45.degree.F
15.degree.F
__________________________________________________________________________
.sup.(h) Flash point determination in accordance with ASTM Method D-56.
.sup.(i) Flash point data obtained from Shell Chemical Co. Brochure
IC-71-18.
.sup.(j) Burned at 75.degree.F, not self-extinguishing.
.sup.(k) Did not burn at 75.degree.F; supported combustion of vapors and
air, but was self-extinguishing.
.sup.(l) Did not burn at 75.degree.F; did not support combustion, but was
self-extinguishing.
Data on two azeotropes were not obtained as indicated by the dashes above.
The flash point data in general show that the inventive azeotropes are
less hazardous in most cases than the alcohol, ether, or ketone
non-chlorofluorohydrocarbon component alone. The azeotropes in most cases
have higher flash points than does the second component alone.
It will be understood that the description given hereinabove of the use of
azeotropic compositions of my invention in cleaning or dissolving solder
flux is given for illustrative purposes only, that the invention itself is
not restricted to such specific embodiments, and that other techniques may
be employed. These unique azeotropic compositions will have applications
as solvents for greases, oils, waxes, aerosol propellants, and the like;
and in cleaning electric motors, compressors, photographic film, oxygen
storage tanks, lithographic plates, typewriters, precision instruments,
gauges, sound tape, cloth, clothing, and the like. It will be readily
apparent that the novel azeotropic compositions can be used for a variety
of purposes as indicated by my general description and suggestions.
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