 |
Description  |
|
|
BACKGROUND OF THE INVENTION
As modern electronic circuit boards evolve toward increased circuit and
component densities, thorough board cleaning after soldering becomes a
more important criterion. Current industrial processes for soldering
electronic components to circuit boards involve coating the entire circuit
side of the board with flux and thereafter passing the flux-coated board
over preheaters and through molten solder. The flux cleans the conductive
metal parts and promotes solder fusion. Commonly used solder fluxes
generally consist of rosin, either used alone or with activating
additives, such as amine hydrochlorides or oxalic acid derivatives.
After soldering, which thermally degrades part of the rosin, the
flux-residues are often removed from the circuit boards with an organic
solvent. The requirements for such solvents are very stringent. Defluxing
solvents should have the following characteristics: a low boiling point,
be nonflammable, have low toxicity and have high solvency power, so that
flux and flux-residues can be removed without damaging the substrate being
cleaned.
While boiling point, flammability and solvent power characteristics can
often be adjusted by preparing solvent mixtures, these mixtures are often
unsatisfactory because they fractionate to an undesirable degree during
use. Such solvent mixtures also fractionate during solvent distillation,
which makes it virtually impossible to recover a solvent mixture with the
original composition.
On the other hand, azeotropic mixtures, with their constant boiling points
and constant compositions, have been found to be very useful for these
applications. Azeotropic mixtures exhibit either a maximum or minimum
boiling point and they do not fractionate on boiling. These
characteristics are also important when using solvent compositions to
remove solder fluxes and flux-residues from printed circuit boards.
Preferential evaporation of the more volatile solvent mixture components
would occur, if the mixtures were not azeotropic and would result in
mixtures with changed compositions, and with attendant less-desirable
solvency properties, such as lower rosin flux solvency and lower inertness
toward the electrical components being cleaned. The azeotropic character
is also desirable in vapor degreasing operations, where redistilled
solvent is generally employed for final rinse cleaning.
In summary, vapor defluxing and degreasing systems act as a still. Unless
the solvent composition exhibits a constant boiling point, i.e., is
azeotropic, fractionation will occur and undesirable solvent distributions
will result, which could detrimentally affect the safety and efficacy of
the cleaning operation.
A number of chlorofluorocarbon based azeotropic compositions have been
discovered and in some cases used as solvents for solder flux and
flux-residue removal from printed circuit boards and also for
miscellaneous degreasing applications. For example: U.S. Pat. No.
3,903,009 discloses the ternary azeotrope of
1,1,2-trichloro-l,2,2-trifluoroethane with ethanol and nitromethane; U.S.
Pat. No. 2,999,815 discloses the binary azeotrope of
1,1,2-trichloro-1,2,2-trifluoroethane and acetone; U.S. Pat. No. 299,817
discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane
and methylene chloride.
Such mixtures are also useful as buffing abrasive detergents, e.g., to
remove buffing abrasive compounds from polished surfaces such as metal, as
drying agents for jewelry or metal parts, as resist-developers in
conventional circuit manufacturing techniques employing chlorine-type
developing agents, and to strip photoresists (for example, with the
addition of a chlorohydrocarbon such as 1,1,1-trichloroethane or
trichloroethylene. The mixtures are further useful as refrigerants, heat
transfer media, foam expansion agents, aerosol propellants, solvents and
power cycle working fluids.
Close-cell polyurethane foams are widely used for insulation purposes in
building construction and in the manufacture of energy efficient
electrical appliances. In the construction industry, polyurethane
(polyisocyanurate) board stock is used in roofing and siding for its
insulation and load-carrying capabilities. Poured and sprayed polyurethane
foams are also used in construction. Sprayed polyurethane foams are widely
used for insulating large structures such as storage tanks, etc.
Pour-in-place polyurethane foams are used, for example, in appliances such
as refrigerators and freezers plus they are used in making refrigerated
trucks and railcars.
All of these various types of polyurethane foams require expansion agents
(blowing agents) for their manufacture. Insulating foams depend on the use
of halocarbon blowing agents, not only to foam the polymer, but primarily
for their low vapor thermal conductivity, a very important characteristic
for insulation value. Historically, polyurethane foams are made with
CFC-11 (trichlorofluoromethane) as the primary blowing agent.
A second important type of insulating foam is phenolic foam. These foams,
which have very attractive flammability characteristics, are generally
made with CFC-11 and CFC-113 (1,1,2-trichloro-l,2,2-trifluoroethane)
blowing agents.
A third type of insulating foam is thermoplastic foam, primarily
polystyrene foam. Polyolefin foams (polyethylene and polypropylene) are
widely used in packaging. These thermoplastic foams are generally made
with CFC-12.
Many smaller scale hermetically sealed, refrigeration systems, such as
those used in refrigerators or window and auto air conditioners, use
dichlorodifluoromethane (CFC-12) as the refrigerant. Larger scale
centrifugal refrigeration equipment, such as those used for industrial
scale cooling, e.g., commercial office buildings, generally employ
trichlorofluoromethane (CFC-11) OR 1,1,2-trichlorotrifluoroethane
(CFC-113) as the refrigerants of choice. Azeotropic mixtures, with their
constant boiling points and compositions have also been found to be very
useful as substitute refrigerants, for many of these applications.
Aerosol products have employed both individual halocarbons and halocarbon
blends as propellant vapor pressure attenuators, in aerosol systems.
Azeotropic mixtures, with their constant compositions and vapor pressures
would be very useful as solvents and propellants in aerosol systems.
Some of the chlorofluorocarbons which are currently used for cleaning and
other applications have been theoretically linked to depletion of the
earth's ozone layer. As early as the mid-1970's it was known that
introduction of hydrogen into the chemical structure of previously
fully-halogenated chlorofluorocarbons reduced the chemical stability of
these compounds. Hence, these now destabilized compounds would be expected
to degrade in the lower atmosphere and not reach the stratospheric ozone
layer intact. What is also needed, therefore, are substitute
chlorofluorocarbons which have low theoretical ozone depletion potential.
Unfortunately, as recognized in the art, it is not possible to predict the
formation of azeotropes. this fact obviously complicates the search for
new azeotropic compositons, which have application in the field.
Nevertheless, there is a constant effort in the art to discover new
azeotropic compositions, which have desirable solvency characteristics and
particularly greater versatilities in solvency power.
SUMMARY OF THE INVENTION
According to the present invention, azeotrope or azeotrope-like
compositions have been discovered comprising admixtures of effective
amounts of perfluoro-1,2-dimethylcyclobutane with 1,1-dichlorofluoroethane
or dichlorotrifluoroethane. The azeotropes are: an admixture of about
50-60 weight percent perfluoro-1,2-dimethylcyclobutane and about 40-50
weight percent 1,1-dichlorofluoroethane; and an admixture of about 23-33
weight percent perfluoro-1,2-dimethylcyclobutane and about 67-77 weight
percent dichlorotrifluoroethane.
The present invention provides azeotropic compositions which are well
suited for solvent cleaning applications.
The compositions of the invention can further be used as refrigerants with
minor modifications in existing refrigeration equipment. They are useful
in compression cycle applications including air conditioner and heat pump
systems for producing both cooling and heating. The new refrigerant
mixtures can be used in refrigeration applications such as described in
U.S. Pat. No. 4,482,465 to Gray.
The compositions of the instant invention comprises an admixture of
effective amounts of perfluoro-1,2-dimethylcyclobutane (C.sub.6 F.sub.12,
boiling point =44.6.degree. C.) and either 1,1-dichloro-1-fluoroethane
(CFCl.sub.2 --CH.sub.3, boiling point=32.degree. C.) or
dichlorotrifluoroethane (C.sub.2 HCl.sub.2 F.sub.3, boiling
point.about.28.5.degree. C.) to form an azeotropic mixture. The
aforementioned halocarbons are known as FC-C-51-12mym, HCFC-141b and
HCFC-123, respectively, in nomenclature conventional to the halocarbon
field.
By azeotropic composition is meant, a constant boiling liquid admixture of
two or more substances, whose admixture behaves as a single substance, in
that the vapor, produced by partial evaporation or distillation of the
liquid has the same composition as the liquid, i.e., the admixture
distills without substantial composition change. Constant boiling
compositions, which are characterized as azeotropic, exhibit either a
maximum or minimum boiling point, as compared with that of the
nonazeotropic mixtures of the same substances.
The language "an azeotropic composition consisting essentially of..." is
intended to include mixtures which contain all the components of the
azeotrope of this invention (in any amounts) and which, if fractionally
distilled, would produce an azeotrope containing all the components of
this invention in at least one fraction, alone or in combination with
another compound, e.g., one which distills at substantially the same
temperature as said fraction.
As used herein, dichlorotrifluoroethane means CF.sub.3 CHCl.sub.2, HCFC-123
containing up to 5% CHClFCClF.sub.2, HFC-123a. Generally from 3-5%
HFC-123a is present in the dichlorotrifluoroethane used herein. The
presence of HFC-l23a in HFC-123 does not alter the azeotropic nature of
the compositions reported herein because of the closeness in boiling
characteristics of HFC-123 and HFC-123a.
It is possible to fingerprint, in effect, a constant boiling admixture,
which may appear under many guises, depending upon the conditions chosen,
by any of several criteria:
The composition can be defined as an azeotrope of A and B, since the very
term "azeotrope" is at once both definitive and limitative, and requires
that effective amounts of A and B form this unique composition of matter,
which is a constant boiling admixture.
It is well known by those skilled in the art that at different pressures,
the composition of a given azeotrope will vary--at least to some
degree--and changes in pressure will also change--at least to some
degree--the boiling point temperature. Thus an azeotrope of A and B
represents a unique type of relationship but with a variable composition
which depends on temperature and/or pressure. Therefore compositional
ranges, rather than fixed compositions, are often used to define
azeotropes.
The composition can be defined as a particular weight percent relationship
or mole percent relationship of A and B, while recognizing that such
specific values point out only one particular such relationship and that
in actuality, a series of such relationships, represented by A and B
actually exist for a given azeotrope, varied by the influence of pressure.
Azeotrope A and B can be characterized by defining the composition as an
azeotrope characterized by a boiling point at a given pressure, thus
giving identifying characteristics without unduly limiting the scope of
the invention by a specific numerical composition, which is limited by and
is only as accurate as the analytical equipment available.
Binary mixtures of 50-60 weight percent perfluoro-1,2-dimethylcyclobutane
and 40-50 weight percent 1,1-dichlorofluoroethane are characterized as
azeotropic, in that mixtures within this range exhibit a substantially
constant boiling point at constant pressure. Being substantially constant
boiling, the mixtures do not tend to fractionate to any great extent upon
evaporation. After evaporation, only a small difference exists between the
composition of the vapor and the composition of the initial liquid phase.
This difference is such that the compositions of the vapor and liquid
phases are considered substantially identical. Accordingly, any mixture
within this range exhibits properties which are characteristic of a true
binary azeotrope. The binary composition consisting of about 54.5 weight
percent perfluoro-1,2-dimethylcyclobutane and 45.5 weight percent
1,1-dichlorofluoroethane has been established, within the accuracy of the
fractional distillation method, as a true binary azeotrope, boiling at
about 26.7..degree. C., at substantially atmospheric pressure.
Also according to the instant invention, binary mixtures of 23-33 weight
percent perfluoro-1,2-dimethylcyclobutane and 67-77 weight percent
dichlorotrifluoroethane are characterized as azeotropic. The binary
composition consisting of about 27.7 weight percent
perfluoro-1,2-dimethylcyclobutane and 72.3 weight percent
dichlorotrifluoroethane has been established, within the accuracy of the
fractional distillation method, as a true binary azeotrope, boiling at
about 27.0..degree. C., at substantially atmospheric pressure.
The aforestated azeotropes have an ozone-depletion potential estimated to
be less than 0.01 and are expected to decompose almost completely prior to
reaching the stratosphere.
The azeotropes of the instant invention permit easy recovery and reuse of
the solvent from vapor defluxing and degreasing operations because of
their azeotropic natures. As an example, the azeotropic mixtures of this
invention can be used in cleaning processes such as described in U.S. Pat.
No. 3,881,949, or as a buffing abrasive detergent.
In addition, the mixtures are useful as resist developers, hwere
chlorine-type developers would be used, and as resist stripping agents
with the addition of appropriate halocarbons.
Another aspect of the invention is a refrigeration method which comprises
condensing a refrigerant composition of the invention and thereafter
evaporating it in the vicinity of a body to be cooled. Similarly, still
another aspect of the invention is a method for heating which comprises
condensing the invention refrigerant in the vicinity of a body to be
heated and thereafter evaporating the refrigerant. A further aspect of the
invention includes aerosol compositions comprising an active agent and a
propellant, wherein the propellant is an azeotropic mixture of the
invention; and the production of these compositions by combining said
ingredients. The invention further comprises cleaning solvent compositions
comprising the azeotropic mixtures of the invention.
The azeotropes of the instant invention can be prepared by any convenient
method including mixing or combining the desired component amounts. A
preferred method is to weigh the desired component amounts and thereafter
combine them in an appropriate container.
Without further elaboration, it is believed that one skilled in the art
can, using the preceding description, utilize the present invention to its
fullest extent. The following preferred specific embodiments are,
therefore, to be construed as merely illustrative, and not limitative of
the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set
forth uncorrected in degrees Celsius and unless otherwise indicated, all
parts and percentages are by weight.
The entire disclosure of all applications, patents and publications, cited
above and below, are hereby incorporated by reference.
EXAMPLES
Example 1
An ebullioscope is used to determine the composition versus boiling point
temperature characteristics for the minimum boiling azeotrope, as follows:
perfluoro-1,2-dimethylcyclobutane is placed in the distillation flask and
brought to boiling at atmospheric pressure and the boiling points (vapor
and liquid) are recorded. Small quantities of the individual binary
component (1,1-dichloro-l-fluoroethane) are added to the distillation
apparatus. The distillation is allowed to to re-equilibrate for 30 minutes
or less and the boiling points (vapor and liquid) are noted for that
particular mixture composition.
When the mixture temperature reaches its lowest boiling point for the given
composition (temperature lower than the boiling points of either pure
component), the temperature recorded is that of the azeotrope, at the
azeotrope composition.
In order to verify the exact azeotropic composition and boiling
temperature, a solution which contained 45.5 wt.%
perfluoro-1,2-dimethylcyclobutane and 54.5 wt.%
1,1-dichloro-l-fluoroethane is prepared in a suitable container and mixed
thoroughly.
The solution is distilled in a 25-plate Oldershaw distillation column,
using about a 10:1 reflux-totake-off ratio. All temperatures are read
directly to 0.1.degree. C. and adjusted to 760mm pressure. Distillate
compositions are determined by gas chromatography. Results obtained are
summarized in Table 1.
TABLE 1
______________________________________
DISTILLATION OF:
(45.5 + 54.5)
PERFLUORO-1,2-DIMETHYLCYCLOBUTANE (PFDMCB)
AND 1,1-DICHLORO-1-FLUOROETHANE (DCFE)
WT.%
TEMPER- DISTILLED
ATURE, .degree.C.
OR
CUTS HEAD RECOVERED PFDMCB DCFE
______________________________________
1 26.6 4.6 54.2 45.8
2 26.7 10.6 54.2 45.8
3 26.6 16.7 54.0 46.0
4 26.6 23.3 54.2 45.8
5 26.7 29.5 54.8 45.2
6 26.6 36.0 54.4 45.6
7 26.7 42.3 54.1 45.9
8 26.6 49.7 53.9 46.1
9 26.6 55.7 53.9 46.1
10 26.6 62.2 53.5 46.5
HEEL -- 88.2 54.8 45.2
______________________________________
A statistical analysis of the distillation data indicates that the true
binary azeotrope of perfluoro-1,2-dimethylcyclobutane and
1,1-dichloro1-fluoroethane has the following characteristics at
atmospheric pressure (99% confidence limit):
______________________________________
Perfluoro-1,2-dimethylcyclobutane =
54.5 .+-. 0.4% wt. %
1,1-Dichloro-1-fluoroethane =
45.5 .+-. 0.4% wt. %
Boiling point, .degree.C. =
26.7 .+-. 0.1%
______________________________________
Example 2
An ebullioscope is used to determine the composition versus boiling point
temperature characteristics for the minimum boiling azeotrope, as follows:
perfluoro-1,2-dimethylcyclobutane is placed in the distillation flask and
brought to boiling at atmospheric pressure and the boiling points (vapor
and liquid) are recorded. Small quantities of the individual binary
component (dichlorotrifluoroethane) are added to the distillation
apparatus. The distillation is allowed to to re-equilibrate for 30 minutes
or less and the boiling points (vapor and liquid) are noted for that
particular mixture composition.
When the mixture temperature reaches its lowest boiling point for the given
composition (temperature lower than the boiling points of either pure
component), the temperature recorded is that of the azeotrope, at the
azeotrope composition.
In order to verify the exact azeotropic composition and boiling
temperature, a solution which contained 34.0 weight percent
perfluoro-1,2-dimethylcyclobutane and 66.0 weight percent
dichlorotrifluoroethane is prepared in a suitable container and mixed
thoroughly.
The solution is distilled in a 25-plate Oldershaw distillation column,
using about a 10:1 reflux-to-take-off ratio. All temperatures are read
directly to 0.1.degree. C. and adjusted to 760mm pressure. Distillate
compositions are determined by gas chromatography. Results obtained are
summarized in Table 2.
TABLE 2
______________________________________
DISTILLATION OF:
(34.0 + 66.0)
PERFLUORO-1,2-DIMETHYLCYCLOBUTANE (PFDMCB)
AND DICHLOROTRIFLUOROETHANE (DCFE)
WT. %
DISTILLED
TEMPER- OR
ATURE, .degree.C.
RECOVERED
CUTS HEAD AT REFLUX PFDMCB DCFE
______________________________________
1 26.9 -- -- --
2 26.9 2.6 -- --
3 27.0 15.6 27.8 72.2
4 27.2 26.4 27.8 72.2
5 26.8 37.8 27.9 72.1
6 26.9 48.8 27.7 72.3
7 26.9 57.2 27.6 72.4
8 27.0 60.4 27.5 72.5
HEEL -- 80.8 55.7 44.3
______________________________________
A statistical analysis of the distillation data indicates that the true
binary azeotrope of perfluoro-1,2-dimethylcyclobutane and
dichlorotrifluoroethane has the following characteristics at atmospheric
pressure (99% confidence limits):
______________________________________
Perfluoro-1,2-dimethylcyclobutane =
27.7 .+-. 0.4% wt. %
Dichlorotrifluoroethane =
72.3 .+-. 0.4% wt. %
Boiling point, .degree.C. =
27.0 .+-. 0.1
______________________________________
Example 3
Several single sided circuit boards are coated with activated rosin flux
and soldered by passing the board over a preheater to obtain a top side
board temperature of approximately 200.degree. F. (93.degree. C.) and then
through 500.degree. F. (260.degree. C.) molten solder. The soldered boards
are defluxed separately with the two azeotropic mixtures cited in Examples
1 and 2 above, by suspending a circuit board, first, for three minutes in
the boiling sump, which contains the azeotropic mixture, then, for one
minute in the rinse sump, which contains the same azeotropic mixture, and
finally, for one minute in the solvent vapor above the boiling sump. The
boards cleaned in each individual azeotropic mixture have no visible
residue remaining thereon.
The preceding examples can be repeated with similar success by substituting
the generically or specifically described reactants and/or operating
conditions of this invention for those used in the preceding examples.
From the foregoing description, one skilled in the art can easily ascertain
the essential characteristics of this invention, and without departing
from the spirit and scope thereof, can make various changes and
modifications of the invention to adapt it to various usages and
conditions.
* * * * *
|
|
 |
|
 |
Description |
|
