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Publication numberUS2999817 A
Publication typeGrant
Publication dateSep 12, 1961
Filing dateAug 15, 1960
Priority dateAug 15, 1960
Also published asUS2999816
Publication numberUS 2999817 A, US 2999817A, US-A-2999817, US2999817 A, US2999817A
InventorsBower Frank A
Original AssigneeDu Pont
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Azeotropic composition
US 2999817 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

United States Patent C "ice j 2,999,817 AZEOTROPIC COMPOSITION corporation of Delaware No Drawing. Filed Aug. 15, 1960, Ser. No. 49,436

1 Claim. '(Cl. 252172) This invention relates to an azeotropic composition and particularly to the azeotropic mixture of 1,1,2-triohloro- 1,2,2-trifluoroethane and methylene chloride.

Several of the chlorofluorome'thanes and chlorofluoroethanes have attained widespread'use as specialty solvents in recent years, particularly trichlorofluoromethane and trichlorotrifluoroethane. Both of these' compounds are relatively low boiling liquids (CCl F, 23.8 C.; CCI FCCIF 47.6" C.), which are nontoxic and nonfiamrnable, and which have good solvent power for greases, oils, waxes and the like. They have therefore found widespread use for cleaning electricmotors, compressors, oxygen storage tanks, photographic film, lithographic plates, typewriters; instruments gauges, sound tape, and as noncorrosivebrines.

For certain solvent purposes however, the chlorofluoromethanes and chlorofluoroethanes have insufficient solvent power alone. This is particularly true in the electronic industry during the manufacture of printed circui L. Printed circuits are well known in the electronics art; and consist of a circuit formed from a soft metal on a solid, nonconducting surface such as a reinforced phenolic 1 resin. During manufacture, the solid surface is coated with the metal, the desired portion of metal is coated with an impervious coating, and the excess metal is removed by etching with a suitable acid. After the excess metal has been removed, it is necessary to remove the impervious coating because solder joints must be made to the printed circuit" and these will not form if the coating is present. After the imprevious coating is removed, the circuits are coated with a rosin flux to permit the joints to be soldered, which rosin flux must then be removed. The chlorofluoromethane and chlorofluoroethane solvents do not have sufiicient solvent power to clean printed circuits; that is, to etfectively remove the rosin flux.

It is an object of this invention to provide a novel azeotropic composition which has new and unusual properties. Another object is to provide an azeotropic composition which is valuable as a solvent, and particularly for cleaning printed circuits. A further object is to provide such a composition which is nonflammable and nontoxic, both in the liquid phase and in the vapor phase. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accord with this invention which comprises an azeotropic composition consisting of about 52% by weight of 1,1,2- trichloro-l,2,2atrifluoroethane and about 48% by weight of methylene chloride and boiling at 37 C. at 760 mm. pressure.

It has been found that l,1,2-trichloro-l,2,2-trifiuoroethane and methylene chloride (CH Cl when admixed in the above proportions form an azeotrope which distils at constant composition, the liquid phase and the vapor phase in equilibrium therewith having the same composition. Such mixture is nonflammable and nontoxic in both the liquid phase and the vapor phase. It is useful as a heat exchange medium and as a hydraulic fluid. It is particularly useful as a solvent for greases, oils, waxes, and the like, in cleaning electric motors, compressors, photographic film, oxygen storage tanks, lithographic, plates, typewriters, precision instruments, gauges, sound tape, components of engines which use liquid oxygen, and

2,999,817, Patented Sept. 12, 1961 printed circuits. The 1,1,2trichloro-1,2,2-trifluoroethane alone has insufiicient solvent power for many of such purposes, and the methylene chloride alone is objectionable for some of such purposes. It has been found that, in the azeotrope, the components modify the solvent properties of each other so that the azeotropic mixture is an excellent solvent for such purposes without having the disadvantages of either.

In the cleaning of components of engines which use liquid oxygen, it is particularly-important that the solvent remove alloxidizable materials so that they will not contact the liquid oxygen and that the solvent leave no residue which will react with liquid oxygen. The azeotropic mixture of this invention has the desired properties which render it useful for this pur'p'oseI r i The azeotropic mixture of l,l,2-trichloro-l,2,2-trifluoroethane and methylene chloride is of special value for cleaning printed circuits. The l, --l,2-trichloro-l,2,2- trifiuoroethane alone is'not an elfective' solvent for cleaning printed circuits, and has no deleteriousfefiect on the boards which form the bases of the printed circuits. Methylene chloride alone deleteriously ,aifects such boards, particularly laminated boards impregnated with phenolic resins, causing softening, swelling "and delamination of such boards and dissolving certain marking inks which are used to code various electronic components in the printed circuit assembly. The azeotropic mixture of this invention does not have these effects and is an excellent solvent for such purpose.

The azeotrope of this invention has several advantages over the solvents heretofore employed for cleaning printed circuits. Trichloroethylene, tetrachloroethylene, and methyl chloroform, are unstable and require stabilizers, whereas the azeotropic composition of this invention does not require a stabilizer, has a more favorable evaporation rate (is lower boiling), and is considerably less toxic than such solvents. The azeotropic composition of this invention is more effective as a solvent for such purposes than trichloroethylene and tetrachloroethylene. Inhibited methyl chloroform (containing dioxane as a stabilizer) is too strong a solvent and attacks the backing of the printed circuits. -Isopropyl alcohol-toluene blends are flammable and irritating. The azeotropic mixture of 1,l,Z-trichloro-1,2,2-trifluoroethane and methylene chloride does not suifer from any of these defects.

The azeotropic composition of this invention was established by the fractional distillation of a mixture containing 20% by weight'of l,l,2-trichloro-1,2,2-trifluoroethane and by weight of methylene chloride. The first fraction collected, amounting to 40% of the original mixture, was the azeotrope containing 52% by weight of 1,1,Z-trichloro-1,2,2-trifluoroethane and 48% by weight of methylene chloride having a boiling point of 37 C. at 760 mm. pressure, freezing point C. to 92 C., 11 1.3860. Distillation of mixtures of different proportions, eg 60% CCl- FCClF and 40% CH Cl always gave, as the first fraction, the azeotrope boiling at 37 C. The fractions boiling at 37 C. could be redisti-lled, giving material which boiled at 37 C. throughout with no separation into the components of the mixture.

Printed circuit boards are usually prepared by impregnating glass cloth, nylon, or paper laminates with a phenol-formaldehyde resin or an epoxy resin. Printed circuits are prepared by a variety of methods. In a typical procedure, the board consists originally of a phenolic resin impregnated base to which is bonded a sheet of copper, 2 to 4 mils thick, covering one surface of the board. The desired circuitis drawn on the copper with an asphalt based ink, using the silk screen method. The

excess copper is then removed by etching with a ferric chloride-hydrochloric acid bath, sometimes containing ammonium chloride, leaving on the board the copper that is covered by the ink. After washing 01f the etch solution, the asphalt ink is removed by cleaning with the azeotropic composition of this invention in an ultrasonic bath (some mechanical scrubbing is often used). The entire surface of the board is then coated with a rosin flux and dried. The electronic components (resistors, capacitors, etc.) are then added at the proper places for soldering to the circuit. The board is then passed over a molten solder bath, contacting the desired joints With the molten metal, whereby the soldering is effected. After cooling, the excess rosin flux remaining on the board must be removed since, if present in the final assembly, it will lead to corrosion, poor electrical resistance and other deleterious properties.

The board is cleaned by placing it in an ultrasonic bath operating at about 32 kilocycles per second and at about 25 C., where it remains for one minute. If 1,1,2-trichloro-1,2,2-trifluoroethane is used alone as the solvent in the bath, it has no effect on the rosin flux. If trichloroethylene is used as the solvent in the bath, about 5% to about 50% of the flux remains after the treatment. If the same cleaning operation is repeated on another circuit board using the azeotropic mixture of 1,1,2-trichloro- 1,2,2-trifluoroethane and methylene chloride as the solvent, the rosin fiux is completely removed. Neither the 1,1,2 trichloro-1,2,2-trifluoroethane nor the azeotropic mixture has any efiect on the board which constitutes the backing of the printed circuit.

It will be understood that the preceding detailed description of the use of the azeotropic composition of this invention in cleaning printed circuits is given for illustrative purposes solely, that this invention is not restricted to such specific embodiment, and that other techniques may be employed. Also, the azeotropic composition can be used for other purposes as indicated in the general description.

From the preceding description, it will be apparent that this invention provides a novel azeotropic composition which has unusual properties and which is useful for a wide variety of purposes. Accordingly, it will be apparent that invention constitutes a valuable contribution to and advance in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A11 azetropic composition consisting of about 52% by Weight of 1,1,2-trich1oro-1,2,2-trifluoroethane and about 48% by weight of methylene chloride and boiling at 37 C. and 760 mm. pressure.

References Cited in the file of this patent UNITED STATES PATENTS 2,155,510 Shepperd Apr. 25, 1939 2,547,887 Reed et a1 Apr. 3, 1951 2,911,331 Dennis et a1. Nov. 3, 1959 OTHER REFERENCES Industrial solvents, Mellan, 2nd ed. (1950), pp. 4879, 314-315, 372-373.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2155510 *Mar 16, 1935Apr 25, 1939Lewis L ScottAir conditioning system
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US2911331 *May 31, 1956Nov 3, 1959Air ReductionDegreasing process
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3212998 *Dec 6, 1962Oct 19, 1965Dow Chemical CoAzeotropic distillation of bromine
US3282853 *Mar 24, 1964Nov 1, 1966Du PontAzeotropic composition and process for attenuating magnetic ink characters
US3330776 *Dec 8, 1964Jul 11, 1967Du PontTrichlorotrifluoroethane hexafluoropropanol composition
US3332881 *Dec 21, 1964Jul 25, 1967Du PontAzeotropic composition
US3351560 *Apr 9, 1965Nov 7, 1967Dow Chemical CoSolvent composition
US3400077 *Jun 1, 1967Sep 3, 1968Allied ChemFluorinated hydrocarbon containing compositions
US3625763 *Dec 4, 1968Dec 7, 1971Bunker RamoConformal coating stripping method and composition
US3846332 *Sep 18, 1972Nov 5, 1974Airco IncAzeotropes of 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether with acetone, methyl ethylketone and tetrahydrofuran
US3915875 *Mar 23, 1973Oct 28, 1975Mc Donnell Douglas CorpLow temperature fluid
US3951843 *Nov 8, 1973Apr 20, 1976Lfe CorporationFluorocarbon composition for use in plasma removal of photoresist material from semiconductor devices
US4055521 *Oct 8, 1975Oct 25, 1977Allied Chemical CorporationTrichlorofluoromethane, isopentane, methylene chloride
US4476036 *Sep 12, 1983Oct 9, 1984Allied CorporationMethylene chloride, cyclopentane, methanol
US4715900 *Jan 8, 1987Dec 29, 1987E. I. Du Pont De Nemours And CompanyCleaning printed circuits
US4808331 *May 24, 1988Feb 28, 1989E. I. Du Pont De Nemours And CompanyAzeotrope or azeotrope-like composition of 1,1,2,-trichloro-1,2,2-trifluoroethane, trans-1,2-dichloroethylene and cyclopentane
US4873021 *Dec 30, 1986Oct 10, 1989E. I. Du Pont De Nemours And CompanyAzeotrope or azeotrope-like composition of trichlorotrifluoroethane and dichlorodifluoroethane
US4954289 *Jun 12, 1989Sep 4, 1990E. I. Du Pont De Nemours And Company1,1,1,2-tetrafluoro-2-chloroethane or 1-chloro-1,1-difluoroeth ane with butane or isobutane
US4986928 *Mar 21, 1990Jan 22, 1991E. I. Du Pont De Nemours And CompanyBinary azeotropic compositions of 1-chloro-1,2,2-trifluorocyclobutane and methanol
US4994202 *Mar 12, 1990Feb 19, 1991E. I. Du Pont De Nemours And CompanySolvent cleaning; refrigerants, aersol propellants, blowing agents for polymers
US5023009 *Oct 3, 1990Jun 11, 1991E. I. Du Pont De Nemours And CompanyCleaning agents, blowing agents, refrigerants, propellants, heat transfer media, fire extinguishers, dielectrics
US5026497 *Mar 12, 1990Jun 25, 1991E. I. Du Pont De Nemours And CompanyAzeotropic compositions of perfluoro-1,2-dimethylcyclobutane with methanol and 1,1-dichloro-1-fluoroethane or dichlorotrifluoroethane
US5026499 *Mar 21, 1990Jun 25, 1991E. I. Du Pont De Nemours And CompanyTernary azeotropic compositions of hexafluoropropylene/ethylene cyclic dimer with trans-1,2-dichloroethylene and methanol
US5037572 *Oct 3, 1990Aug 6, 1991E. I. Du Pont De Nemours And CompanyFor cleaning or surface treatment; refrigerants, heat transfer media, blowing agents
US5037573 *Oct 3, 1990Aug 6, 1991E. I. Du Pont De Nemours And CompanyCleaning agent; blowing agent; refrigerants; aerosol propellant
US5039445 *Oct 3, 1990Aug 13, 1991E. I. Du Pont De Nemours And CompanyTernary azeotropic compositions of N-perfluorobutylethylene and cis-1,2-dichloroethylene with methanol or ethanol or isopropanol
US5066417 *Jul 20, 1989Nov 19, 1991E. I. Du Pont De Nemours And CompanyBinary azeotropic compositions of 2,2-dichloro-1,2-difluoroethane with methanol, ethanol, or trans-1,2-dichloroethylene
US5073288 *Aug 17, 1990Dec 17, 1991E. I. Du Pont De Nemours And CompanyCompositions of 1,1,1,2,2,3,5,5,5-nonafluoro-4-trifluoromethylpentane and use thereof for cleaning solid surfaces
US5073290 *Aug 17, 1990Dec 17, 1991E. I. Du Pont De Nemours And CompanyCompositions of 1,1,1,2,2,5,5,5-octafluoro-4-trifluormethypentane and use thereof for cleaning solid surfaces
US5076956 *Nov 29, 1990Dec 31, 1991E. I. Du Pont De Nemours And CompanyCompositions of octafluorotrifluoromethylpentane and nonafluorotrifluoromethylpentane and use thereof for cleaning solid surfaces
US5084199 *Oct 9, 1990Jan 28, 1992E. I. Du Pont De Nemours And Company1,1,2,2,3,3-hexafluorocyclopentane and use thereof in compositions and processes for cleaning
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US5176757 *Oct 28, 1991Jan 5, 1993E. I. Du Pont De Nemours And Company1,1,2,2,3,3-hexafluorocyclopentane and use thereof in compositions and processes for cleaning
US5221361 *Sep 4, 1991Jun 22, 1993E. I. Du Pont De Nemours And CompanyRemoving flux from printed circuits using azeotrope mixtures
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Classifications
U.S. Classification510/177, 216/13, 252/364, 62/502, 510/408, 252/67, 361/779, 216/54, 252/78.1
International ClassificationC23G5/028, C11D7/50, B41N3/00, C23G5/00
Cooperative ClassificationB41N3/006, C23G5/02819, C11D7/5059
European ClassificationC11D7/50D2K, B41N3/00B, C23G5/028D1B33