Azeotropic compositions

Abstract

This invention relates to azeotropic compositions of 1,2-dichloro-1-fluoroethane or of 1,2-dichloro-1,2-difluoroethane with certain alcohols, ethers, or ketones.

Description

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 nonconducting 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 imitative, 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 AzeotropeAzeotrope.sup.(a) Chlorofuoro- 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 FluxRuns Solvent Systems Dissolved______________________________________1 141/methanol 97.02 141/ethanol 91.53 141/isopropanol 95.74 132/methanol 98.75 132/ethanol 94.06 132/isopropanol 98.07 113.sup.(e) 28.48 1,1,1-trichloroethane 82.69 113/ethanol azeotrope 66.510 113/ethanol/acetone azeotrope 57.011 113/isopropanol azeotrope 69.512 141 51.313 132 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 Per Cent Composition of AzeotropeAzeotrope Chlorofuoro- Chlorofluoro-B.P. (Pressure) hydrocarbon Ether hydrocarbon/Ether______________________________________74.degree. C (739 mm) 141 THF.sup.(f) 61.8/38.270.degree. C (739 mm) 132 THF 45.9/54.1______________________________________ 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______________________________________Runs Solvent Systems Wt. % of Flux Dissolved______________________________________14 141/THF 10015 132/THF 10016 1,1,1-Trichloroethane 82.617 113/ethanol azeotrope 66.518 141 51.319 132 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. % Chloro- Composition fluoro- of AzeotropeAzeotrope hydro- Chlorofluoro-B.P. (Pressure) carbon Ketone hydrocarbon/Ketone______________________________________ (atmos-80.degree. C pheric) 141 MEK.sup.(g) 54.1/45.980.degree. C (743 mm) 132 MEK 39.8/80.266.degree. C (736 mm) 132 Acetone 72.3/27.7______________________________________

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______________________________________Runs Solvent Systems Wt. % of Flux Dissolved______________________________________20 141/MEK 10021 132/MEK 9822 1,1,1-Trichloroethane 82.623 113/ethanol azeotrope 66.524 113/ethanol/acetone azeotrope 57.025 141 51.326 132 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, etherRun Azeotrope or ketone.sup.(i)No. Azeotrope Flash Point, .degree. F.sup.(h) Component Alone______________________________________27 141/methanol 46.degree. F 51.degree. F28 141/ethanol 75.degree. F.sup.(j) 56.degree. F29 141/isopropanol -- 53.degree. F30 132/methanol 46.degree. F 51.degree. F31 132/ethanol 75.degree. F.sup.(k) 56.degree. F32 132/isopropanol 75.degree. F.sup.(l) 53.degree. F33 141/THF 40.degree. F 6.degree. F34 132/THF 36.degree. F 6.degree. F35 141/MEK -- 23.degree. F36 132/MEK 42.degree. F 23.degree. F37 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 wa 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.

Claims

1. The azeotrope which at substantially atmospheric pressure is characterized as about 45.9 weight percent 1,2-dichloro-1,2-difluoroethane and about 54.1 weight percent tetrahydrofuran.

2. The azeotrope according to claim 1 characterized by a boiling point of about 70.degree. C. at substantially atmospheric pressure.

3. The azeotrope according to claim 1 characterized by a boiling point of about 70.degree. C. at about 739 millimeters pressure.