Stabilized azeotrope-like compositions of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane

Description

[0001] In pending U.S. patent application Serial No. 07/297,366, filed February 15, 1989, constant-boiling, azeotrope-like compositions comprising 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b) with methanol and ethanol are described as effective cleaning solvent compositions, particularly with regard to the cleaning of electronic circuit boards.

[0002] As described in the aforementioned application, current industrial processes for soldering electronic components to circuit boards involve coating the entire circuit board with a flux composition and, thereafter, passing the coated side of the board over preheaters and then through molten solder. The flux composition cleans the conductive metal parts and promotes solder adhesion. Commonly used fluxes consist, for the most part, of rosin used alone or rosin with activating additives, such as amine hydrochlorides or oxalic acid derivatives.

[0003] After soldering, which thermally degrades part of the rosin, flux and flux residues are often removed from the board with an organic solvent composition. Since requirements for the removal of contaminants from circuit boards are very stringent, most current industrial circuit board cleaning processes involve the use of vapor defluxing techniques. In the conventional operation of a vapor defluxer, the soldered circuit board is passed through a sump of boiling organic solvent, which removes the bulk of the rosin---including thermally degraded rosin --and thereafter, through a sump which contains freshly distilled solvent and finally through solvent vapor above the boiling sump, which condenses on the circuit board to provide a final rinse with a clean, distilled solvent. Additionally, the circuit board could also be sprayed with distilled solvent, if required, before the final rinse.
* equivalent to EP-0392668-A

[0004] While constant-boiling, azeotrope-like compositions of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane, as described in pending U.S. Patent Application Serial No. 07/335,946, filed April 10, 1989*, are excellent solvent systems for cleaning circuit boards, for practical industrial use these solvent systems, as is the case with many solvent systems, should be stabilized against compositional changes during both use and long term storage. Changes, such as oxidation, polymerization, component interactions, and the like, may generate products which adversely affect the circuit boards being cleaned or the solvent compositions themselves.

[0005] It is therefore an object of the present invention to provide constant-boiling, azeotrope-like compositions of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane, which are compositionally stable during use and long term storage and which minimize the formation of undesirable reaction products, which may adversely affect electronic circuit board cleaning.

INVENTION SUMMARY

[0006] What has been discovered is a stabilized azeotrope-like composition comprising an azeotrope-like composition consisting of effective amounts of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane, such azeotrope-like composition having a boiling point of about 31°C at substantially atmospheric pressure and a stabilizer package comprising one or more of effective stabilizing amounts of nitromethane, diisopropylamine, 1,2-butylene oxide and/or 4-methoxyphenol. The stabilizer package may also comprise effective stabilizing amounts of 1,2-propylene oxide and nitromethane with or without one or more of diisopropylamine, 1,2-butylene oxide and/or 4-methoxyphenol.

DETAILED DESCRIPTION OF THE INVENTION

[0007] By effective amounts is meant the amounts of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b), which, when combined, result in the formation of the azeotrope-like compositions of the instant invention as disclosed in U.S. Patent Application Serial No. 07/335,946, filed April 10, 1989, incorporated herein by reference,(EP-0392668-A).

[0008] By effective stabilizing amounts is meant at least some of one or more of nitromethane, diisopropylamine, 1,2-butylene oxide and/or 4-methoxyphenol. Also, by effective stabilizing amounts is meant at least some of 1,2-propylene oxide and nitromethane with or without one or more of diisopropylamine, 1,2-butylene oxide and/or 4-methoxyphenol. When the effective stabilizing amounts of the disclosed compounds are combined with the azeotrope-like composition of 1,1-dichloro-2,2,2-trifluoroethane (CHCl₂CF₃) and 1,1-dichloro-1-fluoroethane (CCl₂FCH₃), they allow such azeotrope-like composition to be used and stored commercially, i.e., provide commercially acceptable appearance, corrosivity and resistance to loss of integrity of the azeotrope-like composition.

[0009] Commercially available HCFC-123 may contain minor amounts of 1,2-dichloro-1,1,2-trifluoroethane, e.g., as much as about 20.0 weight percent 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a) which mixture is intended to be covered by the language 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) as well as the inclusion of minor amounts of other materials which do not significantly alter the azeotrope-like character of the cleaning solvent compositions.

[0010] The stabilized compositions of the present invention may comprise admixtures of effective amounts of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane, which compositions form azeotrope-like compositions which may contain one or more of about 0.1 to 0.8 weight percent of nitromethane, about 0.05 to 0.4 weight percent 1,2-propylene oxide, about 0.025 to 0.2 weight percent diisopropylamine and about 0.002 to 0.016 weight percent 4-methoxyphenol, said stabilizer weight percentages are based on the weight of the azeotrope-like compositions.

[0011] The present azeotrope-like compositions comprise admixtures of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane, more specifically, the present compositions comprise mixtures of about 1-99 weight percent 1,1-dichloro-2,2,2-trifluoroethane and about 99-1 weight percent 1,1-dichloro-1-fluoroethane.

[0012] The present azeotrope-like compositions may also comprise admixtures of about 20-80 weight percent 1,1-dichloro-2,2,2-trifluoroethane and about 80-20 weight percent 1,1-dichloro-1-fluoroethane which boil at about 31°C, at substantially atmospheric pressure.

[0013] It has been found that azeotrope-like compositions of the instant invention which contain a minimum of about weight percent 1,1-dichloro-2,2,2-trifluoroethane are nonflammable, as determined by a flammability test similar to ASTM E918.

[0014] A preferred azeotrope-like composition of the instant invention has the following composition: about 65 weight percent 1,1-dichloro-2,2,2-trifluoroethane and about 35 weight percent 1,1-dichloro-1-fluoroethane. The azeotrope-like composition boils at about 31°C, at substantially atmospheric pressure.

[0015] The above azeotrope-like compositions are effective solvents for cleaning electronic circuit boards. Such solvent compositions are characterized by desirable properties of relatively low boiling points, non-flammability, relatively low toxicity and high solvency for flux and flux residues. The components also permit easy recovery and reuse without loss of their desirable characteristics because of their azeotrope-like natures and relatively low boiling points.

[0016] While the azeotrope-like compositions of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane perform well in printed circuit board vapor defluxing-degreasing applications, it is recognized that in order to take practical advantage of the unique properties of these solvent compositions, certain other desirable properties should be imparted to the compositions, particularly, when the solvent systems are to be used commercially.

[0017] One such desirable property is storage stability. It is recognized that any material which is to be used commercially must usually be inventoried. Such storage can be for short intervals or for longer periods of months or even years. Thus, for solvent compositions to be useful, they should be stabilized against any significant deleterious changes which may be brought about by oxidation, polymerization or component interaction during storage or use. Such changes may result in solvent discoloration, the formation of undesirable by-products, such as chloride ions and acids and/or the formation of insoluble polymeric materials. It has been found that the addition of an one or more of the compounds listed above, in the aforementioned concentration ranges, perform as effective storage stabilizers.

[0018] Another commercially desirable characteristic to be imparted to the solvent system is in-use stability. For example, as described above, in the vapor defluxing cleaning procedure, the circuit board to be cleaned is first passed through a sump which contains boiling solvent, for removal of bulk rosin, including thermally degraded rosin. In this sump, the organic solvent is in contact with a heat source for a prolonged time. After passage through the first sump, the circuit board is passed through a sump which contains freshly distilled solvent and finally through solvent vapor over a boiling sump, which provides a final rinse with a clean solvent which condenses on the circuit board. Thus, in use, the organic solvent is subjected to constant heating either in maintaining boiling sumps or in vaporizing the solvent to provide freshly distilled solvent or vapor to condense on the circuit board for the final rinse. It is, therefore, highly desirable to minimize any change in the solvent system which can adversely affect the cleaning process or degrade the integrity of the solvent. As mentioned earlier, such changes may be due to oxidation, polymerization or interaction between the solvent system components.

[0019] For example, one such interaction which should be minimized is the interaction between the hydrochlorofluorocarbons and metals, at elevated temperatures, which may generate acidic by-products and chloride ions. Reactive metals such as zinc and aluminum as well as certain aluminum alloys, which are often used as materials of circuit board construction, are particularly susceptible to such interaction. It has been found that nitromethane may be incorporated in the present solvent system in concentrations of about 0.1 to 0.8 weight percent and effectively retard this type of attack and, in addition, prevent the formation of gel.

[0020] The stabilizer package comprising diisopropylamine, in a concentration of about 0.025 to 0.2 weight percent, 4-methoxyphenol, in a concentration of about 0.002 to 0.016 weight percent, 1,2-propylene oxide, in a concentration of about 0.05 to 0.4 weight percent, and nitromethane, in a concentration of about 0.05 to 0.8 weight percent, enhances the stability of the present solvent system. All weight percentages are based on the weight of the of the 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane azeotrope-like composition.

[0021] As shown in the examples, the stabilizers when used together in the present solvent system (4-methoxyphenol, 1,2-propylene oxide, diisopropylamine and nitromethane) appear to enhance the stability of the solvent system. The ranges of acceptable performance for stabilizer concentrations when used together is the same as disclosed herein for when they are used separately. It should be noted that stabilizer concentrations higher than those specified can be employed; under normal circumstances, however, higher stabilizer concentrations do not generally provide additional inhibition advantage.

[0022] Other acceptable inhibitor-stabilizer systems, which provide storage and use stability to the aforedescribed azeotrope-like compositions are:

Inhibitor(s)	Weight Percentage(s)
Nitromethane	0.2
Diisopropylamine	0.05
1,2-Butylene oxide	0.05
4-Methoxyphenol	0.004
Nitromethane + 1,2-propylene oxide	0.2 + 0.05
Nitromethane + 1,2-butylene oxide	0.2 + 0.05
Nitromethane + 1,2-propylene oxide + diisopropylamine	0.2 + 0.05 + 0.05
Nitromethane + 1,2-butylene oxide + diisopropylamine	0.2 + 0.05 + 0.05
Nitromethane + 1,2-propylene oxide + 1,2-butylene oxide	0.2 + 0.05 + 0.05
Nitromethane + 1,2-propylene oxide + 4-methoxyphenol	0.2 + 0.05 + 0.004

[0023] The preferred stabilized, constant-boiling, azeotrope-like composition of the present invention contains about 65 weight percent of 1,1-dichloro-2,2,2-trifluoroethane, about 35 weight percent 1,1-dichloro-1-fluoroethane, about 0.1 to 0.8 weight percent of nitromethane, about 0.05 to 0.4 weight percent 1,2-propylene oxide, and about 0.025 to 0.2 weight percent percent diisopropylamine and about 0.002 to 0.016 weight percent 4-methoxyphenol.

[0024] A more preferred, stabilized, azeotrope-like composition of the present invention contains about 65 weight percent 1,1-dichloro-2,2,2-trifluoroethane, and about 35 weight percent 1,1-dichloro-1-fluoroethane, about 0.2 weight percent nitromethane, about 0.05 weight percent 1,2-propylene oxide, about 0.05 weight percent diisopropylamine and about 0.004 weight percent 4-methoxyphenol.

[0025] The present invention thus provides stabilized, azeotrope-like compositions of 1,1-dichloro-2,2,2-trifluoroethane and 1,1-dichlorolfluoroethane, which can be stored for long periods periods of time, which will undergo little or no change during either prolonged storage or commercial use and which minimize both aluminum corrosion and gel formation.

[0026] The methods of combining the inhibitors with the azeotrope-like compositions of this invention are well-known in the art. They can be prepared by any convenient method including mixing or combining the desired component amounts in suitable containers. A preferred method is to weigh the desired component amounts and thereafter combine them in an appropriate container.

[0027] The aforestated stabilized, azeotrope-like compositions have low ozone depletion potentials and are expected to decompose almost completely prior to reaching the stratosphere.

[0028] The stabilized, azeotrope-like compositions of the present invention permit easy recovery and reuse of the solvent from vapor defluxing and degreasing operations because of their azeotrope-like natures. As an example, the azeotrope-like mixture of this invention can be used in cleaning processes such as described in U.S. Patent No. 3,881,949, which is incorporated herein by deference.

EXAMPLES

[0029] Comparative seven day stability tests of solvent system combinations of about 65 weight percent 1,1-dichloro-2,2,2-trifluoroethane and about 35 weight percent 1,1-dichloro-1-fluoroethane with various inhibitor combinations were carried out by refluxing 150 ml of the solvent combination in a series of 500 ml Pyrex® flasks using 90 percent, at 25°C, water-saturated solvents. The flasks were connected to water-cooled condensers, on top of which were affixed Drierite® desiccant tubes to exclude atmospheric moisture from the test systems. Additionally, stainless steel (SS-304) specimens were located at the refluxing solvent vapor/air interfaces in the condensers and coupled stainless steel (SS-304)/aluminum alloy (AL-7075) specimens were located in the boiling liquids.

[0030] The 1,1-dichloro-1-fluoroethane used in these tests contained about 500 parts per million by weight of vinylidene chloride, an impurity normally found in the crude product; however, no vinylidene chloride was used in test number 1 below. The solvent inhibitor systems tested are described in the Table.

[0031] The following tests were performed on each individual test system subsequent to test exposures:
1. Chloride ion concentration was measured at the end of the test by extracting the solvent with an equal volume of deionized water and analyzing the water for chloride ion concentration. The original, uninhibited, solvent contained less than 0.2 ppm chloride ion. Chloride ion increase generally represents loss of solvent system component stability. Stability loss is generally accompanied by increased acidity.
2. The pH changes of the solvent (final minus original) were determined by extracting the acid from the solvents with equal volumes of pH neutral (pH = 7), deionized water and checking the pH of the water.
3. Corrosion rates were measured by rubbing the metal surfaces with ink and pencil erasers, brushing the surfaces, rinsing the specimens sequentially with 1,1,2-trichlorotrifluoroethane, deionized water and acetone, drying for 24 hours over Drierite® desiccant and weighing the sample to 0.0001 gram, Metal specimen weight loss is expressed in mils/year. An aluminum (Al-7075) corrosion rate of 4 mils/year is considered acceptable.
4. Appearance of the solvent and the aluminum specimens (Al-7075) were rated visually using the following rating criteria:

APPEARANCES
RATINGS	ACCEPTABLE	LIQUID	ALUMINUM-7075 (*)
0	Yes	NO CHANGE OR TRACE CHANGE
		Clear, colorless No gel drops.	Bright and shiny.
1	Yes	VERY, VERY SLIGHT BUT ACCEPTABLE CHANGES
		Very slight, clear, colorless gel drops formed.	Very, very slight corrosion on ca. 1% of surface.
2	Borderline	VERY SLIGHT BORDERLINE CHANGES NOTED, MAY OR MAY NOT BE ACCEPTABLE FOR INTENDED END USE.
		Clear. Slight gel drops formed	Very slight corrosion or black spot deposits on ca. 10-20% of surface.
3	No	SLIGHT, UNACCEPTABLE CHANGES NOTED
		Moderate amount of gel drops in the liquid.	Slight spotting and corrosion on ca. 50% of surface.
4	No	Severe amount of gel in the liquid.	-

(*) All reactivity occurred on the Al-7075 surface which interfaced with the SS-304 in the liquid. The SS-304 specimens were essentially unchanged throughout the tests except in test 13.

TABLE

TEST NO.	STABILIZERS		SOLVENT		Al-7075 CORROS. RATE, MILS/YR	APPEARANCE RATINGS
		WT. %	Δ pH	Cl-		LIQUID(X)	Al-7075(Y)
1	NONE	0	0.0	0.8	0.9	0	1
2	NONE	0	0.5	0.9	0.9	4	0⁺
3	NM	0.2	0.1	0.7	0.3	0	0⁺
4	DIPA	0.05	0.1	1.1	1.0	0	1
5	1,2-PO	0.05	-0.4	0.5	0.8	4	1
6	1,2-BO	0.05	0.1	0.4	1.1	0	0
7	4-MP	0.004	0.2	0.4	0.8	0	0⁺
8	NM	0.2	0.2	0.4	0.9	0	0⁺
	1,2-PO	0.05
9	NM	0.2	0.0	0.3	1.2	0	1
	1,2-BO	0.05
10	NM	0.2	0.0	0.8	0.9	0	1
	1,2-PO	0.05
	DIPA	0.05
11	NM	0.2	-0.1	0.7	1.1	0	0⁺
	1,2-BO	0.05
	DIPA	0.05
12	NM	0.2	0.0	0.8	0.9	0	0
	1,2-PO	0.05
	DIPA	0.05
	4-MP	0.004
13	DIPA	0.05	0.0	2.5	2.5	0	0
	1,2-PO	0.05					(1)*

*On SS-304 surface in air space above condensing vapor.

(X) All ratings are based on gel formation in the liquid phase.

(Y) Relation of metal ratings to appearance changes. All ratings are based on the appearance of the Al-7075 surface in the liquid phase except as noted.

AL-7075 = 1 = very, very, slight corrosion on about 1% of surface

SS-304 = 1 = very, very slight haze on about 20% of the metal surface.

The abbreviations used in the Table are:
1,2-BO = 1,2-butylene oxide
1,2-PO = 1,2-propylene oxide
NM = nitromethane
4-M = 4-methoxyphenol
DIPA = diisopropylamine

Claims

1. A stabilized azeotrope-like composition comprising an azeotrope-like composition consisting of about 80-20 weight percent of 1,1-dichloro-2,2,2-trifluoroethane and about 20-80 weight percent of 1,1-dichloro-1-fluoroethane, said azeotrope-like composition having a boiling point of about 31°C at substantially atmospheric pressure, said azeotrope-like composition in admixture with effective stabilizing amounts of one or more of nitromethane, diisopropylamine, 1,2-butylene oxide and 4-methoxyphenol.

2. The stabilized azeotrope-like composition of Claim 1 wherein about 65 weight percent 1,1-dichloro-2,2,2-trifluoroethane and about 35 weight percent 1,1-dichloro-1-fluoroethane is present.

3. The stabilized azeotrope-like composition of Claim 1 wherein about 0.2 weight percent nitromethane is present, said weight percent based on the weight of the azeotrope-like composition.

4. The stabilized azeotrope-like composition of Claim 1 wherein about 0.05 weight percent diisopropylamine is present, said weight percent based on the weight of the azeotrope-like composition.

5. The stabilized azeotrope-like composition of Claim 1 wherein about 0.05 weight percent 1,2-butylene oxide is present, said weight percent based on the weight of the azeotrope-like composition.

6. The stabilized azeotrope-like composition of Claim 1 wherein about 0.004 weight percent 4-methoxyphenol is present, said weight percent based on the weight of the azeotrope-like composition.

7. A stabilized azeotrope-like composition comprising an azeotrope-like composition consisting of about 80-20 weight percent of 1,1-dichloro-2,2,2-trifluoroethane and about 20-80 weight percent of 1,1-dichloro-1-fluoroethane, said azeotrope-like composition having a boiling point of about 31°C at substantially atmospheric pressure, said azeotrope-like composition in admixture with effective stabilizing amounts of 1,2-propylene oxide and nitromethane with or without one or more of diisopropylamine, 1,2-butylene oxide and 4-methoxyphenol.

8. The stabilized, azeotrope-like composition of Claim 7 wherein about 0.05 to 0.8 weight percent nitromethane, about 0.05 to 0.4 weight percent 1,2-propylene oxide, about 0.025 to 0.2 weight percent diisopropylamine and/or about 0.002 to 0.016 weight percent 4-methoxyphenol is present, said weight percents based on the weight of the azeotrope-like composition.

9. The stabilized, azeotrope-like composition of Claim 7 wherein about 0.2 weight percent nitromethane, about 0.05 weight percent 1,2-propylene oxide, about 0.05 weight percent diisopropylamine and about 0.004 weight percent 4-methoxyphenol is present

10. The stabilized azeotrope-like composition of Claim 7 wherein about 0.2 weight percent nitromethane and about 0.05 weight percent 1,2-propylene oxide are present, said weight percents based on the weight of the azeotrope-like composition.

11. The stabilized azeotrope-like composition of Claim 7 wherein about 0.2 weight percent nitromethane, about 0.05 weight percent 1,2-propylene oxide and about 0.05 weight percent diisopropylamine are present, said weight percents based on the weight of the azeotrope-like composition.

12. The stabilized azeotrope-like composition of Claim 7 wherein about 0.2 weight percent nitromethane, about 0.05 weight percent 1,2-propylamine oxide and about 0.05 weight percent 1,2-butylene oxide are present, said weight percents based on the weight of the azeotrope-like composition.

13. The stabilized azeotrope-like composition of Claim 7 wherein about 0.2 weight percent nitromethane, about 0.05 weight percent 1,2-propylamine oxide and about 0.004 weight percent 4-methoxyphenol are present, said weight percents based on the weight of the azeotrope-like composition.

14. A process for cleaning a solid surface comprising the use of the stabilized azeotrope-like composition of Claim 1.

15. A process for cleaning a solid surface comprising the use of the stabilized azeotrope-like composition of Claim 7.

16. A process for expanding a polymeric foam comprising the use of the stabilized azeotrope-like composition of Claim 1 as a blowing agent.

17. A process for expanding a polymeric foam comprising the use of the stabilized azeotrope-like composition of Claim 7 as a blowing agent.