Background of the Invention This invention relates to azeotropes of 1,1-di- chloro-2,2,2-trifluoroethane (HCFC-123), 1,2-dichloro- 1,1,2-trifluoroethane (HCFC-123a) and 1 ,1-dichloro- 1-fluoroethane (HCFC-141b) with methyl formate and their use as cleaning solvents and blowing agents for polymer foams.

Closed-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 (poly- isocyanurate) 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 reguire expansion agents (blowing agents) for their manufacture. Insulating foams depend on the use of halocarbon blowing agents, not only to foam the poly¬ mer, but primarily for their low vapor thermal conduc¬ tivity, a very important characteristic for insulation

value. Historically, polyurethane foams are made with CFC-11 (CFC1 ) 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 l,l,2-trichloro-l,2,2-trifluoroethane (CFC-113) blowing agents.

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 pre- heaters 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 and 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 require¬ ments for such solvents are very stringent. Defluxing solvents should have the following characteristics: Have a low boiling point, 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 be adjusted by preparing solvent mixtures, these mixtures are often unsatis¬ factory because they fractionate to an undesirable degree during use. Such solvent mixtures also frac¬ tionate during solvent distillation, which makes it virtually impossible to recover a solvent mixture with the original composition.

On the other hand, azeotropes with their constant compositions, have been found to be very useful for these applications. Azeotropes do not fractionate on evaporation or 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 azeotropes. This could result in mixtures with changed compositions and less-desirable solvency properties, such as lower rosin flux solvency and lower inertness toward the electrical components being cleaned. This character is also desirable in vapor degreasing operations, where redistilled solvent is generally employed for final rinse cleaning.

Many solvent compositions used industrially for cleaning electronic circuit boards and for general metal, plastic and glass cleaning are based upon CFC-113.

In summary, vapor defluxing and degreasing systems act as a still. Unless the solvent composition ex¬ hibits a constant boiling point, i.e., is a single material, or is azeotropic, fractionation will occur and undesirable solvent distributions will result, which could detrimentally affect the safety and effi¬ cacy of the cleaning operation.

A number of halocarbon based azeotropic composi¬ tions 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. Patent No. 3,903,009 discloses the ternary azeotrope of 1,1,2- trichloro-l,2,2-trifluoroethane with ethanol and nitro ethane; U.S. Patent No. 2,999,815 discloses the binary azeotrope of 1,1,2-trichloro-l,2,2-trifluoro- ethane and acetone; U.S. Patent No. 2,999,916 discloses the binary azeotrope of 1,1 2-trichloro-l 2 2-tri-

fluoroethane and methyl alcohol; U.S. Patent No. 4,767,561 discloses the ternary azeotrope of l,l,2-trichloro-l,2,2-trifluoroethane, methanol and 1,2-dichloroethylene.

In the early 1970's, concern began to be expressed that the stratospheric ozone layer (which provides protection against penetration of the earth's atmosphere by ultraviolet radiation) was being depleted by chlorine atoms introduced to the atmosphere from the release of fully halogenated chlorofluorocarbons. These chlorofluorocarbons are used as propellants in aerosols, as blowing agents for foams, as refrigerants and as cleaning/drying solvent systems. Because of the great chemical stability of fully halogenated chloro¬ fluorocarbons , according to the ozone depletion theory, these compounds do not decompose in the earth's atmosphere but reach the stratosphere where they slowly degrade liberating chlorine atoms which in turn react with the ozone.

Concern reached such a level that in 1978 the U.S. Environmental Protection Agency (EPA) placed a ban on nonessential uses of fully halogenated chlorofluoro¬ carbons as aerosol propellants. This ban resulted in a dramatic shift in the U.S. away from chlorofluorocarbon propellants (except for exempted uses) to primarily hydrocarbon propellants. However, since the rest of the world did not join the U.S. in this aerosol ban, the net result has been to shift the uses of chloro¬ fluorocarbons in aerosols out of the U.S., but not to permanently reduce the world-wide total chlorofluoro¬ carbon production, as sought. In fact, in the last few years the total amount of chlorofluorocarbons manufac¬ tured worldwide has exceeded the level produced in 1978 (before the U.S. ban).

During the period of 1978-1987, much research was conducted to study the ozone depletion theory. Because of complexity of atmospheric chemistry, many questions

relating to this theory remained unanswered. However, assuming the theory to be valid, the health risks which would result from depletion of the ozone layer are significant. This, coupled with the fact that world¬ wide production of chlorofluorocarbons has increased, has resulted in international efforts to reduce chloro¬ fluorocarbon use. Particularly, in September, 1987, the United Nations through its Environment Programme (UNEP) issued a tentative proposal calling for a 50 percent reduction in world-wide production of fully halogenated chlorofluorocarbons by the year 1998. This proposal was ratified January 1, 1989 and became effective on July 1, 1989.

Because of this proposed reduction in availability of fully halogenated chlorofluorocarbons such as CFC-11, dichlorodifluoromethane (CFC-12) and CFC-113, alternative, more environmentally acceptable, products are urgently needed.

As early as the 1970's with the initial emergence of the ozone depletion theory, it was known that the introduction of hydrogen into previously fully halo¬ genated chlorofluorocarbons markedly 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 stratosphere and the ozone layer. The accompanying Table lists the ozone depletion potential for a variety of fully and partially halogenated halocarbons. Halocarbon Global Warming Potential data (potential for reflecting infrared radiation (heat) back to earth and thereby raising the earth's surface temperature) are also shown.

OZONE DEPLETION AND HALOCARBON GLOBAL WARMING POTENTIALS

Halocarbon Global

Depletion Warming

Blowing Agent Potential Potential

CFC-11 (CFC1 ₃ ) 1. ,0 1.0 CFC-12 (CF ₂ C1 ₂ ) 1. ,0 2.8 HCFC-22 (CHF ₂ C1) 0. ,05 0.3 HCFC-123 (CF ₃ CHC1 ₂ ) 0. ,02 0.02 HCFC-124 (CF ₃ CHFC1) 0. ,02 0.09 HFC-134a (CF ₃ CH ₂ F) 0 0.3 HCFC-141b (CFC1 ₂ CH ₃ ) 0. ,1 0.09 HCFC-142b (CF ₂ C1CH ₃ ) 0. ,06 0.3 HFC-152a (CHF ₂ CH ₃ ) 0 0.03 CFC-113 (CF ₂ C1-CFC1 ₂ ) 0. ,8-0.9 1.4

Halocarbons such as HCFC-123, HCFC-123a and HCFC-141b are environmentally acceptable in that they theoretically have minimal effect on ozone depletion. (Although these values have not been calculated for HCFC-123a, it is estimated that they would be similar to those for HCFC-123.)

Unfortunately, as recognized in the art, it is not possible to predict the formation of azeotropes.

This fact obviously complicates the search for new azeotropes which have application in the field. Nevertheless, there is a constant effort in the art to discover new azeotropic compositions, which have desirable characteristics.

Summary of the Invention

According to the present invention, azeotropes of l,l-dichloro-2,2,2-trifluoroethane (HCFC-123), 1,2-di- chloro-l,l,2-trifluoroethane (HCFC-123a) and 1,1-di- chloro-1-fluoroethane (HCFC-1 1b) with methyl formate have been discovered.

Also included in the invention are processes for using these azeotropes as cleaning agents and foam blowing agents, e.g., to expand a polymer.

All of the azeotropes with methyl formate are maximum boiling azeotropes except for that of HCFC-l4lb which is a minimum boiling azeotrope. With maximum boiling azeotropes, the boiling point is higher than that for the individual components; whereas, the vapor pressure at a particular temperature is lower than that for the components. With a minimum boiling azeotrope, the boiling point is lower than that for the individual components; whereas, the vapor pressure at a particular temperature is higher than that for the components.

The azeotropes of the invention have the composi¬ tions as defined in the following table:

AZEOTROPIC COMPOSITIONS

Atmospheric Components Composition Boiling Point

HCFC-123/Methyl 71.0/29.0 (±1.3 wt. %) 33.5°C

Formate HCFC-123a/Methyl 74.1/25.9 (±1.8 wt. %) 33.5 ^β C

Formate HCFC-14lb/Methyl 61.7/38.3 (±3.4 wt. %) 28.4"C

Formate

Therefore, the compositions consist essentially of

(a) about 69.7 to 72.3 weight percent 1,1-di- chloro-2,2,2-trifluoroethane and about 27.7 to 30.3 weight percent methyl'formate,

(b) about 72.3 to 75.9 weight percent 1,2-di- chloro-l,l,2-trifluoroethane and about 24.1 to 27.7 weight percent methyl formate, or

(c) about 58.3 to 65.1 weight percent 1,1-di- chloro-1-fluoroethane and about 34.9 to 41.7 weight percent methyl formate.

The azeotropes of HCFC-123 and HCFC-141b with methyl formate are useful as cleaning solvents and as blowing agents for polyurethane and phenolic foams. Accordingly, the invention comprises methods of ex¬ panding polymer foams, as well as methods of cleaning substrates with the azeotropic compositions of the invention.

For example, the azeotropic composition may be dissolved in a polyol containing a surfactant and a catalyst to form a B-side system (polyol, catalyst, surfactant and blowing agent) , and subsequently mixed with an isocyanate to produce a foam, e.g., polyure¬ thane foam. Alternatively, the azeotropic composition may be combined with an isocyanate to form one component and subsequently reacted with a polyol, surfactant, and catalyst to produce a foam, e.g., a polyurethane foam.

Production of such foams as discussed above is wholly conventional, from components as disclosed in, e.g., The ICI Polyurethane Book (Wiley & Sons, 1987) and Modern Plastics Encyclopedia 1988-1989 (McGraw-Hill) . Typical polyols include polyester polyols, polyether polyols, mixed polyether/polyester polyols, aminopolyols, sugar-based polyols, polyols derived from polyethylene oxide and/or polypropylene oxide polymers. Typical catalysts include tin salts for the production of polyurethanes, amines for the production of polyurethanes and/or polyureas and alkali metal salts for the production of polyisocyanurates. Typical surfactants include silicon-based surfactants used conventionally to control foam size. Typical isocyanates include toluene diisocyanates (TDI) and ethylene diisocyanates (MDI) , e.g., in the production of polyurethane foams.

Generally, the blowing agent is used in an amount of about 1-30% by weight of the total polymer foam

HCFC-123 may contain as much as about 20.0 wt. % l,2-dichloro-l,l,2-trifluoroethane (HCFC-123a) .

The language "an azeotropic composition consistin 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.

Without further elaboration, it is believed that one skilled in the art can, using the preceding de¬ scription, 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

Foam tests are conducted on a polyisocyanurate foam formulation with the azeotropes of HCFC-123 and HCFC-141b with methyl formate. The polyisocyanurate foam formulation (250 index) is described in Table I. The quantities of blowing agents and the densities of the resultant foams are summarized in Table II.

TABLE I k

POLYISOCYANURATE FOAM'

Ingredient Equivalent Weight Weight Used, g. Polyester polyol 197.0 100.0

DC-193 ^a 1.5

Hex-Cem" 977 ^b 2.7

TMR-30 ^C 0.3

Isocyanate (MDI) 136.5 179.2

Blowing Agent d

* 250 Index Polyisocyanurate foam. a Silicone surfactant, Dow Corning Corporation.

Potassium octanoate, Mooney Chemicals, Incorporated.

Dabco" tris (Dimethylaminomethyl) phenol. Air Products and Chemicals, Incorporated

The quantities of blowing agents are shown in Table II. CFC-11 is used as the reference blowing agent.

TABLE II

POLYISOCYANURATE FOAMS

4 Foam Density

Blowing Agent Wt. % lb./cu. ft.

CFC-11 13.4 2.02

HCFC-123/Methyl Formate 7.2/3.2 2.19

HCFC-123**/Methyl Formate 7.2/3.2 2.19

HCFC-14lb/Methyl Formate 5.6/3.5 2.26

Each blowing agent or azeotrope is used at a concentration which would result in essentially the same number of moles of gas as represented by 13.4 wt. % CFC-11. Each foam is uniform, closed-cell and with fine cell structure.

**

HCFC-123 in this foam contains about 10 wt. % HCFC-123a.

Example 2

Cleaning tests are performed on single-sided circuit boards and nut/washer assemblies using HCFC-123/methyl formate (71.0/29.0), HCFC-123a/methyl formate (74.1/25.9) and HCFC-1 lb/methyl formate (61.7/38.3) azeotropes. The test results are shown in Table III.

TABLE III CLEANING TESTS

Solvent Substrate Results

HCFC-123/Methyl Formate Single-sided Boards clean (71.0/29.0) circuit boards with no vis¬ ible residue

HCFC-123/Methyl Formate Nuts/washers Clean, no oil (71.0/29.0) assemblies

HCFC-123a/Methyl Formate Single-sided Boards clean (74.1/25.9) circuit boards with no vis¬ ible residue

HCFC-123a/Methyl Formate Nuts/washers Clean, no oil (74.1/25.9) assemblies

HCFC-14lb/Methyl Formate Single-sided Boards clean (61.7/38.3) circuit boards with no vis¬ ible residue

HCFC-14lb/Methyl Formate Nuts/washers Clean, no oil (61.7/38.3) assemblies

Boards are fluxed with activated rosin, are preheated to 200 ^β F (93*C), and soldered at 500°F (260*C) prior to cleaning.

Assemblies are dipped in Oak Drawing Oil No. 78-1 prior to cleaning.

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.