EP0600538A1 - Compositions containing a fluorinated ether and use thereof - Google Patents

Abstract

The invention relates to compounds comprising 2,2,2-difluoromethoxytrifluoroethane and an alcohol. These compositions may in particular be used as solvents for cleaning electronic components and for degreasing metals.

Description

The invention relates to compositions comprising a fluorinated ether in combination with an alcohol and the uses of these compositions, in particular as a cleaning agent.

Fully halogenated chlorofluorinated hydrocarbons (CFCs), such as 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), are widely used as solvents in the industry for degreasing and surface cleaning various, particularly for parts of complicated shape and difficult to clean. In addition to their use in electronics in the cleaning of printed circuit boards to eliminate the flux flux which adheres to the printed circuits, they are also conventionally used to degrease metallic parts or to clean mechanical parts of high quality and high precision. In these various applications, CFC-113 is most often combined with other organic solvents, preferably in the form of azeotropic or pseudo-azeotropic compositions which have substantially the same composition in the vapor phase and in the liquid phase and which can thus be easily used at reflux.

Compositions based on CFC-113 are also conventionally used code desiccant agent, in order to remove the water adsorbed on the surface of delicate parts.

However, CFC-113, like other fully halogenated chlorofluoroalkanes, is today suspected of causing environmental problems, on the one hand in the context of the destruction of the stratospheric ozone layer and on the other hand, as part of the warming of the atmosphere (greenhouse effect).

The influence that a product can have on the ozone layer has been quantified from complex mathematical models and is expressed by its ozone-depleting potential (ODP), relative to that of CFC-11. The influence of a product on the greenhouse effect is expressed, still relative to CFC-11, by its global warming potential (GWP).

Depending on the model chosen, the ODP for CFC-113 varies from 0.8 to 0.9 and its GWP from 1.3 to 1.4. Consequently, there is currently an urgent need to find new solvent compositions which do not have a harmful influence on the ozone layer.

To this end, a number of azeotropic compositions based on fluorinated ethers have recently been proposed. For example, patent application EP-A-0450855 proposes to use in solvent cleaning operations compositions comprising fluorinated ethers with low molecular weight and with a boiling point of about 20 to about 120 ° C. In this application, the azeotropic mixtures 1-methoxy-1,1,2-trifluoro-2-chloro-ethane / methanol, methoxytetrafluoroethane / methanol and ethoxytetrafluoroethane / methanol are disclosed. US-A-5,023,010 discloses azeotropic mixtures of 1,1,1,2,3,3-hexafluoro-3-methoxypropane with methanol, isopropanol or n-propanol.

One of the objects of the present invention is to provide other compositions, optionally forming azeotropes or pseudo-azeotropes, which are particularly effective when they are used as a cleaning agent in solvent cleaning processes. The invention also relates to such compositions having properties particularly suitable for cleaning printed circuit boards. Another object of the invention is to provide such compositions having a zero ODP and a particularly low GWP, compositions which can therefore be used in replacement of solvents based on completely halogenated chlorofluoroalkanes.

The present invention relates to compositions comprising difluoromethoxy-2,2,2-trifluoroethane and at least one alcohol. Preferably, the alcohol is a lower alcohol, such as methanol, ethanol, propanol and isopropanol. In a particularly preferred manner, the alcohol is chosen from methanol, ethanol and isopropanol. Most preferably, the alcohol is methanol or ethanol.

Difluoromethoxy-2,2,2-trifluoroethane can be obtained by any means, in particular by reaction between trifluoroethanol and the chlorodifluoromethane code described in patent US Pat. No. 3,761,524.

The difluoromethoxy-2,2,2-trifluoroethane and alcohol contents in the compositions according to the invention can vary within wide limits depending on the intended use.

Generally, the compositions according to the invention contain at least 75% by weight of difluoromethoxy-2,2,2-trifluoroethane. They advantageously contain at least 85% by weight thereof. In a particularly preferred manner, they contain at least 90% thereof. They can contain up to 99.995% by weight. Most often, they contain at most 99.9% by weight, preferably at most 99.5% by weight.

The compositions according to the invention contain from 0.005 to 25% by weight of alcohol. Preferably, they contain from 0.02 to 15%. In a particularly preferred manner, they contain from 0.2 to 10% thereof.

Various additives can optionally be present in the compositions according to the invention. The compositions according to the invention can thus contain stabilizers, surfactants or any other additives making it possible to improve the performance of the compositions according to the invention during their use. The nature and the quantity of these additives depend on the intended use and are easily defined by a person skilled in the art. As a general rule, the amount of additives present in the compositions according to the invention does not exceed approximately 25% of the weight of the composition, most often not more than 10%.

In the compositions according to the invention, difluoromethoxy-2,2,2-trifluoroethane and alcohol have the particularity of forming azeotropic mixtures for well-defined compositions. Preferred compositions according to the invention are therefore those which contain difluoromethoxy-2,2,2-trifluoroethane and alcohol in proportions in which they form an azeotrope or a pseudo-azeotrope. Such compositions are especially obtained when the alcohol is methanol or ethanol. The compositions containing difluoromethoxy-2,2,2-trifluoroethane and methanol in proportions in which they form an azeotrope or a pseudo-azeotrope are particularly preferred.

Basically, the thermodynamic state of a fluid is defined by four interdependent variables: pressure (P), temperature (T), composition of the liquid phase (X) and composition of the gas phase (Y). An azeotrope is a particular system with 2 or more components for which, at a given temperature and at a given pressure, X is exactly equal to Y. A pseudo-azeotrope is a system with 2 or more components for which, at a given temperature and at a given pressure, X is substantially equal to Y. In practice, this means that the constituents of such azeotropic and pseudo-azeotropic systems cannot be separated easily by distillation and therefore their composition remains constant in cleaning operations by solvent, as well as in recovery operations for used solvents by distillation.

For the purposes of the present invention, the term “pseudo-azeotrope” is intended to mean a mixture of two or more constituents whose boiling point (at a given pressure) differs from the boiling point of the azeotrope by 0.5 ° C. to the maximum.

The compositions according to the invention are characterized by their compositions observed at a given pressure. It goes without saying that this does not limit the compositions according to the invention to these particular compositions. It is indeed well known that an azeotrope with 2 or more constituents sees its composition and its boiling point vary as a function of the pressure conditions adopted.

Difluoromethoxy-2,2,2-trifluoroethane and methanol form an azeotrope or a pseudo-azeotrope when their mixture contains 0.1 to 7.5 g of methanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. In particular, they form a azeotrope or a pseudo-azeotrope when their mixture contains from 1 to 5 g of methanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. At atmospheric pressure, the binary composition consisting essentially of approximately 97% by weight of difluoromethoxy-2,2,2-trifluoroethane and approximately 3% by weight of methanol constitutes an azeotrope, the boiling point of which is approximately 29.3 ° C. This composition is very particularly preferred.

Difluoromethoxy-2,2,2-trifluoroethane and ethanol form an azeotrope or a pseudo-azeotrope when their mixture contains from 0.01 to 3 g of ethanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. In particular, they form an azeotrope or a pseudo-azeotrope when their mixture contains from 0.03 to 1 g of ethanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. Under a pressure of 4 bar, the binary composition consisting essentially of approximately 99.7% by weight of difluoromethoxy-2,2,2-trifluoroethane and approximately 0.3% by weight of ethanol constitutes an azeotrope, the boiling point is around 74.9 ° C. This composition is very particularly preferred.

The compositions according to the invention have an adequate boiling point to replace the compositions based on CFC-113 in existing cleaning equipment. With regard to its impact on the environment, difluoromethoxy-2,2, -2-trifluoroethane appears particularly interesting, since it has a zero ozone destruction potential. The compositions according to the invention are also inert against the different types of surfaces to be treated, whether these are made of metal, plastic or glass.

The compositions according to the invention can therefore be used in the same applications and according to the same techniques as the previous compositions based on CFC-113. In particular, the compositions according to the invention can be used as cleaning agent, solvent, degreaser, defluxing or desiccant. Compositions which are particularly suitable in these different applications are those where the constituents are present in proportions in which they form an azeotrope or pseudo-azeotrope.

The following non-limiting examples illustrate the invention in more detail.

Example 1

To demonstrate the existence of azeotropic or pseudo-azeotropic compositions between difluoromethoxy-2,2,2-trifluoroethane and methanol, a glass apparatus consisting of a boiling flask surmounted by a reflux condenser was used. The temperature of the liquid is measured by means of a thermometer immersed in the bottle.

25 ml of pure difluoromethoxy-2,2,2-trifluoroethane were heated to atmospheric pressure until boiling, then small amounts of methanol were gradually introduced into the bottle using a graduated syringe, via a side tube equipped with a septum.

The azeotropic composition was determined by recording the evolution of the boiling temperature of the mixture as a function of its composition. The composition for which a minimum or maximum boiling point has been observed is the azeotropic composition at atmospheric pressure.

avec

tr,

la température relevée en °C

tc,

la température corrigée en °C

P,

la pression atmosphérique au moment de la mesure, en mm Hg.

The influence of atmospheric pressure on the boiling point of mixtures has been corrected using the following formula:

$\text{tc = tr + 0.00012 (760-P) (273 + tr)}$

with

tr,

the temperature recorded in ° C

tc,

the corrected temperature in ° C

P,

atmospheric pressure at the time of measurement, in mm Hg.

Table I shows the corrected boiling temperatures obtained for different compositions of difluoromethoxy-2,2,2-trifluoroethane and methanol.

The best estimate of the composition for which the boiling point is minimum is approximately 97% by weight of difluoromethoxy-2,2,2-trifluoroethane. The boiling point is 29.5 ° C ± 0.2 ° C for compositions containing approximately 93 99.9% by weight of difluoromethoxy-2,2,2-trifluoroethane. TABLE I Methanol added, ml Percentage CF₃-CH₂-O-CHF₂ Corrected temperature (° C) in volume in weight in moles 0 100.00 100.00 100.00 29.8 0.5 98.04 98.88 94.77 29.4 1.0 96.15 97.78 90.06 29.3 1.5 94.34 96.71 85.81 29.3 2.0 92.59 95.66 81.93 29.3 2.5 90.91 94.64 78.40 29.5 3.0 89.29 93.64 75.16 29.6 3.5 87.72 92.65 72.16 29.8 4.0 86.21 91.69 69.40 30.0 5.0 83.33 89.83 64.47 30.3

Example 2

This example highlights the pseudo-azeotrope consisting of difluoromethoxy-2,2,2-trifluoroethane and ethanol.

A solution containing 99.87% by weight of difluoromethoxy-2,2,2-trifluoroethane and 0.13% by weight of ethanol was prepared by mixing the two constituents. This solution was subjected to distillation, at atmospheric pressure, using a Vigreux column. Different fractions of the distillate, each representing around 12 to 15% of the volume of the initial solution, were removed using a "cow-udder" distributor, then analyzed by gas chromatography.

Table II collates the results obtained. TABLE II Fraction of the distillate Ethanol content (g / kg) 1 0.60 2 0.46 3 0.51 4 0.51

Analysis of the results indicates that there are only small differences between the compositions of the different distillate fractions collected as the distillation progresses.

Claims (10)

Compositions comprising difluoromethoxy-2,2,2-trifluoroethane and at least one alcohol. Compositions according to Claim 1, characterized in that the alcohol is chosen from methanol, ethanol, propanol and isopropanol. Compositions according to Claim 1, characterized in that they contain at least 75% by weight of difluoromethoxy-2,2,2-trifluoroethane and from 0.005 to 25% by weight of alcohol. Compositions according to any one of Claims 1 to 3, characterized in that they contain the difluoromethoxy-2,2,2-trifluoroethane and the alcohol in proportions for which they form an azeotrope or a pseudo-azeotrope. Compositions according to Claim 4, characterized in that they contain from 0.1 to 7.5 g of methanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. Compositions according to Claim 4, characterized in that they contain from 0.01 to 3 g of ethanol per 100 g of difluoromethoxy-2,2,2-trifluoroethane. Use of the compositions according to any one of claims 1 to 6 as a cleaning agent. Use of the compositions according to any one of Claims 1 to 6 as a degreasing agent for solid surfaces. Use of the compositions according to any one of claims 1 to 6 as a cleaning agent for printed circuit boards contaminated by flux and their residues. Use of the compositions according to any one of claims 1 to 6 as a desiccant to remove the water adsorbed on the surface of solid objects.