Solvent compositions

The present invention relates to solvent compositions and their use.

International agreements aiming to protect the stratospheric ozone layer require the reduction or even gradual elimination of the use of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Compounds of this kind are used inter alia as solvents or as refrigerants. For example, CFC-11 (CFC-113) is used as a degreasing solvent or for cleaning surfaces. More recently, HCFC-141b has been used for these applications. The latter compound is also used with surfactants in drying agents. CFC-11 (CFC-11) and HCFC-123 are used, for example, as refrigerants in turbocompressors.

Patent Application JP-A-08/020,553 proposes compositions containing an flammable organic compound, a perfluoropolyether and a fluorocarbon such as, in particular, HCFC-141b, these possibly being used as a solvent and as a dispersion agent. These mixtures have a certain flammability.

It was desirable to find non-flammable compositions free of products capable of impairing the stratospheric ozone layer, possibly having advantages as regards their liquid-vapour equilibrium, namely in particular a substantially constant vapour pressure when they are subjected to an evaporation operation. It was also desirable to find compositions suitable for use in processes for manufacturing polymer layers.

The invention therefore relates to a composition comprising at least one, hydrofluoroalkane having a boiling point greater than or equal to 10° C. at 101.3 kPa and at least one perfluoropolyether.

It has been found that the composition according to the invention has advantages as regards its liquid-vapour equilibrium while being non-flammable. It has been found that the composition according to the invention can be used advantageously for suspending, dispersing or dissolving materials intended to be deposited in layer form on a surface, particularly fluoropolymers.

For the purposes of the present invention the term “hydrofluoroalkane” is understood to mean a saturated organic compound consisting only of carbon atoms, hydrogen atoms and fluorine atoms. The hydrofluoroalkanes that can be used in the compositions according to the invention may be linear, branched or cyclic and contain, in general, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms.

The F/H numerical ratio (the number of fluorine atoms in the molecule divided by the number of hydrogen atoms in the molecule) of the hydrofluoroalkane is generally greater than or equal to 0.5. An F/H numerical ratio greater than or equal to 0.6 is very suitable. Preferably, the F/H numerical ratio is greater than or equal to 1. The F/H numerical ratio is generally less than or equal to 20. Preferably the F/H numerical ratio is less than or equal to 4.

In the compositions according to the invention, the hydrofluoroalkane has a boiling point greater than or equal to about 10° C. at 101.3 kPa. Good results are obtained with a hydrofluoroalkane having a boiling point greater than or equal to about 15° C. at 101.3 kPa. In a preferred embodiment, the hydrofluoroalkane has a boiling point greater than or equal to about 20° C. at 101.3 kPa. The hydrofluoroalkane generally has a boiling point less than or equal to about 200° C. at 101.3 kPa. Good results are obtained with a hydrofluoroalkane having a boiling point less than or equal to about 100° C. at 101.3 kPa.

Typical examples of hydrofluoroalkanes are chosen from hydrofluoropropanes, hydrofluorobutanes and hydrofluoropentanes. Specific examples of such hydrofluoroalkanes are 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3-pentafluorobutane (HFC-365mfc) and 1,1,1,2,3,4,4,5,5,5-decafluoropentane (HFC-43-10mee). 1,1,1,3,3-pentafluoropropane and 1,1,1,3,3-pentafluorobutane are preferred. 1,1,1,3,3-pentafluorobutane is most particularly preferred.

For the purposes of the present invention, the term “perfluoropolyether” is intended to mean a compound consisting essentially of carbon, fluorine and oxygen atoms and comprising at least 2, preferably at least 3, C—O—C ether linkages or a mixture of several compounds satisfying this definition. Often the oxygen atoms in the perfluoropolyether are exclusively present within the C—O—C ether linkages.

In the compositions according to the invention, the perfluoropolyether generally has a boiling point greater than or equal to about 40° C. at 101.3 kPa. Good results are obtained with a perfluoropolyether having a boiling point greater than or equal to about 45° C. at 101.3 kPa. The perfluoropolyether generally has a boiling-point less than or equal to about 200° C. at 101.3 kPa. Good results are obtained with a perfluoropolyether having a boiling point less than or equal to about 150° C. at 101.3 kPa.

In the compositions according to the invention, the perfluoropolyether generally has a molecular mass greater than or equal to about 200. When the perfluoropolyether is a mixture of several compounds, the molecular mass is die weight-average molecular mass ( M_w). Good results are obtained with a perfluoropolyether having a molecular mass greater than or equal to about 250. The perfluoropolyether generally has a molecular mass less than or equal to about 2000. Good results are obtained with a perfluoropolyether having a molecular mass less than or equal to about 1500.

When the perfluoropolyether is a mixture of compounds, it is preferred to have a mixture whose boiling point is substantially homogeneous. A mixture of this type may consist, for example, of a distillation fraction having a boiling range less than or equal to 8° C., more often less than or equal to 5° C. and preferably less than or equal to 2° C. In this case, the boiling point of the perfluoropolyether indicated above is the arithmetic mean of the two extreme temperatures of the boiling range.

In a particular embodiment, the kinematic viscosity of the perfluoropolyether is less than or equal to 1 cSt (Centistoke) at 25° C. Often the kinematic viscosity of the perfluoropolyether is less than or equal to 0.9 cSt at 25° C. Preferably, the kinematic viscosity of the perfluoropolyether is less than or equal to 0.8 cSt at 25° C. A perfluoropolyether having a kinematic viscosity of less than or equal to 0.6 cSt at 25° C. is more particularly preferred. In the particular embodiment, the kinematic viscosity of the perfluoropolyether is generally at least 0.3 cSt (Centistoke) at 25° C.

Perfluoropolyethers that can be used in the compositions according to the invention are commercially available or can be obtained by known processes (see, for example, Améduri and Boutevin, Top. Curr. Chem. (1997), Vol. 192, p. 178-179). The perfluoropolyether can be obtained, for example, by a process comprising:

• (a) the photooxidation of a fluoroolefin preferably chosen from hexafluoropropylene and tetrafluoroethylene;
• (b) a chemical and/or physical treatment of the photooxidation product,
• (c) a distillation in order to isolate the desired perfluoropolyether.

The chemical treatment may, for example, be a fluorination. The physical treatment may, for example, be a photolysis or a thermolysis. Perfluoropolyethers that can be used are, for example, those satisfying, the general formulae CF₃—[(OCF(CF₃)—CF₂)_a—(O—CF₂)_b]O—CF₃ (I) and CF₃—[(OCF₂—CF₂)_c—(O—CF₂)_d]O—CF₃ (II) in which a, b, c and d independently denote integers greater than 0.