The present invention relates to a composition for a refrigerator comprising a tetrafluoroethane and a polyether which is compatible at any optional ratio with a tetrafluoroethane, preferably 1,1,1,2-tetrafluoroethane (R-134a), as a cooling medium at a temperature of from -20°C or lower to +40°C or higher and which has a low hygroscopic property.

R-12 (dichlorodifluoromethane) is used as an excellent cooling medium in a refrigerating cycle of e.g refrigerators or car air conditioners. However, R-12 is likely to destroy the ozone layer in the stratosphere and adversely affect the living bodies. Therefore, a study for a substitute material is being made. As a substitute for R-12, R-134a is considered to be most prospective. However, a naphthene mineral oil and a paraffin mineral oil which are refrigerator oils commonly used for R-12, are incompatible with R-134a. Therefore, such a naphthene mineral oil or paraffin mineral oil can not be used as a refrigerator oil for R-134a. Polyether oils having the structures as identified in Table 1, are known as substances relatively well compatible with R-134a.

The polyether oil (a) is disclosed, for example, in Dupont Research Disclosure (17483, Oct., 1978). The polyether oil (b) is disclosed, for example, in US Patent 4,755,316.

However, the polyether oils as identified in Table 1 had the following problems.
(1) Compatibility with R-134a is not adequate. In order to provide a lubricating property as the most important role of the freezer oil, it is essential that the oil is compatible with R-134a and capable of being circulated in the system together with R-134a. With respect to the freezer oils (a) and (b), the upper critical solution temperatures (see the footnote of Table 1) are as shown in Table 1 in the case where the kinematic viscosity at 40°C is 100x10^-6 m²/s (100 cSt). The compatibility can hardly be regarded as adequate.
(2) Hygroscopicity is high. The freezer oils (a) and (b) are highly hygroscopic and apt to absorb moisture. Inclusion of moisture brings about adverse affects such as a deterioration of insulation resistance and an increase of corrosiveness to metal. Conventional polyether oils and their upper critical solution temperatures No. Structure Upper critical solution temperature* of a product with 100 x 10^-6 m²/s (100 cSt) at 40°C (a) C₄H₉-O(C₃H₆O)_nH 12°C (b) 40°C (*) Upper critical temperature: The oil and R-134a are mixed in a weight ratio of 15:85 and sealed. The temperature is gradually raised, and the temperature at which turbidity or phase separation has started, is taken as the upper critical solution temperature. The better the compatibility, the higher the upper critical solution temperature.

To solve the above problems, the present inventors have presumed that the hygroscopicity of the polyether oils is attributable to the terminal hydroxyl groups. Therefore, by using polyethers having from 1 to 3 terminal hydroxyl groups, all or a part of the terminal hydroxyl groups of such polyethers have been acylated or alkylated, and evaluation of such acylated or alkylated compounds for usefulness as freezer oils for R-134a has been conducted. As a result, it has been found that not only the hygroscopicity but also the compatibility with R-134a and the viscosity indexes have been improved. The present invention has been accomplished on the basis of this discovery.

The present invention provides a refrigeration composition, with functions of prevention of friction, abrasion and seizing of sliding portions as defined by the claims.

The disclaimer in claim 2 is based on EP-A 0 377 122.

Now, the present invention will be described in detail with reference to the preferred embodiments.

In the above definitions, the alkyl group includes, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a 2-ethylhexyl group and a nonyl group. The aralkyl group includes, for example, a benzyl group, a phenylethyl group and a methylbenzyl group. The aryl group includes, for example, a phenyl group and a tolyl group. All or a part of hydrogen atoms of these hydrocarbon groups may be substituted by halogen atoms such as fluorine atoms or chlorine atoms. A hydroxyalkyl group includes a hydroxymethyl group, a hydroxyethyl group or a hydroxybutyl group.

The acyl group may be an acyl group of the formula wherein A is the above-mentioned alkyl, aralkyl or aryl group.

The above-mentioned alkyl, aralkyl or aryl group may be employed also for R⁹, R¹⁰, R¹¹ and R¹² in the above-mentioned radicals of the formulas -SO₂R⁹,

Y¹ is a residue obtained by removing both hydroxyl groups from a dicarboxylic compound having at least 3 carbon atoms. The dicarboxylic compound includes, for example, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, suberic acid, methyl succinic acid, methyl adipic acid, maleic acid, fumaric acid and itaconic acid; aromatic dicarboxylic acids such as phthalic acid, diphenyl dicarboxylic acid and diphenyl methane dicarboxylic acid; hydrogenated products of the above aromatic dicarboxylic acids, such as alicyclic dicarboxylic acids; and dicarboxylic acids prepared by introducing carboxyl groups to both terminals of polyalkylene glycols having a molecular weight of from 50 to 1,000.

X¹ in the formula (2) is preferably a residue obtained by removing hydroxyl groups from a dihydroxy compound, such as an ethylene glycol residue or a propylene glycol residue, or a residue obtained by removing hydroxyl groups from the same dicarboxylic compound as mentioned above for the definition of Y¹.

X² in the formula (3) is preferably a residue obtained by removing hydroxyl groups from a trihydroxy compound, such as a glycerol residue or a trimethylol propane residue, or a residue obtained by removing hydroxyl groups from a tricarboxylic compound such as trimellitic acid or trimesic acid.

R¹ in the formulas (1) to (3) and in the radical of the formula is an alkylene group such as an ethylene group, a propylene group, a butylene group or a tetramethylene group. These alkylene groups may be present alone or in combination in the form of a random or block state. In the case of the combination, the main component is preferably a propylene group. R¹ in the formulas (2) and (3) may be the same or different. For the preparation of the compounds of the formulas (1), (2) and (3), the corresponding initiators are respectively, and the numbers of active hydrogen groups thereof are 1, 2 and 3, respectively. If it is attempted to obtain a compound having a kinematic viscosity within range of from 12x10^-6 to 300x10^-6 m²/s (12 cSt to 200 cSt) (40°C) which is common to freezer oils for car air conditioners or refrigerators, by using an initiator having 4 or more active hydrogen groups, the numbers for ℓ, m and n, i.e. the addition molar numbers of alkylene oxides, tend to be too small, whereby the lubricating property will be low, such being undesirable.

The compounds of the formulas (1) to (3) are desired to have a kinematic viscosity of from 12x10^-6 to 300x10^-6 m²/s (12 to 300 cSt) (40°C), so that they provide adequate functions as freezer oils such as the functions for preventing friction, abrasion and seizing of sliding portions of e.g. compressors. Accordingly, it is desirable that the molecular weights of the compounds of the formulas (1) to (3) or the values for ℓ , m and n and the value for p in the formula are selected so as to bring the kinematic viscosity within the above-mentioned range. The values for ℓ , m, n and p are from 6 to 30, and they may be the same or different.

The weight ratio of the compounds of the formulas (1) to (3) to R-134a is usually from 1/99 to 99/1, preferably from 5/95 to 60/40. R-134a may contain a small amount of 1,1,2,2-tetrafluoroethane (R-134). The compounds of the formulas (1) to (3) may be used alone or in combination as their mixtures.

The composition of the present invention is particularly effective when applied to a refrigerating cycle intended for freezing, for refrigerating and for air conditioning. However, it is also useful for other various heat recovery technologies such as a Rankine cycle.

The composition of the present invention has excellent heat stability and requires no stabilizer under a usual application condition. However, if an improvement of the heat stability for use under a severe condition is desired, a small amount of a stabilizer including a phosphite compound such as dimethyl phosphite, diisopropyl phosphite or diphenyl phosphite, a phosphine sulfide compound such as triphenoxy phosphine sulfide or trimethyl phosphine sulfide, and other glycidyl ethers, may be added. Further, the compounds of the formulas (1) to (3) of the present invention may be used in combination with conventional oils such as a naphthene mineral oil, a paraffin mineral oil, an alkylbenzene synthetic oil, a poly-α-olefin synthetic oil, a fluorine type lubricating oil such as a perfluoropolyether oil or a fluorine-containing silicone oil, or polyether oils other than the polyether oils of the present invention.

Further, various additives including a phenol type or amine type antioxidant, a sulfur or phosphorus type high pressure additive, a silicone type anti-foaming agent or a metal inactivating agent such as benzotriazole, may be added to the composition of the present invention.

It is believed that in the present invention, the hydrophilicity is lowered by the modification such as acylation or alkylation of the terminal hydroxyl groups and the hygroscopicity oil is thereby lowered. The mechanism for the compatibility of the oils of the present invention with tetrafluoroethane as a cooling medium, is not clearly understood. However, a certain interaction between tetrafluoroethane and the carbonyl group of the ester bond or the like, is related thereto.

Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples. EXAMPLES 1-1 TO 1-5 AND COMPARATIVE EXAMPLES 1-1 TO 1-5

The structures of the oils used in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-5 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 2.

Into a Petri dish having a diameter of 150 mm, 15 g of an oil having a water content of not higher than 0.03% is introduced. The Petri dish is left open in a constant humidity and temperature room at a temperature of 20°C under a humidity of 50%. The weight increase is calculated by the following equation in which Y is the weight (g) of the oil upon expiration of 30 hours.$$\mathrm{Weight\; increase}=\frac{\mathrm{Y}-15}{15}\times 100\left(\%\right)$$ No. Polyether Upper critical solution temperature (°c) (Compatibility with R-134a) Weight increase (%) (Hygroscopicity) Kinematic viscosity at 40°C (cSt) x 10^-6m²/s Example 1-1 78 0.7 55.4 Comparative Example 1-1 74 2.8 56.0 Example 1-2 56 0.6 100 Comparative Example 1-2 40 1.5 101 Example 1-3 67 1.0 101 Comparative Example 1-3 52 3.2 103 Reference Example 1-4 C₄H₉-O(̵C₃H₆O)̵_21.7COCH₃ 68 0.4 55.8 Comparative Example 1-4 C₄H₉-O(̵C₃H₆O)̵_19.1H 55 1.3 56.1 Example 1-5 51 1.2 102 Comparative Example 1-5 44 2.9 104

Compounds (1) as identified in Tables 3 and 4 were tested for the solubility in R-134a and the stability.

A compound (1) and R-134a were sealed in a glass ampoule at a weight ratio of 30/70, and the solubility of the compound (1) in R-134a was determined by a visual observation of whether or not phase separation was observed. The results are shown in Table 1 together with the results of the Comparative Example. Compound (1): Compound (1) Kinematic viscosity** Solubility R² R¹ R¹¹ Example 2-1*** Butyl Propylene C₂H₅ 32 Dissolved Example 2-2*** Butyl Propylene C₃H₇ 35 Dissolved Example 2-3*** Butyl Propylene C₃H₇ 62 Dissolved Example 2-4*** Butyl Propylene C₃H₇ 102 Dissolved Example 2-5*** Butyl Propylene C₄H₉ 35 Dissolved Example 2-6*** Butyl Propylene C₄H₉ 56 Dissolved Example 2-7*** Butyl Propylene C₅H₁₁ 55 Dissolved Comparative Example 2-1 Suniso 4GS* 56 Insoluble * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x 10^-6 m²/s (cSt), at 40°C
*** Reference example, not covered by the warding of the claims

A compound (1) and R-134a were sealed in a SUS316 pressure container in a weight ratio of 50/50 together with SS41 and Cu as representative metals and left to stand for 14 days at a high temperature of 175°C in a constant temperature tank. After the test, deterioration of the compound (1), R-134a and the metals was determined in comparison with the deterioration of the conventional combination of R-12 and Sniso 4GS. The results are shown in Table 4. Compound (1) Kinematic viscosity** Stability R² R¹ R¹¹ Example 2-1*** Butyl Propylene C₂H₅ 32 Good Example 2-2*** Butyl Propylene C₃H₇ 35 Good Example 2-3*** Butyl Propylene C₃H₇ 62 Good Example 2-4*** Butyl Propylene C₃H₇ 102 Good Example 2-5*** Butyl Propylene C₄H₉ 35 Good Example 2-6*** Butyl Propylene C₄H₉ 56 Good Example 2-7*** Butyl Propylene C₅H₁₁ 55 Good Reference Example Suniso 4GS* 56 Good * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x 10^-6 m²/s (cSt) at 40°C
*** Reference example, not covered by the warding of the claims

Compounds (2) as identified in Tables 5 and 6 were tested for the solubility in R-134a and the stability.

A compound (2) and R-134a were sealed in a glass ampoule in a weight ratio of 30/70, and the solubility of the compound (2) in R-134a was determined by a visual observation of whether or not phase separation was observed. The results are shown in Table 5 together with the Comparative Example. Compound (2): Compound (2) Kinematic viscosity** Solubility R² R¹ R¹⁰ Example 3-1 Butyl Propylene CH₃ 32 Dissolved Example 3-2 Butyl Propylene CH₃ 55 Dissolved Example 3-3 Butyl Propylene CH₃ 102 Dissolved Example 3-4 Butyl Propylene C₂H₅ 56 Dissolved Example 3-5 Butyl Propylene C₆H₅CH₂ 55 Dissolved Example 3-6 Butyl Propylene C₆H₅CH₂CH₂ 53 Dissolved Example 3-7 Butyl Propylene C₆H₅ 55 Dissolved Example 3-8 Butyl Propylene CH₃C₆H₄ 60 Dissolved Example 3-9 Butyl Propylene (CH₃)₂C₆H₃ 62 Dissolved Comparative Example 3-1 Suniso 4GS* 56 Insoluble * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x 10^-6 m²/s (cSt) at 40°C

A compound (2) and R-134a were sealed in a SUS316 pressure container in a weight ratio of 50/50 together with SS41 and Cu as representative metals and left to stand for 14 days at a high temperature of 175°C in a constant temperature tank. After the test, deterioration of the compound (2), R-134a and the metals was ascertained in comparison with the deterioration of a conventional combination of R-12 and Sniso 4GS. The results are shown in Table 6. Compound (2) Kinematic viscosity** Stability R² R¹ R¹⁰ Example 3-1 Butyl Propylene CH₃ 32 Good Example 3-2 Butyl Propylene CH₃ 55 Good Example 3-3 Butyl Propylene CH₃ 102 Good Example 3-4 Butyl Propylene C₂H₅ 56 Good Example 3-5 Butyl Propylene C₆H₅CH₂ 55 Good Example 3-6 Butyl Propylene C₆H₅CH₂CH₂ 53 Good Example 3-7 Butyl Propylene C₆H₅ 55 Good Example 3-8 Butyl Propylene CH₃C₆H₄ 60 Good Example 3-9 Butyl Propylene (CH₃)₂C₆H₃ 62 Good Reference Example Suniso 4GS* 56 Good * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x10^-6m²/s(cSt) at 40°C

Compounds (3) as identified in Tables 7 and 8 were tested for the solubility in R-134a and the stability.

A compound (3) and R-134a were sealed in a glass ampoule in a weight ratio of 30/70, and the solubility of the compound (3) in R-134a was determined by a visual observation of whether or not phase separation was observed. The results are shown in Table 7 together with the Comparative Example. Compound (3): R²-O-(R¹O)_ℓ-R³ Compound (3) Kinematic viscosity** Solubility R² R¹ R³ Example 4-1 Butyl Propylene CH₂CF₃ 32 Dissolved Example 4-2 Butyl Propylene CH₂CF₃ 55 Dissolved Example 4-3 Butyl Propylene CH₂CF(CF₃)₂ 35 Dissolved Example 4-4 Butyl Propylene CH₂CF(CF₃)₂ 62 Dissolved Example 4-5 Butyl Propylene CH₂(CF₂)₆CF₃ 56 Dissolved Example 4-6 Butyl Propylene CH₂(CF₂)₆CF₃ 102 Dissolved Example 4-7 Butyl Propylene CH₂CH(CH₃)CHCl 62 Dissolved Comparative Example 4-1 Suniso 4GS* 56 Insoluble * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x 10^-6 m²/s(cSt) at 40°C

A compound (3) and R-134a were sealed in a SUS316 pressure container in a weight ratio of 50/50 together with SS41 and Cu as representative metals and left to stand for 14 days at a high temperature of 175°C in a constant temperature tank. After the test, deterioration of the compound (3), R-134a and the metals was ascertained in comparison with the deterioration of a conventional combination of R-12 and Sniso 4GS. The results are shown in Table 8. Compound (3) Kinematic viscosity** Stability R² R¹ R³ Example 4-1 Butyl Propylene CH₂CF₃ 32 Good Example 4-2 Butyl Propylene CH₂CF₃ 55 Good Example 4-3 Butyl Propylene CH₂CF(CF₃)₂ 35 Good Example 4-4 Butyl Propylene CH₂CF(CF₃)₂ 62 Good Example 4-5 Butyl Propylene CH₂(CF₂)₆CF₃ 56 Good Example 4-6 Butyl Propylene CH₂(CF₂)₆CF₃ 102 Good Example 4-7 Butyl Propylene CH₂CH(CH₃)CHCl 62 Good Reference Example Suniso 4GS* 56 Good * Naphthene oil, manufactured by Nippon Sun Petroleum Corporation.
** x 10^-6 m²/s (cSt) at 40°C

The structures of the oils used in Examples 5-1 to 5-5 and Comparative Examples 5-1, 5-2 and 5-6 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 9. No. Polyether Upper critical solution temperature (°c) (Compatibility with R-134a) Kinematic viscosity at 40°C (cSt) x 10^-6 m²/s Example 5-1 57 56 Example 5-2 58 54 Example 5-3 60 52 Comparative Example 5-1 C₄H₉O(C₃H₅O)_nH 53 56 Example 5-4 80 32 Example 5-5 85 32 Comparative Example 5-6 >100 2 Comparative Example 5-2 C₄H₉O(C₃H₆O)̵_nH 74 32

The structures of the oils used in Examples 6-1 to 6-5 and Comparative Examples 6-1 to 6-5 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 10. No. Polyether Upper critical solution temperature (°c) (Compatibility with R-134a) Kinematic viscosity at 40°C (cSt) x 10^-6 m²/s Example 6-1 77 57 Comparative Example 6-1 74 56 Example 6-2 53 102 Comparative Example 6-2 40 101 Example 6-3 69 100 Comparative Example 6-3 52 103 Example 6-4 71 54 Comparative Example 6-4 C₄H₉=O(̵C₃H₆O-)_ℓ H 55 56 Example 6-5 50 101 Comparative Example 6-5 44 104

The structures of the oils used in Examples 7-1 to 7-5 and Comparative Examples 7-1 to 7-3 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 11. No. Polyether Upper critical solution temperature (°c) (Compatibility with R-134a) Kinematic viscosity at 40°C (cSt) x 10^-6 m²/s Example 7-1 82 55 Example 7-2 79 56 Example 7-3 80 57 Comparative Example 7-1 74 56 Example 7-4 93 33 Comparative Example 7-2 C₄H₉-O(̵C₃H₆O)̵_ℓ H 74 32 Example 7-5 55 101 Comparative Example 7-3 40 101

The structures of the oils used in Examples 8-1 to 8-5 and Comparative Examples 8-1 to 8-5 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 12. No. Polyether Kinematic viscosity at 40°C (cSt) x 10^-6 m²/s Upper critical solution temperature (°c) (Compatibility with R-134a) Weight increase (%) (Hygroscopicity) Example 8-1 56.0 80 0.7 Comparative Example 8-1 56.0 74 2.8 Example 8-2 100 58 0.6 Comparative Example 8-2 101 40 1.5 Example 8-3 100 63 0.8 Comparative Example 8-3 103 52 3.2 Example 8-4 56 63 0.4 Example 8-5 100 53 1.0 Comparative Example 8-4 104 44 2.9

The structures of the oils used in Examples 9-1 to 9-6 and Comparative Examples 9-1 to 9-6 and the test results for their compatibility with R-134a, hygroscopicity, viscosity indices and kinematic viscosities at 40°C, are shown in Table 13. No. Polyether Weight increase (%) (Hygroscopicity) Viscosity index (VI) Compatibility with R-134a Kinematic viscosity (cSt/ 40°C) x10^-6m²/s Example 9-1 0.9 162 Dissolved 59 Comparative Example 9-1 2.8 135 Dissolved 56 Example 9-2 0.7 196 Dissolved 101 Comparative Example 9-2 1.5 170 Dissolved 101 Example 9-3 1.4 138 Dissolved 100 Comparative Example 9-3 3.2 118 Dissolved 103 Example 9-4 C₄H₉-O(̵C₃H₆O)̵_ℓ -CH₃ 0.5 211 Dissolved 57 Comparative Example 9-4 C₄H₉-O(̵C₃H₆O)̵_m-H 1.3 187 Dissolved 56 Example 9-5 0.9 245 Dissolved 101 Comparative Example 9-5 2.9 228 Dissolved 104 Comparative Example 9-6 Suniso 4SG - - Insoluble 56 Example 9-6 CH₃-O-(C₃H₆O)_n-CH₃ 0.7 214 Dissolved 55

The viscosity index is a value representing the temperature dependency of the viscosity of a lubricating oil. The larger the value, the smaller the change of the viscosity due to the temperature, and accordingly the better the lubricating properties.

An oil and R-134a are mixed in a weight ratio of 15:85 and sealed. The temperature is maintained at 25°C, and the solubility is visually observed.

The structures of the oils used in Examples 10-1 to 10-5 and Comparative Examples 10-1 to 10-6 and the test results for their compatibility with R-134a, hygroscopicity and kinematic viscosities at 40°C, are shown in Table 14. No. Polyether Upper critical solution temperature (°c) (Compatibility with R-134a) Kinematic viscosity at 40°C (cSt) x 10^-6m²/s Example 10-1 78 55 Comparative Example 10-1 74 56 Example 10-2 58 101 Comparative Example 10-2 40 101 Example 10-3 67 102 Comparative Example 10-3 52 103 Example 10-4 61 57 Comparative Example 10-4 C₄H₉-O(̵C₃H₆O)̵_ℓ H 55 56 Example 10-5 52 100 Comparative Example 10-5 44 104 Example 10-6 41 100 Comparative Example 10-6 C₄H₉-O(̵C₃H₆O)_ℓ -H 12 101

The compositions of the present invention provide good compatibility of tetrafluoroethane and polyether oils, and they are capable of adequately providing functions such as the prevention of the friction, abrasion and seizing of sliding portions of e.g. compressors. Further, their hygroscopicity is low, and inclusion of moisture can be minimized, whereby a decrease of insulation resistance can be prevented, and the progress of corrosion of a metal such as a copper pipe by the moisture can be prevented.