KR20000007405A - Coolant 1,1,1,2-tetrafluoroethane of grease for refrigerator - Google Patents

Abstract

PURPOSE: 1,1,1,2,-tetrafluoroethane(HFC-134a) whose ozone depleting potential is zero is used as a coolant in grease for refrigerator. CONSTITUTION: One of polyvalent alcohol selected among pentaerythritol, neopenthylglycol and trimethylolpropane and one of fatty acid selected between n-pentanoic acid and 2-ethylhexanoic acid are reacted to produce an ester compound. HFC-134a is produced by adding grease to this compound. Grease for refrigerator using HFC-134a as a coolant shows excellent characteristics in terms of compatibility with HFC-134a, lubricating ability of a compressor and stability in oxidized state.

Description

Lubricant for refrigerators using 1,1,1,2-tetrafluoroethane as refrigerant

In the present invention, 1,1,1,2-tetrafluoroethane (1,1,1,2-tetrafluoroethane) containing no chlorine and having an ozone depleting potential of zero is referred to as HFC-134a. It relates to a lubricating oil for a refrigerator using a) as a refrigerant.

After the confirmation that Chloro Fluoro Carbon (hereinafter referred to as CFC) and Bromo Fluoro Carbon (hereinafter referred to as Halon) destroys the ozone layer in the stratosphere, the United Nations is the United Nations Environment Agency (UNEP). Supervised in September 1987, the Montreal Protocol banned the production and use of CFCs and Halons.

In CFC, dichlorodifluoromethane (CF ₂ Cl ₂ : hereinafter referred to as CFC-12) is mainly used as a refrigerant refrigerant in refrigerators and car air conditioners, and chlorodifluoromethane (CHF ₂ Cl hereinafter referred to as HCFC-22) It is being used as a refrigerant for a room air conditioner. However, due to high ozone depletion index and global warming potential (GWP), CFC-12 is being replaced by HFC-134a due to environmental issues.

HFC-134a is a polar substance due to its chemical structure, so it is not compatible with mineral oil-based or alkylbenzene-based lubricating oil, which has been used as a refrigeration oil in the past, so it is required to develop a new lubricant for a refrigerator using HFC-134a as a refrigerant. Development of compressors and refrigeration oils suitable for HFC-134a can be traced back to 1988. Initially, lubricating oils based on hydrocarbon fluoride, silicon, ethers and polyalkyleneglycols (PAG) were evaluated. Satisfactory characteristics could not be obtained.

Among them, PAG was excellent in terms of compatibility, but it was found to have a problem in the miscibility and lubrication characteristics with mineral oil-based lubricating oil due to the strong water absorption characteristics, reducing the electrical performance and durability of the compressor.

In order to solve these problems, some of the mixtures of mineral oil and PAG or ester and mineral oil were evaluated to show good lubricity but poor compatibility with HFC-134a (USP 5,372,737).

If refrigerant and lubricant are not completely mixed in the compressor system and separated into two phases, lubricant remains in the evaporator to reduce heat exchange efficiency.In refrigeration compressors, lubricant at the bottom of the compressor may lubricate the compressor due to lack of lubricant. And serious abrasion of mechanical parts such as pistons and cylinders, resulting in high friction losses. HFC-134a has much higher polarity than CFC-12, has a small molecular weight, does not contain chlorine, and the like, and thus suitable refrigeration oil is inevitably limited.

Therefore, the basic characteristics are important for interdissolution between the refrigeration oil and HFC-134a refrigerant, that is, compatibility, and it is necessary to secure high lubricity against the increase in wear of compressor components due to the absence of chlorine in the HFC-134a molecule.

Based on these characteristics, HFC-134a refrigeration oil and polyester and complex ester compounds were examined. Polyhydric alcohols such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol, etc. having 1 to 6 hydroxy groups and carbon number 2 Among ester compounds synthesized from -22 monofatty acids and divalent fatty acids having 2 to 10 carbon atoms, compounds having a 100 ° C kinematic viscosity of 1 to 100 cSt are known to be compatible with HFC-134a. (USP5,486,302, USP5, 185,092, USP5,612,299, USP4,851,144, USP4,053,491, USP4,144,183, USP5,008,028, USP5,716,916 Insufficient, in particular, there is a problem that does not sufficiently satisfy the required performance in terms of lubricity for preventing wear of the compressor.

Furthermore, esters are obtained by condensation of an acid with an alcohol, and the esterification reaction is a reversible reaction, as shown in the following scheme.

In other words, if a reverse reaction occurs, acid is generated, which can have a fatal effect on the compressor components. These problems are accompanied by problems such as destabilization of the decomposition of the compound by hydrolysis and acid, electrical insulation and the like, and countermeasures are also required.

The object of the present invention is ① excellent compatibility to achieve a critical dissolution temperature of -40 ℃ or less, in order to solve the problems of the prior art, which is low in compatibility and lacks the anti-lubrication function by the lubricity and acidic materials, ② long-term The oxidation stability is excellent so that it can be used. ③ For improving the efficiency of the refrigeration compressor, ISO VG 10 (Kinematic Viscosity 9.0 ~ 11.0cSt at 40 ℃), ISO VG 15 (Kinematic Viscosity 13.5 ~ 16.5cSt at 40 ℃) It has low viscosity and excellent lubricity of compressor. ④ It has low water absorption, so it has good stability against hydrolysis and functions to remove acid in case of hydrolysis. ⑤ It does not corrode copper materials. ⑥ Thermal stability It is to provide this excellent refrigeration oil.

In order to achieve the object of paragraph ① of the present invention, the compatibility test between the ester oil having two or more ester bonds in the molecule and HFC-134a was carried out as in Examples 1 to 4 of Table 1 below, and compared with the commercially available products. As in Examples 1 to 6, compatibility tests were performed with HFC-134a.

Table 1 shows the compatibility of chemically synthesized ester compounds and commercially available refrigeration oil products prepared from esters.

The polyhydric alcohols and fatty acids that can be used are as follows.

Sample name Kinematic Viscosity (cSt) @ 40 ℃ Critical melting temperature (℃) (subcritical temperature) Comparative Example 1 Ester-based product (Japan Energy Preol α 15) 15.39 -20 Comparative Example 2 Ester-based product (Japan Energy Preol α 15) 21.78 -33 Comparative Example 3 Ester-based product (sun oil SL-22) 20.58 -33 Comparative Example 4 NPG / nC ₈ 4.7 -30 Comparative Example 5 TMP / nC ₈ 10.9 -20 Comparative Example 6 PE / 2-EH 52.0 -22 Example 1 PE / nC ₅ 15.4 -65 Example 2 NPG / 2-EH 7.08 -62 Example 3 Mixture of NPG / 2-EH and PE / 2-EH 10.32 -48 Example 4 Mixture of NPG / 2-EH and PE / 2-EH, PE / nC ₅ 15.2 -50

NPG: neopentyl glycol (Neopentylglycol)

PE: Pentaerythritol

TMP: Trimethylolpropane

nC ₅ : n-Pentanoic acid

nC ₈ : n-octanoic acid

2-EH: 2-Ethylhexanoic acid

Their structural formula is as follows.

Neopentylglycol trimethylolpropane pentaerythritol

The compatibility of the esters was affected by the structure of the acid reacting with the alcohol, and the best compatibility was obtained when a short acid such as branched acid and pentanic acid was used.

In order to improve the compatibility at low temperatures, the compatibility may be improved by mixing two or three esters in an appropriate ratio to meet the required viscosity.

That is, in order to obtain a refrigerator oil having a kinematic viscosity of 10 cSt at 40 ° C., two esters may be mixed as in Example 3 of Table 1, or three esters may be mixed and used as in Example 4. In this case, however, the composition ratio of the three esters may be different from that of obtaining 15 cSt.

In order to achieve the object of paragraph ② of the present invention, the application of the antioxidant was examined. Compressors installed in refrigerators may be filled or not filled with lubricating oil before they are assembled in the refrigerator system. Peroxides may be produced when stored for a long time with lubricating oil, and during storage and dehydration of lubricants. Anti-oxidation measures for the temperature rise of oil are needed.

As an antioxidant, it was effective to add a phenolic antioxidant that does not affect the insulation material of the compressor motor within the range of 0.10 to 1.5wt%.

As a phenolic antioxidant, as shown in the following structural formula (I) or (II), the structure which can spatially restrict | limit a -OH group is good.

… (Ⅰ)

2,6-di-ter-butyl paracresol

(2,6-di-tert-butylparacresol)

… (Ⅱ)

4,4'-methylenebis [2,6-di-ter-butylphenol]

(4,4'-Methylenebis [2,6-di-tert-butylphenol])

Comparative Example 7 Example 5 Example 6 Example 7 RBOT, min 110 480 530 980 Furtherance Ester base oil 0.3wt% additive 0.5wt% additive 1.0wt% additive Rotating bomb oxidation test (RBOT): The amount of time required for the oxygen pressure to drop by 25 psi while injecting 90 psi (6.2 bar, 620 kpa) of oxygen into the bomb, placing a specified amount of lubricating oil, water, and copper into the oil bath at 150 ° C. Test method for oxidative stability evaluation of lubricating oil specified in ASTM D 2272. The longer it takes for the oxygen pressure to decrease by 25 psi, the better the oxidation stability.

In order to achieve the object of claim 3 of the present invention, as in Examples 1 to 4, a wear resistant agent was added to improve the lubricity while applying a low viscosity lubricant.

The ester compound has -OH group in the molecule, so it can exert relatively strong adsorption power to metal material, so it has good lubricity, but if the viscosity of lubricating oil is lowered, the lubricating film decreases at high temperature and high load. Rapid abrasion may occur and the lubricity should be improved by the selection and application of the appropriate antiwear additives.

The anti-wear agent was effective when 0.5-1.1 wt% of tricresyl phosphate as shown in the following structural formula (III) was applied, and benzotriazole derivatives or tolutriazole derivatives were also lubricating as metal inactivators which did not affect the copper material. It has been shown to affect the improvement. However, the static friction coefficient is relatively high, which is insufficient to improve the lubricity of the refrigerator compressor which is ON / OFF operation.

… (Ⅲ)

The lubrication characteristics evaluation results of tricresyl phosphate using a friction tester are shown in Table 3 below.

Test conditions were steel disc and ball as friction material, amplitude 1.0mm, frequency 50Hz, load 100N (Newton).

Comparison of Lubrication Characteristics Sample Name Coefficient of friction Comparative Example 8 Ester-based product (Japan Energy Preol α 10) 0.125 Comparative Example 9 Ester-based product (Japan Energy Preol α 15) 0.12 Comparative Example 10 Ester-based product (Japan Energy Preol α 22) 0.115 Comparative Example 11 Ester-based product (Texa HFC-22) 0.12 Example 8 PE / nC ₅ + 0.7 wt% additive 0.095 Example 9 NPG / 2-EH + Additive 0.7wt% 0.10 Example 10 NPG / 2-EH and PE / 2-EH Mixture + Additive 0.7wt% 0.095 Example 11 NPG / 2-EH and PE / 2-EH and PE / nC ₅ + Additive 0.7wt% 0.095

As in Examples 5 to 8, the effect of reducing the friction coefficient of 16 to 20% was confirmed by applying 0.5 to 1.1 wt% of an antiwear agent, which directly affects the power consumption of the compressor, and total freezing of work applied to the compressor. In other words, it greatly helps to improve the compressor's freezing coefficient (Coefficient of Performance).

When evaluating the lubrication characteristics of the refrigeration oil, it is necessary to evaluate the refrigerant atmosphere considering the refrigerant used, and laboratory evaluation may cause a lot of error when compared with the evaluation in the actual compressor. Therefore, the results of the practical test using the refrigerator compressor using the above embodiment are shown in Table 4 below.

In Example 12, a metal inactivator, an antioxidant, and an acid trapping agent were added to the antiwear agent in Example 11.

division Example 12 Comparative Example 4 Test Conditions ISO Viscosity Classification Lubricant Refrigerant Discharge Pressure (kg / cm ² ) Suction Pressure (kg / cm ² ) Compressor Temperature (℃) Laboratory Temperature (℃) Test Period (hours) 15 Polyol Ester + Additive HFC-134a 180--15 mm Hg 100 Room temperature 3000 22 Polyol Ester + Additive ←←←←←← Wear rate evaluation (New = 10) Contacting rod, piston end contacting rod, crank end piston Pin cylinder inner diameter Piston face crankshaft, main bearing 869879 668679 Average wear rate 7.83 7.0 Sediment Evaluation (Clean = 10) Exhaust Reed Exhaust Lead Body Intake Reed Cylinder Head Inside Cylinder Head Outside Piston Crown Piston Face 66.6787767 54.68.257765 Average sediment attachment rate 6.81 6.12

Sediment Evaluation of Other Parts (Clean = 10) Phenomenon of Insulation Material String Copper Plating 1010 none 1010 piston and cylinder Lubricant Analysis Viscosity after Test (cSt, @ 100 C) Viscosity (cSt, @ 40 C) Viscosity Change (%) at 40 ° C Color Value (mg KOH / g) 3.7716.7 + 8.3L1.00.05 5.0324.81 + 9.54L1.50.06

Sediment evaluation of the compressor is described in CRC Manual No. 14 was used for evaluation (according to 14 varnish raing test methods issued by the Coordinated Research Council), and the wear rate was visually observed, with a good scratch-free state of 10 and a severe scratch of 1 The intermediate stages were subdivided into 10 grades for evaluation.

As a result of the compressor test, although the refrigeration oil using Example 12 had a lower viscosity than the comparative product, the wear and sediment formation of the compressor was smaller. appear.

The results of the evaluation of the piston, the Wilst Pin, the connecting rod, and the valve plate, which are concerned about the wear and copper plating formation in the compressor, are also good. It was shown to be extremely effective.

In order to achieve the object of claim 4 of the present invention, the structure of the ester, that is, the molecular structure of fatty acids, plays the most important role as the ester compound used to achieve the purpose of item ①. The branched structure at the α-position of the carbonyl group in the fatty acid structure acts as a space limiting element to protect the carbonyl group from water, and thus has excellent hydrolytic stability. In addition, when the phosphate ester is used in the extreme pressure additive to prevent abrasion, the acidic material is generated by decomposition of the additive by moisture, which may cause corrosion as well as a decrease in lubrication performance. In order to prevent such hydrolysis and capture during the generation of acidic substances, the solution was solved using 0.1 to 1.0 wt% of a carbodiimide-based acid trapping agent having the structure shown in the following general formula (IV).

… (Ⅳ)

R is hydrogen or an alkyl group having 1 to 10 carbon atoms

The hydrolysis stability test was performed using a sealed tube test (ASHRAE-97) using an iron, copper and aluminum catalyst under HFC-134a atmosphere and testing at 175 ° C. The test results are shown in Table 5 below.

division Sample composition Moisture (PPM) TAN mg KOH / g ester Scatter Additive 7 days later 14 days later Example 13 Example 1 none 1,000 1.1 2.6 Example 14 Example 2 none 1,000 0.3 0.5 Example 15 Example 3 none 1,000 0.2 0.5 Example 16 Example 4 none 1,000 0.4 2.1 Example 17 Example 1 0.7wt% 1,000 0.02 0.03 Example 18 Example 2 0.6wt% 1,000 0.01 0.01 Example 19 Example 3 0.6wt% 1,000 0.01 0.02 Example 20 Example 4 0.6wt% 1,000 0.02 0.02 TAN: Total Acid Number

In order to achieve the object of claim ⑤ of the present invention by applying 0.01 to 0.5wt% of a benzotriazole derivative or tolutriazole derivative of the following structural formula (V) or formula (VI) as a metal inactivator Prevents oxidation and corrosion of lubricants.

… (Ⅴ)

… (Ⅵ)

Here, R and R 'are hydrogen or an alkyl group having 1 to 12 carbon atoms.

In order to achieve the object of claim 6 of the present invention, the structure of the ester played the most important role as the ester compound used to achieve the purpose of claim ①, the application of antioxidants and phosphorus anti-wear agent is effective.

The additives used to achieve the purpose of Clause 5 and 6 were evaluated using the Sealed Tube Test (ASHRAE-97) below at 175 ° C for 14 days under the refrigerant atmosphere of HFC-134a. Same as

division Sample composition Color of oil Metal catalyst status Example ester additive ASTM color iron Copper aluminum Example 21 Example 1 Antioxidant Antiwear Agent Metal Inert Acid Capture Agent 1.0 Bright Bright Clean Example 22 Example 2 0.5 Bright Bright Clean Example 23 Example 3 0.5 Bright Bright Clean Example 24 Example 4 0.5 Bright Bright Clean

Refrigerator oil of the present invention has excellent compatibility in the refrigerator compressor using the HFC-134a as a refrigerant of -45 ℃ or less and is well mixed without being separated into two layers in the entire temperature range of the low-temperature refrigeration unit, the shaft and bearing of the compressor The formation of a lubricating film in the piston and the cylinder is ensured, and there is no residue of the refrigeration oil in the heat exchanger, that is, the evaporator, thereby improving the heat transfer power for the use of the effective heat of the refrigerant.

In addition, the low viscosity, low coefficient of friction and excellent lubricity have been proved by the practical test using the compressor, which can greatly contribute to the improvement of the COP, which can reduce the power consumption of the refrigerator using the compressor, thereby increasing the freezing capacity. You can.

In addition, the molecular structure of the ester is combined in an optimal state, and the additives, such as antioxidants, antiwear agents, and acid trapping agents, are harmoniously adjusted in consideration of the influence of the compressor parts to improve the performance characteristics and the reliability of the compressor by extending the service life of the refrigeration oil. It can be improved.

Refrigerator oil having the above structure can be effectively applied to the HFC-134a refrigerant ODP is zero and GWP is 1/3 lower than the conventional chlorine-containing refrigerant to protect the global environment. In addition, it can contribute to the reduction of carbon dioxide emissions by reducing the power consumption according to the improved efficiency of the refrigerator.

As mentioned above, although this invention made by this inventor was demonstrated concretely according to the said Example, this invention is not limited to the said Example, It can change variously in the range which does not deviate from the summary.

Claims (6)

Ester obtained by the reaction of a polyhydric alcohol selected from pentaerythritol, neopentyl glycol, trimethylolfuropane, a fatty acid selected from n-pentanoic acid and 2-ethylhexanoic acid in a refrigerator lubricant Refrigerator lubricant using HFC-134a as a refrigerant by adding lubricant additives to at least one compound. The 2,6-di-ter-butylparacresol of formula (I) or 4-4'-methylenebis of formula (II): Refrigerant lubricant for freezer, which is prepared by adding 0.1 to 1.5% by weight of 2-6-di-ter-butylphenol (4-4'-Methylene bis [2-6-di-Tert-butylphenol) to the ester compound as an antioxidant. … (Ⅰ) … (Ⅱ) The lubricating oil for a refrigerator according to claim 1, wherein tricresyl phosphate of the following formula (III) is added by 0.5 to 1.1 wt% of an antiwear agent to an ester compound. … (Ⅲ) The lubricating oil for a refrigerator according to claim 1, wherein the carbodiimide compound of the following general formula (IV) is added by 0.1 to 1.5% by weight based on the ester compound as an acid trapping agent. … (Ⅳ) Here, R is hydrogen or an alkyl group having 1 to 10 carbon atoms. The lubricating oil for a refrigerator according to claim 1, wherein 0.01 to 0.5% by weight of the benzotriazole compound of formula (V) or the tolutriazole compound of formula (VI) are added to the ester compound with a metal deactivator. … (Ⅴ) … (Ⅵ) Here, R and R 'are hydrogen or an alkyl group having 1 to 12 carbon atoms. The lubricating oil of claim 1, wherein the lubricating oil composed of the ester compound and the additive has a low-temperature critical melting temperature of -40 ° C or lower and a kinematic viscosity of 7.0-17.5 cSt at 40 ° C.