Refrigerant containing organopolysiloxane, and cooling device

Abstract

The purpose of the present invention is to provide an organopolysiloxane for a refrigerant which has relatively good fluidity even at low temperature, has a high flash point, and is easy to handle and store. SOLUTION: A refrigerant containing a branched organopolysiloxane represented by formula (1) and having a molecular weight in the 600-1,500 range (R1 3SiO1 / 2)a(R1 2SiO2 / 2)b(R1SiO3 / 2)c(SiO4 / 2)d (1) (where R1 are each independently a C1-4 alkyl group and a, b, c, and d are integers such that c+d is 1 or more and a+b+c+d is 8-20).

Description

Refrigerants and cooling devices containing organopolysiloxanes

[0001] The present invention relates to an organopolysiloxane for use as a refrigerant, a refrigerant containing the organopolysiloxane, and a cooling device.

[0002] Cooling systems that use circulation pumps to forcibly circulate refrigerants are used in a wide range of applications, including cooling electronic equipment, heat exchange in manufacturing plants, and air conditioning. Their operating temperatures range widely from as low as -30°C to as high as 150°C, but special applications require cooling down to extremely low temperatures of -30°C to -100°C. While mineral oils, alcohols, and halogenated hydrocarbons are known as refrigerant oils, mineral oils become highly viscous at low temperatures, placing a heavy load on circulation pumps. Alcohols have relatively low flash points, requiring careful handling and storage. Furthermore, halogenated hydrocarbons are considered a contributing factor to global warming, and their use is restricted. For these reasons, fluorocarbons, a type of halogenated hydrocarbon with low viscosity and low flammability even at extremely low temperatures, have been widely used as refrigerant oils. However, in recent years, the poor biodegradability of fluorinated compounds such as fluorocarbons has become a concern, and restrictions on their use are being considered.

[0003] For these reasons, there is a demand for alternative refrigerants to fluorocarbons, and silicone oil, which maintains fluidity even at low temperatures, is attracting attention. As described in Patent Document 1, studies on using silicone oil as a refrigerant have been conducted before. In the specification of Patent Document 1, the standard was that the flash point should be 60°C or higher, but considering Japan's Fire Service Act and other regulations, this standard is insufficient. Patent Document 2 describes a mixture of decamethyltetrasiloxane and hexamethyldisiloxane, but although these have low fluidity at low temperatures, they are highly volatile and have a flash point of less than 100°C. Patent Document 3 describes a refrigerant mainly composed of siloxane oligomers, which also have excellent fluidity at low temperatures but a low flash point.

[0004] JP 07-166061 JP 02-242878 JP 2001-262168

[0005] To increase the flash point of silicone oil, a method of increasing its degree of polymerization is known. However, since general silicone oil has a linear structure, it is difficult to control the molecular weight distribution, isolate a single polysiloxane, or remove low-molecular-weight components in the range of the degree of polymerization suitable for refrigerants. In addition, in the usual polymerization method, low-molecular-weight cyclic siloxanes whose remaining amounts are being regulated remain, so it has been difficult to develop silicone oil suitable for refrigerants in this regard. The development of fluorocarbon alternatives for refrigerant applications is an urgent issue, and there is a demand for the development of refrigerants that maintain fluidity even at low temperatures and have a high flash point.

[0006] An object of the present invention is to provide an organopolysiloxane for a refrigerant that has relatively excellent fluidity even at low temperatures, has a high flash point, and is easy to handle and store.

[0007] In order to solve the above problems, the present inventors have found that a branched organopolysiloxane having a specific structure shown below exhibits fluidity at extremely low temperatures while having a high flash point and is suitable as a refrigerant oil for a cooling device.

[0008] That is, the present invention provides: [1] A refrigerant containing a branched organopolysiloxane represented by the following formula (1) and having a molecular weight in the range of 600 to 1,500 (R １ ３ SiO １／２ ) ａ (R １ ２ SiO ２／２ ) ｂ (R １ SiO ３／２ ) ｃ (SiO ４／２ ) ｄ (In the formula, R １ are each independently an alkyl group having 1 to 4 carbon atoms, and a, b, c, and d are such that c + d is 1 or more, and a + b + c + d is an integer of 8 to 20).

[0009] Furthermore, the present invention provides a refrigerant or refrigerant device having at least one of the following configurations [2] to [7]: [2] The refrigerant according to [1], wherein the branched organopolysiloxane has a flash point of 150°C or higher as measured by a method conforming to ASTM D3828-16a (2021). [3] The refrigerant according to [1] or [2], wherein the content of a compound having a molecular weight of less than 600 in the refrigerant is 5% by mass or less of the total mass of the refrigerant. [4] The refrigerant according to any one of [1] to [3], wherein the branched organopolysiloxane has a viscosity of 100 mPa·s or less at -60°C as measured by a rotary rheometer. [5] The refrigerant according to any one of [1] to [4], for use in a cooling device. [6] A cooling device using the refrigerant according to [5]. [7] The cooling device according to [6], wherein the cooling device has a mechanism for forced circulation of the refrigerant.

[0010] The branched organopolysiloxane of the present invention has a high flash point while maintaining good fluidity at extremely low temperatures. Therefore, it can be used as a refrigerant oil over a wide temperature range.

[0011] The present invention is a refrigerant comprising a branched organopolysiloxane represented by the following formula (1). (R １ ３ SiO １／２ ) ａ (R １ ２ SiO ２／２ ) ｂ (R １ SiO ３／２ ) ｃ (SiO ４／２ ) ｄ (1) In the above formula (1), R １ These are alkyl groups having 1 to 4 carbon atoms, independently of each other. １ Examples of these groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, and t-butyl groups. Among these, methyl and ethyl groups are preferred.

[0012] In the above formula (1), a, b, c, and d are integers such that c+d is 1 or greater and a+b+c+d is between 8 and 20. a is preferably an integer between 3 and 10, more preferably between 3 and 6. b is preferably an integer between 0 and 10, more preferably between 0 and 4. c is preferably an integer between 0 and 5, more preferably between 0 and 2. d is preferably an integer between 0 and 4, more preferably between 0 and 2. Note that c+d is 1 or greater, preferably between 1 and 6, more preferably between 1 and 4. Also, a+b+c+d is between 8 and 20, preferably between 8 and 11.

[0013] In this invention, the values ​​a, b, c, and d were measured under the following conditions. ２９ This was determined by Si-NMR spectroscopy and gas chromatography. ２９ [Si-NMR Spectrum Measurement Conditions] Measurement Solvent: Deuterated Chloroform Sample Concentration: 30% by mass Relaxation Reagent: Chromium(III) Acetylacetonate Number of Accumulations: 2,000 Instrument Name: JNM-ECX-500II (manufactured by JEOL Ltd.)

[0014] [Gas Chromatography Measurement Conditions] Instrument: Shimadzu Corporation Gas Chromatograph Nexus GC-2030 Carrier gas: Helium Flow rate: 0.6 mL / min Detector: Flame ionization detector (FID) Detector temperature: 320°C Column: DB-5MS (Inner diameter 0.53 mmφ × Length 30 m, Packing material: Silica) (Agilent Technologies) Column temperature: 50 → 280°C (Heating rate: 10°C / min) Sample injection volume: 1.0 μL Internal standard: n-tetradecane

[0015] The branched organopolysiloxane of the present invention has a molecular weight in the range of 600 to 1,500, preferably in the range of 600 to 1,000. The branched organopolysiloxane of the present invention preferably has a single molecular weight within the above range. If the molecular weight of the branched organopolysiloxane is greater than the above upper limit, the viscosity may be too high and it may not be usable as a refrigerant. If the molecular weight of the branched organopolysiloxane is less than the above lower limit, the flash point may decrease.

[0016] The refrigerant of the present invention contains a branched organopolysiloxane represented by formula (1) in an amount of 88% to 100% by mass, preferably 90% to 100% by mass, and preferably 92% to 100% by mass, based on the total mass of the refrigerant. The refrigerant of the present invention preferably contains a compound having a molecular weight of less than 600 in an amount of 5% by mass or less, based on the total mass of the refrigerant. The lower limit is not particularly limited, and the lower the amount, the better. Preferably, the compound having a molecular weight of less than 600 contains 0% to 5% by mass, and more preferably 0 to 1% by mass. The refrigerant of the present invention may further contain other additives in amounts that do not impair the effects of the present invention.

[0017] The purity of the branched organopolysiloxane of the present invention described above is measured by gas chromatography under the above conditions. Furthermore, the product obtained in the production of the branched organopolysiloxane may be used directly as a refrigerant, and in this embodiment, the purity of the branched organopolysiloxane is equivalent to the content of the branched organopolysiloxane represented by formula (1) in the refrigerant (product).

[0018] The method for producing the branched organopolysiloxane used in the refrigerant of the present invention can be carried out according to conventionally known methods. For example, it can be produced by hydrolysis and condensation reactions of chlorosilane or alkoxysilane, or by condensation reactions of organohydrogensiloxane and alkoxysilyl groups using a borane catalyst, followed by purification by distillation or the like. This makes it possible to obtain a refrigerant that mainly consists of a branched organopolysiloxane represented by the above formula (1) and having a molecular weight in the range of 600 to 1,500, with a content of compounds having a molecular weight of less than 600 being 5% by mass or less.

[0019] The branched organopolysiloxane of the present invention preferably has a viscosity of 100 mPa·s or less at -60°C. A viscosity exceeding 100 mPa·s at -60°C is undesirable because it increases the load on the circulation pump. More preferably, it has a viscosity of 50 to 80 mPa·s at -60°C. In this invention, viscosity is measured using a rotary rheometer in an environmental test chamber cooled with liquid nitrogen under the following conditions. In this invention, viscosity refers to dynamic viscosity. [Measurement conditions] Apparatus: DHR-2, environmental test chamber (manufactured by TA Instruments) Shear rate: 1,000 s －１ Plate: Aluminum parallel plate (upper diameter 25 mm, lower diameter 40 mm, gap 0.5 mm)

[0020] It is desirable that the flash point of the refrigerant be higher than the operating temperature. Therefore, the flash point of the branched organopolysiloxane of the present invention is preferably 150°C or higher, and more preferably 160°C to 250°C. In this invention, the flash point is the value measured using a Ceta closed-type flash point measuring device in accordance with the ASTM D3828-16a (2021) method.

[0021] The present invention more preferably provides a refrigerant for a cooling system, and more preferably a refrigerant for a cooling system having a mechanism for forced circulation of the refrigerant. The refrigerant of the present invention can be suitably used as a refrigerant for a cooling system having a mechanism for forced circulation of the refrigerant. Examples of cooling systems include a refrigerant storage tank, a refrigerant circulation device, and a commonly known cooling system having a mechanism for forced circulation of the refrigerant, such as a refrigerator or heat exchanger for cooling the refrigerant.

[0022] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0023] [Example 1] Tetramethoxysilane (30 g) and toluene (119 g) were charged into a reaction vessel, and tris(pentafluorophenyl)borane (0.026 g) was added under a nitrogen atmosphere. The temperature was raised to 50°C, and 1,1,1,3,3-pentamethyldisiloxane (129 g) was added dropwise over 4 hours at 50-75°C. The mixture was stirred at 50-80°C for 1 hour, and it was confirmed that the reaction was complete. １ Confirmation was made by 1H-NMR. Vacuum distillation (oil bath temperature 90-95°C, 5 hPa) was performed to obtain 125 g of a colorless, transparent liquid fraction. The obtained fraction was obtained under the conditions described above. ２９ Si-NMR spectral analysis and gas chromatography confirmed that the target product is a branched organopolysiloxane with the structure shown below, with a purity of 92% and a yield of 25%. Here, purity refers to the mass percentage of the branched organopolysiloxane with the structure shown below relative to the total mass of the fraction (product) obtained. This invention utilizes the product as a refrigerant. The branched organopolysiloxane is, in formula (1) above, R １ The compound is such that all are methyl groups, a is 4, b is 4, c is 0, and d is 1. The above branched organopolysiloxane has a molecular weight of 680.

[0024] [Comparative Example 1] A commercially available dimethylpolysiloxane (viscosity of 5 mPa·s at 25°C, trade name: KF-96P-5cs, manufactured by Shin-Etsu Chemical Co., Ltd.) was used. The organopolysiloxane is represented by the following formula, and the average value of n is 7. The number average molecular weight is 680.

[0025] The characteristic values of the organopolysiloxanes of Example 1 and Comparative Example 1 are shown in Table 1. The flash point was measured using a Setar closed flash point measuring device in accordance with the method described in ASTM D3828-16a (2021). The viscosities at 25°C, 0°C, -20°C, -40°C, -60°C, and -80°C were measured using a rotational rheometer according to the above-described conditions. Also, the content of the compound having a molecular weight of less than 600 accompanying the organopolysiloxanes of Example 1 and Comparative Example 1 was determined by gas chromatography under the above-described conditions. The mass % of the compound having a molecular weight of less than 600 in the fraction (product) obtained above is shown in Table 1 below.

[0026]

[0027] The product obtained in Example 1 above was used as a refrigerant in a cooling water circulation device (manufactured by Tokyo Science Machine Co., Ltd., CCA-1112) having a mechanism for forced circulation of the refrigerant, and when operated at -20°C and 30°C for 30 days each (12 hours / day), it was confirmed that it could be used as a refrigerant.

[0028] As described above, the refrigerant containing the branched organopolysiloxane in the present invention exhibits a low viscosity even at low temperatures and has a sufficiently high flash point. Therefore, it can be suitably used as a refrigerant oil for a cooling device having a mechanism for forced circulation of the refrigerant.

Claims

1. A refrigerant (R) containing a branched organopolysiloxane represented by the following formula (1) and having a molecular weight in the range of 600 to 1,500 １ ３ SiO １／２ ) ａ (R １ ２ SiO ２／２ ) ｂ (R １ SiO ３／２ ) ｃ (SiO ４／２ ) ｄ (1) (where R １ are, independently of each other, alkyl groups having 1 to 4 carbon atoms, and a, b, c, and d are integers such that c + d is 1 or more and a + b + c + d is 8 to 20).

2. The refrigerant according to claim 1, wherein the branched organopolysiloxane has a flash point of 150°C or higher as measured by a method in accordance with ASTM D3828-16a (2021).

3. The refrigerant according to claim 1, wherein the content of a compound having a molecular weight of less than 600 contained in the refrigerant is 5% by mass or less of the total mass of the refrigerant.

4. The refrigerant according to claim 1, wherein the branched organopolysiloxane has a viscosity of 100 mPa·s or less at -60°C as measured by a rotary rheometer.

5. A refrigerant according to any one of claims 1 to 4, for use in a cooling device.

6. A cooling device using the refrigerant described in claim 5.

7. The cooling device according to claim 6, wherein the cooling device has a mechanism for forced circulation of a refrigerant.

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