WO2025229884A1 - Coolant containing organopolysiloxane - Google Patents

Abstract

[Problem] To provide a coolant which is relatively excellent in terms of fluidity even at low temperatures, has a high flash point, and is easy to handle and store. [Solution] Disclosed is a coolant which contains an organopolysiloxane represented by formula (1). (In formula (1), each R¹ independently represents a group that is selected from among an alkyl group having 1 to 8 carbon atoms and a phenyl group, and n is an integer of 5 to 1,000.) The organopolysiloxane has a kinematic viscosity at 25°C of 10-50 mm²/s, and has a molecular weight distribution that satisfies formula (2) as determined by gel permeation chromatography (GPC) measurement. (2): 0.40 ≤ (LT/HT) ≤ 0.65 In formula (2), LT and HT are defined as described in the description of the present application. [Selected drawing] Fig. 1

Description

Refrigerant containing organopolysiloxane

The present invention relates to a refrigerant for use in a cooling device that contains an organopolysiloxane. More specifically, it relates to a refrigerant for use in a cooling device that has a mechanism for forced circulation of the refrigerant.

Cooling devices that use circulation pumps or other devices to force the circulation of refrigerants have a wide range of applications, including cooling electronic devices, heat exchange in manufacturing plants, and air conditioning, and can be used at temperatures ranging from -60°C to approximately 150°C. Known refrigerant oils include mineral oil, alcohols, and halogenated hydrocarbons. Mineral oils become highly viscous at low temperatures, placing a heavy load on circulation pumps, while alcohols pose problems due to their toxicity and flammability. Of the halogenated hydrocarbons, chlorinated hydrocarbons are a contributing factor to global warming, and their production and use are regulated. For these reasons, fluorocarbons, which have low viscosity and low flammability even at low temperatures, have been widely used as refrigerant oils. However, the persistence of fluorocarbons has become a problem in recent years, and restrictions on their use are being considered.

For these reasons, there is a demand for alternative refrigerants to fluorocarbons, and silicone oils, which maintain their fluidity even at low temperatures, are attracting attention. The use of silicone oils as refrigerants has been investigated to date (Patent Document 1). However, the specification stipulated that a flash point of 60°C or higher would be sufficient, which is insufficient in light of Japan's Fire Service Act and other regulations. Mixtures of decamethyltetrasiloxane and hexamethyldisiloxane have also been proposed, but while these have low fluidity at low temperatures, they are highly volatile and have flash points below 100°C (Patent Document 2). Refrigerants primarily composed of siloxane oligomers have also been proposed, but these also have excellent fluidity at low temperatures but a low flash point (Patent Document 3). The development of alternatives to fluorocarbons for refrigerant use is an urgent issue, and there is a need for refrigerants that maintain fluidity at low temperatures and have a high flash point.

Japanese Patent Application Publication No. 07-166061 Japanese Patent Application Publication No. 02-242878 Japanese Patent Application Laid-Open No. 2001-262168

The objective of the present invention is to provide a refrigerant that has relatively good fluidity even at low temperatures, a high flash point, and is easy to handle and store.

The inventors have discovered that organopolysiloxanes with a specific bias in molecular weight distribution exhibit fluidity at low temperatures while also possessing a high flash point, making them suitable for use as refrigerants.

That is, the present invention provides:
[1] Provided is a refrigerant containing an organopolysiloxane represented by the following formula (1):
(wherein ^R1 's are each independently a group selected from an alkyl group having 1 to 8 carbon atoms and a phenyl group, and n is an integer of 5 to 1,000).
And,
the organopolysiloxane has a kinematic viscosity of 10 to 50 mm ² /s at 25°C as measured with a Cannon-Fenske viscometer in accordance with the method described in JIS Z8803:2011;
The refrigerant has a molecular weight distribution calculated by gel permeation chromatography (GPC) measurement that satisfies the following formula (2):
In the above formula (2), LT and HT are defined as follows:
In the chromatogram obtained by the GPC measurement,
The maximum point where the intensity of the peak of the distribution curve is greatest is designated as (P),
The elution time corresponding to the maximum point (P) is defined as (PT),
The point (P h5 ) is located on a line drawn perpendicular to the baseline of the chromatogram from the maximum point (P) and is 5/100 of the length (h) from the baseline to the maximum point (P). A line drawn parallel to the baseline passing through point (P _h5 ) intersects with the distribution curve of the chromatogram at points (P _H ) on the early elution time side (i.e., the high molecular weight component side) and point (P _L ) on _{the late elution time side (i.e., the low molecular weight component side). HT is the time from point (P h5 ) to point (P H ) (} i.e., the elution time of the high molecular weight component), and LT is the time from point (P _L ) to point (P _h5 ) (i.e., the elution time of the low molecular weight component).

The present invention further provides the above refrigerant, which further has at least one component selected from the following:
[2] The refrigerant described above, wherein the organopolysiloxane has a flash point of 200°C or higher.
[3] The above refrigerant, wherein the organopolysiloxane has a flash point of 250°C or higher.
[4] The above refrigerant, wherein all of the R ^1s in the formula (1) of the organopolysiloxane are methyl groups.
[5] The above refrigerant, wherein the organopolysiloxane has a kinematic viscosity at −20° C. of 30 to 120 mm ² /s.
[6] The above refrigerant, wherein the organopolysiloxane has a flash point of 200°C or higher and a kinematic viscosity at -40°C of 60 to 250 mm ² /s.
[7] The above refrigerant, wherein the organopolysiloxane has a flash point of 250°C or higher and a kinematic viscosity at -40°C of 60 to 250 mm ² /s.
[8] The above refrigerant, which is a refrigerant for a cooling device.
[9] The above-mentioned refrigerant, wherein the cooling device has a mechanism for forced circulation of the refrigerant.
More preferably, the present invention provides a refrigerant comprising an organopolysiloxane represented by the above formula (1).

The organopolysiloxane contained in the refrigerant of the present invention maintains good fluidity at low temperatures and has a high flash point. Therefore, it is useful as a refrigerant over a wide temperature range.

FIG. 1 is a chromatogram showing the relationship between the molecular weight distribution and elution time of the organopolysiloxane contained in the refrigerant of the present invention.

The present invention relates to a compound represented by the following formula (1):
(wherein ^R1 's are each independently a group selected from an alkyl group having 1 to 8 carbon atoms and a phenyl group, and n is an integer of 5 to 1,000).
The refrigerant contains an organopolysiloxane represented by the formula:

In the above formula (1), ^R1 's are each independently a group selected from an alkyl group having 1 to 8 carbon atoms and a phenyl group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group. Preferably, 70% or more of the total number of moles of ^R1 's are methyl groups, and more preferably, all of the R1 ^'s in formula (1) are methyl groups.
n is an integer of 5 to 1,000, preferably an integer of 6 to 500, more preferably an integer of 7 to 200, more preferably an integer of 10 to 150, and even more preferably an integer of 14 to 100.

In the present invention, the value of n is determined from a ²⁹ Si-NMR spectrum measured under the following conditions.
[Measurement conditions]
Measurement solvent: deuterated chloroform Sample concentration: 30% by mass
Relaxation agent: chromium(III) acetylacetonate
Number of times accumulated: 2,000 times Device name: JNM-ECX-500II (manufactured by JEOL Ltd.)

The organopolysiloxane contained in the refrigerant of the present invention has a kinematic viscosity at 25°C of 10 to 50 mm ² /s, preferably 10 to 30 mm ² /s. If the kinematic viscosity at 25°C is lower than the above lower limit, the fluidity in the low temperature range will be improved but the flash point will be low. On the other hand, if the kinematic viscosity at 25°C is higher than the above upper limit, the flash point will be high but the viscosity at low temperatures will increase. Note that in the present invention, the kinematic viscosity is the value at 25°C measured using a Cannon-Fenske viscometer according to the method described in JIS Z8803:2011.

The organopolysiloxane contained in the refrigerant of the present invention maintains good fluidity at low temperatures, preferably having a kinematic viscosity of 30 to 120 mm ² /s at -20°C and 60 to 250 mm ² /s at -40°C.
In the present invention, the kinematic viscosity at temperatures below 0° C., for example, −20° C. or −40° C., is a value measured using a rheometer in an environmental test chamber cooled with liquid nitrogen under the following conditions.
[Measurement conditions]
Apparatus: DHR-2, environmental test chamber (manufactured by TA Instruments)
Shear rate:: 1,000s ^-1
Plate: Aluminum parallel plate (upper diameter 25 mm, lower diameter 40 mm, gap 0.5 mm)
The absolute viscosity obtained as a measurement result was converted to kinematic viscosity using the following formula (a) from the absolute viscosity and specific gravity at the measurement temperature T°C. The specific gravity (T°C) at the measurement temperature T°C was calculated using the following formula (b).
Kinematic viscosity (T°C) = Absolute viscosity (T°C) / Specific gravity (T°C) Formula (a)
Specific gravity (T℃) = 0.0009 x (25-T) + specific gravity (25℃) Formula (b)

It is desirable for the flash point of the refrigerant to be higher than the operating temperature, preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher in Japan. The flash point is measured using a Cleveland open cup method as described in JIS K2265-4:2007. Accurate measurement of flash point using this method is difficult at temperatures above 300°C, so the preferred upper limit for flash points is 300°C, but flash points above that can also be used.

The organopolysiloxane of the present invention is characterized by a specific bias in its molecular weight distribution, i.e., the organopolysiloxane of the present invention has a molecular weight distribution in which the ratio of the elution time (LT) of the low molecular weight component to the elution time (HT) of the high molecular weight component in a chromatogram obtained by gel permeation chromatography (GPC) measurement satisfies the relationship of the following formula (2):

In the above formula (2), LT and HT are defined as follows:
In the chromatogram ( FIG. 1 ) obtained by the GPC measurement, the maximum point where the intensity of the peak of the distribution curve is greatest is defined as (P), the elution time corresponding to the maximum point (P) is defined as (PT), and a point (P h5 ) is located on a line drawn perpendicular to the baseline of the chromatogram from the maximum point (P) at a position that is 5/100 of the length (h) from the baseline to the maximum point (P). Points where a line drawn parallel to the baseline passing through the point (P _h5 ) intersects with the distribution curve of the chromatogram are point (P _H ) on the early elution time side (i.e., the high molecular weight component side) and point (P _L ) on the late elution time side (i.e., the low molecular weight component side), and the HT is the time from point (P _h5 ) to point (P _H ) (i.e., the elution time of the high molecular weight _component ), and the LT is the time from point (P _L ) to point (P _h5 ) (i.e., the elution time of the low molecular weight components).
The chromatogram obtained by the GPC measurement of the organopolysiloxane of the present invention preferably contains a single peak. The organopolysiloxane can be obtained by removing low-molecular-weight components by vacuum distillation, as described below, to bias the molecular weight distribution. However, this also includes cases where the peak has a broad peak, a shoulder peak, or a split peak, to the extent that it does not intersect with a line drawn parallel to the baseline of the chromatogram that passes through the above point (P _h5 ).

If the ratio of the elution time (LT) of the low molecular weight component to the elution time (HT) of the high molecular weight component (i.e., LT/HT) is greater than the upper limit above, the proportion of low molecular weight components in the organopolysiloxane will be high, and therefore the flash point of the organopolysiloxane will be low. On the other hand, if the value of LT/HT is less than the lower limit above, the proportion of high molecular weight components will be too high, and the viscosity of the organopolysiloxane will be high. The organopolysiloxane contained in the refrigerant of the present invention has a ratio of HT to LT that is 0.40≦(LT/HT)≦0.65, and more preferably 0.45≦(LT/HT)≦0.60.

In the present invention, GPC measurement of organopolysiloxane was carried out under the following conditions.
[Measurement conditions]
Developing solvent: toluene Flow rate: 0.6 mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-H
TSKgel SuperH5000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2000 (6.0mm I.D. x 15cm x 1)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (toluene solution with a concentration of 0.3% by mass)

The organopolysiloxanes used in the present invention can be produced by commonly known methods, such as co-hydrolysis of trimethylchlorosilane and dimethyldichlorosilane, or by equilibration reaction of hexamethyldisiloxane with a cyclic polysiloxane compound, such as octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane, in the presence of an acid or base catalyst.

Examples of catalysts for the equilibration reaction include acidic catalysts such as sulfuric acid, fuming sulfuric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and hydrochloric acid; metal hydroxides such as sodium hydroxide and potassium hydroxide; and basic catalysts such as the reaction product of dimethylsiloxane and an alkali metal. The amount of catalyst added can be determined according to conventional methods, and is preferably 0.01% to 5% of the organopolysiloxane raw material. The equilibration reaction temperature is not particularly limited, but is typically 0°C to 100°C for acid catalysts and 100°C to 180°C for basic catalysts. The organopolysiloxane obtained by cohydrolysis or equilibration reaction is washed with water or neutralized to remove by-product acids and catalytic acids or bases, and then heated at 100°C to 120°C under reduced pressure to remove solvents and low-molecular-weight components. The organopolysiloxane of the present invention can be further biased in its molecular weight distribution by reducing the pressure to 1.5 kPa or less and stripping at 200° C. or higher. Alternatively, a bias in the molecular weight distribution can be imparted by extracting only the low molecular weight components using an organic solvent such as methanol or acetone.
The refrigerant of the present invention may further contain other additives in amounts that do not impair the effects of the present invention. The type of additive is not particularly limited, and may be appropriately selected from conventionally known additives for refrigerants.

The refrigerant of the present invention can be suitably used as a refrigerant for cooling devices that have a mechanism for forced circulation of the refrigerant. Examples of cooling devices include commonly known forced circulation cooling devices that use a refrigerant storage tank, a refrigerant circulation device, a refrigerator that cools the refrigerant, or a heat exchanger.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

In the following examples and comparative examples, the value of n was determined from the ²⁹ Si-NMR spectrum measured under the conditions described above.
The kinematic viscosity of the organopolysiloxane at 25°C was measured using a Cannon-Fenske viscometer in accordance with the method described in JIS Z8803:2011.
The kinematic viscosities at 20°C, 50°C, and 100°C were also measured using a Cannon-Fenske viscometer according to the method described in JIS Z8803:2011.
The kinematic viscosities at 0° C., −20° C., and −40° C. were measured using a rotational rheometer according to the measurement conditions described above.
The GPC measurement of the organopolysiloxane was carried out under the above-mentioned measurement conditions. The definitions of LT and HT are as explained above.
The flash point of the organopolysiloxane was measured using a Cleveland open flame detector in accordance with JIS K2265-4:2007.

[Example 1]
A reaction vessel was charged with hexamethyldisiloxane (80 g) and decamethylcyclopentasiloxane (700 g), and under a nitrogen atmosphere, 97% sulfuric acid (15 g) was added as an acid catalyst and stirred at 25 to 30°C for 4 hours, after which ion-exchanged water (6 g) was added and stirred at 25 to 30°C for 30 minutes, after which the waste acid was separated and neutralized by washing with water. Low molecular weight components were removed at a reduced pressure of 0.5 kPa or less and an internal temperature of 200°C or higher, yielding a colorless, transparent organopolysiloxane (330 g).
The resulting organopolysiloxane was represented by the above formula (1), in which all ^R1s were methyl groups and the average value of n was 19. The organopolysiloxane had a kinematic viscosity at 25°C of 16.5 ^mm2 /s, and the ratio (LT/HT) of the elution time (LT) of the low molecular weight components to the elution time (HT) of the high molecular weight components was 0.55.

[Example 2]
A reaction vessel was charged with hexamethyldisiloxane (80 g) and decamethylcyclopentasiloxane (650 g), and under a nitrogen atmosphere, 97% sulfuric acid (15 g) was added as an acid catalyst and stirred at 25 to 30°C for 4 hours, after which ion-exchanged water (6 g) was added and stirred at 25 to 30°C for 30 minutes, after which the waste acid was separated and neutralized by washing with water. Low molecular weight components were removed at a reduced pressure of 0.5 kPa or less and an internal temperature of 140°C or higher, yielding a colorless, transparent organopolysiloxane (290 g).
The resulting organopolysiloxane was represented by the above formula (1), in which all ^R1s were methyl groups and the average value of n was 13. The organopolysiloxane had a kinematic viscosity at 25°C of 12 ^mm2 /s, and the ratio (LT/HT) of the elution time (LT) of the low molecular weight components to the elution time (HT) of the high molecular weight components was 0.46.

The properties of the organopolysiloxanes obtained in the examples are shown in Table 1.
Furthermore, the following dimethylpolysiloxane was used as a comparative component and its kinematic viscosity, flash point, and molecular weight distribution were measured.
Comparative Example 1: Dimethylpolysiloxane having a kinematic viscosity of 10 mm ² /s at 25°C (KF-96-10cs, manufactured by Shin-Etsu Chemical Co., Ltd.)
Comparative Example 2: Dimethylpolysiloxane having a kinematic viscosity of 20 mm ² /s at 25°C (KF-96-20cs, manufactured by Shin-Etsu Chemical Co., Ltd.)

As described above, the organopolysiloxane of the present invention has a low viscosity at low temperatures and a flash point of 200° C. or higher, preferably 250° C. or higher. Therefore, refrigerants containing this organopolysiloxane can be safely used as refrigerant oil in circulation-type cooling systems.

Claims (9)

A refrigerant containing an organopolysiloxane represented by the following formula (1):
(wherein ^R1 's are each independently a group selected from an alkyl group having 1 to 8 carbon atoms and a phenyl group, and n is an integer of 5 to 1,000).
where:
the organopolysiloxane has a kinematic viscosity of 10 to 50 mm ² /s at 25°C as measured with a Cannon-Fenske viscometer in accordance with the method described in JIS Z8803:2011;
and has a molecular weight distribution calculated by gel permeation chromatography (GPC) measurement that satisfies the following formula (2):
In the above formula (2), LT and HT are defined as follows:
In the chromatogram obtained by the GPC measurement,
The maximum point where the intensity of the peak of the distribution curve is greatest is designated as (P),
The elution time corresponding to the maximum point (P) is defined as (PT),
The point (P h5 ) is located on a line drawn perpendicular to the baseline of the chromatogram from the maximum point (P) and is 5/100 of the length (h) from the baseline to the maximum point (P). A line drawn parallel to the baseline passing through point (P _h5 ) intersects with the distribution curve of the chromatogram at points (P _H ) on the early elution time side (i.e., the high molecular weight component side) and point (P _L ) on _{the late elution time side (i.e., the low molecular weight component side). HT is the time from point (P h5 ) to point (P H ) (} i.e., the elution time of the high molecular weight component), and LT is the time from point (P _L ) to point (P _h5 ) (i.e., the elution time of the low molecular weight component). The refrigerant according to claim 1, wherein the organopolysiloxane has a flash point of 200°C or higher. The refrigerant according to claim 1, wherein the organopolysiloxane has a flash point of 250°C or higher. 2. The refrigerant according to claim 1, wherein all R ¹ 's in said formula (1) of said organopolysiloxane are methyl groups. 2. The refrigerant according to claim 1, wherein the organopolysiloxane has a kinematic viscosity at -20°C of 30 to 120 mm ² /s. 2. The refrigerant according to claim 1, wherein the organopolysiloxane has a flash point of 200° C. or higher and a kinematic viscosity at −40° C. of 60 to 250 mm ² /s. 2. The refrigerant according to claim 1, wherein the organopolysiloxane has a flash point of 250° C. or higher and a kinematic viscosity at −40° C. of 60 to 250 mm ² /s. The refrigerant according to any one of claims 1 to 7, which is a refrigerant for use in a cooling device. The refrigerant described in claim 8, wherein the cooling device has a mechanism for forced circulation of the refrigerant.