Detergent composition and recycling system

Abstract

The present invention provides: a detergent composition which has high detergency in the cleaning of a component or the like to which dirt such as a metal working oil adheres, has less harmful properties and fire risk of a detergent, and is excellent in terms of recyclability by a means other than distillation; and a power-saving recycling system in which the detergent composition is recycled by a means other than distillation.　The recycling system for a detergent composition includes: a step (1) for cleaning an object to be cleaned by dispersing a solvent component for a detergent composition in water while maintaining the detergent composition at a temperature that is equal to or higher than the cloud point, wherein the detergent composition contains a poorly water-soluble solvent, and has a water content within the range of not less than 60 vol% but less than 90 vol% and a cloud point of 20°C to 70°C; a step (2) for cooling the detergent composition after cleaning to the cloud point or lower, thereby phase-separating dirt from the detergent composition; a step (3) for removing the dirt phase-separated from the detergent composition by a separation means other than distillation; and a step (4) for reusing the detergent composition, from which dirt has been removed, in the step (1) for a non-cleaned object.

Description

Cleaning composition and recycling system

[0001] The present disclosure relates to a cleaning composition that can remove processing oils and the like adhering to processed parts, products, and the like in various industrial fields and can be recycled by a means other than distillation, and a recycling system for the same. More specifically, the disclosure relates to a recycling system that, after cleaning an item with a cleaning composition that contains water and has a cloud point, separates contaminant components mixed in the cleaning composition from the cleaning composition by a method other than distillation.

[0002] Various metalworking oils, fluxes, and other processing agents are used in the manufacture of parts and the like used in various industrial fields, such as automobiles, machinery, precision instruments, electricity, and electronics. Generally, parts and the like that have these contaminants (hereinafter referred to as "contamination") attached to them are cleaned before being further processed or manufactured.

[0003] Various types of cleaning agents and cleaning systems, including aqueous, semi-aqueous, halogenated, hydrocarbon, and solvent-based cleaning agents, are used to remove stains, but no cleaning system exists that is fully satisfactory in terms of the safety of the cleaning agent, cleaning power, recyclability, power consumption, etc.

[0004] Aqueous and semi-aqueous detergents containing surfactants cannot be recycled because it is difficult to separate the dirt by distillation, and cleaning is carried out while periodically replacing the detergent. This makes the replacement process cumbersome and generates a considerable amount of waste liquid.

[0005] Halogen-based, hydrocarbon-based, and solvent-based cleaners that do not contain surfactants can be recycled by distillation separation, taking advantage of the large difference in boiling point between them and the high-boiling contaminants. However, halogen-based cleaners have problems such as toxicity, legal restrictions, and high cleaning costs, while hydrocarbon-based and solvent-based cleaners are flammable and pose a high fire risk, so they require explosion-proof equipment and fire prevention facilities, which require costly and thorough management.

[0006] To address these issues, cleaning agents have been proposed that are made non-flammable by blending water with water-soluble solvents and do not contain surfactants, etc. However, all of the recyclable cleaning agents are recycled by distillation, which requires energy depending on the boiling point and latent heat of vaporization of the cleaning agent, resulting in high power consumption and a significant burden on the global environment (see Patent Documents 1 to 4).

[0007] International Publication No. 2015 / 060379 Japanese Patent Application Publication No. 2019-052277 Japanese Patent Application Publication No. 2019-031690 Japanese Patent Application Publication No. 2013-129815

[0008] An object of the present disclosure is to provide a cleaning agent composition that has high detergency, is less harmful and less likely to cause fire, and is excellent in recyclability other than by distillation when used to clean parts and the like contaminated with metal processing oil or the like, and to provide an energy-saving recycling system that recycles the composition by a means other than distillation.

[0009] In light of these circumstances, the present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have discovered the desired detergent composition and a recycling system therefor, thereby completing the present invention.

[0010] That is, the present disclosure includes the following embodiments.

[0011] [1] A cleaning composition comprising a poorly water-soluble solvent and water, the water content being in the range of 60% by volume or more and less than 90% by volume, and the cloud point being 20°C to 70°C.

[0012] [2] The cleaning composition according to the above [1], wherein the poorly water-soluble solvent is a solvent that does not dissolve in water at any ratio at 70°C in an amount of 1 g / 100 g water or more.

[0013] [3] The cleaning composition according to the above [1], wherein the poorly water-soluble solvent is one or more selected from the group consisting of diethylene glycol methyl propyl ether, diethylene glycol methyl butyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, ethylene glycol hexyl ether, diethylene glycol hexyl ether, propylene glycol butyl ether, dipropylene glycol propyl ether, propyl lactate, and butyl lactate.

[0014] [4] The cleaning composition according to the above [1] or [2], further comprising a water-soluble solvent.

[0015] [5] The cleaning composition according to the above [4], wherein the readily water-soluble solvent is a solvent that dissolves in water in any ratio.

[0016] [6] The cleaning composition according to the above [4], wherein the water-soluble solvent is one or more selected from the group consisting of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, ethylene glycol, diethylene glycol, propylene glycol, methoxybutanols such as 3-methoxy-1-butanol and 3-methoxy-3-methylbutanol; methyl lactate, ethyl lactate, tetrahydrofurfuryl alcohol, furfuryl alcohol, 2-dimethyl-1,3-dioxolane-4-methanol, gamma-butyrolactone, and diacetone alcohol.

[0017] [7] A system for recycling a cleaning composition, comprising: (1) a step of dispersing a solvent component of the cleaning composition in water while maintaining the cleaning composition according to any one of the above items [1] to [6] at a temperature equal to or higher than the cloud point, and cleaning an object to be cleaned; (2) a step of cooling the cleaning composition after cleaning to a temperature equal to or lower than the cloud point, and phase-separating dirt from the cleaning composition; (3) a step of removing the dirt that has phase-separated from the cleaning composition by a separation means other than distillation; and (4) a step of reusing the cleaning composition from which the dirt has been removed for the step (1) on the object to be cleaned.

[0018] [8] In the step (3), the means other than distillation is a separation means using at least one selected from a gravity separation tank, a coalescer, a centrifuge, a filtration membrane, and an adsorption column. The recycling system according to the above [5].

[0019] [9] The recycling system described in [8] above, wherein the filtration membrane is a hollow fiber membrane.

[0020]

[10] A recycling system according to any one of [7] to [9] above, wherein the item to be cleaned is an item having water-insoluble soiling attached thereto.

[0021] The present disclosure can provide a cleaning agent composition and a recycling system thereof that have high detergency, are less harmful and pose less of a fire hazard, and are excellent in recyclability other than distillation when used to clean parts or the like having dirt attached thereto, and are capable of cleaning with less power consumption.

[0022] A cleaning composition and a recycling system thereof according to one embodiment of the present disclosure will be described in detail below.

[0023] In the present disclosure, the cleaning composition contains a poorly water-soluble solvent and water, has a water content in the range of 60% by volume or more and less than 90% by volume, and has a cloud point of 20°C to 70°C.

[0024] In the present disclosure, the cloud point refers to the temperature at which a previously transparent solution becomes cloudy due to a change in temperature, and refers to the temperature at which, similar to the phenomenon known for aqueous solutions of nonionic surfactants, when the temperature of the aqueous solution is raised, the solution separates into a phase mainly composed of the solvent component and a phase mainly composed of water, and the previously miscible solution begins to become cloudy.

[0025] In the present disclosure, a higher water concentration in a cleaning composition is preferable in terms of the separation of dirt from the cleaning agent, and is also more effective in eliminating the flash point of the solvent blended in the cleaning agent. A cleaning composition with a water content of less than 60% by volume will not separate dirt from the cleaning agent sufficiently when cooled below its cloud point, resulting in poor recyclability. If the water concentration exceeds 90% by volume, the cloud point of the cleaning agent will rapidly rise with the increase in water concentration, exceeding 70°C, or even disappearing from the cloud point, making cleaning difficult.

[0026] The cloud point of a detergent composition is in the range of 20° C. to 70° C. If the cloud point is lower than 20° C., a lower temperature cooling means is required to separate the dirt, resulting in increased energy consumption. If the cloud point is higher than 70° C., washing at a temperature higher than the cloud point requires washing at a higher temperature, resulting in significant evaporation of water, which leads to significant fluctuations in water concentration, making management more complicated, and also resulting in increased energy consumption.

[0027] From these viewpoints, the water content of the detergent composition is in the range of 60% by volume or more and less than 90% by volume, and the cloud point is in the range of 20°C to 70°C, more preferably in the range of 30°C to 60°C.

[0028] In the present disclosure, the cleaning composition used has a high water concentration and no flash point (as determined by a confirmation test for Class 4 hazardous materials under the Fire Service Act), and therefore is preferred as it poses little risk of fire.

[0029] In the present invention, the cleaning composition exhibits a cloud point in the specific range described above, and such a cleaning composition is composed of a solvent blended with a solvent that does not dissolve in water at any ratio and has a solubility in water of approximately 1 g / 100 g water or more at 70°C (hereinafter referred to as a "poorly water-soluble solvent"), or a solvent blended with a poorly water-soluble solvent and a solvent that dissolves in water at any ratio (hereinafter referred to as a "readily water-soluble solvent"). Water-insoluble solvents such as paraffinic, naphthenic, and aromatic hydrocarbon solvents are unsuitable because they have extremely low water solubility and do not exhibit a cloud point.

[0030] Examples of the poorly water-soluble solvent include glymes such as diethylene glycol methyl propyl ether, diethylene glycol methyl butyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and triethylene glycol dimethyl ether; glycol ethers such as ethylene glycol hexyl ether, diethylene glycol hexyl ether, propylene glycol butyl ether, and dipropylene glycol propyl ether; and lactic acid esters such as propyl lactate and butyl lactate. These can be used alone or in combination of two or more.

[0031] Among these, detergent compositions containing glymes such as diethylene glycol methyl propyl ether, diethylene glycol methyl butyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether are particularly suitable for use because they have high detergency at or above the cloud point and further excellent separability from dirt.

[0032] Furthermore, cleaning compositions containing poorly water-soluble glycol ethers, such as ethylene glycol hexyl ether, diethylene glycol hexyl ether, propylene glycol butyl ether, and dipropylene glycol propyl ether, and poorly water-soluble lactic acid esters, such as propyl lactate and butyl lactate, have the effect of suppressing an increase in cloud point that accompanies an increase in water concentration. Therefore, by blending these cleaning compositions with other solvents, the range of water concentration within which the cloud point of the cleaning agent is in the range of 20°C to 70°C can be broadened, making them more preferable for use.

[0033] In the present disclosure, a cleaning composition containing only a poorly water-soluble solvent may not necessarily exhibit a cloud point in the range of 20°C to 70°C over the entire range of water concentrations from 60% to less than 90% by volume. If the cloud point is lower than this range at a certain water concentration, the cloud point range can be adjusted to fall within the above-mentioned cloud point range by adding a poorly water-soluble solvent or a water-soluble solvent with higher water solubility. Conversely, if the cloud point is high at a certain water concentration, the cloud point range can be adjusted to fall within the cloud point range of the present invention by adding a poorly water-soluble solvent with lower water solubility.

[0034] The water-soluble solvent is not particularly limited as long as it is a water-soluble solvent that is miscible with water in any proportion at about 20°C. However, since the flash point may be raised or drying properties may be deteriorated depending on the blending ratio, a solvent having a boiling point of generally 150°C or higher and 230°C or lower is preferred. Examples of the water-soluble solvent include glycol ethers such as ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol monoethyl ether; glycols such as ethylene glycol, diethylene glycol, and propylene glycol; methoxybutanols such as 3-methoxy-1-butanol and 3-methoxy-3-methylbutanol; lactic acid esters such as methyl lactate and ethyl lactate; cyclic ether alcohols such as tetrahydrofurfuryl alcohol, furfuryl alcohol, and 2-dimethyl-1,3-dioxolane-4-methanol; and gamma-butyrolactone and diacetone alcohol. These may be used alone or in combination of two or more.

[0035] These poorly water-soluble solvents and readily water-soluble solvents preferably have a boiling point of 150° C. or higher. If the boiling point is lower than 150° C., the flash point will not disappear even when water is added, increasing the risk of ignition. If the boiling point is higher than 230° C., drying after cleaning becomes difficult, making it necessary to rinse with pure water or other low-boiling-point solvents.

[0036] In the present disclosure, the cleaning composition has a high water concentration and is used at a relatively high cleaning temperature equal to or higher than the cloud point, and therefore, depending on the conditions of use, the cleaning composition is likely to be oxidized and deteriorated, and the metal object to be cleaned is likely to be corroded, etc. It is more preferable to further add an antioxidant such as 2,6-di-tert-butyl-p-cresol, thymol, methoxyphenol, n-propyl gallate, or hydroquinone, or a corrosion inhibitor such as benzotriazole, tolyltriazole, or imidazoles, within the scope of the characteristics of the cleaning composition.

[0037] In the present disclosure, the detergent composition may further contain a surfactant such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenol, polyoxyethylene fatty acid ester, ethylene oxide-propylene oxide polymer, polyoxyethylene alkylphenol, or polyhydric alcohol fatty acid ester, as long as the surfactant does not deviate from the characteristics of the detergent composition.

[0038] In the present disclosure, the cleaning composition may further contain other polyhydric alcohol derivatives, esters, ethers, amines, amides, etc., within the range that does not impair the performance of the cleaning composition.

[0039] In the present disclosure, the cleaning composition can be applied to stains such as processing oil, as well as stains that are poorly soluble in water, such as flux, wax, grease, ink, resist, and buffs.

[0040] In the present disclosure, the recycling system for a cleaning composition includes: a step (1) of dispersing the solvent component of the above-described cleaning composition in water while maintaining the cleaning composition at a temperature equal to or higher than the cloud point, and cleaning an object to be cleaned; a step (2) of cooling the cleaning composition after cleaning to a temperature equal to or lower than the cloud point, and phase-separating the dirt from the cleaning composition; a step (3) of removing the dirt that has phase-separated from the cleaning composition by a separation means other than distillation; and a step (4) of reusing the cleaning composition from which the dirt has been removed for the step (1) on an object not to be cleaned.

[0041] In the present disclosure, the recycling system cools the cleaning composition to a temperature below the cloud point after cleaning the object to be cleaned, thereby causing phase separation of the dirt contained in the cleaning agent, and removes the phase-separated dirt from the cleaning composition for recycling.

[0042] When cleaning an object at a temperature above the cloud point, the cleaning composition is in a phase-separated state into a solvent-based phase (solvent phase) and a water-based phase (aqueous phase). By cooling below the cloud point, the solvent phase and the aqueous phase become a homogeneous solution, reducing the solubility of the dirt and separating the composition into a cleaning agent phase (cleaning agent phase) and a dirt-based phase (dirt phase). The separated dirt (dirt phase) is then separated from the cleaning agent phase using a removal means and recycled to the cleaning process.

[0043] In step (2), the cooling temperature should be lower than the cloud point of the detergent composition. However, because a temperature lower than the cloud point improves soil separation, the cooling temperature is preferably 5° C. or lower than the cloud point, more preferably 10° C. or lower than the cloud point. Since cooling to a lower temperature does not significantly affect the separation performance, it is preferable to cool to a temperature approximately 5° C. to 20° C. lower than the cloud point.

[0044] Although no special cooling means is required for cooling the cleaning composition if its temperature naturally drops below the cloud point after cleaning, rapid cooling can be achieved by providing an air-cooled, water-cooled, or other heat exchanger. As the heat exchanger, for example, a conventional heat exchanger such as a fin-tube type, plate type, coil type, or shell-and-tube type can be used.

[0045] In step (3), the means for separating the detergent composition from the dirt is composed of one or more separation means other than distillation, selected from the group consisting of a gravity separation tank, a coalescer, a centrifuge, a filtration membrane, and an adsorption column.

[0046] The separation means is selected depending on the droplet size of the soiled phase, the difference in specific gravity between the soiled phase and the detergent composition, the required cleanliness of the detergent composition, and the recycling rate, and two or more types can also be combined.

[0047] When the droplet size of the contaminant phase is large, an oil-water separator is preferable because it has low equipment costs and is easy to manage, but because the separation speed is slow and takes time, it is preferable to separate it using a centrifuge or a filter membrane. It is also possible to increase the droplet size using a coalescer to speed up the separation speed.

[0048] The centrifuge is not particularly limited and any conventional batch or continuous type centrifuge can be used as long as it is capable of liquid-liquid separation. However, a continuous type centrifuge is preferred as it can increase the throughput and is easy to automate, and conventional types such as a disk type and a cylindrical type can be used.

[0049] Generally, the higher the centrifugal acceleration of the centrifuge, the better the separation of dirt and the faster the processing speed. However, good separation is possible if the centrifugal acceleration is generally 400 G or more and the product of centrifugal acceleration (G) x processing time (minutes) is generally 2000 or more.

[0050] Most oil-based processing oils have a specific gravity of approximately 0.95 or less, while the specific gravity of the detergent composition of the present invention is approximately 1.0. Due to the difference in specific gravity, separation can be achieved quickly under the above conditions. However, if the specific gravities of the dirt and the detergent are similar, separation can be achieved by increasing the centrifugal acceleration or centrifugation time.

[0051] A filtration membrane can also be used as the separation means. As the filtration membrane, one that is solvent-resistant and has a pore size of less than 0.5 μm can be preferably used, and those made of polypropylene, polyamide, Teflon (registered trademark), ceramic, or SUS can be preferably used because they are durable against many solvents.

[0052] Furthermore, hollow fiber membranes are preferred because they have a large membrane surface area per volume and can be used for a long period of time by taking measures against pore clogging, such as a cross-flow method or backwashing.

[0053] The pore size of the filtration membrane is preferably one generally classified as a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane). The smaller the pore size, the better the separation of the detergent from the dirt, but the slower the filtration rate. Therefore, a pore size of approximately 0.01 μm to 0.2 μm is more preferable.

[0054] Depending on the type of dirt, a filter for removing solid foreign matter, an ion exchange resin for removing ionic dirt, activated carbon for removing trace amounts of dissolved dirt, etc. may be provided.

[0055] The configuration of the cleaning system for other cleaning, drying, etc. is not particularly limited, and for example, ultrasonic cleaning, jet cleaning, immersion cleaning, swing cleaning, rotational cleaning, shower cleaning, reduced pressure ultrasonic cleaning, etc. can be used, and a single method or a combination of several methods can be used taking into consideration the required cleanliness and required time, etc.

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, "%" and "parts" mean "volume %" and "volume parts" unless otherwise specified.

[0057] Examples 1 to 28 and Comparative Examples 1 to 7 Various cleaning compositions were prepared, and the cloud points, cleaning properties, and separation properties were measured.

[0058] The compositions of the cleaning compositions used in the tests and the results are shown in Tables 1 and 2. The solvents used in the cleaning compositions are as follows:

[0059] (Poorly Water-Soluble Solvents) BuL Butyl Lactate DAP Diacetoxypropane DEBM Diethylene Glycol n-Butyl Methyl Ether DEDG Diethylene Glycol Diethyl Ether DEHe Diethylene Glycol Hexyl Ether DEMiP Diethylene Glycol Methyl i-Propyl Ether DEMnP Diethylene Glycol Methyl Normal Propyl Ether DPDM Dipropylene Glycol Dimethyl Ether DPP Dipropylene Glycol Monopropyl Ether PGB Propylene Glycol n-Butyl Ether (Readily Water-Soluble Solvents) DAA Diacetone Alcohol DPM Dipropylene Glycol Monomethyl Ether MMB 3-Methoxy-3-methylbutanol PGPR Propylene Glycol n-Propyl Ether.

[0060]

[0061]

[0062] [Cloud Point Measurement] The cleaning composition was placed in a 30 ml glass container, heated with hot water at 80° C., or cooled with cold water at 5° C., and the appearance of the cleaning composition was visually observed. The temperature at which the cleaning composition began to become cloudy was taken as the cloud point.

[0063] [Evaluation of cleaning performance] An M4 x 20 mmL bolt with nut was coated with oil-based processing oil (FBH-9S, manufactured by Nippon Kogyo Yusha Co., Ltd.) and immersed in 100 ml of a cleaning composition maintained at a predetermined temperature (10 to 15°C higher than the cloud point) for 3 minutes to perform ultrasonic cleaning (40 kHz, 200 W). The bolt was then immersed in the same cleaning composition for 1 second to rinse, and after air blowing, was dried with warm air. The amount of oil remaining on the dried object was measured using an oil content test, and cleaning performance was evaluated according to the following evaluation criteria.

[0064] Evaluation criteria (residual oil content on the object to be cleaned) ◎: Less than 0.01 (mg / piece) ○: 0.01 or more to less than 0.02 △: 0.02 or more to less than 0.03 ×: 0.03% or more -: Evaluation not performed.

[0065] [Evaluation of Separation Ability] 0.6 parts by weight of oil-based processing oil (FBH-9S, manufactured by Nippon Kogyo Oil Co., Ltd.) equivalent to approximately 4000 ppm of dirt was added and dissolved in 150 parts by volume of the cleaning composition (solvent component only), and the mixture was heated to 70°C, then mixed with 350 parts by volume of 70°C ion-exchanged water and stirred for 10 minutes. The mixture was then cooled to 30°C or below, and the dirt was separated under the following conditions (1), (2), and (3). The nonvolatile content of the cleaning composition after separation was measured by a gravimetric method, and the separation ability was evaluated according to the following evaluation criteria. In the case of (1), the time required to obtain 100 ml of filtrate was also measured.

[0066] Separation conditions: (1) Separation using hollow fiber membrane Hollow fiber membrane: MF membrane: Asahi Kasei Corporation's Microza USP-043 (nominal pore size 0.1 μm), Asahi Kasei Corporation's Microza UMP-053 (nominal pore size 0.2 μm), Unitika Ltd.'s MFW040-2 (nominal pore size 0.04 μm), Unitika Ltd.'s MFW100-2 (nominal pore size 0.1 μm), UF membrane: Unitika Ltd.'s UF30 (nominal molecular weight cutoff 30,000), Hollow fiber pressure: 0.05 to 0.06 MPa, Measurement of filtration rate: The time required to obtain 100 ml of filtrate was measured.

[0067] (2) Separation by centrifuge Centrifuge: AS ONE Centrifuge CN-1050 (angle rotor RA-5004), Centrifugation time: 5 to 30 minutes, Rotation speed: 2000 to 5000 rpm (maximum centrifugal acceleration 420 G to 2620 G).

[0068] (3) Separation by ceramic membrane Ceramic membrane: Cefilt MF0.1 (nominal pore size 0.1 μm) manufactured by NGK Filtec Co., Ltd. Filtration pressure: 0.10 to 0.15 MPa Evaluation criteria (non-volatile content of detergent composition) ◎: Less than 100 ppm, ○: 100 ppm or more and less than 300 ppm, △: 300 ppm or more and less than 500 ppm, ×: 500 ppm or more, -: Not evaluated.

[0069] Evaluation criteria (filtration rate of hollow fiber membrane): ◎: Less than 15 minutes; ○: 15 minutes or more but less than 30 minutes; ×: 30 minutes or more; -: Not evaluated.

[0070] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0071] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-187592, filed on November 1, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. A cleaning composition comprising a poorly water-soluble solvent and water, the water content being in the range of 60% by volume or more and less than 90% by volume, and exhibiting a cloud point of 20°C to 70°C.

2. The cleaning composition according to claim 1, wherein the poorly water-soluble solvent is a solvent that does not dissolve in water at any ratio at 70°C in a proportion of 1 g / 100 g water or more.

3. The cleaning composition according to claim 1, wherein the poorly water-soluble solvent is one or more selected from the group consisting of diethylene glycol methyl propyl ether, diethylene glycol methyl butyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, ethylene glycol hexyl ether, diethylene glycol hexyl ether, propylene glycol butyl ether, dipropylene glycol propyl ether, propyl lactate, and butyl lactate.

4. The cleaning composition according to claim 1, further comprising a highly water-soluble solvent.

5. The cleaning composition according to claim 4, wherein the readily water-soluble solvent is a solvent that dissolves in water in any desired ratio.

6. The cleaning composition according to claim 4, wherein the water-soluble solvent is one or more selected from the group consisting of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, ethylene glycol, diethylene glycol, propylene glycol, methoxybutanols such as 3-methoxy-1-butanol and 3-methoxy-3-methylbutanol; methyl lactate, ethyl lactate, tetrahydrofurfuryl alcohol, furfuryl alcohol, 2-dimethyl-1,3-dioxolane-4-methanol, gamma-butyrolactone, and diacetone alcohol.

7. A system for recycling a cleaning composition comprising: a step (1) of dispersing a solvent component of the cleaning composition according to any one of claims 1 to 6 in water while maintaining the cleaning composition at a temperature equal to or higher than the cloud point, thereby cleaning an object to be cleaned; a step (2) of cooling the cleaning composition after cleaning to a temperature equal to or lower than the cloud point, thereby phase-separating dirt from the cleaning composition; a step (3) of removing the dirt that has phase-separated from the cleaning composition by a separation means other than distillation; and a step (4) of reusing the cleaning composition from which the dirt has been removed for the step (1) of cleaning an object not to be cleaned.

8. The recycling system according to claim 7, wherein in step (3), the separation means is at least one selected from the group consisting of a gravity separation tank, a coalescer, a centrifuge, a filtration membrane, and an adsorption column.

9. The recycling system according to claim 8, wherein the filtration membrane is a hollow fiber membrane.

10. The recycling system according to claim 7, wherein the item to be cleaned is an item having water-insoluble dirt attached thereto.

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