JP2832190B2 - Cleaning method using supercritical and subcritical fluids - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning hard-to-clean items such as shoes using supercritical and subcritical fluids.

[0002]

2. Description of the Related Art When an object to be cleaned such as a semiconductor is housed in a pressure-resistant cleaning container, a supercritical fluid is brought into contact with the object to be cleaned by a supercritical supply means, and the supercritical fluid is brought into contact with the object to be cleaned. Moisture and organic matter adhering to the cleaning material dissolve in the supercritical fluid,
Move to supercritical fluid. When the supercritical fluid in which water and organic substances are dissolved is removed from the pressure-resistant cleaning vessel by an appropriate means, an object to be precisely cleaned can be obtained. Since moisture has been removed, a cumbersome dry finish is not required. This is because the pressure and temperature conditions are near the critical point as shown in the phase diagram of the pure substance and the graph of the supercritical fluid in FIG.
> P _c (critical pressure), T> T _o (critical temperature), a supercritical fluid that means a high-density fluid that has no other characteristics. (1) A slight change in pressure causes a large change in density. can get.
In general, since the solubility of a substance is proportional to the density, a large difference in solubility can be obtained only by a change in pressure. (2) The density of a supercritical fluid is similar to that of a liquid, but has low viscosity and high diffusivity. Therefore, it is more advantageous in terms of mass transfer. This is the latest cleaning technology that has come to be used for cleaning semiconductor substrates and the like that make good use of the technology.

[0003] Conventional cleaning of a semiconductor substrate is performed by sequentially passing through a solvent bath corresponding to the object to be cleaned and washing it off. For example, for an oil or fat, an organic solution tank (trichlene, acetone, etc.) is used to remove metals. The target is an acid or alkali solution tank (for example, H ₂ O ₂ —NH ₄ OH, HCl—H ₂
In O, etc. ₂ mixture), also with respect to the natural oxide film generated on the substrate surface, washed with HF solution tank, rinse these chemicals with ultrapure water, spin drying and the like in the final stage, the semiconductor This method is called a so-called wet cleaning method in which water that hinders performance and production is completely removed and is passed to each production process. However, it has been developed instead of this method, and there are many proposals. The principle is that, first of all, the low viscosity of the supercritical fluid indicates that it is easy to penetrate into narrow parts, and the high density of the fluid indicates that the supercritical fluid adheres to the substrate.
The high solubility of the impregnating contaminants, especially organic fluids, secondly, the above-mentioned cleaning action results in a supercritical fluid containing the contaminants, but the dissolving action is reduced by reducing its density. Accordingly, the above-mentioned components are deposited in liquid and solid forms. Therefore, it utilizes the fact that these components can be recovered and the circulating fluid can be cleaned in a decompressed separation tank.

[0004] The above physical properties also have a subcritical fluid. The subcritical fluid refers to a fluid that is in a state near a critical point in a pressure-temperature phase diagram. In this region, the fluid is in a physically unstable state and is therefore distinguished from a supercritical fluid. Thus, in the cleaning method disclosed in JP-A-3-261128, the solvent is designated as "supercritical gas containing a subcritical state". As the adopted gas, carbon dioxide, nitric oxide, ethane, propane, etc. are used. In particular, carbon dioxide is nonflammable, harmless, inexpensive, and
The critical temperature is 31 ° C., the critical pressure is 79.2 atm,
It is preferably used because it is easy to handle.

[0005]

In the prior art described above, cleaning is achieved by completely immersing an object to be cleaned in a cleaning fluid and dissolving contaminants in the fluid. The separation of contaminants is not regarded as being caused by complete dissolution, and many of them are undissolved, separated into solids, and transferred into a fluid. In other words, a large amount of solid contaminants also exist and float in the applied cleaning fluid, and the solid contaminants adhere to the object to be cleaned.

[0006] In the case where such re-adhesion is not allowed, there is a disadvantage that a step of washing again with a washing fluid must be added. Further, simply relying only on the dissolving action is time-consuming and inefficient. However, if forced agitation is added to the fluid, the difficulty in designing the pressure-resistant washing container increases, and practical application becomes difficult. However, this does not solve the aforementioned redeposition. In particular, when the object to be washed is a difficult-to-wash object such as shoes, it is difficult to completely clean the shoe.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and the object of the present invention is to provide a forcible method even for difficult-to-clean items such as shoes. Supercritical and subcritical fluids that can be completely removed out of the system without forcing contaminants to adhere to the object to be cleaned by a forced peeling action without disposing a stirring means in the pressure-resistant cleaning vessel are also provided. It is intended to provide the used cleaning method.

[0008]

In order to achieve the above object, a cleaning method according to the present invention comprises immersing an object to be cleaned in a supercritical fluid and a subcritical fluid to which an entrainer is added as required in a pressure-resistant cleaning device. Then, the fluid in the pressure washer is rapidly discharged out of the washer, or the fluid density is rapidly expanded by rapidly expanding the inner volume of the washer, thereby strengthening the contaminant surface. Disturbance or a large amount of air bubbles are generated, and contaminants are promptly forcibly peeled off and dissolved by the flow action or the bubbling action to clean the object to be cleaned.

At this time, when the inorganic compound or the polar substance which is hardly soluble in the supercritical fluid or the subcritical fluid is a contaminant, the lipophilic surfactant capable of preventing the re-adhesion by incorporation of the substance into the reverse micelle. Should be mixed. It is also preferable to control the flow action or the bubbling action by intermittently applying the expansion of the supercritical and subcritical fluids.

[0010] A supercritical fluid and a subcritical fluid to which an entrainer is added as necessary are jetted in a jet stream from an injection nozzle onto an object to be cleaned in the pressure-resistant washer. Fluid is quickly discharged out of the washer, or is rapidly expanded by increasing the volume inside the washer to generate strong turbulence or a large amount of air bubbles. In this method, the contaminants are quickly forcibly peeled and dissolved by using the impact energy of the object, and the object to be cleaned is cleaned.

In this case, when the inorganic compound or the polar substance which is hardly soluble in the supercritical fluid or the subcritical fluid is a contaminant, the lipophilic surfactant capable of preventing the re-adhesion by incorporating these substances into reverse micelles. Should be mixed.

[0012]

The most distinctive feature of supercritical fluids is that the density can be varied greatly, and therefore one solvent can be compared to many liquid solvents. Thus, the fluid in the pressure washer can act as a solvent for various contaminants in hard-to-clean items such as shoes that are immersed in density fluctuations. The same applies to a subcritical fluid.

On the other hand, when the fluid density is rapidly expanded, a peculiar phenomenon is exhibited. That is, when the fluid is rapidly discharged out of the vessel, the fluid in the container changes its density (expands) to maintain the pressure. This also occurs when the container volume is rapidly increased, that is, when the cleaning container is communicated with the collection tank to substantially increase the volume.

During this expansion, very strong disturbances and microbubbles occur in the supercritical region, and disturbing and a large amount of larger bubbles, so-called bubbling, occur near the subcritical region.
This is understood to be caused by the instability of the fluid in the subcritical and near supercritical regions, that is, the rapid transition to a state of high density fluctuation due to the mixture of clusters of different sizes.

Therefore, under this condition, in addition to the solvent's inherent dissolving power, a physical washing action such as strong disturbance and bubbling is added. This disturbance and bubbling causes not only forced separation but also forced levitation for solid waste that may be reattached, and it goes out of the vessel through the discharge line as it is, eliminating the risk of reattachment, Eliminate the need for rewashing.

When a surfactant is mixed in a fluid, solid contaminants, insoluble inorganic compounds and polar substances are taken into the micelles, and large bubbles suitable as a carrier are formed. Up further. Also,
When the disturbance and the bubbling are operated intermittently, what is dissolved during the non-operation is trapped at a stroke, and the chemical cleaning and the physical cleaning are advantageously combined, resulting in highly efficient cleaning.

In the invention according to claim 4, the above-mentioned phenomena occur in the adhered liquid and the impregnating liquid on the surface and the inside of the object to be cleaned. The dirt on the surface is removed, and the jet spray rinses away the dirt-laden liquid on the surface of the object to be cleaned. Since the object to be cleaned is not immersed in the fluid, there is no fear of redeposition. Washing is completed as quickly as in shower washing.

In the fifth aspect of the present invention, the action of the above-described surfactant is added to the action of the fourth aspect of the present invention.

[0019]

An embodiment will be described with reference to the drawings. FIG.
Shows an example of an apparatus configuration for carrying out the method of the present invention. A fluid cylinder 1 is connected to a pressure-resistant washing vessel 3 by a pipe system 2, and is opened by opening a shut valve 4 provided in the pipe system 2. The critical and subcritical fluid 6 is supplied to the pressure-resistant cleaning vessel 3. The container 3 contains an object 5 to be washed, such as shoes, which is difficult to wash.

The object to be cleaned 5 is immersed in the fluid 6 in the case of the first to third aspects of the present invention.
In the cases of the inventions described in (5) to (5) above, they are supported without being immersed. In order to add an entrainer to the fluid 6 or mix a surfactant, the entrainer or the surfactant tank 7 may be connected to the pipe system 10 having a pump 8 and a valve 9.

On the other hand, a discharge pipe system 11 is connected to the container 3, and is provided with a shutoff valve 12 and a flow control valve 13, which are connected to a storage tank 15 through a filter 14 for emission to the atmosphere or for recovery. You. On the bottom of the container 3,
A pipe system 16 for discharging the fluid 6 of the cleaning agent is connected, and is radiated to the atmosphere through a shut valve 17 and a flow control valve 18.
Alternatively, the storage tank 15 may be connected to the discharge pipe system 11.
Will be collected.

In the case of the invention described in claims 4 and 5, a plurality of injection nozzles (not shown) are provided on the container 3 or the nozzles are rotated so as to be able to irradiate the inside and outside of the object 5 to be cleaned. It may be supported (not shown).

[0023]

Since the present invention is configured as described above, it has the following effects. According to the first to third aspects of the present invention, since the disturbance and the bubbling effect effective for cleaning are achieved without introducing a separate stirring device, it is possible to avoid an increase in the size and cost of the device. A powerful cleaning effect that exceeds the cleaning power of

According to the fourth and fifth aspects of the present invention, a showering effect is added to the above-mentioned effect, and speeding up is achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a method of the present invention.

FIG. 2 is a phase diagram of a pure substance and a graph of a supercritical fluid.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fluid cylinder 2 Pipe system 3 Pressure-resistant washing container 4 Shut valve 5 Object to be cleaned 6 Supercritical and subcritical fluid 7 Surfactant tank 8 Pump 9 Valve 10 Pipe system 11 Discharge pipe system 12 Shut valve 13 Flow control valve 14 Filter 15 Storage tank 16 Pipe system 17 Shut valve 18 Flow control valve

Continuation of the front page (56) References JP-A-7-171527 (JP, A) JP-A-4-187275 (JP, A) JP-A-3-261128 (JP, A) JP-A-6-126256 (JP) JP-A-8-274055 (JP, A) JP-A-8-57437 (JP, A) JP-A-7-284739 (JP, A) JP-A-5-269446 (JP, A) 5-86241 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B08B 1/00-11/04 B01D 11/00

Claims (5)

(57) [Claims] 1. An object to be cleaned is immersed in a supercritical fluid and a subcritical fluid to which an entrainer is added as required in a pressure-resistant cleaning device, and then the fluid in the pressure-resistant cleaning device is quickly discharged out of the cleaning device. Or by rapidly expanding the fluid density by increasing the volume inside the washer, causing strong disturbances or large amounts of air bubbles on the surface of the contaminant, and the flow or bubbling action of the contaminant. A cleaning method using a supercritical or subcritical fluid, wherein the object to be cleaned is cleaned by rapidly forcibly peeling and dissolving the material. 2. When an inorganic compound or a polar substance which is hardly soluble in a supercritical fluid or a subcritical fluid is a contaminant, a lipophilic surfactant capable of preventing the re-adhesion by incorporating these substances into reverse micelles. The cleaning method using a supercritical fluid and a subcritical fluid according to claim 1, wherein the fluid is mixed. 3. A cleaning method using a supercritical fluid and a subcritical fluid according to claim 1 or 2, wherein the expansion of the supercritical fluid and the subcritical fluid are intermittently applied to control the flow action or the bubbling action. 4. A supercritical fluid and a subcritical fluid to which an entrainer is added as necessary are jetted in a jet stream state from an injection nozzle onto an object to be cleaned in the pressure-resistant cleaning device. The fluid is rapidly expanded by the method according to claim 1 to generate strong turbulence or a large amount of air bubbles, and the flow action or the bubbling action and the impact energy of the jet injection promptly forcibly separate the contaminants. A cleaning method using a supercritical fluid and a subcritical fluid, wherein an object to be cleaned is cleaned by forcible dissolution. 5. When a pollutant is an inorganic compound or a polar substance which is hardly soluble in a supercritical fluid or a subcritical fluid, a lipophilic surfactant capable of preventing the re-adhesion by incorporating these substances into reverse micelles. The cleaning method using a supercritical fluid and a subcritical fluid according to claim 4, wherein the fluid is mixed.