GB2156204A - Cleaning objects - Google Patents

Abstract

Objects are cleaned by treatment with a gas in which are suspended mist particles not more than 0.5 mu in size. The gas with suspended mist droplets maybe produced by passing the gas through a chamber in which water is sprayed to form a gas containing microscopic droplets, which is then passed through a filter to form the requisite mist. The gas may be air, carbon dioxide, nitrogen, oxygen, or a rare gas. Air with the mist particles suspended therein may be circulated into rooms in which semiconductors are made, or surgical operations performed, or in which sterile food and biopharmaceuticals are prepared to clean the objects therein.

Description

SPECIFICATION Method of cleaning object Background ofthe Invention: The present invention relates to a method of cleaning factories manufacturing LSIsorVLSIs,factor- ies manufacturing biopharmaceuticals, surgical operating rooms, precision machinery-washing factories and factories manufacturing sterile food, or objects placed in these factories and rooms, as well as the operatives, patients and the like therein wearing clothes.

More particularly, the invention pertains to a method wherein air which contains 50,000 mist particles or more of essentially not more than 0.5 micron per cubic feet is sent to VLSI-manufactu ring factories, sterile food-manufacturing factories, airshower rooms in these factories intowhich operatives go before the commencement of work, orthe sickrooms of seriously ill patients, to clean objects.

In general, hospitals, pharmaceutical-manufacturing factories, laboratories and so forth require a clean atmosphere containing no dust or microbes. Therefore, a means is employed such that air is cleaned by the use ofan airfilteroran aircurtain is installed at the entrances and exists thereof. However, these means cannot provide a sufficiently cleaned gas, and the employment ofan air-shower room still cannot attain the purpose of providing such a clean gas.

The present inventor has found, as one result of a zealous study into the cleaning of objects, that the smaller a waterdrop, the lower its surface tension and that when a waterdrop becomes a mist particle of 0.5 micron or less, it adheres strongly to microscopic objects, and, moreover, if a gas containing 50,000 or more such mist particles per cubic feet is applied to an object, the gas adheres not only to microscopic dust, but also to viruses as well as bacteria, mold fungi, and spores presenttherein and carries them away, thereby allowing the objectto be cleaned.Moreover, it has been found that a gaseous atmosphere in which such microscopic waterdrops are suspended can clean the atmosphere as well as offer such the unexpected advantageous effect that although there are water drops present, the object will never be wetted even if the number of mist particles is large, provided that each ofthe mist particles is esentially not more than 0.5 micron. It has also been found, as the result of further examinations, thatwhen an ordinary gas is passed through a gaseous atmosphere in which are suspended microscopic water drops, the ordinary gas is highly cleaned so that it is ultraclean, and such a highly cleaned gas can be directly applied to various rooms, sections and other related places.The present invention has been completed on the basis ofthis new knowledge, and as the result ofthe repetition of various experiments and researches concerning, in particular, an industrially effective method of producing a gas in which are suspended microscopic waterdrops.

Summary ofthe Invention: Accordingly, it is a primary object ofthe invention to provide a method of cleaning an object wherein the object istreatedwith a gas in which are suspended a large number of mist particles of essentially not more than 0.5 micron.

The air within which a large number of mist particles of essentially not more than 0.5 micron are suspended, employed in the present invention, can be produced by means of an apparatus such as that described hereinafter. It is a matter of course that when an inert gas is required, it is only necessary to employ nitrogen gas instead of air.

Brief Description of the Drawings: Fig. 1 shows one embodiment of an apparatus producing a mist-containing gas; Fig. 2 shows another embodiment ofthe apparatus producing a mist-containing gas; Fig. 3 is a section through the upper part ofthe apparatus of Fig. 2; Fig. 4 is a section through the apparatus of Fig. 2, taken alongthe central partthereof; Fig. 5 is a schematic illustration of a complete system in which the present invention is applied to an actual semiconductor-manufactu ring factory; Fig. 6 is an illustration of a heat exchangerwhich can be provided afterthe apparatus producing the mistcontaining gas; and Fig. 7 is a section an upper part ofthe heat exchanger of Fig. 6.

Description ofthe Preferred Embodiments: Referring first to Fig. 1, the most basic apparatus for producing a gas containing a mist has a plurality of water injection nozzles 2 provided on the side surfaces of a tank 1. It is preferable thatthese nozzles 2 are arranged alternately so that the nozzles provided on opposite side surfaces are slightly offset from each other, that is, it is desirable that facing nozzles should not be arranged on the same straight lines.The water injected from each water injection nozzle 2 crosses the interior of the tank 1, as shown by the dashed lines D and strikes the opposite side surface to form microscopicwaterdrops Ewhich fillthetank 1. Underthis state, when a gas is sentfrom the bottom ofthetank 1, as shown bythe arrowA, upthrough thetank 1, the gas easily picks up the microscopic waterdrops and is then discharged from an outletformed in the upper part ofthe tank 1, enabling the provision ofthe desired gas in which a mist is suspended.If necessary, the apparatus may be constructed such that one or more baffle plates (not shown) are provided within the tank 1, either vertically or at an angle (in series, or parallel, oralternately), andthe jets of waterare arranged to strike each baffle plate to form the microscopic waterdrops. The resultant gas containing microscopic waterdrops is passed through a filter so that it contains mist particles of essentially not morethan 0.5 micron, and it is then usedforcleaning an object. In this case, any type of filter can be used. When forced through a filter, large waterdrops such as those bigger than 1 micron, are broken upon impact when they come into contact with the filter, and disappear through evaporation; so that large waterdrops are substantially removed.

Figs. 2,3 and 4 in combination show a more efficient apparatusfor producing a gas in which a mist is suspended, with which the temperature is controlled.

As an example, the production of a cooled mist containing gas will be described hereununder. It is to be noted that a heated mist-containing can be easily produced by replacing the following cooling system with a heating system.

Referring nowto Fig. 2, a cyclone 40 has an air inlet 42 tangentially provided in an upper part of a cylindrical portion 41 thereof. The center of the cylindrical portion 41 is provided with an outlet pipe 43 which extends downward. The outlet pipe 43 is provided with a cold water injection pipe 44 surround- ing the outlet pipe 43, coaxiallytherewith. The injection pipe44 is provided with a plurality of injection nozzles 45. An evaporation pipe 47 of a refrigerator is arranged within the cylindrical portion 41 ofthe cyclone 40.The evaporation pipe 47 and the injection nozzles 45 can be arranged so that the pesitionsthereof are eithercompletely orslightly offset from each other, and they are positioned so that the waterfrom the injection nozzles 45 is injected perpendicularly onto the corresponding portions of the evaporation pipe 47 in the form of sprays orjets. A filter 48, a watertank49 and a pump 50 are provided in that order in the lowered of a conical portion 51 of the cyclone -.0. Accordingly the cold water is recircu lated in the direction of the arrows B, that is, through the sequence of the pump 50, a recirculation pipe 46, the injection pipe 44, the cylindrical portion 41 of the cyclone, the conical portion 51 of the cyclone, the filter 48,thewatertank49, and the pump 50. A refrigerant, in particular, a high-temperature refrigerant (1 Cto 5at), circulates through the evaporation pipe 47 in the direction ofthe arrows C. A gas is sent into the cyclone 40 through the inlet 42 in the direction ofthe arrow A, and it picks up microscopic waterdrops as is also cooled in the cyclone 40 to become the required gas which is then passed through the outlet pipe 43 for use.When the water injected orsprayed at D from the injection nozzles 45 provided in the injection pipe 44 strikes the evaporation pipe 47 of the refrigerator and/orthe side surfaces ofthe cylindrical portion 41, as at E, mist particles are produced (simultaneously therewith, the water stream striking the evaporation pipe 47 exchanges heat with the refrigerant flowing through the pipe 47 and is thus cooled), and the waterdrops are cooled. Asthe gas passesthrough such an atmosphere, as shown by the arrows A, it picks up microscopicwaterdrops as also exchanges heat with the cooled waterdrops so that it is cooled and becomes the required gas.

Fig. 5 is a schematic illustration of a complete system in which the method ofthe invention is applied in practice to a factory mass-producing 64-kilobit RAMs. The mist-containing gas produced in the cyclone 40 by the operation described above is sent into a waterdrop-removing cyclone 50, as shown by the arrows A. More specifically, the gas discharged from the cyclone 40 enters the waterdrop-removing cyclone 50th rough an inlet which is provided tangentially in a sidewall of the cyclone 50. While the gas is circulating in the waterdrop-removing cyclone 50, excess waterdrops and large waterdrops are removed to provide a gas in which is suspended at leat 90% mist particles of not more than 0.5 p, and the gas is removed from an outlet pipe provided in the central part of the cyclone 50.

The mist-containing gas thus removed is sent to an air-shower room 60through a pipe P provided with a filter F to clean people who will work in an ultraclean room 70 adjacent to the air-shower room 60. Simultaneously, part of the mist-containing gas is sent directly to the ultraclean room 70. Thus cleaned gas which contains no dust is sent into the room and is also used to wash the silicon substrates employed in the manufacture of LSls. Moreover, if necessary, it is possible that, instead using the mist-containing gas directly, ordinary air is sent through a shower ofthe gas so that it is cleaned, andthecleaned air is used.

The gas which has been used in the ultraclean room 70 is removed therefrom and is returned to the cyclone 40 through a pipe P and a fan F, and the cycle is repeated.

It has been confirmed that this method makes it possible to maintain an ultraclean room in such an extremely clean state that a space of 1 feet3 contains less than one particle of dust biggerthan 0.5 p. On the other hand, several tens ofthousands of dust particles are suspended in a cubicfootofairin an ordinary factory. From this point of view, it will be understood that the method ofthe present invention is extraordinarily good.

Further, it is possible to raise the gas to an optimum temperature as well as make the mist particles smaller to increase its effects, by providing a heat exchanger 100 afterthe waterdrop-removing cyclone 50, as shown in Figs. 6 and 7, and passing the mistcontaining gas through the heat exchanger 700. The heat exchanger 100will now be described. The center of a barrel 101 is provided with an air discharge pipe 105 which extends vertically. The air discharge pipe 105 communicates with an air duct 105' provided outside the barrel 101. Accordingly, airfrom an air intake pipe 104 reaches the lower part of the barrel 101 while swirling therein, and rises from the lower part of the air discharge pipe 105 in the direction ofthe arrows. In addition, the interior ofthe barrel 101 is provided with an outer pipe 106 and an inner pipe 107.

The lower end of each of the pipes 106, 107 communicateswith a pump 108 provided outside the barrel 101, in orderto pass hot water or cold watertherethrough, which is discharged from drain ports 109, 110 provided in the upper part ofthe barrel 101.A plurality of water injection nozzles 111 a,111 b . . . formed in a wash water pipe 111 are provided in upper and lower partsofthebarrel 101.The nozzles 111a,111 b . . . are arranged so as to face the upper and lower sides ofthe vertical rows of each ofthe pipes 106 and 107, so that wash water can be jetted out toward the pipes 106, 107 and the inner surfaces ofthe barrel 101, as well as the outer surfaces ofthe air discharge pipe 105. A drain pipe 112' is provided in a lower part of the conical portion 102 so that it is possible to drain the wash water, ora drain produced by the cooling ofthe gas, from the barrel 101. Accordingly, the dust, etc. in the airfrom the air intake pipe 104 is separated in the barrel 101 by means of a cyclonic effect, and is heated or cooled to an optimum temperature by means ofthe pipes 106, 107. The air heated or cooled to the optimum temperature is sent outthrough the air discharge pipe 105. On the other hand, the separated dust and the like can be washed away by supplying waterto the wash water pipe 111, and jetting the water out of the nozzles 111 a,111 b .

Since the thus treated gas has a large number of mist particles of not more than 0.5 micron suspended therein, any object can be cleaned by treating the object with the gas.

Although in the present invention air is generally employed as the gas, when oxidation is undesirable it is possible to use carbon dioxide, nitrogen ora rare gas. On the other hand, oxygen may also be em ployed. In otherwords, it is possibleto employ various appropriate gases and mixtures thereof as desired.

The mist particles of not more than 0.5 micron employed in the method of the present invention have an extremely low surface tension and therefore adhere easilyto objects or dust suspended in the air. It is presumed that the weight of any dust to which mist particles have adhered will increase, and hence the dust can be removed by means of a blast. In particular, since the method ofthe invention employs microscopic mist particles, it is possible to remove not only microscopic dust, but also bacteria and viruses, so that an object can be cleaned both physically and biologically. Hitherto, viruses are removed by an air filterorthe like. Since viruses are only 0.5 to 0.01 u in size, however, it is impossible to remove them sufficiently by this conventional method.Accordingly, if a room is cleaned by the method ofthe present invention, the possibility is reduced that people in the room will catch a cold. Thus, the invention is extremely suitable for use in hospitals, pharmacies, laboratories, maternity hospitals, etc.

Moreover, since the method of the present invention makes it possible to avoid the inclusion of various bacteria, this method can be employed for washing the food and apparatuses in food-manufacturing factories. Therefore, the method of the present invention is also extremely suitable for use in food stores, supermarkets and so forth for, for instance, thawing frozen meat and keeping salads, vegetables, fresh fish, and dressed meat. In particular, the method ofthe present invention makes it possible to manufacture uncooked ham, which conventionally has limitations on the manufacture thereof because of the danger ofthe inclusion of various bacteria.

As has been described, the method ofthe present invention can be applied to the washing of imple mentsforsurgical operations in addition to precision machinery because of its ultracleanness. Moreover, it is expectedthatthe method ofthe present invention will be utilized in the medical field forwashing lungs, for example.

Claims (3)

1. Amethodofcleaning an objectcomprising treating the object with a gas in which are suspended a large numberofmist particles of essentially not more than 0.5 micron.

2. Amethodofcleaning anobjectcomprising treating the object with a gas in which are suspended 50,000 mist particles or more of essentially not more than 0.5 micron per cubic feet, said gas being obtained in such a manner that water is sprayed so as to strike against an object to obtain microscopic waterdrops which are suspended in a gas, and then large waterdrops are removed from the gas.

3. A method of cleaning an object substantially as hereinbefore described.