Patent Application
20130240479
1. Field of the Invention
The present invention relates to a method for producing a filtration filter.
2. Description of Background Art
Filtration filters are often used to produce clean water from factory and household wastewater (sewage) by removing contaminants and foreign matter or to produce freshwater from seawater by removing salt content or the like. As for filtration filters, reverse osmosis membranes made of polymeric material such as polymeric membranes of methyl acetate are known. A reverse osmosis membrane has numerous penetrating holes with a diameter of a few nanometers. When pressure is added to sewage or seawater to make it flow through such penetrating holes, contaminant molecules the size of a few dozen nanometers and hydrated sodium ions surrounded by water molecules cannot pass through the penetrating holes, while water molecules each with an approximate diameter of 0.38 nm can pass though the penetrating holes. Accordingly, the reverse osmosis membrane produces clean water or freshwater from sewage or seawater by separating water molecules from contaminants or salt content.
However, when polluted water is purified using reverse osmosis membranes to provide clean water in developing countries and areas stricken by natural disasters, problems arise such as a notably reduced life span for reverse osmosis membranes due to bacteria contained in polluted water that cause decay in polymeric membranes.
Also, since salt and fine sand tend to be mixed into lubricating oil in windmill-type wind power generators located along shore lines, it is strongly required that salt and fine sand be removed from lubricating oil. However, if reverse osmosis membranes are used to remove salt and fine sand, ingredients of the lubricating oil may dissolve polymeric membranes, causing problems such as a notably short life span for the reverse osmosis membranes.
According to one aspect of the present invention, a method for producing a filtration filter includes using masking film formed on a surface of a rigid substrate and having a plurality of openings with a uniform size to expose portions of the surface, etching the portions of the substrate corresponding to the openings, and forming a plurality of holes or grooves in the substrate.
According to one aspect of the present invention, a method for producing a filtration filter includes laminating a plurality of rigid substrates by means of organic material to have a predetermined distance from each other, and removing the organic material.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.
First, a method for producing a filtration filter is described according to a first embodiment of the present invention.
In
Next, silica film 3 is deposited on the surface of substrate 1 and inner surfaces of circular holes 2 by CVD (Chemical Vapor Deposition) using thermal oxidation. During that time, more silica film 3 is deposited near the opening end than inside circular hole 2, making the actual diameter of circular hole 2 the smallest near the opening end (
Next, silica films 3 of two substrates 1, where the diameter of circular holes 2 is reduced by silica film 3, make contact with each other, and the temperature of the ambient atmosphere is raised to 400° C.˜1000° C. so that silica films 3 are thermally bonded. At that time, two substrates 1 are laminated so that the position of each circular hole 2 in upper substrate 1 in the drawing is aligned with the position of each circular hole 2 in lower substrate 1 in the drawing (
Next, the lower surface of lower substrate 1 in the drawing is polished by CMP (chemical mechanical polishing) or the like to remove the silicon portion of that substrate 1 so that diameter-adjustment portion 5 made only of silica film 3 remains in lower substrate 1 in the drawing. At that time, the silicon portion is removed so that minimum-diameter portion 4 remains in diameter-adjustment portion 5 (
Next, lamination of substrates 1 shown in
In filtration filter 6, flow channels 7 are formed by connecting minimum-diameter portions 4 of diameter-adjustment portions 5, making the minimum diameter of flow channels 7 to be 1 nm˜100 nm. Accordingly, filtration filter 6 is used to remove vibrio cholerae and typhoid bacillus with a size of a few hundred nanometers by flowing sewage or seawater through flow channels 7. Moreover, if the minimum diameter of flow channels 7 is controlled to be 1 nm˜5 nm, not only contaminants and salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed.
In the present embodiment, diameter-adjustment portions 5 are laminated downward by polishing the lower surface of lower substrate 1 in
According to the method for producing a filtration filter of the present embodiment, the diameter of numerous circular holes formed in substrate 1 is directly controlled by adjusting the diameter of the opening portions of masking film. Accordingly, when forming circular holes 2 with a diameter of a few nanometers˜100 nm, irregularities are prevented in the diameter of circular holes 2. As a result, by selecting the hole diameters, vibrio cholerae with a size of a few hundred nanometers, viruses with a size of a few dozen nanometers and contaminants are prevented from passing through substrate 1, and a combined use of a distillation method or the like is not required when producing clean water or freshwater purified by filtration filter 6 formed by laminating substrates 1. Thus, procedures for obtaining clean water or freshwater are simplified. Also, since filtration filter 6 is made of rigid silica film 3, primary pressure applied on sewage or seawater can be increased, improving the purification efficiency of producing clean water or freshwater.
In the above-described method for producing a filtration filter according to the present embodiment, silica is deposited by CVD. Since the deposition amount is adjustable by adjusting the CVD treatment duration, it is easy to set the diameter of circular holes 2 at a required value.
Also, in the above-described method for producing a filtration filter according to the present embodiment, since the lower surface of substrate 1 is polished after numerous circular holes 2 are formed in substrate 1, each circular hole will surely penetrate through substrate 1 by adjusting the polishing amount.
Moreover, in the above-described method for producing a filtration filter according to the present embodiment, since 10 or more layers of diameter-adjustment portions 5 are laminated, the strength of filtration filter 6 is enhanced.
In the above-described method for producing a filtration filter according to the present embodiment, silica film 3 is formed on a surface of substrate 1, and silica film 3 on each substrate 1 is thermally bonded to each other when two substrates 1 are laminated. Thus, substrates 1 are firmly bonded to each other, further improving the strength of filtration filter 6.
In the above-described method for producing a filtration filter according to the present embodiment, plasma etching is conducted on substrates. However, any other etching method may be employed as long as openings of masking film are accurately transcribed to a substrate.
In the above-described method for producing a filtration filter according to the present embodiment, silica film 3 is deposited on a surface of substrate 1 and inner surfaces of circular holes 2 by CVD. However, as long as it can be deposited by CVD, it may be any rigid film such as silicon-nitride film, polysilicon film or the like. Although silicon is used for substrate 1, metal or metal oxide may also be used to form substrate 1 as long as it is a rigid material that can be etched. Also, CVD by thermal oxidation is used when depositing silica film 3, but plasma CVD may also be used.
In the above-described method for producing a filtration filter according to the present embodiment, minimum-diameter portion 4 is included in all diameter-adjustment portions 5 of flow channel 7. However, minimum-diameter portion 4 is not required for all diameter-adjustment portions 5, and it is an option that only one diameter-adjustment portion 5 of flow channel 7 has minimum-diameter portion 4.
Moreover, in the above-described method for producing a filtration filter according to the present embodiment, the entire silicon portion is removed from each substrate 1. However, it is not always required to remove the entire silicon portion. It is sufficient if the silicon portion is removed to such a degree that at least circular holes 2 penetrate through substrate 1.
In the above-described method for producing a filtration filter according to the present embodiment, circular holes 2 are formed in each substrate 1. However, each opening portion of masking film may be formed as a slit so that grooves are formed in substrate 1 through etching by using such opening portions. In such a case, it is preferred to adjust the minimum width of grooves at 1 nm˜100 nm, more preferably at 1 nm˜5 nm, by depositing silica on the inner surfaces of the grooves.
Next, a method for producing a filtration filter is described according to a second embodiment of the present invention.
In
In the present embodiment, since each opening portion of the masking film is made into a slit shape with an approximate width of 20 nm˜40 nm, numerous DTs 9 with an approximate width of 20 nm˜40 nm are formed in substrate 8 (
Next, silica film 10 is deposited on a surface of substrate 8 and on inner surfaces of DTs 9 through ALD (Atomic Layer Deposition), and only the silica 10 deposited on the surface of substrate 8 is further removed (
Next, a lower surface of substrate 8 is polished by CMP or the like, and such polishing is stopped when the tip portions of DTs 9 are exposed at the lower surface of substrate 8. In doing so, filtration filter 11 is formed when each DT 9 penetrates through substrate 8 (
In filtration filter 11, minimum width (D1) of DTs 9 penetrating through substrate 8 is set at 1 nm˜5 nm. Thus, when sewage or seawater flows through DTs 9 of filtration filter 11, not only contaminants and salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed.
In the method for producing a filtration filter according to the present embodiment, silica film is deposited through ALD. Since ALD can deposit by a unit of one atom, minimum width (D1) at tip portions of DTs 9 is adjusted precisely at a required value.
In the above-described method for producing a filtration filter according to the present embodiment, DTs 9 were formed in substrate 8. However, each opening portion of masking film may be formed in a circular shape so that circular holes are formed in substrate 8 through etching by using such opening portions. In such a case, it is preferred to adjust the minimum diameter of circular holes to be 1 nm˜5 nm by depositing silica on the inner surfaces of circular holes.
When removing vibrio cholerae, typhoid bacillus and the like with a size of a few hundred nanometers, minimum width (D1) of DTs 9 or the minimum diameter of penetrating holes may be set at 1 nm˜100 nm. Except that the opening size for forming such DTs is roughly 100 nm˜1 μm, the method is not different from that for forming DTs 9 with minimum width (D1) of 1 nm˜5 nm.
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
Next, a method for producing a filtration filter is described according to a third embodiment of the present invention.
In
Next, multiple substrates 12 are laminated in such a way that amorphous carbon film 13 of one substrate 12 makes contact with a lower surface of another substrate 12, their peripheral borders are secured by a frame (not shown) or the like (
In filtration filter 14, slit-shaped flow channel 15 is formed between two adjacent substrates 12 after each amorphous carbon film 13 is removed, and the width of flow channel 15 is 1 nm˜100 nm. When sewage or seawater flows through flow channels 15 in a direction indicated by arrows in the drawing, vibrio cholerae, typhoid bacillus and the like with a size of a few hundred nanometers are removed by filtration filter 14. Moreover, by controlling the width of flow channels 15 to be 1 nm˜5 nm, not only contaminants and salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed.
According to the method for producing a filtration filter of the present embodiment, after multiple silicon substrates 12 are laminated by means of amorphous carbon film 13 to set their distance at 1 nm˜100 nm, each amorphous carbon film 13 is removed. Thus, the width of slit-shaped flow channel 15 formed between adjacent substrates 12 is directly controlled, preventing irregularities in the width of slit-shaped flow channels.
Also, in the above-described method for producing a filtration filter according to the present embodiment, since slit-shaped flow channels 15 with a width of 1 nm˜100 nm are used for filtration, a greater amount of sewage or seawater can flow through flow channels 15 than when using circular holes with a minimum diameter of 1 nm˜100 nm for filtration. As a result, the purification efficiency of producing clean water or freshwater is enhanced.
Moreover, in the above-described method for producing a filtration filter according to the present embodiment, the distance between adjacent substrates 12 is maintained when the peripheral borders of multiple substrates 12 are secured by a frame or the like. However, pillar-shaped distance retainers with a height of 1 nm˜100 nm may be placed between adjacent substrates 12 so that the distance is maintained between adjacent substrates 12.
In the above-described method for producing a filtration filter according to the present embodiment, each amorphous carbon film 13 is removed by ashing. However, each amorphous carbon film 13 may be removed by wet etching using a supercritical chemical solution or the like. Since supercritical chemical solutions enter fine space smoothly, each amorphous carbon film 13 is surely removed.
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
Next, a method for producing a filtration filter is described according to a fourth embodiment of the present invention.
In
Next, amorphous carbon film 19 with a thickness of 1 nm-100 nm is deposited on a surface of substrate 17 and inner surfaces of trenches 18 (
Next, the surface of substrate 17 is made flat by depositing silica film 20 through CVD on inner surfaces of trenches 18 and the surface of substrate 17, and photoresist film 22 having opening portions 21 is further formed on the flat surface of substrate 17 (
Next, using photoresist film 22 as masking film, portions of silica film 20 and amorphous carbon film 19 are etched away to expose silicon-nitride film 16 (
Next, using photoresist film 24 as masking film, portions of silicon-nitride film 23 are etched away to expose silica film 20 (
Next, using photoresist film 26 as masking film, portions of silicon-nitride film 25 and silica film 20 are etched away to expose portions of amorphous carbon film 19 (
Next, the lower surface of substrate 17 is polished by CMP or the like, and such polishing is stopped when hollows 27 are exposed at the lower surface of substrate 17. In doing so, flow channels 28 with a width of 1 nm˜100 nm are formed, penetrating through substrate 17 in a thickness direction (
According to the method for producing a filtration filter of the present embodiment, amorphous carbon film 19 with a thickness of 1 nm˜100 nm is deposited on inner surfaces of trenches 18, and amorphous carbon film 19 is removed after it is covered by silica film 20 so that flow channels 28 with a width of 1 nm˜100 nm are formed. When sewage or seawater flows through flow channels 28, vibrio cholerae, typhoid bacillus and the like are removed. Also, by controlling the width of flow channels 28 at 1 nm˜5 nm, contaminants, salt content and even viruses are removed. Therefore, without a combined use of a distillation method or the like, clean water or freshwater is obtained.
In the above-described method for producing a filtration filter of the present embodiment, trenches 18 are formed in substrate 17. However, circular holes may be formed in substrate 17. In such a case, amorphous carbon film 19 is deposited on the inner surfaces of the circular holes, and such amorphous carbon film 19 is removed in a later step so that flow channels in a circular shape are formed.
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
Next, a method for producing a filtration filter is described according to a fifth embodiment of the present invention.
In
Next, silicon-nitride film 29 and silica film 30 are removed by etching or the like, and amorphous carbon film 35 with a thickness of 1 nm˜100 nm is deposited on the inner surfaces of circular holes 34 (
Next, circular holes 34 are filled with silica 38 through CVD (
According to the method for producing a filtration filter of the present embodiment, after amorphous carbon film 35 with a thickness of 1 nm˜100 nm is deposited on the inner surfaces of circular holes 34 and then covered by silica 38, the amorphous carbon film 35 is removed. Thus, flow channels 39 with a width of 1 nm˜100 nm are formed. When sewage or seawater flows through flow channels 39 in a direction indicated by arrows in the drawing, vibrio cholera, typhoid bacillus, contaminants, salt content and viruses are removed. Accordingly, a combined use of a distillation method or the like is not required to produce clean water or freshwater.
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
Next, a method for producing a filtration filter is described according to a sixth embodiment of the present invention.
In
Next, substrate 45 having multiple penetrating holes 44 with a diameter of a few dozen nanometers to 300 nm is formed by etching the same as substrate 40 using masking film. Then, substrate 45 is compressed and laminated to substrate 40 by means of amorphous carbon film 42, and the substrates are further bonded. Although amorphous carbon film 42 is squeezed to be compressed in a thickness direction during that time, micropillars 43 are not compressed. Thus, the distance between substrate 40 and substrate 45 is maintained at 1 nm˜100 nm (
Next, porous ceramic material 46 is fully filled in each penetrating hole 44 through PVD (physical vapor deposition) (
Next, after amorphous carbon film 42 is formed on a surface of substrate 45, the above-described steps shown in
In filtration filter 50, gaps 47 with a thickness of 1 nm˜100 nm, which are formed when each amorphous carbon film is removed, work as flow channels, and sewage or seawater flows through ceramic material 46 and gaps 47 in a direction indicated by an arrow in the drawing. Thus, vibrio cholerae, typhoid bacillus and the like with a size of a few hundred nanometers are removed by gaps 47. Moreover, by controlling gaps 47 to be 1 nm˜5 nm, not only contaminants or salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed.
According to the method for producing a filtration filter of the present embodiment, since amorphous carbon film 42 includes micropillars 43 with a height of 1 nm˜100 nm, the thickness of gaps 47 is securely maintained at 1 nm˜100 nm by micropillars 43 even after amorphous carbon film 42 is removed.
In the above-described method for producing a filtration filter according to the present embodiment, substrates are laminated in such a way that the penetrating holes of each substrate do not align with each other in a planar view. Thus, ceramic material 46 of each substrate is prevented from aligning with each other to form penetrating holes made only of ceramic material 46. Accordingly, vibrio cholerae and typhoid bacillus with a size of a few hundred nanometers, viruses with a size of a few dozen nanometers and contaminants are prevented from passing through filtration filter 50 in a thickness direction.
In
Next, silicon substrate 54 is laminated on substrate 51 and bonded by means of amorphous carbon film 53 (
Next, a surface of substrate 54 is covered by porous ceramic material 56 through PVD and penetrating holes 55 are filled with ceramic material 56 (
Next, amorphous carbon film 53 is removed by ashing. Here, since ceramic material 56 in each penetrating hole 55 is bonded with substrates 51 and 54, substrates 51 and 54 will not be separated from each other. Ceramic material 56 prevents substrates 51 and 54 from touching each other, and gap 57 with a thickness of 1 nm˜100 nm is formed between substrates 51 and 54 (
Next, after amorphous carbon film 53 is formed on a surface of substrate 54, the above-described steps shown in
In filtration filter 60, porous ceramic material 56 and gaps 57 with a thickness of 1 nm˜100 nm, which are formed when each amorphous carbon film is removed, work as flow channels. Since sewage or seawater flows through ceramic material 56 and gaps 57 in a direction indicated by an arrow in the drawing, not only contaminants or salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed by gaps 57.
In the method for producing a filtration filter according to the present modified example, penetrating holes of each substrate are also formed not to align with each other in a planar view. Thus, ceramic material 56 of each substrate is prevented from aligning with each other to form penetrating holes made only of ceramic material 56. Accordingly, vibrio cholerae and typhoid bacillus with a size of a few hundred nanometers, viruses with a size of a few dozen nanometers and contaminants are prevented from passing through filtration filter 60 in a thickness direction.
In the above-described filtration filters 50 and 60, multiple penetrating holes 61 are formed to go through each substrate (45, 48, 49 or 54, 58, 59) all at once, and a rigid member made of metal such as tungsten is inserted in each penetrating hole 61 to form pillars 62 which penetrate through filtration filter 50 or 60 in a thickness direction (
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
In
Since maximum width (W1) of penetrating flow channels 65 is 1 nm˜100 nm in filtration filter 66, vibrio cholerae and typhoid bacillus with a size of a few hundred nanometers are removed by flowing sewage or seawater through penetrating flow channels 65 of filtration filter 66 along a direction indicated by an arrow in the drawing. Moreover, by controlling minimum width (W1) of penetrating flow channels 65 at 1 nm˜5 nm, not only contaminants and salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed. Accordingly, clean water or freshwater is obtained without a combined use of a distillation method or the like.
The method for producing a filtration filter according to the present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
In
Next, cover 70 is compressed against base plate 69. At that time, substrate 67 is compressed in a thickness direction so as to be expanded in a horizontal direction. However, since its peripheral borders are covered by cover 70, each inner wall of penetrating holes 68 protrudes, reducing the diameter of penetrating holes 68 accordingly (
Next, base plate 69 and cover 70 are removed from substrate 67, and filtration filter 71 is formed as a reverse osmosis membrane (
Since the diameter of penetrating holes 68 is 1 nm˜100 nm in filtration filter 71, not only contaminants and salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed by flowing sewage or seawater through penetrating holes 68 of filtration filter 71.
According to the method for producing a filtration filter of the present embodiment, the diameter of penetrating holes 68 is adjusted by compressing substrate 67 in a thickness direction so that penetrating holes 68 are deformed and the inner walls of penetrating holes 68 protrude. Thus, it is easy to produce filtration filter 71.
In the above-described method for producing a filtration filter according to the present embodiment, as long as the diameter of each penetrating hole 68 is set at 1 nm˜100 nm at maximum, it is acceptable if some penetrating holes 68 are blocked. Thus, the amount to compress substrate 67 is preferred to be set relatively great.
Next, long narrow base 72 is compressed sideways in a direction perpendicular to the direction of its length (directions indicated by arrows in the drawing). At that time, the inner wall of each penetrating hole 73 protrudes inside penetrating hole 73, resulting in a reduced diameter of penetrating hole 73 (
Since the diameter of penetrating holes 73 is at 1 nm˜100 nm in filtration filter 74, vibrio cholerae and typhoid bacillus with a size of a few hundred nanometers are removed by flowing sewage or seawater through penetrating holes 73 of filtration filter 74. Moreover, the diameter of the penetrating holes is controlled to be 1 nm˜5 nm so that not only contaminants or salt content but also picornaviruses and parvoviruses with an approximate size of 20 nm are removed.
In
Next, cover 70 is compressed against base plate 69. At that time, each inner wall of penetrating holes 68 protrudes, thus reducing the diameter of penetrating holes 68 accordingly (
The method for producing a filtration filter according to the above-described present embodiment has the same effects as the method for producing a filtration filter according to the above-described first embodiment.
In
According to the method for producing a filtration filter of the present embodiment, since two ceramic members (78, 79) are bonded to filtration filter 6 where flow channels 7 with a minimum diameter of 1 nm˜100 nm are formed, the strength of resulting complex filtration filter 80 is enhanced. Also, since ceramic filters made of fine permeating holes are used as porous ceramic members (78, 79) in addition to filtration filter 6, filtration is conducted at least twice in complex filtration filter 80. Thus, contaminants, salt content, vibrio cholerae, typhoid bacillus, viruses and the like are surely removed.
In the method for producing a filtration filter of the present embodiment, filtration filter 6 is sandwiched by two ceramic members (78, 79). However, any one of the filtration filters obtained as shown in
Filtration filter 6 is sandwiched by two ceramic members (78, 79) in the present embodiment. However, it is an option for filtration filter 6 to be bonded to one ceramic member to form complex filtration filter 80.
In
According to the method for producing a filtration filter of the present embodiment, since filtration filter 6 having flow channels 7 with a minimum diameter of 1 nm˜100 nm is bonded to reverse osmosis membrane 81 made of polymeric film, filtration is conducted twice when sewage or seawater flows through filtration filter 6 and reverse osmosis membrane 81. Thus, contaminants, salt content or even viruses are surely removed. Also, since it is known that reverse osmosis membranes made of polymeric film are usually characterized by blocking ions by repelling or absorbing ions in water, filtration filter 6 can be used as ion blocking properties of reverse osmosis membrane 81, thus surely removing sodium ions and chloride ions in seawater.
In the method for producing a filtration filter of the present embodiment, filtration filter 6 is bonded to reverse osmosis membrane 81. However, any one of the filtration filters obtained as shown in
In a method for producing filtration filters according to each embodiment, slits or circular holes are formed in each filtration filter. However, flow channels may be formed in a filtration filter through etching by processing a substrate to have a pectinate shape in a planar view. In such a case, first, multiple grooves with a width of 1 nm˜5 nm are formed in a substrate, where the periphery of one end of the substrate is open in a planar view as shown in
The purification efficiency of producing clean water or freshwater by a filtration filter in each embodiment described above decreases after being used for providing purified clean water or freshwater due to clogs caused by trapped contaminants or salt content. Thus, filtration filters are restored by conducting etching or ashing again so that trapped contaminants or salt content are removed. Since filtration filters of each embodiment are made of relatively rigid material such as silicon, they do not sustain damage or deterioration even with another etching or ashing. Namely, filtration filters of each embodiment described above are reusable. Also, if the diameter of flow channels 7 or the like is enlarged due to another etching or ashing while restoring a filtration filter, the enlarged diameter of flow channels 7 or the like will be roughly a few dozen nanometers when the initial diameter of flow channels 7 is 1 nm˜5 nm, for example. Thus, the restored filtration filter may be used for filtering sewage containing filtration targets with a size of a few hundred nanometers or greater, or it may be used for dialysis treatments. Accordingly, waste that contains contaminants or the like can be prevented by methods for producing filtration filters according to the above-described embodiments. Also, by applying water pressure from a direction opposite the filtration direction of sewage or seawater, trapped contaminants or the like may be removed. In such a case as well, since filtration filters are made of rigid material, filtration filters are tolerant to relatively high pressures, allowing efficient removal of contaminants or the like.
In addition, when penetrating holes are formed in filtration filters of each embodiment, the opening at one end of a penetrating hole is set at a predetermined size effective for filtration and the diameter of the penetrating hole is set to increase from that end toward the other end as shown in
Also, as described above, since filtration filters of each embodiment contain relatively rigid substrates such as silicon, sterilizing or antimicrobial metals such as silver may be coated through PVD or CVD, allowing filtration filters to produce purer clean water or freshwater. Here, filtration filters may also be coated with titania, and ultraviolet rays are irradiated during the purification process of producing clean water or freshwater so that a strong sterilization effect through photocatalysis is achieved. Thus, clean water or freshwater is surely sterilized.
Moreover, it is an option for substrates contained in filtration filters of each embodiment to be formed using conductive material or semiconductive material. Accordingly, electric power is provided to filtration filters, and clean water or freshwater is sterilized by electromagnetic waves generated by the electric power.
Electronic circuits with sensor functions may be built beforehand into substrates in filtration filters of each embodiment. For example, using electronic circuits with water quality sensors built into filtration filters, the degree of purification of clean water or freshwater can be monitored real time, thus preventing low-quality clean water or freshwater.
Also, when electronic circuits with flow sensors are built into filtration filters, the amount of purified clean water or freshwater is monitored, and the timing for replacing or restoring filtration filters can be determined properly. In addition, when electronic circuits with vibration sensors are built into filtration filters, vibrations in the substrates of filtration filters are directly monitored, and the timing for replacing filtration filters can be determined properly. When forming built-in electronic circuits with sensor functions, electronic circuits are directly formed on substrates if they are made of silicon. Forming filtration filters and forming electronic circuits are achieved in the same procedures, thus simplifying the formation of electronic circuits. Therefore, substrates are preferred to be made of silicon.
Since reverse osmosis membranes are mainly formed with polymeric membranes, their strength is low. Thus, when a load is applied to sewage or seawater by increasing pressure (primary pressure) for improving purification efficiency, problems such as damaged membranes may arise.
Reverse osmosis membranes of recent development are made of porous ceramics, which will not be decayed by bacteria nor be dissolved in lubricating oil and which are highly rigid (see Japanese Patent Publication No. 2007-526819, for example). The entire contents of this publication are incorporated herein by reference.
A method for producing a filtration filter according to embodiments of the present invention can simplify the process for providing clean water or freshwater.
According to a first embodiment of the present invention, a method for producing a filtration filter includes as follows: using masking film formed on a surface of a rigid substrate and having multiple openings with a uniform size to expose portions of the surface, the portions of the substrate corresponding to the openings are etched so that multiple holes or grooves are formed in the substrate.
In the first embodiment of the present invention, the etching is preferred to be plasma dry etching.
In the first embodiment of the present invention, the diameter of the holes or the width of the grooves is preferred to be adjusted to be 1 nm˜100 nm by depositing a predetermined substance on the inner surfaces of the holes or grooves.
In the first embodiment of the present invention, the diameter of the holes or the width of the grooves is preferred to be adjusted to be 1 nm˜5 nm.
In the first embodiment of the present invention, the predetermined substance is preferred to be deposited by CVD.
In the first embodiment of the present invention, the predetermined substance is preferred to be deposited by ALD.
In the first embodiment of the present invention, it is preferred that an organic film with a thickness of 1 nm˜100 nm be formed on the inner surfaces of the holes or the grooves, and that the organic film be removed after the organic film in the holes or the grooves is covered by another material.
In the first embodiment of the present invention, the thickness of the organic film is preferred to be 1 nm˜5 nm.
In the first embodiment of the present invention, it is preferred that the diameter of the holes or the width of the grooves be 10 nm˜100 nm, and that the diameter of the holes or the width of the grooves be adjusted to be 1 nm˜5 nm by compressing the substrate in a thickness direction so that the holes or the grooves are deformed, causing the inner walls of the holes or the grooves to protrude.
In the first embodiment of the present invention, it is preferred that the diameter of the holes or the width of the grooves be 10 nm˜1000 nm, and that the diameter of the holes or the width of the grooves be adjusted to be 1 nm˜100 nm by compressing the substrate in a thickness direction so that the holes or the grooves are deformed, causing the inner walls of the holes or the grooves to protrude.
In the first embodiment of the present invention, after multiple holes or grooves are formed in the substrate, the lower surface of the substrate is preferred to be polished so that the holes or the grooves penetrate through the substrate.
In the first embodiment of the present invention, multiple substrates having holes or grooves formed as above are preferred to be laminated.
In the first embodiment of the present invention, it is preferred that an oxide film be formed on at least either the upper or lower surface of the substrate, and that the oxide film of each substrate be thermally bonded to each other when laminating multiple substrates.
In the first embodiment of the present invention, multiple holes or grooves formed as above penetrate through the substrate, and when multiple substrates are laminated, it is preferred that the holes or grooves of each substrate are aligned in a planar view to form penetrating portions that go through all the multiple substrates, and that the width of such penetrating portions be adjusted to be 1 nm˜100 nm in a planar view.
In the first embodiment of the present invention, the width of the penetrating portions is preferred to be 1 nm˜5 nm.
In the first embodiment of the present invention, the rigid substrate is preferred to be made of silicon, a metal or a metal oxide.
In the first embodiment of the present invention, the substrate with multiple holes or grooves is preferred to be bonded to another substrate made of ceramic.
In the first embodiment of the present invention, a reverse osmosis membrane made of polymeric film is preferred to be bonded to the substrate having multiple holes or grooves.
In the first embodiment of the present invention, an electrical circuit with a sensor function is preferred to be built into the substrate having multiple holes or grooves.
A method for producing a filtration filter according to a second embodiment of the present invention includes laminating multiple rigid substrates by means of organic material to have a predetermined distance from each other, and removing the organic material.
In the second embodiment of the present invention, it is preferred that holes or grooves that penetrate through each substrate be formed, and that multiple substrates be laminated in such a way that the holes or grooves of each substrate do not align in a planar view.
In the second embodiment of the present invention, the organic material is preferred to contain distance retainer with a size of 1 nm˜100 nm.
In the second embodiment of the present invention, the distance retainer is preferred to have a size of 1 nm˜5 nm.
In the second embodiment of the present invention, it is preferred that multiple substrates be laminated, penetrating holes be formed to penetrate through the multiple substrates all at once, and pillars be formed by inserting rigid members into the penetrating holes.
In the second embodiment of the present invention, multiple laminated substrates are preferred to be bonded to another substrate made of ceramic.
In the second embodiment of the present invention, a reverse osmosis membrane made of polymeric film is preferred to be bonded to multiple laminated substrates.
In the second embodiment of the present invention, an electrical circuit with a sensor function is preferred to be built into at least one of the substrates.
According to an embodiment of the present invention, using etching technology capable of achieving highly accurate processing, especially using plasma dry etching, the size and shape of opening portions of masking film are adjusted so that the diameter of multiple holes or the width and shape of grooves formed in a substrate can be directly controlled. Accordingly, when holes or grooves are formed to have a required size of diameter or width, irregularities are prevented from occurring in the diameter of holes or the width of grooves to be formed. As a result, filtration targets such as viruses with a size of a few dozen nanometers, vibrio cholerae with a size of a few hundred nanometers and contaminants are prevented from passing through the substrate. When a filtration filter containing such a substrate is used to provide clean water or freshwater, a combined use of a distillation method or the like is not required, thus simplifying the purification process for obtaining clean water or freshwater.
Also, according to another embodiment of the present invention, after multiple rigid substrates are laminated by means of organic material to set the distance between substrates at a predetermined value, the organic material is removed. Thus, the width of slits formed between adjacent substrates is directly controlled. Accordingly, when slits with a width of a few nanometers or a few dozen to one hundred nanometers are formed, irregularities are prevented from occurring in the width of slits to be formed. As a result, depending on the width of the formed slits, viruses with a size of a few dozen nanometers, vibrio cholerae with a size of a few hundred nanometers and contaminants are prevented from passing through the slits. Accordingly, a combined use of a distillation method or the like is not required when a filtration filter made of the slits is used for purification to obtain clean water or freshwater, thus simplifying the purification process for obtaining clean water or freshwater.
Furthermore, according to another embodiment of the present invention, since a rigid substrate is used for a filtration filter, primary pressure applied to sewage or seawater can be increased. Thus, the purification efficiency of producing clean water or freshwater improves.
In addition, since the shape of holes or slits is accurately controlled, maintenance efficiency improves. By setting the shape of holes or slits to be suitable for the local situation, the purification efficiency of producing clean water or freshwater is enhanced.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-253080 | Nov 2010 | JP | national |
The present application is a continuation of PCT International Application No. PCT/JP2011/076129, filed Nov. 8, 2011, which is based upon and claims the benefit of priority from Japanese Application No. 2010-253080, filed Nov. 11, 2010. The entire contents of these applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2011/076129 | Nov 2011 | US |
| Child | 13890529 | US |
