Filter sheet

Abstract: The invention relates to a deodorant comprising 5 to 100% by weight of a calcium phosphate compound having a molar ratio of Ca/P of 0.8 to 2.0, a deodorant sheet and filter sheet containing such calcium phosphate compound, and a functional paper containing 10 to 80% by weight of a calcium phosphate compound as well as a filtering medium for an exhaust gas which comprises a ceramic material containing 5 to 100% by weight of a calcium phosphate compound. Based on excellent properties of the incorporated calcium phosphate compound, the agents and products according to the present invention exhibit a highly improved adsorptivity to an oil-soluble substance, odor substance, animal or vegetable cell, virus, biopolymeric substance or other substances and therefore can be advantageously used in various fields of technology. For example, the functional paper can be used as a deodorant, filter medium and adsorbent as well as flame-retardant paper.

Description: The present invention relates to a filter sheet which selectively traps a biological polymeric substance, bacterium, virus, animal or vegetable cell, toxic gas, odor component, dust or mist in a gas or liquid, but allows a permeation of other components. Hitherto, to remove any odor components or substances from the surrounding atmosphere or the like, many odor removing processes have been widely used, and typical examples of the well-known deodorizing processes include (1) the use of an aromatizing agent or fragrance to mask the odor, (2) the use of a catalyst to chemically decompose odor components to thereby make them odorless, and (3) the use of an adsorbent capable of adsorbing and removing any odor components. However, each of these three processes has problems to be solved. For example, the aromatizing agent can sometimes emit an unpleasant smell to a person, because generally it must be an agent capable of give out strong fragrance in comparison with the odor components. The catalytic decomposition of the odor components is limited to only some of the odor components, because there is no catalyst which is effective for all odor components. In addition, an activated carbon which is a typical example of the well-known adsorbent-type deodorants cannot effectively adsorb any basic gases such as ammonia gas, although it can adsorb substantially all of other odor components. Further, the activated carbon must be used under the conditions of low temperature, because it can be easily removed at an elevated temperature because of a combustion thereof. It is therefore desirable to provide an improved deodorant which is effective for all types of odor components and does not restrict the conditions of the usable working temperature. In connection with the above-described adsorbents as the deodorant, it should be noted that hitherto, a fibrous substance such as filter paper or filter cloth, granular substance such as activated carbon, clay, gravel or diatomaceous earth or porous substance such as porous pottery have been used as a filtering medium. Apparently, almost of these filtering mediums are used to trap solid substances, and suitable filtering mediums are selected depending on the specific solid substances to be trapped or filtrated. However, the prior art filtering mediums suffer from some drawbacks. The activated carbon has been frequently used as the filtering medium, because it exhibits an excellent adsorptivity. However, since it has no adsorption power for any oil-soluble substances and any bad smell components such as ammonia, the activated carbon cannot be used to remove these substances and components from any gas or liquid containing the same. Recently, a membrane filtering system has been developed, but it suffers from a high production cost, because it is essential to use an ultrafiltration membrane or reverse osmosis membrane. On the other hand, a bacterial filter such as Seitz Filter has been also developed. However, the use of this filter is limited to only traping of bacteria, and if used, the filtration must be carried out under the application of the reduced pressure or centrifugal force. As is appreciated from this and above descriptions, the prior art filtering mediums can be applied to only the limited range of the substances to be filtered off, or need expensive filtering equipments. The use of calcium phosphate compounds as deodorants, fillers and absorbents is known. WO-A-81/02 891 discloses a composition containing a deodorizing agent which produces a non-odorous ammonia salt thereby eliminating gaseous ammonia from organic waste materials. SU-A-854965 discloses a paper containing SiO 2 , TiO 2 , tricalcium phosphate and phosphogypsum. Similarly, JP-A-62 227 932, JP-A-63 044 997 and JP-A-60 035 016 disclose a sheet which comprises organic polymeric material having dispersed therein a calcium phosphate compound. An object of the present invention is to provide an improved filter sheet which can be produced at a low cost, has a simplified structure, can be easily handled, and can effectively trap any gaseous substances, bacteria, viruses, animal and vegetable cells and other substances, in addition to the solid substances. Still another object of the present invention is to provide an improved filter sheet which does not accompany blocking of the pores thereof, can be easily produced, has a high trapping efficiency of soot or carbon dusts and other dusts, and exhibits a high adsorption performance (action) with regard to gaseous substances such as carbon monoxide or hydrocarbons. The above-described objects of the present invention and other objects which will be appreciated from the following description can be accomplished by a filter sheet according to claim 1. According to the present invention, as described hereinafter in detail, many advantages which could not been obtained in the prior art deodorants and other related agents and products can be obtained. First, the filter sheet according to the present invention exhibits its excellent deodorizing effects at a wide working temperature of from a lower temperature to a higher temperature and accordingly can be widely used in different fields. Note, the filter sheet is effective for an adsorption and separation of specific gases such as carbon monoxide which could not be removed by the prior art deodorants. Further, since the calcium phosphate compound used as a principal component has a white color, it is esthetically acceptable and therefore can be used in the production of deodorant-incorporated papers such as white-colored papers or valuable papers, for example, colored papers and textured or pattern-printed papers. Second, the filter sheet of the present invention is low-priced, has a simple structure, can be easily produced and handled, and can effectively trap any gaseous substances, viruses or bacteria, and animal or plant cells, in addition to the filtering off of the solid substances. Further, since it has a sheet structure, the filter sheet can be easily inserted into and removed from the filter equipment, and also can be freely and easily replaced with a new one, when its adsorptivity was reduced. Based on these advantages, the filter sheet can be applied to different filter and separation apparatuses, for example, air cleaning equipments, water purifiers, deodorizing apparatuses, virus or bacteria filters, cell separators, serum filters and masks. Since the filter sheet of the present invention contains a calciua phosphate compound having an excellent adsorption action of the exhaust gas, it can effectively adsorb gaseous substances such as carbon monoxide or hydrocarbons, in addition to dusts such as soot dusts, and therefore ensures a notably increased purification efficiency for the exhaust gas in contrast with the prior art filtering medium. A1so, it can avoid a problem of the blocking of the pores thereof. Further, since the filter sheet can be fabricated into a filter cartridge, the used filter sheet can be easily exchanged for a new one after a predetermined time of operation. Accordingly, it is always possible to conduct an effective purification of the exhaust gas, while the used filtering medium can be regenerated in a heat treatment or other regeneration treatments. Furthermore, the filter sheet of the present invention can provide a high purification efficiency due to excellent characteristics of the filter sheet per se used therein, and also can significantly increase a purification efficiency of exhaust gas due to a diffusion of the exhaust gas throughout the filter sheet. In addition to these advantages, since a load is uniformly applied over the filter sheet, it becomes possible to avoid a local blocking of the pores due to incorporation of soot and other dusts in the pores. Namely, it becomes possible to notably extend a duration of life of the filter sheet and accordingly to use the filter for an extended period of time. Moreover, in this connection, since a deterioration of the filtering sheet is caused at a substantially same degree and speed of deterioration over a full cross section of the filter, it becomes possible to exchange the used filter sheet for a new one at once and then regenerate the same. The invention will now be further described with reference to the drawings wherein Figure 1 is a cross-sectional view of a filter device containing a filter sheet according to the present invention, and Fig. 2 is a flow diagram of a deodorizing apparatus in which the filter sheet of the present invention is used as a deodorant sheet. The filter sheet according to the present invention is characterized by comprising a sheet-like matrix of organic polymeric material and granules of a calcium phosphate compound having a Ca/P ratio of 0.8 to 2.0 dispersed in the matrix. The organic polymeric matrix which can be used in the filter sheet of the present invention includes a wide variety of sheet-like materials, and typical examples of useful sheet-like materials are papers or cellulose materials, nonwoven fabrics and plastics foams such as urethane foams. The polymeric matrix used must contain air gaps enough to contain particles of the calcium phosphate compound therein, but for the papers and nonwoven fabrics, gaps between the fibers are effective as such air gaps. Similarly, open cells of the plastics foams are effective as such air gaps. The size of the gaps between the fibers and pore size of the open cells of the plastic foams are not limited in the practice of the present invention and therefore can be suitable selected depending on a specific size or amount of the granules to be dispersed in the matrix, but it is necessary that the gap size and pore size are enough to ensure a permeation of the gas or liquid through the filter sheet and a contact of the gas or liquid with the granules of the calcium phosphate compound. The thickness of the filter sheet of the present invention is not limited in the practice of the present invention and can be suitable selected depending on a specific use of the filter sheet. If desired, the filter sheets having a thickness of microns order may be combined or superimposed to make a desired thickness. For the filter sheet of the present invention, it is essential that the calcium phosphate compound used has a Ca/P ratio of 0.8 to 2.0, but any calcium phosphate compounds can be used in the practice of the present invention, insofar as they exhibit a Ca/P ratio of 0.8 to 2.0. Suitable calcium phosphate compounds are those previously described with regard to the deodorant of the present invention, i.e., apatite, tricalcium phosphate, tetracalcium phosphate or a mixture thereof. The calcium phosphate compound is used as granules, and preferably the granules of the calcium phosphate compound have a granule size of 0.1 to 100 µm. The granules, if they have a granule size of less than 0.1 µm, aggregate with each other to thereby prevent a dispersion of the granules in the polymeric matrix. On the other hand, the granule size of more than 100 µm, the granules are hardly adhered to and carried by the polymeric matrix because of an excessively large size thereof. Moreover, the selection of the suitable granule size depends on a specific matrix used, and for example, if the paper is used as the matrix, the granule size of the calcium phosphate compound used is preferably in the range of from 0.1 µm to 30 µm. The granule size of less than 0.1 µm will result in a discharge of the granules from a mesh of the paper making machine during the paper making process, while the granule size of more than 30 µm will result in an ununiform dispersion of the granules in the matrix because of an excessively high weight of the granules. Preferably, the granules of the calcium phosphate compound have a porous structure. The porous granules of the calcium phosphate compound can be produced from a starting material, i.e., crystalline particles of the calcium phosphate compound, in accordance with the process which is similar to the process previously described with regard to the production of the porous granules and blocks for use in the production of the filter sheet of the present invention. Note, the pore size of the porous granules varies depending on a specific substance to be trapped with the filter sheet, and for example, if the specific substance is a virus or other organisms, the porous granules should have a pore size of 0.01 µm or more. Further, the porous granules of the calcium phosphate compound have a porosity of 10 to 75%. The porosity of less than 10% results in only insufficient surface area and water retention of the granules, while the porosity of more than 75% results in an unacceptably lowered strength of the porous granules. Preferably, the porous granules have a specific surface area of 1 to 150m 2 /g. Furthermore, the granules of the calcium phosphate compound may contain at least one additional active substance partially adsorbed on a surface thereof to modify physicochemical properties and immunological properties of the granule surface and accordingly skillfully modify an adsorption activity of the granules. Suitable active substances include, for example, polysaccharides such as living body-originated hyaluronic acid, chondroitin sulfate, chitin derivatives, fibronectin, osteonectin and the like, mucopolysaccharides and proteins as well as derivatives thereof. The filter sheet of the present invention can be advantageously produced in accordance with the following methods which however do not restrict the production of the filter sheet. For example, if nonwoven fabric is used as a matrix, granules of the calcium phosphate compound can be added to the fabric during their production. More particularly, when the paper is used as the matrix, the granules of calcium phosphate are dispersed in a pulp slurry and the mixture is processed to produce a desired filter sheet of the present invention. Similarly, when the nonwoven fabric is used as the matrix, the calcium phosphate compound is added to the starting material during the production of the fabric. When the plastic foam is used as the matrix, the plastic foam is immersed in a slurry of the calcium phosphate compound and then the impregnated plastic foam is dried to produce a desired filter sheet. If desired, in the production of the filter sheet of the present invention, the filter sheet may be additionally perforated with a needle punch or other perforators to more improve a permeability of the filter sheet to the gas or liquid to be filtered. The perforations in the matrix do not cause an undesirable permeation of the substances to be adsorbed with the calcium phosphate compound, because the calcium phosphate compound has a high adsorptivity and also is uniformly dispersed in the matrix, if a diameter of the perforations is not remarkably increased. Since the granular calcium phosphate compound dispersed in the filter sheet has a good selective adsorptivity to biopolymeric substances, bacteria, viruses, animal and plant cells, toxic gases, bad smell components, dusts, mists and other noxious substances, the filter sheet of the present invention can be used as a filter in a wide variety of products which include, for example, an air cleaning equipment, water purifier, deodorizing apparatus, bacterium or virus filter, cell separator, serum filter and mask. In addition to these wide uses, the used filter sheet with the reduced adsorptivity can be easily replaced with a new filter sheet, since its sheet structure makes the handling easy. Moreover, if desired, the filter sheet of the present invention may be inserted between two gauze layers of the commercially available gauze mask or may be contained in a pocket of the gauze mask to more improve the gauze mask. More particularly, the gauze mask with the filter sheet of the present invention can prevent an invasion of viruses, bacteria and the like into a human body, because the viruses end the like are adsorbed with the filter sheet. Remarkable effects are expected when such gauze mask is used in the prevalence period of influenza. Of course, the filter sheet can be easily inserted into and removed from the gauze mask. Figure 1 is a cross-sectional view of the filter device containing a filter sheet according to the present invention. The filter device comprises a rectangular box 2 with the opened upper and lower walls. These two openings are used to introduce an ill-odored air into the filter device, and discharge the deodorized air therefrom, respectively. As is illustrated, there are four filter sheets 1 of the present invention, and one end of each filter sheet 1 is alternately fixed an opposed side wall of the box 2. This alternate arrangement of the filter sheets 1 is intended to form a zig zag flow path 3 of the air. The filter device is used in, for example, an air conditioner to remove bad swell from an air-conditioned air. Figure 2 is a flow diagram of the deodorizing apparatus in which the filter sheet of the present invention is used as a deodorant sheet. The illustrated deodorizing apparatus comprises a Tedlar bag 11, a filter holder 12 with the filter sheet 12a, a pump 13, a flowmeter 14 and a Tedlar bag 15 which connected through a tube in the recited order. Especially, the deodorizing apparatus is used to evaluate a deodorizing effect of the filter sheet. The present invention will be further described with reference to some working examples which do not restrict the scope of the present invention. Example 1: A hydroxyapatite having a Ca/P ratio of 1.67 was synthesized in accordance with the well-known production process. The hydroxyapatite was sintered at 700 °C to produce granules of hydroxyapatite having a porosity of 60% and granule size of 1 to 4mm. The thus obtained granules had an average pore size of 2 µm and specific surface area of 40 m 2 /g. Example 2: A calcium phosphate having a Ca/P ratio of 1.5 was sintered at 1100 °C to produce granules of calcium phosphate having a porosity of 30% and granule size of 1 to 4mm. The thus obtained granules had an average size of fine pores of 300mm, average size of small pores of 8 µm and specific surface area of 12 m 2 /g. Example 3: A 1000g of porous hydroxyapatite granules having an average granule size of 1.0 µm, porosity of 45%, Ca/P ratio of 1.67 and average pore size of 0.09 µm was dispersed in 1000ml of water containing 20g of polyvinyl alcohol to produce a slurry of hydroxyapatite. A sheet-like polyurethane foam having a thickness of 10mm, and containing open cells with an average pore size of 300 µm and porosity of 97% was immersed in the hydroxyapatite slurry. The polyurethane foam was removed from the slurry and then dried at 25°C. A desired filter sheet was thus obtained. Example 4: A 900g of porous hydroxyapatite granules having an average granule size of 1.0 µm, porosity of 45%, Ca/P ratio of 1.67 and average pore size of 0.09 µm and 100g of porous hydroxyapatite granules having an average granule size of 10.3 µm, porosity of 60%, ca/P ratio of 1.67 and average pore size of 1.0 µm were dispersed in 1000ml of 3% by weight of aqueous solution of polyvinyl alcohol to prepare a slurry of hydroxyapatite. A needle-punched polyester nonwoven fabric ("Panelon" commercially available from Dynic Co.; weight: 200g/m 2 ) was immersed in the hydroxyapatite slurry. The nonwoven fabric was removed from the slurry and then dried at 25 °C. A desired filter sheet was thus obtained. Example 5: A 400g of porous hydroxyapatite granules having an average granule size of 2.2 µm, porosity of 50%, Ca/P ratio of 1.67 and average pore size of 0.09 µm was mixed with 600ml of 10% by weight of an aqueous solution of polyvinyl alcohol. After mixing, the mixture was printed and adhered to a polyester nonwoven fabric ("Panelon" commercially available from Dynic), and then dried at 25°C. A desired filter sheet was thus obtained. Note, a printing plate used in the printing process is that containing 4mm × 4mm squares at a distance of 1mm. Test Example 1: This example is intended to evaluate a remarkable excellent deodorizing effect of the filter sheets of the present invention. The deodorizing apparatus of Fig. 2 was used to make this evaluation. The filter sheets of Examples 3 to 5 were cut to discs having a diameter of 45mm, and each disc, i.e., filter sheet 12a of Fig. 2, was set in a filter holder 12 of the deodorizing apparatus. A test gas containing 14.7ppm of ammonia (NH 4 ) in a Tedlar bag 11 was guided through the filter sheet 12a to a Tedlar bag 15. A 10 liters of the test gas was passed through the filter sheet 12a. To evaluate a deodorizing effect, i.e., removal of ammonia, of the filter sheet, a concentration of the ammonia gas remaining in the filtered test gas in the Tedlar bag 15 was determined in accordance with an indicator tube method. The results are summarized, together with a removal percentage of ammonia, in the following Table 1. The removal percentage of ammonia means a percentage of the ammonia gas adsorbed on the filter sheet. test gas conc. of NH 4 (ppm) removal of NH 4 (%) control (not filtered) 14.7 - filtered with filter sheet of Ex. 3 5.3 63.9 filtered with filter sheet of Ex. 4 3.8 74.1 filtered with filter sheet of Ex. 5 4.0 72.8 The results of this table indicate that 90% or more of the ammonia gas can be adsorbed on the filter sheets depending upon a specific structure thereof, and in summary, a remarkable excellent deodorizing effect can be obtained by using the filter sheets of the present invention. Test Example 2: This example is intended to explain the usefulness of the filter sheets of Example 4 as a virus adsorbent. A floating solution of influenza virus PR8 in a physiological saline was used as a test solution. The filter sheet was cut to obtain a test piece with a diameter of 5cm. The test piece was applied onto a filter funnel, and 3ml of the floating solution of influenza virus PR8 was pored into the funnel. The received virus floating solution from the funnel was tested to determine a titer thereof in accordance with the following method. The results are summarized in Table 2. Determination of Titer: When the influenza virus was adhered to red blood cells, the blood cells cause their aggregation with each other. The determination of titer is made based on this aggregation reaction. Namely, the virus floating solution as a test solution is diluted with a physiological saline (0.9% aqueous solution of sodium chloride) to make a twice (2 time, 4 time, 8 time, 16 time, ···) -increased volume, and the diluted solution each is mixed with the same amount of 0.4% floating solution of chick red blood cells. The degree of dilution at which the aggregation reaction was caused is regarded as a titer of test solution (not-diluted solution). sample titer test solution (not filtered) 128 test solution filtered through 32 the filter sheet of Example 4 Note, the titer is proportional to a concentration of influenza virus in each sample solution. The results of the Table 2 indicate that in comparison with the virus concentration of the test solution (not filtered), virus concentration of the solution filtered through the filter sheet of Example 7 was reduced to 1/4. Namely, the influenza virus was effectively adsorbed by the filter sheets of the present invention.

Claims: A filter sheet which comprises a sheet-like matrix of organic polymeric material having dispersed therein and adhering thereto by impregnation a calcium phosphate compound having a molar ratio of calcium to phosphorus of 0.8 to 2.0 and the form of porous granules with a porosity of 10 to 75 %. A filter sheet according to claim 1, in which the calcium phosphate compound is apatite, tricalcium phosphate, tetracalcium phosphate or a mixture thereof. A filter sheet according to claim 1 or 2, in which the calcium phosphate compound has an average particle size of 0.1 to 100 µm. A filter sheet according to claim 1 to 3, in which the matrix of the organic polymeric material is a sheet of paper, nonwoven fabric or plastic foam.

Inventors: OGAWA TETSURO, SAKURAI TAKESHI, TSURU SUMIAKI, YOKOO AKIHIKO, OGAWA, TETSURO, SAKURAI, TAKESHI, TSURU, SUMIAKI, YOKOO, AKIHIKO, OGAWA, TETSURO, C/O ASAHI KOGAKU KOGYO K.K., SAKURAI, TAKESHI C/O YUUGEN KAISHA FUJIMI SHOUKAI, YOKOO, AKIHIKO, C/O ASAHI KOGAKU KOGYO K.K.
Applicants: ASAHI OPTICAL CO LTD, YUUGEN KAISHA FUJIMI SHOUKAI, ASAHI KOGAKU KOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: B01D53
IPC codes: B01D53, A61L9, B01J20, B01D39