Adsorbent article with dust collecting function

Abstract: Preferably configured in ridge and recess irregularity, the adsorbent article of the invention provides adsorption of malodor components in air and also exhibits a dust collecting function. It comprises a woven sheet having a coarse three dimensional structure whose areas of the sheet surface as well as internal fiber structure which are allowed to come into contact with incoming outer air are provided with a binder layer made of a latex or emulsion or a non-solvent adhesive, to which binder layer activated carbon particles are adhered which are partially exposed. The process of adhereing activated carbon particles is conveniently performed by a fluidizing bed. The inventive sheet form fabric incorporates the particles with a high void ratio and uniformity and thereby exhibits a high adsorptive rate and capacity, and exceedingly low pressure loss with such result that it is applicable regardless of high or low air wind rate. Preferable use of the adsorbent article of the invention is in a filter element of an air-conditioner for cars.

Description: This invention relates to an adsorbent article or adsorptive product for mainly eliminating a slight amount of malodorous components contained in air or other gases with the advantage of high adsorption rate as well as convenient handling. Particularly this invention relates to a sheet form adsorbent woven fabric with air cleaning and dust collecting function. Main application thereof is a filter element of an air-conditioner or air-cleaner for household or car use, wherein featured are low pressure loss, long use life, and high cleaning performance by one passage with high air velocity. Heretofore activated carbon has been widely used as adsorbent for effecting a slight amount of undesirable components in air or other gases, wherein powder or particle form activated carbon is not always convenient to handle. Then, attempts have been made to carry such activated carbon particles firmly onto a porous base material, such as foamed plastics or nonwoven fabric. Such carried articles are convenient for the lack of troublesome dusting from powder particles and have the advantage of lower pressure loss due to better permeability of air through voids inside the porous base material. However, a conventional adsorbent of this type has disadvantage that surfaces of activated carbon particles are covered with a binder layer applied on the base material. For that cause, adsorptive capability exhibits only a fraction. It is a result from the preparative process wherein activated carbon powder particles are pre-mixed with a binder and then applied to the base material, that the majority of particle surfaces is unavoidably covered under the binder layer, and thus useless to the expected function. Another attempt has been known of mixing the powder particles with polyurethane prepolymer in the process of producing polyurethane foam, wherein with an adequate amount of the powder particles mixed, foaming capability of the polyurethane is inhibited and likewise the majority of particle surfaces is covered or micropores of activated carbon particles are plugged, thus the result is a large decrease in the adsorptive capability as expected. Then, the art of having the activated carbon particles carried by a coarse knitted article has been proposed, but in the case of a planar or two dimensional structure, a coarse structure of such base material provides a low pressure loss, but does not attain sufficient adsorption, and to the contrary, a fine structure of such base article improves the adsorption, but increases the pressure loss excessively, and results in unapplicable case for uses wherein dust collection is also needed. The present invention utilizes a woven sheet with steric or three dimensional structure and activated carbon particles adhered to such woven sheet with particle surfaces partially exposed or uncovered more than before. Thereby an adsorbent article exhibits lower pressure loss and in turn, higher adsorptive performance as dust collecting filter. The present inventors noticed that, when much turbulent air (or gas) flow passes through an adsorbent having a lower packing density, the contact efficiency between air and adsorbent is so remarkably promoted that it would realize a structure with low pressure loss and suitability for treating with a high rate air wind. In view of such findings, the inventors have experimented in pursuit of such structures based on sheet material having a coarse three dimensional structure wherein adsorbent particles are kept to be like afloat in internal space so as to be suitable to treat with higher air passage rate with a minimum hindrance to permeability. Consequently, the inventors have found it advantageous of adhereing activated carbon particles pointwise by means of a binder to a coarse three dimensional woven sheet and thereby it is found that the activated carbon particles are successfully kept at an adequate void ratio in internal structure. Therein, turbulent wind flow is further promoted by providing ridge and recess configuration or wavy section with the woven fabric and thus the present invention is attained. In summary, the present invention provides an adsorbent article, preferably in ridge and recess configuration, with a dust collecting function comprising a woven sheet having a coarse three dimensional structure whose areas of the sheet surfaces as well as the internal fiber structure which are allowed to come into contact with incoming outer air being provided with a binder layer made of a latex or emulsion or a non-solvent adhesive, to which binder layer activated carbon particles are adhered which are partially exposed, wherein the carbon particles are adhered on the internal structure uniformly. Further, the surface of the sheet is subsequently re-coated with such binder, and the inventive sheet product is suitable to be used in a car air-conditioner or air-cleaner. The present invention also provides a process for manufacturing an adsorbent article, preferably in ridge and recess configuration, with dust collecting function comprising a woven sheet having a coarse three dimensional structure, said process comprising the steps of: forming a binder layer made of a latex or emulsion or a non-solvent adhesive on areas of the sheet surface as well as the internal structure which are allowed to come into contact with incoming outer air, by dipping the sheet into a bath containing latex or emulsion or a non-solvent adhesive, followed by squeezing through rollers and, thereafter, blowing air to break or remove films formed between intertwined internal fiber; passing the woven sheet provided with the binder layer laterally through a fluidized bed of activated carbon particles, prepared by blowing up air from below to fluidize the particles and keeping the blow rate at a level relatively close to or slightly over the minimum fluidization rate, and pressing the sheet with rollers under heated condition to adhere particles mostly exposed on the surface of the binder layer. Further, the inventive adsorbent partially includes aniline, phosphoric acid, malic acid, ferric or ferrous salts carried by the carbon particles. Fig. 1 shows a photograph by scanning electron microscope of a woven fabric of this invention viewed perspectively from askant above. Fig. 2 shows key portions of Fig. 1, to illustrate a pattern of a woven structure. Fig. 3 shows a photograph by scanning electron microscope of a sectional view of the woven fabric. Fig. 4 shows key portions of Fig. 3, to illustrate a pattern of a woven structure. Fig. 5 shows a photograph by scanning electron microscope of activated carbon particles adhered to a fiber through a binder layer. Fig. 6 shows key portions of Fig. 5, to illustrate a internal structure wherein carbon particles are adhered to a fiber through a binder layer. A base material for the inventive adsorbent is a sheet, preferably of ridge and recess configuration, of a woven fabric having a coarse three dimensional structure, and there is little limit about textile materials and included examples are: polyethylene, polypropylene, polyurethane, nylon, polyester, polyvinyl chloride, polyvinylidene chloride, fluororesin, vinylon, polymer of acryl compound, cellulose acetate, promix fiber, and other synthetic or semisynthetic fibers, rayon, cotton, hemp, silk, and other natural fibers, or inorganic fibers, and further various metal fibers such as fabric woven from fine aluminum filament. The woven fabric in the present invention may be manufactured from 20 to 500 denier fiber made of nylon, polyester, or polypropylene, for instance, through specific weaving art. Therein preferably the warp density is 10 to 50 per inch, and the weft density is 10 to 50 per inch. Then, the phrase: "preferably the sheet surface has ridge and recess configuration and a coarse three dimensional structure inside the sheet" means a woven fabric which was finished so by the weaving art or which is configured and structured so after the weaving process, for instance, by pleating (a kind of aftertreatment for a woven fabric), wherein ridges may be provided in two different orientations or irregularly. As noted before, it is preferable to enhance the adsorption so that an air stream hits the sheet surface in the state of turbulent flow, for which effect the ridge and recess configuration is helpful. Also larger voids in the internal structure of the sheet are preferable to treat with larger air wind rate, by which internal structure the turbulence by the ridge and recess configuration at the sheet surface will grow further. The activated carbon of the inventive adsorbent may be any kind which has a large internal surface of several hundreds square meters or more per 1 gram of the sample and exhibits high adsorption. Such activated carbon is usually manufactured from a carbonized product of coconut shells and timber, or coal, which are activated by water vapor or carbon dioxide at high temperature, or treatment by zinc chloride, phosphoric acid, concentrated sulfuric acid. Activated carbons prepared by either process are acceptable for this invention. The activated carbon is a nonpolar material and is known to be unique to exhibit superior adsorption to nearly all gases and liquids. As for the size of the activated carbon particles, there is little limit and a broad range of sizes is acceptable or effective, wherein a preferable particle size is smaller than 20 mesh and larger than 100 mesh for the purpose of controlling the pressure loss. In order to carry the activated carbon particles to internal fibers inside the sheet having a coarse three dimensional structure, an adhesive made of a latex or emulsion or a non-solvent polymer base is necessary to avoid plugging micropores of the activated carbon, wherein in the case of latex or emulsion, a higher solid content such as more than 30%, preferably more than 50%, is recommendable. Latex or emulsion means a dispersion including rubber-based particles or adhesive polymer particles suspended in a water medium. The latex includes SBR, chloroprene, nitrile rubber, and other synthetic rubber-based latexes, and the term emulsion means a copolymer of acrylic acid ester and acrylic acid, or ethylene and vinyl acetate, or polyvinyl acetate suspended in a water medium. Non-solvent polymer based adhesives include adhesive prepolymer with no water or solvent, wherein anadhesive made of synthetic rubber is preferable, for instance, polyurethane pre-polymer with excess NCO groups. More preferable is polyurethane prepolymer with MDI (methylene diisocyanate) as the base. MDI base prepolymer is more preferable than TDI (tolylene diisocyanate) base prepolymer because a MDI base prepolymer has a tendency to yield less liberated isocyanate and to be less adsorbed by the adsorbent particles. The present invention involves forming a binder layer made of the binder material or adhesive noted above on the surface of the coarse sheet form fabric as well as the surface of fibers constituting the internal structure. In order to carry out this work, the sheet is dipped into a bath containing a binder such as latex or emulsion, followed by squeezing excess picked-up binder through rollers. Alternatively, the adhesive is sprayed over the sheet and squeezed to permeate into the internal structure. Thereafter, air blowing is effective to break or remove films formed between intertwined internal fibers, thus the binder layer is provided on areas of the surfaces of the woven fabric as well as on the internal structure which is allowed to come into contact with incoming outer air. Adhesion of the activated carbon particles to the binder layer thus formed is carried out by passing a fluidized bed of particles or spraying or dropping them through a sieve. Therein, the method of passing a fluidized bed includes passing the sheet kept laterally in a fluidized activated carbon bed and thereby permeating the carbon particles into the sheet. The fluidized bed is prepared in a vessel or tank with the carbon particles filled in a predetermined depth and air is blown into the particle bed from below to fluidize the particles, wherein it is found that, in the case of keeping the gas blow rate at a level relatively close to or slightly over the minimum fluidization rate, the particles conveniently enter into the internal structure of the sheet fabric with uniformity. In other methods, the particles adhere mostly on the surface of the sheet fabric and poorly on fibers in the internal structure. However, the method of passing a fluidized bed allows adjustment of air blow rates and dwelling time according to particle sizes so that the particles may adhere on the internal structure uniformly. Thus, this method is most suitable for this purpose. In the case of the spray method or the through sieve method, it is recommended to turn over the side of the sheet so as to spray or drop the particles onto two sides of the sheet for the purpose of uniformly entering the particles into the internal structure. Additionally, by vibrating the sheet after the step of adhereing the particles, the inward move of the particles is promoted. Following the adhesion of the particles onto the sheet, pressing the sheet thus treated between a paired pinch rolls lightly will effect adhesion of the particles, wherein a part or all of the rolls may be heated to promote the adhesion. The activated carbon particles carried by the sheet form fabric are exposed on the surface of the binder layer formed on fibers of the internal structure. This target is attained in this invention because such particles are delivered in the form of not a mixture with the binder component, that is, after the binder layer has been formed, such particles are delivered and then adhesion is effected by press under heated condition. As a result, the particles are mostly exposed on the surface of the binder layer. This status affords the most featuring point in the present invention. Conventionally in the process of having the activated carbon particles carried by a sheet fabric, mostly the particles have been applied in the state mixed with latex or emulsion and in turn the particles are covered with the binder component to result unavoidably in hindered adsorption. In contrast, the sheet form woven fabric mostly contains the activated carbon particles exposed on the surface, and accordingly features larger adsorptive capacity and higher adsorptive rate. Therein the sheet form woven fabric has a coarse or uncompacted structure as a whole to provide a large passage sector for air wind and thus brings about a low pressure drop to high air rate, wherein air passes internally in much turbulent flow. As for the squeezing step as noted above, clearance between the pinch rolls is set conveniently, which is preferable 50 to 80% of the sheet thickness, and in the process of adhereing the carbon particles to a polyurethane prepolymer layer, treatment with heated steam is recommended for enhancing the adhesion. In order to protect the carbon particles adhered to the surface of the coarse sheet form fabric from dropping out during the use, latex or emulsion or non-solvent polymer based adhesive is re-coated and re-subjected to air blowing. The re-coating binder is not always the same as the binder priorily applied into the internal structure, but may be different from such one. In essence, the binder for re-coating is selected in view of suitability, since re-coating will somewhat attenuate the adsorption, but the share percentage of particles lying on the sheet surface which are to be affected by the re-coating is so small as a whole that a loss will normally be under the level of performance requirement. In designing the adsorbent article, the number of sheet ply may be a plurality or in the form of a laminate. In the treatment of pleating, molding may be carried out in a state that the adsorbent sheet is overlaid with paper, nonwoven fabric, electret nonwoven fabric, electrically conductive sheet, magnetic sheet, or sheet having oxidizing catalyst. The inventive adsorbent article bases on a sheet form woven fabric having a coarse three dimensional structure whose surfaces of the sheet as well as internal fibers are adhered with activated carbon particles, and features exceeding low pressure drop in the use circumstances regardless of air passage rate being low or high. For such merits, the inventive adsorptive article is suitable for a deodoring article with dust collecting function to be equipped with air-conditioner or air-cleaner for cars. Example 1 A sheet form fabric (3mm thick) with coarse wavy three dimensional structure, is used as a carrier of activated carbon particles to prepare a deodoring article with dust collecting function, for an air-conditioner and the like. This sheet was dipped into a SBR latex and squeezed by rubber rolls to adjust the latex amount picked up per unit square, and subjected to air blowing to remove films yielded in the internal structure of the porous sheet and then a binder layer is provided on the surface of the sheet as well as the fibers of the internal structure. The sheet thus obtained was passed through a fluidized bed in which crushed activated carbon particles prepared from coconut shell (28 to 70mesh) were fluidized in order for such particles to adhere to the binder layer provided on the surface of the sheet as well as the internal structure. Therein, the fluidization vessel is rectangular with many holes at the bottom and the activated carbon particles were packed 6-8 cm high, the air blow rate was about 0.4 m/s by which the top of the face of the fluidizing mass was viewed to be mildly active, and the sheet was passed laterally through a middle portion thereof at about 1m/s. Then, the fabric incorporated with the particles was passed through the press rollers to accomplish adherence between the binder and the particles, and excess particles or weakly adhered particles were shaken off by vibrating the sheet and then dried at 120 °C to result in a coarse sheet form fabric incorporated with activated carbon particles. Appended Fig. 1 shows a photograph by scanning electron microscope of a woven fabric of this invention viewed perspectively from slantingly above. Fig. 2 shows key portions of Fig. 1, to illustrate the pattern of a woven structure made of fibers 1. Fig. 3 shows a photograph by scanning electron microscope of a sectional view of the woven fabric, and key portions of Fig. 3 are shown in Fig. 4, whereby wavy or "ridge and recess configuration" is realized by intercrossings of the warps 2 and the wefts 3. Fig. 5 shows a photograph by scanning electron microscope of activated carbon particles adhered to a fiber through a binder layer. Fig. 6 shows key portions of Fig. 5, which illustrates the state wherein individual carbon particles 4 are adhered and exposed on the substrate binder layer 5. The amount of retaining the activated carbon particles obtained in Example 1 was 0.11 g/ml, and the adsorptive capacity for benzene(measured by JIS K 1474-1975) was 0.03 g/ml which deserves excellent adsorptivity. Example 2 A porous sheet form woven fabric (5 mm thick) having a coarse wavy three dimention al structure, is used as a carrier of activated carbon particles to prepare a deodoring article with dust collecting function, for an air-cleaner. This sheet was dipped in SBR latex and squeezed by rubber rolls to adjust the latex amount picked-up per square areas, and then subjected to air blowing to remove films yielded in the internal structure of the porous sheet and thus a binder layer is provided on the surfaces of the sheet as well as the fibers of the internal structure. The sheet obtained was passed through a fluidized bed in which crushed activated carbon particles prepared from coconut shell (70 to 100 mesh) were fluidized in order for such particles to adhere to the binder layer provided on the surfaces of the sheet as well as the internal structure. The activated carbon used was a mixture in view of carried substances: 60 wt% of the whole activated carbon did not carry any substance; the rest of 40 wt% was divided into four kinds of each 10 wt%; that is, each of the 10 wt% carried aniline, phosphoric acid, malic acid and ferric (or ferrous) salt, respectively. Then, the fabric incorporated with the particles was passed through the press rollers to accomplish adherence between the binder and the particles, and excess particles or weakly adhered particles were shaken off by vibrating the sheet, and the fabric was sprayed with a thinned SBR latex by a spray (re-coating of latex), and then dried at 120°C to result in a coarse sheet form fabric incorporated with activated carbon particles. The structure thus obtained was similar to Fig. 5. The amount of retaining the activated carbon particles obtained in Example 2 was 0.07 g/ml, and adsorptive capacity for benzene(measured by JIS K 1474-1975) was 0.02 g/ml. The fabric (200 X 200 X 5 mm) obtained in Example 2 was tested for deodoring purpose. Malodoring components; hydrogen sulfide 250 ppm, or trimethyl amine 50 ppm, and acetoaldehyde 25ppm, were contained in a box (1 X 1 X 1 meter) in which the fabric was suspended and air was circulated. In either case the malodor was nearly completely removed in about 30 min. Example 3 A sheet form fabric incorporated with activated carbon particles, excluding the re-coating of latex, was prepared under much the same conditions as in Example 2. The fabric thus obtained exhibited 0.023 g/ml of benzene adsorption. This result indicates that 13% drop in the adsorption was caused by the re-coating of latex, but the adsorptivity was proved to be acceptable regardless of the re-coating application. Example 4 A sheet form fabric laminate comprised of a two ply construction (each ply:3 mm thick) having a wavy coarse three dimensional structure, is used as a carrier of activated carbon particles to prepare a deodoring article with a dust collecting function, for an air-conditioner equipped in a car. This laminate was dipped in a bath containing a non-solvent binder (prepolymer composed of polyisocyanate and polyester) and squeezed by rubber rolls to adjust the amount of picked-up binder and subjected to air blowing to remove films yielded in the internal structure of the porous laminate. Thereby the binder layer is formed on the sheet surfaces as well as on the internal structure. Then, the laminate was passed through a fluidizing bed in which the activated carbon particles are fluidizing to adhere such particles to the sheet surfaces as well as the internal structure, wherein the activated carbon particles (made from coconut shells, 28-70 mesh)were a mixture: 90wt% carried nothing and the rest of 10 wt% carried phosphoric acid in an amount of 10 wt%). Then, the fabric incorporated with the particles was passed through the press rollers to accomplish adherence between the binder and the particles, and excess particles or weakly adhered particles were shaken off by vibrating the sheet. The amount of retaining the activated carbon particles obtained in Example 4 was 0.14 g/ml, and the adsorptive capacity for benzene(measured by JIS K 1474-1975) was 0.035 g/ml. The fabric (200 X 200 X 5 mm) obtained in Example 4 was tested for deodoring purpose. A malodoring component (hydrogen sulfide 50ppm, or ammonia 50 ppm) was contained in a box (1 X 1 X 1 meter) in which the fabric was suspended and air was circulated. In either case malodor was completely removed in about 30 min.

Claims: A process for manufacturing an adsorbent article with a dust collecting function comprising a woven sheet having a coarse three dimensional structure, said process comprising the steps of: forming a binder layer made of a latex or emulsion or a non-solvent adhesive on areas of the sheet surface as well as the internal structure which are allowed to come into contact with incoming outer air, by dipping the sheet into a bath containing latex or emulsion or a non-solvent adhesive, followed by squeezing through rollers and, thereafter, blowing air to break or remove films formed between intertwined internal fiber; passing the woven sheet provided with the binder layer laterally through a fluidized bed of activated carbon particles, prepared by blowing up air from below to fluidize the particles and keeping the blow rate at a level relatively close to or slightly over the minimum fluidization rate, and pressing the sheet with rollers under heated condition to adhere particles mostly exposed on the surface of the binder layer. An absorbent article with a dust collecting function comprising a woven sheet having a coarse three dimensional structure whose areas of the sheet surfaces as well as the internal fiber structure which are allowed to come into contact with incoming outer air being provided with a binder layer made of a latex or emulsion or a non-solvent adhesive, to which binder layer activated carbon particles are adhered which are partially exposed, wherein the carbon particles are adhered on the internal structure An adsorbent article according to claim 2, wherein the surface of the woven sheet incorporated with activated carbon particles being re-coated with a binder. An adsorbent article as claimed in claim 2 or 3, wherein the woven sheet has a sectionally ridge and recess configuration. An adsorbent article as claimed in one or more of claims 2 to 4, wherein the activated carbon particles are carrying at least partially one ore more of aniline, phosphoric acid, malic acid, ferrous or ferric salt. Use of an adsorbent article as claimed in one or more of claims 2 to 5 as an element in an air-conditioner or air-cleaner for cars.

Inventors: FUKUURA MASAKI, NISHIMURA SHUSHI, OKADA TERUHIRO, TAKAMOTO SHOHICHI, FUKUURA, MASAKI, NISHIMURA, SHUSHI, OKADA, TERUHIRO, TAKAMOTO, SHOHICHI
Applicants: KURARAY CHEMICAL KK, KURARAY CHEMICAL CO., LTD.
Application year: 1997
Main classification: B01J20
IPC codes: B01D39, B01D53, B01J20, A61L9