GB2032298A

GB2032298A - Adsorbent air filter

Info

Publication number: GB2032298A
Application number: GB7932904A
Authority: GB
Original assignee: Takeda Chemical Industries Ltd
Current assignee: Takeda Pharmaceutical Co Ltd
Priority date: 1978-10-09
Filing date: 1979-09-21
Publication date: 1980-05-08
Also published as: IT1123296B; DE2938234C2; FR2438493A1; GB2032298B; IT7925941A0; FR2438493B1; DE2938234A1

Abstract

An air-cleaning filter element is prepared by applying an adhesive agent to at least a pair of three- dimensionally mesh-structured elastic- flexible webs, e.g. formed of polyurethane foam, having a thickness of 3 to 10 mm as superimposed, evenly distributing an adsorbent material, such as activated carbon in a size range of 0.5 mm to 10 mm in diameter, between said pair of elastic-flexible webs and pressing the same elastic-flexible webs together as superimposed.

Description

SPECIFICATION Air filter This invention relates to an air-cleaning filter element prepared by bonding an adsorbent material to and between a plurality of elastic-flexible webs with an adhesive agent, which has the inherent adsorptive performance of said adsorbent.

Heretofore, adsorbent materials, e.g. activated carbon, have been commonly used as filter materials for air cleaners and for other uses, the material being packed in plate-shaped or zigzag-shaped filter housings.

However the adsorbents tend to generate dust on vibration or friction of the housings in the course of transportation or use, thereby soiling the housing. Gaps are also formed in the carbon layer and the resultant 'short-cuts' of the fluid to be treated resulted in the failure of the filter to display its expected cleaning performance.

In order to overcome the above disadvantages, various methods have heretofore been proposed for moulding an adsorbent with a binding agent to provide a dimensionally stable adsorbent product. Recently, it has been proposed to place a granular adsorbent in a nonwoven fabric case and seal the case to provide a sealed filter element, orto retain a side of an adsorbent-packed filter element with a spring member so as to prevent the formation of gaps.

However, the binding agents heretofore used are disadvantageous in that the solvents contained in such binders tend drastically to reduce the adsorptive capacity of the adsorbent or to cause a considerable pressure drop on the passage of the fluid.

Furthermore, the filter housing is of necessity complicated in structure. Thus, the prior art devices have not provided fully satisfactory results.

According to one aspect of the present invention there is provided an air-cleaning filter element, which comprises at least two sheets of three-dimensionally mesh-structured elastic-flexible webs having a thickness of 3 mum to 10 mm as superimposed, and adsorbent which is bonded to and between the webs with an adhesive agent.

According to another aspect of the present invention there is provided a method of making an air-cleaning filter element which comprises applying an adhesive agent to and between at least two sheets of three-dimensionally mesh-structured elastic-flexible webs, disposing an adsorbent between said elasticflexible webs and pressing the webs together as superimposed.

The mesh-structured elastic-flexible web to be employed has a three-dimensional skeletal structure which can be attained by selective hydrolysis of a polyurethane foam and which contains 9 to 31 air spaces (hereinafter referred to as cells) per 25 linear millimetres, the number or density of such cells being selected according to the grain size of the activated carbon or other absorbent employed. Thus, for example, a web having 9 cells/25 linear mm is preferred for the adsorbent having a grain size of 4 to 5 mm and a web having 31 cells/25mm for non-uniform irregularly shaped adsorbent grains of the order of 1 mm.

As regards the thickness of said mesh-structured elastic-flexible web, a web material of the described type may be sliced or otherwise processed to a thickness suitable for the grain size of carbon to be bonded thereto and the intended application. An appropriate thickness can be selected within the range of 3 to 10 mm.

The adsorbent employed in the present filter element may for example be activated carbon, active clay, acid clay, silica, alumina or any moulded or crushed metal oxide catalysts, or a mixture of two or more of such materials, although activated carbon is particularly advantageous.. The activated carbon may be one based on coal, petroleum oil distillation residue, wood, fruit shells or the lime, provided only that it has a BET specific surface area of 500 to 2000 m2/gram. The adsorbent is normally used as cylindrical, spherical or irregular-shaped grains from 0.5 mm to 10 mm, preferably from 1 mm to 5 mm in diameter.

The adhesive agent employed may be of any type which is able to secure said adsorbent in position on said mesh-structured elastic and flexible web. Thus, solent-sensitive adhesives pressure-sensitive adhesives, heat-sensitive adhesives, and reaction-sensitive adhesives may be mentioned as examples, although pressure-sensitive adhesives and solvent-sensitive adhesives are particularly desirable.

Such pressure-sensitive adhesive materials are mostly solution-type adhesives using aromatic hydrocar bons (e.g. toluene and xylene) or esters or ketones (e.g. ethyl acetate and acetone) as the solvent components. The solid body components of such adhesives may for example be any of the following materials, or mixture of two or more of them.

1. Rubber type Natural rubber and neoprene, chlorinated rubber, SBR, NBR, MBR and other synthetic rubbers.

2. Cellulose type Ethyl cellulose, butyl cellulose, benzyl cellulose, nitrocellulose. cellulose acetate and acetic acid, butyric acid and other mixed cellulose esters.

3. Vinyl type Polyvinyl chloride, polyacrylate ester, polyvinyl ether, polyvinyl acetal, polyisobutylene, ethylene-vinyl acetate copolymer and other materials.

Example of solvent-sensitive adhesives which are preferably used in making the present air filter include various synthetic rubber latices which are aqueous emulsions of synthetic rubber of 0.03 to 1 Zo 1.51n~ particle size. Examples of the solid component of the latices are described below: (1) Butadiene polymers, or copolymers of butadiene and styrene, styrene derivatives, acrylonitrile, methacrylonitrile, isoprene, isobutylene, etc.

(2) Copolymers of isoprene and styrene, styrene derivatives, etc.

(3) Chloroprene polymers, or copolymers of chloroprene and styrene, styrene derivatives, acrylonitrile, isoprene, etc.

(4) Copolymers of acrylates and styrene, styrene derivatives, vinyl chloride, vinyl acetate, acrylonitrile and methacrylates.

(5) Methacrylonitrile polymers, and copolymers of methacrylonitrile and styrene, etc.

(6) Vinyl acetate polymers and vinyl chloride polymers.

The above latices may be used as such or after modification such as by carboxylation.

These latices may be in the form of an aqueous emulsion obtained by emulsion polymerization, and are used with the resin solid content adjusted to 20 to 50% and preferably, 35 to 45%.

The present air-cleaning filter element can be prepared by the steps of applying said adhesive agent to mesh-structured elastic-flexible webs, disposing the adsorbent over the coated surfaces of said webs and bonding the webs together by the application of pressure.

The application of the adhesive agent to the elastic-flexible webs can be accomplished by direct roller- or calender-coating, spray-coating or any other suitable procedure. It is, however, more desirable to coat a release paper with the adhesive by brushing, roller-coating, spray-coating or the like, pressing the paper against the elastic-flexible web in face-to-face relationship and, then, peeling off the release paper to let the adhesive be transferred from the release paper to the surface of the elastic-flexible web.

While the amount of adhesive should vary with its type, the amount as solid matter thereof can be from 5 g to 550 g per square metre of web. For example, pressure-sensitive adhesives can usually be used in an amount ranging from 5 g/m2to 250 g/m2 as solid matterthereof, preferably from 10 glm2to 200 glum2, and synthetic rubber latex can usually be used in an amount ranging from 100 gim2 to 500 g/m2 as solid matter thereof, preferably 250 g/m2 to 500 g/m2.

With a smaller amount of adhesive, the carbon cannotbe effectively locked in position on the web, and with an excess of adhesive, the open cells of webs are covered with the adhesive to cause an undesirably great pressure drop on passage of fluid.

When the adhesive contains a solent, the solvent should be evaporated off prior to deposition of the adsorbent, for otherwise the solvent will be adsorbed on the adsorbent to interfere with the latter's adsorptive ability. When the adhesive is applied to the elastic-flexible web from a release paper, the evaporation of solvent may take place after the application of adhesive to the release paper and before the pressing of the paper against the web, or after joining and before peeling-off or thereafter. The solvent evaporation may be accomplished either by allowing the material to stand at ambient temperature and pressure or, if necessary, at elevated temperature andlor pressure. The deposition of the adsorbent on the elastic-flexible web may be accomplished by a suitable procedure, e.g. by hand or by mechanical vibration.

While the deposited amount of adsorbent is optional according to the intended application, it is normally 200 to 2500 grams per square metre of the web.

The bonding of the carbon to the adhesive-coated webs can be accomplished by supporting the webs between wood, plastic, metal or other plates and applying an external load of 0.01 to 0.02 kg/cm2.

There are cases in which the edges of thus-formed filter element are heat-sealed.

The present air-cleaning filter element may be one prepared by using not less than 3 sheets of elastic-flexible webs. For example, in case of using 5 sheets of webs A, B, C, D and E as superimposed in the order mentioned, adsorbent is fixed in each space between webs, which are adjacent to each other, i.e. the space between webs A and B, the space between webs B and C, the space between webs C and D, and the space between webs D and E. The adsorbent in each space of the webs is bonded to two webs existing on both sides of the adsorbent. in this case, the adhesive agent may be different in kind in each layer of adhesive agent.It is preferably to use a pressure-sensitive adhesive agent in order to bond the interior webs B, C, D to adsorbents and to use adhesive agent other than a pressure-sensitive adhesive, such as synthetic rubber latex, in order to bond the outer side webs A and E with adsorbent.

The following examples are further illustrative of this invention.

Example 1 An elastic-flexible web was coated by brushing with an adhesive agent at an application rate as resin solids of 350g/m2, followed by scattering activated carbon uniformly on the surface at a rate of 3#/m2, then overlapped by another elastic-flexible web coated with an adhesive agent in the similar manner, and put between plates to be allowed to stand at ambient temperature for 10 hours under load of 0.01 kg/cm2 applied. Of the materials used, the elastic-flexible web was one having a size (15 cm x 30 cm x 5 mm (thickness) and a standard cell number of 9 cells 25 mm, while the activated carbon was in the form of cylinders having a BET specific surface area of 1180 m21g, a grain size of 4 to 6 mexh (4 mm in average particle size), and a packing density of 450 91e, and the adhesive agent was as indicated in Table 1.

TABLE 1 Sample No. Type and solid content of latices used 1 Carboxy-modified SBR 47 2 " MBR 48 3 Polyvinyl acetate 50 4 NBR 45 5 Acrylic acid ester copolymer 45 With the filter materials produced in this way, performance testing was carried out in accordance with the following methods, and the results obtained are shown in Table 2: 1. Pressure loss The filter element was cut into a disc 66 mm across and placed in a column of the same inside diameter.

Dry air at room temperature was introduced into the column at a linear flow rate of 0.5 to 2 misec. and the linear flow rate of the effluent air was measured with an electronic anemometer for pressure drop determination.

2. Acetone adsorption rate The filter element was cut into a disc 66 mm across and fitted into an adsorption column. A gas containing about 1.0 vol.% of acetone in a gas holder was circulated to the adsorption column at a linearflow rate of 15 cm/sec. and the adsorption rate was determined from the time when the acetone concentration has reached one-tenth of its initial concentration.

3. Acetone equilibrial adsorption The filter element was cut into a disc-shaped piece 66 mm across and, in accordance with JIS K-1474, the equilibrial adsorption of acetone with an initial concentration of 1000 ppm was determined.

TABLE 2 Pressure Acetone Acetone equilibrial Sample loss mm adsorption adsorption No. aq.1 misec rate, min. g/100 cm2 filter 1 0.5 8.0 4.3 2 0.7 7.5 4.3 3 0.9 11.0 4.0 4 0.7 8.0 4.2 5 0.8 9.0 4.1 Unfabricated 0.6 7.0 4.3 Example 2 By varying the amount of a synthetic rubber latex (carboxy-modified SBR latex) using the same procedure as described in Example 1, filter materials were produced to carry out the performance testing as mentioned in Example 1, to botain the results shown in Table 3.

TABLE 3 Sample Amount of Pressure Acetone Acetone equili No. latex g/m2 loss mmaq. adsorp brial adsorption 1 miser. tion g/l 00cm2 filter rate, min.

6 300 0.7 8.0 4.2 7 400 0.7 7.5 4.3 8 500 1.2 12.0 4.2 9 600 25.6 21.0 4.0 Unfabri cated - 0.6 7.0 4.3 Reference Example 1 In accordance with the same procedure as described in Example 1, but by crushing the cylindrical-formed activated carbon as used in Example 1 to a uniform grain size of 24 to 48 mesh (average particle size of 0.42 mm), and by the use of a carboxy-modified SBR latex as an adhesive agent and an elastic-flexible web of 50 cell125 linear mm in standard cell number as a mesh-structured elastic-flexible one, with the amount of the adhesive agent being 400 g (solids)/m2, a filter was produced to determined the pressure drop and equilibrium adsorption quantity for acetone, as indicated in the following: Pressure loss: (at a flow rate of 1 m/sec as a linear flow rate) 75.6 mm aq.

Acetone equilibrial adsorption; (2.0 9/100 cm2 - filter) Example 3 By means.of a coating brush, an elastic-flexible web having 9 cells/25 linear mm (standard number) size 25cm x 25cm x 5mm (thickness) was coated with 25 g/m2 (as solid resin content) of a vinyl pressure-sensitive adhesive (Composition: butyl methacrylate/ethylene-vinyl acetate copolymer dissolved in toluene-ethyl acetate; nonvolatile matter 25 wt.%) After application of a release paper, the web was dried in an oven at 800C for 30 minutes, after which time it was taken out and allowed to cool. The elastic web was peeled off the release paper.Then, cylindrical activated carbon pellets (BET specific surface area 1180 m2lg, grain size 4 to 6 mesh, packing density 450 gK) were evenly deposited on the coated web at the rate of 3 elm2. Another elastic web, similarly coated with the same adhesive, was superimposed on the above web and the assembly was placed between a pair of plates and a load of 0.01 kg/cm2 was applied to the plates from behind to join the webs and carbon together under pressure. By the above procedure was obtained a filter element according to this invention.

The following performance tests on the above filter element were carried out by the same manner as in Example 1. The results are shown in Table 4.

TABLE 4 Sample Pressure Acetone Acetone equilibrial No. loss* adsorption adsorption (mm,water) rate(min.) (g11 00 cm2 filter) 10 0.6 9.0 2.15 Unfabri cated 0.6 8.5 2.15 * Pressure loss at a flow rate of 1 m/sec.

Example 4 In the same manner as Example 3, filter elements were produced using various amounts of vinyl pressure-sensitive adhesive and a pressure loss test was performed on each of the filter elements. The results are set forth in Table 5.

TABLE 5 Sample No. Amount of adhesive Pressure loss* (9)m2) (mm, water) 11 10 0.6 12 50 0.6 13 100 0.7 14 200 1.5 15 300 31.0 Unfabricated - 0.6 * Pressure loss at the flow rate of 1 m/sec.

Claims

1. An air-cleaning filter element, which comprises at least two sheets of three-dimensionally meshstructured elastic-flexible webs having a thickness of 3 mm to 10 mm as superimposed, and adsorbent which is bonded to and between the webs with an adhesive agent.

2. An element as claimed in claim 1, wherein the adsorbent is activated carbon.

3. An element as claimed in claim 1 or 2, wherein the adsorbent is used in an amount ranging from 200 to 2500 g. per square metre of web.

4. An element as claimed in any one of claims 1 to 3, wherein the adhesive agent is a solent-sensitive adhesive.

5. An element as claimed in any one of claims 1 to 4, wherein the adhesive agent is a synthetic rubber latex.

6. An element as claimed in claim 5, wherein the synthetic rubber of said latex is a butadiene polymer or a copolymer of butadiene and styrene, a styrene derivative, acrylonitrile, methacrylonitrile, isoprene or isobutylene.

7. An element as claimed in any one of claims 1 to 3, wherein the adhesive agent is a pressure-sensitive adhesive.

8. An element as claimed in any one of claims 1 to 7, wherein the adhesive agent is used in an amount ranging from 5 g to 550 g per square metre of web.

9. An element as claimed in claim 5 or 6, wherein the synthetic rubber latex is used in an amount of from 100 g. to 500 g. per square metre of web.

10. An element as claimed in claim 5,6 or 9, wherein the synthetic rubber latex is used in an amount of from 250 g. to 500 g. per square metre of web.

11. An element as claimed in claim 7, wherein the pressure-sensitive adhesive agent is used in an amount of from 5 g. to 250 g. per square metre of web.

12. An element as claimed in claim 7 or 11, wherein the pressure-sensitive adhesive is used in an amount of from 10 g. to 200 g. per square metre of web.

13. An element as claimed in any one of claims 1 to 12, wherein not less than three sheets of the webs are employed.

14. An element as claimed in claim 13, wherein the interior web or webs are bonded to adsorbent with a pressure-sensitive adhesive and each of the outer side webs is bonded to adsorbent with an adhesive agent other than a pressure-sensitive adhesive.

15. An element as claimed in claim 14, wherein each of the outer side webs is bonded to adsorbent with a synthetic rubber latex.

16. An element as claimed in any one of claims 1 to 15, wherein the adsorbent is activated carbon having a grain size of 0.5 to 10 mm in diameter.

17. An element as claimed in any one of claims 1 to 16, wherein the adsorbent is activated carbon having a grain size of 1 to 5 mm in diameter.

18. An air-cleaning filter element in accordance with claim 1, substantially as hereinbefore described in any one of the foregoing Examples.

19. A method of making an air-cleaning filter element which comprises applying an adhesive agent to and between at least two sheets of three-dimensionally mesh-structured elastic-flexible webs, disposing an adsorbent between said elastic-flexible webs and pressing the webs together as superimposed.

20. A method of making an air-cleaning filter element in accordance with claim 14 substantially as hereinbefore described in any one of the foregoing Examples.