GB2352987A

GB2352987A - Ion-exchange filter

Info

Publication number: GB2352987A
Application number: GB9918901A
Authority: GB
Inventors: Iwao Yoshizawa; Shinji Hattori; Naoki Irie; Yoshiyuki Onishi
Original assignee: Takuma Co Ltd
Current assignee: Takuma Co Ltd
Priority date: 1998-02-19
Filing date: 1999-08-12
Publication date: 2001-02-14
Also published as: JPH11226338A; GB9918901D0; JP3912886B2

Abstract

An ion-exchange filter for use in semiconductor manufacture is made by impregnating a sheet-like substrate 2 of cancellous polyurethane foam having a number of large-diameter continuous pores 1 with an acrylic, urethane or vinyl acetate adhesive agent so that the adhesive agent is uniformly adhered to substantially the entire surface of the substrate; and introducing an excessive amount of ion-exchange resin 3 into the pores 1 so that excess particles pass the substrate through the thickness thereof for subsequent removal without being adhered to the substrate, the particles 3 having a diameter which is 2-50% of the diameter of the pores 1, and being dried in advance to a moisture content below 30%. In use, the filter is wrapped in a cloth of smaller mesh than the particles 3 and housed in an air-permeable casing.

Description

2352987 ION-EXCHANGE FILTER, METHOD OF MANUFACTURING THE FILTER, AND

FILTER APPARATUS USING THE FILTER

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention relates to an ion-exchange filter employed for e.g. eliminating volatile ions in e.g. a clean room of a semiconductor manufacturing factory The invention relates also to a method of manufacturing such filter as well as a filter apparatus using the filter.

DESCRIPTION OF THE RELATED ART

In the semiconductor industry, there has occurred continuous improvement in the art of integration through higher miniaturizing process. In order to support such trend of ever higher integration, efforts have been made to prevent dust generation in the dean room so as to eliminate solid fine particles therefrom. However, with prevention of dust generation in the dean room alone, there has been a limit in the degree of improvement of integration made possible.

Faced with this situation, the convention has attempted to eliminate not only dust but also volatile organic and inorganic chemical contaminants. One known type of such art for eliminating volatile organic and inorganic chemical contaminants is the use of a chemical filter utilizing activated carbon in the form of pellets or grains impregnated with acid or alkali, which is typically phosphoric add, potassium hydroxide or the like, for adsorption of acidic or alkaline ions.

This method relies on a neutralizing reaction of the acid or alkali, for I the elimination of the volatile acidic or alkaline ions. With this method, the neutral salt will be deposited inside or on the surface of the agent-impregnated activated carbon, and such deposited salt is only physically supported on the carbon.

Further, as the amount of deposited neutral salt increases relative to that of the impregnated agent, the deposited substance will tend to scatter over due to a certain physical factor such as change in the air flow amount, or vibration associated With a slight change in the pressure loss, etc, so that the scattered substance may cause contamination clogging of a HEPA filter disposed downstream, resulting in increased pressure loss. For these reasons, the use of such chemical filter has heretofore been problematic for a so-called "super clean room" which requires high-purity atmosphere. Further, the use of such conventional chemical filter in a system for introducing ambience air has been limited in the respect of location of its installment, because, for instance, in such application the filter will be necessarily subject to significant influence from the relative humidity.

Especially, activated carbon impregnated with acid or alkali exhibits higher hygroscopic property due to the effect of the chemical agent contained therein. Then, the activated carbon, in such application, may absorb an unexpectedly large amount of moisture, so that the impregnated agent may 'drain out' of the carbon. Accordingly, in the Japanese climate providing significant humidity variation from 37% RH to 95% RH yearly, it has been impossible to install such chemical filter at the entrance of ambient-air conditioner in the dean room system, and the filter may be employed only in a low-humidity region downstream a humidity conditioner. Further, in an air-circulating system, if the absorbing agent of the activated carbon absorbs and discharges moisture, the degree of moisture suppression required for the actual dean room system tends to be significant, so that it is often 2 difficult to provide a stable environment.

Also, as the agent generally employed as the impregnating agent for acid-impregnated activated carbon, orthophosphoric acid may be cited. This orthophosphoric acid, however, has the disadvantage that it has a relatively large vapor pressure even at the normal temperature of 200C. This means that orthophosphonic add is apt to vaporize under the normal temperature of the dean room. The experiments conducted by the present inventors have indicated that in the case of acid-impregnated filter, the concentration of the acid can be several ng/m' higher on the downstream side than the upstream side.

Therefore, it is presently unfeasible to employ such acid impregnated filter for a super-clean room.

As an alternative to the above, there has been developed also an adsorbing filter having a high air-permeability, in which filter an adsorbing agent such as activated carbon is adhered to a cancellous or entangled wire-work like substrate made of polyurethane foam having a number of large-diameter continuous pores. It has been reported that such adsorbing filter can provide high adsorbing capacity since the activated carbon densely distributed over and adhered to the substrate can come into contact with the contaminated air in an efficient manner while the large-diameter continuous pores of the cancellous polyurethane foam assure good air-permeability (see e.g. Japanese published patent gazette No. Hei. 4-35201).

Further, the convention has also proposed to incorporate a filter using an ion-exchange resin in an air-circulatory system of a clean room for eliminating the chemical contaminants. With such filter using an ion-exchange resin, volatile ions are removed through an ion-exchange reaction provided by the ion-exchange resin, so that the filter will not release again the ions once captured thereby. Because of this, there is a growing interest in this type of filter as a new promising filter capable 3 of solving the above-described problem of the filter using the agent impregnated activated carbon. However, in order to form the ion exchange resin into a filter, this ion-exchange resin needs to be processed into the form of fibers. This necessity has caused various manufacturing difficulties as described next. Namely, in order to assure the spinnability required for forming the ion-exchange resin into such ion-exchange fibers, its manufactuning process necessanily requires the total ion-exchange capacity of the fibers to be small (for instance, in the case of a strongly acidic, positive ion or cation exchange fiber, the total capacity will be as small as 1/2 of that of the ion exchange resin). For this reason, in forming the ion-exchange resin into the fibers, in order to increase its ion-exchange capacity, there arises the necessity of e.g. forming the ion-exchange resin into a high density nonwoven sheet fabric. However, if the nonwoven fabric as a filter material has a density above 0. 1, there occurs a sharp rise in the pressure loss, so that the fabric becomes unfeasible as a filter.

Accordingly, since there exists a limit in increasing the charging density of the ion-exchange fibers due to the pressure loss inevitably associated therewith, the resultant filter will necessa'rily have a small ion exchange capacity per unit area. This means that the filter win provide only a short usable life.

As described above, the prior art has failed to provide an ion exchange type filter capable of providing low pressure loss as well as extended service life. Then, there has been continuous demand for improvement of such ion-exchange type filters.

On the other hand, in order to obtain the activated carbon of the above-noted type, the prior art has also proposed use of ion-exchange resin in the form of carbonized particles (see Japanese laid-open patent gazette No. Hei. 8-168633 (this particular reference will be referred to as "the prior art" hereinafter)).

4 However, the description of the above prior art is limited to that the activated carbon is obtained from ion-exchange resin. And, since the ion-exchange resin, once carbonized, has lost its ion-exchange capacity, its ion eliminating ability is no greater than that of the activated carbon. Therefore, with this filter proposed by the prior art, a large ion-exchange capacity can not be expected.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above described state of the art and its primary object is to provide an improved ion-exchange filter capable of providing a large ion-exchange capacity as well as a longer filter life without involving significant increase in the pressure loss. Specifically, the invention provides an ion-exchange filter comprising a substrate made of a cancellous polyurethane foam and a sufficient amount of ion-exchange resin uniformly distributed over and adhered to the substrate.

That is to say, the present inventors conducted extensive and intensive research and experiments and discovered that an ion exchange filter making the most of the air-permeability of the cancellous polyurethane foam and the ion-eliminating ability of the ion-exchange resin can be obtained through the arrangement of causing particles of ion-exchange resin to adhere to a cancellous substrate made of polyurethane foam. And, the present invention has been made based on this discovery.

Generally, if one attempts to simply cause the ion-exchange resin particles to adhere to the cancellous polyurethane foam substrate, this would not succeed in causing a sufficient amount of particles to uniformly adhere to the polyurethane foam substrate, presumably because the ion-exchange resin has a relatively low fluidity and also the surface of the resin has low adhesiveness due to its hydrophilicity. For this reason, it was difficult to obtain an ion-exchange filter which provides a large ion-exchange capacity and in which a sufficient amount of ion-exchange resin is stably adhered to its substrate. Further, it would require a large amount of trouble to cause the ion-exchange resin particles to uniformly adhere to the substrate for obtaining an ion exchange filter stable in its performance. However, the prior art lacks the recognition of such drawback in the manufacturing aspect, to say nothing of any disclosure or teachings for solving such drawback.

Then, the present inventors also discovered that the poor adhesiveness and fluidity of the ion-exchange resin particles is related to the moisture content of the ion-exchange groups present on the surface of the particles and that through adjustment of this moisture content the adhesiveness and fluidity may be improved for facilitating the handling of the particles, thus enabling a sufficient amount of ion exchange resin to be adhered uniformly to the cancellous polyurethane foam substrate.

For achieving the above-noted object, according to one aspect of the present invention, there is proposed an ion-exchange filter comprising a substrate made of cancellous polyurethane foam having a number of large-diameter continuous pores, and a number of ion exchange resin particles distributed over and adhered to the substrate, each said particle having a particle diameter which is 2-50% of the diameter of the pore of the substrate.

Preferably, the ion-exchange resin particles are dried to a moisture content below 30%.

Preferably, the cancellous polyurethane foam has 4-10 continuous large-diameter pores per inch and is provided in the form of a sheet having a thickness of 5-50mm.

Preferably, the ion-exchange resin particles are adhered to the 6 substrate with an adhesive agent selected from the group consisting of acrylic adhesive agent, urethane adhesive agent, and vinyl acetate adhesive agent.

Preferably, the ion-exchange resin particles comprise a mixture of cation-exchange resin and anion-exchange resin.

Accorcling to a further aspect of the present invention, there is proposed a method of manufacturing such ion-exchange filter, the method comprising:

an adhesive-agent applying step for causing a sheet-like substrate made of cancellous polyurethane foam having a number of large-diameter continuous pores to be impregnated with an adhesive agent selected from the group consisting of acrylic adhesive agent, urethane adhesive agent, and vinyl acetate adhesive agent so that the adhesive agent may be uniformly adhered to substantially entire surface of the substrate; an adhering step for introducing an excessive amount of ion exchange resin particles into the large-diameter continuous pores of the substrate in such a manner that excessive particles pass the substrate through the thickness thereof without being adhered to the substrate, the ion-exchange resin particles having a particle diameter which is 2 50% of the pore diameter of the large-diameter continuous pores of the substrate, the resin particles being dried in advance to a moisture content below 30%; and an excessive -particles removing step for removing any excessive particles loosely retained within the large-diameter continuous pores without being fixedly adhered to the substrate; and.

said applying step, adhering step and removing step being effected in the mentioned order.

Preferably, the cancellous polyurethane foam has 4-10 continuous large-diameter pores per inch and is provided in the form of 7 a sheet having a thickness of 5-50mm; said adhering step is effected by downwardly spraying the ion exchange resin particles to the substrate relative to the direction of thickness of the substrate; and said removing step is effected by collecting the ion-exchange resin particles dropped through the substrate.

Preferably, the ion-exchange filter thus manufactured is used as an ion-exchange falter comprising: the ion-exchange filter; a cloth member wrapping said filter therein, the cloth member having a mesh smalier than the ion-exchange resin particle; and an air-permeable casing housing therein said cloth member wrapping the filter.

Further and other objects, features and effects of the invention will become more apparent from the following more detailed description of the embodiments of the invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view showing a cancellous polyurethane foam, and Fig. 2 are enlarged view of large-diameter continuous pores, Fig.

2(a) showing the pores before adhesion of ion-exchange resin particles thereto, Fig. 2(b) showing the pores after the adhesion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An ion-exchange filter, according to the present invention, is capable of allowing the cancellous polyurethane foam substrate and that of the ion-exchange resin to provide their respective functions fully, 8 since the ion-exchange resin is adhered to the substrate.

In the above, the ion-exchange resin includes a number of exchange groups on the surface thereof, and as these ion-exchange groups exchange ions With moisture to produce OH groups, COOH groups or the like having polarities, thereby to enhance the interaction between the particles and also to facilitate retention of the moisture by these exchange groups, so that this moisture contributes to increase of the adhesive force between the particles. Consequently, the fluidity may be effectively restricted. However, the amount of exchange and retention of the moisture (this will be referred to as "moisture content" hereinafter) is believed to affect directly the ion-exchange capacity.

Then, as it does not adversely affect the ion-exchange capacity, it has been a conventional practice to handle the resin with maintaining such high moisture content. For this reason, it has been inevitably necessary to employ ion-exchange resin having low fluidity, which makes the handling thereof difficult.

However, the present inventors discovered that by limiting the moisture content of ion-exchange resin below 30% it becomes possible to readily handle the ion-exchange resin particles with high fluidity without sacrificing its ion-exchange performance, whereby an ion exchange filter having high efficiency and ion-exchange capacity may be obtained. And, this discovery led to the perfection of the present invention.

The substrate is made of a cancellous, sponge-like or entangled wire-work like polyurethane foam having a number of large-diameter continuous pores and to this substrate, there are adhered a number of ion-exchange resin particles which have a particle diameter of 2-50% of the pore diameter of the large-diameter continuous pores of the substrate and which were dried in advance to a moisture content below 30%. With these, the ion-exchange resin particles retain good 9 adhesiveness and high fluidity, so that they may be readily fed uniformly over the cancellous polyurethane foam. Moreover, as the particle diameter of the ion-exchange resin particles is set to be 2-50% of the pore diameter of the large-diameter continuous pores of the substrate, the fed particles may readily enter the cancellous polyurethane foam and a sufficient amount of the particles may be adhered in a reliable manner to the polyurethane foam. Further, after the adhesion of the ion-exchange resin particles thereto, the large diameter continuous pores still provide sufficient voids or free space to allow the particles to readily come into effective contact with the contaminated air. For these reasons, there has been provided an ion exchange filter having good air-p erme ability as well as large ion exchange capacity.

Further, as the ion-exchange resin, a phenol type ion-exchange resin, a styrene type ion-exchange resin and so on may be employed.

Also, if the cancellous polyurethane foam is provided in the form of a sheet having 4-10 large-diameter continuous pores per inch and a thickness ranging between 5 mm and 50 mm, the ion-exchange resin particles may be readily fed uniformly over the entire cancellous polyurethane foam substrate, simply by gravity-feeding or spraying the particles to the foam substrate. Further, the excess particles may be readily collected on the opposite side of the substrate away from the particle feeding side. Also, With this arrangement, both the required or desired ion-excliange capacity and air-p erme ability may be readily achieved, so that the resultant filter may be appropriately employed as a filter for use in e.g. an air circulatory system of a clean room.

If the ion-exchange resin particles are adhered to the substrate with acrylic, urethane or vinyl acetate type adhesive agent, reliable adhesion may be assured between the phenol type ion-exchange resin and the polyurethane substrate. Further, as such types of adhesive agents generate little volatile components, they will hardly deteriorate the performance of the ion-exchange resil.

For manufacturing such ion-exchange filter as described above, the present invention provides a method comprising:

an adhesive-agent applying step for causing a sheet-like substrate made of cancelious polyurethane foam having large-diameter continuous pores to be impregnated with an adhesive agent selected from the group consisting of acrylic adhesive agent, urethane adhesive agent, and vinyl acetate adhesive agent so that the adhesive agent may be uniformly adhered to substantially entire surface of the substrate; an adhering step for introducing an excessive amount of ion exchange resin particles 'into the large-diameter continuous pores of the substrate so that excessive partides pass the substrate through the thickness thereof without being adhered to the substrate, the ion exchange resin particles having a particle diameter which is 2-50% of the pore diameter of the large-diameter continuous pores of the substrate, the resin particles being dried in advance to a moisture content below 30%; and an excessive-partides removing step for removing any excessive particles loosely retained within the large-diameter continuous pores without being fixedly adhered to the substrate; and said applying step, adhering step and removing step being effected in the mentioned order.

According to the above-described method, by effecting the simple process of impregnating the adhesive agent to the substrate in the applying step, the adhesive agent may be caused to be adhered to the entire surface of the substrate, and then the adheiing step may be carried out also readily by the simple process of introducing the ion exchange resin to the cancellous polyurethane foam. Moreover, with this method, there will hardly occur such inconvenience of the effective 11 surfaces of the ion-exchange resin particles being coated with the adhesive agent, thereby to impair the ion-exchange performance of the particles, or further inconvenience of an excessive amount of ion exchange resin being adhered to the substrate. The excessive particles may be readily eliminated by simply allowing them to the substrate along the thickness thereof, and these excess particles may be collected for reuse appropriately.

Advantageously, the cancellous polyurethane foam has 4-10 continuous large-diameter pores per inch and is provided in the form of a sheet having a thickness of 5-50mm. With this, when the ion exchange resin particles are fed to the cancellous polyurethane foam, it becomes easy to select such particles of a size which can be readily handled and which can also enter the large-diameter continuous pores smoothly with low resistance. Further advantageously, said adhering step is effected by downwardly spraying the ion-exchange resin particles to the substrate along the thickness thereof. With this, it becomes possible to effect the excess-particle removing step by collecting the particles dropped through the substrate. Accordingly, this provides a further advantage of simplifying the construction employed for manufacturing the ion-exchange filter.

Next, a preferred embodiment of the present invention will be described in details with reference to the accompanying drawings.

As shown in Fig. 1, the cancellous or entangled wire-work like polyurethane foam substrate 2 includes a number of large-diameter continuous pores 1, with 'walls' partitioning the adjacent pores being eliminated, with only a 'skeleton' (i.e. wire-work like structure) of the substrate 2 remaining. This cancellous polyurethane foam may be manufactured, for instance, by a method described next.

First, a polyurethane foam weighing 20-60 g per liter and having a number of pores 1 of 1.5-3 mm diameter is prepared. Then, 12 an explosive mixture gas is introduced into the respective pores and then ignited to explode therein. With this explosion, the walls partitioning the pores from each other are eliminated, so that there is obtained a polyurethane foam having a cancellous or entangled wire work like structure consisting substantially solely of the skeleton-like substrate 2 having 4-8 large-diameter continuous pores per inch (see Fig. 2 (a)).

Then, after the large-diameter continuous pores I are impregnated with a non-solvent type adhesive agent (to be referred to as "binder" hereinafter) so that the binder is supplied to substantially entire surfaces of the skeleton substrate 2, the excess binder is removed (adhesive-agent applying step). This removing of excess binder may be done by compressing the cancellous polyurethane foam to 'squeeze out' the binder therefrom. Thereafter, due to the resilience of the cancellous polyurethane foam, the pores or voids will be restored therein to realize a condition allowing introduction of ion-exchange resin particles 3 therein.

Then, to this cancellous polyurethane foam applied with the binder, fine particles of ion-exchange resin are fed- In this, by simply gravity-feeding the particles onto the sheet-like cancellous polyurethane foam being supported and transported horizontally, the ion-exchange resin fine particles may be fed uniformly over the cancellous polyurethane foam to be adhered thereto (adhering step).

Further, the excess ion-exchange resin particles will be dropped below the foam, so that they may be readily collected for reuse appropriately.

As the ion-exchange resin particles 3, both cation exchange resin and anion exchange resin may be employed. And, their amounts to be adhered and the mixture ratio therebetween may be determined appropriately, depending on the particular application intended. Also, the resin may be of various types such as phenol type, styrene type, 13 methacrylic type, or acrylic type. Among these, phenol type is particularly preferred. Further, these ion-exchange resin particles 3 may be of one kind or combination of plural kinds. In this respect, many of anion exchange resins generate amine-like odor, which may be effectively restricted by co-use of cation exchange resin. Such co use of cation and anion exchange resins provides a further advantage of allowing simultaneous filtering of cation and anion.

As the ion-exchange resin described above, generally those having a moisture content of about 50% are commercially available.

However, such ion-exchange resins are low in fluidity, so that they will tend to solidify or at least provide resistance when they are introduced to the cancellous polyurethane foam. However, by drying the resin to a moisture content below 25%, the fluidity of the resin particles may be enhanced to allow smooth feeding thereof, without deteriorating its physical properties or entailing any disadvantageous change in the property thereof such as carbonization.

Even with the above, there still remains the tendency of excess, non-adhered ion-exchange resin particles being loosely 'hooked' or entrapped within the pores of the cancellous polyurethane foam.

Then, by shaking the cancellous polyurethane foam by repeatedly compressing and allowing it to resiliently restore its original shape, such excess particles 3 entrapped therein will be removed therefrom, so as to assure air-permeability of the foam as a filter. As a result, there is obtained an ion-exchange filter comprising the substrate 2 with a number of ion-exchange particles being adhered thereto (see Fig. 2(b)).

Preferably, the ion-exchange filter thus manufactured is used as being wrapped in a cloth member having a mesh smaller than the ion-exchange resin particle and being housed within an air-permeable casing. This is for the following reason. Namely, because of the manufacturing precision, the filter may be put into use, with loosely 14 held or incompletely adhered particles remaining thereon. Then, such excess particles may fall out during use of the filter. In such case, the cloth member may catch the fallen-out particles, to prevent adverse influence resulting from the fallen-out particles. To more effectively prevent such Mifluence, it is preferred that the ion-exchange filter be used as being housed within a case. Further, this arrangement of housing the Ion-exchange filter within an air-permeable casing is advantageous also for preventing such fall-out of the particles and for preventing an accident due to an erroneous handing by the user to inadvertently deform the filter thus causing or promoting fall-out of the particles.

Next, some specific examples will be discussed.

Examples 1. 2

A substrate 2 comprised a cancellous polyurethane foam having, on the average, 4-10, preferably, 6-8 large-diameter continuous pores per inch. The substrate 2 had a thickness of 10 mm in Example 1 and mm in Example 2. To this substrate 2, a predetermined amount of binder was uniformly applied and impregnated in advance. Then, after dxying, but while the applied binder still had some tackiness, cation type ion-exchange resin was over-supplied to the surface of the cells of the substrate and excess (non-adhered) resin was removed.

Soecifically, due to certain requirement of the manufacturing process, the ion-exchange resin comprised sodium in the case of cation-exchange resin and chloride in the case of anion-exchange resin. The resin was regenerated with an excessive amount of strong acid or strong alkali solution of about 5% and then ion-exchanged with water to be rendered into sulfonic groups or hydroxyl groups and then washed in water.

Thereafter, the resin was dried to a moisture content of about 25%. On the other hand, the continuous pore polymer sheet was impregnated with an adhesive agent of e.g. acrylic type and after draining the liquid content therefrom, the above-described dried ion-exchange resin was sprayed to be point-adhered to the polymer substrate described above.

Incidentally, the amount of the ion-exchange resin to be used should be 1.0-1.5 kg per 10 liters of polymer sheet.

Examples 3. 4 Example 3 comprised a substrate (polyurethane foam) having, on the

average, 4-10, preferably, 6-8 cells per inch and having a thickness of 10 mm. Example 4 comprised the same type of substrate as Example 3, different only in the thickness which is 20 mm, like Examples 1 and 2. To each substrate, a predetermined amount of binder was uniformly applied and impregnated in advance. Then, after drying but while the applied binder still had some tackiness, a mixture of anion type ion-exchange resin 10 and the cation type ionexchange resin 1 was over-supplied to the surface of the cells of the substrate and excess (non-adhered) resin was removed. 20 In all of the examples above, same raw materials identified below were employed.

16 Table I polyurethane foam Everlight SF (manufactured by Bridgestone Co., Ltd.) binder CH 18 (manufactured by Konishi Co., Ltd.

binder EM772X (manufactured by Cemedine Co., Ltd.) cation type ion-exchange resin C-20 (manufactured by Sumitomo Chemical Co., Ltd.) (strongly acidic) anion type ion-exchange resin A- 116 (manufactured by Sumitomo Chemical Co., Ltd.) (strongly basic) The amounts of the above materials employed are shown in Table 2 below.

Table 2 substrate 0.6kg/m' (20mm) adhesive agent 0.2kg/m'(20mm) ion-exchange resin amount 30g/M2 (20mm) (note: the amount used in the 10 mm, type is 1/2 of that of the 20 mm type) total ion-exchange capacity 3.6 eq/kg NH3 air-passage removal ratio: 99.0% (20 mm) The total ion-exchange capacity of the ion-exchange resin denotes 2.0 eq/1 for the strongly acidic cation-exchange resin and 1.4 eq/1 for the strongly basic anion-exchange resin. As this is to be used in a gas treatment at a moisture content corresponding to the relative humidity, the value may be simply converted into a ratio relative to the unit dry weight as 3.6 eq/kg for the strongly acidic cation-exchange 17 resin and 2.3 eq/kg for the strongly basic anion-exchange resin.

As a result, when a filter was made with charging about 150g/l of ionexchange resin therein per unit volume of the filter, its pressure loss was measured as 0.1 to 0.15 mm/Aq/10 mm (filter thickness) at 0.5 m/sec.

Further, the ion-exchange filters made in the respective examples above provided the following performance.

Table 3 thickness amount of removal ion-exchange mm attached ion- ratio cap acity exchange eq/kg resin g/100cm, Example 1 C 10 15.1 83.6 3.63 Example 2 C 20 29.8 99.2 3.73 Example 3 A 10 14-9 88.3 2.35 Example 4 A 20 30.0 99.6 2.41 (note: C = cation-exchange resin; A = anion-exchange resin) The total ion-exchange capacities of these ion-exchange filters were measured as 9.8 kg/m' in terms of conversion for ammonium ion (NH4')in Examples 1, 2 and 17kg/m' in terms of conversion for sulphate ion (SO,') in Examples 3, 4. Hence, it may be understood that ion exchange filters having large ion-exchange capacities and small pressure loss have been achieved.

Incidentally, for the sake of comparison, as filters of identical dimensional specifications, a filter comprising a cancellous polyurethane foam and agent-impregnated activated carbon adhered thereto (described hereinbefore as the prior art), a filter using ion exchange resin and the ion-exchange filter according to the present invention were compared in the performances thereof, providing the results indicated in Tables 4 and 5 below. Table 4 shows the 18 performances for removal of ammonium as an example of target alkaline ion, while Table 5 shows the performances for removal of chlorine as an example of target acidic ion, respectively.

When the filters manufactured by the respective methods are charged into a filter frame of identical dimensions to be provided as filter products, as may be apparent from Tables 4 and 5, it may be understood that the total ion-exchange capacity of the product according to the present invention is 2.6 times or more for the removal of ammonium and 3.0 times for the removal of chlorine, so that this product may provide a longer service life.

19 Table 4 filter according conventional filter to the present I. Lnvention ion-exchange absorbing agent ion-exchange resin (dried) (agentfiber nonwoven charging method impregnated fabric (pleat activatedfilter) carbon) charging method dimensions 61Ox61Ox5O 61Ox61Ox5O 61Ox61Ox5O amount of 450g/lOmm x 4 600g/10mm x 5 fiber weight charged sheets sheets 300g/m' material multilayer multilayer purity 80% ammoniumtotal exchange amount of charged area: 4 converted amount: impregnated In 2 removal amount 3.6eq/kg x activated 300 g/M2 X 0.8 x 0.45kg x 4 carbon: 4m'=960g sheets = 0.6kg x 4 =2.4 kg total exchange.

6.48 eq impregnated capacity:

.6.48 eq agent: H,P04 2.2eq/kg xO.96kg x 17g/eq impregnated x 17g/eq =35.9g 110.2 amount: 10% for the weight of activated carbon 2400gxO.10 x (17/98) = ALfig_ practical 60% for total practical 60% for total exchange exchange adsorption exchange capacity capacity amount: 60% cap acity (converted for 110.2g x 0.6 41.6gxO.6.25g 35.9gxO.6-1-25g ammonium) 66g pressure loss <1.OmmAq <4.5mmAq <3.OmmAq (0.5cm./sec) I Table 5 filter according conventional filter to the present invention ion-exchange absorbing agent ion-exchange resin (dried) (agent- fiber nonwoven charging method impregnated fabric (pleat activated- filter) carbon) charging method dimensions 610x61Ox5O 61Ox61Ox5O 61Ox61Ox5O amount of 450g/10mm x 4 600g/10mm x 4 fiber weight charged sheets sheets 300g/m' material multilayer multilayer purity 80% chlorine- total exchange amount of charged area: 4 converted amount: impregnated in 2 removal amount 2.3eq/kg x activated 300 g/M2 X 0.8 x 0.45kg x 4 carbon: 4m'=960g sheets = 0.6kg x 4 =2.4 kg total exchange.

4.14 eq impregnated capacity:

4.14 eq x agent: K2CO3 3.6eq/kg xO.96kg 35.5g/eq impregnated x 35.5g/eq =124g 147,Og amount: 4% for the weight of activated carbon . 2400g x 0.44 x (35.5 x 2 --1- 138) = A"4 practical 147.Og x 0.6 practical exchange 88.2g adsorption 124g x 0.6 capacity amount: 60% 7 3.6 g (converted for 49.4g x 0.6 chlorine) 1. 2 9.6 g pressureloss, <1.OmmAq <4.5mmAq <3.5mmAq (0.5cm/sec) 21 Some other embodiments will be described next.

In the foregoing embodiment, as the ion-exchange resmi, either a cation-exchange resin or an anion-exchange resin was employed.

Instead, both may be used at a time in the form of a mixture thereof.

Further, if a cation-exchange resin is employed together with an anion exchange resin, it is also possible to reduce the odor characteristic of the anion-exchange resin.

Further, in addition to the ion-exchange resin, any other type of gas absorbing agent or the like may be employed simultaneously. In this case, if some miscellaneous gas is generated from the cancelious polyurethane foam or the binder, such miscellaneous gas too may be removed.

The invention may be embodied in any other specific forms without departing from the spirit or essential characteristics thereof.

The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

22

Claims

An ion-exchange filter comprising a substrate made of cancellous polyurethane foam having a number of large-diameter continuous pores, and a number of ion-exchange resin particles distributed over and adhered to the substrate, each said particle having a particle diameter which is 2-50% of the diameter of the pore of the substrate.
2. The filter according to claim 1, wherein the ion-exchange resin particles are dried to a moisture content below 30%.
3. The filter according to claim 1 or 2, wherein the cancellous polyurethane foam has 4-10 continuous large-diameter pores per inch and is provided in the form of a sheet having a thickness of 5-50mm.
4. The filter according to any one of claims 1 through 3, wherein the ion-exchange resin particles are adhered to the substrate with an adhesive agent selected from the group consisting of acrylic adhesive agent, urethane adhesive agent, and vinyl acetate adhesive agent.
5. The filter according to any one of claims 1 through 4, wherein the ion-exchange resin particles comprise a mixture of cation-exchange resin and anion-exchange resin.
6. A method of manufacturing such ion-exchange filter, the method comprising:

an adhesive-agent applying step for causing a sheet-like substrate made of cancellous polyurethane foam having a number of large-diameter continuous pores to be impregnated with an adhesive 23 agent selected from the group consisting of acrylic adhesive agent, urethane adhesive agent, and vinyl acetate adhesive agent so that the adhesive agent may be uniformly adhered to substantially entire surface of the substrate; an adhering step for introducing an excessive amount of ion exchange resin particles into the large-diameter continuous pores of the substrate in such a manner that excessive particles pass the substrate through the thickness thereof without being adhered to the substrate, the ion-exchange resin particles having a particle diameter which is 2 50% of the pore diameter of the large-diameter continuous pores of the substrate, the resin particles being dried in advance to a moisture content below 30%; and an excessive -particles removing step for removing any excessive particles loosely retained within the large-diameter continuous pores without being fixedly adhered to the substrate; and said applying step, adhering step and removing step being effected in the mentioned order.
7. The method according to claim 6, wherein the cancellous polyurethane foam has 4-10 continuous large-diameter pores per inch and is provided in the form of a sheet having a thickness of 5-50mm; said adhering step is effected by downwardly spraying the ion exchange resin particles to the substrate relative to the direction of thickness of the substrate; and said removing step is effected by collecting the ion-exchange resin particles dropped through the substrate.
8. A filter apparatus comprising:

the ion-exchange filter according to any one of claims 1 through 5; 24 a cloth member wrapping said filter therein, the cloth member having a mesh smaller than the ion-exchange resin particle; and an air-permeable casing housing therein said cloth member wrapping the filter.
9. An ion-exchange filter substantially as hereinbefore described with reference to the accompanying drawings and/or examples herein.
10. An ion-exchange filter wherein produced by at least method claim 6.