GB2382315A

GB2382315A - Filtration materials and methods for the production and use thereof

Info

Publication number: GB2382315A
Application number: GB0127862A
Authority: GB
Inventors: Richard Mellor
Original assignee: Purification Products Ltd
Current assignee: Purification Products Ltd
Priority date: 2001-11-21
Filing date: 2001-11-21
Publication date: 2003-05-28
Also published as: AU2002339186A1; GB0127862D0; WO2003045532A1

Abstract

The present invention relates to filtration materials, in particular filtration materials comprising a substrate 10 impregnated with an activated particulate substance. The invention also relates to the use of such materials and to a process for their production. The process comprises the steps of providing a substrate 10, providing a reservoir (16,figure 5) charge with a an emulsion or solution of an activated particulate material wherein the reservoir (16) has an openable discharge port (17, figure 5) actuating the openable discharge port (17) to discharge a desired quantity of the emulsion or solution onto the substrate 10, allowing the emulsion or solution to impregnate the substrate 10 and drying the impregnated substrate to remove a volatile component of the emulsion.

Description

DESCRIPTION FILTRATION MATERIALS AND METHODS FOR THE PRODUCTION AND USE THEREOF The present invention relates to filtration materials, in particular filtration materials comprising a substrate impregnated with an activated particulate substance, to the use of such materials and to a process for their production.

There are a large number of known filtration materials and processes for their production. For example, GB-B-2238802 describes a method of producing particulate-solid-bearing air-permeable sheet material capable of achieving high concentrations of particulate solid and/or air-permeability from a low density (i. e.

0. 25gm/cm3 or less) preformed non-woven fabric or open cell foam. The particulate solids described in this document may be absorbents of gases and, in one example, are activated carbon particles incorporated in fibrous sheets and in cellular foam sheets. The method of manufacture of such sheets comprises disposing one face of a preformed air-permeable sheet material in the path of a stream of a gaseous carrier and entrained particulate solid, whilst maintaining a pressure drop across the thickness of the preformed air-permeable sheet.

GB-B-2238802 itself describes a number of prior art methods for incorporating particulate solids in permeable sheet material. Such prior art methods include laminating the particulate solid with two sheets of woven cloth by applying to one of them a free flowing powder before the lamination of the two sheets is effected. However, this method is said to have the disadvantage that the powdered

material is not firmly bound but can shake out of the laminate. Another method described is to impregnate a fibrous web with a suspension of particulate material in a solvent carrier which also incorporates a binder. However, this method suffers from the disadvantage that the particulate material loses some of its activity by prolonged contact with organic liquids in the suspension and may also become coated with the binder itself, thus preventing those particles which are so coated from being activated.

USSN 09/864,348 discloses a process for producing a woven material with an incorporated particulate solid or solids. This process also comprises disposing a first face of the woven material in the path of a stream of gaseous carrier and entrained particulate solid whilst maintaining a pressure drop across the woven material. This document also discusses certain prior art in the fields of manufacturing woven and non-woven materials impregnated with particulate solids. Liquid dispersion or suspension methods are said to result in encapsulation and consequent deactivation of the particulate solid.

The methods and materials described in GB-B-2238802 and in USSN 09/864, 348 are suited to some extent to the large scale production of web materials for use, for example, in protective clothing, air and fridge filters, respiratory masks, medical dressings and the like. However, neither of these documents describes materials or methods well suited to the production of smaller, lightweight filtration materials such as are used, for example, in electronic hardware and in components and accessories such as computer hard disc drives. Nor are they well suited for

applications in which it is desirable to include in the filtration method further functional ingredients such as, for example, antimony pentoxide in a hard disk drive filter, silver nitrate in a shoe insole or potassium iodate in a respiratory face mask.

Furthermore, the processes described in the prior art as outlined above are somewhat inflexible in their application as to the type of material impregnation which can be achieved and the processes therein suffer from concomitant environmental concerns.

Coating compositions comprising modified carbon products are described in WO-A-99/07794. However, this document does not relate to filtration materials.

It is an object of the present invention to provide a filtration material, and a process for the production and use thereof, which overcomes or alleviates at least some of the aforesaid disadvantages. In particular, it is an object of the present invention to provide such filtration materials which would be suitable for use in connection with electronic devices and their components and accessories, and which can suitably be provided with additional functional ingredients when desired.

Accordingly, the present invention provides a process for manufacturing a filtration material comprising the steps of : a) providing a substrate ; b) providing a reservoir charged with an emulsion or solution of an activated particulate material, the reservoir having an openable discharge port; c) actuating the openable discharge port to discharge a desired quantity of the emulsion or solution onto the substrate; d) allowing the emulsion or solution to impregnate the substrate; and

e) drying the impregnated substrate to remove a volatile component of the emulsion or solution.

Suitable substrate materials include polyesters, glass fibre, polypropylene, viscose, cellulose, cotton and Lycra'. Preferably, the thickness of the substrate is no more than about 2mm, preferably less than about 1.5 mm, more preferably less than about lmm and still more preferably less than about 0.5 mm. One particularly preferred filtration material according to the invention for use in electronic hardware components comprises a substrate of mass to surface area ratio of approximately 16g/m2 and a thickness of less than about 0. lmm. One suitable substrate material in this case would be viscose.

The activated particulate material is preferably selected from materials having an extended or enhanced pore structure. Suitable materials generally have an internal

surface area of greater than about 20m2/g, preferably greater than about 500m2/g, more preferably greater than about 1000m2/g. Suitable materials include activated carbon, zeolites, silica gels, activated alumina and aluminosilicate materials such as clays. The preferred maximum particle size is no more than about 50, um, preferably no more than about 25, um, still more preferably no more than about 8, um. The preferred mean particle size is from about 0. 5, um to about 20, um, preferably from about 0. 7 j. tm to about 10, um and more preferably from about l, um to about 3, um.

Preferably, the concentration of activated particulate material in the emulsion is less than about 10% w/w, preferably from about 2% w/w to about 5% w/w. Where the activated particulate material is activated carbon it is preferably untreated with any

organic reagent, and more preferably has no intentionally attached aromatic or Cl-cl alkyl groups.

The volatile component of the emulsion or solution is preferably selected from liquids which do not substantially deactivate the particulate material in the emulsion or solution. Suitable liquids include water, alcohols such as methanol, ethanol, propanol, butanol in all its isomeric forms, pentanol and all its isomeric forms, hexanol and all its isomeric forms and glycols such as ethylene glycol, propylene glycol, and short chain aldehydes and ketones, for example methy ethyl ketone.

The openable discharge port of the reservoir is preferably adapted to discharge the desired quantity of the emulsion or solution onto the substrate as a jet

or as a spray. The discharge port is preferably less than about 50mm2, more preferably less than about 30mm2, still more preferably less than about 20mm2. Also the reservoir may be provided with a plurality of such discharge ports which may be activated simultaneously or individually, as desired, in operation of the process of the invention. Suitable types of reservoir include those found in known inkjet printers and drop on demand units, such as the Jet-A-MarkTM DOD-2002A available from Matthews Swedot AB, Gamlestadsvägen 8, S-415 02 Göteburg, Sweden. In one preferred process according to the invention, the openable discharge port comprises at least one aperture in the reservoir which, in a closed position of the discharge port, is sealed by a plunger mounted inside the reservoir. When the discharge port is actuated, the plunger is raised allowing the emulsion or solution within the reservoir

to communicate with the aperture. The plunger is then lowered, sealing the aperture and supplying a jet or spray of emulsion or solution onto the substrate. This process can be repeated as many times as is necessary sufficiently to impregnate the substrate with the emulsion or solution. If the surface area of substrate to be treated is greater than the area covered by the jet or spray then the process can be repeated after moving one or both of the substrate and the reservoir. In a suitable adaptation of existing inkjet and drop on demand technology to the process of the invention, in a preferred process according to the invention, the reservoir is moved across a desired width of the substrate, while the substrate is held in position. When the desired width of the substrate has been treated then the substrate is moved lengthways and the reservoir is then moved back across the width of the substrate to treat the newly presented area of the substrate.

When the substrate has been treated, the volatile component of the emulsion or solution is suitably removed therefrom by an air drying process. In one preferred process according to the invention, warm air is blown onto the impregnated substrate to remove the volatile component.

In a preferred process according to the invention the volatile component is at least partially recovered from the drying step and is preferably recycled for further use in making up the emulsion or solution.

It may be necessary or desirable to bind the particulate material in the

substrate. Suitable binders include natural rubber latex, neopren, styrene butadiene, acrylic/acrylonitrile copolymer, modified n-butyl acrylonitrile copolymer,

acrylonitrile polyvinyl acetate, polyacrylate, acrylonitrile butadiene, acrylic methyl methacrylate, self cross linking copolymers of vinyl acetate and ethylene, polyvinyl alcohol, polyvinyl acetate, vinyl chloride copolymers, melamine-formaldehyde resin, solutions of starch, carboxymethyl cellulose, methyl cellulose, sodium silicate, siloxanes, including functionalised siloxanes, and PTFE-based binders or combinations of the above (provided that each component of the combination should be compatible with each other component).

In the case of incorporation of a binder, the process of the invention preferably comprises providing a second reservoir charged with the binder, the second reservoir having an openable discharge port. Actuation of the second reservoir openable discharge port can be conducted before, during and/or after a discharge of the emulsion onto the substrate. The construction and operation of the second reservoir may suitably be the same as or similar to those of the reservoir charged with the emulsion or solution of activated particulate material.

If a binder is incorporated then it is preferred that the treated substrate be cured, for example by infra-red curing. In a preferred process according to the invention, the impregnated substrate is passed through an infra-red heater to cure the binder on the substrate.

It may additionally be desirable to provide further materials, particularly functional materials, for impregnation in the substrate. For example, fire retardant materials (such as, for example, antimony pentoxide), potassium carbonate (for use in neutralising acidic vapours contacting the filtration material), indicator compounds

such as reactive dyes (to call attention to the presence of, for example, hazardous or otherwise undesirable compounds in the vicinity of the filtration material), silver nitrate (for use as a bacteriostat in shoe insoles) or other useful chemicals such as potassium iodate (for use in face masks to combat mercury vapour) may be used.

Such additional materials may be mixed with the emulsion in the reservoir (if they do not have an unacceptable deleterious effect on the activated particulate material) or they can be provided in a second reservoir (with a binder, if present) or in a third reservoir. If desired, a plurality of reservoirs, each charged with the same or different materials, may be employed in the process of the invention. It may also be desirable to employ a plurality of co-functional reservoirs in the process of the invention. Thus, for example, the process of the invention may be operated with a plurality of reservoirs, each charged with the emulsion or solution of the activated particulate material and each arranged to discharge the emulsion or solution onto a separate or overlapping area of the substrate in operation of the process.

The process of the invention may be a continuous process or a batch process.

In another process according to the invention functional materials may be applied to a substrate which is pre-impregnated with an activated particulate material. Thus, the invention further provides a process for manufacturing a filtration material comprising the steps of : a) providing a substrate pre-impregnated with an activated particulate material; b) providing a reservoir charged with an emulsion or solution of one or

more functional materials, the reservoir having an openable discharge port ; c) actuating the openable discharge port to discharge a desired quantity of the emulsion or solution onto the substrate; d) allowing the emulsion or solution to impregnate the substrate; and e) drying the impregnated substrate to remove a volatile component of the emulsion or solution.

The preferred characteristics of the process are as described in connection with the first process acccording to the invention. However, the pre-impregnated substrate may be manufactured according to the first process according to the invention or it may be manuractured by alternative means, for example those described in GB-B-2238802 or USSN 09/864,348. Preferred funtional materials include bacteriocides, bacteriostats (silver compounds being preferred, particularly silver nitrate), fire retardants (such as antimony pentoxide), neutralisers (such as potassium carbonate), mercury vapour combatants (such as potassium iodate) and indicator compounds.

According to the present invention, there is also provided a filtration material obtained by means of the process of the invention.

Further provided in accordance with the invention is a filtration material comprising a substrate impregnated with an activated particulate material having a mean particle size of from about 0. 5 um to about 201lm.

Preferably, the mean particle size of the activated particulate material in the filtration material of the invention is from about 0.7 um to about lOum. Still more

preferably, the mean particle size of the activated particulate material in the filtration material of the invention is from about 1 Ilm to about 3 Ilm.

Also provided in accordance with the invention is a filtration material comprising a substrate impregnated with an activated particulate material and a functional material, the functional material being applied to the substrate pre- impregnated with the activated particulate material by means of a jet or spray of an emulsion or solution of the functional material.

The invention further provides the use of a filtration material according to the invention in an item of electronic hardware, such as a computer hard disk drive.

Further uses of the filtration materials of the invention can be found in shoe insoles and in respiratory face masks, for example.

The invention will now be more particularly described with reference to the following drawings, in which: Figure 1 shows a plan view of an apparatus constructed and arranged to perform the process of the invention; Figure 2 shows view from one end of the apparatus depicted in Figure I ; Figure 3 shows a rear view of the apparatus depicted in Figures 1 and 2; Figure 4 shows a detailed perspective view of the carriage assembly depicted in Figures, 1 2 and 3; and Figure 5 shows a schematic underneath view of a reservoir for use in accordance with the process of the invention.

Referring to Figures 1,2 and 3 there is shown an apparatus 1 comprising a

carriage assembly 2 mounted by means of runners 3a, 3b, 3c, 3d on tracks 4,5 running between opposite transverse ends of apparatus 1 and mounted at each respective end on plinths 6,7. Carriage assembly 2 is moveable in either transverse direction on tracks 5,6 by means of stepper motor 8 and timing belt 9.

A substrate sheet 10 is mounted underneath carriage assembly 2 on supports 11,12 and is passed at one end in between roller pair 13. Roller pair 13 can be activated by stepper motor 14 and timing belt 15 to convey substrate 10 longitudinally underneath carriage assembly 2.

Referring now to Figure 4, carriage assembly 2, its runners 3a, 3b, 3c, 3d and its associated timing belt 9 are shown in more detail. Carriage assembly 2 is provided with a reservoir 16 which is charged with an emulsion comprising, for example, activated carbon and water. Reservoir 16 is of known construction and is commonly used in inkjet printers and drop on demand.

In this embodiment reservoir 16 has seven openable discharge ports 17 arranged linearly as is shown in Figure 5. Each discharge port 17 in this example comprises an aperture closed by means of solenoid plunger 16 mounted inside reservoir 16.

In the process of the invention, substrate 10 is mounted on its supports 11, 12 with one end passing in between roller pair 13. Upon a signal from a central processing station (not shown) carriage assembly 2 is moved by means of stepper motor 8 and timing belt 9 in a transverse direction from one side of apparatus I to the other. Simultaneously, the openable discharge ports are activated and a jet of the

emulsion is directed onto a transverse strip of substrate 2. As carriage assembly 2 completes one transverse sweep of the substrate, roller pair 13 is activated by means of stepper motor 14 and timing belt 15 to convey a predetermined length of substrate 2 longitudinally through apparatus 1. Carriage assembly 2 is then operated to perform a reverse transverse sweep of substrate 2 spraying a jet of emulsion on to a newly presented transverse strip of substrate. The process can then be repeated until a desired length of substrate is produced (in a batch wise process) or may be repeated continuously, with the treated substrate being wound on to a reel (not shown) or cut in to predetermined lengths.

Claims

1. A process for manufacturing a filtration material comprising the steps of : a) providing a substrate; b) providing a reservoir charged with an emulsion or solution of an activated particulate material, the reservoir having an openable discharge port; c) actuating the openable discharge port to discharge a desired quantity of the emulsion or solution onto the substrate; d) allowing the emulsion or solution to impregnate the substrate; and e) drying the impregnated substrate to remove a volatile component of the emulsion or solution.

2. A process according to claim 1, wherein the substrate material is selected from polyesters, glass fibre, polypropylene, viscous, cellulose, cotton and lycra 1M.

3. A process according to claim 1 or claim 2 wherein the thickness of the substrate is no more than about 2mm.

4. A process according to claim 3 wherein the thickness of the substrate is no more than about 1. 5mm.

5. A process according to any one of claims 1 to 4 wherein the activated particulate material has an extended or enhanced pore structure.

6. A process according to any one of claims 1 to 5 wherein the activated particulate material has an internal surface area of greater than about 20m2/g.

7. A process according to any one of claims 1 to 6 wherein the activated particulate material is selected from activated carbon, zeolites, silica jels, activated

alumina and alumina silicate materials.

8. A process according to any one of claims 1 to 7 wherein the maximum particle size of the activated particulate material is no more than about 50 u. m.

9. A process according to claims I to 8 wherein the mean particle size of the activate particulate material is from 0. 5 um to about 20 um.

10. A process according to any one of claims I to 9 wherein the concentration of activated particulate material in the emulsion or solution is less than about 10% w/w.

11. A process according to any one of claims I to 10 wherein a plurality of reservoirs are employed.

12. A process according to claim 11 wherein at least one reservoir is charged with a functional material other than the activated particulate material.

13. A process according to claim 12 wherein the functional material is selected from bacteriocides, bacteriostats, fire retardant compounds, indicator compounds, neutralising compounds and mercury vapour competent compounds.

14. A process for manufacturing a filtration material comprising the steps of : a) providing a substrate pre-impregnated with an activated particulate material; b) providing a reservoir charged with an emulsion or solution of one or more functional materials, the reservoir having an openable discharge port ; c) actuating the openable discharge port to discharge a desired quantity of the emulsion or solution onto the substrate; d) allowing the emulsion or solution to impregnate the substrate; and

15. A filtration material obtained by a process according to any one of claims 1 to 14.

16. A filtration material comprising a substrate impregnated with an activated particulate material having a mean particle size of from about 0.5 u. m to about 20 f. 1m.

17. A filtration material according to claim 16 wherein the mean particle size of the activated particulate material is from about 0.7 um to about 10 urn.

18. A filtration material according to claim 17 wherein the mean particle size of the activated particulate material is from about I um to about 3 um.

19. A filtration material comprising a substrate impregnated with an activated particulate material and a functional material, the functional material being applied to the substrate pre-impregnated with the activated particulate material by means of a jet or spray of an emulsion or solution of the functional material.

20. An item of electronic hardware incorporating a filtration material according to any one of claims 15 to 19.

21. A computer hard disk drive according to claim 20.

22. A shoe insole incorporating a filtration material according to any one of claims 15 to 21.

23. A respiratory face mask incorporating a filtration material according to any one of claims 15 to 21.

24. A process for manufacturing a filtration material, and filtration materials

derived therefrom, substantially as described herein and with reference to the accompanying drawings.

G \CLIENTt405-409\PS7\406295\GB\MASTER