WO2003045532A1

WO2003045532A1 - Functionalised filtration materials and methods for the production and use thereof

Info

Publication number: WO2003045532A1
Application number: PCT/GB2002/005198
Authority: WO
Inventors: Richard Mellor
Original assignee: Purification Products Limited
Priority date: 2001-11-21
Filing date: 2002-11-19
Publication date: 2003-06-05
Also published as: AU2002339186A1; GB2382315A; GB0127862D0

Abstract

The present invention relates to filtration materials, in particular filtration materials comprising a substrate impregnated with an activated particulate substance and/or another functional material. 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, providing a reservoir charged with a an emulsion or solution of an activated particulate material, and/or, another functional material, wherein the reservoir has an openable discharge port, actuating the openable discharge port to discharge a desired quantity of the emulsion or solution onto the substrate, allowing the emulsion or solution to impregnate the substrate and drying the impregnated substrate to remove a volatile component of the emulsion.

Description

DESCRIPTION

FUNCTIONALISED FILTRATION MATERIALS AND METHODS

FOR THE PRODUCTION AND USE THEREOF

The present invention relates to functionalised filtration materials, in particular filtration materials comprising a substrate impregnated with an activated particulate substance and/or one or more further functional materials, 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 then- 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.

US Patent No. 4,659,584 describes a process and apparatus for charging eye-

rods with solutions or suspensions of an active substance by dropwise addition with tthe aid of a micrometering device.

US Patent No. 4,772,455 relates to a fitration material comprising a mesh

having activated carbon fibres dispersed therein. The carbon fibres may be treated with additional materials prior to incorporation in the mesh structure.

WO-A-97/16393 discloses mullite composites formed by impregnating mullite fibre preforms with a mullite precursor sol and then drying off any solvents

in the sol.

GB-B-380739 relates to paper materials coated with an oil-based varnish.

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

functionalised filtration material comprising the steps of: a) providing a filtration substrate in the form of a web or sheet;

b) providing a reservoir charged with an emulsion or solution of at least

one substantially non- volatile functional material selected from activated particulate

materials, bacteriocides, bacteriostats, fire retardant compounds, indicator

compounds, neutralising compounds and mercury vapour combatant compounds, the reservoir having an openable discharge port and means for pressurizing the emulsion or solution through the port on actuation thereof;

c) positioning the filtration substrate adjacent the discharge port of the reservoir to receive thereon ajet or spray of the emulsion or solution upon actuation

of the discharge port; d) actuating the openable discharge port to discharge, by means of a jet or spray, a desired quantity of the emulsion or solution onto the filtration substrate; e) allowing the emulsion or solution to impregnate the filtration

substrate; and f) drying the impregnated filtration substrate to remove a volatile component of the emulsion or solution and yield a filtration material having the at least one functional material impregnated therein.

Suitable substrate materials include polyesters, glass fibre, polypropylene, viscose, cellulose, cotton and Lycra ^m . Preferably, the thickness of the substrate is

no more than about 4mm, preferably less than about 3 mm, more preferably less than about 2mm and still more preferably less than about 1mm. 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 0.5mm, for example less than about

0. lmm. One suitable substrate material in this case would be viscose.

The emulsion or solution is preferably allowed to impregnate at least about 25%, more preferably at least about 40%, still more preferably at least about 50%, for

example at least about 75%, or substantially the whole, of the thickness of the

substrate.

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 aluminosilicale materials such as

clays. The preferred maximum particle size is no more than about 50μm, preferably no more than about 25μm, still more preferably no more than about 8μm. The preferred mean particle size is from about 0.5μm to about 20μm, preferably from about 0.7μm to about lOμm and more preferably from about lμm to about 3μm.

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 C,-C₁₂

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-Mark™ DOD-2002A available from Matthews Swedot AB, Gamlestadsvagen 8, S-415 02 Goteburg, 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 ajet 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.

Alternatively, the reservoir could be maintained under pressure such that

contolled actuation of the discharge port releases ajet or spray of the emulsion or solution onto the filtration 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, neoprene, 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 functional 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.

Further functional materials, in addition to activated particulate materials,

include 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 functional materials may be mixed with the one or more

other functional materials, such as activated particulate materials, in the emulsion in

the reservoir (if they do not have an unacceptable deleterious effect on the activated

particulate or other functional materials) 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 and/or or other functional 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.

If the filtration substrate is not pre-impregnated with activated particulate material then the invention further 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.

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 0.5μm to about 20μm.

Preferably, the mean particle size of the activated particulate material in the filtration material of the invention is from about 0.7 μm to about lOμm. Still more preferably, the mean particle size of the activated particulate material in the filtration material of the invention is from about lμm to about 3μm.

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 1 ; 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 1 to the

other. Simultaneously, the openable discharge ports are activated and ajet 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 ajet 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 functionalised filtration material comprising

the steps of:

a) providing a filtration substrate in the form of a web or sheet; b) providing a reservoir charged with an emulsion or solution of at least

one substantially non-volatile functional material selected from activated particulate materials, bacteriocides, bacteriostats, fire retardant compounds, indicator compounds, neutralising compounds and mercury vapour combatant compounds, the

reservoir having an openable discharge port and means for pressurizing the emulsion or solution through the port on actuation thereof; c) positioning the filtration substrate adjacent the discharge port of the reservoir to receive thereon ajet or spray of the emulsion or solution upon actuation

of the discharge port;

d) actuating the openable discharge port to discharge, by means of a jet or spray, a desired quantity of the emulsion or solution onto the filtration substrate; e) allowing the emulsion or solution to impregnate the filtration

substrate; and f) drying the impregnated filtration substrate to remove a volatile component of the emulsion or solution and yield a filtration material having the at

least one functional material impregnated therein.

2. A process according to claim 1 wherein the emulsion or solution is allowed to impregnate at least about 25% of the thickness of the filtration substrate.

3. A process according to claim 2 wherein the emulsion or solution is allowed to impregnate at least about 40% of the thickness of the filtration substrate.

4. A process according to claim 3 wherein the emulsion or solution is allowed

to impregnate at least about 50% of the thickness of the filtration substrate.

5. A process according to claim 4 wherein the emulsion or solution is allowed to impregnate at least about 75% of the thickness of the filtration substrate.

6. A process according to claim 5 wherein the emulsion or solution is allowed to impregnate substantially the whole of the thickness of the filtration substrate.

7. A process according to any one of claims 1 to 6, wherein the filtration substrate material is selected from polyesters, glass fibre, polypropylene, viscose, cellulose, cotton and lycra™.

8. A process according to any one of claims 1 to 7 wherein the thickness of the substrate is no more than about 4mm.

9. A process according to claim 8 wherein the thickness of the substrate is no more than about 3mm.

10. A process according to any one of claims 1 to 9 wherein the filtration substrate is provided pre-impregnated with an activated particulate material.

11. A process according to any one of claims 1 to 10 wherein the at least one functional material comprises an activated particulate material.

12. A process according to any one of claims 1 to 11 wherein the activated

particulate material has an extended or enhanced pore structure.

13. A process according to any one of claims 1 to 12 wherein the activated

particulate material has an internal surface area of greater than about 20m²/g.

14. A process according to any one of claims 1 to 13 wherein the activated particulate material is selected from activated carbon, zeolites, silica gels, activated

alumina and alumina silicate materials.

15. A process according to any one of claims 1 to 14 wherein the maximum particle size of the activated particulate material is no more than about 50 μm.

16. A process according to claims 1 to 15 wherein the mean particle size of the activate particulate material is from 0.5 μm to about 20 μm.

17. A process according to any one of claims 1 to 16 wherein the concentration of the at least one functional material in the emulsion or solution is less than about

10% w/w.

18. A process according to any one of claims 1 to 17 wherein a plurality of reservoirs are employed.

19. A process according to claim 18 wherein at least one reservoir is charged with an activated particulate material and at least one other reservoir is charged with a functional material selected from bacteriocides, bacteriostats, fire retardant compounds, indicator compounds, neutralising compounds and mercury vapour combatant compounds.

20. A filtration material obtained by a process according to any one of claims 1 to 19 comprising a substrate impregnated with an activated particulate material

having a mean particle size of from about 0.5 μm to about 20 μm.

21. A filtration material according to claim 20 wherein the mean particle size of the activated particulate material is from about 0.7 μm to about 10 μm.

22. A filtration material according to claim 21 wherein the mean particle size of the activated particulate material is from about 1 μm to about 3 μm.

23. An item of electronic hardware incorporating a filtration material according

to any one of claims 20 to 22.

24. A computer hard disk drive according to claim 23.

25. A shoe insole incorporating a filtration material according to any one of

claims 20 to 22.

26. A respiratory face mask incorporating a filtration material according to any

one of claims 20 to 22.