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WO2006128237A1 - Milieu filtrant electrostatique et procede de fabrication - Google Patents

Milieu filtrant electrostatique et procede de fabrication Download PDF

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Publication number
WO2006128237A1
WO2006128237A1 PCT/AU2006/000738 AU2006000738W WO2006128237A1 WO 2006128237 A1 WO2006128237 A1 WO 2006128237A1 AU 2006000738 W AU2006000738 W AU 2006000738W WO 2006128237 A1 WO2006128237 A1 WO 2006128237A1
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WO
WIPO (PCT)
Prior art keywords
web
days
filter
period
fibres
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/AU2006/000738
Other languages
English (en)
Inventor
Jurg Arthur Schutz
Niall Finn
Raymon Douglas Wood
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commonwealth Scientific and Industrial Research Organization CSIRO
Original Assignee
Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2005902810A external-priority patent/AU2005902810A0/en
Application filed by Commonwealth Scientific and Industrial Research Organization CSIRO filed Critical Commonwealth Scientific and Industrial Research Organization CSIRO
Publication of WO2006128237A1 publication Critical patent/WO2006128237A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/44—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling
    • D04H1/46—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres
    • D04H1/48—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres in combination with at least one other method of consolidation
    • D04H1/485—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres in combination with at least one other method of consolidation in combination with weld-bonding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/34—Constructional details or accessories or operation thereof
    • B03C3/40—Electrode constructions
    • B03C3/60—Use of special materials other than liquids
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
    • D04H1/4282—Addition polymers
    • D04H1/4291—Olefin series
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/44—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling
    • D04H1/46—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/44—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling
    • D04H1/46—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres
    • D04H1/48—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres in combination with at least one other method of consolidation
    • D04H1/49—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties the fleeces or layers being consolidated by mechanical means, e.g. by rolling by needling or like operations to cause entanglement of fibres in combination with at least one other method of consolidation entanglement by fluid jet in combination with another consolidation means
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/54—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
    • D04H1/74—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being orientated, e.g. in parallel (anisotropic fleeces)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/02—Types of fibres, filaments or particles, self-supporting or supported materials
    • B01D2239/0241—Types of fibres, filaments or particles, self-supporting or supported materials comprising electrically conductive fibres or particles

Definitions

  • Electrostatic filters are widely used for separating fine dust particles from a gas phase. For example, electrostatic filters were used during the First World War to protect soldiers against exposure to toxic arsenic fumes . Yet another example in which electrostatic filters are still being used is domestic and general air conditioning systems and in particular to remove dust particles including pollens from the indoor environment.
  • Electrostatically enhanced coarse fibre filter media can provide the capacity to filter relatively fine particles at a comparably low pressure drop.
  • electrostatically enhanced filter media made of coarse fibre also have a comparably higher strength than filter media made from fine fibres.
  • Coarse fibre filters can also be formed into thick structures with high bulk, which provide an inherent ability to contain higher dust quantities .
  • electrostatically enhanced filter media are generally seen as the preferred solution in gas filtration applications .
  • a disadvantage of electrostatically enhanced filters is that the electrostatic charge can dissipate over time and, therefore, become less affective as the filter medium ages. According to our experience the rate at which the electrostatic charge of conventional electrostatic filters deteriorates increases when the filter medium is exposed to high humidity, heat or ionising radiation. While some types of electrostatic filter media remain practically unaffected by dissipation of charge over time, they are still affected by the amount of stored charge that is consumed by captured dust particles settling on the fibre surface . The net effect from a reduced amount of stored charge combined with the build up of dust structures in the body of the medium can go both ways in terms of particle capture efficiency.
  • the present invention is based on the realisation that a liquid can play a role in achieving compaction of the filter medium that can result in a lasting electrostatic charge.
  • a process for treating a fabric that can be used as an electrostatic filter medium including the steps of: a) compacting a non-woven web of fibres, or at least a portion thereof, by way of a mechanical means while the non-woven web or said portion is in contact with a liquid phase, and wherein the non-woven web contains one or more than one type of staple fibre; b) drying the web of fibres; and c) electrostatically charging the compacted web of fibres to enhance the capacity of the web to filter dust particles from a gas .
  • steps a) to c) may be carried out disjunctively or contiguously and that the steps can be carried out at one or more different locations .
  • step b) the process include a step of washing the non-woven fibrous web to remove antistatic agents using a washing liquid.
  • the washing liquid be the liquid phase that is in contact with the non-woven web during step a) .
  • An advantage provided by the preferred features mentioned above is that the web itself can be made from fibres on which waxes , oils , spin finishes and other contaminants are still present and that affective compaction of the fibres can be achieved while the fibres are wet from the washing liquid. Previously, it was common practice to first wash and dry staple fibres prior to assembling the fibres into a web which is then electrostatically charged.
  • the preferred features of the present invention mentioned above are based, at least in part, on the realisation that affective compaction of the web can be achieved in the presence of a liquid phase such as a washing liquid that is used to wash contaminants from a fully assembled web of fibres .
  • the term "staple fibres" embraces any type of fibre other than continuous fibres or filaments.
  • the web may be made from spunbonded fibres, carded fibres, or air-laid fibres.
  • the fibres usually contain antistatic contaminants such as waxes and spin finishes , whereas continuous fibres or filaments are more likely to be spunbonded or meltblown in a finished form that will not have external antistatic agents and therefore, will not require washing.
  • the staple fibres in the web be any one or a combination of cellulosic fibres , keratin fibres , proteinaceous fibres and synthetic fibres including polymers such as, but by no means limited to polyolefins , polyesters , polycarbonates, polyamides , polyurethanes , polyaramids , polyacrylonitriles , polyacrylics , polyvinyls , polyvinylidenes , polytetrafluoroethylene and respective polymer-copolymer- combinations and variations thereof.
  • polymers such as, but by no means limited to polyolefins , polyesters , polycarbonates, polyamides , polyurethanes , polyaramids , polyacrylonitriles , polyacrylics , polyvinyls , polyvinylidenes , polytetrafluoroethylene and respective polymer-copolymer- combinations and variations thereof.
  • the structure of the synthetic fibres can be homopolymer, bi- or multi- component core-sheath, side-by-side, "segmented pie” or ⁇ islands-in-the-sea” . It is also possible to use the "island"-polymer filaments which remain after the surrounding "sea"-polymer has been dissolved and washed off.
  • the filtering capacity of the filter is at least twice that of an equivalent filter without an electrostatic charge. More particular, in terms of the quality factors Q and Q x which are described below in more detail , the quality factor Q of a polypropylene filter without an electrostatic charge is usually in the order of 7 kPa "1 (for a test face velocity of 0.15 m/s) and the Q x value approximately equal to 20 nm.
  • a polypropylene filter electrostatically charged according the present invention has an enhanced capacity to retain the electrostatic charge which results in the filter medium having quality factors Q and Q x of at least 14 kPa "1 (for a test face velocity of 0.15 m/s) and 40 nm respectively for a period of up to 12 months or more.
  • washing liquid include any one or a combination of the following: an organic solvent, liquid carbon dioxide, water, or a detergent. It is preferred that the step of washing the web involves the web travelling through one or more than one reservoir of the washing liquid.
  • the step of washing the web involves the web travelling through two or more washing reservoirs
  • the step of compacting the web be to some extent carried out on the web after travelling through each washing reservoir.
  • the mechanical means used for carrying out step a) define an opening through which the web passes and the opening has a height that is less than the thickness of the web prior to compaction.
  • the mechanical means be a nip between one or more pairs of rollers and that step a) involves passing the web through the nip(s) . It is still even further preferred that in the situation where the step of washing the web involves the web travelling through two or more washing reservoirs, compaction of the web according to step a) be carried out by a mechanical means in the form of a pair of rollers between which the web travels.
  • the or each pair of rollers apply a compacting force ranging from 5 to 100 kN/m to the web. It is even more preferred that the or each pair of rollers apply a compacting force to the web of approximately lOkN/m.
  • the web of fibres undergoes an initial consolidation stage.
  • the initial consolidation stage may involve needle punching or spunlacing the web which may also be known as hydroentangling .
  • the initial consolidation stage may also, for example, involve calendering the web which will flatten the web in a direction normal to the plane of the web.
  • the initial consolidation stage may be carried out by thermal bonding.
  • the packing density of the fabric after initial consolidation is preferably between 2% and 10% .
  • the web, once treated according to step a) have a packing density ranging from 5 to 30%. It is even more preferred that the packing density of the web range from 10 to 20%.
  • packing density is a ratio of the density of a fabric to the density of the fibres contained within the fabric. Further details and an explanation of how to calculate the packing density of web is explained under the heading TRIALS in this specification .
  • step of drying the web can be carried out using any suitable fan-forced or convective heating means .
  • step c) may be carried out using any suitable means including needle punching or some form of rubbing, it is preferred that step ⁇ ) be carried out by way of a corona discharge.
  • the fibres may be of any diameter, it is preferred that the fibres have a diameter of 9 ⁇ m or more.
  • the mass per unit area of the non-woven web range from 100 to 1000 g/m 2 . It is even more preferred that the mass per unit area of the non-woven web range from 150 to 400 g/m 2 .
  • the electrostatic filter medium have a filtration efficiency calculated according to a methylene blue particle filtration efficiency of 20% or more .
  • an electrostatic filter medium made according to the process of the present invention described above.
  • the electrostatic filter medium may also include any one or a combination of the preferred features described above .
  • electrostatic charge refers to situations where the electrostatic charge has been induced or created by means other than incidental means such as charge created by drying or handling of the filter medium. It is even more preferred that the electrostatic charge contributes to the filtration properties for a period of at least 365 days, or even more preferably for 2 years , 3 years or more .
  • any one or more of the following properties of the filter medium be greater or superior than a filter medium of the same makeup and at substantially the same base weight (g/m 2 ) without wet compaction: filtration efficiency (%) , quality factor Q (kPa "1 ) or quality factor Q x (nm) . It is preferred that the filtration efficiency be at least 20% using a Methylene Blue Filter Test Instrument which is substantially based on the design specification of Australian Standard AS 1324.2-1996. In the situation where the base weight of the filter ranges from 200 to 300 g/m 2 and a packing density greater than 5% , the filter has any one or a combination of the following properties using the Methylene Blue Filter Test Instrument:
  • the filtration efficiency be at least 30% for a period at least 365 days;
  • the quality factor Q be at least 14kPa ⁇ 1 for a period of at least 365 days; • it is preferred that the quality factor Q x be at least 40nm for a period of at least 365 days.
  • the filter has any one or a combination of the following properties using the Methylene Blue Filter Test Instrument:
  • the filtration efficiency be at least 40% for a period at least 4 days;
  • the quality factor Q be at least 1OkPa "1 for a period of at least 4 days;
  • the quality factor Q x be at least 28nm for a period of at least 4 days.
  • the base weight of the filter ranges from 300 to 400 g/m 2 , has a packing density greater than 10%, and has a hydrophobic spin finish:
  • the filtration efficiency be at least 55% for a period at least 4 days;
  • the quality factor Q be at least 1OkPa "1 for a period of at least 4 days; • it is preferred that the quality factor Q x be at least 28nm for a period of at least 4 days .
  • the base weight of the filter ranges from 300 to 400 g/m 2 , has a packing density greater than 10%, and has a hydrophili ⁇ spin finish: • it is preferred that the filtration efficiency be at least 55% for a period at least 20 days, and even more preferably at least 70%; • it is preferred that the quality factor Q be at least 14IcPa "1 for a period of at least 20 days;
  • the quality factor Q x be at least 40nm for a period of at least 20 days.
  • the base weight of the filter ranges from 300 to 400 g/m 2 , has a packing density greater than 10% r and has a hydrophilic spin finish:
  • the filtration efficiency be at least 80% for dust loading of up to 8 g/m 2 for a period at least 128 days;
  • the quality factor Q be at least 1OkPa "1 for a dust loading of up to 8 g/m 2 for a period at least 128 days;
  • the quality factor Q x be at least 28nm for a dust loading of up to 8 g/m 2 for a period at least 128 days.
  • a plant for treating a fabric that is suitable for manufacturing an electrostatic filter medium
  • the plant including: mechanical compacting means in which a non-woven web of fibres, or at least a portion thereof, can be compacted while the non-woven web or said portion thereof is in contact with a liquid, and wherein the non-woven web contains one or more than one type of staple fibres; a drying stage in which the liquid can be dried from the compacted non-woven web; and means for electrostatically charging the compacted fibres to enhance the capacity of the web to filter dust particles from a gas .
  • the mechanical compacting means can be achieved using any suitable format, it is preferred that the compacting means be in the form of one or more than one nip formed between a pair of rollers .
  • the plant further include a washing stage in which a washing liquid can remove antistatic agents, such as but by no means limited to, waxes, oils and spin finishes from the exterior of the fibres of the web.
  • a washing liquid can remove antistatic agents, such as but by no means limited to, waxes, oils and spin finishes from the exterior of the fibres of the web.
  • washing liquid be the liquid in contact to the non-woven web during the compacting stage .
  • the washing stage include one or more than one vessel through which the web can travel .
  • each vessel include one or more rollers that define a path submerged in the washing liquid along which the web can travel.
  • the washing stage include two or more than two vessels and that the mechanical compacting means include a series of substages each located after the vessels and are adapted for compacting the web to some extent after each washing vessel .
  • the or each nip provide a compression force ranging from 5 to 100 kN/m to the web as it passes through the compacting stage.
  • the plant include an initial consolidation stage for improving the web strength prior to compacting while the web is in contact with a liquid phase .
  • the initial consolidation stage may, for example, be carried out by way of needle punching, spunlacing or thermal bonding. It is preferred that the web has a packing density between 2% and 10% after the initial consolidation stage .
  • the plant of the present invention may also include any one or a combination of the preferred features of the process described above.
  • Figure 1 is a block diagram showing the steps of a process
  • Figure 2 is a side alleviation of a combined washing and compacting stage comprising 3 substages that are utilised by the process ;
  • Figures 3 to 5 illustrate alternative configurations of combined washing and compacting substages for compacting a web.
  • Figures 6a and 6b are schematic drawings of a Laser Opacity Meter that can be used for testing the filtering capacity of the filter medium carrying out a methylene blue filter test.
  • Figure 7 through to Figure 14 illustrate a series of results of trials carried out on sample electrostatic filter media made according to the preferred embodiment, namely examples 3 to 7 and comparative filter media, namely examples 1, 2 and Cl .
  • Figure 7 through to Figure 26 illustrate a series of results of trials carried out on sample electrostatic filter media made according to the preferred embodiment, namely examples 3 to 15 and comparative filter media, namely examples 1, 2, Cl, C2 and C3.
  • Figure 27 is a series of photographs showing side views of compacted examples 11, 12 and the corresponding uncompacted precursor C3. A true scale of 0.5mm per division is shown on the right side of photograph.
  • the preferred embodiment of the present invention differs from technology presently available in many respects including, but by no means limited to, a combined washing and compacting stage.
  • the initial consolidation stage involves consolidating the web of non-woven fibres to a packing density, which is preferably as high as 5%.
  • the initial consolidation stage may involve the use of conventional machinery to carry out needle punching, spunlacing or calendering so as to flatten the web in a direction normal to the plan of the web.
  • the initial consolidation stage may be carried out by thermal bonding between the fibres .
  • the primary purpose of the initial consolidation stage is to consolidate the web and attain sufficient tensile strength that will avoid the web breaking, stretching or drafting during subsequent processing of the web.
  • electrostatic depleting contaminants as used herein embraces antistatic agents that may cause one or a combination of: (i) a reduction in the extent to which an electrostatic charge can initially be applied to a web; and (ii) reduces the capacity of the fabric to retain an electrostatic charge once applied.
  • Each sub-stage includes a vessel 2 containing a washing liquid 3 , at least one guide roller for guiding web into the vessel and a pair of submerged stainless steel rollers 5.
  • web 1 is fed into the first sub-stage via a driven guide roller 4.
  • Two pairs of stainless steel rollers 5 are submerged in the washing liquid and define a nip between which the web travels .
  • the rollers 5 are intended to remove air bubbles from the web 1 and thereby increase wetting of the fabric with the washing liquid.
  • Each pair of rollers 5 comprises a driven top roller 5a and a spring loaded bottom roller 5b .
  • a purge stream may be continuously or periodically discharged from the vessel 2 and a fresh make up stream of washing liquid fed into each vessel 2.
  • the purpose of this procedure is to ensure that the concentration of electrostatic depleting contaminants in the washing liquid is kept at an appropriate level .
  • the washing liquid may be conveyed from one vessel 2 to another in a direction opposite to the direction of motion of the web between the vessels 2. That is, fresh washing liquid may be supplied to the last vessel 2 as seen in the direction of motion of the web and discharged from the first vessel 2 entered by the web.
  • roller 6b is an idling roller
  • roller 6a is a driven roller
  • the rollers 6a and 6b express liquid from the web and apply a compacting force to the web.
  • the compacting force is in the range of 5 to 15 kN/m.
  • the compacting force is generated by rollers 6a and 6b being moveable relative to each other in a direction perpendicular to the direction of travel of the web by hydraulic actuators. In the event that the additional compacting force is required, it may be necessary to replace the rubber coated rollers 6a and 6b with stainless steel rollers.
  • roller 7 facilitates the detachment of the web from high pressure roller 6b and guides the web towards the next set of rollers 5 submerged in the washing liquid in the following substage.
  • the third substage is equipped with a large roller 8b located above the driven roller 8a, which makes roller 7 obsolete as a result.
  • the washing liquid may be any suitable liquid including, but by no means limited to organic solvents, liquid carbon dioxide, water or a detergent.
  • the contaminant is a silicone-based hydrophobic spin finish
  • the web may require washing with a non-polar solvent such as dichloromethane .
  • the pressure from the rollers on the wet fabric renders the physical structure more compact.
  • the level of compaction is significantly higher when the fabric is wet as compared to when it is dry.
  • a substantial portion of the liquid picked up by the fabric during washing is expressed from the web as it passes through the last pair of squeeze rollers 8a and 8b.
  • the remaining liquid is dried off using any suitable air blow and/or heating means.
  • the dried fabric is then electrostatically charged by exposing the web to ions from a DC corona breakdown.
  • the breakdown cell may include a pair of electrodes one of which is a stainless steel wire and the other a stainless steel plate with rounded edges .
  • the polarity of the voltage applied to the wire electrode can then be used to determine the polarity of the ions generated in the breakdown. Positive, negative as well as combinations of positive and negative polarity can be suited to electrostatically charge the web.
  • the preferred embodiment described above involves combined washing and compacting stages , it will be appreciated that these stages may be configured separately and that the liquid contacting the web during compaction may be a liquid phase other than the washing liquid.
  • FIG. 3 illustrates an alternative washing vessel configuration including an additional pair of the rollers 5 and top rollers 9 that in essence increases the length of the web in the washing vessel.
  • the configuration shown in figure 3 is therefore suited to situations where the web requires a greater period of contact with the washing liquid in order to remove contaminants .
  • Figure 4 illustrates an alternative washing vessel that is preferred when the contaminants settle to the bottom of the vessel.
  • a series of the rollers 10 and 11 define a path for the web whereby the web is initially directed toward the base of the washing vessel were the concentration of heavy contaminants may be high and then progressively upward into washing liquid having a lower concentration of the contaminants .
  • the embodiment shown in figure 4 also includes a baffle plate 13 which separates the washing vessel into sections where the web moves downwardly and upwardly in the vessel.
  • a baffle plate 13 which separates the washing vessel into sections where the web moves downwardly and upwardly in the vessel.
  • the embodiment shown in Figure 5 includes two aprons 14 and 15 which guided the web through the washing vessel and absorbed stress imposed in its main and cross directions.
  • An advantage provided by this embodiment is that the aprons 14 and 15 can be used to support low strength webs that may not have undergone the initial consolidation.
  • the aprons have an open scrim- type structure so as not to hinder penetration of the washing liquid through the apron to the web.
  • the performance of a filter can be assessed by monitoring the pressure drop and filtration efficiency of a filter medium when it is loaded with a methylene blue dust.
  • Methylene Blue Filter Test Instrument Methylene Blue Filter Test Instrument
  • Figures 6a and 6b illustrate the Opacity Meter in two different operative orientations , namely an orientation in which methylene blue dust is loaded onto a membrane (i.e. Figure 6a) and another orientation in which the transmission of the loaded membrane is assessed (i.e. Figure 6b) .
  • a sample of filter medium being tested is exposed to a stream of particles in a conduit and two Opacity Meters are flow connected to the conduit, one located on either side of the filter medium being tested i.e., upstream and downstream of the filter medium. This allows the capacity of the filter medium to be assessed through use of the Opacity Meter.
  • the Opacity Meters include a light source in the form of a diode-laser module having a 3 milliwatt optical power capacity and produce light with a 670 nm wavelength.
  • the module also contained an integrated internal feedback system for the purpose of stabilizing the output intensity of the laser beam.
  • a combination of lenses provided for an adjustable beam geometry within a focus range of 35 mm to infinity. With the focus set to infinity, the beam assumed a rectangular shape of 4 mm x 2 mm in size. The beam diameter in the focus was ⁇ 50 um and the beam divergence ⁇ 0.5 mrad.
  • the standard required a negligible response outside the wavelength range of 400 to 700 nm, which had been implemented in the standard by a limited spectral response of the receiver. Lasers fulfil this requirement naturally via the spectral discrimination of the emitted laser light by the gain medium.
  • the standard required further a maximum spectral response in the wavelength range of 500 to 600 nm.
  • the light emitted by the laser module consisted of a few narrow emission lines in a wavelength range of 660 to 680 nm, which were located close to the main absorption band of methylene blue in aqueous solution, with its peak at 660 nm.
  • the optical transmission of the methylene blue stained filter membrane was therefore very sensitive to the amount of dust deposited. It should be noted, that the absorption spectrum of dry methylene blue was different from that of the methylene blue solution, as was apparent from its slight purplish colour, and produced consequently a slightly different spectral response .
  • test dust from the respective sampling tube enters the Opacity Meter via a 3-way cock 16 as shown in Figure 6a where it is directed to filter membrane 17 in holder 18.
  • the dust particles settled on top and within the filter membrane.
  • the particle-free air left the Opacity Meter via the outlet 19 of T-section 20 below the membrane holder 18.
  • a beam 21 of the laser module 22 propagates along the straight path of the 3-way cock 16 and hit the centre of filter membrane 17 as shown in Figure 6b .
  • Part of the light was absorbed by the methylene blue deposits 24 that have been accumulated on the membrane during sampling and 0O the rest emerged as scattered light on the other side of the membrane.
  • a given percentage of the scattered light was detected by photodetector 25 from where the signal was amplified and transmitted via an electrical lead 26 to a display or a processing unit.
  • the Opacity Meter can be switched easily from the sampling mode to the opacity measurement mode, and vice versa, via the 3-way cock 16. This was done either manually or via an actuator.
  • the 3-way cock 16 also protected the laser module from contamination with dust.
  • the photodetector was protected from methylene blue contamination by the filter membrane.
  • the adopted testing procedure had a few more deviations from the Australian Standard:
  • the filter membranes were not steamed after loading since the dust deposited on the membrane was sufficiently uniform.
  • a benefit of reusing the filter membranes was a reduced statistical error for the calculated non-linear statistical averages of the filtration efficiency, in comparison to the use of different membranes for each sampling.
  • the physical properties of the filter medium including weight, thickness and packing density were also calculated.
  • the packing density of the filter medium was obtained by cutting circular discs of the filter medium with a diameter of 109 mm and measuring the thickness. The thickness was measured by placing one of the discs between a flat metal base and a 2.5 mm thick glass plate placed on the top of the disc. A thickness reading was taken and the fabric density calculated. A corresponding packing density was calculated by dividing the fabric density by the average density of the fibres contained in the material of the filter medium. In other words, the packing density increases as the voids between the fibres in the filter medium decrease in size. As will be shown with reference to the test results below, the ability for a filter medium to retain an electrostatic charge is to a large extent dependent on the packing density of the filter medium. Examples 1 - 4
  • Examples 1 -bo 4 involve the use of electrostatic filter media with packing densities ranging from 3.7 % to 5.8 % and comprising solvent cleaned polypropylene fibres . All samples were made from 3 denier polypropylene fibres of 55 mm length containing hydrophobic, silicone- based spin finish . The fibres were carded on a woollen card and subsequently needle punched (Laboratory fibre locker, serial P8701, available from James Hunter Machine Co., North Adams, Massachusetts, USA). Examples 1, 3 and 4 were needle punched at 50 insertions per square centimetre (ins. /cm 2 ) and Example 2 at 250 ins. /cm 2 .
  • Example 3 was also treated, by being passed through two substages of the combined washing and compacting substages shown in Figure 2.
  • the washing vessels were filled with water at 50 0 C temperature containing 0.1 % of non-ionic detergent (TN450) .
  • Detergent residues were removed in a separate process, by washing the web in tap water and leaving them to dry at room temperature .
  • Example 4 was treated as per Example 3, but was passed through the combined washing and compacting stages twice .
  • the sample mass per unit area of the test media varied between 195 and 252 g/m 2 as shown in Table 1 below. Fabric and packing densities of each example are also listed in the legend of Figure 7. It was expected that the media of Examples 2 and 4 would have a lower mass per unit area, due to a more rigorous treatment by the needle punching or the squeeze rollers, respectively. The additional treatment which Example 4 received during the second pass did not only reduce the mass per unit area of the fabric in comparison to that of Example 3, but had also an adverse effect on its packing density. This result suggests that an indiscriminate application of additional compacting steps does not necessarily increase the packing density of the fabric.
  • the Examples 5 to 7 and Cl comprise filter media having a mass per unit area of more than 200 g/m 2 and
  • Example 5 The manufacture of the Example 5 involved treating the medium twice through 3 compacting and washing substages as shown in Figure 2.
  • the washing vessels contained water at 60-65 0 C temperature.
  • Example 6 was manufactured and treated in the same manner as Example 5 with the only exception that 0.1% of non-ionic detergent (BD40) had been added to the water of the first washing vessel of the 6-substage washing and compacting stages .
  • BD40 non-ionic detergent
  • Examples 5 and 6 were then dried in a through-air bonding oven (Thermo Bond Oven, Serial No 6930/12/98, available from Gyson, Dandenong 3175, Australia) at 100 0 C.
  • Thermo Bond Oven Serial No 6930/12/98, available from Gyson, Dandenong 3175, Australia
  • Example 7 was manufactured from a different type of polypropylene fibre having an external hydrophilic spin finish. The spin finish was readily removed in warm water.
  • the 3 denier fibres Polyolefin Staple Fibre, type T-1001, available from Kolon Glotech, Inc., Kyunggi-do,
  • Example 7 was passed twice through the washing and compacting substages in Figure 2 , wherein the washing stages contained water only. Example 7 was subsequently dried in the same manner as Examples 5 and 6.
  • Example Cl were electrostatically charged by a positive polarity DC corona breakdown in 6 passes at 1.3 m/min transport speed.
  • Example 10 the poorest performance, followed by those of Examples 6 and 5.
  • Examples 5 and 7 exhibited relatively similar filtration efficiencies , but Example 7 had a better overall performance due to a lower pressure drop (see Figure 12) .
  • the Comparative Example Cl had the lowest
  • Example 7 had the best overall performance in terms of the quality factors Q (see Figure 13) and Q x (see Figure 14) , which indicated that the
  • Examples 8 to 13, C2 and C3 comprise filter media having a mass per unit area of approximately 400 g/m 2 and comprising polypropylene fibres having external hydrophobic or hydrophilic spin finishes .
  • Hydrophobic spin finish Examples 8, 9 and C2 were manufactured in accordance with the same sequence of steps used to manufacture Examples 5, 6 and Cl described above.
  • Example 10 was manufactured in accordance with the same sequence of steps as Example 9, except the medium was passed only once through the combined compacting and washing substages shown in Figure 2.
  • Comparative Example C3 was manufactured from guillotined polypropylene fibres having an external hydrophilic spin finish .
  • the fibres were initially carded into a web of the required mass per unit area and needle punched at 125 ins . /cm 2 from both sides .
  • the web was then subjected to a corona discharge treatment at this point.
  • Examples 11 to 13 were manufactured in accordance with the method of manufacture of C3 described above, however, in the case of the Example 11, the medium was further treated in a total of 6 substages of washing and compacting in accordance with Example 7.
  • Example 12 was treated in a total of 3-substages of washing and compacting.
  • Example 13 was manufactured in accordance with Example 12, however, the first washing and compacting substage contained water with 0.1% detergent (BD40) rather than water only.
  • BD40 0.1% detergent
  • Examples 8 to 13 and Comparative Examples C2-C3 have been summarised in Table 3 below.
  • the mass per unit area of the samples was spread across a range of 327 to 386 g/m 2 .
  • the packing densities were typically 15% for the compacted media and slightly higher than 9% for the uncompacted comparative examples.
  • the thicknesses of the compacted and uncompacted media varied accordingly.
  • Compacted filter media also differ from spunlaced filter media by leaving the fabric structure essentially unchanged as well as by the lack of grooves that are typically present on spunlaced media from the action of the water jets.
  • Example 14 was compacted by being passed once through the washing and compacting substage shown in
  • Example 15 was passed twice through the washing and compacting substages shown in Figure 2 which is equivalent to a 6- substages process. While the treatment of Example 14 involved the use of non-ionic detergent (BD40) in the first stage only, the same 0.1% concentration of detergent was used for Example 15 in stages 1 and 2. All other treatments for examples 14 and 15 were otherwise the same.
  • PCFTI Particle Counter Filtration Efficiency Test Instrument
  • the main distinguishing feature of the PCFTI from the MBFTI is the determination of the particle concentration in the test duct by means of a laser particle counter-sizer .
  • the atomiser and test duct were constructed according to AS 1324.2-1996 and design parameters in relation to the handling of sodium chloride dust were obtained from BS 3928:1969.
  • Table 5 PCFTI test results of Example 14 at 50 days, before dust loading. Note face velocity (v £ ) of 0.27 m/s.
  • Example 15 was however significantly higher than that of Example 14 at various intermediate stages of the test, which was a
  • Table 7 PCFTI test results of Example 14 at 50 days, after dust loading. Note face velocity (v f ) of 0.27 m/s.
  • Table 9 PCFTI test results of Example 14 at 129 days, 15 before dust loading. Note face velocity (v f ) of 0.15 m/s.
  • Table 10 PCFTI test results of Example 15 at 128 days, before dust loading. Note face velocity (v f ) of 0.15 m/s.
  • Table 12 PCFTI test results of Example 15 at 128 days, after dust loading. Note face velocity (v f ) of 0.15 m/s.
  • Table 13 Comparison of PCFTI and MBFTI filtration efficiencies (FE) for Example 14 and 15, before and after dust loading.

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Filtering Materials (AREA)

Abstract

La présente invention concerne un milieu filtrant électrostatique (1) et un procédé de fabrication d'un filtre électrostatique (1). Le milieu filtrant électrostatique de l'invention se présente sous la forme d'une bande de non-tissé (1) contenant au moins un type de fibres discontinues, la bande de non-tissé étant chargée électrostatiquement et étant comprimée de telle manière que la charge électrostatique contribue aux propriétés de filtrage du milieu pendant une période d'au moins 100 jours.
PCT/AU2006/000738 2005-05-31 2006-05-31 Milieu filtrant electrostatique et procede de fabrication Ceased WO2006128237A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2005902810A AU2005902810A0 (en) 2005-05-31 Electrostatic filter media and a process for the manufacture thereof
AU2005902810 2005-05-31

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Publication number Priority date Publication date Assignee Title
CN106512569A (zh) * 2015-09-11 2017-03-22 松下知识产权经营株式会社 过滤件以及空气净化器
CN106567189A (zh) * 2016-11-04 2017-04-19 东华大学 一种聚四氟乙烯高性能纤维纸的制备方法
CN110062649A (zh) * 2016-11-11 2019-07-26 霍林斯沃思和沃斯有限公司 具有密度变化的过滤介质
CN111206294A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种具有阻燃功能的聚烯烃静电滤材及其制备方法和用途
CN111206292A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种聚烯烃骨架过滤材料及其制备方法和用途
CN111206293A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种可打折的双组分滤材及其制备方法和用途

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WO2001027371A1 (fr) * 1999-10-08 2001-04-19 3M Innovative Properties Company Procede et appareil de fabrication d'une bande a electret fibreuse, non tissee, a partir de fibres non conductrices et d'un liquide polaire
US20020190434A1 (en) * 1999-10-08 2002-12-19 3M Innovative Properties Company Method and apparatus for making a fibrous electret web using a wetting liquid and an aqueous polar liquid
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Publication number Priority date Publication date Assignee Title
WO2001021283A1 (fr) * 1999-09-14 2001-03-29 Intersurgical Limited Moyens de filtration et fabrication correspondante
WO2001027371A1 (fr) * 1999-10-08 2001-04-19 3M Innovative Properties Company Procede et appareil de fabrication d'une bande a electret fibreuse, non tissee, a partir de fibres non conductrices et d'un liquide polaire
US20020190434A1 (en) * 1999-10-08 2002-12-19 3M Innovative Properties Company Method and apparatus for making a fibrous electret web using a wetting liquid and an aqueous polar liquid
WO2004037372A2 (fr) * 2002-10-22 2004-05-06 Polymer Group, Inc. Milieu filtrant enchevetre par voie hydraulique ayant une diminution de reserve statique amelioree et procede correspondant

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106512569A (zh) * 2015-09-11 2017-03-22 松下知识产权经营株式会社 过滤件以及空气净化器
CN106512569B (zh) * 2015-09-11 2020-11-27 松下知识产权经营株式会社 过滤件以及空气净化器
CN106567189A (zh) * 2016-11-04 2017-04-19 东华大学 一种聚四氟乙烯高性能纤维纸的制备方法
CN110062649A (zh) * 2016-11-11 2019-07-26 霍林斯沃思和沃斯有限公司 具有密度变化的过滤介质
CN111206294A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种具有阻燃功能的聚烯烃静电滤材及其制备方法和用途
CN111206292A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种聚烯烃骨架过滤材料及其制备方法和用途
CN111206293A (zh) * 2018-11-21 2020-05-29 上海精发实业股份有限公司 一种可打折的双组分滤材及其制备方法和用途

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