WO2010020737A1

WO2010020737A1 - Apparatus and method for making filter elements

Info

Publication number: WO2010020737A1
Application number: PCT/GB2008/002792
Authority: WO
Inventors: Sergei Botov
Original assignee: Botovs Ltd
Priority date: 2008-08-19
Filing date: 2008-08-19
Publication date: 2010-02-25

Abstract

An apparatus is provided for the manufacture of filter elements from plastics materials, the apparatus comprising: (i) a means for depositing a mixture comprising plastics material into a mould (1008a); (ii) a tamper (1004) for compressing the mixture comprising plastics material once the mixture is in the mould; and (iii) a means for moving the mould and tamper relative to one another. A method of making a filter element is also provided, said method comprising: (i) providing a mixture comprising a plastics material; (ii) introducing said mixture into a mould; (iii) subjecting the mixture to a raised pressure to form a filter element precursor body; and (iv) heating the filter element precursor body.

Description

Apparatus and method for making filter elements

The present invention relates to an apparatus and ^'method for making filter elements, especially (but not exclusively) filter elements that may be used to remove particles from fluids .

Filter elements may be used to remove contaminants (in particular particulate) from fluids. Plastics blocks are ^■ conventionally made by heating a plastics material until molten and forming the molten material into a desired shape using a mould, typically using low pressure to draw the molten material into the mould. This technique has not proved to be a useful method of making filter elements from plastics materials.

The present invention provides an apparatus and method for making filter elements from plastics materials.

In accordance with a first aspect of the present invention, there is provided an apparatus for the manufacture of filter elements from plastics materials, the apparatus comprising:

(i) a means for depositing a mixture comprising plastics material into a mould;

(ii) a tamper for compressing the mixture comprising plastics material once the mixture is in the mould; and

(iii) a means for moving the mould and tamper relative to one another between a first position in which the mixture in the mould may be tamped by the tamper and a second position in which the mixture in the mould may not be tamped by the tamper.

This provides an effective apparatus for making filter elements from plastics materials. Those skilled in the art will realize that the mould and the mixture are not parts of the apparatus of the present invention.

The means for moving the mould and tamper relative to one another may be capable of moving one or both of the mould and tamper.

The means for depositing a mixture comprising plastics material into a mould may comprise a conveyor, such as a screw conveyor. Such conveyors are suitable for transporting essentially granular or solid material-s.

The means for moving the mould and tamper relative to one another may comprise a conveyor belt or a turntable.

The tamper may be arranged to provide a compressive force for from 0.2 to 1.0 seconds, more preferably from 0.2 to 0.6 seconds and most preferably from 0.3 to 0.5 seconds. It has been found that the application of pressure over a short timescale is beneficial to the formation of filter elements with suitable pore sizes- that enable the filter elements to be used as oil, fuel and hydraulic fluid filters.

The tamper may be arranged to provide a maximum compressive force of from 1OkN to 100OkN, more preferably from 1OkN to 50OkN and most preferably from 1OkN to 15OkN. In certain circumstances, in particular for the production of larger filter elements, a maximum compressive force of from 3OkN to 50OkN (and more preferably from 3OkN to 15OkN) may be preferred.

The tamper may comprise a tamping head for contacting the mixture and a means for urging the tamping head into compressive contact with the mixture. The means for urging the tamping head into compressive contact with the mixture may comprise a piston. It is preferred that the piston is electrically driven. This facilitates the tamping head being brought into contact with, and removed from, the material quickly. Such rapid movement has been found to be beneficial to the formation of filter elements: It has been discovered that certain other means of driving the piston (for example, a hydraulically-driven piston) do not facilitate the rapid movement of the tamping head. Hydraulically-driven pistons produce filters which are less satisfactory than those produced using electrically-driven pistons. The tamping head may have an annular shape. This is of particular benefit in the manufacture of filter elements for oil or fuel filters.

The apparatus may comprise' a return mechanism for urging the tamping head away from the mixture in the mould. Such a return mechanism may comprise a bias means, such as a spring. A helical spring may conveniently be used, for example. When the tamping head is urged into compressive contact with the material the return mechanism acts so as to try to urge the tamping head away from the mixture in the mould. Once the force urging the tamping head into contact with the mixture in the mould is removed, the return mechanism urges the tamping head away from the mixture. The apparatus may further comprise a receiver for guiding the mixture into the mould from the means for depositing a mixture comprising plastics material into a mould. The receiver may, in use, be located adjacent the mould. The receiver may flare outwardly, and, for example, may have a funnel like portion.

The apparatus may further comprise a heater for heating the tamped mixture.

The apparatus may further comprise a mixer for mixing the mixture comprising plastics material. The mixer should be suitable for mixing granular materials.^'

The apparatus may further comprise a controller for controlling the operation of one or more of the means for depositing a mixture comprising plastics material into a mould, the tamper for compressing the mixture comprising plastics material once in the mould, the means for moving the mould and tamper relative to one another, the heater (if present) and the mixer (if present) .

In accordance with a second aspect of the present invention, there is provided a method of making a filter element, said method comprising:

(i) providing a mixture comprising a plastics material;

(ii) introducing said mixture into a mould; (iii) subjecting the mixture to a raised pressure to form a filter element precursor body; and

(iv) heating the filter element precursor body. A filter element produced by such a method may be effective at removing contaminants (such as particulate) from fluids.

The mixture may comprise a liquid. The liquid may be present up to 5% by weight of the weight of the mixture, more preferably up to 2%, and further more preferably from 0.02 to 1%. The liquid has been found to ease removal of the filter element from the mould. The liquid may be an organic acid, such as a carboxylic acid (acetic acid, for example) .

It is anticipated that step (iv) may remove some or all of the liquid from the filter element precursor body. For example, some of the liquid may be retained.

It is preferred that the mixture comprises from 2% to 30% by wt. of a poly (chloroalkylene) , such as a poly (chloroethylene) . The chloroethylene groups may comprise 1, 2, 3 or 4 chlorine atoms, and each chloroethylene group may be the same or different.

The poly (chloroalkylene) may, for example, be polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer, or a copolymer in which all or substantially all, that is, more than 90% by weight of the copolymer is derivable from chlorohydrocarbon monomer units. Those skilled in the art will realize that the poly (chloroalkylene) (such as polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polyer) may comprise impurities or defects, such as the presence of unchlorinated branch groups. The polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer may comprise up to 5% (and preferably up to 1%) by weight of groups having a structure other than a chloroethylene structure (chloroethylene meaning -CH₂-CHCl-, -CH₂-CCl₂-, -CHCl-CHCl-, -CHCl-CCl₂- or -CCl₂-CCl₂-.) .

It is preferred that at least 50% by weight (and preferably at least 80% by weight and more preferably at least 90% by weight) of the poly (chloralkylene) is provided by group X having the general structure (i) wherein A, B, E and D are H or Cl provided that at least one of A, B, E and D is Cl.

Structure (i) -

Each repeat group X may be mutually the same. For example, the repeat group X may always be a -CH₂-CHCl- repeat group. Alternatively, the mixture may comprise repeat groups X of mutually different structure. For example, the mixture may comprise two or more of the repeat groups -CH₂-CHCl-, -CH₂- CCl₂-, -CHCl-CHCl-, -CHCl-CCl₂- and -CCl₂-CCl₂-.

The repeat group X may substantially be provided, for example, by polyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC) . It has been found that polyvinyl chloride and its related derivatives produce efficient filters. This is of importance in that PVC and derivatives are common waste products that may be recycled. The method of the present invention is not limited to one using recycled materials; virgin materials may be used, such as Evipol-SH, -EP and -EH polymers (Ineos Vinyls, Runcorn, UK) .

It is preferred that the mixture comprises from 2% to 20% by weight of a poly (chloroalkylene) , preferably from 2% to 15%, more preferably from 3% to 12%, further more preferably from 4% to 12% and most preferably from 8% to 12% by weight of poly (choloroalkylene) .

It is preferred that the mixture comprises from 60 to 98% (preferably from 70 to 95%, more preferably from 80 to 90% and most preferably from 80 to 85%) by weight of a further thermoplastic .

It is preferred that the further thermoplastic comprises one or more of poly acrylonitrile butadiene styrene, acrylic, celluloid, cellulose acetate, a polyester (such as poly ethylene vinyl acetate, polyacrylates, polybutylene terephthalate, polyethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylenechlorinates and polyhydroxyalkanoates) , poly ethylene vinyl alcohol, fluoroplastics (for example, polyfluorotetraethylene (PTFE) ) , polyacetal , polyacrylonitrile, polyamide (such as nylon 6 or nylon 12), polyamide-imide, polyaryletherketone, polybutadiene, polybutylene, , polycarbonate, polyketone, polyethylene, polyetheretherketone, polyetherimide, polyethersulfone, polyimide, polylactic acid, polymethylpentene, polyphenylene oxide, polyphenylene sulfide, polyphthalamide, polypropylene, polystyrene and polysulphone. It is preferred that the further thermoplastic comprises one or more of a polyamide, a polyester (such as polyalkylene terephthalate) and a polyalkylene. The polyamide may be a nylon, such as nylon 6,6. The polyalkylene may be polypropylene or polyethylene, for example. The polyalkylene terephthalate may be polyethylene terephthalate. The polyalkylene may be a high density or a low density polyalkylene. Examples of high density polyethylenes include HMA 014, HMA 025 and HMA 035 (Exxon Mobil Corporation) . Examples of low density polyethylenes include LL6101, LL6201 and LDlOOAC (Exxon Mobil Corporation) .

It is preferred that the mixture further comprises from 2 to 10% by weight of a compatilising agent. The compatibilising agent enables blending of a poly (chloroalkylene) (such as polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer) with the further thermoplastic (if present) .

The plasties material (such as the polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer or further thermoplastic) may be supplied in step (i) in a granular form. The granules may have a mean largest dimension of from 0.1mm to lmm and preferably from 0.2 to 0.6mm. It is anticipated that in many circumstances the mixture will comprise granules of different sizes. For ■ example, several granular sizes of PVC may be used to make- up the PVC component of the mixture (if PVC is present) . If a poly (chloroalkylene) (such as polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer) is used in the present method, it is preferred that such material is provided in a granular form in step (i) . It is preferred that the mean largest dimension of said granules of the poly (chloroalkylene) (such as polyvinyl chloride, chlorinated polyvinyl chloride, plasticized polyvinyl chloride, unplasticized polyvinyl chloride or related polymer) is from 0.2 to 0.8mm, and preferably from 0.2 to O.βmm.

If a further thermoplastic is provided, then it is preferred that it is provided in step (i) in granular form. The mean largest dimension of the granules of the further thermoplastic may be from 0.2 to lmm and preferably from 0.3 to 0.8mm.

Step (iv) may comprise heating the filter element precursor body to a maximum temperature of 120°C, more preferably to a maximum temperature of from 80°C to 110⁰C. It is preferred that step (iv) is performed at ambient pressure i.e. not under reduced or increased pressure.

In step (iii), the material may be under compression for from 0.2 to 1.0 seconds, more preferably from 0.2 to 0.6 seconds and most preferably from 0.3 to 0.5 seconds. It has been found that the application of pressure over a short timescale is beneficial to the formation of filter elements with suitable pore sizes that enable the filter elements to be used as oil and fuel filters. The maximum compressive force applied in step (iii) is preferably from 1OkN to 100OkN, more preferably from 1OkN to 50OkN and most preferably from 1OkN to 15OkN. In certain circumstances, in particular for the production of larger filter elements, a maximum compressive force of from 3OkN to 50OkN (and more preferably from 3OkN to 15OkN) may be preferred.

The mould determines the shape of the filter element precursor body. One or more of the surfaces of the mould which, in use, comes into contact with the mixture comprising a plastics material may have a low surface energy. A low surface energy may be provided by a substrate that has been coated with a material that provides a low surface energy. Alternatively, a substrate of a material that provides a low surface energy may be used. Materials that provide a low surface energy include polytetrafluoroethylene (PTFE, such _.as Teflon®) . Surfaces with a low surface energy may be formed by coating a substrate with a silane or polytetrafluoroethylene (PTFE, such as Teflon®) .

The mould may be shaped so as to form a cylindrical filter element precursor body.

The mould may also be provided with one or more end-fitting casting elements to prevent egress of mixture from the mould once the filter element precursor body has been formed in step (iii) . This is important if the mould containing the filter element precursor body is physically removed from an apparatus so that the mould-precursor element ensemble can be put into an oven or the like to perform step (iv) . The method may further comprise providing a tamper for compressing the mixture in step (iii). The tamper may comprise a tamping head for contacting the mixture and a means for urging the tamping head into compressive contact with the mixture. The means for urging the tamping head into compressive contact with the mixture may comprise a piston. It is preferred that the piston is electrically driven. This facilitates the tamping head to be brought into contact with, and removed from, the material quickly. Such rapid movement has been found to be beneficial to the formation of filter elements. It has been discovered that certain other pistons (for example, a hydraulically-driven piston) do not facilitate the rapid movement of the tamping head. The tamping head may have an annular shape. This is of particular benefit in the manufacture of filter elements for oil or fuel filters.

The method may further comprise providing a return mechanism for urging the tamping head away from the mixture in the mould. Such a return mechanism may comprise a bias means, such as a spring. A helical spring may conveniently be used, for example. When the tamping head is urged into compressive contact with the material the return mechanism acts so as to try to urge the tamping head away from the mixture in the mould. Once the force urging the tamping head into contact with the mixture in the mould is removed, the return mechanism urges the tamping head away from the mixture.

The method may further comprise providing a conveyor for moving said mixture comprising a plastics material towards the mould. The conveyor may comprise a screw conveyor. A screw conveyor has been found to provide an effective mechanism for moving mixtures having a granular or other solid consistency towards the mould.

The method may further comprise providing a receiver for guiding the mixture into the mould. The receiver may be placed adjacent the mould. The receiver may flare outwardly, and, for example, may have a funnel like portion. The receiver may receive the mixture from the conveyor, if present.

The method may comprise providing a plurality of moulds. The method may further comprise providing a transporter for moving the moulds into a position in which material may be delivered into the moulds .

The method of the second aspect of the present invention may use the apparatus of the first aspect of the present invention.

The present invention is now described by way of example only with reference to the following Figures of which: Figure 1 is a schematic side-view of an embodiment of an apparatus in accordance with the present invention for use in an embodiment of a method in accordance with the present invention;

Figure 2A is a schematic cross-section through a part of the apparatus of Figure 1; and Figure 2B is a side view of a portion of the apparatus of Figure 1 showing a means for monitoring the amount of mixture loaded into a mould. Figure 1 is a schematic side-view of an embodiment of an apparatus in accordance with the present invention. The apparatus is denoted generally by reference numeral 1001 and is now briefly described with reference to Figure 1. The apparatus comprises a chute 1002 into which a mixture comprising a plastics material may be fed. The chute 1002 guides the mixture into a screw conveyor 1003. The electrically powered screw conveyor moves the mixture into a mould 1008a via a receiver 1007 which acts as a funnel to direct the mixture to the mould. Mould 1008a is one of four moulds mounted on a turntable platter 1010 driven by turntable motor 1011, but only two of the moulds (1008a, 1008b) are shown for the purposes of clarity. The turntable platter 1010 is rotated by the turntable motor 1011 to move respective moulds into (and out of) the mixture-receiving position underneath the end of the screw conveyor 1003. Mould 1008a is shown in Figure 1 as being in the mixture- receiving position. An indexing pin 1012 engages with a locking hole (reference numeral 1029 in Figure 2a) in the turntable platter 1010 to prevent unwanted movement of the turntable platter 1010 once a mould is located in the mixture-receiving position. An indexing pin driver 1013 causes the indexing pin to engage with the locking hole.

When in the mixture-receiving position, the mould 1008a is aligned with a tamper 1004 that is used to compress the mixture in the mould 1008a to form a filter element precursor body. Once the mixture in a mould has been compressed, the indexing pin 1012 is withdrawn to permit rotation of the turntable platter 1010, moving an empty mould into the mixture-receiving position and moving the mould containing the filter element precursor body into an unloading position.

The operation of the apparatus is controlled by control panel 1015.

The structure of the moulds 1008a, 1008b and the portion of the apparatus associated with tamping will now be described in more detail with reference to Figures 1 and 2a. Figure 2a shows a cut-away diagram of the tamper 1004, with a mould 1008a in a mixture-receiving position. The mould 1008a comprises a cylindrical outer wall 1031 and a cylindrical inner piece 1009a. At the lower end of the mould 1008a, an annular end-piece 1030 extends between the outer wall 1031 and the inner piece 1009a. The inner piece 1009a, outer wall 1031 and end-piece 1030 form a receptacle for the receipt of the mixture comprising a plastics material. The surfaces of the inner piece 1009a and the outer wall 1031 that come into contact with the mixture have been coated with a low surface energy material (in this case, polytetrafluoroethylene) . This low surface energy material helps resist adhesion of the mixture and any subsequently-produced filter element to the walls of the mould 1008a. The lowermost part of the inner piece 1009a locates in a cavity 1028 in the turntable platter 1010 provided for accurate and convenient siting of a mould.

Once the mixture has been delivered to the mould 1008a via the receiver 1007, the mixture may be compressed. The tamper 1004 comprises a cylindrical tamping member 1006 which is provided with an annular tamping head 1022. The tamping member 1006 and tamping head 1022 are sized so that they may be received in the gap between the mould inner piece 1009a and the mould outer wall 1031. The electrically-operated piston 1020 engages with the tamping member 1006 and urges the tamping head 1022 into compressive contact with the material in the mould 1008a.

The apparatus is provided with a return mechanism in the form of a helical spring 1025 mounted around a cylindrical insert 1026. When the tamping member 1006 is urged towards the mould 1008a, the lower end of the helical spring 1025 abuts against the upper surface of lip 1027 provided on the mould inner piece 1009a. The upper end of the helical spring 1025 abuts against the tamping member 1006. As the tamping member 1006 is urged further downwards the helical spring 1025 becomes more compressed, increasing the force in the spring 1025. Once the piston 1020 is retracted, the compressed spring 1025 urges the tamping member 1006 away from the mould 1008a. The cylindrical insert 1026 is provided to support the spring 1025.

The tamping member 1006 is provided with two fill-level pins 1023a, 1023b which protrude through fill-level slots 1024a, 1024b respectively provided in cylindrical body 1005. This arrangement may also be seen in Figure 2B. Referring to Figure 2A, during compression, the tamping member 1006 is moved onto the mixture. The displacement of the tamping member 1006 is dictated primarily by the amount of mixture in the mould 1008a. The position of the fill-level pins 1023a, 1023b are indicative of the amount of mixture in the mould 1008a, and (referring to Figure 2B) the position of the fill-level pin 1023a relative to the scale 1032 provided on the body 1005 permits the user to verify that the correct amount of mixture has been loaded into the mould 1008a.

The cylindrical body 1005 is sized so that it may abut against the end of the mould outer wall 1031.

The piston 1020 is associated with a piston cover 1021. The piston cover is cylindrical and sized to that it may abut against cover 1005.

Those skilled in the art will realize that the gaps shown in Figure 2a between different elements of the apparatus have, in many cases, been exaggerated for the purposes of clarity. The true gaps between elements are, in many cases, smaller than those shown.

Those skilled in the art will realize that the moulds 1008a, 1008b are not part of the apparatus in accordance with the present invention.

The operation of the apparatus of Figure 1 will now be described in further detail with reference to Figures 1, 2A and 2B.

An empty mould 1008a is in a mixture-receiving position. The turntable is locked in this position by indexing pin 1012 which is inserted into locking hole 1029.

A mixture comprising a plastics material is formed by mixing 10% by weight of granules of polyvinyl chloride (PVC) , 80% by weight of granules of polyethylene terephthalate (PET), 8-9% by weight of a commercially available compatibilising agent and 0.02 to 2% by weight of a liquid (typically an organic acid) . The compatibilising agent facilitates the blending together of PET and PVC. Examples of such compatibilising agents include modified polyolefins ("Elvaloy", "Fusabond", "Surlyn" and "Elvanol" agents from DuPont) and styrenic block copolymers ("Styrolux" and "Styroflex" from BASF) . Other compatibilising agents of interest are polycaprolactones (such as the TONE P-767 and P-787 polycaprolactones from Dow Chemical Company) . Also of particular interest are the block-graft copolymers disclosed as compatibilisers in Polymer, Vol. 37, No. 17, August 1996, page 3871-3877 (Braun et al.). Chlorinated polyethylenes have also been recognized as having compatibilising properties in a PVC/high density polyethylene mixture.

The liquid essentially acts as a lubricant to reduce the likelihood of material sticking to the mould. Examples of liquids which may conveniently be used are organic acids, such as acetic acid.

The liquid content is so small that the mixture has a powdery, granular consistency. The mixture is delivered via chute 1002 to the screw conveyor 1003. The screw conveyor transfers the mixture to mould 1008a, via a receiver 1007. It is desirable to use the mixture shortly after preparation; leaving the mixture to stand may result in the liquid evaporating. Once the appropriate amount of mixture had been delivered to the mould 1008a, the mixture may be compressed. Piston 1020 contacts tamping member 1006 and urges tamping head 1022 into the gap between the mould inner piece 1009a and the mould outer wall 1031. The tamping head 1022 is urged into compressive contact with the mixture in the mould 1008a, and the mixture is compressed to form a filter element precursor body. The piston is then withdrawn, and the return mechanism provided by the helical spring 1025 ensures that the tamping member is retracted from the mould 1008a.

The maximum force applied during the compression stroke is of the order of 50-10OkN. The mixture is under compression for a period of about 0.5 seconds. The piston is electrically actuated. It has been found that a hydraulically-actuated piston may be used but applies a force over a longer timescale, the resulting filter element being less satisfactory than if an electrically-actuated piston is used.

The indexing pin 1012 is then removed from the locking hole 1029 and the turntable rotated so that an empty mould (not shown) is located in the mixture-receiving position and mould 1008a, containing the filter element precursor body, being moved to an unloading position. The mould 1008a is then removed from the turntable platter 1010 and placed in an oven (not shown) so that the filter element precursor body may be heated. The filter element precursor body is heated to 100⁰C and kept at 100⁰C for 20 minutes. The temperature is then reduced to 6O⁰C and kept at 60⁰C for 30 minutes. The temperature is then reduced to 40⁰C and kept at 40⁰C for 30 minutes. The temperature is then reduced to 20°C, and kept at 20⁰C for 40 minutes. The filter element may then be removed from the mould; this process includes removing the end-piece 1030 from the filter element. It is expected that the heating process removes substantially all of the liquid from the filter element.

The size of the pores in the filter element may be varied by varying the relative proportions • of PVC and PET used. The size of the pores may also be varied by varying the size of the granules of PVC and PET used, the smaller the granules the smaller the pores in the filter element.

Those skilled in the art will realize that the apparatus of Figure 1 is merely exemplary. It may be more efficient to provide a conveyor belt or the like with many moulds which are subsequently filled with paste. The filled moulds may then be moved to a tamping station provided with one or more tampers. Once tamped, the filter element precursors may be moved to a heating station where the filter elements precursors are heated to remove some or all of the fluid (if present) . Such an apparatus may be substantially automated.

The method described above may be readily adapted in order to change the properties of the filter element. For example, changing the composition of the plastics material can be used to change the properties of the filter element. For example, increasing the mean maximum dimension of the PVC granules used in the mixture gives rise to an increase in pore size. An increase in pore size has been observed when one replaces 0.5mm PVC granules in a mixture with 0.8mm PVC granules .

Claims

1. A method of making a filter element, said method comprising:

5 (i) providing a mixture comprising a plastics material; (ii) introducing said mixture into a mould; (iii) subjecting the mixture to a raised pressure to form a filter element precursor body; and (iv) heating the filter element precursor body. 10

2. A method according to claim 1 wherein the mixture provided in step (i) further comprises a liquid.

3. A method according to claim 1 or claim 2 wherein the

15 mixture provided in step (i) comprises from 2% to 30% by wt . of a poly (chloroalkylene) .

4. A method according to claim 3 wherein the mixture comprises from 60 to 98% by weight of a further

'20 thermoplastic.

5. A method according to claim 3 and claim 4 wherein one or both of the further thermoplastic and the poly (chloroalkylene) is provided in step (i) in granular 25 form.

6. A method according to any one preceding claim wherein step (iv) comprises heating the filter element precursor body to a maximum temperature of .120⁰C.

30

7. A method according to claim 6 wherein step (iv) comprises heating the filter element precursor body to a maximum temperature of from 80°C to 110⁰C.

5 8. A method according to any one preceding claim wherein in step (iii), the material is under compression for from 0.2

L- ^•,'- to 1.0 seconds .

9. A, method according to claim 8 wherein in step (iii) the "10 material is under compression for from 0.2 to 0.6 seconds.

10. A method according to any one preceding claim wherein in step (iii), the material is under compression for from 0.3 to 0.5 seconds .

15

11. A method according to any one preceding claim wherein the maximum compressive force applied in step (iii) is from 1OkN to 100OkN.

20 12. A method according to claim 11 wherein the maximum compressive force applied in step (iii) is from 1OkN to 50OkN.

13. A method according to claim 11 wherein the maximum 25 compressive force applied in step (iii) is from 1OkN to

15OkN.

14. A method according to any one preceding claim wherein one or more of the surfaces of the mould which, in use,

30 comes into contact with the mixture comprising a plastics material is a surface with a low surface energy.

15. A method according to any one preceding claim, wherein the mould is shaped so as to form a cylindrical filter element precursor body.

16. A method according to any one preceding claim wherein the mould is provided with one or more end-fitting casting elements to prevent egress of mixture from the mould once the filter element precursor body has been formed in step (iii) .

17. A method according to any one preceding claim further comprising providing a tamper for compressing the mixture in step (iii) .

18. A method according to claim 17 wherein the tamper comprises a tamping head for contacting the mixture and a means for urging the tamping head into compressive contact with the mixture.

19. A method according to claim 18 wherein the means for urging the tamping head into compressive contact with the mixture comprises an electrically-driven piston.

20. A method according to any one preceding claim further comprising providing a return mechanism for urging the tamping head away from the mixture in the mould.

21. A method according to any one preceding claim further comprising providing a conveyor for moving said mixture comprising a plastics material towards the mould.

22. A method according to claim 21 wherein the conveyor comprises a screw conveyor.

23. A method according to any one preceding claim further comprising providing a receiver for guiding the mixture into the mould.

24. A method according to any one preceding claim comprising providing a plurality of moulds.

25. A method according to any one preceding claim comprising providing a transporter for moving at least one mould into a position in which material may be delivered into at least one or the moulds.

26.. An apparatus for the manufacture of filter elements from plastics materials, the apparatus comprising:

(i) a means for depositing a mixture comprising plastics material into a mould; (ii) a tamper for compressing the mixture comprising plastics material once the mixture is in the mould; and (iii) a means for moving the mould and tamper relative to one another between a first position in which the mixture in the mould may be tamped by the tamper and a second position in which the mixture in the mould may not be tamped by the tamper wherein the tamper is arranged to provide a compressive force for from 0.2 to 1.0 seconds and the tamper is arranged to provide a maximum compressive force of from 1OkN to 100OkN.