FIELD OF THE INVENTION
The present invention relates to a multi layered media having nanofibers for use in filters and a process for its preparation. The invention also relates to an apparatus for the preparation of said multi layered media.
BACKGROUND OF INVENTION
In automotive industry, need for an improved engine management system to protect the injection system from ultimate failure is growing. In automotives, engines are subjected to contaminants from two different sources such as contaminants produced from combustion and outside environment. Contaminants are produced when the engine is in operating condition.
The demand for new development of engine management systems has been increased and to prevent the injection systems from untimely failure, filters with increased filter efficiency and life are needed. In automotive sector, the emission norms are more stringent, due to which working tolerance between the moving parts in the engine is reduced. This needs very high efficiency of filtration of finer particles in automotive filtration to reduce wear of the engine and also it requires longer change over of filters. Hence, the development of filters with fine and ultra fine fibers such as melt blown fibers and nanofibers are essential to enhance their contaminant holding capacity.
OBJECTS OF THE INVENTION
The main object of the invention is to develop a multi layered media for the filters.
Another object of the invention is to develop an apparatus for the production of said multi layered filters.
Another object of the invention is to prepare polymeric nanofibers using a simple, cost effective, safe and eco friendly technique.
Still another object is to develop multilayer composite filters having high capacity for dust holding and that efficiently filter finer particles.
Yet another object is to develop filters with higher surface area with uniform pore size distribution.
Still another object of the invention is to develop composite filter media that are more stable than the conventional filter.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Schematic representation of multi layer media laminating machine integrated with nanofiber generation setup. The description of the reference numerals is as follows:
1. Roller with cellulose media
2. Idler roller (Coarse side media contact)
3. Reservoir with adhesive
4. Roller for coating adhesive on coarse side of media
5. Idler roller (Fine side media contact)
6. Fine side media contact

6. Nanofiber generation setup
7. Roller with melt blown media

9. Idler roller (Coarse side media contact)
10. Pressing Rollers
11. Heater
12. Winding roller for winding multi layer media 13.Nano fibers
14. Multi needle spinnerets
Figure 2: Schematic depiction of single set of multi needle spinneret for the generation of nanofibres.
Figure 3: Schematic representation of double set of multi needle spinneret for the generation of nanofibres.
The description of the reference numerals in Fig 3 an 4 are as follows:
1. Spinneret
2. Positive voltage
3. Metallic collector
4. Media
5. Negative voltage
6. Enclosure
SUMMARY OF THE INVENTION
The present invention provides a multi layered media for filters and a process for its preparation.
The invention also provides an apparatus for the preparation of said multi layered media.
In preferred embodiment filters are used in automotive industry.
In one embodiment the multi layered media comprises nanofibers.
In another embodiment the nanofibers are based on aqueous or non aqueous polymers such as PVA and PAN etc..
In another embodiment the diameter of the fibers is in the range 50 nm to 800 nm with a tolerance of 50 nm.
In another embodiment nanofibers are sandwiched between a synthetic media and cellulose media using chemical bonding for mass production.
In another embodiment the nanofibers are uniformly distributed over the media surface.
In another embodiment electrospinning apparatus for producing nanofibres comprises a reservoir for storing polymeric solution; a single syringe horizontal setup which is connected to said reservoir for delivering said solution; a power source generating high voltage for transmitting said voltage to said syringe setup; and a collector/substrate for collecting said polymeric nanofibers.
In another embodiment the electrospinning process setup/ nanofiber generation setup comprises multi needle spinneret.
In another embodiment a multi needle spinneret is designed and developed for the generation nanofibers in the range of 0.01 GSM to 2 GSM.
In another embodiment an electric field of strength 5 kV to100kV is applied to the tip of needle so that the charge overcomes the surface tension of the deformed drop of polymer solution can be discharged into nanofibers.
In another embodiment the multi needle spinneret moves on cellulose media at the linear speed in the range of 1 m/min to 10 m/min.
In another embodiment the electrospinning process setup/ nanofiber generation setup is integrated with the laminating media process setup.
In another embodiment different layers of multi layered media are joined by using a different polymeric permeable adhesive between the layers.
In another embodiment the adhesive is water based and is free of any solvent. In preferred embodiment the adhesives used are different polymer solutions of acrylic, PVA and reactive polyurethane.
In yet another embodiment the filter media comprises two layers wherein first layer comprises phenol formaldehyde resin impregnated cellulose media and second layer comprising polyacronylonitrile nanofibers. In another embodiment filter media comprises a third layer of melt blown media.
In another embodiment when the filter media is used as an air filter media, said filter media comprises a second layer of polyacronylonitrile nanofibers and a third layer of melt blown media comprising polymeric nanofibers coated cellulose media in the range of 0.01 GSM to 2 GSM.
In another embodiment multilayered media has an efficiency to filter a range of 98.5% to 99.99% of 0.1 micron particle size in terms of air, 97% to 99.99% of 3 micron particle size in terms of fuel and 94% to 98% of 15 micron particle size in terms of oil filtration media. DETAILED DESCRIPTION OF INVENTION
The present invention relates to a multi layered media for automotive filters and a process for its preparation. The invention also provides an apparatus for the preparation of said multi layered media.
Multi layer media approach was adopted to make a media with gradient density pores. The multi layer media contains three layers joined together in which the primary layer consists of more porous melt blown that helps in increasing the dust holding capacity and the secondary layer of nanofibers coated on cellulose media that helps in attaining the efficiency targets. The two medias were joined with special adhesives, which did not alter the filtration properties and also had the desired fuel resistant properties.
The process of joining the multi layered media is being carried out by using different polymer solutions such as acrylic, PVA and reactive polyurethane. The nanofibers are coated on the cellulose media having the nano fibre diameter in the range of 100 run to 600 nm with a tolerance of 50 nm. The media in terms of melt blown, spun bond, spun less, air laid etc. is laminated over the nano coated cellulose media by using laminating machine. Preliminary experiments were carried out in developing the multi layered media by varying the process parameters in terms of roller speed of media, coater speed, air pressure, needle diameter, electrode spacing distance and polymer concentration on filter media in terms of air, oil and fuel for enhancing the performance.
During the initial stage, the machine was developed for joining the double layered media such as cellulose media acting as base paper media and melt blown media having different GSM. This machine is further modified by installing the electrospinning process setup for depositing the nanofibers over the cellulose media and melt blown media line which is fixed adjacent to nanofiber setup through which the melt blown media is joined by using the polymer based adhesive and finally, this multi layered media gets winded in the reel form. Experiments were
conducted on lab scale for the development of multi layered media and analyze the performance of the media in terms of efficiency and contaminant holding capacity. The development of multi layered media having nanofibers sandwiched between the prefiltering melt blown and cellulose media is one of the most significant characteristics in automotive filters which show the performance in terms of pressure drop, efficiency and contaminant holding capacity.
In the present invention, the development of multi layered media was adopted by joining the electrospinning process setup and laminating media process setup. The electrospinning process is used for generating nanofibers using multi needles having diameter in the range of 0.5 mm to 1.5 mm in different spinneret design and these nanofibres are sandwiched between a prefiltering melt blown media and a fine supporting cellulose filter media This approach has significantly improved particle retention efficiency and water separation efficiency in comparison to standard filter media with enhanced dust holding capacity in fuel applications.
The process for developing a multi layer composite media using multi needle spinnerets having different needle diameters have been developed with the unique features. The process combines both MFSI developed laminating machine and the electrospinning setup generating nanofibers with the other layers of the composite media in terms of melt blown and cellulose media.
To achieve more efficiency targets beyond the target of present global competitors, multi layer media setup integrated with nanofiber has been developed at Mahle Filter Systems India that has given cutting edge performance in efficiency targets, which is in the range of 98.5% to 99.98% of 0.1 micron particle size in terms of air, 97 % to 99.5% of 3 micron particle size in terms of fuel and 94% to 98% of 15 micron particle size in terms of oil filtration media.
The multi layer media setup has been developed in such a sequence that coarse side cellulose media moves towards the coating roller and the roller which is partially dipped in the adhesive bath. At the time of operation, the roller picks up the adhesive and supplies on the coarse side of cellulose media by ensuring uniform coating of the adhesive in very thin layer so as to minimize the drop in permeability of media. . The adhesive used for joining process is specially developed so that there is no blockage of pores occurred on the surface of media. This type of adhesive is water based and does not require any solvent for dilution. The speed of the coating roller is controlled through variable frequency drive and the control panel is fixed on the operating side of machine which controls the quantity of adhesive to be applied on the surface of the cellulose media. The adhesive based cellulose media further moves towards the nanofibre
generating machine so that nanofibres adhere on the surface of the media. If the quantity of adhesive is more, it will cause blockage of pores on the surface of coarse side of cellulose media.
The nanofibers are generated by electrospinning process. Electrospinning is a process by which a charged liquid polymer solution is introduced into an electric field. In this electrostatic technique, a high electric field is generated between a polymer liquid contained in a spinning dope reservoir with a capillary tip or spinneret and a metallic fiber collection ground surface. When the voltage reaches a critical value, the charge overcomes the surface tension of the deformed drop of the suspended polymer solution formed on the multi needle spinneret aperture and a jet is produced. This stretching process is accompanied by the rapid evaporation of the solvent molecules that reduces the diameter of the jet, in a cone shaped volume called the "envelope cone". The liquid polymer solution is dispensed via a spinneret attached to a syringe tube at certain voltage and is deposited on a conductive material at ground (0-100 kV) located at a certain distance form the spinneret location.
The multi needle spinneret design has been developed and executed for the generation of nanofibers in collaboration with IIT Delhi. It consists of non conductive cylindrical body connected with multi needle spinneret having eight needles which is filled with polymer solution and it is pressurized in the range of 0.1 bar to 1 bar using a filter regulator and dry air/gas. The needle diameter is in the range of 16G to 22G and the needles are aligned and spring loaded with copper plate. High voltage generator which consists of positive and negative polarity in the range of 0-500 kV having the power in the range of 10W- 5kW watts is fixed besides the multi needle spinneret to supply positive polarity to the needles and negative polarity to the collector plate.
The process uses an electric field to draw a polymer solution from the multi needle spinneret tip of a capillary to a collector plate. A high voltage in the range of 5 kV to 100 kV is applied to the polymer, which causes a jet of the solution to be drawn toward a grounded collector. The fine jet stream of nanofibers is formed in nanometer range, which is collected on a web of conventional filter media passing over the grounded collector.
The metallic collector plate is a fixed plate which is kept normal to the syringe needles. When high voltage is applied to the syringe needles having polymer solution, the solution gets charged and ejects a charged jet which generates nanofiber and collects on the substrate over electrically grounded metallic plate. This setup is covered with non conductive cabinet and the nanofibers are deposited on the surface of adhesive based coarse side cellulose media moving from the coating roller. Using this setup, the droplet free nanofibers were generated and
deposited on the surface of the filter media in terms of air, oil and fuel filter applications and it is used for mass production.
The roller having melt blown media is fixed on the unwinder stand and the roller rotates by the movement of drag. The media is passed through the idler roller and touches the nano coated coarse side cellulose media before pressing and the multi layer media together pass through the pressing roller and winded by the winding roller to maintain tension and alignment of the media respectively.
Air Filter:
In air filter applications, the efficiency of 0.1 microns was increased to close level 99.92 % from 99.32% and 0.3 microns was increased to 100% as per ISO 5011 after depositing the nanofibers generated using different polymers over the air filtration media. This corresponds to higher improvement in efficiency in depositing the nanofibers.
Fuel Filter:
In fuel filter applications, the efficiency of 3 micron particle size was increased to close level in the range of 98% to 99% from 87% and 5 microns was increased to 100% as per ISO TR 13353 after depositing the nanofibers generated using different polymers over the fuel filtration media. This leads to 14% improvement in efficiency in depositing the nanofibers. It is due to the fact that the media forms a higher surface area and hence larger void volume is generated and forms uniform pore size distribution by use of nanofibers.
Oil filter:
In oil filter applications, the efficiency of 15 micron particle size was increased to close level of 94% to 96% from 85% and 5 microns was increased to 100% as per ISO 4548 after depositing the nanofibers generated using different polymers over the fuel filtration media. This leads to 12% improvement in efficiency in depositing the nanofibers.
The invention is described hereinafter with reference to the figures of accompanying drawings and should not be taken as limiting to the scope of invention.
Figure 1 shows the schematic representation of multi layer media laminating machine integrated with nanofiber generation setup. The description of the reference numerals is as follows:
1. Roller with cellulose media
In the initial stage, the cellulose media is loaded on the roller in which the coarse side
media on the top surface while media is moving at linear speed. Roll holding
arrangement is provided on the shaft to keep the rolls of cellulose media to its position. The roll rotates by the drag tension of the web.
2. Idler roller (Coarse side media contact)
Idler roller is fixed before the coating roller in order to avoid tension so that the coarse side media contact of cellulose media is moving freely to the coating roller.
3. Reservoir with adhesive
The reservoir is fixed below the coating roller in which it is filled with adhesive for coating the coarse side of the cellulose media on the moving web.
4. Roller for coating adhesive on coarse side of media
The coating roller which is equipped with the variable frequency drive with speed control mechanism supplies the adhesive to the coarse side of cellulose media in the moving web. The coating roller is dipped partially in the reservoir having adhesive so that while rotating, the roller picks up the adhesive and supplies the adhesive to the moving web. The quantity of adhesive is controlled by the speed of the roller.
The cellulose media is already treated with silicon to ensure surface coating of thin film on coarse side of media. The design of roller and the media surface properties after silicon treatment are such that the cellulose media picks up very limited quantity of the adhesive required for sufficient joining of two layers and ensures minimum drop in permeability.
5. and 6. Idler roller (Fine side media contact)
Idler roller is fixed after the coating roller to maintain uniform tension so that the fine side media contact of cellulose media is moving freely from the coating roller to nanofiber generation setup. 7. Nanofiber generation setup
It consists of non conductive cylindrical body connected with multi needle spinneret having eight needles which is filled with polymer solution and it is pressurized in the range of 0.1 bar to 1 bar using filter regulator and a dry air/gas. The needle diameter is in the range of 18G to 20G and the needles are aligned and high voltage line is connected to spring loaded with copper plate. High voltage generator which consists of positive and negative polarity (0-500 kV) having the power of 100 watts is fixed besides the multi needle spinneret to supply positive polarity to the needles and negative polarity to the collector plate.
The metallic collector plate is a fixed plate which is kept normal to the syringe needles. When high voltage is applied to the syringe needles having polymer solution, the solution gets charged and ejects a charged jet which generates nanofiber and collects on the substrate over electrically grounded metallic plate. This setup is covered with non conductive cabinet and the nanofibers are deposited on the surface of adhesive based coarse side cellulose media moving from the coating roller. Using this setup, the droplet free nanofibers were generated and deposited on the surface of the filter media in terms of air, oil and fuel filter applications and it is used for mass production.
8. Roller with melt blown media
The roller having melt blown media is fixed on the unwinder stand and the roller rotates by the movement of drag. The media is passed through the idler roller and touches the nano coated coarse side cellulose media before pressing and the multi layer media together pass through the pressing roller and winded by the winding roller.
9. Idler roller (Coarse side media contact)
Idler roller is fixed after the melt blown media roller to maintain uniform tension so that the coarse side media contact of melt blown media is moving freely to the pressing roller surface.
10. Pressing Rollers
Pressing roller consists of set of top and bottom rollers. The bottom roller is slightly larger in diameter than the top roller and the top roller can be moved vertically to adjust the clearance between the two rollers. These rollers rotate by the weight of moving paper. This arrangement helps in keeping the two layers joined together before going to the winder and the heater is provided for drying the multi layered media which is kept adjacent to the bottom roller.
11. Heater
Heater is provided for the drying of double layered media after joining the media with pressing roller.
12. Winding roller for winding multi layer media
Winding roller contains rubber covered bottom roller and top shaft. Variable frequency drive is provided to the bottom roller with speed control arrangement. The core tube is placed on the top shaft, on which paper gets winded by friction between the core
covered shaft and the rubber covered roller. This arrangement helps in proper winding of the composite layers with required slight pressing during winding. 14. Multi needle spinnerets
Multi needle spinnerets having twelve needles are used for generating the nanofibers at the deposition rate in the range of 0.01 GSM to 2 GSM with the linear speed in the range of 0.5 m/min to 10 m/min.
Figure 2 shows the schematic sketch of single set of multi needle spinneret for the generation of nanofibres. It consists of non conductive cylindrical body connected with multi needle spinneret having eight needles which is filled with polymer solution and it is pressurized in the range of 0.1 bar to 1 bar using filter regulator lubricator unit (FRL). The needle diameter is in the range of 16G to 22G and the needles are aligned and spring loaded with copper plate.
High voltage generator which consists of positive and negative polarity in the range of 0-500 kV having the power in the range of 10-100 watts is fixed besides the multi needle spinneret to supply positive polarity to the needles and negative polarity to the collector plate. The metallic collector plate is a fixed plate which is kept normal to the syringe needles. When high voltage is applied to the syringe needles having polymer solution, the solution gets charged and ejects a charged jet which generates nanofiber and collects on the substrate over electrically grounded metallic plate.
Figure 3 shows the schematic representation of double set of multi needle spinneret for the generation of nanofibres. These spinnerets are used for generating the nanofibers at higher deposition rate in the range of 0.01- 2 GSM on the surface of media moving at the linear speed in the range of 0.5 m/min to 10 m/min.
ADVANTAGES OF THE INVENTION
■ The preparation of polymeric nanofibre using a simple technique which is cost effective, harmless and eco friendly.
■ Multilayer composite filter of the present invention increases high capacity for dust holding and is highly efficient for filtration of finer particles.
■ Filtration media has its application in oil/fuel filtration.
■ Media forms a higher surface area with uniform pore size distribution which increases the efficiency of the filter.
■ Composite filter media of the present invention is more stable than the conventional filter.
EXAMPLE
The polymeric nanofibers for multilayer filter media are prepared by preparing a solution of aqueous polymer. The polymeric solution is prepared by dissolving said polymeric fibers in a solvent like N-N-di-methyl formamide and Water. The said solution is stored in a syringe. The syringe is provided with a needle to deliver polymeric solution. An electric field of strength 20 kV to lOOkV is applied to the tip of needle so that the charge overcomes the surface tension of the deformed drop of polymer solution can be discharged into nanofibres. The electric field produce charged jet stream of polymeric solution wherein said stream is drawn toward a substrate/collector plate. The charged polymer solution is collected on the substrate in the form of nanofibers. The said substrate/collector comprises conductive material at 0- 100 kV. The said nanofibers are in the diameter range of 50 nm to 800 ran.
A filter media comprises two layers is prepared wherein first layer comprising phenol formaldehyde resin impregnated cellulose media; second layer comprising polyacronylonitrile nanofibers. The second layer comprises polymeric nanofibres coated on cellulose media in the range of 0.1 GSM to 0.5 GSM. The filter media also comprises a third layer of melt blown media. This third layer comprises polymeric nanofibres coated cellulose media in the range of 0.01 GSM to 2 GSM. The layers of multi layer media are affixed by an adhesive and are laminated by passing through rollers and winders.
REFERENCES
1. Doshi, J., and Reneker, D.H., "Electrospinning process and applications of Electrospun fibres", Journal of Electrostatics, Vol. 35, 1995, pp. 151-160.
2. Reneker, D. H., and Chun, I., "Nanometre Diameter Fibres of Polymer, Produced by Electrospinning", Nanotechnology, Volume 7, 1996, pages 216-233.
3. Yarin, A. L., and D.H. Reneker, 'Taylor cone and jetting from liquid droplets in electrospinning of nanofibres' - Journal of Applied Physics. 90 (2001) 4836-4846.
4. Kowalewski, T. A, A.L. Yarin, and S. Blonski. 'Electrospinning of Polymer Nanofibres' Paper presented at The 5th Euromech Fluid Mechanics Conference, Toulouse, France, August 24-28, 2003.
5. Gu, S.Y., J. Ren and G. J. Vancso, "Process optimization for electrospun polyacrylonitrile (PAN) nanofibres precursor of carbon nanofibres", European Polymer Journal, Vol. 41, 2005, pp. 2559-2568.
6. Theron S.A., E. Zussman and A.L. Yarin, "Experimental Investigation of the governing parameters in the electrospinning of polymer solutions", Polymer 45, 2004, pp. 2017-2030.
7. Timothy Grafe, Mark Gogins, Marty Barris, James Schaefer and Ric Canepa "Nanofibres in filtration applications in transportation", Filtration 2001.
8. Yarin. A.L., "Upward needleless electrospinning of multiple nanofibers", Polymer, 45, 2004, pp. 2977- 2980.
9. Dosunmu, O.O., G.G.Chase, W.Kataphinan and D H Reneker, "Electrospinning of Polymer nanofibres from multiple jets on a porous tubular surface, Nanotechnology, 17, 2006, pp.1123-1127.
10. Waclaw Tomaszewski and Marek Szadkowski, "Investigation of Electrospinning with the use of multi-jet electrospinning head", Fibres and Textiles, Vol. 13, No. 4(52), 2005, pp. 22-26.
11. GeunHyung Kim, Young- Sam Cho and Wan Doo Kim, "Stability analysis for multi jets electrospinning process modified with a cylindrical electrode", European Polymer Journal, 2006, pp. 1-8.
12. Theron, S.A., A.L. Yarin, E. Zussman and E. Kroll, "Multiple jets in electrospinning: Experiment and Modelling, Polymer 46, 2005, pp.2889- 2899.

We claim:
1. A method for producing polymeric nanofibers for multilayer filter media comprising:
(i) preparing a solution of aqueous polymer;
(ii) storing the solution of step (i) in a syringe provided with needle for delivering said
solution; (iii)applying an electric field to the needle at a tip thereof so that the charge overcomes the
surface tension of a deformed drop of polymer solution to be discharged into nanofibres; (iv) collecting the charged polymer solution on a substrate, generated in the form of
nanofibres.
2. A method as claimed in claim 1 wherein said polymeric solution is prepared by dissolving said polymeric fibers in a solvent.
3. A method as claimed in claim 2 wherein said solvent is N-N-di-methylformamide and water.
4. A method as claimed in any preceding claim wherein said polymeric solution is exposed to electric field of strength 20 kV to 100kV.
5. A method as claimed in claim 1 or 4 wherein the electric field produces charged jet stream of polymeric solution, said stream being drawn toward a substrate/collector plate.
6. A method as claimed in claim 5 wherein said substrate/collector comprises conductive material at 0-100 kV.
7. A method as claimed in claim 5 wherein the charged polymer solution converts and generates in the form of nanofibres.
8. A method as claimed in any preceding claim wherein said nanofibres are collected on a web of conventional filter media over the said substrate/collector plate.
9. A polymeric nanofiber prepared by a method as claimed in any preceding claim.
10. A polymeric nanofibre as claimed in claim 9 wherein said nanofibre is in the diameter range of 50 nm to 800 nm.
11. A filter media comprises two layers wherein the first layer comprising phenol formaldehyde resin impregnated cellulose media and the second layer comprising polyacronylonitrile nanofibre fibres as claimed in claim 1.
12. A filter media as claimed in claim 11 wherein said second layer comprises polymeric nanofibres coated on cellulose media in the range of 0.1 GSM to 0.5 GSM.
13. A filter media as claimed in claim 10 or 11 wherein said media is for air filter applications.

14. A filter media as claimed in claim 13 wherein efficiency of said air filter media is in the range of 98.5% to 99.98% on 0.1 micron particle size.
15. A filter media as claimed in claim 12 comprising a second layer of polyacronylonitrile nanofibres as claimed in claim 1 and a third layer of melt blown media.
16. A filter media as claimed in claim 16 wherein said third layer comprises polymeric nanofibres coated cellulose media in the range of 0.01 GSM to 2 GSM.
17. A filter media as claimed in claims 12 and 16 wherein said layers are affixed by adhesive.
18. A filter media as claimed in claims 12 and 16 wherein said layers are laminated by passing through rolls and winders.
19. A filter media as claimed in claims 16 and 17 wherein said media is oil filtration media.
20. A filter media as claimed in claim 20 wherein efficiency of said oil filter media is in the range of 94 % to 98% on 15 micron particle size.
21. A filter media as claimed in claim 16 and 17 wherein said media is fuel filtration media.
22. A filter media as claimed in claim 22 wherein efficiency of said fuel filter media is in the range of 97 % to 99.5 % on 3 micron particle size.
23. A filter media wherein said media is prepared by a method of any preceding claim.
24. An electrospinning apparatus for producing polyacrylonitrile nanofibres of claim 1 comprising:

• a reservoir for storing polymeric solution;
• a single syringe horizontal setup which is connected to said reservoir for delivering said solution;
• a power source generating high voltage for transmitting said voltage to said syringe setup;
• a collector/substrate for collecting said polymeric nanofibers.

25. An electrospinning apparatus substantially as described herein before with reference to the drawings.
26. Nanofibre deposit on cellulose media at fine pore size side to increase filtration efficiency and join with melt blown media for duct holding capacity improvement.
27. Nanofibre deposit on cellulose media at corse pore size side to increase filtration efficiency.