FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLEOF THE INVENTION :
NANOFIBER MEMBRANE LAYERED FILTER MEDIA
2. APPLICANT
(a) Solus Filtech
(b) 306 Pashaka, Near Nirmal Hospital, Ring Road, Surat-395002 Gujarat
(c) a partnership firm

(a) Ahmedabad Textile Industry's Research Association (ATIRA)
(b) Vikram Sarabhai Road, P.O. Ambawadi Vistar, Ahmedabad 380015
(c) a Co-Operative Research Organization
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed

FIELD OF THE INVENTION
The invention relates to filter media, and more particularly to filter media incorporating nanofibers of diameter less than 1 micron for high performance.
BACKGROUND OF THE INVENTION
A membrane is usually intended for separation purposes. Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of twentieth century. A wide variety of synthetic membranes are known. They can be produced from organic materials such as polymers and liquids, as well as inorganic materials. The most of commercially utilized synthetic membranes in separation industry are made of polymeric structures. They can be classified based on their surface chemistry, bulk structure, morphology, and production method. The chemical and physical properties of synthetic membranes and separated particles as well as a choice of driving force define a particular membrane separation process. The most commonly used driving forces of a membrane process in industry are pressure and concentration gradients. The respective membrane process is therefore known as filtration. Synthetic membranes utilized in a separation process can be of different geometry and flow configuration. They can be also categorized based on their application and separation regime.
Filter media with nanofibers is known in the prior art. The use of nanofibers has increased because of the properties of the nanofibers that have ultra fine fibers with a high surface area per unit mass that increases the efficiency of the applications. Nanofibers have significant use in the area of filtration since the surface area is substantially greater compared to conventional filter media and a very high pore density. Highly porous structure makes it suitable for the use in variety of filtration techniques.
The nanofibers are provided in a thin layer laid down on a supporting substrate and/or used in conjunction with protective layers in order to attain a variety of benefits, including increased efficiency, reduced initial pressure drop, cleanability, and reduced filter media thickness and/or to provide an impermeability barrier to certain fluids, such as water droplets.

The present invention relates to filter media, and more particularly to filter media incorporating nanofibrous membrane for higher efficiency and performance. The invention may be used in a variety of applications for filtering fluid, including gas such as air, exhaust, and crankcase ventilation gas, and including liquid such as oil, fuel, coolant, water, and hydraulic fluid.
SUMMARY OF THE INVENTION
Filter efficiencies are typically defined as the proportion of the particulate, entrained in the mobile fluid phase, removed by the filter. Filter lifetime is typically considered to be related to the period of time that the pressure drop across the filter remains below a certain predetermined level to permit acceptable operating parameters for the filter and operating equipment. A filter must obtain a sufficient removal efficiency while maintaining a sufficiently low pressure drop to obtain useful performance. A high pressure drop is characteristic of poor operating efficiency for the equipment using the filter.
The tightly interlocked nature of efficient fiber layers can cause increased pressure drop across the fiber layer will substantially and rapidly increase when contacted with such a fluid particulate stream. While these filters are excellent in initial operation, the filter lifetime, not efficiency is often a problem. The filters are adequate for the task but must be replaced. In view of the rapidity that such structures can increase in pressure drop, i.e. have substantially reduced service lifetimes, improvements to such filters are needed.
As is typical in any technological application, the improvement of both filter efficiency and lifetime is a long sought goal for filter manufacturers. In view of this, substantial need exists in the art for filter technology and structures that can obtain increased filter lifetime while maintaining or improving filter efficiency.
To solve the above problems a substantially improved filter media can be obtained by using a filter media having a controlled amount of nanofiber membrane layer onto a media substrate or structure. By forming the nanofiber membrane layer filter efficiency and lifetime can be increased.

In a preferred embodiment, the nanofiber membrane layer is placed on an upstream surface of the substrate. In other case, the nanofiber membrane layer is placed on a downstream surface of the substrate. The media can be formed into a filter structure in a variety of filter structure geometries and formats.
The nanofiber membrane layer is formed on the substrate. Filtration performance is obtained largely as a result of the nanofiber barrier on the substrate blocking the passage of particulate. Substrate structural properties of stiffness, strength, pleatability are provided by the substrate to which the nanofiber adhered. The nanofiber interlocking networks have as important characteristics - relatively small openings, orifices or spaces between the fibers. Such spaces typically range, between fibers, of less than 10 microns, about 0.01 to 5 microns, preferably about 0.1 to 2 microns.
The filter products comprise a nanofiber membrane layer formed on a substrate. Fibers from synthetic, natural sources (e.g., polyester and cellulose layers) are thin, appropriate substrate choices. The nanofibers adds less than 3 microns in thickness to the overall filter structure comprising nanofiber membrane layer plus substrate. In service, the filters can stop incident particulate from passing through the nanofiber membrane layer and can attain substantial surface loadings of trapped particles. The particles comprising dust or other incident particulates rapidly form a dust cake on the nanofiber surface and maintains high initial and overall efficiency of particulate removal. Even with relatively fine contaminants having a particle size of about 0.01 to about 1 micron, the filter media comprising the nanofiber membrane layer has a very high dust capacity. The overall structure of the filter materials provides an overall thinner media allowing improved media area per unit volume, reduced velocity through the media, improved media efficiency and reduced flow restrictions.
Brief description of drawings

Figure 1 shows experimental data comparing the fractional filter efficiency of the conventional filter media vs the nanofiber membrane layered media.
Detail Description of the preferred embodiments
The present invention is directed to a filter medium comprising of flat surfaced filter substrate, the substrate was coated with a layer of polymeric nanofiber membrane; the nanofiber membrane was prepared using free surface electrospinning process.
According to the invention, a multilayered membrane construction is provided comprising a first layer consisting of a porous substrate layer and a second of the said nanofiber membrane, a multilayered construction in which the nanofiber membrane is sandwiched between two porous layers are possible, further a sandwiched structure wherein a porous substrate layer coated with nanofiber memebrane layer is folded face up to form a double layer wherein the nanofiber membrane layer facing each other, further a sandwich structure wherein two or more nanofiber coated porous substrate layers are stacked to create a composite media as per the required performance criterion of the final composite filter media thus formed.
The nanofiber membrane of the invention comprises of a composition that has physical properties that provide improved efficiency and service lifetime in the unique filter structure. The polymeric materials of the invention are compositions that have physical properties that can also permit the polymeric material, in a variety of physical shapes or forms, to have resistance to the degradative effects of humidity, heat, air flow, chemicals and mechanical stress or impact while maintaining effective filtration during use.
Nanofibers can be made from a wide array of materials ranging from organic polymers, inorganic polymers, carbon, ceramic, silica, metal oxides and nonmetallic solids. The nanofibers produced by the invention include, but are not limited to polyvinyl chloride (PVC), polyolefin, polyacetal, polyester, cellulose ether and ester, polyalkylene sulfide, polyarylene oxide, polysulfone, modified polysulfone polymers and polyethylene, polypropylene, polyvinyl alcohol,

various nylons (polyamides such as nylon 6, nylon 6-6 and other nylons), PVDC, polystyrene, polyacrylonitrile (PAN), PMMA, PVDF. There are also a wide variety of solvents available that can be employed.
The solvent chosen and used depends upon the desired polymer(s) as the solvent should be suitable for sufficiently dissolving the polymer. For example, water is not usable as a solvent for many polymers including common nylon (e.g. such as nylon 6 or nylon 6-6). In such instances, another solvent such as formic acid may be chosen for polymers such as common nylon. Solvents for making a polymeric solution for electrospinning may include acetic acid, formic acid, m-cresol, tri-fluoro ethanol, hexafluoro isopropanol chlorinated solvents, alcohols, water, ethanol, isopropanol, acetone and N-methyl pyrrolidone, and methanol. The solvent and the polymer can be matched for appropriate use based on sufficient solubility of the polymer in a given solvent.
An important characteristic of an embodiment is that the nanofiber membrane is formed on a substrate that is preferably a filter media substrate having some filtration capabilities. Many filter media substrates comprise at least in part or in full natural cellulose fibers. There are many possibilities to include natural fiber and synthetic fiber substrates, to include spun bonded fabrics, non-woven fabrics of synthetic fiber, and non-wovens made from the blends of cellulose materials, synthetics and glass fibers, non-woven and woven glass fabrics, plastic screen like materials both extruded and hole punched, and various other materials, not limited to those mentioned here. All of these materials typically come in sheet form; this sheet can further be either plain of corrugated based on the application. The material can be readily purchased in roll form. Substrate sheets with a fine fiber layer can be formed into a filter structure that is placed in a fluid stream including an air stream or liquid stream for the purpose of removing suspended or entrained particulates from that stream.
The filter media according to one of the embodiment of the present invention includes a first substrate layer, typically a permeable coarse fibrous media, made from a natural or synthetic fiber such as cellulose, polyester, nylon, etc. Preferably the substrate layer by itself (that is

without the nanofiber membrane layer) has an average diameter of at least 50 microns, typically and preferably about 10 to about 100 microns. Also preferably the substrate layer by itself has a basis weight of 115 grams/ meter, preferably about 25 to about 200 g/ meter . As for other typical characteristics, preferable thickness of fibrous substrate media is at least 0.40 mm thick, and typically and preferably is about 0.10 mm to about 0.85 mm thick; and preferably has a burst strength of between about 50 kPa and about 500 kPa.
In preferred filter media arrangements, the substrate layer, typically of permeable coarse fibrous material, comprises a material, which would exhibit a permeability of 280 liters/meters2/sec at 200 Pa.
In a preferred embodiment of the invention, the permeable coarse fibrous material comprises a material which, if evaluated separately from a remainder of the construction by the Frazier permeability test, would exhibit an air permeability of at least 1 liters/meters2/sec, and typically and preferably about 2-1000 liters/meters /sec. at 50 Pa pressure. Herein when reference is made to efficiency, unless otherwise specified, reference is meant to efficiency when measured according to ANSI/ASHRAE Standard 52.2, with 0.35 micron NaCl aerosols at 5 m/min.
In typical application, nanofiber membrane is placed on the substrate, the nanofiber membrane comprises a nanofiber having a diameter of about 0.05 micron to 1 micron, preferably between about 0.1 micron and about 0.06 micron, or even between about 0.1 micron and about 0.4 micron, or even between about 0.1 micron and 0.3 micron formed in a layer that has thickness of less than about 5 microns, preferably about 0.05 micron to 2.5 micron and preferably the nanofiber layer by itself has a basis weight of about 0.0005 g/ meter2 to about 3.0 g/ meter2. Each nanofiber membrane comprises an interlocking randomly oriented mesh of fibers that results in a mesh having broad distribution of pore size opening. While any nanofiber layer can have openings of a variety of sizes, the nanofiber layers of the invention have substantial number of pores of a size that range from very small, i.e. about 0.001 micron to about 5 micron, but often range between about 0.1 micron and 2 micron for effective filtering.

The nanofiber membrane layer can be made by the process of electrospinning a polymer solution on a moving substrate, and optionally one or more other components also dissolved or dispersed in the polymer solution. In such a process a polymer solution is introduced into an electric field, and nanofibers are formed under the effect of said electric field.
The nanofibers so formed are typically deposited on a substrate. By performing the electrospinning process in a semi-continuous manner, and using a movable substrate, a semicontinuous layer of deposited nanofibers is formed. For the electrospinning process any suitable technology may be applied, including methods known to the skilled person, multi-nozzle electrospinning with the use of multi-nozzle devices, typically a spinneret with a series of nozzles, and via nozzle-free electrospinning with the use of nozzle free devices, for example using a Nanospider™ apparatus or bubblespinning.
Multi nozzle spinning may optionally be combined with a forced airflow around the nozzles, as in electro-blowing. Classical electrospinning is illustrated in US104,127,706, hereby incorporated by reference. In such processes Taylor cones are formed from the solution either from the nozzles of from a freestanding liquid when applying a high voltage. To create such Taylor cones the voltage typically has to be atleast 2.5 kV. The voltage may be as high as 50 kV or 60 kV or even higher, e.g. 65 kV.
Suitably the voltage is at least 10 kV, preferably at least 20 kV and more particular atleast 30 kV. A voltage sufficiently high to form Taylor cones is also referred as a high voltage.
Typically such an electrospinning process being either a nozzle-free electrospinning with the use of nozzle free device or a multi-nozzle electrospinning process with the use of a multi-nozzle device, comprises steps wherein- applying a high voltage between a spinneret comprising a series of spinning nozzles and a collector, or between a separate electrode and a collector-feeding a stream of polymer solution comprising a polymer and a solvent to the spinneret-whereby the polymeric solution exits from the spinneret through the spinning nozzles and transforms under the influence of the high voltage into charged jet streams, whereby the jet

stream are being deposited on or taken up by the collector or a support layer- whereby the polymer in the jet stream solidifies prior to or while being deposited on or taken up by the collector or the support layer whereby the nanofibers are formed.
In a special embodiment, the invention relates to a process for the preparation of nanofibers using a nozzle free or free surface electrospinning process comprising the steps below:
-a high voltage is applied
-a polymer solution comprising a polymer and a solvent is fed to the nozzle free device and
transformed under the influence of the high voltage into charged jet streams
-the jet streams are deposited on a substrate or taken up by a collector, and
-the polymer in the jet streams solidifies thereby forming nanofibers.
After the preparation of the nanofiber, in preferred embodiments an annealing step is applied. It has been observed that annealing of the nanofiber membrane layer at elevated temperature results in a significant improvement in efficiency and performance of the said filter media. For the annealing step the nanofiber membrane layer media is heated for a certain period to a temperature range above 120°C, and preferably to a temperature in the range of 140°C to 250°C. Heating the polymer fibers results in a significant increase of the molecular weight in combination with improved mechanical properties. Suitably, for the annealing the membrane layer is kept for a period of 15 minutes to 2 hours, at a temperature of 160°C to 230°C, a higher temperature, such as from 180°C to 230°C, allow for shorter annealing times of 10 - 30 minutes.
Preferably the layer of nanofiber membrane prepared from free surface electrospinning process, secured to the surface of the layer of permeable coarse fibrous media have average fiber diameters of no greater than about 1 microns, generally and preferably no greater than about 0.75 micron, and typically and preferably have fiber diameters smaller than 0.5 micron and within the range of about 0.05 to 0.5 micron. Also, preferably the nanofiber membrane layer secured to the permeable coarse fibrous material has an overall thickness that is no greater than about 5 microns, more preferably about 0.05 micron to 2.5 micron, and preferably that is within a

thickness of about 1-8 times (and more preferably no more than 5 times) the average fiber diameter of the layer.
FIG. 1 illustrates the fractional filter efficiency of nanofiber filter media of the invention and commercial filter media with no nanofiber membrane layer. The first structure is a commercial filter media (labelled - blk), this media has no nanofiber membrane layer. The commercial filter media is layered with a nanofiber membrane of the invention (labelled - nf), it is evident from the graph that the nanofiber membrane layered media provides significantly improved filtration efficiency compared to the commercial filter media. The nanofiber membrane layer shows upto 4 fold or 400% improved efficiency for 0.35 micron particle size, at 5 m/min according to ANSI/ASHRAE Standard 52.2.
Certain preferred arrangements according to the present invention include filter media as generally defined, in an overall filter construction. Some preferred arrangements for such use comprise the media arranged in a cylindrical, pleated configuration with the pleats extending generally longitudinally, i.e. in the same direction as a longitudinal axis of the cylindrical pattern. For such arrangements, the media may be imbedded in end caps, as with conventional filters. Such arrangements may include upstream liners and downstream liners if desired, for typical conventional purposes.
In some applications, media according to the present invention may be used in conjunction with other types of media, for example conventional media, to improve overall filtering performance or lifetime. For example, media according to the present invention may be laminated to conventional media, be utilized in stack arrangements; or be incorporated (an integral feature) into media structures including one or more regions of conventional media It may be used upstream of such media, for good load; and/or, it may be used downstream from conventional media, as a high efficiency polishing filter.
According to the present invention, methods are provided for filtering. The methods generally involve utilization of media as described to advantage, for filtering. As will be seen from the

descriptions and examples below, media according to the present invention can be specifically configured and constructed to provide relatively long life in relatively efficient systems, to advantage.
Example
The following example is provided to illustrate the present invention and should not be constructed as limiting the scope of invention.
The media can be a polyester synthetic media, polypropylene spunbonded non-woven media, a microglass fiber media, a media made from cellulose, or blends of these types of materials.
The example cited here is of a resin cured cellulose media: a basis weight of about 115 gsm, a thickness of 0.41 mm; air permeability of about 280 l/(m2*s) at 200 Pa pressure when tested per EN ISO 9237; pore size of about 40 - 50 microns; burst strength of about 180 kPa. The cellulose media has been treated with PA6 nanofiber membrane layer, for example, fibers having a size (diameter) of 0.5 micron or less. A variety of methods can be utilized for application of the nanofiber to the media. Further, this composite media is subjected to annealing at a temperature of 180°C for a period of 10 minutes. Enough nanofibers typically would be applied until the resulting media construction would have an efficiency of 95% according to ANSI/ASHRAE Standard 52.2, with 0.35 micron NaCl aerosols at 5 m/min.

We Claim:
1. A composite filter media comprising of flat surfaced filter substrate coated with a
layer of nanofiber membrane wherein;
the said flat surface filter substrate is cellulosic having air permeability in the range 100 l/(m *s) to 2000 l/(m *s) at 200 Pa air pressure when tested as per EN ISO 9237;
- the said layer of nanofiber membrane is polymeric and made of fiber having GSM ranging between 0.0005 gsm to 3 gsm;
- the said filter media thus formed has filter efficiency in the range of 50% to 95% for 0.35 micron NaCl aerosols at 5m/min. as per ANSI/ASHRAE Standard 52.2.

2. The said flat surface filter substrate as claimed in claim 1 is either resin treated or is untreated.
3. The filter media of claim 1, wherein the said filter media is subjected to annealing at a temperature of 120°C to 230°C for period of 15 minutes to 2 hours, a higher temperature, such as from 180°C to 230°C, for shorter annealing times of 3 - 30 minutes, if the cellulosic substrate is resin treated.
4. The said layer of nanofiber membrane as claimed in claim 1 are made of synthetic polymeric material such as, but not restricted to: Polyamide, Polyvinyl alcohol, Polyvinylidine fluoride, Polystyrene, and Polyphenylene sulfide.
5. The said layer of nanofiber as claimed in claim 1 is having fiber dia in the range 50 nm to 500 nm.

6. The filter media of claim 1, wherein the nanofiber membrane was prepared using free surface electrospinning process.
7. The said composite filter media having resin treated substrate annealed at temperature 180°C for 12 minute coated with PA6 nanofiber of average size of fiber 80nm with weight 0.05 gsm shows filter efficiency of 95%when measured by 0.35 micron NaCl aerosols at 5m/min. as per ANSI/ASHRAE Standard 52.2.