WO2007074997A1

WO2007074997A1 - Filter element for cleaning air and process for preparing the same

Info

Publication number: WO2007074997A1
Application number: PCT/KR2006/005604
Authority: WO
Inventors: Gyu-Beom Gwag; Jae-Min Lee; Jae-Jung Moon
Original assignee: Clean & Science Co., Ltd.
Priority date: 2005-12-26
Filing date: 2006-12-20
Publication date: 2007-07-05
Also published as: JP2009521305A; KR20070067884A

Abstract

The present invention relates to a filter material for cleaning air from contaminants which can be used for an extended period of time and a process for preparing the same. More particularly, it relates to a dual- or multi-layer filter material comprising at least one non-woven fabric layer with a density gradient located on the air- inlet side and a meltblown layer as a final layer located on the air-outlet side, wherein said meltblown layer comprises heterogeneous components having different melting points, and a process for preparing the same. The filter material for air cleaning according to the present invention does not have problems of low strength and fiber shedding which occur when a meltblown material is used as a final layer and as well it shows excellent post-processibility. The filter material of the invention which is excellent in the lamination pro- cessibility and bonding performance involved in the filter preparation process and filter efficiency can improve dust holding efficiency and dust holding capacity which are drawbacks in the conventional filter products, and thus can be used in various filtering apparatuses for vehicles or air ventilation units in buildings.

Description

FILTER ELEMENT FOR CLEANING AIR AND PROCESS FOR

PREPARING THE SAME

Technical Field

[1] The present invention relates to a filter material for cleaning air from contaminants which has an elongated lifetime, and a process for preparing the same. More particularly, it relates to a dual- or multi-layer filter material comprising at least one non- woven fabric layer with a density gradient located on the air- inlet side and a meltblown layer as a final layer located on the air-outlet side, wherein said meltblown layer comprises heterogeneous components having different melting points, and a process for preparing the same. Background Art

[2] Generally, internal combustion engine is operated by supplying liquid fuel such as gasoline and diesel or gaseous fuel such as LPG with a combustion chamber, where the fuel becomes into a gas mixture with oxygen in the air and undergoes combustion/ explosion. The air introduced into the engine to form the gas mixture contains impurities such as dusts which cause incomplete combustion and impeding smooth operation of vehicles or equipments. Also, the impurities may flow into the engine and be piled on the cylinder wall of the engine to deteriorate the durability of engine.

[3] Conventional engines for vehicles are provided with an air filter medium in the air cleaner and an oil filter medium in the oil filter to remove impurities contained in the lubricating oil within the engine.

[4] Such a filter medium comprises various types of filter paper which are technically designed according to the size and quantity of materials to be removed. This filter medium should satisfy sufficient filtration efficiency and life span for maximizing the fluidity and amount of air or lubricating oil which is needed while the engine is operated.

[5] However, in practice, when the size of pore in the filter medium is minimized to collect impurities sufficiently, the pore can be easily clogged. Thus, the filter medium with fine pores has problems in that it cannot be used for a long period of time. On the contrary, the medium with large pores has poor filtration efficiency since fine dusts can easily escape. Therefore, it is desired to have a filter material satisfying both the filtration efficiency and life span.

[6] Conventionally, filter paper and non- woven fabric are widely used as a filter material for vehicles. Filter paper is prepared by blending a natural pulp and a synthetic fiber in accordance with the final application field and subjecting the blend to the dissociation-beating-sheet forming-impregnation-drying-winding processes. Non- woven fabric is classified into various types according to its preparation method, such as spun-bond, spunlace, chemical bond, thermal bond, needle punching and meltblown. Particularly, non-woven fabric largely used as a material for internal combustion engines is prepared by carding a proper combination of fibers, followed by lamination in a multi-layered structure and subjecting the laminate to subsequent processes such as needle punching, heat pressing, chemical treatment, drying and the like.

[7] Upon comparison of performance between the filter paper and the non- woven fabric, the filter paper prepared according to the above-described method has a thin thickness, a high density and a low air permeability and shows excellent particle holding efficiency. However, the filter paper has a defect in that it requires a large area upon application as a filter material, but has an excellent processibility.

[8] Meanwhile, non-woven fabric has a great thickness, a low density and a high air permeability, and thereby, shows a long effective dust holding life. However, it has defects of a low holding efficiency of micro-particles and a poor post-processibility.

[9] By the meltblown process, it is possible to form a ultra-fine fiber which is widely used as various filter materials such as air purification system. However, such a ultra- fine fiber has many problems of strength, fiber shedding and fiber breakage upon pleating, whereby it cannot be used alone.

[10] As a prior art, Korean patent application no. 2000-0068955(November 20, 2000) discloses a filter material for air cleaning purpose in which two or more fabric layers form a density gradient from the air-inlet side to the air-outlet side and each fabric layer is laminated by a thermal bond method without using a resin binder. Korean patent application no. 1999-0058756(December 17, 1999) discloses a filter material in which a meltblown layer and a non- woven layer are laminated by a resin binder. In additon, Korean patent application no. 1999-0039101 (September 13, 1999) discloses a filter material in which a dense layer, an intermediate layer and a bulky layer are laminated by a thermal bond method without using a resin binder.

[11] However, when a needle punching method according to the above conventional technology is used in order to laminate a meltblown fabric and an air permeable non- woven fabric, the meltblown fabric which is a short fiber is ruptured and big holes are formed by the needles, thereby lowering filtering efficiency. Therefore, the meltblown material was unsuitable to use as the final layer in order to improve filtering efficiency. This is because that the meltblown fabric, in its characteristic, is made of short fibers and hence its strength and tensile power are weak.

[12] Therefore, the process in which the meltblown fabric is laminated with other air permeable nonwoven fabric was, until now, mainly the thermal bonding or the resin bonding method, but these processes have problem in the filter efficiency since they require high cost price, and the use of low melting resins and adhesives results in pore closing of the fibers. On the other hand, in a case of the conventional filter material which does not contain the meltblown fabric and which is prepared by thermal bonding or thermal bonding after needle punching process, 50% or more of ultra- fine low melting point fiber and ultra- fine fiber are used in order to constitute the final layer(fine layer) in the multi-layer filter material with a density gradient which also results in air permeability lowering due to the pore closing, low productivity and high cost.

[13] The above prior art non- woven fabric lamination processes can be summerized as follows: when a non- woven fabric is laminated with other non- woven fabric, 1) lamination by needle punching after formation of a density gradient, 2) lamination by chemical adhesives, 3) lamination by thermal bonding after formation of a density gradient with a low melting point fiber, and 4) lamination by hot melt adhesives and resin binders or the combination thereof can be used, but the final layer in the multilayers as the proportion of ultra-fine fiber(the fiber below 1.5 denier) increases, results in the problems of low productivity upon fiber mixing and opening, and high cost due to the use of the resin. Upon the needle punching lamination, rupture of the melt-blown by needles and hole formation in the non-woven fabric make filter efficiency decrease. In addition, the use of the low melting point resin in a large amount makes problems of pore closing in the final layer and elevation of differential pressure. Lamination by the chemical bond or the hot melt binders may provoke the problems of fiber pore closing(aeration resistance elevation), high cost and environmental hazard.

[14] Therefore, it is still desired to improve the foregoing problems in applying such a meltblown material into the ultra-fine fiber material of high filtering performance. Disclosure of Invention Technical Problem

[15] The present inventors have intensively conducted studies to solve the problems involved in the conventional non- woven fabric and to develop a more improved filter material, and found that a dual- or multi-layer filter material by laminating at least one non- woven fabric with a density gradient at the air-inlet side(outer layer) with an ultra- fine meltblown at the air-outlet side(inner layer) side, wherein said meltblown layer comprises heterogeneous components having different melting points can solve the problems of strength loss, fiber shedding, and post processibility which are involved in the prior art filter material containing the meltblown fabric as the final layer and, as well, can improve the lamination work efficiency, and bonding performance which are involved in the filter preparation process, and filter efficiency, and consequently is excellent in micro-particle holding efficiency as compared to the conventional filter material and completed the present invention. Technical Solution

[16] Therefore, it is an object of the present invention to provide an air filter material which can solve the problems of strength loss, fiber shedding, and post processibility which are involved in the prior art filter material containing the meltblown fabric as the final layer and, and as well, can improve lamination work efficiency, and bonding performance which are involved in the filter preparation process, and filtering efficiency, and consequently is excellent in micro-particle holding efficiency as compared to the conventional filter material, and to provide a process for preparing the same.

Advantageous Effects

[17] The air filter material according to the present invention can solve the problems of strength loss, fiber shedding, and post processibility which are involved in the prior art filter material containing the meltblown fabric as the final layer. Also, lamination work efficiency and bonding performance which are involved in the filter preparation process, and filtering efficiency can be improved and consequently the filter is excellent in micro-particle holding efficiency as compared to the conventional filter material. Therefore, the filter material can be used as a filter medium in the fields of vehicles or building ventilator, etc. Brief Description of the Drawings

[18] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which:

[19] FIG. 1 is a schematic view showing an embodiment of the process for preparing air filter material according to the present invention. Best Mode for Carrying Out the Invention

[20] In an aspect of the present invention, there is provided a dual- or multi-layer filter material for cleaning air comprising at least one non- woven fabric layer with a density gradient located on the air-inlet side and a meltblown layer as a final layer located on the air-outlet side, wherein said meltblown layer comprises heterogeneous components having different melting points.

[21] The term "final layer" used herein refers to a layer through which air passes to the outside, where an air-inlet side layer is an outer layer or an external layer. It also can be called "fine layer" meaning that it is a layer having a very high fiber density and these two terms can be used reciprocally. Further, this layer refers to an air outlet layer or an inner layer in the art. Here, when a support layer is added to the final layer at the fluid-outlet side, as needed, it is called as a backup layer or a support layer, but is not called as a " final layer".

[22] The filter material according to the present invention can suitably be used in various fields such as internal combustion engines or air cleaner in the buildings.

[23] In order to accomplish the above object of the present invention, at least one non- woven fabric layer with a density gradient is located on the air-inlet side and a meltblown layer as a final layer(fine layer) is located on the air-outlet side of the dual- or multi-layer filter material for cleaning air. The non- woven fabric at the air inlet layer increases filter life span and the meltblown at the final layer increases filtration efficiency.

[24] In the filter medium to be installed on an engine to clear air, it is preferred to use a meltblown non-woven fabric which can form an ultra-fine fiber in order to increase the filtering efficiency and to use a non- woven fabric, a filter paper or the mixture thereof in order to increase the dust holding quantity. It is also needed to optimize the filter performance by forming a density gradient in each layer. By the constitution of the above filter components, it is possible to solve the problems of strength and air permeability increase and fiber shedding and to improve processibility, dust holding efficiency, dust holding quantity, pleating property and pressure resistance, as compared to the conventional filter material.

[25] The filter material according to the present invention comprises at least one outer layer(or pre-layer) having a density gradient from the air inlet side. The outer layer can be made of a non- woven fabric selected from the group consisting of a spun-bond, a spunlace, a chemical bond, a thermal bond, a needle punching, an air-laid and a bulky meltblown material, or a filter paper or a mixture thereof. This material can also be prepared by air cleaner method which comprising material mixing-multilayer carding- needle punching-impregnation (foam coating)-drying(can, hot air)-taking-up or alternatively in an order of material mixing-multilayer carding-needle punching- drying(can, hot air)-calendring-taking-up. It is more preferred that the non-woven fabric may be prepared by a conventional method such as needle punching method, chemical bonding method, thermal bonding method, spun bonding method, bulky meltblown method, and the like.

[26] The non- woven fabric which constitutes the outer layer can be prepred from the component selected from the group consisting of polyester, acryl, polyethylene, polypropylene, polybutylene, viscose rayon, polyethylene terephthalate, polybutylene terephthalate, nylon, polyphenylenesulphide, polycarbonate and polyester glycol (PETG), which can be used alone or as a mixture thereof.

[27] The non- woven fabric used in the pre-layer may have various properties according to the type of the non- woven fabric and desired performance. For the material for the internal combustion engine, the non-woven fabric preferably has a weight of 30 to 500g/D. an air permeability of 50 to 450 cfm, at 125 Pa, a fiber diameter in the range of 1 to 40 D and a pore size in the range of 60 to 200 D, and is preferably in a multi-layered structure.

[28] The meltblown non- woven fabric composed of the heterogeneous components as used in the present invention can be prepared by the conventional process and briefly can be prepared by the order of material mixing-melting-extrusion and blowing(web formation)-winding.

[29] The above meltblown layer can be formed by two or more components selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, nylon, polyphenylenesulphide, polycarbonate and polyester glycol(PTEG) are spun after mixing or spun in the form of bi-component(side by side, sheath/core, or spilt microfilament yarn) to constitute the heterogeneous fiber having different melting points, and includes, for example, low melting point PET-high melting point PET, low melting point PET-high melting point PBT, low melting nylon-high melting nylon, PBT-nylon, etc. It is more preferable that the meltblown includes 30-90% by weight of high melting point resin.

[30] The meltblown material used in the final layer constitutes preferably 5 to 40 wt% based on the weight of the whole filter material and has preferably a pore size in the range of 20 to 150 D, a weight in the range of 10 to 300 g/D, an air permeability in the range of 10 to 500 cfm, at 125 Pa, and a fiber diameter in the range of 0.5 to 20 D.

[31] Each layer of the filter material can be laminated by either of a heat treatment process such as calender, fusing oven, belt press manner or bonding process such as needle punching, low melting point resin or water-soluble resin, or the mixture thereof. In addition, it is preferred that a heat treatment in the post treatment may be used in order for easy bonding. Lamination process by the heat treatment can be accomplished by heat treatment of the thus formed non- woven web and the meltblown web using fusing oven, belt press, calender or hot air, etc. at 100 ~ 300⁰C, and the low melting point resin present in the meltblown layer is then melted to give the lamination. As a consequence of the heat treatment, the heterogeneous polymeric fibers with different melting points are tangled and twisted by heat which gives effects of more improved porosity, increases in filtering efficiency and filter life span compared to the conventional filter material. Furthermore, the method according to the present invention simplifies lamination process of the non- woven web and the meltblown and can prevents the secondary problems which can occur in the lamination process. The filter material laminated by the conventional needle punching was poor in its filter performance due to the holes generated by the needles. However, the heat treatment after the needle punching by the process according to the present invention results in considerable recovery of the holes by the melted fiber which does not necessitate the additional adhesive resin during the process and the meltblown performs adhesive function. Of course, a chemical resin such as hot melt may be used, if necessary, in order to maximize the bonding strength.

[32] The filter material according to the present invention may preferably comprises a support layer in the back of the meltblown layer, as needed. The support may be formed by the non- woven fabric as described above and preferably has a weight of 5 to 60 g/D.

[33] The non-woven fabric can also be prepared according to the conventional preparation method. For example, spun bond, spun lace, needle punching, chemical bond, thermal bond, air- laid and meltblown processes, etc. can be used.

[34] The finally prepared composite filter material has preferably a total weight of 150 to

500 g/D, a pore size of 10 ~ 150 D, an air permeability of 30 to 150 cfm, at 125 Pa, a fiber diameter of 0.5 ~ 40 D, and a thickness of 1.0 to 4 mm.

[35] In another aspect of the present invention, there is provided a method for preparing the above-described filter material.

[36] As briefly shown in Fig. 1, the method for preparing the filter material according to the present invention may be performed by combining conventional preparation methods. In embodiments for preparing the multi-layered material, a pre-layer comprising a single layer or two or more layers of non- woven fiber web or filter paper and(or) a support layer may be laminated to the meltblown layer which serves as the final layer.

[37] More specifically, the method for preparing the filter material according to the present invention comprises the steps of:

[38] a) transferring at least one non-woven fabric and meltblown from respective winding rolls;

[39] b) if necessary, applying an adhesive(hot melt or water soluble binder) to the non- woven fabric or meltblown layer by spray or dot type application;

[40] c) laminating the above layers (i,e., the adhesive applied filter material and the other material) by a tension roll;

[41] d) fusing the laminated filter materials by fusing oven, belt press, calender or hot air maintained at 100-300 ⁰C; and

[42] e) winding the fused filter material.

[43] Lamination of layers by the conventional methods such as calender, fusing oven or belt press required a large amount of the low melting point fiber at the bonding face of the non- woven fabric and a high treatment temperature. However, if a filter material is prepared according to the present invention, lamination at a low temperature is possible as the low melting point resin in the meltblown is arranged in the form of ultra-fine fiber and, therefore, the use of the low melting point fiber in non-woven fabric can be minimized. In addition, the process provides effects in the productivity and the cost save since it does not require an additional adhesive.

[44] In the above preparation method, a support layer may be preferably attached to the back of the meltblown layer in any one step of the processes to further increase the strength of the back layer.

[45] Also, when it is required to increase bonding strength by needle punching, the present invention provides a method for preparing a filter material for air cleaning comprising the steps of:

[46] a) transferring at least one non- woven fabric and meltblown from respective winding rolls;

[47] b) laminating the non-woven fabric and(or) meltblown layer and bonding the resulting laminate by a plurality of needles to form a web; (needle punching non- woven web lamination method);

[48] c) fusing the laminated filter materials by fusing oven, belt press, calender or hot air; and

[49] d) winding the needle bonded filter material.

[50] According to the above method which laminates a meltblown fiber with a non- woven fabric layer, the rupture of fibers which is a fatal defect in the filtering efficiency upon needle punching can be recovered by the use of calender, fusing oven, or belt press process in the post processing after lamination of fibers, and low melting point meltblown is melted to increase the bonding strength to the non-woven web. In addition, since the filter material contains a high melting point fiber, pore closing according to the film formation of fibers can be minimized. Of course, the bonding strength and porosity can be regulated according to mixing ratio of the meltblown.

[51] When the filter material is prepared by hot melt process, the method for preparing the material according to the present invention comprises the steps of:

[52] a) transferring at least one non- woven fabric and meltblown from respective winding rolls;

[53] b) applying an adhesive to the non- woven fabric or meltblown layer by spray or dot type application;

[54] c) laminating the above layers (i. e., the adhesive applied filter material with the other material) by a tension roll;

[55] d) fusing the laminated filter materials by fusing oven, belt press, calender or hot air; and

[56] e) winding the fused filter material.

[57] According to the above preparation method, when the non-woven fabric of the pre- layer is a multi-layered chemical bond non-woven fabric, the meltblown fabric which serves as a final layer is separately prepared by a conventional method (for example, Korean patent no. 10-0438331, in the order of raw material mixing- extrusion-spinning-web bonding- winding) and combined with a raw material for the non- woven fabric, followed by carding. The meltblown web is then introduced into a step prior to the chemical bonding process(for example, in the order of raw material mixing for chemical bond fiber, filamentation, filament blending, carding, wrapping, impregnation, drying and winding) and bonded by resin bonding to form the material according to the present invention.

[58] The thus prepared material may be further subjected to the steps of:

[59] f) pleating the composite material to a desired shape using a pleating machine; and

[60] The additional steps may be selectively performed according to the post-process procedure.

[61] The filter material according to the present invention can be pleatable. Therefore, the pleating process includes pleating the non- woven material in accordance with a desired shape, cutting the pleated material to a desired size and curing the product at a predetermined temperature for a predetermined time. Here, the curing step can be omitted according to the used resin and process. Therefore, in an additional aspect of the present invention, there is provided a filter element prepared by pleating the material. The filter element may be in a star shape or a flat panel shape.

[62] In the pleating process for shaping, the pleating machine may be a rotary, minipleat, or knife pleating machine. Among them, the knife pleating machine is preferably used. The curing temperature to fix the pleated shape is in the range of 130 to 18O⁰C, which is similar to the curing temperature of the non- woven fabric.

[63] The final filter material thus prepared preferably has a pore size of 10 to 150 D, a total weight of 150 to 500 g/D, a total thickness of 1.0 to 4 mm and an air permeability of 30 to 150 cfm, at 125 Pa. Fibers having a fiber diameter of 0.5 to 40 D may be preferable. Mode for the Invention

[64] The present invention will hereinafter be described in further detail by examples.

However, the examples are given for illustration and the present invention is not limited thereto.

[65] The filter materials produced by different bonding methods based on the raw material in the mixing ratio below were tested for the filter performance. Dust used in the test was AC fine. The amount of flow tested was 25 D/min, filtering area was 176.6 D, and dust input amount was 0.5g/2min. The test was performed until the final pressure loss is 400 mmAg.

[66] Comparative Example, Examples 1 and 2: [67] The raw materials as described in the table 1 below were properly combined and subjected to multi-layer carding-needle punching-drying(can, hot air) -calendaring- winding. The products were examined for properties, and the results thereof are set forth below.

[68] Also, the meltblown non- woven fabric was prepared by the conventional preparation method of extrusion-spinning- web bonding- winding using a resin, and the fabric was then examined for its properties and filter performance. The comparative results according to the mixing ratio of the low melting point resin are shown below tables 2 and 3. Table 2 is the results by the use of heat calender process, and table 3 represents the result by the needle punch process only.

[69] Table 1

[70] Table 2 Lamination by heat calender(150 ⁰C)

[71] Upon review of the above results, the reason that the filter of comparative example 1 is poor in its dust holding quantity compared to those of Examples is originated from the pore closing of melt-blown when the low melting point resin in the second layer is attached. In addition, the filters according to the examples of the invention which comprises the heterogeneous meltblown components resulted in high efficiency. This is because the low melting point PET component is fused to laminate the two filter layers and in addition to reduce the twisting and torting of the fiber and the size of pores. Especially, the filter of Example 2 in which 10% of PBT(IV 0.54) are added to the final layer in order to increase the content of a fine fiber in the final layer resulted in higher efficiency. In aspect of the bonding strength, that of the comparative example which comprises low melting point resin(LM(4D) 25%) on the non-woven web layer and the filters of Examples 1 and 2 which do not contain the low melting point resin represented a similar bonding strength.

[72] Table 3 Bonding strength and efficiency upon using needle punching only

[73] [74] When the melt-blown and non- woven fabric layer were laminated by needle punching only, the bonding strength and efficiency were very low and the dust holding quantity was relatively high. This is based on the generation of holes according to the rupture of fibers by the needles.

[75] Meantime, table 4 below is the compared results on the bonding strength and filtering efficiency when thermal bonding(hot press) was applied after the needle punching. Each of the first and the second layers was laminated with needle punching, and heat calender(150 ⁰C) was then applied thereto.

[76] Table 4

[77] [78] Very excellent results were obtained compared to the previous cases when thermal bonding was applied after the needle punching. That is, it was found that filter efficiency and life span as well as bonding strength were improved. This result is interpreted as a consequence that, upon lamination by the needle punching, each fiber in the non- woven fabric layer is incorporated into the melt-blown layer and, upon thermal fusion, the low melting point resin in the melt-blown layer is fixed to improve bonding strength. In addition, it is possible to minimize the pore closing that is generated due to the increase of fusion temperature and pressure which is required to increase the fusing strength when thermal fusion is used only. Industrial Applicability

[79] As described above, the filter material for air cleaning according to the present invention does not have problems of low strength and fiber shedding which occur when a meltblown material is used as a final layer and as well it shows excellent post- processibility. The filter material of the invention which is excellent in the lamination processibility and bonding performance involved in the filter preparation process and filter efficiency can improve dust holding efficiency and dust holding quantity which are drawbacks in the conventional filter products, and thus can be used in various filtering apparatuses for vehicles or air ventilation units in buildings.

Claims

[1] A dual- or multi-layer filter material for cleaning air which comprises at least one non-woven fabric layer with a density gradient located on the air-inlet side and a meltblown layer as a final layer located on the air-outlet side, wherein said meltblown layer comprises heterogeneous components having different melting points.

[2] The filter material according to Claim 1, wherein the meltblown has a weight of

10 to 300 g/D, and the filter material has a weight in the range of 150 to 500 g/D, a pore size in the range of 10 to 150 D, an air permeability in the range of 30 to 150 cfm, at 125 Pa, and a fiber diameter in the range of 0.5 to 40 D and thickness of 1.0 - 4 mm.

[3] The filter material according to Claim 1, wherein said meltblown layer is formed by two or more components selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, nylon, polyphenylenesulphide, polycarbonate and polyester glycol(PTEG) are spun after mixing or spun in the form of bi-component to constitute the heterogeneous fibers having different melting points.

[4] The filter material according to Claim 1, in which each layer of the material is laminated by a method of thermal bonding, needle punching, chemical bonding, hot melt lamination by dotting or spraying or a combination of two or more thereof.

[5] The filter material according to Claim 1, in which the melt-blown comprises

30-90% by weight of high melting point resin.

[6] The filter material according to Claim 1, which further comprises a support layer at the backside.

[7] A filter element prepared by pleating the filter material according to Claim 1.

[8] A process for preparing a filter material for air cleaning which comprises the steps of: a) transferring at least one non- woven fabric and meltblown from respective winding rolls; b) if necessary, applying an adhesive to the non-woven fabric or meltblown layer by spray or dot type application; c) laminating the above adhesive applied material and the other material by a tension roll; d) fusing the laminated filter materials by fusing oven, belt press, calender or hot air maintained at 100-300 ⁰C; and e) winding the fused filter material.

[9] A process for preparing a filter material for air cleaning which comprises the steps of: a) transferring at least one non-woven fabric and meltblown from respective winding rolls; b) laminating the non- woven fabric and(or) meltblown layer and bonding the resulting laminate by a plurality of needles to form a web; c) fusing the laminated filter materials by fusing oven, belt press, calender or hot air; and d) winding the needle bonded filter material.

[10] A process for preparing a filter material for air cleaning which comprises the steps of: a) transferring at least one non- woven fabric and meltblown from respective winding rolls; b) applying an adhesive to the non- woven fabric or meltblown layer by spray or dot type application; c) laminating the above adhesive applied filter material and the other material by a tension roll; d) fusing the laminated filter materials by fusing oven, belt press, calender or hot air; and e) winding the fused filter material.