FILTER WITH FORM-RETAINING STABILIZING MEANS

Abstract: A filter comprises a filter medium (110) folded in a pleated manner into sheets (112). The sheets are kept apart from one another to form the optimum angle by a stabilizer (120) which is applied in a semi-liquid form, hardens into a desired shape and retains that shape after hardening independent of the final form of the filter medium.

Description: FILTER WITH FORM-RETAINING STABILIZING MEANS The invention relates to filter means comprising a filter medium of non-flat contour and stabilizing means, (a) which are formed by applying a semi-liquid material onto the filter medium, and (b) which are hardenable in a shape, according to the contour of the filter medium. The invention also relates to a method of producing such a filter means. Filters usually contain a filter medium, such as glass paper, micro spun bonded polypropylene or cotton fibre mat. Such filter medium is used particularly for filtering air. To achieve a high filtering effect, i.e. to retain as many particles as possible in the filter medium, the sheets of filter medium are pleated in a zig-zag-manner. The pleated sheets are unstable and need support. Commonly the sheets are glued into a cardboard-frame with support strings. These support strings reduce the effective filter surface and therefore lead to inferior filtering characteristics. This problem has been solved in the past by putting lines of glue onto the pleated medium and pleating the sheet with a very narrow pleating angle so that adjacent portions are glued together and thereby the firmness of the filter medium is improved. This procedure has several disadvantages. The glue needs to be applied on both sides of the filter medium to avoid bending of the complete filter medium. Furthermore the glue is still flexible after hardening and can therefore not be applied to pleated filter media with a larger pleating angle. Another disadvantage is the viscosity of the glue which leads to difficulties when inserting the glue into the very end of the angles formed by the sheet. Another form of support for the filter medium is the use of a metal grid. The metal grid is formed from thin wires, which are sufficiently strong to support the medium but still thin enough to be flexible. This grid is put onto the flat sheet of filter medium usually cotton mat and the two layers are then pleated into the desired configuration afterwards. The metal grid has the advantage of being strong enough to support the filter medium on one side only. The disadvantage of this kind of support is that the pleating of the grid together with the filter medium is difficult. Furthermore the metal grid has sharp ends which could cause injuries during its handling or damage the filter medium, especially when the filter medium needs to be cut into the desired dimensions. Also, it is necessary to glue the metal grid to the filter medium. It is another disadvantage that the metal grid can become rusty. This can cause extra particles in the filtered air and is not desirable from an aesthetic point of view. The recycling of such filters is obviously difficult because the different materials have to be separated before further treatment. It is an object of the invention to overcome the aforementioned problems and to provide a safe and cheap stabilizing means which is easy to handle and has improved characteristics. According to the invention this object is achieved in that (c) the stabilizing means retain their shape after hardening independently of the desired form of the filter medium. Advantageously stabilizing means are firmly connected with the filter medium after hardening. Preferably, the stabilizing means are connected with the filter medium from one side only. Conveniently, the stabilizing means are connected with the filter medium at the downstream side of the filter medium. Preferably, the filter medium is formed from a sheet which is pleated in a zig-zag-manner to form a contour of a plurality of V-shapes. Most preferably, the filtered medium is air and that the pleating angle is optimized with respect to filtering parameters. Advantageously, the stabilizing means are applied in the form of one or more parallel strips. Alternatively, the stabilizing means are applied in form of one or more non parallel strips and thereby forming a grid. In a preferred embodiment, the stabilizing means is made from the same material as the filter medium. In a yet more preferred embodiment the stabilizing means is made of polypropylene. Conveniently, the filter medium is also polypropylene. In another embodiment the stabilizing means has a colour in accordance with a specified code. The invention also provides a method of producing a filter means characterized by the steps of: (a) pleating sheets of filter medium (b) applying the stabilizing material onto the filter medium in form of a plurality of strips (c) allowing the material to harden while keeping the filter medium in the desired contour. A preferred method comprises the further step of heating the stabilizing material before application. Conveniently, the method comprises the further step of cutting the filter means to obtain the desired dimensions after hardening of the stabilizing material. Such a filter stabilizing means need to be applied from one side of the filter medium only. This saves costs and efforts while still achieving excellent stability. By using the same material, for example polypropylene, for the stabilizing means and for the filter medium very good bonding characteristics are obtained, which are far superior to the adhesive characteristics of the commonly used glue. The filter medium in this case can be made of micro spun bonded polypropylene. It is another advantage of using the same material, that it can easily and environmentally friendly incinerated. The use of stabilizing means according to the invention also has the advantage, that it reaches the corners of, for example, the N-shaped profile which is otherwise difficult to achieve. The shape of the filter medium, i.e. the pleating angles, can be easily set before the stabilizing means and the filter medium are combined. The contour remains firm after hardening and does not require any further retaining means, such as the cardboard strings used in the prior art. Cutting the filter means according to the invention is also very easy. Furthermore the filter means do not decay when exposed to changing conditions such as moisture or temperature conditions, as long as the temperature is lower than the melting point of the stabilizing means. The polypropylene can be dyed in accordance with a specified code. This code can be used for example to identify the characteristics of the filter means, such as retaining capacity, air flow, size or price. The invention will now be described more particularly with reference to the accompanying drawings which show by way of example only, embodiments of the invention. In the drawings: Fig. 1 shows a perspective view of a filter medium, pleated in a zig-zag-manner Fig. 2 shows a cross sectional view of a stabilizing means formed from a strip after heating Fig 3 shows a grid for producing an alternative stabilizing means with increased stability Fig. 4 shows a perspective view of the filter medium of Fig. 1 after applying the stabilizing means by heat welding. Fig. 5 shows a cross sectional view of the filter medium and stabilizing means of Fig. 5 Fig. 6 shows a cross sectional view of a filter medium and stabilizing means similar to the one in Fig. 6 but with a different pleating pattern. Fig. 7 is a perspective view of a further embodiment of a filter according to the invention in which the pleats of the filter are opened out in a zig-zag manner; Fig. 8 is a front end view of three of the pleats of the embodiment shown in Fig. 7 in which the stabilizers of adjoining pleats are in a contiguous relationship in the direction of arrow A in Fig. 7; and Fig. 9 is a perspective view of one pleat of the Fig. 7 embodiment. In Fig. 1 numeral 10 denotes a filter medium. The filter medium 10 can consist of a sheet 12 of any material suitable for filtering, such as spun-glass, polyester, polyethylene, cotton or the like. In this particular embodiment the sheet material is micro spun polypropylene which has excellent filtering characteristics for filtering air and which is particularly suitable for the use with polypropylene stabilizing means. The sheet 12 is pleated in a zigzag-manner in order to improve the filtering capacity. This is well known and need not be described here in detail. The optimum number of N-s 14 with respect to air flow resistance, i.e. the optimum number of pleats for this particular sheet per metre is 36, not all of them being shown in the drawing. One of the N-s 14 is highlighted in Fig. 1. The number of N-s depends on the material used for the sheet, its thickness and various other parameters. The angles α,α' 16 and 18 defined by the pleated sections are the same and are in the range of 15 degrees. The filter medium 10 by itself suffers from low stability, i.e. it can be twisted, pushed together or pulled apart like an accordion. It therefore needs to be stabilized. A stabilizing means 20 according to the invention is shown in Fig. 2. The stabilizing means 20 is formed from a strip of polypropylene which has been applied to the filter medium in a semi-liquid form. The stabilizing means 20 have a thickness of about 0,5cm. For a sheet 12 of 25 cm height three such stabilizing means 20 are sufficient. When applying, the material has a sufficient viscosity to fill the space 22 in the corners of the N-s in a bridge-like manner which, after hardening, contributes to the stability of the set-up. In Fig. 3 a grid 24 is shown. The grid consists of thin strips 26 of polypropylene which are heat welded together at connection points 28 The diameter of the strips is in this particular grid about 1 mm. The two dimensional grid 24 can be used instead of the one dimensional strips for forming the stabilizing means. In Fig. 4 and 5 the stabilized filter means 30 is shown. The heated stabilizing means 20 is combined from one side with the sheet of filter medium, the stabilizing means matching the contour of filter medium whereby the corners of the N-s are reached. When the polypropylene is hot and soft, it fills the gaps. At the same time the polypropylene of the filter medium is welded to the polypropylene of the stabilizing means. After cooling down the polypropylene hardens and therefore stabilizes the filter medium in its configuration. The angles 16 and 18 are then fixed and the "accordion" effect is avoided. The polypropylene can be dyed in accordance with a pre-set code in order to facilitate identification of the various filter means. A different embodiment is shown in Fig. 6. The filter means is more densely packed and the pleating does not form V-s but U-s. But still the principles of the invention apply. As can be seen from the drawing , the stabilizing means 20 are only applied from one side only and the gaps between the sections of the filter medium are almost completely filled. The stabilizing means 20 are applied by being extended over the pleats of the medium in the desired configuration and then hardened by blowing cold air over the assembly. Referring to the further embodiment shown in Figs. 7 to 9, the filter medium 110 consists of a sheet 112 of filter material. The sheets 112 are pleated in a zig-zag manner. A stabilizer 120 is applied to the front face 113 of the sheets 112 and a further stabilizer 130 is applied to the rear face 114. The stabilizers 120 are a series of parallel strips of polypropylene formed on the front face 113 and the stabilizers 130 are a series of parallel strips of polypropylene on the rear face 114. When brought into contiguous relationship the stabilizers 120 contact one another and keep the pleats at the desired spacing from one another. The stabilizers 130 also contact one another and maintain the pleats apart at the rear face of the filter. To form the filter of this embodiment, the stabilizer 120 and 130 are sprayed onto a flat sheet of filter medium 110, the pleats are formed by a pressure plate contacting the sheet at regular intervals to form crease lines 125 and 135 on the front and rear faces 113 and 114. It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention, as defined in the appended claims.

Claims: CLAIMS: 1. A filter comprising a filter medium of a non- flat contour and stabilizing means being formed from a semi-liquid material applied onto the filter medium and being hardenable into a shape according to the contour of the filter medium, characterised in that the stabilizing means retain their shape after hardening independent of the final form of the filter medium. 2. A filter according to claim 1, in which the stabilizing means are firmly connected with the filter medium after hardening on either one or both sides of the filter medium. 3. A filter according to claim 1 or claim 2, in which the filter medium is formed from a sheet which is pleated in a zig-zag manner to form a contour of a plurality of V shapes. 4. A filter according to claim 3 in which the pleating angle of the N shapes is optimized with respect to filtering parameters of the fluid being filtered. 5. A filter as claimed in any one of the preceding claims in which the stabilizing means comprise a plurality of parallel strips. 6. A filter as claimed in any one of claims 1 to 4 in which the stabilising means comprise a plurality of non-parallel strips interengaging to form a grid structure on one or both sides of the filter medium. 7. A filter as claimed in any one of the preceding claims in which the stabilizing means and the filter medium are generally of the same material. 8. A filter as claimed in claim 7, in which the stabilizing means and filter medium are both made from a polypropylene material. 9. A filter as claimed in any one of the preceding claims in which the stabilizing means is given a specific colour, so that a user can distinguish specific filters for specific purposes. 10. A method of producing a filter comprising the steps of applying stabilizing material onto a filter medium, pleating the filter medium into distinct sheets and allowing the stabilizing material to harden.

Inventors: HARROLD BRIAN, HERBERT DIARMUID, MCGOEY DONAL RICHARD, HARROLD, BRIAN, HERBERT, DIARMUID, MCGOEY, DONAL, RICHARD
Applicants: HARROLD BRIAN, HERBERT DIARMUID, MCGOEY DONAL RICHARD, HARROLD, BRIAN, HERBERT, DIARMUID, MCGOEY, DONAL, RICHARD
Application year: 1998
Main classification: B01D46
IPC codes: B01D29, B01D46