METHOD FOR IMPREGNATING A POROUS FILTER MATERIAL WITH A FLUID AND A FILTER MANUFACTURED BY THE METHOD

Abstract: The invention related to a method for impregnating a porous filter material with fluid and a filter manufactured according to the method. According to the principles of the method according to the invention, the filter material is placed in a chamber essentially sealed against the atmosphere, the material is heated to a predetermined temperature, the impregnation solution in the form of a dispersed fluid is sprayed into the chamber, and the pressure in the chamber is raised to a predetermined level, whereby said parameters regarding temperature and pressure are maintained in the chamber for a predetermined interval of time that is chosen to allow the impregnation solution to diffuse completely into and fill the filter material. In this way, a good impregnation of fluid in the filter material is obtained in a very simple manner, and the filtering effect of said filter is also good.

Description: Method for impregnating a porous filter material with a fluid and a filter manufactured by the method The present invention relates to a method for impregnating a porous filter material with fluid according to the introduction to claim 1 and a filter manufactured according to the method. The type of filter saturated or impregnated with fluid that is primarily referred to here is a type that is used for filtering dust powders and particles from gases, especially from ventilation air taken up into vehicles. However, filters of the type referred to by the invention can also be used in other situations for cleaning air or other gases. The invention refers especially to saturated filters that can function both as particle filters, whereby the particles get caught in the filter due to their size, and/or as absorption filters, where very small particles and similar stick to the filter by the act of adhesion, i.e. primarily because the filters are saturated with fluid. One objective of the present invention is to achieve an even and controlled saturation of the filter material with fluid to obtain a good and stable filtration effect. This and other objectives are achieved by carrying out the saturation of the filter at an elevated temperature and at an elevated pressure in accordance with that evident in more detail from the claims that follow. The method for saturating filter material according to the invention is especially advantageous when it is carried out on filters that comprise several layers of the same or different materials. A layered, fluid-saturated filter is known from US 4 758 460 where the individual layers of filter are rolled together between two rollers or cylinders, whereby impregnation of the fluid in the filter also takes place by the fluid being applied on one of the said rollers. The disadvantage of this known method is obvious in that the filter material or, more specifically, the very fine threaded elements or fibres that themselves form the filter mass, are physically deformed by the action of the rollers during the actual impregnation process. This adversely affects properties of the filter mass such as the flow- through of air and the ability to collect dust powders. A procedure for treating filter masses comprised of thread-like expanded foam material is known from WO 95/04586. According to this document, the filter masses are saturated with a fluid of relatively high density to increase the ability of the filter to collect dust powders, whereby heat is used to reduce the viscosity of the fluid and thereby facilitate its penetration of the filter. 2 Neither of these documents name or refer to the combination of measures taken during impregnation that are referred to by the present invention. One embodiment of the present invention is described below with reference to the enclosed drawings that show schematically the principles for treating the filter material according to the invention. The filter material 1 is inserted for treatment into a chamber 2 that is sealed from the surrounding atmosphere in an air-tight manner. The filter material 1 is heated by the action of convection heating elements arranged in the chamber (not shown in the figure), or by the action therein of microwaves generated by a oscillator unit arranged in some suitable manner in the space of the chamber. By means of one or preferably several inlet pipes 3 connected to the chamber and opening into it, impregnation fluid 4 is sprayed into the chamber, in addition to which, the pressure in the chamber is increased to a predetermined level, as indicated by the arrows 5. When the specified values of temperature and pressure have been attained in the chamber, they are maintained for a specified interval of time so that the treatment fluid has the opportunity to diffuse into and be fully taken up by the filter material 1 from different directions. The choice of the parameters regarding the temperature, pressure and treatment time in the chamber is decided primarily on the basis of the viscosity of the chosen impregnation fluid as well as the dimensions and density of the filter and, as such, in relation to the time needed for the fluid to diffuse fully into the porous filter mass. It should also be realised that it is beneficial for the speed of manufacture if the dispersed fluid that is sprayed into the chamber is heated to a higher temperature before it is sprayed into the chamber. The above method can be performed for different filter materials and different impregnation fluids, as well as for different levels of temperature, pressure and different treatment times. Examples of filter materials that have been used include those commercially available under the brand names "FILTREN T20, FILTREN T75 and BULPREN S90" from the company RESTICELL INTERNATIONAL. The composition of the filter material preferably comprises a 3-layered material mounted in a frame or similar construction where the filter is, for example, joined together at the edges by gluing and held firmly in the said frame by a net-like element of a relatively stiff material such as rigid plastic or metal. The impregnation fluids can, for example, comprise vegetable oils such as rape seed oil as well as polymers or other known oils. Depending on the application area of the filter and on the filtration demands placed on the filter unit formed, the use of more layers than the said three-layers can also be considered, for example, six-layered material. Typical heating temperatures normally lie in the range from about 75 °C to about 155 °C and the pressure can normally vary from about 20 MPa to 45 MPa, while suitable treatment times amount to about 25 to 90 seconds. According to one example of an embodiment, a very good filtration effect has been obtained with a filter mass from the said manufacturer that was treated at 75 °C and a pressure of 20 MPa with both parameters maintained for a time of 25 seconds. It should be realised that the invention is not limited to that stated above but can be changed and modified in a number of ways within the scope of the concept of the invention as specified in the following claims.

Claims: Claims 1. Method for impregnating a porous filter material with fluid characterised in that the filter material is placed in a chamber that is essentially sealed against the atmosphere, that the material is heated to a pre-determined temperature, that the impregnation solution in the form of a dispersed fluid is sprayed into the chamber, and that the pressure in the chamber is raised to a pre-determined level, whereby the said parameters regarding temperature and pressure are maintained in the chamber for a predetermined interval of time that is chosen to allow the impregnation solution to diffuse completely into and fill the filter material. 2. Method according to claim 1 characterised in that the filter material is heated to a temperature between 75 °C and 155 °C, and that the pressure is increased to between 20 MPa and 45 MPa, and that the temperature and pressure are maintained for a time interval of between 25 and 90 seconds. 3. Method according to claims 1 or 2 characterised in that the temperature in the chamber is 75 °C, the pressure is 20 MPa and that these are maintained for a time of 25 seconds. 4. Method according to any of the previous claims characterised in that the filter material comprises a thread-like porous expanded foam material. 5. Method according to any of the previous claims characterised in that the impregnation material comprises a vegetable oil. 6. Method according to claims 1 to 4 characterised in that the impregnation material comprises a synthetic oil. 7. Method according to any of the previous claims characterised in that microwaves are used to heat the filter material in the chamber. 8. Filter of a thread-like porous material manufactured according to the method in any of the above claims. 9. Filter according to claim 8 characterised in that it is comprised of three layers mounted one above another in a frame.

Inventors: SYDLEN OLLE, SYDLEN, OLLE
Applicants: OENELL TOMAS, SYDLEN OLLE, OENELL, TOMAS, SYDLEN, OLLE
Application year: 1999
Main classification: B01D39
IPC codes: B01D39, B01D46