Process for manufacturing a filter medium, the medium manufactured thereby, and filters using said medium

Abstract: A process for manufacturing a filter medium comprises the following operations: preparing in a pulper or beater a pH 3-5 aqueous suspension of cellulose fibres with a concentration of between 3% and 5%; preparing in a pulper or beater a pH 2.8-3.8 aqueous suspension of glass fibres with a fibre concentration of between 0.5% and 1.2%; preparing a first pulp consisting exclusively of cellulose fibres, to which a moisture-resistant resin is added; preparing a second pulp consisting of cellulose fibres and glass fibres in proportions of between 30% and 70%, to which a moisture-resistant resin is added; forming two superposed layers of said pulps by methods used in paper manufacture; collecting said two layers on a layer of material able to absorb water; pressing the two superposed layers of pulp to a pressure of between 0.1 and 1 kg/cm 2 ; drying the resultant sheet to a moisture content of 1%; impregnating the dried material with a 50 wt% solution of acrylic latex; again drying and winding on a reel.

Description: This patent pertains to the technological sector of filtration in general, and relates in particular to fluid filtration in the engine field. In both Diesel cycle and Otto cycle internal combustion engines it is well known that the lubricating oil must be kept filtered. The problem of effective lubricating oil filtration is not easy to solve, as it involves opposing requirements. European patent 341349 in the name of the present applicant offers a solution to the problem, consisting of locating within a filter of commonly known type, such as a full-flow filter, three filter cartridges, two of which are connected in series with each other, the combination being connected in parallel with the third. By careefully coordinating the porosity of the three cartridges, with the parallel cartridge having a porosity between that of the two series-connected cartridges and the most porous cartridge being located externally, the filter of the said patent attains an efficiency not achievable by other full-flow filters, and achievable only by the most costly and complicated known filters such as double filtration filters. The problem inherent in the various filtration systems will be more apparent on reading said European patent 341349, which is to be considered as transcribed herein. The present patent relates in particular to filters the subject of said European patent. Although said filters have proved very effective operationally, they present certain constructional difficulties which considerably increase their cost. In this respect they use three separate filter cartridges of different type, of both paper and unwoven fabric, which not only have to be manufactured separately and then individually mounted in the filter, but require the filter to be provided with an inner metal reinforcement to maintain them in their operating position. US 3,640,839 discloses a filter paper for oil filters obtained by a process comprising the steps of preparing a first pulp of cotton, it is to say of a specific form of cellulose, intended to create the finer porosity layer; preparing a second pulp of a mixture of cotton (40 to 60%) and rayon (60 to 40%); and feeding these pulps to a paper machine to obtain a multilayer sheet having a continuous web of coarse porosity (allowing 40 particles to pass) supporting a layer consisting of a set of separated parallel strips of finer porosity (allowing 15 particles to pass); the ratio of planar exposed surface area of the strips to the web is 10:5 to 10:10. A filter according to US 3,640,839 has never been introduced into the market, because of its deficiencies in working in wet conditions at high temperature and pressure. The object of the present invention is to provide a filter medium from which a single filter cartridge can be formed having the characteristics of the combined three said filter cartridges of the said European patent and which can be manufactured in a single piece for insertion into the filter device as it is. A further object of the present invention is to provide a filter medium having better filtration and mechanical characteristics than known materials. A further object is to enable filter devices of "cup" type to be formed presenting improved filtration characteristics, within the framework of a simplified construction. Said objects are attained according to the invention by a filter medium in the form of a multilayer sheet, comprising at least one layer of filter paper and at least one layer of glass fibres, said second layer possibly only partly covering said first layer. Polyester, polyethylene and polyamide fibres are also suitable according to the invention, instead of glass fibres. Said multilayer filter sheet, the characteristics of which will be apparent from the ensuing description of its method of manufacture, is then cut into strips and folded to form a filter cartridge of the well known toroidal form. The technology employed in the manufacture of the filter medium is that typically used in paper manufacture. According to the invention the process is carried out in a paper manufacturing plant for processing synthetic cellulose fibres. At least two pulpers are provided in said plant. One of these is used for preparing the cellulose fibre suspension in the manner known in paper manufacture. In the present case the cellulose fibres are provided in sheets and are processed to a concentration of between 3% and 5% at a pH of between 5 and 7. According to the invention, the cellulose fibres have a high alpha-cellulose content to ensure sufficient inter-fibre bonds without having to use extensive beating. In this respect, it is known that beating modifies the fibre dimensions, to create inter-fibre bonds which are so close as to compromise porosity and hence the filtering characteristics of the paper. The other pulper is provided to disperse bales of staple glass fibre or the like in water by opening their fibres. According to the invention the glass fibres are processed at very low fibre concentration, of between 0.5 and 1.2%, in an acid environment of pH between 2.8 and 3.8, maintained within said range by adding sulphuric acid. Starting from the resultant materials, two separate pulps are prepared, one containing only cellulose fibres, the other containing both cellulose fibres and glass fibres. A proportion generally suitable for achieving good results is 50% of glass fibres and 50% of cellulose fibres, it being apparent that the glass fibre percentage influences the filtering effectiveness in a directly proportional manner, in this respect it being the glass fibres which provide the lowest porosity. The two pulps are then purified of undesirable particles by treatment in known cleaners or cyclones, which exploit the specific gravity differences between the treated particles and the particles of dirt. Before the formation stage a moisture-resistant resin of known type, such as an acrylic resin or an epoxy resin, is added to each pulp to increase the physical-mechanical characteristics of the fibre and make it suitable for the subsequent forming and drying stages. The forming stage is effected in the manner well known in paper works by conveying the two pulps separately in succession onto a temporary support, substantially a plastic web, which grazes a mesh-forming cylinder dipping into a forming box containing the desired pulp. The web firstly collects the pulp formed only of cellulose fibres, which are to form the substrate of the filter medium. On the first layer there is then applied a second layer using the pulp containing both the cellulose fibres and the glass fibres. This second layer can conveniently be formed as strips, by suitably masking the forming roller. The two layers formed and combined in this manner are collected by a synthetic felt web which acts as a conveyor belt and absorbs the two pulps by capillarity, so joining them together. According to the invention, the glass microfibres, used for the most severe filtration stage, have a size of between 0.5 and 14 nm and retain the contaminating particles while allowing the liquid undergoing filtration to pass, they also retaining particles smaller than the pore size by virtue of known phenomena such as Brownian motion. Combining glass fibres with cellulose fibres prevents the glass fibres releasing miniparticles, commonly known as shots, which are extremely damaging if they reach the hydraulic lubrication circuits, and which up to the present time have greatly limited the use of glass fibres in filter media. The two pulps, which are initially simply laid one on the other, are then pressed to a pressure of between 0.1 and 1 kg/cm 2 , for example between facing rollers. The sheet obtained in this manner is then dried, generally by a mixed method using rollers heated to about 120°C by steam, and hot air drying ovens of adjustable temperature. After drying, the material is impregnated with acrylic latex in a 50% solution (percentage of dry material) to give the sheet material to form the filter plate sufficient mechanical strength to resist subsequent folding of the sheet, and to withstand operating pressures of the order of between 100 and 800 kPa (kilopascals). Further drying reducing the moisture content to the order of 1% makes it possible to wind the material onto a reel. The filter medium of the invention enables important results to be achieved in the field of oil filters for motor vehicles. Firstly, a single filter cartridge can be obtained comprising three separate filter regions, of which two are in series and a third is in parallel with the first two, as prescribed by the said European patent 341349. By virtue of the invention it is also possible to construct lubricant filters for internal combustion engines for full flow which are of simple configuration, and are provided with a single cartridge operating as a plurality of parallel cartridges of mutually different filtration characteristics. Finally, the invention results in extraordinary simplification in the construction of known filter devices. These and further characteristics of the invention will be apparent from the detailed description given hereinafter with reference to the accompanying drawings, which illustrate preferred but non-limiting embodiments thereof. Figure 1 is a schematic side view showing part of the material processing cycle. Figure 2 is a section on the line II-II of Figure 1. Figure 3 is a section on the line III-III of Figure 1. Figure 4 is an exploded view of the material sheet when in position IV of Figure 1. Figure 5 is an enlarged perspective view of a portion of the filter medium. Figure 6 shows a filter cartridge comprising the portion of Figure 5. Figure 7 shows a second embodiment of a filter cartridge comprising the invention. The figures show two forming boxes 1 and 2, of which the box 1 contains only cellulose fibres and the box 2 contains a 50% pulp of cellulose fibres and glass fibres. Polyester, polyethylene or polyamide fibres can be used instead of glass fibres. A single endless support web 3 is guided along a path which successively grazes the forming rollers 4 and 5. These latter have a mesh surface able to retain a layer of pulp which is deposited on the web 3, which also performs a first draining function. The forming roller 5 comprises regions or strips 6 masked for example by a plastic cloth, which prevents the roller retaining the pulp contained in the box 2. In this manner, downstream of the box there is created a web 7 of filter medium having a first layer or substrate 8 composed of cellulose pulp, and a second layer 9 composed of strips 10 of pulp containing cellulose and glass fibres. Said web is then collected by a felt conveyor belt 11 which absorbs the pulps and fixes them together. Downstream of the conveyor 11 the web of filter medium is pressed between two steel rollers 12 and 13, as stated. As stated, the pressing stage can take place at a pressure of between 0.1 and 1 kg/cm 2 , and is very delicate in that it determines the degree of compactness and hence the porosity of the two layers. As can be seen from Figure 2, it is implemented between two steel rollers 12 and 13, in the illustrated case one of the rollers, namely the roller 12, being of slightly differential diameter so that the regions occupied by both layers are subjected to a lesser pressure than the regions occupied by a single layer, for the reasons stated hereinafter. Figure 1 shows a drying roller 14 heated to about 120°C, a drying oven 15 being provided downstream. Downstream of the drying oven the filter medium web is immersed in an acrylic latex solution 16 after which it reaches drying means 14 and 15 identical to the preceding. The process terminates by final winding onto a reel 18. The web obtained in this manner is cut into strips 17 such as that shown in Figure 5, occupied for about a third of their width by a layer A of cellulose material or paper, and for the remaining two thirds by a layer A of cellulose material and a layer B of cellulose material with glass fibres, said two layers being pressed to a lighter extent than the single layer of cellulose material because of the differing diameter of the presser roller 12. The hence constructed sheet is folded in the usual manner to obtain from it a single filter cartridge to be inserted into a filter device such as that shown in Figure 6. During folding, care must be taken to locate the cellulose material substrate externally, so that the resultant cartridge comprises a first filtering region A of intermediate porosity in parallel with a filtering region AB which is of fine porosity internally and coarse porosity externally. According to a further embodiment, the presser rollers 12 and 13 are perfectly cylindrical, so enabling filter cartridges to be created having regions 20 consisting only of the cellulose substrate, and characterised by coarse porosity, between regions 21 formed from two layers consisting respectively of the cellulose material alone and cellulose material with glass fibres providing finer porosity. It is evident that by controlling the pressing by using rollers of different diameters, all desired porosity ratios can be achieved. In the example shown in Figures 5 and 6, the thickness of the portion A after pressing is about 0.4 mm, while the thickness of the portion AB is about 0.8 mm. In this latter portion the cellulose material itself has a thickness of 0.6 mm. In the example shown in Figure 7, the two-layer regions and the single-layer regions have the same thickness after pressing, namely about 0.6 mm. A further embodiment of the invention, not shown, comprises three layers, of which the outer layers are of cellulose alone, whereas the intermediate layer is of cellulose with glass fibres, or another equivalent as stated. With reference to Figure 6, it should be noted that the longitudinal dimensions of the filtering regions A and AB in the direction of the filter axis can be different from those shown. For example the filtering region A could be much longer than the filtering region AB.

Claims: A process for manufacturing a filter medium characterised by comprising the following operations: preparing in a pulper or beater a pH 3-5 aqueous suspension of cellulose fibres with a concentration of between 3% and 5%; preparing in a pulper or beater a pH 2.8-3.8 aqueous suspension of glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres having a fibre concentration of between 0.5% and 1.2%; preparing a first pulp consisting exclusively of cellulose fibres, to which a moisture-resistant resin chosen from the group comprising acrylic resins and epoxy resins is added; preparing a second pulp consisting of cellulose fibres and glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres in a proportion of between 30% and 70%, to which a moisture-resistant resin chosen from the group comprising acrylic resins and epoxy resins is added; forming two superposed layers of said pulps by methods used in paper manufacture; collecting said two layers on a layer of material able to absorb water; pressing the two superposed layers of pulp to a pressure of between 0.1 and 1 kg/cm2; drying the resultant sheet to a moisture content of 1%; - impregnating the dried material with a 50 wt% solution of acrylic latex; again drying and winding on a reel. A process as claimed in claim 1, characterised in that the glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres have a size of between 0.5 and 14 mm. A process as claimed in claim 1, characterised in that the pulp containing glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres and cellulose fibres contains 50% of glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres. A process as claimed in claim 1, characterised in that drying takes place at a temperature of 120°C. A filter medium comprising at least one layer obtained from a pulp exclusively of cellulose fibres and at least one layer obtained from a pulp containing cellulose fibres and glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres in a proportion of between 30% and 70% characterised in that said pulps contains acrylic latex and a moisture resistant resin chosen from the group comprising acrylic resins and epoxy resins. A filter medium as claimed in claim 5 , characterised in that the layer obtained from a pulp of cellulose fibres and glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres comprises parallel strips which do not completely cover the layer obtained from the pulp containing exclusively cellulose fibres. A filter medium as claimed in claim 5 , characterised by comprising two layers of cellulose fibres. A filter medium as claimed in claim 5 , characterised by comprising two layers of cellulose fibres mixed with glass fibres or polyester fibres, or polyamide fibres or polyethylene fibres. A filter medium as claimed in claim 5 , characterised in that each layer has a thickness of of between 0.4 and 0.8 mm. A lubricant filter for internal combustion engines, characterised by comprising a filter cartridge consisting of a filter medium in accordance with claims 5 to 9 , the filter cartridge comprising at least one region in which the filter medium has only a layer of cellulose material and at least one region in which the filter medium comprises a layer of cellulose material and a layer of material containing glass fibres and cellulose fibres. A lubricant filter for internal combustion engines, characterised by comprising a filter cartridge formed from a filter medium in accordance with claims 5 to 9, consisting of three layers of filter medium.

Inventors: GIRONDI GIORGIO
Applicants: UFI UNIVERSAL FILTER INTERNAT, UFI UNIVERSAL FILTER INTERNATIONAL S.P.A.
Application year: 1997
Main classification: B01D39
IPC codes: D21H13, D21H27, B01D39, B32B5, D21H17, B32B23