Filter Element and method for producing the same

Abstract

A filter element (1), in particular for a motor vehicle, comprises at least one end cap (2, 3) and a filter medium (4) joined to the end cap (2, 3), wherein the at least one end cap (2, 3) comprises rubber and at least one heat-conducting additive. In a method for producing the filter element (1), at least one end cap (2, 3) is at least partially produced from rubber and a heat-conducting additive, wherein a thermal vulcanization process is carried out.

Claims

1. A method for producing a filter element, wherein the filter element comprises: at least one end cap; and a filter medium joined to the at least one end cap; the method comprising the steps of: providing a filter medium of a woven or non-woven natural or synthetic fibers; pleating the filter medium into a plurality of zig-zag folds; providing an outer end cap layer of a fiber reinforced polyamide material for the at least one end cap; providing a raw nitrile butadiene rubber material; providing a heat-conducting additive selected to improve transport of heat during vulcanizing, the heat-conducting additive selected from the group consisting of: diamond, hexagonal or cubic boron nitride, hexagonal or cubic aluminum nitride, aluminum oxide, silicon carbide; wherein the heat-conducting additive further includes iron metal particles and graphite; mixing the heat-conducting additive into the raw nitrile butadiene rubber material to form raw curable nitrile butadiene rubber adhesive mixture, forming a curable nitrile butadiene rubber adhesive film; forming an uncured end cap comprising a curable nitrile butadiene rubber adhesive film from the raw curable nitrile rubber adhesive mixture by the steps of: applying the raw curable nitrile butadiene rubber adhesive mixture onto a filter medium facing side of the outer end cap layer; thermal vulcanizing and cross-linking the curable nitrile butadiene rubber adhesive film of the uncured end cap to for the at least one end cap by applying a heating energy by a means selected from the group consisting of: heating plates, induction heating, infrared radiation, or microwave radiation; wherein the thermal vulcanizing step includes: increasing volume of the curable nitrile butadiene rubber adhesive film by thermal foaming, the thermal foaming partially foaming the curable nitrile butadiene rubber adhesive film on the filter medium facing side of the outer end cap layer; pressing the filter medium into the partially foamed curable nitrile butadiene rubber adhesive film of the at least one end cap; continuing the thermal vulcanizing, increasing volume of the curable nitrile butadiene rubber adhesive film by thermal foaming, the thermal foaming conforming the curable nitrile butadiene rubber adhesive film onto pleat edges of the plurality of zig-zag folds of the filter medium; and forming a fluid-tight joint between the at least one end cap and the filter medium by the thermal foaming.

2. The method according to claim 1, wherein before the step of forming an uncured end cap, the method further comprises: adding at least one at least at least one vulcanization accelerator to the raw curable nitrile butadiene rubber adhesive mixture, the at least one vulcanization accelerator selected from the group consisting of: dithiocarbamates, xanthogenates, sulfenamides and/or thiazoles.

3. The method according to claim 1, wherein in the step of providing a raw nitrile butadiene rubber material, the raw nitrile butadiene rubber material includes zinc oxide as a vulcanization activator.

4. The method according to claim 1, wherein the raw curable nitrile butadiene rubber adhesive mixture includes a phenolic resin.

5. The method according to claim 1, wherein the raw curable nitrile butadiene rubber adhesive mixture includes hexamethylenetetramine.

6. The method according to claim 1, wherein the raw curable nitrile butadiene rubber adhesive mixture includes sulfur or sulfur compounds.

7. The method according to claim 1, wherein the raw curable nitrile butadiene rubber adhesive mixture includes a processing aid selected from the group consisting of: alkyl sulfonic acid esters and hydrocarbon mixtures.

8. The method according to claim 1, wherein before the step of forming an uncured end cap, the method further comprises: adding xanthogenates as a vulcanization accelerator to the raw curable nitrile butadiene rubber adhesive mixture.

9. The method according to claim 1, wherein the raw curable nitrile butadiene rubber adhesive mixture includes alkyl sulfonic acid esters as a processing aid.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the drawings:

(2) FIG. 1: shows a schematic perspective representation of one embodiment of a filter element for a motor vehicle; and

(3) FIG. 2: shows a schematic representation of one embodiment of an end cap for a filter element.

DETAILED DESCRIPTION

(4) FIG. 1 shows a schematic perspective representation of one embodiment of a filter element 1 for a motor vehicle. The filter element 1 can be an air filter or a liquid filter, in particular a fuel filter.

(5) The filter element 1 includes a filter medium 4, which is designed as a mini-pleat pack composed of pleated filter material. Non-woven polymer materials folded in a zigzag-shaped manner are frequently used as filter materials. In the orientation of FIG. 1, an end cap 2, 3 is provided at a respective end side of the filter medium 4 on the upper face and lower face on pleat profiles 9 of the filter medium 4, which forms a continuous bellows. The filter element 1 includes at least one end cap 2, 3; preferably, however, it includes two end caps 2, 3. The end caps 2, 3 are joined to the filter medium 4 in particular in a fluid-tight manner. A bonded joint between the end caps 2, 3 and the filter medium 4 can take place, for example, such as by way of an adhesive film facing the filter medium 4. The end caps 2, 3 lend the filter element 1 a certain level of stability, allowing the same to be used in a corresponding fluid circuit. The filter medium 2 can be pressed into partially foamed material of the end caps 2, 3. A connector 6 forms part of the upper end cap 2, for example. Analogously, the lower end cap 3 can have an opening 7, which can serve as a connection.

(6) In the orientation of FIG. 1, pleatedges 9 of the filter medium 4 are shown on the upper face. During operation, for example as an air filter or a liquid filter, the fluid to be filtered, such as air, flows through the filter surface, which is increased by the pleated filter material 4. The filter materials and geometries of the filter medium 4 or of the filter element 1 are generally adapted to a predefined flow direction. FIG. 1, for example, shows the untreated air RO from the side, and the filtered clean air RL upward and downward. In the orientation of FIG. 1, the surface facing the interior space 8 thus forms the outflow side, and the outer lateral surface of the cylindrical filter medium 4 forms the incident flow side of the filter element 1. An optional support element 5, which is present between the end caps 2, 3, is provided inside the bellows 4.

(7) FIG. 2 is a schematic representation of an end cap for a filter element. FIG. 2 shows an end cap 2 that includes multiple layers or sections. The end cap 2 has a carrier material 2A, for example a fiber-reinforced plastic material, which is joined to the filter medium 4 by way of a joining or gluing section 2B. The pleat edges 9 (see FIG. 1) are covered, so that fluid can flow exclusively through the filter medium 4 or the connections 6, 7. The adhesive section 2B can also be referred to as adhesive film. It may in particular be referred to as a film end cap when the end cap material is composed of a vulcanized rubber material, for example.

(8) In the embodiment as shown in FIG. 2, a section 2B includes nitrile rubber (NBR) is provided, which is completely vulcanized during the course of the production method for a corresponding filter element 1. Vulcanizing is preferably carried out thermally, for example using vulcanization accelerators. Hereafter, it is referred to as an adhesive film 2B to simplify matters. Nitrile rubber is hereafter simply referred to as a rubber material by way of example. In principle, rubber materials in general are suitable for use in filter end caps.

(9) The adhesive film 2B in particular forms part of the end cap 2 in the cured and cross-linked state. This is also referred to as a film end cap. In embodiments, the rubber raw material of the film end cap 2B is made of a rubber having a viscosity between 10 and 80 MU, and more particularly between 20 and 60 MU.

(10) The adhesive film 2B is at least partially produced from nitrile rubber, a synthetic rubber. Nitrile rubber, or NBR, is substantially resistant to working fluids in the motor vehicle field, such as oils, greases, hydrocarbons, combustion air for engines, urea solution and the like.

(11) So as to start a cross-linking reaction or the vulcanization, an activation energy E.sub.A must be overcome, wherein the reaction rate k is dependent on the temperature and described by way of the Arrhenius equation: d(In k)/dT=E.sub.A/R.Math.T.sup.2(R: gas constant, T: temperature). A temperature increase thus drastically impacts the cross-linking rate. For this reason, a heat-conducting additive is introduced into the formulation of the raw substance for the end cap 2, which has a high thermal conductivity . is dependent on the heat conductivity , the density , and the specific heat capacity c starting at: =/(.Math.c). At 1.18 10.sup.6 m.sup.2/s, graphite has a particularly favorable thermal conductivity, for example.

(12) The NBR mixture of the adhesive film 2B includes a heat-conducting additive so as to accelerate thermal vulcanization. The heat-conducting additive is in particular carbon, metal powder, (hexagonal) boron nitride, (hexagonal) aluminum nitride, (-)aluminum oxide and/or silicon carbide. PHR is understood to refer to the mass fraction of a particular mixture relative to the base polymer, which is in particular NBR here.

(13) Optionally, it is possible to use vulcanization accelerators in particular from the substance group of dithiocarbamates, sulfenamides, benzothiazoles and/or zinc oxide as the vulcanization accelerator activator.

(14) The applicant has analyzed various formulations for NBR-based adhesive films for use in filter elements as parts of end caps. A first preferred formulation includes at least one heat-conducting additive from the group consisting of: carbon (graphite, carbon black or diamond), boron nitride (white graphite), aluminum nitrite, aluminum oxide, silicon carbide, graphite, and carbon black combined with NBR rubber.

(15) A second preferred formulation for filter end caps or filter adhesive films including rubber include the heat-conducting additives from the first formulation and at least one further vulcanization accelerator from the group of dithiocarbamates, sulfenamides and/or benzothiazoles.

(16) A third formulation includes NBR rubber, at least one heat-conducting additive, and a vulcanization accelerator, as well as zinc oxide as the activator for the vulcanization process. 150 PHR graphite, 1 PHR zinc oxide, and 0.5 PHR zinc dibenyzldithiocarbamate in the NRB raw substance are conceivable.

(17) A fourth formulation includes nitrile rubber including a vulcanization accelerator from the group of dithiocarbamates, sulfenamides and/or benzothiazoles. Furthermore, elemental sulfur, phenolic resin, hexamethylenetetramine (urotropine), at least one heat-conducting additive from the group consisting of carbon (graphite, carbon black or diamond), boron nitride, aluminum nitride, aluminum oxide and/or silicon carbide were admixed to the NBR. The fourth formulation furthermore optionally includes zinc oxide as the activator for the vulcanization accelerators that are used.

(18) A fifth formulation includes the same substances as the first through fourth formulations and additionally provides for a substance as a processing aid, such as a tackifying agent or water. The end cap may be at least partially produced from a raw material that comprises a processing aid selected from: alkyl sulfonic acid esters and/or hydrocarbon mixtures. Pigments may optionally be added to adapt the color of the rubber.

(19) In particular the proposed fourth and fifth formulations are suitable for appropriately adapting the hardness, elasticity and chemical properties of the end cap.

(20) Heat-conducting additives are used in the described formulations in dosages between 10 and 150 phr. Phenolic resin is used in the described formulations in dosages between 20 and 250 phr. And vulcanization accelerators are used in the described formulations in dosages between 1 and 30 phr. If necessary, a vulcanization retarder may also be admixed so as to increase the storage stability.

(21) The proposed formulations allow the vulcanization process to be used in a targeted manner. It has been shown that the heating time for thermal vulcanization is reduced over conventional adhesive film formulations. In addition, at least partial foaming takes place by way of the proposed film end caps or the adhesive films that are used, so that the respective end cap is joined to the pleat profiles or pleat edges in a fluid-tight manner.

(22) During the production process of the corresponding filter elements, initially a filter medium is provided, to which the adhesive film is attached and which is subsequently thermally cured. For this purpose, the adhesive film is heated by the irradiation of energy. In this way, the rubber material is vulcanized, whereby the film and the filter medium are joined to each other. In particular, the vulcanized rubber material encloses the pleat edges or pleat profiles 8 (see FIG. 1).

(23) As an alternative or in addition, the film may be used as an adhesive means between a further end cap material, as is shown in FIG. 2 as 2A, for example. The vulcanization is carried out in particular at temperatures between 50 and 350 C., and preferably between 120 and 160 C.

(24) The duration of the vulcanization process ranges between 10 and 350 s in embodiments of the production method.

(25) The proposed filter elements, film end caps, adhesive films, and production methods allow improved and simplified production of filter elements. By way of the described formulations, it is possible to achieve homogeneous cross-linking degrees in the rubber material.

(26) While the present invention was described in more detail based on preferred exemplary embodiments, it is not limited to these, but may be modified in a variety of ways. The use of a or an does not exclude a plurality. It is moreover possible to add further substances to the NBR formulations, such as pigments or processing aids.