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EP-4741035-A1 - PULSE FILTER

EP4741035A1EP 4741035 A1EP4741035 A1EP 4741035A1EP-4741035-A1

Abstract

The present invention relates to a filter medium comprising a base web of cellulose fibers, wherein the base web comprises a first and a second layer of cellulose fibers and a transition region between the first and the second layers, wherein the cellulose fibers of the first layer and the cellulose fibers of the second layer are intertwined in the transition region, wherein the first layer comprises more cellulose fibers, expressed as mass of cellulose fibers per unit area, than the second layer, and wherein the base web has a high specific volume of from 4 m 3 /g to 9 m 3 /g. The present invention further relates to a filter arrangement, a filter element, an air filter and a pulse filter comprising the above filter medium.

Inventors

  • NIEDERHUBER, Armin
  • Kampe, Anja

Assignees

  • Neenah Gessner GmbH

Dates

Publication Date
20260513
Application Date
20241107

Claims (15)

  1. A filter medium comprising a base web of cellulose fibers, wherein the base web comprises a first and a second layer of cellulose fibers and a transition region between the first and the second layers, wherein the cellulose fibers of the first layer and the cellulose fibers of the second layer are intertwined in the transition region, wherein the first layer comprises more cellulose fibers, expressed as mass of cellulose fibers per unit area, than the second layer, and wherein the base web has a specific volume from 4 m 3 /g to 9 m 3 /g.
  2. The filter medium according to claim 1, wherein the base web of cellulose fibers is a two-layered base web consisting of the first and the second layer of cellulose fibers with the transition region between them.
  3. The filter medium according to claim 1 or 2, wherein the base web has at least one of the following features (i) to (v): (i) the air permeability thereof is from 400 to 800 l/m 2 s; (ii) the thickness thereof is from 150 µm to 300 µm; (iii) the basis weight thereof is from 25 to 55 g/m 2 ; (iv) the tensile strength ratio MD/CD thereof is from 2 to 3.2 (v) the maximum pore size thereof is from 90 µm to 130 µm.
  4. The filter medium according to any one of claims 1 to 3, wherein the second layer contains curled fibers, preferably in an amount of 15 wt.-% to 40 wt.-%, in terms of the weight of the cellulose fibers of the second layer.
  5. The filter medium according to any one of claims 1 to 4, wherein the second layer comprises uncurled fibers, preferably in an amount of 60 to 85 wt.-%, in terms of weight of the cellulose fibers of the second layer.
  6. The filter medium according to any one of claims 1 to 5, wherein the base web contains 15 to 40 wt.-%, preferably 25 to 35 wt.-%, of curled fibers, in terms of the weight of the cellulose fibers of the base web in total.
  7. The filter medium according to any one of claims 1 to 6, wherein the cellulose fibers of the second layer are softwood fibers.
  8. The filter medium according to any one of claims 1 to 7, wherein the base web is a non-impregnated base web of cellulose fibers and/or wherein the base web consists of cellulose fibers.
  9. The filter medium according to any one of claims 1 to 8, which consists of the base web of cellulose fibers.
  10. The filter medium according to any one of claims 1 to 9, which is a cleanable filter medium, which is optionally cleanable by pressure shock pulsing.
  11. A filter arrangement comprising a first and a second filter, wherein the first filter is a filter medium according to any one of claims 1 to 10 and wherein the second filter is optionally a glass filter, paper filter or meltblown filter.
  12. The filter arrangement according to claim 11, which further comprises one or two nonwoven filter layers that are optionally arranged upstream of the first and/or downstream of the second filter.
  13. A filter element comprising a filter medium according to any one of claims 1 to 10.
  14. An air filter comprising a filter medium according to any one of claims 1 to 10.
  15. A pulse filter comprising a filter medium according to any one of claims 1 to 10.

Description

Technical Field of the Invention The present invention relates to a filter medium, in particular to a cleanable filter medium. The present invention moreover relates to a filter arrangement, a filter element, an air filter and a pulse filter comprising the filter medium. Prior Art Nowadays, there are also requirements on filter materials to be more environmentally friendly in being biodegradable. At the same time, the filter material should maintain good filter performance and efficiency. A filter for cleaning air and gases with a filter material of cellulose fibers is described in US 2012-167771 A1. Another example for a disintegrable filter material which is water dissolvable and made of cellulose acetate fiber tows is given in JP-H09103280 A. CN 102691234 A describes a multi-layer paper filter material (for cigarettes) and its process with a focus on environmental protection. The filter materials described in US 2012-167771, JP-H09103280 A and CN 102691234 A are intended to be used in cigarettes, so that they are not cleanable or reusable. One example for a method to produce multilayer paper is given in US 2010-000693 A1 which uses cellulose fibers. Another method for the production of a multilayer-ply web, in which different pulp suspensions can have different compositions and a fiber web machine for its production is described in EP 3540119 A1. A multi-phase filter medium based on hardwood and softwood fibers is described in US 2010-116138 A1. Rotoformers are used in the working examples of US 2010-116138 A1 to prepare the filter media. Another document wherein multilayer paper webs based on hard and softwood fibers are formed is US 6464830 B1. However, these documents are not concerned with cleanable filters. There are filter materials that due to their structure are cleanable filter materials. Surface filter materials have smaller pores in the first filtration layer in flow direction. The pores in the following layer are larger. Due to this structure of the filter material, virtually all particles, regardless of their size, are separated at the outer surface (first layer) of the filter material and hardly any particles reach the inner layer(s). This results in the formation of a filter cake on the outer surface of the filter material. The filter cake is removable, i.e. the filter material is cleanable, by cleaning steps such as tapping, shacking, washing, pressure shock, or backwashing. For removing the filter cake by pressure shock or backwashing, clean gas or liquid is pressurized against the initial flow direction from the downflow side of the filter. Therefore, the cleanable filters are also denoted as pulse filters. The cleaned surface of the filter material can then be used for another pulse cycle (which corresponds to a dust loading cycle). Apart from the general filtering properties such as air permeability and dust absorption, the number of cycles that the cleanable filter material can be used without unacceptably high increase in pressure drop throughout the material, e.g. due to particles that can no longer be removed by the cleaning steps, is an important performance characteristic of the filter material. As will be appreciated, the number of cycles that the cleanable filter material can be used effectively translates into the lifetime of the filter material. WO 2013/029697 A2 describes a multilayer cleanable filter material and surface filter elements usable for separation of solid impurities in gases and liquids. For better separation of fine particulate matter, the filter material according to WO 2013/029697 A2 comprises a melt blown layer on the upstream side. This requires the use of thermoplastic material. However, the use of several layers of different materials including melt blown materials, leaves room for improvement from an environmental perspective. Technical Problem Accordingly, there is a need for a cleanable filter medium that is environmentally friendly and nonetheless has excellent general filtering properties, such as air permeability and dust absorption, and when applied as a cleanable filter exhibits a long lifetime. Summary of the Invention The present invention solves the problems of the prior art by the following means. In a first aspect, the present invention relates to a filter medium comprising a base web of cellulose fibers, wherein the base web comprises a first and a second layer of cellulose fibers and a transition region between the first and the second layers, wherein the cellulose fibers of the first layer and the cellulose fibers of the second layer are intertwined in the transition region, wherein the first layer comprises more cellulose fibers, expressed as mass of cellulose fibers per unit area, than the second layer, and wherein the base web has a specific volume from 4 m3/g to 9 m3/g, preferably from 4.5 m3/g to 8 m3/g, more preferably from 5 m3/g to 7 m3/g and most preferably from 5.5 m3/g to 6.5 m3/g. In a second aspect, the present invention rela