WO2010026133A2

WO2010026133A2 - A high-strength and high-accumulation capacity multi-layer filter medium and a process for realisation thereof

Info

Publication number: WO2010026133A2
Application number: PCT/EP2009/061259
Authority: WO
Inventors: Giorgio Girondi
Original assignee: Ufi Innovation Center S.R.L.
Priority date: 2008-09-05
Filing date: 2009-09-01
Publication date: 2010-03-11
Also published as: EP2318113A2; WO2010026133A3; ITRE20080081A1

Abstract

A multilayer filter medium comprising, from upstream to downstream relative to a direction of filtration, at least a first layer made of glass fibre (C, C'), a second intermediate layer made of coarse mesh nonwoven fabric (D, D') and a third support layer (E, E') made of nonwoven fabric, characterized in that the intermediate layer (D, D') of coarse mesh nonwoven fabric is joined by fusion and/or bonding both to the first layer in glass fibre (C, C') and to the third support layer (E, E') in nonwoven fabric. The object of the invention includes a process for realizing a multilayer filter medium.

Description

A HIGH-STRENGTH AND HIGH-ACCUMULATION CAPACITY MULTILAYER FILTER MEDIUM AND A PROCESS FOR REALISATION THEREOF

Technical Field

The present invention is a high-strength and high-accumulation capacity multilayer filter medium and a procedure for its realization.

The filter medium of the invention can be used in all applications of filter mediums in which glass fibre is used, and in particular in all applications wherein operating pressures are high and/or wherein pressure peaks are possible.

Background Art

As is known, the binding of a plurality of layers for the realization of multilayer filter mediums normally involves a stage of heating or pressure with ultrasound using beams or pointed elements that ensure localized fusion of the supporting nonwoven fabric (NWF) with the glass fibre.

Consequently, known filter mediums consisting of a plurality of layers have the layers bound together discontinuously with localized fused areas. This configuration presents a number of disadvantages including the fact that known filter mediums, as a consequence of discontinuous bonding between layers, do not have optimum resistance to folding.

Furthermore, when these filter mediums are used under high operating pressures, or with high pressure peaks, they tend to structurally disintegrate, with the nonwoven fabrics tending to detach from the glass fibre, resulting in a significant decline in filtering efficiency.

Furthermore, known filter mediums normally require a plurality of support layers, which can result in sub-optimal distribution of polluting retentate inside the filter. Disclosure Of The Invention

An aim of the present invention is to obviate the problems described above, by providing a filter medium with improved differential pressure performance. A further aim of the present invention is to provide a filter medium with high accumulation capacity with improved internal distribution of retentate. A further aim of the present invention is to provide a filter medium with high resistance to folding. These aims are achieved by a multilayer filter medium comprising, from upstream to downstream in the direction of filtration, at least a first layer of glass fibre, a second intermediate layer of coarse mesh nonwoven fabric, and a third supporting layer in nonwoven fabric, characterized in that the intermediate layer in coarse mesh nonwoven fabric is joined by fusion and/or bonding both to the first layer in glass fibre and to the third supporting layer in nonwoven fabric.

The invention also has the aim of providing a process for realization of a multilayer filter medium, starting from a plurality of reels each unwinding a material destined to form one of the layers of the filter medium, comprising a stage of combination of the various layers into a single flat multilayer material, a pre-heating stage for the multilayer filter medium, a compression stage with a pair of counterpositioned rollers, at least one of which is heated, and a stage of bonding of the materials. The dependent claims delineate preferred and particularly advantageous embodiments of the invention.

Brief Description Of The Drawings

Further characteristics and advantages of the invention will better emerge from the detailed description made herein, provided by way of non-limiting example, with the support of the accompanying figures of the drawings, wherein:

- figure 1 is a cross-section view of the filter medium in a first embodiment of the invention;

- figure 2 is a cross-section view of an alternative embodiment of the filter medium of the invention; - figure 3 is a layout diagram of a system for realization of the filter medium of the invention;

- figure 4 is a layout diagram of a system for realization of an alternative embodiment of the filter medium of the invention;

- figure 5 illustrates filter efficiency as a function of differential pressure with reference both to a known filter medium and to a filter medium of the invention; - figure 6 illustrates the development of differential pressure as a function of the distribution of retentate with reference to both a known filter medium and a filter medium of the invention.

Best Mode Of Carrying Out The Invention

With reference to figure 1 , a first embodiment of the multilayer filter medium of the invention comprises, in a direction going from upstream to downstream in relation to the filtration direction as indicated by the arrow, a support layer

A in nonwoven fabric, preferably made of polyester, with permeability of 1500 to 6000 l/m²/s, a differential pressure of 50 to 500 Pa, and a weight of 20 to

100 g/m². There is also a layer B in coarse mesh nonwoven fabric, preferably made of polypropylene.

Subsequently a layer C made of glass fibre is provided, with a porosity within a range of from 1 to 40 μm and a weight from 40 to 150 g/m².

Downstream of the glass fibre layer C there is a layer D in coarse mesh nonwoven fabric, made of polypropylene, fused or adhered to the adjacent layers (C and E) upstream and downstream of the filtration direction.

Finally, the multilayer filter medium of figure 1 provides a support layer E in nonwoven fabric, made of polyester, with permeability within the range from

1500 to 6000 l/m²/s, a differential pressure of 50 to 500 Pa, and a weight of 20 to 100 g/m².

Consequently both layer B and layer D act as continuous bonding elements for the adjacent layers.

A variant of the multilayer filter medium of the invention is illustrated in figure

2. The material of figure 2 comprises layers as follows arranged upstream and downstream relative to the direction of filtration as indicated by the arrow in figure 2.

There is a first layer C in glass fibre with porosity within a range of from 1 to - A -

40 μm and a weight of 40 to 150 g/m², a second layer D' made of coarse mesh nonwoven fabric, preferably polypropylene, fused or bonded to the glass fibre layer C.

Finally, there is a support layer E' made of nonwoven fabric, preferably realized polyester, with a permeability of 1500 to 6000 l/m²/s, a differential pressure of 50 to 500 Pa, and a weight of 20 to 100 g/m2, acting as a continuous bonding element for the adjacent layers.

Further, layer D' is fused or bonded to the support layer E'.

The production of the above-described filter mediums is now described with reference to a specifically-designed system for this production and comprising a plurality of reels, each of which pays out one of the components making up the superimposed layers of the filter medium of the invention.

In particular (figure 3) the system comprises a reel 11 dispensing the supporting nonwoven fabric (NWF) destined to form layer E in figure 1 , made of a high-fusion temperature polymer material, for example polyester; the roller 11 is idle and unwinds the flat material in response to traction from driven rollers described below.

Alongside the reel 11 is another idle reel 21 for unwinding a low-fusion- temperature coarse-mesh nonwoven polymer material destined to form layer D in figure 1.

The material unwound from the reel 21 can be, for example, polypropylene.

The system also comprises a reel 3 dispensing the glass fibre layer C; this reel 3 is also idle.

Finally, there is a reel 22, for an equivalent but not necessarily identical material to that of reel 21 , relative to the nonwoven fabric destined for layer B of figure 1 , and a reel 12, for an equivalent but not necessarily identical material to that of reel 11 , destined for layer A of figure 1.

In more detail, the reel 22 can serve to pay out a coarse-mesh nonwoven fabric in low-fusion-temperature polymer material, such as for example polypropylene, and the reel 12 can serve to unwind a material like for example polyester.

The various layers of material being dispensed by the reels described above pass between idle transmission rollers 51 and 52 serving to collect the various layers into a single flat material.

To ensure stretching of the multilayer filter medium fully across the width thereof, the system includes a pair of idle spiral rollers 61 ,62 with a plurality of spirals on the outer surfaces configured such that the rotation of the rollers causes the surface thereof in contact with the multilayer filter medium to push the filter medium outwards.

Pre-heating of the multilayer filter medium is done by heating elements 63,64 located on both sides of the multilayer filter medium in the positions indicated in figure 1 , and in particular between rollers 61 and 62.

The plant also provides a driven roller 41 , heated to the softening or fusion temperature of the low fusion temperature nonwoven fabric. For example, in the case of polypropylene the roller is preferably heated to a temperature of approximately 160⁰C. In counterposition to roller 41 another roller 42 is provided, similar to roller 41 as regards both temperature and speed, but having an additional function of exercising pressure on the multilayer filter medium in the direction indicated by the arrow in figure 3. The material comprising the various layers of the filter medium, once accumulated by the idle rollers 51 , 52, is first heated and then compressed at a pressure which can be of between 1 and 7 bar.

Downline of and in proximity of the heated rollers 41 , 42, a pair of rollers 71 and 72 are provided, arranged in sequence in the direction of travel of the multilayer filter medium, such as to obtain a perfect and uniform joining of the layers. In this way the action of the rollers is in successive stages, roller 71 acting first and positioned such as to apply pressure on the polymer material and the glass fibre arriving respectively from reels 12 and 3, such as to ensure safe and continuous bonding of these layers to the coarse mesh nonwoven fabric arriving from the reel 22. Downline of roller 71 is roller 72, so-positioned to apply pressure on the glass fibre and the polymer material arriving respectively from rollers 3 and 11 such as to ensure secure and even bonding of these layers to the coarse mesh nonwoven fabric arriving from the reel 21.

Furthermore, the rollers 71 and 72, in order to ensure an effective bonding action, are staggered such as to oblige the multilayer material to follow an S shaped path, or in any case not rectilinear, thereby increasing the bonding between the different layers.

At the end of the system there is a driven stretcher roller 8, exercising a constant pressure on the multilayer filter medium such as to keep it stretched, and a driven winding roller 9 serving to accumulate the finished multilayer filter medium. The speed of roller 9 is electronically controlled such as to be a function of the speed of the heated rollers 41 and 42, and of the pressure of the stretcher roller 8 (which is substantially constant).

During system operation the high- and low-fusion temperature nonwoven fabrics and the glass fibre arriving from the rollers 11 ,21 ,3,22, and 12 are collected by the transmission rollers 51 and 52, subsequently the resulting multilayer medium is preheated by the heating elements 63,64 when the multilayer filter medium passes through the space between the spiral rollers 61 and 62. Subsequently the multilayer filter medium passes through the heated rollers 41 and 42 when the temperature thereof, and the pressure exercised by roller 42, cause the low fusion temperature nonwoven fabrics to soften such that, following transit through rollers 71 and 72, they bond to the high fusion temperature nonwoven fabric. The high fusion temperature nonwoven fabrics do not change state in response to the temperature of rollers 41 and 42, as the melting temperature of polyester is approximately 280⁰C, (assuming that polyester is in fact the material used for this layer).

Subsequently the bonded multilayer filter medium is kept stretched by the stretcher roller 8, and slowly the temperature of the filter medium falls, after which the medium is wound on the winding reel 9.

An alternative embodiment of the system is illustrated in figure 4, wherein certain components illustrated are also present in the system illustrated in figure 3, but absent from figure 4 are the reels for the low and high fusion temperature nonwoven fabrics corresponding to one side of the glass fibre material.

In particular, in the system of figure 4 the reel 22 and the reel 12 are absent. However, the operation of the system is entirely similar to that of figure 3, producing the material of figure 2, where in particular the material comprising layer E' is unwound from reel 11 , the material comprising layer C is unwound from reel 3, and the material in coarse mesh nonwoven fabric comprising layer D' is unwound from reel 21 , layer D' being fused or bonded between the two layers C and E'.

In this case too, starting from the reels, the various layers are subsequently combined to form a single flat multilayer material. There follows a preheating stage of the multilayer filter medium, a compression stage with a pair of counterpositioned rollers with at least one roller heated, and a stage of bonding the materials.

Among the advantages of the process of the invention, firstly there is no bonding stage using heated pointed elements or slats, or by ultrasound, since the addition of the heated rollers and the layers of bonding material result in the continuous bonding of the layers at the same speed as the transition of the band of filter medium.

A further advantage of the invention is the presence of rollers 71 and 72 close to the outlet of the filter medium from the heated rollers. These rollers are configured such as to assist bonding and the distribution of the bonding layers on both sides of the filter medium. The continuous and regular distribution of the bonding layers results in the mechanical resistance of the multilayer filter medium being considerably greater than in the prior art, such that the filter medium offers greater resistance to loads applied during bending and in particular is very resistant to high differential pressure. This advantage is clearly illustrated in the graph of figure 5, in which the curve 1 plots filtering efficiency as a function of differential pressure in a known multilayer filter medium, and curve 2 plots the behaviour of a multilayer filter screen configured as in the invention: note that from approximately 5,500 hPa upwards curve 1 indicates a significant fall in filtration efficiency, this resulting from the structural breakdown of the filter medium caused by detachment of the NWF supporting the glass fibre; the efficiency curve 2, however, remains level, indicating that there is no structural breakdown.

A further advantage of a filter screen configured as in figure 2 consists of the simplified structure of the component layers. This advantage is guaranteed by the absence of reinforcing nonwoven fabric and relative bonding agent upstream: the high mechanical resistance of the multilayer material, making additional reinforcement layers superfluous, offers improved distribution of the retentate in the glass fibre layer. This is illustrated in the graph of figure 6 in which curve 1 , referring to a prior- art multilayer filter medium exhibiting numerous support layers, from 5 mg/cm² and above shows an exponential increase in differential pressure, demonstrating that the filter medium is clogged. Contrastingly curve 2, referring to a multilayer filter medium configured as in figure 2, shows an exponential increase in differential pressure starting only from 11 mg/cm², signifying that this filter medium guarantees a very high dust holding capacity (DHC) compared to multilayer filter mediums in the prior art.

Obviously, a technical expert in the sector might introduce numerous modifications and variants in order to satisfy contingent needs and specifications, without forsaking of the ambit of the invention as claimed below.

Claims

1. A multilayer filter medium comprising, from upstream to downstream relative to the direction of filtration, at least a first layer of glass fibre (C, C), a second and intermediate layer of coarse mesh nonwoven fabric (D, D'), and a third support layer (E, E') of nonwoven fabric, characterized in that the intermediate layer (D, D') of coarse mesh nonwoven fabric is joined by fusion and/or bonding both to the glass fibre first layer (C, C) and to the nonwoven fabric third support layer (E, E').

2. The multilayer filter medium of claim 1 , characterized in that it further comprises an additional layer (B) of coarse mesh nonwoven fabric which is fused or bonded upstream of the glass fibre layer (C).

3. The multilayer filter medium of claim 2, characterized in that it comprises an additional support layer (A) of nonwoven fabric positioned upstream of the layer of coarse mesh nonwoven fabric (B) to which layer (A) is fused or bonded.

4. The multilayer filter medium of claim 3, wherein the support layer (A) of nonwoven fabric is made of polyester, with a permeability of 1500 to 6000 l/m²/s and a differential pressure of 50 to 500 Pa and a weight of 20 to 100 g/m².

5. The multilayer filter medium of claim 1 , wherein the layer (B) of coarse mesh nonwoven fabric is made of polypropylene.

6. The multilayer filter medium of claim 1 , wherein the glass fibre layer (C, C) has a porosity within a range of between 1 and 40 μm and a weight of from 40 to 150 g/m².

7. The multilayer filter medium of claim 1 , wherein the layer (D, D') of coarse mesh nonwoven fabric is made of polypropylene, fused or bonded to the adjacent layers upstream and downstream in the direction of filtration.

8. The multilayer filter medium of claim 1 , wherein the support layer (E, E') of nonwoven fabric is made of polyester, with a permeability within the range of from 1500 to 6000 l/m²/s, a differential pressure of from 50 to 500 Pa, and a weight of from 20 to 100 g/m².

9. A process for realizing a multilayer filter medium, starting from a plurality of reels each dispensing a material destined to form a layer of the filter medium, the process comprising a stage of gathering the layers into a single flat multilayer medium, a stage of preheating the multilayer filter medium, a compression stage using a pair of counterpositioned rollers of which at least one is heated, and a stage of bonding the materials.

10. The process for realizing a multilayer filter medium of claim 9, characterized in that the stage of gathering the layers includes collecting at least a layer of high-fusion-temperature polymer material, a layer of coarse mesh nonwoven fabric in low-fusion-temperature polymer material, and a layer of glass fibre, each layer having been dispensed by a respective idle reel.

11. The process for realizing a multilayer filter medium of claim 10, characterized in that the stage of gathering of the various layers comprises collecting an additional layer of coarse mesh nonwoven fabric, and a layer of high-fusion-temperature polymer material.

12. The process for realizing a multilayer filter medium of claim 9, characterized in that the stage of preheating the multilayer filter medium is done via heating elements located on both sides of the multilayer filter medium.

13. The process for realizing a multilayer filter medium of claim 9, characterized in that the stage of compressing the material is done using a pair of counterpositioned rollers of which at least one is heated a temperature of approximately 160⁰C, with compression of the material to a pressure of between 1 and 7 bar.

14. The process for realizing a multilayer filter medium of claim 9, characterized in that the stage of bonding of the materials is performed using one or more rollers.

15. A plant for realizing a multilayer filter medium of claims from 1 to 8 and according to the process of claims from 9 to 14, characterized in that it comprises at least one reel (11 ) for a layer of nonwoven fabric made of a high-fusion-temperature polymer material, a reel (21 ) for dispensing a coarse mesh nonwoven fabric in low-fusion-temperature polymer material, and a reel (3) for dispensing a layer of glass fibre, transmission rollers (51 ,52) for gathering the layers into a single flat material constituting the multilayer filter medium, at least a pair of rollers (61 ,62) provided with a plurality of spirals on an external surface thereof such as to stretch a width of the surface of the multilayer filter medium fully, at least a pair of preheating elements (63,64) counterpositioned on opposite sides of the multilayer filter medium, at least a pair of rollers (41 , 42) counterpositioned and exerting pressure on the multilayer material medium, at least one of the counterpositioned rollers (41 , 42) being heated, at least a pair of rollers (71 , 72) for exerting pressure on the multilayer filter medium, a powered stretcher roller (8) exercising a constant pressure on the multilayer filter medium, thereby maintaining it stretched, and a powered winding roller (9) for winding up the multilayer filter medium.

16. The plant for realizing a multilayer filter medium of claim 15, characterized in that the rollers (71 , 72) are located immediately downline of the counterpositioned rollers (41 , 42), are subsequent in an advancement direction of the multilayer filter medium, and are staggered such that the material is forced to follow a non-rectilinear path in order to obtain a compression of the polymer material and of the glass fibre such as to ensure a secure and continuous bonding of the materials with the coarse mesh nonwoven fabric.