DE102009001756A1 - Filter screen e.g. dirt filter, for sample separation device e.g. high-performance liquid chromatography system, has filter arranged at inlet and/or outlet of separating column and impermeable for particles with size above threshold value - Google Patents

Abstract

The screen (80) has a filter arranged at an inlet and/or an outlet of a sample separating column (30) and comprising layers (86) arranged parallel to each other. The layers comprise a sieve-like fabric e.g. wire cloth, that has two metal filaments (90, 92) running along respective directions, where one direction run orthogonal to another direction. The filter is permeable for fluid sample and impermeable for particles with a size above a threshold value, where the filter is designed in a cylindrical shape and made from metallic material e.g. stainless steel. Independent claims are also included for the following: (1) a sample separating device for separation of a component of fluid sample (2) a method for filtering in a sample separation device for separation of components of a fluid sample.

Description

TECHNICAL BACKGROUND

The The present invention relates to a filter screen for a Sample separation device.

In an HPLC, a liquid (mobile phase) is typically run at a very precisely controlled flow rate (for example in the range of microliters to milliliters per minute) and at a high pressure (typically 20 bar to 1000 bar and beyond, currently up to 1200 bar ) is moved through a stationary phase (for example, a chromatographic column) to separate individual components of a sample liquid introduced into the mobile phase. Such an HPLC system is known, for example from the EP 0,309,596 B1 same Applicant, Agilent Technologies, Inc.

One System for liquid chromatography in particular the LC system of the Agilent 1200 series of the assignee Agilent Technologies, Inc., dar. Core piece of such an LC system the chromatographic separation column, which with separation media different morphology - among others for the separation process important properties - filled is.

This Separation medium in the separation column acts in such a system in operation according to a resistance with resulting pressure drop different thickness along the column. Therefore are conventional at the column inlet and at the column exit so-called frits provided, d. H. Sintered body to avoid rinsing the release material from the column.

With respect to the prior art is on US 5,423,982 . EP 0,982,587 and DE 4112258 directed.

In Such and other sample separation devices can be a safe Retention of release material in the column always still a challenge.

EPIPHANY

It It is an object of the invention to provide a sample separation device to keep it dirty. The task is done by means of the independent Claims solved. Further embodiments are shown in the dependent claims.

According to one exemplary embodiment of the present invention is a filter screen for a sample separation device for separating at least one component (or also two or more components) of a fluidic sample by pumping the fluidic Sample through a arranged in a sample separation column Separating material created, wherein the filter screen is a filter of several Has layers, each of which has an ordered structure, and that permeable to the fluidic sample and for particles larger than one predetermined threshold is impermeable.

According to one Another exemplary embodiment is a sample separation device for separating at least one component (or two or more Components) of a fluidic sample, wherein the sample separation device a sample separation column having a separation material disposed therein for separating the at least one component of the fluidic sample by means of Pumping the fluidic sample through the separator, and a filter screen with the features described above for filtering along a fluidic Path of the sample separation device has.

According to Another exemplary embodiment is a Method for filtering in a sample separation device for Separate at least one component (or two or more components) a fluidic sample by pumping the fluidic sample provided a release material arranged in a sample separation column, wherein in the method a filter screen as a filter of several Layers is formed, each of which has an ordered structure, and that permeable to the fluidic sample and for particles with a size above a predetermined threshold is impermeable.

In accordance with an exemplary embodiment of the invention, a filter is provided which may, for example, be located at an input and / or output of a sample separation column or elsewhere (eg, upstream of a column entrance) of a sample separation device to flush out a sample separation material, such as a sample separation device For example, to avoid sorbent for the chromatographic separation of different fractions of a fluidic sample and / or to prevent dirt particles with an extent above a threshold before penetrating into the separation column. Furthermore, such a filter screen can serve to act pressure stable to avoid compressing separator material inside the column, which could lead to cavities in the column and thus its poorer separation performance. Of course, the filter screen together with a sealing ring can also seal against the escape of the solvent and the samples dissolved therein. According to the invention, such a filter screen is formed from a multi-layer construct, wherein each layer has a defined order structure per se. In other words, the invention does not rely on random or random distributions of certain pore diameters, their random structures and their distributions, as for example in conventional sintered frits, but instead proposes, even at the level of a layer, a given spatially-geometrically defined structure of the layer filaments and thus also make the interspaces, whereby a uniform flow distribution in the longitudinal and transverse direction can be ensured through the filter. For example, by providing such a pattern of pattern, a structure can be provided in which exactly one fixed hole size is present in a respective layer, whereby the rinsing properties and the pressure stability characteristics can be adjusted. For example, the spaces between the building filaments of the individual layers can be selected so that they are smaller than a bead size, whereby a rinsing of the beads is avoided. Embodiments of the invention thus make it possible to specify the retention capacity and the pressure stability of a filter screen on a deterministic and not purely statistical basis, so that a certain separation performance can be guaranteed with increased reliability.

According to the invention For example, a column closure with a defined pore size be provided, so that is clearly definable, which solved Components in a mobile phase or sample the column closure happen and which not. This is especially given the trend to ever higher pressures in the area of sample separation technology advantageous because such high pressures also to high forces in the column closure and thus to mechanical loads of Can lead column closure and release material. Thus it can be ensured that the separating beads not washed out of the pipe inside the column become.

According to one Embodiment may be a wire mesh, in particular by interweaving chain and weft links, what is formed allows a reproducible production of the pores. The Longitudinal direction of such a fabric web can be called chain be, the transverse direction can be called shot. Wire strength and mesh spacing define the CutOff size of the manufactured, first single layer, sieve. The provision several layers ensures a controlled pressure stability of the sieve, without the resistance caused by the sieve would significantly increase and postpone the final CutOff size to the desired size. In the design of the multilayer frit replacement can also the Flow geometry can be influenced. As an embodiment this would be about a corresponding character by means of a dome or a dome-like geometry to call, with which could be pressed on the sieve. This would be specifically structured locations on the screen generable what allow a local reduction in pore size could.

in the Further embodiments of the filter are described. These also apply to the sample separation device and the procedure. The filter can be used as a column closure element set up to close the sample separation column be. This can be a rinsing of sorbent (also called Beads are called) can be avoided from the separation column and an undesirable entry of dirt particles into the separation column be avoided.

alternative or in addition, the filter as a dirt filter for Arranging in a fluidic path of the sample separation device downstream of a sample injector and upstream of the Sample separation column to be set up. In such an embodiment The filter can be used as a dirt barrier behind a valve (downstream of a Probeninjektornadel) and even before an input of the separation column be arranged. Of course, such a filter also at any other desired location within a Sample separation system to be established.

at The filter screen may have voids in the filter from several layers a defined pore size (or better, a defined minimum passage or vice versa a defined retention capacity) exhibit. Thus, each layer can be a specific one Define pore size for different Layers can be the same or different. So can for example different pore sizes at different, but precisely defined positions in the sieve-like closure element adapted to an appropriate particle distribution.

Of the The term particle distribution does not refer exclusively here on the size distribution of the sorbent but also on the distribution of introduced into the separation system dirt particles or during operation, especially under high pressures occurring particles due to abrasion of moving parts, such as pneumatic pump or injection valve (s).

Of the defined minimum passage can, for example, in a range between about 0.1 μm and about 1 μm, in particular in a range between approximately 0.2 μm to about 0.5 μm. This makes it possible, usual Sorbent before rinsing through the pores in the filter screen through it.

Further is also possible by skillful choice or arrangement the multi-layer sieves of a manufacturing process-related particle size distribution of the sorbent in such a way that very small particles in the order of about less than 500 nm - too Called nanospheres - during the manufacturing process a filled with this separation medium sample separation vessel be rinsed out of this, and do an otherwise upstream separation process - for example by sedimentation or centrifugation - for further classification of the particles replaced.

Of the Filter can be configured pressure stable, d. H. can be sufficient be mechanically stable provided that this even when applying a high pressure protected against negative influence is. In particular, the filter can withstand pressure a pressure of at least about 100 bar, in particular of at least about 600 bar, more particularly of be configured at least about 1200 bar. So it is suitable the filter screen is also suitable for state-of-the-art HPLC applications, without that a limitation to below 1200 bar would be technically necessary.

At least a part of the layers of the filter screen may have a sieve-like fabric. Such a tissue may be characterized as having a Having a plurality of filamentous structures crosslinked together, which are networked in a defined manner to one of the layers form.

To the For example, the sieve-like fabric may be a wire mesh, in particular a wire mesh made of a metallic material such as stainless steel. Metallic materials can provide adequate pressure stability with simultaneous biocompatibility and inertness provide biological or chemical substances. stainless steels can also have a high rust stability.

The sieve-like tissue may be first extending in a first direction Filaments and along another, second direction extending having second filaments, wherein the first filaments with the second Filaments can be interwoven. The first direction can to the second direction substantially perpendicular, which to a high stability and a reliable Degree of order leads. However, there are other angles as well between first and second direction possible, for example an angle of 45 °.

The Number of layers can be arranged parallel to each other. In other words, the layers can be essentially be two-dimensional planar structures, each of which is a normal vector have different normal vectors of different Layers can be aligned parallel to each other.

alternative The multiple layers can be angularly offset from each other be arranged. In such an embodiment can the multiple layers have, for example, filament trajectories, with each other an acute angle greater than 0 ° and less than 90 ° (for example in a range between 5 ° and 85 °), for example 45 °. By such crossed arrangements may have the sample separation properties be further refined.

The multiple layers may be configured such that along a flow direction of the fluidic sample through the Filter a longitudinal Porösitätsgradient formed is. As a result, changing areas can be higher and lower Permeability are formed (by about different layers have different minimum passages). alternative or in addition, the multiple layers may be so be configured to be transversal to a flow direction the fluidic sample through the filter a radial porosity gradient is formed. This can also be a Durchströmcharakteristik be modified along the filter surface. For example Can a dome be used as an embossing surface? around the filter surface a radial porosity gradient impress.

The several layers can be permanently connected to each other. For example, the multiple layers can be glued, pressed, welded or by another treatment with each other be connected so that a one-piece filter screen results. Such permanent bonding can be achieved, for example, by pressing and / or tempering under pressure.

different The multiple layers can be one different from each other Have mesh size and / or mesh size and / or ply thickness. Thus, mesh size and mesh size and thickness of the Laying design parameters to specific properties specific to the site, which governs a fluidic separation effect are to be set. This allows quite complex tasks through the filter are met, for example in terms Stability, permeability and control of a Separation procedure. For example, a liquid gradient, that from the friction of the liquid with a container wall results, thereby at least partially compensated that the mesh sizes in a central section differ from the mesh sizes are selected in the edge section, which an unwanted widening of a mobile phase during passage can be avoided or compensated by the separation column.

The frit replacement can, for example, kreiszy be lyrical, ie be circular in a cross section (other geometries, for example rectangular or polygonal, are also possible). The thickness of the circular cylinder may be smaller, larger or equal to the diameter of the circular cylinder. In particular, the circular cylinder may have a height of 0.5 mm to 100 mm. On the other hand, the circular diameter of the circular cylinder may be, for example, at most about 100 mm, more preferably at most about 10 mm. The wire thickness may be, for example, in the range between 1 μm and 1 mm (for example, 0.07 mm or 0.7 mm). It has been found that these dimensions can be achieved a good pressure stability and simultaneously a good separation efficiency with a good protection against rinsing.

In In one embodiment, the filter may be seven layers having two different thicknesses. Such a filter has proven to be powerful for HPLC applications exposed. Of course, there are also different ones Number of layers and thicknesses possible.

in the Further will become embodiments of the sample separation device described. These also apply to the filter screen and the Method.

The Release material may comprise beads, for example, a particle size in a range between about 1 μm and about May have 50 microns. For example, you can such beads of silica gel or other porous material getting produced. The beads can turn completely non-porous, partly porous, consisting of an unporous one Core surrounded by a porous shell or totally porous with a dimension in a range between about 10 nm and several 100 nm or even more. This is advantageous in the light of good separation performance of fluidic Samples, for example biological or chemical samples.

The Filter sieve of the sample separation device may be a first column closure component an input of the sample separation column and a second column closure component have at an exit of the sample separation column. alternative it is possible that only at the entrance or only at the exit a sample separation column is provided, or alternatively or additionally in a central section of the sample separation column, d. H. between input and output, such a filter screen provided is.

A Position of the first column closure component with one largest Thickness or thickness (compared to the strengths the other layers of the column closure component) an end region facing away from the interior of the sample separation column facing the first pillar closure component. About that In addition, a layer of the second pillar fastener component with a maximum thickness or thickness (opposite the strengths of the other layers of the column closure component) at an end region facing the interior of the sample separation column the second pillar fastener component are arranged. Thus, upstream of a column entrance and upstream of a column exit, respectively a mechanically reinforced area of the column closure component be provided, d. H. the mechanical strength of the column closure component chosen inhomogeneous along a flow direction be. This can cause the column exit that no particles can escape and the strainer is not clogged. At the pillar entrance should be avoided pollution and constipation.

The Sample separation device may be a microfluidic or a Being a nanofluidic measuring device can be considered a life science device be designed, a liquid chromatography device (For example, an HPLC, High Performance Liquid Chromatography), a Gas chromatography device, or an electrophoresis device (for example, a gel electrophoresis device or capillary electrophoresis device) be. However, embodiments of the invention not limited to these applications, but you can apply to any type of sample separation device.

at In the sample separation apparatus, the separation material may be a stationary one Phase in the chromatographic sample separation column. One or more pumps can be used to move a mobile Phase be provided through the separation column. Also can one Sample injector for injecting the sample into a mobile phase provided be. For this purpose, for example, a needle from a seat drive out, take a sample and then into the with a sample loop associated seat of the sample separation device returned be (sample loop). After disconnecting can be a detector, for example an optical detector for detecting separate fractions of the Sample are used, the detector having an input in fluid communication may have with the sample separation column. For example, you can Fluorescence measurements are performed to separate the Identify fractions of the sample. Furthermore For example, a sample fractionator may be used to fractionate the separated components be provided, for example, to fill the different Components in different sample vessels. Alternatively to a sample fractionator, the separate sample be supplied to a waste container.

Incidentally, a porous closure element designed in this way or in a similar manner can in principle also be used as a filtration element at any point within a chromatographic separation system be used.

in the Further embodiments of the method will be described. These also apply to the filter screen and the sample separation device.

The Number of layers can during a Temperschritts be pressed together under pressure. This ensures a reliable cohesion of the multiple layers.

One circumferential edge of the number (for example, net-like) Layers can be provided with a protective ring, for example. One such guard ring may be, for example, a metal ring, a plastic ring or be a plastic ring with a metal ring. This one can not only the mechanical stability and the tightness increase at the edge, but at the same time as a seal after be used outside. In other words, can a peripheral edge of the plurality of layers with a support ring be provided, in particular with a support ring made of stainless steel be welded or with a support ring Plastic are fused.

With regard to the embodiment relating to fusion with plastic, this can be realized (for example, via inductive heating), for example, as in FIG EP 1,910,731 . WO 2007/009493 . US 2007/0131688 respectively. US 2007/0193237 disclosed.

The described sieve is not limited to applications under high pressure but can (under certain circumstances with additional features) also in, the analytical Chromatography at significantly lower pressures, or the preparative chromatography apply.

BRIEF DESCRIPTION OF THE FIGURES

Other Objectives and many of the attendant advantages of embodiments The present invention will be readily apparent and be better understood with reference to the following more detailed description of embodiments in Related to the attached drawings. Characteristics, which are essentially or functionally the same or similar are provided with the same reference numerals.

1 shows an HPLC system according to an exemplary embodiment of the invention.

2 shows schematically a HPLC separation column with filter screens according to an exemplary embodiment of the invention at the entrance and exit of the sample separation column.

The Representation in the drawing is schematic.

1 shows the basic structure of an HPLC system 10 , as it can be used for example for liquid chromatography. A pump 20 drives a mobile phase through a separation vessel 30 (such as a chromatographic column) containing a stationary phase. A sample application unit 40 is between the pump 20 and the separation device 30 arranged to introduce a sample liquid in the mobile phase. The stationary phase of the separation vessel 30 is intended to separate components of the sample fluid. A detector 50 Detects separated components of the sample, and a fractionator 60 may be provided to dispense separated components of the sample liquid, for example, in designated containers or a drain. A control unit 70 can the entire HPLC system 10 Taxes.

1 further shows filter screens 80 at an entrance or at an exit of the sample separation column 30 , Their structure will be described in more detail below.

It is alternatively or additionally possible that filter screens 80 at various positions inside or outside (upstream and / or downstream) of the column 30 are located.

2 shows an enlarged view of the separation column 30 with the filter sieves 80 , of which in the direction of flow 82 one at the entrance of the separation column 30 and one at the exit of the separation column 30 is arranged. Thus close the filter screens 80 the entrance and exit of the sample separation column 30 ,

2 further shows an enlarged view of the filter screens 80 , see reference number 84 , As can be seen from this illustration, the filter screen 80 from several separate layers 86 formed, according to 2 five layers. For one of these five layers 86 is in 2 again shown an enlarged view, compare reference numerals 88 , Each of the five layers 86 has an ordered structure, such as the interwoven horizontal metal filaments 90 and the vertical metal filaments 92 can be seen. These geometrically shape pores together 94 a constant size. These are just as permeable to the fluidic sample as to the fluidic transport medium. The size of the pores is significantly smaller than the size of the retained beads 96 (ie, sample separation material), which also increases in size 2 are shown (compare reference numerals 98 ), Thereby the sample separation material (beads) is retained quantitatively.

The thickness or wire thickness b of the horizontal and vertical threads 90 can for example play 0.7 mm while the distance s between adjacent threads 90 . 92 for example, can be 0.8 microns. The diameter of a bead D may be, for example, 10 μm. The diameter of a pore h of a bead 96 , see enlargement 100 , for example, may be 0.05 μm. Thus, the beads 96 before rinsing through the pores 94 protected. The retention capacity of the screen described here is not based on the fact that, for example, the mesh size of one of the layers is smaller than or equal to the nominal particle diameter, but the combination of the number of layers makes up the retention capacity. The largest passage, measured with a gas, is z. B. at several micrometers. The filter screen 80 is exemplary circular cylindrical with a thickness or length l of 1 mm and a diameter L of 10 mm. Its geometric shape ultimately depends on the bore geometry of the separation body (column tube).

Due to the robust, multi-layered, in the present case five-layered structure and the stainless steel material of the threads or filaments 90 . 92 is the filter screen 80 stable up to 1200 bar and more. The individual layers 86 are permanently connected to each other by means of tempering, wherein before and / or during the annealing for amplifying the connection, a defined pressure can be exerted for a defined time.

The Arrangement of stainless steel layers can z. B. also under different Angles to be crossed.

As further in 2 shown is the mechanically strongest and the smallest pores having position 86a the layers 86 arranged outside at the entrance, whereas the mechanically strongest and the smallest pores having position 86a of the output filter screen 80 is arranged in the column interior. This is a penetration of dirt particles in the separation column 30 and a rinse of sorbent 96 from the separation column 30 avoided.

It It should be noted that the term "exhibit" does not excludes other elements and that the "one" does not exclude a plurality. Also, elements, in connection with different embodiments are described combined. It should also be noted the reference numerals in the claims are not considered the scope of protection to be interpreted as limiting the claims.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0309596 B1 [0002]
• US 5423982 [0005]
• EP 0982587 [0005]
• - DE 4112258 [0005]
• EP 1910731 [0041]
• WO 2007/009493 [0041]
• US 2007/0131688 [0041]
• US 2007/0193237 [0041]

Claims (32)

Filter screen for a sample separation device for separating at least one component of a fluidic sample by pumping the fluidic sample through an in a sample separation column arranged separating material, wherein the filter screen comprises: one Filter of several separate layers, each of which is an ordered Having structure, and permeable to the fluidic sample and for particles with a size above a predetermined threshold is impermeable. Filter according to claim 1, arranged as a pillar closure element for closing the sample separation column. Filter according to claim 1, arranged as a dirt filter for placing in a fluidic path of the sample separation device downstream of a sample injector and upstream the sample separation column. Filter according to one of claims 1 to 3, wherein voids in the filter of several layers one have defined minimum passage. Filter according to claim 4, wherein the minimum passage in a range between 0.1 μm and 1 μm; especially in a range between 0.2 microns to 0.5 microns, is located. Filter according to one of claims 1 to 5, wherein the filter is configured pressure stable. Filter according to claim 6, wherein the filter is pressure-stable against a pressure of at least 100 bar, in particular of at least 600 bar, more particularly of at least 1200 bar, is designed. Filter according to one of claims 1 to 7, wherein at least a part of the layers has a sieve-like fabric. The filter screen of claim 8, wherein the screen-like Fabric is a wire mesh. Filter according to claim 8 or 9, wherein the sieve-like Tissue along a first direction extending first filaments and second filaments extending along a second direction having the first filaments with the second filaments are intertwined. The filter screen of claim 10, wherein the first direction orthogonal to the second direction. Filter according to one of claims 1 to 11, wherein the plurality of layers are arranged parallel to each other. Filter according to one of claims 1 to 11, wherein the plurality of layers arranged offset from each other at an angle are. Filter according to one of claims 1 to 13, wherein the plurality of layers are permanently connected to each other. Filter according to one of claims 1 to 14, wherein different of the multiple layers are different from each other Mesh sizes and / or mesh thicknesses and / or layer thicknesses exhibit. Filter according to one of claims 1 to 15, wherein the filter is circular cylindrical or rectangular. Filter according to one of claims 1 to 16, wherein the filter is a circular cylinder with a height of at most 100 mm, in particular of at most 10 mm. Filter according to claim 17, wherein the circular cylinder a circle diameter of at most 100 mm, in particular of not more than 10 mm. Filter according to one of claims 1 to 18, wherein the filter is a metallic material, in particular stainless steel, further particularly stainless steel of composition 1.4404, has. Filter according to one of claims 1 to 19, wherein the filter seven layers with two different thicknesses having. Filter according to one of claims 1 to 20, wherein the plurality of layers are configured so that along a flow direction of the fluidic sample through the Filter a longitudinal Porösitätsgradient formed is. Filter according to one of claims 1 to 21, wherein the plurality of layers are configured to be transversal to a flow direction of the fluidic sample through the filter formed a radial porosity gradient is. A sample separation apparatus for separating at least one component of a fluidic sample, the sample separation apparatus comprising: a sample separation column having a separation material disposed therein for separating the at least one component of the fluid sample by pumping the fluid sample through the separation material; a filter screen according to any one of claims 1 to 22 for filtering along a fluidic path of the sample paration device. A sample separation device according to claim 23, wherein the release material comprises beads having a particle size in a range between 1 .mu.m and 50 .mu.m. A sample separation device according to claim 23 or 24, wherein the release material comprises sorbent, the pores with a Dimension in a range between 0.01 μm and 0.2 μm having. A sample separation device according to any one of the claims 23 to 25, adapted for pumping the fluidic sample through the Sample separation column with a pressure of at least 100 bar, in particular of at least 600 bar, more particularly of at least 1200 bar. A sample separation device according to any one of the claims 23-26, wherein the filter screen is a first column closure component at an entrance of the sample separation column and a second column closure component having at an exit of the sample separation column. A sample separation device according to claim 27, wherein a layer of the first pillar fastener component with a greatest strength and / or lowest Minimum passage on a smaller one of the sample separation column remote end portion of the first pillar fastener component and a layer of the second pillar fastener component a maximum strength and / or a lowest Minimum passage at an interior of the sample separation column facing end portion of the second pillar fastener component is arranged. A sample separation device according to any one of the claims 23 to 28, further comprising at least one of the features: the Release material forms a stationary phase in the sample separation column; the Sample separation column is a chromatographic sample separation column; the Sample separation column has metal, such as stainless steel, plastic, about PEEK, glass, some borosilicate glass, ceramics or a combination of these materials; a pump for moving a mobile Phase; a sample injector for injecting the sample into a mobile Phase; a detector for detecting separate fractions of the Sample, with a detector input to the sample separation column connected is. a sample fractionator for fractionating the separated components; one or more thermostats, wherein one or more separation columns are located; one or a plurality of additional switching valves for switching to different separation columns; one Electrophoresis mechanism for electrophoretically driven propagation a mobile phase and a sample in the mobile phase. Method for filtering in a sample separation device for separating at least one component of a fluidic sample by pumping the fluidic sample through an in a sample separation column arranged release material, the method comprising: Form a filter as a filter of several separate layers, from each of which has an ordered structure, and that for the fluidic sample permeable and for particles with a size above a predefinable threshold is impermeable. The method of claim 30, wherein the plurality of layers be pressed together during a tempering process. A method according to claim 30 or 31, wherein a more extensive Edge of the plurality of layers is provided with a support ring, especially welded to a support ring made of stainless steel or fused with a plastic backing ring.