US20230172262A1

US20230172262A1 - Filter for the sorption of components of tobacco smoke which are harmful to health

Info

Publication number: US20230172262A1
Application number: US17/922,183
Authority: US
Inventors: Alireza Eslamian; Martin Schifko; Mehdi Salimi
Original assignee: ESS Holding GmbH
Current assignee: Innovation Technology Steyr GmbH
Priority date: 2020-04-28
Filing date: 2021-04-26
Publication date: 2023-06-08
Also published as: EP4142527C0; AT523163B1; AT523163A4; EP4142527B1; WO2021217190A1; EP4142527A1; CN115697097A

Abstract

A filter for sorption of components of tobacco smoke which are harmful to health comprises ceramic particles bonded to form a porous structure (12). In order to avoid contamination within a short period of time even when the filter is not properly disposed of, and without causing a loss in sorption or in the smoking sensation, the filter has decreasing water solubility from a tobacco-side portion (1) to an opposite mouth-side portion (2).

Description

FIELD OF THE INVENTION

The invention relates to a filter for sorption of components of tobacco smoke which are harmful to health, comprising ceramic particles bonded to form a porous structure.

DESCRIPTION OF THE PRIOR ART

Cigarette filters are used to remove harmful substances from tobacco smoke. Conventional filters are made of cellulose acetate, a plastic that is difficult to biodegrade.
This has the disadvantage that improperly disposed of cigarette butts cause considerable environmental pollution and animals can be harmed if they ingest the cigarette butt.
To circumvent this circumstance, alternative materials for filters have been developed. U.S. Pat. No. 2,996,067 describes a filter for the sorption of harmful substances made of ceramic particles bonded to form a porous structure. Although ceramic particles are essentially naturally occurring inorganic substances that are unproblematic in comparison with various types of plastic, the problem nevertheless remains that such filters lead to pollution if they are not disposed of properly.
Filters made of hemp and cotton, for example, are therefore known from U.S. Pat. No. 2,996,067.
Although such filters are biodegradable, such biodegradation processes require several days for complete degradation and an appropriate environment for the microorganisms responsible for the degradation, which, however, is not prevalent, especially in urban areas.
Other filters comprising ceramic particles are disclosed in EP0539191A1, EP0766929A2, US3428054A and GB1243358A. GB1005786A and EP0539191A1 disclose filters comprising ceramic particles bonded to form a porous structure. EP1504682A1 and KR200476478Y1 disclose manufacturing processes of conventional cigarette filters.

SUMMARY OF THE INVENTION

The invention is thus based on the object of proposing a filter of the type described at the beginning, which avoids contamination within a short time even in the case of improper disposal, without causing losses in terms of sorption properties and smoke sensation.
The invention solves the problem posed in such a way that the filter has a decreasing water solubility from a tobacco-side portion to an opposite mouth-side portion. As a result of this measure, the filter dissolves on contact with larger quantities of water, for example rain. Undesirable dissolution of the filter upon contact with saliva during smoking is prevented in such a way that the water solubility decreases toward the mouth-side portion of the filter, whereby the filter maintains its sorptive capacity along the entire length of the filter during smoking. For example, it may be provided that the mouth-side portion will have poor or no water solubility. The change in water solubility may be sectional or continuous. The mouth-side portion may thereby comprise the end of the filter that is enclosed by the mouth of a smoker. The tobacco-side portion may comprise the end of the filter that is adjacent to the tobacco of the cigarette.
In order to be able to set the required water solubility of the filter without requiring a complex production process, it is proposed that the ceramic particles are bound with a water-soluble binder, the mass proportion of which increases from the tobacco-side portion to the opposite mouth-side portion of the filter. On contact with larger quantities of water, the binder goes into solution and the insoluble ceramic particles are carried away by the water as suspended solids or sediment as non-toxic inorganic substances. In principle, the water solubility can be reduced by increasing the mass fraction of the binder, so that the section of the filter with the lower mass fraction of the binder is dissolved first when it comes into contact with larger quantities of water. Starch, for example, can be used as a water-soluble binder.
Particularly simple manufacturing conditions with sufficiently differentiated water solubility of the filter are achieved if the filter comprises at least three portions with mutually different and in each case constant binder content. This means that a substantially constant binder content is provided within a portion. The portion on the mouth side has the highest binder content and the portion on the tobacco side has the lowest binder content. The binder content of the middle portion lies between the binder contents of the other two portions.
In order for the filter to completely disintegrate during weak rain showers and still be resistant to large amounts of saliva during smoking, the binder content in the tobacco-side portion can be in a range of 1-2 wt %, in at least one middle portion in a range of 2-3 wt %, and in the mouth-side portion in a range of 3-4 wt %. With this composition, the filter does not dissolve even when smoked for a particularly long time. However, if it comes into contact with larger amounts of water, rapid dissolution of the binder occurs. With this composition, a filter according to the invention with conventional cigarette filter dimensions requires about 20 seconds to be completely dissolved in a cup filled with water and equipped with a stirring rod set at 150 revolutions per minute.
In order to enable the filter to bind the toxic substances reliably without negatively affecting the degradability of the filter and the smoking sensation, it is proposed that the porosity of the filter increases from the tobacco-side portion to the opposite mouth-side portion. Due to the lower porosity of the filter in the tobacco-side portion, there is a larger effective surface area for binding the toxic substances. The further the tobacco smoke flows toward the mouth-side portion, the less toxic substances it has due to sorption in the tobacco-side portion, so that the porosity can increase in favor of low-resistance draw of the smoker, or the effective surface area can decrease, without exposing the smoker to the risk of overexposure to toxic substances. The greater porosity and thus lower stability at the mouth-side portion of the filter, which after all has a lower water solubility, also has the positive effect that it can be pulverized in a simple manner, for example by a pressure load, whereby even the mouth-side portion, which is more difficult to dissolve with water, can be dissolved without residue. Due to the porous structure of the filter, however, not only can a desired binding of harmful substances take place, but in addition the water required for degradation can penetrate, thus accelerating the degradation process. Porosity is the ratio of void volume to total volume of the filter.
In order that the porosity can be adjusted in the same process step as the water solubility and with the same accuracy, it is advisable in a particularly easy-to-manufacture embodiment of the device according to the invention for the filter to have at least three portions with different and in each case constant porosity. The tobacco-side portion has the lowest porosity and the mouth-side portion has the highest porosity. The porosity of the middle portion lies between the porosities of the other two portions.
It has been found that the filter according to the invention achieves similar properties in terms of sorption of harmful substances from tobacco smoke and in terms of smoke sensation when the porosity in the tobacco-side portion is in a range of 35-50%, in the middle portion in a range of 50-65% and in the mouth-side portion in a range of 65-80%. The proposed porosity in the tobacco-side portion in the range of 35-50% provides enough effective surface area to bind even the high concentration of harmful substances in the filter. Porosity in the range of 65-80% in the mouth-side portion causes lower flow resistance for the already almost completely detoxified tobacco smoke and also allows easy pulverization by external forces. Porosity in the range of 50-65% in the middle portion represents a compromise between effective surface area and low flow resistance.
The filter according to the invention can be manufactured in a method according to the invention, wherein successively differing mixtures comprising ceramic particles, placeholder particles and water-soluble binder are filled into a mold, whereupon the mold contents are pressed and heated to decompose the placeholder particles and form the porous structure of bound ceramic particles. The mixtures may differ from each other in terms of binder content, such that the mixture for forming the mouth-side portion of the filter has a larger binder content than the mixture for forming the tobacco-side portion of the filter. The mixtures may also differ with respect to the placeholder particle content or placeholder particle size distribution, such that the mixture for forming the mouth-side portion of the filter after decomposition of the place-holder particles has a greater porosity than the mixture for forming the tobacco-side portion of the filter after decomposition of the placeholder particles. For example, NH₄HCO₃can be used as the placeholder particle, which is decomposed into NH₃, H₂O and CO₂by heat treatment and outgases to form the porous structure.
To give a smoker a pleasant mouthfeel when smoking, the elasticity of the filter can decrease inward in the radial direction. Due to the more elastic and therefore more bendable nature at the outer shell of the cigarette filter, a haptic sensation similar to conventional cigarette filters can be created. The radial progression of elasticity can be continuous, but also discrete. Particularly simple conditions for improving the haptic mouthfeel result when felted ceramic fibers are provided as the outer filter shell layer.
It has been found that the mouthfeel can be further positively influenced if the porosity of the filter increases radially outward from a filter core to a filter shell. Due to the lower porosity in the filter core, a sufficiently effective surface for binding the toxic substances can be achieved. Due to the increasing porosity in the direction of the filter shell, the texture of a conventional cigarette filter can be mimicked. The higher porosity at the outer filter shell has the further advantage that water needed for degradation can penetrate into the filter core, thus accelerating the degradation process. Naturally, the mixture for the filter shell must be selected so that it cannot be degraded by a smoker's saliva during the smoking process. In principle, however, the change in porosity can also take place continuously in discrete steps.
A possible embodiment of a porosity changing in radial direction can be achieved if at least one intermediate portion is provided between a filter core portion with a predetermined placeholder particle fraction and a filter shell portion surrounding the filter core with a higher placeholder particle fraction, the placeholder particle fraction of which lies between the placeholder particle fractions of the filter core portion and filter shell portion. Filter core portion, intermediate portion and filter shell portion can mean portions extending in the axial direction of the filter which occupy only part or the entire length of the filter. It is thus conceivable that the porosity varies continuously or in discrete portions in both the axial direction and the radial direction.
A filter according to the invention can be produced by means of a device having a continuous casting mold which has inlet channels downstream of which a heating unit and a separating device are arranged in the casting direction, wherein at least two inlet channels for the continuous casting mold are provided which extend into one another at a distance and are arranged coaxially with respect to one another and with respect to the continuous casting mold. Since the inlet channels extend into one another at a distance according to the invention, a filter can be produced with a filter core having different material properties than the outer filter shell when the inlet channels are fed with different mixtures, as a result of which a porosity and/or water solubility that varies in the radial direction of the filter can be set. Due to the distance between the inlet channels extending into each other, the mixtures differing from each other can be introduced into the continuous casting mold through the free spaces created between the inlet channel walls. It is recommended that each inlet channel is fed with a different compound, so that the composition of the filter can be changed by adding or removing certain inlet channels.
In principle, therefore, the device can also be used to set a porosity and/or water solubility that varies in the axial direction of the filter if, for example, the continuous casting mold is first filled with a first mixture through only one inlet channel and then filled with a second mixture that differs from the first mixture through another inlet channel. Another way to control the filter composition changing in the radial or axial direction is when the mixtures enter the continuous casting mold from the inlet channels at different inlet speeds. In order to achieve a homogeneous transition at the boundary layers between the mixtures drawn from the inlet channels despite a desired water solubility gradient or a desired varying porosity, it is proposed that the inlet channels with a larger diameter project beyond the inlet channels with a smaller diameter in the casting direction. In this way, the inlet channels with the larger diameter in each case span a mixing area in which the mixtures can mix at their transition areas. Favorable design conditions arise when the inlet channel with the largest diameter forms the continuous casting mold.
In order to increase the production throughput of the filters according to the invention, several continuous casting molds extending parallel to one another can be arranged to form a continuous casting module and several continuous casting modules can be arranged on a common base body, wherein the base body has a heating unit for all continuous casting molds and a rotor blade extending between the heating unit and the continuous casting molds as a separating device. In this way, the production process is parallelized. Due to the arrangement of the continuous casting modules on a common base body, one heating unit and one rotor blade can be used for all continuous casting molds, resulting in a particularly energy-saving production process.
The device according to the invention can be used to carry out a method for the continuous production of a filter for the sorption of tobacco smoke. According to the invention, mixtures differing from one another and comprising ceramic particles, place-holder particles and water-soluble binder are first introduced into the continuous casting mold through at least two inlet channels extending at a distance into one another and arranged coaxially to one another and to a continuous casting mold, wherein the inlet velocities of the mixtures differing from one another in the respective inlet channels are varied in the radial and/or axial direction of the filter to adjust the water solubility and/or the porosity, and thereafter the continuous casting mold contents are fractionated and heated to decompose the placeholder particles and form the porous structure of bound ceramic particles. For example, if a filter is to be produced with water solubility decreasing from a tobacco-side portion to an opposite mouth-side portion, one inlet channel may be charged with a mixture having a high binder content and another inlet channel may be charged with a mixture having a lower binder content. To produce an end with lower water solubility, the inlet speed of the inlet channel with the mixture with a high binder content is first increased, while the inlet speed of the inlet channel with the mixture with a lower binder content is 0 or selected to be lower. If the water solubility of the filter is now to decrease in the axial direction, the inlet velocity of the inlet channel with the mixture with a high binder content is reduced and the inlet velocity of the inlet channel with the mixture with a lower binder content is increased. The inlet channels extending into each other also allow the mixtures to be layered one inside the other, which makes it possible to adjust the water solubility in the radial direction as well. By arranging the inlet channels and varying the inlet velocities, it is therefore possible to adjust the water solubility both in the axial direction and in the radial direction. The same naturally applies to the porosity. If, for example, the porosity of the filter is to increase radially outward from a filter core to a filter shell, the inner inlet channel can be charged with a mixture with a smaller proportion of placeholder particles or with a smaller placeholder particle size distribution, and the outer inlet channel with a mixture with a larger proportion of placeholder particles or placeholder particle size distribution. After this adjustment of the composition of the continuous casting mold content, it is fractionated by a separating device and then heated.

BRIEF DESCRIPTION OF THE INVENTION

In the drawing, the subject matter of the invention is shown by way of example, wherein:

FIG. 1 shows a filter according to the invention for sorption of tobacco smoke in a first embodiment,

FIG. 2 shows a schematic section along line II-II of FIG. 1 ,

FIG. 3 shows a schematic representation of a device for carrying out the method according to the invention for filling three mixtures in a first embodiment,

FIG. 4 shows a schematic representation of a device for carrying out the method according to the invention for pressing and heating in a first embodiment,

FIG. 5 shows a schematic cross-section of a second embodiment of a filter according to the invention,

FIG. 6 shows a partial exploded view of a device according to the invention for producing a filter according to the invention in a second embodiment, and

FIG. 7 shows a schematic section through a continuous casting module of the device shown in FIG. 6 on an enlarged scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A filter for sorption of tobacco smoke according to the invention shown in FIG. 1 has a tobacco-side portion 1 and a mouth-side portion 2. In order for the filter to be degraded by larger amounts of water, but not by the saliva of a smoker, the water solubility of the filter decreases from the tobacco-side portion 1 to the mouth-side portion 2.
This can be achieved in a particularly simple manner if the ceramic particles are bonded with a water-soluble binder 3, the mass fraction of which increases from the tobacco-side portion 1 to the opposite mouth-side portion of the filter 2.
As can be seen from FIG. 1 , the increase in the mass fraction of the binder 3 can take place portion by portion, with the mouth-side portion 2 having the largest binder fraction and the tobacco-side portion 1 having the lowest binder fraction. The binder content of the middle portion 4 is therefore between the binder content of the tobacco-side portion 1 and the mouth-side portion 2. The binder content within the respective portions 1, 2, 4 is constant.
A particularly well-degradable filter results if the binder content in the tobacco-side portion 1 is in a range of 1-2 wt %, in the middle portion 4 in a range of 2-3 wt % and in the mouth-side portion 2 in a range of 3-4 wt %.
As can be seen from FIG. 2 , the porosity can increase from the tobacco-side portion 1 to the mouth-side portion 2. The low porosity of the tobacco-side portion 1 results in a particularly large effective surface area, which means that even high concentrations of harmful substances from the tobacco smoke can be bound. The concentration of toxic substances therefore decreases in the direction of the mouth-side portion 2, which means that a higher porosity can be provided there in favor of lower flow losses.
The increase in porosity can also take place portion by portion, analogously to the binder content. The mouth-side portion 2 has the highest porosity and the tobacco-side portion 1 the lowest porosity. Consequently, the porosity of the middle portion 4 lies between the porosity of the tobacco-side portion 1 and the mouth-side portion 2. The porosity within the respective portions 1, 2, 4 is constant.
Effective binding of toxic substances without giving the smoker an unfamiliar smoking sensation is achieved when the porosity in the tobacco-side portion 1 is in a range of 35-50%, in the middle portion 4 in a range of 50-65%, and in the mouth-side portion 2 in a range of 65-80%.
FIGS. 3 and 4 refer to a method for manufacturing the filter according to the invention. As shown in FIG. 3 , first a first mixture 5 a is filled into a mold 6. Whereupon a second mixture 5 b and third mixture 5 c are filled into the mold 6. Between filling of the different mixtures 5 a, 5 b, 5 c, any dump cone 7 formed during filling can be leveled. This can be carried out, for example, by a vibrating plate 8. The mixtures 5 a, 5 b, 5 c comprise ceramic particles, placeholder particles and water-soluble binder, wherein for each mixture 5 a, 5 b, 5 c the binder fraction and/or the placeholder particle fraction and/or the placeholder particle size distribution can vary. In the exemplary embodiment shown in FIG. 2 , mixture 5 a has the largest binder fraction and, to produce a large porosity, placeholder particles with the largest particle size distribution. Accordingly, mixture 5 a is intended to form the mouth-side portion 2. Mixture 5 b has both a lower binder fraction and placeholder particles with a smaller particle size distribution than mixture 5 a and is thus intended for the middle portion 4. Mixture 5 c has the lowest binder fraction and placeholder particles with the lowest particle size distribution and is provided for forming the tobacco-side portion 1. Obviously, the layering of mixtures 5 a, 5 b, 5 c can also be done in reverse order. A method with more than three mixtures can also be provided if a more differentiated design of porosity or water solubility is desired. Preferably, the particle size distribution of the placeholder particles can range from 15 to 300 nm. However, variation of the porosity can also be achieved by changing the mass fraction of the placeholder particles while maintaining the same particle size distribution.
After filling, as can be seen from FIG. 4 , the layered mixtures 5 a, 5 b, 5 c are pressed together by, for example, a ram 9 and heated by a heating unit 10. Due to the applied heat, the placeholder particles, for example NH₄HCO₃, are transferred to the gas phase as NH₃, H₂O and CO₂, thereby leaving gaps 11 in the porous structure 12, as disclosed in FIG. 2 .
FIG. 5 shows a second embodiment of a filter according to the invention, in which the elasticity decreases inwardly. Furthermore, the filter has a decreasing water solubility from a tobacco-side portion 1 to an opposite mouth-side portion 2. The radial inward decrease in elasticity can be achieved in a simple manner by providing an elastic, matted ceramic fiber layer 13. Another possibility is when the porosity, i.e. the volume of the gaps 11 of the filter increases radially outward from a filter core 14 to a filter shell 15.
The increase in porosity in the radial direction outward can be discrete in that at least one intermediate portion 18 is provided between a filter core portion 16 having a predetermined placeholder particle fraction and a filter shell portion 17 surrounding the filter core 14 and having a higher placeholder particle fraction, the placeholder particle fraction of which lies between the placeholder particle fractions of the filter core portion 16 and filter shell portion 17.
FIG. 6 shows a device according to the invention for producing a filter according to the invention with continuous casting molds 19, downstream of which in the casting direction 20 are a separating device 21 and a heating unit 10. As can be seen from FIG. 7 , each continuous casting mold 19 has inlet channels 22 which extend into one another at a distance, i.e. with the formation of an intermediate channel between the shell inner surface of the outer inlet channel 22 and the shell outer surface of the inner inlet channel 22. The continuous casting mold 19 may thus form the inlet channel 22 with the largest tube diameter. The inlet channels 22 can be flow-connected via different supply channels 24, which supply the inlet channels 22 with different mixtures via pumps, for example.
For improved mixing of mixtures conveyed through the different inlet channels 22 and to adjust material properties that vary in the axial direction, the larger diameter inlet channels 22 may project beyond the smaller diameter inlet channels 22 in the casting direction 20.
A plurality of continuous casting molds 19 extending parallel to each other may be combined to form a continuous casting module 25. As disclosed in FIG. 6 , a plurality of continuous casting modules 25 can advantageously be arranged on a base body 26, wherein the base body 26 has apertures 27 corresponding to the continuous casting molds 19 for guiding the continuous casting mold contents or the heated filter. In this regard, the base body 26 has a common heating unit 10 for all continuous casting molds 19 and a rotor blade extending between the heating unit 10 and the continuous casting molds 19 as a separating device 21. The base body 26 may also have a heat sink 28.
After adjusting the filter composition in the continuous casting mold 19 via the inlet channels 22, the continuous casting mold contents are forced through the apertures 27. During the pushing through, the continuous casting mold content is fractionated by a separating device and then heated and hardened by a heating unit 10. Subsequently, a cooling step can be provided by a heat sink 28.

Claims

1. A filter for sorption of components of tobacco smoke that are harmful to health, said filter comprising:

ceramic particles bonded to form a porous structure;

wherein the filter has decreasing water solubility from a tobacco-side portion to an opposite mouth-side portion.

2. The filter according to claim 1, wherein the ceramic particles are bonded with a water-soluble binder, the water-soluble binder having a mass fraction that increases from the tobacco-side portion to the opposite mouth-side portion of the filter.

3. The filter according to claim 2, wherein the filter further comprises a third portion, said tobacco-side portion, said mouth-side portion, and the third portion each having a respective different and constant binder content.

4. The filter according to claim 3, wherein the third portion comprises at least one middle portion, and the binder content in the tobacco-side portion is in a range of 1-2 wt %, in the at least one middle portion in a range of 2-3 wt %, and in the mouth-side portion in a range of 3-4 wt %.

5. The filter according to claim 1, wherein the filter has a porosity that increases from the tobacco-side portion to the opposite mouth-side portion.

6. The filter according to claim 5, wherein the filter further has a third portion, said tobacco-side portion, said mouth-side portion, and the third portion each having a respective porosity that differs from the porosities of the other portions and is constant in said portion.

7. The filter according to claim 6, wherein the third portion comprises at least one middle portion, and the porosity in the tobacco-side portion is in a range of 35-50%, in the middle portion in a range of 50-65% and in the mouth-side portion (23 in a range of 65-80%.

8. The filter according to claim 1, wherein the filter has an elasticity that decreases inwardly in a radial direction of the filter.

9. The filter according to claim 1, wherein the filter has a porosity that increases radially outwardly from a filter core to a filter shell of the filter.

10. The filter according to claim 9, wherein at least one intermediate portion (18) is supported between a filter core portion having a predetermined placeholder particle fraction and a filter shell portion surrounding the filter core and having a placeholder particle fraction higher than the predetermined placeholder particle fraction, wherein the placeholder particle fraction of said intermediate portion lies between the placeholder particle fractions of the filter core portion and the filter shell portion.

11. A method for producing a filter for sorption of tobacco smoke, said method comprising:

filling successively mutually different mixtures comprising ceramic particles, placeholder particles and water-soluble binder into a mold; and

pressing and heating contents of the mold so as to decompose the place-holder particles and to bond the ceramic particles so as to form a porous structure.

12. A device for producing a filter according to claim 1, comprising

a continuous casting mold that has inlet channels; and

a heating unit and a separating device supported downstream of said inlet channels in a casting direction, a heating unit and a separating device;

wherein the continuous casting mold has characterized in that at least two inlet channels that extend at a distance into one another and are arranged coaxially with respect to one another and with respect to the continuous casting mold.

13. The device according to claim 12, wherein wherein some of the inlet channels have a larger diameter and some of the inlet channels have a smaller diameter, wherein the inlet channels with the larger diameter project beyond the inlet channels with the smaller diameter in the casting direction.

14. The device according to claim 13, wherein the continuous casting mold is one of a plurality of continuous casting molds extending parallel to one another that are formed into a continuous casting module, and said continuous casting module is one of a plurality of continuous casting modules that are arranged on a common base body, wherein the base body supports the heating unit and the separating unit comprises a rotor blade extending between the heating unit and the continuous casting molds.

15. A method for the continuous production of a filter for the sorption of tobacco smoke, said method comprising:

initially introducing mixtures differing from one another and comprising ceramic particles, placeholder particles and water-soluble binder into a continuous casting mold through at least two inlet channels that extend into one another at a distance and are arranged coaxially with one another and with respect to the continuous casting mold;

varying inlet velocities of the mixtures differing from one another in the respective inlet channels in a radial and/or axial direction of the filter so as to adjust water solubility and/or the porosity of the filter, and then

fractionating and heating the continuous casting mold contents are so as to decompose the placeholder particles and bind the ceramic particles so as to form the porous structure of said bound ceramic particles.

16. The filter according to claim 4, wherein the filter has a porosity that increases from the tobacco-side portion to the opposite mouth-side portion, and said tobacco-side portion, said mouth-side portion, and the third portion each have a respective porosity that differs from the porosities of the other portions, wherein the porosity in the tobacco-side portion is in a range of 35-50%, in the middle portion in a range of 50-65% and in the mouth-side portion in a range of 65-80%.

17. The filter according to claim 16, wherein the filter has

an elasticity that decreases inwardly in a radial direction of the filter, and

a porosity that increases radially outwardly from a filter core to a filter shell of the filter.

18. The filter according to claim 17, wherein at least one intermediate portion is supported between a filter core portion having a predetermined placeholder particle fraction and a filter shell portion surrounding the filter core and having a placeholder particle fraction higher than the predetermined placeholder particle fraction, wherein the placeholder particle fraction of said intermediate portion lies between the placeholder particle fractions of the filter core portion and the filter shell portion.