WO2008030090A1

WO2008030090A1 - Sound-limiting device, filter and method of manufacture

Info

Publication number: WO2008030090A1
Application number: PCT/NL2007/000218
Authority: WO
Inventors: Arnoud Jan Kalden
Original assignee: Sincear B.V.
Priority date: 2006-09-08
Filing date: 2007-09-10
Publication date: 2008-03-13
Also published as: EP2068796A1

Abstract

The present invention relates to a sound-limiting device for protecting an ear against excessive noise, comprising: - an auditory canal member for insertion thereof in the auditory canal, - a filter allowing passage of a limited amount of sound, which can be arranged in the auditory canal member, wherein; - the filter comprises at least a metal component. The filter preferably comprises a ceramic material comprising the metal component.

Description

Sound-limiting device, filter and method of manufacture

The present invention relates to a sound-limiting device for protecting an ear against excessive noise. The present invention also relates to a filter for a sound-limiting device. The present invention further relates to a method for manufacturing a filter for a sound-limiting device. The present invention further relates to a method for manufacturing a sound-limiting device.

Earplugs are generally used to protect the ear from excessive noise. High-intensity sound of short duration can result in damage to hearing, as can longer-term exposure to sound with a lower intensity. The known earplugs used to protect the ear have a number of operating principles. It is for instance possible to use earplugs consisting of a kneadable, solid material. It is also possible to use earplugs consisting of a foam-like material. It is further known to use earplugs consisting of a number of circular lamellas arranged in an array. Also available commercially are earplugs which have a shape adapted to the auditory canal and which are provided with an open channel with a small diameter through which the sound can pass in damped form. The damping here depends partly on the diameter. A drawback of such existing earplugs is that the known production technologies of such filters result in relatively inaccurate production results, with the consequence of an unreliable damping factor, and therefore unintended damage to hearing. In order to obviate such drawbacks the present invention provides a sound-limiting device for protecting an ear against excessive noise, comprising:

- an auditory canal member for insertion thereof in the auditory canal,

- a filter allowing passage of a limited amount of sound, which can be arranged in the auditory canal member, wherein;

- the filter comprises at least a metal component.

The filter preferably comprises a ceramic material comprising a metal.

In this document a metal component is defined as a metal which is suitable to be able to form part of a ceramic material, but also as a metal per se. Examples of suitable ceramic materials are oxides such as zirconium oxide, silicon oxide, silicon carbide, aluminium oxide and mixtures thereof.

Advantages of such a sound-limiting device include being able to achieve a precise sectional profile or diameter of the channel on the basis of production parameters. Greater damping factors can also be achieved in that the diameters of such a filter according to the present invention can be small. Diameters are possible here of for instance smaller than 0.3 mm, preferably smaller than 0.2 mm, more preferably smaller than 0.1 mm.

In a preferred embodiment the filter is manufactured making use of a binder, preferably an organic agent. An advantage hereof is that a ceramic powder can obtain both fluid and adhesive properties under the influence of the binder, which enables a practical production method. It hereby becomes possible, among other things, to manufacture the filter making use of an injection moulding process.

At least one heat treatment is preferably applied in the manufacture of the filter, preferably two heat treatments. The first heat treatment serves for debinding and the second heat treatment preferably serves to coalesce the ceramic material, for instance by means of sintering. A further advantage of the heat treatments, and the sintering in particular, is that a large measure of shrinkage can be achieved here, this shrinkage being to a large extent achieved in predictable manner under the influence of process parameters to be set. Owing to this large measure of predictable shrinkage, on the one hand a diameter of the channel is achieved which is smaller than the diameter of the mould in which the channel is formed and on the other a high degree of accuracy of the desired and achieved channel diameter can be obtained with the production parameters to be selected. In a further preferred embodiment the auditory canal member extends in the position of use in an auditory canal of the ear beyond the first bend in the auditory canal, and preferably beyond the second bend in the auditory canal. This achieves that the damping through the channel is not counteracted by a leakage of sound between the auditory canal member and the wall of the auditory canal. The auditory canal member here preferably comprises a plastic, and more preferably a gel-like material, thereby also achieving a good material tolerance by the bodily material of the auditory canal.

A further aspect according to the present invention relates to a filter for a sound-limiting device, comprising:

- a housing having preferably a substantially cylindrical form, - a channel extending through the housing and comprising at least one part with a sound-limiting sectional profile, wherein the housing comprises a metal component.

A further aspect according to the present invention relates to a sound- limiting device according to the present invention, comprising a filter according to the present invention.

A further aspect according to the present invention relates to a method for manufacturing a filter for a sound-limiting device or a filter according to claim 13, comprising steps for:

- forming a material mixture into a shaped material which is suitable for obtaining a filter,

- debinding the material mixture,

- coalescing the material mixture to form a hardened filter.

An advantage of such a method is that a filter or a sound-limiting device according to the present invention can be obtained with great sound- damping properties and high production accuracy.

A further aspect according to the present invention relates to a method for manufacturing a sound-limiting device comprising a filter according to the present invention, comprising steps for:

- manufacturing an auditory canal member,

- manufacturing a filter,

- placing the filter in the auditory canal member.

Further advantages, features and details of the invention will be elucidated in greater detail hereinbelow with reference to the accompanying figures, in which:

- Fig. 1 is a schematic representation of a method according to the present invention;

- Fig. 2 is a schematic view of a first preferred embodiment according to the present invention of a filter;

- Fig. 3 is a top view of a limiting device comprising a filter as according to Fig. 2;

- Fig. 4 is a schematic view of a first preferred embodiment according to the present invention of a filter.

A preferred embodiment (Fig. 2) according to the present invention relates to a filter 1 for application in hearing protectors. Such a filter provides such protection in that sound waves are only allowed in damped form through the narrow channel inside filter body 2. The channel comprises for this purpose a narrowed portion which can be manufactured according to the present invention with great precision and great reproducibility. The chance of damage to hearing occurring due to deviations is hereby greatly reduced.

According to the present invention and in the preferred embodiment, body 2 comprises ceramic materials such as for instance aluminium oxide. Other materials or metals are also possible in alternative embodiments. A preferred embodiment of a method for manufacturing such a filter and hearing protection is described by way of example below.

The filter of the embodiment of Fig. 1 is given a technically functional form as a substantially cylindrical tube which is truncated at the position of respective outer walls 4, 3, with a channel extending substantially around the central axis thereof. This channel has a form substantially similar to the form of a venturi with an elongate narrow central part in which the sound waves are damped to a significant extent. It is important here that the damping factor is readily predictable so as to enable a reliable protection. The channel is bounded by wall parts 5 and 6, which form respectively the narrowing and widening of the channel, and wall part 7 which forms the narrowed part.

A method for manufacturing a filter according to the embodiment of Fig. 2 is described on the basis of the flow diagram of Fig. 1. The method begins in step 11 with a powdered material being provided and a binder being provided in step 12. The powdered material in this example is a very fine aluminium oxide powder (AIO₂). Alternative ceramic materials or precursors thereof are likewise possible. The binder can be chosen in suitable manner and has as its most important property that it is suitable for application as a binder in a method according to the present invention. The binder of the example is a so-called solvent debinder.

In step 13 these materials are then mixed to form a mixture wherein the binder is melted. The mixture is subsequently kneaded and further mixed. After the mixing of the mixing method of step 13, the mixture meanwhile obtained is formed in step 14 into small granules or globules, i.e. granulated. According to this embodiment it is important here that the granules are suitable for processing in an injection moulding-like process. By means of an injection moulding process using a suitable mould this globule mixture is then brought substantially into the form of the filter in step 15, although shrinkage will occur in subsequent steps.

In step 16 a large part of the binder is then extracted from the formed material under precise control of process parameters. An alternative designation for the extraction is debinding. The workpiece is subjected for this purpose to a heat treatment at temperatures up to 500 degrees Celsius. The result hereof is a fragile hollow tube substantially in the form of the injection mould, albeit that the workpiece may undergo some shrinkage during this step.

In step 17 the workpiece resulting from step 16 is sintered at temperatures up to 1750 degrees Celsius while applying an accurately predetermined temperature-time curve. Further shrinkage of the workpiece occurs here as a result of compaction. The sintering further causes a mutual adhesion of the material of the granules, thus creating a very strong and stable tube, or the filter as described with reference to Fig. 2. Use is made here of, among other factors, internal stress in the ceramic particles. Solvent residue debinding of the material will also take place due to the sintering. In step 18 the product is then finished by means of for instance smoothing of the outside, and the method is ended in step 19.

In the debinding step an acid such as a nitric acid is preferably applied in a gas in the applied atmosphere. During the debinding step this acid will act on the organic components, such as the resins serving as binder.

The filter in Fig. 4 differs from that of Fig. 2 in that on one side the inclining wall runs such that it leaves space for an edge 9 which extends around an end of channel 7. The advantage of this edge is that it can be used to support the filter thereon during one or more production stages of the filter.

Shrinkage occurs in the workpiece during the extrusion and sintering. This shrinkage has been determined during tests as being in the order of magnitude of 20 to 30 percent. Other percentages may be possible when other process parameters are applied, and these can be determined experimentally during application of the present invention. An advantage of achieving this shrinkage is that a smaller diameter of the damping channel can be obtained than without such a shrinkage. A very predictable shrinkage factor can further be obtained with the application of suitably chosen process parameters. By applying such a method for obtaining the filters for the application, a reliable filter can surprisingly be hereby obtained for use thereof in a hearing protector according to the present invention. A further advantage of the shrinkage is that filter body 2 is further strengthened.

The ceramic materials applied according to the present invention for the filter of hearing protectors have for instance been applied in the field of semiconductor technology because of the material properties of a good conductivity of electric current and good properties for generating magnetic fields. In addition to the attainable accuracy of manufacture, very small channel diameters of 0.1-0.4 mm, preferably 0.15-0.18 mm or 0.1-0.15 mm, are further possible by means of the described method and with use of these materials. Other possible dimensions are 0.18-0.21 mm, 0.21-0.25 mm, 0.25-0.30 mm, 0.30-0.35 mm and for instance 0.35-0.40 mm.

Fig. 3 shows a schematic view of a hearing protector 21 or earplug according to the present invention. Hearing protector 21 here comprises an auditory canal part for insertion thereof into the auditory canal. The auditory canal can hereby be closed against sound vibrations, except substantially those which can pass through the hearing protector. The hearing protector further comprises a handle and/or fastening part 28 for handling and/or fastening of a cord thereto so as to prevent loss of the hearing protector.

The auditory canal part further comprises at the substantially narrow end part thereof an opening which forms the beginning of a sound channel 25. This sound channel debouches on the other side thereof into a filter chamber 24, which is in turn provided with an opening 23. This filter chamber is suitable for permanent or semi-permanent placing of a filter 1 as known from Fig. 2 and/or which can be manufactured as according to the method of Fig. 1. A fixing means and/or sound-damping means can be applied between the filter and the wall of the filter chamber for the purpose of fixing the filter.

It is of further importance for the hearing protector that it is per se manufactured in a manner such that it fits closely onto an individual ear and/or auditory canal of the user. For this purpose a cast is made of the auditory canal, preferably up to a position beyond the second bend of the auditory canal. On the basis of this cast a body is then manufactured with the shape of the auditory canal, which body can serve as the hearing protector according to the present invention with a filter according to the present invention. The filter chamber for attaching the filter is formed in this body. This can be carried out during or after forming of the body.

It is for instance further possible to manufacture filters with very small channel dimensions via for instance three-dimensional print technologies. The filters are here constructed integrally on the basis of a predefined shape.

The present invention is described in the foregoing on the basis of several preferred embodiments. Different aspects of different embodiments are deemed as described in combination with each other, wherein all combinations which can be made by a skilled person on the basis of this document should be included. These preferred embodiments are not limitative for the scope of protection of this text. The rights sought are defined in the appended claims.

Claims

1. Sound-limiting device for protecting an ear against excessive noise, comprising:

- an auditory canal member for insertion thereof in the auditory canal,

- the filter comprises at least a metal component.

2. Sound-limiting device as claimed in claim 1 , wherein the filter comprises a ceramic material comprising the metal component.

3. Sound-limiting device as claimed in claim 2, wherein the filter is manufactured making use of a binder, preferably an organic binder.

4. Sound-limiting device as claimed in claim 2 or 3, wherein the filter is manufactured making use of an injection moulding process.

5. Sound-limiting device as claimed in claim 2, 3 or 4, wherein the filter is manufactured making use of at least one heat treatment, preferably two heat treatments.

6. Sound-limiting device as claimed in one or more of the foregoing claims, having a length and/or form such that the auditory canal member extends in the position of use in an auditory canal of the ear beyond the first bend in the auditory canal, and preferably beyond the second bend in the auditory canal.

7. Sound-limiting device as claimed in one or more of the foregoing claims, wherein the auditory canal member comprises a plastic, preferably a gel-like material.

8. Sound-limiting device as claimed in one or more of the foregoing claims, comprising a support edge on at least one side of a sound channel of the filter.

9. Filter for a sound-limiting device, comprising:

- a housing having preferably a substantially cylindrical form,

- a channel extending through the housing and comprising at least one part with a sound-limiting sectional profile, wherein the housing comprises a metal component.

10. Filter as claimed in claim 9, wherein the filter comprises a ceramic material comprising the metal component.

11. Filter as claimed in claim 9 or 10, wherein the filter is manufactured making use of a binder, preferably an organic binder.

12. Filter as claimed in claim 9, 10 or 11 , wherein the filter is manufactured making use of an injection moulding process.

13. Filter as claimed in claim 9, 10, 11 or 12, wherein the filter is manufactured making use of at least one heat treatment, preferably two heat treatments.

14. Sound-limiting device as claimed in one or more of the foregoing claims 1-8, comprising a filter as claimed in one or more of the claims 8-13.

15. Method for manufacturing a filter for a sound-limiting device or a filter as claimed in claim 14, comprising steps for:

- debinding the material mixture,

- coalescing the material mixture to form a hardened filter.

16. Method as claimed in claim 15, comprising steps for manufacturing the material mixture, wherein the material mixture comprises a precursor for a ceramic material.

17. Method as claimed in claim 15 or 16, wherein the steps for debinding comprise steps for heating the shaped material.

18. Method as claimed in claim 15, 16 or 17, wherein the steps for coalescing the material mixture comprise a heating process, and preferably a sintering process.

19. Method as claimed in one or more of the claims 15-18, wherein the material mixture comprises ceramic and/or metal powder.

20. Method as claimed in one or more of the claims 15-19, comprising steps for shrinking the shaped material.

21. Method for manufacturing a sound-limiting device comprising a filter as claimed in one or more of the foregoing claims, comprising steps for:

- manufacturing an auditory canal member,

- manufacturing a filter,

- placing the filter in the auditory canal member.