WO2006125677A1

WO2006125677A1 - Piezoelectric spray device

Info

Publication number: WO2006125677A1
Application number: PCT/EP2006/006146
Authority: WO
Inventors: Nicolas Duru
Original assignee: L'oreal
Priority date: 2005-05-25
Filing date: 2006-05-19
Publication date: 2006-11-30

Abstract

The invention concerns a spray device including a ring (6) made at least partially of a piezoelectric material and a perforated membrane (7) caused to vibrate by the ring (6), wherein the perforated membrane (7) is held in the ring (6) by force fit.

Description

Piezoelectric spray device

The invention concerns spray devices wherein the droplets are generated by the vibrations of a perforated membrane integral with a piezoelectric vibrator.

There are several known means of rendering the perforated membrane integral with the vibrator.

International application WO 00/53337 discloses a process wherein the perforated membrane is rendered integral with a ring of piezoelectric material by welding. One drawback of this process lies in the risk of depolarisation of the ceramic in the event that its Curie point is exceeded. In this case, post- welding repolarisation is required, which generates an additional cost. Furthermore, welding calls for a particularly clean surface condition of the ceramic and there is a risk that the holes in the membrane will be blocked by welding residues.

It is also known to render the perforated membrane integral with the ring by gluing. Nevertheless, the adhesive used can prove incompatible with the product to be sprayed, particularly in the case of perfumes.

Moreover, gluing is difficult to implement in that the adhesive joint must be particularly thin while at the same providing sufficient mechanical continuity to transmit the vibrations to the perforated membrane. Finally, the gluing operation can be associated with difficulties related to the positioning of the perforated membrane, the drying time, the necessity for sufficient contact pressure between the perforated membrane and the ring, and also poses risks of running.

US patent 4 533 082 describes a spray device in which the ring of piezoelectric material is glued to the perforated membrane.

US patent 5 518 179 describes a spray device in which the ring of piezoelectric material is fixed to an annular support carrying the perforated membrane.

The invention aims to further improve piezoelectric spray devices.

In one of its aspects, the object of the invention is a spray device including a ring made at least partially of a piezoelectric material and a perforated membrane caused to vibrate by the ring, a device wherein the perforated membrane is held in the ring by force fit.

By virtue of the invention, the aforementioned drawbacks associated with welding or gluing, encountered in the prior art, are avoided without thereby adversely affecting the operation of the piezoelectric spray device.

In an example embodiment of the invention, the piezoelectric material is a ceramic, for example a ceramic of zirconate (PZT), metaniobate (PN), barium titanate or zinc oxide.

Again in an example embodiment of the invention, the perforated membrane has a non-flat shape. This shape can result from mechanical stresses associated with force fitting the membrane into the ring.

In an example embodiment of the invention, the perforated membrane is devoid of a rim at is periphery. As a variant, the perforated membrane can include a rim at its periphery and this rim can advantageously bear axially against a face of the ring. This can facilitate the positioning of the perforated membrane relative to the ring during assembly and can improve its attachment to the ring.

In an example embodiment of the invention, the perforated membrane includes an annular lip bearing radially against the ring. Like the aforementioned rim, this lip can be formed for example by stamping, electroforming or chemical etching.

The perforated membrane can be perforated for example in a central region only, or as a variant both in a central region and in a peripheral region, which can for example make it possible to obtain a wider dispersion of droplets. The number of holes in the membrane is for example greater than 100, for example between 100 and 300, for example in the order of 200.

The perforated membrane has for example a thickness less than or equal to

100 μm, preferably less than or equal to 50 μm, for example between 20 and 40 μm.

Before mounting, the perforated membrane has for example an outside diameter between 3 and 7 mm, or between 4 and 6 mm, in particular between 4.5 and 5.5 mm. The negative play between the ring and the membrane, before mounting, is for example greater than or equal to 0.025 mm, being for example approximately 0.5 mm, thereby making it possible to obtain a sufficient force fit of the membrane in the ring. The perforated membrane can have for example an outside diameter of 5.1 mm before mounting in the ring, and the latter a diameter less than 5 mm, which corresponds to a negative play of 0.05 mm.

The membrane can only bear radially against the ring at angularly spaced locations. This can make it possible to achieve an effective force fit, for example enabling the negative play between the membrane and the ring to be increased.

The membrane includes for example at its periphery a plurality of notches, which can for example have a rounded outwardly-concave shape, for example a semi-circular shape, for example of radius between 0.2 and 0.3 mm, for example close to 0.25 mm.

The angular difference between the notches is for example between 20 and 25°, for example close to 22.5°.

In the case where the membrane does not bear by its entire circumference on the ring, the negative play between the membrane and the ring can be larger, for example greater than or equal to 0.1 mm. The outside diameter of the membrane is for example 5.2 mm and the inside diameter of the ring 5 mm.

In an example embodiment of the invention, the piezoelectric spray device can include at least one retaining block for the perforated membrane, arranged on one side of the latter and, in a particular example, two retainers located on each side of the perforated membrane. The membrane can bear axially against at least one of these retainers.

The retaining block or blocks can be integral with a casing containing the ring of piezoelectric material.

In an example embodiment of the invention, the ring presents a stepped radially inner surface. The membrane can bear axially against the step, which can facilitate its positioning and retention.

The piezoelectric device can include a container to supply the perforated membrane with product to be sprayed, and this container holds for example a cosmetic product or a medicine, in particular a perfume, make-up, aromatherapy or skin care product.

The piezoelectric device can include a source of alternating current to excite the ring of piezoelectric material, for example at a frequency greater than or equal to 100 kHz, in particular in the order of 125 kHz.

The device can be of hand-held construction, and can be powered for example by cells, optionally rechargeable.

In another of its aspects, a further object of the invention is a method of spraying, for example a cosmetic product, by means of a piezoelectric spray device such as defined above.

In another of its aspects, a further object of the invention is a method of fixing a perforated membrane on a ring made at least partially of piezoelectric material, a method in which the perforated membrane is inserted by force into the ring.

The aforementioned piezoelectric material is a ceramic for example.

The perforated membrane can be initially flat and can deform outside its plane during fitting into the ring.

The perforated membrane can be brought to bear axially against a face of the ring on completion of assembly, for example by a rim or an annular edge surrounding a lip bearing radially on the ring. The perforated membrane can also be brought to bear against a stepped shoulder on the radially inner surface of the ring.

One or more retaining blocks can be arranged on at least one side of the membrane, and the latter can bear axially against at least one retainer.

In another of its aspects, a further object of the invention is a piezoelectric spray device including a ring of piezoelectric material and a perforated membrane bearing at least partially on a radially inner surface of the ring.

The membrane can in particular bear on the ring by less than a complete circumference, for example by virtue of the presence of notches at the periphery of the membrane. This can make it possible to obtain an effective force fit of the membrane. The invention will be better understood from the following detailed description of non-limitative embodiments, and by reference to the attached drawing in which:

- Figure 1 is a block diagram of a piezoelectric spray device according to the invention,

- Figure 2 is a schematic and partial lengthwise cross-section of an example device,

- Figures 3 to 8 are schematic axial cross-sections illustrating different possibilities for mounting the perforated membrane on the ring, and

- Figure 9 depicts an alternative embodiment of the membrane, in isolation, viewed from above.

The piezoelectric spray device 1 depicted in Figure 1 includes a power supply 2, an electric generator 3 delivering an electrical signal to a piezoelectric vibrator 4 maintaining the latter in vibration, in order to spray droplets of a liquid contained in a reservoir 5.

As can be seen in Figure 2, the vibrator 4 includes a ring 6 of axis X made at least partially of a piezoelectric material, arranged so as to mechanically induce vibrations in a perforated membrane 7, thereby enabling the formation of droplets 8 of product.

The ring 6 is for example made of ceramic, in particular zirconate (PZT), metaniobate (PN), barium titanate or zinc oxide. Electrodes serve to electrically excite the ceramic, thereby creating vibrations in the perforated membrane on the axis X of the ring.

The ring 6 is for example marketed under the reference 27121 by the Danish company

Ferroperm, the material being of the type PZ27.

The piezoelectric material of the ring 6 is for example polarised in the direction of its thickness, that is to say on the axis X, so that application of a potential on its principal faces 10 and 1 1, by means of electrical conductors 35 and 36 connected to the generator 3, causes the ring 6 to vibrate in the radial direction which tends to reduce the inside diameter of the ring 6. The perforated membrane 7 being in contact with the radially inner surface of the ring 6, the force exerted will cause the perforated membrane 7 to bulge very slightly, thereby creating at its centre the axial vibration necessary for the formation of the droplets 8.

The generator 3 delivers an a.c. voltage of 20V peak-to-peak and of frequency 125 kHz for example.

The frequency can be fixed, but as a variant the generator 3 can be arranged to adapt the frequency so as to maximise the amplitude of the vibrations of the perforated membrane 7 by a resonance phenomenon.

The perforated membrane 7 includes, in its central region, holes 13 the size and number of which are adapted to the size distribution of the droplets and the desired flowrate to be generated.

The holes 13 are for example arranged concentrically relative to the axis X, being grouped within a circle for example. In the example illustrated, the perforated membrane 7 bears by its free edge 15 against the radially inner surface 16 of the ring 6, this radially inner surface being for example cylindrical of axis X.

The perforated membrane 7 has the shape of a flat disc before mounting, and after mounting assumes a slightly domed shape by reason of mechanical stresses associated with force fitting of the perforated membrane 7 against the ring 6. In the example considered, mounting is accomplished from the side 17, so that the perforated membrane 7 assumes a convex shape on the outward side 18 towards which the droplets 8 are sprayed.

Before mounting in the ring 6, the outside diameter of the perforated membrane 7 is slightly larger than the inside diameter of the latter, so as to obtain the desired force fit. For example, before it is mounted in the ring 6, the perforated membrane 7 can have an outside diameter of 5.1 mm, for a thickness of 30 μm, and the ring 6 can have for example an outside diameter of 10 mm, an inside diameter of 5 mm, and a thickness of 1 mm.

The perforated membrane is for example a disc of nickel electroformed or obtained by chemical etching. The holes 13 can have a constant cross-section or a diminishing cross-section in the direction of expulsion of the droplets. The membrane 7 includes for example 200 cylindrical holes of 30 μm diameter, arranged in a circle of 2 mm diameter. Such a membrane is obtained for example by chemical etching.

Product is delivered to the perforated membrane 7 for example by capillary action, by means of a wick 38 immersed in the reservoir 5, as illustrated in Figure 2, or in the manner described in the US patent 5 518 179 or in international application WO 00/53337, the content of which is incorporated herein by reference.

Figures 3 to 8 depict variants of attachment of the perforated membrane 7 on the ring.

In the example in Figure 3, the perforated membrane 7 includes an annular Hp 20, of axis X, which bears tightly against the radially inner surface 16 of the ring 6. The lip has for example a height greater than 0.5 mm.

The perforated membrane 7 includes an annular edge 21, radially exterior to the lip 20, which bears against the face 10 of the ring. The presence of the lip 20 and the edge

21 enables the perforated membrane 7 to be mounted in the ring 6 and serves to position it axially. The lip 20 can be formed by stamping of the perforated membrane 7 or by electroforming.

In the example in Figure 4, a rim 22 is formed at the periphery of the perforated membrane 7. This rim includes a riser 23 which bears tightly against the radially inner surface 16 of the ring 6 and abuts axially against the face 1 1 of the ring. This also serves to axially position the perforated membrane 7 relative to the ring 6. The rim 22 is for example formed by stamping or electroforming.

In the example in Figure 5, the perforated membrane 7 includes, as in the example in Figure 4, a rim 22 bearing on the face 11 of the ring. In contrast to Figure 4, the perforated membrane 7 has a domed shape towards the inside 18, with holes 13 in a central region and holes 24 in a peripheral region, so as to obtain a wider dispersal of droplets 8.

The example in Figure 6 differs from that in Figure 4 by the shape of the perforated membrane 7, which is conical, the holes 13 being formed in an upper region of the perforated membrane 7, substantially flat and perpendicular to the axis X. In particular when the perforated membrane 7 does not bear axially against one of the end faces 10 or 11 of the ring, which is the case in the example in Figure 2, it can be useful to provide a means of axially positioning the perforated membrane 7 relative to the ring 6, not only during mounting but also to avoid displacement of the perforated membrane 7 during operation of the device, under the effect of the vibrations.

The vibrator 4 can include for example at least one retaining block 30, in this instance two retaining blocks 30 and 31 in the example in Figure 7, bearing on the perforated membrane 7 on each side of the latter. The retainers 30 and 31 are for example attached to the casing 48 housing the vibrator 4. So as not to interfere with the vibrations of the membrane 7, the retainers 30 and 31 have for example a thickness less than or equal to 0.5 mm. The inside diameter of the ring 6 is thus reduced by a maximum of 1 mm.

The ring of piezoelectric material can have a different shape, and in particular a stepped radially inner surface, so as to facilitate axial positioning of the membrane, as illustrated in Figure 8.

The membrane 7 can then bear against the step 39 in the ring 6.

The invention is not limited to the examples described above.

In particular the perforated membrane can have other shapes and provision can be made, in the examples depicted in Figures 3 to 6, to axially hold the rim against the ring by means of a retainer or a washer bearing on the lower face of the membrane 7, ensuring that the membrane is not unduly prevented from vibrating.

Although the perforated membrane is depicted as monolithic in the examples illustrated, the scope of the present invention is not exceeded when this membrane is made in a non-monolithic manner, for example by assembling several materials or with the holes arranged differently.

The membrane 7 can bear radially against the ring 6 on less than a complete circumference, for example by virtue of the presence of notches 40 at its periphery, as illustrated in Figure 9. For the sake of clarity, only two notches 40 and only some of the holes 13 are shown in this figure.

For example the notches 40 are each semi-circular in shape, for example 0.5 mm in diameter, the centres of two consecutive notches being angularly spaced at an angle α equal to 22.5° in the example illustrated.

Non-continuous bearing contact over the entire circumference can make it possible to obtain an effective force fit in the ring 6, for example be enabling the membrane 7 to be made with a larger diameter, for example 5.2 mm for an inside diameter of the ring of 5 mm.

Delivery of product to the membrane can be accomplished by means other than a wick.

The expression "including one" should be understood as being synonymous with the expression "including at least one", unless otherwise specified.

Claims

1. Spray device including a ring (6) made at least partially of a piezoelectric material and a perforated membrane (7) caused to vibrate by the ring (6), device wherein the perforated membrane (7) is held in the ring (6) by force fit.

2. Spray device according to claim 1, characterised in that the piezoelectric material is a ceramic.

3. Spray device according to claim 1 or 2, characterised in that the perforated membrane (7) has a non-planar shape.

4. Spray device according to any one of claims 1 to 3, characterised in that the perforated membrane (7) is devoid of a rim at its periphery.

5. Spray device according to any one of claims 1 to 3, characterised in that the perforated membrane (7) includes a rim (22) at its periphery.

6. Device according to claim 5, characterised in that the rim (22) bears axially against a face of the ring.

7. Device according to any one of the preceding claims, characterised in that the perforated membrane (7) includes an annular lip (20) bearing radially against the ring (6).

8. Device according to the preceding claim, characterised in that the Hp (20) is formed by stamping.

9. Device according to claim 7, characterised in that the lip (20) is formed by electroforming or chemical etching.

10. Device according to any one of the preceding claims, characterised in that the perforated membrane (7) is perforated only in a central region.

1 1. Device according to any one of claims 1 to 9, characterised in that the perforated membrane is perforated both in a central region and in a peripheral region.

12. Device according to any one of the preceding claims, characterised in that the perforated membrane (7) has a thickness less than or equal to 100 μm, preferably less than or equal to 50 μm, in particular between 20 and 40 μm.

13. Device according to any one of the preceding claims, characterised in that, before it is mounted in the ring (6), the perforated membrane (7) has an outside diameter between 3 and 7 mm, or between 4 and 6 mm, in particular between 4.5 and 5.5 mm.

14. Device according to any one of the preceding claims, in which the ring (6) has a stepped radially inner surface.

15. Device according to any one of the preceding claims, in which the membrane (7) only bears radially on the ring at angularly spaced locations.

16. Device according to claim 15, in which the membrane includes notches (40) at its periphery.

17. Device according to claim 16, in which the notches are semi-circular.

18. Device according to claim 16 or 17, in which the centres of two consecutive notches are spaced at 22.5°.

19. Device according to any one of the preceding claims, in which the membrane (7) has an outside diameter at least approximately 0.1 mm larger than the inside diameter of the ring.

20. Device according to any one of the preceding claims, characterised in that it includes at least one retainer (30; 31) for the perforated membrane, arranged on one side of the latter.

21. Device according to the preceding claim, characterised in that it includes two retainers (30, 31) located on each side of the perforated membrane (7).

22. Device according to any one of the preceding claims, characterised in that it includes a container (5) to supply product to the perforated membrane (7).

23. Method of fixing a perforated membrane (7) on a ring (6) made at least partially of piezoelectric material, a method in which the perforated membrane is inserted by force into the ring.

24. Method according to claim 23, characterised in that the aforementioned piezoelectric material is a ceramic.

25. Method according to claim 23 or 24, characterised in that the perforated membrane is initially flat and deforms out of its plane when mounted in the ring.

26. Method according to any one of claims 23 to 25, characterised in that the perforated membrane is brought to bear axially against a face or a stepped shoulder of the ring on completion of assembly.

27. Method according to claim 26, characterised in that the perforated membrane is brought to bear axially by a rim (22) against a face or a stepped shoulder of the ring on completion of assembly.

28. Method according to claim 26, characterised in that the perforated membrane is brought to bear axially against a face or a stepped shoulder of the ring, on completion of assembly, by an annular edge (21) surrounding a lip (20) bearing radially on the ring.

29. Method according to any one of claims 23 to 28, in which the membrane bears radially against the ring at angularly spaced locations.