AU2006201741A1 - Apparatus for Diffusion of Volatile Liquids - Google Patents

Description

o 1 0

APPARATUS

This invention relates to apparatus for the disseminating of volatile liquids into an atmosphere.

One very common apparatus for disseminating a volatile liquid, such as a fragrance or an insecticide, into an atmosphere consists of a porous transfer member, such as a porous wick, that is in contact with a reservoir of volatile liquid. Liquid rises up this wick and evaporates into the O atmosphere. This system has drawbacks, such as the low surface area for evaporation and the I tendency for the wick to fractionate complex mixtures, such as fragrances, so that some S 10 components are disseminated earlier than others and the full effect of the fragrance is lost.

It has been proposed to overcome this disadvantage by using external capillaries, that is, capillary channels cut or moulded into a suitable substrate. One example is described in United States Patent 4,913,350, in which an external capillary channel-containing member is inserted into a liquid. In another embodiment, described in copending UK Patent Application GB 0306449, there is fittedto a known transfer member a capillary sheet, that is, a sheet extending essentially perpendicularly from the transfer member and that comprises channels of capillary dimensions, to which volatile liquid can pass and travel along for evaporation: This sheet generally contacts the transfer member by means of a hole in the sheet through which the transfer member protrudes and within which it fits snugly, at least some of these channels contacting the transfer member such that liquid can transfer from the member to the sheet ("liquid transfer contact").

Although this technology offers significant advantages over the porous wicks of the art, these advantages have never been completely realized. It has now been found that it is possible to obtain the' full benefits of the technology by adherence to certain fundamental parameters. The invention therefore provides an apparatus adapted to disseminate volatile liquid into an atmosphere from a reservoir, the transfer to atmosphere being achieved by means of a porous transfer member that transfers liquid from the reservoir to an evaporation surface, the evaporation surface being a capillary sheet in liquid transfer contact with and extending substantially transversely from the transfer member, and being further characterized in that the o 2 0 material of the sheet is a plastics material having a Shore D hardness of from 50 to 80 and a thickness of from 0.75 1.25 mm.

The capillary sheet and transfer member are separate components able to be put together when necessary. Typical transfer members include porous wicks of plastics, graphite and ceramics, made by any suitable method, for example, by extrusion or sintering. A preferred material is a o porous plastic, such as polyester. The transfer member may be of any suitable shape or construction. Some examples of suitable configurations include; 0 the transfer member being slightly frusto-conical in shape, narrower end farthest from the reservoir; this enables a capillary sheet with a circular aperture to be easily slipped on andb fitted to the transfer member; the provision in the transfer member of a suitable locating orifice for a capillary sheet, for example, an annular groove or a slot for a matching tab in the capillary diffusion member, to allow for easy fitting.

A combination of all or any of these elements may be used. In addition, other constructions that are not mentioned here but which lie within the skill of the art are also included.

The plastics material may be chosen for any suitable plastics material having the desired hardness properties Shore D hardness is a very well known property in the plastics industry and its measurement is common. It is a surprising feature of this invention that this parameter should have any effect on the efficacy of an evaporation surface, yet it has been found that this has a marked influence. The desired Shore D hardnesses are quite soft by the standards of the plastics industry. Naturally the plastics material should also be suitably inert with respect to any of the materials in the liquid. It should also be a material that permits the formation of capillary channels by any suitable means, for example, by engraving or injection moulding. Injection moulding is the preferred method of forming a capillary sheet. Capillary channels are typically V-shaped channels whose typical dimensions are 0.1-0.5mm wide, 0.1-0.5mm deep with the o 3 0 angle of the channel being 10-25 degrees. The skilled person will readily appreciate what kind of plastics material is suitable for any use.

In a preferred embodiment of the invention, the plastics materials for use in the making of capillary sheets suitable for use in this invention have a surface energy of from 15-50 dyne/cm.

The surface energy of a plastics material is dependent upon its molecular structure and is a o measure of the ability of a surface to be wetted. The more inert is a plastics material chemically, Ithe lower is its surface energy. Thus, materials such as polyethylene, polypropylene and PTFE ohave low surface energies, whereas the plastics with more polar groups have higher surface energies. Preferably the surface energy lies in the range of from 30-45 dynes/cm.

The apparatus is generally supplied with the capillary sheet dismounted and a protective cap over the porous member. The apparatus is put into service by removing the cap and placing the capillary sheet on the transfer member, such that it is in liquid transfer contact with the transfer member. This can be assured by use, for example, of one of the attachment means hereinabove described.

The invention is suitable for use with any volatile liquid that may be disseminated into an atmosphere by means of a porous Wick. Commercial materials of this type, especially the fragrances, are generally carefully formulated proprietary compositions containing a plurality of ingredients, the precise nature of such compositions being kept confidential. However, whatever the nature of these compositions, it is a feature of this invention that they are much more effectively disseminated by the apparatus according to this invention than by a wick alone.

The invention therefore additionally provides a method of disseminating a volatile liquid into an atmosphere by means of its absorption in and travel along an essentially cylindrical porous wick and then along an evaporation surface extending substantially transversely from the wick and in liquid transfer contact therewith, the evaporation surface comprising a capillary sheet of a plastics material having a Shore D hardness of from 50-80 and a thickness of from 0.75 1.25 mm.

Va 0\ 4 The invention is further described with reference to the following non-limiting examples.

Example 1.

1.00 mm thick external capillary sheets were prepared from the materials in the following table and the Shore hardness measured. This was done by means of a Shore (Durometer) test according to ASTM D2240 00. The apparatus used used was a Mitutoyo Hardmatic HH-337- 01. An indenter is pressed in the plastic and this forces the needle of the gauge round and the indicator records maximum value. This is the Shore D Hardness. The individual sheets comprised central holes that permitted them to be mounted on frusto-conical wicks by simply placing them on the wicks.

Trade Name BOREALIS* MG 9641-R SAN* 386R 774 EXACT* 8210 POLYAC* PA-758 IUPITAL* F40-03 LUPOY* GP5001 A-F IPETHENE* 320 RAD ATER* E AX1 100 LL6201 ESCORENE* VL02020 PS 146L IUPILON* S3000 PP 7075 L1 ITOCHU* H202 IOTEK* 8020 Material Type Polyethylene PE (HDPE) Styrene Acrylonitrile Copolymer

SAN

Octene-1 Plastomer Acrylonitrile-butadiene-styrene

ABS

Polyoxymethylene POM (Acetal)

PC/ABS

Polyethylene PE (LDPE) Polyethylene terepthalate

PETG

Polyethylene PE (LLDPE) Ethylene Vinyl Acetate EVA Polystyrene PS Polycarbonate PC Polypropylene PP Polyethylene terepthalate

PETG

lonomer (sodium) Hardness (Measured) (Shore D) 56 87 44 81 79 47 41 83 84 74 62 Trade marks o 0 Frusto-conical wicks of polyester (ex Micropore) were placed in a container containing a vanilla fragrance formulation used for air freshening applications (this fragrance has the advantage of being easily visible). They were allowed to equilibrate overnight. The external capillary sheets were pushed on to a frusto-conical wick until firm contact between sheet and wick (suitable to ensure liquid transfer) was made. The percentage of the capillaries in which liquid was present was assessed visually assessed after 6 minutes for no transfer from wick to the capillary, o 100% for the presence of liquid in all capillaries and liquid has travelled to end of all capillaries). The results are shown on the graph of Figure 1.

0 The graph shows that, for optimum liquid transfer, the material has to have a Shore D hardness of between 50 and Example 2.

Two frusto-conical wicks were placed in individual containers containing the fragrance formulation of Example 1. They were allowed to equilibrate overnight. To one of these wicks was added a polypropylene capillary sheet having a thickness of Imm and a Shore hardness of to the other an otherwise identical sheet having a thickness of 1.5mm. The percentage of each sheet wetted by the liquid is shown in the following table.

Thickness of External Capillary Sheet capillary sheet wetted mm mm 100% Hence the capillary thickness specification for direct liquid transfer as described in US 4,913,350 is not suitable for use in a hybrid wick system as it does not give optimum liquid transfer contact. The ideal thickness is 1.25 mm maximum. The lower limit of thickness is 0.75 mm set by the limit that good capillaries formed in a suitable production process such as injection molding.

o 6 0 The invention is further described with reference to the accompanying drawings. It will be appreciated that the drawings are provided for the purpose of comprehending the context in which the present invention may be applied. It will be understood that the present invention will have other applications that will be apparent to those skilled in the art. The accompanying drawings depict particular embodiments and are not meant to limit the invention in any way.

oFigure 2 is a perspective view of a one embodiment.

oFigure 3 depicts a longitudinal cross-section of a transfer member at the point where it contacts a diffusion surface.

Figure 4 depicts an arrangement wherein surface capillarity is conferred by a porous material affixed to a non-porous surface.

Figure 5 depicts a variety of possible surface capillarity arrangements.

Figures 3-5 are schematic and are not to scale, certain dimensions being exaggerated for the purposes of clarity.

In Figure 2, a reservoir 1 (a bottle or jar) has a neck 2 into which is fitted a rod-like porous wick 3, this being a tight fit into the neck by means of a tightly-fitting elastomeric plug 4 that surrounds the wick. The wick is circular in cross-section and that part of the wick protruding from the reservoir is slightly conical as shown at Figure 3, having a narrower end 5 remote from the reservoir and a broader end 6 closer to the reservoir. This permits the easy mounting on the wick of a diffusion surface 7, which has an aperture 8 of diameter greater than that of end 5 but greater than that of end 6. The aperture 8 is shaped so that it closely matches the frusto-conical surface of the wick, ensuring good contact and liquid transfer. The diffusion surface is a curved sheet of non-porous plastic that bears on its surface a series of open capillaries 9.

In Figure 4, a frusto-conical wick 3 bears a non-porous diffusion surface 10. To this is affixed a capillarity-providing material 11. This material covers that surface of the diffusion surface o 7 0 Sfacing downwards in normal operation and extends into the aperture 8 of the diffusion surface, such that it contacts the wick and is able to absorb and transfer liquid for evaporation. The weight of the diffusion surface acting downwards helps secure the surface and establish a good liquid transfer contact.

In Figure 5, there can be seen a variety of surface capillarities. These are presented by way of o example only and they are not limiting of the many practical and ornamental possibilities.

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Claims (4)

1. 2. An apparatus according to claim 1, in which the arrangement of transfer member and capillary sheet is selected from the group consisting of: a transfer member that is slightly frusto-conical in shape, narrower end farthest from the reservoir, on to which a capillary sheet having a circular aperture is slipped and fitted; (ii) a transfer member comprising a suitable locating orifice into which a capillary sheet may be fitted.
2. 3. An apparatus according to claim 1, in which the plastics materials of the capillary sheet has a surface energy of from 15-50 dyne/cm.
3. 4. An apparatus according to claim 3, in which the surface energy lies in the range of from
4. 30-45 dynes/cm. An apparatus according to any of claims 1 to 4, in which the capillary channels are V- shaped channels that are from 0.1-0.5mm wide, from 0. 1-0.5mm deep, and that have a angle of the channel of from 10-25 degrees. VO 9 6. A method of disseminating a volatile liquid into an atmosphere by means of its absorption in and travel along an essentially cylindrical porous wick and then along an evaporation surface extending substantially transversely from the wick and in liquid transfer contact therewith, the evaporation surface comprising a capillary sheet of a plastics material having a Shore D hardness of from 50-80 and a thickness of from 0.75 -1.25 mm.