CA1316454C

CA1316454C - Air freshener

Info

Publication number: CA1316454C
Application number: CA000594030A
Authority: CA
Inventors: Kenneth L. Purzycki
Original assignee: L Givaudan and Co SA
Current assignee: Givaudan SA
Priority date: 1988-03-18
Filing date: 1989-03-17
Publication date: 1993-04-20
Anticipated expiration: 2010-04-20
Also published as: EP0386158B1; AU3195589A; US4913350A; DE68913294D1; EP0386158A1; JP2756328B2; AU619530B2; DE68913294T2; JPH02503522A; WO1989008462A1

Abstract

Ref. 6550/27 ABSTRACT

An air freshening device which allows a liquid fragrance material to be dispensed into the ambient air of a room or other designated area in a linear fashion, i.e., without distortion of the odor character and without a change in the rate of delivery. More particularly, the device comprices a reservoir, a fragrance material, and an external capillary member, wherein said external capillary member has one or more external capillary cavities, the lower portion of said capillary being in contact with the liquid fragrance material to be dispensed, and the upper portion of said capillary being exposed to the air in the room or area into which it is desired to dispense the fragrance.

Description

~ 316~5~ Ref. 6550/27 Devices designed to dispense ~ragrance materials into the ambient air to impart a desirable and pleasant fragrance ace well known in the art. Such devices, commonly known as air fresheners or room deodorizers, are commercially available in a variety of forms. Some of these devices are quite simple while others, which involve mechanical systems, are more complex.

Ideally, the device should be as simple as eossible, require little or no maintenance and should pecform in a 15 manner that allows the fragrance material to be dispensed at a steady and controlled rate into the designated area while maintaining its odor integrity over the life span of the device. Unfortunately, nearly all of the relatively simple non-aerosol devices that are commercially available suffer 20 from the same limitation. The odor becomes distorted over the life span of the device due to the fact that the more volatile components are removed first, leaving the less volatile components behind. This change of the composition with time eventually results in a weakening of the intensity 25 of the fragrance since the less volatile components evaporate more slowly. It is these t~o problems, i.e., the weakening of intensity and distortion over the lifetime of the fragrance material, that have~occupied much of the attention of those who seek to devise better air freshener 30 devices.

Practically all devices which depend on evaeoration from a surface suffer from the shortcomings mentioned above. In most of these devices, a wick, gel or porous surface simply 35 provides a greater sur~ace area from which the feagrance Ur/28.2.89 ~k 131~454 material can evaporate moce quickly, but fractionation still occurs, as it would from the sucface of the liquid itself, resulting in an initial burst of frageance followed by a period of lower intensity once the more vola~ile components have evaporated. Due to this fractionation and perhaps a clogging of the wick and/or other evaporative surfaces, the fragrance becomes distorted and its intensity weakens perceetibly.

Various methods have been tried in an effort to overcome such eroblems and some have met with limited success. For example, surface active agents have been used to control the release of the fragrance, but these non-volatile substances often clog up delivery devices such as wicks and the use of such materials has not provided the desired degree of linearity of evaporation. ~nother method reported to be successful in minimizing distortion, invol~ed creating a fragrance ~aterial using only components having similar volatility so that they ~ould all evaporate at the same rate- The use of non-volatile solvents such as high boiling lo~-parrafin hydrocarbons has also been reported to slow down the initial burst of fragrance caused by the more volatile components. (See U.S.P. 2,529,536 (1~: 4,250,165 (2): 4,304,688 (3): 4,320,873 (4): 4,323,193 ~5); U.S.P.
4.286,754 (~); U.S.P. 4,609,245 (7).

(1) discloses a fluid evaeoratir.g device utilizing a reversible conventional wick system.

(2) teaches a method of stabilizing fr~grance oils by incorporation of an amount of an alkylphenol ether of poly-ethylene glycol.

(3) teaches uniform odor-releasing liquid deodori?ing ~5 compositions containing isoparaffin-type solvents having a boiling point of 150-300C.

131~

(4) teaches the use of certain non-ionic surfactants, having a particulac degree of ethoxylation, to control the rate of Lelease of perfumes from absorbant substeates.

(5) discloses a wick-type slow dif~usion disæenser for perfume materials which utilizes wicks in the form of sheets to provide a maximum evaporative surface.

(6) addresses the problem of linearity, as the abstract states, "through use of a distinctive wicking structure that comprises a matrix of closely packed, solid particles bonded together with a bonding material that only eartially fills interstices between the particles and thereby leaves a uniform interconnected network of pores." It offers but one solution, a solution that cequires strict adherence to very specific parameters, in particular regarding the particle size of the porous material used. These parameters must be determined for each particular liquid.

(7) Discloses, as the abstract states, "a novel package fcr dispensing odors such as naturally occurring odors, commonly for the purpose of either masking from wild animals the odor of human in the vincinity, or the purpose of attracting wild animals. In principle, the systems consists of a wick in a tube.

The most common devices are those which, as stated above, deeend on an evaporative surface and a delivery system for transferring the fragrance material to that 30 evaporative surface. Despite the fact that most of these devices suffer from the limitation that theee is distortion and a weakening of the fragrance with time, they are still very widely used inasmuch as they are simple and do provide a fragrance over a long period of time, an advantage they 35 have over aerosol-type systems. ~erosol-type systems, while they do maintain fragrance integrity over their useful life, are useful only while they are being sprayed and, unless ~ 3 ~

constan~ly sprayed, they lose their effectiveness in a few minutes. Each spray of the aerosol does, however, emit the same composition so that continued use does not result in distortion or decreased odor intensity. It simply is not practical, ho~ever, to use an aerosol, as a continous dispenser of fragrances.

Mechanical devices have been developed to overcome the limitations mentioned above including the problems of non-linear delivery and distortion of the air freshening material. These systems are devices which introduce a premeasured amount of the fragrance material into the ambient air at regularly timed intervals. Such devices are either electrically or battery operated. The material may be dispensed as an aerosol by a mechanical system or the device may e~ploy fans to dispense a premeasured amount of liquid. These devices are usually com2lex and designed for commercial rather than home use.

None of the pcior art devices fully satisfies ~he need for an air freshening system which is simple in design and yet can deliver an air freshening material to the ambient air over a long period of time without change in the rate of delivery, or in the odor character of the fragrance, during the life of the device.

As pointed out above, at the heart of the ~resent invention is the discovery that t~e external capillary structure when used to deliver a fragrance in an air 30 freshening device releases that fragrance uniformly and linearly into the air, i.e., wi~hout distortion of the odor character and without a change in the rate of delivery.
Nothing in the art cited would indicate that such a transfer would be linear and would be made without distortion.
The present invention is, as pointed out above, a novel air freshening device which allows a liquid fragrance 1~16~54 material to be diseensed ineo the ambient air of a room or other designated area in a linear fashion by means of an external capillary member. More particularly the invention comprises a reservoir, a fcagrance material and an external capillary member, wherein said external caeillary member has one or more external capillary cavities, the lower portion of said capillary being in contact with the liquid fragrance material to be dispensed and the upper portion of said capillary being exposed to the air in the coom or area into which it is desired to dispense the fragrance. Surprisingly and unexpectedly, ~his device releases the fragrance uniformly and linearly into the air, i.e., without distortion of the odor character, without a change in the rate of delivery, and without suffering from many of the limitations of the prior art devices which have been discussed above. Another advantage of this device is the fact that its life span depends only on the amount of fragrance material in the container and, provided that the container is large enough, ~he device can operate for 30 days or more without the fragrance weakening and without noticeable distortion of the fragrance.

BRIEF DESCRIPTION OF THE DR~WINGS

Figure l shows a simple reservoir l with the external capillary members 3a and 3b protruding from the top.

Figure 2 is a cross-sectional view of Figure l taken along line 2, and shows the external capillary members 3a 30 and 3b having one end in contact wi~h the liquid fragrance material 2 and the other end exposed to the ambient air.

Figures 3a and 3b show examples of two external capillaries, one of which, 3a, is in the form of a 35 cylindrical rod, and the other, 3b, which has a f lat or 13164~4 rectangulac box-like structure.

Figure 4a shows an end view of Figure 3a and Figure 4b shows an end view of Figure 3b.
s Figure 5 shows a cross-sectional view of an extruded plastic external capillary cod of the type used in the examples.

Figure 6 is an exploded perspective view of the device that was used in the examples.

Figures 7 and 8 are embodiments of aic freshening devices utilizing the preferred, rod-like, external 15 Capillaries 3, Figure 9 shows the GLC peofile of the ~emon Citeus peefume of Example 3A (SupelcoWax-lO 0.25 mm i.d. x 30 m fused silica capillary column, 50 to 230C @ 4/min.) 20 Components selected for monitoring are numbered l to ]1.

Figure lO shows the GLC profile of the Orange Citrus perfume of Example 3B (SupelcoWax--lO 0.25 mm i.d. x 30 m fused silica capillaLy column, 50 to 230C ~ 4/min.
25 Components selected for monitoring are numbered l to 8.

Gcaph l shows the change in the weight loss of several common fragcance materials ovee ti~e when 2 mm external capillary rods, having 1.0 inch exposed to the ambient air, 30 are used as the external capillaries as described in ~xample LA.

Graeh 2 shows the change in the weight loss of limonene and Dimetol over time using respectively l mm and 3.25 35 mm external capillary rods, each having l.O inch exposed to the ambien~ air, as desceibed in Example lB.

131~5~

, ~ raph ~ shows the change in ~he weight loss of limonene over time when 2 mm external capillary rods, having either 0.5 inch or l.0 inch exposed to the ambient air, are used as described in ~xample lC.

Graph 4 shows the change in the weight loss of a l:l molar solution of limonene and Dimetol ovec time, and the change in the weight ]oss of a l:l:l molar solution of limonene, Dimetol and linalool over time when Z mm external capillary rods, having ~.0 inch exposed to the atmosphere, are used as described in Examples 2A and 2B
respectively.

Graph S shows the change in ~he weight loss of the Lemon Citrus perfume of Figure 8 over time and the change in the weight loss of the Orange Citrus perfume of Figure 9 over time when 2 mm external capillary rods, with l.0 inch exposed to the atmosphere, are used as described in ~xamples 3A and 3B, respectively.
Referring now to the dcawings, wherein like re~erence characters refer to like parts of the Figures, the invention can be described in i~s simplest form as comprising an external caeillary member 3, one portion of which is in contact with a liquid fragrance material 2 held in a reservoir l of some type and another portion of which is in contact with the air of the space into which it is desired to dispense the ~ragrance. In the practice o the invention, the liquid 2 rises ~rom the reservoir l, up the external ca~illary member 3 until it has ~eached the portion exposed to the air, and is evaporated from this portion into the air to be fragranced. The external capillary member is suitably any device having an external capillary cavity 4.

An external capillary is simply a capillary which is not completely enclosed along the sides. The capillary could simply be two plates which are close enough to allow the 1316~4 liyuid to rise between ~hem but which are not attached at the ends. Alternatively, an external capillary could be any device of any shape or configuration having a surface with one or more gcoove-like cavities having dimensions, as set forth below, which allow the liquid to rise in the cavity by capillary action from the surface of the liquid 2 to that portion of the capillary which is exposed to the air.

The pureose of the reservoir is simply to provide a container to hold the fcagrance material used in the air freshening device. The design of the reservoir is not critical, but should be such that the liquid in the reservoir will be able to come in contact with the external capillary member and will be allowed to rise in the external capillary member so as to be exposed to the air to be freshened, i.e., the design should be such that the distance from the level of the liquid to the part of the external capillary that is exposed to the air does not exceed the height that the liquid is capable of rising in the capillary. Said designs are well within the scope of the art of a designer once said designer knows the criteria, as set forth below, that the design must meet.

The fragrance material can be any fragrance material suitable for imparting the desired odor. The material may be used in concentrated form oc may be diluted with a suitable solvent. It is pcefecred to use the material in a somewhat concentrated form, i.e., with little or no solvent, since the solvent imparts no odor and would serve no useful purpose other than to provide fluidity.

l'he external capillary membeL is prefe~ably any device having a plurality of external capi]lary cavities on its surface. The shaee or configucation of the external capillary membec is not critical. External caeillary cavities can be cut into any solid, three--dimen6ional figure, such as a prism, sheet, block or decorative figure which is to serve as an external capillary member. Figuces 3 and 4 provide simple illustrations of possible external capillary !nembers, whecein "V" shaped external capillary cavities are shown cut into cylindrical and rectangular cods.

Figures 3 and 4 are for illustration only, and there is no re~uireme~t that the capillary cavities be "V" shaped, or that the external capillary member be in a rod-like shape.
The external capillary member can be of an~ shape, including that of an artistic ~igure. Any external capillary member will be operational so long as any external capillary cavities cut in its surface have the necessary dimensions, said necessary dimensions being discussed below.

While the "V"-shaped external capillary cavity is preferred for reasons which are given below, an external capillary cavity of any shape which fulfills the criteria set forth below, would be suitable. The practice of this invention is not dependent on either the shape of the capillary cavity or how it is made, but rather on ~he dimensions of the capillary cavity, as set ~oeth below.

Figure 5 ~rovides an accurate cross-sectional view of an ~5 external capillary member that has been manufactured by extruding an extrudable plastic through a die. The dianeter or cross-sectional dimension of the external capillary is controlled by the physical res~raints of the die and the speed of extrusion. The selection of such parameters are 30 well within the ski]l of those knowledgeable in the art of plastic extrusions. Extruded plastic external capillary rods are commercially available from Capillaty Technology, Inc., Portsmouth, Rhode Island and are suitable for use in the present invention. Because these extruded external capillary rods are commercially available, and because the extrusion process is the most economical method for making such external capillary cavities, such extrudable ex~ernal ~3~64~4 capillary rods are especially preferced in preparing ~he devices o~ this invention and reference to them are made herein to i]lustra~e the preferred e~bodiment6 of this invention.

The ~od i]lustrated in Figure 5 is comprised of ~hree central longitudinal tubes surrounded by twelve protrusions. Six of the radiating protrusions are further comprised of two additional protrusions each. The protrusions form a "~" whereby the apex of the "~" is connected to the central core. The open side o~ the "V" is on the outside surface and cuns along the length of the rod. The "V" forms a cavity to conduct fluid via capillary action from a reservoir up the capillary rod. The oeen end of the "V" provides an evaporative surface which allows the liquid to evaporate into ambient air and act as an air freshener.

~lthough the cross-sectional view in Figure 5 shcws a plurality of external capillary cavities, only one is essential to deliver a fragrance material from the reservoir to the atmosphere to be fragranced. It is preferred however, to have as many external capillary cavities per rod as possible so as to more eficiently transfer the f~agrance 25 matecial from the reservoir to the atmosphere to be fragranced.

~ s mentioned above, capillary members are not limited to the vertical rod-like structuces set forth in Figure l, 2, 3 30 and 4 but may be any shape. Figures 7 and 8 illustrate the use of extruded capillary members in a more decorative setting. Figure 7 shows both the vertical members and members which have been bent to form an arch, both ends extending into the liquid. Figure 8 shows a single flexible external capillary member which has been coiled much as a eope would be coiled. The device could be designed where both ends of the external capillary membee were elaced in ~316~

the liquid and the capillary cavities would be filled from both ends. The surface of the coiled capillary device would be exposed to the ambient air, as illustrated in the drawing.

While Figures ~ and 8 provide illustrations using the especially preferred extruded external capillary members, other sha~es and embodiments are possible as mentioned earlier. Any solid having the requisite external capillary cavity grooves, whether vectical, twisting in a spiral or thread-like manner, or existing as part of a decorative design etched on ~he surface of the capillary member, would be suitable as an external capillary member provided the external capillary cavity met the criteria set forth below.

~s mentioned above, the critical factor in this invention is the configuration of the capillary cavity. The configuration of the caDillary cavity must be such that the fragrance material will travel high enough from the surface of the liquid in the reservoir to a point at which it is exeosed to the ambient air. The capillary cavity should be designed so that the liquid will rise to the desired height.

Well-established theo-y of capillary attraction teaches that the height (h) that a liquid will cise in a capillary 25 will depend on a number of factors and can be calculated according to the following equation:

h = p~(cos a)/bdg 30 wherein:
h = height that the liquid will cise in the capillacy [cm]
p = perime~er of the cross section of the capillary cavity [cm]
~ = surface-tension coefficient of the liquid [dynes/cm], [g/sec2]
a = contact angle of the film with the capillary wall 1 3~ 6~

b = the cross-sectional area of the cavity at the base [ cm ]
d - density of the ]iquid rg/cm ]
g = gravity [cm/sec ]

The above formula assumes that the capillacy cavity is regular, i.e., the ccoss-sectional area (b) does not change as h changes. This equation can be used to detecmine whether the value of h for any particular capillary will be sufficient to carry the liquid from the reservoir to the atmosphere to be fragranced.

The only terms in the above equation that refec to the dimensions of the capillary per se are p and b (the perimeter and base area, respectively). The relationship between the height and these two dimensions of the capillary cavity can be seen more clearly by simplifying the above equation to h = k(p/b) wherein k = a(cos a)/dg = ~a/d) ([cos a]/g) For any particular liquid under standard conditions, k can be considered a constant since: a) the surface tension (a) and the density (d) depend on the liquid: b) the gravity (g) is a constant and c) cos a can be assumed to equal 1, in most instances.
For any particular liquid, therefore, h will be directly proportional to p and inversely proportional to b, i.e., h will increase with an increase in p and/or a decrease in b.

While the ratio [cos a]/g can be assumed to be constant for all ]iquids, the term a/d will vary from liquid to liquid. The results set forth in Table 5 of ~ 31 ~

- ~3 -Example 4 show, however, that the ratio ~/d for most fragrance materials falls within the range of 35 + 5 dyne-cm /gram. In order to develop a general exeres-sion, a/d has been assumed to be 35 dyne-cm /yram for all ~ragrance materials, and the term k has been treated as a constant equal to 0.036 cm . (For purposes of this illustcation, the term p, as applied to an external capillary, will be understood to mean the length of the interface, i.e. contact length, between the upper surface of the liquid and the wall of the external capillary cavity.) The value of h needed will depend, for the most part, on the design of the ceservoir desired. ~s indicated above, the size, dimension~ or shape of the reservoir l is not critical other than to insure that the distance between the liquid surface and any part of the external capillary cavity exposed to the ambient air should not exceed the value of h as defined above. For example, consider a capillary which is divided as indicated in Figure 2 wherein hb is the base f the caeillary cavity, h is the height of the capillary cavity which meets the sueface of the liquid, ha is the lowest height on the capillary cavity where the capillary cavity is in contact with the ambient air, and ht is the top of the caeillary cavity. Using these points, let ht -25 ha represent the portion of the capillary which is incontact with the ambient air, let ho - hb represent the portion of the capillary cavity in contact with the liquid in the reservoir, let ha ~ ho represent the portion o~
the capillary which is not e~posed to the liquid in the capillary nor to the ambient air, and let ht - hb represent the total length of the capillary. Using these terms, with h being the height that the liquid will rise in the capillary cavity, the ~eservoir should be designed such that h > ha - ho~ in order to allow the liquid to come into contact with the ambient air. It is pre~erred that the reservoir be designed such that h > ht - hb since as the reservoir empties, a constant amount of material will be ~ 3~4~

exposed to the ambient air ovec the life of the device providing a uniform and constant level of fragrance being emitted.

For any particular resecvoir, therefoce, the dimensions of the caeillary cavity must be such that the portion ha -h is less than k(etb). It is preferred that the portion ha ~~ hb be less than k(p/b) so that the fragrance will continue to be emitted into the air until the liquid level 10 has reached the bottom of the capillary. It is eseecially preferred that the len~th ht - hb be less than k(p/b), and that hb be at the bottom of the reservoir so that over the useful lifetime o~ the air freshening device a constant amount of fragrance will be emitted into the air and will 15 continue to be emitted until the reservoir is empty.

As indicated above, the ratio of e/b desired for any earticular device will depend on the design and size of the reservoir used and the amount of external capillary cavity 20 to be exposed to the air. Assuming that k = 0.036 cm , some examples of suitable p/b ratios are as follows. For example, a p/b ratio of 109 ~ranslates into an h of about 3.5 cm. ~ p/b ratio of 200 corresponds to an h greater than 7 cm, while a p/b catio of 280 corces~onds to an h of ~0 cm.
~The capillaries used in the examples were about ~5 cm. This would require a e/b ratio of about 400 in order for h to be greater than ht - hb') While there is no practical upper limit on h or p/b, a 30 ratio of p/b - 1,000 correseonds to an h > 35 cm and theee is no apparent value in designing a device which requires a p/b exceeding l,000. For most applications, a p/b of about 550, which corresponds to an h of about 20 cm is more than sufficient. Based on the above, it is preferred to design a 35 device wherein the p/b ratio is between 200 and l,000, with a device requiring a p/b ratio of between 250 to 550 being especially ereferred.

~316~5~

~ s indicated above, a single external capillary cavity is theoretically all that is required to deliver fragrance into the ambient aie. ~s a practical matter, however, a plurality of caeillary cavities will probably be needed to provide the desired level of fragrance to be dispersed into che room. The number of capillaey ca~ities required would depend on a number of factors such as the size of the evaporative surface and the strength of the fragrance.

While the shape of the capillaey cavity is not critical, those shapes which increase the ratio of p/b and provide a maximum evaeocative surface are preferred. Example 5 illustrates how the shape of a capillary affects the value of h. For example, a square capillary will support a higher column of fragrance material than a cylindrical cavity of the same cr9ss- sectional area, but not as high a column as a cavity in the shape of a triangle. Especially preferred is a "V" shaped external capillary cavity having the shape approaching an isosceles triangle with the base missing.
(The si~es need not be straight but may be irregular as shown in Figure 5. ~ny irregularity which increases the ratio of p~b and does not decrease the amount of fragrance exposed to the air would be advantageous.) ~n isosceles triangle with the base missing, and having a small angle at 25 the apex provides the configuration that offers the maximum advantage as to capillary capacity while also offering the maximum eva~orative surface for the li~llid.

The rate at which the fragrance is dispersed is directly 30 proportional to the amount of external capillary surface exposed to the ambient air, i.e., the size and number of capillaries used and the length of each that contains said fragrance matecial and, is in contact with the ambient air.
It is therefore well within the ability of the person of 3~ ordinary s~ill, knowing the a~erage rate of dispersion per unit length of the external capillary for any particular fragrance, to be able to design a device so that the pcoper 13164~
- ~6 -amount of material ;s dispensed per unit time. It is also well within the ski]l of the ordinary artisan to control the amount of air to which the external capillary is exposed by means of cap devices which can be opened via ~wisting or lifting means to expose only so much of the delivery system to the air, or to allow only so much air to eass by the delivery system. It should also be understood that the delivery system of the device can be augmented by fans in order to better distribute the fragrance.

At the heart of this invention is the surerising and unexpected ability of the external capillary to deliver the fragrance into the ambient air at a steady rate and without distortion. This significant absence of fractionation is 15 attributable to the ability of the external capillary member to ]inearly transfer volatile materials. There is no obvious explanation as to why this happens when in most all other systems fractionation and a slowing down of the delivery occurs. The constant composition assures that the 20 fragrance being delivered is unchanged throughout the entire period of delivery and is theeefore not distorted.

~ ll conventional fragrance materials, i.e., volatile odorous substances including essential oils, aromatic 25 chemicals and the like, are applicable for use in the instant system. ~ wide vaciety of such materials are known to those skilled in the art of perfumery. They may comprise one or more natural materials or synthetic aromatic chemicals or a mixture of both.
The following examples are erovided herein to illustrate the preferred embodiments of this invention, and to illustrate the unique ability of the cla;med device to dispense a fragrance into the ambien~ air without distortion 35 and without the evaporation of the fragrance slowing do~n over time.

~3~6~4 - ~7 -In examples ~ through 3, the loss of the volatile substance from an enclosed container was monitored over a period of time. The container used was a one ounce clear glass bottle affixed with a cap containing a glass tube, as shown in Figure 6. (The pl~rpose of the glass tube is to focm a holding device for the exte~nal capillary rods.) The external capillary rods used in these examples weee extruded plastic external capillary rods having a cross-sectional view similar to that shown in Figuce 5. The rods used had cross-sectional diameters of l mm, 2 mm or 3.25 mm.

The rate of transfer of the volatile liquid ~rom the containee into the ambient air was measured by monitoring the weight--loss of the liquid in the container over a given period of time. Yor example, limonene, a volatile terpenoid used in the fragrance industry, is transferred linearly into the ambient air over a period of four weeks from the enclosed container shown in Figure 6. (See Examele l and Graphs l, 2 and 3.) The rate of transfer of limonene remains linear even when the rate is changed by varying the area of the external capillary rods exposed to the ambient air, i.e., exposing one inch of the rods results in a linear tcansfer of the material which is approximately twice as fast as when only one half oL an inch of the rods are exposed. (See Example LC.) TAe lack of fractionation and distortion experienced with ot~ler liquid delivery systems when multi-component fragrance mixtures are used is also illustrated. For 30 e~am~le, by monitoring the composition of the liquid system by gas-liquid chromatography (GLC), it was confiemed that the composition of simple binary, te{nary and complex fragrance materials did not change over a four-week test period. (See Examples 2 and 3). This is in contrast to 3~ conventional wick systems which exhibit fast release of the low boiling components followed by the slow release of the medium and high boiling components.

13:~6~

Examples 4 and 5 are p~ovided herein to i]lustrate how varying certain parameters in the design of the capillary cavity of the external capillary member affect the height to which the fragrance material will rise in the capillary.
~xample 5 illustrates that the preferred shape of a capillary cavity is the V-shape of an isosceles trian~le.
The examele further illustrates that an isoceles triangle with the base missing and having a small angle at the apex offers the maximum advantage as to capillary capacity. The data provided in the example can assist in determining a suitable length for the external capillacy member of the air freshening device.

~ xamele 4 provides the data which shows that the surface tension and density of common fragrance materials fall within a relatively narrow range. These properties of a fragrance material are two factors in determining the height to w~ich that material will rise in a particular capillary cavity. The fact that they fall within a narrow range 20 allows one to assume a standard value for these eroperties in determining the height to which any volatile fragrance material will rise ;n a ~articular capillary cavity design.

The following examples will further illustrate the 25 preferred embodiments of this invention.

EXAMPL~ 1 This example illustrates that external capillaries 30 transfer a fragrance material linearly to the ambient air over a given period of time regardless of the size of the exteLnal capillary rod, the length of rod exposed to the ambient air, or the iragrance material being transferred.
The example also illustrates that the rate at which the transfer occurs is dependent upon the area of external capillary exposed to the ambient air.

13~64~4 1~: This example (see ~Jraph 1) shows that the eate of transfer to ambient air of commonly used fragrance materials is linear. In this example, 15 grams each of limonene, Dimetol~ (Givaudan, 2,6 dimethylheptan-2-ol), linalool, ben~yl acetate, phenyl ethyl alcohol, linalyl acetate, menthone and leaf acetate were respectively weighed into bottles containing fourteen 2mm x 6 inch (1 inch = 2.54 cm) external capillary rods with one inch exposed to the ambient atmosphere. The weight lost by each was monitored over a four-week (28 day) period and the results plotted on Graph 1. The rate of transfer for each fragcance material was essentially linear.

lB: This example (see Graph 2) ilLustrates that the rate of transfer of a fragrance material is linear regardless of the size of the capillary rod. In this example, limonene (15 grams) was weighed into a bottle containing thirty lmm x 6 inch external capillary rods, and Dimetol (15 grams) was weighed into a bottle containing four 3.25mm x 4.25 inch e~ternal capillary rods. In both cases, one inch of the external capillary rod was exposed to the atmosphere. Both bottles were monitoeed over a four-week (2~ day) period as described in Example l~A. The results aee plotted on Geaph 2 which shows that both the lmm 25 and 3.25mm external capillary cods transfer common fragrance materials in a linear fashion.

lC: This example (see Graph 3) illustrates how the rate of teansfee can be conteolled by varying the length of the 30 exteenal capillary exposed.

Limonene (15 gcams) was weighed into each of two bottles. Bottle numbee 1 contained foueteen 2mm x 5.5 inch external capillary rods with 0.5 inch exposed to the 35 atmosphere. Bottle number 2 contained fourteen 2mm x 6.0 inch external capillary rods with 1.0 inch exposed to the atmosphere. The weight of limonene lost from each bottle ~31~

- ZO

was monitored ovee a four week (Z8 day) peeiod.

The results are plotted on Geaph 3 which shows that the tcansfer of limonene was linear over the four week test period regardless of length of capillary exposed to the ambient air. The example also shows that ~he rate of transfer can be controlled by the amount of surface area exposed to the ambient aie, inasmuch as evaporation from the bottle having l inch of capillary exposed occurred at a faster rate than from the bottle having 0.5 inch exposed.

This example illustrates that the rate of trans~er of simple binary and ternary compositions over a given period of time is linear and that the comeositions of the liquid remaining in the container is unchanged with time.

ZA: BinarY Composition A l:l moLac solution ~15 grams) of limonene and Dimetol~ was elaced into bottles containing fourteen 2 mm external capillary rods with one inch exposed to the ambient atmospheee. Weight loss was monitored and the composition 25 analyzed by ~as-liquid chromatography (GLC) over a 28 day period. The GLC analysis showed that the mixture remained at a constant 53/47 ratio of limonene to Dimetol dueing the test eeriod.

The result of the weight-loss monitoring for the l:l mixture is elotted on Graph 4. Graph 4 shows that the transfer o~ a l:l molar solution, via evaporation, using external capillary rods is linear. The composition of the liquid in the container did not change with time and was identical to the initial composition. This simele binacy solution shows that external capillary rods linearly transfec mixtures o~ volatile materials without distortion.

131~

B: Ternacy Com~osition A 1:1:1 molar solution ~15 grams) of limonene, Dimetol , and linalool was placed into bottles containing fourteen Z mm external capillary rods with one inch exposed to the ambient atmosehere. Weight-loss was monitored and the composition analyzed by gas-liquid chromatography (GLC) over a 28 day eeriod. The GLC analysis showed that the mixture remained at a constant 34/30/34 ratio of limonene to Dimetol to linalool during the test period.

The result of the weight-loss monitoring for the 1:1:1 mixture is also plotted on Graph 4. Graph 4 shows that the transfer of a l:L:l molar solution, via evaporation, using external capillary rods is linear. The composition of the liquid in the container did not change with time and was identical to the i.nitial composition. This simple three comeonent solution shows that external capillary rods linearly transfer volatile materials without distortion.

F.X~MPI.E 3 This example i.llustrates that complex, multi-component fragrance materials of the type commonly used in air freshening devices, perfocm in the same way as the simple binary and ternary compositions. ~ "Lemon Citrus" perfume was formulated to contain a greater proportion of less volatile components (see Figure 9 and Table 2) while in contrast an "Orange Citrus~ perfume was formulated to contain few, less volatiLe components (see Figure 10 and Table 4~. ~Peak 1 i.n both perfumes is limonene.) The rate of transfer is shown to be essentially linear and the composition remains essentially undistorted throughout the test period.

13~6454 3A: Lemon Citrus Perfume The Lemon Citrus perfume (15 qrams) was placed into a bottle containing fourteen 2 mm x 6 inch external capillary rods~ One inch of ~he external capillary rods was exposed to the atmosphere.The weight loss was monito~ed over a four-week (28 day) period. The results are given in Table 1 and plotted on Geaph 5.

Table 1 Days Grams LostPercent Loss 1 0.194 1.29 2 0.296 1.97 3 0.388 Z.59 6 0.672 4.48 7 0.755 5.03 14 1.219 8.12 21 L.684 11.22 28 2.179 14.52 The composition of the Lemon Citrus eerfume was monitored by gas-liquid chromatogca~hy ~GLC). The chromato--gram of fresh Lemon Citrus is shown in Figure 9. Components of the perfume oil selected for monitoring over the four--week test period are labelled as peaks 1 to 11 (see Figure 9~. The results of the monitoring are given in Tahle 2.

~316~
-~ 23 Table 2 Component composition study of Lemon Citrus pecfume Time Pe~k Number (Percent) (Days) 1 2 3 4 5 6 7 ~ 9 10 11 Fresh19.3 4.1 5.6 4.9 4.2 5.7 4.2 5.4 5.9 8.1 12.2 18.9 4.0 5.5 ~.9 4.2 5.8 4.2 S.5 6.0 8.1 12.1 2 19.4 4.0 5.5 4.9 4.2 5.~ 4.2 5.4 5.9 8.0 12.1 10 3 18.4 3.8 5.2 5.0 4.4 5.8 4.1 5.5 6.4 8.5 12.9 6 19.1 4.0 5.5 4.9 4.2 5.8 4.2 5.5 6.0 8.3 12.5 7 19.3 4.1 5.6 4.9 4.1 5.8 4.2 5.4 6.0 8.1 12.3 14 18.9 3.9 5.3 4.7 4.1 5.7 4.2 5.5 6.2 8.5 12.6 21 18.7 3.8 5.2 4.7 4.2 5.7 4.1 5.4 6.3 8.5 12.7 15 28 18.6 3.9 5.1 4.7 4.2 5.7 4.1 5.5 6.4 8.7 13.3 Graæh 5 shows that the transfer of Lemon Citrus perfume by external capillary rods into the ambient atmosphere is linear.

Table 2 shows that the composition of the liquid perfume in the container remains consistent and is essentially similar to the initial comeosit~ion.

25 3B: Oran~e Citrus Perfume An Orange Citrus perfume (15 grams) was placed into a bottle containing fourteen 2 mm external capillary rods.
One inch of the external capillary rods was exposed to the 30 atmosphere. The weight loss was monitored over a four-week (28 day) period. The results are given in Table 3 and plotted on Graph 5.

1316~5~

Table 3 Days Gcams Lost Percent Loss 1 0.494 3.29 2 0.856 5.70 3 1.179 7.84 6 ~.288 15.22 7 2.644 17.59 1~ 4O117 27.39 21 5.455 36.29 28 6.644 44.20 The composition of Orange Citrus perfume was monitored by gas-liquid chromatography (GLC). The chromatogeam of fresh Orange Citrus is shown in Figure 10. Components of the peefume oil selected foe monitoring over the four-week test period labelled as peaks 1 to 8 (see Figure 10~. The results of the monitoring are given in Table 4.

Table 4 Component composition study of Orange Citrus perfume Time Peak Number (Percent) 25(DaVs) 1 2 3 4 5 6 7 8 Fresh 77.9 0.6 0.7 6.5 0.8 0.4 0.2 1.1 1 81.5 0.7 0.7 6.7 0.8 0.4 0.2 1.3 2 80.7 0.7 0.8 6.8 0.B 0.4 0.2 1.2 3 80.2 Q.7 0.8 7.1 0.9 0.5 0.2 1.2 6 78.5 0.7 0.9 7.8 1.0 0.5 0.2 L.4 7 78.9 0.7 0.8 7.6 0.9 0.5 0.3 1.4 14 77.8 0.7 0.8 8.2 1.0 Q.5 0.3 l.S
21 74.5 0.7 0.8 9.1 1.1 0.5 0.3 1.6 28 72.8 0.8 0.9 10.3 1.3 0.6 0.3 2.0 Graph 5 shows that the transfer of Orange Citrus perfume by external capillary rods into the ambient atmosphere is ~6~5~

essentially linear. Table 4 shows that the composition of the liquid per~lme in the containeL remains consistent and is essentially similar to the initial composition.

The densities (d) and surface tensions (a) of a number of materials commonly used to make fcagrance compositions, were measured and are recorded in Table 5. The density determinations were made using a Met~ler~Parr ~ensity Meter, Model DMA 45. The surface-tension measurements were made using Cenco-Du Nouy Model 70530 Tensiometer. The surface tension measurements repocted in Table 5 are the average of three measurements. Also given in Table 5 is the ratio of the surface tension to the density, i.e., a/d.

The list in Table 5 is not intended to be a definitive list of density and surface tension values, but rather to serve as a basis for showing that the values for the surface tension and density of those materials commonly used in fragrances fall within the relatively narrow range of a/d = 35 + 5 dyne-cm /gram. The data in Table 5 provides justiEication for assuming that most fragrance materials will have a o/d ratio of about 35 dyne-cm2/gram and that such a number can be used as a standard value for a/d in deteemining the height that a fragrance material will rise in a particular capillary.
(See Exam~le 5 where this assumption is applied.) Also included in l'able 5 are the Lemon Citrus perfume and the Orange Citeus perfume of Example 3 which both have a a/d between 34 and 35 dyne-cm /gram.

~3164~

Table 5 Chemical Name d ~ atd (gm/cm3) (dynes/cm) (dyne-cm2/gm) AMYL ACETATE 0.8760 25.7 29.338 ETHANOL 0.79Q0 23.2 29.367 ALLYL CAPROAI'E 0.8860 27.5 31,038 ISOBORNYL ACETATE 0.9900 30.9 31.212 TETRAHY~ROLINALOOL 0.8300 26.0 31.325 OCTAN-3-OL 0.8200 25.8 31.463 MENTHANYL ACETATE 0.9350 30.1 32.193 LINALYL ACETATE 0.9100 29.4 32.308 10 DIMETOL 0.8130 26.4 32.472 CEDRYL ACETATE 1.0500 34.6 32.952 DIMETHYLOCTENONE 0.8480 28.0 33.019 LEAF ACETATE 0.8900 29.5 33.146 TERPINYL ACETATE 0.9600 31.9 33.229 LINALOOL 0.8650 29.1 33.642 (UNDECALACTONE) 0.9420 31.9 33.864 LEAF ALCOHOL 0.8580 29.1 33.916 GERANYL ACETATE 0.9050 30.7 33.923 DIETHYL PTHALATE l.L200 38.1 34.018 MENTHONE 0.9000 30.7 34.111 AMYL SALICYLATE 1.0500 36.0 34.286 METHYL OCTINE CARBONATE 0.9140 31.4 34.354 METHYL HEPTENONE 0.8500 29.6 34.824 20 METHYL SALICYLATE 1.1820 41.2 34.856 ALCOHOL C-8(n-OCTANOL) 0.8240 28.8 34.951 ALLYL CYCLOHEXYLPROPIONATE 0.9470 33.1 34.95Z
CITRONELLAL 0.8510 29.8 35.018 CITRONELLOL 0.8580 . 30.2 35.19B
EUGENOL 1.0900 38.6 35.413 GERANIOL 0.8750 31.0 35.429 25 LIMONENE 0.8400 29.8 35.476 ALDEHYDE C-8 (n-OCTANAL) 0.8200 29.1 35.488 (ETHYL-MET~IYLPHENYL--GLYCIDATE) 1.0900 38.7 35.505 ALDEHYDE C-10 (n-DECANAL) 0.8250 29.3 35.515 CITRONELLYL ACETATE 0.8580 30.5 35.548 ALPHA TERPINEOL 0.9400 33.5 35.638 30 METHYL BENZOATE 1.0870 38.8 35.695 PHENYL ETHYL AcElrATE 1.0500 37.6 35.810 PARA CYMENE 0.8200 29.4 35.854 LILIAL [a-METHYL-B-(p-TERT.BUTYLPHENYL)-PROPIONALDEHYDE] 0.9450 34.1 36.085 ESTRAGOLE 0.9580 34.6 36.117 35 METHYL IONONE 0.9280 33.6 36.207 CYCLAMEN ALDEHYDE 0.9480 34.8 36.709 BENZYL ACETATE 1.0540 38.7 36.717 DIPHENYL OXIDE 1.0730 40.0 37.279 13~6~

DIMETHYL BENZYL CARBINOL 0.9760 ~6.4 37.295 HYDROXYCITRON~LLAL0.9Z00 34.4 37.391 ETHYLENE BRASSYLATE1.0500 39.5 37.619 BENZYL BENZOATE 1.1800 44.4 37.627 CITRAL 0.8870 33.6 37.880 BENZYL SALICYLATE 1.1800 44.7 37.881 AMYL CINNAMIC ~LD~HYDE 0.9650 36.8 38.L35 ANETHOLE 0.9900 38.0 38.384 HYDROTROPIC ~LD~HYD~1.0100 39.0 38.614 MET~IYL ~NTHRANILATE1.1650 45.4 38.970 BENZALDEHYDE 1.0430 41.6 39.885 BENZYL ALCOHOL 1.0450 41.8 40.000 PHENYL ETHYL ALCOHOL1.0300 42.0 40.777 ANISIC ~LDEHYDE 1.1210 46.1 41.124 10 CINNAMIC ~LDEHYVE 1.1100 46.2 41.622 WATER 1.0000 63.9 63.900 LEMON CITRUS PERFUME.869 30.3 34.868 ORANGE CITRUS PERFUME .856 29.3 34.229 The eurpose of this example is to show how changes in the configuration of a eapillary cavity affect the height (h) that a liquid will rise in a capillary cavity above the surfaee of that liquid in a container.

The value of h as shown previously can be determined as follows:

h = pa(cos )/bdg = (p/b)(a/d)([eos a]/g) = k(p/b) wherein:
h = height that the liquid will rise in the capillary p = perimeter of the cross section of the capillacy eavity o = surface tension coefficient of the liquid 30 a = eontaet angle of the film with the capillary wall b = the eross-seetional area of the cavity at the base d = density of the liquid g = gravity k = (a/d)([cos a]/g) In applying the above formula to calculate h, it has been assumed that cos a = 1, that the capillary cavity is 13~4~

regular, i.e., the cross-sectional area b does not change as h changes, and that the gravity, g, is 9~0.66~ cm/sec .
It is also helpful to note that the equation can be broken into three ratios - one of which is a function of the capillary, i.e., ~/b; one of which i5 a ~unction of the liquid in the capillary, i.e., o/d; and one of which is a constant, i.e., (cos a)/g.

Based on the measurements in Example 4 and the values for g and cos ~ given above, ~/d will be considered to have the value 35 dyne-cm /gram and k which equals (~d)([cos a~/g) will have the value 0.036 cm . Since the only parameters that are affected by the design of the capillaey are p and b, the equation h = 0.036 cm2 (p/b) then allows one to determine the effect that changes in the parameters defining the capillar~ cavity will have on the height. The equation can also be used to show that the height attained in a closed capillary should not be much greater than that attained in an open or external capillary if the parameters of the latter are properly chosen.

To illustrate how the equation h = 0.036 cm (p/b) can be used to calculate the height to which a ~ragrance will rise in a closed capillary and/or an open or external capillary cavity, it is assumed that each of the capillary cavities has a "V" shape wherein the sides of the IlV" are 0~05 cm each and the apex angle of the "V" is 15 degrees.
If it is assumed that a side opposite to the apex angle has been added so as to create a closed capillary in the shape 30 of an isosceles triangle, the height, h, that a fragrance would rise in such a capillary can be calculated as follows:

(a) If the equal sides of the isosceles triangle have length A, the angle between these two sides is a, and the side opposite said angle is of length B, then where A = 0.05 cm and a = l~ degrees, 1 3 ~ 4 B -~ 2A (1 - ~05 a) = 0~013 c~l p = 2A ~- B = 2~ ~ = 0.113 cm b = 1/2 A2 sin a = 0.000324 cm2 (b) For a closed capillary h = 0.036 cm (p/b) = ~0.036) (0~113) / 0.000324 = 12.5 cm (c) For an open capillacy, i.e. the length of side B is assumed to be zero and p = 2A + B _ (2)(0.05) + 0 =
0.100 cm, h = 0.036 cm (2/b) = (0.036) (0.100) / 0.000324 = 11.1 cm As just illustrated, cemoval of the side B to convert a closed capillary into an external capillary does not have a major effect on a capillary o the above stated dimensions.

Similar calculations were made to obtain the data in Tables 6, 7 and ~ to illustrate the affect that alte~ing various parameters has on the heigh~. In Table 6, the size of the apex angle is altered. (This has a dramatic affect on the height, the smaller angles producing gceater heights.) In Table 7, the length of side A is varied while the angle is held constant at 15 degrees. (Again, the length of side A appears to have a significant affect on the height, although one can envision for a V-shaped capillary that only a portion o~ the ~'V" near the apex could be used effectively to act as a capillacy and the height to which the liquid rises may be higher than the calculated value.) Table 8 illustrates how the shape of the capillary can affect the height.

~3~45~

Table 6 Heiqht a ~ngle Length T.ength ~rea Perimeter Closed Open a A B _ 2 cm CaPillarY Capillar~
1 .050.0009 0.000022 0.101 164.6 163.2 2 .050.0017 0.000044 Q.102 83.0 81.6 .050.0044 ~.000109 0.104 34.2 32 7 .050.0087 0.000217 0.109 17.8 16.4 .050.0131 0.OD0324 0.113 12.5 11.1 .050.0174 0.000428 0.117 9.8 8.3 .050.0216 0.000528 0.122 8.2 6.7 10 30 .050.0259 0.000625 0.126 7.2 5.7 .050.0383 0.000884 0.138 5.6 4.0 .0~0.0500 0.001083 0.150 4.9 3.3 .050.0707 0.001250 0.171 4.8 2.8 _ a The closed capillary assumes that side B is intact while the open capillary assumes that side B is cemoved.
Table 7 Heiqht Angle Length Length Area Perimeter Closed Open 20 ~ A B cm cm CapillarYCapillary 0.010.0026 0.000013 0.023 62.4 55.0 0.030.0078 0.000116 0.068 20.8 18.3 0.050.0131 0.000324 0.113 12.5 11.1 0.070.0183 0.000634 0.158 8.9 7 9 0.10.0261 0.001294 0.2~6 6.2 5.5 150.150.0392 0.002912 0.339 4.2 3.7 15 0.20.0522 0.005176 0.452 3.1 2.8 15 0.30.0783 0.011647 0.678 2.1 1.8 15 0.50.1305 0.032352 1.130 1.2 1.1 a The closed capillacy assumes that side B is intact while the open capillary assumes that side B is removed.

~3~4~4 Table 8 Triangle Trianglea Area ~cm2) Circle~Equilateral) S~uare ~Isosceles) 0.00~022 27.07 37.3 30.5 164.6 0.000044 19.12 26.4 ~1.6 ~3.0 0.000109 12.1 16.7 13.6 34.1 0.000217 8.6 11.8 9.7 17.8 0.000324 7.0 9.7 7.9 12.5 0.000428 6.1 8.4 6.9 9.8 0.000528 5.5 7.6 6.Z 8.2 0.000625 5.0 7.0 5.7 7.2 0.000958 4.0 5.6 4.6 4.8 ` 0.001175 3.7 5.1 4.2 4.7 -a For the isosceles triangle, the parameters were the same as in Table 6, i. e. length A was kept constant at 0.05 cm and the angle was varied.
Table 8 confirms the fact that the V-shaped external capillary is the preferred shape for an external capillary.
Tables 6 and 7 illustrate that the height will be greater the smallec the capillary dimensions, i.e., the smaller the apex angle a and the smaller the side ~.

The values shown in the tables assume perfect shapes (triangles, V-shapes, etc.) while an actual capillary as shown in Figure 5 has irregular sides. The irregular sides of 5 provides for a larger p and a smaller b than would be calculated for a perfect V-shape, hence the h expected should be greater than the one calculated in the examples.

Claims

1. A device for the evaporation of a liquid into the ambient air which comprises (a) a container which maintains a supply of said liquid in isolation from said ambient air, (b) said liquid to be evaporated, (c) a non-porous, non-absorbing external capillary member extending from the interior of said container, through the container wall, to the outside of said container and having at least one external capillary cavity, said external capillary cavity having i) a portion in contact with said liquid in the container, and ii) a portion in contact with said ambient air such that the portion in contact with said liquid in the container and the portion in contact with said ambient air are connected to one another by the same external capillary cavity and, wherein the length of the portion of said external capillary that is in between the portion that is in contact with the said liquid in the container and the portion that is in contact with said ambient air into which said liquid is to be dispensed is less than the height that said liquid will rise in said capillary cavity.

2. The liquid evaporating device of claim 1 wherein said liquid to be evaporated is a multi-component fragrance material and said liquid evaporation device is used as an air freshner.

3. The liquid evaporating device of claim 2, wherein said external capillary cavity has (a) a length ht - hb, wherein ht represents the top of the capillary cavity and is exposed to the ambient air, and hb represents the base of the capillary cavity and is exposed to the liquid in the container:

(b) a portion ho - hb which is exposed to the liquid in the container, wherein ho represents the top point of the capillary cavity that is exposed to the liquid in the container;

(c) a portion ht - ha which is exposed to the ambient air, wherein ha is the bottom point of the capillary cavity that is exposed to the ambient air.

(d) a portion ha - ho which represents any portion of the capillary cavity which is not exposed to the ambient air or to the liquid;

(e) a uniform cross-sectional area equal to b; and (f) a contact length between the upper surface of the liquid and the wall of the capillary cavity equal to p;

wherein ha - ho is less than 0.036 (p/b) cm.

4. The liquid evaporating device of claim 3 wherein said external capillary cavity has essentially 3 sides, one of which is partially open to the ambient air.

5. The liquid evaporating device of claim 4 wherein said external capillary cavity has greater than 50% of the third side open to the ambient air.

6. The liquid evaporating device of claim 5 wherein said external capillary cavity is essentially an isosceles triangle with the side opposite to the apex angle open to the ambient air.

7. The liquid evaporating device of claim 6 wherein the angle between the two unopened sides is less than 30 degrees.

8. The liquid evaporating device of claim 7 wherein said angle between the two unopened sides is less than 15 degrees.

9. The liquid evaporating device of claims 7 or 8, wherein ha - hb is less than 0.036 (p/b) cm.

10. The liquid evaporating device of claims 7 or 8, wherein ht - hb is less than 0.036 (p/b) cm.

11. The liquid evaporating device of claim 10, wherein p/b exceeds 200 cm-1.

12. The liquid evaporating device of claim 10, wherein p/b is between 250 and 550 cm-1.