WO1987004450A1

WO1987004450A1 - Ice-combative measures

Info

Publication number: WO1987004450A1
Application number: PCT/GB1987/000018
Authority: WO
Inventors: John Harold Sewell
Original assignee: The Secretary Of State For Defence In Her Britanni
Priority date: 1986-01-17
Filing date: 1987-01-15
Publication date: 1987-07-30
Also published as: GB8721453D0; DK483387D0; FI874067A0; NO873902D0; NO873902L; FI874067A; EP0252968A1; DK483387A; JPS63502355A; GB2193970A; GB8601161D0

Abstract

A liquid including a freezing point depressant base material such as glycerol is foamed to produce a stable foam and applied as such to a surface to convey anti-icing protection or to de-ice. The foam resists run-off from inclined surfaces and resists dilution by incident moisture. A foam promoting surfactant is beneficial as is also a foam stabilizer such as methyl cellulose. The foam may be generated and dispensed from a conventional compressed air equipment or an aerosol canister according to application. The invention is especially directed to aircraft and automobile applications.

Description

ICE-COMBATIVE MEASURES This invention relates to what are called herein ice-combative measures, that is measures for combating icing on the surfaces of aircraft, cars, or other vehicles machinery and structures. This term is intended to embrace measures for combating all forms of frozen water (ice snow frost etc) whether by removal of a deposit (de-icing) or by resisting deposition (anti-icing).

It is well known that ice can be combated by application to a dry or an iced surface of a liquid or solid which is soluble in water and has the property of depressing the freezing point of water when dissolved therein. Both anti-icing and de-icing measures using a liquid freezing point depressant are common place in current commercial air line practice. The liquid having the depressant effect on the freezing point of water is called herein an anti-icing liquid whether it is intended for use in an anti-icing application or in a de-icing application. Such a liquid comprises an active base ingredient but may also include a diluent, such as water, and other ingredients. Current commercial airline anti-icing liquids have propylene glycol as base ingredient in combination with water as diluent, in various proportions. However it is well known that other liquids such as glycerol could be used for the base ingredient. The active base for an anti-icing liquid could be a salt such as potassium carbonate, the liquid comprising this salt in a solution or dispersion but such base materials are not generally attractive because they tend to be corrosive. It will be apparent to those skilled in the art, that the effectiveness of an ice combative measure will be dependent upon the quantity of anti-icing liquid applied and the proportion of base ingredient in that liquid. It is known however that the effectiveness is also dependent upon the degree to which the liquid runs off the treated surfaces especially inclined surfaces. It is important for aircraft operational flexibility and for economic reasons that the duration for which an anti-icing operation remains effective be maximised and preferably increased beyond that achievable in the current state of the art. The term "holdover time" is applied to the estimated time for which an anti-icing treatment will prevent frost ice or snow from forming or accumulating upon protected surfaces of an aircraft under average weather conditions within specified limits. It is known that holdover time can be improved by adding to the anti-icing liquid an ingredient which conveys thixotropic properties. However it is desirable to increase holdover times yet further. It is important also that the anti-icing liquid, whilst staying in place for as long as possible on a stationary aircraft, is removed fully from all vulnerable surfaces by aircraft movement on the ground at speeds below rotation speed. This point has assumed increased importance with adoption of new wing forms which are less tolerant of fluid residues. It is well known also that de-icing procedures may be used for automotive windscreen applications. Preparations for this usage conventionally use an alcohol such as methanol as the freezing point depressant. Such preparations can be applied from a hand pump container or from an aerosol. It is known from DE 3344564 that road surfaces and machinery may be de-iced by the application of a foamed carbamide. In this document the foam used Is short lived and is employed as an agent to Improve application of the de-icing material. By this means it is hoped to promote an effective coverage of de-icing treatment with a minimal quantity of material in order to minimise any harmful environmental effects.

The present invention is an ice-combative treatment comprising forming a stable foam of an anti-icing liquid (as hereinbefore defined) and applying that stable foam to a surface to de-ice that surface or convey anti-icing protection to that surface.

The terms 'foam' and 'foamed' are used herein in conventional sense to denote a gas/liquid admixture in which the gas is entrailed within the liquid in bubbles. The term 'stable foam' is used to qualify the resistance of the foam to self decay. The foam must have sufficient such resistance to remain in the foamed condition for a significant period. By foaming the anti-icing liquid its susceptability to run-off is reduced without reliance upon a thickening agent - although for some applications of the invention a thickening agent might still be used. It is anticipated that the treatment of the invention would lead in aircraft usage to an increase in hold-over times without causing any increase in the difficulty of removing the anti-icing liquid residues by aircraft ground movements. It has been found moreover, that the use of the anti-icing treatment of the invention has other beneficial and unforeseen benefits, especially when used as an anti-icing treatment for automobile windscreens etc. Firstly the anti-icing liquid has sufficient resistance to run-off evaporation and dilution when suitably foamed that it may be used to give overnight anti-icing protection not possible with conventional products. Secondly, even if conditions are such that the foamed anti-icing liquid is frosted after application, it is found that the ice forms from the outer surface inwards and penetrates the foamed liquid only slowly so there usually remains an unfrozen liquid layer adjacent the protected surface which enables the ice to be detatched readily from the protected surface.

In order to derive the benefit conferred by the invention, the foam should have sufficient temporal stability to confer resistance to self decay for the duration of a reasonable anti-icing treatment. Thus a foam stability of 8 hours or more is preferred although a lesser foam stability could have utility in some applications such as de-icing applications. It has been found that the conventional base used in aircraft de-icing fluid, propylene glycol, is not suitable for use in the practice of the invention - at least on its own - because it does not foam easily, if at all. Indeed it can suppress foams produced from other liquids. The alcohol bases used in conventional automobile windscreen de-icing products would not be a suitable base ingredient because of their rapid evaporation. A preferred base ingredient is glycerol. This may be used in admixture with water, in proportions suitable for the temperature protection required, and with foam promoting and or stabilizing ingredients as required. A range of 20-60 weight percent of glycerol is preferred.

In order to create a foam of adequate life for use in an effective anti-icing treatment, at least in preparations based on glycerol, a foam promoting and/or foam stabilizing agent is incorporated in the anti-icing liquid. It is suggested that up to 5 percent by weight of a suitable surfactant be incorporated as a foam promoting agent.

The following classes of surfactants are identified as having utility in the practice of the invention: 1. alkyl and alkyl ethoxy sulphate salts of the following: alkali metals, ammonia, lower molecular weight amines and alkanol amines - example of class sodium lauryl ether sulphate; 2. alkyl and alkyl aryl sulphonates - example of class sodium dodecyl benzene sulphonate;

3. amphoteric surfactants - example of class TEGOBETAINE

L7 (trade designation) a fatty amido-propyl dimethyl aminoacetic acid betaine (C₁₁-C₁₇) 4. amine oxides - example of class EMPIGEN OB (trade designation) NN dimethyl (C₁₂-C₁₄) alkyl amine oxide;

5. fatty acids amides eg of the following - mono, di and poly-ethanolamides and polydiethanolamides - example of class coconut fatty acid diethanolamide;

6. alkali salts of fatty acids - example of class sodium oleate; and,

7. sarcosinates - example of class sodium lauryl sarcosinate. A foam stabilizer can be used to increase the resistance of the foamed anti-icing liquid to self decay in order to secure sufficient foam life for utility in the process of the invention. Foam stabilizers can also be adopted in order that the foamed anti-icing liquid is rendered more resistant to external interference by wind and rain.

A preferred foam stabilizing agent is methyl cellulose which is a water soluble polymer having both foam stabilizing and promoting action. Alternative foam stabilizers might be found from the following classes: 1. hydrophillic colloids or polymers eg carboxymethyl cellulose, sodium alginates, also materials which might be generally grouped with these such as proteins, hydrolised proteins and modified starches; and 2. fatty acid esters or ethers of medium to high molecular weight polyethylene glycols, eg polyethylene glycol (molecular weight 6000) distearate. In order that the duration and effectiveness of the treatment of the invention may be predicted and utilised to the full the foam should be produced in such a way that the gas bubbles are of reasonably even size and distribution. Three ways of producing such foams are described herein. A typical bubble size in the sub-millimeter range is preferred. Typical bubble sizes currently utilized are in the range of one half to two thirds of a millimeter. It is envisaged that a typical bubble size which is less than one half millimeter could be more advantageous for commerical scale use.

The invention is now described with reference to the drawings of which: Figure 1 shows a foam generator and dispenser operated by compressed air; and

Figure 2 shows an aerosol canister foam generator and dispenser.

Figure 3 shows an industrial scale foam generator and dispenser operated by compressed air.

The apparatus shown in Figure 1 is of laboratory scale and comprises a bottle 1 having a removable cap 2 and an outlet tube 3 which connects with the interior of the bottle 1 through the cap 2. Within the bottle 1 is a quantity of anti-icing liquid indicated at 4. Beneath the level of the liquid 4 is a first gas inlet 5 which leads to a porous block diffuser 6. Compressed air is supplied to the bottle 1 through inlet 5 and diffuser 6 from a cylinder or compressor (neither shown). The gas flow rate is controlled by a regulation valve 7. A second gas inlet designated 8 leads to the interior of the bottle 1 at a position above the surface of liquid 4. Compressed air is introduced to the bottle through inlet 8 from a source (not shown) at a flow rate which is controlled by regulation valve 8. In operation of the apparatus a sample of anti-icing liquid is introduced to the bottle 1 to approximately the level shown. Then an airflow Is commenced through Inlets 5 and 8 and the regulation valves are adjusted to create the desired foam flow through the outlet tube 3 and the desired bubble size. The flow through inlet 5 is responsible for foaming the anti-icing liquid. The flow through inlet 8 aids in the creation of the required excess pressure for expulsion of the foam through the outlet tube 3. Alternative diffusers 6 of different pore size can be fitted for variation of the bubble size within the foam. Using the laboratory apparatus described foams have been prepared from various anti-icing liquids. Each was based upon an equal mass mixture of glycerol and water but various combinations of foam promoting and stabilising ingredients were used. Good results, in terms of foam stability toughness and resistance to run-off have been achieved using the sample anti-icing liquids documented in Table 1 when foamed to produce a typical bubble size in the range ½ mm to 2/3 mm. It proved easier to produce this small bubble size in anti-icing liquid of low viscosity. Some of the foams containing methyl cellulose as sole additive or with methyl cellulose in combination with Teepol were physically tougher than the other foams. All of the samples detailed below were readily foamed using the apparatus described to yield a foam having at least 24 hours life at ambient temperature and also at cold room conditions.

Teepol is a trade designation for a proprietary surfactant believed to fall in class 1 and/or 2 as described. Sodium oleate is a soap falling in class 6.

Figure 2 illustrates a typical aerosol spray apparatus. This comprises a cannister 20, a nozzle 21 and a valve 22. In the ready position the valve 22 is held closed by action of a compression spring 23 which urges a sealing portion 24 of the valve against a seat 25. When the nozzle 21 is depressed against the force of the spring it breaks the seal and opens a passage through the valve 22 to the nozzle 21. In this condition liquid 26 is forced from the cannister through a siphon tube 27 and out through the valve 22 and nozzle 21 by the internal pressure generated in the cannister 20 by a propellant 28 such as liquified petroleum gas. Using apparatus as shown in Figure 2 with liquified petroleum gas as propellant the process of the invention has been performed with the following formulations: Example 1

Glycerol 50.0, methyl cellulose (foam stabilizer) 0.50, sodium lauryl sarcosinate (class 7 surfactant) 1.00; water 48.50; Example 2

Glycerol 50.0, methyl cellulose 0.50, TEGOBETAINE L7 - trade designation (class 3 surfactant) 2.0; coconut diethanolamide (class 5 surfactant) 0.3; water 47.20 Example 3

Glycerol 50.0, methyl cellulose 0.50, sodium lauryl ether sulphate (3 ethylene oxide) (class 1 surfactant) 0.50 water 49.0 All the above formulations are stated in weight percent proporations. These formulations have been sprayed from an aerosol spray apparatus onto a vertical enamelled metal plate held at room temperature. All survived as foams and remained in place without run off for at least 24 hours. The formulations have also been sprayed In the same manner onto an automobile windscreen left in freezing conditions. After overnight exposure to freezing conditions the foam was iced-over but the ice was easy to remove by use of the windscreen wiper as there remained an unfrozen layer adjacent the windscreen glass.

Figure 3 illustrates an industrial scale foam generator 30 operated by compressed air, of the type used to dispense foamed cleaning fluids. Equipment of this type has been used to foam anti-icing liquids and dispense them in the manner of the invention. The foam generator comprises a pressurisable reservoir 31 a flexible outlet hose 32 and a rigid lance 33. The reservoir 31 has a compressed air inlet 34 which is connected to a compressor (not shown). This connection can be of the type that is maintained during use of the generator 30 or of the alternative disconnectable type that is used only for charging the reservoir 31. Within the reservoir 31 there is held a quantity of anti-icing liquid indicated at 35. A siphon tube 36 extends beneath the surface of liquid 35 and, at a position above the surface a side passage 37 joins the siphon tube 36. Compressed air within the reservoir 31 expels liquid 35 through the siphon tube 36 and also enters that tube via the side passage 37 through an entrance restriction 38 to produce downstream of the junction a frothy liquid. The siphon tube 36 and a compressed air passage 39 extend out of the reservoir 31 through the section of flexible hose 32 to the lance 33. At the remote end of the lance 33 the compressed air from passage 39 is injected at a nozzle 40 into the stream of frothy anti-icing liquid from siphon tube 36 to cause a spray of foamed anti-icing liquid to issue from the nozzle 40. Equipment of the above-described type has been used to foam and dispense anti-Icing liquids comprising an equal mass mixture of glycerol and water together with a proprietory foam generating surfactant of a variety not known by the Applicant. This anti-icing liquid was foamed by the equipment and dispensed onto an aircraft and also a car windscreen easily. A separate test using the same equipment and mixture was conducted in an icing chamber in a simulation of car windscreen usage. At a chamber temperature of -15°C the foamed anti-icing liquid was sprayed onto a glass plate held at 30° to the vertical to cover a portion of the plate with a thin layer of the foam. The remaining portion of the plate was left unprotected. Then a spray of fine droplets of water was directed onto the glass plate under a gentle wind produced by a fan behind the spray. This spray was maintained for some 10 minutes until a layer of ice covered the glass plate. Thereupon the spray was stopped. The ice layer was easily removed by hand from the protected area of the glass in large pieces by breaking the ice at a few discreet points. The pieces of ice slid from the glass because there remained an unfrozen layer adjacent the glass. The ice on the unprotected area of the glass plate was firmly attached to the glass and needed conventional scraping to remove it.

Claims

1. An ice-combative treatment comprising forming a stable foam of an anti-icing liquid (as hereinbefore defined) and applying that stable foam to a surface to de-ice that surface or convey anti-icing protection to that surface.

2. An ice-combative treatment as claimed In claim 1 in which the anti-icing liquid is so foamed as to be stable for at least eight hours.

3. An ice-combative treatment as claimed in claim 1 or claim2 in which the anti-icing liquid comprises glycerol as base ingredient.

4. An ice-combative treatment as claimed in claim 2 or claim3 in which the anti-icing liquid includes a surfactant as a foam promoting ingredient.

5. An ice-combative treatment as claimed in claim 4 in which the foam promoting ingredient comprises up to 5 percent by weight of the anti-icing liquid.

6. An ice-combative treatment as claimed in claim 4 or claim5 in which the foam promoting ingredient is an alkyl or alkyl ethoxy sulphate salt of one of the group consisting of alkali metals, ammonia, lower molecular weight amines, and alkanol amines.

7. An ice-combative treatment as claimed in claim 4 or claim 5 in which the foam promoting ingredient is an alkyl sulphonate or an alkyl aryl sulphonate.

8. An ice-combative treatment as claimed in claim 4 or claim 5 in which the foam promoting ingredient is an amphoteric surfactant.

9. An ice-combative treatment as claimed in claim 4 or claim 5 in whcih the foam promoting ingredient is an amine oxide.

10. An ice-combative treatment as claimed in claim 4 or claim 5 in which the foam promoting ingredient is a fatty acid of one of the group consisting of mono, di, and poly-ethanolamides.

11. An ice-combative treatment as claimed in claim 4 or claim 5 in which the foam promoting ingredient is an alkali salt of fatty acid.

12. An ice-combative treatment as claimed in claim 4 or claim

5 in which the foam promoting ingredient is a sarcosinate.

13. An ice combative treatment as claimed in claim 4 or claim 5 in which the foam promoting ingredient is an oleate.

14. An ice-combative treatment as claimed In any one of the preceeding claims in which the anti-icing liquid includes a foam stabilizing ingredient.

15. An ice-combative treatment as claimed in claim 14 in which the foam stabilizing ingredient is methyl cellulose.

16. An ice-combative treatment as claimed in any one of the preceeding claims in which the anti-icing liquid comprises 20-60 percent glycerol, up to 5 percent surfactant, up to 2.0 percent foam stabilizer balance water, wherein all proportions are stated in weight terms.

17. An ice-combative treatment as claimed in any one of the preceeding claims comprising foaming and dispensing the anti-icing liquid with an aerosol dispenser and applying the foamed anti-icing liquid as a de-icing or anti-icing treatment for a vehicle window glass.

18. An ice combative treatment as claimed in any one of claims 1-16 comprising foaming and dispensing the anti-icing liquid with a compressed air equipment and applying the foamed anti-icing liquid as a de-icing or anti-icing treatment for aircraft or other large equipment or structures.