NO311893B1 - Polymer-thickened deicing agent and icing protection for aircraft - Google Patents

Description

The present invention relates to an anti-icing and anti-icing agent for aircraft, based on glycols and water and with water-soluble cross-linked acrylic polymers as thickeners.

De-icing and anti-icing agent for aircraft (hereinafter, for brevity, simply called de-icing agent or anti-icing liquid) is used to remove ice, snow and/or frost from specific aircraft surfaces, and to avoid this type of deposits on these surfaces. The period of time during which the de-icing fluids provide protection against the re-formation of ice, snow and/or frost on the aircraft is termed re-icing protection time or "hold overtime". In "Recommendations for De-/Anti-Icing of Aircraft on the Ground" (Edition, March 1993) Association of European Airlines (AEA) and in International Standardization Organization (ISO) Spezifikationen 11075, 11076 and 11078, two types of aircraft de-icing fluids are specified . Type-I liquids consist essentially of glycol, water and corrosion inhibitors as well as any surfactants and pH-value regulators, and type-II liquids also contain a water-soluble polymer as a thickener to achieve a highly viscous pseudoplastic consistency.

Of aircraft de-icers of the aforementioned type-II, it is especially expected that they will provide the longest possible protection against new ice formation on the airfoils before take-off under extreme weather conditions, snowfall or freezing rain, and good de-icing from the end of the airfoils when the aircraft takes off. Thus, the ISO standard 11078, which entered into force in 1993, requires, with regard to protection time against new ice formation, at least 30 minutes at

-5°C in the so-called "Water Spray Endurance Test" (the de-icing liquid is exposed to a shear load of 3500 rpm for 5 minutes in advance). With regard to the displacement conditions, ISO 11078 describes for the first time a laboratory test, the so-called "Aerodynamic Acceptance Test", which prescribes a maximum thickness (Boundary Layer Displacement Thickness, d<*>) of the remaining deicing agent film after a simulated start, of at most 10 mm at -30"C and at most 9.5 mm at -10°C. ;The "holdover" time and flow conditions of the type-II deicers are achieved due to the influence of the thickener. Finding a good polymer thickener is, among other things, made difficult by the fact that the two properties, "holdover" time and take-off ratio, essentially stand in opposition to each other. - Report AN 83335W) as well as in EP-B-0,050,700 (US-S-4,358,389), EP-B-0,213,869 (US-A-4,744,913) and EP-B-0,360,183. They essentially consist of: a) 35 to 70% by weight of at least one glycol from the alkylene glycol group with 2 to 3 C atoms and oxalkylene glycol with 4 il ;6 C atoms, ;b) 0.05 to 1.5 wt-# of at least one water-soluble polymer as thickener, c) 0.02 to 1.5 wt-% of at least one surfactant from the group of anionic or non- ionic surfactants, d) at least one corrosion inhibitor in an effective amount, e) at least one basic compound from the group of alkali metal carbonates, alkali metal hydroxides and amines for setting a pH value of 7 to 11 and f) water as residual amount to 100 weight #, where the weight percentages are in relation to the (finished) de-icing agent. FR-patent 2057577 describes a liquid deicing agent consisting of an aqueous solution of ethylene glycol, propylene glycol and glycerin used alone or in various combinations and the polyethylene glycol ester of diisoalkyl phenol. The aqueous solution also contains a copolymer of methacrylic acid or acrylic acid with the alkyl ether of said acids. GB Patent 1 285 862 relates to a de-icing fluid having a lasting effect on aircraft surfaces which is based on polyalcohols with or without the addition of a wetting agent and which contains 0.05 to 10% by weight of an alkali metal salt of a film-forming polymer of a unsaturated carboxylic acid where the viscosity of a 1% aqueous solution of the polymer at pH 7.5 to 9.0 and at 20°C is from 100 to 5000 centistokes. US patent 5,118,434 describes that precipitation of salts from glycol-based fluids when mixed with water is prevented by the addition of copolymers or terpolymers of acrylic acid or alkali metal salt thereof and one or more of the monomers selected from the group consisting of 2-acrylamido-2- methylpropyl sulfonic acid or metal salt thereof, 4-styrenesulfonic acid or metal salt thereof, a lower alkyl hydroxy acrylate and mixtures thereof. ;The de-icing and icing protection agent for aircraft surfaces described in DE-A-24.23.893 contains, as a thickening agent, water-soluble cross-linked or non-cross-linked homo- or copolymers of acrylic acid or methacrylic acid, where the comonomers can be present in an amount from 5 to 70 mol -% (in relation to the total monomer mixture). As comonomers, methyl, ethyl or butyl esters of acrylic, methacrylic or maleic acid, vinyl acetate, styrene, low olefins and acrylic or methacrylamides are mentioned. In EP-B-0-360,183, water-soluble cross-linked polyacrylic acid products are used as thickeners and in EP-B-0,050,700 water-soluble cross-linked copolymers of acrylic acid or methacrylic acid with a comonomer proportion of 2 to 50 wt-# ( relative to the copolymer); nothing further is said about the type of comonomer. In EP-B-0,231,869, a mixture consisting essentially of a water-soluble cross-linked acrylic acid homopolymer and a copolymer of acrylic acid and acrylamide is described as a thickener. The known thickeners described give the aircraft deicers a certain pseudoplastic property, i.e. a relatively high viscosity (Viscosity at rest, called yield value), which decreases with shear stress. In this way, a good "holdover" time should be achieved with sufficient departure conditions at the same time. However, the requirements in specification ISO 11078 are so extreme that the described thickeners either only have a sufficient "holdover" time (due to high viscosity at rest), but do not satisfy the requirements in terms of flowability, or only provide a satisfactory flowability ( due to the viscosity at rest being set low), but cannot meet the requirements in terms of "holdover" time. The described known polymer thickeners thus fail to simultaneously meet the requirements prescribed in ISO 11078 "Water Spray Endurance Time" and in ISO 11078 the recently determined limitation to "Boundary Layer Displacement Thickness" in the "Aerodynamic Acceptance Test". As the state of the art, the new publication WO 93/24543 should also be mentioned, where special macromonomers containing linear cross-linked polycarboxylates as thickeners for type-II aircraft deicing fluids are described. The macromonomers contain a hydrophobic end residue from the alkaryl group and are connected by means of a linker with polycarboxylate (polyacrylate, polymethacrylate etc.) (compare e.g. pages 9 and 19). These polymer thickeners also require monomers with a relatively complicated structure, and can only be produced over several reaction steps. ;As mentioned above, both characteristics, "holdover" time and departure ratio, are opposite to each other. In order to achieve sufficient runoff conditions, the viscosity and thus the concentration of the thickener must be chosen as low as possible. A sufficient "holdover" time, on the other hand, requires the highest possible flow limit for the deicing agent, and thus generally a high viscosity and high thickening agent concentration. The aim of the present invention therefore consists in providing simply structured and easily produced thickening agent polymers, which in the finished aircraft deicing agent give an increased pseudo-plasticity, i.e. give a stronger reduction in viscosity with increasing shear load, and thereby with shear load, despite a higher viscosity at rest , becomes thinner significantly faster and thus flows better. The new de-icing agent with increased pseudo-plasticity must, due to its sufficiently high viscosity at rest, fulfill the "Water Spray Endurance Test" and, due to the faster de-flow in the wind channel or at take-off, at the same time give the required low value of " Boundary Layer Displacement Thickness" in the "Aerodynamic Acceptance Test". The new aircraft de-icing agent of type-II must be based on a simple and easily available polymer thickener, and meet the requirements according to ISO standard 11078 regarding "holdover" time and take-off conditions with good safety. ;It has now been found that water-soluble cross-linked copolymers of acrylic acid and methacrylic acid as the main monomers, and an ester or amide of the acrylic acid or methacrylic acid with a long alkyl residue in the ester group and one or two long alkyl residues in the amide group as the second monomer, give a particularly pronounced pseudoplasticity, and provides type-II aircraft deicer with the above-described combination of properties. Thus, the present invention relates to an anti-icing and ice protection agent for aircraft based on glycols and water and which contains water-soluble cross-linked acrylic polymers as thickening agent, characterized in that the thickening agent is a water-soluble cross-linked copolymer essentially consisting of from 85 to 99 wt-# of polymerized units of acrylic acid or methacrylic acid and from 1 to 15 wt-# of an ester or amide of acrylic acid or methacrylic acid, the latter represented by the formulas wherein R<1>, R2, R3 and R<5> are C6-<C>22-alkyl ; ;r<4> and r<6> is an alkyl radical having 1 to 4 carbon atoms. ;Further embodiments of the present invention are given in the independent claims 2-8. The copolymers used in the invention are known and commercially available. They are produced by copolymerization of the specified monomers in the presence of crosslinkers. This type of copolymerization is, for example, described as carried out in the above-mentioned US-A-4,744,913. A further manufacturing method is based on first preparing an acrylic acid or methacrylic acid homopolymer in sat, and then subjecting this to the specified esterification or amidation. It must of course be understood that the main monomer, acrylic acid or methacrylic acid, can also be polymerized in the form of the corresponding acrylate, preferably alkali metal acrylate (the alkali metal is preferably potassium or sodium) with the other monomer, the ester or the amide (for simplicity, only acrylic acid is spoken of and methacrylic acid). Of the cross-linkers mentioned in US-A-4,744,913, the polyunsaturated ethers mentioned here are also preferred, where diallyl ethers, di- or triallyl glycerin ethers, di- or triallyl trimethylol ethane ethers, di- or triallyl trimethylol propane ethers are particularly preferred , tetraallyl oxetane and di-, tri-, tetra-, penta- or hexaallyl ethers of sugar alcohols as well as the corresponding metalyl ethers. The amount of crosslinkers in the copolymers generally amounts to 0.01 to 10% by weight, preferably 0.1 to 1% by weight, of the copolymer. The water-soluble copolymers used in the invention then consist, taking into account the amount of crosslinker, essentially of polymerized acrylic acid or methacrylic acid as the main component, a smaller amount of polymerized second monomer and a possibly smaller amount of polymerized crosslinker. A preferred copolymer, taking into account the amount of crosslinker, consists essentially of 75 to 98.99% by weight, preferably 89 to 97.9% by weight, of polymerized acrylic acids or methacrylic acids, 1 to 15% by weight, preferably 2 to 10% by weight , polymerized ester compound or amide compound and 0.01 to 10 wt-#, preferably 0.1 to 1 wt-#, polymerized cross-linker, where the weight percentage is of the (finished) copolymer. ;The deicing fluid of the invention contains, in addition to the described thickener, primarily glycol and water, and in addition preferably also surfactants, corrosion inhibitors and, if necessary, pH regulators for setting a pH value from 7 to 11, preferably 7.5 to 9. As glycol, the deicing fluid of the invention preferably contains those from the group of alkylene glycols with 2 to 3 C atoms and oxalkylene glycols with 4 to 6 C atoms. Preferred glycol compounds are ethylene glycol, propylene glycol (1,2-propylene glycol or 1,3-propylene glycol), diethylene glycol, dipropylene glycol or a mixture of two or more of these glycols, with propylene glycol being particularly preferred. The glycols primarily serve to lower the freezing point, and together with water constitute the main component of the liquid. Fully desalinated water is preferably used as water. As a surfactant, fatty alcohol alkoxylate or aryl alkyl sulphonate, or a mixture of these, is preferably used. The alkoxylate is preferably one with 1 to 10, preferably 1 to 5 ethylene oxide units, propylene oxide units or a mixture thereof, where ethylene oxide alone is preferred. The alkyl residue in the fatty alcohol generally contains 6 to 22 C atoms, preferably 8 to 18 C atoms, and can be straight or branched, whereby the straight ones are preferred, and saturated or unsaturated with preferably 1 to 3 double bonds. Examples include: Octyl, decyl, dodecyl, isotridecyl and stearyl alcohol, in addition to oleyl, cocoalkyl and tallow alkyl alcohol as well as a fatty alcohol mixture with a C-^-alkyl residue °S C14-alkyl residue (C-^/C- ^-f ett alcohol ) ethoxylated with 1 to 5 moles of ethylene oxide. The alkarylsulfonate is preferably potassium and/or sodium alkylarylsulfonate with one or more, preferably one or two, sulfonate groups (SO3-K or SO3~Na groups), one or more, preferably one or two, alkyl groups with 5 to 18 C -atoms, preferably 12 to 18 C atoms, and one or more, preferably one or two, benzene rings. Alkali metal (potassium and/or sodium) alkylbenzene sulfonates with 12 to 18 C atoms in the alkyl group are preferred. Since the production of alkyl-arylsulfonates is also based on hydrocarbon mixtures, such as those which are, for example, formed as fractions during petroleum processing, the alkyl groups can also be this type of mixture. Thereby, the number of hydrocarbons is preferably 12 to 18 (that is, an average number of 15). As corrosion inhibitors, compounds which are applicable to liquids based on glycols and water can be used. Suitable corrosion inhibitors are alkali metal phosphates, lower alkyl phosphates such as ethyl phosphate, dimethyl phosphate, isopropyl phosphate and the like, imidazoles such as 1H-imidazole, methylimidazole, benzimidazole and the like. and triazoles such as benzotriazole and tolyltriazole, with the triazoles being preferred. ;For setting the pH value of 7 to 10, preferably 7.5 to 9, basic compounds are used. Preferred are those from the group of alkali metal hydroxides such as NaOH and KOH, alkylamines such as butylamine, hexylamine, octylamine and isononylamine and alkanolamines such as mono-, di- and triethanolamine. The alkali metal hydroxides are particularly preferred. The production of the invention's de-icing agent and anti-icing agent takes place by mixing the individual (known and commercially available) components in the desired order, and can, for example, be carried out in a container equipped with a stirrer. Taking into account all the components described above, the de-icing liquid of the invention essentially consists of: a) 35 to 70 wt-#, preferably 40 to 60 wt-#, of at least one glycol from the group of alkylene glycols with 2 to 3 C atoms; and oxalkylene glycol with 4 to 6 C atoms, ;b) 0.05 to 1.5 wt-#, preferably 0.1 to 1 wt-# of at least one water-soluble cross-linked copolymer of the type ;described as a thickener, ;c) 0 .02 to 1.5 wt-#, preferably 0.05 to 1 wt-# of at least one surfactant from the group of fatty alcohol alkoxylates and arylalkylsulfonates as described above, ;d) 0.01 to 1 wt-#, preferably 0.03 to 0.7 weight # of at least one corrosion inhibitor for liquids based on glycols and water, e) at least one basic compound for setting a pH value of from 7 to 11 and f) water as a residue of 100 weight #, ;where the weight percentages are in relation to the entire agent. As mentioned above, the copolymer used in the invention must be water-soluble. Water solubility exists when, upon dissolving up to 10 g of copolymer in 1000 g of water at around 20°C after setting a pH value of 7 with alkali metal hydroxide, a clear solution is formed. As a further property, the copolymer in a 0.2 wt # aqueous solution at 20° C and a pH value of 7 (adjusted with alkali metal hydroxide, if such a pH value does not already exist) has a viscosity of 1000 to 20,000 mPas, measured with a Brookfield viscometer at 20 rpm. The invention's de-icing liquid of type II fulfills the requirements described above by a good margin. With the new thickener, unexpectedly good de-flowing conditions are achieved even with a high viscosity at rest (flow limit) of the de-icing liquid, which ensures a long "holdover" time. With the new thickener, it is also possible to eliminate the contradiction between both properties, "holdover" time and flow ratio. This surprising result is clearly a result of the unexpected pronounced pseudoplastic conditions of the thickeners, which lead to a marked reduction in viscosity with increasing shear forces, and thus to the desired low layer thickness of the deicing agent film in the "Aerodynamic Acceptance Test". The invention is further explained below by examples 1 and 2 of the invention, and a comparative example. ;EXAMPLE 1 ;A type-II deicer was prepared with the following composition and the following method: ;The copolymers as well as benzotriazole and the surfactant were dissolved in water with vigorous stirring at 20°C. Then 1,2-propylene glycol was added and adjusted to a pH value of 7 to 7.4 with sodium and potassium hydroxide (always in the form of an approximately 10% by weight aqueous solution). ;The formed deicer was tested for viscosity, "Water Spray Endurance Time" and "Boundary Layer Displacement Thickness, d<*>" in the "Aerodynamic Accetpance Test". The results are summarized in the following Tables 1 and 2:

TABLE 1

Viscosity value at 0°C and 0.084, 0.84, 8.4 and 16.8 s"<1>shearness and reduction of viscosity at the aforementioned increasing shear strengths, expressed as a percentage, compared to the value at 0.084 s --'- cutting speed.

EXAMPLE 2

A type II aircraft deicer was prepared with the following composition as in example 1:

The de-icing agent formed (pH value 7.2) was tested as in example 1. The results are summarized in tables 3 and 4 below:

TABLE 3

Viscosity value at 0°C and 0.084, 0.84, 8.4 and 16.8 s"<1 >shear rate and reduction of viscosity at the aforementioned increasing shear rates, expressed as a percentage, in relation to the viscosity value at 0.084 s~<l> cutting speed.

Comparative example

A Type II aircraft deicer was prepared with the following composition and prepared according to the above procedures:

The polyacrylic acid as well as the benzotriazole and the surfactant were dissolved in water with vigorous stirring at 20°C.

Then 1,2-propylene glycol was added and adjusted to a pH value of 7 to 7.4 with the help of sodium and potassium hydroxide (always in the form of about 10% by weight aqueous solution).

The deicing agent formed was tested as in example 1. The results are summarized in tables 5 and 6 below:

TABLE 5

Viscosity value at 0°C and 0.084, 0.84, 8.4 and 16.8 s"<1 >shear speed and reduction of viscosity at the aforementioned increasing shear speeds, expressed as a percentage, in relation to the viscosity value at 0.084 s"<1> cutting speed.

Claims (8)

1. Anti-icing and anti-icing agent for aircraft based on glycols and water and containing water-soluble cross-linked acrylic polymers as a thickener, characterized in that the thickener is a water-soluble cross-linked copolymer consisting essentially of from 85 to 99 wt-# of polymerized units of acrylic acid or methacrylic acid and from 1 to 15% by weight of an ester or amide of acrylic acid or methacrylic acid, the latter represented by the formulas wherein R<1>, R2, R3 and R<5> are C6-<C>22 alkyl; R<4> and R<6> is an alkyl radical having 1 to 4 carbon atoms. 2. Composition according to claim 1, characterized in that the thickening agent is a water-soluble cross-linked copolymer which essentially consists of from 75 to 98.99 wt-# polymerized units of acrylic acid or methacrylic acid, from 1 to 15 wt-$ polymerized units of an ester or amide of acrylic acid or methacrylic acid and from 0.01 to 10% by weight of polymerized cross-linking agent, the percentages being based on the copolymer. 3. Composition according to one or more of claims 1 and/or 2, characterized in that the alkyl radical or alkyl radicals have from 10 to 18 carbon atoms. 4. Composition according to one or more of claims 1 to 3, characterized in that it contains from 0.05 to 1.5 wt-# of water-soluble cross-linked copolymer, where the weight percentages are based on the de-icing composition. 5 . Composition according to one or more of claims 1 to 4, characterized in that it contains as further components at least one surfactant from the group consisting of fatty alcohol alkoxylates and aryl alkyl sulphonates, at least one corrosion inhibitor for liquid based on glycols and water and at least one basic compound to give a pH of from 7 to 11, in an amount that is effective in each case. 6. Composition according to claim 1, characterized in that it essentially includes a) from 35 to 70 wt-# of at least one glycol from the group consisting of alkylene glycols having 2 to 3 carbon atoms and oxyalkylene glycols having 4 to 6 carbon atoms, b) from 0.05 to 1.5 wt-# of at least one water-soluble cross-linked copolymer as a thickener, consisting essentially of polymerized units of acrylic acid or methacrylic acid in an amount of from 85 to 99 wt-# and polymerized units of an ester or amide of acrylic acid or methacrylic acid with a C^-Cg alkyl radical in the ester group and one or two C^-Cg alkyl radicals in the amide group in an amount of from 1 to 15 wt-$, c) from 0.02 to 1.5 wt-# of at least one surfactant from the group consisting of fatty alcohol alkoxylates and aryl alkyl sulfonates, d) from 0.01 to 1 wt-# of at least one corrosion inhibitor for liquids based on glycols and water, e) at least one basic compound to establish a pH of from 7 to 11, and f) water up to 100% by weight, where the weight percentages are based on the de-icing composition. 7 . Composition according to claim 6, characterized in that the fatty alcohol ethoxylate is a fatty alcohol ethoxylate having 1 to 10 ethylene oxide units. 8. Composition according to claim 6, characterized in that the alkyl radical or alkyl radicals in the ester or amide each have 10 to 18 carbon atoms and the fatty alcohol alkoxylate is a fatty alcohol ethoxylate having 1 to 5 ethylene oxide units.