HIGH FUNCTIONALITY COMPOSITIONS BASED ON FLUORINATED AND SILANIZED POLYISOCYANATES AND VARNISHES PREPARED THEREFROM

Abstract: High-functionality compositions based on fluorinated and silanized polyisocyanates, prepared by reacting a hydroxy-­ terminated perfluoropolyether having an average molecular weight ranging from 500 to 7000 and a silico-carbinol having an average molecular weight ranging from 500 to 7000, with an organic diiso­ cyanate and a polyol having a functionality of at least 3. Var­ nishes containing said compositions based on fluorinated and silanized polyisocyanates, having a high functionality.

Description: The present invention relates to high-functionality compositions based on fluorinated and silanized polyisocyanates and to varnishes and paints prepared therefrom. The use of urethane polymers or of polyisocyanates as base products for preparing varnishes and paints is known in the art. Generally, varnishes the paints consist of a solvent/dispersing agent base in which a polymeric product and, optionally, additives, such as pigments, anti-corrosion agents, antifouling agents, etc., are dissolved or dispersed, the function thereof being that of improving the varnish and paint properties when applied as a film or a surface coating. Examples of polymeric products are the urethane resins, acrylic resins and polyvinylchloride. The polyurethane or polyisocyanate paints and varnishes have the property of hardening during the evaporation of the solvent or of the dispersing agent, and consequently of forming a surface coating which, besides adhering well to the surface on which it is applied, shows an excellent resistance to weathering agents as well as excellent physical characteristics such as hardness, water-repellency and stability to ultraviolet radiations. An important field of use for the paints, in particular for those based on polyurethane resins, is represented by the marine sector, where the paint, besides exhibiting excellent anticorrosion coating properties, must also exert an antifouling activity in order to prevent any animal and/or vegetable forms from forming and growing on the hulls of boats and ships. Such vegetable/animal forms give rise to serious drawbacks because they not only damage the protective film or the paint which coats the keel, but they also cause a high friction which remarkably influences the fuel consumption. To remove such vegetable or animal forms, boats of any size are sheltered in dry docks, where they are freed from such foulings and are painted again. Such maintenance work, besides being expensive in itself, requires also long working times which, in the case of commercial boats, detrimentally affect the running costs. As regards racing boats, in particular, the presence of such animal/vegetable forms, with the consequent surface roughness of the keel, adversely affects the sports purposes, i.e., the speed. In fact, for this type of boat, already the protective film itself must exhibit a coefficient of friction close to that of very smooth surfaces, for example glass or mirror-like aluminum, in order to reduce as much as possible the resistance to the advancing of the hull in the water. Thus, there were proposed, and broadly described in the literature, paints mainly intended for marine use, or resins and polymers as basic products for preparing them, by means of which the attempt was made to solve the foregoing problems and above all to reduce and simplify the maintenance work for cleaning and repainting large size boats. Some of these paints, such as, e.g., those described in EP-A-46,354 or in US-A-4,407,997, contain biocides; in most cases biocides based on copper or tin, which are released very slowly according to different mechanisms and which inhibit the growth of vegetable and/or animal forms on the parts on which they are applied. These paints, however, suffer from the drawback of being effective only over a limited period of time and by having a biocide-polluting action on the sea flora and fauna. As an alternative to paints containing antifouling additives, paints have been proposed based on fluorinated resins and polymers. Such fluorinated resins, in particular fluorinated polyurethane resins such as, for example, those described in US-A-4,132,681, permit one to prepare paints endowed with good coating properties and which, when applied on boat hulls, permit easy removal of the vegetable/animal scales formed thereon. This latter characteristic can be improved by adding to such paints powdered fluorinated polymers, such as tetrafluoroethylene, which, as is known, is a material having excellent anti-adhesion properties. Also, in this case, however, the suggested solution is something less than satisfactory because it does not prevent the growth of such animal and/or vegetable forms. It has now been discovered in accordance with the present invention that compositions based on fluorinated and silanized polyisocyanates, to be utilized as base polymers for preparing varnishes endowed with high water-repellency, low critical surface tension, and low coefficient of friction, are those having high functionality and obtainable by reacting a hydroxy-terminated perfluoropolyether, a silico-carbinol, an organic diisocyanate, and a trivalent or tetravalent polyol, preferably of low molecular weight. Thus, the present invention provides high functionality compositions based on fluorinated and silanized polyisocyanates, obtainable by reacting a hydroxy-terminated perfluoropolyether (A₁), having an average molecular weight ranging from 500 to 7000, of formula HO - R f - OH and a silico-carbinol (A₂), having an average molecular weight of from 500 to 7000, of formula HO - R s - OH with an organic diisocyanate (A₃) and a trivalent or tetravalent polyol (A₄), in molar ratios A₁/A₂/A₃/A₄ ranging from 1/0.07/6/2 to 1/0.15/ 7/3.5. In the above formulae R f is a difunctional radical selected from those of formulae (I) to (IX): wherein R₁ is selected from -(CH₂) x -, -(CH₂O) y CH₂- and -(CH₂) x OCH₂-, wherein x, y are integers from 1 to 4; m and n are integers, the ratio m/n ranging between 0.2 and 2, and preferably between 0.5 and 1.2; R' f is a perfluoroalkylene radical containing preferably 1 to 15 carbon atoms, more preferably 1 to 8 carbon atoms; X is F or CF₃; k, j, w, u, d, b, t, c, v, z, a, e, are integers such as to allow one to obtain the above molecular weights; and R s is a difunctional radical of formula wherein R₂ is an alkylene radical containing from 1 to 5 carbon atoms; r is an integer of from 2 to 6; and g is an integer of from 4 to 10. In the above reaction one may employ perfluoropolyether/silico-carbinol weight ratios selected over very wide ranges; however, the preferred ratios are from 98/2 to 85/15. Preferred compositions are those obtained by starting from hydroxy-terminated perfluoropolyethers with an average molecular weight of from 1000 to 2500 and from silico-carbinols with an average molecular weight of from 1000 to 2500. Further preferred compositions are those obtained by starting from polyols having a low molecular weight, for example lower than 400; such compositions have an NCO content, calculated on the dry basis, ranging from 1.5 to 8%, and preferably from 3 to 6%. According to one preferred embodiment of the invention, the compositions of the present invention may be prepared through a two-step process: (a) in a first step, an organic diisocyanate is reacted with a mixture consisting of 85-98% by weight of hydroxyterminated perfluoropolyether and 2-15% of silico-carbinol, the reaction temperature being maintained at from 40 to 100°C; and (b) after the end of the reaction, the product so obtained is admixed with the polyol, or a mixture of polyols, having a low molecular weight. Also in this second step, the temperature ranges from 40 to 100°C. According to another preferred embodiment, the compositions of the present invention may be prepared by a three-step process: (i) in the first step, the mixture of perfluorinated polyetherdiol and silico-carbinol is first charged into an autoclave with a portion of diisocyanate in order to provide a molar ratio of diisocyanate to the mixture equal to about 2:1; (ii) in the second step, to the intermediate product so obtained there is added all the low molecular weight polyol; and (iii) in the third step, at the end of the reaction the remaining portion of the diisocyanate is charged. The reaction temperature in the three steps generally ranges from 40 to 100°C. Since the hydroxy-terminated perfluoropolyether is immiscible both in diisocyanate and in silico-carbinol, and the mixing thereof provides a non-homogeneous milky suspension which tends to separate into an upper part (diisocyanate and silico-carbinol) and a lower part (perfluoropolyether), the reaction is usually conducted in the presence of a solvent. Such solvent, although it dissolves a small amount of perfluorinated polyether diol, enables molecules of the first three reagents to be present in the reaction medium. The initial NCO-terminated intermediate reaction product is perfectly soluble and able by itself to act as a solvent for the not-yet-reacted perfluoropolyether. The solvent utilized is compatible with the reaction temperature and is inert with respect to the reagents and to the final reaction product. Examples of suitable solvents are: dimethylformamide, chlorinated solvents such as trichloroethylene and tetrachloroethane, or organic solvents containing in the molecule an ester-ether group such as polyoxyethylene monoethylether acetate, polyoxyethylene monobutylether acetate, polyoxybutylene monoethylether acetate, polyoxybutylene monobutylether acetate, polyoxyethylene diacetate, polyoxybutylene diacetate, cellosolve ® acetate, ethylene glycol diacetate and butylene glycol diacetate. In order to accelerate the reaction, it is preferred to operate in the presence of appropriate catalysts. Examples of such catalysts are: tertiary amines, such as triethylenediamine, N-ethyl-ethyleneimine, tetramethylguanidine and dimethylcyclohexylamine, organometal activators such as dibutyl-tin-dilaurate, tin octoate, cobalt naphthenate, vanadium acetylacetonate, dimethyl-tin-diethylhexanoate, and mixtures thereof. Preferred catalysts are triethylenediamine and dibutyl-tin-dilaurate. The catalysts are used in catalyst concentrations, and generally not higher than 0.1% by weight. Any diisocyanate of general formula: OCN-R-NCO in which R is selected from alkylene, cycloalkylene, alkylene-cycloalkylene or arylene radicals containing from 1 to 20 carbon atoms, may be utilized for preparing the compositions of the present invention. Examples of utilizable diisocyanates are: 2,4-toluenediisocyanate either alone or in admixture with its isomer 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexyl-methane-diisocyanate; 1-isocyanato-3-isocyanato-methyl-3,5,5-trimethylcyclohexane (or isophorone diisocyanate); 2,2,4-trimethylhexamethylene-diisocyanate in admixture with its isomer 2,5,5-trimethylhexamethylene-diisocyanate, ethylidene-diisocyanate, butylene-diisocyanate pentamethylene-diisocyanate, cyclohexylene-1,4-diisocyanate, cyclohexylene-1,2-diisocyanate, xylylene-diisocyanate, dichloro-hexamethylene-diisocyanate, dicyclohexyl-4,4'-diisocyanate, 1,2-di(isocyanato-methyl)cyclobutane, 1-methyl-2,4-diisocyanatocyclohexane and 1-methyl-2,6-diisocyanato cyclohexane; aliphatic diisocyanates containing ether groups such as 1,3-bis-( γ-isocyanato-propoxy)-2,2-dimethylpropane. Among those, the aliphatic diisocyanates, such as isophorone diisocyanate, are preferred. Any hydroxy-terminated perfluoropolyether of formula HO - R f - OH wherein R f is as defined above may be used for preparing the compositions of the present invention. As an example may be mentioned α , ω -bis-(hydroxymethyl)-polyoxyperfluoroalkylene, marketed by Montefluos S.p.A., Milan, under the trade name Fomblin ® Z-DOL. Any silico-carbinol of formula HO - R s - OH wherein R s is as defined above may be used for preparing the compositions of the present invention. As an example may be mentioned the product of formula: marketed by Dow Corning under the trade name DOW ® Q4-3667. Any polyol having a trivalent or tetravalent functionality, and preferably a low molecular weight, may be utilized in the synthesis of the compositions of the present invention. Preferred polyols are those having a molecular weight lower than 400, such as trimethylol propane, trimethylol ethane, glycerine, 1,2,6-hexanetriol, and ethoxylated or propoxylated pentaerythritol. Said polyols are utilizable either individually or in admixture with one another. Compositions based on fluorinated and silanized polyisocyanates having a high functionality in admixture with their reaction solvent are directly utilizable as varnishes. The varnishes obtained from the high-functionality compositions based on fluorinated and silanized polyisocyanates in admixture with their reaction solvent or further diluted are another object of the present invention. As dilution solvents it is possible to use either the reaction solvents themselves or products compatible with them, such as toluene, xylenes, acetates of general formula CH₃-COO-R₃ , wherein R₃ is a linear or branched alkyl radical containing from 2 to 6 carbon atoms, or also ketones of formula R₄-CO-R₅, wherein R₄ and R₅ are linear or branched alkyl radicals containing from 1 to 5 carbon atoms. To the varnish so obtained one may also add conventional additives such as pigments and fillers; the latter must be inert products, i.e., they must not contain groups that react with the isocyanate groups of the basic composition. Pigments and fillers are useful to improve the surface characteristics, such as consistency, hardness and stability to moisture and to heat, of the varnish after application and drying thereof on the treated surface. The pigments may be selected from natural, synthetic inorganic and synthetic organic pigments. The polyisocyanate-based compositions utilized for preparing the varnishes of the present invention are sufficiently fluorinated so as to be compatible with fillers such as polytetrafluoroethylene or polyfluoroethylene-propylene. These fillers may be added in large amounts such as, for example, up to 50% by weight. The fillers, as well as the inert pigments and any other type of additive, are added to the dispersion in very fine particle form, generally having sizes below 100 µm. The varnishes according to the present invention are characterized by a high water-repellency, a low critical surface tension, and a low coefficient of friction. The fact of being highly water-repellent imparts to the varnishes an excellent antifouling capability. The varnishes of the present invention, after application and drying, are characterized by the following properties: - contact angle: from 100° to 110°, measured according to method ATICELCA MC 21-72; - coefficient of friction: from 0.1 to 0.3, measured according to ASTM D 1894-78; - Sward hardness: from 40 to 70, measured according to ASTM D 2134-66. For a still better understanding of the present invention some illustrative but not limitative examples are given hereinafter. Example 1 Into a 500-ml reactor equipped with stirrer, thermometer, and reflux cooler there were charged, in a nitrogen atmosphere, 59.56 g (0.0339 moles) of Fomblin ® Z-DOL having an equivalent weight of 877; 45.83 g (0.206 moles) of isophorone diisocyanate; 20 g of cellosolve ® acetate, and 0.058 g of dibutyl-tin-dilaurate. The whole mixture was gradually heated to 73°C within half an hour. At this temperature the mixture, which was milky at the beginning, became clear. It was heated to 80°C and this temperature was maintained for 0.5 hours. Then, at 80°C, there were added 4.86 g (0.00242 moles) of Dow ® Q4-3667 having a molecular weight of 2000, 0.05 g of dibutyl-tin-dilaurate, and 20 g of cellosolve ® acetate. The whole mixture was maintained at said temperature for 1 hour, then it was cooled to 55°C whereupon 9.75 g (0.07276 moles) of trimethylolpropane, dissolved, at 60°C, in 40.2 g of cellosolve ® acetate, were added. The resulting mixture was gradually heated to 80°C within half an hour and this temperature was maintained for 3 hours and 30 minutes. 40 g of cellosolve ® acetate were added to bring the dry solids content to 50%. The resulting solution, which had an NCO content of 2.25% (theoretical value: 2.16%), was cooled to 40°C and then was discharged. The resulting reaction mixture was diluted with cellosolve ® acetate up to 30% by weight of dry solids, and then spread onto a glass plate as a film which, after drying in air for 7 days at room temperature of 25°C, had a thickness of 30 µm. The characteristics of the resulting varnish are reported in the following Table. Example 2 Into a 500-ml reactor equipped with stirrer, thermometer, and reflux cooler there were charged, in a nitrogen atmosphere, 100 g (0.057 moles) of Fomblin ® Z-DOL having an equivalent weight of 877, 81.3 g (0.365 moles) of isophorone diisocyanate, 50.0 g of cellosolve ® acetate, and 0.087 g of dibutyl-tin-dilaurate. The resulting mixture was gradually heated to 72°C within half an hour. At this temperature the mixture, which was milky at the beginning, became clear. It was further heated to 80°C and this temperature was maintained for 0.5 hour. 17.3 g (0.0075 moles) of Dow ® Q4-3667, having a molecular weight of 2300 , 17.5 g of cellosolve ® acetate, and 0.058 g of dibutyl-tin-dilaurate were then added. The whole mixture was maintained at this temperature for 1 hour, whereupon it was cooled to 55°C and 17.3 g (0.129 moles) of trimethylolpropane, dissolved in 76.5 g of cellosolve ® acetate at 60°C, were added. The resulting mixture was gradually heated to 80°C within half an hour and this temperature was maintained for 3.5 hours. The solution had an NCO content of 2.63% (theoretical value: 2.51%). 72 g of cellosolve ® acetate were added in order to bring the dry solids content to 50%, whereafter the resulting solution was cooled to 40°C and discharged. A varnish was prepared and applied following the procedure of Example 1. The characteristics of said varnish are reported in Table 2.

Claims: High-functionality compositions based on fluorinated and silanized polyisocyanates obtainable by reacting a hydroxy-terminated perfluoropolyether (A₁) having an average molecular weight of from 500 to 7000 and the general formula HO-R f -OH wherein the R f radical is selected from those having the following formulae: wherein R₁ represents -(CH₂) x -, -(CH₂O) y CH₂- or -(CH₂) x OCH₂-, x and y being integers of from 1 to 4; m and n are integers, the ratio m/n being between 0.2 and 2, preferably between 0.5 and 1.2; R' f is a perfluoroalkylene radical; X is F or CF₃; and k, j, w, u, d, b, t, c, v, z, a and e are integers such as to result in the above molecular weights; and a silico-carbinol (A₂) having an average molecular weight of from 500 to 7000 and the general formula HO-R s -OH wherein R s is a difunctional radical of the following formula: wherein R₂ represents an alkylene radical containing from 1 to 5 carbon atoms, r is an integer of from 2 to 6, and g is an integer of from 4 to 10; with an organic diisocyanate (A₃) and a trivalent or tetravalent polyol (A₄) in molar ratios A₁/A₂/A₃/A₄ ranging from 1/0.07/6/2 to 1/0.15/7/3.5. Compositions according to claim 1, in which the weight ratio A₁/A₂ ranges from 98/2 to 85/15. Compositions according to any one of claims 1 and 2, in which the hydroxy-terminated perfluoropolyether (A₁) and the silico-carbinol (A₂) have average molecular weights of from 1000 to 2500. Compositions according to any one of claims 1 to 3, wherein the polyol (A₄) is trivalent and has a molecular weight lower than 400. Compositions according to any one of claims 1 to 4, wherein the organic diisocyanate (A₃) is of aliphatic nature. Compositions according to claim 5, wherein the diisocyanate is isophorone diisocyanate. Compositions according to any one of claims 1 to 6, wherein the NCO content, calculated on the dry basis, ranges from 1.5 to 8%, and preferably from 3 to 6%. Varnishes comprising high-functionality compositions based on fluorinated and silanized polyisocyanates as defined in any one of claims 1 to 7. Varnishes according to claim 8, wherein the fluorinated and silanized polyisocyanates are dissolved in a solvent selected from dimethylformamide, chlorinated solvents, and organic solvents containing an ester and ether group in the molecule. Varnishes according to claim 8 or 9, diluted with a solvent selected from toluene, xylenes, acetates of formula CH₃-COO-R₃, wherein R₃ is a linear or branched alkyl radical containing from 2 to 6 carbon atoms, and ketones of formula R₄-CO-R₅ wherein R₄ and R₅ are linear or branched alkyl radicals containing from 1 to 5 carbon atoms. Varnishes according to any one of claims 8 to 10, which additionally contain up to 50% by weight of fluorinated fillers. Varnishes according to claim 11, wherein the fluorinated filler is selected from polytetrafluoroethylene and polyfluoroethylene-propylene. Process for preparing the compositions of claim 1, comprising the steps of: (a) reacting, at a temperature of from 40 to 100°C, a diisocyanate (A₃) of formula OCN - R - NCO wherein R is selected from alkylene, cycloalkylene, alkylene-cycloalkylene and arylene radicals containing from 1 to 20 carbon atoms; with a mixture consisting of 85 to 98% by weight of hydroxy-terminated perfluoropolyether (A₁) and 2 to 15% by weight of silico-carbinol (A₂); and (b) reacting the resulting reaction product with a trivalent or tetravalent polyol (A₄), or a mixture thereof, preferably with a low molecular weight, at a temperature of from 40 to 100°C. Process for preparing the compositions of claim 1, comprising the steps of: (i) reacting a mixture of perfluoropolyether (A₁) and silico-carbinol (A₂) with a portion of diisocyanate (A₃), in a molar ratio of said diisocyanate to said mixture of about 2:1; (ii) adding all of the polyol (A₄) to the obtained product; and (iii) adding, at the end of the reaction, the remaining portion of diisocyanate (A₃). Process according to claim 14, wherein the reaction temperature ranges from 40 to 100°C. Process according to any one of claims 13 to 15, wherein the reaction is conducted in the presence of a catalyst. Process according to claim 16, wherein the catalyst is selected from triethylene diamine and dibutyl-tin-dilaurate. Process according to any one of claims 13 to 17, wherein the reaction is conducted in the presence of a solvent selected from dimethylformamide, chlorinated solvents and organic solvents containing an ester and ether group in the molecule.

Inventors: COZZI, ENNIO, FEDERICI, FRANCO, PIN, GIORGIO, TROVATI, ALDO
Applicants: AUSIMONT S.P.A.
Application year: 1987
Main classification: C08G18
IPC codes: C09D175, C08G18, C09D5