USE OF PERFLUOROPOLYETHER DERIVATIVES FOR PROTECTING BUILDING MATERIALS FROM ATMOSPHERICAL AGENTS

Abstract: A process for protecting marble, stones, tiles, cement and similar materials against the action of atmospherical and polluting agents, by applying a perfluoropolyether onto the surface of the substrate to be protected, said perfluoro­ polyether having at one or at both ends functional groups capable of acting as anchoring agents for the substrate.

Description: It is known that perfluoropolyethers impart water-repellent properties to the surface of materials onto which they are applied. Furthermore, the perfluoropolyethers exhibit a high Bunsen coefficient for the gas components of air and therefore permit the passage of air through the surface of the treated materials. These properties render the perfluoropolyethers interesting as liquids suited to protect stoneworks and, in general, articles constructed of stones, marble, cement, tiles, gypsum or wood, from atmospherical agents. Such action is all the more appreciated as the protection is reversible, since it is due to the deposition of a thin liquid film on the surface of the article, such film being removable, if necessary. Furthermore, the low refractive index of the perfluoropolyethers, which corresponds to a value of about 1.3 measured at 20°C with the light of a sodium lamp, causes the manufactured article to retain its original appearance, avoiding optical interference phenomena which lead to color alterations. The above-mentioned use of the perfluoropolyethers has been described in Applicant's IT-A-19 933 A/81. The perfluoropolyethers disclosed in this application are of the type with "inert" end groups, i.e. perfluoroalkyl groups. It has been observed that the porosity of the material to be protected leads to a phenomenon consisting in a slow absorption of the type of perfluoropolyether utilized so far, such phenomenon causing a more or less slow migration (as a function of the type of porosity of the material) of the protecting liquid towards the innermost layers of the article. The consequence thereof is a lower effectiveness in the protection of the outermost areas of the treated article. While on particular materials, such as for example sandstones, the migration towards the inside is sufficiently slow so as to provide sufficient protection over a long period of time, in other cases (for example with tiles) this phenomenon impairs the surface protection, so that further surface treatments become necessary after some time, it being understood that the protection of the underlying layers remains sufficient to considerably slow down the absorption phenomenon. It has now been found that it is possible to obtain a permanent protective action of the above-mentioned materials, if perfluoropolyether derivatives with functional end groups capable of forming chemical and/or physical bonds with the substrate are utilized as protecting agents or as coadjuvants. Such functional end groups are fixed to the substrate to be protected, thus reducing the mobility of the perfluoropolyether and increasing the duration of the protective effect on the treated surface. Optionally, depending on the type of bond formed with the substrate it is possible to remove the protecting agent later, if so desired, by solubilization in a proper solvent, such as e.g. mixtures of 1,1,2-trichloro-1,1,2-trifluoroethane and acetone (or methanol), in a ratio of from 1:1 to 4:1 by volume. The other characteristics of use of these functionalized perfluoropolyether fluids remain analogous to those of the perfluoropolyethers disclosed in IT-A-19 933 A/81 filed on February 24,1981. In particular, such fluids exhibit: 1) capability of forming a thin protective layer having a low volatility and high resistance to the most aggressive chemical agents, such as e.g. acids and alkali; this results in a high resistance to the atmosphere and to the pollutants thereof; 2) high thermal stability and retaining of the fluid state even at low ambient temperatures; 3) low surface tension; 4) high water-repellency; 5) high oil-repellency; 6) permeability to air and water vapour; 7) resistance to light radiation and in particular to U.V. radiation. In particular, the perfluoropolyethers useful for the permanent protective action belong to one of the following groups: I) Rf-O(C₃F₆O) m (CFXO) n -CFX-Y-Zp wherein Rf is a perfluoroalkyl group with 1 to 3 carbon atoms; (C₃F₆O) and (CFXO) are oxyperfluoroalkylene units statistically distributed along the chain, and X = F or CF₃; m and n are integers or n = O (m is always ≠ O) and m/n varies from 5 to 40 when n ≠ 0; p may be 1 or 2; the mean molecular weight varies from 500 to 10 000 (preferably from 900 to 6000); Y is a divalent or trivalent organic linking radical; Z is a functional group capable of forming a chemical and/or physical bond with the material to be protected and is selected from: Z 1) a non-aromatic, non-fluorinated organic radical, free of active hydrogen atoms, containing two or more electron pair-donor heteroatoms, or an aromatic radical, optionally containing heteroatoms, capable of forming coordinative bonds or charge transfer bonds, thus causing various kinds of adsorption phenomena on the substrate; Z 2) -CONR²R³, -COOR R is H or an alkyl group with 1 to 8 carbon atoms, an aromatic or alkylaromatic group such as benzyl, the aromatic groups optionally containing, as substituents, alkyl or polyethoxy groups, R² and R³ are H or an alkyl group containing 1 to 8 carbon atoms or a substitued phenyl group; with t ranging from 0 to 2 and R being the same as defined hereinbefore; Z 3) a group containing ethylenic unsaturations of the polymerizable type; Z 4) a radical of class Z 1) containing one ore more of the substituents indicated in class Z 2). II) AO-(C₂F₄O) p (CF₂O) q -A' where unit (C₂F₄O) and unit (CF₂O) are statistically distributed along the chain; p and q are integers such that p/q may vary from 5 to 0.3, preferably from 2.5 to 0.7; A' is -CFX-Y-Zp; A is A' or perfluoroalkyl with 1 to 3 carbon atoms; p, X, Y and Z are the same as defined hereinabove; the mean molecular weight varies from 1000 to 20000 (preferably from 1800 to 8000). III) Perfluoropolyether compounds containing the units (C₃F₆O), (C₂F₄O) and (CFXO) statistically distributed along the chain with the indicated end groups A and A' as specified hereinbefore, and having a molecular weight ranging from 500 to 20000. IV)Difunctional or monofunctional perfluoropolyether compounds having functional end groups comprising the units: where R₄ and R₅ may be the same or different from each other and are selected from H, Cl, F, said units being statistically distributed along the polymer chain; having a mean molecular weight ranging from 1500 to 8000; and where a fluorine atom of the perfluoromethylene units may be substituted by H, Cl or by perfluoroalkoxy or perfluoroalkyl. The above-identified end groups Z of class Z 1) are described in detail in IT-A-21480 A/84 and 21481 A/84. Those of class Z 3) are preferably selected from methacrylic, acrylic, cinnamic, vinyl, allyl, vinylether or allylether groups. Group Y may be for example -CH₂O-, -CH₂-O-CH₂-, -CH₂(OCH₂CH₂) g - (g being an integer from 1 to 3), -CF₂-, -CF₂O-, -CH₂-, -CONR-, -COO-, -COS-, -CO-, -CH₂NR-, -CH₂S-, where R is the same as defined hereinabove. Other linking groups Y are described in US-A-4 094 911 as radicals X or Y. The starting compounds for obtaining monofunctional perfluoropolyethers of class IV are for example: for obtaining the difunctional perfluoropolyethers they are for example: in which R f and R' f are monovalent and divalent fluoroalkyl radicals, respectively. In the above compounds, end group COF can be converted for example to end groups Y-Z indicated in classes Z 1) or Z 2). The functionalized products of class IV) may be prepared according to the methods specified in EP-A-148 482. It is understood that the difunctional products of classes II, III and IV indicated hereinabove can be also utilized in the form of their polycondensation products to provide, for example, polyurethanes, polyureas, polyesters, polyamides, polyethers, polyimides or polyamino acids. When starting from a difunctional product with end groups -OH, a diisocyanate is used, or vice-versa. The polycondensation reaction can be carried out by using the fluorinated difunctional products of the invention, or a difunctional compound of the invention and a hydrogenated coreactant. In the like manner the other polycondensation products are obtained as is well known in the art and described in US-A-4 080 319 for the polyamides, in US-A-3 876 617 for the polyamides and, in general, in US-A-3 810 874. If end groups Z of class Z 3) are utilized, then it is possible to use both monofunctional and difunctional products of classes I, II, III, IV. The utilization of the polymeric products is particularly suited when a consolidating effect for the substrate is to be obtained. It is also possible to use copolymers obtained starting from the fluorinated monomers of the invention with hydrogenated coreactants, or vice-versa, as is stated for the polymers obtained by polycondensation. These polymeric products can be applied to the substrate to be protected in the form of solutions, if the polymeric products are soluble (linear polymers). Otherwise, it is possible to carry out a polymerization on the substrate starting from the monomeric procuts, optionally in solution. The compounds of classes I, II, III and IV can be used as such or dissolved in fluorocarbons or fluorochlorocarbons having a boiling point preferably not higher than 80°C. Furthermore they can be used in admixture with perfluoropolyethers with end groups of the inert type, having one of the following structures V, VI, VII: V) Rf-O-(C₃F₆O) m (CFXO) n -Rf' where (C₃F₆O) and (CFXO) are units statistically distributed along the chain; Rf' may be like or different from Rf and both are selected from CF₃, C₂F₅ and C₃F₇; X = F or CF₃; m and n are integers; when n = 0, Rf and Rf' are C₂F₅ or C₃F₇; when n ≠ O, the m/n ratio varies from 5 to 40; the mean molecular weight varies from 4000 to 10000. VI) CF₃-(C₂F₄O) p (CF₂O) q CF₃ where units (C₂F₄O) and (CF₂O) are statistically distributed along the chain and p and q are the same as defined hereinabove; the mean molecular weight varies from 4000 to 16000. VII) A perfluoropolyether containing repeating units: -(CF₂CF₂CF₂O)- having a molecular weight ranging from 4000 to 16000, the end groups being a perfluoroalkyl group or a perfluoroaryl group. Such products can be prepared, for example, according to the method of EP-A-148 482. The repeating units of class VII may also contain, instead of F, perfluoroalkyl or perfluoroalkoxy groups, as indicated above for class IV. The weight ratio between the compounds with functional end groups of type I, II, III or IV and the compounds with neutral end groups of type V, VI, VII expressed as I+II+III+IV/V+VI+VII is equal to or higher than 0.01. It is also possible to use as inert perfluoropolyethers, the corresponding copolymers of class III. The application of products I, II, III and IV, optionally in the presence of products V, VI and VII, is preferably accomplished in a solution of 1,1,2-trifluorotrichloroethane containing 50 to 80 % by weight of the perfluoropolyether products. It can be carried out by spraying an atomised liquid jet with or without compressed air, or by other appropriate means. By the process of the present invention it is possible to obtain a better protection of works and articles made of stones, marble, cement, gypsum and wood as compared to the use of perfluoropolyethers as described in IT-A-19933 A/81. Such better protection is achieved by the use of products having a telomer structure containing a perfluoropolyether chain similar to the one described in the above-cited patent application and having functional end groups capable of exerting an anchoring action on the surface of the manufactured article, thus rendering the surface protection more stable in time. The amount of perfluoropolyether protective agent to be used is very different depending on the nature of the material to be treated, in particular on its porosity. The amounts may be even lower than 10 g/m² for very compact materials (carrara marble) and may increase up to 300 g/m² and above for very porous materials. The following examples are given for merely illustrative purposes and are not to be considered as a limitation of the possible embodiments when mixtures with perfluoropolyethers having neutral (inert) end groups are utilized. EXAMPLE 1 There were utilized two test pieces of Carrara marble having the same composition, a porosity lower than 1 % and a cubic shape with one side measuring 50 mm. One of the testpieces was treated on its surface with a derivative of a perfluoropolyether of type II provided with piperonyl end groups linked to the perfluoropolyether chain through radical -CH₂O- and X in the group -CFX- was equal to F, having a mean molecular weight of 2300, and prepared according to example 1 of IT-A-21481 A/84. The piperonyl derivative of the perfluoropolyether was applied as a 5 % solution in 1,1,2-trichlorotrifluoroethane by means of a compressed-air sprayer so as to deposit an amount of protective fluid equal to 30 g/m² on the surface of the test piece. The amount of water absorbed on the two test pieces was measured after seven days. This measurement was effected by contacting a face of each test piece with an apparatus consisting of a glass cylinder filled with water and connected to a graduated microburette which permitted to measure the amount of water absorbed by the contact surface of the test piece. Said apparatus is described in more detail in the document published by the group Unesco-Rilem PEM, No. 78/182. The reading of the absorbed water was made at prefixed intervals of time and the read magnitude is expressed in microliters/cm² of surface. In the treated test piece, the water absorbed per cm² was practically equal to zero up to 30 minutes; in the non-treated test piece, the absorbed amounts were 1.5 after 10 minutes, 4.6 after 20 minutes and 7.6 after 30 minutes, respectively (expressed in microliters for cm²). From a comparison of the two test pieces it is apparent that the surface treatment with the protective agent strongly reduced the rate of water penetration into the stone. EXAMPLE 2 Two Carrara marble test pieces having a cubic shape with one side measuring 5 cm, were respectively treated, on one face only, with: test piece 1 perfluoropolyether "Fomblin®Met", manufactured by Montefluos S.p.A., Milan, in amounts equal to 30 g/m². "Fomblin®Met" is a mixture of 30 parts by weight of 1,1,2-trichlorotrifluoroethane and of 70 parts by weight of Fomblin®YR, which is in turn a perfluoropolyether having a mean molecular weight of about 6000 and a kinematic viscosity of about 1000 cSt at 25° C and neutral end groups, test piece 2 the piperonyl derivative of example 1 in an amount equal to 30 g/m². Both test pieces were allowed to rest having care to maintain the treated surfaces in a vertical position. 15, 30 and 60 days after the treatment a slice of 3 mm thickness was cut from each test piece, the cut having been carried out perpendicular (and therefore in the direction of the protective agent penetration) to the face treated with the protective agent. Onto the slices so obtained there was deposited a very thin layer of metallic gold by using a conventional high-vacuum metalization device type "Galileo" V201r/00440. Since the metalization occurs only in those areas which are free of the protective agent, such method evidences the penetration front of the protective agent. The penetration depths (expressed in mm) of the two protective agents on the test piece were as follows: The results of this example prove the higher residence (lower mobility) in the surface area of the stone material, of a protective agent functionalized according to the present invention as compared to a non-functionalized perfluoropolyether. EXAMPLE 3 Example 1 was repeated using, as a protective agent, a compound of class II with benzyl end groups C₆H₅-CH₂-, prepared as described in example 1, where instead of chloromethyl-1,2-methylenedioxybenzene, benzyl chloride was utilized, the linking group being -CH₂O-. The mean molecular weight was equal to 2200. The results obtained were analogous with those obtained in example 1 for the absorption of H₂O after 30 minutes. EXAMPLE 4 Example 2 was repeated using the same protective agent of example 3. The penetration depth (expressed in mm) of the protective agent into the test pieces was as follows:

Claims: A process for protecting marble, stones, tiles, cement, gypsum or wood and other similar materials employed in particular as building materials against the degradation caused by atmospheric agents and pollutants, which comprises applying onto the surface of said materials a protective agent comprising perfluoropolyethers which have functional end groups and are selected from one of the following groups: I) Rf-O-(C₃F₆O) m (CFXO) n -CFX-Y-Zp where Rf is a perfluoroalkyl group having 1 to 3 carbon atoms; (C₃F₆O) and (CFXO) are oxyperfluoroalkylene units statistically distributed along the chain, and X = F or CF₃; m and n are integers or n = 0 (m is always ≠ 0) and m/n varies from 5 to 40 when n ≠ 0; p may be 1 or 2, the mean molecular weight varies from 500 to 10000 (preferably from 900 to 6000); Y is a divalent or trivalent organic linking radical; Z is a functional group capable of forming a chemical and/or physical bond with the material to be protected and is selected from: Z1) a non-aromatic, non-fluorinated organic radical, free of active hydrogen atoms, containing two or more electron pair-donor heteroatoms, or an aromatic radical, optionally containing heteroatoms, capable of forming coordinative bonds or charge-transfer bonds, thus causing adsorption phenomena of various kinds on the substrate; Z2) -CONR²R³, -COOR wherein R is H or an alkyl group with 1 to 8 carbon atoms, an aromatic or alkylaromatic group such as benzyl, where the aromatic groups may contain, as substituents, alkyl or polyethoxy groups, R² and R³ are H or an alkyl group having 1 to 8 carbon atoms or a substituted phenyl group; with t ranging from 0 to 2, and R being the same as defined hereinabove; Z3) a group containing ethylenic unsaturations of the polymerizable type; Z4) a radical of class Z1) containing one or more substituents indicated in class Z2); II) AO-(C₂F₄O) p (CF₂O) q -A' where units (C₂F₄O) and (CF₂O) are statistically distributed along the chain; p and q are integers such that p/q may vary from 5 to 0.3, preferably from 2.5 to 0.7; A' = -CFX-Y-Z p ; A is A' or perfluoroalkyl having 1 to 3 carbon atoms; p, X, Y and Z are the same as defined hereinabove; the mean molecular weight varies from 1000 to 20000 (preferably from 1800 to 8000); III) perfluoropolyether compounds containing units (C₃F₆O), (C₂F₄O) and (CFXO) statistically distributed along the chain with the indicated end groups A and A' as specified hereinbefore, and having a molecular weight ranging from 500 to 20000; IV) difunctional or monofunctional perfluoropolyether compounds having functional end groups of the type Y-Z p as defined above and comprising the units: where R₄ and R₅ may be the same or different from each other and are selected from H, Cl, F, and where said units may be statistically distributed along the polymer chain; having a mean molecular weight ranging from 1500 to 8000; and where a fluorine-atom of the perfluoromethylene units can be substituted by H, Cl or by perfluoroalkoxy or perfluoroalkyl. The process according to claim 1, characterized in that the perfluoropolyether of general formulae I, II, III or IV is used in admixture with a perfluoropolyether having neutral end groups and belonging to one of the following classes: V) - Rf-O-(C₃F₆O) m (CFXO) n -Rf' where (C₃F₆O) and (CFXO) are units statistically distributed along the chain; Rf' may be like or unlike Rf and both consist of groups CF₃, C₂F₅, C₃F₇; X = F or CF₃; m and n are integers; when n = 0, Rf and Rf' are C₂F₅ or C₃F₇; when n ≠ 0, the m/n ratio varies from 5 to 40; the mean molecular weight varies from 4000 to 10000; VI) - CF₃-(C₂F₄O) p (CF₂O) q CF₃ where units (C₂F₄O) and (CF₂O) are statistically distributed along the chain and p and q are the same as defined hereinabove; the mean molecular weight ranges from 4000 to 16000; VII) a perfluoropolyether containing repeating units -(CF₂CF₂O)- having a molecular weight ranging from 4000 to 16000, the end groups being a perfluoroalkyl or perfluoroaryl group; the repeating units of class VII may also contain, instead of F, perfluoroalkyl or perfluoroalkoxy. The process according to claim 1, in which Y is selected from -CH₂O-, -CH₂-O-CH₂-, -CH₂(OCH₂CH₂) g - (with g being from -CH₂O-, -CH₂-O-CH₂- -CH₂(OCH₂CH₂) g - (with g being an integer from 1 to 3), -CF₂-, -CF₂O-, -CH₂-, -CONR-, -COO-, -COS-,, -CO-, -CH₂NR-, -CH₂S-, where R is the same as defined hereinabove. The process according to any one of claims 1-3, in which Z3) is selected from methacrylic, acrylic, cinnamic, vinyl, allyl, vinylether or allylether groups. The process according to claims 2-4, in which the weight ratio between perfluoropolyethers with functional end groups and perfluoropolyethers with neutral end groups is equal to or higher than 0.01.

Inventors: CAPORICCIO, GERARDO, DR., PASETTI, ADOLFO, PIACENTI, FRANCO, DR., STREPPAROLA, EZIO, DR.
Applicants: AUSIMONT S.P.A.
Application year: 1986
Main classification: C04B41
IPC codes: B27K5, C04B41