PROCESS FOR PROTECTING AND CONSOLIDATING STONY MATERIALS

Abstract: The surfaces of stony materials, tiles, cement conglomerates and related manufactured articles are protected from the action of atmospheric agents and pollutants by applying onto said surfaces a protective material comprising a mixture of a vinylidene fluoride homo- or copolymer con­ taining 55-100% by moles of vinylidene fluoride, 0-45% by moles of hexafluoropropene and 0-30% by moles of tetrafluoro­ ethylene and an aqueous microemulsion or emulsion of certain (per)fluoropolyethers. Said mixtures are applied by conven­ tional methods.

Description: The present invention relates to a process for consolidating and protecting stony materials, tiles, cement conglomerates and articles manufactured therefrom which on their outer sides are exposed to the degrading action of atmospheric agents and pollutants. As it is known, the decay of building materials, in particular marble, sandstones and tiles, and of (e.g. the artistic and decorative) articles manufactured from such materials, is caused by two different kinds of phenomena, i.e. chemical phenomena and physical phenomena, both occurring in the presence of water. A physical phenomenon acting on all building materials is the alternating freezing and thawing of the water absorbed in the pores of the materials, which leads to a variation of the specific volume and to tensions which often cause fractures and/or loss of cohesion or in any case a separation of the individual particles forming the material. Another physical phenomenon is the dissolution in water of limestone which is an essential component of marbles and a binder in stones, with consequent loss of the cohesion between the granules. Equally important for the decay of the above materials and manufactured articles exposed to the open atmosphere is a combination of chemical phenomena. These phenomena substantially consist in the attack of the carbonated parts of the material or of the manufactured article by the pollutants present in the air (for example carbon dioxide, sulphur dioxide, nitrogen oxide). Said pollutants react with the material in the presence of water and their concentration in the rain is particularly high at the beginning of the precipitation. It is also known that in order to eliminate or to at least significantly reduce the above drawbacks it is necessary to substantially reduce the entering and penetration rate of water into and inside, respectively, the material to be protected. To achieve this object, chemical substances which possess a twofold property, i.e. a hydrophobic and consolidating action, are usually applied onto the outer surface of the material to be protected. In order to exert the desired action and not to cause, at the same time, collateral decay phenomena or any undesired side effects, the consolidating/protective substance must possess the following essential characteristics: 1. Ability to restore the cohesion between the particles of the outermost layer of the decayed material and the underlying integral part. 2. Ability to impart an adequate mechanical strength to the outermost layer thus consolidated. 3. Ability to retain elasticity in the consolidated outermost layer in order to prevent the formation - as occurs with other products - of a rigid surface layer having mechanical characteristics different from the ones of the substrate. 4. Chemical inertness towards the material to be protected/consolidated. 5. Low volatility. 6. Stability with respect to the action of atmospheric agents, sunlight and heat. 7. No effect on the colour of the treated material. 8. Ability to retain its own solubility characteristics for a long time in order to secure the reversibility of the treatment. As is known, for the consolidation and protection of stony materials, film-forming substances such as glues, drying oils, resins and polymeric materials are often used. References to the use of said substances are contained in the book by Amoroso and Fassina "Stone Decay and Conservation", Elsewier Ed., Amsterdam 1983. Among said substances, none of which is completely satisfactory for the above purposes, the most commonly used are the following: polyethylene glycols and their methylethers, which, however, are highly soluble in water, wherefore the use thereof is limited to the protection of articles not used outdoors; polyvinyl acetate and polyvinyl alcohol, which exhibit the drawback of being sensitive to water in which the former, moreover, hydrolyses under liberation of acetic acid; polymethylmethacrylate and acrylic resins in general, which, however, tend to yellow in the course of time and are not capable of providing a complete protection from SO₂ contained in the atmosphere, while the thermosetting acrylic copolymers, having better characteristics, exhibit the drawback that their application is irreversible; silicone resins, which, however, besides releasing methanol under certain circumstances, crosslink and form a product which can not be removed anymore; epoxy resins, which tend to yellow and, because of their structure (thermosetting resins), make it difficult or impossible to carry out reversible treatments; polyester resins, which are sensitive towards water (tendency to saponify) and also tend to crosslink, wherefore they lose their reversibility characteristics. Said products which are utilized in the treatment of stony and cement articles, besides in general not exhibiting, as explained above, stability to chemical and physical attacks, drastically reduce the permeability of the treated surface for air and for water vapour. As consequence thereof, very pronounced alteration phenomena occur in the manufactured articles underneath the impermeable film when they are located outdoors owing to the condensation water inside the materials. The use of perfluoropolyethers applied in the form of solutions in chlorofluorocarbons, as described in EP-A-59100 and 192493, or in the form of aqueous microemulsions, as described in EP-A-337311, for the above purposes has solved the problem concerning the protection. Said compounds, due to their physical nature (liquids), cannot however, exert any consolidating action. The use of vinylidene fluoride copolymers as described in EP-A-192494 has solved tho problem concerning the consolidation, but involves the use of considerable amounts of inflammable solvent. There has now, unexpectedly, been found a method of consolidating and protecting stony materials, marbles, sandstones, tiles, cement conglomerates and articles manufactured from said materials, from the degrading action of polluting and atmospheric agents, which method is free of the drawbacks of the above methods. Said method, which is the object of the present invention, comprises the use, as protecting material, of an aqueous mixture obtained from: a) an aqueous dispersion of a vinylidene fluoride homopolymer or copolymer comprising from about 55 to 100% by moles, and preferably up to about 80% by moles, of vinylidene fluoride, from 0 to about 30% by moles of tetrafluoroethylene and from 0 to about 45% by moles of hexafluoropropene, and b) an aqueous emulsion or microemulsion of a (per)fluoropolyether comprising sequences of one or more statistically distributed fluorooxyalkylene units of the following formulae: (CF₂CF₂O), (CF₂O), (CF₂CF₂CF₂O), (CF₂CF₂CH₂O); and having (preferably C₁₋₃) perfluoroalkyl and/or functional end groups. The aqueous mixture obtained from a) + b) contains vinylidene fluoride (homo- or co)polymer and (per)fluoropolyether in a total amount generally ranging from about 2% to about 40%, and preferably from about 15% to about 40% by weight, based on the total weight. The weight ratio between vinylidene fluoride (homo- or co)polymer and (per)fluoropolyether in the aqueous mixture generally ranges from about 20:1 to about 1:20, more usually from about 10:1 to about 1:10, and preferably from about 5:1 to about 1:5. "(Per)fluoropolyether functional group" means a group which is capable of forming a chemical and/or physical bond with the material to be protected and is selected, e.g., from the ones which are capable of forming coordinative or charge transfer bonds with said material. Preferred functional groups are: -COOH, -CH₂OH, polyoxyalkylene-OH, -C(OH)₂-CF₃, -CONR²R³, -CONHR⁹, -CONH₂, -COOR⁴ and quaternary ammonium groups, wherein R² and R³, the same or different from each other, are alkyl groups usually containing 1 to 8, preferably 1 to 4, carbon atoms; R⁴ represents an alkyl group usually containing 1 to 8, preferably 1 to 4, carbon atoms or a (preferably C₆₋₁₂-)aromatic or (preferably C₇₋₁₃-)alkyl-aromatic group, such as phenyl, benzyl and phenethyl; and R⁹ represents and alkyl group usually containing 1 to 8, and preferably 1 to 4, carbon atoms. The end group -COOH preferably is salified. The quaternary ammonium group preferably is a -COONR⁵R⁶R⁷R⁸ group, wherein R⁵, R⁶, R⁷ and R⁸ represent alkyl groups usually containing a total of 4 to 32 carbon atoms (i.e. R⁵ to R⁸ together). Examples of the above alkyl groups are methyl, ethyl, n-and i-propyl, butyl, hexyl, 2-ethylhexyl and octyl. It is also possible to utilize as starting products (per)fluoropolyethers with -COCF₃, -COF or -SO₂F end groups which during the preparation of the (micro)emulsion hydrolyse to -C(OH)₂-CF₃, -COOH and -SO₃H groups and are then salified. The average molecular weight of the (per)fluoropolyether chain ranges from about 1,000 to about 10,000, preferably from about 2,000 to about 6,000. The (per)fluoropolyethers utilized in the present invention may contain, besides the above functional groups, perfluoroalkyl end groups, e.g., CF₃, C₂F₅, and/or C₃F₇. Preferred (per)fluoropolyethers to be utilized in the present invention are those which belong to the following classes: (1) having a random distribution of the perfluorooxyalkylene units; (2) R f O(CF₂CF₂O) n (CF₂O) m R′ f having a random distribution of the perfluorooxyalkylene units; (3) having a random distribution of the perfluorooxyalkylene units; (4) (5) R f O(CF₂CF₂O) n R′ f (6) R f O(CF₂CF₂CF₂O) n R′ f or R f O(CH₂CF₂CF₂O) n R′ f ; wherein m, n, o and p have values such that the average molecular weight of the corresponding chains is in the range given above. R f and R′ f in formulae (1) to (6) are perfluoroalkyl groups, preferably having 1 to 3 carbon atoms and/or end groups containing functional groups of the type defined hereinbefore. As it is known, the functional end groups of functionalized perfluoropolyethers are bound to the perfluoropolyether chain by a divalent linking group, particularly by a group, wherein X = F or CF₃. Other divalent linking groups or radicals are described in e.g. US-A-4,094,911. Perfluoropolyethers of class (1) are commercially available under the trademark Fomblin® Y, the ones of class (2) under the trademark Fomblin® Z, both of which being produced by Montedison. Products of class (4) are commercially known as Krytox® (Du Pont). The products of class (5) are described in US-A-4,523,039; the ones of class (6) are described in EP-A-148,482. The products of class (3) may be prepared according to US-A-3,665,041. Useful products also are the perfluoropolyethers described in US-A-4,523,039 or in J.Am.Chem.Soc.1985, 107, 1195-1201. The products of classes (1), (2) and (3) which have been obtained by photochemical oxidation processes may be employed as crude products of the photooxidation process, which products contain peroxy groups -OO- in the chain, inserted between the (per)fluorooxyalkylene units. Perfluoropolyethers also suitable for use in the present invention are the ones described in EP-A-244839, which polyethers comprise functional groups of the type described hereinbefore, or perfluoroalkyl end groups. In the preparation of the aqueous mixture to be employed according to the present invention it is particularly advantageous to use the (per)fluoropolyether in the form of an aqueous microemulsion. The microemulsions for use in the present invention are obtainable according to, e.g., the method described in EP-A-250766. Essential ingredient of said microemulsions is an ionic or non-ionic fluorinated surfactant and/or surfactant selected from hydrogenated (non-fluorinated) alcohols containing 1 to 12, preferably 1 to 6, carbon atoms and fluoroalkanols. In particular, the following ones may be mentioned as fluorinated surfactants of the ionic or non-ionic type: (a) perfluorocarboxylic acids containing from 5 to 11 carbon atoms and salts thereof; (b) perfluorosulphonic acids having from 5 to 11 carbon atoms and salts thereof; (c) the non-ionic surfactants described in EP-A-51,526, consisting of a perfluoroalkyl chain and a hydrophilic polyoxyalkylene terminus; (d) mono- and di-carboxylic acids derived from perfluoropolyethers and salts thereof; (e) non-ionic surfactants consisting of a perfluoropolyether chain linked to a polyoxyalkylene chain; (f) perfluorinated cationic surfactants or surfactants derived from perfluoropolyethers having 1, 2 or 3 hydrophobic chains. The amount of protective agent ((per)fluoropolyether plus homo- and/or co-polymer) to be used varies as a function of the nature of the material to be treated, in particular as a function of its porosity. The amount of agent generally ranges from about 4 g/m² (for low-porosity materials to be treated) to about 200 g/m² (for high-porosity materials) and, more usually, from 7 to 100 g/m². The vinylidene fluoride homopolymers and copolymers with the above monomers are well known. They are described, inter alia, in GB-A-888,765; Kirk Othmer "Encyclopedia of Chemical Technology" vol.11, page 64, 1980; Polymer Bulletin (1984), vol.11, page 35; J. of Polymer Sci. - Polymer Physics Edition, vol.22, page 357 (1984). The average molecular weight of the vinylidene fluoride homo- and copolymers generally ranges from about 10,000 to about 1,000,000. The aqueous fluoropolymer dispersion can directly be prepared by polymerization, as is described in Kirk Othmer (Vol.8, page 500), operating in the presence of surfactants. The latex can then be stabilized with stabilizers for polymer latices such as, for example, TRITON® X 100. The protective aqueous mixture to be used according to the present invention, obtained by mixing the above ingredients (a) and (b), allows to obtain,at the same time and with only one protective product, the consolidating effect caused by the CH₂=CF₂ homo- or copolymer and the protective effect against atmospheric agents, evidenced by the low water absorption of the treated building material, caused by the (per)fluoropolyether. Another important advantage is that both of the above protective agents are used in the form of aqueous dispersions, thus avoiding the use of organic solvents. The aqueous mixture may be applied onto the surface of the material to be treated by means of any conventional technique, for example by means of a brush, a spray method and by immersion. The amount of product to be applied per surface unit of the material to be consolidated/protected is a function of the physical characteristics of the surface such as, e.g., porosity and state of disaggregation of the material. The higher the porosity and the state of disaggregation, the higher are the amounts of protective/consolidating mixture to be applied and the ratio polymer/(per)fluoropolyether. The invention is illustrated by the following examples, which are given for merely illustrative and not limitative purposes. Utilized products A. VDF/TFE/PFP terpolymer (molar ratio: 65/15/20) in the form of an aqueous dispersion, prepared by polymerization in the presence of ammonium persulphate according to the method described in Kirk Othmer etc., and stabilized with 2% of Triton® X 100. The aqueous dispersion contained 30% by weight of terpolymer. B. Microemulsion, prepared according to EP-A-337311 (example 5), having the following composition (by weight): crude perfluoropolyether (PFPE) 21.3 % fluorinated surfactants 14.6 % aqueous phase 64.1 % C. Microemulsion, prepared in a similar manner as in the case of Microemulsion B, but having the following composition: crude perfluoropolyether (PFPE) 28.1 % fluorinated surfactants 9.6 % isopropanol 16.1 % aqueous phase 46.2 % D. MIX 1: a mixture of B and A having a weight ratio of terpolymer to PFPE of 21/100. E. MIX 2: a mixture of B and A having a weight ratio of terpolymer to PFPE of 43/100. F. MIX 3: a mixture of B and A having a weight ratio of terpolymer to PFPE of 100/11. G. MIX 4: a mixture of C and A having a weight ratio of terpolymer to PFPE of 233/100. TESTS The effectiveness of protection was evaluated according to the pipette method described in EP-A-59100. The aggregation effectiveness or consolidating power was determined according to the method described in EP-A-192494. UTILIZED MATERIALS Vicenza Stone: biocalcarenite having a porosity of about 30%; Siena Brick: having a porosity of about 40%; Lecce Stone: calcareous rock of the group of biocalcarenites, having a porosity of about 35%. EXAMPLE 1 (Table 1) A total of 5 specimens (size: 5x5x5 cm) of Vicenza Stone was employed; one of them was not protected, while on the others the products indicated in the table were applied by means of a brush. From a comparison of tests 3 and 5 (reference tests) on the one hand and tests 2 and 4 on the other hand it is apparent that with the total product content being the same the presence of the terpolymer significantly increases the degree of protection. EXAMPLE 2 (Table 2) A total of 5 specimens as described above was treated, but the products employed were different; specimen 1 was not treated. From a comparison of tests 3 and 5 (reference tests) and tests 2 and 4 it is apparent that with the total product content being the same the presence of PFPE significantly increases the degree of protection. EXAMPLE 3 (Table 3) A total of 4 specimens (2, 3, 4 and 5) of Vicenza Stone was treated with different amounts of MIX 1; specimen 1, not treated, served as control. The reported results show that the protective effectiveness increases as the total amount of applied product increases, as expected. EXAMPLE 4 (Table 4) A total of 4 specimens (2, 3, 4 and 5) of Vicenza Stone was treated with different amounts of MIX 2; specimen 1, not treated, served as control. The reported results show that the protective effectiveness increases as the total amount of applied product increases, as expected. TABLE 5 (Table 5) Two specimens (2 and 3) of Siena Brick were treated. One of them was treated with microemulsion B and the other with MIX 3 (mixture of B and of terpolymer A). Specimen 1 was not treated. From a comparison of test 2 (reference test) and test 3 it is apparent that with the total amount of product being the same the presence of terpolymer remarkably increases the degree of protection. EXAMPLE 6 (Table 6) The weight loss of 6 specimens (size: 5x5x5 cm) of Lecce Stone, artificially aged by 300 cycles of frosting and defrosting (as described in Acta of the Meeting "Manutenzione e conservazione del costruito" - Bressanone (Italy) 1986; pages 527-541) was measured. Specimen 1 was not treated, while the other specimens were treated with terpolymer A, with MIX 4 in two different amounts and with microemulsion C. A comparison of test 4 (reference test) and test 2 evidences the aggregating effect attributable to the combination of PFPE and terpolymer. A comparison of test 2 and tests 5 and 6 shows that the sum of the effects of the two individual components (PFPE and terpolymer) is smaller than the effect thereof when mixed with each other.

Claims: A process for protecting marble, stones, tiles, cement, gypsums, wood and other related materials utilized in particular in the building industry from the destructive action of atmospheric agents and pollutants, by applying onto said materials a protective agent comprising a mixture of: a) an aqueous dispersion of a vinylidene fluoride homo-or copolymer comprising, by moles, from about 55 to 100% of CH₂=CF₂, from 0 to about 30% of C₂F₄ and from 0 to about 45% of C₃F₆; and b) an aqueous emulsion or microemulsion of a (per)fluoropolyether comprising sequences of one or more of the following fluorooxyalkylene units: (CF₂CF₂O), (CF₂O), (CF₂CF₂CF₂O), (CF₂CF₂CH₂O); having an average molecular weight of from about 1,000 to about 10,000 and having perfluoroalkyl end groups and/or end groups containing functional groups capable of forming physical and/or chemical bonds, particularly of the coordinative or charge-transfer type, with the material to be protected. The process of claim 1, wherein the (per)fluoropolyether has functional groups selected from -COOH, -CH₂OH, -polyoxyalkylene-OH, quaternary ammonium groups, -C(OH)₂-CF₃, -CONR²R³, -CONHR⁹, -CONH₂ and -COOR⁴, wherein R² and R³, the same or different from each other, represent alkyl groups; R⁴ is an alkyl, aromatic or alkyl-aromatic group and R⁹ is an alkyl group. The process of any of claims 1 and 2, wherein a vinylidene fluoride copolymer containing about 65% by moles of CH₂=CF₂, about 15% by moles of C₂F₄ and about 20% by moles of C₃F₆ is used. The process of any one of claims 1 to 3, wherein use is made of one or more (per)fluoropolyethers of the following general formulae: (a) b) R f O(CF₂CF₂O) n (CF₂O) m R′ f (c) (d) e) R f O(CF₂CF₂O) n R′ f f) R f O(CF₂CF₂CF₂O) n R′ f or R f O(CH₂CF₂CF₂O) n R′ f wherein n, m, p and o have values such that the molecular weight is within the range indicated in claim 1 and R f and R′ f are C₁₋₃-perfluoroalkyl and/or end groups containing functional groups of the type defined in claims 1 and 2. The process of any one of claims 1 to 4, wherein the (per)fluoropolyether is employed in the form of an aqueous microemulsion. A composition for protecting marble, stones, tiles, cement, gypsum, wood and related materials, comprising a mixture of a) an aqueous dispersion of a vinylidene fluoride homo- or copolymer and b) an aqueous emulsion or microemulsion of a (per)fluoropolyether as defined in any one of claims 1 to 4. The composition of claim 6, wherein the weight ratio of vinylidene fluoride polymer to (per)fluoropolyether ranges from 1:20 to 20:1, particularly from 1:5 to 5:1. The composition of any one of claims 6 and 7, wherein the total amount of vinylidene fluoride polymer and (per)fluorpolyether ranges from 2 to 40, particularly 15 to 40% by weight, based on the total weight of the composition.

Inventors: INGOGLIA, DESIDERATA, LENTI, DARIA, MOGGI, GIOVANNI
Applicants: AUSIMONT S.P.A.
Application year: 1989
Main classification: C04B41
IPC codes: B27K3, C08L27, C08L71, C04B41