Use of perfluoropolyethers in the form of an aqueous microemulsion for protecting stony materials from atmospheric agents

Protecting marble, stone, tiles, cement, and similar materials utilized in the building industry from the action of atmospheric agents and pollutants, which comprises applying a perfluoropolyether having perfluoroalkyl end groups onto the surface of the article, said perfluoropolyether being in the form of an aqueous microemulsion.

DESCRIPTION OF THE INVENTION 
1. Field of the Invention 
It is known that perfluoropolyethers impart remarkable water-repellent and 
oil-repellent properties to the surface of materials onto which they are 
applied. 
Furthermore, perfluoropolyethers exhibit a high Bunsen coefficient toward 
the air-component gases, so that they permit a good passage of air through 
the surface of the treated materials. 
Thanks to these properties, perfluoropolyethers are interesting as liquids 
suitable for protecting masonry and building works and, in general, 
articles constructed in stone, marble, cement, tile, gypsum or wood. 
Furthermore, the low refractive index of perfluoropolyethers, which 
corresponds to a value of about 1.3 measured at 20.degree. C. with the 
light of a sodium-vapor lamp, causes the treated article to retain its 
original appearance, preventing interference optical phenomena which lead 
to color alterations. 
2. Background of the Invention 
The above utilization of perfluoropolyethers has already been described in 
an earlier Italian patent application No. 19,933 A/81. 
The systems described in patent application No. 19,933 A/81 comprise, as a 
solvent, a fluorocarbon or a chlorofluorocarbon. 
The application of said compounds to the substrate is preferably carried 
out by using 1,1,2-trifluorotrichloroethane solutions in admixture with 
other organic solvents containing from 50 to 80% by weight of 
perfluoropolyether products. The application is effected by means of 
atomized liquid jet spraying, either with or without compressed air, or by 
means of some other appropriate method. 
The amount of perfluoropolyether protective agent utilized is highly 
dependent on the porosity of the material to be treated, and varies from 
10 g/m.sup.2 to 300 g/m.sup.2 as the substrate proposity increases. 
The advantage, from the viewpoint of ecology and environmental protection, 
which would originate from the use of systems free from 
chlorofluorocarbons and, possibly, from the total absence of volatile 
organic solvents, is very evident. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, it has now, surprisingly, been 
discovered that it is possible to achieve this and further advantages in 
the protection of works and articles made of stone, marble, cement, gypsum 
and wood by using, instead of perfluoropolyethers as such or in 
fluorochlorocarbons, water-microemulsions of functional 
perfluoropolyethers having perfluoroalkyl end groups. 
The term "microemulsion" is generally used to designate products which are 
macroscopically composed of a single liquid transparent or opalescent and 
optically isotropic phase comprising two immiscible liquids and at least 
one surfactant, one of said two immiscible liquids being dispersed in the 
other in the form of droplets having diameters ranging from about 50 to 
about 2,000.ANG.. 
In principle, the presence of particles having greater or smaller sizes up 
to the molecular dispersion limit cannot be excluded. Furthermore, 
structures may be possible in which the two liquids are interdispersed as 
bicontinuous tridimensional, immiscible films, which are co-solubilized at 
a molecular level. 
Such products spontaneously form merely by mixing the components when the 
interface tension between the two immiscible liquids sinks to values close 
to zero and such values are indefinitely stable over a certain temperature 
range. 
Whenever used in the present description, the term "microemulsion" has a 
broader meaning, including also nonoptically isotropic systems (i.e., 
birefractive), characterized by a component orientation of the 
liquid-crystalline type. 
It is advantageous to have available microemulsions instead of emulsions 
because the former do not require a high dispersion energy for being 
prepared; moreover they are regenerable and indefinitely stable in the 
course of time, while emulsions must be prepared taking into account the 
order of addition of the components and supplying a high dispersion 
energy; furthermore, they exhibit a limited stability over time and when, 
due to aging, give rise to a phase separation, often they cannot be 
brought again to the starting emulsion state even by employing the high 
energy necessary for their preparation. 
The microemulsions utilized in the present invention may be of the 
oil-in-water type or water-in-oil type. Preferably they are of the 
oil-in-water (o/w) type, and consist, in the present case, of 
perfluoropolyether chain compounds having end groups composed of mixtures 
of products with different molecular weights, a perfluorinated surfactant 
and/or a co-surfactant such as an alkanol with 1-12 carbon atoms, and an 
aqueous phase optionally comprising an electrolyte and/or a water-soluble 
inorganic base. The microemulsions used according to the present invention 
may be obtained conforming to the procedures indicated in Italian patent 
applications No. 20,910 A/86 and 19,494 A/87. 
The perfluoropolyethers of the present invention are products which per se 
are well known in the technical and patent literature and are generally 
obtained as mixtures of compounds having the necessary perfluoropolyether 
structure and a molecular weight which is variable over a certain range. 
The perfluoropolyethers utilized in the present invention contain, besides 
the above-mentioned functional groups, perfluoroalkyl end groups, 
perferably with 1 to 3 carbon atoms. 
Preferably, the molecular weight of the perfluoropolyethers range from 500 
to 10,000, and still more preferably from 800 to 3,000. 
The perfluoropolyethers utilized in the present invention consist of 
fluorooxyalkylene units selected from the following: 
##STR1## 
and (CF.sub.2 CF.sub.2 CH.sub.2 O), and in particular belonging to one of 
the following classes: 
##STR2## 
with a random distribution of the perfluorooxyalkylene units, where m, n, 
p have such medium values as to meet the above-cited requirements 
concerning the mean molecular weight; where R.sub.f and R'.sub.f, alike or 
different from each other, are perfluoroalkyl end groups; 
(2) R.sub.f O(CF.sub.2 CF.sub.2 O).sub.n (CF.sub.2 O).sub.m R'.sub.f with a 
random distribution of the perfluorooxyalkylene units, where m, n have 
such values as to meet the above-said requirements; 
##STR3## 
where m, n, p, o have such values as to meet the abovesaid requirements; 
##STR4## 
where n has such a value as to meet the above-said requirements; 
(5) R.sub.f O(CF.sub.2 CF.sub.2 O).sub.n R'.sub.f where n has such a mean 
value as to meet the above-said requirements; 
(6) R.sub.f O(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.n R'.sub.f or R.sub.f 
O(CH.sub.2 CF.sub.2 CF.sub.2 O).sub.n R'.sub.f where n has such a value as 
to meet the above-said requirements. 
Perfluoropolyethers of class (1) are known under the tradename 
Fomblin.RTM.Y, those of class (2) under the tradename Fomblin.RTM.Z, all 
of them being produced by Montedison. Commercially known products of class 
(4) are Krytox.RTM. (DuPont). 
The products of class (5) are described in U.S. Pat. No. 4,523,039; those 
of class (6) are described in European patent EP 148,482 to Daikin. 
The products of class (3) are prepared according to U.S. Pat. No. 
3,665,041. The perfluoropolyethers described in U.S. Pat. No. 4,523,039 or 
in J. Am. Chem. Soc. 1985, 107, 1195-1201 are also useful. 
The microemulsions for use in the present invention are obtainable as 
described in Italian patent applications Nos. 20,910 A/86 and 19,494 A/87. 
Essential ingredient is an ionic or non-ionic fluorinated surfactant. 
In particular, the following may be cited: 
(a) perfluorocarboxylic acids with 5-11 carbon atoms and the salts thereof; 
(b) perfluorosulfonic acids with 5-11 carbon atoms and the salts thereof; 
(c) the non-ionic surfactants indicated in European patent application No. 
51,526 and consisting of a perfluoroalkyl chain and a hydrophilic 
polyoxyalkylene head; 
(d) monocarboxylic and bicarboxylic acids derived from perfluoropolyether 
and the 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. 
As a co-surfactant it is possible to use a hydrogenated alcohol having 1-12 
carbon atoms, preferably 1-6 carbon atoms, or a fluoroalkanol. 
The amount of perfluoropolyether protective agent to be used varies as a 
function of the nature of the material to be treated; in particular, it 
depends on its porosity. The total perfluoropolyether amount ranges from 7 
g/m.sup.2 for low-porosity materials to be protected, to 100 g/m.sup.2 for 
materials having a greater porosity.

EXAMPLES 
The following examples are given merely to illustrate present invention and 
are not to be considered as a limitation of the scope thereof. 
EXAMPLE 1 
Two rectangular asbestos cement test pieces (15.times.10 cm) were prepared. 
One of the two test pieces was used as a check while the other was 
brush-treated with a microemulsion prepared by adding to 3.78 g of a 
carboxylic acid having a mean equivalent weight of 580 and 1.62 g of a 
carboxylic acid having a mean equivalent weight of 361, both having a 
perfluoropolyether structure belonging to class (1) where R.sub.f is 
CF.sub.3 and R'.sub.f is CF.sub.2 COOH, 3 ml of an ammonia solution at 10% 
by weight of NH.sub.3, 101 ml of doubly distilled H.sub.2 O, 2.16 g of an 
alcohol having a mean molecular weight of 678 and a perfluoropolyether 
structure belonging to class (1), and 10.8 of a perfluoropolyether oil 
having a mean molecular weight of 600 and belonging to class (1) where 
R.sub.f is CF.sub.3 and R'.sub.f is CF.sub.2 CH.sub.2 OH. 
The system so obtained consisted of a single limpid phase, which was stable 
at 40.degree. C. and exhibited the following composition by weight: 
______________________________________ 
fluorinated surfactants 
4.4% 
aqueous phase 85.0% 
alcohol 1.8% 
oil 8.8%. 
______________________________________ 
The amount of total fluorinated components deposited on the test piece was 
7 g/m.sup.2. 
The protective efficiency was determined by means of water absorption tests 
on the test pieces before and after the treatment. Percent protective 
efficiency means the ratio of the difference of water absorbed before and 
after the treatment to the amount of water absorbed by the untreated 
material, multiplied by one hundred. 
The amount of water absorbed by a test piece was measured in accordance 
with the method proposed by UNESCO-RILEH (International Symposium on 
Deterioration and Protection of Stone Instruments, Paris, 5-9 June 1978, 
Vol. 5, Test II.4). 
The data obtained are indicated hereinbelow: 
______________________________________ 
Percent Protective 
Efficiency 
______________________________________ 
15 minutes 1 hour 10 days 
68.8% 64.0% 56.7% 
______________________________________ 
EXAMPLE 2 
A low porosity marble test piece was used as a check. The surface of a 
second test piece was brush-treated with a protective material consisting 
of a microemulsion prepared by adding to 3.78 g of carboxylic acid having 
a mean equivalent weight of 580 and to 1.62 g of a carboxylic acid having 
a mean equivalent weight of 361, both having a perfluoropolyether 
structure belonging to class (1) where R.sub.f is CF.sub.3 and R'.sub.f is 
CF.sub.2 COOH, 3 ml of an ammonia solution at 10% by weight of NH.sub.3, 
101 ml of doubly distilled H.sub.2 O, 2.16 g of an alcohol having a mean 
molecular weight of 678 and a perfluoropolyether structure belonging to 
class (1), and 10.8 g of a perfluoropolyether oil having a mean molecular 
weight of 600 and belonging to class (1) where R.sub.f is CF.sub.3 and 
R'.sub.f is CF.sub.2 CH.sub.2 OH. 
The system so obtained consisted of a single limpid phase, which was stable 
at 40.degree. C. and exhibited the following composition by weight: 
______________________________________ 
fluorinated surfactants 
4.4% 
aqueous phase 85.0% 
alcohol 1.8% 
oil 8.8%. 
______________________________________ 
The amount of total fluorinated components deposited on the test piece was 
equal to 18.7 g/m.sup.2. 
The percent protective efficiency measured after 1 hour proved to be equal 
to 40.7%. After 7 hours, such percent protective efficiency remained 
unchanged. 
EXAMPLE 3 
Two high-porosity marble test pieces were utilized. The first one was used 
as a check, while the second one was treated with a microemulsion prepared 
by adding to 3.78 g of a carboxylic acid having a mean equivalent weight 
of 580 and to 1.62 g of a carboxylic acid having a mean equivalent weight 
of 361, both having a perfluoropolyether structure belonging to class (1) 
where R.sub.f is CF.sub.3 and R'.sub.f is CF.sub.2 COOH, 3 ml of an 
ammonia solution at 10% by weight of NH.sub.3, 101 ml of doubly distilled 
H.sub.2 O, 2.16 g of an alcohol having a mean molecular weight of 678 and 
a perfluropolyether structure belonging to class (1) where R.sub.f is 
CF.sub.3 and R'.sub.f is CF.sub.2 CH.sub.2 OH, and 10.8 g of a 
perfluoropolyether oil having a mean molecular weight equal to 600 and 
belonging to class (1). 
The thus-obtained system consisted of a single limpid phase, which was 
stable at 40.degree. C. and exhibited the following composition by weight: 
______________________________________ 
fluorinated surfactants 
4.4% 
water phase 85.0% 
alcohol 1.8%. 
oil 8.8% 
______________________________________ 
The amount of total fluorinated components deposited on the test piece was 
17.4 g/m.sup.2. 
The percent protective efficiency after 1 hour was 79.3% and after 7 hours 
remained unchanged. 
Although the invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives and variations will be 
apparent to those skilled in the art in light of the foregoing 
description. Accordingly, the invention is intended to embrace all of the 
alternatives and variations that fall within the spirit and scope of the 
appended claims. The above references are hereby incorporated by reference 
.