Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2003-06-20
2004-08-10
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S421000, C428S540000, C427S393600
Reexamination Certificate
active
06773805
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns the application of substantially amorphous fluoropolymer compositions to stone in order to protect the stone from the deleterious effects of water and pollution. This invention is useful for the preservation of historic monuments, buildings, and sculptures and for the construction of weather and pollution resistant stone construction materials.
TECHNICAL BACKGROUND OF THE INVENTION
It has long been recognized that a combination of man-made and natural atmospheric conditions are having deleterious effects on stone structures including many monuments of considerable artistic and historical importance. A variety of efforts have been undertaken over the years to identify ways to protect and preserve these structures, but these efforts have met with only partial success. Most recently, a well-organized and concerted effort has been undertaken by Franco Piacenti and his coworkers, with sponsorship from the Target Project for the Cultural Heritage of the Consiglio Nazionale della Recerche of Rome, Italy, and represents the current state of the art.
The deleterious effects of water, in the form of both rainfall and condensation, are of primary concern, although organic pollutants are also of concern. For example, all building materials are subject to stress and concomitant cracking resulting from penetration by water followed by cycles of freezing and thawing. Also, water in combination with CO
2
, which occurs naturally, and nitrous and sulfurous gases, which are man-made pollutants, form acids which rapidly eat away at the stone.
A successful attack on the problem will necessitate some tradeoffs. While it is highly desirable to minimize the contact between water and stone, by achieving maximum water repellency, it is also necessary to provide high water vapor permeability in order to permit venting of that water which finds its way into the microstructure of the stone. Substances with high permeability to water vapor are often not those of the highest water repellency. High resistance to acid and abrasion are also of considerable importance. Furthermore, cost of materials is a factor in any practical application. And, for several reasons, the smaller the amount of material required to achieve the desired effect, the better.
There are other tradeoffs. For example, it is particularly desirable that the coating material coat but preferably not block the pores. To achieve this, a coating viscosity should be in a range which permits wetting of the pores via capillary action. High wetting is also required to ensure thorough and uniform coverage. However, the coating must be provided with sufficient adhesion to the outside surface upon which it is deposited that at least some amount will remain thereon.
Other requirements for such materials include chemical inertness, low volatility, photooxidative stability and thermal stability. There should also be sufficient solubility in environmentally friendly solvents for the purposes of both application and subsequent removal if warranted. The coating must also be clear and colorless, and remain so for its lifetime. In the current state of the art, the application solvent of choice is supercritical CO
2
, as described in Carbonell et al., WO 99/19080.
In a series of patents, U.S. Pat. No. 4,499,146, U.S. Pat. No. 4,746,550, U.S. Pat. No. 4,745,009, U.S. Pat. No. 4,902,538, Piacenti et al. disclose compositions based upon perfluoropolyethers having molecular weights in the range of 500-5000 for use in the protection of stone from the effects of water and atmospheric pollutants. In the art of Piacenti, excellent combinations of water repellency and water vapor permeability are achieved.
In U.S. Pat. No. 4,902,538, good results are achieved in compositions having highly crystalline particles of polytetrafluoroethylene and copolymers thereof intermixed with the perfluoropolyethers. However, when stone of porosity of greater than ca. 30% is treated, impractically high levels of coating material are required to achieve the desired coverage with the desired water repellency. Levels in the range of at least 150 g/m
2
are disclosed, more than 10 times the amount required for low-porosity marble. The effect of this high coating level on permeability is not disclosed. Its effect on cost, however, is clearly undesirable. Furthermore, use of highly crystalline polymers, such as polytetrafluoroethylene, is undesirable because, unless they are sintered at high temperatures, they will be too readily susceptible to removal from the treated surface by abrasion and erosion. Further still, they are not readily soluble in the delivery medium of choice, CO
2
, or any other desirable medium.
Also disclosed in the art in Piacenti et al., U.S. Pat. No. 4,764, 431, are copolymers of vinylidene fluoride which are less effective than the perfluoropolyethers.
Fluorinated acrylic polymers are disclosed by Ciardelli et al., Prog. in Org. Coatings, 32, 43-50 (1997). The polymers disclosed therein are characterized by hydrocarbon backbones and fluorinated pendant groups. These polymers exhibit similar functionality to the perfluoropolyethers.
Guidetti et al. disclose the use of polyfluorosubstantially amorphous fluoropolymers for protecting stone in “Polyfluorosubstantially amorphous fluoropolymers as stone protectives”, 7th International Congress on Deterioration and Conservation of Stone, 1053-62 (1992).
There is considerable incentive in the art to discover new materials which possess several of the above attributes desired for the application
SUMMARY OF THE INVENTION
The present invention provides a process for protecting stone comprising: contacting stone with a substantially amorphous fluoropolymer, comprising, repeat units of the formulas
wherein: Y is fluorine, hydrogen, chlorine, a perfluoroalkyl radical having 1-8 carbon atoms, or a perfluoroalkoxy radical having 1-8 carbon atoms, the radicals optionally substituted by one or more ether oxygens; R is hydrogen or —C(O)R
1
where R
1
is hydrocarbyl or substituted hydrocarbyl; with the proviso that the molar ratio of (I):(II) is in the range of 1:1 to 1:10.
DETAILED DESCRIPTION
For the purpose of the present invention, the term “stone” means a natural stone used in construction or sculpture (such as granite, marble, limestone, or sandstone) as well as tile, cement, brick, stucco, and the like.
The method of the present invention provides surprising benefits over the methods of the art. In the method of the present invention, a substantially amorphous fluoropolymer composition is employed as a coating agent for stone in order to provide high liquid moisture barrier, good moisture vapor permeability, and resistance to environmental pollutants. The non-fugitive, very low areal density coating formed on the stone surface is surprisingly effective over the materials of the art. Furthermore, the substantially amorphous fluoropolymer of the present invention is readily soluble in a variety of solvents by virtue of its amorphous nature, and is thereby both readily applied in the form of an environmentally friendly solution and readily removed by conventional solvents should that be deemed necessary after application. Further still, the highly desirable effects of the method of the present invention are achieved employing a substantially amorphous fluoropolymer in relatively small quantities in order to achieve the desired combination of water vapor permeability and liquid water resistance.
The polymers suitable for use in the present invention are substantially amorphous, in contrast to most fluorinated polymers in common use which are known to be moderately to highly crystalline. One of skill in the art will appreciate that the degree of polymer crystallinity which can be tolerated in a given situation will depend upon the specific polymer structure, solvents, other adjuvants, application methods, requisites of the particular application, and substrate in a given practical embodiment of the invention. For the purpose of the present invention, substantially amorphous polymers suit
Feiring Andrew Edward
Tuminello William Howard
E. I. du Pont de Nemours and Company
Zacharia Ramsey
LandOfFree
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