Coating processes – Optical element produced – Transparent base
Reexamination Certificate
2000-08-31
2004-01-20
Zacharia, Ramsey (Department: 1773)
Coating processes
Optical element produced
Transparent base
C427S169000, C427S168000, C427S389700
Reexamination Certificate
active
06680080
ABSTRACT:
TECHNOLOGICAL FIELD
This invention relates to a method of antiglare treatment of an organic or inorganic substrate, and to a material having antiglare properties that can be obtained by the method of the invention.
In the description that follows, the term organic substrate designates, more precisely, a plastic substrate, for example, one chosen from among the polyacrylates, polycarbonates, polyallylcarbonates and polyamides. In any case, this list is not limitative and covers polymeric materials in a more general way.
The term inorganic substrate covers, more precisely, a vitreous substrate, that is to say, for example, an amorphous or even a crystalline material and, in particular, a silica based glass such as silicate glass, a borosilicate glass, a sodium/calcium glass, and a phosphate based glass, such as a fluorophosphate substrate, and a phosphate substrate, for example, a crystal of potassium dihydrogen phosphate (KH
2
PO
4
or KDP) which may or may not be deuterated.
The method of the invention is particularly advantageous for treating a substrate sensitive to increases in temperature such as a phosphate substrate.
Phosphate substrates, for example a crystal of potassium dihydrogen phosphate, find application, for example, in the fields of laser amplification, laser frequency conversion or in the manufacture of Pockels cells.
Phosphate substrates are very sensitive to thermal shocks. For example, crystals of deuterated KDP undergo an irreversible crystal phase transition at a temperature which is lower the more strongly deuterated they are. The antiglare treatment of these substrates must, as a consequence, be carried out at a moderate temperature or indeed at ambient temperature.
Furthermore, phosphate substrates are fragile and are damaged by atmospheric humidity. In effect, in the presence of moisture, they are hydrolyzed on the surface and become opaque, thereby losing their optical properties. These substrates must, as a consequence, be protected from moisture.
The method of the invention is also applicable, for example, to a silica based glass, and to the organic or inorganic substrates previously described, that is to say, particularly to plastic substrates and to vitreous substrates.
These substrates are also referred to below as “material having antiglare properties”. They find numerous applications. These applications are for example in the field of high power lasers, solar, thermal and photovoltaic applications, integrated optical systems and in architectural applications such as panels glazed on the outside. In the field of solar applications, vitreous or plastic substrates are already used in optical systems in order to minimize heat losses, to concentrate and to focus light energy and finally to protect certain absorbent components.
To summarize, the antiglare treatment which allows one to increase optical transmission, can in certain cases enable one to increase the life of the substrate by an effect of protecting it against humidity. It must in addition, be resistant to a laser flux when it is to be used in laser applications, and must be produced at a temperature that is compatible with the thermal fragility of the substrate.
The invention also relates to a material having antiglare properties that can be obtained by the method of the invention, for example, to a doubly refracting crystal.
STATE OF THE ART
Patent application FR-A-2 680 583 describes an antiglare treatment for organic or inorganic substrates. This treatment is a method of the sol-gel type which uses a dense layer of alkylsilicone resin as a protector for the substrate and a porous sol-gel film as an antiglare layer, and which includes a heat treatment at 150° C. or 180° C.
This method does not allow one to treat substrates sensitive to temperature increases. Also, a compromise is always necessary to the detriment of the protective function against moisture, for example, an antiglare sol-gel deposit, without a silicone layer in the case of deuterated KDP crystals.
DISCLOSURE OF THE INVENTION
The precise purpose of this invention is to provide a method of antiglare treatment for an organic or inorganic substrate that allows one to increase the optical transmission through said substrate and to increase the life of said substrate by protecting it against moisture.
The organic or inorganic substrates are, for example, those described previously.
The method of the invention comprises a step of depositing a layer of fluorinated polymer with a low refractive index, onto said substrate.
According to the invention, the deposition of the layer of fluorinated polymer can be carried out from a deposition solution comprising the fluorinated polymer and a perfluorinated solvent using a technique which can be chosen from a dipping-withdrawing technique, a centrifugal coating technique or a laminar coating technique.
The dipping-withdrawing technique consists of immersing the substrate in a deposition solution and removing it from this solution to leave it to dry. The centrifugal coating technique consists of depositing the deposition solution on the substrate which is rotating. The laminar coating technique consists of coating the substrate horizontally by capillarity using a tube containing the deposition solution. This technique is the subject of patent application FR-A-2 693 558 assigned to the CEA.
The method can be carried out at ambient temperature, and it can be carried out under atmospheric pressure.
The layer of fluorinated polymer is preferably deposited in the form of a thin film, uniformly distributed over the substrate.
The preferred fluorinated polymer according to the method of the invention is an organic fluorinated polymer having a low refractive index, within a range of values from about 1.2 to about 1.4, preferably about 1.3 and preferably soluble in most perfluorinated solvents at ambient temperature.
The organic fluorinated polymer may, for example, be a derivative of polytetrafluoroethylene which may be at a concentration of from 0.1 to 10% by weight in the deposition solution. This polymer may be, for example, an amorphous copolymer arising from a copolymerization of a perfluoro alkene with a perfluoro dioxole. An example of such a polymer is the copolymer with the name TEFLON AF (registered trade mark) arising from the copolymerization of a mixture of tetrafluoroethylene (TFE) and 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD). The PDD sterically prevents the crystallization of the polymer formed. According to the PDD content in the mixture, the properties of the resultant copolymer vary. Hence, when the concentration of PDD increases, the solubility of the copolymer decreases, the refractive index decreases and its vitreous transition temperature increases.
CYTOP (trade mark) is another example of a fluorinated polymer which can be used in the method of the invention. It is sold by Asahi Glass Company and its particular features are a great facility for use in coating, good transparency in the visible and ultraviolet, a low refractive index, approximately equal to 1.34 and good chemical and thermal resistance. Its chemical composition has not been disclosed.
The perfluorinated solvent can be chosen from the group including a perfluoro-alkylamine, for example, Fluorinert series FC (registered trade mark) from the company 3M, a perfluoro-polyether, for example, the Galden series HT or DO (registered trade mark) from the company Ausimont-Montedison, a fluoro-alkane such as Freon, and Flutec (registered trade mark) from the company Rhône-Poulenc.
The deposition solution is prepared by mixing a suitable quantity of a fluorinated polymer with a perfluorinated solvent to obtain a deposition solution having a viscosity that permits a uniform and homogeneous deposition on the surface of the substrate.
This viscosity is a function of the concentration of the fluorinated polymer in the deposition solution. Also, according to the method of the invention, when the fluorinated polymer is, for example, a derivative of polytetrafluoroethylene (PTFE) and the perfluorinated solvent is a
Anderson Kill & Olick
Commissariat a l'Energie Atomique
Lieberstein Eugene
Meller Michael N.
Zacharia Ramsey
LandOfFree
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