Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonelectrolytic coating before forming nonmetal...
Reexamination Certificate
2000-02-08
2001-07-10
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonelectrolytic coating before forming nonmetal...
C205S210000, C205S224000, C205S229000, C205S208000
Reexamination Certificate
active
06258242
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The invention is in the field of devices having a radiation-absorbing coating, particularly a coating of polyaniline absorbing radiation in a band extending from the ultraviolet to the infrared. It also relates to a process for the preparation of surfaces receiving the deposit.
2. Prior Art
A wide range of surface treatments or surface coatings only having a limited specular reflection and only a limited diffuse reflection is known. These treatments or coatings are sought, particularly for optical or infrared applications. They contribute to mechanical elements such as input optics supports of optical devices not reflecting or only reflecting a little light and thus not increasing the signal to noise ratio of the optical or infrared signal intercepted by the detectors of such devices.
Problems known in connection with such coatings and which it is wished to solve by improvements to surface treatment and/or coating deposition processes are e.g. described in column 1 of U.S. Pat. No. 4,589,972 of May 20, 1986, granted to Martin Marietta. The problems referred to in this patent and which it is wished to solve according to the present invention are given hereinafter.
With regards to black paints, it is known that they have a tendency to crack or be detached from in particular metal substrates, due to stresses induced by thermal cycles, particularly for infrared systems operating with sensors cooled to the temperature of helium or liquid nitrogen.
These phenomena become worse with the thickness of the paint coating, said thickness generally increasing with the wavelength of the radiation which it is wished to absorb.
Another problem encountered is due to the degassing of the coating, particularly when the coated material operates at high altitudes or in space. The products resulting from the degassing can chemically react and damage microelectronic components or condense on cooled optical surfaces so as to obscure them.
The Martin Marietta U.S. Pat. No. 4,589,972 proposes, like an earlier U.S. Pat. No. 4,111,762, of Martin Marietta to which U.S. Pat. No. 4,589,972 refers, improving the solution to these problems in two ways. These two improvements are applicable to previously anodized, anodizable metals, particularly aluminium and beryllium.
The process provides for a treatment of the surface by an aluminium oxide jet with a grain size of 100 to 200 mesh. This initial treatment aims at creating a roughness of the surface prior to anodization.
It is indicated at the top of column 7 of said patent, that the increased roughness of the treated surface has a significant effect on the absorption and reflectivity of the surface. The specular reflection is reduced and the dispersion of the incident radiation due to the relief created increases absorption.
The importance of the roughness state of the surface has been recognized by most experts. Reference is also made in this connection to the Johnson U.S. Pat. Nos. 4,233,107 and 4,361,630, the latter being a continuation of the former. In the process described in said patent a substrate is firstly treated by means of a plating of a phosphorous nickel alloy. The thus coated surface is then made rough by means of a bath in a nitric acid aqueous solution which brings about an acid etching of the deposited plating. This leads to a very good absorption in the range 320 to 2140 nanometres.
Thus, it is generally known in the art that a roughening treatment of the surface to be treated before (Marietta patent) or after (Johnson patent) coating or other surface treatment is likely to improve the absorption qualities. However, for each wavelength range to be absorbed and for each treatment and also as a function of the substrate, it is necessary to adapt the roughening treatment.
In a first aspect the present invention is directed at such a roughening treatment.
Under another aspect it is directed at a process for depositing a polyaniline absorbing coating, said deposition preferably taking place after the surface has been roughened prior to the polyaniline coating application operations.
The use of polyaniline for absorbing electromagnetic radiation is in itself known. In this connection reference is made to the patents of EPSTEIN et al U.S. Pat. No. 5,079,334 and various continuations thereof U.S. Pat. Nos. 5,147,968, 5,294,694 and 5,563,182. In these various patents EPSTEIN explains the reasons for the absorbing qualities of polyaniline and the possible applications. U.S. Pat. No. 5,294,694 claims a method for the absorption of electromagnetic waves by means of a polyaniline composition. This patent expressly envisages the ultraviolet to the infrared range.
This patent only very briefly mentions the treatments to be applied to the surfaces to be coated and the deposition method. Thus, it is stated in column 7, lines 55 to 63 of said patents that aniline can be applied by virtually any known method. Among these methods, it refers to electrochemical deposition on conductive substrates. Column 8, lines 5 to 20 also refers to the deposition of films.
The applicant has carried out experiments in which a polyaniline was used as the absorbing coating. It was found that polyaniline had good absorbing qualities, but the total reflection value remains high in the infrared. There is not a good adhesion to the substrate and there is a definite coating foliation tendency.
These experiments revealed that there is a need for a deposit of a polyaniline coating absorbing electromagnetic radiation in the ultraviolet to infrared ranges, which adheres well to the substrate and has no reflection peak in the infrared range.
BRIEF DESCRIPTION OF THE INVENTION
Therefore the invention relates to a process for the preparation of the surface of a substrate for receiving a polyaniline coating, able to absorb in the ultraviolet to infrared range, characterized in that the surface of the substrate is roughened prior to the performance of the polyaniline coating deposition stages.
It has been found that the best results from the absorption standpoint were obtained when the roughness value of the substrate surface is between 10 and 30 &mgr;m. This is the mean square value of the variations between the topmost points of the surface and the bottommost points of the slow undulations of the surface known under the name of roughness Ra. With this initial roughness of the substrate there is a good diffusion effect, particularly in the range 0.25 to 16 &mgr;m. In addition, this diffusion aids absorption.
This Ra value can e.g. be obtained on a titanium substrate by sandblasting with an abrasive. This operation can be carried out with corundum with a grain size between 30 and 120 mesh.
In an embodiment, sandblasting was carried out with such a corundum under a pressure of 6 bars at a distance from the surface to be treated of approximately 20 cm. A double passage was effected with a coverage level of 100%.
This initial substrate preparation phase is necessary for reducing or eliminating the specular reflection peak in the infrared. Aniline deposition, according to a second aspect of the invention, can be carried out after this preparatory phase relative to the obtaining of the roughness of the substrate surface. It may also not be carried out if the specular reflection or absorption value obtained without this prior roughening treatment are considered to be adequate.
According to this second aspect, the invention relates to a process for depositing a polyaniline coating on a titanium or titanium alloy substrate, characterized in that the operating range of deposition successively comprises:
a fluoronitric etching,
a chemical conversion treatment,
a hydrolysis and
a polyaniline deposition by electropolymerization.
If the substrate is not perfectly clean, it is appropriate to carry out a prior cleaning stage (alkaline, solvent or mechanical cleaning).
REFERENCES:
patent: 4111762 (1978-09-01), Wade et al.
patent: 4233107 (1980-11-01), Johnson, Sr.
patent: 4361630 (1982-11-01), Johnson, Sr.
patent: 4589972 (1986-05-01), Pompea et al.
patent: 5294694
Marchandise Didier
Marrugat Robert
Aerospatiale Matra
Burns Doane , Swecker, Mathis LLP
Wong Edna
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