Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-03-27
2003-09-02
Morgan, Kriellion S. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S089000, C524S094000, C524S101000, C524S254000
Reexamination Certificate
active
06613818
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coating composition for preparing a back coating film of a mirror. The back coating film prepared by curing the coating composition provides the mirror with anticorrosion property.
Conventional back coating films for mirror contain corrosion-inhibitive lead pigments, such as red lead, white red, basic lead sulfate, lead cyanamide, and calcium plumbate. The incorporation of such lead pigment has so-called advantageous cation effect, reducing effect, neutralization effect, and anion effect. By this cation effect, ionization and deterioration of metal(s) (i.e., silver, copper and/or at least one other metal) of mirror are suppressed by lead having an ionization tendency greater than those of these metals. By the reducing effect, a reducing atmosphere is produced at the interface between the back coating film and the silver mirror film or the metallic (e.g., copper) protective film, thereby to suppress oxidation of the silver mirror film and the metallic protective film. By the a neutralization effect, a rust of the silver film and/or of the metallic protective film is neutralized by a basic substance generated from a lead pigment, thereby to suppress oxidation of the silver mirror film and/or the metallic protective film. By the anion effect, an anion (e.g., that of cyanamide) reacts with a metal ion derived from the silver mirror film and/or from the metallic protective film. With this, there is formed a passive film that suppresses corrosion of the silver mirror film and the metallic protective film. By the above-mentioned cation, reducing, neutralization, anion effects, the occurrence of corrosion and deterioration of the peripheral and inner portions of the mirror can be prevented.
Japanese Patent Unexamined Publication JP-A-7-261007 discloses a coating composition for preparing a back coating film of a mirror. This coating composition contains a binder of a bisphenol-type epoxy ester resin, benzotriazole and/or its derivative, red lead, and the like (see Tables 1-2). The use of lead in mirror, however, is not desirable from an environmental point of view, as will be mentioned hereinafter. Nevertheless, if the lead pigment is omitted in this coating composition, its anticorrosion property becomes inferior to those containing a lead pigment.
JP-A-7-234306 discloses a mirror that has a special film 4 interposed between a copper protective film 3 and a back coating film 5, in order to improve the mirror in chemical durability. This special film 4 is prepared by applying benzotriazole and/or its derivative to the copper protective film 3. In this publication, it is stated that the back coating film 5 may be formed by using one of various conventional alkyd resin paints, epoxy resin paints, and epoxy ester resin paints. It is known that these paints contain a lead pigment(s). As stated above, the use of lead in mirror is not desirable. In spite of that, if the lead pigment is omitted in the back coating film, the mirror may become unsatisfactory in anticorrosion property.
The use of lead in mirror may cause an environmental hazard. According to an analysis conducted by an examination organization (TCLP) certified by U.S. Environmental Protection Agency (EPA), it was found that conventional mirrors having a back coating film containing a lead pigment contain 30-60 mg/L of lead. Under the EPA's regulation, this concentration is far greater than the permissible upper limit of the lead concentration (i.e., 5.0 mg/L) of wastes to be dumped. Thus, in the United States, it is prohibited to dump cullet and wastes of such mirrors. In view of this, there is a strong demand for a mirror that is substantially free of lead and has advantageous characteristics, in mechanical processability and chemical and mechanical durabilities, which are comparable to those of a mirror having a back coating film containing a lead pigment.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a coating composition for preparing a back coating film of a mirror that is superior in anticorrosion property and is substantially free of lead to reduce a risk of the environmental impact.
It is another object of the present invention to provide such anticorrosive mirror having the back coating film prepared by curing the coating composition.
It is a more specific object of the present invention to provide an anticorrosive mirror that is substantially free of lead and has advantageous characteristics, in mechanical processability (e.g., in cutting and chamfering) and chemical and mechanical durabilities, which are comparable to those of a mirror having a back coating film containing a lead pigment.
According to the present invention, there is provided a coating composition for preparing a back coating film of a mirror. This mirror serving as an anticorrosive mirror has a glass substrate, a silver mirror film that comprises silver and is formed on a back surface of the glass substrate, a metallic protective film that comprises a first metal and is formed on the silver mirror film, and the back coating film formed on the metallic protective film. The coating composition is substantially free of a lead component and comprises (a) a vehicle containing a synthetic resin, (b) a first salt formed by a neutralization of an acid with a base containing a second metal having an ionization tendency that is greater than the silver and the first metal, and (c) a basic compound selected from the group consisting of azoles and diamines. The acid is one compound selected from the group consisting of organic acids each containing an azole ring and unsubstituted and substituted carbamic acids.
According to the present invention, there is further provided such an anticorrosive mirror comprising (a) a glass substrate, (b) a silver mirror film that comprises silver and is formed on a back surface of the glass substrate, (c) a metallic protective film that comprises a first metal and is formed on the silver mirror film, and (d) a back coating film that is formed on the metallic protective film and is prepared by curing the above-mentioned coating composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An anticorrosive mirror according to the present invention can be formed at first by forming on a glass substrate a silver mirror film and then a metallic protective film, for example, by spraying, and then by forming on the metallic protective film a back coating film for providing the mirror with anticorrosion property. The silver mirror film contains silver and may further include at least one other metal such as chromium and titanium. The metallic protective film contains a first metal which is not particularly limited. Copper, which is the most commonly used for conventional metallic protective films, may be used as the first metal. The back coating film is formed at first by applying a coating composition according to the present invention to the metallic protective film and then by curing the coating composition. This application may be conducted, for example, by roller coating, flow coating, and spraying.
As stated above, a coating composition according to the present invention for preparing the back coating film is substantially free of a lead component and comprises (a) a vehicle containing a synthetic resin, (b) a first salt formed by a neutralization of an acid with a base containing a second metal (e.g., zinc or iron) having an ionization tendency that is greater than the silver and the first metal (e.g., copper), and (c) a basic compound selected from the group consisting of azoles and diamines. The acid is one compound selected from the group consisting of organic acids each containing an azole ring and unsubstituted and substituted carbamic acids. Each of the first salt and the basic compound can serve as an anticorrosive agent for the mirror. When both of the first salt and the basic compound are used together, there may be obtained the above-mentioned advantageous cation, reducing, neutralization and anion effects, which are com
Hayashi Ken-ichi
Mori Yutaka
Sakatoku Motoyuki
Tamura Yoshihisa
Central Glass Company Limited
Crowell & Moring LLP
Morgan Kriellion S.
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