Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1995-07-12
2002-12-10
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C106S287190, C106S287340, C106S435000, C106S454000, C106S457000, C106S475000, C106S489000, C106S900000, C252S299010, C427S375000, C427S376200, C427S379000, C427S553000, C428S426000, C428S688000
Reexamination Certificate
active
06492029
ABSTRACT:
The invention relates to the deposition of enamels on a glass substrate, particularly a glass pane. The invention particularly concerns a novel method of producing an enamel layer on a substrate comprised of glass; further an enamel composition suitable for use in producing an enamel layer on a glass substrate; and the enameled products obtained.
The term “enamel” as used herein will be understood to mean
the enamel composition or paste which one applies to the glass, and/or
the enamel layer formed, at various stages of the production method described hereinbelow.
The term “substrate comprised of glass material(s)” will be understood to mean any glass-based substrate, particularly substrates comprised of glass proper (e.g. glass panes), but also a substrate comprised partly of crystalline materials and partly of glass, such as a substrate comprised of vitroceramic materials (used, e.g., for certain cooktops).
Enamels are well known in the art, and are particularly used on substrates comprised of glass proper, such as vehicle glass panes, architectural glass panes, and mirrors. Enamels have been used to form borders, decorative layers, and protective layers (masks) against UV radiation. These may be used particularly for protection of adhesive layers used to mount the glass in a window opening of a vehicle body, e.g. in the case of a windshield or a rear window, or to mount of accessories, e.g. rear-view mirrors; or to protect collector strips for arrays of heating elements; etc. Enamels are also used for coating vitroceramic substrates, such as cooktops.
The enamel used for these applications is generally formed from
a powder comprising a glass frit (vitreous matrix) and (possibly) colorant pigments, wherewith the frit and the pigments are based on metal oxides, and
a medium, known as the vehicle, which facilitates application of the enamel composition to the substrate, and adhesion of the composition to the substrate at the time of application.
Various methods may be used to apply the enamel to the substrate, e.g. spray painting, serigraphy, roll-coating, etc.
Preferably, serigraphy is used, which enables a wide variety of layer shapes and structures to be produced, and is highly reproducible.
In a preferred method of producing the enamel layer,
the enamel is applied to the substrate by serigraphy,
the wet coating which has been applied is dried to the point of good adhesion to the substrate and a general cohesion sufficient such that the enameled substrate can be handled without marring the coating,
(possibly) additional coats are likewise applied and dried, and, finally,
the enamel coat(s) is/are subjected to a heat treatment at high temperature, whereby the enamel is vitrified to produce the final coating.
The enamel coatings may result in deterioration of certain mechanical properties of the enameled substrate as compared to the un-enameled substrate. For glass substrates which must meet certain safety requirements in architectural or automotive applications, particularly applications for automobile sunroofs, such requirements may be quite stringent, particularly as to impact resistance (dropping sphere test, ANSI 26.1).
A related problem is that of satisfying requirements for protection against UV radiation, which specify that an enamel coating must have a certain opacity. Quite evidently, the opacity depends on the thickness of the enamel coating. In the case of a coating intended to protect a strip of adhesive, the coating thickness must generally be greater than 30 micron in the wet state (when the coating has been applied to the substrate prior to drying and firing of said coating), which approximately corresponds to 20 micron coating thickness after the firing and is regarded as a criterion for proper thickness of an enamel coating. Consequently, the amount of enamel required to be used is high, with attendant high cost.
Another requirement in current practice relates to manufacture of a glass pane with regions of different opacity, e.g. in producing a sunroof pane for an automobile, having an enamel with a fine screen pattern in the central region of the pane and a peripheral strip of highly opaque enamel. To achieve this variegated enameling it is generally necessary to make at least two passes (execute two serigraphy operations). In a first pass, enamel is deposited at least in the central zone, in the form of a fine screen pattern applied in a thin layer in order to achieve good definition of the pattern. Then in a second pass the peripheral strip is deposited, using a different serigraphy fabric, achieving a thicker coating having the required opacity. This method is time-consuming and costly, because two serigraphy stations are required, and two drying steps.
The opacity of an enamel can be increased by increasing the pigment content of the composition used to coat the glass; at the same time, the thickness of the coating can be reduced. However, increased pigment content in the enamel tends to result in poorer mechanical properties of the resulting enameled substrate.
A further problem associated with enameling of a glass substrate develops when enameled substrates are subjected to shaping operations (e.g. bending), generally concurrently with the firing of the enamel. In the course of the shaping, frequently the enamel covering the glass substrate undergoing shaping will stick to elements which contact the enameled article, which elements may be, e.g., curving-molds or may be other articles undergoing shaping at the same time. The adhesion results in, among other things, deterioration of the enamel layer.
Certain known enamels have anti-stick characteristics (also called “anti-adhesive” characteristics). They do not adhere, or only minimally adhere, to elements which contact them during shaping. These enamels are principally enamels comprising oxidizable metals or comprising components which form crystalline phases. However, they cause embrittlement of substrates to which they are applied, which embrittlement often exceeds that caused by traditional non-anti-adhesive enamels, and, further, they contribute to adverse changes in the mechanical properties of the resulting enameled substrates.
The invention eliminates the described drawbacks of the state of the art. The invention proposes a novel method of producing at least one enamel layer on at least a part of a glass substrate, which substrate may particularly be a glass frame. The method enables enameled substrates to be fabricated which have improved mechanical properties.
The invention consists of using graphite in enamel compositions for coating glass substrates. According to the invention, the graphite enables enameled substrates to be fabricated which have improved mechanical properties.
The invention proposes a method of enameling a glass substrate, particularly a glass pane, according to which method, with the aim of improving the mechanical properties of the enameled substrate, an enamel composition containing graphite is deposited on at least a part of the surface of the substrate, the resulting layer is (optionally) dried, and subsequently the enamel coating is fused or vitrified.
The invention also relates to an enamel composition for a glass substrate, which composition comprises
a powder comprised of a glass frit and a pigment or pigments,
a medium enabling the production of a material of a viscosity well-suited for the application of the composition to the substrate and facilitating a binding or adhesion to the substrate, and
graphite;
and which composition is intended to enable production of an enameled substrate having improved physical properties. Advantageously, with the aim of obtaining enameled substrates having improved mechanical properties, the composition comprises at least 0.2 wt. %, preferably at least 0.5 wt. % of graphite (based on the total weight of the enamel composition).
The use of graphite in enamel compositions and in the described method affords a number of advantages. Notably, the glass substrate enameled with a graphite-containing enamel according to the invention disp
Pianalto Bernard
Saint-Gobain Glass France
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