Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-07-07
2002-12-24
Bareford, Katherine A. (Department: 1762)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S026000
Reexamination Certificate
active
06498117
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the deposition of enamel on a glass substrate, especially on glazing. In particular, it relates to a novel enamel composition and to the process for obtaining it, a process for manufacturing an enamelled layer on a glass substrate, and the enamelled products obtained, particularly enamelled glazing.
BACKGROUND OF THE INVENTION
Enamels are well known in the prior art and are used, especially, for coating glass substrates, such as glazing in the motor-vehicle industry or the building industry. They make it possible to form decorative layers or inscriptions, conductive layers, protective layers, especially layers for protecting the adhesive layers or adhesive beads intended for mounting glazing in body openings from ultraviolet radiation, masks, especially masks for concealing current-collecting strips of heating grids or for concealing the above mentioned adhesive beads and similar products.
Before application to the substrate and firing, these enamels used for coating glass substrates are generally formed from a powder comprising a glass frit, which is included to provide a glassy matrix, and pigments, which are used as colorants. The pigments also possibly form part of the frit. Both the frit and the pigments are generally based on metal oxides. Also, a medium or “vehicle” is used to allow application and temporary adhesion of the enamel to a substrate. The medium, chosen according to the intended use of the enamel, must ensure that the particles of the frits and pigments used are properly in suspension and must be consumed at the latest during firing of the enamel. This medium may include solvents, diluents, oils, resins and the like.
One problem with existing enamelled glass substrates is the difficulty of recycling such products, particularly in the manufacture of glass substrates in the form of sheets or glazings. Since such products must meet many requirements in terms of coloration, light and/or energy transmission, etc., it is important in fact that the glass waste reintroduced in ground form or cullet into the melting furnaces used for manufacturing new glazings does not disturb the glass compositions normally already present and does not give products that do not meet the necessary requirements. Although non-enamelled glass cullet can thus be reintroduced into a furnace for manufacturing float glass in amounts generally of about 20-30% by weight of the charge of the furnace, enamelled glass cullet, on the other hand, generally causes the appearance of undesirable residual colorations or of residual unmelted islands in the glass sheets formed. Consequently, the amount of enamelled glass cullet that can be reintroduced into these furnaces does not generally exceed 2 to 3% by weight of the charge of the furnaces. Usually, the enamelled glass cullet constitutes from 0.1 to 0.5% by weight of the charge.
An improved enamel composition and an enamelling process are already known from WO 98/25864, which makes it possible to obtain improved enamelled glass substrates, particularly enamelled substrates which can be recycled (especially in the manufacture of glazing) more easily than the existing enamelled substrates. This composition comprises as pigments one or more manganese compounds and has a firing temperature, also called melting point, of less than 750° C. In motor-vehicle applications, the composition is preferably chosen so as to obtain a black enamel having the following colorimetric coordinates, in absolute values:
L*≦5; |a*|2 and |b*|≦2 (and, preferably,
|a*|≦1 and |b*|≦1).
This is generally the case in the compositions described in the above document, which essentially comprise Bi
2
O
3
as intermediate oxide. They are obtained either by adding the manganese compounds in the form of powder to a glass frit powder including Bi
2
O
3
, or by a process, called the “direct process,” by melting a mixture of suitable raw materials (including the manganese compounds) in order to obtain the desired combination of frit and pigments.
On the other hand, the black coloration sought after in motor-vehicle applications is not obtained systematically with other types of recyclable compositions. In particular, tests carried, out by replacing all or some of the Bi
2
O
3
with a less expensive oxide, such as zinc oxide, have not made it possible to obtain the desired black coloration, whether the Bi
2
O
3
is replaced with a less expensive oxide in the glass frit powder before adding the manganese compounds in the first process described in the previous paragraph, or whether the raw material or materials used for obtaining Bi
2
O
3
is or are replaced with one or more raw materials used for obtaining a less expensive oxide in the mixture of raw materials in the direct process described in the preceding paragraph.
Thus, there is a need to develop recyclable black enamel compositions which are less expensive than previous bismuth-based compositions. This need is satisfied by the present invention.
SUMMARY OF THE INVENTION
The enamel compositions provided by the invention are black enamel compositions, i.e., enamel compositions having a black color after firing, which are recyclable and comprise at least zinc.
Until now, such compositions were inconceivable due to the above mentioned coloration problems or due to recycling problems (less expensive compositions do exist but they cannot be recycled). The present invention has succeeded in developing such compositions by devising a particular process for obtaining an enamel, this process comprising the following steps of melting glass forming materials comprising at least bismuth, silicon, boron and manganese, at temperatures greater than 900° C., and then adding a glass frit comprising at least zinc to the mixture obtained after this direct melting.
In one embodiment of the invention, the process for manufacturing a recyclable zinc-containing black enamel composition comprises the steps of melting glass forming materials comprising at least bismuth, silicon, boron and manganese together at temperatures greater than about 900° C. to form a first mixture; and then adding a glass frit comprising at least zinc to the first mixture to obtain a second mixture that can be applied to form an enamel coating.
In the process, the melting step can be carried out above about 1050° C. Glass frit containing no pigments, and optionally with a medium, is added to the first mixture. The zinc-based glass frit can be added in an amount sufficient to represent about 20% to about 55% by weight of the second mixture. The process may further comprise grinding the first mixture before the zinc-based glass frit is added thereto.
Enamel compositions can be obtained by the above described process. Preferably, the enamel compositions are essentially free of chromium, copper, nickel or cobalt and may further comprise a medium.
The enamel compositions may comprise a mixture of a first composition obtained by melting glass forming materials comprising at least bismuth, silicon, boron and manganese at temperatures greater than about 900° C. and a second composition in the form of at least one glass frit comprising at least zinc. The enamel compositions may further comprise a medium.
In another embodiment of the invention, a glass substrate may be enamelled wherein at least part of a glass substrate is at least partially coated with an enamel composition as described above, and then the substrate is subjected to a heat treatment so as to bake the enamel composition thereon and form an enamel coating. The invention may also include glazings comprising at least one glass sheet coated, on at least part of at least one side, with at least one layer of an enamel having a composition as described above.
DETAILED DESCRIPTION OF THE INVENTION
The raw materials used in the process according to the invention may be natural materials, for example, sand, colemanite, etc., or synthetic materials, for example, Bi
2
O
3
, etc. The bismuth, silicon, boron and manga
Beyrle Andre
Dages Daniel
Bareford Katherine A.
Pennie & Edmonds LLP
Saint-Gobain Vitrage
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