Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-09-10
2001-09-11
Marcheschi, Michael (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S020000, C501S018000, C501S023000, C501S022000, C501S025000, C501S026000, C501S032000, C427S376200, C428S428000
Reexamination Certificate
active
06287996
ABSTRACT:
The present invention relates to a ceramic color composition and a process for producing a curved glass plate employing it, useful particularly for a window glass for automobiles.
Heretofore, a glass plate with a colored opaque layer for automobiles, obtained by printing a pasted ceramic color composition (ceramic color paste) around the periphery of a window glass for automobiles such as a front windshield glass, a side light glass, a back light glass or a roof glass, by screen printing following by drying, and by heating the glass plate to bake the ceramic color paste on the glass plate, has been widely used.
When this pasted ceramic color composition is baked around the periphery of a glass plate, it will form a colored opaque layer. The composition is used to prevent deterioration of a urethane sealant which holds the periphery of the window glass, due to ultraviolet rays, or to prevent the terminals of a heating wire equipped around the periphery of the window glass from being seen from the outside of the car. Further, in recent years, it is used to improve the appearance of the window glass, by forming a graded pattern of fine dots on a glass plate from the periphery toward the center by baking the ceramic color paste thereon.
As the ceramic color composition for such an application, one based on an amorphous glass powder which will not crystallize at the time of baking the glass, and one based on a crystalline glass powder which will crystallize at the time of baking the glass, having various heat-resistant pigments added thereto, are available. With respect to the ceramic color composition, as disclosed in Japanese Patent No. 2,748,647 and JP-A-6-256039, by using a glass (crystalline glass) which will crystallize at a temperature for the bending process of a glass plate, coating step of a so-called release agent and washing step after the bending processing can be omitted, whereby the production efficiency is significantly improved.
On the other hand, with the lightening of automobile components in recent years, it has been required to make the window glass for automobiles thin. However, there is a possible fear that the strength of the window glass for automobiles will decrease, or the strength of the glass plate against wind or coolness will be inadequate. It has been known that a glass plate with a colored opaque layer is usually poor in the strength as compared with a glass plate without the colored opaque layer. To overcome this problem, a method to decrease the coefficient of thermal expansion of said ceramic color composition has been known.
However, it is hard to apply this method to a case where the glass plate is made thin. The reason is that the bending temperature becomes low as the glass plate is made thin, and accordingly it is necessary to use a glass powder which will be fused at a lower temperature. Commonly, a glass powder which will be fused at a lower temperature has a higher coefficient of thermal expansion, and accordingly a glass powder which can be applied to the above method can hardly be available.
Further, it is necessary to bake the ceramic color composition on a glass plate during the bending processing of the glass plate by heating. Accordingly, the ceramic color composition is preferably a material which can be baked at a temperature of from 570 to 700° C., preferably from 600 to 700° C.
Further, in recent years, influences of acid rain due to environmental pollution are becoming significant, and accordingly, the problem is becoming significant, such that when a colored opaque layer formed by baking the ceramic color composition is used outside, acid rain will corrode the colored opaque layer, whereby the color of the layer will change. As the main component of the acids in acid rain is sulfuric acid, a ceramic color composition which gives a colored opaque layer excellent in sulfuric acid resistance, has been strongly desired.
On the other hand, as a bending processing for a window glass for automobiles, to improve productivity and to improve accuracy of the bending processing, a system called a bending processing in a furnace, has been employed, wherein a pressing apparatus or a adsorption shaping apparatus for bending is installed in a furnace, and the bending processing is carried out in the furnace. The bending processing (pressing bending processing) requiring a pressing apparatus, is usually followed by tempering processing. In the bending processing (bending processing by gravity) in which an adsorption shaping apparatus for bending is used, usually the tempering processing is not carried out.
In the pressing bending processing, if a ceramic color composition employing an amorphous glass powder having a low apparent viscosity is used, the ceramic color composition will adhere to a heat resistant cloth which is usually used for the surface of a pressing mold, such as a glass cloth or a stainless cloth, and so-called release properties will deteriorate, and thereby the productivity will decrease. Accordingly, it is necessary to use a crystalline glass powder having a high apparent viscosity for the ceramic color composition to be used.
Further, as a glass having a low melting point and having a relatively excellent sulfuric acid resistance, an amorphous bismuth-containing glass containing no lead, is available. However, this glass is poor in release properties, whereby productivity tends to be poor. Further, as a crystalline bismuth-containing glass has a high coefficient of thermal expansion, the strength of a glass plate having the ceramic color composition baked thereon will deteriorate, and with the increase in the content of bismuth, the sulfuric acid resistance will decrease.
Under such circumstances, it is an object of the present invention to overcome the above problems of prior art, and to provide a ceramic color composition with which the strength of a glass plate will not deteriorate, or the strength is less likely to decrease, and a process for producing a curved glass plate employing it.
The present invention provides a ceramic color composition which comprises from 5 to 40 wt % of a heat-resistant color pigment powder, from 50 to 94.5 wt % of a glass powder, from 0 to 25 wt % of a refractory filler, and from 0.1 to 40 wt % of at least one whisker-like refractory filler selected from the group consisting of aluminum borate whiskers, &agr;-alumina whiskers, potassium titanate whiskers, zinc oxide whiskers, Na
2
Ca
2
P
2
O
18
whiskers, magnesium oxide whiskers, magnesium borate whiskers, basic magnesium sulfate (MgSO
4
.5MgO.8H
2
O) whiskers and titanium diboride whiskers.
The present invention further provides a process for producing a curved glass plate, which comprises coating the ceramic color paste containing the above ceramic color composition on a predetermined portion of a glass plate, then heating the glass plate to bake the ceramic color paste on the glass plate, and forming the glass plate into a desired shape after or during the baking of the color paste.
In the present invention, ‘an amorphous glass’ is a glass which will not crystallize at a temperature of from 570 to 700° C., and ‘a crystalline glass’ is a glass which will crystallize at a temperature of from 570 to 700° C.
Now, the present invention will be explained in further detail with reference to preferred embodiments.
In order to keep the strength of a glass plate, the glass powder in inorganic components in the ceramic color composition of the present invention, is preferably one having heat properties such that it can be baked at a temperature at which a glass plate of soda lime silica glass which is commonly used for a window glass for automobiles is subjected to a bending processing. Namely, as the heat properties of the glass powder in inorganic components, the glass powder is required to soften and fluidize at a temperature lower than the temperature for bending processing of the glass plate.
Further, the glass powder may be one (crystalline glass) which will crystallize at the temperature for bending processing of the glass plate, or one (a
Chiba Jiro
Ishida Mineyuki
Manabe Tsuneo
Mukai Kenji
Onoda Hitoshi
Asahi Glass Company Ltd.
Marcheschi Michael
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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