Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2002-01-24
2004-03-30
Jones, Deborah (Department: 1775)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S031000, C522S048000, C522S068000, C522S083000, C524S442000, C524S492000, C524S386000, C524S388000, C524S497000, C106S287160, C106S287290, C106S287100, C106S280000, C106S281100
Reexamination Certificate
active
06713526
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to compositions useful for molding ceramic microstructures on a substrate.
BACKGROUND
Advancements in display technology, including the development of plasma display panels (PDPs) and plasma addressed liquid crystal (PALC) displays, have led to an interest in forming electrically-insulating ceramic barrier ribs on glass substrates. The ceramic barrier ribs separate cells in which an inert gas can be excited by an electric field applied between opposing electrodes. The gas discharge emits ultraviolet (uv) radiation within the cell. In the case of PDPs, the interior of the cell is coated with a phosphor which gives off red, green, or blue visible light when excited by uv radiation. The size of the cells determines the size of the picture elements (pixels) in the display. PDPs and PALC displays can be used, for example, as the displays for high definition televisions (HDTV) or other digital electronic display devices.
One way in which ceramic barrier ribs can be formed on glass substrates is by direct molding. This has involved laminating a planar rigid mold onto a substrate with a glass- or ceramic-forming composition disposed therebetween. The glass- or ceramic-forming composition is then solidified and the mold is removed. Finally, the barrier ribs are fused or sintered by firing at a temperature of about 550° C. to about 1600° C. The glass- or ceramic-forming composition has micrometer-sized particles of glass frit dispersed in an organic binder. The use of an organic binder allows barrier ribs to be solidified in a green state so that firing fuses the glass particles in position on the substrate. However, in applications such as PDP substrates, highly precise and uniform barrier ribs with few or no defects or fractures are required. These requirements can pose challenges, especially during removal of the mold from the green state ribs and during firing of the green state ribs.
Mold removal can damage ribs due to difficulty in mold release. Because barrier ribs tend to shrink during firing, the green state ribs must be taller than the size desired for the fused ribs. Taller structures make demolding even more difficult. Mold removal can also damage the mold. When material cannot be completely removed from the mold, the mold must be discarded. In addition, at temperatures required for firing, the barrier ribs can fracture, delaminate from the substrate, or warp. The substrate also goes through dimensional changes during firing due to thermal expansion and release of internal stresses.
SUMMARY OF THE INVENTION
The present invention provides a curable slurry for forming ceramic microstructures on a substrate. Such microstructures can be used, for example, as spacer ribs in electronic displays such as ceramic barrier ribs in PDPs. Preferred embodiments of the slurry of the present invention can provide several useful properties such as the ability to adhere to the substrate in the cured green state as well as during and after firing, the ability to demold from the microstructure-forming mold after curing, the ability to debind quicker and more completely at relatively low temperatures, the ability to retain good dielectric properties, the capability for environmentally-friendly disposal, or the ability to maintain precise dimensions throughout processing. In addition, further preferred embodiments of the slurry of the present invention can enhance adhesion to the substrate.
In a first aspect, the present invention provides a slurry for patterning microstructures on a substrate using a mold. The slurry is a mixture of (a) a ceramic powder having a softening temperature in a range of about 400° C. to 600° C. and a coefficient of thermal expansion in a range of about 10% less than to about 10% more than the coefficient of thermal expansion of the substrate; (b) a fugitive binder capable of being hardened by radiation curing, electron beam powder is present in an amount of about 40 to 96% by weight, the fugitive binder is present in an amount of about 2 to 50% by weight, and the diluent is present in an amount of about 2 to 50% by weight.
In another aspect, the present invention provides an assembly for patterning ceramic microstructures onto a substrate. The assembly includes a mold, the mold having a patterned surface characterized by a plurality of protrusions and indentions thereon, and the above-described slurry capable of filling the indentions of the patterned surface of the film.
In yet another aspect, the present invention provides a substrate assembly for plasma displays panels which includes a glass substrate with green state microstructures thereon. The green state microstructures are formed by molding and curing the above-described slurry. After curing, the diluent remains in the green state microstructures as a liquid in an interpenetrating network dispersed in the binder.
DETAILED DESCRIPTION
As used herein, the term ceramic refers generally to ceramic materials or glass materials. Thus, in the slurry used in one aspect of the method of the present invention, the included ceramic powder can be glass or ceramic particles, or mixtures thereof. Also, the terms fused microstructures, fired microstructures, and ceramic microstructures refer to microstructures formed using the method of the present invention which have been fired at an elevated temperature to fuse or sinter the ceramic particles included therein.
The slurry of the present invention is a mixture containing a ceramic powder, a curable organic binder, and a diluent. When the binder is in its initial uncured state, the mixture is simply referred to as a slurry. After curing the binder, the slurry is in a more rigid state which can retain the shape in which it was formed. This cured, rigid or semi-rigid state is referred to as the green state, just as shaped ceramic materials are called “green” before they are sintered. The green state material can subsequently be debinded and/or fired. Debinding occurs when the green state material is heated to a temperature at which the binder can diffuse to a surface of the material and volatilize. Debinding is usually followed was formed. This cured, rigid or semi-rigid state is referred to as the green state, just as shaped ceramic materials are called “green” before they are sintered. The green state material can subsequently be debinded and/or fired. Debinding occurs when the green state material is heated to a temperature at which the binder can diffuse to a surface of the material and volatilize. Debinding is usually followed by increasing the temperature to a predetermined firing temperature to sinter or fuse the particles of the ceramic powder. After firing, the material is simply referred to as fired material. Fired microstructures are also referred to herein as ceramic microstructures.
The present invention provides a slurry for molding ceramic microstructures on a substrate. The slurry includes at least three components. The first component is a ceramic powder. The ceramic powder will ultimately be fused or sintered by firing to form microstructures and adhered to the substrate having desired physical properties. The second component is a fugitive binder which is capable of being shaped and subsequently hardened by curing, heating or cooling. The binder allows the slurry to be shaped into rigid or semi-rigid green state microstructures which are adhered to the substrate so that the mold used to form the microstructures can be removed in preparation for debinding and firing. The third component is a diluent which can promote release from the mold after hardening of the binder material or promote fast and substantially complete burn out of the binder during debinding before firing the ceramic material of the microstructures. The diluent preferably remains a liquid after the binder is hardened so that the diluent phase-separates from the binder material during hardening.
The ceramic powder is chosen based on the end application of the microstructures and the properties of the substrate to which the microstructure
Chiu Raymond C.
Dillon Kenneth R.
King Vincent Wen-Shiuan
Moh Kyung H.
Rusin Richard P.
3M Innovative Properties Company
Pechman Robert J.
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