Glass manufacturing – Control responsive to condition sensing means – Temperature or heater control
Reexamination Certificate
2000-12-29
2004-01-20
Vincent, Sean E (Department: 1731)
Glass manufacturing
Control responsive to condition sensing means
Temperature or heater control
C065S024000, C065S029190, C065S169000, C065S255000, C065S273000, C065S356000, C065S370100, C065S374110, C065S374120, C065S374130
Reexamination Certificate
active
06679085
ABSTRACT:
The invention relates to a shaping tool with a structured surface for creating structures on glass in the context of a hot-shaping method, which is employed in particular for making precision structures in a channel plate of flat screens.
Plate glass provided with precision structures is needed for precision applications, in particular in the field of glasses (that is, kinds of glass) that have optical functions. Such glasses are for instance display screens of new flat screen generations (PDPs or plasma display panels, and PALCs or plasma addressed liquid crystals). In the so- called channel plate of these flat screen glasses, microscopic channel structures for triggering individual rows or columns are made, which extend over the entire active width or height of the screen and in which plasma is ignited via an electrical discharge. The boundary on both sides of an individual channel is accomplished via rectangular ribs, whose width is as slight as possible. To achieve an adequate discharge volume, the height of the ribs is substantially greater than their width. The spacing of the ribs should be as slight as possible.
The channel plate thus represents the microstructured glass backpanel of a PALC or PDP display. It is shown in basic form and in detail on a greatly enlarged scale in FIG.
7
.
The channel-like microstructuring shown in this drawing figure must be accomplished cost-effectively and in large numbers for different display sizes (diagonal screen sizes up to 55 inches). For a 42-inch HiVision PDP display, for instance, approximately 5760 channels with a pitch “X” of approximately 161 m&mgr; and a rib height Y of 150 m&mgr; and a rib width “Z” of 30 to 50 m&mgr;, with tolerances of only a few micrometers over a length of about 520 mm must be made. These enormously stringent specifications dictate a high- precision method and a corresponding apparatus.
It is known to create structures on glass on the basis of a shaping tool with a structured surface, using hot- shaping techniques.
Conventional hot-shaping methods, so-called creative forming methods, are conceived such that hot (molten) glass is given its desired form out of the melt by means of a cooled shaping tool that is pressed into the molten glass. The shaping tool takes on the function of “solidification shaping”; that is, before contact with the tool, the glass has a temperature above the glass transition range (T
g
) and is cooled by the contact with the shaping tool in such a way that the negative of the structured surface of the shaping tool is copied dimensionally stably in the glass.
The invention takes as point of departure another hot- shaping method, which can be characterized as a reshaping warm-shaping process. In this reshaping shaping process, the temperature of the glass before it contacts the shaping tool having the structured surface is optionally below the glass transition range, and is raised to the requisite temperature range for shaping (T>T
g
) only by contact with the shaping tool. It is decisive here that only local heating of whatever region is to be structured occurs. In this reshaping process as well, the glass when it leaves the shaping tool is in its structured form and in a dimensionally stable state.
Physical variables, which pertain to both the conventional hot-shaping method and the reshaping warm-shaping method in terms of the process sequence are:
the temperature of the glass and of the shaping tool;
the pressure load on the glass and the shaping tool;
the time of contact of the glass and shaping tool (dwell time).
The following description of the dwell time may make this clearer:
If the glass comes into contact with the shaping tool only briefly, or in other words if the shaping tool is removed from the glass before the solidification occurs, then because of the flowing of the glass structure, major rounding occurs in the structure after contact.
If contact is long-lasting, then major temperature differences and different thermal expansions of the shaping tool and glass result in intolerable lateral strains, which adversely affect the precision of the structures, or in other words the precision with which the channels in channel plates can be positioned and reproduced.
A shaping tool which is intended to be appropriate for precise process control must assure an independent setting/regulation of the above-described variables. The known hot-shaping tools do not meet these requirements. Because of their conventional solid structure with chromium nickel steels, which necessitates heating the entire shaping tool completely, they furthermore have inadequate thermal dimensional stability, because at even relatively slight temperature fluctuations in the shaping tool, relatively major changes in length of the shaping structures occurs, changes that exceed the allowable tolerances for forming the channels or ribs.
The same applies to the shaping tool, disclosed by German Patent DE 197 13 309 C1 and German Patent Application DE 197 13 312 A1, with a structured surface for creating structures on glass on the principle of reshaping warm- shaping, which in the exemplary embodiment has a rolling cylinder, comprising a solid cylinder of preferably nonmetal material, to which a molding tool with the structure-imparting surface is clamped, resting relatively loosely. On each of the two face ends of the solid cylinder, a respective bearing journal for the rotational mounting of the rolling cylinder is provided. An external heating source is provided for the requisite local heating of the shaping tool.
Such an embodiment of the shaping tool does not make it possible in practice to create precision structures with the desired replicable precision, since the necessary thermal dimensional stability has not been adequately taken into account in the design of the individual components and in the bearing of the rolling cylinder. The enormously stringent specifications described at the outset can accordingly not be met.
With the shaping tool disclosed by European Patent Disclosure EP 0 866 487 A1 as well, the enormously stringent specifications discussed at the outset cannot be met.
This known shaping tool has a solid rolling cylinder comprising a metal alloy, and the shaping structures are formed directly on its circumferential surface. Nothing is said in the European Patent reference about the rotational support of the rolling cylinder. The glass substrate is plasticized by means of an external heat source before the rolling cylinder, which is not itself heated directly, in conjunction with a counterpart roller impresses the desired structure into the glass substrate.
This European reference again makes no statement as to the requirement for fine-tuning of the coefficients of thermal expansion and the bearing of the rolling cylinder in order to achieve the requisite thermal dimensional stability. In particular because of the solid rolling cylinder, even at slight temperature fluctuations, relatively major changes in length in the shaping structures occur, which exceed the allowable tolerances for forming the channels or ribs.
Producing channel plates by means of shaping tools with structured surfaces has therefore not gained a foothold in the industry.
The production of channel plates is therefore currently done in general by screen printing, in which between 10 and 20 layers of glass solder are deposited, one layer at a time, onto the glass substrate.
This method has the following disadvantages:
long process times
high solder costs
uneven sintering of the channel plates
environmental pollution (lead in the solder, etching solutions)
and therefore from a commercial standpoint allows the production only of prototypes; that is, it is not suited to commercial mass production.
It is the object of the invention to create a shaping tool with a structured surface for creating structures on glass that economically makes it possible to form high-precision microstructures in the glass by local heating of the region of glass to be structured, on the principle of reshaping warm-shaping.
This object is success
Baum Christiane
Disam Joachim
Singer Rudolf
Schott Glas
Vincent Sean E
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