Glass spacer

Details Glass spacer Glass spacer

2000-04-27

2004-01-13

Ahmad, Nasser (Department: 1772)

Stock material or miscellaneous articles

Nonrectangular sheet

C052S172000, C052S786130, C428S066400, C428S066700, C428S409000, C428S410000, C428S432000

Reexamination Certificate

active

06677024

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a glass spacer having an approximately polygonal bearing cross section, intended to keep two flat substrates spaced apart.
Although the invention is not limited to such applications, it will more particularly be described with reference to spacers used for maintaining a space between two glass sheets, more particularly a space of small thickness, generally of less than a few millimetres, over the entire surface of the glass sheets.
2. Discussion of the Background
Such a configuration is widely sought in the production of display screens, whatever the technology involved. They may be plasma screens or field-emission (FED) screens, such as microdot screens. Such a configuration may also be sought for the production of vacuum glazing or for flat lamps. The expression “flat lamps” should be understood as encompassing lamps that may have a curvature over at least part of their surface, whatever, moreover, the technology of these lamps.
This is because, in this type of screen, a small space must be maintained, especially in order to create a vacuum between the two glass sheets.
It is known, as described in document WO-81/01910, that this type of screen, more particularly the outer glass sheet, i.e. the glass sheet seen by an observer, must have a high optical transparency.
The spacers making it possible to maintain a space between the two glass sheets must consequently be the least visible possible.
It has been proposed to produce glass spacers in the form of polished cylinders or balls so as to be the least visible possible.
Although these spacers seem to be readily producible on an industrial scale, there are stability problems in their use. This is because the rounded shapes cause rolling movements during installation or possibly after fitting.
To remedy this problem, it has therefore been envisaged to produce glass spacers having a rectangular cross section. Because of their flat surfaces in contact with the glass sheets, these spacers provide better stability.
Another drawback resides in the preparation of these spacers. They are generally produced by machine, which does not allow polished surfaces to be obtained in a simple manner.
To alleviate these drawbacks, document EP-0,627,389 A has therefore proposed a process for manufacturing a glass polyhedron in which a preform of polygonal cross section, advantageously polished on all its lateral faces, is firstly drawn and then cut into several rods, which rods, after they have been collected together, are in turn cut to the desired length and then polished at their ends.
This technique is advantageous in so far as it allows glass spacers to be produced, at lower cost, with dimensions that are nevertheless quite difficult, each of these glass polyhedra having very small dimensions, directly equal to those required by the intended application.
This is because, in the case of display screens, such as microdot screens, the spacers have to be installed very precisely on separating strips. These separating strips are provided either in one direction, or in two perpendicular directions, in order to delimit the colour pixels. Installing the spacers has to be carried out so that they do not encroach on the pixel areas.
SUMMARY OF THE INVENTION
The inventors were thus tasked with the mission of defining glass spacers which fulfil their space-maintaining function between, for example, two flat substrates and which may be installed precisely, for example without any risk of disturbing the pixels, and the installation of which may be carried out in an industrializable manner.
The word “industrializable” should be understood to mean that the spacers must be able to be installed precisely and reproducibly, for example with the aid of an industrial robot, bearing in mind the precision of the latter.
This objective is achieved according to the invention by a glass spacer, obtained by a drawing process, having an approximately polygonal bearing cross section with at least one rectilinear surface which falls within a rectangle of dimensions a, b, the said spacer having a height
1
, and the dimensions of the spacer satisfying the following relationships:
a<300 &mgr;m
0.2 mm<1<20 mm
b/a<1000 and preferably b/a<200.
A spacer thus defined according to the invention may fulfil its function, for example between two glass sheets in the case of a display screen. Moreover, it is possible to install such spacers with the aid cf an industrial robot; it is especially possible to position such spacers on the separating strips without any risk of obstructing the pixels, bearing in mind the uncertainty in the precision of the robots and the minimal dimensions required in order to fulfil the function. For applications relating to screens of the medium-voltage and high-voltage FED type, the dimensions of the spacer advantageously satisfy the relationship: 0.5<1<5 mm and preferably 1<1<3.
According to a preferred embodiment, the dimensions of the spacer satisfy the relationship:
0.1<b/1, and preferably 1<b/1.
Such a condition allows the stability of the spacer to be improved, this improvement being useful particularly when the robot grips the spacer, in order to be certain of the automatic orientation of the said spacer, and when the latter is deposited on a substrate so that it does not fall over.
Also to improve the gripping of the spacer by a robot, since its orientation is fixed, the dimensions of the spacer advantageously satisfy the relationship:
b/
1
≦50.
Such spacers may be produced using a technique such as that proposed in document EP-0,627,389 A. This document describes a process which consists in drawing a glass preform or rod having a cross section with a shape approximately identical to that which it is desired to obtain to within a homothetic ratio. This preform has a large enough size to be able to be accurately machined to the desired cross section. In addition, this preform is initially polished on its lateral faces.
This drawing step takes place with the temperature of the preform raised to a temperature close to its softening temperature and the actual drawing then takes place in one or more steps.
The drawn rod obtained after drawing the preform has a cross section with a shape similar to that of the preform to within a homothetic ratio, which corresponds to the cross section of the desired spacers. Moreover, the rod has a polished appearance on its side faces because it passes through a high temperature which creates a “fire polish.” This phenomenon may make it possible to use a preform not polished on its lateral faces but having another appearance, such as a “finely ground” appearance. The invention refers, through the term “fire polish,” to a surface roughness (rms value) of less than 5 Å measured by AFM (atomic force microscopy) on a scanned area of approximately 6 &mgr;m
2
. Preferably, this roughness is of the order of 2Å.
These rods are collected together so as to be mutually parallel. Preferably, these rods are collected together in a cylinder, especially a glass cylinder, and are joined together using a binder such as a wax or adhesive.
Next, the bundle of rods is cut to the desired length so that they form the desired spacers.
Having obtained the length, the bundle of spacers is ground then polished at the two ends. It is thus possible to obtain spacers polished over all their faces. In addition, if the cutting operation is not very precise, it is thus possible to rectify the length of the spacers during the polishing operation.
Next, the spacers are separated from one another, especially by melting the binder, or by chemical dissolution.
The process thus described makes it possible to obtain spacers with precise dimensions and at a lower cost. This is because the manual operations carried out by an operator are very limited. On the one hand, this reduces the production costs and, on the other hand, the operations leading to the dimensions, by not being manual, are both precise and regular.
According to one

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