Coating processes – Optical element produced
Reexamination Certificate
2000-03-09
2002-03-19
Beck, Shrive (Department: 1762)
Coating processes
Optical element produced
C427S277000, C427S286000, C427S356000, C118S044000, C118S056000, C118S100000
Reexamination Certificate
active
06358560
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to display devices, and more particulary to a method of manufacturing a display device with a substrate having barrier ribs.
BACKGROUND AND SUMMARY OF THE INVENTION
A method of manufacturing a display device comprising a substrate having barrier ribs is known. EP-A 0 472 781 describes a thick-film printing method which comprises the steps of printing a glass paste on a transparent flat plate by using a printing screen and a so-called squeegee (or doctor blade or structured knife), and subsequent drying of the paste. The printing and drying steps are repeated five to ten times. However, the five to ten repetitions of superposed printing of the glass paste disturb the required shape of the barrier ribs and cause an inaccuracy of their height. This may lead to a reduction of the quality of the images that are displayed on the display device. The cited document describes an improvement of the printing method by providing, prior to the printing step, the substrate with a layer of an organic film having grooves. The grooves are filled with a glass paste using a printing method several times, and a drying step for solidifying the glass paste, after which the organic layer is removed. However, this method has the drawback that it comprises many process steps and is therefore time-consuming and costly.
It is an object of the invention to reduce the problems and drawbacks indicated above. The invention relates to a method of manufacturing a display device comprising a substrate having barriers ribs, the method comprising the steps of providing a substrate having a surface, and providing a pattern of barrier ribs of frit material by means of a squeegee, the barrier ribs extending in a longitudinal direction parallel to the surface and having a predefined profile in a cross-section perpendicular to the longitudinal direction.
The method of manufacturing a display device according to the invention is characterized in that the squeegee or the substrate is moved in the longitudinal direction, a contact portion of the squeegee being in contact with the surface of the substrate, said contact portion comprising a profile for defining the predefined profile, the profile having a groove structure comprising grooves in a cross-section which corresponds to the predefined profile in the cross-section of the barrier ribs. In practice, the cross-section of the barrier ribs after curing may slightly differ from the cross-section of the grooves. This method of manufacturing a display device has the advantage that it is simple and that an accurate profile of the barrier ribs can be obtained in one manufacturing step, apart from an additional solidifying step.
An embodiment of a method of manufacturing a display device according to the invention is characterized in that the contact portion of the squeegee has a front surface, the front surface and the surface of the substrate enclosing an angle (&bgr;) in the range between 5° and 120°. This embodiment provides much freedom in the design of the squeegee. In addition, in this embodiment, the squeegee acts as a wedge. The wedge shape causes the build-up of a pressure gradient in the frit material when the squeegee is moved across the substrate, which forces the frit paste to flow through the grooves. Different pressure gradients can be obtained by variation of the angle (&bgr;).
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the angle (&bgr;) is substantially equal to 90°, the contact portion comprising a contact surface which is in contact with the surface of the substrate, the contact surface having a length s extending in the longitudinal direction and being at least equal to 0.05 mm. In this embodiment, the frit paste is in contact with the grooves of the squeegee for a relatively long time. Experimentally, it has been observed that an extended residence time improves the curing process of the frit paste. In addition, a contact portion of the squeegee is in contact with the surface of the substrate, which helps building up a pressure in the frit material and thus improves the formation of the barrier ribs.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the length s of the contact surface is at least equal to 0.5 mm. This embodiment has the advantage that the contact portion of the squeegee is extended. The extra residence time obtained in this way can be used to cure the barrier ribs while they are still within the grooves of the squeegee.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the squeegee has a slanting surface, the slanting surface and the contact surface enclosing an angle of 180°-&agr;, &agr; being in the range of −5° to 25°. The wedge shape of the squeegee causes the build-up of a pressure gradient in the frit material when the squeegee is moved across the substrate, which forces the frit paste to flow through the grooves. Different pressure gradients can be obtained by variation of the angle &agr;.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the angle &agr; is in the range of 20° to 90°. Good results were obtained when the angle &agr; was chosen in this range.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the squeegee is provided with a detachable knife having the predefined profile. This embodiment of the squeegee provides a quick way of changing the predetermined profile. Such a situation may occur if a switch to a different width or height of the predetermined profile is required.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the squeegee is provided with a frit expansion room. In this embodiment, the method of manufacturing is less dependent upon the angle (&bgr;), which results in a more stable process.
Another embodiment of a method of manufacturing a display device according to the invention is characterized in that the squeegee has a rear surface opposite the front surface, the grooves extending from the front surface to the rear surface, the grooves being funnel-shaped, and the cross-section of the grooves near the front surface having an area which is equal to or larger than the area of the cross-section of the grooves near the rear surface.
In this embodiment, the grooves have a funnel shape, which helps to increase a further build-up of the pressure in the frit material and consequently improves the solidification of the barrier ribs.
A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the frit expansion room has a smallest distance h
3
to the substrate and the groove structure comprises a structure of protrusions spaced at regular intervals w, the protrusions having a length h
1
and a width between the protrusions equal to w
1
, where
0.3×
h
3
×
w<h
1
×
w
1
<0.75
×h
3
×
w
In this embodiment, a stable process for forming the barrier ribs is obtained.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.
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Bosman Joseph C. M.
Bouten Petrus C. P.
Buijs Maarten
Meinders Erwin R.
Pankert Joseph R. R.
Beck Shrive
Markham Wesley
U.S. Philips Corporation
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