BARRIER RIB FORMATION

Abstract: A method of manufacturing a display device comprising a substrate (1) having barrier ribs (9). The method provides a pattern of barrier ribs (9) of frit material (5) by moving a squeegee (7) relative to a substrate (1). The barrier ribs (9) extend in a longitudinal direction and have a predefined profile (11) in a cross-section which is perpendicular to the longitudinal direction. A contact portion (13) of the squeegee (7) comprises a profile (15) for defining the predefined profile (11). The profile (15) has a groove structure comprising grooves (17) in a cross-section corresponding to the predefined profile (11) in the cross-section of the barrier ribs (9).

Description: Barrier rib formation. 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. 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 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 (β) 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 (β). A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the angle (β) 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°- α, α 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 α. A further embodiment of a method of manufacturing a display device according to the invention is characterized in that the angle α is in the range of 20° to 90°. Good results were obtained when the angle α 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 (β), 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 h3 to the substrate and the groove structure comprises a structure of protrusions spaced at regular intervals w, the protrusions having a length hi and a width between the protrusions equal to wl, where 0.3 x h3 x w < hi x wl < 0.75 x h3 x 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. In the drawings, Figure 1 is a perspective view of a first embodiment of a squeegee according to the invention; Figure 2 is a sectional view in the longitudinal direction of a second embodiment of a squeegee according to the invention; Figure 3 is a sectional view in the longitudinal direction of a third embodiment of a squeegee according to the invention; Figure 4 is a perspective view of a fourth embodiment of a squeegee according to the invention; Figure 5 shows schematically, in a perspective view, a fifth embodiment of a squeegee according to the invention; Figures 6 A, 6B and 6C show various embodiments of the detachable knife according to the invention; Figure 7 shows a cross-section of a squeegee according to the invention having a frit expansion room; and Figure 8 shows a groove structure according to the invention. In general, like reference numerals identify like elements. Figure 1 shows a substrate 1 , usually comprising glass, for use in display devices like, for example, displays of the Plasma Addressed Liquid Crystal Display (PALC) type or the Plasma Display Panel (PDP) type. The substrate 1 has a surface 3, which is covered with a layer of frit material 5 of a suitably chosen composition. By moving a squeegee 7 across the layer of frit material 5 in a direction parallel to the surface 3, a pattern of barrier ribs 9 is provided in the layer of frit material 5. Alternatively, an amount of frit material is shifted by the squeegee to form the barrier ribs 9. In Figure 1, the direction of movement of the squeegee 7 is indicated by an arrow A. The barrier ribs 9 extend in a longitudinal direction, which corresponds to the direction A, and have a predefined profile 1 1 in a cross-section which is perpendicular to the longitudinal direction. The squeegee 7 is moved in the longitudinal direction, a contact portion 13 being in contact with the surface of the substrate 3. Alternatively, the substrate 1 is shifted below a fixed squeegee. The contact portion 13 comprises a profile 1 for defining the predefined profile 11. The profile 15 has grooves 17 in a cross-section which corresponds to the predefined profile 1 1 in the cross-section of the barrier ribs 9. Good results were obtained with a squeegee 7 comprising grooves having a pitch between the grooves of 360 μm, a height of 170 μm and a width of 80 μm at the top of the barrier rib. After formation, the barrier ribs 9 are solidified. The particular solidification step depends upon the composition of the initial frit material and can be done by drying, UN- polymerization and subsequently baking, sintering or any other suitable further solidification step. In practice, the cross-section of the barrier ribs after solidifying may slightly differ from the cross-section of the grooves. Figure 2 is a cross-section of an embodiment of the squeegee. A front surface 21 facing forward in the direction of movement of the squeegee and the surface 3 of the substrate 1 enclose an angle β. The angle β may be chosen within a range of 5° to 120° so as to optimize the process of formation of the barrier ribs. In the shown embodiment, the contact portion 13 comprises an extending profile 15. The profile 15 having the grooves 17 may be a separate piece of metal or a synthetic material in which the grooves 17 are made, which is thereafter connected to the squeegee 7. Alternatively, the profile 15 with the grooves 17 is provided directly in the contact portion 13 which, in this case, has no extending parts. Figure 3 shows the contact portion 13 which has a contact surface 19 being in contact with the surface 3 of the substrate 1. The contact surface 19 has a length s extending in the longitudinal direction. The squeegee 7 has a front surface 21 facing forward in the direction of movement of the squeegee, indicated by an arrow A in the drawing. The squeegee 7 has a slanting surface 22. The slanting surface 22 and the contact surface 19 of the squeegee 7 enclose an angle of 180°- α. Good results were obtained with α varying between -5° and 25°, and the length s being at least equal to 0.05 mm. The extension s can be used to guide the barrier ribs 9 and control the possible swell after release by the squeegee 7. When the squeegee 7 is moved through the frit material 5, a pressure gradient is built up, which forces the frit material 5 through the grooves 17. Different pressure gradients can be obtained by variation of the angle α. The shape of the grooves 17 can be adapted to compensate for possible slumping of the barrier ribs 11 after formation. Another embodiment of the squeegee according to the invention is shown in Figure 4. Here, s is extended and the angle β is substantially equal to 90°. The extra residence time created in this way can be used to solidify the barrier ribs while they are still within the grooves 17 of the squeegee 7. In one embodiment, s is at least equal to 0.5 mm. The squeegee 7 shown in Figure 5 has a rear surface 23 opposite the front surface 21. The contact portion 13 of the squeegee 7 comprises grooves 17 which extend from the front surface 21 to the rear surface 23. These grooves 17 are funnel-shaped and the cross- section 27 of the grooves 17 near the front surface 21 has an area which is equal to or larger than the area of the cross-section 25 of the grooves 17 near the rear surface 23. Suitable values for the angle α are similar to those used in the embodiment shown in Figure 3. This embodiment has the advantage that, in view of the funnel shape, extra pressure can be built up in the frit material, which reduces the curing time of the barrier ribs 9. Figures 6 A, 6B and 6C show various embodiments of the detachable knife 30 according to the invention. This embodiment of the squeegee provides a quick way of changing the predetermined profile 11 of the barrier ribs 9. Such a situation may occur if a switch to a different width or height of the predetermined profile 11 is required. Figure 7 shows a cross-section of a squeegee according to the invention having a frit expansion room 32. In the expansion room 32, expansion of the frit paste is allowed to take place. This leads to a higher accuracy in the manufactured profile of the barrier ribs 9. In practice good results were obtained when the expansion room 32 was located close to the knife 30. A smallest distance of the frit expansion room 23 to the substrate 1 is indicated by h3. Figure 8 shows a groove structure comprising a structure of protrusions spaced at regular intervals w, the protrusions having a length hi and a width between the protrusions equal to wl. A stable operating regime for the method of manufacturing is obtained if the following relation holds: h3 x w = 0.5 x hl x wl This relation is useful in designing the groove structure and the knife 32 and squeegee 7. Example: wl = 60 μm, hi = 200 μm, 0.5° < α < 3.5°, w= 360 μm, and h3 « 70 μm. A useful working area is defined by 0.3 x h3 x w < hi x wl < 0.75 x h3 x w In summary, the invention comprises a method of manufacturing a display device comprising a substrate 1 having barrier ribs 9. The method provides a pattern of barrier ribs 9 of frit material 5 by moving a squeegee 7 relative to a substrate 1. The barrier ribs 9 extend in a longitudinal direction and have a predefined profile 11 in a cross-section which is perpendicular to the longitudinal direction. A contact portion 13 of the squeegee 7 comprises a profile 15 for defining the predefined profile 11. The profile 15 has a groove structure comprising grooves 17 in a cross- section corresponding to the predefined profile 11 in the cross-section of the barrier ribs 9. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims: CLAIMS: 1. A method of manufacturing a display device comprising a substrate (1) having barriers ribs (9), the method comprising the steps of: providing a substrate (1) having a surface (3); and providing a pattern of barrier ribs (9) of frit material (5) by means of a squeegee (7), the barrier ribs (9) extending in a longitudinal direction (A) parallel to the surface (3) and having a predefined profile (11) in a cross-section perpendicular to the longitudinal direction (A), characterized in that the squeegee (7) or the substrate (1) is moved in the longitudinal direction (A), a contact portion (13) of the squeegee (7) being in contact with the surface (3) of the substrate, said contact portion (13) comprising a profile (15) for defining the predefined profile (11), the profile (15) having a groove structure comprising grooves (17) in a cross-section which corresponds to the predefined profile (11) in the cross-section of the barrier ribs (9). 2. A method of manufacturing a display device as claimed in claim 1, wherein the contact portion (13) of the squeegee (7) has a front surface (21), the front surface (21) and the surface (3) of the substrate (1) enclosing an angle (β) in the range between 5° and 120°. 3. A method of manufacturing a display device as claimed in claim 2, wherein the angle (β) is substantially equal to 90°, the contact portion (13) comprising a contact surface (19) which is in contact with the surface (3) of the substrate (1), the contact surface (19) having a length (s) extending in the longitudinal direction and being at least equal to 0.05 mm. 4. A method of manufacturing a display device as claimed in claim 3, wherein the length (s) of the contact surface (19) is at least equal to 0.5 mm. 5. A method of manufacturing a display device as claimed in claim 3, wherein the squeegee (7) has a slanting surface (22), the slanting surface (22) and the contact surface (19) enclosing an angle of 180°- α, α being in the range of -5° to 25°. 6. A method of manufacturing a display device as claimed in claim 5, wherein the angle α is in the range of 20° to 90°. 7. A method of manufacturing a display device as claimed in claim 1 , wherein the squeegee (7) is provided with a detachable knife (30) having the predefined profile (11). 8. A method of manufacturing a display device as claimed in claim 1, wherein the squeegee (7) is provided with a frit expansion room (32). 9. A method of manufacturing a display device as claimed in claim 2, wherein the squeegee (7) has a rear surface (23) opposite the front surface (21), the grooves (17) extending from the front surface (21 ) to the rear surface (23), the grooves (17) being funnel-shaped, and the cross-section (27) of the grooves (17) near the front surface (21) having an area which is equal to or larger than the area of the cross-section (25) of the grooves (17) near the rear surface (23). 10. A method of manufacturing a display device as claimed in claim 8, wherein the frit expansion room (23) has a smallest distance h3 to the substrate (1) and the groove structure comprises a structure of protrusions spaced at regular intervals w, the protrusions having a length hi and a width between the protrusions equal to wl, where 0.3 x h3 x w < hi x wl < 0.75 x h3 x w.

Inventors: BOSMAN JOSEPH C M, BOUTEN PETRUS C P, BUIJS MAARTEN, MEINDERS ERWIN R, PANKERT JOSEPH R R, BOSMAN, JOSEPH, C., M., BOUTEN, PETRUS, C., P., BUIJS, MAARTEN, MEINDERS, ERWIN, R., PANKERT, JOSEPH, R., R.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H01J9
IPC codes: C03C17, G02F1, H01J9, H01J11