Dosing device for dosing a granular material, spraying device and method for applying a granular material to a substrate

Abstract

A dosing device for dosing a granular material containing a reservoir for storing the granular material, a dosing disc, and a suction device and a spraying device containing such a dosing device and a method for applying a granular material to a substrate.

Claims

1. A spraying device (100) for applying a granular material (16) to a surface of a substrate (112), the spraying device (100) comprising a dosing device (10), the dosing device (10) supplying a gas stream comprising the granular material (16), at least one nozzle (108), at least one supply line (104) connecting the dosing device (10) to the at least one nozzle (108) and means for moving a substrate (112) relative to the at least one nozzle (108), wherein the spraying device (100) comprises means for electrostatically charging the particles (17) of the granular material (16), and wherein the dosing device (10) comprises a reservoir (12) for storing the granular material (16), a dosing disc (20), and a suction device (24), wherein the dosing disc (20) is rotatable around a rotational axis (22), the reservoir (12) has a dosing opening (14) facing the dosing disc (20), the dosing opening (14) being arranged above the dosing disc (20) such that a dosing gap is formed between a surface of the dosing disc (20) and a surface (26) surrounding the dosing opening (14), the dosing opening (14) being arranged eccentric with respect to the rotational axis (22), the suction device (24) having an opening (25) facing the dosing disc (20), the opening (25) being arranged above the dosing disc (20) and being arranged eccentric with respect to the rotational axis (22), the size of the dosing gap being such that a monolayer (18) of the particles (17) of the granular material (16) is dosed from the reservoir (12) through the dosing opening (14) onto the surface of the dosing disc (20), the suction device (24) being constructed and arranged such that the monolayer (18) of particles (17) is being sucked into the suction device (24) and mixed with a gas stream when the particles (17) are being transported to the suction device (24) by rotation of the dosing disc (20).

2. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the dosing disc (20) has a surface flatness of 0 to 5 μm and/or has a surface roughness in of from 0.1 to 4 μm.

3. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the surface of the dosing disc (20) is patterned such that the surface has a plurality of indentations (34), the shape of the indentations (34) being such that exactly one particle (17) of the granular material (16) fits in one of the indentations (34).

4. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the size of the dosing gap is larger than the average diameter of the particles (17) and smaller than or equal to two times the average diameter of the particles (17).

5. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the suction device (24) is a Venturi nozzle.

6. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the amount of dosed particles (17) is controlled by parameters selected from the rotational speed of the dosing disc (20), the shape of the dosing opening (14), the distance between the axis of rotation (22) and the center of the dosing opening (14) and combinations of at least two of these parameters.

7. The spraying device (100) according to claim 1, wherein, in the dosing device (10), the reservoir (12) comprises an agitator (28) for stirring the particles (17) of the granular material (16) in the vicinity of the dosing opening (14).

8. The spraying device (100) of claim 1, wherein the at least one supply line (104) is at least partially constructed from a conductive material such that the particles (17) are charged by collisions with the conductive material of the at least one supply line (104).

9. The spraying device (100) of claim 1, wherein the spraying device (100) comprises a vibration system constructed and arranged to apply vibrations to the at least one nozzle (108).

10. The spraying device (100) of claim 1, wherein the distance of the at least one nozzle (108) to the substrate (112) is 25 mm to 500 mm.

11. The spraying device (100) of claim 1, wherein the opening angle of the at least one nozzle (108), the distance of the at least one nozzle (108) to the substrate (112) and, if more than one nozzle is present, the distance between two nozzles (108) are such that an aerosol spray (110) comprising the granular material (16) is generated by the at least one nozzle (108), wherein the aerosol spray (110) covers the entire width of the substrate (112) and wherein no overlap is present between the aerosol sprays (110) generated by two nozzles (108) if more than one nozzle (108) is present.

12. The spraying device (100) of claim 1, wherein the spraying device (100) comprises at least two nozzles (108), wherein each nozzle (108) is connected to the dosing device (10) via a supply line (104) and wherein the supply lines (104) of all nozzles (108) are of equal length.

13. The spraying device (100) of claim 1, wherein the spraying device (100) comprises a spraying chamber (102), wherein the at least one nozzle (108) is located inside the spraying chamber (102), the spraying chamber (102) being constructed to receive the substrate (112) and the spraying chamber (102) being constructed to contain excess particles of the granular material (16).

14. The spraying device (100) of claim 1, wherein the spraying device (100) comprises a spraying chamber (102), wherein the at least one nozzle (108) is located inside the spraying chamber (102), the spraying chamber (102) being constructed to receive the substrate (112) and the spraying chamber (102) being constructed to contain excess particles of the granular material (16).

15. A method for applying a granular material (16) to a surface of a substrate (112), the method comprising supplying the granular material (16) and the substrate (112) to a spraying device (100), and applying the granular material (16) to the surface of the substrate (112) by the spraying device (100), wherein the substrate (112) is a substrate of a switchable window, wherein the spraying device (100) comprises a dosing device (10), the dosing device (10) supplying a gas stream comprising the granular material (16), at least one nozzle (108), at least one supply line (104) connecting the dosing device (10) to the at least one nozzle (108) and means for moving a substrate (112) relative to the at least one nozzle (108), and wherein the dosing device (10) comprises a reservoir (12) for storing the granular material (16), a dosing disc (20), and a suction device (24), wherein the dosing disc (20) is rotatable around a rotational axis (22), the reservoir (12) has a dosing opening (14) facing the dosing disc (20), the dosing opening (14) being arranged above the dosing disc (20) such that a dosing gap is formed between a surface of the dosing disc (20) and a surface (26) surrounding the dosing opening (14), the dosing opening (14) being arranged eccentric with respect to the rotational axis (22), the suction device (24) having an opening (25) facing the dosing disc (20), the opening (25) being arranged above the dosing disc (20) and being arranged eccentric with respect to the rotational axis (22), the size of the dosing gap being such that a monolayer (18) of the particles (17) of the granular material (16) is dosed from the reservoir (12) through the dosing opening (14) onto the surface of the dosing disc (20), the suction device (24) being constructed and arranged such that the monolayer (18) of particles (17) is being sucked into the suction device (24) and mixed with a gas stream when the particles (17) are being transported to the suction device (24) by rotation of the dosing disc (20).

16. The method of claim 15, wherein the substrate (112) is a substrate of an optical device (200) and the particles (17) of the granular material (16) are spacers (210) for separating two substrates of the optical device (200).

17. The method of claim 15, wherein the granular material (16) is mixed with nitrogen gas in the dosing device (10) of the spraying device (100).

18. The method of claim 15, wherein the means for moving the substrate (112) relative to the at least one nozzle (108) is achieved by a conveyor or substrate carrier.

19. A spraying device (100) for applying a granular material (16) to a surface of a substrate (112), the spraying device (100) comprising a dosing device (10), the dosing device (10) supplying a gas stream comprising the granular material (16), at least one nozzle (108), at least one supply line (104) connecting the dosing device (10) to the at least one nozzle (108) and a conveyor or substrate carrier for moving a substrate (112) relative to the at least one nozzle (108), wherein the spraying device (100) comprises at least one supply line which is at least partially constructed from an electrically conductive material such that the particles are charged by collisions with the conductive material of the supply line thereby electrostatically charging the particles (17) of the granular material (16), and wherein the dosing device (10) comprises a reservoir (12) for storing the granular material (16), a dosing disc (20), and a suction device (24), wherein the dosing disc (20) is rotatable around a rotational axis (22), the reservoir (12) has a dosing opening (14) facing the dosing disc (20), the dosing opening (14) being arranged above the dosing disc (20) such that a dosing gap is formed between a surface of the dosing disc (20) and a surface (26) surrounding the dosing opening (14), the dosing opening (14) being arranged eccentric with respect to the rotational axis (22), the suction device (24) having an opening (25) facing the dosing disc (20), the opening (25) being arranged above the dosing disc (20) and being arranged eccentric with respect to the rotational axis (22), the size of the dosing gap being such that a monolayer (18) of the particles (17) of the granular material (16) is dosed from the reservoir (12) through the dosing opening (14) onto the surface of the dosing disc (20), the suction device (24) being constructed and arranged such that the monolayer (18) of particles (17) is being sucked into the suction device (24) and mixed with a gas stream when the particles (17) are being transported to the suction device (24) by rotation of the dosing disc (20).

20. The spraying device (100) of claim 19, wherein the spraying device (100) comprises a vibration system constructed and arranged to apply vibrations to the at least one nozzle (108).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings show:

(2) FIG. 1 a dosing device in a schematic sectional view,

(3) FIG. 2 the dosing device in a perspective view,

(4) FIG. 3 delivery of particles onto a dosing disc,

(5) FIG. 4 delivery of particles onto a patterned dosing disc,

(6) FIG. 5 schematic overview of a spraying device,

(7) FIG. 6 a cross section view of a liquid crystal cell, and

(8) FIG. 7 spacer distribution and test fields on a substrate.

(9) FIG. 1 depicts a dosing device 10 in a schematic sectional view. The dosing device 10 comprises a reservoir 12, a dosing disc 20 and a suction device 24. The reservoir 12 and the suction device 24 are arranged above the dosing disc 20. The dosing disc 20 may rotate around a vertical rotation axis 22.

(10) The reservoir 12 comprises a funnel section 13 leading towards a dosing opening 14. The dosing opening 14 faces the upper surface of the dosing disc 20. Inside the reservoir 12 granular material 16 is stored. The granular material 16 is delivered through the dosing opening 14 onto the dosing disc 20 by means of gravitation. In the embodiment of FIG. 1, an agitator 28 is mounted within reservoir 12 in order to support the delivery of the granular material 16. In order to avoid generation of conductive particles by the agitator 28 scraping the inner wall 15 of the reservoir 12, at least the part of the inner wall 15 which is in the vicinity of the agitator 28 is preferably made from a non-conductive material.

(11) Granular material 16 is delivered onto the dosing disc 20 in form of a monolayer 18 of granular material 16. The monolayer 18 is transported from the underside of the dosing opening 14 to the suction device 24 by means of rotating the dosing disc 20.

(12) The suction device 24 has an opening 25 facing the dosing disc 20. Inside the suction device 24, the gas pressure is reduced with respect to the gas pressure in the vicinity of the dosing disc 20 so that a stream of gas is sucked into the suction device. The stream of gas drags particles of the monolayer 18 along into the suction device 24 generating a mixture of gas and particles. The gas is, for example, dry air or nitrogen.

(13) By means of the monolayer 18, a defined amount of particles of the granular material 16 is transported to the suction device 24 and is then mixed with a defined amount of gas so that a mixture of gas and particles having a defined particle density with low deviations is formed.

(14) As can be seen from FIG. 1, a plane of the dosing opening 14 as well as a plane of the opening 25 of the section device 24 are orientated parallel to the plane of the dosing disc 20. Further, both the reservoir 12 as well as the suction device 24 are arranged eccentrically with respect to the rotation axis 22. The center of the dosing opening 14 and the center of the opening 25 of the suction device 24 have the same distance from the rotation axis 22.

(15) FIG. 2 shows a perspective view of the dosing device 10. The reservoir 12 and the suction device 24 are mounted above the dosing disc 20. The reservoir delivers a monolayer 18 of granular material onto the dosing disc 20. The monolayer 18 of granular material is transported from below the reservoir 12 towards a position below the suction device 24 by means of rotating of the dosing disc 20. A gas stream, such as air or nitrogen flows into the suction device 24 and carries the particles of the monolayer 18 into the suction device 24.

(16) FIG. 3 shows an enlarged schematic view of the delivery of particles onto the dosing disc 20. The funnel section 13 of the reservoir 12 leads towards the dosing opening 14 which is arranged above the surface of the dosing disc 20. The dosing opening 14 is mounted at a distance 30 from the surface of the dosing disc 20 and forms a dosing gap.

(17) Particles 17 of the granular material drop out of the reservoir 12 through the dosing opening 14 onto the surface of the dosing disc 20. By means of rotation of the dosing disc 20, the particles 17 are moved away from below the dosing opening 14. The direction of rotation is indicated by an arrow 23. In the example shown in FIG. 3, the particles 17 have a spherical shape so that their size is defined by their diameter.

(18) The size of the dosing gap is chosen such that only a monolayer 18 of particles 17 may be transported by the dosing disc 20. The surface 26 surrounding the dosing opening 14 acts like a squeegee. The squeegee blocks any further layers of particles 17 from following the rotation of the dosing disc 20 and thus blocks the transport of further particles to the suction device 24.

(19) Preferably, the size of the dosing gap is chosen such that the distance between the dosing opening 14 and the surface 26 of the dosing disc 20 is larger than the diameter of the particles 17 and smaller than or equal to twice the diameter of the particles 17. Due to the chosen size of the dosing gap the surface 26 or squeegee wipes off any particles 17 in excess of those particles 17 forming the monolayer 18.

(20) In the embodiment shown if FIG. 3, the surface of the dosing disc 20 has a roughness 32 in order to provide sufficient friction so that the particles 17 stay in place when the dosing disc 20 rotates. Preferably, the surface roughness Ra of the dosing disc 20 is in the range of from 0.1 to 4 μm, especially preferred in the range of from 2 to 3.5 μm. Ra is the arithmetic average of the surface roughness measured along a line profile.

(21) In FIG. 4 an alternative embodiment of the dosing disc 20 is shown. The surface of the dosing disc 20 is patterned and features a plurality of indentations 34. The indentations 34 match the shape of the particles 17 of the granular material such that exactly one particle 17 fits into one of the indentations 34. The distance of the dosing opening 14 to the surface of the dosing disc 20 is measured from the bottom of the indentations to the dosing opening 14.

(22) As already described with respect to FIG. 2, the dosing disc 20 rotates as indicated by the arrow 23 and transports particles 17 from below the dosing opening 14 to the suction device 24. The surface 26 surrounding the dosing opening 14 wipes off any excess particles which may form additional layers in excess of the monolayer 18.

(23) FIG. 5 shows a spraying device 100 comprising a dosing device 10, a distributor 120 and a spraying chamber 102. Inside the spraying chamber 102 several nozzles 108 are mounted onto a spray bar 106. Further, a conveyor 114 is arranged inside the spraying chamber 102 and configured to receive a substrate 112 and to transport the substrate 112 through the spraying chamber 102.

(24) Each nozzle 108 is connected to the distributor 120 through a separate supply line 104. The dosing device 10 is connected to the distributer 120 and supplies a mixture of gas and particles 17 of the granular material to the distributor 120.

(25) Each of the nozzles 108 is configured to produce an aerosol spray 110 having a defined opening angle. The distance 116 between the nozzles 108 and the substrate 112 as well as the distance 118 between two of the nozzles 108 are chosen such that the aerosol sprays 110 cover the entire width of the substrate 112 while an overlap between aerosol sprays 110 of two nozzles 108 or gaps between the aerosol sprays 110 are avoided.

(26) In order to coat a surface of the substrate 112 with particles 17 of the granular material, the substrate 112 is moved through the aerosol sprays 110 by means of the conveyor 114. The density of the particles 17 on the surface of the substrate 112 may be controlled by adjusting the supplied mixture of gas and particles and by adjusting the movement speed of the conveyor 114.

(27) The process of coating the surface of the substrate 112 is performed inside the spraying chamber 102. The spraying chamber 102 contains any excess particles which are not delivered to the substrate 112 in order to avoid contamination of the environment.

(28) FIG. 6 shows an example of a liquid crystal device 200. The liquid crystal device 200 comprises a first substrate 202, a second substrate 204 and liquid crystalline layer 206 sandwiched between the two substrates 202, 204. Particles 17 are placed between the two substrates 202, 204 and act as spacers 210 to maintain a gap between the two substrates 202, 204 of constant width. The liquid crystal is located inside the formed gap. The liquid crystal device 200 additionally comprises a seal 208 which closes the gap.

(29) FIG. 7 shows the distribution of particles 17 acting as spacers on a first substrate 202. The distribution of the spacers must be uniform in order to guarantee a constant gap width in a liquid crystal device 200. For analysis, nine test fields 301 to 309 have been distributed over the surface of the first substrate 202. The number of particles 17 in each of the test fields 301 to 309 is determined by taking a microscopy image of the respective test field and counting the particles 17 in the microscopy image.

(30) The number and distribution of particles 17 in each of the test fields is analyzed. If the number of particles 17 in a field is too low, forces exerted onto the liquid crystal device 200 may compress the gap in this field. The width of the gap is then smaller than intended resulting in visible defects of the liquid crystal device 200. If the number of particles 17 in a test field is too high, the properties of the liquid crystal surrounding the particles may be disturbed resulting in visible optical defects of the liquid crystal device.

(31) Further, clusters of particles 17 must be avoided. Clusters are agglomerates of two or more particles 17. These clusters are usually large enough to be visible to the naked eye and are thus a visible optical defect. In the field #309 a cluster of 4 particles 17 is depicted.

EXAMPLES

(32) A spraying device having 16 nozzles arranged on a spray bar is used to coat glass substrates with a testing powder. The distance between two nozzles (nozzle pitch) is set to 94 mm. Thus, the maximum width of a substrate which may be coated with this testing setup is about 1500 mm. The powder particles are located in a reservoir of a dosing device. The dosing device is used to provide a mixture of gas and spacer particles to the spraying device.

(33) The dosing opening and the opening of the suction device of the dosing device are mounted at a distance of 20 mm from the axis of rotation. The rotation speed of the dosing disc, the size of the dosing gap between the surface of the dosing disc and the dosing opening are adjustable. As suction device, a Venturi nozzle is used with an adjustable Venturi pressure.

(34) The distance between the nozzles and the glass substrate is adjustable. A conveyor belt is used to move the glass substrates relative to the nozzles.

(35) For analysis of the achieved distribution of particles, a microscopy camera imaging an area of about 5 mm.sup.2 is placed on different positions on the substrate. The image of the microscope camera is acquired using a USB microscope and then analyzed. In a recorded frame, the number of particles is counted for each of the tested positions. Further, the presence of clusters of more than one particle is recorded.

(36) Four glass substrates of size 400 mm×400 mm are coated with polyimide. The polyimide is rubbed in order to create an alignment layer for liquid crystals.

(37) In this example, the anti set-off powder S5/20 available from KSL staubtechnik gmbh, Germany is used as a testing powder. This powder used is based on native starch. The median particle size is 20.6 μm and the amount of particles having a size of less than 10 μm is 6.3% by volume.

(38) 16 nozzles are used and the distance of the nozzles to the substrate glass is set to 200 mm and the speed of the conveyor is set to move the glass substrate relative to the nozzles at a speed of 6 m/min.

(39) The dosing device is operated with the rotation speed of the dosing disc set to 5 rpm and a size of the dosing gap of 30 μm. The Venturi pressure is set to 0.45 bar.

(40) Nine measurement fields having an imaging area of about 5 mm.sup.2 are evenly distributed in three rows (A, B, C) and three columns (1, 2, 3) over the surface of the glass substrates. The number of spacers in each field is counted and clustering is recorded. The measurement results are listed in tables 1 to 4. The average number of particles in a field for each of the substrates as well as the respective standard deviation is given in table 5. Clustering of the particles is not observed.

(41) TABLE-US-00001 TABLE 1 1 2 3 C 9 16 12 B 9 3 8 A 11 6 11

(42) TABLE-US-00002 TABLE 2 1 2 3 C 4 9 6 B 6 5 7 A 4 5 3

(43) TABLE-US-00003 TABLE 3 1 2 3 C 8 4 6 B 10 4 6 A 10 14 12

(44) TABLE-US-00004 TABLE 4 1 2 3 C 12 10 13 B 11 11 5 A 12 9 6

(45) TABLE-US-00005 TABLE 5 Average number of Substrate number particles Standard deviation 1 9.4 3.5 2 5.4 1.7 3 8.2 3.3 4 9.9 2.6

LIST OF REFERENCE NUMERALS

(46) 10 dosing device 12 reservoir 13 funnel 14 dosing opening 15 inner wall 16 granular material 17 particle of granular material 18 monolayer of granular material 20 dosing disc 22 rotation axis 23 direction of rotation 24 suction device 25 opening 26 surface 28 agitator 30 dosing gap 32 surface roughness 34 indentations 100 spraying device 102 spraying chamber 104 supply line 106 spray bar 108 spray nozzle 110 aerosol spray 112 substrate 114 conveyor 116 distance from nozzle to substrate 118 nozzle stitch 120 distributor 200 liquid crystal device 202 first substrate 204 second substrate 206 liquid crystalline layer 208 seal 210 spacer