PROCESS AND DEVICE FOR COATING DISKS

Abstract: Device for coating disks (3), particularly optically readable data carriers, with a holding device (2) for holding a disk to be coated (3), an annular nozzle unit (8) for the application of coating liquid to the disk (3) and a collection zone (7). The coating liquid is applied continuously from the nozzle unit (8) and reaches the collection zone (7) via an annular wetting zone (15), being returned from the collection zone (7) to the nozzle unit (8) via a storage tank (19). The movement unit (6) permits the disk (3) to be brought concentrically into contact with the wetting zone (15) and again removed from it. A ring (16) of coating liquid remains on the disk (3) as a result of adhesive forces. This ring (16) is uniformly distributed over the disk, for example, by means of a centrifuge. The continuous flow of coating liquid permits a constant viscosity of the coating liquid to be achieved. Those problems which can occur with straight-line application are avoided. Moreover, the design of the coating device is simple.

Description: Process and Device for Coating Disks The invention concerns a device according to the description in claim 1 and a process according to the description in claim 8. During the production of compact disks or optically readable data carriers, for example, CD-R disks or digital video disks (DND), the disk is placed on a rotating support in a clean-air room and a coating liquid applied to the rotating disk from above by means of a nozzle. The centrifugal force acting upon the rotating disk is supposed to distribute the coating liquid outward and evenly over the disk. The demands imposed relative to maintaining the desired coating depth are great. Following the application of those layers acting as information carriers, a protective coating, in particular a lacquer coating, is applied. In the case of DVDs with multiple layers, or coated on both sides, the two disk parts must be bonded together with an extremely precise interval separating them. To prevent disturbances, it is necessary to ensure that the layer thicknesses themselves are formed very accurately and that the bond will result without trapping gas bubbles. Contaminants which could settle onto the coating from above must be prevented with expensive installations in the clean-air rooms. A coating device is known from EP 356,140 which coats a disk lying on a rotating support inside a sealed chamber through a discharge or nozzle port. A small clearance above the disk is supposed to prevent any droplets thrown off by the rotating movement of the disk edge from reentering on or below the disk through the circulation system. It was then however found that a sealed space above the disk can lead to increased temperature or an uneven temperature distribution on the support as a result of the heat arising from the drive for the disk support. Temperature differences on the disk or in the applied coating liquid can lead to differences in flow behavior and correspondingly uneven coating thicknesses. At the start of the coating process, the fluid present in the supply line to the nozzle can have a temperature different from that of the liquid flowing in from the storage container. Moreover, droplet formation on the nozzle opening can lead to disturbances at the beginning or end of the coating operation. Because the liquid cannot be applied exactly during precisely one revolution of the disk, steps in the applied coating composition can result in the starting or end zones. These .are broken up by flow, but often not completely, particularly in the case of coating materials of high viscosity. Temperature-dependent flow behavior will also lead then to problems when the discharge nozzle is moved radially over the disk with a precision movement device. When coating with a movable nozzle, the coating liquid is applied to the disk in precise bands precisely where it is supposed to be. The construction of the movement device must be extremely complex and, in addition, together with the rotating movement and a metering pump for the coating liquid, controlled by a complex mechanism. Because the fluids to be applied may also possibly harden at the outlet when the rate of flow decreases, the danger also arises that the supply lines may become plugged. The invention therefore addresses the problem of finding a device and/or process, which makes it possible at low cost to provide the disk with a precise and rotationally symmetrically distributed coating of constant quality and without contamination. This problem is solved by the characteristics of claims 1 through 8. The dependent subclaims describe advantageous execution variants. During the solution of the problem it was recognized that a linear application, or the application of the coating liquid with a nozzle having the form of a hole, leads to the significant quality problems and to the complex design of the known solutions. If the coating liquid can be conveyed essentially continuously by an annular wetting zone and collected in a collection zone, a rotationally symmetrical application of the coating liquid can be achieved by the contact of the disk to be coated with the wetting zone. The device components required to achieve that and also the control are very simple. It is possible to do without a rotating support, a movable discharge opening and a metering device. A constant viscosity of the coating liquid can be achieved by a continuous flow of the same, and no problems result as a result of droplet formation, blockage and temperature variations in the supply lines. These advantages result in production with constant quality. Because no extremely exact dosage of small throughput quantities is necessary, the coating device need not be adapted to the coating liquid used. Correspondirigly, both dyes and lacquers as well as bonding materials can be applied with a standard device. Following the application of the coating materials to an annular zone of the disk, a distribution takes place in a radial direction, according to the respective purpose of the coating. Use is made in this case of a centrifugal process, at least for coatings of dye and protective lacquer. During the centrifugal process, the material applied in a ring is moved radially outward as a result of centrifugal force, until a layer with a constant thickness is formed. The initial application must thus take place at the inner edge of the disk. The portion thrust outward is preferably collected and reused after a filtration and/or degassing step. To permit the preparation of an uncoated outer edge, a cleaning step per the state of the art is provided, particularly with a cleaning jet aimed radially outward. To prevent the mixing of the clean coating material with that portion washed off with the cleaning fluid, the centrifuging and cleaning take place within different recovery zones. If necessary, the centrifuging takes place already in the coating and the cleaning in a different device. For both steps, however, the disks are optionally transported into a centrifuge, in which two different annular slots, perhaps alternating, are arranged radially outside the disk, a first annular slot being used for distribution by centrifugal action and a second annular groove for the cleaning of the disk surface. The radial distribution of bonding coatings takes place optionally by means of a pressing and/or suction operation. For that purpose, at least one of the disks to be bonded together is impacted with bonding material in an annular pattern. The disks are then Oplaced one upon the other and optionally pressed together. The pressing together will then in that case preferably take place by means of a suction process in the central, or optionally in the outer zone of the ring, so that the bonding material will be distributed radially over the desired area, and the disks are bonded together at a desired distance from one another after the bonding material has hardened. The selected width and diameter of the wetting zone will depend upon the additional processing desired. The annular nozzle unit preferably forms an overflow arrangement during which the coating liquid will flow out in an upward direction, radially outward or optionally inward over a nozzle boundary and, due to the force of gravity, reach the collection zone. The wetting zone thereby lies above the nozzle boundary as an overflow level. It is obvious that an arrangement set up differently can also be provided in place of the overflow arrangement, in which case the fluid after exiting, or running through the wetting zone, will not continue to flow due to gravity, but is actively guided by a suction device. When the upper side of the disk is coated, as in the case of the known solutions, the danger arises that droplets of liquid will reach the lower side of the disk due to the force of gravity. When the lower side of the disk is coated, as provided for per a preferred execution variant, no coating liquid will reach the upper side which is not to be coated. There is also no danger that dirt particles will settle onto the coating from above. From the collection zone the coating liquid is sent, preferably via a separation device, to a storage container which will include, for example, a filtering and/or degassing device. The coating liquid will be prepared anew from the storage container and sent via a conveyer arrangement to the nozzle unit. In the case of a simple annular nozzle, the latter is supplied over a rotationally symmetrical distribution arrangement in order to generate a rotationally symmetrical outflow pattern from a central feed. There are also advantageous execution variants in which the nozzle unit is built up from individual nozzles arranged in the shape of a ring. In that case, these individual nozzles can be supplied over a common, but also each over a separate, feed line. In the case of individual nozzles and optionally also in that of an undivided annular nozzle, there is also the possibility for the formation of a pulsing wetting zone. For example, a device for varying the throughput is provided, which makes it optionally possible to obtain varying or pulsing partial flows on the periphery of the wetting zone with a rotating part of the nozzle. This can be advantageous when making contact and, in particular, when releasing the contact between the disk and the wetting zone on the basis of the defined contact boundaries and their shift. Execution variants are also possible, in which the disk is in contact with the liquid in the wetting zone, not along a closed periphery, but only within rotating segments of the same. This is achieved for example when a projecting fluid contact zone moves along the wetting zone as a wave front. An effect like that achieved for example with a pulsing wetting zone can also be obtained with a tumbling movement of the disk: Provision is thereby made in a possible execution variant for the holding device to contain a tumbling unit. Because in particular the transition from laminar to turbulent flow has an influence upon the distribution of the applied coating liquid, it is sufficient in some cases for a tumbling or tipping movement to be executed during the separation of the disk from the wetting zone. The result of the tumbling movement during separation of the disk from the fluid is that a contact-free zone of increasing length arises on the boundary line. In some cases, in the case of a tumbling disk, it is expedient to dispense entirely with a circular closed contact between the disk and the fluid and to provide merely an increasingly and decreasingly rotating contact length during approach and removal. If the contact is to take place simultaneously along the entire periphery, the danger arises that gas bubbles will be included. This can be prevented with a tumbling movement already during the approach of the disk. When joining two disks by means of a bonding material, it can in some cases be expedient for an optimal distribution of the material applied to a disk if one of the two disks executes an analogous tumbling movement, but with a minimal deflection. The drawings explain the invention with the aid of an execution variant. In the drawings: Fig. 1 is a vertical section through a coating device before the disk comes into contact with the coating liquid, Fig. 2 presents a vertical section through an annular nozzle device and a disk which comes into contact with the coating liquid, Fig. 3 is a vertical section through an annular nozzle unit and a disk which is coated with the coating liquid in an annular pattern, Fig. 4 is a schematic view of the rotating arrangement for a coating liquid, Fig. 5 shows a vertical section through two disks to be bonded together, Fig. 6 and 7 each show a vertical section through a holding arrangement for bringing two disks together, before and after they are brought together. Fig. 1 shows a coating device 1 with a holder 2 for holding a disk 3 to be coated. The holding device 2 includes a contact zone 4 against which the disk 3 lies. To obtain the holding force, a partial vacuum is induced in a channel of the contact zone provided for the purpose. The holding force could also however be generated by a mechanical clamping device. The holder 2 preferably includes a rotating drive 5, so that a centrifugal process can thus be carried out after application of the coating liquid. A movement device 5 of the holding arrangement 2 makes it possible to receive the disk 3, to move it into the coating device 1 or into a coating zone, and to hand it off to a device for additional processing once it is coated. Formed around and beneath the coating zone is a collection zone 7 which collects both the fluid 9 flowing downward from a circular ring nozzle 8 as well as that fluid cast off by the disk. A connecting line 10 to the collection zone 7 is provided in order, if necessary, to permit also the recovery of fluid from the interior of the ring nozzle 8. From the collection zone 7, the liquid flows further through a drainage line 11. The ring nozzle 8 is the outlet port of an annular channel 12, which leads from a disk-shaped distribution zone 13 to the ring nozzle 8. The distribution zone 13 is supplied with coating liquid centrally through a feed line 14. In the execution variant shown, the inner edge of the ring nozzle 8 extends upward somewhat further than the outer edge, so that the coating liquid flowing upward through the annular channel 12 will flow radially outward over the outer edge on exiting the ring nozzle 8. The liquid projecting above the ring nozzle 8 in an annular pattern forms a wetting zone 15. To obtain a uniform coating on all disks coated one after the other it is extremely important for the coating liquid in the wetting zone 15 to have a defined viscosity. For that it must be possible to set the temperature precisely. A heater 13a is assigned to the distribution zone 13 in the execution variant shown. At least one temperature value of the coating liquid is detected as a control value for controlling the heat output. Unwanted temperature changes prior to exit from the ring nozzle 8 are avoided as a result of the large flow through the annular channel 12 or its sufficiently large slot width. Temperature variations between the site of temperature adjustment and the wetting zone 15 are kept to a minimum by setting the temperature near the ring nozzle 8. It is obvious that the heating device 13a can also be positioned at a different location on the coating-liquid circuit. If there is a possibility that the temperature of the circulating coating liquid will rise above the temperature desired, use can also be made expediently or exclusively of a cooling device. For the application of coating liquid, as in Fig. 2, the lower side of the disk 3 is then brought into contact with the wetting zone 15. The total flow of coating liquid clearly exceeds the partial flow briefly remaining on a disk 3. Then, as seen in Fig. 3, the disk 3 is again separated from the wetting zone 15. A ring 16 of coating liquid remains on the disk 3 as a result of adhesive forces. If a centrifugal distribution is desired, a centrifuging operation can then be carried out directly. But it would also be possible to remove the disk 3 from the coating device 1 before the centrifuging operation and optionally hand it off to a separate centrifuge or to a bonding device. As already described in the introduction to the specification, the holding device 2 could also include a tumbling device and/or the ring nozzle 8 a device for varying the throughput in order to generate variable or pulsing partial flows on the boundary line of the wetting zone. Fig. 4 shows the a solution for obtaining a circulation of the coating liquid. The drainage line 11 leads to a storage tank 19 via a reflux filter 17 and a degassing baffle system 18. The coating liquid is sent from the storage tank 19 to the ring nozzle 8, through an inflow filter 21 and a feed line 14, by means of a conveyer pump 20. The 1 nozzle unit, the collection zone 7, the conveyer pump 20 and a thermostatically controlled heating and/or cooling unit 13a form a circulation system making it possible to carry the coating liquid through the wetting zone 15 continuously and at essentially constant temperature and viscosity, in which case the total flow of the coating liquid will preferably clearly exceed the partial flow remaining briefly on a disk 3. The execution variant according to Fig. 4 contains a holder 5a inside the annular channel 12. The holder 5a forms, optionally, merely a stop for the disk 3 during coating. If necessary, the holder 5a belongs to the holding device 2 and includes for that purpose a fixed or optionally rotating holding surface. Correspondingly, a manipulator 5b is arranged above it for the introduction and removal of disks 3. Fig. 5 shows two disks 3 to be bonded together, the upper one exhibiting a ring 16 of coating liquid on its lower side. To bond these disks together, a holding arrangement is provided, for example, with an upper holding surface 22 and a lower holding surface 23 which each hold a disk 3. The latter are respectively provided with an annular channel 22a, 23a, to which a partial vacuum can be applied to hold the disks 3. According to Fig. 7, after the two disks 3 have been brought together, a partial vacuum is applied via a suction line 24, at the hole 3a of the disks 3, which draws the two disks together and leads to a uniform distribution of the coating liquid. When UN-hardening bonding material is used, the holding surfaces 22, 23 can optionally contain a UN-source, so that the hardening can be carried out with a defined disk interval. It is obvious that devices per the invention can be combined, as desired, with k . nown centrifuge, handling or bonding equipment.

Claims: Patent Claims Device for coating disks (3), particularly optically readable data carriers, with a holding device (2) for holding a disk to be coated (3), and a conveying device and applicator for applying the coating liquid to the disk (3), characterized by the fact that the applicator comprises an annular nozzle unit (8) and a collection zone (7), in which case the coating liquid can be conveyed by the nozzle unit (8), essentially continuously, through an annular wetting zone (15) and recovered in the collection zone (7), and that a movement unit (6) is provided between the nozzle unit (8) and the disk (3), which can be brought into contact with the disk (3) concentrically relative to the wetting zone (15). Device according to claim 1, characterized by the fact that the holding device (2) contains the movement unit (6) and enables the lower side of the disk (3) to be moved toward the nozzle (8) from above, and the nozzle unit (8) forms an overflow device from which the coating liquid flows upward and outward and reaches the collection zone (7) due to the force of gravity. Device according to claim 1 or 2, characterized by the fact that the nozzle unit (8), the collection zone (7), a pumping unit (20) and a thermostatically controlled heating and/or cooling device belong to a circulation device which enables the coating liquid to be conveyed through the wetting zone (15) continuously, with essentially constant viscosity and temperature, in which case the total flow of coating liquid preferably clearly exceeds the partial flow remaining briefly on a disk (3). 4. Device according to one of the claims 1 through 3, characterized by the fact that the holding device (2) includes a tumbling unit, with which the time-shifted contacting with and/or separation from the wetting zone (15) can be achieved in the peripheral region of the wetting zone. 5. Device according to one of the claims 1 through 4, characterized by the fact that the nozzle unit (8) makes it possible to produce a device for variation of the throughput for the generation of varying or pulsing partial flows at the boundary line of the wetting zone. 6. Device according to one of the claims 1 through 5, characterized by the fact that the holding device (2) comprises a centrifuge, or the disk (3) can be conveyed to a centrifuge, so that the coating liquid deposited in the shape of a ring on the disk (3) can be distributed radially outward by the rotation of the disk (3), in which case the collection zone (7) preferably extends around the zone of the centrifuge in order to catch any coating liquid thrown off. 7. Device according to one of the claims 1 through 5, characterized by the fact the holding device (2) makes it possible to move a disk (3) covered with coating liquid concentrically toward a second disk (3) in such a way that the two disks (3) are mutually positioned with an intervening gap in which the coating liquid of the disk (3) is arranged in the shape of a ring, and a radial distribution of the coating liquid and a desired interval between the disks (3) can be achieved with a pressing device and/or suction device for the application of a partial vacuum to the gap. 8. Process for coating disks (3), particularly optically readable data carriers, with a holding device (2) for holding a disk to be coated (3), and a conveying device and applicator for applying the coating liquid to the disk (3), characterized by the fact that the application of the coating liquid takes place via the concentric contacting of an annular disk zone having an annular wetting zone (15) with coating liquid, in which case the coating liquid is conveyed essentially continuously from an annular nozzle device (8), through the wetting zone (15) into a collection zone (7). 9. Process according to claim 8, characterized by the fact that the coating liquid, applied in the shape of a ring, is distributed radially over the disk (3) by means of a centrifuging process. 10. Process according to claim 8 or 9, characterized by the fact that the coating liquid, applied in the shape of a ring, is distributed radially between the two disks (3) to be bonded together by means of a pressing ope ation and/or the application of a partial vacuum to a gap between the two disks (3).

Inventors: SAWATZKI BRUNO, SAWATZKI HARRY, SAWATZKI, BRUNO, SAWATZKI, HARRY
Applicants: FIRST LIGHT TECHNOLOGY INC, SAWATZKI BRUNO, SAWATZKI HARRY, FIRST LIGHT TECHNOLOGY, INC., SAWATZKI, BRUNO, SAWATZKI, HARRY
Application year: 1999
Main classification: B05C9
IPC codes: B05C5, B05C9, B05C11, G11B7