Rotation holding table for rotating and holding a storage disc thereon and a boss thereof

Abstract: An apparatus, namely, a rotation holding table (A) comprising a base table (1) and a boss (2) thereof wherein the base table (1) holds and rotates a storage disc (D) and uniformly develops an adhesive (R) onto an area of the storage disc (D) adjacent to a central hole of the storage disc where two substrates (D1, D2) are bonded. The storage disc (D) is formed by two discoid resin substrates (D1, D2) which are by way of the adhesive (R) interposed therebetween and have central holes therein. With such an arrangement of the rotation holding table (A), the adhesive (R) can be uniformly developed onto the central portion of the storage disc having no air therein, thereby manufacturing the storage disc (D) having a high quality.

Description: The present invention relates to a rotation holding table comprising a boss for rotating and holding a storage disc thereon. Computers, especially personal computers are remarkably spread recently, and a storage media to be used thereby, particularly capacity of a storage disc has been high dense and kinds of the storage media are increased. There are a magnetic disc, an optical disc (e.g., CD-ROM), an optical magnetic disc (e.g., MO) as the storage disc. The demand of the optical disc as the storage disc is increased recently. Exemplifying an optical disc called as a DVD, a discoid resin substrate that is a single plate constituting the DVD is required to have a thickness of 0.6 mm and an outer diameter of 120 mm and an inner diameter of its central hole of 15 mm. If such a discoid resin substrate is formed of a single discoid resin substrate, it is low in a mechanical strength and is easily deformable. Accordingly, the discoid resin substrates each having the same thickness (0.6 mm) are bonded to each other. For example, Fig. 6 schematically shows a DVD of the optical disc formed of two discoid resin substrates (a first discoid resin substrate D1 and second discoid resin substrate D2) which are bonded to each other. The first discoid resin substrate D1 is formed by a transparent polycarbonate resin by e.g., an injection molding machine. Irregular signal pits (signal holes) serving as information signals such as sound are transferred to one surface of the first discoid resin substrate D1. A reflection reducing coating D11 (e.g., aluminum film, etc.) is formed on the signal pits, and a protection coating D12 is formed on the reflection reducing coating D11 to prevent the signal surface from being damaged. The second discoid resin substrate D2 formed of the transparent polycarbonate resin, etc. which is same as the first discoid resin substrate D1 is bonded onto the first discoid resin substrate D1 in which the signals or information is stored by way of an adhesive R. The second discoid resin substrate D2 may be directly bonded onto the first discoid resin substrate D1 by way of the adhesive R without forming the protection coating D12 on the first discoid resin substrate D1. The optical disc D formed by bonding two first and second discoid resin substrates D1 and D2 receives light reflected on the reflection reducing coating D11 using laser beam by a light detector, not shown, to thereby reproduce the signal. It is needless to say that the optical disc D called as the DVD can employ the second discoid resin substrate D2 in which signals or information is stored. Since the high density storage disc including the DVD not used by the single substrate or plate but it is frequently used by the plural substrates or plates, the first discoid resin substrate D1 and the second discoid resin substrate D2 are needed to be bonded to each other. A series of steps are performed to form an integrated optical disc (i.e., an optical disc) by bonding each single plate (see Fig. 7). (1) a step of placing the first discoid resin substrate D1 on a placing table C. (2) a step of coating the adhesive R onto the first discoid resin substrate D1. (3) a step of placing the second discoid resin substrate D2 on the first discoid resin substrate D1 to thereby bond the former onto the latter. (4) a step of developing the adhesive R which is interposed between both first and second discoid resin substrates D1 and D2. (5) a step of curing the developed adhesive R. Briefly explaining the steps set forth above, first in the step (1), the first discoid resin substrate D1 on which the reflection coating and the protection coating are coated is uniformly sucked and held on the placing table C. In the step (2) coating the adhesive R, the adhesive R, e.g., an ultraviolet curing resin is jetted from a jetting nozzle N while the placing table C on which the first discoid resin substrate D1 is placed is rotated at a low speed. It is preferable that the adhesive is jetted in a doughnut-shaped track although tracks of the adhesive R to be jetted onto the first discoid resin substrate D1 are differentiated from one another depending on the movement of the jetting nozzle N. In the step (3), the transparent second discoid resin substrate D2 is placed on the first discoid resin substrate D1 on which the adhesive R is coated. In the step (4), the adhesive R interposed between the first and second discoid resin substrates D1 and D2 is developed to be uniformly extended between the first and second discoid resin substrates D1 and D2. The development of the adhesive R is performed by rotating the placing table C at a high speed (normally the speed of rotation is several thousand rpm or more for about several seconds) in a state where the first and second discoid resin substrates D1 and D2 are bonded to each other, namely, where the optical disc D is placed on the placing table C. With the rotation of the placing table C, a surplus adhesive R which is present between the bonded first and second discoid resin substrates D1 and D2 is scattered outward when the adhesive R is developed, and also the air sealed between the first and second discoid resin substrates D 1 and D2 (air bubble, etc.) is discharged outward. In the step (5), the adhesive R, e.g., ultraviolet curing resin layer is cured by being irradiated with ultraviolet in a state where the bonded and integrated first and second discoid resin substrates D1 and D2 are rotated (e.g., at about several tens rpm) or not rotated. More specifically, a ultraviolet light source L having a reflecting mirror L1 at the back surface thereof emits light, thereby effectively curing the ultraviolet curing resin layer. Meanwhile, the curing step is different depending on the kind of an adhesive R to be used, and hence the curing method conforming to the characteristics of the adhesive R is employed. As mentioned above, the steps for bonding and integrating the both substrates are completed. The developing step among the above steps is very important because the adhesive R is uniformly extended between the two substrates. However, the adhesive R is not always uniformly developed by the development using the conventional placing table C. The reason is that the adhesive R is jetted in the doughnut-shape, and further the adhesive R is not sufficiently jetted usually until it reaches the central hole of the optical disc D in the sense that the adhesive R is ultimately effectively used. Accordingly, in the developing step, there is a problem that the adhesive R is not sufficiently extended in the region adjacent to the central hole of the optical disc D when the adhesive R is developed outward owing to the centrifugal force, etc., and hence the optical disc D is short of the development inside thereof, whereby air remains in the optical disc D. The inventors of the present application ascertained from the test that the adhesive R is nonuniformly scattered from the central hole toward the inside thereof to thereby contaminate the surface adjacent to the central hole of the optical disc D when the adhesive R is jetted to a part adjacent to the central hole. Considering the performance of the optical disc D, if the adhesive R is not uniformly extended to the region of the central hole, the strength of the region of the central hole is remarkably lowered or the strength of the optical disc is nonuniform as a whole when the adhesive R is cured later. In addition to that, there is not normally present a reflection coating on the central portion of the optical disc D, thereby forming a spotted pattern on the central portion, leading to an inferior beauty or spoiling the beauty of the optical disc D. The storage disc has been diversified recently as set forth above, and there are various standards in the size thereof (dimensions, etc.), for example, there appears a kind of storage disc having an inner diameter of, e.g., 4 mm which is different from the inner diameter of the 15 mm of the central hole of the present optical disc D. As far as the storage disc formed of an integrated plate, which is made of bonded and integrated two discoid resin substrates, is concerned, the two substrates must be bonded to each other using the adhesive, which needs the developing step by the rotation of the storage disc. However, in the method having the developing step which is caused by the rotation of the optical disc, it is difficult to uniformly develop the adhesive at the region adjacent to the central hole of the optical disc, leading to the deterioration of quality. Accordingly, it is a very important key point that the adhesive is thoroughly and uniformly extended to improve the quality of the optical disc. However the decisive solution has not been proposed so far. The present invention has solved the problems under the aforementioned background of the invention. That is, it is an object of the present invention to provide an apparatus for uniformly developing an adhesive at the region where two substrates are bonded to each other adjacent to the central hole of an optical or storage disc, namely, a table for holding and rotating the storage disc and a boss of the table. Meanwhile, the inventors of the present patent have endeavored themselves to a research, and found out that the development of the adhesive is effectively enhanced at the region adjacent to the center of the storage disc when the center of the storage disc is negatively pressurized when the adhesive is developed. The inventors completed the present invention in view of the aforementioned finding. To achieve the above object, there is provided a rotation holding table comprising a boss for rotating and holding a storage disc thereon so as to develop an adhesive, wherein the storage disc is formed by two discoid resin substrates with the adhesive resin interposed therebetween, and wherein the boss is provided with a barrel portion and a suction cylindrical portion protruding from the barrel portion and mounted on a central hole of the storage disc, and the barrel portion is detachably engaged in a recess of the rotation holding table, and the suction cylindrical portion is provided with a ring groove provided at the periphery thereof, and the ring groove is provided with suction holes on the bottom thereof for sucking adhesive in the region of the central hole of the storage disc, and the suction holes having an inner diameter enlarging outwardly. EP-A-0 744 739, which is comprised in the state of the art according to article 54(3) EPC, discloses a rotation holding table comprising a boss for rotating and holding a storage disc thereon so as to develop an adhesive, wherein the storage disc is formed by two discoid resin substrates with the adhesive resin interposed therebetween and wherein the boss is provided with a barrel portion and a suction cylindrical portion protruding from the barrel portion and mounted in a central hole of the storage disc, and the barrel portion is detachably engaged in a recess of the rotation holding table and the suction cylindrical portion is provided with a ring groove provided at the periphery thereof and the ring groove is provided with suction holes on the bottom thereof, for sucking adhesive in the region of the central hole of the storage disk. JP-A-012 940/87 discloses a simple holding table of a disc sticking device. According to said document an adhesive is pressed on the entire surface of the disc by pressing the disc by a pressing plate. Preferably the rotation holding table comprises a rotatable base table having said recess. Conveniently the base table comprises a table for sucking and fixing the storage disc and a supporting portion for supporting the table. In a preferred embodiment the suction cylindrical portion and the table are respectively connected and opened to the same single negative pressure source, thereby dispensing with two different negative pressure sources. Preferably the rotation holding table further includes a space which is partitioned between the storage disc, the rotation holding table and the base table and is opened outward in a state where the storage disc is placed on the base table. It is possible to effectively develop the adhesive adjacent to the central holes of the both discoid resin substrates by employment of the base table on which the storage disc is held and rotated and the boss of the base table. Fig. 1 is a cross sectional view showing a state where a storage disc is placed on a rotation holding table; Fig. 2 is a perspective view of a boss; Fig. 3(a) is a cross sectional view of the boss, and Fig. 3(b) is a cross sectional view of a suction cylindrical portion; Fig. 4 is a perspective view of a boss of a rotation holding table according to a preferred embodiment of the invention; Fig. 5 is a schematic view showing a suction state; Fig. 6 is a crosssectional schematic view of an storage disc; and Fig. 7 is a schematic processing view showing general processes for manufacturing a storage disc by bonding a second discoid resin substrate onto a first discoid resin substrate by way of an adhesive, wherein the bosses shown in Figs. 1 - 3 and 5 are not part of the invention, but necessary for the understanding of the invention. Fig. 1 is a cross sectional view of a state where first and second discoid resin substrates D1 and D2 which are bonded to each other by way of an adhesive R and are placed on a rotation holding table A. Although a vertically movable receiving dome B is disposed around the rotation holding table A for preventing the adhesive R from being scattered when the adhesive R is developed, the receiving dome B is not relevant to the present invention, and hence the explanation of the receiving dome B is omitted. As shown in Fig. 1, the rotation holding table A comprises a rotatable base table 1 and a boss 2 which is engaged in the base table 1. The base table 1 comprises a table 11 and a supporting portion 12, respectively described later, wherein the supporting portion 12 comprises a large diameter portion 121 for receiving the table 11, a small diameter portion 122 to be mounted on a central hole 11A of the table 11 and a most small diameter portion 123 to be inserted into a supporting sleeve 3, described later, serving as a rotary shaft. In the base table 1, the table 11 is placed on the supporting portion 12 from the upper portion thereof and is attached thereto. The supporting portion 12 of the base table 1 is supported by the supporting sleeve 3 having a bearing 31, and is positively rotatable by a driving source, not shown. An insertion hole 12A is formed at the center of the supporting portion 12 and is connected to a suction source (negative pressure source), not shown, wherein a vacuum suction apparatus is employed as the negative pressure source. A recess 12C is provided in the head of the small diameter portion 122 of the supporting portion 12, and the boss 2 is engaged in and attached to the recess 12C. Fig. 2 is a perspective view of the boss 2 in Fig. 1. Fig. 3 (A) is a cross sectional view of the boss 2, and Fig. 3 (B) is a cross sectional view taken along B-B of a suction cylindrical portion 21 of the boss 2 in Fig. 3 (A). As shown in these figures, the boss 2 comprises a barrel portion 22 composed of a large diameter portion 221 and a small diameter portion 222, and the suction cylindrical portion 21 projecting from the barrel portion 22 having a suction function. The boss 2 has a suction passage 2A at the central portion thereof. A plurality of suction holes 21H are bored in the outer periphery of the boss 2, and they are opened to the suction passage 2A. There are provided a plurality of (three in figures) suction holes 21H, and it is preferable that each of the suction holes 21H is e.g. about 1.5 mm at the maximum diameter and each shape of the suction holes 21H is enlarged outwardly. The suction cylindrical portion 21 of the boss 2 is a portion which is accurately mounted on the central hole of the storage disc. Although the boss 2 is engaged into the base table 1, the recess 12C of the small diameter portion of the base table 1 and the large diameter portion 221 of the boss 2, and the recess 12C of the base table 1 and the small diameter portion 222 of the boss 2 are respectively designed to be brought into contact with one another, and hence there is no likelihood of leaking of the air at the contact surfaces therebetween when the adhesive is sucked. The boss 2 engaged into the base table 1 can be integrally rotated with the base table 1. To strongly fix the base table 1, the boss 2 and the base table 1 are fastened with bolts, etc. In a state where the storage disc D is placed on the base table 1, a space S defined between the boss 2, the base table 1 and the lower surface of the storage disc D is partitioned and formed in the rotation holding table A. The space S forms a part for introducing fresh air when performing the suction, described later. The space S is opened to the outside by a passage 12B defined in the supporting portion 12. When the boss 2 is engaged into the supporting portion 12 of the base table 1, the suction holes 21H, the suction passage 2A and the insertion hole 12A communicate with one another. Meanwhile the table 11 is a part on which the storage disc D is directly placed, and has a flat surface as a seating surface. The central hole 11A is defined in the table 11 at the center thereof, and it is engaged into the supporting portion 12, and they are fixed to each other by bolts, etc., not shown, so that the table 11 is attached to the supporting portion 12. A plurality of suction holes 11B are defined in the upper surface of the table 11 so as to uniformly suck and fix the storage disc D placed on the table 11. The suction holes 11B are opened to the insertion hole 12A, which is defined in the supporting portion 12, thorough a space 11C inside the table 11. When the suction source, not shown, communicating with the insertion hole 12A is operated, the suction holes 11B are negatively pressurized to perform the suction operation. At this time, the suction holes 21H which are opened to the insertion hole 12A are negatively pressurized so as to generate the suction force. The force for drawing or sucking the adhesive R from the suction holes 21H is generally higher than force for sucking and fixing the storage disc D on the seated surface of the table 11 in the minimum necessary negative pressure. Accordingly, if the force for attracting the surface of the storage disc D is conformed to the force for sucking the adhesive R, the storage disc D is surely fixed onto the table 11. It is needless to say that the timing between the drawing or suction time of the suction holes 21H and the suction time of the suction holes 11B can be differentiated from each other. In this case, it is preferable that the passage through which air flows is open or closed by a solenoid, etc., or the passage of the suction holes 21H and the passage of the suction holes 11B respectively independently form different passages which are connected to the suction source (negative pressure source). Meanwhile, when the rotation holding table A is assembled, the table 11 is first engaged into the supporting portion 12 of the base table 1. Whereupon since the supporting portion 12 appears or protrudes from the upper surface of the table 11 at the central portion thereof, the barrel portion 22 of the boss 2 is engaged into the recess 12C of the supporting portion 12, thereby easily performing the assembly of the rotation holding table A. Then, the storage disc D is placed on the table 11 and the rotation holding table A is rotated to perform a given developing step. In case that the dimensions of the central holes of the storage discs D are differentiated to exchange the boss 2, the boss 2 is removed from the supporting portion 12 and another boss 2 having different dimensions is engaged into the supporting portion 12 in a state where the storage disc D is not placed on the table 11. In the case where the table needs to be exchanged by another one having different dimensions depending the kind of storage disc D, the table to be replaced must conform to the storage disc D must be attached. Fig. 4 is a perspective view of a boss having a suction cylindrical portion 21 which is larger than the boss 2 in Fig. 2. The boss in Fig. 4 is different of the boss in Fig. 2 in that the ring groove 21A is formed on the periphery of the suction cylindrical portion 21 of the boss 2, and the suction holes 21H are bored into the bottom of the ring groove 21A. The reason that the ring groove 21A is formed on the suction cylindrical portion 21, is to permit the suction force to uniformly act onto the entire periphery of the suction cylindrical portion 21. The suction cylindrical portion 21 normally has a width which is slightly smaller than a thickness of the storage disc D. The reason is that when the storage disc D is placed on the rotation holding table A and rotated, there is a likelihood of the entrance of the storage disc D into the ring groove 21A owing to oscillation, etc. Since the barrel portion 22 of the boss 2 has the same size as the boss having the small diameter showing in Fig. 2, the barrel portion 22 can be surely engaged into the recess 12C of the supporting portion 12 of the base table 1. As explained above, when the barrel portion 22 of the boss 2 is standardized, it is very convenient to set the boss 2 having the suction cylindrical portion 21 to the recess 12C of the supporting portion 12, even if the suction cylindrical portion 21 has various diameters. Describe next is a manner of the development of the adhesive R using the rotation holding table A. As shown in Fig. 1, the second discoid resin substrate D2 is placed on the first discoid resin substrate D1 on the rotation holding table A by way of the adhesive R, e.g., ultraviolet curing resin. When the suction source is operated and the rotation holding table A is rotated at high speed, the adhesive R interposed between the first and second discoid resin substrates D1 and D2 is developed owing to the centrifugal force, and hence the surplus adhesive is scattered outward. Air interposed between the first and second discoid resin substrates D1 and D2 is also discharged outward together with the surplus adhesive owing to the centrifugal force. Since the suction source is operated, fresh air around a plurality of suction holes 21H defined in the outer periphery of the boss and the vicinity thereof is sucked sequentially through the suction holes 21H, the suction passage 2A and the insertion hole 12A. At the time of suction, fresh air introduced from the upper surface of the storage disc D passes through a gap defined between the upper second discoid resin substrate D2 and the boss 2, then it is sucked through the suction holes 21H, while fresh air introduced from the lower surface of the storage disc D (this fresh air is introduced from the space S by way of the passage 12B) passes through the gap defined between the lower first discoid resin substrate D1 of the storage disc D and the boss 2, and then it is sucked through the suction holes 21H. With such a suction operation, the adhesive R interposed between the first and second discoid resin substrates D1 and D2 is sucked through the plurality of suction holes 21H, the suction passage 2A and the insertion hole 12A. It is a difficult manner of suction in the developing step is that the adhesive R is developed in a state where it stops at the portion immediately before the end of the central hole so as to prevent the adhesive R from being leaked outward through the central hole of the storage disc D owing to the suction operation. If the adhesive R is leaked outward through the central hole of the storage disc D, it contaminates the surface of the part adjacent to the central hole, which remarkably deteriorates the quality. The degree of suction is decided carefully considering the viscosity of the adhesive R, the revolutions of the rotation holding table, etc., and it is an essential portion of the developing step. Fig. 5 shows a schematic view showing a state where the adhesive R is uniformly developed at the part adjacent to the central holes of the first and second discoid resin substrates D1 and D2 when air is sucked through the suction port of the boss at the start of suction using the boss 2 and a part of the storage disc. When the suction is performed for a given time, the adhesive R which is present at the part adjacent to the central holes of the first and second discoid resin substrates D1 and D2 is uniformly extended. The present invention is not limited to the embodiment of Figure 4 but can be variously modified without departing from the scope of the essence thereof. For example, the adhesive to be used by the present invention is not limited to the ultraviolet curing resin as described in the embodiment of the invention but may be any kind if it can bond the first and second discoid resin substrate D1 and D2. Further, the small diameter portion 222 of the barrel portion 22 are part to be mounted in the insertion hole, it may be omitted if the large diameter portion 221 is present. Still further, although the barrel portion 22 is cylindrical in the embodiment, it may be of any shape if it can be engaged into the recess 12C of the supporting portion 12 so as to align with the recess 12C. There is no description of the provision of so-called adhesive stop groove (not shown) in the optical disc according to the preferred embodiment, namely, the embodiment does not refer to the presence or non-presence of the adhesive stop groove. In an optical disc having a standard to provide the adhesive stop groove, the suction of air through the boss is normally carried out in a manner that the development of the adhesive stops at the adhesive stop groove. However, if the adhesive is intended to overcome the adhesive stop groove so as to be sucked to the position immediately before the circumference of the central hole of the optical disc, the strength of the suction of air may be changed to cope therewith.

Claims: A rotation holding table (A) comprising a boss (2) for rotating and holding a storage disc thereon so as to develop an adhesive (R), wherein the storage disc is formed by two discoid resin substrates (D1, D2) with the adhesive resin (R) interposed therebetween, and wherein the boss (2) is provided with a barrel portion (22) and a suction cylindrical portion (21) protruding from the barrel portion (22) and mounted on a central hole of the storage disc, and the barrel portion (22) is detachably engaged in a recess (12c) of the rotation holding table (A), and the suction cylindrical portion (21) is provided with a ring groove (21A) provided at the periphery thereof, and the ring groove (21A) is provided with suction holes (21H) on the bottom thereof for sucking adhesive in the region of the central hole of the storage disc, and the suction holes (21H) having an inner diameter enlarging outwardly. A rotation holding table (A) according to claim 1, wherein the rotation holding table (A) comprises a rotatable base table (1) having said recess (12c). A rotation holding table (A) according to claim 2, wherein the base table (1) comprises a table (11) for sucking and fixing the storage disc (D) and a supporting portion (12) for supporting the table (11). A rotation holding table (A) according to claim 2 or 3, wherein the suction cylindrical portion (21) and the table (11) are respectively connected and opened to a single negative pressure source. A rotation holding table (A) according to claim 2, further including a space which is partitioned between the storage disc (D), the boss (2) and the base table (1) and is opened outward in a state where the storage disc (D) is placed thereon on the base table (1).

Inventors: AMO MIKUNI, INOUCHI MASAMI, AMO, MIKUNI, INOUCHI, MASAMI, Amo, Mikuni, c/o Kitano Engineering Co., Ltd., Inouchi, Masami, c/o Kitano Engineering Co., Ltd.
Applicants: KITANO ENG CO LTD, KITANO ENGINEERING CO., LTD.
Application year: 1996
Main classification: F16B11
IPC codes: B29C65, G11B7, B29D17