Apparatus for curing an optical disc

Abstract: It is an object of the invention to provide an apparatus for curing an optical disc (D) capable of efficiently curing ultraviolet curing resin (R) serving as an adhesive relative to disc substrates through which ultraviolet does not transmit. It is another object of the invention to provide a method of and an apparatus for curing an optical disc (D) capable of efficiently curing ultraviolet curing resin (R) serving as an adhesive relative to disc substrates through which ultraviolet hardly transmits. The apparatus for curing an optical disc (D) placed on a rotary holding table (1) and formed by bonding a first disc substrate (D1) and a second disc substrate (D2) by the medium of an ultraviolet curing resin (R) comprises an ultraviolet irradiation peripheral unit (2) disposed around the rotary holding table (1) for irradiating ultraviolet from the peripheral surface of the optical disc (D) toward the inner portion thereof so as to cure the ultraviolet curing resin (R).

Description: The invention relates to an apparatus for curing an optical disc D, more particularly to an apparatus for curing an ultraviolet curing resin R efficiently and uniformly, which resin is sandwiched between two disc substrates constituting the optical disc D. 2. Description of the Related Art: An optical disc D has generally information signal therein such as image, sound, or the like which is transferred onto one side of a disc substrate made of polycarbonate in the form of signal pits (signal holes). In a relatively simple structure of an optical disc D, a metallic reflection film made of, e.g. aluminum, is provided on the surface of the signal pits, and a protection film such as an ultraviolet curing resin R film is formed on the metallic reflection film for preventing metallic reflection film from being damaged. However, as an optical disc D such as a DVD having a large storage capacity of information has been recently spread rapidly, the structure of disc substrates constituting the optical disc D is multi-layered and becomes complex. For example, in a random access memory type DVD, a twin sursassite, a tellurium layer, a reflection film, a protection film and so forth are formed on the resin substrate. Further, if the structure of the disc substrate becomes complex, there occurs a case where ultraviolet does not at all path through the disc substrate. Meanwhile, an optical disc D is formed of a first substrate to which information is applied as mentioned above, and a second disc substrate which are bonded to each other using an ultraviolet adhesive. A method of bonding these two disc substrates is described simply hereinafter. An ultraviolet curing resin R is first applied to at least one of two disc substrates at the portion where it is joined with another disc substrate so as to bond two disc substrates. After the adhesive is applied to the joining portion of the two disc substrates, both the disc substrates are rotated while they are bonded, then the ultraviolet curing resin R is distributed or developed uniformly between the two disc substrates. Thereafter, ultraviolet is irradiated from the upper portion of the disc substrate so as to cure the adhesive, thereby obtaining an optical disc D formed of the two disc substrates which are bonded firmly. When disc substrates having a complex structure through which ultraviolet does not transmit, even if ultraviolet is irradiated from the upper portion of the optical disc D, the ultraviolet curing resin R serving as an adhesive is not cured. Even if disc substrates through which ultraviolet hardly transmits is used, if characters or patterns are printed on the disc substrates, there occurs a lack of uniformity when ultraviolet transmits the disc substrates, so that the ultraviolet curing resin R is not efficiently and uniformly cured. If there occurs a problem in the curing of the ultraviolet curing resin R, it causes the occurrence of strain or distortion such as warp, tilt, and exfoliation when the optical disc D is manufactured by the disc substrates. JP 11 053778 A discloses an apparatus for curing an optical disc placed on a rotary holding table and formed by bonding a first disc substrate and a second disc substrate by the medium of an ultraviolet curing resin comprising an ultraviolet irradiation peripheral unit disposed around the rotary holding table for irradiating ultraviolet from the peripheral surface of the optical disc toward the inner portion thereof so as to cure the ultraviolet curing resin. JP 63 275052 A discloses an apparatus for curing an optical disc according to the preamble of claim 1. The apparatus according to the last mentioned two documents suffer from the drawback that the direction and interval of the irradiation can not be regulated. This is disadvantageous in particular when a fine foreign matter, such as dust, is in the ultraviolet curing resin R. Accordingly, it is the aim of the present invention to at least reduce said drawback. This aim is achieved by an apparatus as defined in claim 1. Said apparatus for curing an optical disc D may comprise an ultraviolet irradiation central unit disposed at the center of the rotary holding table for irradiating ultraviolet from the central hole of the optical disc D toward the outer portion thereof so as to cure the ultraviolet curing resin. According to a further aspect said apparatus for curing an optical disc D may comprise a boss elastically pressed and journaled by and attached to the central portion of the rotary holding table and suction means provided on the rotary holding table and connected to a negative pressure source, wherein the suction means allows the boss to move toward or away from the rotary holding table and the optical disc D to be placed on and attached the rotary holding table. According to a further aspect of said apparatus for curing an optical disc D the ultraviolet irradiation peripheral unit can be divided into eight, and respective two divided bodies 2A of the ultraviolet irradiation peripheral unit 2 may be arranged in parallel with each other and eight units may be disposed square as a whole. Inasmuch as the invention has the going structure, it has the following operations. Ultraviolet is irradiated from the peripheral surface of the optical disc D toward the inner portion thereof after the two disc substrates which are bonded to each other by the medium of the ultraviolet curing resin R are placed on the rotary holding table while the rotary holding table is rotated. Ultraviolet is irradiated from the peripheral surface of the optical disc D toward the inner portion thereof and from the center, i.e., central hole of the optical disc D toward the outer portion thereof after the two disc substrates which are bonded to each other by the medium of the ultraviolet curing resin R are placed on the rotary holding table while the rotary holding table is rotated. Fig. 1 (A) and Fig. 1 (B) are views for respectively explaining a principle of irradiation of ultraviolet, wherein Fig. 1 (A) is a sectional view of an optical disc D, and Fig. 1 (B) is a front view of the same; Fig. 2 is a plan view of schematically showing the apparatus for curing the optical disc D in Fig. 1; Fig. 3 is a side view of schematically showing the apparatus for curing the optical disc D as shown in Fig. 2; Fig. 4 is a sectional view of the apparatus for curing the optical disc D as shown in Fig. 2 for explaining a state at the time before the optical disc D is irradiated with ultraviolet; Fig. 5 is a sectional view of the apparatus for curing the optical disc D in Fig. 1 for explaining a state at the time when the optical disc D is irradiated with ultraviolet; Fig. 6 is a view showing a state where an ultraviolet irradiation peripheral unit is arranged outside the optical disc D; Fig. 7 is a view showing a state where divided ultraviolet irradiation peripheral units are paired and respective pairs are arranged square as a whole; and Fig. 8 shows a bonding step in a schematic processing of the optical disc D. The apparatus for curing an optical disc D according to preferred embodiments of the invention are now described hereinafter with reference to the attached drawings. First of all, an optical disc D is manufactured by a step of forming a first disc substrate by injection molding machine using a stamper manufactured by a mastering step, a step of forming a reflection film and a protection film on a signal surface formed in the first disc substrate, and a step of bonding the first substrate with the second disc substrate and integrating the first and second disc substrates with each other. The method of and apparatus for curing an optical disc D is preferable to be used after the step of bonding in the manufacturing process of the optical disc D. The bonding step is described in more detail for precaution's sake before explaining the apparatus for curing an optical disc D. "Bonding" means that two disc substrates are placed, one over the other by the medium of an adhesive (e.g., ultraviolet curing resin), and it does not matter whether the adhesive is cured or not. Fig. 8 shows a bonding step in a schematic processing of the optical disc D. In the first step, a first disc substrate D1 having a signal surface thereon is positioned on an upper surface of a rotary holding table. In the second step, an ultraviolet curing resin R (adhesive) is applied to the first disc substrate D1. For example, the ultraviolet curing resin R is applied to the upper surface of the first disc substrate D1 through a discharge nozzle N while the rotary holding table is rotated at a low speed. By this, the ultraviolet curing resin R is drawn in a ring-shape on the upper surface of the first disc substrate D1. In the third step, a second disc substrate D2 is placed on the first disc substrate D1 to which the ultraviolet curing resin R is applied. In the fourth step, the rotary holding table is rotated at high speed (preferably not less than 2000 rpm) in a state where the first and second disc substrates D1 and D2 are placed, one over the other. When the rotary holding table is rotated at a high speed, the ultraviolet curing resin R is developed between both disc substrates uniformly as a whole. When the second disc substrate D2 is placed on the first disc substrate D1, air which enters between two disc substrates and, air bubble which is inherent previously in the ultraviolet curing resin R are discharged. In the fifth step, both disc substrates D1 and D2 which are bonded to each other are irradiated with ultraviolet L while they are rotated on the rotary holding table so as to cure the ultraviolet curing resin R. [First Embodiment: Figs. 1 to 6] An apparatus for curing an optical disc according to a first embodiment of the invention is now described with reference to Figs. 1 to 6. Ultraviolet emitted from an ultraviolet light source, not shown, is irradiated from a peripheral surface of the optical disc D toward the inner portion by the medium of optical transmission cables or parts 7 such as an optical fiber, then it is irradiated from the center (central hole) of the optical disc D toward the outer portion so as to cure the ultraviolet curing resin R (see Fig. 1) The apparatus for curing an optical disc D is described next with reference to Figs. 2 and 5. Figs. 2 and 3 are plan and side views respectively schematically showing the apparatus for curing an optical disc D wherein the optical disc D is irradiated with ultraviolet. Meanwhile, Figs. 4 and 5 are sectional views of the apparatus for curing an optical disc D, wherein Fig. 4 shows a state at the time before ultraviolet is irradiated and Fig. 5 shows a state at the time when ultraviolet is irradiated (particularly, Fig. 5 shows a state where a press member 8 as shown in two-dotted one chain line is placed on the optical disc D). The apparatus for curing an optical disc D comprises mainly a rotary holding table 1 having a boss 11 at the center thereof, a ultraviolet irradiation unit for irradiating ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof (hereinafter referred to an ultraviolet irradiation peripheral unit 2), and an ultraviolet irradiation unit for irradiating ultraviolet from the central hole of the optical disc D toward outer portion thereof (hereinafter referred to an ultraviolet irradiation central unit 3). Ultraviolet is transmitted to both the ultraviolet irradiation peripheral unit 2 and ultraviolet irradiation central unit 3 from an ultraviolet light source that is built in a UV irradiation apparatus 100, not shown through an optical transmission parts 7. The rotary holding table 1 is rotatably journaled by a rotary shaft 16 and is disposed at the center of a doughnut-like base table 5, described later. The rotary holding table 1 has a suction surface at the upper surface thereof for drawing the optical disc D (from the side of a lower disc substrate D1) to hold and fix the optical disc D onto the rotary holding table 1, and the suction operation is effected by suction means including a suction passage 15 connected to a negative pressure source, not shown. As mentioned above, since the boss 11 is attached to the central portion of the suction surface of the rotary holding table 1, when the optical disc D is accurately positioned on the rotary holding table 1 by inserting the boss 11 into the central holes O of both the disc substrates D1, D2. The boss 11 is elastically pressed upward and journaled by and attached to a central space 13 of the rotary holding table 1, e.g., by the medium of a spring body 12 so that the boss 11 is movable toward and away from the upper surface of the rotary holding table 1. When the boss 11 is drawn by suction force, the spring body 12 is compressed and buried in the central space 13 of rotary holding table 1 while the boss 11 can be protruded from the central space 13 when stopping the application of suction force to restore the spring body 12. The suction operation is effected by suction means including the suction passage 15 communicating with the suction surface for drawing the disc substrates D1, D2. The suction force is preferably set at 40 to 70 kPag. The ultraviolet irradiation peripheral unit 2 is disposed along the peripheral surface of the rotary holding table 1. More in detail, the ultraviolet irradiation peripheral unit 2 is divided into plural numbers and independent of one another and stand side by side uniformly or at a given interval along the peripheral surface of the rotary holding table 1, and a doughnut-like fastening member 6 presses the ultraviolet irradiation peripheral units 2 against the base table 5. When the divided bodies divided bodies 2A can be fixed between the fastening member 6 and base table 5, ultraviolet can be irradiated in parallel with both the disc substrates D1, D2, and hence it directly acts on the ultraviolet curing resin R sandwiched between both the disc substrates D1, D2. Since the doughnut-like fastening member 6 is fixed to the base table 5 by fixing bolts P, the ultraviolet irradiation peripheral unit 2 can be easily removed when the fixing bolts P are loosened. Accordingly, when the fixing angle of the divided bodies 2A of the ultraviolet irradiation peripheral unit 2 in the right and left directions, i.e. horizontal direction of ultraviolet can be changed. The ultraviolet irradiation peripheral unit 2 is positioned as set forth above and it can irradiate ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof to cure the ultraviolet curing resin R. Further, ultraviolet emitted from the UV irradiation apparatus 100 built in the ultraviolet irradiation apparatus, not shown, is transmitted to the ultraviolet irradiation peripheral unit 2 using the optical transmission parts 7. Under the circumstances, ultraviolet can be directly and accurately irradiated from the peripheral surface of the optical disc D toward the inner portion thereof to cure the ultraviolet curing resin R. Although the output of the ultraviolet irradiation peripheral unit 2 can be regulated by a controller of the UV irradiation apparatus 100, the intensity of illumination can be regulated by moving the entire ultraviolet irradiation peripheral unit 2, i.e., divided bodies 2A away from the optical disc by loosening the fixing bolts P as shown in Fig. 6. It is needless to say that the angle of illumination of ultraviolet relative to the optical disc D can be changed by selecting the angles of disposition of respective divided bodies 2A of the ultraviolet irradiation peripheral unit 2 as set forth above. Meanwhile, the ultraviolet irradiation central unit 3 is disposed at the center of the rotary holding table 1 and it irradiates ultraviolet from the central hole O of the optical disc D to cure the ultraviolet curing resin R. Ultraviolet can be irradiated in parallel with both the disc substrates D1, D2, and hence it directly acts on the ultraviolet curing resin R sandwiched between both the disc substrates D1, D2. Ultraviolet is also transmitted from the ultraviolet light source, not shown, build in the UV irradiation apparatus 100 to the ultraviolet irradiation central unit 3 by the medium of the arm-like transmission part 4 (an optical fiber 3A for transmitting ultraviolet is disposed in the arm-like transmission part 4). As mentioned above, ultraviolet can be irradiated from the center of the optical disc D to the outer portion thereof. A step of curing by the irradiation of ultraviolet using both the ultraviolet irradiation peripheral unit 2 and ultraviolet irradiation central unit 3 as described in detail above is described next. As described in Figs. 4 and 5, disc substrates D1, D2 are placed on the suction surface of the rotary holding table 1. The press member 8 is placed on both the disc substrates D1, D2 for pressing both the disc substrates D1, D2 against each other as shown by two dotted and chain line. The press member 8 is provided for pressing both the disc substrates D1, D2 to prevent both the disc substrates D1, D2 from warping or tilting or the like, but it may be dispensed with depending on the kind of an optical disc D. The press member 8 is formed such that it has a diameter which is slightly smaller than the diameters of both the disc substrates D1, D 2, and it has a hole 81 at the center thereof through which the ultraviolet irradiation central unit 3 can irradiate ultraviolet. The press member 8 is normally preferable to have a weight of 500 to 1000g. Since the curing step by irradiating ultraviolet is different from the conventional curing step by irradiating ultraviolet from the upper portion of the optical disc D, it is possible to employ a press member 8 through which light is not transmitted, for example, a metal disc can be employed. Then, the rotary holding table 1 starts a low speed rotation (preferably about 100 to 200 rpm). Then, ultraviolet is irradiated from the ultraviolet irradiation peripheral unit 2. Ultraviolet is irradiated from the peripheral surface of the optical disc toward the inner portion thereof so as to cure the ultraviolet curing resin R sandwiched between sandwiched between the disc substrates D1, D2. Different from the conventional irradiation of ultraviolet from the upper portion of the optical disc toward the optical disc, ultraviolet is directly irradiated toward the ultraviolet curing resin R along the direction of the application of the ultraviolet curing resin R, the ultraviolet curing resin R can be very efficiently cured by ultraviolet. Further, ultraviolet is irradiated from the peripheral surface central hole O of the optical disc while the optical disc D is rotated, the curing of the ultraviolet curing resin R in all directions can be enhanced. Meanwhile, ultraviolet is irradiated from the center of the optical disc D toward the outer portion thereof by the ultraviolet irradiation central unit 3. In this case, the arm-like transmission part 4 is turned horizontally and is positioned over the central axis of the optical disc D. When the arm-like transmission part 4 is lowered, the ultraviolet irradiation central unit 3 is positioned over the central hole O of the optical disc D. At this time, it is preferable that the boss 11 is buried downward in the central space 13 of the rotary holding table 1 by suction forth not to impede the ultraviolet irradiation central unit 3 from disposing over the central hole O of the optical disc. It is needless to say that the boss 11 can be depressed directly by the ultraviolet irradiation central 3. The ultraviolet irradiation central unit 3 thus positioned in the central hole O of the optical disc D irradiates ultraviolet from the center of the optical disc D toward the outer portion thereof so as to cure the ultraviolet curing resin R sandwiched between both the disc substrates D1, D2. When using both the irradiation means of the ultraviolet irradiation peripheral unit 2 and ultraviolet irradiation central unit 3, ultraviolet is preferably irradiated at the same time from both the irradiation means. It is needless to say that the ultraviolet curing resin R serving as an adhesive can be sufficiently cured even by the irradiation of ultraviolet only from ultraviolet irradiation peripheral unit 2 toward the optical disc D. However, if the irradiation of ultraviolet from the ultraviolet irradiation central unit 3 is added to that from the ultraviolet irradiation peripheral unit 2, more sufficient curing of the ultraviolet curing resin R can be effected. That is, light or ultraviolet emitted from the UV irradiation apparatus 100 is transmitted to the optical transmission parts 7 or the like and it is irradiated toward the ultraviolet curing resin R sandwiched between disc substrates D1, D2 from the ultraviolet irradiation peripheral unit 2 or both the ultraviolet irradiation peripheral unit 2 and ultraviolet irradiation central unit 3. [Second Embodiment: Fig. 7] A ultraviolet irradiation peripheral unit 2 is divided in plural units or bodies and disposed along the peripheral surface of the optical disc D so as to irradiate ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof. As the divided units or bodies 2A of the ultraviolet irradiation peripheral unit 2, it is particularly advantageous that respective two divided bodies 2A, which are obtained by dividing the ultraviolet irradiation peripheral unit 2 into eight pieces, are arranged in parallel with each other and disposed square as shown in Fig. 7. The reason is that if the divided bodies 2A of the ultraviolet irradiation peripheral unit 2 are disposed particularly in the direction of the central portion of the optical disc D, for example, if a fine foreign matter such as dust is mixed in the ultraviolet curing resin R serving as an adhesive, the inside of the location of the foreign matter in the central direction becomes a shade S of ultraviolet so that the ultraviolet curing resin R in the area of the shade S is delayed in curing. That is, since the shade S of ultraviolet is always formed inside the location of the foreign matter during irradiation of ultraviolet, the shade S is localized. Accordingly, the divided bodies 2A of the ultraviolet irradiation peripheral unit 2 are disposed as shown in Fig. 7, it is possible to dispense with the shade S that is localized inside the location of the foreign matter in the central direction thereof. Accordingly, the curing of the ultraviolet curing resin R in the area of the shade A can be enhanced to obtain a uniform ultraviolet curing resin R. Since the angle of fixing the divided bodies 2A of the ultraviolet irradiation peripheral unit 2 between the base table 5 and fastening member 6 can be changed, it is possible to change the direction of irradiation by the ultraviolet irradiation peripheral unit 2, thereby excluding the localized shade S. Although the invention has been described with reference to the first and second embodiments, it is not limited thereto and can be modified variously within the scope of the claims. For example, the design of the shape of the arm-like transmission part can be appropriately changed if it attains the function of the ultraviolet irradiation central unit. Further, the number of the divided bodies of the ultraviolet irradiation peripheral unit is not limited to eight but can be appropriately selected. Still further, if the ultraviolet irradiation central unit is not used, it is not necessary to structure the boss so as to move toward and away from the upper surface of the rotary holding table, but may be structured to be fixed to the rotary holding table while it protrude from the rotary holding table. The angle of vertical direction of irradiation of ultraviolet by the ultraviolet irradiation peripheral unit can be changed. In this case, the angle of vertical direction of irradiation of ultraviolet can be easily changed by enlarging an interval between the base table and presser member and inserting a tapered spacer between the ultraviolet irradiation peripheral unit and the base table or presser member. According to the invention, the ultraviolet curing resin serving as an adhesive can be efficiently cured relative to the disc substrates through which ultraviolet does not transmit. Further, the ultraviolet curing resin serving as an adhesive can be efficiently cured relative to the disc substrates through which ultraviolet hardly transmits. Still further, the ultraviolet curing resin serving as an adhesive can be efficiently and uniformly cured relative to the disc substrates on which printing or the like is applied. Further, when the ultraviolet irradiation peripheral unit and the ultraviolet irradiation central unit are used, the ultraviolet curing resin can be efficiently cured. Still further, a productivity can be markedly improved because the ultraviolet curing resin can be efficiently cured. The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof within the scope of the claims.

Claims: An apparatus for curing an optical disc (D) placed on a rotary holding table (1) and formed by bonding a first disc substrate (D1) and a second disc substrate (D2) by the medium of an ultraviolet curing resin (R) comprising: an ultraviolet irradiation peripheral unit (2) disposed around the rotary holding table (1) for irradiating ultraviolet from the peripheral surface of the optical disc (D) toward the inner portion thereof so as to cure the ultraviolet curing resin (R) and comprising a plurality of divided units, characterized in that said divided units are disposed around the rotary holding table (1), the irradiation direction of ultraviolet is changeable in a horizontal plane and that the ultraviolet irradiation peripheral unit (2) is clamped between a base table (5) and a fastening member (6). The apparatus for curing an optical disc (D) according to claim 1, further comprising: an ultraviolet irradiation central unit (3) disposed at the center of the rotary holding table (1) for irradiating ultraviolet from the central hole of the optical disc (D) toward the outer portion thereof so as to cure the ultraviolet curing resin (R). The apparatus for curing an optical disc (D) according to claim 1 or 2, further comprising a boss (11) elastically pressed and joumaled by and attached to the central portion of the rotary holding table (1) and comprising suction means provided on the rotary holding table (1) and connected to a negative pressure source, wherein the suction means allows the boss (11) to move toward or away from the rotary holding table (1) and the optical disc (D) to be placed on and attached to the rotary holding table (1). The apparatus for curing an optical disc (D) according to claim 3, wherein the ultraviolet irradiation peripheral unit (2) is divided into eight, and wherein respective two divided units are arranged in parallel with each other and eight units are disposed square as a whole.

Inventors: INOUCHI MASAMI, KITANO RYOKO, YOSHIDA MASAYUKI, INOUCHI, MASAMI, KITANO, RYOKO, YOSHIDA, MASAYUKI, Inouchi, Masami, c/o Kitano Engineering Co., Ltd., Kitano, Ryoko, c/o Kitano Engineering Co., Ltd., Yoshida, Masayuki, Kitano Engineering Co., Ltd.
Applicants: KITANO ENG CO LTD, KITANO ENGINEERING CO., LTD.
Application year: 2000
Main classification: C09J5
IPC codes: B29C65, B29C35