DISK CARTRIDGE

Abstract: A disk cartridge comprises a case (1) and a disk (2) encased in the case, the disk (2) having a hub (17) comprising a flange (18) of thin metal sheet and a control ring (19) integrated with the flange (18) by outsert molding the control ring (19) from a compound plastic containing 5 to 40% by weight of a filler, and a dimensional ratio of flange plate (18) thickness to control ring (19) inner diameter being 1/50 to 1/30. The hub (17) has a higher plane precision, a higher attrition resistance, and a higher heat resistance.

Description: BACKGROUND OF THE INVENTION This invention relates to a disk cartridge encasing disk such as a magnetic disk, an optical disk, etc., and more particularly to an improvement in the material of a hub to be fixed at the center of the disk to rotate the disk. A prior construction of the Applicants is illustrated is Japanese Patent Application No. 60-27547 (publication No 61-188790) (published on 22.08.86 and therefore not part of the State of the Art) where the hub, as shown in Fig. 9, comprises a control ring 19 made from a plastic and destined for defining the free movement of a disk 2 in a case 1, and a flange 18 made from a thin magnetic stainless steel sheet and destined for being chucked by magnetic attraction, the control ring 19 and the flange 18 being integrally built up by outsert molding. The control ring 19 has, on its inside surface, a positioning surface for centering with respect to the driving shaft S for disk drive, and the flange 18 has, on its plate surface, a driving hole 23 which is engaged with a driving pin P on the driving shaft. The flange 18 and the control ring 19 are so integrated that the flange 18 may cover the opening at one side of the control ring 19 . In the formation of a hub by integrating the control ring and the flange made from different kinds of materials by outsert molding, as described above, there are the following problems as to the molding owing to differences in the material characteristics therebetween, particularly to a large difference in the coefficient of thermal expansion. For example, the coefficient of thermal expansion of iron is 1.2 × 10 to the minus fifth power (1,2 × 10⁻⁵), whereas that of nylon 6-6 is 10∿15 × 10 to the minus fifth power (10∿15 × 10⁻⁵), and thus there is a difference of about 10 times therebetween. When there is a large difference in the coefficient of thermal expansion between the control ring and the flange, the control ring has a larger contraction ratio when solidified, and thus the plate surface of the flange will undergo warping deformation in the plate thickness direction owing to the internal stress developed by the solidification. Once the flatness of the plate surface of the flange is deteriorated by the warping deformation, track deviation or disk flapping is liable to occur while the disk is used, and will be a fatal drawback for a high density recording disk. Furthermore, when a hub obtained by the said outsert molding is applied to a disk cartridge of relatively small size, it is necessary to prepare a smaller hub to meet the size-down of a disk diameter, but there has been a restriction with respect to the mechanical strength to make the sizes of a positioning or control, ring, for example, thickness, ring width, etc. smaller. That is, the disk can be made smaller in sizes, but it has been impossible to make the hub smaller in size than a given limit value. Furthermore, the positioning surface on the control ring is liable to undergo attrition by the driving shaft, thereby giving a poor centering. When the control ring is a plastic moulded article, it is hard to obtain a positioning surface with good durability and reliability against attrition over a long time. GB-A-2 127 206 discloses a disc cartridge in accordance with the prior art portion of claim 1. This prior construction avoids use of a metal plate filling the centre of the positioning ring and thus gives no assistance to avoiding the difficulties arising from deformation of the metal plate overcome by the present invention as characterised in claim 1. The present invention has as an object to provide a magnetic disc hub which comprises a positioning ring made of a plastic and a plate made of a thin metal sheet, which can be produced in a mass production scale with a high reliability and can meet requirements for the plane precision of the plate, good location of the disc being provided by engagement of a disc drive shaft with the metal plate, not possible where an annular flange is used, there also being provided good mechanical strength of the positioning ring. The desired hub of the present invention can be produced by outsert moulding a control ring from a compound plastic containing a filler, particularly a reinforcing filler, with the filler being provided in a quantity to modify and reduce the moulding shrinkage of the compound plastic, when mixed with the filler, during moulding of the plate. While in our EP-A-0 142 637 we disclose the use of a filled plastics material for a disc cartridge hub, this is in connection with a structure which dispenses with the metal plate such that one does not have the problem of differential thermal contraction between metal and plastic components. This prior proposal provides no suggestion as to the problems to be overcome when a metal plate is integrated with the plastic ring and certainly provides no solution to these problems. Specifically, the plastic base material can be selected mainly from thermoplastic resins such as polyacetal, nylon, polybutylene terephthalate, polyester, polypropylene, polyethylene, polyfluoroethylene, etc. The filler can be selected from potassium titanate, calcium carbonate, graphite, talc, glass fibers, etc., and can be in a granular, whisker or plate shape. 5 to 10% by weight, preferably 10 to 30% by weight, of the fillers is contained in the compound plastic. Below 5% by weight of the filler, the mold shrinkage will be increased, and the heat resistance will be lowered. That is, when the ambient temperature exceeds 60°C, the molded article is liable to be deformed, and the mechanical strength will be lowered, causing breakages or wearing. Above 40% by weight of the filler, the flowability of the molten compound plastic will be lowered, causing poor molding, and considerably deteriorating the impact resistance. That is, cracks are liable to develop. In mixing the filler into the plastic base material, it is most important to make the coefficient of thermal expansion of the control ring as near that of the material of construction of the metal plate as possible to minimize the molding shrinkage. The molding shrinkage can be defined by the numerical value obtained according to the following equation, and will be hereinafter based on this value: It is necessary that the molding shrinkage is not more than 1.8%, preferably not more than 1.5%. When the molding shrinkage is over 1.8%, a warping deformation develops on the metal plate to cause a track deviation particularly in the case of a hub 17 applied to a disk 2 of large nominal size. Most preferable compound plastic composition comprises polybutylene terephthalate or polyacetal as a plastic base material and 20% by weight of potassium titanate in a whisker state on the basis of the weight of the compound plastic composition, where a molding shrinkage of 0.8 to 1.4% can be obtained. Material for the metal plate 18 is preferably magnetic stainless steel such as SUS 430, etc. in the case of chucking by magnetic attraction, and may be other metals in a sheet form, such as steel, copper alloy, aluminium alloy, etc. in the case of mechanical chucking. The amount of warping deformation of the plate 18 , for example, an amount of difference in the thickness direction of the plate 18 between the center of the plate 18 and the position of inner side edge of the control ring 19 depends upon the diameter of the control ring 19 , even if the molding shrinkage of the control ring 19 is constant. To control the amount of warping deformation due to the mechanical structure, it is effective to set a dimensional ratio of the plate thickness T of the plate 18 (Fig. 4) to the inner diameter D of the control ring 19 (Fig. 3), i.e. T/D to at least 1/50, preferably 1/50 - 1/30. When the dimentional ratio T/D is below 1/50, it is difficult to control the amount of warping deformation only by adapting the proper filler control when molding from the compound plastic containing the filler. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 4 show a first application embodiment 1 of a disk cartridge according to the present invention, where Fig. 1 is a bottom plan view of a disk cartridge, Fig. 2 is a plan view of a hub, Fig. 3 is a bottom plan view of the hub, and Fig. 4 is a cross-sectional view along the line IV-IV of Fig. 3. Figs. 5 and 6 show a second application embodiment of a hub according to the present invention, where Fig. 5 is a bottom plan view of a hub and Fig. 6 is a cross-sectional view along the line II-II of Fig. 5. Figs. 7 and 8 show a third application embodiment of a hub according to the present invention, where Fig. 7 is a bottom plan view of a hub and Fig. 7 is a cross-sectional view along the line VIII-VIII of Fig. 7. Fig. 9 shows a vertically cross-sectional front view of a hub and its neighbourhood structure according to the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some application embodiments of a disk cartridge according to the present invention will be described in detail below, referring to the drawings. Application Embodiment 1 Figs. 1 to 4 show a first application embodiment of a disk cartridge. In Fig. 1, a disk cartridge (nominal size: 2.5 inch) is composed of a rectangular case 1 and a disk 2 rotatably encased therein. The case 1 is composed of upper and lower shells 3a and 3b joined together at the edges to form a hollow inside. The lower shell 3b has a circular driving shaft insert opening 4 substantially at the center thereof, and both upper and lower shells 3a and 3b each have a rectangular head insert 5 at the position near the front end. The head insert openings 5 are brought into an open or closed state by the shutter 6 . The shutter 6 is injection molded from a compound plastic containing a reinforcing filler, and supported slidably in the lateral direction of the case 1 , and kept by the force of a spring 7 at a position to close the head insert openings 5 when the disk cartridge is not charged into a disk drive, while the shutter 6 undergoes opening operation against the force of the spring 7 when charged into the disk drive. The lower shell 3b further has insert holes 8 for a positioning pin, an operational groove 10 for operating a write protect notch 9 , etc. The upper shell 3a has a detection hole 11 of the same shape as the operating groove 10 capable of being opened or closed by the write protect notch 9 and a recess for pasting a label. Cleaning members 13 capable of sandwiching the disk 2 through liner sheets not shown in the drawings are provided on the inside surfaces of the upper and lower shells 3a and 3b at a position on the disk-coming side in the disk rotating direction as viewed from the head insert opening 5 . These cleaning members 13 are supported from the outside of the case through operational openings 14 provided through the walls of the upper and lower shells 3a and 3b to make cleaning of the disk 2 and prevent the flapping of a magnetic sheet 16 as driven. The disk 2 is composed of a circular magnetic sheet 16 and a hub 17 facing the said driving shaft insert opening 4 as fixed at the center of the magnetic sheet 16 . The hub 17 is composed of a flange 18 made from a thin magnetic stainless steel sheet of SUS 430 and a control ring 19 as fixed thereto by outsert molding. The magnetic sheet 16 is fixed to a flange portion of the plate 18 by adhesion. The control ring 19 has a chevron-shaped positioning part 21 for concentrically positioning the entire disk with respect to the driving shaft of the disk drive, whereas the flange 18 has a diamond-shaped driving hole 23 with which a driving pin is engaged. To improve the connection between the plate 18 and the control ring 19 , connection lugs 25 are formed by blanking from the sheet of flange 18 toward the peripheral side and are embedded into the wall of the control ring 19 as shown in Figs. 2 and 4. The connecting lugs 25 are provided at 6 positions in the peripheral direction of the control ring 19 including the position corresponding to the positioning part 21 . The connection lug corresponding to the positioning part 21 is formed broader and longer than other connection lugs. The main dimensions of the hub 17 applied to the disk cartridge of 2.5-inch nominal size shown in Figs. 1 to 4 are as follows: Application Embodiment 2 Figs. 5 and 6 show a second embodiment of another hub to a disk cartridge of 3.5-inch nominal size, where the basic structure of hub 17 is the same as that to the disk cartridge of 2.5-inch nominal size of Application Embodiment 1, except that the shape of driving hole 23 is changed to a sector shape. The main dimensions of hub 17 are as follows; Application Embodiment 3 Figs. 7 and 8 show a third application embodiment of other hub for a disk cartridge of 5-inch nominal size, where the hub 17 has basically the same structure as that for the disk cartridge disk of 2.5-inch nominal size as shown in Figs. 1 to 4, but there are small changes in the shape, that is, the shape of the driving hole 23 is changed to an oblong shape and a projection 26 for attrition reduction is provided at the center of the plate surface of flange 18 . The main dimensions of hub 17 are as follows: Example 1 Hubs 17 shown in Figs. 2 to 4 were outsert molded from compound plastics composed each of polybutylene terephthalate as a plastic base material and 0 to 30% by weight of potassium titanate in a whisker form as a filler, on the basis of the weight of the respective compound plastic, as shown in the following Table 1. The whiskers of potassium titanate had an average fiber length of 10 to 20 µm, a fiber diameter of 0.2 to 0.5 µm, a Mohs hardness of 4.0, a tensile strength of 500 to 700 kgf/mm², a modulus in tension of about 28,000 kgf/mm², and a volume resistivity of 3.3 x 10¹⁵ Ω·cm. The flange 18 was made from a stainless steel sheet (3 mm-thick, SUS 430). Example 2 In the material No. 4 of Example 1, a hub 17 was outsert molded in the same manner as in Example 1, except that polybutylene terephthalate was replaced with polyacetal as the plastic base material. The thus obtained hub was identified as material No. 6. Another hub molded from the same compound plastic without the filler, that is, single polyacetal was identified as Comparative Example 2. Example 3 Hubs 17 were outsert molded in the same manner as in Example 1, except that the whiskers of potassium titanate were replaced with talc, calcium carbonate, graphite or glass fibers as the filler in Example 2. They were identified as given in the following Table 2. Evaluation The amounts of warping deformation δ of the hubs 17 obtained by outsert molding the said materials Nos. 1 to 10 and Comparative Examples 1 to 2 were measured. As shown in Fig. 4, the amounts of warping deformation δ were determined by measuring a difference in the thickness direction of the flange between the center of the plate 18 and the position of inner side edge of the control ring 19 by a dial gage. Furthermore, the heat resistance was determined by keeping the hubs at 60°C for 48 hours, leaving them at the ordinary temperature for 24 hours, and observing a change in the inner diameter of control ring 19 . As to the mechanical strength, attrition resistance was determined by engaging a rotating shaft S with the hub 17 by 20,000 repetitions and visually observing the attrition state of the positioning part 21 . The test results are shown in the following Table 3 together with the molding shrinkages of the respective materials. As to the heat resistance, a round mark "O" shows no change; a triangular mark "Δ" shows a little change; a crossed mark "X" shows a substantial change. As to the attrition resistance, a double round mark "o ○" shows no substantial attrition; a round mark "O" shows a slight attrition; a triangular mark "Δ" shows a substantial attrition. In outsert molding of a hub 17 comprising a plastic control ring 19 and a plate 18 of thin metal sheet, the control ring 19 is outsert molded from a compound plastic containing a reinforcing filler capable of improving a molding shrinkage in the present invention, whereby the coefficient of thermal expansion of the control ring 19 can be made as near that of the material of constructions for the plate 18 as possible, and thus the warping deformation of the plate 18 can be lowered to a negligible degree during the mold solidification, attaining a higher plane precision and preventing a track deviation, etc. Furthermore, the mechanical strength and the attrition resistance can be increased by the reinforcing action of the filler, as is obvious from Table 3, and thus the control ring 19 can be given an improved durability and a smaller size with ease.

Claims: A disc cartridge comprising a case (1) and a disc (2) rotatable within the case, the disc (2) having a hub (17) comprising a positioning ring (19) for concentrically positioning the hub (17) and disc (16) with respect to the driving shaft of a disc drive and a sheet metal plate (18) including a flange portion extending radially outwardly of the positioning ring (19) and integrated therewith by moulding the ring (19) from a plastics material, characterised in that the metal plate (18) also has an internal portion substantially filling the centre of the positioning ring, in that the plastics material is a compound plastic which comprises plastics base material mixed with filler to the extent to provide a moulding shrinkage of not more than 1.8% during moulding, and in that the dimensional ratio of plate thickness to the inner diameter of the positioning ring is in the range of 1/50 to 1/30. A disc cartridge according to claim 1, wherein the plastics base material for the compound plastic is polybutylene terephthalate. A disc cartridge according to claim 1, wherein the plastics base material for the compound plastic is polyacetal. A disc cartridge according to claim 1, 2 or 3, wherein the filler is potassium titanate. A disc cartridge according to any preceding claim, wherein the plastics material contains 5 to 40% by weight of the filler. A disc cartridge according to any preceding claim, wherein the positioning ring (19) has a chevron-shaped positioning part (21) for concentrically positioning the hub (17) and disc with respect to the driving shaft(s) of a disc drive.

Inventors: KATO, YOSHITAKE
Applicants: HITACHI MAXELL LTD.
Application year: 1987
Main classification: G11B23
IPC codes: G11B23