Magneto-optical recording medium and method for processing the surface

Abstract: A surface of a magneto-optical recording medium of the present invention is textured with fine and physical protrusions and recessions. The shapes of physical protrusions and recessions vary at each radial locations on the medium such that, for example, rough protrusions and recessions are formed in inner parts of the recording medium and fine protrusions and recessions are formed in outer parts thereof. Therefore, floating force given to a floating head from the medium being rotated based on the constant angular velocity method through an air layer in the outer parts equals floating force in the inner parts. Consequently, since the floating height of the floating head becomes constant irrespective of radial locations on the medium, information can be recorded under constant recording conditions, permitting the accuracy of the recording to improve. Regarding a method for processing the surface of a magneto-optical recording medium relating to the present invention, for example, a texture tape whose roughness is large is used in inner parts of the medium while a texture tape whose roughness is small is used in outer parts thereof. As a result, a magneto-optical recording medium having the above characteristics is produced.

Description: FIELD OF THE INVENTION The present invention relates to a magneto-optical recording medium to be used with a magneto-optical recording/reproducing device comprising a floating type magnetic head, and to a method for processing the surface of the magneto-optical recording medium. BACKGROUND OF THE INVENTION In the magneto-optical recording method, a substrate made of glass, plastic, ceramic or other material and coated with a vertically magnetized film composed of metal magnetic material serves as a recording medium, and recording and reproducing operations on and from the recording medium are carried out in the following process. In the recording operation, first the magnetization direction of the vertically magnetized film of the recording medium is arranged to a predetermined direction (upward direction or downward direction) by using a strong external magnetic field or the like (hereinafter this process is referred to as initialization). Then the temperature of a recording portion where the recording is to be carried out is raised to exceed the vicinity of the Curie point or is raised to exceed its magnetic compensation point by projecting a laser beam on the recording portion. As a result, the magnetic coercive force (Hc) on the recording portion becomes zero or substantially zero. With this state, the magnetization direction is reversed by applying an external magnetic field (bias magnetic field) whose magnetization direction is opposite to the initialized magnetization direction. When the projection of the laser beam is stopped, the recording portion of the recording medium returns to room temperature. Thus, since the reversed magnetization direction is fixed, information is recorded. The above-mentioned recording operation is also called thermomagnetic recording. In the reproducing operation, a linearly polarized laser beam is projected onto the recording medium. The rotating direction of a polarization plane of reflected light or transmitted light from or through the recording medium varies according to the magnetization direction (upward or downward) of the recording medium (this is called magnetic Kerr effect or magnetic Faraday effect). Information is optically read out by the use of the magnetic effect. Recording media used in the magneto-optical recording method have been noted as large capacity memory elements of a re-writable type. At present, there are two methods for re-writing over the information recorded on the recording medium, described in (i) and (ii) below. (i) A method wherein the previously recorded information is deleted by initializing the recording medium again. (ii) A method wherein a recording medium or an external magnetic field generating device is improved so that overwriting is performed, i.e. the information is re-written directly without performing the deletion. If method (i) is adopted, either an initialization device or two heads must be installed, thereby causing a rise in cost. Moreover, in case of deleting information with a single head, the same time taken for recording is required for deleting, resulting in the inefficient operation of re-writing information. In the mean time, if method (ii), improving the recording medium, is adopted, it is difficult to control recording medium composition, film thickness and so on. For the above reasons, the most effective means is improving the external magnetic field generating device of method (ii), i.e. switching a direction of the external magnetic field at high speed according to information signals while keeping the intensity of the laser beam constant. In order to switch the direction of the external magnetic field at high speed, a magnetic head (a coil and a coil core) of the external magnetic field generating device must be miniaturized to a great degree. In this case, however, a generating area of the magnetic field becomes smaller. In order to counteract this, a magnetic head and a recording medium must be brought closer to each other. Thus, as shown in Fig. 10(a) and Fig. 10(b), generally a floating head 32 of a sliding type which can glide over a recording medium in the shape of a disc (not shown) is employed as the external magnetic field generating device. The floating head 32 comprises a slider section 33 provided with a magnetic head section 34. The floating head 32 is pressed down toward the recording medium and supported by a suspension 31. According to the configuration, when the recording medium is rotated, the floating head 32 floats over the surface of the recording medium. A constant floating height of the floating head 32 is maintained due to the fact that floating force balances with depressing force. The floating force is exerted upwards on the slider section 33 by the air flowing between the slider section 33 and the recording medium. The depressing force is exerted downwards on the slider section 33 by the suspension 31. The floating head of this type is also used for conventional hard disks of magnetic recording/reproducing devices. In the case of the hard disks, the floating height is of a submicron order. However, when the recording medium is a magneto-optical disk, a floating height of 5µm to 15µm is necessary, i.e. a larger floating height is needed for the magneto-optical disk than for the hard disk. The reasons for this are as follows. Since the magneto-optical disks are transportable, dust tends to stick more frequently on the disk. As a result, troubles such as a head crash, where the magneto-optical head 34 is damaged by dust as the floating height is too small, may occur. A surface of the magneto-optical disk which faces the floating head 32, is textured with fine and physical protrusions and recessions, preventing the surface of the disk from sticking to the floating head. As shown in Fig. 11(a) and Fig. 11(b), when forming the disk surface with the texture, a texture tape 36 having fine protrusions and recessions on the surface thereof is used. More precisely, when forming the disk surface with the texture, the texture tape 36 is pressed onto a magneto-optical disk 35 by a tape pressure roller 37 and then the magneto-optical disk 35 is rotated while feeding the texture tape in the direction of arrow C. In this case, since the rotating direction of the magneto-optical disk 35 is in parallel with the feeding direction of the tape 36, the protrusions and recessions are evenly formed on the magneto-optical disk 35 as shown by the two-dot long and two short dashes line of fig. 12, substantially forming concentric circles. The use of such a technique for texturing the surface of an Ni-P film formed on the surface of an aluminium alloy disk for a magnetic recording medium is disclosed in JP-A-62/262227. As aforesaid, in the case of the magneto-optical disk, the floating height of the floating head is 5µm to 15µm, greater than a floating height required when a hard disk is used. Therefore, variations in the floating height greatly depend on the relative velocity between the magneto-optical disk and the floating head. The relation is shown in Table 1 below. Referring to table 1, if depressing force F of the suspension is constant and the relative velocity increases by two times, the floating height increases by a substantial one and half times (here, the dimensions of the slider section are 6mm x 4mm). Thus, in case the magneto-optical disk is rotated based on the Constant Angular Velocity method (hereinafter referred to as CAV method), the relative velocity is higher in outer parts of the magneto-optical disk than in inner parts thereof, resulting in a higher floating height in the outer parts. Consequently, a magnetic field intensity applied to the magneto-optical disk by the floating head varies at each radial locations on the magneto-optical disk, and therefore a problem arises, i.e. the recording operation with a conventional magneto-optical disk cannot be carried out under constant conditions. DE-A-3629582 discloses a process for the surface treatment of a disk-shaped nickel-plated aluminium substrate to be used as a base for a magnetic recording hard disk. The substrate is given a surface texture which has a defined surface roughness and structure, using an automatic lapping machine. the applied texture has a bucket wheel-shaped structure, by which is meant that scratches close to one another run outward from the centre of the disk-shaped substrate in an arc-like manner to the disk circumference. SUMMARY OF THE INVENTION The present invention aims to provide a magneto-optical recording medium for use with a floating type magnetic head (hereinafter referred to as a floating head) and to be rotated based on the CAV method, in which a constant floating height of the floating head is maintained irrespective of the radial location on the magneto-optical medium. The present invention also aims to provide a method for processing the surface of the magneto-optical medium so as to form a surface texturing to achieve regulation of the floating force. According to one aspect of the invention, therefore, there is provided a magneto-optical recording medium for use in a recording and/or reproducing apparatus employing a magnetic head which in use floats over the surface of the medium on a flow of air generated by rotation of the medium and entrained between said magnetic head and said surface at a relative linear velocity which varies in accordance with the radial position on the medium, said medium having fine physical protrusions and recessions forming a surface texture which affects a floating force applied, in use, to said magnetic head to cause it to float, characterised in that physical characteristics of said surface texture vary according to the radial position on said surface so as to regulate said floating force with respect to radial position by compensating for said variation in linear velocity. For example, in case that the physical protrusions and recessions are generally elongate, they are formed so that their lengthwise average orientation crosses the rotating direction of the recording medium at substantially right angles in radially inner parts of the recording medium and is substantially parallel to the rotating direction in outer parts thereof. As another example, the physical protrusions and recessions may be formed such that the maximum value R MAX of their heights is larger in the radially inner parts than in the outer parts, i.e. relatively rough protrusions and recessions are formed in the radially inner parts while relatively fine protrusions and recessions are formed in the radially outer parts. With such texturing, the floating force in the radially inner parts where the relative velocity between the recording medium and the floating head is small can be made to equal the floating force in the radially outer parts where the relative velocity is large. Therefore, even when the relative velocity between the floating head and the recording medium changes due to the rotation of the magneto-optical recording medium in the CAV method, the floating height of the floating head does not vary. As a result, the recording condition is maintained to be constant irrespective of the locations on the recording medium in a radial direction, thereby permitting the accuracy of the recording to be improved. In another aspect, the present invention provides a method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to the present invention, wherein a tape having a surface whereon fine and physical protrusions and recessions are formed is used. In this method, fine and physical protrusions and recessions to be formed on the surface of the recording medium by pressing the tape onto the recording medium with pressure means and moving the pressure means, are aligned in a direction which crosses the rotating direction of the recording medium at substantially right angles in the radially inner parts and which is substantially parallel to the rotating direction of the medium in the radially outer parts. The present invention also provides a method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to the present invention, the method being characterized in that a tape whose roughness is large is used in the radially inner parts of the recording medium and a tape whose roughness is small is used in the radially outer parts thereof so as to form rough protrusions and recessions in the radially inner parts and fine protrusions and recessions in the radially outer parts. Instead of using tapes having different conditions each other in roughness, the depressing force of the pressure means may be strengthened in the radially inner parts while it may be weakened in the radially outer parts. The present invention further provides a method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to the present invention, the method being characterized in that by using a stamper whereon fine and physical protrusions and recessions corresponding to desired shapes to be formed on the recording medium are etched, the protrusions and recessions of the desired shapes are copied on the surface of the recording medium. This method using a stamper can be adopted for the mass production of magneto-optical recording media having the above-mentioned surface texturing characteristics. Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figs. 1 to 3 show one embodiment of the present invention. Fig. 1 is a schematic longitudinal sectional view showing the structure of the magneto-optical disk. Fig. 2 is a typical plan depiction showing the features of the texture of the magneto-optical disk surface. Fig. 3(a) and Fig. 3(b) are explanatory views showing a method for forming the recording medium surface with the texture. Fig. 4 and Fig. 5 show another embodiment of the present invention. Fig. 4 is a schematic longitudinal sectional view showing the structure of a magneto-optical disk. Fig. 5 is a typical schematic plan depiction showing the features of textures of the magneto-optical disk surface. Fig. 6 to Fig. 9 show another embodiment of the present invention. Fig. 6 is a typical schematic perspective depiction showing the features of the texture of a magneto-optical disk surface. Fig. 7(a) is a schematic perspective view showing a method for forming the magneto-optical disk surface with the texture by the use of a stamper. Fig. 7(b) to Fig. 7(d) are typical schematic bottom plan depictions showing the features of textures etched on the stamper, corresponding to the features of textures of a recording medium to be formed. Fig. 8 and Fig. 9 are schematic perspective views showing a method for mass-producing the texture by the use of stampers. Fig. 10(a) is a schematic perspective view showing a floating head and a suspension. Fig. 10(b) is a perspective view showing the floating head. Fig. 11 and Fig. 12 show a conventional example. Fig. 11(a) and Fig. 11(b) are explanatory views showing a method for forming a magneto-optical disk surface with a texture by using a texture tape. Fig. 12 is a typical plan depiction showing the features of the texture of the magneto-optical disk surface. DESCRIPTION OF THE EMBODIMENTS The first embodiment of the present invention will be described below with reference to Fig. 1 to Fig. 3. As shown in Fig. 1, a magneto-optical disk as a magneto-optical recording medium of the present invention is configured such that a substrate 1, a magneto-optical recording film 2 and a protective film 3 are laminated in order. The substrate 1 is made of an optically transparent material such as glass, polycarbonate, polymethyl methacrylate and amolphous polyolefine. The magneto-optical recording film 2 of single-layer structure or multilayer structure including a dielectric film, reflection film and the like, is formed on the substrate 1 by sputtering, evaporation or other process. Regarding the protective film 3 formed on the magneto-optical recording film 2, it is made of an organic material such as UV hardening resin or an inorganic material such as SiO 2 , carbon and ceramic. Fine physical protrusions and recessions forming a texture 4 are formed on the surface of the protective film 3. The process for giving the texture 4 to the surface of a magneto-optical disk is called the surface processing. As shown by the two-dot long and two short dashes line of Fig. 2, for example, the protrusions and recessions forming the texture 4 are aligned in a direction which crosses the rotating direction of the disk at substantially right angles in inner parts of the disk, while they are aligned in a direction which is substantially parallel to the rotating direction of the disk in outer parts thereof. In other words, in case fine physical protrusions and recessions whose respective lengths are longer than their respective widths (i.e. which are generally elongate) form the texture 4, the average orientation of the respective physical protrusions and recessions with respect to their lengths varies progressively so that it crosses the rotating direction of the disk at substantially right angles in the inner radially parts of the disk and it is substantially parallel to the rotating direction in the radially outer parts thereof. Briefly, the fine and physical protrusions and recessions are formed on the surface of the magneto-optical disk in different directions at respective radial locations. Accordingly, floating force given to a floating head from the magneto-optical disk being rotated based on the CAV method through an air layer becomes the same in both in the inner parts and in the outer parts. Consequently, the floating height of the floating head becomes constant irrespective of radial locations on the magneto-optical disk. Next, a method for processing the disk surface is described below. As shown in Fig. 3(a), a texture tape 6 having fine physical protrusions and recessions on its surface is used for forming the texture 4. When protrusions and recessions forming the texture 4 are formed in outer parts of a magneto-optical disk 5, the texture tape 6 is pressed onto the surface of the disk 5 by a pressure roller 7 as pressure means and then the texture tape 6 is fed in the direction of arrow A shown in Fig. 3(a) while rotating the disk 5. On the other hand, when forming protrusions and recessions forming the texture 4 from the outer parts of the disk 5 toward the inner parts, the pressure roller 7 is moved toward the inner parts from the outer parts, i.e. toward the position of Fig. 3(b) from the position of Fig. 3(a). With this operation, since the rotating direction of the disk 5 crosses the feeding direction of the texture tape 6 shown by arrow A at substantially right angle in the inner parts, the protrusions and recessions forming the texture 4 are aligned in a direction shown by the two-dot long and two short dashes line of Fig. 2. In the present embodiment, the protrusions and recessions forming the texture 4 are formed on the surface of the magneto-optical disk 5 in a clockwise direction, but they may be formed in a counterclockwise direction. Referring to Fig. 4 and Fig. 5, the following description will discuss the second embodiment of the present invention. As to members whose functions are the same as the members shown in the drawings for the aforesaid embodiment, for convenience' sake, the same numbers are given thereto and the explanations are omitted here. As shown in Fig. 4, similar to the above embodiment, a magneto-optical disk of the present embodiment comprises a substrate 1, a magneto-optical recording film 2 and a protective film 3. Protrusions and recessions forming textures 8 and 9 are formed on the surface of the protective film 3. As shown in Fig. 5, mainly rough protrusions and recessions forming the texture 8 are formed in inner parts of the disk, while mainly fine protrusions and recessions forming the texture 9 are formed in outer parts of the disk. The maximum value R MAX for the heights of the rough protrusions and recessions is 100nm to 2500nm, and the maximum value R MAX for the heights of the fine protrusions and recessions is not more than 200nm. In Fig. 5, the area of the fine texture 9 and the area of the rough texture 8 are indicated distinguishably so that the features of the disk surface are easily understood. However, the protrusions and recessions can be formed such that each of the protrusions and recessions becomes smaller gradually from the inner parts toward the outer parts of the disk according to the relative velocity between the magneto-optical disk and the floating head. As described above, the shapes of the fine and physical protrusions and recessions formed on the surface of the protective film 3 vary at each radial locations on the disk. As a result, since floating force given to the floating head from the magneto-optical disk being rotated in the CAV method through an air layer is the same in both in the inner parts and in the outer parts, the floating height of the floating head becomes constant irrespective of radial locations on the magneto-optical disk. For performing the above-mentioned surface processing in the inner parts of the magneto-optical disk, a texture tape of a large roughness is pressed onto the inner parts of the disk surface by the pressure roller and like the conventional cases the texture tape is fed while rotating the disk. With this operation, rough protrusions and recessions form the texture 8. On the contrary, a texture tape having a small roughness is used in the outer parts of the disk. Therefore, fine protrusions and recessions forming the texture 9 are formed in the outer parts in the same way as the way for the inner parts. Instead of using texture tapes of different roughnesses in the inner parts and the outer parts of the disk, tapes having the same roughness may be employed. In this case, the depressing force of the pressure roller is strengthened in the inner parts and is weakened in the outer parts so that rough protrusions and recessions are formed in the inner parts and fine protrusions and recessions are formed in the outer parts. Referring to Fig. 6 to Fig. 9, the third embodiment of the present invention is described below. Similar to the first embodiment and the second embodiment, a magneto-optical disk of the present embodiment is configured such that a magneto-optical recording film, and a protective film are laminated on a substrate. As shown in Fig. 6, a resin layer 10 is formed on the protective film, and protrusions and recessions 11 in the shape of folds and having the maximum heights R MAX of 100nm to 2500nm are formed on the surface of the resin layer 10. Shortly, as shown by the two-dot long and two short dashes line of Fig. 6, the protrusions and recessions 11 are formed such that lines representing the tops of each folds extend radially in radial directions of the magneto-optical disk. The height of the fold decreases gradually from inner parts of the disk toward outer parts thereof. That is to say, the shapes of the physical protrusions and recessions formed on the surface of the resin layer 10 vary at each radial locations on the magneto-optical disk. As a result, since floating force given to a floating head from the magneto-optical disk being rotated based on the CAV method through an air layer becomes the same both in the inner parts and in the outer parts, the floating height of the floating head becomes constant irrespective of radial locations on the magneto-optical disk. The following description will discuss a method for processing a disk surface in the similar way to the above. As shown in Fig. 7 ( a ), the magneto-optical disk 12 is coated with a resin 13 made of an ultra violet (UV) hardening resin ( for example, unsaturated polyester and oligoacrylate). The UV hardening resin is a kind of optical hardening resins. The resin 13 is hardened by irradiating ultra violet light thereon. A stamper 14 whose texture corresponds to the protrusions and recessions 11 in the shape of folds is pressed onto the hardened resin 13. The bottom surface of the stamper 14 is textured with desired features, for example the one shown in Fig. 7(b), by chemical etching, precision machine processing or other process. The features of a texture to be etched on the stamper 14 may correspond to the features of the textures discussed in the first embodiment and the second embodiment, shown in Fig. 7(c) and Fig. 7(d). In such cases, a magneto-optical disk having the texture features discussed in the first embodiment or the second embodiment can be formed. Next, a method for processing the surface of a magneto-optical recording medium which copes with mass production is described below. As shown in Fig. 8, magneto-optical disks 15 are produced on a production board 18 by leaving predetermined spaces longitudinally and transversely between the disks. The magneto-optical disks 15 have already been coated with a resin (not shown). A roller 16 comprises stampers 17 for giving texture. The stampers 17 are positioned so as to correspond to the respective magneto-optical disks 15. When forming the disk surfaces with the texture, the roller 16 is rotated and the stampers 17 for giving texture are pressed onto the magneto-optical disks 15 on the production board 18 with constant pressure P, so that the magneto-optical disks 15 having a texture of desired features can be produced. Another method for processing the surface of a magneto-optical recording medium which copes with mass production is described below. Like the above case, magneto-optical disks 19 are formed on a production board 24, and a roller 20 comprises stampers 21 on the surface thereof. A pot 22 containing a thermoplastic resin 23 is disposed above the roller 20. The resin 23 is supplied to the roller 20 from the bottom section of the pot 22. The magneto-optical disks 19 are not coated with a resin for giving texture. When forming a texture, the resin 23 is supplied to each the stampers 21 from the bottom section of the pot 22 at the time the roller 20 rolls on the production board 24. The resin 23 whereon the features of the texture of the stampers 21 are transferred is applied to the magneto-optical disks 19 with the rolling of the roller 20. In this case, the stampers 21 and the pot 22 are heated. Since the resin 23 is a thermoplastic resin, the resin 23 attached on the magneto-optical disks 19 are hardened by being cooled. Consequently, the surfaces of the magneto-optical disks 19 are textured with desired features. As described above, a magneto-optical recording medium of the present invention is basically configured such that the physical characteristics of the surface texture formed by the fine physical protrusions and recessions formed on the surface of the medium vary accordingly to the radial position locations on the magneto-optical recording medium. For this reason, in case the magneto-optical recording medium is rotated in the CAV method, the relative velocity between the floating head and the magneto-optical recording medium becomes higher toward the outer parts. However, the floating pressure in the outer parts equals the floating pressure in the inner parts due to the shapes of protrusions and recessions formed on the surface of the recording medium. Therefore, the floating height of the floating head is substantially constant irrespective of radial locations on the recording medium. Consequently, since the intensity of the magnetic field applied to the magneto-optical recording medium from the floating head becomes substantially constant, information is recorded under substantially constant conditions irrespective of radial locations, thereby permitting the accuracy of the recording to improve.

Claims: A magneto-optical recording medium for use in a recording and/or reproducing apparatus employing a magnetic head which in use floats over the surface of the medium on a flow of air generated by rotation of the medium and entrained between said magnetic head and said surface at a relative linear velocity which varies in accordance with the radial position on the medium, said medium having fine physical protrusions and recessions forming a surface texture which affects a floating force applied, in use, to said magnetic head to cause it to float, characterised in that physical characteristics of said surface texture vary according to the radial position on said surface so as to regulate said floating force with respect to radial position by compensating for said variation in linear velocity. A magneto-optical recording medium according to claim 1, wherein the protrusions and recessions forming the texture of the recording medium surface are aligned in a direction which crosses the rotating direction of the recording medium at substantially right angles in the radially inner parts of the recording medium, and which is substantially parallel to the rotating direction in the radially outer parts thereof. A magneto-optical recording medium according to claim 1, wherein the protrusions and recessions are generally elongate in form and are formed so that their lengthwise average orientation vary progressively from an orientation which crosses the rotating direction of the recording medium at substantially right angles in the radially inner parts of the recording medium to an orientation which is substantially parallel to the rotating direction in the radially outer parts thereof. A magneto-optical recording medium according to claim 1, wherein the surface texture in the radially inner parts of the recording medium is rougher than the surface texture in the radially outer parts. A magneto-optical recording medium according to claim 4, wherein the roughness of the surface texture decreases from the radially inner parts of the magneto-optical recording medium toward the outer parts thereof in accordance with the variation with radial position in the relative velocity between the magneto-optical recording medium and the floating type magnetic head when the magneto-optical recording medium is rotated at constant angular velocity. A magneto-optical recording medium according to claim 4, wherein the maximum height R MAX of the protrusions and recessions forming the surface texture in the radially inner parts of the recording medium is 100nm to 2500nm and the maximum height R MAX of protrusions and recessions forming the surface texture in the outer parts is no more than 200nm. A magneto-optical recording medium according to claim 1 wherein the physical protrusions and recessions are folds, lines representing the tops of the folds extend radially of the recording medium, the maximum height R MAX of the folds is 100nm to 2500nm, and the height of the folds decreases from the radially inner parts of the recording medium toward the radially outer parts thereof. A magneto-optical recording medium according to any preceding claim, further comprising: a substrate made of an optically transparent material; a magneto-optical recording film on said substrate; and a protective film on said magneto-optical recording film, wherein a surface of the protective film which in use will face the floating type magnetic head is formed with said surface texture. A method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 2, comprising the steps: pressing a tape having fine physical protrusions and recessions on the surface thereof onto the surface of the rotating magneto-optical recording medium by pressure means; and moving the tape and the pressure means so that fine physical protrusions and recessions to be formed on the recording medium surface are aligned in a direction which crosses the rotating direction of the recording medium at substantially right angles in radially inner parts of the recording medium and which is substantially parallel to the rotating direction in radially outer parts thereof. A method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 4, comprising the step: pressing a tape having fine physical protrusions and recessions on the surface thereof onto the surface of the rotating magneto-optical recording medium by pressure means, wherein a tape having a relatively large roughness is used in radially inner parts of the recording medium while a tape having a relatively small roughness is used in radially outer parts thereof. A method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 4, comprising the step: pressing a tape having fine physical protrusions and recessions on the surface thereof onto the surface of the rotating magneto-optical recording medium by pressure means, wherein the depressing force of the pressure means is strengthened in radially inner parts of the recording medium while it is weakened in radially outer parts thereof. A method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 1, comprising the step: copying features etched on a stamper, corresponding to the features of protrusions and recessions to be formed, onto the magneto-optical recording medium. A method according to claim 12 further comprising the step: coating a resin on the surface of the magneto-optical recording medium, wherein the features of the stamper are copied onto the surface of the resin. A method according to claim 13, wherein the resin is of an ultra violet hardening type. A method for processing a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 1, comprising the steps: producing a magneto-optical recording media coated with a resin on a production board for magneto-optical recording media; disposing stampers, whereon features corresponding to the respective features of fine physical protrusions and recessions to be formed on the respective surfaces of the magneto-optical recording media are etched, in positions on the surface of copying means corresponding to the respective magneto-optical recording media; and copying the respective features of the stampers onto the respective surfaces of the resin on the magneto-optical recording media by pressing the copying means onto the production board with a constant pressure. A method for processing the surface of a magneto-optical recording medium so as to produce a magneto-optical recording medium according to claim 1, comprising the steps: producing magneto-optical recording media on a production board for magneto-optical recording media; disposing stampers, whereon features corresponding to the features of fine physical protrusions and recessions to be formed on the surfaces of the respective magneto-optical recording media are etched, in positions on the surface of copying means corresponding to the respective magneto-optical recording media; supplying a heated thermoplastic resin to the copying means; and pressing the copying means onto the production board so that the thermoplastic resin is coated on the magneto-optical recording media while copying the features of the stampers on the resin.

Inventors: KATAYAMA HIROYUKI, MURAKAMI YOSHITERU, NAKAYAMA JUNICHIRO, OHTA KENJI, KATAYAMA, HIROYUKI, MURAKAMI, YOSHITERU, NAKAYAMA, JUNICHIRO, OHTA, KENJI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1991
Main classification: G11B13
IPC codes: B29C59, B29L17, G11B5, G11B11, G11B7