FR2542900A1 - Glass disc for manufacturing information recording media - Google Patents

Abstract

The invention relates to a disc 7 drilled at its centre and serving as support for an information recording layer 12, its method of manufacture and the use of such discs in the manufacture of information recording media. The support disc 7 comprises chemically tempered glass and has an average thickness of between 0.8 and 2.2 mm. Its thickness at any point does not vary by more than 0.05 mm from its average value. The disc according to the invention is of particular interest in the production of recording media used as originals ("masters") from which dies are prepared for manufacturing copies.

Description

 The present invention relates to a disc pierced in the center, serving as a support for an information recording layer, its manufacturing process and the use of such discs in the manufacture of information recording media.

Recording media comprising a recording layer on a dimensionally stable support disc, pierced in its center for positioning the disc in the recording apparatus, are well known. In the sound recording and other data industries, the recordings made on such recording media are used as originals ("masters") from which matrices are prepared for the manufacture of multiple copies of recordings. Discs with magnetic recording layers are also widely used for recording data in the computer industry
Traditional recording media use an aluminum disc as a medium. When using aluminum discs, difficulties arise in making recording media # s having the quality and general specifications sometimes required by the users. Other support materials have been proposed, but for some technical reason, they have not been found to be satisfactory.

 The present invention provides a support disc with improved properties.

 The present invention provides a disc pierced at its center, serving as a support for an information recording layer, characterized in that this support comprises chemically toughened glass and has an average thickness of between 0.8 and 2.2 mm. and in that the thickness at all points does not vary by more than 0.05 mm from its average value.

 The invention offers a number of advantages.

A chemically toughened glass disc, in addition to having the required dimensional stability, has good vibration damping properties. For example, when forming an engraved or pressed recording track in a sound recording layer, it Track distortions may result from vibration echo during pen writing. If the support of the recording layer is a disc according to the invention, such an echo is avoided or reduced and a particularly high recording fidelity can be obtained. In addition, glass discs have good receptivity to different compositions coating which can be used in the manufacture of a recording medium. This improved receptivity facilitates the formation of coatings lacking or almost free from defects, which favorably influences the standards of recording quality which can be obtained. In addition, a recording layer which is of high quality # as well as from the point of view of its geometry than the absence of defects in composition and structure, can accept a higher density of impressions # of recording, for example helical tracks with closer turns2 than a layer of lower quality On found that chemical toughening of glass does not deteriorate these properties and has no detrimental effect on the flatness of glass, as could be the case with thermal toughening. It has in fact been found that the chemical toughening of glass can improve its receptivity towards certain recording media.

 The foregoing advantages are combined with the additional advantages of strength, low weight and flexibility. The main use of recording media is in the sound recording industry where they are used to make originals ("masters") as described above. Recording media for this market must be produced and distributed to recording studios in large quantities. The choice for the glass of a chemical toughening treatment makes it possible to obtain an adequate resistance to rupture and deterioration, despite the thinness of the support. In fact, the support can be as thin as traditional aluminum supports (about 1 mm). It will also be noted that the glass support offered by the present invention has a thickness which is compatible with its use in devices designed for origin to handle such traditional aluminum supports.

Because the chemically toughened glass disc is very thin, it is flexible. This flexibility is particularly advantageous when a prerecorded disc comprising the support disc
Glass is used as an original ("master") in the production of a recording matrix, and in particular during the processing of the original during the manufacturing of the matrix.

 In the manufacture of recording media, the quality of the surface of the media on which the recording layer is formed has a significant influence on the quality of the recording layer itself. It has been found that in mass production of media discs for recording media, a high surface quality can be obtained more easily and more regularly when making chemically toughened glass discs than when making discs. 'aluminum. It is obviously necessary to carry out appropriate quality control measures to ensure that the glass pieces meet the required quality standards.

One of the essential factors regarding the quality of the surface of the support
is its flatness. The surface should be as close as possible to a real plane. In general, for glass sheets of thickness between 0.8 and 2.2 mm, it has been found easier to manufacture glass of high flatness when the glass has a thickness closer to the upper limit of this range. The fact that the thickness at all points of the tempered glass disc does not vary by more than 0. OS mm from its average value contributes in large part to obtaining this good flatness.

 Preferably, the glass used in the manufacture of a disc according to the invention is drawn glass. That is to say glass cut from a glass ribbon which has been drawn from a mass of molten glass and passed over a folding roller before entering a horizontal gallery of sound annealing, as in a process Colburn traditional manufacturing of sheet glass. Such drawn glass can have a very high surface flatness, particularly on the face which has not been in contact with the folding roller. At least this face of the glass is therefore particularly suitable for carrying a recording layer.

Another important factor for the surface quality for the purposes of the invention consists in the presence of local defects in the glass. Experiments have shown that this surface quality is especially susceptible to deterioration by local defects of a particular type, called "puncture holes". Therefore, it is particular
rely advantageous to include the inspection of these defects as a step of quality control in the selection of glass pieces intended to form support discs according to the invention.

 It is not essential that the glass disc is completely free of puncture holes. The presence of puncture holes is not incompatible with the production of high quality recording media provided that their number and their individual and collective dimensions are within certain limits.

 Based on this discovery, a test was devised to determine the suitability of pieces of glass for use in the manufacture of high quality discs.

 This test will now be described with reference to Figure 1 of the accompanying drawings.

 Representative glass surfaces measuring 25 x 25 cm chosen at random from a sheet (or ribbon) are subjected to the test in order to determine the suitability of this sheet or ribbon to be cut into high quality discs. Each representative surface such as 1 is tested while it is supported in front of a white screen 2 in a plane parallel to this screen. The interval between the glass sheet and the screen, measured perpendicular to them, is 17.8 cm. A light beam 3 whose axis 4 is inclined at 450 relative to the planes of the glass sheet and of the screen, is projected through the glass sheet onto the screen from a slide projector 5. The light is emitted by a 150 W lamp placed behind an aperture 6 for emitting the light beam and an image of this aperture, which is 5 mm in diameter, is focused on the screen by an objective f 2. 8/100 mm. The distance between the opening 6 and the glass sheet 1, measured along the axis 4 of the light beam, is approximately 1.8 m. Each puncture hole in the glass sheet appears on screen 2 in the form of a shadow spot. Each of these tasks is assigned a certain number of points (which can be considered as penalty points) depending on its diameter.

Penalty points are assigned according to the following scale
Diameter of the task (mm) Number of stitches 0, 75 or less 1 more than 0.75 but not more 2 of 1.25 more than 1.25 3
The sheet is considered to pass the test and therefore to be very suitable for use in the manufacture of carrier discs for high quality recording media, if none of the randomly selected tested surfaces is assigned a total number penalty points greater than 5.

 The glass must be chemically toughened when it is in the required form of a disc, that is to say after the disc has been cut from a piece of unhardened glass, and after having carried out all the required operations for running in the edges. Preferably, the edges of the central opening, as well as the periphery of the disc, are lapped to remove sharp edges and surface cracks.

 Advantageously, the glass is chemically toughened by exposure of the glass, at high temperature, to a chemical toughening medium releasing potassium ions to cause the substitution, by these ions, of sodium ions in the surface layers of the glass, at a lower temperature. at the lower annealing temperature of the glass. Particulars on the conditions suitable for chemical quenching are given, for example, in British patent application no. 1,274,733.

 In certain embodiments of the invention, the central opening in the glass disc receives a body of another material which delimits a smaller hole intended for positioning the disc. This body can be a prefabricated component, for example a metallic component, which has been adapted in the opening of the glass support. Alternatively, the said body may be a body which has been hardened or allowed to harden in situ, for example a UV polymerizable resin. In the latter case, after its hardening, the body may wander, suitably drilled to form a positioning hole of the required diameter, The above-mentioned methods facilitate the establishment of a central positioning hole which closely conforms to a dimension determined especially when this dimension is small (for example , 7.8 mm as is commonly used in sound recording originals). In addition, such methods provide protection of the glass at the central hole.

 The invention comprises a method of manufacturing a disc pierced at its center serving as a support for an information recording layer, characterized in that a disc is cut from a sheet of unhardened glass having an average thickness comprised between 0.8 and 2.2 mm, in that a hole is cut in the glass to form the said central opening of the disc, and in that, after the said cutting operations, the glass is chemically toughened. Preferably, the glass is lurked around the periphery of the disc and said opening to remove the sharp edges before the chemical tempering of the glass.

 Preferably, the non-tempered glass sheet is a sheet which satisfies the pitting hole detection test described above.

 The invention includes such a method in which said opening is cut to a dimension larger than the required positioning hole in the finished disc and said hole is formed in a material or component introduced or fixed in the opening made in glass, after the chemical tempering step.

 In certain processes according to the invention, the opening cut out of the glass is closed by filling it with a composition which is made or which is then left to harden in situ, and a hole of the final diameter required is drilled in hardened material. The use of a malleable filling composition which is converted in situ to a substantially rigid form facilitates a solid connection of the central part with the glass disc. The material of the central part can for example be applied so that it fills the opening in the glass disc and extends over portions of the faces of the disc surrounding this opening.

 The invention also includes a recording medium comprising a support disc according to the invention, as described above, carrying an information recording layer on at least one of its faces. The recording layer can be and is preferably formed directly on the glass support. However, a bonding sub-layer can be present if necessary.

 For the sound recording layers, particular use should be made of different resins or other polymeric substances known per se as suitable for printing or etching a sound recording track. Some of these most common compositions favorable can form particularly high quality recording layers because they can easily uniformly wet the chemically toughened glass support.

 The invention also includes an information recording, for example a sound recording, which is in the form of a track modulated in the image of the information in the recording layer of a recording medium such as described above.

 Such a recording can be used to fabricate a matrix according to methods which are known per se. These methods include coating the modulated surface in the image of the information by means of a metallic film, for example # by means of a silver film formed by vacuum evaporation, and the electrolytic coating of this. film, for example with nickel. The electrolytic deposit is then removed along with the underlying metal film as a unitary component which constitutes the matrix used in the molding of copies of the recording.

 In order for the matrix formed by the electrolytic deposit and the metallic film to be used for the production of copies of the recording, such a matrix must be frankly separated from the glass support and from its adherent surface layer modulated in the image of information. This separation is facilitated by the inherent flexibility of the thin, chemically toughened glass used according to the invention.

 In certain circumstances, it is desirable to separate the modulated surface coating from the glass support, as a coherent film. It is therefore desirable that the adhesion between the coating and the glass is well controlled. Such adhesion must be strong enough to maintain the integrity of the product during storage, transport, recording and plating, but not too strong to allow separation between the glass and the recorded layer.

In order to carry out such a control, it is preferred that the disc comprises at least one exposed face of chemically toughened glass which comprises organosilane groups intended to join a layer of resin to this face. Organosilane groups will be attached to the surface of the glass if the glass is contacted with an organosilane solution, as preferred. The choice of silane will naturally depend on the material of which the recording layer is made.
In the sound recording industry, such recording layers are typically made of nitro cellulose resins, although polyamide resins can also be used. Among the silanes which can be used with sound layers in nitrocellulose resin, are found
gamma -Aminopropyltriethoxys ilane
N, N-bis - (beta-Hydroxyethyl) -gamma-
aminopropyltriethoxysilane
N-beta-aminoethyl- gamma-amino
propyltrimethoxysilane
vinyltrichlorosilane
Ilane Vinyltriethoxys
Vinyl-tris - (beta- methoxyethoxy) s ilane
the vinyltr imethoxys ilane
Vinyltriacethoxysilane
gamma - Methacryloxyp ropyltrimethoxys ilane
beta (3, 4 -Epoxy- cyclohexyl) - ethyltr imethoxys ilane
gamma - Glycidoxypropyl-trimethoxys ilane
the gamma- rcaptopropyl- tr imethoxys ilane
gamma- chlo rop r opyl- tr imethoxys ilane.

 The use of one of the first three silanes mentioned is preferred. The glass can be treated using a solution of such a silane comprising water and / or alcohol as solvent.

 As a variant of its use in the manufacture of an original ("master"), modulated in the form of a track, which can be used to manufacture a pressing matrix of copies of the recorded information, a disc pierced at its center according to the invention can serve as a support for a magnetic recording layer, for example intended for an information storage device for a computer. A drilled disc in chemically tempered glass having a thickness between 0.8 and 2.2 mm has a low mass and therefore an angular moment and a moment of inertia, around a central axis perpendicular to the plane of the disc, relatively low. This provides advantages from the point of view of the usual conditions of use, particularly the high operating speeds, of computer memory disks.

 In certain particularly preferred embodiments of the invention, said support is a laminated assembly.

Such a laminated assembly may for example be made up of two sheets of chemically toughened glass joined to one another by an intermediate adhesive layer, or by a single sheet of chemically toughened glass to which an adhesive layer is applied. The adhesive layer can in both cases be applied in the form of a film or in the form of a fluid composition which is made or left to harden in situ. It will be noted that if the laminated assembly consists of two sheets, of equal thickness, of chemically toughened glass, each of these sheets must have a thickness of less than 1.1 mm by an amount necessary to take account of the thickness of the intermediate adhesive layer, so that the total thickness of the assembly does not exceed Z, 2 mm. Such a laminated assembly can be manufactured by a process known per se in the glass lamination technique using an adhesive such as polyvinyl butyral, polyurethane, polyvinyl chloride, or any other known adhesive. If a laminated support breaks, although the chemically toughened glass will shatter, the fragments obtained will be retained by the adhesive layer.

 Laminated media are therefore particularly advantageous for data storage disks working at high speeds.

Preferably, the or each sheet of chemically toughened glass has an average thickness of at least 0.5 mm.

The invention comprises a method of manufacturing a disc pierced at its center serving as a support for an information recording layer, characterized in that at least one disc is cut from unhardened glass having an average thickness d '' at least 0.5 mm, in that a hole is cut in the or each disc to form said central opening, and in that the glass is chemically toughened and conforms to a laminated assembly having an average thickness between 0.8 8 and 2.2 mm,
Some examples of the invention will now be described with reference to Figures 2 to 5 of the accompanying drawings in which
Figure 2 is a sectional view of a medium for an information recording layer;
Figure 3 is a similar view showing the carrier and materials applied to that carrier in a later stage of manufacturing a recording medium.

FIG. 4 represents a recording original ("master") carrying a coating, constituted at the start of the complete recording medium, assembled to a chassis for the purpose of forming a matrix by electrolytic coating; and
Figure 5 is a sectional view of a second embodiment of a medium carrying an information recording layer.

 #Disc 7 is a non-tempered glass disc which has been cut to a diameter of 36.6 cm from soda-lime glass of ordinary composition, stretched horizontally. The glass is very thin and between 0.8 and 2.2 mm. In a specific example, it has a thickness of 1.3 + 0.02 mm. A hole 8 was drilled in the center of the disc by means of a diamond drill bit and the edges of the hole were pruned using a tool with rounded abrasive surface, as suggested by the broken lines 9 in the figure. eliminates all surface imperfections or cracks in a region of the device which can be subjected to relatively concentrated stresses when the disc is possibly fixed in a support template for the production of a matrix by electrolytic coating.

 The periphery 10 of the glass disc has also been crimped to give the rounded profile illustrated.

 After these steps, the glass disc is chemically toughened. To this end, the glass is immersed in a bath of KN03 melted at 4650C for a period of eight hours, the bath being exposed to an atmosphere enriched in CO2.

 After the tempering step, a masking element 11 (FIG. 3) is removably secured to a central zone of one of the faces of the glass disc. A material is applied to this face of the disc to form the recording layer 12. The composition of the recording layer can be of any traditional type used in the art. Types of compositions based on ni-trocellulose or polyamide are particularly suitable because in particular of their very good wetting properties with respect to glass. As a result, they can easily form very uniform recording layers. They are also suitable because they are easy to engrave with a stylus for recording sound. As an alternative to this application of a coating to form the recording layer 12, this layer can be applied in the form of a preformed film which is secured to the toughened glass support 7. In order to control the adhesion of the recording layer 12 to its support?, the glass can be treated with a solution of a silane composition, for example gamma - With minopropyltriethoxys ilane, N, N -bis - (beta-Hydroxyethyl) - gamma-aminopropyltriethoxys ilane (at 62% in methanol), or N - beta-aminoethyl- gamma-aminop ropyltrime - thoxysilane, immediately before applying the coat.

 After applying the composition for the recording layer, the masking element 11 is removed together with any recording layer composition covering it.

 A quantity of UV-curable resin is then applied to the central zone of the disc in order to secure a centering piece 13 in the hole 12. This resin is then irradiated by UV radiation so as to polymerize it in situ. A hole of 7.8 8 mm in diameter is then drilled through the centering piece which thus forms the hub of the finished recording medium as shown in FIG. 4.

 After forming a sound track in the recording layer 12, the recording medium can be used as an original ("master") to form a matrix. To this end, the recording layer carrying the sound track is first coated with a silver film 14, formed by vacuum evaporation. The original is then mounted in a template 15 comprising a cup 16 provided with a threaded central boss 17 which is arranged below the hub 13 of the original.

The original is held firmly against this boss by means of a bolt 18 screwed into the boss. A washer 19 is placed between the bolt and the original in order to distribute the tightening pressure. Inside the jar of the template, an upright circular crown 20 supports the peripheral marginal zone of the original. The height of this crown is such that when the bolt 18 is lightly pressed against the original, the latter is therefore under stress and it is therefore supported firmly. The resulting assembly is then ready to be immersed in an electrolytic coating bath.

 In a variant of the method, the centering piece 13 is formed in situ by means of UV-polymerizable resin. In another variant of the method, the hole 8 in the support disc 7 is filled with the material of the recording layer 12 which is made or allowed to harden and which is then drilled to form a hole of dimension wanted.

 FIG. 5 illustrates an alternative embodiment of an information recording disc comprising a magnetic recording layer 21 of known composition.

This layer is deposited on a support 22 consisting of two sheets 23, 24 of toughened glass chemically secured to one another by means of an intermediate adhesive layer 25. The thickness of the support 22 is between 0.8 and 1.2 mm. In a specific practical embodiment, each glass sheet has a thickness of 0.6 mm.

The intermediate adhesive layer is made of polyvinyl butyral and has a thickness of 0.38 mm. The support 22 has a hub 26 intended for mounting on a chassis. Such a disk can be used for example as a component of a computer memory.

 In order to manufacture the support 22, glass sheets are cut to size, drilled, and their edges are lapped for example as described with reference to FIG. 2.

The discs 23, 24 obtained are then chemically quenched. The discs are then assembled in register, with the help of the hub 26, on the opposite faces of a film of adhesive material 25 and subjected to joining conditions. A magnetic recording layer such as 21 is then applied to one or each face of the support.

 It will obviously be noted that such a recording layer could also be applied to a monolithic support as shown in FIG. 2. It will also be noted that the magnetic recording layer of FIG. 5 can be replaced by a layer intended for the 'information recording by modulating its surface either in digital or in analog mode. This can be done, for example, for the subsequent manufacture of a die as described with reference to Figure 4 in order to form a mold for pressing copies of the original recording.

 In preferred embodiments of the invention, the support has a thickness of not more than 2.0 mm and advantageously not more than 1.7 mm.

 Such a support may be in the form of a disc which is cut from glass the thickness of which does not exceed 2.0 mm, and preferably does not exceed 1.7 mm, or by forming a laminated assembly of such thickness.

 It has been found that this gives considerable advantages as regards the flexibility of the support and its lightness, which entralne a low angular moment and a weak moment of inertia around a central axis normal to the disc.

Claims (19)

 1. Disc pierced in its center, serving as a support for an information recording layer (12, 21), characterized in that this support (7, 22) comprises chemically toughened glass and has an average thickness of between 0 , 8 and 2.2 mm and in that the thickness at all points does not vary by more than 0, OS mm from its mean value.  2. Disc according to claim 1, characterized in that the glass is drawn glass.  3. Disc according to one of claims 1 or 2, characterized in that the glass has been chemically toughened by exposure of the glass, at elevated temperature, to a chemical toughening medium releasing potassium ions to cause substitution, by these ions, sodium ions in the surface layers of glass.  4. Disc according to one of claims 1 to 3, characterized in that the central opening (8) in the glass disc receives a body (13, 26) of another material which delimits a smaller hole intended for the disk positioning.  5. Disc according to claim 4, characterized in that the said body is a body which has been made or which has been allowed to harden in situ.  6. Disc according to one of claims 1 to 5, characterized in that said support is a laminated assembly (22).  7. Disc according to one of claims 1 to 6, characterized in that it comprises at least one exposed face of chemically toughened glass which comprises organosilane groups intended to secure a layer of resin (12, 21) to this face.  8. Disc according to one of claims 1 to 7, characterized in that the support has a thickness not exceeding 2.0 mm and, preferably, not exceeding 1.7 mm.  9. A method of manufacturing a disc pierced at its center serving as a support for an information recording layer, characterized in that a disc is cut from a sheet of unhardened glass having an average thickness of between 0, 8 and 2.2 mm, in that a hole is cut in the glass to form the said central opening of the disc, and in that, after the said cutting operations, the glass is chemically toughened.  10. Method according to claim 9, characterized in that said disc is cut from glass whose thickness does not exceed 2.0 mm, and preferably does not exceed 1.7 mm.  11. A method of manufacturing a disc pierced at its center serving as a support for a recording recording layer, characterized in that at least one disc is cut from unhardened glass having an average thickness of at least 0 , 5mm, in that a hole is cut in the or each disc to form said central opening, and in that the glass is chemically toughened and conforms to a laminated assembly having an average thickness between 0 , 8 and Z, 2 mm.  12. Method according to claim 11, characterized in that the laminated assembly is shaped so that its thickness does not exceed 2.0 mm, and preferably 1.7 7 mm.  13. Method according to one of claims 9 to 12, characterized in that the glass is lapped around the periphery of the disc and said opening to remove the sharp edges before the chemical tempering of the glass.  14. Method according to one of claims 9 to 13, characterized in that said opening is cut to a larger dimension than the required positioning hole in the finished disc and in that said hole is formed in a material or a component introduced or fixed in the opening made in the glass, after the chemical toughening step.  15. The method of claim 14, characterized in that the opening cut in the glass is closed by filling it with a composition which is made or which is then allowed to harden in situ, and in that a hole of the required final diameter is drilled in the hardened material.  16. Method according to one of claims 9 to 15, characterized in that a piece of non-tempered glass is chosen from the stock having undergone the stitching detection test, defined in the present description, as a piece in which the glass disc is cut.  17. Method according to one of claims 9 to 16, characterized in that the glass is brought into contact with a solution of an organosilane.  18. Recording medium comprising a support disc according to one of claims 1 to 8, carrying an information recording layer on at least one of its faces.  19. Recording of information which is in the form of a track modulated in the image of the information in the recording layer of a recording medium according to claim 18.