Method of manufacturing a recording medium

Abstract: The invention is to a method of manufacturing a recording medium, such as an optical information recording medium and a magnetic recording medium. By providing the surface of an optical information recording medium with a chemical adsorption film containing an alkyl fluoride through a siloxane coupling, a recording medium excelling in humidity resistance and corrosion resistance is obtained. By providing the surface of a magnetic recording medium with a chemical adsorption film containing an alkyl fluoride through siloxane coupling, a recording medium excelling in lubricity, durability, running performance and wear resistance may be obtained. Employing the vapor phase process, a plastic substrate may be used, and the formation of pin holes may be prevented.

Description: FIELD OF THE INVENTION The present invention relates to a method of manufacturing an optical information recording medium, i.e., an optical disk, video disk or a digital audio disk, of high recording density which is used in the information industries. BACKGROUND OF THE INVENTION Optical information recording media for forming a recording layer on one side of a transparent substrate using light energy, and recording and reproducing using laser beams on the substrate side have been recently developed. Not only materials for a recording layer have been developed, but also protective films for preventing the recording layer from deteriorating due to moisture or oxygen have been developed (JP-A- 59-68850). The protective layer is typically composed of a material having low moisture permeability, which may include, as inorganic matter, oxide films such as SiO 2 , MgO or Al 2 O 3 . Examples of organic matter may be polypropylene, ethylene-vinyl acetate copolymer, and polyvinylidene chloride. In an optical information recording medium, protection from moisture is explained below. First, to prevent invasion of moisture through the substrate, oxides or fluorides are formed on the surface of the substrate. These inorganic materials are generally low in moisture permeability, and if the optical information recording medium is left in a high humidity atmosphere, corrosion of the recording medium may be prevented to a certain extent. Instead of these inorganic materials, similarly, by using organic high polymers relatively low in moisture permeability, such as polyvinylidene chloride, corrosion of the recording layer may be prevented. Moreover, as an organic high polymer protective film, crosslinking type resins such as epoxy resin are proposed (JP-A-57-70694). Such protective films, however, involve the following problems. (1) Inorganic materials such as oxides and fluorides weakly adhere to the transparent substrate, and peeling or cracking may occur if left at a high temperature, high humidity condition. (2) Oxides and fluorides do not readily form dense thin films. (3) In organic high polymer materials, moisture barrier performance is limited although moisture permeability is low, and the moisture-proof effect is lost when stored for a long time under high temperature, high humidity conditions. (4) When storing for a long time under high temperature, high humidity conditions, the crosslinking type resin is porous and is high in moisture permeability, and the recording layer is likely to deteriorate due to moisture. Due to these reasons, when the optical information recording medium is stored under high temperature, high humidity conditions, the recording layer may corrode and deteriorate. JP-A-50-75001 discloses the provision of a monomolecular film composed of a saturated fatty acid or its metal salt on a thin film of a ferromagnetic metal. US-A-4992300 discloses a magnetic recording layer coated with a chemically adsorbed silane film. US-A-4429024 discloses a method of manufacturing a magnetic recording medium comprising the step of contacting the surface of a plastic film base for the magnetic recording medium in a vacuum chamber with a gas or vapor of organosilane compounds to form a plasma-polymerized layer, which is strongly adhesive to the surface of the film base. JP-A-60-223027 discloses a method of manufacturing a magnetic recording medium comprising the step of contacting the surface of a magnetic film with trimethylchlorosilane vapor to form an organic silicon compound layer. JP-A-62-159332 discloses a method of manufacturing a magnetic recording medium whereby the medium is treated with a steam of a trichlorosilane compound to form a lubricating monolayer. SUMMARY OF THE INVENTION It is the object of the invention to solve the problems of the prior art by presenting a method of preventing the formation of pin holes without injuring the substrate or recording layer by performing a chemical adsorption using a vapor phase method. The present invention provides a method of manufacturing an optical information recording medium having an optical information recording layer provided on one surface of a transparent plastic substrate, characterized in that said method comprises the steps of forming an inorganic oxide layer on the surface of said optical information recording layer, and forming a chemically adsorbed monomolecular film on the surface of said transparent plastic substrate and/or on the surface of said inorganic oxide layer by contacting a halogenated silane chemical adsorbent with the surface of said transparent plastic substrate and/or the surface of said inorganic oxide layer under vapor phase conditions in order to induce a dehydrochlorination reaction and subsequently reacting with moisture to form a chemically adsorbed monomolecular film. It is preferable in this invention that the chemical adsorbent is a compound containing a fluorocarbon group. It is further preferable that the inorganic oxide layer includes at least one compound selected from the group consisting of SiO 2 , TiO 2 and Al 2 O 3 . Moreover, it is preferable that the thickness of the inorganic oxide layer is from 1 to 500 nm. According to the manufacturing method of the invention, the chemically adsorbed film formed on the surface of the transparent substrate and/or on the surface of the oxide layer is dense, hardly forms cracks, and scarcely passes water molecules. Since a chemical bond is achieved through siloxane coupling between the chemically adsorbed film and the inorganic oxide layer or transparent substrate, it does not peel off. Hence, the recording medium obtained by the method of the invention is excellent in moisture proof quality and corrosion resistance. Moreover, since the chemically adsorbed film is formed under a vapor phase, it can be used in a substrate which is soluble in an organic solvent. According to a preferred embodiment of the invention in which the chemical adsorbent contains an alkyl fluoride group, the moisture proof quality and corrosion resistance may be further improved by making use of the water repelling property of fluorine. Since the chemically adsorbed film is a monomolecular film, a very thin, transparent, excellently protective film may be formed. In another preferred embodiment of the invention in which the inorganic oxide layer contains at least one member selected from the group consisting of S SiO 2 , TiO 2 , and Al 2 O 3 , such inorganic oxide layers also present a moisture proof quality and corrosion resistance, so that a superior moisture proof quality and corrosion resistance may be attained. In particular, in the case of a SiO 2 layer, since the density of a siloxane coupling may be enhanced, a dense chemically adsorbed film may be formed. In another preferred embodiment of the invention in which the transparent substrate is made of a resin, an easy-to-handle recording medium may be presented in the optical information recording medium. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional diagram showing an embodiment of the invention at the molecular level, just before the chemical adsorption reaction. Fig. 2 is a sectional diagram showing an embodiment of the invention at the molecular level, just after the chemical adsorption reaction. Fig. 3 is a sectional diagram showing an embodiment of the invention at the molecular level, after reacting with moisture. Fig. 4 is a diagram showing transmittance changes of light (830 nm) at 70 °C, 80% RH conditions in an embodiment of the invention and a reference example. DETAILED DESCRIPTION OF THE INVENTION The invention is intended to present a method of manufacturing an optical information recording medium. By providing the surface of an optical information recording medium with a chemically adsorbed film containing alkyl fluoride through a siloxane coupling, a recording medium excelling in humidity resistance and corrosion resistance is obtained. Employing the vapor phase process, a plastic substrate may be used, and formation of pin holes may be prevented. Referring now to the drawings, some of the embodiments of the invention are described in detail below. Figs. 1 to 3 are sectional views of an optical information recording medium. In Fig. 1 to Fig. 3, numeral 11 denotes a transparent substrate, 12 is an optical information recording layer, 13 is an inorganic oxide layer, 14 is a chlorosilane surfactant, 15 is a siloxane coupling, and 16 is a chemically adsorbed film. When the transparent substrate 11 having provided thereon the optical information recording layer 12 and the oxide layer 13 is exposed to the vapor of the chlorosilane surfactant 14 , the hydroxyl groups of the substrate surface and of the inorganic oxide layer surface and the chlorosilane surfactant react to dehydrochlorinate, and the chemically adsorbed film 16 is formed through the siloxane coupling 15. When left standing in the air, consequently, it reacts with moisture in the air to form the siloxane coupling also between adsorbed molecules. Examples of the transparent substrates 11 usable in the invention include e.g. polycarbonate and acrylic resin. As the inorganic oxide film 13, SiO 2 , TiO 2 , and Al 2 O 3 are preferred from the viewpoint of transparency. In particular, in the case of SiO 2 , same as in an ordinary glass substrate, since the hydroxyl groups are present on the surface at a high density, the chlorosilane surfactant may be bonded at a high density without pretreating with tetrachlorosilane. The inorganic oxide film 13 may be formed by, for example, a sputtering method or a vacuum deposition method. When forming the inorganic oxide film 13 on the optical information recording layer 12, the film thickness is preferably 1 to 500 nm. If the film thickness is more than 500 nm, peeling or cracking may be likely to be formed. If less than 1 nm, pin holes are likely to occur, thereby making it difficult to form the chemical adsorption film. In the optical information recording medium, as the material for composing the chemically adsorbed film 16, for example, a chlorosilane surfactant possessing an alkyl fluoride group or fluorocarbon group may be used. Examples of trichlorosilane-based surface active materials include CF 3 (CF 2 ) 7 (CH 2 ) 2 SiCl 3 , CF 3 CH 2 O (CH 2 ) 15 SiCl 3 , CF 3 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 15 SiCl 3 , CF 3 (CF 2 ) 3 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 9 SiCl 3 , CF 3 (CF 2 ) 7 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 9 SiCl 3 , CF 3 (CF 2 ) 7 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 10 SiCl 3 , CF 3 COO(CH 2 ) 15 SiCl 3 , CF 3 (CF 2 ) 5 (CH 2 ) 2 SiCl 3 , CH 3 (CH 2 ) 9 SiCl 3 , CH 3 CH 2 O(CH 2 ) 15 SiCl 3 , CH 3 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 15 SiCl 3 , CH 3 (CH 2 ) 6 Si(CH 3 ) 2 (CH 2 ) 9 SiCl 3 , CH 3 (CH 2 ) 10 Si(CH 3 ) 2 (CH 2 ) 9 SiCl 3 , CH 3 COO(CH 2 ) 15 SiCl 3 . Examples of lower-alkyl substituted monochlorosilane- or dichlorosilane-based surface active materials include CF 3 (CF 2 ) 7 (CH 2 ) 2 SiCl n (CH 3 ) 3-n , CF 3 (CF 2 ) 7 (CH 2 ) 2 SiCl n (C 2 H 5 ) 3-n , CF 3 CH 2 O(CH 2 ) 15 SiCl n (CH 3 ) 3-n , CF 3 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 15 SiCl n (CH 3 ) 3-n , CF 3 CH 2 O(CH 2 ) 15 SiCl n (C 2 H 5 ) 3-n , CF 3 (CF 2 ) 7 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 9 SiCl n (CH 3 ) 3-n , CF 3 (CF 2 ) 3 (CH 2 ) 2 Si(CH 3 ) 2 (CH 2 ) 9 SiCl n (C 2 H 5 ) 3-n , CF 3 (CF 2 ) 5 (CH 2 ) 2 SiCl n (CH 3 ) 3-n , CF 3 COO(CH 2 ) 15 SiCl n (CH 3 ) 3-n where n represents 1 or 2. Among these examples, trichlorosilane-based surface active materials are preferred in that chlorosilyl bonds other than those bonded to their hydrophilic groups form inter-molecular bonds with adjacent chlorosilane groups by siloxane bonds, thereby permitting formation of a more firmly adsorbed film. Further, CF 3 (CF 2 ) n (CH 2 ) 2 SiCl 3 where n represents an integer, most suitably 3 to 25, is preferred because of its water-repelling, anti-contaminating and other functional properties. Further, with an ethylene or acetylene group added to or incorporated in the alkyl fluoride chain portion, the chemically adsorbed film may be crosslinked after formation by irradiating it with an electron beam of about 5 Mrads, further improving the hardness of the chemically adsorbed film. It is thus possible to further improve the hardness of the chemically adsorbed film. The chlorosilane-based surface active material is not limited to those in the form of a straight chain as noted above. It is possible to use a branched fluorocarbon or hydrocarbon group or those having a substituted fluorocarbon or hydrocarbon group with a -Si- bond at one end (i.e., those represented by the formula R 2 S i C l 2 , R 3 S i C l, R 1 R 2 S i Cl 2 or R 1 R 2 R 3 SiCl where R, R 1 , R 2 and R 3 represents an fluorocarbon group or hydrocarbon group). To increase the adsorption density, however, the straight chain form is preferred. Further, by chemically adsorbing a material for forming an inner layer material having a plurality of chlorosilyl groups, e.g., SiCl 4 , SiH Cl 3 , SiH 2 Cl 2 , and Cl(S i Cl 2 O) n C l 3 (where n represents an integer in a range from 1 to 20), SiCl m (CH 3 ) 4-m , SiCl m (C 2 H 5 ) 4-m (where m represents 1, 2 or 3), and HSiCl p (CH 3 ) 3-p , HSiCl p (C 2 H 5 ) 3-p (where p represents 1 or 2), and then reacting it with water, surface chlorosilyl bonds are converted to hydrophilic silanol bonds, thus making the polymer composition hydrophilic. Among the materials containing a plurality of chlorosilyl groups, tetrachlorosilane (SiCl 4 ) is preferred in that it is highly reactive and low in molecular weight. It can, therefore, provide silanol bonds at a high density. In this way, it is possible to provide a highly hydrophilic composition compared to oxidation treatment of a polymer-containing substrate. To this surface, a chlorosilane-based surface active material containing fluorocarbon groups may be chemically adsorbed. In this way, a chemically adsorbed film suitably having an increased density can be obtained. When the hydrophilic group density is increased in this way, the hydroxyl group density may be higher than in an oxidation treatment of transparent substrate. Thereon, for example, a chlorosilane surfactant containing an alkyl fluoride group may be further chemically adsorbed. The chemically adsorbed film obtained in this manner is higher in density, and the moisture proof quality, corrosion resistance, durability and wear resistance may be further enhanced. As a means of oxidizing the surface of the transparent substrate, ordinary methods may be applied. For example, oxygen plasma processing and the corona process may be used. As the chemically adsorbed film formed on the recording medium surface, a sufficient function is exhibited using only one layer of the monomolecular chemically adsorbed film. The chemically adsorbed film may be also formed by accumulation of monomolecular films. When the chemically adsorbed film forms cumulative films, groups presenting given functions are oriented, and density is enhanced, so that higher functions may be exhibited. Hereinafter, using CF 3 (CF 2 ) n CH 2 CH 2 S iCl 3 , as an example of the chemical adsorbent, the reaction process used in the invention is described. In a container or tank, a transparent substrate having provided thereon a recording layer and an oxide layer possessing hydroxyl groups (-OH) on its surface is placed. Its surface is brought into contact with the chemical adsorbent gas under a vapor phase, then the reaction occurs as shown in formula [1]. Exhausting the gas of the chemical adsorbent, when gas containing moisture (or atmosphere) is introduced, the reaction occurs as shown in formula [2]. When the transparent substrate is exposed to air or left standing, the reaction of formula [3] occurs, and a chemically adsorbed monomolecular film is formed. The invention is described in further details below by referring to some of the practical embodiments thereof. Example 1 On one side of a polycarbonate substrate 11 of 1.2 mm in thickness and 120 mm in diameter, an optical information recording layer 12 mainly composed of Te, TeO 2 was formed by vacuum deposition. A SiO 2 film having a thickness of 10 nm was formed further thereon as an inorganic oxide film 13 by the sputtering method. Using the prepared disk, the surface was oxidized in a UV dry stripper (UV-1, manufactured by Samco International) by treating with oxygen plasma for 10 minutes at an oxygen flow rate of 1 liter/min, and was exposed for 120 minutes to heptadecafluorodecyl trichlorosilane vapor as a chlorosilane surfactant containing alkyl fluoride group in a desiccator. A chemically adsorbed monomolecular film 16 was formed on the surface of the SiO 2 layer 13 and the surface of the polycarbonate substrate 11 through a siloxane coupling 15 containing an alkyl fluoride group. In succession, by letting stand for 60 minutes in the air, a siloxane coupling 15 was formed also among adsorbed molecules. Example 2 A coated substrate was formed as in Example 1, except that the inorganic oxide layer was changed from SiO 2 to T i O 2 . Example 3 A coated substrate was formed as in Example 1, except that the inorganic oxide layer was changed from S i O 2 to Al 2 O 3 . Example 4 A coated substrate was formed as in Example 1, except that the oxygen plasma processing was first followed by exposure tetrachlorosilane vapor for 60 minutes, then left standing in the air for 60 minutes. Example 5 A coated substrate was formed as in Example 1, except that heptadecafluorodecyl trichlorosilane was replaced by 9-(heptadecafluorodecyl dimethylsilylnonyltoilyl chlorosilane. Comparative example 1 A sample was prepared according to Example 1, without forming a chemically adsorbed film. These samples were left standing at 70°C, at 80% RH. The transmittance changes of light (832 nm) were measured. The results are shown in Fig. 4. In Fig. 4, curve F shows the time-course changes of transmittance of Examples 1 to 5, and curve G those of Comparative example 1. As is clear from Fig. 4, in all recording media prepared according to the invention, the transmittance was hardly changed after 1,000 hours, and the recording films were found to be stable without corroding or deteriorating in the high temperature, high humidity conditions. By contrast, in the comparison sample, in 10 to 100 hours, the recording film corroded and deteriorated due to peeling of protective film, cracking, or the like, and transmittance was notably lowered. In the embodiments, meanwhile, as the optical information recording layer, the recording film of Te, TeO 2 compound is explained, but it is not limiting, and the same effects are expected by using other optical information recording films such as Tb-Fe-Co and Al compound films. According to the invention, by forming the inorganic oxide layer on the optical information recording layer formed on one side of the transparent substrate, and disposing the chemically adsorbed film possessing the siloxane coupling on the surface of the inorganic oxide layer on both surfaces of the inorganic oxide layer and transparent substrate by the vapor phase method, a moisture proof quality and corrosion resistance may be enhanced without deteriorating the substrate, of which practical effects are outstanding. As described herein, according to the embodiments of the invention, the chemically adsorbed film formed on the outer surface is dense. Cracks are hardly formed, and water molecules can scarcely pass through. Moreover, since the chemically adsorbed film and the inorganic oxide film or transparent substrate are chemically bonded through a siloxane coupling, peeling hardly occurs, and a moisture proof quality, corrosion resistance, and durability are excellent. Since the chemically adsorbed film is formed in the vapor phase without using an organic solvent, a substrate soluble in an organic solvent can be used. Moreover, since the chemically adsorbed film is formed in the vapor phase, entry of contamination into the obtained ultrathin film may be prevented. In the recording medium produced according to the invention, since the chemically adsorbed film is bonded by covalent bonds on the surface, the durability and wear resistance are excellent, and these characteristics may be maintained for a long period. In addition, the water- and moisture-proof properties are further improved by forming a metal oxide layer on the optical recording layer which is provided on one surface of a transparent substrate. A chemically adsorbed film containing siloxane bonds is provided on the metal oxide layer surface or on the surfaces of both the metal oxide layer and the transparent substrate, thus providing great usefulness in practice. As has been shown, the invention is greatly beneficial to industry.

Claims: A method of manufacturing an optical information recording medium having an optical information recording layer provided on one surface of a transparent plastic substrate, characterized in that said method comprises the steps of forming an inorganic oxide layer on the surface of said optical information recording layer, and forming a chemically adsorbed monomolecular film on the surface of said transparent plastic substrate and/or on the surface of said inorganic oxide layer by contacting a halogenated silane chemical adsorbent with the surface of said transparent plastic substrate and/or the surface of said inorganic oxide layer under vapor phase conditions in order to induce a dehydrochlorination reaction and subsequently reacting with moisture to form a chemically adsorbed monomolecular film. The method of claim 1, wherein the chemical adsorbent is a compound containing a fluorocarbon group. The method of claim 1, wherein the inorganic oxide layer includes at least one compound selected from the group consisting of SiO 2 , TiO 2 and Al 2 O 3 . The method of claim 1, wherein the thickness of the inorganic oxide layer is from 1 to 500 nm.

Inventors: OGAWA KAZUFUMI, SOGA MAMORU, OGAWA, KAZUFUMI, SOGA, MAMORU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G11B7
IPC codes: G11B5, G11B7