Information recording media

Abstract: In accordance with the present invention, there are provided information recording media having a substrate (2) and thereon a recording layer (3), and a metallic layer (4) composed of an aluminum alloy containing at least hafnium. The information recording media provided are excellent in corrosion resistance and also small in dependence of the recording power on linear velocity.

Description: FIELD OF THE INVENTION This invention relates to information recording media having a metallic layer and more particularly to information recording media excellent in corrosion resistance or stability, and small in dependence of their recording power on linear velocity. BACKGROUND OF THE INVENTION In information recording media such as magnetooptical recording discs comprising a substrate and thereon a recording layer and a metallic layer and capable of rewriting information, it is to be desired that the dependence of the recording power on linear velocity is made small so that the recording power for recording information in said media does not largely vary with the inner peripheral and outer peripheral portions of the medium. Usually, in the information recording medium such as the magnetooptical recording disc, a metallic layer is formed, in addition to a magnetooptical recording layer, on a substrate. The metallic layers which have been used so far in the information recording media of the type such as magnetooptical recording discs are composed of nickel alloys, aluminum metal or aluminum alloys containing 0.1-10% by weight of titanium. However, the metallic layers composed of aluminum metal or aluminum-titanium alloys had such a disadvantage that they are poor in corrosion resistance and cannot withstand a long term-service. The metallic layers composed of nickel alloys had also such a serious disadvantage that the recording power required at the time of writing information in the information recording medium largely varies with the inner peripheral and outer peripheral portions of said medium, and thus the dependence of the recording power on linear velocity is still large. Japanese Application JP-A-62067750 reveals a photomagnetic disk comprising a recording layer and a protecting layer. The protecting layer comprises metal nitrides, and a chromium aluminium alloy is indicated to be usable. European patent application EP-A-0064777 discloses an optical information recording medium comprising a layer of metal alloy. This layer is selected from a group of alloys comprising Ag-Cu, Cu-Cr, Al-Cr, Al-CU, Al-B, Al-Mn and Al-lanthanide. The compositions are chosen in such a way as to ensure high light reflection. European patent application EP-A-226168 describes an optical information recording medium comprising a transparent substrate, an optical information recording layer and a reflecting metal layer formed from an aluminium titanium alloy. Japanese patent application JP-A-62172545 discloses a photomagnetic recording medium. A recording layer is situated on a transparent substrate and a protective layer is formed thereon. The protective layer may constitute aluminium, chromium, hafnium, niobium and titanium, as well as several other metals. With the view of developing information recording media which are excellent in corrosion resistance or long-term stability and which are small in linear dependence of the recording power on linear velocity, the present inventors prosecuted extensive researches to find that the information recording media having a metallic layer composed of an aluminum alloy containing at least hafnium are excellent in corrosion resistance and small in dependence of the recording power on linear velocity. Thus, the present invention has been accomplished. OBJECT OF THE INVENTION The present invention is intended to solve such problems associated with the prior art as mentioned above, and an object of the invention is to provide information recording media which are excellent in corrosion resistance and small in dependence of the recording power on linear velocity. SUMMARY OF THE INVENTION The first information recording medium of the present invention which has a recording layer and a metallic layer on a substrate is characterized in that the metallic layer is composed of an aluminum alloy containing at least one element selected from among hafnium (Hf) and niobium (Nb) in an amount of 0.1-10 atom% based on all atoms constituting the aluminum alloy. The second information recording medium of the invention which has a recording layer and a metallic layer on a substrate is characterized in that the metallic layer is composed of an aluminum alloy containing 0.1-9.5 atom% of hafnium and 0.1-5 atom% of chromium based on all atoms constituting the aluminum alloy layer, the combined content of said hafnium and chromium being less than 10 atom%. The third information recording medium of the invention which has a recording layer and a metallic layer on substrate is characterized in that the metallic layer is composed of an aluminum alloy containing 0.5-5 atom% of hafnium and 0.5-5 atom% of titanium based on all atoms constituting the aluminum alloy layer, the combined content of said hafnium and titanium being 1-5.5 atom%. The fourth information recording medium of the invention which has a recording layer and a metallic layer on a substrate is characterized in that the metallic layer is composed of an aluminum alloy containing 0.1-10 atom% of hafnium and 0.1-10 atom% of magnesium based on all atoms constituting the aluminum alloy layer, the combined content of said hafnium and magnesium being less than 15 atom%. The information recording medium of the present invention as illustrated above, which individually have a metallic layer composed of an aluminum alloy containing at least hafnium are excellent in corrosion resistance, small in the dependence of the recording power on linear velocity and excellent in performance of protecting the recording layer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a rough sketch of one embodiment of the information recording medium in cross section of the present invention. Fig. 2 is a rough sketch of another embodiment of the information recording medium in cross section of the present invention. 1 ...Information recording medium 2 ... Substrate 3 ... Recording layer 4 ... Metallic layer 5 ... Protective film DETAILED DESCRIPTION OF THE INVENTION The information recording media of the present invention are illustrated below in detail. Fig. 1 is a rough sketch of the information recording medium in cross section of one embodiment of the invention, and Fig. 2 is also a rough sketch of the information recording medium in cross section of another embodiment of the invention. In the information recording media of the invention, the information stored in said recording media is read out by means of light such as laser beam. Information recording media of this type include, in concrete, postscript type optical disc capable of additional recording but incapable of erasing information recorded, rewriting type optical discs such as magnetooptical recording discs and phase change discs, capable of recording information as well as of erasing and reproducing the information recorded. As can be seen from Fig. 1, for example, in an information recording medium 1 of the invention, a recording layer 3 and a metallic layer 4 are formed on a substrate 2 in that order. Materials for the above-mentioned substrate 2 used in the invention are not particularly limited to specific ones. However, when laser beam is incident upon the substrate 2 (from the direction of an arrow A), the materials used therefor are preferably those which are transparent. Besides inorganic materials such as glass, aluminum and the like, such transparent materials include, for example, organic materials such as poly(methyl methacrylate), polycarbonate, polymer alloys of polycarbonate with polystyrene, such cycloolefin random copolymers as disclosed in U.S. Patent No. 4,614,778, such cycloolefin random copolymers (A) as mentioned below, poly-4-methyl-1-pentene, epoxy resins, polyether sulfone, polysulfone, polyether imide and the like. Of these organic materials, preferred are poly(methyl methacrylate), polycarbonate, such cycloolefin random copolymers as disclosed in U.S. Patent No. 4,614,778 and the cycloolefin random copolymers (A) as mentioned below. From the standpoint of good adhesion particularly to the recording layer and a small double refractive index, particularly desirable materials for the substrate used in the present invention are cycloolefin random copolymers (A) of ethylene and a cycloolefin represented by the following general formula [I], [I-a] or [I-b]. wherein n is 0 or a positive integer, R 1 to R 12 are the same or different, and each reperesents a hydrogen atom, a halogen atom or a hydrocarbon group and R 9 to R 12 , when taken together, may form a mono- or poly-cyclic hydrocarbon ring which may optionally have double bond or bonds, or R 3 and R 10 or R 11 and R 12 , when taken together, may form an alkylidene group. Further explanation of the cycloolefin represented by the general formula [I] will be given below. The cycloolefin represented by the general formula [I] may also be represented by the following general formula [I-a]. General formula In the general formula [I-a], n is 0 or 1, m is 0 or positive integer, R 1 to R 18 represent each a atom or a group selected from the group of a hydrogen atom, a halogen atom and a hydrocarbon group. R 15 to R 18 , when taken together, may form a mono- or poly-cyclic hydrocarbon ring which may optionally have double bond or bonds. Further more, R 15 and R 16 , or R 17 and R 18 , when taken together, may form an alkylidene group. wherein p is an integer of at least 0, q and r are each 0,1 or 2,R 1 to R 15 represent each an atom or a group selected from the group of a hydrogen atom, a halogen atom, an aliphatic hydrocarbon group, an aromatic hydrocarbon group and an alkoxy group, and R 5 (or R 6 ) and R 8 (or R 7 ) may be bonded together directly without an intermediate group or through an alkylene group of one to three carbon atoms. The concrete example of the cycloolefins represented by the general formula [I] includes 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, such octahydronaphthalenes as 2-methyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-ethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-propyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-hexyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2,3-dimethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-methyl-3-ethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-chloro-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-bromo-1,4,5,8-dimethano1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-fluoro-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2,3-dichloro-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-cyclohexyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-n-butyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2-isobutyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, etc. Furthermore, the cycloolefin represented by the general formula [I] includes, bicyclo[2,2,1]hepto-2-en derivatives, tetracyclo[4,4,0,1 2.5 ,1 7.10 ]-3-dodecene derivatives, hexacyclo[6,6,1,1 3.6 ,1 10.13 ,0 2.7 ,0 9.14 ]-4- heptadesene, derivaties, octacyclo[8,8,0,1 2.9 ,1 4.7 ,1 11.18 ,1 13.16 ,0 3.8 ,0 12.17 ]-5-docosene derivaties, pentacyclo[8,8,0,1 2.9 ,1 4.7 ,1 11.18 ,1 13.16 ,0 3.8 ,0 12.17 ]-5-docosene derivatives, pentacyclo[6,6,1,1 3.6 ,0 2.7 ,0 9.14 ]-4-hexadecene derivatives, heptacyclo-5-icosene derivatives, heptacyclo-5-henicosene derivatives, toricyclo[4,3,0,1 2.5 ]-3-decene derivatives toricyclo[4,3,0,1 2.5 ]-3-undecene derivatives, pentacyclo[6,5,1,1 3.6 ,0 2.7 ,0 9.13 ]-4-pentadecene derivatives, pentacyclopentadecadiene derivatives, pentacyclo[4,7,0,1 2.5 ,0 8.13 ,1 9.12 ]-3-pentadecene derivatives, pentacyclo[7,8,0,1 3.6 ,0 2.7 ,1 10.17 ,0 11.16 ,1 12.15 ]-4-icosene derivatives, and nonacyclo[9,10,1,1, 4.7 ,0 3.8 ,0 2.10 ,0 12.21 ,1 13.20 ,0 14.19 ,1 15.18 ]-5-pentacosene derivatives. The concrete examples of such componds as mentioned above are illustrated hereunder. Bicyclo [2,2,1]hept-2-ene derivatives such as: Tetracyclo[4,4,0,1 2.5 ,1 7.10 ]-3-dodecene derivatives such as: Hexacyclo[6,6,1,1 3.6 ,1 10.13 ,0 2.7 ,0 9.14 ]-4-heptadecene derivates such as: Octacyclo[8,8,0,1 2.9 ,1 4.7 ,1, 11.18 ,1 13.16 ,0 3.8 ,0 12.17 ]-5-docosen derivates such as: pentacyclo[6,6,1,1 3.6 ,0 2.7 ,0 9.14 ]-4-hexadecene derivates such as: heptacyclo-5-icosene derivates or heptacyclo-t-henicosene derivates such as: toricyclo[4,3,0,1 2.5 ]-3-decene derivatives such as: tricyclo[4,4,0,1 2.5 ]-1-undecene derivatives such as: pentacyclo[6,5,1,1 3.6 ,0 2.7 ,0 9.13 ]-4-pentadecene derivatives such as: diene compounds such as: Pentacyclo(7,4,0,1 2.5 ,0 8.13 ,1 9.12 ]-3-pentadecene derivatives such as: heptacyclo[8,7,0,1 3.6 ,0 2.7 ,1 10.17 ,0 11.16 ,1 12.15 ]-4-icosene derivatives such as: nonacyclo[10,9,1,1 4.7 ,0 3.8 ,0 2.10 ,0 12.21 , 1 13.20 ,0 14.19 ,1 15.18 ]-5-pentacosene derivatives such as: The following compounds can be mentioned as concrete examples of cycloolefins represented by the formula [I-b]. The cycloolefin random copolymers (A) comprise ethylene units and the above-mentioned cycloolefin units as the essential components as aforesaid, however, if necessary, in addition to these two essential components, said copolymers may contain other copolymerizable unsaturated monomer components so long as they will not throw hinderances in the way of accomplishing the object of the present invention. The unsaturated monomers which may be copolymerized, if necessary, with the copolymers (A) may include, for example, alpha-olefins having from 3 to 20 carbon atoms such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene which may be used in an amount of up to an equimolar to the ethylene component unit in the resulting random copolymer. In the cycloolefin random copolymer [A] having a softening point (TMA) of at least 70°C, the recurring units [a] derived from ethylene are present in an amount of from 40 to 85 mol%, preferably from 50 to 75 mol%, while the recurring units [b] derived from the cycloolefin are present in an amount of from 15 to 60 mol%, preferably from 25 to 50 mol%, and these recurring units [a] and [b] are arranged at random in the substantially linear chain of the copolymer [A]. The molar percentage of the recurring units [a] and [b] were determined by 13 C-NMR. The fact that this cycloolefin random copolymer [A] is completely soluble in decalin at 135°C confirms that it is substantially linear and free from a gel-forming crosslinked structure. The cycloolefin random copolymer [A] has an intrinsic viscosity [η] of from 0.05 to 10 dl/g, preferably from 0.08 to 5 dl/g as measured in decalin at 135°C. The softening temperature (TMA) of the cycloolefin random copolymer [A] as measured by a thermal mechanical analyzer is at least 70°C, preferably from 90 to 250°C, and further preferably from 100 to 200°C. The softening temperature (TMA) referred to above was determined by monitoring thermal deformation behavior of a 1 mm sheet of the copolymer [A) using a thermomechanical analyzer manufactured and sold by Du Pont. More specifically, a quartz needle was vertically placed on the sheet under a load of 49 g and the assembly was heated at a rate of 5°C/min, and a temperature at which the needle penetrated into the sheet by the depth of 0.635 mm was taken as TMA This cycloolefin random copolymer [A] has a glass transition temperature (Tg) of normally from 50° to 230°C, preferably from 70° to 210°C. The crystallinity of this cycloolefin random copolymer [A] as measured by X-ray diffractometry is normally from 0 to 10%, preferably from 0 to 7%, and further preferably from 0 to 5%. The cycloolefin copolymers (A) constituting the cycloolefin random copolymer composition used in the present invention for forming the substrate may all be prepared by the processes proposed by the present inventors in Japanese Patent L-O-P Publns. Nos. 168708/1985, 120816/1986, 115912/1986 and 115916/1986, 252406/1987, 252407/1987, 271308/1986 and 272216/1986, while suitably selecting the conditions. Furthermore, in the present invention, there may also be used as the substrate material a cycloolefin random copolymer composition comprising a cycloolefin random copolymer [A] prepared by copolymerizing ethylene with a cycloolefin represented by the following formula [I], [I-a] or [I-b] and having an intrinsic viscosity [η] of 0.05-10 dl/g measured in decalin at 135°C and a softening temperature (TMA) of at least 70°C, and a cycloolefin random copolymer [B] prepared by copolymerizing ethylene with a cycloolefin represented by the formula [I], [I-a] or [I-b] and having an intrinsic viscosity [η] of 0.05-5 dl/g measured in decalin at 135°C and a softening temperature (TMA) of less than 70°C. Furthermore, the substrate of the magnetooptical recording media according to the invention may be made of polymers having recurring units of the general formula [III] resulting from ring opening of the cycloolefin monomers [I], or polymers having recurring units of the general formula [IV] resulting from hydrogenation of the units [III]. In the general formula [III] or [IV], n and R 1 to R 12 are as defined in the general formula [I]. A thickness of the substrate, though not particularly limited, is preferably 0.5-5 mm and especially 1-2 mm. In the invention, materials for the recording layer 3 are not particularly limited to specific ones. However, when the substrate 3 used is a magnetooptical recording layer having a monoaxial anosotropy perpendicular to the layer surface, this recording layer 3 is preferably composed of at least one member selected from among (i) 3d transition metals and at least one element selected from among (iii) rare earth elements, or composed of at least one member selected from among (i) 3d transition metals, (ii) a corrosion-resistant metal, and at least one element selected from among (iii) rare earth elements. The 3d transition metals used include Fe, Co, Ti, V, Cr, Mn, Ni, Cu and Zn. Of these metals, preferred is Fe or Co, or are both of them. The corrosion-resistant metal (ii) is capable of improving oxidation resistance of this magnetooptical recording layer as the recording layer 3 by incorporation into this recording layer 3 of said corrosion-resistant metal. Such corrosion-resistant metal used includes Pt, Pd, Ti, Zr, Ta, Mo, Nb and Hf. Of these metals, preferred are Pt, Pd and Ti, and particularly Pt or Pd, or both of them. The rate earth elements (iii) used include, for example, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, Ce, Pr, Nd, Pm, Sm and Eu. Of these elements, preferred are Gd, Tb, Dy, Ho, Nd, Sm and Pr. Such magnetooptical recording layer as mentioned above desirably contains the 3d transition metal (i) in an amount of 30-85 atom%, preferably 40-70 atom%, the corrosion-resistant metal (ii) in an amount of less than 30 atom%, preferably 5-25 atom%, and the rare earth element (iii) in an amount of 5-50 atom%, preferably 25-45 atom%. When the recording layer 3 used is other than the magnetooptical recording layer, for example, said recording layer is a phase change type recording layer, this recording layer 3 is composed of such an alloy film, for example, as consisting essentially of Te or Se, and of Te-Ge-Sb alloy film, In-Sb-Te alloy film Te-Ge-Cr alloy film or Te-Ge-Zn alloy film. Further an organic dye film composed of polymethine compounds or cyanine compounds may also be used as the phase change type recording layer. A thickness of the recording layer 3, though not particularly limited, is 50-5000 Å, preferably 100-2000 Å. In the first information recording medium of the present invention, the metallic layer is formed from an aluminum alloy containing 0.1-10 atom% of at least one element (metal) selected from among hafnium and niobium. Concretely, the metallic layer 4 is composed of an aluminum alloy containing 0.1-10 atom%, preferably 1-6 atom% of hafnium (Hf), an aluminum alloy containing 0.1-10 atom%, preferably 1-6 atom% of niobium (Nb), or of an aluminum alloy containing both hafnium and niobium in an amount totaling to 0.1-10 atom%. The metallic layer 4 as mentioned above may contain small amounts of at least one of other metals (elements) in addition to aluminum, hafnium and/or niobium. Such other metal as mentioned above include, for example, chromium (Cr, only in case of Al-Nb alloy), silicon (Si), tantalum (Ta), copper (Cu), tungsten (W), zirconium (Zr), manganese (Mn), magnesium (Mg, only in case of Al-Nb alloy) and vanadium (V). The amount of these other metals contained, if any, in the metallic layer is usually less than 5 atom%, preferably less than 2 atom%. In the second information recording medium of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-9.5 atom%, preferably 1-5 atom% of hafnium and 0.1-5 atom%, preferably 1-3 atom% of chromium. In this aluminum alloy, the combined content of hafnium and chromium is preferably less than 10 atom%. In an embodiment of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-9.5 atom%, preferably 1-5 atom% of hafnium, 0.1-5 atom%, preferably 1-3 atom% of chromium and 0.1-9.5 atom%, preferably 1-5 atom% of titanium. In this aluminum alloy, the combined content of hafnium, chromium and titanium is preferably less than 10 atom%. The metallic layers of the second information recording medium of the invention and of the embodiment as illustrated above may also contain, in addition to the aluminum, hafnium, chromium and titanium, small amounts of at least one of other elements (metals). Such other elements (metal) include, for example, silicon (Si),tantalum (Ta), copper (Cu), tungsten (W), zirconium (Zr), manganese (Mn), and vanadium (V). The amount of these other elements (metals) contained, if any, in the metallic layer is usually less than 5 atom%, preferably less than 2 atom%. In the third information recording medium of the invention, the metallic layer is formed from an aluminum alloy containing 0.5-5 atom%, preferably 1-3 atom% of hafnium, and 0.5-5 atom%, preferably 1-3 atom% of titanium. In this aluminum alloy, the combined content of hafnium and titanium is 1-5.5 atom%, preferably 2-4 atom%. The metallic layer of a further embodiment of the invention as illustrated above may also contain, in addition to aluminum, hafnium and titanium, small amounts of at least one of other elements (metals) Such other elements (metals) include, for example, silicon (Si), tantalum (Ta), copper (Cu), tungsten (W), zirconium (Zr), manganese (Mn), and vanadium (V). The amount of these other elements (metals) contained, if any, in the metallic layer is usually less than 5 atom%, preferably less than 2 atom%. In the fourth information recording medium of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-10 atom%, preferably 1-5 atom% of hafnium and 0.1-10 atom%, preferably 1-5 atom% of magnesium. In this aluminum alloy, the combined content of hafnium and magnesium is less than 15 atom%, preferably 1-10 atom%. In a further embodiment of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-10 atom%, preferably 1-5 atom% of hafnium, 0.1-10 atom%, preferably 1-5 atom% of magnesium and 0.1-10 atom%, preferably 1-5 atom% of titanium. In this aluminum alloy, the combined content of hafnium, magnesium and titanium is desirably less than 15 atom%, preferably 1-10 atom%. In a further embodiment of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-10 atom%, preferably 1-5 atom% of hafnium, 0.1-10 atom%, preferably 1-5 atom% of magnesium and not more than 10 atom%, preferably 0.1-10 atom%, more preferably 1-5 atom% of chromium. In this aluminum alloy, the combined content of hafnium, magnesium and chromium is desirably less than 15 atom%, preferably 1-10 atom%. In a further embodiment of the invention, the metallic layer is formed from an aluminum alloy containing 0.1-10 atom%, preferably 1-5 atom% of hafnium, 0.1-10 atom%, preferably 1-5 atom% of magnesium, less than 10 atom%, preferably 1-5 atom% of chromium and 0.1-10 atom%, preferably 1-5 atom% of titanium. In this aluminum alloy, the combined content of hafnium, magnesium, chromium and titanium is desirably less than 15 atom%, preferably 1-10 atom%. In the fourth information recording media of the invention and in the further embodiments as illustrated above, the metallic layers may each contain small amounts of at least one of other elements (metals) in addition to hafnium, magnesium, titanium and chromium. Such small amounts of other elements (metals) include, for example, silicon (Si), tantalum (Ta), copper (Cu), tungsten (W), zirconium (Zr), manganese (Mn) and vanadium (V). The amount of such other elements (metals) contained, if any, in the metallic layer is usually less than 5 atom%, preferably less than 2 atom%. A thickness of the above-mentioned metallic layers is 100-5000 Å, preferably 500-3000 Å and especially 700-2000 Å. The metallic layers used in the present invention fulfil their function as good heat conductive layers, and in the presence of these metallic layers, the center portion of pits formed in the recording layers may be prevented from being excessively heated to high temperature by the action of the recording laser beam applied thereto. As the result, it is considered that the dependence of the information recording media of the invention on linear velocity is made small. The metallic layers of the invention which are also excellent in corrosion resistance have such a characteristic feature that the dependence of the information recording media on linear velocity is small even after being used for a long period of time, and that said metallic layers are excellent in performance of protecting the recording layers. The structure of the information recording media of the invention shown in Fig. 1 is given by way of illustration but not of limitation. For instance, they may be prepared by providing a protecting film (enhancing film) 5 on the aforementioned substrate 5 and then providing further the recording layer 3 and the metallic layer 4 in that order. The protective film (enhancing film) 5 is formed desirably from Si 3 N 4 , SiN x (0<x<4/3), AlN, ZnSe, ZnS, Si or CdS, though not limited thereto. A thickness of this protective film is 100-2000 Å, preferably about 300-1500 Å. Of these materials used for forming the protective film, particularly preferred are Si 3 N 4 and SiN x (0<x<4/3) from a viewpoint of crack resistance. The function of the protective film is to protect the recording layer and, at the same time, it enhances the information recording medium in sensitivity and functions as an enhancing film. Such a protective layer desirably has a refractive index larger than that of the substrate. The information recording media of the present invention may be prepared by forming on the substrate the recording layer and the metallic layer and, if necessary, the protective layer using such film-forming methods, for example, vacuum deposition, sputtering, electron beam deposition or the like. EFFECT OF THE INVENTION The information recording media of the present invention comprising the metallic layer composed of a specific aluminum alloy are excellent in corrosion resistance, small in the dependence of the recording power on linear velocity and in performance of protecting the recording layer The present invention is illustrated below with reference to examples, but it should be construed that the invention is in no way limited to those examples. The term "optimum recording power" used in the following Examples designates a recording power with which writing signals at a frequency of 1 MHz and a duty factor of 50% are recorded and which makes minimum the secondary harmonics of signals reproduced from the recorded signals. Recording media show a lower degree of dependence on the linear velocity when the information recording media show smaller difference of the optimum recording powers determined at different linear velocities. Example 1 Hereinafter, corrosion resistance of the metallic layer was examined first by the following procedure. On a glass substrate, a metallic layer composed of an aluminum-hafnium alloy was deposited to a thickness of 700 Å by the sputtering process using an aluminum-hafnium composite target. The hafnium content in the above-mentioned aluminum-hafnium alloy (layer) constituting the metallic layer as formed was 4 atom% and the alumium content was 96 atom%. This metallic layer as formed was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby the corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer. The reflectance of the metallic layer did not change before and after the immersion in the sodium chloride aqueous solution of said metallic layer. Example 2 On a glass substrate, a metallic layer composed of an aluminum-niobium alloy was deposited to a thickness of 700 Å by the sputtering process using an aluminum-niobium composite target. The niobium content in the aluminum-niobium alloy (layer) constituting the metallic layer as formed was 4 atom%. This metallic layer was immersed four hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby the corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer. The reflectance of the metallic layer did not change before and after the immersion in the sodium chloride aqueous solution of said metallic layer. Comparative Example 1 On a glass substrate, a metallic layer composed of aluminum was deposited to a thickness of 700 Å by the sputtering process using an aluminum target. This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer. The reflectance of the metallic layer measured after the immersion in the aqueous sodium chloride solution of said metallic layer was lower by about 30% than that measured before said immersion. Example 3 On a disk substrate composed of an amorphous copolymer of ethylene with 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (structure formula: abbreviated to DMON hereinafter), the amorphous copolymer having 59 mol% of an ethylene unit content determined by NMR analysis, an intrinsic viscosity [η] of 0.42 dl/g measured in decalin at 135°C and a softening temperature (TMA) of 154°C, were deposited successively a protective film composed of Si 3 N 4 to a thickness of 1100 Å and a (atom %) recording layer composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) to a thickness of 260Å by the sputtering process, and thereon was deposited a metallic layer composed of an aluminum-hafnium alloy to a thickness of 700 Å by the sputtering process using an aluminum-hafnium composite target. The hafnium content in the aluminum-hafnium alloy (layer) constituting the metallic layer was 4 atom% and the aluminum content was 96 atom%. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer for the recording layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of the information recording medium did not change before and after holding said metallic layer under the circumstance of 80°C and a relative humidity of 85%. This fact means that the metallic layer are excellent in corrosion resistance and in performance of protecting the recording layer. Example 4 Example 3 was repeated except that the metallic layer formed had a thickness of 500 Å. The information recording medium obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85% to measure reflectance of said information recording medium, whereby the reflectance of said information recording medium did not change. The optimum recording power of this information recording medium at a linear velocity of 5.7 m/sec was 3.7 mW, and the optimum recording power at a linear velocity of 11.3 m/sec was 5.2 mW. Comparative Example 2 On a substrate used in the Example 3, were deposited successively a protective film composed of Si 3 N 4 and a recording layer composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer composed of aluminum to a thickness of 700 Å by the sputtering process using an aluminum target. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer for the recording layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of said information recording medium measured after holding said recording medium was lower by about 15% than that measured before said holding. Example 5 Hereinafter, corrosion resistance of a metallic layer composed of an aluminum-hafnium-chromium alloy was examined by the following procedure. On a glass substrate, was deposited a metallic layer composed of an aluminum-hafnium-chromium alloy to a thickness of 1000 Å by the sputtering process using an aluminum-chromium-hafnium composite target. The hafnium and chromium contents of the metallic layer thus formed were each 2 atom%. This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer. The reflectance of the metallic layer did not change before and after the immersion in the aqueous sodium chloride solution of said metallic layer. The number of pinholes observed in the metallic layer after the above-mentioned immersion was less than 50 pieces (49 pieces) per unit surface area 15 cm x 5 cm). Example 6 On a substrate used in the Example 3, were deposited successively a protective film (1100 Å in thickness) composed of Si 3 N 4 and a recording layer (260 Å in (atom %) thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (500 Å in thickness) composed of an Al-Cr-Hf alloy by the sputtering process using a composite target of Al-Cr-Hf. The Cr and Hf contents in the Al alloy (layer) constituting the metallic layer obtained were each 2 atom%. The information recording medium obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer for the recording layer were evaluated by measuring a change in reflectance of the information recording medium and surface profile of the metallic layer. The reflectance of the information recording medium did not cha before and after holding the same under the circumstances of 80°C and a relative humidity of 85%. The optimum recording power of this information recording medium at a linear velocity of (5.7) m/sec was (3.6) mW, and the optimum recording power at a linear velocity of (11.3) m/sec was (5.3) mW. Example 7 On a substrate used in the Example 3, were deposited successively a protective film (1000 Å in thickness) composed of Si 3 N 4 and a recording layer (500 Å in thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (700 Å in thickness) composed of an Al-Cr-Hf alloy by the sputtering process using a composite target of Al-Cr-Hf. The Cr and Hf contents in the Al alloy (layer) constituting the metallic layer obtained were each 2 atom%. The information recording medium obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer for the recording layer were evaluated by measuring a change in reflectance of the information recording medium and surface profile of the metallic layer. The reflectance of the information recording medium did not change before and after holding the same under the circumstances of 80°C and a relative humidity of 85%. Comparative Example 3 On a glass substrate, a metallic layer composed of an aluminum-chromium alloy was formed to a thickness of 1000 Å by the sputtering process using an aluminum-chromium composite target. The chromium content of the metallic layer thus formed was 2 atom%. This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride. After the 4-hour immersion, changes in reflectance and surface profile of the metallic layer were measured. The reflectance of the metallic layer thus measured decreased by about 2%. The number of pinholes observed on the metallic layer was about 70 pieces per unit film surface area (5 cm x 5 cm). Comparative Example 4 A metallic layer containing 4 atom% of chromium was obtained in the same manner as in Comparative Example 3 but using a composite target of an aluminum-chromium alloy different in composition from the composite target used in Comparative Example 3. This metallic layer was immersed in an aqueous sodium chloride solution in the same way as in Comparative Example 3 to measure changes in reflectance and surface profile of the metallic layer after the immersion thereof. The reflectance of the metallic layer did not change before and after the immersion in the aqueous sodium chloride solution of said metallic layer, and the number of pinholes observed in the metallic layer after the immersion thereof was about 70 pieces per unit film surface area (5 cm x 5 cm). Example 8 Hereinafter, corrosion resistance of the metallic layers composed of an aluminum-hafnium-titanium alloy was examined. On a glass substrate, a metallic layer composed of an aluminum-hafnium-titanium alloy was formed by the sputtering process using a composite target of aluminum(Al)-hafnium(Hf)-titanium (Ti). The titanium content of the metallic layer thus obtained was 1 atom%, and the hafnium content thereof was 2 atom%. This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer and surface profile of said metallic layer. The reflectance of the metallic layer did not change before and after the immersion in the aqueous sodium chloride solution of said metallic layer, and the number of pinholes observed in the metallic layer after the immersion thereof was less than 40 pieces (38 pieces) per unit film surface area (5 cm x 5 cm). Example 9 A metallic layer containing 2 atom% of titanium and 1 atom% of hafnium was obtained in the same manner as in Example 8 but using a composite target composed of an aluminum-titanium-hafnium alloy different in composition from the composite target used in Example 8. This metallic layer was immersed in the same manner as in Example 7 in the aqueous sodium chloride solution to evaluate corrosion resistance of the metallic layer by measuring changes in reflectance and surface profile of the metallic layer after the immersion thereof. The reflectance of the metallic layer did not change before and after the immersion in the aqueous sodium chloride solution of said metallic layer, and the number of pinholes observed in the metallic layer after the immersion was less than 40 pieces (33 pieces) per unit film surface area (5 cm x 5 cm). Example 10 On a substrate used in the Example 3, were deposited successively a protective film (1100 Å in thickness) composed of Si 3 N 4 and a recording layer (260 Å in thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (500 Å in thickness) composed of an Al-Hf-Ti alloy by the sputtering process using a composite target of Al-Hf-Ti. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of the information recording medium did not change before and after holding said recording medium under the circumstances of 80°C and a relative humidity of 85%. The optimum recording power of this information recording medium at a linear velocity of (5.7) m/sec was (3.3) mW, and the optimum recording power at a linear velocity of (11.3) m/sec was (4.7) mW. Comparative Example 5 A metallic layer containing 2 atom% of titanium was obtained in the same manner as in Example 8 but using a composite target of aluminum-titanium in place of aluminum-titanium-hafnium used in Example 8. This metallic layer was immersed in the aqueous sodium chloride solution in the same way as in Example 8 to evaluate corrosion resistance of the metallic layer by measuring changes in reflectance and surface profile of said metallic layer after the immersion thereof. The reflectance of the metallic layer decreased by about 8% by the immersion of said metallic layer. The number of pinholes observed in the metallic layer was 51 pieces per unit film surface area (5 cm x 5 cm). Comparative Example 6 A metallic layer composed of an aluminum-titanium alloy containing 4 atom% of titanium was formed in the same manner as in Comparative Example 5. This metallic layer was immersed in the same way as in Example 8 in the aqueous sodium chloride solution to evaluate corrosion resistance of the metallic layer by measuring changes in reflectance and surface profile of said metallic layer after the immersion thereof. The reflectance of the metallic layer decreased by about 2% by the immersion of said metallic layer. The number of pinholes observed in the metallic layer was more than 115 pieces per unit film surface area (5 cm x 5 cm). Example 11 On a substrate used in the Example 3, were deposited successively a protective film (1000 Å in thickness) composed of Si 3 N 4 and a recording layer (500 Å in thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (700 Å in thickness) composed of an Al-Hf-Ti alloy by the sputtering process using a composite target of Al-Hf-Ti. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of the information recording medium did not change before and after holding said recording medium under the circumstances of 80°C and a relative humidity of 85%. Example 12 On a glass substrate, a metallic layer (1000 Å in thickness) composed of an aluminum-hafnium-magnesium alloy was formed by the sputtering process using a composite target of aluminum (Al)-hafnium (Hf)-magnesium (Mg). This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride, whereby corrosion resistance of the metallic layer was evaluated by measuring a change in reflectance of said metallic layer and surface profile of said metallic layer. The reflectance of the metallic layer did not change before and after the immersion in the aqueous sodium chloride solution of said metallic layer, and the number of pinholes observed in the metallic layer was less than 30 pieces (25 pieces) per unit film surface area (5 cm x 5 cm). Examples 13-14 Metallic layers were formed in the same manner as in Example 12 but using composite targets as shown in Table 1. The atom content and the number of pinholes of the metallic layers thus formed are shown in Table 1. Composite target used and Composition of Metallic layer Atom content (at%) Number of pinholes Mg Hf Ti Example 12 Al-Mg-Hf 4 4 - not more than 30 pieces (25 pieces) Example 13 Al-Mg-Hf 4 2 - not more than 30 pieces (30 Pieces) Example 14 Al-Mg-Hf-Ti 4 2 1 Less than 30 pieces (30 pieces) Comparative Example 7 Al-Mg 5 - - 70 pieces Example 15 On a substrate used in Example 3, were deposited successively a protective film (1100 Å in thickness) composed of Si 3 N 4 , and a recording layer (260 Å in (atom %) thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and was deposited thereon a metallic layer (500 Å in thickness) composed of an Al-Mg-Hf alloy by the sputtering process using a composite target of aluminum (Al)-hafnium (Hf)-magnesium (Mg). The Mg content was 4 atom% and the Hf content was 2 atom% in the Al alloy (layer) constituting the metallic layer as formed above. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%. The reflectance of the information recording medium did not change before and after holding the information recording medium under the circumstances of 80°C and a relative humidity of 85%. The optimum recording power of this information recording medium at a linear velocity of (5.7) m/sec was (4.0) mW, and the optimum recording power at a linear velocity of (11.3) m/sec was (5.6) mW. Comparative Example 7 On a glass substrate, was formed a metallic layer (1000 Å in thickness) composed of an aluminum-magnesium alloy by the sputtering process using a composite target of aluminum-magnesium. The magnesium content in the metallic layer thus obtained was 5 atom%. This metallic layer was immersed for 4 hours at 60°C in an aqueous solution containing 10% by weight of sodium chloride. The reflectance of the metallic layer immersed decreased by about 2% by the above-mentioned immersion. The number of pinholes observed in the metallic layer was about 70 pieces per unit film surface area (5 cm x 5 cm). Further Example 1 On a substrate used in the Example 3, were deposited successively a protective film (1100 Å in thickness) composed of Si 3 N 4 and a recording layer (260 Å in thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (500 Å in thickness) composed of an Al-Hf-Ti alloy (Al content 96 atom%, Hf content 2 atom%, Ti content 2 atom%) by the sputtering process using a composite target of Al-Hf-Ti. The information recording medium thus obtained was held for about 720 hours under the circumstances of 80°C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of the information recording medium did not change before and after holding said recording medium under the circumstances of 80°C and a relative humidity of 85%. The optimum recording power of this information recording medium at a linear velocity of (5.7) m/sec was (3.3) mW, and the optimum recording power at a linear velocity of (11.3) m/sec was (4.7) mW. Further Example 2 On a substrate used in the Example 3, were deposited successively a protective film (1000 Å in thickness) composed of Si 3 N 4 and a recording layer (500 Å in thickness) composed of Pt 10 Tb 29 Fe 55 Co 6 (atom %) by the sputtering process, and thereon was deposited a metallic layer (700 Å in thickness) composed of an Al-Hf-Ti alloy (Al content 96 atom%, Hf content 2 atom%, Ti content 2 atom%) by the sputtering process using a composite target of Al-Hf-Ti. The information recording medium thus obtained was held for about 720 hours under the circumstances of 800C and a relative humidity of 85%, whereby corrosion resistance of the metallic layer and protective function of the metallic layer were evaluated by measuring a change in reflectance of said information recording medium. The reflectance of the information recording medium did not change before and after holding said recording medium under the circumstances of 80°C and a relative humidity of 85%.

Claims: An information recording medium having a substrate and thereon a recording layer and a metallic layer, characterised in that the metallic layer is composed of an aluminum alloy containing 0.1-10 atom% of at least one element selected from among hafnium and niobium based on all atoms constituting the aluminum alloy. An information recording medium having a substrate and thereon a recording layer and a metallic layer characterized in that the metallic layer is composed of an aluminum alloy containing 0.1-9.5 atom% of hafnium and 0.1-5 atom% of chromium based on all atoms constituting the aluminum alloy, the combined content of said hafnium and chromium being less than 10 atom%. An information recording medium according to claim 2, wherein the metallic layer additionally comprises 0.1-9.5 atom% of titanium based on all atoms constituting the aluminum alloy and the combined content of the hafnium, chromium and titanium is less than 10 atom%. An information recording medium having a substrate and thereon a recording layer and a metallic layer characterized in that the metallic layer is composed of an aluminum alloy containing 0.5-5 atom% of hafnium and 0.5-5 atom% of titanium based on all atoms constituting the aluminum alloy, the combined content of said hafnium and titanium being 1-5.5 atom%. An information recording medium having a substrate and thereon a recording layer and a metallic layer characterized in that the metallic layer is composed of an aluminum alloy containing 0.1-10 atom% of hafnium and 0.1-10 atom% of magnesium based on all atoms constituting the aluminum alloy, the combined content of said hafnium and magnesium being less than 15 atom%. An information recording medium according to claim 5, wherein the metallic layer additionally comprises 0.1-10 atom% of titanium based on all atoms constituting the aluminum alloy, and the combined content of the hafnium, magnesium and titanium is less than 15 atom%. An information recording medium according to claim 5, wherein the metallic layer additionally comprises not more than 10 atom% of chromium based on all atoms constituting the aluminum alloy, and the combined content of the hafnium, magnesium and chromium being less than 15 atom%. An information recording medium according to claim 5, wherein the metallic layer additionally comprises 0.1-10 atom% of titanium and less than 10 atom% of chromium based on all atoms constituting the aluminum alloy, and the combined content of the hafnium, magnesium, titanium and chromium is less than 15 atom%. The information recording medium as claimed in any of claims 1-8 wherein the recording layer is a magnetooptical recording layer. The information recording layer as claimed in any of claims 1-8 wherein the metallic layer has a film thickness of 100-5000 Å.

Inventors: HASHIMOTO HIDEHIKO, IGARASHI KOICHI, MIZUMOTO KUNIHIKO, SHINDO KIYOTAKA, HASHIMOTO, HIDEHIKO, IGARASHI, KOICHI, MIZUMOTO, KUNIHIKO, SHINDO, KIYOTAKA, HASHIMOTO, HIDEHIKO, C/O MITSUI PETROCHEM. IND. LT, IGARASHI, KOICHI, C/O MITSUI PETROCHEMICL IND. LTD, MIZUMOTO, KUNIHIKO, C/O MITSUI PETROCHEM. IND. LTD, SHINDO, KIYOTAKA, C/O MITSUI PETROCHEMICL IND. LTD
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1990
Main classification: G11B7
IPC codes: G11B7, G11B11