MAGNETIC RECORDING MEDIUM

Abstract: A magnetic recording medium comprises a support and a magnetic layer, coated on said support, comprising magnetic powder, a binder, (I) an ester compound having the formula: in which R1 and R2 are each a saturated alkyl group having 1 to 25 carbon atoms, branched or straight, the total carbon number of R1 and R2 being from 22 to 34, and R3 is a saturated or unsaturated alkyl group having 7 to 29 carbon atoms, branched or straight, and (II) an ester compound having the formula: R₄- ―O―R₅ ..... ( II ) in which R4 is an aliphatic hydrocarbon group having 1 to 29 carbon atoms, straight or brached, and R5 is an aliphatic hydrocarbon group having 1 to 23 carbon atoms, straight or branched, or a straight aliphatic hydrocarbon group having 24 to 36 carbon atoms, the total carbon number of R4 and R5 being 15 to 65.

Description: The present invention relates to a magnetic recording medium. A magnetic recording medium is usually produced by coating a substrate such as polyester film with a magnetic paint composed of magnetic powder, a binder resin, an organic solvent, and other components. In the case of a floppy disk, the magnetic layer is required to have good durability with a minimum of wear, because the magnetic layer of a floppy disk rubs against the magnetic head and jacket liner during recording and play-back. The wear resistance of the magnetic layer is commonly improved by incorporating a lubricant into the magnetic layer. Examples of such lubricants are fatty acids, oleyl oleate, butoxide stearate, fatty acid amides, liquid paraffins, and wax. These lubricants, however, are not necessarily satisfactory in their performance. For example, oleyl oleate and butoxide stearate do not improve the durability of the medium to a satisfactory extent. Fatty acids such as stearic acid and oleic acid and hydrocarbon lubricants such as liquid paraffin effectively improve the durability but exhibit poor miscibility with the binder. When used in large amounts, they bleed out from the surface of the magnetic layer and therefore tend to stain the magnetic head. A magnetic recording medium according to the invention comprises a support coated with a magnetic layer comprising a magnetic powder, a binder, (I) a first ester having the formula: in which R1 and R2 are each independently a C₁ to C₂₅ branched or straight-chain saturated alkyl group in which the total carbon number of R1 and R2 is from 22 to 34, and R3 is a C₇ to C₂₉ branched or straight-chain saturated or unsaturated alkyl group and (II) a second ester having the formula: R₄ ― ―O―R₅ (II) in which R4 is a C₁ to C₂₉ branched or straight-chain aliphatic hydrocarbon and R5 is a C₁ to C₂₃ is a branched or straight-chain aliphatic hydrocarbon group or a straight-­ chain C₂₄ to C₃₆ aliphatic hydrocarbon group in which the total carbon number of R4 and R5 is from 15 to 65. It is preferred that the magnetic layer further comprises (III) an aliphatic acid having 10 to 30 carbon atoms and the total carbon number of R4 and R5 of the ester compound (II) is from 16 to 65. It is preferred that the magnetic layer comprises the ester compounds (I) and (II) in a total amount of 1 to 15 percent by weight based on the magnetic powder at a weight ratio of (I) to (II) in the range between 10/90 and 90/10. It is preferred that the magnetic layer comprises (I) and (III) in a total amount of 1 to 15 percent by weight based on the magnetic powder at a weight ratio of (I) to (III) in the range between 95/5 and 10/90. The invention provides a magnetic recording medium having an intermediate layer. It may further comprise, between said support and said magnetic layer, an intermediate layer comprising (1) one or more resin selected from a hydroxy-containing polyester and a hydroxy-containing polyurethane, (2) a polyisocyanate compound and (3) trisacetylacetonatoiron (III). Alternatively the intermediate layer may comprise(1) one or more resins selected from a hydroxy-­ containing polyester and hydroxy-containing polyurethane, (2) a polyisocyanate compound and (4) cellulose nitrate. The intermediate layer preferably comprises 100 parts by weight of (1), 2 to 40 parts by weight of (2) and 0.01 to 8 parts by weight of (3), or alternatively preferably comprises 100 parts by weight of (1), 2 to 40 parts by weight of (2) and 5 to 50 parts by weight of (4). The magnetic recording medium of this invention is characterized in that the magnetic layer contains a first ester compound represented by the formula (I) above {referred to as ester compound (I) hereinafter} and second ester compound represented by the formula (II) (referred to as ester compound (II) hereinafter}. These ester compounds used in combination impart good lubricity to the magnetic layer, improving the durability of the magnetic recording medium to a great extent. It is not known why they impart such good lubricity. Ester compound (I) may be obtained by the esterification reaction between a branched-chain alcohol and a fatty acid. This branched-chain alcohol is , in general, called Guerbet alcohol. In Ester compound (II), R₄ is preferably an aliphatic hydrocarbon having 7 to 23 carbon atoms, i.e. either with a straight-chain or a branched-chain with a low-molecular weight branch such as methyl or ethyl group. Examples include tridecyl stearate, isotridecyl stearate, oleyl stearate, tridecyl palmitate, isotridecyl palmitate, cetyl myristate, isocetyl stearate, isostearyl palmitate, isostearyl oleate, and eicosyl myristate. The above-mentioned ester compound (I) and ester compound (II) should usually be used in an amount (in total) of 1 to 15 wt% based on the magnetic powder. The ratio of ester compound (I) to ester compound (II) should preferably be in the range of 10/90 to 90/10. The magnetic powder involved in the present invention includes, for example, fine acicular metal oxide such as γ-Fe₂O₃, Fe₃O₄, and CrO₂; processed γ-Fe₂O₃ such as Co-coated γ-Fe₂O₃ and Co-doped γ-Fe₂O₃; iron metal powder; fine platy barium ferrite; magnetic powder with a portion of Fe atoms therein replaced by one or more members of Ti, Co, Zn, V, and Nb; and microfine powder of metal or alloy such as Co, Fe-Co, and Fe-Ni. The iron metal powder may be doped with or surface-treated with nickel, cobalt, titanium, silicon, or aluminum in the form metallic atom, salt, or oxide, to improve its chemical stability. Such a treated one can also be used. For the purpose of stabilization, the iron metal powder may also be coated with thin oxide film by treatment in a weak oxidizing atmosphere. Such a treated one can also be used. The binder that can be used in this invention includes, for example, polyurethane, polyester, polyvinyl chloride, vinyl chloride-­ vinyl acetate copolymer, polyacrylonitrile, nitrile rubber, epoxy resin, alkyd resin, polyamide, polyacrylate ester, polymethacrylate ester, polyvinyl acetate, polyvinyl butyral, polyvinylidene chloride, vinylidene chloride copolymer, cellulose nitrate, maleic acid-modified vinyl chloride-vinyl acetate copolymer, and ethyl cellulose. They may be used individually or in combination with one another. In addition, they may be incorporated with a plasticizer or hardener to control the hardness of the resin. The amount of the binder is usually 15 to 60 parts by weight for 100 parts by weight of magnetic powder. No matter how great the binding power might be, the binder should be used in an amount more than 15 parts by weight; otherwise, the resulting magnetic coating lacks sufficient strength and adhesion with the substrate. On the other hand, the binder in excess of 60 parts by weight reduces the concentration of magnetic powder in the magnetic coating, which leads to a decreased output of reproduction and aggravates the characteristic properties of the coating. The magnetic recording medium of this invention is characterized by that the magnetic layer contains an ester compound represented by the formula (I) above and a fatty acid having 8 to 30 carbon atoms. These compounds used in combination impart good lubricity to the magnetic layer, improving the durability of the magnetic recording medium. The reason for this is not known well. The aliphatic acid to use in the invention preferably includes one having a saturated or unsaturated, straight-claim or branched-claim, having 8 to 24 carbon atoms. Examples of the fatty acid include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, behenic acid, 12-stearic acid, oleic acid, linoleic acid, and erucic acid. The carbon number of 12 to 22 is especially preferred. The above-mentioned ester compound and fatty acid should be used in an amount (in total) of 1 to 15 wt% based on the magnetic powder. The ratio of the ester compound to the fatty acid should be from 95/5 to 10/90, preferably from 95/5 to 50/50. The above-mentioned ester compound (I), ester compound (II), and aliphatic acid(III) should usually be used in an amount (in total) of 1 to 15 wt% based on the magnetic powder. Ester compound (I), ester compound (II), and aliphatic acid (III) should account for 1 to 40 wt%, 10 to 80 wt%, and 1 to 40 wt%, respectively, in the total amount of the three compounds. Preferably, ester compound (I), ester compound (II), and aliphatic acid(III) should account for 5 to 35 wt%, 15 to 70 wt%, and 5 to 35 wt%, respectively, in the total amount of the three compounds. The invention is further improved in prevention of swelling and dissolution by a solvent by insertion of the below described intermediate or primer layer between the support and the magnetic layer. It contains a specific resin having hydroxyl groups, a polyisocyanate compound, and trisacetylacetonatoiron (III), and such a intermediate layer provides a magnetic recording medium having good surface smoothness and good durability. The present invention was completed on the basis of these findings. Accordingly, the present invention relates to a magnetic recording medium having a primer layer between the non-magnetic substrate and the magnetic layer, characterized in that said primer intermediate layer contains the following components. (1) One kind or more than one kind of resin selected from the group consisting of polyester resin having hydroxyl groups and polyurethane resin having hydroxyl groups; (2) Polyisocyanate compound; and (3) Trisacetylacetonatoiron (III). The polyester resin and polyurethane resin used in this invention are not specifically limited so long as they have hydroxyl groups at the terminals or branched chain of the molecule. Examples of commercial polyester resin include Biron 103, Vylon 200, Vylon 280, Vylon 290, Vylon 300, and Vylon 500 available from Toyobo Co., Ltd., and Unitika Elitel UE-3200, Unitika Elitel UE-3201, Unitika Elitel UE-3300, and Unitika Elitel UE-3400 available from Unitika Ltd. Examples of commercial polyurethane resin include Nippollan 5032, Nippollan 5033, and Nippollan 2301 available from Nippon Polyurethane Industry Co., Ltd. The polyisocyanate compound used in this invention is a compound having two or more than two isocyanate groups in one molecule. It may be aromatic, aliphatic, or alicyclic. Examples of commercial polyisocyanate compounds include Coranate L, Coranate HL, and Coranate EH available from Nippon Polyurethane Industry Co., Ltd., and Sumidule L, Sumidule IL, Desmodule HL, Sumidule N, Sumidule HT, and Sumidule W available from Sumitomo Bayer Urethane Co., Ltd. According to this invention, the polyisocyanate compound should preferably be used in an amount of 2 to 40 parts by weight for 100 parts by weight of the polyester resin having hydroxyl groups or the polyurethane resin having hydroxyl groups or a mixture thereof. If the amount of the polyisocyanate compound is less than 2 parts by weight, the crosslinking reaction does not take place completely. With an amount in excess of 40 parts by weight, it takes a long time for the isocyanate groups in the polyisocyanate compound to complete the reaction. This is undesirable. If the polyisocyanate compound partly remains unreacted, the intermediate layer is liable to blocking and sticks to the roll in the step of applying the magnetic paint. The trisacetylacetonatoiron (III) is a red compound represented by the formula Fe(C₅H₇O₂)₃. This compound should preferably be used in an amount of 0.01 to 8 parts by weight for 100 parts by weight of the polyester resin having hydroxyl groups or the polyurethane resin having hydroxyl groups or a mixture thereof. With the amount less than 0.01 parts by weight, the curing reaction of the intermediate layer is very slow; and with the amount in excess of 8 parts by weight, blooming will take place on the surface of the primer layer. The intermediate layer is formed by applying a intermediate solution to the non-magnetic substrate by gravure coating, reverse-roll coating, or other coating method, followed by drying. The intermediate solution is prepared by dissolving the above-mentioned components (1) to (3) in an organic solvent such as acetone, methyl ethyl ketone, cyclohexanone, and ethyl acetate. The intermediate solution may be incorporated with an inorganic pigment such as carbon black and titanium oxide for the prevention of static build-up or the light shielding. The above shown intermediate layer may comprise (4) cellulose nitrate instead of trisacetylacetonatorion (III). This intermediate layer may further comprise (5) an organometallic compound or a tertiary amine. The cellulose nitrate used in this invention is one called nitrocellulose for industrial use according to JIS K6703. It contains 10.7 to 12.2% of nitrogen. Examples of commercial ones include Celnova BTH1/2, Celnova HIG1/16 and Cellnova LIL1/4 available from Asahi Chemical Industry Co., Ltd., and Celline FM-400 and Seluline FM-1600 available from Daisel Chemical Industry Co., Ltd. The cellulose nitrate should preferably be used in an amount of 5 to 50 parts by weight for 100 parts by weight of the polyester resin containing hydroxyl groups or the polyurethane resin containing hydroxyl groups or a mixture thereof. If the amount of the cellulose nitrate is less than the lower limit, the primer layer swells or dissolves under the influence of solvents. With an amount of the cellulose nitrate in excess of the upper limit, the intermediate layer is poor in adhesion to the base film. The organometallic compound used in this invention includes, for example, trisacetylacetonatoiron (III) [Fe(C₅H₇O₂)₃], trisacetyl­ acetonatomanganese (III) [Mn(C₅H₇O₂)₃], dibutyltin dioctate, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, tin octoate, tin oleate, lead naphthenate, lead oleate, tetrapropyl titanate, and tetra-­ n-butyl titanate. The tertiary amine used in this invention includes, for example, triethylenediamine, triethylamine, In the case where one kind or more than one kind of the compound selected from the group consisting of the above-mentioned metallic compounds and tertiary amines are used, their amount should preferably be 0.001 to 8 parts by weight. An amount in excess of 8 parts by weight causes blooming on the surface of the primer layer, and an amount less than 0.001 parts by weight is not effective. These organometallic compounds or tertiary amines may act as a catalyst for urethane bond formation reaction. The intermediate layer is formed by applying a solution to the non-magnetic substrate by gravure coating, reverse-roll coating, or other coating method, followed by drying. The solution is prepared by dissolving the above-mentioned components (1), (2) and (4), or (1), (2), (4) and (5) in an organic solvent such as acetone, methyl ethyl ketone, cyclohexanone, and ethyl acetate. The primer solution may be incorporated with an inorganic pigment such as carbon black and titanium oxide for the prevention of static build-up or the light shielding. (Examples) The invention is now described in more detail with reference to the following examples, which are not intended to limit the scope of the invention. Examples 1 to 20 Mixtures of the following composition were prepared. The kind and amount of the ester compounds as lubricants added to the mixtures are shown in Tables 1, 2 and 3. Co-coated γ-Fe₂O₃ 100 parts by weight Vinyl chloride/vinyl acetate copolymer *¹ 30 Polyurethane resin 1 *² 27 Polyurethane resin 2 *³ 5 Carbon black 8 α-Al₂O₃ 4 Toluene 67 Methyl ethyl ketone 67 Cyclohexanone 100 Note: *¹ VAGH, a product of Union Carbide Corp. in the U.S. *² N2301, a product of Nippon Polyurethane Industry Co., Ltd. *³ N2304, a product of Nippon Polyurethane Industry Co., Ltd. Each of the mixtures was mixed for 5 hours in a sand mill. After the addition of lubricants, mixing was continued for 10 hours with a ball mill. To the resulting mixture was added 5.4 parts by weight of polyisocyanate compound (N3200, a product of Sumitomo Bayer Urethane Co., Ltd.) Thus there were prepared 20 magnetic paints. Each paint was applied to a 75-µm thick polyethylene terephthalate film. The coating weight was adjusted so that the film thickness is 1.5 µm after drying. After drying, the coating film was subjected to calendering and then allowed to stand at 60°C for 4 days to complete the curing reaction. The coated film was punched into disks, which were subsequently polished. In this way floppy disks were prepared. Each of the floppy disks was examined for durability by running it on a special drive for accelerated durability test at 5°C and 25°C. The durability is indicated by the running time required for the reproduction output to decrease to 70% of the initial value. The results are shown in Tables 1, 2 and 3. A reference to amount is based on parts by weight. Comparative Examples 1 to 9 Nine magnetic paints were prepared in the same manner as in Example 1, except that lubricants were changed as shown in Table 4. Floppy disks were prepared from the magnetic paints and examined for durability in the same manner as shown in Example 1. Results are shown in Table 4. Example 21 The intermediate layer was prepared with the following solution composition. Biron, a tradename of a polyester available from Toyobo Co., Ltd. 100 parts by weight Colonate L, a tradename of polyisocyanate available from Nippon Polyurethane Industry Co., Ltd. 15 carbon black 20 trisacetylacetonatoiron(III) 3 methylethylketone 700 cyclohexanone 350 The solution was coated on both sides of a sheet of polyethylene terephthalate having 75 micron thickness to have a dry thickness of 0.5 micron, followed by drying to obtain a primer layer. Separately the following composition was kneaded to form a uniform dispersion with a ball mill and then mixed with 5.4 parts by weight of Colonate L to obtain a magnetic paint. The magnetic paint was coated further on both sides of the sheet to have a dry thickness of 1.0 mircon. After drying, the sheet was treated with calendar rolls at 70°c at a linear pressure of 250 kg/cm and cured at 50°c for two days. A circle having a diameter of 5.25 inches was cut out of the sheet to form a magnetic disk and then treated on the surface with an abrasive tape. It was put into a jacket. The magnetic composition comprised: γ-Fe2O3 coated with Co 100 parts by weight VAGH 17 N2301 21 N2304 3 carbon black 7 α-A12O3 4 tridecyl stearate 4 palmitic acid 2 2-decyl-tetradecyl oleate 2 methylethylketone 100 toluene 100 cyclohexanone 100 The magnetic disk was examined about durability in the same way as shown in Example 1 and then about output voltage and output fluctuation in the below shown manner. Results are shown in Table 5. The output voltage and output fluctuation was measured at 125 kHz, using a commercial floppy disk drive. The output fluctuation is shown with the formula: where A : Average output voltage produced by about 2000 times of magnetic flux inversion including the maximum output voltage in one round of the track. B : Average output voltage produced by about 2000 times of magnetic flux inversion including the minimum output voltage in one round of the track. Example 22 A magnetic disk was prepared in the same way as shown in Example 21, except that 4 parts by weight of 2-decyl-tetradecyl stearate was used, not containing palmitic acid and 2-decyl-­ tetradecyl oleate, in the magnetic composition. Results are shown in Table 5. Example 23 An intermediate layer composition comprised 80 parts by weight of Biron, 18 parts by weight of Colonate L, 20 parts by weight of cellulose nitrate, Celluline (tradename) available from Daicel Chemical Industries Ltd., 700 parts by weight of methylethylketone and 200 parts by weight of cyclohexanone. The magnetic layer composition had the same composition as used in Example 21, except that 8 parts by weight of carbon black, 5 parts by weight of 2-decyl-tetradecyl oleate and 3 parts by weight of behenic acid were used, not containing tridecyl stearate and palmitic acid. A magnetic disk was prepared from the above prepared compositions and examined in the same way as shown in Example 23. Results are shown in Table 5. The intermediate layer to use in the invention will be illustrated below in reference to reference examples. Example 24 A primer solution of the following composition was prepared. Vylon 200 100 parts by weight Coranate L 15 Trisacetylacetonatoiron (III) 2 Methyl ethyl ketone 600 Cyclohexanone 300 The primer solution was applied to both sides of a 75-µm thick polyethylene terephthalate base film. The coating weight was adjusted so that the primer layer has a thickness of 0.5 µm after drying. A magnetic paint was prepared separately by thoroughly mixing and dispersing the following components in a ball mill and continuing mixing after the addition of 10 parts by weight of Coranate L as a polyisocyanate compound. The thus prepared magnetic paint was applied to both of the previously formed primer layers. The coating weight was adjusted so that the film thick is 1.0 µm after drying. After drying, the primer layers were calendered at 70°C under a linear pressure of 250 kg/cm, followed by curing at 50°C for 2 days. The coated film was punched into disks 5.25 inch in diameter, and each disk was polished and put into a jacket. The performance of the magnetic disk thus produced was evaluated. (Composition of magnetic paint) Co-containing γ-Fe₂O₃ powder 100 parts by weight Lecithin 2 Esrex A *¹ 20 Nippollan 2304*² 20 Conductex 975 *³ 4 α-Fe₂O₃ 10 Butyl stearate 5 Methyl ethyl ketone 100 Toluene 100 Cyclohexanone 100 *¹ Vinyl chloride-vinyl acetate-vinyl alcohol copolymer made by Sekisui Chemical Co., Ltd. *² Polyurethane resin made by Nippon Polyurethane Industry Co., Ltd. *³ Carbon black made by Columbia Carbon Co., Ltd. Example 25 Magnetic disks were prepared in the same manner as in Example 24 except that the primer solution was prepared by mixing and dispersing the following components in a ball mill. Conductex 975 30 parts by weight Emalgen 910 *¹ 1 Vylon 200 100 Nippollan 2301*² 100 Coranate EH *³ 10 Trisacetylacetonatoiron (III) 1 Methyl ethyl ketone 900 Cyclohexanone 500 *¹ Nonionic surface active agent made by Kao Co., Ltd. *² Polyurethane resin made by Nippon Polyurethane Industry Co., Ltd. *³ Polyisocyanate compound made by Nippon Polyurethane Industry Co., Ltd. Example 26 Magnetic disks were prepared in the same manner as in Example 24 except that the primer solution of the following composition was used. Nippollan 2301 100 parts by weight Sumidule W *¹ 20 Trisacetylacetonatoiron (III) 0.2 Methyl ethyl ketone 600 Cyclohexanone 300 *¹ Polyisocyanate compound made by Sumitomo Bayer Urethane Co., Ltd. Example 27 A primer solution of the following composition was prepared. Vylon 200 80 parts by weight Coranate L 18 Seluline FM-200 *³ 20 Methyl ethyl ketone 700 Cyclohexanone 200 *³ Cellulose nitrate made by Daisel Chemical Industry Co., Ltd. The primer solution was applied to both sides of a 75-µm thick polyethylene terephthalate base film. The coating weight was adjusted so that the primer layer has a thickness of 0.5 µm after drying. A magnetic paint was prepared separately by thoroughly mixing and dispersing the following components in a ball mill and continuing mixing after the addition of 10 parts by weight of Colonate as a polyisocyanate compound. The thus prepared magnetic paint was applied to both of the previously formed primer layers. The coating weight was adjusted so that the film thick is 1.0 µm after drying. After drying, the primer layers were calendered at 70°C under a linear pressure of 250 kg/cm, followed by curing at 50°C for 2 days. The coated film was punched into disks 5.25 inch in diameter, and each disk was polished and put into a jacket. The performance of the magnetic disk thus produced was evaluated. (Composition of magnetic paint) Co-containing γ-Fe₂O₃ powder 100 parts by weight Lecithin 2 Esrex A *¹ 20 Nippollan 2304*² 20 Conductex 975 *³ 4 α-Fe₂O₃ 10 Butyl stearate 5 Methyl ethyl ketone 100 Toluene 100 Cyclohexanone 100 *¹ Vinyl chloride-vinyl acetate-vinyl alcohol copolymer made by Sekisui Chemical Co., Ltd. *² Polyurethane resin made by Nippon Polyurethane Industry Co., Ltd. *³ Carbon black made by Columbia Carbon Co., Ltd. Example 28 Magnetic disks were prepared in the same manner as in Example 27 except that the primer solution was prepared by mixing and dispersing the following components in a ball mill. Conductex 975 30 parts by weight Emalgen 910 *¹ 1 Vylon 200 40 Nippollan 2301 30 Coranate EH 10 Seluline FM-400 30 Methyl ethyl ketone 1100 Cyclohexanone 600 *¹ Nonionic surface active agent made by Kao Co., Ltd. Example 29 Magnetic disks were prepared in the same manner as in Example 27 except that the primer solution of the following composition was used. Nippollan 2301 100 parts by weight Sumidule W *¹ 30 Celnova BTH1/2 *² 10 Methyl ethyl ketone 600 Cyclohexanone 300 *¹ Polyisocyanate compound made by Sumitomo Bayer Urethane Co., Ltd. *² Cellulose nitrate made by Asahi Chemical Industry Co., Ltd. Example 30 Magnetic disks were prepared in the same manner as in Example 27 except that the primer solution of the following composition was used. Unitika Eryther UE-3200 *¹ 90 parts by weight Sumidule IL *² 5 Seluline FM-200 10 Trisacetylacetonatoiron (III) 0.05 Methyl ethyl ketone 700 Cyclohexanone 100 Methyl isobutyl ketone 200 *¹ Polyester resin made by Unitika Ltd. *² Polyisocyanate compound made by Sumitomo Bayer Urethane Co., Ltd. Example 31 Magnetic disks were prepared in the same manner as in Example 30 except that the trisacetylacetonatoiron (III) (00.5 parts by weight) was replaced by dibutyltin dilaurate (0.5 parts by weight). Example 32 Magnetic disks were prepared in the same manner as in Example 30 except that the trisacetylacetonatoiron (III) (0.05 parts by weight) was replaced by triethylenediamine (1 part by weight). Each magnetic disk obtained above was examined in the same was as shown in Example 21. It is noted from results appearing in Table 6 that the intermediate layer improve the resulting disk in the output voltage and the output fluctuation and then a resistance to a solvent.

Claims: -1- A magnetic recording medium which comprises a support coated with a magnetic layer, comprising a magnetic powder, a binder, (I) a first ester having the formula: in which R1 and R2 are each independently a C₁ to C₂₅ branched or straight-chain in which the total carbon number of R1 and R2 is from 22 to 34, and R3 is a C₇ to C₂₉ branched or straight-chain saturated or unsaturated alkyl group and (II) a second ester having the formula: R₄-―O―R₅ (II) in which R4 is a C₁ to C₂₉ branched or straight-chain aliphatic hydrocarbon and R5 is a C₁ to C₂₃ is a branched or straight-chain aliphatic hydrocarbon group or a straight chain C₂₄ to C₃₆ aliphatic hydrocarbon group in which the total carbon number of R4 and R5 is from 15 to 65. -2- A magnetic recording medium as claimed in Claim 1, in which said magnetic layer further comprises (III) a C₁₀ to C₃₀ aliphatic acid and the total carbon number of R4 and R5 is from 16 to 65. -3- A magnetic recording medium as claimed in Claim 1, in which said magnetic layer includes (IV) a C₈ to C₃₀ aliphatic acid modified in that it contains no second ester (II). -4- A magnetic recording medium as claimed in Claim 1, in which said magnetic layer comprises the ester compounds (I) and (II) in a total amount of 1 to 15 percent by weight based on the magnetic powder at a weight ratio of (I) to (II) from 10/90 to 90/10. -5- A magnetic recording medium as claimed in Claim 2, in which said magnetic layer comprises 1 to 40 percent by weight of (I), 10 to 80 percent by weight of (II) and 1 to 40 percent by weight of (II) in a total amount of 1 to 15 percent by weight based on the magnetic powder. -6- A magnetic recording medium as claimed in Claim 3, in which said magnetic layer comprises (I) and (IV) in a total amount of 1 to 15 percent by weight based on the magnetic powder at a weight ratio of (I) to (IV) from 95/5 to 10/90. -7- A magnetic recording medium as claimed in Claim 1, which further comprises, between said support and said magnetic layer, an intermediate layer comprising (1) at least one resin which is a hydroxy-containing polyester and/or hydroxy-containing polyurethane, (2) a polyisocyanate compound and (3) trisacetylacetonatoiron (III). -8- A magnetic recording medium as claimed in Claim 1, which further comprises, between said support and said magnetic layer, an intermediate layer comprising (1) at least one resin which is a hydroxy-containing polyester and/or a hydroxy-containing polyurethane, (2) a polyisocyanate compound and (3) cellulose nitrate. -9- A magnetic recording medium as claimed in Claim 7, in which said intermediate layer comprises 100 parts by weight of (1), 2 to 40 parts by weight of (2) and 0.01 to 8 parts by weight of (3). -10- A magnetic recording medium as claimed in Claim 8, in which said intermediate layer comprises 100 parts by weight of (1), 2 to 40 parts by weight of (2) and 5 to 50 parts by weight of (3).

Inventors: ABE, CHIAKI, ISHIKAWA, AKIRA, KANAI, HIROYUKI, MINAMI, TAKAHIDE, SUZUE, SHIGETOSHI, TAKEUCHI, TAKASHI
Applicants: KAO CORPORATION
Application year: 1986
Main classification: G11B5
IPC codes: G11B5