JPH038016B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improved magnetic recording media. More specifically, the present invention relates to a magnetic recording medium with excellent magnetic properties and durability, which is manufactured using a magnetic paint that improves the dispersibility of magnetic powder and the adhesion between the magnetic powder and a binder. Magnetic powder in magnetic recording media such as magnetic tapes and magnetic disks is required to have a high degree of dispersibility. Magnetic recording media are generally manufactured by kneading magnetic powder, a binder, various additives, and solvents, then applying a magnetic paint uniformly onto a plastic film or sheet substrate, drying it, and then finishing the magnetic layer with a mirror finish. However, unless the magnetic powder in the magnetic paint is sufficiently dispersed and peptized to remove aggregated particles, it is not possible to create a uniform and smooth magnetic layer with a high packing density. Non-uniformity in the magnetic layer due to agglomerated particles of magnetic powder has a serious adverse effect on the electromagnetic conversion characteristics and magnetic properties of the magnetic tape. In other words, it causes a decrease in output, an increase in noise, dropouts, etc. Additionally, if the adhesive strength between the magnetic powder and the binder is weak, the magnetic powder may peel off from the magnetic coating layer (so-called "powder shedding") when the magnetic recording medium and the recording head or playback head slide. This easily occurs, and the coating surface becomes rough, impairing the durability of the magnetic recording medium. In reality, conventional magnetic recording media have been put into practical use with insufficient durability. As described above, the dispersibility of the magnetic powder in the magnetic paint and the adhesion with the binder are very important in improving the performance of the magnetic recording medium. Improvements in the dispersibility of magnetic powder have been studied from various viewpoints, and it has been proposed to improve the dispersibility by adding a suitable surfactant to the magnetic paint formulation. As such a surfactant, an alkyl imidazoline compound is used (Japanese Patent Application Laid-Open No. 1989-1999).
32304), those using an alkyl polyoxyethylene phosphate ester neutralized with an alkylamine (Japanese Patent Application Laid-Open No. 53-78810), those using a long-chain alkyl phosphate ester (Japanese Patent Application Laid-Open No. 1983-147507, Patent Application No. 1983) −
49629), amines and their derivatives, phosphate esters, and polyoxyethylene phosphate esters are often used. In addition, there has been a proposal that dispersibility is improved by surface-treating magnetic powder and then turning it into a paint.
56-49769), and a method in which metal powder is treated with a titanium coupling agent to measure dispersion stability and at the same time prevent the deterioration of the magnetic coating film over time (Japanese Patent Application Laid-open No. 56-88471). In addition, a method to improve the durability of the magnetic coating film by improving the adhesion between the magnetic powder and the binder is to use a silane coupling agent that has a functional group reactive with the binder (Japanese Patent Laid-Open No. 54-7310 ),
Coated with a reaction product of an aminofunctional silane coupling agent, an isocyanate compound, and an epoxy compound (Japanese Patent Application Laid-Open No. 1989-1999)
143533), a method in which magnetic powder is treated with a titanium coupling agent having a double bond in the binder and an unsaturated bond capable of radical polymerization (JP-A-56-
111129), and one using a compound having at least four radiation-sensitive acrylic double bonds in the molecule as a binder (Japanese Patent Application Laid-Open No. 57-40744). As described above, although much research has been carried out on improving the dispersibility of magnetic powder in magnetic coatings and the durability of magnetic coatings, no satisfactory improvement has yet been reached. In view of the above-mentioned problems of magnetic recording media, the present inventors conducted extensive research to obtain a magnetic recording medium with excellent dispersibility of magnetic powder and durability of the coating layer, and as a result, the present inventors discovered a specific A magnetic recording medium containing magnetic powder coated with a reaction product of a compound and one or more compounds selected from a specific group of compounds having a functional group capable of reacting with an isocyanate group. The present invention was completed by discovering that the magnetic powder has good dispersibility, the coating layer has excellent durability, and furthermore, the electromagnetic conversion characteristics are excellent. That is, the present invention relates to the following () and () () a polyisocyanate compound having a molecular weight of 100 to 1000 having two or more isocyanate groups in one molecule; () a hydrolyzable alkoxy compound in one molecule; One or more isocyanate compounds selected from the group consisting of isocyanate compounds with a molecular weight of 140 to 1,500 having a silane group and one or more isocyanate groups, and the following (), (), ( ), () and () () C6-22 aliphatic alcohol, () C6-22 aliphatic carboxylic acid, () C6-22 hydroxy fatty acid or its salt or ester, ( ) a fatty acid partial ester of a polyhydric alcohol; () a magnetic powder coated with a reaction product with one or more compounds selected from the group consisting of aliphatic amines having 4 to 22 carbon atoms; The present invention provides a magnetic recording medium characterized by the following. Isocyanate compounds belonging to the group consisting of () and () above according to the present invention include toluene diisocyanate, methylene bisphenylene diisocyanate, hexamethylene diisocyanate, 1 mol of trimethylolpropane and toluene diisocyanate. Reaction product with 3 moles, OCN-( _CH2 ) ₆ -NHCONH( _CH2 ) _3Si
(OCH ₃ ) ₃ , etc. can be mentioned. Examples of the aliphatic alcohol having 6 to 22 carbon atoms according to the present invention include monohydric alcohols such as stearyl alcohol, oleyl alcohol, and dodecyl alcohol. Examples of the aliphatic carboxylic acids having 6 to 22 carbon atoms according to the present invention include fatty acids such as stearic acid and palmitic acid. Examples of the hydroxy fatty acid having 6 to 22 carbon atoms, a salt thereof, or an ester thereof according to the present invention include 12-hydroxystearic acid, magnesium 12-hydroxystearate, butyl 12-hydroxystearate, and the like. Examples of the fatty acid partial ester of polyhydric alcohol according to the present invention include pentaerythritol tripalmitate, sorbitan trioleate, glycerin dilaurate, and the like. The aliphatic amine having 4 to 22 carbon atoms according to the present invention has the general formula R-NH ₂ ,

【formula】

[Formula] (R, R', R'' represent an alkyl group) primary amine, secondary amine or tertiary amine, as well as amine compounds such as alkyldiamine and alkyltriamine.The present invention Examples of magnetic powders include fine needle-shaped metal oxides such as γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and CrO ₂ , as well as Co-coated γ-Fe ₂ O ₃ and Co-doped γ-Fe _{2 .} O ₃
γ-Fe ₂ O ₃ , iron metal powder, microplate-like barium ferrite and its
Magnetic powder in which a part of Fe atoms are substituted with one or more of Ti, Co, Zn, V, Nb, etc., Co, Fe-
Examples include ultrafine powder of metals or alloys such as Co, Fe-Ni, etc. Among these, iron metal powder has particularly poor chemical stability, so small amounts of nickel, cobalt, titanium, silicon, aluminum, etc. in the form of metal atoms, salts, and oxides are added or surface treated to improve this. However, these can also be used. In order to stabilize iron metal powder, a thin oxide film may be formed on the surface in a weakly oxidizing atmosphere, and metal powder treated in this way can also be used. The size of these magnetic powders is 1μ to 0.15μ on the long axis,
It is preferable that the minor axis is 0.15μ to 0.015μ. If the long axis is larger than 1μ, dispersion becomes easier, but it is not preferable because recording of short wavelengths becomes disadvantageous and noise becomes large. When the long axis is smaller than 0.15μ, even the magnetic recording medium of the present invention cannot be said to have sufficient dispersibility. In the present invention, the method for obtaining the magnetic powder coated with the reaction product of the isocyanate compound () and () above and a compound selected from the compound group () to () above is not particularly limited. For example, the method shown below is exemplified. (a) Magnetic powder (i) is first heat-treated with isocyanate compound (ii) in an inert organic solvent, and then one or two selected from the group of compounds () to () above is applied.
A method of heat treating more than one species of compound (iii). (b) A method in which the above (i), (ii), and (iii) are mixed all at once in an inert organic solvent and then heated. (c) A method in which (ii) and (iii) are first reacted in an inert organic solvent, and then (i) is added and heat treated. The magnetic recording medium of the present invention can be obtained by adding a binder and a solvent to the magnetic powder processed by the above processing method to form a paint, and applying it to a polyester film, etc. This will be explained in Examples together with the powder processing method. The amount of the isocyanate compound () and () used in the present invention is 0.05 to 0.05 to
About 3% by weight, preferably 0.2 to 1.5% by weight
It is. In addition, the amount of the compound selected from the group of compounds () to () above should be such that they do not remain as unreacted substances in terms of stoichiometry, and the isocyanate group in the polyisocyanate compound is It is preferable that the amount is such that at least one remains. It goes without saying that it is preferable to set reaction conditions such as reaction temperature and reaction time so that the reaction rate is the highest. Examples of inert solvents that can be used in the treatment of magnetic powder include methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, cyclohexanone, benzene, xylene, and toluene. The binder used when turning the treated powder into a paint is a resin binder that is soluble in organic solvents, and is used to fix the above-mentioned magnetic powder onto the substrate and the magnetic powder together with the necessary strength to form a magnetic layer. It is sufficient that it fulfills its role in as small a quantity as possible, and even those that are concerned about deteriorating the dispersibility of magnetic powder in conventional paints can be used in normal paint-forming methods. Examples of these resin binders include polyurethane,
Polyester, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, polyacrylonitrile, nitrile rubber, epoxy resin, alkyd resin, polyamide, polyacrylic ester, polymethacrylic ester, polyvinyl acetate, polyvinyl butyral, vinylidene chloride, chloride Vinylidene copolymers, nitrified cotton, ethyl cellulose, etc. may be used alone, but two or more types are usually used as a mixture. Further, in order to adjust the hardness of the resin, a plasticizer or a hardening agent may be added. The amount of the binder is generally 15 to 60 parts by weight per 100 parts by weight of the magnetic powder. Even if the binder has the highest binding strength, if it is less than 15 parts by weight, the strength of the magnetic coating will be weak and the adhesive strength between the substrate and the magnetic coating will be insufficient. If the amount is more than 60 parts by weight, the concentration of magnetic powder in the magnetic coating film becomes small, resulting in a decrease in reproduction output, which is disadvantageous, and the properties of the coating film may also deteriorate. The solvent used for making paint has the ability to dissolve the binder used and has a boiling point of 50°C to 150°C.
Something in between is desirable. If the boiling point is too low, the coating will dry before the magnetic powder is oriented in the magnetic field after coating, making this treatment impossible. The binder is selected from the above viewpoints depending on the type of binder, but it goes without saying that it should be selected in consideration of toxicity and environmental issues. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. Example 1 150 g of Co-coated γ-Fe ₂ O ₃ with a major axis diameter of 0.35 μm and an axis ratio of 1/10, 300 g of methyl ethyl ketone, and 1.5 g of methylene bisphenylene diisocyanate were placed in a 4-necked flask with a cooling tube, and Stir for 1 hour at °C.
Thereafter, the magnetic powder was washed with a large amount of methyl ethyl ketone. Next, 120 g of the magnetic powder, 300 g of methyl ethyl ketone, and 1.4 g of stearyl alcohol were mixed into 4
Transfer to a two-necked flask and stir at 80-90℃ for 1 hour.
A treated magnetic powder was obtained. The treated magnetic powder was then washed with a large amount of methyl ethyl ketone. 1 of the treated magnetic powder and a vinyl chloride-vinyl acetate copolymer (VAGH manufactured by Union Carbide Co., Ltd., USA) and a polyurethane resin (Nituporan 2304 manufactured by Nippon Polyurethane Industries Co., Ltd.) as binders:
A magnetic paint was obtained by mixing 25% by weight of a mixture of 1:1 (weight ratio) based on the magnetic powder and 130 g of a 1:1 (weight ratio) mixture of methyl ethyl ketone and cyclohexanone as a solvent and kneading the mixture in a ball mill for 24 hours. . Further, this magnetic coating material was applied onto a polyester film using a 30 μm applicator, subjected to magnetic field orientation, dried with hot air, and then calendered to smooth the coating film to obtain a magnetic recording medium. Next, the magnetic recording medium was measured for its squareness ratio, which is a measure of evaluating the dispersibility of the magnetic powder, and its abrasion loss, which is used to evaluate the durability of the magnetic recording medium. The results are shown in Table-1. The abrasion loss was measured by rubbing a magnetic recording medium 3 cm wide and 50 cm long with emery paper CC-1000 under a constant load for 30 minutes. Further, in order to examine the electromagnetic conversion characteristics, the magnetic recording medium was cut into a width of 6.25 mm, mounted on a commercially available open reel deck, and the reproduction output at 3 KHz was measured. The results are shown in Table-1. This value is Comparative Example 1
The playback output of the magnetic recording medium prepared in (described later) is set to 0.
It is expressed as a relative value. Example 2 A treated magnetic powder, a magnetic paint, and a magnetic recording medium were obtained in the same manner as in Example 1, except that 1.6 g of 12-hydroxystearic acid was used in place of the stearyl alcohol used in Example 1. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1. Example 3 Magnesium 12-hydroxystearate 3 was used instead of stearyl alcohol used in Example 1.
A treated magnetic powder, a magnetic coating material, and a magnetic recording medium were obtained in the same manner as in Example 1 except that g was used. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1.
The results are shown in Table-1. Example 4 4 g of pentaerythritol tripalmitate instead of stearyl alcohol used in Example 1
A treated magnetic powder, a magnetic coating material, and a magnetic recording medium were obtained in the same manner as in Example 1 except that the following was used.
The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1. Example 5 Instead of methylene bisphenylene diisocyanate used in Example 1 A treated magnetic powder, a magnetic coating material, and a magnetic recording medium were obtained in the same manner as in Example 1, except that 2 g of dodecylamine was used instead of stearyl alcohol, and 1 g of dodecylamine was used instead of stearyl alcohol. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1. Example 6 A treated magnetic powder, a magnetic paint, and a magnetic recording medium were obtained in the same manner as in Example 5, except that 1.4 g of palmitic acid was used in place of the dodecylamine used in Example 5. Example 1 for the magnetic recording medium
The squareness ratio, wear loss, and regenerated output were measured according to the method. The results are shown in Table-1. Example 7 A treated magnetic powder, a magnetic paint, and a magnetic recording medium were obtained in the same manner as in Example 5, except that 5 g of sorbitan trioleate was used in place of the dodecylamine used in Example 5. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1. Example 8 Instead of 1.5 g of methylene bisphenylene diisocyanate used in Example 1, tolylene diisocyanate (2,4-tolylene diisocyanate 80
Example 1 except that 1.0 g of a mixture of 20% by weight and 2,6-tolylene diisocyanate was used.
A treated magnetic powder, a magnetic paint, and a magnetic recording medium were obtained in the same manner as described above. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1. Example 9 Used in Example 5 Instead of (CH ₃ O) ₃ Si(CH ₂ ) ₃ NHCONH
A treated magnetic powder, a magnetic paint, and a magnetic recording medium were obtained in the same manner as in Example 5, except that 2 g of (CH ₂ ) ₆ NCO was used. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The time is shown in Table-1. Comparative example 1 Long axis diameter 0.35 μm used in Example 1, axial ratio 1/10
A magnetic paint was prepared in the same manner as described in Example 1 by adding only 4.5 g of soybean oil lecithin as a dispersant to 150 g of Co-adhered γ-Fe ₂ O ₃ without surface treatment of the magnetic powder. And a magnetic recording medium was obtained. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1.
The results are shown in Table-1. Comparative Example 2 A magnetic paint and a magnetic recording medium were obtained in the same manner as in Comparative Example 1, except that 4.5 g of octyl phosphate was used in place of the soybean oil lecithin used in Comparative Example 1. The squareness ratio, abrasion loss, and reproduction output of the magnetic recording medium were measured in accordance with Example 1. The results are shown in Table-1.

[Table] As is clear from Table 1, the magnetic recording medium of the present invention is excellent in both the dispersibility of the squareness ratio and the abrasion resistance of the coating layer. Example 10 In a 4-necked flask equipped with a cooling tube, 300 g of methyl ethyl ketone, 2 g of the isocyanate compound used in Example 5, and 1 g of dodecylamine were placed at 90°C.
Then, 150 g of Co-coated γ-Fe ₂ O ₃ used in Example 1 was added, and the mixture was further stirred at 90° C. for 1 hour to obtain treated magnetic powder. The treated magnetic powder was then washed with a large amount of toluene. The treated magnetic powder was mixed with vinyl chloride-vinyl acetate copolymer (manufactured by Union Carbide Co., USA) as a binder.
VAGH) and polyurethane resin (Esten 5033)
50% by weight of the magnetic powder in a 1:2 mixture of
0.4% by weight of carbon black (Lion Akzo's KETSUCHEN BLACK E) as an antistatic agent based on the magnetic powder, 0.2% by weight of alumina with an average particle size of 0.7μ as an abrasive based on the magnetic powder, and butyl as a lubricant. 0.7% by weight of stearate based on magnetic powder,
A 1:1:1 (weight ratio) mixture of methyl ethyl ketone/cyclohexanone/toluene (weight ratio) was mixed with the magnetic powder in an amount of 400% by weight, and the mixture was kneaded in a ball mill for 72 hours. A magnetic paint was obtained by adding 8% by weight of Coronate L) to the magnetic powder and stirring until the system became homogeneous. Further, the magnetic paint was applied onto a polyester film using a 30 μm applicator, dried with hot air without magnetic field orientation, and then calendered to smooth the coating and punched out into a disk shape to obtain a magnetic recording medium. The glossiness, residual magnetic flux density (Br), durability (output drop after 10 million passes/track), and FR-out were measured for the magnetic recording medium. The results are shown in Table-2. however,
The measurement conditions for FR-out are as follows. Relative speed: 4.0 m/sec Recording frequency: 4 MHz Recording head: Sendust Playback head: Ferrite Comparative Example 3 Co-coated γ-Fe ₂ O ₃ powder used in Example 1 was used as a dispersant without surface treatment. GAFAC
3% by weight of RE610 (polyoxyethylene-added alkylaryl sesquiphosphate) was added to the magnetic powder, and a magnetic paint and a magnetic recording medium were prepared by the method of Example 10, and the four items shown in Example 10 were prepared. I took measurements. The results are shown in Table-2.

[Table]
Example 11 500 g of toluene, 0.8 g of the isocyanate compound used in Example 10, and 1.2 g of dodecylamine were placed in a 4-necked condenser flask and stirred at 90° C. for 1 hour. Next, ultrafine grained Fe-Co alloy (average grain size 250 Å, Hc: 1500 Oe, σs: 15 emu) 50
g was added thereto, and the mixture was further stirred at 90°C for 1 hour to obtain treated magnetic powder. The treated magnetic powder was then washed with a large amount of toluene. A magnetic paint and a magnetic recording medium were obtained according to the method of Example 10. The four measurements shown in Example 10 were performed on the magnetic recording medium.
The results are shown in Table-3. Comparative Example 4 The ultrafine-grained Fe-Co alloy used in Example 11 was subjected to no surface treatment, and the dispersant used in Comparative Example 3 was added in an amount of 3% by weight to the magnetic powder. A magnetic paint and a magnetic recording medium were prepared, and the four items shown in Example 10 were measured. The results are shown in Table-3.

[Table] Yes.

Claims (1)

[Scope of Claims] 1 The following () and () () A polyisocyanate compound with a molecular weight of 100 to 1000 having two or more isocyanate groups in one molecule, () Hydrolyzed into one molecule one or more isocyanate compounds selected from the group consisting of isocyanate compounds with a molecular weight of 140 to 1,500 having an alkoxysilane group and one or more isocyanate groups, and the following (), () , (), () and () () Aliphatic alcohol having 6 to 22 carbon atoms, () Aliphatic carboxylic acid having 6 to 22 carbon atoms, () Hydroxy fatty acid having 6 to 22 carbon atoms or salt thereof or ester thereof , () fatty acid partial ester of a polyhydric alcohol, () a magnetic powder coated with a reaction product with one or more compounds selected from the group consisting of aliphatic amines having 4 to 22 carbon atoms. A magnetic recording medium characterized by containing: