JPS63113926A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having good running durability by providing an org. compd. which is an acryl ester compd. polymer contg. a perfluoroalkyl groups and >=50% of which is >=4,000mol.wt. on a thin ferromagnetic metallic film. CONSTITUTION:The thin ferromagnetic metallic film 2 is formed on a nonmagnetic substrate 1 and further, a top coat 3 consisting of the acryl ester compd. polymer contg. the perfluoroalkyl groups is formed on the film 2. Glass, Al or a high-polymer supporting base material of acrylic, etc. is formed to 5-100mum thickness as the substrate 1. The thin ferromagnetic metallic film 2 is formed of Fe, Ni, etc., to 0.05-1.0mum thickness by a sputtering method or the like. The top coat layer 3 has the org. compd. which is the acryl ester compd. polymer contg. the perfluoroalkyl group and >=50% of which is >=4,000 mol.wt. The recording medium having the excellent recording and reproducing characteristics and the satisfactory performance even in the corrosion resistance, repetitive running durability and environmental resistance is obtd.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a magnetic recording medium having excellent durability and environmental resistance, and particularly to a thin film deposition type magnetic recording medium for high-density one-time recording. [Prior Art] Conventionally, coated magnetic recording media have been developed which have a magnetic layer on which ferromagnetic fine particles are uniformly dispersed in a polymeric binder on a non-magnetic support usually made of a plastic film such as polyester. It is widely used, and in recent years, ferromagnetic thin-film magnetic recording media, in which a thin film of metal or the like is formed on a non-magnetic support by methods such as vapor deposition or sputtering, have been developed, and some have been put into practical use. There are some things. These ferromagnetic thin film magnetic recording media are attracting attention as high-density recording media because they can dramatically improve recording density compared to coated magnetic recording media. However, if the ferromagnetic metal thin film layer is Co-Ni alloy or C
Conventional ferromagnetic metal magnetic recording media such as o-Cr alloys have had practical problems in terms of corrosion resistance and wear resistance. In other words, a ferromagnetic metal film such as Co-Ni does not have corrosion resistance by itself, and as the surface of the ferromagnetic metal film is flattened due to the demand for higher density, the wear resistance deteriorates. . In order to solve these problems,
Those in which the surface of the alloy film is oxidized (for example, JP-A-53-
85403), those with a protective layer of nitride (e.g., JP-A-57-167134), and those whose surface is coated with various organic materials (e.g., JP-A-57-123536).
etc. are being considered. However, with VTR tapes in which the lubricant is coated on a ferromagnetic metal film, the reproduced image flickers for a short time (i.e., the head is clogged) in the early stages of repeated running.
It cannot be said that the durability is sufficient. In addition, with regard to improving corrosion resistance, the methods for improving corrosion resistance, such as the above-mentioned surface coating, did not guarantee sufficient corrosion resistance when the product was left in high humidity for a long time or in other conditions where dew condensation was likely to occur. [Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the conventional magnetic recording medium described above, has excellent recording and reproducing characteristics, and has practical properties in terms of corrosion resistance, repeated running durability, and environmental resistance. The purpose of the present invention is to provide a magnetic recording medium with sufficient performance. [Means for Solving the Problems] The present invention provides an acrylic ester compound polymer containing perfluoroalkyl groups, in which 50% or more has a molecular weight of 4000 or more, on a ferromagnetic metal thin film laminated on a non-magnetic substrate. A magnetic recording medium characterized by containing a certain organic compound. The magnetic recording medium of the present invention will be explained below with reference to the drawings. In the following description, quantitative ratios are based on weight unless otherwise specified. FIG. 1 is a schematic diagram showing an example of the magnetic recording medium of the present invention, in which a ferromagnetic metal thin film 2 is formed on a nonmagnetic substrate l, and an acrylic material containing perfluoroalkyl groups is further formed on the ferromagnetic metal thin film 2. A top coat 3 made of an ester compound polymer is formed. FIG. 2 is a diagram showing another example of the magnetic recording medium of the present invention, in which an intermediate layer 4 is formed between a ferromagnetic metal thin film 2 and a top coat 3. As the non-magnetic substrate 1 of the magnetic recording medium of the present invention, in addition to glass, aluminum, surface oxidized aluminum, etc.
Polyester, cellulose, acrylic, polyamide, polyimide, polyamideimide, polyolefin, polyfluoroolefin, pyrivinyl chloride, polyvinyl acetate, vinyl chloride/vinyl acetate copolymer, polyvinylidene chloride, polycarbonate, phenolic resin, polyvinyl acetate, polyvinyl chloride/vinyl acetate copolymer, Ether sulfone, polyether ether ketone, polyacecool, polyphenylene oxide,
Examples include polyphenylene sulfide. The thickness of the nonmagnetic substrate 1 is preferably 5 to 100 μm. The ferromagnetic metal thin film 2 laminated on the nonmagnetic substrate 1 is F.
e, Ni, Co, Fe-Co, Co-Ni,
Co-Cr. Co-P, Fe-Co-B, Co-N1-P,
Co-V. Examples include Co-Re and Co-Pt. Furthermore, Fe is added between the ferromagnetic metal thin film and the non-magnetic substrate to improve properties.
-Ni series, Co-Zr series which is an amorphous magnetic permeability material, Fe
-P-C system, Co-3i-B system, etc., Af, Cr. An intermediate film such as a thin film of a nonmagnetic metal such as Ti or Ge may be provided. The thickness of the ferromagnetic metal thin film is 0.05 to 1.0 μm
is preferred. For forming a ferromagnetic metal thin film on a nonmagnetic substrate, known methods such as sputtering and electron beam evaporation can be used. From the viewpoint of enabling high-density recording, a Co--Cr alloy, especially a Co--Cr alloy containing 15 to 23 wt% Cr, is excellent as a material for the ferromagnetic metal thin film layer 2. The reason for this is that the Co-Cr alloy with the above-mentioned structure forms a perpendicularly magnetized film with an axis of easy magnetization perpendicular to the film surface, and there is no effect of demagnetizing field, which is a disadvantage of the longitudinal recording method, and high-density recording is possible due to woody structure. It is a point. When a Co-Cr alloy is used for a ferromagnetic metal thin film, it is necessary to prepare the film at a high temperature in order to obtain a large coercive force, and the nonmagnetic substrate is required to have heat resistance. In this case, the non-magnetic substrate is preferably polyimide, which has excellent heat resistance, especially paraphenylenediamine (PPD).
) or PPD and diaminodiphenyl ether (D
A copolymerized polyimide of a diamine component (A'DE) and a tetracarphonic acid component consisting of biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PNDA) is excellent. This copolyimide film has high heat resistance and tensile strength, and has an elastic modulus of 300 to 900 kg/mm2, which is an appropriate value as a base film for magnetic recording media. Furthermore, this copolymerized polyimide film has a coefficient of thermal expansion of 1 to 3
It can be adjusted in the range of 10-', cm/cm/°C, and can prevent medium curl caused by the difference in thermal expansion with the ferromagnetic metal thin film or internal stress generated during film formation. In order to make the mechanical and thermal properties of the polyimide nonmagnetic substrate 1 suitable for the above-mentioned magnetic recording medium, the diamine component used to produce the aromatic polyamic acid must be in proportion to the total diamine component. PPl7 in a usage proportion of about 40 to 95 mol %, especially in the range of 45 to 90 mol %.
and about 5 to 60 mol%, especially 1
It is preferable to consist of two components with DADE in a usage ratio of 0 to 55 mol%. Further, the tetracarboxylic acid component for producing the aromatic polyamic acid is about 10 to 90 mol%, especially 15 to 85% by mole based on the total tetracarboxylic acid component.
Preferably, it comprises BPDA in an amount of mol % and PMDA in an amount of about 10 to 90 mol %, in particular 15 to 85 mol %, based on the total tetracarboxylic acid component. As the intermediate layer 4, known materials such as oxides, nitrides, borides, carbides, sulfides, phosphides, fluorides, metal films, carbon films, etc. are used. The manufacturing method involves modifying the surface of the ferromagnetic metal thin film using physical deposition methods such as sputtering, vacuum evaporation, or ion blating, chemical deposition such as CVD, plasma treatment, or ion implantation. Examples include a method of forming a layer. The thickness of the middle layer 4 is preferably 30 to 1000 people,
More preferably, it is 50-300A. If the thickness is increased, the protective durability function will be improved, but the spacing loss will also be increased (which is undesirable because the reproduction signal output will be lowered).If it is too thin, the protective function will be decreased and the durability may also be reduced, which is undesirable. Cobalt oxide is particularly suitable as a material for the intermediate layer 4 formed on the CoCr alloy ferromagnetic metal thin film.The cobalt oxide intermediate layer 4 is formed by sputtering in an inert gas containing oxygen at a predetermined pressure. Vacuum deposition method under diluted oxygen or physical vapor deposition method such as ion brating method,
Alternatively, the surface of the Co alloy ferromagnetic metal thin film is subjected to plasma oxidation treatment to directly deposit or form an oxide layer on the surface of the ferromagnetic metal thin film. The cobalt oxide layer prevents adhesion between the magnetic recording layer and the head and is extremely effective in improving wear resistance. The cobalt oxide intermediate layer 4 plays a major role in protecting the magnetic recording layer 2, and is also good for compatibility with metal heads, ferrite heads, etc. (and also reduces the surface friction coefficient. The effect is remarkable when the outermost part of the cobalt layer is Co3O4.The acrylic ester compound containing a perfluoroalkyl group used for the top coat 3 in the present invention is acrylic acid or methacrylic acid containing a perfluoroalkyl group. These are oligomers and polymer derivatives of acid esters and their derivatives. Examples include: (i) CH2=CHCoO(CH2)nR1(ii)
) CH2=C(CH,)Coo (CH2). R

[(iii) CH2=C(CF3)Coo (CH2
) n(iv) CH2=C(C1'T3)CoO(C
H2) It is a polymer, oligomer, or polymer obtained by polymerizing monomers such as nR+. However, (i) to (iv) above
n is preferably 1 to 10. Rr represents a perfluoroalkyl group. The number of carbon atoms in Rr is preferably 2 to 15. Of these (CH2). is an n-(normal) linear type, i
s. - type and tert- type branched type. Also,(
A part of CH2)n may have a hydroxy group, a carboxyl group, an amino group, an amide group, a sulfonic acid group, a phosphoric acid group, etc. As the top coat 3 of the magnetic recording medium, it is preferable that a perfluoroalkyl group-containing acrylic ester compound polymer having a large molecular weight is included, and it is particularly effective when it contains a large amount of components with a molecular weight of 4000 or more. That is, more than half (50% or more) of the perfluoroalkyl group-containing acrylic ester compound polymer
is preferably occupied by molecules having a molecular weight of 4,000 or more, more preferably 8,000 or more. An acrylic ester compound polymer in which 50% or more of the molecules have a molecular i of 4000 or more means that the center of the molecular weight distribution is 4000 or more.
4,000 or more, or a mixture of a high molecular weight component of 4,000 or more and a low molecular weight component of 4,000 or less,
There are cases where the ratio of the above components is large. When the main component is an acrylic ester compound polymer having a molecular weight of 4000 or less, head clogging is likely to occur and durability is poor. Methods for measuring molecular weight include conventional methods such as ultracentrifugation, viscosity, light scattering, and osmotic pressure measurement. Further, the content of perfluoroalkyl groups is preferably in the range of 25% or more in terms of molecular weight ratio to the entire molecule. 25
%, durability deteriorates and corrosion resistance also deteriorates due to a decrease in water repellency. The amount of deposition on the ferromagnetic metal thin film is as follows:
0.1-50mg, /rr? is preferable, and more preferably 0.
2 to 20 mg/rrr is preferred. Coating amount is 0.1mg
If it is less than 50 mg/rr, it is difficult to obtain effective durability and output uniformity (and if it is more than 50 mg/rr, the top coat will become thicker and the top cord will slide onto the head due to head sliding. As the top coat 3 is deposited on the ferromagnetic metal thin film 2, a spacing loss occurs and a decrease in high frequency output is observed.Reverse roll method, bar coating method, etc. are typical methods for depositing the top coat 3 on the ferromagnetic metal thin film 2. The following methods can be applied: coating using a conventional method, vacuum deposition using resistance heating, or polymerization using electron beams or ultraviolet light with a monomer coated.Contains perfluoroalkyl groups. The coating state of the top coat made of the acrylic ester compound polymer does not necessarily have to be a uniform continuous film, but may be discontinuous like spots. It is also possible to use various organic lubricants in combination. Furthermore, when the substrate 1 is a non-magnetic substrate film, a structure in which various back coat layers are added for protection, lubricity, reinforcement, and other purposes is also effective. Examples] The present invention will be explained below with reference to Examples. Molecule 1 was measured by ultracentrifugation. When the molecular weight is measured by ultracentrifugation, the obtained molecular weight is the weight average molecular weight. The following Examples The evaluation method is as follows. <Tape evaluation method> Output frequency characteristics: Record a single signal of 4, 5 MHz, 7, 5 MHz, and measure the playback output. The standard is a commercially available metal coating type. This is expressed as OdB using a tape. Pass durability test: The number of runs until the output decreases by 3 dB or more from the initial output level in a repeated running durability test at 20°C, 965% RH and -5°C. Corrosion resistance Test: Check for rust on the media surface after storage test at 50°C and 80% RH. Disc evaluation method> Output frequency characteristics: Record and reproduce a single signal of 1, 3 MHz, 7, 0 MHz. Measure the output. Durability: Measure the change in still playback output over time in an environment of 20°C and 285% RH. If the output decreases within 3 dB after 50 hours, ○
shall be. Example 1 70 mol of PPD and 30 mol of DADE as diamine components
A polyimide film with a thickness of 10 μm produced by copolymerizing 20 moles of BPDA and 80 moles of PMD A as the mole and tetracarboxylic acid components was used as a nonmagnetic substrate, and an electron beam was applied to the heating device on this nonmagnetic substrate. Co78wt%-C was produced using a magnetic tape connection film-forming device with
A perpendicularly magnetized film with r22wt% was heated at 0.1 μm/sec while heating the polyimide film to 230°C.
A ferromagnetic metal thin film was formed to a thickness of about 0.4 μm at a film formation rate of c. The coefficient of thermal expansion of the polyimide film used is 1
, 6 X 10-5cm/cm/0C,
The tensile elastic constant was 490 kg/m m2. Co was sputtered on top of the Co--Cr perpendicularly magnetized film in argon gas containing 10% oxygen to form a 100A thick cobalt oxide thin film as a protective layer. Furthermore, 5 mg of an acrylic ester compound containing a perfluoroalkyl group (molecular weight 50,000, 100% component with a molecular weight of 4,000 or more) was dissolved in a solvent of toluene:methyl isobutyl ketone = 1:l and placed on the cobalt oxide layer by the reverse roll method. /rr
R coated and dried. The magnetic sheet thus obtained was slit into a width of 8.0 mm. The curl of this tape is □<0. lm
The amount was as small as m-' and caused no practical problems. This tape was mounted in an 8 mm VTR tape cassette, and tested for output frequency characteristics, still durability, pass durability test, corrosion resistance test, etc. using an 8 mm video deck. The evaluation results are shown in Table 1, and it can be seen that it has excellent recording/reproducing characteristics, good pass durability, and corrosion resistance. Example 2 The acrylic ester compound in Example 1, ? 1. Molecules [8000 (approximately 95% of components with a molecular weight of 4000 or more)
), a magnetic tape was prepared and evaluated under the same conditions as in Example 1, except that it was dissolved in toluene, applied at a rate of 15 mg/rd by the reverse roll method, and dried. Evaluation results first
As shown in the table, it can be seen that the results are good as in Example 1. Example 3 The acrylic ester compound in Example 1 was added to 1,000 CH2
-CHji. CoOCH2CH2-n C3F7 was used to change the molecular fi 10,000 (to about 97% of components with a molecular weight of 4000 or more), dissolved in toluene: methyl ethyl ketone, coated with a bar coater method at 2 mg/rd, and magnetically coated under the same conditions as in Example 1, except that it was dried. A tape was produced and evaluated. The evaluation results are shown in Table 1. It can be seen that similar to Example 1, the results are good. Example 4 Co80w on 11.5 μm thick polyester film
A ferromagnetic metal thin film having a thickness of 0.15 μm was obtained by continuously diagonally depositing a t%-Ni 20 wt% alloy in a trace oxygen atmosphere. On top of this, an acrylic ester compound (molecular weight 50,000, 100% of components with a molecular weight of 4000 or more) consisting of 1,000 CH2-CH''+.C00CH2CH2-n CB F+7 was added to toluene: methyl isobutyl ketone 1
The magnetic tape was dissolved in a solvent of 1 and coated with a bar coater method at 8 mg/nf and dried to produce a magnetic tape and evaluated. The evaluation results are shown in Table 1. Even if the ferromagnetic metal thin film was changed, the same good results as in Example 1 were obtained. Examples 5 to 8 The molecular weight of the acrylic ester compound in Example 1 was
4000 (Example 5), 8000 (Example 6), 1
ooooo. (Example 7), 1000.00 Magnetic tapes were produced and evaluated in the same manner as in Example 1, except that they were changed to those of Example 8. The proportions of components having a molecular weight of 4000 or more were approximately 52%, approximately 92%, approximately 95%, and 100% in order from Example 5. The evaluation results are shown in Table 1. Examples 9 and 10 The same acrylic ester compound used in Example 1, with a molecular weight of 1000 and a molecular weight of 6000.
(Example 9), by mixing the components with a molecular weight of 111,000 and with the molecular weight of 10,000 at a ratio of 1:1, the proportion of components having a molecular weight of 4,000 or more was approximately 55% (Example 9). and the proportion of components with a molecular weight of 4000 or more is approximately 62
% (Example 1.0), a magnetic tape was produced and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. It can be seen that those containing 50% or more of components with a molecule i of 4000 or more are good. Example 11. 12 The same acrylic ester compound as the acrylic ester compound used in Example 1, one with a molecular weight of 500 and one with a molecular weight of 6,000 were mixed at a ratio of 1:2, so that the proportion of components with a molecular weight of 4,000 or more was about 70%. (Example 11), by mixing those with molecules fi500 and those with molecules fi 10,000 at a ratio of 1:2, the proportion of components with molecules fi 14,000 or more was approximately 72%.
A magnetic tape was produced and evaluated in the same manner as in Example 1, except that (Example 12). The evaluation results are shown in Table 1. Comparative Example 1 The acrylic ester compound in Example 1 was
A magnetic tape was prepared and evaluated in the same manner as in Example 1, except that the magnetic tape was changed to 12,000 (approximately 3% of components having molecules of 14,000 or more). The evaluation results are shown in Table 1. Comparative Example 2 Example 1 except that the acrylic ester compounds in Example 1 with molecular weights of 1,000 and 4,000 were mixed at a ratio of ]:1 to make the proportion of components with molecules of 14,000 or more approximately 27%. A magnetic tape was prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Comparative Example 3 The same acrylic ester compound as the acrylic ester compound used in Example 1, one with a molecular weight of 500 and one with a molecular weight of 2,000 were mixed at a ratio of 1:2, so that the proportion of components with a molecular weight of 14,000 or more was about 2%. Except for the above, a magnetic tape was produced and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Comparative Example 4 A magnetic tape produced in the same manner as in Example 4 without being coated with an acrylic ester compound top coat was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Example 13 50 moles of PPD and 5 moles of DADE as diamine components
0 mol and 40 mol of tetracarboxylic acid component Toshite BPDA.
On a 40 μm thick polyimide film produced by copolymerizing 60 moles of mol and PMDA, a perpendicularly magnetized film of 80 wt% Co-20 wt% Cr was formed using a sputtering device, and the polyimide film was heated to 150°C. ．．
A thickness of 5 μm was formed. The polyimide film used had a thermal expansion coefficient of 2.6 x 10 cm/am/'C and a tensile elastic constant of 400 kg/mr+. Co is sputtered at 100A to form a cobalt oxide thin film.
Formed thickly. Acrylic ester compound containing a perfluoroalkyl group (130,000 molecules, approximately 99% of components with a molecular weight of 4,000 or more)
was dissolved in a solvent of toluene:methyl ethyl ketone = 1:1 and applied to the cobalt oxide layer at 18 mg/r using a bar coater method.
n' was applied. The sample thus obtained had a diameter of 47φ.
A disk was punched out and evaluated using a still video deck (testing machine). The evaluation results are shown in Table 2. It can be seen that the reproduction output is not impaired and the durability is good. Example 14 The acrylic ester compound in Example 13 was
-CI)-,. □ C00CH2CH2-nCB F17 Change the molecular weight to 50,000 (100% of components with molecular i of 4000 or more), dissolve this acrylic ester compound in toluene, and use a bar coater method to obtain 20 mg/rr? A disk was prepared and evaluated in the same manner as in Example 13, except for coating and drying. The evaluation results are shown in Table 2, and as in Example 13, the reproduction output was not impaired and the durability was good. Example 15 The same acrylic ester compound as that used in Example 13, with the molecules filooooo and 3
A magnetic disk was prepared and evaluated in the same manner as in Example 13 using a mixture of 000 and 1:1). At this time, components having a molecular weight of 4000 or more accounted for about 77%. The evaluation results are shown in Table 2. It can be seen that the reproduction output is not impaired and the durability is good. Comparative Example 5 A magnetic desk was produced and evaluated in the same manner as in Example 13, except that the molecular weight of the acrylic ester compound in Example 13 was changed to 2000. At this time, the component having molecules of 24,000 or more was about 5%. The evaluation results are shown in Table 2. [Effects of the Invention] As explained above, the magnetic recording medium according to the present invention contains perfluoroalkyl groups on the ferromagnetic metal film layer laminated on the nonmagnetic substrate, and more than 50% of the ferromagnetic metal film layer has a molecular fi4000.
By coating the above acrylic ester compound polymer, it has excellent recording and reproducing properties as well as corrosion resistance.
This will lead to the realization of a magnetic recording medium that has practically sufficient performance in terms of repeated running durability. Further, as can be seen from the pass durability test at -5°C, the magnetic recording medium of the present invention also has excellent durability at low temperatures.

[Brief explanation of the drawing]

FIG. 1 is a side view showing one example of the magnetic recording medium of the invention, and FIG. 2 is a side view showing another example of the magnetic recording medium of the invention. 1...Nonmagnetic substrate 2...Ferromagnetic metal thin film layer 3...Perfluoro group-containing acrylic ester compound layer 4...Intermediate layer FIG.

Claims (1)

[Claims] 1) In a magnetic recording medium in which a ferromagnetic metal thin film is laminated on a non-magnetic substrate, 50% or more of an acrylic ester compound polymer containing a perfluoroalkyl group is formed on the ferromagnetic metal thin film. 1. A magnetic recording medium comprising an organic compound having a molecular weight of 4000 or more. 2) The magnetic recording medium according to claim 1, wherein an intermediate layer is formed between the ferromagnetic metal thin film and the organic compound. 3) The magnetic material according to claim 2, wherein the nonmagnetic substrate is a polyimide film, the ferromagnetic metal thin film is a Co-Cr alloy, and the intermediate layer is made of an oxide containing Co as a main component. recoding media.