JPH0444624A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in durability by specifying the quantity of a binder eluted to tetrahydrofuran (THF) from the magnetic layer consisting essentially of ferromagnetic metal powder and the binder with a specified value or below to the magnetic layer. CONSTITUTION:The quantity of the binder eluted with tetrahydrofuran (THF) from the magnetic layer is specified to <=4.5pts.wt. to the magnetic layer. In this condition, various reactions take place sufficiently, that is, an urethane generation where isocyanate group is reacted with hydroxide group in other binder, further an allophanate generation reaction where isocyanate group is reacted with the produced urethane coupling, an urea generation reaction with, a isocyanate group and water and a burette generation reaction where an isocyanate group is reacted with a generated isocyanol group. By this method, wear resistance of the magnetic layer is improved.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to magnetic recording media such as coated magnetic tapes and magnetic disks using ferromagnetic metal powder as magnetic powder. BACKGROUND OF THE INVENTION In general, the magnetic recording medium described above is manufactured by applying a magnetic paint containing magnetic powder and a binder as main components onto a non-magnetic support such as polyethylene terephthalate, followed by drying and molding. In recent years, the demand for high-density recording has increased, and in magnetic recording media such as magnetic tapes and magnetic disks used in video recorders, audio equipment, and computers, recording wavelengths and track widths have been miniaturized, and magnetic layers have become increasingly important. In addition, it has become essential to realize thinning of the support. Therefore, compared to conventional oxide-based magnetic powders, ferromagnetic metal powders with larger coercive force (Hc-) and saturation magnetization (σS) and finer particles have come to be used. However, although magnetic recording media using ferromagnetic metal powder exhibit excellent electromagnetic conversion characteristics, durability is a problem because the ferromagnetic metal powder itself has low hardness. In other words, the wear resistance of the magnetic layer of the magnetic recording medium becomes insufficient, and scratches occur on the surface of the magnetic layer and ferromagnetic metal powder easily falls off from the magnetic layer.
As a result, problems such as dropouts are more likely to occur. Furthermore, with the spread of portable magnetic recording and reproducing devices and camera-integrated devices, the environments in which magnetic recording media are used are expected to become wider and harsher than ever before, so the durability of the magnetic layer is important. It is extremely important to improve this even further. Therefore, various methods have been proposed for the purpose of improving the durability of the magnetic layer. For example, methods of using multiple binders include a method of specifying the mechanical strength (tensile strength, elongation at break) of the binder as disclosed in JP-A No. 60-111325, and a method of determining the mechanical strength (tensile strength, elongation at break) of JP-A No. 6L-59522. A method for identifying the binder molecule ji (Mn) has been proposed as disclosed in Japanese Patent Application Laid-open No. 193530/1983 as a method for improving wear resistance within an extremely short period of time. As disclosed, a method has been proposed in which a polyisocyanate and an isocyanate reaction promoting compound are added to a binder. Problem to be Solved by the Invention However, in the method using multiple binders as described above, it is difficult to simply specify the characteristics of each binder, and it is difficult to identify the differences in the reactivity of the binder with the hardening agent or the ferromagnetic metal. In many cases, the expected effect may not be obtained due to differences in adsorption ability to the powder surface, and in the case of methods in which a curing agent or curing reaction accelerator is added to promote the crosslinking reaction, the curing environment may In many cases, the curing reaction does not proceed sufficiently due to the problem of setting the time, which is problematic as a method for improving the durability of the magnetic layer. The present invention is intended to solve the above problems, and aims to provide a magnetic recording medium whose magnetic layer has excellent durability. Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has developed a magnetic layer mainly composed of ferromagnetic metal powder and a binder obtained from the detailed study results of the inventors.
The amount of binder eluted in the magnetic layer is 4.5wt%
The following are essential requirements. The amount of binder eluted into tetrahydrofuran (THF) is measured as follows. Add 20 ml of tetrahydrofuran (GHF) to a 20 ml glass sample bottle.
1.5 m of 1/2-inch wide magnetic tape is left on the non-magnetic support with only the magnetic layer remaining, and the tape is immersed. The sample bottle is subjected to ultrasonic vibration for 30 minutes using an ultrasonic vibrator to carry out elution treatment. Keep the water temperature in the ultrasonic vibrator constant so that the sample temperature does not rise during vibration. Remove the tape from the sample bottle and let it stand until the peeled coating settles to the bottom. Take out 10 ml of supernatant liquid from the sample bottle, evaporate to dryness, measure the weight of solid content, and double the value to determine the elution amount. However, since the above-mentioned solid content also contains a lubricant component, the above-mentioned solid content is converted into GPC (Gel Permeation).
Chromatography) to calculate the binder ratio in the solid content and determine the elution amount of the binder. Function According to the present invention, tetrahydrofuran (TH) is removed from the magnetic layer.
The amount of binder eluted in F) is 4.5w with respect to the magnetic layer.
When the temperature is below t, the hardening reaction of the magnetic layer coating, that is, the urethane production reaction in which isocyanate groups react with hydroxyl groups in other binders, the allophanate production reaction in which isocyanate groups react with the generated urethane bonds, and the isocyanate groups and water In addition, the abrasion resistance of the magnetic layer is improved because the urea production reaction and the urea production reaction in which isocyanate groups react with the produced urea bonds are sufficiently progressing. As a result, scratches on the surface of the magnetic layer during tape running and an increase in the coefficient of friction of the magnetic layer. A significantly improved magnetic recording medium is obtained. Examples Examples of the present invention will be described. The magnetic paint used in the present invention mainly consists of ferromagnetic metal powder, binder, and coating solvent, and may also contain additives such as lubricants, abrasives, dispersants, and antistatic agents. . There are no particular restrictions on the binder, and thermoplastic resins,
Thermosetting resins or reactive resins or mixtures thereof are used. For example, polyurethane resin, cellulose resin, polyester resin, polyvinyl chloride copolymer,
Acrylic copolymers and epoxy resins are used alone or in combination, and other additives may be added. Fatty acids and fatty acid esters are used as lubricants, and fused alumina, chromium oxide, and silicon carbide are used as abrasives. The magnetic layer of the present invention is formed by dissolving the above composition in an organic solvent, mixing and dispersing the coating, coating the coating on a non-magnetic support, and drying the coating. Mixing and dispersion are performed by cross-dispersion using a planetary mixer, ball mill, or sand mill. Further, as the non-magnetic support, polyesters such as polyethylene terephthalate, polyamide, polyimide, etc. are used. Hereinafter, embodiments of the present invention will be specifically described using an 8 mm videotape as an example. In the Examples and Comparative Examples, each part of the material indicates the number of parts by weight based on 100 parts of the ferromagnetic metal powder.

[Example 1] Ferromagnetic metal powder...100 parts [average major axis diameter 0.18 μm, average axial ratio 1:10 Copolyurethane resin...10 parts (manufactured by Nippon Polyurethane Co., Ltd., N-2304) Vinyl chloride -Hinyl acetate-hinyl alcohol copolymer resin・10 parts (manufactured by UCC, VAGH) a-A120g ・= 6 parts carbon black ・・ 3 parts stearic acid ・・ 2 parts palmitic acid ・・ 2 parts oleic acid 〇-Butyl... 1 part Polyisocyanate compound... 5 parts (manufactured by Nippon Polyurethane Co., Ltd.,
coronate) mixed organic solvents
...300 parts (MEK (methyl ethyl ketone)/l.
Luene/cyclohexanone = 3 / 3 /' 2
) The above composition was mixed and dispersed using a planetary mixer, Santo Mill and Disper to prepare a magnetic paint. Next, a filter with an average pore diameter of 0.4 parts and 4 m (manufactured by Nippon Wave Equipment, HT
40) was applied onto polyethylene terephthalate with a thickness of 10 μm, subjected to magnetic field orientation, drying, and mirror polishing treatment using a calender. Further 60°C x 2
After curing for 4 hours, a back coat layer containing carphone black as a main component was provided on the polyethylene terephthalate surface opposite to the magnetic layer, and slits were made into 8 mm width.
A metal tape for an 8mm video tape recorder (VTR) was created. The amount of binder eluted from the magnetic layer of this tape into tetrahydrofuran (THF) was 4.0wt9.6 with respect to the magnetic layer.

[Example 2] 8 mmV
A metal tape for TR was created. The amount of bisida eluted from the magnetic layer of this tape into tetrahydrofuran (T HF ) was 3.0 wt % based on the magnetic layer.

[Example 3] The same method as in Example 1 was used except that the curing conditions in Example 1 were changed to 40°C for 120 hours.
A metal tape for VTR was created. The amount of binder eluted from the magnetic layer of this tape into tetrahydrofuran (THF) was i, 5wt96 relative to the magnetic layer.

[Example 4] 0.05 parts by weight of triethylenediamine, which is an isocyanate reaction accelerating compound, was added to the magnetic paint of Example 1 immediately before coating (equivalent to adding 1 part by weight of triethylenediamine to 100 parts by weight of coronate). Hereinafter, Example 1
Coating and curing were performed in the same manner as 8 mm.
A metal tape for VTR was created. The amount of binder eluted from the magnetic layer of this tape into tetrahydrofuran (THF) was 2.8 wt % based on the magnetic layer.

[Comparative Example 1] An 8 mm VTR metal tape was produced in the same manner as in Example 1, except that the curing process in Example 1 was omitted. Tetrahydrofuran (
The amount of binder eluted in THF) is 8.
It was 5wt%.

[Comparative Example 2] The same method as in Example 1 was used except that the curing conditions in Example 1 were changed to 60°C for 2 hours.
A metal tape for TR was created. The amount of binder eluted from the magnetic layer of this tape into tetrahydrofuran (THF) was 5.0 wt% based on the magnetic layer.

[Comparative Example 3] 8 mmV was produced in the same manner as in Example 1, except that the curing conditions in Example were changed to 40°C x 72 hours.
A metal tape for TR was created. The amount of binder eluted from the magnetic layer of this tape into tetrahydrofuran (THF) was 5.5 wt % based on the magnetic layer. Each 8mm VTR obtained in the above examples and comparative examples
The following measurements were performed on the metal tape for (1) C/N (5.0MHz/4.5MHz)5.
The ratio of the signal at 0 MHz to the noise at 4.5 MHz was measured. Using MVS-5000 (manufactured by KODAK) as an 8 mm VTR for C/N measurement, each videotape sample was run for 200 passes in an environment of 40°C and 80% RH (durability test). The C/N was measured for each videotape sample, and the C/N was measured before the durability test.
The C/N after the durability test is shown as a relative value with N as a reference (OdB). (2) Dropout For each videotape sample before and after the durability test according to (1) above, the number of dropouts per minute in which an output drop of 16 dB or more occurred over 15 μs was measured. (3) Head Powder Adhesion After the durability test according to (1) above, the amount of powder adhesion on a part of the magnetic head and cylinder was observed using a microscope, and the degree of powder adhesion was evaluated on a five-point scale. As an evaluation, a sample with no visible powder adhesion and no practical problem was given a rating of 5, and a case with a large amount of powder adhesion and a practical problem was given a rating of 1. (4) Running scratches Running scratches on the surface of the tape magnetic layer after the durability test according to (1) above were visually observed, and the degree of running scratches was evaluated on a five-point scale. The evaluation was rated 5 if there were no running scratches and no practical problems, and 1 if there were many running scratches and there were practical problems. (5) Wrap the magnetic layer around a stainless steel rod with a dynamic friction coefficient of 4 mmφ and contact it at an angle of 180 degrees, set the entrance tension to the stainless steel rod at 13 g, and set the tape running speed at I cm/sec. The exit tension Xg was measured, and the friction coefficient was determined using the following equation. μ・1/π×βn (Output tension Xg/Input tension crab 13g)
Measurements were made for the 1st pass and the 100th bus. (6) Still life Using an 8 mm VTR modified for still life measurement, play the pre-recorded video in still mode at -10°C and a load of 30g, and find that the video signal drops by 6 dB. The time was measured. Table 1 shows the measurement results of the characteristics. (Margins below) As is clear from Table 1, the amount of binder eluted from the magnetic layer into tetrahydrofuran (THF) for the tapes of Examples 1 to 4, in which the temperature and time of the curing treatment were adjusted, was higher than that of the magnetic layer. Good properties were obtained for tapes containing 4.5 wt% or less. Effects of the Invention As described above, according to the present invention, the amount of binder eluted from the magnetic layer into tetrahydrofuran (THF) is 4.5 wt% or less based on the magnetic layer, which is good for magnetic recording media, such as magnetic tapes. Characteristics such as C/N, dropout, and coefficient of dynamic friction can be obtained. Therefore, it is possible to obtain characteristics such as the occurrence of scratches on the surface of the magnetic layer during running, an increase in the coefficient of friction of the magnetic layer, and the possibility of dropouts due to falling particles from the magnetic layer. It is possible to provide a magnetic recording medium that does not have any problems such as generation, has a long still life, and has significantly improved durability of the magnetic layer.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic metal powder and a binder is formed on a non-magnetic support, in which tetrahydrofuran (THF) is formed from the magnetic layer.
The amount of binder eluted in the magnetic layer is 4.5wt%
A magnetic recording medium characterized by the following: