JPH03286419A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To obtain a medium in which mechanical characteristics are satisfactory by using three kinds of binder resins having different Tg, specifying Tg of the mixed resin composition to 30-47 deg.C, and adding these resins in the descending order of Tg. CONSTITUTION:The magnetic recording medium consists of a nonmagnetic supporting body and a magnetic layer containing a ferromagnetic metal powder and a binder formed on the substrate. As for the binder, three kinds of binder resins having different Tg are used, and these three binder resins are mixed to prepare the resin composition having Tg of 30 - 47 deg.C. In the process of preparing the magnetic coating material, the three binder resins are added one by one in the descending order of Tg. Namely, a hard-type binder is first added to form an adsorption layer on the magnetic powder, then a binder having intermediate hardness is added and then a soft binder is added to obtain the binding function. Thereby, formation of the surface can be easily performed, and the obtd. coating film has excellent mechanical characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media such as so-called coated magnetic tapes and magnetic disks that use ferromagnetic metal powder as magnetic powder, and a method for manufacturing the same.

Conventional technology (i-g) Magnetic recording media such as magnetic tapes and magnetic disks used in video, audio equipment, and computers are increasingly becoming more densely packed, resulting in shorter recording wavelengths and narrower recording track widths. The trend is to make the media thinner and the minimum recording unit smaller.Also, magnetic recording and reproducing devices have become portable.With the spread of integrated cameras, they have come to be used in all kinds of environments, both indoors and outdoors. As a result, the environments in which the above-mentioned recording media are used have become wider and more severe than ever before.

For this reason, various measures have been taken to improve the durability of the coating film, including the use of binder resins and lubricating oils. Fair 1-28585
Publications, etc.). Conventional binders improve the dispersibility, filling properties, orientation, heat resistance, head abrasion resistance, and
Thermoplastic and thermosetting resins are often used in consideration of adhesion to the base film.

The main binder is vinyl chloride/vinyl chloride, which is a polymer with a molecular weight of several and has good dispersibility, and has an appropriate amount of anchor segments (adsorption points) that are well adsorbed to the magnetic powder surface coordinated in the molecular chain.
Alcohol copolymers, vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinylidene chloride copolymers, and the like are used. On the other hand, polyurethane resins, epoxy resins, phenol resins, polyamide resins, urea resins, isocyanate resins, etc. are used as sub-binders for the purpose of obtaining highly durable coatings, and in actual coatings, multiple types of binder resins are mixed. (Special Publication No. 61-9826)
Publication No.). However, in order to achieve high C/N and high durability using micronized magnetic powder for high-density recording, it is difficult to obtain sufficient durability using conventional methods. There was a problem.

Problems to be Solved by the Invention In order to secure a high C/N and achieve high durability using micronized magnetic powder, in addition to the excellent dispersibility of the binder used, it is necessary to use a coating film. In some cases, it is necessary that the surface roughness be sufficiently small and that the mechanical strength be excellent.

Reducing the required roughness can be achieved by a coating film surface formation process (calendering) using a soft binder, but on the other hand, the Young's modulus of the coating film decreases significantly, especially at high temperatures. In this environment, the paint film is scraped due to contact with the traveling system such as the magnetic head and the traveling post, and the scraped powder adheres to the magnetic head, resulting in an increase in drop irregularity (D, ○,) and output fluctuation. This always brings about problems. Mechanical properties, that is, high Young's modulus, can still be achieved by using a hard binder, but this not only makes surface formation difficult, but also makes the coating hard and brittle, so the above problems occur at low temperatures. Occur.

The purpose of the present invention is to provide a medium whose mechanical properties are sufficiently satisfied even when the surface roughness of the magnetic layer is small. To achieve this, it is necessary to specify the composition of the soft binder and the hard binder and the procedure thereof. Means for Solving the Problems This invention was made based on the discovery that a magnetic layer containing ferromagnetic metal powder and a binder is formed on a non-magnetic support. A magnetic recording medium consisting of three types of binder resins having different Tg as the binder,
The Tg of the resin composition formed by mixing different types of binder resins must be 30°C to 47°C.
It is constructed by adding different types of binder resins in descending order of Tg.

Effect: According to the structure of the present invention, the durability of the magnetic coating film can be dramatically improved. The effect will be explained below.

Regarding a magnetic recording medium in which a magnetic layer containing ferromagnetic metal powder and a binder is formed on a non-magnetic support, three types of binder resins with different Tg are used as the binder, and these three types of binder resins are mixed. The Tg of the resin composition is 30°C to 47°C, and when preparing the magnetic paint, three types of binder resins are added in order of increasing Tg, that is, the hard binder is added first to form an adsorption layer on the magnetic powder. By adding a binder with intermediate strength second and finally adding a soft binder that acts as a binder, surface formation is facilitated and a coating film with excellent mechanical properties can be obtained. .

A magnetic recording medium obtained by manufacturing a magnetic coating material using three types of binder resins selected according to the Tg of the present invention has dramatically improved durability.

Example Average particle size: long axis -0.2 μm, acicular ratio = 10, magnetic coercion 15500e, specific surface area = 55 nf/g ferromagnetic metal powder was used as the magnetic powder, and binder resins with different Tg were used as the binder resin. An 8mm videotape is produced by using a combination of these methods and adding additives and solvents.

First, we use magnetic powder, an anti-wear agent, and a solvent to create a planetary
After stirring with a mixer (PLM), binder resins are added in descending order of Tg, followed by wetting and kneading. Next, add the remainder of the solvent to reduce the solids concentration and dispersion using a sand mill.
Do time. Alumina is added to this, and sand mill dispersion is further performed for 4 hours. Next, add a wetting agent and a hardening agent, and add 0.4
A 1011m thick polyester film (PET) is passed through a μm filter (HT-40 manufactured by Nippon Wave).
The magnetic layer is coated on top, oriented in a magnetic field, dried, and then subjected to surface treatment using a super calender (surface treatment machine), followed by hardening treatment. Furthermore, a back coat layer containing carbon black as a main component was coated on the PET on the side opposite to the magnetic layer, and the tape was then cut into 8-inch pieces to obtain a magnetic tape.

Here, the three types of binder resins used in Examples and Comparative Examples were combinations in which the Tg of the clear mixed resin coating film was 25°C to 51°C. Characteristics of each rope produced in this way (surface properties, Young's modulus under environmental conditions, durability:
The adhesive, O, amount of change, and amount of head powder adhesion before and after the test were evaluated.

As a result, when the three types of resins used are the same but the mixing ratios are different, or when the mixing ratios are the same but the types of resins used are different, the Tg of the three types of mixed resin coating films combined is less than 30°C. Especially for 40
The Young's modulus was low under an environment of 80% RH and the durability was also unsatisfactory.

When the temperature was higher than 47°C (however, 47°C was not included), Young's modulus was high, but durability and surface roughness were both at low levels. In addition, for those within 30'C to 47°C, good results were obtained for both Young's modulus and durability, which corresponded well to surface roughness, so these depend on the Tg of the binder resin mixed coating film. It turned out that I was doing it. When three types of binder resin M fat were added in ascending order of Tg, poor results were obtained in terms of surface roughness, Young's modulus, and durability. Therefore, it was found that the order in which the binder resin was added had a large effect on durability.

Examples and comparative examples will be specifically described below.

Note that all numbers of component ratios shown in the examples are parts by weight.

Example 1-1 Eight video tapes were produced using the formulation shown in Table 1. The Tg of the three types of binder resins used here is: Binder 1 - 59℃ 1 Binder - 2 = 32℃ 1 Binder 3 = 5
°C, g in the mixed composition was 38 °C.

Table 1 Varnish 200-3 on PP (polypropylene) film
Coat it uniformly to a thickness of 00 μm, dry in a hot air dryer at 100°C, and after cooling, measure 4 mm x 60 mm (including the chuck grip: measurement area - 4 mm x 40 mm)
). After that, peel off the PP film and use Rheopybron (manufactured by Toyo Baldwin) to measure frequency: 1.
00Hz, temperature increase rate: 1°C/mm, starting temperature: approximately 40°C lower than the estimated Tg value.

Examples 1-2 to 5 8 mm video tapes were produced in the same manner as in Example 1-1 using the binder resin compositions shown in Table 2. The binder resins used here each have a Tg of 4--25°C for binder and 35°C for binder 5, and the Tg in the mixed composition is 2-25°C.
It was as shown in the table.

This Tg is the same as in Example 1-1 using the composition shown in Table 3 as the binder resin m precept. An 8 mm videotape was produced. The Tg of the binder resin used here is
The temperature of the binder was 6-57°C, and the Tg of the mixed composition was as shown in Table 3.

Comparative Example 2-1 Below, the binder resins were added in the order of addition according to the recipe of Example 1-1: binder 3, binder 2, and binder 1, and wetting and kneading were performed. An 8 mm videotape was produced in the same manner as in Example 1-1 except for this.

Comparative Example 2-2 Binder resin was added all at once according to the recipe of Example 1-1,
Wetting and kneading were performed. Except for this, an 8-kaku videotape was produced in the same manner as in Example 1-1.

The characteristics of the above samples are summarized in Table 4.

Margin below The evaluation method is also shown below.

(1) Surface Roughness of Magnetic Layer The center average roughness (Ra value) of the magnetic layer surface of each 8 mm videotape was measured using a stylus type surface roughness meter (Crystep, manufactured by Taylor Hobson).

(2) Using a magnetic layer Young's modulus tensile tester (Tensilon, manufactured by Orientic Aji), at a tensile speed of 1.0 m/mm, at 23°C, 60% R.
Young's modulus was measured under H environment and 40″C80%RH environment.

(3) C/N (5.0MHz/4.5M) 5M
The ratio of the signal at Hz to the noise at 4.5 MHz was measured using an 8 mm video tape recorder (MV
S-5000: Measured using KODAK■).

The recording/reproducing head uses an amorphous alloy, and Example 1
Relative values are shown using the C/N of the -1 8 fight videotape as a standard (OdB).

(4) Using an 8 mm videotape recorder similar to that used for dropout C/N measurements, each videotape sample was run for 200 passes in an environment of 40'C and 80% RH, and the recording rate was 1 min.
The number of times a decrease in output of 16 dB or more occurred over 5 μs was measured.

(5) Powder adhesion on head After the test in (3) above, the amount of powder adhesion on the sliding surface of the magnetic head and tape was observed under a microscope and evaluated on a five-point scale. Items with no practical problems were rated 5, and items with practical problems were rated 1.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, as described in detail, three types of binder resins having different Tg are used, and the Tg of the resin composition formed by mixing these three types of binder resins is 30''C to 47C, Furthermore, by adding these three types of binder resins in descending order of Tg, the magnetic recording medium produced has excellent surface properties and mechanical strength, and can also improve durability.

Claims (2)

[Claims] (1) A magnetic recording medium in which a magnetic layer containing ferromagnetic metal powder and a binder is formed on a nonmagnetic support, the binder being three types of binder resins having different glass transition temperatures (Tg), The Tg of the resin composition made by mixing these three types of binder resins is 30°C to 4
A magnetic recording medium characterized by a temperature of 7°C. (2) A method for manufacturing a magnetic recording medium, characterized in that three types of binder resins having a mixed composition with a Tg of 30 to 47° C. are added in descending order of Tg.