JPH043314A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having excellent durability by mixing three kinds of binders varying in the reactivity (gel molar fraction) from a crosslinking agent (polyisocyanate compd.) and specifying the reactivity of the binder compsn. and the crosslinking agent to >=80%. CONSTITUTION:The three-dimensional network structure which is insoluble and inmeltable in a solvent is formed by the addition reaction between functional groups (isocyanate group and hydroxyl group) and consequently, the tough coated films are formed and the durability of the magnetic layer is improved. The generation of flaws on the surface of the magnetic layer and the generation of drop-outs by the powder dislodged from the magnetic layer are obviated. Further, three kinds of the binders are added in order of the lower reactivity with the crosslinking agent at the time of preparing a magnetic coating material, by which the adsorption layer effective for the dispersion of the magnetic particles is first adsorbed by the binder having the low reactivity with the crosslinking agent without strongly adsorbing and fixing the binder having the good reactivity with the crosslinking agent. The durability of the magnetic layer is, therefore, greatly improved while the electromagnetic conversion characteristics are assured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media such as coated magnetic tapes and magnetic disks using ferromagnetic metal powder as magnetic powder, and a method for manufacturing the same. It provides magnetic recording media with excellent durability.

2. Description of the Related Art Magnetic recording media are generally manufactured by applying a magnetic paint containing magnetic powder and a binder as main components onto a non-magnetic support such as polyethylene terephthalate and drying the coating.

In recent years, the demand for high-density recording has increased, especially for video.

BACKGROUND ART In magnetic recording media such as magnetic tapes and magnetic disks used in audio equipment and computers, it has become essential to miniaturize recording wavelengths and track widths, and to make magnetic layers and supports thinner.

Therefore, compared to conventional oxide-based magnetic powder, coercive force (H
e) and ferromagnetic metal powders with large saturation magnetization (σS) and fine particles have come to be employed.

However, since ferromagnetic metal powder has low hardness, the running durability of the magnetic layer or the wear resistance of the magnetic layer of a magnetic recording medium using this powder is insufficient, causing scratches on the surface of the magnetic layer and ferromagnetic metal powder. The powder is less likely to fall off from the magnetic layer, and 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.
It is extremely important to further improve the durability of the magnetic layer.

Therefore, in order to improve the durability of the magnetic layer, a method of using a plurality of binders has been conventionally used. Furthermore, as disclosed in JP-A-60-111325, the mechanical strength (tensile strength, elongation at break) of the binder
It has been proposed to specify the molecular weight (Mn) of the binder as disclosed in JP-A No. 60-59522.

Problems to be Solved by the Invention However, even with the method using multiple binders as described above, it is difficult to identify the characteristics of each binder individually, or the difference in reactivity of the binder with the crosslinking agent or the ferromagnetic material. In many cases, the expected effect cannot be obtained due to differences in adsorption ability to the surface of the metal powder, and the problem is that it is difficult to improve the durability of the magnetic layer by relying on trial and error.

The present invention does not simply specify the characteristics of each binder, but by adjusting the reaction rate (gel fraction) of a mixed composition in which multiple binders and crosslinking agents (polyisocyanate compounds) coexist. The aim is to develop a binder that can improve the strength of the coating film and truly improve the durability of the magnetic layer. Furthermore, the aim is to truly determine how to add a binder in order to further improve the durability (running durability, still characteristics) of the magnetic layer without worsening the dispersibility of the ferromagnetic metal powder. .

Means for Solving the Problems In order to solve the above 21N, the present invention uses three types of binders having different reaction rates (gel fractions) with the crosslinking agent (polyisocyanate compound), and furthermore, the above three types of binders are The essential requirements are that the reaction rate between the mixed binder composition and the crosslinking agent is 80% or more, and that the above three types of binders are added in order of decreasing reaction rate with the crosslinking agent when preparing magnetic paint. It is configured as follows.

Effect of the present invention With the above-described configuration, a three-dimensional network structure that is insoluble in solvents is formed by the addition reaction between functional groups (isocyanate groups and hydroxyl groups), and as a result, the coating film becomes tough, so that the magnetic layer is Durability is improved, and scratches on the surface of the magnetic layer due to tape running (poor appearance), dropouts due to powder falling off from the magnetic layer (wear powder), etc. do not occur.

Furthermore, by adding three types of binders in descending order of reaction rate with the crosslinking agent when preparing the magnetic paint, the binder with good reactivity with the crosslinking agent can be crosslinked without being strongly adsorbed and fixed on the surface of the magnetic powder. A magnetic recording medium that significantly improves the durability of the magnetic layer while ensuring electromagnetic conversion characteristics because it is possible to first form an adsorption layer that is effective in dispersing magnetic particles using a binder that has a low reaction rate with the agent. can be obtained.

Example Examples of the present invention will be described in detail below.

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) Binder ■ 12 parts Vinyl chloride-vinyl acetate copolymer Combined resin〉Binder ■
...4 parts Polyurethane resin Binder ■ ...4 parts Polyurethane resin Abrasive material ...8 parts <α-AN203> Carbon black ...3
Part lubricant...5
Part stearic acid 2 parts Palmitic acid 2 parts n-butyl oleate 1 part Crosslinking agent 5 parts Polyisocyanate compound (Japanese) (manufactured by Polyurethane Co., Ltd.: Coronate L) Mixed solvent: 300 parts MEK/l toluene/cyclohexanone = 3/3/2 Among the above compositions, ferromagnetic metal powder and carbon black were mixed in a planetary mixer (PLM). ),
First, after moistening with 30 parts of mixed solvent, binder ■
, ■, ■ were added in this order, and kneaded for 10 hours. Next, 200 parts of an abrasive and mixed solvent were added and dispersed using a sand mill to obtain a magnetic paint stock solution. Further, 70 parts of a lubricant, a crosslinking agent, and a mixed solvent were added and mixed and stirred using a disper to prepare a magnetic coating material. Next, the paint filtered through a filter with an average pore size of 0.4 μm (manufactured by Nippon Roki: HT40) was applied onto polyethylene terephthalate (PET) with a thickness of 10 μm, oriented, and dried.

Mirror finish treatment using super calender.

After the hardening process, a bank coat layer mainly composed of carbon blank was provided on the polyethylene terephthalate on the opposite side from the magnetic layer, and the bank coat layer was slotted to a width of 8++a and Bw
A metal tape for VTR was created.

The three types of binders used here (binder ■, ■,
Reaction rate (gel fraction) between
is as follows.

Binder ■: 68% Binder ■: 81% Binder ■: 95% In addition, the three types of binders listed above (Binder ■).

The reaction rate (gel fraction) between the mixed binder composition consisting of (1) and (2) and the crosslinking agent (polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was 87%.

Example 2 Binder in place of the binder in Example 1 ■ 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin binder ■ 4 parts <Polyurethane resin> Binder ■ 8 m V
I created a metal tape for R.

The three types of binders used here (binder ■, ■,
Reaction rate (gel fraction) between
is as follows.

Binder ■: 70% Binder ■: 74% Binder ■: 91% In addition, the three types of binders listed above (Binder ■).

The reaction rate (gel fraction) between the mixed binder composition consisting of (1) and (2) and the crosslinking agent (polyisocyanate compound (Coronet L, manufactured by Nippon Polyurethane Co., Ltd.)) was 83%.

Comparative Example 1 Binder in place of the binder in Example 1 ■...12 parts (vinyl chloride-vinyl acetate copolymer resin) binder
■ 4 parts of polyurethane resin Binder ■ 4 parts of polyurethane resin A metal tape for an 8-kaku VTR was created using a similar method.

The three types of binders used here (binder ■, ■,
■) and crosslinking agent (polyisocyanate compound (Coronet L))? ! - The reaction rate (gel fraction) is as follows.

Binder ■: 68% Binder ■: 71% Binder ■ = 77% In addition, the three types of binders listed above (Binder ■).

The reaction rate (gel fraction) between the mixed binder composition consisting of (2) and (2) and the crosslinking agent (polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.)) was 73%.

Comparative Example 2 Binder instead of the binder in Example 1 ■ ...10f
fl Vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin binder ■...4 parts polyurethane resin> Binder ■...6 parts polyurethane resin> , ■, ■ by the same method as in Example 1 except that 8wr V T
I created a metal tape for R.

The three types of binders used here (binder ■, ■,
Reaction rate (gel fraction) between
is as follows.

Binder ■: 70% Binder ■: 74% Binder ■: 81% In addition, a mixed binder composition consisting of the above three types of binders (binder ■■, ■) and a crosslinking agent (polyisocyanate compound (manufactured by Nippon Polyurethane Co., Ltd.: Coronet) L) ) was 75%.

Comparative Example 3 The method of adding binder in Example 1 was changed to binder ■, ■
A metal tape for Bwa VTR was prepared in the same manner as in Example 1 except that the order of .

Comparative Example 4 An 8■VTR metal tape was made in the same manner as in Example 2, except that the binder addition method in Example 2 was changed to adding the binder all at once (simultaneous addition of binders ■, ■, and ■). did.

A method for measuring the reaction rate (gel fraction) between the binder described above and the crosslinking agent (polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.)) is shown below.

(1) Reaction rate of single binder composition (gel fraction) A clear coating film prepared with a composition of single binder/crosslinking agent = 10/1 is subjected to heat treatment (curing treatment) at 60°C for 24 hours.
Thereafter, the MEK insoluble content is calculated for the obtained coating film.

(2) Reaction rate of mixed binder composition (gel fraction) A clear coating film prepared with the mixed binder/crosslinking agent composition set in Examples and Comparative Examples is subjected to heat treatment (curing treatment) at 60°C for 24 hours, and then, MEK insoluble content is calculated for the obtained coating film.

The following measurements were performed on each of the metal tapes for VTRs obtained in the above Examples and Comparative Examples.

(11C/N (5,OM)tz/4.5 MHz)5
．． The ratio of the signal at 0 part 7 to the noise at 4.5 MHz was measured. MVS-5000 (manufactured by KODAK) was used as an 8 m VTR for C/N measurement. In addition, the recording/reproducing head uses an amorphous alloy, and Example 1
Based on the C/N of 8 m VTR metal tape (
It is expressed as a relative value (OdB).

(2) Using the same 8 ws VTR as used for dropout C/N measurement, each videotape sample was tested at 40°C and 80% RH for 2 hours.
00 passes (endurance test), 16 dB for 15 μs for each videotape sample before and after the durability test.
The number of pieces per minute at which the above decrease in output occurred was measured.

(3) Head Powder Adhesion After the durability test according to (2) 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, no lees adhesion was observed.
A rating of 5 indicates that there is no practical problem at all, and a large amount of powder adhesion (,
Items with practical problems were given a rating of 1.

(4) Running scratches Running scratches on the surface of the tape magnetic layer after the durability test according to (2) above were visually observed, and the degree of running scratches was evaluated on a five-point scale. The evaluation was rated 5 if no running scratches were observed and no practical problem at all, and 1 if there were many running scratches and posed a practical problem.

(5) Still life Using a modified 8wra VTR for still measurement,
A pre-recorded still image was played back under the conditions of 10° C. and 30 g load, and the time required for the image signal to drop by 6 dB is shown. Table 1 shows the results.

(Margins below) In the above example, only the 8■VTR metal tape was explained, but other coated magnetic tapes using ferromagnetic metal powder, M! The present invention can be similarly applied to magnetic recording media such as optical disks.

Effects of the Invention As described above, the present invention uses three types of binders having different reaction rates (gel fractions) with a crosslinking agent (polyisocyanate compound), and furthermore, a binder composition formed by mixing these three types of binders. A magnetic recording medium with excellent durability of the magnetic layer because the reaction rate with the crosslinking agent is 80% or more, and by adding these three types of binders in descending order of the reaction rate with the crosslinking agent when preparing the magnetic coating material. This makes it possible to provide the following.

Claims (2)

[Claims] (1) A magnetic recording medium in which a magnetic layer containing ferromagnetic metal powder and a binder is formed on a non-magnetic support, the reaction rate (gel fraction) with a crosslinking agent (polyisocyanate compound) as the binder. ) A magnetic recording medium characterized in that the reaction rate between a binder composition obtained by mixing three types of binders and a crosslinking agent is 80% or more. (2) Using three types of binders with different reaction rates (gel fractions) with the crosslinking agent (polyisocyanate compound), the reaction rate between the binder composition obtained by mixing the three types of binders and the crosslinking agent is 80% The above is the method for producing a magnetic recording medium, characterized in that the three types of binders are added in order of decreasing reaction rate with the crosslinking agent.