JPH04120179A - Production of magnetic coating - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a magnetic paint for coated magnetic tapes and magnetic disks using ferromagnetic metal powder.

Conventional technology-i: Magnetic recording media such as magnetic tapes and magnetic disks used in video, audio equipment, computers, etc. are increasingly becoming more densely packed, and as a result, the recording wavelength is short, the recording track width is narrow, and the recording medium thickness is increasing. The trend is to make the paper thinner and make the minimum recording unit smaller. In addition, with the spread of portable magnetic recording and reproducing devices and built-in cameras, they are now being used in all kinds of environments, both indoors and outside. It becomes.

For this reason, efforts are being made to improve the tm conversion characteristics (C/N ratio) and the durability of the coating film. Discussions are being conducted from the perspective of improvement.

Conventionally, we have focused on the dispersibility and filling properties, orientation, heat resistance, and magnetic head abrasion resistance of ferromagnetic metal powder in coating films.

In consideration of adhesion to the base film, etc., thermosetting binders are often used, and two types of general binders are used: a main binder and a sub binder.

The main binder is PVC, vinyl acetate, or alcohol, which is a polymer with a low molecular weight, has good dispersibility, and has an appropriate amount of anchor segments (adsorption points) that are well adsorbed to the surface of the ferromagnetic metal powder coordinated in the molecular chain. Copolymers are used.

On the other hand, in order to obtain a highly durable coating film, a strong and flexible polyurethane resin is used as a secondary binder.
In actual production of paints, a plurality of types of resins, the main binder and the sub-binder, were simultaneously mixed together with ferromagnetic metal powder (see Japanese Patent Laid-Open No. 61-9826).

Problems to be Solved by the Invention However, as ferromagnetic metal powders with smaller particle sizes (larger BET values) have come to be used for higher density recording, conventional methods have not been able to achieve sufficient ferromagnetic properties. A problem has arisen in that it is difficult to disperse metal powder and obtain a magnetic coating film with high mechanical strength.

As ferromagnetic metal powder becomes finer, in order to disperse it, it is necessary to increase the amount corresponding to the main binder that contributes to dispersibility in accordance with the specific surface area (BET value) of ferromagnetic metal powder. This causes a decrease in the packing density of the ferromagnetic metal powder in the magnetic coating film, resulting in a decrease in the C/N ratio. Since the amount of binder adsorbed to the magnetic metal powder is significantly larger than the amount not adsorbed, it becomes difficult to obtain an effect in the coating surface formation process (calendering treatment), and the C/N ratio decreases due to spacing loss between the magnetic head and tape. A decline occurs.

In addition, the mechanical properties of the surface layer of the magnetic coating film itself deteriorates due to a decrease in the amount of resin that binds the dispersed ferromagnetic metal powder, so under various environments it is difficult to interact with the running systems such as magnetic heads and running posts. Contact causes scraping of the paint film and adhesion of scraped powder to the magnetic hand, leading to problems such as increased dropout (DO) and output fluctuations.

In view of the above problems, the present invention provides a method for producing a magnetic paint for obtaining a magnetic recording medium that has a high C/N ratio and excellent running durability.

Means for Solving the Problems In order to solve the above problems, the method for manufacturing a magnetic paint of the present invention includes a step of kneading ferromagnetic metal powder, a binder resin, and a solvent, a primary dispersion step using a bead mill, and after adding an abrasive. 60 to 90% of the binder resin is kneaded in the kneading process, and the remainder is added after the primary dispersion is completed, and the amount of the binder resin adsorbed to the ferromagnetic metal powder is and the non-adsorbed amount is 0.2 per soil.

Function The present invention aims to satisfy both the C/N ratio and durability by controlling the amount of adsorbed binder resin, which greatly affects the dispersibility of ferromagnetic metal powder, and the amount of non-adsorbed binder, which greatly affects durability. This was done considering the binder design of the magnetic coating film, and its specific function will be explained below.

Conventionally, in order to control the amount of binder resin required to make the ferromagnetic metal powder into a sufficiently highly dispersed state and the amount of binder resin for binding, multiple types of binder resins with different adsorption amounts were used from the beginning of the dispersion process. was added. However, in this method, the amount of binder adsorbed is determined by the adsorption ability of the binder resin used and the surface condition of the magnetic material.

However, as a result of investigating the change in the amount of binder resin adsorbed to ferromagnetic metal powder during the paint dispersion process, it was found that the value was almost determined by the initial kneading process, and that most of the binder resin added after that was not adsorbed and was absorbed into the solvent. I discovered that it exists inside.

This makes it possible to freely control the amount of binder resin adsorption by changing the amount of binder resin added during kneading.

Example The present invention will be specifically explained below using examples.

In addition, all the component ratios shown in the examples are shown in parts by weight.

Example 1 As a ferromagnetic metal powder, the long sleeve is 0.2 μm and the needle ratio is 1.
0, coercive force is 15500e, specific surface area is 50rrr/g
An 8 m videotape was produced using the powder of 100 ml and the blending ratio shown in Table 1 and the steps shown in FIG. 1.

First, a ferromagnetic metal powder, an anti-wear agent, and a mixed solvent (methyl ethyl ketone, toluene, cyclohexanone) are stirred in a planetary mixer (PLM).
A total of 12 parts of the binder resins shown in the table (hereinafter simply referred to as binders) 1, 2.3 were added, and the mixture was wetted and kneaded. Perform primary dispersion for 4 hours, add aluminum oxide (α-/1208) and remaining 6 parts of binder 1.2.3, and further perform secondary dispersion using a sand mill for 4 hours.
Let's do it. Next, a lubricant and a hardening agent were added, and the film was passed through a -10.4 μm filter and applied onto a 10 μm thick polyester film (PET). After magnetic field orientation and drying, a super calender (surface treatment machine) was used to coat the surface of the magnetic layer. After processing, a hardening treatment was performed, and a back coat layer containing carbon black as a main component was coated on the PET layer opposite to the magnetic layer, and the tape was cut into a width of 8 m to obtain a magnetic tape. In Table 2, the glass transition temperature was measured using a pieburon, the molecular weight was measured using GPC, and the amount of adsorption was measured using a dilute solution system of magnetic material and binder. did.

(Left below) Examples 2 to 6, Comparative Example 1. Comparative Example 2 By the same manufacturing process as in Example 1, using the binder shown in Table 2, and using the binder addition method and blending ratio shown in Table 3 below, 8.
A videotape was made.

(Left below) Table 4 below summarizes the ratio of binder adsorption amount to non-adsorption amount and the characteristics of each of the samples listed above.

The evaluation method is also shown. Further, FIG. 2 shows the relationship between the amount of binder used during kneading and the ratio of the amount of binder adsorbed to the ferromagnetic metal powder in the dispersed paint and the amount not adsorbed.

(Hereafter, extra white) The evaluation of the characteristics was carried out by the following method.

(a) 10 g of paint after dispersion and 20 g of mixed solution (methyl ethyl ketone: toluene: cyclohexanone = 1:1:1) in a plastic container with adsorption and non-adsorption amount of binder to ferromagnetic metal powder in magnetic paint of 50 ml. and 1 pupil φ
Add 30g of Sus beads, shake it for 30 minutes in a paint shaker, and then centrifuge (2X10' rpm).
(1 hour) to separate the supernatant. 10m of this supernatant liquid
1 was evaporated to dryness on a hot plate, the mold amount was measured to determine the non-adsorbed amount, and the difference from the total amount of binder contained in the magnetic paint was calculated, which was determined as the adsorbed amount per 1 g of ferromagnetic metal powder.

Function) Surface Roughness of Magnetic Layer The center average roughness (Ra value) of the magnetic layer surface of each 81wl1 videotape was measured using a stylus type surface roughness meter (Talystep, manufactured by Taylor Hobson).

(C) Br and Bm were measured using a rectangular ratio vibrating sample magnetometer under the conditions of a measurement magnetic field of 5 kOe and a sweep rate of 1 minute/5 kOe, and were determined by calculating the ratio (Br/8 m).

(a) C/N (5 MHz/4 MHz) The ratio of the signal at 5 MHz to the noise at 4 MHz was measured using a C/N measuring video tape recorder (MVS-5000:
(manufactured by KODAK@). The recording and playback head uses an amorphous alloy, and the C/N of a commercially available 8m video tape.
It is shown as a relative value using as a reference (Od B).

(e) Still life Using a modified 8-kaku videotape recorder for still measurement, play back still images that have been pre-recorded under a 30g load condition in a -10°C environment, and the image signal is 3D.
B: Shown by the time it takes to become depressed.

) Using the same 81 videotape recorder as used for dropout C/N measurements, each videotape sample was heated to 40'C.

The number of occurrences of a decrease in output of 16 dB or more at 15 μs per minute was measured before and after running the bus 200 times in an environment of 80% RH.

(Chain Head Powder Adhesion After the test in (f) above, the amount of powder adhesion on the magnetic head and tape sliding surface was observed with 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.

From Table 4, regardless of the binder composition, for those with a ratio of adsorption amount to specific adsorption amount in the range of 0.8 to 1.2, C
Good results were obtained in terms of /N ratio and durability. However, it was found that those outside this range were significantly inferior in both properties. In addition, from Figure 2, it was confirmed that when the amount of binder during kneading accounts for 60 to 90% of the total amount of binder, the ratio of adsorbed amount to non-adsorbed amount falls within the range of 1.0 ± 0.2. It was done. In addition, the binder used in the present invention contains three types of resins: a first resin that contributes to dispersibility, a second resin that contributes to dispersibility and durability, and a third resin that mainly contributes to durability. The adsorption amount to the ferromagnetic metal powder serves as a guideline, the glass transition temperature (Tg) governs the mechanical strength of the magnetic coating film and serves as a guideline for hardness, and the hardening agent (diisocyanate: e.g. TDrMDI, IPDI, etc.) It was selected after conducting a reactivity test.

As a result, the first binder selected has the largest adsorption amount to the ferromagnetic metal powder and has a high Tg, and the third binder has the smallest adsorption amount, a low Tg, and a hardenability. The most excellent one, that is, the role of firmly binding the dispersed ferromagnetic metal powder. As the second binder, one having intermediate adsorption amount, Tg, and hardenability is used.

The composition ratio of these three types of binders is determined by considering the dispersibility and mechanical strength of the magnetic coating film. The content of the third binder is desirably 40-60.30-20.30-20%.

In order to improve the performance of magnetic tape, the main focus is on improving the C/N ratio and durability.
This can be freely controlled by changing the adsorption amount and non-adsorption amount to the ferromagnetic metal powder as shown above. That is, even if the same amount of binder is used, if the balance between the adsorbed amount and the non-adsorbed amount to the ferromagnetic metal powder is lost, either the C/N ratio or the durability will be poor.

Although the example of the 8m videotape has been described above, the effects of the present invention are through high-density recording and high durability, and it is suitable for professional use,
A similar effect can be obtained with consumer video tapes, digital audio tapes, etc.

Effects of the Invention As explained above, according to the method for producing a magnetic paint of the present invention, in the process of kneading the paint, after kneading 60 to 90% of the binder, primary dispersion is performed using a bead mill, and then the remaining part is mixed with the abrasive. Add a binder and perform secondary dispersion, and the ratio of the amount of binder adsorbed to the ferromagnetic metal powder to the amount not adsorbed is 1 ± 0.2.
By doing so, a highly dispersed paint can be obtained, and a coating film with strong mechanical strength can be obtained, so that the C/N ratio and durability can be greatly improved.

[Brief explanation of drawings]

Figure 1 is a process diagram for explaining the method for producing magnetic paint according to the present invention, and Figure 2 is a ratio between the amount of binder used during kneading and the amount of binder adsorbed to the ferromagnetic metal powder in the paint after dispersion and the amount not adsorbed. FIG.

Claims (1)

[Claims] It consists of a step of kneading the ferromagnetic metal powder, binder resin, and solvent, a primary dispersion step using a bead mill, and a step of secondary dispersion after adding the abrasive, and 60 to 90% of the binder resin is kneaded in the above kneading step. and the remaining part is added after the primary dispersion is completed, so that the ratio of the amount of binder resin adsorbed to the ferromagnetic metal powder and the amount not adsorbed is 1±0.2.