JPH10334463A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in electromagnetic conversion characteristics, durability and reliability. SOLUTION: In the production process of a magnetic recording medium by applying a magnetic coating material essentially comprising a Co-coated γ-Fe2 O3 magnetic powder and a binder on a nonmagnetic support, the magnetic coating material is prepared by mixing a magnetic powder and a binder, filtering, and further stirring. The coating material is prepared in such a manner that the amt. of the binder in the supernatant of the magnetic coating material is 104 to 110 when the amt. of the binder in the supernatant of the magnetic coating material after filtering is 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, particularly a coating type magnetic recording medium.

[0002]

2. Description of the Related Art A so-called coated magnetic recording medium having a magnetic layer having a structure in which a magnetic powder is dispersed in a binder on a non-magnetic support such as polyethylene terephthalate is described.
Many proposals have been made to improve reliability and stability.

[0003] In the field of magnetic recording, particularly in a VTR (video tape recorder), there is a demand for higher density recording and a shorter recording wavelength in order to achieve higher image quality. On the other hand, higher reliability and stability are required. Therefore, for the purpose of improving the characteristics of the magnetic recording medium, it is required to make the magnetic powder in the magnetic paint finer, to make the magnetic paint highly dispersed, and to stabilize the magnetic paint.

[0004] In a coating type magnetic recording medium, the dispersion state of particles in a magnetic paint prepared by mixing these greatly differs depending on the type of magnetic powder, binder, and additive used. It is necessary to pay attention to the optimum dispersion state in order to obtain the required characteristics.

Further, in order to improve the magnetic characteristics of the magnetic recording medium, the magnetic powder in the magnetic coating material for forming the magnetic layer is subjected to a pulverization and dispersion treatment so that the magnetic powder approaches uniform fine particles, so-called primary particles. There is a need.

[0006]

However, a high dispersion treatment is applied to the magnetic powder for forming the magnetic layer,
Even if a magnetic paint is prepared by mixing with a binder or the like, re-aggregation of the magnetic powder occurs if the magnetic paint is allowed to stand. When reagglomeration of the magnetic powder occurs in the magnetic paint, there is a possibility that the magnetic properties of the finally obtained coating type magnetic recording medium may be adversely affected.

Therefore, in order to avoid such inconvenience in the magnetic paint, it is necessary to moderately reduce the adsorbing force of the magnetic powder in the magnetic paint and to stabilize the magnetic paint.

[0008]

According to the present invention, a magnetic coating mainly comprising Co-coated γ-Fe ₂ O ₃ magnetic powder and a binder is applied on a non-magnetic support to form a magnetic layer. In the method of manufacturing a magnetic recording medium to be formed, at least steps a to e are performed. That is, a. A step of preparing a magnetic paint by mixing the magnetic powder and a raw material of a magnetic paint mainly containing the binder. b. A step of dispersing the magnetic paint. c. Thereafter, a filtration step of filtering the magnetic paint. d. Thereafter, a step of stirring and storing the magnetic paint without relying on standing storage. e. Applying the magnetic paint on a non-magnetic support. Through the following steps, a target magnetic recording medium is manufactured. In the present invention, when the ratio (weight) of the binder in the supernatant liquid of the magnetic paint after the step b and before the next step is 100, the supernatant of the magnetic paint after the step d is The ratio (weight) of the binder in the liquid is 104 to 1
It is assumed to be 10.

[0009] Each of the supernatant liquids is a liquid obtained by partially removing each of the magnetic paints after the above-mentioned steps b and d and separating them by a centrifugal separator. It has been found that the adsorbing force of the particles in the magnetic paint that forms the layer can be moderately reduced, and that the magnetic paint can be stabilized, whereby the electromagnetic conversion characteristics, durability, A highly reliable magnetic recording medium was obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as described above, a magnetic paint mainly composed of Co-coated γ-Fe ₂ O ₃ magnetic powder and a binder is applied on a non-magnetic support. A method for manufacturing a magnetic recording medium on which a magnetic layer is formed, comprising: a. A step of preparing a magnetic paint by mixing the magnetic powder and a raw material of a magnetic paint mainly containing the binder. b. A step of dispersing the magnetic paint. c. Thereafter, a filtration step of filtering the magnetic paint. d. Thereafter, a step of stirring and storing the magnetic paint without relying on standing storage. e. Applying the magnetic paint on a non-magnetic support. Through the following steps, a target magnetic recording medium is manufactured. In the present invention, when the ratio (weight) of the binder in the supernatant liquid of the magnetic paint after the step b and before the next step is 100, the supernatant of the magnetic paint after the step d is The ratio (weight) of the binder in the liquid is 104 to 1
It is assumed to be 10.

Hereinafter, the present invention will be described with reference to specific examples of the present invention and comparative examples that facilitate understanding of the features of the present invention. However, the present invention is not limited to the following examples.

First, a magnetic paint is prepared. The composition of the magnetic paint and its respective amounts are shown.

Magnetic powder Co-coated γ-Fe ₂ O ₃ : 100 parts by weight (average major axis length: 0.28 μm, specific surface area: 40.7 m ² / g, coercive force Hc: 48.2 kA / m, saturation magnetization σs: 76.0 Am ² / kg, water content: 0.58% by weight, pH: 8.9) Binder Polyester polyurethane: 6 parts by weight (sulfonic acid group: 0.074 mmol / g, average molecular weight Mn: 20,000) ) Polyester polyurethane: 4 parts by weight (carboxylic acid group: 0.05 mmol / g, sulfonic acid group: 0.009 mmol / g, average molecular weight Mn: 26000) Vinyl chloride copolymer: 2 parts by weight (carboxylate group: 0) 0.07 mmol / g, average molecular weight Mn: 23000) Nitrocellulose: 2 parts by weight (secondary hydroxyl group: 3.97 mmol / g, average molecular weight Mn: 28,000) Agent Cr ₂ O _3: 15 parts by weight antistatic agent carbon black 5 parts by weight lubricant stearate: 1 part by weight Butyl stearate: 2 parts by weight Solvent Methyl ethyl ketone: 102 parts by weight Toluene: 102 parts by weight Cyclohexanone: 50 parts by weight

The raw materials for the magnetic layer were pre-treated and mixed in a tank equipped with a stirrer for about 2 hours. Thereafter, mixing and dispersion were performed with a sand mill. With respect to the liquid obtained by partially removing the magnetic paint thus obtained and separating it by a centrifuge, that is, the so-called supernatant liquid, the ratio R _{0 of} the binder contained in the liquid, that is, the concentration (by weight) thereof was determined by liquid chromatography. And set this to 100. next,
The magnetic paint after the above dispersion is further filtered using a 5.0 μm filter. Thereafter, each of the filtered magnetic paints was separated and stored in a stirring tank by stirring at medium to low speed for each stirring time shown in Table 1 below. With respect to these magnetic paints, the concentration of the binder, that is, the ratio R of the supernatant was measured in the same manner as described above.

Thereafter, 20 parts by weight of a polyisocyanate compound was added to each of the magnetic paints and mixed and dispersed. The magnetic paint thus obtained was placed on a 9.3 μm thick non-magnetic support made of, for example, polyethylene terephthalate.
Coating was performed so that the thickness of the finally obtained magnetic layer was 5.5 μm, and then a magnetic field orientation treatment was performed. Next, the magnetic layer was dried and calendered, and then cured, and then cut to a 1/2 inch width to produce a magnetic tape.

In the production of the magnetic tape described above, in the method of the present invention, R ₀ measured as described above is 100
In this case, the above R is set to 104 to 110. More specifically, control and selection of the above-described conditions such as the medium-to-low speed stirring time are performed so that the above-mentioned R becomes 104 to 110.

A description will be given of [Example 1], [Example 2], [Comparative Example 1], [Comparative Example 2] and [Comparative Example 3]. In these [Example 1], [Example 2], [Comparative Example 1], [Comparative Example 2] and [Comparative Example 3], magnetic tapes were produced by the method described above.
As shown in Table 1, the concentration of the binder in the supernatant was changed to 166 hours in Example 1, 72 hours in Example 2, and Comparative Example 1 by changing the low-speed stirring time.
Is 19 hours, Comparative Example 2 is 0 hours, that is, when the medium-low speed stirring is not performed, and Comparative Example 3 is 200 hours. In this case, the ratio R of the supernatant binder is as shown in Table 1,
Further, for each magnetic tape, the electromagnetic conversion characteristics (YR
F), head grinding power, and video head dusting were measured and evaluated. The measurement results of each property, the viscosity of each magnetic paint after the above-described stirring of the magnetic paint, the glossiness of the magnetic layer surface after application on the non-magnetic support,
Table 1 shows the results of measurement of surface properties.

[0018]

[Table 1]

Here, as for the electromagnetic conversion characteristics, when the output of the reference tape is 0 dB, the output level of each sample tape when a 50% white signal is input is represented by a relative value. In addition, BVW-40 (trade name of VCR made by Sony Corporation) was used as a measuring instrument.

With respect to the head polishing force [μm], the operation of recording a signal for each sample tape for 15 minutes, rewinding, and again recording the signal was performed four times, and the wear of the video head after running for one hour was performed. The amount was measured. In addition, BVW-70 (trade name of VCR made by Sony Corporation) was used as a measuring instrument.

Regarding the video head dusting, first, the running system of the measuring machine, the head and the drum are cleaned, the produced sample tape is run (recording and reproduction), and the video head after running is observed with a microscope. Then, it is assumed that the powder loss of the video head is evaluated. Evaluation,
A mark that has little powder drop and is practically preferable is marked with a circle, and a mark that has powder drop but does not cause a problem in practice is marked with a mark.
Those that are practically problematic are indicated by crosses. In addition,
BVW-70P (trade name of VCR made by Sony Corporation) was used as a measuring instrument.

Regarding the viscosity of the magnetic coating material [Pa · s], the stirring times produced as described above, which are different from each other in the stirring times [Example 1], [Example 2], [Comparative Example 1], [Comparative Example 2] and [ Each of the magnetic paints in Comparative Example 3 was replaced with a rotor type (B
(Type) Measure using a viscometer. Note that a digital viscometer (manufactured by Tokyo Keiki Co., Ltd.) was used as a measuring instrument.

With respect to the glossiness of the surface of the magnetic layer, the stirring times produced as described above and differing in the stirring time [Example 1], [Example 2], [Comparative Example 1], [Comparative Example 2] and [Comparative Example] Each of the magnetic paints in 3) was applied on a surface of polyethylene terephthalate having a thickness of 20 μm using a doctor blade, and 45 ° light was incident on each sample prepared by performing an orientation treatment while the coating film was not dried. The gloss at the corner was measured. In addition, digital variable-angle gloss meter VG-1 was used as a measuring instrument.
D (trade name, manufactured by Nippon Denshoku Industries Co., Ltd.) was used.

Regarding the surface properties of the magnetic layer, the stirring times produced as described above differ with respect to [Example 1], [Example 2], [Comparative Example 1], [Comparative Example 2] and [Comparative Example 3].
Each of the magnetic paints was coated on a surface of polyethylene terephthalate having a thickness of 20 μm by using a doctor blade, and the surface of the magnetic layer was visually observed for each sample prepared by performing an orientation treatment while the coating film was not dried. And observation with an optical microscope to perform a relative evaluation when compared with the surface properties of the magnetic layer in [Example 1]. in this case,
When the evaluation of [Example 1] was evaluated as 同等, the equivalent was evaluated as ○, followed by △ and × in the order of good surface properties.

As shown in Table 1, when the ratio R of the binder in the supernatant of the magnetic paint after stirring in Examples 1 and 2 was 110 and 104, respectively,
It was found that the magnetic tape produced in this manner had good electromagnetic conversion characteristics, had an appropriate head polishing force, and had relatively good powder dusting of the video head. Also, the viscosity of the paint was relatively low and the applicability was good.

However, as shown in [Comparative Example 1] and [Comparative Example 2], when stirring was not performed, or when R after stirring was less than 104, relatively good electromagnetic conversion characteristics were obtained. You can see that it cannot be done. Further, in these cases, the viscosity of the coating material becomes too high, so that the surface property after coating is deteriorated, and the characteristics of the powder drop of the video head are lower than those of the above [Example 1] and [Example 2]. It can be seen that the headwear is too large.

Further, as shown in [Comparative Example 3], when the ratio R of the binder in the supernatant of the magnetic paint after stirring exceeds 110, the amount of particles adsorbed in the paint becomes small.
It can be seen that the durability is somewhat inferior, and relatively good electromagnetic conversion characteristics cannot be obtained.

From the above, when the ratio R ₀ of the binder in the supernatant of the magnetic paint before stirring is 100,
The ratio R of the binder of the magnetic paint after stirring is set to 104 to 110.
When a magnetic layer is formed with a magnetic paint, the adsorption force of particles in the magnetic paint can be moderately reduced and the magnetic paint can be stabilized, so that the electromagnetic conversion characteristics, durability and reliability can be improved. A magnetic recording medium having excellent properties was obtained.

In the above-described embodiment, polyethylene terephthalate is used as the nonmagnetic support constituting the magnetic recording medium. However, the present invention is not limited to this example, and polyester such as polyethylene 2,6-naphthalate is used. , Polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polyamide and polycarbonate, metals such as Cu, Al and Zn, glass,
Any of ceramics such as BN and SiC can be used.

The form of the nonmagnetic support can be applied to various forms such as a film form, a tape form, a sheet form and a card form.

[0031]

According to the present invention, the adsorbing force of the particles in the magnetic coating material forming the magnetic layer can be moderately reduced and the magnetic coating material can be stabilized, so that the electromagnetic conversion characteristics, A magnetic recording medium having excellent durability and reliability was obtained.

Claims (1)

[Claims] 1. Co-coated γ-Fe ₂ O on a non-magnetic support
_{3. A} method for producing a magnetic recording medium having a magnetic layer mainly composed of a magnetic powder and a binder, comprising: a. Mixing the raw material of the magnetic powder and the magnetic paint mainly containing the binder to prepare a magnetic paint; b. Dispersing the magnetic paint; c. Thereafter, a filtration step of filtering the magnetic paint, d. Stirring and storing the magnetic paint; e. Coating the magnetic paint on a non-magnetic support, and when the ratio (by weight) of the binder in the supernatant of the magnetic paint after the step b is 100, after the step d) The ratio (by weight) of the binder in the supernatant of the magnetic paint of
To 110, characterized by the following: