JPH03288330A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To attain high-frequency characteristics with the coating type intra-surface recording medium by applying and forming a magnetic layer on a nonmagnetic base, then subjecting the layer to a nonorienting treatment which does not apply magnetic fields and two stages of orienting treatments varying in conditions. CONSTITUTION:The main constitution of an orienting device consists of the 1st orienting stage consisting of a permanent magnet 1, the same poles of which face each other, and the 2nd orienting stage arrayed with 10 pieces of electromagnets 2 in a longitudinal direction. The magnetic layer essentially consisting of acicular or particulate magnetic particles and a resin binder is first applied on the nonmagnetic base. The magnetic layer is then subjected to the nonorienting stage which does not apply the magnetic fields from the outside for >=2 to <=7 seconds. The magnetic layer is thereafter subjected to the 1st orienting stage which applies the DC magnetic fields within the coated surface and in the longitudinal direction having the max. magnetic field of >=3 times and <=5 times the coercive force HC of the magnetic particles. The magnetic layer is subjected to the 2nd orienting stage in which the DC magnetic fields within the coated surface and in the longitudinal direction having the min. magnetic field of >=1/2 the coercive force HC of the magnetic particles continue for at least >=0.7 second. The magnetic recording medium of an excellent coating type having the excellent orientability in the coated surface is produced while the ultra-smooth surface is attained without impairing the surface characteristics of the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a coated magnetic recording medium used in video equipment, audio-related equipment, information-related equipment, and the like.

Conventional technology With the advancement of higher image quality in the field of video equipment, digital signal processing in the field of audio equipment, and miniaturization and faster processing of computer peripheral equipment, the coated type has been widely used as external memory for these devices. For magnetic recording media, it has become important to improve recording and reproducing characteristics in high-density recording areas.

In the field of magnetic tapes based on the currently mainstream in-plane magnetic recording method, iron oxide magnetic particles coated with Co to improve coercive force and metal magnetic particles with high saturation magnetization and coercive force are used. There is a trend to adopt these as recording elements.

In order to further increase the recording density, the following measures have been taken.

■ Improve magnetic properties by making magnetic particles finer, lowering the axial ratio, and increasing the particle packing density in the magnetic layer.

■ The magnetic particles are aligned as much as possible in the longitudinal direction, which is the recording direction, to increase the residual magnetization strength of the magnetic properties.

■ Minimize the surface roughness of the magnetic layer as much as possible to suppress magnetic loss due to the gap between the magnetic layer and the head during recording and reproduction.

Problems to be Solved by the Invention However, in each approach, ■ Challenges in the ability of the alignment system to increase the filling degree while aligning ultrafine magnetic particles with high coercive force and low axial ratio with precision ■ Between the magnetic particles of ultrafine particles repulsive interaction (reorientation)
Initial orientation/orientation alignment technology that overcomes problems ■ Issues have emerged in orientation technology, such as an orientation fixing method that does not cause the aligned magnetic particles to reorient. - Improvement of orientation at low axial ratios - Suppression of reorientation due to coating film formation with high viscosity paint - Suppression of reorientation due to increased viscosity during coating drying are being studied.

However, with these countermeasures, ・Roughness of the oriented surface due to magnetic particle coarse movement (flowing of the coating film) caused by high magnetic fields ・Decrease in initial orientation due to high viscosity coating ・Decrease in leveling ability of the coating film ・Surface roughness due to drying, etc. However, there are problems with the balance of surface properties and orientation behavior.

It is an object of the present invention to solve the above-mentioned problems and to realize a coated longitudinal recording medium with high-frequency characteristics on the same level as a medium having a magnetic metal thin film as a magnetic layer.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention coats and forms a magnetic layer containing acicular or granular magnetic particles and a resin binder as main ingredients on a non-magnetic support, and then coats the magnetic layer on a non-magnetic support for 2 seconds. A non-orientation treatment step in which no external magnetic field is applied for 7 seconds or less, and a DC magnetic field in the longitudinal direction within the coated surface whose maximum magnetic field is 3 times or more and 5 times or less than the coercive force ('Hc>) of the magnetic particles. a first orientation step; and a second orientation step in which a direct current magnetic field in the coated surface and in the longitudinal direction in which the minimum magnetic field is 1/2 or more of the coercive force of the magnetic particles continues for at least 0.7 seconds, and the magnetic particles are aligned in the longitudinal direction within the coating surface.

Furthermore, by coating a magnetic layer containing acicular or granular magnetic particles and a resin binder as main ingredients on a non-magnetic support, a magnetic paint containing magnetic particles and a resin binder as main ingredients can be produced with a solid content of 25% to 45%. The following configuration makes the effect more effective.

Further, the effect is made even more effective by using the magnetic layer formed by coating on the non-magnetic support mainly consisting of acicular metal magnetic particles having an axial ratio of 5 or more and 14 or less and a resin binder.

Effects The present invention has the following three effects based on the above-mentioned power.

(1) Before the first orientation step, by introducing a non-orientation treatment step in which no external magnetic field is applied for 2 seconds or more and 7 seconds or less, the initial orientation is not impaired and the leveling property of the magnetic coating film itself is improved. It produces an effect that suppresses surface roughness (orientation surface roughness) caused by coarse movement of magnetic particles by maximizing the effect and balancing with the effect of the first alignment process.

Here, the time required for the non-orientation process needs to be adjusted depending on the solid content of the paint and the molecular weight of the resin material during coating film formation. However, in view of the paint properties during coating film formation considered from the coating technology and material technology related to the present invention, the above effects can be sufficiently obtained by applying a non-orientation treatment step of 2 seconds or more and 7 seconds or less.

(2) The first orientation step is based on the premise that a high magnetic field is applied as an initial orientation to highly orient the ultrafine particles, high coercive force, and low axial ratio magnetic material in the longitudinal direction, and an appropriate magnetic field is applied to the magnetic particles. A DC maximum magnetic field that is 3 times or more and 5 times or less the coercive force (Hc) of is applied within the coated surface and in the longitudinal direction. Here, if the hard magnetization axis of the magnetic particles is oriented in the direction of the magnetic field in the initial state before orientation, effective orientation behavior will not start if the maximum magnetic field is less than three times the coercive force. In addition, if the maximum magnetic field is more than 5 times the coercive force, the magnetic coating itself begins to move like a magnetic fluid, and the smoothness and homogeneity of the coating obtained by leveling properties are impaired, resulting in a magnetic coating with poor surface properties. It becomes a layer.

From the above, it has been found that the maximum magnetic field of the DC magnetic field in the longitudinal direction within the coated surface used for orientation is 3 times or more and 5 times or less than the coercive force of the magnetic particles, without impairing the surface properties of the magnetic layer and at the initial stage of the magnetic particles. Acts to enhance orientation.

(3) Furthermore, in the second orientation process provided to fix the particle alignment of the magnetic coating film that has achieved both initial orientation and surface properties through (1) and (2), the minimum magnetic field is the coercive force of the magnetic particles. When the particle size is 1/2 or more, the repulsion between particles after orientation can be suppressed and alignment can be maintained.

・DC magnetic field within the coating surface and in the longitudinal direction is at least 0.7
By continuing for more than a second, it is possible to correct the orientation state of the magnetic particles that could not be reliably aligned in the initial orientation, and it is possible to fix the orientation state even if strong drying is performed, which may cause surface roughness of the coating film.

It has such an effect. As a result, the highly oriented state of the magnetic particles with high coercive force and low axial ratio can be maintained and fixed while ensuring smooth surface properties.

Forming a coating film using a magnetic paint with a solid content of 25% or more and 45% or less, and a magnetic recording medium whose main ingredients are acicular metal magnetic particles with an axial ratio of 5 or more and 14 or less and a resin binder. By producing a magnetic recording medium based on the present invention, it is possible to obtain a magnetic recording medium with excellent longitudinal orientation and surface properties, which could not be achieved using conventional methods.

EXAMPLE Hereinafter, a comparison between an example of the present invention and a conventional example will be explained with reference to the drawings.

FIG. 1 shows a specific configuration of an orientation apparatus based on the present invention.

The main configuration of the orientation device is rare earth permanent magnets 1 with the same polarity facing each other.
It consists of a first orientation step in which 10 electromagnets 2 made by winding a conducting wire into a solenoid shape are arranged in the longitudinal direction. Here, the components of the first and second alignment steps are installed by a magnet installation stand 4 on alignment device installation guide rails 3 installed on both sides of the non-magnetic support running system parallel to the running surface. The structure is such that the distance from the coating film forming device (coating device) 5 can be changed arbitrarily.

Using such an orientation device, <Example 1> based on the present invention
~6 sample tapes were created. These orientation conditions are shown in Table 1.

To perform the orientation processing method shown in Table 1 using this orientation device, ■ Non-orientation processing time: Move the setting position of the orientation device back and forth in a guide rail shape. ■ ■ ■ First orientation process: Maximum magnetic field Second Orientation step: Minimum magnetic field Second orientation step: Adjust application time.

Between opposite permanent magnets with the same polarity Adjust according to distance.

Applied to the solenoid-like electromagnet Depending on the current value, The value of the magnetic field that has fallen after hearing a thousand words control.

10 solenoid-like electromagnetic Electric current is applied to the stone from the applicator side. flow and control the magnetic field length.

Table 1 For this example, the thickness of the non-magnetic support is 10 μm.
m polyethylene terephthalate film (hereinafter referred to as PE
(abbreviated as T film) with a thickness of 3.0 μm on its surface.
A sample was prepared as an 8m5 VTR tape in which the magnetic layer was continuously coated and a back coat layer with a thickness of 0.5 μm was formed on the back surface.

The method for preparing the sample will be explained in detail below.

(1) Materials forming the magnetic layer The materials forming the magnetic layer and their ratios are as follows.

Metal magnetic material: 100 parts by weight Resin-based pine mites 20 parts by weight Alumina: 7 parts by weight Carbon: 3 parts by weight Aliphatic lubricant: 4 parts by weight Hardening agent = 5 parts by weight Metal magnetic material is relatively small for conventional VTR use. We selected a material with a low axial ratio, making it difficult to ensure orientation.

Table 2 shows its characteristics.

The resin binders in Table 2 were made by mixing the resins shown in Table 3 to form a standard composition as a binder for VTR tapes.

Table 3 Blending ratio: weight ratio with magnetic powder weight as 100.

Each amount is determined to be the most excellent ratio based on the results of a tensile test of a coating film using a binder resin system and a scratch strength test of a magnetic coating film.

Resin d was selected for pre-treating the alchemist.

Alumina has a particle size of 0.10-0.30 pm and has BE
A general material having a T specific surface area of 9 to 15 rrf/g was used, and it was pretreated with 1 part by weight of resin d, and dispersed at an appropriate viscosity using a ξru dispersion machine.

For the remaining 19 parts by weight of the binder, mix the magnetic powder and
It was added during pre-dispersion.

Regarding carbon, the particle size of the -order particles is 200 to 300
Å was used.

Three types of aliphatic lubricants commonly used in magnetic recording media were selected and mixed in the following blending ratio.

CI4: 1 part by weight C18: 1 part by weight Cl8-C4: 1 part by weight A commonly used isocyanate compound was used as a curing agent.

(2) Creation of VA paint The magnetic paint was prepared as follows.

A mixture of metal magnetic powder, carbon and methyl ethyl ketone: toluene: cyclohexanone = 3:3:1 was added to a mixer and stirred for one hour to thoroughly wet the powder with the solvent, and then the resin a. While adding Resin B, Resin C and the remaining amount of the mixed solvent to a mixer, the mixture was stirred for 5 hours to increase the powder size. Thereafter, crosstalk treatment was performed for 4 hours while adjusting the viscosity of the paint.

After diluting this magnetic kneaded material, dispersion was carried out using a sand mill, which is commonly used for paint dispersion.

Upon completion of sand mill secondary dispersion, alumina paste which had been separately dispersed with resin d was added and stirred, and secondary dispersion treatment was performed again using a sand mill.

Immediately before coating, a lubricant solution and a curing agent were added and stirred to the metal magnetic paint stock solution obtained in this manner to complete the preparation of the magnetic paint.

The solid content of the paint (N, ν,) at this time was 30.0%.

(3) Formation method of magnetic layer The method of forming the magnetic layer is to continuously coat the prepared and dispersed magnetic paint onto the 7PPT film using a gravure coater, and immediately after coating, the first orientation treatment in the present invention is performed. The treatments shown in the table were performed. Thereafter, after passing through a main drying step, a calender treatment was performed to give a mirror finish, and this was subjected to a curing reaction in a curing furnace.

(4) Method of Forming Back Coat Layer The back coat layer was formed by continuously applying a special paint containing carbon black as a main component using a gravure coater after forming and curing the magnetic layer.

The sample prepared as described above was slit into a width of 8 cm, and then the difference from the comparative example described below was examined.

Comparative Examples Comparative examples were prepared using the alignment apparatus described in Examples and the alignment treatment shown in Table 4.

(Margins below) Table 4 For these comparative examples, samples were prepared using the same material composition and magnetic coating preparation method as in the examples.

Each of the samples thus prepared was slit into 8-width slits, and its properties were compared with those of Examples.

For each sample, (1) the in-plane longitudinal component of the tape squareness ratio (Br/Bm) (2) and the surface roughness of the magnetic layer were evaluated.

The evaluation results will be explained step by step below.

Table 5 shows the squareness ratio in the longitudinal direction of the tape and the average surface roughness of each sample of the Examples and Comparative Examples, organized according to orientation conditions. Squareness ratio is swept magnetic field 10 k Oe
The average surface roughness was measured using an optical interference type non-contact three-dimensional surface roughness meter using a vibrating magnetization measuring device.

As is clear from Table 5, the conditions of the examples shown below: (1) Non-orientation time = 2.0 seconds to 7.0 seconds (2) Maximum magnetic field strength in the first orientation step: magnetic powder coercive force 3 to 5 times (3) Minimum magnetic field strength in the second orientation process: VA magnetic powder coercive force 1/2 or more (4) Application time in the second orientation process: 0.7 seconds or more A sample that satisfies all of the following is a tape long A high squareness ratio of 0.86 or more in the direction and excellent surface properties of an average surface roughness of 6n+m are both compatible.

Looking at comparative examples in which high orientation and ultra-smoothness are not compatible, the following phenomena occur because conditions (1) to (4) above are not satisfied.

Comparative Example 1: Because the non-orientation time was short, the orientation returned after the orientation process.

Comparative Example 2: The non-orientation time was too long, and the orientation was fixed before the orientation was completed during the orientation process.

Comparative Example 3: Because the maximum magnetic field in the first orientation step was low, magnetic particles with a low axial ratio were not fully oriented.

Comparative Example 4: Although a very high squareness ratio was obtained, the maximum magnetic field in the first orientation step was too high, causing the magnetic particles to flow, resulting in poor surface roughness.

・Comparative Example 5: Because the minimum magnetic field in the second orientation step was too low,
In this section, the reorientation of the magnetic particles cannot be suppressed, and the degree of orientation created in the first orientation step decreases.

・Comparative Example 6: The application time of the second alignment step was too short, so
After the orientation process, the orientation returns.

In this way, when using magnetic particles with a small axial ratio that are difficult to align, the orientation method of the comparative example cannot achieve high orientation because the conditions for the orientation treatment are outside the settings for highly accurate orientation. Can not. Even if a high degree of orientation can be ensured, the surface of the magnetic layer will become rough, and as a result, the electromagnetic conversion characteristics in the short wavelength range will be impaired.

On the other hand, in the Examples, tape characteristics clearly superior to those in the Comparative Examples were obtained because the optimum orientation method of the present invention was used to obtain high orientation while maintaining the surface roughness.

In this embodiment, a combination of a rare earth permanent magnet and a solenoid type electromagnet is used as the alignment device, but it is also possible to use only a permanent magnet or only an electromagnet, and the shape of the electromagnet may also be used as long as the alignment processing method according to the present invention can be realized. It does not have to be solenoid-like, and the present invention is not limited to the constituent materials of the magnetic layer or the methods of making it into paint or tape, and any material, method of making it into paint, application method, etc. that can make a coated magnetic tape can be used. The effects of the present invention can be obtained no matter what kind of material is used.

(The following is a blank space) Table 5 Effects of the Invention As is clear from the above examples, according to the present invention, a coating with excellent in-plane orientation can be achieved while achieving an ultra-smooth surface without impairing the surface properties of the magnetic layer. type magnetic recording media can be manufactured continuously and stably, and its electromagnetic conversion characteristics exhibit excellent recording and reproducing characteristics even in high-density recording areas.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an orientation apparatus used in carrying out the present invention. I... Rare earth permanent magnet with the same poles facing each other, 2...
... Solenoid-shaped electromagnet, 3 ... Guide rail for installing orientation device, 4 ... Magnet installation stand, 5 ...
...Coating film forming device.

Claims (3)

[Claims] (1) After coating and forming a magnetic layer mainly composed of acicular or granular magnetic particles and a resin binder on a non-magnetic support, a non-orientation treatment step in which no external magnetic field is applied for 2 seconds or more and 7 seconds or less , a first alignment step in which a direct current magnetic field is applied in the longitudinal direction within the coated surface where the maximum magnetic field is 3 to 5 times the coercive force (Hc) of the magnetic particles, and a minimum magnetic field is 1/1/2 of the coercive force (Hc) of the magnetic particles. a second alignment step in which a direct current magnetic field in the longitudinal direction within the coating surface of 2 or more continues for at least 0.7 seconds, and magnetic particles are aligned in the longitudinal direction within the coating surface. Method of manufacturing media. (2) By coating and forming a magnetic layer containing acicular or granular magnetic particles and a resin binder as main ingredients on a non-magnetic support, the solid content of the magnetic paint containing magnetic particles and a resin binder as main ingredients is 25% or more. A claim characterized in that it is 45% or less (
1) The method for manufacturing the magnetic recording medium described above. (3) The magnetic recording medium according to claim (2), wherein the magnetic layer formed by coating on the non-magnetic support mainly comprises acicular metal magnetic particles with an axial ratio of 5 or more and 14 or less and a resin binder. manufacturing method.