JPS58200425A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having superior traveling performance, durability, etc. as well as high sensitivity, by forming a magnetic layer consisting of an under layer contg. magnetic powder at a higher filling rate and an upper layer contg. magnetic powder at a lower filling rate together with a lubricant, an antistatic agent and an abrasive material on a substrate. CONSTITUTION:A layer 3 consisting of magnetic powder and a binder is formed on a substrate 1. The filling rate of the powder is 80-90wt%, and the ratio of thermosetting resin/thermoplastic resin in the composition of the binder is 50/ 50-0/100. An upper magnetic layer 2 similar to the layer 3 and consisting of 75-85wt% magnetic powder, a binder a lubricant, an antistatic agent and an abrasive material is formed on the layer 3 in 0.5-1.5mum thickness. The coercive force of the layer 2 is 0-50% larger than that of the layer 3, and the ratio of thermosetting resin/thermoplastic resin in the composition of the binder is 50/ 50-100/0. Thus, a magnetic recording medium having superior adhesive strength to its substrate, superior wear resistance, high sensitivity and high output level is obtd. The medium is suitable for high density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, particularly to the formation of a magnetic coating film with high magnetic flux density, and provides a magnetic recording medium with high sensitivity and suitable for high-density recording using a simple method.

In general, magnetic recording media are made by using a magnetic coating liquid obtained by uniformly dispersing magnetic powder, lubricant, antistatic agent, abrasive, etc. in a binder, which is an organic polymer compound, using a solvent. Coating on the base material, orientation,
It is obtained by cutting to a predetermined width after drying and mirror-finishing the surface. As the binder □, vinyl chloride-vinyl acetate copolymer 3/1, polyurethane resin, epoxy resin, etc. are used, and as the magnetic powder, γ-Fe2O3゜CoT
Acicular fine particles such as Fe2O3, CrO2 and Fe are used, silicone oil, carbon granite, etc. are used as lubricants, carbon black etc. are used as antistatic agents, and Al2O3, Cr2O are used as abrasives.
3rd grade is mainly used. In addition, lecithin and surfactants are used as dispersants, and various fatty acids and fatty acid esters are used as plasticizers, but these are common matters when manufacturing magnetic coating liquids, and unless otherwise specified, this is not the case. In the description of the invention, it is assumed that the invention will be used, and the description will be omitted.

In order to increase the filling rate of magnetic powder in the magnetic layer, it is necessary to reduce the solid content ratio of binders other than magnetic powder, lubricants, antistatic agents, abrasives, etc., or use a more sophisticated dispersant or dispersion machine. One possible method is to increase the filling rate by dispersing the magnetic powder at a higher level. However, in the former case, after completion---1, the physical characteristics of the magnetic tape,
In particular, the adhesion strength of the coating film, 4. JP-A-58-200425 (and) scratch strength etc. decreases, the coefficient of friction and surface resistivity increase, and the running durability deteriorates significantly. In the latter case, the dispersion process requires a very long time, and there are problems such as destruction of the original characteristics of the magnetic powder, especially the acicular shape, and worsening of the noise level. ○ The present invention aims to improve electromagnetic conversion characteristics such as sensitivity, and provides a highly sensitive and high-density magnetic recording medium by highly filling magnetic powder without deteriorating physical characteristics. It is simple and highly effective.

An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, the magnetic recording layer is composed of two layers, an upper layer 2 and a lower layer 3, on a base material 1, and the upper layer 2 contains additives that control the running durability, such as a lubricant, an antistatic agent, and an abrasive. However, the above-mentioned additives are not blended into the lower layer 3, which does not particularly affect the running durability characteristics.

As a result, it is possible to increase the filling rate of magnetic powder in the lower layer 3 as a replacement amount for lubricants, antistatic agents, and abrasives, and the magnetic flux density of the lower layer 3 is high, resulting in high sensitivity and high density as a whole magnetic layer. magnetic recording media can be obtained. In this case, the filling rate of magnetic powder in each layer is 76 for upper layer 2.
From the viewpoint of overall properties, it is desirable that the content of the lower layer 3 be 80 to 90% by weight. In other words, in terms of magnetic properties, higher filling of magnetic powder is better, but if the binder ratio is too low, the physical properties of the magnetic layer, especially the adhesion strength of the coating film,
This results in a decrease in scratch strength, etc., making it impossible to satisfy durable running performance. In the setting range of the filling rate of magnetic powder in each layer in the present invention, if the setting range is below the lower limit, the magnetic properties will not satisfy the characteristics required for a magnetic recording medium, and if it is above the upper limit, the physical properties will not satisfy the characteristics required for a magnetic recording medium. The inventor's numerous experimental results have revealed that comprehensively superior characteristics can be obtained by combining each layer.

Furthermore, the upper layer 2 is a region involved in short wavelength recording, and the coercive force of the magnetic powder is made larger than that of the lower layer in order to compensate for the low filling rate of magnetic powder with respect to the lower layer 3 and to improve short wavelength recording characteristics. This is effective. In this case, if magnetic powder with completely different characteristics is used in each layer, special measures will often have to be taken in view of the equipment used, such as the magnetic head and electric circuit. Therefore, it is practical to limit the amount of magnetic powder to a range of magnetic powders with different coercive forces. In this case, according to the experimental results of the present inventor, if the coercive force of the upper layer magnetic powder is within a range of 0 to 60 degrees greater than that of the lower layer, the two-layer structure of different coercive force magnetic layers will cause distortion of frequency characteristics, beats, etc. It became clear that good magnetic properties could be obtained without any problems.

Further, in order to increase the magnetic flux density of the entire magnetic layer, it can be effectively achieved by increasing the ratio of the thickness of the lower layer 3, which is highly filled with magnetic powder, to the total magnetic layer. It is only the surface of the upper layer 2 that governs running durability, and the upper layer 2 fully exhibits its function with the minimum necessary thickness. However, there is currently a limit to the particle size of solid additives such as lubricants, antistatic agents, and abrasives that are added to R@2. be. According to the study results of the present inventors, it is necessary for the thickness of the upper layer 2 to be at least equal to or greater than the particle size of the additive in order for the additive to perform its function in the coating film. In order to ensure uniformity, the thickness must be greater than the particle size of the additive.

On the other hand, it is desirable that the upper limit of the thickness of the upper layer be as small as possible in terms of magnetic properties, but if it is up to about 1.6 μm, the decrease in sensitivity caused by the upper layer 2, which has a low magnetic flux density compared to the current head cap, will not be particularly noticeable. It's not big.

Furthermore, high filling of the magnetic powder can be effectively achieved by using a binder for the lower layer 3 that is mainly composed of a thermoplastic resin that can be easily filled. on the other hand,
Since the upper layer 2 is required to have durable running properties, it is desirable that the binder has a thermosetting resin as its main component. The thermoplastic resin of the lower layer 3 is also effective in ensuring adhesion strength with the base material.
It is also easy to adjust the flexibility of the magnetic recording medium as a whole.

In addition, the surface of the upper layer 2 tends to be more mirror-finished in order to improve high-density recording characteristics, and even in this case, it is necessary to obtain a strong coating that can withstand close contact with a magnetic head. The use of thermosetting resins is most effective. In this case, according to the inventor's experimental results, the ratio of thermosetting resin/thermoplastic resin in each layer is so that the upper layer 2 is
, 'so~10010, and the lower layer 3 is so, 'so~o
/1'00, it was possible to obtain well-balanced mechanical properties, especially physical properties, required for a magnetic recording medium. That is, the running durability of the upper layer 2, the adhesion of the lower layer 3 to the base material, the adhesion to the upper layer 2, etc. all satisfied the necessary properties.

Furthermore, the lubricants, antistatic agents, and abrasives added to the upper layer 2 are mainly solid at room temperature, and as mentioned above, reducing the thickness of the upper layer 2 leads to improved magnetic properties. Therefore, it is desirable that the particle size of additives such as 1□''' be small.As long as the thickness of the upper layer 2 is up to 1.6 μm, there will be no significant deterioration in the magnetic properties. It is desirable that the particle size of the additive does not exceed this value, and the present inventor believes that it is necessary that the particle size of the additive does not exceed O,S ~ 1.0 μm in order to satisfy the overall properties of the coating film. This was confirmed by the experimental results. Carbon graphite used as a solid lubricant and Al2O3 used as an abrasive often have large maximum particle diameters, and in the case of a thin magnetic layer such as upper layer 2. Since the particles protruding from the surface of the magnetic film break during travel and become powdery foreign matter, causing head clogging, it is necessary to use particles with a particularly small particle size.

Specific examples of the present invention are shown below.

First, the following materials were mixed and sufficiently dispersed to obtain a magnetic liquid for the upper layer.

400 parts by weight or less of Fe magnetic powder (coercive force 11500e) was mixed and sufficiently dispersed to obtain a magnetic liquid for the lower layer.

Fe magnetic powder (coercive force 1060Qi) 60Q
Parts by weight VAGH 755 Parts by weight Nilaporan 230 25 parts Organic solvent 1400 parts by weight The above magnetic liquid was applied to a 6 μm thick polyester base film so that the final thickness after drying was 2.0 μm thick for the lower layer and 1.0 μm thick for the upper layer. The final magnetic recording medium was obtained through coating, orientation, drying, surface mirror polishing, and cutting steps.

Regarding the preparation of the above-mentioned magnetic liquid, it goes without saying that commonly used dispersants, dispersion aids, plasticizers, curing agents, etc. are included in amounts that are generally used, and their descriptions are omitted here. do. The dispersion process and the processes from coating to final cutting are not particularly different from the manufacturing method of general magnetic recording media, and the explanation of the conditions etc. will be omitted here.

Next, as a comparative example for the present invention, the following materials were mixed and sufficiently dispersed to obtain a magnetic liquid, and a final magnetic recording medium was obtained through the same steps as in the example of the present invention. In this case, there is only one magnetic layer, and its thickness is 3.0μ.
It was set as m.

Fe magnetic powder (coercive force 10500e) 400 parts by weight VAGH 266 parts by weight Niraporan 230 75 parts by weight Carbon graphite (particle size: 14 μm) 3
Parts by weight Carbon black 10 parts by weight Alumina (particle size o, 02-1.0μm)
5 parts by weight Organic solvent 1400 parts by weight Since this is a -T single layer structure, the magnetic layer is required to have physical strength, so the binder composition needs to have a thermosetting resin as the main component. Since additives are also required, the filling rate of the magnetic powder is also large, and the above-mentioned formulation is generally unavoidable.

Representative characteristics of electromagnetic conversion characteristics and physical characteristics were evaluated for the magnetic recording medium of the present invention and the magnetic recording medium of the comparative example. The electromagnetic conversion characteristics are the sensitivity at I KHz, the maximum output level, and the sensitivity at 10 KHz, and the physical characteristics are based on the Sellotape peeling method in the longitudinal direction of the magnetic tape width a and a1 mm. l [Strength and durability running performance include wear loss when running in contact with a magnetic head for 150 hours at a running speed of 2.4 cm/sea, and 10 KH, which is the overall effect of physical characteristics such as head touch.
Level fluctuations in z were measured. The above-mentioned electromagnetic conversion characteristics were measured using a commercially available small cassette deck R8M212 (manufactured by Matsushita Electric Industrial Co., Ltd.), and detailed measurements were made in accordance with the generally established conditions of the magnetic tape test method. Note that there is no particular difference in the electromagnetic conversion characteristics other than the high sensitivity and high density recording characteristics that are the features of the present invention, and the description thereof will be omitted in the main text.

The above measurement results are shown in the table below.

As is clear from this table, the magnetic recording medium of the present invention has high 1k)h sensitivity and maximum output level due to the high filling effect of the magnetic powder in the lower layer, and high coercive force of the magnetic powder used in the upper layer at 10kHz. It has improved sensitivity and excellent electromagnetic conversion characteristics. Furthermore, by using a thermoplastic resin as the main component of the lower layer binder, it is possible to improve the adhesion strength with the base material and to achieve a low level of fluctuation due to appropriate contact with the magnetic head. Furthermore, regarding wear loss, the use of additives with a small maximum particle size on the upper layer, which controls this property, is effective.
Sufficient wear resistance was obtained with a magnetic layer thickness of 1.0 μm.

As is clear from the above description, the magnetic recording medium according to the present invention has high sensitivity and is suitable for high-density recording, and
It also shows excellent physical properties and has extremely high industrial value.

[Brief explanation of drawings]

The drawing is a sectional view showing an embodiment of the magnetic recording medium of the present invention. 1... Base material, 2... Upper layer, 3...
··Underlayer.

Claims (1)

[Claims] (1) A magnetic recording layer consisting of two layers is formed on a base material: a lower layer made of magnetic powder and a binder, and an upper layer made of magnetic powder, a binder, a lubricant, an antistatic agent, and an abrasive. A magnetic recording medium characterized by: (2) The filling rate of magnetic powder in the upper and lower layers is 76 to 8 for the upper layer.
The magnetic recording medium according to claim 1, characterized in that the content of the lower layer is 6% by weight, and the content of the lower layer is 80 to 90% by weight. (3) The magnetic recording medium according to claim 1, wherein the magnetic powder of the upper layer and the lower layer are made of the same material system, and the coercive force of the upper layer is 0 to 50% larger than the coercive force of the lower layer. (4) The magnetic recording medium according to claim 1, wherein the thickness of the upper layer is 0.5 to 1.6 μm. (2) The composition of the binder in the upper layer and the lower layer is a thermosetting resin/thermoplastic resin ratio of 50150 to 1001 for the upper layer.
2. The magnetic recording medium according to claim 1, wherein the lower layer has a density of 50,150 to 0/100. (6) The lubricant, antistatic agent, and abrasive contained in the upper layer that are solid at room temperature have a maximum particle size that does not exceed the thickness of the upper layer. magnetic recording medium.