JP2002298332A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium in which the frictional coefficient can be decreased and sticking of a head and durability can be improved by controlling the exudation of a lubricant to the surface of a magnetic layer by a new method so as to respond the requirements for higher smoothness and higher density in the magnetic layer in a coating type magnetic recording medium. SOLUTION: In the magnetic recording medium in which a nonmagnetic layer containing carbon black and a binder resin and a magnetic layer containing ferromagnetic powder and a binder resin and having >=0.05 μm and <=0.5 μm dry thickness are successively laminated on a nonmagnetic supporting body, decrease in the contact angle of the magnetic layer surface with water is specified to <=3 deg. when the medium is immersed in methanol at 20 deg.C, for one minute, then taken out from the liquid and left for one to five minutes compared to the angle before immersion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium (hereinafter, referred to as a magnetic recording medium) in which a magnetic paint obtained by dispersing a ferromagnetic powder in a binder resin is coated on a nonmagnetic support via a nonmagnetic layer.
More specifically, the present invention relates to a magnetic recording medium having good head adhesion, excellent durability, and reduced friction coefficient, and particularly suitable for recording and reproducing digital signals at a high recording density.

[0002]

2. Description of the Related Art With the recent increase in the density of magnetic recording media,
In realizing a magnetic layer having high smoothness using fine magnetic powder, fatty acids and fatty acid esters are used as such lubricants in order to reduce the increase in friction coefficient and the deterioration in durability by effectively mixing lubricants. It is essential to use.

However, fatty acids and fatty acid esters retained in a magnetic recording medium are not actually added to all components due to various factors. For example, the specific surface area of a nonmagnetic powder, a magnetic powder, and other various powders used in the composition of a magnetic recording medium is represented by a BET value. It is well known that the value varies significantly depending on the powder material itself. This is a fact and varies considerably depending on the shape and manufacturing method of the powder. Also,
The amount of fatty acid adsorption greatly depends on the pH of the powder. Furthermore, since the fatty acid ester penetrates into a resin component such as a binder resin due to its structure, the amount acting as a lubricating component is considerably smaller than the amount added.

As described above, simply specifying the amount of the lubricant to be added is not sufficient as a technique for improving the durability of a magnetic recording medium. Therefore, for example, Japanese Patent Application Laid-Open
In Japanese Patent No. 102514, the amount of the fatty acid ester extracted by immersing the magnetic recording medium in n-hexane is set within a specific range, and the weight ratio with the amount of the fatty acid ester extracted by refluxing with methanol is defined. In addition, it has been proposed to improve the durability by controlling how the lubricant seeps from the inside of the magnetic recording medium to the surface.

In Japanese Patent Application Laid-Open No. 11-250439, the distribution of the amount of the lubricant in the intermediate layer and the upper layer is estimated by the extraction speed with n-hexane, and the durability and the like are improved by optimizing the amount of the lubricant on the surface. It has been proposed that

Further, in Japanese Patent Application Laid-Open No. 7-296360, the amount of fatty acid extracted by cyclohexane is within a specific range, and the amount of water-soluble metal ions extracted from the magnetic layer is within a specific range. Improvements in properties and storage have been reported.

[0007]

However, with the recent increase in output of magnetic recording media, a higher degree of smoothness of the magnetic layer has been required, and the friction coefficient has been reduced and the durability has been increased more than ever. Has been required to be improved. Accordingly, the magnetic layer has been required to have a higher density, and in such a situation, in a conventional magnetic recording medium, the supply of a lubricant from the inside of the layer to the surface of the magnetic layer and its control are controlled. It is not sufficient, and there is a concern that the durability of the magnetic layer is deteriorated due to a shortage of the lubricant component on the surface of the magnetic layer and that the head adheres. In particular, in the case of a coating type magnetic recording medium, it has become necessary to supply and control the lubricant from the inside of the magnetic recording medium to the surface thereof more highly than ever.

Accordingly, an object of the present invention is to provide a new method of extruding a lubricant onto the surface of a magnetic layer in order to meet the demand for higher smoothness and higher density of the magnetic layer in a coating type magnetic recording medium. It is an object of the present invention to provide a magnetic recording medium capable of reducing the coefficient of friction, improving the adhesion of the head, and improving the durability by controlling by a method.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in a coating type magnetic recording medium in which the thickness of the magnetic layer is equal to or less than a predetermined value, the amount of lubricant on the surface is reduced. The inventors have found that the above object can be achieved by defining the change amount of the contact angle of the magnetic layer surface with water before and after immersion in methanol, and completed the present invention.

That is, the magnetic recording medium of the present invention comprises, on a nonmagnetic support, a nonmagnetic layer containing carbon black and a binder resin, and a dry thickness of not less than 0.05 μm and not more than 0.5 μm containing a ferromagnetic powder and a binder resin. In the magnetic recording medium in which the magnetic layers are sequentially laminated, before the magnetic recording medium is immersed in methanol at 20 ° C., immersed for 1 minute, taken out and before and after 1 to 5 minutes, The contact angle of water on the surface of the magnetic layer is reduced within 3 degrees.

In the magnetic recording medium of the present invention, the non-magnetic layer and / or the magnetic layer preferably contain a fatty acid, a fatty acid amide, and a fatty acid ester as lubricants. In order to maintain good lubrication, it is effective to add these to the non-magnetic layer and supply the lubricant from the non-magnetic layer. The solubility of the fatty acid in the fatty acid ester is preferably 5.0% by weight or more at 40 ° C.

As described above, the present invention utilizes the fact that a lubricant such as a fatty acid present on the surface of a magnetic recording medium affects the numerical value of the contact angle with respect to water. This is the first to clarify the relationship between friction coefficient, head adhesion and durability.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. In the magnetic recording medium of the present invention,
Before soaking in methanol at 20 ° C, soak for 1 minute,
A decrease in the contact angle of the surface of the magnetic layer with water before and after 1 to 5 minutes from the removal is controlled within 3 degrees. That is, when the decrease in the contact angle of the magnetic layer surface with water measured within 1 to 5 minutes after immersing the magnetic recording medium in methanol at 20 ° C. for 1 minute is within 3 degrees, the fatty acid supply rate to the magnetic layer surface is reduced. Sufficiently, even during the durable running of the magnetic recording medium, the fatty acid in the magnetic layer and / or the non-magnetic layer appropriately exudes, and the desired durability can be realized while preventing an increase in the coefficient of friction. That is, it was found that in order for the fatty acid to be effectively supplied to the magnetic layer, the decrease in the contact angle had to be within 3 degrees. Further, the friction of the magnetic layer is an important factor greatly affecting the durability because the friction of the magnetic layer is related to the running friction in the magnetic tape. It was also found that it could be reduced to 0.30 or less. In other words, this decrease in contact angle is 3
Exceeding the degree, the exudation of the fatty acid from the magnetic layer and / or the non-magnetic layer is insufficient, the running friction increases,
This means that the desired durability cannot be obtained. If the contact angle falls within 1 degree, it is not necessarily satisfactory in terms of head adhesion.
~ 3 degrees.

Here, "1 to 5 minutes after immersion" means that methanol evaporates sufficiently after several tens of seconds after the magnetic tape is taken out after immersion. Since the magnetic tape is sufficiently dried, the lower limit is set to 1 minute. On the other hand, if the time is too long after immersion, the lubricant seeps out of the magnetic layer and / or the non-magnetic layer for a long time. This is because there is no longer any difference in the value of the contact angle in any of the magnetic recording media. That is, the contact angle reduction can be recovered to within 3 degrees within a short time of 5 minutes after drying of methanol,
It is important to achieve the intended purpose.

As a method for minimizing a decrease in the contact angle of water on the surface of the magnetic layer after water is immersed in and washed with methanol at 20 ° C. for 1 minute, the following method is mentioned. By increasing the amount of fatty acid added, the concentration of fatty acid in the layer is increased, and the amount supplied to the surface of the magnetic layer is increased. Select a combination having good compatibility between the fatty acid and the fatty acid ester. By increasing the amount of the fatty acid ester acting as a fatty acid carrier, the supply of the fatty acid in the layer to the surface of the magnetic layer is promoted. Lubricant is compatible with the binder resin to some extent,
In the coating composition, reducing the amount of the binder resin with respect to the powder reduces the amount of the lubricant that is trapped by the binder resin. In the drying after coating on the non-magnetic support, the drying temperature,
Change the layer structure by changing the drying time. The present invention is not limited to the above method, and it is also effective to use a combination of several methods.

In order to improve the durability, adhesion and the coefficient of friction, which are the objectives of the present invention, the lubricant to be used is preferably a fatty acid, a fatty acid and a fatty acid ester, or a combination of a fatty acid amide and a fatty acid ester. , Fatty acids, fatty acid amides and fatty acid esters are preferably used together as lubricants. Fatty acids that can be used as fatty acids, fatty acid esters and fatty acid amides in the present invention include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid,
Elaidic acid, behenic acid and the like.

Such a lubricant is added to the non-magnetic layer and / or the magnetic layer. It is preferable to add the lubricant to the non-magnetic layer in order to maintain good lubrication during durability running. In order to obtain the range of the contact angle according to the present invention, such a lubricant is added in an amount of 1.0 to 9 to 100 parts by weight of the main pigment (carbon black or a nonmagnetic inorganic powder described later) in the composition of the nonmagnetic layer. 0.0 parts by weight, especially 2.0 to 8.0 parts
It is preferable to include them in parts by weight. As described above, the compatibility between the fatty acid and the fatty acid ester is preferably good. Specifically, the solubility of the fatty acid in the fatty acid ester is not less than 5.0% by weight at 40 ° C., and particularly preferably not less than 6. It is preferably at least 0% by weight.

The non-magnetic support used in the magnetic recording medium of the present invention can be appropriately selected from known resin films such as polyester, polyamide or aromatic polyamide or a laminated resin film of these, together with the thickness and the like. It is within a known range and should not be particularly limited.

The ferromagnetic metal powder contained in the magnetic layer of the magnetic recording medium of the present invention is preferably acicular,
The average major axis length is 0.15 μm or less, more preferably 0.05 μm or less.
5 to 0.10 μm. If the average major axis length exceeds 0.15 μm, the electromagnetic conversion characteristics (particularly, S / N and C / N characteristics) required for the magnetic recording medium cannot be sufficiently satisfied.

Such a ferromagnetic metal powder may be contained in the magnetic layer composition at about 70 to 90% by weight. If the content of the ferromagnetic metal powder is too large, the content of the binder is reduced, so that the surface smoothness due to the calendar processing is liable to be deteriorated.

As the binder resin for the magnetic layer, conventionally known thermoplastic resins, thermosetting resins, radiation-curable resins and mixtures thereof can be suitably used, and there is no particular limitation. Also, as the crosslinking agent for curing these binder resins, various known polyisocyanates can be used, and there is no particular limitation. The content of the crosslinking agent is preferably 5 to 30 parts by weight based on 100 parts by weight of the binder resin. If necessary, an abrasive, a dispersant such as a surfactant, a higher fatty acid, and other various additives may be added to the magnetic layer.

The coating material for forming the magnetic layer is prepared by adding an organic solvent to the above components. The organic solvent used is not particularly limited, and one or more of various solvents such as ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone and cyclohexanone and aromatic solvents such as toluene may be appropriately selected and used. Good.

The thickness (dry thickness) of the magnetic layer in the present invention is 0.05 to 0.50 μm, preferably 0.10 to 0.3 μm.
5 μm. If the magnetic layer is too thick, self-demagnetization loss and thickness loss increase.

In the magnetic recording medium of the present invention, a non-magnetic layer is provided between the above-described magnetic layer and the non-magnetic support.
The electromagnetic conversion characteristics of the thinned magnetic layer have been improved, which has further contributed to the improvement of reliability.

The non-magnetic layer contains at least carbon black and a binder resin. The thickness (dry thickness) of such a nonmagnetic layer is preferably 2.5 μm or less,
More preferably, it is 0.1 to 2.3 μm. Even if the thickness is greater than 2.5 μm, no improvement in performance can be expected. On the contrary, when a coating film is provided, the thickness tends to be non-uniform, the application conditions are severe, and the surface smoothness tends to deteriorate. .

In addition to carbon black, the non-magnetic layer
Seed non-magnetic inorganic powder can be used, preferably,
Acicular nonmagnetic powder, for example, acicular nonmagnetic iron oxide (α-F
e_TwoO_Three) Is used. In addition, calcium carbonate (CaC
O_Three), Titanium oxide (TiO) _Two), Barium sulfate (BaS)
O_Four), Α-alumina (α-Al_TwoO_Three), Etc.
Powder may be appropriately blended.

As the binder resin, similarly to the magnetic layer, conventionally known thermoplastic resins, thermosetting resins, electron beam-curable resins and mixtures thereof are used. Among them, the electron beam-curable resins are preferable. The amount of the resin for reducing the amount of the lubricant captured by the resin is 10 to 35 parts by weight based on 100 parts by weight of the total amount of the carbon black and / or the nonmagnetic inorganic powder in the coating for the nonmagnetic layer. , Preferably 15 to 25 parts by weight. However, since this amount can vary depending on the type of the binder resin, the amount is not necessarily limited to this value. The same tendency applies to the magnetic layer, but in the present invention, as described above, it is preferable to add a lubricant to the non-magnetic layer. For this reason, the amount of the resin in the non-magnetic layer paint becomes dominant.

In the non-magnetic layer in the present invention, if necessary, a dispersant such as a surfactant and other various additives may be added.

In the magnetic recording medium of the present invention, a back coat layer can be provided as necessary to improve running stability and prevent the magnetic layer from being charged by a known method.

[0030]

The present invention will be described below with reference to examples and comparative examples. Example 1 <Nonmagnetic layer paint 1> 80 parts by weight of α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DBN650RX) (average short axis diameter = 21 nm, BET = 55 m ² / g) Carbon black (Mitsubishi Chemical ( Co., Ltd .: # 850B) 20 parts by weight (Average particle size = 16 nm, BET = 200 m ² / g, DBP oil absorption = 70 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Co., Ltd .: HIT60A) 15 parts by weight (average particle size = 0.18 μm, BET = 12 m ² / g) 12 parts by weight of an electron beam-curable vinyl chloride copolymer (degree of polymerization = 300, polar group: —OSO ₃ K = 1.5 pieces) / Molecule) Electron beam-curable polyurethane resin 5 parts by weight (Mn = 25000, polar group: sodium phosphite = 1/1 / molecule) MEK 120 parts by weight Toluene 120 parts by weight Cyclohexanone 60 parts by weight After kneading the Narubutsu, it was dispersed in a sand grinder mill.

Next, the following additives and solvents were added to adjust the viscosity, and a non-magnetic coating material 1 was prepared. Butyl stearate 2 parts by weight Stearic acid 2 parts by weight Stearic acid amide 1 part by weight MEK 30 parts by weight Toluene 30 parts by weight Cyclohexanone 30 parts by weight

<Magnetic Layer Coating 1> 100 parts by weight of Fe-based metal magnetic powder (containing 10 atm% of Co and 5 atm% of Al when Fe is 100) (Hc = 144.6 kA / m, σs = 130 Am ²⁾ / Kg, BET = 57 m ² / g, average major axis = 0.10 μm) 10 parts by weight of vinyl chloride copolymer (manufactured by Zeon Corporation: MR110) (degree of polymerization = 300, polar group: —OSO ₃₎ K = 1.5 / molecule) 7 parts by weight of SO ₃ Na-containing polyurethane resin (Mn = 25000, concentration of polar group = 1 / molecule) α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd .: HIT82) ) 12 parts by weight (average particle size = 0.12 .mu.m, after the ^{BET = 20m 2 / g) MEK} 90 parts by weight toluene 90 parts by weight cyclohexanone 120 parts by weight the above composition was kneaded, a sand grinder mill It was dispersed Te.

Next, the following additives and solvents were added to adjust the viscosity, and a magnetic layer coating material 1 was prepared. MEK 110 parts by weight Toluene 110 parts by weight Cyclohexanone 160 parts by weight

<Coating for Backcoat Layer> 80 parts by weight of carbon black (Conductex SC average particle size = 20 nm, BET = 220 m ² / g, manufactured by Columbian Carbon Co.) 1 part by weight of carbon black (Sevacarb, manufactured by Columbian Carbon Co., Ltd.) MT average particle size = 350 nm, BET = 8 m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100, average particle size = 0.1 μm) 1 part by weight vinyl chloride-vinyl acetate-vinyl alcohol Polymer 65 parts by weight (Monomer weight ratio = 92: 3: 5, average degree of polymerization = 420) Polyester polyurethane resin (UR-8300 manufactured by Toyobo Co., Ltd.) 35 parts by weight MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight After kneading the above composition, disperse in a sand grinder mill I went.

Next, the following additives and solvents were added to adjust the viscosity. MEK 210 parts by weight Toluene 210 parts by weight Cyclohexanone 210 parts by weight

The non-magnetic layer coating material 1 is first extruded onto a 6.1 μm-thick PET (polyethylene terephthalate) film, and has a thickness of 2.0 μm (dry film thickness) by a die nozzle method.
After drying at a drying temperature of 100 ° C., a temperature of 100 ° C.
A calendering process was performed at a linear pressure of 2940 N / cm, and thereafter, electron beam irradiation (5 Mrad) was performed to produce a nonmagnetic layer raw material.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic layer paint 1, and 1 part by weight of Coronate L was added to 100 parts by weight of the back coat paint. The magnetic layer paint is extruded and applied with a thickness of 0.25 μm (dry film thickness) by a die nozzle method.
After orientation, the coating film was dried at a drying temperature of 100 ° C., and calendered at a temperature of 100 ° C. and a linear pressure of 2940 N / cm.

Next, a back coat paint was applied to the base surface opposite to the magnetic layer by extrusion die nozzle method to a thickness (dry film thickness) of 0.5 μm and dried at 100 ° C. to produce a raw roll. . After leaving this roll at room temperature for 24 hours, after curing in a heating oven at 60 ° C. for 24 hours,
Cut into 1/2 inch width and assembled into DLT cassette,
A magnetic tape sample was used.

Example 2 A magnetic tape sample was produced in the same manner as in Example 1 except that the amount of butyl stearate in the coating composition for the nonmagnetic layer was changed to 3.0 parts by weight.

Example 3 A magnetic tape sample was produced in the same manner as in Example 1 except that the amount of butyl stearate in the coating material for the nonmagnetic layer was changed to 4.0 parts by weight.

Example 4 A magnetic tape sample was produced in the same manner as in Example 1 except that the amount of stearic acid in the coating composition for the nonmagnetic layer was changed to 3 parts by weight.

Example 5 A magnetic tape sample was produced in the same manner as in Example 1 except that the amount of stearic acid in the coating composition for the nonmagnetic layer was changed to 4 parts by weight.

Comparative Example 1 A magnetic tape sample was produced in the same manner as in Example 1 except that the addition amount of butyl stearate in the coating material for the nonmagnetic layer was changed to 0.5 part by weight.

The following measurements were performed on the magnetic tape samples obtained in the above Examples and Comparative Examples. (Running durability) Using Quantum DLT4000 drive, write / rea a part of the tape
1 million passes were performed in the same way. If the number of write / read retries increases or write / read cannot be performed before the number of passes reaches one million, it is regarded as defective.

(Coefficient of friction) The magnetic layer side of the tape was measured using a horizontal high-speed tensile tester (Model No. HTB-S) manufactured by Island Industry Co., Ltd. Measurement environment is 2
0 ° C, humidity 60%. The measurement conditions were as follows: a holding angle: 90 degrees, a load: 40 g, a measuring speed of 500 mm / min, and a distance of 50 mm. The friction coefficient was calculated from the initial tensile load at this time.

(Head attachment) Quantum DL
Using a T4000 drive, 10 tape samples
Write / Read was run for 2400 cycles in an environment of 20 ° C. and 20%, and the adhesion of the head after running was checked with an optical microscope having a magnification of 100 ×. The evaluation criteria were: adhesion on the entire surface of the head: × partial adhesion on the head: Δ no adhesion of the head: ○.

(Contact Angle) The tape sample having a width of 1/2 inch was measured for the contact angle with water using a contact angle measuring device (a contact angle measuring device manufactured by Kyowa Interface Science Co., Ltd.). The measurement was performed before the tape sample was immersed in methanol at 20 ° C. for 1 minute, and about 1 minute after the immersion, and the contact angle reduction was calculated according to the following equation. (Decrease in contact angle) = (Contact angle before immersion)-(Contact angle after immersion)

(Water-soluble iron ion content) Tape sample 6
m was cut into small pieces, sealed in a beaker together with 40 ml of pure water, heated at 80 ° C. for 1 hour, and then subjected to ultrasonic treatment. Using this filtrate, the amount of ions was quantified by a high-frequency inductively coupled plasma emission spectrometer (manufactured by SEIKO, SPS1200A plasma spectrometer).

[0049]

[Table 1]

Comparative Examples 2 and 3 Magnetic tape samples were produced in the same manner as in Example 1 except that the amount of the binder used in the non-magnetic layer paint of Example 1 was changed as shown in Table 2 below.

[0051]

[Table 2]

Examples 6 to 8, Comparative Examples 4 and 5 In the compositions of Example 1, except that the combinations of fatty acids and fatty acid esters were changed as shown in Table 3 below,
A magnetic tape sample was manufactured in the same manner as in Example 1.

[0053]

[Table 3]

[0054]

As described above, according to the present invention, in the coating type magnetic recording medium, the method of controlling the amount of the lubricant to seep to the surface of the magnetic layer by using the contact angle with water is controlled. A reduction in coefficient, an improvement in head adhesion, and an improvement in durability were achieved. This, in particular,
A magnetic recording medium suitable for recording and reproducing digital signals at a high recording density can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10M 105/68 C10M 105/68 G11B 5/70 G11B 5/70 5/738 5/738 // C10N 20: 00 C10N 20:00 Z 30:00 30:00 Z 40:18 40:18 F term (reference) 4H104 BB17A BB32A BE11A LA20 PA16 4J038 EA011 HA026 JA36 JA54 JB12 KA20 NA22 PB11 5D006 BA09 CA04 FA06

Claims (3)

[Claims] 1. A nonmagnetic layer containing carbon black and a binder resin on a nonmagnetic support, and a dry thickness of at least 0.05 μm containing a ferromagnetic powder and a binder resin.
In a magnetic recording medium in which a magnetic layer of 5 μm or less is sequentially laminated, before and after immersing the magnetic recording medium in methanol at 20 ° C. for 1 minute and removing it for 1 to 5 minutes, A magnetic recording medium, wherein the contact angle of the surface of the magnetic layer with water is reduced within 3 degrees. 2. The magnetic recording medium according to claim 1, wherein the non-magnetic layer and / or the magnetic layer contains a lubricant as a lubricant, a fatty acid amide, and a fatty acid ester. 3. The magnetic recording medium according to claim 2, wherein the solubility of the fatty acid in the fatty acid ester is at least 5.0% by weight at 40 ° C.