JPH06338043A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility, filling rate and running durability of magnetic powder in the magnetic layer of a magnetic recording medium. CONSTITUTION:Particles of magnetic powder 2 contained in a magnetic layer are bonded to each other with a three-dimensional crosslinked body 1 having siloxane bonds as repeating units formed by polycondensing silicic acid or its deriv. The crosslinked body 1 can be formed by a sol-gel method using polyalkoxysilane, o-silicic acid or o-sodium silicate as a basic monomer for polycondensation. When an org. compd. having a reactive functional group or a polar group is allowed to coexist at the time of forming the crosslinked body, particles of the magnetic powder 2 are more tightly bonded to each other by mutual bonding of molecules of the org. compd. as well as bonding with the crosslinked body. An underlayer or a back coat layer can also be formed using the crosslinked body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a floppy disk,
The present invention relates to a magnetic recording medium represented by a magnetic disk such as a hard disk or a magnetic tape such as a video tape and a data tape.

[0002]

2. Description of the Related Art In recent years, with the spread of electronic devices such as personal word processors, personal computers and home videos, magnetic recording media such as floppy disks or video tapes have been widely used as recording media for recording a large amount of information. Has become. Above all,
Since the coating type magnetic recording medium has excellent mass productivity, it occupies most of the market.

In the manufacture of this coating type magnetic recording medium, conventionally, γ-Fe ₂ O ₃ , CrO ₂ , Co-γ-Fe ₂ O is formed on a support such as a polyester film.
Magnetic powder such as ₃ and iron powder is applied together with a resin binder. This resin binder is added in order to ensure the dispersibility of the magnetic powder and the running property of the medium, and it is usually necessary that the addition amount be greater than 10 parts by weight with respect to 100 parts by weight of the magnetic powder. ing.

By the way, in recent years, along with the increase in the amount of information to be handled, there has been an increasing demand for high-density recording on magnetic recording media. Such requirements can be met by improving the orientation of the magnetic powder or the linear recording density. Then, in order to fully exert such high density recording characteristics, in the coating type magnetic recording medium, the magnetic powder is dispersed to a state close to primary particles, thereby improving the orientation ratio and improving the surface of the magnetic layer. It is necessary to make the roughness as small as possible.

In order to further improve the recording / reproducing output of the medium, the volume ratio of the magnetic powder particles in the resin binder should be maximized, that is, the filling rate of the magnetic powder particles in the resin binder should be increased as much as possible. Is required.

However, it is usually very difficult to highly disperse ultrafine particle powder in a dispersion medium. Therefore, there is a great difficulty in dispersing the ultrafine magnetic powder to which the magnetic cohesive force is further applied in the resin binder. When the dispersed state of the magnetic powder in the resin binder is not good, not only the smoothness of the formed magnetic layer is impaired and the filling rate of the magnetic powder is lowered, but also it is formed in the magnetic field orientation step after applying the magnetic paint. Moreover, the orientation ratio of the magnetic powder in the magnetic layer is reduced. As a result, in the produced magnetic recording medium, the output during recording / reproduction is reduced, and further, noise is increased, which causes inconvenience.

In order to improve the durability of the formed coating film, it is effective to increase the contents of the resin binder and the curing agent used in the magnetic paint. However, such an increase in the amount of the non-magnetic material means a reduction in the filling rate of the magnetic powder in the magnetic layer, resulting in a reduction in the reproduction output of the manufactured magnetic recording medium, which is not preferable. Therefore, there is a limit to the amount of the nonmagnetic material as a means for improving the durability of the coating film, and it has been impossible to obtain a coating film having sufficient durability only by increasing the amount of the nonmagnetic material.

That is, at present, it cannot be said that the dispersion technique of the ultrafine magnetic powder used to meet the demand for high density recording has been sufficiently established. Therefore, it is difficult to say that the smoothness and running durability of the coating film, and further the filling rate of the magnetic powder in the magnetic layer are sufficiently improved. In addition, there is a new inconvenience in terms of recording / reproducing characteristics due to the poor dispersibility of the magnetic powder.

[0009]

Therefore, until now, ultrafine magnetic powder has been filled in the magnetic layer at a high filling rate, and the durability has been improved without increasing the amount of the non-magnetic material. In order to obtain a coating film for the magnetic layer, research has been advanced from various fields in search of magnetic powder having improved dispersibility in a resin binder.

As one of attempts to improve the dispersibility of the magnetic powder, it has been proposed to coat the magnetic powder particles with various dispersants or coupling agents. For example, JP-A-4-147426 discloses coating magnetic powder with a fluorine-modified silane coupling agent.

However, this is mainly for the purpose of preventing deterioration of a magnetic recording medium using a metal magnetic powder for long-term storage, and a medium in which various magnetic powders are highly dispersed and a high packing rate is obtained. No mention is made of the means of manufacture. Nor is there any mention of means for ensuring sufficient durability of the medium.

Therefore, the present invention has been made to address such a problem, and not only enhances the dispersibility of the magnetic powder but also sets the filling rate of the magnetic powder in the magnetic layer to an extent not conventionally attempted. It is an object of the present invention to provide a magnetic recording medium that achieves high-density recording by increasing the maximum and further has sufficient durability.

[0013]

That is, the magnetic recording medium of the present invention comprises a non-magnetic support on at least one surface thereof,
In a magnetic recording medium in which a magnetic layer containing magnetic powder is formed, the mutual magnetic powder contained in the magnetic layer is mainly
It is characterized in that they are bonded via a three-dimensional crosslinked body having a repeating unit of a siloxane bond generated by polycondensation of silicic acid or its derivative.

In the present invention, a three-dimensional crosslinked product mainly containing a siloxane bond (-Si-O-) as a repeating unit means a substantially continuous layer in which fine particles are joined by crosslinking in the presence of some fine particles. It means a crosslinked body existing between fine particles so as to have a binder function of being formed, and does not mean a particulate crosslinked body called so-called colloidal silica. In addition, 3 according to the present invention
In the dimensional cross-linked product, at least 20% or more of silicon atoms (Si) form a cross-linking skeleton by bonding to four oxygen atoms (O), respectively. However, it is also different from some crosslinked products such as silicone resins.

The three-dimensional crosslinked product having the above siloxane bond as a repeating unit according to the present invention can be formed by a so-called sol-gel method. The sol-gel method is generally a method in which a starting material such as a metal alkoxide is dissolved in a solvent such as an alcohol, and a hydrolysis / polycondensation reaction proceeds in the solution to change from a sol state to a gel state at room temperature, followed by heating. -A method of obtaining a dried gel body by sintering. When a silicon alkoxide is used as the starting metal alkoxide, a glass or ceramic-like amorphous homogeneous dry gel body can be obtained without requiring high temperature.

The three-dimensional crosslinked product according to the present invention can be formed by the above-mentioned sol-gel method using a silicic acid or a silicic acid derivative such as a silicon alkoxide (silicic acid ester) as a starting material. Among the silicic acids or silicic acid derivatives as starting materials, the most basic monomer is polyalkoxysilane (2-4 alkoxyl groups) shown in the following chemical formula 1 as an example thereof: tetraethoxysilane (tetraethylsilicate). Group-containing alkoxysilane), orthosilicic acid shown in Chemical formula 2, or sodium orthosilicate shown in Chemical formula 3.

[0017]

[Chemical 1]

[Chemical 2]

[Chemical 3] In the present invention, the polyalkoxysilane means an organoalkoxysilane having 2 or 3 alkoxyl groups, or a tetraalkoxysilane (tetraalkyl silicate) having 4 alkoxyl groups. Those having 1 to 3 carbon atoms are preferable. As a starting material, other than these monomers,
These oligomers can also be used. When a monomer is used, nitric acid or the like is usually added as a catalyst for the polycondensation reaction.

The above-mentioned monomers or oligomers are subjected to polycondensation by the sol-gel method to give silicon (S).
Form a three-dimensional crosslinked product of i), that is, silica gel. The fine particles dispersed in the raw material solution at the time of forming the crosslinked body are taken into the crosslinked body in a uniformly dispersed state, and as a result, a gel body of a three-dimensional crosslinked body in which the fine particles are joined by the crosslinked body is obtained. It was found that it could be done.

Therefore, magnetic fine particles such as metal powder and Ba ferrite powder are dispersed in the above raw material solution to form a paint, which is applied onto a non-magnetic support, so that the magnetic fine particles, that is, magnetic powder, are made uniform. A gel-like thin film layer dispersed and held in this state is formed. By drying this to obtain a dried gel body, the magnetic layer of the magnetic recording medium in which the magnetic powder is dispersed in a uniform state and firmly held in the layer is formed.

FIG. 1 is a schematic diagram showing the structure of a three-dimensional crosslinked product according to the present invention. In FIG. 1, a dotted frame indicated by reference numeral 1 indicates a repeating unit of the crosslinked product. As shown in FIG. 1, a siloxane bond (-Si-
When the oxygen atom (O) of O−) is bonded, the magnetic powder 2 is taken into the inorganic three-dimensional crosslinked body, and the magnetic powders 2 and 2 are bonded to each other.

By the way, as described above, in order to form the magnetic layer of the magnetic recording medium, an organic compound such as a resin binder, a curing agent or a lubricant is generally used together with the above-mentioned magnetic powder. Since the three-dimensional crosslinked product of the present invention itself has a binder function, a conventional resin binder is not essential for forming the magnetic layer. Even if a resin binder is used, it can be used in a small amount as compared with the conventional amount.

For example, when a plate-shaped fine powder such as hexagonal ferrite is used as the magnetic powder, it is 10 parts by weight or less relative to 100 parts by weight of the magnetic powder, and when metal powder is used, 15 parts by weight or less. In addition, the amount of resin binder may be reduced. Such a reduction in the amount of resin binder makes it possible to improve the filling rate of the magnetic powder and obtain a high output.

According to the sol-gel method, a solvent-soluble organic compound that dissolves a starting material is incorporated into a three-dimensional crosslinked body at a molecular level and integrated. Therefore, when a magnetic coating material is prepared according to the sol-gel method to form a magnetic layer of a magnetic recording medium, a magnetic powder and an organic compound are held in a three-dimensional crosslinked body in a uniform state, respectively, to obtain a dispersion property. An excellent magnetic layer can be obtained. That is, the magnetic powder is firmly retained in the magnetic layer by using a small amount of the resin binder. The organic compound is not limited to the above resin binder and the like, and if it is soluble in a solvent that dissolves the starting material, for example, an organic dye or the like can be added.

As described above, in the present invention, 3
As the polyalkoxysilane, which is one of the raw material monomers for the three-dimensional crosslinked product, an alkoxyl group having 1 to 3 carbon atoms is used.
It is possible to use one having four, but the presence of an alkoxyl group which remains bound to the Si atom without participating in polycondensation and the presence of other organic groups such as an alkyl group, etc., a three-dimensional crosslinked product and an organic compound. Useful for giving affinity to.

As described above, in the three-dimensional crosslinked product according to the present invention, not all Si atoms are bonded to four oxygen atoms, and all the alkoxyl groups are involved in polycondensation during crosslinking. not a functional group such as the three-dimensional crosslinked body of the present invention represented by a ₁ to a _m 1 is present in a part. The _{A 1 ~A m, -H, -X} ( halogen) - R (alkyl group), - OR (alkoxyl group), - OH-functional (such as silanol groups), or -OM (M is alkali metal) The group is typical.

Among these, since the silanol group is particularly acidic, when a resin molecule having a basic group or a carbonyl group is mixed with the magnetic powder during the formation of a three-dimensional crosslinked body, the acid or base By interaction or hydrogen bonding, this molecule is more firmly incorporated and integrated into the cross-linking skeleton. As a result, the dispersibility of the magnetic powder in the formed magnetic layer is further improved.

The organic compound used together with the magnetic powder for forming the magnetic layer has a reactive functional group such as an isocyanate group or a polar group such as an epoxy group, a carboxyl group, an amino group and a hydroxyl group. When the organic compound is contained, the molecules of the organic compound are crosslinked by the interaction between the molecules to form an organic three-dimensional crosslinked body having a bond of carbon or oxygen atom as a skeleton. Therefore, when a magnetic coating containing the above-mentioned organic compound is prepared according to the sol-gel method to form a magnetic layer of a magnetic recording medium, a three-dimensional crosslinked body having a siloxane bond as a repeating unit and this organic three-dimensional crosslinked body are formed. By combining and, a magnetic layer in which the magnetic powders are evenly dispersed and firmly bonded to each other can be obtained.

The amount of the three-dimensional crosslinked component having siloxane bonds as repeating units in the magnetic layer is the above-mentioned organic 3
The effect of the present invention can be obtained if the amount of the dimensional crosslinked component or the amount of other binder components is 10% by weight or more, but it is more preferably 20% by weight or more, and by 50% by weight or more. , The effect is further improved.

In forming the three-dimensional crosslinked product according to the present invention,
When, for example, a polyisocyanate compound is allowed to coexist as an organic compound having a reactive functional group or a polar group, a magnetic layer in which magnetic powder is firmly incorporated by both a siloxane bond and a urethane bond is formed.

As the organic compound having a reactive functional group such as an isocyanate group or an epoxy group, for example, a trialkoxy or dialkoxysilane coupling agent and an organic compound having a group reactive with the terminal of the coupling agent are used. When the compound coexists, the magnetic layer in which the magnetic powder is firmly incorporated is formed by the bond based on these coupling reactions.

On the other hand, as a starting material for the sol-gel method, Al, Ti, Zr,
When an alkoxide such as Sn, In, or Sb is further added to form the three-dimensional crosslinked body of the present invention, a three-dimensional crosslinked body in which these elements are incorporated into the silanol chain is formed. In this case, the adhesion between the magnetic particles or between the magnetic layer and the non-magnetic support is further enhanced, and a magnetic recording medium with improved coating strength can be obtained.

In the present invention, the fine particles incorporated into the three-dimensional crosslinked body are not limited to magnetic fine particles. For example, when a metal oxide powder such as alumina is mixed with the magnetic powder as an abrasive, these inorganic fine particles are also taken into the three-dimensional crosslinked body in a uniform dispersed state in the same manner as the magnetic powder. Be done. Alternatively, an organic or inorganic pigment or the like can be similarly incorporated.

By the way, as described above, in the present invention, the fine particles incorporated into the three-dimensional crosslinked body are not limited to the magnetic powder, and therefore, like the underlayer and the intermediate layer of the magnetic recording medium,
By applying the present invention, it is possible to form a layer containing no magnetic fine particles but non-magnetic fine particles such as a metal oxide or a carbon compound. In this case, any method may be used to form the magnetic layer of the magnetic recording medium, the present invention may be applied, or another method may be applied.

Furthermore, the present invention can be applied not only to the formation of the magnetic layer and the underlayer of the magnetic recording medium but also to the formation of the back coat layer. Usually, a carbon compound such as carbon black is often added to the back coat layer as a conductive powder, but by applying the present invention, the fine powder of carbon black is incorporated into the three-dimensional crosslinked body in a uniformly dispersed state. Be done.

Next, a method of manufacturing the magnetic recording medium of the present invention will be described. First, raw materials such as polyalkoxysilane, orthosilicic acid, sodium orthosilicate, or their oligomers are dissolved in an organic solvent, and a polymerization catalyst such as nitric acid, magnetic powder and necessary additives are mixed and dispersed, and a sand grinder is used. It is used as a paint to prepare a magnetic paint. A magnetic recording medium of the present invention can be obtained by applying the obtained magnetic coating material onto a non-magnetic support such as a polyester film according to a conventional method and drying it.

[0036]

In the present invention, when a three-dimensional crosslinked body is formed by using the sol-gel method, the fine particles dispersed and present in the raw material solution are taken into the crosslinked body in a uniform dispersed state as follows. It is presumed to be due to the mechanism of.

That is, the siloxane bond (--Si--O) which is the main constituent of the cross-linking skeleton of the three-dimensional cross-linked product according to the present invention.
-) Has a large difference in electronegativity between Si and O, and therefore has a larger ionic bond than covalent bond than, for example, a C-C bond. On the other hand, the surface of ultrafine particles such as magnetic powder is very active. Therefore, it is considered that the crosslinked portion and the surface of the fine particles easily interact with each other by some electrostatic or chemical interaction. When a crosslinked portion having a certain size is formed microscopically, they interact with one fine particle surface, and one fine particle is bonded to the crosslinked portion. It is considered that such bonding is repeated as the cross-linking progresses, and individual fine particles are taken into the cross-linked body in a uniformly dispersed state. In this way
The three-dimensional crosslinked body having a siloxane bond as the main crosslink skeleton joins and integrates the fine particles.

According to the sol-gel method, the organic compound soluble in the solvent that dissolves the starting material is incorporated into the three-dimensional crosslinked body at the molecular level and integrated. At this time, the affinity between the three-dimensional crosslinked product and the organic compound is improved by the presence of an alkoxy group that remains bonded to the Si atom without participating in polycondensation and other organic groups such as an alkyl group. To be done.

Therefore, by using the sol-gel method, the magnetic layer in which the magnetic powder and the other organic compound added at the same time are firmly held in the three-dimensional crosslinked body is formed.

[0040]

EXAMPLES The magnetic recording medium of the present invention will be described in detail below with reference to examples.

Example 1 Magnetic coating materials having the following compositions were mixed and dispersed with a sand grinder for 2 hours.

[0042] Using a spin coater, obtain a magnetic coating material having a diameter of 2.5.
After coating on an inch glass disk substrate and drying,
The coating film was cured by heating in a nitrogen oven in a cure oven at 300 ° C. for 1 hour. Then, a fluorine-based lubricant was applied onto the obtained disk to obtain a magnetic recording hard disk.

Example 2 Magnetic coating materials having the following compositions were mixed and dispersed with a sand grinder for 2 hours.

[0044] The thickness of the obtained magnetic paint was adjusted to 10 using a reverse coater.
It was coated on a polyimide film of μm. Then, ethanol was evaporated while passing under the solenoid magnet to carry out the orientation treatment. Then, the coating film was cured by heating in a curing oven at 110 ° C. for 5 hours and subjected to calendering according to a conventional method to obtain a raw material of a magnetic recording medium. Then, the obtained original fabric was cut into a predetermined width to obtain a magnetic recording tape of an example of the present invention.

Example 3 A magnetic coating material having the following composition was mixed and dispersed with a sand grinder for 2 hours.

[0046] A magnetic recording tape of an example of the present invention was obtained in the same manner as in Example 2 except that the magnetic coating material thus obtained was used as the magnetic coating material.

Comparative Example 1 The same amount of polyurethane resin was used in place of 10 parts by weight of tetraethoxysilane in the [magnetic coating composition] of Example 1.
A magnetic recording hard disk was obtained in the same manner as in Example 1 except that 200 parts by weight of methyl ethyl ketone was used instead of 300 parts by weight of ethanol.

Comparative Example 2 The same amount of polyurethane resin was used in place of 5 parts by weight of tetraethoxysilane in the [magnetic coating composition] of Example 2, and Coronate L (trade name: polyisocyanate type) was added to the obtained magnetic coating. A magnetic recording tape of a comparative example of the present invention was obtained in the same manner as in Example 2 except that 3 parts by weight of a curing agent, manufactured by Nippon Polyurethane Co., Ltd. was added.

Comparative Example 3 Instead of 5 parts by weight of tetraethoxysilane in [Magnetic coating composition] of Example 3, the same amount of polyurethane resin was used, and Coronate L (trade name: polyisocyanate type) was added to the obtained magnetic coating. A magnetic recording tape of a comparative example of the present invention was obtained in the same manner as in Example 3 except that 3 parts by weight of a curing agent, manufactured by Nippon Polyurethane Co., Ltd. was added.

The characteristics of the magnetic disks of Example 1 and Comparative Example 1 and the magnetic recording tapes of Examples 2 and 3 and Comparative Examples 2 and 3 obtained as described above were evaluated and their characteristics were evaluated. I investigated the effect of. In the case of a magnetic disk, the evaluation items are pencil hardness of coating film, saturation magnetization Ms, and CS.
Number of S (contact start / stop), and
It is a reproduction output at 50 kfci, and in the case of a magnetic recording tape, the pencil hardness of the coating film, the saturation magnetization Ms, the still durability under the environment of 0 ° C., and the recording wavelength of 0.4 μm.
Is the recording / reproducing output. The evaluation results are shown in Table 1 below.
Shown in. When measuring the recording / reproducing characteristics, a 2.5-inch HDD (hard disk drive) manufactured by Toshiba was used for the magnetic disk, and a Hi-8 mm deck manufactured by Toshiba was used for the magnetic recording tape.

[0051]

[Table 1] According to Table 1, it is understood that the magnetic recording medium of the present invention has excellent surface property due to high pencil hardness, and high magnetic powder packing density due to high saturation magnetization Ms. It was also clear that the magnetic recording medium was excellent in running durability and recording / reproducing characteristics.

[0052]

As described above, in the present invention,
The magnetic powder in the magnetic layer is not merely mixed and dispersed with the resin binder, but has a binder function.
It is in a state of being firmly bonded to the three-dimensional crosslinked body in a uniformly dispersed state. Therefore, the dispersibility is remarkably improved as compared with the conventional one, and an excellent magnetic recording medium having an improved surface property and orientation of the magnetic layer can be obtained.

Further, according to the present invention, a resin binder as in the conventional magnetic recording medium is not essential, and even when it is used, it is possible to bond the magnetic powder densely and firmly by using a very small amount. Therefore, it is possible to increase the filling rate of the magnetic powder in the magnetic layer. Since the filling rate of the magnetic powder is high, the calendering property becomes good and the smooth magnetic layer can be formed more easily. Since the magnetic powder in the magnetic layer is densely and strongly bonded, the strength of the coating film is increased and the running durability is improved.

Further, the present invention can be applied not only to the magnetic layer of the magnetic recording medium but also to the underlayer, the back coat layer and the like. Therefore, an excellent magnetic recording medium can be obtained only by the present invention or by combining the present invention with a conventional method.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of a three-dimensional crosslinked product.

[Explanation of symbols]

 1 ………… Repeating unit of crosslinked product 2 ………… Magnetic powder

Claims (8)

[Claims] 1. A magnetic recording medium in which a magnetic layer containing magnetic powder is formed on at least one surface of a non-magnetic support, wherein the magnetic powder contained in the magnetic layer is mainly silicic acid or its A magnetic recording medium, wherein the derivative is bonded via a three-dimensional crosslinked body having a repeating unit of a siloxane bond formed by polycondensation. 2. A magnetic recording medium in which a magnetic layer containing magnetic powder and a nonmagnetic layer containing nonmagnetic particles are formed on at least one surface of a nonmagnetic support. Magnetic particles are mainly
A magnetic recording medium characterized by being bonded via a three-dimensional crosslinked body having a siloxane bond formed by polycondensation of silicic acid or a derivative thereof as a repeating unit. 3. A magnetic recording medium in which a magnetic layer containing magnetic powder is formed on one surface of a non-magnetic support, and a back coat layer containing non-magnetic particles is formed on the other surface of the non-magnetic support. A magnetic recording medium characterized in that the non-magnetic particles contained in the coating layer are bonded to each other mainly via a three-dimensional crosslinked body having a repeating unit of a siloxane bond formed by polycondensation of silicic acid or its derivative. . 4. The magnetic layer further comprises an organic compound having a reactive functional group or a polar group, and the mutual bond of the organic compound molecules is further compounded in the three-dimensional crosslinked body. The magnetic recording medium according to claim 1. 5. The non-magnetic layer further comprises an organic compound having a reactive functional group or a polar group, and the mutual bonding of the organic compound molecules is further compounded in the three-dimensional crosslinked body. A magnetic recording medium according to claim 2. 6. The back coat layer further contains an organic compound having a reactive functional group or a polar group, and the mutual bond of the organic compound molecules is further compounded in the three-dimensional crosslinked body. A magnetic recording medium according to claim 3. 7. Al, T in a part of the three-dimensional crosslinked body
7. At least one element selected from the group consisting of i, Zr, Sn, In, and Sb is incorporated therein, Claims 1, 2, 3, 4, 5 or 6. Magnetic recording medium. 8. The method according to claim 1, wherein the silicic acid or its derivative is any one of polyalkoxysilane, orthosilicic acid, sodium orthosilicate, or an oligomer thereof. 4,
The magnetic recording medium according to 5, 6, or 7.