JPH0773442A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility, the packing ratio and the traveling durability of the magnetic powder in the magnetic layer of a magnetic recording medium. CONSTITUTION:The magnetic powder 2 incorporated in the magnetic layer is joined each other through a three-dimentional crosslinking body having the repeating unit 1 of the siloxane bond obtained by condensation polymerization of silicic acid or its deriv. mainly. And the bonding 4 between the org. group which is introduced to the three-dimentional crosslinking body and has more than one group among amino, epoxy or mercapto group and the isocyanate group of the polyisocyanate compd. incorporated in the magnetic layer is formed. The crosslinking body is manufactured using a sol-gel method, and the particulates to be joined are not limited to magnetic particles, and a primary layer or a back coating is also can be formed by the crosslinking body. In this way, the coating film high in hardness and excellent in flexibility and lubricity is obtained and the improvement of the traveling durability is remarkable.

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
Silicic acid or a derivative thereof is bonded through a three-dimensional crosslinked body having a siloxane bond formed by polycondensation as a repeating unit, and the three-dimensional crosslinked body is introduced into the three-dimensional crosslinked body to form an amino group and an epoxy group. Group, or an organic functional group having at least one of a mercapto group, and a crosslinked portion formed by binding an isocyanato group of a polyisocyanate compound contained in the magnetic layer are characterized by being compounded. There is.

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 as a starting material. The most basic monomer among those silicic acids or silicic acid derivatives as starting materials can be represented by the following general formula 1.

[0017]

[Chemical 1] However, in Chemical formula 1, A _{1 to} A ₄ are —H, —X (halogen), —R (alkyl group having 1 to 3 carbon atoms), —OR.
It represents either (alkoxyl group having 1 to 3 carbon atoms), -OH (silanol group), or -OM (M is an alkali metal).

Specific examples of the compound represented by the general formula 1 are polyalkoxysilanes (polyalkyl silicates) of which one is shown in the following chemical formula 2, orthosilicic acid shown in the chemical formula 3, or ortho shown in the chemical formula 4. Examples include sodium silicate.

[0019]

[Chemical 2]

[Chemical 3]

[Chemical 4] As the starting material, in addition to these monomers, oligomers obtained by polymerizing them to form a 2-30mer can be used. When a monomer is used, nitric acid or the like is usually added as a catalyst for the polycondensation reaction. 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 the chemical formula 2, tetraethoxysilane (tetraethyl silicate) is mentioned as a representative example of polyalkoxysilane.

In the present invention, an organic functional group having at least one of an amino group, an epoxy group, and a mercapto group in a three-dimensional crosslinked body having a repeating unit of a siloxane bond formed by polycondensation of silicic acid or its derivative. In order to introduce a group, a trialkoxysilane coupling agent represented by the following general formula 5 or a compound represented by the following chemical formula 6 is used in the formation of a three-dimensional crosslinked body by the compound represented by the above general formula 1. A silane coupling agent such as the dialkoxysilane coupling agent shown may be added.

[0021]

[Chemical 5] However, the reduction 5, -Y ₁ represents an organic functional group having any of an amino group, an epoxy group or a mercapto group,, -Z represents -OR (alkoxyl group having 1 or 2 carbon atoms).

[0022]

[Chemical 6] However, in Chemical Formula 6, -Y ₁ is an organic functional group having any of an amino group, an epoxy group, or a mercapto group, Y ₂ is an organic functional group having any of an amino group, an epoxy group, or a mercapto group, or 1-3 carbons
Represents an alkyl group, and -Z represents -OR (alkoxyl group having 1 or 2 carbon atoms).

Tables 1 and 2 show specific examples of the compounds which can be used as the silane coupling agent represented by the general formula 5 or 6 in the present invention.

[0024]

[Table 1]

[Table 2] In the present invention, as the polyisocyanate compound having a plurality of isocyanato groups in one molecule for binding to the various organic functional groups having the above contents introduced into the three-dimensional crosslinked product, the following compounds can be used. is there. That is, an aliphatic polyisocyanate represented by hexamethylene diisocyanate having an isocyanato group content of 10% by weight or more, an aromatic polyisocyanate represented by tolylene diisocyanate, and an isophorone diisocyanate are represented. The alicyclic aliphatic polyisocyanate or the adduct thereof can be used.

In the presence of these polyisocyanate compounds, the monomer or oligomer represented by the general formula 1 is polycondensed with the silane coupling agent represented by the general formula 5 or 6 by the sol-gel method. As a result, a three-dimensional crosslinked body in which a crosslinked portion composed of an atomic group derived from a polyisocyanate compound is further composited is formed. The fine particles dispersed in the raw material solution at the time of forming the crosslinked body were taken into the crosslinked body in a uniform dispersed state, and as a result, the fine particles were firmly bonded to each other by the composite crosslinked body.
It has been found that a dimensional cross-linked gel body is obtained.

Therefore, for example, magnetic fine particles such as metal powder or 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 the 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, the magnetic powder 2 is incorporated into a three-dimensional crosslinked body by bonding an oxygen atom (O) of a siloxane bond (—Si—O—) to the surface of the magnetic powder 2, They are joined together. An organic functional group (-Y ₁ ) having any of an amino group, an epoxy group, or a mercapto group introduced into a part of the three-dimensional crosslinked body, and an isocyanate group (-N = C = O) of the polyisocyanate compound 3. ) Interact with each other and are bonded as shown by the dotted frame 4 to form a new crosslinked portion. As a result, a crosslinked body in which a crosslinked portion composed of an atomic group derived from a polyisocyanate compound is combined with a three-dimensional crosslinked body having a siloxane bond as a repeating unit is formed.

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 with respect 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 the 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, according to the present invention, an atom derived from a polyisocyanate compound molecule is formed in a part of the skeleton of the three-dimensional crosslinked body. Since the groups are combined, the affinity for the added organic compound is significantly improved. Therefore, the organic compound and the magnetic powder are uniformly held in the three-dimensional crosslinked body, and an excellent magnetic layer having appropriate hardness and flexibility 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.

Since lubricants such as fatty acids and fatty acid esters can be stably stored in the micropores in such a three-dimensional crosslinked body, these lubricants are gradually supplied to the surface of the magnetic layer coating film. It As a result, it is possible to obtain a magnetic recording medium excellent in running durability, in which the coefficient of friction between the magnetic layer surface and a running system device such as a recording / reproducing head or guide post is kept low.

The amount of the three-dimensional crosslinked component having a siloxane bond as a repeating unit 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 the present invention, the fine particles incorporated into the three-dimensional crosslinked body are not limited to magnetic fine particles. For example, when a compound containing Al, Ti, Zr, Sn, In, Sb, etc., or a metal oxide powder such as alumina as an abrasive is mixed with the magnetic powder, these inorganic fine particles are also mixed with the magnetic powder. Similarly, it is incorporated in the three-dimensional crosslinked body in a uniformly dispersed state. Alternatively, an organic or inorganic pigment or the like can be similarly incorporated.

By the way, as described above, since the fine particles incorporated into the three-dimensional crosslinked material in the present invention are not limited to the magnetic powder, 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, polyalkoxysilane (polyalkyl silicate), orthosilicic acid, sodium orthosilicate or a crosslinked body-forming main raw material such as an oligomer, a silane coupling agent, and a polyisocyanate compound are dissolved in an organic solvent, and nitric acid is dissolved. A magnetic catalyst is prepared by mixing and dispersing a polymerization catalyst such as the above, a magnetic powder, and a required additive and converting the mixture into a paint using a sand grinder or the like. 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.

[0037]

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 that it depends on the mechanism.

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.

The presence of a cross-linking portion having carbon or oxygen as a skeleton derived from the polyisocyanate compound molecule, which is compounded in the three-dimensional cross-linked product, is not involved in polycondensation, and remains alkoxy bonded to the Si atom. Combined with the presence of organic groups such as groups and alkyl groups, the affinity between the three-dimensional crosslinked product and the organic compound is significantly improved.

Due to such an improvement in the affinity with the organic compound, the magnetic powder and the other organic compound added at the same time are firmly held in the three-dimensional crosslinked body, and therefore, the hardness and the hardness are moderate. A magnetic layer having flexibility is formed.

[0041]

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.

[Magnetic coating composition] Ba ferrite powder 100 parts by weight Tetraethoxysilane oligomer 3 parts by weight N- (2-aminoethyl) -3-aminopropyltrimethoxysilane 3 parts by weight Methyl ethyl ketone 300 parts by weight Gaffac RE610 (trade name: Phosphate ester-based surfactant, manufactured by Toho Kagaku Co., Ltd.) 4 parts by weight Nitric acid (polymerization catalyst) 0.01 parts by weight Stearic acid 3 parts by weight Then, a trimethylolpropane adduct of tolylene diisocyanate is further added to the dispersion having the above composition. Was added in an amount of 5 parts by weight, and the obtained magnetic paint was applied onto a polyester film. After applying a calendar treatment to the formed coating film, 4
After curing in a constant temperature bath of 0 ° C for 3 days, slit and
A mm-width magnetic recording tape was obtained.

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

[Magnetic coating composition] Ba ferrite powder 100 parts by weight Tetraethoxysilane 4 parts by weight 3-Glycidoxypropyldimethoxysilane 2 parts by weight Methyl ethyl ketone 300 parts by weight Gafac RE610 (trade name: phosphate ester surfactant, Toho Chemical Co., Ltd.) 2 parts by weight Nitric acid (polymerization catalyst) 0.01 parts by weight Stearic acid 3 parts by weight Thereafter, isophorone diisocyanate adduct (isocyanato content 12% by weight) 7 was added to the dispersion having the above composition.
Parts by weight were added. The obtained magnetic paint was used as Co-γ-Fe.
A layer containing ₂ O ₃ magnetic powder was coated on the surface of a magnetic recording medium which was subbed on a polyester film so as to have a film thickness of 0.2 μm after drying. After coating, calendering, curing and slitting were performed in the same manner as in Example 1 to obtain an 8 mm wide magnetic recording tape.

Example 3 An 8 mm wide magnetic recording tape was obtained in the same manner as in Example 1 except that the following composition was used as the magnetic coating material.

[Magnetic coating composition] Metal powder 100 parts by weight Tetraethoxysilane 5 parts by weight 3-Mercaptopropyltrimethoxysilane 3 parts by weight Methyl ethyl ketone 350 parts by weight Lecithin 3 parts by weight Nitric acid (polymerization catalyst) 0.01 parts by weight Stearic acid 3 Parts by weight Example 4 The content of tetraethoxysilane is 2 parts by weight, and
An 8 mm wide magnetic recording tape was obtained in the same manner as in Example 2 except that 5 parts by weight of a polyurethane resin (molecular weight 20,000) was further added.

Comparative Example 1 Instead of the tetraethoxysilane oligomer and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in Example 1, 10 parts by weight of a polyurethane resin (molecular weight 20,000) was added. In the same manner as in Example 1, an 8 mm wide magnetic recording tape was obtained.

Comparative Example 2 Example 1 was changed except that the compounding amount of the tetraethoxysilane oligomer in Example 1 was changed to 6 parts by weight and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane was not added. An 8 mm wide magnetic recording tape was obtained in the same manner as in.

The characteristics of the magnetic tapes of Examples and Comparative Examples obtained as described above were evaluated and the effects of the present invention were investigated. The evaluation items are the pencil hardness of the coating film, the saturation magnetization Ms, the still durability under the environment of 0 ° C., and the recording / reproducing output at the recording wavelength of 0.4 μm. The evaluation results are shown in Table 1 below. A Hi-8 mm deck manufactured by Toshiba was used for measuring the recording / reproducing characteristics.

[0051]

[Table 3] From Table 3, it can be understood that the magnetic recording medium of the present invention has a high pencil hardness and thus is excellent in surface properties, and that the magnetic recording medium of the present invention has a high saturation magnetization Ms and thus a high magnetic powder packing density. 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 simply mixed and dispersed with the resin binder, but has a binder function.
Moreover, the three-dimensional crosslinked product having a high affinity with the organic compound is firmly bonded 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.

Furthermore, according to the present invention, since the magnetic powder can be bonded densely and firmly even with the use of a very small amount of resin binder, the filling rate of the magnetic powder in the magnetic layer can be increased. 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 layer having high hardness and flexibility and capable of stably holding the lubricant is formed inside, the running durability of the magnetic recording medium is remarkably 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 cross-linked product 2 ………… Magnetic powder 3 ………… Polyisocyanate compound 4 ………… Bond between organic functional group and isocyanato group

Claims (1)

[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 The derivative is bonded through a three-dimensional crosslinked body having a siloxane bond formed by polycondensation as a repeating unit,
In addition, the three-dimensional crosslinked body includes an organic functional group having at least one of an amino group, an epoxy group, and a mercapto group introduced into the three-dimensional crosslinked body, and a polyisocyanate contained in the magnetic layer. A magnetic recording medium characterized in that a cross-linked portion formed by bonding with an isocyanato group of a compound is compounded.