JPS6284427A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility, magnetic characteristics and electromagnetic conversion characteristic by incorporating a non-magnetic solid additive subjected to a surface treatment with a specific phosphate into a magnetic layer. CONSTITUTION:The non-magnetic solid additive subjected to the surface treatment with the phosphate expressed by the formula is incorporated into the magnetic layer. The phosphate is uniformly stuck to the surface of the additive. The deposition amt. thereof is made 0.1-2.0pts.wt. by 100pts.wt. solid additive. Non-magnetic inorg. powder having about 0.05-4mum particle size and >=5 Mohs hardness is used for the non-magnetic solid additive. The non-magnetic solid additive is usually used at a ratio of 1-20pts.wt. per 100pts.wt. magnetic powder. The magnetic layer in which the solid additive is uniformly dispersed without forming flocculated lumps and has good surface smoothness is thereby formed. The medium having the good magnetic characteristics and electromagnetic conversion characteristic is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, such as a magnetic tape or a magnetic disk, in which a support L is provided with a magnetic layer containing magnetic powder and a binder resin.

[Conventional technology]

In this type of magnetic recording medium, non-magnetic solid additives such as α-Fe203 powder, Al2O3 powder, TiO2 powder, Ba5O, powder, etc. are included in the magnetic layer containing magnetic powder and binder resin. Efforts are being made to improve the durability of the layer and running stability. However, the above-mentioned solid additives generally have poorer affinity with the binder resin than magnetic powders, and cause agglomerates due to poor dispersibility in the magnetic layer, impairing surface smoothness.
In addition to the drawbacks of frequent deterioration of magnetic properties and electromagnetic conversion properties and frequent dropouts, there is also the drawback that the original purpose of using this solid additive, particularly running stability, cannot be sufficiently improved.

By the way, as a means to improve the dispersibility of magnetic powder in the magnetic layer, it is often carried out to treat the surface of magnetic powder with a surface treatment agent, and a phosphate ester type is particularly effective as a surface treatment agent. Dispersants are known.

Representative examples of phosphoric acid ester-based dispersants include JP-A-54-150104 and JP-A-58-1613.
As seen in Publication No. 03, alkylene oxide adducts obtained by addition-polymerizing alkylene oxide to alcohols such as aliphatic alcohols and alkylphenols are reacted with phosphoric anhydride, for example, as shown in the following formula. ;% formula %) (Ra is an alkyl group or alkylphenyl group, Rb is an ethylene, propylene or ranalalkylene group, n is an integer) and other diesters or triesters having the same structure as above.

If such a conventionally known phosphate ester dispersant is applied to the non-magnetic solid additive, the solid additive in the magnetic layer can be treated by surface treating the additive with the dispersant. It is expected that the dispersibility will be improved.

[Problem that the invention seeks to solve]

Based on the above idea, the inventors actually developed α-Fe.
An attempt was made to surface-treat a non-magnetic solid additive such as 203 powder with the above-mentioned conventionally known phosphate ester dispersant. As a result, an improvement effect on dispersibility was certainly observed, but this improvement effect was sufficiently satisfactory to be able to greatly improve the magnetic properties, electromagnetic conversion properties, dropout, and running stability of this type of magnetic recording medium. It wasn't necessarily a thing.

Therefore, the present invention applies a specific dispersant different from the conventionally known phosphate ester dispersant to the non-magnetic solid additive to be added to the magnetic layer.
The objective is to obtain a magnetic recording medium such as a magnetic tape that has improved dispersibility of this additive in the magnetic layer, has excellent magnetic properties and electromagnetic conversion properties, has less dropout, and has good running stability. .

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors discovered that a specific phosphoric acid ester having an alkylene oxide structure part and a (meth)acryloyl structure part in the molecule was used as a non-magnetic solid additive for the magnetic layer. When used as a surface treatment agent for a vehicle, the affinity and dispersibility of the additive for the binder resin are greatly improved, resulting in excellent magnetic properties and electromagnetic conversion properties, less dropout, and improved running stability. Having learned that a good magnetic recording medium can be obtained, the present invention was completed.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing magnetic powder and binder resin is provided on a support.
In the above magnetic layer, the following formula; % formula % [In the formula, R1 is the following structural formula: An integer of 1 to 30), R2 and R3 are hydrogen or the same group as R1 above. This relates to a magnetic recording medium.

[Structure and operation of the invention]

The phosphoric acid ester represented by the above formula used in this invention has an alkylene oxide structure (R'O) (
It has an essential difference in molecular structure from the conventionally known phosphate esters in that it has a meth)acryloyl group bonded to it, and this difference in molecular structure is what makes it a non-magnetic solid additive. It is presumed that this appears as a difference in the dispersibility improvement effect.

In other words, improvement in the dispersibility of non-magnetic solid additives by a dispersant is achieved as a result of the dispersant increasing the affinity of the non-magnetic solid additives with the binder resin and organic solvent during the preparation stage of the magnetic paint. It is something. Therefore, the dispersant must have appropriate hydrophilicity and lipophilicity to have excellent affinity for the above-mentioned solid additive, binder resin, and organic solvent.

From this point of view, when looking at the phosphoric acid ester according to the present invention, it is adsorbed to solid additives due to its phosphoric acid structure and the strong polarity of the hydroxyl group that may be contained in the molecule, and its alkylene oxide structure is absorbed into solid additives. By adjusting the type and number of moles added, affinity for the binder resin and organic solvent can be imparted. On the other hand, the (meth)acryloyl group bonded to this alkylene oxide structure further increases the affinity with the binder resin and organic solvent, and as a result, the hydrophilic and lipophilic balance of the dispersant as a whole improves the dispersibility of the solid additive. It is thought that this will be kept within a suitable range to improve the situation.

In addition, the above (meth)acryloyl group contains a carbon-carbon double bond, and in this respect, it is mixed with a non-magnetic solid additive to form a dispersant on the surface of the additive. It is thought that the adhesion of the dispersant layer to the additive surface becomes stronger, and this and the above-mentioned suitable hydrophilic/oleophilic balance improve the dispersibility of the solid additive in the magnetic paint and magnetic layer. Furthermore, the dispersion stability is expected to be significantly improved.

Among the phosphoric acid esters according to the present invention that exhibit such effects, monoesters in which R2 and R3 in the above formula are both hydrogen, or monoesters in which one of R2 and R3 in the above formula is hydrogen and the other are hydrogen. Diesters, which are groups having the same structural formula as R1, are particularly preferred. Since such monoesters and diesters contain free hydroxyl groups in their molecules, they give better results in adhesion to the surface of solid additives. Of course, in addition to the mixture of the seven-ester and diester described above, a small amount of a triester in which both R2 and R3 are groups having the same structural formula as R1 may be mixed.

Further, depending on the case, it is also possible to use the above triester alone.

R' in the above structural formula is an alkylene group having 2 to 4 carbon atoms, and is preferably a propylene group having 3 carbon atoms from the viewpoint of improving the balance of hydrophilicity, especially lipophilicity. However, depending on the case, an ethylene group having 2 carbon atoms or a butylene group having 4 carbon atoms can be selected. Further, the repeating unit represented by R'0 may be composed of a mixture of at least two of a propylene oxide group, an ethylene oxide group, and a butylene oxide group. n indicates the number of repeating units mentioned above, and is 1 to 30, usually 1 to 30.
It is preferably in the range of 20, and particularly preferably from 4 to 15. If the number of units is too large, it becomes difficult to balance the hydrophilicity and lipophilicity, making it difficult to improve the dispersibility of the solid additive, and the phosphoric acid ester changes from liquid to solid, making it difficult to handle.

The above-mentioned phosphoric acid ester according to the present invention can be obtained by, for example, synthesizing in advance an alcohol represented by the following formula; The above-mentioned -hydric alcohol can be obtained by an esterification reaction between glycols made of a corresponding alkylene oxide polymer and (meth)acrylic acid.

In addition, in the reaction of the above-mentioned -hydric alcohol and phosphoric anhydride, a part of the above-mentioned -hydric alcohol is converted into aliphatic-
Alkylene oxide adducts obtained by addition-polymerizing alkylene oxide to alcohols such as alcohols and alkylphenols, such as polyalkylene glycol lauryl ethers and polyalkylene glycol alkylphenyl ethers, may also be used. By this substitution, a part of R, (or this and R2 or R3) in the above formula is substantially composed of the above alkylene oxide adduct, and the phosphoric acid ester according to the present invention and the above conventionally known phosphoric acid A mixed phosphoric ester is obtained which is a mixture with an ester. In this invention, there is no problem even if such a mixed phosphoric ester is used.

However, if the amount of substitution becomes too large, the effect of this invention may be impaired, so it is preferable that the amount of substitution does not exceed the amount of the specific monomer alcohol of this invention in terms of moles, and especially More preferably, the amount of substitution is less than half the number of moles of the alcohol in this invention.

In this invention, a nonmagnetic solid additive is surface-treated using the above-mentioned phosphoric acid ester. This treatment allows the phosphate ester to adhere uniformly to the surface of the additive, but
The amount of this adhesion is 01 to 2 parts by weight per 100 parts by weight of the solid additive.
The amount is preferably 0 parts by weight, preferably 2 to 10 parts by weight. If the amount used is too small, a sufficient effect of improving dispersibility cannot be obtained, and if it is too large, the surface smoothness of the magnetic layer may be impaired or the durability may be reduced, both of which are undesirable.

As the non-magnetic solid additive to be surface-treated, a non-magnetic inorganic powder having a particle size of about 0.05 to 4 μm and a Mohs hardness of 5 or more is used. For example, α-Fe203 powder, A
I! 203 powder, TiO□ powder, Cr2O3 powder, mullite (
3Al! 203・2Si02) powder, aluminum titanate (A1203・Ti02) powder, BaSO4 powder, zircon (ZrO□・SiO□) powder, forsterite (2M
go・5i02) powder, enstatite (MgO-S 1
02) Powder, spodumene (L+20・Al2O3・4
SiO2) powder, eucryptite (Li20・Al2O
3.2SiO□) powder, cordierite (2Mg0.2
A1203・5SiO□) powder, Saphirin (4Mg0・
5AI! 203.2SiO2) powder, Petalite (Li2
0.Al2O3.BS io□) powder, beryl (3BeO
・Al2O3・6SiO□) powder, Celsian (BaO-
Examples include A1203.2SiO□) powder. This non-magnetic solid additive is usually used in an amount of 1 to 20 parts by weight per 100 parts by weight of magnetic powder.

Generally, the surface treatment method is to prepare a solution by dissolving phosphate ester in an appropriate solvent, add non-magnetic solid additives to this solution, mix and disperse with a homo mixer, and then heat and dry. Preferably adopted.

This method has the advantage of forming a uniform layer of phosphoric acid ester on the surface of the solid additive.

Solvents for dissolving the above phosphoric acid esters include water, alcohols having 1 to 5 carbon atoms, acetone, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, and aromatic substances such as benzene and toluene. and ethers such as tetrahydrofuran and dioxane. Among these, carbon number 1~
Alcohols No. 5 give particularly good results in terms of the dispersibility of the final non-magnetic solid additive. The concentration of phosphoric acid ester in these solvents varies considerably depending on the type of solvent, but it is generally recommended to be about 1 to 2.0% by weight, particularly preferably about 0.5 to 1% by weight. .

The magnetic recording medium of the present invention is produced by preparing a magnetic paint in which a non-magnetic solid additive surface-treated with a phosphate ester as described above is mixed and dispersed in an organic solvent together with a magnetic powder and a binder resin. By coating it on a non-magnetic support such as polyester film to form a magnetic layer,
Orientation treatment, mirror polishing treatment and cutting (
It can be obtained by performing a punching process or the like.

As the magnetic powder used here, any conventionally known magnetic powder can be used, such as γ-Fe203 powder, Fe3
O4 powder, CO-containing 7-Fe2O3 powder, Co-containing Fe
In addition to oxide-based magnetic powders such as 3O4 powder, hexagonal ferrite powders such as barium ferrite and strontium ferrite, metal powders such as Fe powders, CO powders, and Fe-Ni powders may be used.

These magnetic powders are in the form of acicular powders as well as plate-like single grains.

It has a shape such as a rice grain.

As mentioned above, this invention is characterized in that the non-magnetic solid additive to be added to the magnetic outer layer is surface-treated with a specific phosphoric acid ester. The powder may be similarly surface-treated with the above-mentioned phosphoric acid ester to exhibit the same effect as above. According to this, even better results can be obtained by reducing magnetic properties, electromagnetic conversion properties, running stability, and dropouts. When surface treating magnetic powder in this way,
It is operationally convenient to mix the magnetic powder and the non-magnetic solid additive and surface-treat both at the same time.

Next, the binder resin for dispersing and binding the above-mentioned magnetic powder and non-magnetic solid additives is vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin, polyurethane resin, polyester based resin,
Any conventionally widely used binder resin such as polyisocyanate compounds can be used. Furthermore, various electron beam curable resins can also be used.

Further, as organic solvents for preparing magnetic paint, ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, Solvents suitable for dissolving the binder resin used are particularly suitable, such as alcohol solvents such as isopropyl alcohol, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and dioxane. They may be used alone or in a mixture of two or more without any restriction.

Needless to say, magnetic paints containing such magnetic powder, binder resin, organic solvent, and non-magnetic solid additives surface-treated with the above-mentioned phosphate ester do not contain the commonly used additives. Agents such as lubricants and ultrafine antistatic agents such as carbon black may be added as appropriate.

〔Effect of the invention〕

As detailed above, in this invention, by using the above-mentioned specific phosphoric acid ester as a surface treatment agent for the non-magnetic solid additive to be added to the magnetic layer, it is possible to provide support in the magnetic paint and this paint. The dispersibility of the solid additives in the magnetic layer coated on the body can be greatly improved, resulting in good surface smoothness where the solid additives are uniformly dispersed without forming agglomerates. Since a magnetic layer can be formed, it is possible to provide a magnetic recording medium such as a magnetic tape that has excellent magnetic properties and electromagnetic conversion properties, has little dropout, and has good running stability.

[Examples] Next, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight. Moreover, the phosphoric acid esters AC used in the following examples and comparative examples are as follows.

<Phosphoric acid ester A> As a monolayer alcohol, polyethylene consisting of the following molecular formula consisting of R'=propylene group, n=6, R''=methyl group in the above formula; and the following molecular formula; H+0CH2CH2 0+C9H19 Glycol nonylphenyl ether is used at a molar ratio of 2:1, and a mixed phosphoric ester mainly composed of monoester and diester is obtained by reacting this -hydric alcohol with phosphoric anhydride. Let it be A.

<Phosphoric acid ester B> In the above phosphoric acid ester A, the alcohol used in combination with polyethylene glycol nonylphenyl ether is formed by the following molecular formula in which R' = ethylene group, n = 6, and R'' = hydrogen: Phosphoric ester B is a mixed phosphoric ester containing monoester and diester as main components obtained in the same manner as the above phosphoric ester A, except that the phosphoric ester B was changed to a mixture consisting of a monoester and a diester.

Cricate ester C> The above-mentioned phosphoric acid ester A as the alcohol.

Use the polyethylene glycol nonylphenyl ether used to obtain B alone and react it with phosphoric anhydride to obtain a phosphoric acid ester whose main components are monoester and diester, and use it as phosphoric acid ester C. .

Example 1 α-Fe203 powder (average particle size 0.8 pn)
Part 5 AI! 203 powder (average particle size 03 units)
3 parts Phosphoric acid ester A 1 part Isopropyl alcohol 100 parts The dispersion liquid consisting of the above components was mixed and dispersed in a homomixer for 4 hours.
Let it stand for a while. Then, it was dried at 80°C for 15 hours to obtain a surface-treated mixed solid additive. This processing additive contains 1 1/2 powder of each powder for both α-Fe203 powder and Al2O3 powder.
A magnetic paint was prepared by mixing and dispersing in a ball mill for about 100 hours using the processing additive, in which 15 μm of phosphoric acid ester A was uniformly adhered to each door, and the following composition was used.

Surface treatment mixed solid additive 8 parts Co containing 7
-Fe2O3 magnetic powder 100 parts Nitrified cotton 9 parts Polyurethane resin 8 parts Trifunctional low molecular weight incyanate compound 3 parts Myristic acid 3
90 parts cyclohexanone
en 90
Next, the above magnetic paint was applied onto a 12-thick polyester film to a dry thickness of about 3 fim.
After drying and mirror-finishing, it was cut into a predetermined width to produce a magnetic tape.

Example 2 CO-containing Fe203 magnetic powder 100 parts α
-Fe203 powder (average particle size 0.8F) 5 parts Al2O3 powder (average particle size 0.3μ) 3 parts Phosphoric acid ester A 10 parts Isopropyl alcohol 1,000 parts Example 1 was prepared from a dispersion of each of the above components. A surface-treated mixed powder consisting of a surface-treated magnetic powder and a surface-treated mixed solid additive was obtained in a similar manner. This treated powder contains -
Fe203 magnetic powder, α-Fe203 powder and Al2O
1.5 rng per 1772' of each powder for all three powders
Phosphate ester A was uniformly adhered.

The magnetic coating was carried out in the same manner as in Example 1, except that 108 parts of this surface-treated mixed powder was used in place of 8 parts of the surface-treated mixed solid additive and 100 parts of Co-containing -Fe203 magnetic powder in the magnetic paint of Example 1. A tape was made.

Comparative Example 1 No surface treatment with phosphoric acid ester A was performed, and 5 parts of untreated α-Fe203 powder and 5 parts of untreated α-Fe203 powder were used instead of 8 parts of the surface treatment mixed solid additive in the magnetic coating composition of Example 1. A
I! A magnetic tape was produced in the same manner as in Example 1, except that 3 parts of 203 powder was used.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1, except that phosphoric ester C was used in the same amount instead of phosphoric ester A.

Example 3 Ti02 powder (average particle size 05 pn) 8 parts Phosphoric acid ester B 1 part Isopropyl alcohol 1-00 parts A dispersion containing the above components was mixed and dispersed in a homomixer for 4 hours, allowed to stand for 24 hours, and then filtered. Then, it was dried at 80°C for 15 hours to obtain a surface-treated solid additive. To this processing additive, 15 rng of phosphate ester B was uniformly adhered per door of TiO□ powder.

A magnetic tape was prepared in the same manner as in Example 1, except that 8 parts of this surface-treated solid additive was used in place of 8 parts of the surface-treated mixed solid additive in the magnetic paint of Example 1.

Comparative Example 3 No surface treatment with phosphate ester B was performed, except that 8 parts of untreated TiO□ powder was used instead of 8 parts of the surface treatment solid additive in the composition of the magnetic paint of Example 3. A magnetic tape was produced in the same manner as in Example 3.

The magnetic properties, surface smoothness, C/N ratio, dropout, and running stability of each of the magnetic tapes of Examples 1 to 3 and Comparative Examples 1 to 3 were investigated. The results are shown in Table 1 and below. It was as shown in Table 2.

The magnetic properties are based on the square shape (Br/Bs) and the residual magnetic flux density (
Br) was measured. The surface smoothness was measured using a stylus surface roughness meter at a cutoff of 80 pn, and was expressed as center line average roughness (Ra). The C/N ratio was measured at a recording wavelength of 4 MHz, and Comparative Example 1 was used for Examples 1 and 2 and Comparative Examples 1 and 2, Comparative Example 3 was used for Example 3 and Comparative Example 3,
Each was expressed as a relative value with 0 dB (reference). In addition, the number of dropouts of 5 door seconds or more per minute was investigated, and the running stability was investigated by wow and flutter.

As is clear from the above results in Table 1 and Table 2, the magnetic tape of the present invention has excellent magnetic properties and surface smoothness, good electromagnetic conversion characteristics expressed by C/N ratio, and less dropouts. Moreover, it can be seen that the running stability is also excellent.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder resin is provided on a support, in the magnetic layer:
The following formula; ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, R_1 is the structural formula below; ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, R' is an alkylene group with 2 to 4 carbon atoms. , R'' is hydrogen or a methyl group, n is an integer of 1 to 30), R_2, R_3 are hydrogen or the same group as R_1 above] A magnetic recording medium characterized by containing a solid additive.