JPS59162641A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a high modulus of elasticity, superior mechanical strength and durability by using a liq. acrylic oligomer and a radiation curing resin as binder components and an organotitanium compound as a dispersant for magnetic powder. CONSTITUTION:A magnetic layer contg. an organotitanium compound, dipentaerythritol hexaacrylate, the mono to pentaester of dipentaerythritol with acrylic acid, a radiation curing resin and magnetic powder is formed. Titanium alkoxide, a titanium coupling agent or the like is suitable for use as the organotitanium compound. An acrylic oligomer prepd. by mixing the hexaacrylate with the ester is liq. and has many double-bond groups per one molecule, so a magnetic coating material can be prepd. with a small amount of a solvent. It is preferable that the radiation curing resin has <10,000mol.wt. and 2-4 functional groups.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and its purpose is to have a high elastic modulus, excellent mechanical strength and durability, good dispersibility and filling properties of magnetic powder, and electromagnetic conversion characteristics. The objective is to provide an excellent magnetic recording medium.

In recent years, in magnetic recording media such as magnetic tape, recording,
In order to lengthen playback time as much as possible, thinner magnetic tapes are sought after, and magnetic tapes that tend to be thinner must have particularly high elastic modulus, excellent mechanical strength, and durability to ensure running stability. A material with excellent properties in terms of performance and electromagnetic conversion properties is required.

For this reason, attempts have been made to improve the elastic modulus of the magnetic layer by using a high modulus binder resin such as a high molecular weight polyurethane resin or a two-component reactive binder resin such as a polyol and an isocyanate compound. When using a high modulus binder resin, a large amount of organic solvent is used, making it difficult to obtain good electromagnetic characteristics, and when using a two-component reactive binder resin, a large amount of solvent is required. On the other hand, there are drawbacks such as the need for heat treatment after the magnetic layer is formed, and the reaction is not complete, making it impossible to sufficiently improve durability.

Therefore, as a method to improve this, in recent years, radiation-curable resins such as radiation-sensitive modified resins such as acrylic double bond-introduced vinyl chloride-vinyl acetate copolymers and radiation-sensitive elastomers such as acrylic double bond-introduced urethane elastomers have been developed. A magnetic paint is prepared by mixing and dispersing this radiation-curable resin with magnetic powder treated with a dispersant such as a titanium coupling agent using a mold resin, and after coating the magnetic paint on the substrate, it is irradiated with radiation. A method has been proposed in which a magnetic layer is formed by radiation polymerization of a radiation-curable resin, but this method improves the elastic modulus and wear resistance of the magnetic layer, and also improves the dispersibility and filling properties of the magnetic powder. However, the results are still insufficient and no fully satisfactory results have yet been obtained.

The inventors conducted various studies in view of the current situation, and found that dipentaerythritol hexaacrylate,
When dipentaerythritol and an ester of 5 or less acrylic acid are mixed, it becomes liquid, and this liquid acrylic oligomer and a radiation-curable resin are used together as a binder component, and an organic titanium compound is used as a dispersant for magnetic powder. When using acrylic oligomer, magnetic paint can be prepared with a small amount of organic solvent because the above-mentioned acrylic oligomer is used in combination with an organic titanium compound that has an excellent effect of reducing the viscosity of the liquid main magnetic paint. Since the binder component is a radiation-curable resin, the dispersibility and filling properties of the magnetic powder are sufficiently improved, and when a magnetic paint containing these and the magnetic powder is applied onto a substrate and then irradiated with radiation,
The above-mentioned acrylic oligomer and radiation-curable resin are polymerized and cured by radiation to form a magnetic layer with good dispersibility and filling properties of the magnetic powder and further improved electromagnetic conversion characteristics, and the wear resistance of the magnetic layer is also improved. The present inventors have discovered that a magnetic recording medium can be obtained which has further improved durability and improved elastic modulus, resulting in even more excellent mechanical strength, and has thus arrived at the present invention.

Preferred organic titanium compounds used in this invention include titanium alkoxides and titanium coupling agents. This type of organotitanium compound acts as a bridge between organic and inorganic substances through strong chemical bonds, and when it comes into contact with magnetic powder, it strongly reacts with the hydroxyl groups on the surface of the powder particles, forming a strong bond on the surface of the magnetic powder. join to. Therefore, when this type of organic titanium compound is contained in the magnetic layer, it adheres firmly to the particle surface of the magnetic powder, forming a film and sufficiently improving the dispersibility of the magnetic powder. In addition, this type of organic titanium compound has a particularly excellent effect of reducing the viscosity of the magnetic paint, so the amount of organic solvent used can be reduced, and the filling properties of the magnetic powder can be sufficiently improved, further improving the electromagnetic conversion characteristics. Such organic titanium compounds include, for example, titanium alkoxides such as tetraisopropyl titanate, tetrastearyl titanate, polydibutyl titanate, and isopropyltriisostearoyl titanate, isopropyltridecylhenzensulfonyl titanate, isopropyl tris(dioctylpyrophosphate) titanate, Tetraisopropylbis(dioctylphosphite) rape I, Tetraoctylbis(ditridecylphosphite) titanate, Tetra(2,2
Examples include titanium coupling agents such as -diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, and bis(dioctylpyrophosphate) ethylenecinate; Specific examples of commercially available products include PlenAct TTS, PlenAct 9S, PlenAct 38S1 BlenAct 41B1 PlenAct 46B1 manufactured by Kenri Sohi Petrochemical Co., Ltd.
Examples include Plain Act 55, Plain Act 138S, and Plain Act 2383.

These organic titanium compounds can be prepared by dissolving them in a suitable solvent and adding the solution obtained by this dissolution when preparing magnetic paint, or by soaking magnetic powder in this solution and preparing magnetic powder in advance. The magnetic powder is contained in a magnetic layer and used by a method such as preparing a magnetic paint using the magnetic powder after surface treatment. At this time, when used in combination with a binder resin having hydroxyl groups, if an attempt is made to incorporate the organic titanium compound into the magnetic layer using the former method, the organic titanium compound and the binder resin will react and the dispersion of the magnetic powder will be affected. It is preferable to incorporate the organic titanium compound into the magnetic layer using the latter method, since this does not improve the properties of the organic titanium compound.

If the amount used is less than 0.1% by weight based on the magnetic powder in the magnetic layer, the desired effect will not be obtained, and if it exceeds 10% by weight, there is a risk of bleed-out. It is preferably used within the range, and more preferably within the range of 0.5 to 5% by weight.

In addition, the acrylic oligomer used in this invention, which is a mixture of dipentaerythritol hexaacrylate and an ester of dipentaerythritol and 5 or less acrylic acid, is liquid and has a large number of double bond groups per molecule. Magnetic coatings can be prepared with a small amount of solvent, and have a high crosslinking density when polymerized and cured by radiation irradiation. Therefore, the dispersibility and filling properties of magnetic powder can be improved, and electromagnetic conversion characteristics can be improved. The abrasion resistance and elastic modulus of the magnetic layer are also improved, and the durability and mechanical strength are further improved.

Pen erythritol type acrylate used in a mixture as described above is solid when the number of double bond groups is 4 or more, and dipentaerythritol hexaacrylate is solid; When esters of erythritol and 5 or less acrylic acid are mixed, a liquid acrylic oligomer is obtained, and a magnetic paint can be prepared with a small amount of solvent as described above, and a high crosslinking density can be obtained by irradiation with radiation. The mixing ratio of such dipentaerythritol hexaacrylate and the ester of dipentaerythritol and 5 or less acrylic acid is such that it becomes easily liquefied by mixing and sufficiently improves the filling properties and crosslinking density of the magnetic powder. In order to
It is preferable to mix dipentaerythritol hexaacrylate to ester of dipentaerythritol and 5 or less acrylic acid within the range of 10:1 to 1:IO, and furthermore, the crosslinking density is sufficient to ensure mechanical stability. In order to sufficiently improve strength and durability, it is more preferable to blend the materials so that the average number of acrylic groups is 5 or more.

Further, the radiation-curable resin used in combination is not particularly limited, but those having a molecular weight of less than 10,000 and a number of functional groups of 2 to 4 are preferably used. This type of radiation-curable resin is liquid and has excellent dispersibility and filling properties for magnetic powder, and when it is coated on a substrate together with magnetic powder and then irradiated with radiation, it crosslinks and forms a moderately polymerized and hardened magnetic layer. The mechanical strength and wear resistance of the magnetic layer are improved. In addition, it has good compatibility with the liquid acrylic oligomer, and the acrylic oligomer does not become hard even when irradiated with radiation. The content ratio of curable resin can be increased, and
The amount of the M/8 agent used can be further reduced, and the dispersibility and filling properties of the magnetic powder can be further improved, and the mechanical strength and abrasion resistance of the magnetic layer can be further improved. Specific examples of radiation-curable resins include urethane acrylic oligomers, epoxy acrylic oligomers, oligoester acrylic oligomers, and spiroacecool acrylic oligomers. Specific examples of commercially available products include, for example, M manufactured by Toagosei Co., Ltd. -6250, M-7100, M-1100, M-1
200, Thiokol tJ-782, U-783, U
-788, U-893, 5P-4010 manufactured by Showa Kobunshi Co., Ltd.
, U-3000, E-4000, Celanese 320
0.3500.3600.3700 etc. are mentioned.

the dipentaerythritol hexaacrylate;
The mixing ratio of the liquid acrylic oligomer, which is a mixture of dipentaerythritol and an ester of 5 or less acrylic acid, and the radiation-curable resin is 1:99 to 99:1:1 to the radiation-curable resin, by weight. vs 1
The ratio should be within the range of 10 to 90 to 90.
It is preferable to blend within the range of T'l 1.0,
If the amount of the liquid acrylic oligomer is too small, the filling and dispersibility of the magnetic powder and the mechanical strength and wear resistance of the magnetic layer will not be sufficiently improved, while if it is too large, the magnetic layer will become too hard and brittle. Problems arise with durability.

The radiation used in polymerizing and curing the liquid acrylic oligomer and radiation-curable resin is preferably β-rays such as electron beams, and T-rays such as ultraviolet rays or X-rays. When doing so, a sensitizer is used at the same time to make the effect of irradiation more efficient. Irradiation with such radiation requires an accelerating voltage of 150 to 75
Using 0KV radiation, the absorbed dose is 3-15 Mrad
It is preferable to irradiate in such a way that if the absorbed dose is too small, the crosslinking of the liquid acrylic oligomer and the radiation-curable resin will be insufficient and the desired effect will not be obtained.

To form the magnetic layer of the present invention, a liquid acrylic oligomer prepared by mixing the dipentaerythritol hexaacrylate, an ester of dipentaerythritol and 5 or less acrylic acid, and a radiation-curable resin are combined into an organic Dissolve in a solvent and disperse and mix the organic titanium compound and magnetic powder in this solution, or disperse and mix magnetic powder whose surface has been previously treated with the organic titanium compound to prepare a magnetic coating, and apply this to a polyester film. This is done by applying it to a substrate such as, and then irradiating it with radiation to polymerize and harden it.

As the magnetic powder used here, for example, r-Fe
203 powder, Fe3O4 powder, CO-containing -Fe203
powder, Co-containing Fe3O4 powder, CrO2 powder, F
Various conventionally known magnetic powders such as metal powders such as e powder, Co powder, and Fe-Ni powder are widely used.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethylformamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 800 parts by weight Dipentaerythritol Hexa 20 Acrylate Dipentaerythritol Benta 20 Acrylate M-6250 (manufactured by Toagosei Co., Ltd., 160 Bifunctional oligoester acrylate) Prene Act 9S- (Kenri Sohi 2) Petrochemical Co., Ltd., titanium coupling agent) Myristic acid 15 n-butyl stearate 10 ~ Methyl isobutyl ketone
450 Toluene 450
A magnetic paint was prepared by mixing and dispersing this composition in a ball mill for 72 hours, and this magnetic paint was applied onto a polyester base film with a thickness of 10 μm to a coating thickness of 3 μm. After calendering, the tape was cured by irradiating it with radiation at a dose of 7 Mrad using F, PS-7'50 manufactured by Nisshin High Voltage Co., Ltd., and cut into a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, M-625
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of M-1100 (urethane acrylate manufactured by Toagosei Co., Ltd.) was used in place of M-0.

Example 3 In the composition of the magnetic paint in Example 1, M-625
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of 3200 (epoxy acrylate manufactured by Celanese) was used instead of 0.

Example 4 In the composition of the magnetic paint in Example 1, M-625
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of U-3000 (spiroacecool acrylate manufactured by Showa Kobunshi Co., Ltd.) was used instead of U-3000.

Comparative Example 1 In the composition of the magnetic paint in Example 1, M-625
0 was omitted and 20 parts by weight of dipentaerythritol hexaacrylate was replaced with acrylic double bond-introduced vinyl chloride.
A magnetic tape was prepared in the same manner as in Example, except that 100 parts by weight of the vinyl acetate copolymer was used and 100 parts by weight of an acrylic double bond-introduced urethane elastomer was used instead of 20 parts by weight of diventaerythritol benquaacrylate I. I made it.

The magnetic tape obtained in each example and comparative example was loaded into a video deck, a 4.5 MHz carrier signal was recorded, the playback output was extracted, and the ratio of the peak value C to the integral value N of the total noise was calculated as C/ N was measured. Further, the obtained magnetic tape was loaded into a video deck and its steel properties were measured, and the elastic modulus of the obtained magnetic tape at 1% elongation was measured using a tensile tester. Steel properties are an indicator of wear resistance, and the longer this time, the better the wear resistance.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained in Examples 1 to 4 have higher elastic modulus than the magnetic tape obtained in Comparative Example 1, and have longer steel properties and higher C/N. The magnetic recording medium obtained by this invention is
It has excellent mechanical strength and durability, good dispersibility and filling properties of magnetic powder, and excellent electromagnetic conversion characteristics.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing an organic titanium compound, dipentaerythritol hexaacrylate, an ester of dipentaerythritol and 5 or less acrylic acid, a radiation-curable resin, and a magnetic powder.