JPS59162628A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic transducing characteristics by forming a magnetic layer contg. an organoaluminum compound, a liq. acrylic oligomer, a thermoplastic resin and magnetic powder so as to improve the dispersibility and fillability of the magnetic powder. CONSTITUTION:An aluminum coupling agent prepd. by bonding at least one easily hydrolyzable group and at least one hardly hydrolyzable lipophilic group to aluminum is suitable for use as the organoaluminum compound, and it is used by 0.1-10wt% of the amount of the magnetic powder in the magnetic layer. In case of <0.1wt%, the expected effect is not produced, and in case of >10wt%, the compound is liable to bleed out. The preferred amount is 0.5-5wt%. The acrylic oligomer is prepd. by mixing dipentaerythritol hexaacrylate with the ester of dipentaerythritol with pentaacrylic acid or lower.

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 chargeability 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 thermoplastic resin are used together as a binder component, and an organic aluminum compound is used as a dispersant for magnetic powder. When using , the above-mentioned acrylic oligomer is in liquid form, and since it is combined with an organic aluminum compound that has an excellent effect of reducing the viscosity of magnetic paint, magnetic paint can be prepared with a small amount of organic solvent. Since the thermoplastic resin has excellent dispersibility of magnetic powder, the dispersibility and filling properties of the magnetic powder are sufficiently improved, and a magnetic paint containing these and the magnetic powder is applied onto a substrate, and then it is irradiated with radiation. Then, the acrylic oligomer is polymerized and hardened by radiation to form a magnetic layer with good dispersibility and filling properties of the magnetic powder and further improved electromagnetic conversion characteristics,
Furthermore, the inventors have discovered that the abrasion resistance of the magnetic layer is improved to further improve durability, and the elastic modulus is also improved to provide a magnetic recording medium with even greater mechanical strength, leading to the creation of this invention.

The organoaluminum compound used in the present invention is preferably an aluminum coupling agent in which at least one group that is easily hydrolyzed and at least one group that is difficult to be hydrolyzed and exhibits lipophilicity are bonded to aluminum. used as something. This type of organoaluminium 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 aluminum compound is contained in the magnetic layer, it adheres firmly to the particle surface of the magnetic powder,
A film is formed and the dispersibility of the magnetic powder is sufficiently improved. In addition, this type of organoaluminum 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 are sufficiently improved, further improving the electromagnetic conversion characteristics. Examples of such organic aluminum compounds include aluminum coupling agents such as stearyl acetoacetate aluminum diisopropylate, myristyl acetoacetate aluminum diisopropylate, and caprylacetoacetate aluminum diisopropylate. Specific examples of commercially available products include AL-M manufactured by Ajinomoto Co., Ltd., and the like.

These aluminum compounds can be prepared by dissolving them in a suitable solvent and adding the solution obtained by this melting when preparing magnetic paint, or by dipping magnetic powder in this solution and preparing magnetic powder in advance. The magnetic powder is contained in a magnetic layer and used in a method such as preparing a magnetic paint using this magnetic powder. At this time, when using a binder resin having a hydroxyl group, if an attempt is made to incorporate an organoaluminum compound into the magnetic layer using the former method, the organoaluminum compound and the binder resin will react and the dispersion of the magnetic powder will be reduced. It is preferable to incorporate the organoaluminum compound into the magnetic layer using the latter method, since this does not improve the properties of the magnetic layer. The amount used is 0゛, 1% by weight based on the magnetic powder in the magnetic layer.
If it is less than 10% by weight, the desired effect cannot be obtained, and if it exceeds 10% by weight, there is a risk of bleed-out.
It is preferably used within the range of 0.5 to 5% by weight, 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.

Pentaerythritol 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, but in addition to this, solid or liquid dipentaerythritol type acrylate 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 1:10, 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.

As the thermoplastic resin used in combination with the liquid acrylic oligomer, vinyl chloride resin, polyvinyl acecool resin, cellulose resin, polyurethane resin, polyester resin, etc. are preferably used. All of these thermoplastic resins have good affinity with magnetic powder and have excellent dispersibility of magnetic powder. Therefore, when these types of thermoplastic resins are used together, the dispersibility of magnetic powder is further improved and the electromagnetic conversion characteristics are improved. is improved. Examples of vinyl chloride resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer,
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-
Vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl propionate copolymer, etc. are preferably used.
YHH1VAGH, VMCH2 Sekisui Chemical Co., Ltd. S-Resoku A, S-Lec CN, Toyo Soda Co., Ltd. J4-Lon Q
Examples include S-430 and Luron QA-431. In addition, as the polyvinyl acecool resin, for example, polyvinyl butyral resin is suitably used, and specific examples include S-Resoku BL, S, S-Re-Tsuku BMS, and S-Resoku BL-1 manufactured by Block Chemical Industry Co., Ltd. , Mobital B manufactured by Hoechst Japan Co., Ltd., and the like. Preferred cellulose resins include nitrocellulose, acetylcellulose, acetylbutylcellulose, methylcellulose, ethylcellulose, benzylcellulose, carboxymethylcellulose, and hydroxycellulose. Specific examples include nitrocellulose manufactured by Asahi Kasei Corporation. Cellulose L1/
2, L1/4, Ll, H1/4, H1/2, Hl, H5
, Daicel Nitrocellulose R3I/1.6, R5
Examples include I/2, R3I, R32, and the like. Furthermore, as a polyurethane resin, the molecular weight is 1000 to 100.
(Too) from low molecular weight to high molecular weight are preferably used, and specific examples include Takenate L-1007, Takenate L-2710, Takerac E-551T, manufactured by Shikinichi Pharmaceutical Co., Ltd. Examples include Takelac E-550, Pandenox T-5201 manufactured by Dainippon Ink and Chemicals, Vandesox T-5250, and MH-101 manufactured by Honey Kasei.As polyester resins, commonly used molecular weights are 10,000 to 10,000.
30,000 or so saturated or unsaturated polyester resin,
Alternatively, a polyester resin containing a sulfonic group or a sulfonic acid metal group is preferably used,
As a specific example, for example, Byron #2 manufactured by Toyobo Co., Ltd.
00, Byron #300, Byron #400, polyester GX-W1, and the like.

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 thermoplastic resin is 8:2 to 2: the liquid acrylic oligomer to the thermoplastic resin, by weight. The ratio should be within the range of 2:8, preferably within the range of 6:4 to 4:6. If the liquid acrylic oligomer is too small, the filling properties of the magnetic powder and the mechanical properties of the magnetic layer will be affected. The magnetic strength and abrasion resistance are not sufficiently improved, and on the other hand, if too much is used, the magnetic layer becomes too hard and brittle, and the dispersibility of the magnetic powder is not improved.

The radiation used to polymerize and harden the liquid acrylic oligomer is preferably β rays such as electron beams, and γ rays such as ultraviolet rays or X rays.
When using ultraviolet light, a sensitizer is used at the same time to make the effect of the irradiation more efficient. Such radiation irradiation uses radiation with an accelerating voltage of 150 to 750 KV,
It is preferable to irradiate at an absorbed dose of 3 to 15 Mrad; if the absorbed dose is too small, crosslinking of the liquid acrylic oligomer 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 thermoplastic resin are mixed in an organic solvent. The organoaluminum compound and the magnetic powder are dispersed and mixed in this solution, or the magnetic powder whose surface has been previously treated with the organoaluminum compound is added to the solution for 18 minutes. This is done by mixing to prepare a magnetic paint, coating it on a substrate such as a polyester film, 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, COO Fe50 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 Eslenc CN (Shimiki Kagaku Kogyo 901/Shasei, vinyl chloride-vinyl acetate copolymer) Dipentaerythritol hexa 55 acrylate Dipentaerythritol penta 55/l Acrylate AL-M< Manufactured by Ajinomoto Co., Ltd., aluminum 20 - nium coupling agent) myristic acid 15 n-butyl stearate 10 methyl isobutyl ketone
450 Toluene 450 This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint, and this magnetic paint was applied onto a 10μ thick polyester base film to give a coating thickness of 3μ. Next, after calendering, Nishin High Voltage Co., Ltd. E
Using PS-750, the material was cured by irradiation with radiation at an IMrad dose, and then cut into a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, Eslenok BLS (manufactured by Suihiro Kagaku Kogyo Co., Ltd.,
A magnetic tape was prepared in the same manner as in Example 1 except that the same amount of polyvinyl butyral resin was used.

Example 3 A magnetic tape was produced in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of nitrocellulose I]1 (manufactured by Asahi Kasei Corporation, nitrocellulose) was used in place of Eslenok CN. .

Example 4 In the composition of the magnetic paint in Example 1, the same amount of MH-101 (manufactured by Honey Kasei Co., Ltd., -08 pendant polyurethane resin) was used in place of Eslenok CN, and the same amount of cyclohexanone was used in place of methyl isobutyl ketone. A magnetic tape was produced in the same manner as in Example 1 except for the following.

Example 5 A magnetic tape was prepared in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of polyester GX-Wl (manufactured by Toyobo Co., Ltd., sulfonic group-containing polyester resin) was used in place of Eslenok CN. I made it.

Comparative Example 1 In the composition of the magnetic paint in the example process, SRESOC CN was omitted and BlenAct 9S (
Using the same amount of titanium coupling agent (manufactured by Kenri Sohy Petrochemical Co., Ltd.), and replacing 1-55 parts by weight of dipentaerythritol hexaacrylate, 100 parts by weight of acrylic double bond-introduced vinyl chloride-vinyl acetate copolymer. use,
A magnetic tape was prepared in the same manner as in Example 1, except that 100 parts by weight of an acrylic double bond-introduced urethane elastomer was used in place of 55 parts by weight of dipentaerythritol pentaacrylate.

The magnetic tape obtained in each example and comparative example was loaded into a video deck, a carrier signal of 4.5 Ml (z) 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. The C/N was measured.The obtained magnetic tape was loaded into a video deck and the steel properties were measured.Furthermore, 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 table above, the magnetic tapes obtained in Examples 1 to 5 have a higher elastic modulus than the magnetic tape obtained in Comparative Example 1, and have longer steel properties and higher C/N (, From this, the magnetic recording medium obtained by this invention is
It can be seen that it has excellent mechanical strength and durability, has good dispersibility and filling properties of the magnetic powder, and has excellent electromagnetic conversion characteristics.

Claims (1)

[Claims] ■, organoaluminum compound, dipentaerythritol hexaacrylate, dipentaerythritol and 5
A magnetic recording medium having a magnetic layer containing the following ester with acrylic acid, thermoplastic resin, and magnetic powder: