JPS59162639A - 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 thermoplastic resin as binder components and an organoaluminum compound as a dispersant for magnetic powder and by carrying out irradiation. CONSTITUTION:A magnetic layer contg. an organoaluminum compound, dipentaerythritol hexaacrylate, the mono to pentaester of dipentaerythritol with acrylic acid, a radiation curing resin, a thermoplastic resin and magnetic powder is formed. 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. An acrylic oligomer prepd. by mixing the dipentaerythritol hexaacrylate used therefor and the mono to pantaester of dipentaerythritol with acrylic acid is liq., and high cross- linking density is attained by polymn. and curing under radiation.

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 increase the playback time and increase the playback time, thinner magnetic tapes are being made, and magnetic tapes that are intended to be made thinner have particularly high elastic modulus and excellent mechanical strength for running stability. It is required to have excellent durability and electromagnetic conversion characteristics.

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.

As a result of various studies in view of the current situation, the inventors have already found that when dipentaerythritol hexaacrylate and an ester of dipentaerythritol and 5 or less acrylic acid are mixed, they become liquid, and such liquid acrylic An oligomer and a thermoplastic resin are used together as a binder component, and an organoaluminum compound is used as a dispersant for magnetic powder. A magnetic paint containing these and the magnetic powder is applied onto a substrate, and then it is exposed to radiation. When irradiated with , the oligomer is polymerized and hardened by radiation, forming a magnetic layer with good dispersibility and filling properties of the magnetic powder and further improved electromagnetic conversion characteristics.The abrasion resistance of the magnetic layer is also improved, making it durable. It was discovered that a magnetic recording medium with even better mechanical strength could be obtained by further improving the properties and modulus of elasticity, but as a result of further investigation,
When a radiation-curable resin is further used as a binder component, the dispersibility and filling properties of the magnetic powder are further improved, and the abrasion resistance and elastic modulus of the magnetic layer are further improved, resulting in even better electromagnetic conversion characteristics. The present inventors have discovered that a magnetic recording medium with excellent durability and mechanical strength can be obtained, leading to the present 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 organoaluminum 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 ~ it firmly adheres to 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 organoaluminum compounds can be prepared by dissolving them in a suitable solvent and elevating the solution by this dissolution.
force applied when preparing magnetic paint), or immerse magnetic powder in this 78 liquid to prepare magnetic 1! I.

The magnetic powder is contained in a magnetic layer and used by surface-treating the powder and then using the magnetic powder to prepare a rupturable paint. 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. 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 achieved, 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.

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 should be sufficiently high 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. In addition, the amount of the liquid acrylic oligomer blended in this way is preferably within the range of 1 to 80% by weight based on the total amount of the binder components. Mechanical strength and abrasion resistance are not sufficiently improved, and if the amount is too high, the magnetic layer becomes too hard and brittle, causing problems in durability.

In addition, the radiation-curable resin used in combination is not particularly limited, but has a molecular weight of less than 5,000 and a functional group number of 2 to 2.
4 is 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. This improves the mechanical strength and wear resistance of the magnetic layer. 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 of the curable resin can be increased, the amount of organic solvent used can be further reduced, the dispersibility and filling properties of the magnetic powder can be further improved, and the mechanical strength and wear resistance of the magnetic layer can be improved. You can further improve your sexuality. Specific examples of such radiation-curable resins include:
For example, urethane acrylic oligomer, epoxy acrylic oligomer, oligoester acrylic oligomer,
Examples include spiroacecool acrylic oligomer,
Specific examples of commercially available products include Toagosei i! J
M-6250, M-7100, M-8030, M-11
00, M-1200, Thiokol U-782, U-
783, U-788, U~893, Showa Kobunshisha gsp
-4010, U-3000, E-4000, Celanese 3200.3500.3600.3700, and the like. The amount used is 1 to 40% by weight based on the total amount of binder components.
It is preferable to use the amount within the following range; if it is too small, the filling properties of the magnetic powder will not be sufficiently improved, and if it is too large, the elastic modulus will not be sufficiently increased and the mechanical strength will not be sufficiently improved.

Suitable thermoplastic resins used together with the liquid acrylic oligomer and radiation-curable resin include vinyl chloride resin, polyvinyl acecool resin, cellulose resin, polyurethane resin, and polyester resin. 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 resins include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl propionate copolymer, etc. are preferably used, and specific examples include, for example, U.C.C., Inc., 1VYHH, VAGH, V.
MCJ (S-LEC A, S-LEC CN manufactured by X-Kyomizu Kagaku Kogyo Co., Ltd.).

Ryuron QS-430, Ryuron QΔ manufactured by Toyo Soda Co., Ltd.
-431 and the like. In addition, as the polyvinyl acecool resin, for example, polyvinyl butyral resin is preferably used, and specific examples include S-Resoku BLS, S-Resoku BMS, S-Resoku BL-1 manufactured by Tanezu Chemical Co., Ltd., and Hoechst Japan Co., Ltd. Examples include Mobital B manufactured by Manufacturer. 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/
Examples include nitrocellulose R31/16, R3I/2, R3I, and R52 manufactured by Daicel Corporation.

Furthermore, as a polyurethane resin, the molecular weight is 100.
Both those with a low molecular weight of 0 to 100,000 and those with a high molecular weight are preferably used, and specific examples include Takenate L-1007 manufactured by Yayoi Yakuhin Kogyo Co., Ltd.
, Takenate I, 2710, Takerac E~551T,
Examples include Takelac E-550, Bandex T-5201 manufactured by Dainippon Ink and Chemicals, Bandenox T-52501, and MH-101 manufactured by Honey Kasei. The molecular weight of polyester resins commonly used is 10.
Saturated or unsaturated polyester resins having a molecular weight of about 000 to 30,000 or polyester resins containing sulfonic groups or sulfonic acid metal bases are preferably used. , Byron #300, Byron #400,
Examples include polyester GX-W1. The amount of such thermoplastic resin used is 1 to 8 with respect to the total amount of binder components.
It is preferable to use it within the range of 0 weight percent; if it is too small, the dispersibility of the magnetic powder will not be sufficiently improved, and if it is too large, a sufficiently high elastic modulus will not be obtained and the mechanical strength will not be sufficiently improved.

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. Such radiation irradiation is performed at an accelerating voltage of 150 to 7'
Using 50KV radiation, the absorbed dose is 3-15 Mrad
It is preferable to irradiate so that the absorbed dose is too small, and the cross-linking between the liquid acrylic oligomer and the radiation-curable resin is insufficient, and the desired effect cannot be obtained.

To form the magnetic layer of the present invention, the dipentaerythritol hexaacrylate described above, a liquid acrylic oligomer prepared by mixing an ester of dipentaerythritol and 5 or less acrylic acid, a radiation-curable resin, and a heat-curable resin are used. A magnetic paint is prepared by dissolving the plastic resin in an organic solvent and dispersing and mixing the organoaluminum compound and magnetic powder in this solution, or by dispersing and mixing the magnetic powder whose surface has been previously treated with the organoaluminum compound. This is done by coating this 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, rF
e2'03 powder, Fe3O4 powder, Co-containing rFe2O
3 powder, Co-containing Fe5Q4 powder, CrO2 powder, Fe powder, 0. Various conventionally known magnetic powders such as metal powders such as O 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 1 800 parts by weight of α-Fe magnetic powder
t vinyl copolymer) dipentaerythritol hexa 60 acrylate dipentaerythritol penk 60 acrylate M-6250 (manufactured by Toagosei Co., Ltd., 40 〃bifunctional oligoester acrylate) AL-M (manufactured by Ajinomoto Co., Ltd., aluminum 20〃nium cup Ring agent) Myristic acid 15 Stearic acid ~ n-butyl 10 Methyl isobutyl ketone
425〃Toluene 425
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 hair film to give a coating thickness of 3μ. Next, after calendering, the material was cured by irradiating it with radiation at a dose of 7 Mrad using EPS-750 manufactured by Nishin High Voltage Co., Ltd., and was cut into a predetermined width to produce a magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, Eslenoku CN was replaced with Eslenoku BLS (manufactured by Block Chemical Industry Co., Ltd.,
A magnetic tape was produced 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 the same amount of nitrocellulose H1 (manufactured by Asahi Kasei Corporation, nitrocellulose) was used in place of Esresoku CN in the composition of the magnetic paint.

Example 4 In the composition of the magnetic paint in Example 1, the same amount of MH-101 (manufactured by Honey Kasei Co., Ltd., -OH pendant polyurethane resin) was used in place of S-LEC 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 Same as Example 1 except that the same amount of polyester GX-Wl (manufactured by Toyobo Co., Ltd., sulfone group-containing polyester resin) was used instead of Eslenok CN in the composition of the magnetic paint in Example 1. and made magnetic tape.

Example 6 In the composition of the magnetic paint in Example 1, M-62
A magnetic tape was prepared in the same manner as in Example 1, except that the same amount of M-1200' (urethane acrylate 1~ manufactured by Toagosei Co., Ltd.) was used instead of 50.

Example 7 With the composition of the magnetic paint in Example 1), M-62
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 in place of 50.

Example 8 The composition number of the magnetic paint in Example 1 was M-6.
A magnetic tape was prepared in the same manner as in Example 1, except that 4 times the same amount of U-3000 (spiroacetal acrylic 1/- manufactured by Showenchi Polymer Co., Ltd.) was used in place of 250.

Comparative Example 1 In the composition number of the magnetic paint in Example 1, S-LEC CN and M-6250 were omitted, and instead of AL-M, Prene Act 9S (manufactured by Kenri Nohi Petrochemical Co., Ltd.,
Using the same amount (titanium cup linking agent), and replacing 60 parts by weight of dipentaerythritol hexaacrylate with 100 parts by weight of acryl double bond-introducing salt vinyl-vinyl acetate copolymer. A magnetic tape was prepared in the same manner as in Example 1, except that 100 parts by weight of urethane elastomer having an acrylic double bond was used instead of 60 parts by weight of acrylate.

The magnetic tape prepared 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 8 had a higher elastic modulus than the magnetic tape obtained in Comparative Example 1 (M), had longer steel properties, and had a higher C/N.
This shows that the magnetic recording medium obtained by the present invention has excellent mechanical strength and durability, good dispersibility and filling properties of the magnetic powder, and excellent electromagnetic characteristics.

Claims (1)

[Claims] 1. Organoaluminium compound, dipentaerythritol hexaacrylate, dipentaerythritol and 5
A magnetic recording medium having a magnetic layer containing the following ester with acrylic acid, radiation-curable resin, thermoplastic resin, and magnetic powder.