JPS5829139A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having superior magnetic characteristics, superior surface smoothness of the magnetic layer and superior durability and contg. magnetic powder with high dispersibility and fillability by hardening a coated film contg. a specified coupling agent and a specified oligomer under radiation so as to produce the magnetic layer. CONSTITUTION:A coated film contg. a titanium coupling agent represented by the general formula, an oligomer of epoxy acrylate or epoxy methacrylate obtd. by reacting a compound contg. >=2 epoxy groups with acrylic acid or methacrylic acid, and magnetic powder is formed on a substrate and hardened by irradiation to produce a magnetic layer. Besides said oligomer, to the film may be added an oligomer obtd. by bonding acrylic acid or methacylic acid to a terminal of polyalkylene glycol or polyol by esterification. The preferred amount of the coupling agent to be used is 0.1-10wt% of the amount of the magnetic powder in the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and the object thereof is to have good dispersibility and filling properties of magnetic powder, excellent magnetic properties and surface smoothness of the magnetic layer, and excellent durability. The purpose of this invention is to provide a magnetic recording medium.

Magnetic recording media are usually made by applying a magnetic coating consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film and drying it. A product with excellent quality and durability is required.

Therefore, it is necessary to select a binder component with excellent dispersibility of the magnetic powder, or to change the magnetic powder to, for example, alkyl titanium F.
Attempts have been made to improve the magnetic properties and surface smoothness of the magnetic layer and to improve the wear resistance by improving the dispersibility of magnetic powder by treating it with dispersants such as However, this method is still not completely satisfactory, and in addition, this method involves the use of a large amount of a harmful organic solvent that dissolves the binder component during the preparation of the magnetic coating material, resulting in pollution problems.

Therefore, as a way to improve this, in recent years various oligomers such as urethane ataryleide oligomers have been developed. A method has been proposed in which a magnetic paint is prepared by mixing and dispersing - with a magnetic powder and other necessary components, and this magnetic paint is applied onto a substrate and then irradiated with radiation to polymerize the oligomers to form a magnetic layer. However, although this method improves the pollution problem, the improvement in the dispersibility and filling properties of the magnetic powder are still insufficient, and satisfactorily results have not yet been obtained.

The inventors conducted various studies in view of the current situation, and found that the general formula %) (wherein R is a hydrocarbon group or -CH, -C(C).

'H,)-(CB,-0-CH,-C1(-CH,),
, X is PSY (1+0-Rl), OH, and R8 is an alkyl group. ), an oligomer of epoxy acrylate or niboxy methacrylate obtained by reacting a compound containing two or more egoxy groups with acrylic acid or methacrylic acid, and magnetic powder. When a magnetic coating is applied and then irradiated with radiation to polymerize and harden the oligomer to form a magnetic layer, there are no pollution problems, and the dispersibility and filling properties of the magnetic powder are sufficiently improved to improve the magnetic properties and the magnetic layer. The surface smoothness of the oligomer is further improved, and in addition to the above oligomer, the oligomer has an ester bond of acrylic acid or methacrylic acid at the end of a polyalcohol-molecular glycol or a polyhydric alcohol.
It has been discovered that when used in combination with -, the magnetic properties and surface smoothness of the magnetic layer as well as durability are further improved, and this invention has been completed.

When the titanium coupling agent of the general formula used in this invention comes into contact with magnetic powder, it reacts strongly with the hydroxyl groups on the surface of the powder particles, breaking the bond between the titanium atom and -(OR)4, and forming a titanium atom. Strongly bonds to the surface of magnetic powder via oxygen. Therefore, when this type of titanium coupling agent 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.
Furthermore, since this type of titanium coupling agent has the effect of lowering the viscosity of the magnetic paint, the filling properties of the magnetic powder are also improved, and the magnetic properties and surface smoothness of the magnetic layer are further improved.

Furthermore, since this type of titanium coupling agent has excellent flexibility, the flexibility of the magnetic layer becomes appropriate and the durability is also improved. A specific example of such a titanium coupling agent is, for example, BreneAct 41B1 PreneAc, manufactured by Kenritzhi Petrochemical Co., Ltd., which is represented by the following structural formula.
46B1 Blenaku) 55, etc.

Prene Act 41B (tetraisopropylene bilbis (dioctyl phosphite) titanium) Prene Act 46B (
乎) Ujcutyl bis(ditridecyl phosphite) titanate] preneac) 55 [tetra(2,2-diallyloxymethyl-1-butyl)bis(di-silidecy/&/
) phosphite titanium] These titanium coupling agents can be obtained by dissolving them in a suitable solvent and adding the solution obtained by this dissolution when preparing magnetic paint, or by dipping magnetic powder in this solution. The magnetic powder is used by surface-treating the magnetic powder in advance and then containing it in a magnetic paint by preparing a magnetic paint using this magnetic powder. 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 within the range, and more preferably within the range of 0.5 to 5% by weight.

In addition, the oligomer of epoxy acrylate or epoxy methacrylate used in this invention, which is obtained by reacting a compound containing two or more epoxy groups with acrylic acid or methacrylic acid, may be OH (however, Ro is H or CH3, n is 1 ~20 integers,
m is an integer from 1 to 20. ) Bisphenol-type and novolac-type compounds having a molecular weight of 500 to 20,000 are preferably used. When this type of epoxy acrylate or epoxy methacrylate oligomer is used in combination with the titanium coupling agent mentioned above, the viscosity is reduced by the titanium coupling agent, so the filling property at the end of the magnetic field is sufficiently improved, and the magnetic properties and magnetic layer are improved. surface smoothness is further improved. Furthermore, when the substrate is coated with the magnetic powder and the titanium coupling agent and then irradiated with radiation, the double bonds at both ends are opened and cross-linked, forming an appropriately polymerized and hardened magnetic layer. The wear resistance is also improved. The amount used is preferably within the range of 20 to 60% by weight based on the total amount of magnetic powder. If it is too small, the desired effect will not be obtained, and if it is too large, the content of magnetic powder will be too low. Good electromagnetic conversion characteristics cannot be obtained.

In this invention, the oligomer in which acrylic acid or methacrylic acid is ester bonded to the end of polyalkylene glycol used together with the epoxy acrylate or epoxy methacrylate-F oligomer has the general formula % (where R1 is H or CH3, Rz is a hydrocarbon group, l
is an integer from 1 to 50. ) An oligomer with a molecular weight of 100 to 1500 is preferably used, and an oligomer in which acrylic acid or methacrylic acid is ester-bonded to the terminal of a polyhydric alcohol has the general formula % (kill group, R, OH or R40R, at least one of which is necessarily R40R, and %R3 and R4
is a hydrocarbon group, R5 is H, -CH-Co- or CH
, -C(CH,)-CO-1p is an integer of 1 to 10. ) Oligomers having a molecular weight of 100 to 2,000 are preferably used. This type of oligomer, in which acrylic acid or methacrylic acid is ester-bonded to the terminal end of polyalkylene glycol or polyhydric alcohol, has a coating hardness that changes depending on the degree of polymerization of the polyalkylene glycol. When the degree is 7 or higher, it becomes soft. When this kind of oligomer with low viscosity is used in combination with the above-mentioned relatively hard epoxy acrylate or epoxy methacrylate oligomer, the viscosity of the mixed oligomer is adjusted and lowered, and the filling properties of the magnetic powder are improved. When the titanium coupling agent mentioned above is used in combination, the viscosity is further lowered, so that the filling properties of the magnetic powder are sufficiently improved, and the magnetic properties and surface smoothness of the magnetic layer are further improved. Furthermore, these oligomers were coated on a substrate together with magnetic powder and the titanium coupling agent mentioned above, and then irradiated with radiation, the double bond at the end of each oligomer was opened and oligomers of the same or different types were crosslinked, allowing them to be used in combination. The flexibility is improved by the low viscosity oligomer, and a polymerized and hardened magnetic layer with appropriate flexibility is formed, and the abrasion resistance of the magnetic layer is further improved.

The mixing ratio of the oligomer having acrylic acid or methacrylic acid ester bonded to the end of polyalkylene glycol or polyhydric alcohol to the oligomer of epoxy acrylate or epoxy methacrylate is within the range of 1:3 to 3:1 by weight. It is preferable that the amount of epoxy acrylate-F or epoxy methacrylate oligomer is too small, the wear resistance will decrease,
If the amount is too large, the viscosity of the oligomer will increase and the dispersibility and filling properties of the magnetic powder will not be sufficient. In addition, the amount of the oligomer mixed with both is preferably within the range of 20 to 60% by weight based on the total weight of the magnetic powder. If it is too small, the desired effect cannot be obtained, and if it is too large, the magnetic powder If the content of 2 is too low, good electromagnetic conversion characteristics cannot be obtained.

The radiation used to polymerize and crosslink the oligomers is preferably beta rays such as electron beams, and rms such as ultraviolet rays or X-rays. A sensitizer is used at the same time to make it more efficient. It is preferable to use radiation with an accelerating voltage of 150 to 750 KV in such radiation irradiation so that the absorption 411IfIk is 3 to 15 Mrad; if the absorbed dose is too small, the crosslinking of the oligomers will be insufficient and the The effect of the period cannot be obtained.

Examples of the magnetic powder used in this invention include r-F
e, OB powder, Fe3O4 powder, Co-containing -Fe, 0
1 powder, Co-containing Fe, 04 powder, CrO2 powder,
Various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni powder are widely included, and in particular, metal powders, when used with a thin film layer formed on the surface, can be used as the titanium coupling agent. The effect is greater when used together.

- In order to form the magnetic layer of the present invention on a substrate, the above-mentioned epoxy acrylate or epoxy methacrylate oligomer or polyalkylene glycol or polyhydric alcohol may be attached to the terminal of acrylic at or methacrylic/S.
A magnetic powder and the above-mentioned titanium coupling agent dissolved in a solvent are dispersed and mixed into an oligomer mixed with an oligomer reacted with /#, or a magnetic powder whose surface has been previously treated with the above-mentioned titanium coupling agent is mixed. Prepare a magnetic paint by dispersing and mixing, apply this onto a substrate such as a polyester film, and then irradiate it with radiation to polymerize and harden it.
Alternatively, one or a mixture of two of the above oligomers is dissolved in an organic solvent, and magnetic powder and titanium coupling agent or magnetic powder whose surface has been treated with a titanium coupling agent are dispersed and mixed in the solution in the same manner as described above. This is done by preparing a paint, coating it on a substrate such as a polyester film, preheating it to remove the organic solvent contained in the magnetic paint, and then irradiating it with radiation to polymerize and harden it. In this case, when an organic solvent is used, the viscosity of the magnetic paint becomes lower, so that the filling properties of the magnetic powder are further improved, and the magnetic properties and surface smoothness of the magnetic layer are further improved.

As such an organic solvent, any of the solvents conventionally used in preparing magnetic paints, such as methyl isobutyl ketone, cyclohexanone, toluene, and dimethylformamide, can be suitably used. Since ethanol, n-
Solvents with low boiling points and low toxicity such as hebutane and n-hexane can also be suitably used. Therefore, if these low boiling point and low toxicity solvents are used, pollution problems will be solved.
Moreover, since these low boiling point solvents are easily removed by preheating after applying the magnetic paint, recovery of the solvents is also facilitated.

It should be noted that various commonly used additives, such as dispersants, abrasives, antistatic agents, etc., may be appropriately added to the magnetic coating material as necessary.

Next, embodiments of the invention will be described.

Example 1 An epoxy acrylic oligomer represented by the structural formula was used.
6B (manufactured by Kenritsu 21 Hypetoshi Chemical Co., Ltd., Tesilaoctyl bis(ditridecyl phosphite) titanium) A composition consisting of ethyl alcohol/methyl ethyl 25 1 ketone mixed solvent (mixing ratio 1/1) was mixed and dispersed in a ball mill for 72 hours. A magnetic paint was prepared, and this magnetic paint was coated on a polyester base film with a thickness of 15μ so that the film thickness was 4μ.Then, it was preheated at 90”C for 1 minute to form a mixture of ethyl alcohol/methyl ethyl ketone. After removing the mixed solvent, it was cured by irradiating it with an electron beam at a dose of 7 Mrad using EPS-750 manufactured by Nissin Hemertage, and after calendering, it was cut into predetermined shapes to produce magnetic tape.

Example 2 In the composition of the magnetic paint in Example 1, the amount of epoxy acrylic oligomer used was changed from 40 parts by weight to 20 parts by weight, and 20 parts by weight of nonaethylene glycol dimethacrylate represented by the following structural formula was newly added. A magnetic tape was produced in the same manner as in Example 1 except for the following.

Example 3 In the composition of the magnetic paint in Example 2, the ethyl alcohol/methyl ethyl ketone mixed solvent was omitted, the amount of epoxy acrylic oligomer used was changed from 20 parts by weight to 15 parts by weight, and nonaethyleneglyfur dimethacrylate F was added. A magnetic tape was produced in the same manner as in Example 2, except that the amount used was changed from 20 parts by weight to 30 parts by weight, and preheating was omitted.

Comparative Example 1 A magnetic tape was made in the same manner as in Example 1, except that PlenAc) 46B was omitted in the composition of the magnetic paint in Example 1. ◇ Comparative Example 2 In the composition of the magnetic paint in Example 1, PlenAc) 46B was used. Tetrastearyl titane) (Tl
Example 1 except that the same amount of (QCl, H,,)4) was used.
I made magnetic tape in the same way.

The video SN ratio and the color SN ratio were measured for the magnetic tapes obtained in each example and each comparative example, and each magnetic tape was loaded into a tape recorder to examine the durability. Set the driving speed to about 3. "(011/@e)" output fluctuation was measured after running 300 times.Video SN ratio and color S
The N ratio was determined by loading the obtained magnetic tape into a video deck (V'R-SOOO manufactured by Hitachi, Ltd.) and recording and reproducing it.
Measurements were made using a Color Video Noise Meter 925C manufactured by Shibaku Co., Ltd., and the video SN ratio and color SN ratio of the magnetic tape obtained in Comparative Example 1 were set to 0 and expressed as the difference therebetween.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 to 23) are different from the conventional magnetic tapes (Comparative Example 1).
and 2), the sensitivity, frequency characteristics, video SN ratio, and color SN ratio are all high, and the output fluctuation is small.
In particular, the results obtained in Examples 2 and 3 were good;
Therefore, the magnetic recording medium obtained by the present invention has excellent dispersibility and filling properties of the magnetic powder, and has further improved magnetic properties, surface smoothness of the magnetic layer, and durability.
In particular, it can be seen that the improvements obtained in Examples 2 and 3 are remarkable.

Claims (1)

[Scope of Claims] On the L substrate, a compound of the general formula % formula %) (wherein R is a hydrocarbon group or -CB2-C(C,
H,) -(CB, -0-CH, -CH-CH,),
,X4iP. Y is -Go-R1), OR, and R1 is a furkyl group. ) An oligo of epoxy acrylate or niboxy methacrylate made by reacting a titanium coupling agent represented by the formula with acrylic acid or methacrylic acid with a compound containing two or more epoxy groups! forming a coating film containing - and 1 magnetic powder;
Magnetic recording medium 2 characterized in that a magnetic layer hardened by irradiation with radiation is provided on the substrate. (C,
H,) -(CH, -0-CH, -CH-CH,),
x is P, Y is -40-R1), and R1 is an alkyl group. ), an oligomer of epoxy acrylic acid or methacrylic acid obtained by reacting a compound containing two or more epoxy groups with acrylic acid or methacrylic acid, and a terminal of darykylene glycol or polyhydric alcohol. A magnetic recording medium characterized in that a coating film containing an oligomer made of ester-bonded acrylic acid or methacrylic acid and a magnetic powder is formed on the cedar, and a magnetic layer is hardened by irradiating the disc with radiation.