JPS5829145A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a magnetic layer with superior wear resistance, magnetic characteristics and surface smoothness by applying 2 kinds of specified oligomers to a substrate together with magnetic powder and by binding and hardening them by irradiation. CONSTITUTION:An oligomer of urethane acrylate or urethane methacrylate having urethane bond in the molecule and acrylic double bond at one or both of the terminals and an oligomer obtd. by bonding acrylic acid or methacrylic acid to a terminal of polyalkylene glycol or polyol by esterification are applied to a substrate together with magnetic powder. The oligomers are bonded by irradiation to form a binder for the magnetic powder. For example, urethane acrylic oligomer represented by formulaIand tetraethylene glycol dimethacrylate represented by formula II are used as said oligomers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium and a method for manufacturing the same.
The objective is to provide a magnetic recording medium having a magnetic layer with excellent wear resistance, magnetic properties, and surface smoothness.

Magnetic recording media usually consist of a magnetic powder, a binder component, an organic solvent, and other necessary components. - It is made by coating and drying on a substrate such as ester film, and is required to have excellent magnetic properties and surface smoothness, as well as excellent durability.

Therefore, the magnetic properties and surface smoothness of the magnetic layer can be improved by selecting a binder component that has excellent dispersibility for magnetic powder and excellent wear resistance, such as a vinyl chloride-vinyl acetate copolymer. Attempts have been made to improve the durability, but it is still not fully satisfactory.Furthermore, this method uses a large amount of harmful organic solvents that dissolve the binder component during the preparation of magnetic paint, so it is officially prohibited. There is a problem.

Therefore, as a method to improve this problem, in recent years, a magnetic paint has been prepared by mixing and dispersing oligomers such as urethane attalliage or urethane methacrylate together with magnetic powder and an organic solvent, and this magnetic paint is applied onto a substrate. After that, irradiate the waves and use the oligo! A method has been proposed in which a magnetic layer is formed by polymerizing - under irradiation, but this method does not sufficiently improve wear resistance because the oligomers used, such as urethane acrylate, are too flexible, and the viscosity is high. The dispersibility and filling properties of the magnetic powder are not always sufficient, and fully satisfactory results have not yet been obtained.

The inventors conducted various studies in view of the current situation, and found that oligomers of urethane acrylate-F or urethane methacrylate that have a urethane bond in the molecule and have an acrylic double bond at the * end type or at both ends. and an oligomer in which acrylic acid or methacrylic acid is ester-bound at the end of polyalkylene glycol or polyhydric alcohol, and a magnetic paint containing these oligomers and magnetic powder is applied onto the substrate. Alternatively, a magnetic paint containing a solvent is further applied onto the substrate and preheated to remove the solvent contained in the magnetic paint, and then the magnetic paint applied on the substrate is irradiated with radiation to bond and harden the oligomers. When a magnetic layer is formed using this method, there is no problem with arrow damage, the dispersibility and filling properties of the magnetic powder Q are sufficiently improved, the magnetic properties and the surface smoothness of the magnetic layer are further improved, and the wear resistance is also improved. It was found that the durability was further improved by
This led to this invention.

Urethane acrylate-F or urethane acrylate-F or ZI which has a urethane bond in the molecule and an acrylic double bond at one or both ends used in the present invention.

Examples of oligomers of tan methacrylate include:
Those having a molecular weight of 500 to 20,000 represented by the general formula (where k is Hl or CH3, and n is an integer of 1 to 10) are preferably used. The structure of the urethane acrylate or urethane methacrylate oligomer is not limited to this, but may include polyol compounds such as polyethers, polyesters, and polyols, isocyanate compounds such as 4-)luene diisocyanesi, hexamethylene diisocyanate, and adipine. The urethane oligomer may be a urethane oligomer made of a fatty acid or the like, and may have an acrylic double bond at the end or both ends. This kind of urethane methacrylate or urethane methacrylate oligomer has a high viscosity and the dispersibility and filling properties of the magnetic powder are not sufficient, but it has γ-talylic acid or By using an oligomer made of ester bonded methacrylic acid, the 6 viscosity is reduced and the dispersibility and filling properties of the magnetic powder are excellent, and the spreadable hardness after curing can be appropriately adjusted to make it moderately high. The magnetic properties and surface smoothness of the magnetic layer are further improved. In addition, when a magnetic paint with an appropriate viscosity is prepared and applied to a substrate and then irradiated with radiation, each oligo! The double bond at the end of - opens, allowing the same or different oligo! - is crosslinked to form an appropriately hardened magnetic layer, and at the same time a magnetic layer having appropriate elasticity is formed, and the wear resistance of the magnetic layer is further improved.

A sweet oligo with ester bonding of acrylic acid or methacrylic acid at the end of the polyalkylene glycol used in this invention! - is the general formula % formula % (However, - is H or %ls is a hydrocarbon group, I is 1 to 5
It is an integer of 0. ) Oligos indicated by! -, with a molecular weight of 100 to 1,500, are preferably used, and oligomers in which acrylic acid or methacrylic acid is ester-bonded to the terminal of a polyhydric alcohol have the general formula R group% 1. OR or d R
40Rs and at least one of them must be R
,OR, where R3 and R4 are hydrocarbon groups, R3 is CH2-CH-C0-1 or CB, -C(CH,)-
CO-1p is an oligomer represented by an integer of 1 to 10, and those having molecules of 1iiioo to 2,000 are preferably used. This type of oligomer, in which acrylic acid or methacrylic acid is ester-bonded to the end of polyalkylene glycol or polyhydric alcohol, has a coating film hardness that changes depending on the degree of polymerization of the polyalkylene glycol. When it becomes 7 or less, it becomes hard. According to the above flexible urethane acrylate or urethane methacrylate oligo! - When used in combination with an oligomer that provides such a relatively hard coating film, the viscosity of the mixed oligomer can be adjusted appropriately, and the elasticity of the magnetic layer formed by irradiation with radiation after applying the magnetic paint on the substrate can be increased. The properties are improved, and the abrasion resistance of the magnetic layer is further improved, and the dispersibility and filling properties of the magnetic powder are also sufficiently improved, so that the magnetic properties and surface smoothness of the magnetic layer are further improved.

The mixing ratio of the oligomer of polyalkylene glycol or polyhydric alcohol to the oligomer of urethane acrylate) or urethane methacrylate is 1:3 to 3:1 by weight. It is preferable that the amount of the urethane arylate or urethane methacrylate oligomer be within the range of 0.05, and if the amount of the urethane arylate or urethane methacrylate oligomer is too small, the abrasion resistance of the coating film will not be sufficient. If the number of particles is too high, the viscosity of the oligomer becomes high and the dispersibility and filling properties of the magnetic powder are insufficient. In addition, the amount of Oligo i-, which is a mixture of both materials, is 2 times the amount of magnetic powder.
It is preferable that the amount is in the range of 0 to 60% by weight; if it is too small, the desired effect cannot be obtained, and if it is too large, the content of magnetic powder decreases, making it impossible to obtain good electromagnetic conversion characteristics.

The radiation used to polymerize and crosslink the oligomers is preferably beta rays such as electron beams, and r rays such as ultraviolet rays or X-rays. When ultraviolet rays are used, the effects of irradiation A sensitizer is used at the same time to make it more efficient. It is preferable to irradiate such radiation using radiation with an accelerating voltage of 150 to 750 KV so that the absorbed dose is 3 to 15 Mrad. If the absorbed dose is too small, the crosslinking of the oligomers may be insufficient. The desired effect cannot be obtained.

As the magnetic powder used in this invention, for example, r-
FezOa powder, Fe 804 powder, Co containing -Pe
In addition to SOS powder, Co-containing Fe 304 powder, CrO2 powder, various conventionally known R magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni powder are widely included.

In order to form the magnetic layer of the present invention on a substrate, the above-mentioned urethane acrylate or urethane methacrylate oligomer and polyalkylene glyfur or polyhydric acetate are used.
: A magnetic paint was prepared by dispersing and mixing magnetic powder in an oligomer in which acrylic acid or methacrylic acid was ester-bonded at the end of a 2-lol, and this was coated on a substrate such as a polyester film. After that, either by irradiating radiation to cure the bond, or by dissolving the mixed oligomers in an organic solvent and dispersing and mixing magnetic powder in this solution, a magnetic PIA paint is prepared, and this is applied to a substrate such as a polyester film. After being coated on top of the magnetic paint, it is preheated to remove the organic solvent contained in the magnetic paint, and then irradiated with radiation to cure the bond. In this case, when an organic solvent is used, the viscosity of the magnetic paint becomes lower, so that the dispersibility and filling properties of the magnetic powder are further improved, and the magnetic properties and surface smoothness of the magnetic layer are further improved.

When using 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, but none of the above oligomers can be used. Since it has good solubility in organic solvents, low boiling point and weakly toxic solvents such as ethanol, n-hebutane, and rhohexane can also be suitably used.
Therefore, the use of these low-boiling point, low-toxicity solvents eliminates pollution-related problems, and also facilitates solvent recovery because these low-boiling point solvents are easily removed by preheating after applying the magnetic paint. .

In addition, various commonly used additives such as dispersants, abrasives, antistatic agents, etc. may be added to the magnetic paint as necessary. Example 911 Using urethane acrylic oligomer represented by the structural formula and te)raethylene glycol dimethacrylic acid represented by the structural formula, Co-containing r-Fe203 magnetic powder 60 parts by weight urethane acrylic Oligomer 20 1 tesila ethylene glycol di 2 GM methacrylate ethyl alcohol/methyl ethyl alcohol 25 l methyl ketone mixed solvent (mixing ratio 1/1) A magnetic paint was prepared by mixing and dispersing the composition in a ball mill for 72 hours. The paint was applied on a polyester base film with a thickness of 15 degrees, cured by irradiation with radiation at a dose of 7 Mrmd, and then cut into a predetermined width after calendering to make a magnetic tape.Example 2 Example 2 In the composition of the magnetic paint in 1, the ethyl alcohol/methyl ethyl ketone mixed solvent was omitted, the amount of urethane acrylic oligomer used was changed from 20 parts by weight to 15 parts by weight, and the amount of teethylene glycol dimethacrylate used was changed to 20 parts by weight. Change 35 to part by weight,
Furthermore, a magnetic tape was produced in the same manner as in Example N1 except that preheating was omitted.

Comparative Example 1 The composition of the magnetic paint in Example 1 was the same as in Example 1, except that tetraethylene glycol dimethacrylate was omitted and the amount of urethane acrylic oligomer used was changed from 20 parts by weight to 40 parts by weight. °Made magnetic tape.

Comparative Example 2 Co-containing r-Fe203 magnetic powder 78 parts by weight VA
GH (manufactured by U, C, C, USA, chloride 12 〃vinyl-vinyl acetate-vinyl alcohol copolymer) Nissan 5702 (manufactured by Rich Chemi, Cal, Inc., urethane elastomer) Coconate L (Japan Polyurethane 2 〃 manufactured by Trifunctional Low Molecular Weight Isocyanate Compound) 90〃Toluene
90 This composition was mixed and dispersed in a gold mill for 72 hours to prepare a magnetic hammer. This magnetic paint was applied to a polyester base film with a thickness of 15 tones to a dry thickness of 4μ, dried, calendered, and then cut to a predetermined width to make a magnetic tape. The angle 111 (Br/Bm) of the magnetic tapes obtained in each comparative example was measured, and in order to further examine the durability, each magnetic tape was loaded into a tape rehooder and run 600 times at a running speed of #J48''/sec. The output fluctuations after the test were measured.

The table below shows the results.

As is clear from the table above, the magnetic tapes obtained by the present invention (Examples 1 and 2) have larger square shapes and smaller output fluctuations than conventional magnetic tapes (Comparative Examples 1 and 2). From this, it can be seen that the magnetic recording medium obtained by the present invention has good dispersibility and filling properties of the magnetic powder, further improved adverse properties and surface smoothness of the magnetic layer, and also has improved durability. Recognize.

Claims (1)

[Scope of Claims] L An oligomer of urethane acrylate or urethane acrylate having a urethane bond in the molecule and an acrylic double bond at the terminal or both terminals, and an oligomer of polyalkylene glycol or polyhydric alcohol at the terminal. Acrylic i! ! Magnetic recording medium 2 characterized in that a binder for magnetic powder is obtained by radiation-bonding an oligomer formed by ester bonding or methacrylic acid by irradiating radiation on a substrate coated with magnetic powder. An oligo of urethane acrylate-F or urethane methacrylate that has a urethane bond inside and an acrylic double bond at the terminal or both ends! -, an oligomer in which acrylic acid or methacrylic acid is ester-bonded to the end of polyalkylene glycol or polyhydric alcohol, and magnetic powder are coated with a magnetic paint, which is then irradiated with radiation to form the oligomer. - A method for manufacturing a magnetic recording medium characterized by bonding and curing to form a magnetic layer & Urethane acrylate having a urethane bond in the molecule and an acrylic double bond at one or both ends on a substrate Or urethane methacrylate oligo! -, an oligomer of polyalkylene glycol or polyhydric alcohol with ester bonded to the end of acrylic acid or methacrylic acid, a magnetic paint containing magnetic powder, and a solvent, and then before irradiating with radiation six times, A method for producing a magnetic recording medium according to claim 2, which comprises performing preheating to center the solvent contained in the magnetic paint.