JPH05182175A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent durability by providing a magnetic layer containing a radiation-curing resin obtd. from the reaction of vinyl chloride copolymers and monomers and having 200-400eq./10<6>g urethane link density and a magnetic powder, and then curing the magnetic layer with radiation. CONSTITUTION:Ethylene double bonds are introduced by urethane link reaction of monomers and vinyl chloride copolymers having 10000-100000mol.wt. and hydroxyl groups and polar groups except for hydroxyl groups. When the urethane link density is within the range of 200-400eq./10<6>g, good balance of dispersibility and hardening property is obtd. If the amt. of unreacted hydroxyl groups in the vinyl chloride copolymers increases, viscosity of the soln. increases because of hydrogen bonding among hydroxyl groups. Thereby, it is necessary to maintain NCO/OH as >=0.5/1.0. However, it is also necessary to render NCO /OH as <=0.9/1.0. Therefore, the reaction is effected in a NCO/OH range from 0.5/1.0 to 0.9/1.0, considering the viscosity and reactivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of magnetic recording media used for audio tapes, video tapes, computer tapes, magnetic disks, floppy disks, magnetic cards and the like. More specifically, the present invention relates to a magnetic recording medium using a binder that is cured by radiation.

[0002]

2. Description of the Related Art In recent years, in a magnetic recording medium, a radiation-curable resin is mixed and dispersed with magnetic powder and other essential components to prepare a magnetic coating material, and the obtained magnetic coating material is applied onto a support and dried. Then, radiation curing is performed to form a magnetic layer. A resin obtained by introducing an unsaturated double bond into a vinyl chloride-based copolymer is used as the radiation curable resin. JP 61-596
In JP-A No. 21-52, a vinyl chloride-based copolymer having a hydroxyl group having a molecular weight of 300 to 10,000 is added to 2-isocyanate.
A radiation-curable vinyl chloride copolymer obtained by reacting triethylmethacrylate (MOI) is obtained. However, a coating film having sufficient mechanical properties cannot be obtained with a resin in this range.

[0003]

DISCLOSURE OF THE INVENTION The present invention is intended to improve the above-mentioned various drawbacks, and is suitable for achieving a high recording density with excellent dispersibility and orientation of magnetic powder and excellent durability. A magnetic recording medium is provided.

[0004]

The present invention has a hydroxyl group and a polar group other than the hydroxyl group, the concentration of the polar group other than the hydroxyl group is 10 to 200 equivalents / 10 ⁶ g, and the molecular weight is 10,
000-100,000 vinyl chloride copolymer (A)
And a monomer (B) having at least one ethylenically unsaturated double bond and one isocyanate group in one molecule and no urethane bond in the molecule, an NCO group / OH group (equivalent ratio). ) Is obtained by reacting in the range of 0.5 to 0.9 / 1.0, and the urethane bond concentration is 200 to 400 equivalent / 10 ⁶ g.
A magnetic recording medium in which a magnetic layer containing a radiation curable resin and magnetic powder in the above range is provided on a support, and the magnetic layer is cured by irradiation with radiation.

In the present invention, the compound has a hydroxyl group and a polar group other than the hydroxyl group and has a molecular weight of 10,000 to 100,000.
Examples of the vinyl chloride-based copolymer (A) of 0 include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer. Combined, vinyl chloride-
Vinyl acetate - vinylalcohol - le - glycidyl (meth) Akuriree - include preparative copolymers, also -OSO ₃ M group as a polar group, -SO ₃ M group, -OPO ₃ M group, -P
O ₃ M group, —COOM group, etc. (M is H, Li, N
A represents an atom such as a, K, Ba, or Cs). These polar groups may be contained alone or in combination of two or more.

In the present invention, a monomer having at least one ethylenically unsaturated double bond and one isocyanate group in one molecule and no urethane bond in the molecule.
Examples of (B) include 2-isocyanatoethyl (meth) acrylate and methacryloyl isocyanate. As in this molecule, the distance between the isocyanate group and the acrylic group must be short.

The reaction between the vinyl chloride copolymer (A) having a hydroxyl group and a polar group other than the hydroxyl group and having a molecular weight of 10,000 to 100,000 and the monomer (B) causes an urethane bond to form an ethylenic diene. Although a heavy bond is introduced, radiation curability can be freely designed depending on the weight ratio of the vinyl chloride copolymer (A) and the monomer (B). However, if the urethane bond concentration is too high, the dispersibility will decrease. Therefore, if you balance the dispersibility and curability,
The urethane bond concentration should be in the range of 200 to 400 equivalents / 10 ⁶ g. Further, when the unreacted hydroxyl groups of the vinyl chloride-based copolymer are increased, the solution viscosity increases due to hydrogen bonds between the hydroxyl groups, so that the NCO group / OH group (equivalent) is 0.
It must be 5 / 1.0 or more. However, from the viewpoint of reactivity, the NCO group / OH group needs to be 0.9 / 1.0 or less. Considering this solution viscosity and reactivity, NCO
The vinyl chloride-based copolymer (A) and the monomer (B) must be reacted in the range of 0.5 to 0.9 / 1.0 group / OH group.

In the reaction of the vinyl chloride copolymer (A) and the monomer (B) in the present invention, the vinyl chloride copolymer (A) may be added to a known organic solvent that does not participate in the reaction, if necessary. The reaction is carried out at a reaction temperature of 60 ° C. or lower by dissolving and using a known urethanization catalyst and a known radical polymerization inhibitor such as hydroquinone.

In the present invention, the magnetic powder is γ-Fe.
₂ O ₃ , Fe ₃ O ₄ , mixed crystal of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , cobalt-doped γ-Fe ₂ O ₃ , cobalt-doped Fe ₃ O ₄ , chromium dioxide Examples thereof include barium ferrite, metal magnetic materials such as iron and cobalt, and various alloy magnetic materials.

In addition to the above radiation curable resin and magnetic powder, radiation curable resins such as polyester acrylate, polyurethane acrylate and epoxy acrylate,
Add a diluting monomer such as styrene, a lubricant, an abrasive, an antistatic agent, etc., to form a magnetic layer on the support by a method such as coating, and if necessary, after drying, cure by irradiation of radiation to record magnetically. Get the media.

As the support used in the magnetic recording medium of the present invention, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polypropylene, polyvinyl chloride, polyimide, polyamideimide, aluminum alloy, etc. may be used. Any thing can be given. The thickness of the magnetic layer after coating and drying is usually 2 to 20 μm.

The radiation used in the present invention includes an electron beam having an electron beam accelerator as a radiation source, γ-rays having Co ⁶⁰ as a radiation source, X-rays having an X-ray generator as a radiation source, ultraviolet rays and the like. is there.

[0013]

The present invention will be described below with reference to examples. The middle part of an example represents a weight part. Synthesis Example 1 100 parts of the following vinyl chloride copolymer (I) was dissolved in 200 parts of methyl ethyl ketone and 50 parts of toluene, and then 200 ppm of phenothiazine and hydroquinone were mixed with the following acrylic compound. Thereafter, 5 parts of 2-isocyanatoethyl methacrylate (MOI) and di-n-butyltin laurate (DBT) as a urethanization catalyst.
L) is 1000 ppm relative to the above isocyanate compound
The mixture was mixed and stirred at a reaction temperature of 60 ° C. for 8 hours. IR
It was confirmed by spectrum that there was no absorption of isocyanate groups. Vinyl chloride copolymer (I) Copolymerization composition: vinyl chloride 55 wt%, vinyl acetate 39w
t%, sodium salt of sulfonylstyrene 1 wt%, hydroxyethyl acrylate 5 wt% Molecular weight: 25,000

Synthesis Example 2 200 parts of vinyl chloride-vinyl acetate copolymer "VROH" (manufactured by Union Carbide Co.) containing a hydroxyl group and almost no polar groups other than hydroxyl groups was dissolved in 400 parts of methyl ethyl ketone and 180 parts of toluene. Then, 200 ppm of phenothiazine and hydroquinone were mixed with each of the following acrylic compounds. Thereafter, 20 parts of MOI was added, and DBTL was added to the above isocyanate compound in an amount of 1
000 ppm was mixed and stirred at a reaction temperature of 60 ° C. for 8 hours. It was confirmed by IR spectrum that there was no absorption of isocyanate groups.

Synthesis Example 3 To 174 parts of tolylene diisocyanate heated to 80 ° C., 0.13 part of hydroquinone was added, and then 130 parts of 2-hydroxyethyl methacrylate was gradually added dropwise, An adduct was obtained by reacting at 80 ° C. for 2 hours. 200 parts of vinyl chloride-based copolymer "VROH" (manufactured by Union Carbide Co.) was added to 400 parts of methyl ethyl ketone.
Parts, and 180 parts of toluene at 60 ° C., and 50 parts of the adduct obtained was added to the solution to give D of the urethanization reaction catalyst.
0.1 part of BTL was added. Stir at 60 ° C for 8 hours, IR
It was confirmed by spectrum that there was no absorption of an isocyanate group.

Example 1 One-component cobalt-doped acicular γ-Fe ₂ O ₃ (specific surface area 21 m ² / g) 100 parts Carbon black (antistatic agent) 4 parts Alumina powder (abrasive) 8 parts Lecithin 3 parts Methyl ethyl ketone 50 parts Toluene 50 parts Ingredients Solvent solution of resin obtained in Synthesis Example 1 60 parts Urethane acrylate "Aronix M-1200" (Toagosei Chemical Industry Co., Ltd.) 7 parts Butyl stearate 2 parts Methyl ethyl ketone 90 parts Toluene 90 parts The above components were mixed and dispersed in a ball mill for 3 hours, then the above components were added and mixed and dispersed for 5 hours to obtain a magnetic coating material. The NCO group / OH group (equivalent ratio) is 0.75. A magnetic layer is provided by applying the obtained magnetic coating material to a polyester film support having a thickness of 15 μm,
It was oriented by magnetic field and cured by irradiating with 5 Mrad of electron beam. For the obtained magnetic film, surface gloss (gloss 60 degrees) was used to evaluate the performance of the magnetic recording medium.
The squareness ratio (Rs) and running durability were evaluated. In addition,
The above-mentioned magnetic paint was very stable even after standing for 24 hours with almost no precipitation of the magnetic paint or separation of the binder.

Comparative Example 1 In Example 1, the solvent solution of the resin obtained in Synthesis Example 1 was used in place of the solvent solution of the resin obtained in Synthesis Example 1, and the magnetic paint was prepared under the same composition and dispersion conditions. Was adjusted and the same evaluation was performed. The stability of the magnetic paint was poor.

Comparative Example 2 In Example 1, the solvent solution of the resin obtained in Synthesis Example 1 was used in place of the solvent solution of the resin obtained in Synthesis Example 1, and the magnetic paint was prepared under the same composition and dispersion conditions. Was adjusted and the same evaluation was performed. The stability of the magnetic paint was poor. Table 1 shows the evaluation results of the magnetic films obtained in Examples and Comparative Examples.

[0019]

[Table 1] As is clear from Table 1, by using the binder of the present invention, the dispersibility and orientation of the magnetic powder are excellent, and the durability as a magnetic recording medium can be remarkably improved.

[0020]

EFFECT OF THE INVENTION The specific vinyl chloride-based copolymer having a hydroxyl group and a polar group other than the hydroxyl group in the present invention is a compound having an isocyanate group and an ethylenically unsaturated double bond so that a specific amount of urethane bond concentration is obtained. The radiation-curable resin modified to not only significantly improve the stability of the magnetic coating, which was difficult to achieve with conventional vinyl chloride binders, but also excels in the dispersibility of magnetic powder and resistance to radiation, and by radiation curing. Since a tough resin coating film can be formed, it is possible to provide a magnetic recording medium which has excellent durability and is suitable for high recording density.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuichi Kodera 1-1-1, Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd.

Claims (1)

[Claims] 1. A hydroxyl group and a polar group other than the hydroxyl group, and the concentration of the polar group other than the hydroxyl group is 10 to 200 equivalents / 10 ⁶ g.
And having at least one vinyl chloride copolymer (A) having a molecular weight of 10,000 to 100,000, an ethylenically unsaturated double bond and one isocyanate group in one molecule, and Monomer with no urethane bond in the molecule
(B) has an NCO group / OH group (equivalent ratio) of 0.5 to 0.
A magnetic layer containing a radiation-curable resin having a urethane bond concentration in the range of 200 to 400 equivalents / 10 ⁶ g and a magnetic powder, which is obtained by reacting in the range of 9 / 1.0, is provided on a support. A magnetic recording medium in which a magnetic layer is cured by irradiation with radiation.