JPS6159621A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a binder which can form a magnetic recording medium having excellent wear resistance, mechanical characteristics and electrical characteristics when irradiated with radiations by bringing isocyanate ethyl methacrylate into reaction with a prepolymer having OH groups. CONSTITUTION:The magnetic layer constituted by binding magnetic powder with the polymer obtd. by bringing a copolymer of vinyl chloride and vinyl alcohol or the like having >=2 OH groups in one molecules as the prepolymer and the isocyanate ethyl methacrylate into reaction as a binder is formed on a base. The magnetic paint formed by dissolving such binder into cyclohexane and toluene, etc. to prepare a soln. and dispersing the magnetic powder into such soln. is coated on the base and dried; thereafter electron rays, etc. are irradiated to the coating to cure the same. The binder which has good adhesiveness to the base, the excellent wear resistance and electromagnetic conversion characteristic, decreases output fluctuation and permits the manufacture of a magnetic tape, etc. having a goo S/N ratio is thus obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a binder for magnetic recording media.

[Prior art]

Conventional magnetic recording media 1 For example, in magnetic tape, a binder for the magnetic layer is a urethane crosslinked product obtained by subjecting a polymer having two or more hydrophyle groups in one molecule to a thermochemical reaction with a di- or triisocyanate compound. has been done. However, this binder has a high proportion of isocyanate groups, resulting in a short pot life.
On the other hand, if the amount of isocyanate is reduced in order to lengthen the pot life, curing will be poor and the strength of the coating film will be insufficient, making it difficult to achieve both strength and pot life.

In addition, it is impossible to adjust the degree of hardening of these thermochemical reaction-based materials, and none of them have sufficiently satisfactory wear resistance, and their electrical properties are still unsatisfactory.

Furthermore, since a large amount of harmful paid solvents are used when preparing the magnetic paint, there is also a problem of pollution. In recent years, as a method to improve this problem, studies have been actively conducted on paints in which the conventional thermochemical crosslinking reaction is replaced by a radical polymerization crosslinking reaction that utilizes radicals generated by radiation irradiation.

For example, a urethane acrylate oligomer with ester bonds of acrylic acid at both ends of the urethane oligomer is mixed and dispersed with magnetic powder, an organic solvent, etc. to prepare a magnetic paint, and after this magnetic paint is applied onto a substrate, it is irradiated with radiation. A method has been proposed in which a magnetic layer is formed by subjecting urethane acrylate oligomers to radiation polymerization and crosslinking. However, although these methods can solve the problem of the balance between pot life and coating strength and the problem of adjusting the degree of curing, the dispersion of the magnetic powder into the oligomer is not very good.
Therefore, the filling properties of the magnetic powder are poor.

Satisfactory results in terms of electrical characteristics have not been obtained.

In addition, vinyl groups can be introduced by using part of the hydroxyl groups of a prepolymer such as vinyl acetate-vinyl alcohol copolymer, which has a good track record of dispersing magnetic powder with binders that utilize conventional thermochemical reactions. Attempts have been made to improve the drawbacks by changing only the crosslinking method while retaining the good properties of the conventional system such as dispersibility, but in all cases, methacrylates, polymers, or acrylates having epoxy or carboxyl groups in the hydroxyl groups of the prepolymer have been tried. These reactions have poor reactivity, and when the reactivity is increased, (
For example, it tends to gel during the addition reaction (e.g., increase in reaction temperature), and it also tends to gel when preparing a paint by adding magnetic powder to it and dispersing it, which has made it difficult to put it into practical use.

A method of introducing a vinyl group using an isocyanate group that is more reactive than an epoxy group or a carboxyl group is also being considered, but this method is based on monomers containing a hydroxyl group and a methacrylic group or an acrylic group. (For example, 2-hydroxyl enal acrylate) VC diisocyanate is added in an approximately equivalent amount to create a monovinyl monoisocyanate adduct, and this is added to the hydroxyl group of the prepolymer. There were problems such as easy to cause turbidity, easy to become cloudy, and variations in properties.

[Purpose of the invention]

The present invention was made as a result of intensive studies to solve the problems described above. The purpose is to provide a binder for

[Structure of the invention]

The present invention relates to a radiation-curable binder for magnetic recording media obtained by reacting a prepolymer having a hydroxyl group with isocyanate ethyl methacrylate.

The radiation-curable binder for magnetic recording media according to the present invention is used in a magnetic layer of a magnetic recording medium containing a binder and magnetic powder. Examples of magnetic recording media include magnetic tapes and magnetic disks.

The prepolymer used in the present invention may be one having a hydroxyl group, but preferably a copolymer containing vinyl chloride as a constituent unit or a copolymer containing vinyl alcohol as a constituent unit. Such copolymers include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, and vinyl chloride-vinyl acetate-maleic copolymer. Acid copolymer, vinyl chloride-vinyl acetate-terminated OH side chain alkyl group copolymer (for example, VROH manufactured by UCC).

VYNC, VYMC, VYEC-X, VYM8-X, V
ERR, etc.) polyvinyl alcohol, butyral resin, acetal resin, formal resin, copolymers of these components, etc. The molecular weight of the prepolymer is curable, 0 mechanical properties,
From the viewpoint of stickiness, the range is preferably from 300 to 10,000,
A range of 1,000 to 6,000 is particularly preferred.

The prepolymer having hydroxyl groups used in the present invention is already a known compound.For example, butyral resin, which is an example thereof, is produced by polymerizing vinyl acetate to form polyvinyl acetate.
This is obtained by saponifying 90% or more of vinyl groups to produce vinyl groups, and reacting this with butyraldehyde to about 80% of the vinyl groups.

The reaction between the prepolymer having hydroxyl groups for VC of the present invention and isocyanate ethyl methacrylate is carried out at such a rate that isocyanate ethyl methacrylate reacts with a portion of the hydroxyl groups of the prepolymer. It is preferable that 10 to 50% of the hydroxyl groups react. The reaction temperature is preferably in the range of 1'1.50' to 90°C, and the solvent used is one that does not contain active hydrogen, such as toluene or cyclohequinone. As a catalyst, a catalyst for a reaction between a hydroxyl group and an incyanate group is used.

For example, dibutyltin silaurylate, dibutyltin oxide, etc. are used. The reaction time is usually 5 to 10 hours.

From the viewpoint of electrical properties, the amount of the prepolymer used is preferably within the range of 20 to 60% by weight based on the total amount of the prepolymer and magnetic powder.

As a magnetic powder used in magnetic recording media.

γ-Fe20s, Fes 04 * Co-containing r-
Fe203, Co-containing Fe304, CrCh
Various conventionally known magnetic powders such as powders of , Fe, Co, and FeNi are used.

It is effective to appropriately use various antistatic agents, lubricant 1 dispersants, paint film strength reinforcement additives, etc., which are commonly used in binders for magnetic recording media, in the binder of the present invention, depending on the purpose.

Radiation sources used for curing the binder of the present invention include X-rays, electron beams, ultraviolet rays, and infrared rays, and electron beams are particularly preferred. The irradiation storage for the electron beam accelerator is preferably in the range of 1.0Mrad to 20Mrad in consideration of damage to the substrate, and 2.0M+a in consideration of line speed.
The range of d to 6 Mrad is more preferable.

As a specific system, an electrocurtain system manufactured by Energy Sciences, Inc. of the United States, a scanning electron beam accelerator manufactured by Polyma Physics, Germany, or the like are suitable. When polymerizing and crosslinking by electron beam irradiation, it is better to perform it under an inert gas such as N2 or He.

This is suitable for preventing damage to the equipment due to generation of O3 and prevention of monopolymerization inhibition. Furthermore, when an organic solvent is used, any of the solvents conventionally used for preparing magnetic paints, such as methyl isobutyl ketone, cyclohexanone, and toluene, can be suitably used. A vinyl group-containing low-molecular compound may be added to the binder as a reactive diluent, thereby making it possible to eliminate or reduce the amount of organic solvent used. Such reactive diluents include tetraethylene glycol di(meth)acrylate (referring to dimethacrylate or diacrylate; the same applies hereinafter), 1
．． 6-hexenediol di(meth)acrylate, pentaerythritol (meth)acrylate, trimethylolpropane tri(meth)acrylate, polyfunctional (meth)acrylates such as M-5100 and M-6100 manufactured by Toagosei Chemical Co., Ltd. , Kyoeisha Oil and Fat Chemical Industry ((1) 4O
There are epoxy acrylates such as EM, 70PA, and 80MP'A.

A known material is used as the substrate, such as a polyester film such as polyethylene terephthalate.

Polyolefin/film such as polypropylene, cellulose fat conductor film such as cellulose triacetate, paper,
Polycarbonate plates, polyvinyl chloride plates, polyimide plates, polyamide plates, gold FA plates made of copper, aluminum, etc. are used.

〔Effect of the invention〕

The bimetal material according to the present invention has dispersibility of magnetic powder.

It has excellent filling properties, and when it is coated on a substrate together with magnetic powder and then irradiated with radiation, the double bonds in the side chains of the polymer polymerize and crosslink. A magnetic layer having hardness can be easily formed, thereby providing a magnetic recording medium with further improved electrical properties and excellent wear resistance.

〔Example〕

Next, the present invention will be explained with reference to Examples. "Part" indicates part by weight.

Example 1 (1) Polymer synthesis A polyvinyl alcohol resin (Denka Butyral +2000-L manufactured by Denki Kagaku Kogyo Co., Ltd., vinyl acetate composition 3.0 wt% or less, vinyl alcohol composition 18 to 24 wt%) was used as a prepolymer.
t, vinyl butyral composition 73wt or more, average degree of polymerization 300) 3009 with a stirrer.

A thermometer, a rapid flow condenser, and a 1-hole reaction flask equipped with a dropping funnel were charged with toluene 2009. Add 200 g of methyl imbutyl ketone and raise the temperature to 60°C to dissolve the resin well. Subsequently, 1 g of dibutyltin silaurylate was added to this solution, and then 34.19 g of isocyanate ethyl methacrylate was added dropwise over 1 hour. After the dropwise addition, the temperature was raised to SO'C and kept for 6 hours while stirring.

Next, the temperature was lowered to 60°C, then methanol (19) was added, stirred for 30 minutes, and then cooled.

(2) Preparation of magnetic coating material r-Fe203 magnetic powder 355g Cyclohexone 4709 Toluene 350g This composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic coating material.

(3) Preparation of magnetic tape The magnetic paint obtained in (2) was applied onto a 15 μm thick polyester film (Toshisha M Lumirror) as a base so that the film thickness was 4 μm. Next, heat drying was performed at 90°C for 1 minute to remove the solvent, and then Nz purge was performed using Electro Curtain CB-150 manufactured by Energy Science Co., Ltd.
Irradiate an electron beam of 3.0 Mrad under 400 ppm,
After calendering, it was cut to a predetermined width to make magnetic tape.

Example 2 The prepolymer of Example 1 was a vinyl chloride copolymer (75% by weight of vinyl chloride) instead of the polyvinyl alcohol resin.
, vinyl acetate2. ．． 5% by weight, vinyl alcohol 2Z5
Polymerization degree 300. A magnetic tape was produced in the same manner as in Example 1, except that Denka Kagaku Kogyo Co., Ltd.'s Denkabinyl-1000LT-3 (partial silicon/compound) was used.

Comparative Example 1 r Fe20g magnetic powder 355 parts cyclohexanone 470g toluene 4709 This composition was mixed and dispersed in a ball mill for 72 hours to form a magnetic paint. J! I made 4 adjustments. This magnetic paint f was coated on a polyester base film with a thickness of 15 μm to a coating thickness of 4 μm, then heated and dried at 90° C. for 5 minutes, cross-linked, and cut into a predetermined width to make a magnetic tape. .

Comparative Example 2 The procedure was the same as in Example 1 except that instead of adding 34.19 drops of incyanate ether methacrylate in the section (1) Prepolymer synthesis of Example 1, 66.99 drops of the compound synthesized by the following method was added. A magnetic tape was created.

(1) Compound Synthesis 5 with a stirrer, thermometer, R-flow condenser and 1 dropping funnel
00 cc reaction flask was charged with 174 g of 2.4-1 lylene diisocyanate, and the temperature was raised to 60°C. To this, 0.059 of dibutyltin silaurylate was added, then 1309 α-hydroxy methacrylate was added dropwise over 1 hour, and then the temperature was raised to 80°C and kept warm for 4 hours.
Cool and obtain a monovinyl monoisocyanate compound.

The squareness ratio (Br78m) was 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 wear resistance.
The output fluctuations after running 600 times at a running speed of 8 an/sec were measured and are shown in the table below.

table

Claims (1)

[Scope of Claims] 1. A radiation-curable binder for magnetic recording media obtained by reacting isocyanate ethyl methacrylate with a prepolymer having a hydroxyl group. 2. The radiation-curable binder for magnetic recording media according to claim 1, wherein the prepolymer is a copolymer containing vinyl chloride or vinyl alcohol as a constituent unit.