JP2959062B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Object of the Invention> (Industrial application field) The present invention relates to an audio tape, a video tape, a computer tape, a magnetic disk, a floppy disk,
The present invention relates to improving the performance of a magnetic recording medium used for a magnetic card and the like, and more particularly, to a magnetic recording medium using a binder which is cured by radiation.

(Prior Art) In recent years, in a magnetic recording medium, a radiation curable resin is mixed and dispersed with a magnetic powder and other essential components to prepare a magnetic paint, and the obtained magnetic paint is applied on a support.
After drying, radiation hardening is performed to form a magnetic layer.

And, as these radiation-curable resins, a vinyl chloride copolymer having a hydroxyl group such as a vinyl chloride-vinyl acetate-vinyl alcohol copolymer is added to a monoisocyanate compound having an ethylenically unsaturated group, for example, 1 mol of tolylene diisocyanate. A radiation-curable resin is obtained by reacting an adduct with 1 mol of 2-hydroxyethyl acrylate, or a vinyl chloride copolymer having a hydroxyl group is reacted with an acid anhydride, and then a glycidyl acrylate compound is reacted. Or radiation curable resin.

However, when these radiation-curable resins are used as a binder, they do not have a polar group, so that a dispersant must be used, and sufficient performance such as dispersibility, orientation, and durability cannot be obtained. In addition, it is common to use polyester acrylate and urethane acrylate together as binders for magnetic recording media, and these resins have poor compatibility with vinyl chloride-based copolymers, resulting in poor curability in blends. have.

(Problems to be Solved by the Invention) The present invention is an improvement on the above-mentioned various drawbacks, and provides a magnetic recording medium which is excellent in dispersibility, orientation, and curability in a Bukerend system with urethane acrylate or the like. It is.

(Means for Solving the Problems) The present invention relates to a diisocyanate prepolymer (C) obtained by reacting a polyester diol (A) having a polar group with a diisocyanate compound (B), one hydroxyl group and an ethylenically unsaturated double bond. Is reacted with a monomer (D) having at least one of the above, and one end is an isocyanate group, and the other end is a prepolymer (E) having an acrylate group and a vinyl chloride copolymer (F) having a hydroxyl group. A magnetic recording medium obtained by providing a magnetic layer containing a radiation-curable resin obtained by the reaction and a magnetic powder on a support and being cured by irradiation with radiation.

In the present invention, the carboxylic acid component of the polyester diol (A) having a polar group includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, and p-hydroxybenzoic acid. (Hydroxyethoxy) aromatic oxycarboxylic acids such as benzoic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid;
Examples thereof include unsaturated aliphatic and alicyclic dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, and hexahydrophthalic acid. The glycol component of the polyester diol (A) having a polar group includes ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
Neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl 1,3-pentanediol, 1,4-cyclohexane dimethanol, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide of hydrogenated bisphenol A And propylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Examples of the polar group include sulfonic acid, phosphorus, carboxylic acid, tertiary amines and quaternary amines. These polar groups are at least one kind, and two or more kinds can be used in combination. Specifically, compounds represented by the following structural formulas and the like can be mentioned.

In the present invention, the diisocyanate compound (B) refers to 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, biphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4,
4'-biphenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5 ' -Naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanatomethylcyclohexane,
1,4-diisocyanatodicyclohexane, 4,4'-diisocyanatocyclohexanemethane, isophorone diisocyanate and the like.

In the present invention, the monomer (D) having one hydroxyl group and one or more ethylenically unsaturated double bond includes hydroxyethyl (meth) acrylate, glycerin diacrylate, pentaerythritol triacrylate and the like.

In the present invention, the vinyl chloride copolymer having a hydroxyl group (F) is a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, a vinyl chloride-vinyl alcohol copolymer, a vinyl chloride-vinyl propionate-vinyl alcohol copolymer. Polymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate copolymer and so on. Among these, the number of hydroxyl groups in the vinyl chloride copolymer (F) is 1
It is preferred to use from 1 to 60, especially from 2 to 30, molecules per molecule. A molecular weight of 2,000 to 50,000, particularly preferably 4,000 to 30,000 is used. As a polar group, -S
O ₃ M, −OSO ₃ M, −OPO ₃ M, −OPO ₂ M, −COOM, −NR ₂ , −N
R ₃ X and the like, which can be used alone or in combination of two or more. (M is a hydrogen atom, or L
i represents Na, k, or Ba; R represents a hydrogen atom or an alkyl group; and X represents a halogen atom. The polyester diol (A) having a polar group is reacted with the diisocyanate compound (B) by reacting the diisocyanate compound (B) with an equivalent of 2.0 to 2.2 times the hydroxyl concentration of the polyester diol (A) to obtain an isocyanate prepolymer at both ends. (C), which is reacted with a monomer (D) having a hydroxyl group and an ethylenically unsaturated double bond at a hydroxyl group concentration of 0.5 to 0.7 equivalents to obtain a isocyanate at one end and an acrylate prepolymer at one end (E). I do. Prepolymer (E) having this isocyanate group
And a vinyl chloride copolymer having a hydroxyl group (F) are reacted in a molar ratio (E / F) of 1.0 to 3.0, preferably 1.0 to 2.0. If it is out of this proper range, when used as a binder, there arises a problem that the dispersibility of the magnetic powder decreases due to an increase in the degree of branching.

In the present invention, a reaction between a polyester diol (A) having a polar group and a diisocyanate compound (B), a diisocyanate prepolymer (C) and a monomer (D) having at least one hydroxyl group and at least one ethylenically unsaturated double bond, The reaction between the isocyanate at one end, the acrylate prepolymer at one end (E) and the vinyl chloride copolymer (F) having a hydroxyl group is carried out by using a known organic solvent not involved in the reaction, for example, methyl ethyl ketone, toluene, cyclohexanone and the like. use. As the urethanization reaction catalyst, a known catalyst such as di-n-butyltin laurate (DBTL) is used. As the radical polymerization inhibitor,
Phenothiaban, hydroquinone and the like can be used.

In the present invention, as the magnetic powder, γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
Mixed crystal of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , γ-Fe doped with cobalt
₂ O ₃ , cobalt-doped Fe ₃ O ₄ , chromium dioxide, barium ferrite, or iron, cobalt or other metal magnetic material,
Alternatively, various alloy magnetic materials can be used.

In addition to the radiation-curable resin and the magnetic powder, a radiation-curable resin such as polyester acrylate, polyurethane acrylate, and epoxy acrylate, a diluent monomer such as styrene, a lubricant, an abrasive, and an antistatic agent are added. A magnetic layer is provided on a support by a method, dried if necessary, and then cured by irradiation with radiation to obtain a magnetic recording medium.

As the support used in the magnetic recording medium of the present invention,
Any material such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polypropylene, polyvinyl chloride, polyimide, polyamide imide, and aluminum alloy can be used. The thickness of the magnetic layer after coating and drying is usually 2 to 20 μm.

As the radiation used in the present invention, an electron beam using an electron beam accelerator or the like as a source, a γ-ray using CO ⁶⁰ as a source,
X-rays and ultraviolet rays using an X-ray generator as a radiation source.

Hereinafter, the present invention will be described with reference to examples. The middle part in Examples means parts by weight.

Synthesis Example 1 100 parts of polyester (I) was dissolved in 74 parts of toluene and 74 parts of methyl ethyl ketone, and 25 parts of diphenyltamene diisocyanate (MDI) and di-n-butyltin laurate (DBTL), a urethanation catalyst, were added to MDI. Then, add 2000 ppm and stir at 80 ° C. for 2 hours. Thereafter, 200 ppm of phenothiazine and 200 ppm of hydroquinone (each relative to the acrylic compound to be added) are added to this solution, and then 12 parts of glycerin diacrylate (GDA) are added, followed by stirring at 80 ° C. for 2 hours.

200 parts of a vinyl chloride copolymer "VROH" (trade name, manufactured by Union Carbide) are dissolved in 100 parts of toluene and 300 parts of methyl ethyl ketone at 60 ° C. The urethane-modified solution was added to this solution, and the mixture was stirred at 60 ° C. for 8 hours. The IR spectrum confirmed that there was no absorption of isocyanate groups.
A radiation-curable vinyl chloride resin is obtained.

Polyester (I) composition and molar ratio Synthesis Example 2 After adding 0.13 part of hydroquinone to 174 parts of tolylene diisocyanate heated to 80 ° C, 130 parts of 2-hydroxyethyl methacrylate was gradually added dropwise, and reacted at 80 ° C for 2 hours to form an adduct. Obtained.

200 parts of a vinyl chloride copolymer "VROH" (trade name, manufactured by Union Carbide Co., Ltd.) were dissolved in 480 parts of methyl ethyl ketone at 100 ° C. in 100 parts of toluene at 60 ° C., and the resulting adduct 5
0 parts were added, and 0.1 part of urethanation reaction catalyst DBTL was added. 60
The mixture was stirred at 8 ° C. for 8 hours, and it was confirmed by IR spectrum that there was no absorption of isocyanate groups.

Synthesis Example 3 200 parts of a vinyl chloride copolymer “VROH” (trade name, manufactured by Union Carbide Co.) was dissolved in 290 parts of methyl ethyl ketone and 290 parts of toluene at 60 ° C., and then phthalic anhydride 2
5 parts, 25 parts of glycidyl methacrylate, 0.02 parts of hydroquinone and 0.12 parts of triethanolamine were added to add 80 parts.
The reaction was performed at 20 ° C. for 20 hours, and it was confirmed that the acid value was less than 10.

Example 1 The above components were mixed and dispersed in a ball mill for 3 hours,
Next, the above components were added and mixed and dispersed for 5 hours to obtain a magnetic paint. The obtained magnetic paint was applied to a support made of a polyester film having a thickness of 15 μm to form a magnetic layer, oriented in a magnetic field, and cured by irradiating an electron beam at 5 Mrad.

The obtained magnetic film was measured for surface gloss (gloss 60 ° C.) and squareness ratio (Rs) in order to evaluate the performance of the magnetic recording medium.

In order to evaluate the degree of hardening of the magnetic layer, the above magnetic paint was applied to a polypropylene film support, dried at 80 ° C. for 20 minutes, irradiated with an electron beam at 5 Mrad, and then the magnetic layer was peeled off and a methyl ethyl ketone solvent was used. Soxhlet extraction was performed for 24 hours, and the weight fraction (gel fraction) of the non-extracted binder was measured for the used binder.

Even when the magnetic paint was left for 24 hours, precipitation of magnetic powder and separation of the binder were hardly observed.

Comparative Example 1 In Example 1, instead of the solvent solution of the resin obtained in Synthesis Example 1, a magnetic coating material was prepared using the solvent solution of the resin obtained in Synthesis Example 2 under the same composition and dispersion conditions, The same evaluation was performed. The stability of the magnetic paint was poor.

Comparative Example 2 In Example 1, instead of the solvent solution of the resin obtained in Synthesis Example 1, a magnetic coating material was prepared under the same composition and dispersion conditions using the solvent solution of the resin obtained in Synthesis Example 3, The same evaluation was performed. In addition, the stability of the magnetic paint was poor.

Table 1 shows the results of evaluation of the obtained magnetic films in Examples and Comparative Examples.

As is clear from Table 1, when the binder of the present invention was used, the dispersibility and orientation of the magnetic powder were good,
It can be seen that the recording density is high and the curability can be increased.

(Effects of the Invention) According to the present invention, it is possible to provide a magnetic recording medium which is excellent in dispersibility and orientation of magnetic powder, is excellent in radiation and curability, and is excellent in durability.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-178171 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/702 C09D 5/00

Claims (1)

(57) [Claims] 1. A diisocyanate prepolymer (C) obtained by reacting a polyester diol (A) having at least one kind of polar group with a diisocyanate compound (B) and at least one hydroxyl group and at least one ethylenically unsaturated double bond. Reaction of the prepolymer (E) having one end of an isocyanate group and the other end of which is a (meth) acrylate group reacted with a monomer (D) having the monomer (D) with a vinyl chloride copolymer (F) having a hydroxyl group A magnetic recording medium obtained by providing a magnetic layer containing a radiation-curable resin and magnetic powder obtained on the support on a support, and being cured by irradiation with radiation.