JPS62298921A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has durability even at a low temp., is less softened at a high temp. and is small in torque both in the starting stage and rotating stage by incorporating a binder component crosslinked by a arom. polyisocyanate and polyisocyanate contg. isocyanurate skeleton into a magnetic layer. CONSTITUTION:The magnetic layer of the magnetic recording medium constituted by forming the magnetic layer coated with a magnetic coating compd. prepd. by dispersing ferromagnetic powder into a binder on a nonmagnetic substrate contains the binder component crosslinked by the arom. polyisocyanate and the polyisocyanate contg. the isocyanurate skeleton. The magnetic recording medium has the magnetic layer in which the binder component contains a polyurethane having a sulfonate group and the binder component is crosslinked by the arom. polyisocyanate and the polyisocyanate having the isocyanurate skeleton.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium such as a magnetic disk having excellent reliability and durability.

(Prior Art) In recent years, with the spread of portable word processors and handheld computers, there is a strong desire for low power consumption of floppy disk drivers. In order to cope with this, a floppy disk (hereinafter referred to as FD)
It is desirable to reduce the coefficient of friction between the FD and the magnetic head, reduce the torque when starting and rotating the FD, and reduce the power consumption of the motor.

Particularly in the case of a 3.5-inch FD, since the FD and the magnetic head are always in close contact with each other once the FD is installed in the dry nozzle, it is desirable to reduce the starting torque.

Conventionally, as binders (binder components), resins with relatively good dispersibility such as vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral resins, and polyurethane resins have been used, and the resins have been used as polyisocyanate. Cross-linked compounds have been used.

(The key point to be solved by the invention) In the conventionally widely used magnetic recording medium, which consists of a magnetic layer using a binder, in order to reduce the starting torque, it is difficult to reduce the durability at low temperatures and the durability at high temperatures. Sexuality worsens. Conversely, if you try to improve the durability at low and high temperatures, the starting torque will increase. As described above, it has been extremely difficult to obtain a magnetic recording medium that has good durability even at high and low temperatures and has low starting torque and rotational torque. As the binder, a resin with good dispersibility that can uniformly disperse powder such as ferromagnetic powder is selected, and the resin is crosslinked with a crosslinking agent to achieve appropriate flexibility at low temperatures and resistance to softening at high temperatures. Efforts have been made to obtain less. The present applicant has already proposed a polyurethane resin containing a sulfonic acid group as a binder with excellent dispersibility for powders such as ferromagnetic powder (Japanese Patent Publication No. 41565/1982).

However, this resin has very good dispersibility and can obtain a uniform magnetic layer, but when a polyisocyanate compound, which is conventionally known as a crosslinking agent component for crosslinking the resin, is used, it is difficult to maintain durability over a wide temperature range. It has been difficult to obtain a magnetic recording medium with excellent performance and low starting torque and low rotational torque.

(Means for solving the gap m point) In order to obtain a magnetic recording medium that is durable even at low temperatures, has little softening even at high temperatures, and has low torque per revolution at startup, we have developed a magnetic recording medium with excellent dispersibility. As a result of research into a crosslinking agent that can be used to crosslink a resin to form a binder that meets the above objectives, the present invention was achieved. That is, the present invention provides a magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint containing ferromagnetic powder dispersed in a binder on a non-magnetic support, in which the magnetic layer is composed of aromatic polyisocyanate and incyanurate skeleton. A magnetic recording medium characterized in that it contains a binder component cross-linked with a polyisocyanate containing a The present invention is a magnetic recording medium having a magnetic layer crosslinked with a group polyisocyanate and a polyisocyanate having an incyanurate skeleton. Examples of the aromatic polyisocyanate used in the present invention include 2.4-tolylene diisocyanate, 2.6-)lylene diisocyanate, P-phenylene diisocyanate, diphenylmethane diisocyanate, and an adduct of tolylene diisocyanate to trimethylolpropane. can be mentioned.

Examples of the polyisocyanate having an incyanurate skeleton used in the present invention include a trimer of hexamethylene diisocyanate, a 3ffi form of inphorone diisocyanate, and the like. As a specific example, Coronet)EH(
(manufactured by Nippon Polyurethane Co., Ltd.).

The mixing ratio of both aromatic polyisocyanate/polyisocyanate having an incyanurate skeleton is 9515 to 5.
/95 is preferable, more preferably 80/20 to 20/
It is 80.

Further, the amount of the crosslinking agent (mixture of aromatic polyisocyanate and polyisocyanate having an incyanurate skeleton) used is 5 to 50%, more preferably 10 to 40% in the binder component.

The ferromagnetic powder used in the present invention is γ-FewOs,
Fes 04, Co-containing Fet 03, Crow,
Oxide powder such as barium ferrite, Fezco, F
These are various conventionally known magnetic powders such as metal powders such as e-Ni.

In addition, the resin used in the binder component of the present invention (component for bonding and holding powder such as ferromagnetic powder, whose main component is a cured resin product crosslinked with the crosslinking agent of the present invention) is , vinyl chloride-vinyl acetate copolymers, cellulose resins, polyester resins, polyether ester polymers, polyurethane resins, and the like, which can be crosslinked by reacting with the polyisocyanate of the present invention. Among these, polyurethane having a sulfonic acid metal base is particularly preferred; this resin can disperse powder contained in the magnetic layer, such as magnetic powder, extremely uniformly, and is compatible with the crosslinking agent used in the present invention. This is a particularly preferred resin for obtaining a magnetic recording medium that has particularly excellent durability over a wide temperature range and low torque during startup and rotation due to the combination of the following.

The polyurethane resin of the present invention is obtained by the reaction of a polyhydroxy compound and a polyisocyanate,
Part or all of the polyhydroxy compound contains a sulfonic acid metal base.

As the polyhydroxy compound containing a sulfonic acid metal group, a polyester polyol containing a sulfonic acid metal group is particularly desirable. The polyester polyol containing a sulfonic acid metal base is composed of a carboxylic acid component having no sulfonic acid metal base, a glyfur component, and a dicarboxylic acid component having a sulfonic acid metal base.

Examples of carboxylic acid components not having a sulfonic acid metal base include terephthalic acid, isophthalic acid, orthophthalic acid, 1,
Aromatic dicarboxylic acids such as 5-naphthalic acid, aromatic oxycarboxylic acids such as P-oxybenzoic acid and P-(hydroxyethoxy)benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, etc. Examples include aliphatic dicarboxylic acids, tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid.

Glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-bentanediol, 1,6-hexaneol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2 ,2.4-)
riftyl-1,3-bentanediol, 1,4-cyclohexane dimetatool, ethylene oxide and propylene oxide adducts of bisphenol A, ethylene oxide and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, Examples include polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination.

Examples of the dicarboxylic acid component containing a sulfonic acid metal group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid. The copolymerization m of the dicarboxylic acid component containing these sulfonic acid metal bases is 0.5 mol% or more, preferably 1 to 50 mol%, based on the total carboxylic acid components.

The above-mentioned polyhydroquine compound having a sulfonic acid metal group may be used alone or in combination of two or more.

It may also be used in combination with polyhydroquine compounds that do not have sulfonic acid metal groups, such as ordinary polyester polyols, polyether polyols, acrylic polyols, castor oil derivatives, tall oil derivatives, and their hydroxyl group compounds.

The polyisocyanates used in the polyurethane resin of the present invention include 2,4-tolylene diiso/anate, 2
．． 6-) lylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate,
m-phenylene diiso/anate, hexamethylene diisonanate, tetramethylene diisocyanate), 3.
3'-dimedonkey 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-quinlylene diisocyanate, m-xylylene diisocyanate), 1.3
-diisocyanatemethylcinclohexane, 1,4-diisocyanatemethylcinclohexane, 4.4'-diisonanatedinclohexane, 4.4'-diisocyanatecinclohexylmethane, inphorone diisocyanate, etc., but if necessary, 2, 4゜4″
Small amounts of -triisocyanate-diphenyl, benzenetriisonanate, etc. can also be used.

A polyurethane resin can be obtained by reacting a polyhydroxy compound and a polyisocyanate in a solvent or in the absence of a solvent by a known method, but the desirable blending ratio is NC0 group of polyisocyanate/OH group of polyhydroxy compound = 0.5 ~2/1. The molecular weight of the resulting polyurethane resin is preferably 8,000 to +00,000.

If the softening point of the polyurethane resin of the present invention is low, depending on the application, there is a risk that it will soften due to the heat between it and the head, or that it will block when wrapped with tape. In such a case, it is desirable to add a resin that is compatible with the polyurethane resin of the present invention within a range that does not impair the dispersibility of the fine powder magnetic particles. The amount of the mixture m is generally 2 to 100 parts by weight based on 100 parts by weight of the polyurethane resin.

Examples of resins that are compatible with polyurethane resins include vinyl chloride resins, polyester resins, cellulose resins, and the like.

Examples of organic solvents used in the present invention include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; Solvents suitable for dissolving the resin in the binder component to be used, such as ether solvents such as hydrofuran and dioxane, are not particularly limited.
It can be used alone or in a mixed system of two or more. The magnetic paint (magnetic layer) may contain appropriate amounts of various commonly used additives such as dispersants, lubricants, abrasives, antistatic agents, etc.

Dispersants include fatty acids with 8 to 18 carbon atoms (R-COOH) such as caprylic acid, capric acid, lauric acid, myristic acid, valmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, and lylunic acid. represented, R
is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms): an alkali metal of the above-mentioned fatty acid (L i + Na
+ K, etc.) or alkaline earth metals (Mg, Ca+
A metal soap consisting of Ba, etc.) such as lecithin is used.

In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters may also be used.

These dispersants may be used alone or in combination of two or more.

As a lubricant, silicone oil, carbon bra,
Graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, 12 carbon atoms
Fatty acid esters consisting of a monobasic fatty acid of ~16 and a monohydric alcohol having a total number of carbon atoms of 21 to 23 can also be used.

The abrasives used are commonly used materials such as fused alumina, silicon carbide chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite). These abrasives have an average particle size of 0.05-5
The size of μ is used, particularly preferably 0.1 to
It is 2μ.

Antistatic agents include graphite, carbon black, tin oxide-antimony oxide compounds, tin butyride-titanium oxide-antimony oxide compounds, carbon black graft polymers, dielectric powders such as Nisabonine, and natural surfactants such as alkylene oxides. Nonionic surfactants such as , glycerin type, glycidol type, etc. Cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfonium types: Carboxylic acid, sulfonic acid, phosphoric acid ,
Anionic surfactants containing acidic groups such as sulfuric acid ester groups and phosphoric acid ester groups, diamino acids, aminosulfonic acids, and amphoteric surfactants such as sulfuric acid or phosphoric acid esters of amino alcohols are used.

Examples of non-magnetic supports include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, films such as polycarbonate,
Examples include sheet-like laminates.

(Function) The excellent effect as a crosslinking agent due to the combination of the aromatic polyisocyanate of the present invention and the polyisocyanate having an incyanurate skeleton is due to the excellent effect of the aromatic polyisocyanate as a crosslinking agent, although the detailed mechanism is still unclear. Problems due to high crosslinking speed when using isocyanate alone, and problems due to differences in compatibility between the two when aromatic polyisocyanate and aliphatic iso/anate are used together, even if the speed is appropriate, and incyanurate. The main reason for this is thought to be that this occurred by avoiding the problems caused by the low speed of using only polyisocyanate as a backbone.

The good compatibility of both polyisocyanates of the present invention and the coexistence of the aromatic polyisocyanate with a fast crosslinking rate and the polyisonanate having an incyanurate skeleton with a slow crosslinking rate make it possible to obtain a uniform and appropriate crosslinking density. It is essential to obtain a magnetic recording medium with excellent durability and low torque during startup and rotation.

(Example) Examples 1 to 15, Comparative Examples 1 to 6 A. (Production of polyester polyol) 582 parts of dimethyl terephthalate and 5-sodium sulfoisophthalate were placed in a reaction vessel equipped with a thermometer, a stirrer, and a partial reflux condenser. Dimethyl acid 296 parts, ethylene glycol 434 parts, neopentyl glycol 728 parts, zinc acetate 0.66 parts
part, add 0.08 part of sodium acetate and heat to 140-220°.
The transesterification reaction was carried out at C for 3 hours. Next, 1212 parts of sebacic acid was added and reacted at 210 to 250°C for 2 hours, and then the reaction system was depressurized to 20 m++ Hg over 30 minutes, and further 5 to 20 ms Hg.

The polycondensation reaction was carried out at 250°C for minutes with SO. The obtained polyester polyol (A) is ηs p / c =
0°182, and a hydroquine value of 38. NHR
From analysis, etc., its composition was as follows. Terephthalic acid 30 mol%, 5-sodium sulfoisophthalic acid 10
mol%, sebacic acid 60 mol%, ethylene xericol 44 mol%, neopentyl glycol 56 mol%.

Polyester polyols (B) shown in Table 1 were obtained by a similar manufacturing method.

(Production of polyurethane resin) In a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser, 1280 parts of toluene, 850 parts of methyl isobutyl ketone, 1000 parts of polyester polyol (A), 71 parts of diphenylmethane diisocyanate, and dibutyltin were added. 1.2 parts of silaurylate was added and reacted for 8 hours at 70-90"C. The sulfonic acid metal base of the obtained polyurethane resin (I) was 378 equivalents/106 g, and the molecular weight was 18
．． The polyurethane resin (I
I) was obtained.

Margin Table 1 Below Margin Table 2 C, (Manufacture and evaluation of magnetic recording media) [Methyl ethyl ketone 100//
A magnetic coating material was obtained by mixing and dispersing the mixture consisting of composition 1 for 722 hours in a ball mill. Next, Furonate (an adduct of tolylene diisocyanate to trimethylolpropane (manufactured by Nippon Polyurethane Co., Ltd.)) and Coronate EH (manufactured by Nippon Polyurethane Co., Ltd., a trimer of hexamethylene diisonanate) either singly or as a mixture were added in the proportions shown in Table 3. (parts by weight) and further mixed and dispersed for 1 hour. The magnetic paint thus obtained was applied to a 75μ thick polyester film to a dry thickness of approximately 2μ, dried, surface treated, and then left at 60°C for 72 hours to fully cure. I let it happen. Next, a disk shape was punched out to obtain a magnetic disk.

The thus obtained magnetic disk was attached to a floppy disk driver by inserting the shell, and the starting torque and durability were measured.

The starting torque was measured using a torque tester (manufactured by Shinmei Electric Co., Ltd., MDT2-AMP) after the disk was left in an atmosphere of 45° C. and 80% RH for 8 hours.

Durability is determined by keeping the playback output at the initial value of 7 while touching the magnetic head with a pad pressure of 25 g/cJ and rotating at 300 rpm.
The number of runs until it decreased by 5% was measured. The squareness ratio is a vibration data type magnetometer VSM-BHV-30 manufactured by Riken Denshi 91.
It was measured by determining the ratio of saturation magnetization to residual magnetization.

The results are shown in Table 3.

Table 3 (Effects of the Invention) As is clear from the results in Table 3, the binder component is crosslinked with an aromatic polyisocyanate and a polyisonoanate containing an incyanurate skeleton. Magnetic recording media made of magnetic compounds have excellent durability at low temperatures,
It is an excellent magnetic recording medium with low starting torque at high temperatures. In particular, when the resin in the binder component is a polyurethane resin having a sulfonic acid metal base, excellent dispersibility (high squareness ratio) can be achieved by using the polyisocyanate of the present invention. Provides uniform magnetic field,
Moreover, an excellent magnetic recording medium having excellent durability at low temperatures and low starting torque at high temperatures can be obtained.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic layer is formed by applying a magnetic paint in which ferromagnetic powder is dispersed on a non-magnetic support, the magnetic layer is composed of an aromatic polyisocyanate and a polyisocyanate containing an isocyanurate skeleton. A magnetic recording medium characterized by containing a binder component crosslinked by. (2) The magnetic recording medium according to claim 1, wherein the binder component contains polyurethane having a sulfonic acid metal base.