JPS60173721A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder and the durability of a coated film layer by incorporating the magnetic powder which is surface- treated with the specified phosphoric ester compd. of a specified copolymer and a specified silane coupling agent or a titanium coupling agent into the magnetic layer. CONSTITUTION:The magnetic powder is surface-treated with the hosphoric ester of a copolymer of (meth)acrylate expressed by formula( I ) (where, R1 is hydrogen or a methyl group, and R2 is an aliphatic hydrocarbonic group having 4-22C) or styrene and the (meth)acrylate contg. hydroxyl group expressed by formula (II) (where, R1 is hydrogen or a methyl group, A is an alkylene group having 2-3C, and (n) is 0 or 1-20 integer), and 1 or >=2 kinds of a coupling agent selected from a group of a silane coupling agent contg. an isocyanate group, a silane coupling agent contg. an amino group, a silane coupling agent contg. an epoxy group, and a titanium coupling agent contg. an amino group. The surface-treated magnetic powder is incorporated into the magnetic layer.

Description

[Detailed description of the invention] The present invention relates to an improved magnetic recording medium.

More specifically, the present invention relates to a magnetic recording medium with excellent magnetic properties and durability, which is manufactured using a magnetic paint that improves the dispersibility of magnetic powder and the adhesion between the magnetic powder and a binder.

Magnetic powder in magnetic recording media such as magnetic tapes and magnetic disks is required to have a high degree of dispersibility.

Magnetic recording media are generally manufactured by kneading magnetic powder, a binder, various additives, and solvents, then applying a magnetic paint uniformly onto a plastic film or sheet substrate and drying it. The magnetic layer is formed by mirror-finishing it, but unless the magnetic powder in the magnetic paint is sufficiently dispersed and peptized to remove aggregated particles, it is not possible to create a uniform and smooth magnetic layer with a high packing density. .

Non-uniformity of the magnetic layer due to agglomerated particles of magnetic powder has a serious adverse effect on the electromagnetic conversion characteristics and magnetic properties of the magnetic tape. That is, it causes a decrease in output, an increase in noise, dropouts, etc. In addition, if the adhesive strength between the magnetic powder and the binder is weak, the magnetic powder may peel off from the magnetic coating layer (so-called "powder shedding") when the magnetic recording medium and the recording head or reproduction head slide. This easily occurs, and the coating surface becomes rough, impairing the durability of the magnetic recording medium.

In reality, conventional magnetic recording media have been put into practical use with insufficient durability. is important in improving the performance of charges.

Improvements in the dispersibility of magnetic powder have been studied from various viewpoints, and it has been proposed to improve the dispersibility by adding a suitable surfactant to the magnetic paint formulation. Such surfactants include those using an alkylimidacillin compound (Japanese Patent Application Laid-open No. 53-78810), and those using an alkyl polyoxyethylene phosphate neutralized with an alkyl amine (Japanese Patent Application Laid-Open No. 53-78810). , using a long-chain alkyl phosphate ester (JP-A-54-147507)
, Japanese Patent Application No. 53-49629), amines and their derivatives, phosphoric acid esters, polyoxyethylene phosphoric esters, etc. are often used. In addition, there has been a proposal that dispersibility can be improved by surface-treating magnetic powder and then turning it into a paint.
769), and one that measures metal powder with a titanium coupling agent to measure dispersion stability and at the same time prevent the deterioration of the magnetic coating film over time (Japanese Patent Laid-Open No. 56-88471). In addition, as a method for improving the durability of the magnetic coating film by improving the adhesion between the magnetic powder and the binder, there is a method using magnetic powder treated with a silane coupling agent having a functional group (Japanese Patent Application Laid-Open No. 49-1993).
-59608), one using a silane coupling agent having a functional group reactive with the binder (Japanese Patent Application Laid-Open No. 54-731
0) b Coated with a reaction product of an aminofunctional silane coupling agent, an incyanate compound, and an epoxy compound (JP-A-56-1A3S3S)
), a method in which magnetic powder is treated with a titanium coupling agent having a double bond in the binder and an unsaturated bond capable of radical polymerization (JP-A-56-111129), a method in which a magnetic powder is treated with a titanium coupling agent having a double bond in the binder and an unsaturated bond capable of radical polymerization (Japanese Patent Application Laid-Open No. 56-111129); A compound using a compound having a double bond as a binder (Japanese Unexamined Patent Publication No. 57-4
0744). In this way, regarding the dispersibility of magnetic powder in magnetic paint and the improvement of human resources for magnetic coating films,
Although much research has been carried out, a satisfactory stage of improvement has not yet been reached.

In view of the problems of the magnetic recording medium described above, the present inventors have developed a magnetic recording medium that has excellent dispersibility of magnetic powder and durability of the coating layer. As a result of intensive research to obtain a magnetic recording medium containing in its magnetic layer magnetic powder whose surface is treated with a phosphoric acid ester compound of a certain copolymer and a certain silane coupling agent or titanium coupling agent, We have completed the present invention by discovering that the magnetic powder has good dispersibility and the coating layer has excellent durability.

That is, the present invention.

(A) The following formula (x) 1 0H2 = C-000R2 (1) (in the formula, 5n11d hydrogen or methyl group, R2 has 4 or more carbon atoms
22 aliphatic hydrocarbon group) or styrene, (wherein R1 is hydrogen or a methyl group, and A has 2 or 3 carbon atoms
alkylene group, n represents 0 or an integer from 1 to 20)
A phosphoric acid ester of a copolymer with a hydroxyl group-containing (meth)acrylate represented by, and (B) an incyanate group-containing silane coupling agent,
A magnetic powder surface-treated with one or more coupling agents selected from the group consisting of an amino group-containing silane coupling agent, an epoxy group-containing silane coupling agent, and an amino group-containing titanium coupling agent. The object of the present invention is to provide a magnetic recording medium characterized in that it is contained in a magnetic layer.

The (meth)acrylate represented by the above formula (1) according to the present invention can be produced by esterification of (meth)acrylic acid and an aliphatic alcohol having a return atom number of 4 to 22; The hydroxyl group-containing (meth)acrylate represented by is hydroxyethyl (meth)acrylate or a compound to which ethylene oxide or propylene oxide is added.

The copolymer according to the present invention comprises (meth)acrylate or styrene represented by the above formula (1) and the above formula (If
), the copolymerization molar ratio is (I) or styrene/(II) = q s / s ~ 5
0150 is preferred. When a copolymer having a copolymerization ratio outside this range is used, the magnetic properties of the magnetic recording medium tend to deteriorate somewhat. Moreover, the molecular weight of the copolymer is 100
0 to 30,000 is preferable, more preferably 2,000 to
It is 10,000. Molecular weight is less than 1000 or 5
When a copolymer exceeding 0,000 is used, the dispersibility of the magnetic powder tends to be slightly inferior. The phosphate ester (A) of the copolymer is, for example.

It can be produced by heating and reacting the copolymer and phosphorus pentoxide in an inert organic solvent.

In phosphoric acid esterification, 1. The hydroxyl group derived from the hydroxyl group-containing (meth)acrylate in the copolymer is esterified, but all the hydroxyl groups in the molecule may be esterified, or a portion of the hydroxyl groups in the molecule may be esterified. esterified hydroxyl groups may remain. The degree of esterification is 0.2 or more (1 when all hydroxyl groups in the molecule are esterified).
, where no esterification is taken as 0). If the degree of esterification is less than 0.2, the dispersion of the magnetic powder tends to be somewhat poor.

The phosphoric acid ester (A) of the copolymer according to the present invention is
It also includes a phosphoric acid ester of a copolymer consisting of five components: (meth)acrylate represented by the above formula (r), styrene, and a hydroxyl group-containing (meth)acrylate represented by the above formula (n). Moreover, the expression (meth)acrylate means acrylate or methacrylate.

Next, specific examples of the coupling agent (B) according to the present invention are shown below.

- As an incyanate group-containing silane coupling agent.

001J-(0H2)6-NHOONI((0R2)
, sl(OCR,), and the like.

- As an amino group-containing silane coupling agent 7.

H,,N02E,NEO,H6Eli(OCR,”l,
, u2Nc2nllNHo, n6s1(on,)(oa
n, ),,H2No,)16Si(002H6),,
a2NaoNnc, H651(oC2n,),,H2N
Compounds such as QSi(OOH,)i can be heated.

・As an epoxy group-containing silane coupling agent, can be exemplified.

・As an amino group-containing titanium coupling agent, 02H
,0-Ti(002H1lNIHO2H1lNU2),
, 1-0. H2O・Tl(002H,NHa,,H,
NH,,),%(t-c,H7o)2・Ti(002
H, N) 1-0. , H, NH2)3. n-01lH,
0-Ti(002)111NHO2H,,NH,),,
(n-CuH,O)p Fist Ti(002)1a NHO
2Hu NHO2H1l NJ12”)2 bl-0
,H,O・Ti(002H,NH○2H,NH2),
etc. can be mentioned.

The magnetic powder according to the present invention is fine needle-shaped 7-F.
Metal oxides such as +320 s, Fe s Ou, Or 02, and 00 deposited y-Fe20. , O
O-doped 7-Fe 205, O, iron metal powder, barium ferrite in the form of microplates and some of its Fe atoms are Ti, Oo, Z
Magnetic powder substituted with one or more atoms such as n, V, Wb, Fe, co, ye-Oo, Fe-
Examples include ultrafine powder of metals such as Ni or alloys. Among these, iron metal powder has particularly poor chemical stability, so nickel is used for this improvement.

Cobalt, titanium, silicon, aluminum, etc. may be added in small amounts in the form of metal atoms, salts, and oxides, or may be surface-treated, but these may also be used. In order to stabilize iron metal powder, a thin oxide film may be formed on the surface in a weakly oxidizing atmosphere, and metal powder treated in this way can also be used.

The size of these magnetic powders is from 1μ to 0.15μ on the long axis.
It is preferable that the minor axis is 0.15μ to 0.015μ.

If the long axis is larger than 1 μm, dispersion becomes easier, but recording of short wavelengths becomes disadvantageous and noise becomes large, which is not preferable. When the long axis is smaller than 0.15μ, even the magnetic recording medium of the present invention is insufficient in terms of dispersibility.

In the present invention, the method for obtaining the magnetic powder surface-treated with the phosphoric acid ester compound (A) and the coupling agent (B) is not particularly limited. Ester (A) and coupling agent (B
) and then heat-treated. Furthermore, the order in which the magnetic powder, phosphoric acid ester (A), and coupling agent (B) are added is not limited.

The total amount of the phosphoric acid ester (4) and the coupling agent (B) according to the present invention is suitably about 1 to 10% by weight based on the magnetic powder. In addition, the ratio of the phosphoric acid ester (A) and the coupling agent (B) is as follows:
); phosphoric acid ester (A) = 1: 1. s~15
degree is preferred.

The magnetic recording medium of the present invention can be obtained by adding a binder and a solvent to the magnetic powder treated by the above-described treatment method to form a paint, and applying the same pressure to a polyester film.

Examples of inert organic solvents that can be used in the treatment of magnetic powder include methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, cyclohexanone, benzene, xylene, and toluene.

The binder used when turning the treated powder into paint is a resin binder that is soluble in organic solvents.

In order to fix the above-mentioned magnetic powder on the substrate and the magnetic powders together with the necessary strength to form a magnetic layer, it is sufficient to use the magnetic powder in as small a quantity as possible to fulfill its role. Even substances that are likely to deteriorate the quality of the paint can be used in the usual coating method. Examples of these resin binders include polyurethane, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyacrylonitrile, nitrile rubber, epoxy resin, alkyd resin, polyamide, polyacrylic ester, polymethacrylic ester, and polyester. Examples include vinyl acetate, polyvinyl butyral, vinylidene chloride, vinylidene chloride copolymer, nitrified cotton, and ethyl cellulose. Furthermore, in order to improve the physical properties of these binders, -0)i, -NH,.

It is also possible to use a resin binder into which functional groups such as -0PO, H2, -Coon, etc. are introduced. Although these binders may be used alone, two or more kinds of binders are usually used in combination. Furthermore, a plasticizer or a hardening agent may be added to adjust the hardness of the resin.

The amount of binder added is generally 10 to 50 parts by weight per 100 parts by weight of the magnetic powder. Even if the binder has the highest bonding strength, if it is less than 1 part by weight, the strength of the magnetic coating will be weak and the adhesive force between the substrate and the magnetic coating will be insufficient. Moreover, when the amount is more than 50 parts by weight, the concentration of magnetic powder in the magnetic coating film decreases, which is disadvantageous because the redistribution force decreases, and the properties of the coating film such as running properties of the magnetic recording medium may also decrease. be.

It is desirable that the solvent used for forming the coating has a dissolving power for the binder used and a boiling point between 50°C and 150°C. If the boiling point is too low, the coating will dry before the magnetic powder is oriented in the magnetic field after coating, making this treatment impossible. The binder is selected from the above viewpoints depending on the type of binder, but it goes without saying that it should be selected in consideration of toxicity and environmental issues.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Example 1 4 tube flask with cooling tube, long axis i0.35μm, 1 axis ratio 1
/8 Oo coating 7-'Fe2O, 100fs methyl ethyl ketone 20011 lauryl methacrylate (LMA
) and 2-hydroxylethyl methacrylate (West MA)
copolymer (copolymerization molar ratio LMA/HEiMA=Qo/
20, molecular weight 6500) phosphoric acid ester (esterified W 1.o ) 3 and a silane coupling agent n2Na, a6s1 (oo2n, ), 1f were taken 9
The mixture was stirred at 0'C for 1 hour to obtain treated magnetic powder. Then,
The treated magnetic powder was washed with a large amount of methyl ethyl ketone.

Next, a mixture of 100 t of the treated magnetic powder, 25 f of binder, 130 f of solvent, and 3.75 f of curing agent was kneaded in a ball mill for 48 hours to obtain a magnetic paint. The binder, solvent and curing agent used here are as follows.

<Binder> Vinyl chloride-vinyl acetate copolymer (VAGH, manufactured by Union Carbide, USA) / Polyurethane resin (Nituhoran 2304, manufactured by Nippon Polyurethane Industries, Ltd.) / Nitrocellulose, S (Re 1/2, manufactured by Tycel Co., Ltd.)
= having a weight mix ratio of 4/4/2.

Solvent> Methyl ethyl ketone/cyclohexanone with a weight mixing ratio of 515.

<Curing agent> Urethane prepolymer (Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.) Furthermore, the magnetic paint was applied onto a polyester film using a 50 μm applicator, and after magnetic field orientation, hot air drying was performed, and then The coating film was smoothed by calender treatment to obtain a magnetic recording medium.

Next, the magnetic recording medium was evaluated on the following six items.

(1) A 50 cm long magnetic recording medium with an abrasion loss width of 3 is coated with emery paper Co.
This was done by rubbing at -1000 for 30 minutes under a constant load.

(2) Surface roughness The coating film before calendering was measured using a Surf Yum manufactured by Tokyo Seimitsu Co., Ltd.

(3) Glossiness (gooθθ1nθθθ, hereinafter referred to as "cross") The magnetic recording medium was irradiated with light at an angle of 60 degrees and calculated based on the amount of light reflected.

(4) Squareness ratio (5) Residual magnetic flux density (6 mm Reproduction output The magnetic recording medium was cut into a width of 6.25 mm, and the reproduction output at 5 KHz was measured by attaching it to a commercially available oven reel deck. This value was 7 prepared in Comparative Examples 1 and 2 (described below)
The reproduction output of the magnetic recording medium is expressed as a relative value with zero as the reproduction output.

The above results are shown in Table-1.

Examples 2 to 5 CO deposition used in Example 1 - Fe20. was treated according to the method of Example 1 using the phosphoric acid ester and coupling agent shown in Table 2 to produce treated magnetic powder.
A magnetic paint and a magnetic recording medium were manufactured according to the method of Example 1. The above-mentioned six items were evaluated for the magnetic recording medium. These results are shown in Table-1.

Comparative Example 1 Sesquiphosphoric acid ester of polyoxyethylene alkyl ether (RE-10 manufactured by GAFAO) was added as a dispersant to 20.100 t of COO-coated 7-Fe used in Example 1.
) A magnetic paint and a magnetic recording medium were produced in the same manner as in Example 1, except that the magnetic powder was not subjected to any surface treatment.

For the magnetic recording medium, the method of Example 1 was simply performed using the method described above.
The items were evaluated. These results are shown in Table-1.

Example 6 Iron metal powder 100F in a 4-tube flask with a cooling tube.

Methyl ethyl ketone 200 F, lauryl acrylate
) (LA) and 2-hydroxyethyl methacrylate) (
HFiMA) copolymer (copolymerization mo/l/ratio LA/HK
MA=90/10, molecular weight 14500) phosphoric acid ester (degree of esterification o, s) 1o and Kap 1
f was removed, treated iron metal powder was obtained in the same manner as in Example 1, and the treated iron metal powder was washed with a large amount of methyl ethyl ketone.

Next, a magnetic coating material and a magnetic recording medium were obtained according to the method of Example 1 using the treated iron metal powder.

The above-mentioned six items were evaluated for the magnetic recording medium.

These results are shown in Table-3.

Examples 7 to 9 The iron metal powder used in Example 6 was treated according to the method of Example 1 using the phosphate ester and coupling agent shown in Table 1-4 to produce treated iron metal powder. A magnetic coating material and a magnetic recording medium were manufactured according to the same method as in Example 1. The above-mentioned six items were evaluated for the magnetic recording medium. These results are shown in Table-3.

Comparative Example 2 The following Example 1 was prepared by simply adding octyl phosphate as a dispersant to the iron metal powder 100F used in Example 6 without surface treatment of the magnetic powder.
A magnetic paint and a magnetic recording medium were manufactured using the same method as described above. The magnetic recording medium was evaluated on the above six items in accordance with the method of Example 1. These results are shown in Table-3.

Claims (1)

[Claims] 1(A) The following formula (I). 1 0H2==O-00OR,, (I) (In the formula, Machi is hydrogen or a methyl group, R2 has 4 to 22 carbon atoms
(representing an aliphatic hydrocarbon group) or styrene, and the following formula (n) 1 0H2==O-Coo-OH2-o)1. , -o-(A
O) nn (n) (wherein, R1 is hydrogen or a methyl group, A
is an alkylene group having 2 or 3 carbon atoms, n is 0 or 1 to 20
phosphoric acid ester of a copolymer with a hydroxyl group-containing (meth)acrylate represented by (representing an integer of
A magnetic powder book surface-treated with one or more coupling agents selected from the group consisting of an amino group-containing silane coupling agent, an epoxy group-containing silane coupling agent, and an amino group-containing titanium coupling agent is made magnetic. A magnetic recording medium characterized in that the magnetic recording medium is contained in a layer.