JPH02113424A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good traveling durability, high adhesiveness, decreased drop-outs and a magnetic layer consisting of a thinner film by incorporating specific polyurethane into an intermediate layer or the magnetic layer. CONSTITUTION:The intermediate layer 4 is provided on a nonmagnetic base 1 and the magnetic layer 2 is provided via the layer 4 thereon; further, a BC layer 3 is provided on the surface of the base on the side opposite to the layer 2. The intermediate layer 4 is formed to >=0.05mum and <=3.0mum thickness. The polyurethane in which the negative functional group forms an intramolecular salt is incorporated into the intermediate layer 4 or the magnetic layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

In recent years, magnetic recording media, especially video magnetic recording media that require short wavelength recording, have become more fine-grained than ever before.
There is a growing tendency to use magnetic powder with high magnetic force. However, as magnetic powder becomes finer and has higher magnetic force,
The cohesive force of individual particles becomes stronger, and as a result, the dispersibility and surface smoothness required for obtaining high reproduction output and good S/N ratio for short wavelength recording are no longer fully satisfied. In addition, since such recording media come into violent sliding contact with the magnetic head during recording and reproduction, repeated use causes the magnetic coating to wear out and the magnetic powder contained in the coating to easily fall off, resulting in undesirable effects such as clogging of the magnetic head. bring forth.

For this reason, it is possible to improve the dispersibility of the magnetic powder in the binder by adjusting the particle size distribution of the magnetic powder, to use a surfactant as a dispersant, or to improve the dispersibility of the magnetic powder in the binder. Methods have been proposed in which the properties are modified by introducing a phospho group, a sulfo group, a carboxy group, or the like.

However, these known techniques are still unsatisfactory in terms of achieving high-level electrical characteristics. Moreover, although a smooth surface can be obtained, a smooth surface on the other hand leads to an increase in friction, resulting in extremely poor running performance.

Moreover, the adhesion between the magnetic layer and the base film was likely to be poor, which, combined with poor dispersion of the magnetic powder, further deteriorated running durability and still durability. Furthermore, there is a limit to how thin the magnetic layer can be made due to poor adhesion.

C.6 Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium that has good running durability, high adhesion of the magnetic layer, little dropout, and allows the magnetic layer to be made thinner. be.

20 Structure of the Invention and Its Effects The present invention is characterized in that an intermediate layer with a thickness of 0.05 μm or more and 3.0 μm or less is provided between the magnetic layer and the substrate, and the negative functional group forms an inner salt. This relates to a magnetic recording medium in which a small amount of polyurethane is contained in one of the intermediate layer and the magnetic layer.

First, "polyurethane in which the negative group forms an inner salt" will be described.

First, the manufacturing method will be described.

Similar to the usual polyurethane synthesis method, it is synthesized by reacting a high molecular weight polyol (molecules 1500 to 3000) such as polycarbonate polyol, polyester polyol, polylactone polyol, polyether polyol, etc. with a polyfunctional aromatic or aliphatic isocyanate. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized.

These polyurethanes are primarily produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and may also be in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups; It may also be in the form of a urethane elastomer, which does not contain any reactive end groups. As the isocyanate component, various diisocyanate compounds such as hexamethylene diisocyanate (HMDL), diphenylmethane diisocyanate) (
MDI), hydrogenated MD I (H+zMD I) toluene diisocyanate (TDI), 1.5 naphthalene diisocyanate (ND■), tolidine diisocyanate (TODI), lysine diisocyanate methyl ester (LDI), isophorone diisocyanate (IPD)
I) etc. can be used.

In addition, if necessary, 1,4-butanediol, 1゜6-
A low-molecular polyfunctional alcohol such as hexanediol or 1,3-butanediol is used to adjust the molecular weight, resin physical properties, etc.

The functional group forming the inner salt may be introduced into the incyanate component, but it can also be introduced into the polyol component, and further into the above-mentioned low-molecular-weight polyfunctional alcohol.

Polyester polyols in which the negative functional groups form an inner salt contain various dicarboxylic acid components, polyhydric alcohol components, and dicarboxylic acid components and/or negative functional groups in which the negative functional groups form an inner salt. It can be synthesized by polycondensing polyhydric alcohol components forming an inner salt.

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, sebacic acid, luic acid that dimerizes to 7-dipic acid, maleic acid, and the like. As a polyhydric alcohol component,
Glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, trimethylolpropane, hexanetriol,
Examples include polyhydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol, or any two or more types selected from these glycols and polyhydric alcohols.

Polycarbonate polyols in which the negative functional group forms an inner salt are generally synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or diallyl carbonate, or can be obtained by condensation of a polyhydric alcohol and phosgene. can.

When producing the above polyester polyol and polycarbonate polyol (including polycarbonate polyester polyol), the following aromatic polyhydric alcohols can be used. Further, when the above-mentioned polyester polyol or polycarbonate polyol is reacted with the polyisocyanate, the following aromatic polyhydric alcohol can be used.

Aromatic polyhydric alcohol: [R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R represents a hydrogen atom or an alkyl group or aryl group having 1 to 7 carbon atoms] [n is , represents an integer from 1 to 10,] [n-1, 2] [n represents 1 or 2,] [R is -(cut) z-1-CI(CH:I)-C
llz-Cut- is shown.

X is -so, -, -co-1-C(CHx)z-C(
CHz)z-CJa-C (represents CHzh-) [n represents 1 or 2] [n represents 1 or 2] [n represents 1 or 2] [n represents 1 or 2 In the polyurethane having these aromatic polyhydric alcohol components in the main chain, the content of these components is preferably 10 mo f!% or more of the entire polyhydric alcohol component.

To produce a lactone polyester polyol in which the negative functional group forms an inner salt, S caprolactam,
The above functional group may be introduced into lactams such as α-methyl-1-caprolactam, S-methyl-3-caprolactam, and T-butyrolactam.

In order to produce a polyether polyol in which a negative functional group forms an inner salt, the above functional group may be introduced into ethylene oxide, propylene oxide, butylene oxide, or the like.

As the functional group forming the inner salt, a betaine group mentioned below can be exemplified.

A general method for synthesizing polyester is a condensation reaction between an acid component having an aliphatic or aromatic polyfunctional acid or a derivative thereof and an aliphatic or aromatic polyfunctional alcohol component. Internal amphoteric bases (betaine groups, etc.)
may be contained in either the acid component or the alcohol component, and a method of introducing betaine groups etc. into the polymer as a polymer reaction may be used. However, in consideration of unreacted components and the introduction rate, It is easier to control when the functional group is present in the polymer monomer.

Examples of the betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. The general formula of these beta-yne type functional groups is expressed as follows.

X: -3o3-0-3o3 -Co.

e θ -0-PO3H-0PO,.

θ (e.g. methyl group, ethyl group, etc.).

m; an integer from 1 to 10.

R: an alkyl group, an alkenyl group, or an alkyl group having 1 to 12 carbon atoms.

n, , m: an integer from 1 to 10.

Examples of usable betaine group-containing monomers include the compounds listed below, but it goes without saying that the polyurethane resin used in the present invention is not limited to those using these monomers.

The monomer in which the negative functional group forms an inner salt can be obtained manually as a commercially available chemical, but it can be easily obtained by the method described below.

(Left below) 1) Synthesis method using monochloroacetic acid RN (CHz C00H)+CI CHt
C0OH/CH2-COOH Synthesis method using propane sultone R = Alkyl group such as methyl, ethyl 2) Synthesis method using monochlorosuccinic acid CI (z (blank space below) -COO)I Also, as a polymer reaction, The reaction for introducing betaine groups etc. into the coalescence will be described. In this method, a compound having a betaine group or the like is reacted with an OH group present at the end or side chain of a polyurethane whose chain has been extended to a predetermined molecular weight by a polymerization reaction. In this case, first, a compound having a hydroxyl group and a betaine group is synthesized, and this is reacted with a polyfunctional isocyanate such as diisocyanate in equimolar amounts to obtain a reaction product between one NCO group of the diisocyanate and the hydroxyl group in the above compound. . Then, by reacting the OH groups of the polyurethane with the unreacted NGO groups, a polyurethane into which betaine groups and the like are introduced can be obtained.

Examples of the above-mentioned compounds having a hydroxyl group and a betaine group include, but are not limited to, the following compounds.

The amount of betaine groups etc. introduced into the polyurethane resin of the present invention is preferably (LOI~1.oo+a+o1/g, more preferably 0.1-0.5ms+oI
! /g range. The amount of the above polar group introduced is 0-O
If it is less than 1.0g++ao1/g, it is difficult to see a sufficient effect on the dispersibility of the ferromagnetic powder (in addition, if the amount of the polar group introduced exceeds 1.0g++ao1/g, intermolecular or intramolecular aggregation may occur. This not only adversely affects dispersibility but also causes selectivity to the solvent.
There is also a risk that normal general-purpose solvents may no longer be usable.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 50
00-100000, more preferably 10000-50
The number average molecular weight is preferably in the range of 5,000
If the number average molecular weight is less than 100,000, the coating film-forming ability of the resin tends to be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur in paint manufacturing processes such as mixing, transport, and coating.

Synthesis Example (a) 1 mole of N-methyljetanolamine and 1 mole of propanesultone were reacted at a temperature of 120° C. for 3 hours to obtain a sulfobetaine type polyfunctional monomer.

Next, 1.5 mol of adipic acid, 1.7 mol of 1.4-butanediol, and 0.06 mol of the above sulfobetaine type acid-base polyfunctional monomer were charged, and the mixture was heated at 150 to 200°C for about 3 hours. The temperature was raised at 200°C for 4 hours, and 3-5
Unreacted raw materials were removed at mmHg, and the reaction was carried out until the acid value reached 2 or less. The molecular weight of the obtained copolymerized polyester is M w
It was 2500. 165 g of copolymerized polyester was dissolved in 300 parts of methyl ethyl ketone, 80 parts of diphenylmethane diisocyanate was added, and the mixture was reacted for 2 hours at 80°C. 20 parts of 1,4-butanediol was added and the reaction was further continued for 2 hours. 4 parts of 3-butanediol were added and reacted for 1 hour. The molecular weight of the obtained polyurethane is Mw=3.5
10,000, Mn=22,000.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
An intermediate layer 4 is provided on a non-magnetic support 1 such as polyethylene terephthalate, and a magnetic layer 2 is provided via this intermediate layer 4. If necessary, a BCC 84 is provided on the support surface opposite to the magnetic layer 2. It is provided. An overcoat layer (QC layer 2, not shown) may be provided on the surface side of the magnetic layer 2 of the magnetic recording medium shown in FIG. 1, and the nonmagnetic support 1 may be subjected to a corona discharge treatment.

The magnetic recording medium of the present invention has the following remarkable features.

That is, when an intermediate layer with a specific thickness is provided between the magnetic layer and the substrate, and at least one of the magnetic layer and the intermediate layer contains the specific polyurethane, the adhesion between the magnetic layer and the substrate is as expected. This was a dramatic improvement. As a result, the magnetic layer became more hardened, the running durability was improved, and the slitterability of the medium, especially the tape, was improved, powder falling was prevented, and dropouts were greatly reduced. Furthermore,! It has also become possible to make the magnetic layer thinner than usual while maintaining a certain level of physical properties and electromagnetic conversion characteristics.

Although the cause of the above-mentioned improvement in adhesion is not clear, it can be assumed that it is related to the interaction between the amphoteric functional groups of the polyurethane and the binder of the intermediate layer or magnetic layer.

When the thickness of the intermediate layer is 0.05 μm or less, the effect of improving adhesion is not significant because it is thin, and when it is 3 μm or more,
If it is too thick, it may cause problems when used in a recording/reproducing device.

Furthermore, "polyurethane in which a negative functional group forms an inner salt" can also be included as a binder in the magnetic layer. In this case, the dispersibility of the magnetic powder is dramatically improved compared to conventional methods, and high electromagnetic conversion characteristics can be obtained, as well as the hardening of the magnetic layer (compared to conventional polyurethane). , driving durability is further improved.

Regarding the effect of improving dispersibility by the polyurethane mentioned above,
It can be explained as follows.

The surface of magnetic powder such as metal oxide is complex, and the surface is charged with positive and negative charges due to hydration (surface hydroxyl groups, structural defects, ion substitution, etc.). When selecting, consider the acidity, basicity, and acidity of the surface of the magnetic powder.
Basic strength, acidity, number of basic sites, etc. are important factors8. For example, to uniformly disperse magnetic powder in a short time, binders with acidic and basic (polar) groups of various strengths are used. Ideally, these acid and base sites should be adsorbed to the surface active sites of the magnetic powder.

However, simply introducing functional groups of the same polarity into the binder was far from this ideal.

It is also conceivable to use a binder having a polar functional group and to simultaneously use binders having functional groups of the same polarity and different strengths. However, in this case, the magnetic powder is competitively adsorbed preferentially to the side of the binder having a stronger functional group, making it difficult to achieve sufficient adsorption as a whole, resulting in poor dispersion stability of the magnetic paint. Furthermore, it is also conceivable to use a binder having a polar functional group and to simultaneously use a binder having a different type of functional group. However, with this, the interaction between the polar groups is strong (the adsorption of the binder to the surface of the magnetic powder is difficult to occur, and the viscosity of the magnetic paint increases. The above problem can be solved.In other words, the acid site and base site in the inner salt in the binder adsorb to the surface active site (base site and acid site) of the magnetic powder, so the adsorption force to the magnetic powder increases. It is thought that the dispersibility is significantly improved.Furthermore, since the negative functional groups of the same binder form an inner salt, the above-mentioned problem does not occur.

The Young's modulus of the intermediate layer is preferably at least IXIO" dynel-, and more preferably at least IXIO9dyNe/c. The intermediate layer having such a Young's modulus is
For example, by appropriately combining suitable resins as a binder, by mixing and dispersing suitable inorganic powder as a reinforcing material in the intermediate layer, and by adding a curable resin that hardens by electron beam irradiation, ultraviolet ray irradiation, etc. to the intermediate layer. It can be obtained by incorporating it into a layer.

The average surface roughness Ra of the intermediate layer is preferably 0.02 μm or less. Such an Ra intermediate layer can be obtained by appropriately selecting the particle size, content, type, etc. of the inorganic powder that can be contained in the intermediate layer.

When the above polyurethane is used as a binder for the magnetic layer, it is preferably used in an amount of 100 to 1 part by weight, more preferably 50 to 2 parts by weight, per 100 parts by weight of magnetic powder.

Next, the overall structure of the magnetic recording medium of the present invention will be further described.

As the binder for the magnetic layer and the intermediate layer, known binders can be used in addition to the above-mentioned polyurethane. All known binders for magnetic layers can be used as the binder for the intermediate layer.

The binder that can be used in combination has an average molecular weight of about 10,000.
~200,000, such as urethane resins, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, chloride-acrylonitrile copolymers, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, and cellulose. Derivatives (cellulose acetate butyrate, cellulose diacetate,
cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction Examples include resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -303M, -COOM.

OM, -PO(○M')z (However, M is preferably a resin containing hydrogen or an alkali metal such as lithium, potassium, or sodium, or a group. In other words, such a resin has magnetic property due to the polar group in the molecule. This improves the compatibility with the powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid, which in turn improves the durability of the medium. obtain.

In addition, when the resin containing the hydrophilic polar group described above is contained in the intermediate layer and the "polyurethane in which the negative functional group forms an inner salt" of the present invention is contained in the magnetic layer, the magnetic layer The adhesive strength is even higher. Although the reason for this is not clear, it is thought to be due to the action of the above-mentioned hydrophilic polar group.

Examples of the resin having a hydrophilic polar group include vinyl chloride copolymers and polyurethanes.

The above-mentioned polyurethane having a hydrophilic polar group is a copolymerizable monomer containing a sulfo group, a phospho group, a carboxyl group, an alkali metal salt of a sulfo group, an alkali metal salt of a phospho group, an alkali metal salt of a carboxyl group, etc. It can be obtained by copolymerizing a polyol, a polyisocyanate, and, if necessary, other copolymerizable materials.

Alternatively, the hydroxyl group of the polyol can be sulfonated or phosphonated in advance, or converted into an alkali metal salt of a sulfo group or an alkali metal salt of a phospho group, and then copolymerized with a polyisocyanate and other copolymerizable monomers as necessary. You can also get

For the synthesis of polyurethane, the polyols, polyisocyanates, and other copolymerizable materials as required can be used as described above.

The above vinyl chloride copolymer resin having a hydrophilic polar group contains a sulfo group, a phospho group, a carboxyl group, an alkali metal salt of a sulfo group, an alkali metal salt of a phospho group, an alkali metal salt of a carboxyl group, and a hydroxyl group. It can be obtained by copolymerizing the copolymerizable monovinyl chloride monomer and, if necessary, other copolymerizable monomers.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned sulfonic acid or phosphoric acid salt is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield, etc.

The above-mentioned copolymerizable monomer containing a sulfonate salt is as follows:
(CHI)CH2Son MCH2=CHCHz 0C
OCH(CH2COOR) SOYO M CH1=CHCH 0CHZ CH(OH)cHz S
on M CHz = C(Cl1i) COOCz Ha S
Ox MCHz -CHCOOC4Ha S Os M
cHz =CHC0NHC(C113)! CH□5o
ft M is mentioned.

Also, as a phosphate, CHz ”CHCHz 0CHz CH(OH)CH2
0POz MY' CHz = CHCON HC(CH3) t CHz
O-P Ox MY"PO□MX' CHi =CHCHz O(CH2CH20).

poz MX” In the above, M is an alkali metal, R is a carbon atom number of 1 to
20 alkyl groups, Yl is H, M or CHz=CH
CH□OCHz CH(OH) CHzY2 is HXM or CHt =CHC0NHC(CIL)z C11zxi
is 0H or OM, X” is CI(z = CHCIIz O(CI(zc H
zO)nOH or OM. Also, n is 1 to 100, m
is an integer from 1 to 100.

Examples of carboxyl groups and monomers containing alkali metal salts of carboxyl groups include acrylic acid, methacrylic acid, maleic acid, and alkali metal salts thereof.

In other words, as the monomer containing the above hydroxyl group, as X in the monomer having -X-OH group, C
n1ltn s C00CnHzn and C0NHCnH
Examples include organic residues represented by zn (n is an integer of 1 to 4). Examples of monomers having -X-OH groups include α,β unsaturated acids having 2 to 2 carbon atoms, such as (meth)acrylic acid-2-hydroxyethyl ester and (meth)acrylic acid-2-hydroxypropyl ester. 4, alkanol esters of unsaturated dicarboxylic acids such as maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester, itaconic acid mono-2-hydroxybutyl ester, 3-buten-1-ol , olefin alcohols such as 5-hexene-1ol, alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether, and acrylamides such as N-methylolacrylamide and N-methylolmethacrylamide. In addition, IX bonded to the resin
The amount of hydroxyl group based on -OH group is 0.1 to 2.0% by weight
is preferable; if it is less than 0.1% by weight, the crosslinking effect of the coating film by the isocyanate compound will not be exhibited, and if it is less than 2.0% by weight,
If it is more than that, the pot life of the paint will be too short and it will be difficult to use.

Although the amount of this hydroxyl group is much smaller than that of vinyl chloride-vinyl alcohol-vinyl acetate copolymer, which has been known for use in magnetic paints, the crosslinking reaction with isocyanate compounds is difficult. fully achieved. The reason for this is not clear, but it is thought to be due to the fact that the hydroxyl groups that participate in the reaction are farther away from the main chain of the copolymer, increasing the degree of freedom, and that the distribution of the hydroxyl groups in the polymer is more uniform. .

Copolymerizable monomers to be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters, vinylidene chloride, 7-acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, and various acrylic monomers. Examples include acid esters, methacrylic esters, ethylene, propylene, isobutyne, bookdiene, isoprene, vinyl ethers, esters, aryl esters, acrylamide, methacrylamide, maleic acid, and maleic esters.

By the way, conventional vinyl chloride copolymers (for example, VAG H manufactured by U, C, C) are composed of the following copolymer components.

: Indicates a copolymerization unit.

However, it is thought that the CH and C0-0- groups here do not easily contribute to the crosslinking reaction with the curing agent and the like. So C
It is preferable to contain an epoxy group such as the following in place of HffCO. For example, a copolymer having the following units may be mentioned.

(The following is a blank space) 0f ((X: Monomer unit portion containing an alkali metal salt of a sulfo group or a phospho group) The above binder is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of the hydrophilic polar group-containing monomer in the binder is 0.
If the amount of the hydrophilic polar group-containing monomer, which is preferably 01 to 30 mol %, is too large, the solubility in solvents will be poor and gelation will easily occur, while if it is too small, it will be difficult to obtain the desired properties.

In the magnetic layer, "polyurethane in which a negative functional group forms within the molecule" is preferably used in combination with a vinyl chloride resin or a vinyl chloride copolymer (vinyl chloride-vinyl acetate copolymer, etc.). In this case, the ratio of the polyurethane of the present invention to the vinyl chloride resin and the vinyl chloride copolymer is preferably (2:8) to (8:2) by weight, and (3;7) to ( 7:3) is more preferable. As the vinyl chloride copolymer, those containing the above-mentioned hydrophilic polar groups are also preferred.

Note that it is also possible to incorporate the above betaine type functional group into the vinyl chloride resin.

In the magnetic layer, "polyurethane in which negative functional groups form an inner salt" may be used in combination with epoxy resin (especially phenoxy resin), polyester resin, or nitrocellulose resin (hereinafter referred to as other resins). In this case, the blending ratio of the urethane resin and other resin is 90 to 10 parts by weight, more preferably 80 to 20 parts by weight.
If the above-mentioned compounding ratio exceeds 90 parts by weight, the coating film will become too thick, and the durability of the coating will deteriorate significantly, and the adhesion to the support will also deteriorate. If it is less than 10 parts by weight, the magnetic powder tends to fall off.

Durability can be improved by further adding a polyisocyanate curing agent to the paint for the intermediate layer and magnetic layer containing a binder. Examples of such polyisocyanate curing agents include difunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; Any conventionally used curing agent such as isocyanate or urethane prepolymer containing isocyanate groups at both ends, or polyisocyanate that can be used as a curing agent can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

Examples of inorganic powders that can be contained in the intermediate layer include carbon black, graphite, titanium oxide, barium sulfate, ZnS% MgCO5, Zn02Ca O% γ-iron oxide, tungsten disulfide, molybdenum disulfide, boron nitride, magnesium oxide, and ZnO2. , S t Of , C
rzOz, CX-AlzOx, SjC.

Cerium oxide, corundum, artificial diamond, α-
iron oxide, garnet, garnet, silica, silicon nitride,
Examples include boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly, diatomaceous earth, and dolomite.

Among these, carbon black, CaC0, titanium oxide, barium sulfate, α-A1201, α-iron oxide, T-
Iron oxide and the like are preferred.

Incorporating carbon black in the magnetic layer is further advantageous in terms of improving running properties and electromagnetic conversion characteristics, and also slightly improves dispersibility and reduces the amount of residual melt in the magnetic layer.

If light shielding carbon black is used as such carbon plastic, the degree of light shielding can be further increased. As a light-shielding carbon blank, for example, Raben 2000 (specific surface area: 19
Onf/g, particle size 1Bmμ), 2100.1170.
1000, Mitsubishi Kasei side type #100, #75, #40
, #35, #30, etc. can be used.

Further, as the conductive carbon black, for example, Conductex (Conduct) manufactured by Columbia Carbon Co., Ltd.
ex) 975 (BET value (hereinafter abbreviated as BET) 2
50 i/g, DI3P oil absorption (hereinafter abbreviated as DBP) 170
ml/100gr, particle size 24 mμ), Conductesox 900 (BET125 ml g, particle size 27 mμ), Conductesox 40-220 (particle size 2
0m, u), Conducte 7x SC (BET220
rd/gr%DBP115 mf/100gr.

Particle size: 20 mμ), Cabot's Hulkan (Cabo
tVulcan) X C-72 (specific surface area 254rr
r/g, particle size 30 mμ), Palcan P (BET143
of/gr, DBP118ml! /100g
r, particle size 20 mμ), Raven 1040°420, Blank Pearls 2000 (particle size 15 mμ), and #44 manufactured by Mitsubishi Kasei ■.

In addition, other carbon fibers that can be used in the present invention include Conductex-3C and (BE T220) manufactured by Columbian Carbon.
rl/g, DB P 115 ml/10
0 g, particle size 20 mμ), Palcan manufactured by Caboto Co., Ltd. (
Vulcan) 'l (B E T140 rd/
g, DB P114 ml/100g
, particle size 19rncr), #80 manufactured by Asahi Carbon Co., Ltd. (B
ETL1 ft/g, [)E3p113 ml! /
100g, particle size 23mμ), H3100 manufactured by Denki Kagaku Co., Ltd.
(BET32%/gSDBP180 mff/100g
.

particle size 53 mμ), #22I3 manufactured by Mitsubishi Kasei Co., Ltd. (BET
55m/g, DBP131 ml/100g, particle size 4
0mμ), #20B (BET56n(/g, DBP
115 mff/100g, particle size 40m #), #3
500 (B ET47m/g, D B P2H
4ml/100g, particle size 40mμ), as well as Mitsubishi Chemical's CF-9, #4000, M
A-600, blank pearls manufactured by Cavont (
Black Pearls and Monarch
ck) 800, Pla Tsuk Pearls 700, Black Pearls 1000. blank pearls 8805
Black Pearls 900, Black Pearls 130
0. Frank Perls 2000, Sterling (S
terling) V, Raven 410, Raven 3200, manufactured by Columbia Carbon Co., Ltd.
Raben 430, Raben 450, Raben 825, Raben 1255, Raben 1035, Raben 1000
, Raven 5000, Ketchen Black FC, etc.

The magnetic powder used in the magnetic layer, especially the ferromagnetic powder, is r
-Fez02, Co-containing r Fezes, Fe, 0
．． , Co-containing Fe, O, etc. iron oxide magnetic powder: Fe, N
i=Co, Fe-Aj2, Fe-A1-Ni, Fe-
Al-Co, Fe-Aji! -Ni□-Co.

Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Nf-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co Ni alloy, etc.
Metal magnetic powder mainly composed of Fe, Ni, Co, etc.: cr
Examples include various ferromagnetic powders such as oz.

The l3ET value of the magnetic powder should be 40 i/g or more (,45~8
0m/g is even better.

The magnetic layer can contain a fatty acid and/or a fatty acid ester as a lubricant.This allows the respective characteristics of both to be exhibited while offsetting the defects that would occur when used alone, thereby enhancing the lubricating effect. Improves still image durability,
Running stability, S/N ratio, etc. can be improved. In this case, the amount of fatty acid added is 0 to 100 parts by weight of magnetic powder.
．． 2 to 10 parts by weight is better, and 0.5 to 8.0 parts by weight is even better. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and output decreases. The amount of fatty acid ester added is preferably 0.1 to 10 parts by weight per 100 parts by weight of the magnetic powder.
．． 5 parts by weight is even better. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be set as fatty acid/fatty acid ester =
10/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are exemplified as follows.

Caproic acid Caprylic acid Capric acid Lauric acid Myristic acid Palmitic acid Stearic acid Isostearic acid Lyrinnic acid Linoleic acid Oleic acid Elaidic acid Behenic acid Malonic acid Succinic acid Maleic acid Glutaric acid Adipic acid Pimelic acid Azelaic acid (21) Sebacic acid (22) 1. 12-dodecanedicarboxylic acid (23)
Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl palmitate (7) Butyl myristate (8) Octyl myristate ( 9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Isobutyl oleate (17) Ethyl oleate ( 18) Isotridecyl oleate (19) 2-ethylhexyl stearate (20)
2-ethylhexyl myristate (21) ethyl stearate (22) 2-ethylhexyl palmitate (23)
Isopropyl palmitate (24), isopropyl myristate (25) butyl laurate (26) cetyl-2-ethyl hexalate (27) dioleyl adipate (28) diethyl adipate (29) diisobutyl adipate, (30) diisodecyl adipate, In addition to the fatty acids and fatty acid esters mentioned above, other lubricants (for example, silicone oil, carboxylic acid modified, ester modified), graphite, fluorinated carbon, molybdenum disulfide, tungsten disulfide, fatty acid amide , α-olefin oxide, etc.) may be added to the magnetic layer.

Non-magnetic abrasive particles can also be added to the magnetic layer. Preferably, these include, for example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, and carbon nitride.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Furthermore, carbon bra and rim can also be used together.

In addition, the non-magnetic particles contained in the back coat layer are
It is more preferable to set the average particle diameter within the range of 10 mμ to 1000 mμ, because within the above range, the nonmagnetic particles will not become too fine and the addition effect will be good.

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Zinc oxide, α-F 13403, talc, kaolin,
Examples thereof include calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as benzoguanamine resins, melamine resins, phthalocyanine pigments, etc. can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use carbon black in combination with the above-mentioned non-magnetic particles, as this further stabilizes the running properties of the medium, and in combination with the effect of the above-mentioned non-magnetic particles, it is possible to further improve the durability of the medium. be.

The thickness of the magnetic layer is preferably thin in order to achieve a high S/N ratio, and thicker in terms of running performance and still durability. Therefore, 6.0 to 1.0 μm is preferable.
, 5.9-2. The surface roughness of the magnetic layer is more preferably O11m, and the average surface roughness Ra is o, oos to 0.0.
Preferably, the thickness is 20 μm. This does not reduce running performance and improves the S/N ratio.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

Preparation of videotape> Resin for the intermediate layer shown in Table 1 below and a predetermined amount of CaC0,
was dispersed and dissolved in methyl ethyl ketone/toluene and applied onto a 10 μm thick polyethylene terephthalate base to obtain an intermediate layer having various compositions, film thicknesses, average surface roughness Ra, and Young's modulus shown in Table 1. Ta. However, in Comparative Example 2.4, no intermediate layer was provided on the support, and the magnetic layer was directly formed on the support.

That is, using the specified magnetic powder shown in Table 1 below, Table 1
A magnetic paint is prepared by dispersing each of the resins and various additives shown in the table below, the magnetic paint is filtered through a 1 μm filter, 6 parts of trifunctional isocyanate is added, and the mixture is coated onto a support to a predetermined thickness and superimposed. Calendering was performed to obtain magnetic layers having various compositions and film thicknesses shown in Table 1.

Thereafter, a paint for the BC layer having the following composition was applied to the opposite surface of the magnetic layer to a dry thickness of 0.4 μm.

Carbon blank (Raven 1035)
40 parts barium sulfate (average particle size 300 mμ)
10 parts nitrocellulose
25 parts N-2301 (manufactured by Nippon Polyurethane) 25 parts Coronate L (〃 ) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts In this way, a wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was prepared. I got this and rolled it up.

This film was cut into 1/'2 inch width to produce the video tapes shown in Table 1. However, the numbers shown in the table represent parts by weight.

(Margin below) Each component shown in Table 1 is as follows.

Secret Co-T-Fez03 (adhered) Specific surface area l3ET value 45rd/g Coercive force (Hc) 750 erste, polyester Byron 200 (manufactured by Toyobo Co., Ltd.) Yoyu Buny Kue Masha thermoplastic polyurethane [Nistan 5701J (Manufactured by Good Lynch Co., Ltd.) Wari IWI Dan Vinyl chloride resin containing sulfo groups and epoxy groups Vinyl chloride component 77-t% Sulfuric acid groups 0.8 wt% Epoxy groups 3.9 wt% Hydroxyl groups 0.5 wt% Sulfo 4 Polyurethane U R -8300 (manufactured by Toyobo Co., Ltd.) The polyurethane resins (a) to (c) according to the present invention are as follows.

Synthesis example (a) of the polyurethane (-a) according to the present invention
(B) and (C) were synthesized in the same manner.

(a) Sulfobetaine-type modified group-containing number average molecule N: 22,000 Tg -20°C Polar group concentration: 0.04 vao 12 / gCH.

+c Hz N-CHz +/ Polyester type (
CHd3 Polyurethane chain 0=S=O O8 (b) Number average molecular weight containing carboxybetaine type modification group
15,000 Tg 10℃ polar group concentration 0.1mv
so 1 / gCH2 -8-CHz -N CHz+ Polyester type CH
.

7\0 (c) Phosphobetaine type modified group content number average molecular weight 30,000 Tg O℃ polar group concentration
0.07 mmo j! / gCHiCONHCHzC
Hz +CHz N CHz+-Polyester type CH.

HO-P = 0 (Cutoff is 0.25 Dragon).

Young's modulus of middle layer Measurement was performed using a Leo Pipelon made by Toyo Baldwin.

Evaluation of Videotape Performance> The characteristics shown in Table 2 below were evaluated for each videotape shown in Table 1.

The measurement method for each evaluation data is as follows.

Electromagnetic conversion characteristics〉 HR36 can be used as a VTR deck for RF measurement.
000, the output during playback with a 100% white signal was measured using the videotape of Example 1 as a reference (0).

Lumi S/N: Using a noise meter (manufactured by Shibatsu), the videotape of Example 1 was used as a reference (0), and the difference in S/N of the sample in a 100% white signal was determined by comparison with this. .

Still life: The time until the RF specific output decreases by 1 dB in still mode using NV 6200 (manufactured by Nichiden Denki).

Powder falling: The stain was observed and evaluated after the videotape was run 2100 times over the entire length under conditions of a temperature of 40° C. and a humidity of 80%.

0 -------1 - No stains 8 = Slight stains × -1111 Dirt RF output drop: After repeatedly running the tape 100 times, perform playback output at 100% white signal. It was determined in comparison with the tape of Example 1.

Dropout: Using a VTR dropout counter (manufactured by Shibatsu Corporation), one dropout is measured over the entire length of the tape when the output drops by 14 dB or more from the RF envelope output over a long period of 10 μsec / or 3 μs4. Then, the average value per minute was determined.

Adhesiveness to film; After attaching cellophane tape to the sample surface (magnetic layer side), it was strongly peeled off and the sample surface was observed.

Evaluation Amount transferred to tape ○・−−−−−−2% or less △　　　　　2～10　% ×10~50% xx　　--50% or more Average surface roughness of magnetic layer〉 It was measured in the same manner as the average surface roughness of the intermediate layer.

As shown in Table 2, the samples of the examples are significantly superior in electromagnetic conversion characteristics and running durability compared to the samples of the comparative examples.

Next, a videotape having the same configuration and prescription as the videotape of Example 1 was created. However, only the thickness of the intermediate layer was varied, and each sample was checked for adhesion of the magnetic layer and the presence or absence of defective reproduced images. The results are shown in Table 3 below.

Reproduction image defects: Each videotape was reproduced using a VTR (HR-3-6000) and image defects were examined.

○ No image defects 8. Image shaking can be confirmed. × Image defect Table-3 From Table 3, it can be seen that limiting the thickness of the intermediate layer is important.

[Brief explanation of drawings]

FIG. 1 is a partially enlarged sectional view showing an example of a magnetic recording medium. In addition, in the reference numerals shown in the drawings, they are: 1-11--Nonmagnetic support 2--Magnetic layer 3 Back coat layer 4--1-Intermediate layer. Agent: Hiroshi Aisaka, Patent Attorney (Volunteer) Proceedings (Hosho 4, April 6, 1999, 1, Indication of the case, 1988 Patent Application No. 266439, 2, Title of invention: Magnetic recording medium 3, Person making amendment case) Relationship with Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name
(127) Konica Co., Ltd. 4, Agent address: FINIE Building 6, 2-4-11 Shibasaki-cho, Tachikawa-shi, Tokyo, Detailed explanation of the invention column (1) of the specification subject to amendment, from the bottom of page 12 of the specification 4th line and above

Claims (1)

[Claims] 1. An intermediate layer with a thickness of 0.05 μm or more and 3.0 μm or less is provided between the magnetic layer and the substrate, and polyurethane in which a negative functional group forms an inner salt is used as the intermediate layer and the magnetic layer. A magnetic recording medium contained in at least one of the layers.