JPH0242625A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a traveling property and durability and to obtain electromagnetic conversion characteristics by providing a back coating layer contg. specific nonmagnetic powder and resin having a negative functional group to the recording medium. CONSTITUTION:The nonmagnetic powder contains a carbon black having 20-40mmu average primary particle size, carbon black having 50-100mmu average primary grain size and zinc oxide powder having 0.5-1.0mum average grain size. The back coating layer contg. this nonmagnetic powder and the resin having the negative functional group is provided. The back coating layer is provided on the other surface of a nonmagnetic base on the side opposite to the surface to be provided with a magnetic layer. The traveling property and durability are improved in this way and the good electromagnetic conversion characteristics are obtd. at the time of cope with high density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media. More specifically, the present invention relates to a magnetic recording medium that has excellent running properties and durability and can realize good electromagnetic conversion characteristics even when supporting high-density recording.

[Prior Art and Problems to be Solved by the Invention] Magnetic recording media are widely used in various applications such as video tapes, audio tapes, and floppy disks.

Further, in such magnetic recording media, there is an increasing demand for magnetic recording media that can support high-density recording.

In general, magnetic recording media capable of supporting high-density recording use ferromagnetic powder with a small particle size as the ferromagnetic powder contained in the magnetic layer.

Therefore, the surface of the FB magnetic layer tends to be smooth.

Also, the surface of the magnetic layer has a smaller surface roughness.

Good electromagnetic conversion characteristics can be obtained in response to high-density recording.

However, if the surface of the magnetic layer becomes smooth.

The coefficient of friction increases and running resistance increases, leading to uneven running and deterioration of electromagnetic conversion characteristics such as chroma S/N, and excessive rubbing of the magnetic recording medium during running. There is a problem that durability may be reduced.

Therefore, better running performance is desired in magnetic recording media, particularly in magnetic recording media that are compatible with high-density recording.

The running performance of such a magnetic recording medium is determined not only by the surface condition of the magnetic layer provided on one side of the non-magnetic support, but also by the condition of the other side (back side) of the non-magnetic support on which the magnetic layer is not provided. The surface condition also has a large effect.

Therefore, in order to improve running properties, it has been proposed to provide a back coat layer on the back surface of the nonmagnetic support.

The back coat layer is usually formed from nonmagnetic powder and a binder.

The non-magnetic powder has the effect of making the surface of the back coat layer appropriately rough, reducing the contact area and lowering the coefficient of friction.

It is said that by providing such a back coat layer, the running properties of the magnetic recording medium can be improved.

However, by providing a back coat layer, for example, the surface roughness of the back coat layer increases due to agglomeration of non-magnetic powder, resulting in unevenness, which is transferred to the magnetic layer and generates noise. (1) When used, the back coat layer becomes easily scraped, and the scraped material adheres to the magnetic layer or magnetic head, resulting in a decrease in electromagnetic characteristics.

These problems are thought to be due to poor dispersibility of the non-magnetic powder in the back coat layer and insufficient bonding force between the non-magnetic powder and the binder.

By the way, as a method for providing a back coat layer to improve the running properties of a magnetic recording medium, for example, Japanese Patent Laid-Open No. 57-130234 and Japanese Patent Laid-Open No. 58-1611 disclose
No. 35, JP-A-57-53825, JP-A-58241
No. 5 shows an example of using sa powder as a non-magnetic powder in the back coat layer, and many of these also include:
A limited particle size is shown.

For the back coat layer using the above-mentioned inorganic powder,
A back coat layer has been proposed that uses carbon black in the back coat layer to have an antistatic effect, a light shielding effect, and a surface roughening effect due to its particles.

For example, Japanese Patent Laid-Open No. 17401/1983 has been proposed. However, because the average particle size of the carbon black used is small (10 to 20 m IL), the dispersibility of carbon black in the back coat paint is extremely poor, and the carbon black does not appear in the formed back coat layer. of agglomerated particles are present.

There is a problem in that unevenness occurs on the surface of the back coat layer.

Additionally, in order to solve the above-mentioned problems, attempts have been made to use a combination of carbon black with an average primary particle size of relatively small 10 to 60 μm and carbon black with an average primary particle size of 100 gm or more. (Unexamined Japanese Patent Publication 1986-
No. 45938, JP-A-60-459:19, JP-A-6
0-25023, JP-A-60-38125, JP-A-6
0-107729, JP 59-185027, JP 59-223931, JP 57-111828
No. 147:1 (No. 18, etc.).

However, the problem is that the carbon black cannot be sufficiently dispersed in the back coat layer by simply focusing on the particle size of the carbon black.

Furthermore, the combination of inorganic powder and carbon black has been proposed (JP-A-59-2105:1, JP-A-60
25022, JP-A No. 60-25023), however, the monodispersity has not been significantly improved.This invention was made based on the above-mentioned circumstances.

That is, an object of the present invention is to provide a magnetic recording medium that has excellent running properties and durability and can realize good electromagnetic conversion characteristics even when supporting high-density recording.

[Means and effects for solving the above problems] In order to solve the above problems, the present inventor has diligently studied and developed a back coat layer containing a specific non-magnetic powder and a specific binder. The provided magnetic recording medium has a good dispersion state of the non-magnetic powder in the back coat layer, a sufficiently large bonding force between the non-magnetic powder and the binder, and excellent runnability and durability.
This invention was achieved by discovering that it is possible to realize good electromagnetic conversion characteristics.

That is, the invention for solving the above problem is as follows.

Carbon black with an average primary particle size of 20 to 40 m JL, carbon black with an average primary particle size of 50 to 100 m JL, and carbon black with an average primary particle size of 0.5 to 1. The present invention is a magnetic recording medium characterized in that it is provided with a back coat layer containing a nonmagnetic powder containing zinc oxide powder, which is OILm, and a resin having a negative functional group.

The back coat layer, nonmagnetic support, and magnetic layer that constitute the magnetic recording medium of the present invention will be explained below.

(Backcoat layer) The backcoat layer is provided on the surface of the nonmagnetic support on which the magnetic layer is provided and the other surface.

The back coat layer contains non-magnetic powder and a binder.

One of the important points in this invention is that the non-magnetic powder is carbon black [hereinafter sometimes referred to as carbon black A] having an average primary particle size of 20 to 40 ml. ] and carbon black having an average primary particle size of 50 to 100 mg [hereinafter sometimes referred to as carbon black B]. ] and the average particle size is 0.5 to 1. The zinc oxide powder has a diameter of 0 μm.

As a specific example of carbon black A, for example, manufactured by Columbia Carbon Co., Ltd. [trade name]; Raven 525
0,1255. +250.1200°1170.104
0,10:Is, 1030°1020.890,850
, 825 Manufactured by Cabot [Product name]; Black Burls.

Legal 400, 600.50OR, 500°3:10
,99゜Hulcan :12,30,4
00DMA-100,7,8,11.

Specific examples of carbon black B include, for example, "Raben 14." manufactured by Columbia Carbon Co., Ltd. [trade name];
1 hill, 22,410,420,430450°Nister Ring NS, V manufactured by Cabot Corporation.

In the back coat layer, the carbon black A
The blending weight ratio of carbon black B and carbon black B (carbon black A/carbon black B) is preferably 50/
1 to 2/3, more preferably 20/I to I/1
It is.

The zinc oxide may be manufactured by either a dry method or a wet method, and preferred is non-uniform 11F lead oxide manufactured by the French method.

The average particle size of the zinc oxide is expressed as a value determined by the air permeation method described below.

The air permeation method uses the general Kozeny+Caraan method to determine the relationship between the permeability of fluid (air) passing through a powder packed bed and the specific surface area of the powder for powder made of spherical uniform particles. ) is a method of determining the 41 average particle diameter using equation (1).

Where: Sw: Specific surface area of powder (cm2/g) ε: Porosity of powder packed bed ρ: Powder density (g/c-') η: Viscosity coefficient of air (g/c-・5ee) L: Thickness of powder packed bed (C■) Q: Powder filled permeation air amount (c, c) ΔP: Pressure difference between both sides of packed bed (g/c■2)^: Cross-sectional area of packed bed (cm2) t; Air permeation time (sec) of Qc, c, through the packed bed
W: Powder weight (g) In the above formula (1), ρ, η, ^, and ε can be measured independently, so give Q and 1 and set the PIN for this. Then, Sv can be found. This Sv
By entering the value in the following relational expression (2), the average particle diameter d is calculated.

Examples of measurement types include 5S-100 (Ichitsu Seisakusho).

In the back coat layer, the amount of zinc oxide is usually such that the weight ratio (zinc oxide/carbon black A + carbon black B) to the amount of carbon black including the carbon black A and the carbon black B is 1. , 1150~1/1, and further 1150~2
/3 is preferable.

In the back coat layer, the blending amount of the non-magnetic powder is preferably 50 to 5 parts by weight based on 100 parts by weight of the binder.
00 parts by weight, more preferably 60 to 400 parts by weight.

In addition to carbon black A, carbon black B, and the zinc oxide, the back coat layer described in Irj contains an organic filler,
It can contain an inorganic filler.

As the organic filler, acrylic styrene resin,
Examples include benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluoroethylene resin powder.

In particular, benzoguanamine-based and/or melamine-based resin powders are preferred for use in combination with carbon black.

Examples of the inorganic filler include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, zinc sulfate, tin oxide,
Chromium oxide, silicon carbide, calcium carbide, α-Fe, O
, talc, kaolin, boron nitride, zinc fluoride, and molybdenum dioxide.

One of the important points in this invention is as follows.

The back coat layer is made of a resin having a negative functional group (hereinafter sometimes simply referred to as resin (A)). ].

In this invention, the resin (A) is used as a binder.

The resin (A) is considered to have the function of uniformly dispersing the non-magnetic powder in the binder and increasing the bonding force between the non-magnetic powder and the binder.

Examples of the negative functional group in the resin (A) include -8OYM, -050. M,-COOM.

OM' (However, in the formula, 1M represents a hydrogen atom, lithium, sodium or potassium, Ml and Ml each represent a hydrogen atom, lithium, sodium, potassium or an alkyl group, and MI and Ml are the same. (It's okay to be different, it's okay to be different, etc.).

Specific examples of the resin (A) include resins obtained by introducing the negative functional groups into polyester resins, polyurethane resins, vinyl chloride resins, and the like.

These resins can be obtained by various methods. For example, polyester resins containing sulfonic acid metal bases are
It can be obtained by using a dicarboxylic acid containing a sulfonic acid metal group as part of the dicarboxylic acid component and condensing this with a dicarboxylic acid that does not have a sulfonic acid metal base together with a diol.

A polyurethane resin containing a sulfonic acid metal base can be produced by combining, for example, a dicarboxylic acid containing a sulfonate metal base, which is a starting material for the polyester containing a sulfonate metal base, a dicarboxylic acid containing no sulfonate metal base, and a diol. It can be obtained by a condensation reaction and an addition reaction using three types of compounds and a diisocyanate.

Furthermore, a method of modifying a polyester resin, a polyurethane resin, or a vinyl chloride resin to introduce a negative functional group can also be considered.

That is, these resins and, for example, CL;L-CH
ICH, S03M.

CJI-CHt CHI O20, M.

C-cHt CH2C00M.

OM'CfL-CH,-P=00M'' (where M, M' and M2 have the same meanings as above). This is a method of introducing by condensation through reaction.

The carboxylic acid components used to obtain polyester resins and polyurethane resins include terephthalic acid, isophthalic acid, orthophthalic acid, 1. Aromatic dicarboxylic acids such as S-naphthalic acid: p-oxybenzoic acid, p-(
Aromatic oxycarboxylic acids such as (hydroxyethoxy)benzoic acid: succinic acid, adipic acid, azelaic acid, sebacic acid.

Examples include aliphatic dicarboxylic acids such as dodecanedicarboxylic acid, tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid.

Among these, terephthalic acid is preferred.

These are isophthalic acid, adipic acid, and sebacic acid.

Examples of the dicarboxylic acid component containing the sulfonic acid metal base include 5-sodium sulfoisophthalic acid,
Examples include 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, and 2-potassium sulfoterephthalic acid.

Examples of the diol component include ethylene glycol, propylene glycol, 1.3-propanediol, 1.4-butanediol, 1.5-bentanediol, 1.6-hexanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol. ,2
, 2,4-trimethyl-1,3-bentanediol, l
, 4-cyclohexane dimetatool, bisphenol A
Examples include ethylene oxide adducts of hydrogenated bisphenol A, ethylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and/or tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaesothritol can be used in combination.

Examples of the isocyanate component used to obtain the polyurethane resin include 2.4-tolylene diisocyanate, 2.6-tolylene diisocyanate,
p-phenylene diisocyanate.

Diphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate 3.3'-dimethoxy-
4,4'-biphenylene diisocyanate, 4,4'-
Diisocyanate-diphenyl ether, 1. Cornaphthalene diisocyanate, ρ-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanatemethylcyclohexane, 1,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate dicyclohexylmethane, Examples include inphorone diisocyanate.

When modifying a vinyl chloride resin to introduce a sulfonic acid metal base, examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, It is possible to use a vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol concentric polymer, a vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer, and the like.

Vinyl alcohol OH contained in these copolymers
group and the above-mentioned C-C112CII□SO3M.

C - chlorine of a chlorine-containing sulfonic acid metal salt such as CIl, CH, 03OJ, etc., in a polar solvent such as dimethylformamide, dimethyl sulfoxide, etc., to an amine salt such as pyridine, picoline, triethylamine, etc.

It is possible to suitably use a method of carrying out a dehydrochlorination reaction in the presence of a dehydrochlorination agent such as an epoxy compound such as ethylene oxide or propylene oxide.

The molecular weight of the resin (A) is usually 1, s, ooo to 80.
000, preferably from 10,000 to 10,000. If this molecule exceeds go, ooo, the viscosity of the back coat paint will increase beyond the allowable range, leading to an increase in the coefficient of friction of the back coat layer and deterioration of workability during production. be. On the other hand, 1 molecular weight or s, o
If it is less than oo, in the step of applying the back coat paint onto the non-magnetic support and curing it using a curing agent,
Unreacted portions may occur and low molecular weight components may remain, which may deteriorate the physical properties of the coating film.

As a binder in the Hauk coat layer.

In addition to the resin (A), for example, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or mixtures thereof, which have been conventionally used in magnetic recording media, can be used. Ru.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-axolonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. Copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-axolonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin ,
Polyvinyl butyral, cellulose derivatives (cellulose acetate tstylate), cellulose diacetate,
Examples include cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester mlli, vinyl ether chloride-acrylic acid ester copolymers, amino resins, and synthetic rubber-based thermoplastic resins.

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

] i1 The thermosetting resin or reactive resin includes, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and incyane 1. ~ mixtures with prepolymers,
Mixtures of methacrylate copolymers and diisocyanate brevolimers, mixtures of polyester polyols and boisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, and polyamine resins. Can be mentioned.

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

Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, and polyamide acrylic type: ether Examples include polyfunctional monomers such as acrylic type, urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and hydrocarbon type.

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

In this invention, the various resins described above may be used as they are as a binder, but furthermore, a curing agent may be used together with the various resins described above to serve as a binder.

Examples of the curing agent include bifunctional incyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, and trifunctional isocyanates such as Coronate (product name: Nippon Polyurethane Industry V4) and Desmodur Shikki (product name: Bayer). , or polyisocyanate-based curing agents conventionally used as curing agents, such as urethane prepolymers containing isocyanate groups at both ends.

The amount of the curing agent used is usually 5 to 80 parts by weight based on the total amount of binder.

In addition to the nonmagnetic powder and the binder, the back coat layer may contain a dispersant, an antistatic agent, and the like.

Examples of the dispersant include lecithin, phosphoric acid ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfosuccinic acid ester, known surfactants, and salts thereof. Also, the negative function 2 & (for example -
It is also possible to use salts of polymers with COOH2-PO,II> as dispersants.

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

As the 11″I antistatic agent, the carbon tura:
.

Conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponin, and nonionic surfactants such as alkylene oxides and glycidols. Agents: Higher alkylamines: Quaternary ammonium salts, pyridine, other heterocycles, phosphonium or sulfoniums, etc. Cationic surfactants: Acidic acids such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, phosphoric ester groups, etc. Examples include anionic surfactants containing diamino acids, aminosulfonic acids, bifacial active agents such as sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

In addition, in this invention, it is preferable not to use a commonly used lubricant in the back coat layer.

By using a commonly used lubricant, the fi friction coefficient of the back coat layer increases, which may lead to a decrease in running durability such as an abnormality in running due to an increase in torque.

The thickness of the back coat layer is 1, usually 0.1 to 5.0.
It is preferably 0.2 to 3.0 m.

The surface roughness of the back coat layer is preferably 0.05 μm or less in terms of center line average roughness (Ra) of CQj off 0.08 mm in terms of runnability and electromagnetic characteristics.

Such a back coat layer is provided on a nonmagnetic support described below. However, the surface of the nonmagnetic support on which the back coat layer is provided is the other surface of the nonmagnetic support from the surface on which the magnetic layer is provided.

(Nonmagnetic Support) Materials for forming the Moeki nonmagnetic support include, for example, polyethylene terephthalate and polyethylene-2,6-
Mention may be made of polyesters such as naphthalates, polyolefins such as vopropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonates. In addition, metals such as Cu, An, and X-oxide, glass, and various ceramics such as so-called new ceramics (eg, boron nitride, silicon carbide, etc.) can also be used.

There is no particular restriction on the form of the non-magnetic support, and it may be tape-like, sheet-like, cart-like, disk-like, or the like.

The thickness of the non-magnetic support is, for example, usually 1 to 3 to 1100 mm, preferably 5 to 50 mm in the case of a tape or sheet shape, and 1 to 30 mm in the case of a disk or card shape. 〜+00#Lm.

(Magnetic Layer) The magnetic layer is provided on one surface of the nonmagnetic support.

The magnetic layer is a layer formed by dispersing the ferromagnetic powder in a binder.

Examples of the ferromagnetic powder include γ-Fe and 0U.

Co-containing y FQ20y, FQzOa, Co
Containing y-Fe, O, etc. iron oxide magnetic powder, Fe-hexa alloy powder, Fc-A11-P alloy powder, Fe-Ni-
Co alloy powder, Fe-Mn-Zn alloy powder, Fe-N
i-Zn alloy powder, Fe-Go-Ni-Cr alloy powder.

Examples include Fe-Co-N1-P alloy powder, Go-Ni alloy powder, Go-P alloy powder, and ferromagnetic alloy powder containing ferromagnetic metals such as Fe, Ni, and Co as main components.

There is no particular restriction on the shape of the ferromagnetic powder, and for example, it may be acicular, spherical, or ellipsoidal.

There is no particular restriction on the shape of the ferromagnetic powder, and for example, acicular, spherical, or ellipsoidal shapes can be used.

The binder includes, for example, a thermoplastic resin, a thermosetting resin 1-reactive resin, which has been conventionally used in magnetic recording media,
It is possible to use an irradiation curable resin or a mixture thereof, and it is possible to use a resin similar to that used in the back coat layer.

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

In the magnetic layer, in addition to the ferromagnetic powder and binder, a lubricant, an antistatic agent, a hardening agent, etc. can be blended.

Furthermore, if necessary, an abrasive can be added to the magnetic layer.

As the abrasive, for example, fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are used.

The average particle size of these abrasives is usually 0.05 to 5.0.
#Lm.

When blending No. 14 abrasive, the blending ratio of the abrasive is usually 0.5 to 100 parts by weight of the ferromagnetic powder.
~20 scratched parts.

Note that in the back coat layer and the magnetic layer,
The lubricant, the antistatic agent, etc. do not have a single function, for example.

In some cases, the compound acts as a lubricant and an antistatic agent.

Therefore, the above classification in this invention is as follows.

It shows the main effects, and is not limited by the effects of the classified compound or the effects shown in the classification.

Next, a method for manufacturing the magnetic recording medium of the present invention will be explained.

(Manufacturing method, etc.) The magnetic recording medium of Issue 11 can be prepared by, for example, preparing a magnetic paint by kneading and dispersing the magnetic layer forming components such as the ferromagnetic powder and binder in a solvent, and then applying the obtained magnetic paint to the magnetic recording medium. After applying and drying on one side of the non-magnetic support, and cross-dispersing the back-coat layer forming components such as the non-magnetic powder and the binder in a solvent to prepare a back-coat paint, the obtained It can be manufactured by applying a coating material to the other surface of the non-magnetic support and drying it.

Examples of the solvent used for dispersing the magnetic layer forming components include acetone and methyl ethyl ketone (for ME).
, methyl isobutyl ketone (CMIBK) and cyclohexanone; alcohols such as methanol, ethanol, propatool and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol monoacetate; Ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. Halogenated hydrocarbons and the like can be used.

When mixing the composition of the magnetic paint components, the ferromagnetic powder and other magnetic paint components are charged simultaneously or individually into an R kneading machine. for example.

First, the ferromagnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and continued to be roughly kneaded to obtain a magnetic paint.

For crosstalk distribution, various crosstalk machines can be used, such as Miki roll mill, Miki roll mill, ball mill, pebble mill, side grinder, Sqegvari attritor, high speed impeller disperser, high speed stone mill, high speed speed impact mill,
Disper kneader 1 high speed mixer, homogenizer,
Examples include ultrasonic dispersion machines.

The coating solution of the magnetic layer forming component thus prepared is coated on one side of the non-magnetic support by a known method.

The back coat layer forming component can also be prepared by the same method as the magnetic layer forming component, and the coating liquid of the back coat layer forming component is applied to the other surface of the nonmagnetic support by a known method.

Application methods that can be utilized in this invention include, for example, gravure roll coating, wire per coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeegee coating, kiss coating, and fan coating. Examples include tin coating.

After the magnetic layer-forming components and backcoat layer-forming components have been applied in this way, a magnetic field orientation treatment is performed as necessary in an undried state, and a surface smoothing treatment is usually performed using a super calender roll or the like.

The magnetic recording medium of the present invention can be obtained by performing the above-described surface smoothing treatment and then cutting the medium into a desired shape.

The magnetic recording medium of the present invention can be used, for example, by cutting it into a long shape, as a magnetic tape such as a video tape or audio tape, or by cutting it into a disk shape.
It can be used as a floppy disk or the like6.Furthermore, it can also be used in a cart-like, cylindrical, or other form like a normal magnetic recording medium.

[Example] Next, the present invention will be described in more detail by showing χ examples and comparative examples of the present invention.

In addition, in the examples and comparative examples described below, "
"Parts" means "parts by weight."

(Example 1) A magnetic paint was prepared by mixing and dispersing the following 31N magnetic layer composition using a ball mill, adding 6 parts of a polyfunctional isocyanate as a hardening agent, and filtering with a 1Bm filter. did.

CO-containing γ-Fe, Oyu......Polyurethane...Vinyl chloride-vinyl acetate copolymer/Butyl stearate...Myristic acid・・・・・・・・・・・・ Stearic acid・・・・・・・・・・ Alumina・・・・・・・・・・・・ Carbon fiber・・・・・・ Lecithin・・・・・・・・・・・・ Cyclohexanone・・・・・ 100 parts・・8 parts・・12 parts・ 0.8 parts・ 0.5 parts・ 0.5 parts・・5 parts・ 0 .5 parts...4 parts...40 parts Methyl ethyl ketone...60 parts Toluene...60 parts The obtained magnetic coating liquid was rolled on a reverse roll. Using a coater, coat one side of a polyethylene terephthalate film with a thickness of 1:1#Lm to a dry thickness of 4.5 JLm after calendering, remove the solvent under heating, and apply it to a supercalenter to make a surface monitor. A smoothing process was performed.

Next, a back coat paint was prepared by dispersing the back coat layer composition having the composition shown in Table 1 using a ball mill for 24 hours.

The obtained back coat paint liquid was dried using a reverse roll coater to a thickness of 1. A back coat layer was formed by coating the polyethylene terephthalate film on the side on which the magnetic layer was provided and on the other side so that the film had a film thickness of Ogm.The solvent was removed under heating to form a back coat layer.

Next, Jujutsu PJ! A sample tape was prepared by slitting it into a 1/2 inch width using a machine.

(a) Pack the sample tape into a VIIS cassette and place the NV-6200 (
The bus was run 200 times using a deck (manufactured by Under-Desk Electric). Regarding the tape (200 pass tape), the output fluctuation range, dynamic friction coefficient of the back coat layer, dropout, skew, and jitter were measured, and tape damage and back coat layer abrasion were visually evaluated.

In addition, the dynamic friction coefficient and dropout of the back coat layer were measured for the sample tape (virgin tape) that had not been run yet.

In addition, the measurement of each characteristic was performed as follows.

Output fluctuation range: Under conditions of temperature 20°C and humidity 60%.

The width of the output fluctuation during reproduction of the 200-pass tape was determined.

Dynamic friction coefficient: Under the conditions of temperature 23°C and II degree 60%, the running performance tester manufactured by Yokohama System Co., Ltd. (TDT-: 100-
D), set the inlet tension to 20g, and wrap the sample tape 180° around a stainless steel pin with a diameter of 3.8@s: 1. :lea/second, and the exit tension of -minute diameter was measured and calculated from the following equation (3).

Dropout: Measured using a VTR dropout counter (manufactured by Shibaku Corporation).

Skew measurement: The color bar signal was recorded on a sample tape and was run using a video deck (HR-6500, manufactured by Victor Japan) under conditions of a temperature of 40℃ and a humidity of 80%, and the number of times was 200. When this happens, the distortion of the image at the switching point on the monitor screen is expressed in 3-seconds.

Jitter measurement: Sample tape after running 200 times on VTR
It was measured using a jitter measuring meter (manufactured by Ikkoku Electric Co., Ltd.).

The living room adhesion test was conducted as follows. Wrap a 1/2 inch wide tape with a pressure of 1 kg (b), leave it for 20 hours at a temperature of 60°C, and a humidity of 80%, then leave it at room temperature for another 24 hours, unwind it, and measure the resistance when it is pulled apart. Those that were present were evaluated as yes, and those that were not were evaluated as none.

(C) The surface roughness [Ra] of the back coat layer surface was measured as follows. Three-dimensional roughness measuring instrument SE-:IF
(manufactured by Kota Research Institute) with a cutoff of 0.25 and a stylus force of 3hg.
It was determined by measuring 2.51 lengths of the sample surface (back coat layer surface).

(d) Chroma S/N was measured as follows.

+11-7100 (manufactured by Japan Victor ■) was used to record at a maximum recording current of 4.5 Mtlz, and the noise voltage during reproduction was measured.

The results are shown in Table 2.

(Examples 2 to 4 and Comparative Example 1.2) Prototype tapes were prepared in the same manner as in Example 1, except that the back coat layer composition having the composition shown in Table 1 was used. The quality was measured using the following methods.

The results are shown in Table 2.

or metal salts.

(Evaluation) As is clear from Table 2, in the magnetic recording medium of the present invention, the non-magnetic powder is uniformly dispersed in the back coat layer, and the bonding force between the non-magnetic powder and the binder is large. The surface of the back coat layer has moderate roughness, the coefficient of friction is small, there is very little abrasion of the back coat layer or damage to the tape, and there are very few dropouts. Furthermore, it has excellent skew and jitter characteristics due to stable running, small output fluctuation range, no deterioration of chroma S/N, sufficient durability, and good electromagnetic conversion characteristics.

[Effects of the Invention] According to this invention, (1) the back coat layer containing carbon black provides an antistatic effect and a light shielding effect, and (2) the nonmagnetic powder is sufficiently and uniformly dispersed. However, it is possible to form a back coat layer with a large bonding force between the non-magnetic powder and the binder. (3) Due to the moderate roughening effect of the back coat layer,
It has excellent running performance, excellent durability, and good electromagnetic conversion characteristics.

(4) Even when dealing with high-density recording, it is possible to provide a magnetic recording medium that has advantages such as excellent running properties, excellent durability, and the ability to realize good electromagnetic conversion characteristics. Ru.

Claims (1)

[Claims] (1) Non-magnetic material comprising carbon black with an average primary particle size of 20 to 40 mμ, carbon black with an average primary particle size of 50 to 100 mμ, and zinc oxide powder with an average particle size of 0.5 to 1.0 μm. A magnetic recording medium comprising a back coat layer containing powder and a resin having a negative functional group.