JPH0388120A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the mechanical strength, coatability, surface characteristics, etc., of magnetic layers by using binders having specific groups at the time of dispersion of ferromagnetic powders into the magnetic layers and specifying the molar number of the groups thereof with the upper magnetic layer and the lower magnetic layer. CONSTITUTION:The magnetic layers consisting of the upper layer and the lower layer are provided on a nonmagnetic base. A resin contg. ferromagnetic powder and the negative functional group-contg. binder is used for the upper layer. The resin contg. the Co-contg. Mn iron oxide and the negative functional group- contg. binder is used for the lower layer. The molar number of the negative functional group of the binder per unit magnetic powder weight in the upper layer is so determined as to be equal to the molar number of the negative functional group in the binder of the lower layer or above. The mechanical strength, coatability, surface characteristic, adhesiveness to the base, etc., of the magnetic layers are improved in this way and particularly the electromagnetic conversion characteristics and the traveling stability are improved. Drop- outs and edge breakage are reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium, and more specifically, the dispersibility of ferromagnetic powder is improved, and it has excellent characteristics characterized by electromagnetic conversion characteristics, such as video tape. The present invention relates to a magnetic recording medium that enables high-quality recording and reproduction when used for.

[Conventional technology 1 Problems to be solved by the invention] In recent years, magnetic recording media have been increasingly used in other fields along with product development, and accordingly, strict requirements have been placed on the characteristics characterized by electromagnetic conversion characteristics. It started to be done.

For this reason, various studies have been made regarding binders, which are one of the magnetic materials.

As a binder traditionally used for filling ferromagnetic powder,
Cellulose derivative, vinyl chloride-vinyl acetate copolymer,
Polyurethane, acrylic resin, copolymers thereof, epoxy resin, phenoxy resin, polyester, etc. are known.

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

As an example, the comparatively recently released Japanese Patent Publication No. 1-10
5320 discloses a combination of polyurethane and vinyl chloride-vinyl acetate copolymer as a binder that also serves as a dispersant.

However, despite these combinations, the dispersibility of the binder, the surface properties of the magnetic layer, the abrasion resistance, etc. required for magnetic recording media have not yet been satisfied.

On the other hand, recently, by atomizing ferromagnetic powder, S/
Attempts have been made to increase the N ratio or to densely fill the magnetic layer with ferromagnetic powder, but on the other hand, the strength of the magnetic layer deteriorates, or dropouts occur when the magnetic recording medium is made into tape. There are many cases of edge bending.

The purpose of the present invention is to improve the mechanical strength, coating properties, surface properties, adhesion to a support, etc. of a magnetic layer by filling a specific binder with high density of ferromagnetic powder with excellent dispersibility. It is an object of the present invention to provide a magnetic recording medium which is improved and has particularly excellent electromagnetic conversion characteristics and running stability, and which can significantly reduce dropouts and edge bending.

[Means for Solving the Problems] The present invention has a magnetic recording medium having a magnetic layer consisting of an upper layer and a lower layer on a non-magnetic support, in which the upper layer contains a ferromagnetic powder and a binder containing a negative functional group. At the same time, the lower layer contains cobalt-containing gamma iron oxide and a binder containing a negative functional group, and the number of moles of the negative functional group of the binder per unit weight of magnetic powder in the upper layer is greater than the number of moles of the negative functional group of the binder in the lower layer. The number of moles is equal to or greater than the number of moles. The present invention will be explained in more detail below.

The magnetic recording medium of the present invention has a magnetic layer consisting of an upper layer and a lower layer on a non-magnetic support.

The magnetic layer is a layer made of ferromagnetic powder dispersed in a binder or the like.

In order to achieve the object of the present invention, a resin containing a negative functional group is used as a binder.

Suitable examples of the negative functional group include -503M, -0S
Os M, -COOM, -PO(Ou')g (however,
M is hydrogen or an alkali metal, M' is hydrogen or an alkali metal, or a hydrocarbon group), and in the present invention, a resin containing at least one kind of negative functional group selected from these can be used.

Moreover, what is important in the present invention is that the number of moles of negative functional groups of the binder per unit magnetic powder in the upper magnetic layer and the lower magnetic layer has specific conditions. That is, the number of moles of the former must be equal to or greater than the number of moles of the latter.

If this condition is not met, a well-balanced improvement effect on the properties of the magnetic layer, especially the mechanical strength, coating properties, surface properties, electromagnetic conversion properties, and running durability of the magnetic layer will not be achieved, and the effect of reducing dropouts etc. will not be achieved. I can't even see it.

In addition, when using a binder that does not have the above-mentioned negative functional group,
A magnetic recording medium with sufficient output characteristics cannot be obtained.

Traditionally, examples of resins used as binders include vinyl chloride resins, vinyl acetate resins, cellulose resins, urethane resins, ester resins, butadiene resins, epoxy resins, phenoxy resins, and acrylic resins. Are known.

In the present invention, among these resins, one or more resins having the negative functional groups introduced therein can be used. Particularly preferred are vinyl chloride resins having the negative functional groups and polyurethane resins having the negative functional groups.

The reason is that the vinyl chloride resin having the negative functional group and the polyurethane resin having the negative functional group are particularly effective in improving the dispersibility of the ferromagnetic powder in the magnetic layer and achieving high electromagnetic conversion characteristics. This is because it is effective.

The negative functional group is a vinyl alcoholic hydroxyl group contained in the vinyl chloride resin, and C1-CII2CHt R [where R is -So, M,
-0303M, -COOM, -RO (representing OM'>2 (however, M and M' represent the same meanings as above), etc.). Vinyl chloride is produced by a dehydrochlorination reaction in a polar solvent such as phoxide in the presence of a dehydrochlorination agent such as an axon salt such as pyridine, picoline, or triethylamine, or an epoxy compound such as ethylene oxide or propylene oxide. It can be introduced into the system resin.

Moreover, the gold mM in this negative functional group is an alkali metal such as lithium, potassium, or sodium,
Particularly, potassium is preferable in terms of solubility, reactivity, yield, and the like.

Examples of vinyl chloride-based resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Vinyl-vinyl propionate-vinyl maleate-acrylic glycidele ether-(2-acrylamido-2-methylpropane potassium)-(allyl-
Vinyl chloride copolymers such as (2-hydroxypropyl ether) copolymers can be used.

A vinyl chloride copolymer having a negative functional group can also be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable heptamer containing the above-mentioned negative functional group, and, if necessary, another copolymerizable hetamine. be able to. Since this copolymer is based on vinyl synthesis, it is easy to manufacture, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The copolymerizable heptad containing the negative functional group is, for example, C1l*-CtlCLR cH, -C(CH3)CIl, R CIl*=CHCH0COCtl(CH*C00R)
RCllffi-CIICH,OCH,CH(Oll
)CH, RcH! -C(CHi)COOC,H,RCH
Examples include *-CHCooCJaR CH*lICIC0NIC(CHz)*CHJ.

[However, R represents the same meaning as above.] Also, examples of copolymerizable monomers to be copolymerized as necessary include various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, Methacrylic acid, various acrylic esters, methacrylic esters, ethylene, propylene, isobutyne,
Examples include butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic ester, and the like.

Next, the polyurethane resin containing the negative functional group is prepared by using three types of compounds: a dicarboxylic acid containing a negative functional group, a dicarboxylic acid not containing a negative functional group, and a diol, and a diisocyanate. It can be obtained by a condensation reaction and an addition reaction.

Furthermore, in addition to the above method, a method of modifying the polyurethane resin itself to introduce a negative functional group may also be considered.

In other words, these polyurethane resins.

C-CH.

A compound containing the above negative functional group and chlorine in the molecule, such as CH2S03C-CH,-COOM (wherein M and M' have the same meanings as above), is reacted with a dehydrochloric acid reaction. This method involves condensation and introduction.

The carboxylic acid component used to obtain the polyurethane resin includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-nuclic acid; p-oxybenzoic acid, p-(hydroxyethoxy )
Aromatic oxycarboxylic acids such as benzoic acid; succinic acid, adipic acid.

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

Among these, preferred are terephthalic acid, isophthalic acid, adipic acid, and sebacic acid.

As the dicarboxylic acid component containing the negative functional group,
Examples include 5-sodium sulfoisophthalic acid, 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, diethylene glycol, 2 ，
2.4-trimethyl-1,3-opentanediol,
l,4-cyclohexane dimetatool, ethylene oxide adduct of bisphenol A, hydrogenated bisphenol A
ethylene oxide adduct, polyethylene glycol,
Examples include polypropylene glycol and polytetramethylene glycol. Also, trimethylolethane,
Tri- and/or tetraols such as trimethylolpropane, glycerin, and pentaerythritol can also be used in combination.

The isocyanate component used to obtain the polyurethane resin includes, for example, 4,4-diphenylmethane diisocyanate, 2,4-)-lylene 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, 1,3-naphthalene diisocyanate, p-xylene Examples include diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanatemethylcyclohexane, 1,4-diisocyanatemethylcyclohexane, 4,4'-diisocyanatedicyclohexane, 4,4'-diisocyanatedicyclohexylmethane, and isophorone diisocyanate.

When the negative functional group is a metal salt, the metal is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferred in terms of solubility, reactivity, yield, etc.

Examples of the copolymerizable polymer containing a sulfonate as the negative functional group include CH, -CH5O
J CHI-CHCHJOJ CI4. Tomi C (CHs) CHtSO3MCH*-CHC
H*0COCH(CHtCOOR) SOsMCH*-
CHCHtOCH*CH(OH)CIl*SOs厘CH
*-C(CHi)COOCJJOJtJ,-CHC00
Examples include C411aSOJ CH*-CHCoNHC(CHs)tcHJOJ [where M in the formula is the same as above].

In addition, as a phosphate, CHm-CHCH*OCH*CH(OH)CHI-0-
POJ'Y'CH, CHCONHC (CHi) CHI
-0-POJ'Y Spirit CH*-CICH*0(CHI(:
HtO)-PO3M"X" [However, in the sulfonate and phosphate, Ml represents an alkali metal, Yl represents a hydrogen atom Ml, and CH, -CHCH,
0C) IICI(OH)CH, -,
Y2 is a hydrogen atom, Mt, and CI, -CICONI (
C(CH3)represents either CHI-, and OM
', and I2 represents C1, -CH-Cl1.
-0-(CH, CH, O), -, OHg and OM', and m and n are integers of 1 to 100. ] In addition, as copolymerizable polymers to be copolymerized as necessary, for example, various vinyl esters, vinylidene chloride,
Acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, various acrylic esters,
Examples include methacrylic acid ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The binder in the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In either method, if necessary, a molecular weight regulator 1 a polymerization initiator,
Known techniques such as divisional addition or continuous addition of seven snails can be applied.

The molecular weight of the polyurethane resin is preferably 2.0
00-70,000, especially 4,000-so, ooo.

If this molecular weight exceeds 70,000, the viscosity of the magnetic coating material becomes unacceptably large, and the object of the present invention may not be achieved. On the other hand, if the molecular weight is less than 2000, unreacted portions will occur during the step of applying the magnetic paint onto a non-magnetic support and curing it using a curing agent, resulting in low molecular weight components remaining. May deteriorate the physical properties of the film.

In this R1 light, the blending ratio of the binder is 10% of the ferromagnetic powder.
1 to 0 parts by weight, usually 5 to 40 parts by weight, preferably 10 to 30 parts by weight.

By keeping this blending ratio within the above range, it is possible to improve the dispersion rate while maintaining a good dispersion state of the ferromagnetic powder in the magnetic layer.

In the present invention, the durability of the 1-meter layer can be improved by adding a polyisocyanate curing agent together with the polyurethane resin to the binder.

Examples of the polyisocyanate curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name: manufactured by Nippon Polyurethane Industries), and Desmodur L (trade name: Bayer Co., Ltd.! 1).
Trifunctional isocyanates such as trifunctional isocyanates, or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, and polyisocyanates that can be used as curing agents are all used. be able to.

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

The mixing ratio of the ferromagnetic powder and the binder in the magnetic layer is usually 1 to 200 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the ferromagnetic powder.

If the amount of binder blended is too large, the blended amount of ferromagnetic powder may be lowered and the recording density of the magnetic recording medium may be lowered. If it is too small, the strength of the magnetic layer may be reduced and the magnetic recording medium may be The running durability of the vehicle may be reduced.

In the present invention, the binder containing the above negative functional group can be used in combination with a known binder not containing a 6-negative functional group.

In that case, the weight ratio of the former to the latter is 2298
~98:2, preferably 5:95~g525. If the blending amount is out of the above range, the electromagnetic conversion characteristics of the magnetic recording medium may deteriorate or the dispersibility of the ferromagnetic powder may be impaired.

1. Ferromagnetic Powder 1. In the magnetic recording medium of the present invention, a known ferromagnetic powder is used for the upper magnetic layer, and a cobalt-containing gamma iron oxide (CO-coated powder) is used for the lower magnetic layer. Fs*
Os) is used.

The known ferromagnetic powder is, for example, Co-coated powder.
Fe, 03 powder, Co-coated Fe50. Powder, Co-coated Fe0x (4/co<x<3/2) powder, Fe-A metal powder, Fe-Ni metal powder, Fe-An-Ni metal powder, Fe-AIL-P metal powder, Fe- Ni-Ai metal powder, Fe-Ni-34-All-Mn metal powder, N
i-Co metal powder, FeJn-Zn metal powder, Fe-
Examples include old-Zn metal powder, Fe-Co-Ni-Cr metal powder, Fe-Co-N1-P metal powder, Go-Ni metal powder, and Co-P metal powder.

Among these, preferred are Co-coated-Fe, 0.
It is a powder.

Also, from the point of view of coercive force (Hc), preferably 30
A ferromagnetic powder with a coercivity of 0 or more, particularly 400 or more is desirable, and each of the metal powders mentioned above satisfies these coercive force conditions.The specific surface area of this ferromagnetic powder is preferably 25m in BET value. /g or more, especially 3
When the specific surface area of the 0 ferromagnetic powder is preferably within the range of 0 to 70 m''/g, monodispersity is good and noise in the reproduced signal can be reduced.

Note that the shape of the ferromagnetic powder is not particularly limited, and for example, needle-like, columnar, or ellipsoidal shapes can be used.

In the magnetic layer containing at least the ferromagnetic powder or cobalt-containing gamma iron oxide and the binder, the average filling rate of the ferromagnetic powder (the average weight of the ferromagnetic powder present in a unit volume of the magnetic layer) is Preferably 2 g/cm" or more, particularly preferably a depth of 1 g/cm" from the surface on the non-magnetic support side.
By setting the average filling rate of the ferromagnetic powder in the range of 3 to 5 g/cm'' in the range of 3 to 5 μm, particularly in the range from the surface on the non-magnetic support side to a depth of l←m, for example, It is possible to improve the reproduction output of signals on the wavelength exceeding side such as color signals.

Other Components - In the present invention, it is preferable that the lower layer contains a non-magnetic powder with a Mohs hardness of 6 or more, which is less than 1/2 of the upper layer by weight relative to the ferromagnetic powder, since this improves the chroma audio output. .

Examples of the non-magnetic powder include lubricants, abrasives, antistatic agents, and the like.

Examples of the lubricant include bridge lubricants such as carbon black, graphite, carbon black graft polymers, molybdenum disulfide, and tungsten disulfide.

Among these, carbon black is preferred.

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

The amount of the lubricant used is 100 jl of the ferromagnetic powder (usually 0.05 to 10 parts by weight per imaging unit).

Examples of the polishing agent include aluminum oxide, titanium oxide (TjO, TiO□), and silicon oxide (SiO1S).
Examples include inorganic powders such as iO□), silicon nitride, chromium oxide, and boron carbide, and organic powders such as benzoguanamine resin powder, melamine resin powder, and phthalocyanine compound powder.

The average particle diameter of the abrasive is usually 0.1 to 1.0 m.
is within the range of

Further, the amount of the abrasive is usually in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder.

Examples of the antistatic agent include carbon black,
Examples include conductive powders such as graphite, tin oxide-antimony oxide compounds, tin oxide-titanium oxide-antimony oxide compounds, and carbon black graft polymers.

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

The amount of the antistatic agent added is usually 0.5 to 20!1 parts by weight per 100 parts by weight of the ferromagnetic powder.

Note that the lubricant, antistatic agent, etc. do not have a single function; for example, one compound may act as a lubricant and an antistatic agent.

Thickness of one magnetic logging - The thickness of the magnetic layer having the above structure is usually 4JLm or less, preferably 2←m or less. This thickness is 41Lm
If it exceeds 1, the adhesion between the magnetic recording medium of the present invention and the magnetic head may deteriorate, resulting in a decrease in output.

(Nonmagnetic Support) Materials for forming the nonmagnetic support include, for example, polyethylene terephthalate and polyethylene-2,6.
- Polyesters such as naphthalates, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamides and polycarbonates. Furthermore, Cu, AJl, Zn
Various ceramics such as metals such as glass, so-called new ceramics (for example, 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, card-like, disc-like, drum-like, etc., and various materials may be used depending on the form and as necessary. can be selected and used.

When the support is in the form of a tape or sheet, the thickness is preferably 3 to 1100p, particularly preferably 3
~50#Lm. Moreover, in the case of a disk shape or a cart shape, it is preferably 30 to 11007L. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

A back coat layer may be provided on the surface (back surface) of the nonmagnetic support on which the magnetic layer is not provided for the purpose of improving the running properties of the magnetic recording medium, preventing electrification, preventing transfer, and the like.

Furthermore, an intermediate layer (for example, an adhesive layer) may be provided on the surface of the nonmagnetic support on which the magnetic layer is provided, for the purpose of improving the adhesion between the magnetic layer and the nonmagnetic support.

(Method for manufacturing a magnetic recording medium) The magnetic recording medium of the present invention is produced by preparing a magnetic paint by cross-dispersing ferromagnetic powder, a binder, etc. in a solvent, and then applying the magnetic paint onto a non-magnetic support and drying it. It can be manufactured by

Examples of the above solvent include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (purchased from IBK
) and ketones such as cyclohexanone: methanol,
Alcohols such as ethanol, propatool and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, propyl acetate and ethylene glycol heptanoacetate; ethers such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, etc. System: Aromatic hydrocarbons such as benzene, toluene and xylene; Halogenated hydrocarbons such as methylene chlorite, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, etc. can be used.

To cross-wire the magnetic paint components, the ferromagnetic powder and other magnetic paint components are charged simultaneously or individually into a cross-wire machine. For example, first, the magnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined period of time, the remaining components are added and mixing is continued to obtain a magnetic paint.

Various types of crosstalk devices can be used to disperse crosstalk. Examples of this mixing machine include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sight grinder, a Sqegvari attritor, a high-speed impeller dispersion machine, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer, a homogenizer, Examples include ultrasonic dispersion machines.

Note that a dispersant can be used for the crosstalk dispersion of the ferromagnetic powder.

Examples of the dispersant include lecithin, phosphoric acid ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, and
Ocuccinic acid, sulfosuccinic acid esters, known surfactants, salts thereof, organic groups such as -COO
H, -PO311) salts of polymer dispersants, and the like.

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

The amount of the dispersant added is usually 1 to 20 parts by weight per 100 parts by weight of the ferromagnetic powder.

The magnetic paint thus prepared is coated onto a non-magnetic support by a known method.

Coating methods that can be used in the present invention include, for example, gravure roll coating, knife coating, wire bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, calendar coating, squeegee coating, -V Examples include scoating and fantin coating.

The thickness of the magnetic layer coated in this way is usually 0.1 to 1107 z in terms of dry thickness.

Further, back coating may be applied to the back surface of the support in order to protect the support, prevent m'at, and improve runnability.

After applying the magnetic paint 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.

Next, a magnetic recording medium can be obtained by cutting into a desired shape.

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

In the present invention, since a specific bond cutting is used under specific conditions, ferromagnetic powder can be blended into the magnetic layer with high packing density and excellent dispersibility. As a result, a magnetic layer with excellent mechanical strength, coating properties, surface properties, and adhesion to the support can be obtained.

The magnetic recording medium of the present invention has particularly excellent electromagnetic characteristics and durability, and is less prone to dropouts, sliding noise, and edge bending.

[Example] Next, the present invention will be described in more detail based on Examples and Comparative Examples. In addition, in the following, "parts" are "parts by weight"
shall represent.

(Examples 1 to 9, Comparative Examples 1 to 10) The upper layer composition and lower layer composition shown below were mixed and dispersed in the following manner to prepare a magnetic paint for the upper layer and a paint for the lower layer. However, the vinyl chloride copolymer (a) in the upper layer composition and the vinyl chloride copolymer (b) in the lower layer composition
) was changed in 19 ways as shown in Table 1.

Upper Me 1 Fe-Al ferromagnetic metal powder...100 parts (electromagnetic crab 1600 o e, specific surface area: 65 m"/g) Vinyl chloride copolymer containing sodium salt of sulfo group (a)... 10 parts Thermoplastic polyurethane resin 7 parts (XE-I-2 manufactured by Saiji Yakuhin Co., Ltd.) α-Ai 20 parts ・ ・ ・ ・ ・ ・ ・ ・ ・
・ ・ 5ill stearic acid・・・・・・・・・
◆・ 1 part butyl stearate・・・・・・・・・
1 part methyl ethyl ketone 150 m
Cyclohexanone: 80 parts Toluene: 120 parts The upper layer composition was thoroughly mixed in a sand mill, and a polyfunctional isocyanate (Coronate manufactured by Nippon Polyurethane Co., Ltd.) was added to the mixture. A magnetic paint for the upper layer was prepared by adding and mixing 3 parts of L).

This upper layer magnetic paint had excellent stagnation stability.

Technique 1" υ Shark koji containing cobalt - γ-Fe, O, ... 100 parts ferromagnetic powder (electromagnetic crab 800 o e, specific surface area 50 m"/
g) Vinyl chloride copolymer containing sodium salt of sulfo group (b)... 10 parts Thermoplastic polyurethane (mentioned above)... 7 parts α-A1203
・・・・・・・・・ 5 parts stearic acid・・・・
・・・・・・・・・1 part methyl ethyl ketone・・・・・・
...110 parts cyclohexanone...
・70 parts toluene・・・・・・・・・・・・11
0 The lower layer composition was thoroughly mixed with a sand mill, and 2 parts of the polyfunctional isocyanate (mentioned above) were added and mixed to the mixture to prepare a magnetic paint for the lower layer.

In addition, this magnetic paint for the lower layer had excellent stagnation stability.

Next, use magnetic paint for the upper layer and magnetic paint for the lower layer to a thickness of 1
Heavy N was coated on a 4JLm polyethylene terephthalate support using a precision extrusion coater, and after orientation treatment in a magnetic field, it was dried, and after supercalender treatment, a back coat layer was formed on the back surface of the support. did.

The thickness of the magnetic layer of the laminate obtained in this way was 0.5 mm for the upper layer.
The thickness of the lower layer was 2.6←m, and the thickness of the back coat layer was 0.7 Im.

Next, this laminate was slit into 1/2 inch width to prepare a videotape, and its video tape properties were measured.

The results are shown in Tables 2 and 3.

In addition, the strength characteristics were measured as follows.

Electromagnetic conversion characteristics: RF output, Lumi S/N, and chroma output were measured using a video deck and a Shibasou 25D-1 as a noise meter.

Dropout; In the HR-57000, the average value of the dropout number (155 end S, -14dB) of the 100% white signal for 1 minute is calculated using the dropout counter (VHO).
IBz).

Running durability: Playback of the entire length of 2 hours was set as 1 bus on a video deck at 40° C. and 70% RH, and repeated rewinding and playback was performed up to a maximum of 400 buses.

Coating properties: A coating that could be coated uniformly to a predetermined coating thickness and had no coating failures was rated A. When the sample was visually inspected after coating, fine streaks were seen, and compared to A, Gross (
6G@) was rated B if it decreased by 10 or more. C was given to cases in which coating streaks occurred frequently and coating was virtually impossible, or cases in which the heat roll of the calendar was stained over the entire surface and it was virtually impossible to obtain a sample.

Surface roughness: Ra was measured using Surfcom I 500A manufactured by Tokyo Seimitsu Co., Ltd. with a cutoff of 0.08 mm.

(Hereinafter, blank space) As is clear from Tables 2 and 3, the magnetic recording medium of the present invention has significantly superior electromagnetic conversion characteristics (especially at room temperature), running stability, and mechanical properties compared to those of the comparative example. It can exhibit high mechanical strength (especially under high temperature and high humidity conditions).

It is also excellent in terms of low dropout, surface roughness of the magnetic layer, coatability, etc.

It was also confirmed that there was significantly less sliding noise and edge breakage.

[5P, bright effect] According to the present invention, a binder having a specific group is used when dispersing the ferromagnetic powder in the magnetic layer, and moreover, the number of moles of the group (per unit magnetic powder) is lower than that in the upper magnetic layer. and the lower magnetic layer, it is possible to provide a magnetic recording medium with particularly excellent electromagnetic characteristics, durability, mechanical strength, and significantly less dropouts and edge bending.

Claims (1)

[Claims] (1) In a magnetic recording medium having a magnetic layer consisting of an upper layer and a lower layer on a non-magnetic support, the upper layer contains a ferromagnetic powder and a binder containing a negative functional group, and the lower layer contains cobalt-containing gamma iron oxide. and a binder containing a negative functional group, and the number of moles of the negative functional group of the binder per unit weight of magnetic powder in the upper layer is equal to or greater than the number of moles of the negative functional group of the binder in the lower layer. magnetic recording media.