JPH04195721A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high memory capacity and a high record/playback output and improve durability by a method wherein a non-magnetic layer made mainly of carbon black and a magnetic layer containing specific magnetic particles and having a specific thickness are provided and, further, the ratio of the quality of all binder in the magnetic layer is adjusted to not be larger than a specific value. CONSTITUTION:A non-magnetic layer made mainly of carbon black is provided on a non-magnetic supporter 1 and, further, a magnetic layer which contains magnetic particles which are plate-shaped and have easy-to-magnetize axes approximately perpendicular to the plate surfaces and has a thickness of 0.1-4.0 mum is provided on the layer 2. At the same time, the ratio of the quantity A of all binder in the non-magnetic layer 2 to the quantity B of all binder in the magnetic layer 4, i.e. A/B, is adjusted to be not larger than 7. That is, the non-magnetic layer 2 which is a conductive layer containing carbon black and the magnetic layer 4 containing ferromagnetic barium ferrite particles are applied to the non-magnetic supporter 1 in this order. With this constitution, a high memory capacity and a high record/playback output can be obtained and durability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium suitably used as a magnetic recording medium for a floppy disk.

[Prior Art and Problems to be Solved by the Invention] Magnetic recording media generally consist of a polymeric material called a binder (F#1 resin material) on a non-magnetic support. Magnetic paint is obtained by uniformly dispersing body powder, abrasives, antistatic agents such as carbon black, lubricants, curing agents, and other additives, and adding appropriate solvents as necessary. , coated on a support and dried.

In recent years, there has been a strong demand for increasing the storage capacity and recording/reproduction output of 1M1 recording media.

In order to increase storage capacity, it is necessary to increase the information recording density per unit area of the magnetic recording medium, and to increase the information recording density, the write magnetic flux generated from the magnetic head must be concentrated in a small area. Heads must be made smaller and the amount of magnetic flux generated must be reduced. Therefore, in order to reverse the direction of magnetization with a minute amount of magnetic flux, it is necessary to reduce the thickness of the magnetic layer.

Furthermore, in order to increase the recording and reproducing output, it is necessary to increase the residual magnetic flux of the magnetic layer, and it is necessary to increase the thickness of the magnetic layer.

However, increasing the thickness of the magnetic layer deteriorates high frequency characteristics. Therefore, in order to increase the residual magnetic flux and improve the high frequency characteristics, it is necessary to make the Mim layer thinner and to increase the coercive force of the magnetic material.

Furthermore, in order to prevent the low frequency characteristics from deteriorating, a magnetic recording medium is developed in which a thin magnetic layer made of a high coercive magnetic material is provided on a thick magnetic layer made of a magnetic material with a relatively low coercive force and a large residual magnetic flux. requested.

In JP-A No. 62-212933, when providing a thin magnetic layer consisting of at least two magnetic layers on a magnetizable support and with the dry film of the outermost layer being 2 μJl or less, simultaneous multilayer coating is applied. It is stated that a magnetic recording medium with high characteristics can be obtained by providing at least two or more magnetic layers simultaneously and applying a magnetic field while the material is undried.

However, it has been known that binders play an important role in the dispersion of strong FFI powders, and vinyl chloride resins and nitrocellulose are used in combination with polyurethane, which is a relatively soft binder.

However, with these binder combinations, 1Mi
There is a problem that the surface roughness, TS/N, and C5,/N of the magnetic layer are somewhat insufficient.

Therefore, in the binder composition of the conventional multi-layer structure, all the binders contained in both the upper layer (25a layer) and the lower layer (1fB layer) are used in an equal ratio to the ferromagnetic powder (for example, 212993, Japanese Patent Application Laid-open No. 54-145104, etc.), and the total binder used in the upper layer is used in a considerably larger amount than the total binder used in the lower layer (Japanese Patent Application Laid-Open No. 58-56231). Publication No.).

However, if the binder is used in the same ratio for both the soil layer and the lower layer, the surface roughness of the m-type layer is good, but there is a problem that (2) S/N and C5/N are not integrated.

Furthermore, if there is a large difference in the amount of total binder used in the upper and lower layers of the magnetic layer, the surface roughness will also deteriorate, resulting in TS/N,
There is also the problem that the C/S/N deteriorates to N chopsticks.

On the other hand, as mentioned above, when forming two magnetic layers by applying the magnetic layer paint by simultaneous multilayer coating,
Differences in density caused by the inorganic filler contained in the magnetic paint, BET between carbon black and magnetic powder, and large differences in the amount of binder caused by differences in the amount of oil supplied can deteriorate coating properties, resulting in a single layer. There is a problem in that the disturbance at the boundary surface is reflected on the surface of the magnetic layer, deteriorating the surface properties of the magnetic recording medium and deteriorating the electromagnetic conversion characteristics.

The present invention has been made based on the above circumstances.

The purpose of the present invention is to increase storage capacity and recording/playback output,
An object of the present invention is to provide a magnetic recording medium with improved resistance to I-contamination.

[107 Steps to Solve Problem 1iii] The invention as set forth in claim 1 to achieve the above object provides a method of providing a nonmagnetic layer containing carbon black as an -r component on a nonmagnetic support. , and further thereon, a film thickness l~4.0 containing magnetic particles having a flat plate shape and whose axis of easy magnetization is approximately perpendicular to the flat plate surface.
A magnetic layer of Bm is provided, and the ratio A/B of the total binder content (A) in the nonmagnetic layer to 1ffi (B) of the total binder in the magnetic layer is 7 or less. It is a magnetic recording medium.

Further, the invention according to claim 2 is the magnetic recording medium according to claim 1, wherein the binder constituting the double layer has a functional group or a functional group forming an inner salt introduced therein. It is a modified resin.

The present invention will be explained in detail below.

Magnetic recording medium of the present invention ('', on a non-iflable support 1-.

It is formed by coating in this order a conductive layer containing carbon black, a multilayer nonmagnetic layer, and a magnetic layer containing ferromagnetic barium ferrite grains.

-Nonmagnetic support- Examples of the nonmagnetic support include polyesters such as polyethylene derephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamide, and polycarbonate. Examples include plastics such as

In addition, metals such as Cu, AI, and Zn, glass, boron nitride,
Ceramics such as Si carbide can also be used.

The thickness of these non-magnetic supports is approximately 3 to 100μ in the case of a film or sheet, preferably 5 to 50μ.
30gm-10g for discs and cards
If it is drum-shaped, it is used in a cylindrical shape, and its shape is determined depending on the recorder used.

Incidentally, an intermediate layer or a subbing layer may be provided on the surface of the non-magnetic support in order to improve adhesiveness.

1. Non-magnetic layer 1. The non-magnetic layer is formed by coating a conductive layer containing carbon black and a binder on a non-magnetic support.

The nonmagnetic layer is a conductive layer containing carbon black as a main component.

As the carbon black used for such a conductive layer, for example, Fundactex fconductex 1975 (specific surface area 250 ha/
g, particle size 24 mμ), Conductex 900 (specific surface area 125r11t/g, particle size 27 mμ), Fundex 40-220 (particle size 20 mμ), Conductex SC (particle size 20 mμ), Cabot Vulcanl X C- 72 (specific surface area 254 m”/g.

There are conductive carbon blacks such as Palcan P (particle size 20 mμ) (Raben 1040.420, Black Bars L2000 (particle size 16 mμ), #44 from Mitsubishi Chemical Corporation).This carbon black has its oil absorption. It is preferable that the amount is 90 m j2 fDBPl / 100 g or more because it is easy to form a stracture structure and exhibits higher conductivity.

The average particle size of the carbon black to be contained in this non-magnetic layer is 5 to 301μ, preferably 10 to 25μ. Also, among the carbon blacks having the above average particle size, those whose pH is less than 5 are is preferred.

As carbon black having such a specific pH, for example, IJONARCH1 manufactured by Cabot Corporation in the United States is used.
40G (average particle size; 13.Onm, pH; 2.5
), MONARCH1300 (average particle size; 13.
Onm, pH; 2.5), MONARCH10
00 (average particle size; 16.Onm, pH; 2.5
), MOG[IL L (BLACHPEARL
SL, average particle size, 24.0n-1pH; 3.0)
, REGAL 400R (REGAL 400
, average particle size; 25. Ons, pH, 3,0), etc., and ROYAL 5PECTR manufactured by Columbia Carbon.
A (average particle size, 10.0 nm, pH
; 4.0), NEO5PEDTRA
MARKI (average particle size; 11.Onm, pH;
4. ), NEO5PECTRA MARKII (average particle size; 13.Onm, pH; 3.0), NE
O5PECTRA AG (average particle size; 13.On
m, pH; 3.0), 5UPERBA (average particle size; 15-Or+m, pH; 32), NE
O5PECTRA MARK ■ (average particle size, 16.0 rho, pH, 4,5), RAVEN 5000 (average particle size, 12.0 nm, pH: 2.8), R
AVEN 7000 (average particle size, 15.On*, p
H; 2.1), RAVEN 5750 (average particle size, ls, 0 nm, pH; 2.1),
RAVEN 5'50 (average particle size; 200nm, p
H; 2.2), RAVEN 3500 (average particle size, 16.Onm, pH, 2.5), RAV
EN 1255 (average particle size, 23.0 rho, pH,
2,5), RAVEN 1040 (average particle size, 2
8.0 nm, pH; 2.8), RAVEN 10
35 (average particle size; 27, Onm, pH; 3.
5) and RAVEN 14 powder (average particle size: 59.0 nse, pH: 3.0).

The amount of carbon black added is usually 10 to 400 parts by weight, preferably 1 part by weight, per 100 parts by weight of the binder described below.
00 to 350 parts by weight.

As the binder (sometimes referred to as a binder), which is one of the components forming the non-magnetic layer, conventionally used binders can be used. Preferred is a resin modified by introducing.

The functional group in the resins mentioned above is, for example, -5
o, M, -03O,M, -COO~1, and -PO(
OM' ) [wherein, M is either a hydrogen atom r, an alkali metal, or an ammonium group, and Ml is a hydrogen atom, an alkali metal, or an alkyl group, respectively. Further, Ml in the two OM's bonded to the phosphorus atom may be the same or different. )
Examples include.

Examples of resins into which these functional groups are introduced include resins such as vinyl chloride resins, polyester resins, and polyurethane resins.

Among various resins modified by introducing functional groups, polyurethane resins having the aforementioned functional groups are preferred. Moreover, among polyurethane resins having functional groups, polyurethane resins having repeating units having S 03 Na are preferred.

For example, such a polyurethane resin can be prepared as follows.
It can be manufactured using

Generally, polyurethane resins can be produced by reacting a polyisocyanate compound and a polyol component. As this polyol component, a polyester polyol obtained by a reaction between a polyol and a polybasic acid is used.

Polyurethane resin is produced by preparing a polyester polyol having a specific polar group using a polybasic acid having a specific polar group as part of the polybasic acid according to a conventional method, and the resulting polynisder polyol and polyisocyanate. It can be obtained by reacting with a compound.

Examples of polybasic acids having polar groups include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfoisophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate,
Mention may be made of alkyl 4-sulfophthalates, alkyl 3-sulfophthalates, and their sodium and potassium salts.

Examples of polyol components include trimethylolpropane, hexanetriol, glycerin, trimethyl]-lubroban, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol.

Furthermore, examples of dicarboxylic acids among polybasic acids include phthalic acid, isophthalic acid, terephthalic acid, adipic acid, trimerized lyluic acid, sebacic acid, and maleic acid.

The number average molecular weight of the polyester polyol having a polar group obtained in this way is usually 500 to 8,000.
within the range of

Examples of polyisocyanate compounds include the reaction product of 3 moles of diisocyanate such as diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, xylylene diisocyanate and 1 mole of trimethylolpropane, and the reaction product of 3 moles of hexamethylene diisocyanate. Examples include a lett adduct compound, an isocyanurate adduct compound containing 5 moles of tolylene diisocyanate, an isocyanurate adduct compound containing 3 moles of tolylene diisocyanate, and a polymer of diphenylmethane diisocyanate.

The reaction between a polyester polyol and a polyisocyanate compound occurs when the number average molecular weight of the oily polyurethane resin is
Usually 10,000 to 20Q, [100, preferably 1
It is carried out under conditions adjusted to be within the range of 5,00 to 60,000 mouths.

In addition to the above production method, for example, a polyurethane resin into which -OH is introduced is produced, and this polyurethane resin is reacted with a compound containing a polar group and chlorine described below (dehydrochloric acid reaction) to produce polyurethane. A method of introducing a polar group into the resin may also be adopted.

1-CH, CH25O, M, Cj2-CH, CH2O5
03M, product (However, Ml and M' each have the same meaning as above.) Polyurethane resins having functional groups usually have a content of 0% to 5% by mole in the repeating resin having functional groups.
, preferably within the range of 0.1 to 2.0 mol%.

Regarding the introduction of functional groups into polyurethane resin,
As mentioned above, Special Publication No. 51-157603 and No. 58-4
No. 1565, JP-A-57-92422, JP-A No. 57-92
There are methods described in No. 423, etc., and in the present invention, polyurethane resins containing functional groups obtained by the methods described therein can be suitably used.

Preferred specific examples of functional group-containing binders include -C
OOH-containing OH urethane (rTIM-3 manufactured by Sanyo Chemical
005J), -3o, Na-containing polyurethane (“UR-8300” manufactured by Toyobo Jll■, rUR-8600J
), -COOH-containing OH-containing vinyl acetate copolymer (
Nippon Zeon's "400x 110AJ), -3o
, Na-containing vinyl chloride-vinyl acetate copolymer ("MR-110J" manufactured by Nippon Zeon ■), and the like.

The functional group content is preferably in the range of 1 to 10,000 equivalent l/106gr. Also, the molecular weight is 300-200.000
is preferred.

Polyurethane resins modified by introducing functional groups that form intramolecular salts include polyurethane resins modified by introducing functional groups that form intramolecular salts, and polyurethane resins that are modified by introducing functional groups that form intramolecular salts. Examples include vinyl chloride resins modified by polyvinyl chloride.

A polyurethane resin modified by introducing a functional group that forms an inner salt can be produced as follows.

Similar to the usual polyurethane synthesis method, high molecular weight polyols (molecular weight 500 to 3,000) such as polycarbonate polyols, polyester polyols, polylactone polyols, and polyether polyols and polyfunctional aromatic,
Manufactured by reacting with aliphatic incyanate. This yields polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate.

These polyurethanes are primarily produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and contain free incyanate groups and/or
Alternatively, it may be in the form of a urethane resin or urethane prepolymer containing hydroxyl groups, or it may be in the form of a urethane elastomer that does not contain these reactive end groups.

As the incyanate component, various diisocyanate compounds such as hexamethylene diisocyanate (HM
DI), diphenylmethane diisocyanate (MDI)
, water-added MDI (H,2MDI), toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TOD)
I), lysine diisocyanate methyl ester (L
DI), isophorone diisocyanate (IPDI), etc. can be used.

Further, if necessary, a low-molecular polyfunctional alcohol such as 1,4-butanediol, 1.6-hexanediol, 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 furthermore may be introduced into the above-mentioned low-molecular polyfunctional alcohol.

Polyester polyols whose functional groups form inner salts can be made from various dicarboxylic acid components and polyhydric alcohol components, and dicarboxylic acid components whose functional groups form inner salts and/or functional groups form inner salts. It can be synthesized by polycondensing the polyhydric alcohol components forming the compound.

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, trimerized lyluic acid, and maleic acid.

Polyhydric alcohol components include glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol. An example of any two types selected from among these is soil.

Polycarbonate polyol, in which the functional groups form an inner salt, can generally be synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or a diallyl carbonate, or by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or a diallyl carbonate. It can also be obtained by condensation.

In producing the above polyester polyol and polycarbonate polyol (including polycarbonate polyester polyol), the following aromatic polyhydric alcohols can be used. Moreover, when reacting the above-mentioned polyester polyol or polycarbonate polyol with polyisocyanate, the following aromatic polyhydric alcohol can be used.

Aromatic polyalcohol: [However, n is 1 or 2. J However, R is -f(:H!l , -, -CHtCH,
l-CH2CH2-, X is =SO, -doCO-,
-Cfc)l□L-, -CICI-iz-C-H4-C
(CH,), - is shown. J OH I(" [However, R' represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R2 represents a hydrogen atom or an alkyl group or aryl group having 1 to 7 carbon atoms, 1 HO+ICH9〈Σ0) 1 [However, m indicates an integer from 1 to 10,] HO-fcseniΣ(CH2+, -0) IEftashi5, k indicates 1 or 2.] Ho-(CH21, -o+o-+co2+
, -OH [k represents 1 or 2. ] old i,, +C)I2) [(, and -C)) -fcH2
) k-OH [1 or 2 is not indicated for . ] l0IC82 one -〇-bet==〉-ノ'7o-+c1
1. ) k-oH, ℃z [However, 1, k indicates 1 or 2. ] [However, k represents 1 or 2.] In the polyurethane having these aromatic polyhydric alcohol components in one chain, the content of these components is 5 mol% or more of the entire polyhydric alcohol component -F This is desirable.

In order to produce a rough polyester polyol in which the functional groups form an inner salt, S-caprolactam,
The above functional group may be introduced into lactams such as α-methyl-1-caprolactam, S-methyl-8-caprolactam, and γ-butyrolactam.

In order to produce poly1-→-ruboliol whose functional group has an inner salt ()■ε, the above-mentioned method can be used as described above. It is sufficient to introduce a functional group.

Examples of functional groups forming an inner salt include a betaine group.

A polyester polyol whose functional groups form an inner salt will be further described.

As a method for synthesizing polyesters, there is a method that utilizes a condensation reaction between an acid component having an aliphatic or aromatic polyfunctional acid or a derivative thereof and an aliphatic or aromatic alcohol component.

Introduction of an intramolecular amphoteric base such as a betaine group can be carried out by using the acid component containing a betaine group or the alcohol component containing a betaine group,
It is also possible to introduce hetain groups, etc. into polyester using a polymer reaction.However, considering the adverse effects of remaining unreacted components and the introduction rate, it is necessary to introduce intramolecular amphoteric bases such as betaine groups in advance. It is preferred to use a monomer consisting of:

Examples of the betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. The general formula of these betaine type functional groups can be expressed as follows.

A-N'''-1CH1,B- [However, the nitrogen atom in the above formula is incorporated into the urethane chain, A represents a hydrogen atom and an alkyl group having 1 to 60 carbon atoms, B- is - SO,-2-O-SO,-.

-COO-, -0-PO3H-5-opo, -do0PO
aHi- represents an integer from 1 to 10; represents a group, D represents -C00-1 or -CONH-, B- and k represent the same meanings as above.] As usable betaine group-containing monomers, the compounds exemplified below are can be mentioned. It goes without saying that the polyurethane resin having a functional group that forms an inner salt is not limited to those obtained using these monomers.

[^) CHs-N' ICHzCHzOHl zCH,CH,
CHOSO! - 1B) CH, -N" +CH, C00H) m, CHICH2
CH! 503- IC) ClH%-N” (C)l*cOOH1xCH,COO
- +DI CH, -N" fcH, cH, OH1゜CHIC) If
fiCOO- fE) CHx-N'[fCHtCHJIJ]*CI(, C1,
C0O- (Fl Hd'Ustl The monomer in which the functional group forms an inner salt can be obtained as a commercially available chemical, but it can also be easily synthesized by the method described below.

(a) Synthesis method using monochloroacetic acid R'-N(CH
, C0OH+ , +i -CIl, -CDDH [However, R4 represents a lower alkyl group such as a methyl group or an ethyl group] lbl Synthesis method using monochlorosuccinic acid R'-Ni
CH,C)1. OH), +Cj2-CH(CH,C0
0H1-COOH----→R'-N" (CH2
CH2COOH1*, CH-COO-' CH, COOH [However, R4 represents the same meaning as above. ](cl
A synthetic method using propane sultone [Tatashi2, R4 represents the same meaning as above] Also, a reaction for introducing a betaine group etc. into the Togane compound as a polymer reaction will be described.

This is a method in which 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 which has been previously extended to a predetermined molecular weight by a 5-unit 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 an equimolar amount to obtain a reaction product of one NGO group of the diisocyanate and the hydroxyl group in the above compound. Then, by reacting the OH groups of the polyurethane with the unreacted NCO groups, a polyurethane into which betaine groups or the like are introduced can be obtained.

The compound described above and having a hydroxyl group and a betaine group 2
For example, the following compounds can be exemplified. However, it is not limited to these.

CH,N”tcH,c)1.0)!+.

CH2Cl, C)1. SO, - ■ C, 11, N" fc) 12C) 1.0H12 ■ CH2Cl, 503- ■ CHsN" fcLcH20H12 CH2Cl, COO- ■ C2H, C0NHCH2CH2N" fcH, c) i2
0 old.

C)1. CH2PO311- The amount of betaine groups etc. introduced into the polyurethane resin is
It is preferably 0 to 10 mmol%/g, more preferably 1 to 0.5 mmol%/g. If the amount of betaine groups etc. introduced is less than 001 mmol %/g, it becomes difficult to notice any significant effect on the dispersibility of the ferromagnetic powder. In addition, the amount of introduced functional group is 1.0 mmol%/g
If it exceeds this amount, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make it impossible to use ordinary general-purpose solvents.

The number molar average molecular weight of the polyurethane resin used in the present invention is 5
,000 to 100,000, preferably 10.000
~50.000. If the number average molecular weight is less than 5,000, the coating film forming ability of the resin will be insufficient, and if the number average molecular weight exceeds 100,000, the preparation of magnetic paint will be difficult.
F. Problems may occur during processes such as mixing, transferring, and coating.

Next, a vinyl chloride resin having a functional group forming an inner salt will be explained.

The vinyl chloride resin having a functional group forming an inner salt is a vinyl chloride monomer, a copolymerizable monomer J having a functional group forming an inner salt, and other copolymerizable monomers as necessary. It can be obtained by copolymerizing polymerizable monomers.In addition, once a vinyl chloride copolymer is produced, a functional group forming an inner salt is added to the vinyl chloride copolymer by a polymer reaction. May be introduced.

[Functional group forming an inner salt] may include a betaine group, and specific examples of such betaine groups include a sulfobetaine group, a phosphobetaine group, a carboxybetaine group, and the like. Further, as the [copolymerizable monomer having a functional group forming an inner salt], the following compounds can be exemplified.

■ CH,=CHC0NHCH,CH2CH2-N"ic
H, 12CH, COO- ■ CH2=CHC0NI(CH2CH2CI2-N” f
cH,)2[CH21,501- ◎ CH2・CHCON)ICI(2GHz-N” (CH
-12(CL) 3SO, - CHz:CHCONHCHtCHzCHz-N"fcH
l)zl HCOO- CHl ■ (:)12=C(CHyu)C00CH,C)1. -N”
1CH312CH,COO- ■ CH,=CfcH,1cOOcH,cH2cH,-N”
fcH31゜- (CH21zsos- ■ ■ CH2: CHCONHCHxCHz-N'-fcHzc
HtOH1aCH, CH2PO, H- Also, as a method for introducing betaine groups etc. by polymer reaction, firstly, betaine groups etc. are introduced at the end or side chain of a vinyl chloride copolymer whose chain has been extended to a predetermined molecular weight by a polymerization reaction. There is a method in which a compound having a betaine group or the like is reacted with a double bond.

Examples of the compound used in this method include the above-mentioned copolymerizable molecules having a functional group forming an inner salt.

In the vinyl chloride resin having a functional group forming an inner salt, the content of the copolymerizable monomer having a functional group forming an inner salt is 0.01 to 30 mol%. preferable. If the content of the copolymerizable monomer having a functional group forming an inner salt is too large, the solubility in solvents may deteriorate and gelation may easily occur. If the content is too low, desired characteristics may not be obtained.

As mentioned above, there are various types of copolymerizable monomers that have a functional group that forms an inner salt, so in order to optimally adjust the properties of a vinyl chloride resin that has a functional group that forms an inner salt. , it is better to select and use them appropriately.

The vinyl chloride resin having a functional group that forms an inner salt may be obtained by copolymerizing an epoxy group-containing monomer and/or a hydroxyl group-containing monomer as another copolymerizable monomer.

The hydroxyl group present in the vinyl chloride resin having a functional group that forms an inner salt may be derived from the hydroxyl group-containing monomer, but may be derived from other copolymerizable monomers.
For example, it may be introduced by partial hydrolysis of a vinyl chloride resin obtained using vinyl fatty acid such as vinyl acetate.

Examples of the above-mentioned epoxy group-containing monomers include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methacryl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, and glycidyl-
Glycidyl esters of unsaturated acids such as p-vinyl benzoate, methyl glycidyl vinyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene monoxide, vinylcyclohexene monooxide, 2-methyl- Examples include 5,6-epoxy to chiracene epoxide olefins.

As a hydroxyl group-containing child, -R'-OH [however,
R5 is -C9H2p=OR1-COOC,H,, -O
H, or -CONHC, H,, -OH (where p is an integer from 1 to 4).

). Examples include monomers having an organic residue represented by *.

This type of monomer having -R'-OH includes (meta)
Acrylic acid-2-hydroxyethyl ester, and (
C2-4 alkanol esters of α,β-unsaturated acids such as meth)acrylic acid-2-hydroxypropyl ester, maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester, and itacon. Alkanol esters of unsaturated dicarboxylic acids such as acid mono-2-hydroxybutyl esters, 3
- Olefinic alcohols such as puten-1-ol and 5-hexen-1-ol, alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether, acrylamide such as N-methylol acrylamide and N-methylol methacrylamide, etc. can be mentioned. In addition, -I'! bound to a vinyl chloride resin containing a functional group that forms an inner salt! The content of hydroxyl groups based on '-OH is O1-2.
0% by weight is preferred. If the amount is less than 0.1%, the crosslinking effect of the coating film by the isocyanate compound will not be exhibited, and the
If the amount exceeds % by weight, the pot life of the magnetic paint will be too short, causing problems in its use. Although the amount of this hydroxyl group is much smaller than that of the vinyl rubinyl chloride alcohol-vinyl acetate copolymer known for magnetic coatings, the crosslinking reaction with the incyanate compound is achieved in 1 minute. The reason for this is not clear, but it is thought to be due to the fact that the hydroxyl groups involved in the reaction are farther away from the main chain of the copolymer, increasing the degree of freedom, and that the hydroxyl groups are uniformly distributed in the polymer. .

Examples of copolymerizable monomers that can be copolymerized as needed for use include known polymerizable monomers, some of which are exemplified below.

The vinyl chloride copolymer is preferably a vinyl chloride-vinyl acetate copolymer (hereinafter referred to as "copolymer").

[Vinyl chloride-vinyl acetate copolymer]. ) can be mentioned. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, and vinyl chloride-acetic acid. Examples include vinyl-vinyl alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers,
Partially hydrolyzed ones are also preferred.

The above copolymers that can be used in the present invention are:
It can be obtained by polymerization methods such as emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization. In either method, a molecular weight regulator or a polymerization initiator may be used as necessary, or known techniques such as dividing or continuous addition of seven polymers may be used.

By the way, conventional vinyl chloride-based copolymer resins (for example, U, C, C, manufactured by Co., Ltd. (7) VAGH) are composed of the following copolymer components.

However, it is believed that the -0-COC:Hs group is unlikely to contribute to the crosslinking reaction with a curing agent or the like. Therefore, instead of -0-COCH.

It is preferable to contain an epoxy group such as.

Specifically, a resin represented by the following general formula [1F] is preferable.

However, in formula [I], E can be represented by the following formula.

! ... Also, in formula [1], D is -COO- or -CON)l
-1R6 and R10 are alkyl groups having 1 to 3 carbon atoms, R
7 is X cold x hydrogen atom or methyl group, Rl + is an alkyl group having 1 to 3 carbon atoms, R1 and R' are an alkyl group having 1 to 6 carbon atoms, e is an integer of 2 to 6, Rto is hydrogen atom or methyl group, f is O~3 when R'' is a hydrogen atom
is an integer of 0 when Rto is a methyl group. J
is -coo, -so, or -PO,H.

It is ri. However, R12 and R13 each represent a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, or a phenyl group, R14 represents an alkylene group having 1 to 15 carbon atoms, and h represents an integer of 0 to 20.

Z is an introduced monomer other than vinyl chloride, an epoxy group, or a monomer having a functional group capable of forming an inner salt. a is 2
00-800, b is 1-100, c is 1-10
0 and d represent integers from 0 to 200.

2 is a known polymerizable monomer that is introduced as necessary, and specific examples include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate, methyl ether,
Vinyl ethers such as inbutyl vinyl ether and cetyl vinyl ether, vinylidene such as vinylidene chloride and fukkavinylidene, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth)acrylate,
(meth)ethyl acrylate, (meth)acrylic acid uryl, (meth)acrylic l! ! -Unsaturated carboxylic acid esters such as 2-hydroxypropyl, olefins such as ethylene and propylene, unsaturated nitrites such as (meth)acrylonitrile, styrene, a-methylstyrene, p-
Examples include aromatic vinyls such as methylstyrene.

The degree of polymerization of the vinyl chloride copolymer used in the present invention is
It is preferably 100-500, more preferably 150-400.

In addition, as a method for measuring the degree of polymerization, vinyl chloride resin is dissolved in cyclohexanone by heating, and the specific viscosity of the solution is measured at 30°C according to JIS K6721. Convert to specific viscosity to determine the degree of polymerization.

In the above general formula [H, it is preferable that a betaine group and an epoxy group exist together in the copolymer, in which case the betaine group is 0.5 to 4% by weight, and the epoxy group is 0.5% to 4% by weight.
5-3% by weight, vinyl chloride monomer units 95-8
It is desirable that the content is 0% by weight.

In the copolymer represented by the above general formula [1], when the copolymer is used as a binder for a magnetic recording medium and exhibits the necessary effect, the vinyl chloride repeating unit is used as a binder for the magnetic recording medium. If the vinyl chloride component is too small, the mechanical strength required for magnetic recording media cannot be obtained, and if it is too large, the solubility in solvents will be poor, and the glass of the resin will deteriorate. The transition temperature (Tg) also tends to become higher.

In addition, the repeating unit containing an epoxy group improves the thermal stability of vinyl chloride and also reacts with crosslinking curing agents such as incyanate. It is involved in bonding with the binder resin and increases durability such as thermal stability and abrasion resistance.

It also has the effect of controlling the glass transition temperature (Tg) and plasticizing effect of the binder resin by controlling the content. For this purpose, reactive hydroxyl groups such as vinyl alcohol are not required, but their presence does not pose a problem.

The repeating unit having a betaine group contributes to dispersibility, and if its content is too small, the effect will be small;
If the amount is too large, it will not contribute to any further improvement in dispersibility, and will even worsen moisture resistance, which is not preferable.

In addition to the above repeating unit, the vinyl chloride copolymer represented by the general formula [1] further contains Moeki-(z). - For the purpose of improving dispersibility, carboxyl groups or salt residues thereof, such as -COOM (where M represents a hydrogen atom, an alkali metal atom, or an ammonium group), or repeats having a hydrophilic functional group such as a hydroxyl group, are used. A carboxyl group, which may include a return unit, is more effective in improving the retention and dispersibility of a binder for magnetic powder (iron oxide, metal powder) than a hydroxyl group.

Furthermore, repeating units having the effect of improving the strength or solvent solubility of the resin or the compatibility with other resins, improving the lubricity, or improving the flexibility may be introduced.

Next, specific examples of copolymers having blocks represented by the above general formula will be given, but the copolymers are not limited to the following examples.

□C9Cho0-C)1. CHCH2 0' -fcH7-CHI, -+CH21, SO, -CON
HCH2CH,C)I2-N" +co, +.

0-CH2CHCN.

ゝn/ ― Cp and twenty (1-C
H, to 1(C)I2Ol -1cH2-C15- □ C・0 0-C)1. CH20H (d) CH.

-(Ct(□-C1la- -O 0-CH2CHCl1□ (Ne) 711° CH.

1CH2-CI2. −.

j.

Sound 0-CH2CHCl1□ 0' -fc)lx-CH) s-(CH2) 3S03-
．． CON I C11□CH2Cl1□-N” fcH
il2H3-(CH,-C1,,-j,.

0-CH, CHCH.

ゝ0′ 哩　　　　c=.

噸0-CH,CHCH2ゝ0/H Next, the synthesis of a vinyl chloride copolymer containing a functional group capable of forming an inner salt will be further explained.

When a vinyl chloride copolymer containing no betaine groups is synthesized and then a functional group that forms an inner salt, such as a betaine group, is introduced through a polymer reaction, since this is a polymer reaction, unreacted compounds There are problems such as difficulty in removing by-products and difficulty in adjusting the reaction rate. Also, the introduced epoxy group may interact with hydrochloric acid during the reaction, or the epoxy ring may be opened during synthesis. There is a problem that a ring reaction occurs.Therefore, in order to avoid these problems even if only a little, it is advantageous to use a method of copolymerizing a copolymerizable monomer having a functional group such as betaine.

That is, for example, a predetermined amount of a reactive monomer having an unsaturated bond that induces a repeated injection position expressed by the above 5Z-V formula [1] is injected into a reaction vessel such as an autoclave, and the polymerization is initiated by injection. A polymerization initiator such as a radical polymerization initiator such as benzoyl peroxide or azobisisobutyronitrile, a redox polymerization initiator, an anionic polymerization initiator, or a cationic polymerization initiator is used, and thereby the pre=e reaction A copolymer can be synthesized by polymerizing a monomer.

A specific example of the reactive monomer for introducing the epoxy group is chrycidyl acrylate.

Various compounds mentioned above including glycidyl methacrylate and the like can be mentioned. As the reactive monomer for introducing the betaine group, all of those mentioned above can be used.

If a carboxylic acid or its salt is introduced,
Acrylic acid, methacrylic acid, etc. are preferably used.

Moreover, as for the oil-thermal radical polymerization initiator, the following azo compounds or organic peroxides can be used.

For example, 2,2′-azobisisobutyronitrile, 2
, 2°-azobis(2-methyl-valeronitrile), 2
,2°-azobis(2,4-dimethylbutyronitrile)
, 2.2”-azobis(2-methylcapronitrile),
2,2°-azobis(2,3,3-trimethylbutyronitrile), 2,2′-azobis(2,4,4-trimethylvaleronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile) nitrile), 2,2°-azobis(2,4
-dimethyl-4-ethoxyvaleronitrile), 2.2'
-Azobis(2,4-dimethyl-4-n-butoxyvaleronitrile) and the like can be used. Examples of organic peroxides include acetyl peroxide, propionyl peroxide, isobutyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5.5-trimethylhexanoyl peroxide, and benzoyl peroxide. Diacyl peroxides such as hexanoyl bardiisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxyisobutyrate, t-butyl peroxyvivalate, t-butyl peroxylaurate, etc. Peroxy esters and the like can be used. Of course, two or more of the above-mentioned oil-thermal radical polymerization initiators can also be used in an appropriate combination. Among these, azo compounds are preferred from the viewpoint of handling safety and performance, with 2°2°-azobisisobutyronitrile or 2°2°-azobis(2,4-dimethylvaleronitrile) being particularly preferred. Although it is difficult to define the amount of such an initiator to be used, it is generally used within a range of 0.2 to 2.0% by weight based on the monomer.

In addition, regarding the pH of the polymerization system, if the pH is too strong, it will cause ring opening of the epoxy group during polymerization, and if the pH is too strong, it will cause hydrolysis of the produced polymer.
It is recommended to set it within the range of H2 to 9, preferably 2 to 7.

The polymerization temperature depends on the type of initiator, but the higher the temperature, the more likely the ring-opening reaction of the epoxy group will occur, or a portion of the monomer will be emulsified and emulsion polymerization will occur, producing a latex-like fine polymer. Generally, 80"
A temperature range of 40-70'C or less is recommended.

In addition, it is desirable to use water as the polymerization solvent, but water is miscible with F! It is also permissible to coexist an A'r8 medium or an electrolyte salt.

By using a resin modified by introducing the above-mentioned functional group or a functional group that forms an inner salt into the nonmagnetic layer, it is possible to improve the dispersibility of carbon black and obtain a highly smooth magnetic recording medium. I can do it.

In the present invention, in addition to the binder described above, conventionally used unmodified vinyl chloride resins, polyurethane resins, or polyester resins may be used in combination, if necessary, and cellulose resins, phenoxy resins, or Thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, etc. that have specific usage methods may be used in combination.

The resins described above can be used as a binder constituting the nonmagnetic layer by selecting the optimum type and amount of the resins, with their lengths complementary to each other.

The amount of binder in this nonmagnetic layer is determined by
If the total amount of binder in the non-&B layer is (A), then (A)
It is important that the amount of i (B) be at a specific weight ratio with i (B) of the total binder in the magnetic layer, which will be described later.

This non-magnetic layer, which is a conductive layer, is made by fixing the carbon black with a binder resin, which is a binder, and may further contain an optional component such as a lubricant.

The lubricant added to the non-magnetic layer includes fatty acids and/or
Alternatively, a fatty acid ester can be contained. In this case, the amount of fatty acid and/or fatty acid ester added is preferably 0 to 30 parts by weight based on the carbon black.
If the magnetic layer is made thin, the total amount of lubricant will be reduced, leading to deterioration of durability, and if the amount of lubricant in the magnetic layer is increased beyond a certain range, the lubricant will easily seep out and the output will drop. Therefore, from the viewpoint of improving the durability of the magnetic layer, it is effective to add a lubricant to the non-magnetic layer so as to serve as a lubricant supply source for the magnetic layer.

The fatty acid may be a -basic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms. Examples of fatty acids are caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Stearic acid, isostearic acid, lylunic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid,
Examples include succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, and octanedicarboxylic acid.

Examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate,
Inbutyl oleate, stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, ethyl stearate, 2-ethylhexyl palmitate , isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2-ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate,
Examples include 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol monobutyl ether palmitate, diethylene glycol monobutyl ether palmitate, and the like.

In addition to the above-mentioned fatty acids and fatty acid esters, other lubricants such as silicone oil and fatty acid amides may be added to the magnetic layer.

The lubricant described above may be used alone or in combination of two or more, and may be the same or different from the lubricant for the magnetic layer.

An inorganic filler may be added as another optional component added to the nonmagnetic layer. As a specific example, y-FezO
i, Co-y-FeJz, metal, magnetic powder such as Ba-ferrite, 5iC2a -Al2O3,0-Fe2oz
, CrJs and other abrasives, low BET type carbon black, and the like.

In the magnetic recording medium according to the present invention, the dry thickness of the nonmagnetic layer is from 0.1 to 4.0 .mu.m, preferably from 0.3 to 20 .mu.m.

-Magnetic layer- The magnetic recording medium of the present invention has the above-mentioned nonmagnetic layer, which is the conductive layer, and a magnetic layer containing specific magnetic particles and having a specific thickness on a nonmagnetic support, in this order. Become.

In the &Fi layer stack of the magnetic recording medium of the present invention, ferromagnetic barium ferrite (hereinafter abbreviated as Ba-ferrite) is used as the magnetic particles.

A preferable Ba-ferrite magnetic powder that can be used in the present invention is a Ba-ferrite powder having an average particle size (height of the diagonal line of the plate surface of the ferrite-based ferrite) in which a part of Fe is replaced with at least CO and Zn. ) 400 to 900 people, plate ratio (the value obtained by dividing the length of the diagonal line of the plate surface of ferrite type ferrite by the plate thickness) 2.0 to 10.0. Riki Yasuda 450-150
00 Ba-ferrite.

In Ba-ferrite, the coercive force is controlled to an appropriate value by partially replacing Fe with Co, and furthermore, Z
By partially substituting n, it is possible to achieve high saturation magnetization that cannot be obtained by Co substitution alone, and to obtain a magnetic recording medium with excellent electromagnetic conversion characteristics and high reproduction output. Moreover, by further substituting a part of Fe with Hb, a magnetic recording medium having higher reproduction output and excellent electromagnetic conversion characteristics can be obtained. Furthermore, in the Ba-ferrite of the present invention, a part of Fe is Ti, In, Mn, Cu,
There is no problem even if it is substituted with a transition metal such as Ge or Sn.

In addition, when Ba-ferrite used in the present invention is expressed by the following general formula (M is a substitution metal), BaO・n(fFe+
-mMjJzl [However, m>0.36 (However, Co+Zn = 0.0
8 to 0.3, Co/2n to 0.5 to 10)] where n is 5.4 to 6.0, and M is a combination of two or more elements with an average number of 3. preferable.

In the present invention, the reason why it is preferable for the average grain size, plate ratio, and coercive force of Ba-ferrite to be within the above-mentioned preferable ranges is as follows. In other words, if the average particle diameter is less than 400, the reproduction output when used as a magnetic recording medium will be insufficient.
On the other hand, if the number exceeds 900, the surface smoothness of the magnetic recording medium will deteriorate significantly, and the noise level may become too high. Also, if the plate ratio is less than 2.0, the magnetic recording medium will When this happens, a perpendicular orientation ratio suitable for high-density recording cannot be obtained, and conversely, if the platelet ratio exceeds 6.0, the surface smoothness when used as a magnetic recording medium will deteriorate significantly and the noise level will increase. Furthermore, if the coercive force is less than 3,500e, it becomes difficult to retain the recording signal, and if it exceeds 20,000e, the head limit may decrease to saturation, making recording difficult.

As a method for manufacturing the magnetic powder used in the present invention, for example, oxides and carbonates of each element necessary to form the target Ba-ferrite are melted together with a glass-forming substance such as boric acid. Then, the resulting melt is rapidly cooled to form a glass, then this glass is heat-treated at a predetermined temperature to precipitate the target Ba-)nyrite crystal powder, and finally the glass components are removed by heat treatment. In addition to the glass crystallization method, a coprecipitation-calcination method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method, etc. are applicable.

In accordance with 8 of the present invention, without impairing the effects of the present invention, any known magnetic material may be used as the magnetic particles in addition to [magnetic particles having a flat plate shape and whose axis of easy magnetization is substantially perpendicular to the flat plate surface. It can also be included in the magnetic layer.

For example, yFetus, Co-containing 7-Fe
zes or Co-coated y Fe20i
Co-γ-FexOa, such as y-FezOs, FezO4, GO-containing FezO4 or Co-coated@Fe50;
Oxide magnetic materials such as CrO*, others such as Fe,
Ni, Fe-Ni alloy, Fe-Co alloy, Fe-N1
-P alloy, Fe-Ni-Co alloy, Fe-Mn-2n alloy, Fe-Ni-Zn alloy, Fe-Go-Ni-Cr alloy, Fe-Co-N1-P alloy, Co-P alloy, Co
Examples include metal magnetic powders containing Fe, Ni, and Co as main components, such as -Cr alloys. Moreover, Si, Cu, Zn, A1.
Elements such as P, Mn, and Cr or compounds thereof may be included.

As the binder used in the magnetic layer, the same binder as that used in the non-magnetic layer is used.

The amount of binder (B) relative to the ferromagnetic powder in the magnetic layer is 5 to 30% by weight.

In the present invention, it is important to adjust the amount (B) of the binder in the magnetic layer to the total amount (A) of the binder in the nonmagnetic layer to a specific weight ratio.

That is, the ratio of the total amount of binder in the nonmagnetic layer (A) to the total amount of binder in the magnetic layer (B), A/B (weight ratio), is 7 or less. More preferably, A/B is 2 to 5
It is.

If the binder quantity ratio A/B exceeds 7, a difference in shrinkage rate due to drying of the coating film will occur due to the difference in the strength of the binder, and the interface between the magnetic coating layers will be disturbed during simultaneous multilayer coating. The surface properties of the resulting magnetic layer deteriorate.

When A/B is less than 2, the total amount of binder in the non-Mi layer decreases, the dispersibility of the paint deteriorates, and the surface properties of the magnetic layer deteriorate.

Furthermore, the adhesion of the non-magnetic layer deteriorates.

Durability deteriorates.

Incidentally, in order to improve the durability of the magnetic layer of the magnetic recording medium of the present invention, various hardening agents are contained in the magnetic paint.
The magnetic layer may be formed by a method described later.

Examples of such curing agents include isocyanates such as aromatic isocyanates and aliphatic isocyanates.

Examples of the aromatic incyanate include tolylene diisocyanate + TD11 and adducts of these incyanates with active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are suitable.

Examples of aliphatic incyanates include hexamethylene diisocyanate iHMD11 and adducts of these incyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these incyanates and active hydrogen compounds, those having molecular stars in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic layer may contain a dispersant contained in the magnetic paint used to form the magnetic layer, and may also contain additives such as lubricants, abrasives, and antistatic agents as necessary. It may also contain .

Dispersants used in the present invention include phosphoric acid esters, amine compounds, argyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, Nisdel sulfosuccinates, known surfactants, and the like. There are salts and also negative organic groups (e.g. -COOH
) can also be used.

Examples of dispersants include fatty acids having 12 to 22 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, balmitic acid, stearic acid, and oleic acid, and their alkali metal salts or alkaline earth metal salts. Amides of these; polyalkylene oxide alkyl phosphate esters; lecithin; trialkyl polyolefin oxy quaternary ammonium acids; azo compounds having carboxyl groups and sulfonic acid groups, and the like are used. These dispersants are added in an amount of 0.5 to 5% by weight based on the ferromagnetic powder.

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

Furthermore, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty a, and fatty acid ester can be used as lubricants in the magnetic layer.

The fatty acid may be a -basic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms. As an example of fatty acids 1:! caproic acid.

caprylic acid, capric acid, lauric acid, myristic acid,
Palmitic acid, stearic acid, isostearic acid, linolic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, pentasuccinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1
．． Examples include 12-dodecanedicarboxylic acid and octanedicalic acid.

Examples of the fatty acid esters include oleyl oleate, isocedyl ester, dioleyl malate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate,
Isobutyl oleate 5 stearyl stearate, lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate-1, isotridecyl oleate, 2-ethylhexyl stearate, ethyl stearate, 2-ethylhexyl palmidate , isopropyl palmitate, isobrobyl myristate, butyl laurate, cetyl-2-ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, Examples include isopentyl stearate, diethylene glycol mono-butyl ether palmitate, diethylene glycol mono-butyl ether palmitate, and the like.

These lubricants contain 0.00 parts by weight per 100 parts by weight of binder.
It is added in an amount of 2 to 20 parts by weight.

Non-magnetic abrasive particles may also be added.

The abrasive may be a material used for -V,
Alumina (α-AJ2.O,, β-Aβ203, y
-AjL Ox, b-Ajl! zOs,
i: −Aβ203, η−/l! 20. ．． θ−Aβ20
3, pc-Aβ201, χ-Aj2. O,,ρ−Aβ2
01, etc.), alumina hydrate, alumina silicate, other silicates, silicon carbide, boron carbide, other carbides, non-magnetic oxides such as chromium oxide and iron oxide, nitrides such as boron nitride, etc. be done. These abrasives have an average particle size of 0
．． A size of 0.05 to 5 μm is used, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.

There is no need to add ordinary antistatic agents to the magnetic layer. That is, according to the present invention, since the conductive layer containing carbon black is provided between the magnetic layer and the nonmagnetic support, the surface electrical resistance of the magnetic layer is sufficiently reduced by this conductive layer. Because you can. And the magnetic layer is B
a- The packing density and dispersibility of the ferrite magnetic powder are improved.

However, in the magnetic recording medium of the present invention, further:
By adding carbon black to the magnetic layer, the durability of the magnetic recording medium can be improved.

In this case, the particle size of the carbon black added to the magnetic layer is preferably in the range of 20 to 500 ns, preferably 40 to 100 ns.

A specific example of carbon black added for the purpose of improving durability is PEA to BLAC manufactured by Kisabot Corporation in the United States.
RLS 280 (average particle size; 41 nm), BL
ACKPEARLS 170 (average particle size; 50 r
u++ ), BLACK PEARLS160 (average particle size; 50 nm), BLACK PEARLS 1
30 (average particle size; 75n++), BLACK
PEARLS 120 (average particle size near 5na+), etc.
Also, RAVEN 500 manufactured by Columbia Carbon Co.
(Average particle size; 52.9 nm), RAVEN
450 (average particle size; 75.4 nm), RAVEN
430 (average particle size; 82, In5), RAV
EN 420 (average particle size; 85.7nw), RA
VEN 410 (average particle size; 100.6 n+*
), RAVEN T230 (average particle size; 56.2
nm), RAVEN H2OPowder (average particle size; 59.9 nm), RAVEN 22 Pow
der (average particle size; 82.6 nm), RAVE
N 16 powder (average particle size; 678 nap
), RAVEN 14 powder (average particle diameter; 54.6nw), RAVEN MT-P (average particle diameter; 280.Onm), etc., #22B (average particle diameter; 40.Onm) manufactured by Mitsubishi Chemical Corporation, CF -9
' (Average particle size; 40.Ons+), #35QO
(Average particle size: 40, Onw) etc., HS-1 manufactured by Denka
00 (average particle size; 53, Onm), HS-500 (average particle size; 76, Onm) manufactured by Asahi Carbon Co., Ltd., and the like.

An important point in the present invention is that the dry film thickness of the magnetic layer is 0.1
-4.0 μm, preferably 0.1-2.0 am.

When the thickness of the magnetic layer exceeds 4.0 μm, the surface resistivity of the magnetic layer becomes high and dropout of the magnetic recording medium increases. On the other hand, when the thickness of the magnetic layer is thinner than 0.1μ, the influence of the non-magnetic layer appears strongly, the surface of the magnetic layer becomes rough, and the lumi S/N and chroma S/N of the magnetic recording medium
N decreases.

-Method for manufacturing a magnetic recording medium- When forming a nonmagnetic layer and a magnetic layer on a support, -
There are two methods: a method in which the drying process is repeated layer by layer (so-called wet-on-dry coating method), and a method in which the next layer is applied simultaneously or sequentially on top of the wet layer that has not been dried (so-called wet-on-wet). Coating method =
However, in manufacturing the magnetic recording medium of the present invention, simultaneous multilayer coating using a wet-on-wet multilayer coating method is preferably used, particularly from the viewpoint of effectiveness.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
A conductive layer 2 containing carbon black, which is the above-mentioned non-&a multilayer, and a Ba-
A magnetic layer 4 containing ferrite magnetic powder and, if necessary, an overcoat layer (not shown) are laminated in this order.

The magnetic recording medium shown in FIG. 1 includes a conductive layer 2 and a support 1.
An undercoat layer (not shown) may be provided between the two or no undercoat layer may be provided (the same applies hereinafter).
, the support may also be subjected to corona discharge treatment.

Next, a preferred example of the present invention will be explained with reference to FIG.

In this manufacturing apparatus, when manufacturing the medium shown in FIG. 1, as shown in FIG. After coating each paint for the conductive layer 2 and the magnetic layer 4, which are magnetic layers, in a wet-on-wet method, the material passes through a non-orientation magnet or a vertical orientation magnet 33, and is introduced into a dryer 34. Next, the dried support 1 with each coated layer is guided to a super calender device 37 consisting of a combination of calender rolls 38, where it is calendered. After that, it is wound up on a take-up roll 39. Thereafter, the conductive layer 2,
A magnetic layer 4 is applied, dried, and calendered. The thus obtained magnetic film is punched out into a desired shape, for example a disk shape, and placed in a cassette to manufacture a 35-inch floppy disk.

In the above method, each paint may be supplied to the extrusion coaters 10 and 11 through an in-line mixer (not shown). In addition, in the figure, 71[D indicates the conveyance direction of the nonmagnetic base film. The extrusion coaters 10.11 are each provided with a reservoir 13.14 to deposit the paint from each coater in a wet-on-wet manner.

In other words, immediately after applying the conductive layer paint (when it is not dry)
Apply multiple layers of magnetic layer paint.

The wet-on-wet multilayer coating method uses two extrusion coaters [Fig. 3(a)] as well as the two extrusion coaters described above [Fig. 3(b)].
Extrusion coaters of the type I and FCL can also be used.

In addition, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, etc. can also be used. Furthermore, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater, etc. can be combined.

In multilayer coating using this wet-on-wet method, the lower layer conductivity! Since the upper magnetic layer is applied while the multilayer is still wet, the surface of the lower layer (i.e., the interface with the upper layer) becomes smooth and the surface properties of the upper layer are good. Adhesion is also improved. As a result, it satisfies the performance requirements of a magnetic disk, which requires high output and low noise, especially for high-end recording, and, unlike magnetic tape, requires high durability performance. Eliminate membrane peeling even when it comes to things! I
Strength is in the 1st direction, and RI1 durability is in the 1st direction. In addition, the wet-on-wet multilayer coating method reduces dropouts and improves reliability.

In addition to cases in which there is substantially a clear boundary between the upper and lower layers formed by the above-mentioned wet-on-wet multilayer coating method, there is a boundary area where components of both layers are mixed at a certain thickness. However, any case in which the upper or lower layer excluding such a boundary region is a magnetic layer or a conductive layer as described in L is included within the scope of the present invention.

The solvents blended in the above paint 4 or the diluting solvents used during application of this paint include acetone, methyl ethyl ketone,
Ketones such as methyl isobutyl ketone and cyclohexanone; Alcohols such as methanol, ethanol, propatool, butanol; Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; Glycol dimethyl ether, glycol monoethyl Ethers such as ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene.

These various solvents can be used alone or
The magnetic field in the non-oriented magnet or the vertically oriented magnet, which can also be used in combination with two or more of them, is approximately 20 to 5000 Gauss in alternating current or direct current, and the drying temperature in the dryer is approximately 30 to 120°C. and
Drying time is about 0.1-10 minutes.

〔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 scope of the present invention. In addition, in the following examples, all "parts" are parts by weight.

(Examples 1 to 12) The components shown below were sufficiently mixed and dispersed using a Nigu machine and a ball mill.5 Then, just before coating, a polyisocyanate compound (Coronate Shi Nippon Polyurethane) was added.
A magnetic paint (I) for the magnetic layer and a carbon black paint (II) for the non-magnetic layer/conductive layer were prepared by adding and mixing the following parts.

The magnetic paint (I) and the carbon black paint (If) used a polyurethane resin and a vinyl chloride-vinyl acetate-vinyl alcohol copolymer as a binder.

The blending amount of the binder and A/B in Examples 1-12 are as shown in Table 1.

110LL1L: 100 parts of Ba-Fe magnetic powder (B
ET specific surface area: 32g/g, coercive force IHcl: 6000e) Polyurethane resin It (parts) shown in Table 1 contains Tuboran 230
4: Made by Nippon Polyurethane) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (manufactured by VAGH U, C, C, USA) Amount shown in Table 1 (parts) Nitrocellulose Amount shown in Table 1 (parts) α- Alumina 7 parts Cyclohexanone 200 parts Toluene
50 parts methyl ethyl ketone
50 parts carbon black ° ′ ■
): Carbon black 100 parts (Conductex 900 Specific surface area 125 m" 7 g Particle size 27 mμ) Polyurethane resin Table 1 display @ (part) shows Tuboran 2304
: Nippon Polyurethane ■) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH: manufactured by U, C, C, USA) Table 1 Displayed ml (parts) Nitrocellulose Table 1 Displayed amount (parts) Cyclohexanone 600 parts toluene
200 parts methyl ethyl ketone 200 parts Next, thickness 75 μm
The above carbon black paint (■-A) and magnetic paint (I) were applied on the polyethylene terephthalate base film of
As shown in Figure 3 below, various coatings were sequentially applied using a wet-on-wet method using an extrusion type extrusion coater, and after drying, a calender treatment was performed. Thereafter, paints (II) and (1) were similarly applied to the opposite side of the polyethylene prephthalate base film in sequence, and after drying, calender treatment was performed.

The thus obtained magnetic film was punched out into a disk shape with a diameter of 86 cm and placed in a cassette to produce a magnetic disk.

Each of the obtained magnetic disks was measured according to the following items.

Measuring method Fl1 Dispersion The gloss was evaluated by measuring the degree of gloss with a digital variable angle gloss meter VG-ID manufactured by Suidenshoku Kogyo.

(2) Smoothness It is expressed as surface roughness Ra.

Stylus type surface roughness meter [-manufactured by Koita Research Institute.

5E3PK type].

The upper row shows the surface roughness when the layers are stacked, and the numbers in parentheses show the surface roughness of a single nonmagnetic layer.

(3) Recording was performed using a sine wave signal with a reproduction output of 500 KHz, and the reproduction RF output was measured.

Drive: TO5) IIBA ll1l PD-21
1. The measured reproduction RF output is shown as a relative value when the floppy disk manufactured in Example (6) is taken as 100%.

It has a large culm with a high RF specific output and a good magnetic disk.

(4) Conductivity (Surface Electrical Specific Resistance) Electrodes with a width of 10+w+m were put together with a sample to be measured between them, and the surface electrical resistance was measured at a voltage of 100 V.

If the value is large, the electrical resistivity of the crosspiece surface is large.

(5) Coatability The coating surface was visually observed and evaluated during and after coating.

0: Very good △・Poor ○: Good ×: Very poor (6) Calendar stain (calendar heat roll stain) The degree of stain on the calender roll used for calender treatment in the magnetic medium manufacturing process was visually observed.

0: No stains at all △: Some stains ○: Almost no stains ×: Lots of stains (7) Durability Load the magnetic head into the recording/reproducing device and insert the Toshiba 4MB
With the drive PI)-211, the disk was brought into sliding contact with a pressure of 20 g/c 2 and rotated at a disk rotation speed of 300 rpm, and the running time until the playback output reached 70% of the initial output was taken as the durability time and the temperature and temperature were measured. was evaluated by changing the

(Comparative Examples 1 to 4) In Examples, measurements were made in the same manner as in other Examples except that the A/B ratio of the binder was 7 or more.

The evaluation results are shown in Table 1.

(Examples 13 to 20) Examples 13 to 20 were carried out in the same manner as in Example 1, except that the types of binders shown in Table 2 of the above Examples were blended in the proportions shown in Table 2.

Binder combination! and A/B are as shown in Table 2.

The evaluation results are shown in Table 2.

[Effects of the Invention] According to the present invention, it is possible to provide a magnetic recording medium with increased storage capacity, increased recording/reproduction output, and improved durability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a cross section of a magnetic recording medium according to an embodiment of the present invention, and FIG. 2 is a schematic illustration showing a manufacturing apparatus as an example that can manufacture the magnetic recording medium of the present invention. FIG. 3A, tb+ and fcl are schematic explanatory diagrams showing a wet-on-wet multilayer coating method using an extrusion coater. 1... Nonmagnetic support, 2... Nonmagnetic layer, 3... Magnetic layer. Building 1 Ward Building 2 Drawing D Drawing 3 (a) (b) (C)

Claims (2)

[Claims] (1) A nonmagnetic layer containing carbon black as a main component is provided on a nonmagnetic support, and a flat plate is further provided on the nonmagnetic layer,
A magnetic layer with a thickness of 0.1 to 4.0 μm containing magnetic particles whose easy axis of magnetization is almost perpendicular to the plane of the flat plate is provided, and the total amount of binder in the nonmagnetic layer (A) and the amount in the magnetic layer are A magnetic recording medium characterized in that the ratio A/B to the total amount of binder (B) is 7 or less. (2) The magnetic recording medium according to claim 1, wherein the binder constituting the nonmagnetic layer is a resin modified by introducing a functional group or a functional group that forms an inner salt.