JPH0266721A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To shorten the time required for dispersion of the magnetic powder and to pack the magnetic powder uniformly into a magnetic layer at a high density by incorporating a prescribed volume of moisture into the magnetic powder of the magnetic recording medium having the magnetic layer contg. the magnetic powder and binder and incorporating polyurethane the negative functional group of which forms an intramolecular salt therein. CONSTITUTION:The magnetic layer contg. the magnetic powder and the binder is formed on the magnetic recording medium. The polyurethane which contains 0.1 to 2.0wt.% moisture and the negative functional group of which forms the intramolecular salt is incorporated as the binder into the magnetic powder of this magnetic recording medium. The magnetic layer 2 is formed on a nonmagnetic base 1 consisting of polyethylene terephthalate, etc., and a back coating layer 4 is formed at need on the side opposite to the layer 2. The time required for the dispersion of the magnetic powder as the magnetic recording medium is thus shortened and the magnetic powder is packed uniformly into the magnetic layer at the high density.

Description

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

Prior Art Recently, magnetic recording media such as magnetic tapes have become denser and have higher S/S.
With the shift to nitrogen, magnetic powders with smaller particle diameters are being used.

Generally, it is said that the S/N ratio of a magnetic recording medium is proportional to the square value of the number of particles of magnetic powder in the recording material involved in recording and reproduction. Therefore, when applying the same weight of magnetic powder,
The use of magnetic powder with a smaller particle size is more advantageous in improving the S/N. Further, by making the magnetic powder into fine particles and increasing its BET value, the surface of the magnetic layer becomes smoother and spacing loss is reduced, which is advantageous in obtaining high electromagnetic conversion characteristics.

However, since the surface area of particles increases in inverse proportion to the square of the particle diameter, dispersion of particles becomes rapidly difficult as the particle diameter decreases, and dispersion stability also deteriorates. In this case, the orientation of the ferromagnetic material in the magnetic layer, the smoothness of the surface of the magnetic layer, etc. deteriorate, and as a result, an excellent squareness ratio and S/N ratio cannot be obtained, which is disadvantageous.

Conventionally, polyester-type polyurethane resins and vinyl chloride-based resins have been mainly used as binders for magnetic tapes.

However, since sufficient dispersibility cannot be obtained with conventional polyurethane resins, it is necessary to adjust the particle size distribution of the magnetic powder to improve its dispersibility in the binder, or to use a surfactant as a dispersant. There are many things being done. Furthermore, the binder may be a hydrophilic group such as a hydroxyl group, a phosphor group, a sulfo group,
Alternatively, a method has been proposed in which the properties are improved by modifying the material by introducing a carboxy group or the like.

However, even with such a binder, it may be difficult to obtain sufficient dispersibility, and the emergence of a binder that has even higher adsorption power to the surface of magnetic powder is expected.

C1 Purpose of the invention The purpose of the present invention is to achieve smooth adsorption of the binder onto the surface of the magnetic powder, shorten the time required for dispersing the magnetic powder (high dispersion stability, and excellent electromagnetic conversion characteristics). An object of the present invention is to provide a magnetic recording medium.

21 Structure of the invention and its effects The present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, wherein the magnetic powder contains 0.1 to 2.0% by weight of water, The present invention relates to a magnetic recording medium characterized in that the binder contains polyurethane in which the negative functional groups form an inner salt in the molecule.

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

First, the manufacturing method will be described.

Same as the usual polyurethane synthesis method, polycarbonate polyol, polyester polyol, Borilac I.
It is synthesized by reacting a high molecular weight polyol (molecular weight 500 to 3000) such as polyol and polyether polyol with a polyfunctional aromatic or aliphatic incyanate. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized.

These polyurethanes are primarily produced by the reaction of polyisocyanates with polyols and optionally other copolymers, and can also be in the form of urethane resins or urethane prepolymers containing free isocyanate 1-groups and/or hydroxyl groups. Alternatively, it may be one that does not contain these reactive end groups (for example, urethane elastomer type 0). As the isocyanate component, various diisocyanate compounds such as hexamethylene diisocyanate (HMD I), diphenylmethane diisocyanate (MDI) hydrogenated M DI (H+zM DI
), toluene diisocyanate (TDI), 1.5
Naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine diisocyanate methyl ester (LDI), isophorone diisocyanate (IPDI), etc. can be used.

In addition, if necessary, 1,4-butanediol, 1゜6-
A low-molecular polyfunctional alcohol such as hexanediol, (1), or 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 isocyanate component, but it can also be introduced into the polyol component, and further into the above-mentioned low-molecular polyfunctional alcohol.

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

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, second-generation luic acid, and maleic acid. As a polyhydric alcohol component,
Glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol; polyhydric alcohols such as trimethylolpropane, hexanediol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol; and Examples include two or more arbitrary alcohols selected from among alcohols.

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

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

An example of the functional group forming the inner salt is the hetain group described below.

A polyester polyol in which the negative functional group forms an inner salt will be further described.

- A simple method for synthesizing polyester involves a condensation reaction between an acid component having an aliphatic or aromatic polyfunctional acid or a derivative thereof and an aliphatic or aromatic polyfunctional alcohol component. The intramolecular amphoteric base (hetaine group, etc.) of the present invention may be contained in either the acid component or the alcohol component, or a method may be used in which a betaine group or the like is introduced into the polymer as a polymer reaction. However, in view of unreacted components and introduction rate, it is easier to control if the functional group is contained in a monopolymer monomer.

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 is expressed as follows.

X: SO30So?　　　CoCPO■ OP　03　HOP　O3 0POzHz.

A: Hydrogen or an alkyl group having 1 to 60 carbon atoms (eg, methyl group, ethyl group, etc.).

m: an integer from 1 to 10.

”− B Knee Coo or C0NH.

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

n, m: integer from 1 to 10.

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

) CI(2CH20H C)12cl120B The monomer in which the negative functional group forms an inner salt is available as a commercially available drug, but it can be easily obtained by the method described below.

1) Synthesis method using monochloroacetic acid RN (CHz C0QH)z+Cj2 CHz
C00HR-Alkyl groups such as methyl and ethyl 2) Synthesis method using monochlorosuccinic acid 3) Synthesis method using propane sultone CH□CH2011 Not applicable.

＼　　　　e CH□C)12cH2so.

Furthermore, as a polymer reaction, a reaction for introducing betaine groups and the like into a polymer will be described. In this method, a compound having a hetain group or the like is reacted with an OH group present at the end or side chain of polyurethane whose chain has been extended to a predetermined molecular weight by a polymerization reaction. In this case, first, a compound having a hydroxyl group, a betaine group, etc. is synthesized, and this is reacted with a polyfunctional isocyanate such as diisocyanate in equimolar amounts 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 NGO groups, a polyurethane into which hetain groups and the like are introduced can be obtained.

Examples of the above-mentioned compounds having a hydroxyl group and a hetaine group include the following.
'-) \CH2Cl□SO'1 C112CII□O11 \. O\CII□C)120H The amount of hetain group etc. introduced into the polyurethane resin of the present invention is preferably 0.01 to 1.0 mmoβ/g,
More preferably, it is in the range of 0.1 to 0.5 mmoff/g. The amount of introduced polar group is 0.01 mmof!
If it is less than /g, sufficient effect on the dispersibility of the ferromagnetic powder will not be recognized. In addition, the amount of the polar group introduced is 1.0
When mmoβ/g is exceeded, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also
There is also the possibility that selectivity with respect to the solvent may occur, making it impossible to use ordinary general-purpose solvents.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 5
000-100000, more preferably 10000-5
Preferably, it is in the range of 0000. 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, problems will occur in paint manufacturing processes such as mixing, transport, and coating. There is a risk that this may occur.

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

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

The amount of "polyurethane whose negative group forms an inner salt" according to the present invention is preferably 100 to 1 part by weight, more preferably 50 to 2 parts by weight, per 100 parts by weight of the magnetic powder. .

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

That is, since the functional groups contained in the polyurethane of the present invention form an inner salt, the adsorption power to the magnetic powder surface,
Retention force is extremely high. Moreover, since the moisture content of the magnetic powder is limited to a specific range of 0.1 to 2.0% by weight (13%), the moisture on the surface of the magnetic powder and the inner salt of the polyurethane are formed. The polyurethane has a sufficient interaction with the functional groups contained in the magnetic powder, and the adsorption power of the polyurethane to the magnetic powder is further increased.

As a result, the time required for dispersing the magnetic powder is shortened, the dispersion stability is improved, the magnetic powder is more densely and uniformly filled into the magnetic layer, and the output, S/N ratio, etc. are improved.

The reason why the above-mentioned remarkable effects can be achieved by the magnetic recording medium of the present invention is considered to be as follows.

The surface of magnetic powder such as metal oxide is complex, and the surface is charged with positive and negative charges due to ponds due to surface hydroxyl groups due to hydration, structural defects, ion substitution, etc. Therefore, when selecting a binder for magnetic powder, consider the acidity, basicity, and
Basic strength, acidity, number of basic sites, etc. are important factors. For example, in order to uniformly disperse magnetic powder in a short time, it is necessary to use binders with acidic and basic (polar) groups of various strengths, and to adsorb these acidic and basic sites to the surface active sites of the magnetic powder. is ideal.

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

It is also conceivable to use a binder having a polar functional group and to simultaneously use binders having functional groups of the same polarity and different strengths. However, in this case, the magnetic powder is competitively adsorbed preferentially to the side of the binder having a stronger functional group, making it difficult to achieve sufficient adsorption as a whole, resulting in poor dispersion stability of the magnetic paint. Furthermore, it is also conceivable to use a binder having a polar functional group and to simultaneously use a binder having a different type of functional group. However, in this case, the interaction between the polar groups is strong, and adsorption of the binder to the surface of the magnetic powder is difficult to occur, and the viscosity of the magnetic paint increases, making it impossible to prepare a magnetic paint.

The present invention solves these problems.

In other words, the acid sites and basic sites in the inner salts in the binder efficiently adsorb to the surface active sites (base sites and acid sites) of the magnetic powder, and the inner salts in the same binder Since acid sites and basic sites coexist, the above-mentioned (1G) problem does not occur. Moreover, by specifying the water content in the magnetic powder as described above, the number of surface active sites (water acid sites and basic sites) on the surface of the magnetic powder can be appropriately controlled, and the base content in the polyurethane of the present invention can be controlled appropriately. It is possible to strengthen the interaction between points, acid points and the surface of magnetic powder. It is thought that this significantly improves the dispersibility of the magnetic powder. If the moisture content on the surface of the magnetic powder is too small, sufficient interaction with the polar groups of the polyurethane of the present invention cannot be achieved, making it difficult for the polyurethane to exhibit the above-mentioned features. On the other hand, the water content of magnetic powder is 2
．． If it exceeds 0% by weight, water will be dispersed in the magnetic paint during dispersion, and this dispersed water will interact with the polar groups of the polyurethane, so that the polyurethane will no longer be adsorbed onto the surface of the magnetic powder.

The water content in the magnetic powder is more preferably 0.2 to 1.8% by weight.

Next, the "magnetic powder" used in the magnetic recording medium of the present invention will be further described.

The water content of magnetic powder can be measured as follows. That is, the weight of the magnetic powder sample is measured, and then the magnetic powder sample is dried at 110° C. for 1 hour, and the dried magnetic powder sample is immediately weighed again.

If the sterile weight of the magnetic powder sample is X, then the water content (weight percentage) - (x/initial magnetic powder sample weight) Cohar, which is iron oxide magnetic powder doped with or coated with cobalt atoms [containing iron oxide magnetic powder, ferromagnetic chromium dioxide powder, iron nitride, iron carbide, alloy metal magnetic powder, barium ferrite, or it is combined with titanium, cobalt, etc. Examples include those modified with metals.

As ferromagnetic iron oxide particles, when expressed as FeOx, the value of X is generally in the range of 1.33≦X≦1.50, that is, magnetite (γ-Fez (h x = 1.50)
Magnetite (Fe: +04x = 1.33), and solid solutions thereof (FeOx = 1.33 < x < 1
．． 50).

γ-Fe203 and Fe30a are usually obtained by the following manufacturing method.

Ferrous hydroxide is generated by adding an alkali to a ferrous salt solution, and oxidized by blowing air at a predetermined temperature and pH to obtain acicular hydrated iron oxide, which is heated in air at 250-400℃. It is heated, dehydrated, and then heated and reduced at 300 to 450°C in a reducing atmosphere to obtain acicular magnetite particles. Furthermore, if necessary, the magnetite is reoxidized at 200 to 350 DEG C. to form acicular magnetite (.gamma.-Fe203).

The method for producing Co-doped iron oxide particles includes (1) a method in which ferric hydroxide containing cobalt hydroxide is hydrothermally treated in an alkaline atmosphere, and the resulting powder is reduced and oxidized.

(2) When synthesizing goethite, a cobalt salt solution is added in advance, and while adjusting the pH, goethite containing cobalt is synthesized, and this is reduced and oxidized.

(3) A method in which Co-free goethite is used as a core, a reaction similar to that in (2) is performed on the core, Co-containing goethite is grown, and then reduced and oxidized.

(4) C on the surface of acicular goethite or magnetite
A method in which the Co compound is adsorbed by treatment in an alkaline aqueous solution containing o-salts, followed by reduction/oxidation or heat treatment at a relatively high temperature.

There is.

Co-coated iron oxide magnetic particles are prepared by mixing acicular magnetic iron oxide and cobalt salt in an alkaline aqueous solution and heating the mixture to adsorb cobalt compounds such as cobalt hydroxide to the iron oxide particles.
This is obtained by washing and drying with water, and then heat-treating in a non-reducing atmosphere such as air or N2 gas.

Co-coated particles are superior to Co-doped particles in demagnetizing the media magnetic layer by heating and/or pressure, and it is preferable to use Co-coated particles except in special fields.

The cobalt content is 1% of the total cobalt-containing iron oxide magnetic powder.
．． The content is preferably 0 to 5.0% by weight.

Coercive force (c) of cobalt-containing iron oxide magnetic powder is 600
It is preferable to set it as -1200 oersted. The specific surface area of the cobalt-containing iron oxide magnetic powder is 10~”I in BET value.
It is preferably within the range of OmZg, 35%/g or more, and more preferably 40r+? /g or more is more preferable.

The average particle diameter is 0.8 to 0.2 μm on the long axis and 0.8 μm on the short axis.
It is preferable to set it as about 2-0.01 micrometer.

Ferromagnetic chromium dioxide powder has high filling properties and is free from crystal defects that cause dropouts and noise.

The coercive force of ferromagnetic chromium dioxide magnetic powder is 600-1200
It is preferable to set it as oe. Specific surface area is 15~ in BET value
It is preferably within the range of 60rd/g, and 2Or+
(/g or more, more preferably 30 m/g or more).

The amount of saturation magnetization is preferably 60 to 75 emu/g.

The average particle diameter is from 0.8 to 0.2 μm on the long axis to 0.8 μm on the short axis.
It is preferable to set it as about 2-0.01 micrometer. The acicular ratio is preferably about 2/1 to 20/1.

Examples of metal magnetic powders that can be used in the present invention include Fe, Ni,
Including Co, Fe-A/! system, Fe-A/! Nl system,
Fe-Aj! -Co system, Fe-Ni-3i system, Fe-A
ff-Zn system, Fe-Ni-Co system, Fe-Mn
-Z n-based, pe-Ni-based, Fe-N1Af-based, Fe
-Ni-Zn system, Fe-Ni -Mn system, Fe-C0
Examples include ferromagnetic powders such as metal magnetic powders whose main components are -NiP type, Co-Ni type, Fe-Ni-Co, etc. Among them, Fe is 80at+n% or more (furthermore, 9Qa
tm% or more) has excellent electrical properties, and is particularly superior to Fe-Al1-Fe- in terms of corrosion resistance and dispersibility.
Aff-Ni, , FeAff-Zn, , Fe-Aj2-
Co, Fe Ni, Fe-N1-Aff, Fe-Ni
-Zn,Fe-N+A/! -3i-Zn, Fe-N1-
A/! SiMn-based metal magnetic powder is preferred.

Saraniha, iron-aluminum system (F e-A I system, F
e-Aff-Ni system, Fe-Aff-Zn system, FeAj
! -Co-based, etc.) metal magnetic powder is particularly preferred.

Hereinafter, the iron-aluminum system will be simply referred to as Fe-Aj! It is called a system.

In particular, the uses of video tapes in recent years have expanded to include a wide range of uses, and the conditions for their use have varied. Therefore, video tapes are required to have high corrosion resistance. In this regard, Fe-Aff magnetic powder exhibits high corrosion resistance,
Moreover, the dispersibility is also good. This is very important for realizing high-density recording, since even if the specific surface area of the magnetic powder is increased, its dispersibility can be sufficient.

Moreover, in the above-mentioned Fe-AA metal magnetic powder, it is preferable that the A1 content of the magnetic powder is within the range of 0.1 to 20 at %.

The coercive force (Hc) of the metal magnetic powder is preferably 600 to 2000 oersted. Specific surface area is 1 in BET value
It is preferably within the range of 0 to 80 m/g, and 35 m/g.
It is more preferable to set it to 40rd/g or more, more preferably 40rd/g or more. The average particle diameter is preferably about 0.8 to 0.2 μm on the long axis and about 0.2 to 0.01 μm on the short axis.

The above specific surface area is expressed as a BET value, which refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter.For example, even if the average particle diameter is the same, there are Some have a small surface area. To measure the specific surface area, for example, first, heat the powder at around 250°C for 30 to 30 minutes.
After heat treatment for 60 minutes, the powder is degassed to remove substances adsorbed on the powder, and then introduced into a measuring device, and the initial pressure of nitrogen is set to 0.5 kg/rrr, and the nitrogen is used to remove the liquid. Adsorption measurements are carried out at nitrogen temperature (-195 °C) (generally B, E).

A method for measuring specific surface area called the method. For details, please refer to J and A.
ll1e, Chem, Soc, 60309 (1938
). As a device for measuring the specific surface area (BET value), it is possible to use the "powder measuring device (Cantersoap)" manufactured jointly by Digestion Battery (1) and Digestion Ionics (2). A general explanation of the specific surface area and its measurement method can be found in "Measurement of Granules J (J, M.

It is described in detail in DALLAVALLE, CLYDEORR Jr. (translated by Benyo and others; published by Sangyo Toshosha).
Also, "Chemistry Handbook" (Application Edition, pp. 1170-1171,
It is also described in Nippon Kagaku Complete Edition, Maruzen, published on April 30, 1966) (In addition, in the above-mentioned "Chemistry Handbook", specific surface area is simply described as surface area (rl/gr), but in this specification (It is the same as the specific surface area in the water.)

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

"Polyurethane in which negative functional groups form an inner salt"
Other known binders can also be used.

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

The above resins are -303M, -COOM, PO(O
M) Resin containing a hydrophilic polar group such as 2 (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue) It is good to be. That is,
These resins have polar groups in their molecules that improve their compatibility with the metal magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the metal magnetic powder, further improving the stability of the coating liquid. This can also improve the durability of the medium.

The "polyurethane in which a negative functional group forms an inner salt" of the present invention is a vinyl chloride resin, a vinyl chloride copolymer (
It is preferable to use it in combination with vinyl chloride-vinyl acetate copolymer, etc.). In this case, the weight ratio of the polyurethane of the present invention to the vinyl chloride resin and vinyl chloride copolymer is (
2: 8) to (8: 2), preferably (3
:7) to (7:3) is more preferable. As the vinyl chloride copolymer, those containing the above-mentioned hydrophilic polar groups are particularly preferred.

The binder used in combination, especially the vinyl chloride copolymer, is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable polymers as necessary. be able to.

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

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

The above copolymerizable monomer containing a sulfonic acid salt is as follows: CHz = CHS O3M CHz = CHCH2S OxM CH□-C(CH:l) CHz S 03MCHz
” CHCHzOCH2CH(CH2COOR)803M CHz = CHCHzOCH2CH(OH)CH2
S O3MCHz -C(CH3)COOCzH4S
OzMCH2=CHC○OC4Hs S 03MCH
2=CHCONH,C(CH3)ZCH2SO,M is mentioned.

In addition, as a phosphate, CH2=CHCH20CH2CH(CH)CH2C)-
PO3MY' CH2=CHC0NHC(CH,)2CH2−○PO,
MX' CH2= CHCHzO<CH2CH2O)IIIP
02MX 2 In the above, M is an alkali metal, R is an alkyl group having 1 to 20 carbon atoms, and yl is H, M or C
Hz =CHCH20C)f2cH(OH)CH2Y2
is H, M or CHz = CHCON HC(CH3) Z G H
z○■ (or ○M, X2 is CHz ”= CHCHzO (CHzCHzo) II
OH or 0M. Also, n is 1 to 100 + m is 1
~100 positive number.

Copolymerizable monomers to be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, and various acrylic esters. , methacrylic ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic ester and the like.

The binder is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of monomer containing the salt of the acidic group in the binder is 0.0
It is preferably 1 to 30 mol%. If the amount of the salt-containing monomer is too large, the solubility in solvents will be poor and gelation will likely occur. Furthermore, if the amount of salt-containing monomer is too small, desired characteristics cannot be obtained.

Preferably, the vinyl chloride copolymer further contains an epoxy group or a hydroxyl group. By the way, conventional vinyl chloride copolymers (for example, U, C, C.

VAGH) manufactured by Co., Ltd. consisted of the following copolymerized components.

However, the CH3C0-0- group here does not contribute to the crosslinking reaction with the curing agent etc. Therefore,
In place of CH3CO, copolymers having the following units may be mentioned.

It is further advantageous in terms of improved running performance and electromagnetic conversion characteristics.
The dispersibility is also improved to some extent, and the residual solvent size in the magnetic layer is reduced by CH2-C.
Hteπ, 1Xte "H (X: 1,000 unit part containing an alkali metal salt of a sulfo group or phospho group) "Polyurethane in which negative functional groups form an inner salt"
It is also preferable to use epoxy resin (particularly phenoxy resin), polyester resin, or nitrocellulose resin (hereinafter referred to as other resin) in combination. In this case, the blending ratio of the urethane resin and other resins is preferably 90 to 10 parts by weight, more preferably 80 to 20 parts by weight.

If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too bulky and the durability of the coating film is significantly deteriorated, and also the adhesion to the support becomes poor. Further, when the above blending ratio is less than 10 parts by weight,
Magnetic powder easily falls off.

When carbon blank is included in the magnetic layer, the degree of light shielding can be increased by using carbon black.

As a light-shielding carbon blank, for example, Raben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 190rrr) is used.
/g, particle size 18m μ), 2100.117o, 10
00, made by Mitsubishi Kasei ■] 00, #75, #40, #
35, #30, etc. can be used.

Further, as a conductive carbon blank, for example, Conductex (Columbia Carbon Co., Ltd.) is used.
x) 975 (BET value (hereinafter abbreviated as BET) 250
rrf/g = DBP oil absorption (hereinafter abbreviated as DBP) 17
0ml! /100gr, particle size 24mμ), Conductesox 900 (B ET125ml g, particle size 2
7 mμ), : 1 Dactesox 40-220 (particle size 2
0mμ), Conductex SC (BET220ml
gr, DBP115 mn/100gr.

Particle size: 20 mμ), Parcan (Cabo
tVulcan) X C-72 (specific surface area 254m/
g, particle size 3゜mμ), Harkan P (BET143 r
tr/gr,, DBP118ml/IQQgr
, particle size 20rnc+), Lachen 104o, 420,
Examples include Buranoku Pearls 2000 (particle size 15m, CR) and #44 manufactured by Ryo Kasei ■.

Other carbon blacks that can be used in the present invention include Conductenox (manufactured by Columbia Carbon Co., Ltd.).
Conductex) -S C, (B E T220
m/g, DB P115 ml! /100
g, particle size 20 m, u), Halkan (V
ulcan) 9 (BET 140m/g-D
BP114 mn/100g, particle size 19mμ), #80 manufactured by Asahi Carbon Co., Ltd. (BET117 rd/g, DB
P113mβ/100g, particle size 23mμ), H5100 manufactured by Denki Kagaku Co., Ltd. (B ET32m/g, D B
P2H4m 12 /100g, particle size 53m, u), #22B manufactured by Mitsubishi Chemical Corporation (BET55m / g,
D B P131 m l! /100g, particle size 4(1
mμ), #2OB (BET56m/g, D
BP115ml! /100g.

Particle size 40mμ), #3500 (BET47rrr/
g, DBP187 m t2 /100g, particle size 40
mμ), and in addition, CF-9 manufactured by Mitsubishi Chemical Corporation,
#4000, MA-600, Bra 7 made by Capo Soto
Black Pearls L2 Monarch 800, Black Pearls 7
00, Black Pearls 1000, Black Pearls 880, Blank Burls 900, Blank Pearls 1300, Black Pearls 2000, Sterling V, Columbian Carbon Raven 410, Raven 3200, Lachen 430, Raven 450, Lachen 825, Lachen 1255, Raven 1035, Raven 1000, Seechen 5000. Examples include Ketsutien Blank FC.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic coating paste containing a binder.

Such polyisocyanate curing agents include, for example, bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; trifunctional isocyanates such as Coronat (specially manufactured by Nippon Polyurethane Industries) and Desmodur (manufactured by Bayer); Any conventionally used curing agent, such as a urethane prepolymer containing mucoisocyanate groups at both ends, or polyisocyanate that can be used as a curing agent can be used.

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

The magnetic recording medium of the present invention has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, as shown in FIG. 1, if necessary. This is a configuration in which a BCC 20 is installed. Further, as shown in FIG. 2, the magnetic layer 2 of the magnetic recording medium of FIG.
An overcoat layer (QC layer) 4 may be provided thereon.

Further, the magnetic recording media shown in FIGS. 1 and 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. It's okay. Further, the support may be subjected to corona discharge treatment.

In addition to the metal magnetic powder and binder described above, the magnetic layer 2 also contains:
Fatty acids and/or fatty acid esters can be contained as lubricants. This allows us to bring out the strengths of both while offsetting the defects that would occur when used alone.
Improves lubrication effect, still image durability, running stability, S
/N ratio etc. can be increased. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight, and even more preferably 0.5 to 8.0 parts by weight, per 100 parts by weight of the magnetic powder. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and output decreases. The amount of fatty acid ester added is 0.00 parts by weight per 100 parts by weight of magnetic powder.
1 to 10 parts by weight is better, and 0.2 to 8.5 parts by weight is even better. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount increases, the ester will easily seep out and the output will decrease.

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

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Hehenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid Acid (21) Sebacic acid (22) 1.12-Dodecanedicarboxylic acid (23)
Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

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

Non-magnetic abrasive particles can also be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, etc. are used. . The average particle diameter of this abrasive is preferably 0.6 μm or less. Moreover, it is preferable that the Mohs hardness is 5 or more.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Furthermore, a carbon blank can also be used in combination.

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

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples include zinc oxide, α-Fe203, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as henzoguanamine resins, melamine resins, and phthalocyanine pigments can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use a carbon blank together with the above-mentioned non-magnetic particles. This further stabilizes the running properties of the medium, and in combination with the effect of the non-magnetic particles described above, it is possible to further improve the durability of the medium.

The thickness of the magnetic layer is preferably thin in order to achieve a high S/N ratio, and thicker in terms of running performance and still durability. Therefore, 6.0 to 1.0 μm is preferable,
More preferably, the thickness is 5.0 to 2.0 μm. The surface roughness of the magnetic layer is an average surface roughness Ra of 0.005 to 0.02.
It is preferable to set it to 0 μm. This does not reduce running performance and improves the S/N ratio.

Examples of the material forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene 2.6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; plastics such as polycarbonate, etc. can be mentioned. Furthermore, Cu,
Metals such as A1 and Zn, glass, and various ceramics such as so-called new ceramics (for example, borosulfur nitride, silicon carbide, etc.) can also be used.

The form of the non-magnetic support is not particularly limited, and may include tape,
It may be a sheet, card, disk, drum, etc. (various materials can be selected and used depending on the form and as necessary.

When the non-magnetic support is in the form of a tape or sheet, the thickness is usually in the range of 3 to 100 μm, preferably in the range of 5 to 50 μm. Further, in the case of a disk or card shape, the thickness is usually within the range of 30 to 100 μm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., so that it can be made into a shape B3 corresponding to the recorder used.

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

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, [parts-4] are all parts by weight.

Preparation of Videotape First, a magnetic layer was formed on a polyethylene terephthalate film having a thickness of 10 μm as a support in the following manner.

That is, using the specified magnetic powder shown in Table 1 below, Table 1
A magnetic paint is prepared by dispersing each resin and various additives shown in the following. This magnetic paint is filtered through a 1 μm filter, 1.6 parts of trifunctional isocyanate is added, and 4.0
Coat it to a thickness of μm and shade it with a super calendar.
The magnetic layers had the various compositions shown below.

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

Carbon black 40 parts Barium sulfate 10 parts Nitrocellulose 25 parts N-230
1 (Made of mother wood polyurethane) 25 parts Coronate
) 10-part cyclohexanone
400 parts methyl ethyl ketone
250 parts toluene
250 parts A wide magnetic film having a magnetic layer and a BC layer of a predetermined thickness was obtained in this way, and this was wound up.

One copy of this film was cut into a 2-inch width to make each videotape (Table 1). However, the numerical values shown in Table 1 represent parts by weight.

Table 1 Each magnetic powder has the following characteristics.

A BCD CO-γ-Fe203 Same as left Same left Same left Moisture content 0.05 (wt%) Coercive force 650 (Oersted) Specific surface area 32 (BET value, rn'/g) Magnetization amount 75.6 (emu/g) Particle size 0.4 (Long axis, μm) 0.3 76.8 0.3 1.3 2.5 Ferromagnetic chromium dioxide 1.5 79.0 77.0 74.5 0.3 0.25 0.5 F GHI JK Ferromagnetic dioxide Same as left Same left Ferromagnetic Same left Same left Chromium
Metal magnetic powder moisture content 0.05 1.8
2.7 2.9 1.7 0゜9 (weight%) Coercive force 760 850 910 1300
1500 (Oersted) Specific surface area 42 38 45 43 5
0 (BET value, m/g> Magnetization amount 75.3 74.2 73.8 131
135 (emu/g) Particle diameter (1, 40, 40, 30, 50, 3 (long axis, μm) The polyurethane resins (a) to (c) according to the present invention are as follows.

Polyurethane (a) according to the present invention was synthesized by the method of Synthesis Example 1, and (b) and (c) were also synthesized by the same method.

(a) Sulfohecine type modified group content Number average molecular weight 22,000 Tg-20℃ Polar group concentration 0.04 mmol/g CH3 ■ 1'fCH2-N-CH2-+/ Polyester type (C
H2)3 Polyurethane chain 0-8-〇(b) Carboxybetaine type modification group content number average molecular weight 1
．． 50,000 Tg -10'C polar group concentration 0.1nu+
+ol/g H2 CH□ Polyurethane chain (iii) Phosphohetaine type modified group-containing number average molecule N30,000 Tg O℃ polar group concentration 0.
07 mmol/g H2 Polyurethane chain H2 HO-P=0 e <Evaluation of videotape performance> Characteristic evaluations shown in Table 2 below were performed for each videotape, not shown in Table 1.

The measurement method for each evaluation data is as follows.

Electromagnetic Conversion Characteristics> The output during playback in a white signal with 100% RF specific output was determined using the tape of Comparative Example (3) as a reference and in comparison with the tape of Comparative Example (3).

Lumi-3/N: Using a noise meter (manufactured by Shihasoku Co., Ltd.), the difference in S/N of the sample at 100% white signal was determined by comparing the tape with a reference tape (manufactured by Konica ■).

Chroma-3/N: Using a noise meter (manufactured by Shihasoku), the difference in S/H of the sample in the chroma signal was determined in comparison with a reference tape (manufactured by Konica ■).

Fast running and durability Jitter: VTR jitter manufacturer MK-612A
Measured at (Meguro Radio).

Still life: The time it takes for the RF output to decrease by dB in still mode using NV-6200 (manufactured by Matsushita Electric).

<100 Pass Tape> and <Virgin Tape> RF output fluctuation, dynamic friction coefficient, and dropout were measured for unused tape (virgin tape). In addition, the sample tape was packed in a VHS cassette and placed in N
Using V-6200 (manufactured by Matsushita Electric) deck, 100
The tape was run repeatedly (100 pass tape). In addition to carrying out the above measurements, the presence or absence of damage to the tape was also examined.

Dynamic friction coefficient: 25℃ Otsu trowel tape runnability tester TBT3
A tape was wound 180° around a chrome-plated stainless steel 4φ pin at 00D (Yokohama System Research Institute), and measurement was performed at a tape speed of 1 crn/sec and an inlet tension of 20 g, and μ was calculated using the following formula.

Dropout: Using a dropout counter VD-5M manufactured by Victor Japan, the output that is longer than 15 p sec and is 20 dB or more lower than the output of the RF envelope is defined as one dropout, and the total length is measured, and the total length is measured. The average value was calculated.

(Left below) Samples of Examples 1 to 6 using the polyurethane resin according to the present invention and dispersing magnetic powder conforming to the structure of the present invention had better electromagnetic conversion characteristics, jitter, Excellent still life. Further, in the 100-pass running test e, there was no occurrence of tape damage such as edge bending or one-sided stretching, and the coefficient of dynamic friction was small.

In addition, the output fluctuation range is small. Regarding dropouts, the level remains at a low level.

Next, based on the videotape of Example 1.3.5, the water content in the magnetic powder was changed to various values, the other configurations and prescriptions were kept the same, and videotapes were prepared for each, and the RF
Specific power was measured. The results are shown in FIG.

From the results shown in FIG. 3, it can be seen that by limiting the water content in the magnetic powder as described above, the effects of the present invention are significantly exhibited.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially enlarged sectional views showing examples of magnetic recording media. Figure 3 shows R for changes in water content in magnetic powder.
It is a graph showing F output change. In addition, in the symbols shown in the drawings, 1-----1 Nonmagnetic support 2-- Magnetic layer 3-- Hack coat layer (BC layer) 4-------- Overcoat layer (00 layer ).

Claims (1)

[Claims] 1. In a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, the magnetic powder contains 0.1 to 2.0% by weight of water, and the negative functional group forms an inner salt. 1. A magnetic recording medium, comprising polyurethane as the binder.