JPH03224128A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having good electromagnetic conversion characteristics and traveling property by incorporating a low mol.wt. compd. of <=2,000 mol.wt. having an epoxy group and a polar group in one molecule into a magnetic layer. CONSTITUTION:A low mol.wt. compd. of <=2,000 mol.wt. having an epoxy group and a polar group in one molecule is incorporated into the magnetic layer. The polar group is one or more kinds selected from -COOM, -SO3M, -OSO3M, -OPO(OM)2, and -PO(OM)2, wherein M is an alkali metal atom or ammonium. By this method, dispersion state of the ferromagnetic fine power in the magnetic layer is improved so that the characteristics of the ferromagnetic powder are enough displayed, and the obtd. medium has excellent traveling property with improved electromagnetic conversion characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a magnetic recording medium comprising a nonmagnetic support and a magnetic layer.

[Conventional technology]

Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, floppy disks, etc. A magnetic recording medium basically consists of a magnetic layer in which ferromagnetic powder is dispersed in a binder, which is laminated on a non-magnetic support.

Basically, magnetic recording media are required to have high levels of various properties such as electromagnetic conversion properties, running durability, and running performance. In particular, with the recent spread of 8mm video tape recorders, video tapes are required to have particularly excellent electromagnetic conversion characteristics, such as high video output and excellent original picture playback ability. has been done.

There are various methods for improving the electromagnetic conversion characteristics of a magnetic recording medium, but the method of improving the characteristics of ferromagnetic powder, which is a magnetic recording material, is direct and effective. Therefore, ferromagnetic powder has gradually become finer to enable high-density recording, and the material for ferromagnetic powder has also shifted from iron oxide to iron oxide modified with different metals such as cobalt. Recently, ferromagnetic metals such as iron, nickel, and cobalt, or alloys containing these metals, have come to be used.

By using ferromagnetic powder improved in this way, it is essentially possible to obtain a magnetic recording medium with good electromagnetic conversion characteristics, but in reality, it is possible to obtain a magnetic recording medium with good electromagnetic conversion characteristics. It is difficult to manufacture magnetic recording media with improved electromagnetic conversion characteristics.

This is because as the ferromagnetic powder becomes finer, its dispersibility in the binder tends to decrease, and the characteristics of the ferromagnetic powder include, for example, γ-iron oxide, cobalt-coated γ-iron oxide,
Since the dispersibility tends to decrease in the order of fine ferromagnetic metal powder, improving the ferromagnetic powder may actually worsen the dispersion state of the ferromagnetic powder in the magnetic layer. This is due to the fact that the excellent properties of the powder are not fully exhibited.

In order to improve the dispersion state of these ferromagnetic fine powders, there is a method of performing cross-talk dispersion for a long time when preparing magnetic paint, but since a considerable shearing force acts on the ferromagnetic fine powders during cross-dispersion, the ferromagnetic fine powder The characteristics of the fine powder may be impaired, and furthermore, it takes a long time to manufacture the magnetic recording medium, which poses problems in terms of work efficiency.

Therefore, methods of effectively dispersing the above-mentioned fine ferromagnetic powder without making major changes to the manufacturing method of ordinary magnetic recording media have been studied. There are methods using ferromagnetic fine powder that has been surface-treated with a surface treatment agent such as a ring agent, methods using components (dispersants) that improve the dispersibility of ferromagnetic fine powder such as fatty acids, and methods using various functional groups. A method using a vinyl chloride copolymer containing as a binder (Japanese Patent Application Laid-Open No. 63
-83913) etc. are known. A magnetic recording medium containing a polymer having a polar functional group and a degree of polymerization of 100 or less in the magnetic layer (Japanese Patent Laid-Open No. 57-53824) has also been proposed.

However, according to studies conducted by the present inventors, it has been found that even if the above method is used, the dispersion state of the ferromagnetic fine powder may not be sufficiently improved in some cases.

That is, for example, in the case of a ferromagnetic fine powder that has been surface-treated using the silane coupling agent, since the surface of the ferromagnetic fine powder is hydrophobized by the silane coupling agent,
Although the stability of the dispersion state of the ferromagnetic fine powder particles in the magnetic paint is usually improved, the compatibility with the resin component may be adversely reduced. Therefore, the final state of dispersion of the ferromagnetic fine powder in the magnetic layer may not be sufficiently improved. Furthermore, since the silane coupling agent is very expensive, it is difficult to use it as a treatment agent for ferromagnetic fine powder used in ordinary magnetic recording media.

Furthermore, fatty acids, which are normally contained as lubricants in the magnetic layer of magnetic recording media, have a dispersing effect on the ferromagnetic fine powder. Therefore, it is possible to improve the dispersion state of the ferromagnetic fine powder by adjusting the amount used, but in general, when fatty acids are used as a dispersant, they are more difficult to disperse than when added to the magnetic layer as a lubricant. A sufficient effect cannot be obtained unless a large amount is used. On the other hand, fatty acids are known to act as plasticizers on binders when used in excess, and there is a problem that when fatty acids act as dispersants for ferromagnetic fine powder, the binders inevitably become plasticized. There is.

On the other hand, by improving the dispersion state of the ferromagnetic fine powder,
A problem has arisen in that the smoothness of the surface of the magnetic recording medium improves, resulting in poor running performance. For example, it has been possible to improve the dispersion state by using a large amount of fatty acids, but this has been insufficient in terms of durability and runnability.

In addition, the polymer proposed in JP-A No. 57-53824 has a free acid polar group, so it is extremely easy to thicken.
Sufficient surface gloss and SQ were not obtained.

Furthermore, when a low molecular weight vinyl chloride copolymer containing various functional groups is used during kneading or dispersion as proposed in JP-A No. 63-83913, the low molecular weight vinyl chloride copolymer is easily dehydrochlorinated. This was not desirable as it caused head corrosion.

(Objective of the Invention) An object of the present invention is to provide a magnetic recording medium particularly having good electromagnetic conversion characteristics and running properties.

More specifically, the present invention improves the dispersion state of the ferromagnetic fine powder in the magnetic layer so that the characteristics of the ferromagnetic fine powder used are fully exhibited, improves the electromagnetic conversion characteristics, and also provides excellent runnability. The purpose is to provide a magnetic recording medium that maintains the

(Structure of the Invention) The above object of the present invention is to provide a magnetic recording medium in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support. and 1000M as a polar group.

508M, O3O+ M, OPO(OM)2
.

This can be achieved by a magnetic recording medium characterized by containing a low molecular weight compound having a molecular weight of 2,000 or less and containing one or more of PO(OM)2 (where M is an alkali metal atom or ammonium).

More preferably, the above object of the present invention is a magnetic recording medium characterized in that the low molecular compound is at least one compound selected from an ether compound, an ester compound, an amine compound, or a vinyl polymer not containing vinyl chloride. This can be achieved by

That is, although the compound of the present invention has a low molecular weight, it does not contain components that are easily dehydrochlorinated, such as vinyl chloride, so the epoxy group exists stably, and it has excellent adsorption to ferromagnetic powder.
In addition to improving dispersibility, it also acts as a mediator between the ferromagnetic powder and the binder because it has a polar group. It is also an excellent compound that has a suitable affinity with the binder, but does not plasticize the magnetic layer or deteriorate its durability even when used in large amounts.

Alternatively, the epoxy group quickly reacts with the isocyanate group of the curing agent to form a urethane bond, which more firmly binds the binder and the ferromagnetic powder, thereby improving durability.

The compound in the present invention has an epoxy group in the same molecule,
COOM-3o, M as a polar group.

-08O,M, -0PO(OM)2.

It is characterized by containing any one of PO(OM)2 (where M is an alkali metal or ammonium).

The reason why these groups are introduced as a salt is that if a free acid is used, the viscosity may increase during surface treatment or kneading with a binder.

As a method for introducing an epoxy group, various commercially available epoxy compounds can be used. Also known is a synthesis method in which an aliphatic alcohol, aromatic phenol, aliphatic amine, or aromatic amine is reacted with epihalohydrin.

1000M, -8o, M for these compounds.

08Ch M, OPO (OM) 2.

As a method for introducing PO(OM) 2 , a generally known method for synthesizing salts of carboxylic acids, sulfonic acids, and phosphonic acids can be adopted.

It is also possible to apply these methods to an aliphatic alcohol, aromatic phenol, aliphatic amine, or aromatic amine component before introducing an epoxy group to introduce a polar group in advance. The molecular weight of these compounds is 2,000 or less, preferably 1,000 or less. Molecular weight is 2,00
When it is 0 or more, the effect of improving the dispersibility of the ferromagnetic powder becomes small.

The chemical structure of the compound used in the present invention is shown by a general formula.

Ester compounds Ether compounds Amino compounds (where R1 and R2 are aliphatic and aromatic groups, X is a polar group, -SO, M, -03OIM).

-0PO(OM) 2. -PO(OM)2 is shown. )
Also, various vinyl monomers are used as vinyl compounds containing epoxy groups -〇〇〇M, -8o, M.

504M, -0PO(OM) 2. It may be copolymerized with a vinyl compound containing -PO(OM)2.

As various vinyl monomers, C00CH, C00CH, CN can be given.

Also, as a vinyl monomer containing an epoxy group, CH.

CH2 CH CH2=C CH,=CH can be used.

0CR2CH-CH2 \1 Oa As a vinyl monomer containing M, CH.

CH2 CH CH2 QC2H, So, M QC2H, So, M Hs CH,=CH CH2 QC,H,SO3M QC, H, So, M CH.

CH2=CH CH2=C CH2803M CHt So, M CH.

CH2 CH CH2 C0NHC(CH3)zcH2sO, NaC0NHC(
CHs)2cH2s(hNa).

O.S.O.

As a vinyl monomer containing M, CH.

CH2 CH CH2 o (CH2CH2 scolding SO, M 0 (CH2CH20 piece SO3M CH.

CH,=CH CH2(XCH, CH2O well SO, M CH.

CH20 (CH2CH20i SO3MCH3 can be mentioned.

Also, -op.

(OM) Vinyl monomers containing - As for can be mentioned.

Examples of vinyl monomers containing PO (OM) include.

Examples of vinyl monomers containing -COOM include.

When the above compound is dissolved in an organic solvent, ferromagnetic powder is added, and surface treatment or cross-dispersion is performed, such compound is adsorbed or bonded to the surface of the ferromagnetic powder. When a binder is further added and kneaded, the dispersibility of the ferromagnetic powder is significantly improved.

This is because the polar groups strongly adsorb to the surface of the ferromagnetic powder and coat the surface of the magnetic material, which prevents agglomeration between the magnetic particles, and when a magnetic layer is formed, the resin component of the ferromagnetic powder It is presumed that the affinity is moderately improved and the state of dispersion of the ferromagnetic fine powder in the magnetic layer is improved.

Furthermore, when an isocyanate-based crosslinking agent is added, the dispersion state is improved and the physical properties of the film are surprisingly improved.
This is due to the interaction between the polar groups not adsorbed on the ferromagnetic powder and the binder, especially the epoxy group opening the ring and reacting with the isocyanate group in the crosslinking agent to form a urethane bond, or the isocyanate group and the epoxy group. This is presumed to be because the groups react to form oxazolidone. The content of the above compound in the magnetic layer is usually 0.00 parts by weight per 100 parts by weight of the ferromagnetic powder. A content within the range of 1 to 10 parts by weight is desirable.

In particular, by setting the content within the range of 0.2 to 6 parts by weight, the glossiness of the surface of the magnetic layer increases, the dispersion state of the ferromagnetic powder becomes favorable, and the electromagnetic conversion characteristics are significantly improved. Content is 0. If it is less than 1 part by weight, the effect of the blend may not be effective, and if it is blended in more than 10 parts by weight, the dispersion state of the ferromagnetic fine powder will not be improved any further, and it will act as a plasticizer, causing the magnetic layer to deteriorate. may deteriorate the physical properties of

In the present invention, the method for improving the dispersibility of ferromagnetic powder using the above compound is to dissolve or disperse this compound in a low boiling point organic solvent, add the ferromagnetic powder to this solution, and then mix. , a method for manufacturing a magnetic recording medium by preparing a pretreated ferromagnetic fine powder by removing an organic solvent, dispersing the ferromagnetic fine powder in a binder solution, and applying it to a non-magnetic support; When preparing a paint, there is a method in which the above-mentioned compound is dissolved or dispersed together with a ferromagnetic powder in a part of a solvent for preparing a magnetic paint, and then a binder is added to perform cross-dispersion and coating.

The magnetic recording medium according to the present invention has an epoxy group and -So
3M, -08O,M, -0PO(OM)2.

-PO(OM) By using a compound containing one of the polar groups, this compound acts as a dispersant for the ferromagnetic powder, improving the dispersion state of the ferromagnetic fine powder in the magnetic layer, and The physical properties of the film are improved by the interaction or reaction between the polar groups not adsorbed on the ferromagnetic powder and the binder, particularly the isocyanate in the crosslinking agent in the binder.

Specifically, by using the above compound, the ferromagnetic powder is dispersed well, the surface of the magnetic layer becomes smooth, and the maximum magnetic flux density and squareness ratio of the magnetic layer are increased. Furthermore, by improving the physical properties of the film, running durability is also improved.

The magnetic recording medium according to the present invention basically has a structure in which a non-magnetic support and a magnetic layer made of ferromagnetic powder (ferromagnetic material) dispersed in a binder are provided on the support. .

The material forming the non-magnetic support can be one that is normally used as a material for the non-magnetic support of magnetic recording media.

Examples of the material include polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, and metal foils such as aluminum foil and stainless steel foil.

The thickness of the nonmagnetic support is usually in the range of 3 to 50 μm (preferably 5 to 30 μm).

The nonmagnetic support may be provided with a back coat layer (backing layer) on the side where the magnetic layer is not provided.

The magnetic recording medium according to the present invention includes a magnetic layer in which ferromagnetic powder is dispersed in a binder on a non-magnetic support as described above.

Examples of ferromagnetic powders include γ-Fe20+, Fe50<
and metal oxide-based ferromagnetic powders such as bertolide, barium ferrite, dissimilar metal/iron oxide-based ferromagnetic powders such as γ-Feint containing Co, and ferromagnetic metals such as iron. Mention may be made of ferromagnetic metal powders.

Although there is no particular restriction on the shape of the ferromagnetic powder used in the present invention,
Usually, needle-shaped, granular, dice-shaped, rice grain-shaped, and plate-shaped ones are used. In particular, it is preferable to use needle-shaped ones.

In particular, the present invention is advantageous when applied to a magnetic recording medium using ferromagnetic metal powder whose dispersibility is inferior to other ferromagnetic powders. When using a ferromagnetic metal powder, it is a ferromagnetic metal powder containing iron, cobalt or nickel, and has a specific surface area of 42rd/g or more (particularly preferably 45mr/g).
above) is highly effective.

As a specific example of such a ferromagnetic metal powder, the metal content in the ferromagnetic metal powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal or alloy, (Example: Fe, Co, Ni, Fe-Co
, Fe-Ni.

Co-Ni, Co-N1-Fe), and the metal content is 2
Other components (e.g. ACS i, S
, Sc, Ti, V, Cr, Mn.

Cu, Zn, Y, MO, Rh, Pd, Ag, W.

Sn, 5bXB, Te, Ba, Ta, Re, P.

Au, Hg, Bi, La, Ce, Pr, Nd.

Mention may be made of alloys that may contain Pb, Zn). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide. Methods for producing these fine ferromagnetic metal powders are already known, and the ferromagnetic metal powder used in the present invention can also be produced according to these known methods.

As the binder, commonly used binders can be used in an amount of usually 10 to 40 parts by weight (preferably 15 to 30 parts by weight) per 100 parts by weight of the ferromagnetic powder.

Examples of resins used include cellulose derivatives, vinyl chloride copolymers (e.g., vinyl chloride, vinyl chloride, and vinyl chloride containing a third component such as vinyl acetate/maleic anhydride copolymers).
Vinyl acetate copolymers and vinyl chloride/vinyl acetate copolymers or their saponified products, or CO2M,
SO, M, PO.

Vinyl chloride copolymers containing polar groups such as M2), vinylidene chloride copolymers, polyester resins, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, phenoxy resins, epoxy resins, butadiene, Examples include acrylonitrile copolymers, polyurethane resins, and urethane epoxy resins, and in the present invention, these can be used alone or in combination.

Among the above resins, it is preferable to use a polyurethane resin and a vinyl chloride copolymer together.

Further, when a polyurethane resin and a vinyl chloride copolymer are used, it is particularly preferable that at least one of these resins is a resin containing a repeating unit having a polar group.

Examples of repeating units having polar groups contained in the vinyl chloride copolymer include -COOM, -3o, MO3O, M',
and -PO(OM") 2 [M represents a hydrogen atom, an alkali metal atom or ammonium. Even if the vinyl chloride polymer contains one of these repeating units, two or more of them may be included. Among these, it is preferable to use a vinyl chloride copolymer containing a repeating unit having -8OsNa and/or a repeating unit having -COOH.

The content of repeating units having polar groups in the vinyl chloride copolymer is usually in the range of 0.001 to 5.0 mol% (preferably 0.05 to 3.0 mol%).

If the content of repeating units having polar groups is lower than 0.001 mol%, the dispersion state of the ferromagnetic powder may deteriorate, and if it is higher than 5.0 mol%, the copolymer may become hygroscopic. The weather resistance of the magnetic tape tends to deteriorate.

It is preferable that the above-mentioned vinyl chloride copolymer further contains a repeating unit having an epoxy group.

The epoxy group in the vinyl chloride copolymer mainly acts to stabilize the vinyl chloride copolymer and suppress the dehydrochlorination reaction of the copolymer that progresses over time.

When containing a repeating unit having an epoxy group, the content of the repeating unit having an epoxy group in the copolymer is preferably within the range of 1 to 30 mol%, and vinyl repeating unit 1
The ratio of repeating units having epoxy groups to moles is 0.01 to 0.5 moles (particularly preferably 0.01 to 0.5 moles).
3 mol).

The number average molecular weight of such a vinyl chloride copolymer is usually io, ooo to 100,000 (preferably 15.
000 to 60,000).

Further, the binder is preferably a cured product obtained by adding a polyisocyanate compound to the above vinyl chloride copolymer and polyurethane resin.

In this case, ordinary polyisocyanate compounds can be used, and specific examples thereof include 3 mol of diisocyanate such as diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, and xylylene diisocyanate, and trimethylolpropane. 1 mole of the reaction product, 3 moles of hexamethylene diisocyanate in a biuret adduct compound, 5 moles of tolylene diisocyanate in an isocyanurate adduct compound, 3 moles of tolylene diisocyanate and 2 moles of cehexamethylene diisocyanate in an isocyanurate adduct compound, and diphenylmethane diisocyanate. Polymers may be mentioned.

The amount of the polyisocyanate compound used is usually equal to or less than that of the above-mentioned polyurethane resin.

By using polyurethane resin, vinyl chloride copolymer and polyisocyanate compound in this way,
The polyisocyanate compound forms a three-dimensional crosslink between the polyurethane resin and the vinyl chloride copolymer, making it a strong binder.

In the present invention, the above compound is dissolved in an organic solvent and mixed with ferromagnetic powder, then dispersed using the above vinyl chloride copolymer and polyurethane resin as a binder, and then mixed with a magnetic coating liquid using a polyisocyanate compound. By doing so, the binder can effectively crosslink and form a strong magnetic layer.

Further, it is preferable that the magnetic layer of the magnetic recording medium of the present invention contains a fatty acid. In the magnetic layer, the fatty acid acts as a lubricant, but when preparing a magnetic paint, it acts to improve the dispersibility of the ferromagnetic powder.

When containing fatty acids, the content of fatty acids is usually set within the range of 0.1 to 5 parts by weight (particularly preferably 0.3 to 4 parts by weight) based on 100 parts by weight of the ferromagnetic fine powder.

Examples of fatty acids used in the present invention include capric acid, lauric acid, undecylic acid, myristic acid, palmitic acid, stearic acid, behenic acid, montanic acid, oleic acid,
Mention may be made of elaidic acid, linoleic acid, lylunic acid and stearolic acid.

Furthermore, when a fatty acid is used, the lubricity is improved by using a combination of this fatty acid and a fatty acid ester as a lubricant.

When using a fatty acid ester, the content of the fatty acid ester is usually 0.00 parts by weight per 100 parts by weight of the ferromagnetic powder. 1~
The amount is set within the range of 5 parts by weight (particularly preferably 0.3 to 4 parts by weight).

Furthermore, when using fatty acids and fatty acid esters together,
Usually fatty acid and fatty acid ester have a weight ratio of 1=9 to 9:
It is used at a blending ratio within the range of 1.

Examples of fatty acid esters used in the present invention include octyl myristate, butyl myristate, methyl myristate, butyl stearate, ethyl palmitate, butoxyethyl palmitate, oleyl oleate, tridecyl stearate, and butoxyethyl stearate. I can list many things.

The magnetic layer of the magnetic recording medium according to the present invention preferably further contains inorganic particles having a Mohs hardness of 5 or more.

The inorganic particles used are not particularly limited as long as they have a Mohs hardness of 5 or more. Examples of inorganic particles having a Mohs hardness of 5 or more include ACCh (Mohs hardness 9), Ti0 (Mohs hardness 6),
TiO2 (6.5).

SiO□ (7), SnO2 (6.5).

cr H03, (same 9), and aFe20m (same 5
．． 5), and these can be used alone or in combination.

Particularly preferred are inorganic particles having a Mohs hardness of 8 or more. When inorganic particles with a Mohs hardness lower than 5 are used, the inorganic particles tend to fall off from the magnetic layer and have almost no abrasive action on the head, resulting in head clogging and poor running durability. Become.

The content of inorganic particles is usually 0.00 parts by weight per 100 parts by weight of ferromagnetic powder. It ranges from 1 to 20 parts by weight, preferably from 1 to 10 parts by weight.

In addition to the above-mentioned inorganic particles, the magnetic layer preferably contains carbon black (particularly one having an average particle size of 10 to 3001 m (nanometers; 10-'m)).

The magnetic recording medium according to the present invention is produced by mixing ferromagnetic powder, a binder, and the above-mentioned additives used as desired in a commonly used organic solvent such as toluene, butyl acetate, ethyl acetate, methyl ethyl ketone, cyclohexanone, and tetrahydrofuran. After dispersing and preparing a magnetic paint, this magnetic paint is coated on a non-magnetic support so that the dry thickness of the magnetic layer is usually 0.1 to 10 μm, and then subjected to magnetic field orientation treatment, drying, surface smoothing treatment and Perform hardening treatment etc.
It can then be manufactured using a conventional method of cutting.

However, when carrying out the above method, a method such as using a ferromagnetic powder pretreated as described above or adding the above compound at the time of crosstalk dispersion is used.

Preferred embodiments during kneading are as follows.

(11 ferromagnetic powder 1.0 to 0.3 to 1°0 solvent,
It is preferable to further add and knead the above compound.

(2) 0.3 to 1 liter of solvent per 1.0 liter of ferromagnetic powder.

0. It is preferable to further add and knead the above compound and an isocyanate curing agent.

Generally, the magnetic layer is applied directly onto the nonmagnetic support, but it can also be applied via an adhesive layer or an undercoat layer.

Methods for preparing magnetic paints, coating methods, magnetic field orientation treatment methods, drying methods, surface smoothing treatment methods, hardening treatment methods, etc. are already known, and the magnetic recording medium of the present invention can also be manufactured according to these methods.

(Effect of the invention) The magnetic layer of the present invention contains a low-molecular compound with a molecular weight of 2000 or less that contains an epoxy group and a polar group in the same molecule, but the low-molecular-weight polar group is highly adsorbed on the surface of the ferromagnetic powder. In addition, the epoxy group easily reacts with polyisocyanate, and the bond with the binder is strong. That is, since the compound of the present invention has a low molecular weight, it has high reactivity and plays a strong mediating role between the ferromagnetic powder and the binder. The polar groups are adsorbed to the ferromagnetic powder and improve its dispersibility, improving surface gloss and SQ.As the dispersibility increases, the filling degree increases and Bm improves, and the ferromagnetic powder is evenly distributed. Since the compound and binder of the present invention are adsorbed and wrapped, head clogging and magnetic layer yield stress are also improved. In addition, the epoxy compound reacts with the binder and polyisocyanate to further strengthen the network structure, thereby preventing head clogging and greatly improving the yield stress of the magnetic layer.

In addition, in the present invention, since the polar group has a salt structure, and more preferably does not contain a vinyl chloride bond in the molecule, the ring-opening reaction of the epoxy group is difficult to occur. It is estimated that it will be used effectively and its durability will be improved.

〔Example〕

Next, Examples and Comparative Examples of the present invention will be shown. In addition, in the Examples and Comparative Examples described below, "part" represents "part by weight".

Example 1 Ferromagnetic metal fine powder (composition: Fe94%, Zn Hc: 1500Qe) Specific surface area: 50rr? /g) Compound A 4%, Ni 2%, 100 parts (here n=10) Toluene 25 parts Cyclohexanone 25 parts After the above composition is thoroughly cross-dispersed, the following composition is added and dispersed again.

Butyl stearate 2 parts Methyl ethyl ketone 225 parts Vinyl chloride copolymer (average degree of polymerization = 310 Vinyl chloride 77% by weight, -3O
aNa o, 8% by weight, epoxy group 3.9% by weight
, hydroxyl group 0.5% by weight)
10 parts Polyester polyurethane (weight average molecular weight 40,000, -3O3Na divalent per molecule) 10 parts α
-Altos 5 parts Stearic acid 2 parts After the remaining components of the above composition were mixed and dispersed for 48 hours using a ball mill, 5 parts of a polyisocyanate compound (Coronate, manufactured by Nippon Polyurethane) was added thereto, and mixed for another 1 hour. After the dispersion, the mixture was filtered using a filter having an average pore size of 1 μm to prepare a magnetic paint.

The obtained magnetic paint was applied onto the surface of a polyethylene terephthalate support having a thickness of 10 μm using a reverse roll so that the thickness after drying was 3.0 μm. The non-magnetic support coated with the magnetic paint was subjected to a magnetic field alignment treatment using a 3,000 Gauss magnet while the magnetic paint was still wet, and after drying, it was subjected to a super calender treatment and slit into 8 mm widths. produced a videotape.

Example 2 Instead of using compound A in Example 1, compound B H2 I OCH.

(X here.

An 8 mm video tape was produced in the same manner except that the number of parts was 5 parts.

Example 3 An 8 mm video tape was produced in the same manner as in Example 1 except that Compound C was used instead of Compound A.

Example 4 1 part by weight of Compound A was added and dissolved in 99 parts by weight of methyl ethyl ketone.

To 100 parts by weight of this solution, 1 of the ferromagnetic powder used in Example 1 was added.
After adding and mixing at a ratio of 0.00 parts by weight, methyl ethyl ketone was removed to obtain a ferromagnetic metal fine powder treated with the above compound A.

Using the above ferromagnetic metal fine powder, 8 m
Manufactured video tape.

Example 5 An 8-fight videotape was produced in the same manner as in Example 1, except that the step of kneading the ferromagnetic metal fine powder with only Compound A and a solvent was omitted, and all the components were charged and dispersed at the same time.

Comparative Example 1 An 8 mm videotape was produced in the same manner as in Example 1, except that Compound A was not used and the pre-dispersion step was omitted.

Comparative Example 2 In the same manner as in Example 1, 8 m
m-video tape was manufactured.

Comparative Example 3 In Example 1, Compound A was replaced with butyl acrylate acrylic acid copolymer (molar ratio 80:20, number average degree of polymerization L
An 8 mm video tape was produced in the same manner except that the tape was adjusted to about 30).

〔Evaluation item〕

Surface glossiness The glossiness of the surface of the magnetic layer was measured at an incident angle of 45 degrees and a reflection angle of 45 degrees using a standard glossmeter (manufactured by Suga Test Instruments ■). Note that the values shown are values when the glossiness of the surface of the magnetic layer of the magnetic recording medium obtained in Comparative Example-1 is taken as 100%.

Large residual magnetic flux density (Bm) and shaped (S) were determined by measuring the magnetic properties at a magnetic field strength (Hm) of 5 kOe using a vibration test magnetometer (VSM) (manufactured by Toei Kogyo ■).

C/N ratio commercially available 8-kaku video tape recorder (Fujix-8)
A 5 MHz signal was recorded using a 5 MHz signal, the noise generated within the range of 5±I MHz when this signal was reproduced was measured, and the ratio of the reproduced signal to this noise was measured. The measurement was performed using an NV-870HD output level measuring device (manufactured by Matsushita Electric Industry Co., Ltd.). Note that the values shown are for comparative examples.
This is the value when the C/N ratio of the magnetic recording medium obtained in 1 is expressed as OdB.

Recording and playback were performed with the above VTR under conditions of an air temperature of 20° C. and a relative humidity of 10%, and head clogging was observed for every 30 minutes of playback. For evaluation, the number of times the output decreased by 3 dB or more was determined, and the number of times the output decreased per 30 minutes was 0, ◯, 1 to 2 times, △, and 3 or more times, X.

Rotating Seal! The 8-kaku tape sample and the remaining base after peeling off the magnetic layer from the tape sample were each tested at a tensile speed of 100% using a tensile strength tester (Tensilon manufactured by Toyo Baldwin).
Measured at 23°C and 60% RH.

From the obtained data, a stress strain curve of the magnetic layer was determined using the following formula, and from this, the yield stress of the magnetic layer was determined.

m The evaluation results are shown in Table 1.

As shown in Table 1, according to the present invention, the molecular weight is 2000 or less, preferably 1.000 or less, and the epoxy group and polar group are present in the same molecule as -3o, M-3o, M, -OP(
By using fine ferromagnetic powder whose surface is treated with a compound containing one of the following: OM), -PO(OM)21, the dispersion state of the ferromagnetic powder in the magnetic layer is improved and the electromagnetic conversion characteristics are improved. It was possible to manufacture a magnetic recording medium that maintained excellent running properties.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support, an epoxy group and a polar group are present in the same molecule in the magnetic layer.
M-SO_3M, -OSO_3M, -OPO(OM)_
2. A magnetic recording medium characterized by containing a low molecular weight compound having a molecular weight of 2,000 or less and containing any one or more of -PO(OM)_2 (here, M is an alkali metal atom or ammonium). (2) The magnetism according to claim (1), wherein the low molecular compound is at least one compound selected from an ether compound, an ester compound, an amino compound, or a vinyl polymer not containing vinyl chloride. recoding media.