JPH0630138B2 - Magnetic recording medium - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet and a magnetic disk.

B. BACKGROUND ART In general, a magnetic recording medium includes a support formed by molding polyethylene terephthalate or the like into a tape shape or a sheet shape,
The magnetic layer is formed by coating a magnetic coating material containing magnetic powder and a binder as main components on the support.

The magnetic powder contained in the magnetic layer is superior to the iron oxide magnetic powder in terms of squareness ratio, saturation magnetization, coercive force, and the like. However, when the particle size of the metal magnetic powder is 1 μm or less, not only the dispersion becomes worse, but also the metal magnetic powder easily participates and easily rusts, which deteriorates the saturation magnetization over time, resulting in storage stability and still durability. descend. Further, under certain conditions, the metal magnetic powder tends to ignite in the atmosphere even at room temperature. As described above, the reason why the metal magnetic powder becomes unstable with respect to oxidation is that the properties of the metal magnetic powder itself, that is, the physical properties change in the temperature range of room temperature to 70 ° C. In addition to this, pinholes existing on the surface of the metal magnetic powder are also considered to be a factor.

On the other hand, when the metal-based magnetic powder is used, although it has the above-mentioned various excellent performances, sufficient durability (running durability and still durability) as a magnetic layer is not obtained. For this reason, it is possible to use various additives such as higher resin acids in the magnetic layer, but it has been difficult to obtain a magnetic recording layer having desirable characteristics even if such additives are added. For example, if a large amount of these additives is used, the mechanical strength of the magnetic recording layer may be reduced, or a blooming phenomenon in which the additive gradually exudes after the magnetic recording layer is formed is observed. There was also.

C. Object of the Invention An object of the present invention is to achieve improvement in oxidation stability, running durability, and still durability in a magnetic recording medium having a magnetic layer containing a metal-based magnetic material such as the above-mentioned metal-based magnetic powder. Especially.

D. Structure of the Invention and Its Effect: That is, in the present invention, the magnetic layer contains A1 containing metal magnetic powder, carbon black, and a polyurethane resin having a tensile strength of 200 kg / cm ² or more and a breaking elongation of less than 900%. The present invention relates to a magnetic recording medium characterized by the above.

According to the present invention, since the metal-based magnetic powder contains aluminum, the magnetic powder is thermally stable and excellent in oxidation resistance.

The present inventor, as a means for investigating the oxidation stability of the metal-based magnetic powder, electron microscope observation of the surface state of the metal-based magnetic powder, and the results of the investigation of the stability of the differential thermal analysis curve,
It has been found that there is an extremely close relationship between them as follows.

It has been confirmed that the surface state of conventionally known metal magnetic powder (metal magnetic powder whose differential thermal analysis curve changes between 20 ° C and 70 ° C as shown in Fig. 1) is formed by overlapping needle-shaped powder particles. The unit acicular particles have a relatively smooth surface. On the contrary, in the case of the metal magnetic powder suitable for the present invention in which the differential thermal analysis curve does not change up to at least 80 ° C. as shown in FIG. It is considered that the number of pinholes, which are closely related to the oxidative stability of the powder, has decreased. It is considered that such a reduction in pinholes improves the thermal stability (and thus the oxidation stability) of the differential thermal analysis curve of the metal magnetic powder.

As the magnetic powder that can be used in the magnetic layer of the magnetic recording medium of the present invention, Fe—Ni—Co alloy, Fe—Mn—Zn alloy, F
e-Co-Ni-P alloy, Fe-Ni-Zn alloy, Fe
-Ni-Cr-P alloy, Fe-Co-Ni-Cr alloy,
Fe-Co-P alloy, Fe-Ni alloy, Fe-Ni-M
n alloy, Co-Ni alloy, Co-Ni-P alloy, Fe-
Such as Al alloy, Fe-Al-Co alloy, Fe-Al-Ca alloy, Fe-Mn-Zn alloy, Fe-Al-P alloy, etc. Can be mentioned.

The following methods (1) to (3) are conceivable as a method for obtaining a stable metal-based magnetic powder whose differential thermal analysis curve does not change up to at least 80 ° C.

(1), a method of coating the outer surface of the metal magnetic powder with a thermally stable polymer compound (for example, polyamide resin).

(2) A method of gradually oxidizing the outer surface of the metal-based magnetic powder to form a stable oxide layer shown by dots (the degree of oxidation increases as it goes to the surface of the magnetic powder: the degree of oxidation increases continuously).

(3) Mainly aluminum (along with nickel, silicon, magnesium, copper, and
A method of adding various elements such as phosphorus and / or their compounds together) or adding the compounds by a method such as containing or adhering.

The metal-based magnetic powder contained in the magnetic layer of the magnetic recording medium of the present invention is the magnetic powder obtained by the method (3) above. However, it is preferable to supplementarily employ either one or both of the methods (1) and (2) as necessary.

According to the present invention, the differential thermal analysis curve is at least 80 ° C. (that is, 80 ° C. or lower, or higher than 80 ° C.) due to the inclusion of aluminum as the metal-based magnetic material
Is used, the magnetic substance is not easily oxidized even if the magnetic recording medium is repeatedly used, and the electromagnetic conversion characteristics are not easily deteriorated. Occasionally, heat generation temperature (equilibrium temperature of 60 ℃ to 75 ℃) caused by friction between the magnetic head and the magnetic recording medium.
Then, the magnetic substance does not change, and the still durability is excellent. Since the magnetic substance is thermally stable in this way,
The catalytic action on the binder in the magnetic layer is also suppressed, the characteristics of the binder used in the present invention do not change over time,
It will be fully maintained and demonstrated.

Here, the above-mentioned “differential thermal analysis curve” means that the temperature difference generated between the reference substance and the sample (metal magnetic substance) is simultaneously heated at a constant rate, and the temperature (or Is a curve showing the change in the temperature difference or the calorific value difference on the vertical axis. This differential thermal analysis curve is generally referred to as DTA (Differential Thermal Ana
lysis) curve or thermogram, which is a DSC (Differential Scanning Calo).
rimeter) corresponding to the curve measured. The measuring method is described in detail, for example, in “New Experimental Chemistry Course 2, Basic Technology” edited by The Chemical Society of Japan.

Amount of aluminum to be added to the metal-based magnetic powder, in the metal component of the metal magnetic powder, Al atoms (e.g., additive if Al ₂ O _3, Al ₂₎ is the ratio of, the total metal components It is preferably in the range of 0.5 to 20 atomic% by weight, and particularly preferably in the range of 1 to 20 atomic% by weight. If the Al atom content is less than 0.5 atom% by weight, the resulting metal-based magnetic powder is insufficient in thermal or oxidative stability as described above, and the characteristics of the magnetic recording medium produced using this magnetic powder, for example, storage stability. Raw, reproduction output, and still durability are likely to be insufficient.

Further, when an Si element and / or its compound is used together with Al as an additive, the metal component portion (Al, Si, S, Fe, Ni, Co, Ra, H of the metal-based magnetic powder is used.
f, Cu, P, Zn, Mn, Cr, Bi, Mg and the like), the weight percentage of Si atoms is 1
It may be less than or equal to 0.5% by weight, preferably less than or equal to 0.5% by weight, and may be less than or equal to 0.1% by weight in some cases. If Si is out of this range, it may be difficult to modify the magnetic powder.

Further, in the case of containing Ni element and / or its compound as an additive, the upper limit is 30 atomic% or less, preferably 20 atomic% or less from the viewpoint of magnetic properties.

FIG. 2 is a special curve a showing the relationship between the still durability (minutes) of the magnetic recording medium (magnetic tape) of the present invention and the stable temperature of the differential thermal analysis curve of the metal magnetic powder used for the tape. From this figure, it can be confirmed that when the minimum temperature at which a change in the differential thermal analysis curve appears is 80 ° C. or higher, the still durability of the tape is dramatically increased.

The present inventor has further found that, surprisingly, the running durability of the medium is significantly improved and the still durability is also greatly improved by including carbon black in the magnetic layer in the above-mentioned metal magnetic powder. It was That is, carbon black is a fine particle (preferably a particle size of 10 mμ to 1 μm, especially 20
.About.200 m.mu.), and when added in a predetermined amount to the magnetic layer, the surface of the magnetic layer has appropriate irregularities, which lowers the friction coefficient of the surface and improves the running property of the medium. As a result, changes in electromagnetic conversion characteristics are reduced even when running for a long time (improved running durability) and still durability is improved. Therefore, the still durability improved by the above-mentioned aluminum-containing tammel-based magnetic powder, etc. In addition, it became possible to obtain extremely effective durability as a medium.

Up to now, when the above-mentioned metal-based magnetic powder is used in the magnetic layer, carbon black has not been added to the magnetic layer. The reason is that although carbon black has properties such as imparting conductivity to the magnetic layer, the addition of carbon black is unnecessary because the metal-based magnetic powder is generally conductive by itself. There was an existing concept that the packing density of magnetic powder would rather decrease due to the addition of black and electromagnetic conversion characteristics would deteriorate.

However, the inventor of the present invention defeated the existing concept as described above and used carbon black in combination with the metal-based magnetic powder, and as a result, an unexpected effect (that is, improved running durability and eventually electromagnetic conversion). It was found that the characteristics can be maintained well). This is because carbon black not only has conductivity and light-shielding properties, but also has a function of appropriately roughening the surface of the magnetic layer to reduce its friction coefficient.

The particle size of carbon black used in the present invention is 10 mμ to 1
μ is particularly preferable, and 20 to 200 mμ is particularly preferable, but if the particle size is too small, the friction coefficient on the surface of the magnetic layer does not decrease. Getting worse.

Carbon blacks that can be used include carbon blacks that impart conductivity (hereinafter referred to as CB ₁ ) and, in some cases, carbon blacks that sufficiently impart light-shielding properties to the magnetic layer (hereinafter referred to as CB ₂ ). Is preferably added.

The amount of carbon black added is 0.1 per 100 parts by weight of magnetic powder.
-15 parts by weight is preferable, and 0.2-10 parts by weight is more preferable.

When using the above-mentioned carbon blacks CB ₁ and CB ₂ , the specific surface areas of both carbon blacks are
200 to 500 m ² g (further 200 to 300 m ² / g), and the latter is preferably 40 to 200 m ² / g. That is, as shown in FIG. 7, if the specific surface area of CB ₁ is less than 200 m ² / g, the particle size is too large and the conductivity becomes insufficient even if carbon black is added, and if it exceeds 500 m ² / g, the particle size becomes too large. Since the diameter is too small, the dispersibility of carbon black tends to deteriorate. The carbon black CB ₁ is preferably particles in which the particles are so-called grape tuft-like, and is preferably porous and has a large specific surface area, that is, a so-called high structure level. As such carbon black,
For example, Conductex (Con
ductex) 975 (specific surface area 270 m ² / g, particle size 46 mμ), Conductex 950 (specific surface area 245 m ² / g, particle size 46 mμ),
Cabot Valcan XC-72 (specific surface area
257 m ² / g, particle size 18 mμ) etc. can be used. Also,
CB ₂ has a specific surface area of 40 as shown in Fig. 7.
When it is m ² / g or less, the particle size is too large and the light-shielding property is apt to deteriorate, and it is necessary to increase the addition amount more than necessary.
On the other hand, when it is 200 m ² / g or more, the particle size is too small and the dispersion in the layer tends to be poor. Such a light-shielding carbon black CB ₂ has a small particle size, a relatively low structure level, and a relatively low specific surface area, for example, Raven 2000 manufactured by Columbia Carbon Co.
(Specific surface area 180 m ² / g, particle size 19 mμ, 2100, 1170, 100
0, # 100, # 75, # 44, # 40, # 35, # 30, etc. can be used.

The mixing ratio (weight ratio) of each of the above carbon blacks has a certain preferable range, and CB ₁ / CB ₂ = 90/10 to 50
/ 50 is good, and 80 / 20-60 / 40 is even better. If this mixing ratio is greater than 90/10, the ratio of the conductive carbon black CB ₁ will increase, resulting in insufficient light-shielding properties.
If it is smaller, the amount of conductive carbon black CB ₁ is small and the surface specific resistance increases.

However, in the magnetic recording medium of the present invention, the light-shielding property of the magnetic layer can be sufficiently obtained if the metal-based magnetic powder is contained at a high density, and in this case, the addition of CB ₂ is not necessary.

Next, in the present invention, the above metal-based magnetic powder was treated with a copolymer containing at least one monomer unit having a negative organic group as a copolymerization component and the negative organic group forming a salt. It is desirable that the magnetic layer is contained in the state. That is, since the above-mentioned copolymer forms a salt of a negative organic group, the hydrocarbon residue portion of the copolymer is well compatible with the binder, and the above-mentioned salt portion is simply ( It has a reasonably large dissociation constant as compared to the free organic group that is not formed, and can be sufficiently bonded to the hydrophilic surface of the magnetic substance when the magnetic powder is treated with the above copolymer in an aqueous system. Further, since it is more hydrophilic than free organic groups, it is less prone to desorption and transfer to the binder / solvent phase when the surface-treated magnetic material is dispersed in the binder / solvent.
On the one hand, the above-mentioned copolymer is sufficiently bonded to the surface of the magnetic substance, and on the other hand, it is well adapted to the binder of the magnetic layer without being desorbed. Therefore, the dispersibility of the magnetic substance treated with this copolymer is Various characteristics such as squareness ratio, output, and surface bleeding are improved.

In the present invention, the above-mentioned copolymer used for pretreating the surface of the magnetic powder will be described in detail.

In the negative organic group-containing monomer (hereinafter referred to as monomer unit A) constituting this copolymer, the negative organic group includes, for example, a carboxyl group, a phosphoric acid residue, a sulfonic acid residue, and the like. Groups and phosphoric acid residues are preferable, and salts thereof include ammonium salts, alkali metal salts and the like, and ammonium salts are preferable. Examples of the monomer unit A include acrylic acid, methacrylic acid, maleic anhydride, 2-hydroxyethylacryloyl phosphate, and the like, among which acrylic acid and maleic anhydride are preferable.

The negative organic group is preferably a carboxyl group or a phosphoric acid residue, and the salt is preferably an ammonium salt. Acrylic acid and maleic anhydride are preferable as the monomer unit A because they are particularly excellent in storability and dispersibility. In the case of additives conventionally used to improve the blooming phenomenon, etc., the blooming phenomenon can be improved to some extent, but the storage stability is deteriorated, sticking is likely to occur, and aggregation is likely to occur during dispersion. The copolymer that can be used in the present invention is excellent in these points.

In this copolymer, the action and effect of the salt of the negative organic group will be described as follows. Simply, the negative organic group (for example, free --COOH) and its salt (for example, ammonium salt, N
and each dissociation constant is different.

[Dissociation constant K]

_{^{-COOH <-COO - N + H 4}} <-COONa Then, using each surface-treated magnetic powder monomer unit A having each of these groups in the copolymer as a component, a method described in detail later It was confirmed that the squareness ratio (Bm / Br) of the magnetic recording medium provided with the magnetic layer prepared in (1) was as shown in FIG. 3, for example. That is, based on the present invention, compared to the case of using a simple copolymer having —COOH,
It can be seen that the squareness ratio is improved by using the copolymer in which COOH is a salt. This is because when -COOH is salted, the dissociation constant is large and the hydrophilicity is large,
This is because the copolymer easily becomes sufficiently bonded to the hydrophilic surface of the magnetic powder during the surface treatment of the magnetic powder, and the adsorbed substance is less likely to be desorbed during dispersion (that is, the hydrophilic property is good). it is conceivable that. On the contrary, -COOH has a property of easily adhering to or binding to the surface of the magnetic powder. That is, although they are easily attached or bonded, they are more hydrophilic than salts and are easily desorbed during dispersion in an organic solvent. Further, among the organic groups according to the present invention, as shown in FIG. 3, the ammonium salt has better magnetic properties than the alkali metal salt, and when the ammonium salt is used, the dissociation constant decreases or increases before and after the maximum. It can be seen that the squareness ratio tends to decrease with the increase. The reason for this is that the alkali metal salt has a higher hydrophilicity (probably because the dissociation constant is considerably large). However, it is considered that the ammonium salt preferentially binds to the surface of the magnetic powder due to an appropriate dissociation constant. Moreover, desorption in an organic solvent is small. In addition,
When the magnetic powder is not surface-treated at all, the characteristics of the medium tend to deteriorate (see FIG. 3).

As the ammonium salt, the -COO ^- formula containing _{^{N + H 4: -COOH - N}} + (R 1) (R 2) (R 3) (R 4) where ^{R 1, R 2, R 3} , R Each of ⁴ is a hydrogen atom or a lower alkyl group which is the same as or different from each other. ) Is applicable. Where R ¹ ,
When R ² , R ³ and R ⁴ are lower alkyl groups, R ¹ to
It is preferable that the total number of carbon atoms of R ⁴ is 6 or less, because the basicity of the ammonium salt is not impaired by steric hindrance.

The above-mentioned copolymer used in the present invention is the above-mentioned monomer unit A. And monomer unit A If expressed using It can be expressed as. However, m and n are positive real numbers, respectively. The average value of (m + n) is 100 or more, preferably 50 or less. When it exceeds 100, it becomes difficult to be uniformly dispersed in the magnetic layer of the magnetic recording medium, and in the recording medium,
Performance (for example, output) tends to be partially uneven,
Not preferable. Further, (m + n) is particularly preferably 30.
The dispersion effect at this time is particularly excellent, and the performance of the magnetic recording medium according to the present invention is remarkably improved. The average value of (m + n) is preferably, for example, 4 or more from the viewpoint of preventing the blooming phenomenon.

Here, by selecting m and n and the value, respectively, and selecting the type of salt of the organic group in the unit A, both hydrophilic and hydrophobic properties of the copolymer, that is, HLB (Hydrophile Lipophi) are obtained.
le Balance) can be controlled appropriately.

The monomer units other than the monomer unit A of the copolymer (hereinafter referred to as the monomer unit B) are, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2 , 4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, p- n-dodecyl styrene, p-methoxy styrene, p-phenyl styrene,
Examples thereof include styrene and styrene derivatives such as p-chlorostyrene and 3,4-dichlorostyrene. Other vinyl-based monomers other than these include, for example, ethylene-based unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl fluoride. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, acrylic Dodecyl acid, 2-ethylhexyl acrylate, stearyl acrylate, 2- / chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-methacrylate -Butyl, methacrylic acid Α-methylene fats such as isobutyl, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate. Group monocarboxylic acid esters; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; vinyl methyl ketone, vinyl hexyl ketone, methyl iso Vinyl ketones such as propenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N
-N-vinyl compounds such as vinylindole and N-vinylpyrrolidone; vinylnaphthalene and the like.

In order to surface-treat the magnetic powder with the above-mentioned copolymer, an aqueous solution of the copolymer may be added to the magnetic powder, kneaded with a kneader or the like for a predetermined time, and water may be removed by filtration and / or drying. The treated magnetic powder after filtration and / or drying can be pulverized to a desired particle size and classified. Alternatively, the above copolymer is dissolved in a solvent such as toluene, methyl ethyl ketone, ethyl cellosolve, acetone, or methanol, and magnetic powder is immersed in the solution at a predetermined ratio, stirred and mixed, then filtered or evaporated to evaporate the solvent. According to the above, further drying treatment can be performed.

Further, it was found that the surface treatment effect of the above-mentioned copolymer is excellently exhibited when the specific surface area of the metal-based magnetic powder to be treated is set to 30 m ² / gr or more.
That is, if the specific surface area is 30 m ² / gr or more, the particle size is small,
The magnetic characteristics are improved to some extent in terms of high density recording, but the dispersibility of the magnetic powder tends to become poor. As shown in FIG. 4, when the magnetic powder is not surface-treated at all, the characteristics are improved to some extent depending on the specific surface area, and the organic group in the monomer unit A is a copolymer having only —COOH. The properties of the treated magnetic powder (treated magnetic powder II) are further improved, but they are improved almost linearly with respect to the specific surface area of the magnetic powder. On the other hand, in the present invention, it was confirmed that when the magnetic powder surface-treated with the copolymer (treated magnetic powder I) was used, the characteristic surface area was 30 m ² / gr or more and the characteristics were sharply improved as compared with the treated magnetic powder II. ing. This clearly shows that the decrease in the dispersibility of the magnetic powder can be effectively prevented by the surface treatment with the copolymer according to the present invention, and the dispersibility can be significantly improved. Incidentally, if the specific surface area of the magnetic powder used is unnecessarily large, dispersion failure will occur rather. Therefore, it is desirable to set the upper limit to 100 m ² / gr.

In the above, the "specific surface area" means a 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, the specific surface area is large, Some have a small surface area. To measure the specific surface area, first, for example, magnetic powder at around 250 ° C for 30-6
Degas while heating for 0 minutes to remove those adsorbed on the powder, and then introduce it into the measuring device, set the initial pressure of nitrogen to 0.5 kgr / m ² , and use liquid nitrogen with nitrogen. Adsorption measurement is performed at temperature (-195 ° C) (generally called BET method for measuring specific surface area. For details, see J. Ame. Ch.
See em.Soc, 60 309 (1938)). This specific surface area (BET
As a measuring device for the “value”, a “powder and granular material measuring device (canter soap)” jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. can be used. A general explanation of the specific surface area and its measurement method is described in detail in "Measurement of powder particles" (co-authored by JMDALLAVALLE, CLYDEORR Jr, translated by Benda et al., Published by Sangyo Tosho Co., Ltd.). Ed., Pages 1170 to 1171, edited by The Chemical Society of Japan, published by Kyuzen Co., Ltd. on April 30, 1964.
(In the above "Chemical Handbook", the specific surface area is simply described as the surface area (m ² / gr, but it is the same as the specific surface area in the present specification.) In the present invention, it is used for the magnetic layer. It is preferable to use polyurethane as the binder component, especially rigid polyurethane having a tensile strength of 200 kg / cm ² or more and an elongation at break of less than 900%, because this rigid polyurethane reduces stickiness and decrease in stiffness (Stiffness). It is possible to suppress the tackiness and strengthen the rigidity of the medium. In addition, in order to facilitate the calendering process and improve the adhesiveness of the magnetic layer,
Tensile strength is less than 200 kg / cm ² and elongation at break is 900%
The above soft polyurethanes can be used in combination.
The mechanical properties (tensile strength, elongation at break) of the polyurethane are specified in Japanese Industrial Standard (JIS) K6301-1975, and the elongation at break corresponds to "elongation at break" in the standard. is doing.

Polyurethane used as a binder of the magnetic layer in the magnetic recording medium of the present invention, particularly hard polyurethane,
It can be synthesized by reacting a polyol with a polyisocyanate. As usable polyols, phthalic acid, adipic acid, dimerized linoleic acid, organic dibasic acids such as maleic acid, ethylene glycol, propylene glycol, butylene glycol, glycols such as diethylene glycol or trimethylolpropane, hexanetriol, Polyhydric alcohols such as glycerin, tomethyl roll ethane and pentaerythritol, or polyester polyols synthesized by reaction with any two or more polyols selected from these glycols and polyhydric alcohols; or s-caprolactam, α-methyl-1-caprolactam, s-metal-s
-Lactone polyester polyols synthesized from lactams such as caprolactam and γ-butyrolactam; and polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide and the like.

These polyols are reacted with an isocyanate compound such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc., thereby urethanized polyester polyurethane and polyether polyurethane are synthesized. These polyurethanes according to the invention are usually produced mainly by the reaction of polyisocyanates with polyols, and also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and / or hydroxyl groups or their reactivity. It may have no terminal group (for example, in the form of urethane elastomer).

Since methods for producing polyurethane, urethane prepolymer, urethane elastomer, effective crosslinking method and the like are known, detailed description thereof is omitted.

The above-mentioned polyurethane is hard depending on its components,
You can get soft ones respectively. For example, rigid polyurethane can be synthesized by using the same type of polyol, by increasing the amount of isocyanate added, by using an isocyanate that is easily crystallized, or by using an isocyanate having a benzene ring in the molecule.
Further, the soft polyurethane is obtained by randomly allowing a plurality of types of polyester polyol components to exist in the molecule, or by using an isocyanate in which the molecular chain between the isocyanate groups is a chain aliphatic hydrocarbon group. You can

As the binder of the magnetic layer, in addition to the above-mentioned polyurethane, a thermosetting resin, a thermoplastic resin, a reactive resin,
A mixture with an electron beam radiation curable resin may be used.

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and has an infinite molecular weight due to reactions such as condensation and addition after coating and drying.
Further, among these resins, those which are not softened or melted before the resin is thermally decomposed are preferable. In particular,
For example, phenoxy resin, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic resin, mixture of methacrylate copolymer and diisocyanate prepolymer, urea formaldehyde resin, polyamine resin, and the like. And the like. Of these, phenoxy resin is preferable.

The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 200 to 2,000, for example, an acrylic ester-acrylonitrile copolymer, an acrylic ester-vinylidene chloride copolymer. Coalescence, acrylic ester-styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer Coal, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin, various synthetic rubber thermoplastic resins and these Used by mixtures, etc. It is.

As the electron beam irradiation curable resin, an unsaturated prepolymer,
For example, maleic anhydride type, urethane acryl type, polyester acryl type, polyether acryl type, polyurethane acryl type, polyamide acryl type, etc., or as a polyfunctional monomer, ether acryl type, urethane acryl type, phosphate ester acryl type, aryl type , Hydrocarbon type, and the like.

When a fibrin resin and / or a vinyl chloride copolymer is also contained as a desirable binder to be used in combination with the above-mentioned polyurethane, the dispersibility of the magnetic powder in the magnetic layer is improved and its mechanical strength is increased. To do. However, the layer becomes too hard only with the fibrin-based resin and the vinyl chloride-based copolymer, which can be prevented by containing the above-mentioned polyurethane.

As usable fibrin-based resins, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. As the cellulose ether, methyl cellulose, ethyl cellulose, propyl cellulose, isopropyl cellulose, butyl cellulose, methyl ethyl cellulose, methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose sodium salt, hydroxyethyl cellulose, benzyl cellulose, cyanoethyl cellulose, vinyl cellulose, Nitrocarboxymethyl cellulose, diethylaminoethyl cellulose, aminoethyl cellulose and the like can be used.
As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate or the like can be used.
In addition, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, cetacryloyl cellulose, chloroacetyl cellulose, β-oxypropionyl cellulose, benzoyl cellulose, p-toluenesulfonate cellulose, acetylpropionyl cellulose, acetylbutyrate. Lil cellulose or the like can be used. Of these fibrin-based resins, nitrocellulose is preferred. Specific examples of the nitrocellulose include Cell Nova BTH1 / 2 and Nitrocellulose SL-1 manufactured by Asahi Kasei Corporation and Nitrocellulose RS1 / 2 manufactured by Daicel Corporation. The viscosity of nitrocellulose (specified in JIS, K-6703 (1975)) is 2
It is preferably from 1/64 second, and particularly preferably from 1/4 second. If the amount is out of this range, the magnetic layer does not have sufficient film adhesion and film strength.

Further, as the above-mentioned vinyl chloride-based copolymer that can be used, a compound represented by the general formula: There is something represented by. in this case, Unit and The molar ratio derived from l and m in the unit is
It is 95 to 50 mol% for the former unit and 5 to 50 mol% for the latter unit. X represents a monomer acid group copolymerizable with vinyl chloride, and is represented by vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride ester, maleic acid, maleic acid ester, vinylidene chloride, acrylonitrile, acrylic acid, acrylic acid. It represents at least one selected from the group consisting of acid esters, methacrylic acid, methacrylic acid esters, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate. The degree of polymerization, expressed as (l + m), is preferably
When the degree of polymerization is less than 100, the magnetic layer or the like tends to be tacky, and when it exceeds 600, the dispersibility deteriorates. The vinyl chloride copolymer may be partially hydrolyzed. The vinyl chloride-based copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate-based copolymer").
Is mentioned. Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, vinyl chloride-vinyl acetate-vinyl. Examples thereof include alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferable. Specific examples of the above vinyl chloride-vinyl acetate copolymer include "VA manufactured by Union Carbide Co., Ltd.
GH ”,“ VYHH ”,“ VMCH ”, Sekisui Chemical Co., Ltd.
"S-REC A", "ES-REC A-5", "ES-REC C", "ES-REC M" manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Vinyl 1000G", "Denka Vinyl 1000W" and the like can be used. The above vinyl chloride copolymer and the fibrous resin may be used in an arbitrary mixing ratio. For example, as shown in FIG. 5, the vinyl chloride resin: the fibrous resin is 90/10 by weight. ~ 5/95 is desirable 80 / 20-10 /
90 is more desirable.

In addition, the ratio of polyurethane to other resins (particularly the synthetic amount of fibrin resin and vinyl chloride copolymer) is 6th
As shown in the figure, the weight ratio of 90/10 to 50/50 is good, and 85/15
~ 60/40 is even better.

The mixing ratio of the metal magnetic powder according to the present invention and the binder is 5 to 400 parts by weight, preferably 10 to 200 parts by weight, based on 100 parts by weight of the magnetic powder.
If the amount of the binder is too large, the recording density when used as a magnetic recording medium will decrease, and if the amount of the binder is too small, the strength of the magnetic layer will be inferior, and durability will be reduced, and powder will fall off.

Further, in order to improve the durability of the magnetic recording medium according to the present invention, in addition to the above-mentioned isocyanate in the magnetic layer, triphenylmethane triisocyanate, tris-
(P-isocyanate phenyl) thiophosphite, polymethylene polyphenyl isocyanate may be contained.

The paint used for forming the magnetic layer may contain additives such as other dispersants, lubricants, abrasives and antistatic agents, if necessary.

Other dispersants used include lecithin, phosphoric acid esters, amine compounds, alkyl sulphates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acid esters, known surfactants and salts thereof, and also, Negative organic groups (eg -COOH, -PO
It is also possible to use salts of polymeric dispersants with ₃ H). These dispersants may be used alone or in combination of two or more. These dispersants are magnetic powder 100
It is added in the range of 1 to 20 parts by weight with respect to parts by weight. These dispersants may be used for pretreating the magnetic powder in advance. Further, as the lubricant, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acid having 12 to 16 carbon atoms and the number of carbon atoms of the fatty acid A fatty acid ester or the like composed of a monohydric alcohol having a total of 21 to 23 carbon atoms can also be used.
These lubricants are added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of magnetic powder. As abrasives that may be used, commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial Danyamond, garnet, emery (main components: corundum and magnetite) are used. To be done. As these abrasives, those having an average particle diameter of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 1 to 20 parts by weight with respect to 100 parts by weight of magnetic powder. As the antistatic agent that may be used, conductive powder such as carbon black, graphite, tin oxide-antimony oxide compound, titanium oxide-tin oxide-antimony oxide compound; natural surfactant such as saponin; Alkylene oxide-based, glycerin-based, glycidol-based, etc. nonionic surfactants; higher alkyl amines, quaternary ammonium salts, pyridine, other heterocycles, cations such as phosphonium or sulfonium compounds; carboxylic acids, sulfones Examples thereof include anionic surfactants containing an acidic group such as acid, phosphoric acid, sulfuric acid ester group, and phosphoric acid ester group; amphoteric active agents such as aminic acid, aminosulfonic acid, aminoalcohol sulfuric acid or phosphoric acid ester.

A hardener may be added to the magnetic paint to accelerate the hardening of the magnetic layer.

Examples of usable curing agents include polyfunctional isocyanates and adducts of these active hydrogen compounds. Examples of isocyanate compounds include compounds shown in Table 1 below.

The solvent for the magnetic paint or the solvent used when applying the magnetic paint includes ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate, ethyl acetate, acetic acid. Butyl, ethyl lactate, esters such as ethylene glycol monoacetate; ethers such as ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, ethylene chloride, tetra Those such as halogenated hydrocarbons such as carbon chloride, chloroform and dichlorobenzene can be used.

Further, as the material of the support forming the above-mentioned magnetic layer, polyethylene terephthalate, polyethylene-2,
Polyesters such as 6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, metals such as Al and Zn, glass, silicon nitride, silicon carbide, porcelain, pottery, etc. Ceramic or the like is used. The thickness of these supports is about 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
m, and in the case of a disk or card, 30 μm to 10 mm
In the case of a drum, it is cylindrical, and its type is determined according to the recorder used.

As a coating method for coating the magnetic coating on the support to form a magnetic layer, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, revas roll coat, transfer roll coat, gravure coat, Kiss coat, cast coat, spray coat, etc. can be used, and other methods are also possible. If necessary, the magnetic layer coated on the support by such a method is subjected to a treatment for orienting the metal-based magnetic powder in the layer, and then the formed magnetic layer is dried. If necessary, the surface is smoothed or cut into a desired shape to manufacture the magnetic recording medium of the present invention.

8 to 10 exemplify the specific structure of the magnetic recording medium according to the present invention.

The magnetic layer containing the above-mentioned metal-based magnetic powder, carbon black, binder, etc. is provided as the layer 12 on the support 11 in FIG. 8 and is supported for the winding appearance and running stability when the tape is wound. The back coat layer (BC
Layer) 13 is provided. The magnetic recording medium of FIG. 8 may have an undercoat layer (not shown) provided between the magnetic layer 12 and the support 11, or may not have the undercoat layer ( The same applies below).

As the non-magnetic powder contained in the BC layer 13 of FIG. 8, carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples thereof include those made of zinc oxide, α-Fe ₂ O ₃ , talc, kaolin, calcium sulfate, boric nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably those made of carbon black or titanium oxide.
By including these non-magnetic powders in the BC layer, the surface of the BC layer can be appropriately roughened (matted) to improve the surface property, and in the case of carbon black, the BC layer can be made conductive. An antistatic effect can be obtained. The combined use of carbon black and other non-magnetic powder is advantageous because both the effect of improving the surface property (stabilization of running property) and the improvement of conductivity can be obtained.
However, as for the surface roughness of the BC layer, the average roughness or height (Ra) of the center line of the surface irregularities is 0.01 to 0.1 μm, preferably 0.025.
Maximum roughness (Rmax) 0.20 to 0.80μ
It is better to set m. Regarding Ra, Ra ≦ 0.025 μ is desirable in order to improve chroma S / N. Ra
If the value of Rmax is too small, the running stability and the winding appearance at the time of winding the tape will be insufficient, and if it is too large, the BC layer will be transferred to the magnetic layer (when the tape is wound) and the surface will be further roughened. . The particle size of the filler (including non-magnetic powder) in the BC layer 13 is 0.5 μm or less, preferably 0.2 μm or less in order to obtain the above surface roughness. Also, BC
The layer 13 can be formed by coating in the same manner as described above, but the film thickness after coating and drying is 0.1 to 3.0 μm, preferably 1 μm or less, and more preferably 0.6 μm or less. The amount of nonmagnetic powder added to the BC layer is generally 100 to 400 mg / m ² , and preferably 200 to 300 mg / m ² . Further, as the binder of the BC layer 13, the same binder as that of the magnetic layer 12 can be used.

The BC layer 13 is necessary as a high quality tape, but it is not always necessary to provide it.

FIG. 9 shows another magnetic recording medium.
Overcoat layer (OC layer) on the magnetic layer 12 of the medium in the figure
14 are provided.

The OC layer 14 is provided to protect the magnetic layer 12 from damage and the like, but for that purpose, it is necessary that the lubricity is sufficient. Therefore, as the binder of the OC layer 14, it is preferable to use the polyurethane used in the magnetic layer 12 described above (desirably in combination with the fiber resin and / or the vinyl chloride copolymer).

FIG. 10 shows a magnetic recording medium configured as a magnetic disk, and the same magnetic layer 12 as described above is formed on both surfaces of the support 11.
Are provided respectively. An OC layer similar to that shown in FIG. 9 may be provided on each of these magnetic layers.

The magnetic recording medium according to the present invention produced as described above has extremely good wear resistance and durability as compared with conventionally known magnetic recording media, and also has excellent dispersibility and surface properties,
Dropouts can be reduced. Further, the magnetic recording medium according to the present invention has a significantly improved S / N ratio as compared with the conventional magnetic recording medium, and a reproduction output higher than the conventional one can be obtained.

E. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" represent "parts by weight".

First, the iron-based metal magnetic powder was surface-treated with each of the following copolymers (a) to (d) to obtain a corresponding treated magnetic powder. That is, an aqueous solution of each copolymer was added to 100 parts of the metal magnetic powder so that the solid content was 2.5 parts, and the mixture was kneaded with a kneader (manufactured by Inoue Seisakusho) for 2 hours. The surface-treated magnetic powders are transferred to a rotary vibration dryer to evaporate the water content, and the magnetic powders are disentangled with a colloid mill and sieved with a mesh to classify the magnetic powders with the desired particle size. Got the powder.

(a) Ammonium salt of copolymer of 2-hydroxyethyl acryloyl phosphate and lauryl acrylate (b) Ammonium salt of copolymer of acrylic acid and propylene (c) Butylamine of copolymer of methacrylic acid and butylene Salt (Ammonium Salt) (d) Ammonium Salt of Copolymer of Acrylic Acid and Ethylene Then, the treated magnetic powders were used to prepare the following compositions.

Treated metal magnetic powder (above) Polyurethane 30 parts (as a solution) (Dainippon Polyurethane Nippolan N-2304: Tensile strength 400 kg / cm ² , breaking elongation 700%) (Solid content 30%) Phenoxy resin 20 parts (〃 ) (PKHH) (solid content 20%) Conductex 975 2.5 parts (BET value 270 m ² / gr, particle size 46 mμ) Lecithin 5 parts Myristic acid 2 parts Palmitic acid butyric ester 1 part Alumina 4 parts Methyl ethyl ketone 50 parts Cyclohexanone 100 parts This composition was thoroughly stirred and mixed with a ball mill. At this time, the sample was applied at regular intervals and applied on a glass plate, and the degree of dispersion was compared with a standard plate under a microscope of 100 times to determine the end point of dispersion. Then, 5 parts of a polyfunctional isocyanate (curing agent) was added to this composition to give an average pore diameter of 1 μm.
It filtered with the filter of. The obtained magnetic paint was applied on a polyester film with a thickness of 10 μm with a reverse roll coater while applying a magnetic field and dried (dry film thickness 3.2.
μm). Thereafter, the magnetic layer was surface-treated with a super calendar roll to obtain a wide magnetic film having a magnetic layer of a predetermined thickness. Cut this film to 12.65 mm width,
I made a magnetic tape for video.

The presence or absence of each magnetic powder and carbon black in the above magnetic paint is summarized in Table 2 below.

Comparative Examples 7 to 12 A1 in the A1-containing iron-based metal magnetic powder used in Example 1 was changed to Zn (Comparative Example 7), Cu (Comparative Example 8), Sn (Comparative Example 9), Mn (Comparative Example 10), Cr. (Comparative Example 11),
A magnetic tape was obtained in the same manner as in Example 1 except that the iron-based metal magnetic powder replaced with Mo (Comparative Example 12) was used.

Comparative Example 13 Instead of the polyurethane used in Example 1 (Nipporan N-2304 manufactured by Dainippon Polyeletan Co., Ltd .: tensile strength 400 kg / cm ² , elongation at break 700%) (solid powder 35%), a soft polyurethane (Dainippon Ink and Chemicals) was used. A magnetic tape was obtained in the same manner as in Example 1 except that Pandex T-5610 manufactured by Kogyo Co., Ltd .: tensile strength 120 kg / cm ² , breaking elongation 1050%) (solid content 35%) was used.

The video characteristics and durability of each of the above magnetic tapes were measured, and the results are shown in Table 3 below. These measuring methods were as follows.

RF output: R playback output of 5 MHz per virgin tape
It is measured under the condition of F, and the measured value of Comparative Example 5 is 0,
Displayed as a relative value.

Still durability: The time until the reproduction output of a still image decreases by 2 dB per virgin tape is shown in minutes.

RF output reduction (running durability): The tape was recorded and reproduced 100 times at room temperature and normal humidity on a VCR, and the first RF output and 100
The output difference from the RF output after rotation is displayed in dB. 100
The output after rotation showed a value lower than the RF output at the time of the first reproduction.

From these results, it can be seen that the medium in which the magnetic layer contains the aluminum-containing metal magnetic powder and carbon black according to the present invention has a high RF output and improved still durability and running durability. Contrary to this, as in Comparative Examples 1 to 4, those not containing carbon black are still durable,
It can be seen that the running durability is deteriorated, the RF output is deteriorated in the case of not containing aluminum as in Comparative Examples 5 and 6, and the running durability is extremely deteriorated in the case of not containing carbon black. .

[Brief description of drawings]

The drawings are for explaining the present invention. FIG. 1 is a graph showing a differential thermal analysis curve of a metal-based magnetic powder, and FIG. 2 is a differential of a metal-based magnetic powder contained in a magnetic layer of a magnetic recording medium. FIG. 3 is a characteristic curve diagram showing the relationship between the temperature at which a change in the thermal analysis curve can be observed and the still durability of the magnetic recording medium. FIG. 3 is a graph showing the squareness ratio of the magnetic recording medium according to the type of magnetic powder surface-treated. Figure 4 shows the output S / of various magnetic powders according to the specific surface area of the magnetic powders.
Fig. 5 is a graph showing changes in N, Fig. 5 is a graph showing changes in tape characteristics depending on the compounding ratio of resins other than polyurethane, and Fig. 6 is a graph showing changes in still durability depending on the compounding ratio of polyurethane and other resins. FIG. 7 is a graph showing a change in tape characteristics depending on the specific surface area of carbon black, and FIGS. 8, 9, and 10 are enlarged cross-sectional views of a part of the magnetic recording medium according to each example. In the reference numerals used in the drawings, 1 ... Metal magnetic powder 11 ... Support 12 ... Magnetic layer.

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Claims (1)

[Claims] 1. A1 containing metal magnetic powder, carbon black, tensile strength of 200 kg / cm ² or more, elongation at break 9
A magnetic recording medium comprising a magnetic layer containing less than 00% of a polyurethane resin.