JP2010049731A - Magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has an upper-layer magnetic layer having excellent surface smoothness and excellent electromagnetic conversion characteristics by improving the surface smoothness of a lower-layer nonmagnetic layer using fine nonmagnetic inorganic powder, and to provide a method of manufacturing the magnetic recording medium. <P>SOLUTION: The magnetic recording medium includes: a nonmagnetic supporter; the lower-layer nonmagnetic layer provided on one surface of the nonmagnetic supporter; and the upper-layer magnetic layer on the lower-layer nonmagnetic layer. The upper-layer magnetic layer contains ferromagnetic powder and a binder, and the lower-layer nonmagnetic layer contains carbon black, nonmagnetic inorganic powder other than the carbon black, and a binder. In the lower-layer nonmagnetic layer, a polyurethane resin is used as a binder, which includes a polar group selected from a sulfonic acid metal base and a sulphuric acid metal base in the range of 200-250 eq/t and which has a reduced viscosity of 0.42-0.55 measured in the following conditions: a measured solvent in which toluene/MEK/cyclohexanone=40/40/20 (ratio by weight); a measured solution concentration of 4g/L; and a measured temperature of 30°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium and a manufacturing method thereof, and more particularly to a magnetic recording medium excellent in surface smoothness and electromagnetic conversion characteristics of a magnetic layer and a manufacturing method thereof.

In recent years, high-density recording of magnetic recording media has been demanded in order to cope with an increase in the amount of recording data. In particular, LTO ^R used for data recording of a computer ^{(R: Linear Tape Open), DLT R} ( R: Digital Linear Tape) and a recording density of a magnetic recording medium such as a magnetic tape called is determined Yes. For high density recording, the recording wavelength is shortened, and the magnetic layer is thinned. Further, as the recording wavelength is shortened, the surface of the magnetic layer is required to be smoother from the viewpoint of spacing loss.

  When the magnetic layer is thinned, the surface roughness of the support is reflected on the surface of the magnetic layer, the smoothness of the surface of the magnetic layer is impaired, and the electromagnetic conversion characteristics deteriorate. For this reason, a nonmagnetic layer as an undercoat layer is provided on the surface of the support, and the magnetic layer is provided therebetween. Therefore, the surface of the nonmagnetic layer (the surface of the nonmagnetic layer in contact with the magnetic layer) is also required to be smoother.

  Japanese Patent Application Laid-Open No. 2005-149623 discloses a magnetic recording medium using a nonmagnetic inorganic powder having an average particle diameter of 80 nm or less as a lower nonmagnetic layer (Claim 1).

  JP-A-2004-67941 discloses that when the total amount of each of the acid component and glycol component of the polyester polyol is 100 mol%, the acid component is 50 to 80 mol of an aliphatic and / or alicyclic dibasic acid. %, A polyester polyol (A) having an aromatic dibasic acid having a sulfonic acid metal base of 20 to 50 mol% and a number average molecular weight of 300 to 800 is reacted with an aromatic polyisocyanate (B). And a polyurethane resin having a sulfonic acid metal base concentration of 200 to 500 eq / t with respect to the entire polyurethane resin is disclosed (claim 1). The publication also discloses that the polyurethane resin is used as a binder component in a magnetic recording medium formed using a magnetic coating material in which a ferromagnetic powder having a major axis length of 100 nm or less is dispersed in a binder. (Claim 3).

JP 2005-149623 A JP 2004-67941 A

  According to Japanese Patent Application Laid-Open No. 2005-149623, a non-magnetic non-magnetic powder having an average particle size of 80 nm or less is used as a non-magnetic layer coating component, and is processed under optimum dispersion conditions, thereby providing a non-magnetic lower layer having good surface smoothness. As a result, good surface smoothness of the upper magnetic layer is realized. The refinement of non-magnetic inorganic powder is accompanied by an increase in specific surface area.Therefore, if the non-magnetic layer coating material is not treated under appropriate dispersion conditions, it causes aggregation of fine particles and an increase in coating viscosity. The temporal stability of the magnetic layer coating is deteriorated. If a nonmagnetic layer coating with poor temporal stability is used, it is difficult to obtain good surface smoothness of the lower nonmagnetic layer, and good surface smoothness of the upper magnetic layer cannot be realized (Comparative Example 4 in the same publication). ).

  According to Japanese Patent Application Laid-Open No. 2004-67941, by using a polyurethane resin having a specific structure with a sulfonate metal base concentration of 200 to 500 eq / t as a binder, ultrafine ferromagnetic powder having a major axis length of 100 nm or less is bound. It is disclosed that it can be dispersed in an agent (paragraphs [0026], [0035]). The publication does not disclose the dispersion of nonmagnetic inorganic powder or the nonmagnetic layer.

  When the fine non-magnetic inorganic powder is dispersed using a binder resin with a high concentration of polar groups such as metal sulfonate, the resulting non-magnetic coating material has interactions between polar groups and surface energy. The fine particles tend to re-agglomerate due to the interaction between the large non-magnetic fine inorganic powders, and the viscosity of the paint increases. When the viscosity of the nonmagnetic paint increases, the leveling of the paint does not become sufficient when the nonmagnetic paint is applied onto the nonmagnetic support, and a smooth nonmagnetic layer surface cannot be obtained. Therefore, good surface smoothness of the upper magnetic layer is not realized. Furthermore, when the viscosity of non-magnetic paints increases, filter clogging tends to occur when filtering non-magnetic paints, requiring frequent filter replacement, increasing filter costs, and operating rate of the coating line. Incurs a decline. The paint stagnated during filter replacement becomes a vicious circle in which the paint viscosity further increases due to the stagnation.

  An object of the present invention is to provide a magnetic recording medium that improves surface smoothness of a lower nonmagnetic layer using fine nonmagnetic inorganic powder and is excellent in surface smoothness and electromagnetic conversion characteristics of an upper magnetic layer, and a method for producing the same. There is to do.

  In order to improve the dispersibility of the fine nonmagnetic inorganic powder for the lower nonmagnetic layer and to improve the stability of the nonmagnetic layer coating, the present inventor has determined the amount of polar groups in the binder resin of the nonmagnetic layer coating. Attention was paid to the reduced viscosity.

The present invention includes the following inventions.
(1) A magnetic recording medium having at least a nonmagnetic support, a lower nonmagnetic layer on one surface of the nonmagnetic support, and an upper magnetic layer on the lower nonmagnetic layer,
The upper magnetic layer includes at least a ferromagnetic powder and a binder,
The lower nonmagnetic layer includes at least carbon black, nonmagnetic inorganic powder other than carbon black, and a binder,
The binder contained in the lower non-magnetic layer has a polar group selected from a sulfonate metal base and a sulfate metal base in a range of 200 eq / t to 250 eq / t, and the following conditions:
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C
A magnetic recording medium in which a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less measured in (1) is used.

  (2) The nonmagnetic inorganic powder other than the carbon black contains at least one of iron oxide having an average major axis length of 40 nm to 95 nm and iron oxyhydroxide having an average major axis length of 40 nm to 95 nm. The magnetic recording medium according to (1) above.

(3) The iron oxide, BET specific surface area is of less 80 m ² / g or more 100 m ² / g, the magnetic recording medium according to (2).

(4) The magnetic recording medium according to (2), wherein the iron oxyhydroxide has a specific surface area of 80 m ² / g or more and 100 m ² / g or less by a BET method.

  (5) The magnetic recording medium according to any one of (1) to (4), wherein the polyurethane resin has a radiation functional group.

  (6) The magnetic recording medium according to any one of (1) to (5), wherein the upper magnetic layer has a thickness of 0.30 μm or less.

  (7) The magnetic recording medium according to any one of (1) to (6), wherein the lower nonmagnetic layer has a thickness of 0.3 μm to 1.3 μm.

(8) A method of manufacturing a magnetic recording medium having at least a nonmagnetic support, a lower nonmagnetic layer on one surface of the nonmagnetic support, and an upper magnetic layer on the lower nonmagnetic layer,
Carbon black, a nonmagnetic inorganic powder other than carbon black, and a binder having a polar group selected from sulfonate metal base and sulfate metal base in the range of 200 eq / t to 250 eq / t, and the following conditions :
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C
A step of preparing a coating for a nonmagnetic layer containing at least a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less measured in
Applying a prepared nonmagnetic layer coating on one surface of the nonmagnetic support to form a lower nonmagnetic layer;
Applying a magnetic layer coating material containing at least a ferromagnetic powder and a binder on the lower nonmagnetic layer and drying to form an upper magnetic layer.

  According to the present invention, as described above, the binder for the lower non-magnetic layer has a polar group selected from metal sulfonate and metal sulfate in the range of 200 eq / t to 250 eq / t, and A polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less measured under the above conditions is used. By using a polyurethane resin having a specific number of polar groups and a specific range of reduced viscosity, fine non-magnetic inorganic powders can be dispersed well in the non-magnetic layer coating material, and are uniformly dispersed and stable. A non-magnetic layer coating having excellent properties is produced. Therefore, good surface smoothness of the lower nonmagnetic layer is obtained, and good surface smoothness of the upper magnetic layer is realized. As a result, a magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained.

  The magnetic recording medium of the present invention has at least a nonmagnetic support, a lower nonmagnetic layer on one surface of the nonmagnetic support, and an upper magnetic layer on the lower nonmagnetic layer. Usually has a backcoat layer on the other side. The lower nonmagnetic layer has a thickness of, for example, 0.3 to 2.5 μm, and preferably 0.3 to 1.3 μm, and the upper magnetic layer has a thickness of, for example, 0.30 μm or less, preferably 0.03 to 0.3 μm. The thickness of the back coat layer is, for example, 0.3 to 0.8 μm, and the total thickness of the magnetic recording medium is preferably 4.0 to 10.0 μm. A lubricant coating or various coatings for protecting the magnetic layer may be provided on the upper magnetic layer as necessary. In addition, an undercoat layer (an easy adhesion layer) is provided on the one surface on which the magnetic layer of the nonmagnetic support is provided for the purpose of improving the adhesion between the lower nonmagnetic layer and the nonmagnetic support. Also good. At that time, the thickness of the undercoat layer is preferably 0.05 to 0.30 μm. The thickness of the undercoat layer is preferably 0.05 μm or more in order to exhibit effects such as improvement in adhesiveness, and a sufficient effect is obtained when the thickness is 0.05 μm or more and 0.30 μm or less.

[Lower nonmagnetic layer]
The lower nonmagnetic layer includes at least carbon black, nonmagnetic inorganic powder other than carbon black, and a binder.

As carbon black contained in the lower nonmagnetic layer, furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like can be used. The specific surface area is preferably ⁵ to 600 m ² / g, the DBP oil absorption is 30 to 400 ml / 100 g, and the particle diameter is preferably 10 to 100 nm. Specifically, the carbon black that can be used can be referred to “Carbon Black Handbook”, edited by the Carbon Black Association.

  The compounding quantity of carbon black is 5-30 mass% in a lower nonmagnetic layer, Preferably it is 10-25 mass%.

  The lower nonmagnetic layer contains at least one of iron oxide and iron oxyhydroxide as a nonmagnetic inorganic powder other than carbon black. The use of iron oxide and / or iron oxyhydroxide as the nonmagnetic inorganic powder contained in the lower nonmagnetic layer is important from the viewpoint of running durability of the magnetic recording medium.

The iron oxide contained in the lower non-magnetic layer is acicular α-Fe ₂ O ₃ , the average major axis length is preferably 40 to 95 nm, and the specific surface area by the BET method is preferably 80 to 100 m ² / g.

When the average major axis length of iron oxide exceeds 95 nm, the dispersibility in the nonmagnetic layer coating is improved, but the smoothness of the surface of the nonmagnetic layer tends to be lowered. On the other hand, if the average major axis length is less than 40 nm, it is too fine and the dispersibility is poor, and the stability of the nonmagnetic layer coating tends to be lowered. descend. Although the iron oxide increases the specific surface area by the BET method generally enough to be miniaturized, in the present invention, the BET method specific surface area of the iron oxide is preferably in the range of 80~100m ² / g. In the case of iron oxide having an average major axis length of 40 nm, a BET specific surface area of about 100 m ² / g is appropriate. When the average major axis length exceeds 100 m ² / g, the powder surface has many irregularities, Dispersibility tends to be poor. On the other hand, when the average major axis length of the iron oxide of 95 nm, the BET specific surface area is suitably about 80 m ² / g, is less than 80 m ² / g, powder agglomeration easily occurs again dispersibility in paint Tend to get worse.

The average major axis length of iron oxide is more preferably in the range of 45 to 80 nm, and more preferably in the range of 45 to 70 nm. The BET specific surface area of iron oxide is more preferably in the range of 80 to 90 m ² / g.

The iron oxyhydroxide contained in the lower nonmagnetic layer is acicular α-FeO (OH), the average major axis length is 40 to 95 nm, and the specific surface area by the BET method is 80 to 100 m ² / g. preferable.

When the average major axis length of the iron oxyhydroxide exceeds 95 nm, the dispersibility in the nonmagnetic layer coating is improved, but the smoothness of the surface of the nonmagnetic layer is likely to be lowered. On the other hand, if the average major axis length is less than 40 nm, it is too fine and the dispersibility is poor, and the stability of the nonmagnetic layer coating tends to be lowered. descend. As the iron oxyhydroxide becomes finer, the specific surface area by the BET method generally increases. However, in the present invention, the BET method specific surface area of iron oxyhydroxide is preferably in the range of 80 to 100 m ² / g. When the average major axis length of 40nm iron oxyhydroxide, the BET specific surface area is suitably about 100 m ² / g, when it exceeds 100 m ² / g, a shape that there are many irregularities on the surface of the powder, Dispersibility in paint tends to be poor. On the other hand, when the average major axis length of the iron oxyhydroxide of 95 nm, the BET specific surface area is suitably about 80 m ² / g, is less than 80 m ² / g, powder agglomeration easily occurs, in also the paint Dispersibility tends to deteriorate.

The average major axis length of iron oxyhydroxide is more preferably in the range of 45 to 80 nm, and more preferably in the range of 45 to 70 nm. Further, the BET specific surface area of iron oxyhydroxide is more preferably in the range of 80 to 90 m ² / g.

Acicular iron oxide α-Fe ₂ O ₃ is produced by dehydrating acicular iron oxyhydroxide α-FeOOH at a high temperature.

  The compounding quantity of the said iron oxide and / or iron oxyhydroxide is 50-80 mass% in a lower layer nonmagnetic layer as a total amount, Preferably it is 50-70 mass%.

The lower nonmagnetic layer includes nonmagnetic inorganic powders other than carbon black, the iron oxide, and the iron oxyhydroxide, for example, inorganic powders such as CaCO ₃ , titanium oxide, barium sulfate, and α-Al ₂ O _3. It may be.

  The blending ratio of carbon black and nonmagnetic inorganic powder other than carbon black (the total of the iron oxide + the iron oxyhydroxide + the other nonmagnetic inorganic powder) is the mass ratio (non-carbon black / carbon black other than carbon black). The magnetic inorganic powder is preferably 95/5 to 5/95. When the blending ratio of carbon black is less than 5 parts by mass, a problem may occur in the surface electrical resistance. If the blending ratio of the nonmagnetic inorganic powder other than carbon black is less than 5 parts by mass, the surface smoothness of the lower nonmagnetic layer may be deteriorated and the mechanical strength may be decreased. The deterioration of the surface smoothness of the lower nonmagnetic layer causes the deterioration of the surface smoothness of the upper magnetic layer.

A polyurethane resin having a specific number of polar groups and a specific range of reduced viscosity is used as a binder for the lower nonmagnetic layer. That is, the polyurethane resin has an S-containing polar group selected from a sulfonic acid metal base and a sulfate metal base in a range of 200 eq / t to 250 eq / t based on the mass of the polyurethane resin, and the following conditions: :
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C
The reduced viscosity measured at is from 0.42 to 0.55.

  The polyurethane resin is a resin obtained by a reaction between a hydroxy group-containing resin such as polyester polyol and / or polyether polyol and a polyisocyanate-containing compound. Usually, the number average molecular weight is about 5,000 to 200,000 and the Q value (mass average molecular weight / number average molecular weight) is about 1.5 to 4.

The polar group in the polyurethane resin is selected from a sulfonic acid metal base (—SO ₃ M) and a sulfate metal base (—OSO ₃ M). Here, M represents an alkali metal such as Li, Na, or K. Since the S-containing polar group has an affinity for the surface of the nonmagnetic inorganic powder, it contributes to improving the dispersibility of the nonmagnetic inorganic powder. The polyurethane resin may contain only one of the S-containing polar groups or may contain both, and when both are contained, the content ratio is arbitrary. The S-containing polar group is contained at a rate of 200 to 250 eq / t based on the mass of the polyurethane resin having the polar group. 1t = 1000 kg. These polar groups may be present in the main chain of the skeleton resin or in the branches.

  Such a polyurethane resin is obtained by a known method by reacting a raw material containing a specific polar group-containing compound and / or a raw material resin reacted with a specific polar group-containing compound in a solvent or without a solvent. It is done. In synthesizing the polyurethane resin, the proportion of the polar group contained in the polyurethane resin can be appropriately changed by adjusting the proportion of the polar group-containing compound used.

  When the number (concentration) of the S-containing polar groups contained in the polyurethane resin is 200 to 250 eq / t, the nonmagnetic inorganic powder is good because of the affinity between the polar groups and the surface of the nonmagnetic inorganic powder. To be distributed. When the number (concentration) of the S-containing polar group is less than 200 eq / t, the dispersion of the nonmagnetic inorganic powder becomes insufficient. On the other hand, when the number (concentration) of the S-containing polar groups exceeds 250 eq / t, the polyurethane resin tends to aggregate due to the interaction between the excess polar groups, and the number of polar groups used for dispersion of the nonmagnetic inorganic powder. Decreases, the dispersion of the nonmagnetic inorganic powder becomes insufficient, and the nonmagnetic inorganic powder aggregates.

  The polyurethane resin has a reduced viscosity measured under the above conditions of 0.42 or more and 0.55 or less. The reduced viscosity is an amount representing the contribution of the unit concentration to the viscosity increase of the solute, that is, the greater the reduced viscosity, the greater the viscosity increase of the solution. It is considered that as the reduced viscosity is larger, the polyurethane resin is sufficiently solvated in the nonmagnetic coating material and the molecular size is expanded.

  Generally, the reduced viscosity of the polymer solution indicates the size of the polymer molecule in the measurement solvent, and the larger the value, the larger the molecular size. The reduced viscosity is [ηsp / c], the reduced viscosity at infinite dilution is the intrinsic viscosity [η], and is expressed as the following Houwink-Mark-Iwata equation.

c: Concentration (g / cm ³ )
ηsp = (η−η ₀ ) / η ₀
ηsp: Specific viscosity η ₀ : Viscosity of solvent η: Viscosity of solution K: Proportional constant M: Molecular weight a: Parameter that varies depending on polymer type, degree of polymerization, and solvent

  In the polymer solution, the difference that occurs in the reduced viscosity and the intrinsic viscosity, which is the reduced viscosity at infinite dilution, is not only the M (molecular weight) of the polymer but also the a value (a parameter that varies depending on the type of polymer, degree of polymerization, and solvent) Also depends. For example, the difference that occurs in the intrinsic viscosity in an infinite dilution state, that is, in an ideal state where only one molecular chain exists, includes, for example, polar group concentration in the polymer, aliphatic segment (flexible segment) / Factors such as the ratio of aromatic segments (rigid segments) and the type of polymer side chains have an effect. The higher the polar group concentration, the higher the proportion of the aliphatic segment in the skeleton, and the more the side chain is flexible and has a polar group, the greater the intrinsic viscosity. Similarly, the reduced viscosity increases.

  Thus, the reduced viscosity depends not only on the molecular weight but also on the a value, and in the present invention, attention was paid to the importance of the reduced viscosity.

  In the present invention, as described above, in order to disperse the nonmagnetic inorganic powder well, the number (concentration) of the S-containing polar groups contained in the polyurethane resin is set as high as 200 to 250 eq / t. When the polar group concentration is high in this way, the polar groups interact with each other and the polyurethane resin tends to aggregate. Then, about the polyurethane resin which has a high polar group density | concentration as 200-250 eq / t, the interaction between polyurethane resins can be suppressed by making reduced viscosity into the small value of the range of 0.42 or more and 0.55 or less. it can. Furthermore, within the range of 200 to 250 eq / t, the higher the concentration of the S-containing polar group, the better the dispersion of the nonmagnetic inorganic powder proceeds even when the solid content concentration in the nonmagnetic coating is high. By combining the specific range of the S-containing polar group concentration and the specific range of the reduced viscosity, for example, a nonmagnetic coating material in which fine iron oxide and / or iron oxyhydroxide having an average major axis length of 40 nm to 95 nm is dispersed. The stability over time can be remarkably improved. For example, the nonmagnetic coating material used in the present invention can form a nonmagnetic layer having a smooth surface property with little increase in viscosity even if it stays for one week.

  When the reduced viscosity of the polyurethane resin is less than 0.42, the solvation of the polyurethane resin is too small, and the nonmagnetic inorganic powder in the nonmagnetic paint tends to settle. On the other hand, when the reduced viscosity exceeds 0.55, the solvation of the polyurethane resin is too large, and the polyurethane resin tends to aggregate. As a result, the dispersion is not successful and the nonmagnetic inorganic powder also aggregates.

  The number of the S-containing polar groups in the polyurethane resin is in the range of 200 to 250 eq / t. The larger the number of S-containing polar groups in this range, the reduced viscosity is 0.42 or more and 0.55 or less. It is preferable to make it smaller within the range. For example, if the number of the S-containing polar groups in the polyurethane resin is 200 eq / t, the reduced viscosity may be in the range of 0.45 to 0.55, and the number of the S-containing polar groups in the polyurethane resin is If it is 250 eq / t, the reduced viscosity is preferably in the range of 0.42 to 0.50.

  Adjustment of the reduced viscosity of the polyurethane resin can be performed, for example, by changing the proportion of the polyisocyanate-containing compound that is a synthetic component of the polyurethane resin.

An example of the polyurethane resin for the lower nonmagnetic layer will be further described.
Examples of polyurethane resin for the lower non-magnetic layer are:
Polyester polyol (A);
An aromatic polyisocyanate compound (B);
In which the S-containing polar group is in the range of 200 eq / t to 250 eq / t, and the reduced viscosity under the above conditions is 0.42 to 0.55. It is.

  The polyester polyol (A) is obtained by polycondensation of a dicarboxylic acid component and a glycol component, and a polyester polyol containing 90 to 100 mol% of an aliphatic dicarboxylic acid as an acid component is preferable.

  Examples of the aliphatic dicarboxylic acid used in the polyester polyol (A) include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dodecinyl succinic acid, fumaric acid, maleic acid, itaconic acid, and 3-hexenedicarboxylic acid. It is done. Among these, adipic acid, sebacic acid, dodecinyl succinic acid, and itaconic acid are preferable from the viewpoint of dispersibility of the nonmagnetic inorganic powder. Moreover, you may copolymerize sulfonic-acid metal salt containing aromatic dicarboxylic acid, such as 5-sodium sulfo isophthalic acid, 5-potassium sulfo isophthalic acid, and sodium sulfo terephthalic acid, as an acid component.

Examples of the glycol component used in the polyester polyol (A) include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2 -Propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2 Aliphatic glycols such as 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate, 2,2-diethyl-1,3-propanediol;
1,3-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxymethyl) cyclohexane, 1,4-bis (hydroxyethyl) cyclohexane, 1,4-bis (hydroxypropyl) cyclohexane, 1,4-bis ( Hydroxymethoxy) cyclohexane, 1,4-bis (hydroxyethoxy) cyclohexane, 2,2bis (4-hydroxymethoxycyclohexyl) propane, 2,2-bis (4-hydroxyethoxycyclohexyl) propanebis (4-hydroxycyclohexyl) methane And alicyclic glycols such as 2,2-bis (4-hydroxycyclohexyl) propane, 3 (4), 8 (9) -tricyclo [5.2.1.0 ^2,6 ] decanedimethanol. .

  Among these, in particular, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl -3-Hydroxypropanate, 1,6-hexanediol and 1,4-bis (hydroxymethyl) cyclohexane are preferred.

  In addition, as a part of the raw material of the polyester polyol (A), trifunctional or higher functional compounds such as trimellitic anhydride, glycerin, trimethylolpropane, pentaerythritol, etc. have characteristics such as organic solvent solubility and application workability of the polyester resin. You may use in the range which does not impair.

  Examples of the aromatic polyisocyanate compound (B) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, m- Phenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, 2,6-naphthalene diisocyanate, 3,3′-dimethyl-4,4′-biphenylene diisocyanate, 4, Examples include 4'-diphenylene diisocyanate, 4,4'-diisocyanate diphenyl ether, 1,5-naphthalene diisocyanate, m-xylene diisocyanate, and the like. Of these, 4,4'-diphenylmethane diisocyanate is particularly preferred.

  The reduced viscosity of the polyurethane resin can be adjusted by changing the use ratio of the aromatic polyisocyanate compound (B). That is, when the use ratio of the compound (B) is increased, the reduced viscosity of the polyurethane resin is increased.

  When the polyurethane resin is made radiation curable, a compound (C) having a radiation functional unsaturated bond and a functional group capable of reacting with an isocyanate may be used as a synthetic component of the polyurethane resin.

  As said compound (C), the (meth) acrylate compound which has a hydroxyl group is mentioned. For example, glycerol monomethacrylate, glycerol monoacrylate, etc. are mentioned. Alternatively, as a compound having one hydroxyl group, 2-hydroxyethyl acrylate, 2-hydroxymethyl methacrylate, 2-hydroxypropyl acrylate, hydroxyethylene glycol methacrylate, butoxyhydroxypropyl acrylate, phenoxyhydroxypropyl acrylate, hydroxypropyl acrylate, 2-hydroxy Examples include propyl-1,3-dimethacrylate, glycerol dimethacrylate, and monohydroxypentaerythritol triacrylate. Among these, it is preferable to use monohydroxypentaerythritol triacrylate because it exhibits excellent electron beam curability. The compound (C) preferably has a molecular weight of 500 or less. When the molecular weight of the compound (C) exceeds 500, the glass transition temperature of the polyurethane resin is lowered, the coating strength of the lower nonmagnetic layer is likely to be lowered, and a huge side chain or terminal portion containing no polar group is present. As a result, the dispersibility of the non-magnetic inorganic powder tends to decrease. A decrease in the coating strength of the lower nonmagnetic layer leads to a decrease in the durability of the magnetic recording medium.

  Furthermore, you may use the branched compound (D) represented by following General formula (1) as a synthetic component of a polyurethane resin.

In the general formula (1), R ¹ , R ² and R ³ may be the same or different and each represents an ethylene group or a 1,2-propylene group, m, n and o represent the number of repeating units; The sum of m, n, and o is 2 ≦ m + n + o ≦ 8. When m + n + o is less than 2, there is a tendency to reduce the radiation curability when the compound (C) is used. On the other hand, when m + n + o exceeds 8, the glass transition temperature of the polyurethane resin decreases, the coating strength of the lower nonmagnetic layer tends to decrease, and the Q value (mass average molecular weight / number average molecular weight) becomes larger than 4. The dispersibility of the nonmagnetic inorganic powder tends to decrease. Specific examples of the compound include an ethylene oxide adduct and a propylene oxide adduct to glycerin.

  Furthermore, a compound (E) having a molecular weight of 800 or less and having two or more functional groups that react with isocyanate groups may be used as a synthetic component of the polyurethane resin.

  Examples of the compound (E) include 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, and 2,2-dimethyl-1,3-propanediol. 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, 2-normalbutyl-2-ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol 2,2-diethyl-1,3-propanediol, 3-octyl-1,5-pentanediol, 3-phenyl-1,5-pentanedio Le, 2,5-dimethyl-3-sodium sulfo-2,5-hexanediol, and the like. Among these, 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate, 2-normalbutyl-2- Ethyl-1,3-propanediol and 2,2-diethyl-1,3-propanediol are particularly preferred from the viewpoint of dispersibility of the nonmagnetic inorganic powder. When the molecular weight of the compound (E) exceeds 800, the urethane group concentration in the polyurethane resin decreases, the mechanical properties of the polyurethane resin decrease, and the coating strength of the lower nonmagnetic layer tends to decrease. A decrease in the coating strength of the lower nonmagnetic layer leads to a decrease in the durability of the tape medium. Further, polyester polyol, polypropylene glycol or the like may be used as long as the molecular weight is 800 or less.

  Among the compounds (E), 2,2-dimethyl-1,3-propanediol, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanoate, 2-normalbutyl- Compounds having side chains such as 2-ethyl-1,3-propanediol and 2,2-diethyl-1,3-propanediol contribute to improving the solubility of the polyurethane resin, and the polyester polyol (A) and the above-mentioned It is possible to copolymerize at a high ratio with respect to the combination of the aromatic polyisocyanate (B). An increase in the copolymerization ratio of the compound (E) component leads to an increase in the urethane bond group concentration, making the urethane resin tougher. That is, by adjusting these quantitative ratios, a polyurethane resin having both high solubility in general-purpose solvents and strong mechanical properties can be obtained. These characteristics as a urethane resin contribute to the improvement of the high dispersibility and tape durability as a binder resin for magnetic tapes.

  The polyurethane resin can be obtained by copolymerizing each component by a known method. As the reaction catalyst, stannous octylate, dibutyltin dilaurate, triethylamine or the like may be used. Moreover, you may add a ultraviolet absorber, a hydrolysis inhibitor, antioxidant, etc. before manufacture of a polyurethane resin, during manufacture, or after manufacture.

  The number average molecular weight of the polyurethane resin is preferably in the range of about 10,000 to 80,000, and the glass transition temperature Tg is preferably in the range of −20 ° C. ≦ Tg ≦ 80 ° C. When the glass transition temperature of the polyurethane resin is lowered, the mechanical properties of the polyurethane resin are lowered, and as a result, the coating strength of the lower nonmagnetic layer is likely to be lowered.

  In the present invention, the polyurethane resin is preferably used in an amount of 30% by mass or more and 70% by mass or less, and 40% by mass or more and 60% by mass or less, based on the total amount of the binder for the lower nonmagnetic layer. It is more preferable. The binder used in combination with the polyurethane resin is preferably a vinyl chloride copolymer in order to maintain rigidity. When the polyurethane resin is thermosetting, a thermosetting vinyl chloride copolymer is used. When the polyurethane resin is radiation (electron beam or ultraviolet ray) curable, radiation curable vinyl chloride copolymer is used. Use coalescence.

  By using the polyurethane resin in such a range, the effect of improving the dispersibility of fine nonmagnetic inorganic powder and the stability of the nonmagnetic layer coating can be obtained. When the amount of the polyurethane resin is less than 30% by mass, the nonmagnetic coating film tends to be hard and brittle. If the non-magnetic layer becomes hard and brittle, the edge portion tends to rise when it is cut (slit) into the width of the magnetic tape, so that it becomes a so-called high edge. On the other hand, when the amount of the polyurethane resin exceeds 70% by mass, the rigidity of the nonmagnetic coating film is lowered and the durability of the magnetic tape is likely to be lowered.

  The vinyl chloride copolymer preferably has a vinyl chloride content of 50 to 95% by mass, particularly 55 to 90% by mass, and the average degree of polymerization is preferably about 100 to 500%. Particularly preferred is a copolymer of vinyl chloride and a monomer containing an epoxy (glycidyl) group. The vinyl chloride copolymer can be subjected to electron beam sensitive modification by introducing a (meth) acrylic double bond or the like by a known method.

The vinyl chloride copolymer preferably contains a polar group in order to improve the dispersibility of the nonmagnetic inorganic powder. Examples of the polar group include S-containing polar groups such as -OSO ₃ M, -SO ₃ M, and -SR, P-containing polar groups such as -POM, -PO ₂ M, and -PO ₃ M, -COOM (M is hydrogen or alkali ^{_{metal), - NR 2, -N +}} R 3 X - (R is hydrogen or a hydrocarbon group, X is a halogen atom), phosphobetaine, sulfobetaine, phosphamine, sulfamic, and the like.

  When the polyurethane resin and the vinyl chloride copolymer are thermosetting, a crosslinking agent that cures these binders is used. As the crosslinking agent, various polyisocyanates, particularly diisocyanates can be used, and it is particularly preferable to use one or more of tolylene diisocyanate, hexamethylene diisocyanate, and methylene diisocyanate. These cross-linking agents are particularly preferably used as cross-linking agents modified with one having a plurality of hydroxyl groups such as trimethylolpropane or isocyanurate-type cross-linking agents in which three molecules of a diisocyanate compound are bonded, and the functionalities contained in the binder resin. Bonding with a group or the like crosslinks the resin. It is preferable that content of a crosslinking agent shall be 10-30 mass parts with respect to 100 mass parts of binder resin. In order to cure such a thermosetting resin, it may be generally heated at 50 to 70 ° C. for 12 to 48 hours in a heating oven.

  In addition to the vinyl chloride copolymer and the polyurethane resin, various known resins may be contained in the nonmagnetic layer in the range of 20% by mass or less of the total binder.

  The content of the binder resin used for the lower nonmagnetic layer is preferably 10 to 100 parts by weight, more preferably 100 parts by weight, based on the total of 100 parts by weight of the nonmagnetic inorganic powder other than carbon black and carbon black in the lower nonmagnetic layer. Is 12-30 parts by mass. If the content of the binder is too small, the ratio of the binder resin in the lower nonmagnetic layer is lowered, and sufficient coating strength cannot be obtained. When the content of the binder is too large, the tape medium tends to be strongly curved in the tape width direction, and the contact with the head tends to be poor.

  The lower nonmagnetic layer preferably contains a lubricant as necessary. As the lubricant, regardless of whether it is saturated or unsaturated, fatty acids such as stearic acid and myristic acid, fatty acid esters such as butyl stearate and butyl palmitate, and sugars such as saccharides may be used alone or in combination of two or more. It is also possible to use a mixture of two or more fatty acids having different melting points, or a mixture of two or more fatty acid esters having different melting points. This is because it is necessary to continuously supply a lubricant corresponding to any temperature environment used for the magnetic recording medium to the surface of the medium.

  The content of the lubricant in the lower nonmagnetic layer may be adjusted as appropriate according to the purpose, but is 1 to 20 mass relative to the total mass of the nonmagnetic inorganic powder other than carbon black and carbon black in the lower nonmagnetic layer. % Is preferred.

  The coating material for forming the lower nonmagnetic layer is prepared by adding an organic solvent to each of the above components and mixing, stirring, kneading, dispersing, and the like by a known method. The organic solvent to be used is not particularly limited, and one or more of various solvents such as ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone and cyclohexanone, and aromatic solvents such as toluene are appropriately selected. Use it. The addition amount of the organic solvent may be about 100 to 900 parts by mass with respect to 100 parts by mass of the total amount of carbon black, various inorganic powders other than carbon black, and the binder resin.

  In the present invention, since the specific polyurethane resin is used, no aggregation of the iron oxide powder and / or iron oxyhydroxide powder occurs during the preparation of the coating, and no increase in the viscosity of the coating occurs. A nonmagnetic layer coating material that is uniformly dispersed and excellent in stability is prepared.

  The thickness of the lower nonmagnetic layer is usually 0.3 to 2.5 μm, preferably 0.3 to 2.0 μm, more preferably 0.3 to 1.3 μm. If the nonmagnetic layer is too thin, it is easily affected by the surface roughness of the nonmagnetic support. As a result, the surface smoothness of the nonmagnetic layer is deteriorated and the surface smoothness of the magnetic layer is also easily deteriorated. The conversion characteristics tend to be reduced. Further, since the light transmittance becomes high, it becomes a problem when the edge of the medium is detected by a change in the light transmittance. On the other hand, even if the nonmagnetic layer is thickened to some extent, the performance is not improved.

[Upper magnetic layer]
The upper magnetic layer contains at least a ferromagnetic powder and a binder.

In the present invention, it is preferable to use metallic magnetic powder or hexagonal plate-like fine powder as the ferromagnetic powder. As the metal magnetic powder, the coercive force Hc is 118.5 to 278.5 kA / m (1500 to 3500 Oe), the saturation magnetization σs is 70 to 160 Am ² / kg (emu / g), and the average major axis length is 0.02 to 0.02. It is preferable that the average minor axis length is 0.1 to 20 μm, the aspect ratio is 1.2 to 20. Moreover, Hc of the medium produced using metal magnetic powder is preferably 118.5 to 278.5 kA / m (1500 to 3500 Oe). The hexagonal plate-like fine powder has a coercive force Hc of 79.6 to 278.5 kA / m (1000 to 3500 Oe), a saturation magnetization σs of 40 to 70 Am ² / kg (emu / g), and an average plate particle size of 15 It is preferable that it is -80nm and a plate ratio is 2-7. The Hc of the medium produced using the hexagonal plate-like fine powder is preferably 94.8 to 318.3 kA / m (1200 to 4000 Oe).

  The ferromagnetic powder may be contained in an amount of about 70 to 90% by mass based on the magnetic layer. If the content of the ferromagnetic powder is too large, the content of the binder is decreased, so that the surface smoothness due to calendering tends to deteriorate. On the other hand, if the content of the ferromagnetic powder is too small, a high reproduction output is obtained. I can't.

  The binder resin material for the upper magnetic layer is not particularly limited, and a thermoplastic resin, a thermosetting or reactive resin, a radiation (electron beam or ultraviolet ray) curable resin, and the like are appropriately combined in accordance with the characteristics of the medium and process conditions. Selected and used.

  The content of the binder resin used in the upper magnetic layer is preferably 5 to 40 parts by mass, particularly preferably 10 to 30 parts by mass with respect to 100 parts by mass of the ferromagnetic powder. When the content of the binder is too small, the strength of the magnetic layer is lowered, and the running durability tends to be deteriorated. On the other hand, when the content of the binder is too large, the content of the ferromagnetic powder is lowered, so that the electromagnetic conversion characteristics tend to be lowered.

  Further, in order to increase the mechanical strength of the magnetic layer and to prevent clogging of the magnetic head, the upper magnetic layer contains an abrasive having a Mohs hardness of 6 or more such as α-alumina (Mohs hardness 9). Such an abrasive is usually indefinite shape, prevents clogging of the magnetic head, and improves the strength of the coating film.

  The average particle diameter of the abrasive is, for example, 0.01 to 0.2 μm, and preferably 0.05 to 0.2 μm. If the average particle size is too large, the amount of protrusion from the surface of the magnetic layer becomes large, leading to a decrease in electromagnetic conversion characteristics, an increase in dropout, an increase in head wear, and the like. If the average particle size is too small, the amount of protrusion from the surface of the magnetic layer becomes small, and the effect of preventing head clogging becomes insufficient.

The average particle size is usually measured with a transmission electron microscope. The content of the abrasive is 3 to 25 parts by mass, preferably 5 to 20 parts by mass with respect to 100 parts by mass of the ferromagnetic powder.
Further, in the magnetic layer, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, silicon oil, and other various additives may be added as necessary.

  The coating material for forming the upper magnetic layer is prepared by adding an organic solvent to each of the above components and mixing, stirring, kneading, dispersing and the like by a known method. The organic solvent to be used is not particularly limited, and those similar to those used for the lower nonmagnetic layer can be used.

  The thickness of the upper magnetic layer is 0.03 to 0.30 μm, more preferably 0.05 to 0.25 μm. If the magnetic layer is too thick, self-demagnetization loss and thickness loss increase.

  The centerline average roughness (Ra) of the upper magnetic layer surface is preferably 1.0 to 5.0 nm, more preferably 1.0 to 4.0 nm. If the Ra is less than 1.0 nm, the surface is too smooth, the running stability is deteriorated, and trouble during running tends to occur. On the other hand, when the thickness exceeds 5.0 nm, the surface of the magnetic layer becomes rough, and in a reproduction system using an MR type head, electromagnetic conversion characteristics such as reproduction output deteriorate.

[Back coat layer]
The backcoat layer is provided as necessary for improving running stability and antistatic of the magnetic layer, and the structure and composition are not particularly limited.For example, carbon black, nonmagnetic inorganic powder other than carbon black, And those containing a binder resin.

  The backcoat layer preferably contains 30 to 80% by weight of carbon black based on the backcoat layer.

In addition to the carbon black, various nonmagnetic inorganic powders can be used for the backcoat layer in order to control the mechanical strength. Examples of the inorganic powder include α-Fe ₂ O ₃ , CaCO ₃ , titanium oxide, Examples thereof include barium sulfate and α-Al ₂ O ₃ .

  The coating material for forming the backcoat layer is prepared by adding an organic solvent to each of the above components and mixing, stirring, kneading, dispersing and the like by a known method. The organic solvent to be used is not particularly limited, and those similar to those used for the upper magnetic layer and the lower nonmagnetic layer can be used.

  The thickness of the back coat layer (after calendering) is 1.0 μm or less, preferably 0.1 to 1.0 μm, more preferably 0.2 to 0.8 μm.

[Non-magnetic support]
The material used as the non-magnetic support is not particularly limited, and is selected from various flexible materials and various rigid materials according to the purpose. What is necessary is just to set it as a shape and a dimension. Examples of flexible materials include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins such as polypropylene, polyamide (PA), polyimide (PI), polyamideimide (PAI), polycarbonate, and the like. These resins can be mentioned. As the nonmagnetic support, a resin film selected from PEN, PA, PI, and PAI is preferable. The thickness of the nonmagnetic support is, for example, 3.0 to 15.0 μm, and preferably 2.0 to 6.0 μm.

[Manufacture of magnetic recording media]
In the present invention, each coating film (coating layer) is prepared by coating, drying, calendering, curing, etc., using each of the prepared non-magnetic layer forming coating material, magnetic layer forming coating material, and backcoat layer forming coating material. And forming a magnetic recording medium.

  In the present invention, the lower nonmagnetic layer and the upper magnetic layer are preferably formed by a so-called wet-on-dry coating method. However, it may be formed by a wet-on-wet coating method. In the case of the wet-on-dry coating method, first, the coating for the non-magnetic layer is applied on one surface of the non-magnetic support, dried, and calendered as necessary, so that the uncured lower layer is not coated. A magnetic layer is obtained. Thereafter, the uncured lower nonmagnetic layer is cured. When a radiation (electron beam) curable resin is used as the binder resin for the lower nonmagnetic layer, radiation (electron beam) irradiation is performed to cure the lower nonmagnetic layer. Next, the magnetic layer coating material is applied, oriented and dried on the cured lower nonmagnetic layer to form an upper magnetic layer. The order of forming the backcoat layer is arbitrary, that is, before the formation of the lower nonmagnetic layer, after the formation of the lower nonmagnetic layer, before the formation of the upper magnetic layer, and after the formation of the upper magnetic layer. Good.

  In the magnetic recording medium, the binder contained in the lower nonmagnetic layer and the binder contained in the upper magnetic layer are both cured.

  As a coating method, various known coating means such as gravure coating, reverse roll coating, die nozzle coating, and bar coating can be used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

[Measurement method of powder characteristics]
(Measurement of average long axis length)
A 100,000 times transmission electron microscope (TEM) photograph of the powder to be measured was taken, and the long axis length was measured for 100 particles randomly extracted from the photograph. The average value of these values was taken as the average major axis length.

(Measurement of BET specific surface area)
The specific surface area was determined by the BET method using NOVA2000 series manufactured by Quantachrome. BET measurement is, for example, a method of degassing sample powder, adsorbing molecules whose adsorption occupation area is known, and determining the specific surface area of the sample from the subsequent desorption amount.

[Measurement method of resin properties]
(Number average molecular weight)
It was measured by water permeation gel permeation chromatography (GPC) using polystyrene as a standard substance and tetrahydrofuran as a solvent. The low-molecular peak having a number average molecular weight of less than 300 was deleted during analysis, and the peak of a polymer having a molecular weight of 300 or more was subjected to data processing to obtain a number average molecular weight Mn.

(Composition analysis of polyurethane resin)
Using a nuclear magnetic resonance analyzer (NMR) Gemini-200 manufactured by Varian, ¹ H-NMR analysis was performed in a deuterated chloroform solvent, and the integral ratio was determined.

(Sodium sulfonate concentration)
A 0.1 g sample was carbonized and dissolved in an acid, and then determined by atomic absorption analysis. The polar group (sodium sulfonate base) concentration was determined by the following formula. The Na atomic weight was 23.
Polar group concentration (eq / t) = Na concentration (weight ppm) / 23

(Reduced viscosity measurement method)
Reduced viscosity was measured by solution viscosity measurement using an Ubbelode viscometer.
The measurement conditions were as follows.
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C

The reduced viscosity was determined by the following calculated value.
Reduced viscosity (dl / g) = ((t1 / t2) -1) /0.4
here,
t1: Average flow time of measurement solution (sec)
t2: Solvent flow time (sec)
It is.

[Viscosity measurement method]
The viscosity (unit cp; centipoise) of the coating for the nonmagnetic layer was measured at 20 rpm using No. 2 or No. 4 with a B-type viscometer manufactured by Tokyo Keiki.
When the viscosity of the paint was 1000 cp or less, No. 2 rotor was used, and when it was higher than 1000 cp, No. 4 rotor was used.

Abbreviations used in the examples are as follows.
AA: Adipic acid
SA: sebacic acid IA: itaconic acid DMS: 5-sodium sulfoisophthalic acid dimethyl ester EG: ethylene glycol HD: 1,6-hexanediol DMH: 2-butyl-2-ethyl-1,3-propanediol NPG: 2, 2-dimethyl-1,3-propanediol HPN: 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate GP-400: propylene oxide adduct of glycerin (Sanyo Chemical ( Co., Ltd., molecular weight 400)
MDI: 4,4′-diphenylmethane diisocyanate PETA: monohydroxypentaerythritol triacrylate (three double bonds in one molecule)
701A: 2-hydroxy-3-acryloyloxydipropyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., two double bonds in one molecule)
MR110: Vinyl chloride copolymer (manufactured by Zeon Corporation)

  First, production examples of polyurethane resins (I) to (XI) are shown. The polyurethane resins (I) to (XI) are electron beam curable. In Examples, “parts” means “parts by mass” unless otherwise specified.

  Table 1 shows the constituent components of the sulfonic acid metal base-containing polyester polyols (a) to (d) used in the production of the polyurethane resins (I) to (XI).

[Production Example 1: Production Example of Polyurethane Resin (III) of Example 1]
(Synthesis of polyester polyol (b))
In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 117 parts of adipic acid, 58 parts of dimethyl ester of 5-sodium sulfoisophthalic acid, 71 parts of 1,6-hexanediol, 2,2-dimethyl-1,3- 94 parts of propanediol and 0.2 part of tetrabutyl titanate were charged and heated at 180 to 220 ° C. for 180 minutes to carry out an esterification reaction. Thereafter, the reaction system was depressurized to 5 mmHg in 20 minutes, and the temperature was raised to 240 ° C. during this time. Furthermore, the pressure in the reaction system was gradually reduced, and after 10 minutes, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was performed at 240 ° C. for 30 minutes. In this way, a polyester polyol (b) was synthesized.

(Synthesis of polyurethane resin (III))
In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 100 parts of the polyester polyol (b), 20 parts of 2-butyl-2-ethyl-1,3-propanediol, and 30 parts of monohydroxypentaerythritol triacrylate. In this, 73 parts of methyl ethyl ketone and 73 parts of toluene were added and dissolved. 0.05 part of phenothiazine was added, and after stirring, 45 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 2 hours, and then methyl ethyl ketone 272 Part, 272 parts of toluene, and 13 parts of GP-400 were further reacted at 80 ° C. for 4 hours to obtain polyurethane resin (III).

[Production Example 2: Production Example of Polyurethane Resin (IV) of Example 2]
Using the polyester polyol (b), a polyurethane resin (IV) was obtained in the same manner as in Production Example 1.

[Production Example 3: Production Example of Polyurethane Resin (V) of Example 3]
(Synthesis of polyester polyol (c))
In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 160 parts sebacic acid, 7 parts itaconic acid, 47 parts dimethyl ester of 5-sodium sulfoisophthalic acid, 4 parts ethylene glycol, 2,2-dimethyl-1,3 -47 parts of propanediol, 105 parts of 2,2-dimethyl-3-hydroxypropyl-2 ', 2'-dimethyl-3-hydroxypropanate, and 0.2 part of tetrabutyl titanate are charged at 180-220 ° C. The mixture was heated for 5 minutes to conduct esterification reaction. Thereafter, the reaction system was depressurized to 5 mmHg in 20 minutes, and the temperature was raised to 240 ° C. during this time. Furthermore, the pressure in the reaction system was gradually reduced, and after 10 minutes, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was performed at 240 ° C. for 30 minutes. In this way, a polyester polyol (c) was synthesized.

(Synthesis of polyurethane resin (V))
In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 100 parts of polyester polyol (c), 14 parts of 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate, And 27 parts of 2-hydroxy-3-acryloyloxydipropyl methacrylate were added, and 73 parts of methyl ethyl ketone and 73 parts of toluene were added and dissolved. 0.05 part of phenothiazine was added, and after stirring, 45 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 2 hours, and then methyl ethyl ketone 272 Part, 272 parts of toluene and 11 parts of GP-400 were further added and reacted at 80 ° C. for 4 hours to obtain a polyurethane resin (V).

[Production Example 4: Production Example of Polyurethane Resin (VIII) of Example 4]
(Synthesis of polyester polyol (d))
In a reaction vessel equipped with a thermometer, stirrer, Liebig condenser, 102 parts of adipic acid, 89 parts of 5-sodium sulfoisophthalic acid dimethyl ester, 156 parts of 2,2-dimethyl-1,3-propanediol, and tetrabutyl 0.2 part of titanate was charged and heated at 180 to 220 ° C. for 180 minutes to carry out an esterification reaction. Thereafter, the reaction system was depressurized to 5 mmHg in 20 minutes, and the temperature was raised to 240 ° C. during this time. Further, the pressure in the reaction system was gradually reduced, and after 10 minutes, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was performed at 240 ° C. for 30 minutes. In this way, a polyester polyol (d) was synthesized.

(Synthesis of polyurethane resin (VIII))
In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 100 parts of polyester polyol (d), 20 parts of 2-butyl-2-ethyl-1,3-propanediol, and 30 parts of monohydroxypentaerythritol triacrylate. To this, 73 parts of methyl ethyl ketone and 73 parts of toluene were added and dissolved. 0.05 part of phenothiazine was added, and after stirring, 38 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 2 hours, and then methyl ethyl ketone 272 Part, 272 parts of toluene, and 13 parts of GP-400 were further reacted at 80 ° C. for 4 hours to obtain polyurethane resin (VIII).

[Production Example 5: Production Example of Polyurethane Resin (IX) of Example 5]
Using the polyester polyol (d), a polyurethane resin (IX) was obtained in the same manner as in Production Example 4.

[Production Example 6: Production Example of Polyurethane Resin (X) of Example 6]
(Synthesis of polyester diol (e))
In a reaction vessel equipped with a thermometer, stirrer and Liebig condenser, 888 parts of 5-sodium sulfoisophthalic acid dimethyl ester, 2,2-dimethyl-3-hydroxypropyl-2 ′, 2′-dimethyl-3-hydroxypropanate 1836 parts and 0.2 part of tetrabutoxytitanium were charged and transesterified at 240 ° C. for 5 hours. The temperature was lowered to 100 ° C. and diluted with 633 parts of toluene to obtain a polyester diol (e) solution (solid content concentration 80% by weight).

(Synthesis of polyurethane resin (X))
In a reaction vessel equipped with a thermometer, a stirrer, and a Liebig condenser, 100 parts of the polyester polyol (b), 20 parts of 2-butyl-2-ethyl-1,3-propanediol, 10 parts of the polyester polyol (e) ( As a solid content) and 27 parts of 2-hydroxy-3-acryloyloxydipropyl methacrylate were added, and 73 parts of methyl ethyl ketone and 73 parts of toluene were added and dissolved. 0.05 part of phenothiazine was added, and after stirring, 38 parts of 4,4′-diphenylmethane diisocyanate was added, 0.05 part of dibutyltin dilaurate was added as a catalyst and reacted at 80 ° C. for 2 hours, and then methyl ethyl ketone 272 Part, 272 parts of toluene and 13 parts of GP-400 were further reacted at 80 ° C. for 4 hours to obtain a polyurethane resin (X).

The polyurethane resin used in each comparative example was synthesized by the same method with the resin composition shown in Table 2.
Polyurethane resin (I) of Comparative Example 1
Polyurethane resin (II) of Comparative Example 2
Polyurethane resin (VI) of Comparative Example 3
Polyurethane resin of comparative example 4 (VII)
Polyurethane resin (XI) of Comparative Example 5

  Table 2 shows the resin composition, number average molecular weight, polar group concentration (concentration of sodium sulfonate base), and reduced viscosity of the polyurethane resins (I) to (XI).

  Next, production examples of polyurethane resins (i) to (xi) are shown. The polyurethane resins (i) to (xi) are thermosetting.

[Production Example 7: Production Example of Polyurethane Resin (iii) of Example 7]
In the synthesis of polyurethane resin (III) in Production Example 1, the same method as in Production Example 1 except that monohydroxypentaerythritol triacrylate was not added and the amount of 4,4′-diphenylmethane diisocyanate added was 38 parts. Thus, a polyurethane resin (iii) was synthesized.

[Production Example 8: Production Example of Polyurethane Resin (iv) of Example 8]
In the synthesis of polyurethane resin (IV) in Production Example 2, the same method as in Production Example 2 except that monohydroxypentaerythritol triacrylate was not added and the amount of 4,4′-diphenylmethane diisocyanate was changed to 46 parts. As a result, a polyurethane resin (iv) was obtained.

[Production Example 9: Production Example of Polyurethane Resin (v) of Example 9]
In the synthesis of polyurethane resin (V) in Production Example 3, the same method as in Production Example 3 except that monohydroxypentaerythritol triacrylate was not added and the amount of 4,4′-diphenylmethane diisocyanate added was 38 parts. As a result, a polyurethane resin (v) was obtained.

[Production Example 10: Production Example of Polyurethane Resin (viii) of Example 10]
In the synthesis of polyurethane resin (VIII) in Production Example 4, the same method as in Production Example 4 except that monohydroxypentaerythritol triacrylate was not added and the addition amount of 4,4′-diphenylmethane diisocyanate was 32 parts. Thus, a polyurethane resin (viii) was synthesized.

[Production Example 11: Production Example of Polyurethane Resin (ix) of Example 11]
In the synthesis of polyurethane resin (IX) in Production Example 5, the same method as in Production Example 5 except that monohydroxypentaerythritol triacrylate was not added and the amount of 4,4′-diphenylmethane diisocyanate added was 38 parts. As a result, a polyurethane resin (ix) was obtained.

[Production Example 12: Production Example of Polyurethane Resin (x) of Example 12]
In the synthesis of polyurethane resin (X) in Production Example 6, the same method as in Production Example 6 except that monohydroxypentaerythritol triacrylate was not added and the amount of 4,4′-diphenylmethane diisocyanate added was 32 parts. As a result, a polyurethane resin (x) was obtained.

The polyurethane resin used in each comparative example was synthesized by the same method with the resin composition shown in Table 3.
Polyurethane resin (i) of Comparative Example 6
Polyurethane resin (ii) of Comparative Example 7
Polyurethane resin (vi) of Comparative Example 8
Polyurethane resin of comparative example 9 (vii)
Polyurethane resin (xi) of Comparative Example 10

  Table 3 shows the resin composition, number average molecular weight, polar group concentration (concentration of sodium sulfonate base), and reduced viscosity of the polyurethane resins (i) to (xi).

[Synthesis Example of Electron Beam (EB) Curing Type Vinyl Chloride Resin]
A reaction vessel equipped with a thermometer, a stirrer, and a condenser was charged with 100 parts of vinyl chloride resin MR110 (manufactured by Nippon Zeon Co., Ltd., polar group concentration 63 eq / t) and dissolved in 245 parts of methyl ethyl ketone. Subsequently, 200 ppm (mass) of phenothiazine and hydroquinone were mixed with respect to the following acrylic compound (MOI). Thereafter, 5 parts of 2-isocyanatoethyl methacrylate (MOI) and diuretization catalyst di-n-butyltin dilaurate were mixed at 1000 ppm (mass) with respect to the isocyanate compound (MOI), and the reaction temperature was 8O 0 C at 8 ° C. Stir for hours. In this way, an EB curable vinyl chloride resin was obtained. When the molecular weight and glass transition temperature of the obtained EB curable vinyl chloride resin were measured, the number average molecular weight was 25000 and the glass transition temperature was 60 ° C.

[Examples 1-6, Comparative Examples 1-5]
(Preparation of coating for nonmagnetic layer)
Acicular α-iron oxide 80.0 parts by mass (average particle size: 65 nm, BET specific surface area: 85 m ² / g)
20.0 parts by mass of carbon black (trade name: # 950B, manufactured by Mitsubishi Chemical Corporation, average particle size: 17 nm, BET specific surface area: 250 m ² / g, DBP oil absorption: 70 ml / 100 g, pH: 8)
Binder Electron beam curable vinyl chloride resin 12.0 parts by mass (synthesized above, MOI modified product of MR110)
Binders Each electron beam curable polyurethane resin shown in Table 4 10.0 parts by mass (synthesized above)
Dispersant Phosphate-based surfactant 3.2 parts by mass (trade name: RE-610, manufactured by Toho Chemical Industry Co., Ltd.)
Abrasive material α-alumina 5.0 parts by mass (product name: HIT60A, average particle size: 0.18 μm, manufactured by Sumitomo Chemical Co., Ltd.)
NV (solid content concentration) = 70% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 2/2/1 (mass ratio)

  After kneading the above materials with a kneader, the kneaded product is NV (solid content concentration) = 30 wt% or 35 wt% (shown as “NV [%] before dispersion” in Table 4) as above. Dilution was performed using a solvent having a mixing ratio to obtain a diluted product. The viscosity of this diluted product was measured and shown in Table 4 as “viscosity before dispersion [cp]”.

  The diluted product was dispersed in a residence time of 60 minutes by a horizontal pin mill filled with 0.8 mm zirconia beads at a filling rate of 80% (porosity: 50 vol%). Sampling was performed during the dispersion, and the viscosity was measured appropriately. The highest viscosity value among the measured viscosities is shown in Table 4 as “viscosity during dispersion [cp]”.

Then further lubricant materials:
Lubricant Fatty acid 0.5 part by mass (Nippon Yushi Co., Ltd. product name: NAA180)
Lubricant Fatty Acid Amide 0.5 part by mass (trade name: Fatty Acid Amide S, manufactured by Kao Corporation)
Lubricant Fatty acid ester 1.0 part by mass (trade name: NIKKOLBS manufactured by Nikko Chemicals Co., Ltd.)
Add
NV (solid content concentration) = 24% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 2/2/1 (mass ratio)
After diluting so as to become dispersed, it was dispersed and put into a tank. The viscosity of the paint at the time of delivery was measured. This viscosity is shown in Table 4 as “viscosity after dilution after dispersion [cp]”.

  Subsequently, the obtained coating material was further filtered through a filter having an absolute filtration accuracy of 1.0 μm to prepare each nonmagnetic coating material. This was used for the production of magnetic tape.

  Furthermore, in order to evaluate the stability of the paint, the obtained paint was allowed to stand in a tank for 1 week, and the viscosity of the paint at the time of standing for 1 week was measured. The viscosity value is shown in Table 4 as “viscosity after 1 week [cp]”.

  Further, in order to evaluate the stability of the paint, when the obtained paint was left in a tank for 1 day, it was visually observed whether or not precipitation occurred in the paint. The results are shown in Table 4.

(Preparation of coating for magnetic layer)
Ferromagnetic powder Fe-based acicular ferromagnetic powder 100.0 parts by mass (Fe / Co / Al / Y = 100/24/5/12 ( atomic ratio), Hc: 188kA / m, σs: 140Am 2 / kg, BET (Specific surface area value: 60 m ² / g, average major axis length: 0.45 μm)
Thermosetting type vinyl chloride resin Vinyl chloride copolymer 10.0 parts by mass (trade name: MR110, manufactured by Nippon Zeon Co., Ltd.)
Thermosetting polyurethane resin Polyester polyurethane 6.0 parts by mass (trade name: UR8300, manufactured by Toyobo Co., Ltd.)
Dispersant Phosphoric acid surfactant 3.0 parts by mass (manufactured by Toho Chemical Co., Ltd., trade name: RE610)
Abrasive material α-alumina 10.0 parts by mass (trade name: HIT60A, average particle size: 0.18 μm, manufactured by Sumitomo Chemical Co., Ltd.)
NV (solid content concentration) = 70% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 4/4/2 (mass ratio)

  After kneading the above materials with a kneader, the kneaded product is diluted with a solvent having the same mixing ratio as described above so that NV (solid content concentration) = 30%. Of zirconia beads were dispersed by a horizontal pin mill filled with 80% filling rate (50 vol% porosity).

Then, further, the pre-dispersed paint
NV (solid content concentration) = 15% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 22.5 / 22.5 / 55 (mass ratio)
After diluting so that it becomes, finish dispersion was performed. Subsequently, 4 parts by mass of a thermosetting agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to and mixed with the obtained paint, and then filtered with a filter having an absolute filtration accuracy of 0.5 μm. Produced.

(Preparation of paint for back coat layer)
75.0 parts by mass of carbon black (trade name: BP-800, average particle size 17 nm, DBP oil absorption 68 ml / 100 g, BET specific surface area 210 m ² / g, manufactured by Cabot)
15.0 parts by mass of carbon black (trade name: BP-130, average particle size 75 nm, DBP oil absorption 69 ml / 100 g, BET specific surface area 25 m ² / g, manufactured by Cabot)
Calcium carbonate (Shiraishi Kogyo Co., Ltd., trade name: white luster 0, average particle size 30 nm) 10.0 parts by mass Nitrocellulose 65.0 parts by mass (Asahi Kasei Kogyo Co., Ltd. trade name: BTH1 / 2)
35.0 parts by mass of polyurethane resin (aliphatic polyester diol / aromatic polyester diol = 43/57)
NV (solid content concentration) = 30% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 1/1/1 (mass ratio)

  The material was sufficiently kneaded in a high-viscosity state with a kneader in a state where a part of the organic solvent was removed from the material. Next, the organic solvent removed from the kneaded material was added, and the mixture was sufficiently stirred with a dissolver, and then the material was kneaded with a kneader. Thereafter, as a pre-dispersion, dispersion was performed by a horizontal pin mill filled with 0.8 mm zirconia beads at a filling rate of 80% (porosity: 50 vol%).

Then further pre-dispersed material,
NV (solid content concentration) = 10% (mass percentage)
The solvent ratio was diluted so that MEK / toluene / cyclohexanone = 50.0 / 40.0 / 10.0 (mass ratio), and then final dispersion was performed. Subsequently, 10 parts by mass of a thermosetting agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to and mixed with the obtained coating material, followed by filtration with a filter having an absolute filtration accuracy of 0.5 μm, and the coating material for the back coat layer. Was made.

(Non-magnetic layer forming process)
On one side of a 5.0 μm-thick base film (polyethylene naphthalate film), the above-mentioned non-magnetic layer coating material is extruded by a nozzle so that the thickness after calendering becomes 1.1 μm. Applied and dried. After that, a calendar combining a plastic roll and a metal roll is used to perform processing at a nip number of 4 times, a processing temperature of 100 ° C., a linear pressure of 3500 N / cm, and further irradiation with an electron beam at an irradiation dose of 4.0 Mrad and an acceleration voltage of 200 kV. To form a lower non-magnetic layer.

(Magnetic layer forming process)
On the lower non-magnetic layer formed as described above, the magnetic layer coating material is applied by an extrusion coating method with a nozzle so that the thickness after processing becomes 0.1 μm, oriented, and dried. did. Thereafter, a calender combining a plastic roll and a metal roll was used to perform processing at a nip number of 4 times, a processing temperature of 100 ° C., and a linear pressure of 3500 N / cm to form an upper magnetic layer.

(Back coat forming process)
On the other surface of the base film, the above-mentioned coating material for the backcoat layer was applied by an extrusion coating method with a nozzle so that the thickness after processing was 0.4 μm, and dried. Thereafter, a back coat layer was formed by calendering a combination of a plastic roll and a metal roll at a nip number of 4 times, a processing temperature of 100 ° C., and a linear pressure of 3500 N / cm.

  The magnetic recording tape original fabric obtained as described above was thermally cured at 60 ° C. for 48 hours, and then slit (cut) to a width of 1/2 inch (= 12.650 mm). And the tape for data as a magnetic recording tape sample of Comparative Examples 1-5 was produced, respectively.

[Evaluation of magnetic tape]
The following evaluation was performed for each magnetic recording tape sample.

(Surface roughness (centerline average roughness: Ra))
Using the “TALYSTEP system” (made by Taylor Hobson), the center line average roughness Ra of the magnetic layer surface of the tape was measured based on JIS B0601-1982.
The measurement conditions were a filter of 0.18 to 9 Hz, a stylus 0.1 × 2.5 μm stylus, a stylus pressure of 2 mg, a measurement speed of 0.03 mm / sec, and a measurement length of 500 μm. In addition, the measurement of Ra on the surface of the magnetic layer was performed after the final calendar process and the curing process.

(Measurement of bit error rate b-ERT)
For each magnetic tape sample incorporated in the cartridge, a single recording wavelength of 0.25 μm is recorded with a magnetic recording head, and a P-P value (amplitude) of 50% or less with respect to the P-P value (amplitude) of the signal ) Signal was a missing pulse, and four or more consecutive missing pulses were detected as a defect Long Defect. The number of Long Defects per meter of the magnetic tape sample of Comparative Example 1 as a reference tape is N, the number of Long Defects per meter of each magnetic tape sample is X, and Log ₁₀ (X / N) for each magnetic tape sample. ) As a bit error rate. The calculated bit error rates were compared. A magnetoresistive head (MR head) was used as the reproducing head.

  The results are shown in Table 4.

  As can be seen from Table 4, in Examples 1 to 6, as a binder for the lower non-magnetic layer, a metal sulfonate group was in the range of 200 eq / t to 250 eq / t and measured under the above conditions. When a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less is used, the dispersibility of the fine nonmagnetic inorganic powder in the nonmagnetic layer coating is improved, and no increase in viscosity is observed and the stability is excellent. A magnetic layer paint was produced. When these nonmagnetic coating materials were used, the leveling when applied was good, and a smooth nonmagnetic layer could be formed. Therefore, an upper magnetic layer excellent in surface smoothness was obtained. As a result, all of the magnetic recording media of Examples 1 to 6 were excellent in electromagnetic conversion characteristics.

  In Examples 1 to 6, the nonmagnetic layer coating material was excellent in stability with no increase in viscosity, and there was no clogging of the filter when filtering the nonmagnetic layer coating material. Thus, there was also an advantage in the manufacturing process.

[Examples 7 to 12, Comparative Examples 6 to 10]
(Preparation of coating for nonmagnetic layer)
Acicular α-iron oxide 80.0 parts by mass (average particle size: 65 nm, BET specific surface area: 85 m ² / g)
20.0 parts by mass of carbon black (trade name: # 950B, manufactured by Mitsubishi Chemical Corporation, average particle size: 17 nm, BET specific surface area: 250 m ² / g, DBP oil absorption: 70 ml / 100 g, pH: 8)
Binder Thermosetting vinyl chloride resin 12.0 parts by mass (MR110)
Binder Each thermosetting polyurethane resin shown in Table 5 10.0 parts by mass (synthesized above)
Dispersant Phosphate-based surfactant 3.2 parts by mass (trade name: RE-610, manufactured by Toho Chemical Industry Co., Ltd.)
Abrasive material α-alumina 5.0 parts by mass (product name: HIT60A, average particle size: 0.18 μm, manufactured by Sumitomo Chemical Co., Ltd.)
NV (solid content concentration) = 70% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 2/2/1 (mass ratio)

  After kneading the above materials with a kneader, the kneaded product is NV (solid content concentration) = 30 wt% or 35 wt% (shown as “NV [%] before dispersion” in Table 5) as above. Dilution was performed using a solvent having a mixing ratio to obtain a diluted product. The viscosity of this diluted product was measured and shown in Table 5 as “viscosity before dispersion [cp]”.

  The diluted product was dispersed in a residence time of 60 minutes by a horizontal pin mill filled with 0.8 mm zirconia beads at a filling rate of 80% (porosity: 50 vol%). Sampling was performed during the dispersion, and the viscosity was measured appropriately. The highest viscosity value among the measured viscosities is shown in Table 5 as “viscosity during dispersion [cp]”.

Then further lubricant materials:
Lubricant Fatty acid 0.5 part by mass (Nippon Yushi Co., Ltd. product name: NAA180)
Lubricant Fatty Acid Amide 0.5 part by mass (trade name: Fatty Acid Amide S, manufactured by Kao Corporation)
Lubricant Fatty acid ester 1.0 part by mass (trade name: NIKKOLBS manufactured by Nikko Chemicals Co., Ltd.)
Add
NV (solid content concentration) = 24% (mass percentage)
Solvent ratio MEK / toluene / cyclohexanone = 2/2/1 (mass ratio)
After diluting so as to become dispersed, it was dispersed and put into a tank. The viscosity of the paint at the time of delivery was measured. This viscosity is shown in Table 5 as “viscosity after dilution after dispersion [cp]”.

  Subsequently, 4 parts by mass of a thermosetting agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to and mixed with the obtained coating material, and then filtered through a filter having an absolute filtration accuracy of 1.0 μm. Produced. This was used for the production of magnetic tape.

  Furthermore, in order to evaluate the stability of the paint, the obtained paint was allowed to stand in a tank for 1 week, and the viscosity of the paint at the time of standing for 1 week was measured. This viscosity value is shown in Table 5 as “viscosity after 1 week [cp]”.

  Further, in order to evaluate the stability of the paint, when the obtained paint was left in a tank for 1 day, it was visually observed whether or not precipitation occurred in the paint. The results are shown in Table 5.

(Preparation of coating for magnetic layer)
A magnetic layer coating was prepared in exactly the same manner as in Example 1.

(Preparation of paint for back coat layer)
A paint for the backcoat layer was prepared in exactly the same manner as in Example 1.

(Non-magnetic layer forming process)
On one side of a 5.0 μm-thick base film (polyethylene naphthalate film), the above-mentioned non-magnetic layer coating material is extruded by a nozzle so that the thickness after calendering becomes 1.1 μm. Applied and dried. After that, with a calender combining a plastic roll and a metal roll, the nip number is 4 times, the processing temperature is 100 ° C., the linear pressure is 3500 N / cm, and the thermosetting is further performed at 60 ° C. for 24 hours. A layer was formed.

(Magnetic layer forming process)
On the lower non-magnetic layer formed as described above, the magnetic layer coating material is applied by an extrusion coating method with a nozzle so that the thickness after processing becomes 0.1 μm, oriented, and dried. did. Thereafter, a calender combining a plastic roll and a metal roll was used to perform processing at a nip number of 4 times, a processing temperature of 100 ° C., and a linear pressure of 3500 N / cm to form an upper magnetic layer.

(Back coat forming process)
On the other surface of the base film, the above-mentioned coating material for the backcoat layer was applied by an extrusion coating method with a nozzle so that the thickness after processing was 0.4 μm, and dried. Thereafter, a back coat layer was formed by calendering a combination of a plastic roll and a metal roll at a nip number of 4 times, a processing temperature of 100 ° C., and a linear pressure of 3500 N / cm.

  The magnetic recording tape original fabric obtained as described above was thermally cured at 60 ° C. for 48 hours, and then slit (cut) to a width of 1/2 inch (= 12.650 mm). Examples 7 to 12, And the tape for data as a magnetic recording tape sample of Comparative Examples 6-10 was produced, respectively.

[Evaluation of magnetic tape]
Each magnetic recording tape sample was evaluated in the same manner as in Example 1. In the measurement of the bit error rate b-ERT, the magnetic tape sample of Comparative Example 6 was used as a reference tape.

  The results are shown in Table 5.

  As can be seen from Table 5, in Examples 7-12, the binder of the lower nonmagnetic layer had a sulfonic acid metal base in the range of 200 eq / t to 250 eq / t, and was measured under the above conditions. When a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less is used, the dispersibility of the fine nonmagnetic inorganic powder in the nonmagnetic layer coating is improved, and no increase in viscosity is observed and the stability is excellent. A magnetic layer paint was produced. When these nonmagnetic coating materials were used, the leveling when applied was good, and a smooth nonmagnetic layer could be formed. Therefore, an upper magnetic layer excellent in surface smoothness was obtained. As a result, all the magnetic recording media of Examples 7 to 12 were excellent in electromagnetic conversion characteristics.

  In Examples 7 to 12, the nonmagnetic layer coating material was excellent in stability with no increase in viscosity, and there was no clogging of the filter when filtering the nonmagnetic layer coating material. Thus, there was also an advantage in the manufacturing process.

Claims (8)

A magnetic recording medium having at least a nonmagnetic support, a lower nonmagnetic layer on one surface of the nonmagnetic support, and an upper magnetic layer on the lower nonmagnetic layer,
The upper magnetic layer includes at least a ferromagnetic powder and a binder,
The lower nonmagnetic layer includes at least carbon black, nonmagnetic inorganic powder other than carbon black, and a binder,
The binder contained in the lower non-magnetic layer has a polar group selected from a sulfonate metal base and a sulfate metal base in a range of 200 eq / t to 250 eq / t, and the following conditions:
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C
A magnetic recording medium in which a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less measured in (1) is used.   The nonmagnetic inorganic powder other than the carbon black contains at least one of iron oxide having an average major axis length of 40 nm to 95 nm and iron oxyhydroxide having an average major axis length of 40 nm to 95 nm. 2. A magnetic recording medium according to 1. The magnetic recording medium according to claim 2, wherein the iron oxide has a specific surface area by a BET method of 80 m ² / g or more and 100 m ² / g or less. The magnetic recording medium according to claim 2, wherein the iron oxyhydroxide has a specific surface area of 80 m ² / g or more and 100 m ² / g or less by a BET method.   The magnetic recording medium according to claim 1, wherein the polyurethane resin has a radiation functional group.   The magnetic recording medium according to claim 1, wherein the upper magnetic layer has a thickness of 0.30 μm or less.   The magnetic recording medium according to claim 1, wherein the lower nonmagnetic layer has a thickness of 0.3 μm to 1.3 μm. A method for producing a magnetic recording medium comprising at least a nonmagnetic support, a lower nonmagnetic layer on one surface of the nonmagnetic support, and an upper magnetic layer on the lower nonmagnetic layer,
Carbon black, a nonmagnetic inorganic powder other than carbon black, and a binder having a polar group selected from sulfonate metal base and sulfate metal base in the range of 200 eq / t to 250 eq / t, and the following conditions :
Measuring solvent: toluene / methyl ethyl ketone / cyclohexanone = 40/40/20 (weight ratio)
Measurement solution concentration: 4 g / L
Measurement temperature: 30 ° C
A step of preparing a coating for a nonmagnetic layer containing at least a polyurethane resin having a reduced viscosity of 0.42 or more and 0.55 or less measured in
Applying a prepared nonmagnetic layer coating on one surface of the nonmagnetic support to form a lower nonmagnetic layer;
Applying a magnetic layer coating material containing at least a ferromagnetic powder and a binder on the lower nonmagnetic layer and drying to form an upper magnetic layer.