JP2005235322A - Magnetic recording tape and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording tape for an MR head having low noise, high capacity and satisfactory running durability even though a back layer is thin. <P>SOLUTION: (1) In the magnetic recording tape having a non-magnetic layer, a magnetic layer and the back layer on a substrate, the non-magnetic layer has a binder which is occupied by ≥30 mass% binder having ≥100°C glass transition temperature and has no thermosetting curing agent and the surface of the back layer has 10 to 1,000 pieces/90 μm square density of protrusions having 30 to 100 nm height measured by an atomic force microscope. (2) In a manufacturing method of the magnetic recording medium, a webb formed by forming the non-magnetic layer which does not contain the thermosetting curing agent, the magnetic layer and the back layer on the substrate is cut out in a desired width, then the cut out web is wound up and subjected to thermal treatment at 40 to 70°C for ≥24 h. (3) The magnetic tape is obtained by cutting out the web having the non-magnetic layer, the magnetic layer and the back layer on the substrate in the desired width, then winding up the cut out web and then subjecting the cut out web to thermal treatment at 40 to 70°C for ≥24 h. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-density magnetic recording tape excellent in electromagnetic conversion characteristics and running durability.

  Conventionally, magnetic heads using electromagnetic induction as the operating principle (inductive magnetic heads) have been used and spread, but there is a limit to using them in a higher density recording / reproducing area, and MR (magnetoresistance) is used as the operating principle. Is proposed and used in hard disks and the like. MR heads can produce a reproduction output several times that of induction type magnetic heads and do not use induction coils, so that equipment noise such as impedance noise is greatly reduced. It has become possible to obtain an S / N ratio. A magnetic recording layer suitable for an MR head has been studied even in a coating type magnetic recording medium that is excellent in productivity and can be provided at a low price. A magnetic recording medium in which a magnetic layer formed by dispersing a substantially non-magnetic lower layer and ferromagnetic fine powder in a binder on a non-magnetic support in this order is provided on the magnetic layer while maintaining the smoothness of the surface. Many methods have been applied to today's high-density coated magnetic recording media as a method for realizing thinning (Patent Document 1).

In order to realize high-density recording, it is important to reduce the particle size of the magnetic powder. However, for example, during the development of a coating type magnetic recording medium exceeding the surface recording density of 0.3 Gbit / inch ² , there has been a problem that noise is increased particularly when the particle size of the magnetic particles is reduced. If the particle size of the magnetic powder is reduced, it becomes difficult to disperse in the binder during the preparation of the magnetic layer coating, and the smoothness of the magnetic layer surface cannot be maintained, resulting in the intended low noise medium. It becomes difficult. In order to suppress this noise, it is necessary to (1) eliminate the aggregation of the magnetic materials and (2) smooth the surface of the magnetic layer.

  In addition to excellent electromagnetic conversion characteristics, magnetic recording tape is also required to have good running durability. For this purpose, there is an attempt to improve running durability by providing a back layer and providing protrusions on the base surface, or adding coarse particle carbon having a particle size of 0.1 μm or more to the back layer to roughen the surface. Has been made. When the surface of the back layer is roughened by such a method, when the magnetic recording tape is wound around a hub and stored or processed, the back layer and the magnetic layer are pressed against each other so that irregularities of the back layer appear in the magnetic layer. There has been a drawback that "back-through" occurs and as a result, the electromagnetic conversion characteristics deteriorate. Attempts have been made to smooth the surface of the back layer in order to solve such a problem of “show-through”.

  For example, Patent Document 2 discloses a back surface that includes primary particles or agglomerated carbon black having a diameter larger than the major axis diameter of the metal magnetic powder and that has a center line average roughness of 0.01 μm or less. It has been proposed to use layers. In this case, it is possible to suppress an increase in noise due to winding and storage, but it is not possible to exhibit the effect of showing-through already when the tape is manufactured. Further, there is no description about the durability of the back layer. If the back layer surface is made smooth, the coefficient of friction with respect to the guide of a regenerator such as a VTR increases, and the running stability decreases.

Patent Document 3 contains an oxide powder made of titanium oxide, α-iron oxide or a mixture thereof, and carbon black, and further 10 to 40 masses with the total mass of the oxide powder and carbon black being 100 parts by mass. It has been proposed to use a back layer having a high adhesive strength and containing a part of binder. In this case, although it has been shown that the output can be improved and the running durability of the back layer can be maintained, the entire system is a system of an induction magnetic head that is relatively insensitive to noise. The influence on the recording medium is not described, and it is unavoidable that improvement is necessary for a coating type magnetic recording medium having a surface recording density of 0.3 Gbit / inch ² or more.

On the other hand, the demand for thinning is demanded not only for the magnetic layer but also for the entire layer constituting the magnetic recording tape. Computer storage media in recent years are required to have a high capacity, and it is necessary to reduce the thickness of the entire tape. In order to reduce the thickness of the magnetic recording tape, conventionally, the flexible support is thinned, or the nonmagnetic layer provided between the flexible support of the coating type magnetic recording tape and the magnetic layer is thinned. It was done. However, if the flexible support is made thinner than a certain range, the running durability is lowered, and if the nonmagnetic layer is made thinner, the output is lowered, the error rate is increased, and the dropout is increased. The back layer cannot be omitted in order to maintain good running performance. In addition, if the back layer is made thin, the adhesive strength between the back layer and the support decreases, so the back layer peels off during repeated running, or the projection on the back layer surface shows through the magnetic layer and outputs. It will decline.
As described above, the conventional technology has not yet provided a magnetic recording tape having sufficiently good electromagnetic characteristics and running durability. In particular, today, where the thickness of the entire magnetic recording tape is required to be reduced, there is a need for a magnetic recording tape that has a thin back layer and good electromagnetic characteristics and running durability. No satisfactory magnetic recording tape is provided.

Japanese Examined Patent Publication No. 4-71244 Japanese Patent Laid-Open No. 10-116414 Japanese Patent Laid-Open No. 11-259851

  The object of the present invention is to solve the problems of the prior art, and to provide a magnetic recording tape for MR heads with low noise, high capacity, thin back layer and good running durability.

  As a result of intensive studies to achieve the above object, the present inventors use a binder having high Tg and high toughness on the magnetic layer side, appropriately set the surface protrusion density of the back layer, and then heat treatment By adding the above, it was found that a magnetic recording tape capable of extremely improving electromagnetic conversion characteristics and running stability can be provided, and the present invention has been achieved. That is, the present invention comprises the following means.

1) A magnetic recording tape in which a magnetic layer mainly composed of ferromagnetic metal powder or hexagonal ferrite powder and a binder is formed on a support, wherein the nonmagnetic layer is interposed between the magnetic layer and the support. In the magnetic recording tape having a back layer on the opposite surface, the non-magnetic layer accounts for 30% or more of the total binder mass with a binder having a glass transition temperature (Tg) of 100 ° C. or more and thermosetting. A magnetic recording tape which does not contain a curing agent and has a projection density of 30 to 100 nm in height measured by an atomic force microscope existing on the surface of the back layer is 10 to 1000 per 90 μm square.
2) A nonmagnetic layer not containing a thermosetting curing agent, a ferromagnetic metal powder or a hexagonal ferrite powder and a magnetic layer mainly composed of a binder are formed in this order on one side of the support, and the other support. A method of manufacturing a magnetic recording tape, comprising: cutting a surface having a back layer formed thereon into a desired width, winding up, and then performing a heat treatment at 40 to 70 ° C. for 24 hours or more.
3) After cutting the substrate having the magnetic layer, nonmagnetic layer and back layer described in 1) above to a desired width, winding the film, and then performing a heat treatment at 40 to 70 ° C. for 24 hours or more. A magnetic recording tape obtained.

  The present invention provides a magnetic recording tape suitable for reproduction by an MR head, having a high capacity due to its thin total thickness, low noise because the surface smoothness of the magnetic layer is ensured, and excellent running durability. can do.

The invention described in 1) above (hereinafter referred to as the present invention 1) specifies the binder composition of the nonmagnetic layer and specifies the surface characteristics of the back layer from the viewpoint of the distribution of protrusions.
That is, in the present invention 1), a binder having a Tg of 100 ° C. or higher, preferably 100 to 160 ° C., more preferably 110 to 140 ° C. is used without adding a thermosetting curing agent to the nonmagnetic layer. 30% or more, preferably 30 to 70%, more preferably 40 to 65%, and the back layer surface has a protrusion density of 30 to 100 nm in height measured by an atomic force microscope, 10 per 90 μm square. ˜1000, preferably 30 to 800, more preferably 30 to 200.
Since the present invention 1) has the above-described structure, it can form a multi-layer consisting of a nonmagnetic layer and a magnetic layer which are highly elastic and hardly cause plastic deformation. A high-output, low-noise magnetic recording tape in which the show-through of the surface protrusion to the magnetic layer is reduced can be supplied. In the magnetic recording tape of the present invention 1), since the surface of the back layer is specified, the coefficient of friction of the back layer can be set to a moderate size. This increases the inter-layer friction coefficient between the back layer and the magnetic layer, so that the tape rolled up on the roll, slit pancake, and built-in reel is good even when handling magnetic recording tape at high speed. . Similarly, the winding form of the tape on the reel after the video cassette recorder is fast-forwarded or rewinded at high speed is also good.

The invention described in the above 2) (hereinafter referred to as the present invention 2) is characterized in that the nonmagnetic layer is formed without containing a thermosetting curing agent, and the tape that has been cut is wound, and then heat-treated. A method for manufacturing a magnetic recording tape.
That is, the present invention 2) is a method in which a non-magnetic layer and magnetic layer containing no thermosetting curing agent and a back layer (hereinafter also referred to as a web) formed on a support are cut into a desired width, and then wound. Then, a heat treatment at 40 to 70 ° C., preferably 50 to 65 ° C., more preferably 55 to 65 ° C. is performed for 24 hours or more, preferably 24 to 48 hours, more preferably 36 to 48 hours.
The heat treatment of the present invention 2) is carried out after the web is cut into a desired width, but it is preferable that the thermo-treatment is performed before the cutting. Here, what is heat-treated is the tape width of the final product.
This thermo process is normally performed as a means for reducing the heat shrinkage rate, and there is a method of performing a thermo process in a form in which webs are laminated. Although this thermal treatment can greatly improve the heat shrinkage rate, there is a problem that the unevenness of the back surface is considerably reflected on the magnetic layer.
In the present invention, when this web is cut, wound, and heat-treated, the nonmagnetic layer does not contain a thermosetting curing agent. Therefore, the frequency and size of irregularities on the magnetic layer due to the annealing effect of the binder. And a smooth magnetic layer can be obtained.

In the invention described in 3) above (hereinafter referred to as the present invention 3), the material having the magnetic layer, the nonmagnetic layer and the back layer of the present invention 1) on the support is cut into a desired width and then wound. And then the heat treatment of the present invention 2).
The present invention 3) can produce an effect obtained by combining the effects of the present invention 1) and the present invention 2). In other words, the multi-layer composed of the nonmagnetic layer and the magnetic layer has high mechanical strength, so that the back surface protrusion on the magnetic layer by the thermo treatment is reduced, and the show-through is further reduced by the heat treatment. And a highly durable magnetic layer can be obtained.

  The magnetic recording tape of the present invention widely includes those having a nonmagnetic layer and a magnetic layer on one side of a support and a back layer on the opposite side. Therefore, the magnetic recording tape of the present invention includes those having layers other than the magnetic layer and the back layer. For example, a nonmagnetic layer containing nonmagnetic powder, a soft magnetic layer containing soft magnetic powder, a second magnetic layer, a cushion layer, an overcoat layer, an adhesive layer, and a protective layer may be included. These layers can be provided at appropriate positions so that their functions can be effectively exhibited. The magnetic recording tape of the present invention is preferably a magnetic recording tape having a nonmagnetic layer containing a nonmagnetic inorganic powder and a binder between the support and the magnetic layer. The thickness of the layer can be, for example, 0.03 to 1 μm for the magnetic layer and 0.5 to 3 μm for the nonmagnetic layer. The nonmagnetic layer is preferably thicker than the magnetic layer. When a soft magnetic layer is provided between the support and the magnetic layer, for example, the magnetic layer is 0.03 to 1 μm, preferably 0.05 to 0.5 μm, and the soft magnetic layer is 0.8 to 3 μm. be able to. The thickness of the back layer formed on the magnetic recording tape of the present invention is preferably set in the range of 0.05 to 1.0 μm.

It is preferable to use carbon black for the back layer in order to prevent electric resistance. As the carbon black used for the back layer, those commonly used for magnetic recording tape can be widely used. For example, furnace black for rubber, thermal black for rubber, carbon black for color, acetylene black, and the like can be used. In order to prevent unevenness of the back layer from appearing on the magnetic layer, the particle size of the carbon black is preferably set to 0.3 μm or less. A particularly preferable particle size is 0.01 to 0.1 μm. Carbon black preferably has a pH of 2 to 10, a moisture content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml. The specific surface area is 100 to 500 m ² / g, preferably from 150~400m ² / g, DBP oil absorption 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. As specific examples, BLACK PEARL S2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72 manufactured by Cabot Corporation; # 3050B, # 3150B, # 3250B, # 3250B, #, manufactured by Mitsubishi Chemical Corporation 3750B, # 3950B, # 950, # 650B, # 970B, # 850B, MA-600; Columbian Carbon's CONDUCTEX SC, RAVEN8800, 8000, 7000, 5750, 5250, 3500, 2100, same 2000, 1800, 1500, 1255, 1250; Akzo Ketchen Black EC, Asahi Carbon Corporation # 55, # 50, # 30; Colombian Carbon Corporation RAVEN450, 430; Kerncarb Corporation Thermax MT, etc. I can make it.

  For the binder for the back layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used. Preferred binders are vinyl chloride resins, vinyl chloride-vinyl acetate resins, fiber-based resins such as nitrocellulose, phenoxy resins, and polyurethane resins. Among them, it is more preferable to use a vinyl chloride resin, a vinyl chloride-vinyl acetate resin, or a polyurethane resin because the hardness of the back layer becomes close to the hardness of the magnetic layer and the back shot can be reduced.

Polyurethane resin, _-SO 3 _M in the _{molecule, -OSO 3 M, -COOM, -PO} 3 MM ', - OPO 3 MM', - NRR ', - N + RR'R "COO - ( wherein, M And M ′ are each independently a hydrogen atom, an alkali metal, an alkaline earth metal, or ammonium, R and R are each independently an alkyl group having 1 to 12 carbon atoms, and R ″ is an N bond having 1 to 12 carbon atoms. It preferably contains at least one polar group selected from (which represents an alkylene group), particularly preferably —SO ₃ M or —OSO ₃ M. The amount of these polar groups is preferably 1 × 10 ⁻⁵ to 2 × 10 ⁻⁴ eq / g, particularly preferably 5 × 10 ⁻⁵ to 1 × 10 ⁻⁴ eq / g. If the amount is less than 1 × 10 ⁻⁵ eq / g, the powder tends to be insufficiently adsorbed, so that the dispersibility tends to decrease. If the amount exceeds 2 × 10 ⁻⁴ eq / g, the solubility in the solvent decreases. Therefore, dispersibility tends to decrease.

  The number average molecular weight (Mn) of the polyurethane resin is preferably 5,000 to 100,000, more preferably 10,000 to 50,000, and particularly preferably 20,000 to 40,000. If it is less than 5000, the strength and durability of the coating film are low. Moreover, when more than 100,000, the solubility to a solvent and a dispersibility are low. As the polyurethane resin, those having a cyclic structure and an ether group are preferable. The cyclic structure of the polyurethane resin contributes to rigidity, and the ether group contributes to flexibility.

  The back layer of the magnetic recording tape of the present invention can appropriately contain components other than carbon black and a binder. In particular, the inclusion of a fatty acid is essential for suppressing an increase in the coefficient of friction during repeated running while maintaining the strength. Further, by containing a fatty acid ester or an abrasive having a Mohs hardness of 8 or more, an increase in the coefficient of friction during repeated running can be suppressed and sliding durability can be improved. Furthermore, an increase in friction coefficient can be suppressed by adding an aromatic organic acid compound or a titanium coupling agent to improve dispersibility and increase strength. Moreover, an organic powder can be contained to suppress an increase in the coefficient of friction and to reduce the reflection. Examples of fatty acids that can be added include monobasic fatty acids having 8 to 24 carbon atoms. Among these, monobasic fatty acids having 8 to 18 carbon atoms are preferable. Specific examples thereof include lauric acid, caprylic acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, and elaidic acid.

Examples of fatty acid esters include monobasic fatty acids having 10 to 24 carbon atoms (which may include unsaturated bonds or branched) and monovalent, divalent, trivalent, and tetravalent carbon atoms having 2 to 12 carbon atoms. And mono-fatty acid ester, di-fatty acid ester or tri-fatty acid ester formed of any one of monovalent, pentavalent, and hexahydric alcohols (which may include an unsaturated bond or may be branched). . Specific examples thereof include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate. Rate. The amount of fatty acid ester added is 0.1 to 5 parts by mass, preferably 0.1 to 3 parts by mass, when the total amount of oxide powder such as α-iron oxide and carbon black is 100 parts by mass. Here, the oxide powder does not contain an abrasive having a Mohs hardness of 8 or higher. This oxide powder is generally used in an amount of 0 to 20 parts by mass, preferably 0 to 15 parts by mass with respect to 100 parts by mass of carbon black.
Examples of the abrasive having a Mohs hardness of 8 or more include α-alumina, chromium oxide, artificial diamond, and carbon-modified boron nitride (CBN). Among them, it is preferable to use those having an average particle size of 0.2 μm or less and a particle size of the back layer thickness or less. This abrasive is usually used in an amount of 0 to 10 parts by mass, preferably 0 to 5 parts by mass with respect to 100 parts by mass of carbon black.

In the present invention, since the back layer can be made thin, sufficient sliding durability can be ensured only by adding a small amount of abrasive. As the aromatic organic acid compound, phenylphosphonic acid is preferable. The amount used is 0.03 to 10 parts by mass, preferably 0.5 to 5 parts by mass, when the total amount of the oxide powder and carbon black is 100 parts by mass. Examples of the organic powder include acrylic-styrene copolymer resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment. The glass transition temperature of the back layer is preferably 60 to 120 ° C., and the dry thickness is usually about 0.05 to 1.0 μm. The magnetic recording tape of the present invention can have a thickness of 4 to 9 [mu] m because the back layer is not easily reflected on the magnetic layer even when wound and stored at high tension.

The ferromagnetic powder used for the magnetic layer of the magnetic recording tape of the present invention is a ferromagnetic metal powder or a hexagonal ferrite powder such as barium ferrite. The ferromagnetic powder usually has an SBET (BET specific surface area) of 40 to 80 m ² / g, preferably 50 to 70 m ² / g. The crystallite size is usually 10 to 25 nm, preferably 11 to 22 nm. The major axis length is usually 0.03 to 0.25 μm, preferably 0.04 to 0.08 μm. The pH of the ferromagnetic powder is preferably 7 or more. Examples of the ferromagnetic metal powder include a simple substance or an alloy such as Fe, Ni, Fe—Co, Fe—Ni, Co—Ni, and Co—Ni—Fe, and within a range of 20% by mass or less of the metal component, aluminum, Silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, rhenium, silver, lead, phosphorus, lanthanum, Cerium, praseodymium, neodymium, tellurium, bismuth, and the like can be included. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. Methods for producing these ferromagnetic powders are already known, and the ferromagnetic powders used in the present invention can also be produced according to known methods. There are no particular restrictions on the shape of the ferromagnetic powder, but needle-shaped, granular, dice-shaped, rice-grained and plate-shaped ones are usually used. It is particularly preferable to use acicular ferromagnetic powder. In the present invention, the binder and the ferromagnetic powder are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone, ethyl acetate ordinarily used in the preparation of a magnetic coating material to obtain a magnetic layer forming coating material. The kneading and dispersing can be performed according to a usual method. In addition to the above components, the coating material for forming the magnetic layer includes an abrasive such as α-Al ₂ O ₃ and Cr ₂ O _3, an antistatic agent such as carbon black, a lubricant such as fatty acid, fatty acid ester, and silicone oil, and a dispersant. Or the like or a commonly used additive or filler.

Next, the nonmagnetic layer (also referred to as the lower layer) will be described. The inorganic powder used in the lower layer of the present invention is selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and nonmagnetic metals in the case of nonmagnetic powders, for example. can do. As an inorganic compound, for example, titanium oxide (TiO ₂ , TiO), α-alumina, β-alumina, γ-alumina, α-iron oxide, chromium oxide, zinc oxide, tin oxide, oxidized with an α conversion rate of 90-100% Tungsten, vanadium oxide, silicon carbide, cerium oxide, corundum, silicon nitride, titanium carbide, silicon dioxide, magnesium oxide, zirconium oxide, boron nitride, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, goethite, hydroxide Aluminum or the like can be used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred are titanium dioxide described in JP-A-5-182177, and JP-A-6-60362 and JP-A-9-170003. Α-iron oxide described in the publication. Nonmagnetic metals include Cu, Ti, Zn, Al and the like. The average particle size of these nonmagnetic powders is preferably 0.005 to 2 μm. However, if necessary, nonmagnetic powders having different average particle sizes may be combined, or even a single nonmagnetic powder may have a wide particle size distribution. The same effect can be given. Particularly preferred is a nonmagnetic powder having an average particle size of 0.01 μm to 0.2 μm. The pH of the nonmagnetic powder is particularly preferably 6-9. The specific surface area of the nonmagnetic powder is usually 1 to 100 m ² / g, preferably 5 to 50 m ² / g, and more preferably 7 to 40 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.01 μm to 2 μm. The oil absorption using DBP is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedron shape, and a plate shape.

When a soft magnetic layer is provided, the soft magnetic powder includes granular Fe, Ni, granular magnetite, Fe-Si, Fe-Al, Fe-Ni, Fe-Co, Fe-Co-Ni, Fe-Al-Co. (Sendust) alloy, Mn—Zn ferrite, Ni—Zn ferrite, Mg—Zn ferrite, Mg—Mn ferrite, and others, “Non-angled physics (lower) magnetic properties and applications” (1984), 368-376). The surface of these nonmagnetic powders and soft magnetic powders is surface-treated so that at least a part thereof is coated with Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO. It is preferable to leave. Of these, particularly providing good dispersibility is _{Al 2 O 3, SiO 2,} TiO 2, ZrO 2, further preferred is _{Al 2 O 3, SiO 2,} ZrO 2. These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated depending on the purpose may be used, or a method of first treating the surface layer with alumina and then treating the surface layer with silica, or vice versa. May be. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

  By mixing carbon black in the lower layer, the surface electrical resistance Rs can be lowered and the desired micro Vickers hardness can be obtained. The average particle diameter of carbon black is 5 nm to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Specifically, the same carbon black that can be used for the above-described back layer can be used.

As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the above back layer and magnetic layer can be applied. In particular, known techniques relating to the back layer and the magnetic layer can be applied to the binder amount, type, additive, and dispersant addition amount and type.
As the binder having a glass transition temperature (Tg) of 100 ° C. or higher used in the present invention, a polyurethane resin is preferable. Examples of the polyurethane resin used include those obtained by reacting a polyol having a molecular weight of 500 to 5000 having a cyclic structure and an alkylene oxide chain with a polyol having a molecular weight of 200 to 500 having a cyclic structure as a chain extender and an organic diisocyanate. A polyurethane resin (A), a polyester polyol composed of an aliphatic dibasic acid and an aliphatic diol having an alkyl branched side chain and no cyclic structure, and a branched alkyl side chain having 3 or more carbon atoms as a chain extender Polyurethane resin (B) obtained by reacting an aliphatic diol and an organic diisocyanate compound, or polyurethane obtained by reacting a polyol compound having a cyclic structure and an alkyl chain having 2 or more carbon atoms with an organic diisocyanate List resin (C) Door can be.
These will be described in detail below.

1) Polyurethane resin (A)
As the polyol having a cyclic structure and an alkylene oxide chain as a raw material of the polyurethane resin (A), a polyol obtained by adding an alkylene oxide such as ethylene oxide or propylene oxide to a diol having a cyclic structure can be used. Specifically, bisphenol A, hydrogenated bisphenol A, bisphenol S, hydrogenated bisphenol S, bisphenol P, hydrogenated bisphenol P, tricyclodecane dimethanol, cyclohexane dimethanol, cyclohexane diol, 5,5 ′-(1- Methylethylidene) bis- (1,1′-bicyclohexyl) 2-ol, 4,4 ′-(1-methylethylidene) bis-2methylcyclohexanol, 5,5 ′-(1,1′-cyclohexylidene) ) Bis- (1,1′-bicyclohexyl) 2-ol, 5,5 ′-(1,1′-cyclohexylmethylene) bis- (1,1′-bicyclohexyl) 2-ol, hydrogenated terpene diphenol , Diphenyl bisphenol A, diphenyl bisphenol S, diphenyl bisphenol P, 9,9-bis- (4 Hydroxyphenyl) fluorene, 4,4 '-(3-methylethylidene) bis (2-cyclohexyl-5-methylphenol), 4,4'-(3-methylethylidene) bis (2-phenyl-5-methylcyclohexanol) ), 4,4 ′-(1-phenylethylidene) bis (2-phenol), 4,4′-cyclohexylidenebis (2-methylphenol), terpene diphenol and other diols can be used. Of these, hydrogenated bisphenol A and hydrogenated bisphenol A polypropylene oxide adducts are preferred. The molecular weight of the polyol is preferably 500 to 5,000. When it is 500 or more, the urethane group concentration is low, and thus the solvent solubility is high.
As the polyol having a cyclic structure used as a chain extender, a diol having the above cyclic structure and an alkylene oxide such as ethylene oxide and propylene oxide with a molecular weight of 200 to 500 can be used. Preferred are hydrogenated bisphenol A and propylene oxide adducts of hydrogenated bisphenol A.

2) Polyurethane resin (B)
The polyester polyol as a raw material for the polyurethane resin (B) is composed of an aliphatic dibasic acid and an aliphatic diol having no cyclic structure having an alkyl branched side chain. As the aliphatic dibasic acid, aliphatic dibasic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, malonic acid, glutaric acid, pimelic acid, and suberic acid can be used. Of these, succinic acid, adipic acid and sebacic acid are preferred. Of the total dibasic acid component of the polyester polyol, the aliphatic dibasic acid content is preferably 70 mol% or more. When it is 70 mol% or more, the concentration of the dibasic acid having a substantially cyclic structure is low, so that the solvent solubility is high and a good dispersibility improvement effect can be obtained.
Examples of the aliphatic polyol having no cyclic structure having an alkyl branched side chain that can be used for the polyester polyol include 2,2-dimethyl-1,3-propanediol, 3,3-dimethyl-1,5-pentanediol, 2-methyl-2-ethyl-1,3-propanediol, 3-methyl-3-ethyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 3-methyl-3 -Propyl-1,5-pentanediol, 2-methyl-2-butyl-1,3-propanediol, 3-methyl-3-butyl-1,5-pentanediol, 2,2-diethyl-1,3- Propanediol, 3,3-diethyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-ethyl-3-butyl-1 5-pentanediol, 2-ethyl-2-propyl-1,3-propanediol, 3-ethyl-3-propyl-1,5-pentanediol, 2,2-dibutyl-1,3-propanediol, 3, 3-dibutyl-1,5-pentanediol, 2,2-dipropyl-1,3-propanediol, 3,3-dipropyl-1,5-pentanediol, 2-butyl-2-propyl-1,3-propane Diol, 3-butyl-3-propyl-1,5-pentanediol, 2-ethyl-1,3-propanediol, 2-propyl-1,3-propanediol, 2-butyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 3-butyl-1,5-pentanediol, 3-octyl-1, 5- Ntanediol, 3-myristyl-1,5-pentanediol, 3-stearyl-1,5-pentanediol, 2-ethyl-1,6-hexanediol, 2-propyl-1,6-hexanediol, 2-butyl Use branched aliphatic diols such as -1,6-hexanediol, 5-ethyl-1,9-nonanediol, 5-propyl-1,9-nonanediol, and 5-butyl-1,9-nonanediol. Can do. Among these, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol are preferable. The content of the polyol having a branched side chain in the polyol used for the polyester polyol is preferably 50 to 100 mol%, more preferably 70 to 100 mol%. Within the above range, the solvent solubility is high and good dispersibility can be obtained.
In the polyurethane resin (B), an aliphatic diol having a branched alkyl side chain having a total carbon number of 3 or more can be used as a chain extender. The branched alkyl side chain means an alkyl group that branches into a carbon chain that connects each carbon having two hydroxyl groups. When the total number of carbon atoms is 3 or more and the branched alkyl side chain is present, the solvent solubility is improved and good dispersibility can be obtained. Examples of the aliphatic diol having a branched alkyl side chain having a total carbon number of 3 or more include 2-methyl-2-ethyl-1,3-propanediol, 3-methyl-3-ethyl-1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 3-methyl-3-propyl-1,5-pentanediol, 2-methyl-2-butyl-1,3-propanediol, 3-methyl-3 -Butyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 3,3-diethyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol 3-ethyl-3-butyl-1,5-pentanediol, 2-ethyl-2-propyl-1,3-propanediol, 3-ethyl-3-propyl-1,5-pentanediol, 2 2-dibutyl-1,3-propanediol, 3,3-dibutyl-1,5-pentanediol, 2,2-dipropyl-1,3-propanediol, 3,3-dipropyl-1,5-pentanediol, 2-butyl-2-propyl-1,3-propanediol, 3-butyl-3-propyl-1,5-pentanediol, 2-propyl-1,3-propanediol, 2-butyl-1,3-propane Diol, 3-propyl-1,5-pentanediol, 3-butyl-1,5-pentanediol, 3-octyl-1,5-pentanediol, 3-myristyl-1,5-pentanediol, 3-stearyl- 1,5-pentanediol, 2-ethyl-1,6-hexanediol, 2-propyl-1,6-hexanediol, 2-butyl-1,6-hexa Diol, 5-propyl-1,9-nonanediol, it can be used 5-butyl-1,9-nonanediol and the like. Of these, 2-ethyl-2-butyl-1,3-propanediol and 2,2-diethyl-1,3-propanediol are preferable. The content in the polyurethane resin is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. Within the above range, the solvent solubility is high and good dispersibility can be obtained.

3) Polyurethane resin (C)
The polyol compound having a cyclic structure and an alkyl chain having 2 or more carbon atoms as a raw material for the polyurethane resin (C) is preferably a diol having a molecular weight of 500 to 1,000. A diol is preferred because gelation due to crosslinking during polyurethane polymerization does not occur. Moreover, when the carbon number of the alkyl chain of the diol is 2 or more, the solvent solubility is high and the dispersibility is good. When the molecular weight is 500 or more, the solvent concentration is high because the urethane group concentration is low, and when it is 1000 or less, the coating film strength is good. As the polyol having a cyclic structure and an alkyl chain having 2 or more carbon atoms, a dimer diol represented by the structure of the following formula obtained by hydrogenating and reducing dimer acid is preferable.

The diol having a cyclic structure and an alkyl chain having 2 or more carbon atoms is preferably contained in the polyurethane resin in an amount of 5 to 60% by mass, more preferably 10 to 40% by mass. When the content of the diol having a cyclic structure and an alkyl chain having 2 or more carbon atoms is within the above range, the solvent solubility is high, the dispersibility is good, and the durability is high, which is preferable.
In the present invention, the organic diisocyanate used for reacting with the polyol to form a polyurethane resin is not particularly limited, and those usually used can be used. Specifically, for example, hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6- Examples include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthalene diisocyanate, and 3,3-dimethylphenylene diisocyanate.

The polyurethane resin preferably has a polar group. There are various methods for introducing a polar group into a polyurethane resin. For example, a polyurethane resin having a polar group can be produced by using a raw material monomer having a polar group introduced therein to produce a polyurethane resin. it can. For example, a dihydric alcohol or dibasic acid produced from a polar group-containing polyol such as polyester polyol or polyether polyol having a polar group and a polyol such as polyester polyol or polyether polyol not having a polar group and a diisocyanate. It is possible to use a method such as production by changing the part to a polar group-containing diol or a polar group-containing dibasic acid. Polar group-containing polyol or a polar group-containing dibasic acid, for example _-SO 3 _M in the main chain or side chain of the polyol or dibasic _{acid, -OSO 3 M, -PO (OM} ) 2, -OPO (OM) 2 And at least one polar group selected from —COOM (wherein M represents a hydrogen atom, an alkali metal or ammonium). The content of the polar group is preferably 0.075 to 0.200 meq / g, more preferably 0.100 to 0.150 meq / g.

  The average molecular weight of the polar group-containing polyurethane resin used in the present invention is preferably 5,000 to 100,000, more preferably 10,000 to 50,000. By setting it within this range, the solubility in a solvent is high, the dispersibility is ensured, the physical strength of the magnetic coating film is high, and the durability of the magnetic recording tape is good. Further, the viscosity of the paint at a predetermined concentration is appropriate, the workability is good, and handling is easy.

In the present invention, a polyurethane resin other than the polyurethane resin can be used in combination. The polyurethane resin used in combination preferably has the same polar group as that of the polyurethane resin.
The total binder used for the nonmagnetic layer is preferably 10 to 30 parts by mass, more preferably 15 to 25 parts by mass, with respect to 100 parts by mass of the inorganic powder.
The polyurethane resin used in the nonmagnetic layer may be used in the magnetic layer, and the amount added in that case is preferably 5 to 50 parts by mass, more preferably 100 parts by mass of the ferromagnetic powder. 10-30 parts by mass.

  In the present invention, the magnetic layer can be composed of two or more layers according to the purpose. In this case, it is known that the performance is changed between the upper magnetic layer and the lower magnetic layer. For example, in order to improve the long wavelength recording characteristics, it is desirable to set the Hc of the lower magnetic layer lower than the Hc of the upper magnetic layer, and to set Br of the lower magnetic layer higher than Br of the upper magnetic layer. It is valid. In addition, the advantage by taking a well-known multilayer structure can be provided. As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the lower magnetic layer, those of the above magnetic layer can be applied. In particular, with respect to the binder amount, type, additive, dispersant addition amount, type, known techniques relating to the magnetic layer can be applied.

  Examples of the support that can be used in the present invention include biaxially stretched polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyamide (including aromatic polyamide), polyimide, polyamideimide, polybenzoxazole, and the like. be able to. These supports may have been previously subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like. The support that can be used in the present invention has a centerline average surface roughness of 0.1 to 20 nm, preferably 1 to 10 nm at a cutoff value of 0.25 mm, and has excellent surface smoothness. It is preferable to have it. These supports preferably have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more. The thickness of the support is 4 to 15 μm, preferably 4 to 9 μm. When it is thin, the unevenness of the back layer is easily reflected by the handling tension, and this can be effectively suppressed by using the above-mentioned polyurethane resin in at least the lower layer. When the thickness is 7 μm or less, it is preferable to use an aromatic polyamide such as PEN or aramid. Most preferred is aramid.

The magnetic recording tape of the present invention can be manufactured, for example, by applying a paint to the surface of the support under running so that the layer thickness after drying is within the above-mentioned predetermined range. . A plurality of magnetic paints or non-magnetic paints may be applied successively or simultaneously. As an application machine for applying magnetic paint, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, Spray coating, spin coating, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to. When manufacturing a magnetic recording tape having two or more layers on one side, for example, the following method can be used.
(1) First, the lower layer is first applied by a coating apparatus such as a gravure, roll, blade, or extrusion, which is generally applied in the application of magnetic paint, and before the lower layer is dried, Japanese Patent Publication No. 1-44686, A method of coating the upper layer using a support pressure type extrusion coating apparatus or the like disclosed in JP-A-60-238179, JP-A-2-265672, and the like.
(2) Using a single coating head having two coating liquid passage slits disclosed in JP-A-63-88080, JP-A-2-17971, and JP-A-2-265672, A method of applying the lower layer almost simultaneously.
(3) A method of applying the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

  The back layer can be prepared by applying a coating material for forming a back layer in which particulate components such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent to the surface opposite to the magnetic layer. The applied magnetic layer is dried after subjecting the ferromagnetic powder contained in the magnetic layer to a magnetic field orientation treatment. The magnetic field orientation treatment can be appropriately performed by a method well known to those skilled in the art. The magnetic layer is subjected to a surface smoothing treatment using a super calender roll or the like after drying. By performing the surface smoothing treatment, voids generated by the removal of the solvent at the time of drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer is improved. For this reason, a magnetic recording tape having high electromagnetic conversion characteristics can be obtained. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like is used. Moreover, it can also process with a metal roll.

  The magnetic recording tape of the present invention preferably has a surface with good smoothness. In order to improve the smoothness, for example, it is effective to subject the magnetic layer formed by selecting a specific binder as described above to the calendar treatment. In the calendar treatment, the temperature of the calender roll is set to 60 to 100 ° C., preferably 70 to 100 ° C., particularly preferably 80 to 100 ° C., and the pressure is set to 98 to 490 kN / m (100 to 500 kg / cm), preferably 198 to 441 kN. / M (200 to 450 kg / cm), particularly preferably 294 to 392 kN / m (300 to 400 kg / cm). The obtained magnetic recording tape can be cut into a desired size using a cutting machine or the like. The magnetic recording tape that has undergone the calendering process is generally heat-treated. Recently, it has been emphasized to lower the thermal shrinkage rate for the linearity of the high-density magnetic recording tape (to ensure off-track margin). In particular, as the track becomes narrower, it is required to suppress the shrinkage rate in the MD direction (longitudinal direction) in the use environment, but the shrinkage rate can be suppressed by using the present invention 2) in combination with the thermo treatment. Is possible.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples. In addition, unless otherwise indicated, the display of "part" in an Example shows a "mass part".

[Synthesis Example 1]
Synthesis of Polyurethane Resin A (Polyurethane Resin Containing Dimerdiol as Diol Component) Dimerdiol / hydrogenated bisphenol / sulfoisophthalic acid ethylene oxide adduct (DEIS) / diphenylmethane diisocyanate (MDI) = 14.9 / 36.2 / A diol component excluding MDI having a 2 / 46.7 (molar ratio) composition was equipped with a reflux condenser and a stirrer, and dissolved in a 30% cyclohexanone solution at 60 ° C. under a nitrogen stream in a container purged with nitrogen in advance. Next, 60 ppm of dibutyltin dilaurate was added as a catalyst and further dissolved for 15 minutes. Further, MDI was added and reacted by heating at 90 ° C. for 6 hours to obtain a polyurethane resin A solution. Tg of polyurethane resin A was 155 ° C.

[Synthesis Example 2]
Synthesis of polyurethane resin B (including polyurethane resin) Propylene oxide adduct of bisphenol A / tricyclodecanediol / DEIS / MDI = 40/60/2/100 (molar ratio) diol components excluding MDI were reflux-cooled The vessel was equipped with a vessel and a stirrer, and was dissolved in a 30% cyclohexanone solution at 60 ° C. under a nitrogen stream in a container previously purged with nitrogen. Next, 60 ppm of dibutyltin dilaurate was added as a catalyst and further dissolved for 15 minutes. Further, MDI was added and reacted by heating at 90 ° C. for 6 hours to obtain a polyurethane resin B solution. The Tg of polyurethane resin B was 110 ° C.

[Example 1]
Magnetic paint 1 (ferromagnetic metal powder)
Ferromagnetic acicular metal powder 100 parts Hc: 2300 Oe (184 kA / m)
Crystallite size: 120 mm, average long axis length: 0.06 μm
BET specific surface area: 70 m ² / g
Polyurethane resin A 18 parts Phenylphosphonic acid 5 parts α-Al ₂ O ₃ (average particle diameter: 0.2 μm) 10 parts Carbon black (average particle diameter: 20 nm) 1 part Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part

Lower layer paint 1
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
10.5 parts of vinyl chloride copolymer (MR110, manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin A 8.6 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

Back layer paint 1
(Dispersion) The following composition was placed in a ball mill and dispersed for 24 hours.
80 parts of carbon black 1 (average particle size: 20 nm)
Carbon black 2 5 parts (average particle size: 100 nm)
α-Fe ₂ O ₃ (average major axis length: 0.1 μm) 1 part nitrocellulose resin 65 parts polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 35 parts MEK 260 parts toluene 260 parts cyclohexanone 260 parts

The following composition was mixed and stirred in the dispersed slurry, and then dispersed again for 3 hours in a ball mill.
Stearic acid 1 part Butyl stearate 2 parts MEK 210 parts Toluene 210 parts Cyclohexanone 210 parts Add 1 part of isocyanate compound (Nihon Polyurethane Co., Ltd., Coronate-L) to 100 parts of the filtered paint, and stir and mix for back layer Paint was used.

About each of the said magnetic layer coating material and the coating material for lower layers, after kneading each component for 60 minutes with an open kneader, it dispersed for 240 minutes with the sand mill. Furthermore, 40 parts of cyclohexanone was added to each, and it filtered using the filter which has an average hole diameter of 1 micrometer, and prepared the coating liquid of a magnetic layer and a lower layer.
Thickness of the obtained nonmagnetic layer coating solution so that the thickness of the lower layer after drying is 1.2 μm, and immediately after that, the thickness of the magnetic layer is 0.12 μm. Simultaneous multilayer coating was performed on a support having a center surface average surface roughness of 3.8 nm at 2 μm, and the layers were oriented with a magnet having a magnetic force of 0.3 T while both layers were still wet. After drying, a surface smoothing treatment was performed at a speed of 100 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a temperature of 90 ° C. using a seven-stage calendar composed only of metal rolls. Thereafter, a back layer having a thickness of 0.5 μm was applied, dried, and then subjected to heat treatment at 70 ° C. for 24 hours before winding and cutting. Thereafter, it was slit to a 1/2 inch width, wound up, and then subjected to a heat treatment at 60 ° C. for 48 hours. A tape sample was obtained by cleaning the surface of the magnetic layer with a tape cleaning device attached so that the nonwoven fabric and the razor blade were pressed against the magnetic surface on a device having a slit product feeding and winding device.

[Example 2]
A magnetic recording tape was prepared in the same manner as in Example 1 except that the magnetic coating material and the lower layer coating material were changed as follows in Example 1.
Magnetic paint 2 (hexagonal ferrite powder)
Barium ferrite magnetic powder 100 parts Hc, plate diameter: 2500 Oe, 0.03 μm
Polyurethane resin A 12 parts α-Al ₂ O ₃ (average particle diameter: 0.2 μm) 7 parts Carbon black (average particle diameter: 20 nm) 1 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Lower layer paint 2
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
13.3 parts of vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin A 5.8 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 3]
In Example 1, a magnetic recording tape was produced in the same manner except that the coating material for the lower layer was changed as follows and the thickness of the back layer was changed to 0.3 μm.
Lower layer paint 3
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
14.4 parts of vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin A 4.7 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 4]
In Example 3, a magnetic recording tape was produced in the same manner except that no heat treatment was performed.

[Example 5]
In Example 2, a magnetic recording tape was prepared in the same manner except that the lower layer coating material and the back layer coating material were changed as follows.
Lower layer paint 4
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
5.7 parts of vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin A 13.4 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

Back layer paint 2
(Dispersion) The following composition was placed in a ball mill and dispersed for 24 hours.
85 parts of carbon black 1 (average particle size: 20 nm)
Carbon black 2 0.5 part (average particle size: 100 nm)
α-Fe ₂ O ₃ (average major axis length: 0.1 μm) 1 part nitrocellulose resin 65 parts polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 35 parts MEK 260 parts toluene 260 parts cyclohexanone 260 parts

The following composition was mixed and stirred in the dispersed slurry, and then dispersed again for 3 hours in a ball mill.
Stearic acid 1 part Butyl stearate 2 parts MEK 210 parts Toluene 210 parts Cyclohexanone 210 parts Add 1 part of isocyanate compound (Nihon Polyurethane Co., Ltd., Coronate-L) to 100 parts of the filtered paint, and stir and mix for back layer Paint was used.

[Example 6]
In Example 3, the magnetic recording tape of Example 6 was produced in the same manner except that the lower layer coating material was changed as follows and the heat treatment after cutting was omitted.
Lower layer paint 5
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
Polyurethane resin A 19.1 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 7]
In Example 1, 1 part of an isocyanate compound (Nihon Polyurethane Co., Ltd., Coronate-L) was added as a thermosetting curing agent to 100 parts of the paint after filtration of the paint for the lower layer, and the mixture was stirred and mixed to obtain a paint for the lower layer. Produced the magnetic recording tape of Example 7 in the same manner as in Example.

[Example 8]
In Example 2, the magnetic recording tape of Example 8 was produced in the same manner except that the lower layer coating material was changed as follows.
Lower layer paint 6
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
10.5 parts of vinyl chloride copolymer (MR110, manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin B 8.6 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 9]
In Example 2, the magnetic recording tape of Example 9 was produced in the same manner except that the lower layer coating material was changed as follows and the thickness of the back layer was changed to 0.3 μm.
Lower layer paint 7
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
10.5 parts of vinyl chloride copolymer (MR110, manufactured by Nippon Zeon Co., Ltd.)
Polyurethane (UR8600, manufactured by Toyobo, Tg: 32 ° C.) 8.6 parts phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part cyclohexanone 140 parts methyl ethyl ketone 170 parts butyl stearate 2 parts stearin 1 part acid

[Example 10]
A magnetic recording tape of Example 10 was produced in the same manner as in Example 1 except that the magnetic layer coating material was changed as follows.
Magnetic paint 3 (ferromagnetic metal powder)
Ferromagnetic acicular metal powder 100 parts Hc: 2300 Oe (184 kA / m)
Crystallite size: 120 mm, average long axis length: 0.06 μm
BET specific surface area: 70 m ² / g
Polyurethane resin B 20 parts Phenylphosphonic acid 5 parts α-Al ₂ O ₃ (average particle diameter: 0.2 μm) 10 parts Carbon black (average particle diameter: 20 nm) 1 part Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 11]
The magnetic recording tape of Example 11 was produced in the same manner as in Example 10 except that the coating material for the lower layer was changed as follows and the thickness of the back layer was changed to 0.3 μm.
Lower layer paint 9
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
14.3 parts of vinyl chloride copolymer (MR110 manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin B 4.8 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 12]
In Example 10, the coating for the lower layer was changed as follows, and 1 part of an isocyanate compound (Nihon Polyurethane Co., Ltd., Coronate-L) was added as a thermosetting curing agent to 100 parts of the paint after filtration, followed by stirring and mixing. A magnetic recording tape of Example 12 was produced in the same manner except that the lower layer coating material was used.
Lower layer paint 10
Nonmagnetic inorganic powder: 85 parts of α-iron oxide Average long axis length: 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 15 parts Average particle size: 20 nm
10.5 parts of vinyl chloride copolymer (MR110, manufactured by Nippon Zeon Co., Ltd.)
Polyurethane resin B 8.6 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle size: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

[Example 13]
In Example 10, the magnetic recording tape of Example 13 was produced in the same manner except that the lower layer coating material was changed to the coating material 10 and the heat treatment after cutting was not performed.

[Example 14]
In Example 13, the magnetic recording tape of Example 14 was produced in the same manner except that the heat treatment after cutting was performed.

[Example 15]
In Example 10, the magnetic recording tape of Example 15 was produced in the same manner except that the lower layer coating material was changed to the coating material 10 and the heat treatment conditions after cutting were set at 40 ° C. for 150 hours.

[Example 16]
A magnetic recording tape of Example 16 was produced in the same manner as in Example 15 except that the heat treatment conditions after cutting were set at 80 ° C. for 12 hours.

[Example 17]
In Example 15, the magnetic recording tape of Example 17 was produced in the same manner except that the coating material for the back layer was changed as follows and the heat treatment conditions after cutting were changed to 70 ° C. for 24 hours.
Back layer paint 3
(Dispersion) The following composition was placed in a ball mill and dispersed for 24 hours.
85 parts of carbon black 1 (average particle size: 20 nm)
20 parts of carbon black 2 (average particle size: 100 nm)
α-Fe ₂ O ₃ (average particle size: 0.1 μm) 1 part nitrocellulose resin 65 parts polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 35 parts MEK 260 parts toluene 260 parts cyclohexanone 260 parts

[Example 18]
The magnetic recording tape of Example 18 was produced in the same manner as in Example 1 except that the coating material for the back layer was changed to Paint 2.

[Example 19]
The magnetic recording tape of Example 19 was produced in the same manner as in Example 1, except that the back layer coating material was changed to the coating material 3.

The performance of the obtained magnetic recording tape was evaluated as follows, and the results are shown in Table 1.
〔Measuring method〕
1. Measurement of SNR, DO (Dropout) SNR was measured using a reel-to-reel tester and a commercially available head mounted under the following conditions. An AMR head was used as the reproducing head.
Relative speed: 3 m / sec, recording track width: 18 μm, reproduction track width: 10 μm
Distance between shields: 0.27 μm
Recording signal generator: HP 8118A
Reproduction signal processing: spectrum analyzer For the measurement of DO, the number of outputs of 40% or less with respect to the average value of reproduction output was obtained using a DO tester manufactured by AMT.
The SNR is 20 dB or more and the DO is 5 pieces / m or less.

2. Durability Durability evaluation was performed by wrapping the tape on a SUS420J rod of 6 mmφ (roughness 0.6 s) at 45 °, and running at a load of 70 g under the conditions of 23 ° C. and 50% RH for 10,000 passes for the magnetic layer and 1000 passes for the back layer. It was. The surface of the tape after running was observed, and the number of scratches of 2 or less, no deposits and stains were evaluated as “good”, and the number of scratches of 3 or more, or those with deposits and stains were rated as “x”.

3. Back Protrusion Density Three-dimensional surface roughness was measured using an atomic force microscope and Nanoscope III manufactured by Digital Instruments Inc., USA, and the number of protrusions existing at 30 to 100 nm was determined from the average surface of the back layer surface roughness. Here, the average surface is a surface in which the volume of unevenness in the measurement surface is equal. The measurement was performed in a contact mode and a scanning speed of 2 Hz in a range of 90 μm × 90 μm.

In the table, the binder ratio of the lower polyurethane is the ratio of the binder (polyurethane resin A or B) having a glass transition temperature (Tg) of 100 ° C. or higher with respect to the total mass of the lower binder. In addition, those satisfying the present inventions 1) to 3) were evaluated as ◯, and those not satisfied as x.
From the above table, it can be seen that the present invention 3) satisfying the present invention 1) and 2) is excellent in SNR, DO and durability.

Claims (3)

  A magnetic recording tape in which a magnetic layer mainly composed of ferromagnetic metal powder or hexagonal ferrite powder and a binder is formed on a support, and there is a nonmagnetic layer between the magnetic layer and the support In the magnetic recording tape having a back layer on the opposite side, the non-magnetic layer comprises 30% or more of the total binder mass with a binder having a glass transition temperature (Tg) of 100 ° C. or more and a thermosetting curing agent. And a protrusion density of 30 to 100 nm in height measured by an atomic force microscope existing on the back layer surface is 10 to 1000 per 90 μm square.   A nonmagnetic layer not containing a thermosetting curing agent, a ferromagnetic metal powder or a hexagonal ferrite powder and a magnetic layer mainly composed of a binder are formed in this order on one side of the support and on the other side of the support A method for producing a magnetic recording tape, comprising: cutting a back layer formed into a desired width, winding up, and then performing a heat treatment at 40 to 70 ° C. for 24 hours or more.   The substrate having the magnetic layer, the nonmagnetic layer and the back layer according to claim 1 on a support is cut into a desired width, wound, and then subjected to a heat treatment at 40 to 70 ° C. for 24 hours or more. Magnetic recording tape characterized by that.