JP2011216152A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the quality of an original sheet, and to improve production efficiency as a result of the long winding of the original sheet by suppressing the generation of longitudinal wrinkles and the generation of recesses in a magnetic layer.SOLUTION: This method includes a lower nonmagnetic layer forming process, an upper magnetic layer forming process, a back coating layer forming process, a first winding process which winds the original sheet in which each layer is formed, a thermosetting process which performs thermosetting processing on the original sheet, a calender process which calenders the original sheet, and a second winding process for winding the calendered original sheet. In the first winding process, each layer is formed so that the thickness of the center of the wound original sheet is larger than that of the end by a range of 0.25 mm or larger and 0.35 mm or smaller per 10,000 turns (so that an original sheet accumulative shape value is within the range). In the second winding process, calendering is performed so that the thickness of the center of the wound original sheet is larger than that of the end by a range of 0.2 mm or larger and 0.3 mm or smaller per 10,000 turns.

Description

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

  In general, a magnetic tape is formed by forming a coating layer including a magnetic layer on a long and wide flexible support body, winding it around a core, and then, for example, a desired width such as 1/2 inch width. It is obtained by cutting (cutting) into multiple lines. In recent years, the capacity of the medium has further increased, and the thickness of each layer tends to be reduced in addition to the thickness of the support and the magnetic layer. This is to increase the tape length to be wound in a certain volume and to increase the capacity. If the length of the web becomes longer, the number of turns (the number of layers that the web is wound around the core) increases when the roll is wound around the core, and there is a portion with uneven thickness in the width direction of the web. When the sheet is cut to a desired tape width, the tension becomes uneven in the original width direction, and the width of the magnetic tape after cutting varies. On the other hand, if there is a part that is partially recessed in the web wound around the core, vertical wrinkle deformation will occur in the longitudinal direction of the web, and there will be no contact with the head when it becomes a tape. It will be equal. For this reason, it is preferable to wind up the core in a shape that does not cause partial dents and the central portion is slightly convex.

  JP-A-61-293577 is an example of a conventional technique for producing an original fabric having a convex central portion. According to this, it is disclosed that when the coating agent is applied on the long and wide support, coating is performed such that the dry coating thickness of the coating agent in the width direction becomes thicker from the end toward the center. Yes. In the example of the publication, when the length of the long wide support is 4000 m and the average thickness in the width direction is 1.0 μm, the deviation of the thickness of the central portion with respect to the end is 0.1 μm. . However, when the length of the long and wide support exceeds 10,000 m, the number of turns (number of windings) for winding the long and wide support around the core (core) is 10,000 even if the thickness deviation is 0.1 μm. In such a case, the protrusion amount of the central part due to the accumulation of deviation (the difference between the thickness of the end part and the thickness of the central part becomes excessive (for example, when the number of turns is 10,000, the central part becomes the end part) 1 mm in the circumferential direction).

  Japanese Patent Application Laid-Open No. 2000-285445 discloses a method of preventing the transfer and deformation of the original fabric by limiting the number of turns to be stacked within a certain range. However, the core diameter of the take-up will be extremely large, or the length of the roll taken up will be shortened, the handling of the roll taken up on the core will be worse, and the length of the roll will be shortened. Therefore, the production efficiency decreases as the ratio increases with respect to the length of the core that cannot be used in the product and the length of the outermost peripheral portion that can be commercialized.

  Therefore, it is preferable to take up the raw material as long as possible. However, if the micro-projections are formed on the surface of the backcoat layer, the magnetic tape support is wound up to produce the magnetic tape raw material roll. The microprotrusions are pressed against the opposing magnetic layer surface. When the magnetic tape original roll is left in that state for a long time or heated, there is a problem that a minute dent is formed on the surface of the magnetic layer. If the surface of the data recording layer of a tape-shaped recording medium represented by a computer backup magnetic tape has a dent, the frequency of dropouts (signal loss) during data reading / writing increases, and the tape-shaped recording medium Quality will deteriorate. Further, since the influence of the dent increases as the track width becomes narrower, it becomes a great obstacle to increasing the recording capacity (recording density) of the tape-shaped recording medium. Therefore, Japanese Patent Application Laid-Open No. 2007-004874 proposes a processing method for recovering the dents in the magnetic layer generated by transferring the backcoat layer by heating the pancake cut and wound on the hub. The temperature change caused by reheating the plate tends to cause stepping or popping out of the pancake, resulting in damage to the side of the tape.

JP-A-61-29377 (page 2-3, FIG. 1-7) JP 2000-285445 A (page 2-12, FIG. 1-6) JP 2007-004874 A (page 5-12, FIG. 1-6)

  Accordingly, an object of the present invention is to realize stabilization of the quality of the original fabric by suppressing the occurrence of vertical wrinkle-like deformation in the longitudinal direction of the original fabric and the occurrence of dents in the magnetic layer due to the transfer of the backcoat layer. A further object is to provide a method of manufacturing a magnetic recording medium that can improve the production efficiency by taking up a long roll of the original fabric.

  The present invention relates to a lower layer non-magnetic layer in which a coating solution for a nonmagnetic layer containing at least a nonmagnetic powder and a binder is applied on one surface of a flexible support, dried and then cured to form a lower nonmagnetic layer. A magnetic layer forming step, an upper magnetic layer forming step in which an upper magnetic layer is formed by applying a coating solution for a magnetic layer containing at least a ferromagnetic powder and a binder on the non-magnetic material and then drying the magnetic layer; and the flexibility A backcoat layer forming step of forming a backcoat layer by applying a backcoat layer coating solution containing at least a nonmagnetic powder and a binder on the other surface of the support; and A first winding step of winding the raw material having the respective layers formed on both sides around the core, a thermosetting step of performing a thermosetting process on the raw material wound on the core, and winding the core on the core Unwind the original fabric, A magnetic recording medium manufacturing method for manufacturing a magnetic recording medium, including a calendar process for performing calendar processing on a magnetic material, and a second winding process for winding the raw material subjected to the calendar processing on a core. The thickness of the central portion in the width direction of the original fabric wound around the core in the first winding step is within the range of 0.25 mm or more and 0.35 mm or less per 10,000 turns than the thickness of the end portion in the width direction. The thickness of each layer is defined so as to be thick, and the thickness of the central portion in the width direction of the raw material wound around the core in the second winding step is the end in the width direction. The magnetic recording medium is manufactured by performing the calendar process so that the thickness is within a range of 0.2 mm or more and 0.3 mm or less per 10,000 turns than the thickness of the portion. It is a method.

  In the calendar process, the present invention uses a plurality of metal rolls in which a central portion in a length direction along the width direction of the original fabric is formed in a crown shape having a larger diameter than an end portion of the length. A method of manufacturing a magnetic recording medium, wherein the calendaring is performed.

  The present invention is the method for producing a magnetic recording medium, wherein the treatment for curing the lower nonmagnetic layer in the lower nonmagnetic layer forming step is a curing treatment using radiation.

  According to the present invention, at the time of the thermosetting treatment, the roll shape of the raw material wound around the core is a slightly larger central convex shape than the final shape, so that the vertical wrinkle-like deformation that occurs in the longitudinal direction of the original material. As a result, the quality of the original fabric can be stabilized, and as a result, the yield can be improved. In addition, since the quality of the raw material is stabilized, a tape with good head touch can be manufactured. In addition, by performing a calendar process after the thermosetting process, it is possible to avoid the occurrence of dents in the magnetic layer due to the transfer of the backcoat layer, thereby reducing the frequency of dropouts and the recording capacity of the tape-shaped recording medium ( As a result of stable recording density), the quality can be improved. In addition, since the quality can be stabilized even if the length of the raw roll is increased, the loss of the product can be reduced. As a result, the cost can be reduced and the production efficiency can be improved.

It is a perspective view of the measuring apparatus used for this invention. It is the 1st explanatory view explaining the measuring method of original fabric accumulated shape value. It is the 2nd explanatory view explaining the measuring method of original fabric accumulated shape value.

  Hereinafter, embodiments of the present invention will be described in detail.

  As an example of the magnetic recording medium produced in the present invention, a lower nonmagnetic layer is provided on one surface of a nonmagnetic support (flexible support), and a thickness of 0.03 to 0.03 is formed on the lower nonmagnetic layer. An upper magnetic layer of 0.30 μm is provided, and a backcoat layer is provided on the other surface of the nonmagnetic support. In the present invention, a lubricant coating or various coatings for protecting the magnetic layer may be provided on the magnetic layer as necessary. The one surface on which the magnetic layer of the nonmagnetic support is provided has an undercoat layer (adhesive layer) for the purpose of improving the adhesion between the coating film (lower nonmagnetic layer) and the nonmagnetic support. May be provided.

[Lower nonmagnetic layer]
The lower nonmagnetic layer contains carbon black, nonmagnetic inorganic powder other than carbon black, and a binder resin.

As carbon black contained in the 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 amount of water-soluble sodium ions and water-soluble calcium ions contained in carbon black is preferably small, and the content of water-soluble sodium ions is preferably 500 ppm or less, more preferably 300 ppm or less. The water-soluble calcium ion content is preferably 300 ppm or less, more preferably 200 ppm or less. If it exceeds the above range, an organic acid (particularly fatty acid) and salt contained in the coating film are formed and discharged onto the surface of the coating film, which causes dropout and increased error rate.

  In order to reduce water-soluble sodium ions and water-soluble calcium ions contained in carbon black, the purity of water used as a reaction stop fluid in the production process of carbon black or water used in the granulation process is reduced. You only have to increase it. Carbon black production methods are described in JP-A-11-181323, JP-A-10-46047, and JP-A-8-12898.

Various inorganic powders other than carbon black can be used for the nonmagnetic layer. For example, acicular nonmagnetic iron oxide (α-Fe ₂ O ₃ ), CaCO ₃ , titanium oxide, barium sulfate, α-Al ₂ O ₃ etc. inorganic powder is mentioned. The inorganic powder preferably contains less water-soluble sodium ions and water-soluble calcium ions, and the water-soluble sodium ion content is preferably 70 ppm or less, more preferably 50 ppm or less. When the above range is exceeded, an organic acid (particularly fatty acid) and salt contained in the coating film are formed and discharged onto the surface of the coating film, resulting in a dropout and an increased error rate. In order to reduce water-soluble sodium ions and water-soluble calcium ions contained in the inorganic powder, a water washing step may be added.

  The blending ratio of carbon black and inorganic powder other than the carbon black is preferably 100/0 to 5/95 in terms of mass ratio (carbon black / inorganic powder). When the blending ratio of carbon black is less than 5 parts by mass, a problem occurs in surface electrical resistance.

  In the lower nonmagnetic layer, a thermoplastic resin, thermosetting or reactive resin, radiation (electron beam or ultraviolet ray) curable resin, etc., as a binder in addition to the above materials, can be selected according to the characteristics and process conditions of the medium. It is selected and used in appropriate combination.

  As the thermoplastic resin, those having a softening temperature of 150 ° C. or less, an average molecular weight of 5,000 to 200,000, and a degree of polymerization of about 50 to 2,000 are used, and as the thermosetting resin, reactive resin or radiation curable resin, the average It has a molecular weight of 5,000 to 200,000 and a polymerization degree of about 50 to 2,000. After coating, drying and calendering, the molecular weight is increased by a reaction such as condensation or addition by heating and / or radiation (electron beam or ultraviolet ray) irradiation. What to do is used.

  Among these, what is preferably used is a combination of nitrocellulose and a polyurethane resin as shown below, and a combination of a vinyl chloride copolymer and a polyurethane resin.

  The vinyl chloride copolymer preferably has a vinyl chloride content of 60 to 95% by mass, particularly 60 to 90% by mass, and the average degree of polymerization is preferably about 100 to 500%.

  Such vinyl chloride resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride- Vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-hydroxyalkyl (meth) acrylate-maleic acid copolymer, vinyl chloride- Vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, etc. , Especially with vinyl chloride Copolymers of monomers containing epoxy (glycidyl) group.

The vinyl chloride copolymer contains a sulfate group (—SO ₄ Y) and / or a sulfo group (—SO ₃ Y) as a polar group (hereinafter referred to as an S-containing polar group) in order to improve dispersibility. Is preferred. In the S-containing polar group, Y may be either H or an alkali metal, but it is particularly preferable that Y = K, that is, —SO ₄ K, —SO ₃ K. The vinyl chloride copolymer may contain only one of the S-containing polar groups, or may contain both, and the content ratio is arbitrary when both are included.

  The polyurethane resin used in combination with the vinyl chloride resin is a general term for resins obtained by a reaction between a hydroxy group-containing resin such as polyester polyol and / or polyether polyol and a polyisocyanate-containing compound, and has a number average molecular weight of 5000 to 5000. It is about 200,000 and has a Q value (mass average molecular weight / number average molecular weight) of about 1.5 to 4.

  The polyurethane resin may have a polar group at the terminal or side chain, and particularly preferably contains a polar group containing sulfur and / or phosphorus.

As the polar groups contained in the polyurethane _{resin, -SO 3 M, -SO 4 M} , S -containing groups -SR _{like, -PO 3 M, -PO 2 M} , -POM, -P = O (OM 1) ( OM ² ), P-containing polar groups such as —OP═O (OM ¹ ) (OM ² ), —COOM, —OH, —NR ₂ , —N + R ₃ X— (where M, M ¹ and M ² are , H, Li, Na, K, R represents H or a hydrocarbon group, and X represents a halogen atom), an epoxy group, —CN, and the like. It is preferable to use a polyurethane resin in which at least one polar group selected from these polar groups is introduced by copolymerization or addition reaction. These polar groups are preferably contained in the molecule in an amount of 0.01 to 3% by mass, and these polar groups may be present in the main chain or branching of the skeleton resin.

  The polyurethane resin preferably has a glass transition temperature Tg in the range of −20 ° C. ≦ Tg ≦ 80 ° C.

  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 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.

  Examples of thermoplastic resins other than vinyl chloride copolymers and polyurethane resins include (meth) acrylic resins, polyester resins, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymers. Polymer, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, polyfunctional polyethers such as polycaprolactone, polyamide resin, polyimide resin, phenol resin, polybutadiene elastomer, chlorinated rubber, acrylic rubber , Isoprene rubber, epoxy-modified rubber and the like.

  Thermosetting resins include phenol resins that undergo condensation polymerization, epoxy resins, polyurethane curable resins, urea resins, butyral resins, formal resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, polyamide resins, and epoxy resins. -Polyamide resins, saturated polyester resins, urea formaldehyde resins and the like.

  As the crosslinking agent for curing these binder resins, various polyisocyanates, particularly diisocyanates can be used, and in particular, one or more of tolylene diisocyanate, hexamethylene diisocyanate, and methylene diisocyanate are used. It is preferable to use it. 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.

  Furthermore, it is also possible to use the binder resin obtained by introducing a (meth) acrylic double bond by a known method and performing electron beam sensitive modification. In order to perform this electron beam sensitive modification, the resin is modified with urethane or ethylenic non-reactant, which reacts a reaction product (adduct) of tolylene diisocyanate (TDI) and 2-hydroxyethyl (meth) acrylate (2-HEMA). Improved urethane modification and hydroxyl group using a monomer (2-isocyanatoethyl (meth) acrylate, etc.) having one or more saturated double bonds and one isocyanate group in one molecule and no urethane bond in the molecule An ester modification in which a compound having a (meth) acrylic group and a carboxylic acid anhydride or dicarboxylic acid is reacted with a resin having a carboxylic acid group is well known. Among these, improved urethane modification is preferable because it does not become brittle even when the content ratio of the vinyl chloride resin is increased, and a coating film excellent in dispersibility and surface properties can be obtained.

  When these electron beam curable binder resins are used, a conventionally known polyfunctional acrylate is mixed in an amount of 1 to 50 parts by mass, preferably 5 to 40 parts by mass with respect to 100 parts by mass of the binder resin in order to improve the crosslinking rate. May be used.

  The content of the binder resin used for the lower nonmagnetic layer is preferably 10 to 100 parts by mass, more preferably 12 to 12 parts by mass with respect to a total of 100 parts by mass of the inorganic powder other than carbon black and carbon black in the lower nonmagnetic layer. 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. If the binder content is too large, a dispersion failure occurs during the preparation of the lower non-magnetic layer coating solution, and a smooth lower non-magnetic layer surface cannot be formed.

  The lower nonmagnetic layer preferably contains a lubricant as necessary. As the lubricant, regardless of whether it is saturated or unsaturated, known ones such as fatty acids, fatty acid esters and saccharides can be used alone or in admixture of two or more, and two or more fatty acids having different melting points are used in admixture. It is also preferable to use 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.

  Specifically, as fatty acids, saturated linear fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, erucic acid, saturated fatty acids having side chains such as isosecetic acid, isostearic acid, oleic acid, linoleic acid Unsaturated fatty acids such as linolenic acid can be used as appropriate.

  Fatty acid esters include linear saturated fatty acid esters such as butyl stearate and butyl palmitate, saturated fatty acid esters having side chains such as isocetyl stearate and isostearyl stearate, and unsaturated fatty acid esters such as isostearyl oleate. Fatty acid esters of unsaturated alcohols such as oleyl stearate, esters of unsaturated fatty acids and unsaturated alcohols such as oleyl oleate, esters of dihydric alcohols such as ethylene glycol distearate, ethylene glycol monooleate, ethylene glycol di Esters of dihydric alcohols and unsaturated fatty acids such as oleate and neopentyl glycol dioleate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan Such as sugars and esters of saturated or unsaturated fatty acids such as Rioreeto the like.

  The content of the lubricant in the lower nonmagnetic layer may be appropriately adjusted according to the purpose, but is preferably 1 to 20% by mass with respect to the total mass of carbon black and inorganic powder other than carbon black.

  The coating liquid for forming the lower non-magnetic layer is prepared by adding an organic solvent to the above components. 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, methyl isobutyl ketone and cyclohexanone, and aromatic solvents such as toluene may be appropriately selected and used. . 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.

  The thickness of the lower nonmagnetic layer is usually 0.1 to 2.5 μm, preferably 0.3 to 2.3 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. Moreover, since the light transmittance becomes high, it becomes a problem when the tape end 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 resin.

  The average major axis length of the ferromagnetic powder is preferably 0.1 μm or less. By using a ferromagnetic powder having a short major axis, the filling rate of the coating film is increased, and transfer from the backcoat layer is difficult to receive. The average long axis length of the preferred ferromagnetic powder is 0.03 to 0.10 μm. When the average major axis length of the ferromagnetic powder exceeds 0.1 μm, the filling rate of the coating film does not increase, and transfer from the backcoat layer is easily received. On the other hand, if the average major axis length is less than 0.03 μm, the magnetic anisotropy is weakened and orientation is difficult, and the output tends to decrease.

In the present invention, it is preferable to use metallic magnetic powder or hexagonal plate-like fine powder as the ferromagnetic powder. The metal magnetic powder has a coercive force Hc of 118.5 to 237 kA / m (1500 to 3000 Oe), a saturation magnetization σs of 120 to 160 Am ² / kg (emu / g), and an average major axis length of 0.03 to 0.3. It is preferable that 1 μm, the average minor axis length is 10 to 20 nm, and the aspect ratio is 1.2 to 20. The Hc of the medium produced using the metal magnetic powder is preferably 118.5 to 237 kA / m (1500 to 3000 Oe). The hexagonal plate-like fine powder has a coercive force Hc of 79 to 237 kA / m (1000 to 3000 Oe), a saturation magnetization σs of 50 to 70 Am ² / kg (emu / g), an average plate particle size of 30 to 80 nm, a plate The ratio is preferably 3-7. The Hc of the medium produced using the hexagonal plate-like fine powder is preferably 94.8 to 173.8 kA / m (1200 to 2200 Oe).

Here, the average major axis length of the ferromagnetic powder can be obtained by separating and collecting the magnetic powder from the tape piece and measuring the major axis length of the powder from a photograph taken with a transmission electron microscope (TEM). it can. An example of the procedure is shown below.
(1) The back coat layer is wiped off from the tape piece with a solvent and removed.
(2) The tape piece sample in which the lower nonmagnetic layer and the upper magnetic layer remain on the nonmagnetic support is immersed in a 5% NaOH aqueous solution, and heated and stirred.
(3) The coating film removed from the nonmagnetic support is washed with water and dried.
(4) The dried coating film is sonicated in methyl ethyl ketone (MEK), and the magnetic powder is adsorbed and collected using a magnetic stirrer.
(5) The magnetic powder is separated from the residue and dried.
(6) Collect the magnetic powder obtained in (4) and (5) on a dedicated mesh, prepare a TEM sample, and take a photograph with the TEM.
(7) The major axis length of the magnetic powder in the photograph is measured and averaged (number of measurements: n = 100).

The metal magnetic powder uses, as a starting material, iron oxyhydroxide obtained by blowing an oxidizing gas into an aqueous suspension in which a ferrous salt and an alkali are mixed. As the type of this iron oxyhydroxide, α-FeOOH is preferable, and as its production method, a ferrous salt is neutralized with an alkali hydroxide to form an aqueous suspension of Fe (OH) _2. There is a first production method in which an oxidizing gas is blown into a needle-like α-FeOOH. On the other hand, there is a second production method in which ferrous salt is neutralized with alkali carbonate to form an aqueous suspension of FeCO ₃ , and oxidizing gas is blown into this suspension to form spindle-shaped α-FeOOH.

  As the ferrous salt used in these methods, any of ferrous chloride, ferrous nitrate, and ferrous sulfate may be used. In addition, as the alkali hydroxide used in the first production method, potassium hydroxide, sodium hydroxide, and aqueous ammonia can be used. Further, as the alkali carbonate used in the second production method, sodium carbonate, sodium bicarbonate, ammonium carbonate or the like can be used.

The conditions for producing α-FeOOH suitable for obtaining a metal magnetic powder that is fine, unbranched, and excellent in dispersibility and packing properties using the first production method described above are necessary for neutralization of the ferrous salt. It is to use 2 to 10 times the amount of alkali and advance the oxidation reaction of Fe (OH) ₂ under conditions with a high alkali concentration. The reaction in a high alkali concentration region is a necessary condition for obtaining unbranched particles. The particle size can be controlled by controlling the reaction temperature and the amount of the oxidizing gas blown as generally known. In addition, Ni, Co, Al, It is also possible to control the size of the particles by allowing a metal salt such as Si to exist and neutralizing it with an alkali before proceeding with the oxidation reaction.

  In the second production method, the produced spindle-shaped α-FeOOH has no branching, and it is easy to obtain fine particles having a uniform particle size. The particle size in the second production method can be controlled by changing the iron concentration in the aqueous suspension, the reaction temperature, and the amount of oxidizing gas blown. In addition, the shape of the particles can be controlled by adding Ni, Co or the like as in the first production method.

Hereinafter, a method for producing a metal magnetic powder using the acicular α-FeOOH obtained by the first production method as a raw material will be described as an example. First, the ferrous salt is neutralized with an alkali hydroxide more than twice the amount necessary for neutralization to obtain an Fe (OH) ₂ alkaline suspension, and an oxidizing gas is blown into the needle suspension to form needles. Of α-FeOOH. At this time, in order to control the acicular ratio and shape of α-FeOOH, Ni, Co, Zn, Cr, Mn, Zr, Al, Si, P, Ba, Ca, Mg, Cu, Sr, Ti, Mo, A metal such as Ag or a rare earth element can be doped. The addition method of these different metals may be mixed uniformly in the ferrous salt, or may be added during the reaction. The amount added is determined empirically by the desired shape and size.

In this method, the ferrous salt is neutralized with an alkali to produce a suspension of Fe (OH) ₂ , which is oxidized to produce α-FeOOH. By using the amount twice or more of the neutralization equivalent, a raw material α-FeOOH having a high coercive force when obtained as a metal magnetic powder can be obtained. As the amount of such an excess of alkali increases, the branching of α-FeOOH decreases, but even if it is added 10 times or more, no further effect is manifested. Therefore, the reaction of adding an excess of 10 times or more is efficient. Not.

In addition, the size of the α-FeOOH particles necessary for obtaining a preferable metal magnetic powder is required to have a specific surface area BET value in the range of 60 to 130 m ² / g. When the specific surface area is less than 60 m ² / g, the particles are too large to obtain a high coercive force, which is not preferable as a magnetic material for a single wavelength region. Also, if the specific surface area exceeds 130 m ² / g, the particles may become too fine and superparamagnetism may be manifested, but high coercivity cannot be obtained, and it may be due to irregularity of particles, but the coercive force distribution It will become a wide thing.

  Next, Ni, Co, Zn, Cr, Mn, Zr, Al, Si, P, Ba, Ca, Mg, Cu, Sr, Ti, Mo, Ag, rare earth elements, etc. are doped or doped No α-FeOOH contains at least one of Ni, Co, Al, Si and rare earth elements. As a content method at this time, a method is generally used in which various metal salts are neutralized with an acid or an alkali and deposited as a fine crystal film of hydroxide on the particle surface. Ni, Co, and rare earth elements may be not newly deposited on the surface of α-FeOOH particles when necessary amounts are doped in the reaction for generating α-FeOOH. When it is necessary to contain a large amount, the amount to be doped is limited, so that these elements are further deposited on the surface. The content of each metal element in the metal magnetic powder is preferably in the following range. The following numerical value is a mass ratio of each metal when iron is set to 100.

  Ni = 0.3-8.0Co = 3.0-45.0 Al = 0.5-8.0Si = 0.5-8.0 Rare earth element = 0.2-10.0 However, Al + Si = 2. 0 to 15.0

  The rare earth element is at least one of La, Ce, Pr, Nd, Sm, Gd, Dy, and Y, and these combinations are also effective. As the metal to be added, it is convenient to use a water-soluble salt such as chloride, sulfate or nitrate. In the case of Si, sodium metasilicate, orthosilicate, and water glass can be used. The order of deposition is preferably to first deposit Ni and Co, which are alloyed to control the magnetic properties of the metal magnetic powder, and then deposit Al and Si to prevent sintering of the particles due to heat. . In the case of rare earth elements, there is an effect of increasing the α force, and even when Al and / or Si is applied, there is an effect, but the effect is greater when it is present inside.

Next, after depositing a predetermined amount of each of the above metals, the metal is sufficiently washed with water and dried, and heat-treated at a temperature of 300 to 800 ° C. in a non-reducing atmosphere. When the heat treatment temperature is less than 300 ° C., the number of vacancies in the α-Fe ₂ O ₃ particles produced by dehydration of α-FeOOH increases, and as a result, the properties of the reduced metal magnetic powder become inferior. Further, when the heat treatment temperature exceeds 800 ° C., the melting of α-Fe ₂ O ₃ particles starts and the shape of the particles changes or the sintering proceeds. As a result, the properties of the obtained metal magnetic powder deteriorate. To do.

  Next, the metal magnetic powder after the heat treatment is reduced at a temperature of 300 to 600 ° C. under a hydrogen gas stream, and an oxide film is formed on the surface of the particles by a known method to obtain a metal magnetic powder. In order to reduce water-soluble sodium ions and water-soluble calcium ions contained in the metal magnetic powder, the purity of water used in the above production method may be increased, or an alkali containing no sodium or calcium may be used.

Examples of the method for producing hexagonal ferrite include the following methods, and any method may be used.
(1) After mixing barium oxide, iron oxide, metal oxide replacing iron, and boron oxide as a glass forming substance so as to have a desired ferrite composition, it is melted and rapidly cooled to an amorphous body, Next, a glass crystallization method in which barium ferrite crystal powder is obtained by washing and pulverizing after reheating treatment.
(2) Water obtained by neutralizing barium ferrite composition metal salt solution with alkali and removing by-products, followed by liquid phase heating at 100 ° C. or higher, followed by washing, drying and grinding to obtain barium ferrite crystal powder. Thermal reaction method.
(3) A coprecipitation method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, then dried, treated at 1100 ° C. or less, and pulverized to obtain a barium ferrite crystal powder.

  In order to reduce water-soluble sodium ions and water-soluble calcium ions contained in the hexagonal ferrite powder, the purity of water used in the above production methods (1) to (3) is increased, or sodium or calcium is contained. Use no alkali.

  The content of water-soluble sodium ions contained in the ferromagnetic powder is preferably 70 ppm or less, more preferably 50 ppm or less. The water-soluble calcium ion content is preferably 30 ppm or less, more preferably 20 ppm or less. If it exceeds the above range, an organic acid (particularly fatty acid) and a salt contained in the coating film are formed and discharged onto the surface of the coating film, causing dropout and an increase in error rate.

  Such ferromagnetic powder should just be contained about 70-90 mass% on the basis of a magnetic layer. If the content of the ferromagnetic powder is too large, the content of the binder is reduced, 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 for the 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 selected according to the characteristics and process conditions of the medium. Have been used. It can be used by appropriately selecting from the same binders as described for the lower nonmagnetic layer.

  The content of the binder resin used in the 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, the magnetic layer contains an abrasive having a Mohs hardness of 6 or more in order to increase the mechanical strength of the magnetic layer and to prevent clogging of the magnetic head. As an abrasive, for example, α-alumina (Mohs hardness 9), chromium oxide (Mohs hardness 9), silicon carbide (Mohs hardness 9.5), silicon oxide (Mohs hardness 7), aluminum nitride (Mohs hardness 9), It is preferable to contain at least one abrasive having a Mohs hardness of 6 or more, preferably a Mohs hardness of 9 or more, such as boron nitride (Mohs hardness 9.5). These are usually indefinite shapes, prevent clogging of the magnetic head, and improve 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 solution for forming the magnetic layer is prepared by adding an organic solvent to the above components. 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 magnetic layer is 0.03 to 0.30 μm, more preferably 0.10 to 0.25 μm. If the magnetic layer is too thick, self-demagnetization loss and thickness loss increase.

  In the present invention, the smoothness of the magnetic layer surface is important. The centerline average roughness (Ra) of the magnetic layer surface is preferably 1.0 to 8.0 nm, more preferably 2.0 to 7.0 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 8.0 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.

  The ten-point average center line average roughness (Rz) of the magnetic layer surface is preferably 5 to 25 nm, more preferably 5 to 20 nm. If Rz is less than 5 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 25 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.

  As the recording wavelength corresponding to the recent high-density recording becomes shorter, in the accurate evaluation of the output and error rate of the magnetic layer, in addition to the surface roughness (Ra and Rz) of the surface of the magnetic layer, a fine region It is preferable to consider the surface roughness (for example, about 10 μm × 10 μm). In the case of a recording / reproducing system with the shortest recording wavelength of 0.6 μm or less, the AFM surface roughness Ra value as the surface roughness of the magnetic layer should be 6.0 nm or less from the viewpoint of the surface roughness of only a minute region. Is preferable, 2.0 to 6.0 nm is more preferable, and 2.0 to 5.0 nm is more preferable. When the AFM surface roughness Ra exceeds 6.0 nm, the spacing is increased, and the error rate is particularly likely to be lowered. On the other hand, if the thickness is less than 2.0 nm, scratch resistance and friction may be deteriorated, resulting in a decrease in running reliability.

  The AFM surface roughness Ra value of the surface of the magnetic layer is obtained from Ra defined by JIS-B-0601 from a surface roughness curve measured using an atomic force microscope. More specifically, using a probe having a radius of curvature of 10 nm or less, preferably 2 to 10 nm, measurement is performed in a range of 10 μm × 10 μm, image processing is performed, and centerline average surface roughness Ra is obtained.

In the present invention, the number of recesses having a depth of 30 nm or more on the surface of the magnetic layer is preferably 5 or less per 1 cm ² of surface area. A dent with a depth of 30 nm or more becomes a spacing loss and tends to cause an error rate to deteriorate. If there are 6 or more dents per 1 cm ² of surface area, the error rate will increase. The lower limit of the number of dents is not particularly limited and is preferably as small as possible. However, in the examples, 0.1 piece / cm ² is shown.

  The number of the dents is determined by measuring dents having a diameter of 10 to 60 μm and a depth of 30 nm or more with an optical interference type three-dimensional roughness meter, adjusting the interference intensity of an optical microscope (magnification 50 to 100 times), For example, in a 1 to 5 cm length of a 1/2 inch wide tape, 3 or more fields are counted and obtained by arithmetic mean.

[Back coat layer]
The backcoat layer is provided for improving running stability, preventing the magnetic layer from being charged, and the like, and includes carbon black, nonmagnetic inorganic powder other than carbon black, and a binder resin.

  The back coat layer preferably contains 30 to 80% by mass of carbon black based on the back coat layer. If the content of carbon black is too small, the antistatic effect tends to decrease, and the running stability tends to decrease. Further, since the light transmittance of the medium is likely to be high, there is a problem in the method of detecting the tape end by the change in the light transmittance. On the other hand, when the content of carbon black is too large, the strength of the backcoat layer decreases, and the running durability tends to deteriorate. The carbon black may be any one as long as it is normally used, and the average particle size is preferably about 5 to 500 nm. The average particle size is usually measured with a transmission electron microscope.

  The amount of water-soluble sodium ions and water-soluble calcium ions contained in carbon black is preferably small, and the content of water-soluble sodium ions is preferably 500 ppm or less, more preferably 300 ppm or less. The water-soluble calcium ion content is preferably 300 ppm or less, more preferably 200 ppm or less. If it exceeds the above range, an organic acid (particularly fatty acid) and salt contained in the coating film are formed and discharged onto the surface of the coating film, causing dropout and an increase in error rate.

In addition to the carbon black, various nonmagnetic inorganic powders can be used for the backcoat layer in order to control mechanical strength. Examples of inorganic powders include α-Fe ₂ O ₃ , CaCO ₃ , titanium oxide, Examples thereof include barium sulfate and α-Al ₂ O ₃ . The content of the nonmagnetic inorganic powder is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of carbon black. The average particle size of the nonmagnetic inorganic powder is preferably 0.01 to 0.5 μm. If the content of such nonmagnetic inorganic powder is too small, the mechanical strength of the backcoat layer tends to be insufficient, and if it is too large, the amount of wear such as guides in the tape sliding contact path tends to increase, and the magnetic layer Will cause scratches.

  In addition to the above materials, the back coat layer may be made of a thermoplastic resin, a thermosetting or reactive resin, a radiation (electron beam or ultraviolet ray) curable resin, etc., as appropriate in accordance with the characteristics and process conditions of the medium. It is selected and used in combination. It can be used by appropriately selecting from the same binders as described for the lower nonmagnetic layer.

  The content of the binder resin used in the backcoat layer is preferably 15 to 200 parts by mass, more preferably 50 to 180 parts by mass with respect to 100 parts by mass in total of the carbon black and the nonmagnetic inorganic powder in the backcoat layer. is there. When the content of the binder resin is too large, friction with the guide roll or the like in the tape sliding contact path becomes too large, and traveling stability is lowered, and a traveling accident is likely to occur. In addition, problems such as blocking with the magnetic layer occur. If the content of the binder resin is too small, the strength of the backcoat layer is lowered and the running durability is likely to be lowered.

  If necessary, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, or silicon oil, and other various additives may be added to the back coat layer.

  As the lubricant, it can be used by appropriately selecting from the same lubricants described for the lower nonmagnetic layer. The content of the lubricant in the backcoat layer may be appropriately adjusted according to the purpose, but is preferably 1 to 20% by mass with respect to the total mass of carbon black and inorganic powder other than carbon black.

  The coating liquid for forming the back coat layer is prepared by adding an organic solvent to the above components. 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 addition amount of the organic solvent may be about 740 to 1600 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.

  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. If the back coat layer is too thick, the friction with the guide roll and the like in the tape sliding contact path becomes too large, and the running stability tends to decrease. On the other hand, if the backcoat layer is too thin, the backcoat layer is likely to be scraped when the medium is running. On the other hand, if the backcoat layer is too thin, the surface smoothness of the backcoat layer decreases due to the influence of the surface roughness of the nonmagnetic support. For this reason, when the backcoat layer is thermally cured, the roughness of the backcoat layer surface is transferred to the surface of the magnetic layer, and high frequency output, S / N, and C / N tend to be reduced.

[Non-magnetic support]
The material used as the nonmagnetic support is not particularly limited, and may be selected from various flexible materials and various rigid materials according to the purpose, and may have a predetermined shape and size such as a tape according to various standards. Examples of the flexible material include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, and various resins such as polyamide, polyimide, and polycarbonate.

  The thickness of these nonmagnetic supports is preferably 3.0 to 15.0 μm. The form of the nonmagnetic support is not particularly limited, and may be any of a tape form, a sheet form, a card form, a disk form, and the like, and various materials are selected depending on the form and if necessary. Can be used.

The surface roughness of the nonmagnetic support used in the present invention is 20 nm or less, preferably 15 nm or less in terms of the center line average surface roughness Ra. The surface roughness of the nonmagnetic support can be freely controlled by the size and amount of filler added to the nonmagnetic support as necessary. Examples of these fillers include oxides and carbonates of Ca, Si, Ti, Al, and the like, and organic resin fine powders such as acrylic, preferably a combination of Al ₂ O ₃ and organic resin fine powders. It is.

[Production method]
The magnetic recording medium configured as described above is manufactured by the method of the present invention. First, a nonmagnetic layer coating solution is applied on one surface of a nonmagnetic support, dried and cured to form a lower nonmagnetic layer, and a magnetic layer coating is applied on the cured lower nonmagnetic layer. The step of applying and drying the liquid to form an upper magnetic layer and the step of applying and drying the backcoat layer coating liquid on the other surface of the nonmagnetic support to form the backcoat layer are performed. .

  The steps of producing the backcoat layer coating solution, the lower nonmagnetic layer coating solution, and the magnetic layer coating solution are at least a kneading step, a dispersing step, and mixing performed before and after these steps, respectively. It consists of a process, a viscosity adjustment process, and a filtration process. Each process may be divided into two or more stages. All materials such as ferromagnetic powder, nonmagnetic inorganic powder, binder, abrasive, carbon black, lubricant and solvent used in the present invention may be added at the beginning or middle of any step. Moreover, you may divide | segment and add each material by two or more processes.

  For kneading / dispersing the coating liquid, it is of course possible to use conventionally known manufacturing techniques for some or all of the processes, but in the kneading process, a material with a strong kneading force such as a continuous kneader or a pressure kneader is used. It is preferable to do. When a continuous kneader or a pressure kneader is used, a ferromagnetic powder or a nonmagnetic inorganic powder, a binder and a small amount of solvent are kneaded. The slurry temperature during kneading is preferably 50 ° C to 110 ° C.

  Moreover, it is desirable to use a dispersion medium having a high specific gravity for dispersion of the coating liquid in each step, and ceramic media such as zirconia and titania are suitable. Conventionally used glass beads are not preferred because water-soluble sodium ions and water-soluble calcium ions are mixed in the coating solution as impurities due to bead wear during dispersion.

  First, a nonmagnetic layer coating solution is applied on one surface of a nonmagnetic support, dried and cured to form a lower nonmagnetic layer. Next, a magnetic layer coating solution is applied onto the cured lower nonmagnetic layer and dried to form an upper magnetic layer. As described above, when the nonmagnetic layer and the magnetic layer are formed by a so-called wet-on-dry coating method, and when the magnetic layer is applied while the nonmagnetic layer is wet, the magnetic layer is applied. In comparison, it is preferable in terms of uniformity of the interface between the nonmagnetic layer and the magnetic layer. A backcoat layer coating solution is applied on the other surface of the nonmagnetic support and dried to form a backcoat layer.

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

  Regarding the order of forming the lower nonmagnetic layer, the upper magnetic layer, and the backcoat layer, as described above, the lower nonmagnetic layer, the upper magnetic layer, and then the backcoat layer are formed. It is generally preferable to carry out in this order.

  The magnetic tape that is finally cut into ½ inches has a magnetic layer surface that is convex outward so that the head contact with the drive is improved. This is so that the magnetic layer surface side provided on the opposite surface side of the support becomes convex outward by providing the backcoat layer with shrinkage. In general, each of the lower nonmagnetic layer, the upper magnetic layer, and the backcoat layer has shrinkage. In order to finally make the magnetic layer surface convex, the design is such that the largest shrinkage force is applied to the backcoat layer provided with the support interposed therebetween, rather than the shrinkage force of the lower nonmagnetic layer and upper magnetic layer.

  When the back coat layer is first applied, the back coat layer is provided only on one side of the support, and thus the support itself is greatly curled in the width direction. If an attempt is made to provide the lower nonmagnetic layer on the other surface of such a support, the variation in coating thickness in the support width direction becomes large, which causes a problem.

  Therefore, it is preferable to first apply the lower nonmagnetic layer having a smaller shrinkage than the backcoat layer first.

After providing the lower nonmagnetic layer, it is preferable to provide a magnetic layer thereon. The upper magnetic layer has the strictest application accuracy, and if the thickness is too thick, the self-demagnetization loss and the thickness loss increase.
On the other hand, if the thickness is small, the amount of magnetization becomes small and a sufficient output cannot be obtained. When the coating liquid is applied and dried, the thermal history during drying when each coating layer is provided, or the stress at the time of winding into a roll after providing the coating layer, the strain of the support is subjected to each step. From the viewpoint of coating accuracy, it is preferable to apply the upper magnetic layer next.

  For the above reasons, the back coat layer is applied last in the three layers. As described above, since the back coat layer is applied with the support having the largest strain, the back coat layer should be applied with a coating method that can be reliably applied even if the support is strained. Is preferred. In the present invention, the bar coat method is used for coating the back coat layer.

  The magnetic tape original fabric on which the layers are formed on both surfaces of the nonmagnetic support is subjected to a thermosetting treatment in a roll state to cure the upper magnetic layer and the backcoat layer. The roll tape is held in a heat treatment chamber at 40 to 80 ° C., preferably 50 to 70 ° C., for a predetermined time, preferably 24 hours or more, for example, 24 hours to 48 hours. In this thermosetting process, since the magnetic layer surface and the backcoat layer surface are in contact with each other, the surface of the magnetic layer is likely to be dented by minute protrusions existing on the backcoat layer surface.

  Therefore, in the present invention, each layer is calendered in a batch after the thermosetting treatment. By a calendar process at this stage, a magnetic layer having a flat surface is obtained.

  The calendar processing is preferably performed under the following calendar processing roll and calendar processing conditions.

  As the calendering roll, heat-resistant plastic elastic rolls such as epoxy, polyester, nylon, polyimide, polyamide, polyimide amide (which may be kneaded with carbon, metal or other inorganic compounds) and metal rolls Use a combination. Moreover, it is preferable to process between metal rolls because a flatter magnetic layer surface can be obtained. A metal roll is disposed on the side in contact with the magnetic layer surface in order to obtain a flatter surface. A plastic elastic roll is usually disposed on the side in contact with the back coat layer surface, but a metal roll is preferably disposed.

  The treatment temperature is preferably 70 ° C. or higher, more preferably 90 ° C. or higher and 110 ° C. or lower. The linear pressure is preferably 198 kN / m (200 kg / cm) or more, more preferably 245 kN / m (250 kg / cm) or more and 392 kN / m (400 kg / cm) or less, and the treatment speed is in the range of 20 m / min to 900 m / min. is there.

  In the calendering after the formation of the lower nonmagnetic layer, the upper magnetic layer, and the backcoat layer, the nonmagnetic support base and the calendering roll are not in direct contact, and the base and the filler contained in the base are scraped. There is nothing. Therefore, calendar processing is performed very well. When the nonmagnetic support base and the calendering roll are in direct contact, the base and the filler contained in the base are scraped, and the shaved filler adheres to the nip portion of the calender roll. The presence of the filler in the nip portion may cause a dent in the magnetic layer. In particular, the dent generated in the lower nonmagnetic layer and the upper magnetic layer due to the cutting of the filler or the like is as large as 10 to 60 μm in diameter, but the depth is as shallow as 30 to 100 nm. However, in the recording / reproducing system having the shortest recording wavelength of 0.6 μm or less, the error rate is significantly affected.

  In the method described in Japanese Patent Application Laid-Open No. 2004-319017, since the calendering is performed before the thermosetting treatment, the nonmagnetic layer and the magnetic layer are calendered and processed after the thermosetting treatment and before the calendering treatment. It has already been compressed and the amount of crushing is less. The ten-point average center line roughness (Rz) of the magnetic layer surface is preferably 5 to 25 nm, but the average particle size of the carbon black contained in the backcoat layer is 500 nm at the maximum, in addition to the carbon black. When various nonmagnetic inorganic powders are used to control the strength, the average particle size is 0.5 μm at the maximum. The maximum height at which carbon black or non-magnetic inorganic powder is exposed on the surface of the backcoat layer is about ½ of the particle size (because it is about 250 nm in depth on the surface of the magnetic layer due to contact during thermal curing). A dent may be generated. In order to relieve such dents by calendering, the peripheral part of the dents may be compressed and the depth of the dents may be mitigated, but before the calendering after thermosetting treatment, the lower non-magnetic layer and magnetic layer In both cases, the calender treatment has been completed and the coating film has already been compressed, and the crushing margin is small, so that it is not possible to greatly expect the relaxation effect against the dent on the surface of the magnetic layer.

  Therefore, in this application, it was set as the process which does not perform the calendar process before a thermosetting process, performs a thermosetting process first, and calenders each layer collectively after a thermosetting process. Thus, after the thermosetting treatment, the non-magnetic layer, the magnetic layer, and the back coat layer have not been subjected to the calendar treatment at all, so that both the magnetic layer surface and the back coat layer surface are in a rough state. The degree of filling of the coating film is in a low state (porous), and thereafter, the calendar process can be performed in a state where a crushing margin is secured when performing the calendar process.

  In addition, if the binder resin used for the lower nonmagnetic layer is a radiation curable binder resin, the lower nonmagnetic layer can be adjusted by adjusting the radiation dose irradiated from the outside during the curing process of the lower nonmagnetic layer. The degree of curing of can be adjusted. If the degree of cure of the lower nonmagnetic layer is low, the lower nonmagnetic layer can be effectively compressed during the calendar process, and the microprojections present on the backcoat layer surface due to the contact between the magnetic layer surface and the backcoat layer surface. Therefore, the dent generated on the surface of the magnetic layer can be relaxed.

  In the manufacturing method of the present application, the coating liquid is applied to any one of the nonmagnetic layer, the magnetic layer, and the backcoat layer so that the central portion in the support width direction is slightly thick. By applying the coating liquid in this manner, the shape of the original roll wound up around the core (hereinafter also referred to as “original roll cumulative shape”) has a shape in which the central portion in the width direction of the original roll protrudes from the end portion. The amount of protrusion (the difference between the thickness of the central portion and the thickness of the end portion in the width direction of the raw material wound around the core: hereinafter, also referred to as “raw material cumulative shape value”) is within a predetermined range. I am letting you. However, it is not necessary for the non-magnetic lower layer, the magnetic layer, and the back coat layer to have a slightly thick central portion in the width direction of the support, as long as the central portion in the width direction of the support is slightly thick in the sum of the three layers. good. For example, assuming that the accumulated shape value of the original fabric at the time when the nonmagnetic layer and the magnetic layer have been applied is +0.35 mm per 10,000 turns, the back coat layer has a uniform thickness distribution in the width direction of the support as it is. (Flat) may be applied, but it is determined that it is the allowable upper limit of the raw material accumulated shape value, the back coat layer is applied so as to be slightly thinner at the center in the width direction of the support, You may apply | coat and adjust so that the raw material accumulated shape value before a thermosetting process may become about +0.30 mm per 10,000 turns. In addition, since the shape of the support also has a large effect on the original accumulated shape value, it is also important to grasp the accumulated shape of the support itself. The cumulative shape of the support itself may be convex or concave at the center in the width direction of the support, and after determining the cumulative shape of the support to be used, set the thickness pattern in the width direction of the support for each coating layer, It is necessary that the accumulated shape value of the raw material wound around the core before the thermosetting treatment is within a predetermined range (for example, +0.25 mm to +0.35 mm) per 10,000 turns of the original material.

  In the cumulative shape in which the support itself is wound around the core, the central portion in the width direction of the support protrudes from the end, and the cumulative shape value is in the range of +0.25 mm to +0.35 mm per 10,000 turns of the support. If necessary, the nonmagnetic layer, the magnetic layer, and the backcoat layer applied to the support may be applied in a uniform (flat) pattern in the width direction of the support. The accumulated shape of the support itself may not be a simple shape that gradually protrudes from the end portion toward the center portion or gradually decreases from the end portion toward the center portion. In this case, the formation of the nonmagnetic layer, the magnetic layer, and the backcoat layer is completed by, for example, applying a thin nonmagnetic layer to the protruding portion and a thick nonmagnetic layer to the recessed portion. Then, when the raw fabric is wound around the core, the accumulated shape is adjusted so as to project smoothly from the end toward the center.

  As a method of coating so that the thickness of the coating liquid is thick at the center in the width direction of the support, for example, in the case of nozzle coating, the slit gap through which the coating liquid flows out is wide at the center in the width direction of the support and at both ends of the support. By adjusting it narrowly, the amount of the coating liquid flowing through the central portion is large and both end portions are small, so that the pattern of the coating thickness in the support width direction can be made convex.

  When the support is supported by guide rolls located upstream and downstream of the nozzle, the tip of the nozzle is pressed against the support surface between these guide rolls, and the coating liquid pushed out from the slit is applied to the support surface In addition to the above method, the shape of the upstream guide roll and / or the downstream guide roll is inverted crown (the guide roll diameter is small in the center in the support width direction, and the both ends in the support width direction are the diameters). By forming a large shape, the support thickness at the center in the width direction of the support is lowered, and the coating thickness pattern in the width direction of the support is made convex by adjusting the support tension at both ends in the width direction of the support to be higher. be able to.

  In the method of adjusting the coating thickness by making a difference in the tension in the width direction of the support, a tension adjusting mechanism is provided in a part or several places in the width direction of the support so that the coating thickness is simply convex in the width direction of the support. It can be controlled like an M-shaped pattern, a W pattern, or a sine curve shape, not just a concave. Specifically, a touch roll having a width narrower than the width of the support is partially brought into contact with the vicinity of the extrusion coating head coating portion to partially press the support, or from a blowout port having a width narrower than the width of the support. By jetting the gas and partially pressing the support, the tension of the support is partially increased at the application portion of the nozzle, and as a result, the coating thickness can be partially reduced. A desired pattern in the support width direction can be achieved by providing a plurality of these support tension adjusting mechanisms in the support width direction and adjusting them individually. Instead of ejecting gas, a suction nozzle can be opened near the other surface of the support, and a part of the support in the width direction can be sucked to partially increase the tension of the support.

  When applying with a reverse roll, adjust the cylindricity of the applicator roll and metering roll. If the applicator roll has a straight shape and the metalling roll has a reverse crown shape, the gap between both rolls will be in the width direction of the support. The center portion is wide and the both ends in the support width direction are narrow, and the thickness pattern of the coating layer applied thereby can be applied so that the center portion in the support width direction is convex. Also, hot or cold air is blown onto the applicator roll and / or metering roll, and the shape of the applicator roll and / or metering roll is changed using the thermal expansion or contraction of the roll, and the coating thickness pattern in the support width direction Can also be adjusted.

  In the bar coat, it is a mechanism to measure the excess coating liquid pre-applied on the support surface by the groove formed on the bar surface, so if the contact strength between the support and the bar is adjusted, it is the same The thickness pattern in the width direction of the support can be adjusted. Specifically, if the bar is directed toward the support surface and the center of the support in the width direction of the support is a bow, the contact state between the outer peripheral surface of the bar and the support surface is Weaker, it can be made stronger at both ends of the support. As a result, the amount of coating liquid scraped off by the bar is small at the center in the width direction of the support and large at both ends of the support, and the amount of coating in the width direction of the support is convex in the center in the width direction of the support. Become. If the upstream guide roll and / or the downstream guide roll of the bar have an inverted crown shape, a difference in tension occurs in the width direction of the support, with a lower tension at the center of the support and a higher tension at both ends of the support. As the coating amount in the support width direction, the center in the support width direction is convex.

  Further, in the method of adjusting the coating thickness by making a difference in the tension of the support at a desired portion in the support width direction, if a tension adjusting mechanism is provided at a plurality of locations in the support width direction, the coating thickness can be reduced. It can be controlled in the form of an M-shaped pattern, a W pattern, or a sine curve instead of a simple convex or a simple concave in the support width direction. As described above, this uses a plurality of touch rolls, gas ejection mechanisms, and suction mechanisms that are narrower than the width of the support, and adjusts them individually to create a tension distribution in the width direction of the support. A desired coating thickness pattern is obtained in the width direction. The coating method for providing the coating layer is not limited to nozzle coating, reverse roll coating, and bar coating, and various coating methods can be used.

<Measuring method of accumulated fabric shape value>
As a method of measuring the roll accumulated shape value of the roll-shaped web wound around the core, a method of directly measuring the outer diameter of the roll-shaped web using a micrometer, a roll combining a linear guide mechanism and a sensor. There are a method for measuring the shape of the outer peripheral surface of the original sheet, a method for measuring by combining a linear sensor, a laser sensor equipped with a light projecting unit and a light receiving unit, and the like. Either method can be applied, but a combination of a linear guide mechanism and a sensor is preferable because the configuration is simple and easy to use. As the sensor, either a non-contact type sensor or a contact type sensor can be used. However, in the present application, a case of a contact type sensor will be described below as an example. As an example of the contact type sensor, the LGF type manufactured by Mitutoyo Corporation can be exemplified.

  Next, referring to FIG. 1, the configuration of a measuring apparatus for measuring the roll accumulated shape value of the roll-shaped roll wound around the core and the procedure for measuring the roll accumulated shape value using this measuring apparatus will be described with reference to FIG. explain.

  The measuring device includes a base plate 1, V blocks 2 and 2 for supporting both ends of the core 8 to fix the original fabric 9, and a contact sensor 7 for measuring the outer peripheral surface shape of the original fabric 9. The X-axis linear guide mechanism 4 for moving the contact sensor 7 in the width direction of the support is fixed by support columns 3 and 3 rising from the base plate 1. The X-axis linear guide mechanism 4 is further provided with a Z-axis linear guide moving mechanism 5, and the holder 6 and the contact sensor 7 fixed to the holder 6 are configured to be movable in the Z-axis direction. Yes. The Z-axis linear guide mechanism 5 is a mechanism for enabling measurement within the measurement range of the contact sensor 7 in accordance with the outer diameter of the original fabric 9 to be measured. Then, the state is fixed at a predetermined position. Further, the contact sensor 7 is retracted upward in FIG. 1 so as not to hinder the work when preparing the measurement of the original fabric 9 or when removing and attaching the original fabric 9 after the measurement is completed. The movement direction of the X-axis linear guide mechanism 4 is adjusted so as to be horizontal, and the movement direction of the Z-axis linear guide mechanism 5 is adjusted so as to be vertical.

  In the measurement, first, the raw fabric 9 wound around the core 8 is set so that both ends of the core 8 are supported by the V blocks 2 and 2. The contact sensor 7 is moved to the measurement start point (near one end of the original support in the width direction) by the X-axis linear guide mechanism 4. Thereafter, the Z-axis linear guide mechanism 5 is lowered to lower the contact type sensor 7 from the position where it is retracted upward to a position where it comes into contact with the original fabric 9, and the contact state of the contact type sensor 7 is set to the middle of the sensor measurement range. Fine adjustment is performed in the Z-axis direction (height direction) so that the position is reached. The contact sensor 7 is driven in the X-axis direction along the X-axis linear guide mechanism 4 by a drive mechanism (not shown), and measures the outer peripheral surface shape of the original fabric 9 in the support width direction of the original fabric 9.

  The measurement data is processed by taking the displacement amount in the Z-axis direction output from the contact sensor 7 and the X-axis position information output from the X-axis linear guide mechanism 4 into a PC or the like. As an example, assuming that the X-axis position of the contact sensor 7 at the start of measurement is X = 0 mm, displacement amounts in the Z-axis direction are taken every 0.5 mm. The measurement length in the width direction of the original fabric measures the effective width that is finally cut and commercialized as a tape. For example, when the tape is cut to a 1/2 inch width by cutting and 50 pieces are taken in the width direction of the support, the width is 12.65 mm × 50 = 632.5 mm. Therefore, by subtracting the effective width to be manufactured as a tape from the finished original fabric width, the position offset by one half of the original width in the support width direction from the one end of the original fabric to the center of the support width. The measurement start position in the X-axis direction is set, and the effective width that is produced as a tape along the X-axis direction from that position is traced as the measurement length. When the core 8 is set to the V blocks 2 and 2, the V blocks 2 and 2 are adjusted so that the center axis AA of the core 8 is horizontal, and the center axis AA of the core 8 is adjusted. The front / rear direction is also adjusted so that the measurement line B-B of the contact sensor 7 is in the plane of the reference vertical plane 10 including the center axis AA of the core 8 even if it is mounted on a different original fabric. The shape of the outer peripheral surface of the raw fabric 9 can be measured as a displacement in the radial direction with respect to the core center AA within the plane of the reference vertical plane 10 including

  It is preferable to use a straight core having a cylindricity as close as possible to the core used for winding the original fabric so that there is no variation in accuracy among the cores used. This is because the accumulated shape of the raw material is measured in a state in which the raw material is wound around the core, and if the accuracy of the core varies, it affects the setting of the width direction pattern of the coating thickness of each layer, and the setting is complicated. This is to avoid becoming. Since the processing accuracy of the core is also limited, the cylindricity is not 0, but the cylindricity is preferably 0.05 mm or less.

  As shown in FIG. 2, the unevenness judgment of the accumulated shape of the original fabric from the measurement data and the calculation of the radius difference are performed by using the measurement data as the X axis in the width direction of the original fabric and the displacement amount ΔZ in the original fabric radial direction as the Y axis. A graph is plotted on the XY plane, and the maximum value or the minimum value of the displacement amount ΔZ of the original fabric radial direction is read to obtain the accumulated stock shape value. As shown in FIG. 3, when both the raw fabric radial displacement amount ΔZ at the measurement start position and the measurement end position are both 0, the maximum value or the minimum value may be simply read, but as shown in FIG. When the original radial displacement amount ΔZ at the measurement end position is not 0, the data of the measurement start position and the measurement end position are connected by a line, and the original radial direction displacement amount Δ is corrected by using this line as a reference. Read the maximum or minimum value of Z. When the raw fabric cumulative shape value is positive, it means that the outer diameter of the central portion in the width direction is larger than the outer diameter of the end portion in the width direction, and conversely, the cumulative shape value of the raw fabric is negative. In this case, the outer diameter of the central portion in the width direction is smaller than the outer diameter of the end portion in the width direction. In addition, the original fabric cumulative shape value defined in the present application is a difference in thickness of the original fabric in the wound state (difference in radius of the original fabric in the wound state).

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

<Preparation of coating solution for lower nonmagnetic layer>
(Binder solution preparation)
Electron beam curable vinyl chloride resin NV 30 wt% (vinyl chloride-epoxy-containing monomer copolymer, average degree of polymerization = 310, epoxy content = 3 wt%, S content = 0.6 wt%, acrylic content = 6 / 1 molecule, Tg = 60 ° C.) 45 parts by mass Electron beam curable polyester polyurethane resin (NV 40 wt%) (polar group-OSO ₃ Na-containing polyester polyurethane, number average molecular weight = 26000) 16 parts by mass methyl ethyl ketone (MEK) 2 parts by mass toluene 2 parts by mass cyclohexanone 2 parts by mass

  The above composition was charged into a hypermixer and stirred to obtain a binder solution.

(Kneading)
The following composition was put into a pressure kneader and kneaded for 2 hours.

Acicular α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DB-65, average major axis length = 0.11 μm, BET (specific surface area) = 53 m ² / g) 85 parts by mass carbon black (manufactured by Mitsubishi Chemical Corporation: # 850B, average particle size = 16 nm, BET = 200 m 2 / g, DPB oil absorption = 70 ml / 100 g) 15 parts by mass α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd .: HIT-60A, average particle size = 0.20 μm) 5 parts by mass o-phthalic acid 2 parts by mass binder solution 67 parts by mass

  The following composition was added to the kneaded slurry to adjust the viscosity to be optimal for the dispersion treatment.

MEK 40 parts by mass Toluene 40 parts by mass Cyclohexanone 40 parts by mass

(dispersion)
The slurry was subjected to dispersion treatment with a horizontal pin mill filled with 75% of zirconia beads (Traceram φ0.8 mm manufactured by Toray Industries, Inc.).

(Viscosity adjusting liquid)
The following composition was put into a hypermixer and stirred to obtain a viscosity adjusting liquid.

Stearic acid 1 part by mass Butyl stearate 1 part by mass MEK 30 parts by mass Toluene 30 parts by mass Cyclohexanone 30 parts by mass

(Viscosity adjustment and final coating solution)
The above solution was mixed and stirred in the slurry after dispersion, and then dispersed again in a horizontal pin mill filled with 75% of zirconia beads (Traceram φ0.8 mm manufactured by Toray Industries, Inc.) to obtain a coating solution. The coating solution was subjected to circulation filtration using a depth filter having an absolute filtration accuracy of 1.0 μm to obtain a final coating solution for the lower nonmagnetic layer.

<Preparation of coating solution for magnetic layer>
(Binder solution preparation)
Vinyl chloride resin (made by Nippon Zeon Co., Ltd .: MR-110) 11 parts by mass Polyester polyurethane resin (Toyobo Co., Ltd .: UR-8300) 17 parts by mass MEK 7 parts by mass Toluene 7 parts by mass Cyclohexanone 7 parts by mass

  The above composition was put into a hypermixer, mixed and stirred to obtain a binder solution.

(Kneading)
The following composition was put into a pressure kneader and kneaded for 2 hours.

α-Fe magnetic powder (Hc = 1858Oe, Co / Fe = 20 at%, σs = 138 emu / g, BET = 58 m ² / g, average major axis length = 0.10 μm) 100 parts by mass α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd .: HIT-60A, average particle size = 0.20 μm) 6 parts by mass α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd .: HIT-82, average particle diameter = 0.13 μm) 6 parts by mass phosphoric acid Ester (Toho Chemical Co., Ltd .: Phosphanol RE610) 2 parts by weight Binder solution 49 parts by weight

  The following composition was added to the kneaded slurry to adjust the viscosity to be optimal for the dispersion treatment.

MEK 100 parts by mass Toluene 100 parts by mass Cyclohexanone 75 parts by mass

(dispersion)
The slurry was subjected to dispersion treatment with a horizontal pin mill filled with 75% of zirconia beads (Traceram φ0.8 mm manufactured by Toray Industries, Inc.).

(Viscosity adjusting liquid)
The following composition was put into a hypermixer and mixed and stirred for 1 hour to obtain a viscosity adjusting liquid.

Stearic acid 1 part by mass Butyl stearate 1 part by mass MEK 100 parts by mass Toluene 100 parts by mass Cyclohexanone 250 parts by mass

(Viscosity adjustment)
The above solution was mixed and stirred in the slurry after dispersion, and then dispersed again in a horizontal pin mill filled with 75% of zirconia beads (Traceram φ0.8 mm manufactured by Toray Industries, Inc.) to obtain a coating solution. The coating solution was circulated and filtered using a depth filter with an absolute filtration accuracy of 1.0 μm.

(Final coating solution)
Add 0.82 parts by mass of an isocyanate compound (manufactured by Nippon Polyurethane, Coronate L) to 100 parts by mass of the coating solution after filtration, stir and mix, and perform circulation filtration using a depth filter with an absolute filtration accuracy of 1.0 μm. The final coating solution for the layer was used.

<Preparation of coating solution 1 for backcoat layer>
(Binder solution 1)
Nitrocellulose (Asahi Kasei Kogyo Co., Ltd .: BTH1 / 2 solid content concentration 70 wt%) 77 parts by mass Polyester polyurethane resin (Toyobo Co., Ltd .: UR-8300 solid content concentration 30 wt%) 120 parts by mass MEK 275 parts by mass Toluene 275 parts by mass Cyclohexanone 100 parts by weight

  The above composition was charged into a hypermixer and stirred to obtain a binder solution.

(dispersion)
The following composition was placed in a ball mill and dispersed for 24 hours.

(Carbon black 1)
Carbon black (Mitsubishi Chemical Corporation: # 950B, average particle size = 17 nm, BET = 250 m ² / g, DBP oil supply = 70 ml / 100 g) 100 parts by weight binder solution 1847 parts by weight

(Viscosity adjusting liquid 1)
The following composition was put into a hypermixer and stirred to obtain a viscosity adjusting liquid.

MEK 430 parts by mass Toluene 430 parts by weight Cyclohexanone 100 parts by weight

(Viscosity adjustment)
The above solution was mixed and stirred in the dispersed slurry, and then dispersed again in a ball mill for 3 hours. The coating solution was circulated and filtered using a depth filter with an absolute filtration accuracy of 3.0 μm.

(Final coating solution)
To the coating solution after filtration, an isocyanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate 3041 solid content concentration: 50 wt%) is added at a ratio of 0.0189 parts by mass with respect to 100 parts by weight of the coating solution after filtration, followed by stirring and mixing. The solid content concentration of the liquid was 10.7 wt%, and circulation filtration was performed using a depth filter with an absolute filtration accuracy of 3.0 μm to obtain a backcoat coating liquid 1.

<Manufacture of magnetic recording tape>
On the surface of a PEN (polyethylene naphthalate) film having a width of 520 mm, a length of 10810 m, and a thickness of 5.0 μm as a nonmagnetic support, the coating liquid for the lower nonmagnetic layer is applied by nozzle coating to a width of 500 mm, after drying Is applied in such a way that the average thickness of the film becomes 1.3 μm (at a line speed of 200 m / min), dried in a furnace in which hot air at a temperature of 100 ° C. is supplied at a wind speed of 15 m / sec, and then an irradiation dose of 4.5 Mrad A lower nonmagnetic layer was formed by performing a curing treatment by irradiation with an electron beam under the above conditions.

  Next, on the cured lower nonmagnetic layer, the magnetic layer coating solution is applied by nozzle coating at a line speed of 200 m / min so that the coating width is 496 mm and the average thickness after drying is 0.10 μm. While the coating film was in a wet state, a magnetic field orientation treatment was performed with a solenoid of 5000 Oe, and dried in a furnace supplied with hot air at a temperature of 100 ° C. at a wind speed of 15 m / sec to form an upper magnetic layer. Next, on the other surface of the polyethylene naphthalate film, the backcoat layer coating solution is applied by backcoating so that the average thickness after drying is 0.42 μm. In the second drying step, drying was performed in a furnace supplied with hot air at a temperature of 100 ° C. at a wind speed of 15 m / sec. Thus, the raw material in which each layer was formed on both surfaces was obtained. Subsequently, the raw material in which the lower non-magnetic layer and the upper magnetic layer are formed on one surface of the flexible support and the back coat layer is formed on the other surface in this manner is used to form an outer diameter of 166.7 mm. It was wound on a 6 inch core.

  The raw material accumulated shape value of the raw material thus obtained was measured with the above-described measuring apparatus, and then allowed to stand at room temperature for 12 hours, and then stored in a heat treatment furnace at 60 ° C. for 60 hours for thermosetting treatment. went. After the thermosetting treatment finished raw material was allowed to stand at room temperature for 36 hours, calendering was performed.

  The calendering process was performed with a calender apparatus constituted by seven metal rolls in which four heat rolls having a heating mechanism inside and three follower rolls were straightly combined. The number of nips was 6 nips, the heat roll temperature was set to 110 ° C., and the linear pressure was set to 330 kg / cm (= 323 kN / m). In this case, since the calender roll is pressurized through the shafts at both ends of the roll, bending occurs. When a flat roll is used, the contact at both ends in the width direction of the roll surface length becomes strong. For this reason, it is common to make the trunk | drum of a roll into the crown shape whose center part is large diameter. In the present application, the crown amount of the roll is determined by measuring the nip width using pressure-sensitive paper and trying to obtain a uniform load in the roll width direction. The processing speed was 150 m / min. In this way, the original fabric after the calendar process was wound around the 6-inch core, and the original shape accumulated shape value of the wound original fabric was measured with the above measuring device. Thereafter, the wound web was left at room temperature for 24 hours, and then cut into a 1/2 inch (12.65 mm) width to obtain a pancake-like magnetic recording tape.

  Next, the tape width NG, vertical wrinkle NG, error rate, variation, and error NG were evaluated as evaluation items for a plurality of types of magnetic recording tapes manufactured by cutting originals having different original film accumulated shape values. In this case, the raw material accumulated shape value (hereinafter referred to as “the turn is the number of times of wrapping the raw material around the core) after 10000 turns (after the formation of each layer and before the thermosetting treatment) after application of each coating liquid”. 1st original fabric cumulative shape value) and original fabric accumulated shape value per 10000 turns after calendar (hereinafter also referred to as "second original fabric accumulated shape value") are 0.25 mm and 0.20 mm respectively. Example 1 is a magnetic recording tape using anti-reflective material, and Example 2 is a magnetic recording tape using original materials having a first original film accumulated shape value and a second original film accumulated shape value of 0.30 mm and 0.25 mm, respectively. Example 3 was a magnetic recording tape using original fabrics having a first original fabric cumulative shape value and a second original fabric cumulative shape value of 0.35 mm and 0.30 mm, respectively. In addition, a magnetic recording tape using an original fabric having a first original fabric accumulated shape value and a second original fabric accumulated shape value of 0.20 mm and 0.15 mm, respectively, is set as Comparative Example 1, and the first original fabric accumulated shape value and Comparative Example 2 was a magnetic recording tape using original fabrics having two original fabric accumulated shape values of 0.40 mm and 0.35 mm, respectively. Further, an original fabric having a first original fabric cumulative shape value of 0.45 mm was defined as Comparative Example 3. For Comparative Example 3, no pancake-like magnetic recording tape was produced for the reasons described later.

  Moreover, the magnetic recording tape as the comparative example 4 was manufactured as follows. First, a lower nonmagnetic layer and an upper magnetic layer were formed on one surface of the polyethylene naphthalate film in the same manner as in the production methods for producing Examples 1 to 3 and Comparative Examples 1 and 2 described above. Next, after applying the coating solution for the backcoat layer on the other surface of the polyethylene naphthalate film, a drying treatment was performed to form a backcoat layer. Subsequently, a calendar process was performed under the above-described conditions, and then a thermosetting process was performed under the above-described conditions to obtain a raw fabric. Next, the raw material was wound around a 6-inch core, and then cut into ½-inch widths without performing calendering to obtain a pancake-like magnetic recording tape.

About each magnetic recording tape of the said Examples 1-3 and Comparative Examples 1-4, tape width NG, vertical wrinkle NG, an error rate, variation, and error NG were evaluated as an evaluation item. The results are shown in Table 1.

In calculating the first original fabric cumulative shape value and the second original fabric cumulative shape value per 10,000 turns,
Raw total thickness (average) × (raw length) = [pi / 4 × ((Hara ^{Hansoto径) 2} - (winding core outside ^diameter) 2)
The outer diameter of the fabric is obtained from the relationship of
Number of turns = ((raw material outer diameter) / 2− (winding core outer diameter) / 2) / total tape thickness (average)
It is calculated from the following formula.
For example, if the finished length is 10,080 m after coating the back coat layer, the outer diameter of the original fabric is 0.3397 m.
数 Number of turns = (0.3397 / 2−0.1667 / 2) /6.82E−6=12,680 (turns).

  In Comparative Example 1, the original fabric was not broken at the time of calendar processing, and the processing was completed, but vertical wrinkles were observed in 12% of the pancake taped to 1/2 inch width. I wrote it and checked it, but an error occurred and it did not become a product. In addition, this vertical wrinkle was already recognized in the original fabric after the thermosetting treatment.

  In Comparative Example 2, the cumulative shape value of the first original fabric was 0.40 mm, and the original fabric after the heat effect treatment did not appear vertically and seemed to be good, but the central portion was slightly slack when the calendar was processed. In addition, some strength in the calendar process was recognized in the width direction of the original fabric. When the width of the tape was confirmed after cutting, 10% was out of specification (in the center in the width direction of the original fabric), resulting in a decrease in yield. Further, the processing of both ends of the original fabric was slightly weaker than that of the central portion, and 6% of both ends were less than -6.5 and the error rate was NG.

  In Comparative Example 3, the original fabric was manufactured so that the accumulated shape value of each original fabric was larger than that of Comparative Example 2. However, the center portion protruded during winding after coating, and the touch roll was in good contact with the entire width. The original fabric was wound up with air. For this reason, the original fabric was in a loosely wound state, causing a winding deviation and becoming NG.

  Comparative Example 4 was carried out by switching the order of the calendering process and the heat treatment process. However, the transfer of the shape of the backcoat layer and the dents were remarkably recognized on the surface of the magnetic layer in the finished original fabric. When the error rate was confirmed, it was a value of -5.8, which was a level that could not be commercialized. About Examples 1-3, it was favorable also about any evaluation item. From these results, the original accumulated shape value in the first winding step of winding the raw material around the core after forming each layer is within the range of 0.25 mm to 0.35 mm per 10000 turns, It is understood that a good magnetic recording tape can be manufactured by setting the raw material accumulated shape value in the second winding process to be wound around the core within the range of 0.2 mm to 0.3 mm per 10,000 turns. The

DESCRIPTION OF SYMBOLS 1 Base plate 2, 2 Block 3, 3 Support | pillar 4 X-axis linear guide mechanism 5 Z-axis linear guide moving mechanism 6 Holder 7 Contact-type sensor 8 Core 9 Original fabric 10 Reference | standard vertical surface (DELTA) Z Original radial displacement amount

Claims (3)

A lower non-magnetic layer forming step of forming a lower non-magnetic layer by applying a coating solution for a non-magnetic layer containing at least a non-magnetic powder and a binder on one surface of a flexible support, drying and then curing. When,
An upper magnetic layer forming step of forming an upper magnetic layer by applying a magnetic layer coating solution containing at least a ferromagnetic powder and a binder on the nonmagnetic layer and then drying the coating layer;
A backcoat layer forming step of forming a backcoat layer by applying a backcoat layer coating solution containing at least a nonmagnetic powder and a binder on the other surface of the flexible support; and
A first winding step of winding a raw material having each layer formed on both sides of the flexible support around a core;
A thermosetting step for performing a thermosetting process on the raw material wound around the core;
A calendering process in which the raw material wound around the core is fed out and calendered on the raw material;
A magnetic recording medium manufacturing method for manufacturing a magnetic recording medium, including a second winding step of winding the calendered raw material around a core,
In the first winding step, the thickness of the central portion in the width direction of the original fabric wound around the core is within the range of 0.25 mm or more and 0.35 mm or less per 10,000 turns than the thickness of the end portion in the width direction. Define the thickness of each layer so as to be thick, and form each layer.
In the second winding step, the thickness of the central portion in the width direction of the raw material wound around the core is within the range of 0.2 mm or more and 0.3 mm or less per 10,000 turns than the thickness of the end portion in the width direction. A method of manufacturing a magnetic recording medium, wherein the calendar process is executed so as to be thick.   In the calendering step, the calendering is performed using a plurality of metal rolls in which a central portion in a length direction along the width direction of the original fabric is formed in a crown shape having a larger diameter than an end portion of the length. The method of manufacturing a magnetic recording medium according to claim 1, wherein:   3. The method of manufacturing a magnetic recording medium according to claim 1, wherein the process of curing the lower nonmagnetic layer in the lower nonmagnetic layer forming step is a curing process using radiation.

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