JP2006286126A - Manufacturing method of magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic recording medium having excellent surface smoothness and a high quality. <P>SOLUTION: When thermally treating a coated and calender-treated base film and thereafter calender-treating it again, a condition for first calender treatment and that for second calender treatment are set differently from each other so that an effect of the first calender treatment may be weaker than that of the second calender treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetic recording medium and a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium having a high recording density used for backup of computer data and the like and a magnetic recording medium.

  A magnetic tape as a magnetic recording medium is generally manufactured by a process of [application] → [calendar] → [heat treatment] → [slit].

  In the coating step, a belt-like flexible base film is fed out from the raw roll, and a magnetic layer is applied to one surface of the base film, and a back coat layer is applied to the other surface.

  In the calendering step, the surface is flattened through a plurality of calender rollers arranged so that the base film on which the magnetic layer and the back coat layer are applied is in contact with each other.

  In the heat treatment step, the calendered base film is wound around a core and left in a roll at a predetermined temperature for a predetermined time to perform heat treatment.

  In the slit process, the roll-shaped base film after the heat treatment is rewound and cut into a plurality of magnetic tapes at the slit portion.

  By the way, in the magnetic tape manufacturing process as described above, heat treatment is performed in a state in which the base film is wound around the core. The rough back coat layer is pressed and deformed (back surface image), and the surface roughness (Ra) of the magnetic layer surface increases. Such an increase in the surface roughness of the magnetic layer surface causes a problem of causing a spacing loss with the head and facilitating a dropout.

Therefore, Patent Documents 1 to 3 propose that the base film that has been coated and calendered is heat-treated in a roll state and then calendered again. At this time, in Patent Documents 1 to 3, the first calendar process and the second calendar process are set to the same condition, and the calendar process is performed twice on the base film.
JP 2004-319015 A JP 2004-319016 A JP 2004-319017 A

  However, as in Patent Documents 1 to 3, if the two calendar processes are performed under the same conditions, the molding margin is used in the first calendar process. There is a drawback that it is difficult to smooth the calendar and is less effective. In addition, there is a drawback in that the calendar process becomes excessively strong, and adverse effects such as a decrease in durability are likely to occur.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of manufacturing a magnetic recording medium having excellent surface smoothness and high quality, and a magnetic recording medium.

  In order to achieve the above object, the first aspect of the present invention provides a step of coating and forming a magnetic layer on the surface of a strip-like flexible base film, and a base film on which the magnetic layer is coated and formed. A magnetic recording medium comprising: a step of performing a calendar process; a step of performing a heat treatment on the base film that has been subjected to the first calendar process; and a step of performing a second calendar process on the base film that has been subjected to the heat treatment. The manufacturing method is characterized in that a condition for the first calendar process and a condition for the second calendar process are changed.

  According to the first aspect of the present invention, when the base film that has been coated and calendered is heat treated and then calendered again, the first calendering and the second calendering are performed under different conditions.

  In order to achieve the above object, the invention according to claim 2 is characterized in that, in the invention according to claim 1, the effect of the first calendar process is weaker than the effect of the second calendar process. The condition of the first calendar process and the condition of the second calendar process are changed.

According to the invention described in claim 2, the conditions of the first calendar process and the conditions of the second calendar process are such that the effect of the first calendar process is weaker than the effect of the second calendar process. Changed and set. Here, “to reduce the effect” means to reduce the change in surface roughness (Ra) when the same base film is processed at the same time. That is, when Ra ₁ is the surface roughness when the same base film is calendered under the _first processing condition, and Ra ₂ is the surface roughness when calendering under the second processing condition, “Ra ₁ > Ra ₂ ”.

According to a third aspect of the present invention, in order to achieve the above object, in the first or second aspect of the present invention, at least one of temperature, linear pressure, speed, number of calendar stages, calendar roller diameter, and hardness is changed. The conditions of the first calendar process and the conditions of the second calendar process are changed.

  According to the third aspect of the invention, at least one of temperature, linear pressure, speed (base film conveyance speed), number of calendar stages, calendar roller diameter, and hardness is changed, and the conditions and conditions of the first calendar processing are changed. The conditions for the second calendar process can be changed.

  The invention described in claim 4 is manufactured by the method described in claim 1, 2 or 3 in order to achieve the object.

  According to the fourth aspect of the present invention, a high-quality magnetic recording medium having excellent surface smoothness can be obtained by the method according to the first, second, or third aspect.

  According to the method for manufacturing a magnetic recording medium and the magnetic recording medium according to the present invention, it is possible to obtain a high-quality magnetic recording medium with excellent surface smoothness, and to effectively suppress the occurrence of dropouts and errors. it can.

  The best mode for carrying out a method of manufacturing a magnetic recording medium and a magnetic recording medium according to the present invention will be described below with reference to the accompanying drawings.

  In the present embodiment, a magnetic tape as a magnetic recording medium is manufactured by a process of [application] → [calendar] → [heat treatment] → [calendar] → [slit].

  In the coating step, a belt-like flexible base film is fed out from the raw roll, and a magnetic layer is applied to one surface and a backcoat layer is applied to the other surface. In this coating process, the base film on which the magnetic layer and the back coat layer are coated is wound around a core and formed into a roll shape.

  In the calendar process after coating (hereinafter referred to as “first calendar process”), as shown in FIG. 1, by passing the base film F between a plurality of calendar rollers C arranged so as to be in contact with each other, The base film F is sandwiched at the nip between the calendar rollers C and heated and pressed to smooth the surface of the base film F. At this time, the base film F rewound from the roll is passed between the calender rollers C while being guided by the guide rollers G, and is calendered at the nip between the calender rollers C, and then the core S again. Rolled up.

Here, processing conditions are set in the first calendar process so that the calendar processing effect is weaker than that in the second calendar process described later. “Calendar processing effect is weak” means that when the same base film is processed simultaneously, the change in surface roughness (Ra) becomes small. That is, Ra ₁ is the surface roughness when the same base film is calendered under the _first calender treatment conditions, and Ra ₂ is the surface roughness when calendered under the second calender treatment conditions. It means that “Ra ₁ > Ra ₂ ”.

  As a method of weakening the treatment effect, a method of changing each treatment condition of temperature, linear pressure, speed (base film conveyance speed), number of calender stages, calender roller diameter, and hardness, and at least one of them can be considered. Change the conditions to weaken the processing effect. For example, when changing the temperature, set the temperature of the first calendar process lower than the second calendar process, and when changing the line pressure, change the line of the first calendar process with respect to the second calendar process. Set the pressure low. When changing the speed, set the speed of the first calendar process faster than the second calendar process, and when changing the number of calendar stages, set the number of calendar stages of the first calendar process to the second calendar process. Set less. Furthermore, when changing the diameter of the calender roller, set the calender roller diameter of the first calender process larger than that of the second calender process, and when changing the hardness of the calender roller, The hardness of the calendar roller in the first calendar process is set low.

  In the heat treatment step, as shown in FIG. 2, the base film F wound around the core S is placed in a temperature-controlled room 10 at a predetermined temperature in a roll state and left for a predetermined time to perform heat treatment.

  In the calendering process after heat treatment (hereinafter referred to as “second calendering process”), as in the first calendering process, a base film is passed between a plurality of calender rollers arranged to be in contact with each other. The base film F is sandwiched at the nip between the calendar rollers and heated and pressed to smooth the surface of the base film. However, as described above, the processing conditions are set so that the second calendar process has a stronger calendar processing effect than the first calendar process. In the second calendar process, the base film is wound around the core after processing and formed into a roll.

  In the slitting process, the base film F that has been subjected to the second calendar process is rewound and fed to the slit portion, and cut into a plurality of magnetic tapes at the slit portion.

  Thus, in the magnetic tape manufacturing method of the present embodiment, the calendar process is performed twice, and the calendar process is performed by changing the conditions of the first calendar process and the conditions of the second calendar process. That is, the calendar process is performed twice by changing the conditions of the first calendar process and the conditions of the second calendar process so that the effect of the first calendar process is weaker than the effect of the second calendar process.

  Thereby, a base film can be effectively smoothed and a high quality magnetic tape excellent in surface smoothness can be manufactured. That is, by making the effect of the first calendar process weaker than the effect of the second calendar process, the margin for the second calendar process can be secured, and the base film can be effectively smoothed. Further, it is possible to prevent a decrease in durability due to excessive treatment. Moreover, the occurrence of dropouts and errors can be reduced due to such excellent surface smoothness.

  In the present embodiment, the case where a magnetic tape is manufactured in the process of [application] → [first calendar] → [heat treatment] → [second calendar] → [slit] is described as an example. The manufacturing process of the magnetic tape to which the invention is applicable is not limited to this. For example, [Coating] → <Heat treatment> → [First calendar] → [Heat treatment] → [Second calendar] → [Slit] → <Surface treatment / heat treatment / servo light> → [Entrainment] The items in the> can be applied in the same manner in the case of manufacturing in the process performed as necessary.

  In this embodiment, the roll-shaped base film is placed in a thermostatic chamber for heat treatment, but the temperature of the heat treatment is not necessarily constant, and may be changed stepwise or gradually. Also good. Further, the temperature and time of the heat treatment are not particularly limited, and it is preferable to appropriately set optimum conditions according to the object to be treated.

  In the present embodiment, the time from the completion of the heat treatment to the start of the second calendar processing is not particularly defined, but this time may be defined. For example, it may be specified that the second calendar process is performed within 80 hours after the heat treatment is completed.

  The core for winding the base film to be heat-treated is not particularly limited. For example, the material is CFRP (Carbon Fiber Reinforced Plastics), and the outer diameter is preferably 400 mm or more and 600 mm or less. .

  Moreover, when winding around a core, you may make it wind up together with a contact roller. In this case, the base film may be wound around the core while applying heat and pressure with a contact roller.

  Further, the material, width and length of the base film of the magnetic tape produced in the present invention are not particularly limited, and bases of various materials such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and aramid are used. A film can be used.

  In addition, the field of use of the magnetic tape manufactured by the present invention is not particularly limited, but a remarkable effect can be obtained by applying the present invention to a magnetic tape manufacturing process used for backup of computer data, for example. it can. In particular, the effect can be obtained by applying the present invention to a manufacturing process of a magnetic tape having a high recording density exceeding 100 GB.

  Hereinafter, a magnetic tape used for backup of computer data will be described. In this case, the magnetic tape basically means a magnetic film having a magnetic layer on one side of the base film and a back coat layer on the other side. For example, a nonmagnetic layer is further provided between the base film and the magnetic layer. It may be a magnetic tape having a configuration. Further, both surfaces may be magnetic layers.

  As the base film, those conventionally used as a base film material for magnetic tape can be used, and a non-magnetic one is particularly preferable. Examples of these are polyesters (eg, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), mixtures of polyethylene terephthalate and polyethylene naphthalate, polymers containing an ethylene terephthalate component and an ethylene naphthalate component), polyolefins (Eg, polypropylene), cellulose derivatives (eg, cellulose diacetate, cellulose triacetate), polycarbonate, polyamide (especially aromatic polyamide, aramid), polyimide (especially wholly aromatic polyimide), and other synthetic resin films. . Among these, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), aromatic polyamide and aramid are preferable.

  The thickness of the base film is not particularly limited, but is preferably in the range of 2 to 8 μm (more preferably 3 to 8 μm, particularly preferably 3 to 7 μm).

  The magnetic layer is basically made of a ferromagnetic powder and a binder. The magnetic layer usually further contains a lubricant, carbon black as a conductive powder, and an abrasive.

Examples of the ferromagnetic powder include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , FeOx (x = 1.33 to 1.5), CrO ₂ , Co-containing γ-Fe ₂ O ₃ , and Co-containing FeOx (x = 1.33-1.5), ferromagnetic metal powder and plate-shaped hexagonal ferrite powder. In the present invention, it is preferable to use a ferromagnetic metal powder or a plate-shaped hexagonal ferrite powder as the ferromagnetic powder. Particularly preferred is a ferromagnetic metal powder.

The ferromagnetic metal powder has a specific surface area of preferably 30 to 70 m ² / g, and the crystallite size determined by X-ray diffraction method is 50 to 300A. If the specific surface area is too small, it will not be possible to sufficiently cope with high density recording, and if it is too large, it will not be possible to disperse sufficiently, so that it will not be possible to form a smooth magnetic layer, and thus it will not be able to cope with high density recording. The ferromagnetic metal powder is required to contain at least Fe, and specifically, a simple metal or an alloy mainly composed of Fe, Fe—Co, Fe—Ni, Fe—Zn—Ni, or Fe—Ni—Co. It is. As for the magnetic properties of these ferromagnetic metal powders, the saturation magnetization (σs) is 110 emu / g or more, preferably 120 emu / g or more and 170 emu / g or less in order to achieve a high recording density. The coercive force (Hc) is in the range of 800 to 3000 oersted (Oe) (preferably 1500 to 2500 Oe). And the long axis length (namely, average particle diameter) of the powder calculated | required with a transmission electron microscope is 0.5 micrometer or less, Preferably, it is 0.01-0.3 micrometer, and an axial ratio (long axis length / short axis length, The needle ratio) is 5 or more and 20 or less, preferably 5-15. In order to further improve the characteristics, non-metals such as B, C, Al, Si and P, or salts and oxides thereof may be added during the composition. Usually, an oxide layer is formed on the particle surface of the metal powder in order to stabilize it chemically.

The plate-shaped hexagonal ferrite powder has a specific surface area of 25 to 65 m ² / g, a plate ratio (plate diameter / plate thickness) of 2 to 15, and a plate diameter of 0.02 to 1.0 μm. is there. The plate-shaped hexagonal ferrite powder has the same reason as the ferromagnetic metal powder, so that high density recording becomes difficult even if the particle size is too large or too small. The plate-shaped hexagonal ferrite is a ferromagnetic material having a flat plate shape and an easy axis of magnetization in a direction perpendicular to the flat plate surface, specifically, barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and the like. The cobalt substitution product of these can be mentioned. Of these, cobalt substitutes of barium ferrite and cobalt substitutes of strontium ferrite are particularly preferable. To the plate-shaped hexagonal ferrite used in the present invention, elements such as In, Zn, Ge, Nb, and V may be added as necessary to improve the characteristics. Further, regarding the magnetic properties of these plate-shaped hexagonal ferrite powders, in order to achieve a high recording density, the particle size as described above is required and at the same time, the saturation magnetization (σs) is preferably at least 50 emu / g or more. Is 53 emu / g or more. The coercive force is in the range of 700 to 2000 Oersted (Oe), and preferably in the range of 900 to 1600 Oe.

The water content of the ferromagnetic powder is preferably 0.01 to 2% by weight. It is preferable to optimize the water content depending on the type of the binder. The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used, and the pH is usually in the range of 4 to 12, preferably in the range of 5 to 10. The ferromagnetic powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount of the surface treatment used is usually 0.1 to 10% by weight based on the ferromagnetic powder. By performing the surface treatment, adsorption of a lubricant such as a fatty acid can be suppressed to 100 mg / m ² or less. The ferromagnetic powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr. However, if the content is 5000 ppm or less, the properties are not affected.

  The lubricant is added to ooze out on the surface of the magnetic layer, thereby relaxing the friction between the magnetic layer surface and the magnetic head, the guide pole of the drive and the cylinder, and smoothly maintaining the sliding contact state. Examples of the lubricant include fatty acids or fatty acid esters. Examples of fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, And aliphatic carboxylic acids such as palmitoleic acid or mixtures thereof.

  Examples of fatty acid esters include butyl stearate, sec-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyldecyl stearate, Acylation of butyl palmitate, 2-ethylhexyl myristate, butyl stearate and butyl palmitate, oleyl oleate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether with stearic acid , Diethylene glycol dipalmitate, hexamethylenediol acylated with myristic acid to give a diol, and various ester compounds such as glycerin oleate Can. These can be used alone or in combination. The normal content of the lubricant is in the range of 0.2 to 20 parts by weight (preferably 0.5 to 10 parts by weight) with respect to 100 parts by weight of the ferromagnetic powder of the magnetic layer.

Carbon black is added for various purposes such as reducing the surface electrical resistance (Rs) of the magnetic layer, reducing the dynamic friction coefficient (μK value), improving the running durability, and ensuring the smooth surface properties of the magnetic layer. The Carbon black preferably has an average particle size in the range of 3 to 350 nm (more preferably 10 to 300 nm). The specific surface area is preferably 5 to 500 m ² / g (more preferably 50 to 300 m ² / g). The DBP oil absorption is preferably in the range of 10 to 1000 mL / 100 g (more preferably 50 to 300 mL / 100 g). The pH is preferably 2 to 10, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc.

  Carbon black obtained by various manufacturing methods can be used. Examples of carbon black that can be used include furnace black, thermal black, acetylene black, channel black, and lamp black. Specific examples of carbon black products include BLACKPEARLS 2000, 1300, 1000, 900, 800, 700, VULCANXC-72 (above, manufactured by Cabot Corporation), # 35, # 50, # 55, # 60 and # 80. (Made by Asahi Carbon Co., Ltd.), # 3950B, # 3750B, # 3250B, # 2400B, # 2300B, # 1000, # 900, # 40, # 30, and # 10B (Mitsubishi Chemical Corporation )), CONDUCTEXSC, RAVEN150, 50, 40, 15 (above, Columbia Carbon Co., Ltd.), Ketjen Black EC, Ketjen Black ECDJ-500 and Ketjen Black ECDJ-600 (above, Lion Azo Co., Ltd.) ). The usual addition amount of carbon black is 0.1 to 30 parts by weight, preferably 0.2 to 15 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.

Examples of the abrasive include fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite). These abrasives preferably have a Mohs hardness of 5 or more (preferably 6 or more) and an average particle size of 0.05 to 1 μm (more preferably 0.2 to 0.8 μm). . The addition amount of the abrasive is usually in the range of 3 to 25 parts by weight (preferably 3 to 20 parts by weight) with respect to 100 parts by weight of the ferromagnetic powder.

  Examples of the binder for the magnetic layer include thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. Examples of thermoplastic resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl A polymer or a copolymer containing acetal and vinyl ether as structural units can be given. Examples of the copolymer include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate ester-acrylonitrile copolymer, acrylate ester-vinylidene chloride copolymer. Polymer, Acrylate ester-Styrene copolymer, Methacrylate ester-Acrylonitrile copolymer, Methacrylate ester-Vinylidene chloride copolymer, Methacrylate ester-Styrene copolymer, Vinylidene chloride-Acrylonitrile copolymer , Butadiene-acrylonitrile copolymer, styrene-butadiene copolymer, and chlorovinyl ether-acrylic ester copolymer.

  In addition to the above, polyamide resins, fiber-based resins (cellulose acetate butyrate, cellulose diacetate, cellulose propionate, nitrocellulose, etc.), polyvinyl fluoride, polyester resins, polyurethane resins, and various rubber resins are also used. be able to.

  Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, Mention may be made of a mixture of polyester resin and polyisocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate.

  Examples of the polyisocyanate include tolylene diisocyanate, 4-4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate. Mention may be made of isocyanates, products of these isocyanates with polyalcohols, and polyisocyanates produced by condensation of isocyanates.

  As the polyurethane resin, known resins having structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used.

In the present invention, the binder of the magnetic layer is vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, and A combination of at least one resin selected from nitrocellulose and a polyurethane resin, or a combination of these with a polyisocyanate is preferable.

As the binder, as necessary to obtain the durability of the layer obtained more excellent _{dispersibility, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, -O _{-P = O (OM) 2 (} M represents a hydrogen atom or an alkali metal salt,.), - OH, -NR 2, -N + R 3 (R is a hydrocarbon group.), an epoxy group, - It is preferable to use at least one polar group selected from SH, —CN and the like by copolymerization or addition reaction. Such polar groups are preferably introduced into the binder in an amount of 10 ^-1 to 10 ^-8 mol / g (more preferably 10 ^-2 to 10 ^-6 mol / g).

  The binder for the magnetic layer is usually used in the range of 5 to 50 parts by weight (preferably 10 to 30 parts by weight) with respect to 100 parts by weight of the ferromagnetic powder. When a combination of vinyl chloride resin, polyurethane resin, and polyisocyanate is used as a binder in the magnetic layer, the vinyl chloride resin is 5 to 70% by weight and the polyurethane resin is 2 to 50% by weight in the total binder. % And polyisocyanates are preferably used in amounts ranging from 2 to 50% by weight.

  A dispersing agent can be added to the coating solution for forming the magnetic layer of the magnetic tape in order to favorably disperse the magnetic powder in the binder. Further, if necessary, conductive particles (antistatic agent) other than plasticizer, carbon black, antifungal agent and the like can be added. Examples of the dispersant include 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearic acid, and the like. A fatty acid (RCOOH, R is an alkyl group having 11 to 17 carbon atoms, or an alkenyl group), a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, a compound containing fluorine of the fatty acid ester, Fatty acid amide, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, copper phthalocyanine, etc. Can be used. These may be used alone or in combination. The dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder of the magnetic layer.

  Next, the back coat layer will be described. The backcoat layer is preferably formed from carbon black and a binder. Moreover, it is preferable that an inorganic powder or a lubricant is further added.

  It is preferable to use a combination of two types of carbon black having different average particle sizes. In this case, it is preferable to use a combination of fine particle carbon black having an average particle size of 10 to 20 nm and coarse particle carbon black having an average particle size of 230 to 300 nm. In general, by adding fine carbon black as described above, the surface electrical resistance of the backcoat layer can be set low, and the light transmittance can also be set low. Some magnetic recording devices utilize the light transmittance of the tape and are used for the operation signal. In such a case, the addition of particulate carbon black is particularly effective. In addition, particulate carbon black is generally excellent in retention of liquid lubricants, and contributes to reduction of the friction coefficient when used in combination with lubricants. On the other hand, the coarse particulate carbon black having a particle size of 230 to 300 nm has a function as a solid lubricant, and forms fine protrusions on the surface of the back layer, reducing the contact area, and reducing the friction coefficient. Contributes to reduction.

Specific products of the particulate carbon black include the following. RAVEN2000B (18 nm), RAVEN1500B (17 nm) (above, manufactured by Columbia Carbon Co., Ltd.), BP800 (17 nm) (manufactured by Cabot), PRINTEX90 (14 nm), PRINTEX95 (15 nm), PRINTEX85 (16 nm),
PRINTEX75 (17 nm) (above, manufactured by Degussa), # 3950 (16 nm) (manufactured by Mitsubishi Chemical Corporation). Examples of specific products of coarse particulate carbon black include thermal black (270 nm) (manufactured by Kerncarb) and Ravenmtp (275 nm) (manufactured by Columbia Carbon).

  When two types of backcoat layers having different average particle sizes are used, the content ratio (weight ratio) of fine particle carbon black of 10 to 20 nm and coarse particle carbon black of 230 to 300 nm is the former: latter = It is preferably in the range of 98: 2 to 75:25, more preferably in the range of 95: 5 to 85:15. The content of carbon black (the total amount thereof) in the back coat layer is usually in the range of 30 to 110 parts by weight, preferably in the range of 50 to 90 parts by weight with respect to 100 parts by weight of the binder.

  It is preferable to use two types of inorganic powders having different hardnesses. Specifically, it is preferable to use a soft inorganic powder having a Mohs hardness of 3 to 4.5 and a hard inorganic powder having a Mohs hardness of 5 to 9. By adding a soft inorganic powder having a Mohs hardness of 3 to 4.5, the friction coefficient can be stabilized by repeated running. Moreover, when the hardness is within this range, the sliding guide pole is not scraped. The average particle size of the soft inorganic powder is preferably in the range of 30 to 50 nm. Examples of the soft inorganic powder having a Mohs hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more. Among these, calcium carbonate is particularly preferable. The content of the soft inorganic powder in the backcoat layer is preferably in the range of 10 to 140 parts by weight, more preferably in the range of 35 to 100 parts by weight with respect to 100 parts by weight of the carbon black.

  By adding a hard inorganic powder having a Mohs hardness of 5 to 9, the strength of the backcoat layer is enhanced and the running durability is improved. When this is used together with carbon black, there is little deterioration even with repeated sliding, and a strong backcoat layer is obtained. In addition, the addition of the inorganic powder provides an appropriate polishing force and reduces the adhesion of shavings to the tape guide pole and the like. The hard inorganic powder preferably has an average particle size in the range of 80 to 250 nm (more preferably, 100 to 210 nm).

Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Among these, α-iron oxide or α-alumina is preferable. The content of the hard inorganic powder is usually in the range of 3 to 30 parts by weight, preferably in the range of 3 to 20 parts by weight with respect to 100 parts by weight of the carbon black.

  The back coat layer can contain a lubricant. The lubricant can be appropriately selected from the lubricants described in the magnetic layer. In the backcoat layer, the lubricant is usually added in the range of 1 to 5 parts by weight with respect to 100 parts by weight of the binder. Moreover, the dispersing agent described in the magnetic layer can also be added to the backcoat layer. The amount of the dispersant added can be the same as the amount added to the magnetic layer.

  As the binder for the backcoat layer, the binder described in the magnetic layer can be used. Binders that can be used include nitrocellulose resins, polyurethane resins, polyester resins, and polyisocyanates as curing agents. The binder of the backcoat layer is usually 5 to 250 parts by weight (preferably 10 to 200 parts by weight) with respect to 100 parts by weight of carbon black.

  As described above, the magnetic tape of the present invention may have a configuration in which a nonmagnetic layer is provided between the base film and the magnetic layer. That is, a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one surface of the base film and a backcoat layer on the other surface may be used.

  The nonmagnetic layer is a substantially nonmagnetic layer containing a nonmagnetic powder and a binder. This non-magnetic layer needs to be substantially non-magnetic so as not to affect the electromagnetic conversion characteristics of the magnetic layer on the non-magnetic layer, but is small enough not to affect the electromagnetic conversion characteristics of the magnetic layer. Even if the magnetic powder is contained, there is no particular problem. In addition, the nonmagnetic layer usually contains a lubricant in addition to these components.

  Examples of the nonmagnetic powder used in the nonmagnetic layer include nonmagnetic inorganic powder and carbon black. The non-magnetic inorganic powder is preferably relatively hard, and preferably has a Mohs hardness of 5 or more (more preferably 6 or more). Examples of nonmagnetic inorganic powders include α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium dioxide, silicon dioxide, Mention may be made of boron nitride, zinc oxide, calcium carbonate, calcium sulfate and barium sulfate. These can be used alone or in combination. Of these, titanium dioxide, α-alumina, α-iron oxide, or chromium oxide is preferable. The average particle diameter of the nonmagnetic inorganic powder is preferably in the range of 0.01 to 1.0 μm (preferably 0.01 to 0.5 μm, particularly 0.02 to 0.1 μm).

  Carbon black is added for the purpose of imparting electrical conductivity to the magnetic layer to prevent electrification and ensuring the smooth surface properties of the magnetic layer formed on the nonmagnetic layer. As the carbon black used in the nonmagnetic layer, the carbon black described in the magnetic layer can be used. However, the carbon black used in the nonmagnetic layer preferably has an average particle size of 35 nm or less (more preferably 10 to 35 nm). The normal addition amount of carbon black is 3 to 20 parts by weight, preferably 4 to 18 parts by weight, and more preferably 5 to 15 parts by weight with respect to 100 parts by weight of the total nonmagnetic inorganic powder in the nonmagnetic layer. Part.

  As the lubricant, the fatty acid or fatty acid ester described in the magnetic layer can be used. The addition amount of the lubricant is usually in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the total nonmagnetic powder of the nonmagnetic layer.

  As the binder for the nonmagnetic layer, the binders described for the magnetic layer described above can be used. The binder is usually used in the range of 5 to 50 parts by weight (preferably 10 to 30 parts by weight) with respect to 100 parts by weight of the nonmagnetic powder of the nonmagnetic layer. In the case of using a combination of vinyl chloride resin, polyurethane resin, and polyisocyanate as binders in the nonmagnetic layer, 5 to 70% by weight of vinyl chloride resin and 2 to 50 polyurethane resin in all binders. It is preferred to use such that the polyisocyanate is included in an amount ranging from 2% to 50% by weight. In the nonmagnetic layer, an optional component that can be added to the magnetic layer may be added.

  In the case of a magnetic tape having a non-magnetic layer, the method for forming the magnetic layer and the non-magnetic layer is not particularly limited, but the magnetic layer is a coating formed after applying the non-magnetic layer coating liquid on the base film. It is preferably formed by using a so-called wet-on-wet coating method in which a magnetic layer coating solution is applied to a layer (nonmagnetic layer) while it is in a wet state.

  Examples of the application method by the wet-on-wet method include the following methods.

  (1) Using a gravure coating, roll coating, blade coating, or extrusion coating apparatus, a nonmagnetic layer is first formed on the base film. While the nonmagnetic layer is in a wet state, the base film pressurizing type A method of forming a magnetic layer with a roux coating device (see Japanese Patent Laid-Open Nos. 60-238179, 1-46186, and 2-265672).

  (2) A method of forming a magnetic layer and a nonmagnetic layer on a base film almost simultaneously using a coating apparatus comprising a single coating head provided with two slits for coating solution (Japanese Patent Laid-Open No. 63-88080, (See JP-A-2-17921 and JP-A-2-265672).

  (3) A method in which a magnetic layer and a nonmagnetic layer are formed almost simultaneously on a base film using an extrusion coating apparatus with a backup roller (see JP-A-2-174965). The nonmagnetic layer and the magnetic layer are preferably formed using a simultaneous multilayer coating method.

  The surface of the back coat layer of the magnetic tape tends to be transferred to the surface of the magnetic layer while the tape is wound. For this reason, it is preferable that the surface of the back coat layer also has relatively high smoothness. The surface of the back coat layer of the magnetic tape is preferably adjusted so that its surface roughness Ra (centerline average roughness with a cutoff of 0.08 mm) is in the range of 0.003 to 0.060 μm. . The surface roughness can be adjusted by the material of the calendar roller to be used, its surface property, pressure, speed, etc., in the surface treatment process using the calendar after the formation of the coating film.

  The magnetic layer of a magnetic tape having a single-layer structure having a magnetic layer on one side of the base film and a backcoat layer on the other side, manufactured according to the manufacturing method of the present invention, has a thickness of 1.0 to 3 It is preferably in the range of 0.0 μm (more preferably, 1.5 to 2.5 μm).

  The total thickness of the magnetic tape having this configuration is preferably in the range of 4.0 to 12.0 μm, more preferably 4.0 to 10.0 μm.

  The thickness of the back coat layer is preferably in the range of 0.1 to 1.0 μm (more preferably 0.2 to 0.8 μm).

  The magnetic layer of the magnetic tape having a nonmagnetic layer preferably has a thickness in the range of 0.01 to 1.0 μm (more preferably 0.05 to 0.5 μm).

  The thickness of the nonmagnetic layer is preferably in the range of 0.01 to 3.0 μm (more preferably 0.5 to 2.5 μm).

  The ratio of the thickness of the magnetic layer to the thickness of the nonmagnetic layer is preferably in the range of 1: 2 to 1:15 (more preferably 1: 5 to 1:12).

  The total thickness of the magnetic tape having the nonmagnetic layer and the thickness of the backcoat layer are preferably in the same range as the magnetic tape having the single layer structure.

  The effect by the structure of this invention is demonstrated by the following tests.

  After the magnetic layer and the back coat layer are formed on the belt-like flexible base film, a first calendar process is performed. After the first calendar treatment, the base film is wound around a core to form a roll, and heat treatment is performed in a roll state (temperature of 70 ° C. for 48 hours). After the heat treatment, a second calendar process is performed under different conditions. Thereafter, through a predetermined process, a tape cassette is prepared, and a dropout occurrence state of the produced magnetic tape is measured by a DLT (Digital Linear Tape) system.

  The processing conditions for the second calendar process are (1) the same processing conditions as for the first calendar process, (2) the processing conditions for which the processing effect is weaker than the first calendar process, and (3) from the first calendar process. However, the processing conditions were changed by changing the temperature, the linear pressure, the speed, the number of calendar stages, the diameter of the calendar roller, and the hardness.

  The results of each processing condition are shown in Table 1 below.

表１に示すように、一回目のカレンダ工程よりも処理効果が強くなるように二回目のカレンダ工程の処理条件を設定したときに、ドロップアウトが少なくなることが確認できた。

As shown in Table 1, it was confirmed that dropouts were reduced when the processing conditions of the second calendar process were set so that the processing effect was stronger than that of the first calendar process.

Diagram showing the outline of the calendar process Diagram showing outline of heat treatment process

Explanation of symbols

  C ... Calendar roller, G ... Guide roller, F ... Base film, S ... Core, 10 ... Constant temperature chamber

Claims (4)

A step of applying and forming a magnetic layer on the surface of the strip-like flexible base film, a step of applying a first calendar process to the base film on which the magnetic layer has been formed, and a process of applying the first calendar process. A method for manufacturing a magnetic recording medium, comprising: a step of performing a heat treatment on a base film; and a step of performing a second calendar treatment on the base film subjected to the heat treatment,
A method of manufacturing a magnetic recording medium, characterized in that the conditions of the first calendar process and the conditions of the second calendar process are changed.   The condition of the first calendar process and the condition of the second calendar process are changed so that the effect of the first calendar process is weaker than the effect of the second calendar process. Item 2. A method for manufacturing a magnetic recording medium according to Item 1.   The condition of the first calendar process and the condition of the second calendar process are changed by changing at least one of temperature, linear pressure, speed, number of calendar stages, calendar roller diameter, and hardness. 3. A method for producing a magnetic recording medium according to 1 or 2.   A magnetic recording medium manufactured by the method according to claim 1, 2 or 3.

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