JP2020186318A - Aromatic polyamide film for magnetic tape - Google Patents

Abstract

To provide an aromatic polyamide film optimal for magnetic tape which has excellent size stability when stored under high temperature and high humidity for a long period, even when length of a magnetic tape with an aromatic polyamide film as a support body becomes 1,000 m or more per cartridge, suppresses a tape width change at a reel core side, and has excellent running durability.SOLUTION: An aromatic polyamide film for magnetic tape, which shows a size change amount in the film width direction of 500 ppm or less after standing under an atmosphere of 60°C and 90%RH for 10 days, has an L value of 40 to 50, and has a thickness of 2 μm to 15 μm.SELECTED DRAWING: None

Description

The present invention relates to an aromatic polyamide film that is excellent in dimensional stability under high temperature and high humidity and is most suitable for magnetic tape applications that require a high recording capacity of several TB class.

In recent years, the means for transmitting terabyte-class information at high speed has been remarkably developed, and while it is possible to transfer images and data with enormous amounts of information, advanced technology for recording, reproducing and storing them is required. It has come to be. Examples of the recording medium and the reproduction medium include a flexible disk, a magnetic drum, a hard disk, and a magnetic tape (hereinafter, also referred to as a magnetic recording medium of the present invention). In particular, the magnetic tape has a large recording capacity per roll and is a hard disk. Since the management cost is low compared to the above, it plays a large role for data backup and archiving. In addition, due to the handling of big data, reliability for data storage under a wide range of environmental conditions (especially high temperature and high humidity conditions) due to the widespread use of magnetic tape, and data for multiple runs due to repeated use at high speed. Stable recording, reliability of reading performance, etc. are also required more than before.

The magnetic tape for a computer conventionally used in a digital data recording system is determined for each recording / playback system, and so-called D8 type, DLT type, or DDS type compatible magnetic tapes are known. These magnetic tapes are provided with at least a magnetic layer containing ferromagnetic powder and a binder on a non-magnetic support, and on the other side, prevention of winding disorder and good running durability are maintained. Therefore, a back coat layer is provided. Further, in order to improve the decrease in the regenerated output due to the thickness loss of the magnetic layer, the lower non-magnetic layer formed by dispersing the inorganic powder in the binder on the non-magnetic support and the non-magnetic layer while the non-magnetic layer is in a wet state. A magnetic recording medium having a thin upper magnetic layer having a thickness of 1.0 μm or less, which is obtained by dispersing a ferromagnetic powder in a binder, is disclosed.

By the way, the magnetic tape is generally cut into a predetermined size in a step of preparing a coating liquid for each layer, a step of applying the obtained coating liquid on a non-magnetic support, a drying step, a calendar treatment (smoothing treatment) step, and a predetermined size. It is manufactured through a processing process and a packaging process in which the obtained tape is wrapped around a cartridge. Then, in the coating step, the drying step, or the calendering step, the treatment of the film (long support) drawn out from the raw fabric roll has a constant tension (for example, the coating step or the drying step) according to the treatment step. Since the film is carried out under a tension of about 5 kg / m), the film is easily stretched in the longitudinal direction, and the magnetic tape wound in the cartridge gradually shrinks with the lapse of time after production, causing winding tightening. , There is a problem that the tape is easily deformed. In order to solve such a problem, in Patent Documents 1, 2 and 3, an aromatic polyamide film that can be made thinner and longer because of its higher strength than PET and PEN is used as a non-magnetic support. It has been proposed to suppress reversible dimensional changes typified by the coefficient of thermal expansion and the coefficient of humidity expansion in the longitudinal direction, width direction and thickness direction of the film.

Japanese Unexamined Patent Publication No. 2004-67872 Japanese Unexamined Patent Publication No. 9-71669 Japanese Unexamined Patent Publication No. 2005-846966

However, in response to the need for higher capacity of data storage systems (several TB class) and storage under a wide range of environmental conditions, an aromatic polyamide film is used for the support to thin the magnetic tape and one cartridge. When the tape length inside was wound longer, further problems became apparent. Especially when a cartridge with a tape length of more than 1,000 m is stored in a high temperature and high humidity environment, surface pressure is applied in the thickness direction on the core side of the cartridge reel, and the tape width changes significantly. The problem of being significantly inferior has become apparent. As a result of cause analysis, aromatic polyamide is superior to PET and PEN in reversible dimensional stability, but when stored for a long time in a state of being wound on a cartridge reel under high temperature and high humidity, it absorbs more moisture than PET and PEN. Since it has high properties, it has been found that it has a property (creep property) in which water molecules easily change in size due to the entry of water molecules between the molecules. That is, when the magnetic tape having an aromatic polyamide film as a support is wound longer than before and the surface pressure applied to the cartridge reel core side becomes high, the amount of dimensional deformation becomes large due to the influence of hygroscopicity and tensile strength. As a result, it spreads in the tape width direction, causing a problem that the servo characteristics are inferior.

An object of the present invention is to overcome the above problems, for example, when the magnetic tape having an aromatic polyamide film as a support is stored for a long period of time under high temperature and high humidity even if the length of the magnetic tape is 1,000 m or more per one cartridge. It is an object of the present invention to provide an aromatic polyamide film which is excellent in dimensional stability, suppresses a change in tape width on the reel core side, and has excellent running durability, which is most suitable for a magnetic tape.

In order to solve such a problem, the present invention has the following configuration.
(1) The amount of dimensional change in the film width direction after being left at 60 ° C. and 90% RH for 10 days is 500 ppm or less, the L value is 40 or more and 50 or less, and the thickness is 2 μm or more and 15 μm or less. A characteristic aromatic polyamide film for magnetic tape.
(2) An aromatic polyamide film roll for magnetic tape having a width of 1,000 mm or more and a length of 1,000 m or more, which is obtained by winding the aromatic polyamide film for magnetic tape according to (1) above.
(3) The aromatic polyamide for magnetic tape according to (1) above, which is subjected to a heat treatment in which the surface temperature of the aromatic polyamide sheet having a solvent content of less than 5% by mass is maintained at 270 ° C. or higher for 3 seconds or longer. How to make a film.
(4) A magnetic recording medium having a magnetic layer formed on at least one side of the aromatic polyamide film for magnetic tape according to (1) above.

The magnetic tape cartridge to which the aromatic polyamide film for magnetic tape of the present invention is applied can be used in a high temperature and high humidity environment even if the length of the tape using the aromatic polyamide as a support is 1,000 m or more per cartridge. The tape width change on the reel core side was suppressed, and the tape width was excellent in dimensional stability and winding characteristics.

The aromatic polyamide film for magnetic tape of the present invention (hereinafter, may be simply referred to as an aromatic polyamide film) can satisfy various properties because the constituent polymer is an aromatic polyamide. Here, as the aromatic polyamide, for example, one having a repeating unit represented by the following chemical formula (1) and / or chemical formula (2) is preferable.

Here, examples of the groups of Ar ₁ , Ar ₂ , and Ar ₃ include those represented by the following chemical formula (3).

Further, the X, group Y _{is, -O -, - CH 2 -} , - CO -, - CO 2 -, - S -, - SO 2 -, - C (CH 3) 2 - is chosen from such , Not limited to these. Furthermore, some of the hydrogen atoms on these aromatic rings are halogen groups such as fluorine, bromine and chlorine (particularly chlorine), nitro groups, alkyl groups such as methyl, ethyl and propyl (particularly methyl groups), methoxy and ethoxy. , Which is substituted with a substituent such as an alkoxy group such as propoxy, is preferable because it lowers the moisture absorption rate and reduces the dimensional change due to the change in humidity. Further, the hydrogen in the amide bond constituting the polymer may be substituted with another substituent. In the aromatic polyamide used in the present invention, the aromatic ring having a para-orientation occupies 80 mol% or more, more preferably 90 mol% or more of the total aromatic ring. The para-orientation referred to here means a state in which the divalent bonds constituting the main chain on the aromatic ring are coaxial or parallel to each other. If the para-orientation is less than 80 mol%, the rigidity and heat resistance of the film may be insufficient. Further, when the aromatic polyamide contains 60 mol% or more of the repeating unit represented by the following chemical formula (4), it is preferable because the stretchability and the physical properties of the film are particularly excellent.

The method for producing the aromatic polyamide film of the present invention is exemplified below, but the present invention is not limited thereto.

The method for obtaining an aromatic polyamide is, for example, when it is obtained from acid chloride and diamine, solution polymerization is carried out in an aprotic organic polar solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), or dimethylformamide (DMF). It is also synthesized by interfacial polymerization using an aqueous medium. When acid chloride and diamine are used as monomers in the polymer solution, hydrogen chloride is produced as a by-product, but when neutralizing this, an inorganic neutralizer such as calcium hydroxide, calcium carbonate, or lithium carbonate, or ethylene Organic neutralizers such as oxide, propylene oxide, ammonia, triethylamine, triethanolamine, diethanolamine are used. Further, when an aromatic polyamide is obtained from the reaction of isocyanate and carboxylic acid, it is carried out in an aprotic organic polar solvent in the presence of a catalyst.

These polymer solutions may be used as they are as a film-forming stock solution, or the polymer may be isolated once and then redissolved in the above-mentioned organic solvent or an inorganic solvent such as sulfuric acid to prepare a film-forming stock solution.

In order to obtain the aromatic polyamide film of the present invention, the intrinsic viscosity of the polymer ηjnh (measured at 30 ° C. with 0.5 g of the polymer as a 100 ml solution in 98% sulfuric acid) is 0.5 (dl / g). The above is preferable.

As a method for adding particles, there are a method in which the particles are sufficiently slurryed in a solvent and then used as a solvent for polymerization or a solvent for dilution, and a method in which the particles are directly added after preparing a membrane-forming stock solution.

Inorganic salts such as calcium chloride, magnesium chloride, lithium chloride, and lithium nitrate may be added to the film-forming stock solution as a solubilizing agent. Further, as the membrane-forming stock solution, the neutralized polymer solution may be used as it is, or the polymer may be isolated and then redissolved in a solvent. As the solvent, an organic polar solvent such as N-methyl-2-pyrrolidone, dimethylacetamide, or dimethylformamide is preferable because it is easy to handle, but a strong acid solvent such as concentrated sulfuric acid, concentrated nitric acid, or polyphosphate may be used. The polymer concentration in the film-forming stock solution is preferably about 2 to 40% by mass.

The film-forming stock solution prepared as described above is formed into a film by a so-called solution film-forming method. The solution film-forming method includes a dry-wet method, a dry method, a wet method, etc., and any method may be used for film-forming, but if the polymer solution contains an inorganic salt, it is extracted. A wet process is required, and a dry wet method and a wet method are used. Here, the dry / wet method will be described as an example.

When forming a film by the dry-wet method, the undiluted solution is extruded from the base onto a support such as a drum or an endless belt to form a thin film, and then the solvent is scattered from the thin film layer to make the thin film self-supporting polymer concentration (PC). Dry to 35-60% by mass. After the sheet after the dry step is cooled, it is peeled off from the support and introduced into the wet bath of the next wet step, and desalting and solvent removal are performed. The wet bath composition is not particularly limited as long as it is a poor solvent for the polymer, but water or a mixed system of an organic solvent / water can be used. At this time, in order to reduce impurities in the sheet, the composition ratio of the organic solvent / water mixture system (the following numerical values are based on mass) is organic solvent / water = 70/30 to 0/100, preferably 60. It is preferably / 40 to 30/70 and the bath temperature is 40 ° C. or higher. Inorganic salts may be contained in the wet bath, but it is preferable to finally extract the solvent and inorganic salts contained in the sheet with a large amount of water.

The sheet that has passed through the wet process is subsequently dried and heat-treated in the tenter, and may be dried until the solvent content in the sheet becomes less than 5% by mass by the time the sheet is heat-treated in the tenter. is important. If the heat treatment step is started in a state where the solvent content is 5% by mass or more, uneven heat treatment is likely to occur, uneven physical properties are generated in the film width direction, and the sheet is likely to break during the stretching step. It is more preferable that the solvent content is small, and it is desirable that the solvent is completely dried to around 0% by mass.

The sheet formed as described above is stretched during the wet process in order to improve the mechanical properties and dimensional stability desired in the heat treatment process. For stretching, a sequential biaxial stretching method in which the sheet is first stretched in the longitudinal direction and then in the width direction, or first in the width direction and then in the longitudinal direction, or a simultaneous biaxial stretching method in which the longitudinal direction and the width direction are simultaneously stretched is used. be able to. These stretching methods are well known as stretching methods in melt film formation performed by film formation of polyethylene, polypropylene, polyester, etc., but in the case of a film obtained by solution film formation as in the present invention, Since a solvent and a wet bath component are contained in the sheet and they are a process including movement to the outside of the sheet, it is preferable to adopt the method described later in order to obtain the target film.

As the stretching method, the sequential biaxial stretching method is preferable from the viewpoint of equipment and operability. As the stretching conditions, it is necessary to select appropriate conditions depending on the polymer composition and the like, but the stretching ratio in the longitudinal direction of the sheet is 1.0 to 1.5 times, and the stretching ratio in the width direction is 1.2 to 2. It is preferable that the ratio is 0.0 times in order to obtain the desired dimensional stability. The stretching temperature is preferably 270 ° C. or higher for 3 seconds or longer, and more preferably 270 to 320 ° C. for 3 seconds or longer. If the stretching temperature is less than 270 ° C., crystallization may be insufficient, and dimensional characteristics such as sufficient hygroscopicity and tensile strength may not be obtained. If the stretching temperature exceeds 320 ° C., the crystallinity increases too much, so that the film becomes brittle and the film is likely to be torn. Further, the solvent content in the sheet at the time of stretching is preferably less than 5% by mass. It is effective to slowly cool the film after stretching or heat treatment, and cooling at a rate of 50 ° C./sec or less is effective in reducing the heat shrinkage rate.

The aromatic polyamide film in the present invention may of course be a single-layer film, but may be a laminated film. For example, in the case of two layers, one example is a method in which the polymerized aromatic polyamide solution is divided into two, different particles are added to each, and then the layers are laminated. The same applies to the case of three or more layers. Examples of these laminating methods include laminating in a mouthpiece, laminating in a composite pipe, and once forming one layer and then forming another layer on it.

The aromatic polyamide film obtained as described above may be subjected to various treatments such as corona discharge treatment, plasma treatment, dust removal treatment, and reheat treatment.

Next, the physical properties of the aromatic polyamide film of the present invention will be described.

The aromatic polyamide film in the present invention can be used even in a harsh environment, and the amount of dimensional change in the film width direction after being left at 60 ° C. and 90% RH for 10 days is 500 ppm or less, so that the temperature is high. Even when it is used as a magnetic tape in a high humidity environment, it is possible to suppress a total dimensional change including a reversible dimensional change and an irreversible dimensional change (creep). Here, the dimensional change of the aromatic polyamide film referred to in the present invention means that the film is cut out, and after humidity control for 24 hours in an atmosphere of 25 ° C. and 50% RH, one side in the longitudinal direction is fixed and the other side is 0.55 N. It is the amount of dimensional change in the width direction when the above conditions are set and measured in a horizontally stretched state so that a load is uniformly applied. Details will be described later.

Aromatic polyamide film of the present invention is preferably the longitudinal direction of the Young's modulus (E _MD) is not less than 8 GPa. When the Young's modulus in the longitudinal direction is 8 GPa or more, it is easy to handle even if it is thinned, the head touch is good when it is used as a magnetic recording medium, and the winding suitability of the magnetic tape cartridge is good. On the contrary, if the Young's modulus in the longitudinal direction is less than 8 GPa, the winding characteristics of the magnetic tape tend to deteriorate. More preferably, the Young's modulus in all directions of the film is 9 GPa or more, still more preferably 10 GPa or more. There is no particular upper limit to Young's modulus, but it is usually preferable to set it to about 25 GPa because the Young's modulus and elongation are well-balanced.

Also, the aromatic polyamide film of the present invention, the ratio _E TD _{/ E MD} in the longitudinal direction of the Young's modulus and the Young's modulus in the transverse direction _{(E TD)} is at _{1 ≦ E TD / E MD ≦} 3, a better It is preferable because the winding characteristic can be obtained, and it is more preferable that the _ETD / E _MD is 1 < _ETD / E _MD <2.

Further, the aromatic polyamide film in the present invention preferably has a Poisson's ratio of 0.1 or more and less than 0.5 because both reversible dimensional stability and toughness can be achieved. More preferably, it is 0.1 or more and less than 0.3. Films with a Poisson's ratio in this range have a high capacity (several TB class), especially for systems with high surface pressure and running tension of magnetic tape, for example, data storage systems in which the tape length of one roll exceeds 1,000 m. It is useful as a support for magnetic tape corresponding to the above. If the Poisson's ratio is less than 0.1 or 0.5 or more, the tape breakage may occur if the surface pressure applied to the tape and the running tension are high.

When the coefficient of thermal expansion of the aromatic polyamide film in the present invention is preferably −5 ppm / ° C. or higher and 5 ppm / ° C. or lower, more preferably −10 ppm / ° C. or higher and 10 ppm / ° C. or lower, reversible dimensional change due to temperature change occurs. It is preferable because it is small and it is easy to obtain good servo tracking error characteristics when it is used as a magnetic tape.

When the humidity expansion coefficient of the aromatic polyamide film in the present invention is preferably -5 ppm /% RH or more and 5 ppm /% RH or less, and more preferably -10 ppm /% RH or more and 10 ppm /% RH or less, it is reversible due to a change in moisture absorption. It is preferable because the dimensional change is small and good servo tracking error characteristics can be easily obtained when using magnetic tape. If it is out of this range, even if the irreversible humidity change is good, it cannot withstand the reversible humidity change, and the servo tracking Error characteristics may deteriorate.

The heat shrinkage of the aromatic polyamide film in the present invention at 200 ° C. (5 minutes) is preferably 3% or less in at least one direction, preferably in all directions. If the thermal dimensional stability is out of this range, flatness such as curling is likely to occur in the processing process of the product, and the winding characteristics may be inferior.

The elongation of the aromatic polyamide film in all directions in the present invention is preferably 10% or more, more preferably 20% or more because the tape has appropriate flexibility and excellent workability.

The aromatic polyamide film of the present invention may contain particles in order to impart slipperiness to the film. The particle size and content of the particles contained should be appropriately selected depending on the intended use, but the average primary particle size is preferably 0.001 to 2 μm. The content of the particles contained in the film is preferably 0.001 to 5% by mass, more preferably 0.05 to 3% by mass. If the particle size and content of the particles are larger than or larger than the above range, the adhesion between the tape and the magnetic head tends to be poor when the magnetic tape is used, and the electromagnetic conversion characteristics tend to deteriorate. If the particle size and content of the particles are smaller than or less than the above range, the runnability of the film deteriorates and the durability may be deteriorated.

The types of particles include inorganic particles such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , CaSO ₄ , BaSO ₄ , CaCO ₃ , carbon black, zeolite, and other fine metal powders, silicon particles, polyimide particles, and crosslinked particles. Examples thereof include organic polymers such as polymer particles, crosslinked polystyrene particles, and Teflon (registered trademark) particles. As a method for imparting slipperiness to the film, in addition to the method of adding particles, a method of blending a dissimilar polymer with a base polymer and forming protrusions of the dissimilar polymer in the film forming process can also be used.

The surface roughness of the film should be appropriately designed depending on the application, but for magnetic greening applications, Rz is 2 to 500 nm, more preferably 3 to 300 nm, and Ra is 0.1 to 100 nm, more preferably. It is 0.2 to 50 nm, 2 to 500 nm at Rz, and more preferably 3 to 400 nm. Ra and Rz are measured by Atomic Force Microscope NanoScopeIIIa manufactured by Digital Instruments, AFM (deep needle; single crystal silicon, scanning mode; tapping mode, measuring range; 5 × 5 μm, surface element number; 256 × 256, scanning speed. Using 1.0 Hz, measurement environment; room temperature, in the air), 10 points are measured in the film width direction, and the average value is calculated.

The aromatic polyamide film in the present invention undergoes appropriate heat treatment to promote crystallization between polymer chain molecules and improve mechanical properties, but the heat treatment causes the aromatic polyfilm to change its absorption wavelength. It changes deeply with it. In particular, in a thin aromatic polyamide film of 2 μm or more and 15 μm or less, the higher the L value, the less the progress of crystallization is sufficient, and therefore the hygroscopicity and tensile strength of the polyamide film are inferior. That is, since the dimensional change of the tape width becomes large in a high temperature and high humidity environment, a problem that the servo characteristics and the like are remarkably inferior when the magnetic tape is used becomes apparent. On the other hand, if the L value is too low, the color contrast due to the uneven thickness becomes clear, so that the uneven thickness in the width direction is worsened, and the aromatic polyamide film is partially carbonized and becomes fragile, resulting in the Young's modulus of the film. The mechanical properties of the film are significantly reduced. For the above reasons, the aromatic polyamide film of the present invention preferably has an L value of 40 or more and 50 or less in order to maintain good mechanical properties, and more preferably an L value of 41 or more and 49 or less. Good.

The L value of the film was measured using a colorimetric color difference meter ZE2000 manufactured by Nippon Denshoku Industries Co., Ltd. The L value is a value measured by stacking the minimum number of films having a film thickness of 36 μm or more because the sensitivity of the detector becomes dull and an appropriate evaluation cannot be made when the film thickness becomes thin. The details of the measurement method will be described later.

In order to control the amount of dimensional change and the L value in the film width direction described above, a step of heat-treating an aromatic polyamide sheet having a solvent content of less than 5% by mass under predetermined conditions to obtain a film is performed. It is preferable to go through. As the heat treatment conditions at this time, it is preferable to hold the sheet at a surface temperature of 270 ° C. or higher for 3 seconds or longer.

The above heat treatment may be performed, for example, during the longitudinal stretching of the film forming step or during the transverse stretching. Further, it is possible to form a film once, wind it up, and then unwind it again.

Further, as a means for performing the heat treatment, for example, hot air or an electric heater (for example, an infrared heater) can be used, and the amount of heat given to the sheet surface by these can be appropriately adjusted to satisfy the above heat treatment conditions.

In the above, if the heat treatment is performed in a state where the solvent content is 5% by mass or more, drying unevenness is likely to occur in the width direction, color unevenness is likely to occur on the entire surface of the film, and the sheet is likely to be broken during transportation. It is more preferable that the solvent content is low, and it is desirable that the solvent is completely dried to around 0%. Further, since the dimensional characteristics of the film depend on the maximum heat treatment temperature of the sheet surface, it is preferable to treat the film at 270 ° C. or higher for 3 seconds or longer, but more preferably at a temperature of 270 to 320 ° C. for 3 seconds or longer. And. If the heat treatment temperature is less than 270 ° C., crystallization may be insufficient, and dimensional characteristics such as sufficient hygroscopicity and tensile strength may not be obtained. Further, if the temperature exceeds 320 ° C., the film becomes brittle, and in particular, the capacity of a system having a high surface pressure and running tension of a magnetic tape, for example, a data storage system in which the tape length of one roll exceeds 1,000 m (high capacity) It may not be practical as a support for magnetic tape corresponding to several TB class).

The hygroscopicity of the aromatic polyamide film of the present invention is preferably 2.0% or less, more preferably 1.5% or less. If the moisture absorption rate exceeds 2.0%, the dimensional stability under high temperature and high humidity conditions tends to deteriorate, and curls and wrinkles of the magnetic tape may occur, resulting in deterioration of flatness.

The density of the aromatic polyamide film of the present invention is preferably 1.48 kg / m ³ or more, and preferably 1.52 kg / m ³ or less. When the film density exceeds 1.52 kg / m ³ , the rigidity and packing property of the molecular chain are improved, so the influence on the dimensional change due to moisture absorption is small, but it becomes partially carbonized and fragile, and the machine such as Young's modulus of the film The characteristics tend to decrease.

In order to improve the productivity per unit time, the aromatic polyamide film of the present invention is wound as a roll having a width of 1,000 mm or more and a length of 1,000 m or more to obtain an aromatic polyamide film roll for magnetic tape. It can be mass-produced at low cost. In particular, it is most suitable as a support for a magnetic tape corresponding to a high capacity (several TB class) of a data storage system in which the tape length of one roll of the magnetic tape exceeds 1,000 m.

The aromatic polyamide film of the present invention is preferably used for various applications such as flexible printed substrates, capacitors, release films, printer ribbons, and acoustic vibration plates, but magnetic recording media having a magnetic layer on at least one side, particularly When used as a magnetic tape, it is particularly preferable because the effect of the dimensional stability of the present invention having dimensional stability, rigidity, surface smoothness and the like is sufficiently exhibited.

In the present invention, a magnetic layer can be formed (provided) on at least one side of the aromatic polyamide film to form a magnetic recording medium. In particular, the magnetic tape to which the aromatic polyamide film of the present invention is applied is preferably composed of an upper magnetic layer, a lower non-magnetic layer, an undercoat layer, and a backcoat layer in addition to the aromatic polyamide film support. Known techniques can be applied to the method for producing a magnetic tape.

The thickness of the aromatic polyamide film when used as a support for a magnetic tape is preferably 2 to 15 μm, more preferably 2.4 to 4.2 μm. If the film thickness is smaller than 2 μm, the mechanical strength cannot be sufficiently obtained and the running durability is inferior, and if it is larger than 15 μm, it may not be practical as a support for a high-capacity magnetic tape.

When obtaining a magnetic tape to which the aromatic polyamide film of the present invention is applied, particularly a high-density magnetic tape corresponding to a data storage system in which the tape length of one roll exceeds 1,000 m, a non-magnetic layer is formed on the support. As a means for forming a magnetic layer, a backcoat layer, etc., for example, there are a wet method of coating on a support film, a vapor deposition method, a sputtering method, an ion plating method, and other dry methods, and the method is not particularly limited. However, here, a wet method of coating on a support film will be described as an example.

As a means for forming a non-magnetic layer, a magnetic layer, a back coat layer, etc. on the support by coating, an extrusion coating method, a roll coating method, a gravure coating method, a microgravure coating method, and an air knife coating method are used. Known methods such as a method, a die coating method, a curtain coating method, a dip coating method, and a wire bar coating method can be used. In particular, when the non-magnetic layer and the magnetic layer are coated by the sequential layering method, it is preferable to use the extrusion coating method in producing the magnetic layer. For example, the formation of the non-magnetic layer, the magnetic layer, and the back coat layer is continuously applied on the non-magnetic support aromatic polyamide film sent out from the non-magnetic support original roll (film roll). After forming the non-magnetic layer, the magnetic layer, and the backcoat layer, the non-magnetic support is wound to obtain a magnetic recording medium raw fabric roll, which is subjected to calendar treatment and heat treatment, and then the magnetic recording medium raw fabric roll. It is preferable to obtain a tape-shaped magnetic recording medium by cutting a part of the above.

A method in which a non-magnetic support wound in a rolled state is sent out to form a non-magnetic layer and a magnetic layer, then wound once, and then the non-magnetic support is sent out again to form a backcoat layer is inexpensive and a large amount of magnetic force is used. It is difficult to manufacture a recording medium. On the other hand, as described above, after the non-magnetic support wound in the roll state is sent out to form the non-magnetic layer and the magnetic layer, the back coat layer is formed without winding the non-magnetic support even once. As a result, the magnetic recording medium can be mass-produced at low cost.

Further, in order to improve productivity, the transport speed of the non-magnetic support when forming each layer is preferably 100 m / min or more, more preferably 200 m / min or more, still more preferably 300 m / min or more. Particularly preferably, it is 400 m / min or more. The faster the coating speed, the more advantageous for improving productivity. However, if the coating speed is too fast, coating failures (coating streaks, coating unevenness, etc.) are likely to occur. Therefore, the coating speed is preferably 700 m / min or less. Therefore, the ferromagnetic powder in the magnetic layer is placed in a desired orientation state. Therefore, it is usually preferable to orient the magnetic layer coating liquid in the longitudinal direction using a cobalt magnet and a solenoid while the magnetic layer coating liquid is in a wet state after coating.

The coating liquid for forming each layer can be dried, for example, by blowing warm air onto the coated coating liquid. The temperature of the drying air is preferably 60 ° C. or higher. Further, the air volume of the dry air may be set according to the coating amount and the temperature of the dry air. After the magnetic layer coating liquid is applied, an appropriate pre-drying can be performed before introducing the magnetic layer coating liquid into the magnet zone for orientation treatment.

After the coating liquid for forming each layer is applied and dried as described above, the magnetic recording medium is usually subjected to calendar processing. As the roll for calendar processing, a heat-resistant plastic roll or metal roll such as epoxy, polyimide, polyamide, or polyimide amide can be used. The processing temperature during the calendar processing is preferably 50 ° C. or higher, more preferably 90 ° C. or higher. The linear pressure during calendar processing is preferably 200 kg / cm (196 kN / m) or more, and more preferably 300 kg / cm (294 kN / m) or more.

It is preferable to introduce a heat treatment step on the original roll of the magnetic recording medium after the calendar processing. It is preferable that the roll after the calendar treatment is heat-treated at a tension of 2 to 5 kg / m in the range of 40 to 70 ° C. for 8 to 40 hours. Further, it is preferable to combine a step of heat-treating the pancake after cutting into a width of 1/2 inch at a tension of 0.3 to 1.0 N / piece in the range of 40 to 60 ° C. for 5 to 30 hours.

The thickness of the magnetic layer in the magnetic tape of the present invention is preferably, for example, 0.01 to 0.2 μm.

Examples of the ferromagnetic powder contained in the magnetic layer include hexagonal ferrite powder and ferromagnetic metal powder. Examples of the hexagonal ferrite used include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite substituents, and Co-substituted products. The ferromagnetic metal powder used in the magnetic layer is not particularly limited, but it is preferable to use a ferromagnetic metal powder containing α-Fe as a main component. In addition to the predetermined atoms, these ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, RH, Pd, Ag, Sn, Sb, Te, Ba, etc. It may contain atoms such as Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B.

The non-magnetic layer in the magnetic tape of the present invention is a layer containing at least a non-magnetic powder and a binder. The film thickness of the non-magnetic layer is preferably 0.1 to 2.0 μm. If the film thickness of the non-magnetic layer is too thick, the total thickness of the magnetic tape becomes thick and it becomes difficult to increase the capacity. On the other hand, if it is too thin, the influence of the surface roughness of the non-magnetic support appears on the surface of the magnetic layer, and the effect of sinking the abrasive and carbon black on the surface of the magnetic layer is impaired. The more preferable film thickness of the non-magnetic layer is 0.2 to 1.5 μm, and the particularly preferable film thickness is 0.3 to 1.0 μm. The non-magnetic layer is not particularly limited as long as it is substantially non-magnetic, and may contain magnetic powder as long as it is substantially non-magnetic. "Substantially non-magnetic" means that the non-magnetic layer is allowed to have magnetism within a range that does not substantially reduce the electromagnetic conversion characteristics of the magnetic layer. For example, metal oxides and metal carbonates are allowed. It can be selected from inorganic compounds such as salts, metal sulfates, metal nitrides, metal carbides and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, gateite, corundum, and nitride with an pregelatinization rate of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. be able to.

The thickness of the backcoat layer in the magnetic tape of the present invention is, for example, 0.2 to 0.8 μm, preferably 0.3 to 0.6 μm. In general, magnetic tapes for recording computer data are strongly required to have repeatability as compared with video tapes and audio tapes. In order to maintain such high running durability, it is preferable that the backcoat layer contains carbon black and an inorganic powder.

Further, in the magnetic tape of the present invention, an undercoat layer for improving adhesion may be provided between the non-magnetic support and the non-magnetic layer or the magnetic layer. The thickness of the undercoat layer is, for example, 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm. A known undercoat layer can be used.

In the magnetic tape of the present invention, various known additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used for the magnetic layer, the non-magnetic layer, and the backcoat layer, depending on the purpose. can do.

[Measurement method of physical properties and evaluation method of effect]
The method for measuring physical properties and the method for evaluating the effect in the present invention were carried out according to the following methods.

(1) Dimensional change rate in the film width direction In order to measure the part where the dimensional change rate is the largest, the film at a position 5 m from the core side of the roll wound over 1,000 m is divided into 5 parts in the width direction. Five film samples having a width direction of 30 mm and a length direction of 110 mm were collected at the positions.

After adjusting the humidity in an atmosphere of 25 ° C and 50% RH, a square with a length of about 20 mm square is marked in the center of each sample, and the length in the width direction is determined by Keyence Co., Ltd. image dimension measuring instrument IM7010 (repetition accuracy ± 0). The measurement was repeated 10 times with (5.5 μm, measurement accuracy ± 2 μm), and the average value was set to T0. Further, the sample was fixed on one side in the longitudinal direction and horizontally spread on the other side so that a load of 0.55 N was uniformly applied, and left to stand in an atmosphere of 60 ° C. and 90% RH for 10 days, and similarly in the width direction. The average value (T1) of the lengths of was obtained and evaluated with the maximum value.

Dimensional change rate = (T1-T0) / T0 x 10 ⁶ (ppm)
(2) Young's modulus (tensile elastic modulus)
Five film samples having a width of 10 mm were collected in the longitudinal direction and the width direction of the film so that the length in the direction of measurement at each center position of the film divided into five in the width direction was 150 mm.

Using the Orientec robot Tencilon RTF-1210, the collected film is set in a device with a chuck distance of 100 mm, and a tensile test is performed under the conditions of a tensile speed of 200 mm / min, a temperature of 23 ° C., and a relative humidity of 65%. The Young's modulus in the longitudinal direction and the Young's modulus in the width direction were obtained from the tangent line of the rising portion of the obtained load-elongation curve, and evaluated by the average value.

(3) L value measurement The L value of the film was measured using a colorimetric color difference meter ZE2000 manufactured by Nippon Denshoku Industries Co., Ltd.

The film was divided into five in the width direction, five points at the center of each sample were measured, and the minimum and maximum values were calculated. Since the sensitivity of the detector becomes dull and an appropriate evaluation cannot be made when the film thickness becomes thin, the L value is measured by stacking the minimum number of sheets having a thickness of 36 μm or more.

(4) Residual Solvent Concentration of Film Before Heat Treatment Step Five samples of 20 mm in width direction × 20 mm in length direction were collected at each center position of the sheet before the heat treatment step divided into five in the width direction. The mass of the film before drying was measured using an electronic analytical balance AUX-220 manufactured by Shimadzu Corporation, and the mass at that time was G0, and the mass after drying at 200 ° C. for 1 hour was evaluated as follows. ..

((G1-G0) / G0) x 100 (mass%)
(5) Measurement of film density The film density was measured by a pycnometer method using an aqueous solution of sodium polytungstate as an immersion liquid. The film was divided into five in the width direction, five points at the center of each sample were measured, and the minimum and maximum values were calculated.
・ Equipment: Balance AUX-220, an electronic analytical balance manufactured by Shimadzu Corporation
・ Constant temperature bath: Constant temperature water tank BK33 manufactured by Yamato Scientific Co., Ltd.
・ Pycnometer: Lipkin-Devison type pycnometer ・ Measurement temperature: 23 ℃
(6) Winding characteristics of film roll 1,000 m or more If a film with a width of 1,000 mm or more can be formed and wound 1,000 m or more without breaking, ○, 1,000 m or more can be wound. If it cannot be done, it is marked as x.

(7) Magnetic Tape Dimensional Change Rate A non-magnetic coating material having the following composition was applied onto the aromatic polyamide film so that the thickness after drying was 0.8 μm, and the film was dried at 100 ° C. Immediately after that, a magnetic paint having the following composition was applied so that the thickness after drying was 0.08 μm, and the mixture was dried at 100 ° C. At this time, while the magnetic layer was still in a wet state, it was passed through the alternating magnetic field generator to perform the orientation treatment. Further, the backcoat paint is applied and dried on the side opposite to the non-magnetic lower layer and the magnetic layer forming surface of the support so that the thickness after drying is 0.5 μm, and the magnetic recording laminated raw fabric is obtained. Got a roll. The obtained magnetically recorded laminated raw fabric roll was run in a heat treatment zone having a temperature of 130 ° C. at a tension of 3.0 kg / m (the residence time in the heat treatment zone is 15 seconds). Next, surface smoothing was performed at a temperature of 90 ° C., a linear pressure of 300 kg / cm, and a winding tension of 4.0 kg / m with a 7-stage calendar processing machine composed of only metal rolls, and then heated at 60 ° C. for 36 hours. It was processed and cut to a width of 1/2 inch to prepare a magnetic tape. The tension after cutting was adjusted to 1/2 inch width so as to be 0.55 N. Then, the servo signal was recorded on the obtained magnetic tape and wound on the LTO cartridge to prepare a magnetic tape cartridge.
<Preparation of upper layer magnetic paint solution>
Ferromagnetic plate-shaped hexagonal ferrite powder 100 parts by mass polyurethane resin 15 parts by mass phenylphosphonic acid 3 parts by mass α-Al ₂ O ₃ (particle size 0.15 μm) 5 parts by mass plate-shaped alumina powder (average particle size: 50 nm) 1 Parts by mass Carbon black (particle size 20 nm) 2 parts by mass Cyclohexanone 110 parts by mass Methyl ethyl ketone 100 parts by mass Toluene 100 parts by mass Butyl stearate 2 parts by mass Steaic acid 1 part by mass <Preparation of non-magnetic coating liquid for lower layer>
Non-magnetic inorganic powder 85 parts by mass α-iron oxide, surface treatment agent: Al ₂ O ₃ , SiO ₂
Carbon black 20 parts by mass polyurethane resin 15 parts by mass phenylphosphonic acid 3 parts by mass α-Al ₂ O ₃ (average particle size 0.2 μm) 5 parts by mass cyclohexanone 140 parts by mass methyl ethyl ketone 170 parts by mass butyl stearate 2 parts by mass stearic acid 1 Mass part <Adjustment of paint liquid for back coat>
Carbon black (average particle size: 25 nm) 40.5 parts by mass Carbon black (average particle size: 370 nm) 0.5 parts by mass barium sulfate 4.05 parts by mass nitrocellulose 28 parts by mass polyurethane resin (containing SO ₃ Na group) 20 By mass Cyclohexanone 100 parts by mass Toluene 100 parts by mass Methyl ethyl ketone 100 parts by mass.

Immediately after leaving the obtained magnetic tape cartridge at 60 ° C. for 10 days in a 90% RH environment and cutting out the magnetic tape at the portion that is 5 m from the leader tape joint to the outermost peripheral side (preferably within 30 minutes), the cartridge reel is the most. The difference in tape width between the outer peripheral portion and the innermost peripheral portion was measured by the same method as the measurement of the amount of dimensional change of the film. The reason for measuring immediately after cutting out is to measure the tape dimensional change before the surface pressure applied to the tape becomes free and the magnetic tape returns to the original state (before a reversible change occurs). This was repeated 10 times to obtain the average value, and the difference was evaluated below.

500ppm or less: ○
Over 500 ppm: ×
(8) Servo tracking error occurrence rate After storing the obtained magnetic tape cartridge at 60 ° C for 10 days in a 90% RH environment, run the entire length with an LTO-4 drive (manufactured by IBM), and servo tracking by off-track of the servo signal. The error rate was calculated. The error occurrence rate was determined by the ratio of the number of turns in which an error occurred when 10 turns were run.

10% or less: ○
Over 10%: ×
Specific examples and comparative examples according to the present invention will be given below, but the present invention is not limited to these examples.

(Example 1)
2-Chloroparaphenylenediamine (hereinafter CPA) corresponding to 85 mol% and diphenyl ether (hereinafter DPE) corresponding to 15 mol% are dissolved in N-methyl-2-pyrrolidone (hereinafter NMP), and this solution is filtered with precision. After filtering through a filter made of 1.0 μm polypropylene, the mixture was transferred to a polymerization tank and passed through a filter made of polypropylene having a filtration accuracy of 1.0 μm, which corresponds to 98.5 mol% of chloroterephthalic acid chloride (hereinafter referred to as chloroterephthalic acid chloride). CTPC) was added to add polyether sulfone (Sumika Excel 5400P manufactured by Sumitomo Chemical Co., Ltd.) to 5.0% by mass based on the aromatic diamine component and colloidal silica having an average primary particle size of 80 nm before polymerization. It was added in an amount of 0.45% by mass based on the aromatic diamine component, and stirred at 30 ° C. or lower for 2 hours to obtain a polymerized polymer.

Next, 98.5 mol% of lithium carbonate was added to hydrogen chloride in the polymer polymer for 4 hours of neutralization, and 10 mol% of triethanolamine was added to hydrogen chloride in the polymer polymer. Then, the mixture was stirred for 1 hour to obtain an aromatic polyamide solution A having a polymer concentration of 10.8% by mass.

CPA corresponding to 85 mol% and DPE corresponding to 15 mol% were dissolved in NMP, and this solution was filtered through a filter made of polypropylene having a filtration accuracy of 1.0 μm, and then transferred to a polymerization tank. CTPC corresponding to 98.5 mol% passed through a filter made of polypropylene having a filtration accuracy of 1.0 μm was added, and the mixture was stirred at 30 ° C. or lower for 2 hours to obtain a polymerized polymer. Next, 98.5 mol% of lithium carbonate was added to hydrogen chloride in the polymer polymer to neutralize it for 4 hours, and silica having an average primary particle size of 16 nm (“AEROSIL” manufactured by Nippon Aerosil Co., Ltd.” R972 type) was added in an amount of 0.3% by mass to the polymer and stirred for 1 hour, and then 10 mol% of triethanolamine was added to hydrogen chloride in the polymer polymer and stirred for 1 hour. This was carried out to obtain an aromatic polyamide solution B having a polymer concentration of 10.8% by mass.

Next, the polymerized aromatic polyamide solution A is passed through a metal fiber filter made of stainless steel having a filtration accuracy of 1.0 μm, and the aromatic polyamide solution B is passed through a metal fiber filter made of stainless steel having a filtration accuracy of 5.0 μm. Laminated inside the base. At this time, the lamination ratio (thickness ratio) of the aromatic polyamide solutions A and B was set to 50% each.

B of the laminated aromatic polyamide solution was spread on the endless belt so as to be the belt surface, and heated with hot air at 120 ° C. for 2 minutes to evaporate the solvent, and a self-retaining film was continuously formed from the belt. Peeled off.

Next, the film body was introduced into the tank of the solvent extraction treatment apparatus, and water extraction of the residual solvent and the inorganic salt generated by neutralization was performed while stretching 1.15 times in the vertical direction, and the residue before the heat treatment step was performed. The solvent concentration was adjusted to 0% by mass.

After that, the obtained film body is gripped by a clip of a transverse stretching machine, and heat-treated with hot air for 3 seconds so that the surface temperature of the film becomes 270 ° C. while stretching 1.5 times in the width direction in the heat treatment step. After that, the mixture was slowly cooled at a rate of 20 ° C./sec to obtain an aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m. The thickness of this film is 3.6 μm, Young's modulus in the longitudinal direction is 10.3 GPa, Young's modulus in the width direction is 15.5 GPa, L value of the film is 46 to 47, and film density is 1.490 to 1.506 kg / m ³ , 60. The dimensional change rate of the film after being left at ° C. and 90% RH atmosphere for 10 days was 300 ppm in the longitudinal direction. The dimensional change rate of the 1,050 m magnetic tape produced using this film was good, and the servo tracking error occurrence rate was also good. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Example 2)
An aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m was obtained by forming a film in the same manner as in Example 1 except that the residual solvent concentration before the heat treatment step was adjusted to 4.8% by mass. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Example 3)
An aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m was obtained by forming a film in the same manner as in Example 1 except that the film was heat-treated with hot air so that the film surface temperature became 320 ° C. in the heat treatment step. .. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Example 4)
An aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m was obtained by forming a film in the same manner as in Example 1 except that the thickness of the final film was 2 μm. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Example 5)
An aromatic polyamide film roll having a film width of 1,050 mm and a length of 4,000 m was obtained by forming a film in the same manner as in Example 1 except that the thickness of the final film was 12 μm. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Example 6)
In the film forming process, the film is wound once in a roll shape without heat treatment, and then heat-treated with hot air for 3 seconds so that the surface temperature of the film becomes 270 ° C. To obtain an aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Comparative Example 1)
In the heat treatment step, an aromatic polyamide film roll having a film width of 1,050 mm and a length of 10,000 m was formed in the same manner as in Example 1 except that the film was heat-treated with hot air for 30 seconds so that the film surface temperature became 245 ° C. Obtained. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Comparative Example 2)
The film was formed in the same manner as in Example 1 except that the film was heat-treated with hot air so that the film surface temperature became 350 ° C. in the heat treatment step, but the film was partially carbonized and weakened due to excessive crystallization, and the film was broken at the time of slitting. Therefore, only an aromatic polyamide film roll having a length of 500 m could be obtained. It could not be used as a support for magnetic tape.

(Comparative Example 3)
The film was formed in the same manner as in Example 1 except that the residual solvent concentration before the heat treatment step was 15% by mass and the film surface temperature in the heat treatment step was heat-treated with hot air for 100 seconds so that the film surface temperature was 320 ° C. An aromatic polyamide film roll having a length of 10,000 m was obtained. Table 1 shows the physical properties of the obtained film and the evaluation results of the magnetic tape using this film.

(Comparative Example 4)
An aromatic polyamide film roll having a film width of 1,050 mm and a length of 3,000 m was obtained by forming a film in the same manner as in Example 3 except that the thickness of the final film was 20 μm. I tried to make it using this film, but it could not be more than 1,000 m per cartridge, and it could not be used as a support for high-capacity magnetic tape.

(Comparative Example 5)
A film was formed in the same manner as in Example 1 except that the thickness of the final film was set to 1.8 μm, but the film was too thin and had poor winding characteristics, and the film was wrinkled. Therefore, an aromatic polyamide film having a length of 100 m. I only got a roll. It could not be used as a support for magnetic tape.

Claims (4)

The amount of dimensional change in the film width direction after being left at 60 ° C. and 90% RH for 10 days is 500 ppm or less, the L value is 40 or more and 50 or less, and the thickness is 2 μm or more and 15 μm or less. Aromatic polyamide film for magnetic tape. An aromatic polyamide film roll for magnetic tape having a width of 1,000 mm or more and a length of 1,000 m or more, which is obtained by winding the aromatic polyamide film for magnetic tape according to claim 1. The method for producing an aromatic polyamide film for magnetic tape according to claim 1, wherein a heat treatment is performed in which the surface temperature of the aromatic polyamide sheet having a solvent content of less than 5% by mass is maintained at 270 ° C. or higher for 3 seconds or longer. .. A magnetic tape having a magnetic layer formed on at least one surface of the aromatic polyamide film for magnetic tape according to claim 1.