JP5865749B2 - Laminated polyester film and coated magnetic recording tape using the same - Google Patents

Description

  The present invention relates to a laminated polyester film used for a base film of a coating type magnetic recording tape such as data storage.

  Polyester films have been used as base films for magnetic recording tapes because they are relatively inexpensive and have excellent mechanical properties. And when using for the base film of a magnetic-recording tape, it is calculated | required that a polyester film has a flat surface without a rough protrusion and a fault. On the other hand, in a coating type magnetic recording tape formed by applying a magnetic layer to a polyester film, a uniform magnetic layer cannot be efficiently produced if the winding property and running property of the base film are unstable. It is required that the polyester film contains particles as a lubricant to form protrusions on the surface. These two requirements are contradictory, and in order to satisfy these requirements, Patent Documents 1 to 5 disclose that the catalyst species should be specific in order to reduce surface defects, and particles to be included in the film. A film having a small number of coarse particles and a film having a small surface defect subjected to such a treatment have been proposed. Patent Documents 6 to 7 propose a biaxially oriented polyester film that is excellent in the stability of the original fabric shape and the electromagnetic conversion characteristics as a magnetic recording medium by reducing the undulation component of the base film focusing on the spatial frequency. Has been made.

  However, in recent years, the demand for high-density recording is tremendous. Particularly in the case of a coating type magnetic recording tape such as a data storage having a very high recording capacity, the film described in Patent Documents 1 to 5 described above that has no surface defects or Patent Documents 6 to 6 are used. Even the film that is said to have less undulation in 7 can no longer respond sufficiently.

JP 2004-114492 A JP 2003-291288 A JP 2002-36311 A JP 2002-363310 A JP 2002-059520 A JP 2001-341265 A JP 2004091753 A

  The object of the present invention is excellent in productivity as a film, has subsequent processability such as transportability, and has excellent electromagnetic conversion characteristics when used for a coating type magnetic recording tape, particularly a base film for data storage. An object of the present invention is to provide a laminated polyester film that can reduce error rate and dropout.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have provided the surface where the magnetic layer is formed and the surface where the magnetic layer is not formed by containing particles having a specific particle size in a specific ratio. We have found out that we can do it and have reached the present invention.

Thus, according to the present invention, there are two base films used for the coating type magnetic recording tape, that is, the A layer that forms at least the surface on which the magnetic layer is formed and the B layer that forms the surface on which the magnetic layer is not formed. The layer A has a single peak when viewing the particle size distribution , and particles having an average particle size of 0.06 to 0.29 μm and a relative standard deviation of the particle size of 20% or less are 0.001 to 0.001. 0.19% by weight and the background index on the surface of the layer A is in the range of 96 to 99.99%, and the layer B on the side not forming the magnetic layer has a single peak when the particle size distribution is seen. 0.03 to 0.9% by weight of particles having an average particle diameter equal to that of the A layer and having a relative standard deviation of the particle diameter of 20% or less, and the particle content is 1. A laminated polyester film that is 5 times or more is provided.

  Further, according to the present invention, as a preferred embodiment of the present invention, the polyester has ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate as a main repeating unit, and the thickness is 2.0 to 8.0 μm. Or a laminated polyester film comprising at least one of particles containing spherical silica particles, crosslinked polystyrene particles, silicone particles, silica-acrylic composite particles, and the laminated polyester film of the present invention, There is also provided a coated magnetic recording tape comprising a magnetic layer coated on the surface on which the magnetic layer is to be formed.

  Since the laminated polyester film of the present invention uses particles of the same particle diameter in any layer, the portion that did not become a product at the time of film production is recovered, and it can be recovered in any layer. While possessing workability such as transportability necessary for practical use, and even when used for coating type magnetic recording tapes, especially base films for data storage, even minute surface defects that cause errors are reduced. Therefore, it is possible to provide data storage having excellent electromagnetic conversion characteristics and low error rate and dropout.

Hereinafter, the present invention will be described in detail.
As the polyester in the present invention, a known polyester can be adopted as long as it can be formed into a film. For example, an aromatic polyester obtained by polycondensation of a diol component and an aromatic dicarboxylic acid component is preferable. Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the like. 6,6 ′-(alkylenedioxy) di-2-naphthoic acid. Examples of the diol component include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol.

  Among these, ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate is the main repeating unit from the viewpoint of dimensional stability during processing at high temperature, and ethylene-2,6-naphthalene is particularly preferable. Those having carboxylate as the main repeating unit are preferred. The term “main” as used herein means preferably 60 mol% or more, 70 mol% or more, 80 mol% or more, and more preferably 90 mol% or more.

  Further, from the viewpoint of further improving the dimensional stability against environmental changes, the 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component described in International Publication No. 2008/096612 pamphlet, 6,6 ′-( 6,6 ′-(alkylenedioxy) di-2-naphthoic acid components such as trimethylenedioxy) di-2-naphthoic acid component and 6,6 ′-(butylenedioxy) di-2-naphthoic acid component The thing copolymerized is also mentioned. The copolymerization amount of the (alkylenedioxy) di-2-naphthoic acid component is preferably in the range of 5 to 40 mol%, more preferably in the range of 6 to 35 mol%, particularly 7 to 7 mol, based on the number of moles of the total dicarboxylic acid component. It is in the range of 30 mol%. In the case of copolymerizing the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, an ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate component and 6,6 ′-(alkylenediene) The total amount of the (oxy) di-2-naphthoic acid component is preferably 90 mol% or more of the total acid component.

  When the polyester in the present invention does not contain a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, it is 6,6 ′-(alkylenedioxy) di- in o-chlorophenol at 35 ° C. When the 2-naphthoic acid component is contained, the intrinsic viscosity when measured in a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio) at 35 ° C. is 0. It is preferably 40 dl / g or more, more preferably 0.40 to 1.0 dl / g. If the intrinsic viscosity is less than 0.4 dl / g, cutting may occur frequently during film formation, or the strength of the product after forming may be insufficient. On the other hand, when the intrinsic viscosity exceeds 1.0 dl / g, productivity during polymerization is lowered.

  The melting point of the polyester in the present invention is preferably 200 to 300 ° C, more preferably 210 to 290 ° C, and particularly preferably 220 to 280 ° C. If the melting point is less than the lower limit, the heat resistance of the biaxially oriented film may be insufficient, and if the melting point exceeds the upper limit, the temperature during melt kneading becomes very high, which tends to cause thermal degradation.

  The polyester in the present invention is further copolymerized with other copolymer components known per se within a range not impairing the effects of the present invention, for example, 10 mol% or less, further 5 mol% with respect to the number of moles of repeating units. Copolymerization may be carried out in the following range, and other thermoplastic resins and the like may be blended in a range of, for example, 20% by weight or less, and further 10% by weight or less.

  By the way, although the laminated polyester film of the present invention can be produced from the above-mentioned polyester, it maintains a high level of electromagnetic conversion characteristics when data storage is performed while maintaining characteristics such as conveyance and winding within a practically acceptable range. From the viewpoint, the surface on the side on which the magnetic layer is formed needs to contain 0.001-0.19% by weight of particles having an average particle size of 0.07-0.29 μm. When the average particle size is smaller than this range or when the content is small, the transportability is deteriorated, and scratches called “scratches” are likely to enter the film, resulting in deterioration of error rate and dropout. In addition, when the particle diameter or content exceeds these ranges, for example, when used for a base film for data storage with a high recording density such as a storage capacity of 3 TB or more, the surface becomes too rough, and electromagnetic conversion characteristics deteriorate. End up. A preferable range of the average particle diameter is 0.07-0.29 μm, more preferably 0.08-0.24 μm. Moreover, the range of preferable content is 0.001-0.19 weight%, Preferably it is 0.003-0.15 weight%, More preferably, it is 0.005-0.10 weight%, Most preferably, it is 0.008. -0.06% by weight.

  As the particles to be contained, particles that do not contain coarse particles or contain very few particles are preferable. Therefore, particles that are easy to have a sharp particle size distribution curve and are likely to exist in the form of primary particles are preferable. Organic polymer particles such as silicone particles, crosslinked acrylic resin particles, crosslinked polyester particles, and crosslinked polystyrene particles, and spherical silica particles It is preferably at least one particle selected from the group consisting of composite particles of silica and organic polymer, and in particular, a group consisting of silicone particles, crosslinked polystyrene particles and spherical silica particles, and silica-acrylic composite particles It is preferably at least one kind of particle selected from Of course, when these particles are contained, it is preferable to filter with a filter, to treat the surface of the particles with a dispersant, or to enhance kneading with an extruder in order to eliminate coarse particles.

  These particles are preferably the same particle type in the A layer and the B layer, but the type may be different as long as the average particle diameter is the same. In addition, when the average particle diameter in the present invention is the same, when calculating the average particle diameter (μm) of the particles, the values up to two decimal places calculated by rounding off the third decimal place are the same, That is, it means that the average particle size is not different when the size is 0.01 μm or more.

  By the way, the above-mentioned particles are required to have a relative standard deviation of the particle size of all the particles as viewed from the particle size distribution curve of 20% or less, and further 15% or less. From such a viewpoint, it is preferable to have a single peak when viewing the particle size distribution curve. Whether or not there is a single peak is determined by creating a particle size distribution curve with the particle diameter on the horizontal axis and the particle frequency on the vertical axis, and when the measurement pitch of the particle diameter on the horizontal axis is 0.01 μm, there is only one peak. Even if there are a plurality of peaks, it means that there is no dent that is 50% or less with respect to the height of the lower peak between the peaks.

  The particles contained in the B layer have a content of 0.03 to 0.9% by mass, preferably 0.05 to 0.7% by mass, more preferably 0.10, based on the mass of the B layer. In the range of ˜0.6 mass%, the content is 1.5 times or more by mass ratio with respect to the particles contained in the A layer. Below this ratio, it is impossible to balance electromagnetic conversion characteristics, transportability, and windability. In addition, Preferably it is 2 times or more, Furthermore, it is 3 times or more. Further, the upper limit is not particularly limited as long as the content of particles contained in the B layer is in the above range.

  Below, the manufacturing method of a polyester film is demonstrated. First, the polyester production method of the present invention includes, for example, a first reaction in which an aromatic dicarboxylic acid or an ester-forming derivative thereof and an alkylene glycol are esterified or transesterified to synthesize a polyester precursor, and the precursor It consists of a second reaction in which the product is polycondensed, and a method known per se can be adopted.

  The preferable first reaction condition may be performed under normal pressure, but it is preferable to perform the reaction under a pressure of 0.05 MPa to 0.5 MPa because the reaction rate can be easily increased. Moreover, it is preferable to perform the temperature of 1st reaction in the range of 210 to 270 degreeC. By making the reaction pressure within the above range, it is possible to suppress the generation of by-products typified by dialkylene glycol while facilitating the progress of the reaction. At this time, the alkylene glycol component is preferably used in an amount of 1.1 to 6 moles relative to the acid component present in the reaction system in which the first reaction is carried out from the viewpoint of maintaining the reaction rate and the physical properties of the resin. More preferably, it is 2-5 mol times, More preferably, it is 3-5 mol times.

  Further, in order to increase the reaction rate of the first reaction, it is preferable to use a catalyst known per se, for example, a metal compound having a metal component such as Li, Na, K, Mg, Ca, Mn, Co, and Ti. Among these, when performing under pressure, Mn and Ti compounds are preferable from the viewpoint of easy progress of the reaction. In particular, a Ti compound is preferable because it can be used as a polycondensation reaction catalyst, and the catalyst residue is less precipitated. The titanium compound used in the present invention is preferably an organic titanium compound that is soluble in polyester from the viewpoint of suppressing the generation of insoluble coarse particles due to precipitation of catalyst residues. Particularly preferable examples of the titanium compound include titanium tetraisopropoxide, titanium tetrapropoxide, titanium tetrabutoxide, titanium tetraethoxide, titanium tetraphenoxide, and trimellitic acid titanium.

  The amount of catalyst to be added is preferably in the range of 10 to 150 mmol%, more preferably 20 to 100 mmol%, especially 30, in terms of metal elements, based on the number of moles of all acid components present in the first reaction. It is preferable to be in the range of ˜70 mmol% because the reaction rate can be promoted, the formation of coarse insoluble foreign matters due to the catalyst can be suppressed, and the heat resistance of the resulting copolymerized aromatic polyester can be maintained at a high level. In addition, when adding a titanium compound, it is preferable to add so that it may exist from the time of the esterification reaction start of a 1st reaction, and as above-mentioned, it uses continuously as a polycondensation reaction catalyst. Of course, it may be added in two or more times for the purpose of controlling the polycondensation reaction rate.

Next, the second reaction in which the precursor obtained in the first reaction is polycondensed will be described.
In the present invention, for the purpose of imparting a high degree of thermal stability to the obtained polyester, it is preferable to add a thermal stabilizer composed of a phosphorus compound to the reaction system before the start of the polycondensation reaction in the second reaction. The specific phosphorus compound is not particularly limited as long as it has a phosphorus element in the compound. For example, phosphoric acid, phosphorous acid, phosphoric acid trimethyl ester, phosphoric acid tributyl ester, phosphoric acid triphenyl ester, phosphorus Examples include acid monomethyl ester, phosphoric acid dimethyl ester, phenylphosphonic acid, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, ammonium phosphate, triethylphosphonoacetate, methyldiethylphosphonoacetate, and these phosphorus compounds May use 2 or more types together. The addition timing of the phosphorus compound is preferably performed during the initial stage of the polycondensation reaction, which is the second reaction after the first reaction is substantially completed, and the addition may be performed at one time or two or more times. You may divide into.

  By the way, the polycondensation reaction is preferably performed at a temperature in the range of 270 ° C. to 300 ° C., and the pressure during the polycondensation reaction is preferably performed under a reduced pressure of 50 Pa or less. If the pressure during the polycondensation reaction is higher than the upper limit, the time required for the polycondensation reaction becomes long and it becomes difficult to obtain a copolymerized aromatic polyester having a high degree of polymerization. As the polycondensation catalyst, known metal compounds such as Ti, Al, Sb, and Ge can be suitably used, and among them, it is a catalyst that the titanium compound added at the time of esterification reaction or transesterification reaction is used continuously. This is preferable because generation of insoluble coarse foreign matters due to the residue can be suppressed.

  In addition, as for the method of incorporating particles, as a slurry state of alkylene glycol, coarse particles are further reduced by a filter or the like, and added in the polymerization step, whereby particles having a particle content of 0.02 to 1.0% by weight. It is preferable to prepare a containing master polyester and dilute the master polyester with a polyester containing no particles in order to reduce coarse protrusions due to aggregation of particles.

  The polyester thus obtained contains a stabilizer such as an ultraviolet absorber, a lubricant such as an antioxidant, a plasticizer, and a wax, a flame retardant, a release agent, and a nucleating agent as long as the effects of the present invention are not impaired. You may mix | blend as needed. In addition, from the viewpoint of making the background index on the surface on the side where the magnetic layer is formed into a desired range, other thermoplastic polymers that are incompatible with polyester, pigments, fillers, glass fibers, carbon fibers, layered silicates, etc. Is preferably not contained.

  By the way, the background index of the surface forming the magnetic layer of the laminated polyester film of the present invention is in the range of 80 to 99.99%. More preferably, it is in the range of 85 to 99.5%, particularly preferably in the range of 90 to 99.5%, and most preferably in the range of 96 to 99.5%. The background index is a value measured by a non-contact type three-dimensional surface roughness meter, and is a numerical value indicating the area ratio of the surface excluding protrusions and dents on the film surface. It is one of the features of the present invention that the background index is closely related to the electromagnetic conversion characteristics and the error rate after storage of the tape cartridge. When the background index is in the above range, it is possible to achieve both high transportability and the like while reducing the electromagnetic rate and the error rate after storing the tape cartridge.

  In order to make such a background index within a desired range, it is effective to mix the particles on the rough surface layer side within the above-mentioned range, but in addition, the stretching temperature is set in the production process of the laminated polyester film. It is also very effective to stretch the film under the conditions described later. In order to increase the background index, it is sufficient to select conditions such as stretching at a temperature at which the viscoelasticity is as low as possible during transverse stretching of the film and at a relatively high temperature at which the crystal does not progress instantaneously at that temperature itself. On the other hand, if it is desired to reduce the stretching temperature, a condition for lowering the stretching temperature may be selected, such as stretching at a temperature at which a decrease in viscoelasticity starts during transverse stretching of the film.

  The laminated polyester film of the present invention is prepared, for example, by preparing a polymer for the polyester A layer and a polymer for the polyester B layer forming the opposite surface, and laminating these in a molten state and coextruding them from a die into a sheet. It can manufacture by extending | stretching the process of making a lamination | stacking unstretched polyester film and the obtained lamination | stacking unstretched polyester film in a film forming direction and the width direction by cooling and solidifying the obtained sheet-like material. The temperature in the process of extruding in a molten state is not particularly limited as long as there is no unmelted material and the temperature of the polyester does not excessively deteriorate. For example, the melting point of the polyester (Tm: ° C.) to (Tm + 70) ° C. It is preferable to carry out at temperature. Next, for cooling, in order to reduce the thickness unevenness while maintaining the flatness of the obtained laminated unstretched polyester film, a rotating cooling drum installed below the die along the film forming direction is used. It is preferable to cool the sheet-like material in close contact with it. Subsequently, for stretching, the laminated unstretched polyester film is uniaxially (longitudinal or transverse) (polyester glass transition temperature (Tg) −10) ° C. to (Tg + 60) ° C. to 2.5 times or more. Preferably, the film is stretched at a magnification of 3 times or more, and then stretched at a temperature of Tg to (Tg + 60) ° C. at a temperature of 2.5 times or more, preferably at a magnification of 3 times or more in the direction orthogonal to the stretching direction. At this time, in order to keep the above-mentioned background index within a desired range, it is desirable that the transverse stretching temperature is stretched in the range of (Tg + 25) to (Tg + 60 ° C.). More preferred is (Tg + 30) to (Tg + 60 ° C.), particularly preferred is (Tg + 30) to (Tg + 55 ° C.), and most preferred is a range of (Tg + 35) to (Tg + 55 ° C.). At this time, the transverse stretching temperature is preferably increased stepwise, and any temperature is preferably within the above range. If the transverse stretching temperature is too low with respect to Tg, excessive stretching stress concentrates on the particles, and as a result, the voids around the particles become larger and the protrusions are higher and larger. On the other hand, when mildly stretched in the temperature range described above, the rough surface layer side can be flattened by simultaneously increasing the transverse stretch ratio higher than usual, and as a result, it has a desired height and size. Protrusions can be formed.

  Further, if necessary, the film may be stretched again in the machine direction and / or the transverse direction. The total draw ratio when stretched in this way is preferably 9 times or more, more preferably 12 to 35 times, and particularly preferably 15 to 30 times as an area draw ratio (longitudinal draw ratio x transverse draw ratio). . Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tm-70) to (Tm-10) ° C., and is preferably heat-set at, for example, 180 to 250 ° C. The heat setting time is preferably 0.1 to 60 seconds. Moreover, although the above-mentioned extending | stretching was demonstrated by sequential biaxial stretching, you may use simultaneous biaxial stretching which extends | stretches simultaneously in the vertical direction and a horizontal direction.

  The laminated polyester film of the present invention has a longitudinal Young's modulus of 3 to 10 GPa, more preferably 3.5 to 9 GPa, particularly in order to develop excellent dimensional stability when used as a base film of a high-density magnetic recording medium. It is preferably 4 to 8 GPa. On the other hand, the Young's modulus in the width direction is 4 to 15 GPa, more preferably 5 to 14 GPa, particularly 6 to 13 GPa, most preferably 7 to 11 GPa, from the viewpoint of easily setting the temperature expansion coefficient of the base film to the range described later. It is preferable. If the Young's modulus in the width direction is less than the lower limit, it is difficult to reduce the temperature expansion coefficient when the magnetic recording tape is used. On the other hand, if the upper limit is exceeded, the temperature expansion coefficient when the magnetic recording tape is used becomes excessively small. End up.

  The total thickness of the laminated polyester film of the present invention is preferably 2.0 to 8.0 μm. More preferably, it is 2.5-7 micrometers, More preferably, it is 3-6 micrometers, Most preferably, it is 3.0-4.5 micrometers. When the thickness is smaller than the lower limit, the tape becomes dull and electromagnetic conversion characteristics deteriorate. When the thickness exceeds the upper limit, the tape length per one tape is shortened, so that it is difficult to reduce the size and increase the capacity of the magnetic tape.

  Moreover, the laminated polyester film of the present invention has a thickness of 20 to 99% with respect to the thickness of the laminated polyester film, when the polyester layer forming the surface on the flat layer side forming the magnetic layer is an A layer. Furthermore, it is preferable to be in the range of 30 to 98%, particularly 40 to 97%. When the A layer is less than the lower limit with respect to the total thickness, the particles included in the polyester layer (B layer) on the rough surface layer that does not form the magnetic layer are generated, and the electromagnetic conversion characteristics are likely to deteriorate. On the other hand, dropping the particles contained in the A layer can be suppressed by making the thickness of the A layer below the upper limit. Normally, if the recovered resin is reused without impairing the flatness of the surface of the A layer, it can be used only for the B layer, and can be reused by reducing the thickness of the B layer as described above. The rate drops extremely. However, in the present invention, since both the A layer and the B layer contain particles having the same particle diameter, they can be used for any layer, and can be reused even if the A layer is thick and the B layer is extremely thin. The ratio can be kept very high.

  The laminated polyester film of the present invention is preferably used as a base film of a high-density magnetic recording tape, particularly a digital recording magnetic recording tape. Therefore, the magnetic recording medium using the laminated polyester film of the present invention will be further described.

  The magnetic recording medium of the present invention can be produced by forming a magnetic layer on the above-described laminated polyester film. In addition, on the surface of the laminated polyester film of the present invention, in order to improve the adhesiveness with a magnetic layer or the like, a coating layer having a well-known easy-adhesion function, etc., as long as the effect of the present invention is not impaired. It may be formed.

  The magnetic layer in the magnetic recording tape of the present invention is prepared by uniformly dispersing iron or acicular fine magnetic powder or barium ferrite in a binder such as polyvinyl chloride or a vinyl chloride / vinyl acetate copolymer. As described above, by using the laminated polyester film of the present invention, a magnetic recording tape excellent in dimensional stability, electromagnetic conversion characteristics and error rate performance can be obtained. .

  In addition, it is excellent in electromagnetic conversion characteristics such as output in a short wavelength region, S / N, C / N, etc., particularly when the magnetic layer is applied so that the thickness is 1 μm or less, and further 0.1 to 1 μm. This is preferable from the viewpoint of a coating type magnetic recording tape for high density recording with low dropout and error rate. If necessary, it is also preferable to disperse and coat a nonmagnetic layer containing fine titanium oxide particles or the like in the same organic binder as that of the magnetic layer as the underlayer of the coating type magnetic layer.

Further, a protective layer such as diamond-like carbon (DLC) and a fluorine-containing carboxylic acid-based lubricating layer are sequentially provided on the surface of the magnetic layer as required, and a known backcoat layer is provided on the other surface. May be provided.
The coating type magnetic recording tape thus obtained is extremely useful as a magnetic tape for data use such as data 8 mm, DDSIV, DLT, S-DLT, LTO and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The characteristics of the polyester, laminated polyester film and data storage in the present invention were measured and evaluated by the following methods.

(1) Intrinsic viscosity As described above, the intrinsic viscosity of the obtained polyester is measured at o-chlorophenol at 35 ° C. When it is difficult to dissolve uniformly with o-chlorophenol, p-chlorophenol / It was determined by measurement at 35 ° C. using a mixed solvent of 1,1,2,2-tetrachloroethane (40/60 weight ratio).

(2) Particle size, average particle size, and relative standard deviation of particle size in the film Polyester on the film surface layer is removed by a plasma low-temperature ashing method (for example, PR-503, manufactured by Yamato Kagaku), and the particles are removed. Expose. The treatment conditions are such that the polyester is ashed but the particles are not damaged. This is observed with a SEM (scanning electron microscope) at a magnification of about 10,000 times, and an image of the particle (light density produced by the particle) is connected to an image analyzer (for example, QTM900, manufactured by Cambridge Instrument) The observation area is changed, and the area equivalent circle diameter (Di) of at least 5,000 particles is obtained. From this result, a particle size distribution curve was created, the number average was taken as the average particle size, and the value obtained by dividing the standard deviation of the particle size by the average particle size was taken as the relative standard deviation. The identification of the particle type can be performed using SEM-XMA, quantitative analysis of metal elements by ICP, or the like. Further, the average particle size of the particles to be added was calculated by performing the same measurement.

(3) Content of particles (3-1) Total content of particles in each layer The polyester A layer and the polyester B layer were sampled by scraping about 100 g each from the laminated biaxially oriented polyester film, the polyester was dissolved, and the particles were After selecting the solvent not to be dissolved and dissolving the sample, the particles are centrifuged from the polyester, and the ratio of the particles to the sample weight (% by weight) is the total particle content in each layer.

(3-2) Total content of inorganic particles in each layer When inorganic particles of the laminated polyester film are present, the polyester A layer and the polyester B layer are each scraped and sampled about 100 g, and this is sampled in a platinum crucible. Burn in a furnace at about 1,000 ° C. for 3 hours or more, then mix the burned product in the crucible with terephthalic acid (powder) to make a 50 gram tablet plate. The plate is converted from a calibration curve for each element in which the count value of each element is prepared in advance using wavelength-dispersed fluorescent X-rays, and the total content of inorganic particles in each layer is determined. The X-ray tube for measuring fluorescent X-rays is preferably a Cr tube and may be measured with an Rh tube. The X-ray output is set to 4 kW, and the spectral crystal is changed for each element to be measured. When there are a plurality of types of inorganic particles of different materials, the content of the inorganic particles of each material is determined by this measurement.

(3-3) Content of various particles in each layer (when no inorganic particles are present)
When inorganic particles are not present in the layer, the weight ratio of the particles present in each peak region is calculated from the number ratio of each particle constituting the peak determined in (2) above, the average particle diameter and the density of the particles, From this and the total content of particles in each layer determined in (3-1) above, the content (% by weight) of particles present in each peak region is determined.
The typical fine particle density is as follows.
Density of crosslinked silicone resin: 1.35 g / cm ³
Cross-linked polystyrene resin density: 1.05 g / cm ³
Cross-linked acrylic resin density: 1.20 g / cm ³
The resin density is further determined by separating the particles centrifuged from the polyester by the method (3-1), and measured by a method described in “Fine Particles Handbook: Asakura Shoten, 1991 edition, page 150”, for example, with a pycnometer. be able to.

(3-4) Content of various particles in each layer (when inorganic particles are present)
When inorganic particles are present in the layer, the layer is determined from the total content of particles in each layer determined in (3-1) and the total content of inorganic particles in each layer determined in (3-2). The content of the organic particles and the inorganic particles in each is calculated, the content of the organic particles is the method (3-3), and the content of the inorganic particles is the method (3-2). (Wt%) is determined.

(4) Thickness of film and each polyester layer (4-1) Thickness of film 10 films are stacked so that dust does not enter, the thickness is measured with a dot-type electronic micrometer, and the film thickness per sheet is calculated. To do.

(4-2) Thickness of each polyester layer Using a secondary ion mass spectrometer (SIMS), an element caused by the highest concentration of particles in the film ranging from the surface layer to a depth of 3,000 nm The concentration ratio (M + / C +) of the carbon element in the polyester is defined as the particle concentration, and analysis in the thickness direction is performed from the surface to a depth of 3,000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. And the particle concentration once reached the maximum value starts to decrease again. Based on this concentration distribution curve, a depth at which the surface layer particle concentration is ½ of the maximum value (this depth is deeper than the depth at which the maximum value is reached) is determined, and this is defined as the surface layer thickness. Then, the thickness of each layer is calculated from the thickness of the film and the thickness of the surface layer.
The conditions are as follows.
(A) Measuring device: secondary ion mass spectrometer (SIMS)
(B) Measurement conditions Primary ion species: O ²⁺
Primary ion acceleration voltage: 12KV
Primary ion current: 200 nA
Raster area: 400 μm
Analysis area: 30% gate
Measurement degree of vacuum: 0.8 Pa (6.0 × 10 ⁻³ Torr)
E-GUN: 0.5KV-3.0A
In addition, when the most contained particles in the range from the surface layer to a depth of 3000 nm are organic polymer particles, it is difficult to measure by SIMS, so XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy) while etching from the surface. The depth profile similar to the above may be measured by the method) to obtain the surface layer thickness.

(5) Young's modulus A film is cut into a sample width of 10 mm and a length of 15 cm, and the distance between chucks is set to 100 mm, and the film is pulled with an Instron type universal tensile testing device under conditions of a tensile speed of 10 m / min and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent of the rising portion of the obtained load-elongation curve.

(6) Surface roughness (Ra)
Measured using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022) at a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ), and incorporated in the roughness meter The center surface average roughness (Ra) was determined by the surface analysis software Metro Pro, which was defined as the surface roughness (Ra). The measurement was performed 10 times while changing the measurement location, and the average value thereof was defined as the center plane average roughness (Ra). The surface roughness of the flat side (A layer side) of the laminated polyester film was RaA, and the surface roughness of the rough side (B layer side) was RaB.

(7) Background Index After measuring Ra under the condition (6) above using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022), the software Metro Pro built in the roughness meter By drawing a line that is 5 nm away from the center line on the surface in the height direction on the convex side and the concave side, respectively, a thing having a height higher than that is recognized as a protrusion, and further has an area of 0.5 μm ² or more The protrusions were counted as the number of protrusions. The projection areas of all the projections were totaled, and a value obtained by subtracting the measurement area 283 μm × 213 μm = (0.0603 mm ² ) as a percentage of the measurement area was determined as the background index in the present invention. In addition, the measurement was performed 10 times while changing the measurement location, and the average value thereof was used as the background index.

(8) Coefficient of static friction of the film A glass plate fixed on the lower side of two films obtained by superimposing the surface on the polyester A layer side and the surface on the polyester B layer side is placed, and the lower side of the laminated film (glass plate The film in contact with the film) with a low speed roll (10 cm / min), and the detector is fixed to one end of the upper film (the opposite end to the direction of the lower film). Detects the tensile force at the start. The thread used at that time has a weight of 200 g and a lower area of 50 cm ² .
The static friction coefficient (μs) was obtained from the following equation.
μs = (Tensile force at start g) / (Load 200 g)
When the static friction coefficient of the film exceeds 1.0, the slipperiness is extremely lowered, and when the film is rolled up, wrinkles and defects are likely to occur, which is not preferable.

(9) Running film sticking test Using a commercially available friction tester, a film having a width of 12.7 mm and a length of 30 cm was prepared as a test piece, and the load was 100 g, the speed was 10 mm / sec, the running length was 10 cm, and the number of repetitions was 30 times. Under the conditions, the flat surface side of the film was run at a holding angle of 90 ° on a chromium-plating metal guide roller having a roughness of 19 nm and a diameter of 6 mm. When running, the running was stable, but when the film after running was observed with a stereomicroscope, there were 5 or less scratches with a length of 1 cm or more, and the film stuck to the metal guide roller A case where running was unstable or an innumerable number of scratches from 5 was evaluated as x.
○: Sticking does not occur and film conveyance is stable, and there are no scratches with a length of 1 cm or more. Δ: Sticking does not occur, film transportation is stable, and there are five or less scratches with a length of 1 cm or more. , Film transport is unstable, or more than 5 scratches

(10) Preparation of magnetic tape A back coat layer paint having the following composition was applied to the surface of the rough surface layer (A layer) of the laminated biaxially oriented polyester film having a width of 1000 mm and a length of 1000 m obtained in each of Examples and Comparative Examples. After coating and drying with a die coater (tension during processing: 20 MPa, temperature: 120 ° C., speed: 200 m / min), a non-magnetic paint or magnetic paint having the following composition on the surface of the flat layer (B layer) side of the film Is applied at the same time with a die coater while changing the film thickness, magnetically oriented and dried. Further, after calendering with a small test calender (steel roll / nylon roll, 5 stages) at a temperature of 70 ° C. and a linear pressure of 200 kg / cm, curing is performed at 70 ° C. for 48 hours. The tape was slit to 12.65 mm and incorporated into a cassette to obtain a magnetic recording tape. The coating amount was adjusted so that the thicknesses of the dried backcoat layer, nonmagnetic layer and magnetic layer were 0.5 μm, 1.2 μm and 0.1 μm, respectively.

<Composition of non-magnetic paint>
-Titanium dioxide fine particles: 100 parts by weight-Esreck A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight-Nipponran 2304 (Nippon Polyurethane Polyurethane Elastomer): 10 parts by weight-Coronate L (Nippon Polyurethane Poly Isocyanate): 5 parts by weight, lecithin: 1 part by weight, methyl ethyl ketone: 75 parts by weight, methyl isobutyl ketone: 75 parts by weight, toluene: 75 parts by weight, carbon black: 2 parts by weight, lauric acid: 1.5 parts by weight <magnetic Composition of paint>
Iron (major axis: 0.037 μm, needle ratio: 3.5, 2350 oersted): 100 parts by weight Eslek A (vinyl chloride / vinyl acetate copolymer made by Sekisui Chemical: 10 parts by weight) Nipponan 2304 (Nippon Polyurethane) Polyurethane elastomer): 10 parts by weight, Coronate L (polyisocyanate made by Nippon Polyurethane): 5 parts by weight, lecithin: 1 part by weight, methyl ethyl ketone: 75 parts by weight, methyl isobutyl ketone: 75 parts by weight, toluene: 75 parts by weight, carbon Black: 2 parts by weight ・ Lauric acid: 1.5 parts by weight <Composition of back coat layer paint:>
Carbon black: 100 parts by weight Thermoplastic polyurethane resin: 60 parts by weight Isocyanate compound: 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)
Silicone oil: 0.5 parts by weight Methyl ethyl ketone: 250 parts by weight Toluene: 50 parts by weight

(11) Electromagnetic conversion characteristics For measuring the electromagnetic conversion characteristics, a 1/2 inch linear system with a fixed head was used. Recording was performed using an electromagnetic induction head (track width 25 μm, gap 0.1 μm), and reproduction was performed using an MR head (8 μm). The relative speed of the head / tape is 10 m / sec, a signal with a recording wavelength of 0.2 μm is recorded, the reproduced signal is analyzed with a spectrum analyzer, the output C of the carrier signal (wavelength 0.2 μm), and the integration over the entire spectrum. The noise N ratio was defined as C / N ratio, and a relative value was determined with 0 dB as Example 4 created by the above method 10, and evaluated according to the following criteria.
◎: +1 dB or more ○: −1 dB or more, less than +1 dB ×: less than −1 dB

(12) Error rate Data storage with the length of the magnetic recording tape of 850 m, slitting the original tape produced in (10) above to a width of 12.65 mm (1/2 inch) and incorporating it into an LTO case. A cartridge was created. This data storage was recorded using an IBM LTO5 drive in an environment of 23 ° C. and 50% RH (recording wavelength 0.55 μm), and then the cartridge was stored in an environment of 50 ° C. and 80% RH for 7 days. After the cartridge was stored at room temperature for one day, the full length was reproduced, and the error rate of the signal at the time of reproduction was measured. The error rate is calculated from the error information (number of error bits) output from the drive by the following formula. The dimensional stability is evaluated according to the following criteria.
Error rate = (number of error bits) / (number of write bits)
A: Error rate is less than 1.0 × 10 ⁻⁶ ○: Error rate is 1.0 × 10 ⁻⁶ or more, less than 1.0 × 10 ⁻⁴ ×: Error rate is 1.0 × 10 ⁻⁴ or more

(13) Dropout (DO)
The data storage cartridge whose error rate was measured in the above (12) was loaded into an IBM LTO5 drive, a data signal was recorded at 14 GB, and it was reproduced. A signal having an amplitude (PP value) of 50% or less with respect to the average signal amplitude was detected as a missing pulse, and four or more consecutive missing pulses were detected as dropouts. In addition, dropout evaluates 1 volume of 850m, converts into the number per 1m, and determines by the following references | standards.
◎: Dropout less than 3 pieces / m ○: Dropout of 3 pieces / m or more, less than 9 pieces / m ×: Dropout of 9 pieces / m or more

[Example 1]
Polyethylene-2,6-naphthal for polyester A layer having an intrinsic viscosity of 0.62 and containing 0.03% by weight of true spherical silica particles (particle A) having an average particle diameter of 0.08 μm as particles to be added to the flat layer side As phthalate pellets (glass transition temperature: 121 ° C., melting point: 265 ° C.) and particles to be added to the rough surface layer side, 0.30% by weight of spherical silica particles (particles B1) having an average particle size of 0.08 μm were contained. Polyethylene-2,6-naphthalate pellets (glass transition temperature: 121 ° C., melting point: 265 ° C.) for polyester B layer having an intrinsic viscosity of 0.62 were prepared. Each pellet was dried at 170 ° C. for 6 hours, and then supplied to two extruder hoppers, respectively, at a melting temperature of 310 ° C., and a thickness ratio of A layer: B layer = 42: 58 from the die onto the cooling drum. The sheet was coextruded to obtain a laminated unstretched polyester film.
The laminated unstretched polyester film thus obtained was preheated to 120 ° C. and heated from above with an IR heater so that the film surface temperature was 140 ° C. Stretching in the film direction) was performed. Subsequently, it is supplied into a stenter heated to 155 ° C., and is stretched 5.3 times in the lateral direction (first stage) while being gradually increased to 165 ° C. and 170 ° C., and further heated to 180 ° C. After being supplied into the stenter and stretched 1.2 times in the transverse direction again, it was heat-fixed with hot air at 210 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 3.8 μm. The Young's modulus of the obtained laminated biaxially oriented polyester film was 6.0 GPa in the vertical direction and 9.1 GPa in the horizontal direction. The background index of the polyester A layer was 98.51%.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Examples 2-3 and Comparative Examples 1-3]
The same operation as in Example 1 was repeated except that the particle A, the particle B1, and the thickness of each layer were changed as shown in Table 1. Here, the silica-acrylic particles were used for polymerization after substituting the dispersion medium of Soliostar SP-01 manufactured by Nippon Shokubai (5% solid content aqueous dispersion, particle size 0.15 μm) with ethylene glycol.

[Example 4]
Polyethylene-terephthalate pellets for polyester A layer containing 0.01% by weight of true spherical silica particles (particle A) having an average particle diameter of 0.20 μm and particles added to the flat layer side (glass transition) (Temperature: 76 ° C., melting point: 255 ° C.) As a particle to be added to the rough surface layer side, 0.15% by weight of true spherical silica particles (particle B1) having an average particle diameter of 0.20 μm were contained, and the intrinsic viscosity was 0.00. 62 polyethylene-terephthalate pellets (glass transition temperature: 76 ° C., melting point: 255 ° C.) for polyester B layer were prepared. Each pellet was dried at 170 ° C. for 3 hours, and then supplied to two extruder hoppers, respectively, at a melting temperature of 280 ° C., and a thickness ratio of A layer: B layer = 42: 58 from the die onto the cooling drum. The sheet was coextruded to obtain a laminated unstretched polyester film.
The laminated unstretched polyester film thus obtained was preheated to 75 ° C. and heated from above with an IR heater so that the film surface temperature was 90 ° C., and stretched in the machine direction (manufactured at a stretch ratio of 4.8 times). Stretching in the film direction) was performed. Subsequently, it was supplied into a stenter heated to 120 ° C., and while being stepwise raised to 125 ° C. and 130 ° C., it was stretched 5 times in the transverse direction (first stage) and further heated to 180 ° C. After being supplied into the stenter and stretched 1.2 times in the transverse direction again, it was heat-fixed with hot air at 210 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.3 μm. The Young's modulus of the obtained laminated biaxially oriented polyester film was 5.4 GPa in the vertical direction and 7.3 GPa in the horizontal direction.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Examples 5 to 7 and Comparative Example 4]
The same operation as in Example 4 was repeated except that the particle A, the particle B1, and the thickness of each layer were changed as shown in Table 1. Here, the silica-acrylic particles were used for polymerization after substituting the dispersion medium of Soliostar SP-01 manufactured by Nippon Shokubai (5% solid content aqueous dispersion, particle size 0.15 μm) with ethylene glycol. In Comparative Example 4, as shown in Table 1, the B layer contained two kinds of crosslinked polystyrene particles having different particle diameters.

[Comparative Example 5]
In Example 1, with respect to the stretching conditions, the same operation was repeated except that the transverse stretching temperature before transverse stretching again was changed to the conditions of stepwise increasing the temperature to 125 ° C, 130 ° C, and 160 ° C. Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

  The biaxially oriented laminated polyester film of the present invention has few errors and dropouts when used as a magnetic recording medium, and can exhibit excellent electromagnetic conversion characteristics, so that it can be used for high-density magnetic recording media, particularly digital recording magnetic recording tapes. It can be suitably used as a base film.

Claims (5)

A base film used for a coating type magnetic recording tape, comprising at least two layers of an A layer that forms a surface on which a magnetic layer is formed and a B layer that forms a surface on which a magnetic layer is not formed,
The layer A has a single peak when viewing the particle size distribution, and has an average particle size of 0.06 to 0.29 μm, and particles having a relative standard deviation of the particle size of 20% or less are 0.001 to 0.19 weight. The background index on the surface of the A layer is in the range of 96 to 99.99%, and the B layer on the side not forming the magnetic layer has a single peak when the particle size distribution is seen , The average particle diameter is the same as that of the A layer, and 0.03 to 0.9% by weight of particles having a relative standard deviation of the particle diameter of 20% or less, and the particle content is 1.5 times or more of the A layer. A laminated polyester film.   The laminated polyester film according to claim 1, wherein the polyester comprises ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate as a main repeating unit.   The laminated polyester film according to claim 1, which has a thickness of 2.0 to 8.0 µm.   The laminated polyester film according to claim 1, wherein the contained particles are any of spherical silica particles, crosslinked polystyrene particles, silicone particles, and silica-acryl composite particles.   5. A coating type magnetic recording tape comprising the laminated polyester film according to claim 1 and a magnetic layer coated on the surface on which the magnetic layer is formed.