JP2015039801A - Laminate polyester film and coat-type magnetic recording tape using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film capable of exhibiting excellent electromagnetic conversion characteristics and error rate characteristics even when used for a coat-type magnetic recording tape.SOLUTION: The provided laminate polyester film is a base film used for a coat-type magnetic recording tape and consisting of at least two layers, namely a layer A forming the surface of the side where a magnetic layer is formed and a layer B forming the surface of the side where the magnetic layer is not formed, wherein the layer A includes 0.001-0.19 mass% of particles having an average diameter of 0.06-0.29 μm and a relative diameter standard deviation of 20% or below in a state where the textural index of the surface of the layer A is being confined to a range of 80-99.99%, wherein the layer B includes 0.03-0.9 mass% of particles having an average diameter identical to that of the layer A and a relative diameter standard deviation of 20% or below in a state where the content of the included particles is at least 1.5 times higher than that of the layer A, wherein the density of aggregated protrusions of five or more particles of the layer A is 3 protrusions/9 cmor less, and wherein the density of aggregated protrusions of five or more particles of the layer B is 10 protrusions/9 cmor less.

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, the demand for high-density recording in recent years is tremendous. Especially in MR heads and GMR heads, signals can be read by the instantaneous temperature rise caused by touching the protrusions on the surface of the magnetic recording medium due to its characteristics. Disappearance (thermal aspirity) phenomenon is known, and smoothness of the surface of the magnetic recording medium is particularly emphasized as a measure against thermal aspirity, especially coating type magnetic recording such as data storage with extremely high recording capacity In the case of a tape, even a film that has no surface defects in the above-mentioned Patent Documents 1 to 5 and a film that has a small amount of undulation in Patent Documents 6 to 7 cannot sufficiently respond.

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, dropout, and thermal aspiration.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention have included a specific ratio of particles having the same particle diameter on the surface on which the magnetic layer is formed and the surface on which the magnetic layer is not formed. The present inventors have found that it can be provided by improving the dispersibility of the polyester containing the particles on the surface forming the layer.

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. A laminated polyester film comprising layers,
A layer contains 0.001-0.19 mass% of particles having an average particle diameter of 0.06-0.29 μm and a relative standard deviation of the particle diameter of 20% or less, and the background index on the surface of the A layer is In the range of 80-99.99%,
On the other hand, the B layer on the side where no magnetic layer is formed contains 0.03-0.9% by mass of particles having the same average particle diameter as that of the A layer and a relative standard deviation of the particle diameter of 20% or less. The content is 1.5 times or more of the A layer, and the A layer has 3 aggregated projections of 5 or more particles / 9 cm ² or less, while the A layer has 10 aggregated projections of 5 or more particles of the B layer / A laminated polyester film that is 9 cm ² or less is provided.

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 intrinsic viscosity of the A layer is 0.50 or more and 0.00. 54, the intrinsic viscosity of the B layer is 0.50 or more and 0.54 or less, the intrinsic viscosity of the A layer is larger than that of the B layer, and the contained particles are spherical silica particles, crosslinked polystyrene particles, silicone particles, silica A laminated film comprising at least one of the car acryl composite particles is also provided.
Furthermore, according to the present invention, there is also provided a coating type magnetic recording tape comprising the above laminated polyester film of the present invention and 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 with excellent electromagnetic conversion characteristics, low error rate, dropout and thermal aspiration.

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 The copolymer may be copolymerized in the following range, or may be blended with another thermoplastic resin or the like in a range of, for example, 20% by mass or less, and further 10% by mass 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 where the magnetic layer is formed needs to contain 0.001-0.19 mass% of particles having an average particle diameter of 0.06-0.29 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. Furthermore, since the friction with the magnetic head is increased, the thermal aspiration may be deteriorated. 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 mass%, Preferably it is 0.003-0.15 mass%, More preferably, it is 0.005-0.10 mass%, Most preferably, it is 0.008. -0.06 mass%.

  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.

By the way, one of the features of the present invention is that the projections formed by five or more inert particles that have not been a problem until now when the background index described later is made extremely high while containing inert particles. This is because a new problem has been found that the ratio of the increase will increase. These protrusions are not so high as to generate missing pulses and error rates, but are larger than normal protrusions, and have been found to cause deterioration in thermal aspiration. They have also found that these problems can be resolved by reducing the number of aggregated projections of 5 or more particles in the A layer on the magnetic layer forming side to 3/9 cm ² or less. Further, from the same viewpoint, the aggregated protrusions in the B layer on the side where the magnetic layer is not formed have a considerable influence, and the aggregated protrusions of 5 or more particles in the B layer need to be 10/9 cm ² or less. If the aggregated protrusion of 5 or more particles in the A layer exceeds the upper limit, or if the aggregated protrusion of 5 or more particles in the B layer exceeds the upper limit, the thermal aspiration deteriorates. The upper limit of the aggregation protrusions of 5 or more particles in the preferred A layer is 2 or less, and further 1 or less. Moreover, the upper limit of the aggregation protrusion of 5 or more particles in a preferable B layer is 6 or less, and further 4 or less.

  The method for suppressing such aggregated protrusions is not particularly limited, but it is necessary to make the dispersibility of the particles to be contained extremely high. Selecting particles having good dispersibility as the particles to be contained, polyester for dispersing the particles As a polyester, in which particles are easy to disperse, to add particles at the time of polymerization in order to increase the dispersibility of the particles, and to separately perform melt-kneading to increase the dispersibility again. Preferably it is done.

  The cause of the dispersion of the polyester that easily disperses the particles when the particles are added during the polymerization is unknown. However, the polyester catalyst also affects the polyester. For example, it is not suitable for a reaction system that polymerizes using a manganese compound and an antimony compound. It is preferable to manufacture by adding active particles. Therefore, the A layer on the side forming the magnetic layer in the present invention preferably contains the manganese compound and the antimony compound. More preferably, not only the A layer but also the B layer contains the manganese compound and the antimony compound from the viewpoint of the dispersibility of the particles.

  The polyester composition produced by adding the above-mentioned inert particles may be used as the resin for the A layer as it is, but the polyester composition produced by adding the inert particles is used as a master polymer for the inert particles. It is preferable to dilute the polyester so as to have a desired amount of inert particles with a polyester containing no, since dispersibility can be further improved. The catalyst system of the diluted polymer is not particularly limited because it has a relatively small influence on the dispersibility of the inert particles, but it is preferable to use the same manganese compound and antimony compound as the master polymer.

From such a point of view, in the laminated polyester film of the present invention, the A layer on the side forming the magnetic layer contains a manganese compound and an antimony compound as catalyst residues, and the following formulas (I) to (I): It is preferable to contain in the range of II).
1 ≦ Mn ≦ 100 (I)
5 ≦ Sb ≦ 300 (II)
(In formula (I)-(II), Mn is the manganese element amount (ppm) of the manganese compound contained as the catalyst residue, and Sb is the manganese element amount (ppm) of the manganese compound contained as the catalyst residue. ) If Mn or Sb is less than the lower limit, the effect of improving the particle dispersibility is hardly exhibited, and if it exceeds the other upper limit, coarse foreign matters due to the catalyst residue are easily formed.

From such a viewpoint, the manganese element amount of the above formula (I) is preferably in the range of 1 to 100 ppm, more preferably 20 to 90 ppm, and particularly preferably 40 to 80 ppm. Moreover, by setting it as such a range, while promoting reaction rate, the production | generation of the coarse insoluble foreign material derived from a catalyst can be suppressed, and also the heat resistance of the copolymerized aromatic polyester obtained can be maintained highly. From the same viewpoint, the antimony element amount is preferably in the range of 5 to 300 ppm, more preferably 50 to 250 ppm, and particularly preferably 150 to 250 ppm. By being in the said range, the production | generation of the coarse insoluble foreign material resulting from a catalyst can be suppressed, promoting a reaction rate. In addition, the preferable polyester in this invention should just be a catalyst composition which satisfies the said Formula (I) and (II), and may use another catalyst together in the range which does not impair the objective of this invention. However, it is preferable to use these manganese compounds and antimony compounds so as to be 90% by mass or more of the total catalyst residue.
Specific examples of the manganese compound include manganese acetate. Specific examples of the antimony compound include antimony trioxide.

  Below, the manufacturing method of the laminated polyester film of this invention 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. As mentioned above, it is preferable to use a Mn compound for the purpose of improving the dispersibility of the particles.

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. Among them, at least an antimony compound can be used for the purpose of improving the dispersibility of the inert particles. preferable.

  In addition, regarding the method of containing particles, whether the particles are made into an alkylene glycol slurry state, coarse particles are reduced by a filter or the like, and added in the above-described polymerization step to create a polyester having a desired particle content. In order to reduce coarse protrusions due to aggregation of particles, a particle-containing master polyester having a particle content of 0.02 to 1.0% by mass is prepared and the master polyester is diluted with a polyester not containing particles. preferable. In the present invention, since a very high degree of particle dispersibility is required, the polyester composition containing the particles obtained by the above method is directly put into a melt-kneading extruder for forming a film. Instead, it is preferable to further improve the dispersibility of the particles through a separate melt-kneading process before that. As such a separate melt-kneading process, a method of separately melting and kneading the polyester composition containing particles before melt film formation may be used. The method used as a thing may be sufficient. In this case, as the separate melt-kneading, it is preferable to use a biaxial kneading extruder rather than a uniaxial kneading extruder because the dispersibility of the particles is easily improved.

  In addition, from the viewpoint of improving the dispersibility of particles by performing separate melt-kneading in this way, the obtained A layer, more preferably both the A layer and the B layer, have an intrinsic viscosity of the polyester constituting the film layer. It is preferably 0.50 dl / g or more and 0.54 dl / g or less, more preferably 0.51 dl / g or more and 0.53 dl / g or less. The intrinsic viscosity of the polyester of the A layer is preferably larger than the intrinsic viscosity of the B layer from the viewpoint of high shear during melt extrusion and advantageous particle dispersion.

  The polyester composition thus obtained is a stabilizer such as an ultraviolet absorber, an antioxidant, a plasticizer, a lubricant such as a wax, a flame retardant, a release agent, and a nucleating agent as long as the effects of the present invention are not impaired. , May be blended as necessary. 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 (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 film
The polyester on the film surface layer is removed by a plasma low temperature ashing method (for example, PR-503, manufactured by Yamato Kagaku) to expose the particles. 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) Number of aggregation protrusions The polyester on the film surface layer is removed by a plasma low-temperature ashing method (for example, PR-503, manufactured by Yamato Kagaku) to expose the particles. 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. The protrusions on the film surface generate voids around the particles due to stretching. If there is one particle in the void, it is not agglomeration. When there are five or more particles in the void, the projection is caused by aggregation, and aggregation projection of five or more particles occurs. Then, 100 voids were confirmed, and the number of aggregated protrusions of 5 or more particles present per 9 cm ² was calculated from the measurement area required for the voids.

(4) Catalyst residue The concentrations of manganese and antimony atoms as catalyst residues in the film were quantitatively analyzed with a fluorescent X-ray apparatus (Rigaku Corporation 3270E type).

(5) Content of particles (5-1) 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 (mass%) of the particles to the sample weight is used as the total particle content in each layer.

(5-2) 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.

(5-3) 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 (5-1) above, the content (% by mass) 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 (5-1), and measured by a method described in “Fine Particles Handbook: Asakura Shoten, 1991, p. 150”, for example, with a pycnometer. be able to.

(5-4) 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 (5-1) and the total content of inorganic particles in each layer determined in (5-2). The content of the organic particles and the inorganic particles in each is calculated, the content of the organic particles is the method of (5-3) above, and the content of the inorganic particles is the content of the method (5-2) above. (Mass%) is obtained.

(6) Thickness of film and each polyester layer (6-1) 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.

(6-2) 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.

(7) Young's modulus The 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. The film is pulled with an Instron type universal tensile tester under the 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.

(8) 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.

(9) 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.

(10) Coefficient of static friction of the film An acrylic plate fixed on the lower side of two films (each 20 cm in the vertical direction × 10 cm in the horizontal direction) on which the surface on the polyester A layer side and the surface on the polyester B layer side are placed, A thread is placed at the center of the upper side of the two overlapped films, fixed to the acrylic plate with the surface with the larger surface roughness facing down, and the acrylic plate is taken up with a low speed roll (10 cm). / Min), a detector is fixed to one end of the upper film (opposite to the take-off direction of the lower film), and the tensile force at the start of the film / film is detected. The thread used at that time has a weight of 200 g and a lower area of 50 cm ² (rectangle of 10 cm in the vertical direction × 5 cm in the horizontal direction).
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 increases, slipperiness decreases, and wrinkles and defects are likely to occur when the film is wound into a roll.

(11) 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, a load of 100 g, a speed of 10 mm / sec, a running length of 10 cm, and a repetition count of 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

(12) 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 Example and Comparative Example. 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

(13) 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 obtained with 0 dB as Example 9 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

(14) Error rate Data storage with an original tape produced in (12) slit to a width of 12.65 mm (1/2 inch) and incorporated into an LTO case, and the length of the magnetic recording tape is 850 m. 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 error rate 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

(15) Dropout (DO)
The data storage cartridge whose error rate was measured in the above (14) 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

(16) Thermal Asperity The reproduction signal is read from the data storage tape created above using an LTO5 drive manufactured by IBM in the same manner as the error rate. When a low frequency component of 500 kHz or less is generated in each read reproduction waveform, the low frequency component is counted as a thermal aspiration component and calculated by the following equation. The thermal aspiration is evaluated according to the following criteria.
Thermal aspiration = (The number of thermal aspirations) / (Number of reproduced waveforms)
A: Thermal aspiration is less than 1.0 × 10 ⁻⁴ ○: Thermal aspiration is 1.0 × 10 ⁻⁴ or more, less than 1.0 × 10 ⁻² ×: Thermal aspiration is 1.0 × 10 ⁻² that's all

[Example 1]
A mixture of 100 parts of 2,6-dimethylnaphthalate and 56 parts of ethylene glycol is charged with 0.0313 parts of manganese acetate tetrahydrate in a SUS (stainless steel) container capable of pressure reaction, and 0.07 MPa is added. The ester exchange reaction was carried out while increasing the pressure from 140 ° C. to 240 ° C., and then 0.042 part of triethylphosphonoacetate was added to complete the ester exchange reaction.
Thereafter, the reaction product is transferred to a polymerization vessel, heated to 290 ° C., 0.0239 parts of antimony trioxide is added, and a polycondensation reaction is carried out at a high vacuum of 100 Pa, an intrinsic viscosity of 0.62, a diethylene glycol amount of 1. A polyethylene-2,6-naphthalate resin composition for dilution (PEN-0) of 5 mol% (compared with 2,6-ethylene naphthalate component) was obtained.

In the same manner as above, a mixture of 100 parts of 2,6-dimethylnaphthalate and 56 parts of ethylene glycol was charged with 0.0313 parts of manganese acetate tetrahydrate in a SUS (stainless steel) container capable of pressure reaction. The ester exchange reaction was carried out while increasing the pressure from 140 ° C. to 240 ° C. under a pressure of 0.07 MPa, and then 0.042 parts of triethylphosphonoacetate was added to complete the ester exchange reaction.
Thereafter, the reaction product is transferred to a polymerization vessel, 0.01 mass% of spherical silica particles having an average particle size of 0.12 μm are added as a lubricant, the temperature is raised to 290 ° C., and 0.0239 parts of antimony trioxide is added. Polyethylene-2,6-naphthalate resin composition for layer A having an intrinsic viscosity of 0.62 and an amount of diethylene glycol of 1.5 mol% (compared to 2,6-ethylene naphthalate component) A product (PEN-A1) was obtained. Furthermore, PEN-A1 was melt-extruded again using a twin-screw kneading extruder (Kobe Steel, Ltd., model name: HYPERKTX) to obtain PEN-A1a with improved spherical silica dispersibility.
Further, a polyethylene-2,6-naphthalate resin composition for B layer (PEN-B1) is obtained in the same manner except that the amount of the spherical silica particles to be contained with PEN-A1 is changed to 1.0% by mass. It was. Furthermore, PEN-B1 was melt-extruded again using a twin-screw kneading extruder (Kobe Steel Corporation, model name: HYPERKTX) to obtain PEN-B1a with improved dispersibility of true spherical silica.

  For layer A, PEN-A1 was used alone, and for layer B, PEN-B1 and PEN-0 pellets were blended so that the amount of particles was 0.4% by weight. After these chips were dried at 170 ° C. for 6 hours, they were respectively supplied to two extruder hoppers, and were melted at 310 ° C. and sheeted from the die onto the cooling drum at a thickness ratio of A layer: B layer = 42: 58. To form a laminated unstretched polyester film. The laminated unstretched film was pulverized with a split cutter, and again melt-extruded with an extruder (Kobe Steel Works, model name: HYPERKTX) to prepare pellets. This pellet is designated as PEN-C1. And PEN-C1 and the PEN-0 for dilution were mix | blended, and the chip | tip for A layers with a total spherical silica particle density | concentration of 0.01 mass% was created. Further, PEN-C1 and PEN-B1 were blended so as to have a total true spherical silica particle concentration of 0.4% by mass to prepare a chip for B layer. Using these chips, after drying at 170 ° C. for 6 hours, each was supplied to two extruder hoppers and cooled from the die at a melting temperature of 310 ° C. at a thickness ratio of A layer: B layer = 42: 58 Coextruded into a sheet on a drum 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 99.00%.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 2]
Using a twin-screw kneading extruder (Kobe Steel Corporation, model name: HYPERKTX), PEN-A1 in Example 1 was melt-extruded again to obtain PEN-A1a with improved dispersibility of true spherical silica. It was. In addition, PEN-B1a in which PEN-B1 in Example 1 was melt-extruded again using a twin-screw kneading extruder (Kobe Steel Corporation, model name: HYPERKTX) to improve the dispersibility of true spherical silica. Got.
In Example 1, the same operation was repeated except that PEN-A1a was used instead of PEN-A1 and PEN-B1a was used instead of PEN-B1. Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 3]
In Example 2, the same operation was repeated except that silica-acrylic particles having an average particle diameter of 0.15 μm were used in place of the spherical silica particles and the particle content was changed to the amount shown in Table 1. It was. The silica-acrylic particles were used by replacing the dispersion medium of Soliostar SP-01 (5% solids aqueous dispersion) made by Nippon Shokubai with ethylene glycol. In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 4]
In Example 2, the same operation was repeated except that crosslinked polystyrene particles having an average particle diameter of 0.15 μm were used in place of the true spherical silica particles and the particle content was changed to the amount shown in Table 1. . In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 5]
In Example 2, the same operation was repeated except that the content of the spherical silica particles was changed to the amount shown in Table 1. In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 6]
In Example 2, the same operation was repeated except that cross-linked polystyrene particles having an average particle size of 0.06 μm were used instead of true spherical silica particles and the particle content was changed to the amount shown in Table 1. . In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 7]
In Example 2, the same operation was repeated except that cross-linked polystyrene particles having an average particle diameter of 0.24 μm were used instead of true spherical silica particles, and the content of the particles was changed to the amount shown in Table 1. . In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 8]
In Example 2, the same operation was repeated except that the content of the spherical silica particles in the A layer was changed to the amount shown in Table 1. In addition, adjustment of particle content was adjusted with the particle amount added at the time of superposition | polymerization.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Examples 9 and 10]
In Example 2, the same operation was repeated except that the blending ratio with PEN-0 was changed so that the content of the spherical silica particles in the B layer was the amount shown in Table 1.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Example 11]
In Example 2, the same operation was repeated except that the amount of catalyst was changed. In addition, the intrinsic viscosity of PEN-0, PEN-A1, and PEN-B1 was 0.60 dl / g, respectively.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 1]
A mixture of 100 parts of 2,6-dimethylnaphthalate and 56 parts of ethylene glycol is charged with 0.011 part of tetra-n-butyl titanate in a SUS (stainless steel) container capable of pressure reaction, and pressurized to 0.07 MPa. Then, the ester exchange reaction was carried out while raising the temperature from 140 ° C. to 240 ° C., and then 0.042 part of triethylphosphonoacetate was added to complete the ester exchange reaction.
Thereafter, the reaction product is transferred to a polymerization vessel, 0.01 mass% of true spherical silica particles having an average particle size of 0.12 μm are added as a lubricant, the temperature is raised to 290 ° C., and the polycondensation reaction is performed at a high vacuum of 100 Pa. A polyethylene-2,6-naphthalate resin (PEN-A2) composition for layer A having an intrinsic viscosity of 0.62 and a diethylene glycol amount of 1.5 mol% (compared to 2,6-ethylene naphthalate component) was obtained. In the same manner as above, a polyethylene-2,6-naphthalate resin (PEN-B2) composition for layer B is similarly used except that 1.0% by mass of spherical silica particles having an average particle size of 0.12 μm is added as a lubricant. Got. And operation similar to Example 1 was repeated except using PEN-A2 instead of PEN-A1, and PEN-B2 instead of PEN-B1.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 2]
In Example 2, PEN-0 was used instead of PEN-A1, and the same operation as in Example 2 was repeated except that no spherical silica particles were contained.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 3]
In Example 2, the same operation was repeated except that particles having an average particle diameter of 0.08 μm were used as true spherical silica particles and the particle content was changed to the amount shown in Table 1. In addition, the particle content was adjusted by adjusting the amount of particles added during polymerization for the A layer, and by adjusting the blending ratio with the PEN-0 for diluting the B layer.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 4]
In Example 3, the same operation was repeated except that the particle content of the A layer was changed to the amount shown in Table 1. The particle content was adjusted by the amount of particles added during polymerization.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 5]
In Example 4, instead of PEN-B1, PEN-B3 containing 1% by mass of crosslinked polystyrene particles having an average particle diameter of 0.12 μm and PEN containing 1% by mass of crosslinked polystyrene particles having an average particle diameter of 0.3 μm -B4 was prepared, and the same operation as in Example 4 was repeated except that these were blended so as to have the particle content in Table 1 instead of PEN-B1.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 6]
In Example 1, the same operation was repeated except that the blending ratio with PEN-0 was changed so that the content of the spherical silica particles in the B layer was the amount shown in Table 1.
Table 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Comparative Example 7]
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 2 shows the characteristics of the obtained laminated biaxially oriented polyester film.

  In Tables 1 and 2, true spherical silica means true spherical silica particles, silica-acryl means silica-acryl composite particles, and crosslinked polystyrene means crosslinked polystyrene particles.

  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, which is a laminated polyester film 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. There,
A layer contains 0.001-0.19 mass% of particles having an average particle diameter of 0.06-0.29 μm and a relative standard deviation of the particle diameter of 20% or less, and the background index on the surface of the A layer is 80 to 99.99% range,
On the other hand, the B layer on the side where no magnetic layer is formed contains 0.03-0.9% by mass of particles having the same average particle diameter as that of the A layer and a relative standard deviation of the particle diameter of 20% or less. The content is 1.5 times or more of the A layer, and the aggregation protrusions of 5 or more particles of the A layer are 3/9 cm ² or less, and the aggregation protrusions of 5 or more particles of the B layer are 10/9 cm. A laminated polyester film that is ² or less.   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 intrinsic viscosity of the A layer is 0.50 or more and 0.54 or less, the intrinsic viscosity of the B layer is 0.50 or more and 0.54 or less, and the intrinsic viscosity of the A layer is larger than that of the B layer. Laminated polyester film.   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.