JP6087529B2 - Biaxially oriented laminated polyester film and coating type magnetic recording tape using the same - Google Patents

Description

  The present invention relates to a biaxially oriented laminated polyester film that has an extremely flat surface and excellent workability at high temperatures, such as a base film of a coating type magnetic recording tape for 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 coating a magnetic layer on a polyester film, a uniform magnetic layer is efficiently produced if the winding property of the base film and handling properties in the coating process are unstable. In other words, 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 purpose of the present invention is to form a coating film layer with a very flat surface at a high speed, and it is necessary to dry the coating film layer at a higher temperature. Although there is a considerable limitation on speeding up, the surface roughness is 1.5 nm or less, but the surface roughness due to transfer is small and exceeds the glass transition temperature of polyester, for example. An object of the present invention is to provide a biaxially oriented laminated polyester film that is excellent in processability at such a high temperature.

  As a result of diligent research to solve the above-mentioned problems, the inventors of the present invention reduced the thermal shrinkage rate of the film and formed the magnetic layer and the other surface even if the surface on which the magnetic layer was formed was finished extremely flat. By using particles of the same particle size on the surface of the film, it was discovered that a biaxially laminated polyester film having less surface roughness due to transfer and having workability such as transportability could be provided, and the present invention was achieved.

Thus, according to the present invention, a biaxially oriented laminated polyester film composed of the film layer A and the film layer B, and the film layer A has an average particle size of 0 having a single peak when the particle size distribution curve is seen. .05-0.2 μm of inert particles A containing 50 ppm (mass basis) or more, the surface roughness (RaA) is 1.5 nm or less, and the other film layer B is a particle size distribution curve The inert particles B having the same average particle diameter as the inert particles A having a single peak, the surface roughness (RaB) is in the range of 2.0 nm to 6.0 nm, and the film layer A The background index is 80 to 99.99%, the drop of the bearing curve is 10 to 30 nm, and the biaxially oriented laminated polyester film has a heat shrinkage ratio of 3 at 130 ° C. for 30 minutes in the film width direction. % The biaxially oriented laminated polyester film which is a lower are 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 thickness is 2.0 μm or more and 8.0 μm or less. That is, the ratio (tA / tB) of the thickness tA (μm) of the film layer A to the thickness tB (μm) of the film layer B is 0.5 to 9 and the thickness tA (μm) of the film layer A And the ratio (tA / DpB) of the average particle diameter DpB (μm) of the inert particles B contained is 15 or more, and the thermal shrinkage rate at 130 ° C. in the longitudinal direction of the film is 3% or less. The Young's modulus in the longitudinal direction of the film is 5 GPa or more, and the inert particles contained are any of spherical silica particles, crosslinked polystyrene particles, silicone particles, and silica-acrylic composite particles. There is also provided a biaxially oriented polyester film having at least one of the above, and further comprising the biaxially oriented laminated polyester film of the present invention and a magnetic layer coated and formed on the surface on which the magnetic layer is formed. A coated magnetic recording tape is also provided.

  The biaxially oriented laminated polyester film of the present invention has excellent surface properties such as having a very flat surface, but also has a low thermal shrinkage rate even in a high temperature environment of application, so that it is wrinkled when contacting a process roll. In addition, it has workability such as transportability that is necessary for practical use, and even when applied to coating-type magnetic recording tapes, especially data storage base films, even minor surface defects that cause errors are reduced. In addition, surface roughness due to transfer can be suppressed, and data storage excellent in electromagnetic conversion characteristics can be provided.

  Hereinafter, the present invention will be described in detail. For convenience of explanation, the film forming direction of the film may be referred to as a mechanical axis direction, a vertical direction, a longitudinal direction, and an MD direction, and a direction orthogonal to the film forming direction and the thickness direction is referred to as a width direction, a lateral direction, Sometimes referred to as TD direction.

  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 biaxially oriented laminated polyester film of the present invention can be produced from the above-mentioned polyester, the electromagnetic conversion characteristics when the data storage is made while maintaining the processing characteristics such as winding and conveyance within a practically no problem range. From the viewpoint of maintaining a high level, the film layer A contains particles having an average particle size of 0.05 to 0.2 μm, based on the mass of the film layer A, and having a surface roughness (RaA) of 1.5 nm or less while containing 50 ppm or more. Need to be. 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. Further, when the particle diameter or surface roughness (RaA) exceeds these ranges, the surface becomes too rough when used for a base film of a high recording density data storage having a storage capacity of 3 TB or more, for example. The characteristics will deteriorate. A preferred average particle size range is 0.06-0.2 μm, more preferably 0.08-0.18 μm. Moreover, the range of preferable content is 55 ppm or more, More preferably, it is 60 ppm or more, More preferably, it is 65 ppm or more, Most preferably, it is 70 ppm or more. The preferable range of the surface roughness (RaA) is 1.4 nm or less, more preferably 1.3 nm or less.

  On the other hand, film layer B is inactive from the viewpoint of maintaining high electromagnetic conversion characteristics and dropouts when data storage is performed while maintaining processing characteristics such as transportability within a practically acceptable range. The inert particles B having the same average particle diameter as the particles A are contained, and the surface roughness (RaB) is required to be in the range of 2.0 to 6.0 nm. The lower limit of the surface roughness (RaB) of the preferred B layer is 2.2 nm, more preferably 2.5 nm, particularly 4.0 nm, and the upper limit is 5.8 nm. When the average particle size is smaller than this range, or when the surface roughness (RaB) is small, the transportability is deteriorated, and scratches called “scratches” are likely to enter the film, resulting in deterioration of error rate and dropout. . Further, when the particle diameter or surface roughness (RaB) exceeds these ranges, for example, when used for a base film of a high recording density data storage having a storage capacity of 3 TB or more, it takes up when it is rolled up into a roll shape. When the roughness of the film layer B is transferred to the film layer A due to the stress, the surface of the film layer A is roughened.

  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 may be the same or different on the surface on which the magnetic layer is formed and on the surface on which the magnetic layer is not formed. However, the same is preferable from the viewpoint of ease of collection and suppression of transfer. 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. For example, if particles having the same average particle diameter are added to the surface on which the magnetic layer is formed and the surface on which the magnetic layer is not formed, the protrusions formed by the particles formed on the surface have the same height, so the surface on which the magnetic layer is not formed Transfer to the surface to be formed is suppressed, or when the film is recovered and reused, it can be reused in either layer.

  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.

  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 Mn compound is preferable because the dispersibility of the inert particles to be contained is easily improved.

  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. Among these, when Mn—Sb is used, it is preferable because the dispersibility of the particles can be improved.

  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 biaxially oriented 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 within the above range, it is possible to highly reduce the electromagnetic conversion characteristics and the error rate after storing the tape cartridge. In addition, when the film is processed at a high temperature, for example, in the step of applying and drying the magnetic layer, the background index is in the above range, so that the coating layer can be uniformly dried, Even if the film is processed at a high temperature at which the viscoelasticity of the film is lowered, the surface property change before and after the treatment can be suppressed because there are few protrusions that change at a high temperature. 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.

  Further, the biaxially oriented laminated polyester film of the present invention requires that the heat shrinkage rate at 130 ° C. in the width direction of the film is 3% or less. A preferable upper limit is 2.9% or less, further 2.8% or less, and particularly 2.3% or less. By having such a low thermal shrinkage rate while having a background index as described above, wrinkles in the coating process in a high-temperature environment can be reduced, and folding wrinkles at the time of conveyance roll contact can be reduced and conveyance performance can be achieved. Processability at the time of drying can be ensured, and it is possible to achieve a high balance between surface properties. On the other hand, the heat shrinkage rate at 130 ° C. in the film forming direction is also preferably 3% or less. More preferably, it is 2.9% or less, more preferably 2.8% or less, and particularly 2.3% or less. It becomes possible to reduce wrinkles of a film that is tensioned in a high temperature environment such as a coating process.

  Moreover, the bearing drop of the surface which forms a magnetic layer with the biaxially oriented laminated polyester film of this invention is the range of 10-30 nm. More preferably, it is 10-28 nm, Most preferably, it is the range of 10-25 nm. This bearing drop shows a steep curve drop seen in a region where the bearing area is 0.4% in a bearing curve created from surface data measured by a non-contact type three-dimensional surface roughness meter. . A large value indicates a large difference in height between the high and low protrusions, and a low value indicates that the same height protrusions are generally present uniformly. In particular, in a film used for a magnetic tape, if a steep protrusion is present on the magnetic layer side, the spacing between the head and the film increases at the corresponding location, causing electromagnetic conversion characteristics and dropout. On the other hand, if this value is too small, there is only a small protrusion on the film, so that the transportability deteriorates. The above-mentioned range is preferable in order to have transportability and characteristics as a magnetic tape. In order to make such a bearing drop range, it is preferable to blend the particle size and concentration of the particles added to the film within the aforementioned range.

  The biaxially oriented laminated polyester film of the present invention is prepared, for example, by preparing a polyester polymer for a magnetic layer and a polyester polymer for forming the opposite surface, and laminating these in a molten state and coextruding from a die to a sheet. It can be manufactured by stretching and solidifying the obtained unstretched polyester film in the 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 (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 raised 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.

  Further, the biaxially oriented laminated polyester film of the present invention may be relaxed in the width direction while being heat-set or after heat-set. By relaxing in the width direction in this way, the heat shrinkage rate in the width direction of the film can be maintained in an appropriate range. This relaxation itself can also take place in the longitudinal direction. On the other hand, if relaxation is performed, the Young's modulus of the film is lowered, and a desired Young's modulus cannot be ensured, and tension may not be applied during processing. Therefore, the appropriate relaxation rate strongly depends on the polymer type of the film and the film forming conditions. For example, in the case of forming a polyethylene-2,6-naphthalate film, the relaxation temperature is set to 190 ° C., and the relaxation rate is 0. It is preferable to form a film at 3%.

  The biaxially oriented laminated polyester film of the present invention preferably has a Young's modulus in the longitudinal direction of 5 GPa or more in order to exhibit excellent dimensional stability when used as a base film of a high-density magnetic recording medium. If the Young's modulus in the longitudinal direction is lower than that described above, the film tends to be stretched when tension is applied in the longitudinal direction during film handling, resulting in a problem. On the other hand, although there is no restriction | limiting about an upper limit, the higher one is preferable from a viewpoint of the said handling. The Young's modulus in the width direction is 4 to 15 GPa, more preferably 5 to 14 GPa, particularly 6 to 13 GPa, and 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. preferable. If the Young's modulus in the width direction is less than the lower limit, it becomes difficult to reduce the temperature expansion coefficient when it is used as a magnetic recording tape, or wrinkles are likely to enter the film with respect to the conveyance tension in the coating process. On the other hand, when the upper limit is exceeded, the temperature expansion coefficient when the magnetic recording tape is formed becomes excessively small.

  The total thickness of the biaxially oriented laminated polyester film of the present invention is preferably 2.0 μm or more and 8.0 μm or less. The lower limit of the preferable total thickness is 2.5 μm, and further 3 μm. The upper limit of the preferable total thickness is 7 μm, further 6 μm, particularly 4.5 μm. When the thickness is smaller than the lower limit, the tape loses its elasticity, so that the electromagnetic conversion characteristics are deteriorated and wrinkles are easily formed in the coating process. 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.

  In addition, the biaxially oriented laminated polyester film of the present invention is a polyester that forms a surface layer on the rough surface layer side that forms the polyester layer that forms the surface on the flat layer side that forms the magnetic layer as the A layer and the opposite surface. When the layer is a B layer, the thickness ratio (tA / tB) of the A layer and the B layer is preferably in the range of 0.33 to 90. Preferred lower limits are 0.5, further 0.6, even more 0.8, in particular 2.0. A preferred upper limit is 8.0, further 7.0, even 6.0, especially 5.0. When the amount is less than the lower limit, the particles contained in the B layer on the rough surface layer side where the magnetic layer is not formed are pushed up, and electromagnetic conversion characteristics are easily deteriorated. On the other hand, when the amount is not less than the above upper limit, it is preferable that the lubricant of the rough surface layer not forming the magnetic layer is easily removed, and the normally recovered resin is preferably used for the B layer so as not to impair the flatness. If this is the case, problems such as a drastic reduction in the reusable rate occur.

  Further, in the biaxially oriented polyester film of the present invention, the polyester layer that forms the surface on the flat layer side that forms the magnetic layer is the A layer, and the polyester layer that forms the surface property on the rough layer side that forms the opposite surface. Is a B layer, the ratio (tA / DpB) of the thickness tA of the A layer and the average particle diameter DpB of the inert particles added to the B layer is preferably 15 or more. If it is less than the above lower limit, the particles in the B layer that do not form the magnetic layer are pushed up to the magnetic layer, and the flatness tends to be deteriorated. On the other hand, the upper limit is not particularly limited as long as a desired film can be obtained.

  The biaxially oriented laminated polyester film of the present invention is preferably used as a base film for high-density magnetic recording tapes, particularly digital recording magnetic recording tapes. Therefore, the magnetic recording medium using the biaxially oriented 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 biaxially oriented laminated polyester film. The surface of the biaxially oriented laminated polyester film of the present invention has a well-known easy adhesion function as long as it does not impair the effects of the present invention in order to improve the adhesion with a magnetic layer or the like. A layer or the like 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 biaxially oriented polyester film of the present invention, a magnetic recording tape excellent in dimensional stability, electromagnetic conversion characteristics and error rate performance should be obtained. Can do.

  By the way, as described above, in order to increase the recording density, it is necessary to make the magnetic material finer. Therefore, it becomes difficult to remove the solvent from the coating liquid, and if the workability is maintained, drying or the like is performed at a higher temperature. It was necessary to do in. And when it was going to process the film which has a very flat surface at high temperature, there existed new problems, such as wrinkles, and it reached | attained this invention.

  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, biaxially oriented 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 of particles in the film The polyester in 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 of the particles was prepared. The identification of the particle type can be performed using SEM-XMA, quantitative analysis of metal elements by ICP, or the like. Moreover, the average particle diameter of the inert particle to add was measured similarly, the particle diameter of each particle was calculated | required, and the number average was made into the average particle diameter.

(3) Content of particles (3-1) Total content of particles in each layer About 100 g each of the polyester A layer and the polyester B layer are sampled from the biaxially oriented laminated polyester film, and the polyester is dissolved. 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 biaxially oriented laminated polyester film are present, the polyester A layer and the polyester B layer are each scraped off and sampled by about 100 g, and the platinum crucible is sampled. The mixture is burned in a furnace at about 1,000 ° C. for 3 hours or longer, and then the combustion product in the crucible is mixed with terephthalic acid (powder) to prepare a 50-gram tablet plate. This plate is converted using a wavelength-dispersed fluorescent X-ray to calculate the count value of each element from a calibration curve for each element that has been prepared in advance, 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 by the above (2), 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 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, and 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.

(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 MetroPro, 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.

(8) Bearing drop 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 roughness data is analyzed with software for analysis (Image Metrology). (Made by SPIP), a bearing curve was created, and the maximum value of the steep drop of the bearing curve where the bearing area in this bearing curve is 0.4% was quantified as the bearing drop.

(9) 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 were placed, A thread is placed at the center of the upper side of the two superimposed films, and fixed to the acrylic plate with the A layer on the upper side and the B layer on the lower side, 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.

(10) Rate of non-defective product taken as follows according to the ratio of non-blocking and wrinkle-free good products when 100 rolls at a length of 5000 m were taken while slitting a 1 m wide product roll from the parent roll at 80 m / min. To do.
◎; Percentage without defects such as blocking and wrinkles 85-100%
○: Same as above 70-84%
×: Same as above, less than 70%

(11) Heat treatment wrinkle test A film having a width of 10 cm and a length of 25 cm was prepared as a test piece, and heat treatment was performed at 130 ° C for 1 minute in a state where a load of 1 kg / m was applied. The elongation in the longitudinal direction of the heat-treated film and the number of wrinkles generated in the longitudinal direction were measured in the width direction.

(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: 130 ° 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-ESREC A (vinyl chloride / vinyl acetate copolymer made by Sekisui Chemical: 10 parts by weight)-Nipporan 2304 (polyurethane elastomer made by Nippon Polyurethane): 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 <magnetic paint Composition>
Iron (major axis: 0.025 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. A relative value with the noise N ratio as C / N ratio and Example 2 as 0 dB was determined 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 a length of 850 m of magnetic recording tape by slitting the original tape produced in (11) 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

(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

[Example 1]
As particles to be added to the flat layer side, the intrinsic viscosity containing 0.01% by weight of spherical silica particles (particles A) having an average particle size of 0.08 μm (particle size: relative standard deviation: 10%) is 0.62. Polyethylene-2,6-naphthalate pellets for polyester A layer (glass transition temperature: 121 ° C., melting point: 265 ° C.) and particles to be added to the rough surface layer side, an average particle size of 0.08 μm (particle size: relative standard deviation) : Polyethylene-2,6-naphthalate pellets for polyester B layer having an intrinsic viscosity of 0.62 containing 0.50 wt% of true spherical silica particles (particles B1) (glass transition temperature: 121 ° C., 10%) Melting point: 265 ° C.). 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 = 75: 25 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 fed into the stenter and stretched 1.2 times in the transverse direction, it was heat-fixed with hot air at 215 ° C for 4 seconds, and then relaxed in the width direction at 190 ° C and a relaxation rate of 0.27%. Thus, a biaxially oriented laminated polyester film having a thickness of 4.0 μm was obtained. The Young's modulus of the obtained biaxially oriented laminated polyester film was 6.5 GPa in the vertical direction and 8.9 GPa in the horizontal direction. The background index of the polyester A layer was 98.38%.
The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

[Example 2]
A biaxially oriented laminated polyester film was obtained in the same manner as in Example 1 except that the transverse stretching temperature was changed to 124, 128, and 158 ° C. so as to change the temperature stepwise.
The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

[Examples 3 to 5]
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. The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

[Example 6]
As particles to be added to the flat layer side, 0.01% by weight of spherical silica particles (particles A) having an average particle size of 0.08 μm (particle size: relative standard deviation: 10%) were contained, and the intrinsic viscosity was 0.62. Polyethylene-terephthalate pellets for polyester A layer (glass transition temperature: 76 ° C., melting point: 255 ° C.) and polyetherimide pellets (trade name: ULTEM 1040) blended at a weight ratio of 90:10, rough surface layer Polyester having an intrinsic viscosity of 0.62 containing 0.55% by weight of true spherical silica particles (particles B1) having an average particle size of 0.08 μm (particle size: relative standard deviation: 10%) as particles added to the side B-layer polyethylene-terephthalate pellets (glass transition temperature: 76 ° C., melting point: 255 ° C.) and polyetherimide pellets (trade name: ULTEM 1040) The resin composition blended at a weight ratio of 90:10 was dried in a pellet state at 170 ° C. for 3 hours, and then supplied to two extruder hoppers at a melting temperature of 280 ° C. Coextruded in a sheet form from the die onto a cooling drum at a layer thickness ratio of 77:23 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 90 ° C., and while being stepwise raised to 125 ° C. and 130 ° C., it was stretched 5 times in the lateral 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 230 ° C for 4 seconds, and then relaxed at 210 ° C with a relaxation rate of 1%, and then laminated with a thickness of 4.5 µm A biaxially oriented polyester film was obtained. The Young's modulus of the obtained biaxially oriented laminated polyester film was 4.9 GPa in the vertical direction and 7.6 GPa in the horizontal direction.
The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

[Comparative Examples 1-8]
The same operation as in Example 1 was repeated except that the particle A, particle B1, particle B2, the thickness of each layer, the heat setting temperature, and the relaxation rate were changed as shown in Table 1. The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

[Comparative Example 9]
Polyethylene-terephthalate pellets for polyester A layer having an intrinsic viscosity of 0.62 containing 0.01% by weight of true spherical silica particles (particle A) having an average particle size of 0.08 μm as the particles added to the flat layer side (glass transition (Temperature: 76 ° C., melting point: 255 ° C.) As particles to be added to the rough surface layer side, 0.35% by weight of true spherical silica particles (particle B1) having an average particle size of 0.08 μm and an average particle size of 0.20 μm Polyethylene-terephthalate pellets (glass transition temperature: 76 ° C., melting point: 255 ° C.) for polyester B layer having an intrinsic viscosity of 0.62 and containing 0.03% by mass of true spherical silica (particle B2) were prepared. Each pellet was dried at 170 ° C. for 3 hours, and then supplied to two extruder hoppers. At a melting temperature of 280 ° C., a thickness ratio of A layer: B layer = 77: 23 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 90 ° C., and while being stepwise raised to 125 ° C. and 130 ° C., it was stretched 5 times in the lateral 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 230 ° C for 4 seconds, and then relaxed at 210 ° C with a relaxation rate of 1%, and then laminated with a thickness of 4.5 µm A biaxially oriented polyester film was obtained. The Young's modulus of the obtained biaxially oriented laminated polyester film was 4.9 GPa in the vertical direction and 7.6 GPa in the horizontal direction.
The characteristics of the obtained biaxially oriented laminated polyester film are shown in Table 1.

  In Table 1, silica means true spherical silica particles, PEN means polyethylene-2,6-naphthalene dicarboxylate, PET means polyethylene terephthalate, and PEI means polyetherimide.

  The biaxially oriented laminated polyester film of the present invention is excellent in productivity and also has workability such as subsequent transportability, excellent electromagnetic conversion characteristics, and a coating type magnetic recording tape with reduced error rate and dropout, particularly It can be suitably used as a base film for data storage.

Claims (9)

A biaxially oriented laminated polyester film comprising a film layer A and a film layer B, and the film layer A has an average particle diameter of 0.05-0.2 μm having a single peak when the particle size distribution curve is seen. The inert particle A contains 50 ppm (mass basis) or more, its surface roughness (RaA) is 1.5 nm or less, and the other film layer B has a single peak when the particle size distribution curve is seen. Inactive particles B having the same average particle diameter as the inactive particles A have, the surface roughness (RaB) is in the range of 2.0 nm to 6.0 nm, and the background index of the film layer A is 80 to 99. In the range of .99%, the drop of the bearing curve is in the range of 10-30 nm, and the heat shrinkage rate at 130 ° C. for 30 minutes in the film width direction of the biaxially oriented laminated polyester film is 3% or less. Toss Biaxially oriented laminated polyester film.   The biaxially oriented laminated polyester film according to claim 1, wherein the polyester comprises ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate as a main repeating unit.   The biaxially oriented laminated polyester film according to claim 1, which has a thickness of 2.0 µm or more and 8.0 µm.   2. The biaxially oriented laminated polyester film according to claim 1, wherein the ratio (tA / tB) of the thickness tA (μm) of the film layer A to the thickness tB (μm) of the film layer B is 0.5 or more and 9 or less.   5. The biaxially oriented laminated polyester film according to claim 4, wherein the ratio (tA / DpB) of the thickness tA (μm) of the film layer A to the average particle diameter DpB (μm) of the inert particles B contained is 15 or more.   The biaxially oriented laminated polyester film according to claim 1, wherein the heat shrinkage rate at 130 ° C in the film forming direction is 3% or less.   The biaxially oriented laminated polyester film according to claim 1, wherein the Young's modulus in the film forming direction is 5 GPa or more.   The biaxially oriented laminated polyester film according to claim 1, wherein the inert particles contained are any of spherical silica particles, crosslinked polystyrene particles, silicone particles, and silica-acryl composite particles.   A coating type magnetic recording tape comprising the biaxially oriented laminated polyester film according to any one of claims 1 to 8, and a magnetic layer coated and formed on the surface on the side on which the magnetic layer is formed.