US20100167092A1 - Biaxially oriented polyester film and magnetic recording tape - Google Patents

Biaxially oriented polyester film and magnetic recording tape Download PDF

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Publication number
US20100167092A1
US20100167092A1 US12/278,885 US27888508A US2010167092A1 US 20100167092 A1 US20100167092 A1 US 20100167092A1 US 27888508 A US27888508 A US 27888508A US 2010167092 A1 US2010167092 A1 US 2010167092A1
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Prior art keywords
film
biaxially oriented
layer
oriented polyester
polyester film
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US12/278,885
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English (en)
Inventor
Ieyasu Kobayashi
Shinji Muro
Takeshi Ishida
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Toyobo Film Solutions Ltd
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Teijin DuPont Films Japan Ltd
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Assigned to TEIJIN DUPONT FILMS JAPAN LIMITED reassignment TEIJIN DUPONT FILMS JAPAN LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ISHIDA, TAKESHI, KOBAYASHI, IEYASU, MURO, SHINJI
Publication of US20100167092A1 publication Critical patent/US20100167092A1/en
Priority to US13/117,224 priority Critical patent/US8404371B2/en
Abandoned legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
    • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
    • B29C55/14—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively
    • B29C55/143—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively firstly parallel to the direction of feed and then transversely thereto
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/733—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer characterised by the addition of non-magnetic particles
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G11B5/73927—Polyester substrates, e.g. polyethylene terephthalate
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G11B5/73927—Polyester substrates, e.g. polyethylene terephthalate
    • G11B5/73929—Polyester substrates, e.g. polyethylene terephthalate comprising naphthalene ring compounds, e.g. polyethylene naphthalate substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G11B5/73927—Polyester substrates, e.g. polyethylene terephthalate
    • G11B5/73931—Two or more layers, at least one layer being polyester
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates
    • G11B5/73927—Polyester substrates, e.g. polyethylene terephthalate
    • G11B5/73935—Polyester substrates, e.g. polyethylene terephthalate characterised by roughness or surface features, e.g. by added particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
    • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
    • B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
    • B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds

Definitions

  • the present invention relates to a biaxially oriented polyester film which is suitable for use as a base film for magnetic recording tapes of linear recording system and a magnetic recording tape of linear recording system, comprising the same.
  • a polyester film is used in a magnetic recording tape because it has excellent thermal and mechanical properties.
  • Magnetic recording tapes, especially data storage magnetic recording tapes require a larger storage capacity and a higher recording density as the size of data to be recorded is growing, and the requirements for the characteristic properties of base films constituting the magnetic recording tapes are becoming more severe.
  • magnetic recording tapes for data storage such as QIC, DLT, large-capacity super-DLT and LTO employ linear recording system (also called “linear track system”), and the track pitch is becoming very narrow to realize a large capacity and a high density for the magnetic recording tapes.
  • linear recording system also called “linear track system”
  • the dimensional changes rate in the width direction of the magnetic recording tape changes, track dislocation occurs even if the dimensional changes rate in the width direction is so small that it does not cause a problem in the prior art, whereby an error occurs.
  • the dimensional changes rate in the width direction of the magnetic recording tape are caused by temperature and humidity variations and tension variations.
  • the pamphlet of WO99/29488 proposes a biaxially oriented polyester film whose temperature expansion coefficient ⁇ t in the width direction ( ⁇ 10 ⁇ 6 /° C.), humidity expansion coefficient ⁇ h in the width direction ( ⁇ 10 ⁇ 6 /% RH) and shrinkage factor P (ppm/g) in the width direction for a load which is applied in the longitudinal direction are set to specific ranges.
  • the pamphlet of WO00/76749 and the pamphlet of WO02/45959 also propose a biaxially oriented polyester film whose dimensional changes rate in the width direction when it is left under load in the longitudinal direction, temperature expansion coefficient ⁇ t in the width direction ( ⁇ 10 ⁇ 6 /° C.), humidity expansion coefficient ⁇ h in the width direction ( ⁇ 10 ⁇ 6 /% RH) and dimensional changes rate in the width direction (%) for a load which is applied in the longitudinal direction are set to specific ranges.
  • LTO linear tape-open
  • LTO linear tape-open
  • LTO linear tape-open
  • LTO linear tape-open
  • LTO linear tape-open
  • the temperature expansion coefficient ⁇ t in the width direction of the film should be about the same as the temperature expansion coefficient ⁇ t of a magnetic head for reading it (about 7 ppm/° C. in the case of a MR head)
  • the temperature expansions of the back coat layer, magnetic layer and non-magnetic layer are large and their influences are large. Therefore, to provide higher dimensional stability, they have found that it is necessary to ease the temperature expansions of these layers with the base film, that is, it is important to provide an extremely low temperature expansion coefficient to the base film.
  • a biaxially oriented polyester film which has a Young's modulus (YMD) in the film machine direction of 6.5 GPa or more and a Young's modulus (YTD) in the width direction of 8.2 to 9.8 GPa and is used as a base film for magnetic recording tapes of linear recording system.
  • YMD Young's modulus
  • YTD Young's modulus
  • a biaxially oriented polyester film having at least one of features that the polyester is polyethylene-2,6-naphtahlene dicarboxylate, the thickness of the film is 3 to 6 ⁇ m, the total of YMD and YTD is 15 to 18 GPa, YTD is equal to or larger than YMD, the temperature expansion coefficient in the width direction of the film is ⁇ 8 to +1 ppm/° C., the humidity expansion coefficient in the width direction of the film is 5 to 10 ppm % RH, the heat shrinkage factor (105° C. ⁇ 30 minutes) in the width direction of the film is 0.8% or less, the rupture elongation in the width direction of the film is 45% or more, the crystallinity of the film is 28 to 33%, the dimensional change rate in the width direction when a load of 32 MPa is applied in the film machine direction in a 40° C.
  • the biaxially oriented polyester film is a single-layer film having a surface roughness (WRa) of 1 to 10 nm
  • the polyester film is a laminate film consisting of two polyester film layers (layers A and B)
  • the layer A is formed on the side on which a magnetic layer is to be formed and has a surface roughness (WRa(A)) of 0.5 to 4 nm
  • the layer B is formed on the side on which no magnetic layer is to be formed and has a surface roughness (WRa(B)) of 5 to 10 nm
  • the layer A contains inert particles A having an average particle diameter of 0.01 to 0.18 ⁇ m in an amount of 0.01 to 0.15 wt % based on the weight of the layer A
  • the layer B contains inert particles B 1 having an average
  • a magnetic recording tape of linear recording system which comprises the above biaxially oriented polyester film of the present invention, a non-magnetic layer and a magnetic layer formed on one side of the film, and a back coat layer formed on the other side, and a magnetic recording tape in which the ratio of the total thickness of the non-magnetic layer, magnetic layer and back coat layer to the thickness of the biaxially oriented polyester film is 0.2 to 0.8.
  • FIG. 1(A) is a diagram of an apparatus for measuring the chipping resistance of a film
  • FIG. 1(B) is an enlarged view of the blade of the apparatus and guide rollers located on the right and left sides of the blade.
  • the film machine direction of the biaxially oriented polyester film is called “vertical direction, longitudinal direction or MD direction” and the direction orthogonal to the film machine direction is called “width direction, transverse direction or TD direction”.
  • the vertical direction, longitudinal direction, transverse direction and width direction of a magnetic recording tape mean the same as the vertical direction, longitudinal direction, transverse direction and width direction of the biaxially oriented polyester film, respectively.
  • the biaxially oriented polyester film of the present invention is made from an aromatic polyester.
  • aromatic polyester as used herein denotes a polymer obtained by polycondensing a diol and an aromatic dicarboxylic acid.
  • aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4′-diphenyldicarboxylic acid.
  • diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexandimethanol and 1,6-hexanediol.
  • polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferred from the viewpoint of mechanical properties, and polyethylene-2,6-naphthalene dicarboxylate is particularly preferred because it has high mechanical properties and dimensional stability.
  • the aromatic polyester in the present invention is not limited to a homopolymer but may be a copolymer or a mixture as far as it does not impair the effect of the present invention.
  • the amount of another component to be copolymerized or mixed is preferably 10 mol % or less, more preferably 5 mol % or less based on the number of mols of the recurring unit.
  • Comonomers known per se may be used, such as a diol component exemplified by diethylene glycol, neopentyl glycol and polyalkylene glycol and a dicarboxylic acid component exemplified by adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid and 5-sodium sulfoisophthalic acid. It is preferred that syndiotactic polystyrene should be copolymerized or mixed to reduce the humidity expansion coefficient of the obtained biaxially oriented polyester film and that polyimide should be copolymerized or mixed to improve the mechanical properties or thermal properties of the film.
  • a diol component exemplified by diethylene glycol, neopentyl glycol and polyalkylene glycol
  • a dicarboxylic acid component exemplified by adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid
  • the intrinsic viscosity of the polyester resin in the present invention is preferably 0.40 or more, more preferably 0.40 to 0.80, particularly preferably 0.5 to 0.7 in o-chlorophenol at 35° C.
  • the intrinsic viscosity is less than 0.4, breakage may often occur during film formation or the strength of a molded product may become unsatisfactory.
  • the intrinsic viscosity is higher than 0.8, productivity at the time of polymerization tends to lower.
  • the biaxially oriented polyester film of the present invention has a Young's modulus in the film machine direction (YMD) of 6.5 GPa or more, preferably 6.7 GPa or more, more preferably 7.0 GPa or more, particularly preferably 7.5 GPa or more, most preferably 8 GPa or more.
  • YMD Young's modulus in the film machine direction
  • YMD is preferably 9 GPa or less.
  • the Young's modulus in the width direction (YTD) of the biaxially oriented polyester film of the present invention must be 8.2 to 9.8 GPa, preferably 8.5 to 9.5 GPa, more preferably 8.7 to 9.3 GPa.
  • YTD is outside the above range, the difference between the dimensional changes rate in the width direction of the magnetic head and the tape by temperature variations becomes large with the result of the occurrence of track dislocation.
  • the total of YMD and YTD is 15 to 18 GPa, preferably 16 to 18 GPa.
  • the Young's modulus in the film machine direction (YMD) or the Young's modulus in the width direction (YTD) does not become the above value and the dimensional changes rate in the width direction of the film becomes large with the result of the occurrence of track dislocation.
  • the total of YMD and YTD exceeds the upper limit, it is extremely difficult to form a film (film breakage often occurs), which is not preferred from the viewpoint of productivity.
  • YTD of the biaxially oriented polyester film of the present invention should be equal to or larger than YMD because a biaxially oriented polyester film having little track dislocation of interest is stably obtained and the surface properties of the obtained biaxially oriented polyester film can be easily made excellent.
  • YTD is preferably 0.5 GPa or more larger than YMD.
  • the difference between YTD and YMD is preferably 2.5 GPa or less, more preferably 2.0 GPa or less because the dimensional changes rate in the width direction caused by the above creep and temperature and humidity variations can be easily made small.
  • the biaxially oriented polyester film of the present invention has a temperature expansion coefficient ⁇ t in the width direction of the film of ⁇ 8 to +1 ppm/° C. It is more preferably ⁇ 6 to 0 ppm/° C., particularly preferably ⁇ 5 to ⁇ 1 ppm/° C.
  • ⁇ t in the width direction of the film of ⁇ 8 to +1 ppm/° C. It is more preferably ⁇ 6 to 0 ppm/° C., particularly preferably ⁇ 5 to ⁇ 1 ppm/° C.
  • the biaxially oriented polyester film of the present invention has a humidity expansion coefficient ⁇ h in the width direction of the film of 5 to 10 ppm/% RH. It is more preferably 6 to 9 ppm % RH.
  • ⁇ h exceeds the upper limit, the dimensional changes rate in the width direction of the film by humidity variations becomes large, whereby track dislocation readily occurs.
  • ⁇ h falls below the lower limit, at becomes large in the negative direction and the dimensional changes rate in the width direction by temperature variations becomes large, whereby track dislocation readily occurs.
  • the humidity expansion coefficient can be also adjusted by the above Young's modulus in the width direction.
  • the thickness of the whole biaxially oriented polyester film of the present invention is preferably 3.0 to 6.0 ⁇ m, more preferably 3.5 to 5.5 ⁇ m, particularly preferably 4.0 to 5.0 ⁇ m.
  • the thickness exceeds the upper limit the thickness of the tape becomes large and the length of the tape to be stored in a cassette becomes small, whereby a sufficiently large magnetic recording capacity, especially a recording capacity of more than 500 GB is not obtained or the proportion of the base film to the magnetic recording tape becomes large. Therefore, the magnetic layer and the non-magnetic layer become thin and the magnetic surface becomes roughened by the influence of the surface properties of the base film with the result that output characteristics deteriorate, thereby increasing the error rate.
  • the thickness of the film When the thickness falls below the lower limit, the thickness of the film is very small, whereby the film is often broken at the time of film formation, the winding of the film fails, and the suppression of the temperature expansion of a layer other than the base film by the base film of the present invention becomes difficult.
  • the biaxially oriented polyester film of the present invention has a heat shrinkage factor in the width direction of the film of 0.8% or less, preferably 0.7% or less, particularly preferably 0.6% or less when it is heated at 105° C. under no load for 30 minutes because the dimensional stability of the film can be easily improved.
  • the draw ratio in the width direction of the film is reduced, the drawing temperature in the width direction of the film is increased, the heat setting temperature is increased, or the film is relaxed in the width direction during heat setting.
  • the lower limit of heat shrinkage factor is not particularly limited, to carry out relaxation excessively in order to reduce the heat shrinkage factor as much as possible, a higher draw ratio is required to maintain the same Young's modulus, whereby film forming properties are readily impaired. From this point of view, the lower limit of heat shrinkage factor in the width direction of the film is 0.1% or more, more preferably 0.3% or more.
  • the biaxially oriented polyester film of the present invention has a rupture elongation in the width direction of the film of preferably 45% or more, more preferably 47% or more, particularly preferably 50% or more from the viewpoint of film forming properties.
  • a rupture elongation in the width direction of the film preferably 45% or more, more preferably 47% or more, particularly preferably 50% or more from the viewpoint of film forming properties.
  • stretching conditions in the width direction become very severe and film forming properties may be impaired.
  • the draw ratio in the width direction of the film is reduced, the stretching temperature in the width direction of the film is increased, the heat setting temperature is increased, or the film is relaxed in the width direction during heat setting.
  • the upper limit of rupture elongation is not particularly limited as long as the above Young's modulus is obtained, the upper limit is determined naturally from the Young's modulus.
  • the crystallinity of the biaxially oriented polyester film of the present invention is preferably 28 to 33%, more preferably 29 to 32% when the polyester is polyethylene-2,6-naphthalene dicarboxylate, whereby the surface of the film can be made very flat and high electromagnetic conversion characteristics can be obtained for a magnetic recording tape.
  • the crystallinity is greatly influenced by heat setting temperature and can be made high by increasing the heat setting temperature or extending the heat setting time. For instance, the above crystallinity can be obtained by carrying out heat setting at a temperature of preferably 202 to 210° C., particularly preferably 203 to 208° C. for preferably 1 to 20 seconds.
  • the heat setting temperature must be made high, whereby the surface flatness of even a film having a large Young's modulus in the width direction specified by the present invention can be improved by heat setting with the result that a high-density magnetic recording tape provided by the present invention easily exhibits excellent electromagnetic conversion characteristics.
  • the effect of improving the surface flatness of the film by increasing the heat setting temperature becomes unsatisfactory, thereby causing a reduction in Young's modulus, the deterioration of film forming properties by increasing the draw ratio to eliminate the reduction in Young's modulus, or nonuniformity in the thickness of the film due to the reception of an excessive heat history with the result of impaired surface flatness.
  • the dimensional changes rate in the width direction is preferably more than 0.3% and 1.0% or less, more preferably 0.4 to 0.9% from the viewpoints of film forming properties and track dislocation.
  • the dimensional changes rate in the width direction rate at the time of applying the above load can be reduced by increasing the Young's modulus in the film machine direction or reducing the heat shrinkage factor in the width direction of the film.
  • the Young's modulus in the film machine direction must be increased excessively or the heat shrinkage factor in the width direction of the film must be reduced, whereby a high draw ratio is required, thereby impairing the film forming properties.
  • the reason that the dimensional changes rate in the width direction at the time of applying the above load may be made high is that tension applied to the magnetic recording tape becomes smaller as the recording density of the magnetic recording medium becomes higher, which is totally unexpected from a magnetic recording tape having a low recording density in the prior art.
  • the dimensional changes rate in the width direction of the film at the time of applying the above load exceeds the upper limit, even if tension applied to the magnetic tape becomes small, the size in the width direction of the film changes while it is used repeatedly, thereby causing track dislocation.
  • the biaxially oriented polyester film of the present invention has a surface roughness WRa(center plane average roughness) of at least one exposed surface of preferably 1 to 10 nm, more preferably 2 to 6 nm, particularly preferably 3 to 5 nm.
  • WRa center plane average roughness
  • this surface roughness WRa is higher than the upper limit, the surface of the magnetic layer becomes rough, thereby deteriorating the electromagnetic conversion characteristics.
  • the surface roughness WRa is lower than the lower limit, the surface becomes too flat, whereby slippage over a pass roll or a calender becomes worse, the film is wrinkled, the magnetic layer cannot be formed well, or the calendering step becomes unstable.
  • the biaxially oriented polyester film is not limited to a single-layer film but may be a laminate film consisting of two or more layers which differ from each other in the composition of inert particles contained therein.
  • the surface roughness of the both sides of the film is preferably 1 to 10 nm. It is more preferably 2 to 10 nm from the viewpoint of film forming and winding properties and 1 to 7 nm from the viewpoint of electromagnetic conversion characteristics. It is particularly preferably 2 to 7 nm to achieve both film forming and winding properties and electromagnetic conversion characteristics.
  • a polyester film layer which contains substantially no inert particles or a small amount of relatively small inert particles if it contains, that is, a layer forming a flat surface is formed on the side on which a magnetic layer is to be formed, and a polyester film layer which contains a large amount of relatively large inert particles, that is, a surface having excellent running properties is formed on the other running surface, that is, a non-magnetic layer side. Since this laminate film provides both electromagnetic conversion characteristics and film winding properties to a magnetic recording tape more easily than the single-layer film, it can be said that the laminate film is a preferred embodiment of the present invention.
  • the layer A on the side on which a magnetic layer is to be formed has a surface roughness (WRa(A)) of 0.5 to 4 nm and the layer B on the side on which no magnetic layer is to be formed has a surface roughness (WRa(B)) of 5 to 10 nm, whereby both film forming and winding properties and electromagnetic conversion characteristics can be obtained.
  • WRa(A) surface roughness
  • WRa(B) surface roughness
  • the above surface roughness WRa can be adjusted by containing inert particles, for example, inorganic fine particles containing the element of group IIA, IIB, IVA or IVB of the periodic table (such as kaolin, alumina, titanium oxide, calcium carbonate or silicon dioxide) or organic particles of a polymer having high heat resistance such as crosslinked silicone resin, crosslinked polystyrene or crosslinked acrylic resin particles in the film, or carrying out a surface treatment for forming fine irregularities, for example, coating a lubricant coating.
  • inert particles for example, inorganic fine particles containing the element of group IIA, IIB, IVA or IVB of the periodic table (such as kaolin, alumina, titanium oxide, calcium carbonate or silicon dioxide) or organic particles of a polymer having high heat resistance such as crosslinked silicone resin, crosslinked polystyrene or crosslinked acrylic resin particles in the film, or carrying out a surface treatment for forming fine irregularities, for example, coating a lubricant coating.
  • the average particle diameter of the inert particles is preferably 0.01 to 0.8 ⁇ m, more preferably 0.05 to 0.6 ⁇ m, particularly preferably 0.1 to 0.4 ⁇ m.
  • the content of the inert particles is preferably 0.01 to 0.8 wt %, more preferably 0.03 to 0.6 wt %, particularly preferably 0.05 to 0.4 wt % based on the weight of the entire film in the case of a single-layer film or the weight of the film layer containing the inert particles in the case of a laminate film.
  • the inert particles contained in the film are not limited to a single component but may be composed of two or more components. It is preferred that inert particles composed of two components or three or more components should be contained in the film layer on the non-magnetic layer side of the laminate film because both tape electromagnetic conversion characteristics and film winding properties can be obtained at the same time.
  • the surface roughness WRa can be adjusted by suitably selecting the average particle diameter and amount of the inert particles from the above ranges. For instance, the surface roughness WRa can be made large by increasing the average particle diameter or content of the inert particles.
  • the biaxially oriented polyester film of the present invention may have a coating layer which is formed by coating a lubricant coating.
  • the lubricant coating may be applied not only to one side but also to both sides. Coating layers known per se may be advantageously used. For example, those enumerated in the pamphlet of WO00/76749 may be used as the coating layer. It is possible to form a coating layer by coating a lubricant coating without containing inert particles in the film.
  • the biaxially oriented polyester film of the present invention may be a single-layer film or a laminate film consisting of a plurality of layers which differ in the type, particle diameter and amount of inert particles contained therein.
  • the layer A should contain inert particles A having an average particle diameter of 0.01 to 0.20 ⁇ M in an amount of 0.01 to 0.15 wt % based on the weight of the layer A and that the layer B should contain inert particles B 2 having an average particle diameter of 0.2 to 0.4 ⁇ m in an amount of 0.01 to 0.2 wt % based on the weight of the layer B.
  • the average particle diameter of the inert particles A is smaller than 0.01 ⁇ m or the content of the inert particles A is lower than 0.01 wt %, winding becomes difficult, chipping occurs or chipping powders are produced by a pass roll, or a scratch is formed at the time of forming a film, thereby causing an error.
  • the average particle diameter is larger than 0.20 ⁇ m or the content is higher than 0.15 wt %, if high dimensional stability is to be provided to a high-density recording medium which the present invention is aimed to attain, the surface of the layer A becomes rough and an error readily occurs.
  • the content of the inert particles A is preferably 0.09 wt % or less.
  • the layer B preferably contains the above inert particles B 2 .
  • the average particle diameter or content of the inert particles B 2 falls below the lower limit, air squeezability and friction coefficient become high, whereby it may be difficult to wind the film.
  • the average particle diameter or content of the inert particles B 2 exceeds the above upper limit, the surface of the layer A is greatly tossed by the inert particles B 2 , thereby impairing the surface properties of the layer A and making it difficult to increase the recording density.
  • the layer B may be composed of a single component, that is, the inert particles 32 alone but preferably contains inert particles B 1 having an average particle diameter of 0.01 to 0.2 ⁇ m in an amount of 0.01 to 0.3 wt % based on the weight of the layer B from the viewpoints of the influence upon the surface properties of the magnetic surface of the polyester layer B (improvement of electromagnetic conversion characteristics) and film winding properties.
  • the average particle diameter or content of the inert particles B 1 falls below the lower limit, the friction coefficient becomes high, thereby making it difficult to wind the film, or the surface is shaved and foreign matter produced by shaving is transferred to the surface of the layer A, thereby causing an error.
  • the inert particles B 1 When the average particle diameter or content of the inert particles B 1 exceeds the upper limit, the inert particles B 1 or agglomerates of the inert particles B 1 form large projections which toss the surface, thereby impairing surface flatness.
  • the inert particles B 1 preferably have an average particle diameter 0.1 ⁇ m or more smaller than that of the inert particles B 2 because a combination of the inert particles B 1 and B 2 provides the effect of improving electromagnetic conversion characteristics and film winding properties more easily.
  • the average particle diameter of the inert particles B 1 is preferably 0.05 to 0.2 ⁇ m, more preferably 0.10 to 0.15 ⁇ m.
  • Preferred examples of the inert particles A and the inert particles B 1 and B 2 are those listed for the above inert particles.
  • Spherical silica particles and spherical heat-resistant polymer particles are preferred as the inert particles A and B 1 because they provide the effect of the present invention easily.
  • heat-resistant polymer particles having low hardness, for example, a Mohs hardness of less than 3 are particularly preferred because the transfer of the rough surface of the layer B to the surface of the layer A can be suppressed.
  • the inert particles B 1 contained in the layer B are preferably identical to the inert particles A.
  • the recovered polymer can be used as the polymer of the layer B.
  • the inert particles B 2 are existent in the layer A, which may impair the surface flatness of the layer A on which a magnetic layer is to be formed.
  • the average particle diameter of the inert particles A should be set to 0.01 to 0.18 ⁇ m and the thickness (tB) of the layer B should account for 50 to 90%, specifically 60 to 80% of the thickness of the entire biaxially oriented polyester film.
  • the (tB/t) ratio falls below the lower limit, the amount of the recovered polymer to be used in the layer B becomes small and it is difficult to recycle all the amount of the recovered polymer.
  • (tB/t) exceeds the upper limit, the particles of the layer B greatly toss the surface of the layer A, whereby the surface properties of the layer A may be impaired and it may be difficult to increase the recording density.
  • the thickness (tB) of the layer B accounts for preferably more than 20% and less than 50% of the thickness (t) of the entire biaxially oriented polyester laminate film, and the ratio (tB/dB) of tB to the average particle diameter (dB) of all the inert particles contained in the layer B is preferably 2 to 30, more preferably 4 to 25.
  • tB/dB is preferably 0.5 to 15, more preferably 2 to 10
  • tB/t is preferably 10 to 20%, more preferably 12 to 18% to provide extremely excellent surface flatness to the biaxially oriented polyester film of the present invention so as to improve the error rate, thereby making it possible to increase the recording density and to use the recovered polymer in another film.
  • (tB/t) falls below the lower limit, the particles contained in the layer B may falloff, or chipping occurs in a die coater or the calendering step, thereby causing an error.
  • (tB/t) exceeds the upper limit, the thickness of the polyester layer B becomes large and the effect of improving the surface flatness of the film becomes unsatisfactory.
  • the biaxially oriented polyester film of the present invention whose Young's moduli in the film machine direction and the width direction are set to extremely high specific ranges is preferably manufactured, for example, by the following method because the above Young's moduli can be obtained while the film forming properties are retained.
  • the above aromatic polyester as a raw material is dried and supplied into an extruder heated at a temperature of the melting point (Tm: ° C.) of the aromatic polyester to (Tm+50)° C. to be extruded into a sheet form from a die such as a T die.
  • This extruded sheet form is solidified by quenching to obtain an unstretched film which is then stretched biaxially.
  • Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. At least transverse stretching is preferably carried out in two or more stages because this makes it easy to set the Young's modulus in the width direction to the range of the present invention and to stabilize the film forming properties.
  • longitudinal stretching is preferably carried out in two or more stages, that is, longitudinal stretching is carried out again after transverse stretching because this makes it easy to increase the Young's modulus in the film machine direction and to stabilize the film forming properties.
  • the aromatic polyester is first stretched to 4.5 to 6.5 times in the longitudinal direction at a temperature of its glass transition temperature (Tg: ° C.) to (Tg+40)° C., to 3.5 to 5.5 times in the transverse direction at (Tg+10) to (Tg+50)° C. which is higher than the above temperature for longitudinal stretching and then at a total transverse draw ratio of 5.5 to 7.0 times which is obtained by multiplying by the previous transverse draw ratio at (Tg+20) to (Tg+110)° C. which is higher than the temperature for transverse stretching, and heat set at (Tg+70) to (Tg+110)° C. for 1 to 20 seconds and further for 1 to 15 seconds.
  • Tg: ° C. glass transition temperature
  • Tg+40 glass transition temperature
  • Tg+50 glass transition temperature
  • the first transverse stretching should be divided into two or more temperature zones
  • the temperature of the former half stretching zone should be set to (Tg+5) to (Tg+20)° C.
  • the temperature of the latter half stretching zone should be set to (Tg+25) to (Tg+40)° C.
  • the transverse re-stretching should be divided into two or more temperature zones
  • the temperature of the former half stretching zone should be set to (Tg+45) to (Tg+65)° C.
  • the temperature of the latter half stretching zone should be set to (Tg+80) to (Tg+90)° C.
  • the heat setting temperature should be set to (Tg+80) to (Tg+90)° C.
  • Heat setting may be carried out simultaneous with transverse re-stretching. In this
  • heat setting is particularly preferably carried out at 202 to 210° C., specifically 203 to 208° C. for 1 to 20 seconds because both surface flatness and film forming properties can be obtained at the same time.
  • the draw ratio in the longitudinal direction When the draw ratio in the longitudinal direction is high, the Young's modulus in the film machine direction improves but the Young's modulus in the width direction lowers whereas when the draw ratio in the transverse direction is high, the Young's modulus in the film machine direction lowers but the Young's modulus in the width direction improves. Therefore, the draw ratios must be further adjusted according to the target Young's moduli.
  • the sequential biaxial stretching in which longitudinal stretching, transverse stretching, transverse re-stretching and heat setting are carried out in this order can apply to the same manufacturing method in which longitudinal stretching, transverse stretching, longitudinal re-stretching, transverse re-stretching and heat setting are carried out in this order except that the draw ratio of the first longitudinal stretching is 2.0 to 3.5 times, the draw ratio of the first transverse stretching is 3.5 to 5.5 times, and longitudinal re-stretching is carried out at a total longitudinal draw ratio of 4.5 to 6.5 times obtained by multiplying the raw ratio of the previous longitudinal stretching and a total transverse draw ratio of 5.5 to 7.0 times at a temperature between the temperature of transverse stretching and the temperature of transverse re-stretching.
  • Longitudinal stretching is preferably carried out by preheating the film at a temperature of (Tg ⁇ 20) to (Tg+10)° C. before longitudinal stretching and using an IR heater as a heater to adjust the surface temperature of the film to the above range because the effect of the present invention is easily obtained.
  • the above description has been given of sequential biaxial stretching.
  • the biaxially oriented polyester film of the present invention can be manufactured by simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are carried out simultaneously. Refer to the draw ratios and the stretching temperatures explained in the foregoing.
  • the biaxially oriented polyester film of the present invention is a laminate film
  • two or more molten polyesters are joined together in the die and extruded into a film form preferably at a temperature of the melting point of the polyester (Tm: ° C.) to (Tm+70)° C., or two or more molten polyesters are extruded from the die, joined together and solidified by quenching to obtain an unstretched laminate film which is then biaxially stretched and heat set like the above single-layer film.
  • a desired coating solution should be applied to one side or both sides of the above unstretched film or monoaxially stretched film and then the obtained film should be biaxially stretched and heat set like the above single-layer film.
  • a non-magnetic layer and a magnetic layer are formed in this order on one side of the above biaxially oriented polyester film of the present invention as a base film, and a back coat layer is formed on the other side.
  • the composition of the non-magnetic layer is not particularly limited, a thermosetting resin or a high-energy ray curable resin containing inorganic fine powders such as silica, alumina or titanium dioxide powders is used.
  • the thickness of the non-magnetic layer is preferably 0.5 to 3.0 ⁇ m, more preferably 0.5 to 2.5 ⁇ m, particularly preferably 1.0 to 2.0 ⁇ m. The above range is preferred because the effect of the present invention is easily obtained.
  • the type of the magnetic layer formed on the non-magnetic layer a so-called “coating” type magnetic layer formed by applying magnetic powders together with a binder is preferred.
  • the type of the magnetic powders constituting the magnetic layer is not particularly limited, and iron oxide, chromium oxide, cobalt coated iron oxide, and metals and alloys thereof such as iron, cobalt, iron-cobalt, iron-cobalt-nickel and cobalt-nickel are preferably used. Metals and alloys thereof are more preferred than oxides.
  • the binder constituting the magnetic layer is not particularly limited, a thermosetting resin-based binder and a high energy ray curable binder are preferred, and the magnetic layer may further contain additives such as a dispersant, lubricant and antistatic agent.
  • a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, polyurethane, polyisocyanate or a mixture thereof is preferably used.
  • the thickness of the magnetic layer is preferably 0.05 to 0.5 ⁇ m, more preferably 0.05 to 0.3 ⁇ m, particularly preferably 0.05 to 0.2 ⁇ m. The above range is preferred because the effect of the present invention is easily obtained.
  • the back coat layer is not limited to particular composition, a back coat layer containing carbon black and a thermosetting resin-based or high energy ray curable binder is preferred, and the back coat layer may further contain additives such as a dispersant, lubricant and antistatic agent.
  • a copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, polyurethane, polyisocyanate or a mixture thereof is preferably used.
  • the thickness of the back coat layer is preferably 0.1 to 1.0 ⁇ m, more preferably 0.3 to 0.8 ⁇ m. The above range is preferred because the effect of the present invention is easily obtained.
  • the thickness obtained by subtracting the thickness of the base film from the thickness of the magnetic recording tape is preferably 0.2 to 0.8 time, more preferably 0.2 to 0.6 time, particularly preferably 0.3 to 0.5 time the thickness of the base film.
  • the magnetic layer, the non-magnetic layer and the back coat layer become thin, coating becomes difficult, the surface properties of the base film exert a great influence upon the surface properties of the magnetic layer and the back coat layer, thereby causing an error, and the effect of suppressing temperature expansion with the base film becomes excessive, thereby causing track dislocation.
  • the thickness ratio exceeds the upper limit the tape becomes too thick, whereby the length of the tape stored in a cassette becomes short, thereby making it impossible to obtain a sufficiently large magnetic recording capacity and making it difficult to obtain the effect of suppressing temperature expansion with the base film.
  • a biaxially oriented polyester film which has excellent dimensional stability in the width direction when a magnetic recording tape of linear recording system is formed from the biaxially oriented polyester film can be provided, and a magnetic recording tape of linear recording system which rarely sees track dislocation and has excellent dimensional stability can be obtained as a high-density magnetic recording tape having a recording capacity of more than 500 GB by using this biaxially oriented polyester film as a base film. Therefore, the prevent invention is of extremely great industrial value.
  • the film is cut into a sample having a width of 10 mm and a length of 15 cm, and this sample is pulled with an Instron type universal tensile tester at a chuck interval of 100 mm, a pull speed of 10 mm/min and a chart speed of 500 mm/min to calculate the Young's modulus from the tangent line of a rising portion of the obtained load-elongation curve.
  • the measurement direction is the longitudinal direction of the sample, the Young's modulus is measured 10 times, and the average value of the measurement data is used.
  • the center plane average roughness (WRa) is obtained from the following equation by surface analyzing software incorporated in the non-contact 3-D roughness meter (NT-2000) of WYKO Co., Ltd. at a measurement magnification of 25 times and a measurement area of 246.6 ⁇ m in the film machine direction ⁇ 187.5 ⁇ m in the width direction (0.0462 mm 2 ). The measurement is repeated 10 times and the average value of the measurement data is used.
  • Z jk is the height of a 3-D roughness chart at a j-th position and a k-th position in the measurement direction (246.6 ⁇ m) and a direction (187.5 ⁇ m) orthogonal to the measurement direction when these directions are divided into M and N sections, respectively.
  • a particle diameter corresponding to 50 mass percent is read from a cumulative curve showing the particle diameter of each particle and the amount of the particle calculated based on the obtained centrifugal sedimentation curve and taken as the above average particle diameter.
  • the average particle diameter of the inert particles contained in the film can be measured as follows.
  • the polyester of the surface layer of the film is removed by a low-temperature plasma ashing method (for example, PR-503 of Yamato Kagaku Co., Ltd.) to expose particles.
  • the treating conditions are selected to ensure that the polyester is ashed but the particles are not damaged.
  • the exposed particles are observed through SEM (scanning electron microscope) at a magnification of 10,000 times, an image (light shade formed by the particles) of the particles is linked to an image analyzer (for example, QTM900 of Cambridge Instrument Co., Ltd.), and the area circle equivalent diameters (Di) of at least 5,000 (n) particles are obtained by changing the observation site.
  • the particle size distribution curve is formed from the obtained results to calculate the proportion of the number of particles at each peak (the area of each peak is determined with the boundary as a valley portion of the distribution curve).
  • the number average value represented by the following equation is obtained from the measurement results of the particle diameter and the number of particles in each peak area and taken as the average particle diameter (DA) of the particles.
  • the particle diameters (secondary particle diameter) of the agglomerates are measured to obtain the average particle diameter (DA).
  • the identification of the type of the particles can be made by using the quantity analysis of each metal element by SEM-XMA or ICP.
  • the content of the inert particles in the film can be measured as follows.
  • the total content of the inert particles can be measured from the weight ratio (wt %) of the particles to the sample by shaving off 100 g of the single-layer film or 100 g of each layer in the case of the polyester laminate film as a sample, selecting a solvent which dissolves the polyester but not the particles to dissolve the sample and centrifugally separating the particles from the polyester.
  • a sample obtained in the same manner as described above is combusted in a platinum crucible in a furnace at 1,000° C. for 3 hours or more, and the combusted product in the crucible is mixed with terephthalic acid (powdery) to prepare a 50 g lock-like plate.
  • the total content of the inorganic particles in each layer of this plate can be determined from the calibration curve of each element prepared from the count value of the element with wavelength dispersion type fluorescent X-rays.
  • the X-ray tube for measuring fluorescent X-rays is preferably a Cr tube and may be an Rh tube.
  • the X-ray output is set to 4 kW and the analyzing crystal is changed for each element to be measured.
  • the content of each type of inorganic particles can be determined by this measurement.
  • the proportion of particles existent in each peak area is calculated from the ratio of the number and the average particle diameter of particles constituting the peak obtained by the measurement of the average particle diameter of the inert particles contained in the film and the density of the particles, and the content (wt %) of particles existent in each peak area is obtained from this proportion of the particles and the total content of inert particles obtained by the measurement of the total amount of the inert particles.
  • the content of the organic particles and the content of the inorganic particles in each layer can be calculated from the total content of the particles in each layer and the above total content of the inorganic particles.
  • Density of crosslinked silicone resin 1.35 g/cm 3
  • Density of crosslinked polystyrene resin 1.05 g/cm 3
  • Density of crosslinked acrylic resin 1.20 g/cm 3
  • the density of the resin constituting the organic particles can be measured with a picnometer in accordance with the method described in “Fine Particle Handbook”, Asakura Shoten, 1991, p. 150 by further classifying particles centrifugally separated from the polyester by the above method.
  • Samples of the film and the magnetic recording tape are cut into pieces having a length of 15 mm and a width of 5 mm in the width direction which is the measurement direction, and these test specimens are set in the TMA3000 of Shinku Riko Co., Ltd. to be pretreated in a nitrogen atmosphere (0% RH) at 60° C. for 30 minutes and cooled to room temperature. Thereafter, the temperature is raised from 25° C. to 70° C. at a rate of 2° C./min to measure the lengths of the specimens at each temperature in order to calculate their temperature expansion coefficients (at) from the following equation.
  • the measurement direction is the longitudinal direction of the specimen, the measurement is made 5 times, and the average value of the measurement data is used.
  • ⁇ t ⁇ ( L 60 ⁇ L 40 )/( L 40 ⁇ T ) ⁇ +0.5
  • L 40 sample length at 40° C. (mm)
  • L 60 sample length at 60° C. (mm)
  • Samples of the film and the magnetic recording tape are cut into pieces having a length of 15 mm and a width of 5 mm in the width direction which is the measurement direction, and these test specimens are set in the TMA3000 of Shinku Riko Co., Ltd. and kept in a nitrogen atmosphere at 30° C. by maintaining 30% RH and 70% RH to measure the lengths of the samples so as to calculate their humidity expansion coefficients from the following equation.
  • the measurement direction is the longitudinal direction of the specimen, the measurement is made 5 times, and the average value ( ⁇ h) of the measurement data is used.
  • ⁇ h ( L 70 ⁇ L 30 )/( L 30 ⁇ H )
  • L 30 sample length at 30% RH (mm)
  • L 70 sample length at 70% RH (mm)
  • the dimensional change rates (ppm) in the width direction under the following conditions 1 and 2 are calculated from the temperature expansion coefficient and the humidity expansion coefficient measured in (4) and (5) above.
  • the dimensional change rates (ppm) in the width direction of the magnetic head under the following conditions 1 and 2 are calculated from the temperature expansion coefficient (7 ppm/° C.) and the humidity expansion coefficient (0 ppm % RH).
  • the difference (ppm) in dimensional change rate between the magnetic recording tape and the magnetic head under the following conditions 1 and 2 is taken as the amount of off-track between the magnetic recording tape and the head, and the larger change rate out of the change rates under the following conditions 1 and 2 is taken as the maximum amount of off-track.
  • the overall evaluation of the sample is ⁇ when the maximum amount of off-track measured in (6) is less than 700 ppm and the amount of creep measured in (7) is less than 0.20 and X when any one of the above evaluation items is outside the above range.
  • the error rate is obtained by recording (recording wavelength of 0.37 ⁇ ) and reproducing data with an LTO drive.
  • the error rate is obtained from the following equation based on error information (number of error bits) output from the drive and judged by the following criteria based on the error rate of Example 1 (100).
  • Error rate (number of error bits/number of write bits)
  • reference numeral 1 denotes a feed roll, 2 a tension controller, 3 a tension detector 1 (inlet), 4 , 5 , 7 and 8 guide rollers (free rollers), 6 a blade, 9 a tension detector 1 (outlet), 10 a speed controller and 11 a wind-up roll.
  • Running conditions speed of 60 m/min, tension of 60 g, running length of 50 m
  • ⁇ the deposition of powders on the edge of the blade is less than 1.0 mm ⁇ ): the deposition of powders on the edge of the blade is 1.0 mm or more and less than 2.0 mm X: the deposition of powders on the edge of the blade is more than 2.0 mm
  • edge waste produced in the manufacturing process of the biaxially oriented polyester film is ground and used in the layer B as a recovered polymer, recyclability is evaluated from the ratio of the usable recovered polymer to the weight of the polymer of the entire film based on the following criteria.
  • ⁇ 60 wt % or more of recovered polymer is usable ⁇ ): 50 wt % or more and less than 60 wt % of recovered polymer is usable ⁇ : 20 wt % or more and less than 50 wt % of recovered polymer is usable X: less than 20 wt % of recovered polymer is usable
  • the rupture elongation (%) is obtained from the equation (extended length/original length of sample) ⁇ 100 when the film is measured at 25° C. and 65% RH with an Instron type tensile tester in accordance with the method specified in JIS K-7127.
  • 50 rolls are slit to a size of 1,000 mm (width) ⁇ 8,000 m at a rate of 50 m/min and the winding properties of the slit films are evaluated based on the following criteria on the condition that a roll without bumps, projections or wrinkles on the surface of the film is accepted.
  • the film forming state is observed and evaluated based on the following criteria.
  • ⁇ no problem such as breakage during film formation and 16 hours or longer continuous film formation possible
  • ⁇ no problem such as breakage during film formation and 8 hours or longer continuous film formation possible
  • ⁇ narrow and limited film formable conditions and possible to make a roll as long as 8,000 m or more
  • X poor continuous film forming properties and difficult to make a roll as long as 8,000 m or more
  • a film (30 cm long) slit to a width of 12.65 mm (1 ⁇ 2 inch) is set as shown in FIGS. 1(A) and 1(B) in a 23° C. and 50% RH atmosphere.
  • Gold is deposited on the surface of the sample slit to a width of 12.65 mm by sputtering in advance to enable the measurement of the size in the width direction with the detector.
  • a dead weight of 32 MPa is attached to one end (the other end is fixed) of the film to measure the width (L 1 ) of the film with the laser outer-diameter measuring instrument of Keyence Co., Ltd. (body: Model 3100, sensor: Model 3060).
  • the dimensional changes rate in the width direction ( ⁇ W) before and after the temperature and humidity treatment under no load is calculated from the measured sizes before and after the above temperature and humidity treatment based on the following equation.
  • the film is measured at 10 points selected at random with a micrometer and the average value of the measurement data is used.
  • the (M+/C+) concentration ratio of the metal element (M+) derived from highest concentration particles out of the particles contained in the film in an area of 5,000 nm from the surface layer excluding the coating layer to the hydrocarbon (C+) of the polyester is taken as a particle concentration, and a portion from the surface to a depth of 5,000 nm in the thickness direction is analyzed.
  • the concentration of the particles is low in the surface layer due to the boundary of the surface and becomes higher as the distance from the surface increases.
  • the concentration of the particles becomes a stable value of 1 and rises to a stable value of 2, or decreases monotonously.
  • a depth which provides a particle concentration of (stable value of 1+stable value of 2)/2 in the former case or a depth at which the concentration of the particles becomes 1 ⁇ 2 of the stable value of 1 in the latter case (this depth is larger than the depth which provides a stable value of 1) is taken as the thickness ( ⁇ m) of the polyester layer B.
  • the measurement of the polyester layer B is carried out with a secondary ion mass spectroscope (SIMS) (6300 of PERKINELMER INC.) under the following conditions.
  • SIMS secondary ion mass spectroscope
  • the concentration distribution curve is measured with FT-IR (Fourier transform infrared spectroscopy) while etching from the surface or XPS (X-ray photoelectric spectroscopy) depending on the type of particles to obtain the thickness of each layer ( ⁇ m).
  • the thickness of the other polyester layer is obtained by subtracting the thickness of the polyester layer B from the above total thickness.
  • the density of the polyester film is measured by a density gradient tube to obtain crystallinity from the following equation.
  • ⁇ density of polyester film sample ⁇ a: 1.325 (perfect non-crystal density of polyethylene naphthalate) ⁇ c: 1.407 (perfect crystal density of polyethylene naphthalate) The unit is g/cm 3 .
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.1 times between low-speed and high-speed rolls, quenched, supplied to a stenter to be stretched to 5.2 times at 150° C. in the transverse direction and then to 1.2 times at 180° C. in the transverse direction and then heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • a back coating having the following composition was applied to the side A of the film with a die coater and dried
  • a non-magnetic coating and a magnetic coating having the following compositions were applied to the side B of the film with a die coater at the same time to different thicknesses, magnetically oriented and dried.
  • the film was calendered with a small-sized test calender (5 sets of steel rolls/nylon rolls) at a temperature of 70° C. and a line pressure of 200 kg/cm and cured at 70° C. for 48 hours.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • the thicknesses of the back coat layer, non-magnetic layer and magnetic layer after drying were 0.5 ⁇ m, 1.2 ⁇ m and 0.1 ⁇ m, respectively.
  • Titanium dioxide fine particles 100 parts by weight Eslec A (vinyl chloride-vinyl acetate copolymer of Sekisui Chemical Co., Ltd.): 10 parts by weight Nipporan 2304 (polyurethane elastomer of Nippon Polyurethane Industry Co., Ltd.): 10 parts by weight Colonate L (polyisocyanate of Nippon Polyurethane Industry Co., Ltd.): 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
  • Carbon black 100 parts by weight Thermoplastic polyurethane resin: 60 parts by weight Isocyanate compound (Colonate L of Nippon Polyurethane Industry Co., Ltd.): 18 parts by weight Silicone oil: 0.5 part by weight Methyl ethyl ketone: 250 parts by weight Toluene: 50 parts by weight
  • a PEN resin composition 3 containing 0.02 wt % of crosslinked silicone resin particles with an average particle diameter of 0.5 ⁇ m and 0.30 wt % of spherical silica particles with an average particle diameter of 0.1 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g was dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C. in the extruder, extruded onto a casting drum whose surface temperature was kept at 60° C. from a T-shaped extrusion die at a surface finish of 0.3 S and solidified by quenching to obtain an unstretched laminate film.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.5 times between low-speed and high-speed rolls, quenched, supplied to a stentor to be stretched to 4.8 times at 150° C. in the transverse direction and then to 1.2 times at 180° C. in the transverse direction and then heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 7.5 GPa in the longitudinal direction and 8.5 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • An unstretched laminate film was obtained in the same manner as in Example 1.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 3.0 times between low-speed and high-speed rolls, quenched, supplied to a stentor to be stretched to 4.0 times at 135° C. in the transverse direction and then heat set at 160° C. for 3 seconds.
  • the film was stretched to 1.9 times at 155° C. in the longitudinal direction, supplied to the stenter to be stretched to 1.7 times at 160° C. in the transverse direction and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 8.0 GPa in the longitudinal direction and 9.5 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • An unstretched laminate film was obtained in the same manner as in Example 1.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.1 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.6 times at 150° C. in the transverse direction and then heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 8.0 GPa in the longitudinal direction and 6.5 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • An unstretched laminate film was obtained in the same manner as in Example 1.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 4.3 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.7 times at 150° C. in the transverse direction and then to 1.1 times at 180° C. in the transverse direction, and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 6.0 GPa in the longitudinal direction and 9.0 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • An unstretched laminate film was obtained in the same manner as in Example 1.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 3.5 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 5.4 times at 150° C. in the transverse direction and then to 1.2 times at 180° C. in the transverse direction, and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 5.5 GPa in the longitudinal direction and 12.0 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • An unstretched laminate film was obtained in the same manner as in Example 1.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 4.9 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.7 times at 150° C. in the transverse direction and then to 1.1 times at 180° C. in the transverse direction, and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 7.0 GPa in the longitudinal direction and 7.3 GPa in the transverse direction.
  • a non-magnetic coating and a magnetic coating were applied to this film with a die coater at the same time to different thicknesses, magnetically oriented, dry calendered and cured at 70° C. for 48 hours in the same manner as in Example 1.
  • the above tape was slit to a width of 12.65 mm and set in a cassette to obtain a magnetic recording tape.
  • a PEN resin composition containing 0.38 wt % of spherical silica particles with an average particle diameter of 0.3 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition containing 0.1 wt % of crosslinked polystyrene particles with an average particle diameter of 0.8 ⁇ m and 0.9 wt. % of crosslinked polystyrene particles with an average particle diameter of 0.3 ⁇ m and having an intrinsic viscosity (ortrochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • the unstretched film obtained as described above was preheated at 120° C., further heated up to 140° C. with a heating metal roll to be stretched to 4.6 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.0 times at 145° C. in the transverse direction and then to 1.4 times at 170° C. in the transverse direction, heat set at 215° C. for 3 seconds, relaxed at a relaxation rate of 4.0% in the transverse direction in a 160° C. cooling zone, further 1.2% in the transverse direction in a 120° C. zone, cooled to room temperature and wound up as a film having a thickness of 4.3 ⁇ m.
  • Example 1 The operation of Example 1 was repeated except that the draw ratio in the longitudinal direction was changed from 5.1 times to 4.7 times, the draw ratio of re-stretching in the transverse direction was changed from 1.2 times to 1.1 times, the heat setting temperature was changed to 200° C., and the thickness was controlled as shown in Table 1.
  • Example 1 The operation of Example 1 was repeated except that the draw ratio in the longitudinal direction was changed from 5.1 times to 5.5 times, the draw ratio of re-stretching in the transverse direction was changed from 1.2 times to 1.3 times, the heat setting temperature was changed to 215° C., and the thickness was controlled as shown in Table 1.
  • a PEN resin composition 4 containing 0.03 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 5 containing 0.07 wt % of crosslinked silicone resin particles with an average particle diameter of 0.3 ⁇ m and 0.10 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.1 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 5.2 times in the transverse direction at 130° C. in the first half and at 150° C. in the latter half and then to 1.2 times in the transverse direction at 175° C. in the first half and at 205° C. in the latter half.
  • the film was heat set at 205° C. for 3 seconds while it was stretched in the latter half and cooled at 190° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 6 containing 0.09 wt % of spherical silica particles with an average particle diameter of 0.05 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 7 containing 0.15 wt % of crosslinked silicone resin particles with an average particle diameter of 0.2 ⁇ m and 0.20 wt % of spherical silica particles with an average particle diameter of 0.05 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 6.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 6.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 10 containing 0.10 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 11 containing 0.10 wt % of spherical silica particles with an average particle diameter of 0.3 ⁇ m and 0.30 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ M and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 6.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 12 containing 0.05 wt % of spherical silica particles with an average particle diameter of 0.20 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 13 containing 0.06 wt % of crosslinked silicone resin particles with an average particle diameter of 0.5 ⁇ m and 0.35 wt % of spherical silica particles with an average particle diameter of 0.2 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 6.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.5 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.8 times in the transverse direction at 130° C. in the first half and at 150° C. in the latter half and then to 1.2 times in the transverse direction at 175° C. in the first half and at 205° C. in the latter half and heat set at 190° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 7.5 GPa in the longitudinal direction and 8.5 GPa in the transverse direction.
  • Example 6 The operation of Example 6 was repeated to manufacture a magnetic recording tape from the obtained film.
  • An unstretched laminate film was obtained in the same manner as in Example 6.
  • the unstretched laminate film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 3.0 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.0 times in the transverse direction at 135° C., heat set at 160° C. for 3 seconds, stretched to 1.9 times in the longitudinal direction at 155° C., supplied to the stenter to be stretched to 1.7 times in the transverse direction at 160° C. and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 8.0 GPa in the longitudinal direction and 9.5 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 14 containing 0.05 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 15 containing 0.07 wt % of crosslinked silicone resin particles with an average particle diameter of 0.3 ⁇ m and 0.10 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.1 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 5.2 times in the transverse direction at 130° C. in the first half and at 150° C. in the latter half and then to 1.2 times in the transverse direction at 175° C. in the first half and at 205° C. in the latter half.
  • the film was heat set at 205° C. for 3 seconds while stretching at 205° C. in the latter half and then cooled to 190° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 16 containing 0.01 wt % of spherical silica particles with an average particle diameter of 0.18 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 17 containing 0.02 wt % of crosslinked silicone resin particles with an average particle diameter of 0.4 ⁇ m and 0.05 wt % of spherical silica particles with an average particle diameter of 0.18 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 10.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 18 containing 0.15 wt % of spherical silica particles with an average particle diameter of 0.05 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 19 containing 0.15 wt % of crosslinked silicone resin particles with an average particle diameter of 0.2 ⁇ m and 0.30 wt % of spherical silica particles with an average particle diameter of 0.05 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 13.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • a PEN resin composition 24 containing 0.05 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g and a PEN resin composition 25 containing 0.07 wt % of crosslinked silicone resin particles with an average particle diameter of 0.3 ⁇ m and 0.10 wt % of spherical silica particles with an average particle diameter of 0.14 ⁇ m and having an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.60 dl/g were each dried at 180° C. for 5 hours, supplied into the hopper of an extruder, molten at 300° C.
  • a biaxially oriented polyester film having a thickness of 5.0 ⁇ m was obtained from the unstretched film obtained as described above in the same manner as in Example 13.
  • the Young's modulus of the obtained film was 6.7 GPa in the longitudinal direction and 9 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 5.5 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.8 times in the transverse direction at 150° C. and then to 1.2 times in the transverse direction at 180° C., and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 7.5 GPa in the longitudinal direction and 8.5 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • the unstretched film obtained as described above was preheated at 120° C., further heated with an infrared heater having a surface temperature of 830° C. 14 mm from above to be stretched to 3.0 times between low-speed and high-speed rolls, quenched, supplied to the stenter to be stretched to 4.0 times in the transverse direction at 135° C., heat set at 160° C. for 3 seconds, stretched to 1.9 times in the longitudinal direction at 155° C., supplied to the stenter to be stretched to 1.7 times in the transverse direction at 160° C., and heat set at 205° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 ⁇ m.
  • the Young's modulus of the obtained film was 8.0 GPa in the longitudinal direction and 9.5 GPa in the transverse direction.
  • Example 1 The operation of Example 1 was repeated to manufacture a magnetic recording tape from the obtained film.
  • the biaxially oriented polyester film of the present invention can be advantageously used as a base film for magnetic recording tapes of linear recording system and data storage tapes for the back-up of computers, especially linear tape-open (LTO) tapes.
  • LTO linear tape-open

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JP6087529B2 (ja) * 2012-07-23 2017-03-01 帝人フィルムソリューション株式会社 二軸配向積層ポリエステルフィルムおよびそれを用いた塗布型磁気記録テープ
JP6049337B2 (ja) * 2012-07-23 2016-12-21 帝人フィルムソリューション株式会社 二軸配向ポリエステルフィルムおよびそれを用いた塗布型磁気記録テープ
JP6158672B2 (ja) * 2013-10-07 2017-07-05 帝人フィルムソリューション株式会社 積層ポリエステルフィルムおよび強磁性金属薄膜型磁気記録テープ
JP6301711B2 (ja) * 2014-04-11 2018-03-28 帝人フィルムソリューション株式会社 配向積層ポリエステルフィルム
WO2019093447A1 (ja) 2017-11-08 2019-05-16 ソニー株式会社 磁気記録媒体
JP6750740B2 (ja) * 2018-03-30 2020-09-02 ソニー株式会社 磁気記録媒体
JP6610823B1 (ja) 2019-03-29 2019-11-27 ソニー株式会社 磁気記録媒体
JP6590106B1 (ja) 2019-05-08 2019-10-16 ソニー株式会社 磁気記録媒体およびカートリッジ
JP6590105B1 (ja) 2019-05-08 2019-10-16 ソニー株式会社 磁気記録媒体およびカートリッジ
JP6883227B2 (ja) * 2019-10-23 2021-06-09 ソニーグループ株式会社 磁気記録媒体
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US8609264B2 (en) * 2009-05-15 2013-12-17 Toray Industries, Inc. Biaxially oriented polyester film and magnetic recording medium
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US9306083B2 (en) * 2011-03-09 2016-04-05 Fujifilm Corporation Method of producing polyester film, polyester film, and back sheet for solar cell

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EP1983512A1 (de) 2008-10-22
US8404371B2 (en) 2013-03-26
EP1983512A4 (de) 2009-02-25
JPWO2007091381A1 (ja) 2009-07-02
WO2007091381A1 (ja) 2007-08-16
JP2010218684A (ja) 2010-09-30

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