JP2012072219A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film in which when it is made as a magnetic recording medium, there is a little dimensional change by the environmental change, and which has good coating property and film making property.SOLUTION: The biaxially oriented polyester film is characterized in that the thermal shrinkage at 120°C for 30 minutes of the width direction of the polyester film is 0-5%, and the Young's modulus of the width direction thereof is 7-15 GPa.

Description

  The present invention relates to a support used for a magnetic recording medium such as a magnetic tape, and a magnetic recording medium provided with a magnetic layer on the support.

  Biaxially oriented polyester films are used in various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, especially magnetic recording media that have been strengthened using stretching technology, etc. Its usefulness as a support is well known. In recent years, magnetic recording media such as magnetic tapes are required to have high density recording in order to reduce the weight, size, and capacity of equipment. For high density recording, it is useful to shorten the recording wavelength and the recording track. However, if the recording track is made small, there is a problem that the recording track is liable to shift due to deformation caused by heat during tape running or temperature and humidity changes during tape storage. Therefore, there is an increasing demand for improvement in characteristics such as dimensional stability in the width direction in the tape use environment and storage environment. In addition, dimensional stability due to heat at the time of magnetic tape production is also important due to higher density.

  From this point of view, the support may be made of an aromatic polyamide having high rigidity superior to the biaxially oriented polyester film in terms of strength and dimensional stability. However, aromatic polyamide is expensive and expensive, and is not practical as a support for general-purpose recording media.

  To improve the dimensional stability of the polyester film in the width direction, a technology to reduce the coefficient of humidity expansion by polymer alloy or copolymerization has been disclosed, but it tends to cause slitting deterioration and tearing during film formation. There is a problem. (Patent Documents 1 to 3).

  As a result of diligent investigations on the above issues, dimensional stability, coatability, and electromagnetic conversion characteristics when magnetic tape is produced by using a special process that achieves both high orientation and low thermal shrinkage, in which the heat setting temperature is stepped. -It has been found that a biaxially oriented polyester film excellent in film formability can be obtained and many problems can be solved.

JP 2010-37448 A JP 2010-31116 A JP 2009-212277 A

  An object of the present invention is to solve the above problems and provide an excellent biaxially oriented polyester film. More specifically, it is an object of the present invention to provide a biaxially oriented polyester film that has a small dimensional change due to environmental changes when used as a magnetic recording medium, and that has good coating properties and film forming properties.

  The present invention for solving the above-described problems is characterized by the following (1) to (4).

  (1) A biaxially oriented polyester film having a thermal shrinkage rate of 0 to 5% at 120 ° C. for 30 minutes in the width direction of the polyester film and a Young's modulus in the width direction of 7 to 12 GPa.

  (2) The biaxially oriented polyester film according to (1), wherein the heat shrinkage rate at 120 ° C. for 30 minutes in the film longitudinal direction is 0 to 5%.

  (3) The biaxially oriented polyester film according to (1) or (2), wherein the humidity expansion coefficient in the film width direction is 0 to 6 ppm /% RH.

  (4) A magnetic recording medium obtained by applying a magnetic layer to the biaxially oriented polyester film described in (1) to (3).

  According to the present invention, when a magnetic recording medium is used, a biaxially oriented polyester film having little dimensional change due to environmental changes and good coating properties and film forming properties can be obtained.

  In the present invention, the polyester film is composed of, for example, a polymer having an acid component or a diol component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid as a structural unit (polymerization unit). .

  Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 6,6 ′-(alkyl). Rangeoxy) di-2-naphthoic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid, and the like. Among these, terephthalic is preferable. Acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be used. As the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, an alkylene having 2 to 10 carbon atoms is preferable, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 Examples include '-(trimethylenedioxy) di-2-naphthoic acid and 6,6'-(butyleneoxy) di-2-naphthoic acid. As the alicyclic dicarboxylic acid component, for example, cyclohexane dicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like can be used. These acid components may be used alone or in combination of two or more.

  Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2'-bis (4'- β-hydroxyethoxyphenyl) propane and the like can be used, and among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and ethylene glycol is particularly preferable. etc It can be used. These diol components may be used alone or in combination of two or more.

  The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol or phenyl isocyanate, or a trifunctional compound such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, or 2,4-dioxybenzoic acid. A compound or the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or crosslinking. In addition to the acid component and diol component, the present invention includes aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 2,6-hydroxynaphthoic acid, p-aminophenol, and p-aminobenzoic acid. As long as the effect is not impaired, the copolymerization can be further carried out.

  Polyester is preferably polyethylene terephthalate or polyethylene naphthalate (polyethylene-2,6-naphthalate). Moreover, these copolymers and modified bodies may be used.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the width direction of 7.0 to 12 GPa. When the Young's modulus in the width direction is within the above range, when used for a magnetic recording medium, the dimensional stability due to environmental changes during recording / reproduction of the magnetic recording medium becomes good. The upper limit of the Young's modulus in the width direction is more preferably 10 GPa, and still more preferably 9.0 GPa. The lower limit of the Young's modulus in the width direction is more preferably 7.2 GPa, still more preferably 7.5 GPa. A more preferable range is 7.2 to 10 GPa, and a further preferable range is 7.5 to 9.0 GPa. The Young's modulus in the width direction can be controlled by the temperature and magnification of TD stretching.

  The thermal contraction rate in the width direction of the polyester film of the present invention at 120 ° C. for 30 minutes is 0 to 5%. When the thermal shrinkage rate is larger than the above range, a process trouble such as “wrinkle” is caused when processing into a magnetic recording medium, which causes problems such as a decrease in yield of magnetic tape production. On the other hand, if it is smaller than the above range, the relaxation of the amorphous part has progressed too much, the temperature and humidity expansion coefficient becomes too high, the quality may be deteriorated, and problems such as wrinkles such as expansion during the production of the magnetic tape are caused. A more preferable upper limit is 4%, and a further preferable upper limit is 3%. The heat shrinkage rate at 120 ° C. in the width direction can be controlled by the heat setting temperature.

  The heat shrinkage rate in the longitudinal direction of the polyester film of the present invention at 120 ° C. for 30 minutes is 0 to 5%. When the thermal shrinkage rate is larger than the above range, a process trouble such as “wrinkle” is caused when processing into a magnetic recording medium, which causes problems such as a decrease in yield of magnetic tape production. On the other hand, if it is smaller than the above range, there will be a problem of wrinkles such as expansion when the magnetic tape is produced. A more preferable upper limit is 4%, and a further preferable upper limit is 3%. The heat shrinkage rate at 120 ° C. in the longitudinal direction can be controlled by the heat setting temperature.

  The biaxially oriented polyester film of the present invention has a humidity expansion coefficient in the width direction of 0 to 6 ppm /% RH. When the humidity expansion coefficient is larger than 6 ppm /% RH, when used for a magnetic recording medium, deformation due to a change in humidity increases, and dimensional stability deteriorates. A more preferred upper limit is 5.5 ppm /% RH, and even more preferred is 5 ppm /% RH. A more preferred range is 0 to 5.5 ppm /% RH, and even more preferably 0 to 5 ppm /% RH. The humidity expansion coefficient is a physical property influenced by the degree of tension of the molecular chain, and can be controlled by the TD stretch ratio.

  In the present invention, the thickness of the biaxially oriented polyester film can be appropriately determined according to the use, but usually 1 to 7 μm is preferable for the linear magnetic recording medium. When this thickness is smaller than 1 μm, electromagnetic conversion characteristics may be deteriorated when a magnetic tape is used. On the other hand, when the thickness is larger than 7 μm, the tape length per one tape is shortened, so that it may be difficult to reduce the size and increase the capacity of the magnetic tape. Therefore, in the case of high-density magnetic recording medium applications, the lower limit of the thickness is preferably 2 μm, more preferably 3 μm, and the upper limit is preferably 6.5 μm, more preferably 6 μm. A more preferable range is 2 to 6.5 μm, and a more preferable range is 3 to 6 μm.

  The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows.

  First, a polyester film constituting a biaxially oriented polyester film is manufactured. In order to produce a polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, and then cooled and solidified to form a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove unmelted material in the polymer. In addition, it is necessary to add inert particles in order to control the surface properties of the polyester film and to impart easy slipping, wear resistance, scratch resistance, and the like. Inert particles are inorganic particles, organic particles such as clay, mica, titanium oxide, calcium carbonate, carion, talc, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, etc., acrylic Examples thereof include organic particles containing acid, styrene resin, thermosetting resin, silicone, imide compound and the like, particles precipitated by a catalyst added at the time of polyester polymerization reaction (so-called internal particles), and the like. Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, and the like, provided that they do not inhibit the present invention. Conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments, dyes, and the like may be added.

  Then, after extending | stretching the said sheet | seat to the biaxial of a longitudinal direction and the width direction, it heat-processes in steps. In order to improve the dimensional stability in the width direction, the stretching step is preferably divided into two or more stages in the width direction. That is, the method of performing re-lateral stretching is preferable because it is easy to obtain a high-strength film optimal as a high dimensional stability magnetic tape. Furthermore, it is preferable to perform heat treatment stepwise because the heat shrinkage rate can be reduced while maintaining high strength.

  As the stretching method, a sequential biaxial stretching method such as stretching in the width direction and then stretching in the width direction is preferable.

  Hereinafter, the method for producing the support of the present invention will be described as an example in which polyethylene terephthalate (PET) is used as polyester. Of course, the present application is not limited to a support using a PET film, but may be one using another polymer. For example, when a polyester film is formed using polyethylene-2,6-naphthalenedicarboxylate having a high glass transition temperature or a high melting point, it may be extruded or stretched at a temperature higher than the following temperature.

  First, polyethylene terephthalate is prepared. Polyethylene terephthalate is manufactured by one of the following processes. (1) Using terephthalic acid and ethylene glycol as raw materials, a low molecular weight polyethylene terephthalate or oligomer is obtained by direct esterification reaction, and then a polymer is obtained by polycondensation reaction using antimony trioxide or titanium compound as a catalyst. Process (2) A process in which dimethyl terephthalate and ethylene glycol are used as raw materials, a low molecular weight product is obtained by transesterification, and then a polymer is obtained by polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. Here, the reaction proceeds even without a catalyst, but the transesterification usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium, titanium as a catalyst, and the transesterification reaction is carried out. After the completion of the reaction, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction.

  In order to contain the inert particles in the polyester constituting the film, a method in which the inert particles are dispersed in a predetermined proportion in the form of a slurry in ethylene glycol and this ethylene glycol is added during polymerization is preferable. When adding inert particles, for example, water sol or alcohol sol particles obtained at the time of synthesis of the inert particles are added without drying once, the dispersibility of the particles is good. It is also effective to mix an aqueous slurry of inert particles directly with PET pellets and knead them into PET using a vented biaxial kneading extruder. As a method for adjusting the content of the inert particles, a master pellet of a high concentration of inert particles is prepared by the above method, and this is diluted with PET that does not substantially contain inert particles during film formation. A method for adjusting the content of the active particles is effective.

  Next, the obtained PET pellets are dried under reduced pressure at 180 ° C. for 3 hours or more, and then supplied to an extruder heated to 270 to 320 ° C. under a nitrogen stream or under reduced pressure so that the intrinsic viscosity does not decrease. The film is extruded from a slit-shaped die and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and altered polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. To laminate the film, a plurality of different polymers are melt laminated using two or more extruders and manifolds or merge blocks.

  Next, the unstretched film thus obtained is stretched in the machine direction using the difference in peripheral speed of the roll (MD stretching) using a longitudinal stretching machine in which several rolls are arranged, and subsequently A biaxial stretching method in which transverse stretching (TD stretching) is performed using a stenter will be described.

  First, the unstretched film is MD stretched. The stretching temperature for MD stretching varies depending on the type of polymer used, but can be determined using the glass transition temperature Tg of the unstretched film as a guide. It is preferable that it is the range of Tg-10-Tg + 15 degreeC, More preferably, it is TgC-Tg + 10 degreeC. When the stretching temperature is lower than the above range, film tearing frequently occurs and productivity may be lowered. The MD draw ratio is preferably 2.5 to 4.0 times. More preferably, it is 2.8 to 3.8 times, and still more preferably 3.0 to 4.0 times.

  Next, TD stretching is performed using a stenter. The draw ratio of TD stretching is preferably 3.0 to 5.0 times, more preferably 3.2 to 4.5 times, and still more preferably 3.5 to 4.0 times. The stretching temperature for TD stretching is preferably in the range of Tg-10 to Tg + 15 ° C, more preferably Tg ° C to Tg + 10 ° C.

  Although heat setting is performed after TD stretching, it is preferable to perform heat treatment at two stages of temperature in order to suppress orientation relaxation of the film. The first stage of heat setting treatment is preferably TD stretching 2 stretching temperature to TD stretching 2 stretching temperature + 30 ° C., TD stretching 2 stretching temperature + 5 to TD stretching 2 stretching temperature + 25 ° C. while relaxing the film in tension or in the width direction. It is. The heat treatment time is preferably in the range of 0.5 to 10 seconds. Further, the second stage is preferably performed at 110 to 130 ° C. More preferably, it is 115-125 degreeC. More preferably, the heat setting treatment is performed at 120 ° C., which is the treatment temperature during the production of the magnetic tape. By bringing the heat treatment temperature and the heat setting temperature at the time of magnetic tape production close to each other, it is possible to take out molecular chain distortion while maintaining high orientation and suppress deterioration of dimensional stability and applicability. Then, after cooling to 25 ° C., the film edge can be removed to obtain the biaxially stretched polyester film of the present invention.

  Next, a method for manufacturing a magnetic recording medium will be described.

  The magnetic recording medium support (biaxially oriented polyester film) obtained as described above is slit into, for example, a width of 0.1 to 3 m, and conveyed at a speed of 20 to 300 m / min and a tension of 50 to 300 N / m. On the other hand, a magnetic paint and a non-magnetic paint are applied to one surface (A surface) with an extrusion coater. A magnetic paint is applied to the upper layer with a thickness of 0.1 to 0.3 μm, and a nonmagnetic paint is applied to the lower layer with a thickness of 0.5 to 1.5 μm. Thereafter, the support coated with the magnetic coating material and the nonmagnetic coating material is magnetically oriented and dried at a temperature of 80 to 130 ° C. Next, a back coat is applied to the opposite surface (B surface) with a thickness of 0.3 to 0.8 μm, and after calendar treatment, it is wound up. The calendering is performed using a small test calender (steel / nylon roll, 5 stages) at a temperature of 70 to 120 ° C. and a linear pressure of 0.5 to 5 kN / cm. Thereafter, the film is aged at 60 to 80 ° C. for 24 to 72 hours, slit to a width of 1/2 inch (1.27 cm), and a pancake is produced. Next, a specific length from this pancake is incorporated into a cassette to obtain a cassette tape type magnetic recording medium.

  Here, examples of the composition of the magnetic paint include the following compositions.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by weight Modified vinyl chloride copolymer: 10 parts by weight Modified polyurethane: 10 parts by weight Polyisocyanate: 5 parts by weight 2-ethylhexyl oleate: 1.5 parts by weight Palmitic acid: 1 Mass parts-Carbon black: 1 part by mass-Alumina: 10 parts by mass-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of back coat)
Carbon black (average particle size 20 nm): 95 parts by mass Carbon black (average particle size 280 nm): 10 parts by mass Alumina: 0.1 parts by mass Modified polyurethane: 20 parts by mass Modified vinyl chloride copolymer: 30 Mass parts: Cyclohexanone: 200 parts by mass Methyl ethyl ketone: 300 parts by mass Toluene: 100 parts by mass Magnetic recording media are, for example, data recording applications, specifically computer data backup applications (for example, linear tape recording media (LTO4 And LTO5))) and digital image recording applications such as video.

(Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Young's modulus The Young's modulus of a film is measured according to ASTM-D882 (1997). Instron type tensile tester is used and the conditions are as follows. The average value of the five measurement results is defined as the Young's modulus in the present invention.

・ Measuring device: Model 5848, an ultra-precision material testing machine manufactured by Instron
・ Sample size:
When measuring Young's modulus in the film width direction Film length direction 2 mm x film width direction 12.6 mm
(The gripping distance is 8mm in the film width direction)
When measuring Young's modulus in the longitudinal direction of the film 2 mm in the film width direction × 12.6 mm in the film longitudinal direction
(Grip interval is 8mm in the longitudinal direction of the film)
・ Tensile speed: 1 mm / min ・ Measurement environment: Temperature 23 ° C., humidity 65% RH
-Number of measurements: 5 times.

(2) Humidity expansion coefficient in the width direction Measurement is performed under the following conditions in the width direction of the film, and an average value of three measurement results is defined as a humidity expansion coefficient in the present invention.

Measuring device: Thermomechanical analyzer TMA-50 manufactured by Shimadzu (humidity generator: humidity control device HC-1 manufactured by ULVAC-RIKO)
Sample size: 10 mm in the film longitudinal direction x 12.6 mm in the film width direction
・ Load: 0.5g
・ Number of measurements: 3 times ・ Measurement temperature: 30 ° C.
・ Measurement humidity: Measured dimensions by holding at 40% RH for 6 hours, increasing the humidity to 80% RH in 40 minutes and holding at 80% RH for 6 hours, and then measuring the dimensional change ΔL (mm) in the width direction of the support. taking measurement. The humidity expansion coefficient (ppm /% RH) is calculated from the following equation.

Humidity expansion coefficient (ppm /% RH) = 10 ⁶ × {(ΔL / 12.6) / (80-40)}
(3) Thermal contraction rate It measured according to JIS C2318 (2007).

・ Sample size: width 10mm, marked line interval 200mm
-Treatment conditions: Temperature 120 ° C, treatment time 30 minutes, no load condition-Thermal contraction rate was determined from the following equation.

Heat shrinkage rate (%) = {(L ₀ −L) / L ₀ } × 100
L ₀ : Marking interval before heat treatment L: Marking interval after heat treatment However, the sample size may be measured by reducing the mark interval depending on the size of the obtained sample.

(4) Refractive index It measured using the following measuring device according to JIS-K7105 (1981).

・ Device: Abbe refractometer 4T (manufactured by Atago Co., Ltd.)
-Light source: Sodium D line-Measurement temperature: 25 ° C
・ Measurement humidity: 65% RH
・ Measurement range: ~ 1.87
Mount solution: methylene iodide, sulfur methylene iodide birefringence Δn = (nMD−nTD)
nMD: Refractive index in the film longitudinal direction nTD: Refractive index in the film width direction (5) Melting point (Tm)
According to JIS-K7121 (1987), a differential scanning calorimeter, DSC (RDC220) manufactured by Seiko Instruments Inc., and a disk station (SSC / 5200) manufactured by Seiko Instruments Inc. were used, and a sample 5 mg was placed on an aluminum tray 25 The temperature was raised from 0 ° C. to 300 ° C. at a heating rate of 20 ° C./min. At that time, the peak temperature of the endothermic peak of melting observed is the melting point (Tm)
(6) Glass transition temperature (Tg)
Specific heat is measured with the following equipment and conditions, and determined according to JIS-K7121 (1987).

・ Device: Temperature modulation DSC manufactured by TA Instrument
-Measurement conditions-Heating temperature: 270-570K (RCS cooling method)
・ Temperature calibration: Melting point of high purity indium and tin ・ Temperature modulation amplitude: ± 1K
・ Temperature modulation period: 60 seconds ・ Temperature increase step: 5K
・ Sample weight: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature is calculated by the following formula.

Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(7) Stability of width dimension A film slit to a width of 1 m is conveyed with a tension of 200 N, and a magnetic paint and a non-magnetic paint having the following composition are applied on one surface (side A) of the support by an extrusion coater ( The upper layer is made of magnetic paint, the coating thickness is 0.2 μm, the lower layer is made of non-magnetic paint and the coating thickness is 0.9 μm), magnetically oriented, and dried at a drying temperature of 100 ° C. Next, a back coat having the following composition was applied to the opposite surface (B surface), and then at a temperature of 85 ° C. and a linear pressure of 2.0 × 10 ⁵ N / m using a small test calender device (steel / nylon roll, 5 steps). After calendaring with, take up. The original tape is slit to a width of 1/2 inch (12.65 mm) to make a pancake. Next, a length of 200 m from this pancake is incorporated into a cassette to form a cassette tape.

(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by mass [Fe: Co: Ni: Al: Y: Ca = 70: 24: 1: 2: 2: 1 (mass ratio)]
[Long axis length: 0.09 μm, axial ratio: 6, coercive force: 153 kA / m (1,922 Oe), saturation magnetization: 146 Am ² / kg (146 emu / g), BET specific surface area: 53 m ² / g, X-ray Particle size: 15 nm]
Modified vinyl chloride copolymer (binder): 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Modified polyurethane (binder): 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
Polyisocyanate (curing agent): 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass Carbon black (antistatic agent): 1 part by mass (average primary particle size: 0.018 μm)
Alumina (abrasive): 10 parts by mass (α alumina, average particle size: 0.18 μm)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of nonmagnetic paint)
Modified polyurethane: 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass-Polyisocyanate: 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
・ 2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass (composition of back coat)
Carbon black: 95 parts by mass (antistatic agent, average primary particle size 0.018 μm)
Carbon black: 10 parts by mass (antistatic agent, average primary particle size 0.3 μm)
Alumina: 0.1 part by mass (α alumina, average particle size: 0.18 μm)
Modified polyurethane: 20 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 30 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
• Cyclohexanone: 200 parts by mass • Methyl ethyl ketone: 300 parts by mass • Toluene: 100 parts by mass Take out the tape from the cassette tape cartridge, put the sheet width measuring device prepared as shown in FIG. Measure. The sheet width measuring device shown in FIG. 1 is a device that measures the width dimension using a laser, and fixes the magnetic tape 9 to the load detector 3 while setting it on the free rolls 5 to 8, and the end portion A weight 4 serving as a load is hung on. When this magnetic tape 9 is irradiated with the laser beam 10, the laser beam 10 oscillated linearly in the width direction from the laser oscillator 1 is blocked only by the portion of the magnetic tape 9, enters the light receiving unit 2, and the blocked laser beam The width is measured as the width of the magnetic tape. The average value of the three measurement results is defined as the width in the present invention.

・ Measuring device: Sheet width measuring device manufactured by Ayaha Engineering Co., Ltd. ・ Laser oscillator 1, light receiving unit 2: Laser dimension measuring device LS-5040 manufactured by Keyence Corporation
-Load detector 3: Load cell CBE1-10K manufactured by NMB
・ Constant temperature and humidity chamber: SE-25VL-A manufactured by Kato Corporation
・ Load 4: Weight (longitudinal direction)
・ Sample size: width 1/2 inch x length 250 mm
-Retention time: 5 hours-Number of measurements: 3 measurements.

(Width dimensional change rate: dimensional stability)
The width dimension (l _A , l _B ) is measured under two conditions, and the dimensional change rate is calculated by the following equation. Specifically, dimensional stability is evaluated according to the following criteria.

By measuring the lapse of 24 hours after _{l A} in A conditions, measuring the _{l B} after a lapse of 24 hours then B conditions. Three points were measured: a sample cut from the 30 m point from the beginning of the tape cartridge, a sample cut from the 100 m point, and a sample cut from the 170 m point. X is rejected.

A condition: 10 ° C, 10% RH, tension 0.8N
B condition: 29 ° C, 80% RH, tension 0.5N
Width dimensional change rate (ppm) = 10 ⁶ × ((l _B -l _A ) / l _A )
A: Maximum width change rate is less than 500 (ppm) ○: Maximum width change rate is 500 (ppm) or more and less than 600 (ppm) Δ: Maximum width change rate is 600 (ppm) or more Less than 700 (ppm) ×: The maximum value of the width dimensional change rate is 700 (ppm) or more. (8) Coating property
The cassette tape produced in the above (7) was evaluated for applicability of the magnetic layer of the tape according to the following criteria.

  A: There is no unevenness, coating omission, or peeling at all, and coating properties are good.

  ○: There is almost no unevenness, missing coating, or peeling, and there is no problem in coating properties.

  Δ: Unevenness, coating omission, and peeling sometimes occur and there is a slight problem in coating properties.

  X: Unevenness, coating omission, and peeling frequently occur, and there is a problem in applicability.

(9) Film-formation stability The film-formability of the film was evaluated according to the following criteria.

  ○: Stable film formation is possible with almost no film tearing.

  (Triangle | delta): Film tearing generate | occur | produces occasionally and film forming stability is a little low.

  X: Many film breaks occur and the film formation stability is low.

  Based on the following examples, embodiments of the present invention will be described. Here, polyethylene terephthalate is expressed as PET and polyethylene naphthalate PEN.

(Reference Example 1)
194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140 ° C. and dissolved. Then, 0.1 mass part of magnesium acetate tetrahydrate and 0.05 mass part of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at 140 to 230 ° C. Next, 1 part by mass (5 parts by mass as trimethyl phosphate) of 5 parts by mass ethylene glycol solution of trimethyl phosphate was added.

  Addition of trimethyl phosphoric acid in ethylene glycol reduces the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. When the temperature of the reaction contents in the transesterification reactor thus reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

After the transition, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach the final temperature and final pressure was both 60 minutes. After reaching the final temperature and the final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the agitation torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus. The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was a predetermined value). Accordingly, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain polyethylene terephthalate PET pellets X having an intrinsic viscosity of 0.62. (Tm = 255 ° C., Tg = 78 ° C.)
(Reference Example 2)
In the same direction rotation type vent type biaxial kneading extruder heated to 280 ° C., 99 parts by mass of PET pellet X prepared in Reference Example 1 and 10 parts by mass of water slurry of colloidal silica particles having an average diameter of 0.06 μm. 10 parts by mass (1 part by mass as colloidal silica particles), the vent hole is maintained at a reduced pressure of 1 kPa or less, moisture is removed, and 1 part by mass of colloidal silica particles having an average diameter of 0.06 μm is contained. .62 PET pellets Z _0.06 were obtained.

(Reference Example 3)
In the same direction rotation type bent type biaxial kneading extruder heated to 280 ° C., 98 parts by mass of PET pellet X prepared in Reference Example 1 and 10 parts by mass of water of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm. The slurry is supplied in an amount of 20 parts by mass (2 parts by mass as spherical cross-linked polystyrene), the vent hole is maintained at a reduced pressure of 1 kPa or less to remove moisture, and 2 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm are contained. PET pellet Z _0.3 with a viscosity of 0.62 was obtained.

(Reference Example 4)
Two spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were obtained in the same manner as in Reference Example 2, except that spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were used instead of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm. PET pellets Z _0.8 having an intrinsic viscosity of 0.62 and contained in parts by mass were obtained.

(Reference Example 5)
To a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added and gradually increased from a temperature of 150 ° C. to a temperature of 240 ° C. The transesterification was carried out while raising the temperature. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by mass of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Thereafter, a transesterification reaction was carried out, and 0.023 parts by mass of trimethyl phosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290 ° C., subjected to a polycondensation reaction under a high vacuum of 30 Pa, and the stirring torque of the polymerization apparatus is a predetermined value (specifically depending on the specifications of the polymerization apparatus). Although this value was different, the value indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65 in this polymerization apparatus was a predetermined value). Therefore, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in the form of a strand, and immediately cut to obtain PEN pellet X ′ having an intrinsic viscosity of 0.65.

(Reference Example 6)
The PEN pellet X ′ produced in Reference Example 7 was added to 99 parts by mass and 10 parts by mass of colloidal silica particles having an average diameter of 0.06 μm in the same direction rotation type bent type twin-screw kneading extruder heated to 280 ° C. Intrinsic viscosity containing 10 parts by mass of slurry (1 part by mass as colloidal silica particles), holding the vent hole at a reduced pressure of 1 kPa or less, removing moisture, and containing 1 part by mass of colloidal silica particles having an average diameter of 0.06 μm 0.65 PEN pellets Z ′ _0.06 were obtained.

(Reference Example 7)
A PEN pellet X ′ prepared in Reference Example 7 was 98 parts by mass and 10 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm in the same direction rotation type bent type twin-screw kneading extruder heated to 280 ° C. 20 parts by mass of water slurry (2 parts by mass as spherical cross-linked polystyrene) is supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less to remove water, and 2 parts by mass of spherical cross-linked polystyrene particles having an average diameter of 0.3 μm are contained. PEN pellets Z ′ _0.3 having an intrinsic viscosity of 0.65 were obtained.

(Reference Example 8)
Two spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were obtained in the same manner as in Reference Example 9 except that spherical crosslinked polystyrene particles having an average diameter of 0.8 μm were used instead of spherical crosslinked polystyrene particles having an average diameter of 0.3 μm. PEN pellets Z ′ _0.8 having an intrinsic viscosity of 0.65 and contained by mass were obtained.

Example 1
In the extruder E heated to 280 ° C. using two extruders E and F, 80 parts by mass of the PET pellet X obtained in Reference Examples 1 and 2 and 20 parts by mass of the PET pellet Z _0.06 were added at 180 ° C. 3 time was dried under reduced pressure was supplied after, the same 280 ° C. the extruder was heated to F, PET pellets X84 parts by mass obtained in reference example 1, 3, 4, 5, PET pellets _{Z 0.3} 15 parts by weight, Further, 1 part by mass of PET pellet Z _0.8 was dried at 180 ° C. under reduced pressure for 3 hours and then supplied. Two layers are joined together in a T-die (lamination ratio E (A side) / F (B side) = 20/1), and solidified by cooling while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C. Then, a laminated unstretched film was produced.

  Subsequently, the obtained unstretched laminated film was preheated with a heated roll group, then stretched 3.3 times at a temperature of 90 ° C. (MD stretching), and cooled with a roll group at a temperature of 25 ° C. to be uniaxially stretched. A film was obtained. While holding both ends of the obtained uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 85 ° C. in the tenter, and then continuously in the heating zone at a temperature of 90 ° C. in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4.0 times (TD stretch). Subsequently, a heat treatment for 5 seconds was performed in a heat treatment zone in the tenter at a temperature of 180 ° C., and a treatment was further performed at a temperature of 120 ° C. Subsequently, after uniformly cooling to 25 ° C., the film edge was removed, and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 5 μm. When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, it had excellent properties in dimensional stability, applicability, and film formability.

(Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, the Young's modulus in the TD direction was low when used as a magnetic tape. Had the characteristics.

(Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, because of its high Young's modulus in the TD direction when used as a magnetic tape, the film stability is slightly inferior to the dimensional stability and film forming property. It had excellent properties.

Example 4
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, when used as a magnetic tape, the thermal shrinkage rate at 120 ° C. in the TD direction was large, but the coating stability was slightly inferior, but the dimensional stability, It had excellent film properties.

(Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were changed as shown in Table 1.

  When the obtained biaxially oriented polyester film was evaluated, as shown in Table 2, since it has a large coefficient of humidity expansion when used as a magnetic tape, it has excellent coating properties and film forming properties although it is slightly inferior in dimensional stability. Had.

(Example 6)
The PET pellet X, PET pellet Z _0.06 , PET pellet Z _0.3 , and PET pellet Z _0.8 used in Example 1 were used as the PEN pellet X ′ and PEN obtained in Reference Examples 5, 6, 7, and 8. Example 1 except that the pellets Z ′ _0.06 , the PEN pellets Z ′ _0.3 and the PEN pellets Z ′ _0.8 were changed to produce a laminated unstretched film and the film forming conditions were changed as shown in Table 1. In the same manner as above, a biaxially oriented polyester film was obtained.

  When the obtained biaxially oriented polyester film was evaluated, as shown in the table, the film had excellent dimensional stability, applicability, and film formability.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched under the film forming conditions shown in Table 1. Since the thermal shrinkage rate at 120 ° C. in the TD direction was large, the obtained biaxially oriented polyester film was greatly inferior in applicability.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched under the film forming conditions shown in Table 1. Since the thermal shrinkage rate at 120 ° C. in the TD direction has a negative value and expands, the applicability is greatly inferior.

(Comparative Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched under the film forming conditions shown in Table 1. Since the TD Young's modulus was small, the obtained biaxially oriented polyester film was greatly inferior in dimensional stability.

(Comparative Example 4)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the film was stretched under the film forming conditions shown in Table 1. Since the TD stretch ratio was large, the film forming property was deteriorated and a biaxially oriented polyester film could not be stably obtained.

It is a schematic diagram of the sheet | seat width measuring apparatus used when measuring a width dimension.

1: Laser oscillator 2: Light receiving unit 3: Load detector 4: Load 5: Free roll 6: Free roll 7: Free roll 8: Free roll 9: Magnetic tape 10: Laser light

Claims (4)

A biaxially oriented polyester film having a heat shrinkage rate of 0 to 5% at 120 ° C for 30 minutes in the width direction of the polyester film and a Young's modulus in the width direction of 7 to 12 GPa. The biaxially oriented polyester film according to claim 1, wherein the heat shrinkage rate at 120 ° C for 30 minutes in the longitudinal direction of the film is 0 to 5%. The biaxially oriented polyester film according to claim 1 or 2, wherein a humidity expansion coefficient in the film width direction is 0 to 6 ppm /% RH. A magnetic recording medium obtained by applying a magnetic layer to the biaxially oriented polyester film according to claim 1.

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