JP2004130594A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film excellent in dimensional stability in a use environment, reduced in the deformation against load and especially suitable as a base film for a high density magnetic recording tape. <P>SOLUTION: The biaxially oriented polyester film is based on a polyester and the heat shrinkage factor in the longitudinal direction of the film under a 55°C/100 hr condition is -0.03-0.05% and the Young's modulus in the longitudinal direction of the film is 6-15 GPa. <P>COPYRIGHT: (C)2004,JPO

Description

【００６５】
表１において、「長手」は、長手方向を、また、「幅」は、幅方向を意味する。
【００６６】
【表２】

【００６７】
【発明の効果】
本発明によれば、使用環境での寸法安定性に優れ、荷重に対する変形が少ない二軸配向ポリエステルフィルムを得ることができ、特に高密度磁気記録テープ用ベースフィルムとして好適な二軸配向ポリエステルフィルムを得ることができる。具体的には磁気記録媒体用として、走行耐久性、保存性、加工適性の優れたベースフィルムを得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biaxially oriented polyester film, and more particularly, to a biaxially oriented polyester film useful as a base film for a high-density magnetic recording medium.
[0002]
[Prior art]
In recent years, magnetic recording tapes are becoming thinner and have higher recording densities for miniaturization and long-term recording, and there is an increasing demand for improvement in tape elongation deformation due to tension and dimensional change in the usage environment. Has become. Due to these developments in the field of magnetic recording tapes, there is an increasing demand for base films to have higher strength and to improve morphology and dimensional stability in a use environment.
[0003]
Aramid films have conventionally been used as base films that can meet the above requirements from the viewpoint of strength and dimensional stability. This aramid film is expensive and disadvantageous in terms of cost, but is currently used because there is no performance alternative.
[0004]
On the other hand, as a conventional technique for increasing the strength of a biaxially oriented polyester film, it is common to stretch a film stretched in two directions in the vertical and horizontal directions again in the vertical direction to increase the strength in the vertical direction (for example, Patent Document 1). Further, when it is desired to impart strength further in the horizontal direction, a re-longitudinal re-horizontal stretching method or the like has been proposed in which, after re-longitudinal stretching, stretching is performed in the horizontal direction again (for example, Patent Document 2). In such a high-strength polyester film obtained by such a conventional technique, dimensions change due to stress-elongation deformation or environmental conditions, a deviation occurs in a recording track, an error occurs during recording and reproduction, and a desired magnetic conversion characteristic is obtained. There are problems such as not. Therefore, there is a relaxation heat treatment as a technique for improving the dimensional change under environmental conditions. The relaxation heat treatment is a heat treatment in which the produced biaxially oriented polyester film is subjected to a heat treatment in a relaxed state, for example, after the biaxially oriented polyester film is heat set in a heat fixing zone of a tenter by a tenter method, and then released from a tenter clip. A method for producing a biaxially oriented polyester film which is pulled in a relaxed state by a take-off roll at a speed lower than the tenter speed (for example, Patent Document 3), or while giving a restricted shrinkage of 1 to 10% in the width direction of the biaxially oriented polyester film. A method has been proposed in which heat setting is performed and then relaxation heat treatment is performed by a floating treatment method using air pressure (for example, Patent Document 4). However, these methods have problems such as a decrease in the strength of the film and a undulation of the film, resulting in a deterioration in flatness, and it is more difficult to reduce the heat shrinkage at 55 ° C. for 100 hours to a desired level. Was.
[0005]
Further, in recent years, a simultaneous biaxial tenter of a linear motor type has been developed, and has attracted attention due to its high film forming speed (for example, Patent Documents 5 to 7). That is, in the conventional simultaneous biaxial stretching method, a screw method in which a clip is placed in a groove of a screw to increase a clip interval, or a pantograph method in which a clip interval is increased using a pantograph, etc. There are problems such as a low film speed, difficulty in changing conditions such as stretching ratio, and difficulty in stretching at high magnification. On the other hand, the simultaneous biaxial stretching method of the linear motor method may solve these problems at once. Patent Literature 5 discloses that the interval between tenter clips is changed by electric force generated by a linear motor to enable high-efficiency production. Patent Document 6 discloses a stretching system using a linear motor, and Patent Document 7 discloses a system effective for controlling a large number of linear motors along a stretching section. Further, process conditions for producing a polyester film having excellent physical properties and quality using the simultaneous biaxial tenter of the linear motor type are also being studied (for example, Patent Document 8). However, in the manufacturing process of Patent Document 8, as a relaxation heat treatment condition, it is only described that a series of stretching and subsequent relaxation operations is performed twice or more and less than 10,000 times. It was difficult to reduce the heat shrinkage to a desired level.
[0006]
[Patent Document 1] Japanese Patent Publication No. 42-9270
[Patent Document 2] Japanese Patent Application Laid-Open No. 50-133276
[Patent Document 3] Japanese Patent Publication No. 6-43097
[Patent Document 4] Japanese Patent Publication No. 6-67601
[Patent Document 5] Japanese Patent Publication No. 51-33590
[Patent Document 6] US Pat. No. 4,853,602
[Patent Document 7] US Pat. No. 4,675,582
[Patent Document 8] JP-A-2000-885
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a biaxially oriented polyester film which is excellent in dimensional stability in a use environment and has little deformation under load, and is particularly suitable as a base film for a high density magnetic recording tape. Is to provide.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, after stretching with a simultaneous biaxial stretching machine with a linear motor, the film was subjected to relaxation heat treatment in both the longitudinal direction and the width direction, so that the heat shrinkage in the longitudinal direction was reduced. In a certain range, and when a biaxially oriented polyester film in the range where the Young's modulus in the longitudinal direction is within a certain range, it is found that it becomes a biaxially oriented polyester film particularly suitable as a base film for a high-density magnetic recording tape, The present invention has been completed.
[0009]
That is, the biaxially oriented polyester film of the present invention is a biaxially oriented polyester film containing polyester as a main component, and has a heat shrinkage in the longitudinal direction of the film at −55 ° C. for 100 hours of −0.03 to 0.05. %, And the Young's modulus in the longitudinal direction is within a range of 4 to 15 GPa.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The polyester constituting the biaxially oriented polyester film of the present invention is, for example, a polymer having an acid component such as an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid or a diol component as a structural unit (polymerized unit). .
[0011]
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, and 4,4′-diphenyldicarboxylic acid Acids, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid, and the like can be used, and among them, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be preferably used. . As the alicyclic dicarboxylic acid component, for example, cyclohexanedicarboxylic 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.
[0012]
Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-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, among which ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol, etc. can be used, and particularly preferred. , Ethylene glycol Can be used. These diol components may be used alone or in combination of two or more.
[0013]
Further, a monofunctional compound such as lauryl alcohol and phenyl isocyanate may be copolymerized in the polyester, or trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, etc. A trifunctional compound or the like may be copolymerized within a range where the polymer is substantially linear without excessive branching or crosslinking. Furthermore, in addition to the acid component and the diol component, aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, and 2,6-hydroxynaphthoic acid, p-aminophenol, p-aminobenzoic acid, and the like are also used in the present invention. If the amount is small enough not to impair the effect of the above, copolymerization can be further performed.
[0014]
The polyester is not particularly limited, but is preferably polyethylene terephthalate or poly-2,6-naphthalenedicarboxylate. Further, these copolymers and modified products may be used.
[0015]
The method for producing the polyester is not particularly limited, and for example, the following conventional method is employed. Bis-β-hydroxyethyl terephthalate (BHT) is prepared by esterifying terephthalic acid and ethylene glycol or by transesterifying dimethyl terephthalate and ethylene glycol. Next, this BHT is transferred to a polymerization tank, and heated to 280 ° C. under vacuum to advance the polymerization reaction. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained polyester is subjected to solid phase polymerization under reduced pressure in the form of pellets. This solid phase polymerization is carried out by preliminarily precrystallizing at a temperature of 180 ° C. or lower and then performing solid phase polymerization at 190 to 250 ° C. under a reduced pressure of about 1 mmHg for 10 to 50 hours.
[0016]
Further, as a manufacturing method when particles are contained in the polyester constituting the film, a method in which particles are dispersed in ethylene glycol at a predetermined ratio in a slurry state, and the particles-containing ethylene glycol is polymerized with terephthalic acid is preferable. . When the particles are added, for example, a method of adding a water sol or an alcohol sol obtained at the time of synthesizing the particles without once drying them is preferable because the particles have good dispersibility. It is also effective to directly mix the water slurry of the particles with predetermined polyester pellets and knead the polyester with a vented twin-screw extruder. As a method of adjusting the content of particles and the number of particles, a master pellet containing a high concentration of particles is prepared by the above-described method, and at the time of film formation, the content of the particles is diluted with a polyester substantially containing no particles. Adjusting the amount is effective.
[0017]
The biaxially oriented polyester film of the present invention has a heat shrinkage in the longitudinal direction of the film at −55 ° C. for 100 hours within a range of −0.03 to 0.05%, and a Young's modulus in the longitudinal direction of 6 to 100%. It must be in the range of 15 GPa. Within the above range, a biaxially oriented polyester film having good dimensional stability and suitable for a magnetic recording medium can be obtained. When the heat shrinkage in the longitudinal direction exceeds 0.05%, for example, in the case of a magnetic recording medium, the heat history in a film processing step such as applying a magnetic layer to a base film, or the magnetic tape and magnetic recording head during running. Thermal deformation of the tape due to the frictional heat may occur, or the storage stability of the tape may deteriorate. On the other hand, when the content is less than -0.03%, the film expands and wrinkles are easily generated. More preferably, it is -0.01 to 0.04%, and still more preferably 0 to 0.03%. When the Young's modulus in the longitudinal direction is less than 6 GPa, for example, in the case of a magnetic recording medium, elongation occurs in the magnetic tape due to the tension received from the magnetic head and the guide pins during running, which adversely affects the electromagnetic conversion characteristics (output characteristics). It may not be practically usable due to application or poor head contact with the magnetic head. In addition, a biaxially oriented polyester film having a Young's modulus in the longitudinal direction of more than 15 GPa may be industrially difficult to produce or may have a marked decrease in tear resistance and dimensional stability. More preferably, it is 6.5 to 13 GPa, and further preferably, it is 7 to 10 GPa.
[0018]
In the biaxially oriented polyester film of the present invention, in the crystal orientation analysis by the diffractometer method of wide-angle X-ray diffraction, the diffraction peak of the crystal plane in the polyester main chain direction obtained when the sample film is rotated around its normal line is obtained. The half width in the circumferential direction is not particularly limited, but is preferably in the range of 50 to 85 °. The circumferential half-width of the diffraction peak of the crystal plane in the polyester main chain direction represents the spread of the distribution in the direction of the orientation of the crystal of the biaxially oriented polyester film, and when this half-width is less than 50 °, The storage stability is deteriorated due to the poor dimensional stability of the film, and the tear propagation resistance of the film is reduced, so that the tape is easily broken. If the half width exceeds 85 °, a film having high strength in all directions in the plane of the film cannot be obtained. Here, the crystal plane in the polyester main chain direction is a crystal plane whose normal line is closest to the polyester main chain direction among crystal planes detected as diffraction peaks by the wide-angle X-ray diffractometer method. And (-105) plane for polyethylene terephthalate and (-306) plane for polyethylene-2,6-naphthalate. The half width is more preferably in the range of 55 to 83 °, and still more preferably in the range of 60 to 80 °.
[0019]
The biaxially oriented polyester film of the present invention has a surface roughness Ra of one film surface (A surface). _A Is not particularly limited, but is preferably in the range of 1 to 10 nm. The thickness is preferably 1 nm or more from the viewpoint of reducing friction with the magnetic recording head, and is preferably 10 nm or less from the viewpoint of electromagnetic conversion characteristics. More preferably, it is 2 to 9 nm, and further preferably, it is 3 to 8 nm. In addition, the surface roughness Ra of the film surface (Side B) on the side opposite to A side _B Is not particularly limited, but is preferably in the range of 5 to 20 nm. The thickness is preferably 5 nm or more from the viewpoint of handling properties in the processing step, and is preferably 20 nm or less from the viewpoint of reducing transfer by pressing pressure when wound as a tape. It is more preferably 6 to 18 nm, and still more preferably 7 to 15 nm.
[0020]
The biaxially oriented polyester film of the present invention is not particularly limited, but the heat shrinkage in the width direction of the film at 55 ° C. for 100 hours is in the range of −0.03 to 0.05%, and the Young's modulus in the width direction. Is preferably in the range of 4 to 15 GPa. When the heat shrinkage in the width direction exceeds 0.05%, for example, in the case of a magnetic recording medium, the heat history in a film processing step such as applying a magnetic layer to a base film and the magnetic tape and the magnetic recording head during running. Thermal deformation of the tape due to the frictional heat may occur, or the storage stability of the tape may deteriorate. On the other hand, when the content is less than -0.03%, the film expands and wrinkles are easily generated. More preferably, it is -0.01 to 0.04%, and still more preferably 0 to 0.03%. When the Young's modulus in the width direction is less than 4 GPa, for example, in the case of a magnetic recording medium, the tape edge buckles due to the stress received by the guide pin, the tape running property deteriorates, and the temperature and humidity expansion in the tape width direction causes recording. The signal reading may be adversely affected or may not be practically usable. In addition, a biaxially oriented polyester film having a Young's modulus in the width direction of more than 15 GPa may be industrially difficult to produce or may have a marked decrease in tear resistance and dimensional stability. More preferably, it is 4.5 to 13 GPa, and further preferably, it is 5 to 10 GPa.
[0021]
The biaxially oriented polyester film of the present invention may have a single layer or a laminated structure of two or more layers. Although not particularly limited, a laminated structure having two or more layers is more preferable. When a single layer is used, for example, for use in a magnetic recording medium, if particles are included, projections on the surface may not be aligned, and electromagnetic conversion characteristics and running properties may deteriorate. Further, in the case of three layers, the effect of the present invention is further improved, which is preferable. The thickness of the outermost layer is not particularly limited, but is preferably 0.1 to 10 times the average diameter of the particles contained in the outermost layer, because the effects of the present invention are further improved. The reason is that if the value is below the lower limit of this range, the electromagnetic conversion characteristics may be poor, while if the value exceeds the upper limit of this range, there is a possibility that the running performance is poor.
[0022]
The biaxially oriented polyester film of the present invention, within a range that does not impair the effects of the present invention, such as a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, a dye, a fatty acid ester, and a wax. Organic lubricants and the like may be added. In addition, in order to impart lubricity, abrasion resistance, scratch resistance, etc. to the film surface, inorganic particles, organic particles, etc. are added to the outermost layer of the laminated film, for example, useful for magnetic recording media and the like. is there. The additives include clay, mica, titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, inorganic particles such as alumina and zirconia, acrylic acids, styrene and the like. Organic particles, so-called internal particles precipitated by a catalyst or the like added during the polyester polymerization reaction, and a surfactant.
[0023]
The biaxially oriented polyester film of the present invention may be further laminated with another polymer layer, for example, a layer made of polyolefin, polyamide, polyvinylidene chloride or an acrylic polymer, directly or via a layer such as an adhesive. Good.
[0024]
The biaxially oriented polyester film of the present invention may be subjected to any processing such as heat treatment, molding, surface treatment, lamination, coating, printing, embossing, and etching, as necessary.
[0025]
The use of the biaxially oriented polyester film of the present invention is not particularly limited, but it is used for magnetic recording media, capacitors, heat-sensitive transfer ribbons, heat-sensitive stencil printing paper, and the like.
[0026]
The thickness of the biaxially oriented polyester film of the present invention is not particularly limited, but is preferably 1000 μm or less, and more preferably in the range of 0.5 to 500 μm. As will be described later, it can be appropriately determined according to the application and purpose. For example, the range is preferably 0.5 to 20 μm. Particularly, for a magnetic recording medium, the tape is suitable for a high-density magnetic recording tape, for example, a base film for data storage. The data recording capacity is preferably 30 GB (gigabyte) or more, more preferably 70 GB or more. , More preferably 100 GB or more. The linear recording density is preferably at least 25 KB / cm, more preferably at least 34 KB / cm, even more preferably at least 39 KB / cm. The film thickness is usually in the range of 1 to 15 μm for magnetic recording materials, 2 to 10 μm for data or digital video coating type magnetic recording media, and 3 to 9 μm for data or digital video evaporation type magnetic recording media. Is preferred. Further, for capacitors, a film having a thickness of 0.5 to 15 μm is preferably used, and the dielectric breakdown voltage and dielectric characteristics are excellent. A film having a thickness of 1 to 6 μm is preferably used for the thermal transfer ribbon application, and can perform high-definition printing without wrinkles at the time of printing, without causing uneven printing or overtransfer of ink. For use in heat-sensitive stencil paper, a film having a thickness of preferably 0.5 to 5 μm is applied, and it has excellent low-energy piercing properties, and can change the piercing diameter according to the energy level. Excellent printability for color printing.
[0027]
When used as a high-density magnetic recording medium, preferred examples of the magnetic layer include a ferromagnetic metal thin film, a magnetic layer formed by dispersing a ferromagnetic metal fine powder in a binder, and a magnetic layer formed by coating a metal oxide. No. As the ferromagnetic metal thin film, iron, cobalt, nickel and other alloys are preferable. Further, as the ferromagnetic metal fine powder, ferromagnetic hexagonal ferrite fine powder, iron, cobalt, nickel and other alloys are preferable. As the binder, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof and the like are preferable.
[0028]
The magnetic layer can be formed by kneading the magnetic powder with a binder such as thermoplastic, thermosetting, or radiation curable, and applying and drying the metal, alloy, or by vapor deposition, sputtering, or ion pre-coating. Any of dry methods in which a magnetic metal thin film layer is directly formed on a base film by a method or the like can be adopted.
[0029]
In the magnetic recording medium of the present invention, a protective film may be provided on the ferromagnetic metal thin film. With this protective film, running durability and corrosion resistance can be further improved. Examples of the protective film include oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitride protective films such as titanium nitride, silicon nitride, and boron nitride; silicon carbide, chromium carbide, and boron carbide. Examples of the protective film include a carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon.
[0030]
The carbon protective film is a carbon film made of an amorphous structure, a graphite structure, a diamond structure, or a mixture thereof formed by a plasma CVD method, a sputtering method, or the like, and is particularly preferably a hard carbon film generally called diamond-like carbon. . The surface of the hard carbon protective film may be treated with an oxidizing or inert gas plasma for the purpose of further improving the adhesion with the lubricant provided on the hard carbon protective film.
[0031]
In the present invention, in order to improve the running durability and corrosion resistance of the magnetic recording medium, it is preferable to add a lubricant or a rust inhibitor to the magnetic film or the protective film.
[0032]
The method for producing a biaxially oriented polyester film of the present invention comprises the steps of: discharging from a die by melt extrusion using an extruder; cooling and solidifying a molten polymer to form a sheet; and forming the sheet into a simultaneous biaxial tenter. And then stretched biaxially at a magnification of 4.5 to 10 times in the longitudinal direction and 3 to 10 times in the width direction, and then (glass transition temperature (Tg) of polyester resin) to (melting point of polyester resin ( Tm)) is a method for producing a biaxially oriented polyester film which is heat-set at a heat-setting temperature within the range of (Tm)) and further subjected to relaxation heat treatment. More preferred stretching conditions are a magnification of 5 to 9 times in the longitudinal direction and 4.5 to 9 times in the width direction, and further preferred conditions are 5.5 to 7.5 times in the longitudinal direction and 5 to 9 in the width direction. The magnification is 7.5 times.
[0033]
As a stretching method of the biaxially stretched polyester film of the present invention, if a simultaneous biaxial tenter is used, a sequential biaxial stretching combining unidirectional stretching such as a method of stretching in the width direction after stretching in the longitudinal direction. A stretching method, a simultaneous biaxial stretching method for simultaneously stretching in the longitudinal direction and the width direction, and a method combining a sequential biaxial stretching method and a simultaneous biaxial stretching method are included. Among them, a method including a simultaneous biaxial stretching method is particularly preferable from the viewpoint of obtaining the effects of the present invention.
[0034]
In the present invention, it is preferable to use a linear motor type simultaneous biaxial tenter as a stretching machine capable of freely changing the stretching direction and the stretching ratio. As described above, the simultaneous biaxial tenter of the linear motor type is made of (1) a film capable of freely changing the deformation pattern of the film in the stretching, heat treatment, and relaxation steps; It has the advantage that the film speed and film width can be increased to the level of conventional sequential biaxial stretching or more.
[0035]
In the present invention, the stretching temperature when performing stretching on the polyester film is not particularly limited, but when performing stretching on an unstretched film, it is preferable to maintain the temperature at (Tg) ° C to (Tg + 120) ° C, (Tg + 5) ° C to (Tg + 100) ° C is more preferable, and further preferably (Tg + 10) ° C to (Tg + 80) ° C. If the stretching temperature is lower than Tg ° C., the orientation by stretching is too advanced, and it is difficult to stretch to a high magnification.
[0036]
An example of the method for producing the biaxially oriented polyester film of the present invention will be described, but the present invention is not limited thereto. Here, an example is shown in which polyethylene terephthalate is used as the polyester, but the production conditions differ depending on the polyester used.
[0037]
Polyester pellets are prepared in accordance with the above-mentioned conventional method, and the obtained polyester pellets are dried under vacuum at 180 ° C. for 3 hours or more, and then heated to 280 to 320 ° C. under a nitrogen stream or vacuum so that the intrinsic viscosity does not decrease. The extruder is supplied to the extruder, and a film is formed by a conventional method. In this melt extruder, it is preferable to use various filters, for example, a filter made of a material such as a sintered metal, a porous ceramic, a sand, or a wire mesh, in order to remove foreign substances and a deteriorated polymer before extrusion. Further, if necessary, a gear pump may be provided in order to improve the quantitative supply property. In the case of a laminated film, a sheet in which molten polyester is laminated is extruded from a slit die using two or more extruders, manifolds or merging blocks, and cooled on a casting roll to produce an unstretched film I do.
[0038]
Next, this unstretched film is biaxially stretched and biaxially oriented. This biaxial stretching can be performed by a sequential biaxial stretching method or a simultaneous biaxial stretching method using a simultaneous biaxial tenter. Here, a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal direction and the width direction is used. The stretching temperature varies depending on the structural components of the polyester and the components of the lamination, but an example in which a single layer is made of polyethylene terephthalate will be described. The unstretched film is guided to a simultaneous biaxial stretching tenter of a linear motor type by gripping both ends of the film with clips, and is heated to (Tg + 10) to (Tg + 100) ° C. in a preheating zone, and can be moved in any of the longitudinal direction and the width direction. At the same time, the film is stretched 4.5 to 10 times in one step or two or more steps. The stretching ratio may be different between the longitudinal direction and the width direction. At this time, in any case, it is preferable to set the temperature of the clip for gripping the film end in a temperature range of (Tg) to (Tg + 120) ° C. The stretching temperature in the stretching step is preferably maintained within a temperature range of (Tg + 10) to (Tg + 80) ° C., but the film may be cooled once and stretched while suppressing crystallization of the film. Further, in the case of a raw material having a high molecular weight or a raw material which is difficult to be crystallized, it is preferable to increase the stretching temperature to 200 ° C. In the latter half of the stretching step, the stretching is preferably performed while gradually increasing the stretching temperature in two or more stages.
[0039]
Then, from the viewpoint of the manifestation of the effect of the present invention, the biaxially stretched polyester film is added to the (Tm-70) ° C to (Tm) ° C, more preferably (Tm-50) ° C to (Tm-10) ° C range. Is subjected to heat setting. Further, a limited shrinkage of 0.5 to 5%, more preferably 1 to 3% is given in the longitudinal and width directions at the heat setting temperature (hereinafter referred to as relaxation heat treatment I). (Tm−50) ° C., more preferably in a temperature range of (Tg + 10) ° C. to (Tm−80) ° C., in a range of 1 to 7%, more preferably 2 to 6% in the longitudinal and width directions. (Hereinafter referred to as relaxation heat treatment II). The relaxation heat treatment may be performed at different restricted shrinkage rates in the longitudinal direction and the width direction. In particular, it is preferable to perform the relaxation heat treatment I at the heat setting temperature and then perform the relaxation heat treatment II in the cooling process in order to further enhance the effects of the present invention. It is preferable that the relaxation heat treatment II is performed in two or more stages while changing the temperature. Thereafter, the film is cooled to room temperature, the film edge is removed, and the film is wound up, thereby obtaining a target biaxially oriented polyester film.
[0040]
The glass transition temperature Tg in the present invention is a value obtained from the heat flux gap at the time of temperature rise in the differential scanning calorimetry according to JIS-K7121. If it is difficult to make a determination only by a method based on differential scanning calorimetry, a morphological method such as dynamic viscoelasticity measurement or microscopic observation may be used in combination. When determining the glass transition temperature by differential scanning calorimetry, it is also effective to use a temperature modulation method or a high sensitivity method. The melting point Tm in the present invention is a value determined according to JIS-K7122.
[0041]
[Method of measuring physical properties and method of evaluating effects]
The method for measuring characteristic values and the method for evaluating effects are as follows.
(1) Heat shrinkage at 55 ° C for 100 hours
The sample was conditioned at 23 ° C. and 65% RH for 24 hours, then the sample length (L0) was measured, and the sample was heated under the following measurement environment and holding time conditions. The length (L) was measured.
Measuring device: TMA TM-3000 manufactured by Vacuum Riko Co., Ltd., heating control unit TA-1500, AD converter ADX-98E manufactured by Canopus Electronics Co., Ltd.
Sample size: width 4mm x test length 15mm,
Measurement environment: temperature 55 ° C, humidity 65% RH, load 0.5g
Retention time: 100 hours
[0042]
The heat shrinkage was calculated by the following equation.
Heat shrinkage (%) = [(L0−L) / L0] × 100
L0: Sample length before heat treatment
L: Sample length after heat treatment
[0043]
(2) Young's modulus
According to the method specified in ASTM-D882, the measurement was performed using an Instron type tensile tester. The measurement was performed under the following conditions.
Measuring device: Orientec Co., Ltd. film automatic elongation measuring device
"Tensilon AMF / RTA-100"
Sample size: width 10 mm x test length 100 mm,
Pulling speed: 200mm / min
Measurement environment: temperature 23 ° C, humidity 65% RH
[0044]
(3) Using a half-width X-ray diffractometer in the circumferential direction of the crystal plane diffraction peak of the film by the wide-angle X-ray diffraction method (Model 4036A2 (tube type) manufactured by Rigaku Corporation) under the following conditions. Was measured by the diffractometer method.
X-ray diffractometer: 4036A2 type (tube type) manufactured by Rigaku Corporation
X-ray source: CuKα ray (using Ni filter)
Output: 40kV 20mA
Goniometer: manufactured by Rigaku Denki Co., Ltd.
Slit: 2mmφ-1 ゜ -1 ゜
Detector: Scintillation counter
Count recording device: RAD-C type manufactured by Rigaku Denki Co., Ltd.
A circumferential profile is obtained by fixing a sample and a counter cut out to 2 cm × 2 cm at the diffraction peak position of the crystal plane obtained by the 2θ / θ scan, aligned in the same direction and superimposed, and rotating the sample in the plane. (Β scan). The half width (deg) of the peak was calculated using the valleys at both ends of the peak as a background in the peak profile obtained by the β scan.
[0045]
(4) Surface roughness Ra
The surface roughness Ra was measured under the following conditions according to JIS-B0601.
Measuring device: Kosaka Laboratory Co., Ltd. High accuracy thin film step measuring device ET-10
Stylus tip radius: 0.5m
Stylus load: 5mg
Measurement length: 1mm
Cutoff value: 0.08mm
Scanning in the film width direction, the center line average roughness Ra was measured 20 times, and the average value was taken.
[0046]
(5) Glass transition temperature (Tg)
It was measured by a quasi-isothermal method according to JIS-K7121.
Measuring device: Temperature modulated DSC manufactured by TA Instrument
Heating temperature: 0 ° C to 300 ° C (RCS cooling method)
Temperature calibration: melting point of high purity indium and tin
Temperature modulation amplitude: ± 1 ° C
Temperature modulation cycle: 60 seconds
Heating step: 5 ° C
Sample mass: 5mg
Sample container: Aluminum open container (22mg)
Reference container: Aluminum open container (18 mg)
The glass transition temperature (Tg) was calculated by the following equation.
Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
[0047]
(6) Melting point (Tm)
The peak temperature of the endothermic peak of melting was measured according to JIS-K7122 as a melting point (Tm).
Measuring device: Seiko Denshi Kogyo Co., Ltd. "Robot DSC-RDC220" Data analysis "Disk session SSC / 5200"
Sample mass: 5mg
Sample pretreatment: solidification after quenching at 300 ° C for 5 minutes
Heating rate: 20 ° C / min
[0048]
(7) Running durability and storability of magnetic tape
A magnetic paint having the following composition is applied to the surface of the biaxially oriented polyester film so as to have a coating thickness of 2.0 μm, magnetically oriented, and dried. Next, a back coat having the following composition is applied to the opposite surface, calendered, and then cured at 70 ° C. for 48 hours. The obtained raw tape was slit to a width of 1/2 inch, and a 670 m long magnetic tape was assembled into a cassette to form a cassette tape.
(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
-Stearic acid: 1.5 parts by weight
・ Oleic acid: 1 part by weight
・ Carbon black: 1 part by weight
・ Alumina: 10 parts by weight
・ Methyl ethyl ketone: 75 parts by weight
・ Cyclohexanone: 75 parts by weight
・ Toluene: 75 parts by weight
[0049]
(Composition of back coat)
・ Carbon black (average particle size: 20 nm): 95 parts by weight
・ Carbon black (average particle size: 280 nm): 10 parts by weight
・ Α-alumina: 0.1 parts by weight
-Modified polyurethane: 20 parts by weight
・ Modified vinyl chloride copolymer: 30 parts by weight
・ Cyclohexanone: 200 parts by weight
・ Methyl ethyl ketone: 300 parts by weight
・ Toluene: 100 parts by weight
[0050]
The created cassette tape was run at room temperature for 1000 hours using a Magstar 3590 Model B1A Tape Drive manufactured by IBM, and the running durability of the tape was evaluated according to the following criteria. ◎ and ○ are acceptable products.
：: No extension or bending of the tape end face, no scraping marks
：: No tape end surface elongation, no bending, no trace of scraping
△: no tape end surface elongation or bending, but some scraping marks are seen
×: A part of the tape end face is elongated, wakame-like deformation is observed, and scraping marks are observed.
[0051]
Further, after reading the data of the cassette tape prepared above using Magstar 3590 Model B1A Tape Drive manufactured by IBM, the cassette tape was stored in an atmosphere of 60 ° C. and 80% RH for 350 hours. The storage stability of the tape was evaluated based on criteria. ◎ and ○ are acceptable products.
：: Normal playback without any abnormality in tape width and no track deviation
：: There was almost no abnormality in the tape width and there was almost no track deviation, and normal reproduction was performed.
Δ: There is no abnormality in the tape width, but some parts cannot be read.
×: There is a change in the tape width, and reading is impossible
[0052]
(8) Suitability of film processing
While unwinding the film wound up to a width of 500 mm from the unwinder, the film is supplied to an oven processing device manufactured by Inoue Metal Industry Co., Ltd. at a transport speed of 20 m / min, and subjected to a heat treatment at 180 ° C. And the film was evaluated for the suitability for processing according to the following criteria. ◎ and ○ are acceptable products.
◎: Projection at the end was less than 3 mm and no wrinkles were observed during processing
：: The protrusion at the end was 3 mm or more and 5 mm or less, and no wrinkles were observed during processing.
△: The protrusion of the end is 5 mm or more and 10 mm or less.
X: The end of the wound film protruded beyond 10 mm due to meandering or the like, and became irregular.
[0053]
【Example】
Embodiments of the present invention will be described based on the following examples.
[0054]
Example 1
Using two extruders A and B, the extruder A heated to 280 ° C. was charged with polyethylene terephthalate (0.16% by weight of spherical silica particles having an intrinsic viscosity of 0.62 and an average diameter of 0.3 μm) obtained by a conventional method. The blend (I) was supplied after drying the pellet (I) under vacuum at 180 ° C. for 3 hours, and the extruder B also heated to 280 ° C. was supplied with polyethylene terephthalate (intrinsic viscosity 0.62, average diameter) obtained by a conventional method. A pellet (II) containing 0.3% by weight of 0.3 μm spherical crosslinked polystyrene particles and 0.01% by weight of spherically crosslinked polystyrene particles having an average diameter of 0.8 μm) was supplied after vacuum drying at 180 ° C. for 3 hours. Three layers (II) are merged in a T-die so as to form three outermost layers (stacking ratio II / I / II = 1/10/1), and an electrostatic charge is applied to a cast drum having a surface temperature of 25 ° C. While being in close contact, the mixture was cooled and solidified to produce a laminated unstretched film.
[0055]
Both ends of the unstretched film were gripped with clips and guided to a simultaneous biaxial stretching tenter of a linear motor type to form a film under the conditions shown in Table 1. The film is heated to 90 ° C., and is simultaneously biaxially stretched at an area stretching ratio of 12.25 (longitudinal ratio: 3.5 times, lateral ratio: 3.5 times). Subsequently, the film temperature is raised to 160 ° C., and the film is stretched again at an area stretching ratio of 2.16 times (longitudinal ratio: 1.8 times, horizontal ratio: 1.2 times), and heat-fixed at a heat-setting temperature of 210 ° C. for 2 seconds. After the treatment, a relaxation heat treatment I of 2% in the longitudinal direction and the width direction is performed at the heat setting temperature, and then a relaxation heat treatment II of 4% in the longitudinal direction and 2% in the width direction in two stages of 150 ° C. and 100 ° C. Then, a biaxially stretched polyester film having a thickness of 5 μm was obtained. The composition and properties of the biaxially oriented polyester film were as shown in Table 2, and had excellent properties as a base film for a magnetic recording medium.
[0056]
Examples 2 and 3
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the relaxation heat treatment was performed under the relaxation heat treatment conditions shown in Table 1. The biaxially oriented polyester film obtained had a heat shrinkage in the longitudinal direction at 55 ° C. of 100 hours of −0.03% and 0.05%, respectively. As shown in Table 2, the base for magnetic recording media was used. It had excellent properties as a film.
[0057]
Comparative Examples 1-3
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the relaxation heat treatment was performed under the relaxation heat treatment conditions shown in Table 1. The obtained biaxially oriented polyester film was inferior as a base film for a magnetic recording medium because the heat shrinkage at 55 ° C. for 100 hours was out of the range of the present invention.
[0058]
Example 4
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the film was stretched under the stretching conditions shown in Table 1. The obtained biaxially oriented polyester film had a Young's modulus in the longitudinal direction of 6 GPa. However, as shown in Table 2, it had excellent properties as a base film for a magnetic recording medium.
[0059]
Comparative Example 4
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the film was stretched under the stretching conditions shown in Table 1. The obtained biaxially oriented polyester film was inferior as a base film for a magnetic recording medium because the Young's modulus in the longitudinal direction was out of the range of the present invention.
[0060]
Comparative Example 5
A biaxially oriented polyester film was produced in the same manner as in Example 1 except that the heat setting was performed under the heat setting conditions shown in Table 1. The obtained biaxially oriented polyester film was inferior as a base film for a magnetic recording medium because the heat shrinkage at 55 ° C. for 100 hours was out of the range of the present invention.
[0061]
Example 5
Using two extruders A and B, extruder A heated to 300 ° C. was charged with polyethylene-2,6-naphthalate (intrinsic viscosity 0.65, spherical silica particles having an average diameter of 0.3 μm) obtained by a conventional method. The pellet (I) (0.16% by weight) was vacuum-dried at 180 ° C. for 3 hours and supplied to the extruder B, which was also heated to 300 ° C., and polyethylene-2,6- obtained by a conventional method. A pellet (II) of naphthalate (comprising 0.2% by weight of spherical crosslinked polystyrene particles having an intrinsic viscosity of 0.65 and an average diameter of 0.3 μm and 0.01% by weight of spherical crosslinked polystyrene particles having an average diameter of 0.8 μm) was heated at 180 ° C. Supplied after vacuum drying for 3 hours. Three layers (II) are merged in a T-die so as to form three outermost layers (stacking ratio II / I / II = 1/10/1), and an electrostatic charge is applied to a cast drum having a surface temperature of 35 ° C. While being in close contact, the mixture was cooled and solidified to produce a laminated unstretched film.
[0062]
Both ends of the unstretched film were gripped with clips, guided to a simultaneous biaxial stretching tenter of a linear motor type, and formed into a film under the conditions shown in Table 1 to produce a biaxially oriented polyester film. As shown in Table 2, the obtained biaxially oriented polyester film had excellent properties as a base film for a magnetic recording medium.
[0063]
Comparative Example 6
The unstretched polyester film obtained in the same manner as in Example 1 was stretched 3.2 times at a temperature of 90 ° C. in one step in a longitudinal direction using a roll stretching machine, and further stretched in the width direction using a tenter. The film was stretched 3.2 times at a temperature of 100 ° C. Subsequently, the film was stretched 1.7-fold at a temperature of 140 ° C. in two steps in the longitudinal direction with a roll-type stretching machine, and then stretched 1.2-fold at a temperature of 190 ° C. in the width direction using a tenter. Further, after a heat treatment at a temperature of 210 ° C. for 10 seconds, a relaxation treatment of 4% was performed in the width direction to obtain a biaxially oriented polyester film having a thickness of 5 μm. When successive biaxial stretching was performed using a roll stretching machine, it was difficult to perform relaxation heat treatment in the longitudinal direction. The obtained biaxially oriented polyester film was inferior as a base film for a magnetic recording medium because the heat shrinkage at 55 ° C. for 100 hours was out of the range of the present invention.
[0064]
[Table 1]

[0065]
In Table 1, "longitudinal" means the longitudinal direction, and "width" means the width direction.
[0066]
[Table 2]

[0067]
【The invention's effect】
According to the present invention, it is possible to obtain a biaxially oriented polyester film having excellent dimensional stability in a use environment and a small deformation under load, and particularly a biaxially oriented polyester film suitable as a base film for a high-density magnetic recording tape. Obtainable. Specifically, it is possible to obtain a base film having excellent running durability, storability and workability for a magnetic recording medium.

Claims (8)

A biaxially oriented polyester film containing polyester as a main component, wherein the longitudinal heat shrinkage of the film at 55 ° C. for 100 hours is in the range of −0.03 to 0.05%, and the longitudinal direction is Young. A biaxially oriented polyester film having a ratio in the range of 6 to 15 GPa. The half-width in the circumferential direction of the diffraction peak of the crystal plane in the main chain direction of the film obtained by the crystal orientation analysis by the wide-angle X-ray diffraction method is in the range of 50 to 85 °. Biaxially oriented polyester film. The surface roughness Ra _{A of} one film surface (A surface) is in the range of 1 to 10 nm, and the surface roughness Ra _B of the film surface (B surface) on the opposite side of the A surface is in the range of 5 to 20 nm. The biaxially oriented polyester film according to claim 1 or 2, wherein: The film is characterized in that the heat shrinkage in the width direction at 55 ° C. for 100 hours is in the range of −0.03 to 0.05%, and the Young's modulus in the width direction is in the range of 4 to 15 GPa. The biaxially oriented polyester film according to claim 1. The biaxially oriented polyester film according to any one of claims 1 to 4, wherein the polyester is polyethylene terephthalate or polyethylene naphthalate. A resin containing polyester as a main component is discharged from a die by melt extrusion, the molten polymer is cooled and solidified to form a sheet, and the sheet-like molded product is stretched by a linear motor simultaneous biaxial stretching machine. A method for producing a biaxially oriented polyester film, wherein relaxation heat treatment is performed in both the longitudinal direction and the width direction. A magnetic recording medium comprising a biaxially oriented polyester film according to claim 1 and a magnetic layer provided on at least one side of the film. 8. The magnetic recording medium according to claim 7, wherein the heat shrinkage in the longitudinal direction at 55 [deg.] C. for 100 hours is in a range of -0.03 to 0.05%.