JP4934063B2 - Biaxially oriented polyester film - Google Patents

Description

  The present invention relates to a biaxially oriented polyester film using an aromatic polyester copolymerized with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid.

  Polyester film enables the continuous production of large-area films that cannot be obtained from other materials, making use of its strength, durability, transparency, flexibility, surface properties, and other characteristics to create a magnetic film. It is used in fields that are in great demand, such as for recording, industrial materials, packaging, agriculture, and building materials. Among them, biaxially oriented polyester films are used in various fields because of their excellent mechanical properties, thermal properties, electrical properties, and chemical resistance, and are especially useful as base films for magnetic tapes. Does not allow other films to follow.

  However, in recent years, with the increase in processing speed in processes such as polyester film processing processes, magnetic layer coating processes in magnetic recording media applications, and thermal transfer layer coating processes in thermal transfer applications, or in order to improve the required quality of final products Accordingly, the polyester film is required to have better surface properties such as running property and wear resistance.

In order to obtain a film having these good characteristics, it is known that it is effective to form fine protrusions uniformly on the film surface.
A polyester film in which a thin layer containing particles for forming protrusions on the film surface is laminated on a base layer is known (for example, JP-A-2-77431).
In addition, a method of forming desired fine protrusions on the surface using crystallization of polyester without relying on these contained particles is also known (for example, JP-A Nos. 7-1575 and 2000-143848). Publication).

  However, in the method using particles, voids called voids are likely to be generated around the particles. On the other hand, in the method using crystallization of polyester, the surface is heated or ultraviolet rays are irradiated to promote crystallization. Because the number of fine protrusions changes due to equipment fluctuation factors such as temperature unevenness at the time, it is difficult to obtain a high-quality polyester film with uniform quality, and it takes a considerable amount of time to form fine protrusions by crystallization of polyester Therefore, there is a problem that the film forming speed cannot be increased.

  Incidentally, a film using polyethylene-6,6 '-(ethylenedioxy) di-2-naphthoate has been proposed (for example, Japanese Patent Laid-Open No. 61-145724). However, since the melting point is very high and the crystallinity is very high, when trying to form a film or the like, the fluidity in the molten state is poor and the extrusion becomes non-uniform, or even if it is stretched after extrusion There was a problem such as breakage when the film was advanced and stretched at a high magnification.

Japanese Patent Laid-Open No. 2-77431 JP-A-7-1575 JP 2000-143846 A JP 61-145724 A

  An object of the present invention is to provide a biaxially oriented polyester film that has uniform protrusions due to contained particles but has few voids and is excellent in shaving.

  The inventors of the present invention have intensively studied to solve the above-mentioned problems. As a result of using a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component as a copolymerization component, 10-point average roughness (Rz) And found that the void can be made small, and reached the present invention.

（上記構造式（Ｉ）中のＲは、炭素数１〜１０のアルキレン基を示す。）
で表される６，６’−（アルキレンジオキシ）ジ−２−ナフトエ酸成分であり、
少なくとも一方の表面は、１０点平均粗さ（Ｒｚ）を表面粗さ（Ｒａ）で割った値（Ｒｚ／Ｒａ）が、２０未満である二軸配向ポリエステルフィルムが提供される。 Thus, according to the present invention, there is provided a biaxially oriented polyester film containing 0.01% by weight or more of an aromatic polyester composed of an aromatic dicarboxylic acid component and a glycol component and particles having an average particle diameter of 50 nm or more,
The aromatic dicarboxylic acid component is 5 mol% or more and less than 80 mol% of the following formula (I):

(R in the structural formula (I) represents an alkylene group having 1 to 10 carbon atoms.)
Is a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by:
At least one surface is provided with a biaxially oriented polyester film in which a value (Rz / Ra) obtained by dividing 10-point average roughness (Rz) by surface roughness (Ra) is less than 20.

  Further, according to the present invention, as a preferred embodiment of the present invention, the particle size distribution of the contained particles is 0.5 or less in relative standard deviation, and at least one surface has a 10-point average roughness (Rz). It is in the range of 10 to 400 nm, at least one surface has a surface roughness (Ra) in the range of 1 to 20 nm, and the particles are silica particles, silicone particles, crosslinked polystyrene particles, crosslinked acrylic particles, crosslinked polyester. It is at least one selected from the group consisting of particles, the average particle size of the particles is in the range of 50 to 1000 nm, and the content is in the range of 0.05 to 0.5% by weight based on the weight of the film The other film layer is laminated on one side of the biaxially oriented polyester film of the present invention, and the base film of the magnetic recording medium is used. The biaxially oriented polyester film comprising either Rukoto at least also provided.

According to the present invention, the protrusions formed by the particles can be uniform and have few voids, and as a result, a biaxially oriented polyester film excellent in flatness and running property is provided.
Therefore, according to the present invention, a film suitable for a base film of a high density magnetic recording medium is provided which is required to have a high degree of surface flatness, and excellent dimensional stability can be obtained by using the film of the present invention. A high-density magnetic recording medium having high performance can also be provided.

  Further, according to the present invention, the dimensional stability against temperature and humidity changes can be enhanced at the same time by copolymerizing the polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoic acid component. An effect is also produced.

<Aromatic polyester>
In the present invention, the aromatic polyester forming the biaxially oriented polyester film is composed of an aromatic dicarboxylic acid component and a glycol component. Specific examples of the aromatic dicarboxylic acid component other than the aromatic dicarboxylic acid component represented by the formula (I) include terephthalic acid component, isophthalic acid component, 2,6-naphthalenedicarboxylic acid component, and 2,7-naphthalenedicarboxylic acid. An acid component etc. are mentioned. Examples of the glycol component include an ethylene glycol component, a trimethylene glycol component, a tetramethylene glycol component, and a cyclohexane dimethanol component.

  Specific aromatic polyesters formed from aromatic dicarboxylic acid components other than the aromatic dicarboxylic acid component represented by the aforementioned formula (I) include alkylene terephthalates such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. Polyalkylene- having a repeating unit of alkylene-2,6-naphthalate such as polyalkylene terephthalate, polyethylene-2,6-naphthalate, polytrimethylene-2,6-naphthalate, polybutylene-2,6-naphthalate, etc. 2,6-naphthalate is preferred. Among these, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferable from the viewpoint of mechanical properties and the like, and polyethylene-2,6-naphthalate is particularly preferable. From such a viewpoint, 90 mol% or more of the glycolic acid component is preferably an ethylene glycol component. The proportion of the ethylene glycol component is preferably in the range of 90 to 100 mol%, more preferably 95 to 100 mol%.

  By the way, one of the characteristics of the present invention is that the acid component of the aromatic polyester described above is 6,6 ′-(alkylenedioxy) represented by the above formula (I) in the range of 5 mol% or more and less than 80 mol%. The di-2-naphthoic acid component is copolymerized. When the ratio of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is less than the lower limit, the effect of reducing Rz and voids due to copolymerization is poor, and the effect of reducing the coefficient of humidity expansion is hardly exhibited. The upper limit is required to be less than 80 mol% from the viewpoint of moldability and the like. Surprisingly, the effect of reducing Rz and voids by the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component and the effect of reducing the coefficient of humidity expansion are expressed very efficiently even in a small amount. , Less than 50 mol% is almost saturated and preferably less than 50 mol%. From such a viewpoint, the upper limit of the copolymerization amount of the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is preferably 45 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less. 30 mol% or less, and the other lower limit is 5 mol% or more, further 7 mol% or more, still more 10 mol% or more, particularly 15 mol% or more.

  By using an aromatic polyester copolymerized with such a specific amount of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, Rz and voids can be made smaller with the same particle composition. Furthermore, when both the temperature expansion coefficient and the humidity expansion coefficient are viewed at the same Young's modulus, a molded product such as a film can be produced.

  In addition, the 6,6 '-(alkylenedioxy) di-2-naphthoic acid component represented by the structural formula (I) described above is one in which the R portion is an alkylene group having 1 to 10 carbon atoms. Preferably, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid component and 6,6 ′-(butylenedioxy) di -2-naphthoic acid component and the like. Among these, from the viewpoint of the effects of the present invention, those having an even number of carbon atoms of R in the above general formula (I) are preferable, and a 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component is particularly preferable. .

  The aromatic polyester in the present invention may be copolymerized with other copolymerization components known per se as long as the effects of the present invention are not impaired.

  Next, since the aromatic polyester in the present invention is copolymerized with a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, the melt viscosity tends to increase, so the melting point measured by DSC. However, it is preferable from the point of film forming property that it exists in the range of 200-260 degreeC, the range of 210-255 degreeC, especially the range of 220-253 degreeC. When the melting point exceeds the above upper limit, the melt viscosity is large, and the fluidity is inferior when molding is performed by melt extrusion, so that the discharge and the like are likely to be non-uniform, and the film forming property tends to be lowered. On the other hand, when it is less than the above lower limit, although the film-forming property is excellent, the mechanical properties of the aromatic polyester are easily impaired. Usually, if other acid components are copolymerized and the melting point is lowered, the mechanical properties and the like are also lowered at the same time. The same mechanical characteristics as those of the polymer having the main repeating unit of the ester of 6,6 ′-(alkylenedioxy) di-2-naphthoic acid described in 2 can be exhibited.

  Further, the aromatic polyester in the present invention has a glass transition temperature (hereinafter sometimes referred to as Tg) measured by DSC in the range of 90 to 120 ° C, more preferably in the range of 95 to 119 ° C, particularly 100 to 118 ° C. It is preferable from the viewpoint of heat resistance and dimensional stability. Such a melting point and glass transition temperature can be adjusted by controlling the type and amount of copolymerization component, dialalkylene glycol as a byproduct.

<Film>
The biaxially oriented polyester film of the present invention can be obtained by melt-forming the aforementioned aromatic polyester and extruding it into a sheet. And as above-mentioned, since the fluidity | liquidity at the time of a fusion | melting and subsequent crystallinity are improved, it becomes a uniform film excellent in film forming property, for example, without a thickness spot.

  When the biaxially oriented polyester film of the present invention is used as a base film such as a magnetic tape, at least one surface has a 10-point average roughness (Rz) in order to achieve both excellent flatness and running property. And the surface roughness (Ra) ratio (Rz / Ra) should be less than 20, preferably less than 20, and more preferably less than 18. If Rz / Ra exceeds the upper limit on any surface, the height of the film surface protrusion is not uniform, and the film of the present invention having a surface excellent in wear resistance cannot be obtained. Moreover, the lower limit of Rz / Ra is not particularly limited, but is preferably 5 or more, and more preferably 10 or more from the viewpoint of ease of winding and adjusting particles to be contained.

  The biaxially oriented polyester film of the present invention is in the range of 1 to 20 nm, more preferably 2 to 15 nm, depending on the use of the surface roughness (Ra) of at least one surface from the relationship between flatness and running properties. It is preferable. In particular, when used as a base film of a magnetic recording medium, the surface roughness (Ra) of at least one surface is preferably in the range of 1 to 10 nm, particularly 2 to 8 nm. When further improving the electromagnetic conversion characteristics, at least one is preferably in the range of 1 to 5 nm, and more preferably in the range of 2 to 4 nm. On the other hand, both electromagnetic conversion characteristics and transportability when processing into a magnetic recording medium are made compatible. From the viewpoint, it is preferably in the range of 5 to 10 nm, more preferably in the range of 6 to 8 nm. When the surface roughness (Ra) exceeds the upper limit, the flatness is poor, and for example, when used as a base film of a magnetic recording medium, output characteristics, electromagnetic conversion characteristics, etc. tend to be poor. On the other hand, when the surface roughness (Ra) is less than the lower limit, the running property tends to be poor.

  Further, the biaxially oriented polyester film of the present invention has a 10-point average roughness (Rz) of at least one surface of 10 to 400 nm, more preferably 15 to 300 nm, depending on the relationship between flatness and runnability. It is preferable that it exists in the range. In particular, when used as a base film of a magnetic recording medium, at least one surface preferably has a 10-point average roughness (Rz) in the range of 20 to 200 nm, particularly 30 to 150 nm. When the 10-point average roughness (Rz) exceeds the upper limit, flatness is poor, and when used as a base film of a magnetic recording medium, for example, output characteristics and electromagnetic conversion characteristics tend to be poor. On the other hand, when the 10-point average roughness (Rz) is less than the lower limit, the running property tends to be poor.

  By the way, in order to give the above-mentioned surface property to the biaxially oriented polyester film of the present invention, it is necessary to contain 0.01% by weight or more of particles having an average particle diameter of 50 nm or more. If the average particle size or content is less than the lower limit, it becomes difficult to produce the above surface properties by forming protrusions with particles. Further, in order to reduce the ratio of Rz and Ra described above, in addition to copolymerizing the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by the aforementioned formula (I), particles to be contained For example, it is possible to use one having a small variation in particle diameter. From such a viewpoint, the particles to be contained preferably have a relative standard deviation of 0.5 or less, more preferably 0.45 or less, and particularly preferably 0.40 or less when the particle size distribution is observed. Such particles can be adjusted by selecting particles with relatively little variation as described later, or by removing coarse particles by filtration with a filter or the like. In order to reduce the Ra, the particle size of the particles to be contained may be reduced or the content may be reduced. On the other hand, to increase Ra, the particle size of the particles to be contained is increased or contained. Just reduce the amount. In order to reduce Rz, in addition to copolymerizing the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by the above formula (I), the particle size of the particles to be contained is One example is to reduce the proportion of large items.

  The particles to be included in such a film include (1) heat-resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene, crosslinked acrylic resin, melamine-formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, Particles made of crosslinked polyester), (2) metal oxides (for example, aluminum oxide, titanium dioxide, silicon dioxide (silica), magnesium oxide, zinc oxide, zirconium oxide, etc.), metal carbonates (for example, magnesium carbonate, Inorganic such as calcium carbonate), metal sulfates (eg calcium sulfate, barium sulfate etc.), carbon (eg carbon black, graphite, diamond etc.) and clay minerals (eg kaolin, clay, bentonite etc.) Is it a compound And (3) externally added particles in which different materials are added in the form of particles such as core-shell type composite particles using, for example, a core and a shell, in addition to the range not impairing the effects of the present invention or ( 4) Internally precipitated particles formed by precipitation of a catalyst and the like can be mentioned. Among these, at least one kind of particles selected from the group consisting of a crosslinked silicone resin, a crosslinked acrylic resin, a crosslinked polyester, a crosslinked polystyrene, aluminum oxide, titanium dioxide, silicon dioxide, kaolin and clay is particularly preferable. At least one kind of particles selected from the group consisting of silicone resin, cross-linked acrylic resin, cross-linked polyester, cross-linked polystyrene, and silicon dioxide (excluding porous silica etc.) reduces the variation in particle size. It is preferable because it is easy. Of course, these may be used in combination of two or more.

  The average particle size of preferred particles is in the range of 50 to 1000 nm, more preferably 80 to 800 nm, and particularly in the range of 50 to 600 nm and further 80 to 400 nm when used as a magnetic recording medium. The preferred particle content is 0.01 to 0.5% by weight, more preferably 0.03 to 0.45% by weight, based on the weight of the film, particularly 0.01 to 0 when used as a magnetic recording medium. .4% by weight, and further 0.05 to 0.35% by weight. When the biaxially oriented polyester film of the present invention is a laminated film composed of two or more film layers, the content of each particle only needs to be satisfied based on the weight of each film layer.

Furthermore, the preferable aspect of this invention is explained in full detail.
The biaxially oriented polyester film of the present invention has a Young's modulus of 6.0 GPa in at least one direction in the film surface direction so that the base film does not stretch due to stress applied to the film when used as a base film such as a magnetic tape. It is preferable to have a high Young's modulus as described above. In addition, by having such a high Young's modulus, it is possible to sufficiently reduce the coefficient of humidity expansion even when polyalkylene-6,6 ′-(alkylenedioxy) di-2-naphthoate is used as a copolymerization component. it can. The upper limit of the Young's modulus is not limited, but is usually 11 GPa. The preferred Young's modulus is 5.1 to 11 GPa in the longitudinal direction of the film, more preferably in the range of 5.2 to 10 GPa, particularly 5.5 to 9 GPa, and 5.0 to 11 GPa in the width direction of the film, further 6 to 10 GPa. In particular, it is in the range of 7-10 GPa.

  The biaxially oriented polyester film of the present invention preferably has a temperature expansion coefficient (αt) in at least one direction, preferably in the width direction of the film, of 10 ppm / ° C. or less from the viewpoint of exhibiting excellent dimensional stability. When the temperature expansion coefficient in at least one direction of the film is 10 ppm / ° C. or less, excellent dimensional stability against environmental changes can be exhibited. The lower limit of the temperature expansion coefficient is not limited, but is usually −15 ppm / ° C. A preferable temperature expansion coefficient (αt) is in the range of −10 to 10 ppm / ° C., further −7 to 7 ppm / ° C., particularly −5 to 5 ppm / ° C. It is preferable because it can exhibit excellent dimensional stability against dimensional changes due to.

  The biaxially oriented polyester film of the present invention has a humidity expansion coefficient in the range of 3 to 7 ppm /% RH and 3 to 6 ppm /% RH in the direction satisfying the relationship of the temperature expansion coefficient in at least one direction, preferably the width direction of the film. It is preferable from the viewpoint of dimensional stability when a magnetic recording tape is used. In particular, when used as a base film for a magnetic recording tape, it is preferable that the direction satisfying the above-mentioned formula (1) is the width direction of the biaxially oriented polyester film because track deviation can be extremely suppressed. In the present invention, the width direction of the film is a direction orthogonal to the film forming direction of the film (also referred to as a longitudinal direction or a longitudinal direction), and is sometimes referred to as a lateral direction.

  Further, for the direction in which the temperature expansion coefficient is 10 ppm / ° C. or less, at least one direction, preferably as described above, the width direction should be satisfied, but the direction orthogonal thereto is also dimensional stability point, It is preferable that the same temperature expansion coefficient, humidity expansion coefficient, and Young's modulus are satisfied.

The biaxially oriented polyester film of the present invention preferably has an apparent density in the range of 1.340 to 1.360 g / cm ³ . By adopting the stretching and heat setting conditions such that the apparent density falls within the above range, Rz and voids can be more easily suppressed. Specifically, although depending on the draw ratio, the apparent density can be increased by increasing the drawing temperature and the heat setting temperature.

  In addition, the biaxially oriented polyester film of the present invention is not limited to a single layer film, and if the at least one surface is made of the biaxially oriented polyester film of the present invention, the particle composition and the resin type to be contained are included. It may be a laminated film in which different film layers are laminated on one side. In addition, as the other film layers, those known per se can be suitably used, and those similar to those described in the biaxially oriented polyester film of the present invention are preferable from the viewpoint of peeling.

<Method for producing aromatic polyester resin>
Next, a method for producing the aromatic polyester in the present invention will be described in detail.
First, ester 6,6 ′-(alkylenedioxy) di-2-naphthoic acid or an ester-forming derivative thereof such as 2,6-naphthalenedicarboxylic acid or terephthalic acid or an ester-forming derivative thereof and ethylene glycol, for example. The polyester precursor is produced by the reaction of esterification or transesterification. And it can manufacture by superposing | polymerizing the polyester precursor obtained in this way in presence of a polymerization catalyst, You may give a solid phase polymerization etc. as needed. A catalyst known per se can be used as the catalyst. The intrinsic viscosity measured at 35 ° C. using a mixed solvent of aromatic polyester P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60) thus obtained is 0.4. From the viewpoint of the effect of the present invention, it is preferably in the range of -1.5 dl / g, more preferably in the range of 0.5-1.3 dl / g.

  In the aromatic polyester thus obtained, other thermoplastic polymers, stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, flame retardants, mold release, as long as the effects of the present invention are not impaired. Agents, pigments, nucleating agents, fillers, glass fibers, carbon fibers, layered silicates and the like may be blended as necessary. Examples of other types of thermoplastic polymers include aliphatic polyester resins, polyamide resins, polycarbonates, ABS resins, polymethyl methacrylate, polyamide elastomers, polyester elastomers, polyetherimides, polyimides, and the like.

<Film production method>
The biaxially oriented polyester film of the present invention is one in which the molecular orientation in each direction is enhanced by stretching in the film forming direction and the width direction. For example, the film forming property can be maintained by the following method. However, it is preferable because the Young's modulus is easily improved.
First, the above aromatic polyester is used as a raw material, dried, and then supplied to an extruder heated to a temperature of the melting point (Tm: ° C.) to (Tm + 50) ° C. of the aromatic polyester resin. Extrude into a sheet from the die. The extruded sheet is rapidly cooled and solidified with a rotating cooling drum or the like to form an unstretched film, and the unstretched film is further biaxially stretched.

  In order to satisfy the Young's modulus in both directions defined by the present invention, and αt and αh, it is necessary to facilitate the subsequent stretching. From such a viewpoint, the cooling by the cooling drum is very prompt. It is preferable to do so. From such a viewpoint, it is preferable to carry out at a low temperature of 20 to 60 ° C., not as high as 80 ° C. as described in Patent Document 3. By performing at such a low temperature, crystallization in the state of an unstretched film is suppressed, and subsequent stretching can be performed more smoothly.

Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching.
Here, a manufacturing method in which longitudinal stretching, lateral stretching, and heat treatment are performed in this order by sequential biaxial stretching will be described as an example. First, in the first longitudinal stretching, the glass transition temperature (Tg: ° C.) to (Tg + 40) ° C. of the copolymerized aromatic polyester is stretched 3 to 8 times, and then in the transverse direction at a higher temperature than the previous longitudinal stretching. The film is stretched 3 to 10 times at a temperature of (Tg + 10) to (Tg + 50) ° C., and further treated as a heat treatment at a temperature below the melting point of the polymer and at a temperature of (Tg + 50) to (Tg + 150) ° C. for 1 to 20 seconds, and further 1 to 15 It is preferable to carry out a second heat fixing treatment. In particular, in order to satisfy the viewpoint of reducing Rz and voids and the above-described apparent density, it is preferable that the temperature of the heat setting treatment is in a range of 190 to 230 ° C.

  Normally, when the draw ratio is increased, the film-forming stability is impaired. However, in the present invention, the 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component is copolymerized, so that the drawability is increased. Is very high, and there is no such problem, and in particular, the draw ratio can be further increased. Therefore, it is particularly useful for a thin film having a thickness of 10 μm or less, more preferably 8 μm or less. The lower limit of the thickness of the film is not particularly limited, but is usually about 1 μm, preferably 3 μm.

  Although the above description has been described for sequential biaxial stretching, the biaxially oriented polyester film of the present invention can be produced by simultaneous biaxial stretching in which longitudinal stretching and lateral stretching are simultaneously performed, for example, the stretching ratio and stretching temperature described above, etc. Should be referred to.

  Further, when the biaxially oriented polyester film of the present invention is a laminated film, two or more types of molten polyester are laminated in a die and then extruded into a film, preferably the melting point (Tm: ° C.) to (Tm + 70) of each polyester. ) Extrude at a temperature of ° C. or extrude two or more types of molten polyester from a die, laminate them, quench and solidify them to form a laminated unstretched film, and then perform biaxial stretching and Heat treatment may be performed. If such a method is used, it is easy to impart desired surface characteristics to the front and back of the obtained biaxially oriented polyester film, which is a very preferable embodiment. Further, when providing the above-mentioned coating layer, a desired coating solution is applied to one or both sides of the unstretched film or the uniaxially stretched film, and then the biaxial stretching and the same method as in the case of the single-layer film are performed. It is preferable to perform a heat treatment.

  In addition, about the method of containing particle | grains, the method well-known per se can be employ | adopted, for example, in the manufacturing process of the above-mentioned aromatic polyester, you may add to a reaction system, and the obtained aromatic polyester is melt-kneaded. It may be added. From the viewpoint of the dispersibility of the particles, the polyester composition is preferably added to the reaction system of the aromatic polyester to produce a polyester composition having a high particle concentration as a master polymer, and the polyester composition does not contain particles or has a low particle concentration. The method of mixing is preferable.

  According to the present invention, the biaxially oriented polyester film of the present invention is used as a base film, a nonmagnetic layer and a magnetic layer are formed in this order on one side, and a backcoat layer is formed on the other side. Thus, a magnetic recording tape can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the present invention, the characteristics were measured and evaluated by the following methods.

(1) Intrinsic viscosity The intrinsic viscosity of the obtained polyester was measured at 35 ° C by dissolving the polymer using a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio). And asked.

(2) Glass transition point and melting point Glass transition point and melting point were measured by DSC (TA Instruments Co., Ltd., trade name: Thermal lyst 2100) at a heating rate of 20 ° C / min.

(3) Copolymerization amount As for the glycol component, 10 mg of a sample was dissolved at 80 ° C. in 0.5 ml of a mixed solution of p-chlorophenol: 1,1,2,2-tetrachloroethane = 3: 1 (volume ratio). After adding isopropylamine and mixing well, it was measured at 80 ° C. with 600 M ¹ H-NMR (JEOL A600, manufactured by Hitachi Electronics), and the amount of each glycol component was measured.
As for the aromatic dicarboxylic acid component, 50 mg of a sample was dissolved in 0.5 ml of a mixed solution of p-chlorophenol: 1,1,2,2-tetrachloroethane = 3: 1 at 140 ° C., and 400 M ¹³ C-NMR ( Hitachi Electron JEOL A600) was measured at 140 ° C., and the amount of each acid component was measured.

(4) Young's modulus The obtained film was cut out with a sample width of 10 mm and a length of 15 cm, and a universal tensile testing device (product name: Toyo Baldwin, trade name: 100 mm between chucks, tensile speed 10 mm / min, chart speed 500 mm / min). Pull with Tensilon). The Young's modulus is calculated from the tangent of the rising portion of the obtained load-elongation curve.

(5) Temperature expansion coefficient (αt)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the width direction of the film was a measurement direction, set in TMA3000 manufactured by Vacuum Riko, and pretreated at 60 ° C. for 30 minutes in a nitrogen atmosphere (0% RH). Then, the temperature is lowered to room temperature. Thereafter, the temperature is raised from 25 ° C. to 70 ° C. at 2 ° C./min, the sample length at each temperature is measured, and the temperature expansion coefficient (αt) is calculated from the following equation. In addition, the measurement direction is the longitudinal direction of the sample cut out, the measurement was performed 5 times, and the average value was used.
αt = {(L ₆₀ −L ₄₀ )} / (L ₄₀ × ΔT)} + 0.5
Here, L ₄₀ in the above formula is the sample length (mm) at 40 ° C., L ₆₀ is the sample length (mm) at 60 ° C., ΔT is 20 (= 60-40) ° C., 0.5 Is the temperature expansion coefficient (× 10 ⁻⁶ / ° C.) of quartz glass.

(6) Humidity expansion coefficient (αh)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the width direction of the film would be the measurement direction, set in TMA3000 manufactured by Vacuum Riko, and a humidity of 30% RH and a humidity of 70% under a nitrogen atmosphere at 30 ° C. The length of each sample in RH is measured, and a humidity expansion coefficient is calculated by the following equation. In addition, the measurement direction is the longitudinal direction of the cut out sample, the measurement was performed 5 times, and the average value was αh.
αh = (L ₇₀ −L ₃₀ ) / (L ₃₀ × ΔH)
Here, L ₃₀ in the above formula is a sample length (mm) when 30% RH, L ₇₀ is a sample length (mm) when 70% RH, ΔH: 40 (= 70-30)% RH is there.

(7) Center plane average roughness (Ra) and 10-point average roughness (Rz)
Measured using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022) under the conditions of a measurement magnification of 10 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ), and incorporated in the roughness meter The center plane average roughness (Ra) and 10-point average roughness (Rz) are obtained by the surface analysis software MetroPro.

(8) Measurement of void ratio A sample film piece is fixed to a scanning electron microscope sample stage, and the surface of the film is subjected to the following conditions using a sputtering apparatus (JFC-1100 type ion etching apparatus) manufactured by JEOL Ltd. Ion etching treatment is performed. The condition is that a sample is placed in a bell jar, the degree of vacuum is increased to a vacuum state of about 10 ⁻³ Torr, and ion etching is performed at a voltage of 0.25 kV and a current of 12.5 mA for about 10 minutes. Further, using the same apparatus, the film surface was sputtered with gold, observed with a scanning electron microscope at a magnification of 20,000 times, and image analysis processing was performed from the obtained image with a Luzex 500 manufactured by Japan Regulator Co., Ltd. Extract the boundary where void boundaries can be confirmed, obtain the particle area and void area for each particle, and calculate the void ratio according to the following definition.
Void ratio = (particle area + void area) / particle area This measurement was performed on 100 particles, and the average value was defined as the void ratio. The smaller the void ratio, the smaller the void and the better.

(9) Relative standard deviation of particles The relative standard deviation of the particles to be added was calculated from the particle size distribution obtained by the centrifugal sedimentation method based on JIS Z8823-1 by the following formula. On the other hand, the particle size distribution of the particles in the film is as follows. The surface of the film is fixed to a scanning electron microscope sample stage, and the surface of the film is measured using a sputtering apparatus (JFC-1100 type ion etching apparatus) manufactured by JEOL Ltd. Ion etching treatment is performed under conditions. The condition is that a sample is placed in a bell jar, the degree of vacuum is increased to a vacuum state of about 10 ⁻³ Torr, and ion etching is performed at a voltage of 0.25 kV and a current of 12.5 mA for about 10 minutes. Further, using the same apparatus, the surface of the film was subjected to gold sputtering, observed with a scanning electron microscope at a magnification of 20,000 times, and image analysis processing was performed from the obtained images using Luzex 500 manufactured by Japan Regulator Co., Ltd. The area equivalent circle diameter was determined for the particles, and the relative standard deviation (σ) was calculated from the particle size distribution obtained therefrom using the following formula.

(10) Scratch resistance Measurement is performed as follows using an apparatus shown in FIG. 1 in an environment of a temperature of 20 ° C. and a humidity of 60%. In FIG. 1, 1 is an unwinding reel, 2 is a tension controller, 3, 5, 6, 8, 9 and 11 are free rollers, 4 is a tension detector (inlet), 7 is a fixing rod, 10 is a tension detector ( (Exit), 12 is a guide roller, and 13 is a take-up reel. The film cut to a width of 1/2 inch is brought into contact with 7 fixing rods at an angle θ = 60 °, and is run for 200 m at a speed of 300 m / min and an inlet tension of 50 g. The shavings adhering to the fixed bar 7 after running is evaluated. At this time, a 6φ tape guide (surface roughness Ra = 0.015 μm) made of SUS304 and having a sufficiently finished surface is used as a fixing rod.
<Shaving powder judgment>
○: no shaving powder is seen
Δ: Slightly scraped powder is seen
X: The shaving powder is adhering badly

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out to give an intrinsic viscosity of 0.66 dl / g, 73 mol% of the acid component being 2,6-naphthalenedicarboxylic acid component, and 27 mol% of the acid component being 6,6 ′-(alkylenedioxy). A polyester (B-1) for film layer B was obtained in which 98 mol% of the di-2-naphthoic acid component and glycol component were an ethylene glycol component and 2 mol% was a diethylene glycol component. The polyester (B-1) was subjected to filtration with a filter medium having an average pore diameter of 0.7 μm in the state of ethylene glycol slurry before the polycondensation reaction to remove coarse particles. The average particle diameter was 0.32 μm. The average particle diameter of silica particles having a relative standard deviation of 0.12 as particles B1, 0.15% by weight based on the weight of the resin composition obtained, and coarse particles removed by performing the same filtration Silica particles having a relative standard deviation of 0.12 μm and 0.12 μm were included as particles B2 in an amount of 0.10% by weight based on the weight of the resulting resin composition.

  Moreover, as shown in Table 1, instead of particles B1 and particles B2, in the state of ethylene glycol slurry, filtration was performed with a filter medium having an average pore size of 0.7 μm to remove coarse particles, average particle size of 0.12 μm, relative The same operation as that of the polyester (B-1) except that silica particles having a standard deviation of 0.12 are used as the particles A1 so that the amount is 0.10% by weight based on the weight of the obtained resin composition. Was repeated to obtain a polyester (A-1) for film layer A.

The polyesters (A-1) and (B-1) thus obtained were supplied to different extruders, laminated at 295 ° C. in a die so that the thickness ratio was 1: 2, and melted. An unstretched film was formed by extruding into a sheet shape so that the polyester (B-1) side was in contact with the cooling drum on a cooling drum having a temperature of 50 ° C. during rotation. Then, between two pairs of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above with an IR heater so that the film surface temperature becomes 135 ° C., and stretching in the machine direction (film forming direction) is 5 times. A uniaxially stretched film was obtained. Then, this uniaxially stretched film is guided to a stenter, stretched in the transverse direction (width direction) at 145 ° C. at a draw ratio of 8.5, and then heat-set at 200 ° C. for 5 seconds to give a biaxially stretched film having a thickness of 5 μm. Got.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Examples 2 to 5, 9]
In Example 1, except that the inert particles to be contained were changed as shown in Table 1, the same operation as in Example 1 was repeated to obtain a biaxially oriented laminated polyester film.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Example 6]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out, the intrinsic viscosity was 0.77 dl / g, 82 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 18 mol% of the acid component was 6,6 ′-(ethylenedioxy). A polyester (B-2) for film layer B was obtained in which 99 mol% of the di-2-naphthoic acid component and glycol component were an ethylene glycol component and 1 mol% was a diethylene glycol component. In addition, this polyester (B-2) was made to contain particle | grains as shown in Table 1 by repeating operation similar to polyester (B-1).

  Moreover, as shown in Table 1, instead of particles B1 and particles B2, in the state of ethylene glycol slurry, filtration was performed with a filter medium having an average pore size of 0.7 μm to remove coarse particles, average particle size of 0.12 μm, relative Operation similar to polyester (B-2), except that silica particles having a standard deviation of 0.12 are used as particles A1 so as to be 0.10% by weight based on the weight of the resin composition obtained. Was repeated to obtain a polyester (A-2) for film layer A.

The polyesters (A-2) and (B-2) thus obtained are supplied to different extruders, laminated at 290 ° C. in a die so that the thickness ratio is 1: 2, and melted. An unstretched film was extruded into a sheet shape on a rotating drum at a temperature of 50 ° C. while rotating so that the polyester (B-2) side was in contact with the cooling drum. Then, between two sets of rollers having different rotational speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 135 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.0. Then, this uniaxially stretched film is guided to a stenter, stretched at a stretching ratio of 8.0 times in the transverse direction (width direction) at 150 ° C., and then heat-set at 205 ° C. for 5 seconds, and biaxially stretched to a thickness of 5 μm A film was obtained.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Example 7]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was performed, and the intrinsic viscosity was 0.72 dl / g, 90 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 10 mol% of the acid component was 6,6 ′-(ethylenedioxy). A polyester (B-3) for film layer B in which 99 mol% of the di-2-naphthoic acid component and glycol component was an ethylene glycol component and 1 mol% was a diethylene glycol component was obtained. In addition, this polyester (B-3) was made to contain particle | grains as shown in Table 1 by repeating operation similar to polyester (B-1).

  Moreover, as shown in Table 1, instead of particles B1 and particles B2, in the state of ethylene glycol slurry, filtration was performed with a filter medium having an average pore size of 0.7 μm to remove coarse particles, average particle size of 0.12 μm, relative Operation similar to polyester (B-3), except that silica particles having a standard deviation of 0.12 are used as particles A1 so as to be 0.10% by weight based on the weight of the resin composition obtained. Was repeated to obtain a polyester (A-3) for the film layer A.

The polyesters (A-3) and (B-3) thus obtained are supplied to different extruders, laminated at 290 ° C. in a die so that the thickness ratio is 1: 2, and melted. An unstretched film was formed by extruding the sheet on a cooling drum having a temperature of 50 ° C. while rotating in a state such that the polyester (B-3) side was in contact with the cooling drum. Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 4.6. Then, this uniaxially stretched film is guided to a stenter, stretched at a stretching ratio of 7.4 times in the transverse direction (width direction) at 155 ° C., and then heat-set at 205 ° C. for 5 seconds, and biaxially stretched to a thickness of 5 μm. A film was obtained.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Example 8]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was performed, and the intrinsic viscosity was 0.77 dl / g, 65 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 35 mol% of the acid component was 6,6 ′-(ethylenedioxy). A polyester (B-4) for film layer B was obtained in which 99 mol% of the di-2-naphthoic acid component and glycol component were an ethylene glycol component and 1 mol% was a diethylene glycol component. In addition, this polyester (B-4) was made to contain particle | grains as shown in Table 1 by repeating operation similar to polyester (B-1).

  Moreover, as shown in Table 1, instead of particles B1 and particles B2, in the state of ethylene glycol slurry, filtration was performed with a filter medium having an average pore size of 0.7 μm to remove coarse particles, average particle size of 0.12 μm, relative Operation similar to polyester (B-4), except that silica particles having a standard deviation of 0.12 are used as particles A1 so as to be 0.10% by weight based on the weight of the resin composition obtained. Was repeated to obtain a polyester (A-4) for the film layer A.

The polyesters (A-4) and (B-4) thus obtained are fed to different extruders, laminated at 290 ° C. in a die so that the thickness ratio is 1: 2, and melted. An unstretched film was formed by extruding into a sheet shape such that the polyester (B-4) side was in contact with the cooling drum on a cooling drum at a temperature of 50 ° C. during rotation. Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.0. Then, this uniaxially stretched film is guided to a stenter and stretched at a stretching ratio of 7.4 times in the transverse direction (width direction) at 145 ° C., followed by heat setting treatment at 205 ° C. for 5 seconds, and biaxial stretching with a thickness of 5 μm. A film was obtained.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Example 10]
In Example 1, polyester (B-1) was used instead of polyester (A-1), and the same operation was repeated except that it was a single layer film consisting only of polyester (B-1).
The properties of the obtained biaxially oriented polyester film are shown in Table 2. The side in contact with the cooling drum was the B surface side.

[Comparative Example 1]
Dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol are subjected to an esterification reaction and a transesterification reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to obtain an intrinsic viscosity of 0.62 dl / g. Polyethylene-2,6-naphthalate for film layer A and film layer B in which 1.5 mol% of the glycol component was a diethylene glycol component was obtained. The polyethylene-2,6-naphthalate for each film layer was made to contain inert particles as shown in Table 1 by repeating the same operation as in Example 1 before the polycondensation reaction.

The polyethylene-2,6-naphthalate thus obtained is supplied to an extruder so that the layer B side is in contact with the cooling drum on a cooling drum at a temperature of 60 ° C. while rotating in a molten state from a die at 300 ° C. An unstretched film was extruded into a sheet shape. Then, between the two sets of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above by an IR heater so that the film surface temperature becomes 140 ° C., and stretching in the machine direction (film forming direction) is performed. A uniaxially stretched film was obtained at a magnification of 5.0. And this uniaxially stretched film is led to a stenter, stretched at 160 ° C in the transverse direction (width direction) at a stretch ratio of 5.0 times, further stretched at 170 ° C and 1.3 times, and then heat-fixed at 200 ° C for 5 seconds. Processing was performed to obtain a biaxially stretched film having a thickness of 5 μm.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

[Comparative Example 2]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was carried out to give an intrinsic viscosity of 0.66 dl / g, 73 mol% of the acid component being 2,6-naphthalenedicarboxylic acid component, and 27 mol% of the acid component being 6,6 ′-(alkylenedioxy). A polyester was obtained in which 98 mol% of the di-2-naphthoic acid component and glycol component were ethylene glycol components and 2 mol% were diethylene glycol components. Before the polycondensation reaction, the polyester was filtered through a filter medium having an average pore size of 0.7 μm in the state of ethylene glycol slurry to remove coarse particles. The average particle size was 0.5 μm and the relative standard deviation was 0.22% by weight of silica particles of 0.12 based on the weight of the resulting resin composition, and coarse particles were removed by carrying out similar filtration, with an average particle size of 0.12 μm and a relative standard deviation of 0 .12 silica particles were contained so as to be 0.10% by weight based on the weight of the obtained resin composition.

The polyester thus obtained was supplied to an extruder, heated to 295 ° C., extruded into a sheet on a cooling drum having a temperature of 50 ° C. during rotation in a molten state, and an unstretched film was obtained. Then, between two pairs of rollers having different rotation speeds along the film forming direction, the film surface temperature is heated from above with an IR heater so that the film surface temperature becomes 135 ° C., and stretching in the machine direction (film forming direction) is 5 times. A uniaxially stretched film was obtained. Then, this uniaxially stretched film is guided to a stenter and stretched at a stretching ratio of 8.5 in the transverse direction (width direction) at 145 ° C., and then heat-set at 200 ° C. for 5 seconds to form a single layer having a thickness of 5 μm. An axially stretched film was obtained.
The properties of the obtained biaxially oriented polyester film are shown in Table 2. The side in contact with the cooling drum was the B surface side.

[Comparative Example 3]
In Comparative Example 2, the inert particles to be contained are changed to silica particles having an average particle size of 0.32 μm and a relative standard deviation of 0.60, and the same as in Comparative Example 2 except that filtration with a filter medium was not performed. These operations were repeated to obtain a biaxially oriented laminated polyester film.
The properties of the obtained biaxially oriented polyester film are shown in Table 2.

  In Tables 1 and 2, ANA is 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, MD is the film forming direction, TD is the film width direction, and A surface is the film layer A side. The B surface is the surface on the film layer B side, the A layer is the film layer A, and the B layer is the film layer B.

  The biaxially oriented polyester film of the present invention can be used for various applications such as magnetic recording, industrial materials, packaging, agriculture, and building materials, and is particularly suitably used as a base film for high-density magnetic recording media. be able to.

FIG. 1 is an explanatory diagram of a wear resistance measuring apparatus.

Explanation of symbols

1 Unwinding reel
2 Tension controller
4 Tension detector (inlet)
7 Fixed rod
10 Tension detector (exit)
13 Take-up reel

Claims (8)

A biaxially oriented polyester film comprising an aromatic polyester composed of an aromatic dicarboxylic acid component and a glycol component and 0.01% by weight or more of particles having an average particle size of 50 nm or more,
The aromatic dicarboxylic acid component is 5 mol% or more and less than 80 mol% of the following formula (I):

(R in the structural formula (I) represents an alkylene group having 1 to 10 carbon atoms.)
Is a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component represented by:
At least one of the surfaces is a biaxially oriented polyester film, wherein a value (Rz / Ra) obtained by dividing 10-point average roughness (Rz) by surface roughness (Ra) is less than 20.   The biaxially oriented polyester film according to claim 1, wherein the particle size distribution of the contained particles is 0.5 or less in relative standard deviation.   The biaxially oriented polyester film according to claim 1, wherein at least one surface has a 10-point average roughness (Rz) in the range of 10 to 400 nm.   The biaxially oriented polyester film according to claim 1, wherein at least one surface has a surface roughness (Ra) in the range of 1 to 20 nm.   The biaxially oriented polyester film according to claim 1, wherein the particles are at least one selected from the group consisting of silica particles, silicone particles, crosslinked polystyrene particles, crosslinked acrylic particles, and crosslinked polyester particles.   The biaxially oriented polyester film according to claim 1, wherein the average particle diameter of the particles is in the range of 50 to 1000 nm, and the content thereof is in the range of 0.05 to 0.5 wt% based on the weight of the film.   The biaxially-oriented polyester film by which the other film layer was laminated | stacked on the single side | surface of the biaxially-oriented polyester film in any one of Claims 1-6.   The biaxially oriented polyester film according to claim 1 or 7, which is used for a base film of a magnetic recording medium.

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