JP2008069227A - Polyester resin composition and biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester resin composition which has smooth surfaces capable of resisting to practical uses, when processed into formed articles such as films or fibers, and can enhance Young' modulus. <P>SOLUTION: This polyester resin composition is characterized by containing plate-like boehmite particles having an average secondary particle diameter (D) of 25 to 90 nm in an amount of 0.5 to 3 wt.% based on the weight of the polyester resin composition, and the biaxially oriented polyester film using the resin composition. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a polyester resin composition and a polyester film using the same. More specifically, the present invention relates to a polyester resin composition capable of obtaining a polyester film or polyester fiber having a high Young's modulus and a polyester film using the same.

Polyester resins are used for films and fibers because they have excellent moldability and mechanical properties.
In particular, a polyester film is used as a base film for a magnetic recording medium. For the base film of magnetic recording media, for example, it is required that the magnetic recording medium can be made thin by data storage or the like to increase the length of the magnetic recording medium in the same volume, and the recording density can be further increased. ing. In order to satisfy this requirement, the base film must have a high Young's modulus and excellent surface flatness. Such high Young's modulus is required not only for base films of magnetic recording media but also for polyester fibers as well as other polyester films.

  As a method for improving the strength and dimensional stability of a polyester resin, a polyester resin composition (Patent Document 1: JP-A-6-128466) in which fibrous wollastonite and a needle-like filler are blended has been proposed. Further, a polyester composition in which glass fibers having a specific fiber length are blended in a high proportion with polyalkylene terephthalate (Patent Document 2: Japanese Patent Application Laid-Open No. 1-144452 is also proposed).

  However, polyester films obtained from these polyester resins have a rough surface and cannot be used for base films that require flatness such as magnetic recording media. In addition, when these polyester resins are used for the production of polyester fibers, there are problems such as frequent yarn breakage during spinning.

  In addition, a polyester resin composition containing carbon nanotubes (Patent Document 3: Japanese Patent Application Laid-Open No. 2003-82202) has also been proposed. However, the surface of the obtained film is also rough, or the yarn is broken during spinning. There were problems such as frequent occurrences.

  Furthermore, a biaxially oriented thermoplastic resin film (Patent Document 4: Japanese Patent Application Laid-Open No. 2002-225198) in which needle-like inert particles are blended to improve strength and dimensional stability has also been proposed. However, it is insufficient for use in a base film that requires flatness, such as a coarse and high-density magnetic recording medium.

JP-A-6-128466 Japanese Unexamined Patent Publication No. 1-144452 JP 2003-82202 A JP 2002-225198 A JP-A-6-322243 JP-A-11-228711

  An object of the present invention is to solve the above-described problems of the prior art, and to obtain a molded article such as a film or fiber having a high Young's modulus and surface flatness, and a biaxial shaft using the polyester resin composition The object is to provide an oriented polyester film.

  As a result of repeated researches to solve the above problems, the present inventors have surprisingly obtained Young's modulus of a molded product when acicular boehmite particles are dispersed in polyester with a very small particle size. And the present invention has been found that the surface flatness can be provided at the same time.

  Thus, according to the present invention, a polyester resin composition containing acicular boehmite particles having an average secondary particle diameter (D) of 25 to 90 nm in a proportion of 0.5 to 3% by weight based on the weight of the resin composition. Things are provided. Moreover, as a preferable embodiment of the polyester resin composition of the present invention, a polyester resin composition in which the polyester is polyethylene-2,6-naphthalate is also provided.

  Moreover, according to this invention, the biaxially-oriented polyester film which contains the acicular boehmite particle | grains whose average secondary particle diameter (D) is 25-90 nm in the ratio of 0.5 to 3.0 weight% is also provided. Moreover, as a preferable aspect of the biaxially oriented polyester film of the present invention, the Young's modulus of at least one of the film forming direction and the width direction of the film is in the range of 6 to 15 GPa, the thickness is 2 to 10 μm, Also provided is a biaxially oriented polyester film comprising at least one of the polyester being polyethylene-2,6-naphthalate.

  The polyester resin composition of the present invention is selected from acicular boehmite particles as particles and is subjected to a treatment such as a pressure homogenizer described later, so that it is dispersed with a very small secondary particle size. The effect of improving the Young's modulus is manifested, and the surface is hardly roughened. Therefore, by molding into a film or fiber using the polyester resin composition of the present invention, a molded product having a high Young's modulus can be obtained while having excellent surface flatness, and its industrial value is extremely high.

Hereinafter, the present invention will be described in detail.
[Polyester resin composition]
The polyester resin composition of the present invention contains acicular boehmite particles having an average secondary particle diameter (D) of 25 to 90 nm in a proportion of 0.5 to 3.0% by weight based on the weight of the resin composition. It is necessary to. First, if the particles are not acicular boehmite particles, it is difficult to form such a uniform dispersion state even if a treatment such as a pressure homogenizer described later is applied. It becomes difficult to maintain sex. Then, by incorporating acicular boehmite particles having a secondary particle diameter in the above range into the polyester resin composition at the above frequency, the polyester resin composition can be used without using a large amount of acicular particles as in Patent Document 4. The Young's modulus of a polyester molded product obtained using the product can be improved, and the surface smoothness can be improved. Such a dispersion state can be achieved by selection of acicular boehmite particles and a dispersion treatment such as a pressure homogenizer described later.

  The polyester content in the polyester resin composition is in the range of 97 to 99.5% by weight. The component of the polyester resin composition may be only polyester and acicular boehmite particles, but the content ratio of the polyester and acicular boehmite particles is in the above range and does not impair the effects of the present invention. For example, the additive etc. which are mentioned later may be contained.

[polyester]
The polyester in the present invention may be a homopolymer or a copolymer. In the case of a copolymer, the proportion of the copolymer component is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 20 mol% or less, more preferably 10 mol% or less, based on the repeating unit. .

  In the polyester of the present invention, 80 mol% or more of the total dicarboxylic acid component, more preferably 85 mol% or more, particularly 90 mol% or more is 2,6-naphthalenedicarboxylic acid, 80 mol% or more of all glycol components, and further 85 mol% or more. In particular, it is preferable that 90 mol% or more is composed of ethylene glycol. Such a polyester can be produced by a method known per se, for example, the method disclosed in Patent Documents 1 to 4 described above.

  When the polyester is a copolymer, a copolymer component known per se can be employed. Examples of the dicarboxylic acid component include succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, and 5-sodium. Examples of the dicarboxylic acid and the glycol component include alkylene glycols such as trimethylene glycol, diethylene glycol, propylene glycol, and 1,4-butanediol, and 1,4-cyclohexanedimethanol. In addition, these copolymerization components may use not only 1 type but 2 or more types together.

  The intrinsic viscosity of the polyester in the present invention is an intrinsic viscosity measured at 35 ° C. in an orthochlorophenol solvent and is 0.4 dl / g to 0.8 dl / g, and further 0.5 dl / g to 0.7 dl / g. It is preferable. When the intrinsic viscosity is less than the lower limit, the mechanical strength required when the polyester resin composition of the present invention is used for each product after film formation may be insufficient. On the other hand, when the intrinsic viscosity exceeds the upper limit, productivity at the time of melt kneading in the melt polymerization step and the film forming step may be impaired.

  By the way, in the polyester resin composition of the present invention, the needle boehmite particles are used in the range that does not hinder the effects of the present invention in order to improve the rollability of the film and the transportability of the film when the film is produced. Separately, organic or inorganic inert particles can be contained as a lubricant. The inert particles in the present invention mean organic or inorganic inert particles that function as a lubricant other than needle boehmite particles unless otherwise specified.

[Acicular boehmite particles]
In the present invention, the acicular boehmite particles have an average secondary particle diameter (D) of 25 to 90 nm, and the content thereof is in the range of 0.5 to 3.0% by weight based on the weight of the resin composition. It is necessary to be. When the average secondary particle size (D) is less than the lower limit, the Young's modulus improvement effect is poor. Rather, coarse particles that cause aggregation in a melt-kneading process or the like when forming into a film or fiber, and impair flatness. It will form. Moreover, when the average secondary particle diameter (D) exceeds the upper limit, the effect of improving the Young's modulus is poor and the flatness of the surface tends to be impaired. From these points, the average secondary particle diameter (D) is in the range of 30 to 85 nm, more preferably 35 to 80 nm, and particularly 40 to 75 nm, while maintaining the surface flatness while improving the Young's modulus. It is preferable because it is easy. Such a dispersed state can be achieved by selecting acicular boehmite particles and employing a dispersion treatment such as a pressure homogenizer described later.

  Moreover, when the ratio of the acicular boehmite particles in the polyester resin composition is less than the lower limit%, a sufficient Young's modulus improving effect cannot be exhibited in a molded article such as a film or fiber. On the other hand, when the ratio exceeds the upper limit, the roughening of the surface becomes remarkable, the effect of improving the Young's modulus by the acicular boehmite particles approaches a saturated state, and processes such as film formation and yarn production tend to become unstable. From these points, the ratio of the acicular boehmite particles in the polyester resin composition is preferably in the range of 0.7 to 2.5% by weight, more preferably 1.0 to 2.0% by weight.

  In addition, in the case of a polyester composition, the average secondary particle diameter (D) in the present invention is once formed into a film, and then subjected to etching treatment on the surface of the film to expose the acicular boehmite particles. The exposed surface of the particles can be observed with a scanning electron microscope by magnifying about 100,000 times, and the equivalent circle diameter calculated from the area of each secondary particle is calculated as the secondary particle diameter (d), The average secondary particle diameter (D) is a value obtained by dividing the total of these secondary particle diameters (d) by the number thereof. Moreover, in the case of a polyester film, it can measure by the method similar to the case of a polyester composition except using a film as it is. The ratio in the polyester resin composition referred to here is calculated from the amount of acicular boehmite particles remaining after dissolving and removing the polyester with an organic solvent. In addition, when a molded article is a single layer film, it means the ratio in the polyester resin composition constituting the entire film. When the molded article is a laminated film composed of two or more layers, a layer containing acicular boehmite particles The ratio in the polyester resin composition which comprises is meant.

  By the way, the acicular boehmite particles in the present invention are acicular boehmite particles in which the shape of the primary particles is acicular, for example, the average diameter (R) representing the thickness is 5 to 20 nm, the length in the major axis direction. Preferred examples include those having an average length (L) representing 50 to 200 nm and an average aspect ratio (L / R) representing a ratio thereof of 5 to 20. The shape of these primary particles can be observed with a transmission electron microscope or the like.

  Thus, the polyester resin composition of the present invention is a biaxially oriented polyester film or oriented polyester obtained by stretching the average secondary particle diameter (D) and the ratio of the acicular boehmite particles within a specific range. A molded article such as a fiber can be provided with a high Young's modulus and surface flatness.

[Production method of polyester resin composition]
The polyester resin composition of the present invention can be produced by a conventionally known method for producing a polyester resin composition, but the average secondary particle diameter of needle-like boehmite particles is small and compared with adding as a normal lubricant. Since the frequency is extremely high, the acicular boehmite particles easily reaggregate in the polyester, and it is necessary to uniformly disperse the acicular boehmite particles while suppressing the reaggregation of the acicular boehmite particles. In order to achieve such a dispersed state, in addition to selecting acicular boehmite particles, for example, a glycol slurry containing acicular boehmite particles having an average primary particle diameter of 5 to 100 nm is brought to an ultrahigh pressure state of 50 to 250 MPa. After that, the glycol slurries discharged from the nozzles facing each other are discharged so as to collide with each other, and the acicular boehmite particles are crushed by the collision of the particles in the glycol slurry (processing by a color-homogenizing homogenizer), and the pulverization is performed. It is preferable to perform the polymerization reaction by adding the treated glycol slurry to the polyester reaction system. In particular, the above-mentioned crushing treatment can suppress re-aggregation compared to crushing treatment such as a sand grinder while being uniformly dispersed. As a result, even if the abundance is extremely large, the number average secondary particle diameter is Can be in the range. Of course, in order to further improve the dispersibility of the acicular boehmite particles, it is also preferable to perform a filtration treatment in the state of a glycol slurry, and further melt kneading after forming a polymer, more preferably melt kneading by a twin screw extruder. Further, it is also preferable to melt and knead the mixture with a polymer containing no acicular boehmite particles or a very small amount as a high concentration master polymer.
The polyester resin composition of the present invention can be produced by adopting such a production method having excellent dispersibility of the acicular boehmite particles.

[Biaxially oriented polyester film]
The biaxially oriented polyester film of the present invention is composed of the above-described polyester resin composition of the present invention, and the film forming direction (hereinafter sometimes referred to as the longitudinal direction) and the in-plane direction (hereinafter referred to as the width direction or the following). A polyester film oriented in the biaxial direction). If it is not oriented in the biaxial direction, the Young's modulus improvement effect by the acicular boehmite particles cannot be obtained. In addition, as long as there is no notice in particular below, the biaxially oriented polyester film of this invention can be said to be the same as having demonstrated with the polyester resin composition of the above-mentioned this invention.

  The biaxially oriented polyester film of the present invention contains acicular boehmite particles in the polyester resin composition constituting the film. The acicular boehmite particles may be contained in the entire film. However, when the film is a laminated film of two or more layers, it is sufficient that at least one of the layers contains acicular boehmite particles. In the polyester resin composition which comprises these, the acicular boehmite particle | grains should just be contained with the said frequency. As the layer structure, for example, a two-layer structure of a layer containing no acicular boehmite particles and a layer containing acicular boehmite particles (acicular boehmite particle-containing layer), acicular boehmite-containing layers and acicular on both surfaces thereof A three-layer structure in which layers not containing boehmite particles are laminated, a three-layer structure in which needle-like boehmite particle-containing layers are laminated on both surfaces of a layer not containing needle-like boehmite particles, and these layer structures are further needle-like The layer structure of three or more layers which provide the layer which does not contain boehmite particles, or acicular boehmite particle content layer can be mentioned.

  When the biaxially oriented polyester film of the present invention is used as the base fill of a magnetic recording medium, the surface roughness (Ra) of at least one exposed surface of the film is preferably 0.1 to 10 nm. When the surface roughness exceeds the upper limit, when a magnetic layer is provided on the surface to form a magnetic tape, the surface of the magnetic layer becomes rough and electromagnetic conversion characteristics deteriorate, which is not preferable. On the other hand, when the surface roughness is less than the lower limit, the slipping property between the film and the film is lowered, and the winding property of the film is deteriorated. Further preferred surface roughness is in the range of 3 to 9.5 nm, especially 5 to 9 nm.

  As a means for providing the biaxially oriented polyester film of the present invention with such a surface roughness, adjusting the type, shape, size, addition amount and dispersion state of acicular boehmite particles to be contained in the biaxially oriented polyester film Can do. Further, in addition to the acicular boehmite particles, when inert particles are further added as a lubricant, it can be adjusted by the type, shape, size and addition amount of the inert particles. The biaxially oriented polyester film of the present invention can also be adjusted by a surface treatment that forms fine irregularities on at least one surface thereof, for example, a coating treatment with a slippery coating agent. Examples of the aforementioned inert particles include inorganic fine particles (for example, kaolin, titanium oxide, calcium carbonate, silicon dioxide, etc.) containing the elements of IIA, IIB, IVA, and IVB of the periodic table, silicone resins, and crosslinks. Examples thereof include inert particles made of a polymer having high heat resistance such as polystyrene. When the inert particles are included in the polyester film, the average particle diameter of the inert particles is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.8 μm. Moreover, it is preferable that content of an inert particle is 0.05 to 0.5 weight% in the polyester resin composition which comprises a polyester film, and also 0.1 to 0.3 weight%. Further, the inert particles are not limited to one type, and two or more types having different types, shapes, or sizes may be used in combination.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus of at least 6 GPa in at least one of the film forming direction and the width direction. If the Young's modulus in the machine direction and the transverse direction are both below the lower limit, for example, when a biaxially oriented polyester film is used as the base film of a tape for magnetic recording media, the dimension is stabilized by changes in tension and changes in temperature and humidity. Performance is impaired and problems such as track misalignment are likely to occur. Moreover, the effect by adding the acicular boehmite particles becomes difficult to express. From these viewpoints, the Young's modulus of any one of the biaxially oriented polyester films is more preferably 8 GPa or more, and particularly preferably 10 GPa or more. Furthermore, the Young's modulus in the longitudinal direction of the biaxially oriented polyester film is preferably 6 GPa or more, more preferably 8 GPa or more, and particularly preferably 10 GPa or more, since the dimensional change in the width direction due to the tension change in the longitudinal direction of the magnetic tape can be suppressed. On the other hand, the Young's modulus in the transverse direction of the biaxially oriented polyester film is preferably 6 GPa or more, more preferably 8 GPa or more, and particularly preferably 10 GPa or more, since the dimensional change in the width direction of the magnetic tape due to temperature and humidity changes can be suppressed. In addition, although the upper limit of the Young's modulus in the vertical direction and the horizontal direction is not particularly limited, it is usually preferably 15 GPa or less because sufficient Young's modulus can be imparted in the orthogonal direction.

  The sum of the Young's modulus in the vertical direction and the horizontal direction of the polyester film is preferably 10 GPa or more, more preferably 13 GPa or more, and particularly preferably 15 GPa or more. Such a high Young's modulus can be obtained by addition of acicular boehmite particles at a lower magnification than conventional films not containing acicular boehmite particles. The upper limit of the sum of the Young's modulus in the vertical direction and the horizontal direction is not particularly limited, but is usually at most 20 GPa.

  The thickness of the polyester film of the present invention is appropriately designed according to the application to be used, and particularly 2 to 10 μm, further 3 to 8 μm, particularly 4 to 6 μm when used for a base film of a magnetic recording medium tape. Is preferred. If the thickness is less than the above lower limit, the tape strength is insufficient, the tape width contracts due to the tension at the start of running, and the track and the magnetic head are misaligned. If the thickness exceeds the upper limit, the length of the tape stored in the cartridge becomes short, and a desired storage capacity cannot be obtained.

[Production method of polyester film]
The polyester film of the present invention can be produced, for example, according to the following method.
First, a polyester resin pellet containing a high concentration of needle-like boehmite particles and a polyester resin pellet containing no needle-like boehmite particles are mixed at a predetermined ratio, and after drying, for example, extruded at a melting temperature of 260 ° C. to 310 ° C. The film is extruded from a machine through a die, cast onto a cooling drum, and cooled and solidified to produce an unstretched film. This unstretched film is stretched in the longitudinal direction at a temperature of 60 to 140 ° C. at a magnification of 3 to 8 times, and then stretched in the transverse direction at a temperature of 70 to 180 ° C. at a magnification of 3 to 7 times to give a biaxially oriented polyester A film can be obtained. If necessary, longitudinal and / or transverse stretching may be divided into two or more stages (longitudinal multi-stage stretching, longitudinal-horizontal-vertical three-stage stretching, longitudinal-horizontal-vertical-horizontal 4). Step stretching, etc.). Moreover, you may implement by simultaneous biaxial stretching. The total draw ratio when producing the biaxially oriented polyester film is preferably 10 to 35 times, more preferably 12 to 30 times as the area draw ratio. Further, the biaxially oriented polyester film is preferably heat-set at a temperature of 140 to 250 ° C. after biaxial stretching, particularly preferably 180 to 230 ° C. The heat setting time is preferably 1 to 60 seconds.

  Further, when the biaxially oriented polyester film of the present invention is a laminated film, for example, using two extruders, at least one of them is fed with a pellet-like polyester composition containing acicular boehmite particles and melted, Extrusion as a laminated film from a two-layer or multi-layer die creates a laminated unstretched film, and the laminated unstretched film may be subjected to stretching, heat treatment, and the like similar to the case of the single-layer polyester film.

[Magnetic recording medium]
The biaxially oriented polyester film of the present invention has excellent Young's modulus, dimensional stability, flatness, slipperiness, winding property and the like. Because of such characteristics, the polyester film of the present invention is preferably used as a base film for high-density magnetic recording media, particularly as a base film for digital recording type magnetic machine recording media.

  A magnetic recording medium using the biaxially oriented polyester film of the present invention as a base film can be obtained, for example, by the following method. First, on one side of the biaxially oriented polyester film (in the case of a laminated film, the surface with the flatter surface roughness), a magnetic layer is formed, or by vacuum deposition, sputtering, ion plating, etc., A ferromagnetic metal thin film layer made of iron, cobalt, chromium, or an alloy or oxide containing these as a main component is formed, and the surface, purpose, application, and protection of diamond-like carbon (DLC), etc., if necessary A magnetic recording medium can be prepared by sequentially providing a layer and a fluorine-containing carboxylic acid-based lubricating layer and further providing a backcoat layer on the surface opposite to the magnetic layer.

[Polyester fiber]
When the polyester fiber is produced using the polyester resin composition of the present invention, a known method can be appropriately adopted as the production method. However, in order to develop the Young's modulus improvement effect by the acicular boehmite particles, the uniaxial direction ( It must be molecularly oriented in the spinning direction). In order to increase the molecular orientation, it is effective to increase the spinning speed to, for example, 3000 m / min or higher or increase the draw ratio.

  Hereinafter, the present invention will be further described based on examples. Various physical property values and characteristics in the present invention are measured and defined as follows.

(1) Young's modulus Using a tensile tester “Tensilon” manufactured by Toyo Baldwin Co., Ltd., the film was placed in a room adjusted to a temperature of 20 ° C. and a humidity of 50%. From the tangent of the rising portion of the resulting load-elongation curve, the length is cut to 15 cm, the chuck is 100 mm, the film is pulled in the film forming direction and the width direction at a chart speed of 500 mm / min, and the chart speed is 500 mm / min. The Young's modulus in the film forming direction and the width direction is calculated.

(2) Average secondary particle diameter of acicular boehmite particles (D)
When the sample is a polyester composition, this is once made into an unstretched film having a thickness of 200 μm, and this is stretched 3.5 times in the machine direction and transverse direction at a temperature 20 ° C. higher than the glass transition temperature of the polyester composition. Thus, a stretched film is obtained, which is used as a sample. When the sample was a film, it was used as it was as a sample.

Next, the sample film piece is fixed to the sample stage for a scanning electron microscope, and ion etching treatment is performed on the film surface under the following conditions using a sputtering apparatus (JFC-1100 type ion etching apparatus) manufactured by JEOL Ltd. Apply. 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, ion etching is performed at a voltage of 0.25 kV and a current of 12.5 mA for about 10 minutes, and needle-like boehmite particles To expose. Further, using the same apparatus, the film surface was sputtered with gold, magnified 100,000 times with a scanning electron microscope, 1000 secondary particles were observed, and the equivalent circle diameter was calculated from the area of each secondary particle. The secondary particle size was calculated. The average secondary particle diameter (D) was calculated by dividing the sum of the individual secondary particle diameters by the number. In addition, the secondary particle diameter here is a particle diameter of all plate-like boehmite particles measured without being separated from primary particles and secondary particles.

(3) Average particle diameter of inert particles Measured using a CP-50 type Centrifugular Particle Size Analyzer manufactured by Shimadzu Corporation. The particle size corresponding to 50 mass percent is read from the cumulative curve of the particle size and the abundance of each particle size calculated based on the centrifugal sedimentation curve obtained, and this value is taken as the average particle size. To do.

(4) Surface roughness of the film (centerline average roughness: Ra)
Centerline average roughness (Ra) is measured according to JIS-B601. In the present invention, a stylus type surface roughness meter (SURFCORDER SE, 30C) manufactured by Kosaka Laboratory Ltd. is used to measure and obtain under the following conditions.
(A) Stylus tip radius: 2 μm
(B) Measurement pressure: 30 mg
(C) Cutoff: 0.08mm
(D) Measurement length: 8.0 mm
(E) How to summarize data: The same sample is repeatedly measured 6 times, the largest value is removed, and the center line average roughness (Ra) is obtained as an average value using the remaining five data. When the surface roughness (Ra) of the center line exceeds 10 nm, the surface is too rough, and it is determined that it cannot be used as a magnetic recording medium.

(5) Intrinsic viscosity This is a value measured at 35 ° C. in orthochlorophenol. The unit is dl / g.

[Example 1]
(1) Preparation of slurry 100 g of acicular boehmite particles having an average primary particle shape of 90 nm in average length and an average diameter (thickness) of 10 nm are added to 900 g of ethylene glycol, and mixed for 10 minutes with a home tabletop mixer for 10 weight. % Slurry was prepared. This operation was repeated 10 times, and all were mixed to prepare a total amount of 10000 g of slurry. This slurry is put into a high-pressure state at a pressure of 200 MPa with a pressure homogenizer (manufactured by Sugino Machine, continuous atomizer Optimizer System HJP-25005), discharged from nozzles facing each other, and pulverized by collision of particles. All treatments were performed. This crushing treatment was repeated twice, and then this treatment solution was filtered with a cartridge grade 005 (corresponding to 99.98% filtration accuracy of 0.5 μm) of Nihon Pall filter profile II to obtain a final slurry. .

(2) Production of polyester resin composition
A mixture of 100 parts of dimethyl 2,6-naphthalene and 60 parts of ethylene glycol was charged with 0.030 part of manganese acetate tetrahydrate in a transesterification reactor, and gradually heated from 140 ° C to 230 ° C while being gradually heated. The transesterification reaction was carried out while distilling methanol out of the system. During this period, 15 parts of the acicular boehmite particle slurry prepared in Example 1 (1) was added at 190 ° C. in an amount corresponding to 10% by weight, and the reaction was continued. After complete distillation of methanol, phosphorus as a phosphorus compound was obtained. The reaction was terminated by adding 0.020 parts of trimethyl acid. Subsequently, 0.05 part of polymerization catalyst antimony trioxide was added after 5 minutes and heated to 250 ° C. to distill a part of ethylene glycol, and then the oligomer was transferred to a polycondensation reaction kettle. Thereafter, the reaction is terminated when the desired viscosity is reached at a final internal temperature of 295 ° C. while heating in a high vacuum according to a conventional method, and is continuously extruded in a strand form from the discharge part, and cooled and cut to about 3 mm. Before and after, pellets of polyethylene-2,6-naphthalate were obtained. The intrinsic viscosity of this polymer was 0.60.

(3) Production of biaxially oriented polyester film
The polyester resin composition described above was dried at 170 ° C. for 6 hours, then supplied to an extruder hopper, melted at 300 ° C., and maintained at a surface finish of 0.3 S and a surface temperature of 60 ° C. using a T-type extrusion die. The film was rapidly cooled and solidified on a casting drum to obtain an unstretched film made of a polyester resin composition.
This unstretched film is preheated to 120 ° C, further heated by an infrared heater with a surface temperature of 900 ° C from above 14 mm between low-speed and high-speed rolls, stretched 5.0 times in the longitudinal direction, rapidly cooled, and then Was supplied to a stenter and stretched 4.5 times in the transverse direction at 150 ° C. Subsequently, the film was heat-fixed at 225 ° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 4.5 μm.
The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Example 2]
The polyester resin composition prepared in Example 1 was used as the polyester resin composition for layer A, and a polyester resin containing 0.01% by weight of spherical silica particles having an average particle size of 0.1 μm was used instead of the one-way boehmite particles. The composition is a polyester resin composition for layer B, which is dried at 170 ° C. for 6 hours and then fed to separate extruder hoppers, melted at a melting temperature of 300 ° C., and using a multi-manifold coextrusion die. Then, the A layer and the B layer were laminated and rapidly solidified on a casting drum maintained at a surface finish of 0.3 S and a surface temperature of 60 ° C. to obtain a laminated unstretched film. The thickness of each layer is 60% for the A layer and 40% for the B layer.

  The laminated unstretched film thus obtained is preheated to 120 ° C., and further heated by an infrared heater having a surface temperature of 900 ° C. from above 14 mm between low speed and high speed rolls to 5.5 times in the longitudinal direction. Stretched, quenched, then fed to the stenter, stretched transversely at 150 ° C by 4.2 times, further stretched at 170 ° C by 1.14 times in the transverse direction, and stretched by 4.8 times in the total transverse direction. did. Subsequently, the film was heat-fixed at 225 ° C. for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.5 μm. The characteristics of the obtained biaxially oriented polyester film are shown in Table 1.

[Examples 3 to 5]
A polyester resin composition and a biaxially oriented polyester film were obtained in the same manner as in Example 1 except that the acicular boehmite particles were changed as shown in Table 1. Table 1 shows the properties of the obtained polyester resin composition and biaxially oriented polyester film.

[Comparative Example 1]
The same as Example 1 except that no acicular boehmite particles were added, 0.02 wt% of calcium carbonate particles having an average particle diameter of 0.6 μm, and 0.2 wt% of silica particles having an average particle diameter of 0.1 μm were added. Thus, a polyester resin composition and a biaxially oriented polyester film having a thickness of 4.5 μm were obtained. Table 1 shows the properties of the obtained polyester resin composition and biaxially oriented polyester film.

[Comparative Examples 2 to 4]
A polyester resin composition and a biaxially oriented film having a thickness of 4.5 μm were obtained in the same manner as in Example 1 except that the acicular boehmite particles were changed as shown in Table 1. Table 1 shows the properties of the obtained polyester resin composition and biaxially oriented polyester film.

[Comparative Example 5]
The same processing as in Example 1 was performed except that the processing by the continuous atomizer optimizer system was not performed. Table 1 shows the properties of the obtained polyester resin composition and biaxially oriented polyester film.

  PEN in Table 1 indicates polyethylene-2,6-naphthalate, and the content indicates the particle content in the resin composition. Note that the shapes of calcium carbonate and silica were almost spherical.

  Since the polyester resin composition of the present invention has a specific amount of specific needle boehmite particles, a biaxially oriented polyester film or polyester fiber obtained by stretching it has a high Young's modulus while maintaining surface flatness. The industrial value is high. In addition, since the biaxially oriented polyester film of the present invention has a specific amount of specific acicular boehmite particles, the biaxially oriented polyester film has a high Young's modulus while maintaining the flatness of the surface. It can be suitably used for a film or the like.

Claims (5)

  A polyester resin composition comprising needle boehmite particles having an average secondary particle diameter (D) of 25 to 90 nm in a proportion of 0.5 to 3.0% by weight based on the weight of the resin composition object.   The polyester resin composition according to claim 1, wherein the polyester is polyethylene-2,6-naphthalate.   Biaxial orientation characterized by containing acicular boehmite particles having an average secondary particle diameter (D) of 25 to 90 nm in a proportion of 0.5 to 3.0% by weight based on the weight of the resin composition Polyester film.   The biaxially oriented polyester film according to claim 3, wherein the Young's modulus of at least one of the film forming direction and the width direction of the film is in the range of 6 to 15 GPa.   The biaxially oriented polyester film according to claim 3, which has a thickness of 2 to 10 µm.