JP2005349726A - Biaxially oriented film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented film which is excellent in transparency, dimensional stability, and scratch resistance and especially suitable for optical applications. <P>SOLUTION: The biaxially oriented film mainly composed of a polyester (A), a polyimide (B), and two kinds of particles a and particles b which are different in average particle size has a total light transmittance of at least 80% and a haze value of 2% or below. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of a biaxially oriented film, and more particularly to a biaxially oriented film that is excellent in transparency, dimensional stability, and scratch resistance and is particularly suitable for optical use.

  Polyester film is capable of continuous production of large-area films that cannot be obtained from other materials, taking advantage of its strength, durability, transparency, flexibility, and surface characteristics. Used in various fields that are in great demand such as for magnetic recording media, condensers, thermal transfer ribbons, heat sensitive stencil printing base papers, various industrial materials such as circuit boards, agriculture, packaging, and building materials. ing.

  In particular, antistatic for pasting the surface of glass on the front panel of so-called flat panel displays such as transparent touch panels, base films for prism sheets used in liquid crystal display devices, cathode ray tubes, LCDs, and PDPs (plasma display panels). Widely used in various optical applications such as protective film base films with functional layers such as anti-reflection and electromagnetic wave shielding, as well as excellent transparency as well as dimensional stability due to thermal history during processing And flatness are essential.

  However, the polyester film has insufficient dimensional stability due to the heat history during the processing step, and whitening of the film surface causes an increase in haze, thereby impairing transparency.

Conventionally, as a method for improving the dimensional stability of a polyester film, a method using a blend polymer of polyethylene terephthalate (PET) and polyetherimide (PEI) related to the present invention has been proposed (Patent Document 1).
JP 2002-341114 A

  However, with this method, slight scratches on the film surface, which are optical defects, are likely to occur due to friction with the roll during film formation, and are easily scratched during the processing process, resulting in insufficient scratch resistance. Met.

  Accordingly, an object of the present invention is to provide a biaxially oriented film that is excellent in transparency, dimensional stability, and scratch resistance and that is particularly suitable for optical use.

  Here, “biaxially oriented film suitable for optical use” means excellent transparency, little whitening of the film during heat treatment in the post-processing step, and minimal scratches on the film surface. It is a required film. In particular, the present invention improves the scratch resistance, which has been insufficient with the conventional method using a blend polymer of PET and PEI. Specifically, the present invention is used for attaching a front panel glass surface of a flat panel display. It is intended to provide a novel optical film that is optimal as a base film for a protective film provided with functions such as antistatic, antireflection, and electromagnetic wave shielding.

In order to solve the above problems, the biaxially oriented film of the present invention has the following configuration (1).
(1) A film mainly composed of polyester (A) and polyimide (B) and two kinds of particles a and particles b having different average particle diameters, having a total light transmittance of 80% or more and a haze value of 2% A biaxially oriented film comprising:

The biaxially oriented film of the present invention has the following preferred embodiments (2) to (8).
(2) The heat shrinkage ratio after heating at 180 ° C. for 10 minutes is 2% or less, and the change in haze value after heating is 20% or less.
(3) The polyester (A) is polyethylene terephthalate or polyethylene-2,6-naphthalate.
(4) The polyimide (B) is a polyetherimide, and the content of the polyetherimide is 5 to 50% by weight.
(5) The film surface has a center line average roughness Ra of 1 to 30 nm and is an optical film.
(6) Particle a has an average particle size of 0.1 μm or more and less than 1 μm, and particle b has an average particle size of 1 μm or more and 5 μm or less.
(7) The refractive index of the particle a and the refractive index of the particle b are both 1.4 or more and 1.7 or less, and are optical films.
(8) An optical film using the biaxially oriented film according to any one of (1) to (7) above.

  ADVANTAGE OF THE INVENTION According to this invention, the biaxially oriented film excellent in transparency, dimensional stability, and scratch resistance, especially the biaxially oriented film suitable for optics can be provided, and its industrial value is extremely high.

  In order to satisfy the effects of the present invention, the biaxially oriented film of the present invention is composed of polyester (A) and polyimide (B).

  Examples of the polyester (A) in the present invention include polyethylene terephthalate and copolymers thereof, thermoplastic polyester resins such as polyethylene naphthalate and aliphatic polyester, ethylene such as high-density polyethylene, medium-density polyethylene, and low-density polyethylene. Resins, or propylene resins, polymethylpentene-1, polyolefin resins such as ethylene-cyclic olefin copolymers, nylon-6, nylon-6,6, nylon-6,10, nylon-6,12, nylon Polyamide resins such as -6, T, styrene resins, polycarbonate, acrylonitrile resins, polyphenylene ethers, polyphenylene sulfides, polyacetals, fluorine resins, polyether ether ketones, polyether resins De, thermoplastic resins such as polyether-based resin and polyimide resin polyethersulfone and the like. Among these, polyester resins are preferable from the viewpoint of transparency and dimensional stability, and polyethylene terephthalate and polyethylene-2,6-naphthalate are particularly preferably used.

  The polyimide (B) referred to in the present invention is a melt moldable polymer containing a cyclic imide group, and may be any polymer as long as it can meet the purpose of the present invention. Polyetherimides containing aromatic ether units and cyclic imide groups as repeating units are preferred.

  Examples of such polyetherimide include, for example, US Pat. No. 4,141,927, Japanese Patent No. 2622678, Japanese Patent No. 2609912, Japanese Patent No. 2606914, Japanese Patent No. 2596565, and Japanese Patent No. 2596565. Polyetherimide described in Japanese Patent No. 2596566, Japanese Patent No. 2598478, Japanese Patent No. 2598536, Japanese Patent No. 2599171, Japanese Patent Laid-Open No. 9-48852, Japanese Patent No. 2655556, Patent No. 2564636, Patent No. 2564737, Patent No. 2563548, Patent No. 2563547, Patent No. 2558341, Patent No. 2558339 and Patent No. 2854580 Examples thereof include polymers.

  If the effect of the present invention is not impaired, the main chain of polyimide contains structural units other than cyclic imide and ether units, such as aromatic, aliphatic, alicyclic ester units, oxycarbonyl units, and the like. May be.

  Further, if the effect of the present invention is not inhibited, structural units other than cyclic imide and ether units in the main chain of polyetherimide, for example, aromatic, aliphatic, alicyclic ester units, oxycarbonyl units, etc. It may be contained.

  Specific examples of the polyetherimide that can be preferably used in the present invention include polymers represented by the following general formula.

In the above formula, R ₁ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, and R ₂ is a divalent aromatic having 6 to 30 carbon atoms. From a residue, an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 2 to 20 carbon atoms, and a polydiorganosiloxane group chain-terminated with an alkylene group having 2 to 8 carbon atoms A divalent organic group selected from the group consisting of: Moreover, as said R < ₁ >, R < ₂ >, the aromatic residue shown by the following formula group can be mentioned, for example.

  In the present invention, a polyetherimide having a glass transition temperature of preferably 350 ° C. or lower, more preferably 250 ° C. or lower is preferable from the viewpoint of compatibility with a thermoplastic resin, cost, and melt moldability, and a structure represented by the following formula: Condensates of 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride having units with m-phenylenediamine or p-phenylenediamine, and copolymers and modified products thereof Is most preferable from the viewpoints of compatibility with the thermoplastic resin, cost, melt moldability, and the like. This polyetherimide is commercially available from GE Plastics and is known under the registered trade name “Ultem 1000, 5000, and 6000 series”.

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  The content of the polyimide (B) in the biaxially oriented film of the present invention is preferably 5 to 50% by weight based on the total weight of the biaxially oriented film, and 7 to 35 from the viewpoint of transparency and dimensional stability. More preferably, it is% by weight. If the content of the polyimide is less than 5% by weight, the dimensional stability may be inferior, and if it exceeds 50% by weight, the transparency may be deteriorated, and the film forming property and cost may be problematic. Therefore, it is not preferable. Moreover, it is preferable that content of polyester (A) is 95 to 50 weight% with respect to the total weight of a biaxially oriented film from a viewpoint of dimensional stability and film forming property. When the content of the polyester (A) is less than 50% by weight, there may be a problem in the deterioration of transparency, film forming property and cost, and when it exceeds 95% by weight, the dimensional stability may be inferior. This is not preferable.

  In the biaxially oriented film of the present invention, it is essential to contain two kinds of particles a and particles b having different average particle diameters from the viewpoint of achieving both transparency and scratch resistance. In the present invention, “different in average particle diameter” means that a particle group having a particle diameter of less than 1 μm obtained from particle size distribution measurement is a small particle a, and a particle group having a particle diameter of 1 μm or more is a large particle b, and these particle groups The difference between the average particle size of a and the average particle size of the particle group b is 0.8 μm or more and 2.5 μm or less. Here, when the difference between the average particle diameters of the small-diameter particles a and the large-diameter particles b is less than 0.8 μm, the particles having the same average particle diameter are used as one kind in the present invention. Since only one kind of particles having the same average particle diameter may not be provided with scratch resistance, it is not employed in the present invention.

  Further, “two kinds of particles having different average particle diameters” mean that only one kind of particles having the same composition may be used as long as the average particle diameters are different as described above. In addition, the particles having the same average particle diameter are regarded as one particle in the present invention as being the same particle diameter even if the composition is different. In the present invention, the two types of particles a and b having different average particle diameters are mixedly used with the polyester (A) and the polyimide (B), so that the particles a and b, the polyester (A) and the polyimide are mixed. By forming the film mainly from (B), large and small irregularities are formed on the film surface, particles b having a large average particle size provide scratch resistance, and particles a having a small average particle size provide an effect of improving transparency. Thus, a biaxially oriented film excellent in transparency and scratch resistance, which is the desired effect of the present invention, and particularly suitable as an optical film can be obtained.

  The biaxially oriented film of the present invention preferably contains particles a having an average particle size of 0.1 μm or more and less than 1 μm, and particles b preferably have an average particle size of 1 μm or more and less than 5 μm, more preferably particles a The average particle size of the particles b is from 0.2 μm to less than 0.9 μm, the average particle size of the particles b is from 1.2 μm to less than 4 μm, more preferably the average particle size of the particles a is from 0.3 μm to less than 0.8 μm, The average particle size is 1.4 μm or more and less than 3 μm. When the average particle size of the particles a is less than 0.1 μm, the scratch resistance tends to deteriorate. On the other hand, when the average particle size of the particles a is larger than 1 μm, the total light transmittance tends to be lowered and transparency tends to be impaired. Moreover, there exists a tendency for scratch resistance to deteriorate that the average particle diameter of particle | grains b is less than 1 micrometer. On the other hand, when the average particle diameter of the particles b is larger than 5 μm, the total light transmittance tends to be lowered and the transparency tends to be impaired.

  In the present invention, in order to further improve the scratch resistance, the difference between the average particle size of the particles a and the average particle size of the particles b is preferably 1 μm or more and 2.5 μm or less, more preferably 1.2 μm or more and 2. It is 3 μm or less, more preferably 1.4 μm or more and 2 μm or less. If the difference in average particle size is less than 1 μm, scratch resistance may not be imparted, whereas if the difference in average particle size is greater than 2.5 μm, the total light transmittance may be reduced and transparency may be deteriorated.

  Further, the content of particles a contained in the biaxially oriented film of the present invention is 0.005 wt% or more and 0.05 wt% or less, and the content of particles b is 0.002 wt% or more and 0.01 wt% or less. More preferably, the content of the particles a is 0.008 wt% or more and 0.04 wt% or less, the content of the particles b is 0.003 wt% or more and 0.009 wt% or less, more preferably the particles The content of a is 0.01 wt% or more and 0.03 wt% or less, and the content of particles b is 0.004 wt% or more and 0.008 wt% or less.

  If the content of the particles a and particles b is within the above range, it is effective to achieve both transparency and scratch resistance. Furthermore, the weight ratio (a / b) of the content of particles a and particles b contained in the biaxially oriented film is preferably 1 or more and less than 10, more preferably 1.5 or more and less than 9, and still more preferably 2 It is less than 8. If the weight ratio (a / b) of the content of the particles a and the particles b is less than 1, it is not preferable because the total light transmittance may decrease and the transparency may deteriorate. On the other hand, if the weight ratio (a / b) of the content of particles a and particles b is 10 or more, scratch resistance may not be imparted, which is not preferable.

  The refractive index of the particles a and the refractive index of the particles b contained in the biaxially oriented film of the present invention are preferably 1.4 or more and 1.7 or less, more preferably 1.42 or more and 1.65 or less. More preferably, it is 1.44 or more and 1.6 or less. If the refractive indexes of the particles a and b are out of the above range, the difference in refractive index between the hybrid resin composed of the polyester (A) and the polyimide (B) becomes large, and the transparency may be deteriorated. .

  Further, the particles used in the biaxially oriented film of the present invention include inorganic particles and organic particles such as clay, mica, titanium oxide, calcium carbonate, kaolin, talc, silica, calcium phosphate, barium sulfate, alumina, zirconia, and acrylic acids. Styrenic resin and thermosetting resin are added. Among them, silica particles are suitable for obtaining a film having a relatively close refractive index with a polyester resin and excellent in transparency and scratch resistance.

  In addition, the biaxially oriented film of the present invention has various additives such as a compatibilizer, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, and an antistatic agent as long as the effects of the present invention are not inhibited. Agents, brighteners, colorants, conductive agents, crystal nucleating agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments and dyes may be added.

  The biaxially oriented film of the present invention must have a total light transmittance of 80% or more, preferably 85% or more. When the total light transmittance is less than 80%, a film with poor transparency is obtained. The upper limit of the total light transmittance is about 99.9%. In order to make the total light transmittance within the range of the present invention, it can be achieved by appropriately adjusting the kind, addition amount, and average particle diameter of the particles in the film.

  It is essential that the biaxially oriented film of the present invention has a haze of 2% or less, preferably 1.5% or less. If the haze is greater than 2%, the incident light diffuses inside the film and the amount of emitted light decreases, resulting in a film with poor transparency. Usually, the lower limit of haze on the film is considered to be about 0.05%.

  In order to make the haze within the range of the present invention, it can be achieved by appropriately adjusting the kind of particles in the film, the added amount, the average particle diameter, and the like.

  In the biaxially oriented film of the present invention, the heat shrinkage ratio after heating at 180 ° C. for 10 minutes is preferably 2% or less in all directions from the viewpoint of dimensional stability and transparency, and more preferably 1.8% or less. More preferably, it is 1.5% or less. If the heat shrinkage ratio after heating at 180 ° C. for 10 minutes is larger than 2%, the shape change due to the heat history in the processing step becomes remarkable, and it is difficult to obtain the dimensional stability which is the effect of the present invention. In order to make the thermal contraction rate within the range of the present invention, it can be achieved by appropriately adjusting the content of the polyimide (B), the heat treatment conditions in the film forming process, and the cooling process to a multi-stage cooling system or the like.

  In the biaxially oriented film of the present invention, the change in haze after heating at 180 ° C. for 10 minutes is preferably 20% or less, more preferably 15% or less. The change in haze after heating means the difference between the haze value after heating at 180 ° C. for 10 minutes and the haze value before heating. When the change value of haze is larger than 20%, the film becomes markedly whitened, and the transparency is inferior when the biaxially oriented film of the present invention is used as a base material for optical applications in which heat treatment is performed in a post-processing step. This is not preferable because the influence on the appearance and performance cannot be ignored. In order to make the change value of the haze after a heating into the range of this invention, it can achieve by adjusting content of a polyimide (B) and the particle | grains in a film suitably.

  From the viewpoint of transparency, the biaxially oriented film of the present invention preferably has a center line average roughness Ra of 1 to 30 nm, more preferably 2 to 25 nm, and further preferably 4 to 20 nm. An excessively smooth film with an Ra of less than 1 nm is not preferred because the film winding process during film formation becomes difficult and the productivity may deteriorate. Conversely, a film having a large surface roughness such that Ra exceeds 30 nm is not preferable because the total light transmittance is lowered and the transparency is deteriorated.

  In order to set the center line average roughness Ra on the surface of the biaxially oriented film within the range of 1 to 30 nm described above, it can be achieved by appropriately adjusting the kind of particles in the film, the added amount, and the average particle diameter.

  The thickness of the biaxially oriented film of the present invention is preferably 25 to 250 μm, more preferably 50 to 200 μm. When the biaxially oriented film of the present invention is used as a substrate for optical applications, if the thickness of the film is less than 25 μm, it is not preferable because the film itself is not elastic and difficult to handle. Conversely, when the thickness of the film is greater than 250 μm, the amount of light absorbed by the thickness increases and the total light transmittance decreases, which is not preferable.

  Next, the case where polyethylene terephthalate (PET) is used as the polyester (A) and polyetherimide (PEI) “Ultem” (registered trademark made by GE Plastics) is used as the polyimide (B) is exemplified. Although the preferable manufacturing method of an axially oriented film is demonstrated, it cannot be overemphasized that this invention is not limited to the following manufacturing method.

  First, in accordance with a conventional method, magnesium acetate is added to a mixture of dimethyl terephthalate and ethylene glycol, and the temperature is raised by a conventional method to carry out a transesterification reaction. Next, after adding trimethyl phosphate to the transesterification reaction product, germanium oxide is added to move to the polycondensation reaction layer. Subsequently, the reaction system is gradually depressurized while being heated and heated, and the polymerization reaction is advanced at 290 ° C. under a reduced pressure of 1 mmHg. Here, a polyester having an intrinsic viscosity of about 0.6 is obtained. Moreover, as a method for incorporating the particles into the polyester constituting the film, a method in which the particles are dispersed in a predetermined proportion in the form of a slurry in ethylene glycol and this ethylene glycol is polymerized with terephthalic acid is preferable.

  When the particles are added, for example, if the water sol or alcohol sol obtained at the time of synthesis is added without drying, the dispersibility of the particles is good. It is also effective to mix the aqueous slurry of particles directly with predetermined polyester pellets and knead them into the polyester using a vented twin-screw kneading extruder. As a method of adjusting the content and number of particles, a master of high-concentration particles is prepared by the above method, and it is diluted with polyester that does not substantially contain particles at the time of film formation to adjust the content of particles. The method to do is effective.

Next, the pellets of polyethylene terephthalate and the pellets of polyetherimide are mixed at a predetermined ratio and supplied to a vent type twin-screw kneading extruder heated to 270 to 300 ° C. for melt extrusion. The shear rate at this time is preferably 50 to 300 sec ⁻¹ , more preferably 100 to 200 sec ⁻¹ , and the residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. Furthermore, when not compatible under the above conditions, the obtained chip may be put into the twin-screw extruder again and extrusion may be repeated until compatible.

  The obtained polyetherimide-containing polyester pellets, particle master pellets and polyethylene terephthalate pellets for dilution are vacuum-dried at 180 ° C. for 3 hours or more, and then 280 in a nitrogen stream or under vacuum so that the intrinsic viscosity does not decrease. It is supplied to an extruder heated to ˜320 ° C., and a film is formed by a conventional method. Moreover, it is preferable to use various types of filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh, in order to remove foreign substances and denatured polymers. Moreover, you may provide a gear pump as needed in order to improve fixed_quantity | feed_rate supply property. Using an extruder, a sheet of a mixture of molten polyester and polyetherimide is extruded from a slit die and cooled on a casting roll to produce an unstretched film.

  Next, the obtained sheet-like material is stretched in the longitudinal direction (longitudinal direction), then stretched in the width direction (transverse direction), or stretched in the width direction (transverse direction) and then stretched in the longitudinal direction (longitudinal direction). Biaxial orientation is imparted to the film by the sequential biaxial stretching method or the simultaneous biaxial stretching method. Although the specific example by the sequential biaxial stretching method used most generally is shown below, of course, this invention is not limited to the following description.

  First, a film heated by a plurality of roll groups is stretched at a temperature of 90 to 170 ° C., a magnification of 2.0 to 5.0 times, preferably at a magnification of 2.5 to 4.5 times in one step or two or more steps. The film is stretched in the longitudinal direction (longitudinal direction) in multiple stages, and the film is further gripped by a clip and guided to a tenter, stretched at 90 to 180 ° C., and at a magnification of 2.0 to 6.0 times, preferably 2. Stretch in the width direction (lateral direction) at a magnification of 5 to 5.5 times. Under the present circumstances, you may extend | stretch 1.01-2.5 times further at the temperature of 110-180 degreeC in the longitudinal direction and / or the width direction as needed. In the present invention, the heat treatment temperature after stretching is preferably a temperature not higher than the melting point of the thermoplastic resin from the viewpoint of dimensional stability, more preferably a temperature of 190 to 245 ° C, still more preferably a temperature of 210 to 240 ° C. It is preferable to heat-treat for 1 to 30 seconds. Further, in the present invention, it is preferable to perform intermediate cooling at 100 to 160 ° C. after the heat treatment step, it is preferable to perform relaxation treatment, and relaxation treatment may be performed at a ratio of 2 to 10% in the width direction and / or the longitudinal direction. Preferably, it is 4 to 9%.

  In this way, a biaxially oriented film having excellent transparency, dimensional stability, and scratch resistance can be obtained.

[Methods for measuring physical properties and methods for evaluating effects]
(1) Content of polyester and polyimide It melt | dissolves in the suitable solvent (for example, HFIP / deuterated chloroform) which melt | dissolves both polyester and a polyimide, and measures the NMR spectrum of 1H nucleus. In the obtained spectrum, the peak area intensity of absorption peculiar to polyester and polyimide (for example, aromatic proton of terephthalic acid for PET and aromatic proton of bisphenol A for PEI) is determined, and the ratio and proton are determined. The molar ratio of the blend is calculated from the number. Further, the weight ratio is calculated from the formula amount corresponding to the unit unit of the polymer. The measurement conditions are, for example, the following conditions, but are not limited to this because they differ depending on the type of polyester and polyimide.
Apparatus: BRUKER DRX-500 (Bruker)
Solvent: HFIP / deuterated chloroform

Observation frequency: 499.8 MHz
Standard: TMS (0 ppm)
Measurement temperature: 30 ° C
Observation width: 10 KHz
Data point: 64K
acquisiton time: 4.952 seconds
pulse delay time: 3.048 seconds Integration count: 256 times

  Moreover, you may perform a composition analysis by microscopic FT-IR method (Fourier transform microinfrared spectroscopy) as needed. In that case, it calculated | required from ratio of the peak resulting from the carbonyl group of polyester, and the peak resulting from substances other than polyester. In order to convert the peak height ratio to the weight ratio, a calibration curve was prepared in advance from a sample with a known weight ratio, and the ratio of polyester to the total amount of polyester and other substances was determined. The thermoplastic resin ratio was determined from this and the particle content. Moreover, the X-ray microanalyzer was used together as needed.

(2) Transparency (total light transmittance and haze)
According to JIS K6714-1958, total light transmittance Tt (%) and scattered light transmittance Td (%) were determined, and haze (Td / Tt × 100) (%) was calculated.

(3) Surface roughness (centerline surface roughness Ra)
Using an atomic force microscope (AFM), under the following conditions, the scanning range is appropriately selected and 10 places are measured at different locations, and the average value of the 10 fields when measured with a scanning range of 125 μ □ is the surface roughness. Ra.
Apparatus: NanoScope III AFM (manufactured by Digital Instruments)
Cantilever: Silicon single crystal Scanning mode: Tapping mode Scanning range: 30 to 125 μm
Scanning speed: 0.5 Hz to 1.0 Hz

(4) Film thickness Film thickness was measured at 30 g of needle pressure using an electronic micrometer (K-312A type) manufactured by Anritsu Corporation.

(5) Average particle diameter 1.0 liter of an appropriate solvent (for example, HFIP / deuterated chloroform) that dissolves both polyester and polyimide was added to 100 g of a film sample and heated at 120 ° C. for 3 hours. Centrifugation is carried out at 30,000 rpm for 40 minutes using an ultracentrifuge 55P-72 manufactured by Kogyo Co., Ltd., and the resulting particles are vacuum dried at 100 ° C. When the particles are measured with a scanning calorimeter, if a dissolution peak corresponding to polyester and polyimide is observed, an appropriate solvent (for example, HFIP / deuterated chloroform) that dissolves both polyester and polyimide is added to the particles, After heating and cooling, the centrifugation operation is performed again. When no dissolution peak is observed, the particles are regarded as precipitated particles. Usually, two centrifugation steps are sufficient. Next, the obtained precipitated particles were dispersed in ethylene glycol or as a water slurry, and the volume average diameter (μm) was measured using a centrifugal sedimentation type particle size distribution analyzer (CAPA500 manufactured by Horiba, Ltd.).

(6) Content of particles The particle size distribution obtained in the above (5) is separated into a small particle group (particle a) having a particle diameter of less than 1 μm and a large particle group (particle b) having a particle diameter of 1 μm or more. The ratio (weight%) of the particle weight to the total film weight was determined for the particle group.

(7) Refractive index of the particles According to JIS-K-0062, a sample plate having the same composition as the particles is prepared (casting the molten particle raw material), and Abbe refraction is performed using sodium D-line (589 nm) as the light source. Measurement was performed with a meter.

(8) Dimensional stability (heat shrinkage rate)
It measured according to the method prescribed | regulated to JISC-2318. The sampling method was the same as that of the elastic modulus sample. A sample having a sample width of 10 mm and a sample length of 200 mm was heat-treated in a gear oven at 180 ° C. for 10 minutes, and the thermal contraction rate was calculated from the change in the sample length by the following formula.
Thermal shrinkage rate (%) = [(length before heat treatment−length after heat treatment) / length before heat treatment] × 100

(9) Optical film suitability test

[Change in haze after heating]
The film was cut into 10 cm × 10 cm, the total light transmittance Tt (%) and the scattered light transmittance Td (%) were determined according to JIS K6714-1958, and the initial haze before heat treatment (Td / Tt × 100) (%) Was calculated.

  Subsequently, the film was sandwiched between metal frames (outer dimensions 10 cm × 10 cm and inner dimensions 8 cm × 8 cm), and heat-treated at 180 ° C. for 10 minutes in a gear oven under tension. After cooling the film at room temperature, the film is removed from the metal frame, and the total light transmittance Tt (%) and scattered light transmittance Td (%) are determined according to JIS K6714-1958, and the haze after heating (Td / Tt × 100) (%) was calculated.

  And the value of the difference obtained by subtracting the haze value (%) before and after the heat treatment was defined as the haze change value after heating.

[Scratch resistance]
The film is slit to a width of 1000 mm, and the film surface is brought into contact with a hard chrome-plated free roll (surface roughness: Ra of 100 nm) having a diameter of 220 mm and a rotational resistance of 9.8 N using a film running tester. Let it run. The traveling conditions at this time were a traveling speed of 10 m / min, a winding angle of 60 °, and a traveling tension of 98N. After traveling, scratches on the surface of the film are deposited with platinum and observed with a microscope. The number of scratches with a width of 3 μm or more and a length of 500 μm or more is converted per unit area, and the first decimal place is rounded off. Then, the following rank was used for determination. “◎” is preferable, but “○” can be used practically.
A: Less than 10 / m ²
○: 10 or more and less than 20 / m ²
×: 20 or more / m ²

  Specific examples of the present invention will be described below in comparison with comparative examples.

Reference example 1
Production of polyethylene terephthalate (PET) polymer chips:
To a mixture of 100% by weight of dimethyl terephthalate and 60% by weight of ethylene glycol, 0.04% by weight of magnesium acetate was added with respect to the amount of dimethyl terephthalate, and the temperature was raised by a conventional method to conduct a transesterification reaction. Next, 0.020% by weight of trimethyl phosphate was added to the transesterification product with respect to the amount of dimethyl terephthalate, and then 0.02% by weight of germanium oxide was added, followed by transition to a polycondensation reaction layer. Subsequently, the reaction system was gradually depressurized while being heated and heated, and polymerization was performed at 290 ° C. under a reduced pressure of 1 mmHg by a conventional method to obtain a polyethylene terephthalate chip having an intrinsic viscosity [η] = 0.65.

Reference example 2
Production of particle-containing polyethylene terephthalate chips:
[Η] = 0.0 in the same manner as described above except that an ethylene glycol slurry having a particle amount of 5% by weight as a particle amount is added to the dimethyl terephthalate amount before transferring to the polycondensation reaction layer. 65 particle-containing polyethylene terephthalate master chips were obtained.

Reference example 3
Production of polyethylene-2,6-naphthalate (PEN) polymer chips:
To a mixture of 100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by weight of ethylene glycol, 0.03 part by weight of manganese acetate tetrahydrate salt is added, and the temperature is gradually increased from 150 ° C. to 240 ° C. The transesterification was carried out while raising the temperature. In the middle, when the reaction temperature reached 170 ° C., 0.024 parts by weight of antimony trioxide was added. When the reaction temperature reached 220 ° C., 0.042 parts by weight of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (corresponding to 2 mmol%) was added. Thereafter, a transesterification reaction was subsequently carried out. After completion of the transesterification reaction, 0.023 parts by weight of trimethyl phosphate was added. Next, the reaction product is transferred to a polymerization reactor, heated to a temperature of 290 ° C., subjected to a polycondensation reaction under a high vacuum of 0.2 mmHg or less, and polyethylene-2,6 having an intrinsic viscosity of 0.65 dl / g. -A naphthalate chip was obtained.

Reference example 4
Production of particle-containing polyethylene-2,6-naphthalate chips:
Before moving to the polycondensation reaction layer, the same amount as above except that 5% by weight of ethylene glycol slurry is added as 1% by weight as the amount of particles with respect to the amount of dimethyl 2,6-naphthalenedicarboxylate, A particle-containing polyethylene-2,6-naphthalate master chip with [η] = 0.65 was obtained.

Example 1
50 parts by weight of PET having an intrinsic viscosity of 0.65 and 50 parts by weight of polyetherimide (PEI) “Ultem” 1010 manufactured by General Electric were dehumidified and dried at 150 ° C. for 5 hours, and then heated to 320 to 290 ° C. (Screw zone, temperature gradient is set at the extrusion head part) Bent type two equipped with twin-screw three-stage type screw (Plastic and PEI kneading plasticizing zone / Dalmage kneading zone / Fine dispersion compatibilizing zone by reverse screw dalmage) The mixture was supplied to a shaft extruder (L / D = 40, the degree of vacuum of the vent hole was 200 Pa) and melt-extruded with a residence time of 3 minutes to obtain a blend chip containing 50% by weight of Ultem.

  Next, the obtained blend chip, the above-described PET chip having an intrinsic viscosity of 0.65, a master chip containing 1% by weight of the particles a shown in Table 1 (added in the PET polymerization step), and 1 weight of the particles b % Master chip (added in the PET polymerization step) was mixed so as to have the content (% by weight) shown in Table 1, vacuum dried at 180 ° C. for 3 hours, and then put into an extruder. After melt extrusion at 280 ° C. and passing through a fiber sintered stainless steel metal filter (14 μm cut), the sheet is discharged from a T-die into a sheet shape, and the sheet is adhered to a cooling drum having a surface temperature of 25 ° C. by an electrostatic application method. Solidified and cooled to obtain an unstretched polyester film.

  Subsequently, this unstretched polyester film was heated 3.0 times in the longitudinal direction of the film at a temperature of 100 ° C. using a peripheral speed difference of the roll using a longitudinal stretching machine composed of a plurality of heated roll groups. Stretched at a magnification. Thereafter, both ends of the film were gripped with clips, led to a tenter, stretched 3.3 times at a temperature of 105 ° C. in the width direction, and subsequently heat treated at a temperature of 240 ° C. for 3 seconds (in the width direction). 2% relaxation treatment), followed by further 2% relaxation treatment in the width direction at a temperature zone of 150 ° C., and then gradually cooled to room temperature to obtain a biaxially oriented film having a thickness of 100 μm.

The characteristics of the obtained biaxially oriented film are shown in Table 1. The biaxially oriented film of the present invention had properties suitable for transparency, dimensional stability and optical films.
Example 2 and Comparative Example 1
A biaxially oriented film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the contents of PET and PEI were changed as shown in Table 1.

  The characteristics of the obtained biaxially oriented film are shown in Table 1. The biaxially oriented film of Example 2 had properties suitable for transparency, dimensional stability, and optical films. Although the biaxially oriented film of Comparative Example 1 is excellent in transparency, since it does not contain polyimide (B), it has poor dimensional stability and transparency after heat treatment, and is not suitable as an optical film. there were.

Example 3
50 parts by weight of PEN having an intrinsic viscosity of 0.65 and 50 parts by weight of polyetherimide (PEI) “Ultem” 1010 manufactured by General Electric were dehumidified and dried at 150 ° C. for 5 hours, and then heated to 330 to 290 ° C. (Temperature gradient is set in the screw zone and extrusion head part) Bent type two equipped with a twin-screw three-stage type screw (PEN and PEI kneading plasticization zone / Dalmage kneading zone / Fine dispersion compatibilizing zone by reverse screw dalmage) The mixture was supplied to a shaft extruder (L / D = 40, the degree of vacuum of the vent hole was 200 Pa) and melt-extruded with a residence time of 3 minutes to obtain a blend chip containing 50% by weight of Ultem.

  Next, the obtained blend chip, the PEN chip having the intrinsic viscosity of 0.65, the master chip containing 1% by weight of the particles a shown in Table 1 (added in the PEN polymerization step), and 1% of the particles b % Master chips (added in the PEN polymerization step) were mixed so as to have the content (% by weight) shown in Table 1, vacuum dried at 180 ° C. for 3 hours, and then put into an extruder. After melt extrusion at 280 ° C. and passing through a fiber sintered stainless steel metal filter (14 μm cut), the sheet is discharged from a T-die into a sheet shape, and the sheet is adhered to a cooling drum having a surface temperature of 25 ° C. by an electrostatic application method. Solidified and cooled to obtain an unstretched polyester film. The pellets were dried at a temperature of 170 ° C. for 6 hours, then put into an extruder, melt extruded at a temperature of 310 ° C., passed through a fiber sintered stainless metal filter (14 μm cut), and then sheeted from a T die. The sheet was solidified by an electrostatic application method on a cooling drum having a surface temperature of 25 ° C. and cooled to obtain an unstretched film. Subsequently, this unstretched film was stretched 3.0 times in the longitudinal direction at a temperature of 130 ° C. using a longitudinal stretching machine composed of a plurality of heated roll groups. Subsequently, both ends of the film were gripped with clips, guided to a tenter, stretched 3.3 times at a temperature of 140 ° C. in the width direction, and subsequently heat treated at a temperature of 240 ° C. for 3 seconds (in the width direction). 2% relaxation treatment), followed by further 2% relaxation treatment in the width direction at a temperature zone of 150 ° C., and then gradually cooled to room temperature to obtain a biaxially oriented film having a thickness of 100 μm.

The characteristics of the obtained biaxially oriented film are shown in Table 1. The biaxially oriented film of the present invention had properties suitable for transparency, dimensional stability and optical films.
Examples 4-7, Comparative Examples 2-4
A biaxially oriented film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the particle type, average particle diameter, and addition amount of the particles a and b were changed as shown in Table 1.

  The characteristics of the obtained biaxially oriented film are shown in Table 1. The biaxially oriented films of Examples 4 to 7 had characteristics suitable for transparency, dimensional stability, and optical films.

  Although the biaxially oriented film of Comparative Example 2 is excellent in transparency, since the added particles are only the type of particles a1, and the addition amount of the particles a is outside the preferred range of the present invention, the scratch resistance is high. It was inferior and was a characteristic not suitable as an optical film.

  The biaxially oriented film of Comparative Example 3 is inferior in transparency because the amount of added particles a and particles b is outside the preferred range of the present invention, the total light transmittance is reduced, and the haze value is large. It was a characteristic that was not suitable as an optical film.

  In the biaxially oriented film of Comparative Example 4, the average particle diameter of the added particles a and the added amount of the particles b are outside the preferred range of the present invention, the total light transmittance is reduced, and the haze value is large. Further, the transparency was inferior, and the characteristics were not suitable as an optical film.

ここで、表中の略号を以下に示す。
ＰＥＴ：ポリエチレンテレフタレート
ＰＥＮ：ポリエチレン−２，６−ナフタレート
ＰＥＩ：ポリエーテルイミド

Here, abbreviations in the table are shown below.
PET: Polyethylene terephthalate PEN: Polyethylene-2,6-naphthalate PEI: Polyetherimide

  The biaxially oriented film according to the present invention is excellent in transparency, dimensional stability and scratch resistance, and is particularly used as an optical film, and its industrial value is extremely high.

Claims (8)

  A film mainly composed of polyester (A) and polyimide (B) and two kinds of particles a and b having different average particle diameters, having a total light transmittance of 80% or more and a haze value of 2% or less. A biaxially oriented film characterized by that.   2. The biaxially oriented film according to claim 1, wherein a heat shrinkage ratio after heating at 180 ° C. for 10 minutes is 2% or less and a change in haze value after heating is 20% or less.   The biaxially oriented film according to claim 1 or 2, wherein the polyester (A) is polyethylene terephthalate or polyethylene-2,6-naphthalate.   The polyimide (B) is a polyetherimide, and the content of the polyetherimide is 5 to 50% by weight (vs. the total weight ratio of the film). Biaxially oriented film.   The biaxially oriented film according to any one of claims 1 to 4, wherein the center line average roughness Ra of the film surface is 1 to 30 nm.   The average particle size of the particles a is 0.1 μm or more and less than 1 μm, the average particle size of the particles b is 1 μm or more and 5 μm or less, and the weight ratio (a / b) of the content of the particles a and particles b (to the total weight ratio of the film) ) Is 1 or more and less than 10, The biaxially oriented film according to claim 1.   The biaxially oriented film according to any one of claims 1 to 6, wherein the refractive index of the particles a and the refractive index of the particles b are 1.4 or more and 1.7 or less.   The film for optics which uses the biaxially oriented film in any one of Claims 1-7.