JP2009072939A - Releasing polyester film for polarizing plate protection or retardation plate protection, releasing film, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a releasing polyester film for polarizing plate protection or retardation plate protection in which the mechanical axis direction and optical axis direction of a film highly precisely are matched with each other and the optical axis direction of the film is uniform in the film surface, to provide a base film of the polyester film and to provide a manufacturing method of the polyester film. <P>SOLUTION: A biaxially-oriented polyester film which is used by being attached to a polarizing plate or a retardation plate and is used as a base material of the releasing film supplied for an inspection according to a Crossed Nicols method is characterized in that (1) the polyester film has a molecular orientation main axis in the film longitudinal direction and (2) a difference between refractive index of the film longitudinal direction and refractive index of the film width direction is in the range of 0.03 to 0.10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate that is a constituent member of a large-sized liquid crystal display device, a release film suitable for inspection by a crossed Nicol method, which is used by being attached to a retardation plate, a base film thereof, and a manufacturing method thereof.

  A polarizing plate and a retardation plate, which are constituent members of a liquid crystal display device, are provided with an adhesive layer on one surface, and a release film for protecting the polarizing plate or the retardation plate is laminated on the adhesive layer. In the state of the laminated body, it is rolled and transported or stored.

  One of the important items in inspection of polarizing plates and retardation plates is inspection of defects such as scratches and foreign matter. This defect inspection is generally performed by observation under crossed Nicols in the state of a laminate in which a release film is laminated on one surface of a polarizing plate or a retardation plate via an adhesive layer. In the defect inspection under the crossed Nicols, the release film provided on the surface of the laminate is disposed between the two polarizing plates forming the crossed Nicols. Therefore, the release film is required to have a function that does not cause a change in contrast and brightness and does not cause an interference color during observation under crossed Nicols.

  Biaxially oriented polyester films are widely used as release film substrates from the viewpoint of strength function and cost. A biaxially oriented polyester film having a structure in which linear polyester polymers are oriented is a birefringent body that optically exhibits birefringence. Therefore, the biaxially oriented polyester film has two optical axes perpendicular to the direction parallel to and perpendicular to the direction of molecular orientation. Therefore, if the optical axis of the release film substrate is laminated with the polarizing plate or the optical axis of the phase difference plate tilted, it will exhibit transmitted light and interference color when placed under crossed Nicols. It becomes a factor that hinders defect inspection. Furthermore, if the direction of the optical axis of the release film substrate varies within the film plane, the contrast, brightness, and interference color state fluctuate depending on the location of the laminate during the defect inspection. Inspection becomes extremely difficult.

  Therefore, the polyester film that is the substrate of the release film has excellent optical axis accuracy, that is, the mechanical axis direction (longitudinal direction / width direction) of the film and the optical axis direction coincide with each other with high accuracy. In addition, the axial direction of the optical axis is required to be uniform in the film plane.

  However, the biaxially oriented polyester film produced by sequentially stretching in the machine direction-transverse direction tends to be distributed in the direction of the molecular orientation principal axis, that is, the optical axis in the film width direction, and is generated in the stretching and heat treatment processes. Due to the bowing phenomenon, the tilt angle of the optical axis with respect to the width direction increases as the film ends. Therefore, as the base film of the release film for protecting the polarizing plate or protecting the retardation plate, only a product collected from the vicinity of the central part in the film width direction having a relatively small inclination of the optical axis can be used. Therefore, it is a big problem in reducing the procurement cost of the base film, and hence the supply cost of the release film.

  Furthermore, along with the trend toward larger screens of liquid crystal displays in recent years, it is desired that the size of polarizing plates and retardation plates is increased and the release film is also widened. When the release film becomes wider, for the reasons described above, it is necessary to collect the film from a wider area than the vicinity of the central part so far, and the inclination angle of the optical axis in the film width direction within one release film. The variation (variation) in the size also increases. That is, in a release film used by being attached to a polarizing plate or a retardation plate for a large liquid crystal display device, excellent optical axis accuracy is required so that the optical axis is not inclined even in a wider region with respect to the width direction. It has become to.

  A number of approaches have been proposed so far to reduce the Boeing phenomenon that causes the above problems. For example, a uniaxially stretched film is transversely stretched with a tenter, cooled to below the glass transition temperature, and then the gripping of both ends of the film is once released and gripped again, and heat-fixed while raising the temperature in a temperature range of 120 to 240 ° C. A method (for example, see Patent Document 1), a method of increasing the rigidity by reducing the film temperature to a temperature equal to or lower than the glass transition temperature immediately after transverse stretching, and preventing the film on the heat treatment chamber side from being drawn into the stretching chamber (for example, , See Patent Documents 2 and 3), holding the both ends of the film after the transverse stretching with the tenter gripping means, gripping only the narrow part near the center of the film with the nip roll, and forcibly moving the center part Method (for example, refer to Patent Document 4), and the method of heating the film so that the temperature at the end is higher than the center of the film after biaxial stretching. (For example, see Patent Documents 5 and 6), cooling at a temperature not higher than the glass transition temperature (Tg) between stretching in the width direction and heat setting, and then re-stretching in the width direction at the maximum temperature of the heat setting temperature A method (see, for example, Patent Documents 7, 8, and 9), a method in which a cooling region of any one of a triangle, a trapezoid, and an arc shape is provided in a heat fixing region (see, for example, Patent Documents 10 and 11). A method of performing a direction relaxation process (see, for example, Patent Document 12).

JP-A-57-87331 Japanese Patent Laid-Open No. 3-130127 JP-A-3-216326 Japanese Patent Publication No. 63-24459 Japanese Patent Laid-Open No. 62-183327 JP-A-62-183328 JP 2001-328159 A JP 2002-172694 A JP 2002-361737 A Japanese Patent Laid-Open No. 2004-18588 JP 2004-18784 A JP 2004-358742 A

  However, any of these methods is an approach for suppressing the occurrence of bowing as much as possible in a biaxially stretched film having a molecular orientation main axis in the film width direction by sequentially stretching in the machine direction and the transverse direction. When the film is stretched sequentially in the machine direction-transverse direction, the straight line drawn in the width direction of the film before the tenter is put into an arcuate curve by bowing through stretching and heat setting. The geometric distortion (geometric bowing amount) of this curve is expressed by the maximum distance between the chord and arc of the curve. However, as shown in the examples of the present specification (Comparative Examples 2 and 3), the geometric bowing amount and the physical bowing amount represented by the inclination angle of the optical main axis are not necessarily proportional. However, it is necessary to avoid predicting the accuracy of the optical axis from the effect of improving the geometric bowing amount.

  Specifically, Patent Document 1 discloses a film in which a geometric bowing amount (maximum distance between a string and an arc) is halved compared to a conventionally known manufacturing method. However, the fact that Boeing is occurring remains unchanged. Further, there is no suggestion or disclosure of the improvement effect of the tilt angle of the optical axis.

  Patent Document 2 discloses a film in which the geometric bowing distortion is reduced to 2.58%, and Patent Document 3 discloses a film in which the geometric bowing distortion is reduced to 2.66%. ing. However, the bowing phenomenon still occurs in these proposals, and the tilt angle of the optical axis is not disclosed at all.

  Patent Document 4 discloses a film in which the geometric bowing amount is reduced to about one-tenth of the conventionally known method. However, no improvement effect is shown for the tilt angle of the optical axis.

  Patent Documents 5 and 6 disclose films having a trapezoidal geometric bow shape. However, there is no suggestion or disclosure of the improvement effect of the tilt angle of the optical axis.

  Patent Document 7 discloses a film having an orientation angle of 1.3 degrees or less with respect to the lateral direction of the film in a film having a width of 950 mm, excluding 200 mm at both ends. However, it is a conventionally known fact that the orientation angles are aligned in the lateral direction in the vicinity of the central portion in the film width direction, and no special effect is recognized in this proposal.

  Patent Document 7 discloses a film having an orientation angle of 7 degrees at a position 2 m from the center in the film width direction. In this proposal, since the full width of the film is not disclosed, it is unclear how uniform the orientation angle is obtained over the full width.

  Patent Document 8 discloses a film having an orientation angle of 4 degrees at a relative position 0.6 in the film width direction. However, as described above, it is a conventionally known fact that the orientation angles are aligned in the lateral direction at the central portion of the film.

  Patent Document 9 discloses a film having a maximum orientation angle of 4.6 degrees in an 80% region in the film width direction. However, the proposed film has five extreme values in the orientation angle distribution in the film width direction. Therefore, the problem that the orientation angle changes rapidly in the width direction of the film is inherent, and it is not an essential solution of the problem.

  Patent Documents 10 and 11 disclose films whose maximum orientation angles up to 80% in the film width direction are 5.1 degrees and 4 degrees, respectively. However, these methods have not yet fundamentally solved the problem of optical distortion.

  In Patent Documents 7, 9, 10, 11, and 12, in order to suppress the geometric bowing amount of the biaxially oriented polyester film, the stretching ratio in the longitudinal direction is set to be smaller than the stretching ratio in the width direction. Has been. This is intended to reduce the distortion due to bowing that occurs in the film by reducing the draw ratio in the longitudinal direction. Although the geometric bowing amount is suppressed by this, the problem of the optical axis accuracy has not been essentially solved as described above.

  Furthermore, the Example of patent document 7 is disclosing the biaxially stretched film which has a molecular orientation main axis | shaft in the longitudinal direction of a film by extending | stretching sequentially in a horizontal direction-a vertical direction. However, in Patent Document 7, for the purpose of reducing bowing, the draw ratio in the longitudinal direction is set to be equal to or less than the draw ratio in the width direction as described above. In this way, if the orientation main axis is simply in the longitudinal direction, the optical axis direction is easily affected by bowing, and further, the optical axis of the film is strongly influenced by the wave of molecular orientation in the longitudinal direction (variation). As shown in the examples of the present specification (Comparative Example 1), the optical axis direction in the film surface varies and the direction is not uniform.

  In other words, all of these methods are approaches to suppress the geometric bowing amount of the film as much as possible, and there is a problem of optical axis accuracy in the release film for protecting the polarizing plate or protecting the retardation plate. Has not been solved essentially.

An object of the present invention is to protect a polarizing plate in which the mechanical axis direction (longitudinal direction / width direction) of the film and the direction of the optical axis coincide with each other with high accuracy, and the direction of the optical axis is uniform in the film plane. Or a release film for protecting a retardation plate, and a base film thereof.
Another object of the present invention is to provide a method for stably producing a release base film for protecting a polarizing plate or for protecting a retardation plate having the above-mentioned properties at low cost.
And, by these, defect inspection of large-size and high-definition polarizing plate for liquid crystal display and retardation plate is performed efficiently and accurately, contributing to the improvement of image quality of large-screen liquid crystal display and its spread. It is the purpose.

  As a result of intensive studies, the present inventor has found that the above problems can be solved by highly orienting the molecular orientation of the base film in the longitudinal direction. That is, a release base film for protecting a polarizing plate or protecting a retardation plate of the present invention, a releasing film for protecting a polarizing plate or protecting a retardation plate using the same, and a method for producing the same, have the following constitutions Consists of.

1st invention is a biaxially-oriented polyester film used as a base material of the release film used for the test | inspection by the crossed Nicol method used by bonding together to a polarizing plate or a phase difference plate, (1) (2) The difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction is 0.03 or more and 0.10 or less. A biaxially oriented polyester film.
In the second invention, the maximum inclination angle of the optical principal axis with respect to the mechanical axis direction of the biaxially oriented polyester film is 5 degrees or less, and the fluctuation of the inclination angle of the optical principal axis measured at 30 cm intervals in the film width direction is 5 degrees. The biaxially oriented polyester film is characterized by the following.
3rd invention is a release film used for the test | inspection by the cross Nicol method used by bonding together to a polarizing plate or a phase difference plate, Comprising: The base material of this release film is the said biaxially-oriented polyester film It is a release film for polarizing plate protection or retardation plate protection characterized by comprising.
4th invention is the said biaxially-oriented polyester film manufacturing method, Comprising: After the said biaxially-oriented polyester film extends | stretches an unstretched film to the width direction, it extends | stretches to a longitudinal direction and is then manufactured by heat-processing. A method for producing a biaxially oriented polyester film.
5th invention is the said biaxially oriented polyester film manufacturing method, Comprising: After the said biaxially oriented polyester film carries out simultaneous biaxial stretching of the unstretched film to the width direction and a longitudinal direction, it extends | stretches further to a longitudinal direction. Then, it is a method for producing a biaxially oriented polyester film, which is produced by performing a heat treatment.

The release film for protecting the polarizing plate or protecting the retardation plate of the present invention is such that the biaxially oriented polyester film as the substrate is highly molecularly oriented in the longitudinal direction, and the refractive index in the longitudinal direction and the refractive index in the width direction. Since the difference from the rate is controlled within a specific range, the direction of the optical axis of the base film is not affected by geometric bowing, and the fluctuation range of the optical axis direction with respect to the mechanical axis of the film is small. For this reason, the optical axis and the mechanical axis coincide with each other with high accuracy.
Moreover, according to the manufacturing method of this invention, said characteristic can be acquired stably irrespective of the taking position of the width direction of the biaxially-oriented polyester film used as a base material. Therefore, a release film for protecting a polarizing plate or protecting a retardation plate having excellent characteristics can be produced at low cost.
Furthermore, the biaxially oriented polyester film as the substrate of the present invention is excellent in mechanical properties, has few thickness spots, and enables high-level defect inspection corresponding to high definition display.

  The release film for protecting a polarizing plate or protecting the retardation plate of the present invention needs to use a biaxially oriented polyester film as the substrate.

  The polyester is a crystalline polyester that can be obtained by polycondensation of an aromatic dicarboxylic acid or its ester and a diol. The aromatic dicarboxylic acid typically includes terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, and the diol includes ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, and the like. It is done.

  The above polyester is obtained by direct polycondensation of aromatic dicarboxylic acid and glycol, or a method of polycondensation after transesterification of aromatic dicarboxylic acid dialkyl ester and glycol, or diglycol ester of aromatic dicarboxylic acid Can also be obtained by a polycondensation method.

  Specific examples of such polyester include polyethylene terephthalate, polyethylene-2,6-naphthalate, polytetramethylene terephthalate, polytetramethylene-2,6-naphthalate, and the like. The polyester may be a copolyester obtained by copolymerizing various components in addition to the homopolyester. Further, it may be a polymer blend of polyester and another copolymer. Examples of other copolymers that can be blended include polyolefins and other polyesters. A blend of a homopolymer and a polyalkylene copolymer polymer, in particular a polyetherester copolymer or a blend of different polyalkylene glycol copolymer polymers is preferred.

  Among these, in particular, polyethylene terephthalate (PET) is most preferably used from the comprehensive performance such as transparency, mechanical properties, surface smoothness, solvent resistance, scratch resistance, moisture permeability, cost and the like with few impurities. In addition, in the above-mentioned polyester, various additives such as an antioxidant, a heat stabilizer, a weather stabilizer, an ultraviolet absorber, an organic lubricant, a pigment, a dye, and the like within a range not impairing the effects of the present invention. Organic or inorganic fine particles, fillers, antistatic agents, nucleating agents and the like may be blended and used.

  Moreover, in order to provide a slipperiness to a polyester film, microparticles | fine-particles can also be contained. The fine particles not only impart lubricity, but are also important in the sense of adjusting the contrast under the crossed dicol state by utilizing minute alignment irregularities around the fine particles that are generated after being included in the polymer and stretched. Play a role.

  Typical examples of the inorganic particles to be added include silica, colloidal silica, alumina, aluminum sol, kaolin, talc, mica, calcium carbonate, calcium phosphate, and the like. Moreover, acrylic particles, styrene particles, olefin particles, imide particles or the like can be used as the organic particles.

  The additive particles preferably have an average particle diameter of 0.01 μm or more and 10 μm or less, more preferably 0.05 μm or more and 8 μm or less, and most preferably 0.1 μm or more and 3 μm or less. It is good to use.

  If the average particle size of the particles is smaller than 0.01 μm, it is necessary to increase the amount added to maintain slipperiness, and it is difficult to control the haze value, contrast value, and film surface roughness within the required ranges. It is. Further, when the average particle size of the particles is larger than 10 μm, the drop of the added particles during the film forming process is remarkable, which is not preferable because the process is contaminated.

  In addition, the measurement of the average particle diameter of said particle | grain is performed with the following method. Take a picture of the particles with a scanning electron microscope (SEM), at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) The average value is taken as the average particle diameter.

  Further, the content of the particles is preferably 0.01% by weight or more and 5% by weight or less, more preferably 0.05% by weight or more and 1% by weight or less in the polyester film. When the content of the particles is less than 0.01% by weight, the slipperiness is inferior, and scratches are generated due to friction with a roll or the like in the process, which is not preferable. Moreover, when the content of the particles is more than 5% by weight, it is difficult to control the haze value, contrast value, and film surface roughness within the necessary ranges.

  The intrinsic viscosity of the polyester is preferably in the range of 0.45 to 0.70. If the intrinsic viscosity is lower than 0.45, the film is easily torn, and if it is higher than 0.70, the increase in filtration pressure is increased and high-precision filtration becomes difficult.

  As a result of intensive studies on the relationship between optical axis accuracy and bowing, the present inventors surprisingly found that the biaxially stretched film highly molecularly oriented in the longitudinal direction of the film had its position in the width direction, It has been found that the optical axis is highly coincident with the mechanical axis (longitudinal direction, width direction) of the film regardless of the degree of geometric bowing. That is, the biaxially oriented polyester film used as the base material for the release film for protecting the polarizing plate or protecting the retardation plate of the present invention has (1) a molecular orientation main axis in the longitudinal direction of the film, (2) It is important that the difference between the refractive index (nx) in the film longitudinal direction and the refractive index (ny) in the film width direction is 0.03 or more and 0.10 or less.

The reason why the biaxially oriented polyester film in the present invention exhibits the above characteristics is considered as follows.
As described above, since the biaxially oriented polyester film produced by sequentially stretching in the longitudinal direction-lateral direction is stretched in the lateral direction (film width direction) in the subsequent stage, the molecular orientation as a whole is oriented in the width direction. And has a molecular orientation main axis in the film width direction. Therefore, in such a biaxially oriented polyester, the direction of the optical principal axis is distributed in the width direction. Therefore, the bowing caused by transverse stretching and being promoted by heat fixation causes distortion of physical properties in the width direction, so that the optical principal axis distributed in the width direction is easily affected by the bowing, and becomes the end in the film width direction. The distortion of the optical main axis increases. On the other hand, since the biaxially oriented polyester film of the present invention is highly molecularly oriented in the longitudinal direction of the film, it is less susceptible to bowing that causes distortion in the width direction. However, although it is difficult to be affected by Boeing, simply aligning the alignment main axis in the longitudinal direction is strongly affected by the wave (variation) of the molecular orientation in the longitudinal direction. It will not be uniform. Therefore, by further controlling the refractive index difference between the refractive index (nx) in the film longitudinal direction and the refractive index (ny) in the film width direction within the above range, the wave of molecular orientation in the longitudinal direction is suppressed, and optical The direction of the axis was made uniform in the film plane. Therefore, the optical axis of the biaxially oriented polyester film of the present invention is highly consistent with the mechanical axis direction (longitudinal direction and width direction) of the film regardless of the position in the width direction and the degree of geometric bowing. To do. In addition, the manufacturing method of such a film is mentioned later.

  When the difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction is less than 0.03, the inclination of the optical axis of the biaxially oriented polyester film becomes large due to the influence of geometric bowing. It is not preferable. Further, when the refractive index difference is less than 0.03, the wave of molecular orientation in the longitudinal direction (variation) increases, and the variation of the tilt angle of the optical principal axis with respect to the mechanical axis of the film increases. The difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction is preferably 0.04 or more, and more preferably 0.05 or more.

  On the other hand, the difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction needs to be 0.10 or less, more preferably 0.09 or less, and further 0.08 or less. Is preferred. If the difference between the refractive index in the longitudinal direction of the film and the refractive index in the width direction of the film is greater than 0.10, the retardation value becomes too large, whitish under polarized light, and foreign matter and other inspections are difficult. Further, the film tends to tear in the orientation direction of the fill, and the mechanical strength decreases.

  The release film of the present invention obtained by using a biaxially oriented polyester film having the above characteristics as a substrate has the following preferable characteristics. That is, the maximum inclination angle of the optical main axis with respect to the machine axis direction (longitudinal direction, width direction) is within 5 degrees. Moreover, the fluctuation | variation of the inclination-angle of the optical principal axis measured at 30 cm intervals in the film width direction is less than 5 degree | times.

  The maximum inclination angle is more preferably within 4 degrees, further preferably within 3 degrees, and most preferably within 2 degrees. Here, the machine axis direction means two directions orthogonal to the longitudinal direction (machine direction) of the film and the width direction. In the case of a biaxially oriented polyester, the optical axis has two optical axes, a direction perpendicular to the direction of molecular orientation and a direction perpendicular to the direction of molecular orientation. In the present invention, the optical axis is in the longitudinal direction with the molecular orientation main axis, and has another optical axis in the width direction. When the maximum inclination angle of these optical axes with respect to the mechanical axis exceeds 5 degrees, transmitted light and interference color are exhibited during defect inspection under crossed Nicols, which hinders inspection. Further, the variation of the tilt angle of the optical main axis measured at an arbitrary 30 cm interval in the film width direction is more preferably within 4 degrees, further preferably within 3 degrees, and most preferably within 2 degrees. Further, if the fluctuation of the tilt angle of the optical main axis exceeds 5 degrees per 30 cm of the film width, an interference color is partially generated or the difference between light and dark becomes large, which also hinders inspection.

  Next, the biaxially oriented polyester film used as the base material of the release film for protecting the polarizing plate or protecting the retardation plate of the present invention preferably has a haze in the range of 2.0 to 12.0%. More preferably, it is in the range of 4.0 to 10.0%, further preferably in the range of 5.0 to 9.0%.

  When the haze is 2.0% or less, when defect inspection is performed under crossed Nicols, the contrast between the defect portion and the normal portion becomes too high, and defects such as scratches and foreign matters tend to be detected excessively. Therefore, it is not preferable. On the other hand, when the haze is greater than 12.0%, the transparency is poor and the detection accuracy of the defect due to the transmitted light is deteriorated.

  The biaxially oriented polyester film preferably has a thermal shrinkage rate at 150 ° C. for 30 minutes of 3.0% or less in both the longitudinal direction and the width direction. When the heat shrinkage rate exceeds 3.0%, the film is greatly shrunk by heating at the time of mold release processing or adhesive processing, resulting in deterioration of flatness, wrinkles, curls, etc., which is not preferable.

  The thickness of the release film of the present invention is not particularly limited and is arbitrary, but is preferably 9 to 300 μm, and most preferably 12 to 50 μm. If the thickness exceeds 300 μm, there is a problem in cost, retardation is increased, and visibility in crossed Nicol tends to be lowered. On the other hand, when the thickness is less than 9 μm, the mechanical properties are deteriorated and the function as a protective film cannot be performed.

  The biaxially oriented polyester film having the above characteristics can be obtained by the following means, but any biaxially oriented polyester film having the characteristics of the present invention is included in the scope of the present invention even if it is obtained by a method other than the following method. It is.

(1) Longitudinal stretching in the latter stage of stretching In the present invention, in order to orient the orientation main axis of the biaxially oriented polyester film in the longitudinal direction, it is preferable to perform longitudinal stretching in the latter stage of the stretching step. The molecular orientation of the biaxially stretched film tends to be strongly influenced by the stretching direction to be performed later, and the orientation main axis of the film can be easily oriented in the longitudinal direction by the above embodiment.

(2) Stretch ratio in the longitudinal direction As described above, in the conventional technical idea of suppressing geometric bowing, it has been desirable to reduce the stretch ratio in the longitudinal direction. However, in the present invention, it is desirable that the biaxially oriented polyester film has a high longitudinal draw ratio in order to suppress fluctuations in the molecular orientation in the longitudinal direction. By increasing the draw ratio in the longitudinal direction, the orientation main axis of the film is highly oriented in the longitudinal direction, and the optical axis direction becomes uniform in the film plane. In order to produce a biaxially oriented polyester film having the above characteristics, the draw ratio in the longitudinal direction is preferably 3.0 to 6.0 times, particularly 4.0. -5.0 times is more preferable. Moreover, the draw ratio in the width direction is preferably 2.0 to 5.0 times, and more preferably 2.5 to 4.0 times. As for the draw ratio in the longitudinal direction and the width direction, it is desirable that the draw ratio in the longitudinal direction is 1.0 or more, preferably 1.5 or more larger than the draw ratio in the width direction.

(3) Heat setting Boeing is caused by transverse stretching, and strain is increased and fixed by subsequent heat setting. Therefore, from the viewpoint of suppressing bowing, it is ideally preferable not to perform heat setting or to lower the heat setting temperature. However, in the present invention, since there is no influence of bowing, heat setting at a continuous high temperature is possible. This makes it possible to obtain a biaxially oriented polyester film having high thermal dimensional stability.

Hereinafter, as an example, a specific manufacturing method using PET will be described in detail.
In order to obtain a base film having high transparency, PET pellets containing substantially no particles for imparting slipperiness are sufficiently vacuum-dried and then supplied to an extruder at about 280 ° C. It is desirable to form an unstretched PET sheet by melting and extruding it into a sheet and cooling and solidifying it. Furthermore, in order to remove foreign substances contained in the resin, high-precision filtration can be performed at any place where the molten resin is maintained at about 280 ° C. The filter medium used for high-precision filtration of molten resin is not particularly limited, but the filter medium of the sintered stainless steel is excellent in removal performance of aggregates and high-melting-point organic substances mainly composed of Si, Ti, Sb, Ge, Cu. It is.

  Furthermore, the filter particle size (initial filtration efficiency 95%) of the filter medium is preferably 15 μm or less. When the thickness is 15 μm or more, the foreign matters of 20 μm or more cannot be sufficiently removed. (Initial filtration efficiency of 95%) is suitable for obtaining a highly transparent film although productivity may be reduced by performing high-precision filtration of the molten resin using a filter medium of 15 μm or less. Here, the initial filtration efficiency refers to a numerical value measured by ANSI / B93.36-1973.

  In the extrusion method, polyester can be melted and extruded from an extrusion die, and cooled and solidified with a cooling roll to obtain an unstretched sheet. If necessary, lamination may be performed using 2 or 3 extruders, 2 or 3 layers of multi-nihold, or a feed block. In order to improve the sheet flatness, it is preferable to use an electrostatic application adhesion method or a liquid application adhesion method in order to improve the adhesion between the sheet and the rotary cooling drum.

  Next, the film stretching process will be described. The biaxially oriented polyester film used in the present invention is characterized by being highly oriented in the longitudinal direction. Therefore, as a stretching method, an unstretched film is stretched in the width direction using a tenter, the film is heated by a roll group, and further stretched in the longitudinal direction using an infrared heater, etc., and then guided to the tenter again and heat-set. It is preferable to employ any one of a method for performing stretching, that is, a sequential biaxial stretching method in which stretching is performed in the order of TD-MD, or a simultaneous biaxial stretching method in which stretching in the longitudinal direction and the width direction is performed in the same tenter.

First, sequential biaxial stretching in which stretching is performed in the order of the above-described TD-MD will be described.
First, the unstretched sheet is stretched in the transverse direction by gradually widening the width of the tenter rail with a tenter-type stretching machine to obtain a uniaxially oriented polyester film. The temperature of the preheating zone is preferably not less than the glass transition temperature of the resin and not more than 130 ° C. The preheating zone is preferably composed of one or more zones defined by a predetermined preheating temperature. After preheating, the film is subsequently stretched, and the stretching ratio is preferably 2.0 to 5.0 times, particularly preferably 2.5 to 4.0 times. The temperature of the stretching zone is in the range of the glass transition point Tg to (Tg + 50) ° C. of the polyester. When the stretching temperature is lower than Tg, it cannot be uniformly stretched and causes unevenness in thickness. Moreover, when the stretching temperature is higher than (Tg + 50) ° C., the uniformity of the thickness in the width direction is deteriorated, which is not preferable. After stretching, the film is gradually cooled by using one or two or more zones, and after the temperature is lowered to (Tg−20) ° C. or lower, the clip is removed and guided to the next step.

  Next, it is stretched in the longitudinal direction by a roll type stretching machine comprising a group of rolls heated to a temperature equal to or higher than the glass transition point Tg of the polyester. The draw ratio is 3.0 to 6.0 times in the longitudinal direction, particularly 4.0. -5.0 times is more preferable. When the stretching is performed, auxiliary heating is performed using an infrared heater or the like, and the film stretching temperature is set in the range of (Tg + 10) to (Tg + 50) ° C. When the temperature is lower than (Tg + 10) ° C., breakage tends to occur. When the temperature is higher than (Tg + 50), the longitudinal orientation is lowered, which is not preferable for achieving the object of the present invention. After stretching, the film is cooled to Tg or less by a cooling roll and then guided to the next step.

  Subsequently, the film is again guided to the tenter and heat-set, and the temperature of the heat-set zone is preferably in the range of (Tg + 130) to (Tm-10) ° C, more preferably (Tg + 140) to (Tm-20) ° C. Range. (Tm represents the melting point of the polyester.) When the temperature of the heat setting zone is lower than (Tg + 130) ° C., the heat shrinkage rate becomes high, which may cause wrinkling and curling during processing. When the temperature of the heat setting zone is higher than (Tm-100) ° C., crystallization progresses, and it tends to tear in the stretching direction in the trimer process and the slit process, which is not preferable. Moreover, the relaxation process can be performed in the longitudinal direction and the width direction as necessary. The amount of relaxation varies depending on the conditions, but is about 1 to 10%. Moreover, about the process after heat setting, it is a product winder through the process which cuts and processes the film edge currently hold | gripped with the TD clip, the process which performs a corona process, the process which performs a relaxation process between rolls, etc. It is wound up.

Next, simultaneous biaxial stretching will be described.
Both ends of the obtained unnew-stretched polyester film are held by clips and guided to the preheating zone. The temperature of the preheating zone is preferably not less than the glass transition temperature of the resin and not more than 130 ° C. The preheating zone is preferably composed of one or more zones defined by a predetermined preheating temperature.

  After preheating, the film is stretched simultaneously in the longitudinal direction and the width direction, and the stretching ratio is 3.0 to 6.0 times in the longitudinal direction, particularly 4.0. -5.0 times is more preferable. Further, the draw ratio in the width direction is more preferably 2.0 to 5.0 times and 2.5 to 4.0 times. As for the draw ratio in the longitudinal direction and the width direction, it is desirable that the draw ratio in the longitudinal direction is 1.0 or more, preferably 1.5 or more larger than the draw ratio in the width direction.

  The stretching end point is preferably set so that the stretching in the longitudinal direction and the width direction ends simultaneously or the setting where the stretching in the longitudinal direction ends later. In the latter, it is preferable that the stretching in the longitudinal direction performs 15% or more of the entire stretching ratio in the longitudinal direction after the stretching in the width direction is completed.

  The temperature of the stretching zone is in the range of Tg to (Tg + 50) ° C. When the stretching temperature is lower than Tg, it cannot be uniformly stretched and causes unevenness in thickness. Moreover, when the stretching temperature is higher than (Tg + 50) ° C., the uniformity of the thickness in the width direction is deteriorated, which is not preferable.

  After the stretching of the film, the film is continuously heat-set, but before that, it is preferable to provide an intermediate zone between the stretching zone and the heat-setting zone of the film. By providing the intermediate zone, heat exchange between the stretching zone and the heat setting zone can be suppressed, and the temperature accuracy of each zone can be improved.

  The intermediate zone may be unheated, or may be a hot air circulation system in which the temperature is controlled in the range of Tg-50 ° C to Tg + 60 ° C, more preferably in the range of Tg-40 ° C to Tg + 30 ° C. . When the intermediate zone of the hot air circulation system is employed, if the temperature of the circulating air is Tg-50 ° C. or less, a large amount of heat is required for heating the film in the heat setting zone, which is not preferable. Conversely, Tg + 60 ° C. or higher is not preferable because the optical axis accuracy of the biaxially stretched film may deteriorate. The time for the film to pass through the intermediate zone is preferably 2 to 20 seconds, more preferably 4 to 15 seconds. If it is 2 seconds or less, the film temperature is not sufficiently lowered, and if it is 20 seconds or more, the zone length necessary for cooling becomes long, and the equipment becomes large. Further, instead of providing the intermediate zone, stretching and heat setting may be performed by separate tenters, and the film temperature may be adjusted within the above range.

  The temperature of the heat setting zone is preferably in the range of (Tg + 130) to (Tm−10) ° C., more preferably in the range of (Tg + 140) to (Tm−20) ° C. When the temperature of the heat setting zone is lower than (Tg + 130) ° C., the heat shrinkage rate becomes high, which causes wrinkles and curls during processing. When the temperature of the heat setting zone is higher than (Tm−10) ° C., crystallization proceeds, and it tends to tear in the stretching direction in the trimer process and the slit process, resulting in a decrease in yield.

  Moreover, the relaxation process can be performed in the longitudinal direction and the width direction as necessary. The amount of relaxation varies depending on the conditions, but is preferably about 1 to 10%.

  Moreover, about the process after heat setting, it cuts and processes the film edge currently hold | gripped with the TD clip, the process of performing a corona process, the process of performing a relaxation process between rolls, etc. with a product winder It is wound up.

  The biaxially oriented polyester film produced by the above method has adhesiveness, water resistance, and chemical resistance with layers formed on the film such as an adhesive layer, a release layer, an antistatic layer, and a protective layer. In order to improve the above, surface treatment, that is, corona discharge treatment (in air, nitrogen, carbon dioxide, etc.) or easy adhesion treatment may be performed by a known method. Various methods known in the art can be used for the easy adhesion treatment, and a method of applying various easy adhesives before stretching or after uniaxial stretching is suitably employed.

Next, release processing will be described.
The release film of the present invention is a film formed by forming a release layer on one side of the above-described polyester film of the present invention. The release layer preferably contains one or more selected from silicone resins and fluororesins as a main component.

  As the silicone resin, a silicone resin generally used as a release agent can be used, and a silicone generally used in the field described in “Silicon material handbook” (Toray Dow Corning, 19933.8) and the like. It can be used by selecting from resins. Generally, a thermosetting or ionizing radiation curable silicone resin (including resin and resin composition) is used. As the thermosetting silicone resin, for example, condensation reaction type and addition reaction type silicone resins can be used, and as the ionizing radiation curable silicone resin, ultraviolet or electron beam curable silicone resins can be used. A release layer is formed by applying these on a film as a substrate and drying or curing.

  As the condensation reaction type silicone resin, for example, polydimethylsiloxane having an OH group at the terminal and polydimethylsiloxane (hydrogensilane) having a terminal hydrogen are used using an organic tin catalyst (for example, an organic tin acylate catalyst). A composition that can form a three-dimensional crosslinked structure by a condensation reaction is exemplified.

  Examples of the addition reaction type silicone resin include a composition capable of forming a three-dimensional cross-linked structure by reacting polydimethylsiloxane having a vinyl group introduced at its terminal with hydrogensilane using a platinum catalyst.

  Examples of the ultraviolet curable type or electron beam curable type silicone resin include, as the most basic types, resins that are crosslinked and cured by radical reaction in the same manner as ordinary silicone rubber crosslinking, resins that are photocured by introducing an acrylic group, and ultraviolet rays. And a resin composition in which an onium salt is decomposed to generate a strong acid, whereby the epoxy ring is cleaved and crosslinked, and a resin composition that is crosslinked by addition reaction of thiol to vinyl siloxane. Since an electron beam has a stronger energy than ultraviolet rays, a radical crosslinking reaction occurs without using an initiator as in the case of ultraviolet curing.

  The curable silicone resin preferably has a degree of polymerization after curing of about 500 to 200,000, particularly about 1,000 to 100,000, and specific examples thereof include the following resins: Shin-Etsu Chemical ( KS-718, KS-774, KS-775, KS-778, KS-779H, KS-830, KS-835, KS-837, KS-838, KS-839, KS-841, KS- 843, KS-847, KS-847H, X-62-2418, X-62-2422, X-62-2125, X-62-2492, X-62-2494, X-62-5048, X-62- 470, X-62-2366, X-62-630, X-92-140, X-92-128, KS-723A ・ B, KS-705F, KS-708A, KS-883, KS-7 9, KS-719; TPR-6701, TPR-6702, TPR-6703, TPR-3704, TPR-6705, TPR-6721, TPR-6722, TPR-6700, XSR-7029, YSR manufactured by Toshiba Silicon Co., Ltd. -3022, YR-3286; DK-Q3-202, DK-Q3-203, DK-Q3-204, DK-Q3-205, DK-Q3-210, DK-Q3-240, manufactured by Dow Corning DK-Q3-3003, DK-Q3-3057, SFXF-2560; SD-7226, SD-7229, SD-7320, BY-24-900, BY-24- manufactured by Toray Dow Corning Silicone Co., Ltd. 171, BY-24-312, BY-24-374, SRX-375, SYL-OFF23, SRX-244 Such as ICI Japan made of (stock) SILCOLEASE425; SEX-290. Further, silicone resins described in JP-A-47-34447 and JP-B-52-40918 can also be used. These curable silicone resins may be used alone or in combination of two or more.

  As the fluororesin, a fluororesin generally used as a release agent can be used. Examples of such a fluororesin include, for example, a polymer (including an oligomer) composed of a fluorine-containing vinyl polymerizable monomer or a copolymer thereof, a fluorine-containing vinyl polymerizable monomer and a vinyl polymerizable monomer not containing a fluorine atom. Examples thereof include a copolymer with a monomer or a mixture thereof, and a resin having 5 to 80 mol% of fluorine atoms.

  Examples of the polymer comprising the fluorine-containing vinyl polymerizable monomer include the following polymers: poly [2- (perfluorononenyloxy) ethyl methacrylate], poly [2- (perfluorononenyloxy). Ethyl acrylate], poly [2- (perfluorononenyloxybenzoyloxy) ethyl methacrylate], poly [2- (perfluorononenyloxybenzoyloxy) ethyl acrylate], poly [2,2,2-trifluoroethyl methacrylate] ], Poly [2,2,2-trifluoroethyl acrylate], poly [2,2,3,3,3-pentafluoropropyl methacrylate], poly [2,2,3,3,8-pentafluoropropyl acrylate] ], Poly [1-methyl-2,2,3,3,4,4-hexafluorobutylmeta Relate], poly [1-methyl-2,2,3,3,4,4-hexafluorobutyl acrylate], poly [perfluoroheptylethyl methacrylate], poly [perfluoroheptylethyl acrylate], poly [perfluoroheptyl] Vinyl ether], poly [α, β, β-trifluorostyrene], polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene and the like.

  Examples of the vinyl polymerizable monomer that does not contain a fluorine atom and can be copolymerized with the fluorine-containing vinyl polymerizable monomer include hydrocarbon-based vinyl polymerizable monomers and hydrocarbon-based non-conjugated divinyl polymerizable monomers. And functional group-containing vinyl polymerizable monomers. Among these, hydrocarbon-based vinyl polymerizable monomers include, but are not limited to, the following compounds: methyl acrylate, propyl acrylate, butyl acrylate, isoamyl acrylate, 2-ethylhexyl acrylate, acrylic Octyl acid, octadecyl acrylate, lauryl acrylate, N, N-diethylaminoethyl acrylate, methyl methacrylate, propyl methacrylate, butyl methacrylate, isoamyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, octadecyl methacrylate, Lauryl methacrylate, N, N-diethylaminoethyl methacrylate, vinyl acetate, vinyl propionate, vinyl caprate, vinyl laurate, vinyl stearate, styrene, α-methylstyrene, p-methyl Tylene, vinyl chloride, vinyl bromide, vinylidene chloride, allyl heptanoate, allyl acetate, allyl caprate, allyl caproate, vinyl methyl ketone, vinyl ethyl ketone, 1,3-butadiene, 2-chloro-1,3-butadiene 2,3-dichloro-1,3-butadiene, isoprene and the like. Hydrocarbon-based non-conjugated divinyl polymerizable monomers include, but are not limited to, the following compounds: ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, diethyleglycol di Acrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, divinylbenzene, vinyl acrylate, dibromoneopentyl glycol dimethacrylate, etc. Functional group-containing vinyl polymerizable monomers include, but are not limited to, the following compounds: acrylic acid, methacrylic acid, acrylamide, methacrylamide, N-methylol acrylamide, N-butoxymethyl acrylamide, diacetone acrylamide , Methylol diacetone acrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, 3-chloro-2-hydroxypropyl methacrylate, and the like.

  In addition to the silicone resin and fluororesin, the release layer may contain additives that are usually used in the field as long as the effects of the present invention are not impaired. Examples thereof include an antifoaming agent, a coating property improving agent, a thickener, an antistatic agent, an antioxidant, an ultraviolet absorber, a magnetizing agent, and a dye.

  The thickness of the release layer is not particularly limited, but is preferably in the range of 0.05 to 5 μm. When the thickness of the coating film is thinner than this range, the mold release performance is deteriorated and satisfactory performance may not be obtained. On the contrary, when the thickness of the coating film is thicker than this range, it takes time for the curing and the productivity may decrease.

  Furthermore, the release film of the present invention is preferably provided with an antistatic layer for the purpose of suppressing the generation of static electricity. This antistatic layer can be formed by applying an antistatic resin composition to a base film. Examples of the antistatic agent contained in the antistatic resin composition include the following substances: Various cationic charges having a cationic group such as a quaternary ammonium salt, a pyridinium salt, and an aliphatic amine salt. Inhibitors: Anionic antistatic agents having anionic groups such as sulfonate groups, sulfate ester bases, phosphate ester bases, phosphonate bases; amphoteric antistatic agents such as amino acids and aminosulfates, amino alcohols, Various surfactant type antistatic agents such as nonionic antistatic agents such as glycerin and polyethylene glycol. A polymeric antistatic agent obtained by increasing the molecular weight of the antistatic agent as described above is also used. Polymerization of monomers and oligomers (for example, N, N-dialkylaminoalkyl (meth) acrylate monomers) having tertiary amino groups and quaternary ammonium groups that can be polymerized by ionizing radiation and their quaternary compounds. Antistatic agents can also be used.

  In addition to the antistatic agent, the antistatic resin composition contains a binder for improving the strength of the coating film of the antistatic layer, adhesion to the base film, water resistance, solvent resistance, blocking property and the like. It is preferable. The binder is preferably a polymer compound such as a thermoplastic resin and / or a thermosetting resin. Examples of the thermoplastic resin include thermoplastic polyester resins, acrylic resins, and polyvinyl resins, and examples of the thermosetting resin include thermosetting acrylic resins, urethane resins, melamine resins, and epoxy resins. Furthermore, the antistatic resin composition particularly preferably contains at least one crosslinking agent selected from the following compounds: methylolated or alkylolized melamine compounds, urea compounds, glyoxal compounds Acrylamide compounds, epoxy compounds, polyisocyanates, etc.

  The antistatic layer is formed on the surface of the base film, and the pressure-sensitive adhesive layer or the release layer is formed on the opposite surface. Alternatively, an adhesive layer or a release layer is formed on the antistatic layer. Preferably, it is provided on the opposite surface of the antistatic layer and the pressure-sensitive adhesive layer or release layer. This is because, for example, when a release layer is laminated on the antistatic layer, the coating solution of the template may be repelled by the antistatic agent. When an adhesive layer or a release layer is provided on the surface opposite to the antistatic layer, an antistatic layer is selected by selecting an antistatic agent that exhibits the above surface specific resistance value on the opposite surface. Is preferred.

The surface resistivity value of the antistatic layer can be arbitrarily set according to the purpose of use. For example, the surface specific resistance value of the antistatic layer is preferably 1 × 10 ¹¹ Ω / □ or less. If the surface specific resistance value is 1 × 10 ¹¹ Ω / □, dust does not usually adhere.

  The method for forming the pressure-sensitive adhesive layer, the release layer, and the antistatic layer on the surface of the biaxially oriented polyester film, which is a base film, is not particularly limited, but a coating method is preferably used. Examples of the coating method include air doctor coating method, knife coating method, rod coating method, forward rotation roll coating method, reverse roll coating method, gravure coating method, kiss coating method, bead coating method, slit orifice coating method, cast coating method. Etc. are used. The same applies when different layers are stacked.

  In the case of forming a release layer on the surface of the biaxially oriented polyester film, for example, after applying a silicone resin or a fluororesin by the above method, the release layer is formed by drying and curing it. The The resin is cured by heating, ionizing radiation irradiation, or the like. Drying and curing can each be performed individually or simultaneously. When performing simultaneously, it is preferable to carry out at the temperature of 80 degreeC or more. The drying and curing conditions are preferably 80 ° C. or higher and 10 seconds or longer. When the drying temperature is less than 80 ° C. or the curing time is less than 10 seconds, the coating film is not completely cured, and the coating film tends to fall off.

  Next, the description will be further described with reference to examples. However, the present invention is not limited to the following examples without departing from the gist thereof. In addition, the evaluation method of the physical property in a following example and a comparative example is as follows.

(1) Refractive index In accordance with JIS K 7142-1996 5.1 (Method A), the refractive index (nx) in the longitudinal direction of the film and the refractive index (ny) in the width direction were measured with an Abbe refractometer using sodium D line as a light source. , (Nx−ny) to obtain the refractive index difference.

(2) Direction of molecular orientation main axis In the refractive index measurement, when nx> ny, the longitudinal direction was determined, and when nx ≦ ny, the width direction was determined.

(3) Molecular chain principal axis orientation angle (θ), optical principal axis tilt angle (ξ)
About the distance of a film width direction, an edge is set to 0% in the film width | variety of the tenter exit (Examples 1-4 and 2nd tenter exit in the comparative example 1) in preparation of the biaxially oriented polyethylene terephthalate film mentioned later. The edge is 100%. For an area corresponding to 10% to an area corresponding to 90% of the film width (corresponding to the entire width of the release film described below), n 100 mm square film samples were continuously formed at a pitch of 100 mm in the width direction. Cut out. The square film sample was cut at a right angle with respect to either the longitudinal or width axis. For each film sample, using a MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd., the orientation angle (θi) of the molecular chain principal axis relative to the film longitudinal direction, and the machine axis direction (longitudinal direction) defined by the following formula , Or the width direction), the tilt angle (ξi) of the optical principal axis was measured. Note that n is an integer obtained by multiplying the total width of the film by 0.8 and rounding up the value after dividing by 10 mm. I represents a sample number, i = 1 to n.
When | θ | ≦ 45 degrees ξ = | θ |
When | θ |> 45 degrees ξ = | 90 degrees− | θ ||
Of the inclination angles of the optical principal axis measured from the film sample, the maximum value was defined as the maximum inclination angle (ξmax) of the optical principal axis.

  In the measurement of the orientation angle, the orientation angles (θi, θi + 1, θi + 2, θi + 3) of four consecutive film samples were compared, and the difference (Δθi) between the maximum value and the minimum value was obtained. Among Δθ1 to Δθn-3, the maximum value was defined as the change in the tilt angle of the optical principal axis (Δθmax).

(4) Thermal shrinkage at 150 ° C. [HS150 (MD)]
In accordance with JIS C 2318-1997 5.3.4 (dimensional change), the dimensional change rate (%) in the longitudinal direction and the width direction was measured.

(5) Haze The haze was measured according to JIS K 7105 “Testing method for optical properties of plastic” haze (cloudiness value). NDH-300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measuring instrument.

(6) Visibility under polarized light A polarizing plate is orthogonally crossed and installed in a crossed Nicol state on a surface light source backlight (transmitted light BOX A3-2 manufactured by SFC). The film cut out from the film roll is sandwiched between the polarizing plates so that the slit end of the film and the polarizing axis of the polarizing plate are vertical or horizontal, and the coloring state and the inspection property of the full width are observed.
A: Almost no interference color occurs. Even when viewed obliquely, interference colors are hardly generated. There are no partially colored spots.
○: Some interference color is generated, but foreign matter of about 100 μm can be detected. Colored spots are within an acceptable range.
Δ: Foreign matter of about 100 μm can be detected, but foreign matter in the film is excessively detected, or foreign matter can be confirmed due to a decrease in contrast, but is difficult to inspect.
×: Difficult to detect foreign matter of about 100 μm with a strong interference color. Coloring when viewed from an angle is also large. Or there is a partial colored spot and cannot be inspected.

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200 ° C., 86.4 parts by weight of terephthalic acid and 64.6 parts by weight of ethylene glycol were charged, and 0.017 parts by weight of antimony trioxide as a catalyst while stirring. 0.064 parts by weight of magnesium acetate tetrahydrate and 0.16 parts by weight of triethylamine were charged. Next, the pressure was raised and the pressure esterification reaction was carried out under the conditions of gauge pressure 0.34 MPa and 240 ° C., then the esterification reaction vessel was returned to normal pressure, and 0.014 parts by weight of trimethyl phosphate was added. . Further, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by weight of trimethyl phosphate was added.

  Next, after 15 minutes, the dispersion treatment was performed with a high-pressure disperser, and further 0.1 wt% of sodium tripolyphosphate aqueous solution was contained as sodium atoms with respect to the silica particles, and the coarse particles were cut by 35% by centrifugal treatment. 0.2 parts by weight of an ethylene glycol slurry of silica particles having an average particle size of 2.5 μm, which was filtered through an open 5 μm metal filter, was added as the particle content. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and subjected to a polycondensation reaction under reduced pressure at 280 ° C. to obtain a polyethylene terephthalate resin (A) having an intrinsic viscosity of 0.62 dl / g. (Hereafter, abbreviated as PET (A).)

(Production Example 2-Polyester B)
On the other hand, in the production of PET (A), a polyethylene terephthalate resin (B) having an intrinsic viscosity of 0.62 dl / g and containing no silica particles was obtained. (Hereafter, abbreviated as PET (B).)

(Production Example 3-Release agent C)
A thermosetting silicone resin (manufactured by Toshiba Silicone Co., Ltd., TPR6712) is mixed and dispersed in a solvent (toluene / MEK = 50/50; mass ratio) so that the solid content concentration is 1.0% by mass. As a curing catalyst, 1 part by mass of a platinum catalyst was added to 100 parts by mass of the silicone resin to obtain a release agent (C).

Example 1
PET (A) and PET (B) are mixed, the silica particle content is adjusted to 0.08% by weight, dried by a conventional method, supplied to an extruder and melted at 290 ° C. to form a film forming die Then, it was extruded into a sheet shape, closely contacted onto a water-cooled rotary quenching drum using an electrostatic application adhesion method, and quenched to prepare an unstretched film. At this time, a stainless sintered filter medium having a filtration particle size (initial filtration efficiency of 95%) of 15 μm was used as a filter medium for removing foreign substances from the molten resin.

This unstretched film was guided to a tenter stretching machine (first tenter), preheated at 95 ° C. for about 6 seconds in a preheating zone, and then stretched at a stretching ratio of 3.2 times in the width direction in a stretching zone at 100 ° C. Thereafter, the film was cooled to 50 ° C., and then the clip was released. Then, it led to the roll group heated at 100 degreeC, and it adjusted so that extending | stretching temperature might be 115 degreeC using an infrared heater, and performed 4.5 time extending | stretching to the longitudinal direction. Then, after cooling a film to 40 degreeC with a cooling roll, it guide | induced to the tenter (2nd tenter) again, heat-fixed at 220 degreeC, and after cooling to 50 degreeC, the holding | grip of the clip was open | released. Subsequently, both ends corresponding to 15% of the entire film width of the second tenter outlet width were cut and wound into a roll shape to obtain a biaxially oriented polyethylene terephthalate film having a width of about 1500 mm and a thickness of 38 μm.
The properties of the obtained film are shown in Table 1.

  The release agent (C) was applied to one side of the film obtained by the above method. The application was performed using a gravure coater, and after applying a release agent, it was dried at 140 ° C. for 90 seconds to provide a release layer having a thickness of 0.5 μm. Subsequently, both ends corresponding to 5% of the total film width of the tenter outlet width were cut, and then rolled up to obtain a release film. The visibility of the release film thus obtained under polarized light was good over the entire width and had good characteristics as a release film for protecting a polarizing plate or protecting a retardation plate.

(Example 2)
A biaxially oriented polyethylene terephthalate film having a thickness of 38 μm and a release film were obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal direction was 4.7 times.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.
As in Example 1, the visibility of the obtained release film under polarized light was good over the entire width of the film.

(Comparative Example 1)
In Example 1, a biaxially oriented polyethylene terephthalate film having a thickness of 38 μm and a release film were prepared in the same manner except that the draw ratio in the width direction was 3.7 times and the draw ratio in the longitudinal direction was 3.5 times. Obtained.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.
The visibility of the obtained release film under polarized light emitted an interference color and was x.

(Example 3)
A biaxially oriented polyethylene terephthalate film having a thickness of 38 μm and a release film were obtained in the same manner as in Example 1 except that the content of silica particles was adjusted to 0.015% by weight.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.
The visibility of the obtained release film under polarized light is within the allowable range for interference colors and colored spots, and it was possible to inspect foreign matter of about 100 μm. △ was assigned.

Example 4
A biaxially oriented polyethylene terephthalate film having a thickness of 38 μm and a release film were obtained in the same manner as in Example 1 except that the content of silica particles was adjusted to 0.15% by weight.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.
The visibility of the obtained release film under polarized light is such that interference colors and colored spots are within the allowable range, and inspection of foreign matter of about 100 μm is possible, but the contrast is extremely low. , Foreign matter detection ability decreased. Therefore, the visibility was set as Δ.

(Comparative Example 2)
The unstretched film obtained by the same method as in Example 1 is led to a group of rolls heated to 75 ° C., adjusted using an infrared heater so that the stretching temperature becomes 95 ° C., and 3.3 times in the longitudinal direction. Stretched. Next, the film was led to a tenter, stretched 3.9 times in the width direction at 120 ° C., subsequently heat-set at 220 ° C., cooled the film, then released from the clip, and 15% of the total film width at the tenter outlet width. Both ends corresponding to the above were cut and then rolled up to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 38 μm.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.

Next, a roll-shaped release film was prepared by the same method as in Example 1.
The visibility of the obtained release film under polarized light showed good characteristics at the center of the film, but exhibited a remarkable interference color at the end of the film and could not be used.

  In the production of the biaxially oriented polyethylene terephthalate film of this comparative example, the geometric bowing amount was measured by the following method. Before introducing the tenter, a straight line extending in the longitudinal direction was drawn with magic ink over the entire width in the film width direction. When such a straight line was observed after heat setting, it became a curved curve that was bowed in a concave shape with respect to the film traveling direction by bowing. When the maximum distance between the bowed curve and the string was measured, the maximum distance was divided by the total film width distance, and the geometric bowing amount was calculated as a percentage, it was about 15%.

(Comparative Example 3)
The unstretched film obtained by the same method as in Example 1 is led to a group of rolls heated to 75 ° C., adjusted using an infrared heater so that the stretching temperature becomes 95 ° C., and 3.3 times in the longitudinal direction. Stretched. Next, it was led to a tenter, stretched 2.6 times in the width direction at 120 ° C, and further stretched 1.5 times in the width direction at 220 ° C. And both ends corresponding to 15% of the total film width of the tenter exit width were cut and wound into a roll to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 38 μm.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 1.

Next, a roll-shaped release film was prepared by the same method as in Example 1.
The visibility of the obtained release film under polarized light, as in Comparative Example 2, showed good characteristics at the center of the film, but exhibited a significant interference color at the end of the film and was unusable for use. .

  In the production of this comparative example, the geometric bowing amount was measured in the same manner as in comparative example 2. As a result, the bowing amount was about 5%, and a marked improvement was observed in comparison with the bowing amount of Comparative Example 2. However, as shown in Table 1, the improvement effect on the maximum tilt angle of the optical main axis was very slight, and no improvement in distortion as much as the geometric bowing amount was improved.

(Example 5)
PET (A) and PET (B) are mixed, the silica particle content is adjusted to 0.08% by weight, dried by a conventional method, supplied to an extruder and melted at 290 ° C. to form a film forming die Then, it was extruded into a sheet shape, closely contacted onto a water-cooled rotary quenching drum using an electrostatic application adhesion method, and quenched to prepare an unstretched film.

Next, the unstretched film was guided to a tenter-type simultaneous biaxial stretching machine, and both ends of the film were gripped by clips, and simultaneously biaxially stretched by 3.2 times at 95 ° C. in the longitudinal direction and the width direction. Subsequently, the film was stretched 1.4 times in the longitudinal direction while raising the temperature to 120 ° C., then heat-fixed at 220 ° C., cooled to 50 ° C., and then the clip was opened. Subsequently, both ends corresponding to 15% of the total film width of the tenter outlet width were cut and wound into a roll shape to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 38 μm.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 2.
Next, a roll-shaped release film was prepared by the same method as in Example 1.
The visibility of the obtained release film under polarized light was ◎.

(Example 6)
An unstretched film prepared by the same method as in Example 5 was guided to a tenter simultaneous biaxial stretching machine, and both ends of the film were gripped by clips, and simultaneously stretched at 90 ° C in the longitudinal direction and the width direction by 3.0 times. Axial stretched. Subsequently, the film was stretched 1.67 times in the longitudinal direction while raising the temperature to 115 ° C., heat-fixed at 220 ° C., cooled to 50 ° C., and then the clip was opened. Subsequently, both ends corresponding to 15% of the total film width of the tenter outlet width were cut and wound into a roll shape to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 38 μm.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 2.
Next, a roll-shaped release film was prepared by the same method as in Example 1.
The visibility of the obtained release film under polarized light was much better than that of Example 5 and was extremely good.

(Comparative Example 4)
The unstretched film prepared by the same method as in Example 5 was guided to a tenter type simultaneous biaxial stretching machine, and both ends of the film were gripped by clips, and simultaneously two times at 95 ° C. in the longitudinal direction and the width direction. Axial stretched. Subsequently, the film was stretched 1.17 times in the longitudinal direction while raising the temperature to 120 ° C., then heat-fixed at 220 ° C., cooled to 50 ° C., and then the clip was opened. Subsequently, both ends corresponding to 15% of the total film width of the tenter outlet width were cut, and then wound into a roll to obtain a biaxially oriented polyethylene terephthalate film.
The properties of the obtained biaxially oriented polyethylene terephthalate film are shown in Table 2.
Next, a roll-shaped release film was prepared by the same method as in Example 1.
The visibility of the obtained release film under polarized light exhibited a remarkable interference color at the end of the film and was not practical.
In addition, the refractive index difference (difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction) of the film obtained in this comparative example is 0.02, and the refractive index difference in Example 5 (0. 04), but the maximum tilt angle of the optical main axis was remarkably deteriorated.

  The obtained results are shown in Tables 1 and 2. In each of the examples and comparative examples, the heat shrinkage rate was greater in the longitudinal direction than in the width direction.

  The release film for protecting a polarizing plate or protecting the retardation plate of the present invention can be used by being attached to a polarizing plate or a retardation plate, which are constituent members of a large liquid crystal display device.

Claims (5)

  A biaxially oriented polyester film used as a base material for a release film used for inspection by a crossed Nicol method, which is used by being bonded to a polarizing plate or a retardation plate, and (1) molecular orientation in the longitudinal direction of the film (2) A biaxially oriented polyester film characterized in that the difference between the refractive index in the film longitudinal direction and the refractive index in the film width direction is 0.03 or more and 0.10 or less. .   The maximum inclination angle of the optical principal axis with respect to the mechanical axis direction of the biaxially oriented polyester film is 5 degrees or less, and the variation of the inclination angle of the optical principal axis measured at 30 cm intervals in the film width direction is 5 degrees or less. The biaxially oriented polyester film according to claim 1.   A release film used for inspection by a crossed Nicol method, which is used by being bonded to a polarizing plate or a retardation plate, wherein the base material of the release film is the one according to claim 1 or 2. A release film for protecting a polarizing plate or protecting a retardation plate, comprising an axially oriented polyester film.   3. The method for producing a biaxially oriented polyester film according to claim 1, wherein the biaxially oriented polyester film is stretched in the longitudinal direction after stretching the unstretched film in the width direction, and then heat-treated. A method for producing a biaxially oriented polyester film, wherein   3. The method for producing a biaxially oriented polyester film according to claim 1, wherein the biaxially oriented polyester film is obtained by simultaneously biaxially stretching the unstretched film in the width direction and the longitudinal direction, and further in the longitudinal direction. A process for producing a biaxially oriented polyester film, wherein the film is produced by stretching the film, followed by heat treatment.