JP2007056091A - Polyester film and release film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film capable of conducting an inspection with accuracy in the inspection of a polarizing plate by a crossed Nicol procedure and capable of preventing microscopic foreign particles from mixing in a pressure-sensitive adhesive layer of the polarizing plate, and to provide a release film given by using the polyester film. <P>SOLUTION: The polyester film has a maximum light transmittance of ≤50% at a wavelength of 550 nm under crossed Nicols, wherein the film has a number of foreign particles of ≤0.1 counts/m<SP>2</SP>inside the film and that of ≤0.01 counts/m<SP>2</SP>on a surface of the film, when the foreign particles of which the each has a maximum diameter of ≥100 μm and further has such a size that a shape thereof subjected to parallel projection to the surface of the film in a perpendicular direction of the surface includes a regular square of 50 μm×50 μm are counted in a range of a film area of ≥300 m<SP>2</SP>. The release film is formed by applying a release layer to at least one of surfaces of the polyester film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polyester film excellent in optical properties, which is an important property in a film for liquid crystal display applications, and the like, and a release film using the film, in which foreign substances existing in and inside the film are remarkably reduced. In particular, the present invention relates to a film that can be suitably used as a polarizing plate.

  In recent years, with the rapid spread of mobile phones and personal computers, the demand for liquid crystal displays (LCDs) that are thinner, lighter, consume less power, and have higher image quality than CRTs, which are conventional displays, is growing significantly. The technology has also grown significantly in increasing the screen size of LCDs. As an example of increasing the screen size of LCDs, LCDs have recently been used for large TV applications of, for example, 40 inches or more. In a large-screen LCD, a bright LCD with a large screen is often obtained by increasing the luminance of a backlight incorporated in the LCD or incorporating a film for improving the luminance in a liquid crystal unit.

  In such a so-called high-brightness type LCD, there are many cases where a small bright spot existing in the display becomes a problem, and in a component such as a polarizing plate, a retardation plate or a retardation polarizing plate incorporated in the display, Small size foreign matter that has not been a problem in conventional low-brightness LCDs has become a problem. Even if foreign matter is mixed in, it prevents the entry of fine foreign matter in the manufacturing process. Both improvement of the inspection property that can be surely recognized as a defect has become important.

  For example, as a defect inspection of a polarizing plate, a visual inspection by a crossed Nicols method is generally used. Further, for example, for a polarizing plate used for a large TV application of 40 inches or more, an inspection by an automatic particle inspection device using the crossed Nicols method is used. Is also being implemented. This crossed Nicol method is a method in which two polarizing plates are put in a quenching state with their orientation principal axes orthogonal to each other, and if there are foreign matters or defects, they appear as bright spots, so that a defect inspection can be visually observed. Here, a polyester film in which a release layer is installed via an adhesive layer is used for the polarizing plate, and the crossed Nicols inspection is performed with the release polyester film sandwiched between two polarizing plates. In general, when a release polyester film is used for this, it may become an obstacle to the inspection by the crossed Nicols method, and there may be a problem that it is easy to overlook foreign matters and defects. Also, if there is a foreign matter or defect in the polyester film, it may not be possible to determine whether it is a defect of the polarizing plate, and the polarizing plate may be defective. May become a problem.

  A conventional biaxially oriented polyester film for a release film is one that defines the number of foreign matters in the film (see Patent Document 1), and has a retardation value when a polyester film is sandwiched between two polarizing plates. Although it has been disclosed that inspection performance is improved when it is within the range (see Patent Document 2), it becomes a problem when performing inspection for surely finding defects even if these are used. There is a case.

  In order to solve this problem, there has been a technique in which the maximum transmittance of light having a wavelength of 550 nm under crossed Nicols and the size and number of foreign substances present in the film are defined to solve the problem (see Patent Documents 3 and 4). ).

  However, in recent years, with the necessity of improving the yield due to the lower price of LCD and the further increase in brightness and added value of LCD, mixing of minute foreign matters in the manufacturing process has become a big problem. . An adhesive is applied to one side of the polarizing plate, and a release film is attached to protect the adhesive layer. Conventionally, the optical characteristics of the release film and the size and number of foreign substances inside the film have been defined to facilitate the inspection of the defects of the polarizing plate, but the film adhered to the release surface of the bonded release film. No consideration is given to the size, number, or existence probability of foreign matter. If foreign matter is present on the surface of the release layer, not only the problem of foreign matter discrimination in defect inspection, but also foreign matter moves to the adhesive layer, resulting in the final product. This causes a big problem that foreign matter is mixed in the LCD.

Existence probability of the foreign matter (pieces / ^{m 2)} for, usually, are (see Patent Documents 5 and 6) which is determined by the foreign matter detection by visual inspection of 310 mm ² to 2 m ² about an area. However, general products of actual polyester film and silicone release film have a length of about 1000 to 15000 m and a width of about 0.5 to 1.5 m, which is 250 to 70000 times the inspection area. It has the size. The occurrence and existence probability of a foreign substance is not a parameter that expresses a characteristic within a specified range if it is evaluated at a specified position in the product such as physical properties of the film, for example, breaking strength and tensile modulus. Since the foreign matter is generated discontinuously, it greatly depends on the evaluation position in the film product.

Ideally, the existence probability is preferably 0 / full length regardless of the size of the foreign matter, but it cannot be achieved in practice. Therefore, the lower the probability of presence of foreign matter, the better. However, the probability of presence when the inspection length for inspecting the presence of foreign matter is significantly shorter than the total product length reflects the status of foreign matter in the product. I can't say that. For example, in the foreign matter inspection of 300 meters ^2, the confirmation films that foreign matters of a certain size is 0.06 pieces / ^{m 2,} in a short test length of about 10 m ^2, the foreign matter is examined with 0 / ^{m 2} In some cases, it may be determined that no foreign matter exists. Therefore, in order to avoid variation in the presence probability of foreign matter at the evaluation position and oversight of foreign matter due to inspection in a small area, it is necessary to perform foreign matter inspection in a large area.
JP 2002-207119 A JP 2000-338327 A JP 2004-240174 A JP 2004-346117 A Japanese Patent Laid-Open No. 09-314782 Japanese Patent Laid-Open No. 10-155881

  The present invention is intended to solve such problems, and the problem to be solved is that it is possible to carry out an accurate inspection in the inspection of the polarizing plate by the crossed Nicol method, and the foreign matter is applied to the adhesive layer of the polarizing plate. An object of the present invention is to provide a polyester film and a release film using the film so as not to mix any of the above.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be easily solved by a polyester film and a release film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a polyester film having a maximum light transmittance at a wavelength of 550 nm under crossed Nicols of 50% or less, and is a foreign matter having a maximum diameter of 100 μm or more in a film area of 300 m ² or more. The number of foreign matters having a size including a square of 50 μm × 50 μm in a shape projected in parallel from the vertical direction to the film surface of the foreign matter is 0.1 pieces / m ² or less in the film, A polyester film having a surface of 0.01 pieces / m ² or less, and a release film having a release layer provided on at least one surface of the polyester film, and having a release film area of 300 m ² or more In this case, the foreign matter having a maximum diameter of 100 μm or more is projected in parallel from the perpendicular direction to the film surface of the foreign matter. Wherein the number of foreign matter shape has a size encompassing a square 50 [mu] m × 50 [mu] m is 0.1 or within the film / ^{m 2} or less, that is 0.01 pieces / ^{m 2} or less on the film surface It exists in a release film.

Hereinafter, the present invention will be described in detail.
The polyester referred to in the present invention refers to a polymer containing an ester group obtained by polycondensation from a dicarboxylic acid and a diol or from a hydroxycarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, succinic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and the diol includes ethylene. Glycol, 1,3-propanediol, 1,6-hexanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, etc. as hydroxycarboxylic acids Can be exemplified by p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and the like.

  Typical examples of such polymers include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate and the like. These polymers may be homopolymers or may be a copolymer of the third component.

  The film of the present invention is preferably a biaxially oriented polyester film from the viewpoint of excellent strength and dimensional stability, and a biaxially stretched film is preferably used, but a uniaxially stretched film may also be used.

  When the polyester film in the present invention is made into a crossed Nicol state using two polarizing films and a laminated body in which the polyester film is sandwiched between the two polarizing films, the laminated body has a maximum transmission of light having a wavelength of 550 nm. The rate is 50% or less, preferably 30% or less, and most preferably 15% or less. When the maximum transmittance of 550 nm light under crossed Nicols exceeds 50%, light leakage is large during crossed Nicols inspection using a polarizing plate, and in-plane interference color variation tends to increase. As a result, the possibility of overlooking a defective portion such as a bright spot is increased, which is not preferable.

Further, the number of foreign matters having a maximum diameter of 100 μm or more having a size including a rectangle of 50 μm × 50 μm in a shape projected in parallel from the vertical direction to the film surface of foreign matters existing inside the film has a film area of 300 m ² or more. It is 0.1 piece / m ² or less in the range. When such foreign matter exceeds 0.1 piece / m ² , the foreign matter in the polyester film becomes a bright spot at the time of inspection, and it is often difficult to discriminate the polarizing plate or the like from being defective. Since it may be considered, it is not preferable. Further, the number of foreign matters having a maximum diameter of 30 μm or more is preferably 1.5 pieces / m ² or less, and more preferably 1 piece / m ² or less. In addition, the foreign material which exists in the inside of a film arises by mixing of the organic compound etc. by degradation of a molding machine, the inorganic substance derived from a damage, and the thermal decomposition of resin at the time of shaping | molding of a film in the process shape | molded into a film.

  The film haze is preferably 6% or less, and when the film haze exceeds 6%, the bright spot of the defective portion tends to be difficult to find.

Concerning foreign matters existing on the film surface, the number of foreign matters having a maximum diameter of 100 μm or more including a rectangle of 50 μm × 50 μm in parallel projected from the vertical direction on the film surface is 0.01 / m ² or less. Further, the number of foreign matters having a maximum diameter of 20 μm or more is preferably 0.3 pieces / m ² or less. The film surface refers to the interface between the film and the air, and the foreign substance existing on the film surface means a foreign substance that exists at the interface and adheres to the film surface. When foreign matter having a maximum diameter of 100 μm or more exists on the film surface at 0.01 pieces / m ² or more, when the foreign matter attached to the film surface is stuck to the polarizing plate and the adhesive layer, This causes a problem that a large amount of foreign matter is mixed into the final product LCD, resulting in a defective product. Foreign matter adhering to the film surface is a process of drawing and heat-treating the film, such as deterioration of the molding machine, inorganic substances derived from damage, film fragments, organic compounds due to thermal decomposition of the film during film formation, human Dust such as protein is generated due to work, and the dust is caused by flying in the air, settling on the film surface, and then adhering.

In addition, after heat-treating the polyester film at 180 ° C. for 10 minutes, the amount of oligomer extracted with dimethylformamide (hereinafter referred to as surface OL amount) is preferably 10 mg / m ² or less, more preferably 1 mg / m ² or less. . When the amount of surface OL is more than 10 mg / m ² , OL is deposited on the film surface in the heating process at the time of release layer installation, contaminates the release layer installation process, or a release layer is provided and attached to the polarizing plate. When combined, the oligomer may transfer to the pressure-sensitive adhesive, and as a result, foreign matter may be mixed into the pressure-sensitive adhesive.

Furthermore, the number of scratches having a width of 10 μm or more present on the film surface is preferably 20 / m ² or less, more preferably 10 / m ² or less. When the number of scratches with a width of 10 μm is more than 20 / m ² , when the scratched part on the film surface becomes a bright spot during the crossed Nicols inspection, or when the appearance inspection of the polarizing plate or the like is performed by reflected light, It may be recognized as a point and the polarizing plate or the like may be regarded as a defective product.

  Moreover, it is preferable that b value measured by transmitted light using a color difference meter exists in the range of -2.0-2.0. If the b value is outside this range, the color tone of the end face of the release film roll in which the release layer is provided on the polyester film may be extremely yellow or blue, which may cause problems in practice.

  In the polyester film of the present invention, it is preferable to add a filler in the film for the purpose of improving workability and improve the slipperiness of the film. Examples of the filler to be added include silica, calcium carbonate, kaolin, and oxidation. Inorganic particles such as titanium, aluminum oxide, barium sulfate, and zeolite, or organic particles such as silicone resin, cross-linked polystyrene, and acrylic resin may be used alone or in a mixture in the film. In this case, the average particle size, the amount added, and the particle size distribution of the particles to be used are not particularly limited as long as the effects of the present invention are not impaired, but the average particle size is 0.1 to 4.0 μm. The amount is preferably 0.01 to 3.0% by weight.

  Among such additive filler groups, a polyester film with less foreign matter can be produced by blending calcium carbonate particles in the film at an addition amount of 0.03% by weight or more with respect to the polyester. is there. Further, when calcium carbonate particles are used in the polyester film, the film is handled when winding the film roll after the release layer is installed by setting the center surface average roughness (SRa) of the film to 10 nm or more. In some cases, it is preferable in terms of workability.

  The polyester film of the present invention may be a single layer film or a multilayer film in which a plurality of layers are laminated as long as the effects of the present invention are not impaired. A film having a multilayer structure such as a seed 3 layer is preferable.

  In order to reduce foreign matter adhering to the surface of the polyester film, it is preferable to perform the following cleaning within a range that does not impair the effects of the present invention. There are dry and wet cleaning methods as cleaning methods. As a dry cleaning method, 1) a method in which an adhesive resin roll is brought into contact with the film surface to transfer the adhered foreign matter to the resin roll side, and 2) the surface of the film is subjected to high-cleanness air or high-speed ultrasonic vibration. There is a method in which the adhered foreign matter is peeled off from the film surface and the foreign matter is guided to the adjacent suction port, and 3) a blade, cloth or the like is pressed against the film surface to scrape the adhered foreign matter. As a wet cleaning method, 4) A method of spraying high-pressure ultrapure water to remove foreign substances and washing away, 5) Applying ultrasonic vibration to the cleaning liquid and bringing the liquid into contact with the film surface, adhesion of the film surface There is a method for removing and removing foreign substances.

  In particular, the cleaning method of 5) is highly effective in removing foreign matter, and further, when an organic solvent imparted with ultrasonic vibration is brought into contact with the film surface, it is effective in removing foreign matter that is firmly fixed on the film surface such as organic matter. high. In addition, by selecting an organic solvent, the type of foreign matter that can be removed and the removal rate vary greatly.

  The removal of adhered foreign matter on the film surface is preferably performed in combination with the cleaning methods 1) to 5) described above.

Hereinafter, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.
Polyester chips dried by a known method are supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to melt. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is preferably stretched in the biaxial direction to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 1.3 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 90 to 160 ° C. in the lateral direction. It is preferable that the film is stretched 1.3 to 6 times and heat-treated at 150 to 240 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. The stretching method may be sequential biaxial stretching or simultaneous biaxial stretching, and a stretching method based on the simultaneous biaxial stretching method is preferable.

  If the polyester film of the present invention is within the range not impairing the effects of the present invention, it may be stretched in the longitudinal direction as necessary to improve the required properties such as antistatic properties, weather resistance and surface hardness. After the completion, so-called in-line coating may be performed in which coating is performed before entering the tenter for transverse stretching and drying is performed in the tenter. Various coatings may be performed by offline coating after film production. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for offline coating, but is preferably water-based or water-dispersed for in-line coating.

  If the polyester film of the present invention is within a range not impairing the effects of the present invention, foreign matters may be removed by a dry cleaning method after longitudinal stretching and / or lateral stretching in the film forming process. Alternatively, it is preferable to remove foreign matters by a dry or wet cleaning method or a combination of both cleaning methods during a slitting operation and a rewinding operation for adjusting the width and length of the polyester film. The wet cleaning method is preferably a method of peeling and removing foreign substances adhering to the film surface by applying ultrasonic vibration to the cleaning liquid and bringing the liquid into contact with the film surface.

  The polyester film of the present invention can be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent brightening agent, and the like can be mixed.

  When a release layer is installed on the polyester film of the present invention, the material constituting the release layer is not particularly limited as long as it has releasability, and a type mainly composed of a curable silicone resin may be used. Alternatively, a modified silicone type obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin may be used. Among them, when the curable silicone resin is a main component, the release property is good.

  It is preferable to remove foreign matters attached to the film surface by dry or wet cleaning at a stage before installing the release layer and by dry cleaning at a later stage. Furthermore, in the previous stage, dry cleaning is performed, and then ultrasonic cleaning is applied to the cleaning liquid, and the liquid is brought into contact with the film surface, thereby removing the foreign substances using a method of peeling and removing the adhered foreign substances on the film surface. Is preferred.

  Types of curable silicone resins include solvent addition type, solvent condensation type, solvent UV curable type, solventless addition type, solventless condensation type, solventless UV curable type, solventless electron beam curable type, etc. But it can also be used.

In the present invention, even after processing into a release film, in the same manner as the above-mentioned film, in the range of 300 m ² or more of the release film, the maximum diameter is 100 μm or more of foreign matter, The number of foreign matters having a size including a square of 50 μm × 50 μm projected in parallel from the vertical direction is 0.1 piece / m ² or less inside the film and 0.01 piece / m ² or less on the film surface. It is necessary to be. If these conditions are not satisfied, the same problem as described above occurs, which is not preferable.

  The present invention provides a polyester film capable of carrying out an accurate inspection in the inspection of the polarizing plate by the crossed Nicol method, and does not allow minute foreign matters to be mixed into the adhesive layer of the polarizing plate, and a release film using the film. The industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. Various physical properties and characteristics are measured or defined as follows.

(1) Measurement of maximum transmittance at 550 nm under crossed Nicols Cut out a 6 cm square sample from an arbitrary position of the polyester film, and light at 550 nm using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Instruments. The retardation and orientation angle were measured, respectively, and the transmittance at 550 nm light was calculated by the following formula. The highest maximum transmittance in the film was defined as the maximum transmittance of the film.
Transmittance = Sin (2θ) · Sin (π · Re / 550)
(In the above formula, θ means the orientation angle (deg.) Re of the polyester film and Re means the retardation (nm) of the polyester film)

(2) using the measurement number of foreign matter Hu-Tech Co., Ltd. defect detecting device, the light transmission detection system, the camera resolution film width direction 24 [mu] m, as the flow direction 24 [mu] m, was particle inspection of the polyester film and the release film 300 meters ² . In addition, when the shape projected on the film surface of the foreign material in the vertical direction includes a square of 50 μm × 50 μm, the defect detection device was adjusted so that it was detected as a foreign material. When a foreign object was detected, the position information was recorded on the computer and the film edge was marked. After inspection of the foreign matter, a 3 cm square sample is taken from the location information and marking so that the location where the foreign matter is present in the center, and the presence position (surface or inside) and size of the foreign matter in the square sample are measured with an optical microscope. After counting the number of foreign matters having a maximum diameter of 100 μm or more for each existing position, the number was converted into an existence probability (pieces / m ² ). Subsequently, a 10 m ² polyester film and a release film are visually inspected using a crossed Nicol method, and when a foreign object is confirmed, a square sample of 3 cm square so that the location where the foreign object exists is included in the center. Was cut out. Existence position (surface or internal) and size of foreign matter in the square sample are determined by an optical microscope, and the number of foreign matters having a maximum diameter of 30 (internal) or 20 (surface) or more is counted and then present. Converted to probability (pieces / m ² ). In the following examples, foreign matter inspection was performed using a long sample, but the number of foreign matters can be measured by a method similar to the above even for a small sample such as an A4 size.

(3) Measurement of film haze According to JIS-K6714, the haze of the film was measured with the Nippon Denshoku Industries Co., Ltd. divisional turbidimeter NDH-20D.

(4) Measurement of surface oligomer amount Fold the heat-treated polyester film so that the top is opened and the bottom area is 250 cm ² to create a square box. When the coating layer is provided, the coating layer surface is set to the inside. Next, 10 ml of DMF is put into the box prepared by the above method, and the DMF is recovered after being left for 3 minutes. The recovered DMF is supplied to a liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomer in DMF, and this value is divided by the film area in contact with DMF to determine the amount of oligomer on the film surface (mg / m ² ). And The amount of oligomer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing an oligomer (cyclic trimer) collected in advance and dissolving it in DMF accurately weighed. The concentration of the standard sample is preferably in the range of 0.001 to 0.01 mg / ml. The conditions for the liquid chromatograph were as follows.
Mobile phase A: Acetonitrile mobile phase B: 2% acetic acid aqueous solution column: MCI GEL ODS 1HU manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(5) Measurement of the number of scratches Light is applied to the film surface with a width of 1500 mm and a length of 10 m (area 15 m ² ) with a halogen light, the film surface is visually observed, and the number of scratches appearing as bright spots is counted. The width of all the scratches was measured with an optical microscope, and the number of scratches having a width of 10 μm or more was calculated. In this example, the number of scratches having a width of 10 μm or more was counted for a long sample, but the number of scratches having a width of 10 μm or more was measured by the same method as described above even for a film having a size of about A4 size, for example. It is possible.

(6) Measurement of b value Using a spectral color difference meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd., the b value by the transmission method was measured according to the method of JIS Z-8722.

(7) Measurement of center plane average roughness (SRa) Non-contact type three-dimensional roughness meter using a so-called two-beam interference method, which is a direct phase detection interferometry method, by depositing Al on the surface of a 3 cm square film sample. (Micromap Co., Ltd., 512) Under the conditions of measurement wavelength: 554 nm and objective lens magnification: 20 times, from the projection height distribution curve, the center plane average roughness of the A plane and C plane in the measurement area of 232 μm × 177 μm The SRa was measured over 50 points, and the SRa values of the 50 points were averaged to calculate the SRa of the film.

(8) Release film formation Polyester film, 100 parts of curable silicone resin (“KS-774” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-50T” manufactured by Shin-Etsu Chemical), methyl ethyl ketone (MEK) / A release agent comprising 2000 parts of a toluene mixed solvent system was applied so that the coating amount after drying was 0.1 g / m ² and dried at 170 ° C. for 10 seconds to obtain a release film.

(9) Visual inspection property under crossed Nicols Adhering the release film to the polarizing film via an adhesive so that the width direction of the release film obtained in (8) is parallel to the orientation axis of the polarizing film A polarizing plate for inspection is placed on the release film that has been adhered, and the polarizing plate for inspection is superimposed so that the orientation axis is orthogonal to the width direction of the film, and white light is irradiated from the polarizing plate side. The visual inspection property under crossed Nicols was evaluated according to the following criteria. In addition, in the case of a measurement, the sample of A4 size was cut out from the arbitrary places of the obtained polyester film, and it implemented. In addition, when there existed adhering foreign material on the mold release film surface, when the mold release film was peeled off from the polarizing plate, it became clear that the foreign material would move to the adhesive layer side.

<Criteria for visual inspection under crossed Nicols>
(Inspection is good) ◎>○>△>×> XX (Inspection failure)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

(10) Foreign substance recognition 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical), methyl ethyl ketone (MEK) / toluene mixed solvent system 2000 After applying a release agent consisting of parts on one side of the polyester so that the coating amount after drying is 0.1 g / m ² and drying at 170 ° C. for 10 seconds to obtain a release film, A release film was adhered to the polarizing film through a known acrylic pressure-sensitive adhesive so that the width direction of the mold film was parallel to the orientation axis of the polarizing film, thereby preparing a polarizing plate with a release film. Here, when producing the said polarizing plate, the black metal powder (foreign matter) with a magnitude | size of 20 micrometers or more was mixed between the adhesive and the polarizing film so that it might become 10 piece / m < ² >. A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with foreign matters thus obtained so that the orientation axis is orthogonal to the width direction of the releasing film, and white light is irradiated from the polarizing plate side. Ten inspectors visually observed from the polarizing plate for inspection, and evaluated whether the foreign matter mixed between the adhesive and the polarizing film could be found by the following classification. At the time of measurement, the film was evaluated using a total of three films at the center and both ends of the obtained film. It was.
<Foreign substance recognition classification criteria>
(Good foreign body recognition) ◎>○>△> × (poor foreign body recognition)
Among the above criteria, those above ○ are levels that can be used without any problem in actual use.

Example 1
(Polyester chip manufacturing method)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized according to a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and a polyester A having an intrinsic viscosity of 0.65 was obtained by chipping according to a conventional method. Polyester A was solid-layer polymerized by a known method to obtain polyester B having IV = 0.75. When the polyester A was produced, 10000 ppm of calcium carbonate having an average primary particle size of 0.7 μm was added to obtain polyester C. When the polyester A was produced, 8000 ppm of amorphous silica having an average primary particle size of 2.4 μm was added to obtain polyester D. When the polyester A was produced, 20000 ppm of δ-type aluminum oxide having an average primary particle size of 60 nm was added to obtain polyester E.

(Manufacture of polyester film)
Using the polyesters A to E as mixed raw materials for the A layer and B layer at the blending ratio shown in Table 1, each is supplied to two twin-screw extruders and melted at 285 ° C., and then the A layer is the outermost layer. (Surface layer), with B layer as an intermediate layer, 20 layers with a structure of 2 types and 3 layers so that the thickness ratio of A layer / B layer / A layer = 8% / 84% / 8% with respect to the total thickness It was coextruded on a casting drum cooled to 0 ° C. and cooled and solidified to obtain a non-oriented sheet. Next, the film was stretched 2.8 times in the longitudinal direction at 100 ° C., then subjected to a preheating step in the tenter and subjected to transverse stretching of 4.6 times at 120 ° C., followed by heat treatment at 225 ° C. for 10 seconds, At 180 ° C., 10% relaxation was applied in the width direction to obtain a polyester film having a width of 3000 mm and a thickness of 38 μm. In the process of slitting the obtained film to a width of 1500 mm, the film surface adhering foreign matter was removed by ultrasonic cleaning using an adhesive roll and then methyl ethyl ketone. The polyester film was excellent in visual inspection and foreign substance recognition and highly practical. Table 2 below shows the presence probability of foreign matters in the polyester film obtained by the examples, and Table 3 below shows the presence probability of foreign matters in the release film obtained by performing silicone coating on the polyester films obtained by the examples. .

(Examples 2 to 4)
A polyester film was obtained in the same manner as in Example 1 except that the raw material composition, film forming conditions, film thickness, and the solvent used for ultrasonic cleaning were as shown in Table 1 below. The obtained polyester films had the results as shown in Table 1, and each was a highly practical film, although there were differences in visual inspection and foreign matter recognition.

(Comparative Examples 1-2)
A polyester film was obtained in the same manner as in Example 1 except that the raw material composition and film forming conditions were as shown in Table 4 and that the surface adhering foreign matter was not removed in the slitting process. The obtained polyester films were inferior in visual inspection and foreign matter recognition, but were inferior, had high b values, and lacked practicality. Table 5 shows the foreign matter existence probability of the polyester film obtained by the comparative example, and Table 6 shows the foreign matter existence probability of the release film obtained by performing silicone coating on the polyester film obtained by the comparative example.

The present invention provides a polyester film capable of carrying out an accurate inspection in the inspection of the polarizing plate by the crossed Nicol method, and does not allow minute foreign matters to be mixed into the adhesive layer of the polarizing plate, and a release film using the film. Therefore, its industrial value is extremely high.

Claims (2)

A polyester film having a maximum transmittance of 550 nm light of 50% or less under crossed Nicols, and is a foreign matter having a maximum diameter of 100 μm or more in the range of 300 m ² or more, and perpendicular to the film surface of the foreign matter. The number of foreign matters having a size including a square of 50 μm × 50 μm in parallel projection from the direction is 0.1 piece / m ² or less inside the film and 0.01 piece / m ² or less on the film surface. Polyester film characterized by A release film having a release layer on at least one side of the polyester film according to claim 1, wherein the release film is a foreign matter having a maximum diameter of 100 μm or more in a range of 300 m ² or more, and the foreign matter film. The number of foreign substances having a size including a square of 50 μm × 50 μm in parallel projection from the vertical direction to the surface is 0.1 piece / m ² or less in the film and 0.01 piece / m on the film surface. A release film characterized by being ² or less.