JP4805795B2 - Polyether film for release film - Google Patents

Description

  The present invention relates to a polyether film for a release film, and more particularly to a polyester film for a release film that can achieve a high degree of accuracy in detecting defects in inspection of polarizing plates for liquid crystal displays. .

  In recent years, liquid crystal displays have been widely used as various mobile communication terminals such as mobile phones, personal computer monitors, liquid crystal televisions, and other display devices. In particular, liquid crystal displays as flat-screen televisions have been developed to large screens of 37 inches or more, and the demand that can be said to be explosive is increasing.

  In particular, in a liquid crystal display as a thin television, improving visibility in a bright room is a very important required characteristic in terms of a competitive relationship with a plasma display. In order to improve this required characteristic, the liquid crystal display tends to increase the brightness of the display screen. By the way, in such a so-called high-brightness type liquid crystal display, there are many cases where the existing small bright spot becomes a problem, and in a component such as a polarizing plate incorporated in the display, there is a problem in the conventional low-brightness type liquid crystal display There is a problem of a foreign object of a minute size that did not become. For this reason, while preventing the contamination of foreign matters in the manufacturing process, the importance of inspection accuracy that can be surely recognized as a defect even if foreign matters are mixed is further increased.

  A polarizing plate is made of a polarizing film made by adsorbing and orienting a polarizing element such as iodine or a dichroic dye on a polyvinyl alcohol film and coated with a film such as cellulose triacetate as a core. In many cases, a layer is provided, and a release film as a separator is bonded, and a surface protective film is bonded to the opposite surface for the purpose of preventing scratches. Moreover, as a release film as a separator for the pressure-sensitive adhesive layer, a film obtained by applying a release layer such as a silicone resin using a polyester film typified by a polyethylene terephthalate film as a base material is generally used. The release film is peeled off from the pressure-sensitive adhesive layer after completion of the inspection, and the polarizing plate is bonded to the glass panel of the liquid crystal cell.

  As a defect inspection of a polarizing plate, a visual inspection by a crossed Nicol method is generally used. Further, for example, in a polarizing plate used for a large TV application of 40 inches or more, an inspection by an automatic foreign matter inspection machine using the crossed Nicol method is also possible. It is being implemented. In this crossed Nicol method, two polarizing plates are made to extinguish with their orientation principal axes orthogonal, and if there are foreign matters or defects on the polarizing plate, they will appear as bright spots, so that it can be used for defect inspection. Is the method. In the actual inspection, the presence or absence of a bright spot is evaluated with respect to the reference polarizing plate as a quenching state using the polarizing plate to be inspected. In the inspection of the polarizing plate, since the inspection of the pressure-sensitive adhesive layer is also performed, it is inevitable that the release film is also bonded, and the laminated pressure-sensitive adhesive layer and the release film exist in the crossed Nicols. It will be. At this time, for example, even if there is a foreign substance derived from the release film, it becomes a bright spot, so that it cannot be determined whether or not it is a defect of the polarizing plate, resulting in a decrease in the accuracy of the polarizing plate inspection.

  There are various types of optical defects that originate from the release film. Among them, dust and dirt attracted by the charge of the release film, and the polyester film used as the substrate are heated when heated. Regarding the oligomer to be used, the present inventors have already proposed that the coating film provided on the polyester film prevents the film from being charged or reduces the amount of the oligomer that springs out.

By the way, as for the polyester film used as the base material of a release film, in order to ensure slipperiness and a winding characteristic, adding a particle | grain and forming a fine protrusion on the surface is generally performed. At this time, unless the appropriate particle size and blending amount are satisfied, the desired slipperiness cannot be ensured or the winding properties are deteriorated, resulting in deterioration of productivity. However, due to the added particles, this becomes a bright spot, and it has been noted as a problem that it interferes with the foreign substance inspection process.
JP 2003-237005 A JP 2004-177718 A

  The present invention is intended to solve the above-mentioned problems, and a problem to be solved is to provide a polyester film for a release film that can realize a high degree of accuracy in the inspection of a polarizing plate by the crossed Nicols method. .

  As a result of intensive studies in view of the above problems, the present inventors provide a polyester film that is particularly suitable for a polyester film for a release film, without deteriorating excellent film properties, according to a polyester film having a specific configuration. The inventors have found what can be done and have completed the present invention.

That is, the gist of the present invention is a stretched polyester film having a coating layer containing a cationic polymer on at least one side, the surface specific resistance value of the coating layer being 1 × 10 ¹³ Ω or less, and particles present in the polyester film A release film having an average particle size (d50) of 0.2 to 1.5 μm and a particle size distribution value (d25 / d75) of 1.0 to 2.0 Lies in polyester film.

Hereinafter, the present invention will be described in detail.
The stretched polyester film referred to in the present invention is a film that is melt-extruded from an extrusion die, is a film that has been heat-treated after being stretched in at least one direction after being cooled by a so-called extrusion method, Is a film that has been biaxially stretched in the longitudinal direction and the width direction and then heat-treated.

  The polyester constituting the film of the present invention is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. The polyester used may be a homopolyester or a copolyester. In the case of a copolyester, it may be a copolymer containing 30 mol% or less of the third component.

  The dicarboxylic acid component of the copolymerized polyester is selected from isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and oxycarboxylic acid (for example, P-oxybenzoic acid). The glycol component is selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, ethylene oxide adduct of bisphenol A, and the like. Or 2 or more types are mentioned.

  Among the above polyesters, a film using polyethylene terephthalate as a constituent component or a film using the copolyester is preferable from the viewpoint of the balance between characteristics as a base film and cost.

  The intrinsic viscosity of the polyester used in the present invention is usually in the range of 0.40 to 0.90, preferably 0.45 to 0.80, and more preferably 0.50 to 0.75. If the intrinsic viscosity is less than 0.40, the mechanical strength of the film tends to be weak. If the intrinsic viscosity exceeds 0.90, the melt viscosity becomes high, the load in the melt extrusion process is large, and the productivity is high. It tends to decrease.

  The polyester may be chipped after melt polymerization, and may be further subjected to solid phase polymerization under heating or reduced pressure or in an inert gas stream such as nitrogen as necessary. The intrinsic viscosity of the polyester obtained at this time is preferably 0.45 to 0.90 dl / g.

  The polyester film of the present invention may be a film having a structure in which a polyester having a low oligomer content is coextruded and laminated on at least one surface of a layer composed of a polyester having a normal oligomer content. When it has, in the polyester film for release films obtained by this invention, the effect which prevents the bright spot by oligomer precipitation is acquired, and it is especially preferable.

  In the polyester obtained by the present invention, a weathering agent, a light-proofing agent, an antistatic agent, a lubricant, a light-shielding agent, an antioxidant, a fluorescent whitening agent, a matting agent, and a heat-stabilizing agent as long as the gist of the present invention is not impaired. You may mix | blend an agent and coloring agents, such as dye and a pigment.

  In the polyester film of the present invention, particles are added in order to ensure slipperiness and winding properties to form fine protrusions on the film surface. The particles to be blended in the polyester film for this purpose include, for example, inorganic fine particles such as silicon oxide, calcium carbonate, magnesium carbonate, calcium phosphate, magnesium phosphate, kaolin, and titanium oxide, or high cross-linkage such as cross-linked acrylic resin and cross-linked polystyrene resin. Examples thereof include molecular fine particles. These particles may be used alone or in combination of two or more components. And the content is 1 weight% or less normally, Preferably it is 0.005-1 weight%, More preferably, it is the range of 0.01-0.8 weight%. When the content of the particles is small, the number of protrusions formed on the film surface is insufficient, and the surface is liable to be scratched in the film manufacturing process, and the winding characteristics tend to be inferior. Further, when the content of the particles exceeds 1% by weight, the degree of roughening of the film surface becomes too large, and the transparency may be impaired.

  In the present invention, the average particle size of the particles contained in the polyester film needs to be in the range of 0.2 to 1.5 μm, and preferably in the range of 0.3 to 1.3 μm. When the average particle diameter is less than 0.2 μm, the height of the protrusion formed on the film surface becomes insufficient, so that the winding characteristics in the film manufacturing process tend to be inferior. When the average particle diameter exceeds 1.5 μm, when used as a polarizing plate release film, it may become a bright spot and hinder foreign matter inspection.

  Further, the particle size distribution of the particles used must be sharp. Specifically, the particle size distribution value, which is an index representing the sharpness of the particle size distribution, needs to be 1.0 to 2.0, and more preferably 1.1 to 1.8. Here, the particle size distribution value is the particle size distribution value d25 / d75 (d25 and d75 are calculated by calculating the integrated volume of the particle group from the large particle side, and the particle size corresponding to 25% and 75% of the total volume (μm Is a value defined by When the particle size distribution value exceeds 2.0, coarse particles become bright spots, which similarly impedes foreign matter inspection.

  On the other hand, in order to improve the transparency of the film, a method of blending particles only in the surface layer as a laminated film of two or more layers is also preferably employed. The surface layer in this case is at least one of the front and back layers. When the film has three or more layers, particles can be blended in both the front and back layers. In this case, a part or all of the film that has not become a product in the film forming process can be reused as an intermediate layer material.

  In the present invention, the method of blending the particles with the polyester is not particularly limited, and a known method can be adopted. For example, it can be added at any stage for producing the polyester, but it is preferably added as a slurry dispersed in ethylene glycol or the like at the stage of esterification or before the start of the polycondensation reaction after completion of the transesterification reaction. The condensation reaction may proceed. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder Etc.

  In the polyester film of the present invention, it is preferable that the angle formed by the main orientation direction and the width direction is an orientation angle, and this variation is small. Specifically, the orientation angle is measured at measuring points at intervals of 500 mm in the longitudinal and lateral directions in the film plane, and the difference between this and the orientation angle between adjacent measuring points in the longitudinal and lateral directions is examined in a specific range, and the largest orientation angle is obtained. The difference is taken as the variation of the orientation angle (angle / 500 mm). The variation in the orientation angle is preferably 3 degrees / 500 mm or less, and more preferably 2 degrees / 500 mm or less. When the variation in the orientation angle exceeds 3 degrees / 500 mm, the transmitted light intensity varies depending on the position of the polarizing plate when inspecting the polarizing plate, which is an undesirable obstacle to stable inspection of the polarizing plate.

  In the polyester film of the present invention, the refractive index (nβ) in the direction perpendicular to the film in-plane direction with respect to the main orientation axis is preferably 1.640 or less, and more preferably 1.630 or less. If it exceeds 1.640, the variation of the orientation angle of the film tends to increase, which not only becomes an obstacle to stable inspection of the polarizing plate, but also the formation of voids in the particles becomes prominent. It may be visible as a bright spot, which may hinder inspection.

  The thickness of the film of the present invention is not particularly limited as long as it can be formed as a stretched film, but is usually 4 to 100 μm, preferably 10 to 75 μm.

The polyester film in the present invention has a coating layer containing a cationic polymer on at least one side, and the surface specific resistance value of the coating layer is required to be 1 × 10 ¹³ Ω or less.

  In the present invention, a cationic polymer is used as an antistatic agent used in the coating layer. A low molecular weight antistatic agent is not preferable because it has a drawback that the antistatic agent is easily transferred onto the surface that contacts when the film is wound. Among polymer antistatic agents, nonionic polymers are generally not preferred because they often lack antistatic performance. An anionic polymer antistatic agent has strong acidity such as polystyrene sulfonic acid, for example, and has a difficulty in handling. In the case of a neutralized salt thereof, the coating film is formed at the time of coating and stretching by the in-line coating method described later. Again, it is not preferable because it has the disadvantage of being easily whitened. On the other hand, the cationic polymer is preferably used in the present invention because it is excellent in antistatic performance and good in terms of handleability and little whitening during stretching.

  The cationic polymer in the coating layer used in the present invention is a polymer containing a quaternized nitrogen-containing unit as a repeating unit. In particular, a pyrrolidinium ring is added to the main chain represented by the formula (1) or (2). A cationic polymer containing a unit having a main repeating unit as a main repeating unit is preferable in that an excellent antistatic performance can be obtained. These are advantageous in that the amount of other components such as a crosslinking agent and polyvinyl alcohol described later can be increased because there is little decrease in the antistatic performance even if the amount of the cationic polymer in the coating layer is reduced. It is.

In the structure of the above formula (1) or (2), R1 and R2 are usually an alkyl group having 1 to 4 carbon atoms or hydrogen, and these may be the same group or different. Moreover, the alkyl group of R1 and R2 may be substituted with a hydroxyl group, an amide group, an amino group, or an ether group. Further, R1 and R2 may be chemically bonded and have a ring structure. The (1) or (2) the X ^- is a halogen ion, a nitrate ion, methanesulfonate ion, ethanesulfonate ion, monomethyl sulfate ion, monoethyl sulfate ion, trifluoroacetate ion, trichloroacetate ion.

Among the above-mentioned cationic polymers containing a unit having a pyrrolidinium ring in the main chain as a main repeating unit, particularly when the structure of formula (1) and X ⁻ is a chlorine ion, the antistatic performance is excellent. In addition, the humidity dependency of the antistatic performance is small, which is preferable in that the decrease in the antistatic performance is reduced even under a low humidity.

  The polymer having the unit of the formula (1) as a repeating unit is polymerized by using the diallylammonium salt represented by the following formula (3) as a monomer and ring-closing by radical polymerization in a medium mainly containing water. It is obtained by. The polymer having the unit of the formula (2) as a repeating unit can be obtained by cyclopolymerizing the monomer of the formula (3) in a system using sulfur dioxide as a medium.

  In addition, when the polymer having the unit represented by the formula (1) or (2) as a repeating unit is a homopolymer composed of a single unit, better antistatic performance can be obtained. As will be described later, in order to improve the transparency of the coating layer when the polyester film is further stretched after the coating solution containing the cationic polymer is applied to the polyester film, it is expressed by the formula (1) or (2). 0.1 to 50 mol% of the unit to be prepared may be replaced with other copolymerizable components.

  As the monomer component used as the copolymer component, one or more compounds having a carbon-carbon unsaturated bond copolymerizable with the diallylammonium salt of the formula (3) can be selected.

  These are specifically acrylic acid and its salts, methacrylic acid and its salts, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth) Acrylamide, N-methylol (meth) acrylamide, N-methyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, maleic acid and its salt or maleic anhydride, fumaric acid and its salt or fumaric anhydride, monoallylamine And quaternized products thereof, acrylonitrile, vinyl acetate, styrene, vinyl chloride, vinylidene chloride, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, dihydroxypropyl (meth) acrylate, glycidyl (meth) acrylate, (meth) A Liloyloxyethyldialkylamine and its quaternary product, (meth) acryloyloxypropyldialkylamine and its quaternary product, (meth) acryloylaminoethyldialkylamine and its quaternary product, (meth) acryloylaminopropyldialkylamine and its quaternary product A quaternized product can be exemplified, but is not limited thereto.

  The cationic polymer contained in the coating layer is, for example, represented by the formula (4) or (5) in addition to the cationic polymer containing a pyrrolidinium ring as a repeating unit in the main chain represented by the formula (1) or (2). A cationic polymer having a repeating unit as a repeating unit may be used.

In the structure of formula (4) or (5), R3 and R8 are each hydrogen or a methyl group, and R4 and R9 are each usually an alkyl group having 2 to 6 carbon atoms. R5, R6, R7, R10, R11, and R12 are a methyl group, a hydroxyethyl group, or hydrogen, and these may be the same group or different. Further, X ⁻ in the formula (4) or (5) is a halogen ion, nitrate ion, methanesulfonate ion, ethanesulfonate ion, monomethyl sulfate ion, monoethyl sulfate ion, trifluoroacetate ion, or trichloroacetate ion.

  In the cationic polymer having the unit represented by the formula (4) or the formula (5) as a repeating unit, for example, an acrylic acid monomer or a methacrylic acid monomer corresponding to each unit is radically polymerized in a medium mainly containing water. However, the present invention is not limited to this.

  The average molecular weight (number average molecular weight) of the cationic polymer in the coating layer used in the present invention is usually in the range of 1,000 to 500,000, more preferably 5,000 to 100,000. If the average molecular weight is less than 1000, it may cause the cationic polymer to transfer or block on the overlapping surface when the film is wound, and conversely if the average molecular weight exceeds 500,000, the coating solution containing this It becomes difficult to uniformly apply to the film surface.

  In the polyester film of the present invention, it is preferable to add a binder polymer to a coating layer containing a cationic polymer to impart durability, film-forming property, adhesiveness, or oligomer sealing property of the coating layer. Examples of the binder polymer include polyvinyl alcohol, polyalkylene glycol, polyacrylamide, methyl cellulose, hydroxy cellulose, and polyacrylate. Among these, when polyvinyl alcohol is used, the film forming property and oligomer of the coating layer are used. Since sealing property improves, it is especially preferable.

As an oligomer sealing property of the coating layer, the amount of oligomer extracted from the coating layer surface after heat treatment at 150 ° C. for 10 minutes is preferably 0.3 mg / m ² or less.

  In addition, a crosslinking agent can be added to the coating layer containing the cationic polymer for the purpose of improving the heat-resistant adhesiveness, solvent resistance, blocking resistance and the like of the coating layer. This crosslinking agent includes methylolated or alkoxymethylolated melamine compounds, urea compounds, acrylamide compounds, or epoxy compounds, isocyanate compounds, carbodiimide compounds, oxazoline compounds, silane coupling agent compounds, zirconium It is preferable to contain at least one selected from compounds and the like.

  In addition to the above, fine particles and a surfactant can be added to the coating layer containing the cationic polymer. The fine particles to be added include inorganic and organic fine particles such as silicon oxide, alumina, cross-linked acrylic resin, cross-linked polystyrene resin, tin oxide, indium- At least one selected from conductive fine particles such as tin composite oxide fine particles and antimony-tin composite oxide fine particles can be contained. Further, for the purpose of improving the wettability of the coating solution, a nonionic surfactant such as an alkylene oxide addition polymer of acetylene glycol can be preferably used as the surfactant, and the coating layer is stretched in the process. For the purpose of maintaining the transparency of the coating layer, a polyalkylene oxide adduct of glycerin or a polyalkylene oxide adduct of polyglycerin can be preferably used.

  In the polyester film of the present invention, the composition constituting the coating layer containing the cationic polymer, that is, the quantity ratio of the cationic polymer, the binder, the cross-linking agent, the fine particles, and the surfactant is particularly defined because the optimum value varies depending on the selected compound. However, in order to impart antistatic performance to the coating layer surface, the content of the cationic polymer is usually 5% or more, preferably 10 to 80%.

The surface specific resistance value of the coating layer containing the cationic polymer described above needs to be 1 × 10 ¹³ Ω or less, preferably 1 × 10 ¹² Ω or less, more preferably 1 × 10 ¹¹ Ω or less, Preferably, it is 1 × 10 ¹⁰ or less, and the lower limit is not particularly limited, but is usually 1 × 10 ⁸ Ω. When the surface specific resistance exceeds 1 × 10 ¹³ Ω, static electricity generated on the surface where uneven coating has occurred cannot be effectively prevented, and foreign matter such as dust or dust can be removed because the film surface is easily charged. Since it will attract, it is not preferable.

  The coating layer containing the cationic polymer described above is coated on the polyester film as a coating solution mainly using water as a medium. For the purpose of improving the stability of the coating solution or improving the coating properties and coating film characteristics. In addition to water, it is usually possible to add an organic solvent in an amount of 10% by weight or less. Examples of the organic solvent include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin, ethyl cellosolve, t-butyl cellosolve, ethers such as propylene glycol monomethyl ether and tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, Examples thereof include amines such as dimethylethanolamine and trimethanolamine, and amides such as N-methylpyrrolidone. These can be used alone or in combination.

  Any known method can be applied as a method of applying the coating solution to the polyester film as the substrate. Specifically, roll coating method, gravure coating method, micro gravure coating method, reverse coating method, bar coating method, roll brush method, spray coating method, air knife coating method, impregnation method, curtain coating method, die coating method, etc. It can be applied alone or in combination.

  In the present invention, the coating liquid containing the cationic polymer described above is applied to at least one side of the polyester film, but this film is a polyester film before crystal orientation is completed, and is further stretched in at least one direction after coating, It is preferable that it is heat-set after that. As a specific example, after applying an aqueous coating solution to an unstretched film, the film was stretched simultaneously or sequentially in the longitudinal and transverse directions, and then applied to a film that was uniaxially stretched in the longitudinal or transverse direction when heat-fixed. Later, when the film is stretched in the direction orthogonal to the previous stretching and then heat-set, it is applied to a film biaxially stretched in the vertical and horizontal directions, and then stretched again in the vertical, horizontal, or both directions, and then heat-set. In this case, it is possible to exemplify a case where, after being applied to an unstretched film, it is uniaxially stretched in the longitudinal or lateral direction and then heat-set. By using such a so-called in-line coating method, the coating layer is thermally fixed together with the polyester film at a high temperature, so that the adhesion between the coating layer and the polyester film is improved.

  The thickness of the coating layer containing the cationic polymer of the polyester film in the present invention is preferably 0.01 to 0.5 μm, more preferably 0.02 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, antistatic performance and adhesiveness are insufficient, and when it exceeds 0.5 μm, blocking tends to occur.

  Moreover, the coating layer containing a cationic polymer may be coated only on one side of the film, or may be coated on both sides. Furthermore, when coating only on one side of the film, a coating layer different from the coating layer described above can be coated on the opposite surface of the coating layer.

  Next, 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.

  First, the preferable example of the manufacturing method of polyester used by this invention is demonstrated. Here, an example in which polyethylene terephthalate is used as the polyester is shown, but the production conditions differ depending on the polyester used. According to a conventional method, esterification with terephthalic acid and ethylene glycol, or transesterification reaction with dimethyl terephthalate and ethylene glycol, the product is transferred to a polymerization tank, and the temperature is increased while reducing the pressure. In particular, the polymerization reaction proceeds by heating to 280 ° C. under vacuum to obtain a polyester.

  Next, for example, a polyester chip that has been polymerized as described above and dried by a known method is 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 stretched uniaxially or biaxially to form a film. Specifically describing the stretching conditions of the sequential biaxially stretched film, the unstretched sheet is preferably stretched 2 to 5 times in the longitudinal direction at 70 to 145 ° C. to obtain a longitudinally uniaxially stretched film. Next, after performing a hydrophilization treatment such as a corona discharge treatment if necessary, an aqueous coating solution is applied to the uniaxially stretched film. This film is preheated and dried in a tenter, and then stretched 3 to 6 times in the transverse direction at 90 to 160 ° C. At this time, the longitudinal stretching or the lateral stretching may be one-stage stretching, but may be stretched by dividing the stretching ratio into two or more stages. Next, heat setting is performed at 150 to 240 ° C. for 1 to 600 seconds. At this time, in the maximum temperature zone of heat setting and / or the cooling zone of the heat setting outlet, it is possible to relax or extend in a range of 20% or less in the longitudinal direction and / or the transverse direction. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary. Furthermore, it is also possible to perform simultaneous biaxial stretching of the unstretched sheet so that the area magnification is 10 to 40 times.

  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 these, when a curable silicone resin is used as a main component, the releasability is improved, which is preferable.

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

  According to the present invention, it is possible to provide a polyester film for a release film that can be used for foreign matter inspection such as a polarizing plate and a retardation plate, and has as few luminescent spots as possible, and can improve the accuracy of foreign matter inspection. The industrial value of the 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. In the examples and comparative examples, “parts” means “parts by weight”. The measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was accurately weighed and dissolved by adding 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and measured at 30 ° C.

(2) Average particle size (d50, μm) and particle size uniformity (d25 / d75)
The average particle size d50 was defined as the particle size having an integrated volume fraction of 50% in an equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution measuring apparatus (SA-CP4L type) manufactured by Shimadzu Corporation. In addition, the ratio d25 / d75 of the diameter of the point having a weight fraction of 25% and the diameter of the point having a weight fraction of 75%, integrated from the large particle side, was used as the particle size distribution value.

(3) Surface resistivity (Ω)
Using a high resistance measuring instrument HP4339B and measuring electrode HP16008B manufactured by Hewlett-Packard Japan, surface resistivity of the coating layer (Ω) after 1 minute at an applied voltage of 100 V in a measurement atmosphere of 23 ° C. and 50% RH Was measured.

(4) Evaluation of dust adhesion After the humidity of the polyester film is sufficiently adjusted in a measurement atmosphere of 23 ° C. and 50% RH, the coated layer is rubbed 10 times with a cotton cloth. This was brought close to the finely crushed cigarette ash and the ash adhesion was evaluated according to the following criteria.
○: Even if the film is brought into contact with ash, it does not adhere. Δ: When the film is brought into contact with ash, it adheres a little (allowable range).
×: Adhering in large quantities just by bringing the film close to ash

(5) Change in orientation angle in the film (angle / 500 mm)
In the width direction of the polyester film master roll, samples at positions of every 500 mm are cut out from the center position toward both ends in the width direction, and each uses an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Instruments. The main orientation direction was measured, and the angle formed between this and the width direction was taken as the orientation angle, and the orientation angle for every 500 mm was determined in one row in the film width direction. Subsequently, this measurement was repeated seven times every 500 mm in the longitudinal direction of the film (with a length of 3 m in the longitudinal direction), and the orientation angle at the measurement point at which the vertical / horizontal distance was 500 mm was determined. The orientation angle at each of these measurement points was compared with the values of adjacent measurement points in the vertical and horizontal directions, and the difference was obtained. The largest value among the differences in the orientation angles was defined as the orientation angle variation (angle / 500 mm).

(6) Refractive index of film (nβ)
In the width direction of the polyester film, a sample at a position of every 500 mm is cut from the center position toward both ends in the width direction, and the film is used with respect to the main orientation direction in the film plane using an Abbe refractometer manufactured by Atago Optics. The refractive index in the perpendicular direction in the plane was measured for each position, and the average value was obtained and defined as nβ. As the main orientation direction, the one obtained in the above (5) was used.

(7) Surface oligomer amount after heat treatment (mg / m ² )
The polyester film was cut to a size of 25 cm square and heat-treated for 10 minutes in an oven set at 150 ° C. (hot air circulation furnace manufactured by Tabai Espec). Next, the heat-treated polyester film is folded so that the coating layer surface is on the inside, and a square box is created in which the upper part is opened and the bottom area is 250 cm ² . 10 ml of DMF is put in the obtained box, and the DMF is recovered after standing at room temperature for 3 minutes. The recovered DMF was supplied to liquid chromatography (Shimadzu LC-7A) to determine the amount of oligomers in DMF, and this value was divided by the film area in contact with DMF to determine the amount of film surface oligomers (mg / m ² ). It was. The amount of oligomer in DMF was determined from the ratio of the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by dissolving a preliminarily collected oligomer (cyclic trimer) in DMF accurately weighed. 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 IHU manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(8) Visual inspection under crossed Nicols 100 parts of curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical) and 1 part of curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical) on one side of the polyester film Then, a release agent composed of 2200 parts of methyl ethyl ketone (MEK) / toluene mixed solvent system was applied so that the coating amount was 0.1 g / mm ² and dried at 170 ° C. for 10 seconds to obtain a release film. It was. The release film is in close contact with the polarizing film via an adhesive so that the width direction of the release film is parallel to the orientation axis of the polarizing film to form a polarizing plate. The inspection polarizing plate is overlapped so as to be orthogonal to the width direction, white light is irradiated from the polarizing plate side, 10 inspectors visually observe each from the inspection polarizing plate, under crossed Nicols Visual inspection was evaluated according to the following criteria. In the measurement, A4 size samples were cut out from the portions corresponding to the positions of 10, 50, and 90% with respect to the film width direction from the end of the master roll of the obtained polyester film.
<Criteria for visual inspection under crossed Nicols>
(Good inspection) ◎>○>△>×> XX (Inspection failure)
Among the above criteria, those above Δ are levels that can be used without any problem in actual use.

(9) Foreign matter recognition Using the release film created in (8) above, release using a known acrylic pressure-sensitive adhesive so that the width direction of the release film is parallel to the orientation axis of the polarizing film. The film was adhered to the polarizing film to create a polarizing plate with a release film. Here, when the polarizing plate was prepared, black metal powder (foreign matter) having a size of 50 μm or more was mixed between the pressure-sensitive adhesive and the polarizing film so as to be 50 / m ² . A polarizing plate for inspection is superimposed on the polarizing plate release film mixed with the foreign matter thus obtained so that the orientation axis is orthogonal to the width direction of the release 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 master roll of the obtained film. The foreign body was cognitive.
<Foreign substance recognition classification criteria>
(Good foreign body recognition) ◎ ＞ ○ ＞ △ ＞ × (foreign body poor recognition)
Among the above criteria, those above ○ are levels that can be used without any problem in actual use.

Examples 1-4 and Comparative Examples 1-4:
<Manufacture of polyester (A)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours.
After 4 hours, the transesterification reaction was substantially terminated. Ethyl acid phosphate was added to the reaction mixture, which was then transferred to a polycondensation tank, and 0.04 part of antimony trioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C.
On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure to obtain polyester (A). The intrinsic viscosity of this polyester was 0.63.

<Manufacture of polyester (B)>
In the method for producing polyester (A), after adding ethyl acid phosphate, the content of synthetic calcium carbonate particles having an average particle size of 0.8 μm and a particle size distribution value of 1.6 in an amount of 1 wt. The polyester (B) was obtained using the same method as the production method of the polyester (A) except that the addition was made so as to be%. The obtained polyester (B) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (C)>
In the production method of polyester (B), the additive particles are synthetic calcium carbonate particles having an average particle size of 0.4 μm and a particle size distribution value of 1.7, and the content of the polyester is 1% by weight, except that the content is 1% by weight. A polyester (C) was obtained using a method similar to the production method of B). The obtained polyester (C) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (D)>
In the method for producing polyester (B), the additive particles are synthetic calcium carbonate particles having an average particle size of 1.4 μm and a particle size distribution value of 1.9, and the content of the polyester is 1% by weight. Polyester (D) was obtained using the same method as the production method of B). The obtained polyester (D) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (E)>
In the production method of the polyester (B), the additive particles are silica particles having an average particle size of 2.5 μm and a particle size distribution value of 1.3, and the content of the polyester is 0.6% by weight. A polyester (E) was obtained using a method similar to the production method of B). The obtained polyester (E) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (F)>
In the method for producing polyester (B), the additive particles are natural calcium carbonate particles having an average particle diameter of 0.8 μm and a particle size distribution value of 2.5, and the content of the polyester is 1% by weight. A polyester (F) was obtained using a method similar to the production method of B). The obtained polyester (F) had an intrinsic viscosity of 0.63.

<Manufacture of polyester (G)>
In the method for producing polyester (B), polyester (B) is used except that the additive particles are silica particles having an average particle size of 0.12 μm and a particle size distribution value of 2.0, and the content with respect to the polyester is 0.3% by weight. A polyester (G) was obtained using a method similar to the production method of B). The obtained polyester (G) had an intrinsic viscosity of 0.63.

<Compound constituting the coating layer>
Cationic polymer: (a1)
Quaternary ammonium salt-containing cationic polymer using diallyldimethylammonium chloride (Pyrrolidinium ring-containing cationic polymer of formula (1))
Average molecular weight about 30,000.
Cationic polymer: (a2)
Quaternary ammonium salt-containing cationic polymer using diallylmonomethylammonium methanesulfonate (Pyrrolidinium ring-containing cationic polymer of formula (1))
Average molecular weight about 30,000.
Cationic polymer: (a3)
Homopolymer of poly (trimethylammonium ethyl methacrylate) monomethyl sulfate (cationic polymer of formula (5))
-Binder polymer: (b)
Polyvinyl alcohol resin (saponification degree 88 mol%, polymerization degree about 500)
・ Crosslinking agent: (c)
Crosslinkable resin of alkylol melamine / urea copolymer (Bekkamin manufactured by Dainippon Ink & Chemicals, Inc.)

<Manufacture of film>
A mixed raw material in which the polyester (A) and the polyesters (B), (C), (D), (E), (F), and (G) are mixed at a ratio as shown in Table 1 or 2 below. As a raw material for the A layer, 100% of a polyester (A) chip raw material was used as a raw material for the B layer, which was dried at 180 ° C. for 4 hours and then supplied to two extruders. Then, the A layer is the outermost layer (both surface layers) and the B layer is an intermediate layer which is melt-extruded at 290 ° C., and is cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method, and is unstretched A sheet was obtained. Next, longitudinal stretching was performed at the stretching ratio and stretching temperature shown in Table 1 or 2 to obtain a uniaxially stretched film. Here, after performing corona discharge treatment on both surfaces of the film, the coating liquid having the solid content composition shown in Table 1 or 2 was applied so that the thickness after drying and stretching was 0.06 μm (Comparative Example 4 was except). Thereafter, the film is guided to a tenter, dried and preheated, and then subjected to transverse stretching and heat setting under the conditions shown in Table 1 or 2, and the total thickness is 40 μm and the thickness structure is 4 μm / 32 μm / 4 μm (A / B / A) A master roll having a width of 3300 mm was obtained. This was slit with a slitter into film rolls having a width of 1000 mm and a length of 5000 m, and 3 rolls were collected.

  In Comparative Example 4, the film using polyester (A) and (G) as the film surface layer was extremely flat in surface shape and deteriorated in slipperiness, so that the film after stretching and heat treatment was wound into a roll. However, it could not be wound up well and could not be a product. In addition, since scratches were generated on the entire surface of the film, it was impossible to evaluate the visual inspection property and foreign matter recognition of the film.

  The film of the present invention can be suitably used as a polyether film for a release film that can realize a high degree of accuracy in, for example, inspection of a polarizing plate by the crossed Nicols method.

Claims (1)

It is a stretched polyester film having a coating layer containing a cationic polymer on at least one surface, the coating layer has a surface resistivity of 1 × 10 ¹³ Ω or less, and the average particle size (d50) of the particles present in the polyester film is A polyester film for a release film having a particle size distribution value (d25 / d75) in the range of 0.2 to 1.5 μm and a range of 1.0 to 2.0.