JP2011201172A - Optical biaxially-stretched polyester film roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film excellent in optical performance, which does not cause a decrease in processing speed and a deterioration in yield in a front processing and a back coat processing of an optical sheet or the like used for members of LCD and a backlight, and keeps stable a high brightness because of few chromatic variations and stable color tone to give a highly sharp and high-quality image.SOLUTION: In a biaxially-stretched polyester film roll having a coating layer on both surfaces, a difference (R) of the maximum value and the minimum value when a roll hardness is measured at every 50 mm intervals in a film roll width direction is to be 450 or below, and the color tone y value when a plurality of films are overlapped so that the total thickness in measuring may become 900-1,000 μm is to be 0.3230 or less.

Description

  The present invention relates to a biaxially stretched polyester film roll for optics, and more specifically, a diffusion sheet, a prism sheet, a microlens sheet, which is used as a backlight unit of a liquid crystal display (hereinafter sometimes abbreviated as LCD), The present invention relates to a polyester film roll used for a brightness enhancement sheet, a composite sheet and the like.

  Polyester film, especially biaxially stretched film of polyethylene terephthalate or polyethylene naphthalate, has excellent mechanical properties, heat resistance, chemical resistance, magnetic tape, ferromagnetic thin film tape, photographic film, packaging film, Widely used as materials for films for electronic parts, electrical insulating films, metal laminate films, films to be attached to glass surfaces such as glass displays, and protective films for various members.

  In recent years, polyester films have been widely used for various optical sheets in particular. Base films such as diffusion sheets for LCD members, prism sheets, microlens sheets, brightness enhancement sheets, composite sheets, reflectors, and touch panels, and antireflection bases. It is used for various applications such as film and display explosion-proof base film, and PDP filter film.

  These optical sheets are spread on one side, front processing with functions such as diffusion and prisms and microlenses, and on the opposite side to prevent sticking of each sheet, etc. However, if the flatness of the film is not good, the resin (resin) used in these front processing and back coating processing cannot be uniformly applied. In order to adjust these defects, there is a need to reduce the processing speed, resulting in a decrease in productivity and yield. Incorporation into a film causes problems such as image unevenness and inability to obtain a clear image. It is necessary to perform the flatness of the quality management always.

  In order to keep costs down, inexpensive raw materials with reduced polymerizability and recyclable raw materials are sometimes used. However, when these raw materials are used in large quantities, the color tone of the film becomes yellowish and the brightness is increased. There is a problem that a clear and high-definition image cannot be obtained. In addition, chromaticity differences occur between the sheets, and when the sheets are incorporated into the backlight unit, it is necessary to adjust the color tone of the backlight on the light source side each time. In the light, the yellowish color is further increased due to the relationship of the light source color of the LED, and the image becomes yellow. Therefore, there is a problem that these sheets cannot be used in the backlight corresponding to the LED.

JP-A-7-27561

  The present invention has been made in view of the above circumstances, and the problem to be solved is a reduction in processing speed and yield in front processing and back coating processing of optical sheets used for LCD members and backlights. Providing a polyester film with excellent optical performance that can generate high-quality images with high brightness and stable brightness because of stable color tone with little change in chromaticity. There is to do.

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

  That is, the gist of the present invention is a biaxially stretched polyester film roll having coating layers on both sides, and the difference between the maximum value and the minimum value (R) when the roll hardness is measured at intervals of 50 mm in the film roll width direction. Is a biaxially stretched polyester film for optical use, having a color tone y value of 0.3230 or less when a plurality of films are superposed so that the total thickness during measurement is 900 to 1000 μm Be in a role.

  When used as a base film for LCD backlight diffusion sheets, prism sheets, microlens sheets, brightness enhancement sheets, composite sheets, etc., the film of the present invention has good processing characteristics during front processing and back coating processing. In addition, high brightness and stable high quality images can be obtained without causing problems during processing such as processing speed and yield reduction, and the industrial value of the present invention is extremely high.

Hereinafter, the present invention will be described in more detail.
The polyester used for the polyester film in the present invention refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1, 4-cyclohexanedimethanol etc. are mentioned. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), polybutylene terephthalate, and the like. Such a polyester may be a homopolymer that is not copolymerized, 20 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and / or 20 mol% or less of the diol component is other than the main component. It may be a copolyester that is a diol component. Moreover, those mixtures may be sufficient.

  The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low-polymerization degree polyester by reaction of a dicarboxylic acid and a diol, or a lower alkyl ester of a dicarboxylic acid and a diol reacted with a conventionally known transesterification catalyst. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony compound, a germanium compound, or a titanium compound can be used. Preferably, the dullness of the film can be reduced by setting the amount of the antimony compound to zero or 100 ppm or less as antimony. preferable.

  The polyester used in the present invention may be converted into chips after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and more preferably 0.40 to 0.90 dl / g.

  You may mix | blend particle | grains in the polyester layer which comprises the film roll of this invention for the main purpose of provision of slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples thereof include particles of magnesium silicon oxide, kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape and the like may be used. Moreover, there is no restriction | limiting in particular about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used has the preferable range of 0.01-5 micrometers. If the average particle size is less than 0.01 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, if the average particle size exceeds 5 μm, the surface roughness of the film becomes too rough and transparent. May be inferior.

  Further, the particle content in the polyester is usually in the range of 0.0003 to 1.0% by weight, preferably 0.0005 to 0.5% by weight, based on the total polyester constituting the film. When the particle content is less than 0.0003 wt%, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 1.0 wt%, the transparency of the film is insufficient. There are cases.

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. 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 blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, fluorescent brighteners, dyes, pigments, and the like are added to the polyester film in the present invention as necessary. be able to. Depending on the use, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber, may be contained.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually in the range of 180 to 310 μm.

  The total light transmittance of the film of the present invention is preferably 88.5% or more. The film of the present invention is widely used in optical applications because of its excellent light transmittance. However, when the total light transmittance is less than 88.5%, it may be inappropriate for optical use. .

  The film of the present invention has a film haze of usually 2.5% or less, preferably 2.3% or less, and more preferably 2.0% or less. The film roll of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 2.5%, it may be unsuitable for optical use.

  The film of the present invention has a film longitudinal direction (MD) of usually 1.5% or less, preferably 1.0 or less, with respect to the shrinkage after heating at 150 ° C. for 30 minutes. The film width direction (TD) is 1.0% or less, preferably 0.8% or less, and more preferably 0.5% or less. When the longitudinal direction of the film becomes larger than 1.5% and the width direction exceeds 1.0%, particularly when the LCD is used as a member of a product that tends to be very thin, The dimensional stability of the film forming the sheet is lost due to the heat generated by the lamp and surrounding parts, and the wavy phenomenon occurs at the edge of the sheet, causing distortion and unevenness in the image. Image quality may be degraded.

  The polyester film roll of the present invention has a color tone y value (reflection method) in a range of 0.3230 or less when a plurality of films are superposed so that the total thickness at the time of measurement is 900 to 1000 μm. When the y value exceeds 0.3230, the film has a strong yellowish color, and when used as a display, it is inappropriate in that the color tone of the image becomes inferior or the brightness decreases. . In addition, a color tone difference occurs between the sheets, and when each sheet is incorporated into the backlight unit, a problem arises in that it is necessary to adjust the color tone of the backlight light source each time.

  In order to obtain a film having such a color tone, the catalyst and auxiliary agent for producing the raw material polyester are selected, the amount of the catalyst is reduced as much as possible, and the temperature of the polyester becomes higher than necessary during polymerization and film formation. In addition, it is possible to adopt a method such as preventing the melting time from becoming longer or reducing the amount of the recyclable raw material.

In the film roll of the present invention, the sum of the front and back surfaces of the amount of oligomer (cyclic trimer) deposited on the film surface after heat treatment at 180 ° C. for 10 minutes is preferably 15 mg / m ² or less. Is 10.0 mg / m ² or less, particularly preferably 8.0 mg / m ² or less. When the amount of oligomer precipitation on the film surface exceeds 15 mg / m ² , the oligomer may crystallize on the surface and dissolve into a functional layer provided on the film, which may cause problems such as affecting properties.

  In order to make the amount of oligomer deposition on the film surface by heat treatment within the above range, the oligomer is deposited on the film surface by using polyester with low oligomer content or by providing a coating layer inline or offline. By pressing, the amount of oligomer deposition on the film surface after heat treatment can be within the above range.

  The film of the present invention can be formed into a laminated structure using a coextrusion method. In this case, the outermost layer thickness is preferably only one side, and is usually 4 μm or more and 1/10 or less of the total thickness. . If the thickness is less than 4 μm, the oligomer (cyclic trimer) contained in the inner layer is deposited on the film surface due to heat history during processing, etc., and contamination of the production line and an increase in the amount of foreign matter on the film surface are observed. There is a case. On the other hand, if it exceeds 1/10, the film tends to curl easily.

  The film roll of the present invention measured the roll hardness at the top of the roll at 50 mm intervals in the roll width direction of the product roll slit to an arbitrary width and an arbitrary winding length from the master roll obtained in the film forming process. The difference (R) between the maximum value and the minimum value is 450 or less, more preferably 400 or less. When the roll hardness difference R exceeds 450, the resin cannot be uniformly applied during front processing and back coating processing on the film. In addition, problems such as unevenness, missing spots, and streaks occur during application, and adjustment of these problems causes the need to reduce the processing speed, which causes a decrease in productivity and yield.

  In order to set the roll hardness difference of the product roll in the above range, in the present invention, the film is drawn in the biaxial direction to form a film, but the draw ratio in the longitudinal direction and the transverse direction is 3 times or more. In order to adjust the heat shrinkage rate, relaxation is performed 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 exit of the heat treatment, but relaxation is performed at 10% or less. This method can be adopted.

  Hereinafter, although the manufacturing method of the polyester 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, a dried or undried polyester chip 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 biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 3 to 5 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then at 90 to 160 ° C. in the lateral direction. It is preferable to perform 3 to 5 times stretching and heat treatment at 215 to 245 ° C. for 10 to 600 seconds. Further, at this time, a method of relaxing 1 to 10% 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 outlet of the heat treatment is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, as described above, two or more polyester melt extruders can be used to form a three-layer laminated film by a so-called coextrusion method. As a structure of a layer, it can be set as the film of A / B / A structure using A raw material and B raw material.

  In particular, since the film of the present invention is used for a diffusion sheet, a prism sheet, a microlens sheet, etc. used as a backlight for LCD, each resin such as diffusion, prism, microlens, etc. For the purpose of improving adhesion with each resin, it is necessary to provide a coating layer as an undercoat layer on both sides.

  In forming such a coating layer, the method of forming a film, in particular, after stretching in the longitudinal direction and before stretching in the lateral direction can form a very thin coating layer, and the coating solution drying and curing reaction Is preferable in that it can be carried out in the film forming process.

  The coating layer is preferably composed of a combination of a crosslinking agent and various binder resins, and as the binder resin, a polymer selected from polyester, acrylic polymer and polyurethane is usually employed from the viewpoint of adhesion. Each of the above polymers shall also include derivatives thereof. The derivative here refers to a polymer obtained by reacting a reactive compound with a copolymer or a functional group with another polymer.

  In addition, you may coat by an offline coat after manufacture of a film as needed. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, since the film roll of the present invention is used for optics, a functional multilayer thin film for the purpose of preventing dust adhesion due to static electricity and further for electromagnetic wave shielding is formed particularly on the side opposite to the processing surface on the front side. Is more preferable.

  Among the polyesters, acrylic polymers, and polyurethanes that are used as coating agents in the present invention, particularly preferred polymers have a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher. It is a polyurethane having a carboxylic acid residue, at least a part of which is made water-based using an amine or ammonia.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin may be either a monomer, a condensate composed of a dimer or higher multimer, or a mixture thereof.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipperiness, adhesion and the like. The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the light transmittance of the film tends to be lowered.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes. On the other hand, examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound containing two or more carbon-carbon double bonds in one molecule (for example, divinylbenzene).

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Examples include glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, and amides such as N-methylpyrrolidone. Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.

  The coating layer in the present invention may be subjected to chemical treatment or electric discharge treatment before coating in order to improve the coating property and adhesiveness of the coating agent to the film. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually 0.01 to 0.5 μm, preferably 0.015 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  When such a coating film is applied to an optical application, coating leakage on the surface of the coating layer becomes a problem when a diffusion resin and a backcoat resin are provided on the coating layer. The reason for the occurrence of coating leakage is not clear, but foreign matter in the film creates coarse protrusions on the surface of the film, which acts as a core and the coating agent repels and stretches to cause coating leakage or the film surface. It is conceivable that the oligomer or dust adhering to the core becomes a nucleus and the coating agent repels and disappears from the nucleus. Therefore, it is necessary to form a film under such a condition that dust and foreign matters that can become nuclei are removed as much as possible. Such foreign substances include oligomers adhered or deposited on the film, so that reducing the amount of oligomers contained in the film has the effect of reducing the amount of coating.

When the film of the present invention thus obtained has a coating layer, the number (N) of coating spots is preferably 50 / m ² or less, more preferably 30 / m ² or less, and particularly preferably 10 / m ² or less. In any case, in an optical film that will become more and more severe in the future, it is necessary to make coating coating as zero as possible.

  The film of the present invention exhibits particularly excellent effects when used as an optical material. Specific examples of the film include a diffusion sheet, a prism sheet, and a microlens used as a backlight for an LCD. It is a polyester film used for a sheet, a brightness enhancement sheet, a composite sheet, and the like, and is particularly effectively used as a base material that requires high optical performance.

  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. 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) Measurement of third component (copolymerization component) content About a solution in which a resin sample was dissolved in a deuterated chloroform / hexafluoroisopropanol (weight ratio 7/3) mixed solvent to a concentration of 3% by weight, Using a nuclear magnetic resonance apparatus (“JNM-EX270 type” manufactured by JEOL Ltd.), 1 H-NMR was measured to assign each peak, and the content of the copolymer component was calculated from the integrated value of the peak.

(3) Measurement of average particle size (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(4) Total light transmittance, haze Total light transmittance is JIS-K-7361, and haze is based on JIS-K-7136 by Nippon Denshoku Industries Co., Ltd. integrating sphere turbidimeter “NDH2000”. The rate and haze were measured.

(5) Heat Shrinkage The sample was treated for 30 minutes in an oven kept at 150 ° C. in a tensionless state, the length of the sample before and after that was measured, and the heat shrinkage was calculated by the following formula.
Heat shrinkage rate (%) = {(L0−L1) / L0} X100
(In the above formula, L0 is the sample length before the heat treatment, L1 is the sample length after the heat treatment) Five points were measured in the film longitudinal direction (MD) and the width direction (TD), and the average value was obtained for each.

(6) Color tone y value The color tone y value (reflection method) was measured with a spectrophotometer “CM-3700d” manufactured by Minolta according to JIS-Z-5722. For example, when the film thickness is 188 μm, 5 sheets are stacked, 4 sheets are stacked when 250 μm, and 3 sheets are stacked when 300 μm, so that the total thickness is 900 μm to 1000 μm. did.

(7) Difference in roll hardness (R)
Using the electronic paper / film hardness tester “PAROTESTER 2”, from the master roll obtained in the film forming process, to the upper part in the roll width direction of the product roll slit to an arbitrary width and an arbitrary winding length, The roll hardness was measured at intervals of 50 mm, and the difference (R) between the maximum value and the minimum value at the time of measurement was obtained.

(8) Appropriateness in processing A film of 5 m in the longitudinal direction is cut out from a product roll slit to an arbitrary width and an arbitrary winding length from a master roll, the film is allowed to stand on a surface plate, and the degree of deformation of the film flatness From the following viewpoint, it evaluated comprehensively.
A: Level at which there is almost no deformation of the film and there is no defect in film flatness B: Level at which deformation of the film can be confirmed and there is no defect in film flatness

(9) Suitability of optical members (luminance)
The characteristics when used as a prism sheet as an optical member were evaluated. That is, an acrylic binder is applied to one side of the film to form a prism layer, an acrylic binder is applied to the opposite side to form a stick prevention layer, and the resulting prism sheet and two sheets are used as a backlight unit. Incorporating, the quality of the planar light emission obtained was evaluated from the following viewpoints.
-Luminance level: Evaluated using a luminance meter and compared with the case where the film of Example 4 was used. A: The luminance was improved and improved. B: A decrease in luminance could not be confirmed. Declined

  Examples and Comparative Examples are shown below, and the method for producing the polyester used in the Examples and Comparative Examples is as follows.

<Manufacture of polyester>
<Method for producing polyester (a)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out 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 0.69 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (a) was 0.69.

<Method for producing polyester (b)>
In the method for producing polyester (a), after adding 0.04 part of ethyl acid phosphate, 0.3 part of silica particles having an average particle diameter of 2.1 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide are added. In addition, polyester (b) was obtained using the same method as the production method of polyester (a) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.67. The obtained polyester (b) had an intrinsic viscosity of 0.67.

<Method for producing polyester (c)>
In the method for producing polyester (a), the starting material is 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, and the method for producing polyester (a) is used except that germanium oxide is used as a polymerization catalyst. A polyester (c) was obtained using the same method as described above. In addition, the addition method of germanium oxide employ | adopted the well-known method, The addition amount was 100 ppm with respect to the raw material weight as germanium. The intrinsic viscosity of the obtained polyester (c) was 0.67.

Example 1:
Mixing the above-mentioned polyesters (c) and (b) at a ratio of 88% and 12%, respectively, is used as the raw material of the A layer, and the raw material of the B layer is 100% of the polyester (c). Each is supplied to a shaft extruder, melted at 285 ° C., and coextruded in a layer configuration of two types and three layers (A / B / A) with the A layer as the outermost layer (surface layer) and the B layer as the intermediate layer. An unstretched sheet was obtained by extruding from a die and cooling and solidifying on a cooling roll having a surface temperature set to 21 ° C. using an electrostatic application adhesion method. Next, the film was stretched 3.2 times in the longitudinal direction at a film temperature of 81 ° C. using the roll peripheral speed difference, and then applied to the tenter after applying the coating agent having the composition shown below, and 4 ° C. at 120 ° C. in the lateral direction. After stretching 2 times and performing heat treatment at 232 ° C., it was relaxed by 3% in the transverse direction, and the resulting master roll was slitted into a product width of 1300 mm and a winding length of 1200 m, and a thickness of 188 μm A laminated polyester film roll was obtained. The thickness of each layer of the obtained film was 7/174/7 μm. The thickness of the coating layer was 0.09 μm on one side and 0.12 μm on the opposite side.

(Coating agent composition: weight ratio)
a / b / c / d = 47/20/30/3
Here, a is a polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio); b is Methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) emulsion polymer (emulsifier: anionic surfactant); c is hexamethoxymethylmelamine (melamine type) (Crosslinking agent); d is an aqueous dispersion (inorganic particles) of silicon oxide having a particle size of 0.06 μm
It is.

Example 2:
A mixed raw material in which polyesters (c) and (b) are mixed at a ratio of 87% and 13%, respectively, is used as a raw material for the A layer, and 85% polyester (c) and ears and master rolls generated during the production of the polyester of Example 1 A polyester film roll having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the mixed raw material in which the recycled product from the ear part was mixed at a ratio of 15% was used as the B layer. The thickness of each layer of the obtained film was 7/174/7 μm.

Example 3:
A mixed raw material in which polyesters (c) and (b) are mixed at a ratio of 95% and 5%, respectively, is used as a raw material for the A layer, and is cooled and solidified on a cooling roll set at a surface temperature of 18 ° C. to obtain an unstretched sheet. In the same manner as in Example 1, except that the film was stretched 3.1 times in the vertical direction and 3.5 times in the horizontal direction, heat-treated at 229 ° C., and then relaxed 2% in the horizontal direction. A polyester film roll was obtained. The thickness of each layer of the obtained film was 12/276/12 μm.

Example 4:
2. A mixed raw material in which the polyesters (a) and (b) are mixed at a ratio of 88% and 12%, respectively, is used as the raw material of the A layer, the raw material of the B layer is 100% of the polyester (a), and the draw ratio is 3. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the film was stretched 3 times and 4.1 times in the lateral direction. The thickness of each layer of the obtained film was 6/176/6 μm.

Comparative Example 1:
A mixed raw material in which polyesters (c) and (b) are mixed at a ratio of 87% and 13%, respectively, is used as a raw material of the A layer, and a raw material of the B layer is 100% of the polyester (c). A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the film was stretched 4.0 times in the transverse direction and heat-treated at 229 ° C. The thickness of each layer of the obtained film was 6/176/6 μm.

Comparative Example 2:
A mixed raw material in which polyesters (c) and (b) are mixed at a ratio of 87% and 13%, respectively, is used as the raw material for the A layer, and 40% of the polyester (c) and the ears and master generated during the production of the polyester of Example 1 A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that a mixed raw material obtained by mixing recycled products from the roll ears at a ratio of 60% was used as the raw material for the B layer. The thickness of each layer of the obtained film was 7/174/7 μm.

Comparative Example 3:
The mixed raw materials obtained by mixing the polyesters (c) and (b) at a ratio of 88% and 12%, respectively, were used as the raw material for the A layer, the raw material for the B layer was 100% polyester (c), and the surface temperature was set to 28 ° C. After cooling and solidifying on a cooling roll, an unstretched sheet was obtained, stretched 2.9 times in the longitudinal direction and 3.3 times in the lateral direction, heat treated at 225 ° C., and then relaxed 5% in the lateral direction. A polyester film roll having a thickness of 300 μm was obtained in the same manner as in Example 1 except that.

Comparative Example 4:
The mixed raw materials in which polyesters (c) and (b) are mixed at a ratio of 88% and 12%, respectively, are used as the raw material of the A layer, the raw material of the B layer is 100% of the polyester (c), and the heat setting temperature is set to 212 ° C. Except for this, a film was formed under the same conditions as in Example 1 to obtain a polyester film having a thickness of 188 μm. The thickness of each layer of the obtained film was 6/176/6 μm.

Comparative Example 5:
Polyesters (c) and (b) were mixed at a rate of 88% and 12%, respectively, and the raw material of the A layer was used as the raw material of the A layer, and the raw material of the B layer was 100% of the polyester (c). Except for the above, film formation was carried out under the same conditions as in Example 1 to obtain a laminated polyester film having a thickness of 188 μm. The thickness of each layer of the obtained film was 7/174/7 μm.

  Table 1 summarizes the physical property values of the obtained film, suitability for processing, and suitability for optical members. It can be seen that a film satisfying the requirements of the present invention has high suitability for optical use.

  The film roll of the present invention can be suitably used as an optical film.

Claims (1)

A biaxially stretched polyester film roll having coating layers on both sides, and the difference (R) between the maximum value and the minimum value when the roll hardness is measured at intervals of 50 mm in the film roll width direction is 450 or less. An optically biaxially stretched polyester film roll having a color tone y value of 0.3230 or less when a plurality of films are superposed so that the total thickness of the film becomes 900 to 1000 μm.