JP2007031497A - Optical polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film having good optical performances and, when used as an element of LCD, PDP, organic EL, projection displays and the like, causing neither unevenness nor defect, realizing high luminance and giving high quality images having no defect. <P>SOLUTION: The film comprises a polyester containing 2.0-10.0 mol% third ingredient other than main constituents, is obtained by a simultaneous biaxial drawing method and is a biaxially oriented polyester film having 0-3.0% film haze. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical polyester film, and in particular, various optical members used for liquid crystal displays (hereinafter sometimes abbreviated as LCD), plasma displays (hereinafter sometimes abbreviated as PDP), and the like, It is a polyester film used for protective films and release films used in the manufacturing process of products in the optical field, and contributes to improving quality and reducing energy consumption because it has excellent optical properties and no defects in optical products. It relates to an optical polyester film capable of

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Magnetic tape, ferromagnetic thin film tape, photographic film, packaging It is widely used as a material for films, films for electronic parts, electrical insulation 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 films, in particular, prism films for LCD members, light diffusion sheets, reflectors, touch panels, and other base films, antireflection base films, display explosion-proof base films, and PDPs. It is used for various applications such as filter films. In these optical products, in order to obtain a bright and clear image, the base film used as an optical film has good transparency from its usage, and there are no defects such as foreign matter or scratches that affect the image. Necessary. In addition to this, it is necessary to obtain an image having no unevenness even when polarized light is used, so that there is no retardation unevenness due to uneven orientation of the polymer and uneven thickness.

  A polyester film is usually obtained by subjecting an amorphous sheet obtained by melt extrusion to a sheet and quenching and solidifying it in the longitudinal and transverse directions, followed by heat treatment. If the uniformity of cooling and stretching is not sufficient in these steps, the above-mentioned retardation unevenness remains, and there is a problem that the image is deteriorated when used for optics.

  Brightness is an important characteristic in displays, and it is known that the polyester film used as a member affects the brightness. In particular, when a high-quality image is obtained, a high brightness is required. Therefore, the polyester film has been required to have a characteristic for realizing a high brightness. For this purpose, it goes without saying that the polyester film has a high degree of transparency, but it is also necessary to have an optically advantageous characteristic of increasing the brightness.

In addition to this, an important characteristic when used for displays is that there is no defect. If there are defects such as scratches on the film, there is a problem that when used as a member of a display product, a defect of an image is generated and the quality is deteriorated.
JP 2005-144839 A JP 2005-132107 A

  The present invention has been made in view of the above circumstances, and the solution to the problem is that when used as a member of an LCD, PDP, organic EL, projection display or the like, there is no unevenness or defect, and high brightness is realized. It is an object of the present invention to provide a polyester film having good optical performance and capable of giving a high-quality image without defects.

  That is, the gist of the present invention is a film comprising a polyester containing a third component other than the main constituent component in a total range of 2.0 to 10.0 mol%, and obtained by a simultaneous biaxial stretching method, It exists in the biaxially-oriented polyester film for optics characterized by film haze being 0 to 3.0% of range.

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 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. In the present invention, it is necessary to contain 2.0 to 10.0 mol% of a third component other than the main constituent, preferably 2.5 to 10 mol%, more preferably 3.0 to 8.0. Mol%.

  As a method for containing the third component, a copolymer polyester containing a predetermined amount of a copolymer component as a raw material for producing a film may be used, or a copolymer polyester containing a copolymer component larger than a predetermined amount. Further, a raw material obtained by blending a copolymer polyester or homopolyester having a small content of copolymer components may be used.

  Examples of the third component herein include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like as the dicarboxylic acid component, and P-oxybenzoic acid as the oxycarboxylic acid. Examples of the glycol component include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like. Among these, when diethylene glycol, triethylene glycol, or 1,4-cyclohexanedimethanol is used, the optical unevenness of the film due to the orientation and thickness unevenness of the polymer can be efficiently reduced, and the flatness of the film and This is preferable in that heat resistance and dimensional stability can be maintained at a high level. Here, as a third component contained in the polyester, diethylene glycol by-produced from ethylene glycol during polymerization is also included.

  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 reaction of a lower alkyl ester of a dicarboxylic acid and a diol 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 may be used. Preferably, the amount of antimony compound is zero or 100% or less as antimony to reduce film dullness. .

  The polyester 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 preferably 0.40 to 0.90 dl / g.

  You may mix | blend particle | grains in the polyester layer in this invention with the main objective of providing lubricity. The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness, and specific examples thereof include, for example, 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 also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more if necessary.

  Further, the average particle size of the particles used is usually preferably 0.01 to 5 μm. 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. It may become inferior.

  Furthermore, 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. 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 application, 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 9 to 300 μm, preferably 20 to 260 μm, and more preferably 25 to 200 μm. When used as a member of an optical product, it is usually in the range of 75 to 260 μm.

  The film of the present invention has a film haze of 0 to 3.0%, preferably 0 to 1.5%, more preferably 0 to 1.2%, and particularly preferably 0 to 1.0%. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 3.0%, it is unsuitable for optical use.

  The polyester film for optical use of the present invention, particularly for display, has a color tone b * value measured by a single transmission method of preferably -5 to +3, more preferably -4 to +2, particularly preferably -3. The range is 5 to +1. When the b * value exceeds +3, it is often unsuitable in that the yellow color is strong and the color tone of the image becomes inferior or the luminance becomes low when used for a display. On the other hand, in the case of a film lower than -5, there is a problem of color tone. However, in the case of a polyester film, the b * value is not lower than -5, so that a method such as using an additive is used. However, it is not preferable because it may cause problems such as bleeding out of the additive and reliability during long-term use. 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 polyester is heated to an unnecessarily high temperature during polymerization and film formation. Further, it is possible to adopt methods such as preventing the melting time from becoming longer and reducing the amount of the recycled raw material.

In the film of the present invention, the sum of the front and back surfaces of the 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, more preferably 10 .0mg / ^{m 2,} particularly preferably not more than 8.0 mg / ^{m 2.} When the amount of oligomer deposition on the film surface exceeds 15 mg / m ² , the oligomer may crystallize on the surface to reduce the transparency of the film, or it may dissolve in the functional layer provided on the film and affect the properties. It is easy to cause problems such as.

  In order to make the oligomer precipitation amount on the film surface by heat treatment in the above range, a laminated film consisting of at least three layers by coextrusion in particular, and using a polyester with a low oligomer content in the outermost layer constituting the surface layer, By suppressing the oligomer precipitation on the film surface by providing the coating layer inline or offline, the amount of oligomer deposition on the film surface after the heat treatment can be within the above range.

  The film of the present invention can be formed into a laminated structure using a co-extrusion method. In this case, it is preferable that the outermost layer thickness is usually 3 μm or more and ¼ or less of the total thickness on one side. If the thickness is less than 3 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. On the other hand, if it is thicker than 1/4 of the total thickness, the amount of particles to be blended in the outermost layer may increase and the transparency may be impaired.

  When carrying out the present invention with a single layer, it is also preferable that the film should contain as little particles as possible, and the coating layers on the front and back sides should contain particles.

  When it manufactures as this laminated | multilayer film, content of the 3rd component in this invention needs to make the amount of 3rd component contained in the whole film with respect to polyester of the whole film into the above-mentioned range. This is because the prevention of optical unevenness, which is a problem to be improved in the present invention, is related to the transmitted light of the film, and is not limited to the film surface or the inside, but is related to the entire characteristics.

  Moreover, when adding additives, such as the said ultraviolet absorber and dye, it is preferable to mix | blend with the intermediate | middle layer of a laminated | multilayer film.

In the film of the present invention, foreign matters having a maximum diameter of 150 μm or more present in the film are usually 0.0 pieces / m ² , and foreign matters having a maximum diameter of 30 μm or more are usually 1.5 pieces / m ² or less, preferably It is preferable that it is 1.0 piece / m ² or less. When the foreign substance with the maximum diameter of 150 μm or more is 0.0 pieces / m ² or the foreign substance with the maximum diameter of 30 μm or more is 1.5 pieces / m ² or less, it is an image when used as a member of LCD or PDP Defects in the surface cause deterioration of quality.

In addition to this, the film of the present invention preferably has 1.0 mm / 10 m ² or less scratches having a length of 1.0 mm or more present on the surface, and more preferably 0.50 / 10 m ² or less. Further, the number of scratches having a width of 10 μm or more is preferably 10 / m ² or less, more preferably 5 / m ² or less, regardless of the length. If there are many scratches present on the film surface, the LCD or PDP image will have defects, leading to quality degradation. In order to overcome such problems, a method of preventing foreign matters during polyester raw material production and film production and removing foreign matters by using a high-accuracy filter is adopted, and in order to prevent scratches, a stretching process is performed simultaneously. It is effective to use the axial stretching method. In addition to this, it is preferable to take measures such as suppressing uneven speed at the time of contact with each roll in the winding process and preventing foreign matter from entering between the roll and the film.

  The thus-obtained film of the present invention is used for various optical applications. In this case, it is preferable that the optical unevenness of the film due to the orientation of the polymer and the unevenness of the thickness is reduced. The difference between the maximum and minimum retardation values in the plane of the film measured by the method is 100 nm or less, preferably 50 nm or less, more preferably 30 nm or less. When satisfying such requirements, it is possible to obtain a product having excellent image sharpness, brightness and uniformity when used in optical applications.

  Next, 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 and melted. 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. The stretching step in the present invention is a step of performing simultaneous biaxial stretching.

  As a simultaneous biaxial stretching method that can be used in the present invention, a clip is connected in a tenter with a pantograph to open a clip interval, and the clip is driven by a screw-shaped shaft to adjust the interval between the screw grooves. In the form of opening, etc., a system in which stretching is performed simultaneously in the longitudinal direction and the transverse direction can be used. Furthermore, a more preferable form in the simultaneous biaxial stretching method is a driving method using a linear motor. In this system, the clips are not connected individually, but each clip is independently speed-controlled by a magnetic field generated by a linear motor, and has a feature of widening the clip interval. In addition, since it is possible to control how to expand the clip only by controlling the magnetic field, it may be difficult to change the conditions such as the draw ratio in the above-described pantograph-type or screw-type simultaneous biaxial drawing machine, while the change of conditions, etc. Needless to say, stretching can be easily performed in multiple stages, and there is an advantage that stretching in the machine direction and the transverse direction can be performed while finely controlling the stretching conditions and selecting more appropriate conditions.

  As for the line speed, it is difficult to obtain a fast line speed with a pantograph type or screw type simultaneous biaxial drawing machine, whereas with a linear motor drive type simultaneous biaxial drawing machine, a normal sequential biaxial drawing machine. Another advantage is that the line speed can be increased to the same level as that of a stretching machine.

  The stretching temperature of the simultaneous biaxial stretching in the present invention is selected so that the temperature of the stretched resin sheet is within the range of the glass transition temperature (Tg) ° C.-5 ° C. of the polyester to the temperature rising crystallization temperature (Tc) −10 ° C. It is preferable to do so. The stretch ratio of the thermoplastic polyester resin sheet in the present invention may be stretched in the range of 1.2 to 50 times, preferably 4 to 30 times in terms of area by simultaneous biaxial stretching in the longitudinal and lateral directions. Further, the ratio of the stretching ratio in the machine direction and the transverse direction is not particularly limited, but in order to obtain a normal biaxially oriented film in which the machine direction and width are balanced, 1.0 ± 0.4, preferably 1.0 ±. It should be 0.2.

    In the present invention, the stretching itself can be stretched up to a predetermined ratio in a single stretch, but in particular, when a linear motor drive type biaxial stretching apparatus is used, the stretching is divided into two or more times to be predetermined. It is also possible to stretch to a magnification. In this case, it is possible to set conditions according to the state of the resin sheet by changing the stretching temperature and stretching speed in each stretching stage.

  The film stretched in this manner can be heat-set in order to improve flatness, heat-resistant dimensional stability, and the like. For this heat setting, heat setting is preferably performed in the simultaneous biaxial drawing machine used in the drawing step.

  This heat setting is normally performed for 1 to 30 seconds in a temperature range of 150 ° C. or higher and lower than the melting point of the film. Furthermore, after that, relaxation treatment within 30% can be performed in the vertical, horizontal, or both directions at the same temperature as the heat setting temperature or in an arbitrary temperature range of the cooling process.

  In the present invention, as described above, two or three or more polyester melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. As the layer structure, an A / B structure using an A raw material and a B raw material, or an A / B / A structure, and further using a C raw material to form an A / B / C structure or other film. Can do. For example, the surface shape of the A layer can be designed using specific particles as the A raw material, and a film having an A / B or A / B / A structure can be formed using a raw material not containing particles as the B raw material. In this case, since the raw material of B layer can be selected freely, a cost advantage etc. are large. Further, even if the recycled material of the film is blended with the B layer, the surface roughness can be designed by the surface A layer, so that the cost advantage is further increased.

  In particular, since the film of the present invention is used for optical applications, a hard coat layer, an antireflection layer, an antiglare layer, or the like is provided, or a vapor deposition layer or the like is provided. A coating layer as an undercoat layer can be provided for the purpose of improving adhesion or preventing charging in order to keep the surface clean. 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 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 adhesiveness. 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 with an offline coat after manufacture of a film as needed. Moreover, it does not matter on one side or both sides. 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.

  In addition, since the film of the present invention is used for optics, it is also preferable to form a functional multilayer thin film for the purpose of preventing dust reflection due to reflection of external light and static electricity, as well as electromagnetic shielding, in addition to improving adhesiveness. .

  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 transparency of the film is hindered and the sharpness of the image 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. The content of the particles in the coating layer is preferably 10% by weight or less, more preferably 5% by weight or less as an appropriate addition amount that does not impair the transparency.

  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 may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. 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-mentioned 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 optical applications, the coating layer surface is not coated. This is a problem when an antireflection layer or the like is further provided on the surface of the substrate. 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 of coating spots (N) is preferably 0 to 20, more preferably 10 or less, particularly 3 or less per 30 m ^{2 of the} film.

  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 exerts particularly excellent effects when used for optics, and as specific members thereof, a reflector for a backlight for a liquid crystal display, a diffuser, a prism sheet, Lens sheets, brightness enhancement films, protective films for liquid crystal panels, release films for processes during panel manufacturing, and so-called PDP filters for plasma displays, electromagnetic shielding, near infrared shielding, color correction, ultraviolet shielding Effectively used as a substrate that requires a high degree of transparency, such as a film substrate having various functions such as antireflection, and a process for manufacturing a panel, and an image forming screen for a projection television. Is done.

  The film of the present invention has excellent optical properties such as transparency, low haze and optical uniformity, and contributes to quality improvement and energy consumption reduction such as prevention of image defects when it is used as an optical product. When used as various optical members used in LCDs, PDPs, etc., the advanced characteristics are exhibited and the industrial value is extremely 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. 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) Film haze Film haze was measured with an integrating sphere turbidimeter “NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7105.

(5) b * value The color tone was measured according to the method of JISZ-8722 using Tokyo Denshoku Co., Ltd. color analyzer TC-1800MKII.

(6) Measurement of the number of scratches The surface of the film was observed in a range of 20 m ² under a three-wavelength fluorescent lamp, and the number of recognized scratches was marked and counted. When it was unclear whether the length was 1.0 mm or more, the length was confirmed with an optical microscope. In addition, even when the scratch was minute and the width was unclear, the number was counted with an optical microscope.

(7) Measurement of the number of coating spots The film surface having a width of 1500 mm and a length of 20 m (area 30 m @ 2) was irradiated with a halogen lamp, and the surface of the film was visually observed to calculate the number of coating spots of 0.5 mm or more. In this example, the number of scratches having a width of 10 μm or more was counted for the long sample, but it can also be estimated by measurement using an A4 cut plate as described above.

(8) Suitability of optical member As a representative of the optical member, characteristics when used as a diffusion plate were evaluated. That is, an acrylic binder containing particles was applied to one side of the film to form a light diffusion layer. The obtained diffusion sheet was incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints.

Luminance level (evaluated using a luminance meter, compared with the case of using a conventional PET film, that is, the film of Comparative Example 1 in the present invention)
A: Brightness increased by 3% or more, and significant improvement was observed. B: Brightness increased by 1% or more, and improvement was observed. C: Brightness was not improved or decreased.

・ Luminance unevenness A: Almost no unevenness B: Some unevenness is seen but practical level C: Unevenness is significant and affects the image on the liquid crystal display

-Image defects A: No defects exist B: Defects are rarely seen, but are practically usable C: Defects are conspicuous or the number is large, resulting in a problem that the yield as a display product decreases.

Examples and Comparative Examples are shown below, and the production method of the polyester used for this 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 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.68 and a diethylene glycol content of 1.0 mol%.

<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 2.5 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide were 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 and a diethylene glycol content of 1.0 mol%.

<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 obtained polyester (C) had an intrinsic viscosity of 0.67, and the diethylene glycol content in the polymer was 3.8 mol%.

<Method for producing polyester (D)>
The starting material is 100 parts by weight of dimethyl terephthalate, 54 parts by weight of ethylene glycol and 25 parts by weight of 1,4-cyclohexanedimethanol, 0.011 part by weight of tetrabutoxy titanate is used as a catalyst, and the reaction start temperature is 150 ° C. The reaction temperature was gradually increased with the distillation of methanol, and the temperature was raised to 230 ° C. after 3 hours, and the reaction was continued for another hour. Thereafter, the temperature of the reaction product was gradually raised from 230 ° C., and the pressure was gradually reduced from the normal pressure, and finally the temperature was 280 ° C. and the pressure was 0.3 mmHg. After stopping the reaction, the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (D) was 0.72, the content of 1,4-cyclohexanedimethanol was 33 mol%, and the content of diethylene glycol was 1.0 mol%.

<Method for producing polyester (E)>
In the production method of the polyester (A), the polyester (E) is produced using the same method as the production method of the polyester (A) except that the starting dicarboxylic acid is 80 parts by weight of dimethyl terephthalate and 20 parts of isophthalic acid. Obtained. The obtained polyester (E) had an intrinsic viscosity of 0.67 and a content of diethylene glycol of 1.0 mol%.

(Example 1) <Production of polyester film>
Two vents using the above-mentioned polyester (B) and (C) mixed at a ratio of 12% and 88%, respectively, as the raw material for the A layer and 100% of the polyester (C) as the raw material for the B layer. Each is supplied to a twin screw extruder and melted at 285 ° C., and each layer is composed of two layers and three layers (A / B / A) with the A layer as the outermost layer (surface layer) and the B layer as the intermediate layer. The sheet was extruded and extruded from the die, and cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, after applying a coating agent having the composition shown below, it is led to a tenter having a linear motor driven simultaneous biaxial stretching machine, further preheated and heated with hot air of 95 ° C., and longitudinally 3 at 95 ° C. Simultaneous biaxial stretching was performed 3 times and 3.5 times in the transverse direction. Thereafter, the film was heat-set in a hot air atmosphere at 230 ° C. in the same tenter, subjected to 3% relaxation treatment in the longitudinal direction and the transverse direction at the same temperature, and then rolled up into a roll to obtain a polyester film having a thickness of 188 μm. Got. The thickness of each layer of the obtained film was 10/168/10 μm. The thickness of the coating layer was 0.08 μm.

(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 = 31/16/3/22/21/7 (molar ratio); b Is an emulsion polymer (emulsifier: anionic surfactant) of methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio); c is hexamethoxymethylmelamine ( (Melamine-based crosslinking agent); d is an aqueous dispersion (inorganic particles) of silicon oxide having a particle diameter of 0.06 μm.

(Example 2)
In Example 1, the stretching ratio in the longitudinal direction was 3.6, the stretching ratio in the transverse direction was 3.7 times, the thickness of each layer was 10/105/10 μm, and other film forming conditions and coating conditions were set in Example 1. In the same manner, a polyester film having a thickness of 125 μm was obtained.

(Example 3)
In Example 1, the raw material of the B layer is a raw material obtained by mixing polyester (D) and (C) at a ratio of 5% and 95%, respectively, and the A layer is polyester (B), (C), and (D), respectively. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the raw materials were mixed at a ratio of 10%, 85% and 5%.

Example 4
The raw material of the B layer is a raw material in which the polyesters (E) and (C) are mixed at a ratio of 10% and 90%, respectively, and the A layer is 10% and 80% of the polyesters (B), (C), and (E), respectively. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the raw material was mixed at a ratio of 10%.

(Example 5)
In the production of the polyester (C), diethylene glycol was increased as a glycol component to obtain a polyester containing 6 mol% of diethylene glycol. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the polyester was used in place of the polyester (C) in Example 1. When the content of diethylene glycol increased, the thermal stability of the polyester became slightly inferior, and the b * value of the obtained film slightly increased.

(Example 6)
In Example 2, a polyester film having a thickness of 125 μm was obtained in the same manner as in Example 2 except that the longitudinal draw ratio was 3.2 and the transverse draw ratio was 4.0.

(Comparative Example 1)
Example 1 except that polyester (B) and (A) were mixed at a rate of 12% and 88%, respectively, and the mixed raw material was used as the raw material for layer A, and the raw material of 100% polyester (A) was used as the raw material for layer B. In the same manner as above, a polyester film having a thickness of 188 μm was obtained.

(Comparative Example 2)
In Example 3, the raw material of the B layer is a raw material in which the polyesters (D) and (C) are mixed at a ratio of 35% and 65%, respectively, and the A layer is the polyester (B), (C), and (D), respectively. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 3 except that the raw materials were mixed at a ratio of 12%, 53%, and 35%. The resulting film has too much content of the third component, so when used for optics, its properties deteriorate, heat resistance is insufficient, and the flatness of the film during actual use is insufficient. It was seen.

(Comparative Example 3)
An unstretched sheet was manufactured with the same raw material composition and thickness structure as in Example 1, and a biaxially oriented film was manufactured using a sequential biaxial stretching method. That is, the unstretched sheet was stretched 3.4 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 same composition as in Example 1. The film was stretched 3.6 times at 120 ° C., heat treated at 230 ° C., and then relaxed 2% in the transverse direction to obtain a laminated polyester film having a thickness of 188 μm. The coating thickness was adjusted to be the same as in Example 1 by adjusting the solid content concentration of the coating solution.

(Comparative Example 4)
A single layer polyester film using one extruder was prepared using raw materials in which polyesters (B) and (C) were mixed at a ratio of 12% and 88%, respectively. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the film thickness was 188 μm.

The physical properties and optical member suitability of the obtained film are summarized in Table 1. It can be seen that a film satisfying the requirements of the present invention is highly suitable for optical use.
Table 1

In Table 1 above, DEG means diethylene glycol, 1,4-CHDM means 1,4-cyclohexanedimethanol, and IPA means isophthalic acid. Moreover, only the main component was described about the 3rd component shown in Table 1. Further, the third component content of Example 3, Example 4, and Comparative Example 2 includes DEG.

  The film of the present invention can be suitably used as, for example, various optical members used in LCDs, PDPs, and the like, and protective films and release films used in the manufacturing process of products in the optical field.

Claims (4)

A film comprising a polyester containing a third component other than the main constituent components in a total range of 2.0 to 10.0 mol%, obtained by a simultaneous biaxial stretching method, and having a film haze of 0 to 3.0. % Biaxially oriented polyester film for optical use. The optically biaxially oriented polyester film according to claim 1, wherein the number of scratches having a length of 1.0 mm or more present on the surface is 1.0 / 10 m ² or less. The main component is polyethylene terephthalate, and the third component is one or more selected from diethylene glycol, triethylene glycol, and 1,4-cyclohexanedimethanol. The biaxially oriented polyester film for optics described. The optically biaxially oriented polyester film according to any one of claims 1 to 3, wherein the optically biaxially oriented polyester film is used for an optical member for a liquid crystal display, a plasma display, an organic EL, and a projection television.