JP2006182832A - Biaxially drawn polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film having a thickness of ≥50μm, suitable as a part of devices such as LCD, PDP, organic EL and projection display, free from optical defect and polarization unevenness and having good optical properties. <P>SOLUTION: The biaxially drawn polyester film contains ethylene terephthalate as a main constituent and has the half crystallization period of the film of 30-100 sec at 180°C and a film haze of ≤3.0%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a biaxially stretched polyester film, and more specifically, various optical members used for liquid crystal displays (hereinafter abbreviated as LCD), plasma displays (hereinafter abbreviated as PDP), and the like, A polyester film that is suitably used for protective films, release films, etc. used in the manufacturing process of products in the optical field, has excellent optical properties, and can contribute to improving the quality of optical products and reducing energy consumption. The present invention relates to an axially stretched polyester film.

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 members, electrical insulating films, films for metal laminates, films to be attached to glass surfaces such as glass displays, and protective films for various members.
Polyester film has recently been widely used for various optical films. Base films such as prism sheets for LCD members, light diffusion sheets, reflectors and touch panels, base films for antireflection, base films for explosion-proof displays, 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 pattern and does not have defects such as foreign matter and scratches that affect the image. Is required. In addition, even when polarized light is used, it is necessary that there is no polarization unevenness caused by uneven orientation or thickness unevenness of the polymer.
As these optical films, a relatively thick polyester film having a thickness of about 50 to 300 μm is used, but as the thickness increases, it becomes difficult to uniformly heat or cool the film. Among them, crystallization unevenness occurs in the polyester film, causing optical defects and the above-mentioned uneven polarization, and a solution is desired.
JP 2001-261856 A JP 2003-49011 A JP 2003-341000 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that there is no optical defect or polarization unevenness in a polyester film suitably used for members such as LCD, PDP, organic EL, projection display, etc. It is to provide a polyester film having good mechanical properties.

  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 polyester film having specific physical properties, and have completed the present invention.

  That is, the gist of the present invention is a polyester film having ethylene terephthalate as a main constituent, the film having a half crystallization time at 180 ° C. of 30 to 100 seconds, and a film haze of 3.0% or less. The characteristic biaxially stretched polyester film exists.

Hereinafter, the present invention will be described in detail.
First, the polyester resin used in the biaxially stretched polyester film of the present invention (hereinafter sometimes referred to as a film) will be described.

  The polyester resin used in the present invention is obtained by a polycondensation reaction by a conventional method of polyvalent carboxylic acid and polyhydric alcohol. Further, two or more kinds of polyester resins obtained in the same manner and having different melting points can be mixed to form a composition. As the composition of the polyester resin constituting the film, the ethylene terephthalate unit is 80 mol% or more. Preferably. When the ethylene terephthalate unit is 80 mol% or less, the mechanical strength and heat resistance of the film are poor.

  Examples of dicarboxylic acid components other than terephthalic acid and its ester-forming derivatives include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, and dodecadicarboxylic acid. An acid, cyclohexane dicarboxylic acid, etc. are mentioned. Examples of diol components other than ethylene glycol include trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, neopentyl glycol, diethylene glycol, polyethylene glycol, and polytetramethylene ether glycol. And aliphatic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol and the like.

  In particular, as a preferred form for achieving the object of the present invention, the third component other than ethylene terephthalate is selected from isophthalic acid, 2,6-naphthalenedicarboxylic acid, diethylene glycol, triethylene glycol, and 1,4-cyclohexanedimethanol. Those obtained by copolymerizing one or more components are preferred. The amount of these copolymerization components is preferably 3 to 20 mol%, but the copolymerization amount of diethylene glycol is 1 to 8 mol%, preferably 1 to 5 mol%, more preferably 1 to 4 mol%. It is preferable. When the amount of diethylene glycol exceeds 8 mol%, the heat resistance is deteriorated, and when the polyester resin is melt-extruded, coloring and IV decrease may be caused.

  The polyester used in the present invention can be obtained by a conventionally known method, for example, a method of directly obtaining a polyester having a low polymerization degree by reaction of a dicarboxylic acid and a diol, or a lower alkyl ester of a dicarboxylic acid and a diol by a conventionally known transesterification catalyst. After the reaction, it can be obtained by a method of performing a polymerization reaction in the 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 alone or in combination. However, the use of a germanium compound or a titanium compound can reduce the half-crystallization time of the film to a predetermined value. Since it is easy to adjust to the range, it is preferable. Moreover, when using an antimony compound, it is preferable that the content shall be 250 ppm or less, Preferably it is 200 ppm or less, More preferably, it is 150 ppm or less. When the antimony compound is 250 ppm or more, the catalyst residue works as a crystallization nucleus material of the polyester resin, which is not preferable because the crystallinity of the film becomes high. Further, if the antimony compound is 250 ppm or more, it may cause dullness of the film, which is not preferable.

  The polyester to be used may be converted into chips 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 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, phosphoric acid. Examples of the particles include magnesium, silicon oxide, kaolin, aluminum oxide, and titanium oxide. 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 as required.

  Further, the average particle size of the particles used is usually preferably 0.01 to 5 μm. When the average particle diameter is less than 0.01 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, when the average particle diameter exceeds 5 μm, the surface roughness of the film becomes too rough and the transparency May become inferior.

  Furthermore, the content of the particles in the polyester is usually 0 to 1.0% by weight, preferably 0.003 to 0.5% by weight. When the particle content exceeds 1.0% by weight, the transparency of the film may be insufficient.

  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 of producing the polyester, but preferably at the stage of esterification or after completion of the transesterification reaction. Further, it is carried out by a method of blending dried particles and a polyester raw material using a kneading extruder with a vent.

  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 20 to 500 μm, preferably 50 to 300 μm, more preferably 70 to 250 μm.

  The film of the present invention has a film haze of 3.0% or less, preferably 2.0% or less, more preferably 1.5% or less, and particularly preferably 1.0% or less. When the film haze exceeds 3.0%, the transparency is inferior, which is not preferable.

  The polyester film of the present invention has a color tone b * value measured by one transmission method of preferably −5 to +3, more preferably −4 to +2, and particularly preferably −3.5 to +1. . When the b * value exceeds +3, the yellowish color is strong, and when used for a display, the color tone of the image may become inferior or the luminance may be lowered. . On the other hand, there is a problem of color tone in a film lower than -5, but in the case of a normal polyester film, the b * value is not lower than -5, so a method such as using an additive is used. This method may cause problems such as bleeding out of additives and reliability during long-term use. In order to make a film of 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, the polyester becomes a temperature higher than necessary during polymerization and film formation, Methods such as preventing the melting time from becoming long and reducing the blending amount of the regenerated raw material can be employed.

In the film of the present invention, the amount of ethylene terephthalate cyclic trimer deposited after heating at 180 ° C. for 10 minutes is usually 2.0 mg / m ² or less, preferably 1.0 mg / m ² or less, more preferably 0.5 mg / m ^2. m ² or less. The method of bringing the ethylene terephthalate cyclic trimer amount into the above range is not particularly limited, but the method of using a raw material in which the cyclic trimer amount is reduced in advance by a solid layer polymerization method for the polyester resin to be used, catalyst deactivation method A method of coating an oligomer precipitation preventing layer is preferably used.

  An important characteristic of the film of the present invention is the crystallinity of the film. Usually, a polyester film mainly composed of ethylene terephthalate has the fastest crystallization speed in the vicinity of 150 to 190 ° C., and it is necessary to control the crystallinity of the film in this temperature range in order to obtain a high-quality optical film. It is.

  The film of the present invention has a film half-crystallization time at 180 ° C. of 30 to 100 seconds, preferably 30 to 80 seconds, and more preferably 40 to 70 seconds. When the half-crystallization time at 180 ° C. is 30 seconds or less, the crystallization property is too high, and thus, during the film forming process, for example, when the molten resin is cooled with a casting roll to form an amorphous sheet, uneven cooling occurs. In addition, since crystallization unevenness occurs in the film sheet, it causes polarization unevenness and optical defects such as haze unevenness. On the other hand, when the half crystallization time at 180 ° C. exceeds 100 seconds, the crystallinity is insufficient, and thus the heat resistance and mechanical properties are inferior.

In the film of the present invention, it is preferable that the second-order transition temperature Tg [° C.] and the melting point Tm [° C.] measured by a differential scanning calorimeter satisfy the following formulas, respectively.
65 ≦ Tg ≦ 90
200 ≦ Tm ≦ 260

  Here, Tg and Tm are the temperature of DSC raised to 290 ° C. at a heating rate of 50 ° C./min, held for 5 minutes, rapidly cooled with liquid nitrogen, and again up to 290 ° C. at a heating rate of 20 ° C./min. The inflection point accompanying the glass transition observed when the temperature is raised is Tg, and the endothermic peak temperature accompanying melting is Tm. When Tg is 65 ° C. or less, heat resistance and mechanical properties tend to be inferior, and when it exceeds 90 ° C., productivity may be deteriorated. Moreover, when Tm is 200 degrees C or less, there exists a tendency for it to be inferior to heat resistance and a mechanical characteristic, and when it exceeds 260 degreeC, there exists a tendency for it to be inferior to economical efficiency.

  The layer structure of the film of the present invention is not particularly limited, and may be either a single layer or a laminated structure. For example, it is preferable to use a three-layer structure and to mix a recycled resin in the intermediate layer because the economy is improved. Moreover, when adding additives, such as a ultraviolet absorber, when it mix | blends with the intermediate | middle layer of a film as a laminated film, since the bleeding out of an additive can be prevented, it is preferable.

In the film of the present invention, foreign matter having a maximum diameter of 150 μm or more existing on the film surface is usually 0.0 pieces / m ² or less, and foreign matter having a maximum diameter of 30 μm or more is usually 1.5 pieces / m ² or less, preferably Is preferably 1.0 piece / m ² or less. When it is used as a member of LCD or PDP when the foreign matter with a maximum diameter of 150μm or less is 0.0 pieces / m ² or less, or the foreign matter with a maximum diameter of 30μm or more is 1.5 pieces / m ² or less Defects in the image may cause a reduction in quality. Furthermore, the number of scratches having a width of 10 μm or more present on the film surface is preferably 10 / m ² or less, more preferably 5 / m ² or less. If the number of scratches having a width of 10 μm is larger than 10 / m ² , the quality of the LCD or PDP image may be similarly lowered. 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. It is necessary to take measures such as suppressing unevenness in speed at the time of contact with each roll in the process and preventing foreign matter from being mixed between the roll and the film.

  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 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. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 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 stretch 2-6 times and to heat-process at 150-240 degreeC for 1 to 60 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  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 a 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 as an A / B / C structure or other film. be able to. 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 A layer as the surface layer, so that the cost advantage is further increased.

  Moreover, although the thickness of the film of this invention is not specifically limited, As an optical use, the thickness of about 20-250 micrometers is normally used suitably. The effect of the film of the present invention increases as the thickness increases, and the effect is exerted on a film having a thickness of 50 μm or more, and further 100 μm or more.

  When the film of the present invention is used for optical applications, a hard coat layer, an antireflection layer, an antiglare layer, and the like are provided, so that the coatability and adhesiveness when forming these layers are improved, or A coating layer as an undercoat layer can be provided for the purpose of preventing charging in order to keep the surface clean. In forming such a coating layer, the method of performing a film manufacturing process, 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 is dried or cured. This is preferable in that it can be performed in the film forming process. Such a 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 urethane 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 provide an application layer offline after manufacture of a film as needed. Moreover, the surface which provides an application layer does not ask | require one side and both surfaces. The material for the coating layer may be either water-based and / or solvent-based in the case of off-line coating, but is preferably water-based or water-dispersed in the case of in-line coating.

  When 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 used as the coating agent in the present invention, particularly preferred polymers are those having a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher, and carboxylic acid residues. And at least a part of the polymer is made aqueous with amines 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 blending 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 sharpness of the film tends to decrease.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, vanadium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and easy to control the particle size. 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 particles in the coating layer is preferably 10% by weight or less, and more preferably 5% by weight or less as an appropriate addition amount that does not inhibit transparency.

  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 increasing 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 thereof include glycol derivatives such as ethyl cellosolve, methyl cellosolve and propylene glycol monomethyl ether, ketones such as dioxane, tetrahydrofuran and acetone, and amides such as N-methylpyrrolidone. 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, an air doctor coater or other coating device as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” is used. be able to.

  The coating layer may be formed only on one side of the polyester film or on both sides. When only one surface is formed, other properties 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 exceeds 0.5 μm, the films are likely to stick to each other, and particularly when the coated film is re-stretched due to the high strength of the film, it tends to stick to the roll in the process. There is a tendency to become. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  When such a coated film is applied to an optical application, coating missing on the surface of the coating layer is a problem when an antireflection layer or the like is 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. In some cases, oligomers and dust adhering to the core may become the core, causing the coating agent to repel and become loose. 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. Since such foreign substances include oligomers adhered or deposited on the film, reducing the amount of oligomers contained in the film also has the effect of reducing coating loss.

When the film of the present invention thus obtained has a coating layer, the number of coating spots is usually 10 pieces / m ² or less, more preferably 5 pieces / m ² or less, particularly preferably 3 pieces / 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 eliminate the coating loss as much as possible.

  According to the present invention, it is possible to provide a polyester film that is free from optical defects and polarization unevenness and has good optical properties in a polyester film that is suitably used for members such as LCD, PDP, organic EL, and projection display. The industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited at all to these examples, unless the summary is exceeded. In addition, the evaluation method of the film of this invention is as follows.

(1) Intrinsic viscosity ([η])
A measurement sample was dissolved in a solvent of phenol / tetrachloroethane = 50/50 (parts by weight) to prepare a solution having a concentration c = 0.01 g / cm ³ , and a relative viscosity η _r with the solvent was measured at 30 ° C. The intrinsic viscosity [η] was determined from the following formula.
(Η _r −1) / c = [η] + [η] ² k′c
(In the above formula, k ′ is 0.33)

(2) Secondary transition temperature (Tg), melting point (Tm)
Using a differential scanning calorimeter “MDSC 2920 type” manufactured by TA Instruments Inc., about 5 mg of a polyester resin was used as a sample, and it was determined by the method described in the specification.

(3) Measurement of Third Component (Copolymerization Component) Content Regarding a solution in which a resin sample is dissolved in a deuterated chloroform / hexafluoroisopropanol (weight ratio: 7/3) mixed solvent to a concentration of 3% by weight. Then, using a nuclear magnetic resonance apparatus (“JNM-EX270 type” manufactured by JEOL Ltd.), 1H-NMR was measured, each peak was assigned, and the content of the copolymer component was calculated from the integrated value of the peak.

(4) Average particle diameter (d50: μm)
The value of 50% integral (weight basis) in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 type manufactured by Shimadzu Corporation) was defined as the average particle size.

(5) 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.

(6) Semi-crystallization time at 180 ° C. (second)
It measured using the Kotaki Seisakusho make and MK-701 type | mold. That is, a film completely melted by heating at 300 ° C. for 5 minutes is immersed in a thermostatic chamber (set temperature of 180 ° C.) installed between the orthogonal polarizing plates, and an optical anisotropic crystal accompanying the crystallization of the film The amount of increase in transmitted light due to the components was measured, and the time required for the crystallinity to be halved was calculated using the following Abram formula.

（上記式中、Χ_ｃは結晶化度、ｋは結晶化速度常数、ｎはアブラミ指数、ｔは時間（秒）Ｉ_０は透過強度（始点）、Ｉ_ｔは透過強度（t秒後）、Ｉ_ｇは透過強度（終点）である）

(In the formula, chi _c crystallization degree, k is the crystallization rate constant, n represents Avrami exponent, t is the time (in seconds) I ₀ is the transmitted intensity (starting point), I _t is the transmitted intensity (t seconds after), _Ig is transmission intensity (end point))

(7) Film surface defect Light is applied with a halogen lamp to a film surface having a width of 1500 mm and a length of 20 m (area 30 m ² ) in a dark room, and the film surface is visually observed. The number of scratches having a width of 10 μm or more and other surface defects having a diameter of 30 μm or more were counted, and the number of surface defects per 1 m ^{2 of} the film was calculated.

(8) Polarization unevenness An acrylic binder containing particles was applied to form a light diffusion layer, and 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. .
A: Unevenness is hardly seen B: Unevenness is slightly seen but practical level C: Unevenness is noticeable and affects the image on the liquid crystal display

Next, the polyester raw material used in each example will be described.
<Method for producing polyester A>
Using terephthalic acid as the dicarboxylic acid component, ethylene glycol as the polyhydric alcohol component, and antimony trioxide as a catalyst, agglomerated silica particles (average particle size 2.2 μm, content 0.3 wt. %) Was produced.

<Method for producing polyester B>
Polyester B was produced by a conventional melt polymerization method using terephthalic acid as the dicarboxylic acid component, ethylene glycol and diethylene glycol as the polyhydric alcohol component, and antimony trioxide as a catalyst.

<Method for producing polyester C>
Polyester C was produced by a conventional melt polymerization method using terephthalic acid as the dicarboxylic acid component, ethylene glycol and diethylene glycol as the polyhydric alcohol component, and tetrabutyl titanate as a catalyst.

<Method for producing polyester D>
Polyester D was produced by a conventional melt polymerization method and solid phase polymerization method using 2,6-naphthalenedicarboxylic acid as a dicarboxylic acid component, ethylene glycol as a polyhydric alcohol component, and antimony trioxide as a catalyst.

<Method for producing polyester E>
Polyester E was produced by a conventional melt polymerization method using terephthalic acid and isophthalic acid as the dicarboxylic acid component, ethylene glycol as the polyhydric alcohol component, and germanium dioxide as the catalyst.

<Method for producing polyester F>
Polyester F was produced by a conventional melt polymerization method using terephthalic acid as the dicarboxylic acid component, ethylene glycol and 1,4-cyclohexanedimethanol as the polyhydric alcohol component, and tetrabutyl titanate as a catalyst.
The properties of the obtained polyester are shown in Table 1 below.

(In the above table, TPA is terephthalic acid, NDCA is 2,6-naphthalenedicarboxylic acid, IPA is isophthalic acid, EG is ethylene glycol, DEG is diethylene glycol, CHDM is 1,4-cyclohexanedimethanol, Sb is antimony, Ge is Germanium, Ti means titanium respectively)

  The raw materials obtained by mixing the polyesters A and C at a ratio of 10% by weight and 90% by weight, respectively, are used as the A layer raw material, and the raw material of 100% polyester C is used as the raw material for the B layer. Supplied, melted at 285 ° C., co-extruded 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, electrostatically applied through the die Using an adhesion method, the sheet was cooled and solidified on a cooling roll (diameter 1.5 m) having a surface temperature set to 40 ° C. to obtain an unstretched sheet. Next, the film was stretched 3.3 times in the machine direction at a film temperature of 81 ° C. using the difference in peripheral speed of the roll, and then applied to a tenter after applying a coating agent having the composition shown below, and 3. The film was stretched 6 times, heat treated at 225 ° C., and then relaxed 2% in the transverse direction to obtain a laminated polyester film having a thickness of 100 μm. Moreover, the film forming speed of the film was 25 m / min. Each layer thickness of the obtained film was 5/90/5 μm. The film properties obtained were good as shown in Table 2.

(Coating agent composition: weight ratio)
a / b / c / d = 47/20/30/3
Here, a is terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio) polyester dispersion 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-based crosslinking agent)
d is an aqueous dispersion of silicon oxide (inorganic particles) having a particle size of 0.06 μm.

  In Example 1, the A layer raw material is a raw material in which polyesters A, C, and D are mixed at a ratio of 10% by weight, 87% by weight, and 3% by weight, the B layer raw material is 100% polyester C, and the thickness of each layer is 10 / A laminated polyester film having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the film forming conditions and the coating conditions were changed to 105/10 μm. The film properties obtained were good as shown in Table 2.

  In Example 1, the raw materials for layer A were polyesters A, C, and E mixed at a ratio of 10% by weight, 50% by weight, and 40% by weight, respectively, and the raw materials for layer B were 60% by weight for polyesters C and E, respectively. A laminated polyester film having a thickness of 188 μm (5/178/5 μm) was obtained in the same manner as in Example 1 except that the raw materials mixed at a ratio of 40% by weight were used. The film properties obtained were good as shown in Table 2.

  In Example 1, the raw materials for layer A were polyesters A, C, and F mixed at a ratio of 12 wt%, 78 wt%, and 10 wt%, respectively, and the raw materials for layer B were 90 wt% of polyesters C and F, respectively. A laminated polyester film having a thickness of 188 μm (5/178/5 μm) was obtained in the same manner as in Example 1 except that the raw material mixed at a ratio of 10% by weight was used. The film properties obtained were good as shown in Table 2.

  A thickness of 188 μm (10/168/10) was obtained in the same manner as in Example 1, except that the raw material for layer B was mixed with polyester C and F at a ratio of 50% by weight and 50% by weight, respectively. 10 μm) of laminated polyester film was obtained. The film properties obtained were good as shown in Table 2.

(Comparative Example 1)
In Example 1, a raw material in which the A layer raw material was mixed with polyesters A and B in proportions of 15% by weight and 85% by weight, respectively, and the B layer raw material was in proportions of 15% by weight and 85% by weight for polyesters A and B, respectively. A laminated polyester film having a thickness of 100 μm (5/90/5 μm) was obtained in the same manner as in Example 1 except that the raw materials mixed in the above were used. As shown in Table 2, the obtained film characteristics were high in haze, resulting in poor quality as an optical film. Moreover, since the crystallization speed was high, the evaluation of uneven polarization was also poor.

(Comparative Example 2)
Example 1 is the same as Example 1 except that the raw material for layer A is a raw material in which polyesters A and B are mixed at a ratio of 10% by weight and 90% by weight, respectively, and the raw material for layer B is 100% by weight of polyester B. Thus, a laminated polyester film having a thickness of 188 μm (5/178/5 μm) was obtained. As shown in Table 2, the obtained film characteristics were too high in crystallinity of the film, so that optical defects associated with microcrystallization of polyester occurred on the film surface, and the evaluation of polarization unevenness was poor.

(Comparative Example 3)
In Example 1, a laminated polyester film having a thickness of 100 μm (5/90/5 μm) was obtained in the same manner as in Example 1 except that the B layer material was 100% by weight of polyester F. Since there were too many copolymerization components, it was inferior in heat resistance, and thickness was bad and polarization unevenness was bad. Moreover, there were many fractures, and there was a problem in continuity.

The film of the present invention can be suitably used as various optical members used in, for example, LCDs and PDPs.

Claims (1)

A biaxially stretched polyester film characterized by being a polyester film comprising ethylene terephthalate as a main constituent, having a film half-crystallization time at 180 ° C. of 30 to 100 seconds, and a film haze of 3.0% or less. .