JP2008299152A - Optical polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film which causes neither unevenness nor a defect, realizes high luminance and enables to give a high-quality image when used as a lens sheet substrate. <P>SOLUTION: The polyester film is a biaxially oriented polyester film for a lens sheet which comprises a polyester having a coating layer on at least one surface and has a total light transmittance of ≥91.0% and an angle (θ3) between a main orientation axis direction and MD (longitudinal direction) of the film in a range of 40-70°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to an optical polyester film, and in particular, is a polyester film used as a base material for a lens sheet, which is an optical member used for a liquid crystal display (hereinafter abbreviated as LCD). It is related with the polyester film which is excellent in and can contribute to the quality improvement and energy consumption reduction of the said optical product.

  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 in various optical films, especially base films for LCD members, such as lens sheets, light diffusion sheets, reflectors, and touch panels, 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 and scratches that affect the image. Necessary. In addition, it is necessary for obtaining an image having no unevenness even when polarized light is used, in particular, that there is no retardation unevenness due to uneven orientation of the polymer and uneven thickness.

  The polyester film is usually obtained by subjecting an amorphous sheet obtained by melt extrusion to a sheet shape and rapid cooling and solidification to the longitudinal direction and the transverse direction, 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 is 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 in addition to this, it is necessary to have further optically advantageous properties.

Japanese Patent Publication No.59-5216 JP 59-217755 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is that, when used as a lens sheet substrate, there is no unevenness or defect, high brightness is achieved, and a high-quality image is provided. It is in providing the polyester film which can be performed.

  That is, the gist of the present invention is a film made of polyester having a coating layer on at least one surface, has a total light transmittance of 91.0% or more, and is formed by the main orientation axis direction and the MD (longitudinal direction) of the film. The present invention resides in a biaxially oriented polyester film for a lens sheet, wherein the angle (θ3) is in the range of 40 to 70 °.

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 this invention, it is preferable to contain 2.0-10.0 mol% of 3rd components other than a main structural component, More preferably, it is 2.5-10 mol%, Most preferably, it is 3.0-8.0. Mol%.

  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, optical unevenness of the film due to polymer orientation and thickness unevenness 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.

  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.

  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.

  The polyester film of the present invention preferably uses a polyester produced using a titanium compound as a catalyst in order to highly satisfy optical properties. Further, the film of the present invention preferably contains a phosphorus compound in addition to the titanium compound used as a catalyst. The content of titanium element in at least one layer of the film of the present invention is preferably 20 ppm or less, more preferably 10 ppm or less, and the lower limit is usually 1 ppm, preferably 2 ppm. When there is too much content of a titanium compound, an oligomer is by-produced in the process of melt-extruding polyester, and a film having high transparency with a low oligomer cannot be obtained. Further, when no titanium element is contained, the productivity at the time of production of the polyester raw material is inferior, and the polyester raw material reaching the target degree of polymerization cannot be obtained. On the other hand, the amount of phosphorus element is preferably 1 ppm or more, more preferably 5 ppm or more, and the upper limit is usually 300 ppm, preferably 200 ppm, more preferably 100 ppm. By containing a specific amount of the above-described titanium compound and containing a phosphorus compound, it is possible to exert a remarkable effect on the reduction of the contained oligomer. When there is too much content of a phosphorus compound, gelatinization will occur and it may become a foreign material and cause the quality of a film to fall. In the present invention, when the titanium compound and the phosphorus compound are contained in the above-described range, the by-product of the oligomer can be prevented, and the effect of the present invention is highly obtained.

  The thickness of the layer satisfying the contents of the titanium compound and the phosphorus compound is preferably 60% or more, more preferably 80% or more, particularly preferably the entire layer of the film satisfies this requirement with respect to the total thickness of the film. It is desirable to do. When the film of the present invention is used as a prism sheet substrate, light is transmitted through the film, so that all the polyesters constituting the film are involved in the optical properties. For this reason, the one where the ratio of the layer which satisfy | fills the requirements regarding this contained metal is high is preferable.

  Further, the layer containing the titanium compound and the phosphorus compound preferably contains no antimony element, usually 100 ppm or less, preferably 60 ppm or less, and most preferably substantially free, ie 10 ppm or less. If the amount of the antimony element is too large, it may be reduced by the phosphorus compound during melt extrusion and aggregate to cause foreign matters, or the film may become dark and the transparency may be impaired.

  The film of the present invention satisfies the above problems to a high degree and exhibits particularly excellent effects for optical use. That is, by using a titanium compound as a catalyst, darkening as in the case of using antimony can be prevented, and a film having excellent transparency can be obtained, and by adding a phosphorus compound at the same time, the color tone of the film can be improved. Demonstrate the effect of not worsening. Specifically, when the b * value of the film is high, that is, when the film is used for optical purposes, the brightness may decrease and the image may be deteriorated when used for optics. It exhibits excellent properties in terms of transparency and color tone.

  In the present invention, by mixing a polyester produced by using titanium as a catalyst and a polyester containing a predetermined amount of a phosphorus compound, it is possible to obtain a film having the above-described amounts of titanium and phosphorus, thereby obtaining an excellent film. Can exert the effect. In other words, when a polyester is produced by polymerizing using titanium as a catalyst, adding a phosphorus compound in the polymerization process slows down the polymerization rate, leading to deterioration in productivity, or longer polymerization time, which in turn increases the yellowness. Problems may occur. On the other hand, when the polyester of the titanium catalyst is subjected to a melt extrusion process in which a film is produced in the absence of a phosphorus compound, there is a problem that yellowness increases due to thermal deterioration. In the present invention, in order to prevent the occurrence of such a problem, a method in which a polyester containing a predetermined amount of a phosphorus compound is prepared as a master batch and mixed with a polyester using a titanium catalyst is preferable. Examples of the method for producing a master batch of a phosphorus compound include a method of polymerizing with a germanium catalyst, a method of polymerizing with a minimum amount of an antimony catalyst, and a method of adding in a step of melt extrusion to a polyester with a titanium catalyst. It is particularly preferable to employ a catalyst.

  In the polyester film of the present invention, as the polyester constituting the layer containing the titanium compound and the phosphorus compound within the aforementioned range, if a raw material obtained by solid-phase polymerization of the polyester formed into a chip after melt polymerization is used, This is preferable because the amount of oligomer contained in can be reduced.

  In the polyester film of the present invention, the amount of the oligomer contained in the layer containing the titanium compound and the phosphorus compound within the aforementioned range is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, particularly preferably. 0.3 wt% or less. When the amount of oligomer in the polyester layer is small, the amount of oligomer contained in the polyester film of the present invention is reduced and the effect of preventing oligomer precipitation on the film surface is particularly high.

  The polyester used in the present invention may be obtained by forming a chip after melt polymerization and subjecting it to further solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the polyester of the present invention 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 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 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. 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.

  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 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 500 μm, preferably 20 to 350 μm, and more preferably 50 to 250 μm.

  The film of the present invention has a total light transmittance of 91.0% or more, preferably 91.5% or more, more preferably 92.0% or more. The film of the present invention is widely used for optical applications because of its excellent light transmittance, but when the film haze is less than 91.0%, it is unsuitable for optical use.

  In order to satisfy such total light transmittance, the film of the present invention selects the particle type, particle size, content, polyester composition and catalyst and film forming conditions, but the particles have a low refractive index and a content of It is preferable that the polyester composition and the catalyst satisfy the above-described requirements, and it is necessary to prevent temperature unevenness and stretching unevenness in the stretching process during film formation.

  An important requirement for the film used as the substrate of the lens sheet for LCD backlight in the present invention is that the angle between the main orientation angle of the film and MD is in the range of 40 to 70 °, preferably in the range of 45 to 70 °. That is. Especially in the case of a surface light source in which a cold cathode tube is arranged at the edge of the backlight and the light guide plate, reflector, diffuser plate, prism sheet, etc. are used as members, especially when the orientation angle of the base film of the prism sheet is in a specific range It has been found that high brightness can be obtained. Usually, a polyester film has a main orientation direction, so that a certain degree of brightness can be theoretically realized by punching the shape from the film so that this direction becomes a specific angle. If the film is used, a member can be formed in a predetermined size in the vertical and horizontal directions, so that the efficiency is high and it is extremely advantageous in terms of cost, productivity, accuracy, and the like. For this reason, in the film of the present invention, the range in the horizontal direction that satisfies the requirements for the specific main orientation direction is the product width range of the film roll, specifically the range of 500 mm or more, and further the range of 600 mm or more. Is preferably satisfied.

  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 inappropriate in that the color tone of the image becomes inferior or the luminance becomes low when used for a display because of its strong yellowishness. On the other hand, although there is a problem of color tone in a film lower than -5, since a b * value is not lower than -5 in a normal polyester film, a method such as using an additive is used. Then, there may be a problem in the bleed out of the additive and the 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 crystallizes on the surface and lowers the transparency of the film, or dissolves in the functional layer provided on the film and affects the properties. Sometimes.

  In order to make the oligomer precipitation amount on the film surface by heat treatment within the above range, it is particularly a laminated film composed of at least three layers by coextrusion, and a polyester having a low oligomer content is used as the outermost layer constituting the surface layer, By providing the coating layer inline or offline, the oligomer deposition amount on the film surface after the heat treatment can be controlled within the above range by suppressing oligomer precipitation on the film surface.

  The film of the present invention can be formed into a laminated structure using a co-extrusion method. In this case, the thickness of the outermost layer is preferably 3 μm or more, more preferably 5 μm or more and 1/4 of the total thickness in terms of the thickness of only one side. Hereinafter, it is more preferably 1/5 or less, particularly preferably 1/10 or less. When the thickness is less than 3 μm, oligomers (cyclic trimers) contained in the inner layer are 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.

  On the other hand, when carrying out the present invention with a single layer, it is also preferable that the film is made to contain no particles as much as possible and the particles are contained in the front and back coating layers.

  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, relates to the transmitted light of the film and relates not only to the film surface and the inside but also 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.

  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 perform 2-6 times stretching and to heat-process at 150-240 degreeC for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable.
Further, the present invention relates to the main orientation direction, and it is preferable to make the film forming conditions specific in order to realize it. For example, it is more preferable that the stretching ratio in the transverse direction is increased to a range of 3 to 6, the relaxation rate is decreased to 10% or less, and the heat treatment temperature is 225 ° C. or lower. .

  The film obtained in the present invention is more preferably a film near the center. 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 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 by 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 or solvent-based for off-line 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 it is formed only on one side, an application layer different from the above-mentioned application layer can be formed on the opposite side as necessary to give other characteristics. 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. Moreover, 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, the coating layer surface coating is problematic 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 film surface, which repels the coating agent and causes coating leakage, oligomers attached to the film surface, There may be a case where dust becomes a nucleus and the coating agent repels and leaves as a 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 50 or less per 10 m ^{2 of} film, more preferably 30 or less, particularly preferably 10 or less. is there. 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 an excellent effect particularly when used for optics, but as a specific member thereof, as a base material that requires high transparency of a light diffusion plate for liquid crystal display Used effectively.

  The film of the present invention is excellent in optical properties such as transparency, low haze, and optical uniformity, and can contribute to improving the quality of optical products and reducing energy consumption, and is used as a light diffusion plate member. In that case, its advanced characteristics are demonstrated and its 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.), 1H-NMR was measured, each peak was assigned, 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) Quantification of amount of metal element and phosphorus element in film Using a fluorescent X-ray analyzer (model “XRF-1500” manufactured by Shimadzu Corporation), the film FP method was used. The amount of elements in the film was determined by sheet measurement, and the detection limit in this method is usually about 1 ppm.

(5) Total light transmittance Total light transmittance was measured with an integrating sphere turbidimeter “NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7105.

(6) Angle between the main orientation direction and MD Using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Instruments, the length of one side is 300 mm in the width direction of the product, and the length of the side perpendicular to it is 210 mm. The film was cut and measured. When the film has a predetermined thickness, the ratio of the portion where the angle between the main orientation direction and MD is in the range of 40 to 70 ° is 70% or more, A rank, and B is 60% or more. Rank was C rank when less than 60%.

(7) Optical member suitability As a representative optical member, characteristics when used as a prism sheet were evaluated. That is, an acrylic binder containing particles was applied to one side of the film to form a prism layer. The obtained prism sheet was incorporated into a backlight unit, and the quality of the planar light emission obtained and the contribution to the yield of high quality products were evaluated from the following viewpoints.
Luminance level (Evaluated using a luminance meter and compared with the case of using the film of Comparative Example 2 in the present invention)
A: The brightness of the film has been improved and the yield of good products has been improved. B: The brightness of the film has been improved and can be used. C: The brightness has been lowered in many parts of the film, and the yield of good products has been reduced.

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)>
Starting from 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, tetrabutyl titanate as a catalyst is taken into the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. Was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially completed, and then a polycondensation reaction was performed for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.63 and a diethylene glycol content of 4.0 mol%.

<Manufacture of polyester (B)>
Starting from 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol, magnesium acetate / tetrahydrate is added as a catalyst to the reactor, the reaction start temperature is set to 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. Was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. This reaction mixture was transferred to a polycondensation tank, orthophosphoric acid was added, and germanium dioxide was added to carry out a polycondensation reaction for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65 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 (B) was 0.65. The diethylene glycol content was 1.0 mol%.

<Method for producing polyester (C)>
In the manufacturing method of polyester (A), polyester (C) is obtained using the same method as the manufacturing method of polyester (A) except that the starting materials are 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol. It was. The obtained polyester (C) had an intrinsic viscosity of 0.68, and the diethylene glycol content in the polymer was 1.0 mol%.

<Method for producing polyester (D)>
Polyester (D) using a method similar to the production method of polyester (A) except that starting materials were 100 parts by weight of dimethyl terephthalate, 54 parts by weight of ethylene glycol, and 25 parts by weight of 1,4-cyclohexanedimethanol. Got. The intrinsic viscosity of the obtained polyester (D) was 0.70, 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 of the polyester (A), a polyester (E) chip was obtained by the same method as the general production method except that the amount of tetrabutyl titanate was changed. The obtained polyester (E) had an intrinsic viscosity of 0.62 and a diethylene glycol content of 4.0 mol%.

<Method for producing polyester (F)>
In the production of polyester (A), polyester (F) was obtained using the same method as the general production method except that antimony trioxide was used as a polymerization catalyst. The intrinsic viscosity of the obtained polyester (F) was 0.65, and the diethylene glycol content in the polymer was 4.0 mol%.

<Method for producing polyester (G)>
In the production method of polyester (A), 0.18 part of silica particles having an average particle diameter of 2.0 μm dispersed in ethylene glycol was added, and the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.66. Polyester (G) was obtained using a method similar to the method for producing polyester (A). The obtained polyester (G) had an intrinsic viscosity of 0.66 and a diethylene glycol content of 1.0 mol%.

  In the above table, DEG means diethylene glycol, and 1,4-CHDM means 1,4-cyclohexanedimethanol.

Example 1:
Polyester (A), (B), and (G) chips are blended at a rate of 91%, 5%, and 4%, respectively, and melt-extruded at 290 ° C by a twin-screw extruder with a vent, and electrostatically applied. By using this method, it was cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. to obtain an unstretched sheet. Next, the film was stretched 3.2 times in the longitudinal direction at 85 ° C., and then a coating agent having the composition shown below was applied to both sides of the film and then led to a tenter, and stretched 3.6 times in the lateral direction at 115 ° C. Heat treatment was performed at 220 ° C. to obtain a 125 μm thick polyester film. The contents of antimony, titanium, and phosphorus in the obtained film were 0 ppm (below the lower limit of detection), 5 ppm, and 50 ppm, respectively. The diethylene glycol content was 3.6 mol%. The thickness of the coating layer was 0.05 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 (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) D) is an aqueous dispersion (inorganic particles) of silicon oxide having a particle size of 0.06 μm.

Example 2:
In Example 1, polyester (A), (B), (D), and (G) chips were used as raw materials of 85%, 1%, 10%, and 4%, respectively, and stretched 3.5 times in the transverse direction. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the heat treatment was performed at 225 ° C.

Example 3:
A polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the polyesters (B), (E), and (G) in Example 1 were changed to 5%, 90%, and 5%, respectively.

Comparative Example 1:
A polyester film having a thickness of 300 μm was obtained in the same manner as in Example 1 except that the polyesters (B), (C), and (G) were changed to 5%, 91%, and 4%, respectively.

Comparative Example 2:
The film forming conditions were the same as in Example 1 except that the polyesters (A), (B), (D), and (G) were 50%, 5%, 30%, and 15%, respectively. 200 μm. 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:
In Example 1, a polyester film having a thickness of 150 μm was obtained in the same manner as in Example 1 except that the polyesters (F) and (G) were 93% and 7%, respectively.

Example 4:
A polyester film having a thickness of 200 μm was obtained in the same manner as in Example 1 except that the polyesters (A), (B), and (G) were changed to 64%, 35%, and 6%, respectively.

Comparative Example 4:
In Example 1, a polyester film having a thickness of 125 μm was obtained in the same manner as in Example 1 except that the film was stretched 4.5 times in the longitudinal direction and 2.8 times in the transverse direction and heat-treated at 220 ° C. Near the part was used.

The physical properties and optical member suitability of the obtained film are summarized in Table 3 below. It can be seen that a film satisfying the requirements of the present invention has high suitability for optical use.

  In the above table, FD means longitudinal stretching temperature, FDR means longitudinal stretching ratio, TD means transverse stretching temperature, TDR means transverse stretching ratio, and HS means heat treatment temperature.

  The film of the present invention can be suitably used as a base material for a lens sheet, which is an optical member used in, for example, an LCD.

Claims (1)

It is a film made of polyester having a coating layer on at least one surface, has a total light transmittance of 91.0% or more, and an angle (θ3) formed by the main orientation axis direction and the MD (longitudinal direction) of the film is 40 to 70. A biaxially oriented polyester film for a lens sheet, characterized by being in the range of °.