JP2007146056A - Light scattering biaxially-oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light scattering biaxially-oriented polyester film having antistatic properties and being produced with excellent productivity, which can be suitably used as a base film for a film or sheet in which sticking of dust by static electricity generated at the time of peeling of a protective film etc., tends to become a problem, for example, a diffusion plate and a prism sheet of a backlight unit, and a lens sheet for a screen for a projector. <P>SOLUTION: The light scattering biaxially-oriented polyester film comprises organic particles having an average particle size of 2.0-40 μm in an amount of 0.10-10 wt.% and has a surface resistivity of 5×10<SP>12</SP>Ω or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a film or sheet in which dust due to static electricity generated when peeling off a protective film or the like is likely to be a problem, such as a diffuser plate or prism sheet of a backlight unit, or a substrate such as a lens sheet of a projector screen The present invention relates to a light-scattering biaxially stretched polyester film used as a film.

  The polyester film is easily charged with static electricity, so it easily adsorbs dust in the air. Therefore, the quality of the device used as a part may be deteriorated.

  In order to solve these problems, an antistatic light diffusion sheet used in a surface light source device has been proposed. For example, according to Patent Document 1, a transparent conductive resin layer is applied to the surface of a transparent biaxially stretched polyester film, and a concavo-convex layer is provided thereon to form a light diffusive sheet. However, there is a problem that the manufacturing process until the light diffusive sheet is made becomes complicated.

  As for a biaxially stretched polyester film containing a light diffusing agent having antistatic properties, for example, Patent Document 2 proposes a polyester film containing several percent of silica particles having an average particle diameter of 4 μm. However, when inorganic particles are used for the light scattering agent, there is a problem in that the filter pressure rises easily in the resin extrusion line, resulting in poor productivity.

JP 2001-159703 A JP-A-2-207291

  The present invention has been made in view of the above circumstances, and a problem to be solved is to provide a light-scattering biaxially stretched polyester film having antistatic properties and excellent productivity.

  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 biaxially stretched polyester film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is that the organic particle having an average particle diameter of 2.0 to 40 μm is contained in an amount of 0.10 to 10 wt%, and the surface resistivity is 5 × 10 ¹² Ω or less. It exists in a scattering biaxially stretched polyester film.

Hereinafter, the present invention will be described in detail.
The polyester in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1, This polyester is mainly composed of an ester with glycol such as 4-cyclohexanedimethanol. The polyester can be obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by a transesterification reaction between an aromatic dicarboxylic acid dialkyl ester and a glycol, followed by polycondensation, or an aromatic dicarboxylic acid diglycol. It can also be obtained by a method such as polycondensation of an ester. Typical examples of the polyester include polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate (PEN), boribylene terephthalate, and the like. Such a polyester may be a homopolymer that is not copolymerized, 40 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and 40 mol% or less of the diol component is a diol component other than the main component. It may be a certain copolyester or a mixture thereof.

  In the present invention, organic particles are contained in order to develop light scattering properties. The organic particles may be contained in the entire film or in at least one layer of a co-extruded laminated film having two or more layers.

  The average particle size of the organic particles used in the present invention is in the range of 2.0 to 40 μm, preferably 2.5 to 30 μm. When the average particle size is less than 2.0 μm, the light scattering property is lowered. On the other hand, when the average particle diameter exceeds 40 μm, the increase in the pressure of the filter becomes large, resulting in poor productivity. In addition, if the eyes of the filter to be used are enlarged, the foreign matter in the film increases.

  The 5% pyrolysis temperature of the organic particles used in the present invention in an inert atmosphere by a thermogravimetric analyzer is preferably 300 ° C. or higher, more preferably 310 ° C. or higher. When the thermal decomposition temperature is less than 300 ° C., the generation of thermally deteriorated products may cause the transmitted light of the film to become yellowish and the appearance quality may deteriorate.

  The organic particles used in the present invention preferably have a functional group on the surface. It is considered that particles having a functional group are easily charged and an electrostatic repulsive force between the particles acts to improve dispersibility. Without a functional group, the particles tend to aggregate between the particles and the filter life is reduced. Furthermore, the affinity with polyester is reduced, and large voids are formed around the particles, so that the particles are easily dropped in the film manufacturing process and the film processing process, and the film itself is easily damaged. Preferred functional groups are a carboxylic acid group, a hydroxyl group, an epoxy group, and an ester group.

  In addition, the organic particles in the film of the present invention have a hardness that can be deformed under biaxial stretching conditions, and the degree of deformation is preferably in the range of 1.1 to 5.0, and 1.2 to 4 0.0 is more preferable. It is considered that organic particles having a degree of deformation of less than 1.1 are less elastically deformed when subjected to shear stress at a polyester resin dissolution temperature of 250 to 350 ° C., and the filter life is reduced. On the other hand, when the degree of deformation exceeds 5.0, the light scattering property tends to decrease.

  The organic particle content of the film of the present invention is in the range of 0.10 to 10% by weight, preferably in the range of 0.20 to 8% by weight. When the organic particle content is less than 0.10% by weight, a film having light scattering properties intended by the present invention cannot be obtained. On the other hand, when the organic particle content exceeds 10% by weight, the film is easily broken and the productivity is lowered.

  In addition, the organic particle used by this invention may be a single component, and may use two or more components simultaneously. Specific examples of organic particles include organic particles such as melamine resin, polystyrene, organic silicone resin, and acrylic-styrene copolymer.

  Further, the haze of the film of the present invention is preferably 10% or more, more preferably 20% or more. If the haze is less than 10%, the light scattering property tends to be inferior.

  The film of the present invention may contain additives such as an ultraviolet absorber, an antistatic agent, an antioxidant, and a fluorescent brightening agent as necessary.

The surface resistivity of the film of the present invention is 5 × 10 ¹² Ω or less, preferably 1 × 10 ¹² Ω or less, more preferably 5 × 10 ¹¹ Ω or less, and particularly preferably 1 × 10 ¹¹ Ω or less. If the surface resistivity exceeds 5 × 10 ¹² Ω, static electricity is generated when the film is wound or rolled back, and static electricity accumulates on the film, causing surface defects due to electric discharge, or when the protective film is peeled off. Causes dust to adhere to the film surface.

In order to obtain a polyester film having a surface resistivity of 5 × 10 ¹² Ω or less, a method of forming a coating layer having antistatic properties by applying a coating solution having a specific composition to a polyester sheet before stretching and the whole film Or a coextruded layer forming the surface layer may contain an antistatic agent. The coating liquid of the former method contains a nonionic, anionic, cationic, or amphoteric organic compound, a compound generally referred to as an antistatic agent that absorbs static electricity by absorbing moisture. Specific examples of the antistatic agent include the following.

  Nonionic antistatic agents include polyether compounds or derivatives thereof. Specific examples thereof include polyethylene glycol, polypropylene glycol, polyethylene glycol / polypropylene glycol block copolymers, polyoxyethylene diamine, polyether / polyester / polyamide. Block copolymers fall under this category. Examples of the anionic antistatic agent include compounds having sulfonic acid, carboxylic acid, phosphoric acid, boric acid and salts thereof.

  Of these, sulfonic acid antistatic agents are often used because of their strong antistatic properties and industrial availability. Examples thereof include polystyrene sulfonate, lithium polystyrene sulfonate, sodium polystyrene sulfonate, potassium polystyrene sulfonate, cesium polystyrene sulfonate, and ammonium polystyrene sulfonate. Of course, copolymers of other copolymerizable monomers with styrene sulfonic acid and its salts are also included.

  A low molecular weight sulfonic acid compound is also effective. Examples thereof include alkyl sulfonates and alkyl sulfates. For example, sodium dodecylbenzene sulfonate, sodium α-olefin sulfonate, sodium lauryl sulfate, sodium cetyl sulfate, sodium stearyl sulfate, sodium oleyl sulfate, and the like.

  Typical examples of the cationic antistatic agent include primary amine hydrochlorides, secondary amine hydrochlorides, tertiary amine hydrochlorides, and quaternary ammonium salts as low molecular weight compounds. Examples of amines used include monomethylamine, dimethylamine, trimethylamine, laurylamine, dilaurylamine, lauryldimethylamine, stearylamine, distearylamine, stearyldimethylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, N, N-diethylethylenediamine, aminoethylethanolamine, pyridine, morpholine, guanidine, hydrazine and the like can be mentioned.

  Examples of the quaternary ammonium salt include lauryltrimethylammonium chloride, lauryldimethylbenzylammonium chloride, cetylpyridinium chloride, cetylpyridinium bromide, stearamidemethylpyridinium chloride, lauryltrimethylammonium methosulfate, and the like. Examples of the polymeric cationic antistatic agent include a quaternary ammonium salt type styrene polymer, a quaternary ammonium salt type aminoalkyl (meth) acrylate polymer, a quaternary ammonium salt type diallylamine polymer, and the like.

  Specific examples include polyvinylbenzyltrimethylammonium chloride, quaternized polydimethylaminoethyl methacrylate, and polydiallyldimethylammonium chloride.

  Amphoteric antistatic agents include carboxylate-type amphoteric surfactants with amine salt-type cations, carboxylate-type amphoteric surfactants with quaternary ammonium salt-type cations (so-called betaine-type amphoteric surfactants) Is famous. For example, sodium laurylaminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, etc. are mentioned.

  Furthermore, in the coating layer, one or more of water-soluble or water-dispersible binder resins other than those described above can be used in combination as required. Examples of the binder resin include polyester, polyurethane, acrylic resin, vinyl resin, epoxy resin, amide resin, and the like. In these, each skeleton structure may have a composite structure substantially by copolymerization or the like. Examples of the binder resin having a composite structure include acrylic resin graft polyester, acrylic resin graft polyurethane, vinyl resin graft polyester, and vinyl resin graft polyurethane.

  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 of the coating agent to the film and the antistatic property, the film may be subjected to chemical treatment or discharge treatment before 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 in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the antistatic property is inferior.

  In addition, the coating layer may contain a surfactant, an antifoaming agent, a coating property improver, a thickener, an organic lubricant, organic particles, inorganic particles, an antioxidant, and an ultraviolet absorber as necessary. .

  Next, examples of the antistatic agent in the latter method include the following compounds as described in JP-A-2002-225173.

  Cationic compounds such as primary amine salts, tertiary amines, quaternary ammonium compounds, sulfurized oils, sulfated amide oils, sulfated ester oils, fatty alcohol sulfates, alkyl sulfates, fatty acid ethyl sulfones Acid salts, alkyl sulfonates, alkyl naphthalene sulfonates, alkyl benzene sulfonates, phosphate esters, and the like, partial fatty acid esters of polyhydric alcohols, ethylene oxide adducts of fatty alcohols, fatty amines or Nonionic compounds such as fatty acid amide ethylene oxide adduct, alkylphenol ethylene oxide adduct, alkylnaphthol ethylene oxide adduct, polyethylene glycol, fatty acid ester of alkyldiethanolamine, carboxylic acid derivatives, imidazo Those such emissions derivatives of amphoteric systems. Of these, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, lithium alkyl sulfonate, lithium alkyl benzene sulfonate and the like are preferable from the viewpoint of antistatic performance and transparency. The addition amount is 0.05 to 5% by weight in the whole film. If it is less than 0.05% by weight, the antistatic effect is inferior. On the other hand, addition of more than 2% by weight does not significantly improve the antistatic effect.

  Moreover, you may contain additives, such as a ultraviolet absorber, antioxidant, and a fluorescent whitening agent, as needed.

  The thickness of the film of this invention is 20-300 micrometers. If it is less than 20 μm, the workability may be poor. On the other hand, when the thickness exceeds 300 μm, the weight may increase or the handleability may deteriorate.

Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.
1) Method for Producing Film Containing Antistatic Agent A dried polyester containing an antistatic agent in advance is supplied to an extruder and heated to a temperature equal to or higher than the melting point of the polyester to be melted. Next, it is extruded as a molten sheet from a T die, and the molten sheet is rapidly cooled to below the glass transition temperature on a rotary cooling drum to obtain an amorphous unstretched film. At this time, in order to improve the flatness of the unstretched film, the adhesion between the unstretched film and the rotating cooling drum may be improved by an electrostatic application adhesion method, a liquid application adhesion method, or the like. And a uniaxially stretched film is obtained by extending | stretching an unstretched film in the longitudinal direction (longitudinal stretching) using a roll stretching machine. The stretching temperature at this time is stretched in a temperature range of minus 10 ° C. to plus 40 ° C. of the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.0 to 6.0 times. Furthermore, longitudinal stretching may be performed in only one stage, or may be performed in two or more stages. Thereafter, the biaxially stretched film is obtained by stretching the uniaxially stretched film in the width direction (lateral stretching) using a tenter stretching machine. The stretching temperature at this time is stretched in a temperature range of + 50 ° C. from the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 7.0 times, more preferably 3.5 to 6.0 times. Further, the transverse stretching may be performed only in one stage, or may be performed in two or more stages. Moreover, you may perform simultaneous biaxial stretching which performs vertical and horizontal simultaneously. And a film is manufactured by heat-processing a biaxially stretched film. The heat processing temperature at this time is 130-250 degreeC. When the biaxially stretched film is heat-treated, the biaxially stretched film may be relaxed within 20%.

2) Manufacturing method of film provided with antistatic coating layer This is a method of coating at any stage from melt extrusion of polyester to biaxial stretching, heat setting and winding. Usually applied to either a substantially amorphous unstretched sheet obtained by melting and quenching, a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction), or a biaxially stretched film before heat setting. To do. In these, the method of extending | stretching to a horizontal direction after apply | coating to a uniaxially stretched film is excellent. According to such a method, since film formation and coating layer drying can be performed at the same time, there is an advantage in manufacturing cost, and it is easy to apply a thin film for stretching after application, and excellent in transparency. Since the applied heat treatment is at a high temperature that cannot be achieved by other methods, the coating layer and the polyester film are firmly adhered.

  INDUSTRIAL APPLICABILITY The present invention can provide a biaxially stretched polyester film having a small filter pressure increase, excellent productivity, and excellent antistatic properties and light scattering properties, and the industrial value of the present invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement methods and terms used in the examples and the present invention are defined as follows.

(1) Added particle average particle diameter The particles were observed using an electron microscope to determine the maximum diameter and the minimum diameter, and the average was defined as the particle diameter of one particle. This is done for at least 100 particles in the film. The average particle diameter of the particle group is the weight average diameter of these particles.

(2) Deformation After fixing the film piece with an epoxy resin, it is cut with a microtome so that the cut surface of the film is parallel to the principal axis direction of the molecular chain orientation, and the cut surface is observed with a scanning electron microscope. For at least 50 particles that fall within ± 10% of the average particle size for each particle, the ratio of the maximum diameter to the minimum diameter is calculated, and the arithmetic average is taken as the degree of deformation.

(3) Haze The haze is measured by applying light in the longitudinal stretching direction of the film on the surface of the single layer film or the surface of the layer A according to method 3 (60 ° glossiness) of JIS Z-8741-1983.

(4) Thermal decomposition temperature of organic particles After drying organic particles under reduced pressure at 60 ° C. for 4 hours, measurement was performed using a thermobalance (Rigaku Denki Co., TAS100 type) under a nitrogen gas atmosphere under a temperature rising rate of 20 ° C./min Measure the temperature at the time of 5% weight loss.

(5) Surface resistivity 16600A, which is a concentric electrode of Yokogawa Hewlett-Packard's inner electrode 50 mm diameter and outer electrode 70 mm diameter, is placed on the sample in an atmosphere of 23 ° C. and 50% RH, and a voltage of 100 V is applied. Then, the surface resistivity of the sample is measured with 4329A, a high resistance meter manufactured by the same company.

(6) Increase in filter pressure Using a filter with a collection efficiency of 20 μm and a collection diameter of 50 to 60%, a resin with a particle content of 2% by weight is extruded at a discharge rate of 20 kg / h before film production, and before the filter. Measure the pressure of the resin. If the pressure difference exceeds 0.5 megapascals in 1 hour, the filter life is rejected (x), and if it is 0.5 megapascals or less, it is passed (o).

(7) Light-scattering property Place a paper with MS Gothic font printed with numbers 1 to 9 with 8 points on a desk under fluorescent light, and observe the distance from a distance of 30 cm through the test film to distinguish the numbers. Measure the distance between the missing film and the paper. The light scattering property is evaluated as follows.
○: Distance at which numbers cannot be seen is 5 cm or less, light scattering is good ×: Distance at which numbers cannot be seen exceeds 5 cm, poor light scattering

(8) Antistatic property Using a Static Honest Meter (trade name) of Shishido Trading Company, a film was applied by applying a voltage of 10 kV to a discharge electrode 2 cm above the sample in an atmosphere of 23 ° C. and 50% RH. Discharging is stopped after charging and the amount of charge is saturated. Next, the charge attenuation of the sample is measured with an electrometer located 2 cm above the sample, and the following criteria are used to determine the half life.
○: Half-life is 3 seconds or less and excellent in antistatic property △: Half-life is over 3 seconds and 6 seconds or less, antistatic property is slightly good ×: Half-life is over 6 seconds, antistatic property Inferior

(Raw material adjustment)
・ Polyester a
Polyethylene terephthalate having an intrinsic viscosity of 0.65 and a melting point of 253 ° C. synthesized by a conventional polycondensation.

・ Polyester b
Crosslinked styrene-acrylic organic particles having a hydroxyl group on the surface of a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation and having an average particle size of 6 μm and a thermal decomposition temperature of 329 ° C. Kneaded 4.0% by weight.

・ Polyester c
Crosslinked styrene-acrylic organic particles having a glycidyl group on the surface of a polyethylene terephthalate resin synthesized by a conventional polycondensation having an intrinsic viscosity of 0.68 and a melting point of 253 ° C., an average particle size of 10 μm, and a 5% thermal decomposition temperature of 331 ° C. Is kneaded and contained at 8.0% by weight.

・ Polyester d
Spherical porous silica particles having an average particle size of 10 μm and a hydroxyl group on the particle surface were kneaded into a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation to contain 4.0% by weight. Is.

・ Polyester e
Cross-linked acrylic organic having an intrinsic viscosity of 0.68 synthesized by a conventional polycondensation, a polyethylene terephthalate resin having a melting point of 253 ° C., an average particle diameter of 1.7 μm, a 5% thermal decomposition temperature of 290 ° C. having a carboxylic acid group on the particle surface Particles are kneaded and contained at 2.0% by weight.

・ Polyester f
A polyethylene terephthalate resin having an intrinsic viscosity of 0.68 and a melting point of 253 ° C. synthesized by a conventional polycondensation is kneaded with sodium dodecylbenzenesulfonate to contain 4.0% by weight.

・ Coating agent X
Coating mainly composed of water as a medium comprising 40 parts of Charol DC303P manufactured by Daiichi Kogyo Seiyaku Co., Ltd., which is a polymer having a pyrrolidinium ring in the main chain, 20 parts of methoxymethylol, and 40 parts of an acrylic acid alkyl ester / methacrylic acid alkyl ester copolymer liquid.

Example 1:
A mixture of 50% by weight of polyester a and 50% by weight of polyester b is fed to a twin-screw extruder equipped with a vent, melted at a melting temperature of 280 ° C., taken through a die through a pump and a filter, and then drawn into a casting drum. A stretched film was obtained. The unstretched film thus obtained was fed into a longitudinal stretching roll, first stretched 3.7 times at a film temperature of 83 ° C., then coated with coating agent X on one side, led to a tenter, and 4.0 times laterally at 95 ° C. Stretched to obtain a biaxially oriented film. Next, the obtained biaxially oriented film was introduced into a heat setting zone, and heat-set while being relaxed by 3% in the width direction at 230 ° C. for 5 seconds to obtain a polyester film having a thickness described in Table 1 below.

Example 2:
A mixture of 87.5% by weight of polyester a constituting the intermediate layer (B layer) and 12.5% by weight of polyester c is fed to a vented twin-screw extruder (main) to form a surface layer (A layer). Polyester a is fed to another twin-screw extruder with a vent (sub) and melted at a melting temperature of 280 ° C., then the molten polymer from each extruder is merged with a feed block through a gear pump and a filter, and cast through a die. It was taken up on a drum to obtain an unstretched film of 2 types and 3 layers. Thereafter, as in Example 1, coating agent X was applied on one side, led to a tenter, stretched and heat-set to obtain a film having a thickness structure described in Table 1.

Example 3:
A mixture of 67.5% by weight of polyester a forming the surface layer (A layer) and 32.5% by weight of polyester b is fed to a twin-screw extruder with a vent (sub) to form an intermediate layer (B layer) Polyester a is fed to another twin-screw extruder with a vent (main) and melted at a melting temperature of 280 ° C., then the molten polymer from each extruder is merged with a feed block through a gear pump and a filter, and cast through a die. It was taken up on a drum to obtain an unstretched film of 2 types and 3 layers. Thereafter, as in Example 1, the coating agent X was applied to one side, led to a tenter, stretched and heat-set to obtain a film having a thickness structure described in Table 1.

Example 4:
A mixture of 50% by weight of polyester b forming the surface layer (A layer) and 50% by weight of polyester f is fed to a twin-screw extruder with a vent (sub), and the polyester a constituting the main layer (B layer) is separated. The melted polymer from each extruder is merged with a feed block through a gear pump and a filter, and taken up by a casting drum through a die. Two types and two layers of unstretched films were obtained. Thereafter, as in Example 1, the coating agent X was applied to one side, led to a tenter, stretched and heat-set to obtain a film having a thickness structure described in Table 1.

Comparative Example 1:
Before forming a film, a filter pressure increase test was conducted using a mixture of 50% by weight of polyester d and 50% by weight of polyester a. As a result, a pressure increase was observed, so that no film was prepared.

Comparative Example 2:
A film was obtained in the same manner as in Example 1 except that the antistatic coating layer was not provided.

Comparative Example 3:
100% by weight of polyester e forming the surface layer (A layer) is supplied to a biaxial extruder with a vent (sub), and polyester a constituting the intermediate layer (B layer) is supplied to another biaxial extruder with a vent (main) Except having supplied, it carried out similarly to Example 3, and obtained the film of the thickness structure described in Table 1.

Comparative Example 4:
A mixture of 85% by weight of polyester a forming the surface layer (A layer) and 15% by weight of polyester b is supplied to a twin-screw extruder with a vent (sub), and the polyester a constituting the intermediate layer (B layer) is separated. In the same manner as in Example 3 except that the film was supplied to a vented twin-screw extruder (main), a film having a thickness structure described in Table 1 was obtained.

  The obtained results are summarized in Table 1 below.

  In Examples 1 to 4, there is no increase in the pressure of the filter, the production is excellent, and the antistatic property and light scattering property of the film are excellent. On the other hand, since the comparative example 1 used the inorganic particle, the pressure rise of the filter was observed. In Comparative Example 2, since there was no antistatic coating layer, the antistatic property was inferior. Comparative Example 3 was inferior in light scattering property because the average particle size was less than 2.0 μm. In Comparative Example 4, since the concentration of the organic particles was less than 0.10% by weight, there was no light scattering property.

  The film of the present invention is, for example, a film or sheet in which dust due to static electricity generated when peeling off a protective film or the like is likely to be a problem, such as a diffuser plate or a prism sheet of a backlight unit, or a lens sheet of a projector screen It can utilize suitably as base film, such as.

Claims (1)

A light-scattering biaxially stretched polyester film comprising 0.10 to 10% by weight of organic particles having an average particle size of 2.0 to 40 μm and a surface resistivity of 5 × 10 ¹² Ω or less.