TWI679119B - Polyester film - Google Patents

Abstract

The subject of the present invention is that by using this polyester film which is economical, film-forming, whiteness, reflective, lightweight, and excellent in surface shape, it will not be damaged even in contact with other members, and the film Since the flaws are not obvious, it is possible to provide a surface light source with excellent brightness characteristics and excellent performance in preventing uneven brightness.

The solution of the present invention is a polyester film, which is a polyester film having at least two layers of a polyester layer (A) and a polyester layer (B), wherein the polyester layer (A) forms at least one side of the polyester film A surface layer, a coating layer (C) containing particles is provided on one side of the surface layer, the particles contained in the coating layer (C) are amorphous porous particles, and the volume average particle diameter of the particles is 10 μm or more and 30 μm or less; When observing the SEM cross-section photograph of each protrusion generated when the particles were coated, the average value Dh of the distance (height of protrusion) dh from the top to the outermost surface of the polyester layer (A) was 10 μm or more and 30 μm or less. The average length Dw (width of the bottom of the protrusion) dw of the portion in contact with the polyester layer (A) is 10 μm or more and 35 μm or less; the ratio Dh / Dw of Dh / Dw is 0.70 or more and 1.00 or less; and from the polyester layer ( A) The particle length in the direction parallel to the layer A of the particles in the height of dh / 2 from the outermost layer (the width of the central portion of the protrusion) dv has an average value Dv of 10 μm or more and 35 μm or less; the ratio Dh / Dv Dh / Dv It is 0.90 or more and 1.00 or less; the ratio of Dv to Dw Dv / Dw is 0.80 or more and 1.05 or less; the particle is 1 per 1 mm ^{2 of the} film surface More than 1,000 and less than 2000.

Description

Polyester film

The present invention relates to a polyester film, and more particularly to a film used as a reflection plate for a liquid crystal display.

A liquid crystal display commonly used in various electronic devices such as a television, a personal computer, and a tablet terminal is provided with a light source called a backlight at the rear of the display for screen display. In addition, the backlight must illuminate the entire screen evenly. As a method that satisfies this characteristic, a structure known as an edge light type and a direct type surface light source is known. In particular, a thin display is suitable for an edge-light type, that is, a type of backlight that illuminates the screen from the side. Generally, in the case of the edge-light type, various types such as dot printing or surface texturing can be used on one side of a transparent substrate such as a light guide plate and a certain thickness of an acrylic plate. Treated flakes. By irradiating light to the edges of the light guide plate from a light source on the side, the illumination light is uniformly dispersed above, and a screen having uniform brightness can be obtained. In addition, since the illumination is provided only at the side, the light source can be reduced, the cost can be reduced, the weight can be reduced, and the thickness can be made thinner than the direct type. In addition, in order to prevent the illuminating light from escaping to the back of the screen, a reflecting plate is provided below the light guide plate, thereby reducing the loss of light from the light source and making the liquid crystal screen bright.

Such a surface light source for a liquid crystal display, particularly a reflection plate used in an edge-light type, of course needs to be a thin film and light, and has high reflection performance, and especially needs compatibility with a light guide plate. In the past, reflective plates have been coated with porous materials by adding white pigment to the film, or containing fine bubbles inside, and using the interface reflection to achieve high reflection performance, adding inorganic particles to the surface layer, etc. High-quality inorganic particles and the like are provided with an uneven shape to prevent adhesion to the light guide plate (Patent Documents 1, 2, 3, 4, and 5).

On the other hand, when a concave-convex shape reflective film is provided by the method described above, depending on the material of the light guide plate, the surface subjected to various processes such as dot printing or surface embossing is easily damaged. Chips are the cause of uneven screen. In addition, due to vibration during transportation or violent contact with other components during assembly, the coating of the reflective film may be cracked or peeled off, and scratches may occur.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2009-98660

[Patent Document 2] Japanese Patent Laid-Open No. 2004-126345

[Patent Document 3] WO11 / 105294

[Patent Document 4] Japanese Patent No. 5218931

[Patent Document 5] Japanese Patent Laid-Open No. 2011-75779

Then, the subject of this invention is to provide easily, cheaply, and stably. A white polyester film having high reflectivity, excellent unevenness elimination, and film scratch resistance, which cannot be achieved in the above-mentioned conventional studies.

In order to solve the above-mentioned problems, the present invention uses the following configuration.

(1) A polyester film, which is a polyester film having at least two layers of a polyester layer (A) (hereinafter also referred to as layer A) and a polyester layer (B) (hereinafter also referred to as layer B), wherein The polyester layer (A) forms a surface layer of at least one side of a polyester film. A coating layer (C) containing particles is provided on one side of the surface layer, and the particles contained in the coating layer (C) are amorphous porous particles. The volume average particle diameter of this particle is 10 μm or more and 30 μm or less. When observing the SEM cross-section photograph of each protrusion generated when the particle is coated, the distance from the top of the particle to the outermost surface of the polyester layer (A) (hereinafter also referred to as The average value Dh of the projection height) dh is 10 μm or more and 30 μm or less; the average value Dw of the length (hereinafter also referred to as the width of the projection bottom) dw of the portion of the projection that is in contact with the polyester layer (A) is 10 μm or more 35 μm or less; Dh / Dw ratio Dh / Dw is 0.7 or more and 1.0 or less; particle length in a direction parallel to layer A of particles in the height from the outermost surface of the polyester layer (A) to dh / 2 (the following also applies) (The width of the center of the protrusion) The average value of dv Dv is 10 μm or more and 35 μm or less; the ratio of Dh to Dv Dh / Dv is 0.90 or more and 1.00 or less; the ratio Dv to Dw D v / Dw is 0.80 or more and 1.05 or less; the particles are 1,000 or more and 2000 or less per 1 mm ² of the film surface.

(2) The polyester film according to (1), wherein the particles are organic particles.

(3) The polyester film according to (1) or (2), wherein the particles are mainly composed of 6-nylon.

(4) The polyester film according to any one of (1) to (3), wherein the 60 ° gloss change value after the surface abrasion test of the side surface of the coating layer (C) is less than 30%.

A reflective film for a liquid crystal display using the polyester film as described in any one of (1) to (4).

According to the present invention, a polyester film having both high reflectivity and excellent surface shape can be provided. In particular, when the polyester film is used as a reflecting plate or reflector in a surface light source, the liquid crystal screen can be illuminated, so that The liquid crystal image is more vivid and easy to view. In addition, it can also prevent the problem of adhesion or planing to the light guide plate and the film itself from being chipped or damaged when using the backlight of the edge-light type light source, so that the screen does not have unevenness.

The present invention is described in detail below.

[Composition of polyester film]

The polyester film of the present invention includes a polyester layer (A) and a polyester layer (B). Considering the convenience and effect of film formation, a three-layer structure is preferable, and a three-layer structure of a polyester layer (A) / polyester layer (B) / polyester layer (A) is more preferable. In addition, it is necessary to have a particle-containing coating layer (C) on at least one side.

The thickness of the polyester layer (A) of the present invention is preferably 2 to 20 μm. If the thickness of the polyester layer (A) is less than 2 μm, the film may not be customized. When the thickness of the polyester layer (A) exceeds 20 μm, when the polyester film is used as a reflective film, light may not easily reach the polyester layer (B), and a portion will be reflected at the interface between the bubbles and the polyester described later. Reduce, etc., causing light reflectance or When optical characteristics such as brightness are reduced.

[Polyester layer (A)]

The polyester layer (A) of the polyester film of the present invention preferably contains polyester (a) as a main component, and may also contain various additives as appropriate.

[Polyester (a)]

The polyester (a) constituting the polyester layer (A) can be subjected to 1) polycondensation of a dicarboxylic acid component or an ester-forming derivative thereof (hereinafter collectively referred to as a "dicarboxylic acid component") with a diol component; 2) Polycondensation of a compound having a carboxylic acid or carboxylic acid derivative skeleton and a hydroxyl group in one molecule; and 1) a combination of 2).

Examples of the dicarboxylic acid component constituting the polyester (a) include fats such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, methylmalonic acid, and ethylmalonic acid. Dicarboxylic acids, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and other dicarboxylic acids, etc., However, it is not limited to these, and it is also suitable to use a polyfunctional acid such as trimellitic acid, pyromelic acid, and the like. In addition, these can be used singly or in combination.

Examples of the diol component constituting the polyester resin include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, and 1 Aliphatic diols such as 1,3-butanediol; diols such as 1,3-benzenedimethanol, 1,4-benzenedimethanol and other aromatic diols as representative examples, but are not subject to Limited. These may be used alone or in combination.

The polyester (a) can be obtained by appropriately combining and compounding the above-mentioned compounds.

The polyester (a) may be crystalline or non-crystalline and contains at least In the case of one type of non-crystalline polyester, it is suitable for forming a surface shape described later. The term "amorphous" as used herein refers to a resin having a heat of crystal melting of less than 1 cal / g.

Examples of polyesters suitable for the polyester (a) include polyethylene terephthalate (hereinafter referred to as PET), polytrimethylene terephthalate, and polyterephthalic acid. Succinate, etc.

The polyester (a) can maintain non-coloring properties by using the resin described above, and can provide high mechanical strength when formed into a film. More preferably, PET is preferable from the viewpoint of being inexpensive and excellent in water resistance, durability, and chemical resistance.

In the polyester film of the present invention, the content of the polyester (a) is preferably 50% by mass or more based on the polyester layer (A). If the content of the polyester (a) is less than 50% by mass, it may not be possible to form a film, or the strength of a film may be reduced even when a film is formed, which is not suitable.

[Polyester layer (B)]

From the viewpoint of optical characteristics such as brightness and reflectance, it is preferable that the polyester film layer (B) of the present invention contains polyester (a), a cell core agent (b), and cells. It is more preferable to use a polyester (c) or a dispersant described later as appropriate. By using the polyester (a) and the bubble nucleating agent (b) and by a method described later, bubbles containing the bubble nucleating agent (b) as a core are easily contained, and further by using the polyester (c) or dispersing Agent, it is easy to make the bubbles finer and generate a large amount, so it is easy to produce a polyester film that is lightweight and has high reflection characteristics.

As for the resin constituting the polyester layer (B), the use of the polyester (a) used in the polyester layer (A) can maintain the non-coloring property and provide high mechanical strength when it is formed into a film. Better.

Can be obtained from having excellent film forming properties, light reflection properties, From the viewpoint of a heat-resistant and durable polyester film, the content of the polyester (a) constituting the polyester layer (B) is preferably at least 30% by mass based on the polyester layer (B). When the content of the polyester (a) is less than 30% by mass, sufficient bubbles cannot be generated around the bubble nucleating agent (b) and the like described later in the film, and whiteness and light reflection properties may be poor. From the viewpoint of film-forming convenience, the upper limit of the polyester (a) is preferably 90% by mass or less.

[Bubble core agent (b)]

In order to make the polyester film of the present invention have whiteness and reflection properties, it is preferable to have bubbles in the polyester layer (B). The polyester film (a) and the bubble nucleating agent ( b) Biaxial extension is performed to form bubbles.

The bubble nucleating agent (b) may be inorganic particles or organic particles, or these may be used in combination.

Specific examples of the inorganic particles include calcium carbonate, magnesium carbonate, titanium oxide, antimony oxide, magnesium oxide, barium carbonate, zinc carbonate, barium sulfate, calcium sulfate, aluminum oxide, and silicon oxide (silicon dioxide). . Among these, calcium carbonate, titanium oxide, barium sulfate, and silicon dioxide are more preferable from the viewpoint of improving film formation stability and reflection characteristics for a long time; from the viewpoint of small particle diameter and easy dispersion, Titanium oxide is the best. These can be used alone or in combination of two or more. In addition, it can be in the form of porous or hollow porous, etc., and the surface treatment can be performed in order to improve the dispersibility within the range that does not hinder the effect of the present invention. The surface treatment agent is preferably a silane coupling agent or titanate coupling. Mixture, silicone.

Specific examples of the organic particles include linear, branched, or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene. This polyolefin can be homopolymer or copolymer Materials can even be used in combination of two or more. Among these, from the viewpoints of excellent transparency and excellent heat resistance, polypropylene, polymethylpentene, and the like are preferably used for crystalline polyolefins; and amorphous polyolefins are more suitable for crystalline polyolefins. Cycloolefin copolymers (which may also be described as COC) are preferably used. The cyclic olefin copolymer refers to a cyclic olefin selected from the group consisting of cyclic olefins, bicyclic olefins, tricyclic olefins, tetracyclic olefins, and pentacyclic olefins, and linear olefins such as ethylene and propylene. Copolymer. The term "amorphous resin" used herein refers to a resin having a heat of crystal melting of less than 1 cal / g.

Representative examples of cycloolefins in cycloolefin copolymers include bicyclic [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, 5 , 6-dimethylbicyclo [2,2,1] hept-2-ene and the like.

In addition, typical examples of the linear olefin in the cyclic olefin copolymer include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene.

When a cycloolefin copolymer resin is used as the organic particles, the linear olefin component is preferably an ethylene component from the viewpoint of reactivity. In addition, from productivity. Transparency. From the viewpoint of high Tg, the cyclic olefin component is also preferably bicyclo [2,2,1] hept-2-ene (norbornene) or a derivative thereof.

When the amount of the bubble nucleating agent (b) is added, when the total mass of the polyester layer (B) is 100% by mass, 10 to 50% by mass is more preferred, and 5 to 30% by mass is more preferred. If the content of the bubble nucleating agent (b) is less than 10% by mass, sufficient bubbles may not be generated inside the film, and whiteness or light reflection characteristics may be poor. On the other hand, when the content of the bubble nucleating agent (b) exceeds 50% by mass, the strength of the film is reduced, and it is easy to break during stretching, and During post-processing, there may be problems such as dust generation. By setting the content within this range, sufficient whiteness can be exhibited. Reflective. Lightweight.

When organic particles are used as the bubble nucleating agent (b), it is effective to add a dispersant in order to uniformly disperse the same. In the case of the present invention, polyalkylene glycols, especially polyethylene glycols, are particularly preferred. In addition, a copolymer of polybutylene terephthalate and polytetramethylene glycol and the like are also suitable for use because they improve the dispersibility of organic particles. The added amount is preferably 3 mass% or more and 20 mass% or less, and particularly preferably 5 mass% or more and 15 mass% or less with respect to the mass of the polyester layer (B). If the amount of the dispersant is too small, the effect of the addition is weak; if it is too large, the original characteristics of the film base material may be impaired. Such a dispersant can be added to a film base material polymer in advance, and it can be prepared as a base polymer (master particle).

[Polyester (c)]

The polyester (c) can be obtained by 1) polycondensing a dicarboxylic acid component or an ester-forming derivative thereof with a diol component.

In addition, in the present invention, the diol component is not limited to a component existing in the form of a diol, and includes a case where the constituent component of the polyester is contained in the form of a copolymer or a mixture of these resins, for example.

Among the polyester films of the present invention, one or more polyester resins can be used as the polyester (c).

Examples of the dicarboxylic acid component constituting the polyester resin include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedione acid, dimer acid, Eicosanedioic acid, pimelic acid, nonan Aliphatic dicarboxylic acids such as diacid, methylmalonic acid, ethylmalonic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalene Dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, sodium isophthalate 5-sulfonate Dicarboxylic acids such as aromatic dicarboxylic acids such as anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis (4-carboxyphenyl) phosphonic acid, or their ester derivatives, etc. are representative examples, but they are not Among these limitations, for example, polyfunctional acids such as trimellitic acid, pyromelic acid, and ester derivatives thereof can be suitably used. In addition, these may be used alone, or a plurality may be used as required.

In addition, it is also suitable to use an oxo acid, such as l-lactide, d-lactide, hydroxybenzoic acid, and the like, which are added to the carboxyl terminus of the dicarboxylic acid component, and a plurality of the oxo acids, A dicarboxylic compound formed by a compound or the like.

Examples of the diol component constituting the polyester resin include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, and 1 Aliphatic diols such as 3-butanediol, cyclobutanediol, cyclopentanediol, cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclopropanedimethanol, cyclobutanedimethanol, Cyclopentanedimethanol, cyclohexanedimethanol, cycloheptanedimethanol, cyclooctanedimethanol, alicyclic diols having 4 or more and 8 or less carbon atoms, bisphenol A, 1,3-benzenedimethanol, 1 Aromatic diols such as, 4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene, and the like are representative examples, but they are not limited thereto. In addition, these can be used singly or in combination.

Among the above-mentioned diols, polyester (c) is particularly suitable for use from the standpoint of monomer price and easy mixing with polyester resins (especially PET). 1,4-cyclohexanedimethanol (CHDM).

In the polyester film of the present invention, the content of the polyester (c) is preferably 1.2 to 36% by mass based on the polyester layer (B). More preferably, it is 2.4 to 26% by mass. If the content of the polyester (c) is less than 1.2% by mass, the microdispersion effect of the cell core agent (b) is reduced, and the reflection performance is lowered, which is not preferable. Moreover, when it exceeds 36 mass%, the heat resistance of a polyester film will fall, and when exposed to high temperature, a dimensional change may become large, and it is unpreferable. By setting the content of the polyester (c) in the polyester film of the present invention to 1.2 to 36% by mass, a polyester film having higher film-forming stability, reflectivity, and dimensional stability can be produced.

[Coated layer (C)]

The polyester film of the present invention has a coating layer (C) on the surface of the polyester layer (A), and the coating layer must contain amorphous porous particles (d). From the viewpoint of not easily damaging other members, especially the light guide plate, the type of the porous particles (d) that can be used in the present invention is preferably organic particles. For example, acrylic resin particles, silicone resin particles, nylon resin particles, styrene resin particles, polyethylene resin particles, polyamide resin particles, urethane resin particles, polymer Ester-based resin particles, etc., or mixtures of these; etc. However, from the viewpoint that hardness can be appropriately adjusted, nylon particles are particularly preferred.

In addition, the term "amorphous porous particles" as used herein refers to particles in which each particle is not limited to a certain shape, and each particle has a different shape and has pores. A pore is a portion of a particle that is depressed toward the inside of the particle. Examples include hollow shapes, shapes like needles or curves, and depressions toward the inside or center of the particle, or these depressions The shape and the like of the trapped through-particles may be different in size or volume, and are not particularly limited. In this way, by using particles having pores, no special processing is required, and the value of the 60 ° gloss change after the surface abrasion test described later can be less than 30%. Regarding the presence or absence of pores and the shape of the particles, a thin film sample was cut at a 3 ° blade tilt angle in a direction perpendicular to the film plane using a rotary microtome made by Japan Microtome Research Institute (stock); Using a scanning electron microscope ABT-32 manufactured by Topcon Corporation, for example, at an observation magnification of 2500 to 10,000 times, one particle is actually drawn in the entire field of view. In addition, the contrast of the image is appropriately adjusted to observe, and the presence of pores can be confirmed And particle shapes.

In addition, the presence or absence of pores is determined from the observed image based on the presence or absence of speckles and speckle patterns in the particles. The presence of speckles and speckle patterns is defined as the presence of pores and the absence of pores is designated as the absence of pores. hole. Examples of the amorphous porous particles include particles produced by the production method described in Japanese Patent Application Laid-Open No. 2006-328173.

The polyester film of the present invention has at least one surface layer having an uneven shape provided by coating. Among the protrusions, the average value of the distance dh from the apex of the protrusion to the outermost surface of the polyester layer (A) is Dh. It must be 10 μm or more and 30 μm or less, and more preferably 10 μm or more and 20 μm or less. When Dh is less than 10 μm, when an edge light type backlight is used, other members such as a light guide plate and the film may adhere to each other, resulting in uneven brightness. On the other hand, when it is larger than 30 μm, it is difficult to fix to the film body, and the protrusions may fall off. In addition, the average Dw of the length (the width of the bottom of the protrusion) dw of the portion in contact with the A layer must be 10 μm or more and 35 μm. Hereinafter, it is more preferably 10 μm or more and 20 μm or less. In the case of less than 10 μm, when an edge-light backlight is used, other members such as a light guide plate and the film may adhere to each other, resulting in uneven brightness. In addition, the 60 ° gloss change after the surface abrasion test described later cannot be made less than 30%. On the other hand, when it is larger than 35 μm, it is difficult to fix the film body, and the protrusions may fall off. In addition, the average particle length (dv) of the particle length (width of the center of the protrusion) dv in a direction parallel to the layer A of the particles at a height from the layer A to dh / 2 must be 10 μm or more and 35 μm or less, and more preferably 10 μm or more and 20 μm or less . In the case of less than 10 μm, when an edge-light backlight is used, other members such as a light guide plate and the film may adhere to each other, resulting in uneven brightness. In addition, the 60 ° gloss change after the surface abrasion test described later cannot be made less than 30%. On the other hand, when it is larger than 35 μm, it is difficult to fix the film body, and the protrusions may fall off.

In addition, the number N of protrusions per 1 mm ² of the film surface must be 1,000 or more and 2000 or less. In the case of using the polyester film of the present invention as a reflective film of an edge-light backlight, in order to achieve no unevenness in the displayed image even when scratched during assembly, Dh, Dw, Dv, and each 1 mm on the polyester film ² The number N of film surfaces must be set within the above range.

In order to set Dh, Dw, and Dv in the above range, porous particles having an average particle diameter of 10 μm or more and 30 μm or less, and preferably 10 μm or more and 20 μm or less are used. Moreover, it is preferable to use a water-based coating agent. When the average particle diameter is less than 10 μm, it is difficult to keep the gloss within the above-mentioned range, and thus brightness unevenness may occur. On the other hand, when the thickness is larger than 30 μm and the thickness of the binder is as described below, the particles may fall off, and Even if a film can be formed, the brightness becomes low, which is not good.

Here, the water-based coating agent means that among the constituent elements of the coating agent, 50% by mass or more is water. In addition, it is preferable that the binder component contained in the coating agent is 5% to 20% by mass in terms of dry concentration. When the dry concentration of the binder component is less than 5% by mass, particles may fall off. On the other hand, when the dry concentration of the adhesive component exceeds 20% by mass, the protrusions are buried by the adhesive, so it is particularly difficult to keep Dh in the above range, and even the light reflection characteristics of the film body may be impaired. situation. In addition, after coating, it is preferable to go through a drying step of drying at least 180 seconds at a gas ambient temperature for more than 2 seconds. Moreover, by containing 5-20 mass% of the said particle | grains, the number N of film surfaces per 1 mm <^2> can be made into the said range.

The binder resin layer related to the present invention is not particularly limited, but is preferably a resin mainly composed of an organic component, and examples thereof include polyester resin, polyurethane resin, acrylic resin, and formic acid. Acrylic resin, polyamide resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, fluorine resin, etc. These resins may be used alone or as a copolymer or a mixture of two or more. Particularly preferred are polyester resins, polyurethane resins, acrylic or methacrylic resins. From the viewpoints of heat resistance, particle dispersibility, coatability, and refractive index difference from the substrate, it is particularly preferable to use a polymer resin. Ester resin.

The thickness of the adhesive resin layer is preferably from 0.1 μm to 1 μm, and more preferably from 0.1 μm to 0.5 μm. When the thickness of the adhesive resin layer is less than 0.1 μm, the flatness as described above cannot be maintained. Particles of average particle size may fall off. On the other hand, when the thickness of the adhesive is greater than 1 μm, it is difficult to keep the gloss within the aforementioned range, and it also has an adverse effect on other optical characteristics such as brightness, which is not good.

In the polyester film of the present invention, the value of the 60 ° gloss change after the surface abrasion test is preferably less than 30%, more preferably less than 10%. The surface abrasion test referred to here refers to the use of a surface abrasion tester (PA-300A, manufactured by Daiei Scientific Precision Manufacturing Co., Ltd.), by applying a load of 1 kg and an end surface of 1 cm ² (1 cm × 1 cm). A corner post was tested on the surface of the film with 5 cm reciprocating friction.

In addition, the gloss in the present invention refers to a case where a digital reflection angle gloss meter UVG-5B (manufactured by Suga Tester Co., Ltd.) is used in a coating layer having a light reflection film in accordance with JIS Z-8741 (1997) It is a value obtained by measuring from the coating layer side, and in the case where it is not from the polyester (A) layer side. The term "60 ° glossiness" used herein refers to a value when the measurement conditions are set to an incident angle = 60 ° and a light reception angle = 60 °.

The ratio Dh / Dw of Dh to Dw is 0.70 or more and 1.00 or less, which is necessary for the polyester film of the present invention. If Dh / Dw is greater than 1.0, the protrusions and other components will rub, and the protrusions will easily fall off when they are stressed, that is, after the surface of the friction film is rubbed, the value of the 60 ° gloss change will not reach less than 30%. If Dh / Dw is less than 0.70, particles may scratch other components or be scratched by other components. In any case, after rubbing the film surface, there will be a case where the value of the 60 ° gloss change will not reach less than 30% .

In addition, the ratio Dh / Dv of Dh to Dv is 0.90 or more and less than 1.00, which is necessary for the polyester film of the present invention. If Dh / Dw is large At 1.0, there may be cases where the protrusions are easily rubbed off due to friction between the protrusions and other members, that is, there may be cases where the 60 ° gloss change value does not reach less than 30% after the surface of the friction film is rubbed. If Dh / Dv is less than 0.90, particles may scratch other components or be scratched by other components. In any case, after rubbing the film surface, there will be cases where the value of the 60 ° gloss change will not reach less than 30% .

In addition, the ratio Dv / Dw of Dv to Dw is 0.80 or more and less than 1.05, which is necessary for the polyester film of the present invention. If Dh / Dw is greater than 1.05, there may be friction between the protrusions and other components, and the protrusions may easily fall off when they are stressed, that is, after the surface of the friction film is rubbed, the value of the 60 ° gloss change will not reach less than 30%. If Dv / Dw is less than 0.80, particles may scratch other components or be scratched by other components. In any case, after rubbing the film surface, there will be cases where the value of the 60 ° gloss change will not reach less than 30%. .

If the change value of the 60 ° glossiness is more than 30%, not only can the flaw be visually observed, but when the film is assembled as a backlight, the flaw will appear as uneven brightness on the screen, which is not good.

Here, the brightness in the present invention refers to the relative brightness, and the measurement is performed as described below. The reflection film attached to the new 32-type LCD TV LHD32K15JP backlight manufactured by Hisense Japan Co., Ltd. was changed to the polyester film of the present invention, and then the light was turned on. In this state, it stood for one hour, stabilized the light source, and then captured the liquid crystal screen portion with a CCD camera (DXC-390 manufactured by SONY), and acquired an image with an image analysis device Eyescale manufactured by I-System. Then, the brightness level of the captured image is controlled to 30,000 steps, so that it is automatically detected and converted. Is brightness. The brightness evaluation is based on the attached reflective film as a reference sample (100%), and the relative brightness of the thin film sample is obtained according to the following formula, and this value is set as the brightness.

Brightness (%) = (Brightness (%) of the thin film sample) / (Brightness (%) of the reference sample) × 100.

In addition, the brightness unevenness is obtained by using the brightness maximum value, brightness minimum value, and brightness average value that are automatically detected in the above-mentioned manner, and are obtained according to the following formula.

Uneven brightness (%) = (maximum brightness-minimum brightness) / average brightness × 100

The method for forming the aforementioned coating layer is not particularly limited, but various coating methods such as an in-line coating method, a reverse coating method, a gravure coating method, a rod coating method, a rod coating method, a mold coating method, or Spray coating method.

[Film forming method]

The method for obtaining the polyester (a) will be described with one example, but it is not limited to this example. Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, antimony trioxide (polymerization catalyst) was added so that the obtained polyester particles were converted into 300 ppm in terms of antimony atom conversion, and By a polycondensation reaction, polyethylene terephthalate particles (polyester (a)) can be obtained.

In the bubble nucleating agent (b), the inorganic particles are polyester (a) master batches containing inorganic particles, and can be used in the production of the present invention.

The method for obtaining organic particles is described in the bubble nucleating agent (b), but it is not limited to this example. Organic particles can be obtained by a known method (for example, Japanese Patent Application Laid-Open No. 61-271308, International Publication No. 2007/060723). Brochure) is obtained by polymerizing the above-mentioned cyclic olefin and olefin, or is obtained by purchasing a commercially available product (for example, "TOPAS" (manufactured by Poly Plastics)).

The method for obtaining polyester (c) will be described with one example, but it is not limited to this example. Use terephthalic acid as the dicarboxylic acid component, alicyclic diols with 4 to 8 carbon atoms as the diol component, and use magnesium acetate, antimony trioxide, and phosphorous acid as catalysts to convert them into antimony atoms. It is added at 300 ppm and a polycondensation reaction is performed to obtain a polyester (c) obtained by copolymerizing an alicyclic diol having 4 to 8 carbon atoms and terephthalic acid.

The method for obtaining a dispersant is described with one example, but it is not limited to this example. The dispersant that can be preferably used in the present invention is a block copolymer of PBT (polybutylene terephthalate) and PAG (mainly polytetramethylene glycol), and the melt index (MI) is 14 (2.160 g, 240 ° C). The copolymerization ratio is butyl terephthalate: butanediol = 70 mol%: 30 mol (for example, "Hytrel" (manufactured by Toray DuPont)).

The method for obtaining the porous plasmid (d) will be described with one example, but it is not limited to this example. It can be obtained by the method described below, for example, in Japanese Patent Application Laid-Open No. 2006-328173. That is, 15% by weight of the particles of nylon 6 were mixed in ethylene glycol (solvent), and the resulting mixture was stirred at 185 ° C. in a mixing tank equipped with a stirrer and carbon dioxide replacement until the nylon 6 was completely dissolved. As shown in FIG. 1, the obtained uniform solution was cooled on a stainless steel belt conveyor maintained at a constant temperature, and nylon 6 porous particles were granulated. At this time, the temperature of the stainless steel belt conveyor was maintained at 75 ° C, and the speed of the belt conveyor was 5.0 m / min. In addition, on the surface of this belt conveyor, The homogeneous solution forms a liquid film of 1 to 1.5 mm. The mixture of nylon 6 porous particles and ethylene glycol obtained in this way is separated from the conveyor belt by a scraper, and the ethylene glycol is roughly separated by a centrifugal separator, and then dried to obtain Nylon 6 porous particle seed powder. Particles are obtained in this way, and then a part of the particle powder is sampled, and a scanning electron microscope ABT-32 manufactured by Topcon is used, for example, at an observation magnification of 2500 to 10,000 times, so that one particle is actually drawn in the entire field of view. In addition, the contrast of the image is appropriately adjusted for observation, and the presence or absence of pores and particle shapes are confirmed. The presence or absence of pores is determined by the presence or absence of speckles and speckle patterns in the particles based on the observed image. The presence of speckles and speckle patterns is determined to have pores. In the case of pores, the particles were judged to be porous particles.

Next, an example of the method for producing the polyester film of the present invention will be described, but the present invention is not limited to this example.

Regarding the polyester layer (A), a mixture containing the polyester (a) and various additives as necessary is sufficiently vacuum-dried and supplied to a heated extruder. Various additives can be added using the master batch prepared by uniform melting and kneading in advance, or can be directly supplied to the kneading extruder.

As for the polyester layer (B), a mixture containing the polyester (a) and the nucleating agent (b) and, if necessary, the polyester (c) and a dispersant is sufficiently vacuum-dried and supplied to a heated extruder. Out of the plane. The bubble nucleating agent (b) can be added by using the master batch prepared by uniformly melting and kneading in advance, or it can be directly supplied to the kneading extruder.

In addition, when melt extrusion, It is filtered by a filter and then introduced into a T-die nozzle, and a molten sheet is obtained by extrusion molding.

This molten sheet was cooled and solidified on a roller cooled to a surface temperature of 10 to 60 ° C. by static electricity to produce a three-layer film of unstretched A / B / A. The unstretched 3-layer film is guided to a roller group heated to 70 to 120 ° C, preferably 70 to 100 ° C, and stretched 2 to 4 times in the longitudinal direction (longitudinal direction, that is, the direction in which the film proceeds). And it cools in the roll group of the temperature of 20-50 degreeC.

The sheet extending in the longitudinal direction was guided to a coating device, and a coating agent containing the resin particles and the binder resin and being a raw material of the coating layer (C) was applied by a bar coating method.

Next, the two ends of the film are clamped by a clamp and guided to a tenter at the same time. In a gas environment heated to a temperature of 90 to 150 ° C, it extends in a direction perpendicular to the long side direction (wide side direction) 2 to 4 times. At this time, it is considered that the volatile components are removed from the coating layer (C), and the coating layer (C) is completed. The stretching magnification is 2 to 4 times in the long side direction and the wide side direction, and the area magnification (longitudinal stretching magnification × horizontal stretching magnification) is preferably 4 to 16 times, and 8 to 12 times is more preferable. If the area magnification is less than 4 times, the strength of the bubbles and the film is insufficient, and it is difficult to obtain high reflection characteristics. On the other hand, if the area magnification exceeds 16 times, it may be easily broken during stretching. The coating layer (C) may be applied on-line as described above, or may be provided during post-processing. However, in the case of connecting on-line, it is easy to make the number of protrusions fall within the aforementioned range and it is inexpensive, so it is preferable.

In order to end the crystal orientation of the obtained biaxially stretched film and to provide dimensional stability, the temperature was then increased in a tenter at 150 to 240 ° C. Heat treatment is performed at the temperature for 1 to 30 seconds, and it is uniformly slowly cooled and then cooled to room temperature. Then, if necessary, in order to further improve the adhesion with other materials, corona discharge treatment and the like are wound and wound. The polyester film of the present invention is obtained. In the heat treatment step, it is preferable to perform a relaxation treatment of 3 to 12% in a wide side direction or a long side direction.

In addition, generally speaking, the higher the heat treatment temperature, the higher the thermal dimensional stability. In the film formation step, it is preferable to perform the heat treatment at a high temperature (190 ° C. or higher).

The method of biaxial stretching may be either sequential or simultaneous. In addition, after biaxial extension, it can be extended in either the long side direction or the wide side direction.

The polyester film of the present invention has a concave-convex shape provided by coating on at least one side of the surface layer, and air bubbles are formed inside the film. The polyester film has high reflectance and is lightweight. It is used as a reflective plate for liquid crystal displays, especially LEDs In the case of a reflective plate for a type display, compatibility with other members, especially a light guide plate is good, and there is no unevenness in the screen, and high brightness can be obtained.

[Method for measuring physical properties and evaluating effects]

test methods

The method of evaluating the physical properties of the present invention and the method of evaluating the effects are as follows.

A. Brightness and uneven brightness

The reflective film attached to the backlight of the new 32-type LCD TV LHD32K15JP manufactured by Hisense Japan Co., Ltd. was changed to a polyester film to be measured, and then the light was turned on. At this time, the Way setting. Stand in this state for 1 hour, stabilize the light source, and then take a CCD camera (DXC-390, manufactured by Sony) to capture the liquid crystal screen, and acquire an image using Eyescale, an image analysis device. Then, the brightness level of the captured image is controlled at 30,000 levels, so that it is automatically detected and converted into brightness. The brightness evaluation is based on the attached reflective film as a reference sample (100%), and the relative brightness of the thin film sample is obtained according to the following formula, and this value is determined as the brightness.

Brightness (%) = (Brightness (%) of the thin film sample) / (Brightness (%) of the reference sample) × 100.

In addition, the brightness unevenness is obtained by using the brightness maximum value, brightness minimum value, and brightness average value that are automatically detected in the above-mentioned manner and according to the following formula.

Uneven brightness (%) = (maximum brightness-minimum brightness) / average brightness × 100

"AA": Excellent (less than 2%)

"A": Good (more than 2% and less than 5%)

"B": poor (more than 5% and less than 10%)

"C": Very poor (more than 10%)

The above "AA" and "A" were determined as passing.

B. Protrusion size (dh, Dh, dw, Dw, dv, Dv)

Using a microtome, cut out a cross section parallel to the TD direction (lateral direction) of the film, vapor-deposit platinum-palladium, and then use an electric field emission scanning electron microscope "JSM-6700F" manufactured by Japan Electronics Co., Ltd. at 5000 times Zoom in and observe the vicinity of the film surface on the coating layer (C) side. Use the obtained image. For each protrusion on the image, the distance from the top of the protrusion to the outermost surface of layer A (the height of the protrusion) dh; The length of the part where layer A meets ( The width of the bottom of the protrusion) dw; the particle length (width of the central portion of the protrusion) dv in a direction parallel to the layer A of the particles in the height from layer A to dh / 2 was measured for each of the 20 protrusions and calculated The average value of dh was taken as the average value of Dh and dw as the average value of Dw and dv as Dv.

C. Number of protrusions per 1mm ² film surface (N)

Platinum-palladium was vapor-deposited on the surface of the film on the coating layer (C) side, and then an electric field emission scanning electron microscope "JSM-6700F" manufactured by Japan Electronics Co., Ltd. was observed at a magnification of 2000 times, and the obtained image was used. , Count the number of protrusions (N) on the surface of the film, and derive a conversion value converted to 1 mm ² according to the image size and magnification. The number of measurements was set to n = 5, and the average value was obtained. In the case of a coated film, the coated surface is measured.

D. Average particle diameter of particles of the coating layer (C)

Using a microtome, the film was cut in the cross-section direction, and platinum-palladium was evaporated on the obtained cross-section. Then, an electric field emission scanning electron microscope "JSM-6700F" manufactured by Japan Electronics Co., Ltd. was observed at a magnification of 5000 times. In the vicinity of the surface of the film on the coating layer (C) side, from the obtained image, the average particle diameter of the particles was determined in the following procedure (D in the formula).

1) For all the particles observed in the cross section in this image, the cross-sectional area S is obtained, and the particle diameter d is obtained according to the following formula (1).

d = 2 × (S / π) ^1/2 ‧‧‧ (1)

(Where π is the pi)

2) Using the obtained particle diameter d, a volume average particle diameter D is obtained according to the following formula (2).

D = Σ [4 / 3π × (d / 2) ³ × d] / Σ [4 / 3π × (d / 2) ³ ]. ． ． (2)

3) Change 5 places to implement 1) ~ 2) above, and use the average value as the level. Average particle size.

E. Thickness of the adhesive resin layer of the coating layer (C)

Using a microtome, the film was cut in the cross-section direction, and platinum-palladium was evaporated on the obtained cross-section. Then, an electric field emission scanning electron microscope "JSM-6700F" manufactured by Japan Electronics Co., Ltd. was magnified at 20,000 times. Observe the vicinity of the film surface on the side of the coating layer (C). From the obtained image, the thickness of the adhesive resin layer observed in the cross section in the image is measured at any five places with a scale, etc., and obtained. average value.

F. Film formation

In the embodiment. In the comparative example, when the film was formed, the film rupture occurred only once per day or less, and the particles did not cause step contamination, such as "AA". The film rupture occurred only once per day or less, but it can be confirmed with the naked eye. If dirt accumulates on the roll surface, set it to "A"; if film cracking occurs twice / day or more and no more than 3 times / day, or if it can be confirmed with the naked eye that dirt significantly accumulates on the roller surface, set it to "B"; film cracking occurs 4 When the number of times / day or more is set to "C". In mass production, it is necessary to have a film-forming property of "A" or more. If it is "AA", it may even have the effect of reducing costs.

G. Gloss change at 60 ° after plane abrasion test

Using a plane abrasion tester (PA-300A, manufactured by Daiei Scientific Seiki Seisakusho Co., Ltd.), a square prism with an end face of 1 cm ² (1 cm × 1 cm) was applied to the film by reciprocating friction at 5 cm by applying a 1 kg load 10 times. Then, using a digital angle-varying gloss meter UVG-5B (manufactured by Suga Testing Machine Co., Ltd.), the coating layer (C) having a light reflecting film is from the coating layer (C) side, and the absence thereof is from polyester. (A) The layer side is a value measured in accordance with JIS Z-8741 (1997). The term "60 ° glossiness" used herein refers to a value when the measurement conditions are set to an incident angle = 60 ° and a light reception angle = 60 °. The 60 ° glossiness of the portion after the plane abrasion test and the portion not tested was measured, and the difference was taken as the glossiness change value.

[Example]

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

(raw material)

． Polyester (a)

Using terephthalic acid as the acid component and ethylene glycol as the diol component, antimony trioxide (polymerization catalyst) was added, and polycondensation was performed at 300 ppm in terms of antimony atom relative to the obtained polyester particles. The reaction resulted in polyethylene terephthalate particles (PET) having an limiting viscosity of 0.63 dl / g and a carboxyl terminal group amount of 40 equivalents / ton.

． Bubble core agent (b) inorganic particles

Titanium oxide and barium sulfate are commercially available titanium oxide or barium sulfate master batches (the base resin is polyester (a)).

． Bubble core agent (b) organic particles

A cycloolefin-based copolymer "TOPAS" (manufactured by Poly Plastics, Inc.) having a glass transition temperature of 180 ° C was used (denoted as COC in the table).

． Polyester (c)

Using terephthalic acid as the acid component and ethylene glycol as the diol component, antimony trioxide (polymerization catalyst) was added so that the obtained polyester particles were converted to 300 ppm in terms of antimony atom conversion, and polymerized. By condensation reaction, polyethylene terephthalate particles (PET) having an limiting viscosity of 0.63 dl / g and a carboxyl terminal group amount of 40 equivalents / ton are obtained. In addition, use PET with CHDM (cyclohexanedimethanol) copolymerized PET. According to the aforementioned method, PET (referred to as TPA / EG / CHDM in the table) obtained by copolymerizing 60 mol% of cyclohexanedimethanol with respect to the glycol component.

． Dispersant

A PBT-PAG (polybutylene terephthalate-polybutanediol) copolymer (manufactured by Toray DuPont Co., Ltd., trade name: Hytrel) was used. This resin is a block copolymer of PBT (polybutylene terephthalate) and PTMG (mainly polytetramethylene glycol), and has a melt index (MI) of 14 (2.160 g, 240 ° C). In addition, the copolymerization ratio was butylene terephthalate: butanediol = 70 mol%: 30 mol% (denoted as PBT / PTMG in the table).

． Porous particles (d) Porous nylon

15% by weight of the particles of nylon 6 were mixed in ethylene glycol (solvent), and the resulting mixture was stirred at 185 ° C. in a mixing tank equipped with a stirrer and carbon dioxide replacement until the nylon 6 was completely dissolved. As shown in FIG. 1, the obtained uniform solution was cooled on a stainless steel belt conveyor maintained at a constant temperature, and nylon 6 porous particles were granulated. At this time, the temperature of the stainless steel belt conveyor was maintained at 75 ° C, and the speed of the conveyor was 5.0 m / min. In addition, on the surface of this belt conveyor, a uniform solution will form a liquid film of 1 to 1.5 mm. The mixture of nylon 6 porous particles and ethylene glycol obtained in this way is separated from the conveyor belt by a scraper, and the ethylene glycol is roughly separated by a centrifugal separator, followed by drying to obtain Polyamide 6 porous particle powder. Particles are obtained in this manner, and then a part of the particle powder is sampled. Using a scanning electron microscope ABT-32 manufactured by Topcon, for example, the observation magnification is 2500 to 10,000 times, so that one is actually drawn in the entire field of view. Particles, and adjust the contrast of the image appropriately to confirm the presence of pores and particle shape. The presence or absence of pores is determined by the presence or absence of speckles and speckle patterns in the particles based on the observed image. The presence of speckles and speckle patterns is determined to have pores, and the absence of pores is designated to be free of pores. In the case of pores, the particles were judged to be porous particles.

． Spherical particles (d) PBT-PTMG particles

Spherical particles made of PBT-PAG (polybutylene terephthalate-polybutanediol) copolymer (manufactured by Toray DuPont Co., Ltd., trade name: Hytrel) were used. This resin is a block copolymer of PBT (polybutylene terephthalate) and PTMG (mainly polytetramethylene glycol), and has a melt index (MI) of 14 (2.160 g, 240 ° C). In addition, the copolymerization ratio was butylene terephthalate: butanediol = 70 mol%: 30 mol%.

． Binder resin in the coating layer (C)

A polyester resin aqueous dispersion (25% by mass of polyester resin, 5% by mass of third butyl cellosolve, and 70% by mass of water) made by Takamatsu Oil & Fat Co., Ltd. was used.

(Examples 1 to 15)

In a composite film forming apparatus having a main extruder and a sub-extruder, the raw material mixture shown in Table 1 as the polyester layer (B) was vacuum-dried at 180 ° C for 3 hours, and then supplied to The main extruder side was melt-extruded at a temperature of 280 ° C., and then filtered through a 30 μm cut filter, and then introduced into a T-die compound nozzle. On the other hand, as for the polyester layer (A), mother particles containing 99.5% by mass of polyester (a) and 0.5% by mass of SiO ₂ particles having an average particle diameter of 2.0 μm were vacuum-dried at a temperature of 180 ° C. 3 After that, it was supplied to a sub-extruder, melt-extruded at a temperature of 280 ° C, filtered through a 30 μm cutoff filter, and then introduced into a T-die compound nozzle. Next, in this T-die compound nozzle, the polyester layer (A) extruded by the sub-extruder was laminated on both sides of the polyester layer (B) extruded by the main extruder (A / B / A) to make them converge, and then co-extruded into a sheet shape to make a molten laminated sheet, and the molten laminated sheet was cooled and solidified by a static charge method on a roller whose surface temperature was maintained at 20 ° C. Stretch laminated film. Next, the unstretched laminated film was preheated by a roll group heated to 85 ° C according to a conventional method, and then stretched in a longitudinal direction (longitudinal direction) using a 90 ° C heating roll, and a roll at a temperature of 25 ° C The group was cooled, and this uniaxially stretched film was guided to a coating device, and the coating liquid was applied using a metal rod # 8 by a rod coating method, and the resin containing the resin particles and the binder resin was applied to become a raw material for the coating layer (C). Coating. Then, while holding both ends of the coated uniaxially stretched film with a jig, guide it to a preheating zone at a temperature of 95 ° C in the tenter, and then continuously in a heating zone at a temperature of 105 ° C to A direction (wide side direction) perpendicular to the long side direction extends. Next, in the heat treatment zone in the tenter, heat treatment is performed at 200 ° C for 20 seconds, and further 4% relaxation treatment is performed at 180 ° C in the broad direction, and then further widened at 140 ° C. 1% relaxation treatment in the side direction. Next, it was slowly cooled uniformly, and then it was wound to obtain a polyester film. The coating liquid was prepared by mixing a polyester resin aqueous dispersion (described as a polyester binder in the table), particles, and water by Takamatsu Oils and Fats Co., Ltd. at a ratio shown in Table 1. Various characteristics are also shown in Table 1. In this step, the porous nylon particles exist in a dispersed state in the coating liquid. However, it is speculated that adsorption of water and resin components constituting the coating liquid may occur in the coating liquid, so that it can exceed 10 μm. Particles of a size are fixed with a binder of 1 to 2 μm. And then extending. In the heat-fixing step, particles are deformed to form amorphous porous particles by heating the particles. In this way, the polyester film of the present invention can be formed into a film stably, and even if it is damaged, the change in glossiness is small, and it exhibits characteristics of excellent surface shape (brightness unevenness reduction effect).

(Comparative Examples 1 to 13)

In a composite film forming apparatus having a main extruder and a sub-extruder, a film of a polyester film was attempted in the same manner as in Examples 1 to 15 in accordance with the raw material mixture and conditions shown in Table 2. However, Comparative Example 8 was unable to form a film. Various characteristics are shown in Table 2. In the example of successful film formation, although the brightness is not uneven when assembled in the backlight without damage, if the damaged film is assembled in the backlight, the gloss of this part will be different from the surrounding gloss, so Uneven brightness occurred.

[Industrial availability]

The polyester film of the present invention is excellent in economy, film-forming property, reflectivity, and surface shape. By using the polyester film, a surface light source can be provided at low cost, which has excellent brightness characteristics and compatibility with other members. Sex.

The polyester film of the present invention can be applied to applications requiring whiteness, reflectivity, and concealment, and particularly preferred applications include plate-shaped materials that are assembled for surface reflection for light reflection. Specifically, it is preferably used for a side-light reflecting plate for a liquid crystal screen, a reflecting plate for a direct type light source, a cold cathode ray tube, and a reflector around LED lighting.

Claims (6)

A polyester film is a polyester film having at least two layers of a polyester layer (A) and a polyester layer (B). The polyester layer (A) forms at least one surface layer of the polyester film. A coating layer (C) containing particles is provided on one surface layer. The particles contained in the coating layer (C) are amorphous porous particles. The volume average particle diameter of the particles is 10 μm or more and 30 μm or less. When the SEM cross-section photograph of each protrusion was generated, the average value Dh of the distance (protrusion height) dh from the top of the polyester layer (A) to the outermost surface of the polyester layer (A) was 10 μm or more and 30 μm or less. The protrusion was in phase with the polyester layer (A). The average length dw (width of the bottom of the protrusion) dw of Dw is 10 μm or more and 35 μm or less, and the ratio of Dh to Dw Dh / Dw is 0.70 or more and 1.00 or less. The average length of the particle length (width of the center of the protrusion) dv of the particles in the direction of layer A parallel to the height of / 2 is 10 μm or more and 35 μm or less, and the ratio Dh / Dv of Dh / Dv is 0.90 or more and 1.00 or less. The Dw ratio Dv / Dw is 0.80 or more and 1.05 or less, and the particles are 1,000 or more and 2000 or less per 1 mm ² of the film surface. The polyester film of claim 1, wherein the porous particles are organic particles. For example, the polyester film of claim 1 or 2, wherein the porous plasmid is mainly composed of 6-nylon. For example, the polyester film of claim 1 or 2, wherein the 60 ° gloss change value after the surface abrasion test of the side surface of the coating layer (C) is less than 30%. The polyester film of claim 3, wherein the 60 ° gloss change after the surface abrasion test of the side surface of the coating layer (C) is less than 30%. A reflective film for a liquid crystal display using a polyester film according to any one of claims 1 to 5.