JP2013120313A - White polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film excellent in film forming property, whiteness, reflectivity, lightweight property and compatibility with other members, and to provide a surface light source excellent in luminance characteristic and lightweight property by using the white polyester film.SOLUTION: The white polyester film includes a skin layer on at least one surface of a polyester layer (A) containing bubbles. The film has 0.5 or less specific gravity and contains inorganic particles (c) on the skin layer by 5 to 30% with respect to the whole weight of the skin layer, with the inorganic particles (c) having an apparent density of 0.5 g/cmor less.

Description

  The present invention relates to a white polyester film, and more particularly to a white polyester film that is optimal as a surface light source reflector for a liquid crystal display. Specifically, when the white polyester film is used for a backlight of a liquid crystal display, illumination such as a fluorescent tube or an LED (light emitting diode) is arranged on the top or side of the white polyester film, so that it is brighter. The present invention relates to a white polyester film that can provide a screen with less unevenness and that does not damage other members of a liquid crystal display such as a light guide plate.

  Liquid crystal displays, which are frequently used in various electronic devices such as mobile terminals such as televisions, personal computers, and tablet computers, are provided with a light source called a backlight at the rear of the display for screen display. Moreover, the backlight needs to irradiate the whole screen uniformly. As a system satisfying this characteristic, there are surface light source structures called a side light type and a direct type. In particular, a thin display used for a notebook personal computer or the like employs a sidelight type, that is, a type of backlight that emits light from the side of the screen. In general, in the side light type, a sheet called a light guide plate, which has been subjected to various treatments such as halftone printing or embossing on one side of a transparent substrate such as an acrylic plate having a certain thickness, is used. By applying light from the light source on the side to the edge of the acrylic plate or the like, the illumination light is evenly distributed upward, and a screen having uniform brightness can be obtained. In addition, since the illumination is installed only on the edge portion, not on the rear surface of the screen, the number of light sources can be reduced, the cost and weight can be reduced, and the backlight system can be made thinner. Furthermore, in order to prevent the illumination light from escaping to the back of the screen, a reflector is provided on the back of the screen, thereby reducing the loss of light from the light source and brightening the liquid crystal screen.

  Films used as reflectors and reflectors (generally referred to as surface light source reflecting members) used for such surface light sources for liquid crystal screens are not only thin films but also have high reflection performance, especially for portable terminals For example, weight reduction is desired. Conventionally, a film added with a white pigment, a film containing fine bubbles inside, or a film obtained by laminating these films and a plastic plate has been used. Among these, in particular, a film containing bubbles inside obtained by stretching a sheet containing fine particles of incompatible resin and a white pigment is widely used because of its excellent luminance (Patent Documents 1 and 2, 3, 4).

In addition, a light reflector containing a filler using a general-purpose polyolefin resin as a lightweight material is disclosed. (Patent Document 5)
On the other hand, when placed in an environment where the change of temperature and humidity conditions is large on the premise of long-term use, the members are distorted due to the difference in coefficient of thermal expansion of each member. At this time, if the surface irregularity of the film is small, that is, the flatness is high, scratching between members occurs, and this repetition promotes deterioration of the member and deteriorates characteristics from scratches caused by rubbing. Moreover, it becomes easy to adhere | attach with a light-guide plate, the brightness | luminance of an adhesion part becomes higher than another part, and the difference of brightness will generate | occur | produce. Then, examination which prevents adhesion | attachment with a light-guide plate is made | formed by coating and roughening the layer containing a coarse particle (patent document 6).

JP 2009-98660 A JP-A-2005-350615 JP 2009-173015 A JP 2002-098808 A JP 2005-4195 A JP 2004-126345 A

  However, when surface irregularities are imparted by adding general inorganic particles, etc., vibration during transportation and the irregularities will scrape various processing surfaces such as halftone dot printing and embossing on the light guide plate, causing a decrease in brightness. End up. Furthermore, since inorganic particles generally have a large specific gravity, in order to impart the surface shape as described above, it is necessary to contain inorganic particles that greatly affect the specific gravity of the entire film, and it is difficult to reduce the weight. Met. Even when a low specific gravity resin other than polyester is used, there is a problem in productivity, such as adding a large amount of an additive or using a high-purity raw material, in order to increase the reflectance. Moreover, in the conventional technology, in order to achieve high reflection characteristics, compatibility with the light guide plate and weight reduction at the same time, a layer for improving compatibility with other members such as organic particles must be provided by coating, There were problems with productivity and cost. Therefore, the present invention has no processes other than extrusion molding such as coating a white polyester film having excellent film forming properties, reflectivity, light weight, and compatibility with other members that could not be achieved by the above-described conventional studies. It is an issue to provide. Another object of the present invention is to provide a surface light source reflecting member having excellent luminance characteristics at low cost by using the white polyester film.

In order to solve the above problems, the present invention has the following configuration. That is, the white polyester film of the present invention is
(1) A polyester film having a skin layer on at least one surface of the polyester layer (A) containing air bubbles, wherein the specific gravity of the film is 0.5 or less, and inorganic particles (c) are applied to the skin layer of the skin layer. A white polyester film containing 5 to 30% based on the total weight and having an apparent density of inorganic particles (c) of 0.5 g / cm ³ or less.
(2) The white particle film according to (1), wherein the inorganic particles (c) have an average particle size of 10 μm to 20 μm.
(3) The white polyester film according to (1) or (2), wherein the inorganic particles (c) are talc.
(4) The white polyester film according to any one of (1) to (3), wherein the inorganic particles (c) are talc, and the water content of the talc is less than 1.0%.
(5) The 60 ° gloss of the outermost layer of at least one surface of the polyester layer (A) is 20 or less, the center line average roughness (Ra), and the ten-point average roughness (Rz)
500 nm ≦ Ra and
6000 nm ≦ Rz
The white polyester film according to any one of (1) to (4), wherein
(6) A surface light source reflector for a liquid crystal display using the white polyester film according to any one of (1) to (5).

  INDUSTRIAL APPLICABILITY The present invention can easily and inexpensively produce a white polyester film having high reflectivity, light weight, and compatibility with other members. Particularly, the white polyester film is used as a reflector or reflector in a surface light source. When used as, it can brightly illuminate the liquid crystal screen, make the liquid crystal image clearer and easier to see, and can be useful because it can reduce the lightness and damage to other components that are required for mobile terminals with a liquid crystal display Is something.

It is the schematic sectional drawing of the liquid crystal screen incorporating the white polyester film for light reflection, and the schematic of the brightness | luminance measuring method.

Hereinafter, the present invention will be described in detail.
[Configuration of white polyester film]
The white polyester film of the present invention is a polyester film having a polyester layer (A). The polyester layer (A) must contain a polyester resin (a), a polyolefin (b) that is incompatible with the polyester resin (a), and air bubbles in terms of optical properties such as luminance and reflectance. is there.

  In the white polyester film of the present invention, the polyester layer (A) is a layer containing air bubbles, and the skin layer (B) containing inorganic particles (c) is laminated on at least one side thereof. From the viewpoint of optical properties and compatibility with other members.

  By using the polyester resin (a) and the polyolefin (b), it is possible to easily contain bubbles having the polyolefin (b) as a core by a method as described later, and it is a lightweight and white having high reflection characteristics. A polyester film can be produced. Voids may be formed around the inorganic particles (c).

  Considering the ease of film formation and effects, a structure of two or more layers is necessary, and a three-layer structure is preferable. In particular, a form in which the polyester layer (A) is protected by the skin layer (B), that is, a three-layer structure of skin layer (B) / polyester layer (A) / skin layer (B) is preferable. Moreover, when it becomes a multilayer, it is preferable that a core layer part is a polyester layer (A), and the surface layer part of the one side or both sides is a skin layer (B).

  The thickness of the skin layer (B) of the white polyester film of the present invention is preferably 2 to 12 μm. If the thickness of the skin layer (B) is less than 2, it will be remarkably easily broken due to the influence of the polyester layer (A) containing a large number of air bubbles, so that not only stable film formation but also inorganic particles (c) are likely to fall off. This is undesirable because it contaminates the process. When the thickness of the skin layer (B) exceeds 12 μm, when the film is used as a reflector, light is difficult to reach the polyester layer (A), and the components reflected at the interface between the bubbles and the polyester are reduced. This is not preferable because optical characteristics such as reflectance and luminance are deteriorated.

  The white polyester film of the present invention is a white polyester film in which two or more polyester layers having the above-described configuration are laminated, and controls the light diffusibility of reflected light or imparts high mechanical strength to the film. Alternatively, a layer having a film forming property, an antistatic property, a light resistance, or any other function having an accompanying function may be laminated. By using a multi-layer structure, various characteristics of each layer can be controlled.

[Polyester resin (a)]
In the white polyester film of the present invention, one or more polyester resins can be used as the polyester resin (a), but it is preferable that the polyester resin (a1) and the polyester resin (a2) described later are included. By using the polyester resin (a1) and the polyester resin (a2), a white polyester film having high optical properties can be stably obtained.

  The polyester resin (a1) comprises 1) polycondensation of a dicarboxylic acid component or an ester-forming derivative thereof (hereinafter collectively referred to as “dicarboxylic acid component”) and a diol component, and 2) a carboxylic acid or carboxylic acid derivative skeleton in one molecule. And a polycondensation of a compound having a hydroxyl group and 1) 2).

  In 1), as the dicarboxylic acid component constituting such polyester resin, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelain Acids, aliphatic dicarboxylic acids such as methylmalonic acid, ethylmalonic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1 , 8-Naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9′-bis (4-carboxyl) Aromatic dica such as phenyl) fluorenic acid Typical examples include dicarboxylic acids such as boric acid, or ester derivatives thereof, but are not limited thereto, and for example, polymellitic acids such as trimellitic acid, pyromellitic acid, and ester derivatives thereof are preferably used. Can do. Moreover, these may be used independently or may be used in multiple types as needed.

  Also, dicarboxy compounds obtained by adding oxyacids such as l-lactide, d-lactide, hydroxybenzoic acid, and derivatives thereof, and a combination of a plurality of the oxyacids to the carboxy terminus of the dicarboxylic acid component described above. Preferably used.

  Examples of the diol component constituting the polyester resin in 1) include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3. -Aliphatic diols such as butanediol, aromatic diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene, etc. Examples of such diols include, but are not limited to, diols. Moreover, these may be used independently or may be used in multiple types as needed.

  In addition, in 2), examples of the compound having a carboxylic acid or a carboxylic acid derivative skeleton and a hydroxyl group in one molecule include oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, and derivatives thereof, and oxyacids thereof. And a dicarboxy compound to which a plurality of is added.

  The polyester resin (a1) can be obtained by polycondensation by appropriately combining the above compounds. Polyesters suitably used for the polyester resin (a1) include polyethylene terephthalate (hereinafter sometimes abbreviated as PET), polyethylene-2,6-naphthalenedicarboxylate (hereinafter sometimes abbreviated as PEN), and the like. Examples thereof include polypropylene terephthalate (hereinafter sometimes abbreviated as PPT), polybutylene terephthalate (hereinafter sometimes abbreviated as PBT), and the like.

  By using the above-mentioned resin as the polyester resin (a1) used in the present invention, high mechanical strength can be imparted when a film is formed while maintaining no coloration. More preferably, PET or PEN is preferable because it is inexpensive and has excellent water resistance, durability, and chemical resistance. In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester.

Here, in the white polyester film of the present invention, the polyester resin (a) has a polyester resin component (a2), and the polyester resin component (a2) contains an alicyclic diol component having 4 to 8 carbon atoms. It is preferable to do. Here, the alicyclic group having 4 to 8 carbon atoms in the present invention is a cycloalkane, and is a cyclic aliphatic represented by the general formula C _n H _2n (where 4 ≦ n ≦ 8). A general term for hydrocarbons.

  The alicyclic diol having 4 or more and 8 or less carbon atoms refers to a substance having the structure of both a cyclic aliphatic hydrocarbon part having 4 to 8 carbon atoms and a diol part. That is, specific examples of the alicyclic diol having 4 to 8 carbon atoms include cyclobutanediol, cyclopentanediol, cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclopropanedimethanol, cyclobutanedimethanol, cyclopentane. Examples include dimethanol, cyclohexane dimethanol, cycloheptane dimethanol, and cyclooctane dimethanol.

  The diol component bonded to the cycloaliphatic hydrocarbon moiety having 4 to 8 carbon atoms may be bonded to any carbon atom of the cycloaliphatic hydrocarbon moiety. For example, the cycloaliphatic hydrocarbon moiety When is a cyclohexane, it is preferable that a diol component is bonded to positions 1 and 4.

  Of the alicyclic diols having 4 to 8 carbon atoms, 1,4-cyclohexanedimethanol (CHDM) is particularly preferable because it is easy to mix with a monomer price and a polyester resin (particularly PET). Used for.

  In addition, the diol component in this invention is not limited to the component which exists as diol, The case where it contains as a structural component of polyester, for example, a copolymer, or a mixture of these resin is also included.

  In the white polyester film of the present invention, the content of the polyester resin component (a2) is preferably 1.2 to 36% by mass with respect to the entire film. More preferably, it is 1.9-30 mass%, More preferably, it is 2.4-26 mass, Most preferably, it is 3.3-20 mass%. When the content of the polyester resin component (a2) is less than 1.2% by mass, the fine dispersion effect of the polyolefin (b) is lowered and the reflection performance is lowered, which is not preferable. Moreover, when it exceeds 36 mass%, the heat resistance of a white polyester film will fall and a dimensional change may become large when exposed to high temperature, and is unpreferable. In the white polyester film of the present invention, by making the content of the polyester resin component (a2) 1.2 to 36% by mass, a white polyester film having film forming stability, reflectivity and dimensional stability is obtained. Can do.

[Bubble formation]
The white polyester film of the present invention preferably has a relative reflectance of 100% or more. More preferably, it is 100.5% or more, More preferably, it is 101% or more. There is no particular upper limit on the relative reflectance, but in order to increase the reflectance, it is necessary to increase the amount of polyolefin (b) as a bubble-forming nucleating agent, in which case the film forming property may become unstable. Therefore, it is preferably 110% or less. Here, the relative reflectance means that an integrating sphere made of barium sulfate on the inner surface, a spectrophotometer equipped with a 10 ° inclined spacer, aluminum oxide as a standard white plate, and light incident at an incident angle of 10 °. Is a reflectance obtained by averaging the relative reflectance at a wavelength of 560 nm when the reflectance of the standard white plate is 100%. In the white polyester film of the present invention, by setting the relative reflectance to 100% or more, a white polyester film excellent in whiteness and reflection characteristics can be obtained, and particularly when used for a liquid crystal display device, a high luminance improvement is achieved. An effect can be obtained.

  Here, in order to adjust the relative reflectance of the white polyester film of the present invention within the above-mentioned range, it is important that the film is whitened by containing bubbles and inorganic particles, thereby scattering light. Since the effect is exhibited, the reflectance can be improved.

  Formation of bubbles is achieved by finely dispersing a high melting point polyester and polyolefin (b) or inorganic particles in a film base material such as polyester, and stretching (for example, biaxial stretching). During stretching, bubbles are formed around the polyolefin (b), and the number of interfaces between the bubbles and the polyester in the film thickness direction (sometimes referred to as the number of interfaces) is 15 or more per 10 μm of film thickness. Preferably, it is 20 or more, more preferably 25 or more. When the number of the interfaces is 15 or more, this exhibits light reflection and scattering action, so that it is whitened and high reflectance can be obtained. If the number of interfaces is less than 15, the light reflection and scattering actions are insufficient, and this is not preferable because whitening and high reflectance are not achieved.

[Polyolefin (b)]
Although it is necessary for the white polyester film of the present invention to have air bubbles inside the polyester film, as described above, air bubbles can be formed by containing the polyolefin (b) incompatible with the polyester.

  In the white polyester film of the present invention, when a thermoplastic resin is used as the polyolefin (b), the resin is preferably used for both crystalline and amorphous. Specific examples thereof include linear, branched, or cyclic polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene. The polyolefin may be a homopolymer or a copolymer, and two or more incompatible resins may be used in combination. Among these, polyolefin is preferably used in terms of excellent transparency and heat resistance. Specifically, polypropylene or polymethylpentene is preferably used as the crystalline polyolefin, and a cycloolefin copolymer is preferably used as the amorphous polyolefin.

  When the polyester resin (a) is used and the polyolefin (b) is used as an incompatible component for the polyester resin (a), specific examples of the crystalline resin are from the viewpoint of transparency and heat resistance. Polymethylpentene is more preferably used. Here, as polymethylpentene, those containing a derivative unit from 4-methylpentene-1 in the molecular skeleton are preferably 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more. . Examples of other derived units include hydrocarbons having 6 to 12 carbon atoms other than ethylene units, propylene units, butene-1 units, 3-methylbutene-1, or 4-methylpentene-1. The polymethylpentene may be a homopolymer or a copolymer. Further, a plurality of polymethylpentenes having different compositions and melt viscosities may be used, or other olefinic resins and other resins may be used in combination.

  In the white polyester film of the present invention, when an amorphous polyolefin is used as the polyolefin (b), a cyclic olefin copolymer resin can be particularly preferably used. The cyclic olefin copolymer is composed of at least one cycloolefin selected from the group consisting of cycloalkene, bicycloalkene, tricycloalkene, tetracycloalkene and pentacycloalkene, and linear olefin such as ethylene and propylene. Mention may be made of copolymers. The amorphous resin as used herein refers to a resin having a heat of crystal fusion of less than 1 cal / g.

Representative examples of the cyclic olefin in the cyclic olefin copolymer resin include bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, 5,6- Dimethylbicyclo [2,2,1] hept-2-ene, 1-methylbicyclo [2,2,1] hept-2-ene, 6-ethylbicyclo [2,2,1] hept-2-ene, 6 N-butylbicyclo [2,2,1] hept-2-ene, 6-i-butylbicyclo [2,2,1] hept-2-ene, 7-methylbicyclo [2,2,1] hept- 2-ene, tricyclo [4,3,0,1 ^2.5] -3-decene, 2-methyl - tricyclo [4,3,0,1 ^2.5] -3-decene, 5-methyl - tricyclo [4,3, 0,1 ^2.5] -3-decene, tricyclo [4,4,0,1 ^2.5] -3 Decene, 10-methyl - there is tricyclo [4,4,0,1 ^2.5] -3-decene.

  Moreover, as a typical example of the linear olefin in cyclic olefin copolymer resin, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and the like.

  In the present invention, as the polyolefin (b), among those mentioned above, an alicyclic diol and / or an aliphatic olefin copolymer resin, which is an amorphous resin, is contained in a matrix as described later. It is particularly preferably used because it can be more finely dispersed by the interaction with the cyclic dicarboxylic acid, and as a result, the reflection characteristics can be further enhanced.

  In the present invention, the polyolefin (b) preferably has a glass transition temperature Tg of 170 ° C. or higher. More preferably, it is 180 degreeC or more. It is because it can disperse | distribute more finely in matrix resin at the time of kneading | mixing by setting it as 170 degreeC or more, a bubble can be formed in a extending process, and the loss | disappearance of the bubble in a heat treatment process can be suppressed more. The upper limit is preferably 250 ° C. Exceeding 250 ° C. is not preferable because the extrusion temperature during film formation becomes high and the processability is poor.

  In particular, in the present invention, when a cyclic olefin copolymer resin is used as the polyolefin (b), when the glass transition temperature Tg is less than 170 ° C., when heat treatment of the film is performed to impart dimensional stability, The cyclic olefin copolymer resin, which is a nucleating agent, is deformed, and as a result, bubbles formed using the olefin as a nucleus may be reduced or disappeared, and reflection characteristics may be deteriorated. Further, if the heat treatment temperature is lowered to maintain the reflection characteristics, the dimensional stability of the film may be lowered in that case, which is not preferable.

  When the cyclic olefin copolymer resin is used as the polyolefin (b), in order to control the glass transition temperature Tg within the above-mentioned range, for example, the content of the cyclic olefin component in the cyclic olefin copolymer is increased, It is possible to reduce the content of linear olefin components such as ethylene. Specifically, the cyclic olefin component is 60 mol% or more, and the content of linear olefin components such as ethylene is preferably less than 40 mol%. More preferably, the cyclic olefin component is 70 mol% or more, the content of the linear olefin component such as ethylene is less than 30 mol%, more preferably the cyclic olefin component is 80 mol% or more, and the linear chain such as ethylene. The content of the olefin component is less than 20 mol%. Particularly preferably, the cyclic olefin component is 90 mol% or more, and the content of linear olefin components such as ethylene is less than 10 mol%. By setting it as this range, the glass transition temperature Tg of a cyclic olefin copolymer can be raised to the above-mentioned range.

  Moreover, when using cyclic olefin copolymer resin as polyolefin (b), although a linear olefin component is not restrict | limited in particular, an ethylene component is preferable from a reactive viewpoint.

  Furthermore, the cyclic olefin component is not particularly limited, but bicyclo [2,2,1] hept-2-ene (norbornene) and its derivatives are preferable from the viewpoint of productivity, transparency, and high Tg.

  Therefore, in this invention, it is preferable that the white polyester film has polyester resin (a) and polyolefin (b), and polyolefin (b) has a glass transition temperature of 170 degreeC or more and 250 degrees C or less. Furthermore, the polyolefin (b) is preferably amorphous, and more preferably (non-crystalline) cyclic olefin copolymer resin.

  In the present invention, the addition amount of the polyolefin (b) is preferably 5 to 25% by mass when the total mass of the entire polyester film is 100% by mass. If the content of the polyolefin (b) is less than 5% by mass, sufficient bubbles are not generated inside the film, and the whiteness and light reflection characteristics may be inferior. On the other hand, when the content of the polyolefin (b) exceeds 25% by mass, the strength of the film is lowered and breakage at the time of stretching may easily occur. By setting the content within this range, sufficient whiteness, reflectivity, and lightness can be exhibited.

  The polyolefin (b) is more preferably dispersed uniformly and finely. By uniformly and finely dispersing, bubbles are uniformly formed inside the film, and the reflectance becomes uniform.

  The average dispersion diameter of the polyolefin (b) is from 0.2 μm to 5 μm, and more preferably from 0.3 μm to 3 μm.

  When the average dispersion diameter of the polyolefin (b) is smaller than the above range, it is difficult to form bubbles having the polyolefin (b) as a nucleus, which is not preferable. On the other hand, if it is larger than the above range, the bubble size becomes large, the reflectance cannot be increased, and the film strength and the film-forming stability are deteriorated.

[Dispersant (d)]
In order to uniformly disperse the polyolefin (b), it is effective to add the dispersant (d). As the dispersant (d), for example, for polyester, polyalkylene glycol such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, polypropylene glycol, ethylene oxide / propylene oxide copolymer, and sodium dodecylbenzenesulfonate. , Alkylsulfonate sodium salt, glycerol monostearate, tetrabutylphosphonium paraaminobenzenesulfonate, and the like. In the case of the present invention, polyalkylene glycol, particularly polyethylene glycol is particularly preferable. A copolymer of polybutylene terephthalate and polytetramethylene glycol is also preferably used for improving the dispersibility of the incompatible polyolefin (b). The addition amount is preferably 3% by mass or more and 20% by mass or less, and particularly preferably 10% by mass or more and 15% by mass or less, based on the total mass of the polyester film. If the amount of the dispersant (d) added is too small, the effect of the addition is reduced, and if it is too large, the original properties of the film base material may be impaired. Such a dispersant (d) can be added in advance to the film base polymer and adjusted as a master polymer (master chip). [Inorganic particles (c)]
The white polyester film of the present invention requires that the 60 ° glossiness of the polyester layer (A) side surface layer is 20 or less. When a white polyester film with a glossiness outside the above range is used as a surface light source reflector, the component that directly reflects the light of the illumination light source on the liquid crystal screen increases, so the difference in brightness (lamp unevenness depending on the interval of the illumination light source). ) Occurs, the brightness of the liquid crystal screen may not be uniform, which is not preferable. By setting the gloss level within the above range, a film that reflects light from the illumination light source uniformly and uniformly to the liquid crystal cell is obtained.

  Moreover, in the white polyester film of this invention, it is preferable that the center plane average roughness (Ra) of the polyester (A) side surface is 500 nm or more, and 10-point average roughness (Rz) is 6000 nm or more. The numerical values of Ra and Rz are related to the unevenness of the film surface. By providing irregularities on the film surface, the specular reflection component of light reflection on the film surface is reduced, and the glossiness of the film can be lowered. As described above, when the film is used as a backlight member due to low glossiness, luminance unevenness can be reduced, and thus a liquid crystal display capable of displaying a more uniform brightness image is provided. Can do.

  Even if Ra is in the above range, if Rz is less than 6000 nm, the glossiness exceeds 20, which is not preferable.

  Even if Rz is in the above range, if Ra is less than 500 nm, the portions other than the protrusions on the film surface become smooth and high gloss, which is not preferable. When both Ra and Rz values are in the above ranges, the film becomes low gloss, the handling in the subsequent process such as incorporation into the backlight housing is improved, and other members are less likely to be damaged during transportation. preferable. .

  In order to achieve the above, it is necessary to contain inorganic particles (c) in the skin layer (B) of the white polyester film of the present invention.

Further, the apparent density of the inorganic particles (c) is required to be 0.5 g / cm ³ or less. If the apparent density of the inorganic particles (c) exceeds 0.5 g / cm ³ or less, it is difficult to make the specific gravity of the polyester film 0.5 or less. The apparent density is more preferably 0.3 g / cm ³ or less of the inorganic particles (c), 0.1g / cm ³ or less is particularly preferred.

  The water content of the inorganic particles (c) needs to be 1.0% or less. When the water content exceeds 1.0%, hydrolysis is promoted when melt-kneading with the polyester resin (a1) or the polyester resin (a2), which hinders master pellet formation or film formation.

  The type of particles used as the inorganic particles (c) is not particularly limited, and mica, mica titanium, talc, clay, kaolin and the like are preferable. Moreover, they can be used individually or in mixture of 2 or more types. Talc and clay are preferable from the viewpoints of the dispersion diameter stability and lightness of the particles and the stability of film formation, and talc is more preferable. Moreover, it may be in the form of a porous or hollow porous material, and may be subjected to a surface treatment in order to improve the dispersibility with respect to the resin within the range not impairing the effects of the present invention.

  Moreover, it is preferable that the volume average particle diameter of an inorganic particle (c) is 10-20 micrometers. If it is less than 10 μm, it becomes difficult to make Rz in the above-mentioned range, and the film surface becomes smoother, so that the glossiness increases. If the volume average particle diameter of the inorganic particles (c) exceeds 20 μm, the particles are likely to fall off from the film, causing process contamination and tearing, and the productivity is lowered.

  Moreover, content of an inorganic particle (c) needs to be 5-30 mass% when the total mass of a skin layer (B) is 100 mass%. When the content of the inorganic particles (c) is less than 5% by mass, the surface layer (B) side surface has less unevenness, and the Ra and Rz values do not fall within the above ranges, resulting in insufficient light diffusibility and glossiness. Will go up. When the content of the inorganic particles (c) exceeds 30% by mass, the specific gravity of the film increases, the film breaks during stretching, and the process contamination and powder generation during post-processing are likely to occur due to particle dropping from the film. , Productivity and handling are reduced.

  In the white polyester film of the present invention, when talc or the like is used as the inorganic particles (c), air bubbles having these as nuclei may be formed. Moreover, you may make a polyester layer (A) contain an inorganic particle (c) in the range which does not impair a characteristic.

  By using the polyolefin (b) and the inorganic particles (c), the apparent specific gravity of the polyester film is lower than that of a normal polyester film. In order to reduce the weight of this white polyester film while maintaining the mechanical properties as a substrate for a liquid crystal display reflector, it is necessary that the specific gravity be 0.3 or more and 0.6 or less.

  In order to make the specific gravity 0.3 or more and 0.6 or less, it is achieved by containing 5 to 25 mass% of polyolefin (b) with respect to the whole polyester film and setting the draw ratio to 2.5 to 4.5. can do. When the apparent specific gravity is within the range of the present invention, a large number of fine bubbles can be present while maintaining the film strength, and a high reflectance can be obtained. That is, when it is used as a liquid crystal display reflector, it exhibits outstanding performance in terms of screen brightness.

[Method of blending particles]
Various methods can be used as a method of blending the inorganic particles (c) into the polyester composition. The following method can be mentioned as the typical method. (A) A method of adding particles before the end of the ester exchange reaction or esterification reaction during polyester synthesis, or a method of adding particles before the start of the polycondensation reaction. (A) A method in which particles are added to polyester and melt kneaded. (C) A method of producing master pellets in which a large amount of particles are added in the above method (a) or (b) and kneading these with a polyester not containing additives to contain a predetermined amount of additives. (D) A method of using the master pellet of (c) as it is.

  As the blending method of the polyolefin (b) and the inorganic particles (c), it is particularly preferable to take the above method (c) or (d) from the viewpoint of dispersibility of the particles.

[Film forming method]
An example of the method for obtaining the polyester resin (a1) will be described, 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 to the resulting polyester pellets to 300 ppm in terms of antimony atoms, and a polycondensation reaction was performed. Polyethylene terephthalate pellets (polyester resin (a1)) can be obtained.

  An example of the method for obtaining the polyester resin (a2) will be described, but it is not limited to this example. Add terephthalic acid as the dicarboxylic acid component, alicyclic diol having 4 to 8 carbon atoms as the diol component, and magnesium acetate, antimony trioxide, phosphorous acid as the catalyst to add 300 ppm in terms of antimony atoms A polyester resin (a2) obtained by copolymerizing an alicyclic diol having 4 to 8 carbon atoms and terephthalic acid can be obtained by performing a polycondensation reaction.

  An example of the method for obtaining the polyolefin (b) will be described, but it is not limited to such an example. Polyolefin (b) is a product obtained by polymerizing the above-mentioned cycloolefin and olefin by a known method (for example, JP-A-61-271308, WO 2007/060723 pamphlet) or a commercial product (for example, “TOPAS” ( Polyplastics Co., Ltd.)) can be purchased.

  As the inorganic particles (c), polyester resin (a1) master pellets containing the inorganic particles (c) can be used.

  An example of the method for obtaining the dispersant (d) will be described, but it is not limited to such an example. The dispersant (d) is a block copolymer of PBT (polybutylene terephthalate) and PAG (mainly polytetramethylene glycol), and has a melt index (MI) of 14 (2.160 g, 240 ° C.). The copolymerization ratio is butylene terephthalate: alkylene glycol = 70 mol%: 30 mol (for example, “Hytrel” (manufactured by Toray DuPont Co., Ltd.)).

  Next, although an example is demonstrated about the manufacturing method of the white polyester film of this invention, this invention is not limited only to this example.

  A film forming apparatus having an extruder, which is sufficiently vacuum dried, if necessary, for a mixture containing the polyester resin (a1), the polyester resin (a2), the polyolefin (b), the inorganic particles (c), and the dispersant (d). To the heated extruder. The addition of the polyolefin (b) and the inorganic particles (c) may be performed using a master chip prepared by melt-kneading uniformly in advance or may be supplied directly to a kneading extruder. The addition of the polyester resin component (a2) can be performed when the mixture containing the polyester resin (a1) and the polyolefin (b) is uniformly melted and kneaded in advance to add the master chip, or directly into the kneading extruder. Although it may be supplied, the dispersion of the polyolefin (b) is facilitated by adding a mixture containing the polyester resin (a1) and the polyolefin (b) in advance and melt-kneading the master chip. It is more preferable in that it is.

  In addition, it is preferable to obtain a molten sheet by extrusion molding after being filtered through a filter having a mesh of 40 μm or less during melt extrusion and then introduced into a T die die.

  This molten sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to produce an unstretched single layer film. The unstretched single layer film is led to a roll group heated to a temperature of 70 to 120 ° C., and stretched 2.5 to 4 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and a temperature of 20 to 50 ° C. Cool with a group of rolls. Subsequently, the film is held at both ends with a clip, guided to a tenter, and stretched 2.5 to 4 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 90 to 150 ° C. .

  The stretching ratio is 2.5 to 4 times in the longitudinal direction and the width direction, respectively, but the area ratio (longitudinal stretching ratio x lateral stretching ratio) is preferably 9 to 16 times. If the area magnification is less than 9 times, the resulting biaxially stretched film has insufficient reflectance and film strength. Conversely, if the area magnification exceeds 16 times, the film tends to be broken during stretching.

  In order to complete the crystal orientation of the obtained biaxially stretched film and to impart dimensional stability, heat treatment is subsequently performed in a tenter at a temperature of 150 to 240 ° C. for 1 to 30 seconds, and after uniform cooling The white polyester film of the present invention can be obtained by cooling to room temperature, and then, if necessary, performing corona discharge treatment or the like in order to further improve the adhesion to other materials and winding. During the heat treatment step, a relaxation treatment of 3 to 12% may be performed in the width direction or the longitudinal direction as necessary.

  In general, the higher the heat treatment temperature, the higher the thermal dimensional stability. However, the white polyester film of the present invention is preferably heat treated at a high temperature (190 ° C. or higher) in the film forming process. This is because the white polyester film of the present invention is desired to have a certain thermal dimensional stability. The white polyester film of the present invention may be used as a reflective film for a surface light source (backlight) mounted on a liquid crystal display or the like. This is because the ambient temperature inside the backlight may rise to about 100 ° C. depending on the backlight.

  In particular, by setting the glass transition temperature Tg of the polyolefin (b) within the above-mentioned temperature range, the polyolefin (b), which is a nucleating agent for generating voids, is not further thermally deformed (crushed) even in heat treatment at a high temperature. It is preferable because a film having excellent light resistance can be obtained while maintaining high whiteness, reflection characteristics, and light weight as a result.

  In addition, the biaxial stretching method may be either sequential stretching or simultaneous biaxial stretching. However, when the simultaneous biaxial stretching method is used, it is possible to prevent film breakage in the manufacturing process or to adhere to a heating roll. Transfer defects are less likely to occur. Further, after biaxial stretching, it may be re-stretched in either the longitudinal direction or the width direction.

  The white polyester film of the present invention thus obtained was used as a surface light source reflector for a liquid crystal display because the surface layer on at least one side had a low gloss, air bubbles were formed inside the film, the reflectance was light, and it was lightweight. In some cases, high brightness can be obtained. Moreover, it is hard to damage other members.

[Measurement of physical properties and evaluation method of effects]
Measurement Method The physical property value evaluation method and effect evaluation method of the present invention are as follows.

A. Apparent density of the inorganic particles (c) Based on JIS K-5101 (2004), the inorganic particles (c) were ground into the receiver using an apparent density measuring device (30 cm ³ ) manufactured by Tsutsui Rika Kikai Co., Ltd. The weight of the contents was measured, and the apparent density was obtained by dividing the weight by 30.

B. Water content of inorganic particles (c) Based on JIS K-5010 (2004), 10 g of inorganic particles (c) were measured and dried for 2 hours with a drier kept at 105 ° C., and then the weight was measured. The water content was determined by dividing the reduced mass by 10.

C. Volume average particle diameter A cross section of a film or a master pellet was cut out using a microtome. In the case of a film, a cross section in a direction parallel to the TD direction (film width direction (hereinafter sometimes referred to as “lateral direction”)) was cut out. After depositing platinum-palladium on the cross section, a cross-sectional photograph of 3000 to 5000 times was taken with a field emission scanning electron microscope “JSM-6700F” manufactured by JEOL. In the case of powder, the sample was placed on the sample stage of the electron microscope so that the particles did not overlap as much as possible, and photographed by the same method and conditions as the cross section of the film or master pellet. From the obtained image, the volume average particle diameter of the inorganic particles was determined by the following procedure.

1) About the inorganic particle observed in the cross section in this image, the cross-sectional area S was calculated | required, respectively, and the particle diameter d calculated | required by following formula (1) was calculated | required, respectively.
d = 2 × (S / π) ^1/2 (1)
(Where π is the circumference)
2) The volume average particle diameter Dv was calculated | required in following formula (2) using the obtained particle diameter d.
Dv = Σ [4 / 3π × (d / 2) ³ × d] / Σ [4 / 3π × (d / 2) ³ ] (2)
3) The above 1) to 2) are carried out at five different places, and the volume average particle diameter is determined by the average value. Note that the above evaluation is performed in an area of 2500 μm ² or more per observation point.

D. Reflectivity An integrating sphere is attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies, and the reflectivity is measured over 400 to 700 nm when the standard white plate (aluminum oxide) is 100%. The reflectance is read from the obtained chart at intervals of 5 nm, and the average value is calculated to obtain the average reflectance.

E. Specific gravity of film A white film was cut into a size of 5 cm × 5 cm, and measured using an electronic hydrometer SD-120L (Mirage Trading Co., Ltd.) based on JIS K7112 (1980). In addition, 5 sheets were prepared for each white film, each was measured, and the average value was used as the specific gravity of the white film.

F. Glossiness Measured according to JIS Z-8741 (1997) from the polyester (A) layer side of the light reflection film using a digital variable glossiness meter UGV-5B (manufactured by Suga Test Instruments Co., Ltd.). The measurement conditions were an incident angle = 60 ° and a light receiving angle = 60 °.

G. Surface roughness Based on JIS B0601 (2001), centerline average roughness (Ra) and ten-point average surface roughness (Rz) are manufactured by Kosaka Laboratory, stylus type surface roughness meter (model number: SE-3FA). And measured. The conditions were as follows, and the average value of five measurements was taken as the value.
・ Tip tip radius: 0.5μm
-Stylus load: 5mg
・ Measurement length: 0.8mm
・ Cutoff value: 0.08mm
H. Film-forming properties When film formation is carried out in Examples / Comparative Examples, film breakage occurs only once / day or less, and there is no process contamination due to particle dropping, etc., film breakage occurs only once / day or less However, the case where the accumulation of dirt on the roll surface can be confirmed with the naked eye, the case where film breakage occurs 2 times / day or more and 3 times / day or less △, the case where film breakage occurs 4 times / day or more × It was. For mass production, a film forming property of Δ or more is required, and if it is ○ or more, there is a further cost reduction effect.

I. Relative luminance and luminance unevenness (direct type luminance)
As shown in FIG. 1, the reflective film pasted in the backlight of 181BLM07 (manufactured by NEC Corporation) was changed to a predetermined film sample and turned on. In this state, after waiting for 1 hour to stabilize the light source, the liquid crystal screen was photographed with a CCD camera (DXC-390 manufactured by SONY), and an image was captured using an eye scale manufactured by an image analyzer Eye System. Thereafter, the brightness level of the photographed image was controlled to 30,000 steps to be automatically detected and converted to brightness. As a luminance evaluation, # 250E6SL manufactured by Toray Industries, Inc. was used as a reference sample (100%), and the evaluation results were as follows.
Excellent: 102% or more Good: 101% or more and less than 102% Possible: 100% or more and less than 101% Impossible: Less than 100% Further, luminance uniformity was evaluated according to the following formula. Those that could not be recognized as unevenness by visual inspection (good or better) were accepted. For evaluation of uneven brightness, # 250E6SL manufactured by Toray Industries, Inc. was used as a reference sample (100%), and the evaluation results were as follows.
Brightness unevenness (%) = (maximum value−minimum value) / average value × 100
Excellent: Less than 80% Good: 80% or more and less than 90% Possible: 90% or more and less than 100% Impossible: 100% or more As shown in FIG. 1, the reflective film laminated in the backlight of 181BLM07 (manufactured by NEC Corporation) was changed to a predetermined film sample, and a light guide plate was placed on the upper part to light up. At this time, the extent to which bright spots were observed was defined as the following evaluation results.
Excellent: No bright spot is observed. Good: One bright spot with a major axis of less than 5 mm is possible: One bright spot with a major axis of 5 mm or more is impossible: Two or more bright spots. Number of bubble-polyester interfaces inside the film Using a microtome, a cross section in the direction parallel to the film TD direction (lateral direction) was cut out, platinum-palladium was deposited, and field emission scanning electron microscope “JSM” manufactured by JEOL Ltd. Using an image obtained by magnifying and observing at an appropriate magnification (500 to 10000 times) at -6700F ", the image is arbitrarily perpendicular to the film surface from one surface of the film toward the other surface. When a straight line was drawn, the number of interfaces existing on the line was counted, and the number of interfaces per 10 μm was obtained by multiplying by 10 the number obtained by dividing by the thickness of the film. At this time, the number of interfaces was counted as one interface both in the interface from the gas phase to the solid phase and in the interface from the solid phase to the gas phase. The interface by the bubble produced | generated by the polyolefin (b) and the interface by the bubble produced | generated by the inorganic particle (c) were counted as an interface. The number of measurements was n = 5, and the average value was obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples and the like, but the present invention is not limited thereto.

(material)
・ Polyester resin (a1)
Using terephthalic acid as the acid component and ethylene glycol as the glycol component, adding to the polyester pellets that can obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, performing a polycondensation reaction, limiting viscosity Polyethylene terephthalate pellets (PET) having 0.63 dl / g and carboxyl end group amount of 40 equivalents / ton were obtained.

・ Polyester resin (a2)
CHDM (cyclohexanedimethanol) copolymerized PET was used. PET obtained by copolymerizing 60 mol% of cyclohexanedimethanol with the above-described method with respect to the glycol component.

・ Polyolefin (b)
A cycloolefin copolymer “TOPAS” (manufactured by Polyplastics Co., Ltd.) having a glass transition temperature of 180 ° C. was used.

・ Inorganic particles (c)
As the talc, talc having the characteristics shown in Tables 1 and 2 which are sold by Nippon Talc Co., Ltd. was used as a master pellet (the matrix resin is a polyester resin (a1)).
The clay used was a clay made of Hayashi Kasei Co., Ltd. with the characteristics shown in Table 1 and Table 2 as master pellets (the matrix resin is a polyester resin (a1)).
Calcium carbonate was used as a master pellet of calcium carbonate having the characteristics shown in Table 2 sold by Shiraishi Calcium Co., Ltd. (the matrix resin is a polyester resin (a1)).

・ Dispersant (d)
A PBT-PAG (polybutylene terephthalate-polyalkylene glycol) copolymer was used (trade name: Hytrel, manufactured by Toray DuPont Co., Ltd.). The 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.). The copolymerization ratio is butylene terephthalate: alkylene glycol = 70 mol%: 30 mol%.

(Examples 1-8)
In a composite film forming apparatus having a main extruder and a sub-extruder, the raw material mixture shown in Table 1 is vacuum dried at a temperature of 180 ° C. for 3 hours, then supplied to the main extruder side and melted at a temperature of 280 ° C. After extrusion, the solution was filtered through a 30 μm cut filter and then introduced into a T-die composite die. On the other hand, vacuum dried PET was supplied to the sub-extruder for 3 hours at a temperature of 180 ° C., melt-extruded at a temperature of 280 ° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die. Next, the skin layer (B) extruded from the sub-extruder is laminated (B / A / B) on both surface layers of the polyester layer (A) extruded from the main extruder in the T-die composite die. After merging, the sheet was coextruded into a molten laminated sheet, and the molten laminated sheet was closely cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 20 ° C. to obtain an unstretched laminated film. Subsequently, the unstretched laminated film is preheated with a roll group heated to a temperature of 85 ° C. according to a conventional method, and then stretched 3.5 times in the longitudinal direction (longitudinal direction) using a heating roll having a temperature of 90 ° C. And cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched film.

  While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 95 ° C. in the tenter, and continuously in a heating zone at a temperature of 105 ° C. in a direction perpendicular to the longitudinal direction (width direction). 3.2 Stretched 2 times. Subsequently, heat treatment was performed at 125 ° C. for 20 seconds in the heat treatment zone in the tenter, and after relaxation treatment in the 4% width direction at a temperature of 180 ° C., relaxation was further performed in the 1% width direction at a temperature of 140 ° C. Processed. Subsequently, after gradually cooling uniformly, it was wound up to obtain a white laminated polyester film having a total thickness of 188 μm. The polyester layer (A) contained many bubbles inside. The various characteristics are shown in Table 1. As described above, the white polyester film of the present invention can be formed stably and at low cost, and exhibits excellent properties such as reflectivity, lightness, luminance, and low gloss (reduction in luminance unevenness).

(Comparative Examples 1-7)
In a composite film-forming apparatus having a main extruder and a sub-extruder, a white laminated polyester film having a total thickness of 188 μm was formed from the mixture of raw materials shown in Table 2 in the same manner as in Example 1. In Examples 2, 3, 4, and 6, film breakage was 2 times / day or more, and productivity was low. Various characteristics are shown in Table 2. The polyester layer (A) contained many bubbles inside. Comparative Examples 1, 5, and 7 have Ra, Rz, and glossiness, and Comparative Examples 2, 3, 4, 6, and 7 have specific gravity outside the scope of the present invention. In particular, Comparative Examples 1, 5, and 7 When the film was incorporated in a backlight, brightness unevenness and bright spots due to close contact with the light guide plate were generated.

  The white polyester film of the present invention is economical, film-forming, white, reflective, lightweight, and compatible with other members. By using this white polyester film, a surface light source excellent in luminance characteristics can be made inexpensive. Can be provided.

  The white polyester film of the present invention can be applied to applications that require whiteness, reflectivity, concealment, and lightness, but as a particularly preferable application, there is a plate-like material incorporated into a surface light source for light reflection. can give. Specifically, it is preferably used for a liquid crystal screen edge light reflector, a direct light reflector, a cold cathode ray tube, a reflector around LED lighting, and the like that are carried around.

DESCRIPTION OF SYMBOLS 1; White polyester film 2; Cold cathode tube 3; Milky white plate 4; Diffuser plate 5; Prism sheet 6; Polarizing prism sheet 7; CCD camera 8;

Claims (6)

A polyester film having a skin layer on at least one side of the polyester layer (A) containing air bubbles, the specific gravity of the film being 0.5 or less, and the inorganic particles (c) in the skin layer in the total weight of the skin layer On the other hand, a white polyester film containing 5 to 30% and having an apparent density of inorganic particles (c) of 0.5 g / cm ³ or less. 2. The white polyester film according to claim 1, wherein the average particle diameter of the inorganic particles (c) is 10 μm to 20 μm. The white polyester film according to claim 1 or 2, wherein the inorganic particles (c) are talc. The white polyester film according to any one of claims 1 to 3, wherein the inorganic particles (c) are talc, and the water content of the talc is less than 1.0%. The 60 ° glossiness of the outermost layer on at least one side of the polyester layer (A) is 20 or less, the center line average roughness (Ra), and the ten-point average roughness (Rz)
500 nm ≦ Ra and
6000 nm ≦ Rz
The white polyester film according to claim 1, wherein the white polyester film is a white polyester film. The surface light source reflector for liquid crystal displays using the white polyester film in any one of Claims 1-5.

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