JP2012137618A - White polyester film for reflector of surface light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film good at film-forming property, whiteness, reflecting property, lightness and light resistance, and to provide a surface light source good at brightness characteristics (having high uniformity in brightness in particular) by using the film.SOLUTION: A white polyester film for a reflector of a surface light source comprises: a polyester layer (A) including bubbles; a polyester layer (B) with a thickness of 2 μm to 12 μm formed on at least one face of the polyester layer (A); and large-diameter particles (C) included in the polyester layer (B) in 0.1 to 5.0% with respect to a total weight of the polyester layer (B). An average particle size of the large-diameter particles (C) is 4 μm to 10 μm and is 0.8 to 1.3 times as large as the thickness of the polyester layer (B).

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. More specifically, when the white polyester film is used as a backlight of a liquid crystal display, illumination such as a fluorescent tube or an LED (light emitting diode) is disposed on the white polyester film, thereby making the display more bright and uneven. The present invention relates to a white polyester film for a surface light source reflector that can obtain a screen with less screen.

  In recent years, liquid crystal displays that are widely used in various electronic devices such as TVs, personal computers, and mobile devices are equipped with a surface light source called a backlight at the rear of the display to radiate light in order to ensure high brightness. is doing. 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. Generally, in this sidelight type, various treatments such as halftone printing and embossing are performed on one side of a transparent base material such as an acrylic plate having a certain thickness, and lighting such as a cold cathode tube is applied from the edge of the acrylic plate. The illumination light is evenly distributed by applying the light to obtain a screen having uniform brightness. In addition, since the illumination is installed not at the back of the screen but at the edge, it can be made thinner than the backlight method. In addition, in order to prevent the escape of illumination light to the back of the screen, a reflector is provided on the back of the screen, thereby reducing the loss of light from lighting such as cold cathode ray tubes and making the LCD screen brighter. Has been granted.

  On the other hand, large-screen liquid crystal televisions are often of the direct light type because it is not possible to increase the screen brightness with the sidelight method. In this method, illumination such as a cold cathode ray tube is disposed at the lower part of the liquid crystal screen, and the reflector is formed in a flat shape or a portion of the illumination formed into a semicircular concave shape.

  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 high reflection performance, as well as high output emitted from illumination light sources. Conventionally, a film added with a white pigment, a film containing fine bubbles inside, or a laminate of these films and a plastic plate has been used because of exposure to light for a long time. Among these, in particular, a film containing bubbles inside obtained by stretching a sheet containing fine particles of an incompatible resin and a white pigment is widely used because it is excellent in luminance improvement effect and light resistance ( Patent Documents 1, 2, 3, 4).

  On the other hand, if the surface irregularity of the film is small, that is, the flatness is high, the regular reflection of light is likely to occur, so that the glossiness is high, and the proportion of regular reflection in the reflected light increases and diffuse reflection decreases. When such a film is used as a reflective film for a surface light source reflecting member, a component that directly reflects the light of the illumination light source on the liquid crystal screen increases. ) Will occur. Therefore, studies have been made to reduce the lamp unevenness by increasing the diffuse reflection component by coating a layer containing coarse particles and reducing the flatness to reduce the lamp unevenness (Patent Document 5).

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

  However, in the conventional technology, in order to suppress high reflection characteristics, light resistance, and lamp unevenness, a layer for imparting light resistance and low gloss must be provided by coating as described above, and productivity, There was a problem with cost. Therefore, the present invention is other than extrusion molding such as coating a white polyester film having excellent light resistance, film-forming property, whiteness, reflectivity, and low gloss that could not be achieved by the above-mentioned conventional studies. It is an object to provide without a process. 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 in which a polyester layer (B) having a thickness of 2 μm to 12 μm is laminated on at least one side of a polyester layer (A) containing bubbles, and the polyester layer (B) has a large particle size particle (c ) In an amount of 0.1 to 5.0% based on the total weight of the polyester layer (B), the average particle size of the large particle size particles (c) is 4 μm to 10 μm, and the large particle size particles (c) A white polyester film for a surface light source reflector, having an average particle diameter of 0.8 to 1.3 times the thickness of the polyester layer (B).
(2) The white polyester film for a surface light source reflector according to (1), wherein the large particle (c) is an inorganic particle.
(3) The white polyester film for a surface light source reflector according to (1) or (2), wherein the large particle size particles (c) are silica.
(4) The inorganic layer (d) having light resistance in the polyester layer (B) is contained in an amount of 3 to 20% based on the total weight of the polyester layer (B), (1) to (3) The white polyester film for surface light source reflectors in any one.
(5) The 60 ° gloss of the outermost layer of the polyester layer (B) is 30 or less, the center line average roughness (Ra), and the ten-point average roughness (Rz)
200 nm ≦ Ra ≦ 500 nm, and
3000 nm ≦ Rz ≦ 6000 nm
The white polyester film for a surface light source reflector 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).

  The present invention can easily and inexpensively produce a white polyester film having high reflectance, light resistance, and low glossiness. In particular, the white polyester film is used as a reflector or reflector in a surface light source. The liquid crystal screen is brightly and evenly illuminated so that the liquid crystal image can be made clearer and easier to see, and light deterioration in long-term use can be suppressed, which is useful.

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.

  The white polyester film of the present invention is a layer in which the polyester layer (A) contains air bubbles, and a polyester layer (B) containing large particle size particles (c) and inorganic particles (d) is laminated on at least one side thereof. It is preferable in terms of film forming properties, optical properties, and light resistance.

  By using the polyester resin (a) and the polyolefin (b), it becomes possible to easily include bubbles having the polyolefin (b) as a core by a method as described later, and has a low specific gravity and high reflection characteristics. A white polyester film can be produced. Voids may be generated around the large particle (c) and the inorganic particle (d).

  In view of the ease and effect of film formation, a two-layer structure or a three-layer structure is preferable. In particular, a form in which the polyester layer (A) is protected by the polyester layer (B), that is, a three-layer structure of polyester layer (B) / polyester layer (A) / polyester 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 polyester layer (B).

  The thickness of the polyester layer (B) of the white polyester film of this invention needs to be 2-12 micrometers. When the thickness of the polyester layer (B) is less than 2, the polyester layer (A) containing a large number of bubbles is easily broken, so that not only stable film formation but also large particle size particles (c) and inorganic particles are not possible. This is not preferable because the particles (d) easily fall off and contaminate the process. When the thickness of the polyester layer (B) exceeds 12 μm, when the film is used as a reflecting plate, it becomes difficult for light to reach the polyester layer (A), and the component reflected at the interface between the bubbles and the polyester decreases. 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, or a function having an accompanying function may be laminated. By adopting a multilayer structure, the characteristics of each layer are expressed, and various characteristics 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), inorganic particles (c), and inorganic particles (d), which are bubble forming nucleating agents, In some cases, the film forming property may become unstable, and thus 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 amorphous polyolefin (b) or inorganic particles in a film base material such as polyester and stretching it (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 amount of the polyolefin (b) added is preferably 5 to 25% by mass or less 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.

[Dispersant (e)]
In order to uniformly disperse the polyolefin (b), it is effective to add the dispersant (e). Examples of the dispersant (e) include, for polyester, polyalkylene glycol such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, and 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 added amount of the dispersant (e) is too small, the effect of the addition is reduced, and if it is too much, the original characteristics of the film base material may be impaired. Such a dispersant (e) can be added in advance to a film base polymer and adjusted as a master polymer (master chip).

  By making the white polyester film contain bubbles using the polyolefin (b), the apparent specific gravity of the polyester film becomes lower than that of a normal polyester film. In order to reduce the weight of the white polyester film while maintaining the mechanical properties as a substrate for a liquid crystal display reflector, the specific gravity is preferably 0.45 or more and 0.99 or less.

  In order to make the specific gravity 0.45 or more and 0.99 or less, the polyolefin (b) is contained by 5 to 25% by mass with respect to the whole polyester film, and the draw ratio is 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.

  The average dispersion diameter of the incompatible polyolefin (b) contained in the white polyester film is preferably not more than the volume average particle diameter of the large particle diameter particles (c). More preferably, it is not more than the volume average particle size of the large particle size particle (c) and not less than 0.2 μm and not more than 5 μm, more preferably not more than the volume average particle size of the large particle size particle (c) and not less than 0.3 μm and not more than 3 μm. It is as follows.

  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.

[Large particle size (c)]
The white polyester film of the present invention requires that the 60 ° glossiness of the polyester layer (A) side surface layer is 30 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.

  In the white polyester film of the present invention, the center plane average roughness (Ra) of the polyester (A) side surface is 250 nm or more and 1000 nm or less, and the ten-point average roughness (Rz) is 4000 nm or more and 10,000 nm or less. It is necessary. 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 4000 nm, the glossiness exceeds 30, which is not preferable. On the other hand, if Rz exceeds 10,000 nm, coarse irregularities become large and are easily broken, and the films are rubbed with each other when forming a film roll, so that the particles are likely to fall off.

  Even if Rz is in the above range, if Ra is less than 250 nm, the portions other than the projections on the film surface become smooth and high gloss, which is not preferable. On the other hand, if Ra exceeds 1000 nm, the number of coarse protrusions increases, so that the particles due to the coarse protrusions easily fall off, and the film-forming property and workability in the subsequent process are deteriorated. By setting both the Ra and Rz values in the above ranges, the film can have a low gloss, and process contamination due to particle dropout can be prevented, and handling in the subsequent process such as incorporation into a backlight housing is also improved. .

  In order to achieve the above, it is necessary for the white polyester film of the present invention to contain large particle diameter particles (c) having a volume average particle diameter of 4 to 10 μm.

  If the volume average particle diameter of the large particle diameter particle (c) is less than 4 μm, it becomes difficult to make Rz within the above range, and the film surface becomes smoother, resulting in an increase in glossiness. When the volume average particle size of the large particle size (c) exceeds 10 μm, the particles are likely to fall off from the film, causing process contamination and tearing, and the productivity is lowered.

  The volume average particle diameter of the large particle diameter particle (c) is preferably 0.8 to 1.3 times the thickness of the polyester layer (B). If the magnification is less than 0.8, the influence of the particles on the surface shape becomes small, and it becomes difficult to make Rz in the above range, which is not preferable. When the magnification exceeds 1.3 times, the particles are likely to fall off from the film, causing process contamination and tearing, which is not preferable because productivity is reduced.

  The particle used as the large particle size particle (c) is not particularly limited as the kind thereof, and any organic type or inorganic type can be used. As the organic particles, acrylic resins, silicone resins, nylon resins, styrene resins, polyethylene resins and the like can be used. As inorganic particles, silica, barium sulfate, aluminum oxide zinc oxide and the like are preferable. They can be used alone or in admixture of two or more, but inorganic particles are preferable from the viewpoint of dispersion diameter stability of the particles and film formation stability, and silica is more preferable.

  The content of the large particle size particles (c) needs to be 0.1% by mass or more and 5.0% by mass or less when the total mass of the polyester layer (B) is 100% by mass. When the content of the large particle size particles (c) is less than 0.1% by mass, the surface of the polyester layer (A) side is less uneven, and the Ra and Rz values do not fall within the above ranges, so that the light diffusibility is insufficient. As a result, the glossiness increases. When the content of the large particle size particles (c) exceeds 5.0% by mass, the particles easily fall off from the film, causing process contamination and tearing, and the productivity is lowered.

[Inorganic particles (d)]
The white polyester film of the present invention is exposed to ultraviolet rays derived from outside light during storage, and is exposed to ultraviolet rays from illumination attached to the backlight unit during use. Therefore, it is necessary to impart light resistance. In the present invention, in order to impart light resistance, inorganic particles (d) having a different chemical composition can be preferably used in addition to the above-described large particle size particles (c).

  In the white polyester film of the present invention, the inorganic particles (d) are not particularly limited as long as they have a chemical composition different from that of the large particle size particles (c), but calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc) White), antimony oxide, cerium oxide, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, calcium phosphate, Examples thereof include aluminum oxide, mica, mica titanium, talc, clay, kaolin, lithium fluoride and calcium fluoride.

  Among these, it is possible to incorporate inorganic particles (d) having UV absorption ability from the viewpoint of improving light resistance, in addition to improving the winding property of the film, long-term film formation stability, and reflection characteristics. Particularly preferred. From this viewpoint, calcium carbonate, titanium oxide, and zinc oxide (zinc white) are preferable, and titanium oxide is most preferable. These inorganic particles (d) may be used alone or in combination of two or more. 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 shape of this titanium oxide is a rutile type.

  The inorganic particles (d) used in the present invention preferably have a volume average particle diameter in the film of 0.05 to 2 μm, more preferably 0.07 to 1 μm. When the volume average particle diameter of the inorganic particles (d) is out of the above range, it is not preferable because the light resistance may be deteriorated due to the drop of particles or the uniform dispersibility of the inorganic particles (d) due to aggregation or the like. . Moreover, since brightness nonuniformity will arise because glossiness goes up, it is unpreferable.

  Moreover, in this invention, content of an inorganic particle (d) needs to be 3-20 mass% when the total mass of a polyester layer (B) is 100 mass%.

  When the content of the inorganic particles (d) is less than 3% by mass, it may be difficult to improve characteristics such as light resistance, whiteness, and hiding properties of the film, which is not preferable. When the content of the inorganic particles (d) exceeds 20% by mass, the specific gravity of the film increases or it becomes difficult to obtain high reflection characteristics due to the light absorption ability and light hiding property of the inorganic particles (d). In some cases, the glossiness may increase, the film may be broken during stretching, and inconveniences such as powder generation may occur during post-processing.

  In the white polyester film of the present invention, when titanium oxide, barium sulfate, calcium carbonate, or the like is used as the inorganic particles (d), bubbles having these as nuclei may be formed. However, the inorganic particles (d) have a particle shape that is difficult to be spherical and extremely fine, so it is difficult to form bubbles. Moreover, you may make a polyester layer (A) contain an inorganic particle (d) in the range which does not impair a characteristic.

  When the large particle size particle (c) is an inorganic particle, the method for distinguishing from the inorganic particle (d) is that the inorganic particle having a volume average particle size of 4 to 10 μm is the large particle size particle (c), and the volume average particle size is Inorganic particles having a diameter of less than 2 μm are defined as inorganic particles (d). The volume average particle diameter is obtained by directly measuring particles in the white polyester film. However, the volume average particle diameter of the inorganic particles (c) and the inorganic particles (d) may be obtained from the powder or master pellet before film formation.

[Method of blending particles]
Various methods can be used as a method of blending the large particle size particles (c) and the inorganic particles (d) 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 a blending method of the polyolefin (b), the large particle size particle (c), and the inorganic particle (d), 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 large particle (c), a polyester resin (a1) master pellet containing the large particle (c) can be used.

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

  An example of the method for obtaining the dispersant (e) will be described, but it is not limited to such an example. The dispersant (e) 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.

  The mixture containing the polyester resin (a1), the polyester resin (a2), the polyolefin (b), the large particle size particle (c), the inorganic particle (d) and the dispersant (e) is sufficiently vacuum-dried as necessary. And fed to a heated extruder of a film forming apparatus having an extruder. The addition of the polyolefin (b), the large particle size particles (c) and the inorganic particles (d) may be performed by using a master chip prepared by uniform melt melting and kneading in advance or directly supplied to a kneading extruder. Good. 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, the film may be re-stretched in either the longitudinal direction or the width direction.

  The white polyester film of the present invention thus obtained has a surface layer on at least one surface with low gloss and little luminance unevenness, and bubbles are formed inside the film to achieve a high reflectivity. As a surface light source reflector for a liquid crystal display High brightness can be obtained when used. Moreover, it is excellent also in light resistance.

[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. 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.

B. 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.

C. Specific gravity 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.

D. 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 °.

E. 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
Cut-off value: 0.08 mm.

F. 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.

G. 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.

H. Light resistance (Δb value)
The color tone b value of the white polyester film before accelerating deterioration was measured using a spectroscopic color difference meter SE-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) under optical conditions according to JIS Z-8722 (2000). The color difference according to K-7105 (1981) was determined. This film was subjected to UV irradiation (295 to 450 nm, illuminance 100 mW / cm ² (± 5%) at 50 ° C. and RH 80% under super accelerated weathering test apparatus iSuper UV Tester SUV-W131 (Iwasaki Electric Co., Ltd.). )), An initial color tone b value was measured in the same manner, and a difference between the initial value and the value after UV irradiation was defined as a Δb value. The Δb value was determined as follows.
Excellent: Δb value of less than 3 Good: Δb value of 3 or more and less than 4 possible: Δb value of 4 or more and less than 5: Δb value of 5 or more and Δb value of 5 or more, the white polyester film is a surface light source reflector. When used as a material for use, it is severely deteriorated by ultraviolet rays from the light source and cannot withstand long-term use.

I. 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 bubbles generated by the polyolefin (b) and the interface by bubbles generated by the large particle size particles (c) and the inorganic particles (d) were counted as interfaces. 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.

・ Large particle size (c)
The silica used was prepared by adding silica particles having the volume average particle diameters shown in Tables 1 and 2 during the production of the polyester resin (a1).
The silicone resin used was a mixture of Tospearl 145 manufactured by GE Toshiba Silicone Co., Ltd. and polyester resin (a1) in advance.
As the acrylic resin, TECHPOLYMER SSX-105 manufactured by Sekisui Plastics Co., Ltd. was previously mixed with the polyester resin (a1).

・ Inorganic particles (d)
The titanium oxide used was a titanium oxide master pellet having a volume average particle size of 0.25 μm sold by DIC Corporation (the matrix resin is a polyester resin (a1)).

・ Dispersant (e)
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%.

Example 1
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 polyester 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 by a roll group heated to a temperature of 85 ° C. according to a conventional method, and then stretched 3.7 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 for 20 seconds at a predetermined temperature (see table) in the heat treatment zone in the tenter, and further relaxation treatment was performed in the 4% width direction at a temperature of 180 ° C. The relaxation treatment was performed in the% width direction. 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, low gloss (reduction in luminance unevenness), and light resistance.

(Examples 2 to 12)
In a composite film-forming apparatus having a main extruder and a sub-extruder, a mixture of raw materials shown in Table 1 was formed in the same manner as in Example 1 to obtain a white laminated polyester film having a total thickness of 188, 225, and 250 μm. It was. 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, low gloss (reduction in luminance unevenness), and light resistance.

(Example 13)
A white laminated polyester film having a total thickness of 188 μm was obtained by forming a film by the same method as in Examples 1 to 12 except that silicone particles were used as the large particle size particles (c). 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, low gloss (reduction in luminance unevenness), and light resistance.

(Example 14)
A white laminated polyester film having a total thickness of 188 μm was obtained by forming a film in the same manner as in Examples 1 to 12 except that acrylic particles were used as the large particle size particles (c). 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, low gloss (reduction in luminance unevenness), and light resistance.

(Example 15)
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, in the T die composite die, the polyester layer (B) extruded from the sub-extruder and the polyester layer (A) extruded from the main extruder are laminated so as to be a two-layer laminate of B / A. Introduced into T-die base. Next, it is extruded into a sheet from the inside of the T die die to form a melted two-layer laminated unstretched sheet composed of A layer / B layer, and the molten laminated sheet is electrostatically applied onto a drum maintained at a surface temperature of 25 ° C. Then, the film was tightly cooled and solidified to obtain an unstretched laminated film. At this time, the surface of the A layer was in contact with the drum, and the surface of the B layer was in contact with air. That is, the A layer surface was the back surface, and the B layer surface was the front surface. Subsequently, after preheating the unstretched laminated film with a roll group heated to a temperature of 85 ° C., irradiation is performed only from the B layer surface side (front surface) under the conditions of the infrared heater shown in Table 1 (that is, the surface). , While irradiating only from one side of the film), in the longitudinal direction (longitudinal direction), using the peripheral speed difference of the roll, 3.6-fold stretching, cooling with a roll group at a temperature of 25 ° C., uniaxial stretching A film was obtained.

  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). The film was stretched 3.6 times. Subsequently, heat treatment was performed at 190 ° C. for 20 seconds in the heat treatment zone in the tenter, and after further relaxation treatment in the 6% 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, low gloss (reduction in luminance unevenness), and light resistance.

(Comparative Examples 1-11)
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, 225, 250 μm was formed from the mixture of raw materials shown in Table 2 in the same manner as in Example 1. However, except for Comparative Example 1, film breakage was 4 times / day or more, which was not at a level where stable production was possible. Samples to the extent that various characteristics can be evaluated were obtained. The polyester layer (B) contained many bubbles inside. The various characteristics are shown in Table 2. Comparative Example 10 had Ra, Comparative Examples 1, 2, 4, 7, 8, and 11 had Rz, and Comparative Example 1 did not fall within the scope of the present invention. The evaluation was acceptable or unacceptable. If the content and size of the particles are small, it is difficult to exert the effect, and if the content is large, the particles fall off during or after film formation.

  The white polyester film of the present invention is excellent in economic efficiency, film-forming property, whiteness, reflectivity, lightness, and light resistance. By using this white polyester film, a surface light source excellent in luminance characteristics can be provided at low cost. Can do.

  The white polyester film of the present invention can be applied to uses that require whiteness, reflectivity, and concealment, and a particularly preferred use is a plate-like material incorporated in a surface light source for light reflection. Specifically, it is preferably used for edge light reflectors for liquid crystal screens, direct light reflectors, cold cathode ray tubes, reflectors around LED lighting, and the like.

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

Claims (6)

A polyester film in which a polyester layer (B) having a thickness of 2 μm to 12 μm is laminated on at least one surface of a polyester layer (A) containing air bubbles, wherein the polyester layer (B) is made of a polyester having a large particle size (c). 0.1 to 5.0% of the total weight of the layer (B), the average particle size of the large particle size particle (c) is 4 μm to 10 μm, and the average particle size of the large particle size particle (c) Is a white polyester film for a surface light source reflector, wherein the thickness is 0.8 to 1.3 times the thickness of the polyester layer (B). 2. The white polyester film for a surface light source reflector according to claim 1, wherein the large particle size particles (c) are inorganic particles. The white polyester film for a surface light source reflector according to claim 1 or 2, wherein the large particle size particles (c) are silica. The inorganic particle (d) having light resistance in the polyester layer (B) is contained in an amount of 3 to 20% based on the total weight of the polyester layer (B). White polyester film for surface light source reflector. The outermost layer of the polyester layer (B) has a 60 ° gloss of 30 or less, the center line average roughness (Ra), and the ten-point average roughness (Rz)
200 nm ≦ Ra ≦ 500 nm, and
3000 nm ≦ Rz ≦ 6000 nm
The white polyester film for a surface light source reflector according to any one of claims 1 to 4, wherein the white polyester film is a surface light source reflector. The surface light source reflector for liquid crystal displays using the white polyester film in any one of Claims 1-5.

Images