JP5082606B2 - White laminated polyester film for reflective sheet - Google Patents

Description

  The present invention relates to a white laminated polyester film for a reflective sheet. More specifically, the present invention relates to a polyester film having a laminated structure, excellent in reflection characteristics, concealment properties, and good productivity. The present invention relates to a backlight device for image display, a reflection sheet for a lamp reflector, and a lighting device. The present invention relates to a white laminated polyester film that can be suitably used for a reflective sheet, a reflective sheet for lighting signs, a back reflective sheet for solar cells, and the like.

  A white polyester film is a uniform and highly reflective material for applications such as reflectors and reflectors for surface light source devices, back reflectors for lighting signs, and back reflector sheets for solar cells in flat image display systems used in liquid crystal displays. Widely used because of characteristics such as rate, dimensional stability, and low cost. As a method to achieve high reflection performance, the polyester film contains a large number of inorganic particles such as barium sulfate, and light reflection at the interface between the polyester resin and the particles and at the hollow interface of the fine cavities generated using the particles as nuclei. A method of using light (see Patent Document 1), a method of utilizing light reflection at the cavity interface of a fine cavity that is produced by mixing an incompatible resin with polyester and using an incompatible resin as a nucleus (Patent Document) 2), a method of utilizing light reflection at the interface of the cavity formed inside by impregnating the polyester film with an inert gas in a pressure vessel (see Patent Document 3), etc. A method using a difference in refractive index between inorganic particles and polyester resin and a difference in refractive index between fine voids and polyester resin is widely used.

  In recent years, in particular, the use of liquid crystal displays has been dramatically expanded, and in addition to conventional notebook computers, monitors, and portable terminals, they have been widely used for liquid crystal televisions. And higher definition have been demanded. Reflecting sheets have been required to have higher reflectivity and higher concealment as the screen brightness increases. Accordingly, increasing the amount of inorganic particles in the polyester film, increasing the amount of resin incompatible with the polyester, etc., it is necessary to increase the number of reflective interfaces in the polyester film, By increasing the amount of resin that is incompatible with inorganic particles and polyester, film tearing frequently occurs during biaxial stretching, resulting in inferior productivity, resulting in high reflectivity, high concealment, and film productivity. It was difficult to achieve both.

Therefore, an attempt has been made to obtain high concealability with high reflectivity with a small amount of addition by containing titanium dioxide particles having a large refractive index difference with the polyester resin that is the basic structure of the film (Patent Documents 4, 5, 6). However, by containing titanium dioxide particles having strong scattering properties, a part of the scattered light tends to be lost due to loss, and when added in a relatively large amount, the concealing property of the reflective sheet appears. The reflectance decreases due to the loss of light. Conversely, when a small amount is added, there is a problem that the reflectance and concealability of the reflecting sheet are insufficient, and it is difficult to achieve both. There is an increasing demand for a polyester film that has both good reflectivity and concealment and is not easily torn and has good productivity.
JP 2004-330727 A Japanese Patent Laid-Open No. 04-239540 International Publication No. 97/01117 Pamphlet JP 2001-225433 A JP 2002-138150 A JP 2004-294611 A

  An object of the present invention is to provide a white laminated polyester film having a high reflectivity and a high concealing property, and having a high productivity and a highly reflective sheet with less film tearing. Is.

The present invention uses the following means in order to solve this problem. That is, the white laminated polyester film for a reflective sheet of the present invention is a laminated polyester film in which a polyester layer (A) is laminated on at least one side of a polyester layer (B) containing a cavity therein, and the laminated polyester film Is a white laminated polyester film for a reflective sheet that satisfies all of the following (1) to (5).
(1) The thickness of the polyester layer (A) on at least one side is 5 to 15 μm.
(2) The polyester layer (A) contains 3 to 15% by weight of particles having a refractive index of 2.0 or more based on the polyester layer (A).
(3) The thickness of the polyester layer (B) is 150 μm or more.
(4) The amount of particles having a refractive index of 2.0 or more contained in the polyester layer (B) is 2% by weight or less with respect to the polyester layer (B).
(5) In the polyester layer (B), 12 to 25% by weight of the resin incompatible with the polyester resin and / or 30 to 30 inorganic particles having a refractive index of less than 2.0 with respect to the polyester layer (B). Containing 50% by weight.

Moreover, the void-containing laminated white polyester film of the present invention has the following preferable modes (a) to (j).
(A) Particles having a refractive index of 2.0 or more contained in the polyester layer (A) are titanium dioxide particles.
(B) The thickness of the polyester layer (A) is 5 to 10 μm, and the thickness of the polyester layer (B) is 200 to 400 μm.
(C) The titanium dioxide particles contained in the polyester layer (A) are mainly rutile type.
(D) The titanium dioxide particles contained in the polyester layer (A) are mainly rutile type produced by the chlorine method.
(E) The resin constituting the polyester layer (A) and the polyester layer (B) is based on polyethylene terephthalate.
(F) The resin incompatible with the polyester resin contained in the polyester layer (B) is polymethylpentene.
(G) The average particle size of polymethylpentene in the polyester layer (B) is 3 μm or less in the width direction and 2 μm or less in the thickness direction.
(H) The inorganic particles having a refractive index of less than 2.0 contained in the polyester layer (B) are barium sulfate.
(I) A coating layer having ultraviolet absorbing ability is provided on at least one surface.
(J) The polyester layer (A) contains 0.05 to 10% by weight of a light-proofing agent with respect to the polyester layer (A).
(K) The polyester layer (A) side is used as a light reflecting surface.
(L) A back reflection sheet for a backlight for a liquid crystal display, wherein the polyester layer (A) side is a light reflection surface.

  According to the present invention, it is possible to obtain a white laminated polyester film for a reflective sheet that is highly productive and has high reflectivity and high concealability, and is less likely to be broken during production.

  The present inventors have solved the above problems, that is, the result of earnestly examining the white laminated polyester film for a reflective sheet, which is compatible with high reflectivity and high concealment property, and hardly breaks during production and has high productivity. The inventors have found and found that a polyester film having a specific configuration can solve such problems all at once.

  The white laminated polyester film for a reflector of the present invention is a polyester film in which a polyester layer (A) containing titanium dioxide particles is laminated on at least one side of a polyester layer (B) containing a cavity inside. Polyester layer (B) containing many fine cavities derived from inorganic particles and / or resin incompatible with polyester, and exhibiting functions of cushioning and flexibility in addition to light reflection function, and light on the surface By dividing the polyester layer (A) that has a diffuse reflection function and retains the rigidity of the film and expresses the film-forming property and the strength of the film, it is impossible to achieve with a single layer structure, It becomes possible to make a film having both productivity. Moreover, it is preferable that a polyester layer (A) and a polyester layer (B) are extended | stretched to biaxial direction, after laminating | stacking at once in a film forming line by the coextrusion method. In the method of providing the polyester layer (A) by the coating method, it is difficult to stably provide a film thickness necessary for exhibiting sufficient rigidity.

  As a laminated structure of the white laminated polyester film for reflectors of the present invention, the polyester layer (A) and the polyester layer (B) are, for example, two layers of A / B and three layers of A / B / A. May be mentioned as a preferable example. For example, a three-layer structure of A / B / C in which a polyester layer (C) other than the polyester layer (A) or the polyester layer (B) is laminated, or a laminated structure of more than that may be adopted. . It is preferable to arrange | position the polyester layer (A) which has a light-diffusion reflection function of the surface in the one-side outermost layer of the laminated structure laminated | stacked by the coextrusion method. In addition, the polyester layer (B) containing many fine cavities contains many nucleating agents such as inorganic particles and incompatible resins for expressing the cavities, so that the dropout becomes a problem, and the film is formed for a long time. In the meantime, the portion (drum, roll, coater, etc.) in contact with the film forming apparatus may be contaminated and the productivity may be impaired. Therefore, it is preferable to arrange it in the inner layer of the laminated structure laminated by the coextrusion method. .

  The following components are mentioned as a component which comprises the polyester resin used by this invention. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, phthalic acid, diphenic acid and ester derivatives thereof for aromatic dicarboxylic acids, and adipic acid, for aliphatic dicarboxylic acids. Examples of sebacic acid, dodecadioic acid, eicoic acid, dimer acid and ester derivatives thereof include 1,4-cyclohexanedicarboxylic acid and ester derivatives thereof for alicyclic dicarboxylic acids, and trimellitic acid, pyrophosphate for polyfunctional acids. A merit acid and its ester derivative are mentioned as a representative example. Examples of the diol component include ethylene glycol, propanediol, butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, decanediol, cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyethylene glycol, and tetramethylene glycol. Typical examples include polyethers such as polyethylene glycol and polytetramethylene glycol. Considering the mechanical strength, heat resistance, production cost, and the like of the produced polyester film, it is preferable that the polyester layer (A) and the polyester layer (B) in the present invention have polyethylene terephthalate as a basic structure. The basic constitution in this case means that 50% by weight or more of polyethylene terephthalate is contained with respect to the contained polyester resin.

In the present invention, a copolymer component may be introduced into the basic structure of polyethylene terephthalate. As a method for introducing a copolymer component, a copolymer component may be added at the time of polymerization of a polyester pellet as a raw material, and the copolymer component may be used as a pellet in which a copolymer component is polymerized in advance. For example, polybutylene terephthalate is used. Alternatively, a method may be used in which a mixture of pellets independently polymerized and polyethylene terephthalate pellets is supplied to an extruder and copolymerized by transesterification at the time of melting. The amount of these copolymerization components is not particularly limited, but from the viewpoint of each characteristic, the dicarboxylic acid component and the diol component are each preferably 1 to 50 mol%, more preferably 1 to 20 mol, with respect to each component. %.
Moreover, it is preferable to use isophthalic acid as a copolymerization component from a viewpoint of cleavage prevention between a polyester layer (A) and a polyester layer (B), film-forming stability, and manufacturing cost. In addition, it is preferable that the polyester layer (A) and the polyester layer (B) contain a common copolymer component because the cleavage preventing property between the polyester layer (A) and the polyester layer (B) is further improved.

  As a catalyst used for the polycondensation reaction of the said polyester resin, an antimony compound, a titanium compound, a germanium compound, a manganese compound etc. are mentioned preferably, for example. These catalysts can be used alone or in combination. Among these catalysts, a titanium compound and a germanium compound are preferable in that a metal catalyst aggregate is difficult to be generated, and a titanium compound is preferable from the viewpoint of cost. Specific examples of titanium compounds include titanium alkoxides such as titanium tetrabutoxide and titanium tetraisopropoxide, and composite oxides and titanium complexes in which the main metal element such as titanium dioxide silicon dioxide composite oxide is composed of titanium and silicon. Can be used. In addition, ultrafine titanium oxide such as titanium-silicon composite oxide (trade name: C-94) manufactured by Accordis may be used.

  In the present invention, the polyester layer (A) contains particles having a refractive index of 2.0 or more in an amount of 3 to 15% by weight, preferably 5 to 10% by weight, based on the polyester layer (A). . When the amount of particles having a refractive index of 2.0 or more is less than 3% by weight, the film is inferior in reflectivity and concealment, and when it exceeds 15% by weight, the loss of light due to scattering increases, so the reflectivity. Is inferior.

  In the present invention, the amount of particles having a refractive index of 2.0 or more contained in the polyester layer (B) is 2% by weight or less, preferably 1% by weight or less with respect to the polyester layer (B). . When the amount of particles having a refractive index of 2.0 or more contained in the polyester layer (B) exceeds 2% by weight, light scattering loss in the polyester layer (B), which is the main component of the laminated film Increases and the film has poor reflectivity.

  The polyester layer (A) of the present invention contains particles having a refractive index of 2.0 or more. By using particles with a high refractive index, the difference in refractive index from the polyester resin constituting the film increases, and the diffuse reflectance of light at the interface between the particles and the resin increases, resulting in high reflectivity and concealment. It is done. Examples of the particles having a refractive index of 2.0 or more include titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), etc., but reflection characteristics, hiding properties, light stability, Titanium dioxide particles are preferred from the viewpoint of production cost and the like. When particles having a refractive index of less than 2.0 are used, the difference in refractive index from the polyester resin constituting the film is small, resulting in poor reflection characteristics and hiding properties.

  In the present invention, when titanium dioxide is used as particles having a refractive index of 2.0 or more, titanium dioxide having anatase type and rutile type crystal structures is preferable. Compared to the anatase type, the rutile type has a higher refractive index because of its dense crystal structure, and therefore the refractive index difference with the polyester resin becomes larger, and a high reflective action at the interface can be obtained. It is preferable to use type titanium dioxide.

  As a production method of the titanium dioxide particles, mainly a sulfuric acid method and a chlorine method are exemplified. In the sulfuric acid process, ilmenite ore is dissolved in concentrated sulfuric acid, iron is separated as iron sulfate, and the solution is hydrolyzed to precipitate and separate titanium as a hydroxide. Next, titanium dioxide can be obtained by baking this hydroxide with a high-temperature rotary keeln or the like. On the other hand, in the chlorine method process, rutile ore is used as a raw material, reacted with chlorine gas and carbon at a high temperature of about 1000 ° C to form titanium tetrachloride, and then titanium tetrachloride is separated and oxidized while being injected at high speed. Titanium dioxide can be obtained. Compared to the sulfuric acid process, titanium dioxide produced by the chlorine process is synthesized by a gas phase reaction involving only gas, so there are few impurities such as vanadium, iron, and manganese, and high purity titanium dioxide is used. It is particularly preferable because it can be obtained and light absorption loss due to impurities is reduced.

  The titanium dioxide used in the present invention is preferably subjected to a surface treatment in order to suppress the photocatalytic activity of titanium dioxide or to improve the dispersibility in the polyester resin. In order to suppress the photocatalytic activity, for example, a method of coating the surface with an inorganic oxide such as silica or alumina can be mentioned. In order to improve dispersibility, for example, a method of surface treatment with a siloxane compound or a polyol can be used.

  The particle diameter of titanium dioxide in the present invention is preferably 0.1 μm to 0.5 μm. The wavelength at which the light reflecting ability of titanium dioxide is maximized is about twice the wavelength of the titanium dioxide particle size, and therefore the particle size of titanium dioxide is particularly preferably 0.2 μm to 0.4 μm. When the particle diameter of titanium dioxide is less than 0.1 μm, the titanium dioxide particles tend to aggregate and tend to be difficult to disperse, and when it exceeds 0.5 μm, the reflection efficiency in the visible light region tends to decrease.

  The average particle diameter of the titanium dioxide particles referred to here is the number of 50 particles observed after ashing the laminated film and then observing with a scanning electron microscope (SEM) at a magnification of 20000 times. It is the value which calculated | required the average particle diameter.

  In the present invention, the polyester layer (B) contains a cavity inside. By containing a large number of cavities inside, the reflectance can be increased while suppressing scattering loss by utilizing the difference in refractive index between the polyester resin and the cavities. As a method for making the polyester layer (B) contain fine cavities and exhibiting high reflectivity and concealment, (1) adding a foaming agent to the polyester, foaming by heating during extrusion or film formation, or chemical (2) A method of adding a gas or a vaporizable substance during extrusion of a polyester, (3) A thermoplastic resin incompatible with the polyester (incompatible resin) And (4) a method of adding a large amount of bubble-forming inorganic fine particles in place of the incompatible resin, and the like. However, in the present invention, from the comprehensive point of film-forming properties, ease of adjusting the amount of cavities contained inside, ease of forming finer and uniform cavities, and light weight, the above (3) it is necessary to use a method of using the inorganic fine particles used in the incompatible resin and (4) of the. In this method, the more the content of the resin and / or inorganic particles incompatible with the polyester, the higher the stretching ratio in the biaxial stretching process, the more the interface that reflects light is generated inside the polyester. It is possible to exhibit high reflectivity and concealment.

  The incompatible resin referred to here is a thermoplastic resin other than polyester and is incompatible with polyester, dispersed in the form of particles in the polyester, and stretched in the film. A resin having a large effect of forming cavities is preferred. More specifically, the incompatible resin refers to a system in which polyester and the incompatible resin are melted by a known method, preferably a differential scanning calorimeter (DSC), dynamic viscoelasticity measurement or the like. When measured, it is a resin in which Tg corresponding to the incompatible resin is observed in addition to the glass transition temperature corresponding to polyester (hereinafter abbreviated as Tg).

  The melting point of such an incompatible resin should be equal to or slightly lower than the melting point of polyester, and higher than the temperature at which the film is heat-set during crystallization to be crystallized (heat treatment temperature). Particularly preferred. From this point, among the incompatible resins, polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, and fluorine resins are preferably used. It is done. These incompatible resins may be homopolymers or copolymers, and two or more incompatible resins may be used in combination. Among these, polyolefin resins such as polypropylene and polymethylpentene having a low surface tension are preferable, and polymethylpentene is most preferable. Since polymethylpentene has a relatively large difference in surface tension from polyester and a high melting point, polymethylpentene has a feature that the effect of forming cavities per added amount is large, and is particularly preferable as an incompatible resin.

  The content of the incompatible resin in the polyester layer (B) in the present invention is 12 to 25% by weight, preferably 15 to 20% by weight, based on the entire polyester layer (B). When the content is less than the above range, the film has poor reflectivity and concealment. Conversely, when the content is more than the above range, the apparent density of the entire film is too low, so the film is broken during stretching. Etc. are likely to occur, the productivity is reduced, and the produced polyester film has a low rigidity and is difficult to handle.

  In the present invention, fine cavities are formed using the incompatible resin as a core. The fine cavities in the present invention can be observed by a scanning electron microscope (SEM) or a transmission electron microscope (TEM) of the cross section (thickness direction) of the polyester layer (B).

In the present invention, when the polyester layer (B) contains an incompatible resin, the cavities generated using the incompatible resin as a core are preferably independent of each other. The average size of the width of the cavity observed in the section cut along the direction and the width direction is preferably 3 to 25 μm, more preferably 5 to 20 μm, and the average size of the thickness of the cavity Is preferably 0.3 to 10 μm, and more preferably 0.5 to 5 μm. When the average size of the cavity width is larger than 25 μm, or the average size of the cavity thickness is larger than 10 μm, the difference in cushioning properties on the surface of the laminated film partially increases, and the reflectance becomes uneven. , Tearing is likely to occur during film formation. Further, if the average size of the cavity width is less than 3 μm or the average size of the cavity thickness is less than 0.3 μm, sufficient reflectance may not be obtained. In addition, the longitudinal direction said here is a direction through which a film flows in the process at the time of film manufacture, and let the direction orthogonal to a longitudinal direction be a width direction. In addition, the average thickness and width of the cavities described here are obtained by freezing the film, then cutting out a section along the longitudinal direction and the width direction, and then scanning the section with a scanning electron microscope (for example, (SEM) S -2100A type (manufactured by Hitachi, Ltd.) was used to examine the presence or absence of fine cavities from a cross-sectional photograph taken by magnifying 4000 times and observed the cavity size and the size of the incompatible resin. Thus, the lengths in the width direction and the thickness direction are measured, and the size of each cavity and each incompatible resin is obtained by calculating backward from the magnification. The average value of the cavity size and the size of the incompatible resin is 50 from the cross-sectional photograph of the cut surface cut in the longitudinal direction, and 50 from the cross-sectional photo of the cut surface cut along the width direction. The size in the width direction and the thickness direction is determined for the incompatible resin, and the average value is obtained. In addition, when the longitudinal direction and the width direction are unclear, the measurement is performed by cutting a cross section of the sample along two orthogonal surfaces.
About the cavity size and the size of the incompatible resin, the size shown in FIG. 1 is measured. In addition, the case where incompatible resin is not found in the cavity as shown in FIG. 2 is excluded.

  The average size in the width direction of the incompatible resin in the polyester layer (B) used in the present invention is preferably 7 μm or less, and more preferably 3 μm or less. The average thickness is 3 μm or less, more preferably 2 μm or less. If the average size in the width direction of the incompatible resin exceeds 7 μm or the average size in the thickness direction exceeds 3 μm, the reflectivity may be lowered or the film may be easily broken during film formation. The incompatible resin is preferably finely dispersed in the polyester resin. However, when the average size is less than 0.5 μm in both the width direction and the thickness direction, the cavities generated by the stretching process are transferred to the subsequent heat treatment process. This is not preferable because it tends to be blocked and cannot be maintained. In addition, the above-mentioned method is used also about the average size and average thickness of the incompatible resin in the width direction.

  The method for controlling the average dispersion diameter of the incompatible resin within the above-mentioned preferable range is not particularly limited. For example, it is preferable to add a dispersant in addition to the polyester and the incompatible resin described above. As a method. By adding a dispersant, the dispersion diameter of the incompatible resin is reduced, so that the cavities generated by stretching can be made finer, resulting in improved film reflectivity, total light transmittance, and film formation stability. Can be made. Examples of the dispersant exhibiting the above-described effects include olefin polymers or copolymers having polar groups such as carboxyl groups and epoxy groups, and functional groups reactive with polyester, diethylene glycol, polyalkylene glycol, and surfactants. In addition, a heat adhesive resin or the like can be used. Of course, these may be used alone or in combination of two or more. Among them, a copolymer resin of a polyalkylene glycol, an aliphatic diol component having 2 to 6 carbon atoms, and a polyester resin composed of terephthalic acid is compatible with the polyester resin which is the main constituent unit of the polyester layer (B) and polyolefin. From the viewpoint of improving the dispersibility of the resin, a block copolymer of polyethylene glycol and polybutylene terephthalate is particularly preferable. Such a dispersant may be used as a polyester obtained by copolymerizing a dispersant in a polymerization reaction in advance, or may be used directly as it is.

  The amount of the dispersant used in the present invention is preferably 0.05 to 10% by weight, more preferably 0.1 to 7% by weight, based on the entire polyester layer (B) containing the dispersant. Even more preferably, it is 0.2 to 5% by weight. When the amount added is less than 0.05% by weight, the effect of refining the bubbles may be reduced. On the other hand, when the addition amount is more than 10% by weight, the effect of adding the incompatible resin is reduced, and problems such as a decrease in production stability and an increase in cost are likely to occur.

  In the present invention, when the polyester layer (B) contains inorganic particles having a refractive index of less than 2.0, the cavities generated using the inorganic particles as nuclei are preferably independent of each other. The average size of the width of the cavity observed in the section cut along the longitudinal direction and the width direction of the film is preferably 1 to 25 μm, more preferably 2 to 20 μm, and the thickness of the cavity The average size is preferably 0.1 to 10 μm, and more preferably 0.3 to 5 μm. When inorganic particles are used, compared to incompatible resins, the average size is less because re-aggregation is difficult after extrusion, and the core is not thermally deformed during heat treatment in the film forming process, and the void ratio does not decrease. Although it is preferable in that it can contain many small cavities, conversely, when inorganic particles are used, since it is difficult to form cavities between polyester resins, in order to achieve high reflection and high concealment, a large amount of inorganic particles must be added. It is necessary to contain. When the average size of the width of the cavity is larger than 25 μm, or the average size of the thickness of the cavity is larger than 10 μm, the difference in cushioning properties on the surface of the laminated film partially increases, resulting in spots on the appearance. Tear easily occurs during film formation. Further, if the average size of the cavity width is less than 1 μm or the average size of the cavity thickness is less than 0.3 μm, sufficient reflectance may not be obtained. In addition, the longitudinal direction said here is a direction through which a film flows in the process at the time of film manufacture, and let the direction orthogonal to a longitudinal direction be a width direction. It is the value measured by the method similar to said cavity size and the size of incompatible resin.

  Examples of inorganic particles having a refractive index of less than 2.0 that are preferably used in the polyester layer (B) of the present invention include wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, and carbonic acid. Magnesium, zinc oxide (zinc white), magnesium oxide, barium carbonate, zinc carbonate, barium sulfate, calcium sulfate, mica, talc, clay, kaolin and the like can be used, but barium sulfate is particularly preferable.

  The inorganic particles having a refractive index of less than 2.0 preferably have an average particle size in the polyester of 0.05 to 10 μm, more preferably 0.1 to 3 μm. When the average particle diameter exceeds 10 μm, the film is broken at the time of stretching or the productivity is lowered such as filter clogging. Moreover, when the average particle diameter is 0.05 μm or less, the reflectance on the high wavelength side is particularly lowered, which is not preferable. Here, the average particle diameter is the number average particle diameter. In the present invention, the content of inorganic particles having a refractive index of less than 2.0 is 30 to 50% by weight, preferably 35 to 45% by weight, based on the polyester layer (B). When the content is less than the above range, the film has a poor reflectance and total light transmittance, and conversely, when the content is more than the above range, the film is likely to be broken at the time of stretching, resulting in productivity. May decrease. In addition, inorganic particles having a refractive index of less than 2.0 can also be contained in the polyester layer (A).

  In the present invention, the polyester layer (B) may contain both inorganic particles having a refractive index of less than 2.0 and a resin incompatible with the polyester. When an incompatible resin is used as a nucleating agent, it is easy to generate flat and large cavities and can reflect light over a wide range of wavelengths, but because the size of the cavities themselves is large, the number of cavities is small. Increasing the content of polyester incompatible resin tends to decrease, resulting in problems such as tearing in the manufacturing process due to increase in the incompatible resin dispersion size, and even higher reflectivity When obtaining the value, there is a problem that it is difficult to improve the reflectance. In addition, when inorganic particles having a refractive index of less than 2.0 such as barium sulfate are used, the content in the polyester film can be increased as compared with the incompatible resin, so that a large number of small cavities are formed. Although it is excellent in that the reflectance on the low wavelength side is high, it is inferior to the reflectance on the long wavelength side because it is difficult to form a large-sized cavity. For this reason, it becomes possible to compensate each other's fault by combining the big cavity by the resin incompatible with polyester, and the small cavity by the inorganic particle whose refractive index is less than 2.0.

  In the present invention, the thickness of the polyester layer (A) on at least one side is 5 to 15 μm, preferably 5 to 10 μm. When the thickness of the polyester layer (A) is less than 5 μm, the contribution of diffuse reflection of the surface portion by the particles having a refractive index of 2.0 or more in the polyester layer (A) is reduced, resulting in poor reflectivity. Moreover, when the thickness of the polyester layer (A) having a high degree of rigidity is reduced, problems such as a reduction in the rigidity of the polyester film and frequent occurrence of tearing during production occur. When the thickness of the polyester layer (A) exceeds 15 μm, the reflectance decreases due to an increase in loss due to light diffusion in the polyester layer (A).

  In this invention, the thickness of a polyester layer (B) is 150 micrometers or more, Preferably it is 200-400 micrometers. The main light reflection performance is expressed by the cavity in the polyester layer (B). When the thickness of the polyester layer (B) is less than 150 μm, the film is inferior in reflectance and concealment. The upper limit of the thickness of the polyester layer (B) is not particularly limited, but is preferably 500 μm or less from the viewpoint of productivity and cost of the polyester film.

  In this way, a thin polyester layer (A) having a high reflection ability on the surface side while exhibiting basic light reflection performance by a thick layer of the polyester layer (B) with little loss of light diffusion. By increasing the reflection efficiency at the part near the film surface on the side where light is incident, the effect of increasing the reflectivity is high despite the relatively low titanium dioxide content while keeping the light diffusion loss low. Can be obtained. Therefore, it is preferable in terms of reflectance to use the polyester (A) layer side of the white laminated polyester film of the present invention for the light reflecting surface. In addition, the thickness of each polyester layer measures the length of the thickness direction of each polyester layer from the observation photograph with the scanning microscope of the said cross section, and calculates | requires the thickness of each layer by calculating backward from magnification. In addition, when calculating | requiring the thickness of each polyester layer, the cross-sectional photograph arbitrarily selected from the mutually different measurement visual field in the cut surface cut out along the width direction is used, and it calculates as the average value. When the longitudinal direction and the width direction are unknown, a cross section in an arbitrary direction may be measured.

In the present invention, the apparent density of the entire film is preferably 0.5 to 1.3 g / cm ³ , more preferably 0.6 to 1.3 g / cm ³ , and particularly preferably 0.7 to 1.3 g / cm ^3. cm ³ . The apparent density of the void-containing laminated white polyester film is reduced by the fine voids contained in the polyester layer (B) and adjusted to a preferred range. When the apparent density is less than 0.5, it is preferable because the film strength is inferior and breakage occurs, wrinkles occur during three-dimensional processing, or the production of the film frequently breaks and the productivity is inferior. Absent. On the other hand, if the apparent density exceeds 1.3 g / cm ³ , the amount of voids present in the polyester film is insufficient, and thus the reflectance is deteriorated. In addition, the apparent density in this invention cuts a film into the magnitude | size of 100 mm x 100 mm, measures the thickness of 10 points | pieces by attaching the measuring element of diameter 10mm to a dial gauge, and average value d (thickness value d ( After calculating (μm), the film was weighed with a direct balance, and the weight w (g) was read to the unit of 10 ⁻⁴ g, and the calculated value.

  In the present invention, an antioxidant is preferably added to the polyester layer (B) in an amount of 0.05 to 1.0% by weight, more preferably 0.1 to 0.5% by weight, based on the polyester layer (B). By making it contain, it becomes possible to perform more stable polymer extrusion and film formation. As the antioxidant, a hindered phenol-based or hindered amine-based antioxidant is particularly preferable from the viewpoint of dispersibility.

  In the present invention, organic particles can also be used as the particles used. Examples of the organic particles include crosslinked polymer particles, calcium oxalate, acrylic particles, and imide particles.

  Moreover, the light-resistant agent may be contained in at least any polyester layer of the white laminated polyester film for reflectors of the present invention, and it is a preferred embodiment that it is contained in the polyester layer (A). By containing a light resistance agent, the color tone change by the ultraviolet-ray of a film is prevented. The light-proofing agent preferably used in the present invention is not particularly limited as long as other properties are not impaired, but it has excellent heat resistance, good compatibility with the polyester resin, can be uniformly dispersed, and has little coloration. It is desirable to select a light-proofing agent that does not adversely affect the reflective properties of the film. Examples of such a light-proofing agent include salicylic acid-based, benzophenone-based, benzotriazole-based, cyanoacrylate-based, triazine-based UV absorbers, hindered amine-based UV stabilizers, and the like. Specifically, for example, salicylic acid-based pt-butylphenyl salicylate, p-octylphenyl salicylate, benzophenone-based 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy -5-sulfobenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane, 2- (2'-hydroxy-5) of benzotriazole series '-Methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H benzotriazol-2-yl) phenol], a cyanoacrylate-based ester 2- (3,4-diphenyl-1,3,5-triazin-2-yl) -5-[(hexyl) oxy] as triazine series, and tri-2-cyano-3,3′-diphenyl acrylate) -Phenol and the like.

  Examples of the UV stabilizer include hindered amine-based bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, dimethyl succinate 1- (2-hydroxyethyl) -4-hydroxy-2. , 2,6,6-tetramethylpiperidine polycondensate, as well as nickel bis (octylphenyl) sulfide, and 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl- Examples include 4′-hydroxybenzoate. Among these light-proofing agents, 2,2 ′, 4,4′-tetrahydroxy-benzophenone, bis (2-methoxy-4-hydroxy-5-benzoylphenyl) methane, and 2,2 ′ are excellent in compatibility with polyester. -Methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2Hbenzotriazol-2-yl) phenol] and 2- (4,6-diphenyl-1,3,5-triazine Application of -2-yl) -5-[(hexyl) oxy] -phenol is preferred. The above light resisting agents may be used alone or in combination of two or more.

  The content of the light fastener in the white laminated polyester film for a reflector of the present invention is preferably 0.05 to 10% by weight, more preferably 0.1 to 5% by weight with respect to the layer containing the light fastener. More preferably, it is 0.15 to 3% by weight. When the light-proofing agent content is less than 0.05% by weight, the light resistance is insufficient, and the color tone changes during long-term storage, and when the light-proofing agent content exceeds 10% by weight. The color of the film is changed by coloring with the light-proofing agent, and the light-proofing agent itself absorbs light, so that the reflectance may be lowered.

  In the white laminated polyester film for a reflector of the present invention, excellent light resistance and light reflectivity can be achieved by using a light resistance agent and titanium oxide in combination.

  In the present invention, it is preferable that a coating layer having an ultraviolet absorbing ability is provided on at least one surface side because yellowing of the film during long-term use can be prevented. The ultraviolet absorbing layer may be a single layer or a plurality of layers, but in the case of a plurality of layers, any one of them is a layer containing an ultraviolet absorber, preferably two or more layers. Is a layer containing an ultraviolet absorber from the viewpoint of maintaining weather resistance. The UV-absorbing layer includes UV absorbers in resin components such as thermoplastic, thermosetting, and active curable resins, such as benzophenone, benzotriazole, triazine, cyanoacrylate, salicylate, and benzoate. Alternatively, it can be obtained by laminating a resin containing or copolymerizing an inorganic ultraviolet shielding agent or the like. Of these, benzotriazole-based ultraviolet absorbers are more preferable.

  The benzotriazole-based UV-absorbing monomer is not particularly limited as long as it is a monomer having benzotriazole in the basic skeleton and an unsaturated double bond, and preferred monomer is 2- (2′-hydroxy-5). '-Acryloyloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-3'-tert-butyl- 5'-acryloyloxyethylphenyl) -5-chloro-2H-benzotriazole is preferred. Acrylic monomers and / or oligomers copolymerized with these monomers include alkyl acrylates, alkyl methacrylates, and monomers having crosslinkable functional groups such as carboxyl groups, methylol groups, acid anhydride groups, sulfonic acid groups, amides. Examples thereof include monomers having a group, an amino group, a hydroxyl group, an epoxy group, and the like.

  In the coating layer having ultraviolet absorbing ability preferably used in the present invention, one or more of the above acrylic monomers and / or oligomers may be copolymerized at an arbitrary ratio, preferably methyl methacrylate or From the viewpoint of the hardness of the laminated film, it is preferable that styrene is polymerized in an amount of 20% by weight or more, more preferably 30% by weight or more based on the acrylic monomer. The copolymerization ratio of the benzotriazole monomer and the acrylic monomer is such that the ratio of the benzotriazole monomer is 10% by weight to 70% by weight, preferably 20% by weight to 65% by weight, more preferably 25% by weight to 60%. It is preferable from the viewpoint of durability and adhesion with a substrate film that the content is not more than% by weight. Although the molecular weight to this copolymerization polymer is not specifically limited, Preferably it is 5000 or more, More preferably, it is preferable from a durable viewpoint of an application layer that it is 10,000 or more. The preparation of the copolymer can be obtained by a method such as radical polymerization, and is not particularly limited. The copolymer is laminated on the base film as an organic solvent or an aqueous dispersion, and the thickness is usually 0.5 to 15 μm, preferably 1 to 10 μm, more preferably 1 to 5 μm. It is particularly preferable in terms of light resistance to be within the range.

  In the coating layer having ultraviolet absorbing ability in the present invention, organic and / or inorganic particles may be added to the coating layer for the purpose of adjusting the glossiness of the surface. As inorganic particles, silica, alumina, titanium dioxide, zinc oxide, barium sulfate, calcium carbonate, zeolite, kaolin, talc, etc. can be used. As organic particles, silicone compounds, crosslinked styrene, crosslinked acrylic, crosslinked melamine are used. Etc. can be used. The particle size of the organic and / or inorganic particles is preferably 0.05 to 15 μm, and preferably 0.1 to 10 μm. Moreover, as content, 5 to 50 weight% is preferable with respect to the dry weight of the coating layer which has an ultraviolet absorptivity, More preferably, it is 6 to 30 weight%, More preferably, it is 7 to 20 weight%. Setting the particle size of the contained particles in the above range is preferable because it prevents the particles from falling off and adjusts the glossiness of the surface.

  Various additives can be added to the coating layer having ultraviolet absorbing ability in the present invention within a range not impairing the effects of the present invention. As the additive, for example, a fluorescent brightening agent, a crosslinking agent, a heat stabilizer, an antistatic agent, a coupling agent and the like can be used.

  Moreover, the coating layer which has an ultraviolet absorptivity can be apply | coated by arbitrary methods. For example, gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife i-coating, dipping, extrusion lamination, etc. can be used, but in particular kiss coating using a micro gravure roll. The coating method is preferable because it is excellent in coating appearance and gloss uniformity. Moreover, when hardening an application layer after application | coating, the hardening method can use a well-known method. For example, thermosetting, a method using active rays such as ultraviolet rays, electron beams, radiation, or a combination of these methods can be applied. In the present invention, a heat curing method using a hot air oven or an ultraviolet curing method using ultraviolet irradiation is preferable. Moreover, as a method of providing a coating layer, the method of apply | coating simultaneously at the time of manufacture of a base film (in-line coating) may be sufficient, and you may apply | coat (off-line coating) on the base film after completion | finish of crystal orientation.

  In the white laminated polyester film for a reflective sheet of the present invention, the heat shrinkage at 80 ° C. for 30 minutes is preferably 0.5% or less in both the longitudinal direction and the width direction, more preferably 0.0 to 0.3%, Preferably it is 0.0 to 0.1% or less. When the heat shrinkage rate exceeds 0.5%, the dimensional change of the reflective film becomes large, and the flatness of the film is deteriorated. The heat shrinkage rate is preferably larger than 0%. When the content is less than 0.0%, that is, in the direction in which the film stretches when heated, the film is stretched by the heat of the cold cathode tube after being incorporated into the backlight unit, so that bending and undulation are likely to occur. The method for setting the heat shrinkage ratio to less than 0.5% is not particularly limited. Usually, however, the biaxially stretched film is reduced in the draw ratio during production, the heat treatment temperature is increased, and simultaneously in the width direction and / or the longitudinal direction. For example, a relaxation treatment may be performed. In order to obtain a predetermined heat shrinkage rate in both the longitudinal direction and the width direction, it is preferable to perform relaxation treatment also in the longitudinal direction. For this relaxation treatment, a method (in-line treatment) performed during the production of the biaxially stretched polyester film is preferable from the viewpoint of production cost, but a method of performing relaxation treatment by passing the film once formed into the oven again (offline) Processing).

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

  In a composite film forming apparatus having an extruder (A) and an extruder (B), first, in order to form a polyester layer (A), polyester pellets having a melting point of 230 to 280 ° C. and master pellets of titanium dioxide particles are used as titanium dioxide. Mix so that the particles are 3 to 15% by weight and dry thoroughly. You may add another inorganic particle and a ultraviolet absorber to this dry raw material as needed. Next, the dried raw material is supplied to an extruder (A) heated to a temperature of 240 to 300 ° C., filtered through a 10 to 50 μm cut filter after melt extrusion, and then introduced into a T-die composite die. . On the other hand, in order to form the polyester layer (B), vacuum-dried polyester pellets and, if necessary, vacuum-dried polyester pellets that are incompatible with the polyester layer (B) are incompatible with the polyester layer (B). 12 to 30% by weight and / or inorganic particles are mixed so as to be 30 to 50% by weight, and this is fed to an extruder (B) heated to a temperature of 260 to 300 ° C., and the polyester (A) layer It is melted as in the case, filtered and introduced into the T-die composite die. In addition, you may add a 0.05 to 10weight% of dispersing agent to this raw material as needed. In addition, the incompatible resin may be added by previously drying a master chip in a vacuum. In the T die composite die, the polymer of the extruder (B) is laminated in the center so that the amount of the polymer of the extruder (A) is A / B / A on the surface side, and co-extruded into a sheet and melted. A laminated sheet is obtained.

  This melt-laminated 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 laminated film. The unstretched laminated film is led to a group of rolls heated to a temperature of 70 to 120 ° C., stretched 3 to 4 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and a group of rolls having a temperature of 20 to 50 ° C. Cool with.

  Subsequently, the both ends of the film are guided to a tenter while being gripped by clips, and stretched 3 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 3 to 5 times in each of the longitudinal direction and the width direction, and the area ratio (longitudinal stretching ratio x lateral stretching ratio) is preferably 9 to 15 times. If the area magnification is less than 9 times, the resulting biaxially stretched laminated film has insufficient reflectivity, concealability, and film strength. Conversely, if the area magnification exceeds 15 times, the film tends to be broken during stretching. is there.

  In order to complete the crystal orientation of the obtained biaxially stretched laminated film and to give flatness and dimensional stability, heat treatment is continuously performed in a tenter at a temperature of 150 to 240 ° C. for 1 to 30 seconds, and uniform. After cooling to room temperature, it is cooled to room temperature, and then, if necessary, a corona discharge treatment or the like is performed to further improve the adhesion to other materials, and winding is performed to obtain the void-containing white laminated polyester film of the present invention. be able to. 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.

  Biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, but when the simultaneous biaxial stretching method is used, film breakage in the manufacturing process can be prevented, or the polyester layer (A) adheres to the heating roll. This makes it difficult for transfer defects to occur. Further, after biaxial stretching, the film may be re-stretched in either the longitudinal direction or the width direction.

  The white laminated biaxially stretched film thus obtained is provided with a coating layer having ultraviolet absorbing ability by a microgravure plate / kiss coat, dried at 80 to 140 ° C., and then irradiated with ultraviolet rays to cure the coating layer. To do. A pretreatment such as providing an easy-adhesion layer may be applied before applying the layer having ultraviolet absorbing ability.

[Measurement and evaluation method of characteristics]
The characteristic value of this invention is calculated | required with the following evaluation method and evaluation criteria.

(1) Fine void size inside the film, size of incompatible resin and thickness of polyester layer After freezing the film, cut out the cross section along the longitudinal direction and the width direction, and scan the cross section with a scanning electron microscope ( SEM) The presence or absence of fine cavities was examined from a cross-sectional photograph taken by magnifying 4000 times using S-2100A type (manufactured by Hitachi, Ltd.).

  For the cavity size and the size of the incompatible resin, measure the length in the width direction and the thickness direction from the photograph taken with the scanning microscope of the above cross section, and calculate backward from the magnification to calculate each cavity and each incompatible phase. The size of the molten resin was determined. The average value of the cavity size and the size of the incompatible resin is 50 from the cross-sectional photograph of the cut surface cut in the longitudinal direction, and 50 from the cross-sectional photo of the cut surface cut along the width direction. The size in the width direction and the thickness direction of the incompatible resin was determined and used as the average value. In addition, when the longitudinal direction and the width direction are unclear, the measurement may be performed by cutting a cross section of the sample at two orthogonal surfaces.

  As for the cavity size and the size of the incompatible resin, the sizes shown in FIG. 1 were measured. In addition, the case where no incompatible resin was found in the cavity as shown in FIG. 2 was excluded.

  The thickness of each polyester layer was determined by measuring the length in the thickness direction of each polyester layer from the observation photograph of the cross section with a scanning microscope and calculating backward from the magnification. In addition, when calculating | requiring the thickness of each polyester layer, the cross-sectional photograph arbitrarily selected from the mutually different measurement visual field in the cut surface cut out along the width direction was used, and it computed as the average value. In addition, when the longitudinal direction and the width direction are unknown, a cross section in an arbitrary direction may be measured.

(2) Apparent density The film was cut to a size of 100 mm × 100 mm, and a dial gauge (No. 2109-10 manufactured by Mitutoyo Corporation) was attached to a 10 mm diameter probe (No. 7002). The thickness is measured, and the average thickness d (μm) is calculated. Further, this film is weighed with a direct balance, and the weight w (g) is read up to a unit of 10 ⁻⁴ g. The value calculated by the following formula is the apparent density.
(Apparent density) = w / d × 100 (g / cm ³ ).

(3) Average reflectance A spectrophotometer (Shimadzu Corporation UV2450) with an integrating sphere attachment (ISR2200, Shimadzu Corporation) is attached, barium sulfate is used as a standard board under the following conditions, and the standard board is 100%. The relative reflectance was measured. In the wavelength range of 420 to 670 nm, the average reflectance was defined as the average value of the relative reflectance for each wavelength of 10 nm, and the determination was made according to the following criteria. In addition, (double-circle), (circle), (triangle | delta) is a pass.
A: Very good (over 102%)
○: Good (101% or more and less than 102%)
Δ: Slightly inferior (100% or more and less than 101%)
X: Inferior (less than 100%)
<Measurement conditions>
Scanning speed: Medium speed Slit: 5.0nm
Reflection angle: 8 °.

<Standard plate creation method>
34 g of barium sulfate white standard reagent (EASTMAN White Reflectance Standard Cat No.6091) was put into a cylindrical recess having a diameter of 50.8 mm and a depth of 9.5 mm, and compressed using a glass plate, and the compression density was about 2 g / cm. ³ barium sulfate white standard plate was prepared.

  In addition, as an evaluation index of the ultraviolet absorbing ability, an average reflectance of 320 nm to 360 nm was measured in the same manner as described above. If it is less than 10%, it is good.

(4) Concealing property Using a haze meter (HZ-2 manufactured by Suga Test Instruments Co., Ltd.), the polyester film was measured for total light transmittance according to JIS K7105 (1981), and the concealability was determined according to the following criteria. Went. In addition, (double-circle), (circle), (triangle | delta) is a pass.
A: Very good (total light transmittance is less than 2.0%)
○: Good (total light transmittance is 2.0% or more and less than 2.5%)
Δ: Slightly inferior (total light transmittance is 2.5% or more and less than 3.0%)
X: Inferior (total light transmittance is 3.0% or more).

(5) Film-forming stability Evaluation was made based on the number of occurrences of film tearing. Evaluation was performed based on the number of tears per day, and the determination was made according to the following criteria. In addition, (circle) and (triangle | delta) are pass.
○: Good (Nearly torn (less than once / day))
Δ: Slightly inferior (breakage occurs occasionally (1 to 2 times / day))
X: Inferior (Torn frequently (twice / day or more)).

  The present invention will be described with reference to the following examples, but the present invention is not limited thereto.

<Example 1>
(Manufacture of polyethylene terephthalate pellets (PET))
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.

(Production of isophthalic acid copolymerized polyethylene terephthalate pellets (PET / I ¹² ))
A mixture of 88 mol% terephthalic acid and 12 mol% isophthalic acid as the acid component, ethylene glycol as the glycol component, and antimony trioxide as the polymerization catalyst is added to the polyester pellets in an amount of 300 ppm in terms of antimony atoms. Then, a polycondensation reaction was carried out to obtain isophthalic acid copolymerized polyethylene terephthalate (PET / I ¹² ) pellets having an intrinsic viscosity of 0.68 dl / g and a carboxyl end group amount of 40 equivalents / ton.

  In a composite film-forming apparatus having an extruder (a) and an extruder (b), in order to form the polyester layer (A), the mixture of raw materials shown in Table 1 was vacuum-dried at a temperature of 160 ° C. for 5 hours, The mixture was supplied to the extruder (a) side, melt-extruded at a temperature of 280 ° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.

Abbreviations in Table 1 have the following meanings.
Ti0 ₂ -A (50): Titanium dioxide master PET pellet containing 50% by weight of anatase-type titanium particles produced by a sulfuric acid process having an average particle size of 0.25 μm and a refractive index of 2.5 Ti0 ₂ − R1 (50): Titanium dioxide master PET pellet containing 50% by weight of rutile-type titanium particles produced by a sulfuric acid process having an average particle size of 0.25 μm and a refractive index of 2.7. Ti0 ₂ -R2 (50) Titanium dioxide master PET pellets containing 50% by weight of rutile titanium dioxide particles produced by a chlorine process having an average particle size of 0.22 μm and a refractive index of 2.7 BaSO ₄ (60) -PET / I ¹² : Barium sulfate master isophthalic acid copolymer polyethylene terephthalate containing 60% by weight of barium sulfate particles having an average particle diameter of 1 μm and a refractive index of 1.6 Tallates (PET ^{/ I 12)} pellets · PMP: polymethylpentene (Mitsui Chemicals Co., Ltd., TPX DX820)
PBT / PAG: “Hytrel®” (registered trademark) 7277 (manufactured by Toray DuPont Co., Ltd.), which is a block copolymer of polybutylene terephthalate (PBT) and polyalkylene glycol (PAG)
PEG (6): PET pellets obtained by copolymerizing 6% by weight of polyethylene glycol having a molecular weight of 4,000. Light proofing agent (10): Triazine-based ultraviolet absorber (Ciba UVA006, manufactured by Ciba Specialty Chemicals Co., Ltd.) 10 On the other hand, in order to form the polyester layer (B), the mixture of raw materials shown in Table 1 was vacuum-dried at a temperature of 160 ° C. for 5 hours and then supplied to the extruder (b) side. Then, after melt extrusion at a temperature of 280 ° C., foreign matter was 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 (A) is merged so as to be laminated (A / B / A) on both surface layers of the polyester layer (B), and then co-extruded into a sheet to obtain a melt-laminated sheet. The melt-laminated sheet was closely cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 18 ° 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 3.3 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 90 ° C. in the tenter, and continuously in a heating zone at a temperature of 100 ° C. in a direction perpendicular to the longitudinal direction (width direction). 3.2 Stretched 2 times. Subsequently, a heat treatment was performed at a temperature of 200 ° C. for 10 seconds in a heat treatment zone in the tenter, a relaxation treatment was further performed in a 4% width direction at a temperature of 180 ° C., and then a 1% width direction at a temperature of 140 ° C. The relaxation treatment was performed. Subsequently, the film is gradually cooled and wound up, and the A / B / A three-layer composite structure in which the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside is 5/240/5 (μm) is obtained. A white laminated polyester film having a thickness of 250 μm was obtained. This white laminated polyester film contained many fine cavities in the polyester layer (B), the average size in the width direction of the cavities was 11.0 μm, and the average size in the thickness direction was 1.3 μm.

A layer (C) having the following composition was applied to one side of the obtained film by kiss coating using a micro gravure roll so that the thickness after application was 2 μm, and dried at 120 ° C. for 1 minute. Further, on this (C) layer, a surface hardened layer (D) layer having the following composition was applied by kiss coating using a micro gravure roll so that the thickness after curing was 4 μm, and the solvent was removed with a hot air dryer at 80 ° C. After drying, a UV light amount of 300 mJ / cm ² was applied and cured with a conveyor-type metahalide lamp (manufactured by Eye Graphic) to obtain a white laminated polyester film having a light-resistant cured layer on one side.

(C) Coating composition of layer: 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole (30 wt%) copolymerized methyl methacrylate: 95 parts by weight Modified saturated polyester resin “Nikka Coat” (Registered trademark) FS-12 (manufactured by NIPPON KAKO CO., LTD.): 4 parts by weight methylated melamine “Cymel” (registered trademark) 370 (manufactured by Mitsui Cytec Co., Ltd.): 1 part by weight toluene / methyl ethyl ketone = 1/1 : 400 parts by weight.

(D) Coating composition of layer: 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole: 20 parts by weight Dipentaerythritol hexaacrylate: 68 parts by weight Acrylic oligomer “Aronix” (Registered trademark) M-7100 (manufactured by Kyoeisha Chemical Co., Ltd.): 8 parts by weight, 2-hydroxypropyl acrylate: 4 parts by weight, “Irgacure” (registered trademark) 183 (manufactured by Ciba Geigy): 4 parts by weight Toluene / methyl ethyl ketone = 1/1: 312 parts by weight.

  The characteristics of the white laminated polyester film having the light-resistant cured layer thus obtained are as shown in Table 3, having high reflectivity and concealing properties, and excellent film forming stability.

<Example 2>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 15/200/15 ( A white laminated polyester film having a thickness of 230 μm having an A / B / A three-layer composite configuration of (μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 3, and were within the acceptable range although the reflectivity and concealability were slightly inferior.

<Example 3>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having a composite structure of 3 μm A / B / A three layers was obtained. In this example, no light-resistant cured layer was provided.

  The characteristics of the obtained white laminate were as shown in Table 3, and had high reflectivity and concealing properties, and excellent film forming stability. In addition, since the light-resistant cured layer was not provided, the ultraviolet absorption ability was slightly inferior.

<Example 4>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer are as shown in Table 3 and had a tendency to be slightly inferior in film forming stability, but had a particularly high reflectance.

<Example 5>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 15/170/15 ( A white laminated polyester film having a thickness of 200 μm having a composite structure of 3 μm A / B / A was obtained, and a light-resistant cured layer was provided on one side in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 3 and were within the acceptable range although the concealability was slightly inferior.

<Example 6>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 3, and the reflectance was slightly inferior, but was within the acceptable range.

<Example 7>
The polyester layer (A) and the polyester layer (B) having a cavity in the same manner as in Example 1 except that the raw materials and conditions shown in Table 1 were used and the heat treatment temperature was changed to 185 ° C. A white laminated polyester film having a thickness of 190 μm having an A / B / A three-layer composite structure with a thickness of 15/160/15 (μm) was obtained, and light-resistant curing was performed on one side in the same manner as in Example 1. A layer was provided. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 3 and were within the acceptable range although the reflectance and concealability were slightly inferior.

<Example 8>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/284/8 ( A white laminated polyester film having a thickness of 300 μm having an A / B / A three-layer composite structure of (μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the obtained white laminated polyester film having the light-resistant cured layer are as shown in Table 3, and both the reflectance and the concealing property are particularly high and have excellent characteristics.

<Example 9>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/384/8 ( A white laminated polyester film having a thickness of 400 μm having an A / B / A three-layer composite structure of (μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the obtained white laminated polyester film having the light-resistant cured layer are as shown in Table 3, and both the reflectance and the concealing property are particularly high and have excellent characteristics.

<Example 10>
Except that the raw materials and conditions shown in Table 1 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 5/240/5 ( A white laminated polyester film having a thickness of 250 μm having a composite structure of 3 μm A / B / A three layers was obtained. However, no light-resistant cured layer was provided. The characteristics of the obtained white laminated polyester film having the light-resistant cured layer are as shown in Table 3, and both the reflectance and the concealing property are particularly high and have excellent characteristics.

<Comparative Example 1>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 20/210/20 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristic of the white laminated polyester film which has the obtained light-resistant cured layer is as Table 4, Comprising: It was inferior to a reflectance.

<Comparative example 2>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having cavities therein was 3/244/3 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer are as shown in Table 4, and although the reflectivity and concealability were acceptable, the film-forming stability was inferior.

<Comparative Example 3>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 15/220/15 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristic of the white laminated polyester film which has the obtained light-resistant cured layer is as Table 4, Comprising: It was inferior to a reflectance.

<Comparative example 4>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 4, and were inferior in reflectance and concealment.

<Comparative Example 5>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristic of the white laminated polyester film which has the obtained light-resistant cured layer is as Table 4, Comprising: It was inferior to a reflectance.

<Comparative Example 6>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( An attempt was made to produce a white laminated polyester film having a thickness of 250 μm with a composite structure of A / B / A three layers of (μm), but tearing occurred frequently and film formation was impossible.

<Comparative Example 7>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 4, and were inferior in reflectivity and concealability.

<Comparative Example 8>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 8/234/8 ( A white laminated polyester film having a thickness of 250 μm having an A / B / A three-layer composite structure of μm) was obtained, and a light-resistant cured layer was provided on one side thereof in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 4, and were inferior in reflectance and concealment.

<Comparative Example 9>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside was 15/130/15 ( A white laminated polyester film having a thickness of 160 μm having a composite structure of A / B / A of 3 μm) was obtained, and a light-resistant cured layer was provided on one side in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 4, and were inferior in concealability.

<Comparative Example 10>
The polyester layer (A) and the polyester layer (B) having a cavity in the same manner as in Example 1 except that the raw materials and conditions shown in Table 2 were used and the heat treatment temperature was changed to 185 ° C. A white laminated polyester film with a thickness of 180 μm having an A / B / A three-layer composite structure with a thickness of 15/150/15 (μm) was obtained, and light-resistant curing was performed on one side in the same manner as in Example 1. A layer was provided. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer were as shown in Table 4, and were inferior in reflectance and concealment.

<Comparative Example 11>
The polyester layer (A) and the polyester layer (B) having a cavity in the same manner as in Example 1 except that the raw materials and conditions shown in Table 2 were used and the heat treatment temperature was changed to 185 ° C. An attempt was made to produce a white laminated polyester film with a thickness of 180 μm with a 15/150/15 (μm) A / B / A three-layer composite structure. However, tearing occurred frequently and film formation was impossible. It was.

<Comparative Example 12>
Except that the raw materials and conditions shown in Table 2 were used, the thickness of the polyester layer (A) and the polyester layer (B) having no cavity inside was 15/158 / A white laminated polyester film having a thickness of 188 μm having a 15 (μm) A / B / A three-layer composite structure was obtained, and a light-resistant cured layer was provided on one side in the same manner as in Example 1. The characteristics of the white laminated polyester film having the obtained light-resistant cured layer are as shown in Table 4, and the reflectance was greatly inferior.

Cross-sectional view of the cavity around the incompatible resin Cross section of the cavity where incompatible resin is not seen

Explanation of symbols

1 Incompatible resin in polyester 2 Cavity 3 Cavity width 4 Cavity thickness 5 Incompatible resin width 6 Incompatible resin thickness

  The present invention relates to a white laminated polyester film for a reflective sheet. More specifically, the present invention relates to a polyester film having a laminated structure, excellent in reflection characteristics, concealment properties, and good productivity. The present invention relates to a backlight device for image display, a reflection sheet for a lamp reflector, and a lighting device. The present invention relates to a white laminated polyester film that can be suitably used for a reflective sheet, a reflective sheet for lighting signs, a back reflective sheet for solar cells, and the like.

Claims (13)

A laminated polyester film in which a polyester layer (A) is laminated on at least one surface side of a polyester layer (B) containing a cavity therein, and the laminated polyester film comprises all of the following (1) to ( 8 ): White laminated polyester film for reflective sheet to fill.
(1) The thickness of the polyester layer (A) on at least one side is 5 to 15 μm.
(2) The polyester layer (A) contains 3 to 15% by weight of particles having a refractive index of 2.0 or more based on the polyester layer (A).
(3) The thickness of the polyester layer (B) is 150 μm or more.
(4) The amount of particles having a refractive index of 2.0 or more contained in the polyester layer (B) is 2% by weight or less with respect to the polyester layer (B).
(5) In the polyester layer (B), 12 to 25% by weight of the resin incompatible with the polyester resin and / or 30 to 30 inorganic particles having a refractive index of less than 2.0 with respect to the polyester layer (B). Containing 50% by weight.
(6) The resin incompatible with the polyester resin contained in the polyester layer (B) is polymethylpentene.
(7) The average particle size of the polymethylpentene in the polyester layer (B) is 3 μm or less in the width direction and 2 μm or less in the thickness direction.
(8) The polyester layer (B) contains a copolymer resin of a polyalkylene glycol, an aliphatic diol component having 2 to 6 carbon atoms and a polyester resin composed of terephthalic acid, and the content of the copolymer resin is: It is 0.05 to 10 weight% with respect to the whole polyester layer (B). The white laminated polyester film for a reflective sheet according to claim 1, wherein the particles having a refractive index of 2.0 or more contained in the polyester layer (A) are titanium dioxide particles. The white laminated polyester film for a reflective sheet according to claim 1 or 2, wherein the thickness of the polyester layer (A) is 5 to 10 µm and the thickness of the polyester layer (B) is 200 to 400 µm. The white laminated polyester film for a reflective sheet according to claim 2 or 3, wherein the titanium dioxide particles contained in the polyester layer (A) are mainly rutile type. The white laminated polyester film for a reflective sheet according to claim 4, wherein the titanium dioxide particles contained in the polyester layer (A) are mainly composed of a rutile type produced by a chlorine method. The white laminated polyester film for a reflective sheet according to any one of claims 1 to 5, wherein the resin constituting the polyester layer (A) and the polyester layer (B) is based on polyethylene terephthalate. The copolymer resin of the polyalkylene glycol, the aliphatic diol component having 2 to 6 carbon atoms, and the polyester resin composed of terephthalic acid is a block copolymer of polyalkylene glycol and polybutylene terephthalate. The white laminated polyester film for reflective sheets according to any one of the above. The white laminated polyester film for a reflective sheet according to any one of claims 2 to 7, wherein the content of titanium dioxide particles in the polyester layer (A) is 3 to 7% by weight based on the whole polyester layer (A). . The white laminated polyester film for a reflective sheet according to any one of claims 1 to 8, wherein the inorganic particles having a refractive index of less than 2.0 contained in the polyester layer (B) are barium sulfate. The white laminated polyester film for a reflective sheet according to any one of claims 1 to 9, wherein a coating layer having an ultraviolet absorbing ability is provided on at least one surface. The white laminated polyester film for a reflective sheet according to any one of claims 1 to 9, wherein the polyester layer (A) contains 0.05 to 10% by weight of a light-resistant agent with respect to the polyester layer (A). The white laminated polyester film for a reflection sheet according to any one of claims 1 to 11, wherein the polyester layer (A) side is used as a light reflection surface. It is a back surface reflection sheet of the backlight for liquid crystal displays which uses the polyester layer (A) side as a light reflection surface, The white laminated polyester film for reflection sheets in any one of Claims 1-12.

Images