JP5251091B2 - White polyester film - Google Patents

Description

  The present invention relates to an improvement of a white film, and particularly relates to a white film for a reflecting member. More specifically, it is a white film for a reflective member suitable as a reflective member (reflector plate, lamp reflector) for a surface light source, and a surface light source that is brighter, clearer, thinner, and excellent in illumination efficiency is obtained. It is related with the white film which can be manufactured. Moreover, it is related with the white film for reflection members suitable also as a solar cell backsheet.

  In recent years, many displays using liquid crystals have been used as display devices for personal computers, televisions, mobile phones, and the like. Since these liquid crystal displays themselves are not light emitters, they can be displayed by installing a surface light source called a backlight from the back side and irradiating light. Further, the backlight has a structure of a surface light source called a side light type or a direct type in order to meet the requirement that the entire screen should be irradiated uniformly, not just light. In particular, for a thin liquid crystal display used for a notebook personal computer or the like for which a thin and small size is desired, a sidelight type, that is, a backlight of a type that irradiates light from the side of a screen is applied.

  In general, in this sidelight type backlight, a cold cathode ray tube or an LED is used as an illumination light source from the edge of the light guide plate, and a light guide plate that uniformly propagates and diffuses light is used to uniformly irradiate the entire liquid crystal display. The light plate method is adopted. In this illumination method, in order to use light more efficiently, a lamp reflector is provided around the cold cathode ray tube, and in order to efficiently reflect the light diffused from the light guide plate to the liquid crystal screen side, A reflector is provided below. Thereby, the loss of light from the cold cathode ray tube is reduced, and the function of brightening the liquid crystal screen is provided.

  On the other hand, for large screens such as liquid crystal televisions, the edge-light method has been adopted because it is not possible to increase the screen brightness. In this system, a cold cathode ray tube, an LED, and the like are provided at the bottom of the liquid crystal screen, and the cold cathode ray tube and the like are arranged in parallel on the reflector. The reflecting plate may be a flat plate or a cold cathode ray tube formed into a semicircular concave shape.

  Lamp reflectors and reflectors used for such surface light sources for liquid crystal screens (hereinafter sometimes collectively referred to as surface light source reflecting members) are required to have high light reflecting performance as well as thin films. A film to which a pigment is added or a film containing fine bubbles inside has been used alone, or a film in which these films are bonded to a metal plate, a plastic plate, or the like. In particular, a film containing fine bubbles inside is widely used because it has a certain effect in improving luminance and uniforming screen luminance (Patent Documents 1 and 2).

  In particular, in a film containing fine bubbles inside, a nucleating agent is added in order to generate fine bubbles. Such nucleating agents include acyclic olefin resins such as polypropylene (hereinafter sometimes abbreviated as “PP”) and polymethylpentene (hereinafter sometimes abbreviated as “PMP”), barium sulfate, calcium carbonate, and the like. Inorganic particles are used.

  By the way, the application of the liquid crystal screen has been widely used in various devices such as a stationary personal computer, a television, and a mobile phone display in recent years in addition to a conventional notebook personal computer. Accordingly, liquid crystal screens are required to be brighter, clearer, thinner, and more excellent in lighting efficiency (low power consumption).

  In recent years, solar cells, which are clean energy, have attracted attention as the next-generation energy source, and development is progressing from the construction field to electrical and electronic parts. Solar cells convert sunlight into electricity with high efficiency, that is, conversion efficiency is most important, and the reflected light from the back sheet for solar cells laid on the back (back) of the solar cell is also converted into electricity. The conversion efficiency is improved by conversion (here, the solar battery back sheet refers to, for example, the back surface sealing film of FIG. 1 of Patent Document 3).

Therefore, the solar cell backsheet is also required to function as a light reflecting member. Then, although the above-mentioned white film may be used as a solar cell backsheet (reflective member), the film excellent in the further light reflection performance, lightweight property, and thin film property is calculated | required (patent document 3).
JP-A-6-322153 JP-A-7-118433 JP 2002-26354 A

  However, when the above-described conventional white film is used as a reflector or reflector as a surface light source reflecting member, a part of the light from the illumination light source is transmitted to the opposite surface because of poor light reflectivity. In addition, there is a problem that the brightness (brightness) of the liquid crystal screen is insufficient, and further, the efficiency of illumination is reduced due to transmission loss of light from the illumination light source, so problems such as not contributing to reduction of power consumption are pointed out. Therefore, there is a strong demand for higher reflectivity of white films.

  In addition, the conventional white film is inferior in concealment, so when used as a surface light source, the chassis or frame on the back side of the reflective film may be seen through, which is a cause of reducing the sharpness of the liquid crystal screen. It has become. Therefore, there is a strong demand for improving the concealability of white films. In addition, such a phenomenon that the chassis and the frame can be seen through is sometimes referred to as “show-through”. If the chassis or frame is made of a metal or plastic member that is a high light reflector, that portion will be brighter than the other parts, and if the metal or plastic member is a high light absorber, The part “darkens” behind the other parts. That is, the luminance uniformity on the screen is reduced. However, in order to make the liquid crystal image clearer and easier to see, the luminance on the screen must be uniform. Therefore, such a decrease in luminance uniformity is a very large problem in practice.

  Moreover, although a white film may be used as a lamp reflector, the improvement of the concealment property of a white film is an important subject also in this case. That is, the white film as the lamp reflector may be completely covered with another member such as metal, may be partially covered, or may not be covered at all. Here, if it is completely covered, light leakage from the lamp reflector part does not occur so much, but if it is only partially covered or not covered at all, light leakage will be as much as the light source is in the vicinity. It becomes remarkable. The light leaked by such light leakage becomes stray light, which causes a decrease in brightness uniformity on the screen, or light leaks from a part that is not intended at all (for example, a gap part visible from the outside of the liquid crystal television). Cause problems.

  Here, in the film in which bubbles are contained in the film, the light beam incident on the film is reflected at the interface between the resin phase (solid phase) and the bubble phase (gas phase) inside the film. Therefore, in order to further improve the light reflection performance and light hiding performance, or to reduce the thickness while maintaining high light reflection performance and light hiding performance, the nucleating agent is more finely dispersed and the stacking density of bubbles in the film thickness direction That is, it is necessary to increase the number density of the gas-solid interface in the film thickness direction. (1) The fine dispersion of the nucleating agent has recently reached a peak. (2) If the fine dispersion is achieved and bubbles are generated. Even if it succeeds, bubbles are connected in the stretching process, and it is a problem that it does not contribute to an efficient increase in the number of gas-solid interfaces.

  In addition, inorganic particles such as barium sulfate and calcium carbonate may be used as a nucleating agent, but (1) the specific gravity of the white film cannot be reduced (2) in order to make the particle size uniform, (3) Aggregation is more likely to occur as the particle size is reduced, and does not contribute to an efficient increase in the number of gas-solid interfaces. (4) Various treatments are performed on the particle surface to suppress aggregation. When treated with an agent, the surface treatment agent is not completely colorless and transparent, so light absorption caused by the surface treatment agent occurs, resulting in a decrease in the light reflection performance of the white film as a result. .

  In addition, when the above-described conventional white film is used as the back sheet for solar cells (reflecting member), since it is inferior in light reflectivity, it does not contribute much to the improvement of the conversion efficiency of solar cells. There is a strong demand for higher reflectivity. However, if it is attempted to improve the light reflection performance, the same problem as when a white film is used as a reflection member for a surface light source occurs.

Therefore, the present invention employs the following means in order to solve such problems.
That is,
(1) A film having a white polyester layer (W layer) containing a polyester resin (A) and a cyclic olefin resin (B) and having bubbles therein, the cyclic olefin resin (B)
And the cyclic olefin resin (B) is contained in an amount of 10% by weight to 40% by weight based on the white polyester layer (W layer), and the white polyester layer (W Layer), a polyester polyester elastomer (C) having a melting point of 160 ° C. or higher is 20.5 parts by weight or more with respect to 100 parts by weight of the cyclic olefin resin (B) , a white polyester film for a reflecting member ,
(2) The white polyester film for a reflecting member according to (1), wherein the thermoplastic polyester elastomer (C) is a block copolymer of a hard segment and a soft segment,
(3) The white polyester film for a reflecting member according to (2), wherein the hard segment is a polybutylene terephthalate polyester and / or a polyethylene terephthalate polyester,
(4) The white polyester film for a reflecting member according to (2) or (3), wherein the soft segment is poly (ethylene oxide) glycol and / or poly (tetramethylene oxide) glycol.
It is.

  The white film of the present invention is excellent in light reflection performance, concealment performance, lightness (low specific gravity), thin film properties, etc., especially when used as a reflector or reflector in a surface light source, The liquid crystal image can be made clearer and easier to see, which is useful.

  The white film of the present invention needs to be a film containing a polyester resin (A) and a cyclic olefin resin (B) and having a white polyester layer (W layer) having bubbles inside.

  Here, the shape of the bubbles is not particularly limited. Independent bubbles may be used, and bubbles that are two-dimensionally or three-dimensionally continuous may be used.

  Moreover, although a bubble shape is not specifically limited, As mentioned later, it is preferable to form a large number of gas-solid interfaces in the film thickness direction.

  Therefore, the cross-sectional shape of the bubbles is preferably a circle or an ellipse extending in the film surface direction.

  The light reflectivity of the film is that the light ray incident on the film is at the gas-solid interface (the interface between the bubbles (gas phase) and the solid phase such as the polyester resin (A) or cyclic olefin resin (B), which is a matrix resin). It is because it is expressed by being reflected.

  In order to form such bubbles, the white film of the present invention is made of a polyester resin (A) that is a matrix resin constituting the white polyester layer (W layer) and a resin that is incompatible with the polyester resin (A). It is preferable to form a gas-solid interface by melt-extrusion of a mixture containing a certain cyclic olefin resin (B) and then stretching in at least one direction to form bubbles inside.

  The method is a method of generating flat air bubbles by utilizing the fact that peeling occurs at the interface between the polyester resin (A) constituting the white film and the incompatible resin cyclic olefin resin (B) during stretching. is there. Therefore, when this method is used, biaxial stretching is more preferable than uniaxial stretching in order to increase the bubble volume in the film and increase the number of gas-solid interfaces per film thickness.

  The white film of the present invention requires the polyester resin (A) constituting the white polyester layer (W layer). The polyester resin (A) is generally obtained by polycondensation of a dicarboxylic acid component and a diol component. Can do. Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid, diphenic acid, and ester derivatives thereof. Examples of the aliphatic dicarboxylic acid include adipic acid, sebacic acid, dodecadioic acid, eicoic acid, dimer acid, and ester derivatives thereof, and examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid and ester derivatives thereof. Examples of polyfunctional acids include trimellitic acid, pyromellitic acid, and ester derivatives thereof. 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.

  In the present invention, the polyester resin suitably used is polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”), polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1 , 4-cyclohexylenedimethylene terephthalate and the like.

  By using such a polyester resin as a matrix resin, high mechanical strength can be imparted to the film while maintaining high transparency. Among these, PET is more preferable from the viewpoints of mechanical properties, transparency, and cost.

  Moreover, you may introduce | transduce a copolymerization component with respect to polyester basic composition. 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.

  Moreover, in this invention, you may mix the copolymer polyester resin which introduce | transduced the copolymerization component with respect to the polyester resin.

  The amount of these copolymer components is not particularly limited, but from the viewpoints of transparency, stretchability, film forming property, moldability, etc., both dicarboxylic acid component and diol component are preferably 1 to 70 mol with respect to each component. %, And more preferably 10 to 40 mol%.

  In a preferred embodiment of the white film of the present invention, the content of the copolymerized polyester resin is 10% by weight or more based on the white polyester layer (W layer). By setting it as this range, stretchability, film-forming property, and moldability can be improved. The upper limit of the content of the copolyester resin is not particularly limited, but is preferably 50% by weight or less with respect to the white polyester layer (W layer). If the content exceeds 50% by weight, the film forming property and mechanical properties may be inferior.

  Moreover, in this invention, it is required for the white polyester layer (W layer) to contain the cyclic olefin resin (B).

  Here, the cyclic olefin resin (B) used in the present invention refers to a resin having an alicyclic structure in the main chain of a polymer obtained by polymerization from a cyclic olefin as a monomer. Since the benzene ring is not included in the alicyclic structure, the polycarbonate resin is not included in the cyclic olefin resin. The cyclic olefin (monomer) refers to cycloalkene, bicycloalkene, tricycloalkene, tetracycloalkene and the like. The cyclic olefin resin (B) may be composed of one type of cyclic olefin (monomer), or may be composed of two or more types of cyclic olefin (monomer). In addition, the cyclic olefin (monomer) used in the present invention may be a derivative to which various functional groups are imparted, but from the viewpoint of productivity of the cyclic olefin resin (B) and dispersibility in the matrix resin. It is preferable that a highly polar functional group is not added.

Representative examples of cyclic olefins (monomers) include bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, and 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 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- Chill - tricyclo [4,4,0,1 ^2.5] -3-decene, tetracyclo ^{[4,4,0,1 2.5, 1 7.10]} dodecene, 8-methyl - tetracyclo [4,4,0, 1 ^{2.5, 1 7.10]} dodecene, 8-methyl-8-methoxycarbonyltetracyclo ^{[4,4,0,1 2.5,} there is a ^{1 7.10]} dodecene, and the like.

  In particular, cyclic olefin resins using bicyclo [2,2,1] hept-2-ene (norbornene) and its derivatives as monomers, bicyclo [2,2,1] hept-2-ene (norbornene) and its derivatives, and A copolymer resin with a linear olefin such as ethylene is preferable in that it is excellent in productivity and transparency and has a high glass transition temperature. Thus, the cyclic olefin resin (B) used in the present invention may be a copolymer. Although the kind of copolymerization component is not specifically limited, As a suitable copolymerization component, the unsaturated monomer component shown below is mentioned, for example, Ethylene, propylene, 1-butene, 4-methyl-1- Α-olefins having 3 to 20 carbon atoms such as pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, cyclopentene, cyclohexene , 3-methylcyclohexene, cyclooctene, 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 1,7-octadiene, dicyclopentadiene, 5-ethylidene-2 -Norbornene, 5-vinyl-2-norbornel, tetracyclododecene, 2-methyltetracyclododece , And the like 2-ethyl-tetracyclododecene. Among these, linear olefins such as ethylene and propylene are preferably used from the viewpoint of ease of copolymerization.

  Moreover, in this invention, the glass transition temperature of cyclic olefin resin (B) needs to be 140 degreeC or more. By setting the glass transition temperature of the cyclic olefin resin (B) to 140 ° C. or higher, the cyclic olefin resin (B) can be finely dispersed in the polyester resin (A) which is a matrix resin. Thereby, when it is set as a white film, many fine and flat air bubbles can be formed inside, and the light reflection performance, concealment performance, etc. of a white film can be improved dramatically. By incorporating such a white film into the backlight, the screen luminance can be further increased, and by using it as a solar cell backsheet, the conversion efficiency of the solar cell can be further increased.

  The glass transition temperature of the cyclic olefin resin (B) is preferably 160 ° C. or higher, more preferably 180 ° C. or higher, and still more preferably 190 ° C. or higher. This is because the cyclic olefin resin (B) can be more finely dispersed in the polyester resin (A), which is the matrix resin, within the above range.

  The upper limit of the glass transition temperature of the cyclic olefin resin (B) is not particularly defined, but is preferably 250 ° C. or less, more preferably 230 ° C. or less, and particularly preferably 210 ° C. or less. This is because if the glass transition temperature is too high, the cyclic olefin resin (B) may not be sufficiently melted and fine dispersion may not be promoted when melt-kneading with the matrix resin (A).

  In addition, when the glass transition temperature of the cyclic olefin resin (B) is less than 140 ° C., the cyclic olefin resin (B) is not sufficiently finely dispersed and desired light reflection performance and concealment performance cannot be obtained. Uniform stretching cannot be performed in the stretching process at the time of film formation, and remarkable film thickness unevenness (the ratio of the maximum film thickness to the minimum film thickness is 2 or more) tends to occur.

  The glass transition temperature (hereinafter sometimes abbreviated as “Tg”) is the midpoint glass transition temperature (Tmg) described in JIS K7121-1987, and a specific measurement method will be described later.

  The cyclic olefin resin (B) used in the present invention can be produced by a known liquid phase polymerization method (for example, JP-A-61-271308) or a commercial product (for example, “TOPAS” (Polyplastics Corporation). ), “APEL” (Mitsui Chemicals, Inc.), “ARTON” (JSR Corporation), “ZEONEX”, “ZEONOR” (Nippon Zeon Corporation)) can also be used.

  When using a commercially available product, “TOPAS” manufactured by Polyplastics Co., Ltd., in which an ethylene component is copolymerized with a norbornene component, is preferable because it has a high glass transition temperature.

  In order to set the glass transition temperature of the cyclic olefin resin (B) to 140 ° C. or higher, for example, the cyclic olefin resin (B) is a copolymer of a cyclic olefin (monomer) and a linear olefin such as ethylene. In some cases, the amount of cyclic olefin (monomer) component can be increased and the amount of linear olefin component such as ethylene can be decreased (Endo Go, Toshio Masuda, Tadaomi Nishikubo, “Next Generation Polymer Design”). IPC, June 2000, p.221-261, etc.).

  In particular, when a norbornene component is used as a cyclic olefin (monomer) component and an ethylene component is used as a copolymerization component to form a copolymer, the cyclic olefin (monomer) component is 77% by weight or more, and a linear olefin component such as ethylene The copolymerization amount of is preferably 23% by weight or less. More preferably, the cyclic olefin (monomer) component is 80% by weight or more, the copolymerization amount of a linear olefin component such as ethylene is 20% by weight or less, more preferably the cyclic olefin component (monomer) is 82% by weight or more. Yes, the copolymerization amount of linear olefin components such as ethylene is 18% by weight or less. By setting it as this range, the glass transition temperature of cyclic olefin resin (B) can be made high efficiently. The copolymerization amount of the copolymerization component is not limited to the above range, but the cyclic olefin (monomer) component is not more than 95% by weight or the copolymerization amount of a linear olefin component such as ethylene is not less than 5% by weight. It is preferable. If the cyclic olefin (monomer) component is 95% by weight or more or the copolymerization amount of a linear olefin component such as ethylene is 5% by weight or less, the entire resin may become too brittle. In addition to the above two components, other copolymerizable components can be copolymerized as necessary within the range not impairing the object of the present invention.

  Also, a method for improving the glass transition temperature of the cyclic olefin resin (B) by adding various functional groups to the basic skeleton of the cyclic olefin (monomer) (for example, Toshitaka Otsuki, Kohei Goto, Zen Komiya, “Hydrogen The development and industrialization of a metathesis ring-opening polymer, ”JSR Technical Review, March 2001, Vol. 108, pp. 19-26) can also be adopted.

  In the present invention, it is necessary that the cyclic olefin resin (B) having a glass transition temperature of 140 ° C. or higher is contained in an amount of 10% by weight or more based on the total weight of the white polyester layer (W layer). The content of the cyclic olefin resin (B) is preferably 14% by weight or more, more preferably 18% by weight or more, and further preferably 25% by weight or more.

  By setting the content of the cyclic olefin resin (B) in such a range, a sufficient number of fine flat bubbles can be formed inside the film while reducing the specific gravity of the entire white film. Thereby, the light reflection performance, concealment performance, etc. of a white film can be improved dramatically compared with the conventional white film. By incorporating such a white film into the backlight, the screen luminance can be further increased, and by using it as a solar cell backsheet, the conversion efficiency of the solar cell can be further increased.

  In addition, when the content of the cyclic olefin resin (B) is less than 10% by weight, a sufficient number of fine flat bubbles cannot be formed inside the film, the light reflection performance and the concealment performance are inferior, and the whole film The specific gravity does not decrease. On the other hand, when the content of the cyclic olefin resin (B) exceeds 40% by weight, the film-forming property is extremely deteriorated (the film breaks frequently in the stretching step). In addition, bubbles are easily connected, and it does not contribute much to an efficient increase in light reflection performance and concealment performance.

  In the present invention, it is necessary that the white polyester layer (W layer) contains the thermoplastic polyester elastomer (C). The thermoplastic polyester elastomer (C) is a hard segment and a soft segment block. A polymer is preferred. Here, the hard segment is preferably a thermoplastic polyester (c1), and the soft segment is preferably a poly (alkylene oxide) glycol (c2).

  That is, the thermoplastic polyester elastomer (C) is a polyetherester block copolymer obtained by copolymerizing the thermoplastic polyester (c1) as a hard segment and the poly (alkylene oxide) glycol (c2) as a soft segment. It is preferable that By including the thermoplastic polyester elastomer (C) having such a structure in the white polyester layer (W layer), the cyclic olefin resin (B) can be more finely dispersed in the polyester resin (A).

  Moreover, the thermoplastic polyester (c1) which is a hard segment is obtained by polymerizing the dicarboxylic acid component (c11) and the diol component (c12).

  Therefore, the thermoplastic polyester elastomer (C) is preferably a block copolymer consisting of three components of a dicarboxylic acid component (c11), a diol component (c12), and a poly (alkylene oxide) glycol (c2).

  Here, examples of the dicarboxylic acid component (c11) include terephthalic acid, isophthalic acid, phthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, and diphenyl-4,4′-dicarboxylic acid. , Diphenoxyethanedicarboxylic acid, aromatic dicarboxylic acid typified by sodium 3-sulfoisophthalate, alicyclic dicarboxylic acid typified by 1,4-cyclohexanedicarboxylic acid, succinic acid, oxalic acid, adipic acid, sebacine Examples thereof include at least one dicarboxylic acid component selected from acids, dodecanedioic acid, aliphatic dicarboxylic acids represented by dimer acid, and ester-forming derivatives thereof.

  Examples of the diol component (c12) include aliphatic diols such as ethylene glycol, propanediol, butanediol, neopentylglycol, pentanediol, hexanediol, octanediol, and decanediol, cyclohexanedimethanol, and tricyclodecanedimethanol. And at least one low molecular diol component selected from alicyclic diols such as these and ester-forming derivatives thereof.

  Examples of poly (alkylene oxide) glycol (c2) include poly (ethylene oxide) glycol, poly (1,2-propylene oxide) glycol, poly (1,3-propylene oxide) glycol having an average molecular weight of about 200 to 5,000. At least one of poly (alkylene oxide) glycols such as poly (tetramethylene oxide) glycol, a copolymer of ethylene oxide and propylene oxide, and a copolymer of ethylene oxide and tetrahydrofuran.

  Among them, from the viewpoint of heat resistance and further fine dispersion of the cyclic olefin resin (B) in the polyester resin (A) which is a matrix resin, in the present invention, a hard segment of the thermoplastic polyester elastomer (C) (thermoplastic polyester ( c1)) is preferably a polybutylene terephthalate polyester and / or a polyethylene terephthalate polyester, particularly preferably a polybutylene terephthalate polyester.

  Here, the polybutylene-based polyester is a polyester using terephthalic acid as a dicarboxylic acid component (c12) or a dicarboxylic acid component in which terephthalic acid and isophthalic acid are combined, and 1,4-butanediol as a diol component (c12). However, a part of this dicarboxylic acid component (less than 50 mol%) is replaced with another dicarboxylic acid component or an oxycarboxylic acid component, or a part of the diol component (less than 50 mol%) is a butanediol component. Polyester substituted with a low molecular diol component other than the above may be used.

  The polyethylene-based polyester refers to a polyester using terephthalic acid as a dicarboxylic acid component (c11) or a dicarboxylic acid component in which terephthalic acid and isophthalic acid are combined, and ethylene glycol as a diol component (c12). However, a part of this dicarboxylic acid component (less than 50 mol%) is replaced with another dicarboxylic acid component or an oxycarboxylic acid component, or a part of the diol component (less than 50 mol%) is a low molecular diol other than the ethylene glycol component. It may be a polyester replaced with a component.

  In the present invention, the matrix is such that the soft segment (poly (alkylene oxide) glycol (c2)) of the thermoplastic polyester elastomer (C) is a poly (tetramethylene oxide) glycol and / or a poly (ethylene oxide) glycol. From the viewpoint of further finely dispersing the cyclic olefin resin (B) in the polyester resin (A), which is a resin, poly (tetramethylene oxide) glycol is particularly preferable.

  Here, the poly (ethylene oxide) glycol refers to poly (alkylene oxide) glycol having poly (ethylene oxide) glycol as a main component, but a part (less than 50% by weight) of the polyether portion is ethylene oxide. Polyethers replaced with other dioxy components may be used.

  Poly (tetramethylene oxide) glycol refers to poly (alkylene oxide) glycol having poly (tetramethylene oxide) glycol as the main component, but a part of the polyether portion (less than 50% by weight). May be replaced with a dioxy component other than tetramethylene oxide.

  By adding the thermoplastic polyester elastomer (C), the cyclic olefin resin (B) can be particularly finely dispersed in the polyester resin (A). This is presumed to be due to some interaction between the polyester resin (A), the cyclic olefin resin (B), and the thermoplastic polyester elastomer (C).

  In the present invention, the thermoplastic polyester elastomer (C) must have a melting point of 160 ° C. or higher.

  Here, the melting point (hereinafter sometimes abbreviated as “Tm”) is a melting peak temperature (Tpm) described in JIS K7121-1987, and a specific measurement method will be described later.

  The melting point of the thermoplastic polyester elastomer (C) is preferably 180 ° C. or higher, more preferably 195 ° C. or higher, particularly preferably 215 ° C. or higher. By setting the melting point of the thermoplastic polyester elastomer (C) within such a range, the cyclic olefin resin (B) can be particularly finely dispersed in the polyester resin (A).

  When the melting point of the thermoplastic polyester elastomer (C) is less than 160 ° C., the cyclic olefin resin (B) cannot be finely dispersed, and the light reflection performance and the hiding performance are inferior. Moreover, since the thermoplastic polyester elastomer (C) having a melting point of less than 160 ° C. is inferior in heat resistance, a decomposition product is likely to be generated at the time of melting, and the decomposition product may cause a film defect.

  The upper limit of the melting point of the thermoplastic polyester elastomer (C) is not particularly limited, but is preferably 250 ° C. or lower, more preferably 235 ° C. or lower, and particularly preferably 225 ° C. or lower. If the melting point is too high, the thermoplastic polyester elastomer (C) is not sufficiently melted during melt kneading, and as a result, the cyclic olefin resin (B) is not finely dispersed in the polyester resin (A), which is not preferable. is there.

  In order to set the melting point of the thermoplastic polyester elastomer (C) to 160 ° C. or higher, for example, the content of the hard segment is increased while the content of the soft segment is decreased.

  The thermoplastic polyester elastomer can be obtained by polymerization using the above components, and commercially available products (for example, “Hytrel” (Toray DuPont Co., Ltd.), “Perprene” (Toyobo Co., Ltd.), etc.) can be used.

  When using a commercial product, it is a copolymer of a hard segment and a soft segment, and the hard segment is a polybutylene terephthalate polyester, the soft segment is a poly (tetramethylene oxide) glycol, and has a high melting point. It is preferable to use “Hytrel” manufactured by DuPont.

  In the present invention, in the white polyester layer (W layer), the thermoplastic polyester elastomer (C) having a melting point of 160 ° C. or higher is a cyclic olefin having a glass transition temperature of 140 ° C. or higher contained in the white polyester layer (W layer). It is necessary to contain 20.5 parts by weight or more with respect to 100 parts by weight of the resin (B). Preferably it is 25.5 weight part or more, More preferably, it is 29.5 weight part or more, Most preferably, it is 44.5 weight part or more.

  By setting the content of the thermoplastic polyester elastomer (C) in such a range, the cyclic olefin resin (B) can be particularly finely dispersed in the polyester resin (A).

  On the other hand, even if the thermoplastic polyester elastomer (C) is added to polymethylpentene or polypropylene conventionally used as an incompatible resin, the same fine dispersion effect is not exhibited. Only when the cyclic olefin resin (B) is used as the incompatible resin, the reason why such a specific fine dispersion effect is manifested is being elucidated, but is unclear.

  In addition, when the content of the thermoplastic polyester elastomer (C) is less than 20.5 parts by weight, the fine dispersion of the cyclic olefin resin (B) cannot be sufficiently achieved.

  The upper limit of the content of the thermoplastic polyester elastomer (C) is not particularly limited, but is preferably 100 parts by weight or less, more preferably 80 parts by weight or less, and still more preferably 60 parts by weight or less. It is preferable from the viewpoint of the productivity of the white film. When the content of the thermoplastic polyester elastomer (C) becomes too large, tearing frequently occurs in film formation, and productivity may be poor.

  Next, the effects of the present invention will be summarized. That is, by using the white film having the configuration of the present invention, the cyclic olefin resin (B), which is an incompatible resin, can be dispersed extremely finely in the polyester resin (A), and white by stretching or the like. Even if air bubbles are generated inside the polyester layer (W layer), the connection between the air bubbles can be suppressed. Thereby, the gas-solid interface number density per film thickness can be dramatically increased, and the film can be efficiently reduced in specific gravity. In addition, the increase in the number density of the gas-solid interface greatly contributes to the improvement of light reflection performance and hiding performance. Therefore, by incorporating the white film of the present invention into the backlight (surface light source), it has high luminance characteristics and excellent screen. Brightness uniformity and excellent screen sharpness can be achieved. Furthermore, since the surface light source using the film of the present invention has high luminance characteristics, the output of the light source can be suppressed and the power consumption can be reduced. Moreover, the conversion efficiency of a solar cell can be made higher by using the film of this invention as a solar cell backsheet. In addition, since the white film of the present invention is remarkably excellent in light reflection performance and hiding performance, it can be made thin while maintaining high light reflection performance and light hiding performance.

  The specific gravity of the white film of the present invention is preferably less than 0.9. Preferably it is 0.8 or less, More preferably, it is 0.7 or less, Most preferably, it is 0.6 or less. This is because the white film of the present invention is mainly used as a solar cell back sheet or a reflective member for a surface light source, and is preferably as light as possible. Therefore, the lower limit is not particularly defined, but is preferably 0.3 or more from the viewpoint of strength. To make the specific gravity less than 0.9, the white polyester layer (W layer) contains 10% by weight or more of the cyclic olefin resin (B) having a glass transition temperature of 140 ° C. or higher with respect to the white polyester layer (W layer). And 20.5 parts by weight or more of the thermoplastic polyester elastomer (C) having a melting point of 160 ° C. or higher with respect to 100 parts by weight of the cyclic olefin resin (B). Further, in order to further reduce the specific gravity, as shown in the examples described later, the content of the cyclic olefin resin (B) and the content of the thermoplastic polyester elastomer (C) are further increased, or the cyclic olefin resin ( This can be achieved by increasing the glass transition temperature of B) and the melting point of the thermoplastic polyester elastomer (C).

  In the white film of the present invention, other layers may be laminated on one side or both sides of the white polyester layer (W layer).

  Moreover, in the white film of this invention, it is preferable that the gas-solid interface number density of the film thickness direction of a white polyester layer (W layer) is 1.55 / micrometer or more. The light beam incident on the white film is reflected at the interface between the resin (solid phase) and the bubbles (gas phase) inside the film, and the air-solid interface number density in the film thickness direction of the white polyester layer (W layer) is 1 By setting the thickness to .55 / μm or more, the reflection performance and concealment performance can be dramatically improved.

Here, the gas-solid interface number density in the film thickness direction in the white polyester layer (W layer) is determined by the following procedures (1) to (10).
(1) Using a microtome, cut perpendicular to the film surface direction without crushing the film cross section in the thickness direction.
(2) Next, the cut section is observed using an electron microscope, and an image obtained by magnifying and observing the white polyester layer (W layer) 5000 times is obtained. At this time, the thickness direction of the film and the vertical direction of the image are made to coincide. In addition, when the entire thickness direction of the polyester layer (W layer) does not fit in one image, a divided image is obtained in the film thickness direction and bonded later, and the entire thickness direction of the white polyester layer (W layer) is Assume that a stored image is obtained.

Here, the entire thickness direction of the polyester layer (W layer) does not fit in one image means that the boundary (X) with the other layer laminated on one side of the polyester layer (W layer) and the polyester layer This means that the boundary (Y) with another layer laminated on the other surface of (W layer) does not fit in one image. When no other layer is laminated on one side or both sides of the polyester layer (W layer), the boundary (X) or the boundary (Y) indicates the boundary between the polyester layer (W layer) and the outside world. And
(3) In the image obtained in (2), a straight line is drawn perpendicularly to the film surface direction from one point on the boundary (X) line (which is determined at random, which is defined as the XA point). Y) A point that intersects the line and a point YA. A straight line connecting the XA point and the YA point is defined as a Z straight line. Regarding the gas-solid interface existing on the Z line, the gas-solid interface closest to the XA point is defined as a gas-solid interface 1. The gas-solid interface refers to a gas-solid interface existing inside the white polyester layer (W layer), whether it is an interface from the gas phase to the solid phase or an interface from the solid phase to the gas phase. Good. However, the gas-solid interface between the inside of the film and the outside of the film (that is, the film surface) is not included in the gas-solid interface to be measured in this procedure.
(4) The gas-solid interface 2 is the gas-solid interface 2 that is on the YA point side of the gas-solid interface 1 on the Z straight line, has an inter-interface distance of 200 nm or more, and has the smallest inter-interface distance. Here, the inter-interface distance is a distance between the gas-solid interface k and the gas-solid interface k + 1 on the Z straight line (that is, in this case, the distance between the gas-solid interface 1 and the gas-solid interface 2 on the Z straight line). Is). Further, only gas-solid interfaces having an inter-interface distance of 200 nm or more are targeted for measurement. When the inter-interface distance is less than 200 nm, there is a high probability that a light reflection phenomenon based on geometric optics does not occur at the interface, and white This is because it does not contribute to the light reflection performance of the film.
(5) As in (4), the gas-solid interface is the gas-solid interface on the Z straight line which is on the YA point side of the gas-solid interface 2 and the inter-interface distance is 200 nm or more and the inter-interface distance is the smallest. 3.
(6) Similar work (that is, the gas-solid interface m + 1 on the Z line is located on the YA point side of the gas-solid interface m, the inter-interface distance is 200 nm or more, and the inter-interface distance is the smallest). Is repeated until there is no gas-solid interface on the YA point side.
(7) The gas-solid interface 1 to the gas-solid interface n are obtained by the above procedure, and the numerical value of n is used as the number N of gas-solid interfaces in the present measurement. In this measurement, when there is only one gas-solid interface, the number of gas-solid interfaces is 1, and when there is no gas-solid interface in the polyester layer (W layer), the number of gas-solid interfaces is 0.
(8) The length of the Z straight line is measured, and this is defined as the thickness P (μm) of the white polyester layer (W layer).
(9) A value (N / P) obtained by dividing the number N of the gas-solid interface by the thickness P of the white polyester layer (W layer) is defined as a gas-solid interface number density Q (/ μm).
(10) Perform the same operations as (1) to (9) 100 times by randomly changing the film cutting location, and calculate the arithmetic average value of the gas-solid interface number density Q obtained in each case as the final white polyester The gas-solid interface number density in the film thickness direction in the layer (W layer) is used.

  The gas-solid interface number density of the white polyester layer (W layer) is preferably 1.8 / μm or more, more preferably 2.2 / μm or more, and particularly preferably 2.6 / μm or more. By setting the gas-solid interface number density of the white polyester layer (W layer) within such a range, excellent reflection performance and concealment performance can be imparted as a reflective member for a surface light source and a back sheet for a solar cell. In order to set the gas-solid interface number density of the white polyester layer (W layer) to 1.55 / μm or more, in the white polyester layer (W layer), a cyclic olefin resin (B) having a glass transition temperature of 140 ° C. or more is used. Achieved by containing 10 to 40% by weight of thermoplastic polyester elastomer (C) having a melting point of 160 ° C. or more and 24.5 parts by weight or more with respect to 100 parts by weight of the cyclic olefin resin (B). can do. In order to further increase the gas-solid interface number density of the white polyester layer (W layer), the content of the cyclic olefin resin (B) in the white polyester layer (W layer) or This can be achieved by further increasing the content of the thermoplastic polyester elastomer (C), or by increasing the glass transition temperature of the cyclic olefin resin (B) and the melting point of the thermoplastic polyester elastomer (C).

  In addition, although the upper limit of the gas-solid interface number density of a white polyester layer (W layer) is not specifically provided, it is preferable not to exceed 5.00 / micrometer. If it exceeds 5.00 / μm, the bubbles become too fine, and the light reflection phenomenon according to geometric optics does not occur at the gas-solid interface, and sufficient reflection performance may not be exhibited as a whole film.

  The white film of the present invention preferably has a relative reflectance of 100.4% or more with respect to the aluminum oxide white plate. Here, a part number 210-0740 manufactured by Hitachi Instrument Service Co., Ltd. is used for the aluminum oxide white plate. A detailed method for measuring the relative reflectance with respect to the aluminum oxide white plate will be described later. Note that the relative reflectivity of the film having higher reflection performance than that of the white plate of aluminum oxide may exceed 100%.

  The relative reflectance with respect to the aluminum oxide white plate is more preferably 100.8% or more, further preferably 101.3%, particularly preferably 101.8% or more. By setting the relative reflectance with respect to the aluminum oxide white plate in such a range, when the white film of the present invention is used as the reflecting member for a surface light source, particularly high luminance characteristics can be exhibited. Moreover, the conversion efficiency of a solar cell can be made higher by using the white film of this invention as a solar cell backsheet. In addition, since it is preferable that reflection performance is higher, an upper limit is not specifically limited.

  The transmittance of the white film of the present invention is preferably 4.2% or less. More preferably, it is 3.5% or less, More preferably, it is 3.0% or less, Most preferably, it is 2.7% or less. By setting the transmittance in such a range, a high concealment performance can be exhibited when used as a reflection member for a surface light source, and “set-off” can be reduced. In addition, since it is preferable that the transmittance | permeability is lower, a minimum is not specifically limited, However 0.0% becomes a minimum on measurement.

  The optical density of the white film of the present invention is preferably 1.38 or more. More preferably 1.43 or more, further preferably 1.52 or more, and particularly preferably 1.57 or more. By setting the optical density within such a range, high concealment performance can be exhibited when used as a reflective member for a surface light source, and “set-off” can be reduced. In addition, since it is preferable that the optical density is higher, the upper limit is not particularly limited. However, if it exceeds 3.0, the concealability is almost saturated, so 3.0 can be set as the upper limit.

  In the present invention, the thickness of the white polyester layer (W layer) and the total thickness of the white film are not particularly limited, and a thickness at which desired light reflection performance, concealment performance, and luminance characteristics can be appropriately selected may be selected. In general, the thickness is preferably 40 to 600 μm. More preferably, it is 75-400 micrometers, Most preferably, it is 150-300 micrometers. By setting it as this range, it can be used conveniently as a reflective member for surface light sources or a back sheet for solar cells. If the total thickness is less than 40 μm, the strength may be inferior or sufficient light reflection performance / hiding performance may not be exhibited. On the other hand, if the total thickness exceeds 600 μm, the entire surface light source or the entire solar cell may become too thick when incorporated in a surface light source or a solar cell.

  The white film of the present invention may contain additives such as a lubricant, a fluorescent whitening agent, and an ultraviolet absorber as long as the effects of the present invention are not lost.

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

  In order to form a white polyester layer (W layer), using a film forming apparatus having an extruder (main extruder), if necessary, a polyester resin (A) chip and a glass transition temperature that are sufficiently vacuum-dried. Is a mixture of a cyclic olefin resin (B) having a melting point of 140 ° C. or higher and a thermoplastic polyester elastomer (C) having a melting point of 160 ° C. or higher is supplied to a heated extruder. For the addition of the cyclic olefin resin (B) and the thermoplastic polyester elastomer (C), a master chip prepared by melt-kneading and blending uniformly in advance may be used, or it may be supplied directly to a kneading extruder. May be.

  When the white film of the present invention is a laminated film, a thermoplastic film (PET) that is sufficiently vacuum-dried as necessary using a composite film forming apparatus having a sub-extruder in addition to the main extruder. A polyester resin, etc.) and, if necessary, inorganic particles and various additives such as a fluorescent brightening agent and an ultraviolet absorber are mixed and supplied to a heated sub-extruder for coextrusion and lamination. .

  Further, in the case of melt extrusion, it is preferable to obtain a molten sheet (in the case of a laminated film, a molten laminated sheet) by filtering through a filter having a mesh of 40 μm or less and introducing it into a T die die.

  The 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 unoriented (unstretched) film. The unoriented film is guided to a roll group 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 roll group having a temperature of 20 to 50 ° C. Cooling.

  Subsequently, the film is guided to a tenter while gripping both ends with a clip, and in an atmosphere heated to a temperature of 90 to 150 ° C., 3 to 4 times in a direction perpendicular to the longitudinal direction (lateral direction, ie, film width direction). A biaxially oriented (biaxially stretched) film can be obtained.

  The stretching ratio is preferably 3 to 4 times in each of the longitudinal direction and the width direction, and the area ratio (the ratio obtained by multiplying the longitudinal direction stretching ratio by the width direction stretching ratio) is preferably 9 to 15 times. If the area magnification is less than 9 times, the resulting biaxially oriented (biaxially stretched) film has insufficient light reflection performance, concealment performance, and film strength. Conversely, if the area magnification exceeds 15 times, the film will be broken during stretching. It tends to occur easily.

  If necessary, in order to complete the crystal orientation of the obtained biaxially oriented (biaxially stretched) film and to impart planarity and dimensional stability, it is subsequently changed to 1 to 150-240 ° C. in the tenter. Perform heat treatment for 30 seconds, uniformly cool, then cool to room temperature, and then, if necessary, perform corona discharge treatment to further improve the adhesion to other materials, and take up, A white film can be obtained. During the heat treatment step, a relaxation treatment of 0.1 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. Therefore, the white film of the present invention is preferably heat treated at a high temperature (180 ° C. or higher) in the film forming process. This is because the white film of the present invention is desired to have a certain thermal dimensional stability.

  In addition, biaxial stretching may be either sequential stretching or simultaneous biaxial stretching. However, when the simultaneous biaxial stretching method is used, film defects in the manufacturing process can be prevented, or transfer defects caused by sticking to a heating roll. Is unlikely to occur. Further, after biaxial stretching, it may be re-stretched in either the longitudinal direction or the width direction.

  Moreover, you may add aluminum, silver, etc. to the white film of this invention by methods, such as metal vapor deposition and bonding, on the film surface for the objectives, such as electromagnetic wave shielding property and bending workability provision.

  The white film of the present invention is preferably used as a reflecting member incorporated in a surface light source for light reflection. Specifically, it is preferably used for an edge light reflector for a liquid crystal screen, a reflector for a surface light source of a direct type light, a lamp reflector around a cold cathode ray tube, and the like. Moreover, it can use suitably also as a solar cell backsheet.

(Measuring method)
1. Glass transition temperature of cyclic olefin resin (B) (JIS 7121-1999, JIS 7122-1999)
The glass transition temperature of the cyclic olefin resin (B) was measured using a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. according to JIS K7122 (1999). For data analysis, a disk session “SSC / 5200” was used. The measurement is performed in a nitrogen atmosphere.

  First, 5 mg of a sample resin is weighed and packed in a sample pan, and the sample pan is heated from 20 ° C. to 300 ° C. at a heating rate of 10 ° C./min, held at 300 ° C. for 5 minutes, and then 20 It was rapidly cooled to below ℃. The differential scanning calorimetry chart (absorption / exotherm curve) obtained at this time is defined as a 1strun-DSC curve.

  Subsequently, the temperature was raised again from 20 ° C. to 300 ° C. at a rate of 10 ° C./min. The differential scanning calorimetry chart (absorption curve) obtained at this time is defined as a 2ndrun-DSC curve.

  The glass transition temperature of the cyclic olefin resin (B) is determined from this 2ndrun chart.

2. Melting point of thermoplastic polyester elastomer (C) (JIS 7121-1999, JIS 7122-1999)
The melting point of the thermoplastic polyester elastomer (C) was measured using a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. according to JIS K7122 (1999). For data analysis, a disk session “SSC / 5200” was used. The measurement is performed in a nitrogen atmosphere.

  First, 5 mg of a sample resin is weighed and packed in a sample pan, and the sample pan is heated from 20 ° C. to 300 ° C. at a heating rate of 10 ° C./min, held at 300 ° C. for 5 minutes, and then 20 It was rapidly cooled to below ℃. The differential scanning calorimetry chart (absorption / exotherm curve) obtained at this time is defined as a 1strun-DSC curve.

  Subsequently, the temperature was raised again from 20 ° C. to 300 ° C. at a rate of 10 ° C./min. The differential scanning calorimetry chart (absorption curve) obtained at this time is defined as a 2ndrun-DSC curve.

  The melting point of the thermoplastic polyester elastomer (C) is determined from this 2ndrun-DSC curve.

3. Using a gas-solid interface number density microtome of the white polyester layer (W layer), the white film is cut perpendicularly to the film surface direction without crushing the cross section in the thickness direction. Next, after depositing platinum-palladium on the cross section, the cross section was observed at a magnification of 5000 times using a field emission scanning electron microscope “JSM-6700F” manufactured by JEOL Ltd. to obtain an image. Based on the obtained image, the gas-solid interface number density was calculated according to the method described above.

4). A white film relative reflectance spectrophotometer U-3310 (manufactured by Hitachi, Ltd.) was fitted with a φ60 integrating sphere (part number 130-0632 (manufactured by Hitachi, Ltd.)) and a 10 ° inclined spacer, and a wavelength of 560 nm. The light reflectance of the white film was determined.

  Part number 210-0740 manufactured by Hitachi Instrument Service Co., Ltd. was used as the aluminum oxide white plate, and the white plate was used as a standard white plate and a sub white plate.

  In addition, the light reflectance was calculated | required about both surfaces of the white film, and the higher numerical value was made into the reflectance of the said white film.

5. The total light transmittance of the white film was measured using a transmittance haze meter NDH-5000 (manufactured by Nippon Denshoku Industries Co., Ltd.). In addition, the transmittance | permeability calculated | required about both surfaces of the white film, and made the lower numerical value the transmittance | permeability of the said white film.

6). Optical density of white film Macbeth transmission / reflection densitometer TR-927 (Sakata Inx Corporation) was used to measure the transmission density of the white film. The spectral sensitivity characteristic was orthomatic. At the time of measurement, the color display of the filter position was “white”. In addition, before measuring the sample, zero point alignment and numerical value confirmation of the standard plate shall be performed in accordance with the description in the manual attached to the equipment.

7. Five square samples measuring 5 cm in length and 5 cm in width are cut out from the white film specific gravity white film and measured once each using an electronic hydrometer SD-120L (Mirage Trading Co., Ltd.) based on JIS K7112-1980. did. The arithmetic average of the obtained measured values of a total of 5 points was calculated | required, and it was set as the specific gravity of the said white film.

8). Area light source brightness (backlight brightness)
(1) 20-inch size direct backlight (number of cold cathode tubes: 16, cold cathode tube diameter: 3 mm, distance between cold cathode tubes: 2.5 cm, distance between milky white plate and cold cathode tube, 1.5 cm, reflector) And a cold cathode tube at a distance of 5 mm, a white film is installed as a reflector, RM401 (manufactured by Sumitomo Chemical Co., Ltd.) as a milky white plate, and a light diffusion sheet “Light Up” (registered trademark) GM3 (Kimoto Co., Ltd.), prism sheet BEFIII (manufactured by 3M), DBEF-400 (manufactured by 3M).

Next, a cold cathode tube was turned on by applying a voltage of 12 V, and after 50 minutes, using a color luminance meter BM-7 / FAST (manufactured by Topcon Corporation), a viewing angle of 1 °, between the backlight and the luminance meter. The brightness at the center of the backlight screen was measured at a distance of 40 cm.
(2) Thereafter, the application of voltage is stopped, the white film as the reflector is once taken out with the cold cathode tube turned off, and then the same white film is set as the reflector again. The same operation as (1) The brightness was measured.
(3) In accordance with the above method, the luminance measurement was performed 5 times for the same white film, and the arithmetic average value of the five measured values was used as the luminance of the surface light source using the white film.

  In addition, even if the surface light source luminance is a difference of 0.3%, the difference is very large. The surface light source luminance depends also on the output of the cold cathode tube as the light source. Therefore, a surface light source having high luminance can reduce the output of the light source accordingly, and can contribute to lower power of the surface light source. Because.

9. 7. Uniformity of screen brightness In the surface light source luminance measurement, after the fifth luminance measurement is completed, the state where the voltage is applied is continued, and the backlight in the lighting state is observed from the front direction, and the back of the framework (chassis) on the back side is clearly seen. What was observable was marked with x, what was slightly observed was marked with Δ, what was slightly observed was marked with ○, and what was not observed was marked with ◎. Practically, even Δ is acceptable, but ○ or ◎ is more preferable.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, this invention is not limited to this.

(material)
A. Polyester resin (A)
・ PET
Using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component, add it to the polyester pellets to obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, conduct a polycondensation reaction, A polyethylene terephthalate (PET) pellet at 255 ° C. was obtained.

B. Cyclic olefin resin (B)
・ Cyclic olefin copolymer resin “TOPAS”
“TOPAS 5013”, “TOPAS 6013”, “TOPAS 6015”, “TOPAS 6017”, “TOPAS 6018T2”, and “TOPAS 6018T5” (all manufactured by Nippon Polyplastics) were used. As shown in Chemical Formula 1, the resin is a cyclic olefin copolymer resin that is polymerized from a norbornene component that is a cyclic olefin (monomer) component and an ethylene component that is a copolymer component. Table 1 shows the copolymerization weight ratio and glass transition temperature of each component.

  As described in Table 1, the glass transition temperatures of “TOPAS 6013”, “TOPAS 6015”, “TOPAS 6017”, “TOPAS 6018T2”, and “TOPAS 6018T5” are 140 ° C. or higher. It corresponds to the cyclic olefin resin (B). On the other hand, since the glass transition temperature of “TOPAS 5013” is 136 ° C., it does not correspond to the cyclic olefin resin (B) having a glass transition temperature of 140 ° C. or higher.

・ Cyclic olefin copolymer resin "APEL"
“APEL APL6015T” (Mitsui Chemicals) was used. The resin is a cyclic olefin copolymer resin polymerized from a cyclic olefin (monomer) component having norbornene as a basic skeleton and an ethylene component as a copolymer component. The component ratio of each component is 79% by weight of the cyclic olefin component and 21% by weight of the ethylene component, and the glass transition temperature is 155 ° C. Therefore, this resin corresponds to cyclic olefin resin (B) whose glass transition temperature is 140 degreeC or more.

・ Cyclic olefin resin “ZEONOR”
“ZEONOR 1600R” (manufactured by Nippon Zeon) was used. The resin tetracyclo ^{[4,4,0,1 2.5, 1 7.10]} As shown in Chemical Formula 2 is dodecene cyclic olefin resin polymerized from cyclic olefin (monomer) having a basic skeleton. Since the glass transition temperature of the resin is 163 ° C., the resin corresponds to the cyclic olefin resin (B) having a glass transition temperature of 140 ° C. or higher.

C. Incompatible component ・ PP (polypropylene)
“F-704NP” (manufactured by Prime Polymer) was used. The resin is a linear olefin resin having a melting point of 170 ° C. The glass transition temperature is 20 ° C. or lower. Therefore, the resin does not correspond to the cyclic olefin (B) having a glass transition temperature of 140 ° C. or higher.

・ PMP (polymethylpentene)
“TPX DX820” (manufactured by Mitsui Chemicals) was used. The resin is a linear olefin resin having a melting point of 235 ° C. The glass transition temperature is 25 ° C. Therefore, the resin does not correspond to the cyclic olefin (B) having a glass transition temperature of 140 ° C. or higher.

-Barium sulfate having an average particle diameter (diameter) of 0.6 μm was used. The fine particles having a particle size of 0.3 μm or less and the coarse particles having a particle size of 1.0 μm or more were removed through a classification step.

D. Thermoplastic polyester elastomer (C)
“Hytrel G3548L”, “Hytrel 3046”, “Hytrel 4047”, “Hytrel 4767”, “Hytrel 7247”, and “Hytrel 2751” (all manufactured by Toray DuPont) were used.

  The resin is a block copolymer of a hard segment and a soft segment, where the hard segment is a polybutylene terephthalate-based polyester and the soft segment is a poly (tetramethylene oxide) -based glycol. The melting point of the resin is shown in Table 2. Except for “Hytrel G3548L”, all correspond to the thermoplastic polyester elastomer (C) having a melting point of 160 ° C. or higher. On the other hand, since “Hytrel G3548L” has a melting point of 154 ° C., it does not correspond to a thermoplastic polyester elastomer (C) of 160 ° C. or higher.

(Examples 1 to 55)
The raw material mixture shown in Table 3 was vacuum dried at a temperature of 130 ° C. for 8 hours, then supplied to an extruder, melt-extruded at a temperature of 280 ° C., filtered through a 30 μm cut filter, and then introduced into a T die die. .

  Next, from the inside of the T die die, it is extruded into a sheet shape to form a molten single layer sheet, and the molten single layer sheet is closely cooled and solidified by electrostatic application on a drum maintained at a surface temperature of 20 ° C. Stretched) A single layer film was obtained. Subsequently, the unoriented single layer film was preheated with a roll group heated to a temperature of 85 ° C., and then stretched 3.3 times in the longitudinal direction (longitudinal direction) using a heating roll having a temperature of 90 ° C. It cooled with the roll group of the temperature of 0 degreeC, and obtained the uniaxially oriented (uniaxial stretching) film.

  While holding both ends of the obtained uniaxially oriented film with clips, it is guided to a preheating zone at a temperature of 95 ° C. in the tenter, and then continuously in the heating zone at a temperature of 105 ° C. in the width direction (lateral direction) perpendicular to the longitudinal direction. The film was stretched 3.2 times. Subsequently, after heat treatment at 180 ° C. for 20 seconds in the heat treatment zone in the tenter, and further 4% relaxation treatment in the width direction at a temperature of 180 ° C., further 1% in the width direction at a temperature of 140 ° C. The relaxation treatment was performed. Then, after gradually cooling uniformly, it was wound up to obtain a biaxially oriented white polyester film having a thickness of 188 μm. This white polyester film contains many fine bubbles inside and corresponds to a white polyester layer (W layer). Table 4 shows the characteristics of the obtained white film. Thus, the white film of the present invention was excellent in light reflection performance, concealment performance, lightness (low specific gravity), high luminance characteristics, and luminance uniformity.

(Comparative Examples 1, 2, 4-14, 17)
A film was formed in the same manner as in Example 1 using the raw materials shown in Table 3. This white polyester film had bubbles inside, but its characteristics were inferior as shown in Table 4.

(Comparative Examples 3, 15, 16, 18, 19)
Film formation was attempted using the raw materials shown in Table 3 in the same manner as in Example 1. However, film breakage occurred frequently, and a white film after stretching could not be collected.

From the above examples and comparative examples, the following items can be mentioned as the effects of the present invention.
(1) Compared with linear olefins (PP, PMP) conventionally used as incompatible components, the incompatible components can be differentially oxidized in polyester, and as a result, gas can be efficiently absorbed. The solid interface number density can be increased. In addition, light reflection performance and concealment performance are greatly improved, and surface light source luminance and luminance uniformity are also excellent. Further, even if the incompatible resin (B) is contained in a large amount, film breakage does not occur and the film forming property is excellent.
(2) Compared to the case where inorganic particles (barium sulfate) are used as the incompatible component, the gas-solid interface number density can be increased. In addition, light reflection performance and concealment performance are greatly improved, and surface light source luminance and luminance uniformity are also excellent. Furthermore, it has a lower specific gravity.

Claims (4)

A film containing a polyester resin (A) and a cyclic olefin resin (B) and having a white polyester layer (W layer) having bubbles inside, wherein the glass transition temperature of the cyclic olefin resin (B) is 140 ° C. or higher. And the cyclic olefin resin (B) is contained in an amount of 10 wt% to 40 wt% with respect to the white polyester layer (W layer), and the white polyester layer (W layer) has a temperature of 160 ° C. or higher. A white polyester film for a reflecting member , wherein a thermoplastic polyester elastomer (C) having a melting point is contained in an amount of 20.5 parts by weight or more with respect to 100 parts by weight of the cyclic olefin resin (B). The white polyester film for a reflective member according to claim 1, wherein the thermoplastic polyester elastomer (C) is a block copolymer of a hard segment and a soft segment. The white polyester film for a reflecting member according to claim 2, wherein the hard segment is a polybutylene terephthalate polyester and / or a polyethylene terephthalate polyester. The white polyester film for a reflecting member according to claim 2 or 3, wherein the soft segment is a poly (ethylene oxide) glycol and / or a poly (tetramethylene oxide) glycol.