TW201815588A - White polyester film for molding and white resin molded body - Google Patents

Abstract

To provide a white resin molded body that is suitable for a direct-under type backlight unit, or a white polyester film that is suitably processed to be the white resin molded body. This white polyester film for molding is characterized by comprising at least three layers, wherein the glass transition temperature (Tg) of the surface layer is 80-120 DEG C, and the specific gravity of the film is 0.8-1.1.

Description

   White polyester film for molding and white resin molded body using the same   

The present invention relates to a white polyester film for molding and a white resin molded body suitable for use as a direct type backlight unit and the like.

In recent years, as display devices such as computers, televisions, smart phones, tablet computers, and mobile phones, a display using a liquid crystal has been mostly used. Since these liquid crystal displays are not themselves light-emitting bodies, a surface light source called a backlight is provided from the back side to irradiate light, thereby enabling display. In addition, the backlight is not only for irradiating light, but in response to the requirement that the entire screen must be uniformly illuminated, a structure called a side-light type or a direct-type surface light source is adopted. Among them, hope for thin. The thin-type liquid crystal displays used in miniaturized notebook computers, monitors, and tablet computers are suitable for use with edge-lit backlights, that is, types that illuminate the screen from the side. On the other hand, for large screen applications such as liquid crystal televisions, a backlight of a direct type, that is, a type that irradiates light to the screen from the back is suitable.

High-light-reflecting properties are required for lamp reflectors and reflectors used in such surface light sources for liquid crystal displays (hereinafter, collectively referred to as reflective films and surface light-reflecting members, etc.). So far, films with added white pigments have been used alone. 2. A film containing fine bubbles inside, or a film that is bonded to a metal plate, a plastic plate, etc. In particular, a film containing fine air bubbles inside has a certain effect on brightness enhancement effect and uniformity of screen brightness, and is therefore widely used (Patent Documents 1 and 2).

A large TV with a direct-type backlight is equipped with a function called "local dimming". It is a technology that distinguishes the liquid crystal backlight in detail, and according to the brightness of the displayed image, assigns the backlight to the brightness according to the classification, so as to further improve the contrast and display a clear image. As a technical problem of "local dimming", there is a problem that when the difference in brightness between adjacent LEDs is large, light leaks to a region next to each other, and the effect decreases. In addition, the direct type backlight may have unevenness in that only a part of the LED is brightened due to the structure.

As a method for solving these problems, a light reflecting plate (Patent Document 3) having a concave light reflecting surface can be used. However, if a foamed sheet is subjected to a load during molding, voids tend to collapse easily. Topic.

Prior art literature Patent literature

Patent Document 1 JP 2003-160682

Patent Document 2 Japanese Patent Publication No. 8-16175

Patent Document 3 Japanese Patent Application Publication No. 2012-022089

An object of the present invention is to solve the above-mentioned problems, and to provide a white polyester film and a white resin molded body suitable for forming a direct type backlight unit.

The present inventors have carefully studied such a problem, and have the following structure.

(1) A white polyester film for molding, comprising at least three layers, a glass transition temperature (Tg) of a surface layer of 80 ° C. to 120 ° C., and a specific gravity of the film of 0.8 to 1.1.

(2) The white polyester film for molding according to (1), wherein the glass transition temperature (Tg) of the surface layer + 60 ° C and the storage elastic modulus (E ') are 10 MPa to 300 MPa.

(3) The white polyester film for molding according to (1) or (2), characterized in that it comprises at least three layers, and the core layer has bubbles containing a hollow nucleating agent.

(4) The white polyester film for molding according to any one of (1) to (3), which has a reflectance of 98% or more and a transmittance of less than 3%.

(5) A white resin molded body formed by molding the white polyester film for molding according to any one of (1) to (4).

(6) The white resin molded body according to (5), which is used for an LED lighting unit.

(7) The white resin molded body according to (5), which is used for a direct type LED backlight unit.

According to the present invention, it is possible to provide a white polyester film excellent in moldability and shape retention after molding, and by forming the white polyester film, it is possible to provide a white resin molded body suitable for a direct-type backlight unit with less uneven brightness. .

FIG. 1 is a diagram showing the boundary between elastic deformation and plastic deformation from the obtained S-S curve.

A form for implementing the invention

The present inventors conducted a careful study on such a problem, and as a result, found that it is important not only to have a high reflectance and formability but also a high shape retention property in order to obtain a reflecting plate having a shape, and to complete the present invention . When a shaped reflector is used in order to improve the contrast ratio of the direct type backlight unit and eliminate unevenness, its shape is optimized optically by careful calculation. The reflecting plate is assembled to the directly-type backlight unit, and is then exposed to the heat from the circuit and the LED. At this time, if the reflecting plate cannot maintain the shape, the contrast ratio is improved or the effect of eliminating unevenness is reduced.

According to the results of careful research by the present inventors, if a white polyester film for molding is used that is characterized by including at least three layers, the glass transition temperature (Tg) of the surface layer is 80 ° C or higher and less than 120 ° C, and the specific gravity of the film is 0.8 to 1.1. In this case, a white polyester film for molding that is excellent in moldability and shape retention can be supplied.

The details of the present invention are described below.

    [Thin film structure]    

The white polyester film for molding of the present invention must include at least three layers, and the glass transition temperature (Tg) of the surface layer is 80 ° C or higher and less than 120 ° C.

The glass transition temperature refers to the middle of the stepped endothermic peak with a change in specific heat capacity when the polymer is measured in a differential scanning thermal card meter (DSC) under a nitrogen environment at a temperature rise rate of 10 ° C / min. Point temperature. When the glass transition temperature of the surface layer is lower than 80 ° C., the shape retention property after forming the film may be reduced, which is not preferable. Moreover, when it is higher than 120 degreeC, workability may worsen and it may become unpreferable. The glass transition temperature is more preferably 85 ° C or more and less than 115 ° C, and even more preferably 90 ° C or more and less than 110 ° C.

The laminated form of the white polyester film for molding of the present invention is not particularly limited as long as it is three or more layers. For example, when one layer is represented by one letter, X / Y / X, X / Y / Z and other laminated morphologies. When the two surface layers are layers containing different raw materials, the glass transition temperature (Tg) of either surface layer must also be 80 ° C or higher and less than 120 ° C.

The method of setting the glass transition temperature (Tg) of the surface layer within the above range is not particularly limited, but examples thereof include a resin having a glass transition temperature of 80 ° C or higher in the surface layer. The resin having a glass transition temperature of 80 ° C. or higher is preferably a polyester resin, and more preferably an aromatic polyester resin.

The white polyester film for molding of the present invention must contain a polyester resin as a main component. If the polyester resin constituting the white polyester film for molding is at least 50% by weight or more, it can be said to be the main component. Regarding polyester resins, preferred aspects are described below. The polyester resin refers to a polymer having an ester bond in the main chain, but the polyester resin used in the present invention is preferably a polyester resin having a structure in which a dicarboxylic acid and a diol are polycondensed. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and dicarboxylic acid in terms of aromatic dicarboxylic acid. Aromatic dicarboxylic acids such as phenylphosphonium dicarboxylic acid, diphenoxyethanedicarboxylic acid, sodium 5-oxadicarboxylic acid; oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, Components of aliphatic dicarboxylic acids such as fumaric acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and oxycarboxylic acids such as p-oxybenzoic acid. Examples of the dicarboxylic acid ester derivative component include esterified products of the dicarboxylic acid compounds, such as dimethyl terephthalate, diethyl terephthalate, and 2-hydroxyethyl terephthalate. Components such as methyl ester, dimethyl 2,6-naphthalate, dimethyl isophthalate, dimethyl adipate, diethyl maleate, dimethyl dimer, and the like. As the dicarboxylic acid component, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid are the main components, and the glass transition temperature can be set within the above range, so it is preferable. If these dicarboxylic acid components are 50 mol% or more of the dicarboxylic acid components, they can be said to be the main components.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. Aliphatic dihydroxy compounds such as diols, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol); diethylene glycol, polyethylene glycol, polypropylene glycol , Polyoxymethylene alkylene glycols such as polytetramethylene glycol, 1,4-cyclohexanedimethanol, spiro glycerol, 1,4: 3,6-dihydro-D-glucosanol (isosorbide ) And other components such as alicyclic dihydroxy compounds; and aromatic dihydroxy compounds such as bisphenol A and bisphenol S. These may be only one type each, or two or more types may be used. In addition, as long as it does not affect the film-forming properties of the formed thin film, a small amount of trimellitic acid, pyromellitic acid, and its ester derivative may be copolymerized. As the diol component, ethylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, spiroglycerin, and isosorbide are the main components. This is adjusted by the storage elastic modulus described later. Number (E ') is preferred.

The white polyester film for molding of the present invention must have a specific gravity of 0.8 to 1.1. As a method for setting the specific gravity within such a range, it is preferable that bubbles are contained in the inside of the film. As a method for containing bubbles in the inside, (1) A polyester resin is contained in a foaming agent, and foamed by heating during extrusion or film formation, or chemically decomposed to cause foaming. A method for forming bubbles by foaming; (2) a method for adding a gas or a gasifiable substance when extruding a polyester resin; (3) adding an inorganic particle and / or a thermoplastic incompatible with the resin to the polyester resin Resin (A) is a method of uniaxially or biaxially stretching to generate fine bubbles, etc. In the present invention, the film forming property, the ease of adjusting the amount of bubbles contained in the inside, the manufacturing cost, etc. are integrated From the point of view, the method (3) described above is preferably used. Examples of the inorganic particles in the method (3) include silicon dioxide, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, aluminum oxide, magnesium carbonate, zinc carbonate, titanium oxide, Zinc oxide (zinc white), antimony oxide, cerium oxide, zirconia, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica Particles, titanium, mica, talc, clay, kaolin, etc. In addition, they can be used singly or in combination of two or more kinds. Among them, from the viewpoint of obtaining high optical characteristics and film formation stability, barium sulfate particles and titanium dioxide particles are particularly preferred. When bubbles are contained by inorganic particles, the inorganic particles are preferably contained in an amount of 1 to 50% by weight based on the total weight of the white polyester film for molding of the present invention. When the inorganic particles are less than 1% by weight, it becomes difficult to reduce the specific gravity to 1.1 or less. When the inorganic particles are more than 50% by weight, the mechanical strength, heat resistance, and manufacturing cost of the polyester resin may be impaired. good. Thermoplastic resins (A) incompatible with polyester resins can be selected: olefin resins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclic olefins; styrene resins, polyacrylate resins , Polycarbonate resin, polyacrylonitrile resin, polyphenylene sulfide resin, fluorine resin, etc. Among them, an olefin-based resin or a styrene-based resin is preferable, and as the olefin-based resin, polyethylene, polypropylene, and poly 4-methylpentene-1 (hereinafter, abbreviated as "polymethylpentene") are preferable. Or "PMP"), ethylene-propylene copolymer, ethylene-butene-1 copolymer, and cyclic olefin. As the styrene resin, polystyrene, polymethylstyrene, and polydimethylene are preferred. Styrene, etc. These may be a homopolymer or a copolymer, or two or more thermoplastic resins (A) may be used in combination. The thermoplastic resin (A) is preferably contained in an amount of 1 to 50% by weight based on the total weight of the white polyester film for molding of the present invention. When the thermoplastic resin (A) is less than 1% by weight, it becomes difficult to reduce the specific gravity to 1.1 or less. When it exceeds 50% by weight, the mechanical strength, heat resistance, and manufacturing cost of the polyester resin are impaired. The situation is not good. By setting the specific gravity to 0.8 to 1.1, the reflectance, the storage elastic modulus (E '), and the shape-retaining property with respect to the load after molding can be set within a preferable range. When the specific gravity is greater than 1.1, the formation of bubbles is insufficient, and the reflectance of the thin film is not good. In addition, when the specific gravity is less than 0.8, shape retention with respect to a load after molding may be reduced, which is not preferable. More preferably, the specific gravity is 0.82 to 1.05, and even more preferably 0.85 to 1.0.

As a method of determining the weight ratio of the polyester resin and the thermoplastic resin (A), a method of combining a plurality of analyses depending on the type of each resin may be considered. It can be used: a method of removing only the polyester resin with a solvent, separating the remaining thermoplastic resin (A) with a centrifugal separator, and determining a weight ratio from the weight of the obtained residue; using IR (infrared spectroscopy), 1H -NMR, 13C-NMR to identify each resin, dissolve in a solvent in which both the polyester resin and the thermoplastic resin (A) are soluble, remove impurities and inorganic substances by centrifugation, and determine the concentration from the absorbance to determine the weight ratio Methods. As a solvent that can dissolve the polyester resin, trifluoroacetic acid, 1,1,1,3,3,3-hexafluoro-2-propanol, orthochlorophenol can be used.

The white polyester film for molding of the present invention preferably has a glass transition temperature (Tg) of the surface layer and a storage elastic modulus (E ') of 60 ° C of 10 MPa to 300 MPa. If the storage elastic modulus (E ') at a certain temperature is small, it means that it is easy to be deformed by a small force at that temperature, and if it is large, it means that a large force is required for deformation. When the storage layer modulus (E ') of the glass transition temperature (Tg) + 60 ° C of the surface layer is lower than 10 MPa, the self-supporting property such as sagging due to the weight of the film itself may be lowered. Moreover, if it exceeds 300 MPa, it will become difficult to shape | mold for giving a specific shape, and it is unpreferable. It is more preferably 20 MPa to 250 MPa, and even more preferably 50 MPa to 200 MPa. The method for setting the glass transition temperature (Tg) of the surface layer + 60 ° C storage elastic modulus (E ') within such a range is not particularly limited, and the glass transition temperature of the surface layer is set to 80 ° C as described above in combination. As described above, a method of setting the specific gravity to 1.1 or less is premised, and the film can be produced by the method described below, and the storage elastic modulus can be set within the above range. When the specific gravity is adjusted by including bubbles in the film, the storage elastic modulus (E ') can be adjusted according to the increase or decrease of the specific gravity. The reason for this is that the cross-sectional area of the appearance becomes larger by the inclusion of bubbles, and the storage elastic modulus (E ') becomes lower. As the polyester resin used in the present invention, a copolyester resin can be used. In general, it is known that the copolyester resin-based crystallinity tends to be lower than that of a homopolymer, and it is preferable to reduce the storage elastic modulus (E '). The copolymerized polyester resin is preferably copolymerized from two or more kinds of dicarboxylic acid components cited as the polyester resin and / or two or more kinds derived from diol components. In particular, it is easier to set the glass transition temperature to 80 ° C or higher in the combination of terephthalic acid and 2,6-naphthalenedicarboxylic acid and the combination of ethylene glycol and spiroglycerin compared to polyethylene terephthalate homopolymer. 120 ° C or lower is preferred. As a method for introducing a copolymerization component, a copolymerization component may be added when polymerizing the polyester particles of the raw material, and the copolymerization component may be used as a particle in which the copolymerization component has been polymerized in advance, or, for example, polyethylene naphthalate alone may be used. A method in which a mixture of polymerized particles and polyethylene terephthalate particles is supplied to an extruder, and is copolymerized by a transesterification reaction during melting.

The polyester resin used in the surface layer of the molding white polyester film of the present invention may be one in which two or more polyester resins are mixed. When two or more polyester resins are mixed, the glass transition temperature of two or more surface layers may be measured. In this case, the glass transition temperature that becomes the starting point of "glass transition temperature of the surface layer + 60 ° C" is the glass transition temperature at which the temperature is the highest.

In the white polyester film for molding of the present invention, it is preferable that the core layer has air bubbles containing a hollow nucleating agent. The so-called core layer herein refers to all layers except the two surface layers in the polyester film having three or more layers. In the case of four or more layers, the core layer has two or more layers. When the core layer is two or more layers, it is preferable that at least one of the layers has air bubbles containing a hollow nucleating agent. The hollow nucleating agent is not the same as the main resin component constituting the white polyester film for molding, and may be dispersed in the resin component in particulate form. Examples include inorganic fine particles, organic fine particles, and various thermoplastics. Resin, etc. There is no particular limitation on the method for obtaining bubbles containing a hollow nucleating agent, and it is preferable to use a thermoplastic resin (A) which is obtained by adding inorganic particles to the polyester resin and / or incompatible with the resin, and uniaxially or A method of biaxial stretching to generate fine bubbles and the like. With bubbles containing a void nucleating agent, voids are difficult to collapse during the molding process. When the white polyester film for molding is molded into a white resin molded body, it becomes difficult to cause a decrease in reflectance and transmission. The increase in rate is better.

The white polyester film for molding of the present invention preferably has a reflectance of 98% or more and a transmittance of less than 3%. Here, the so-called reflectance is an average reflectance of a wavelength region of light of 400 to 700 nm, and the transmittance is a light transmittance measured in accordance with JIS-K-7361-1 using light having a wavelength (400 to 800 nm) in a visible light region. rate. There is also a case called total light transmittance. When the reflectance is less than 98% or the transmittance is 3% or more, there is a case where a sufficient brightness cannot be generated when it is assembled to a direct type backlight. The method of setting the reflectance and transmittance within the above ranges is not particularly limited, and a polyester resin containing inorganic particles and / or a thermoplastic resin (A) incompatible with the resin can be preferably used. A method of performing uniaxial or biaxial stretching to generate fine bubbles.

The white polyester film for molding of the present invention is intended to reflect from the viewpoints of film forming properties and moldability. The transmittance and the shape-retaining property with respect to the load after forming are set in a preferable range. The thickness of the film is preferably 100 to 500 μm, more preferably 125 to 400 μm, and even more preferably 160 to 350 μm.

Next, an example of the method for producing a white polyester film for molding of the present invention will be described, but it is not particularly limited. In a composite film forming apparatus having at least two uniaxial or biaxial extruders, a main extruder, and a sub-extruder, a resin serving as a raw material for the core layer (Y), The extruder was charged with a resin that is a raw material for the surface layer (X). Each raw material is preferably dried so that the moisture content becomes 50 ppm or less. Feeding the raw materials to each of the extruders in this manner makes it possible to form a three-layer film of X / Y / X with, for example, two extruders, a feed zone provided in the upper part of the T die, and a multi-manifold. The extruded unstretched sheet is closely cooled and solidified on a cooled drum to obtain an unstretched laminated film. At this time, in order to obtain a uniform film, it is desirable to apply static electricity to make it adhere to the drum. After that, the desired polyester film is obtained through a stretching step and a heat treatment step as needed.

This unstretched film is heated with a roller or infrared heating as needed, and is heated to a temperature higher than the glass transition temperature (Tg) of the polymer, and stretched in the longitudinal direction (hereinafter referred to as the longitudinal direction) to obtain a longitudinal direction. Stretch the film. This stretching is performed using a difference in peripheral speed of two or more rolls. The stretching ratio in the longitudinal direction depends on the characteristics required for the application, and is preferably 2 to 6 times, and more preferably 3 to 4 times. If it is less than 2 times, the reflectance may be low, and if it is more than 6 times, cracks may easily occur during film formation. Then, the film stretched in the longitudinal direction is sequentially stretched, heat-fixed, and thermally relaxed in a direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction) to form a biaxially oriented film. These processes are on one side. The film advances while proceeding. At this time, the preheating and stretching temperature for transverse stretching is preferably performed at a temperature higher than the glass transition temperature (Tg) of the polymer (Tg + 20 ° C). The stretching ratio in the transverse direction depends on the characteristics required for the application, preferably 2.5 to 6 times, and more preferably 3 to 4 times. If it is less than 2.5 times, the reflectance may be low. When it exceeds 6 times, it may become easy to produce a crack during film formation. The crystal orientation of the obtained biaxially stretched laminated film was terminated. In order to provide planarity and dimensional stability, heat treatment was performed in a tenter at 180 to 230 ° C. for 1 to 60 seconds to uniformly. After slowly cooling, cool to room temperature, and take up to a roll. Such a heat treatment can be performed simultaneously with slackening the film in its longitudinal direction and / or width direction.

Here, the case where the stretching is performed by the sequential biaxial stretching method is described in detail as an example. However, the polyester film of the present invention can be selected from the sequential biaxial stretching method and the simultaneous biaxial stretching method. One method is used for stretching, and further, if necessary, after biaxial stretching, longitudinal stretching and / or transverse stretching are performed again.

In order to provide planar stability and dimensional stability to the biaxially stretched laminated film obtained in this way, heat treatment (heat fixation) is performed in a tenter, and then slowly and uniformly cooled, and then cooled to near room temperature. When rolled up, the white film of the present invention can be obtained.

In addition, as long as the effect of the present invention is not impaired, various coating liquids may be applied using well-known techniques on at least one side of the resin layer (A) in order to impart slipperiness, antistatic property, ultraviolet light absorption performance, or the like, or In order to improve impact resistance, a hard coat layer or the like is provided. The coating may be applied during film production (in-line coating) or on a white film after film production (off-line coating).

The present invention may be a white resin molded body obtained by molding the white polyester film for molding described above. The forming method is not particularly limited, and a method of forming the film only by vacuum forming, air pressure molding, vacuum pressure forming, press forming, and plug-assisted vacuum pressure forming; Methods such as insert molding, TOM (Three Dimension Overlay Method) molding, and three-dimensional lamination molding are commonly known molding methods such as a substrate molding method. For example, in the case of vacuum pressure forming, a 400 ° C. far-infrared heater is used to heat the film so that the film surface temperature becomes Tg + 50 ° C. or higher, and vacuum pressure is performed along a mold heated to 50 ° C. By air forming (pressure: 1 MPa), the reflecting plate of the present invention can be obtained. The shape of the formed body of the present invention is not particularly limited, and it is preferable to form one or more depressions. The shape of the depression may be a truncated cone shape, a hemispherical shape, a spherical crown shape, a columnar shape, a combination thereof, an intermediate shape, a shape distorted into an ellipse, and a round shape with R at the corners. Among them, if it is a quadrangular frustum shape or a hexagonal frustum shape, it is easy to fill the surface with the same shape, and it is easy to use and it is preferable for the application mentioned later.

The white resin molded body of the present invention can be suitably used as a reflector for an LED lighting unit. In the case of the LED lighting unit using the white resin molded body of the present invention, light leakage from adjacent LEDs is less likely to occur, and therefore it is suitable for lighting applications equipped with a partial driving function. In particular, it is preferable as a reflecting plate for a flat-type LED lighting unit.

The white resin molded body of the present invention can be suitably used as a reflecting plate for a direct type LED backlight unit. In the case of the direct-type LED backlight unit using the reflecting plate of the present invention, a backlight equipped with a local dimming function is less likely to cause leakage of light from adjacent LEDs. In particular, a reflecting plate for a direct type LED backlight unit used in a liquid crystal display, a liquid crystal television, a liquid crystal monitor, or the like is preferable.

    [Example]    

Hereinafter, the present invention is described in detail by examples. In addition, each characteristic value was measured by the following method.

    (1) Glass transition temperature    

Using a differential scanning thermal card meter (manufactured by Seiko Electronics Industries, RDC220), measurement and analysis were performed in accordance with JIS K 7121-1987 and JIS K7122-1987. 5 mg of a polyester layer or a polyester film was used for the sample. Based on the DSC curve obtained when the temperature rises from 25 ° C to 300 ° C at 20 ° C / minute, the elongation of each bottom line in the direction of the vertical axis (the axis showing the heat flow) is obtained from the change in the specific heat of the transition from the glass state to the rubber state. The glass transition temperature is defined as the glass transition temperature at the midpoint of the point where the straight line is equidistant from the straight line and the curve of the step-shaped change portion of the glass transition. In addition, the endothermic peaks with extremely small peak areas (in terms of crystal melting energy converted to 0.5 J / g or less) seen on the bottom line were regarded as noise and removed. When only the surface layer is measured, the surface layer is cut with a blade and measured.

    (2) Storage elastic modulus (E ’)    

A rectangle having a length of 60 mm and a width of 5 mm was cut out of the film in the longitudinal direction and the width direction as a sample. Using a dynamic viscoelasticity measuring device (DMS6100, manufactured by Seiko Instruments), the elastic modulus (E ') of the film surface layer at Tg + 50 ° C was determined under the following conditions.

Frequency: 1 Hz, test length: 20 mm, minimum load: about 100 mN, amplitude: 10 μm, measurement temperature range: 20 ° C to 230 ° C, heating rate: 5 ° C / min. (3) Specific gravity

Five pieces of square samples with a side length of 5 cm were cut out from the film, and were measured using an electronic hydrometer SD-120L (Mirage Trading Co., Ltd.) based on JIS K7112-1980. The added average of the measured values obtained in five points in total was determined as the specific gravity of the film.

    (4) Reflectivity    

A 60mmφ integrating sphere was mounted on a spectrophotometer (U-3310) manufactured by Hitachi High Technologies, and a standard white board (manufactured by Hitachi High Technologies, part No. 210-0740) covering 400 to 700 nm was measured at 100%. Reflectivity. The reflectance was read from the obtained graph at intervals of 5 nm, and the arithmetic mean was calculated as the reflectance.

    (5) Transmittance (total light transmittance)    

A turbidimeter "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure the total light transmittance in accordance with JIS "Test method for total light transmittance of plastic transparent materials" (K7361-1, 1997 edition).

    (6) Formability    

Using a molding machine (FKS-0631-20) manufactured by Asano Laboratories, a 400 ° C far-infrared heater was used to heat the film so that the film surface temperature became Tg + 50 ° C or higher. The mold (bottom surface diameter: 50 mm, cylindrical shape) was subjected to vacuum pressure forming (pressure: 1 MPa). Using the degree of molding (shrinkage ratio: molding height / bottom surface diameter), the state of molding along the mold was evaluated according to the following criteria.

：: Can be formed with a shrinkage ratio of 0.7 or more.

○: Moldable at a shrinkage ratio of 0.7 to 0.4.

△: Can be formed with a shrinkage ratio of 0.4 to 0.1.

×: Cracking occurred, and it was impossible to form at a shrinkage ratio of 0.1. Or the followability is low and cannot be formed.

A pass of △ or more was determined to be acceptable.

    (7) Shape retention (load resistance)    

Using a molding machine (FKS-0631-20) manufactured by Asano Laboratories, a 400 ° C far-infrared heater was used to heat the film so that the film surface temperature became Tg + 50 ° C or higher. The mold (bottom surface diameter: 50 mm, height: 25 mm, conical shape) was subjected to vacuum pressure forming (pressure: 1 MPa). The formed cone was subjected to a compression test using a tensile tester (RTF-1210, manufactured by Baldwin Co., Ltd.) and a compression test fixture. The boundary between elastic deformation and plastic deformation was read from the obtained S-S curve (FIG. 1), and the load resistance was evaluated from the test force (N).

◎: 15N or more test force

○: The test force is 10N or more and less than 15N

△: The test force is 5N or more and less than 10N

×: Test force is less than 5N

A pass of △ or more was determined to be acceptable.

    (8) Shape retention (heat resistance)    

Using a molding machine (FKS-0631-20) manufactured by Asano Laboratories, a 400 ° C far-infrared heater was used to heat the film so that the film surface temperature became Tg + 60 ° C or higher. The mold (bottom surface diameter: 50 mm, height: 25 mm, conical shape) was subjected to vacuum pressure forming (pressure: 1 MPa). The formed cone was put into an oven at 80 ° C for 30 minutes, and the rate of change in height before and after heating was measured. The height was measured using a OneShot 3D shape measuring machine VR-3200 (manufactured by Keyence Corporation).

◎: Change rate is less than 3%

○: Change rate is more than 3% and less than 5%

△: Change rate is more than 5% and less than 8%

×: Change rate is 8% or more

A pass of △ or more was determined to be acceptable.

    (9) Optical unevenness    

Using a molding machine (FKS-0631-20) manufactured by Asano Laboratories, a 400 ° C far-infrared heater was used to heat the film so that the film surface temperature became Tg + 60 ° C or higher. The mold (box type having a wall of 2 × 2 squares with a side of 50 mm, a height of 10 mm, and a thickness of 10 mm) was subjected to vacuum pressure forming (pressure: 1 MPa). A hole with a diameter of 12 mm is opened at the bottom of each square, and the LED and the lens cover are exposed from the hole to be assembled into the backlight of a commercially available TV (made by Haier, LE42A7000), and an optical film group is placed to make the LED light and observe Exterior.

◎: See the four corners of the box brightly

○: Brightly seen

×: Dimly seen

    [Using raw materials]         (1) Polyester resin (a)    

Polyethylene terephthalate (PET) is obtained by polymerizing terephthalic acid and ethylene glycol with antimony trioxide as a catalyst by a common method. The glass transition temperature of the obtained PET was 77 ° C, the melting point was 255 ° C, the intrinsic viscosity was 0.63 dl / g, and the terminal carboxyl group concentration was 40 eq./t.

    (2) Polyester resin (b)    

A transesterification reaction was performed with dimethyl 2,6-naphthalene dicarboxylate and ethylene glycol, using manganese acetate as a catalyst. After the transesterification reaction, antimony trioxide was used as a catalyst to obtain polyethylene terephthalate (PEN) by a common method. The glass transition temperature of the obtained PEN was 124 ° C, the melting point was 265 ° C, the intrinsic viscosity was 0.62 dl / g, and the terminal carboxyl group concentration was 25 eq./t.

    (3) Copolyester resin (c)    

A commercially available 1,4-cyclohexanedimethanol copolyester (GN001 manufactured by Eastmen Chemical Co., Ltd.) was used. The glass transition temperature was 85 ° C and the intrinsic viscosity was 0.75 dl / g.

    (4) Copolyester resin (d)    

A copolymerized isophthalic acid having a terephthalic acid component as a dicarboxylic acid component of 82.5 mol%, an isophthalic acid component of 17.5 mol%, and a glycol component of a glycol component of 100 mol% Polyethylene terephthalate resin. The glass transition temperature was 70 ° C and the inherent viscosity was 0.7 dl / g.

    (5) Copolyester resin (e)    

Copolymerized neopentyl glycol with 100 mol% terephthalic acid component as dicarboxylic acid component, 70 mol% ethylene glycol component as diol component, and 30 mol% neopentyl glycol component Polyethylene terephthalate resin. The inherent viscosity is 0.75 dl / g.

    (6) Polyester resin (f)    

A commercially available polybutylene terephthalate resin, "Toraycon" (registered trademark) 1200S manufactured by Toray Co., Ltd. was used. The melting point is 224 ° C and the inherent viscosity is 1.26 dl / g.

    (7) Copolyester resin (g)    

"Altester" (registered trademark) S2000 manufactured by Mitsubishi Gas Chemical Co., Ltd. was used as a commercially available polyester resin of copolymerized spiroglycerin. The glass transition temperature was 95 ° C and the intrinsic viscosity was 0.75 dl / g.

    (8) Copolyester resin (h)    

Commercially available polyisophthalic acid polycyclohexylene terephthalate ("Eastar AN004" manufactured by Eastman Chemical Co., Ltd.) was used. The glass transition temperature is 83 ° C and the intrinsic viscosity is 0.75 dl / g.

    (9) Titanium dioxide masterbatch (i)    

50 parts by weight of the polyester resin (a) and 50 parts by weight of titanium dioxide particles (number average particle diameter 0.5 μm) were kneaded in a biaxial extruder to obtain titanium dioxide mother particles (k).

    (10) Thermoplastic resin (j)    

Commercially available polymethylpentene raw material "TPX RT18" (Mitsui Chemical Co., Ltd., melting point: 233 ° C).

    (11) Cyclic olefin resin (k)    

A commercially available cyclic olefin resin "TOPAS 6017" (Japan Polyplastic Co., Ltd.) was used.

    (12) Copolyester (l)    

A commercially available polyester resin copolymerized with isosorbide and 1,4-cyclohexanedimethanol ("ECOZEN BS300" manufactured by SK Chemicals) was used.

    (13) Copolyester (m)    

Copolymerization using 2,6-naphthalenedicarboxylic acid component as a dicarboxylic acid component at 100 mol%, ethylene glycol component as a diol component at 85 mol%, and neopentyl glycol component at 15 mol% Polyethylene terephthalate resin of pentanediol. The glass transition temperature was 112 ° C and the inherent viscosity was 0.70 dl / g.

    (Examples 1, 3 to 7, 9)    

After the raw materials of the composition shown in Table 1 were vacuum-dried at 180 ° C for 6 hours, the raw materials of the core layer (Y) were supplied to the main extruder, and melt-extruded at a temperature of 280 ° C, and cut off at 30 μm. The filter (cut filter) is used to filter, the raw material of the surface layer (X) is supplied to the sub-extruder, and melt-extruded at a temperature of 290 ° C, and then filtered with a 30 μm cut-off filter, and then the T-die compound extrusion nozzle So that the surface layer (X) is laminated on the two surface layers (X / Y / X) of the core layer (Y).

Next, it was extruded into a sheet shape to make a molten sheet, and the molten sheet was adhered and cooled and solidified on a drum maintained at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched film. Next, the unstretched film was preheated with a roller group heated to a temperature of 80 ° C., and then irradiated from both sides with an infrared heater, and pulled in the longitudinal direction (longitudinal direction) at a magnification of Table 2 It stretched and cooled with the roller group of 25 degreeC, and obtained the uniaxially stretched film. Then, while holding both ends of the uniaxially stretched film with a clamp, guide it to a preheating zone at 110 ° C in the tenter, and then follow the table at 120 ° C in a direction (lateral direction) perpendicular to the long side direction. Stretching was performed at a magnification of 2. Next, a heat treatment at a temperature of Table 2 was further applied to a heat treatment zone in the tenter, and then slowly and uniformly cooled, and then rolled up to a roll to obtain a white polyester film for molding having a thickness shown in Table 2.

    (Examples 2, 8, 11-20)    

After the raw materials of the composition shown in Table 1 were vacuum-dried at 180 ° C for 6 hours, the raw materials of the core layer (Y) were supplied to the main extruder, and the raw materials of the surface layer (X) were supplied to the sub-extruder. After being melt-extruded at a temperature of 280 ° C., they were filtered with a 30 μm cut-off filter, and then in a T-die compound extrusion nozzle, so that they were laminated with the surface layer (X) on the two surface layers (X) of the core layer (Y). / Y / X).

Next, it was extruded into a sheet shape to make a molten sheet, and the molten sheet was adhered and cooled and solidified on a drum maintained at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched film. Next, the unstretched film was preheated with a roller group heated to a temperature of 70 ° C, and then drawn from both sides with an infrared heater, and pulled in the longitudinal direction (longitudinal direction) at a magnification of Table 2 It stretched and cooled with the roller group of 25 degreeC, and obtained the uniaxially stretched film. Then, while holding both ends of the uniaxially stretched film with a clamp, guide it to a preheating zone at 110 ° C in the tenter, and then follow the table at 120 ° C in a direction (lateral direction) perpendicular to the long side direction. It is stretched at a magnification of 2. Next, a heat treatment at a temperature of Table 2 was further applied to a heat treatment zone in the tenter, and then slowly and uniformly cooled, and then rolled up to a roll to obtain a white polyester film for molding having a thickness shown in Table 2.

    (Example 10)    

After the raw materials of the composition shown in Table 1 were vacuum-dried at 180 ° C for 6 hours, the raw materials of the core layer (Y) were supplied to the main extruder, and melt-extruded at a temperature of 280 ° C, and cut off at 30 μm. The filter is used for filtering, and the raw material of the surface layer (X) is supplied to the sub-extruder. After melting and extruding at a temperature of 270 ° C., it is filtered by a 30 μm cut-off filter, and then the compound is extruded in a T-die composite extrusion nozzle. The surface layer (X) is laminated on the two surface layers (X / Y / X) of the core layer (Y) to merge.

Next, it was extruded into a sheet shape to make a molten sheet, and the molten sheet was adhered and cooled and solidified on a drum maintained at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched film. Next, the unstretched film was preheated with a roller group heated to a temperature of 70 ° C, and then drawn from both sides with an infrared heater, and pulled in the longitudinal direction (longitudinal direction) at a magnification of Table 2 It stretched and cooled with the roller group of 25 degreeC, and obtained the uniaxially stretched film. Then, while holding both ends of the uniaxially stretched film with a clamp, guide it to a preheating zone at 110 ° C in the tenter, and then follow the table at 120 ° C in a direction (lateral direction) perpendicular to the long side direction. Stretching was performed at a magnification of 2. Next, a heat treatment at a temperature of Table 2 was further applied to a heat treatment zone in the tenter, and then slowly and uniformly cooled, and then rolled up to a roll to obtain a white polyester film for molding having a thickness shown in Table 2.

    (Comparative Examples 1, 2, 6)    

After the raw materials of the composition shown in Table 1 were vacuum-dried at 180 ° C for 6 hours, the raw materials of the core layer (Y) were supplied to the main extruder, and the raw materials of the surface layer (X) were supplied to the sub-extruder. After being melt-extruded at a temperature of 280 ° C., they were filtered with a 30 μm cut-off filter, and then in a T-die compound extrusion nozzle, so that they were laminated with the surface layer (X) on the two surface layers (X) of the core layer (Y). / Y / X).

Next, it was extruded into a sheet shape to make a molten sheet, and the molten sheet was adhered and cooled and solidified on a drum maintained at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched film. Next, the unstretched film was preheated with a roller group heated to a temperature of 70 ° C, and then drawn from both sides with an infrared heater, and pulled in the longitudinal direction (longitudinal direction) at a magnification of Table 2 It stretched and cooled with the roller group of 25 degreeC, and obtained the uniaxially stretched film. Then, while holding both ends of the uniaxially stretched film with a clamp, guide it to a preheating zone at 110 ° C in the tenter, and then follow the table at 120 ° C in a direction (lateral direction) perpendicular to the long side direction. Stretching was performed at a magnification of 2. Next, a heat treatment at a temperature of Table 2 was further applied to a heat treatment zone in the tenter, and then slowly and uniformly cooled, and then rolled up to a roll to obtain a white polyester film for molding having a thickness shown in Table 2.

    (Comparative Examples 3 to 5)    

After the raw materials of the composition shown in Table 1 were vacuum-dried at 180 ° C for 6 hours, the raw materials of the core layer (Y) were supplied to the main extruder, and melt-extruded at a temperature of 280 ° C, and cut off at 30 μm. The filter is used to filter, and the raw material of the surface layer (X) is supplied to the sub-extruder. After melting and extruding at a temperature of 290 ° C., it is filtered with a 30 μm cut-off filter. The surface layer (X) is laminated on the two surface layers (X / Y / X) of the core layer (Y) to merge.

Next, it was extruded into a sheet shape to make a molten sheet, and the molten sheet was adhered and cooled and solidified on a drum maintained at a surface temperature of 25 ° C by an electrostatic application method to obtain an unstretched film. Next, the unstretched film was preheated with a roller group heated to a temperature of 80 ° C., and then irradiated from both sides with an infrared heater, and pulled in the longitudinal direction (longitudinal direction) at a magnification of Table 2 It stretched and cooled with the roller group of 25 degreeC, and obtained the uniaxially stretched film. Then, while holding both ends of the uniaxially stretched film with a clamp, guide it to a preheating zone at 110 ° C in the tenter, and then follow the table at 120 ° C in a direction (lateral direction) perpendicular to the long side direction. Stretching was performed at a magnification of 2. Next, a heat treatment at a temperature of Table 2 was further applied to a heat treatment zone in the tenter, and then slowly and uniformly cooled, and then rolled up to a roll to obtain a white polyester film for molding having a thickness shown in Table 2.

Industrial availability

The present invention has not only high reflectivity and moldability, but also high shape retention, and is therefore suitable for use as a light reflecting plate or the like used in a direct type LED backlight unit.

Claims (7)

    A white polyester film for forming is characterized in that it comprises at least three layers, the glass transition temperature (Tg) of the surface layer is 80 ° C or higher and less than 120 ° C, and the specific gravity of the film is 0.8 to 1.1.         For example, the white polyester film for molding according to claim 1, wherein the surface layer has a glass transition temperature (Tg) + 60 ° C and a storage elastic modulus (E ') of 10 MPa to 300 MPa.         The white polyester film for forming as in claim 1 or 2, wherein the core layer has air bubbles containing a hollow nucleating agent.         For example, the white polyester film for molding of claim 1 has a reflectance of 98% or more and a transmittance of less than 3%.         A white resin molded body formed by molding a white polyester film for molding as described in claim 1.         The white resin molded body according to claim 5, which is used for an LED lighting unit.         The white resin molded body according to claim 5, which is used for a direct type LED backlight unit.