TWI488743B - Reflector with white film - Google Patents

Description

White film for reflector

The present invention relates to a white film for a reflecting plate used as a reflecting plate of a backlight unit of a liquid crystal display device.

The backlight unit of the liquid crystal display device is provided with a reflection plate on the back surface in order to prevent light from the light source from leaking to the back surface of the screen. The reflector is required to be thin and has a high reflectance.

A white film for a reflecting plate used in a backlight unit for a liquid crystal display device is known as a white polyester film containing fine bubbles inside the film and has been widely used.

Patent Document 1: JP-A-63-62104

Patent Document 2: Special Fair 8-16175

Patent Document 3: JP-A-2000-37835

Patent Document 4: JP-A-2005-125700

Patent Document 5: JP-A-2004-50479

The reflecting plate is processed into a specific shape by a white film and assembled in a backlight unit. Although the step of cutting the reflecting plate into a specific shape by the white film is used for the processing, the cutting speed in this step is accelerated with the mass production of the backlight unit.

When a high-brightness is obtained from a conventional reflective film, a whisker or a burr is likely to occur on the end face of the film at the time of cutting. The whisker is a small projection which is formed on the cut surface by cutting, and it is necessary to remove it as waste material. Therefore, when a whisker is generated, the productivity is lowered. Further, the burr is a portion of the burr which is generated in the vicinity of the cut surface due to the cutting, and if there is a burr, the distance between the reflecting surface and the light source is changed, which adversely affects the brightness, and there is a possibility that uniform brightness cannot be obtained.

The purpose of the benzene invention is to provide a white film for a reflecting plate which can be used as a reflecting plate in a backlight unit of a liquid crystal display device having high reflectance, which is highly resistant to burrs or whiskers during punching. It is a white film for a reflector having excellent punching properties.

A second object of the present invention is to provide a white film for a reflecting plate which is capable of suppressing thermal bending and having excellent planarity in an environment which is used as a reflecting plate of a liquid crystal display device.

That is, the present invention is a white film for a reflecting plate, which is characterized in that it is composed of a light reflecting layer having a pore volume ratio of 55 to 80% and a supporting layer of a biaxially stretched polyester film provided on at least one surface thereof. The ratio of the total thickness of the reflective layer to the thickness of the support layer is 85:15 to 98:2, the light reflectance of the film is 98.0% or more, and the punching energy obtained by the drop impact test is 0.10 to 0.30 J, and the film thickness is It is 150~250μm.

According to the present invention, it is possible to provide a white film for a reflecting plate which can obtain high luminance when used as a reflecting plate in a backlight unit of a liquid crystal display device having high reflectance, which is difficult to generate burrs or whiskers during punching. It is a white film for a reflector having excellent punchability.

A second object of the present invention is to provide a white film for a reflector of a backlight unit of a liquid crystal display device which is excellent in thermal bending and excellent in flatness, in an environment which is used as a reflector of a liquid crystal display device.

The invention is described in detail below.

The white film for a reflecting plate of the present invention comprises a light reflecting layer and a supporting layer of a biaxially stretched polyester film provided on at least one side thereof.

[light reflective layer]

The light-reflecting layer of the present invention is formed by providing a white coloring agent in a thermoplastic resin or a pore-forming substance in a thermoplastic resin and extending it to form an interface between the thermoplastic resin and the pore-forming substance. The pores present a layer of a thermoplastic resin composition such as white.

The light-reflecting layer of the present invention has a pore volume ratio of 55 to 80%, more preferably 60 to 75%, and most preferably 62 to 70%. When the void volume ratio is less than 55%, a high reflectance cannot be obtained, and the punching workability is also inferior. Further, if the void volume ratio exceeds 80%, film formation becomes extremely difficult.

[thermoplastic polyester]

The thermoplastic resin of the light-reflecting layer of the present invention preferably uses a thermoplastic polyester. When a thermoplastic polyester is used, a polyester composed of a dicarboxylic acid component and a diol component is used. As the dicarboxylic acid, for example, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid or sebacic acid can be exemplified. The diol may, for example, be ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol or 1,6-hexanediol. The polyester is also preferably a thermoplastic aromatic polyester, preferably polyethylene terephthalate. The polyethylene terephthalate may be a homopolymer, but is preferably a copolymerized polymer, preferably polyethylene terephthalate copolymerized with isophthalic acid.

When the polymer is polymerized with polyethylene terephthalate, the ratio of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 15 mol%, based on the total dicarboxylic acid component, more preferably 3~13 moles %. By setting the ratio of the copolymerization component to such a range, excellent film forming properties can be obtained even in the light-reflecting layer, and a film excellent in thermal dimensional stability can be obtained.

When the thermoplastic polyester is used as the thermoplastic resin of the light-reflecting layer, the intrinsic viscosity of the thermoplastic polyester measured in the light-reflecting layer is preferably from 0.40 to 0.53 dl/g. By the intrinsic viscosity in this range, the thermoplastic polyester composition of the light-reflecting layer can be easily melt-extruded even if it contains a high concentration of inorganic particles, and can be formed into a film with high productivity without breaking the film.

[White inorganic particles]

As the white colorant of the light reflection layer, white inorganic particles are used. As the pore forming material, white inorganic particles, organic particles or incompatible resins are used. As the white inorganic particles, barium sulfate particles, titania particles, cerium oxide particles, calcium carbonate particles, and preferably barium sulfate particles can be used.

The average particle diameter of the white inorganic particles is preferably from 0.1 to 3.0 μm, more preferably from 0.2 to 2.5 μm, still more preferably from 0.3 to 2.0 μm. By using white inorganic particles having an average particle diameter in the range, it can be appropriately dispersed in the thermoplastic resin of the light-reflecting layer without causing white inorganic particles, and a light-reflecting layer having no large protrusions on the surface can be obtained, and at the same time, the light-reflecting layer can be obtained. The surface is not coarse and can be an appropriate range of gloss. As the white inorganic particles, the barium sulfate particles having an average particle diameter of 0.1 to 3.0 μm are used, and d50 (median diameter) is used, or 10% of d10 from the small particle diameter, since the particle size is small When 90% of the d90 is expressed, the d90/d10 of the particle size distribution is preferably from 1 to 500, more preferably from 1 to 300, still more preferably from 1 to 100, and most preferably from 1 to 50. If the particle size distribution is in this range, the coarse particles do not block the filter, and the fine particles do not agglomerate, and the film can be stably formed.

The white inorganic particles may be in any particle shape, and may be, for example, a plate shape or a spherical shape. The white inorganic particles can also be subjected to a surface treatment for improving dispersibility.

When organic particles are used as the pore-forming substance, for example, polymer particles can be used, and specifically, for example, crosslinked polystyrene particles or acrylic particles can be used.

When a non-compatible resin is used as the pore-forming substance, it is a resin which is incompatible with the thermoplastic resin of the light-reflecting layer. When a thermoplastic polyester, in particular, polyethylene terephthalate or a copolymerized polymer thereof is used as the thermoplastic resin of the light-reflecting layer, as the non-compatible resin, for example, polyolefin or polystyrene can be used.

When the light reflecting layer is composed of a thermoplastic polyester composition comprising white inorganic particles and a thermoplastic polyester, the white inorganic particles preferably occupy 50 to 60% by weight, and the thermoplastic polyester preferably occupies 50%. ~40% by weight. By having a composition in this range, good reflectance and punching workability can be expected, and film formation can be stably performed. The white inorganic particles in the composition preferably occupy 52 to 60% by weight, more preferably 53 to 59% by weight, most preferably 54 to 58% by weight.

When the light reflecting layer is composed of a thermoplastic polyester composition comprising organic particles and a thermoplastic polyester, the organic particles preferably occupy 50 to 60% by weight, and the thermoplastic polyester preferably occupies 50 to 40%. weight%. By having a composition in this range, good reflectance and punching workability can be expected, and film formation can be stably performed. The organic particles in the composition preferably occupy 52 to 60% by weight, more preferably 53 to 59% by weight, most preferably 54 to 58% by weight.

When the light reflecting layer is composed of a thermoplastic polyester composition comprising a non-compatible resin and a thermoplastic polyester, the non-compatible resin preferably accounts for 50 to 60% by weight of the composition, and the thermoplastic polyester is preferably used. Occupy 50 to 40% by weight. By having a composition in this range, good reflectance and punching workability can be expected, and film formation can be stably performed. The non-compatible resin in the composition preferably accounts for 52 to 60% by weight, more preferably 53 to 59% by weight, most preferably 54 to 58% by weight.

[Support Layer]

The support layer is composed of a biaxially stretched polyester film. The support layer is composed of a thermoplastic polyester, and the thermoplastic polyester is preferably a thermoplastic aromatic polyester composed of an aromatic dicarboxylic acid component and a diol component, and preferably a polyethylene terephthalate. ester. The polyethylene terephthalate may be a homopolymer, but is preferably a copolymerized polymer. In the case of copolymerizing a polymer, the thermoplastic amorphous aromatic polyester of the support layer is preferably based on all dicarboxylic acid components, and has a terephthalic acid component of 95 to 99.9 mol and 0.1 to 5 mol% of isophthalic acid. The component is a copolymerized polyethylene terephthalate composed of a dicarboxylic acid component. Particularly good punchability of the support layer can be obtained by copolymerizing the phthalic acid component in this range. The amount of the copolymerization of the isophthalic acid component is more preferably 0.1 to 4 mol%, more preferably 0.1 to 3 mol%.

The support layer may also contain white inorganic particles. When the support layer is composed of a thermoplastic polyester composition comprising a thermoplastic polyester and white inorganic particles, the white inorganic particles preferably occupy 0.1 to 10% by weight, and the thermoplastic polyester preferably occupies 99.9. 90% by weight. By setting the composition of the support layer in this range, good reflectance and punching workability can be expected, and film formation can be stably performed.

The intrinsic viscosity of the thermoplastic polyester measured in the support layer of the white film for a reflector of the present invention is preferably from 0.54 to 0.65 dl/g. By the inherent viscosity in this range, the molten polymer can be easily extruded at the time of film formation, and the film can be formed with high productivity without breaking the film. In particular, from the viewpoint of obtaining good punchability and film formability, the intrinsic viscosity of the thermoplastic polyester of the support layer is preferably higher than the inherent viscosity of the thermoplastic polyester of the light-reflecting layer.

[layer composition]

The white film for a reflecting plate of the present invention is preferably produced by a co-extrusion method. That is, it is preferred to laminate the light reflecting layer and the support layer by a co-extrusion method.

The white film for a reflector of the present invention comprises a single or a plurality of light reflecting layers comprising a single or a plurality of support layers. The ratio of the total thickness of the light reflecting layer to the total thickness of the supporting layer is 85:15 to 98:2, preferably 95:5 to 98:2. When the ratio of the thickness of the reflective layer to the total thickness of the film is less than 85, it is difficult to obtain high reflectance. On the other hand, when it exceeds 98, the film is often broken and it is difficult to form a film stably.

The white film for a reflector of the present invention may be configured by providing a support layer on at least one side of the light-reflecting layer. Specifically, it may be composed of, for example, two layers of a light-reflecting layer/support layer, and a support layer/light-reflecting layer/ 3 layers of support layer, 3 layers of light reflection layer/support layer/light reflection layer, 4 layers of support layer/light reflection layer/support layer/light reflection layer, support layer/light reflection layer/support layer/ The light reflecting layer/support layer is composed of 5 layers. From the viewpoint of film formation stability and production cost, it is preferably a three-layer structure of the support layer/light reflection layer/support layer.

The total thickness of the white film for a reflecting plate of the present invention is from 150 to 250 μm, preferably from 170 to 230 μm. Good operability and productivity can be obtained by the total thickness of the range. If it is less than 150 μm, the reflectance is insufficient. On the other hand, when it exceeds 250 μm, a sufficient reflectance can be obtained, but the punching property is deteriorated.

The white sheet of the reflector of the present invention is biaxially stretched. High mechanical strength can be obtained by biaxial stretching.

[falling impact test]

The punching energy obtained by the drop impact test of the white film for the reflecting plate of the present invention is generally required to be 0.10 to 0.30 J. If it is less than 0.10 J, the film itself is easily broken, and if it exceeds 0.30 J, a whisker or a burr may occur.

[light reflectance]

The light reflectance of the white film for a reflector of the present invention is preferably 98.0% or more, more preferably 98.5% or more, and most preferably 99.0% or more at a wavelength of 550 nm. By using a light reflectance of 98.0% or more, high luminance can be obtained when used in a backlight unit.

The punching energy and light reflectance can be achieved by a white film composed of the composition and layer of the present invention.

[Maximum peak temperature of loss tangent tan δ]

The maximum peak temperature of the loss tangent tan δ measured by dynamic viscoelasticity of the white film for a reflector of the present invention is preferably 110 ° C or more. When the maximum peak temperature of the loss tangent tan δ is less than 110 ° C, film bending occurs due to temperature rise due to heat from the cold cathode tube.

[Storage Elasticity E' _{(120 ° C)} vs. Storage Elasticity E' _{(50 ° C)} at _{50 ° C} ]

The ratio of the storage elastic modulus E' _{(120 ° C)} at 120 ° C measured by the dynamic viscoelasticity of the white sheet of the present invention to the storage elastic modulus E' _{(50 ° C)} at _{50 ° C} (E' _{(120 ° C) ) / E '(50 ℃)} ) is preferably 0.25 to 1.00, more preferably 0.27 to 1.00. If the ratio (E' _{(120 ° C)} / E' _{(50 ° C)} ) is less than 0.25, the Young's modulus of the film cannot be maintained in the temperature region reached by the film when encountering heat from the cold cathode tube. The reflective film is bent. The nature of the thermoplastic polyester does not exceed 1.00. This ratio (E' _{(120 ° C)} / E' _{(50 ° C)} ) is 0.25 to 1.00, and good flatness can be maintained even by heat from a light source.

[Young's modulus]

The Young's modulus of at least one of the white films for a reflector of the present invention is preferably 3,000 MPa or more. If the Young's modulus is less than 3000 MPa, thermal bending occurs.

[heat shrinkage rate]

The heat shrinkage rate of the white film for a reflecting plate of the present invention at 85 ° C is preferably 0.5% or less, more preferably 0.4% or less, and most preferably 0.3% or less in both directions of the orthogonal direction. It is preferred to maintain the good planarity of the film when exposed to high temperatures by the heat shrinkage rate in this range.

The ratio of the highest peak temperature of the tangent tan δ, the storage elastic modulus E' _{(120 ° C)} to the storage elastic modulus E' _{(50 ° C)} at _{50 ° C} , the Young's modulus and the thermal shrinkage rate can be determined by the conditions described later. This is achieved by making a white film.

[additive]

The whitening film for the reflecting plate of the present invention can also be formulated with a fluorescent whitening agent. When the fluorescent whitening agent is blended, the thermoplastic polyester composition of the layer to be blended is, for example, 0.005 to 0.2% by weight, preferably 0.01 to 0.1% by weight, per 100% by weight. When the amount of the fluorescent whitening agent is less than 0.005% by weight, the reflectance in the wavelength region around 350 nm is insufficient, so that it lacks the meaning of addition, and if it exceeds 0.2% by weight, it is not preferable because it exhibits the characteristic color of the fluorescent whitening agent. . As the fluorescent whitening agent, for example, OB-1 (manufactured by Esterman Co., Ltd.), Uvitex-MD (manufactured by Ciba Geisy Co., Ltd.), and JP-Conc (manufactured by Nippon Chemical Industry Co., Ltd.) can be used.

Antioxidants, UV absorbers, slip agents, etc. may also be added as needed.

[Production method]

An example of a method of producing a white film for a reflecting plate of the present invention will be described below. Hereinafter, the glass transition temperature of the polymer is sometimes referred to as Tg, and the melting point is sometimes referred to as Tm. The mixing of the white inorganic particles with the thermoplastic polyester composition can be carried out during the polymerization of the thermoplastic polyester or after the polymerization. When the polymerization is carried out, it may be prepared before the end of the transesterification reaction or the esterification reaction, or may be prepared before the start of the polycondensation reaction.

After the polycondensation, it is added to the thermoplastic polyester after polymerization and melt-kneaded. At this time, masterbatch particles containing white inorganic particles at a relatively high concentration are prepared, and they are blended in a thermoplastic resin particle containing no white inorganic particles at a desired content ratio to obtain a thermoplastic polyester containing white inorganic particles. Composition.

The thermoplastic polyester used for the production of a white film for a reflector is preferably filtered using a non-woven filter having an average mesh opening of 10 to 100 μm composed of a stainless steel fine wire having a wire diameter of 15 μm or less. By performing this filtration, it is possible to suppress aggregation of particles which are usually aggregated into coarse aggregated particles, and it is possible to obtain a white film having a small amount of foreign matter. Further, the average mesh opening of the non-woven fabric is preferably from 20 to 50 μm, more preferably from 15 to 40 μm. The filtered thermoplastic polyester composition was extruded in a molten state by a simultaneous multi-layer extrusion method using a feed block in a multi-layered state to produce an unstretched laminated sheet.

The unstretched laminated sheet extruded from the die is cooled and solidified by a casting cylinder to form an unstretched laminated film. The unstretched laminated film is heated by roll heating, infrared heating or the like, and is extended in the longitudinal direction to obtain a longitudinally stretched laminated film. This extension is preferably carried out using more than two roll peripheral speed differences.

The extension is preferably carried out at a temperature above the Tg of the thermoplastic polyester. The stretching ratio in the longitudinal direction and the direction orthogonal to the longitudinal direction (hereinafter referred to as the lateral direction) are, for example, 2.5 to 5.0 times, preferably 2.5 to 4.3 times, more preferably 2.7 to 4.2 times. If it is less than 2.5 times, the film thickness is unstable, and a good film cannot be obtained. If it exceeds 5.0 times, cracking tends to occur in the film formation.

The longitudinally stretched laminated film is then subjected to lateral stretching, heat setting, and thermal relaxation treatment to form a laminated biaxially oriented film which can be carried out while moving the film. The pre-heat treatment of the transverse extension begins at a temperature higher than the Tg of the thermoplastic polyester. Therefore, it is preferred to carry out the temperature increase from (Tg + 5 ° C) to (Tg + 70 ° C). The temperature rise during the transverse stretching may be a continuous temperature increase or a stepwise (sequential) temperature increase, but usually a sequential temperature increase. For example, the transverse stretching region of the tenter is divided into a plurality of portions in the film moving direction, and the heating medium having a specific temperature is supplied to each region to raise the temperature. The lateral extension magnification is, for example, 3.5 to 5.0 times, preferably 3.7 to 4.8 times, more preferably 4.0 to 4.6 times. By extending this condition, the ratio of the highest peak temperature of the loss tangent tan δ of 110 ° C or more and the storage elastic modulus E' _{(120 ° C)} at _{120 °} C to the storage elastic modulus E' _{(50 ° C)} at _{50 ° C can} be obtained. (E' _{(120 ° C)} / E' _{(50 ° C)} ) is a film of 0.25 to 1.00, and the film does not break.

The film is held at both ends of the transversely stretched film, and heat treatment is performed at a temperature of (Tm-20 ° C) to (Tm - 100 ° C) at a fixed width or a width reduction of 10% or less to lower the heat shrinkage rate. If the heat treatment temperature is higher than (Tm-20 ° C), the planarity of the film is poor, and the thickness is unstable and the thickness is not good. If it is lower than (Tm - 100 ° C), the case where the heat shrinkage rate becomes large is not preferable.

Further, in order to adjust the amount of heat shrinkage, both ends of the film to be held can be cut off, and the drawing speed in the longitudinal direction of the film can be adjusted to relax in the longitudinal direction. As a means of relaxation, the speed of the roller group on the exit side of the tenter is adjusted. As for the ratio of relaxation, the film speed of the tenter is reduced by the speed of the roll group, preferably 0.1 to 2.5%, more preferably 0.2 to 2.3%, and most preferably 0.3 to 2.0%. Relaxation (this value is called "relaxation rate"), and the thermal contraction rate in the longitudinal direction is adjusted by controlling the relaxation rate. Further, in the transverse direction of the film, the width of both ends of the film is cut off to reduce the width, and the desired heat shrinkage ratio can be obtained.

Although the white film for a reflector of the present invention is formed by the above-described sequential biaxial stretching method, it may be formed by a simultaneous biaxial stretching method instead of the sequential biaxial stretching method. In this case, the stretching ratio is, for example, 2.7 to 4.3 times, preferably 2.8 to 4.2 times in the longitudinal direction and the lateral direction.

Example

The invention is described in detail below by way of examples. Further, each characteristic value was measured by the following method.

Further, PET means poly(ethylene terephthalate), and IPA means isophthalic acid.

(1) Light reflectance

The machine ball was mounted on a spectrophotometer (UV-3101PC manufactured by Shimadzu Corporation), and the light reflectance of the sample film at a wavelength of 550 nm was measured when the BaSO ₄ white plate was set to 100%.

(2) Brightness

The brightness of the display device when used as a reflector in a liquid crystal display device was evaluated. The backlight reflection film of the 32-inch TV (BRAVIN KDL-32V2500) manufactured by SONY was removed, and the sample film of the evaluation object was set, and the brightness meter (the model of MC-940 of Otsuka Electronics) was used, and the measurement was performed near the center of the backlight. The true face is measured at a distance of 500 mm.

(3) Average particle size of inorganic particles

The particle size distribution of the particles was determined by a particle size distribution meter (LA-950 manufactured by Horiba, Ltd.), and the particle diameter of d50 was defined as an average particle diameter.

(4) Punching energy measured by the drop impact test

It was implemented based on the DuPont impact test (JIS K5600-5-3, ISO6272). The sample film (30 mm × 30 mm) adjusted at 25 ° C and 50% RH was set on a support table, and a crucible (a cylindrical shape of 4 mm in diameter and a material SUS) was placed on the sample film. The scale (300 g load) was dropped from the appropriate position onto the core, and the sample film under the core was observed for cracking. The determination of whether or not the crack occurred was not only determined to be broken due to the extension of the sample film but also cracked, and only cracks were formed on the sample film. The drop height of the sample film before the rupture occurred was raised on a 1 cm scale, and a preliminary test before the sample film was broken was performed. When the sample film was broken, the drop height was lowered by 1 cm, and when the crack did not occur, the drop height was increased by 1 cm to perform the reverse operation. Each 50 sheets of the sample film were tested to determine the drop height at which half of the sample film broke. The drop height is multiplied by the load as the punching energy (J) obtained by the drop impact test.

(5) Pore volume ratio

From the polymer density of the light-reflecting layer and the density of the inorganic particles, and the ratio of the blending in the light-reflecting layer, the calculated density of the light-reflecting layer in the absence of voids in the light-reflecting layer is obtained. The density used for this calculation was 1.39 g/cm ³ for polyethylene terephthalate and 4.5 g/cm ³ for barium sulfate particles. On the other hand, the light reflection layer was separated only from the white film, and the weight per unit volume was calculated to determine the solid density of the light reflection layer. The pore volume ratio was calculated by the following formula.

Pore volume ratio (%) = (1 - solid density / calculated upper density without voids) × 100

(6) Thickness ratio of each layer

Using a S-4700 electric field emission type scanning electron microscope manufactured by Hitachi, Ltd., the film profile was observed at a magnification of 500 times, and the thickness ratio of each layer of the film was determined by measuring the average of 5 points.

(7) Film thickness

The film thickness was measured using a contact thickness meter (manufactured by ANRITSU, K-402B).

(8) Punching

Using the punching fixture CARL CP-5, the film was punched 50 times (the diameter of the circular hole was 6 mm, the punching speed was set to 50 times / 1 minute), and the end of the punching was observed by an optical microscope at a magnification of 25 times. Observe the presence or absence of whiskers and the presence or absence of burrs. Regarding the whisker, the punching hole of the whisker that has a length of 1 mm or more from the punching portion is set to "have occurred", and for the flashing edge, part or all of the punching portion is based on the film plane as a reference. The punching hole above the mm is set to "have occurred". Regarding each whisker and burr, the following formula calculates the occurrence ratio.

Occurrence ratio (%) = "has occurred" / 50

(9) Intrinsic viscosity

0.3 g of the thermoplastic polyester of each layer was peeled off from the white film, 25 ml of o-chlorophenol was added, dissolved at 100 ° C, dissolved, and then measured while cooling to 25 ° C. Further, the inorganic particles were dissolved in o-chlorophenol, and then centrifuged at 12,000 rpm for 30 minutes using a centrifugal separator (Hitachi Machinery Group CF-15RXII type) to thermally separate inorganic particles and o-chlorophenol. After the plastic polyester was separated, the intrinsic viscosity was measured and calculated. The intrinsic viscosity is obtained by the following conversion formula.

Intrinsic viscosity = measured value / [(100 - inorganic particle concentration) 100]

(10) Glass transition temperature (Tg), melting point (Tm)

The measurement was performed at a temperature increase rate of 20 m/min using a differential scanning calorimeter (TA Instruments 2100 DSC).

(11) Extensibility

It was observed whether or not the film was custom-made at the time of film formation in the examples, and evaluation was performed based on the following criteria. Further, the longitudinal direction is the continuous film forming direction of the film, and the lateral direction is the direction orthogonal thereto.

A: Custom film can be customized for more than 2 hours.

B: Custom film can be customized for more than 1 hour and less than 2 hours.

C: The cutting occurred in less than 1 hour, and the film could not be customized.

(12) Young's modulus

A test piece in which the film was cut into a width of 150 mm long by 10 mm was used, and a tenter UCT-100 manufactured by Orientic Co., Ltd. was used, and the room was adjusted to a temperature of 20 ° C and a humidity of 50%, and the stretching speed was 100 mm between the jigs. 10 mm/min, the jig speed was 500 mm/min, and the Young's modulus was calculated from the connection of the rising portion of the obtained load-elongation curve. In addition, the Young's modulus in the longitudinal direction is the direction in which the film longitudinal direction (MD direction) is the measurement direction, and the Young's modulus in the lateral direction is the measurement direction in the transverse direction (width direction) of the film. Each Young's modulus was measured 10 times, and the average value was used.

(13) Ratio of the highest peak temperature and storage elastic modulus of the loss tangent tan δ measured by dynamic viscoelasticity

Using the dynamic viscoelasticity measuring device, the highest peak temperature of the loss tangent tan δ was obtained by measuring the frequency of 11 Hz and the dynamic displacement of ±2.5×10 ^-4 cm, and the storage elastic modulus E' _{(120 ° C)} at 120 ° C was obtained. The ratio of the storage elastic modulus E' _{(50 ° C)} at _{50 ° C} indicates the ratio of storage elastic modulus (E' _{(120 ° C)} / E' _{(50 ° C)} ).

(14) Thermal bending

A direct-type backlight (65 吋) unit of a liquid crystal television (AQUOS-65V manufactured by SHARP) prepared for evaluation was taken out, and the originally assembled light-reflecting sheet was taken out, and a film sample to be measured was assembled. After inserting the power source and leaving it in an environment of a temperature of 40 ° C and a humidity of 50% for 24 hours, the sample for evaluation was taken out, and the sample for evaluation was spread on a flat plate having a particularly high plane precision, and the bent state of the film was evaluated. The determination is made based on the following criteria. Only A is judged to be tolerant of the use of the assembled backlight.

A: Almost no bending is seen.

B: I saw some bending

C: I saw a big bend.

Example 1

In a flask equipped with a rectification column and a distillation condenser, 132 parts by weight of dimethyl terephthalate and 18 parts by weight of dimethyl isophthalate (12% of all dicarboxylic acid components based on polyester) were placed. Mol%), 98 parts by weight of ethylene glycol, 1.0 part by weight of diethylene glycol, 0.05 parts by weight of manganese acetate, and 0.012 parts by weight of lithium acetate, and heated to 150 to 235 ° C while stirring to distill off methanol for transesterification. After distilling off methanol, 0.03 part by weight of trimethyl phosphate and 0.04 parts by weight of cerium oxide were added, and the reactant was transferred to a reactor. Subsequently, the inside of the reactor was gradually reduced to 0.5 mmHg while stirring, and the temperature was raised to 290 ° C to carry out a polycondensation reaction to obtain a thermoplastic polyester. Using the obtained thermoplastic polyester as the thermoplastic polyester of the support layer and the light-reflecting layer, a master batch of barium sulfate having an average particle diameter of 1.2 μm was produced, and the content of the thermoplastic polyester composition in the support layer was 4% by weight. The amount of addition was adjusted so that the content of the thermoplastic polyester composition in the light-reflecting layer was 55% by weight.

Using these raw materials, respectively, they are supplied to two extruders heated to 275 ° C, and the thermoplastic polyester composition of the support layer is made of a three-layer feed block device such as a support layer/light reflective layer/support layer. The thermoplastic polyester composition of the light-reflecting layer merges and maintains its laminated state to form a sheet shape from the nozzle. The thickness ratio of the discharge amount adjustment support layer/light reflection layer/support layer of each extruder was 4/92/4 after biaxial stretching. Further, the sheet was heated to a temperature of preheating 1 (73 ° C) and preheating 2 (77 ° C) shown in Table 1 by a cooling cylinder which was cooled and solidified by a cooling cylinder having a surface temperature of 23 ° C, in the longitudinal direction (longitudinal direction). It was extended at a stretching rate of 1000%/sec at 92 ° C at a magnification of 3.0 times, and cooled at a roll group of 25 ° C. Next, both ends of the film which was longitudinally stretched by a jig were simultaneously introduced into a tenter, preheated at 115 ° C, and extended in a direction perpendicular to the length (lateral direction) in an atmosphere heated to 125 ° C for 5 seconds at a magnification of 3.7 times. Then, it was heat-fixed in a tenter at a temperature of 195 ° C, and relaxed in the tenter at a relaxation rate of 2% in the longitudinal direction, and at a temperature of 145 ° C at a shrinkage rate of 2% in the transverse direction, and then cooled to A white film was obtained at room temperature. The resulting white film had a degree of 225 μm and a reflectance of 98.7%. The evaluation results are summarized in Table 3.

Example 2

In the first embodiment, the addition amount of the barium sulfate particles of the support layer and the light reflection layer was changed to 6% by weight and 60% by weight, respectively, and the average particle diameter (d50) of the barium sulfate particles was changed as described in Table 1, and Example 1 was also prepared as a white film. The evaluation results are summarized in Table 3.

Example 3

In the first embodiment, the dicarboxylic acid component and the dimethyl isophthalate are not used in the polyester polymerization stage of the support layer, and only the dimethyl terephthalate is used for polymerization to prepare the master batch of the barium sulfate. The white film was formed in the extension conditions shown in Table 2 in the ratio shown in Table 1. The evaluation results are summarized in Table 3.

Example 4

In the third embodiment, the rutile-type titanium oxide particles having an average particle diameter (d50) of 0.2 μm were changed to the support layer inorganic particles, and the barium sulfate particles having a mean particle diameter (d50) of 1.2 μm were used as the light-reflecting layer. Example 3 was also prepared as a white film. The evaluation results are summarized in Table 3.

Example 5~9

A white film was obtained in the same manner as in Example 1 except that the conditions described in Table 1 were changed. Further, in Example 9, a two-layer laminated film was produced, and both were evaluated from the side of the light-reflecting layer. The evaluation results are summarized in Table 3.

Comparative Example 1~7

A white film was obtained in the same manner as in Example 1 except that the conditions described in Table 1 were changed. Further, in Comparative Example 5, since the film forming property was extremely poor and the film was broken, the sample could not be obtained. The evaluation results are summarized in Table 3.

[Industry possible use]

The white film for a reflecting plate of the present invention can be preferably used for a reflective film of a liquid crystal display device.

Claims (11)

A white thermoplastic polyester film for a reflector, characterized by a light reflection layer having a pore volume ratio of 55 to 80% and a support layer of a biaxially stretched polyester film disposed on at least one side thereof, the light reflection layer The ratio of the total thickness to the thickness of the support layer is 92:8 to 98:2, the light reflectance of the film is 98.0% or more, and the punching energy obtained by the drop impact test is 0.10 to 0.30 J, and the film thickness is 150. ~250 μm; the light reflecting layer is composed of a thermoplastic polyester composition, and the thermoplastic polyester composition is composed of thermoplastic polyester, white inorganic particles, organic particles or non-compatible resin; the above support layer The biaxially stretched polyester film is composed of a thermoplastic polyester or a thermoplastic polyester composition, and the thermoplastic polyester composition is composed of thermoplastic polyester 99.9 to 90% by weight and white particles. It is composed of 0.1 to 10% by weight. A white thermoplastic polyester film for a reflector according to the first aspect of the invention, wherein the light-reflecting layer is composed of a composition of 40 to 48% by weight of thermoplastic polyester and 52 to 60% by weight. It is composed of white inorganic particles. For example, the white thermoplastic polyester film for the reflector of claim 2, wherein the thermoplastic resin of the light-reflecting layer has an intrinsic viscosity of 0.40 to 0.53 dl/g. A white thermoplastic polyester film for a reflector according to claim 2, wherein the thermoplastic polyester of the light-reflecting layer is isophthalic acid copolymerized polyethylene terephthalate. The white thermoplastic polyester film for a reflector according to the second aspect of the invention, wherein the white inorganic particles of the light-reflecting layer are composed of at least one selected from the group consisting of barium sulfate, titanium oxide, calcium carbonate and cerium oxide. Particles having an average particle diameter of 0.1 to 3.0 μm. A white thermoplastic polyester film for a reflector according to the first aspect of the invention, wherein the biaxially stretched polyester film of the support layer is composed of 99.9 to 90% by weight of thermoplastic polyester and 0.1 to 10% by weight of inorganic particles. Composition. The white thermoplastic polyester film for a reflector according to claim 6 of the patent application, wherein the thermoplastic polyester having a specific viscosity of 0.54 to 0.65 dl/g is determined for the support layer. A white thermoplastic polyester film for a reflecting plate according to the first aspect of the patent application, wherein the maximum peak temperature of the tangent tan δ of the film is 110 ° C or more. A white thermoplastic polyester film for a reflector according to the first aspect of the patent application, wherein the ratio of the storage elastic modulus E' _{(120 ° C) of the} film at 120 ° C to the storage elastic modulus E' _{(50 ° C)} at _{50 ° C} (E) ' _{(120 ° C)} / E' _{(50 ° C)} ) is 0.25 ~ 1.00. A white thermoplastic polyester film for a reflector according to the first aspect of the invention, wherein the Young's modulus of at least one direction of the film is 3,000 MPa or more. A white thermoplastic polyester film for a reflector according to the first aspect of the invention is a reflective film of a backlight unit of a liquid crystal display device.