TW201412837A - White reflective film - Google Patents

Abstract

The purpose of the present invention is to provide a white reflective film that has excellent optical properties as a reflective film and is capable of preventing LED deterioration even in the case where the film contains barium sulfate. The white reflective film according to the present invention is formed of a thermoplastic resin and contains barium sulfate, wherein the amount of zinc ion contained in the barium sulfate is 500 mass ppm or greater relative to the mass of the barium sulfate, and not greater than 3000 mass ppm relative to the mass of the thermoplastic resin.

Description

White reflective film

The present invention relates to a white reflective film. In particular, it relates to a white reflective film suitable for use in a light-emitting diode (LED) light source.

The backlight unit of the liquid crystal display device (LCD) is divided into a direct type of a light source and a reflector on the back surface of the liquid crystal display panel, and a light guide plate provided with a reflector on the back surface of the liquid crystal display panel, and the light guide plate is disposed The side is equipped with a side light type of light source. The backlight unit used in previous large LCDs has excellent brightness and uniformity of brightness in the picture, and is also in direct type (mainly direct type CCFL backlight, CCFL: cold cathode fluorescent tube / Cold Cathode) Fluorescent Lamp) is the mainstream. However, in recent years, in large LCDs such as televisions, the edge light type is the mainstream, and the light source is changed to an LED (light emitting diode) (edge light type LED backlight). In addition, an LED is provided for the backlight of the liquid crystal display panel, and a direct-type LED backlight having a reflector on the same plane or even the back surface of the LED is provided.

The lighting fixture is also used to raise the reflector for the amount of light that is emitted from the front. Moreover, the light source used for power saving also tends to the LED.

The white reflective film used as a reflector as described above is known so far It is a substance which uses barium sulfate (for example, patent documents 1-4).

Patent Document 1: JP-A-2006-212925

Patent Document 2: JP-A-2009-86451

Patent Document 3: JP-A-2009-126094

Patent Document 4: JP-A-2009-83369

Invention disclosure

The white reflective film using barium sulfate as shown in the above-mentioned patent documents is widely used as a reflector because it can achieve high reflectance and high brightness, and is easy to recover raw materials, and barium sulfate itself is a very stable substance.

However, in recent years, epoxy resin has been used as a sealing resin for LEDs instead of epoxy resin. In the process, the inventors have newly discovered that when a white reflective film and an LED using barium sulfate have been used at the same time, the LED is deteriorated due to the use conditions, and problems such as color change and brightness reduction occur.

Therefore, it is required to use a LED having a lower sealing performance as a white reflective film for a light source.

Against this background, an object of the present invention is to provide a white reflective film which has excellent optical properties as a reflective film and which suppresses deterioration of LED even if the film contains barium sulfate.

In the white reflective film using barium sulfate as exemplified in the above patent document, since the barium sulfate itself is a very stable substance as described above, the LED is not directly affected, and the LED is not deteriorated and is widely used.

However, the present inventors have found that LED degradation is affected by the reduction of the sealing performance of the LED, and is affected by the only hydrogen sulfide remaining in the film and barium sulfate. In other words, it is inferred that when the sealing resin of the LED is a resin having a low sealing property such as a polyoxyxylene resin, the sealing performance of the LED is lowered, and the impurity is allowed to penetrate into the resin of the LED having low sealing performance, thereby affecting the inside of the LED. The lead frame or the reflecting plate formed of a silver material or a silver plated material is used to deteriorate the color of the LED and the density is lowered.

As a result of intensive review by the present inventors, it has been found that by using a special barium sulfate which moderately reduces the occurrence of impurities of hydrogen sulfide, instead of the barium sulfate previously used, the hydrogen sulfide generated by the film can be reduced, and the deterioration of the LED can be suppressed. The invention has been achieved.

That is, the present invention employs the following structure.

A white reflective film which is a barium sulfate-containing film formed of a thermoplastic resin, wherein the amount of zinc ions in the barium sulfate is 500 ppm by mass or more based on the mass of barium sulfate, and the mass of the thermoplastic resin When it is a reference, it is 3000 mass ppm or less.

2. The white reflective film according to the above 1, wherein the thermoplastic resin is a polyester.

3. The white reflective film according to the above 1 or 2, wherein the barium sulfate is barium sulfate obtained by adding zinc sulfate to a sedimentary barium sulfate slurry obtained by reacting barium sulfide with sulfuric acid or a sulfate.

4. The white reflective film according to any one of the above 1 to 3, wherein a reflectance of a surface having a wavelength of 550 nm is 96% or more.

5. The white reflective film according to any one of the above 1 to 4, wherein The content of barium sulfate in the medium white reflective film is 1 to 50% by mass based on the mass of the white reflective film.

6. The white reflective film according to any one of the above 1 to 5, which is used as a light source of a light emitting diode.

A light-emitting diode light source backlight unit comprising the white reflective film according to the above 6th aspect.

A light-emitting diode light source lighting fixture comprising the white reflective film according to the above 6 aspect.

Best form for implementing the invention

The white reflective film of the present invention is a film containing barium sulfate formed of a thermoplastic resin.

[White reflective film]

The white reflective film of the present invention is a film formed of a thermoplastic resin and which exhibits a white color by a white coloring agent or a void-forming agent in the film. It contains barium sulfate for the void former. Further, barium sulfate may be used in combination with other coloring agents or void forming agents without hindering the object of the present invention. For example, inorganic particles other than barium sulfate for the void-forming agent, organic particles, or a resin which is incompatible with the thermoplastic resin constituting the film (hereinafter referred to as a non-compatible resin) can be used.

Further, the white reflective film of the present invention is a single layer film or a laminate film. From the viewpoint of obtaining high reflectance and high mechanical strength, it is preferred to have a layer containing a large number of voids (reflective layer), and to contain less or no voids. A laminated film of layers (support layer). When it is a laminated film, when the reflective layer is represented by A and the support layer is represented by B, it may be a double layer structure of A/B, a three-layer structure of A/B/A or B/A/B, or the like. A multilayer structure of at least one layer of the reflective layer and the support layer of four or more layers. Further, in the present invention, in the case of A/B or B/A/B, a single surface layer or a double surface layer is a structure of a support layer, and it is particularly preferable to further reduce the effect of reducing the amount of hydrogen sulfide.

(thermoplastic resin)

The thermoplastic resin constituting the white reflective film is, for example, polyester, polyolefin, polystyrene, or acrylic. From the viewpoint of obtaining a film having excellent mechanical properties and thermal stability, polyester is preferred.

When a polyester is used as the thermoplastic resin, the polyester to be used is preferably a polyester formed from a dicarboxylic acid component and a diol component. The dicarboxylic acid component is, for example, a component derived from terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid or sebacic acid. Further, the diol component is, for example, a component derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol or 1,6-hexanediol. Among these polyesters, aromatic polyesters are preferred, and polyethylene terephthalate is particularly preferred.

The polyester may be a homopolyester, but is preferably a copolymerized polyester. The copolymerized polyester is preferably a copolymerized polyethylene terephthalate. By using the copolymerized polyester, it is possible to ensure excellent film formability even if a large amount of voids are contained in order to increase reflectance and brightness. The white reflective film used is a laminated white film having a layer containing a large number of voids (reflective layer) and a layer containing less voids or voids (support layer), and is used in the case of containing more voids. The polyester of the shot layer is more effective in using a copolymerized polyester. The ratio of the copolymerization component is, for example, 1 to 20 mol%, preferably 3 to 15 mol%, more preferably 5 to 13 mol%, based on 100 mol% of the total dicarboxylic acid component. When the ratio of the copolymerization component is within this range, excellent film formability can be obtained even if a large number of voids are contained. Further, a film excellent in thermal stability can be obtained. Further, the copolymerization component may be the above-exemplified dicarboxylic acid component and diol component. A particularly preferred copolymerized polyester is a copolymerized polyethylene terephthalate with an isophthalic acid component.

(Barium sulfate)

In the present invention, in view of preventing color change and brightness reduction of the LED, it is important to reduce the occurrence of hydrogen sulfide impurities (sulfide impurities) in the barium sulfate contained in the film. Sulfide impurity at this time means that it is mainly hydrogen sulfide, which directly affects the deterioration of the LED, and, for example, a sulfide of hydrogen sulfide occurs due to a certain reaction of the environment, which indirectly affects the deterioration of the LED, and therefore also includes The thing.

Therefore, it is not preferable to use barium sulfate as a barium sulfate, and to use a specific barium sulfate which does not substantially contain hydrogen sulfide, or to assume that the barium sulfate is contained in the production, and it is also possible to use a zinc ion removing system. The present invention relates to a white reflective film which suppresses deterioration of LEDs by containing a specific amount of zinc ions in barium sulfate to remove hydrogen sulfide in barium sulfate. "Removal" at this time means that, in addition to removal to the system, the formation of other compounds disappears or decreases from the system.

The white reflective film of the present invention is composed of a thermoplastic resin. In the film having barium sulfate, the amount of zinc ions in the barium sulfate is 500 ppm by mass or more based on the mass of the barium sulfate, and is 3,000 ppm by mass or less based on the mass of the thermoplastic resin.

By using a barium sulfate having a zinc ion amount as described above, the white reflective film using the barium sulfate can suppress deterioration of the LED. Moreover, excellent optical characteristics can be obtained. When the amount of zinc ions is too large, deterioration of the LED can be suppressed, but the thermoplastic resin constituting the film, particularly the polyester resin, is deteriorated, so that the reflectance and the brightness are lowered, and the film forming property is lowered. Further, since an extremely small amount of hydrogen sulfide which is present in the original barium sulfate is excessively added, it is an unnecessary additive component. When the amount of zinc ions is too small, the reaction with hydrogen sulfide present in barium sulfate will be insufficient, and the residual impurities cannot be sufficiently removed. From the viewpoints of the above, the amount of zinc ions is preferably 600 ppm by mass or more, more preferably 700 ppm by mass or more, and most preferably 1000 ppm by mass or more based on the mass of barium sulfate. Further, when it is based on the mass of the thermoplastic resin, it is preferably 2,500 ppm by mass or less, more preferably 2,000 ppm by mass or less, still more preferably 1,500 ppm by mass or less. Further, the method for producing barium sulfate can achieve the above aspect by a method described later.

In the present invention, the average particle diameter of barium sulfate is preferably 3.0 μm or less, more preferably 2.5 μm or less, and still more preferably 2.0 μm or less. When the average particle diameter is too large, it tends to cause cracking, and tends to lower the reflectance. Further, the average particle diameter of barium sulfate is preferably 0.2 μm or more, more preferably 0.3 μm or more, and still more preferably 0.4 μm or more. When the average particle diameter is too small, the particles tend to aggregate, and it tends to boost the filter when the filter is filtered. The condensate itself is also the cause of the rupture. The shape of barium sulfate may be plate or spherical. The spherical shape refers to the particle size (long diameter / short diameter) is 1.3 or less.

The content of the barium sulfate is preferably from 1 to 50% by mass, more preferably from 2 to 45% by mass, based on the mass of the white reflective film, from the viewpoint of improving the reflectance and improving the film forming property. In particular, when it is whitened only by barium sulfate, it is preferably 20 to 50% by mass, more preferably 25 to 45% by mass. In the case of the above structure having a reflective layer and a support layer, the content of the reflective layer is preferably 31 to 70% by mass based on the mass of the reflective layer, and more preferably 35 to 65% by mass, more preferably 40%. 50% by mass, the content in the support layer is preferably from 0 to 30% by mass based on the mass of the support layer, more preferably from 1 to 15% by mass, still more preferably from 1 to 10% by mass. By adopting such a structure, both the reflectance and the film forming property can be simultaneously improved.

(Manufacturing method of barium sulfate)

Next, a method for producing barium sulfate which can be used in the present invention will be described.

The manufacturing method of barium sulfate for general industrial production is as follows. That is, after mixing the barite (the main component is barium sulfate) and coke, the barium sulfate is reduced by high-temperature baking in a rotary kiln to obtain a black calcined product having a main component of barium sulfide. After immersing in warm water to prepare an aqueous solution of barium sulfide, the resulting barium sulfate is filtered, washed, dried and pulverized by a solution of the reaction with an aqueous solution of sulfuric acid or a sulfate (preferably Na ₂ SO ₄ ). A method of obtaining powdered barium sulfate. The reaction of reducing the calcination of barium sulfate to obtain barium sulfide, and reacting the aqueous solution of barium sulfide with an aqueous solution of sulfuric acid to obtain barium sulfate are represented by the following formula (1) and the following formula (2).

BaSO ₄ +2C→BaS+2CO ₂ ...(1)

BaS+H ₂ SO ₄ →BaSO ₄ +H ₂ S...(2)

The barium sulfate obtained by the method of the above formula (2) is generally such that, as a result of the reaction, hydrogen sulfide is formed, and it is difficult to completely remove the gas in the form of a gas, and partial dissolution remains in the liquid. Therefore, the general barium sulfate obtained by the production methods represented by the above formulas (1) and (2) does not suppress the deterioration of the LED in accordance with the object of the present invention.

Therefore, in order to obtain barium sulfate which can be used in the present invention, it is necessary to reduce the amount of hydrogen sulfide by more than the amount which can be reduced by ordinary washing. For example, the method of the above formula (2) focuses on a method of re-washing the obtained barium sulfate valve in water again, or a special washing process using a multi-stage thickener for washing with a large amount of water. However, there are still restrictions on the production surface even if it is washed.

Therefore, in the present invention, it is preferred to use a reaction of the above formula (2) or a reaction of replacing an aqueous sulfuric acid solution with an aqueous solution of a sulfate such as sodium sulfate in the above formula (2) (for example, when sodium sulfate is used, the above formula (2) The H ₂ S on the right side is Na ₂ S, which is a barium sulfate obtained by adding zinc sulfate (ZnSO ₄ ) to the settled barium sulfate slurry obtained by reacting with water in the air to form H ₂ S. More specifically, the focus is on the addition of ZnSO ₄ to sodium hydroxide (NaOH) from the viewpoint of pH adjustment to the solution of the above formula (2), and the hydrogen sulfide mixed in the barium sulfate is converted into a stable salt. This structure is inferred as follows.

ZnSO ₄ +2NaOH→Zn(OH) ₂ +Na ₂ SO ₄

Zn(OH) ₂ →ZnO+H ₂ O

Secondly, with respect to the impurity H ₂ S present in barium sulfate, by

H ₂ S+ZnO→ZnS+H ₂ O This type converts hydrogen sulfide into a form of zinc sulfide-like salt, which is more easily removed by water washing and removes H ₂ S, and since zinc sulfide itself is a stable substance, it does not The re-ionization occurs to adversely affect the LED.

(colorant, void former)

When the coloring agent or the void forming agent which can be used together with barium sulfate is an inorganic particle other than barium sulfate, the inorganic particle is preferably white inorganic particle. The white inorganic particles are particles of titanium dioxide, cerium oxide or calcium carbonate. The average particle diameter of the inorganic particles is preferably from 0.2 to 3.0 μm, more preferably from 0.3 to 2.5 μm, still more preferably from 0.4 to 2.0 μm. Further, the content is preferably from 1 to 30% by mass, more preferably from 3 to 20% by mass, based on the mass of the white reflective film. When such inorganic particles are used in combination, a better reflectance is more easily achieved. Further, in a thermoplastic resin, a suitable dispersion state can be obtained, particle aggregation is less likely to occur, and a film which suppresses coarse protrusions can be obtained. At the same time, since the surface of the film is not excessively rough, the gloss can be controlled to an appropriate range. Further, the inorganic particles may be in any particle shape such as a plate shape or a spherical shape. Further, the inorganic particles can be subjected to surface treatment for improving dispersibility.

When the organic coloring agent is used as the coloring agent or the void forming agent to be used together, the organic particles used are resin particles which are incompatible with the thermoplastic resin constituting the film. The organic particles are preferably polyoxynoxide particles or polytetrafluoroethylene particles. The average particle diameter of the organic particles is preferably 0.2 to 10 μm, more preferably 0.3 to 8.0 μm, still more preferably 0.4 to 6.0 μm. Further, the content thereof is preferably from 1 to 30% by mass, more preferably from 3 to 3, based on the mass of the white reflective film. 20% by mass. When such organic particles are used, it is easier to achieve a better reflectance. Further, in a thermoplastic resin, a suitable dispersion state can be obtained, particle aggregation is less likely to occur, and a film which suppresses coarse protrusions can be obtained. At the same time, since the surface of the film is not excessively rough, the gloss can be controlled to an appropriate range. Also, the organic particles may be in any particle shape such as a plate shape or a spherical shape.

When the coloring agent or the void forming agent used is a non-compatible resin, and the thermoplastic resin constituting the film is a polyester, the non-compatible resin is preferably a polyolefin (including a cyclic polyolefin) or a polystyrene. Further, the content thereof is preferably from 1 to 30% by mass, more preferably from 3 to 20% by mass, based on the mass of the white reflective film. When such a non-compatible resin is used, a better reflectance is more easily achieved.

(membrane thickness)

The thickness of the white reflective film may be any, but it is preferably a thickness having an excellent reflectance. Further, from the viewpoint of handleability, it is preferred to have a moderate thickness. In addition, the view of lightweighting should not be too thick. The viewpoint is preferably 10 μm or more, more preferably 50 μm or more, and still more preferably 100 μm or more. Further, it is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 250 μm or less.

When the white reflective film has a reflective layer and a support layer, the thickness of each layer can be set after considering optical characteristics such as reflectance and elongation. When the reflective layer is thick, it tends to increase the reflectance and brightness, and when the support layer is thick, it tends to increase the elongation. In addition, when the support surface/double layer or the double surface layer is a support layer, such as the support layer/reflection layer or the support layer/reflection layer/support layer, the support layer may be further thickened. Highly suppresses the effect of LED degradation. From the viewpoint of the equalization, when the total thickness of the white reflective film is 100, the reflective layer (which is a total of the plurality of reflective layers) is preferably 40 to 95, more preferably 50 to 90. Further, it is preferable that the support layer (which is a total of the plurality of support layers) has a thickness ratio of 60 to 5, more preferably 50 to 10.

[Production method]

An example of a method of producing a white reflective film of the present invention will be described below. In this example, a white reflective film is a laminated white film. Further, the direction of the film forming machine shaft is referred to as the longitudinal direction or the longitudinal direction or MD. Further, the direction perpendicular to the film forming machine axis direction and the thickness direction is referred to as the lateral direction or the width direction or TD.

The polyester composition used for laminating a white film (a composition containing barium sulfate and other optional components in the polyester for a thermoplastic resin constituting the film) is preferably a stainless steel having a wire diameter of 15 μm or less in a molten state. The non-woven filter having an average pore diameter of 10 to 100 μm, preferably having an average pore diameter of 20 to 50 μm, is filtered. By carrying out this filtration, it is generally possible to suppress aggregation of particles which are easily aggregated to form coarse aggregated particles, and to obtain a laminated white film having less coarse foreign matter. Thus, a polyester composition for forming a reflective layer and a polyester composition for forming a support layer can be obtained.

Each of the polyester compositions after filtration was extruded from a die in a multilayer state by a multi-layer extrusion method using a feed device in a molten state to produce a laminated unstretched sheet.

The laminated unstretched sheet extruded by the die is cooled and solidified by a casting drum Forming a laminated unstretched film. After the laminated unstretched film is heated by roll heating, infrared heating, or the like, the longitudinally stretched film is laminated in the longitudinal direction. This extension is preferably carried out using a peripheral speed difference of two or more rolls. The longitudinal extension is preferably carried out at a temperature above the glass transition point (Tg) of the polyester. More preferably, it is a range of Tg or more and (Tg+70 ° C) or less. The stretching ratio in the longitudinal direction is preferably 2.2 to 4.0 times, more preferably 2.3 to 3.9 times. When it is less than 2.2 times, the film thickness tends to be uneven, and when it exceeds 4.0 times, it tends to cause cracking in film formation.

The laminated film after the longitudinal stretching is introduced into the tenter, and then the pre-heating, the transverse stretching, the heat fixing, and the heat relaxation treatment are sequentially performed to obtain the laminated biaxial alignment film, but the treatment is generally performed on the film walking. In progress. The lateral extension process begins with a temperature above Tg. The temperature rise during the transverse extension can be continuous or staged (sequential) but generally sequential. For example, after the lateral extension of the tenter is divided into plural directions along the traveling direction of the film, a heating medium of a certain temperature is caused to flow into each of the blocks to raise the temperature. The stretching ratio in the transverse direction is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times. When it is less than 2.5 times, the film thickness tends to be uneven, and when it exceeds 4.5 times, it tends to cause cracking in film formation. Further, in the case of the above-described lateral stretching ratio, an excellent effect of suppressing the deterioration of the LED can be obtained.

The transversely stretched film may be subjected to heat treatment at a temperature of (Tm - 100 ° C) to (Tm - 20 ° C) at a temperature of (Tm - 100 ° C) to (Tm - 20 ° C) to reduce the heat shrinkage. At this time, Tm represents the melting point of the polyester. When the heat treatment temperature is higher than (Tm - 20 ° C), the planarity and thickness uniformity of the film tend to be deteriorated. Below (Tm - 100) ° C tends to increase the heat shrinkage rate. Moreover, in order to adjust the amount of heat shrinkage, the film can be cut after the ends of the film are cut. The stretching speed in the longitudinal direction is to relax the longitudinal direction. The method of relaxation is to adjust the speed of the roller group on the exit side of the tenter. The ratio of the relaxation is that the deceleration of the roller group is performed by the film walking speed with respect to the tenter, preferably 0.1 to 2.5%, more preferably 0.2 to 2.3%, and particularly preferably 0.3 to 2.0% of the deceleration and relaxation ( This value is called "relaxation rate"), and the thermal contraction rate in the longitudinal direction is adjusted by controlling the relaxation rate. Further, the film is transversely deformed in the process of cutting both ends to obtain a desired heat shrinkage ratio.

[Characteristics of White Reflective Film] (Reflectivity)

The reflectance (reflectance at a wavelength of 550 nm) of the white reflective film of the present invention is preferably 96% or more, more preferably 97% or more, still more preferably 97.5% or more, and particularly preferably 98% or more. When the reflectance is in the above range and is used in a liquid crystal display device, a lighting fixture, or the like, high luminance and illumination can be obtained. The reflectance can be achieved, for example, by using the above-described white film, preferably in the form of particles of barium sulfate or other void-forming agent, in accordance with a preferred range of the present invention. Further, when the amount of zinc ions is too large, the reflectance tends to be lowered.

(brightness)

Brightness of the white reflective film of the present invention is preferably 5900cd / m ² or more, again 6000cd / m ² or more preferably, more preferably 6050cd / m ² or more, particularly preferably 6100cd / m ² or more. When the brightness is in the above range, when used in a liquid crystal display device, a lighting fixture, or the like, high brightness and illumination can be obtained. The brightness can be achieved, for example, by using the above-described white film, preferably in the form of particles of barium sulfate or other void-forming agent, in accordance with a preferred range of the present invention. Further, the coating layer is also an effective aspect of the present invention. Further, when the amount of zinc ions is too large, the brightness tends to decrease.

Example

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

(1) Reflectance

The integrating sphere was attached to a spectroscopic luminance meter (UV-3101PC manufactured by Shimadzu Corporation) or higher, and the reflectance at 100% of the BaSO ₄ whiteboard was measured at a wavelength of 550 nm, and this value was used as the reflectance.

Further, the measurement surface may be a surface on which the reflection surface is formed as a reflection plate. Embodiments of the invention are carried out in the following manner. That is, when the reflective layer is formed to form at least one surface layer, the surface on the side of the reflective layer is measured. In this case, it is determined to measure any surface.

(2) Average particle size of particles

Using an S-4700 electric field emission type scanning electron microscope manufactured by Hitachi, Ltd., 100 arbitrary particles were measured at a magnification of 5000 times to obtain an average particle diameter. Also, it is used as a circle area.

(3) Brightness

The edge-light type backlight unit (32 inches) of the liquid crystal television (BRAVIA EX7 manufactured by SONY Co., Ltd.) prepared for evaluation was used to remove the previously mounted light-reflecting sheet, and then the film sample to be measured was attached. At this time, the surface on the side of the reflectance was measured on the side of the light guide plate. Thereafter, the light-emitting surface of the backlight unit was divided into 4 blocks of 2 × 2, and the front luminance of each block after lighting for 1 hour was measured using BM-7 manufactured by Teppong Co., Ltd. The measurement angle was 1°, and the distance between the luminance meter and the smooth surface of the backlight unit was 50 cm. A simple average value of the brightness at four places in the plane of the light-emitting surface of the backlight unit is obtained as the brightness.

(4) Thickness of the layer

The film sample was cut into triangles, fixed in a landfill capsule, and then filled with an epoxy resin. Next, using a sheet cutter (ULTRACUT-S), a section of the film sample after the landfill is cut into a section parallel to the longitudinal direction, and then observed and photographed using an optical microscope, and the thickness ratio of each layer is measured from the photo, and the thickness of the entire film is measured. Calculate the thickness of each layer.

(5) Amount of zinc ion using ICP method

After 8 g of monobutyl sulfate was dispersed from the film, it was dispersed in 40 ml of a 0.5 N HCl solution, stirred by a stirrer for 30 minutes, centrifuged, and the amount of zinc ions was measured by an ICP method. The concentration of the mass relative to the barium sulfate and the concentration with respect to the mass of the thermoplastic resin were calculated from the obtained amount of zinc ions.

(6) Confirmation of the presence or absence of hydrogen sulfide in barium sulfate

The barium sulfate powder was weighed in a 250 ml Erlenmeyer flask, and after 2 g, 10 ml of dilute hydrochloric acid and water were added to make the liquid amount 100 ml, and then boiled for 10 minutes, and the lead acid paper was wetted by contact with the gas generated therebetween, and the acetic acid was visually evaluated. Whether the lead paper is black or not.

The thing in which the lead acetate paper is not blackened is considered to be substantially free of hydrogen sulfide (evaluation "none"), and the blackened lead acetate paper is considered to contain substantially hydrogen sulfide (evaluation "yes").

(7) Color change evaluation of silver paste (LED degradation evaluation)

A silver paste (manufactured by Fujikura Kasei Co., Ltd., conductive paste "Dade D-550"), which is opaque to the surface, was applied to a glass slide using commercially available bristles. One glass slide and five reflective films of 5 cm × 5 cm were placed in a 500 cc bottle, and the bottle mouth was covered with a polypropylene sheet, and then placed at 80 ° C and 80% RH for 48 hours. The surface of the silver paste after standing was observed, and evaluated in the form of discoloration (evaluation ○), slight discoloration (evaluation Δ), and confirmation of discoloration (evaluation ×). Further, the color phase (L*) of the placed silver paste was measured by a reflection method (C light source, viewing angle of 2°) using a color difference meter (SPECTRO PHOTOMETER "SE6000").

(8) LED color change evaluation (LED degradation evaluation)

In the state in which the film sample is prepared, the reflective sheet in the above (3) is assembled in a liquid crystal television (BRAVIA EX7 manufactured by SONY), and placed at 80 ° C and 80% RH for one week without a power supply. The color of the LED light source is confirmed as the number of LEDs that change color. Visually Look at the 50 LEDs assembled internally.

○: Confirm that the discoloration is 0~1

△: Confirm that the discoloration is 2~3

×: Confirm that the discoloration is 4 to 50

(9) Film filming evaluation

The film forming conditions (longitudinal stretching ratio 2.9 times and lateral stretching 3.6 times) described in the examples and the comparative examples were determined based on the following criteria.

○: film breakage was 2 times or less at the time of film formation for 10 hours

△: film breakage is 3 to 4 times during film formation for 10 hours

×: The film was broken more than 5 times during film formation for 10 hours.

[Example 1] (Manufacturing Example 1: Production of barium sulfate particles 1)

A sulfuric acid aqueous solution having a concentration of 1.1 mol/L and a temperature of 20 ° C was introduced into the reaction tank at a ratio of 700 L/hour, and a concentration of 120 g/L (0.71 mol/L) and a temperature of 50 ° C were added at a ratio of about 1200 L/hour. After the aqueous solution of barium sulfide was adjusted to have a barium sulfide concentration of 6 g/L (approximately 10% of barium sulfide concentration), the average reaction rate of the reaction to barium sulfide reached 93% with an average residence time of 0.2 seconds. The solution of the reaction vessel was di-differentiated, and the solution of the dimerized solution was heated to a temperature of 70 ° C, and then a 10 mass % Na ₂ SiO ₃ aqueous solution of 30% by mass in terms of SiO ₂ in terms of cerium sulfate was added. After adding hydrochloric acid to the obtained slurry to adjust the pH to 2, 0.25 mass% of ZnSO _{4 was} added to the barium sulfate, and the mixture was aged for 35 minutes, and the pH was adjusted to 7 by adding a 20 mass% aqueous sodium hydroxide solution, followed by aging for 35 minutes. After washing with a filter press and washing with water, the resulting residue was calcined at 800 ° C for 1 hour using a muffle furnace. After cooling, it was pulverized by a hammer mill, filtered again with a filter press, and then the resulting residue was calcined at 800 ° C for 30 minutes using a muffle furnace. After cooling, it was pulverized with a hammer mill to obtain barium sulfate. Particle 1.

The obtained barium sulfate particles 1 had an average particle diameter of 0.8 μm. Further, the impurities of the sulfide were evaluated by the above method, and as a result, they were substantially free of hydrogen sulfide.

(manufacturing polyester)

132 parts by mass of dimethyl terephthalate, 18 parts by mass of dimethyl isophthalate (12 mol% based on the total acid component of the polyester), 96 parts by mass of ethylene glycol, and diethylene glycol 3.0 A mass fraction, 0.05 parts by mass of manganese acetate, and 0.012 parts by mass of lithium acetate were placed in a flask equipped with a rectification column and a distillation condenser, and heated to 150 to 235 ° C with stirring to distill off methanol to carry out a transesterification reaction. After distilling off methanol, 0.03 parts by mass of trimethyl phosphate and 0.04 parts by mass of cerium oxide were added, and the reactant was transferred to a reactor. Next, 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 copolymerized polyester.

(manufacturing film)

In the layer A, the copolymerized polyester was used, and the barium sulfate particles 1 obtained in the above Production Example 1 were added in the amounts shown in Table 1 to form a layer A polymer. Also, this layer A is a reflective layer. Another layer B is the same as the above-mentioned copolymerized polyester. The barium sulfate particles 1 obtained in the above Production Example 1 were added in the amounts shown in Table 1 to form a layer B polymer. Also, the layer B is a support layer.

Each of them was supplied to two extruders heated to 280 ° C, and the layer A polymer, the layer A and the layer B were A/B, and the thickness ratio shown in Table 1 was used to make the layer A polymer, The layer B polymer is combined and formed into a sheet shape by a die while maintaining the laminated state. Further, the sheet was cooled and solidified to a non-stretched film by a cooling drum having a surface temperature of 25 ° C, and then the temperature was 90 ° C at a magnification of 2.9 times to extend the longitudinal direction, and then cooled at 25 ° C. Next, the clips were fixed at both ends of the film while being introduced into the tenter to preheat in the preheating zone, and at the same time, in the environment heated to 120 ° C, the transverse direction was extended by 3.6 times. Thereafter, the film was thermally fixed at a temperature of 200 ° C in a tenter, and then relaxed in the longitudinal direction by 1.5% and in the transverse direction by 2%. After cooling to room temperature, a biaxially stretched polyester film (white reflective film) was obtained. ). The evaluation results of the obtained white reflective film are shown in Table 2.

[Embodiment 2] (Production Example 2: Production of barium sulfate particles 2)

The barium sulfate particles 2 were produced in the same manner as in the production example 1, in which the amount of addition of ZnSO _{4 to} barium sulfate was changed to 0.15% by mass. The obtained barium sulfate particles 2 had an average particle diameter of 0.8 μm. Further, the impurities of the sulfide were evaluated by the above method, and as a result, they were substantially free of hydrogen sulfide.

(manufacturing film)

The barium sulfate of the layer A and the layer B is obtained by using the above Production Example 2. A white reflective film was obtained in the same manner as in Example 1 except for the barium sulfate particles 2. The evaluation results are shown in Table 2.

[Example 3] (Production Example 3: Production of barium sulfate particles 3)

The barium sulfate particles 3 were produced in the same manner as in the production example 1, except that the amount of addition of ZnSO _{4 to} barium sulfate was changed to 0.45 mass%. The obtained barium sulfate particles 3 had an average particle diameter of 0.8 μm. Further, the impurities of the sulfide were evaluated by the above method, and as a result, they were substantially free of hydrogen sulfide.

(manufacturing film)

A white reflective film was obtained in the same manner as in Example 1 except that the barium sulfate particles of the layer A and the layer B were used. The evaluation results are shown in Table 2.

[Example 4] (manufacturing film)

A white reflective film was obtained in the same manner as in Example 2 except that the layer structure of the film was as shown in Table 1 as B/A/B. The evaluation results are shown in Table 2.

[Comparative Example 1] (Production Example 4: Production of barium sulfate particles 4)

In the production example 1 described above, the solution of the dimerization of the solution with respect to the reaction vessel was carried out in the same manner as in Production Example 1 except that ZnSO _{4 was} not added, and the barium sulfate particles 4 were obtained. The obtained barium sulfate particles 4 had an average particle diameter of 0.8 μm. Further, the impurity of the sulfide was evaluated by the above method, and as a result, it contained substantially hydrogen sulfide.

(manufacturing film)

A white reflective film was obtained in the same manner as in Example 1 except that the barium sulfate particles of the layer A and the layer B were used. The evaluation results are shown in Table 2.

[Comparative Example 2] (Production Example 5: Production of barium sulfate particles 5)

The barium sulfate particles 5 were produced in the same manner as in the production example 1, except that the amount of addition of ZnSO _{4 to} barium sulfate was changed to 1.0% by mass. The obtained barium sulfate particles 5 had an average particle diameter of 0.8 μm. Further, the impurities of the sulfide were evaluated by the above method, and as a result, they were substantially free of hydrogen sulfide.

(manufacturing film)

A white reflective film was obtained in the same manner as in Example 1 except that the barium sulfate particles of the layer A and the layer B were used. The evaluation results are shown in Table 2, but the amount of zinc ions was large. Since the polyester is deteriorated, the film forming property is poor, and it is difficult to take a film sample. Further, in Comparative Example 2, the amount of zinc ions relative to the mass of barium sulfate was estimated to be 8,000 to 9000 ppm by mass. Further, the amount of zinc ions relative to the mass of the thermoplastic resin is estimated to be 4,800 to 5,500 ppm.

[Comparative Example 3] (Production Example 6: Production of barium sulfate particles 6)

The barium sulfate particles 6 were produced in the same manner as in the production example 1, except that the amount of addition of ZnSO _{4 to} barium sulfate was changed to 0.65 mass%. The obtained barium sulfate particles 6 had an average particle diameter of 0.8 μm. Further, the impurities of the sulfide were evaluated by the above method, and as a result, they were substantially free of hydrogen sulfide.

(manufacturing film)

A white reflective film was obtained in the same manner as in Example 1 except that the barium sulfate particles 6 obtained in the above Production Example 6 were used as the barium sulfate of the layer A and the layer B. The detailed results are shown in Table 2. However, since the amount of zinc ions is large, the polyester is deteriorated somewhat, so that the film forming property is deteriorated a little, and the hue of the film is affected, and the reflectance and the brightness tend to be slightly deteriorated.

[Comparative Example 4]

A white reflective film was obtained in the same manner as in Example 1 except that the barium sulfate of the layer A and the layer B was a precipitated barium sulfate "B-54" (a readily dispersible material for plastics) manufactured by Nippon Chemical Industry Co., Ltd., and an average particle diameter of 1.2 μm. . The evaluation results are shown in Table 2.

Further, the impurities of the sulfide of barium sulfate used at this time were evaluated by the above method, and as a result, the substance containing hydrogen sulfide was substantially contained.

[Comparative Example 5]

A white reflective film was obtained in the same manner as in Comparative Example 4 except that the layer structure of the film was as shown in Table 1 as B/A/B. The evaluation results are shown in Table 2.

In Table 1, PET represents a polyethylene terephthalate component, and IPA represents an isophthalic acid component.

Effect of invention

The present invention can provide a white reflective film which has excellent optical properties as a reflective film and which suppresses deterioration of the LED even if the film contains barium sulfate.

Since the white reflective film of the present invention has the above-described functions, it is possible to obtain an effect that LED degradation is less likely to occur even when used together with an LED light source. Therefore, when the white reflective film of the present invention is used as a reflector for a backlight unit (LED light source backlight unit) including an LED light source, it is possible to form a backlight unit that suppresses deterioration of the LED of the light source and is less likely to cause a decrease in brightness and color. Therefore, the liquid crystal display device provided with the backlight unit can also obtain an effect of suppressing brightness reduction and color change. Moreover, when the white reflective film of the present invention is used as a reflector for a lighting fixture (LED light source lighting fixture) including an LED light source, it is possible to form an illumination that suppresses deterioration of the LED of the light source and which is less likely to cause a decrease in brightness, a decrease in illumination, and a change in color. appliance.

Industrial use possibility

The white reflective film of the present invention is suitably used as a white reflective film for a reflector such as a liquid crystal display device or a lighting fixture. In particular, it is suitable for a backlight unit including an LED light source, a reflector for using a liquid crystal display device or the like, and a white reflective film for an LED light source.

Claims (8)

A white reflective film which is a film containing barium sulfate formed of a thermoplastic resin, and the amount of zinc ions in the barium sulfate is 500 ppm by mass or more based on the mass of the barium sulfate, based on the mass of the thermoplastic resin. It is 3000 mass ppm or less. The white reflective film of claim 1, wherein the thermoplastic resin is a polyester. The white reflective film of claim 1 or 2, wherein the barium sulfate is barium sulfate obtained by adding zinc sulfate to the settled barium sulfate slurry obtained by reacting barium sulfate with sulfuric acid or sulfate. The white reflective film according to any one of claims 1 to 3, wherein a reflectance of a surface having a wavelength of 550 nm is 96% or more. The white reflective film according to any one of claims 1 to 4, wherein the content of barium sulfate in the white reflective film is from 1 to 50% by mass based on the mass of the white reflective film. A white reflective film according to any one of claims 1 to 5, which is used as a light source for a light emitting diode. An LED light source backlight unit having a white reflective film as claimed in claim 6. An LED light source lighting fixture having a white reflective film as claimed in claim 6.