JP5262715B2 - White reflective film - Google Patents

Description

  The present invention relates to a white reflective film for improving the brightness of a liquid crystal backlight, and more specifically, a reflection plate for edge light type and direct type liquid crystal backlights for liquid crystal displays, and an edge light type liquid crystal backlight. The present invention relates to a white reflector film suitably used for a lamp reflector and further a solar cell backsheet.

  Backlights that illuminate liquid crystal cells are used in liquid crystal displays. Depending on the type of liquid crystal display, an edgelight type backlight is used for liquid crystal monitors, and a direct type backlight is used for liquid crystal televisions. As these reflective films for a backlight, a porous white film formed of bubbles is generally used (Patent Document 1). Furthermore, in order to prevent yellow discoloration of the film due to ultraviolet rays radiated from the cold cathode tube, a white film in which an ultraviolet absorbing layer is laminated has been proposed (Patent Documents 2 and 3).

  The basic structure of the direct type backlight is characterized by a structure in which fluorescent tubes are arranged directly behind the screen without using a light guide plate. By arranging several linear or partially linear lamps in parallel at the back of the screen, it is possible to cope with a large screen and to secure sufficient brightness. However, uneven brightness (brightness unevenness) occurs in the screen due to a lamp installed behind the screen, which is also a feature. In other words, the light above the lamps arranged in a row is bright and the space between adjacent lamps is dark. For this reason, in the direct type backlight, in order to eliminate this luminance unevenness, a light diffusing plate (milky white plate) having extremely strong light diffusibility is installed on the upper side of the fluorescent tube to make the screen uniform. The light diffusion plate is a plate having a thickness of about 2 mm made of an acrylic resin or a polycarbonate resin in which fine particles are dispersed. This light diffusing plate eliminates uneven brightness and makes the screen uniform, but because it diffuses strongly, the total light transmittance is low and the light utilization efficiency deteriorates. As a result, the required front brightness is insufficient. Therefore, on the light diffusing plate, while diffusing light isotropically, a diffusing sheet that exhibits a condensing effect in the front direction, a condensing sheet represented by a prism sheet for improving the condensing property, and a liquid crystal Since the brightness on the panel is insufficient, a brightness enhancement sheet for improving the brightness on the liquid crystal panel is incorporated.

A method of improving luminance unevenness in the backlight by controlling the diffusibility of the film surface on the light source side in the reflection sheet in the direct type backlight is also disclosed (Patent Document 4). The light-resistant particle production method and its application are mainly disclosed for use in a diffuser plate used in a direct type backlight, and some examples of use for coating are also disclosed. (Patent Documents 5 and 6)
JP-A-8-262208 JP 2001-166295 A JP 2002-90515 A JP 2005-173546 A JP 2003-12733 A JP 2006-267592 A

  In the reflective film for liquid crystal televisions, while cost reduction is strongly demanded, improvement in light resistance and reflectance of the reflective film is also demanded at the same time as compared with the conventional film. With respect to light resistance, there is a problem that the number of cold cathode fluorescent lamps increases with an increase in the size of a liquid crystal television and yellowing due to an increase in the amount of ultraviolet rays becomes remarkable. Usually, the coating layer of the white reflective film is composed of a resin binder and particles, and usually only the binder has light resistance. Another reason for selection is that particles having no light resistance are more economical.

  Recently, in order to reduce the total cost of the backlight, it has been practiced to compensate for the reduced brightness by reducing the number of expensive prism sheets and the number of lamps by increasing the brightness of each lamp. . In addition to the increase in lamp spacing due to the change in the configuration of these backlights, the brightness of the lamp has been increased, so that the brightness of the optical sheet configuration (light diffusing plate and reflective film) used so far is high. The problem that the unevenness cannot be resolved is becoming prominent.

  In order to eliminate these uneven brightness, a relatively large amount of light diffusing fine particles is added to the coating layer of the reflective film. However, if there are too many fine particles in the coating layer, the contact area with the surface layer of the white film is reduced, and there is a problem that the adhesion between the white film and the coating layer is poor. Furthermore, since the fine particles themselves generally do not have the ability to absorb ultraviolet rays, if the diffuse reflection performance is improved by adding a large amount of fine particles, the light resistance of the coating layer is lowered accordingly.

  Unlike the above-described conventional methods, the present invention improves the light resistance of the coating layer of the white reflective film used for the backlight by devising the coating layer on the light source side of the white film. More preferably, the diffuse reflection property and adhesion of the coating layer of the white reflective film are also improved.

The present invention employs the following means in order to solve such problems. That is, a white reflective film having a particle coating layer containing an ultraviolet absorber and / or a light stabilizer on at least one surface of the white film, the spherical particle content of the entire coating layer being 65 to 85% by weight. There is .

Further, a preferred embodiment of the white reflective film of the present invention is
( 1 ) The absolute value of the refractive index difference between the spherical particles forming the coating layer and the binder resin is less than 0.10.
( 2 ) The coefficient of variation CV of the spherical particles is 20% or more.
( 3 ) The ultraviolet absorber contained in the spherical particles is selected from the group consisting of benzotriazole series, benzophenone series, oxalic acid anilide series, cyanoacrylate series, triazine series, titanium oxide, zinc oxide, zirconium oxide, and cerium oxide. And at least one ultraviolet absorber.
( 4 ) The light stabilizer contained in the spherical particles is a hindered amine light stabilizer.
( 5 ) The spherical particles are obtained by copolymerizing the ultraviolet absorber and / or the light stabilizer.
( 6 ) The spherical particles are composed of at least one selected from the group consisting of an acrylic copolymer, a polystyrene copolymer, and a copolymer composed of an acrylic vinyl monomer and a styrene vinyl monomer.

  Further, the present invention is a lamp reflector for a liquid crystal backlight provided with the white reflective film of the present invention with the coating layer surface facing the light source side, and the white reflective film of the present invention is directed with the coating layer surface facing the light source side. This is a direct-type liquid crystal backlight.

  According to the present invention, by using a white reflective film in which a specific coating layer is provided on at least one surface of a white film, when used in a backlight, a backlight with less luminance deterioration due to long-term use than before can be provided. . Furthermore, according to a preferred aspect of the present invention, it is possible to provide a backlight with less luminance unevenness and improved luminance than before.

It is a figure which shows typically the backlight for evaluation used for the brightness nonuniformity measurement.

Explanation of symbols

1 Fluorescent tube 2 Center luminance measurement position (black circle)
3 Brightness measurement line (thick dotted line)

  The present invention has been intensively studied on the above-mentioned problem, that is, a white reflective film in which the luminance reduction due to long-term use is less than conventional by devising the coating layer on the light source side of the white film. As a result, when a coating layer containing spherical particles having an ultraviolet absorber and / or a light stabilizer was applied to at least one surface of the white film, the effect of improving the light resistance of the coating layer could be confirmed. It was clarified to solve the problem.

  The white reflective film of the present invention is obtained by laminating a coating layer containing spherical particles having an ultraviolet absorber and / or a light stabilizer on at least one side of a white film. Here, “spherical” does not necessarily mean only a true sphere, but a particle whose cross-sectional shape is surrounded by a curved surface such as a circle, an ellipse, a substantially circle, or a substantially ellipse.

  Particles containing an ultraviolet absorber and / or a light stabilizer according to the present invention are partially disclosed in Patent Document 6, and are acrylic resin particles, silicone resin particles, nylon, which are general organic spherical particles. Reaction when UV absorbers and / or light stabilizers are added to resin particles, styrene resin particles, polyethylene resin particles, benzoguanamine resin particles, urethane resin particles, etc., or when these resins are produced May be chemically bonded by copolymerization with an ultraviolet absorber and / or a light stabilizer having an ionic double bond. In view of less bleeding out from the spherical particles, it is preferable to fix the ultraviolet absorber and / or the light stabilizer by chemical bonding as in the latter case.

  The ultraviolet absorbers and light stabilizers contained in the spherical particles are roughly classified into inorganic and organic types. As inorganic ultraviolet absorbers, titanium oxide, zinc oxide, zirconium oxide, cerium oxide, and the like are generally known, and zinc oxide is most preferable in terms of economy, ultraviolet absorption, and photocatalytic activity. Examples of the organic ultraviolet absorber include benzotriazole, benzophenone, oxalic anilide, cyanoacrylate, and triazine. These ultraviolet absorbers may be used alone or in combination of two or more. Since these ultraviolet absorbers only absorb ultraviolet rays and cannot capture organic radicals generated by ultraviolet irradiation, the white film as a base material may be deteriorated in a chain by these radicals. In order to capture these radicals and the like, it is preferable to use a light stabilizer in combination, and among them, a hindered amine compound is preferably used.

  Here, as the copolymerization monomer for fixing the ultraviolet absorber and / or the light stabilizer, vinyl monomers such as acrylic and styrene are highly versatile and economically preferable. Since the styrene vinyl monomer has an aromatic ring and is easily yellowed, copolymerization with an acrylic vinyl monomer is most preferable in terms of light resistance.

  As an ultraviolet absorber benzotriazole substituted with a reactive vinyl monomer, 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole (trade name: RUVA-93); Otsuka Chemical In addition, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine (in which a reactive vinyl monomer is substituted for the hindered amine compound of the light stabilizer) can be used. "ADK STAB LA-82"; manufactured by ADEKA Corporation) can be used.

  The acrylic vinyl monomer is not particularly limited, and may be an acrylic monomer or a methacrylic monomer. Examples include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (Meth) acrylate having a linear alkyl group such as (meth) acrylate, n-octyl (meth) acrylate, n-nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, styryl (meth) acrylate Acrylate; Branching such as iso-propyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate and t-butyl (meth) acrylate (Meth) acrylic acid alkyl ester having an alkyl group; isobornyl (meth) a (Meth) acrylates having alkyl groups such as (meth) acrylic acid alkyl esters having cyclic alkyl groups such as acrylate and cyclohexyl (meth) acrylate; (meth) acrylic acid-2-hydroxyethyl, (meth) acrylic acid Hydroxyl groups such as hydroxyl group-containing vinyl compounds such as 2-hydroxypropyl, monoesters of (meth) acrylic acid and polypropylene glycol or polyethylene glycol and adducts of lactones and 2-hydroxyethyl (meth) acrylate Containing compounds; (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid and fumaric acid and other carboxyl group-containing (meth) acrylic monomers; N, N-dimethylaminoethyl (meth) acrylate and other amino group containing (meta ) Acrylic monomers and (meth) acrylic Amides, containing amide groups, such as N- methylacrylamide (meth) acryl-based monomer.

  The spherical particles according to the present invention are preferably resin particles made of a copolymer of the vinyl monomer as described above, a specific hindered amine polymerizable compound, and a specific benzotriazole polymerizable compound. It is preferable that this copolymer has a crosslinked structure. Without a cross-linked structure, when a spherical paint and a binder resin are mixed in a solvent to prepare a coating paint, the spherical particles begin to dissolve in the solvent, and the particle shape and particle size may change.

  In order to form a crosslinked structure, it is preferable to form a crosslinked structure using a vinyl compound having a plurality of functional groups in one molecule, and in the present invention, in particular, a vinyl compound having a plurality of functional groups in one molecule. As such, a polyfunctional acrylic compound such as a bifunctional acrylic compound, a trifunctional acrylic compound, or a tetrafunctional or higher polymerizable acrylic compound can be used.

In the white reflective film of the present invention, the average number of particles satisfying “R> H” per 100H square viewed from the surface of the coating layer is 10 or more when the thickness of the coating layer is H and the particle size of the spherical particles is R. If it is, since the brightness | luminance at the time of incorporating in a backlight improves, it is preferable. More preferably, it is 50 or more, more preferably 100 or more, and particularly preferably 300 or more. If the reflectance of the white reflective film is improved, the luminance as a backlight is improved, and the expensive sheet used on the upper part of the light source can be reduced. For example, as an example of the configuration of a backlight for a liquid crystal television, from the light source side to the light source side, a diffusion plate (thickness of about 2 mm) / diffusion film (thickness of about 200 μm to 300 μm) / diffusion film (thickness of about 200 μm to 300 μm) / diffusion film ( If the brightness of the entire backlight is improved by 2 to 3%, one diffusion film can be reduced in the above configuration. The method for obtaining the “coating layer thickness H” and the “spherical particle size R” will be described later.

  The content of the spherical particles in the coating layer according to the present invention is not particularly limited as long as an improvement in reflectance is obtained, but it is preferably 5% by weight or more, more preferably 10% by weight with respect to the entire coating layer. Above, particularly preferably 15% by weight or more. When the content of the spherical particles is less than 5% by weight, the effect of improving the reflectance may not be obtained. Moreover, although an upper limit is not specifically limited, If it exceeds 300 weight part with respect to 100 weight part of components other than the spherical particle in a coating layer, ie, 75 weight% of the whole coating layer, it may be inferior to coating property. The amount is preferably 300 parts by weight or less, that is, 75% by weight or less of the entire coating layer, based on 100 parts by weight of components other than the spherical particles in the coating layer.

  Furthermore, the content of the spherical particles in the coating layer according to the present invention is 50 to 85% by weight with respect to the entire coating layer from the viewpoint of improving diffuse reflection, light resistance, and adhesion with a white film. It is preferably 5 to 80% by weight, particularly preferably 65 to 75% by weight. When the content of the spherical particles is less than 50% by weight, the diffuse reflectance may be insufficient. In addition, when the content of spherical particles is more than 85% by weight, the diffuse reflectance is good and the luminance unevenness when incorporated in the backlight is improved, while the coating film strength is weak and the adhesion to the white film is low. May decrease.

  Although the thickness H of the coating layer concerning this invention is not specifically limited, 0.5-15 micrometers is preferable, More preferably, it is 1-10 micrometers, Most preferably, it is 1-5 micrometers. If the thickness H is less than 0.5 μm, the light resistance of the coating layer may be insufficient. On the other hand, if the thickness H exceeds 15 μm, the luminance when incorporated in the backlight may decrease, which is not preferable from the viewpoint of economy.

  The white reflective film of the present invention has an absolute value of the refractive index difference between the binder resin forming the coating layer and the spherical particles (hereinafter, the absolute value of the refractive index difference is referred to as “refractive index difference”). Preferably it is less than 10. If the refractive index difference is less than 0.10, it is considered that the loss of light that does not propagate to the front decreases as a result of repeated reflection and diffusion at the interface between the binder resin and the spherical particles. That is, the internal diffusion light loss in the coating layer is reduced, and the amount of light reaching the coating layer surface is relatively increased. As a result, when the white reflective film of the present invention is incorporated in a backlight, an effect of improving luminance can be further obtained. The difference in refractive index is more preferably 0.05 or less, and particularly preferably 0.00.

  Here, the refractive index is a ratio of changing the angle of the traveling direction at the boundary between media having different waves traveling straight, and is a value specific to a substance based on a vacuum, that is, an absolute refractive index. Further, since the refractive index is a value specific to the observation wavelength, the refractive index difference is a difference between values measured at the same observation wavelength. For example, for light with a wavelength of 589.3 nm, the refractive index of polymethyl methacrylate, which is a typical acrylic resin, is 1.49.

  The spherical particles according to the present invention preferably have a coefficient of variation CV of 20% or more, more preferably 25% or more, and most preferably 30% or more. If the CV is less than 20%, the uniformity of the particles is good, so that the light diffusibility becomes weak, and the effect of improving luminance unevenness when incorporated in a backlight may not be obtained. In addition, monodisperse particles having a small CV value are generally expensive and economically undesirable. Here, the coefficient of variation CV is a value obtained by dividing the standard deviation of the particle diameter by the average particle diameter. This variation coefficient CV is measured by, for example, the method described in the examples described later.

  The surface roughness Ra of the coating layer according to the present invention is preferably 400 nm or more, more preferably 450 nm or more, and most preferably 500 nm or more. The surface roughness (Ra) according to the present invention is determined by using a two-dimensional surface roughness meter SE-3400 (manufactured by Kosaka Laboratory Co., Ltd.) according to JIS B-0601 (1982). The value measured at 25 mm. If it is less than 400 nm, there may be a squeaking noise with a light diffusing plate that is a member in contact with the coating layer in the backlight, a lamp holder that fixes the lamp, or the like. Moreover, although an upper limit is not specifically limited, If it exceeds 1000 nm, there is a possibility of dropping off of particles.

  The white film of the base material according to the present invention is better if the visible light reflectance is high. For this purpose, a white film containing bubbles inside is used. Although these white films are not limited, porous unstretched or biaxially stretched polypropylene films and porous unstretched or stretched polyethylene terephthalate films are preferably used as examples. About these manufacturing methods etc., [0034]-[0057] of JP-A-8-262208, [0007]-[0018] of JP-A-2002-90515, [0008]-[0034] of JP-A-2002-138150, etc. It is disclosed in detail. Among them, the porous white biaxially stretched polyethylene terephthalate film disclosed in JP-A-2002-90515 is particularly preferable as the white film according to the present invention for the reasons described above.

  The structure of the white film of the base material according to the present invention may be appropriately selected depending on the intended use and required characteristics, and is not particularly limited, but is not limited to a single layer and / or 2 having a structure of at least one layer. A composite film having more than one layer is preferable, and it is preferable that at least one layer thereof contains bubbles and / or inorganic particles. It is preferable to contain inorganic particles in terms of the diffuse reflectivity of the white film of the substrate.

  An example of a single layer configuration (= 1 layer) is, for example, a white film having only a single A layer, and includes a configuration in which inorganic particles and / or bubbles are contained in the A layer. The content of is preferably 2% by weight or more, more preferably 7% by weight or more, and most preferably 10% by weight or more based on the total weight of the white film. An example of a two-layer structure is a white film having a two-layer structure of A layer / B layer in which a B layer is laminated on the A layer, and at least one of these A and B layers contains inorganic particles. And / or a composition containing bubbles, and the content of the inorganic particles is preferably 2% by weight or more based on the total weight of the white film, that is, the total weight of the two layers, more preferably It is 7% by weight or more, most preferably 30% by weight or more. Further, as an example of a three-layer structure, a white film having a three-layer laminated structure in which three layers of A layer / B layer / A layer and / or A layer / B layer / C layer are laminated as described above. In addition, at least one layer of each layer includes inorganic particles and / or bubbles, and the content of the inorganic particles is 2% by weight with respect to the total weight of the white film, as described above. It is preferable that the amount be 7% by weight or more, more preferably 30% by weight or more. In the case of a three-layer configuration, the B layer is most preferably a layer containing bubbles from the viewpoint of productivity.

  The number average particle diameter of the inorganic fine particles contained in the white film is preferably 0.3 to 2.0 μm. Examples of the inorganic particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, silica, alumina, mica, titanium mica, talc, clay, Kaolin, lithium fluoride, calcium fluoride, or the like can be used.

  As an example of such a white film, SY64 (manufactured by SKC) or the like is first given as an example of a single layer structure, and as a white film of a two layer structure, Tetron (registered trademark) film UXZ1 (Teijin DuPont Films Co., Ltd.) Examples of the white film having a three-layer structure include Lumirror (registered trademark) E6SL, E6SR, E6Z, Tetoron (registered trademark) film UX (manufactured by Teijin DuPont Films Co., Ltd.), and the like.

  The white reflective film of the present invention may deteriorate the white film of the substrate due to light emitted from a lamp such as a cold cathode tube during use as a backlight, particularly ultraviolet light (for example, optical deterioration such as yellowing, or It is preferable that the binder resin in the coating layer provided on one side of the white film of the base material also contains an ultraviolet absorber and / or a light stabilizer.

  Although it does not specifically limit as binder resin contained in the coating layer of this invention, Resin which has an organic component as a main component is preferable, for example, polyester resin, polyurethane resin, acrylic resin, methacrylic resin, polyamide resin, polyethylene resin, polypropylene resin , Polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, fluorine resin and the like. These resins may be used alone, or two or more copolymers or a mixture thereof may be used. Of these, polyester resins, polyurethane resins, acrylic or methacrylic resins are preferably used in terms of heat resistance, particle dispersibility, coatability, and glossiness. As described above, in terms of light resistance of the coating layer, it is more preferable that the binder resin layer contains an ultraviolet absorber and a light stabilizer.

  In the present invention, if the difference in refractive index between the binder resin forming the coating layer and the spherical particles is reduced as much as possible, the reflectance is improved and the light resistance of the coating layer is also improved. The copolymer component, the monomer composition, the ultraviolet absorber and the light stabilizer are preferably the same. However, since it is necessary to dilute the binder resin component in a solvent in the coating step, it is preferable that the binder resin component does not have a crosslinked structure. In that sense, it is preferable that the binder resin component does not contain a polyfunctional acrylic compound.

  Various additives can be added to the coating layer according to the present invention as long as the effects of the present invention are not impaired. Examples of additives that can be used include organic and / or inorganic fine particles, fluorescent brighteners, crosslinking agents, heat stabilizers, oxidation stabilizers, organic lubricants, nucleating agents, and coupling agents.

  In the white reflective film of the present invention, the average reflectance at a wavelength of 400 to 700 nm measured from the surface provided with the coating layer is preferably 85% or more, more preferably 87% or more, and particularly preferably 90% or more. is there. When the average reflectance is less than 85%, the luminance may be insufficient depending on the applied liquid crystal display. In addition, when the coating layer is provided in both surfaces of the white film, the average reflectance measured from any coating layer should just be 85% or more.

  In applying the coating layer according to the present invention to the white film of the substrate, the coating solution can be applied by any method. For example, methods such as gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife coating, and dipping can be used. The coating liquid for forming the coating layer may be applied at the time of producing the white film of the substrate (in-line coating), or may be applied on the white film after completion of crystal orientation (off-line coating).

  The thus obtained white reflective film of the present invention is provided with the coating layer surface facing the light source as a lamp reflector of an edge light type liquid crystal backlight or a reflector of edge light type and direct type liquid crystal backlights. Thus, a liquid crystal backlight with little decrease in reflectance can be obtained even when used for a long time. Furthermore, according to a preferable aspect, the luminance unevenness is improved more than before, and a liquid crystal backlight with improved luminance can be obtained. The white reflective film of the present invention can be suitably used as a reflector for edge light type and direct type liquid crystal backlights for liquid crystal screens, and as a lamp reflector for edge light type liquid crystal backlights. In addition, it can be suitably used as a reflection plate for various surface light sources and a sealing film for solar cell modules that require reflection characteristics.

  The measurement method and evaluation method are shown below.

(1) Refractive index of binder resin, refractive index of spherical particles When the refractive index values of the binder resin and spherical particles are unknown, the refractive index is determined by the following procedure.
(I) After extracting the binder resin from the coating layer of the white reflective film using an organic solvent and distilling off the organic solvent, measurement is performed with respect to light having a wavelength of 589.3 nm at 25 ° C. by an ellipsometry method. This is carried out at five different places, and the average value of the five places is taken as the “refractive index of the binder resin”.
(Ii) The coating layer of the white reflective film is immersed in an organic solvent, and the coating layer is peeled and collected from the white reflective film, and then the spherical particles are dropped from the coating layer by pressing and sliding on a slide glass. The spherical particles obtained here were confirmed by the Becke line detection method to confirm that the contours of the particles could not be seen at a temperature where the refractive index of each liquid organic compound was known, and the refractive index of the liquid organic compound used at this time was determined. Ask. This is carried out at five different places, and the average value at the five places is taken as the “refractive index of the spherical particles”.

(2) Volume average particle diameter of spherical particles, coefficient of variation CV of spherical particles
The volume average particle diameter and the coefficient of variation CV are measured for the five different spherical particles collected in (1). For the measurement, Coulter Multisizer III (manufactured by Beckman Coulter, Inc.) is used as a particle size distribution measuring apparatus utilizing the pore electrical resistance method. The number and volume of particles are measured by measuring the electrical resistance of the electrolyte solution corresponding to the volume of the particles as they pass through the pores. First, a small amount of sample is dispersed in a thin surfactant aqueous solution, and then added to the container of the specified electrolyte solution in such an amount that the aperture (detection portion pore) passage rate is 10 to 20% while viewing the monitor display. Then, the particle diameter is continuously measured until the number of passing particles reaches 100,000, and is automatically calculated, and the volume average particle diameter, the standard deviation of the volume average particle diameter, and the coefficient of variation CV are obtained. The value of the variation coefficient CV can be obtained by the following equation.
Coefficient of variation CV (%) = standard deviation of volume average particle diameter (μm) × 100 / volume average particle diameter (μm).

(3) Yellowishness (b value)
Using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.), a b value representing yellowishness is determined by a reflection measurement method using a C / 2 ° light source. B value is calculated about 3 samples, and this is made yellowish.

(4) Light resistance (yellowishness change)
A forced UV irradiation test is performed under the following conditions using an ultraviolet degradation tester iSuper UV Tester SUV-W131 (manufactured by Iwasaki Electric Co., Ltd.), and then the b value is obtained. An acceleration test is performed on three samples, b values before and after the test are measured, and an average value of the difference is defined as light resistance (yellowish change amount).
"UV irradiation conditions"
Illuminance: 100 mW / cm ²
Temperature: 60 ° C
Relative humidity: 50% RH
Irradiation time: 120 hours And the light resistance evaluation result is determined by the following, and class A or class B is passed.
A grade: Yellowish change amount is 5 or less B grade: Yellowish change amount is 6 or more and 10 or less C class: Yellowish change amount is 11 or more.

(5) Coating layer thickness H, spherical particle diameter R, average number of spherical particles with R> H The white reflective film is a rotary microtome manufactured by Nihon Microme Laboratories, and the knife inclination angle is 3 °. Cut in a direction perpendicular to the plane of the film. The cross section of the obtained film is observed using a scanning electron microscope ABT-32 manufactured by Topcon Corporation. The portion where the spherical particles are not visible on the surface of the coating layer but the surface of the coating layer is a binder resin The thicknesses of the five coating layers are measured, and the average value is defined as the thickness H of the coating layer.

  Next, the surface of the coating layer is observed with an optical microscope OPTIPHOTO 200 manufactured by Konica, and a range of 100H square (vertical: 100H, horizontal: 100H square) is arbitrarily selected at five locations. The spherical particles present in the 100H square range are taken out and observed with an optical microscope, and the longest diameter L and the shortest diameter S of the spherical particles are measured. Let R = (L + S) / 2 be the particle size R of the spherical particles.

  The number of spherical particles satisfying “R> H” existing in the five 100H square ranges is counted, an average value per one point is obtained, and the value is determined as spherical particles satisfying “R> H” per 100H square. The average number. In addition, five particles were arbitrarily selected from the spherical particles observed above, and the average value of the particle diameters R is shown in Table 1.

(6) Content rate of spherical particles in coating layer When the content rate of spherical particles in the coating layer is unknown, the content is determined by the following procedure.
(I) The coating layer of the white reflective film is scraped off with a sharp blade, 0.05 g of the coating layer is collected from the white reflective film, and the binder resin component is extracted using an organic solvent.
(Ii) The particles not dissolved in the organic solvent are made spherical particles, the weight A (g) of the spherical particles is weighed, and the content of the spherical particles is calculated from the following mathematical formula.
(Iii) The same operation is carried out from any three samples, and the average value is defined as the “content ratio of spherical particles”.
Spherical particle content (% by weight) = spherical particle weight A (g) /0.05 (g) × 100.

(7) Average brightness 21 inch direct type backlight (lamp tube diameter: 3 mmΦ, number of lamps: 12, distance between lamps: 25 mm, distance between reflection film and lamp center: 4.5 mm, distance between diffusion plate and lamp center: 13.5 mm) and the luminance measurement is performed with the optical sheet configuration of the following two models.
Model 1: Diffusion plate RM803 (Sumitomo Chemical Co., Ltd., thickness 2 mm) / Diffusion sheet GM3 (Kimoto Co., Ltd., thickness 100 μm) 2 models 2: Diffusion plate RM803 (Sumitomo Chemical Co., Ltd., thickness) 2 mm) / Diffusion sheet GM3 (manufactured by Kimoto Co., Ltd., thickness 100 μm) / prism sheet BEF-II (manufactured by 3M, thickness 130 μm) / polarization separation sheet DBEF (manufactured by 3M, thickness 400 μm)
In the luminance measurement, the cold cathode ray tube lamp is turned on for 60 minutes to stabilize the light source, and then the luminance (cd / m ² ) is measured using a color luminance meter BM-7fast (manufactured by Topcon Corporation). An average value is calculated for three samples, and this is used as the average luminance.

(8) Luminance unevenness 15 inch (330 mm × 250 mm: diagonal 400 mm) direct type backlight (housing, white reflective film of the present invention, light diffusion plate (“Clarex” (registered trademark) acrylic resin plate, Japan) Resin Kogyo Co., Ltd., transmittance 85%)) is turned on at 12V, and after 1 hour, the luminance unevenness analyzer Eye-Scale3 manufactured by I-System Co., Ltd. is used as shown in FIG. The luminance unevenness (uniformity) in the front direction on the luminance measurement line is measured.
The luminance was evaluated as the maximum value of the measurement position. The luminance unevenness is expressed by the following formula, where Cmax is the latest luminance maximum value from the central luminance measurement position 2 shown in FIG. 1, Cmin is the latest luminance minimum value, and Cave is the average luminance value on the luminance measurement line 3. calculate.
・ Luminance unevenness (uniformity) (%) = 100 × (Cmax−Cmin) ÷ Cave
The following backlight configuration for evaluation is used.
(Fluorescent tube)
Diameter: 3mm
Number: 8 Adjacent spacing (pitch): 28mm
Distance between tube center and reflector (lower side): 5mm
Distance between tube center and light diffuser (upper side) 10mm
The brightness unevenness result is determined as follows, and class A or class B is set as acceptable.
Class A: Brightness unevenness is less than 43% Class B: Brightness unevenness is 43% or more and less than 46% Class C: Brightness unevenness is 46% or more.

(9) Adhesiveness of coating layer “Cellotape” (registered trademark) CT-405 (manufactured by Nichiban Co., Ltd., 18 mm width) is pasted on the coating layer side of the white reflective film and rubbed with an eraser from the top of the cellophane, and the non-adhesive part Is removed and peeled in the direction of 90 degrees. Three samples were measured for each white reflective film, and the evaluation results were determined as follows.
Class A: The coating layer does not peel in all three samples.
Class B: In any sample, there is a part that peels off in a dot shape.
Class C: 50% or more of the area of the adhesion part peels off.

( Reference Example 1)
"Method for producing spherical particle A"
In a 1 liter four-necked flask equipped with a stirrer, thermometer and nitrogen gas inlet tube, 70 parts by weight of methyl methacrylate, 10 parts by weight of trimethylolpropane triacrylate as a polyfunctional monomer forming a crosslinked structure, a hindered amine system 2,2,6,6-tetramethyl-4-piperidyl methacrylate 3 parts by weight as a polymerizable compound and 2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzo as a benzotriazole-based polymerizable compound 10 parts by weight of triazole and 1 part by weight of lauroyl peroxide as a polymerization initiator were added. Furthermore, 1 part by weight of polyvinyl alcohol (PVA-224, manufactured by Kuraray Co., Ltd.) and 200 parts by weight of water were added as a dispersion stabilizer for this solution. These were stirred for 3 minutes at 9000 rpm using a homomixer to disperse the polymerizable compound in water. Next, the dispersion was heated to 75 ° C. for 2 hours and maintained at this temperature for reaction, and further heated to 90 ° C. for 3 hours for copolymerization.

After reacting as described above, the dispersion was cooled to room temperature. The dispersion was filtered using a mesh filter having an opening of 40 μm to remove aggregates and the like. The obtained dispersion was free from agglomerates, and the filterability of this dispersion was very good.
The average particle diameter of the resin particles dispersed in the dispersion thus filtered was 6.4 μm, and the resin particles were spherical.
The resin particle dispersion was washed according to a conventional method and filtered to separate the resin particles and the dispersion medium, and the separated resin particles were dried. Subsequently, spherical particles A were obtained through classification (variation coefficient 28%).

"Production method of white reflective film"
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 5.0 g, spherical particles A (Refractive index 1.49): A coating liquid prepared by adding 0.3 g with stirring was prepared. This coating solution was applied to one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. The coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 2)
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 5.5 g, spherical particles A (Refractive index 1.49): A coating liquid prepared by adding 0.6 g with stirring was prepared. This coating solution was applied to one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. The coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 3)
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 6.5 g, spherical particles A (Refractive index 1.49): A coating liquid prepared by adding 1.0 g with stirring was prepared. This coating solution was applied to one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. Then, the coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 4)
"Method for producing spherical particle B"
Spherical particles B were obtained in the same manner as the spherical particles A of Reference Example 1 except that 70 parts by weight of methyl methacrylate was changed to 30 parts by weight of methyl methacrylate and 40 parts by weight of styrene. The average particle diameter of the obtained spherical particles was 6.5 μm.

"Production method of white reflective film"
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 5.0 g, spherical particle B (Refractive index 1.49): A coating liquid prepared by adding 1.0 g with stirring was prepared. This coating solution was applied to one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. The coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 5)
"Method for producing spherical particle C"
Spherical particles C were obtained in the same manner as the spherical particles A of Reference Example 1 except that 70 parts by weight of methyl methacrylate was changed to 5 parts by weight of methyl methacrylate and 65 parts by weight of styrene. The average particle diameter of the obtained spherical particles was 6.2 μm.

"Production method of white reflective film"
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 5.0 g, spherical particles C (Refractive index 1.49): A coating liquid prepared by adding 1.0 g with stirring was prepared. On one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.), a coating solution was applied using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. The coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 6)
Hals Hybrid (registered trademark) UV-G720T (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 7.0 g, spherical particles A (Refractive index 1.49): A coating liquid prepared by adding 1.7 g with stirring was prepared. This coating solution was applied to one side of a white film made of 225 μm porous biaxially stretched polyethylene terephthalate (Lumirror (registered trademark) E6SR manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. Then, the coating layer was provided under drying conditions at 120 ° C. for 1 minute.

( Reference Example 7)
A white film was obtained by providing a coating layer in the same manner as in Reference Example 6 except that the amount of ethyl acetate in the coating liquid for forming the coating layer was 10 g and the amount of spherical particles A was 2.7 g.

( Reference Example 8)
A white film was obtained by providing a coating layer in the same manner as in Reference Example 6 except that the amount of ethyl acetate in the coating liquid forming the coating layer was 15 g and the amount of spherical particles A was 4.8 g.

Example 9
A white film was obtained by providing a coating layer in the same manner as in Reference Example 6 except that the amount of ethyl acetate in the coating liquid for forming the coating layer was 25 g and the amount of spherical particles A was 9.2 g.

(Example 10)
A coating layer was provided in the same manner as in Reference Example 6 except that the amount of ethyl acetate in the coating solution for forming the coating layer was 40 g and the amount of spherical particles A was 16 g to obtain a white film.

( Reference Example 11)
A coating layer was provided in the same manner as in Reference Example 6 except that the amount of ethyl acetate in the coating solution for forming the coating layer was 90 g and the amount of spherical particles A was 36 g to obtain a white film.

(Comparative Example 1)
Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 10.0 g A coating liquid was added while adding. This coating solution was applied to one side of a 250 μm porous biaxially stretched polyethylene terephthalate white film (Lumirror (registered trademark) E6SL manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. The coating layer was provided under drying conditions at 120 ° C. for 1 minute.

(Comparative Example 2)
Except for making spherical particles acrylic particles (TECHPOLYMER (registered trademark) MBX series, MB30X-8, refractive index 1.49, average particle size 8.0 μm, coefficient of variation CV 32%, manufactured by Sekisui Plastics Co., Ltd.) It produced similarly to the reference example 3, and obtained the white reflective film.

(Comparative Example 3)
Except that the spherical particles were polystyrene particles (TECHPOLYMER (registered trademark) SBX series, SBX-8, refractive index 1.59, average particle size 8.0 μm, coefficient of variation CV 37%, manufactured by Sekisui Plastics Co., Ltd.) It produced similarly to the reference example 3, and obtained the white reflective film.

(Comparative Example 4)
Except that spherical particles were nonporous benzoguanamine / formaldehyde condensate particles (Epester (trademark registration), Epostor M05, refractive index 1.66, average particle size 5.2 μm, coefficient of variation CV 35%, manufactured by Nippon Shokubai Co., Ltd.) Was prepared in the same manner as in Reference Example 3 to obtain a white reflective film.

(Comparative Example 5)
Hals Hybrid (registered trademark) UV-G720T (acrylic copolymer, 40% concentration solution, refractive index 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 25 g, silicone particles (GE Toshiba) Silicone Co., Ltd. Tospearl (registered trademark), Tospearl 125, refractive index 1.42): A coating solution was prepared by adding 9.2 g with stirring. This coating solution was applied to one side of a white film made of 225 μm porous biaxially stretched polyethylene terephthalate (Lumirror (registered trademark) E6SR manufactured by Toray Industries, Inc.) using a bar coater count 12 manufactured by Matsuo Sangyo Co., Ltd. Then, the coating layer was provided under drying conditions at 120 ° C. for 1 minute.

The following can be understood by comparing each example, comparative example , and reference example .

(Light resistance)
-Whether the spherical particles in the coating layer contain an ultraviolet absorber and a light stabilizer, Reference Examples 1 to 8, 11, and Examples 9 and 10 are the same as Comparative Example 1 in which there are no spherical particles in the coating layer More light resistance. It can be seen that even if spherical particles are contained in the coating layer, the light resistance can be maintained if the spherical particles contain an ultraviolet absorber and a light stabilizer.
-In particular, Reference Examples 1 to 3 , 6 to 8, 11, and Examples 9 and 10 using spherical particles A not containing styrene as a copolymerization monomer use spherical particles B and C containing styrene as a copolymerization monomer. The light resistance is better than those of Reference Examples 4 and 5 and Comparative Example 1 having no spherical particles. It can be seen that the light resistance can be improved by selecting the monomer composition of the spherical particles even if the spherical particles are included in the coating layer.
On the other hand, Comparative Examples 2 to 4 in which the spherical particles in the coating layer do not contain an ultraviolet absorber or a light stabilizer are inferior in light resistance to Comparative Example 1 in which there are no spherical particles in the coating layer.

(Improved brightness)
-By comparing Reference Examples 1 to 3 in which the difference in refractive index between the spherical particles in the coating layer and the binder resin is the same, it can be seen that the luminance improves as the number of spherical particles satisfying R> H increases.
When comparing Reference Examples 3 to 5 in which the number of spherical particles satisfying R> H is substantially the same, it can be seen that the luminance is improved as the refractive index difference between the spherical particles and the binder resin is smaller.
When comparing Reference Example 5 and Comparative Example 4 in which the number of spherical particles satisfying R> H is substantially the same, it can be seen that there is a significant difference in luminance when the refractive index difference is less than 0.10. In particular, Comparative Example 4 is inferior in luminance as compared with Comparative Example 1 in which no spherical particles are present in the coating layer, and merely having spherical particles satisfying R> H does not improve the luminance, and the refractive index difference is 0. It can be seen that it needs to be less than 10. The same can be said when Comparative Example 2 and Comparative Example 3 in which the number of spherical particles satisfying R> H are substantially the same are compared.

(Improves brightness unevenness, adhesion)
-When comparing Reference Examples 6 to 8, 11 and Examples 9 and 10 in which only the content of the spherical particles in the coating layer is compared, the luminance unevenness improves as the content increases, but the adhesion may decrease. I understand. Further, from Example 9, it can be seen that when the content is in a particularly preferable range of 65 to 75% by weight, the luminance unevenness improvement and the adhesion are both good and balanced.
When comparing Example 9 and Comparative Example 5 in which the content of spherical particles in the coating layer is the same, Comparative Example 5 having a coefficient of variation CV of less than 20% is compared with Example 9 having a coefficient of variation of 20% or more. It can be seen that the luminance unevenness improvement is inferior.

Claims (9)

A white reflective film in which a coating layer having spherical particles containing an ultraviolet absorber and / or a light stabilizer is laminated on at least one side of a white film, and the content of the spherical particles in the entire coating layer is 65 to 85 wt. % White reflective film. The white reflective film according to claim 1, wherein an absolute value of a difference in refractive index between the spherical particles forming the coating layer and the binder resin is less than 0.10. The white reflective film according to claim 1 or 2, wherein a coefficient of variation CV of the spherical particles is 20% or more. The ultraviolet absorber contained in the spherical particles is at least selected from the group consisting of benzotriazole, benzophenone, oxalic anilide, cyanoacrylate, triazine, titanium oxide, zinc oxide, zirconium oxide, and cerium oxide. It is one type of ultraviolet absorber, The white reflective film in any one of Claims 1-3 . The white reflective film according to any one of claims 1 to 4 , wherein the light stabilizer contained in the spherical particles is a hindered amine light stabilizer. White reflective film according to any one of claims 1 to 5, wherein said spherical particles are spherical particles obtained by copolymerizing the UV absorbers and / or light stabilizers. It said spherical particles, acrylic copolymer, polystyrene copolymer, and in the claims is composed of at least one member selected from the group consisting of a copolymer of an acrylic vinyl monomer and styrene vinyl monomer 1-6 The white reflective film in any one of. An edge-light type liquid crystal backlight in which the white reflective film according to any one of claims 1 to 7 is provided with the coating layer surface facing the light source. A direct-type liquid crystal backlight in which the white reflective film according to any one of claims 1 to 7 is provided with the coating layer surface facing the light source.

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