KR101260102B1 - white reflective film - Google Patents

Abstract

This invention relates to the white reflective film which laminated | stacked the application layer which has the spherical particle containing a ultraviolet absorber and / or a light stabilizer on at least one surface of a white film. By this invention, the white reflective film which aims at the brightness improvement of a liquid crystal backlight, and brightness maintenance in long-term use is provided.

White Reflective Film, LCD Backlight, Lamp Reflector

Description

White Reflective Film {WHITE REFLECTIVE FILM}

TECHNICAL FIELD The present invention relates to a white reflective film aimed at improving the brightness of liquid crystal backlights, and more particularly, reflecting plates of edge light type and direct type liquid crystal backlights for liquid crystal displays, and lamp reflecting mirrors of edge light type liquid crystal backlights. The present invention further relates to a white reflective film which is preferably used for a solar cell back sheet.

Background Art A backlight for illuminating a liquid crystal cell is used in a liquid crystal display, and an edge light type backlight is used in a liquid crystal monitor, and a direct backlight is used in a liquid crystal television, depending on the type of the liquid crystal display. As these reflective films for backlights, the porous white film formed by the bubble is generally used (patent document 1). Moreover, the white film which laminated | stacked the ultraviolet absorbing layer is also proposed in order to prevent the yellow discoloration of the film by the ultraviolet-ray radiated | emitted from a cold cathode tube (patent document 2, 3).

The basic configuration of the direct backlight is characterized by a structure in which a fluorescent tube is arranged directly on the screen without using a light guide plate. By paralleling some of the linear or partial linear lamps in the screen, it is possible to cope with a large screen and to ensure sufficient brightness. However, brightness unevenness (brightness unevenness) in the screen occurs due to the lamp installed in the screen which is also a feature. That is, immediately above a plurality of lamps in parallel is bright, and between adjacent lamps is dark. For this reason, in the direct backlight, in order to eliminate this luminance nonuniformity, the light diffusion plate (milk white plate) which has very strong light diffusivity is provided above the fluorescent tube, and the screen is made uniform. . The light diffusing plate is a plate having a thickness of about 2 mm containing an acrylic resin or a polycarbonate resin in which fine particles are dispersed. This light diffusing plate eliminates the luminance unevenness and makes the screen uniform. However, in order to diffuse strongly, the total light transmittance is low, the light utilization efficiency is deteriorated, and it is diffused too strongly, so that light is dispersed in an unnecessary direction. As a result, the required brightness of the front becomes insufficient. Therefore, the light condensing sheet represented by the diffusion sheet which shows the light condensing effect in the front direction, and the prism sheet for improving light condensation while isotropically spreading light on a light diffuser plate, and also lacks the brightness | luminance on a liquid crystal panel, liquid crystal The brightness improvement sheet etc. for improving the brightness on a panel are inserted.

In the reflection sheet in a direct backlight, the method of improving the brightness nonuniformity in a backlight is also disclosed by controlling the diffusivity of the film surface on the light source side (patent document 4). The manufacturing method of the light resistant particle | grains and its application are mainly disclosed as the diffuser plate use used for a direct backlight, and the example of use for some coating uses is also disclosed (patent document 5, 6).

Patent Document 1: Japanese Patent Application Laid-Open No. 8-262208

Patent Document 2: Japanese Patent Application Laid-Open No. 2001-166295

Patent Document 3: Japanese Patent Laid-Open No. 2002-90515

Patent Document 4: Japanese Patent Laid-Open No. 2005-173546

Patent Document 5: Japanese Patent Application Laid-Open No. 2003-12733

Patent Document 6: Japanese Patent Application Laid-Open No. 2006-267592

<Start of invention>

Problems to be Solved by the Invention

While the cost reduction is strongly demanded in the reflective film for liquid crystal television, the improvement of the light resistance and reflectance of a reflective film is calculated | required simultaneously more than before. Regarding light resistance, the number of cold cathode tubes increases with the increase in size of the liquid crystal television, and there is a problem that yellowing due to the increase in the amount of ultraviolet rays becomes remarkable. Usually, in the coating layer of a white reflective film, the resin binder and particle | grains were included and normally only the binder had light resistance. This may be cited as a reason for selection that the particles which do not have economic light resistance are advantageous.

In recent years, in order to lower the total cost of the backlight, the luminance lowered by the reduction of the expensive prism sheet and the reduction of the number of lamps is supplemented by increasing the luminance of each lamp. Since the lamps are made high in addition to the increase in the lamp spacing due to the change in the configuration of these backlights, there is a problem that luminance unevenness cannot be eliminated with the optical sheet structure (light diffuser plate or reflecting film) used so far. Is becoming remarkable.

In order to eliminate these luminance nonuniformity, a light diffusion fine particle is added to a coating layer of a reflective film in comparatively large quantity. However, when there are too many microparticles | fine-particles in an application layer, since the contact area with the surface layer of a white film becomes small, there exists a problem that the adhesiveness of a white film and an application layer runs short. Moreover, since the microparticles | fine-particles generally do not have the ultraviolet absorbing ability, when the diffusive reflection performance is improved by mass addition of microparticles | fine-particles, there also exists a problem that the light resistance of a coating layer falls accordingly.

Unlike the conventional method mentioned above, this invention improves the light resistance of the coating layer of the white reflective film used for a backlight by studying the coating layer of the light source side of a white film. More preferably, the diffusive reflectivity and adhesiveness of the coating layer of a white reflective film are also improved.

MEANS FOR SOLVING THE PROBLEMS [

In order to solve this problem, the present invention employs the following means. That is, it is a white reflective film which has a particle | grain coating layer containing a ultraviolet absorber and / or a light stabilizer in at least one surface of a white film.

Moreover, the preferable form of the white reflective film of this invention is

(1) Content of spherical particle with respect to the said coating layer whole is 50 to 85 weight%.

(2) The absolute value of the difference in refractive index between the spherical particles forming the coating layer and the binder resin is less than 0.10.

(3) The coefficient of variation CV of the said spherical particle is 20% or more.

(4) at least the ultraviolet absorber contained in the spherical particles is selected from the group consisting of benzotriazole series, benzophenone series, annilide oxalate series, cyanoacrylate series, triazine series, titanium oxide, zinc oxide, zirconium oxide and cerium oxide Being one kind of ultraviolet absorber.

(5) The light stabilizer contained in the spherical particles is a hindered amine light stabilizer.

(6) The said spherical particle copolymerized the said ultraviolet absorber and / or light stabilizer.

(7) The spherical particles are composed of at least one selected from the group consisting of an acrylic copolymer, a polystyrene copolymer, and a copolymer containing an acrylic vinyl monomer and a styrene vinyl monomer.

Moreover, this invention is the lamp reflector for liquid crystal backlight which installed the white reflecting film of this invention so that the coating layer surface may face the light source side, and the direct type system which installed the white reflecting film of this invention so that its coating layer surface may face the light source side. Is a liquid crystal backlight.

EFFECTS OF THE INVENTION [

According to the present invention, by using a white reflective film provided with a specific coating layer on at least one side of a white film, when used for a backlight, a backlight having a lower luminance deterioration due to long-term use can be provided. Moreover, according to the preferable aspect of this invention, the backlight which has less luminance nonuniformity and improved brightness than before can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the evaluation backlight used for the luminance nonuniformity measurement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

1: fluorescent tube

2: center luminance measurement position (black ring)

3: luminance measurement line (thick dotted line)

BEST MODE FOR CARRYING OUT THE INVENTION [

This invention earnestly examined about the said subject, ie, the white reflective film with little brightness fall by long-term use more than before, by studying the coating layer on the light source side of a white film. As a result, when at least one surface of the white film was coated with a coating layer containing spherical particles having an ultraviolet absorber and / or light stabilizer, the effect of improving the light resistance of the coating layer can be confirmed, thereby solving these problems at once. It is to be saved.

The white reflective film of this invention laminate | stacks the coating layer containing the spherical particle which has an ultraviolet absorber and / or a light stabilizer on at least one surface of a white film. Here, "spherical" does not necessarily mean only a spherical shape, but means that the cross-sectional shape of the particle is surrounded by a curved surface such as a circle, an ellipse, an almost circle, or an almost oval.

Particles containing the ultraviolet absorber and / or light stabilizer according to the present invention are partially disclosed in Patent Document 6, and are acrylic resin particles, silicone resin particles, nylon resin particles, styrene resin particles, polyethylene, which are general organic spherical particles. Copolymerization with ultraviolet absorbers and / or light stabilizers having reactive double bonds in the case where ultraviolet absorbers and / or light stabilizers are added to the resin resin particles, benzoguanamine resin particles, urethane resin particles or the like, or when the resins are prepared. It may make it chemically bond by. In view of the low 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.

Ultraviolet absorbers and light stabilizers contained in spherical particles are broadly divided into inorganic and organic. Titanium oxide, zinc oxide, zirconium oxide, cerium oxide, and the like are generally known as inorganic ultraviolet absorbers, and zinc oxide is most preferable in view of economical efficiency, ultraviolet absorption, and photocatalytic activity. Examples of the organic ultraviolet absorber include benzotriazole type, benzophenone type, oxalate anilide type, cyanoacrylate type, triazine type and the like. These ultraviolet absorbers may be used alone, or two or more thereof may be mixed and used. Since these ultraviolet absorbers cannot capture the organic radical which arises by ultraviolet irradiation as long as they absorb an ultraviolet-ray, the white film which becomes a base material in series by this radical may deteriorate. In order to capture these radicals etc., it is preferable to use an optical stabilizer together, and especially, a hindered amine compound is used preferably.

As the copolymerized 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 a styrene vinyl monomer has an aromatic ring and is easy to yellow, copolymerization with an acrylic vinyl monomer is most preferable at the point of light resistance.

2- (2'-hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole (trade name: RUVA-93) as a reactive vinyl monomer substituted with the benzotriazole of a ultraviolet absorber; Otsuka Chemical Co., Ltd.) and 4-methacryloyloxy-2,2,6,6-tetra as a reactive vinyl monomer substituted with the hindered amine compound of the light stabilizer. Methyl piperidine ("adecaster LA-82"; manufactured by ADEKA Corporation) can be used.

It does not specifically limit as an acryl-type vinyl monomer, An acrylic monomer and a methacryl monomer may be sufficient. Examples are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylic Latex, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, n-nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, styryl (meth) acrylic (Meth) acrylate which has linear alkyl groups, such as a rate; iso-propyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate and t-butyl (meth (Meth) acrylic-acid alkylester which has branched alkyl groups, such as) acrylate; (Meth) acrylate which has alkyl groups, such as (meth) acrylic-acid alkylester which has cyclic alkyl groups, such as isobornyl (meth) acrylate and cyclohexyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, monoesters of (meth) acrylic acid and polypropylene glycol or polyethylene glycol, and lactones and 2-hydroxy (meth) acrylic acid Hydroxyl group-containing compounds such as hydroxyl group-containing vinyl compounds such as adducts with ethyl; Carboxyl group-containing (meth) acrylic monomers such as (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid and fumaric acid; And amino group-containing (meth) acrylic monomers such as N, N-dimethylaminoethyl (meth) acrylate and amide group-containing (meth) acrylic monomers such as (meth) acrylamide and N-methylacrylamide.

It is preferable that the spherical particle which concerns on this invention is a resin particle which consists of a copolymer of the vinylic monomer as mentioned above, a specific hindered amine type polymeric compound, and a specific benzotriazole type polymeric compound, Especially this copolymer is It is preferable to have a crosslinked structure. When it does not have a crosslinked structure, when a spherical particle and a binder resin are mixed in a solvent and the coating paint is combined, a spherical particle may start to melt | dissolve in a solvent, and a particle shape and a particle diameter may change.

In order to form a crosslinked structure, it is preferable to form a crosslinked structure using the vinyl compound which has several functional groups in 1 molecule, and especially in this invention, as a vinyl compound which has several functional groups in 1 molecule, a bifunctional acrylic compound And polyfunctional acrylic compounds such as trifunctional acrylic compounds and polymerizable acrylic compounds having more than four functions can be used.

When the white reflective film of the present invention has the thickness of the coating layer as H and the particle size of the spherical particles as R, the average number of particles satisfying "R> H" per 100H square viewed from the coating layer surface is 10 or more, It is preferable because the luminance at the time of assembly to the backlight is improved. More preferably, it is 50 or more, More preferably, it is 100 or more, Especially preferably, it is 300 or more. When the reflectance of a white reflective film improves, the brightness as a backlight improves and the expensive sheet used for the upper part of a light source can be reduced. For example, as an example of the configuration of a backlight for a liquid crystal television, a diffusion plate (thickness about 2 mm) / diffusion film (thickness about 200 μm to 300 μm) / diffusion film (thickness about 200 μm to 300 μm) is provided on the light source side. When it is laminated | stacked in the order of / diffusion film (thickness about 200 micrometers-300 micrometers), and the brightness | luminance of the whole backlight improves by 2 to 3%, one diffusion film can be reduced by the said structure. In addition, the method of obtaining "thickness H of a coating layer" and "particle size R of spherical particle" is mentioned later.

Although content of the spherical particle in the coating layer which concerns on this invention is not specifically limited if the improvement of a reflectance is obtained, It is preferable that it is 5 weight% or more with respect to the whole coating layer, More preferably, it is 10 weight% or more, Especially preferably, Is 15% by weight or more. When content of spherical particle | grains is less than 5 weight%, the effect of improving a reflectance may not be acquired. In addition, although an upper limit is not specifically limited, Since applicability | paintability may fall when it exceeds 300 weight part, ie, 75 weight% of the whole application layer with respect to 100 weight part of components other than spherical particle in an application layer, in an application layer 300 weight part or less, ie, 75 weight% or less of the whole coating layer is preferable with respect to 100 weight part of components other than spherical particle.

In addition, it is preferable that content of the spherical particle in the coating layer which concerns on this invention is 50-85 weight% with respect to the whole coating layer from the viewpoint of the improvement of a diffuse reflectance, light resistance, and adhesiveness with a white film, More preferably, Is 55 to 80% by weight, particularly preferably 65 to 75% by weight. When content of spherical particle | grains is less than 50 weight%, diffuse reflectance may be inadequate. In addition, when the content of the spherical particles is more than 85% by weight, the diffuse reflectivity is good, the luminance nonuniformity at the time of assembling in the backlight is improved, while the coating film strength is weak, and the adhesion with the white film may be reduced. .

Although the thickness H of the coating layer which concerns on this invention is not specifically limited, 0.5-15 micrometers is preferable, More preferably, it is 1-10 micrometers, Especially preferably, it is 1-5 micrometers. When thickness H is less than 0.5 micrometer, the light resistance of an application layer may be insufficient. On the contrary, when thickness H exceeds 15 micrometers, the brightness | luminance at the time of assembling to a backlight may fall, and it is unpreferable from an economic viewpoint.

Moreover, it is preferable that the white reflective film of this invention is less than 0.10 absolute value (henceforth absolute value of a refractive index difference) of the refractive index difference between the binder resin which forms an application layer, and the said spherical particle. . When the difference in refractive index is less than 0.10, it is considered that the loss of light that does not propagate to the front is reduced as a result of repeating reflection and diffusion at the interface between the binder resin and the spherical particles. That is, the internal diffused light loss in the coating layer decreases, and the light reaching the coating layer surface becomes relatively large. As a result, when the white reflective film of this invention is assembled with a backlight, the improvement effect of a brightness | luminance is acquired further. The refractive index difference is more preferably 0.05 or less, particularly preferably 0.00.

Here, the refractive index is the rate at which the wave going straight changes the angle of the traveling direction at the boundary of the different medium, and is the value intrinsic to the material, that is, the absolute refractive index, based on the vacuum. In addition, since a refractive index is a value inherent in an observation wavelength, a refractive index difference is a difference of the value measured with the same observation wavelength. For example, for light having a wavelength of 589.3 nm, the refractive index of methyl polymethacrylate, which is a typical acrylic resin, is 1.49.

It is preferable that the coefficient of variation CV of the spherical particle which concerns on this invention is 20% or more, More preferably, it is 25% or more, Most preferably, it is 30% or more. If the CV is less than 20%, the uniformity of the particles is good, so the light diffusivity is weakened, and the effect of improving the luminance non-uniformity when assembled to the backlight may not be obtained. In addition, monodisperse particles having a small CV value are generally economically unfavorable because they are expensive. The variation coefficient CV is a value which the standard deviation of particle diameter divided by the average particle diameter. This variation coefficient CV is measured by the method as described in the Example mentioned later, for example.

It is preferable that surface roughness Ra of the coating layer which concerns on this invention is 400 nm or more, More preferably, it is 450 nm or more, Most preferably, it is 500 nm or more. Surface roughness Ra which concerns on this invention means the value measured by 0.25 mm of cutoffs according to JIS B-0601 (1982) using the two-dimensional surface roughness meter SE-3400 (made by Kosaka Corporation). If it is less than 400 nm, the squeak may generate | occur | produce with the light diffusion plate which is a member which contacts a coating layer in a backlight, the lamp holder which fixes a lamp, etc. in a backlight. In addition, an upper limit is although it does not specifically limit, If it exceeds 1000 nm, there exists a possibility of particle | grains falling off.

The higher the visible light reflectance of the white film of the substrate according to the present invention, the better. The white film containing bubbles therein is used for this purpose. Although not limited to these white films, a porous unstretched or biaxially stretched polypropylene film, a porous unstretched or stretched polyethylene terephthalate film is preferably used as an example. These production methods and the like are described in Japanese Patent Laid-Open No. 8-262208 to 0057, Japanese Laid-Open Patent Publication No. 2002-90515 to 0018, Japanese Laid-Open Patent Publication No. 2002-138150 To [0034] and the like. Among them, the porous white biaxially stretched polyethylene terephthalate film disclosed in Japanese Patent Laid-Open No. 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 which concerns on this invention can be suitably selected by the use used and the characteristic requested | required, Although it is not specifically limited, The single film and / or the two or more composite film which have a structure of at least 1 layer or more are preferable. And it is preferable that at least 1 layer or more contains bubble and / or inorganic particle. It is preferable to contain an inorganic particle from the point of the diffusive reflectivity of the white film of a base material.

As an example of a single layer structure (= 1 layer), it is a white film only of A layer which is a single layer, for example, and the thing of the structure which contained the inorganic particle and / or bubble in the said A layer is mentioned, The content rate of the inorganic particle is white It is preferable that it is 2 weight% or more with respect to the total weight of a film, More preferably, it is 7 weight% or more, Most preferably, it is 10 weight% or more. In addition, an example of a two-layered constitution is a white film having a two-layered constitution of A / B layer in which a B layer is laminated on the A layer, and inorganic particles and / or bubbles are contained in at least one of these A and B layers. The content of the inorganic particle is contained, It is preferable that the content rate of the inorganic particle is 2 weight% or more with respect to the total weight of a white film, ie, the total weight of two layers, More preferably, it is 7 weight% or more, Most preferably, 30 weight% or more. In addition, an example of a three-layered constitution is a white film having a three-layer lamination structure formed by laminating three layers of A layer / B layer / A layer and / or A layer / B layer / C layer as above. The thing of the structure which contained the inorganic particle and / or bubble in at least 1 layer is mentioned, It is preferable that the content rate of the inorganic particle is 2 weight% or more with respect to the total weight of a white film similarly to the above, More preferably, it is 7 It is weight% or more, More preferably, it is 30 weight% or more. In the case of a three-layered constitution, it is most preferable that the layer B contains a bubble from the viewpoint of productivity.

It is preferable that the number average particle diameter of the inorganic fine particles contained in such a white film is 0.3-2.0 micrometers. In addition, such 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, mica titanium, talc, clay , Kaolin, lithium fluoride, calcium fluoride and the like can be used.

As an example of such a white film, SY64 (made by SKC) etc. can be mentioned as an example of a single layer structure, Teflon (trademark) film UXZ1 (made by Daijin Dupont Film Co., Ltd.) etc. as a white film of a two-layered structure etc. Examples of the white film having a three-layer structure include Lumir® E6SL, E6SR, E6Z, and Teflon® film UX (made by Daijin Dupont Film Co., Ltd.).

In the white reflective film of the present invention, the white film of the substrate may be deteriorated by light emitted from a lamp such as a cold cathode tube, in particular, ultraviolet rays during use as a backlight (for example, optical degradation such as yellowing or low molecular weight). It is preferable to contain a ultraviolet absorber and / or a light stabilizer also in binder resin in the application layer provided in one side of the white film of a base material).

Although it does not specifically limit as binder resin contained in the coating layer of this invention, Resin which mainly uses an organic component is preferable, For example, polyester resin, a polyurethane resin, an acrylic resin, methacryl resin, a 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 in combination of two or more kinds of copolymers or mixtures. Especially, polyester resin, a polyurethane resin, an acryl, or methacryl resin is used preferably from a viewpoint of heat resistance, particle dispersibility, applicability | paintability, and glossiness. As mentioned above, it is more preferable that a ultraviolet absorber and a light stabilizer are contained also in a binder resin layer from a viewpoint of the light resistance of an application layer.

In the present invention, when the refractive index difference between the binder resin and the spherical particles forming the coating layer is infinitely small, the reflectance is improved and the light resistance of the coating layer is also improved. Thus, the copolymerization component of the binder resin and the spherical particles, the monomer composition, It is preferable that a ultraviolet absorber and a light stabilizer are the same. However, since the binder resin component needs to be diluted in a solvent by an application | coating process, it is preferable not to have a crosslinked structure. In the meaning, it is preferable that a binder resin component does not contain a polyfunctional acrylic compound.

Various additives can be added to the coating layer which concerns on this invention within the range which does not impair the effect of this invention. As the additive, for example, organic and / or inorganic fine particles, fluorescent brighteners, crosslinking agents, heat stabilizers, oxidation stabilizers, organic lubricants, nucleating agents, coupling agents and the like can be used.

It is preferable that the average reflectance in the wavelength of 400-700 nm measured from the surface in which the coating layer was provided of the white reflective film of this invention is 85% or more, More preferably, it is 87% or more, Especially preferably, it is 90% or more to be. When the average reflectance is less than 85%, the luminance may be insufficient depending on the liquid crystal display to be applied. In addition, when providing the coating layers on both surfaces of a white film, the average reflectance measured from either coating layer should just be 85% or more.

In applying the coating layer which concerns on this invention to the white film of a base material, a coating liquid can be apply | coated by arbitrary methods. For example, methods such as gravure coating, roll coating, spin coating, reverse coating, bar coating, screen coating, blade coating, air knife coating, dipping and the like can be used. In addition, the coating liquid for formation of an application layer may be apply | coated (inline coating) at the time of manufacture of the white film of a base material, and may be apply | coated (offline coating) on the white film after completion of crystal orientation.

The white reflective film of the present invention thus obtained is used as a lamp reflector of an edge light type liquid crystal backlight or a reflecting plate of edge light type and direct type liquid crystal backlight so that the coating layer faces the light source side for a long time. A liquid crystal backlight having a small decrease in degree reflectance is obtained. According to a further preferred embodiment, the liquid crystal nonuniformity is improved and the luminance is improved. The white reflective film of this invention can be used suitably as a reflecting plate of the liquid crystal backlight of the edge light type and direct type | mold for a liquid crystal screen, and the lamp reflector of the liquid crystal backlight of an edge light type. In addition, it can be used suitably also as a sealing film of the solar cell module in which the reflecting plate of various surface light sources, and reflection characteristics are calculated | required.

The measurement method and evaluation method are shown below.

(1) the refractive index of the binder resin, the refractive index of the spherical particles

When the value of the refractive index of binder resin and spherical particle is uncertain, it is calculated | required by the following procedure.

(i) Binder resin is extracted from the coating layer of a white reflective film using the organic solvent, the organic solvent is distilled off, and the measurement of the light of 589.3 nm wavelength in 25 degreeC is measured by a flat-pipe analysis method. This is carried out at five other places, and the average value of five places is referred to as "refractive index of binder resin".

(ii) The coating layer of a white reflective film is immersed in the organic solvent, and a peeling extract | collecting the coating layer from a white reflective film is carried out, and spherical particle falls out from a coating layer by crimping | bonding and sliding on slide glass. The spherical particle obtained here is confirmed by the Beckett line detection method, and it is confirmed that the outline of a particle | grain is no longer seen at the refractive index known temperature of each liquid organic compound, and the refractive index of the liquid organic compound used at this time is calculated | required. This is carried out at five other places, and the average value of the five places is referred to as "refractive index of 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 about five other spherical particles collected in the above (1). For the measurement, Coulter Multisizer III (manufactured by Beckman Coulter) is used as a particle size distribution measuring device using the pore electrical resistance method. The number and volume of the particles are measured by measuring the electrical resistance of the electrolyte content corresponding to the particle volume when the particles pass through the pores. First, a small amount of the sample is dispersed in a light surfactant solution, and then added to the container of the designated electrolyte by an amount such that the aperture (pore of the detection portion) passes through 10-20% while viewing the display on the monitor, and then the number of passing particles The measurement of the particle diameter is continued and calculated automatically until 100,000 pieces are obtained, 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 calculated | required by the following formula.

Variation coefficient CV (%) = standard deviation (μm) of volume average particle diameter x 100 / volume average particle diameter (μm)

(3) Yellow rice (b value)

Using an SM color computer (manufactured by Suga Shikeki Co., Ltd.), a b value indicating yellow color is determined by a reflection measurement method using a C / 2 ° light source. B value is computed for 3 samples, and it is set as yellow.

(4) Light resistance (yellowish change)

B value is calculated | required after performing a forced ultraviolet irradiation test on condition of the following using ultraviolet-ray deterioration acceleration tester iceper UV tester SUV-W131 (manufactured by Iwasaki Denki Co., Ltd.). Acceleration tests are performed on three samples, and the b values before and after each test are measured, and the average value of the difference is made into light resistance (amount of yellow rice change).

"UV irradiation conditions"

Illuminance: 100 mW / ㎠

Temperature: 60 ℃

Relative Humidity: 50% RH

Count time: 120 hours

And the light resistance evaluation result is determined by the following, and A grade or B grade are made into the pass.

Class A: Yellow rice change less than 5

Class B: Yellow Rice Variation 6 to 10

Class C: Yellow rice change over 11

(5) Thickness H of coating layer, particle size R of spherical particle, average number of spherical particle of R> H

The white reflective film is cut in the direction perpendicular to the film plane at a knife inclination angle of 3 ° using a Nippon MICROMS Corporation Co., Ltd. rotary microtome. The obtained film cross section was observed using the scanning electron microscope ABT-32 by Topcon Corporation, and the application layer of five places where the surface of an application layer is binder resin instead of the part which a spherical particle is showing on the surface of an application layer. Is measured, and the average value is taken as thickness H of the coating layer.

Next, the surface of an application layer is observed with the optical microscope OPTIPHOTO 200 made from KOICA, and 5 ranges of 100H square (vertical: 100H, horizontal: 100H square) are arbitrarily selected 5 places. The spherical particle which exists in this 100H square range is taken out, observed with an optical microscope, and the longest diameter L and the shortest diameter S of a spherical particle are measured. Let R = (L + S) / 2 as the particle diameter R of a spherical particle.

Count the number of spherical particles satisfying "R> H" existing in these five 100H square ranges to obtain an average value per one place, and calculate the average number of spherical particles satisfying "R> H" per 100H square. Shall be. In addition, five were chosen arbitrarily from the spherical particle observed above, and the average value of these particle diameters R is shown in Table 1 below.

(6) Content of spherical particles in coating layer

When the content rate of spherical particle in an application layer is unclear, it is calculated | required by the following procedures.

(i) The coating layer of a white reflective film is scraped off with a sharp cutting edge, 0.05g of coating layers are extract | collected from a white reflective film, and binder resin component is extracted using the organic solvent.

(ii) Let the thing which is not dissolved in the organic solvent be spherical particle, the weight A (g) of spherical particle be measured, and the content rate of a spherical particle is computed from the following formula.

(iii) The same operation is performed from three arbitrary samples, and the average value is made into the "content rate of a spherical particle."

Content rate (weight%) of spherical particle = weight A (g) /0.05 (g) * 100 of spherical particle

(7) average brightness

21 inch direct backlight (lamp tube diameter: 3 mmΦ, number of lamps: 12, distance between lamps: 25 mm, distance between reflective film and lamp center: 4.5 mm, distance between diffuser and lamp center: 13.5 mm) It uses and performs brightness measurement by the optical sheet structure in following 2 models.

Model 1: Two diffuser plates RM803 (manufactured by Sumitomo Chemical Co., Ltd., thickness 2 mm) / diffusion sheet GM3 (manufactured by Kimoto Co., Ltd., thickness 100 μm)

Model 2: Diffusion plate RM803 (manufactured by 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 Corporation, thickness 400 μm)

In luminance measurement, after cooling a cold cathode ray tube lamp for 60 minutes and stabilizing a light source, luminance (cd / m <2>) is measured using the color | luminance luminance meter BM-7 high speed (made by Topcon Co., Ltd.). An average value is calculated for three samples, and this is taken as the average luminance.

(8) luminance unevenness

15 inches (330mm * 250mm: relative angle 400mm) direct backlight for the evaluation (case, white reflecting film of this invention, light diffuser plate ("Clarex" (trademark registration) acrylic resin board, Nihon Jushi High School) Note) Manufacturing, transmittance 85%)) was turned on at 12 V, and after 1 hour, the eye system was manufactured, and the luminance non-uniformity analyzer, Eye-Scale 3, was shown in Fig. 1. The luminance nonuniformity (evenness) in the front direction on a luminance measurement line is measured.

Luminance was evaluated as the maximum value of the measurement position. The luminance nonuniformity is calculated by using the following equation with Cmax as the nearest luminance maximum value from the center luminance measurement position 2 shown in FIG. 1, C as the nearest luminance minimum value as C minutes, and the average value of the luminance on the luminance measurement line 3 as Cave. .

Brightness nonuniformity (evenness) (%) = 100 x (Cmax-Cmin) ÷ Cave

The evaluation backlight configuration uses the following.

(Fluorescent tube)

Diameter: 3 mm

Count: 8

Adjacent distance (pitch): 28 mm

Distance from center of view to reflector (lower side): 5 mm

Distance from center of view to light diffuser plate (top side): 10 mm

A luminance nonuniformity result is judged by the following, and A grade or B grade are made to pass.

Class A: Less than 43% luminance unevenness

Class B: luminance unevenness is more than 43% and less than 46%

Class C: The luminance nonuniformity is 46% or more

(9) Adhesion of Coating Layer

A cellophane tape (registered trademark) CT-405 (manufactured by Nichiban Co., Ltd., 18 mm wide) is adhered to the coating layer side of the white reflective film, and rubbed with an eraser from the top of the cellophane tape to remove the non-adhesive portion, and the 90 degree direction. Peel off. Three samples were measured about each white reflective film, and the evaluation result was determined by the following.

Grade A: All three samples do not peel a coating layer.

Class B: There is a part that peels off in any one sample.

Class C: 50% or more of the area of the adhered portion peels off.

(Example 1)

"Method for Producing Spherical Particle A"

70 parts by weight of methyl methacrylate in a 1 L four-necked flask equipped with a stirring device, a thermometer, and a nitrogen gas introduction tube, 10 parts by weight of trimethylolpropanetriacrylate as a polyfunctional monomer forming a crosslinked structure, a hindered amine 3 parts by weight of 2,2,6,6-tetramethyl-4-piperidyl methacrylate as the polymerizable compound, 2- (2'-hydroxy-5'-methacryloxy as the benzotriazole polymerizable compound 10 parts by weight of ethylphenyl) -2H-benzotriazole and 1 part by weight of lauroyl peroxide were added as a polymerization initiator. As a dispersion stabilizer of this solution, 1 part by weight of polyvinyl alcohol (PVA-224, manufactured by Kuraray Co., Ltd.) and 200 parts by weight of water were added. These were stirred for 3 minutes at a speed of 9000 rpm using a homo mixer to disperse the polymerizable compound in water. Subsequently, this dispersion liquid was heated to 75 ° C. for 2 hours, held at this temperature and reacted, and further heated to 90 ° C. for copolymerization reaction for 3 hours.

After reacting as described above, the dispersion was cooled to room temperature. This dispersion was filtered using a mesh filter of 40 mu m mesh to remove aggregates and the like. There was no aggregate in the obtained dispersion, and the filterability of this dispersion was very good.

Thus, the average particle diameter of the resin particle disperse | distributed in the filtered dispersion liquid was 6.4 micrometers, and this resin particle was spherical shape.

Thus, after wash | cleaning the dispersion liquid of resin particle in accordance with a conventional method, it filtered, isolate | separated resin particle and a dispersion medium, and dried separated resin particle. Then, spherical particle A was obtained through classification (28% variation coefficient).

"Method of producing a white reflective film"

Hals Hybrid® UV-G13 (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 5.0 g, spherical particle A (refractive index 1.49): 0.3 The coating liquid which adds while stirring g was prepared. This coating was carried out on one side of a white film made of 250 micrometers porous biaxially stretched polyethylene terephthalate (Toray Co., Ltd. Lumirror® E6SL) using Matsuo Sangyo Co., Ltd. The liquid was apply | coated and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Example 2)

Hals Hybrid® UV-G13 (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 5.5 g, spherical particle A (refractive index 1.49): 0.6 The coating liquid which adds while stirring g was prepared. This coating was carried out on one side of a white film made of 250 micrometers porous biaxially stretched polyethylene terephthalate (Toray Co., Ltd. Lumirror® E6SL) using Matsuo Sangyo Co., Ltd. The liquid was apply | coated and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Example 3)

Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 6.5 g, spherical particle A (refractive index 1.49): 1.0 The coating liquid which adds while stirring g was prepared. This coating was carried out on one side of a white film made of 250 micrometers porous biaxially stretched polyethylene terephthalate (Toray Co., Ltd. Lumirror® E6SL) using Matsuo Sangyo Co., Ltd. The liquid was apply | coated and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Example 4)

"Method for producing spherical particle B"

Spherical particles B were obtained in the same manner as the spherical particles A of Example 1 except that 70 parts by weight of methyl methacrylate was set to 30 parts by weight of methyl methacrylate and 40 parts by weight of styrene. The average particle diameter of the obtained spherical particle was 6.5 micrometers.

"Method of producing a white reflective film"

Hals Hybrid® UV-G13 (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 5.0 g, spherical particle B (refractive index 1.49): 1.0 The coating liquid which adds while stirring g was prepared. This coating liquid was used on one side of a white film made of 250 micrometers porous biaxially stretched polyethylene terephthalate (Toray Co., Ltd. Lumirror® E6SL) using Matsuo Sangyo Co., Ltd. Was applied, and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Example 5)

"Method for Producing Spherical Particles C"

Spherical particles C were obtained in the same manner as the spherical particles A of Example 1 except that 70 parts by weight of methyl methacrylate was made 5 parts by weight of methyl methacrylate and 65 parts by weight of styrene. The average particle diameter of the obtained spherical particle was 6.2 micrometers.

"Method of producing a white reflective film"

Hals Hybrid® UV-G13 (acrylic copolymer, solution having a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 5.0 g, spherical particle C (refractive index 1.49): 1.0 The coating liquid which adds while stirring g was prepared. A coating liquid was used on one side of a white film made of 250 µm porous biaxially stretched polyethylene terephthalate (manufactured by Toray Industries, Ltd., Rumirror® E6SL) using Matsuo Sangyo Co., Ltd. It applied, and provided the coating layer on 120 degreeC and 1 minute of drying conditions.

(Example 6)

Hals Hybrid® UV-G720T (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 7.0 g, spherical particle A (refractive index 1.49): 1.7 The coating liquid which adds while stirring g was prepared. This coating liquid was used on one side of a white film (made by Toray Industries, Ltd., Lumirror® E6SR) made of porous biaxially stretched polyethylene terephthalate having a thickness of 225 µm using Matsuo Sangyo Co., Ltd. Was applied, and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Example 7)

An application layer was formed in the same manner as in Example 6 except that the amount of ethyl acetate in the coating solution forming the coating layer was 10 g and the amount of the spherical particles A was 2.7 g, thereby obtaining a white film.

(Example 8)

An application layer was formed in the same manner as in Example 6 except that the amount of ethyl acetate in the coating solution forming the coating layer was 15 g and the amount of the spherical particles A was 4.8 g, thereby obtaining a white film.

(Example 9)

An application layer was formed in the same manner as in 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 the spherical particles A was 9.2 g to obtain a white film.

(Example 10)

An application layer was formed in the same manner as in 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 the spherical particles A was 16 g, thereby obtaining a white film.

(Example 11)

An application layer was formed in the same manner as in 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 the spherical particles A was 36 g, to obtain a white film.

(Comparative Example 1)

Hals Hybrid (registered trademark) UV-G13 (acrylic copolymer, a solution having a concentration of 40%, a refractive index of 1.49, manufactured by Nippon Shokubai Co., Ltd.): 10.0 g, ethyl acetate: 10.0 g was added while stirring to prepare a coating solution. It was. This coating liquid was used on one side of a white film made of 250 micrometers porous biaxially stretched polyethylene terephthalate (Toray Co., Ltd. Lumirror® E6SL) using Matsuo Sangyo Co., Ltd. Was applied, and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

(Comparative Example 2)

Except having made spherical particle into acryl particle | grains (Seikisui Plastics Co., Ltd. TECHPOLYMER (trademark registration) MBX series, MB30X-8, refractive index 1.49, average particle diameter 8.0micrometer, coefficient of variation CV 32%), Prepared in the same manner as 3 to obtain a white reflective film.

(Comparative Example 3)

Similarly to Example 3, except that the spherical particles were made of polystyrene particles (Sekisui Plastics Co., Ltd. Techpolymer (registered trademark) SBX series, SBX-8, refractive index 1.59, average particle diameter 8.0 µm, variation coefficient CV 37%). To give a white reflective film.

(Comparative Example 4)

A spherical particle having a non-porous benzoguanamine formaldehyde condensate particle (Epostar (registered trademark) manufactured by Nippon Shokubai Co., Ltd.), Eposta M05, refractive index 1.66, average particle diameter 5.2 μm, variation coefficient CV 35% A white reflective film was obtained in the same manner as in Example 3 except for the above.

(Comparative Example 5)

Hals Hybrid (registered trademark) UV-G720T (acrylic copolymer, solution with a concentration of 40%, refractive index 1.49, manufactured by Nippon Shokubai): 10.0 g, ethyl acetate: 25 g, silicon particles (GE Toshiba Silicone Co., Ltd.) Manufacture Tospal (trademark), Tospal 125, refractive index 1.42): The coating liquid which adds 9.2g, stirring was prepared. This coating liquid was used on one side of a white film (made by Toray Industries, Ltd., Lumirror® E6SR) made of porous biaxially stretched polyethylene terephthalate having a thickness of 225 µm using Matsuo Sangyo Co., Ltd. Was applied, and the coating layer was provided on 120 degreeC and the drying conditions for 1 minute.

The following is understood by the contrast of each Example and a comparative example.

(Light resistance)

Examples 1 to 11 in which the spherical particles in the coating layer contain an ultraviolet absorber and a light stabilizer are the same or higher light resistance than Comparative Example 1 in which the spherical particles are not present in the coating layer. Even if spherical particles were put in the coating layer, it can be seen that the spherical particles retain the light resistance if they contain an ultraviolet absorber and a light stabilizer.

In particular, Examples 1 to 3, 6 to 11 using spherical particles A without styrene as copolymerization monomers, Examples 4 and 5 and spherical particles using spherical particles B and C containing styrene as copolymerization monomers Light resistance is better than the comparative example 1 which does not exist. By selection of the monomer composition of a spherical particle, even if a spherical particle is put into an application layer, it turns out that light resistance can be improved.

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 without the spherical particles in the coating layer.

(Brightness improvement)

In contrast to Examples 1 to 3 in which the refractive index differences between the spherical particles and the binder resin in the coating layer are the same, it can be seen that the luminance improves as the number of spherical particles satisfying R> H increases.

In contrast to Examples 3 to 5 in which the number of spherical particles satisfying R> H is substantially the same, it can be seen that the smaller the difference in refractive index between the spherical particles and the binder resin, the higher the luminance is.

In contrast to Example 5 and Comparative Example 4, where 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, in Comparative Example 4, the luminance was lowered as compared with Comparative Example 1 without the spherical particles in the coating layer, the luminance was not improved as long as there were spherical particles satisfying R> H, and the refractive index difference had to be less than 0.10. It can be seen that. In addition, it can be said that it is the same compared with Comparative Example 2 and Comparative Example 3, where the number of spherical particles satisfying R> H is almost the same.

(Improve brightness unevenness, adhesiveness)

In contrast with Examples 6 to 11 in which only the content of spherical particles in the coating layer was changed, the luminance nonuniformity was improved as the content was increased, but the adhesion was reduced. In addition, from Example 9, when content is in the range of 65-75 weight% which is especially preferable, it turns out that both the brightness nonuniformity improvement and adhesiveness become favorable, and a balance is obtained.

In contrast to Example 9 and Comparative Example 5 in which the content of spherical particles in the coating layer is the same, it can be seen that Comparative Example 5 having a coefficient of variation CV of less than 20% is inferior in luminance nonuniformity improvement to Example 9 having 20% or more. .

Claims (10)

At least one member selected from the group consisting of an acrylic copolymer, a polystyrene copolymer, and a copolymer comprising an acrylic vinyl monomer and a styrene vinyl monomer on at least one side of the white film and containing an ultraviolet absorber and / or a light stabilizer The white reflective film which laminated | stacked the coating layer which has the spherical particle comprised. The white reflective film of Claim 1 whose content of the spherical particle | grains with respect to the said whole application layer is 50 to 85 weight%. The white reflective film of Claim 1 whose absolute value of the refractive index difference between the spherical particle which forms the said application layer, and binder resin is less than 0.10. The white reflective film of Claim 1 whose content of the spherical particle | grains with respect to the said application layer whole is 50 to 85 weight%, and the absolute value of the refractive index difference between the spherical particle which forms the said application layer and binder resin is less than 0.10. The white reflecting film of any one of Claims 1-4 whose coefficient of variation CV of the said spherical particle is 20% or more. The ultraviolet absorbent according to any one of claims 1 to 4, wherein the ultraviolet absorber contained in the spherical particles is a benzotriazole type, a benzophenone type, an oxalate anhydride type, a cyanoacrylate type, a triazine type, titanium oxide, zinc oxide, A white reflective film which is at least one ultraviolet absorber selected from the group consisting of zirconium oxide and cerium oxide. 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. The white reflective film according to any one of claims 1 to 4, wherein the spherical particles are spherical particles obtained by copolymerizing the ultraviolet absorber and / or light stabilizer. The edge light type liquid crystal backlight which provided the white reflective film as described in any one of Claims 1-4 so that the application layer surface may face the light source side. The direct type | mold liquid crystal back light which provided the white reflective film in any one of Claims 1-4 so that the application layer surface may face the light source side.

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