JP2005292398A - Light diffuser, manufacturing method thereof, light-diffusing material and pixel display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffuser in which, while backward scatter of light is minimized, light diffusibility is ensured, and thin filming is achieved. <P>SOLUTION: In the light diffuser, at least three or more transparent binder layers (14, 16, 18, and 20) are layered on the rugged face of a transparent base material (12), with the transparent binder layers having refraction indexes that change in the order, from the rugged side to outside. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light diffuser, a method for producing the same, a light diffusing material, and an image display element, and more particularly, a light diffuser that diffuses transmitted light forward without light scattering, and light that can easily produce the light diffuser. Manufacturing methods of diffusers, especially light diffusion films that do not effectively lose light and increase the viewing angle in reflective LCDs, light diffusion films that do not depolarize (depolarize) even when placed inside a polarizing film, etc. The present invention relates to a light diffusing material, an image display element suitable for a liquid crystal display element using a thin film light diffuser which has a high light diffusing effect without being deviated even when placed in the inner surface of a liquid crystal cell and does not cause liquid crystal alignment disorder.

  Light diffusing materials are used in various fields such as light control materials, optical elements, and display elements. In recent years, the use of display materials such as liquid crystal displays for improving display quality and viewing angle characteristics has been advanced. As the structure of the light diffusing material, for example, a method of forming fine irregularities on the surface like frosted glass, or a method of dispersing particles from several μm to 10 μm blood in a resin film has been generally used. . However, although these methods can surely scatter light, the amount of transmitted light is reduced and the contrast of the display screen is lowered because the scattering of the light is increased. In addition, the conventional light diffusing material described above is difficult to be applied to a liquid crystal display or the like which has recently been strongly demanded due to depolarization, and since the amount of transmitted light is also small for display materials, The load will increase. Therefore, there is a demand for a light diffusing material that has little backscattering, has high light diffusibility, and does not cause depolarization.

  As a means for solving such a problem, for example, a method is known in which a concavo-convex shape is designed in a lens shape and light refraction is used. However, in this method, the formation of fine irregularities is complicated and inferior in productivity, and the diffusion material is vulnerable to contamination and impact, so that it has irregularities, causing an alignment disorder, There is a problem that it cannot be used because the display quality is remarkably deteriorated.

  A method using fine particles as a light diffusing material is also known. In particular, for the purpose of utilizing refraction rather than light scattering by particles, the internal distribution of particles is not uniform, and light diffusing materials using fine particles in which the refractive index in the particles is changed between the inside and the surface are known. ing. In these methods, light diffusibility is ensured while suppressing the degree of backscattering of light to a small extent.

  For example, it has been proposed to disperse monodispersed fine particles in a binder on a color filter in a reflective liquid crystal cell and to aim at both ensuring light diffusibility and preventing depolarization. (Non-Patent Document 1)

  However, it is difficult to make a gradient of refractive index in particles stably in terms of manufacturing technology, and the range of monomers that can be selected from the viewpoint of compatibility between polymerizability and particle formability is narrow, and a gradient with a large refractive index can be created. There has been a demand for a light diffuser that has disadvantages such as inability to be produced, can be more easily manufactured, and has high light diffusibility and no depolarization.

IDW'00 Proceedings "Color Filter with Light Scattering Layer for Reflection LCDs" p451-p454

A first object of the present invention is to provide a light diffusing body capable of ensuring light diffusibility while suppressing backscattering of light to a small amount, and to achieve a thin film, a manufacturing method thereof, and a light diffusing material. is there.
A second object of the present invention is to provide an image display element such as a liquid crystal display element that can widen the viewing angle without losing light, has no depolarization, and has high contrast.

The above-described problems are achieved by the following invention.
(1) At least three or more transparent binder layers having a concavo-convex formed on the surface of the transparent substrate and having a refractive index sequentially changing from the concavo-convex surface to the outside are laminated on the concavo-convex surface. A light diffuser characterized by that.
(2) In (1), the difference between the refractive index of the transparent binder layer in contact with the uneven surface formed on the surface of the transparent substrate and the refractive index of the transparent substrate is 0.10 or less. The light diffuser described.
(3) The light diffuser according to (1) or (2), wherein the difference in refractive index between adjacent transparent binder layers is 0.10 or less.
(4) The total thickness of the third transparent binder layer from the transparent binder layer in contact with the uneven surface formed on the surface of the transparent substrate is based on the ten-point average roughness (Rz) of the unevenness defined in JIS B0601. The light diffuser according to any one of (1) to (3), wherein
(5) The average interval between the convex and concave portions (average interval S value defined in JIS B0601) is 1/3 to 5 times the ten-point average roughness (Rz) of the irregularities defined in JIS B0601. The light diffusing body according to any one of (1) to (4), wherein: (6) The unevenness formed on the surface of the transparent substrate is formed by any one of an embossing method, a photolithography method, a sand blasting method, and a holographic method (1) to (5) The light diffuser according to any one of the above.
(7) A light diffuser according to any one of (1) to (6), wherein at least two of the three or more transparent binder layers are simultaneously applied in multiple layers. Production method.
(8) A light diffusing material, wherein the light diffusing material according to any one of (1) to (6) is provided on a support.
(9) An image display element using the light diffuser according to any one of (1) to (6).
(10) The image display element according to (9), which is a liquid crystal display element using the light diffuser according to any one of (1) to (6).
(11) The image display device according to (10), wherein the light diffuser is used for an inner surface of a liquid crystal cell.

According to the light diffuser of the present invention, light diffusibility can be ensured while reducing backscattering of light, and a thin film can be achieved.
Moreover, according to the manufacturing method and light-diffusion material of the light-diffusion body of this invention, a light-diffusion body can be manufactured simply.
Furthermore, according to the image display element of the present invention, it is possible to provide an image display element such as a liquid crystal display layer that can widen the viewing angle without losing light, has no depolarization, and has high contrast.

  Hereinafter, preferred embodiments of the present invention will be described.

-Surface irregularities-
In the present invention, any material may be used as the base material for forming irregularities on the surface as long as it is transparent. When this diffuser is disposed inside the polarizing film, the transparent body preferably has no optical anisotropy or depolarization. Moreover, the material of the base material for forming the irregularities on the surface may be the transparent base material itself, or may be a transparent layer laminated on the transparent support, and is laminated on the temporary support. It may be a transparent layer that is peeled off.

  As a method for forming irregularities on a transparent substrate, an embossing method, a photolithography method, a sand blast method, a holography method, or the like can be arbitrarily employed depending on the material of the substrate. The shape of the concave / convex shape is not particularly limited, but from the viewpoint of easy lamination of the transparent binder layer laminated on the concave / convex surface, the concave / convex shape of the concave / convex shape is also based on the so-called ridge-like shape spreading inside. A shape having an open expanse toward the outside is preferable.

  The average roughness of the irregularities is preferably 10 μm to 10 μm, more preferably 1.0 μm to 10 μm, and even more preferably 1.0 μm to 5.0 μm as a ten-point average roughness Rz value defined by JIS B0601. . The average interval between the convex and concave portions is preferably 1/3 times to 5 times the 10-point average roughness Rz value defined in JIS B0601 with the average interval S value defined in JIS B0601, and more preferably 1/2. Double to 2 times.

-Transparent binder layer-
Any transparent binder can be used. What is necessary is just to select arbitrarily from water-soluble polymer, organic-solvent soluble polymer, aqueous latex, aqueous ionomer, etc. Moreover, after apply | coating a polymerizable monomer, an oligomer, or those mixtures, you may superpose | polymerize with light, a heat | fever, an electron beam, etc., and may form a transparent binder layer. Furthermore, the transparent binder layer may be formed by vacuum deposition, sputtering, CVD, or the like.

  In this case, the transparent binder layer can be formed of not only an organic material but also an inorganic thin film material. Among these, when a polymer binder is used as the transparent binder layer, those listed in Polymer Handbook VI / 453-VI / 461 can be suitably used as examples of the polymer binder. Here, since the refractive index of each polymer is also described in detail, a preferred polymer may be appropriately selected from these values.

Furthermore, the polymer binder may be a copolymer of a monomer constituting the polymer and another monomer, or a mixture of different types of polymers in the polymer. Further, the refractive index of the transparent binder layer may be adjusted by mixing ultrafine particles having a particle diameter equal to or smaller than the wavelength of light in the binder. Recently, various kinds of ultrafine particles having a particle diameter of several tens of nanometers have been developed as nanoparticles, and these can be suitably used. Examples of these particles include Si, Ti, Ba, Ca, Na, K, Al, Mg, Zn, Zr, Y, Nb, Fe, Ce, Co, Er, In, Nd, Ni, Pb, Sb, Inorganic oxides selected from Yb, Sn, etc., or mixed oxides of these elements are preferably used, but are not limited thereto.

  In this case, the refractive index can be adjusted by selecting the type of ultrafine particles or adjusting the amount of ultrafine particles added to the binder.

  In the present invention, the refractive index changes sequentially from the concave and convex surface formed on the transparent base material in the outward direction. From the arrival rate of the transparent binder layer in contact with the concave and convex surface formed on the transparent base material, the outer transparent binder It means a case where the refractive index of the layer is sequentially increased or sequentially decreased.

  Furthermore, you may add a crosslinking agent and a network formation agent to all or one part of the binder of each transparent binder layer. Depending on the binder, this can improve heat resistance, scratch resistance, gas permeability, water resistance, solvent resistance, and the like.

-Lamination method of transparent binder layer-
Various methods can be employed for providing the first and second transparent binders on the uneven surface formed on the transparent substrate. For example, there is a method in which the transparent binder layer of the previous layer is formed by applying and drying, and then the transparent binder layer of the next layer is sequentially applied and dried while being laminated. In this case, surface treatment such as corona discharge treatment or plasma discharge treatment may be applied to the previous transparent binder layer in order to improve the wettability during the application of the next transparent binder layer. Further, a surfactant for improving wettability, an antistatic agent for preventing static electricity, and the like may be added to the coating solution for the transparent binder layer.

  In this way, when sequentially applying in a stacked manner, when applying a transparent binder layer to be applied next to the previous transparent binder layer, so as not to overdissolve the previous transparent binder layer and damage the surface state. It is also an effective method to select the solvent contained in the transparent binder layer coating solution or to apply the next transparent binder layer after curing the previous transparent binder layer by heat treatment or the like.

  Furthermore, when the previous transparent binder layer is an aqueous binder, it is also possible to select, for example, an organic solvent-soluble polymer insoluble in water for the next transparent binder layer. There is also a reverse method. Any of the commonly used coating methods may be used for coating the coating solution for the transparent binder layer. Examples thereof include a bar coater, a spin coater, a slit coater, an extrusion coater, a gravure coater, and a blade coater.

  Further, as another method of laminating the transparent binder layer, it is possible to form two or more transparent binder layers simultaneously by coating, and for this purpose, a known multilayer extrusion coater is preferably used. it can. In this case, immediately after applying the coating liquid in a laminar flow state, the coating liquid is once gelled in a low temperature zone or the like to fix the layer structure, and then dried to reliably form a multilayer structure. it can. For this method, a method widely used in the production of a color photographic film can be applied.

  On the other hand, it is also preferable to apply a transparent binder layer coating solution with multiple layers, and then, after intentionally delaying drying and mixing the layers to a certain extent, drying. In this case, the interface between layers becomes ambiguous, and as a result, there is no interface between layers with different refractive indexes, and a continuous refractive index gradient body can be obtained. High display can be obtained.

  The high light diffusibility and small depolarization characteristic of the manifestation of the effect are the form in which the refractive index of the multilayer structure of the transparent binder layer sequentially changes, the distortion of each transparent binder layer, and further from the convex part to the concave part. It seems to be caused by the composite of continuous thickness change of the transparent binder layer.

Next, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view schematically showing an embodiment of a light diffuser of the present invention. Reference numeral 10 is a support or temporary support, 12 is a transparent substrate having irregularities formed on the surface, and 14, 16, 18, and 20 are first to fourth transparent binder layers, respectively. As can be seen from the figure, the multilayer transparent binder layer is fixed as a curved surface of the binder layer itself under the influence of the uneven curved surface. Because of the curved surface of the transparent binder layer, the light incident on the light diffuser diffuses along the curved surface, so the light diffuser seems to act as a forward diffuser (diffuses only in the direction of light travel). It is.

  Further, in the present invention, the refractive index of each transparent binder layer changes sequentially from the concave and convex surface of the transparent substrate 12, and the refractive index difference between adjacent transparent binder layers is suppressed to within 0.10, preferably within 0.05. In this case, light can be transmitted efficiently with almost no backscattering. In addition, since this light diffuser has little interface scattering, depolarization hardly occurs, and it is possible to maintain polarization even if it is placed inside the polarizing film in a display element using polarized light, and a display element with extremely high contrast Can be obtained. The effect of the present invention can be obtained if the number of the transparent binder layers is three or more, but the effect is higher as the transparent binder layer is divided into multiple layers.

Further, the total of the thicknesses from the first layer to the third layer (that is, the thickness of the central portion between the concaves and convexes, indicated by T ₁ in FIG. 1) is the ten-point average of the concaves and convexes defined by JIS B0601. It is preferable not to exceed the roughness (Rz). In this case, it is because the curved surface of each transparent binder layer has a curvature effective for bending light. In addition, the average gap between the convex and concave portions of the concave and convex portions (average interval S value defined in JIS B0601) is 1/3 to 5 times the average height of the convex portion from the viewpoint of manufacturing suitability and diffusion effect. Is preferable, more preferably 1/3 to 2 times, still more preferably 1/2 to 1 times or less.

  FIG. 2 shows another embodiment of the light diffuser of the present invention. Here, the planarizing layer 22A or the adhesive layer 22B is provided as the fifth layer in the uppermost layer of the structure of FIG. The planarizing layer 22A is sometimes important when the light diffuser is actually used. For example, when the light diffuser of the present invention is used on the inner surface of a liquid crystal cell, it is effective for making the thickness of the liquid crystal layer disposed thereon uniform.

  In addition, when the light diffuser is viewed through the light diffuser as viewed from above, external light from above is scattered back and forth by the unevenness of the uppermost part of the diffuser (for example, the fourth transparent binder layer 20). When the contrast is lowered, the flattening layer 22A can prevent the contrast from being lowered due to backscattering. Of course, when the shape of the unevenness is large to some extent, the surface unevenness of the uppermost transparent binder layer may be preferable without the flattening layer 22A because the antiglare effect may be preferable. Good.

  In FIG. 2, when the fifth layer is an adhesive layer 22B or an adhesive layer, the light diffuser can be attached to another base material. Examples of the other substrate herein include a glass plate of a liquid crystal cell, a polarizing plate, a 1 / 4λ plate, a retardation plate, a viewing angle widening plate, a backlight light guide plate of a liquid crystal display device, and a prism plate. It is also possible to transfer only the light diffusing body onto another substrate by so-called transfer lamination in which the support is peeled off after being bonded to another substrate. For this purpose, a cushion layer for improving the compatibility with the release layer and the substrate or a cured layer for surface hardening after the release may be applied in advance on the support.

  These technologies are already widely used in dry laminate films and transfer color filters for printed circuit boards, and can be easily realized by applying them. In the case where the planarizing layer 22A is provided on the uneven surface as described above, the planarizing layer 22A is planarized by the post-application leveling leg (the coating liquid surface is flattened by the flow due to the surface tension), and then the solvent is removed. A method of solidifying without evaporation is preferred. For such a purpose, the flattening layer is preferably a solventless ultraviolet curable resin or electron beam curable resin.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Example 1)
The surface of a glass plate having a refractive index of 1.70 (an oxide mainly composed of Ba, Ti, and Si) was roughened by sandblasting. The ten-point average roughness (Rz) of the irregularities defined by JIS B0601 on the surface of the glass plate was 3.7 μm, and the average interval S value defined by JIS B0601 was 6.2 μm.
Next, TiO ₂ ultrafine particles with an average particle size of 30 nm, acrylic resin (BR-87: manufactured by Mitsubishi Rayon Co., Ltd.), and MEK were mixed at different ratios to prepare the following four types of coating solutions A to D.
A: The refractive index of the film after drying is 1.65.
B: The refractive index of the coating after drying is 1.57
The refractive index of the coating after Ci drying is 1.53
D: Refractive index of the coating after drying is 1.49
Subsequently, A liquid, B liquid, and C liquid were sequentially applied onto the coating layer so that the dry film thickness was 1.0 μm, and each was dried at 120 ° C. Finally, the liquid D was dried on the coating layer at 120 ° C. so as to have a dry film thickness of 5 μm to obtain a light diffuser.

(Example 2)
The glass plate was changed to a cellulose triacetate film, and irregularities were formed on the surface of the film by an embossing method. The ten-point average roughness (Rz) of the unevenness defined by JIS B0601 of this uneven surface was 4.9 μm, and the average interval S value defined by JIS B0601 was 7.3 μm.
Thereafter, liquid A, liquid B, liquid C and liquid D were applied and dried in the same manner as in Example 1. Finally, after this corona discharge treatment was performed on this coating layer, a commercially available acrylic pressure-sensitive adhesive was applied and dried to a thickness of 20 μm. The material (polyethylene terephthalate film) obtained by bonding the adhesive surface of this film to glass was peeled off to obtain a light diffuser formed on a glass plate.

(Example 3)
In the same manner as in Example 1, with respect to a glass plate having irregularities on the surface by the sandblasting method, the dry film thicknesses of the liquid A, the liquid B, the liquid C, and the liquid D are 1.2 μm, respectively, using an extrusion coater for simultaneous multilayers After simultaneous multilayer coating at a flow rate of 1, 2 μm, 1.2 μm, and 5 μm, preliminary drying at 70 ° C. was performed for 1 minute, followed by drying at 120 ° C. for 10 minutes to obtain a light diffuser.

  The backscattering property, light diffusing property, and depolarization property of the obtained light diffuser were evaluated by the following methods. Visual evaluation is made with a score of 5 stages, and the larger the number, the better the characteristics. Back diffusivity and depolarization are items for predicting the blackness of the black display state of the display device, and are important items that greatly contribute to contrast. On the other hand, light diffusivity is an item that contributes to whiteness and a wide viewing angle. If the rating is 3 or more, it can be practically used.

<Backscattering property>
The support surface side of the light diffuser is attached to a black mirror plate with an adhesive and visually confirmed from above. The better the black. The black color of the black mirror plate used for the test was scored 5, and the score was determined by relative comparison between samples.

<Unbiased>
Attach the light diffusive support surface to the aluminum vapor-deposited film with an adhesive, and start with this combination of a quarter-wave plate and a linear polarizing plate in the direction to completely cut the specular reflection light. More visually confirmed. The reflected light is not depolarized and the better it looks black. The black color in the state where the light diffuser was removed from the assembled test sample was assigned a score of 5, and the score was determined by comparing the results between the samples.

<Light diffuser>
The light diffusive support surface is attached to an aluminum vapor-deposited film with an adhesive and visually confirmed from above. It is so good that the metallic luster of aluminum disappears and it looks white. The whiteness of the fine paper was assigned a score of 5, and the score was determined by making a relative comparison between the samples.

  The evaluation results are shown in Table 1. The comparative example in the table described the results of the test using a sample in which the coating liquids A to D were not applied to the surface roughened glass plate described in Example 1.

  From the above results, it can be seen that the light diffuser of the present invention exhibits good forward diffusibility and hardly exhibits depolarization.

Example 4
The glass plate onto which the light diffuser of Example 2 was transferred was used as a substrate on one side of the liquid crystal cell and incorporated into a reflective liquid crystal display device as shown in FIG. In FIG. 3, 30 is a glass substrate, 32 is an Al reflective electrode, 34 is an alignment film, 36 is a liquid crystal, 38 is an alignment film, 40 is an ITO electrode, 42 is a color filter, 44 is a glass substrate, 46 is a light diffuser, Reference numeral 48 denotes a λ / 4 plate, and 50 denotes a polarizing plate. In the drawing, an arrow indicates a traveling direction of light.
As a result, an easy-to-see display element with good contrast and wide viewing angle was obtained.

(Example 5)
The glass plate onto which the light diffuser of Example 2 was transferred was used as a substrate on one side of the liquid crystal cell and incorporated into a reflective liquid crystal display device as shown in FIG. 4 is different from the apparatus of FIG. 3 in that the light diffuser 46 is provided between the color filter 42 and the glass substrate 44, and the other configurations are substantially the same. The reference numerals are the same as those in FIG. 3, and the arrows in the figure indicate the traveling direction of light.
As a result, it was possible to obtain a display device having good contrast and a wide viewing angle, and excellent resolution and color purity.

It is principal part sectional drawing which shows preferable one Embodiment of the light diffusing body of this invention. It is principal part sectional drawing which shows other preferable embodiment of the light diffusing body of this invention. It is principal part sectional drawing which shows preferable one Embodiment of the liquid crystal display device of this invention. It is principal part sectional drawing which shows other preferable embodiment of the liquid crystal display device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Support body 12 Transparent base material 14 1st transparent binder layer 16 2nd transparent binder layer 18 3rd transparent binder layer 20 4th transparent binder layer 22A Planarizing layer 22B Adhesion layer 30 Glass substrate 32 Al reflective electrode,
34 Alignment film 36 Liquid crystal 38 Alignment film 40 ITO electrode 42 Color filter 44 Glass substrate 46 Light diffuser 48 λ / 4 plate 50 Polarizing plate

Claims (11)

It has irregularities formed on the surface of the transparent substrate, and on this four-convex surface, at least three or more transparent binder layers whose refractive index has been sequentially changed outward from the irregular surface are laminated. Characteristic light diffuser. 2. The light according to claim 1, wherein the difference between the refractive index of the transparent binder layer in contact with the uneven surface formed on the surface of the transparent substrate and the refractive index of the transparent substrate is 0.10 or less. Diffuser. The light diffuser according to claim 1 or 2, wherein the difference in refractive index between adjacent transparent binder layers is 0.10 or less. The total thickness of the third transparent binder layer from the transparent binder layer in contact with the irregular surface formed on the surface of the transparent substrate is less than the ten-point average roughness (Rz) of the irregularities defined in JIS B0601. The light diffuser according to any one of claims 1 to 3, wherein The average interval between the convex and concave portions (the average interval S value defined in JIS B0601) is 1/3 to 5 times the ten-point average roughness (Rz) of the irregularities defined in JIS B0601. The light diffuser according to claim 1, wherein the light diffuser is characterized in that: 6. The unevenness formed on the surface of the transparent substrate is formed by any one of an embossing method, a photolithography method, a sand blasting method, and a holographic method. Item 1. A light diffuser according to item 1. 7. The method for producing a light diffuser according to claim 1, wherein at least two of the three or more transparent binder layers are simultaneously applied in multiple layers. A light diffusing material, wherein the light diffusing body according to any one of claims 1 to 6 is provided on a support. An image display device using the light diffuser according to any one of claims 1 to 6. The image display element according to claim 9, wherein the image display element is a liquid crystal display element using the light diffuser according to claim 1. The image display element according to claim 10, wherein the light diffuser is used on an inner surface of a liquid crystal cell.

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