Patent Application
20150049389
The present invention relates to a display device. Specifically, the present invention relates to a display device that is suitable as a display device including a display panel, such as a liquid crystal panel, and a front sheet, such as a touch panel.
Display devices including a display panel (e.g., liquid crystal panel) are widely used in apparatus, such as television, mobile phones, and PC displays. Great progress has been made especially in technology to produce small lightweight or big-screen liquid crystal display devices including a liquid crystal panel. The following techniques relating to such devices have recently attracted attention.
The first one is a technique of disposing a touch panel or a laminate of a protection sheet and a touch panel in front of a display panel in a display device for use as mobile devices, such as smart phones and tablet computers. The protection sheet is a component to protect the display panel, and is usually disposed in front of the touch panel.
The second one is a technique of using a display device including a display panel in an outdoor or semi-outdoor display medium, such as digital signage. A display device for digital signage may include a protection sheet in front of the display panel and may further include a touch panel.
The third one is a technique of using a film which has a moth-eye structure capable of suppressing reflection without optical interference as an anti-reflection film for a display device.
Herein, a component disposed in front of a display panel, such as a touch panel or a protection sheet, is also referred to as a front sheet.
The following arts relating to the above techniques have been known.
Patent Literature 1, for example, discloses a display device which includes a transparent touch panel with an anti-reflection function on a rear surface of a rearmost transparent substrate and a display panel. The transparent substrate has fine irregularities functioning as so-called a moth-eye structure on the rear surface.
Non-Patent Literature 1, for example, discloses a method for forming a moth-eye structure by blue ray disk technology.
Non-Patent Literatures 2 to 6, for example, disclose various methods for calculating the reflective properties of structures smaller than visible light wavelength, such as moth-eye structures.
Non-Patent Literature 7, for example, discloses resistive film touch panels, surface capacitance touch panels, and projective capacitance touch panels.
Patent Literature 2, for example, discloses a method for producing a touch panel glass. The method includes a surface-roughening treatment to adjust the surface roughness Ra of an entire surface or a part of a surface of the glass to 3 to 50000 Å. Patent Literature 2 mentions that the touch panel glass preferably has a Young's modulus of not less than 70 GPa.
Patent Literature 3, for example, discloses a tabular component which includes a substrate, a first moth-eye film on one surface of the substrate, and a second moth-eye film on the other surface of the substrate. Light consisting of reflected light on a surface of the first moth-eye film and reflected light on a surface of the second moth-eye film exhibits flat chromatic dispersion within the visible light range.
Patent Literatures 4, 5, and 6, for example, disclose technologies relating to interference-type anti-reflection films. Patent Literatures 4 and 5, for example, disclose a low refractive index thin film including a fine particle layer film in which a layer of fine particles and a layer of polymers are alternately laminated on a substrate. The fine particle layer film has a gap structure which does not scatter visible light.
Patent Literature 6, for example, discloses a low refractive index thin film including a substrate having a softening temperature of not higher than 200° C. and a thin film having a refractive index of from 1.20 to 1.30 on at least one surface of the substrate.
Regarding a method for forming a mold for forming a moth-eye structure, Patent Literature 7, for example, discloses a method for forming an anodic oxide layer, including the steps of (a) preparing an aluminum substrate having an aluminum surface, (b) anodic oxidizing the surface to form a barrier alumina layer, and (c) further anodic oxidizing the surface after the step (b) to form a porous alumina layer having a plurality of fine recesses.
In a display device including a display panel and a front sheet, an air layer (air gap), if present, between the display panel and the front sheet may become thinner when external pressure is locally applied to the front sheet (for example, when the front sheet is pressed with a finger). Reflected light on the rear surface of the front sheet and reflected light on the front surface of the display panel may interfere with each other to generate interference fringes. Interference fringes reduce the visibility of a screen of the display panel. Interference fringes may be derived from warping of the front sheet and/or display panel (usually display panel) caused during assembly of the display device. A recent demand for entirely thinner and lighter display devices has led to a trend of thinner air layer, display panel, and front sheet, resulting in an increase in the occurrence of interference fringes.
Light reflected on two interfaces which are apart from each other at a distance of more than 100 μm rarely interferes, and thus substantially no interference fringe occurs. In the case of two interfaces apart from each other at a distance of 50 to 100 μm, interference fringes may be visually observed when high coherent light (e.g., laser beam) is reflected, whereas interference fringes are not prominent when low coherent light (e.g., sunlight, fluorescent light) is reflected. In the case of two interfaces apart from each other at a distance of not more than 50 μm (especially not more than 10 μm), interference fringes are prominent even when low coherent light is reflected.
Interference fringes may be prevented from occurring by filling the air layer with an ultraviolet ray curable resin. After this treatment, however, the front sheet cannot be reassembled or replaced with new one. Moreover, if part of the resin is not exposed to ultraviolet rays, the unexposed part remains uncured.
The following describes a display device 101 of Comparative Embodiment 1 examined by the inventors of the present application.
As shown in
This is supposedly because of the following reasons. From an industrial point of view, the heights and the aspect ratios of protrusions in moth-eye structures cannot be sufficiently increased by the current technology. Moth-eye films thus have a little wavelength-dependent reflectance. Under such restriction, the heights and the aspect ratios (especially heights) of protrusions are set so that the luminous reflectance (Y value) of a moth-eye film is as low as possible in a front direction. Moreover, as shown in
The present invention was made in view of the aforementioned current status, and aims to provide a display device capable of suppressing the occurrence of interference fringes not only in a front direction but also in an oblique direction.
After various studies on display devices capable of suppressing the occurrence of interference fringes not only in a front direction but also in an oblique direction, the inventors of the present invention have focused on the reflection properties of moth-eye structures. The inventors have found that, when a minimal value of the reflection spectrum of a moth-eye structure in a front direction, especially a minimal value of the reflection spectrum of 5-degree specular reflection RS(5°), is controlled to be on the longer wavelength side than 550 nm as shown in
That is, one aspect of the present invention is a display device (hereinafter, also referred to as the display device of the present invention) including: a display panel, a front sheet disposed in front of the display panel with an air layer interposed therebetween, and a film (first film) disposed on the front surface of the display panel or on the rear surface of the front sheet. The air layer has a thickness of not more than 50 μm. At least one of the display panel and the front sheet can be warped. The thickness of the air layer varies within a range of 0 μm to 50 μm when at least one of the display panel and the front sheet is warped. The film includes a moth-eye structure (first moth-eye structure) on a surface contacting the air layer. A reflectance at at least one wavelength within a range of 600 to 780 nm is smaller than a reflectance at a wavelength of 550 nm in the reflection spectrum of 5-degree specular reflection of the moth-eye structure.
The configuration of the display device of the present invention is not especially limited by other components as long as it essentially includes such components.
The following describes preferable embodiments of the display device of the present invention. The preferable embodiments may be employed in combination. An embodiment including a combination of two or more of the following preferable embodiments is also a preferable embodiment.
The front sheet has a Young's modulus of less than 70 and may further include a component which deforms with the aforementioned film upon deformation of the film. Such a front sheet enables to more efficiently suppress the occurrence of interference fringes.
For achieving both good productivity and an effect of suppressing the occurrence of interference fringes, the moth-eye structure preferably has a height of from 200 nm to 350 nm, and more preferably has a maximum height of not more than 300 nm.
For similar purposes, the moth-eye structure has an aspect ratio of preferably not more than 3, and more preferably not more than 2.5.
In view of antireflection performance in an oblique direction, the moth-eye structure preferably has an aspect ratio of not less than 0.5.
For improving the visibility of a screen of the display panel in observation from an oblique direction, the moth-eye structure has a pitch of preferably not longer than 150 nm, and more preferably not longer than 120 nm. In this case, the moth-eye structure preferably has a pitch randomness of from 25% to 35%. Such a moth-eye structure can surely and effectively improve the visibility in an oblique direction.
For more effectively suppressing the occurrence of interference fringes, the display device of the present invention preferably further includes a second film disposed on either of the front surface of the display panel or the rear surface of the front sheet on which the film (first film) is not disposed. The second film preferably includes a moth-eye structure (second moth-eye structure) on a surface contacting the air layer.
For particularly effectively suppressing the occurrence of interference fringes, a reflectance at at least one wavelength within a range of 600 nm to 780 nm is preferably smaller than the reflectance at a wavelength of 550 nm in the reflection spectrum of 5-degree specular reflection of the second moth-eye structure.
From similar points of view to those concerning the first film, the second film preferably has properties similar to those of the first film.
Specifically, the second moth-eye structure has a height of from 200 nm to 350 nm, and more preferably has a maximum height of not more than 300 nm.
The second moth-eye structure has an aspect ratio of preferably not more than 3, and more preferably not more than 2.5.
The second moth-eye structure preferably has an aspect ratio of not less than 0.5.
The second moth-eye structure has a pitch of preferably not longer than 150 nm, and more preferably not longer than 120 nm. In this case, the second moth-eye structure preferably has a pitch randomness of from 25% to 35%.
Another aspect of the present invention is a film (hereinafter, also referred to as a film of the present invention) having a moth-eye structure on a surface, the moth-eye structure having a pitch of not longer than 150 nm.
The configuration of the film of the present invention is not especially limited by other components as long as it essentially includes such components.
For similar points of view to those concerning the display device of the present invention, examples of preferable embodiments of the film of the present invention include the preferable embodiments of the first film in the display device of the present invention. The preferable embodiments of the film of the present invention may be employed in combination. An embodiment including a combination of two or more of the preferable embodiments is also a preferable embodiment.
The present invention enables to provide a display device capable of suppressing the occurrence of interference fringes not only in a front direction but also in an oblique direction.
a) shows an SEM photograph of an entire eye of a moth, and
a) and
a) is a schematic perspective view illustrating an anodic oxidation process.
a) and
a) and
a) and
a) and
a) and
a) and
a) and
a) and
a),
The terms used herein will be defined below.
The term “front” means a position closer to a viewer. Further, the term “front surface” means a surface on the viewer side. The “rear surface” or “back surface” means a surface opposite to the viewer side. Thus, the rear surface of a front sheet is a surface facing a display panel. The front surface of the display panel is a surface facing the front sheet.
The reflection spectrum of x-degree (x is any number satisfying the inequation: 0≦x<90) specular reflection means the spectrum of specularly reflected light that reflects at a reflection angle of x°. The reflection angle is formed by the normal direction of the main surface of a sample and the direction of the reflected light, and the incident angle is formed by the normal direction and the direction of the incident light.
The Young's modulus is a value determined by a bending resonance method.
The height of the moth-eye structure is an average of the heights of any ten protrusions.
The aspect ratio of the moth-eye structure is a value obtained by dividing the height of a moth-eye structure by the pitch of the moth-eye structure.
The pitch of the moth-eye structure is an average of the pitches of any ten pairs of protrusions. A pitch of protrusions is a distance between two points at which hypothetical perpendicular lines from the apexes of two adjacent protrusions reach the same plane. The plane is parallel to the main surface of the moth-eye film.
In the case of producing a moth-eye structure using a mold having a large number of depressions on its surface, the pitch of the moth-eye structure is substantially the same as the pitch of the mold. Similarly to the case of the moth-eye structure, the pitch of the mold is an average of the pitches of any ten pairs of depressions. A pitch of depressions is a distance between two points at which hypothetical perpendicular lines from the deepest points of two adjacent depressions reach the same plane. The plane is parallel to the main surface of the mold.
Herein, fractions of the measured values of the heights and the pitches of protrusions and the depths and the pitches of depressions are treated by the following method (method also called Swedish rounding). Namely, when the units digit is 3, 4, 5, 6, or 7, it is round down/up to the nearest 5, and when 8, 9, 0, 1, or 2, to the nearest 0.
The pitch randomness of the moth-eye structure is a value obtained as follows: the distances from the apex of a protrusion to the apexes of the first to third nearest protrusions are measured for multiple protrusions; an average value (average distance) and the standard deviation of the distances are calculated; the standard deviation is divided by the average value; and the result is expressed in percentage.
In the case of producing a moth-eye structure with a mold having a large number of depressions on its surface, the pitch randomness of the moth-eye structure is substantially the same as the pitch randomness of the mold. Similarly to the pitch randomness of the moth-eye structure, the pitch randomness of the mold is a value obtained as follows: the distances from the deepest point of a depression to the deepest points of the first to third nearest depressions are measured for multiple depressions; an average value (average distance) and the standard deviation of the distances are calculated; the standard deviation is divided by the average value; and the result is expressed in percentage.
The number of the protrusions or depressions for calculating the pitch randomness of the moth-eye structure or the mold may be unlimitedly set appropriately. The number may be within a range of 100 to 300 for reducing errors.
The average value herein means an arithmetic mean value unless otherwise stated.
The visible light means light having a wavelength of 380 to 780 nm. A wavelength of not longer than the visible light wavelength specifically means a wavelength of not longer than 380 nm.
The present invention will be mentioned in more detail referring to the drawings in the following embodiments, but is not limited to these embodiments.
A display device 1 of this embodiment includes a display panel 10, a translucent front sheet 30, and a film (moth-eye film) 40 having a moth-eye structure (nanostructure) 41, as shown in
At least one of the display panel 10 and the front sheet 30 can be warped, usually when an external pressure is applied thereto to cause internal stress. As shown in
The region of the air layer 20 with an uneven thickness may be in any size as long as the region can be visually observed by naked eyes. The size is usually not smaller than 1 mm2 (preferably not smaller than 100 mm2) but not larger than the display area of the display panel 10.
The pitches of the protrusions 43 are not longer than the visible light wavelength. The protrusions 43 are each tapered toward the apex. A cross section of each protrusion 43 parallel to the main surface of the moth-eye film 40 (hereinafter, also referred to as horizontal cross section) closer to the apex has a smaller area.
The moth-eye structure 41 enables to effectively reduce light reflection at an interface between the air layer 20 and the moth-eye film 40. The principle will be described below.
When the refractive index suddenly changes within a distance smaller than the wavelength of incident light at an interface between two substances in the normal direction, the light reflects at the interface. Conversely, light reflection can be prevented by reducing the change in the refractive index at the interface. The substrate 42 has a refractive index of about 1.3 to 1.8, which is greatly different from the refractive index (=1.0) of air. The pitches and the heights of the protrusions 43 are in the nanometer scale. The protrusions 43 are spread over the substrate 42 like an eye of a moth as shown in
The moth-eye film 40 can exert greater antireflection performance than conventional LR films and AR films as shown in
The reflectance of the moth-eye film 40 can be determined not only by actual measurement but also by calculation. Examples of the measurement method include calculation based on the effective refractive index medium theory (effective medium theory). According to the theory, a submicron-scale structure is coarse grained and is considered as a medium having an average reflective index of the solute of space including the structure (such as solute forming the structure, or air). According to the theory, the moth-eye structure 41 can be considered as a multi-layered film consisting of a large number of films whose refractive indexes vary by gradation.
Although the moth-eye film 40 exerts excellent antireflection performance over the entire visible light range, the reflectance shows a little wavelength dependence due to insufficient heights and aspect ratios of the protrusions 43. Specifically, the reflection spectrum of the moth-eye structure 41 in a front direction (for example, reflection spectrum of 5-degree specular reflection RS (5°)) and the reflection spectrum in an oblique direction (for example, reflection spectrum of 45-degree specular reflection RS (45°)) each include at least one minimal value as shown in
In this embodiment, a reflectance at at least one wavelength within a range of from 600 nm (preferably from 650 nm) to 780 nm is set to be smaller than a reflectance at a wavelength of 550 nm in the reflection spectrum of 5-degree specular reflection RS(5°). This setting enables to prevent the reflectance at a wavelength of 550 nm from increasing in the reflection spectrum in an oblique direction (e.g., reflection spectrum of 45-degree specular reflection RS (45°)), thereby preventing an increase in the Y value in an oblique direction. Accordingly, occurrence of interference fringes can be suppressed in observation of a screen from an oblique direction even when at least one of the display panel 10 and the front sheet 30 is warped.
Even if the reflection spectrum RS(5°) is set as above, the Y value in the moth-eye film 40 in a front direction does not extremely increase. Thus, occurrence of interference fringes in a front direction can also be suppressed.
As mentioned earlier, the conditions for this embodiment are set such that a low reflectance is achieved in as wide a viewing angle range as possible, not such that the best reflectance is achieved in a front direction.
Moth-eye films in which the heights and the aspect ratios of protrusions are sufficiently high have a reflectance with no wavelength dependence. Unfortunately, industrial production of such films is difficult.
In contrast, this embodiment, in which the heights and the aspect ratios of the protrusions 43 are not necessarily very high, can achieve both good productivity and an effect of suppressing the occurrence of interference fringes.
The specularly reflected light spectrum of the moth-eye film 40 depends on the pitch and height, especially height, of the moth-eye structure 41. Thus, the specularly reflected light spectrum of the moth-eye film 40 can be appropriately controlled by appropriately changing the pitch and height (especially height) of the moth-eye structure 41.
The reflection spectrum of LR films can be controlled. However, since LR films have high reflectance, occurrence of interference fringes cannot be suppressed even if the reflection spectrum is controlled.
As shown in
For achieving ideal antireflection performance with no wavelength dependence, the heights of the protrusions 43 are preferably as high as possible in the nanometer scale, which unfortunately leads to lower industrial productivity. Thus, for achieving both good productivity and an effect of suppressing the occurrence of interference fringes, the moth-eye structure 41 preferably has a height of from 200 nm to 350 nm, and more preferably has a maximum height of not higher than 300 nm. A height of less than 200 nm may fail to achieve sufficient antireflection performance. All the protrusions 43 may or may not have the same height.
For achieving ideal antireflection performance with no wavelength dependence, the aspect ratios of the protrusions 43 are preferably as high as possible in the nanometer scale, which unfortunately leads to lower industrial productivity. Thus, for achieving both good productivity and an effect of suppressing the occurrence of interference fringes, the moth-eye structure 41 has an aspect ratio of preferably not more than 3, and more preferably not more than 2.5. A smaller aspect ratio does not negatively affect the antireflection performance in a front direction but may deteriorate the antireflection performance in an oblique direction. Thus, the moth-eye structure 41 preferably has an aspect ratio of not less than 0.5. All the protrusions 43 may or may not have the same aspect ratio.
The protrusions 43 may have any pitch that is not longer than the visible light wavelength. For improving the visibility of a screen of the display panel 10 from an oblique direction, the pitch of the moth-eye structure 41 is preferably not longer than 150 nm, and more preferably not longer than 120 nm. All the protrusions 43 may have the same pitch; namely, the protrusions 43 may be arranged at a fixed interval. For more surely and effectively achieving the above effects, or specifically, for preventing the visibility of the screen of the display panel 10 from being deteriorated by markedly strong diffracted light when the screen is observed from an oblique direction, the protrusions 43 preferably do not have the same pitch, namely the protrusions 43 are preferably irregularly arranged. More specifically, the moth-eye structure 41 preferably has a pitch randomness of from 25% to 350.
The moth-eye film 40 is not directly touched almost at all after a final product is completed. Thus, the moth-eye structure 41 does not necessarily have a high scratch resistance. Scratch resistance at about a level that endures handling during assembly is sufficient.
The protrusions 43 may have a variety of shapes. All the protrusions 43 may or may not have the same shape.
Examples of the horizontal cross sectional shape of the protrusions 43 include round, elliptical, triangular, quadlangular, and other polygonal shapes. Each protrusion 43 entirely has the same horizontal cross sectional shape, or different horizontal cross sectional shape depending on the position of the cross section. In view of employing a highly productive production method (described later) using a mold, preferably each protrusion 43 entirely has a round horizontal cross section.
A cross section of each protrusion 43 orthogonal to the main surface of the moth-eye film 40 (hereinafter, also referred to as orthogonal cross section) is in a sine-wave like, triangular, or trapezoidal shape or other shapes, for example. The apex of each protrusion 43 may be flat. Adjacent protrusions 43 may have a flat area between them. For improving the antireflection performance in the above cases, the flat area is preferably as small as possible. For similar purposes, the moth-eye structure 41 preferably includes no flat area.
As shown in
For preventing the antireflection effect from being anisotropic, the protrusions 43 are preferably arranged in a dotted pattern as shown in
The substrate 42, which is integrally formed with the protrusions 43, supports the protrusions 43. Preferable examples of the material of the substrate 42 and the protrusions 43 include ultraviolet ray curable resins such as acrylate resin, and methacrylate resin.
The moth-eye film 40 may include another substrate other than the substrate 42. For example, as shown in
The refractive indexes of the protrusions 43 and a substrate such as the substrate 42 may be set appropriately, but are usually 1.3 to 1.8. The difference between the refractive index of the protrusions 43 and that of the substrate is preferably as small as possible, or more specifically the difference is preferably not more than 0.005, and more preferably not more than 0.002.
The display device 1 may further include a moth-eye film 50 that is similar to the moth-eye film 40 as shown in
The features of the moth-eye film 50, such as characteristics of the reflection spectrum and the shapes of the protrusions, may be set appropriately. The moth-eye film 50 preferably has the features described in relation to the moth-eye film 40.
The moth-eye film 40 and the moth-eye film 50 may be attached to the front sheet 30 and the display panel 10, respectively, with an adhesive, preferably with a pressure sensitive adhesive. Use of a pressure sensitive adhesive enables detachment and reattachment of the films and easy change of the films.
The front sheet 30 may have any function, but preferably has a function of, for example, a touch panel, a protection sheet, a parallax barrier, or a component having these functions in combination.
The type of the touch panel may be appropriately selected. Examples of the touch panel include resistance film type, capacitive type, ultrasonic type, and electromagnetic induction type touch panels. Examples of the capacitive type touch panel include surface capacitive type and projection capacitive type touch panels. Resistance film type touch panels cost low. Surface capacitive type touch panels distinctively have high precision, high durability, and high sensitivity. Projection capacitive type touch panels are suitable for mobile devices, especially smart phones and tablet computers.
Non Patent Literature 2, which relates to touch panels, describes an example where a touch panel in a size of 40 inch has a surface deflection (warpage) of 1 mm or more. Thus, interference fringes are considered to occur in a conventional display device with a large touch panel. In contrast, the embodiment of the present invention can exert an effect of suppressing the occurrence of interference fringes regardless of the sizes of the display panel 10 and the front sheet 30.
Non Patent Literature 2 also describes the trend of using glass rather than plastic as a material of protection sheets for touch panels to produce thinner mobile phones with high quality sensation. It describes that use of chemically tempered glass is studied for enhancing the strength, presumably because plastic is vulnerable to scratches while glass is not. Patent Literature 2 describes that the glass for touch panels preferably has a Young's modulus of not less than 70 GPa. Moreover, glass for touch panels having a Young's modulus of 7300 kGf/mm2, i.e., approximately 73 GPa (Trade Name: ULTRA FINE FLAT GLASS, produced by NSG Group) is available from the market. Patent Literature 1 describes that transparent substrates having fine irregularities thereon are preferably rigid, not flexible enough to be deformed by a pressure by pressing a touch panel. Moreover, glass plates having a Young's modulus of approximately 7100 kGf/mm2 are known.
Thinner display devices are and will be continuously desired. Thinner substrates, such as substrates for touch panels and protection sheets for touch panels, may hardly maintain a Young's modulus of not less than 70 GPa. Moreover, scratch resistant plastic films are being developed. If plastic films are used instead of glass substrates, such films may hardly maintain a Young's modulus of not less than 70 GPa. In these cases, a rigidity enough to prevent deformation by pressing cannot be surely achieved. Examples of materials that can substitute for glass include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin, and polycarbonate, among which PET and acrylic resin are preferred. Also, the following materials are known: PET films having a Young's modulus of approximately 55 kGf/mm2, PET films having a Young's modulus of approximately 630 kGf/mm2, PET monofilament having a Young's modulus of approximately 870 kGf/mm2, and PET monofilament having a Young's modulus of approximately 1500 kGf/mm2; PEN films having a Young's modulus of approximately 63 kGf/mm2, PEN films having a Young's modulus of approximately 740 kGf/mm2, and PEN monofilament having a Young's modulus of approximately 2400 kGf/mm2; acrylic plates having a Young's modulus of approximately 340 kGf/mm2; and polycarbonate plates having a Young's modulus of approximately 210 kGf/mm2.
The display device 1 of the present embodiment, which can exert an effect of suppressing the occurrence of interference fringes regardless of the rigidity of the front sheet 30, can greatly contribute to the aforementioned circumstances.
Specifically, the front sheet 30 may include a component (usually, an insulating substrate or an insulating film facing the entire display region of the display panel 10) which deforms with the moth-eye film 40 upon deformation of the moth-eye film 40. The deformable component may have a Young's modulus of less than 70 GPa. This structure can also sufficiently exert an effect of suppressing the occurrence of interference fringes.
The display panel 10 may be of any type, and examples thereof include liquid crystal panels, organic EL panels, inorganic EL panels, and PDPs.
If the display panel 10 is a liquid crystal panel, a pair of substrates 11 and 12 each having a thickness of 0.7 mm are assembled to form a liquid crystal cell as shown in
The air layer 20 provides a space for deformation of the front sheet 30 when external force is applied to the front sheet 30. Deformation of the front sheet 30 disperses and absorbs external force, and thus the display panel 10 is protected.
The air layer 20 may have any thickness of not more than 50 μm. The thickness may be appropriately set depending on the purpose of use of the present embodiment and may be not more than 10 μm. The air layer 20 having such a thickness enables to more effectively suppress the occurrence of interference fringes. In the case of the air layer 20 having a thickness of more than 100 μm, basically interference fringes do not occur. The air layer 20 may have a thickness of not less than 10 μm, considering that the tolerance of the total thickness of the polarizer, optical film, and liquid crystal cell is not more than 10 μm in the liquid crystal display device.
The moth-eye structure may be formed by any method in the present embodiment. In view of the productivity and cost, a preferable method includes preparing a mold and transferring the shape of the mold. A method using a mold with an anodized aluminum layer (hereinafter, also referred to as a porous alumina mold) is particularly preferable. The following describes a method of producing the moth-eye film 40 or 50 using a porous alumina mold.
First, a substrate 70 is prepared. The substrate 70 has two types, a flat plate and a seamless roll. A glass plate 71 having a size of 1.6 m×1 m×2.8 mm (thickness) as shown in
Then, an aluminum film having a thickness of approximately 0.5 μm to 2 μm is formed by sputtering on the surface of the glass plate 71 or the electrodeposited sleeve 73.
Next, anodic oxidation and etching treatment are repeatedly performed on the substrate 70 as shown in
Thereafter, a mold release agent is applied to the substrate 70. In the case of the glass plate 71, it is immersed in a mold release agent as shown in
A porous alumina mold having an inverted shape of the moth-eye structure is completed through the above steps. The mold is used for a shape transfer process.
In the case of the glass plate 71, as shown in
In the case of the aluminum pipe 72 or the electrodeposited sleeve 73, as shown in
The moth-eye structure having an aspect ratio of more than 3 would easily cause clogging of the resin in the porous alumina mold, breaking of the substrate film 75, and peeling of the anodized layer.
For preventing the clogging of the resin, a mold release agent is preferably added to the ultraviolet ray curable resin. A mold release agent usually acts as a foaming agent. Thus, a defoaming agent is preferably added together with a mold release agent if added.
Regarding the moth-eye structure having a higher aspect ratio, the temperature of the resin and the pressure for pressing the embossing device are preferably as high as possible in order to prevent foam generation in the resin.
According to the above method, 14 kinds of moth-eye films (films 1 to 14) were actually produced using a glass plate as a substrate under conditions shown in Table 1. The porous alumina molds used for the films 1 to 14 were produced under different conditions, specifically, different voltages between anode and cathode (hereinafter, also referred to simply as voltage) during the anode oxidation treatment, different times for the anode oxidation treatment (AO time), and different etching times. A TAC film having a thickness of 80 μm was used as a substrate film. The ultraviolet ray curable resin was controlled to have a thickness of 8 μm upon application.
The depth D of the pores of the porous alumina mold is an average value of the depths of any 10 pores in an SEM photograph of a cross section (a face orthogonal to the main face) of the mold.
The height H of the moth-eye structure is an average value of the heights of any 10 protrusions in an SEM photograph of a cross section (a face orthogonal to the main face) of the moth-eye film.
The pitch P of the moth-eye structure is an average value of the pitches of any 10 pairs of pores in an SEM photograph of a cross section (a face orthogonal to the main face) of the mold.
The pitch of the moth-eye structure usually depends on the voltage during the anode oxidation treatment. This test gave a similar result. A higher voltage led to a longer pitch of the moth-eye structure.
Next, 14 samples were prepared from the films 1 to 14. The specularly reflected light spectra of the films 1 to 14 were measured using these samples. As shown in
Table 2 shows the result of the film 1.
Table 3 shows the result of the film 2.
Table 4 shows the result of the film 3.
Table 5 shows the result of the film 4.
Table 6 shows the result of the film 5.
Table 7 shows the result of the film 6.
Table 8 shows the result of the film 7.
Table 9 shows the result of the film 8.
Table 10 shows the result of the film 9.
Table 11 shows the result of the film 10.
Table 12 shows the result of the film 11.
Table 13 shows the result of the film 12.
Table 14 shows the result of the film 13.
Table 15 shows the result of the film 14.
Comparison among the films having the same pitch (films 1 to 3, 4 to 11, and 12 to 14) indicates the following.
As the height of the moth-eye structure increases, the entire spectrum shifts to the right.
As the measurement angle increases, the entire spectrum shifts to the upper left.
These changes are well noted by paying attention to the minimal point of the spectrum.
Table 16 below shows the Y values of the films 1 to 14 calculated based on the spectra. Fourteen kinds of display devices are assembled using the films 1 to 14. Each display device includes a display panel and a touch panel having one of the films 1 to 14 attached to the rear surface. The display devices provided with any of the film 1, 2, 4, 5, 6, and 12 correspond to the comparative examples of the present invention. The display devices provided with any of the film 3, 7, 8, 9, 11, 13, and 14 correspond to the examples of the present invention. The display device provided with the film 10 corresponds to the reference example. Occurrence of interference fringes in each display device was checked by pressing the front face of the touch panel by a finger. The result shows that the interference fringes are weakened to an unnoticeable level when the Y value is not more than 0.25%.
These results indicate that the following films are effective for weakening the interference fringes in an angle from the normal direction of the display panel to a 45 degree direction. The film 3 is the best among the films 1 to 3. Though the film 2 has a low Y value in a 5 degree direction, the film 3 is preferred for suppressing interference fringes in a 5 degree direction and a 45 degree direction. For similar purposes, the films 7 to 11 are preferred among the films 4 to 11, and the films 13 and 14 are preferred among the films 12 to 14. A higher moth-eye structure exerts a higher effect of suppressing the occurrence of interference fringes but deteriorates the film-releasing property in the shape transferring step. A lower possible moth-eye structure is thus preferable in industrial production. Hence, the films 7, 8, and 10 are preferable for achieving both good productivity and an effect of suppressing the occurrence of interference fringes.
Interference fringes in a direction of not more than 45 degree were evaluated because the visibility in the range is especially important for mobile devices such as smart phones and tablet computers.
The above results show that the specularly reflected light spectrum of the moth-eye film depends on the pitch and height of the moth-eye structure, especially greatly on the height.
Similar results were obtained for the moth-eye films produced using the aluminum pipe or the electrodeposited sleeve as a substrate.
The specularly reflected light spectra of the moth-eye structures were calculated based on the effective medium theory. The results are described below. The reflection spectrum of 0-degree specular reflection and reflection spectrum of 45-degree specular reflection of three kinds of moth-eye structures having a height of 180 nm, 240 nm, and 300 nm were obtained.
Similar results as those in the aforementioned test were obtained in all the cases. Namely, the followings are clarified.
As the height of the moth-eye structure increases, the entire spectrum shifts to the right.
As the measurement angle increases, the entire spectrum shifts to the upper left.
The three techniques described below are known for calculating reflection of light on a structure smaller than visible light wavelength.
The effective medium theory is a calculation technique in which a submicron-scale structure is coarse grained and is considered as a medium that has an average reflective index of the solute of space including the structure (such as solute forming the structure, or air). For the calculation, a moth-eye structure is considered as a multi-layered film consisting of a large number of films whose refractive indexes vary by gradation.
RCWA is a technique of solving a relational expression (coupling equation) between incident light to a submicron-scale diffraction grating and diffracted light.
FDTD is a technique of sequentially solving Maxwell's equations.
A report says that all the techniques produce an identical result. The inventors of the present invention used the technique 1: the effective medium theory for the calculation. Herein, the techniques 2 and 3, which are common calculation methods (softs for the calculation are commercially available), are not examined in detail.
Non Patent Literatures 3 and 4 describe the technique 1 in detail. Thus, a method of applying this technique to a moth-eye structure is briefly described herein. The technique 1 includes the following steps 1 to 3.
Step 1
A moth-eye structure is finely divided into multiple layers in the thickness direction (see
Step 2
Herein, the refractive index of each layer is an average refractive index based on the volume ratio of the solutes forming the layers (see
Step 3
Reflected light of light incident to the multi-layered film is calculated. The calculation is of a level that can be calculated by a common spreadsheet application. The parameters for the calculation are as follows.
The input values are incident angle, wavelength, number of the layers, thickness of each layer, and refractive index (may be complex numbers) of each layer.
A phase change δj of each layer is expressed by the following expression.
A characteristic matrix [Mj] of each layer is expressed by the following expression.
A characteristic admittance Yj of each layer is expressed by the following expression.
Y
i=√{square root over (∈0/μ0)}ni cos θi
A product [M] of the characteristic matrixes of the layers is expressed by the following expression.
As shown in
The output value is a reflectance Ro, and is expressed by the following expression.
The relation of the characteristic matrixes [Mj] is determined as described below. In the case of s-polarized light, the following expressions are derived.
The right side and left side of the following Faraday's law formula are modified.
These results derive the following relational expressions.
Also, the following relational expressions are derived from the boundary conditions.
E
j
=E
j
+
+E
j
−
E
j-1
=E
j
+
e
iδ
+E
j
−
e
−iδ
The relational expressions derive the relationship of the characteristic matrixes [Mj] of the layers.
The concept of a pitch does not exist in the effective medium theory, whereas it exists in the techniques 2 and 3.
The following describes haze of a moth-eye film.
When a moth-eye film is irradiated with light, a haze component is a component that is diffused without linearly advancing through the film nor without being specular reflected. As shown in
Haze=Diffused light/(Linearly advancing light+Transmitted light)=(Total light transmitted−Linearly advancing light)/Total light transmitted
The points to be considered concerning the haze of a moth-eye film are that light to be incident to a sample is orthogonally applied to the sample, and that only the transmitted light is measured without measuring back-scattered light.
A viewer of a moth-eye film significantly recognizes haze when the moth-eye film 60 is irradiated with light from an oblique direction as shown in
Thus, not only reduction of the haze measured by the method shown in
Two kinds of moth-eye films (films 15 and 16) were actually produced by the same method as that for the films 1 to 14, except for the following. The conditions for producing the porous alumina mold are different between the films 1 to 14 and the films 15 and 16. Specifically, the voltage in the anode oxidation treatment, the time for the anode oxidation treatment (AO time), and the time for the etching are different among the films. The mold for the film 15 was produced under a voltage of 55 V, an AO time of 120 seconds, and an etching time of 8 minutes. The mold for the film 16 was produced under a voltage of 65 V, an AO time of 90 seconds, and an etching time of 10 minutes. Further, the film 3, film 7, film 15, film 16, and film 13 each are attached to a business-card-size glass plate to prepare five kinds of samples. The voltages for the anode oxidation treatment in the production of the porous alumina molds for the films 3, 7, 15, 16, and 13 are 35 V, 45 V, 55 V, 65 V, and 80 V, respectively. The pitches of the moth-eye structures of the films 3, 7, 15, 16, and 13 are 85 nm, 115 nm, 135 nm, 160 nm, and 190 nm, respectively.
The five kinds of samples were hung in front of a fluorescent light as shown in
Separately, five kinds of samples were prepared from the films 3, 7, 15, 16, and 13. The front hazes and the deviation hazes of the films 3, 7, 15, 16, and 13 were measured using the samples. As shown in
The front haze was measured with a haze meter NDH 2000 produced by Nippon Denshoku Industries Co., Ltd. The deviation haze was measured with a spectrophotometer CM-2600d produced by Konica Minolta Sensing under the specular components excluded (SCE) mode that excludes specular reflection. As shown in
A moth-eye film (film 17) was actually produced using a mold in which the photoresist is patterned by interference exposure. The moth-eye structure of the film 17 had a pitch of 200 nm. The protrusions of the moth-eye structure were randomly arranged in the films 1 to 16 produced using the porous alumina mold, whereas the protrusions of the moth-eye structure were regularly arranged in a lattice pattern in the film 17. Moreover, the film 13 (pitch=190 nm) and the film 17 (pitch=200 nm) each were attached to a business-card-size glass plate to prepare two kinds of samples. The two kinds of samples were hung in front of a fluorescent light as shown in
An aluminum film having a thickness of 1 μm was formed by sputtering on surfaces of a plurality of glass substrates. The substrates having the films were subjected once to anodic oxidation so that an anodized layer (layer 1, 2, 3, 4, or 5) having a porous surface was formed. The layers 1 to 5 were formed under different anodic oxidation conditions as follows. The anodic oxidation was performed by immersing the substrate in an oxalic acid solution at 5° C. for forming the films 1 to 4, whereas the anodic oxidation was performed by immersing the substrate in a tartaric acid solution at room temperature (22° C.) for forming the film 5. The layer 1 was formed under a concentration of the oxalic acid solution of 0.03 wt %, a voltage of 45 V, and an AO time of 200 seconds. The layer 2 was formed under a concentration of the oxalic acid solution of 0.03 wt %, a voltage of 80 V, and an AO time of 350 seconds. The layer 3 was formed under a concentration of the oxalic acid solution of 0.6 wt %, a voltage of 200 V, and an AO time of 16 seconds. The layer 4 was formed under a concentration of the oxalic acid solution of 0.6 wt %, a voltage of 300 V, and an AO time of 5 seconds. The layer 5 was formed under a concentration of the tartaric acid solution of 2 wt %, a voltage of 200 V, and an AO time of 10 minutes.
An SEM photograph (magnification=20000×) of the surface of each layer was taken. Distances from the center of each pore to the centers of the first to third nearest pores were measured for approximately 200 pores in a few micrometers square of the photograph (see
If the layer was further repeatedly subjected to anodic oxidation and etching treatment, the pores would become deeper and larger so that the layer can be a porous alumina mold. Thus, the average distance and the pitch randomness of each layer are substantially identical to the average distance and the pitch randomness of pores of a porous alumina mold produced by repeating anodic oxidation under the same condition as that of the anodic oxidation of the layer, and etching, and are also substantially identical to the average distance and pitch randomness of the protrusions of the moth-eye structure produced using the mold. Thus, the above results revealed that the pitch randomness of the moth-eye structure of a moth-eye film produced using the porous alumina mold is almost constant, in a range of 25% to 35%, regardless of the condition for the anodic oxidation. A pitch randomness of the moth-eye structure within the range enables to prevent the film from being locally very bright like the moth-eye film having regularly arranged protrusions. Furthermore, a pitch randomness of the moth-eye structure within the range and a pitch of the moth-eye structure being not longer than 150 nm (preferably not longer than 120 nm) together enable to suppress the front haze and deviation haze on the entire film.
The anodic oxidation condition for the layer 1 is the same as that for the mold for the film 7. The anodic oxidation condition for the layer 2 is the same as that for the mold for the film 13. Moreover, the pitch randomness of an anodized layer formed according to the method described in Patent Literature 7 is almost the same as the pitch randomness of the layers 1 to 5.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-034547 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/052040 | 1/30/2013 | WO | 00 |
