JP7615530B2 - Optical sheet, polarizing plate with optical sheet, touch panel with optical sheet and display device - Google Patents

Description

The present invention relates to an optical sheet that imparts an optical effect to the image light formed by a display panel. In addition, the present invention relates to a polarizing plate with an optical sheet, a touch panel with an optical sheet, and a display device that include the optical sheet.

Optical sheets that are installed on display panels such as liquid crystal display panels and organic LED (Organic Light Emitting Diode) panels and impart optical effects to the image light formed by the display panel have been known for some time.

For example, Patent Document 1 discloses a louver film as an optical sheet. This louver film has an optical functional layer in which light absorbing sections and light transmitting sections are arranged alternately.

Louver films are used to prevent the image light from the display panel from spreading over a wide area, and to provide a function to prevent peeping.

On the other hand, Patent Document 2 discloses a display device equipped with an organic LED panel and a touch panel. Patent Document 2 proposes bonding multiple components constituting the display device with an adhesive with a low dielectric constant, thereby suppressing malfunction of the touch panel.

JP 2017-45060 A International Publication No. 2019/049726

Incidentally, louver films are sometimes incorporated into display devices with touch panels. In this case, if the dielectric constant of the louver film is high, the touch panel is more likely to malfunction due to the influence of driving noise generated in the display panel. However, optical sheets such as louver films usually have a multi-layer structure, which makes it difficult to adjust the dielectric constant. Furthermore, louver films may contain components in the light absorbing portion that can increase the dielectric constant, in which case adjusting the dielectric constant becomes even more difficult.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an optical sheet, a polarizing plate with an optical sheet, a touch panel with an optical sheet, and a display device that can effectively suppress malfunction of a touch panel.

The optical sheet according to the present invention comprises a substrate and an optical functional layer bonded to the substrate, the optical functional layer having a light absorbing portion and a light transmitting portion, and has a relative dielectric constant at 25°C of 3.18 or more and 3.51 or less in the frequency range of 1 KHz or more and 1 MHz or less, in accordance with JIS C 2138:2007.

The optical sheet according to the present invention may further include a first ultraviolet-cured resin layer provided on the surface of the optical functional layer opposite the substrate.

The optical sheet according to the present invention may further include a second ultraviolet-cured resin layer provided on the surface of the substrate opposite the optical functional layer.

One of the outermost surfaces of the optical sheet may be formed by the first ultraviolet curable resin layer, and the other of the outermost surfaces of the optical sheet may be formed by a surface of the base opposite to the optical functional layer side.
In this case, the thickness of the optical sheet may be 100 μm or more and 500 μm or less, and preferably 250 μm or more and 300 μm or less.

In addition, one of the outermost surfaces of the optical sheet may be formed by the first ultraviolet curing resin layer, and the other of the outermost surfaces of the optical sheet may be formed by the second ultraviolet curing resin layer, and the thickness of the substrate may be 50 μm or more. The thickness of the substrate is preferably 130 μm or more.

In addition, one of the outermost surfaces of the optical sheet is formed by the surface of the optical functional layer opposite the substrate side, and the other of the outermost surfaces of the optical sheet is formed by the surface of the substrate opposite the optical functional layer side, and the thickness of the optical sheet may be 500 μm or less, and the thickness of the substrate may be 50 μm or more. It is preferable that the thickness of the optical sheet is 220 μm or less, and the thickness of the substrate is 50 μm or more.

The optical functional layer may further have a land portion that is integral with the light transmitting portions and that is made of the same material as the light transmitting portions while spanning the plurality of light transmitting portions, and the light absorbing portion is exposed from one of a pair of main surfaces of the optical functional layer, and the land portion forms the other of the pair of main surfaces and is bonded to the substrate, while covering the light absorbing portion from the substrate side.

The light absorbing portion may include a base resin and light absorbing particles held by the base resin, and the light absorbing particles may include carbon black.
In this case, the light absorbing particles may be included in an amount of 10 parts by weight or more and 30 parts by weight or less relative to 100 parts by weight of the light absorbing portion, and the carbon black may be included in an amount of 10 parts by weight or more and 50 parts by weight or less relative to 100 parts by weight of the light absorbing particles.

Another optical sheet according to the present invention is an optical sheet comprising a substrate and an optical functional layer bonded to the substrate, the optical functional layer having a light absorbing portion and a light transmitting portion, and having a dielectric tangent at 25°C of 0.0102 or more and 0.0197 or less in the frequency range of 1 KHz or more and 1 MHz or less, conforming to JIS C 2138:2007.

The polarizing plate with optical sheet according to the present invention comprises a polarizing plate and the optical sheet.

The touch panel with an optical sheet according to the present invention comprises a touch panel and the optical sheet provided on the touch panel.

The display device according to the present invention also includes a display panel and the optical sheet provided on the display panel.

The present invention effectively prevents touch panel malfunctions.

1 is a schematic cross-sectional view showing a layer structure of a display device including an optical sheet according to a first embodiment of the present invention. 1 is a schematic cross-sectional view showing a layer structure of an optical sheet according to a first embodiment. FIG. 11 is a schematic cross-sectional view showing a layer structure of an optical sheet according to a second embodiment. FIG. 11 is a schematic cross-sectional view showing a layer structure of an optical sheet according to a third embodiment. FIG. 2 is a diagram showing a modification of the display device shown in FIG. 1 .

The optical sheets and the like according to each embodiment of the present invention will be described below with reference to the drawings. Note that in the drawings attached to this specification, the scale and aspect ratios have been appropriately altered and exaggerated from those of the actual objects for the convenience of illustration and ease of understanding.

In addition, in this specification, the terms "plate," "sheet," and "film" are not distinguished from one another solely on the basis of differences in name. For example, an "optical sheet" is a concept that includes members that can be called plates or films, and therefore an "optical sheet" cannot be distinguished from members called "optical films" or the like solely on the basis of differences in name.

In addition, the term "sheet surface (plate surface, film surface)" refers to a surface that coincides with the planar direction of the target sheet-like (plate-like, film-like) member when the target sheet-like (plate-like, film-like) member is viewed overall and from a global perspective. The normal to the sheet surface means a line that is perpendicular to the sheet surface, and the direction parallel to the normal is called the normal direction. In the following explanation, the sheet surface (plate surface, film surface) may also be called the main surface.

In addition, terms used in this specification that specify shapes, geometric conditions, and the degree of those conditions, such as "parallel," "orthogonal," and "same," as well as values of lengths and angles, are not to be construed as being limited to their strict meanings, but rather should be interpreted to include the range within which similar functions can be expected.

<<First embodiment>>
Fig. 1 is a schematic cross-sectional view showing a layer structure of a display device DP including an optical sheet 1 according to a first embodiment. The display device DP shown in Fig. 1 is configured by laminating an organic LED (Organic Light Emitting Diode) panel 15, the optical sheet 1, a circular polarizing plate 20, a touch panel 30, and a cover glass 40 in this order.

The optical sheet 1 is disposed on the display surface (front surface) 15A of the organic LED panel 15. The front surface of the optical sheet 1 and the rear surface of the circular polarizer 20 are bonded together with an adhesive layer, the front surface of the circular polarizer 20 and the rear surface of the touch panel 30 are bonded together with an adhesive layer, and the front surface of the touch panel 30 and the rear surface of the cover glass 40 are bonded together with an adhesive layer.

Each of the adhesive layers is a so-called OCA (Optical Clear Adhesive) and has high light transmittance. In this example, the organic LED panel 15 and the optical sheet 1 are not bonded together with an adhesive layer, but they may also be bonded together with an adhesive layer.

The circular polarizing plate 20 has a polarizer and a retardation plate, the retardation plate is disposed on the organic LED panel 15 side, and the polarizer is bonded to the surface of the retardation plate opposite the organic LED panel 15 side. Specifically, the polarizer is a linear polarizer, and the retardation plate is a λ/4 retardation plate.

The touch panel 30 includes a transparent substrate and employs a capacitive touch panel. The touch panel 30 may include a transparent glass plate as the transparent substrate and transparent sensor electrodes arranged on the glass plate in, for example, a mosaic pattern. The cover glass 40 has a protective function, but may also have other functions such as an anti-reflection function.

Incidentally, when the circular polarizer 20 is disposed on the external light incident side (the cover glass 40 side) of the optical sheet 1 as in the illustrated example, when external light is incident from the cover glass 40 toward the organic LED panel 15, the circular polarizer 20 makes it difficult for the external light to reach the optical sheet 1. This can suppress, for example, multiple reflections within the optical sheet 1. As a result, the occurrence of visibility-impairing phenomena such as rainbow unevenness and interference fringes is suppressed, and good visibility of the image can be ensured.

In addition, before the display device DP is assembled, the optical sheet 1 and the circular polarizer 20 may be distributed in the form of a polarizer with an optical sheet, which are integrated with each other. Also, the optical sheet 1 and the touch panel 30 may be distributed in the form of a touch panel with an optical sheet, which are integrated with each other.

<Optical sheet>
The optical sheet 1 will be described in detail below with reference to Fig. 2. The optical sheet 1 shown in Fig. 2 includes a substrate 11, an optical functional layer 12, and a first ultraviolet cured resin layer 13. The substrate 11 and the optical functional layer 12 are bonded to each other, and the first ultraviolet cured resin layer 13 covers the optical functional layer 12 from the side opposite the substrate 11.

The image light from the organic LED panel 15 enters through the first ultraviolet curing resin layer 13 and exits from the substrate 11. The optical function layer 12 has a light absorbing portion 12a and a light transmitting portion 12b. The optical function layer 12 adjusts, for example, the orientation of the image light by absorbing or reflecting a portion of the image light from the organic LED panel 15 at the light absorbing portion 12a.

Optical sheet 1 is configured so that the relative dielectric constant at 25°C conforming to JIS C 2138:2007 is 3.18 or more and 3.51 or less in the frequency range of 1 KHz or more and 1 MHz or less, and/or the dielectric dissipation factor at 25°C conforming to JIS C 2138:2007 is 0.0102 or more and 0.0197 or less in the frequency range of 1 KHz or more and 1 MHz or less.

As described above, when the relative dielectric constant of the optical sheet 1 is 3.18 or more and 3.51 or less, and/or the dielectric dissipation factor is 0.0102 or more and 0.0197 or less, when the optical sheet 1 is incorporated into a display device DP together with a touch panel 30, malfunction of the touch panel can be suitably suppressed. The present inventors have found the relationship between the value of such relative dielectric constant and/or dielectric dissipation factor and the obtained effect through extensive research, and have arrived at the present invention. Such relative dielectric constant and/or dielectric dissipation factor of the optical sheet 1 can be set by appropriately adjusting the material and thickness of the substrate 11, the material and thickness of the optical functional layer 12 and the content of the light absorbing component in the light absorbing portion 12a, the material and thickness of the first ultraviolet cured resin layer 13, etc.

The thickness of the optical sheet 1 is preferably 100 μm or more and 500 μm or less, and more preferably 250 μm or more and 300 μm or less. The relative dielectric constant and/or dielectric loss tangent vary depending on the thickness, but when the thickness of the optical sheet 1 is within the above range, particularly when it is 250 μm or more and 300 μm or less, it becomes easier to set the relative dielectric constant and/or dielectric loss tangent to the desired range, and handling becomes easier due to the appropriate thickness.

(Substrate)
The substrate 11 is a transparent substrate having optical transparency made of resin, glass, or the like, and is composed of, for example, a film mainly composed of polycarbonate, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polyolefin, polyacrylate, or polyamide, glass, etc. The thickness of the substrate 11 is, for example, 60 μm or more and 250 μm or less, and the refractive index of the substrate 11 is, for example, 1.46 or more and 1.67 or less. Note that the main component means a component that is contained in a proportion of 50% or more of the entire substance, or a component that is contained in the largest amount, among multiple components that constitute a certain substance.

In addition, the dielectric constant of the substrate 11 itself at 25°C in accordance with JIS C 2138:2007 is preferably 3.1 or more and 3.6 or less in the frequency range of 1 KHz or more and 1 MHz or less. In addition, the dielectric tangent of the substrate 11 itself at 25°C in accordance with JIS C 2138:2007 is preferably 0.0100 or more and 0.0200 or less in the frequency range of 1 KHz or more and 1 MHz or less.

When the dielectric constant and/or dielectric loss tangent of the substrate 11 itself is within the above range, it is easy to set the dielectric constant of the optical sheet 1 to the above-mentioned range of 3.18 to 3.51, and the dielectric loss tangent to the above-mentioned range of 0.0102 to 0.0197. However, even when the dielectric constant and/or dielectric loss tangent of the substrate 11 itself is within the above range, the dielectric constant and/or dielectric loss tangent of the optical sheet 1 may deviate from the desired range depending on the material and thickness of the optical functional layer 12 and the first ultraviolet cured resin layer 13. However, even in such a case, as long as the material and thickness of the optical functional layer 12 and the first ultraviolet cured resin layer 13 are appropriately set, an optical sheet 1 with the desired dielectric constant and/or dielectric loss tangent can be obtained.

(Optical Functional Layer)
The optical functional layer 12 is a so-called louver film having light absorbing portions 12a and light transmitting portions 12b, and the light transmitting portions 12b and the light absorbing portions 12a are alternately arranged along a first direction D1 parallel to each of a pair of main surfaces of the optical functional layer 12. The symbol D2 in Fig. 1 indicates a second direction parallel to each of the pair of main surfaces and perpendicular to the first direction D1, and the light absorbing portions 12a and the light transmitting portions 12b extend linearly in the second direction D2. Note that the first direction D1 and the second direction D2 do not have to be perpendicular to each other.

The light absorbing portion 12a is a portion that absorbs light, and contains light absorbing particles in a base resin, in other words, a binder resin. For example, acrylic beads containing carbon black can be used as the light absorbing particles. Note that the light absorbing portion 12a may also be a binder resin containing, for example, a black filler, and its composition is not particularly limited.

The optical sheet 1 is installed so as to transmit image light from the optical functional layer 12 towards the substrate 11, and the light absorbing portion 12a adjusts, for example, the orientation of the image light. In this embodiment, the cross-sectional shape of the light absorbing portion 12a is a trapezoid tapered toward the light exit side. On the other hand, the cross-sectional shape of the light transmitting portion 12b is a trapezoid tapered toward the light entrance side. However, the cross-sectional shapes of the light absorbing portion 12a and the light transmitting portion 12b can adopt various shapes depending on the required function, and are not particularly limited, and may be, for example, rectangular.

In the following, the light-entering principal surface of the pair of principal surfaces of the optical functional layer 12 is referred to as the first principal surface 121, and the light-emitting principal surface is referred to as the second principal surface 122. The above-mentioned base material 11 is provided on the second principal surface 122 of the optical functional layer 12, and the first ultraviolet-cured resin layer 13 is provided on the first principal surface 121 of the optical functional layer 12. In this embodiment, one of the outermost surfaces of the optical sheet 1 (the surface located on the lower side in the figure) is formed by the first ultraviolet-cured resin layer 13, and the other of the outermost surfaces of the optical sheet (the surface located on the upper side in the figure) is formed by the surface of the base material 11 opposite the optical functional layer 12 side.

The optical function layer 12 in this embodiment further has a film-like land portion 12c that is integrated with the light transmitting portion b in a state spanning the multiple light transmitting portions 12b and is made of the same material as the light transmitting portions 12b. The light absorbing portion 12a is exposed from a first main surface 121 (the lower surface in the figure), which is one of a pair of main surfaces of the optical function layer 12, and the land portion 12c forms a second main surface 122, which is the other of the pair of main surfaces of the optical function layer 12, is bonded to the substrate 11, and covers the light absorbing portion 12a from the substrate 11 side. However, the optical function layer 12 does not have to have the land portion 12c described above.

The material constituting the base resin in the light absorbing portion 12a is not particularly limited, but is preferably a curable resin. Specifically, for example, an ionizing radiation curable resin, which is a resin cured by ultraviolet light or an electron beam, a mixture of an ionizing radiation curable resin and a solvent drying type resin (a resin that becomes a coating by simply drying the solvent added to adjust the solid content during coating), or a thermosetting resin may be mentioned. The refractive index of the base resin in the light absorbing portion 12a is preferably 1.47 to 1.65, more preferably 1.49 to 1.57. If the refractive index of the base resin is high, the light absorbing portion 12a is likely to crack, so the refractive index is preferably 1.57 or less. From the viewpoint of reducing the relative dielectric constant and/or dielectric loss tangent and suppressing the deterioration of optical performance, it is preferable to form the light absorbing portion 12a from an ultraviolet curable acrylic resin, for example, an ultraviolet curable urethane acrylate.

On the other hand, the light-transmitting portion 12b is a portion that transmits light, and is made of, for example, a resin that transmits visible light. The material of the light-transmitting portion 12b is not particularly limited, but it is preferably a curable resin. Specific examples include an ionizing radiation curable resin that is cured by ultraviolet light or an electron beam, a mixture of an ionizing radiation curable resin and a solvent drying resin (a resin that becomes a coating simply by drying a solvent added to adjust the solid content during application), or a thermosetting resin.

In this embodiment, the light transmitting portion 12b is bonded to the substrate 11, and therefore it is desirable that the light transmitting portion 12b is compatible with the substrate 11 in order to improve the bonding strength with the substrate 11. In addition, since the gaps formed in the light transmitting portion 12b to be filled with the light absorbing portion 12a are formed, for example, by a mold, it is desirable that the light transmitting portion 12b has properties that allow for good release, for example, by including a release agent. For example, when the substrate 11 is mainly composed of polycarbonate, a material containing phenoxyethyl acrylate in terms of improving bonding strength and a phosphate ester in terms of ensuring releasability can be suitably used as the material for the light transmitting portion 12b that can satisfy the above two requirements.

In addition, the refractive index of the light-transmitting portion 12b is preferably 1.47 or more and 1.65 or less, and more preferably 1.49 or more and 1.57 or less. If the refractive index is high, the light-transmitting portion 12b is likely to crack, so the refractive index is preferably 1.57 or less. In addition, it is desirable that the refractive index of the light-transmitting portion 12b is higher than or the same as the refractive index of the base resin of the light-absorbing portion 12a. When the refractive index of the light-transmitting portion 12b is higher than the refractive index of the base resin of the light-absorbing portion 12a, optical design using total reflection of light from the light-transmitting portion 12b toward the light-absorbing portion 12a becomes possible, and for example, the light utilization efficiency can be improved. In addition, when the refractive index of the light-transmitting portion 12b is the same as the refractive index of the base resin of the light-absorbing portion 12a, total reflection and refraction of light do not occur, so that, for example, even if the distance from the surface of the display device to the optical sheet 1 is large, it is possible to prevent the occurrence of double images of transmitted light, total reflected light, and refracted light. From the viewpoint of reducing the relative dielectric constant and/or dielectric loss tangent and suppressing deterioration of optical performance, it is preferable to form the light transmitting portion 12b from an ultraviolet-curable acrylic resin, for example, an ultraviolet-curable urethane acrylate.

The pitch of the arrangement of the light absorbing parts 12a and the light transmitting parts 12b in the optical functional layer 12 is not particularly limited, but from the viewpoint of effectively exerting the function of the louver film, it is preferably 15 μm to 100 μm, more preferably 30 μm to 100 μm. The height (thickness) of the light absorbing parts 12a is preferably 60 μm to 150 μm. The thickness of the land part 12c is preferably 10 μm to 50 μm. The maximum width (width of the end part on the exposed side) of the light absorbing parts 12a in the first direction D1 is preferably 5 μm to 15 μm. If it is less than 5 μm, there is a risk that the optical performance will be impaired, and if it is more than 15 μm, there is a risk that it will be difficult to reduce the relative dielectric constant and/or dielectric loss tangent.

In addition, the relative dielectric constant of the optical functional layer 12 itself at 25°C in accordance with JIS C 2138:2007 is preferably 3.1 or more and 3.6 or less in the frequency range of 1 KHz or more and 1 MHz or less. In addition, the dielectric tangent of the optical functional layer 12 itself at 25°C in accordance with JIS C 2138:2007 is preferably 0.0100 or more and 0.0200 or less in the frequency range of 1 KHz or more and 1 MHz or less.

When the relative dielectric constant and/or dielectric loss tangent of the optical functional layer 12 itself is within the above range, it is easy to set the relative dielectric constant of the optical sheet 1 to the above-mentioned range of 3.18 to 3.51, and the dielectric loss tangent to the above-mentioned range of 0.0102 to 0.0197. However, even when the relative dielectric constant and/or dielectric loss tangent of the optical functional layer 12 itself is within the above range, the relative dielectric constant and/or dielectric loss tangent of the optical sheet 1 may deviate from the desired range depending on the material and thickness of the substrate 11 and the first ultraviolet cured resin layer 13. However, even in such a case, as long as the material and thickness of the substrate 11 and the first ultraviolet cured resin layer 13 are appropriately set, an optical sheet 1 with the desired relative dielectric constant and/or dielectric loss tangent can be obtained.

Here, when the light absorbing particles in the light absorbing portion 12a contain a dielectric such as carbon black, the dielectric may increase the relative dielectric constant and/or dielectric loss tangent of the optical sheet 1. On the other hand, when the amount of the dielectric such as carbon black is reduced in order to reduce the relative dielectric constant and/or dielectric loss tangent, the optical performance of the light absorbing portion 12a may be deteriorated. From the viewpoint of suppressing the relative dielectric constant and/or dielectric loss tangent and suppressing the deterioration of the optical performance, when the light absorbing portion 12a contains a base resin and light absorbing particles held by the base resin, and the light absorbing particles contain carbon black, it is preferable that the light absorbing particles are contained in an amount of 10 parts by weight or more and 30 parts by weight or less when the light absorbing portion 12a is 100 parts by weight. And, it is preferable that the carbon black is contained in an amount of 10 parts by weight or more and 50 parts by weight or less for 100 parts by weight of the light absorbing particles. By not excessively decreasing or increasing the content of the derivative such as carbon black, it becomes easier to achieve both the suppression of the relative dielectric constant and/or dielectric loss tangent and the suppression of the deterioration of the optical performance.

(First UV-curable resin layer)
The first ultraviolet cured resin layer 13 has a function of protecting the optical functional layer 12 by covering the optical functional layer 12. The inventors of the present invention have found that the relative dielectric constant and dielectric loss tangent can be effectively suppressed by covering only the optical functional layer 12 side with a layer made of ultraviolet cured resin, and have bonded the first ultraviolet cured resin layer 13 to the optical functional layer 12. The thickness of the first ultraviolet cured resin layer 13 is, for example, 5 μm or more and 50 μm or less, and the refractive index of the first ultraviolet cured resin layer 13 is, for example, 1.47 or more and 1.65 or less.

The material of the first UV-cured resin layer 13 is not particularly limited, but is preferably a curable resin. Specific examples include ionizing radiation-curable resins that are cured by UV rays or electron beams, and mixtures of ionizing radiation-curable resins and solvent-drying resins (resins that become a coating simply by drying the solvent added to adjust the solid content during application).

In this embodiment, when the optical sheet 1 is incorporated into a display device, it is assumed that the first ultraviolet curing resin layer 13 will be adjacent to other optical members, specifically, the surface material of the organic LED panel 15. In this situation, even if the first ultraviolet curing resin layer 13 comes into contact with other optical members, it is desired that the first ultraviolet curing resin layer 13 does not damage the other optical members and does not come into close contact with the other optical members. Therefore, it is desirable for the first ultraviolet curing resin layer 13 to ensure high sliding properties, and a slip agent may be included to satisfy this. As the slip agent, higher fatty acid ester, higher fatty acid aluminide, wax (paraffin wax, polyolefin wax), silicone oil, etc. may be used. In addition, the first ultraviolet curing resin layer 13 in this embodiment is formed as a matte layer and has a rough surface. This makes it easier to avoid adhesion with the organic LED panel 15. In addition, from the viewpoint of reducing the relative dielectric constant and/or dielectric loss tangent and suppressing the deterioration of optical performance, it is preferable to form the first ultraviolet curing resin layer 13 from an ultraviolet curing acrylic resin, for example, an ultraviolet curing urethane acrylate.

The first ultraviolet cured resin layer 13 itself preferably has a relative dielectric constant at 25°C in accordance with JIS C 2138:2007 of 3.1 or more and 3.6 or less in the frequency range of 1 KHz to 1 MHz. Also, the first ultraviolet cured resin layer 13 itself preferably has a dielectric tangent at 25°C in accordance with JIS C 2138:2007 of 0.0100 or more and 0.0200 or less in the frequency range of 1 KHz to 1 MHz.

When the dielectric constant and/or dielectric loss tangent of the first ultraviolet cured resin layer 13 itself is within the above range, it is easy to set the dielectric constant of the optical sheet 1 to the above-mentioned range of 3.18 to 3.51, and the dielectric loss tangent to the above-mentioned range of 0.0102 to 0.0197. However, even when the dielectric constant and/or dielectric loss tangent of the first ultraviolet cured resin layer 13 itself is within the above range, the dielectric constant and/or dielectric loss tangent of the optical sheet 1 may deviate from the desired range depending on the material and thickness of the substrate 11 and the optical functional layer 12. However, even in such a case, as long as the material and thickness of the substrate 11 and the optical functional layer 12 are appropriately set, an optical sheet 1 with the desired dielectric constant and/or dielectric loss tangent can be obtained.

The optical sheet 1 according to the first embodiment described above includes a substrate 11 and an optical functional layer 12. More specifically, the optical sheet 1 further includes a first ultraviolet curing resin layer 13, and one of the outermost surfaces of the optical sheet 1 is formed by the first ultraviolet curing resin layer 13, and the other of the outermost surfaces of the optical sheet is formed by the surface of the substrate 11 opposite to the optical functional layer 12 side. The optical sheet 1 is configured so that the relative dielectric constant at 25°C conforming to JIS C 2138:2007 is 3.18 to 3.51 in the frequency range of 1 KHz to 1 MHz, and/or the dielectric loss tangent at 25°C conforming to JIS C 2138:2007 is 0.0102 to 0.0197 in the frequency range of 1 KHz to 1 MHz.

Since the relative dielectric constant and/or dielectric tangent of such an optical sheet 1 is not excessively large, malfunction of the touch panel 30 can be effectively suppressed when the optical sheet 1 is incorporated into a display device DP together with the touch panel 30.

<<Second embodiment>>
Next, an optical sheet 2 according to a second embodiment will be described with reference to Fig. 3. The optical sheet 2 shown in Fig. 3 includes a base material 11, an optical functional layer 12, a first ultraviolet cured resin layer 13, and a second ultraviolet cured resin layer 14. In this embodiment, one of the outermost surfaces of the optical sheet 1 (the surface located on the lower side in the figure) is formed by the first ultraviolet cured resin layer 13, and the other of the outermost surfaces of the optical sheet 1 (the surface located on the upper side in the figure) is formed by the second ultraviolet cured resin layer 14.

As in the first embodiment, this optical sheet 2 is configured so that the relative dielectric constant at 25° C., in accordance with JIS C 2138:2007, is 3.18 or more and 3.51 or less in the frequency range of 1 KHz or more and 1 MHz or less, and/or the dielectric dissipation factor at 25° C., in accordance with JIS C 2138:2007, is 0.0102 or more and 0.0197 or less in the frequency range of 1 KHz or more and 1 MHz or less.
Here, the thickness of the optical sheet 2 is preferably 100 μm or more and 500 μm or less, and more preferably 270 μm or more and 450 μm or less. When the thickness of the optical sheet 1 is within the above range, particularly when it is 270 μm or more and 450 μm or less, it becomes easier to set the relative dielectric constant and/or dielectric loss tangent to the desired range. In addition, the thickness of the base material 11 is, for example, 50 μm or more, preferably 60 μm or more, and more preferably 80 μm or more. The other preferable conditions of the base material 11, the optical functional layer 12, and the first ultraviolet cured resin layer 13 are the same as those of the first embodiment.

The second ultraviolet cured resin layer 14 is provided, for example, to protect the substrate 11. The thickness of the second ultraviolet cured resin layer 14 is, for example, 5 μm or more and 50 μm or less, and the refractive index of the second ultraviolet cured resin layer 14 is, for example, 1.47 or more and 1.65 or less. The material of the second ultraviolet cured resin layer 14 is not particularly limited, but it is preferably a curable resin. Specifically, for example, an ionizing radiation curable resin that is a resin that is cured by ultraviolet light or an electron beam, a mixture of an ionizing radiation curable resin and a solvent drying type resin (a resin that becomes a coating by simply drying a solvent added to adjust the solid content during coating), or a thermosetting resin can be mentioned. From the viewpoint of reducing the relative dielectric constant and/or dielectric loss tangent and suppressing the deterioration of optical performance, it is preferable to form the second ultraviolet cured resin layer 14 from an ultraviolet curable acrylic resin, for example, an ultraviolet curable urethane acrylate.

In addition, the second ultraviolet cured resin layer 14 is preferably formed of the same material and to the same thickness as the first ultraviolet cured resin layer 13. In this case, the linear expansion coefficient of the second ultraviolet cured resin layer 14 and the linear expansion coefficient of the first ultraviolet cured resin layer 13 can be made uniform, and defects such as curling can be suppressed. In addition, manufacturing costs can be suppressed.

The optical sheet 2 according to the second embodiment described above also has an excessively large relative dielectric constant and/or dielectric loss tangent, and therefore can effectively suppress malfunction of the touch panel 30 when incorporated into a display device DP together with the touch panel 30. As will be shown in the examples described later, the optical sheet 2 according to the second embodiment tends to have a greater relative dielectric constant and dielectric loss tangent than the optical sheet 1 according to the first embodiment, which is under almost the same conditions except that the second ultraviolet cured resin layer 14 is not provided. However, the optical sheet 2 according to the second embodiment has good durability and ease of use because it has the second ultraviolet cured resin layer 14.

<<Third embodiment>>
Next, an optical sheet 3 according to a third embodiment will be described with reference to Fig. 4. The optical sheet 3 shown in Fig. 4 includes a base material 11 and an optical functional layer 12, and one of the outermost surfaces of the optical sheet 1 (the surface located on the lower side in the figure) is formed by the surface of the optical functional layer 12 opposite to the base material 11 side, and the other of the outermost surfaces of the optical sheet (the surface located on the upper side in the figure) is formed by the surface of the base material 11 opposite to the optical functional layer 12 side.

As in the first embodiment, the optical sheet 3 is configured so that the relative dielectric constant at 25°C conforming to JIS C 2138:2007 is 3.18 to 3.51 in the frequency range of 1 KHz to 1 MHz, and/or the dielectric dissipation factor at 25°C conforming to JIS C 2138:2007 is 0.0102 to 0.0197 in the frequency range of 1 KHz to 1 MHz. The thickness of the optical sheet 3 is preferably 500 μm or less, the thickness of the substrate 11 is preferably 50 μm or more, and it is more preferable that the thickness of the optical sheet 3 is 220 μm or less and the thickness of the substrate 11 is 50 μm or more. The other preferable conditions of the substrate 11 and the optical functional layer 12 are the same as those in the first embodiment.

The optical sheet 3 according to the third embodiment described above also has an excessively large relative dielectric constant and/or dielectric dissipation factor, and therefore can effectively suppress malfunction of the touch panel 30 when incorporated into a display device DP together with the touch panel 30. In this embodiment, the relative dielectric constant and/or dielectric dissipation factor is suppressed by suppressing the overall thickness of the optical sheet 1. The optical sheet 3 according to the third embodiment has a simple two-layer structure, which can improve productivity.

<<Modifications>>
In the first embodiment, the optical sheet 1 is provided between the organic LED panel 15 and the touch panel 30, but the optical sheets 1 to 3 may be provided on the cover glass 40 of the display device as shown in the modified example of FIG. 5. In this case, the optical sheets 1 to 3 exert a peep suppression function. On the other hand, when the optical sheets 1 to 3 are provided on the cover glass 40, if the relative dielectric constant and the dielectric dissipation factor are excessively low, the sensitivity of the touch panel 30 may be impaired. Here, when the relative dielectric constant at 25° C. of the optical sheets 1 to 3 conforming to JIS C 2138:2007 is 3.18 to 3.51 in the frequency range of 1 KHz to 1 MHz, and when the dielectric dissipation factor at 25° C. conforming to JIS C 2138:2007 is 0.0102 to 0.0197 in the frequency range of 1 KHz to 1 MHz, the sensitivity of the touch panel 30 is favorable and malfunction is suppressed. Therefore, the optical sheets 1 to 3 are useful no matter which side of the touch panel 30 they are placed on.

In addition, in each of the embodiments described above, it is assumed that the optical sheets 1 to 3 are used together with the organic LED panel 15, but the optical sheets 1 to 3 may also be used together with a liquid crystal panel to form a display device. In addition, the optical sheet may include only the substrate 11, the optical functional layer 12, and the second ultraviolet cured resin layer 14.

Below, Examples 1 to 4 of the present invention and Comparative Example 1 will be described. Examples 1 to 4 and Comparative Example 1 were produced using a mold having a convex portion corresponding to the shape of the light absorbing portion 12a. The convex portion of the mold used in producing Examples 1 to 4 has a tapered shape, with a width of 4 μm on the tip side and a width of 10 μm on the base side. The height of the convex portion is 102 μm. The convex portions are arranged with a pitch of 39 μm. In the mold used in producing Comparative Example 1, the height of the convex portion is 120 μm.

Example 1
Example 1 corresponds to the first embodiment, and includes a base material 11 , an optical function layer 12 , and a first ultraviolet curable resin layer 13 .
As the substrate 11, a polycarbonate film (Carboglass, manufactured by AGC) having a thickness of 130 μm was used.
An ultraviolet-curable urethane acrylate with a refractive index of 1.56 was used as a material for forming the light-transmitting portion 12b of the optical function layer 12. Then, the ultraviolet-curable urethane acrylate was provided on the substrate 11, and a recess corresponding to the shape of the light-absorbing portion 12a was formed using the above-mentioned mold, and then curing was performed using a release mold and UV irradiation, thereby forming a land portion 12c with a thickness of 12 μm and the light-transmitting portion 12b on the substrate 11.

The material used for forming the light absorbing portion 12a of the optical function layer 12 was a material containing a base resin made of ultraviolet-curable urethane acrylate with a refractive index of 1.49 and light absorbing particles made of acrylic beads containing carbon black with an average particle size of 4 μm. The light absorbing particles were contained in an amount of 20% by weight of the entire forming material. The material for forming the light absorbing portion 12a was then applied to the light transmitting portion 12b, pushed into the recessed portion with a doctor blade, and then cured by UV irradiation to form the light absorbing portion 12a.
An ultraviolet-curable urethane acrylate having a refractive index of 1.51 was used as a material for forming the first ultraviolet-curable resin layer 13. This ultraviolet-curable urethane acrylate was provided on the light-absorbing portion 12a, and a mold was pressed against the urethane acrylate to form a matte surface, followed by curing by UV irradiation, thereby forming the first ultraviolet-curable resin layer 13.

The thickness of each element and the total thickness of the optical sheet in Example 1 are as follows.
The thickness of the substrate 11 is 130 μm.
The land portion 12c of the optical function layer 12 has a thickness of 12 μm.
The thickness of the light transmitting portion 12b of the optical function layer 12 is 102 μm.
The thickness of the light absorbing portion 12a of the optical function layer 12 is 102 μm.
The first ultraviolet curing resin layer 13 has a thickness of 25 μm.
The total thickness of the optical sheet is 269 μm.

Example 2
Example 2 corresponds to the second embodiment, and includes a base material 11, an optical function layer 12, a first ultraviolet curing resin layer 13, and a second ultraviolet curing resin layer 14.
As the substrate 11, a polycarbonate film (Carboglass, manufactured by AGC) having a thickness of 130 μm was used.
The light transmitting portion 12b of the optical function layer 12 was formed from an ultraviolet-curable urethane acrylate having a refractive index of 1.56.
A material containing a base resin made of ultraviolet-curable urethane acrylate with a refractive index of 1.49 and light-absorbing particles made of acrylic beads containing carbon black and having an average particle size of 4 μm was used as a material for forming the light-absorbing portion 12a of the optical function layer 12. The light-absorbing particles were contained in an amount of 20% by weight of the entire forming material.
As a material for forming the first ultraviolet curing resin layer 13, ultraviolet curing urethane acrylate having a refractive index of 1.51 was used.
The procedure for forming the optical function layer 12 and the first ultraviolet curing resin layer 13 is the same as in the first embodiment.
On the other hand, ultraviolet-curable urethane acrylate with a refractive index of 1.51 was used as a material for forming the second ultraviolet-curable resin layer 14. The ultraviolet-curable urethane acrylate was provided on the substrate 11, and a mold was pressed against the urethane acrylate to form a matte surface, followed by curing by UV irradiation, thereby forming the second ultraviolet-curable resin layer 14.

The thickness of each element and the total thickness of the optical sheet in Example 2 are as follows.
The thickness of the substrate 11 is 130 μm.
The land portion 12c of the optical function layer 12 has a thickness of 29 μm.
The thickness of the light transmitting portion 12b of the optical function layer 12 is 102 μm.
The thickness of the light absorbing portion 12a of the optical function layer 12 is 102 μm.
The first ultraviolet curing resin layer 13 has a thickness of 25 μm.
The second ultraviolet curing resin layer 14 has a thickness of 25 μm.
The total thickness of the optical sheet is 311 μm.

Example 3
Example 3 corresponds to the second embodiment, and includes a base material 11, an optical function layer 12, a first ultraviolet curing resin layer 13, and a second ultraviolet curing resin layer 14.
As the substrate 11, a polycarbonate film (Carboglass, manufactured by AGC) having a thickness of 250 μm was used.
The light transmitting portion 12b of the optical function layer 12 was formed from an ultraviolet-curable urethane acrylate having a refractive index of 1.56.
A material containing a base resin made of ultraviolet-curable urethane acrylate with a refractive index of 1.49 and light-absorbing particles made of acrylic beads containing carbon black and having an average particle size of 4 μm was used as a material for forming the light-absorbing portion 12a of the optical function layer 12. The light-absorbing particles were contained in an amount of 20% by weight of the entire forming material.
As a material for forming the first ultraviolet curing resin layer 13, ultraviolet curing urethane acrylate having a refractive index of 1.51 was used.
As a material for forming the second ultraviolet curing resin layer 14, ultraviolet curing urethane acrylate having a refractive index of 1.51 was used.
The procedure for forming each layer was the same as in the second embodiment.

The thickness of each element and the total thickness of the optical sheet in Example 3 are as follows.
The thickness of the substrate 11 is 250 μm.
The land portion 12c of the optical function layer 12 has a thickness of 19 μm.
The thickness of the light transmitting portion 12b of the optical function layer 12 is 102 μm.
The thickness of the light absorbing portion 12a of the optical function layer 12 is 102 μm.
The first ultraviolet curing resin layer 13 has a thickness of 25 μm.
The second ultraviolet curing resin layer 14 has a thickness of 25 μm.
The total thickness of the optical sheet is 421 μm.

Example 4
Example 4 corresponds to the third embodiment and includes a base material 11 and an optical function layer 12 .
As the substrate 11, a polycarbonate film (Carboglass, manufactured by AGC) having a thickness of 100 μm was used.
The light transmitting portion 12b of the optical function layer 12 was formed from an ultraviolet-curable urethane acrylate having a refractive index of 1.56.
A material containing a base resin made of ultraviolet-curable urethane acrylate with a refractive index of 1.49 and light-absorbing particles made of acrylic beads containing carbon black and having an average particle size of 4 μm was used as a material for forming the light-absorbing portion 12a of the optical function layer 12. The light-absorbing particles were contained in an amount of 20% by weight of the entire forming material.
The procedure for forming the optical function layer 12 is the same as in the first embodiment.

The thickness of each element and the total thickness of the optical sheet in Example 4 are as follows.
The thickness of the substrate 11 is 100 μm.
The land portion 12c of the optical function layer 12 has a thickness of 18 μm.
The thickness of the light transmitting portion 12b of the optical function layer 12 is 102 μm.
The thickness of the light absorbing portion 12a of the optical function layer 12 is 102 μm.
The total thickness of the optical sheet is 220 μm.

(Comparative Example 1)
Comparative Example 1 includes a substrate and an optical functional layer similar to those of the embodiment, but a bonding substrate is provided on the optical functional layer via an ultraviolet-curable adhesive.
A polycarbonate film (Carboglass, manufactured by AGC) having a thickness of 130 μm was used as the substrate.
The material for forming the light transmitting portion of the optical functional layer was an ultraviolet-curable urethane acrylate having a refractive index of 1.56.
The material used for forming the light absorbing portion of the optical functional layer was a material containing a base resin made of ultraviolet-curable urethane acrylate with a refractive index of 1.49 and light absorbing particles made of acrylic beads containing carbon black and having an average particle size of 4 μm. The light absorbing particles were contained in an amount of 20% by weight of the entire material.
The UV-curable adhesive has a thickness of 25 μm.
The substrate for lamination is a polycarbonate film having a thickness of 100 μm.

The thickness of each element and the total thickness of the optical sheet in Comparative Example 1 are as follows.
The thickness of the substrate is 130 μm.
The thickness of the land portion of the optical function layer is 42 μm.
The thickness of the light transmitting portion of the optical function layer is 120 μm.
The thickness of the light absorbing portion of the optical functional layer is 120 μm.
The thickness of the ultraviolet curing adhesive is 25 μm.
The thickness of the lamination substrate is 100 μm.
The total thickness of the optical sheet is 417 μm.

The dimensional conditions of Examples 1 to 4 and Comparative Example 1, and the measurement results of the dielectric constant and dielectric dissipation factor are shown in Table 1 below. The dielectric constant and dielectric dissipation factor were measured in an environment of 25°C using the automatic balancing bridge method in accordance with JIS C 2138:2007. A Precision LCR meter E4980A (manufactured by Agilent Technologies, Inc.) was used for the measurements. The dielectric constant and dielectric dissipation factor were measured at 1 KHz, 10 KHz, 100 KHz, and 1 MHz.

In each of Examples 1 to 4, the relative dielectric constant at 25°C conforming to JIS C 2138:2007 is 3.18 to 3.51 in the frequency range of 1 KHz to 1 MHz, and the dielectric dissipation factor at 25°C conforming to JIS C 2138:2007 is 0.0102 to 0.0197 in the frequency range of 1 KHz to 1 MHz. When these optical sheets were used together with the touch panel 30, no malfunction of the touch panel 30 was observed.

Example 1 is under almost the same conditions as Example 2 except that the second ultraviolet curing resin layer 14 is not provided, but the relative dielectric constant and dielectric loss tangent are lower than those of Example 2. According to this result, in order to suppress the relative dielectric constant and dielectric loss tangent, it can be said that it is effective to cover only the optical function layer 12 side with a layer made of ultraviolet curing resin.
In addition, from the results of Example 2 and Example 3, it can be said that when the first and second ultraviolet cured resin layers 13, 14 are both urethane acrylate, the relative dielectric constant and dielectric loss tangent are effectively suppressed to be low. On the other hand, comparing Example 2 and Example 3, Example 3, in which the thickness of the substrate 11 is larger, has a lower relative dielectric constant and dielectric loss tangent than Example 2. According to this result, in a configuration in which the first ultraviolet cured resin layer 13 and the second ultraviolet cured resin layer 14 form the outermost surfaces, it is presumed that the thicker the substrate 11 between them, the lower the relative dielectric constant and dielectric loss tangent. In Example 2, the thickness of the substrate 11 is 130 μm, and the relative dielectric constant at 1 KHz is 3.49 and the dielectric loss tangent is 0.0190. Taking these values into consideration, it is estimated that if the thickness of the substrate 11 is 130 μm or more, the relative dielectric constant will be within the range of 3.18 to 3.51 inclusive and the dielectric tangent will be within the range of 0.0102 to 0.0197 inclusive in the frequency range of 1 KHz to 1 MHz inclusive.
In addition, in Example 4, it is presumed that the dielectric constant and the dielectric loss tangent are suppressed due to the thin thickness of the optical sheet. In general, the dielectric constant and the dielectric loss tangent are lower as the thickness of the dielectric is smaller. In Example 4, the thickness is 220 μm, and the dielectric constant at 1 KHz is 3.51, and the dielectric loss tangent at 1 MHZ is 0.0196. Therefore, when the optical sheet 1 is composed of the substrate 11 and the optical functional layer 12, if the total thickness is 220 μm or less and the thickness of the substrate 11 is 100 μm or more, it is presumed that the dielectric constant in the frequency range of 1 KHz to 1 MHz is 3.18 to 3.51, and the dielectric loss tangent is 0.0102 to 0.0197.

On the other hand, in Comparative Example 1, the relative dielectric constant and dielectric tangent are high. This is thought to be due to the overall thickness, the UV-curable adhesive, and the material of the bonding substrate.

Reference Signs List 1, 2, 3... optical sheet 11... substrate 12... optical functional layer 121... first main surface 122... second main surface 12a... light absorbing portion 12b... light transmitting portion 12c... land portion 13... first ultraviolet curing resin layer 14... second ultraviolet curing resin layer

Claims (3)

A display panel;
an optical sheet provided on the display panel;
The optical sheet includes a base material and an optical functional layer bonded to the base material,
the optical functional layer has a light absorbing portion and a light transmitting portion,
the refractive index of the light transmitting portion is higher than the refractive index of the light absorbing portion,
the light absorbing portion has a trapezoidal shape tapered toward a light output side in a direction in which light transmits from the display panel toward the base material,
The relative dielectric constant of the optical sheet at 25° C. according to JIS C 2138:2007 is 3.18 to 3.51 in the frequency range of 1 KHz to 1 MHz,
The optical sheet further includes a first ultraviolet curing resin layer provided on a surface of the optical functional layer opposite to the substrate side,
the first ultraviolet curing resin layer contains urethane acrylate,
one of the outermost surfaces of the optical sheet is formed by the first ultraviolet curing resin layer, and the other of the outermost surfaces of the optical sheet is formed by a surface of the base material opposite to the optical functional layer side;
The thickness of the optical sheet is 100 μm or more and 500 μm or less,
the light absorbing portion includes a base resin and light absorbing particles held by the base resin;
The light absorbing particles include carbon black;
The light absorbing particles are contained in an amount of 10 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the light absorbing portion,
The display device, wherein the carbon black is contained in an amount of 10 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the light absorbing particles . the optical function layer further includes a land portion that is integral with the light transmitting portion in a state spanning a plurality of the light transmitting portions and is made of the same material as the light transmitting portions,
the light absorbing portion is exposed from one of a pair of main surfaces of the optical function layer,
The display device according to claim 1 , wherein the land portion forms the other of the pair of main surfaces, is joined to the base material, and covers the light absorbing portion from the base material side. A display panel;
an optical sheet provided on the display panel;
The optical sheet includes a base material and an optical functional layer bonded to the base material,
the optical functional layer has a light absorbing portion and a light transmitting portion,
the refractive index of the light transmitting portion is higher than the refractive index of the light absorbing portion,
the light absorbing portion has a trapezoidal shape tapered toward a light output side in a direction in which light transmits from the display panel toward the base material,
The dielectric tangent of the optical sheet at 25° C. according to JIS C 2138:2007 is 0.0102 or more and 0.0197 or less in the frequency range of 1 KHz or more and 1 MHz or less,
The optical sheet further includes a first ultraviolet curing resin layer provided on a surface of the optical functional layer opposite to the substrate side,
the first ultraviolet curing resin layer contains urethane acrylate,
one of the outermost surfaces of the optical sheet is formed by the first ultraviolet curing resin layer, and the other of the outermost surfaces of the optical sheet is formed by a surface of the base material opposite to the optical functional layer side;
The thickness of the optical sheet is 100 μm or more and 500 μm or less,
the light absorbing portion includes a base resin and light absorbing particles held by the base resin;
The light absorbing particles include carbon black;
The light absorbing particles are contained in an amount of 10 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the light absorbing portion,
The display device, wherein the carbon black is contained in an amount of 10 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the light absorbing particles .

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