Optical laminated sheet

Abstract

The present invention provides a thin optical laminated sheet with little or no interference fringes or rainbow-like colors, and a method of manufacturing the optical laminated sheet. An optical laminated sheet is integrally formed by laminating a plurality of optical films having an adhesive layer interposed therebetween, the optical laminated sheet including an adhesive layer A wherein one surface is a flat and smooth surface and the opposite surface has an unevenness shaped by a transfer. The optical laminated sheet may include an integrally formed laminate wherein one surface of the adhesive layer A is planarly bonded to one surface of the optical film and an uneven surface that is the other surface of the adhesive layer A is linearly and/or intermittently bonded to the prism edges of a light collecting film made up of prism rows. The optical laminated sheet may be used in a backlight unit.

Claims

1. A laminated optical sheet comprising: an adhesive layer A, one surface thereof being a smooth surface, the opposite surface being rough and having a plurality of convex spherical surfaces shaped by transcription molding; a condensing film D having a plurality of prism rows adhered to the smooth surface of the adhesive layer A; a condensing film E having a plurality of prism rows wherein ridge lines of the prism rows are adhered to the rough surface; an adhesive layer B with both surfaces being smooth; and a diffusion film C having a cross sectional shape which includes plural convex portions (I) of polygonal cross section or curved cross section arranged in parallel along with random irregularities (II) lower than a maximum height of the convex portion (I) on the same surface; and wherein the films are stacked in an order with condensing film D, adhesive layer A, condensing film E, adhesive layer B, and diffusion film C, integrated to form the laminated optical sheet, and wherein the condensing film D and the diffusion film C are laminated and unified to form a laminated body with an angle between an extending direction of the convex portion (I) and an extending direction of the prism rows of at least one of the condensing films being in the range from 2° to 88°.

2. The laminated optical sheet according to claim 1, wherein at least one of the following occurs: the condensing film D comprises a prism molding layer, a supporting layer, and a coating layer; or the condensing film E comprises a prism molding layer, a supporting layer, and a coating layer.

3. The laminated optical sheet according to claim 2, wherein the laminated optical sheet is combined with a reflecting plate and a light guide plate in a backlight unit.

4. The laminated optical sheet according to claim 2 in combination with a reflecting plate and a light guide plate, wherein the reflecting plate, the light guide plate, and the laminated optical sheet are laminated in this order in a backlight unit.

5. The laminated optical sheet according to claim 1, wherein the laminated optical sheet is combined with a reflecting plate and a light guide plate in a backlight unit.

6. The laminated optical sheet according to claim 1 in combination with a reflecting plate and a light guide plate, wherein the reflecting plate, the light guide plate, and the laminated optical sheet are laminated in this order in a backlight unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a configuration example of an LCD panel and a backlight unit.

(2) FIG. 2 shows a condensing film composed with prism rows.

(3) FIG. 3 shows a laminated optical sheet in which a laminated sheet with prism rows and an adhesive layer A are integrated.

(4) FIG. 4 shows a specific example of the cross-sectional shape of the prism row.

(5) FIG. 5 shows an example of a cross-sectional view of the diffusion film C.

(6) FIG. 6 shows an illustration of the crossing angle.

(7) FIG. 7 shows a schematic diagram of the manufacturing process.

BEST MODE FOR CARRYING OUT THE INVENTION

(8) Embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following embodiments and examples shown in the figures, and the present invention can be variously changed in design.

(9) FIG. 3 shows a cross-sectional view of a laminated optical sheet in which a condensing film having two prism rows is integrated with an adhesive layer A interposed therebetween. This cross-sectional view depicts a case where the extending directions of the two prism rows are parallel.

(10) One surface of the adhesive layer A21 is bonded to a surface of the support layer 13 of the condensing film 50 composed with a prism row, and a surface of another adhesive layer A is a rough surface 20.

(11) The support layer 13 is a film having an easily-adhesive layer on the surface, such as a PET (polyethylene terephthalate) film, a TAO (cellulose triacetate) film, or a COP (cycloolefin polymer) film. The thickness of the support layer film is 5 to 100 μm, desirably 10 to 80 μm. If the thickness exceeds 100 μm, the demand for thinning cannot be satisfied. If the thickness is less than 5 μm, wrinkles are prominent, and it becomes difficult to form a prism row on the support layer and to form the rough surface of the adhesive layer A.

(12) The molding of the condensing film 50 composed with the prism rows can be accomplished by pouring the ultraviolet ray or electron beam curing resin between the roll-like die cut and processing into a shape, a reverse shape of the prism row, (the same shape but the unevenness is reversed) and the film of the support layer 13, and by irradiating with an ultraviolet ray or electron beam, the ultraviolet or electron beam curable resin is cured.

(13) As the ultraviolet ray or electron beam curable resin, an acrylic ultraviolet ray or electron beam curable resin is preferably used, and more preferably a solventless acrylic ultraviolet ray or electron beam curable resin can be used. The solventless type is preferable because it is excellent in handling ability and low shrinkage.

(14) Examples of radical polymerization monomers or oligomers of acrylic ultraviolet or electron beam curable resins include urethane poly (meth) acrylate, polyester (meth) acrylate, and epoxy poly (meth) acrylate. These may be used alone or in a form of a mixture of two or more monomers.

(15) A carbonyl compound such as benzyl, acetoin or benzophenone can be used as a photo-polymerization initiator. These may contain additives, such as antioxidant and a yellowing prevention agent, as needed.

(16) From the viewpoint of luminance improvement, acrylic ultraviolet light or electron beam curable resins mixed with ZrO.sub.2, TiO.sub.2, etc., which are transparent and high refractive index inorganic fine particles, can be suitably used in the visible light region.

(17) The prism row is preferably composed with unit prisms having a triangular cross-sectional shape with an apex angle of 85° to 95°, more preferably 88° to 92°, from the viewpoint of improving luminance.

(18) Further, as shown in FIG. 4, the cross-sectional shape in the vicinity of the top of the unit prism may be semicircular, trapezoidal, or a protrusion on the top of the unit prism. That is, as shown in FIG. 4(2), the semicircular shape is effective in suppressing the generation of white spots, which are optical defects due to scratches, and as shown in FIG. 4(1), the peel strength is improved when trapezoidal or protrusion shapes are present.

(19) The pitch of the prism row is appropriately designed depending on the liquid crystal cell size and so on, but the shorter the pitch is, the lower the prism row height can be designed, which enables the reduction of the thickness of the laminated optical sheet, and also the backlight unit, enabling one to make the backlight unit thinner. The pitch is 5 to 100 μm, more preferably 10 to 60 μm. If the pitch is less than 10 μm, it is difficult to cut the transfer roll mold, and if it exceeds 100 μm, the demand for thinning cannot be met.

(20) As the resin of the adhesive layer A, an ultraviolet ray or electron beam curable acrylic resin adhesive or an acrylic resin pressure-sensitive resin adhesive can be suitably used.

(21) As long as the adhesive (including pressure-sensitive adhesive) is an ultraviolet or electron beam curable type and adheres to an acrylic resin or polyethylene terephthalate resin, the adhesive can be used.

(22) An adhesive including a mixture of a poly-functional epoxy (meth) acrylate oligomer, a poly-functional urethane (meth) acrylate, a (meth) acryl monomer, a (meth) acrylate compound having an acryloyl group, and a photo-polymerization initiator can be used.

(23) The viscosity of the adhesive is from 5 to 800 (25° C., mPa.Math.s), preferably from 10 to 500 (25° C., mPa.Math.s). If it is less than 5 (25° C., mPa.Math.s), the productivity is remarkably lowered, and if it exceeds 800 (25° C., mPa.Math.s), it becomes difficult to control the thickness of the adhesive layer.

(24) The thickness of the adhesive layer is from 1 to 50 μm, preferably from 3 to 30 μm. If the thickness of the adhesive layer is less than 1 μm, the peel strength that can be used as a laminate cannot be achieved, and if it exceeds 50 μm, the requirement for thinning is not satisfied.

(25) When the peel strength is less than 0.3 (N/25 mm), problems arise in handling properties such as peeling of the optical film during handling. When it exceeds 10 (N/25 mm), the drop in luminance expands.

(26) The Ra, Ry, and Rz of the surface of the solidified adhesive layer A having a spherical convex portion have Ra of 0.01 to 0.55 μm, Ry of 0.10 to 2.50 μm, and Rz of 0.05 to 2.50 μm.

(27) When any of Ra, Ry, and Rz is out of the above range, interference fringes and rainbow-like colors become conspicuous and the product is not practical.

(28) For example, the surface having the spherical convex portion can be shaped by transfer from a roll surface of a cylindrical metal having a concave portion formed by sandblasting. Specifically, a spherical recess can be formed by striking substantially spherical blast particles whose surface randomly includes a particle size in the range of 30 to 100 μm on a metal roll.

(29) Incidentally, for the production of the cylindrical metal roll, the specification of JP 2011-221197 A can be used.

(30) The surface having the spherical convex portion of the adhesive layer A can be exposed by peeling off the two optical films integrated through the adhesive layer A. Ra, Ry, and Rz can be calculated from the rough surface of the adhesive layer A that appears. This can be obtained by numerical analysis of a rough surface obtained by observation with a laser microscope. The adhesive layer A can contain fine particles for adjusting the refractive index, such as ZrO.sub.2, within a range that satisfies the above Ra, Ry, and Rz.

(31) It is desirable that the adhesive layer A has a configuration which does not contain fine particles. This is because the formation of the surface having the target spherical convex portion, the improvement of the peel strength, and further the cost reduction, that are hindered.

(32) Here, the term “fine particles” refers to particles having a particle size of micron made of an inorganic or organic material.

(33) The diffusion film is obtained by kneading fine particles in an ultraviolet ray or electron beam curable resin, and applying and curing on a base film.

(34) As the fine particles, inorganic particles such as glass beads and silica can be suitably used.

(35) A diffusion film C that can be suitably used in the present invention is a diffusion sheet disclosed in an international pamphlet (WO2016/088385).

(36) As shown in FIG. 6, the bottom surface of the condensing film composed with the prism rows and the diffusion film C are integrated with each other by adhesion so that the extending direction 29 of the prism row ridge line of the condensing film and the extending direction 30 of the convex portion (I) form an angle in the range of 2° to 88° and both surfaces of the adhesive layer are bonded as smooth surfaces.

(37) The crossing angle 28 (θ) can be determined by assembling an LCD panel including a laminated optical sheet disclosed in the present invention without bonding and solidifying the bottom surface of the condensing film composed with the prism rows and by obtaining a crossing angle at which interference fringes and rainbow-like colors do not occur while changing the extending direction 30 of the diffusion film C.

(38) Also, the crossing angle can be determined by the method disclosed in Japanese Patent Application No. 2016-021386.

(39) One example of a method for producing a laminated optical sheet of the present invention will be described.

(40) As shown in FIG. 7, an ultraviolet curable adhesive 31 is applied on the support layer 13, and the surface of the metal mold cylindrical roll 32 formed with a spherical recess on the surface is brought into contact with the surface of the adhesive 31 while the first UV irradiation is performed by the UV irradiation device 33, and the spherical convex portion is shaped by transfer and, after that, The prism row ridge line of the condensing film 50 formed of the prism row is brought into contact with the spherical convex portion surface of the adhesive layer. The first ultraviolet irradiation is performed by the ultraviolet irradiation device 33, and the spherical convex portion is shaped by transfer, and then the prism row ridge line of the condensing film 50 formed of the prism row is brought into contact with the spherical convex portion surface of the adhesive layer. The laminated optical sheet F is obtained by UV irradiation for a second time while solidifying and integrating the adhesive layer.

(41) The first ultraviolet light amount is from 1/200 to 1/20 of the total amount of ultraviolet light calculated by adding the amount for the first time and the amount for the second time, and more preferably 1/150 to 1/10. When the amount of ultraviolet light is less than 1/200, the shape of the spherical convex portion formed on the surface of the adhesive layer A is not maintained, and the generation of interference fringes and rainbow-like colors cannot be suppressed. If the amount of ultraviolet light exceeds 1/20 of the total amount of ultraviolet light, the predetermined peel strength cannot be obtained.

(42) Subsequently, while the support layer of the laminated. optical sheet F integrated with the adhesive layer is in contact with the metal cylindrical mold roll 35 shaped in the same shape as the prism row, the ultraviolet irradiation device 33 is used. The laminated optical sheet G in which the prism molding layer was integrated was obtained by irradiating ultraviolet rays for solidifying the resin. The mold roll 35 is partially immersed in the ultraviolet curable resin tank 34 and plays a role of applying resin to the lower surface of the support layer of the laminated. optical sheet F.

(43) Subsequently, in the same manner, an adhesive is applied on the bottom surface 36 of the laminated optical sheet 5, and the laminated optical sheet H is solidified and integrated by irradiation with ultraviolet rays while the convex portion (I) of the diffusion film C is in contact with the adhesive. (Not shown).

(44) Similarly, the diffusion film C is obtained by applying ultraviolet curable resin on the support layer and by irradiating ultraviolet rays using an ultraviolet irradiation device (not shown) to be solidified, while the ultraviolet curable resin is being pressed to a metal cylindrical mold roll (not shown), a reverse shape of the same shape as the surface shape of the diffusion film being pressed thereon.

(45) FIG. 5 shows an example of a cross-sectional view of the diffusion film C. As shown in FIG. 5, the diffusion film C60 has a configuration in which a triangular convex portion (I) 26 and a spherical convex portion (II) 27 are provided on the surface of the support layer 13. On the back surface of the diffusion film C60, a resin layer 25 composed with unevenness is provided. As shown in FIG. 5, a resin layer having irregularities on one surface of the diffusion film C60 can be similarly molded by transfer and added.

(46) The laminated optical sheets F, G, and H disclosed in the present invention can be used as constituent members of the backlight unit.

(47) A measurement method and an evaluation method are described together below.

(48) 1. Peel Strength Test

(49) Edges to be clamped by a chuck of a tensile tester for slowly peeling off two optical films at the surface where the rough surface of the adhesive layer A adhering to the optical film and the prism row ridge line of The condensing film composed with the prism row are obtained. The maximum peel strength was measured by conducting a 180° tensile strength test at the tensile speed of 300 mm/min, with a piece width of 25 mm and a test length of 100 mm.

(50) The peel strength defined in the present invention refers to the maximum value obtained by preparing a predetermined test piece in the longitudinal direction and the transverse direction of the optical film and performing a peel strength test.

(51) 2. Viscosity of the Adhesive Material

(52) Measured with a B-type viscometer at 25° C.

(53) 3. Ra, Ry, Rz of Rough Surface of Adhesive Layer A

(54) The two optical films were slowly peeled off at the surface where the rough surface of the adhesive layer A adhering to the optical film and the surface where the prism row ridge line of the condensing film composed with the prism row are adhered. The rough surface of the adhesive layer A that has appeared after being peeled off was photographed at a magnification of 2000 using a VK8710 manufactured by Keyence (registered trademark), and was measured. with an analysis software (K Analyzer) in accordance with JIS standards (JIS B0601: 1994). However, the part that had been joined to The rough surface of the adhesive layer A was excluded. For example, the prism row ridge line trace was excluded from the measurement part. In addition, the bonding state was observed at an imaging magnification of 400 times.

(55) 4. UV Intensity

(56) The illuminance was measured with MV-03A manufactured by Oak Manufacturing Co., Ltd. (registered trademark)

(57) 5. Evaluation of Interference Fringe and Rainbow-Like Colors

(58) A backlight unit used in the LCD panel of a notebook PC (X554L) manufactured by ASUS (registered trademark) was used. The laminated optical sheet was placed on the backlight and visually observed. to see whether or not interference fringes and rainbow-like colors were generated.

(59) 6. Curl

(60) A sheet cut into a 10 cm square was placed on a surface plate, the height of the sheet raised from the surface plate to the four corners was measured with a gap Gauge, and the maximum value was defined as curl.

(61) 7. Refractive Index

(62) The refractive index of the coating layer and the adhesive layer was measured with a NPR30V/type A manufactured by SHIMADZU.

Embodiment 1

(63) An acrylic adhesive having a viscosity of 40 (mPa.Math.s) was applied with a thickness of 10 μm on a support layer made of a 25 μm polyethylene terephthalate film coated with an easily-adhesive layer on both sides.

(64) Subsequently, an ultraviolet ray of 0.19 mW/cm.sup.2 at a line speed of 8 m/min is radiated while bringing a metal roll including a copper surface blasted with a mixture of substantially spherical alumina particles having a particle diameter of 30 to 60 μm in contact with acrylic adhesive to a form spherical convex portion on the surface of the adhesive layer. The adhesive layer was not sufficiently solidified and had tackiness.

(65) Subsequently, the support layer, the adhesive layer, and the prism were irradiated with 20 mW/cm.sup.2 of ultraviolet rays at a line speed of 8 m/min while bringing the prism ridge of the condensing film made of the prism row into contact with the spherical convex surface of the adhesive layer. After integrating the condensing film having the support layer, the adhesive layer and the prism rows, while pouring an ultraviolet curable acrylic resin with a viscosity of 1200 (mPa.Math.s) between the surface without the adhesive of supporting layer opposite the spherical convex surface of the adhesive layer and the metal roll including a copper surface with the prism row of the same shape formed whereon, and solidifying by irradiation of ultraviolet light at the line speed of 8 m/min and 10 mW/cm.sup.2 and an unified optical laminated sheet Y including prism molding layer (I), supporting layer, adhesion layer and prism molding layer (II) was obtained.

(66) In the laminated optical sheet Y, the extending directions of the prism row ridge lines of the two prism molding layers are substantially orthogonal. The cross-sectional shape of the prism molding layer (I) was a triangular shape with an apex angle of approximately 90°, and the pitch was 25 μm. The cross-sectional shape of the prism molding layer (II) was a triangular shape with an apex angle of approximately 90°, and the pitch was 50 μm. The peel strength of the laminated optical sheet Y was 0.6 (N/25 mm). Ra was 0.11 μm, Ry was 0.54 μm, and Rz was 0.70 μm. As a result of observing the joining situation, the prism ridge line was adhered linearly. Generation of interference fringes and rainbow-like colors was not observed.

Embodiment 2

(67) An acrylic adhesive having a viscosity of 30 (mPa.Math.s) was applied with a thickness of 2 μm on a support layer made of a μm polyethylene terephthalate film coated with an easily-adhesive layer on both sides, and the ultraviolet light of 20 mW/cm.sup.2 was irradiated at the line speed of 2 m/min. The adhesive solidified and formed a coat layer without tackiness.

(68) Subsequently, an ultraviolet curable acrylic resin having a viscosity of 1200 (mPa.Math.s) was poured into the gap between the opposing surfaces of the coating layer and a metal roll including a copper surface on which a prism row having the same shape in opposite direction to the prism row was formed, to be cured by ultraviolet rays irradiation at 10 mW/cm.sup.2 at a line speed of 8 m/min to become solidified, and the laminate Z of the prism molding layer (I), the support layer, and the coating layer were wound into a roll.

(69) Subsequently, while feeding out the laminate Z, an acrylic adhesive having a viscosity of 40 (mPa.Math.s) was applied to the surface of the coat layer with a thickness of 10 μm, and while the acrylic adhesive and the metal roll including a nickel surface processed with a blast treatment by a mixture of almost spherical alumina particles with particle sizes from 30 μm to 60 μm were in contact, an ultraviolet ray of 19 mW/cm.sup.2 was irradiated at a line speed of 8 m/min to shape a spherical convex portion at the surface of the adhesive layer. The adhesive layer was not sufficiently solidified and had a viscosity.

(70) Subsequently, an ultraviolet curable acrylic resin having a viscosity of 1200 (mPa.Math.s) was poured into the gap between the opposing surfaces of the coating layer and a metal roll including a copper surface on which a prism row having the same shape in opposite direction to the prism row was formed, to be cured by ultraviolet rays irradiation at 10 mW/cm.sup.2 under a line speed of 8 m/min to become solidified, and a unified optical laminate sheet Y.sub.2 including the prism molding layer (I), the support layer, the adhesive solidified layer, the adhesive layer and the prism molding layer (II) and the supporting layer.

(71) In the laminated optical sheet Y.sub.2, the rolling directions of the prism row ridge lines of the two prism molding layers were substantially orthogonal. The cross-sectional shape of the prism molding layer (I) was a triangular shape with an apex angle of approximately 90°, and the pitch was 25 μm. The cross-sectional shape of the prism molding layer (II) was a triangular shape with an apex angle of approximately 90°, and the pitch was 50 μm. The peel strength of the laminated optical sheet Y.sub.2 was 0.6 (N/25 mm). Ra was 0.11 μm, Ry was 0.54 μm, and Rz was 0.70 μm. Generation of interference fringes and rainbow-like colors was not observed. As a result of investigating the curl of the laminate Z after storing the laminate Z wound 1000 times in a roll shape in an environment of 30° C.×1 for a month, the curl was 0.1 mm or less. The refractive index ratio between the coat layer and the adhesive layer was 1.00.

Embodiment 3

(72) The adhesive used in Embodiment 1 was applied to a thickness of 30 μm on the support layer of the condensing film with the prism rows of the optical laminated sheet Y obtained in an embodiment. A plurality of convex portions (I) having a triangular cross-sectional shape were arranged side by side in parallel, while having the peak portion of the convex portion of the diffusion film having the surface on the same plane contact with a triangular convex portion (I) with the height of the convex portion (I) 22 being 20 μm, the interval 24 of the height of the convex portion (I) being 300 μm, and the spherical convex portion (II) with the maximum height of the spherical convex portion (II) being 20 μm, the width 23 being in the range of from 0.5 μm to 10.0 μm the laminated optical sheet integrated by solidifying by irradiating a UV light of 20 mW/cm.sup.2 at the line velocity of 8 m/min (Refer to FIG. 5). The intersection angle was 7° (Refer to FIG. 6). Interference fringes and rainbow-like colors were not observed.

INDUSTRIAL APPLICABILITY

(73) The present invention is useful for optical films used in liquid crystal panels and the like.

DESCRIPTION OF SYMBOLS

(74) 1 Configuration example of LCD panel 2 Configuration example of backlight unit 3 LED 4 Reflection plate 5 Light guide plate 6 Diffusion film 7 Light collection film 8 Liquid crystal cell 9 Antireflection film 10 Polarizing film 11 Molding layer 12 Bottom surface 13 Supporting layer 14 Vertical angle 15 Prism row ridgeline 16 Pitch 17 Unit prism 18 Prism row 19 Smooth surface 20 Rough surface 21 Adhesive layer A 22 Maximum height 23 Width 24 Interval of convex portion (I) 25 Resin layer composed with unevenness 26 Convex portion (I) 27 Convex portion (II) 28 Crossing angle 29 Extending direction of prism row ridgeline 30 Extending direction of convex portion (I) ridgeline of diffusion film C 31 Adhesive 32 Metal mold cylindrical roll formed with spherical recess on surface 33 Ultraviolet irradiation device 34 Ultraviolet curable resin tank 35 Metal cylindrical mold roll shaped in same shape as prism row 36 Bottom surface of laminated optical sheet 50 Condensing film formed with prism row 60 Diffusion film C