JP2008175968A - Optical film - Google Patents

Abstract

An optical film having a good alignment between a structure such as a lenticular lens on the front surface side and a structure such as a reflective layer on the back surface side and excellent in light use efficiency is provided.
A lens film (1) having a structure surface in which cylindrical lenses or prisms or an assembly thereof are formed in a stripe shape on one surface, and the lens film (1) on the structure back surface of the lens film (1). And 1) a reflective layer (2) containing a white pigment formed in a stripe shape through an opening corresponding to a condensing shape of parallel light incident from the structure surface side. the film.
[Selection] Figure 2

Description

  The present invention relates to an optical film used mainly for applications such as illumination optical path control in a display backlight unit using a liquid crystal display element.

  A display typified by a liquid crystal display device (LCD) is remarkably widespread in a type including a light source (backlight) necessary for recognizing provided information. In battery-operated devices such as laptop computers, the power consumed by the light source accounts for a substantial portion of the power consumed by the entire device. For this reason, it is particularly desirable for battery powered devices to increase battery life by reducing the total power required to provide a given brightness.

  In order to solve this problem, an optical film having a brightness enhancement film (BEF, a registered trademark of 3M USA) is widely used between a light source or a light guide plate and a liquid crystal panel.

  BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a transparent substrate. This prism is formed in a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” or “recycle” towards the viewer. To do. When using the display (when observing), BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally a normal direction to the display screen.

  When the repetitive array structure of prisms is arranged in only one direction, only redirection or recycling in the arrangement direction is possible. Therefore, in order to control the luminance of the display light in the horizontal and vertical directions, two sheets are overlapped and combined so that the arrangement directions of the prism groups are substantially orthogonal to each other. The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption. Many patent documents disclose that a brightness control member having a repetitive array structure of prisms represented by BEF is used in a display (see, for example, Patent Documents 1 to 3).

  In an optical film using BEF as a brightness control member, light from a light source is emitted from the film at an angle controlled by refraction, and can be controlled to increase the intensity of light in the viewer's visual direction. There are also unexpected light rays that are emitted in the horizontal direction without proceeding in the visual direction of the viewer. That is, regarding the intensity distribution of the light emitted from the optical film provided with the BEF, the light intensity is highest in the viewer's visual direction (the angle with respect to the axial direction is 0 °), but ± 90 with respect to the axial direction. There is also a problem that a small light intensity peak occurs in the vicinity of °, and the amount of light emitted unnecessarily from the lateral direction increases. A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° is more desirable.

In order to overcome such drawbacks, an optical film having a repetitive array structure of unit lenses (also referred to as a lenticular lens) instead of a prism has been proposed (see, for example, Patent Document 4). The surface of the optical film on the liquid crystal panel side has an array structure in which a plurality of unit lenses are repeatedly formed so as to guide light emitted from a light source and traveling through the optical film to the liquid crystal panel. The other surface of the optical film is provided with a reflective layer patterned in a stripe shape so that the vicinity of the focal plane of the lens is an opening. In the case where the unit lens is a semi-cylindrical convex cylindrical lens, the reflective layer is formed in a stripe shape so that an opening is formed corresponding to each unit lens in a 1: 1 ratio. Such a reflective layer is formed by printing or transferring a mixture obtained by mixing a white pigment, for example, titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive so as to form a predetermined pattern.

  When this optical film is incorporated into a backlight unit of a liquid crystal display, only the light emitted from the diffusion film that has passed through the opening between the reflective layers is incident on the lens and is focused in a certain direction by the lens. It will be emitted later. Furthermore, the light emitted from the optical film enters the polarizing plate, and only the light having a predetermined polarization component is guided to the liquid crystal panel.

  On the other hand, the light that has not passed through the opening is reflected by the reflection layer, returned to the diffusion film side, and guided to the reflection plate. Then, the light is incident on the diffusion film again by being reflected by the reflecting plate, and after being diffused again on the diffusion film, the incident light is incident on the lens through the opening after the incident angle is reduced. Is squeezed within a predetermined angle and emitted from the optical film.

In the backlight unit using such an optical film, by adjusting the size and position of the opening between the reflective layers, the ratio of the light emitted from the lens in the front direction is increased while improving the light utilization efficiency. Can be controlled to increase.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

  In the conventional optical film, when misalignment occurs between the lenticular lens on the structural surface and the reflective layer and the opening on the back surface of the structure, moiré or luminance unevenness occurs, and the conventional optical film does not function as a luminance enhancement film. For this reason, it is necessary to accurately align the structure of the front surface and the back surface, and there is a manufacturing problem.

  For example, in the method in which the shapes of the front and back surfaces are formed on separate films and then bonded and integrated, there is a problem in maintaining alignment accuracy. In addition, it is necessary to mold the lens and the reflective layer separately, which increases the number of steps.

  In order to solve the problem of alignment of the front and back surfaces, a method of simultaneously molding the front and back surfaces is conceivable. However, when such a method is used, it increases the number of members and processes, which causes a decrease in yield and an increase in cost. In particular, there is a method of sandwiching a film with two molds for molding the front and back surfaces of the front and back lenses and the like when they are molded with a mold using a radiation curable resin. However, since radiation irradiation is essential for curing the radiation curable resin, a method using two molds cannot be employed.

  On the other hand, for the same film, the surface side structure is molded and irradiated sequentially, and the back side structure is molded and irradiated with radiation. The deviation of the shape due to the above, particularly the deviation in the stripe width direction, becomes remarkable, adversely affects the alignment of the front and back surfaces, and cannot be practically adopted.

  An object of the present invention is to provide an optical film that has a good alignment between a structure such as a lenticular lens on the front surface side and a structure such as a reflective layer on the back surface side and is excellent in light utilization efficiency.

  The invention according to claim 1 of the present invention includes a lens film having a structural surface in which cylindrical lenses or prisms or aggregates thereof are formed in a stripe shape on one surface, and the lens film on the structural back surface of the lens film. And a reflective layer containing a white pigment formed in a stripe shape through openings corresponding to the condensing shape of parallel light incident from the structure surface side. Examples of the parallel light incident on the lens film from the structure surface side include laser light having a wavelength of 0.8 μm or more used for processing the reflective layer.

  The invention according to claim 2 provides the optical film according to claim 1, wherein the lens film has a structure in which a transparent support film and a lens layer made of a radiation curable resin are laminated. . In this case, the thickness of the support film is set so that the back surface of the support film is near the condensing position of the entire lens film.

  The invention according to claim 3 provides the optical film according to claim 1 or 2, wherein the thickness of the reflective layer is more than 5 μm and not more than 100 μm.

  The invention according to claim 4 provides the optical film according to any one of claims 1 to 3, wherein the transmittance of the reflective layer is 15% or less.

  According to a fifth aspect of the present invention, a reflective layer containing a white pigment is formed on the back side of the structure of a lens film having a structural surface in which a cylindrical lens or prism or an assembly thereof is formed on one surface, and the lens A laser beam is irradiated from the structure surface side of the film, a part of the reflective layer corresponding to the condensing part of the laser beam is selectively removed to form an opening, and a striped reflective layer is left. A method for producing an optical film according to any one of claims 1 to 4 is provided.

  The invention according to claim 6 provides the method for producing an optical film according to claim 5, wherein the wavelength of the laser light is 0.8 μm or more.

The invention according to claim 7 provides the method for producing an optical film according to claim 5 or 6, wherein the energy amount density (irradiation intensity) of the laser beam is 250 J / cm ² or more.

  According to the invention of claim 1 of the present invention, the lens film structure is striped on the structure rear surface through openings corresponding to the condensing shape of parallel light incident on the lens film from the lens structure surface side of the front surface. Since the formed reflective layer is formed, for example, when used in a backlight unit, an optical film with high light utilization efficiency can be provided. The conventional optical film does not completely correspond to the shape of the parallel light incident on the lens film from the lens structure surface side of the surface and the opening, so when used in a backlight unit, etc. Is inferior in light use efficiency.

  According to the invention which concerns on Claim 2, by setting it as the two-layer structure which laminated | stacked the transparent support film and the lens layer which consists of radiation curable resin, the film thickness adjustment of a lens film becomes easy, stability or Mechanical strength can also be improved.

  According to the invention of claim 3, by setting the thickness of the reflective layer to more than 5 μm, a sufficient white color can be obtained and adjusted to a desired transmittance, and it has a sufficient strength against rubbing and the like. No longer peels or falls off. In addition, by making the thickness of the reflective layer 100 μm or less, the processed shape of the pattern can be improved and the material cost can be reduced.

  According to the invention of claim 4, by setting the transmittance of the reflective layer to 15% or less, the ratio of light that is transmitted without being reflected by the reflective layer is reduced, and the repeated reflection in the optical film is increased. And uniformity of brightness can be improved.

  According to the invention which concerns on Claim 5, the part corresponding to the condensing part of the laser beam of a reflection layer is formed by reflecting the reflection layer formed in the structure back side of a lens film by the laser beam irradiation from the structure surface side of a lens film. A desired shape can be obtained by a simple process by selectively removing and forming an opening and applying a stripe process to the reflective layer.

  According to the invention which concerns on Claim 6, an efficient process can be performed by making the wavelength of the laser beam used for the stripe process of a reflection layer into 0.8 micrometer or more.

According to the invention which concerns on Claim 7, a highly stable process can be performed by the energy amount density of the laser beam used for the stripe process of a reflection layer being 250 J / cm < ² > or more.

  FIG. 1 is a cross-sectional view of an optical film according to an embodiment of the present invention. In this optical film, a reflective layer 2 containing a white pigment is formed in a stripe shape on the rear surface of a lens film 1 having a structure such as a lenticular lens (repetitive array structure of a striped semi-cylindrical convex cylindrical lens). It is. The openings 2 a between the stripe-shaped reflective layers 2 substantially match the condensing shape of parallel light incident on the lens film 1 from the structure surface side.

  FIG. 2 is a cross-sectional view of an optical film according to another embodiment of the present invention. This optical film is formed by striping a reflective layer 2 containing a white pigment on the rear surface of a lens film 1 in which a lens layer 4 having a structure such as a lenticular lens is formed on a transparent support film 3 such as polyethylene terephthalate (PET). It is formed in a shape. In this case, the thickness of the support film 3 is set so that the back surface of the support film 3 is in the vicinity of the condensing position of the entire lens film 1. If the thickness of the support film 3 is set as described above, the parallel light incident on the lens film 1 from the structural surface side can be easily and accurately formed in the opening 2a between the stripe-shaped reflective layers 2. It can be adjusted to match the shape. The thickness of the support film 3 is usually about 50 μm to 200 μm.

  FIG. 3 is a cross-sectional view of an optical film according to still another embodiment of the present invention. This optical film has the same configuration as the optical film of FIG. 2 except that the cross section of the unit lens in the lens layer 5 is trapezoidal. This unit lens has an intermediate structure between a cylindrical lens and a prism.

  Note that the cylindrical lens shown in FIG. 2 and the lens having the structure shown in FIG. 3 may be combined.

  As a material for the lens layer, it is desirable to use a radiation curable resin such as an ultraviolet curable resin or an electron beam curable resin, particularly when fine processing is required. As a radiation curable resin, the composition which added the reaction diluent, the photoinitiator, the photosensitizer, etc. to the urethane (meth) acrylate and / or epoxy (meth) acrylate oligomer can be used, for example.

  The urethane (meth) acrylate oligomer is not particularly limited, but, for example, ethylene glycol, 1,4-butanediol, neopentyl glycol, polycaprolactone polyol, polyester polyol, polycarbonate diol, polytetramethylene glycol and the like, hexamethylene diisocyanate, isophorone diisocyanate It can be obtained by reacting with polyisocyanates such as tolylene diisocyanate and xylene isocyanate.

  The epoxy (meth) acrylate oligomer is not particularly limited, but for example, epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, terminal glycidyl ether of bisphenol A type propylene oxide adduct, fluorene epoxy resin, etc. And can be obtained by reacting (meth) acrylic acid.

As the material of the reflective layer, a material in which a white pigment is dispersed in a resin is used. As the white pigment, TiO ₂ , BaSO ₄ , ZnO, Al ₂ O ₃ , Ag, or the like can be used. By setting the thickness of the reflective layer to more than 5 μm, a sufficient white color can be obtained and adjusted to a desired transmittance, and it has sufficient strength against rubbing and the like and does not easily peel / drop off. In addition, by making the thickness of the reflective layer 100 μm or less, the processed shape of the pattern can be improved and the material cost can be reduced. Since the reflective layer having such a thickness can reflect light inside the layer, it can be called a volumetric reflective layer.

  Next, with reference to FIG. 4 and FIG. 5, an example of the manufacturing method of the optical film which concerns on this invention is demonstrated.

  First, a lens film is manufactured as shown in FIG. As shown in FIG. 4, the support film 3 is supplied from an unwinding roll 101, and an ultraviolet curable resin is applied to the surface of the support film 3 by a coating device 102. The support film 3 is passed between a lens forming roll 103 having a reverse lenticular lens shape formed on the surface and a pressure roll 103 ′, and the lens structure is transferred to the ultraviolet curable resin on the support film 3. Thereafter, ultraviolet rays are irradiated from the ultraviolet irradiation device 104 to cure the ultraviolet curable resin to form a lens layer.

  The support film 3 is preferably a transparent resin film having ultraviolet transparency, and it is more preferable that the surface on which the lens layer is formed is subjected to an easy-adhesion treatment of the ultraviolet curable resin. Examples of the material for the support film 3 include polyethylene terephthalate (PET), polycarbonate (PC), and polyvinyl chloride (PVC).

  Although the ultraviolet curable resin coating apparatus 102 is not particularly limited, a doctor blade, a die coater, or the like is desirable. The thickness of the UV curable resin applied to the support film 3 varies depending on the shape of the lenticular lens to be formed, but is suitably 0.02 to 0.2 mm. The coating thickness of the ultraviolet curable resin can be adjusted by the viscosity of the resin, the feeding speed of the support film, and the like.

  As the lens forming roll 103 having a lenticular lens reverse shape formed on the surface, a metal mold that has been machined or a resin mold that is replicated from the metal mold by a predetermined method is used. be able to.

  Next, a reflective layer containing a white pigment is formed on the structural back surface (flat surface) of the lens film (not shown). If the raw material of the reflective layer can be supplied as a liquid white ink in which a white pigment is dispersed in a resin solution, a printing method, a coating method, a transfer method, and the like can be used, which is advantageous in production. If necessary, the resin may be dried / cured using a dryer or the like after forming the reflective layer.

  As the printing method, a gravure printing method, a silk printing method, an offset printing method, a flexographic printing method, or the like can be selected. Since it is solid printing, a reflective layer having a necessary thickness may be formed by several printings. As a coating method, a roll coater, a die coater, a curtain coater, or the like can be selected. When the transfer method is used, a transfer foil can be used, and a thermal transfer method, a sublimation transfer method, a transfer method using adhesion or adhesion, and the like can be used.

  The thickness of the reflective layer is preferably more than 5 μm and not more than 100 μm. When the thickness of the reflective layer exceeds 5 μm, a sufficient white color can be obtained and adjusted to a desired transmittance, and it has sufficient strength against rubbing and the like and does not easily peel / drop off. If the thickness of the reflective layer is 100 μm or less, the processed shape of the pattern can be improved and the material cost can be reduced.

  Next, the reflective layer is striped by the method shown in FIG. As shown in FIG. 5, the laser light 6 is irradiated as parallel light from the structural surface side of the lens film 1, and a part of the reflective layer 2 corresponding to the condensing part of the laser light 6 is selectively removed while the lens The opening 2a is formed by moving the laser beam 6 relative to the film 1 in the stripe length direction (direction perpendicular to the paper surface). By repeating this operation by moving the laser beam 6 relative to the lens film 1 along the stripe arrangement direction (the left-right direction on the paper surface), the stripe-shaped reflective layer 2 can be left. Thus, a stripe pattern of the reflective layer 2 corresponding to the structure of the lens film 1 can be obtained.

The wavelength of the laser beam 6 is not particularly limited as long as sufficient energy can be given to the reflective layer. However, it is preferable to use a laser beam having a wavelength of 0.8 μm or more obtained with a YAG laser (wavelength 1.064 μm), LD, or the like in consideration of the transmittance of the lens film, the absorption rate of the reflective layer, and the like. In particular, when titanium oxide (TiO ₂ ) is used as the white pigment of the reflective layer, it is effective to use laser light having a wavelength of 0.8 μm or more.

  It is also effective to irradiate with radiation such as ultraviolet rays in order to fix the reflective layer after the stripe processing. By irradiating with a sufficient amount of ultraviolet rays and sufficiently curing the resin on the front and back surfaces, it is possible to stabilize the production and obtain a product with little deterioration even after long-term use.

  The optical film that has been subjected to final processing may be taken up at the take-up portion, or may be connected to a line for bonding / adhesion with the diffusion plate as it is to proceed with the next step.

  The optical film according to the present invention is integrated with a diffusion plate or diffusion film having a diffusion function by bonding or bonding, and this is combined with a member such as a light source (backlight) to constitute a backlight unit. A liquid crystal display can be manufactured in combination with a liquid crystal panel.

  FIG. 6 shows the configuration of the liquid crystal display. The optical film 10 having the reflective layer 2 formed in a stripe shape on the structure rear surface of the lens film 1 through the opening 2 a is bonded to the diffusion film 12 with an adhesive 11. On the back side of the diffusion film 12, a lamp house 21 including a plurality of light sources 20 and a light reflecting plate 22 are provided. These members constitute a backlight unit. A liquid crystal panel 30 sandwiched between polarizing plates 31 and 32 is provided on the structural surface side of the lens film 1. These members constitute a liquid crystal display.

  The material of the diffusion film having a diffusion function is a material that is transparent with respect to the wavelength of the image light and can be used without particular limitation as long as it is used for the optical member. preferable. As the plastic, if polyethylene terephthalate (PET) is used, it is easy to handle from experience, but acrylic resins such as polymethyl methacrylate, polycarbonate resins, acrylic-styrene copolymers, styrene resins, polyvinyl chloride, and the like are also available. Can be used.

  The material of the diffusion plate that has a diffusion function is sufficient if it has practically sufficient transmittance and mechanical strength to reproduce the projected image. Main plastic materials such as methacrylstyrene resin, acrylic resin, and polycarbonate resin are used. can do. In addition to the plastic plate, a glass plate (float glass, blue plate glass, BK7, etc.) can also be used.

  In addition, the optical film which concerns on this invention can be used for a use besides a liquid crystal display. For example, the stripes of the optical film can be appropriately colored and used. In particular, the stripes can be colored black and bonded / adhered to an appropriate diffusion plate for use in a transmission screen.

  Hereinafter, the present invention will be described based on examples.

  In this example, the optical film shown in FIG. 2 was produced.

  As the support film 3, a 75 μm thick polyethylene terephthalate (PET) film (Toyobo A4300) was used.

  4, an ultraviolet curable resin is applied on the support film 3, the lens structure of the lens molding roll 103 is transferred to the ultraviolet curable resin, and then the ultraviolet curable resin is cured by irradiating ultraviolet rays. Thus, a lens film was formed by forming a lens layer. The shape of the lens was an aspherical shape with a pitch of 140 μm and an ellipsoidal surface as a reference surface and corrected by higher order terms. When lenses are formed at a pitch of 140 μm in this way, the vicinity of the back surface of the support film 3 made of PET having a thickness of 75 μm becomes the focal plane of the laser light used for stripe processing.

  A reflective layer having a thickness of 11 μm made of a polyurethane-based resin blended with titanium oxide as a white pigment was formed on the back surface of the lens film thus obtained. The transmittance of this reflective layer was 13%.

  The reflective layer was striped by the method shown in FIG. A part of the reflective layer 2 corresponding to the condensing part of the laser beam 6 is selected by irradiating the laser beam 6 emitted from the YAG laser with a wavelength of 1064 nm from the structural surface side of the lens film 1 and scanning the laser. The stripe pattern of the reflective layer 2 was formed.

  At this time, the incident angle of the laser beam on the lens film 1 was changed variously and the influence on the pattern formation was examined. Specifically, the tilt angle of the laser beam in the direction of the stripe length of the lens with respect to the vertical direction was changed to 0 degrees, 10 degrees, 20 degrees, and 30 degrees, but a stripe pattern can be obtained under any conditions. It was.

In addition, the laser output was variously changed to investigate the influence of the pattern on the processing state. As a result, it was found that a pattern can be obtained efficiently and stably by setting the energy density to 250 J / cm ² or more.

Sectional drawing of the optical film which concerns on one Embodiment of this invention. Sectional drawing of the optical film which concerns on other embodiment of this invention. Sectional drawing of the optical film which concerns on other embodiment of this invention. The schematic diagram which shows the manufacturing method of the lens film which concerns on this invention. The schematic diagram which shows the manufacturing method of the optical film which concerns on this invention. The schematic diagram which shows the structure of the liquid crystal display incorporating the optical film which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Lens film, 2 ... Reflective layer, 3 ... Support film, 4 ... Lens layer, 5 ... Lens layer, 6 ... Laser beam, 10 ... Optical film, 11 ... Adhesive, 12 ... Diffusing film, 20 ... Light source, 21 DESCRIPTION OF SYMBOLS ... Lamp house, 22 ... Light reflecting plate, 30 ... Liquid crystal panel, 31, 32 ... Polarizing plate, 101 ... Unwinding roll, 102 ... Coating apparatus, 103 ... Lens molding roll, 103 '... Pressure roll, 104 ... Ultraviolet irradiation apparatus.

Claims (7)

A lens film having a structure surface in which cylindrical lenses or prisms or an assembly thereof is formed in a stripe shape on one surface;
A reflective layer containing a white pigment is formed on the structural back surface of the lens film in a stripe shape through openings corresponding to the shape of the parallel light incident on the lens film from the structural surface side. An optical film characterized by the above.   The optical film according to claim 1, wherein the lens film has a structure in which a transparent support film and a lens layer made of a radiation curable resin are laminated.   The optical film according to claim 1, wherein the reflective layer has a thickness of more than 5 μm and not more than 100 μm.   The optical film according to any one of claims 1 to 3, wherein the transmittance of the reflective layer is 15% or less. A reflective layer containing a white pigment is formed on the back side of the structure of the lens film having a structure surface in which a cylindrical lens or prism or an assembly thereof is formed on one surface,
Irradiate laser light from the structural surface side of the lens film, selectively remove a part of the reflective layer corresponding to the condensing part of the laser light to form an opening, and leave a stripe-shaped reflective layer The method for producing an optical film according to claim 1, wherein:   6. The method for producing an optical film according to claim 5, wherein the wavelength of the laser beam is 0.8 [mu] m or more. The method for producing an optical film according to claim 5 or 6, wherein the energy density of the laser beam is 250 J / cm ² or more.

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