JP2009003241A - Optical member and surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member suppressed in warpage associated with the change in the environmental conditions. <P>SOLUTION: The optical member 21 comprises a first substrate sheet 21, a lens part 30 that includes a plurality of unit lenses 31 aligned on one surface 22a of the first substrate sheet, and a second substrate sheet 25 bonded to the other surface 22b of the first substrate sheet. The unit lens is constituted of a hardened crosslinkable resin compound. The thickness t1 of the first substrate is smaller than the thickness t2 of the second substrate sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical member having a light collecting function incorporated in a surface light source device, and in particular, an optical member in which the occurrence of warpage due to a change in environmental conditions is suppressed, and a surface light source device including the optical member, , Regarding.

In a surface light source device used for a liquid crystal display device or the like, an optical member (also called a prism sheet or a lens sheet) that narrows the light path direction and intensively improves the luminance in a certain direction (typically, the front direction). ) Is incorporated (for example, Patent Document 1). Usually, the optical member has a base sheet and a plurality of unit lenses formed by forming a crosslinkable resin on the base sheet.
Japanese Patent No. 2742880

  Such an optical member has a problem that warpage occurs with changes in environmental conditions such as temperature and humidity. When such a warp occurs, not only the optical member can not exhibit the intended light collecting function, but also the luminance unevenness and even the wrinkles of the optical member are visually recognized on the display device.

  The warp generated in the optical member is usually on the inside of the unit lens side of the optical member. Although the detailed mechanism for the occurrence of warping is unknown, one factor is the stress remaining in the optical member due to polymerization shrinkage during the shaping of the crosslinkable resin forming the unit lens, and the unit lens and the base. It is considered that the difference in the coefficient of thermal expansion between the material sheets has an effect.

  As a method for suppressing this warp, attempts have been made to increase the thickness of the base sheet, to laminate the base sheet, and the like. However, the warping of the optical member has not been sufficiently suppressed yet.

  The present invention has been made in consideration of the above points, and provides an optical member in which the occurrence of warpage due to a change in environmental conditions is suppressed, and a surface light source device including the optical member. With the goal.

  As a result of extensive research conducted by the present inventor, an optical member comprising a first base sheet in which unit lenses are arranged and a second base sheet laminated on the side opposite to the unit lenses of the first base sheet. It has been found that the occurrence of warpage of the optical member due to changes in environmental conditions can be significantly suppressed by making the thickness of the first base sheet thinner than the thickness of the second base sheet. It was. The present invention is based on such knowledge.

  An optical member according to the present invention includes a first base sheet, a lens unit including a plurality of unit lenses arranged on one surface of the first base sheet and made of a crosslinkable resin cured product, and the first base sheet. And a second base sheet joined to the other surface of the sheet, wherein the first base sheet is thinner than the second base sheet.

  In the optical member according to the present invention, the first base sheet and the second base sheet are made of stretched polyethylene terephthalate, and the thickness of the first base sheet is 50 μm or more, and the thickness of the second base sheet. May be 250 μm or less.

  Moreover, the optical member by this invention WHEREIN: You may make it the said 2nd base material sheet have the curvature characteristic which becomes convex toward the said 1st base material sheet side.

  Furthermore, in the optical member according to the present invention, the protruding height of each unit lens of the lens portion from the first base sheet may be 10 μm or more.

  A surface light source device according to the present invention includes any one of the optical members described above and a light source that projects light onto the optical member.

  According to the optical member of the present invention, it is possible to prevent a large warp from occurring due to changes in environmental conditions such as temperature and humidity.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  1 to 4 are diagrams for explaining an embodiment of an optical member and a surface light source device according to the present invention. 1 is a side view showing an optical member, FIG. 2 is a perspective view showing the optical member, and FIG. 3 is a diagram schematically showing a configuration of a surface light source device in which the optical member is incorporated.

  As shown in FIGS. 1 and 2, the optical member (optical sheet, lens sheet, prism sheet) 20 includes a first base sheet 21 and a lens portion formed on one surface of the first base sheet 21. 30 and a second substrate sheet 25 bonded to the other surface of the first substrate sheet 21. The optical member 20 constitutes a part of the surface light source device 14. The surface light source device 14 illustrated in FIG. 3 projects light onto the optical member 20, the light diffusion sheet 15 disposed on the second base sheet 25 side of the optical member 20, the light diffusion sheet 15, and the optical member 20. And a reflector 17 provided so as to cover the light source 16. In the example shown in FIG. 3, the surface light source device 14 is configured as a direct type, but the present invention is not limited to this, and the optical member 20 can also be applied to an edge light type surface light source device. In addition, the term “lens” used in the specification of the present application is intended to include a so-called prism in addition to a lens in a narrow sense.

  And the surface light source device 14 can comprise the liquid crystal display device 10 with the liquid crystal display panel 12 arrange | positioned at the lens part 30 side of the optical member 20. FIG. Here, the liquid crystal panel 12 includes a pair of support plates made of glass or the like, a liquid crystal disposed between the support plates, and an electrode that is disposed for each pixel in a plane and controls the orientation of liquid crystal molecules by an electric field. It is a panel having. The arrangement of the liquid crystal between the support plates can be changed for each region forming one pixel. As a result, the liquid crystal panel 12 transmits the planar light from the surface light source device 15 for each pixel. Or it functions as a shutter that can be shut off.

  As the light source 16, for example, a linear cold-cathode tube, a dot-shaped LED, an electroluminescent body, or the like can be used. The reflection plate 17 is a member for directing light from the light source 16 toward the optical member 20, and at least the inner surface of the reflection plate 17 is made of a material having a high reflectance such as metal.

  The light diffusion sheet 15 is a sheet for isotropically diffusing light from the light source 16 and eliminating luminance unevenness due to the configuration of the light source 16. Examples of the light diffusion sheet 15 include a light diffusion sheet having an uneven surface (mat surface) formed on the surface, a light diffusion sheet having a base material and light diffusion particles dispersed in the base material, and other known light. A diffusion sheet can be used. Such a light diffusing sheet 15 can be formed of a resin having high light transmissivity, such as polycarbonate resin or acrylic styrene resin.

  Next, the optical member 20 will be described in detail. The optical member 20 restricts the traveling direction of light incident from the light diffusion sheet 15 side to the front direction (the direction orthogonal to the sheet surface of the lens sheet 30 and the normal direction of the light emitting surface of the surface light source device). This is a sheet for improving the luminance in the direction. As described above, the optical member 20 is bonded to the first base sheet 21, the lens unit 30 formed on one surface of the first base sheet 21, and the other surface of the first base sheet 21. The second base sheet 25 is provided.

  The lens unit 30 includes a large number of unit lenses 31 formed on one surface 22 a of the first base sheet 20. As shown in FIGS. 1 and 2, the unit lenses 31 extend linearly in one direction and are arranged side by side along the other direction on one surface 22a orthogonal to the one direction. The unit lens 31 has a triangular shape, more specifically an isosceles triangular shape, in a cross section along a direction orthogonal to the longitudinal direction. The lens unit 30 is formed by curing a crosslinkable resin such as an ultraviolet curable resin on the one surface 22 a of the first base sheet 21. The unit lens 31 made of the cured crosslinkable resin protrudes from the first base sheet 21 by 10 μm or more due to a manufacturing method or the like.

  In the example shown in FIGS. 1 and 2, an adhesive layer 24 is provided between the first base sheet 21 and the second base sheet 25, and the first base sheet 21 is interposed via the adhesive layer 24. And the second base sheet 25 are joined. The first base sheet 21 and the second base sheet 25 are formed from stretched polyethylene terephthalate.

  A film (sheet) made of polyethylene terephthalate tends to be yellowish when the thickness exceeds 250 μm. Therefore, in the optical member 20 incorporated in the display device, the first base sheet 21 and the second base sheet 25 preferably have a thickness of 250 μm or less. In addition, when the lens unit 30 is shaped on the first base sheet 21, the first base sheet 21 is required to have a certain degree of rigidity. Specifically, it is preferable that the first base sheet 21 has a thickness of 50 μm or more.

  In the present embodiment, the thickness t <b> 1 of the first base sheet 21 is thinner than the thickness t <b> 2 of the second base sheet 25. By adjusting the thickness t1 of the first base sheet 21 and the thickness t2 of the second base sheet 25 in this way, the environmental conditions surrounding the surroundings, such as changes in temperature and humidity, are changed. The degree of warping of the optical member 20 that occurs can be greatly reduced. As will be apparent from the examples described later, when the thickness t1 of the first base material sheet 21 is set to be equal to or greater than the thickness t2 of the second base material sheet 25, a large warp may occur as the environmental conditions change. Become. Moreover, when the ratio of the thickness t1 of the first base sheet 21 to the thickness t2 of the second base sheet 25 is 0.75 or less, the degree of warping of the optical member is generally preferable. It can be suppressed to a certain extent (for example, a warp of 5 mm or less in a sample having a plan view of 200 mm × 200 mm).

  By the way, when the crosslinkable resin forming the lens portion 30 is subjected to crosslinking polymerization, the resin undergoes polymerization shrinkage. As a result, as shown in FIG. 4, the first base sheet 21 on which the lens unit 30 is formed has a warp characteristic that is convex toward the side opposite to the lens unit 30 (the other surface 22b side). It becomes like this. Note that a stretched polyethylene terephthalate film (sheet) also usually has warp characteristics. Although the detailed cause for the stretched polyethylene terephthalate film to have warp characteristics is unknown, it is thought that one factor is that the cooling rate during production differs between one side and the other side. It is done. And in this Embodiment, in order to reduce the curvature after forming the lens part 30, 1st base sheet 21 is warped so that the curvature characteristic of the 1st base material sheet 21 may become convex toward the lens part 30 side. It is preferable to determine the surface 22a of the material sheet 21 on the side where the lens portion 30 is formed. Similarly, in order to reduce the warpage caused by the lens unit 30, the second base material sheet 25 is formed such that the warp characteristic of the second base material sheet 25 becomes convex toward the first base material sheet 21 side. Is preferably arranged with respect to the first base sheet 21.

  Note that the warp characteristic referred to here is a property that tends to warp to either side in the state of use or after the environmental conditions have changed.

  According to the present embodiment as described above, the first base sheet 21 in which the unit lenses 31 are arranged, and the second base sheet laminated on the opposite side of the unit lenses 31 of the first base sheet 21. 25 on the optical member 20, and the thickness t1 of the first base sheet 21 is made thinner than the thickness t2 of the second base sheet 25, so that the warp of the optical member 20 due to changes in environmental conditions is achieved. Occurrence can be greatly suppressed.

  The optical member 20 and the surface light source device 14 according to the present embodiment are not limited to the above-described aspects, and various changes can be made.

  For example, in the above-described embodiment, the example in which the unit lens 31 of the lens unit 30 has a triangular cross section is shown, but the present invention is not limited to this. The unit lens 31 of the lens unit 30 may have a shape that forms, for example, a part of an ellipse in the cross section. In addition, the unit lenses 31 may be arranged at intervals along the two directions, and the lens unit 30 may form a fly-eye lens.

  The above-described embodiment will be described in more detail with specific examples.

  A planar optical member having a plan view shape of 200 mm × 200 mm and having the layer configuration shown in FIG. 1 was produced. The first base sheet and the second base sheet were biaxially stretched polyethylene terephthalate films. The lens part was formed by crosslinking and curing an ultraviolet curable acrylate prepolymer by ultraviolet irradiation. The adhesive layer was an acrylic adhesive, and the first base sheet and the second base sheet were adhered to the entire surface.

About each obtained optical member, thickness t1 of the 1st substrate sheet, thickness t2 of the 2nd substrate sheet, and arrangement pitch P of a unit lens were measured. The measurement results are shown in Table 1.

  Further, the degree of warpage generated after changing the environmental conditions of the obtained optical member was evaluated.

  A first test as a heating curl test was performed. In the first test, the optical member was left in a space maintained at 80 ° C. for 1 minute. Thereafter, the optical member was taken out of the space, and when the temperature of the optical member returned to room temperature, the warpage of the optical member was measured.

  On the other hand, the second test, the third test, and the fourth test were performed as the wet heat curl test. In the second test, the optical member was left in a space maintained at 45 ° C. and a relative humidity of 95% for 24 hours. Thereafter, the optical member was taken out of the space, and when the temperature of the optical member returned to room temperature, the warpage of the optical member was measured. In the third test, the optical member was left in a space maintained at 60 ° C. and a relative humidity of 95% for 24 hours. Thereafter, the optical member was taken out of the space, and when the temperature of the optical member returned to room temperature, the warpage of the optical member was measured. In the fourth test, the optical member was left in a space maintained at 80 ° C. and a relative humidity of 95% for 24 hours. Thereafter, the optical member was taken out of the space, and when the temperature of the optical member returned to room temperature, the warpage of the optical member was measured.

The method for measuring warpage is to place a square optical member having a plan view shape of 200 mm × 200 mm on the support surface so that the second base sheet faces the support surface, and from the support surfaces at the four corners of the optical member. The lift was measured as warpage. When the warpage is 0 mm, the optical member is placed on the support surface so that the lens portion faces the support surface, and the lift from the support surfaces at the four corners of the optical member is measured as the warp. did. The measured value at this time is expressed as a minus sign. Table 2 and FIG. 5 show the measurement results of warpage in the first to fourth tests. The measurement results in Table 2 and FIG. 5 were the maximum values of the measured lifts at the four corners.

  When the ratio of the thickness t1 of the first base sheet to the thickness t2 of the second base sheet was 1 or less, the amount of warping could be stably reduced. Moreover, when the ratio of the thickness t1 of the first base sheet to the thickness t2 of the second base sheet is 0.75 or less, the maximum warpage amount is set to 5 mm or less, which is generally preferred. I was able to.

FIG. 1 is a side view showing an embodiment of an optical member according to the present invention. FIG. 2 is a perspective view showing the optical member shown in FIG. FIG. 3 is a schematic configuration diagram showing an embodiment of a surface light source device according to the present invention. FIG. 4 is a perspective view for explaining a preferred lamination method of the first base material sheet and the second base material sheet while explaining the warpage characteristics. FIG. 5 is a graph showing the relationship between the ratio of the thickness t1 of the first base sheet to the thickness t2 of the second base sheet and the degree of warpage.

Explanation of symbols

14 Surface light source device 20 Optical member (lens sheet, prism sheet)
21 1st base material sheet 22a One surface 22b The other surface 25 2nd base material sheet 30 Lens part 31 Unit lens

Claims (5)

A first substrate sheet;
A lens unit including a plurality of unit lenses arranged on one surface of the first base sheet and made of a crosslinkable resin cured product;
A second substrate sheet joined to the other surface of the first substrate sheet,
The thickness of the said 1st base material sheet is thinner than the thickness of the said 2nd base material sheet, The optical member characterized by the above-mentioned. The first base sheet and the second base sheet are made of stretched polyethylene terephthalate,
The thickness of the first base sheet is 50 μm or more,
The optical member according to claim 1, wherein a thickness of the second base sheet is 250 μm or less. The optical member according to claim 1, wherein the second base sheet has a warp characteristic that is convex toward the first base sheet. The optical member according to claim 1, wherein a protruding height of each unit lens of the lens unit from the first base sheet is 10 μm or more. An optical member according to any one of claims 1 to 4,
A surface light source device comprising: a light source that projects light onto the optical member.

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