JP2008203839A - Acrylic resin for light diffusion sheet, light diffusion sheet, lens sheet, surface light source device and liquid crystal display device - Google Patents

Abstract

An object of the present invention is to reduce glare in a liquid crystal display device without causing a significant decrease in luminance of the surface light source device or the liquid crystal display device.
An acrylic resin for a light diffusing sheet comprising 10 to 50% by mass of an alkyl acrylate unit having 1 to 4 carbon atoms of an alkyl group as a monomer unit.
On the first surface of the sheet-like translucent substrate having the first surface and the second surface, a light diffusing layer is formed in which a light transmissive light diffusing material is contained in the acrylic resin for the light diffusing sheet. Light diffusion sheet.
A plurality of prism rows 411 are formed in parallel on the first surface of the sheet-like translucent base material 43 having the first surface and the second surface, and the second surface includes an acrylic resin for the light diffusion sheet. The prism sheet in which the light-diffusion layer 45 in which the translucent light-diffusion material 452 is contained in is formed.
[Selection] Figure 3

Description

  The present invention relates to an acrylic resin suitable as a binder resin for a light diffusing sheet, a light diffusing sheet including the same, a lens sheet having a lens formed on the light diffusing sheet, a liquid crystal display device including the same as a constituent member, and the liquid crystal display The present invention relates to a surface light source device used as a backlight of the device. In particular, the present invention relates to a lens sheet, a surface light source device, and a liquid crystal display device that are intended to reduce a glare phenomenon called speckle or sparkling in image display of a liquid crystal display device.

  In recent years, color liquid crystal display devices have been widely used in various fields as image display means for portable notebook personal computers, desktop personal computer monitors, portable televisions or video integrated televisions. The liquid crystal display element (liquid crystal panel) used in this liquid crystal display device does not emit light by itself, but serves as an optical shutter. Thus, in order to improve the image display performance of the liquid crystal display device, a surface light source device called a backlight is arranged behind the liquid crystal panel, and the liquid crystal panel is illuminated from the back by the light emitted from the surface light source device. Is generally done.

  Such a backlight is, for example, a fluorescent tube as a primary light source, a light guide, as described in JP-A-2-84618 (Patent Document 1) and Japanese Utility Model Laid-Open No. 3-69184 (Patent Document 2). And a prism sheet as a light deflection element. Among these, the prism sheet is disposed on the light emitting surface of the light guide, and is for improving the optical efficiency of the backlight to improve the brightness. For example, one surface of the translucent sheet Is a lens sheet in which prism rows having an isosceles triangle cross section with apex angles of 60 ° to 100 ° are arranged in parallel at a pitch of 50 μm.

As the prism sheet, as described in JP-A-6-324205 (patent document 3), JP-A-10-160914 (patent document 4) and JP-A 2000-353413 (patent document 5). In order to provide a function of a light diffusion sheet or a light diffusion film, it has been proposed to form a surface structure having a light diffusion function on the surface opposite to the surface on which the prism rows are formed. In the prism sheet of Patent Document 3, a projection group having a light diffusing function and a height not less than the wavelength of the light source light and not more than 100 μm is formed to improve the luminance of the surface light source device and reduce the luminance variation. In the prism sheet disclosed in Patent Document 4, the brightness of the surface light source device is increased and the viewing angle is increased by forming a light diffusion layer of a coating type, an embossed type, or a sandblast type. In the prism sheet of Patent Document 5, the luminance is improved and the viewing angle is expanded by applying a light diffusing fine particle layer such as transparent beads. Japanese Patent Application Laid-Open No. 2004-252353 (Patent Document 6) proposes a light diffusion sheet in which occurrence of luminance unevenness and luminance reduction is reduced by applying a cycloalkyl group-containing polymer composition.
Japanese Patent Laid-Open No. 2-84618 Japanese Utility Model Publication No. 3-69184 JP-A-6-324205 JP-A-10-160914 JP 2000-353413 A JP 2004-252353 A

  As one of the functions of the surface structure having the light diffusion function of the prism sheet as described above, light is diffused by the respective protrusions, and desired haze (Haze) is expressed, so that the desired luminance and viewing angle can be obtained. Adjustments can be made. Another one of the functions of the surface structure having the light diffusion function of the prism sheet is due to partial close contact with the light diffusion sheet and the liquid crystal panel located on the upper surface of the prism sheet (surface opposite to the prism row forming surface). It is possible to suppress a phenomenon called sticking that generates interference fringes. As a further function of the surface structure having the light diffusion function of the prism sheet, the mat structure or lens formed on the light emitting surface of the light guide or the back surface on the opposite side can be reduced. Examples include so-called defect concealment, which reduces the visibility of surface structural defects such as a row arrangement structure. This defect concealment increases in importance especially when a high-intensity light source is used as the primary light source.

  Thus, when a surface structure having a light diffusing function is formed on the surface opposite to the prism row forming surface of the prism sheet, it has a very strong directivity emitted from the light guide and internally reflected by the prism row of the prism sheet. Light may interfere with the surface structure having a light diffusing function, and a glare phenomenon called speckle or sparkling may occur in which fine particles in the coating film and irregularities on the surface are extremely glazed. In this case, the display image is very difficult to see, and in recent years, there has been a strong demand for solving this glare phenomenon. The above Patent Documents 3 to 6 do not suggest a technical problem of eliminating or reducing such a glare phenomenon.

  In order to suppress the glare phenomenon caused by the surface structure having the light diffusing function as described above, the light diffusibility is increased by increasing the amount of the light diffusing material fine particles added to the coating film forming the surface structure. As a result, the glare phenomenon can be reduced to some extent. However, when a light diffusion layer is formed by a coating method, as the amount of added light diffusing material increases, the light diffusing materials agglomerate with each other, and the coating film tends to form a non-uniform agglomerated structure. However, there is a drawback that the glare phenomenon of the liquid crystal display device is greatly increased. Moreover, there exists a difficulty that the adhesiveness to a base material falls as the addition amount of a light-diffusion material increases.

  Accordingly, an object of the present invention is to reduce the glare phenomenon in a liquid crystal display device by forming a light diffusion layer in which a light diffusion material is uniformly dispersed on the opposite surface of the prism sheet.

  The first gist of the present invention is an acrylic resin for a light diffusing sheet containing 10 to 50% by mass of an alkyl acrylate unit having 1 to 4 carbon atoms of an alkyl group as a monomer unit.

  The second gist of the present invention is that the light-transmitting light diffusing material is contained in the acrylic resin for the light diffusing sheet on the first surface of the sheet-shaped light transmitting base material having the first surface and the second surface. This is a light diffusion sheet on which a light diffusion layer is formed.

  According to a third aspect of the present invention, a plurality of lens rows are formed in parallel on the first surface of the sheet-like translucent substrate having a first surface and a second surface, and the second surface includes the It is a lens sheet in which a light diffusing layer formed by containing a translucent light diffusing material in an acrylic resin for a light diffusing sheet is formed.

  The fourth gist of the present invention is the light diffusing sheet or the lens sheet, wherein the translucent light diffusing material contains at least one kind of acrylic cross-linked particles or silicon-based particles.

According to a fifth aspect of the present invention, in an arbitrary circular region having an area of 0.015 mm ² of the light diffusion layer, a long diameter formed by aggregating a plurality of the light transmissive light diffusing materials in the acrylic resin. The number of secondary particles of 30 μm or more is 3 or less.

  The sixth gist of the present invention is the lens sheet, wherein the haze of the light diffusion layer is in the range of 30% to 85%.

The seventh gist of the present invention is a primary light source, a light guide that is guided by the light emitted from the primary light source, guided and emitted, and arranged so that the light emitted from the light guide is received. The lens sheet,
The light guide includes a light incident end surface on which light emitted from the primary light source is incident and a light output surface from which the guided light is emitted, and the primary light source is adjacent to the light incident end surface of the light guide. The surface light source device is characterized in that the lens sheet is disposed such that the first surface faces the light emitting surface of the light guide.

The eighth aspect of the present invention comprises the surface light source device and a liquid crystal panel arranged so that light emitted from the second surface of the lens sheet of the surface light source device is incident thereon,
The liquid crystal panel includes an incident surface on which light emitted from the second surface of the lens sheet is incident and an observation surface on the opposite side.

  According to the present invention as described above, since there is no aggregation structure of the light transmissive light diffusing material in the light diffusion layer, the glare phenomenon in the liquid crystal display device can be reduced.

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

  FIG. 1 shows a prism sheet as an embodiment of a lens sheet according to the present invention, an embodiment of a surface light source device according to the present invention using the prism sheet, and a liquid crystal display device according to the present invention using the surface light source device. FIG. 2 is a schematic perspective view showing an embodiment, and FIG. 2 is a schematic partial cross-sectional view thereof. In the present embodiment, the surface light source device includes a light guide 3 having at least one side end face as a light incident end face 31 and a light exit face 33 as one surface substantially orthogonal thereto, and the light guide 3. A linear primary light source 1 disposed facing the light incident end surface 31 and covered with the light source reflector 2, a prism sheet 4 as a light deflection element disposed on the light emitting surface of the light guide 3, and a light guide The light reflecting element 5 is disposed so as to face the back surface 34 opposite to the light emitting surface 33 of the body 3. In the present embodiment, the liquid crystal display device includes a liquid crystal panel (liquid crystal display element) 8 disposed on the light exit surface 42 of the prism sheet 4 of the surface light source device.

  The light guide 3 is arranged in parallel with the XY plane and has a rectangular plate shape as a whole. The light guide 3 has four side end surfaces, and at least one of the pair of side end surfaces parallel to the YZ plane is a light incident end surface 31. The light incident end face 31 is disposed to face the primary light source 1, and the light emitted from the primary light source 1 enters the light incident end face 31 and is introduced into the light guide 3. In the present invention, for example, the light source may be disposed opposite to another side end face such as the side end face 32 opposite to the light incident end face 31.

  Two main surfaces that are substantially orthogonal to the light incident end surface 31 of the light guide 3 are respectively positioned substantially parallel to the XY plane, and one of the surfaces (the upper surface in the drawing) serves as the light emitting surface 33. By providing the light emitting surface 33 with a directional light emitting mechanism including a rough surface or a lens array, the light incident from the light emitting surface 33 is guided while the light incident from the light incident end surface 31 is guided through the light guide 3. Light having directivity is emitted in a plane (XZ plane) orthogonal to the end face 31 and the light emission face 33. The angle between the peak direction (peak light) of the emitted light luminous intensity distribution in the XZ in-plane distribution and the light emitting surface 33 is defined as α. The angle α is, for example, 10 to 40 degrees, and the full width at half maximum of the emitted light luminous intensity distribution is, for example, 10 to 40 degrees.

  The rough surface and the lens array formed on the surface of the light guide 3 have a luminance within the light emitting surface 33 that the average inclination angle θa according to ISO 4287 / 1-1984 is in the range of 0.5 to 15 degrees. It is preferable from the point of aiming at the degree of uniformity. The average inclination angle θa is more preferably in the range of 1 to 12 degrees, and more preferably in the range of 1.5 to 11 degrees. The average inclination angle θa is preferably set in an optimum range by a ratio (L / d) between the thickness (d) of the light guide 3 and the length (L) in the direction in which the incident light propagates. That is, when using a light guide 3 having an L / d of about 20 to 200, the average inclination angle θa is preferably 0.5 to 7.5 degrees, more preferably 1 to 5 degrees. It is a range, More preferably, it is the range of 1.5-4 degree | times. Further, when the light guide 3 having L / d of about 20 or less is used, the average inclination angle θa is preferably 7 to 12 degrees, and more preferably 8 to 11 degrees.

The average inclination angle θa of the rough surface formed on the light guide 3 is obtained in accordance with ISO 4287 / 1-1984 by measuring the rough surface shape using a stylus type surface roughness meter and setting the coordinate in the measurement direction as x. From the obtained slope function f (x), the following equations (1) and (2)
Δa = (1 / L) ∫ ₀ ^L | (d / dx) f (x) | dx (1)
θa = tan ⁻¹ (Δa) (2)
Can be obtained using Here, L is the measurement length, and Δa is the tangent of the average inclination angle θa.

  Further, the light guide 3 preferably has a light emission rate in the range of 0.5 to 5%, and more preferably in the range of 1 to 3%. By setting the light emission rate to 0.5% or more, the amount of light emitted from the light guide 3 is increased, and sufficient luminance tends to be obtained. Further, by setting the light emission rate to 5% or less, emission of a large amount of light in the vicinity of the primary light source 1 is prevented, attenuation of the emitted light in the X direction within the light emission surface 33 is reduced, and light emission is reduced. The brightness uniformity on the surface 33 tends to be improved. Thus, by setting the light emission rate of the light guide 3 to 0.5 to 5%, the angle of the peak light in the emission light intensity distribution (in the XZ plane) of the light emitted from the light emission surface is the same as that of the light emission surface. The full width at half maximum of the emitted light luminous intensity distribution (in the XZ plane) in the XZ plane that is in the range of 50 to 80 degrees with respect to the normal and is perpendicular to both the light incident end face and the light emitting face is 10 to 40 degrees. Light with high directivity and emission characteristics can be emitted from the light guide 3, the emission direction can be efficiently deflected by the prism sheet 4, and a surface light source device having high luminance can be provided. .

In the present invention, the light emission rate from the light guide 3 is defined as follows. The relationship between the light intensity (I ₀ ) of the emitted light at the edge on the light incident end face 31 side of the light emitting face 33 and the emitted light intensity (I) at a distance L from the edge on the light incident end face 31 side is If the thickness (dimension in the Z direction) of the light guide 3 is d, the following formula (3)
I = I ₀ (α / 100) [1- (α / 100)] ^{L / d} (3)
Satisfying such a relationship. Here, the constant α is the light output rate, and the light guide 3 per unit length (length corresponding to the light guide thickness d) in the X direction orthogonal to the light incident end surface 31 on the light output surface 33. It is the ratio (percentage:%) at which the light is emitted from. The light emission rate α is obtained from the gradient by taking the logarithm of the light intensity of the light emitted from the light emission surface 23 on the vertical axis and (L / d) on the horizontal axis, and plotting these relationships. be able to.

  In the present invention, instead of forming the light emitting mechanism on the light emitting surface 33 as described above, or in combination with this, the light diffusing fine particles are mixed and dispersed in the light guide so as to emit directional light. A mechanism may be added.

  Moreover, in order to control the directivity in the surface (YZ surface) parallel to the primary light source 1 of the emitted light from the back surface 34 which is the main surface to which the directional light emitting mechanism is not provided, It is a prism row forming surface in which a large number of prism rows are arranged in a direction crossing the light incident end surface 31, more specifically in a direction substantially perpendicular to the light incident end surface 31 (X direction). The prism row on the back surface 34 of the light guide 3 can have an arrangement pitch in the range of, for example, 10 to 100 μm, and preferably in the range of 30 to 60 μm. Moreover, the prism row | line | column of the back surface 34 of this light guide 3 can make the apex angle into the range of 85-110 degree | times, for example. This is because the light emitted from the light guide 3 can be appropriately condensed by setting the apex angle within this range, and the luminance as the surface light source device can be improved. More preferably, it is the range of 90-100 degree | times.

  The light guide 3 is not limited to the shape shown in FIG. 1, and various shapes such as a rust shape with a thicker light incident end face can be used.

  The light guide 3 can be made of a synthetic resin having a high light transmittance. Examples of such synthetic resins include acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, an acrylic resin is optimal because of its high light transmittance, heat resistance, mechanical properties, and molding processability. In addition, in this application, an acrylic resin is the concept also including a methacryl resin, and means the resin which has acrylic acid ester or methacrylic acid ester as a main component. As such an acrylic resin, a resin having methyl methacrylate as a main component and having a methyl methacrylate content of 80% by weight or more is preferable. When forming a surface structure such as a rough surface of the light guide 3 or a surface structure such as a prism array or a lenticular lens array, the transparent synthetic resin plate is formed by hot pressing using a mold member having a desired surface structure. Alternatively, the shape may be imparted simultaneously with molding by screen printing, extrusion molding, injection molding, or the like. The structural surface can also be formed using heat or a photocurable resin. Furthermore, it is made of an active energy ray-curable resin on the surface of a transparent substrate such as a polyester film, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, a polymethacrylimide resin, or a transparent film or sheet. A rough surface structure or a lens array arrangement structure may be formed, or such a sheet may be bonded and integrated on a separate light-transmitting substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, (meth) acrylic acid metal salts, and the like can be used. In the present application, (meth) acryl is a general term for acrylic and methacrylic.

  The prism sheet 4 is disposed on the light emitting surface 33 of the light guide 3. The prism sheet 4 is made of a sheet-like member, and the first and second surfaces 41 and 42, which are the two main surfaces of the prism sheet 4, are arranged in parallel to each other as a whole and are located in parallel with the XY plane as a whole. The first surface 41 that is one main surface (the main surface that faces the light emitting surface 33 of the light guide 3) is a light incident surface, and the other main surface 42 is a light output surface. . The light incident surface 41 is a prism row forming surface in which a plurality of prism rows extending in the Y direction are arranged in parallel to each other. The light exit surface 42 is an uneven surface.

  In FIG. 3, the typical partial expanded sectional view of the prism sheet 4 and the light guide 3 is shown. The prism sheet 4 includes a sheet-like translucent substrate 43, a translucent prism array forming layer 44 that is a translucent lens array forming layer, and a light diffusion layer 45. A prism row 411 is formed on the lower surface of the prism row forming layer 44, and this lower surface forms the light incident surface 41. Further, the upper surface of the light diffusion layer 45 forms a light exit surface 42.

  The material of the translucent substrate 43 is preferably a material that transmits active energy rays such as ultraviolet rays and electron beams. As such a material, a flexible glass plate or the like can be used, but polyethylene terephthalate and polyethylene naphthalate can be used. Polyester resins such as phthalates, acrylic resins such as polymethyl methacrylate, cellulose resins such as diacetyl cellulose and triacetyl cellulose, styrene resins such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, cyclic or norbornene structures Transparent resins such as polyolefins and olefin resins such as ethylene / propylene copolymers, polyamide resins such as nylon and aromatic polyamide, polycarbonate resins, vinyl chloride resins, polymethacrylimide resins Sheet or film is preferred. In particular, polymethyl methacrylate having a refractive index lower than that of the prism array forming layer 44 and having a low surface reflectance, a mixture of polymethyl acrylate and a polyvinylidene fluoride resin, a polyester resin such as a polycarbonate resin and polyethylene terephthalate It is preferable from the viewpoints of strength and transparency. The thickness of the translucent substrate 43 is preferably, for example, 10 to 500 μm, more preferably 20 to 400 μm, and particularly preferably 30 to 300 μm from the viewpoint of workability such as strength and handleability. In addition, in order to improve the adhesiveness between the prism array forming layer 44 made of the active energy ray-curable resin and the transparent base material 43, the surface of the light-transmitting base material 43 is adhesive such as anchor coating treatment. What performed the improvement process is preferable.

  The light diffusing layer 45 includes a plurality of light transmissive light diffusing materials (light diffusing particles) 452 in the light transmissive resin 451.

  The translucent resin 451 is cured by mixing an acrylic resin containing 10 to 50 parts by weight of an alkyl acrylate unit having 1 to 4 carbon atoms of an alkyl group as a monomer unit with a crosslinking agent if necessary. It becomes. The translucent resin 451 is preferably crosslinked with a crosslinking agent in terms of mechanical strength, scratch resistance, and impact resistance.

  The light diffusion layer 45 is formed by applying a coating liquid containing an acrylic resin, a crosslinking agent, a light transmissive light diffusing material, a solvent, and the like to the surface of the light transmissive substrate 43. The haze of the light diffusion layer can be easily adjusted by the content of each component in the coating liquid, the coating amount, the weight average particle diameter of the light diffusion material, and the like.

  Specific examples of the solvent used for preparing the coating liquid include hydrocarbons such as toluene and xylene, esters such as ethyl acetate, butyl acetate and cellosolve acetate, alcohols such as isopropyl alcohol and n-butanol. And ketones such as acetone and methyl ethyl ketone. Among them, from the viewpoint of solubility of acrylic resin, dispersion stability of the light diffusing material in the coating liquid, adhesion between the light diffusing layer and the translucent substrate, and coating appearance of the light diffusing layer, toluene, methyl ethyl ketone and The mixture is preferred.

  As a coating method, a known method using a gravure coat, a lip coat, a comma coater or the like can be suitably used.

  In general, as the coating liquid becomes lower in viscosity, the light diffusing material tends to aggregate in the light diffusing layer. However, when the acrylic resin of the present invention is used, 100 mPa · s particularly in the case of gravure coating. Also in the coating method using the following low-viscosity coating liquid, the light diffusing material in the light diffusing layer can be well dispersed, and in addition, 20 m / min. Even at the above high-speed coating, defects such as streaks and unevenness of the light diffusion layer hardly occur.

  As the acrylic resin, those containing 10 to 50% by mass of an alkyl acrylate unit are used, so that the dispersibility of the translucent light diffusing material in the light diffusing layer is improved and used as a lens sheet for a liquid crystal display device. Sometimes the glare phenomenon can be reduced.

  Although the reason why the dispersibility of the translucent light diffusing material in the light diffusing layer is improved by using the acrylic resin containing the alkyl acrylate unit is not clear, the acrylic resin and the surface of the translucent light diffusing material are not clear. Affinity is high, and the surface of the light diffusing material is modified by adsorption of acrylic resin in the coating liquid, preventing contact between the surfaces of the light diffusing material, thereby forming the coating in the coating liquid and the light diffusing layer. It can be inferred that the aggregation of the light diffusing material is prevented in the process.

  Moreover, the adhesiveness with the light-diffusion layer at the time of using a polyethylene terephthalate as a material of the translucent base material 43 improves by containing the alkyl acrylate whose carbon number of an alkyl group is 1-4 as a structural unit. .

  An alkyl acrylate having an alkyl group with 5 or more carbon atoms has insufficient dispersibility of the light diffusing material and adhesion to the light-transmitting substrate, and the carbon number needs to be 1 to 4. Among these, ethyl acrylate and methyl acrylate are preferable, and ethyl acrylate is particularly preferable in terms of water absorption of the translucent resin.

  The content of the alkyl acrylate unit in the acrylic resin needs to be in the range of 10 to 50% by mass with respect to the acrylic resin, more preferably 12 to 40% by mass, and particularly preferably 15 to 35% by mass. %.

  When the alkyl acrylate unit is less than 10% by mass, the dispersibility of the light diffusing material becomes insufficient. When the alkyl acrylate unit exceeds 50% by mass, the mechanical properties and wet heat resistance of the translucent resin are deteriorated.

  Content of the alkyl acrylate unit in an acrylic resin or translucent resin can be quantified by NMR or GC-MS method.

  The translucent resin is preferably formed by crosslinking an acrylic resin with a crosslinking agent. However, the crosslinking method is not particularly limited, and a known crosslinking method can be used. By cross-linking, the mechanical strength, scratch resistance and impact resistance of the translucent resin are expressed.

  As the crosslinking method, a method of introducing a hydroxyl group into an acrylic resin and using it in combination with a crosslinking agent capable of reacting with the hydroxyl group is preferable because it is simple in process.

  As a method for introducing a hydroxyl group into the acrylic resin, an appropriate amount can be introduced by copolymerizing a radical polymerizable monomer having a hydroxyl group (hydroxyl group-containing monomer). Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 4-hydroxy (meth) acrylate, and caprolactone addition type monomer such as Plaxel F series manufactured by Daicel Chemical Industries.

  The content of the hydroxyl group-containing monomer in the acrylic resin is preferably in the range of 0.1 to 25% by mass, more preferably 1 to 20% by mass, and particularly preferably 2 to 15% by mass.

  As the crosslinking agent in this case, a known one that can react with a hydroxyl group can be used without particular limitation, but an isocyanate-based crosslinking agent is preferable from the viewpoint of reactivity. Among these, HDI (hexamethylene diisocyanate), XDI (xylylene diisocyanate) oligomers and various derivatives thereof are preferred from the viewpoint of compatibility between reactivity and light resistance. Examples of these commercially available products include “Duranate TPA-100” manufactured by Asahi Kasei Chemicals Corporation, “Takenate D-110N” manufactured by Mitsui Chemicals Polyurethanes, and “Coronate HX” manufactured by Nippon Polyurethanes. .

  When using the said isocyanate compound as a crosslinking agent, it is preferable to adjust the compounding ratio of an acrylic resin and a crosslinking agent according to the quantity of an isocyanate group and a hydroxyl group. That is, the molar ratio of isocyanate groups to hydroxyl groups is preferably in the range of 0.7 to 1.5, more preferably in the range of 0.9 to 1.3. By adjusting the compounding ratio of the acrylic resin and the crosslinking agent within this range, the mechanical properties of the obtained translucent resin and the adhesiveness with the translucent base material are improved.

  The crosslinking agent is preferably added to the coating solution immediately before coating so that the crosslinking reaction in the coating solution does not proceed as much as possible. On the other hand, after coating, the crosslinking proceeds in the translucent resin, and reaches a sufficient degree of crosslinking after an appropriate time. In addition, an appropriate aging treatment may be performed to promote crosslinking.

  The hydroxyl value of the acrylic resin is preferably 3 to 100 mg KOH / g, more preferably 5 to 70 mg KOH / g, and particularly preferably 6 to 50 mg KOH / g. By adjusting the hydroxyl value within this range, the translucent resin has sufficient mechanical strength and hardness, and has an excellent balance between pot life and crosslinking reactivity when a crosslinking agent is added to the coating liquid, Productivity is improved.

  Moreover, when using an isocyanate compound as a crosslinking agent, it is preferable to include a carboxylic acid group in the acrylic resin in order to accelerate the crosslinking reaction. The preferred range of the acid value in this case is 0.1 to 30 mg KOH / g, and in order to adjust the crosslinking reaction rate according to the hydroxyl value of the acrylic resin, the molecular weight, and the type of the crosslinking agent, an appropriate acid value is set. It is preferable to adjust.

  As a method for introducing a carboxylic acid group into an acrylic resin, an acrylic resin having an appropriate amount of a carboxylic acid group is obtained by using a radical polymerizable monomer having a carboxylic acid group (a carboxylic acid group-containing monomer) as a copolymerization component. be able to. Examples of the carboxylic acid group-containing monomer include (meth) acrylic acid.

  The content of the carboxylic acid group-containing monomer in the acrylic resin is preferably in the range of 0.01 to 10% by mass, particularly preferably in the range of 0.1 to 5% by mass.

  As other copolymerization components of the acrylic resin, known radical polymerizable monomers can be used without particular limitation. Various (meth) acrylic acid esters, styrene and the like can be mentioned, and the refractive index can be adjusted to an arbitrary refractive index by copolymerizing a fluorinated alkyl (meth) acrylate.

  As a weight average molecular weight (MW) of an acrylic resin, 20,000-150,000 are preferable, More preferably, it is 40,000-120,000, Especially preferably, it is the range of 50,000-100,000. By using an acrylic resin having a MW in this range, the dispersion stability of the light diffusing agent in the coating liquid is improved, and a lens sheet with less warpage is obtained because the shrinkage due to crosslinking of the translucent resin is small.

  Moreover, as Tg of acrylic resin, Preferably it is 25-100 degreeC, More preferably, it is 30-90 degreeC, Most preferably, it is 35-80 degreeC, By using the acrylic resin which has Tg of this range, it is the present invention. When a lens sheet is used as a surface light source, unevenness of the surface light source due to deformation of the lens sheet due to heat generation of the light source can be reduced, and the translucent resin has an appropriate hardness, Generation of scratches on each other during friction can be prevented.

  When forming the light diffusion layer, it is preferable to use a mixture of an acrylic resin and a leveling agent, thixotropic agent, slip agent, antifoaming agent, antistatic agent, ultraviolet absorber and the like. In particular, by including an acrylic and silicon leveling agent, aggregation of the light diffusing material 452 can be suppressed, and an uneven structure can be easily formed on the surface of the light diffusing layer by the light diffusing material 452. .

  Moreover, the damage at the time of friction with the liquid crystal panel surface can be prevented by adding a slip agent. As the slip agent, commercially available products such as silicon-based, fluorine-based, paraffin-based, and mixtures thereof can be used without any particular limitation. In particular, a silicon-based slip agent containing a hydroxyl group was included to rub against the liquid crystal panel surface. Can prevent damage.

  Next, as the light diffusing material 452, inorganic fine particles such as silica, alumina, glass, crosslinked organic fine particles such as polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, benzoguanamine, melamine, silicone fine particles, etc. Can be appropriately selected and used. Two or more kinds of light diffusing materials may be used in combination according to the purpose.

  Among these, acrylic cross-linked particles and silicone-based fine particles obtained by cross-linking methyl methacrylate are particularly preferable in terms of improving the dispersion stability in the light diffusion layer.

  As the shape of the light diffusing material, a spherical shape, an irregular shape, a spheroid or the like can be used without limitation, but the viewpoint of improving the scratch resistance of unevenness and the dispersibility in the light diffusing layer are good. From this point, a spherical one is desirable. When the light diffusing layer 45 having a concavo-convex surface is formed by coating, as the light diffusing material 452, crosslinked organic fine particles having a specific gravity close to that of a solvent capable of dissolving the translucent resin are precipitated in the coating liquid. Since it is small, it is preferably used.

  The content of the light diffusing material 452 in the light diffusing layer 45 is preferably 3 to 35 wt% with respect to the total solid content of the light diffusing layer so that the haze of the light diffusing layer 45 is 30 to 85%. If the content of the light diffusing material 452 is less than 3 wt%, the haze of the light diffusing layer 45 tends to be lower than 30%, and the viewing angle of the surface light source device tends to decrease, and the content of the light diffusing material 452 is 35 wt%. If it exceeds 50%, the haze exceeds 85% and the brightness tends to decrease.

  1-8 micrometers is preferable, as for the weight average particle diameter D1 of the light-diffusion material 452, 1-6 micrometers is more preferable, and 1-5 micrometers is especially preferable. If the weight average particle diameter D1 of the light diffusing material 452 is smaller than 1 μm, the light beam that has passed through the light diffusing layer 45 may be colored to lower the color temperature of the surface light source device or to reduce the defect concealing property. In addition, when the weight average particle diameter D1 of the light diffusing material 452 is larger than 8 μm, the glare phenomenon tends to occur strongly.

The light diffusing layer 45 obtained by applying the coating liquid containing the various materials described above has very little aggregation of the light diffusing material, but further various apparatus conditions during coating and the viscosity of the coating liquid. And the like, the number of secondary particles 453 having a major axis of 30 μm or more is preferably 3 or less, preferably 2 or less, more preferably 1 in an arbitrary circular region having an area of 0.015 mm ² of the light diffusion layer. In order to suppress the glare phenomenon, it is desirable that the number is not more than one. As shown in the plan view of FIG. 4, the planar shape of the secondary particles 453 formed by aggregating a plurality of light diffusing materials 452 is generally not circular. Therefore, the size of the secondary particles 453 is represented by the major axis D.

  The upper surface of the prism row forming layer 44 is a flat surface and is joined to the lower surface of the translucent substrate 43. The lower surface, that is, the light incident surface 41 of the prism row forming layer 44 is a prism row forming surface, and a plurality of prism rows 411 extending in the Y direction are arranged in parallel to each other. The thickness of the prism row forming layer 44 is, for example, 10 to 500 μm. The arrangement pitch P of the prism rows 411 is, for example, 10 μm to 500 μm.

  The prism row 411 includes two prism surfaces 411a and 411b. These prism surfaces may be optically sufficiently smooth surfaces (mirror surfaces) or rough surfaces. In the present invention, the prism surface is preferably a mirror surface from the viewpoint of maintaining desired optical characteristics by the prism sheet. The apex angle θ of the prism row 411 is preferably in the range of 40 to 150 °. In general, in a backlight of a liquid crystal display device, when the prism sheet is disposed so that the prism row forming surface faces the liquid crystal panel, the apex angle θ of the prism row is in the range of about 80 to 100 °. Preferably it is the range of 85-95 degrees. On the other hand, when the prism sheet 4 is arranged so that the prism row forming surface faces the light guide 3 as in the above embodiment, the apex angle θ of the prism row 411 is in the range of about 40 to 75 °, Preferably it is the range of 45-70 degrees.

  The prism row forming layer 44 is made of, for example, an active energy ray curable resin. The active energy ray curable resin for forming the prism row forming layer 44 is not particularly limited as long as it is cured with active energy rays such as ultraviolet rays and electron beams. For example, polyesters, epoxy resins , (Meth) acrylate resins such as polyester (meth) acrylate, epoxy (meth) acrylate, and urethane (meth) acrylate. Among these, (meth) acrylate resins are particularly preferable from the viewpoint of optical characteristics and the like. The active energy ray-curable composition used for such a cured resin is a polyfunctional acrylate and / or a polyfunctional methacrylate (hereinafter referred to as polyfunctional (meth) acrylate) in terms of handleability and curability. , Monoacrylate and / or monomethacrylate (hereinafter referred to as mono (meth) acrylate), and a photopolymerization initiator by active energy rays are preferred. Typical polyfunctional (meth) acrylates include polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane poly (meth) acrylate, and the like. These are used alone or as a mixture of two or more. Examples of mono (meth) acrylates include mono (meth) acrylates of monoalcohols and mono (meth) acrylates of polyols.

  As described above, the prism sheet 4 has been described as having the prism row forming layer 44 separately from the translucent base material 43. However, in the present invention, the translucent base material 43 and the prism row forming layer 44 are shared. It can consist of members. That is, a prism row can be formed on the surface of the translucent substrate 43. In this case, the translucent base material 43 can be made of a synthetic resin having a high light transmittance. Examples of such synthetic resins include acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, an acrylic resin is optimal because of its high light transmittance, heat resistance, mechanical properties, and molding processability. As such an acrylic resin, a resin having methyl methacrylate as a main component and having a methyl methacrylate content of 80% by weight or more is preferable.

  FIG. 3 schematically shows how light is deflected in the XZ plane by the prism sheet 4. This figure shows an example of the traveling direction of peak light (light corresponding to the peak of the outgoing light distribution) from the light guide 3 in the XZ plane. Most of the peak light obliquely emitted from the light emitting surface 33 of the light guide 3 at an angle α is incident on the first prism surface 411a of the prism row 411 and is almost totally reflected by the second prism surface 411b. The light travels substantially in the direction of the normal line of the light exit surface 42 and is diffused and emitted mainly by the surface of the uneven structure of the light diffusion layer 45. Further, in the YZ plane, there is also the action of the prism rows on the light guide back surface 34 as described above, so that the luminance in the normal direction of the light exit surface 42 can be sufficiently improved in a wide range.

  Note that the shape of the prism surfaces 411a and 411b of the prism row 411 of the prism sheet 4 is not limited to a single plane, and can be, for example, a convex polygonal shape or a convex curved surface shape. A narrow field of view can be achieved.

  In the prism sheet 4, the prism array is formed for the purpose of accurately producing a desired prism array shape, obtaining stable optical performance, and suppressing wear and deformation of the top of the prism array during assembly work or use of the light source device. A top flat portion or a top curved surface portion may be formed on the top of the top. In this case, the width of the top flat part or the top curved surface part is preferably 3 μm or less from the viewpoint of suppressing the occurrence of a non-uniform luminance pattern due to a decrease in luminance or a sticking phenomenon as the surface light source device. The width of the top flat part or the top curved part is 2 μm or less, more preferably 1 μm or less.

  The formation of the prism rows as described above is performed on the surface of the synthetic resin sheet by using a mold member having a shape transfer surface for transferring and forming the light incident surface 41 including the prism row forming surface having the prism rows 411. This can be realized.

  FIG. 5 is a schematic diagram showing an embodiment of forming a prism row in the prism sheet. In FIG. 5, reference numeral 7 denotes a mold member (roll mold) formed by forming a shape transfer surface for transferring and forming the light incident surface 41 on a cylindrical outer peripheral surface. This roll type | mold 7 shall consist of metals, such as aluminum, brass, and steel. FIG. 6 is a schematic perspective view of the roll mold 7. A shape transfer surface 18 is formed on the outer peripheral surface of the cylindrical roll 16. FIG. 7 is a schematic exploded perspective view showing a modified example of the roll mold 7. In this modification, a thin plate-shaped mold member 15 is wound around and fixed to the outer peripheral surface of the cylindrical roll 16. The thin plate-shaped member 15 has a shape transfer surface formed on the outer surface.

  As shown in FIG. 5, the roll mold 7 is supplied with a translucent substrate 9 (43) along its outer peripheral surface, that is, the shape transfer surface. 9, the active energy ray-curable composition 10 is continuously supplied from the resin tank 12 through the nozzle 13. A nip roll 28 for making the thickness of the supplied active energy ray-curable composition 10 uniform is provided outside the translucent substrate 9. As the nip roll 28, a metal roll, a rubber roll, or the like is used. Moreover, in order to make the thickness of the active energy ray-curable composition 10 uniform, the nip roll 28 is preferably processed with high accuracy with respect to roundness, surface roughness, etc. In the case of a rubber roll A rubber having a high hardness of 60 degrees or more is preferable. The nip roll 28 is required to accurately adjust the thickness of the active energy ray curable composition 10 and is operated by the pressure mechanism 11. As the pressure mechanism 11, a hydraulic cylinder, a pneumatic cylinder, various screw mechanisms, and the like can be used, but a pneumatic cylinder is preferable from the viewpoint of simplicity of the mechanism. The air pressure is controlled by a pressure regulating valve or the like.

  The active energy ray-curable composition 10 supplied between the roll mold 7 and the translucent substrate 9 is preferably maintained at a constant viscosity in order to keep the thickness of the obtained prism portion constant. In general, the viscosity range is preferably in the range of 20 to 3000 mPa · S, and more preferably in the range of 100 to 1000 mPa · S. By setting the viscosity of the active energy ray-curable composition 10 to 20 mPa · S or more, it is necessary to set the nip pressure extremely low or extremely increase the molding speed in order to make the prism portion constant in thickness. Disappear. If the nip pressure is extremely low, the pressure mechanism 11 tends to be unable to operate stably, and the thickness of the prism portion is not constant. On the other hand, when the molding speed is extremely increased, the irradiation amount of the active energy ray is insufficient, and the curing of the active energy ray curable composition tends to be insufficient. On the other hand, by setting the viscosity of the active energy ray-curable composition 10 to 3000 mPa · S or less, the curable composition 10 can be sufficiently distributed to the details of the roll-shaped shape transfer surface structure, and the accuracy of the lens shape is improved. Transfer is difficult, defects due to mixing of bubbles are not easily generated, and productivity is not deteriorated due to an extremely low molding speed. For this reason, in order to keep the viscosity of the active energy ray-curable composition 10 constant, a sheathed heater, a hot water jacket, or the like is provided outside or inside the resin tank 12 so that the temperature of the curable composition 10 can be controlled. It is preferable to install a heat source facility.

After supplying the active energy ray-curable composition 10 between the roll mold 7 and the translucent substrate 9, the active energy beam curable composition 10 is interposed between the roll mold 7 and the translucent substrate 9. In the sandwiched state, the active energy ray irradiating device 14 irradiates the active energy ray through the translucent substrate 9 to polymerize and cure the active energy ray curable composition 10, and the shape transfer formed on the roll mold 7. Transfer the surface. As the active energy ray irradiation device 14, a chemical reaction chemical lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a visible light halogen lamp, or the like is used. The amount of active energy ray irradiation is preferably such that the integrated energy at a wavelength of 200 to 600 nm is 0.1 to 50 J / cm ² . The irradiation atmosphere of active energy rays may be air or an inert gas atmosphere such as nitrogen or argon. Next, the prism sheet composed of the translucent substrate 9 (43) and the prism array forming layer (44) formed of the active energy ray curable resin is released from the roll mold 7.

  The application of the light diffusion layer 45 to the translucent substrate 43 can be performed before or after the application of the prism row forming layer 44 to the translucent substrate 43 as described above.

  Returning to FIG. 1, the primary light source 1 is a linear light source extending in the Y direction. As the primary light source 1, for example, a fluorescent lamp or a cold cathode tube can be used. In this case, as shown in FIG. 1, the primary light source 1 is not only installed to face one side end face of the light guide 3, but is further placed on the opposite side end face as necessary. You can also

  The light source reflector 2 guides the light from the primary light source 1 to the light guide 3 with little loss. As the material, for example, a plastic film having a metal-deposited reflective layer on the surface can be used. As shown in the drawing, the light source reflector 2 avoids the prism sheet 4 and winds from the outer surface of the light reflecting element 5 to the edge of the light emitting surface of the light guide 3 through the outer surface of the primary light source 1. It is attached. On the other hand, the light source reflector 2 can also be wound from the outer surface of the light reflecting element 5 to the light emitting surface edge of the prism sheet 4 through the outer surface of the primary light source 1. A reflection member similar to the light source reflector 2 can be attached to the side end face other than the light incident end face 31 of the light guide 3.

  As the light reflecting element 5, for example, a plastic sheet having a metal vapor deposition reflecting layer on the surface can be used. In the present invention, it is also possible to use a light reflecting layer or the like formed by metal vapor deposition or the like on the back surface 34 of the light guide 3 instead of the reflecting sheet as the light reflecting element 5.

  A transmissive liquid crystal is formed on the light emitting surface (the light exit surface 42 of the prism sheet 4) of the surface light source device including the primary light source 1, the light source reflector 2, the light guide 3, the prism sheet 4, and the light reflecting element 5 as described above. By disposing the panel (liquid crystal display element) 8, a liquid crystal display device using the surface light source device of the present invention as a backlight is configured. The liquid crystal display device is observed by an observer from above.

  In the above embodiment, a prism sheet having a prism row is used as a lens sheet having a lens row. However, in the present invention, other lens rows such as a lenticular lens having a lenticular lens row are used. Is also possible.

  In the embodiment of the lens sheet described above, the one in which the lens array is not formed is an embodiment of the light diffusion sheet. The lens sheet of the above embodiment has a light diffusing function based on the light diffusing layer. If attention is paid mainly to this light diffusing function, the above embodiment is a light diffusing sheet to which a prism row is added. It can also be said that it is an embodiment.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, the compound used in an Example is abbreviated as follows.
Methyl ethyl ketone: MEK
Methyl methacrylate: MMA
Ethyl acrylate: EA
n-butyl acrylate: n-BA
4-hydroxybutyl acrylate: 4-HBA
2-Hydroxyethyl methacrylate: HEMA
Methacrylic acid: MAA
Azobisisobutyronitrile: AIBN

[Production Example 1] (Production of acrylic resins A to E)
Weigh 106 parts by weight of toluene, 71 parts by weight of MEK, 69 parts by weight of MMA, 25 parts by weight of EA, 5 parts by weight of HEMA, and 1 part by weight of MAA in a 2 L separable flask in a polymerization reaction vessel, and perform bubbling with nitrogen while stirring with a stirring blade. For 30 minutes. Thereafter, 0.45 part by weight of AIBN was added as a radical polymerization initiator, and then the reaction vessel was heated to 90 ° C. and kept in that state for 5 hours. Further, 1 part by weight of AIBN was added and the reaction was kept for 4 hours, and then cooled to room temperature to complete the reaction, whereby an acrylic resin A solution was obtained.

  The molecular weight of the acrylic resin A is MW = 75,100, the hydroxyl value is 21.6 mgKOH / g, the acid value is 2.1 mgKOH / g, Tg is 61 ° C., and the heating residue of the acrylic resin A solution is 36.0% by weight. there were.

  Acrylic resins B to E were synthesized in the same manner as described above except that the monomer composition and the initiator amount were changed. The results are shown in Table 1.

[Production Example 2] (Production of acrylic resins F to H)
In a 2 L separable flask of the polymerization reaction vessel, 106 parts by weight of toluene, 71 parts by weight of MEK, 92.2 parts by weight of MMA, 6.8 parts by weight of HEMA, and 1 part by weight of MAA were weighed. Thereafter, a polymerization reaction was carried out in the same manner as in Production Example 1 to obtain a solution of acrylic resin F. The molecular weight of the acrylic resin F was MW = 63,000, the hydroxyl value was 29.0 mgKOH / g, the acid value was 1.7 mgKOH / g, Tg was 102 ° C., and the heating residue of the acrylic resin B solution was 36.0% by weight. It was.

  Acrylic resins G and H were synthesized in the same manner as above except that the monomer composition and the initiator amount were changed. The results are shown in Table 2.

  Using the acrylic resins A to H obtained above, the prism sheet, the surface light source device, and the liquid crystal display device described with reference to FIGS.

[Example 1]
(Formation of light diffusion layer)
25 acrylic polymer A particles having an average particle size of 5 μm (Techpolymer developed product XX-49B, manufactured by Sekisui Plastics Co., Ltd.) as a light diffusing material are added to 193.3 parts by weight of the acrylic resin A solution obtained in Production Example 1. 5.4 parts by weight of Duranate TPA-100 manufactured by Asahi Kasei Chemicals Co., Ltd. as a crosslinking agent, 70.5 parts by weight of MEK as an additional solvent, and 105.8 parts by weight of toluene are weighed in a container and stirred with a stirring blade. Thus, a coating solution for forming a light diffusion layer in which the light diffusion material was uniformly dispersed was prepared. The solid content of the coating liquid was 25% by weight, the addition amount of the light diffusing material relative to the total solid content was 25% by weight, and the viscosity was 30 mPa · s at 25 ° C.

  Next, a reverse gravure coating method is used on the surface of a PET film (trade name A4300, manufactured by Toyobo Co., Ltd.) having a thickness of 188 μm as a translucent substrate, and the average thickness after solvent drying of the coating solution is 6 μm. And then dried. Thus, a light diffusion layer having an uneven structure based on the light diffusing materials 452 and 454, that is, having an uneven surface, was formed on one surface of the PET film. As for the appearance of the obtained light diffusion sheet, there was no occurrence of coating spots such as streaks, and a very good appearance was obtained.

The following evaluation was performed about the light-diffusion layer of the obtained light-diffusion sheet.
-Adhesiveness Notches were formed in the light diffusion layer to form 100 2 mm x 2 mm wide gobangs, and a cello tape (registered trademark) peel test was performed. The number of fractional molecules shown in Table 3 indicates the number of cells remaining without being peeled after the peel test.
・ Abrasion resistance Using the Gakushin friction fastness tester described in JISL 0849, the gauze was set on the non-abrasion surface, and the coating film was shaken 200 times with a load of 500 g / cm ^2. The surface state of is shown.
○: No scratch △ to ○: There is no scratch, but some gloss is seen Δ: There are scratches and many glosses are seen ×: The coating film is peeled off and the base is visible ・ Appearance Haze meter (manufactured by Nippon Denshoku Co., Ltd., Using a product name NDH2000), the light diffusion layer was attached to face the light receiving side, and the total light transmittance (JIS K 7316) Tt and haze (JIS K 7136) Haze were measured. As a result, the total light transmittance was 96.7% and haze was 79.8%.
-Aggregation state of light diffusing material The light diffusing material was observed with transmitted light at a magnification of 500 times using an optical microscope (manufactured by Olympus, trade name MX61L). As a result, the number of secondary particles having a major axis of 30 μm or more in three arbitrary circular regions having a radius of 70 μm on the surface of the light diffusion layer was 1 at the maximum.

(Formation of prism rows)
A shape transfer surface corresponding to the shape of the prism array forming surface was formed on the surface of three types of JIS brass thin plates having a thickness of 1.0 mm and 400 mm × 690 mm to obtain a mold member. Here, the shape of the target prism array forming surface is such that a large number of prism arrays 411 having a pitch P = 50 μm and an apex angle θ = 65 ° are arranged in parallel.

  Next, a stainless steel cylindrical roll having a diameter of 220 mm and a length of 450 mm was prepared, and a mold member was wound around the outer peripheral surface and fixed with a screw to obtain a roll mold. The translucent substrate with the light diffusion layer is supplied along the roll mold between the roll mold 7 and the rubber roll, and the translucent substrate is interposed between the rubber roll and the roll mold by a pneumatic cylinder connected to the rubber roll. The material was nipped.

On the other hand, the following ultraviolet curable composition phenoxyethyl acrylate (Biscoat # 192 manufactured by Osaka Organic Chemical Industry Co., Ltd.): 50 parts by weight Bisphenol A-diepoxy-acrylate (epoxy ester 3000A manufactured by Kyoeisha Yushi Chemical Co., Ltd.): 50 parts by weight 2- Hydroxy-2-methyl-1-phenyl-propan-1-one (Darocur 1173 manufactured by Ciba-Geigy Corporation): 1.5 parts by weight were adjusted to a viscosity of 300 mPa · S / 25 ° C.

  This ultraviolet curable composition was supplied to the surface on the opposite side to the surface to which the light-diffusing layer was provided of the translucent base material niped by a rubber roll into a roll mold. While rotating the roll mold, in a state where the ultraviolet curable composition is sandwiched between the roll mold and the translucent substrate, ultraviolet rays are irradiated from an ultraviolet irradiation device to polymerize and cure the ultraviolet curable composition. The prism row pattern on the shape transfer surface of the mold was transferred. Then, it released from the roll type | mold and obtained the prism sheet.

  The prism sheet obtained as described above was cut into a 14.1 W (wide) size, and the light emitting surface of a 14.1 W (wide) size acrylic resin light guide with a cold cathode tube arranged on the side surface. As shown in FIG. 1 and FIG. 2, it was placed so that the prism array forming surface faced downward, and the other side surface and the back surface were covered with a reflection sheet to obtain a surface light source device.

  A transmissive liquid crystal panel was placed on the prism sheet of the surface light source device obtained as described above. This liquid crystal panel has a 60 ° gloss value of 48.6 on the observation surface measured by a gloss meter (trade name VGS-300A, manufactured by Nippon Denshoku Industries Co., Ltd.) and a 60 ° gloss value of 31.2 on the incident surface. It was a size 14.1 W (wide) liquid crystal panel with a pixel count XGA. In this liquid crystal display device, when the surface light source device is made to emit light, a white image is displayed on the liquid crystal panel, and glare is observed, there is almost no glare phenomenon and an easy-to-view image quality with a very smooth texture is obtained. It was.

[Examples 2 to 5]
Except having changed the compounding ratio according to Table 3, the coating liquid for light diffusion layers was produced similarly to Example 1, and this was apply | coated to PET film and the light diffusion layer was formed. The appearance of the obtained light diffusing sheet was very good with no occurrence of coating spots such as streaks. Table 3 shows the solid content and viscosity of the coating solution used.

  The light diffusion layer of the obtained light diffusion sheet was evaluated in the same manner as in Example 1 for adhesion, abrasion resistance, total light transmittance, haze, aggregation state of particles in the light diffusion layer, and glare. The results are shown in Table 3.

[Comparative Example 1]
A light diffusion layer was formed in the same manner as in Example 1 except that the coating solution was prepared according to the blending ratio shown in Table 4 using the acrylic resin F solution prepared in Production Example 2.

  About the light-diffusion layer of the obtained light-diffusion sheet, it carried out similarly to Example 1, and measured adhesiveness, abrasion resistance, and external appearance (total light transmittance and total haze). The results are shown in Table 4.

As a result of observing the aggregation state of the light diffusing material in the light diffusing layer in the same manner as in Example 1, a circular structure having a diameter of about 100 μm in which the light diffusing material was aggregated in a Benard cell shape was formed on the entire light diffusing layer.

  Further, a prism row forming layer is formed in the same manner as in Example 1 to obtain a prism sheet, and a surface light source device is manufactured in the same manner as in Example 1 using this prism sheet, and this surface light source device is used. A liquid crystal display device was produced in the same manner as in Example 1. In this liquid crystal display device, when the glare was observed in the same manner as in Example 1, a very strong glare phenomenon was observed due to the aggregated structure of the light diffusing material in the light diffusion layer, and only an image quality that was very difficult to see was obtained. There wasn't.

[Comparative Examples 2-3]
Except having changed the compounding ratio according to Table 4, the coating liquid for light-diffusion layers was produced similarly to Example 1, and this was apply | coated to PET film and the light-diffusion layer was formed.

  The light diffusion layer of the obtained light diffusion sheet was evaluated in the same manner as in Example 1 for adhesion, abrasion resistance, total light transmittance, haze, aggregation state of particles in the light diffusion layer, and glare. The results are shown in Table 4. Adhesion, abrasion resistance, agglomerated state of particles in the light diffusion layer, and glare were all poor.

[Example 6]
In Example 1, further using acrylic crosslinked particles having an average particle diameter of 8 μm (Techpolymer developed product XX-45B, manufactured by Sekisui Plastics Co., Ltd.) as the light diffusing material, the coating liquid with the mixing ratio shown in Table 3 Otherwise, a light diffusion layer was formed in the same manner as in Example 1.
The light diffusion layer of the obtained light diffusion sheet was evaluated for adhesion, abrasion resistance, total light transmittance, haze, aggregation state of particles in the light diffusion layer, and glare in the same manner as in Example 1. Table 3 shows.

1 schematically shows a prism sheet as an embodiment of a lens sheet according to the present invention, an embodiment of a surface light source device according to the present invention using the prism sheet, and an embodiment of a liquid crystal display device using the surface light source device. It is a perspective view. It is a typical fragmentary sectional view of FIG. It is a typical partial expanded sectional view of a prism sheet and a light guide. It is a schematic plan view which shows a secondary particle. It is a schematic diagram for demonstrating the manufacturing method of a prism sheet. It is a typical perspective view which shows the roll type | mold used for manufacture of a prism sheet. It is a typical disassembled perspective view which shows the roll type | mold used for manufacture of a prism sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary light source 2 Light source reflector 3 Light guide 31 Light incident end surface 32 Side end surface 33 Light output surface 34 Back surface 4 Prism sheet 41 Light incident surface 411 Prism rows 411a and 411b Prism surface 42 Light exit surface 43 Translucent base material 44 Prism row Formation layer 45 Light diffusion layer 451 Translucent resin 452 Light diffusion material 453 Secondary particle 5 Light reflection element 7 Mold member (roll type)
8 Liquid crystal panel 81 Incident surface 82 Observation surface 9 Translucent substrate 10 Active energy ray curable composition 11 Pressure mechanism 12 Resin tank 13 Nozzle 14 Active energy ray irradiation device 15 Thin plate member 16 Cylindrical roll 18 Shape transfer surface 28 Nip roll

Claims (8)

An acrylic resin for a light diffusing sheet containing 10 to 50% by mass of an alkyl acrylate unit having 1 to 4 carbon atoms of an alkyl group as a monomer unit. A light diffusing layer comprising a light transmissive light diffusing material contained in the acrylic resin for a light diffusing sheet according to claim 1 on the first surface of a sheet-like light transmissive substrate having a first surface and a second surface. The formed light diffusion sheet. 2. The acrylic for light diffusion sheet according to claim 1, wherein a plurality of lens rows are formed in parallel on the first surface of the sheet-like translucent substrate having a first surface and a second surface, and the second surface has an acrylic for a light diffusion sheet. A lens sheet in which a light diffusing layer formed by containing a translucent light diffusing material in a resin is formed. The lens sheet according to claim 3, wherein the translucent light diffusing material contains at least one kind of acrylic cross-linked particles or silicon-based particles. In an arbitrary circular region having an area of 0.015 mm ² of the light diffusing layer, the number of secondary particles having a major axis of 30 μm or more formed by aggregating a plurality of the light transmissive light diffusing materials in the acrylic resin is The lens sheet according to claim 3 or 4, wherein the number is 3 or less. The lens sheet according to claim 3, wherein a haze of the light diffusion layer is in a range of 30% to 85%. A primary light source, a light guide that is guided by the light emitted from the primary light source, is guided and emitted, and the light emitted from the light guide is arranged to be incident thereon. It consists of the lens sheet described,
The light guide includes a light incident end surface on which light emitted from the primary light source is incident and a light output surface from which the guided light is emitted, and the primary light source is adjacent to the light incident end surface of the light guide. The surface light source device is characterized in that the lens sheet is disposed such that the first surface faces the light emitting surface of the light guide. The surface light source device according to claim 7 and a liquid crystal panel arranged so that light emitted from the second surface of the lens sheet of the surface light source device is incident thereon,
The liquid crystal panel includes an incident surface on which light emitted from the second surface of the lens sheet enters and an observation surface on the opposite side.

Images