JP6293414B2 - Light guide film for ultra-thin liquid crystal backlight, ultra-thin liquid crystal backlight unit, and portable computer - Google Patents

Description

  The present invention relates to a light guide film for an ultra-thin liquid crystal backlight, an ultra-thin liquid crystal backlight unit, and a portable computer.

  In the liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side is widely used, and a backlight unit such as an edge light type or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 5, the edge light type backlight unit 111 is generally placed on the inner surface side of the top plate 114 that is the casing on the rearmost surface of the liquid crystal display unit, and is disposed on the surface of the top plate 114. A reflecting plate 113, a light guide plate 112 disposed on the surface of the reflecting plate 113, and a light source 115 for irradiating light toward the end face of the light guide plate 112 (Japanese Patent Laid-Open No. 2010-177130). See the official gazette). In the edge light type backlight unit 111, the light emitted from the light source 115 enters the end surface of the light guide plate 112, and the light incident on the light guide plate 112 propagates through the light guide plate 112, The light is emitted from the surface of the guide plate 112. The light beam emitted from the back surface of the light guide plate 112 is reflected by the reflection plate 113 and is incident on the light guide plate 112 again to reduce the light beam loss.

  A portable computer having such a liquid crystal display unit is required to be thin and light in order to improve its portability and convenience, and accordingly, the liquid crystal display unit is also required to be thin. In particular, in an ultra-thin laptop computer in which the thickest part of the casing called Ultrabook (registered trademark) is 21 mm or less, the thickness of the liquid crystal display part is desired to be about 4 mm to 5 mm. The edge light type backlight unit incorporated in the display unit is required to be thinner.

  For this reason, the light guide film used in such an ultra-thin portable computer is also required to be thin in conjunction with the thinning of the liquid crystal display portion. Specifically, such a light guide film is required. The thickness is preferably about 600 μm or less.

  However, the ultra-thin light guide film is likely to be distorted due to aging. Since the surface of the distorted light guide film is curved, there is a risk that the luminance and uniformity of the light beam emitted from the light guide film may be reduced. Moreover, the retardation of the light guide film is increased due to the distortion of the light guide film, and the optical characteristics of the light beam emitted from the light guide film change due to the retardation, which may reduce the luminance and the uniformity thereof. As described above, the uniformity of the luminance of the light emitted from the light guide film is lowered, and as a result, the luminance unevenness of the display screen of the ultra-thin portable computer may occur.

JP 2010-177130 A

  This invention is made | formed in view of such a situation, and it aims at providing the light guide film which can suppress the fall of a brightness | luminance and its uniformity while achieving thickness reduction. Further, the present invention provides an edge light type backlight unit and a portable computer that are less likely to cause uneven brightness by suppressing a decrease in luminance and uniformity of light emitted from a light guide film, and can be reduced in thickness. It is to provide.

The light guide film for an ultra-thin liquid crystal backlight of the present invention made to solve the above problems is
A light guide film for an ultra-thin liquid crystal backlight having an average thickness of 600 μm or less that emits light incident from the end face substantially uniformly from the surface,
Retardation value (Re) is 50 nm or less,
The average residual stress is 8 × 10 ⁵ Pa or less.

Since the light guide film has a retardation value (Re) of 50 nm or less, the optical characteristics of light emitted from the light guide film are less likely to change, and the luminance and uniformity of the light emitted from the light guide film. Is less likely to occur. Further, since the average residual stress is 8 × 10 ⁵ Pa or less, the light guide film is less likely to be distorted due to a change with time, and the light guide film is less likely to be curved. It is difficult for the brightness of the light beam and the uniformity thereof to decrease.

  The light guide film is preferably formed by an extrusion sheet molding method. By forming the light guide film by an extrusion sheet forming method, the light guide film can be easily formed.

  The light guide film preferably has a polycarbonate resin as a main component. Thereby, since polycarbonate-type resin is excellent in transparency and its refractive index is high, total reflection is likely to occur on the surface of the light guide film, and light can be efficiently propagated. In addition, since the polycarbonate-based resin has heat resistance, deterioration due to heat generation of the light source hardly occurs. Further, the polycarbonate resin has high dimensional stability because it has less water absorption than acrylic resin and the like.

The difference between the maximum value and the minimum value of the residual stress is preferably 1 × 10 ⁵ Pa or less. Thereby, since the difference in distortion of the light guide film due to a change with time is reduced, there is little possibility that the brightness of the light emitted from the light guide film and the uniformity thereof are lowered.

  The light guide film preferably has a surface static friction coefficient of 0.5 or less. Thereby, the slipperiness with other optical sheets etc. arrange | positioned at the surface side of the said light guide film can be kept favorable, and scratch resistance can be improved.

  In addition, the light guide film preferably has a fine modulation structure in which the front surface or the front surface and the back surface are wavy. Thereby, light guide property, diffusibility, or light output property is promoted, and it is possible to further suppress a decrease in luminance and uniformity of light emitted from the surface.

  The light guide film preferably has a diffusion pattern on the back surface. Thereby, the light beam introduced from the light source can be efficiently diffused by the diffusion pattern and emitted from the surface side.

  The light guide film may have a configuration in which the diffusion pattern includes a plurality of hemispherical concave portions. Thereby, since a hemispherical diffusion surface is formed on the inner side of the light guide film, it is possible to efficiently diffuse the light beam.

  Further, the light diffusion pattern may be composed of a plurality of light scattering portions colored by laser irradiation. Thereby, a desired diffusion pattern can be formed easily and reliably. Moreover, when forming a diffusion pattern by such a method, thickness reduction of the light guide film can be promoted as compared with the case of forming a diffusion pattern by providing a convex portion or the like on the back surface of the light guide film.

  Further, an ultra-thin liquid crystal backlight unit according to the present invention made to solve the above-described problems is a reflector, the light guide film having the above-described configuration laminated on the surface side of the reflector, and the light guide. A light source for irradiating the film with light is provided.

  In the ultra-thin liquid crystal backlight unit, since the average thickness of the light guide film is 600 μm or less, it is possible to promote thinning. In addition, the light guide film has a retardation value (Re) of 50 nm or less and an average residual stress of 8 × 10 5 Pa or less, so that the luminance and uniformity of light emitted from the light guide film are reduced. Hateful. Therefore, the ultra-thin liquid crystal backlight unit is less likely to cause luminance unevenness.

  Furthermore, a portable computer according to the present invention, which has been made to solve the above problems, includes the ultra-thin liquid crystal backlight unit having the above-described configuration in a liquid crystal display unit.

  Since the portable computer includes the ultra-thin liquid crystal backlight unit having the above-described configuration, the portable computer has the advantages as described above. That is, the portable computer is less likely to cause uneven brightness on the display screen and can be thinned.

The “residual stress” is the stress generated inside without applying external stress, and the calculation formula “retardation (Re) (nm) / (photoelastic coefficient (10 ¹² / Pa) × thickness”. (Cm)) ”. “Average residual stress” means the average value of residual stress at any 15 points. The “difference between the maximum value and the minimum value of the residual stress” is a difference between the maximum value and the minimum value of the residual stress at any 15 points. “Surface” means the display surface side of the liquid crystal display unit. “Back” means the top plate side and the opposite side of the display surface of the liquid crystal display unit. The “static friction coefficient” is a static friction coefficient with respect to the surface of the same material, and means a value measured by a method defined in JIS K7125.

  As described above, the light guide film for an ultra-thin liquid crystal backlight according to the present invention can be reduced in thickness and can suppress reduction in luminance and uniformity thereof. In addition, the ultra-thin liquid crystal backlight unit and the portable computer of the present invention cause uneven brightness by suppressing the decrease in the luminance and uniformity of light emitted from the light guide film for the ultra-thin liquid crystal backlight. Difficult and thin.

It is a schematic perspective view of the laptop computer which concerns on one Embodiment of this invention, (A) shows the state which opened the liquid crystal display part, (B) shows the state which closed the liquid crystal display part. It is typical sectional drawing which shows the ultra-thin liquid crystal backlight unit of the portable computer of FIG. It is a typical partial enlarged view which shows the manufacturing apparatus of the light guide film of the ultra-thin liquid crystal backlight unit of FIG. It is a typical perspective view which shows the ultra-thin liquid crystal backlight unit which concerns on a different form from the ultra-thin liquid crystal backlight unit of FIG. It is typical sectional drawing which shows the conventional edge light type backlight unit.

[First embodiment]
<Portable computer>
A portable computer 1 shown in FIG. 1 is a laptop computer, and includes an operation unit 2 and a liquid crystal display unit 3 connected to the operation unit 2 so as to be rotatable (openable and closable). The portable computer 1 has a casing (a casing that entirely accommodates the components of the portable computer 1) having a thickness (the thickest part (when the liquid crystal display unit 3 is closed)) of 21 mm or less. Registered trademark) (hereinafter sometimes referred to as “ultra-thin computer 1”).

  The liquid crystal display unit 3 of the ultra-thin computer 1 includes a liquid crystal panel 4 and an edge-light ultra-thin liquid crystal backlight unit 11 (hereinafter referred to as a “backlight unit”) that emits light from the back surface toward the liquid crystal panel 4. 11 ”). The liquid crystal panel 4 is held by the casing 5 for the liquid crystal display section of the housing around the front surface, side surfaces, and direction. Here, the casing 5 for the liquid crystal display unit includes a top plate 14 disposed on the surface (and the back surface) of the liquid crystal panel 4, and a surface support member 6 disposed on the surface side around the surface of the liquid crystal panel 4. have. The casing of the ultra-thin computer 1 is provided in a liquid crystal display casing 5 and the liquid crystal display casing 5 so as to be rotatable via a hinge portion 7. CPU) etc. are built in.

  The thickness of the liquid crystal display unit 3 is not particularly limited as long as the thickness of the housing is within a desired range, but the upper limit of the thickness of the liquid crystal display unit 3 is preferably 7 mm, and more preferably 6 mm. More preferably, it is 5 mm. On the other hand, the lower limit of the thickness of the liquid crystal display unit 3 is preferably 2 mm, more preferably 3 mm, and still more preferably 4 mm. If the thickness of the liquid crystal display unit 3 exceeds the above upper limit, it may be difficult to meet the demand for thinning the ultra-thin computer 1. Further, when the thickness of the liquid crystal display unit 3 is less than the lower limit, there is a possibility that the strength of the liquid crystal display unit 3 is lowered, the luminance is lowered, or the like.

<Backlight unit>
The backlight unit 11 of FIG. 2 includes a light guide film 12, a reflector 13 laminated on the back surface of the light guide film 12, and a light source 15 that irradiates the light guide film 12. The backlight unit 11 may have a top plate 14 that is laminated on the back surface of the reflecting plate 13.

(Light guide film)
The light guide film 12 emits light incident from the end face substantially uniformly from the surface side. The light guide film has an average thickness of 600 μm or less. The light guide film 12 has a sheet body 16. A diffusion pattern 17 is formed on the back surface of the sheet body 16.

  The sheet body 16 is formed in a substantially rectangular parallelepiped shape. The average thickness of the sheet body 16 is 600 μm or less. The upper limit of the average thickness of the sheet body 16 is more preferably 580 μm, and further preferably 550 μm. On the other hand, the lower limit of the average thickness of the sheet body 16 is preferably 100 μm, more preferably 150 μm, and even more preferably 200 μm. When the average thickness of the sheet main body 16 exceeds the above upper limit, there is a possibility that the demand for thinning the backlight unit 11 desired in the ultra-thin computer 1 may not be met. Moreover, when the average thickness of the sheet body 16 is less than the lower limit, the light guide film 12 may have insufficient strength, and the light from the light source 15 may not be sufficiently incident.

Since the sheet body 16 needs to have translucency, it is formed to be transparent, particularly colorless and transparent. Although it does not specifically limit as a main component of the sheet | seat main body 16, Synthetic resins, such as a polycarbonate-type resin excellent in transparency, intensity | strength, etc., and an acrylic resin excellent in transparency, scratch resistance, etc., are mentioned. Especially, as a main component of the sheet | seat main body 16, polycarbonate-type resin is preferable. Since the polycarbonate-based resin is excellent in transparency and has a high refractive index, an air layer (a layer formed in a gap with the optical sheet disposed on the front surface side of the light guide film 12 and the back surface side of the light guide film 12). Total reflection is likely to occur at the interface between the reflecting plate 13 and a layer formed in the gap between the reflecting plate 13 and the light beam can be propagated efficiently. In addition, since the polycarbonate-based resin has heat resistance, deterioration due to heat generation of the light source 15 hardly occurs. In addition, since the polycarbonate resin has less water absorption than the acrylic resin, the dimensional stability is high.

  The polycarbonate resin is not particularly limited, and may be either a linear polycarbonate resin or a branched polycarbonate resin, and a polycarbonate resin including both a linear polycarbonate resin and a branched polycarbonate resin. It may be.

The linear polycarbonate-based resin is a linear aromatic polycarbonate-based resin produced by a known phosgene method or melting method, and includes a carbonate component and a diphenol component. Examples of the precursor for introducing the carbonate component include phosgene and diphenyl carbonate. Examples of the diphenol include 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, and 1,1-bis (4-hydroxy). Phenyl) cyclohexane, 1,1-bis (3,5-dimesyl-4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) decane, 1,1-bis (4-hydroxyphenyl) propane, , 1-bis (4-hydroxyphenyl) cyclodecane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) cyclododecane, 4,4′-dihydroxydiphenyl ether, 4,4′-thiodiphenol, 4 , 4'-dihydroxy-3,3'-dichlorodiphenyl ether and the like. These can be used alone or in combination of two or more. Such a linear polycarbonate resin is produced by, for example, the method described in US Pat. No. 3,998,672.

  The branched polycarbonate resin is a polycarbonate resin produced using a branching agent. Examples of the branching agent include phloroglucin, trimellitic acid, 1,1,1-tris (4-hydroxyphenyl) ethane, 1, 1,2-tris (4-hydroxyphenyl) ethane, 1,1,2-tris (4-hydroxyphenyl) propane, 1,1,1-tris (4-hydroxyphenyl) methane, 1,1,1-tris (4-hydroxyphenyl) propane, 1,1,1-tris (2-methyl-4-hydroxyphenyl) methane, 1,1,1-tris (2-methyl-4-hydroxyphenyl) ethane, 1,1, 1-tris (3-methyl-4-hydroxyphenyl) methane, 1,1,1-tris (3-methyl-4-hydroxyphenyl) ethane, 1,1-tris (3,5-dimethyl-4-hydroxyphenyl) methane, 1,1,1-tris (3,5-dimethyl-4-hydroxyphenyl) ethane, 1,1,1-tris (3- Chloro-4-hydroxyphenyl) methane, 1,1,1-tris (3-chloro-4-hydroxyphenyl) ethane, 1,1,1-tris (3,5-dichloro-4-hydroxyphenyl) methane, , 1,1-tris (3,5-dichloro-4-hydroxyphenyl) ethane, 1,1,1-tris (3-bromo-4-hydroxyphenyl) methane, 1,1,1-tris (3-bromo -4-hydroxyphenyl) ethane, 1,1,1-tris (3,5-dibromo-4-hydroxyphenyl) methane, 1,1,1-tris (3,5-dibromo-4-hydroxyphenyl) Tan, 4,4'-dihydroxy-2,5-dihydroxydiphenyl ether, and the like.

  Such branched polycarbonate resins include, for example, aromatic diphenols, polycarbonate oligomers derived from the above branching agents and phosgene, aromatic diphenols, and the like, as described in JP-A No. 03-182524. A method in which an end stop agent is reacted while stirring so that the reaction mixture containing these becomes a turbulent flow, and when the viscosity of the reaction mixture rises, an aqueous alkali solution is added and the reaction mixture is reacted as a laminar flow. Can be manufactured.

  The sheet body 16 preferably contains the branched polycarbonate resin in the polycarbonate resin in the range of 5 wt% to 80 wt%, and more preferably in the range of 10 wt% to 60 wt%. . This is because if the branched polycarbonate-based resin is less than 5% by weight, the elongational viscosity decreases and molding by extrusion molding becomes difficult. If the branched polycarbonate resin exceeds 80% by weight, the shear viscosity of the resin increases and the moldability becomes low. It is because it falls.

  The sheet body 16 may contain other optional components as long as the transparency is not impaired, but preferably contains 90% by mass or more, more preferably 98% by mass of the linear polycarbonate resin and / or branched polycarbonate resin. It is good to include the above. Examples of the optional component include an ultraviolet absorber, a stabilizer, a lubricant, a processing aid, a plasticizer, an impact resistance aid, a phase difference reducing agent, a matting agent, an antibacterial agent, and an antifungal agent.

  The sheet body 16 preferably has a retardation value (Re) of 50 nm or less, more preferably 40 nm or less, and further preferably 30 nm or less. When the retardation value (Re) exceeds the upper limit, the optical characteristics of the light beam emitted from the sheet main body 16 may change, so that the luminance of the light beam and its uniformity may decrease.

The seat body 16 is preferably an average residual stress is not more than 8 × ¹⁰ 5 Pa, more preferably 5 × ¹⁰ 5 Pa or less, more preferably 3 × ¹⁰ 5 Pa or less. When the average residual stress exceeds the above upper limit, distortion of the sheet main body 16 is likely to occur due to a change with time, and the surface of the distorted sheet main body 16 is curved, so that the luminance and uniformity of light emitted from the sheet main body are reduced. There is a fear. In addition, when a resin having a high photoelastic coefficient is used for the sheet body 16, the retardation value (Re) may be increased due to the curvature of the surface, and the optical characteristics of the light emitted from the sheet body 16 change. There is a fear. The sheet body 16 is not particularly limited, but the average residual stress is preferably 0.5 × 10 ⁵ Pa or more, and more preferably 1 × 10 ⁵ Pa or more. When the average residual stress is less than the above lower limit, the production efficiency of the light guide film may be reduced.

Further, the difference between the maximum value and the minimum value of the residual stress of the sheet body 16 is preferably 1 × 10 ⁵ Pa or less, and more preferably 0.7 × 10 ⁵ Pa or less. When the difference between the maximum value and the minimum value of the residual stress of the sheet main body 16 exceeds the above upper limit, the distortion difference of the light guide film becomes large, and the luminance and uniformity of the light beam emitted from the sheet main body may be reduced. is there.

  Moreover, it is preferable that the static friction coefficient of the surface of the sheet | seat main body 16 is 0.5 or less, and it is further more preferable that it is 0.4 or less. If the static friction coefficient of the surface of the sheet main body 16 exceeds the above upper limit, the sliding property with other optical sheets disposed on the surface side of the light guide film is not sufficient, and there is a risk of damaging other optical sheets. is there.

  The diffusion pattern 17 includes a plurality of concave portions and is formed on the back surface of the sheet main body 16. The plurality of recesses are formed in a dotted shape on the back surface of the sheet body 16 and are arranged so that uniform light can be emitted from the light guide film 12 from the front surface side. Specifically, the plurality of recesses are formed so that the existence ratio at a position close to the light source 15 is small, and the existence ratio increases as the distance from the light source 15 increases. The presence ratio of the plurality of recesses can be adjusted by adjusting the arrangement position or changing the size of each recess while keeping the size of each recess the same. However, from the viewpoint of improving the light guide property while promoting the thinning of the light guide film 12, it is preferable to adjust the arrangement position while keeping the size of each recess the same.

  The average diameter of the recess is not particularly limited, but is preferably 50 μm or less. As an upper limit of the average diameter of the said recessed part, 40 micrometers is more preferable and 30 micrometers is further more preferable. On the other hand, the lower limit of the average diameter of the recesses is preferably 0.5 μm, more preferably 1 μm, and even more preferably 5 μm. When the average diameter of the recess exceeds the upper limit, luminance unevenness may occur, and the height of the recess increases, which may make it difficult to promote thinning of the light guide film 12. Conversely, when the average diameter of the recesses is less than the lower limit, the light scattering effect may not be sufficiently obtained. The “diameter” means an intermediate value between the maximum width of the outer shape and the width of the outer shape in the direction orthogonal to the maximum width direction. Furthermore, the “average diameter” refers to the average value of the diameters of the plurality of recesses.

  The shape of the concave portion is not particularly limited, but may be a hemispherical shape, a conical shape, a cylindrical shape, a polygonal pyramid shape, a polygonal columnar shape, a hoof shape, or the like. Especially, it is preferable that the said recessed part is formed as a hemispherical recessed part. By making the said recessed part into a hemispherical recessed part, a moldability is improved and a light beam can be diffused efficiently.

(reflector)
The reflection plate 13 reflects the light beam emitted from the back surface side of the light guide film 12 from the front surface side. The reflector 13 can be made by depositing a metal such as aluminum or silver on the surface of a white sheet in which a filler is dispersed in a base resin such as a polyester resin or a film formed from a polyester resin or the like. Examples thereof include a mirror surface sheet with improved reflectivity.

(Top board)
The top plate 14 is formed from a metal or resin plate. As this metal top plate 14, for example, an aluminum plate can be used. Here, the thickness of the plate material is preferably 500 μm or more and 1200 μm or less, and more preferably 700 μm or more and 900 μm or less. The top plate 14 is formed with the periphery of the plate material curved toward the surface side, and the curved portion functions as a rib and has sufficient strength as the top plate 14. In addition, although parts (center part) other than the curved part of this rib are made into the flat surface, patterns, such as a geometric pattern, can also be embossed.

(light source)
The light source 15 is incorporated in the liquid crystal display casing 5 and is disposed so that the irradiation surface faces (or abuts) the end surface of the light guide film 12. Various light sources 15 can be used. For example, a light emitting diode (LED) can be used. Specifically, a light source 15 in which a plurality of light emitting diodes are arranged along the end face of the light guide film 12 can be used.

  In the backlight unit 11, the one-side edge light system in which the light source 15 is disposed on the side of only one side edge of the light guide film 12, or the light source 15 is disposed on the side of the opposite side edge of the light guide film 12. It is possible to employ a double-sided edge light system or the like that is disposed respectively.

<Method for producing light guide film>
Next, a method for manufacturing the light guide film 12 will be described.

  The method for manufacturing the light guide film 12 includes a step of forming the sheet body 16 (STEP 1) and a step of forming the diffusion pattern 17 on the sheet body 16 (STEP 2). Although STEP 1 and STEP 2 can be performed in separate steps, in this embodiment, the extrusion sheet forming method is adopted in STEP 1, and in STEP 2, the pressing roll is a roll-like shape to which the diffusion pattern is transferred. By using the inversion type, STEP1 and STEP2 are performed simultaneously.

  STEP1 is implemented using the extrusion molding apparatus 21 of FIG. The extrusion molding device 21 includes an extruder and a T-die 22, a pair of pressing rolls 23, a winding device (not shown), and the like. As the T die 22, for example, a well-known one such as a fish tail die, a manifold die, a coat hanger die, or the like can be used. The pair of pressing rolls 23 are disposed adjacent and in parallel. The extruder and the T-die 22 are configured to be able to extrude molten resin into a sheet shape at the nip between a pair of pressing rolls 23. The pair of pressing rolls 23 is provided with a temperature control means, and is configured to be able to control the surface temperature to a temperature optimum for extrusion molding. As the pressing roll 23, it is preferable to use a metal elastic roll comprising a metal roll and a flexible roll whose surface is covered with an elastic body.

  The pair of pressing rolls 23 includes a pressing roll 23a and a pressing roll 23b. Among these, the press roll 23a is formed as an inverted type in which the diffusion pattern is transferred to the surface.

  STEP 1 is performed by an extrusion sheet forming method in which the forming material of the molten sheet body 16 is supplied to the T die 22, the forming material is extruded from the extruder and the T die 22, and then pressed by a pair of pressing rolls 23. . The melting temperature of the forming material of the sheet body 16 extruded from the T die 22 is appropriately selected in consideration of the melting point of the resin used. The average thickness of the sheet body 16 formed in STEP 1 is 600 μm or less, and the retardation (Re) is 50 nm or less. This is adjusted by adjusting the interval between the pair of pressing rolls 23 and the rotational speed.

  STEP2 is performed by transferring the diffusion pattern transferred to the surface of the pressing roll 23a before the forming material of the molten sheet body 16 is cured. In STEP 2, the material for forming the molten sheet main body 16 is pressed by the pair of pressing rolls 23, whereby the diffusion pattern transferred to the surface of the pressing roll 23 a is transferred to the back surface of the sheet main body 16. In STEP 2, a plurality of recesses are formed on the back surface of the sheet body 16 by this transfer.

<Advantages>
Since the light guide film 12 has a retardation value (Re) of the sheet body 16 of 50 nm or less, the optical characteristics of the light emitted from the sheet body 16 are less likely to change, and the brightness of the light emitted from the sheet body 16 and The uniformity is less likely to deteriorate. Further, since the average residual stress of the sheet main body 16 is 8 × 10 ⁵ Pa or less, the sheet main body 16 is less likely to be distorted due to a change with time, and the surface of the distorted sheet main body 16 is less likely to be curved. There is little possibility that the luminance and uniformity of the emitted light beam will be lowered. Further, since the retardation value (Re) is less likely to be increased due to the curvature of the surface of the sheet main body 16, the optical characteristics of the light emitted from the sheet main body 16 are less likely to change, and the luminance of the light emitted from the light guide film is small. In addition, it is difficult for the uniformity to be reduced.

  The light guide film 12 can be easily formed by being formed by an extrusion sheet forming method.

  Furthermore, since the light guide film 12 has the diffusion pattern 17 on the back surface, the light can be efficiently scattered by the diffusion pattern 17 and emitted from the front surface side.

  Further, since the backlight unit 11 includes the light guide film 12, the thickness can be reduced. Further, the backlight unit 11 is less likely to cause luminance unevenness because a decrease in luminance and uniformity of light emitted from the light guide film 12 is suppressed.

  In addition, since the portable computer 1 includes the backlight unit 11, the thickness of the portable computer 1 can be reduced and luminance unevenness of the display screen hardly occurs.

[Second Embodiment]
<Backlight unit>
The backlight unit 31 of FIG. 4 includes a light guide film 32, the reflector 13 laminated on the back surface of the light guide film 32, and the light source 15 that irradiates the light guide film 32 with light. The light source 15 is disposed on the end face side substantially orthogonal to the ridge line direction in the fine modulation structure of the light guide film 32 described later.

<Light guide film>
The light guide film 32 is used as a light guide film of an edge light type ultra-thin liquid crystal backlight unit in a liquid crystal display part of a laptop computer having a casing thickness of 21 mm or less.

  The light guide film 32 emits light incident from the end face substantially uniformly from the surface side. The light guide film 32 has a sheet body 36.

The surface of the sheet body 36 has a wavy fine modulation structure. Further, the direction of the ridge line 38 in the wavy fine modulation structure and the end face on which the light beam is incident are substantially orthogonal. As a result, when the light rays propagating in the light guide film 32 are reflected on the surface, the traveling direction of some of the light rays approaches the ridge line 38 side. improves. In addition to this, the light beam emitted from the surface is slightly diffused in the direction perpendicular to the ridge line due to refraction by the wavy fine structure, so that the diffusibility of the emitted light beam is improved. Thereby, the fall of the brightness | luminance of the light ray radiate | emitted from the surface, and its uniformity can be suppressed more.

  Although it does not specifically limit as the ridgeline space | interval p in the said fine modulation structure, 1 mm or more and 500 mm or less are preferable. The upper limit of the ridge line interval p is more preferably 100 mm, and further preferably 60 mm. On the other hand, the lower limit of the ridge line interval p is more preferably 10 mm, and even more preferably 20 mm. When the ridge line interval p is out of the above range, the light beam propagating through the light guide film 12 is not easily condensed on the ridge line direction side. In addition, although it is preferable that all the ridge line intervals p in the fine modulation structure are within the above range, some of the plurality of ridge line intervals p in the fine modulation structure may be outside the above range. Of the plurality of ridge line intervals, 50% or more, preferably 70% ridge line intervals may be within the above range.

In addition, the average height h of the ridge line 38 based on the approximate virtual plane through which the plurality of valley lines 39 in the modulation structure passes is not particularly limited, but is preferably 5 μm or more and 40 μm or less. The upper limit of the average height h is more preferably 20 μm and even more preferably 15 μm. On the other hand, the lower limit of the average height h is more preferably 7 μm and even more preferably 9 μm. When the average height h is out of the above range, the light beam propagating through the light guide film 12 is not easily collected on the ridge line side.

  In addition, as a manufacturing method of the light guide film which the surface has the said fine modulation structure, although it is possible to manufacture by the method similar to the manufacturing method of the light guide film 12 of FIG. 2, in this case, a pair of press By adjusting the arrangement interval and rotation speed of the rolls 23, the wavy fine modulation structure can be formed. Further, by using a T die whose cross-sectional shape is an inverted shape of the vertical cross-sectional shape with respect to the ridge line of the fine modulation structure, a light guide film having a fine modulation structure with a wavy surface can be formed.

  The main components, additives, and the like of the sheet main body 36 are the same as those of the sheet main body 16 of the light guide film 12 in FIG.

  A diffusion pattern 37 is formed on the back surface of the sheet body 36. The diffusion pattern 37 is composed of a plurality of light scattering portions that are colored by laser irradiation. Specifically, the light scattering portion is formed by allowing the color former to be contained in the forming material of the sheet main body 36, and irradiating the laser after forming the sheet main body 36 to develop the color.

  The color former dispersed and contained in the forming material of the sheet main body 36 is a pigment whose color is changed by laser irradiation. As this color former, a well-known organic substance or inorganic substance used as a laser marking agent can be used. Specifically, for example, yellow iron oxide, inorganic lead compound, manganese violet, cobalt violet, mercury, cobalt, copper, bismuth, nickel and other metal compounds, pearlescent pigments, silicon compounds, mica, kaolins, silica sand, A diatomaceous earth, a talc, etc. can be mentioned, Among these, 1 type (s) or 2 or more types can be used. However, in the present embodiment, the diffusion pattern 37 is formed as a reflection pattern that reflects light rays, and therefore preferably has a color that reflects light rays. Therefore, in the light guide film 32, it is preferable to use a color former that develops white color by laser irradiation, and on the contrary, a color former that is carbonized by laser irradiation and changes to black that absorbs light is inappropriate. Examples of such a color former that develops white color include titanium black, cordierite, and mica.

  As the cordierite, in addition to the inorganic compound represented by the composition formula MG2Al3 (AlSi5O18), one in which a part of Mg is substituted with Fe can be used. Moreover, you may use the thing containing a water | moisture content.

  As the mica, natural mica such as mascobite, phlogopite, biotite and sericite, and synthetic mica such as fluorine phlogopite and tetrasilica mica can be used.

  The content of the color former in the sheet main body 36 is preferably 0.0001% by mass to 2.5% by mass, and more preferably 0.1% by mass to 1% by mass. When the content of the color former is less than the above lower limit, a sufficient color development effect cannot be obtained at the time of laser irradiation, and a desired reflection pattern may not be formed. On the contrary, when the content of the color former exceeds the above upper limit, the transparency and mechanical strength of the sheet main body 36 may be lowered.

  The laser for irradiating the sheet body 36 is not particularly limited, and examples thereof include a carbon dioxide laser, a carbon monoxide laser, a semiconductor laser, and a YAG (yttrium, aluminum, garnet) laser. In particular, a carbon dioxide laser having a wavelength of 9.3 μm to 10.6 μm is suitable for forming a fine diffusion pattern. As the carbon dioxide laser, a lateral atmospheric pressure excitation (TEA) type, a continuous oscillation type, a pulse oscillation type, or the like can be used.

  The shape of the light scattering portion is not particularly limited, but may be hemispherical, conical, cylindrical, polygonal pyramid, polygonal column, hoof, or the like. Especially, as a shape of the said light-scattering part, a hemisphere is preferable. By making the said light-scattering part hemispherical, while improving a moldability, it can prevent that an edge comes out. The arrangement pattern of the diffusion pattern 37 is the same as that of the diffusion pattern 17 in FIG. Further, the average diameter of the light scattering portion is the same as the concave portion of the diffusion pattern 17 in FIG.

  The light guide film 32 can easily and reliably form a desired diffusion pattern 37 by laser irradiation. Moreover, when forming the diffusion pattern 37 by such a method, since it is not necessary to provide a convex part etc. in the back surface of the said light guide film 32, thickness reduction can be accelerated | stimulated.

  In addition, since the light guide film 32 has the diffusion pattern 37 formed by laser irradiation, the diffusion pattern does not need to be transferred to the surface of the pressing roll even when the light guide film 32 is formed by a melt extrusion molding method. .

[Other Embodiments]
In addition, the light guide film for ultra-thin liquid crystal backlights, the ultra-thin liquid crystal backlight unit, and the portable computer of the present invention can be implemented in various modified and improved modes in addition to the above modes.

  In the said embodiment, although the said light guide film demonstrated the structure where the surface of a sheet | seat main body has a wavy fine modulation structure, it can be set as the structure where the surface and back surface of a sheet | seat main body have a wavy fine modulation structure. . By having the wavy fine modulation structure on the front and back surfaces of the sheet main body, it is possible to further suppress a decrease in luminance and uniformity of light emitted from the light guide film.

Further, in the above embodiment, the configuration in which the ridge line direction in the wavy fine modulation structure on the surface of the sheet main body and the end surface on which the light beam is incident is substantially orthogonal, the ridge line direction and the light beam in the wavy fine modulation structure are You may arrange | position a sheet | seat main body so that the incident end surface may be located substantially in parallel. As a result, the ridgeline direction of the fine modulation structure is positioned substantially perpendicular to the traveling direction of the light beam propagating through the light guide film, so that the incident angle of the light beam on the surface varies due to the wavy fine modulation structure. Due to this, the outgoing property from the surface of the light guide film is improved. Thereby, the fall of the brightness | luminance of the light ray radiate | emitted from the surface, and its uniformity can be suppressed more.

  Further, the diffusion pattern may be formed as a convex portion by a printing method. In this case, when a sheet body is formed by the above-described extrusion sheet forming method, a pair of pressing rolls having no diffusion pattern transferred to the surface is used. As a printing method for forming the convex shape, it can be performed by an ink jet printing method or a screen printing method using a white or transparent ink. By forming the diffusion pattern on the concave portion by a printing method, the diffusion pattern can be easily and reliably formed.

  The ultra-thin liquid crystal backlight unit in which the light guide film is disposed can use a top plate as a reflecting plate. By forming the surface of the top plate as a reflection surface, the light beam emitted from the back surface side of the light guide film can be reflected on the surface side by this reflection surface.

  Further, in the above embodiment, the sheet body forming step (STEP 1) and the diffusion pattern forming step (STEP 2) are described simultaneously. However, as described above, STEP 1 and STEP 2 can be performed in separate steps. Specifically, it is possible to wind the sheet body formed in STEP 1 in a roll shape, and then pull out the sheet body from the roll state to perform STEP 2.

  Moreover, you may perform the process of annealing treatment after STEP2 like the said embodiment. This annealing process is not particularly limited, and a known method can be adopted. For example, a heating method including a heating roll, an infrared heater, hot air, and the like can be employed. Among these methods, it is preferable to perform an annealing treatment with a heating roll. By setting the heating roll to a high temperature, the temperature of the surface of the sheet main body can be increased at a stretch, and the shrinkage rate of the sheet main body can be suppressed.

  As described above, the light guide film for an ultra-thin liquid crystal backlight according to the present invention suppresses a decrease in luminance and its uniformity, and as a result of achieving a reduction in thickness, the luminance unevenness of the liquid crystal display surface of the portable computer is reduced. Since it is difficult to occur and thinned, it can be suitably used for, for example, a so-called ultra-thin computer called ultrabook, a mobile information terminal such as a smartphone, and a portable information terminal such as a tablet terminal.

DESCRIPTION OF SYMBOLS 1 Portable computer, ultrathin computer 2 Operation part 3 Liquid crystal display part 4 Liquid crystal panel 5 Liquid crystal display part casing 6 Surface support member 7 Hinge part 8 Operation part casing 11 Ultrathin liquid crystal backlight unit, backlight unit 12 Light guide film 13 Reflecting plate 14 Top plate 15 Light source 16 Sheet main body 17 Diffusion pattern 21 Extrusion device 22 T-die 23 Press roll 23a Press roll 23b Press roll 31 Backlight unit 32 Light guide film 36 Sheet main body 37 Diffusion pattern 38 Ridge line 39 Valley line

Claims (8)

A light guide film for an ultra-thin liquid crystal backlight having an average thickness of 600 μm or less that emits light incident from the end face substantially uniformly from the surface,
Retardation value (Re) is 50 nm or less,
The difference between the maximum value and the minimum value of the residual stress calculated by retardation (Re) / (photoelastic coefficient (10 ¹² / Pa) × thickness) is 1 × 10 ⁵ Pa or less,
The average residual stress is 8 × 10 ⁵ Pa or less,
The front surface or the front surface and the back surface have a wavy fine modulation structure, the interval between the ridge lines in this fine modulation structure is 1 mm or more and 500 mm or less, and the ridge line with reference to the approximate virtual plane through which a plurality of valley lines in this fine modulation structure passes A light guide film having an average height of 5 μm to 40 μm.   The light guide film according to claim 1, wherein the main component is a polycarbonate resin. The light guide film according to claim 1 or 2, wherein the surface has a static friction coefficient of 0.5 or less. The light guide film according to any one of claims 1 to 3 , wherein the back surface has a diffusion pattern. The light guide film according to claim 4 , wherein the diffusion pattern includes a plurality of hemispherical concave portions. The light guide film according to claim 4 , wherein the diffusion pattern includes a plurality of color formers that develop color by laser irradiation. reflector,
An ultra-thin liquid crystal backlight comprising: the light guide film according to any one of claims 1 to 6 ; and a light source that irradiates light to an end surface of the light guide film. unit. A portable computer comprising the ultra-thin liquid crystal backlight unit according to claim 7 in a liquid crystal display unit.

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