JP6209428B2 - Optical sheet with lens and surface light source member - Google Patents

Description

  The present invention relates to an optical sheet with a lens made of a transparent thermoplastic resin composite extruded sheet, and a surface light source member made of the optical sheet.

As a surface light source member of a liquid crystal display device, an optical sheet made of a transparent resin is widely used under the name of a light guide plate. On the other hand, with the recent progress of colorization, enlargement, thinning, and high-definition images, improvement in light utilization efficiency of light sources used in liquid crystal display devices is required. To meet this demand, a lens-shaped light guide plate with a lens shape formed on the surface of the light guide plate has higher light utilization efficiency of the light source than a conventional light guide plate with a flat surface, and the brightness (brightness) is greatly increased. Since it improves, it is used for prizes.
As a method for producing this lens-shaped light guide plate, a transparent resin is heated using an extruder, extruded in a flat plate form continuously from a T-die in a molten state, and formed on the outer circumferential surface of the roll in the immediately subsequent transfer roll process. An extrusion manufacturing method in which a lens shape is transferred to the surface of a transparent resin sheet using a lens mold is well known. In order to further increase the luminance, it is desired to improve the transfer ratio (h / d), which is the ratio of the height h of the lens transferred to the transparent resin sheet to the depth d of the lens mold.
In order to use the optical sheet as a surface light source member of a liquid crystal display device, light from a light source is incident from a side surface, and an emission surface that emits planar light in a direction intersecting the side surface is opposed to the emission surface. It is common to use a so-called edge light type surface light source member in which printed dots that reflect light incident from the side surface to the exit surface side are formed on the back surface.
The printed dots also have a great influence on the brightness, and there is a strong demand for further improvement.

Japanese Patent Laid-Open No. 6-18707 Japanese Patent Laid-Open No. 9-11328 JP 2005-249882 A

The problem to be solved by the present invention is an optical sheet suitable for an edge light type surface light source of a liquid crystal display device, capable of efficiently guiding light from the light source to the light emitting surface side and increasing the luminance, and from the optical sheet. It is providing the surface light source member which becomes.
More specifically, the problem to be solved by the present invention is that a lens transferred to a transparent resin sheet with respect to the depth d of the lens mold formed on the transfer roll when manufacturing an optical sheet with a lens by an extrusion method. An optical sheet with a lens with an improved transfer ratio (h / d), which is a ratio of height h, and an optical sheet with better performance in combination with a PS resin having higher transparency than the conventional one, and A surface light source member is provided. The problem to be solved by the present invention is an edge light system in which the performance of printing dots for reflecting light to the exit surface side is improved as compared with the conventional one when an edge light type surface light source member is formed from the optical sheet with lens. It is also providing the surface light source member of this.

  As a result of intensive studies and experiments conducted to solve the above problems, the present inventors have found that the above problems can be solved by the following configuration, and have completed the present invention. That is, the present invention is as follows.

[1] a core layer comprising a transparent thermoplastic resin, and disposed on both sides of the core layer, the release agent 0.03 weight% content selected from the group consisting of higher aliphatic alcohols及beauty and high-class fatty acid transparent thermoplastic formed from a resin with a lensed optical sheet made of a transparent thermoplastic resin composite extrusion sheet have a table layer, a release agent selected from the group consisting of higher fatty alcohols and higher fatty acids of the core layer Content of 0 . The optical sheet is less than 03% by mass.

  [2] The optical sheet according to [1], wherein the surface layer has a thickness of 5 to 200 μm.

  [3] The optical sheet according to [2], wherein the transparent thermoplastic resin of the core layer and the surface layer is polystyrene.

で表されるトリマー成分（1a-フェニル-4e-(1'-フェニルエチル)テトラリン）が3000μｇ/ｇ以下である、前記［３］に記載の光学シート。 [4] The total amount of dimer and trimer contained in the polystyrene of the core layer and the surface layer is 5000 μg / g or less, and the following general formula (1):

The optical sheet according to [3], wherein the trimer component (1a-phenyl-4e- (1′-phenylethyl) tetralin) represented by the formula is 3000 μg / g or less.

[5] The optical sheet according to [4], wherein the concentration of 4-t-butylcatechol (TBC) contained in the core layer and the surface layer polystyrene is 6 μg / g or less.

  [6] 0.02-0.2 parts by mass of a phosphorus-based antioxidant and / or 0.02-0.2 parts by mass of a phenol-based antioxidant are added to the polystyrene of the core layer and the surface layer. The optical sheet according to [5].

  [7] A side surface on which light from a light source is incident, an exit surface that is formed in a direction intersecting with the side surface, emits planar light, a back surface facing the exit surface, and light incident from the side surface The surface light source member which consists of an optical sheet in any one of said [1]-[6] in which the printing dot reflected to the said output surface side was formed in the said back surface.

  [8] The surface light source member according to [7], wherein the printing dots are formed by inkjet printing.

The optical sheet according to the present invention is suitable as an edge light type surface light source member of a liquid crystal display device because light from a light source can be efficiently guided to the light emitting surface side to increase luminance.
The optical sheet according to the present invention has a lens height h transferred to the transparent resin sheet with respect to the depth d of the lens mold formed on the transfer roll when the optical sheet with a lens is manufactured by an extrusion method. This is an optical sheet with a lens that has an improved transfer ratio (h / d), and the performance is further improved in combination with a PS resin having a higher transparency than the conventional one. In addition, when the edge light type surface light source member is used, the performance of the printed dots for reflecting the light toward the light exit surface is improved as compared with the conventional one.

It is sectional drawing of the light-guide plate which concerns on this invention. It is a schematic diagram of the sheet forming machine used for this invention. It is the schematic which shows the brightness | luminance and chromaticity measurement spot position at the time of light-guide plate evaluation, and LED arrangement | positioning.

Hereinafter, embodiments of the present invention will be described in detail.
A transparent thermoplastic resin is heated in an extruder and continuously extruded from a T-die in a molten state into a flat plate shape. Immediately after that, it is sandwiched between a transfer roll having a lens transfer mold formed on the outer peripheral surface and a glazing roll. The method of transferring the lens shape onto the surface of the sheet while cooling is generally used as a rational means that enables easy continuous production of optical sheets.
As a typical example of the lens shape, because the roll processing is easy, the cross section perpendicular to the extrusion direction of the optical sheet is semicircular, the isosceles triangle, and the top of the isosceles triangle are continuously formed. Of course, the present invention is not limited thereto.

When transferring the lens shape, the lens is transferred to a transfer roll in which a lens transfer mold is formed in a molten state exceeding the glass transition temperature (Tg) that maintains the fluidity of the transparent thermoplastic resin. There is a step of holding the lens shape of the sheet surface by cooling to Tg or less after the shape is transferred.
In order to improve the transfer ratio (h / d), which is the ratio of the height h of the lens transferred to the resin sheet to the depth d of the lens mold formed on the transfer roll, the temperature of the transfer roll can be increased. It is obvious that it is advantageous that the transparent thermoplastic resin has sufficient fluidity by making it as high as possible, but the higher the temperature of the transfer roll, the more difficult it is to peel off the resin sheet from the roll surface. Stripping patterns appear intermittently on the surface, and the quality as an optical sheet cannot be maintained.
Further, when the temperature exceeds the allowable temperature, the resin sheet is wound around the transfer roll without being peeled off, and the continuous production is forced to be interrupted, and a great deal of labor is required for repairing the transfer roll, resulting in a great trouble.
Therefore, although the transfer ratio is unsatisfactory in order to obtain a good optical sheet having a lens formed on the surface, there are situations in which the transfer roll temperature must be lowered to make it easy to peel off.

On the other hand, the use of a release agent can be mentioned as a measure to improve the peeling from the transfer roll, but in the case of an optical sheet used for an edge light in particular, the influence of impurities is caused by designing a long optical path. The optical performance is conspicuous, the transparency of the mold release agent is inhibited, that is, the optical sheet such as turbidity and yellowness is fatally deteriorated, and its use is greatly restricted.
According to the present invention, it is possible to obtain an optical sheet having both the transfer ratio and the excellent performance of transparency. That is, using a co-extrusion equipment equipped with a main extruder and a sub-extruder, a core layer is extruded from the main extruder, and a surface layer containing a release agent having a relatively thin thickness compared to the core layer from the sub-extruder. By extruding into a composite sheet, it is possible to obtain an optical sheet with a lens having a good transfer ratio and satisfying transparency.

  The co-extrusion equipment consists of a gear pump, T-die, lens transfer roll, glazing roll, take-up roll, etc., in addition to the main and sub-extruders. A feed block is installed between the extruder and the T-die. A multi-manifold system in which a composite sheet is used and a composite sheet directly in a T-die is well known. As the lens transfer roll, the glazing roll, and the take-up roll, a metal roll made of a metal such as stainless steel or steel can be used. Further, the surface may be subjected to plating treatment such as chromium plating, nickel plating, nickel-phosphorous plating, copper plating, and the like.

  As the transparent thermoplastic resin used in the present invention, PS (polystyrene) resin, PMMA (polymethyl methacrylate) resin, MS (copolymer of methyl methacrylate and styrene) resin, PC (polycarbonate) Based resins and the like. Specific examples of PS resins include, in addition to polystyrene, one or two or more selected from α-methylstyrene, p-methylstyrene, acrylic acid, methacrylic acid, etc., which are mainly composed of styrene and copolymerizable with styrene. These copolymers are also included. Examples of the PMMA-based resin include a polymer of methyl methacrylate, and one or more copolymers selected from methyl acrylate, ethyl acrylate, butyl acrylate, etc. with methyl methacrylate as a main component.

  As the MS-based resin, a copolymer composed of an approximately equal proportion of methyl methacrylate and styrene is generally used, but depending on the purpose, a proportion biased to either component can also be selected. The PC resin is generally a polymer derived from a dihydric phenol compound typified by bisphenol A. Among these, PS-based resins have low water absorption compared to other transparent thermoplastic resins, and therefore, when used as an optical sheet, it is difficult to cause warping, twisting, etc. due to dimensional changes due to water absorption or dehydration. Advantageously, the margin of the optical sheet support frame of the surface light source can be reduced by the expected size change due to water absorption or dehydration.

Deformation such as warpage of the optical sheet causes uneven brightness unevenness as a surface light source due to the inconsistency of the positional relationship with the light source at the edge, and further presses the liquid crystal surface and optical such as an optical film constituting the surface light source Luminance changes due to contact with the member cause a major obstacle. Moreover, since PS resin has a small specific gravity as compared with other transparent thermoplastic resins, the weight can be reduced.
With the recent increase in size of liquid crystal display devices, it is easier to be affected by dimensional changes due to moisture, and the trend toward reducing the thickness of the optical sheet to reduce weight makes it possible to reduce warpage and the like. PS-based resins are attracting attention. Furthermore, compared to an optical sheet with a flat surface, an optical sheet having a lens shape on the surface is more likely to warp due to absorption and dehydration due to the difference in surface area between the front and back surfaces, but has a low water absorption property. A PS-based resin having is more preferable.

  Among PS resins, polystyrene, which is a styrene homopolymer, is more preferable because of its high transparency and low YI. The total amount of dimer and trimer contained in the polystyrene is 5000 μg / g or less, and the trimer component (1a- (Phenyl-4e- (1′-phenylethyl) tetralin) is 3000 μg / g or less, and the concentration of TBC, which is also contained in the core layer itself and exhibits a yellow color, is regulated to 6 μg / g or less. The addition of 0.02 to 0.2 parts by mass of a system antioxidant and 0.02 to 0.2 parts by mass of a phenolic antioxidant has a low degree of yellowing phenomenon during extrusion and lowers YI. Is more preferable.

  If the total amount of dimer and trimer contained in the polystyrene exceeds 5000 μg / g, or if the content of trimer component (1a-phenyl-4e- (1′-phenylethyl) tetralin) exceeds 3000 μg / g, the resin When the light transmittance in the molded body decreases and the optical path length becomes longer as in the light guide plate, the difference becomes significant. When the concentration of TBC remaining in the polystyrene is 6 μg / g or less and the phosphoric antioxidant is 0.02 to 0.2 parts by mass, the decrease in light transmittance is suppressed due to deterioration during heating such as molding. it can. Moreover, light transmittance can be maintained over a long period as it is 0.02-0.2 mass part of phenolic antioxidant.

The following stabilizers are used for these transparent thermoplastic resins.
Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α′dimethylbenzyl) phenyl] benzotriazole, 2- ( Benzotriazoles such as 3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4 Benzophenone series such as -n-octoxybenzophenone, phenyl salicylate, and salicylic acid series such as 4-t-butylphenyl salicylate. One or more ultraviolet absorbers selected from these are usually 50 to 1000 μg / It can be added at a concentration of g.

  It is also possible to add antioxidants such as phenols, thioethers, and phosphites. In the present invention, it is important to select the type and amount of the release agent, and the release agent is blended on the surface layer side and is less than 0.03% by mass which is not substantially contained in the core layer. It is characterized by that. Types of mold release agents include higher fatty alcohols such as stearyl alcohol, higher fatty acids such as stearic acid and palmitic acid, higher fatty acid amides represented by ethylenebisstearylamide, higher fatty acid metals such as magnesium stearate and calcium stearate. Examples include salts, higher fatty acid esters such as stearyl stearate and stearic acid monoglyceride, and silicone oils such as polydimethylsiloxane.

Among these, higher aliphatic alcohols and higher fatty acids, which are less likely to decrease the transmittance at a relatively short wavelength (420 to 500 nm) in the visible light wavelength range in extrusion molding, are preferable because both increase in yellowness is small. Higher aliphatic alcohols having an excellent balance between the internal release effect and chemical stability are more preferred.
Higher fatty acid amides and higher fatty acid metal salts which are usually available as additives have high yellowness, and higher fatty acid esters are similarly not recommended because of their higher yellowness. Silicone oils are also not recommended because they may cause ink repellency during printing or may reduce ink adhesion. The addition amount of the release agent is preferably 0.03 to 1% by mass, and more preferably 0.1 to 0.5% by mass.
If the amount is less than 0.03% by mass, it is difficult to obtain a desired release effect. If the amount exceeds 1% by mass, roll contamination is likely to occur during the operation of the extruder, and defects such as fogging occur in the manufactured optical sheet. Not recommended because of

  The thickness of the surface layer is preferably 5 to 200 μm, more preferably 10 to 150 μm, and still more preferably 20 to 100 μm. There is a limit to making the thickness distribution in the surface layer width direction uniform by extrusion molding, and it is not recommended to provide a surface layer of less than 5 μm because there may be a portion where there is no surface layer. The surface layer to which the release agent is added has a higher yellowness than the core layer that does not substantially contain the release agent, and if the surface layer exceeds 200 μm, the yellowness of the optical sheet with a lens becomes higher due to the influence. .

The liquid crystal display device includes a surface light source device because the liquid crystal material does not self-emit light.
As the surface light source device, an edge light system is often used, and a light guide plate that emits light from the light source to the liquid crystal display panel side, an LED (light emitting diode), a CCFL (cold cathode tube), etc. disposed on the side surface thereof It consists of other light sources. The light guide plate generally includes a transparent substrate and a light emitting mechanism, and repeatedly reflects light from the light source incident from the side surface inside the light guide plate to guide the light into the light guide plate, and a light scattering pattern as a light emitting mechanism provided on the light guide plate. The light is emitted to the liquid crystal display panel side. As the light scattering pattern provided on the light guide plate, a diffusion gradation pattern by ink dot printing or an uneven pattern such as a texture (rough surface) formed on the light guide plate is used.

  In response to a decrease in the light transmittance of the liquid crystal display cell due to high definition of the display, a light guide plate in which a lens row or a prism row is formed on the light exit surface is used to increase the light use efficiency of the light guide plate. Yes. Further, a light guide plate is also used in which a lens array or a prism array in which a concave / convex pattern such as a texture (rough surface) is formed on the opposite surface of the light emitting surface to further improve the light utilization efficiency.

In the light guide plate of the present invention, in order to make the distribution of the emitted light uniform, a light scattering pattern having gradation is formed in a direction in which the light source moves away from the side surface portion where the light source is arranged.
As the light scattering pattern, for example, a dot or uneven shape is a gradation pattern that gradually increases in area as it moves away from the position of the light source, or a dot or uneven shape of the same size as the distance from the light source increases. One example is a gradation pattern with a narrow pitch.

  As a specific method of forming a light-scattering pattern having gradation on the optical sheet with a lens of the present invention, there is a method of directly imparting a shape to the light guide plate by hot pressing, laser processing, etc., but the liquid crystal size and the type of light source Because it is necessary to make the pattern suitable for each change of the arrangement, etc., the light scattering pattern with gradation is changed and the light guide plate is directly given shape each time so that the brightness is uniform in the surface direction It takes a lot of time and money to optimize while iterating until it is confirmed.

  A method of applying dots of a light scattering pattern having gradation by a commonly used printing method such as silk printing is excellent in application to the optical sheet of the present invention, and in particular, a large liquid crystal size, for example, 20 inches When applying to larger sizes, the time and cost required to optimize the pattern by repeating the test will be significantly greater than the method of applying the shape directly to the light guide plate by hot pressing or laser processing. Can be reduced.

Furthermore, the method of applying dots of light scattering pattern having gradation by inkjet printing is more excellent for application to the optical sheet of the present invention, by forming hemispherical dots having a mirror surface with a high lens effect, The brightness can be further improved.
Further, by making the dots fine, it is possible to reduce the appearance of the dot shape on the exit surface side, which is advantageous for reducing the thickness of the light guide plate. In order to eliminate uneven brightness in the surface direction, that is, so-called uneven brightness, an ink liquid is obtained from a plurality of adjusting means such as the height of the ink jet nozzle, the amount of ink ejected, the number of ink drops, and the ink viscosity. The gradation pattern can be adjusted with a high degree of freedom by selecting the droplet size, the area density of the number of printed dots, and the like, and luminance unevenness can be eliminated within a short time compared to the conventional method.

  The main component of ink used for inkjet is usually cured by ultraviolet rays to become a transparent resin, but if a colorant is added in advance, the color of emitted light can be changed. By providing a primer layer in advance on the optical sheet, it is recommended that ink repellency can be prevented and the dot shape can be controlled from the correlation between the primer layer and the surface tension of the ink. The brightness can be improved by bringing the refractive index of the primer layer and dots close to that of the transparent thermoplastic resin. It is also possible to improve the yellowness of the optical sheet by adding a blue dye, such as an anthraquinone compound, to the primer layer.

Hereinafter, the present invention will be specifically described based on examples and comparative examples.
In addition, the evaluation used by each Example and the comparative example and the test method were as follows.

(1) Method for measuring 4-t-butylcatechol (TBC) concentration 1 g of a composition (pellet, molded product, etc.) was dissolved in 20 ml of chloroform, and then BSTFA (N, O-bis (trimethylsilyl) trifluoroacetamide) was used. Then, the trimethylsilyl derivatization treatment was performed, and the supernatant liquid separated by centrifugation was measured by gas chromatography mass spectrometry (GC / MS). A calibration curve prepared in advance was used to determine the concentration.
GC / MS measurement conditions:
GC device: Agilent 6890
Column: DB-1 (0.25 mm id x 30 m)
Liquid phase thickness 0.25mm
Column temperature: 40 ° C. (5 min hold) → (20 ° C./min temperature increase) →
320 ° C (6 min hold) 25 min total
Inlet temperature: 320 ° C
Injection method: Split method (split ratio 1: 5)
Sample volume: 2 μl
MS equipment: Agilent MSD5973
Ion source temperature: 230 ° C
Interface temperature: 320 ° C
Ionization method: Electron ionization (EI) method Measurement method: SCAN method (scan range m / z 10 to 800)

(2) Method of measuring the concentration of stearic acid, stearyl alcohol, phosphorus antioxidant, phenolic antioxidant After 1 g of the composition (pellet, molded product, etc.) is sufficiently dissolved in 20 ml of methyl ethyl ketone, 5 ml of methanol is dropped. Stir for about 20 minutes. The supernatant liquid separated by centrifugation was measured by gas chromatography (GC). For determination of the concentration, a calibration curve prepared in advance for stearic acid, stearyl alcohol, and each antioxidant was used.
GC measurement conditions:
GC device: Shimadzu Corporation GC-2010
Column: DB-1 (0.25 mm id x 30 m)
Liquid phase thickness 0.10mm
Column temperature: 240 ° C. (1 min hold) →
(10 ° C / min temperature rise) →
320 ° C (5 min hold) 14 min total
Inlet temperature: 320 ° C
Injection method: Split method (split ratio 1: 5)
Sample volume: 1 μl

(3) Measurement of styrene dimer and trimer After 1 g of the composition (pellet, molded product, etc.) was sufficiently dissolved in 10 ml of methyl ethyl ketone, 3 ml of methanol was added dropwise and stirred for about 20 minutes. The supernatant liquid separated by centrifugation was measured by gas chromatography (GC). A calibration curve prepared in advance was used to determine the concentration.
GC measurement conditions:
GC device: Agilent 6850 series GC system
Column: Agilent 19091Z-413E
Inlet temperature: 250 ° C
Detector temperature: 280 ° C
The content of stearic acid, stearyl alcohol, TBC, phosphorus antioxidant, phenolic antioxidant and styrene dimer, trimer in the polymer is corrected by measuring the respective concentrations in the composition, Can be calculated.

(4) Measuring method of average light transmittance of optical path length 300mm It measured using Nippon Denshoku Industries Co., Ltd. long optical path spectral transmission color meter ASA-1. The optical sheet specimen to be used for the measurement has a square shape with a width of 50 mm and a length of 300 mm with the direction parallel to the shaping lens array as the long side, and the short side end face is preliminarily formed with Plabeauty PB-500 manufactured by Megaro Technica Co., Ltd. It finished in the mirror surface and evaluated by the length of 300 mm of an optical path.

(5) Appearance of optical sheet Visual observation of the obtained optical sheet revealed that there was no abnormality on the surface, ○, an abnormality of peeling pattern (gloss unevenness, intermittent stripe pattern, etc.) from the roll was observed. Things were evaluated as x.

(6) Measurement of luminance and chromaticity of light guide plate Measurement was performed using a two-dimensional color luminance meter CA-2000 manufactured by Konica Minolta.

(7) Manufacture of polystyrene-based resin composition a. Manufacture of PS-1 1,1-bis (t--) with respect to 100 parts by mass of a mixture of 85% by mass of styrene (TBC concentration 11 μg / g) and 15% by mass of ethylbenzene The polymerization liquid added with 0.05 part by weight of (butylperoxy) cyclohexane was continuously charged into a 5.4 liter fully mixed reactor at 0.70 liter / hr, and the temperature was adjusted to 101 ° C. The resulting solution was continuously charged into a 3.0 liter laminar flow reactor equipped with a stirrer and temperature controlled in 3 zones. The temperature of the laminar flow reactor was adjusted to 113 ° C / 121 ° C / 128 ° C. Thus, a polymer solution was obtained.
The obtained polymer solution is continuously supplied to a devolatilizing extruder with a two-stage vent, and unreacted monomers and solvents are recovered at an extruder temperature of 225 ° C., a one-stage vent and a two-stage vent with a degree of vacuum of 15 torr. After that, the phosphorus antioxidant (Tris phosphite (2,4-di-t-butylphenyl, trade name: ADK STAB 2112)), phenol antioxidant (3- (3,5- Di-t-butyl-4-hydroxyphenyl) stearyl propionate, trade name: Irganox 1076) with respect to 100 parts by mass of the polymer so that the concentration is 0.05 parts by mass and 0.05 parts by mass, respectively. The monomer polymerization rate was calculated as 68% from the mass yield, and the TBC concentration in the obtained polystyrene resin composition was 1.5 μg / g. The total amount of dimer and trimer is 1710μ g / g, of which Trimer I was 520 μg / g.

b. Production of PS-2 A polystyrene resin composition in the same manner as PS-1, except that stearyl alcohol was added to 100 parts by mass of the polymer so as to have a concentration of 0.5 parts by mass. Got. The TBC concentration in the obtained polystyrene-based resin composition was 1.5 μg / g, the total amount of dimer and trimer was 1710 μg / g, and the trimer I was 520 μg / g.

c. Production of PS-3 Polystyrene resin composition in the same manner as PS-1, except that stearic acid was added to 100 parts by mass of the polymer to a concentration of 0.5 part by mass. Got. The TBC concentration in the obtained polystyrene-based resin composition was 1.5 μg / g, the total amount of dimer and trimer was 1710 μg / g, and the trimer I was 520 μg / g.

d. Production of PS-4 A polystyrene resin composition was obtained in the same manner as PS-1, except that stearyl alcohol was added to 100 parts by mass of the polymer so as to have a concentration of 1.5 parts by mass. It was. The TBC concentration in the obtained polystyrene-based resin composition was 1.5 μg / g, the total amount of dimer and trimer was 1710 μg / g, and the trimer I was 520 μg / g.

e. Production of PS-5 Polystyrene-based resin composition in the same manner as PS-1, except that erucic acid amide was added to 100 parts by mass of the polymer to a concentration of 0.5 part by mass. Got. The TBC concentration in the obtained polystyrene-based resin composition was 1.5 μg / g, the total amount of dimer and trimer was 1710 μg / g, and the trimer I was 520 μg / g.

[Example 1]
Acrylic resin (made by Asahi Kasei Chemicals Corporation, trade name Delpet LP-1, PMMA-1) for the core layer, and acrylic resin (made by Asahi Kasei Chemicals Corporation, trade name Del Powder 70H) and stearyl alcohol 0.5 mass for the surface layer % Was mixed using a tumbler and then melted and kneaded at a resin temperature of 250 ° C. with a vented 30 mmφ twin screw extruder to prepare a material (PMMA-2).
A gear pump and a feed block are connected to the main extruder for the core layer (screw diameter 50 mmΦ, L / D = 32, single shaft) and the sub-extruder for the surface layer (screw diameter 32 mmΦ, L / D32, single shaft), Two-type three-layer sheet molding was performed by a co-extrusion method by a conventional method using a unit in which a T die, a polishing roll and a shaping roll were arranged, and a take-up roll. The shaping roll was formed with a semicircular lens mold having a depth of 100 μm and a pitch of 200 μm on the outer peripheral surface.
These glazing rolls and transfer rolls each had a diameter of 300 mm.
The resin temperature at the time of sheet extrusion is set to 260 ° C., and the resulting sheet is a composite sheet configuration in which the lens shape is transferred to one side of the core layer and the other side is formed with a flat surface layer. It adjusted with the extrusion amount balance of a sub extruder.
In FIG. 2, the roll temperature was adjusted to 85 ° C. for 10 (glazing roll), 95 ° C. for 11 (shaping roll), and 90 ° C. for 12 (take-off roll).

Adjust the gap between the T-die discharge port and the polishing roll, and the rotation speed of the polishing roll, shaping roll and take-up roll, and set the thickness of both surface layers to 50μm and the total thickness of the sheet to 2.5mm. The sheet extrusion speed was 0.8 m / min, and a coextruded sheet having a width of 240 mm was obtained.
When the height of the lens was measured by magnifying observation from the cross-sectional direction, it was 40 μm and the transfer ratio (h / d) was 0.40.
From the co-extruded sheet, a plate of 300 mm in the flow direction at the time of extrusion and 50 mm in a direction perpendicular to the flow is cut out, and the end surface on the short side is polished with a mirror finisher (Pura Beauty PB-500 manufactured by Megaro Technica). Used for evaluation of average light transmittance of a long optical path (optical path length: 300 mm).
The obtained coextruded sheet had a satisfactory appearance as an optical sheet having a good appearance and a high long light path average light transmittance. Further, a test piece having a long side of 240 mm and a short side of 160 mm was cut out from the coextruded sheet and processed into a light guide plate. That is, after polishing the end face of the long side that is the light incident surface using a mirror finisher similar to the above, the surface opposite to the surface that is formed with the lens that is the light exit surface is silkscreen printed as a light guide plate A gradation pattern that increases the diameter of the dots at a location away from the light incident surface was applied so as to reduce in-plane luminance unevenness. At this time, ultraviolet curable ink was used as the ink.
As a backlight module, a light guide plate was placed on a reflection sheet, and four optical sheets, a diffusion sheet, a prism sheet (horizontal groove), a prism sheet (vertical groove), and a diffusion sheet were placed thereon. As a light source, an LED array was arranged on the long side at the bottom of the screen as shown in FIG.
With the LED turned on, brightness and chromaticity at 25 points in the plane were measured using CA-2000. The obtained light guide plate had satisfactory performance as a light guide plate in terms of average luminance, average chromaticity, and color difference.

[Example 2]
A coextruded sheet was obtained in the same manner as in Example 1 except that polystyrene (PS-1) was used for the core layer and polystyrene (PS-2) was used for the surface layer.
However, the resin temperature at the time of sheet extrusion was set at 230 ° C., and the roll temperature was adjusted to 85 ° C., 11 at 90 ° C., and 12 at 90 ° C. in FIG.
The obtained sheet had a satisfactory appearance as an optical sheet having a good appearance and a high long optical path average light transmittance. Further, a test piece having a long side of 240 mm and a short side of 160 mm is cut out from the coextruded sheet, and the end surface of the long side which is a light incident surface is polished using a mirror finisher similar to the above, and then is a light exit surface. A gradation pattern that increases the dot diameter away from the light entrance surface so that the luminance unevenness in the surface as a light guide plate is reduced by silk screen printing on the surface facing the lens shaping surface. Granted. At this time, a heat drying type ink was used as the ink.
As in Example 1, the luminance and chromaticity were measured, and as a result, the average luminance, average chromaticity, and color difference were satisfactory for the light guide plate.

[Example 3]
A coextruded sheet was obtained in the same manner as in Example 2 except that polystyrene (PS-1) was used for the core layer and polystyrene (PS-3) was used for the surface layer.
The obtained sheet had a satisfactory appearance as an optical sheet having a good appearance and a high long optical path average light transmittance. Further, a test piece having a long side of 240 mm and a short side of 160 mm is cut out from the co-extruded sheet, and the end surface of the long side that is the light incident surface is polished using a mirror finisher, and then the lens that is the light emitting surface is shaped. In order to reduce the uneven brightness in the surface as a light guide plate by silk screen printing on the surface facing the surface, after providing a primer layer in advance, increase the dot diameter at a location away from the light incident surface Gradient pattern was added. At this time, ultraviolet curable ink for inkjet printing (refractive index after curing of 1.56) was used as the ink.
As in Example 1, the luminance and chromaticity were measured, and as a result, the average luminance, average chromaticity, and color difference were satisfactory for the light guide plate.

[Example 4]
A coextruded sheet was obtained in the same manner as in Example 3 except that polystyrene (PS-2) was used for the surface layer and the extrusion conditions were adjusted so that the surface layer thickness was 150 μm.
As in Example 1, the luminance and chromaticity were measured, and as a result, the average luminance, average chromaticity, and color difference were satisfactory for the light guide plate.

[Example 5]
As a result of measuring the luminance and chromaticity in the same manner as in Example 1 except that inkjet printing was used as the printing method and ultraviolet curable ink for inkjet printing (refractive index after curing of 1.56) was used as the ink, the average luminance was measured. Both the average chromaticity and the color difference had satisfactory performance as a light guide plate.
The evaluation results of the optical sheets and light guide plates obtained in the above examples are summarized in Table 1 below.

[Comparative Example 1]
Co-extrusion was carried out in the same manner as in Example 1 except that acrylic resin (PMMA-1) was used for the surface layer, but the phenomenon that the sheet sticked to the gloss roll and the shaping roll frequently occurred and the appearance was good. No coextruded sheet was obtained.

[Comparative Example 2]
A coextruded sheet having a good appearance was obtained in the same manner as in Example 1 except that acrylic resin (PMMA-1) was used for the surface layer and the setting temperature of the gloss roll and the shaping roll was uniformly reduced by 15 ° C. However, the transfer ratio was as low as 0.21.
The light guide plate obtained by silk screen printing (using UV curable ink) had a low average luminance and did not have satisfactory performance.

[Comparative Example 3]
Except for using polystyrene (PS-1) for the surface layer, coextrusion was carried out in the same manner as in Example 2 to obtain a coextruded sheet, but there was a phenomenon of sticking to the gloss roll and the shaping roll, Since many peeling patterns from the roll were observed on the sheet surface, the evaluation as a light guide plate was not performed.

[Comparative Example 4]
A coextruded sheet was obtained in the same manner as in Example 2 except that the setting temperature of the polishing roll and the shaping roll using polystyrene (PS-1) for the surface layer was uniformly reduced by 10 ° C. It was as low as 0.22.
The light guide plate obtained by silk screen printing (using heat-drying type ink) did not have the performance with satisfactory average luminance.

[Comparative Example 5]
A light guide plate was obtained in the same manner as in Example 5 except that polystyrene (PS-2) was used for the core layer, but it had the performance of satisfying the average chromaticity (y value) and color difference (Δy value). There wasn't.

[Comparative Example 6]
A light guide plate was obtained in the same manner as in Example 5 except that polystyrene (PS-4) was used for the surface layer. However, the light guide plate did not have satisfactory performance for average chromaticity (y value) and color difference (Δy value). It was.

[Comparative Example 7]
A light guide plate was obtained in the same manner as in Example 5 except that polystyrene (PS-5) was used for the surface layer. However, the light guide plate had satisfactory performance for average luminance, average chromaticity (y value), and color difference (Δy value). I did not.
The evaluation results of the optical sheet and the light guide plate obtained in the above comparative examples are summarized in Table 2 below.

* 1: Measured at the part with no peeling pattern Release agent A: Stearyl alcohol (NAF-45, NOF Corporation)
B: Stearic acid (NAA-175, NOF Corporation)
C: erucic acid amide (NOF Alfro P-10)
Appearance of optical sheet; ○: No abnormality, x: Peeling pattern from roll Transfer ratio (h / d): Lens shaping height h (μm) / lens mold depth d (μm)
Printing method UV: Silk screen printing, UV curable ink used
IR: Silk screen printing, using heat drying ink
IJ: Inkjet printing, UV curable ink used Average luminance: Average value of luminance at 25 points in the screen (FIG. 2) Average chromaticity y: Average value of chromaticity y at 25 points in the screen Chromaticity difference Δy: 25 in the screen Difference between maximum and minimum chromaticity y of a point

  An optical sheet with a lens formed of a transparent thermoplastic resin composite extrusion sheet according to the present invention is a television, a monitor for a personal computer (for desktops and notebooks), a monitor for a car navigation system, a mobile phone, and illumination for indoor and outdoor spaces. As a surface light source member used for an apparatus or the like, it can be suitably used in a wide range of applications such as a display device and a signboard.

DESCRIPTION OF SYMBOLS 1 Surface layer 2 Core layer 3 Side surface 4 Output surface 5 Back surface 6 Print dot 7 Core layer main extruder 8 Surface layer sub-extruder 9 T die 10 Glossing roll 11 Shaping roll 12 Take-up roll 13 Brightness / chromaticity measurement spot 14 LED

Claims (8)

The core layer comprising a transparent thermoplastic resin, and disposed on both sides of the core layer, the release agent a transparent heat containing 0.03 wt% selected from the group consisting of higher aliphatic alcohols及beauty and high-class fatty acid a lensed optical sheet made of a transparent thermoplastic resin composite extrusion sheet have a table layer made of thermoplastic resin, the content of the release agent selected from the group consisting of higher fatty alcohols and higher fatty acids of the core layer Is 0 . The optical sheet is less than 03% by mass.   The optical sheet according to claim 1, wherein the surface layer has a thickness of 5 to 200 μm.   The optical sheet according to claim 2, wherein the transparent thermoplastic resin of the core layer and the surface layer is polystyrene. The total amount of dimer and trimer contained in the polystyrene of the core layer and the surface layer is 5000 μg / g or less, and the following general formula (1):

The optical sheet according to claim 3, wherein the trimer component (1a-phenyl-4e- (1′-phenylethyl) tetralin) represented by the formula is 3000 μg / g or less. The optical sheet according to claim 4, wherein the concentration of 4-t-butylcatechol (TBC) contained in the core layer and the surface polystyrene is 6 µg / g or less.   The phosphorus antioxidant 0.02-0.2 mass part and / or the phenolic antioxidant 0.02-0.2 mass part are added to the polystyrene of the said core layer and the said surface layer. 5. The optical sheet according to 5.   A side surface on which light from a light source is incident, an exit surface that is formed in a direction intersecting with the side surface, emits planar light, a back surface that faces the exit surface, and light incident from the side surface is the exit surface. The surface light source member which consists of an optical sheet of any one of Claims 1-6 in which the printing dot reflected to the side was formed in the said back surface.   The surface light source member according to claim 7, wherein the printing dots are formed by ink jet printing.

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