WO2009122942A1

WO2009122942A1 - Optical sheet, process for producing optical sheet, formed object, and process for producing formed object

Info

Publication number: WO2009122942A1
Application number: PCT/JP2009/055693
Authority: WO
Inventors: 川東　宏至; 木暮　真巳
Original assignee: 出光興産株式会社
Priority date: 2008-03-31
Filing date: 2009-03-23
Publication date: 2009-10-08
Also published as: CN101981097A; JP5296405B2; KR101567351B1; JP2009242752A; CN101981097B; TWI442118B; TW201003161A; KR20100138965A

Abstract

An optical sheet is provided which can be easily processed into formed objects, e.g., a lightguide plate having a reduced thickness and increased area, and has a high light transmittance. Also provided are: a process for producing the optical sheet; a formed object obtained by forming a rugged pattern in a surface of the optical sheet; and a process for producing the formed object. The optical sheet is an optical sheet obtained by extruding an aromatic polycarbonate resin composition from an extruder and then cooling the extrudate at a temperature not higher than the glass transition temperature, the resin composition comprising (A) 100 parts by mass of an aromatic polycarbonate having a viscosity-average molecular weight of 22,000 or lower and (B) 0.01-1 part by mass of an antioxidant and not containing a blue dye or pigment. This optical sheet is characterized in that the optical sheet having a thickness of 0.1-1 mm has a total light transmittance of 91% or higher.

Description

Optical sheet, optical sheet manufacturing method, molded body, and molded body manufacturing method

The present invention relates to an optical sheet used for a light guide plate and the like, a method for manufacturing the optical sheet, a molded body in which irregularities are formed on the surface of the optical sheet, and a method for manufacturing the molded body. More specifically, an optical sheet excellent in transparency and light guide obtained by extruding a specific thermoplastic resin under specific conditions and controlling a higher order structure in the solid structure of the sheet, and the optical sheet The present invention relates to a manufacturing method, a molded body, and a molded body manufacturing method.

In recent years, with the spread of mobile electronic devices such as mobile phones, portable music players, and notebook computers, these product devices have been made thinner and larger in screen. With the development of thinning technology for LED light sources, the backlight for liquid crystal displays mounted on the LED light source is also actively studied for thinning and screen enlargement. Among the members constituting the backlight, the light guide plate dominates the product size, and therefore, consideration has been given to reducing the thickness of the light guide plate and enlarging the screen.
Specifically, the thickness that has already been 0.8 mm has been reduced to 0.6 to 0.4 mm, and recently, the thickness has been further reduced to 0.2 mm, which is 0.3 mm or less. These thinnings are accompanied by the thinning of the LED light source. On the other hand, the screen size, which was about 1.8 to 2.8 inches, is now expanding to 3 to 3.5 inches. Furthermore, the use of LED light sources from CCFL light sources in notebook personal computers is also progressing, and it has been attempted to adopt a light guide plate with a thickness of 0.4 to 0.6 mm for a screen size of 12 inch class.
A light guide plate used for a backlight for mobile devices is mainly made of polycarbonate resin. In these, a polycarbonate resin is molded into a plate shape mainly by an injection molding method, and at the same time, fine irregularities optically designed for the purpose of uniformly emitting a backlight on the surface are formed.
Among the polycarbonate resins used here, in particular, resin compositions that have been improved in light guide properties for light guide plate applications for injection molding are frequently used (Patent Documents 1 and 2). However, these resin compositions are not only limited by the thickness of the light guide plate and the screen size in the injection molding method, but also birefringence (retardation) occurs due to shear orientation during injection molding, and color misregistration tends to occur during light emission. There is a problem.
In addition, for the resin composition, even if the injection molding method is changed to the extrusion molding method and the sheet molding is performed, the sheet becomes cloudy at the time of the extrusion molding, especially, when the thickness exceeds 2 mm, the cloudiness becomes remarkable. There is a problem that the luminance characteristic is deteriorated. It was difficult to obtain an original sheet for a light guide plate with the resin composition by an extrusion method.

In turn, even if the fluidity of the resin composition during injection molding is improved (Patent Document 3), a light guide plate having a thickness of 2.6 inches or more and a thickness of 0.25 mm or less cannot be molded by the injection molding method. It has been extremely difficult to obtain a product that is a limit region and exhibits brightness performance as a light guide plate.
For large screens such as those for notebook computers, light guide plates made of polymethyl methacrylate (PMMA) have been used. However, as the thickness is reduced, impact strength is insufficient and warping (dimensional stability) Insufficient performance), there are problems such as generation of moire fringes and lowering of luminance due to displacement from the light source.
Against this background, attempts have been made to apply polyethylene terephthalate (PET) sheets to these thin light guide plates. However, PET sheets have extremely large birefringence (retardation), and color shifts occur when they are used as light guide plates. There is a drawback that it is easy.
Further, a polycarbonate resin composition for a light guide plate is disclosed (Patent Document 4) in which 0.02 to 2 parts by weight of a phosphorus-based and / or phenol-based antioxidant is blended with 100 parts by weight of a polycarbonate resin. Further, since a blue dye or the like is used and the molding temperature is high, the total light transmittance is only about 90%, and further improvement is desired.

Japanese Patent Laid-Open No. 10-73725 (Japanese Patent No. 3330498) JP 2002-60609 (Patent 3516908) JP 2005-247947 A JP 2008-24911 A

An object of the present invention is to provide an optical sheet which can be easily processed into a molded body such as a light guide plate having a thin wall and a large screen and has a high light transmittance, and a method for producing the same.

As a result of intensive studies to achieve the above object, the present inventors have achieved the above-mentioned problems by using an aromatic polycarbonate having a specific molecular weight and an antioxidant and molding at a specific temperature. Found to get. The present invention has been completed based on such findings.
That is, the present invention
(1) (A) Aromatic polycarbonate resin composition containing 100 parts by weight of aromatic polycarbonate having a viscosity average molecular weight of 22,000 or less and (B) 0.01-1 part by weight of an antioxidant, and containing no blue dye or pigment. Is an optical sheet that is cooled below the glass transition temperature after being extruded from the extruder, and has a total light transmittance of 91% or more at a thickness of 0.1 to 1 mm. Sheet,
(2) The optical sheet according to (1), wherein the birefringence (phase difference; retardation value at a wavelength of 550 nm) is 150 nm or less, and the standard deviation value of the retardation value at an arbitrary position in the sheet surface is 10 or less,
(3) Spectral light transmittance of 70% or more at a wavelength of 300 nm or aromatic polycarbonate in a visible-UV spectral spectrum measured at a thickness of 0.4 mm of a sample plate prepared from an aromatic polycarbonate resin composition used in the optical sheet (1) measured in a good solvent (measured by the solution method: the light guide length of the solution cell is 5 cm, the sample solution concentration is 12 g / dl, the solvent is dichloromethane, and the wavelength is 450 nm) is 94% or more (1 ) Optical sheet,
(4) The optical sheet according to the above (1), comprising 0.01 to 1 part by mass of (C) a thermoplastic polyacrylic resin with respect to 100 parts by mass of the component (A).
(5) The optical sheet according to (1), wherein the antioxidant of the component (B) is a phosphorus-based antioxidant and / or a phenol-based antioxidant,
(6) A molding step of melt-extruding the aromatic polycarbonate resin composition into a sheet, a cooling step of rapidly cooling the melt-extruded sheet-like molded product to a glass transition temperature or lower, and a cooled sheet-like molded product, The method for producing an optical sheet according to the above (1), comprising a heat treatment step of heat treatment at a temperature equal to or higher than ° C. and equal to or lower than a glass transition temperature of the aromatic polycarbonate resin composition,
(7) A molded article obtained by forming a concavo-convex pattern on the surface of the optical sheet according to (1) above,
(8) The molded product according to (7), which is any one of a light guide plate, a diffusion sheet, a retroreflecting plate, a prism sheet, and a Fresnel lens sheet,
(9) The present invention provides a method for producing a molded article, wherein a concavo-convex pattern is formed on the surface of the optical sheet according to (1).

The present invention excels in optical properties (light guiding properties, color tone) such as transferability, high transparency, low birefringence, and the like suitable for the production of molded articles such as a light guide plate having a thickness and area that cannot be achieved by the injection molding method. An optical sheet, a light guide plate, and the like are provided.

It is a schematic diagram which shows the transfer process by a steel belt method. It is a figure which shows the transcription | transfer process by a pinching roll method. It is a schematic diagram which shows the transfer process by a belt transfer method. It is a schematic diagram of the manufacturing apparatus which performs the process of forming a sheet | seat shaping | molding and an uneven | corrugated pattern simultaneously.

Explanation of symbols

1: Tension roll 2: Heating roll 3: Cooling roll 4: Pressure roll 5: Endless belt 6: Sheet supply roll 7: Tension roll 8: Heating device S: Sheet d before transferring uneven shape: Pressure roll Length of sheet 21 pinched by endless belt: extruder 22: pinching roll 23: pinching roll 24: take-up roll 25: pinching roll 26a: transfer roll 26b: transfer roll 26c: transfer roll 31: heating Roll 32: Transfer roll 33 for forming irregularities: Pre-heating roll 34: Cooling roll 35: Conveying roll 36: Endless belt

In the optical sheet of the present invention, (A) an aromatic polycarbonate having a viscosity average molecular weight of 22,000 or less contains (B) an antioxidant, and an aromatic polycarbonate resin composition containing no blue dye or pigment is extruded from an extruder. After that, the optical sheet is cooled below the glass transition temperature, and the total light transmittance at the thickness of the optical sheet of 0.1 to 1 mm is 91% or more.
The birefringence (phase difference; retardation value at a wavelength of 550 nm) is preferably 150 nm or less, and the standard deviation value of the retardation value measured at an arbitrary position in the sheet surface is preferably 10 or less.
Since the optical sheet of the present invention does not contain a blue dye or pigment, there is no reduction in luminance characteristics when processed into a light guide plate or the like. By the way, when a blue dye or pigment is contained, the luminance number decreases on the order of 10% depending on the blending amount.
In addition, since (A) an aromatic polycarbonate is used as a base resin and (B) an aromatic polycarbonate resin composition containing an antioxidant is used as an optical sheet, it is possible to reduce yellowing during molding into a sheet. Thus, the luminance is reduced when this sheet is processed into a light guide plate or the like.

As the aromatic polycarbonate as the component (A), bisphenol A type polycarbonate is preferable from the viewpoint of optical transparency, mechanical strength, and heat resistance.
The aromatic polycarbonate can be usually produced by reacting a dihydric phenol and a polycarbonate precursor such as phosgene or a carbonate compound. For example, in a solvent such as methylene chloride, in the presence of a known acid acceptor or molecular weight regulator, a branching agent may be added if necessary, and a reaction between a dihydric phenol and a carbonate precursor such as phosgene, or It is produced by a transesterification reaction between a dihydric phenol and a carbonate precursor such as diphenyl carbonate.
There are various kinds of dihydric phenols, and 2,2-bis (4-hydroxyphenyl) propane (common name: bisphenol A) is particularly preferable. Examples of bisphenols other than bisphenol A include bis (4-hydroxyphenyl) methane; 1,1-bis (4-hydroxyphenyl) ethane; 2,2-bis (4-hydroxyphenyl) butane; (4-hydroxyphenyl) octane; 2,2-bis (4-hydroxyphenyl) phenylmethane; 2,2-bis (4-hydroxy-1-methylphenyl) propane; bis (4-hydroxyphenyl) naphthylmethane; 1 1,2-bis (4-hydroxy-t-butylphenyl) propane; 2,2-bis (4-hydroxy-3-bromophenyl) propane; 2,2-bis (4-hydroxy-3,5-tetramethylphenyl) ) Propane; 2,2-bis (4-hydroxy-3-chlorophenyl) propane; 2,2-bis (4-hydro) Bis-3,5-tetrachlorophenyl) propane; bis (hydroxyaryl) alkanes such as 2,2-bis (4-hydroxy-3,5-tetrabromophenyl) propane, 1,1-bis (4-hydroxyphenyl) ) Cyclopentane; 1,1-bis (4-hydroxyphenyl) cyclohexane; bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) -3,5,5-trimethylcyclohexane, 4, 4'-dihydroxyphenyl ether; dihydroxyaryl ethers such as 4,4'-dihydroxy-3,3'-dimethylphenyl ether, 4,4'-dihydroxydiphenyl sulfide; 4,4'-dihydroxy-3,3'- Dihydroxydiaryl sulfides such as dimethyldiphenyl sulfide, 4,4 ′ Dihydroxydiphenyl sulfoxide; dihydroxydiaryl sulfoxides such as 4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfoxide; 4,4′-dihydroxydiphenyl sulfone; 4,4′-dihydroxy-3,3′-dimethyldiphenyl sulfone And the like, and dihydroxydiphenyls such as 4,4′-dihydroxydiphenyl. These dihydric phenols may be used alone or in combination of two or more.

Examples of the carbonate compound include diaryl carbonates such as diphenyl carbonate, and dialkyl carbonates such as dimethyl carbonate and diethyl carbonate. And as a molecular weight regulator, what is normally used for superposition | polymerization of a polycarbonate may be used, and various things can be used. Specifically, as monohydric phenol, for example, phenol, on-butylphenol, mn-butylphenol, pn-butylphenol, o-isobutylphenol, m-isobutylphenol, p-isobutylphenol, ot -Butylphenol, mt-butylphenol, pt-butylphenol, on-pentylphenol, mn-pentylphenol, pn-pentylphenol, on-hexylphenol, mn-hexylphenol, pn-hexylphenol, pt-octylphenol, o-cyclohexylphenol, m-cyclohexylphenol, p-cyclohexylphenol, o-phenylphenol, m-phenylphenol, p-phenylphenol, on-nonylphenol M-nonylphenol, pn-nonylphenol, o-cumylphenol, m-cumylphenol, p-cumylphenol, o-naphthylphenol, m-naphthylphenol, p-naphthylphenol; 2,5-di -T-butylphenol; 2,4-di-t-butylphenol; 3,5-di-t-butylphenol; 2,5-dicumylphenol; 3,5-dicumylphenol; p-cresol, bromophenol, tribromo Examples include phenol. Among these monohydric phenols, pt-butylphenol, p-cumylphenol, pt-octylphenol, phenol and the like are preferably used.

Other branching agents include, for example, 1,1,1-tris (4-hydroxyphenyl) ethane; α, α ′, α ″ -tris (4-hydroxyphenyl) -1,3,5-triisopropylbenzene; -[Α-methyl-α- (4'-hydroxyphenyl) ethyl] -4- [α ', α'-bis (4 "-hydroxyphenyl) ethyl] benzene; phloroglysin, trimellitic acid, isatin bis (o-cresol) A compound having three or more functional groups such as) can also be used.

The aromatic polycarbonate as the component (A) used in the present invention is required to have a viscosity average molecular weight of 22,000 or less, and preferably 12,000 to 20,000. If it is less than 12,000, the mechanical strength is inferior, and if it exceeds 22,000, the total light transmittance is less than 91%, which is not preferable as an optical sheet. Birefringence (phase difference; retardation value at a wavelength of 550 nm) is 150 nm or less, preferably 130 nm or less, and the standard deviation value of the retardation value measured by sampling at an arbitrary position in the sheet surface is 10 or less. It is preferable. The glass transition temperature of the aromatic polycarbonate as the component (A) is about 141 to 149 ° C. After the aromatic polycarbonate is extruded from the extruder, it is cooled below such a glass transition temperature, so that the birefringence is 150 nm or less, and the standard deviation value can be 10 or less.
The lower limit of the standard deviation value is preferably as low as possible, but about 15 is sufficient for practical use from the viewpoint of optical isotropy and economy required for the optical sheet.
In the present invention, an arbitrary location is a total of 9 locations on a 3 cm × 3 cm grid of 1 cm pitch of two 4 cm × 4 cm portions, each of which is 60 cm or more away from a sample of an optical sheet of 100 cm × 100 cm. 18 points shall be measured.

Examples of the antioxidant as the component (B) include phosphorus-based, phenol-based, and pentaerythritol-based ones.
Among them, phosphorus-based antioxidants, more specifically, phosphorus-based antioxidant stabilizers such as phosphites and phosphates are preferably used. Examples of phosphites include triphenyl phosphite, trisnonylphenyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, trinolyl phosphate, tridecyl phosphite, trioctyl phosphite. Phyto, trioctadecyl phosphite, distearyl pentaerythritol diphosphite, tricyclohexyl phosphite, monobutyl diphenyl phosphite, monooctyl diphenyl phosphite, distearyl pentaerythritol diphosphite, bis (2,4-di-) tert-butylphenyl) pentaerythritol phosphite, bis (2.6-di-tert-butyl-4-methylphenyl) pentaerythritol phosphite, 2,2-methylenebis (4,6-di-ter - butylphenyl) octyl phosphite, tri-esters of phosphorous acid such as tetrakis (2,4-di -tert- butylphenyl) -4,4-diphenyl Eni alkylene phosphonites, diesters, such as mono-ester.

Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, tris (nonylphenyl) phosphate, 2-ethylphenyl diphenyl phosphate, and the like. These phosphorus antioxidants may be used alone or in combination of two or more.

Among these phosphorus antioxidants, distearyl pentaerythritol diphosphite, bis (2,4-di-tert-butylphenyl) pentaerythritol phosphite, bis (2.6-di-tert-butyl-4-) Methylphenyl) pentaerythritol phosphite and tris (2,4-di-tert-butylphenyl) phosphite are preferred, pentaerythritol type, especially bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol Phosphite is particularly preferred. The phosphorus antioxidants can be used alone or in combination of two or more.

Commercially available phosphoric antioxidants can be used as they are, for example, Asahi Denka Kogyo Co., Ltd. [trade name: ADK STAB 2112], Clariant Japan Co., Ltd. product (Sand Stub P-EPQ), Sumitomo Chemical Co., Ltd. Products [Sumilyzer P-168], Ciba-Geigy products [Tris (2,4-di-tert-butylphenyl) phosphite, trade name: Irgafos 168), products of Asahi Denka Co., Ltd. [trade name: Adegas Tab PEP36, etc. Is mentioned.

Examples of phenolic antioxidants include α-tocopherol, butylhydroxytoluene, sinapyl alcohol, vitamin E, n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2- tert-Butyl-6- (3′-tert-butyl-5′-methyl-2′-hydroxybenzyl) -4-methylphenyl acrylate, 2,6-di-tert-butyl-4- (N, N-dimethyl) Aminomethyl) phenol, 3,5-di-tert-butyl-4-hydroxybenzylphosphonate diethyl ester, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-methylenebis (4 -Ethyl-6-tert-butylphenol), 4,4'-methylenebis (2,6-di-ter -Butylphenol), 2,2'-methylenebis (4-methyl-6-cyclohexylphenol), 2,2'-dimethylene-bis (6-α-methyl-benzyl-p-cresol) 2,2'-ethylidene-bis (4,6-di-tert-butylphenol), 2,2′-butylidene-bis (4-methyl-6-tert-butylphenol), 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), Triethylene glycol-N-bis-3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, 1,6-hexanediol bis [3- (3,5-di-tert-butyl- 4-hydroxyphenyl) propionate], bis [2-tert-butyl-4-methyl 6- (3-tert-butyl-5-methyl) -2-hydroxybenzyl) phenyl] terephthalate, 3,9-bis {2- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1, -dimethylethyl}- 2,4,8,10-tetraoxaspiro [5,5] undecane, 4,4′-thiobis (6-tert-butyl-m-cresol), 4,4′-thiobis (3-methyl-6-tert) -Butylphenol), 2,2′-thiobis (4-methyl-6-tert-butylphenol), bis (3,5-di-tert-butyl-4-hydroxybenzyl) sulfide, 4,4′-di-thiobis ( 2,6-di-tert-butylphenol), 4,4′-tri-thiobis (2,6-di-tert-butylphenol), 2,2-thiodiethylenebis- [ -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis (n-octylthio) -6- (4-hydroxy-3 ', 5'-di-tert-butylanilino) -1,3,5-triazine, N, N′-hexamethylenebis- (3,5-di-tert-butyl-4-hydroxyhydrocinnamide), N, N′-bis [3- (3,5 -Di-tert-butyl-4-hydroxyphenyl) propionyl] hydrazine, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2 , 4,6-Tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, Tris (3,5-di-tert-butyl-4-hydroxyphenyl) isocyanurate Tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5 5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, 1,3,5-tris-2 [3 (3,5-di-tert-butyl-4-hydroxyphenyl) Examples include propionyloxy] ethyl isocyanurate and tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxymethyl] methane. All of these are readily available. Among them, n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl) -4-hydroxybenzyl) benzene, 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, tetrakis [3- (3,5-di-tert-butyl-4 -Hydroxyphenyl) propionyloxymethyl] methane is preferred, in particular n-octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate. The said hindered phenolic antioxidant can be used individually or in combination of 2 or more types.
Commercially available phenolic antioxidants can be used as they are, for example, Asahi Denka Kogyo Co., Ltd. [trade name: ADK STAB AO-80], its products [trade name: ADK STAB AO-30], Ciba Specialty Chemicals. Products [trade name: Irganox 1010, 1076] and the like.

The antioxidant which is (B) component may use 1 or more types of the said phosphorus antioxidant, may use 1 or more types of phenolic antioxidant, and 1 or more types of phosphorus antioxidants. And one or more phenolic antioxidants may be used in combination.
The addition amount is in the range of 0.01 to 1 part by mass, preferably in the range of 0.05 to 0.3 part by mass, with respect to 100 parts by mass of the aromatic polycarbonate as the component (A). By setting it as such a range, the preferable characteristic as an optical sheet is acquired.

The optical sheet of the present invention has a total light transmittance of 91% or more at a thickness of 0.1 to 1 mm. After being extruded from the extruder, the total light transmittance can be 91% or more by cooling below the glass transition temperature. Preferably, it is 91.5 to 92%.
By setting it to 91% or more, it is possible to prevent the luminance from being lowered. If it exceeds 92%, industrial production is difficult at present because of absorption from the molecular skeleton of the aromatic polycarbonate.

In general, injection molded products are cooled in the mold while maintaining the molecular orientation due to the shear during injection molding, and the residual stress strain tends to increase because the molecular orientation is frozen. Then, the degree of residual stress strain becomes non-uniform. Usually, since the residual stress strain in the gate peripheral portion increases, the retardation value tends to show a larger measured value.
On the other hand, although the sheet by extrusion molding can depend on the conditions at the time of extrusion molding and the viscosity of the material (depending on the viscosity average molecular weight), the retardation value can be lowered, and the distribution of the retardation within the sheet product Is easy to homogenize. For this reason, it is possible to obtain a light guide plate with higher display quality than a light guide plate by injection molding. By using a retardation value of 150 nm or less and a standard deviation value of the retardation value measured by sampling at an arbitrary position in the sheet surface to be 10 or less, a backlight using a light guide plate processed with an optical sheet is used as a liquid crystal panel. It is possible to prevent the display quality when the display device is mounted on the display device from being deteriorated. The retardation value is preferably 100 nm or less, more preferably 50 nm or less.

The optical sheet of the present invention has a spectral light transmittance (solution) in a visible-UV spectral spectrum measured at a thickness of 0.4 mm, measured by dissolving a spectral light transmittance of 70% or more at a wavelength of 300 nm or an aromatic polycarbonate in a good solvent. Measurement by method: Aromatic polycarbonate resin having a light guide length of the solution cell of 5 cm, a sample solution concentration of 12 g / dl, a solvent dichloromethane, and a wavelength of 450 nm) of 94% or more is used as the component (A) of the polycarbonate resin composition. preferable.
Usually, in a light guide plate formed using an optical sheet, light having a wavelength of 400 to 700 nm in the visible light region enters from the end face, is guided and propagates in the end face direction, and the direction of light in the thickness direction (plane direction) Surface emission is achieved by controlling the nature. The light incident in the direction of the end face is emitted from the end face on the opposite side, and the spectral characteristics of the light are measured, so that evaluation suitable for the light propagation of the light guide plate can be performed.
However, in such a measurement, a measurement with a thin molded piece of 1 mm or less needs to prepare a special measuring device, which is actually difficult. Therefore, in the present invention, the sheet characteristics are evaluated based on the spectral characteristics in the thickness direction (plane direction) that can be easily measured and evaluated. In general, when the thickness of the sheet is as thin as 1 mm or less, it becomes difficult to detect the spectral characteristic difference specific to the sheet base material in the measurement of the spectral light transmittance that transmits visible light in the thickness direction. However, even when measuring spectral characteristics in the thickness direction, it is possible to evaluate this spectral characteristic difference by paying attention to a wavelength of 380 nm or less in the ultraviolet region. That is, the evaluation result of the spectral transmittance at 300 to 380 nm by the measurement in the thickness direction does not directly reflect the spectral transmittance in the visible light region, but is relatively linked with the spectral transmittance at 300 to 380 nm in the end face direction. There is a tendency to reflect the spectral characteristics in the visible light wavelength region, and a substitution thereof is possible.
Specifically, an optical resin base material having a high spectral transmittance of 300 to 380 nm measured in the thickness direction tends to have high spectral characteristics in the visible light wavelength region when measured in the end face direction. If the spectral light transmittance is less than 70%, the light guide performance is insufficient, and thus the luminance decreases. More preferably, it is 73% or more.

The viscosity average molecular weight of the aromatic polycarbonate (A) in the optical sheet of the present invention is 22000 or less, preferably 14000 to 20000. More preferably, it is 15000 to 19000. If it is less than 14,000, the strength of the product will be insufficient, and the yield will be reduced due to the adhesion of chips during the external processing of the product. In particular, when the thickness of the optical sheet is 0.3 mm or less, the strength tends to be insufficient, and the optical sheet tends to be easily damaged.
When the viscosity average molecular weight exceeds 22,000, depending on the extrusion molding conditions, the yellowing and retardation values of the resin base material are likely to increase, and it becomes difficult to reach a total light transmittance of 91%.
A light guide plate or the like is formed by transferring a fine uneven pattern (prism, dot, dome-shaped convex lens) of several to several hundred microns on a sheet surface by roll embossing or press forming a resin sheet to form an uneven pattern. Although manufactured, when the viscosity average molecular weight exceeds 22,000, the transferability at this time also deteriorates.

The optical sheet of the present invention is produced by extrusion molding of an aromatic polycarbonate resin composition, but it is thermoplastic as component (C) in addition to the aromatic polycarbonate as component (A) and the antioxidant as component (B). A small amount of polyacrylic acid alkyl ester resin may be added. Spectral characteristics are further improved by adding a small amount of component (C).
Component (C) is preferably added so that the ratio of component (A) / component (C) is 99.99 / 0.01 to 99.00 / 1.00 (mass ratio). More preferably, it is 99.95 / 0.05 to 99.50 / 0.50, and particularly preferably 99.90 / 0.10 to 99.70 / 0.30. By setting the addition ratio of component (C) to 0.01 or more, the transparency of the molded body is improved, and by setting it to 1.00 or less, transparency can be maintained without impairing other desired physical properties. it can.

The thermoplastic polyacrylic acid alkyl ester resin as component (C) is a polymer having a repeating unit of at least one selected from monomer units of acrylic acid, acrylic acid ester, acrylonitrile and derivatives thereof, a homopolymer or A copolymer with styrene, butadiene or the like may also be used. Specifically, polyacrylic acid, polymethyl methacrylate (PMMA), polyacrylonitrile, ethyl acrylate-acrylic acid-2-chloroethyl copolymer, acrylic acid-n-butyl-acrylonitrile copolymer, acrylonitrile-styrene copolymer And acrylonitrile-butadiene copolymer and acrylonitrile-butadiene-styrene copolymer. Among these, polymethyl methacrylate (PMMA) can be particularly preferably used. As polymethyl methacrylate (PMMA), known ones can be used. Usually, those produced by bulk polymerization of methyl methacrylate monomer in the presence of a peroxide or azo polymerization initiator are used. preferable.
The thermoplastic polyacrylic acid alkyl ester resin as component (C) preferably has a molecular weight of 200 to 100,000, more preferably 20,000 to 60,000. When the molecular weight is 200 to 100,000, phase separation between the component (A) and the component (C) does not become too fast at the time of molding, so that sufficient transparency can be obtained in the optical sheet.

The method for producing the optical sheet of the present invention is not particularly limited, but a desired optical sheet can be produced according to the following method for producing an optical sheet of the present invention.
The method for producing an optical sheet of the present invention includes a molding step of melt-extruding the aromatic polycarbonate resin composition into a sheet, a cooling step of rapidly cooling the melt-extruded sheet-like molded body to a glass transition temperature or lower, and cooling A heat treatment step of heat-treating the sheet-like molded body at 50 ° C. or more and below the glass transition temperature of the polycarbonate resin.
The said cooling process can cool the said sheet-like molded object by allowing the said sheet-like molded object to pass through the slit where cooling water flows down. The heat treatment step can be carried out by sandwiching and heating the front and back surfaces of the sheet-like molded body with a metal endless belt and / or metal roll having a mirror surface.
As an extrusion molding method, an optical sheet that can be used as a light guide plate can be manufactured by selecting molding conditions even with a sheet molding machine that is generally equipped with three rolls. The cylinder temperature and die temperature of the extruder are about 220 to 340 ° C., preferably about 240 to 320 ° C., depending on the difference in resin composition, glass transition temperature, and the like.
Resin containing (A) component / (C) component in a ratio of 99.99 / 0.01 to 99.00 / 1.00 (mass ratio) and (B) an antioxidant in the above-described ratio When performing extrusion molding using the composition as a raw material, a cooling step of rapidly cooling the sheet-like molded body obtained by the above melt extrusion to a glass transition temperature or lower is important. Extrusion molding including such a cooling step When the apparatus is applied, an optical sheet having higher optical transparency can be obtained.
The cooling temperature needs to be lower than the glass transition temperature, preferably 140 ° C. or lower, more preferably 120 ° C. or lower. By setting the cooling temperature to the glass transition temperature or lower, the total light transmittance at a thickness of 0.1 to 1 mm of the optical sheet can be set to 91% or higher. The lower limit of the cooling temperature is about 50 ° C. although it depends on the difference in resin composition, glass transition temperature, and the like. By setting the temperature to 50 ° C. or higher, it is possible to reduce the residual strain in the molded optical sheet and ensure optical isotropy. Cooling is usually performed using a plurality of rolls.
The cylinder temperature of the extruder is about 220 to 340 ° C, preferably about 240 to 320 ° C.
In addition, the cooled sheet-like formed body is subjected to a heat treatment step in which heat treatment is performed at a temperature of 50 ° C. or higher and below the glass transition temperature of the aromatic polycarbonate. An optical sheet having a uniform thickness and no retardation value can be obtained.
By applying an extrusion molding machine equipped with these production steps, a resin composition having a ratio of (A) component / (C) component of 99.99 / 0.01 to 99.99 / 1.00 (mass ratio) It is possible to suppress the phase separation that occurs in the cooling process from the molten state of the object, and it is possible to suppress a decrease in light transmittance.
Examples of the production method including these steps include an elastic roll method and a steel belt method, and application of an extruder having these steps is more preferable.
Examples of the steel belt method include a manufacturing method disclosed in Japanese Patent Application Publication No. 2004-230598.
In this manufacturing method, the endless belt wound around a plurality of rolls and heated by the heating roll unit is caused to travel while the formed sheet is in close contact with the endless belt and the roll. A method for producing a sheet in which the sheet is peeled from the endless belt after linear pressure welding, and the heated sheet is kept warm and / or heated while traveling from the side opposite to the endless belt ( (See FIG. 1). Heat insulation and / or heating is performed by a heat insulation plate, hot air blowing, and infrared rays.
In FIG. 1, 1 is a tension roll, 2 is a heating roll, 3 is a cooling roll, 4 is a rolling roll, 5 is an endless belt, 6 is a sheet supply roll, 7 is a tension roll, and 8 is a heating device. S indicates a sheet before the concavo-convex shape is transferred, and d indicates the length of the sheet sandwiched between the rolling roll 4 and the endless belt 5.
Examples of the elastic roll method include a method disclosed in Japanese Patent Publication No. 2004-155101.
In this manufacturing method, a T-die is attached to an extruder to form a sheet, the sheet is passed through a first clamping roll, a second clamping roll, and a third clamping roll, and a plurality of transfer rolls are linearly formed. In this method, sheets are manufactured side by side and manufactured through a take-up roll (see FIG. 2).
In FIG. 2, 21 is an extruder, 22, 23 and 25 are pinching rolls, 24 is a take-up roll, and 26a, 26b and 26c are transfer rolls.

Next, the molded body of the present invention such as a light guide plate having a concavo-convex pattern formed on the surface of the optical sheet will be described.
The optical sheet obtained by the above characteristics, composition, and manufacturing method is formed into a molded body by forming a fine uneven pattern on the surface, light distribution control is possible, a light guide plate, a diffusion sheet, a retroreflector, It can be used as a prism sheet and a Fresnel lens sheet. Examples of the concavo-convex pattern include a dot shape, a convex lens shape, a concave lens shape, a V-groove prism shape, and a polygonal prism shape such as a triangular pyramid and a quadrangular pyramid.
In the light guide plate, it is preferable to add gradation (shading) to the uneven pattern.
It is preferable to form a uniform pattern if it is a normal diffusion sheet, retroreflecting plate, and prism sheet.
In the case of a diffusion sheet used in a direct type backlight, it is possible to make the luminance uniform by forming the uneven pattern in the distance from the light source shadow on the light source to the distance between the light sources.
Examples of a method for forming such a concavo-convex pattern include a roll embossing method, a vacuum press molding method, and a belt transfer method. Above all, a mold with a fine uneven pattern formed on a nickel-plated foil on the surface of a belt-like thin plate stainless steel is manufactured, and heat, pressure transfer and peeling are performed while the resin film is synchronously conveyed between the mold belts rotating up and down. It is preferable to apply a belt transfer method (for example, Japanese Patent Application Laid-Open No. 2005-321681) using an apparatus provided with means for continuously performing each of these steps. This method does not require time for evacuation, temperature increase, and temperature decrease, and can transfer to a large area with high productivity (see FIG. 3).
In FIG. 3, 31 is a heating roll, 32 is a transfer roll for forming irregularities, 33 is a preheating roll, 34 is a cooling roll, 35 is a transport roll, and 36 is an endless belt. The left arrow indicates the optical sheet before transferring the concavo-convex shape, and the right arrow indicates the optical sheet after transfer, that is, a molded body such as a light guide plate.

In addition, there are a lithography method in which an acrylic UV curable resin is pressed against the optical sheet of the present invention using a mold having a fine concavo-convex pattern, and a screen printing method using a white ink. Applicable.
A molded body such as a light guide plate can also be manufactured by simultaneously performing the optical sheet molding and the step of forming a concavo-convex pattern on the surface. As a manufacturing apparatus provided with such simultaneous processes, for example, a continuous extrusion embossing machine SPU-03026W manufactured by Toshiba Machine Co., Ltd. can be suitably used (see FIG. 4).
In the apparatus shown in FIG. 4, the pressing length is increased due to the flexibility of the special touch roll, and the transfer rate is improved. In addition, the roll clearance adjustment method (Pressure sensor and Positioning sensor) enables measurement and control of clearance and pressing force.

Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

The compounding materials used in Examples and Comparative Examples are as follows.
<Combination material>
(1) Aromatic polycarbonate PC1
Taflon FN1700A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., glass transition temperature: 142 ° C., viscosity average molecular weight: 17,300, refractive index: 1.585]
(2) Aromatic polycarbonate PC2
Toughlon FN1900A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., glass transition temperature: 145 ° C., viscosity average molecular weight: 19,500, refractive index: 1.585]
(3) Aromatic polycarbonate PC3
Toughlon FN2500A [Bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., glass transition temperature: 148 ° C., viscosity average molecular weight: 23,500, refractive index: 1.585]
(4) Phosphorus antioxidant Adegas tab PEP36 [Bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol phosphite manufactured by Asahi Denka Co., Ltd.]
(5) Phenol antioxidant Irganox 1076 [Phenol antioxidant manufactured by Ciba Specialty Chemicals, Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] Table 1 is described as “IRG1076”.
(6) Thermoplastic polyacrylic resin DIANAR BR83 [Mitsubishi Rayon Co., Ltd., molecular weight: 25,000, refractive index: 1.490, molecular weight: intrinsic viscosity of chloroform solution at 25 ° C. using an Ostwald type viscosity tube [ η] was measured, and the average degree of polymerization PA was calculated by the following relational expression. log PA = 1.613 log ([η] × 10 ⁴ /8.29)]
In Table 1, it is described as “acrylic ester resin”.
(7) Blue dye HOSTALUX KSN [manufactured by Clariant Japan Co., Ltd., mixture of 4- (benzoxazol-2-yl) -4 '-(5-methylbenzoxazol-2-yl) stilbene and blue pigment]

<Kneading extrusion>
Using a tumbler, the materials are mixed at the blending ratios in each Example and Comparative Example shown in Table 1, and melt-kneaded and extruded at 280 ° C. using a single screw extruder with a screw diameter of 65 mmφ to produce pellets used in each example. did.

<Optical sheet extrusion>
Condition 1 (applied in Examples 1 to 4 and Comparative Examples 1 and 2)
An optical sheet (thickness 0.4 mm) was produced by a “three roll device” provided with the extruder 21 shown in FIG. A first pinching roll 22 having a screw diameter of 65 mm for the extruder 21, a width of a T-shaped die of 650 mm, and a diameter of 300 mm was used. Each of the second pinching roll 23 and the third pinching roll 25 was a metal roll having a diameter of 300 mm. As the transfer roll 26, a roll in which three metal rolls having a diameter of 70 mm were arranged in a straight line was used. The total distance between the first transfer roll 26a and the final transfer roll 26c was 3 m.
Condition 2 (applied in Example 5)
This was carried out using a UF roll clamping press machine (elastic roll method—see FIG. 2) manufactured by Hitz Industrial Equipment Techno Co., Ltd. The screw diameter of the extruder is 90 mm.
Condition 3 (applied in Example 6)
A stamper with a triangular pyramid prism array (height 50 μm) formed by nickel plating was pressed against a sheet obtained by sheet molding using a continuous extrusion embossing machine SPU-03026W (see FIG. 4) manufactured by Toshiba Machine Co., Ltd. Simultaneously, pattern transfer was performed to produce a prism sheet (pattern formation 2). The screw diameter of the extruder is 26 mmφ, and the temperatures of the other parts are as described in Table 1.
Condition 4 (applied in Comparative Example 3)
The same procedure as in Condition 1 was performed except that the temperature at each location was changed to the temperature shown in Table 1.
Condition 5 (applied in Comparative Example 4)
Injection molding was performed at a molding temperature of 360 ° C. (mold temperature: 120 ° C.) using an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., product number SG100M-HP) having a clamping force of 100 tons.

<Pattern transfer by press molding>
Each optical sheet produced in each Example other than Example 6 and each Comparative Example was vacuum-sucked with a vacuum press for fine pattern transfer manufactured by Meiki Seisakusho, and then a triangular pyramid prism array (height 50 μm) was formed by nickel plating. A light guide plate was produced by pressing against a stamper and performing press molding at 160 ° C. (pattern formation 1).

<Evaluation method>
(1) Total light transmittance Measured according to JIS-K-7105 using a haze meter (HGM-2DP) manufactured by Suga Test Instruments Co., Ltd.
(2) Spectral Light Transmittance of Sheet An optical sheet sample having a thickness of 0.4 mm was measured for spectral light transmittance (%) at a wavelength of 300 nm using a UV-visible spectrophotometer (UV-2450) manufactured by Shimadzu Corporation.
(3) Birefringence (Retardation) and Standard Deviation Value The birefringence (retardation value) for 550 nm was measured with a retardation measuring device (RETS-100) manufactured by Otsuka Electronics Co., Ltd.
In the present invention, an arbitrary location is a total of 9 locations on a 3 cm × 3 cm grid of 1 cm pitch of two 4 cm × 4 cm portions, each of which is 60 cm or more away from a sample of an optical sheet of 100 cm × 100 cm. 18 points were measured.
a formula:
Standard deviation (σ) =
√ [{(Re ₁ −Re _av ) ² + (Re ₂ −Re _av ) ² +... + (Re _n −Re _av ) ² } / n]
n represents the total sampling number Re _n , the Re value Re _{av at} the n-th sampling location, and the average value of Re.
(4) Optical characteristics by the solution method (spectral light transmittance)
a) Sample preparation The cut sample (6 g) was put into a volumetric flask (50 ml) and dissolved by adding dichloromethane, and ultrasonic irradiation was performed for 3 hours at the time of dissolution.
b) Measuring device: Shimadzu Corporation UV-2450
c) Measurement condition Cell length: 5 cm
Measurement wavelength: 900-200μm
Scanning speed: Set to low-speed mode Slit width: 2.0 nm
Switching wavelength: 360 nm
d) Measurement procedure After starting up and stabilizing the apparatus 2 hours before the measurement, the baseline is measured, and then auto-zero is measured at 500 nm, and it is confirmed by measuring whether the zero point is taken.
Wash the cell thoroughly with dichloromethane and acetone, wait until the cell temperature reaches room temperature, and when the cell temperature returns, add the measurement solution, put the cell in the measurement chamber, cover it, and leave it for about 1 minute. Start measurement. After completion of the measurement, the measurement solution is taken out and washed, and this is repeated by changing the sample.
(5) Transferability of concavo-convex pattern For each of the light guide plates obtained in Examples 1 to 6 and Comparative Examples 1 to 4, the pattern transfer rate reflecting the luminance characteristics was carried out instead of the luminance evaluation.
Transfer rate (%) = [height of the triangular pyramid of the transferred light guide plate (μm) / height of the triangular pyramid in the stamper (50 μm)] × 100

[Examples 1 to 6]
Using each pellet produced by melt-kneading extrusion using the compounding materials shown in Table 1, an optical sheet is produced by applying the molding conditions of “Condition 1”, “Condition 2” or “Condition 3”, A light guide plate was produced by applying the pattern formation 1 (Examples 1 to 5) or the pattern formation 2 (Example 6) to the optical sheet. The temperature at each location under each condition is as described in Table 1.

[Comparative Examples 1 to 4]
Using each pellet produced by melt kneading extrusion using the compounding materials shown in Table 1, an optical sheet is produced by applying the molding conditions of “Condition 1”, “Condition 4” or “Condition 5”. A light guide plate was prepared by applying the pattern formation 1 to an optical sheet. The temperature at each location under each condition is as described in Table 1.

The optical sheet of the present invention controls the higher order structure in the solid structure by extruding a resin composition containing a specific aromatic polycarbonate under specific conditions, and optimizes the uneven pattern formed on the surface according to the application By doing so, it is processed into a light guide plate, a diffusion sheet, a retroreflecting plate, or a brightness enhancement prism sheet.

Claims

(A) An aromatic polycarbonate resin composition containing 100 parts by weight of an aromatic polycarbonate having a viscosity average molecular weight of 22,000 or less and (B) 0.01 to 1 part by weight of an antioxidant and containing no blue dye or pigment is an extruder. An optical sheet which is extruded from the above and cooled at a glass transition temperature or lower, wherein the total light transmittance at a thickness of 0.1 to 1 mm of the optical sheet is 91% or more.
2. The optical sheet according to claim 1, wherein the birefringence (phase difference; retardation value at a wavelength of 550 nm) is 150 nm or less, and the standard deviation value of the retardation value at an arbitrary position in the sheet surface is 10 or less.
In a visible-UV spectroscopic spectrum measured with a sample plate thickness of 0.4 mm prepared from an aromatic polycarbonate resin composition used in the optical sheet, a spectral light transmittance of 70% or more at a wavelength of 300 nm or an aromatic polycarbonate is used as a good solvent. The spectroscopic light transmittance (measured by a solution method: the light guide length of the solution cell is 5 cm, the sample solution concentration is 12 g / dl, the solvent is dichloromethane, and the wavelength is 450 nm) is 94% or more as measured by dissolving in an aqueous solution. Optical sheet.
2. The optical sheet according to claim 1, comprising 0.01 to 1 part by mass of (C) a thermoplastic polyacrylic resin with respect to 100 parts by mass of the component (A).
The optical sheet according to claim 1, wherein the antioxidant of the component (B) is a phosphorus-based antioxidant and / or a phenol-based antioxidant.
A molding step of melt-extruding the aromatic polycarbonate resin composition into a sheet, a cooling step of rapidly cooling the melt-extruded sheet-like molded product to a glass transition temperature or lower, and the cooled sheet-like molded product at 50 ° C. or higher, The method for producing an optical sheet according to claim 1, comprising a heat treatment step in which heat treatment is performed at a temperature equal to or lower than a glass transition temperature of the aromatic polycarbonate resin composition.
A molded product obtained by forming an uneven pattern on the surface of the optical sheet according to claim 1.
The molded article according to claim 7, which is any one of a light guide plate, a diffusion sheet, a retroreflector, a prism sheet, and a Fresnel lens sheet.
A method for producing a molded body, comprising forming a concavo-convex pattern on the surface of the optical sheet according to claim 1.