JP5253925B2 - Multilayer optical sheet - Google Patents

Description

  The present invention relates to a multilayer optical sheet used particularly for a light guide plate. More specifically, it is excellent in transparency, light guide, and transferability obtained by extruding a specific thermoplastic resin under specific conditions and controlling the higher order structure and layer structure in the solid structure of the sheet. The present invention relates to a multilayer optical sheet.

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 that is 0.3 mm or less. These thinnings are accompanied by the thinning of the LED light source. On the other hand, a screen size of about 1.8 to 2.8 inches has recently been expanded to 3 to 3.5 inches. Furthermore, the use of LED light sources instead of CCFL light sources is progressing in notebook personal computers, and an attempt has been made to adopt a light guide plate having a thickness of 0.4 to 0.6 mm for a 12-inch class screen size.
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.

  Patent Documents 1 to 5 disclose a polycarbonate resin laminate obtained by laminating an acrylic resin layer on a polycarbonate resin layer, which is excellent in surface hardness, transparency, impact resistance, weather resistance, and the like.

JP-A-2005-219330 Japanese Patent Laid-Open No. 2005-2225018 JP 2006-103169 A JP 2007-160892 A JP 2007-237700 A

However, the present inventors have found that the aromatic polycarbonate used in the inventions described in Patent Documents 1 to 5 is inferior in transparency because the viscosity average molecular weight is too large.
The present invention has been made to solve such problems, and provides a multilayer optical sheet that is excellent in transparency, transferability, punching suitability, etc., and can be applied to a light guide plate that is thin and has a large screen. With the goal.

  The inventors of the present invention have intensively studied to solve such problems, and as a result, an aromatic polycarbonate resin having a specific viscosity molecular weight and a transparent resin having a specific capillary viscosity are used to form layers each having a specific film thickness. The present invention has been completed by finding that the above-mentioned problems can be solved by forming a laminate.

That is, the present invention
1. A multilayer optical sheet having a thickness of 0.1 to 1.1 mm and a total light transmittance of 91.0% or more, comprising a base material layer made of an aromatic polycarbonate resin composition and a surface layer laminated on at least one surface thereof Because
(A) The aromatic polycarbonate resin composition contains 0.01 to 1 part by mass of an antioxidant with respect to 100 parts by mass of the aromatic polycarbonate having a viscosity average molecular weight of 17,000 to 23,000 and 100 parts by mass thereof. And (b) the surface layer has a thickness of 20 to 100 μm, and the transparent resin constituting the surface layer has a capillary viscosity of 300 Pa · s or less measured at a temperature of 280 ° C. and a shear rate of 100 s ^−1. about,
A multilayer optical sheet characterized by
2. The multilayer optical sheet according to 1 above, obtained by coextrusion of the base material layer and the surface layer,
3. The multilayer optical sheet according to 1 or 2, wherein the aromatic polycarbonate resin composition further contains 0.01 to 1 part by mass of a thermoplastic acrylic resin with respect to 100 parts by mass of the aromatic polycarbonate.
4). The multilayer optical sheet according to any one of 1 to 3, wherein the transparent resin is an acrylic resin or an aromatic polycarbonate,
5. 5. The multilayer optical sheet according to any one of 1 to 4 above, wherein a concavo-convex pattern by thermal transfer is formed on the surface layer, and 6. The multilayer optical sheet as described in 5 above, wherein when the concave / convex pattern depth of the transfer mold is 100%, the corresponding height of the concave / convex pattern of the transferred multilayer optical sheet is 90% or more,
Is to provide.

  According to the present invention, it is possible to provide a multilayer optical sheet that is excellent in transparency, transferability, punching suitability, and the like and can be applied to a light guide plate that is thin and has a large screen.

The multilayer optical sheet of the present invention has a base layer composed of an aromatic polycarbonate resin composition and a surface layer laminated on at least one surface thereof, and has a thickness of 0.1 to 1.1 mm and a total light transmittance of 91. 0.0% or more of multilayer optical sheet,
(A) The aromatic polycarbonate resin composition contains 0.01 to 1 part by mass of an antioxidant with respect to 100 parts by mass of the aromatic polycarbonate having a viscosity average molecular weight of 17,000 to 23,000 and 100 parts by mass thereof. And (b) the surface layer has a thickness of 20 to 100 μm, and the transparent resin constituting the surface layer has a capillary viscosity of 300 Pa · s or less measured at a temperature of 280 ° C. and a shear rate of 100 s ^−1. about,
It is characterized by.
Since the multilayer optical sheet of the present invention has a base material layer made of an aromatic polycarbonate resin composition containing an aromatic polycarbonate as a base resin and containing an antioxidant, it is possible to reduce yellowing during sheet molding, In this case, the luminance can be improved.

  In addition, the aromatic polycarbonate resin composition in the present invention has a high transmittance of blue visible light in the vicinity of 380 to 450 nm and a low yellowness as compared with a general aromatic polycarbonate resin. Does not need to contain a blue dye (or pigment) as a material for the base material layer, and therefore there is no reduction in the luminance characteristics of the light guide plate. When a blue dye (or pigment) is contained, the luminance number decreases on the order of 10%, depending on the blending amount.

(Aromatic polycarbonate)
The aromatic polycarbonate may be one having a viscosity average molecular weight of 17,000 to 23,000 from the viewpoint of optical transparency, mechanical strength, and heat resistance. Usually, various aromatic polycarbonates produced by the reaction of a dihydric phenol and a carbonate precursor can be used.

Various divalent phenols may be mentioned, and in particular, 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], bis (4-hydroxyphenyl) methane, 1,1-bis (4- Hydroxyphenyl) ethane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 4,4′-dihydroxydiphenyl, bis (4-hydroxyphenyl) cycloalkane, bis (4-hydroxyphenyl) ether Bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfone, bis (4-hydroxyphenyl) sulfoxide and bis (4-hydroxyphenyl) ketone. These dihydric phenols may be used alone or in combination of two or more.
Particularly preferred dihydric phenols are those based on bis (hydroxyphenyl) alkanes, especially bisphenol A or bisphenol A.

  Examples of the carbonate precursor include carbonyl halide, carbonyl ester, and haloformate, specifically phosgene, dihaloformate of dihydric phenol, diphenyl carbonate, dimethyl carbonate, and diethyl carbonate.

  The aromatic polycarbonate may have a branched structure, and examples of the branching agent include 1,1,1-tris (4-hydroxyphenyl) ethane, α, α ′, α ″ -tris (4- Bidroxyphenyl) -1,3,5-triisopropylbenzene, phloroglysin, trimellitic acid, and isatin bis (o-cresol).

The viscosity average molecular weight of the aromatic polycarbonate is 17,000 to 23,000, preferably 17,000 to 20,000. When the viscosity average molecular weight exceeds 23,000, although depending on the extrusion molding conditions, the base material layer tends to yellow or the retardation value tends to increase.
In addition, a light guide plate is manufactured by forming a fine uneven pattern (prism, dot, dome-shaped convex lens) of several to several hundred μm on the surface of the multilayer optical sheet of the present invention by roll embossing or press forming. However, if the viscosity average molecular weight is 20,000 or less, the thermal transferability at this time is improved. Further, when the viscosity average molecular weight is 17,000 or more, the product strength is improved, and even when the wall thickness is reduced to 0.3 mm or less, the product strength is maintained, and there is a tendency that cracking is difficult.

(Aromatic polycarbonate resin composition)
The aromatic polycarbonate resin composition for forming the base material layer on the multilayer optical sheet of the present invention is 0.01 to 1 part by weight, preferably 0.05 to 0.5 part by weight, with respect to 100 parts by weight of the aromatic polycarbonate. Contains.
Examples of the antioxidant include phosphorus antioxidants and hindered phenol antioxidants.

Examples of phosphorus antioxidants include phosphorous acid, phosphonous acid, phosphonic acid and esters thereof, and tertiary phosphine.
Among these, phosphorous acid, phosphoric acid, phosphonous acid, phosphonic acid, triorganophosphate compound and acid phosphate compound are preferable.
In addition, the organic group in the acid phosphate compound includes any of mono-substituted, di-substituted, and mixtures thereof.
Any of the following exemplified compounds is also included.

Triorganophosphate compounds include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tridecyl phosphate, tridodecyl phosphate, trilauryl phosphate, tristearyl phosphate, tricresyl phosphate, triphenyl phosphate, trichlorophenyl phosphate, diphenyl Examples include cresyl phosphate and tributoxyethyl phosphate.
Among these, trialkyl phosphate is preferable.
The carbon number of the alkyl group in the trialkyl phosphate is preferably 1 to 22, more preferably 1 to 4.
A particularly preferred trialkyl phosphate is trimethyl phosphate.

Examples of the acid phosphate compound include methyl acid phosphate, ethyl acid phosphate, butyl acid phosphate, butoxyethyl acid phosphate, octyl acid phosphate, decyl acid phosphate, lauryl acid phosphate, stearyl acid phosphate, oleyl acid phosphate, behenyl acid phosphate, behenyl acid phosphate Nonylphenyl acid phosphate, cyclohexyl acid phosphate, phenoxyethyl acid phosphate, alkoxy polyethylene glycol acid phosphate, bisphenol A acid phosphate, and the like.
Among these, long-chain dialkyl acid phosphates having 10 or more carbon atoms are effective for improving thermal stability, and the acid phosphate itself is preferable because of high stability.

  Examples of the phosphite compound include triphenyl phosphite, tris (nonylphenyl) phosphite, tridecyl phosphite, trioctyl phosphite, trioctadecyl phosphite, didecyl monophenyl phosphite, dioctyl monophenyl phosphite, diisopropyl Monophenyl phosphite, monobutyl diphenyl phosphite, monodecyl diphenyl phosphite, monooctyl diphenyl phosphite, tris (diethylphenyl) phosphite, tris (di-iso-propylphenyl) phosphite, tris (di-n-butyl) Phenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, tris (2,6-di-trt-butylphenyl) phosphite, distearylpenta Rithritol diphosphite, bis (2,4-ditert-butylphenyl) pentaerythritol diphosphite, bis (2,6-ditert-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2, 6-di-tert-butyl-4-ethylphenyl) pentaerythritol diphosphite, bis {2,4-bis (1-methyl-1-phenylethyl) phenyl} pentaerythritol diphosphite, phenylbisphenol A pentaerythritol diphosphite Examples thereof include phosphite, bis (nonylphenyl) pentaerythritol diphosphite, and dicyclohexyl pentaerythritol diphosphite.

Furthermore, as other phosphite compounds, those that react with dihydric phenols and have a cyclic structure can be used.
For example, 2,2′-methylenebis (4,6-di-tert-butylphenyl) (2,4-di-tert-butylphenyl) phosphite, 2,2′-methylenebis (4,6-di-tert- Butylphenyl) (2-tert-butyl-4-methylphenyl) phosphite and 2,2-methylenebis (4,6-di-tert-butylphenyl) octyl phosphite.

Examples of the phosphonite compound include tetrakis (2,4-di-tert-butylphenyl) -4,4′-biphenylenediphosphonite, tetrakis (2,4-di-tert-butylphenyl) -4,3′-biphenylenedi. Phosphonite, tetrakis (2,4-di-tert-butylphenyl) -3,3′-biphenylenediphosphonite, tetrakis (2,6di-tert-butylphenyl) -4,4′-biphenylenediphosphonite, Tetrakis (2,6-di-tert-butylphenyl) -4,3′-biphenylenediphosphonite, tetrakis (2,6-di-tert-butylphenyl) -3,3′-biphenylenediphosphonite, bis ( 2,4-di-tert-butylphenyl) -4-phenyl-phenylphosphonite, bis (2,4-di-tert Butylphenyl) -3-phenyl-phenylphosphonite, bis (2,6-di-n-butylphenyl) -3-phenyl-phenylphosphonite, bis (2,6-di-tert-butylphenyl) -4- Examples thereof include phenyl-phenylphosphonite, bis (2,6-di-tert-butylphenyl) -3-phenyl-phenylphosphonite, and tetrakis (di-tert-butylphenyl) -biphenylenediphosphonite, bis (di -Tert-butylphenyl) -phenyl-phenylphosphonite, tetrakis (2,4-di-tert-butylphenyl) -biphenylenediphosphonite, bis (2,4-di-tert-butylphenyl) -phenyl- More preferred is phenylphosphonite.
The phosphonite compound is preferable because it can be used in combination with a phosphite compound having an aryl group in which two or more alkyl groups are substituted.

  Examples of phosphonate compounds include dimethyl benzenephosphonate, diethyl benzenephosphonate and dipropyl benzenephosphonate.

The tertiary phosphine includes triethylphosphine, tripropylphosphine, tributylphosphine, trioctylphosphine, triamylphosphine, dimethylphenylphosphine, dibutylphenylphosphine, diphenylmethylphosphine, diphenyloctylphosphine, triphenylphosphine, tri-p-tolyl. Examples include phosphine, trinaphthyl phosphine, and diphenylbenzyl phosphine.
A particularly preferred tertiary phosphine is triphenylphosphine.

Preferred phosphorus antioxidants are triorganophosphate compounds, acid phosphate compounds, and phosphite compounds represented by general formula (1).
Especially, it is preferable to mix | blend a triorganophosphate compound.

（式中、Ｒ及びＲ’は炭素数６〜３０のアルキル基又は炭素数６〜３０のアリール基を表し、互いに同一であっても異なっていてもよい。）

(In the formula, R and R ′ represent an alkyl group having 6 to 30 carbon atoms or an aryl group having 6 to 30 carbon atoms, and may be the same as or different from each other.)

  As described above, the phosphonite compound is preferably tetrakis (2,4-di-tert-butylphenyl) -biphenylenediphosphonite, and the stabilizer containing phosphonite as a main component is Sandostab P-EPQ (trademark, Clariant). And Irgafos P-EPQ (trademark, manufactured by CIBA SPECIALTY CHEMICALS), both of which are available.

  Among the phosphite compounds preferred among the general formula (1), distearyl pentaerythritol diphosphite, bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis (2,6-di) -Tert-butyl-4-methylphenyl) pentaerythritol diphosphite, and bis {2,4-bis (1-methyl-1phenylethyl) phenyl} pentaerythritol diphosphite.

As the hindered phenol antioxidant, various compounds usually blended in the resin can be used.
Examples of the hindered phenol compound include α-tocopherol, butylhydroxytoluene, napyr alcohol, vitamin E, 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-dimethylaminomethyl) ) 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-t) rt-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-6tert-butylphenol), Triethylene glycol bis-3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate, 1,6-hexanediol bis [3- (3,5-di-tert-butyl-4-hydroxy Phenyl) 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 (3,5-di-tert-butyl-4hydroxyphenyl) 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 (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, 3,5-Tris 2 [3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy] ethyl isocyanurate, tetrakis [methylene-3- (3,5-di-tert-butyl-4- Hydroxyphenyl) propionate] methane, 3,9-bis [2- {3- (3-tert-butyl-4-hydroxy-5-methylphenyl) acetyloxy} -1,1-dimethylethyl] -2,4 8,10-tetraoxaspiro [5,5] undecane, tetrakis [methylene-3- (3-tert-butyl-4-hydroxy-5-methyl) Ruphenyl) propionate] methane, 1,3,5-trimethyl-2,4,6-tris (3-tert-butyl-4-hydroxy-5-methylbenzyl) benzene and tris (3-tert-butyl-4-hydroxy And -5-methylbenzyl) isocyanurate.

Among them, tetrakis [methylene-3- (3-tertbutyl-4-hydroxy-5-methylphenyl) propionate] methane, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 3 , 9-bis [2- {3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [ 5,5] Undecane is preferably used.
In particular, 3,9-bis [2- {3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1dimethylethyl] -2,4,8,10-tetraoxa Spiro [5,5] undecane is preferred.
A hindered phenolic antioxidant can be used individually or in combination of 2 or more types.

It is preferable that either a phosphorus-based antioxidant or a hindered phenol-based antioxidant is blended.
Especially, it is preferable to mix | blend phosphorus antioxidant and it is more preferable to mix | blend a triorganophosphate compound.

  Such an aromatic polycarbonate resin composition is further improved in spectral characteristics by adding a trace amount of a thermoplastic acrylic resin to a composition obtained by adding an antioxidant to an aromatic polycarbonate. The compounding amount of the thermoplastic acrylic resin is preferably 0.01 to 1 part by mass and more preferably 0.05 to 0.5 part by mass with respect to 100 parts by mass of the aromatic polycarbonate. When the blending amount of the thermoplastic acrylic resin is 0.01 parts by mass or more, the transparency of the multilayer optical sheet is improved, and when it is 1 part by mass or less, the transparency is maintained without impairing other desired physical properties. be able to.

The thermoplastic acrylic resin is a polymer having a repeating unit of at least one selected from monomer units of acrylic acid, acrylic ester, acrylonitrile and derivatives thereof, and may be a homopolymer or a copolymer with styrene, butadiene, or the like. Good. Specifically, polyacrylic acid, polymethyl methacrylate (PMMA), polyacrylonitrile, ethyl acrylate-acrylic acid-2-chloroethyl copolymer, acrylic acid-n-butyl-acrylonitrile copolymer, acrylonitrile-styrene copolymer Examples thereof include meronitrile, 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 monomers in the presence of a peroxide or azo polymerization initiator are used. preferable.
The thermoplastic acrylic resin preferably has a molecular weight of 200 to 100,000, more preferably 20,000 to 60,000. When the molecular weight is 200,000 to 100,000, phase separation between the aromatic polycarbonate and the thermoplastic acrylic resin does not become too fast at the time of molding, so that sufficient transparency can be obtained in the optical sheet.

(Transparent resin)
As the transparent resin constituting the surface layer (transfer layer) of the multilayer optical sheet of the present invention, those having a capillary viscosity at 280 ° C. and a shear rate of 100 s ⁻¹ of 300 Pa · s or less, preferably 200 Pa · s or less are used. . When the capillary viscosity of the transparent resin exceeds 300 Pa · s, even if a concavo-convex shape is formed on the surface layer using a transfer roll, the concavo-convex shape having a low transfer rate and a sufficient height (depth) cannot be obtained. . As a specific example of the transparent resin, an aromatic polycarbonate or an acrylic resin (including a rubber component copolymer) having a viscosity average molecular weight of 13,000 to 16,000 is preferable, and an acrylic resin (including a rubber component copolymer). Is more preferable. As the aromatic polycarbonate used as the transparent resin, the same ones as described above are used.
As the acrylic resin, a commercially available acrylic resin can be used, and from the viewpoint of transparency and heat resistance, for example, Acrypet manufactured by Mitsubishi Rayon Co., Ltd. or Sumipex manufactured by Sumitomo Chemical Co., Ltd. can be suitably used. Moreover, the defect by the crack at the time of the punching process of the multilayer optical sheet of this invention, a chip, etc. can be reduced by making a surface layer into an impact-resistant acrylic resin. Preferably 2 kJ / m ² or more as impact strength of the transparent resin (JIS K7110), and more preferably 3 kJ / m ² or more. As heat resistance, a load deflection temperature (JIS K7191, load 1.80 MPa) is preferably 80 ° C. or higher, more preferably 90 ° C. or higher.

  The transparent resin constituting these surface layers (transfer layers) may contain an ultraviolet absorber from the viewpoint of improving light resistance in the case of applications such as a Fresnel lens for a sunlight collecting lens.

(Sheet characteristics)
The multilayer optical sheet of the present invention has a thickness of 0.1 to 1.1 mm, preferably 0.2 to 1.0 mm. When the thickness of the multilayer optical sheet is less than 0.1 mm, the strength is remarkably lowered and is easily broken, and when it exceeds 1.1 mm, the light transmittance is lowered.
The total light transmittance of the multilayer optical sheet of the present invention is 91.0% or more. The upper limit of the total light transmittance is not particularly limited, but is usually about 95% from the viewpoint of industrial availability. If the total light transmittance is less than 91.0%, the luminance decreases.
The multilayer optical sheet of the present invention preferably has birefringence (phase difference; retardation value at a wavelength of 550 nm) of 150 nm or less. In general, injection-molded products are cooled in the mold while maintaining the molecular orientation due to shear during injection molding, and the molecular orientation is frozen, which tends to increase residual stress strain. Then, the degree of residual stress strain becomes non-uniform. Usually, the residual stress strain in the peripheral portion of the gate increases, so that the retardation value tends to show a larger measured value. On the other hand, the sheet by extrusion molding can reduce the retardation value depending on the conditions at the time of extrusion molding and the viscosity of the material (depending on the viscosity average molecular weight), 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. When the retardation value is 150 nm or less, the display quality when the liquid crystal panel is mounted is good, preferably 100 nm or less, more preferably 50 nm or less.

(Production method)
As a method for producing the multilayer optical sheet of the present invention by coextruding a base material layer made of an aromatic polycarbonate resin composition and a surface layer made of a transparent resin, the aromatic polycarbonate resin composition, the transparent resin layer, A molding process for melt-extruding the sheet into a sheet, a cooling process for quenching the melt-extruded sheet, and a glass transition of the aromatic polycarbonate resin at 50 ° C. or higher as necessary. The method by the heat processing process heat-processed below temperature is mentioned.
In the cooling step, the sheet-like body can be cooled by passing the sheet-like body through a slit through which cooling water flows. Moreover, the said heat processing process can be implemented by pinching and heating the front and back of the said sheet-like body with the metal endless belt and / or metal roll which have a mirror surface.
As an extrusion molding method, it is possible to produce a multilayer optical sheet that can be used for a light guide plate by selecting molding conditions using a sheet molding machine that is generally equipped with three rolls. However, in the case where extrusion sheet molding is performed using an aromatic polycarbonate resin composition containing 100 parts by weight of an aromatic polycarbonate resin and 0.01 to 1 part by weight of an antioxidant as a raw material, the above-described melt-extruded sheet is used. The cooling step of rapidly cooling the body to the glass transition temperature or lower is important, and it is more efficient to obtain a multilayer optical sheet having higher optical transparency by applying an extrusion molding apparatus having such a cooling step. it can.
It is essential that the cooling temperature is not higher 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 91.0% 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.

In addition, there is no wrinkle by once releasing the residual strain due to the aforementioned rapid cooling process and shaping by a heat treatment step of heat-treating the cooled sheet-like body at 50 ° C. or more and below the glass transition temperature of the polycarbonate resin. A multilayer optical sheet that is uniform, thick, and has a low retardation value can be obtained.
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.

As an elastic roll method, the method currently disclosed by patent publication 2004-155101 is mentioned, for example.
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.

By applying an extrusion molding machine equipped with these production steps, a cooling process from a molten state of an aromatic polycarbonate resin composition containing 100 parts by weight of an aromatic polycarbonate resin and 0.01 to 1 part by weight of an antioxidant. It is possible to suppress the phase separation that occurs in When the phase separation domain exceeds 200 nm, light having a wavelength in the visible light region is scattered, the light guide performance required for the light guide plate is reduced, and useless scattered light is increased, so that the luminance characteristics are deteriorated. The phase separation domain size is preferably less than 200, more preferably 100 nm or less, and still more preferably 50 nm or less.
Such phase separation can be observed by using a transmission electron microscope when the aromatic polycarbonate resin composition contains a thermoplastic acrylic resin, and the aromatic polycarbonate rich phase is a thermoplastic acrylic resin. Compared with the resin-rich phase, observation is possible by contrast generated because it is difficult to be stained with osmic acid.
Usually, in the case of a two-component polymer pair exhibiting a substantially incompatible specific gravity, the blend ratio and the contrast ratio of the phase separation domain are almost the same. For example, if it is 100 parts by weight of an aromatic polycarbonate resin and 0.1 part by weight of a thermoplastic acrylic resin, the morphological image separated into two phases with an area ratio of 1000: 1 can be obtained.

However, in the case of a polymer pair comprising an aromatic polycarbonate resin composition containing 100 parts by weight of an aromatic polycarbonate and 0.01 to 1 part by weight of a thermoplastic acrylic resin, it is known to show semi-compatibility. Therefore, by selecting the molecular weight of the thermoplastic acrylic resin and the freezing conditions at the time of molding, it is possible to control the domain size to a smaller size that does not cause visible light scattering. In this system, it is a spinodal decomposition process (a process in which phase separation proceeds due to concentration fluctuation), which is well-known as a dissipative structure due to self-organization of a nonequilibrium system, and by freezing the structure in the initial state of this fluctuation, An optically transparent optical sheet can be formed. In addition, since the application of extrusion molding does not promote the phase separation by shearing than during injection molding, it is possible to control the size of the micro-phase separation domain that is finer than that, and an optically transparent resin substrate can be formed. Can be obtained.
In the case of this system, compared with the aromatic polycarbonate resin matrix, since it is a system in which a small amount of thermoplastic acrylic resin is blended, the above-mentioned contrast becomes ambiguous in the observation image by the transmission electron microscope, and the concentration is clear. The phase separation domain of the difference is not shown, and a mosaic-like thin cloud of thermoplastic acrylic resin molecules floats in the sea of the aromatic polycarbonate resin matrix, and a phase having a domain size of 100 nm or less is imaged. Observed throughout. That is, the blend ratio and the contrast ratio of the phase separation domain do not match.

The multilayer optical sheet of the present invention obtained by the above characteristics, composition and production can control light distribution by forming fine irregularities on the surface. As the irregular shapes, dot shapes, convex lenses, concave lenses, V Examples thereof include a polygonal prism such as a groove prism, a triangular pyramid, and a quadrangular pyramid.
In the case of the light guide plate, gradation (shading) may be given to the uneven shape.
If it is a normal diffuser sheet or a retroreflector, a uniform pattern may be formed.
Further, in the case of a diffusion sheet used in a direct type backlight, it is possible to make the luminance uniform by forming uneven shapes in the distance between the light source shadow on the light source and the distance between the light sources.
Examples of the method for forming such irregularities include a roll embossing method, a vacuum press molding method, and a belt transfer method. In particular, a die with fine irregularities 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 synchronously transporting a resin film between the upper and lower mold belts. It is preferable to apply an apparatus provided with means for performing each step continuously. In this step, time for evacuation, temperature increase and temperature decrease is not required, and transfer to a large area can be performed 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 multilayer optical sheet before transferring the concavo-convex shape, and the right arrow indicates the multilayer 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 ultraviolet curable resin is pressed against the optical sheet of the present invention using a mold having a fine concavo-convex shape, and a screen printing method using a white ink. Applicable.
A molded body such as a light guide plate can also be manufactured by the method for manufacturing a molded body, wherein the sheet molding and the step of forming irregularities on the surface are performed simultaneously. 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).

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by 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., viscosity average molecular weight: 17,500, capillary viscosity: 280 ° C., 100 s ⁻¹ , 390 Pa · s]
(2) Aromatic polycarbonate (PC2)
Toughlon FN1900A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., viscosity average molecular weight: 19,500, capillary viscosity: 280 ° C., 100 s ⁻¹ , 780 Pa · s]
(3) Aromatic polycarbonate (PC3)
Taflon FN2200A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., viscosity average molecular weight: 22,500, capillary viscosity: 280 ° C., 100 s ⁻¹ , 1300 Pa · s]
(4) Aromatic polycarbonate (PC4)
Taflon FN 1500A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., viscosity average molecular weight: 14,500, capillary viscosity: 280 ° C., 100 s ⁻¹ , 250 Pa · s]
(5) Aromatic polycarbonate (PC5)
Taflon FN2600A [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., viscosity average molecular weight: 26,500, capillary viscosity: 280 ° C., 100 s ⁻¹ , 2500 Pa · s]
(6) Aromatic polycarbonate (PC6)
Taflon FD1400 [bisphenol A polycarbonate resin manufactured by Idemitsu Kosan Co., Ltd., viscosity average molecular weight: 13,000, capillary viscosity: 280 ° C., 100 s ⁻¹ , 150 Pa · s]
(7) Phosphorus antioxidant Adegas tab PEP36 [bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol phosphite manufactured by ADEKA Corporation]
(8) Thermoplastic acrylic resin DIANAR BR83 [Mitsubishi Rayon Co., Ltd., molecular weight: 25,000, refractive index: 1.490, molecular weight: intrinsic viscosity [η] of chloroform solution at 25 ° C. using an Ostwald type viscosity tube 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)]
(9) Acrylic resin (PMMA1)
Acrypet IR S404 [Mitsubishi Rayon Co., Ltd., capillary viscosity: 280 ° C., 100 s ⁻¹ , 200 Pa · s]
(10) Acrylic resin (PMMA2)
Acrypet IR H30 [Made by Mitsubishi Rayon Co., Ltd .: 280 ° C., 100 s ⁻¹ , 450 Pa · s]

<Multilayer optical sheet extrusion>
A multilayer optical sheet was produced by an extruder provided with the apparatus shown in FIG. An extruder 21 having a screw diameter of 65 mm, a T-shaped die having a width of 650 mm, and a first pinching roll 22 having a diameter of 300 mm were 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 rolls 26a, 26b, and 26c, three metal rolls having a diameter of 70 mm are arranged in a straight line. The total distance between the first transfer roll 26a and the final transfer roll 26c was 3 m.

<Evaluation method>
(1) Total light transmittance It measured based on JIS-K-7105 using the Suga Test Instruments Co., Ltd. haze meter (HGM-2DP).
(2) Transfer rate The transfer rates shown below were measured for the optical sheets obtained in Examples 1 to 8 and Comparative Examples 1 to 6.
Transfer rate (%) = [Average height of triangular pyramid of transferred optical sheet (μm) / Average depth of triangular pyramid on stamper (50 μm)] × 100
(3) Punching property When a 3 inch (7.62 cm) light guide plate was punched with a Thomson blade at a press pressure of 100 kg / cm ² , the presence or absence of cracks at the ends, whiskers, and chips were visually determined. . Judgment criteria are shown below.
○: No problem ×: Edge crack

Example 1
Phosphorous antioxidant PEP36 (manufactured by ADEKA Co., Ltd.) was added to the aromatic polycarbonate (PC1) at the ratio shown in Table 1, and melt kneaded at 260 ° C. to obtain a base material layer material. Similarly, phosphorus antioxidant (PEP36) and thermoplastic polyacrylic resin (BR83) were added to the aromatic polycarbonate (PC4) in the proportions shown in Table 1, and melt-kneaded at 260 ° C. to obtain surface layer materials. Using the main 65 mmφ and sub 25 mmφ of a single screw extruder manufactured by HITZ Industrial Machine Techno, these materials were extruded with a base layer and a surface layer resin, respectively, cooled and solidified with three horizontal rolls, and each of the base layer and the surface layer was 350, A two-type two-layer optical sheet having a thickness of 50 μm was obtained. During roll cooling, the triangular pyramid prism shape with an average depth of 50 μm formed on the second roll was transferred to the surface layer. A punching test was performed on the sheet after transfer to determine the punching suitability.

Example 2
A multilayer optical sheet was prepared in the same manner as in Example 1 except that a thermoplastic polyacrylic resin (BR83) was added to PC1 to obtain a base material, and the total light transmittance, transfer rate, and punchability were evaluated. .

Example 3
A multilayer optical sheet was prepared in the same manner as in Example 2 except that the substrate layer material was obtained using PC2 instead of PC1, and the total light transmittance, transfer rate, and punchability were evaluated.

Example 4
A multilayer optical sheet was produced in the same manner as in Example 2 except that the base material layer material was obtained using PC3 instead of PC1, and the total light transmittance, transfer rate, and punchability were evaluated.

Example 5
A multilayer optical sheet was prepared in the same manner as in Example 2 except that the thickness of the base layer was 900 μm and the thickness of the surface layer was 100 μm, and the total light transmittance, transfer rate, and punchability were evaluated.

Example 6
A multilayer optical sheet was produced in the same manner as in Example 1 except that acrylic resin Acrypet IR S404 manufactured by Mitsubishi Rayon was used as the surface layer material, and the total light transmittance, transfer rate, and punchability were evaluated.

Example 7
A multilayer optical sheet was prepared in the same manner as in Example 1 except that the surface layer material was obtained using aromatic polycarbonate (PC6) instead of PC4, and the total light transmittance, transfer rate and punchability were evaluated.

Example 8
In the same manner as in Example 1, except that the thickness of the base material layer was set to 300 μm, and a surface layer having a thickness of 50 μm was provided on both surfaces of the base material layer using acrylic resin Acrypet IR S404 manufactured by Mitsubishi Rayon. A multilayer optical sheet of layers was prepared, and the total light transmittance, transfer rate, and punchability were evaluated.

Comparative Example 1
Phosphorous antioxidant (PEP36) and thermoplastic polyacrylic resin (BR83) were added to the aromatic polycarbonate (PC1) in the proportions shown in Table 1, and melt-kneaded at 260 ° C. This material was extruded using a 65 mmφ single screw extruder manufactured by HITZ Industrial Machine Techno, and cooled and solidified with three horizontal rolls to obtain an optical sheet having a thickness of 350 μm. During roll cooling, the triangular pyramid prism shape having a depth of 50 μm formed on the second roll was transferred. The single-layer optical sheet after transfer was evaluated for total light transmittance, transfer rate, and punchability.

Comparative Example 2
An optical sheet was prepared in the same manner as in Example 2 except that acrylic resin (PMMA2) was used as the surface layer material, and the total light transmittance, transfer rate, and punchability were evaluated.

Comparative Example 3
A base sheet material was obtained using PC4 instead of PC1, and an optical sheet was prepared in the same manner as in Example 2 except that acrylic resin (PMMA1) was used as the surface layer material. And the punchability was evaluated.

Comparative Example 4
An optical sheet was prepared in the same manner as in Comparative Example 3 except that PC5 was used instead of PC4, and the total light transmittance, transfer rate, and punchability were evaluated.

Comparative Example 5
An optical sheet was prepared in the same manner as in Comparative Example 2 except that the thickness of the base layer was 45 μm, the thickness of the surface layer was 5 μm, the total thickness was 50 μm, and acrylic resin (PMMA1) was used as the surface layer material. The transmittance, transfer rate and punchability were evaluated.

Comparative Example 6
An optical sheet was prepared in the same manner as in Comparative Example 2 except that the thickness of the base layer was 1080 μm, the thickness of the surface layer was 120 μm, the total thickness was 1200 μm, and acrylic resin (PMMA1) was used as the surface layer material. The transmittance, transfer rate and punchability were evaluated.
Table 1 shows the mixing ratio of the base material and the surface material, the thickness of the base material and the surface layer, the molding conditions, and the optical sheet characteristics in Examples 1 to 8 and Comparative Examples 1 to 6.

  Since the multilayer optical sheet of the present invention is excellent in high optical transparency (light guide property, color tone), birefringence, and transferability, the optical material for the light guide plate of a thin backlight having an LED as a light source and a thickness of 1 mm or less. It is useful as a sheet and a molded body (light guide plate). In addition, by optimizing the concavo-convex pattern formed on the surface according to the application, it is suitable as a base material for retroreflective sheets, diffusion sheets, and brightness enhancement prism sheets.

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

Claims (6)

A multilayer optical sheet having a thickness of 0.1 to 1.1 mm and a total light transmittance of 91.0% or more, comprising a base material layer made of an aromatic polycarbonate resin composition and a surface layer laminated on at least one surface thereof Because
(A) An aromatic polycarbonate resin composition having a viscosity average molecular weight of 17,000 to 23,000, a capillary viscosity of 390 to 1300 Pa · s measured under conditions of a temperature of 280 ° C. and a shear rate of 100 s ⁻¹ And 100 parts by mass of the antioxidant, 0.01 to 1 part by mass of the antioxidant, and (b) the surface layer has a thickness of 20 to 100 μm and the transparent resin constituting the surface layer The capillary viscosity measured under the conditions of a temperature of 280 ° C. and a shear rate of 100 s ⁻¹ is 300 Pa · s or less,
A multilayer optical sheet characterized by   The multilayer optical sheet according to claim 1, obtained by coextrusion of the base material layer and the surface layer.   The multilayer optical sheet according to claim 1 or 2, wherein the aromatic polycarbonate resin composition further contains 0.01 to 1 part by mass of a thermoplastic acrylic resin with respect to 100 parts by mass of the aromatic polycarbonate.   The multilayer optical sheet according to claim 1, wherein the transparent resin is an acrylic resin or an aromatic polycarbonate.   The multilayer optical sheet according to claim 1, wherein a concavo-convex pattern is formed on the surface layer by thermal transfer.   6. The multilayer optical sheet according to claim 5, wherein when the uneven pattern depth of the transfer mold is 100%, the corresponding height of the uneven pattern of the transferred multilayer optical sheet is 90% or more.

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