JP2008003358A - Method for producing optical film, optical film and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical film having excellent transparency, and having extremely low controlled birefringence. <P>SOLUTION: The method for producing the optical film includes: a kneading step of kneading inorganic grains and a high polymer resin; and an orienting step of orienting the high polymer resin comprising the inorganic grains obtained by the kneading step. Also, the method is characterized in that the inorganic grains are needle-shaped or bar-shaped grains having optical anisotropy, and the kneading step is performed in a state where carbon dioxide is incorporated into the high polymer resin. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an optical film, and more particularly to a method for producing an optical film having excellent transparency and improved birefringence, and an optical film produced by this production method. Further, the present invention relates to an optical element using the optical film having improved birefringence.

  In recent years, as a material of optical parts for optoelectronics as well as general optical parts such as eyeglass lenses and transparent plates due to its light weight, strong impact resistance, workability, mass productivity, etc., it has become a conventional glass-based material Instead, there is an increasing tendency to use polymer resins.

  Liquid crystal displays are also widely used. In addition, with the expansion of applications, further weight reduction and thickness reduction and further improvement in performance in terms of strength such as impact resistance have been demanded. Thus, in recent years, a tendency to use a polymer resin as a material for an optical film has been increasing.

  Expectations for polymer resins are increasing, but at present, there are problems to be solved such as dimensional stability, coefficient of linear expansion, rigidity, birefringence, and the like, which has hindered widespread use.

  In many polymer resin materials usually used as optical materials, the monomer forming the polymer has an optical anisotropy with respect to the refractive index, and the optical anisotropy of the monomer in a certain direction of the polymer. Birefringence is produced in the polymer resin material by being expressed by the arrangement or orientation. More specifically, in the polymer as it is generated by the polymerization reaction, the bond chains are intertwined at random, and the polymer bond chains are not oriented. The anisotropy cancels each other, so the polymer does not exhibit birefringence, but when the stretching operation is performed during film formation, random polymer bond chains are oriented due to the external force applied at this time. The polymer exhibits birefringence (orientation birefringence).

  On the other hand, inorganic materials often exhibit much larger birefringence than organic compounds, and do not produce birefringence when oriented like polymers, but have birefringence due to the original crystal structure. ing. In particular, birefringence occurs when the system has non-uniformity significantly smaller than the wavelength of light, such as inorganic fine particles (structural birefringence). In particular, long and narrow particles such as needles are oriented in one direction inside the matrix. When mixed in such a state, large structural birefringence is exhibited.

  In order to solve the above problems, a technique for mixing inorganic fine particles in a polymer resin has been studied. In particular, in order to improve the birefringence of the optical film, studies on techniques for mixing inorganic fine particles in a polymer resin are active.

  Patent Document 1 discloses an optical resin material in which birefringence is reduced by performing an alignment process in a state in which molecular alignment suppression particles having a size smaller than the wavelength of light to be used are mixed in a transparent polymer resin material. Disclosed to obtain. In this technique, the birefringence developed by the alignment treatment is reduced by suppressing the degree of alignment generated in the polymer chain of the polymer resin material due to the presence of the molecular alignment suppressing granules.

  Patent Document 2 discloses a technique for obtaining an optical resin material having reduced orientation birefringence by adding an inorganic substance having birefringence that cancels the orientation birefringence of the polymer resin to a transparent polymer resin. It is disclosed. The inorganic substance added here has the property that it is aligned in the same direction as the alignment direction of the bonding chain as the bonding chain is aligned by external force during molding of the polymer resin, and such alignment in the same direction. Those having birefringence that can cancel the orientation birefringence of the polymer resin are selected.

  In the techniques described in Patent Document 1 and Patent Document 2, the dispersibility of the particles in the resin is poor and the orientation state of the particles is not good, so that a sufficient birefringence reduction effect cannot be obtained.

On the other hand, Patent Documents 3 and 4 disclose techniques in which carbon dioxide is impregnated to increase the plasticity of the resin and increase the dispersibility of the fine particles. However, these techniques are for molding processes. This technique is completely different from an optical film made of a polymer resin containing needle-like or rod-like inorganic particles having optical anisotropy as in the present invention.
JP 2001-208901 A WO 01/25364 pamphlet Japanese Patent Laid-Open No. 2000-53871 JP 2004-307720 A

  The present invention seeks to solve the problems that could not be sufficiently achieved by the prior art as described above, and the object of the present invention is to have excellent transparency and control the birefringence very low. It is providing the manufacturing method of an optical film, the optical film manufactured by this manufacturing method, and also the optical element using this optical film.

  The above object of the present invention can be achieved by the following means.

  That is, the method for producing an optical film of the present invention includes a kneading step of kneading inorganic particles and a polymer resin, and a stretching step of stretching the polymer resin containing the inorganic particles obtained by the kneading step. In the method for producing an optical film, the inorganic particles are needle-like or rod-like inorganic particles having optical anisotropy, and the kneading step is performed in a state where carbon dioxide is contained in the polymer resin. To do.

  According to the present invention, as the inorganic particles to be contained in the polymer resin, needle-like or rod-like inorganic particles having optical anisotropy are used, so that the orientation birefringence of the polymer resin can be reduced. In addition, since the present invention performs the kneading step in a state where carbon dioxide is contained in the polymer resin, the stretching step is also performed in a state where carbon dioxide is contained in the polymer resin. The mobility of the needle-like or rod-like inorganic particles having optical anisotropy in the polymer resin is increased, and the dispersibility and the orientation with respect to the polymer resin are remarkably improved. As a result, according to the present invention, an optical film having excellent properties with high transparency and reduced birefringence can be obtained.

  Hereinafter, the present invention will be described in detail.

1. Polymer resin The polymer resin used in the method for producing an optical film of the present invention is not particularly limited as long as it is a highly transparent resin generally used as an optical material. In addition, from the viewpoints of heat resistance and processability, acrylic resins, polycarbonate resins, polyester resins, polyether resins, polyamide resins, polyimide resins, alicyclic polyolefin resins, and cellulose ester resins are preferable. Furthermore, alicyclic polyolefin resins and cellulose ester resins are more preferred because of their low water absorption and excellent transparency.

  Examples of the alicyclic polyolefin resin include norbornene resins, cyclohexadiene polymers, and olefin maleimide alternating copolymers.

  Examples of the norbornene resin include a ring-opening polymer of a norbornene monomer and a hydrogenated product thereof, an addition polymer of a norbornene monomer, an addition polymer of a norbornene monomer and an olefin, and the like. .

  For example, as a polymer resin used for an application that may be exposed to a high temperature in a manufacturing process such as a substrate for a TFT liquid crystal display device, a heat-resistant addition polymer of a norbornene monomer is preferable.

  Norbornene monomers include norbornene, alkyl-substituted derivatives of norbornene, alkylidene-substituted derivatives of norbornene, aromatic-substituted derivatives of norbornene, and halogen, hydroxyl group, ester group, alkoxy group, cyano group, amide group, imide group And a substituted product substituted with a polar group such as a silyl group. For example, 2-norbornene, 5-methyl-2-norbornene, 5,5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, 5- Methoxycarbonyl-2-norbornene, 5-cyano-2-norbornene, 5-methyl-5-methoxycarbonyl-2-norbornene, 5-phenyl-2-norbornene, 5-phenyl-5-methyl-2-norbornene and the like It is done. In addition, a monomer obtained by adding one or more cyclopentadiene to norbornene, a derivative or a substitute similar to the above, for example, 1,4: 5,8-dimethano-1,2,3,4,4a, 5 , 8,8a-2,3-cyclopentadienonaphthalene, 6-methyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 1, 4,5,10: 6,9-trimethano-1,2,3,4,4a, 5,5a, 6,9,9a, 10,10a-dodecahydro-2,3-cyclopentadienoanthracene and the like. Can be mentioned. Furthermore, the monomer of the polycyclic structure which is a multimer of cyclopentadiene, its derivatives and substitutes similar to the above, for example, dicyclopentadiene, 2,3-dihydrodicyclopentadiene and the like can be mentioned. Further, adducts of cyclopentadiene and tetrahydroindene and the like derivatives and substitutes thereof, for example, 1,4-methano-1,4,4a, 4b, 5,8,8a, 9a-octahydrofluorene 5,8-methano-1,2,3,4,4a, 5,8,8a-octahydro-2,3-cyclopentadienonaphthalene and the like.

  The cellulose ester resin is preferably at least one selected from cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and cellulose phthalate.

  As the substitution degree of the mixed fatty acid ester, more preferred cellulose acetate propionate and lower fatty acid ester of cellulose acetate butyrate have an acyl group having 2 to 4 carbon atoms as a substituent, and the substitution degree of the acetyl group is X, When the substitution degree of propionyl group or butyryl group is Y, it is a cellulose resin containing a cellulose ester that simultaneously satisfies the following formulas (I) and (II). In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are determined by ASTM-D817-96.

Formula (I) 2.5 ≦ X + Y ≦ 2.9
Formula (II) 0.1 ≦ X ≦ 2.0
Of these, cellulose acetate propionate is particularly preferably used. Among them, 1.0 ≦ X ≦ 2.5 and 0.5 ≦ Y ≦ 2.5 are preferable. Cellulose esters having different degrees of substitution of acyl groups may be blended so that the entire optical film falls within the above range. The part not substituted with the acyl group is usually present as a hydroxyl group. These can be synthesized by known methods. The measuring method of the substitution degree of an acetyl group can be measured according to ASTM-D817-96.

2. Inorganic particles The inorganic particles according to the present invention are acicular or rod-like inorganic particles having optical anisotropy. The acicular or rod-like inorganic particles having optical anisotropy are preferably those having birefringence.

There is no restriction | limiting in particular as a raw material of an inorganic particle, For example, all kinds of well-known inorganic particles, such as various metals, a metal oxide, carbonate, borate, a glass composition, and those mixtures or composite fine particles, should be used. Is possible. Specifically, silica, alumina, titania, zirconia, ceria, zinc oxide, cobalt oxide, iron oxide, YVO ₄ , LiNbO ₄ , PbMoO ₄ , MgCO ₃ , CaCO ₃ , SrCO ₃ , BaCO ₃ , MnCO ₃ , CoCO ₃ , ZnCO ₃ , BaB ₂ O _{4 and the} like.

  The inorganic particles need to be aligned in a state in which the axial direction of the inorganic particles is parallel to the bond chains as the polymer bond chains are aligned. This orientation can be caused by, for example, an external molding force that causes the orientation of the bonding chain in the polymer. From this, the shape of the inorganic particles is rod-like or needle-like, and the aspect ratio between the axial length (major axis diameter) and the diameter perpendicular to the axial direction (minor axis system) is 1.5 or more. Preferably, it is preferably 2 or more, more preferably 3 or more. The upper limit is not particularly limited, but is about 10 in general.

  In addition, “the axial direction of the inorganic fine particles is aligned in parallel with the bonding chain along with the alignment of the polymer bonding chain” means that the axial direction of all the inorganic particles is not necessarily aligned in parallel with the bonding chain of the polymer. It does not mean that, from a statistical point of view, it includes that there are a large number of inorganic particles whose axial directions are oriented in parallel. The crystal structure of the inorganic particles preferably has a crystal structure belonging to a tetragonal system, a trigonal system, a hexagonal system, an orthorhombic system, a monoclinic system, or a triclinic system. Further, not only these single crystal structures but also polycrystals or aggregates thereof may be used.

  In general, the average particle size of the inorganic particles is preferably about a wavelength or less, more preferably 200 nm or less, and particularly preferably 100 nm or less in order to keep light scattering low. In addition, even if the average particle size is controlled to be small, if coarse particles are mixed, the influence of light scattering increases, so the proportion of particles having a particle size of 300 nm or more is 30% by number or less. Is preferable, and it is more preferable that it is 10 number% or less. Here, the particle diameter refers to the major axis diameter of needle-like or rod-like inorganic particles, and the average particle diameter is an average value thereof.

  There is no limitation in particular as a manufacturing method of the inorganic particle used by this invention, It is possible to apply all the well-known manufacturing methods. Since it is preferable to use inorganic particles having a narrow particle size distribution, it is preferable to produce them by a liquid phase method such as a reaction crystallization method or a sol-gel method.

  The inorganic particles of the present invention may have a silica layer formed on the surface thereof, and the surface of the silica layer may be subjected to a hydrophobic treatment. As a treating agent for forming a silica layer on the surface of inorganic particles, a known treating agent that forms a layer of a compound containing silicon such as a trifunctional silane coupling agent, a tetrafunctional silane coupling agent, or polysilazane. Can be used. Specifically, polysilazane, methyltrimethoxysilane, tetramethoxysilane, and tetraethoxysilane are preferably used, and polysilazane is particularly preferably used from the viewpoint of the speed of forming the silica layer and the denseness of the silica layer.

  The content of the inorganic particles dispersed in the polymer resin is preferably 5 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the polymer resin. If the content of the inorganic particles is 10 parts by mass or more, the birefringence reduction effect can be exhibited, and if it is 80 parts by mass or less, the properties such as processability which are the advantages of the original polymer resin are obtained. It will not be damaged.

3. Additives In the optical film production process and molding process, various additives (hereinafter also referred to as compounding agents) can be added as necessary. Although there is no limitation in particular about an additive, Mainly a plasticizer, antioxidant, a light-resistant stabilizer, etc. are mentioned. In addition, heat stabilizers, weathering stabilizers, UV absorbers, stabilizers such as near infrared absorbers, resin modifiers such as lubricants, soft polymers, anti-clouding agents such as alcoholic compounds, dyes and pigments And other colorants, antistatic agents, flame retardants, fillers and the like. These compounding agents can be used alone or in combination of two or more thereof, and the compounding amount thereof is appropriately selected within a range not impairing the effects described in the present invention. In particular, at least a plasticizer or an antioxidant is preferably contained.

(3-1) Plasticizer The plasticizer is not particularly limited, but is a phosphate ester plasticizer, a phthalate ester plasticizer, a trimellitic ester plasticizer, a pyromellitic acid plasticizer, Examples include glycolate plasticizers, citrate ester plasticizers, and polyester plasticizers.

  The plasticizers can be used alone or in combination of two or more. The blending amount is appropriately selected within a range not impairing the object of the present invention.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like. Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl benzyl phthalate, diphenyl phthalate, and dicyclohexyl phthalate. Examples of trimellitic acid plasticizers include tributyl trimellitate, triphenyl trimellitate, and triethyl trimellitate. Examples of the pyromellitic acid ester plasticizer include tetrabutyl pyromellitate, tetraphenyl pyromellitate, and tetraethyl pyromellitate. Examples of glycolate plasticizers include triacetin, tributyrin, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, and butyl phthalyl butyl glycolate. Examples of the citrate plasticizer include triethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, and acetyl tri-n- (2-ethylhexyl) citrate. .

(3-2) Antioxidants Examples of antioxidants include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, etc. Among them, phenolic antioxidants, particularly alkyl-substituted phenolic compounds. Antioxidants are preferred. By blending these antioxidants, coloring and strength reduction due to oxidative degradation during molding can be prevented without reducing transparency, heat resistance, and the like.

  Antioxidants can be used alone or in combination of two or more. The blending amount is appropriately selected within a range not impairing the object of the present invention, but is preferably in the range of 0.001 to 5 parts by mass with respect to 100 parts by mass of the polymer resin, and 0.01 to 1 More preferably, it is in the range of parts by mass.

  A conventionally well-known thing is applicable as a phenolic antioxidant, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds, octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis (4-methyl-6-t-butylphenol) ), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di) t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenylpropionate)) methane [i.e. pentaerythrimethyl-tetrakis ( 3- (3,5-di-t-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate) and the like Alkyl substituted phenol compounds, 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio-1,3 5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3,5-triazine, etc. Triazine group-containing phenol compounds, and the like.

  Phosphorus antioxidants include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t -Butylphenyl) phosphite, monophosphite such as 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide Compounds, 4,4'-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl phosphite), 4,4'-isopropylidene-bis (phenyl-di-alkyl (C12-C15) And diphosphite compounds such as) phosphite). Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

  Sulfur-based antioxidants include dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3-thiodipropionate Pentaerythritol-tetrakis- (β-lauryl-thio-propionate), 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane and the like. .

(3-3) Light-resistant stabilizer Examples of the light-resistant stabilizer include benzophenone-based light-resistant stabilizers, benzotriazole-based light-resistant stabilizers, and hindered amine-based light-resistant stabilizers. In the present invention, it is preferable to use a hindered amine light resistance stabilizer from the viewpoints of transparency, color resistance and the like. Among hindered amine light-resistant stabilizers (hereinafter referred to as HALS), those having a molecular weight Mn in terms of polystyrene by liquid chromatography using tetrahydrofuran as a solvent are preferably 1,000 to 10,000, and preferably 2,000 to 5,000. Some are more preferred, with 2,800-3,800 being particularly preferred. When Mn is too small, when HALS is blended by heating and kneading into a block copolymer, a predetermined amount cannot be blended due to volatilization, or foaming or silver streak occurs during heat melting molding such as injection molding. This is because there arises a problem that the stability is lowered.

  The HALS mentioned above includes N, N ′, N ″, N ′ ″-tetrakis- [4,6-bis- {butyl- (N-methyl-2,2,6,6-tetramethylpiperidin-4-yl]. ) Amino} -triazin-2-yl] -4,7-diazadecane-1,10-diamine, dibutylamine and 1,3,5-triazine, N, N'-bis (2,2,6,6- Polycondensate with tetramethyl-4-piperidyl) butylamine, poly [{(1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2, 2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}], 1,6-hexanediamine-N, N′- Bis (2,2,6,6-tetramethyl-4-pipe Di) and morpholine-2,4,6-trichloro-1,3,5-triazine, poly [(6-morpholino-s-triazine-2,4-diyl) (2,2, 6,6, -tetramethyl-4-piperidyl) imino] -hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino] and other piperidine rings are bonded via a lyazine skeleton. Molecular weight HALS; polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, 1,2,3,4-butanetetracarboxylic acid, 1,2,2 , 6,6-pentamethyl-4-piperidinol and 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane S Piperidine ring, such as Le compound is bound high molecular weight HALS, and the like via an ester bond.

  Among these, a polycondensate of dibutylamine, 1,3,5-triazine and N, N′-bis (2,2,6,6-tetramethyl-4-piperidyl) butylamine, poly [{(1 , 1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {( 2,2,6,6-tetramethyl-4-piperidyl) imino}], dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, etc. Is preferably in the range of 2,000 to 5,000.

  The blending amount of the light-resistant stabilizer is preferably in the range of 0.01 to 20 parts by mass, more preferably in the range of 0.02 to 15 parts by mass with respect to 100 parts by mass of the polymer resin. 0.05 to 10 parts by mass is particularly preferable. This is because if the addition amount is too small, the effect of improving the light resistance cannot be sufficiently obtained, and particularly when used as a substrate of an image display device, coloring occurs due to irradiation of a backlight, for example, and the blending amount of HALS If the amount is too large, a part of the gas is generated as a gas, and the dispersibility in the polymer resin is lowered, so that the transparency of the substrate is lowered.

  Moreover, it is preferable to mix | blend the compound whose lowest glass transition temperature is 30 degrees C or less. This is because white turbidity in a high temperature and high humidity environment for a long time can be prevented without degrading various properties such as transparency, heat resistance and mechanical strength.

4). Carbon dioxide In the present invention, when the inorganic particles and the polymer resin are kneaded in the kneading step, carbon dioxide is contained.

  Carbon dioxide dissolves in the polymer resin under high pressure conditions, but Henry's law is established in which the pressure and the amount of dissolution are proportional up to a pressure of about 20 MPa. In the present invention, carbon dioxide can be contained in the polymer resin by bringing carbon dioxide in a high pressure state of 2 to 10 MPa or carbon dioxide in a supercritical fluid into contact with the molten polymer resin and mixing. it can.

  Examples of the apparatus that can be used for mixing include a closed apparatus such as a lab plast mill, a Banbury mixer, a kneader, and a roll, and a batch apparatus. Further, mixing and kneading can be performed simultaneously by using a continuous melt kneader such as a single screw extruder or a twin screw extruder.

  In the present invention, the content of carbon dioxide in the polymer resin is important. If the content of carbon dioxide is small, the improvement effect is small, and if the content of carbon dioxide is large, the polymer resin is used as a film. It is not preferable because it may foam. The content of carbon dioxide in the polymer resin is generally from 0.5% by mass to 5% by mass, preferably from 0.5% by mass to 3.0% by mass, more preferably from 0% by mass, based on the polymer resin. 0.5 mass% to 2.5 mass%.

  Carbon dioxide may be in a supercritical fluid state. The supercritical fluid here refers to a fluid having an intermediate property between a gas and a liquid at a critical temperature or higher and a critical pressure or higher.

5. Kneading step In the kneading step of kneading the polymer resin and the inorganic particles, the polymer resin containing carbon dioxide and the inorganic particles may be added and kneaded all at once, or added in stages and kneaded. Also good. In the case where the addition is performed in stages, in a melt-kneading apparatus such as an extruder, it is also possible to add the components to be added in stages from the middle of the cylinder. Also, after kneading the polymer resin and the inorganic particles in advance, when adding other components that were not previously added as components other than the polymer resin and further melt-kneading them, these may be added all at once and kneaded. Alternatively, it may be added in stages and kneaded. As a method of adding in divided portions, a method of adding one component in several times, a method of adding one component at a time and adding other components in a stepwise manner, or a method in which these are combined is used. it can.

  In addition, the inorganic particles may be added in a powder or agglomerated state, or may be added in a dispersed state in the liquid. However, when adding inorganic particles in a state dispersed in a liquid, it is preferable to perform deaeration after kneading. Moreover, when adding in the state disperse | distributed in the liquid, it is preferable to disperse | distribute agglomerated particle | grains to a primary particle beforehand, and to add. Various types of dispersers can be used for dispersing the aggregated particles, but a bead mill is particularly preferable. There are various kinds of beads in the bead mill, but the size is preferably 1 mm or less, more preferably 0.1 mm or less and 0.001 mm or more.

  Also, polymer resin powders or pellets containing inorganic compounds that are the raw materials for optical films are hot-air dried or vacuum dried, then heated and melted with optical film components such as plasticizers, antioxidants, and light stabilizers. It is also possible to enter the kneading step after mixing while contacting with carbon dioxide to contain carbon dioxide in the polymer resin.

  In the present invention, the introduction timing of carbon dioxide in the kneading step may be any time before or during melt kneading.

  The specific procedure of the kneading step is preferably one of the following two.

  One is a procedure in which a polymer resin and carbon dioxide are brought into contact and mixed before melt-kneading, carbon dioxide is contained in the polymer resin, and then inorganic particles and the polymer resin are kneaded. The other is a procedure in which carbon dioxide is brought into contact with a mixture of a polymer resin and inorganic particles and mixed, and carbon dioxide is contained in a polymer resin containing inorganic particles and kneaded.

  According to the latter procedure, carbon dioxide is contained in the plasticized polymer resin, so that the viscosity of the kneaded product can be reduced. When this procedure is used, carbon dioxide can be directly introduced into the polymer resin in the kneading apparatus.

  Prior to the kneading step, it is preferable to remove in advance the gas adsorbed on the polymer resin or inorganic particles. When inorganic particles are used as a dispersion for kneading, it is preferable to remove dissolved oxygen.

6). Forming method of optical film The forming method of the optical film of the present invention is not particularly limited, and a known method of forming a resin film can be used as appropriate. For example, extrusion molding that extrudes into a film using a die coater. Various methods such as a method (melt film forming method) can be given.

  In order to obtain a film excellent in characteristics such as low birefringence, mechanical strength, and dimensional accuracy, a melt film forming method is preferable. The melting temperature during the melt film formation is preferably in the range of 120 ° C to 280 ° C, more preferably 200 ° C to 250 ° C.

  For example, it is extruded into a film form from a T-die, and is brought into close contact with a cooling drum or an endless belt by an electrostatic application method or the like, and is cooled and solidified to obtain an unstretched film. The temperature of the cooling drum is preferably maintained at 90 to 150 ° C.

  The unstretched film obtained by peeling from the cooling drum may be reheated through one or a plurality of roll groups and / or a heating device such as an infrared heater, and cooled after being stretched in one or more stages in the longitudinal direction. preferable.

  The draw ratio is usually 1.1 to 10 times, preferably 1.1 to 4 times, and the draw temperature is (Tg-30) to (Tg + 100) ° C., where Tg is the glass transition temperature of the optical film of the present invention. More preferably, it is preferably heated in the range of (Tg−20) to (Tg + 80) ° C. and stretched in the transport direction (longitudinal direction; MD) or the width direction (TD). It is preferable to perform transverse stretching within the temperature range of (Tg-20) to (Tg + 20) ° C. and then heat-set.

  The stretching method is not particularly limited, but a known pin tenter or clip type tenter can be preferably used.

  It is also preferable to perform relaxation treatment after the stretching step. Moreover, after forming a film, you may perform the process which improves the smoothness of a surface, such as giving a smoothing coating to the surface.

The optical film obtained by the production method of the present invention preferably has a linear expansion coefficient at 25 ° C. to 160 ° C. of 5.00 × 10 ⁻⁵ / ° C. or less, preferably 4.00 × 10 ⁻⁵ / ° C. or less. More preferably, it is 3.00 × 10 ⁻⁵ / ° C. or less. The linear expansion coefficient is measured by, for example, the TMA method described in JIS standard K-7197, and can be calculated from the following formula 1. In formula _{1, △ Is (T 1)} , △ Is (T 2) each represent the temperature T ₁ of the at sample measurement (℃) and T ₂ TMA measurement at (℃) a (μm), L ₀ is The length (mm) of the sample at room temperature.

  The surface roughness of the optical film obtained by the production method of the present invention is preferably 1000 nm or less, more preferably 500 nm or less, and particularly preferably 200 nm or less. When the film becomes rougher than this, for example, when it is used as a substrate for a liquid crystal display element, thickness unevenness occurs in a liquid crystal portion in contact with the film, which may cause a problem of display failure.

  The optical film obtained by the production method of the present invention is a gas barrier layer, a hard coat layer, an anti-curl layer, a conductive film layer, or an adhesive layer for increasing the adhesion between each layer, if necessary in various applications. Various functional layers may be laminated.

7). Use of optical film The optical film obtained by the production method of the present invention is not particularly limited, and can be applied to various fields. Specifically, light guide plates used for image display devices such as color filter substrates, touch panel substrates, solar cell substrates, and liquid crystal displays; optical films such as polarizing films, retardation films, and light diffusion films; for image display devices A substrate etc. can be mentioned.

  Since the optical film obtained by the production method of the present invention is particularly excellent in transparency, it is particularly preferably used as various optical films and substrates for image display devices among the various applications described above.

  Hereinafter, the present invention will be described in detail with reference to examples, but the embodiment of the present invention is not limited thereto.

(Example 1)
In this example, needle crystals of strontium carbonate are used as the inorganic particles, and the superiority of carbon dioxide contained in the polymer resin during stretching and orientation will be described.

  With reference to Example 2 of JP 2004-35347 A, the reaction temperature and reaction time are appropriately adjusted by a uniform precipitation method, and two types of strontium carbonate particles having an average particle diameter (major axis diameter) of 200 nm and 40 nm are obtained. Produced.

<Sample 1>
30 g of strontium carbonate having an average particle diameter of 200 nm and an aspect ratio of 7 dried at a temperature of 200 ° C. under reduced pressure was dispersed in 720 ml of xylene with an ultrasonic wave to be gelled. To the resulting solution, 180 ml of 5% polysilazane solution (NP110: manufactured by AZ Electromaterials) was added under an argon atmosphere. The solution was stirred for 10 minutes, and further heated at a temperature of 200 ° C. for 1 hour with stirring in an air atmosphere. Thereafter, spray drying was performed, and the obtained particles were further heated at 200 ° C. for 1 hour in an air atmosphere.

  Next, 4 g of methyltrimethoxysilane (LS-530: manufactured by Shin-Etsu Chemical Co., Ltd.) was added to 30 g of the obtained powder while stirring in an argon atmosphere. Furthermore, after heating at a temperature of 200 ° C. for 30 minutes, by reducing the pressure to 100 ° C., unreacted hexamethyldisilazane and by-product ammonia adsorbed on the particles were removed, and the surface was hydrophobized. A powder was obtained. This is designated as Sample 1.

<Sample 2>
A powder whose surface is hydrophobized in the same manner as in Sample 1 is obtained except that strontium carbonate in Sample 1 is replaced with strontium carbonate having an average particle diameter of 40 nm and an aspect ratio of 8 instead of strontium carbonate having an average particle diameter of 200 nm. It was. This is designated as Sample 2.

<< Production of optical composition and optical film >>
Sample 1 and Sample 2 prepared by the above-described production method were used with a polylab system (manufactured by HAAKE) with respect to 100 parts by mass of alicyclic polyolefin resin (ZEONEX 330R: Nippon Zeon Co., Ltd.), which is a polymer resin. A polymer resin containing inorganic particles was obtained by melt-kneading mass% inorganic particles.

  The obtained polymer resin containing inorganic particles was dried in air at 110 ° C. for 2 hours under normal pressure and allowed to cool to room temperature in a stock tank maintained at a reduced pressure to produce pellets. This pellet is put into a twin screw extruder and heated and melted at a melting temperature of 230 ° C., then carbon dioxide is supplied from a carbon dioxide cylinder, carbon dioxide is mixed and contained in the polymer resin, It knead | mixed in the state which contained the carbon dioxide. The amount of carbon dioxide contained in the polymer resin was adjusted by the cylinder pressure. After kneading, it was melt-extruded from a T-die and then stretched to obtain an optical film. The stretching conditions are a stretching ratio of 1.4, a stretching temperature of 140 ° C., and heat setting of 140 ° C.

  The content of carbon dioxide was calculated from this difference by taking out a part of the melt-kneaded product, measuring the mass immediately after taking it out, and measuring the mass at the time when there was no decrease in mass after a certain period of time.

  The obtained optical films were made into films 1 to 14 as shown in Table 1.

"Evaluation methods"
1) Light transmittance After each film 1-14 was heat-melted, each film 1-14 was formed into a plate shape having a thickness of 3 mm. About each of the obtained plate-shaped films 1-14, the transmittance | permeability of the thickness direction in wavelength 588nm was measured with the spectrophotometer (Shimadzu Corporation make: UV-3150).

2) Refractiveness The micro birefringence was judged by observing a sample under crossed Nicols using a polarizing microscope.

  The films 1 to 14 were evaluated for light transmittance and birefringence, and the evaluation results are shown in Table 1.

Birefringence Low birefringence (good) ◎>○>△> × High birefringence (bad)
From Table 1, in the present invention kneaded with carbon dioxide, the orientation of the inorganic particles in the film is good, and the problem of coexistence of high transparency and reduced birefringence is solved. I understand. Furthermore, when the content of carbon dioxide is 0.5 to 3.0 mass%, and further 0.5 to 2.5, the effects of improving transparency and reducing birefringence are more prominent. It can be seen that it is expressed.

(Example 2)
As a result of conducting a comparative study using the films 1, 2, and 5 in Example 1 simply as a substrate for a liquid crystal display element, the same experimental results as in Example 1 were obtained.

Claims (5)

In a method for producing an optical film, comprising: a kneading step for kneading inorganic particles and a polymer resin; and a stretching step for stretching the polymer resin containing the inorganic particles obtained by the kneading step. A method for producing an optical film, which is an anisotropic needle-like or rod-like inorganic particle, wherein the kneading step is performed in a state where carbon dioxide is contained in the polymer resin. The method for producing an optical film according to claim 1, wherein the needle-like or rod-like inorganic particles having optical anisotropy have birefringence. The method for producing an optical film according to claim 1 or 2, wherein the amount of carbon dioxide contained in the polymer resin is 0.5 to 3.0 mass% with respect to the polymer resin. An optical film manufactured by the method for manufacturing an optical film according to any one of claims 1 to 3. An optical element using the optical film according to claim 4.