JP5640743B2 - Optical film for polarizing plate, production method thereof, polarizing plate and liquid crystal display device using the same - Google Patents

Description

  The present invention relates to an optical film, a method for producing the same, a polarizing plate using the same, and a liquid crystal display device.

  The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and personal computer liquid crystal displays. In general, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. The optical element (polarizing plate protective film) is sandwiched between a child (also referred to as a polarizing film or a polarizing film). As this polarizing plate protective film, a cellulose triacetate film is usually used.

  On the other hand, with the recent advancement of technology, the enlargement of the liquid crystal display device is accelerated, and the use of the liquid crystal display device is diversified. For example, it can be used as a large display installed in a street or a store, or used as an advertising display in a public place using a display device called digital signage.

  However, as the liquid crystal display device is enlarged as described above, and the applications to the outdoors are expanded, it is necessary to increase the amount of light of the backlight so that the image can be fully recognized even outdoors. It was used under severe conditions, and higher moisture resistance and heat resistance were required.

  As a technique for improving moisture resistance and heat resistance, a resin in which an acrylic resin is combined with an impact-resistant acrylic rubber-methyl methacrylate copolymer or butyl-modified acetylcellulose has been proposed (see, for example, Patent Documents 1 and 2). .

  However, even with this method, sufficient improvement in brittleness cannot be obtained, and handling properties are not sufficient for producing an optical film used for a large-sized liquid crystal display device. Further, haze due to the mixed components is also generated, and when used outdoors where a higher contrast is required, there is a problem that the contrast of the image is lowered.

  In addition, a technique has been proposed in which an acrylic resin is mixed with a conventional cellulose ester film to control a plasticizer and optical properties (see, for example, Patent Document 3).

  However, for these purposes, the acrylic resin is not added to such an extent that the moisture resistance can be sufficiently improved, so that sufficient moisture resistance cannot be obtained. Problems such as changes in optical values occurred. Conventionally, when a large amount of other resin is added to the cellulose ester resin in order to improve the moisture resistance, it is considered that the transparency is lowered, and the moisture resistance is such that the optical value does not change in a high humidity environment. A cellulose ester film having improved properties has not been obtained.

  Under the above circumstances, along with the recent expansion of applications of liquid crystal display devices, problems such as low hygroscopicity, transparency, high heat resistance, brittleness, etc. in the optical film used are becoming more and more prominent and improvement is required. It was done.

  On the other hand, a resin composed of an acrylic resin and a cellulose ester resin is a material having both low birefringence and high heat resistance. However, when melt film formation is performed, there is a problem that breakage frequently occurs during transportation.

  Although there is a known example of adding a phosphorus-based additive to cellulose, there is a problem that birefringence is high and light leakage of a polarizing plate using this is severe (see, for example, Patent Document 4).

  Moreover, although the technique of adding a phosphorus additive to an acrylic resin is known, there existed a problem that it was inferior in heat resistance (for example, refer patent document 5).

  Acrylic resin and cellulose ester resin are resins that are excellent in low birefringence and high heat resistance, respectively, but when these two resins are mixed and melt-formed, there is a problem that the film breaks due to conveying stress. It occurred frequently.

  Melt film formation is a method of extruding molten resin from a die and then winding it around a cooling roll to form a film, but at the mass production stage, to increase film productivity and to adjust the film thickness The cooling roll is formed by increasing the roll rotation speed with respect to the die extrusion speed. From this, it is considered that the film is stretched between the die and the cooling roll. The cellulose and acrylic resin melted in the extruder is weakly entangled, and when stretched while cooling between the dice and the cooling roll, the entanglement between the acrylic resin and the cellulose ester resin is weakly formed, and there It was presumed that the film was easily broken by the transfer stress.

Japanese Patent Laid-Open No. 5-119217 JP 2008-88417 A JP 2003-12859 A JP 2008-55890 A JP 2004-213866 A

  The present invention has been made in view of the above-described problems and situations, and the problem to be solved is an optical film mainly composed of an acrylic resin and a cellulose ester resin, and is conveyed during the melt film formation of the optical film. An object of the present invention is to provide an optical film in which breakage of the film due to stress is prevented and there is no light leakage when used in a polarizing plate. Furthermore, it is providing the polarizing plate and liquid crystal display device using the same.

  The above-mentioned problem according to the present invention is solved by the following means.

1. The acrylic resin (A) having a weight average molecular weight (Mw) in the range of 110000 to 1000000 and the cellulose ester resin (B) are mixed in a mass ratio of 50:50 to 95: 5, And,
A phosphite represented by any one of the following general formulas (I) to (V), a phosphonite represented by any one of the following general formulas (VI) to (XII), or any one of the following general formulas (XIII) to (XV) The optical film for polarizing plates characterized by containing the phosphorus additive chosen from the phosphinite represented by these.
[Wherein each group is independently of each other, R ¹ , R ^4, and R ⁵ may be C1-C24 alkyl (straight or branched, heteroatoms, N, O, P, or S may be included). ), C5-C30 cycloalkyl (which may include heteroatoms, N, O, P or S), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, or C6-C24 aryl or Heteroaryl (C1-C18 alkyl (straight or branched), C5-C12 cycloalkyl or substituted with C1-C18 alkoxy group)), R ² is H, C1-C24 alkyl ( Linear or branched, heteroatoms, N, O, P or S may be included), C5-C30 cycloalkyl (heteroatoms, N, O, P or S.), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, or C6-C24 aryl or heteroaryl (C1-C18 alkyl (straight or branched)), C5- R ³ represents a C1-C30 alkylene type n-valent group (straight or branched, heteroatom, N, O, P or S.), C1-C30 alkylidene (heteroatom, N, O, P or S may be included), C5-C12 cycloalkylene or C6-C24 arylene (C1-C24). Substituted with C18 alkyl (straight or branched), C5-C12 cycloalkyl or C1-C18 alkoxy. . And) represents, A is a direct bond, alkylidene of C1-C30 (hetero atom, N, O, may include P or ^{S),>NH,> NR} 1, -S -.,> S (O),> S (O) ₂ , or —O— , X represents Cl, Br, F, or OH (including the resulting tautomeric form> P (O) H); k represents an integer of 0 to 4, n represents an integer of 1 to 4, m represents an integer of 0 to 5, and p represents 0 or 1. ]

2. 2. The optical film for a polarizing plate according to 1 above, containing phosphite and phosphonite as the phosphorus-based additive.

3 . 3. Said 1 or 2 characterized by containing acrylic particle (C) in the range of 0.5-30 mass% with respect to the total mass of resin which comprises the said optical film for polarizing plates. Optical film for polarizing plate .

4 . It is a manufacturing method of the optical film for polarizing plates which manufactures the optical film for polarizing plates as described in any one of said 1 to 3 , Comprising: It is the melt casting film forming method using a touch roll, It is characterized by the above-mentioned. The manufacturing method of the optical film for polarizing plates to perform.

5 . A polarizing plate using the optical film for a polarizing plate according to any one of 1 to 3 above.

6 . 6. A liquid crystal display device using the polarizing plate described in 5 above.

  By the above-mentioned means of the present invention, an optical film comprising an acrylic resin and a cellulose ester resin as main components, the film is prevented from being broken by a conveyance stress during melt film formation of the optical film, and used for a polarizing plate. Sometimes an optical film free from light leakage can be provided. Furthermore, a polarizing plate and a liquid crystal display device using the same can be provided.

  Although the mechanism of manifestation of the effect of the present invention has not been elucidated, a phosphorus-based additive selected from phosphinite, phosphonite, and phosphite is added to a mixture obtained by mixing an acrylic resin and a cellulose ester resin at a specific mass ratio. When added, the phosphorus additive strengthens the entanglement between the compatibilized acrylic resin and the cellulose ester resin, and the film is less likely to break even when a film is formed by melt extrusion and is subjected to conveying stress. Guessed.

  In addition, the phosphorus additive is effective only when it has a structure of any one of phosphinite, phosphonite, and phosphite, and has another phosphate additive, for example, a phosphate structure represented by triphenyl phosphate. The thing did not have the effect which improves a fracture | rupture.

Optical film manufacturing apparatus using elastic touch roll

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are mixed (blended) in a mass ratio of 50:50 to 95: 5, and phosphinite, phosphonite, and An optical film comprising a phosphorus-based additive selected from phosphites. This feature is a technical feature common to the inventions according to claims 1 to 7.

  An embodiment of the present invention is preferably an embodiment containing phosphite and phosphonite as the phosphorus-based additive. Moreover, it is preferable that the weight average molecular weight (Mw) of the said acrylic resin (A) exists in the range of 110000-1000000. Furthermore, it is preferable to contain acrylic particles (C) within a range of 0.5 to 30% by mass with respect to the total mass of the resin constituting the optical film.

  The method for producing the optical film of the present invention is preferably a melt casting film forming method using a touch roll.

  The optical film of this invention can be used suitably for a polarizing plate and a liquid crystal display device using the same.

  Hereinafter, the present invention, its components, and the best mode and mode for carrying out the invention will be described in detail.

(Acrylic resin (A))
The acrylic resin used in the present invention includes a methacrylic resin. Although it does not restrict | limit especially as resin, What consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer units copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Unsaturated group-containing divalent carboxylic acids such as saturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, Maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride and the like can be mentioned, and these can be used alone or in combination of two or more monomers.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

  The acrylic resin (A) used in the optical film of the present invention has a weight average molecular weight (Mw) particularly from the viewpoint of improving brittleness as an optical film and improving transparency when it is compatible with the cellulose ester resin (B). Is 80000 or more.

  The weight average molecular weight (Mw) of the acrylic resin (A) is more preferably in the range of 110000 to 1000000, and particularly preferably in the range of 100,000 to 600000. Although the upper limit of the weight average molecular weight (Mw) of an acrylic resin (A) is not specifically limited, It is a preferable form that it shall be 1 million or less from a viewpoint on manufacture.

  The weight average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin (A) in this invention, You may use any well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. Regarding the polymerization temperature, suspension or emulsion polymerization may be performed at 30 to 100 ° C, and bulk or solution polymerization may be performed at 80 to 160 ° C. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dynal BR52, BR80, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. Two or more acrylic resins can be used in combination.

(Cellulose ester resin (B))
The cellulose ester resin (B) used in the present invention has an acyl group total substitution degree (T) of 2.0 to 2.0, particularly from the viewpoint of transparency when improved in brittleness or compatible with the acrylic resin (A). 3.0, the degree of substitution of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the degree of substitution of the acyl group having 3 to 7 carbon atoms is 2.0 to 3.0. Is preferred. That is, the cellulose ester resin of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, but a propionyl group is particularly preferably used. .

  When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups at the 2, 3, and 6 positions of the cellulose ester molecule is more than 1.0, the acrylic ester When the resin (A) and the acrylic resin (B) are not sufficiently compatible and used as an optical film, haze becomes a problem. Moreover, even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, still sufficient compatibility cannot be obtained, Brittleness will decrease. For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased. Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

  As for the acyl substitution degree of the cellulose ester resin (B) of the present invention, the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but it is preferable that the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms is 1.3 or less.

  The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin (B) has an aromatic acyl group as a substituent, it is preferable that the number of the substituents X substituted to an aromatic ring is 0-5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0. For example, since the benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzoyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the cellulose ester resin (B) as described above, having a structure having at least one kind of an aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used in the cellulose resin of the present invention.

  The substitution degree of the cellulose ester resin (B) according to the present invention is such that the total substitution degree (T) of the acyl group is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 2.0. 3.0.

  Moreover, it is a preferable structure that the sum total of the substitution degree of other than an acyl group having 3 to 7 carbon atoms, that is, an acetyl group and an acyl group having 8 or more carbon atoms is 1.3 or less.

  The cellulose ester resin (B) according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, Those having an acyl group having 3 or 4 carbon atoms as a substituent are preferred.

  Among these, cellulose ester resins that are particularly preferred are cellulose acetate propionate and cellulose propionate.

  The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is 75000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and is preferably in the range of 75,000 to 300,000. More preferably, it is in the range of ˜240,000, particularly preferably in the range of 160000 to 240000. When the important average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the effect of improving heat resistance and brittleness is not sufficient, and the effect of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 50:50 to 95: 5 from the viewpoint of the effect expression of the present invention, moisture resistance, etc. Preferably, it is 90: 10-60: 40.

  If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the acrylic resin is less than 50:50, the moisture resistance is insufficient.

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

  Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state can be determined by, for example, the glass transition temperature Tg.

  For example, when the two resins have different glass transition temperatures, when the two resins are mixed, there are two or more glass transition temperatures for each resin because there is a glass transition temperature for each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which is the glass transition temperature of the compatible resin.

  The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. The point glass transition temperature (Tmg).

  The acrylic resin (A) and the cellulose ester resin (B) are each preferably an amorphous resin, and either one may be a crystalline polymer or a partially crystalline polymer. In the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably compatible with each other to become an amorphous resin.

  In the optical film of the present invention, the weight average molecular weight (Mw) of the acrylic resin (A), the weight average molecular weight (Mw) of the cellulose ester resin (B), and the degree of substitution are different in solubility in the solvent of both resins. It is obtained by measuring each after use. When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be. A combination of these solvents may be combined in two or more steps to separate the resin. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying. These fractionated resins can be identified by general structural analysis of polymers. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), it can be separated by the same method.

  If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

  In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin. By measuring the molecular weight distribution of each of the resins separated in advance based on the difference in solubility in a solvent by GPC, it is possible to detect each of the compatible resins.

  In the present invention, “containing acrylic resin (A) and cellulose ester resin (B) in a compatible state” means mixing each resin (polymer), resulting in a compatible state. This means that a state in which a precursor of acrylic resin such as monomer, dimer or oligomer is mixed with cellulose ester resin (B) and then polymerized by polymerization is not included. .

  For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin such as a monomer, dimer, or oligomer with the cellulose ester resin (B) and then polymerizing it involves a complicated polymerization reaction. The resin is difficult to control the reaction, and it is difficult to adjust the molecular weight. In addition, when a resin is synthesized by such a method, graft polymerization, cross-linking reaction or cyclization reaction often occurs. In many cases, the resin is soluble in a solvent or cannot be melted by heating. Since it is difficult to elute the resin and measure the weight average molecular weight (Mw), it is difficult to control the physical properties and it cannot be used as a resin for stably producing an optical film.

  Unless the function as an optical film is impaired, the optical film of this invention may contain resin and additives other than an acrylic resin (A) and a cellulose-ester resin (B), and may be comprised.

  When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is contained, even if the added resin is in a compatible state, it may be mixed without being dissolved.

  The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the optical film of the present invention is preferably 55% by mass or more of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  When using resins and additives other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the addition amount within a range not impairing the function of the optical film of the present invention.

(Acrylic particles (C))
The optical film of the present invention preferably contains acrylic particles. In the present application, “acrylic particles (C)” means an acrylic component present in the state of particles (also referred to as an incompatible state) in the optical film containing the acrylic resin (A) and the cellulose ester resin (B). Say.

  The acrylic particles (C) are obtained, for example, by collecting a predetermined amount of the produced optical film, dissolving it in a solvent, stirring, and sufficiently dissolving / dispersing it, so that the pore diameter is less than the average particle diameter of the acrylic particles (C). It is preferable that the weight of the insoluble matter filtered and collected using the PTFE membrane filter is 90% by mass or more of the acrylic particles (C) added to the optical film.

  The acrylic particles (C) used in the present invention are not particularly limited, but are preferably acrylic particles (C) having a layer structure of two or more layers, particularly the following multilayer structure acrylic granular composite. It is preferable.

  The multilayer structure acrylic granular composite is formed by laminating an innermost hard layer polymer, a cross-linked soft layer polymer exhibiting rubber elasticity, and an outermost hard layer polymer from the center to the outer periphery. It refers to a particulate acrylic polymer having a structure.

  That is, the multilayer structure acrylic granular composite is a multilayer structure acrylic granular composite comprising an innermost hard layer, a crosslinked soft layer, and an outermost hard layer from the central portion toward the outer peripheral portion. This three-layer core-shell multilayer acrylic granular composite is preferably used.

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following. (A) Monomer composed of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of polyfunctional grafting agent An innermost hard layer polymer obtained by polymerizing a mixture of the body, (b) in the presence of the innermost hard layer polymer, an alkyl acrylate having an alkyl group of 4 to 8 carbon atoms of 75 to 98.5% by mass. A crosslinked soft layer polymer obtained by polymerizing a mixture of monomers comprising 0.01 to 5% by mass of a polyfunctional crosslinking agent and 0.5 to 5% by mass of a multifunctional grafting agent, (c) In the presence of a polymer comprising an inner hard layer and a crosslinked soft layer, a mixture of monomers comprising 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Outermost obtained by polymerizing The layered polymer has a three-layer structure, and the obtained three-layered polymer is the innermost hard layer polymer (a) 5 to 40% by mass, the soft layer polymer (b) 30 to 60% by mass. And the outermost hard layer polymer (c) 20 to 50% by mass, having an insoluble part when fractionated with acetone, and an insoluble granular part having a methyl ethyl ketone swelling degree of 1.5 to 4.0 Complex.

  As disclosed in Japanese Patent Publication No. 60-17406 or Japanese Patent Publication No. 3-39095, not only the composition and particle size of each layer of the multilayer structure acrylic granular composite are defined, but also the multilayer structure acrylic granular composite. By setting the tensile modulus of the body and the degree of swelling of methyl ethyl ketone in the acetone-insoluble part within a specific range, it is possible to realize a further sufficient balance between impact resistance and stress whitening resistance.

  Here, the innermost hard layer polymer (a) constituting the multi-layer structure acrylic granular composite is 80 to 98.9% by mass of methyl methacrylate and 1 to 20% of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. % And a mixture of monomers consisting of 0.01 to 0.3% by mass of a polyfunctional grafting agent is preferred.

  Here, examples of the alkyl acrylate having 1 to 8 carbon atoms in the alkyl group include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like. And n-butyl acrylate are preferably used.

  The proportion of the alkyl acrylate unit in the innermost hard layer polymer (a) is 1 to 20% by mass. When the unit is less than 1% by mass, the thermal decomposability of the polymer is increased, while the unit is 20% by mass. If it exceeds 50%, the glass transition temperature of the innermost hard layer polymer (c) is lowered, and the impact resistance imparting effect of the three-layer structure acrylic granular composite is lowered.

  Examples of the polyfunctional grafting agent include polyfunctional monomers having different polymerizable functional groups, such as allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and allyl methacrylate is preferably used. . The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the ratio used during the innermost hard layer polymerization is 0.01 to 0.3% by mass. .

  The crosslinked soft layer polymer (b) constituting the acrylic granular composite is an alkyl acrylate 75-98.5 having 1 to 8 carbon atoms in the presence of the innermost hard layer polymer (a). What is obtained by polymerizing a monomer mixture consisting of mass%, polyfunctional crosslinking agent 0.01 to 5 mass% and polyfunctional grafting agent 0.5 to 5 mass% is preferred.

  Here, as the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, n-butyl acrylate or 2-ethylhexyl acrylate is preferably used.

  In addition to these polymerizable monomers, it is possible to copolymerize 25% by mass or less of other monofunctional monomers capable of copolymerization.

  Other monofunctional monomers that can be copolymerized include styrene and substituted styrene derivatives. As for the ratio of the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group and styrene, the glass transition temperature of the polymer (b) decreases as the former increases, that is, the ratio can be softened.

  On the other hand, from the viewpoint of the transparency of the resin assembly, the refractive index of the soft layer polymer (b) at room temperature is set to the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard heat. It is more advantageous to make it closer to the plastic acrylic resin, and the ratio between them is selected in consideration of these.

  As the polyfunctional grafting agent, those mentioned in the item of the innermost layer hard polymer (a) can be used. The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c), and the proportion used during the innermost hard layer polymerization is impact resistance. 0.5-5 mass% is preferable from a viewpoint of the property provision effect.

  As the polyfunctional crosslinking agent, generally known crosslinking agents such as divinyl compounds, diallyl compounds, diacrylic compounds, and dimethacrylic compounds can be used, and polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used.

  The polyfunctional cross-linking agent used here is used to generate a cross-linked structure at the time of polymerization of the soft layer (b) and develop an effect of imparting impact resistance. However, if the above-mentioned polyfunctional grafting agent is used during the polymerization of the soft layer, the polyfunctional crosslinking agent is not an essential component because the crosslinked structure of the soft layer (b) is generated to some extent. Is preferably 0.01 to 5% by mass from the viewpoint of imparting impact resistance.

  In the presence of the innermost hard layer polymer (a) and the soft layer polymer (b), the outermost hard layer polymer (c) constituting the multilayer structure acrylic granular composite is 80 to 99 masses of methyl methacrylate. % And a mixture of monomers consisting of 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferred.

  Here, as the acrylic alkylate, those described above are used, and methyl acrylate and ethyl acrylate are preferably used. The ratio of the alkyl acrylate unit in the outermost hard layer (c) is preferably 1 to 20% by mass.

  Further, for the purpose of improving the compatibility with the acrylic resin (A) during the polymerization of the outermost hard layer (c), it is also possible to use an alkyl mercaptan or the like as a chain transfer agent in order to adjust the molecular weight.

  In particular, it is preferable to provide the outermost hard layer with a gradient such that the molecular weight gradually decreases from the inside toward the outside in order to improve the balance between elongation and impact resistance. Specifically, the outermost hard layer is divided into two or more monomer mixtures for forming the outermost hard layer, and the amount of chain transfer agent to be added each time is increased sequentially. It is possible to decrease the molecular weight of the polymer forming the layer from the inside to the outside of the multilayer structure acrylic granular composite.

  The molecular weight formed at this time can also be examined by polymerizing a mixture of monomers used each time under the same conditions and measuring the molecular weight of the resulting polymer.

  The particle diameter of the acrylic particles (C) preferably used in the present invention is not particularly limited, but is preferably 10 to 1000 nm, more preferably 20 to 500 nm, particularly 50 to Most preferably, it is 400 nm.

  In the acrylic granular composite that is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core and the shell is not particularly limited, but when the entire multilayer structure polymer is 100 parts by mass, The core layer is preferably 50 to 90 parts by mass, and more preferably 60 to 80 parts by mass. In addition, the core layer here is an innermost hard layer.

  Examples of such commercially available multilayered acrylic granular composites include, for example, “Metablene” manufactured by Mitsubishi Rayon Co., “Kane Ace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Rohm and Haas “Acryloid” manufactured by KK, “Staffyroid” manufactured by Ganz Kasei Kogyo Co., Ltd., “Parapet SA” manufactured by Kuraray Co., Ltd., and the like can be used alone or in combination of two or more.

  Further, specific examples of the acrylic particles (c-1) which are graft copolymers suitably used as the acrylic particles (C) preferably used in the present invention include unsaturated carboxylic acids in the presence of a rubbery polymer. Mixtures of monomers consisting of acid ester monomers, unsaturated carboxylic acid monomers, aromatic vinyl monomers, and other vinyl monomers copolymerizable with these if necessary Examples thereof include a graft copolymer obtained by copolymerization.

  The rubbery polymer used for the acrylic particles (c-1) as the graft copolymer is not particularly limited, but diene rubber, acrylic rubber, ethylene rubber, and the like can be used. Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned. These rubbery polymers can be used alone or in a mixture of two or more.

  Moreover, when adding an acrylic particle (C) to the optical film of this invention, the refractive index of the mixture of an acrylic resin (A) and a cellulose-ester resin (B) and the refractive index of an acrylic particle (C) must be near. From the viewpoint of obtaining a film with high transparency. Specifically, the refractive index difference between the acrylic particles (C) and the acrylic resin (A) is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

  In order to satisfy such a refractive index condition, a method of adjusting the monomer unit composition ratio of the acrylic resin (A) and / or a rubbery polymer or monomer used for the acrylic particles (C) The refractive index difference can be reduced by a method of adjusting the composition ratio, and an optical film excellent in transparency can be obtained.

  The refractive index difference referred to here is a solution in which the optical film of the present invention is sufficiently dissolved in a solvent in which the acrylic resin (A) is soluble to obtain a cloudy solution, which is subjected to an operation such as centrifugation. After separating the solvent-soluble part and the insoluble part and purifying the soluble part (acrylic resin (A)) and insoluble part (acrylic particles (C)), the measured refractive index (23 ° C., measuring wavelength: 550 nm). ) Difference.

  There is no restriction | limiting in particular in the method of mix | blending an acrylic particle (C) with an acrylic resin (A) in this invention, After blending an acrylic resin (A) and another arbitrary component previously, Usually at 200-350 degreeC, A method of uniformly melt-kneading with a single-screw or twin-screw extruder while adding acrylic particles (C) is preferably used.

  A commercially available thing can also be used as an acrylic particle concerning this invention. For example, metabrene W-341 (C2) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C3), MS-300X (C4) (manufactured by Soken Chemical Co., Ltd.) and the like can be mentioned.

  In the optical film of the present invention, it is preferable to contain 0.5 to 30% by mass of acrylic particles (C) with respect to the total mass of the resin constituting the film, and in the range of 1.0 to 15% by mass. It is more preferable to contain.

(Antioxidant)
In the present invention, the resin mixture such as an acrylic resin preferably contains an antioxidant.

  In the present invention, a preferable antioxidant is a phosphorus-based or phenol-based antioxidant, and it is more preferable to combine a phosphorus-based and a phenol-based antioxidant at the same time.

  Hereinafter, the antioxidant that can be suitably used in the present invention will be described.

<Phenolic antioxidant>
In the present invention, a phenolic antioxidant represented by the following general formula (AO1) can be used.

In the general formula (AO1), R ₁ , R ₂ and R ₃ represent an alkyl substituent which is further substituted or unsubstituted. Specific examples of hindered phenol compounds include n-octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate, n-octadecyl 3- (3,5-di-t-butyl- 4-hydroxyphenyl) -acetate, n-octadecyl 3,5-di-t-butyl-4-hydroxybenzoate, n-hexyl 3,5-di-t-butyl-4-hydroxyphenylbenzoate, n-dodecyl 3, 5-di-t-butyl-4-hydroxyphenylbenzoate, neo-dodecyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, dodecyl β (3,5-di-t-butyl- 4-hydroxyphenyl) propionate, ethyl α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octade Sil α- (4-hydroxy-3,5-di-t-butylphenyl) isobutyrate, octadecyl α- (4-hydroxy-3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2- (n -Octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (n-octylthio) ethyl 3,5-di-t-butyl-4-hydroxy-phenylacetate, 2- (n- Octadecylthio) ethyl 3,5-di-t-butyl-4-hydroxyphenyl acetate, 2- (n-octadecylthio) ethyl 3,5-di-t-butyl-4-hydroxy-benzoate, 2- (2- Hydroxyethylthio) ethyl 3,5-di-t-butyl-4-hydroxybenzoate, diethyl glycol bis- (3,5-di-t-butyl-4) -Hydroxy-phenyl) propionate, 2- (n-octadecylthio) ethyl 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearamide N, N-bis- [ethylene 3- (3 5-di-t-butyl-4-hydroxyphenyl) propionate], n-butylimino N, N-bis- [ethylene 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2- (2-stearoyloxyethylthio) ethyl 3,5-di-tert-butyl-4-hydroxybenzoate, 2- (2-stearoyloxyethylthio) ethyl 7- (3-methyl-5-tert-butyl-4- Hydroxyphenyl) heptanoate, 1,2-propylene glycol bis- [3- (3,5-di-tert-butyl-4-hydroxyl Nyl) propionate], ethylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], neopentyl glycol bis- [3- (3,5-di-t-butyl-) 4-hydroxyphenyl) propionate], ethylene glycol bis- (3,5-di-t-butyl-4-hydroxyphenyl acetate), glycerin-1-n-octadecanoate-2,3-bis- (3 5-di-t-butyl-4-hydroxyphenyl acetate), pentaerythritol-tetrakis- [3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate], 1,1,1 -Trimethylolethane-tris- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], sorbite Ruhexa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-hydroxyethyl 7- (3-methyl-5-tert-butyl-4-hydroxyphenyl) propionate, 2- Stearoyloxyethyl 7- (3-methyl-5-t-butyl-4-hydroxyphenyl) heptanoate, 1,6-n-hexanediol-bis [(3 ', 5'-di-t-butyl-4-hydroxy Phenyl) propionate], pentaerythritol-tetrakis (3,5-di-t-butyl-4-hydroxyhydrocinnamate). Hindered phenol compounds of the above type are commercially available, for example, from Ciba Japan under the trade names “Irganox 1076” and “Irganox 1010”.

<Phosphorus antioxidant>
As the phosphorus-based antioxidant that can be used in the present invention, a phosphorus-based compound such as phosphite, phosphonite, or phosphinite can be used.

  Conventionally known compounds can be used as the phosphorus-based antioxidant. For example, Japanese Patent Application Laid-Open Nos. 2002-138188, 2005-344444, paragraph numbers 0022 to 0027, Japanese Patent Application Laid-Open No. 2004-18279, paragraph numbers 0023 to 0039, Japanese Patent Application Laid-Open No. 10-306175, Japanese Patent Application Laid-Open No. 1-254744, and Japanese Patent Application Laid-Open No. -270892, JP-A-5-202078, JP-A-5-178870, JP-T-2004-504435, JP-T-2004-530759, and JP-A-2005-353229 Is preferred.

  Preferable phosphorus compounds include, but are not limited to, compounds represented by the following general formula.

Examples include phosphites of general formulas (I) to (V), phosphonites of general formulas (VI) to (XII), and phosphinites of general formulas (XIII) to (XV). Each group is independently of each other, and R ¹ is C ¹ -C 24 alkyl (straight or branched, hetero atoms may include N, O, P, S), C 5 -C 30 cycloalkyl (hetero atoms , N, O, P, S), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, C6-C24 aryl or heteroaryl (C1-C18 alkyl (linear or Branched), substituted with a C5-C12 cycloalkyl or C1-C18 alkoxy group).

R ² is H, C 1 -C 24 alkyl (straight or branched, hetero atom, N, O, P, S may be included), C 5 -C 30 cycloalkyl (hetero atom, N, O, P , S may be included), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, C6-C24 aryl or heteroaryl (C1-C18 alkyl (straight or branched), C5-C12 Or a C1-C18 alkoxy group).

R ³ is a C1-C30 alkylene type n-valent group (straight or branched, heteroatom, N, O, P, S may be included), C1-C30 alkylidene (heteroatom, N, O, P, S may be included), C5-C12 cycloalkylene or C6-C24 arylene (C1-C18 alkyl (straight or branched), C5-C12 cycloalkyl or C1-C18 alkoxy) Replaced with

R ⁴ is C 1 -C 24 alkyl (straight or branched, hetero atom, N, O, P, S may be included), C 5 -C 30 cycloalkyl (hetero atom, N, O, P, S C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, C6-C24 aryl or heteroaryl (C1-C18 alkyl (straight or branched), C5-C12 cyclo) Substituted with an alkyl or C1-C18 alkoxy group).

R ⁵ is C 1 -C 24 -alkyl (straight or branched, hetero atoms, N, O, P, S may be included), C 5 -C 30 cycloalkyl (hetero atoms, N, O, P, S C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, C6-C24 aryl or heteroaryl (C1-C18 alkyl (straight or branched), C5-C12 cyclo) Substituted with an alkyl or C1-C18 alkoxy group).

A is a direct bond, C1-C30 alkylidene (which may include heteroatoms, N, O, P, and S),>NH,> NR ¹ , —S—,> S (O),> S ( O) ₂ or —O—.

  X is Cl, Br, F, or OH (including the resulting tautomeric form> P (O) H).

  k is an integer of 0 to 4, n is an integer of 1 to 4, m is an integer of 0 to 5, and p is 0 or 1.

  Among these compounds, particularly preferable compounds include the following compounds. These compounds may be used in combination of two or more. The addition amount of a phosphorus compound is 0.01-10 mass parts normally with respect to 100 mass parts of cellulose esters, Preferably it is 0.05-5 mass parts, More preferably, it is 0.1-3 mass parts.

  In addition to the above examples, specific examples of phosphorus compounds that can be used in the present invention include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) phosphite, tris (di Nonylphenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, 10- (3,5-di-tert-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa -10-phosphaphenanthrene-10-oxide, 6- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8,10-tetra-t-butyldibenz [d , F] [1.3.2] monophosphite compounds such as dioxaphosphine and tridecyl phosphite; 4 4'-butylidene-bis (3-methyl-6-t-butylphenyl-di-tridecyl phosphite), 4,4'-isopropylidene-bis (phenyl-di-alkyl (C12-C15) phosphite), etc. Diphosphite compounds of: triphenylphosphonite, tetrakis (2,4-di-tert-butylphenyl) [1,1-biphenyl] -4,4′-diylbisphosphonite, tetrakis (2,4-di-tert) Phosphonite compounds such as -butyl-5-methylphenyl) [1,1-biphenyl] -4,4'-diylbisphosphonite; phosphinites such as triphenylphosphinite and 2,6-dimethylphenyldiphenylphosphinite Compounds such as triphenylphosphine and tris (2,6-dimethoxyphenyl) phosphine Fin-based compounds; and the like.

  Phosphorus compounds of the above type are, for example, from Sumitomo Chemical Co., Ltd. “Sumilizer GP”, from ADEKA Co., Ltd. “ADK STAB PEP-24G”, “ADK STAB PEP-36”, “ADK STAB 3010”, “ADK STAB 2112”. ”,“ IRGAFOS P-EPQ ”and“ IRGAFOS 168 ”from Ciba Japan Co., Ltd., and“ GSY-P101 ”from Sakai Chemical Industry Co., Ltd.

《Other antioxidants》
Dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, pentaerythrityltetrakis (3-laurylthiopropioate) Nate) and the like, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy) 3,5-di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenyl acrylate, 3,4-dihydro-2H-1 described in JP-B-08-27508 -Benzopyran compounds, 3,3'-spirodichroman compounds, 1,1-spiroindane compounds, morpholine, thiomorpho Emissions, thiomorpholine oxide, thiomorpholine dioxide, a compound having a piperazine skeleton partial structure, oxygen scavenger dialkoxy benzene type compound in JP-03-174150 Patent describes the like. These antioxidant partial structures may be part of the polymer or regularly pendant into the polymer and introduced into part of the molecular structure of additives such as plasticizers, acid scavengers, and UV absorbers. It may be.

(Other additives)
《Plasticizer》
In the optical film of the present invention, a plasticizer can be used in combination in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the optical film of the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

<Ultraviolet absorber>
The optical film of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole, 2-hydroxybenzophenone, and salicylic acid phenyl ester. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine A hybrid system having both structures can be mentioned, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

  Furthermore, various antioxidants can also be added to the optical film of the present invention in order to improve the thermal decomposability and thermal coloring during molding. It is also possible to add an antistatic agent to give the optical film antistatic performance.

  For the optical film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphates, halogen-containing condensed phosphonates, halogen-containing phosphites, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

  According to the optical film of the present invention, improvement in low hygroscopicity, transparency, high heat resistance, and brittleness that could not be achieved with conventional resin films can be achieved at the same time.

  In the present invention, the brittleness index is determined based on the criterion of whether or not it is “an optical film in which ductile fracture does not occur”. By obtaining an optical film with improved brittleness that does not cause ductile fracture, even when manufacturing a polarizing plate for a large-sized liquid crystal display device, breakage and cracking during production do not occur, and the handling property is excellent. It can be an optical film. Here, the ductile fracture is a fracture caused by applying a stress larger than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material until the final fracture. The fracture surface is characterized by numerous indentations called dimples.

  In the present invention, whether or not it is “an optical film that does not cause ductile fracture” is evaluated based on the fact that no breakage or the like is observed even when a large stress is applied such that the film is folded in two. . Even if it is used as a polarizing plate protective film for a large-sized liquid crystal display device, if it is an optical film that does not cause ductile fracture even when such a large stress is applied, problems such as breakage during production Furthermore, even when the optical film is used after being peeled off after being pasted once, no breakage occurs and the optical film can be sufficiently reduced in thickness.

  In the present invention, the tension softening point is used as an index of heat resistance. In addition to the increasing size of liquid crystal display devices and the increasing brightness of backlight light sources, the use of digital signage and other outdoor applications demands higher brightness. However, if the tension softening point is 105 ° C. to 145 ° C., it can be determined that sufficient heat resistance is exhibited. In particular, it is more preferable to control at 110 to 130 ° C.

  As a specific measuring method of the temperature indicating the tension softening point of the optical film, for example, the optical film is cut out at 120 mm (length) × 10 mm (width) using a Tensilon tester (ORIENTEC, RTC-1225A). The temperature can be raised at a rate of 30 ° C./min while pulling with a tension of 10 N, and the temperature at the time when the pressure reaches 9 N is measured three times, and the average value can be obtained.

  From the viewpoint of heat resistance, the optical film preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. Point glass transition temperature (Tmg).

  As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used. In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  According to the optical film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property. By increasing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and the acrylic particles (C), an increase in haze value can be prevented.

  In addition, since the surface roughness also affects the haze value as surface haze, the particle diameter and addition amount of acrylic particles (C) should be kept within the above range, and the surface roughness of the film contact portion during film formation should be reduced. Is also effective.

  In addition, the hygroscopicity of the optical film in the present invention is evaluated by dimensional change with respect to humidity change.

  The following method is used as an evaluation method of dimensional change with respect to humidity change.

  In the casting direction of the produced optical film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the mark (cross) before and after treatment was measured with an optical microscope. Obtain the dimensional change rate (%). The dimensional change rate (%) is expressed by the following formula.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
a1: Distance before heat treatment a2: Distance after heat treatment When an optical film is used as a protective film for a polarizing plate of a liquid crystal display device, unevenness or a change in retardation value occurs due to a dimensional change due to moisture absorption. This causes problems such as a decrease in contrast and uneven color. In particular, the above problem becomes significant when the polarizing plate protective film is used in a liquid crystal display device used outdoors. However, if the dimensional change rate (%) under the above conditions is less than 0.5%, it can be evaluated that the optical film exhibits sufficiently low hygroscopicity. Furthermore, it is preferable that it is less than 0.3%.

  In the optical film of the present invention, it is preferable that the number of defects in a film plane of 5 μm or more is 1/10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

  When the number of defects is greater than 1/10 cm square, for example, when the film is tensioned during processing in a later process, the film may break with the defects as a starting point, and productivity may decrease. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

  Moreover, even when it cannot be visually confirmed, when a hard coat layer or the like is formed on the film, the coating agent may not be formed uniformly, resulting in a defect (missing coating). Here, the defect is a void in the film (foaming defect) generated due to the rapid evaporation of the solvent in the drying process of the solution casting, a foreign matter in the film forming stock solution, or a foreign matter mixed in the film forming. This refers to foreign matter (foreign matter defect) in the film.

  In the measurement according to JIS-K7127-1999, the optical film of the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  The thickness of the optical film of the present invention is preferably 20 μm or more. More preferably, it is 30 μm or more.

  The upper limit of the thickness is not particularly limited, but in the case of forming a film by a solution casting method, the upper limit is about 250 μm from the viewpoint of applicability, foaming, solvent drying, and the like. In addition, the thickness of a film can be suitably selected according to a use.

  The optical film of the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact part (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roll, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the acrylic resin.

  The optical film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

  Such physical properties include the optical film containing the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and the weight average molecular weight Mw of the acrylic resin (A) is 80000. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.00 to 3.00, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. And having a weight average molecular weight (Mw) of 75,000 or more.

<Optical film formation>
An example of a method for producing an optical film will be described, but the present invention is not limited to this.

  As a method for forming the optical film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the standpoints of suppressing optical defects such as die lines and suppressing optical defects, melt casting by casting is preferred. In the present invention, the melt casting film forming method using a touch roll is particularly preferable.

  In the present application, “melt film formation” means that a composition containing additives such as an acrylic resin, a cellulose ester resin, and a plasticizer is heated and melted to a temperature showing fluidity, and then a fluid cellulose ester resin, Casting a melt containing an acrylic resin or the like is defined as melt film formation.

  More specifically, the heat melting molding method can be classified into a melt extrusion molding method, a press molding method, an inflation method, an injection molding method, a blow molding method, a stretch molding method, and the like. Among these, in order to obtain an optical film excellent in mechanical strength and surface accuracy, the melt extrusion method is excellent.

≪Film forming process≫
Hereinafter, the film forming process of the film will be described.

<Acrylic resin, cellulose ester resin and additive melt pellet manufacturing process>
It is preferable that a plurality of raw materials used for melt extrusion are usually kneaded and pelletized in advance.

  The pelletization may be performed by a known method. For example, an acrylic resin, a cellulose ester resin, an acrylic resin, a plasticizer, and other additives are supplied to an extruder with a feeder and kneaded using a single-screw or twin-screw extruder. It is possible to extrude into a strand form from a die, and then perform water cooling or air cooling and cutting.

  It is important to dry the raw material before extruding to prevent decomposition of the raw material. In particular, since the cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer, and to keep the moisture content at 200 ppm or less, and further 100 ppm or less.

  The additives may be mixed before being supplied to the extruder, or may be supplied by individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

  Mixing of the antioxidants may be performed by mixing solids, and if necessary, the antioxidant may be dissolved in a solvent and impregnated with a resin such as an acrylic resin, or may be sprayed. You may mix.

A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Further, if the contact with air, such as the exit from the feeder unit or die, it is preferable that the atmosphere such as dehumidified air and dehumidified N ₂ gas.

  In addition, it is preferable to keep the supply hopper and the like to the extruder warm because moisture absorption can be prevented. Matting agents, UV absorbers, and the like may be applied to the obtained pellets or added in an extruder during film formation.

  The extruder is preferably processed at as low a temperature as possible so that the shearing force is suppressed and the resin can be pelletized so as not to deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  Kneader discs can improve kneadability, but care must be taken against shearing heat generation. Mixability is sufficient without using a kneader disk. The suction from the vent hole may be performed as necessary. Since there is almost no volatile component at low temperatures, there may be no vent hole.

The color of the pellet is preferably such that the b * value, which is an index of yellowness, is in the range of -5 to 10, more preferably in the range of -1 to 8, and in the range of -1 to 5. More preferred. The b ^* value can be measured at a viewing angle of 10 ° using a spectrocolorimeter CM-3700d (manufactured by Konica Minolta Sensing Co., Ltd.) and a light source of D65 (color temperature 6504K).

  A film is formed using the pellets obtained as described above. Of course, the raw material powder can be directly fed to the extruder by a feeder without being pelletized to form a film as it is.

<Process of extruding a melt of a resin mixture such as acrylic resin from a die>
Dehydrated hot air or polymer dried under vacuum or reduced pressure using a uniaxial or biaxial extruder, with a melting temperature Tm of about 200 to 300 ° C, filtered through a leaf disk type filter, etc. After removal, the film is cast from a T die into a film.

  When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum or reduced pressure or in an inert gas atmosphere. Tm is the temperature at the die exit portion of the extruder.

  The extrusion flow rate is preferably performed stably by introducing a gear pump or the like. Further, a stainless fiber sintered filter is preferably used as a filter used for removing foreign substances.

  A stainless steel fiber sintered filter is an integrated stainless steel fiber body that is intricately entangled and then compressed and sintered at the contact point. The density is changed according to the thickness of the fiber and the amount of compression, and the filtration accuracy is improved. Can be adjusted.

  It is preferable to use a multilayer body in which the filtration accuracy is repeated coarsely and densely a plurality of times. Further, it is preferable to adopt a configuration in which the filtration accuracy is sequentially increased or a method in which coarse and dense filtration accuracy is repeated, so that the filtration life of the filter can be extended and the accuracy of supplementing foreign matters and gels can be improved.

  If flaws or foreign matter adhere to the die, streaky defects may occur. Such defects are also referred to as die lines, but in order to reduce surface defects such as die lines, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

  The inner surface that contacts the molten resin such as an extruder or a die is preferably subjected to surface treatment that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material having a low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

  Additives such as plasticizers may be mixed with the resin in advance, or may be kneaded in the middle of the extruder. In order to add uniformly, it is preferable to use a mixing apparatus such as a static mixer.

<Process of casting a melt extruded from a die between a cooling roll and an elastic touch roll to form a film>
In this step, the film-like melt extruded from the die is nipped between a cooling roll and an elastic touch roll to form a predetermined film shape and film thickness.

(Cooling roll)
The cooling roll of the present invention is not particularly limited, but is a roll having a structure with a high-rigidity metal roll that allows a temperature-controllable heat medium or refrigerant to flow inside, and is not limited in size. It is sufficient that the film is large enough to cool the formed film, and the diameter of the cooling roll is usually about 100 mm to 1 m.

  Examples of the surface material of the cooling roll include carbon steel, stainless steel, aluminum, and titanium. Further, in order to increase the surface hardness or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

  The surface roughness of the surface of the cooling roll is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable to further polish the surface that has been subjected to surface processing so as to have the above-described surface roughness.

  The cooling roll of the present invention is at least one, and preferably has two or more. When there is only one, the surface temperature Tr of the cooling roll is set to Tg-50 ≦ Tr ≦ Tg. In the case of two or more, the surface temperatures of the first cooling roll and the second cooling roll are set to Tg−50 ≦ Tr1 ≦ Tg and Tg−50 ≦ Tr2 ≦ Tg.

  Tg refers to the glass transition temperature (° C.) of the mixture of acrylic resin and cellulose ester resin.

  The glass transition temperature Tg was measured according to JIS K7121 using a differential scanning calorimeter DSC220 manufactured by Seiko Electronics Industry.

  Set about 10 mg of sample, raise the temperature from room temperature to 250 ° C. at 20 ° C./min under a nitrogen flow rate of 50 ml / min and hold for 10 minutes (1st scan), then 30 at a rate of 20 ° C./min. The temperature was lowered to 0 ° C. and held for 10 minutes (2nd scan), and further raised to 250 ° C. at 20 ° C./min (3rd scan) to obtain a DSC curve. The glass transition temperature was obtained from the obtained 3rd scan DSC curve.

[Elastic touch roll]
Examples of the elastic touch roll according to the present invention include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97-026950, JP-A-11-235747, Although the surface described in JP-A-2002-36332, JP-A-2005-172940 and JP-A-2005-280217 can use a thin-film metal sleeve-coated silicon rubber roll, the following elastic touch rolls are used. It is preferable.

  A melt containing cellulose ester has a higher melt viscosity and is less likely to be stretched than other thermoplastic resins.

  Therefore, when the draw ratio is large, there is a problem that the film thickness is likely to vary in the conveying direction, and also when the film is stretched in the tenter process, the film tends to be broken, and the drawing ratio is about 7 to 8 at most. However, in this invention, it is preferable to convey the film obtained by extruding the melt containing a cellulose ester from die | dye into a film form, and having a draw ratio of 10-30, pressing to a cooling roll with an elastic touch roll.

  The draw ratio is a value obtained by dividing the lip clearance of the die by the average film thickness of the film solidified on the cooling roll. By setting the draw ratio within this range, a polarizing plate protective film having good productivity and no bright and dark stripes and uneven spots when an image is displayed on a liquid crystal display device can be obtained.

  The draw ratio can be adjusted by the die lip clearance and the take-up speed of the cooling roll. The die lip clearance is preferably 900 μm or more, and more preferably 1 mm or more and 2 mm or less. Even if it is too large or too small, spotted unevenness may not be improved.

  The elastic touch roll used in the present invention has a double structure of a metal outer cylinder and an inner cylinder, and has a space so that a cooling fluid can flow between them.

  Furthermore, because the metal outer cylinder has elasticity, the temperature of the surface of the touch roll can be controlled with high accuracy, and the distance to press the film in the longitudinal direction can be increased by utilizing the property of elastically deforming appropriately. Thus, when an image is displayed on the liquid crystal display device, there is obtained an effect that there are no bright and dark stripes and uneven spots.

  If the range of the thickness of the metal outer cylinder is 0.003 ≦ (thickness of the metal outer cylinder) / (touch roll radius) ≦ 0.03, it is preferable because the elasticity is appropriate. If the radius of the touch roll is large, even if the thickness of the metal outer cylinder is large, the touch roll bends appropriately.

  The diameter of the elastic touch roll is preferably 100 mm to 600 mm. If the thickness of the metal outer cylinder is too thin, the strength is insufficient and there is a concern of breakage. On the other hand, if it is too thick, the roll mass becomes too heavy and there is a concern about uneven rotation. Therefore, the thickness of the metal outer cylinder is preferably 0.1 to 5 mm.

  The surface roughness of the surface of the metal outer cylinder is preferably 0.1 μm or less in terms of arithmetic average roughness Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film.

  The material of the metal outer cylinder is required to be smooth, moderately elastic, and durable. Carbon steel, stainless steel, titanium, nickel produced by electroforming, etc. can be preferably used. Furthermore, in order to increase the hardness of the surface or to improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, ceramic spraying, or the like. It is preferable that the surface processed is further polished to have the surface roughness described above.

  The inner cylinder is preferably a lightweight and rigid metallic inner cylinder such as carbon steel, stainless steel, aluminum, titanium or the like. By giving rigidity to the inner cylinder, it is possible to suppress the rotational shake of the roll. A sufficient rigidity can be obtained by setting the thickness of the inner cylinder to 2 to 10 times that of the outer cylinder.

  The inner cylinder may be further coated with a resin elastic material such as silicone or fluororubber.

  The structure of the space through which the cooling fluid flows can be any structure as long as the temperature of the roll surface can be uniformly controlled. For example, the roll can be made to flow in a spiral direction by going alternately in the width direction and returning. Temperature control with a small surface temperature distribution is possible.

  The cooling fluid is not particularly limited, and water or oil can be used according to the temperature range to be used.

  The surface temperature Tr0 of the elastic touch roll is preferably lower than the glass transition temperature (Tg) of the film. If it is higher than Tg, the peelability between the film and the roll may be inferior. More preferably, it is Tg-50 degreeC-Tg.

  The elastic touch roll used in the present invention preferably has a so-called crown roll shape in which the central portion in the width direction has a diameter larger than that of the end portion.

  The touch roll generally presses both ends of the touch roll against the film with a pressurizing unit, but in this case, the touch roll is bent, so that there is a phenomenon that the touch roll is pressed more strongly toward the end. By making the roll into a crown shape, highly uniform pressing becomes possible.

  The width of the elastic touch roll used in the present invention is preferably wider than the film width because the entire film can be in close contact with the cooling roll. Further, when the draw ratio is increased, both end portions of the film may become ear height (thickness of the end portion becomes thick) due to a neck-in phenomenon.

  In this case, the width of the metal outer cylinder may be made narrower than the film width so as to escape from the height of the ear. Alternatively, the outer diameter of the metal outer cylinder may be reduced to escape the ear height.

  Specific examples of the metal elastic touch roll include molding rolls described in Japanese Patent No. 3194904, Japanese Patent No. 3422798, Japanese Patent Application Laid-Open No. 2002-36332, and Japanese Patent Application Laid-Open No. 2002-36333.

  In order to prevent bending of the elastic touch roll, a support roll may be arranged on the opposite side of the touch roll with respect to the cooling roll.

  You may arrange | position the apparatus which cleans the stain | pollution | contamination of an elastic touch roll. As the cleaning device, for example, a method of pressing the roll surface with a member such as a nonwoven fabric infiltrated with a solvent if necessary, a method of bringing the roll into contact with a liquid, a plasma discharge such as corona discharge or glow discharge, A method for volatilizing dirt can be preferably used.

  In order to make the surface temperature Tr0 of the elastic touch roll even more uniform, a temperature control roll may be brought into contact with the touch roll, temperature-controlled air may be blown, or a heat medium such as a liquid may be brought into contact.

  In the present invention, it is preferable that the touch roll linear pressure at the time of pressing the elastic touch roll is 1 kg / cm or more and 15 kg / cm or less, and the touch roll side film surface temperature Tt is Tg <Tt <Tg + 110 ° C.

  By setting the elastic touch roll linear pressure within this range, a polarizing plate protective film having no bright and dark stripes and uneven spots when an image is displayed on a liquid crystal display device can be obtained.

  The linear pressure is a value obtained by dividing the force with which the elastic touch roll presses the film by the film width at the time of pressing. The method for setting the linear pressure within the above range is not particularly limited, and for example, both ends of the roll can be pressed with an air cylinder or a hydraulic cylinder.

  You may press a film indirectly by pressing an elastic touch roll with a support roll.

  The higher the film temperature when pressing the film with the elastic touch roll, the lighter and darker streaks caused by the die line are improved. However, if the film temperature is too high, the spotted unevenness deteriorates. This is expected because volatile components are volatilized from the film and are not uniformly pressed when pressed with a touch roll. If it is too low, light and dark stripes resulting from the die line will not be improved.

  The method of setting the film temperature at the time of pressing in the above range is not particularly limited. For example, the distance between the die and the cooling roll is made closer, and the cooling between the die and the cooling roll is suppressed, or between the die and the cooling roll. Examples of the method include heat insulation by surrounding with a heat insulating material, or heating by hot air, an infrared heater, microwave heating, or the like.

  The film surface temperature and roll surface temperature can be measured with a non-contact infrared thermometer. Specifically, using a non-contact handy thermometer (IT2-80, manufactured by Keyence Co., Ltd.), 10 locations in the width direction of the film are measured at a distance of 0.5 m from the object to be measured.

  The elastic touch roll side film surface temperature Tt refers to the film surface temperature measured with a non-contact infrared thermometer from the touch roll side in the state where the touch roll is removed from the film being conveyed.

<The process and the extending process of heating the cooled film in the range of Tg + 30 degreeC or more and Tg + 60 degreeC or less>
In a normal film-forming process, after being melt-cast and formed into a film shape, it is said that it should be quickly cooled with a cooling roll.

  However, the present invention is characterized in that after being cooled by a cooling roll, the heat treatment is performed again. That is, after the cooling step, a step of heating the cooled film again in the range of Tg + 30 ° C. or higher and Tg + 60 ° C. or lower is provided. The heating time is preferably 5 to 60 seconds, more preferably 10 to 30 seconds.

  This step of heating again is preferably a stretching step. A step of heating again while stretching is preferred. This stretching step is preferably a transverse stretching step (film width direction).

  In the present invention, it is preferable to stretch at least 1.01 to 5.0 times. Preferably, the film is stretched 1.1 to 3.0 times in both the longitudinal and lateral (width direction) directions.

  You may have multiple processes which heat the cooled film in Tg + 30 degreeC or more and Tg + 60 degreeC or less. In this case, it is preferable to cool by the cooling roll maintained at the temperature below Tg between each heating process.

  As a method of stretching, a known roll stretching machine or tenter can be preferably used.

  The temperature and magnification of the optical film of the present invention can be selected so that desired retardation characteristics can be obtained.

  The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

<Post-stretching process (including winding process)>
In the optical film produced by the above method, after the aggregates such as plasticizer are reduced to such an extent that haze failure does not occur, the film is oriented in the longitudinal direction or the width direction for the purpose of adjusting retardation and reducing the dimensional change rate. It may be contracted.

  In order to shrink in the longitudinal direction, for example, there is a method of contracting the film by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

  The latter method can be performed by using a general simultaneous biaxial stretching machine and driving the clip portions in the longitudinal direction by, for example, a pantograph method or a linear drive method to smoothly and gradually narrow the clip portion. it can. You may combine with extending | stretching of arbitrary directions (diagonal direction) as needed. The dimensional change rate of the optical film can be reduced by shrinking 0.5% to 10% in both the longitudinal direction and the width direction.

  Prior to winding, the ends may be slit and cut to the width of the product, and knurling (embossing) may be applied to both ends to prevent sticking or scratching during winding. The knurling method can process a metal ring having an uneven pattern on its side surface by heating or pressing.

  In addition, since the film has deform | transformed and cannot use as a product normally, the holding | grip part of the clip of both ends of a film is cut out and reused as a raw material.

  In the present invention, it is preferable to reduce the humidity change rate and dimensional change rate of retardation (Ro, Rt) by reducing the free volume of the film.

  In order to reduce the free volume, it is effective to have a step of performing a heat treatment near the Tg of the film after the stretching step. The heat treatment time shows an effect from 1 second or more, and the effect becomes higher as the time is longer. However, since the effect is saturated at about 1000 hours, Tg-20 ° C to Tg is preferably 1 second to 1000 hours.

  Further, Tg-15 ° C to Tg is preferably 1 minute to 1 hour. In addition, it is preferable to perform heat treatment while slowly cooling the temperature range from Tg to Tg-20 ° C., because the effect can be obtained in a shorter time than heat treatment at a constant temperature.

  The cooling rate is preferably −0.1 ° C./second to −20 ° C./second, more preferably −1 ° C./second to −10 ° C./second. There is no particular limitation on the heat treatment method, and the heat treatment can be performed by a temperature-controlled oven or roll group, hot air, an infrared heater, a microwave heating device, or the like.

  The film may be heat-treated in the form of a sheet or roll while being conveyed. In the case of carrying, it can be carried while carrying out heat treatment using a roll group or a tenter. When heat-treating in a roll shape, the film may be wound in a roll shape at a temperature in the vicinity of Tg and gradually cooled by cooling as it is.

  FIG. 1 is a schematic flow sheet showing the overall configuration of the optical film manufacturing apparatus of the present invention. In FIG. 1, an optical film is manufactured by mixing a film material such as an acrylic resin, and then melt-extruding it from a casting die 4 onto a first cooling roll 5 using an extruder 1. In addition to circumscribing, the film 10 is further circumscribed by a total of three cooling rolls, that is, the second cooling roll 7 and the third cooling roll 8, and is cooled and solidified to form a film 10. Next, the film 10 peeled off by the peeling roll 9 is then stretched in the width direction by holding both ends of the film by the stretching device 12 and then wound by the winding device 16. In addition, a touch roll 6 is provided that clamps the molten film on the surface of the first cooling roll 5 in order to correct the flatness. The touch roll 6 has an elastic surface and forms a nip with the first cooling roll 5.

<Characteristics of manufactured optical film>
The optical film of the present invention is useful as a polarizing plate protective film for protecting a polarizer mainly composed of polyvinyl alcohol, and is also used as an optical compensation film for a liquid crystal display device by adjusting the retardation. be able to.

〔Polarizer〕
When using the optical film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  On the other surface, the optical film of the present invention may be used, or another polarizing plate protective film may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

[Liquid Crystal Display]
By incorporating the polarizing plate bonded with the optical film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate according to the present invention includes a reflective type, a transmissive type, a transflective type LCD or a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), an IPS type (including an FFS type), and the like. It is preferably used in LCDs of various driving methods. In particular, in a large-screen display device having a screen size of 30 or more, especially 30 to 54, there is no white spot at the periphery of the screen, and the effect is maintained for a long time.

  In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
[Preparation of acrylic resin]
The following commercially available acrylic resin was used for the acrylic resin used for this invention.

Dianar BR83 (Mitsubishi Rayon Co., Ltd.) Mw40000
Dianar BR85 (Mitsubishi Rayon Co., Ltd.) Mw280000
Acrypet VH-4 (Mitsubishi Rayon Co., Ltd.) Mw 140000
Acrypet V (Mitsubishi Rayon Co., Ltd.) Mw105000
The ratio of the MMA unit in the molecule in the acrylic resin used in the present invention was 90% by mass or more and 99% by mass or less.

[Preparation of acrylic particles]
<Preparation of acrylic particles (C1)>
A reactor with a reflux condenser with an internal volume of 60 liters was charged with 38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate, and the temperature was raised to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. The effect of oxygen was virtually eliminated. 0.36 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of MMA 1657 g, BA 21.6 g, and ALMA 1.68 g was added all at once, and after the detection of the exothermic peak, it was held for another 20 minutes to polymerize the innermost hard layer Was completed.

  Next, 3.48 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of BA1055 g, PEGDA (200) 31.9 g, and ALMA264.0 g was continuously added over 120 minutes. Hold for 120 minutes to complete the polymerization of the soft layer.

  Next, 1.32 g of APS was added, and after stirring for 5 minutes, a mixture of monomers consisting of 2106 g of MMA and 201.6 g of BA was continuously added over 20 minutes. The polymerization of 1 was completed.

  Next, 1.32 g of APS was added, and after 5 minutes, a mixture of monomers consisting of 3148 g of MMA, 201.6 g of BA, and 10.1 g of n-OM was continuously added over 20 minutes, and held for another 20 minutes after the addition was completed. . Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost hard layer 2.

  The polymer latex thus obtained was poured into a 3% by weight aqueous sodium sulfate solution, salted out and coagulated, then dried after repeated dehydration and washing, and three-layer acrylic particles ( C1) was obtained. When the average particle size was determined by the absorbance method, it was 100 nm.

  The above abbreviations are the following materials.

MMA; methyl methacrylate MA; methyl acrylate BA; n-butyl acrylate ALMA; allyl methacrylate PEGDA; polyethylene glycol diacrylate (molecular weight 200)
n-OM; n-octyl mercaptan APS; ammonium persulfate [Preparation of optical film]
<Preparation of optical film 1>
(Molten resin composition 1)
Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) 94 parts by mass Cellulose ester (cellulose acetate propionate acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 200000 )
5 parts by mass The above-prepared acrylic particles (C1) 1 part by mass Irganox 1010 (manufactured by Ciba Japan Co., Ltd.) 0.5 parts by mass GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.) 0.075 parts by mass ADKSTAB 2112 (( Co., Ltd. ADEKA Co., Ltd.) 0.075 parts by mass Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0.2 parts by mass UV absorber Ti928 (manufactured by Ciba Japan Co., Ltd.) 1.5 parts by mass Matting agent Seahoster KEP-30 Japan Made by Catalyst Co., Ltd.
(Average particle size 0.3 μm silica fine particles) 0.1 part by mass (melting of optical film)
The cellulose ester and acrylic resin were dried under reduced pressure at 70 ° C. for 3 hours and cooled to room temperature, and then each additive other than the matting agent was mixed.

  The above mixture was formed into a film by a manufacturing apparatus using an elastic touch roll shown in FIG. In a nitrogen atmosphere, it was melted at 240 ° C., extruded from the casting die onto the first cooling roll, and molded by pressing the film between the first cooling roll and the touch roll. Further, a matting agent was added as a slip agent from the hopper opening in the middle of the extruder 1 so as to be 0.1 part by mass.

  The heat bolt was adjusted so that the gap width of the casting die was 0.5 mm within 30 mm from the end in the width direction of the film and 1 mm at other locations. As the touch roll, a touch roll was used, and 80 ° C. water was allowed to flow therein as cooling water.

  On the peripheral surface of the first cooling roll from the position where the resin extruded from the casting die contacts the first cooling roll to the upstream end position in the first cooling roll rotation direction of the nip between the first cooling roll and the touch roll. The length L along was set to 20 mm. Thereafter, the touch roll was separated from the first cooling roll, and the temperature T of the melted part immediately before being sandwiched in the nip between the first cooling roll and the touch roll was measured. The temperature T of the melted part immediately before being squeezed by the nip between the first cooling roll and the touch roll is 1 mm upstream from the upstream end of the nip and is measured by a thermometer (HA-200E manufactured by Anritsu Keiki Co., Ltd.). It was measured. As a result of the measurement, the temperature T was 141 ° C. The linear pressure of the touch roll against the first cooling roll was 14.7 N / cm.

  Furthermore, after being introduced into a tenter and stretched 1.3 times at 160 ° C in the width direction, it was cooled to 30 ° C while relaxing 3% in the width direction, and then released from the clip. Was subjected to a knurling process with a width of 10 mm and a height of 5 μm, and wound on a winding core with a winding tension of 220 N / m and a taper of 40%. The winding core had an inner diameter of 152 mm, an outer diameter of 165 to 180 mm, and a length of 1550 mm. A prepreg resin obtained by impregnating glass fibers and carbon fibers with an epoxy resin was used as the core material for the core. The surface of the core was coated with an epoxy conductive resin, the surface was polished, and the surface roughness Ra was finished to 0.3 μm. The optical film 101 was manufactured with a film thickness of 80 μm and a winding length of 3500 m.

<Preparation of optical films 2 to 21>
In the production of the optical film 1, the composition ratio of the acrylic resin (A) and the cellulose ester resin (B), and the types and addition ratios of the additives are as shown in Table 1, and the types of the acrylic resin (A). Optical films 2 to 21 were produced in the same manner except that the conditions were changed as described in Table 2.

"Evaluation method"
The following evaluation was implemented about the obtained optical films 1-21.

(Turn resistance during transportation)
At the time of film formation of the optical film, the breakage resistance at the time of conveyance was ranked according to the following criteria with respect to the frequency of breakage of the film during conveyance.
◎◎: No breakage or breaks during film formation, transport, winding, and film handling.
(Double-circle): Although a fracture | rupture is not seen at the time of film forming, conveyance, winding at the time of film handling, a break is sometimes made at the time of winding.
○: Breakage is not observed during film formation, conveyance, winding, and film handling, but breaks often occur during winding.
(Triangle | delta): A fracture | rupture is seen in one or more places at the time of film forming, conveyance, winding, and film handling.
X: Breaking occurs frequently during film formation, conveyance, winding, and film handling.

(Light leakage resistance)
The obtained optical film is sandwiched between two polarizers arranged in a crossed Nicol state with a polarizing plate, that is, in an orthogonal state (crossed Nicol state), irradiated with light from the outside of one polarizing plate, Visual observation was performed from the outside, and light leakage resistance was ranked according to the following criteria.
A: There is no light transmission and the entire dark field is uniform. B: Partially weak streak-like light / darkness is recognized. X: Strong streaky light-darkness is partially observed (polarizer deterioration resistance).
For the polarizing plate produced by the above method, first, the parallel transmittance and the direct transmittance were measured, and the degree of polarization was calculated according to the following formula. Thereafter, each polarizing plate was subjected to forced degradation for 1000 hours at 60 ° C. and 90%, and then the parallel transmittance and the direct transmittance were measured again, and the degree of polarization was calculated according to the following formula. The amount of change in polarization degree was determined by the following formula.

Polarization degree P = ((H ₀ −H ₉₀ ) / (H ₀ + H ₉₀ )) ^1/2 × 100
Polarization degree change amount = P ₀ -P ₁₀₀₀ H ₀ : Parallel transmittance H ₉₀ : Direct transmittance P ₀ : Polarization degree before forced deterioration P ₁₀₀₀ : Polarization degree after 1000 hours of forced deterioration A: Polarization degree change rate 10% Less than ○: Polarization degree change rate of 10% or more and less than 25% ×: Polarization degree change rate of 25% or more (tensile elongation at break)
It measured using a No. 1 type test piece according to JIS K3127.

  The above evaluation results are shown in Tables 1 and 2.

  As is clear from the results shown in Table 1, it can be seen that the examples of the optical film according to the present invention are superior in each evaluation performance to the comparative example.

DESCRIPTION OF SYMBOLS 1 Extruder 2 Filter 3 Static mixer 4 Casting die 5 Rotating support body (1st cooling roll)
6 Nipping pressure rotating body (touch roll)
7 Rotating support (second cooling roll)
8 Rotating support (3rd cooling roll)
9, 11, 13, 14, 15 Transport roll 10 Film 12 Stretching machine 16 Winding device

Claims (6)

The acrylic resin (A) having a weight average molecular weight (Mw) in the range of 110000 to 1000000 and the cellulose ester resin (B) are mixed in a mass ratio of 50:50 to 95: 5, And,
A phosphite represented by any one of the following general formulas (I) to (V), a phosphonite represented by any one of the following general formulas (VI) to (XII), or any one of the following general formulas (XIII) to (XV) The optical film for polarizing plates characterized by containing the phosphorus additive chosen from the phosphinite represented by these.
[Wherein each group is independently of each other, R ¹ , R ^4, and R ⁵ may be C1-C24 alkyl (straight or branched, heteroatoms, N, O, P, or S may be included). ), C5-C30 cycloalkyl (which may include heteroatoms, N, O, P or S), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, or C6-C24 aryl or Heteroaryl (C1-C18 alkyl (straight or branched), C5-C12 cycloalkyl or substituted with C1-C18 alkoxy group)), R ² is H, C1-C24 alkyl ( Linear or branched, heteroatoms, N, O, P or S may be included), C5-C30 cycloalkyl (heteroatoms, N, O, P or S.), C1-C30 alkylaryl, C6-C24 aryl or heteroaryl, or C6-C24 aryl or heteroaryl (C1-C18 alkyl (straight or branched)), C5- R ³ represents a C1-C30 alkylene type n-valent group (straight or branched, heteroatom, N, O, P or S.), C1-C30 alkylidene (heteroatom, N, O, P or S may be included), C5-C12 cycloalkylene or C6-C24 arylene (C1-C24). Substituted with C18 alkyl (straight or branched), C5-C12 cycloalkyl or C1-C18 alkoxy. . And) represents, A is a direct bond, alkylidene of C1-C30 (hetero atom, N, O, may include P or ^{S),>NH,> NR} 1, -S -.,> S (O),> S (O) ₂ , or —O— , X represents Cl, Br, F, or OH (including the resulting tautomeric form> P (O) H); k represents an integer of 0 to 4, n represents an integer of 1 to 4, m represents an integer of 0 to 5, and p represents 0 or 1. ]   The optical film for a polarizing plate according to claim 1, comprising phosphite and phosphonite as the phosphorus-based additive.   The acrylic particles (C) are contained within a range of 0.5 to 30% by mass with respect to the total mass of the resin constituting the optical film for polarizing plate. The optical film for polarizing plates as described in 2.   It is a manufacturing method of the optical film for polarizing plates which manufactures the optical film for polarizing plates as described in any one of Claim 1- 3, Comprising: It is the melt casting film forming method using a touch roll. The manufacturing method of the optical film for polarizing plates characterized by these.   A polarizing plate using the optical film for a polarizing plate according to any one of claims 1 to 3.   A liquid crystal display device using the polarizing plate according to claim 5.