Method for manufacturing optical film, optical film, polarizing plate, and liquid crystal display device

Abstract

This invention relates to a method for manufacturing an optical film, an optical film, a polarizer, and a liquid crystal display device. The objective is to provide a method for manufacturing a wide-width optical film with low retardation values ​​in both the in-plane and thickness directions, and to suppress display unevenness caused by environmental variations in the display device, using a plant-derived resin. The method for manufacturing the optical film of this invention is characterized by comprising: a step of forming a strip film from a cellulose ester resin containing a total acetyl substitution degree of 2.30 to 2.60 and a sugar ester having a furanose or pyranose structure; and a step of stretching said strip film, wherein the retardation value R... o The range is 0–10 nm, R t The process of stretching the long strip film, with a wavelength of -10 to 10 nm, includes the following steps: a first step to obtain a first stretched film; and a second step to further stretch the first stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is in the range of 190 to 220°C.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an optical film, an optical film, a polarizer, and a liquid crystal display device. More specifically, it relates to a method for manufacturing a wide-width optical film, and an optical film thereof, which uses a plant-based resin to provide low in-plane and thickness retardation values ​​and suppresses display unevenness caused by environmental variations in the display device. Background Technology

[0002] It is known that cellulose acetate resins, by varying the degree of acetyl substitution, can be applied to optical films with a wide range of retardations. Generally, triacetylcellulose with a high degree of acetyl substitution is suitable for use as a protective film for polarizers mounted in IPS-mode liquid crystal display devices due to its low retardation value. However, when used as an optical compensation film for various liquid crystal modes such as VA mode and TN mode, the retardation is insufficient to manifest by stretching alone, thus requiring the addition of retardation enhancers (see, for example, Patent Document 1).

[0003] On the other hand, diacetylcellulose with low acetyl substitution can be stretched at high ratios and exhibits high retardation. Therefore, it can be expected to be used as an optical compensation film even without the addition of the aforementioned retardation agent, and various technologies have been studied (see, for example, Patent Document 2).

[0004] Furthermore, the diacetyl cellulose described above can be stretched at high ratios, which is beneficial for widening the optical film. Therefore, conversely, it has also been studied to adjust the additives and manufacturing methods appropriately to achieve a low retardation value even when stretched at high ratios (see, for example, Patent Document 3).

[0005] However, due to the high hydrophilicity of cellulose acetate with low acetyl substitution, the water content of the membrane increases, resulting in slightly poorer resistance to environmental changes such as dimensional stability and fluctuations in optical properties. Therefore, it is considered difficult to use it directly as an optical membrane.

[0006] However, given the current requirements for reducing environmental impact, the demand for optical films using plant-based resins is constantly increasing. Furthermore, with the increasing size of display devices such as televisions and monitors, there is a demand for wider optical films and higher display performance. Specifically, there is a strong desire for optical films that, even with wider screens, reduce the occurrence of uneven screen display (screen spots) caused by changes in the surrounding environment.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Description of European Patent No. 911656

[0010] Patent Document 2: International Patent Publication No. 2011 / 135980

[0011] Patent Document 3: Japanese Patent Application Publication No. 2014-149325 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] The present invention was made in view of the above-mentioned problems and conditions, and its solution is a method for manufacturing a wide optical film, an optical film, a polarizer, and a liquid crystal display device that uses a plant-based resin to provide a wide optical film with small retardation values ​​in the in-plane and thickness directions and suppresses screen display unevenness (display spots) caused by environmental changes of the display device.

[0014] Methods for solving problems

[0015] In order to solve the above-mentioned problems, the inventors, during their research on the causes of the above-mentioned problems, discovered that: by preparing a paste containing a specific cellulose ester resin and a specific compound, casting the paste to make a long strip film, and then stretching the film under specific conditions in a way that controls the retardation value, a method for manufacturing a wide optical film with small retardation values ​​in both the in-plane and thickness directions and suppressing uneven screen display caused by environmental changes in the display device can be achieved using plant-based resins.

[0016] That is, the aforementioned problems involved in this invention are solved by the following means.

[0017] 1. A method for manufacturing an optical film, comprising a method for manufacturing an optical film containing at least a cellulose ester resin, characterized in that it includes: a step of casting a paste containing at least a cellulose ester resin and a sugar ester on a support to form an elongated film; and a step of stretching the formed elongated film, wherein the total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, the sugar ester is a compound in which all or part of the hydroxyl groups in compound (A) or compound (B) have been esterified with aliphatic acyl groups, wherein compound (A) has one furanose structure or pyranose structure, and compound (B) incorporates at least two and no more than twelve furanose structures or pyranose structures, and the optical film has a retardation value R defined by the following formula (i). o The delay value R is defined by the following equation (ii) within the range of 0 to 10 nm. t Within the range of -10 to 10 nm, the process of stretching the formed elongated film sequentially includes a first step to obtain a first elongated stretched film, and a second step to further stretch the first elongated stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is within the range of 190 to 220°C.

[0018] Formula (i)R o =(n x -n y )×d

[0019] Equation (ii)R t ={(n x +n y ) / 2-n z}×d

[0020] In the formula, n x The refractive index n represents the refractive index along the hysteresis axis within the film surface. y The refractive index n represents the refractive index along the advanced phase axis within the film surface. z The refractive index represents the thickness of the film. The refractive index is measured at a wavelength of 590 nm under conditions of 23 °C and 55% RH. d represents the thickness of the film (nm).

[0021] 2. The method for manufacturing the optical film according to the first claim, characterized in that the content of the sugar ester is in the range of 10 to 25% by mass.

[0022] 3. The method for manufacturing the optical film according to the first claim, characterized in that the adhesive further contains polyester.

[0023] 4. The method for manufacturing the optical film according to the third item, characterized in that the content of the polyester is in the range of 5 to 15% by mass.

[0024] 5. The method for manufacturing an optical film according to the first or second claim, characterized in that the step of stretching the formed elongated film has a precipitation suppression zone after the second step, the temperature of which is in the range of -100 to -50°C compared with the stretching temperature of the second step.

[0025] 6. The method for manufacturing an optical film according to the first or second claim, characterized in that the stretching temperature of the second step is in the range of +60 to +100°C compared to the stretching temperature of the first step.

[0026] 7. The method for manufacturing an optical film according to the first or second claim, characterized in that, after placing the optical film in environments of 23°C·20%RH and 23°C·80%RH for 24 hours, the difference ΔR between the retardation values ​​measured in the same way is... o and ΔR t The absolute values ​​are all below 5nm.

[0027] 8. The method for manufacturing an optical film according to the first or second claim, characterized in that the optical film employs... 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50 to 80 seconds.

[0028] 9. An optical film comprising at least a cellulose ester resin, characterized in that the total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, the optical film further comprising a glycol ester, wherein the glycol ester is a compound in which all or part of the hydroxyl groups in compound (A) or compound (B) are esterified with aliphatic acyl groups, wherein compound (A) has one furanose structure or pyranose structure, and compound (B) is composed of at least two and no more than twelve furanose structures or pyranose structures, and the optical film has a retardation value R defined by the following formula (i). o The delay value R is defined by the following equation (ii) within the range of 0 to 10 nm. t Within the range of -10 to 10 nm, the difference ΔR between the delay values ​​measured after placing the optical film in environments of 23°C·20%RH and 23°C·80%RH for 24 hours is considered. o and ΔR t The absolute values ​​of all are below 5nm, and the optical film adopts 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50–80 seconds.

[0029] Formula (i)R o =(n x -n y )×d

[0030] Equation (ii)R t ={(n x +n y ) / 2-n z}×d

[0031] In the formula, n x The refractive index n represents the refractive index along the hysteresis axis within the film surface. y The refractive index n represents the refractive index along the advanced phase axis within the film surface. z The refractive index represents the thickness of the film. The refractive index is measured at a wavelength of 590 nm under conditions of 23 °C and 55% RH. d represents the thickness of the film (nm).

[0032] 10. The optical film according to claim 9, characterized in that the content of the sugar ester is in the range of 10 to 25% by mass.

[0033] 11. A polarizer, characterized in that an optical film according to claim 9 or 10 is attached to at least one side of the polarizer.

[0034] 12. A liquid crystal display device, characterized in that a polarizer according to claim eleven is applied to at least one side of a liquid crystal cell.

[0035] 13. The liquid crystal display device according to item 12, characterized in that it is an IPS-mode liquid crystal display device.

[0036] Invention Effects

[0037] A method for manufacturing a wide-width optical film that provides low in-plane and thickness retardation values ​​using plant-based resins and suppresses uneven image display caused by environmental changes in the display device; an optical film; a polarizer; and a liquid crystal display device.

[0038] The mechanism by which the effects of this invention are manifested and the mechanism of action are not yet clear, but are speculated as follows.

[0039] Generally, by stretching the film at a temperature higher than its glass transition temperature, the tensile stress applied to the film can be reduced (in this invention, it is also referred to as "low-stress stretching"). Therefore, it is believed that while suppressing the increase in haze and the deterioration of brittleness caused by stress, an optical film with a small retardation value can be obtained.

[0040] The inventors have discovered that cellulose acetate, a plant-derived resin, exhibits a three-dimensional structure due to intermolecular interactions, which becomes ordered during high-temperature stretching. Even stretching at temperatures higher than the glass transition temperature generates stress. By adjusting the degree of substitution at the 6-position of the pyranose ring, this ordering of the resin is suppressed, enabling low-stress stretching at high temperatures. Furthermore, by combining it with a specific additive (a glycol ester in this invention), during high-temperature stretching, the additive readily enters the intermolecular space of cellulose, causing randomization and low stress in the cellulose orientation, thus reducing the manifestation of phase difference. Moreover, it is speculated that through the strong interaction between the cellulose backbone and the additive, orientation changes are less likely to occur in response to changes in ambient temperature and humidity, resulting in a film with minimal phase difference variation associated with environmental changes.

[0041] If we focus on the degree of substitution at the 6-position of the aforementioned pyranose ring, for example, triacetylcellulose, through high-temperature treatment, causes the nearby acetyl groups to become crosslinking points and become ordered, exhibiting polymer chain bundle properties. Therefore, a stretching ratio of around 40% is the limit; if stretched beyond this, the polymer chains will be cut, and the film will break. For diacetylcellulose, even with high-temperature treatment, since there are no nearby acetyl groups that can become crosslinking points, the aforementioned ordering does not occur. Therefore, through low-stress stretching, a stretching ratio of around 200% can be achieved. By combining it with appropriate additives, the generation of retardation can be suppressed, making it a resin advantageous for widening optical films. Attached Figure Description

[0042] Figure 1 This illustrates the use of optical films containing cellulose ester resins. 13A schematic diagram showing the measurement location of the cellulose skeleton at C-NMR determination of longitudinal relaxation time T1.

[0043] Figure 2 This is a schematic diagram illustrating an example of the apparatus and process for the preparation of the slurry, the casting process, the stretching process, and the drying process in a solution casting film production method.

[0044] Explanation of reference numerals in the attached figures

[0045] 1 Dissolving vessel

[0046] 3, 6, 12, 15 filters

[0047] 4.13 storage kettle

[0048] 2, 5, 14 Liquid delivery pumps

[0049] 8, 16 catheters

[0050] 10. Ultraviolet absorber feeder

[0051] 20 Combination pipe

[0052] 21 Mixer

[0053] 30 Pressure Die Head

[0054] 31 Metal strip (support body)

[0055] 32. Mesh or long strip membrane

[0056] 33. Peeling location

[0057] 34. Tensioning device for the first stretching process

[0058] 35. Tensioning device for the second stretching process

[0059] 36 Precipitation inhibition region

[0060] 37. Drying apparatus

[0061] 38 conveying rollers

[0062] 39 Optical film winding device

[0063] 40 Optical film rolls

[0064] 41 Feeding kettle

[0065] 42 storage kettle

[0066] 43 pumps

[0067] 44 Filters Detailed Implementation

[0068] The method for manufacturing the optical film of the present invention is a method for manufacturing an optical film containing at least a cellulose ester resin, characterized in that it includes: a step of casting a paste containing at least a cellulose ester resin and a sugar ester on a support to form a strip film; and a step of stretching the formed strip film, wherein the total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, the sugar ester is a compound in which all or part of the hydroxyl groups in compound (A) or compound (B) are esterified with aliphatic acyl groups, compound (A) has one furanose structure or pyranose structure, and compound (B) incorporates at least two and no more than twelve furanose structures or pyranose structures, and the optical film has a retardation value R as defined by the above formula (i). o The delay value R, defined by equation (ii) above, is in the range of 0–10 nm. t Within the range of -10 to 10 nm, the process of stretching the formed elongated film sequentially includes a first step of obtaining a first elongated stretched film, and a second step of further stretching the first elongated stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is within the range of 190 to 220°C. This feature is a common or corresponding technical feature of the following embodiments.

[0069] As an embodiment of the present invention, from the viewpoint of demonstrating the effects of the present invention, it is preferable that the content of the above-mentioned sugar ester in the membrane is in the range of 10 to 25% by mass.

[0070] The aforementioned adhesive also contains polyester, which is preferred from the viewpoints of reducing the Tg of the optical film, controlling the stretching temperature, and reducing energy costs. Furthermore, the preferred polyester content in the film is in the range of 5 to 15% by mass.

[0071] From the viewpoint of suppressing the generation of precipitates such as additives in the optical film and obtaining a high-quality optical film, it is preferable that the process of stretching the strip film formed above has a precipitation suppression range after the second process, and the temperature of the precipitation suppression range is in the range of -100 to -50°C compared with the stretching temperature of the second process.

[0072] Furthermore, from the viewpoint of keeping the delay value low while being able to stretch at a high ratio, it is preferable that the stretching temperature of the second process is in the range of +60 to +100°C compared to the stretching temperature of the first process.

[0073] From the viewpoint of suppressing uneven screen display caused by environmental changes in the display device, it is preferable to measure the difference ΔR in the delay value when the optical film is placed in environments of 23°C·20%RH and 23°C·80%RH for 24 hours. o and ΔR t The absolute values ​​are all below 5nm.

[0074] Furthermore, from the viewpoint of determining the resin structure that solves the problem of the present invention, the use of the above-described optical film is preferred. 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50 to 80 seconds.

[0075] Figure 1 For use in optical films containing cellulose ester resins 13 A schematic diagram showing the locations of the cellulose skeleton measured by C-NMR at longitudinal relaxation time T1. The diagram shows the longitudinal relaxation time measurements taken from locations labeled [ring 1]. In the diagram, Ac represents an acetyl group, and R represents a substituent.

[0076] In this invention, in the examples described later (reference examples), for triacetyl cellulose (TAC), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), and diacetyl cellulose (DAC), the cast web was not stretched, but only dried. Optical films No. 27 to No. 32 were fabricated, and the longitudinal relaxation time T1 at [ring 1] of the cellulose backbone was measured (the composition and evaluation of the optical films are shown in Tables II and III).

[0077] The results showed that, without the addition of glycolipids, diacetylcellulose (DAC) had a shorter longitudinal relaxation time (higher motility) compared to triacetylcellulose (TAC) (comparison of No. 31 and No. 32).

[0078] However, with the addition of glycolipids, a significant increase in the longitudinal relaxation time of the [ring 1] of the cellulose backbone was observed. In this case, the longitudinal relaxation time of diacetylcellulose (DAC) was further prolonged compared to triacetylcellulose (TAC) (comparison of No. 27 and No. 31) (comparison of No. 30 and No. 32). This indicates a strong interaction between diacetylcellulose (DAC) and glycolipids, suggesting that this enhanced interaction can suppress the effects of environmental changes (delayed changes: ΔR). o and ΔR t (value).

[0079] The optical film of the present invention is an optical film containing at least a cellulose ester resin, characterized in that the total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, and it further contains a glycol ester, wherein the glycol ester is a compound in which all or part of the hydroxyl groups in compound (A) or compound (B) are esterified with aliphatic acyl groups, wherein compound (A) has one furanose structure or pyranose structure, and compound (B) is combined with at least two and no more than twelve furanose structures or pyranose structures, and the optical film has a retardation value R as defined by the above formula (i).o The delay value R, defined by equation (ii) above, is in the range of 0–10 nm. t Within the range of -10 to 10 nm, the difference ΔR between the delay values ​​measured after placing the optical film in environments of 23°C·20%RH and 23°C·80%RH for 24 hours is considered. o and ΔR t The absolute values ​​of all are below 5nm, and the optical film adopts 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50 to 80 seconds.

[0080] The polarizer of the present invention is characterized in that the optical film of the present invention is attached to at least one side of the polarizer, and the liquid crystal display device of the present invention is characterized in that the polarizer is applied to at least one side of the liquid crystal cell. The above-described liquid crystal display device is preferably an IPS-type liquid crystal display device.

[0081] The present invention, its constituent elements, and the forms and methods for carrying out the invention will be described in detail below. It should be noted that in this application, "~" is used to indicate the lower and upper limits of the numerical values ​​described before and after it.

[0082] Summary of the method for manufacturing the optical film of the present invention

[0083] The method for manufacturing the optical film of the present invention is a method for manufacturing an optical film containing at least a cellulose ester resin, characterized in that it includes: a step of casting a paste containing at least a cellulose ester resin and a sugar ester on a support to form a strip film; and a step of stretching the formed strip film, wherein the total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, the sugar ester is a compound in which all or part of the hydroxyl groups in compound (A) or compound (B) are esterified with aliphatic acyl groups, compound (A) has one furanose structure or pyranose structure, and compound (B) incorporates at least two and no more than twelve furanose structures or pyranose structures, and the optical film has a retardation value R as defined by the above formula (i). o The delay value R, defined by equation (ii) above, is in the range of 0–10 nm. t The process of stretching the formed elongated film within the range of -10 to 10 nm includes, in sequence, a first process of obtaining a first elongated stretched film, and a second process of further stretching the first elongated stretched film to obtain a second stretched film, wherein the stretching temperature of the second process is within the range of 190 to 220 °C.

[0084] First, the methods for measuring various parameters involved in the manufacturing method of the optical film of the present invention will be described.

[0085] <Delay value>

[0086] The in-plane retardation value R of the optical film o The retardation value R in the thickness direction t It can be obtained using the following equations (i) and (ii).

[0087] Formula (i)R o =(n x -n y )×d

[0088] Equation (ii)R t ={(n x +n y ) / 2-n z}×d

[0089] In the formula, n x The refractive index n represents the refractive index along the hysteresis axis within the film surface. y The refractive index n represents the refractive index along the advanced phase axis within the film surface. z The refractive index represents the thickness of the film, and d represents the thickness of the film (nm).

[0090] Regarding the refractive index and film thickness mentioned above, the average refractive index of randomly sampled optical films was measured using an Abbe refractometer (4T). Additionally, the average film thickness was measured using a commercially available micrometer.

[0091] Regarding the delay of the optical film, the delay of the film at a wavelength of 590 nm was measured using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Measurement Equipment Co., Ltd.) after the film had been placed in an environment of 23°C and 55%RH for 24 hours.

[0092] In addition, after placing the aforementioned optical film in environments of 23°C and 20% RH and 23°C and 80% RH for 24 hours, the difference in retardation value ΔR was calculated using the same method. o and ΔR t The absolute value is used as an indicator of the fluctuation of the delayed value when the environment changes.

[0093] ΔR o (nm)=|R o (23℃·20%RH)-R o (23℃·80%RH)|

[0094] ΔR t (nm)=|R t (23℃·20%RH)-R t (23℃·80%RH)|

[0095] <Adopted 13The longitudinal relaxation time T1 of C-NMR is >

[0096] The use of optical films 13 The longitudinal relaxation time T1 of C-NMR was determined as described below.

[0097] Measure 50 mg of membrane sample and perform CP / MAS analysis using a JEOL RESONANCE JNM-ECA400W membrane analyzer. 13 C1-NMR measurements were performed, and the Torchia method was used to calculate the above... Figure 1 The longitudinal relaxation time T1 of the [ring 1] portion of the cellulose skeleton.

[0098] It should be noted that the measurement conditions were 23℃, relaxation delay of 3 seconds, cumulative number of measurements of 512, and resonance frequency of 100MHz.

[0099] The following describes in detail the manufacturing method of the optical film of the present invention, and then the materials used in the optical film of the present invention.

[0100] [1] Manufacturing method of optical film

[0101] (Manufacturing method of optical film)

[0102] First, the method for manufacturing the optical film of the present invention will be described.

[0103] The method for manufacturing the optical film of the present invention is characterized by comprising: a step of casting a paste containing at least a cellulose ester resin and a sugar ester on a support to form an elongated film; and a step of stretching the elongated film formed thereon, wherein the cellulose ester resin and the sugar ester are specific compounds described later, and the optical film has a retardation value R defined by the above formula (i). o The delay value R, defined by equation (ii) above, is within the range of 0–10 nm. t The process of stretching the above-mentioned long strip film in a manner within the range of -10 to 10 nm includes a first process of obtaining a first long strip of stretched film, and a second process of further stretching the first long strip of stretched film to obtain a second stretched film, wherein the stretching temperature of the second process is within the range of 190 to 220°C.

[0104] Therefore, the optical film manufacturing method of the present invention relates to a manufacturing method for manufacturing optical films using a solution casting method.

[0105] The manufacturing process of the optical film of the present invention will be described according to the process flow, which includes the following steps: dissolving cellulose ester resin and additives in a solvent to prepare a paste; casting the paste on an infinitely transferable annular metal support; forming the cast paste into a mesh and drying it; peeling the mesh from the metal support to obtain a film; stretching or maintaining the width of the film; adjusting the temperature of the film using an anti-deposition zone; drying the film; and finally, winding the completed film.

[0106] The process of stretching the film is characterized by comprising, in sequence, a first step of obtaining a long strip of first stretched film, and a second step of further stretching the long strip of first stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is in the range of 190 to 220°C. Hereinafter, the "first step" will sometimes be referred to as the "first stretching step", and the "second step" will sometimes be referred to as the "second stretching step".

[0107] 1) Dissolving process

[0108] The process for preparing the adhesive paste is described below. A high concentration of cellulose ester in the adhesive paste is preferable as it reduces the drying load after casting on the metal support. However, if the concentration of cellulose ester is too high, the load during filtration increases, and the filtration accuracy deteriorates. A concentration that balances these two factors is preferably 10–35% by mass, more preferably 15–25% by mass.

[0109] The solvents used in the adhesives of this invention can be used alone or in combination of two or more. For production efficiency, it is preferable to use a mixture of good and bad solvents for cellulose esters. Regarding the solubility of cellulose esters, a higher proportion of good solvents is preferred. In terms of the preferred mixing ratio of good to bad solvents, the good solvent is 70–98% by mass, and the bad solvent is 2–30% by mass. The terms "good solvent" and "bad solvent" refer to solvents that dissolve cellulose esters alone, and solvents that swell or do not dissolve alone. Therefore, the good and bad solvents vary depending on the average degree of acetylation (degree of acetyl substitution) of the cellulose ester. For example, when using acetone as a solvent, it is a good solvent in cellulose acetate (degree of acetyl substitution 2.4) and cellulose acetate propionate, but a bad solvent in cellulose acetate (degree of acetyl substitution 2.8).

[0110] The good solvents used in this invention are not particularly limited, and examples include organohalogen compounds such as dichloromethane, dioxolane compounds, acetone, methyl acetate, and methyl acetoacetate. Particularly preferred examples include dichloromethane or methyl acetate.

[0111] Furthermore, there are no particular limitations on the unsuitable solvents used in this invention; for example, methanol, ethanol, n-butanol, cyclohexane, and cyclohexanone are preferred. Additionally, it is preferable that the slurry contains 0.01 to 2% by mass of water. Furthermore, for the solvent used in the dissolution of the cellulose ester, the solvent removed from the membrane by drying during the membrane fabrication process is recovered and reused. The recovered solvent may sometimes contain trace amounts of additives added to the cellulose ester, such as plasticizers, UV absorbers, polymers, and monomer components; even if these are present, they can preferably be reused, and can be purified for reuse as needed.

[0112] As a method for dissolving cellulose esters in the preparation of the above-described paste, a conventional method can be used. Combining heating and pressurization allows heating to be performed above the boiling point at atmospheric pressure. Dissolving by heating and stirring at a temperature above the boiling point of the solvent at atmospheric pressure and within the range where the solvent does not boil under pressure is preferable, as it prevents the formation of gel-like, undissolved lumps called "mamako". Alternatively, a method of mixing the cellulose ester with a poor solvent, wetting or swelling it, and then further adding a good solvent for dissolution is also preferred.

[0113] Pressurization can be achieved by injecting inert gases such as nitrogen, or by increasing the vapor pressure of the solvent through heating. Heating is preferably performed externally; for example, jacketed heating is preferred because temperature control is easier.

[0114] From the viewpoint of the solubility of cellulose esters, a higher heating temperature for adding the solvent is preferred. If the heating temperature is too high, the required pressure increases, and the productivity decreases. The preferred heating temperature is 45–120°C, more preferably 60–110°C, and even more preferably 70–105°C. In addition, the pressure is adjusted so that the solvent does not boil at the set temperature.

[0115] Alternatively, a cooling dissolution method is preferred, which allows cellulose esters to dissolve in solvents such as methyl acetate.

[0116] Next, the cellulose ester solution is filtered using a suitable filter material such as filter paper. For the filter material, a low absolute filtration precision is preferred to remove insoluble matter; if the absolute filtration precision is too low, clogging of the filter material is likely to occur. Therefore, a filter material with an absolute filtration precision of 0.008 mm or less is preferred, more preferably 0.001 to 0.008 mm, and even more preferably 0.003 to 0.006 mm.

[0117] There are no particular restrictions on the material of the filter media; common filter media can be used. Plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel are preferred because they do not shed fibers. Filtration is preferred to remove or reduce impurities, especially bright foreign matter, contained in the cellulose ester of the raw material.

[0118] A bright spot or foreign object refers to a point (foreign object) visible when two polarizers are arranged in an orthogonal Nicol configuration, with an optical film placed between them, and light is shone from one side of the polarizer. When viewed from the other side, light leaks from the opposite side. Preferably, the number of bright spots with a diameter of 0.01 mm or more is 200 per cm. 2 The following is preferred. More preferably, 100 pieces / cm 2 The following is a further preferred option: 50 units / m 2 The following is a further preferred option: 0 to 10 per cm. 2 Below. Additionally, it is preferable to have fewer bright spots smaller than 0.01mm.

[0119] The filtration of the adhesive can be carried out using conventional methods. A method of filtration while heating is preferred because it minimizes the increase in the pressure difference (called differential pressure) before and after filtration, where the solvent's boiling point is above its atmospheric pressure and does not boil under pressure. Preferred temperatures are 45–120°C, more preferably 45–70°C, and even more preferably 45–55°C.

[0120] The filtration pressure is preferably low. The filtration pressure is preferably 1.6 MPa or less, more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

[0121] Here, the process of casting the adhesive paste will be explained.

[0122] 2) Casting process

[0123] Regarding the metal support in the casting process, a product with a mirror-finished surface is preferred. A roller with a surface plated and finished using stainless steel strips or castings is preferred as the metal support. The casting width can be set from 1 to 4 meters. The surface temperature of the metal support in the casting process is above -50°C and below the boiling point of the solvent. Higher temperatures result in faster drying of the mesh (the adhesive film formed by casting the adhesive on the support is called the "mesh"). Therefore, it is preferable that if the temperature is too high, the mesh may foam or its planarity may deteriorate. A preferred support temperature is 0 to 40°C, more preferably 5 to 30°C. Alternatively, cooling the mesh to gel it and peeling it off from the roller while it still contains a large amount of residual solvent is also a preferred method. There are no particular limitations on the method for controlling the temperature of the metal support; methods include spraying warm or cold air, or contacting the back side of the metal support with warm water. When using warm water, heat transfer is efficient, so a short time until the metal support reaches a certain temperature is preferred. When using warm air, sometimes the air temperature is higher than the target temperature.

[0124] 3) Solvent evaporation process

[0125] It is a process of heating the mesh on a casting support to evaporate the solvent.

[0126] When evaporating the solvent, methods include blowing air from the side of the mesh and / or using liquid heat transfer from the back of the support, or using radiant heat to transfer heat from the surface to the back. The back-side liquid heat transfer method is preferred due to its good drying efficiency. Alternatively, a combination of these methods is also preferred. It is preferable to dry the cast mesh on the support in an atmosphere of 40–100°C. When maintaining the atmosphere at 40–100°C, it is preferable to spray warm air at that temperature onto the mesh or to use infrared radiation or other means for heating.

[0127] From the perspectives of surface quality, moisture permeability, and peelability, it is preferable to peel the mesh from the support within 30 to 120 seconds.

[0128] 4) Stripping process

[0129] This is a process of peeling off the mesh, which has undergone solvent evaporation on a metal support, at the peeling location. The peeled mesh is then fed into the next process.

[0130] The temperature at the peeling location on the metal support is preferably in the range of 10 to 40°C, and more preferably in the range of 11 to 30°C.

[0131] Furthermore, the amount of residual solvent during the peeling of the mesh on the metal support depends on the strength of the drying conditions and the length of the metal support. It is preferably within the range of 50% to 120% by mass. If the mesh is too soft when peeling with a higher amount of residual solvent, it will impair the planarity during peeling and easily cause shrinkage cracks and longitudinal stripes caused by peeling tension. Therefore, the amount of residual solvent during peeling should be determined while taking into account both economic speed and quality.

[0132] The amount of residual solvent in the network is defined by the following formula.

[0133] Residual solvent content (%) = (Mass of the network before heat treatment - Mass of the network after heat treatment) / (Mass of the network after heat treatment) × 100

[0134] Furthermore, the heat treatment for determining the amount of residual solvent is indicated by a heat treatment at 140°C for 1 hour.

[0135] The peeling tension when separating the metal support and the film is typically in the range of 50 to 245 N / m. In cases where wrinkles are easily generated during peeling, a peeling tension of less than 190 N / m is preferred.

[0136] In this invention, it is preferable that the temperature at the peeling location on the metal support is in the range of -50 to 40°C, more preferably in the range of 10 to 40°C, and most preferably in the range of 15 to 30°C.

[0137] In order to ensure good planarity of the optical film, the amount of residual solvent when peeling the mesh from the metal support is preferably 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130% by mass, and particularly preferably 20 to 30% by mass or 70 to 120% by mass.

[0138] 5) Stretching and drying processes

[0139] (Stretching operation, refractive index control)

[0140] The optical film stretching process of the present invention is characterized by a first step of obtaining a long strip of first stretched film, and a second step of further stretching the long strip of first stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is in the range of 190 to 220°C.

[0141] The first step described above is a process that, to some extent, evaporates the residual solvent in the optical film and ensures the planarity of the film. The second step described above is a process that reduces the phase difference by mitigating the orientation of the cellulose ester resin caused by the high-temperature treatment and obtaining a wide optical film produced by high-magnification stretching.

[0142] That is, cellulose acetate, as a plant-derived resin, exhibits a three-dimensional structure due to intermolecular interactions, which becomes ordered during high-temperature stretching. Even stretching at temperatures higher than the glass transition temperature generates stress. By adjusting the degree of substitution at the 6-position of the pyranose ring, the ordering of the resin is suppressed, enabling low-stress stretching at high temperatures. Furthermore, by combining it with the sugar ester involved in this invention, during high-temperature stretching, the additive readily enters the intermolecular space of cellulose, causing randomization and low stress in the cellulose orientation, thus reducing the manifestation of phase difference. In addition, through the strong interaction between the cellulose backbone and the additive, orientation changes are difficult to occur in response to changes in ambient temperature and humidity, resulting in a film with minimal phase difference variation associated with environmental changes.

[0143] Therefore, by adjusting the degree of substitution at the 6-position of the pyranose ring or using appropriate additives, even at high temperatures and high stretching ratios, breakage and property degradation can be mitigated. Furthermore, if a sudden high-temperature treatment is performed in the first step, foaming and curling deformation caused by residual solvents can easily occur, leading to deterioration of the physical and optical properties of the optical film. Therefore, the first step and the subsequent second step are necessary.

[0144] The optical film of the present invention is characterized in that the retardation value R expressed by the above formula is... o R is in the range of 0 to 10 nm. t The range is -10 to 10 nm.

[0145] Furthermore, to improve the effectiveness of the present invention, a delay value R is more preferred. o The range is 0–5 nm, and R t In the range of -5 to 5 nm.

[0146] To obtain the above delay value R o R t In this case, it is preferable that the optical film adopts the structure of the present invention, and then the refractive index is controlled by the stretching operation involved in the present invention.

[0147] Generally, in terms of stretching operations, the film can be stretched sequentially or simultaneously in its longitudinal direction (film-forming direction) and in a direction orthogonal to it within the film surface, i.e., its width direction. In this invention, the film stretching process sequentially includes: a first step to obtain a long strip of first stretched film; and a second step to further stretch the long strip of first stretched film to obtain a second stretched film, wherein the stretching temperature in the second step is within the range of 190–220°C. That is, sequential stretching is required.

[0148] Regarding the stretching temperature in the first process of obtaining the first stretched film, when the glass transition temperature of the film is set to Tg, stretching is preferably performed in the temperature range of (Tg+10) to (Tg+50) °C. If the temperature is below (Tg+10) °C, delay is likely to occur, and the tensile stress increases, thus increasing haze. If stretching is performed at a temperature exceeding (Tg+50) °C, film foaming-induced breakage or planarity degradation occurs, leading to enhanced film coloring. The stretching temperature is preferably performed in the range of (Tg+15) to (Tg+40) °C.

[0149] It should be noted that the glass transition temperature Tg mentioned here is the intermediate glass transition temperature (Tmg) determined using a commercially available differential scanning calorimeter at a heating rate of 20°C / min, according to JIS K7121 (1987).

[0150] The specific method for determining the glass transition temperature Tg of the optical film was in accordance with JIS K7121 (1987), using a differential scanning calorimeter DSC220 manufactured by Seiko Instruments Co., Ltd.

[0151] A sample of optical film of about 10 mg was prepared. Under the condition of nitrogen flow rate of 50 ml / min, the temperature was increased from room temperature to 250℃ at 20℃ / min and held for 10 minutes (first scan). Then, the temperature was decreased to 30℃ at 20℃ / min and held for 10 minutes (second scan). Then, the temperature was increased to 250℃ at 20℃ / min (third scan). DSC curves were prepared. The glass transition temperature Tg can be determined from the DSC curve of the third scan.

[0152] In this invention, the material constituting the optical film is prepared experimentally in advance, and the stretching of the optical film within the above-mentioned temperature range is preferably performed to determine the Tg of the optical film.

[0153] The stretching temperature of the second process for obtaining the second stretched film is preferably +60 to +100°C compared to the stretching temperature of the first process for obtaining the first stretched film. Furthermore, the higher the stretching temperature of the second process, the more capable it is of low-stress stretching. Therefore, it is preferably 200°C or higher, and more preferably in the range of 205 to 215°C.

[0154] The stretching operation, apart from the first and second stretching steps, can be divided into multiple stages, and biaxial stretching can also be performed in the casting direction and the width direction. Furthermore, in the case of biaxial stretching, it can be performed simultaneously or in stages. Regarding the stretching ratio, combining the casting direction and the width direction relative to the original width of the film, it is preferably in the range of 1.1 to 4 times, more preferably 1.2 to 3 times.

[0155] In this case, the term "staged" can refer to, for example, performing stretching in different directions sequentially, or dividing the stretching in the same direction into multiple stages, and applying stretching in different directions in any one of those stages. That is, for example, the following stretching steps can also be performed.

[0156] Stretch in the casting direction → Stretch in the width direction → Stretch in the casting direction → Stretch in the casting direction

[0157] Stretch in the width direction → Stretch in the width direction → Stretch in the casting direction → Stretch in the casting direction

[0158] The preferred stretching ratio is 1.1 to 2.5 times the original width in both the width and longitudinal directions. Particularly preferred, from the viewpoint of reducing retardation, is a stretching ratio of 1.1 to 2.5 times the original width of the film in the width direction, more preferably 1.5 to 2.1 times. Furthermore, a stretching ratio of 1.1 to 2.0 times in the longitudinal direction is preferred, and more preferably 1.2 to 1.5 times.

[0159] There are no particular limitations on the method for stretching the mesh. Examples include: applying a difference in circumferential speed to multiple rollers and stretching longitudinally using this difference; fixing both ends of the mesh with clamps and needles, and increasing the spacing between the clamps and needles in the direction of travel to stretch longitudinally; similarly, expanding laterally and stretching laterally; or expanding both longitudinally and laterally simultaneously and stretching in both directions. Of course, these methods can be combined. Furthermore, in the case of the tenter frame method, if the clamping mechanism is driven linearly, smooth stretching can be achieved, reducing the risk of breakage, and is therefore preferred.

[0160] The width maintenance or lateral stretching in the film-making process is preferably performed using a tenter frame, which can be a pin plate tenter frame or a clamp tenter frame.

[0161] After stretching, the long strip film is cooled in the precipitation suppression zone to alleviate the tensile stress. From the viewpoint of maintaining and improving the planarity and optical properties of the film, it is preferable that the temperature of the precipitation suppression zone is in the range of -100 to -50°C compared to the temperature of the second stretching process described above. More preferably, it is in the range of -70 to -50°C. The time taken to pass through the precipitation suppression zone is adjusted appropriately while monitoring the film temperature.

[0162] Secondly, the optical film is dried using a drying device that alternately passes and transports multiple rollers within the drying apparatus.

[0163] In the drying process of the optical film, it is preferable that the residual solvent content of the film is 1% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0 to 0.01% by mass or less.

[0164] There are no particular restrictions on the means of drying the membrane. Hot air, infrared rays, heating rollers, microwaves, etc. can usually be used. For simplicity, hot air is preferred.

[0165] The drying temperature in the membrane drying process is preferably between 40 and 200°C, and is gradually increased. It is more preferably in the range of 50 to 140°C to improve dimensional stability.

[0166] The dried optical film is wound using an optical film winding device 39 to form an optical film roll.

[0167] There is no particular limitation on the thickness of the optical film, and 10–200 μm is used. A thickness of 10–100 μm is particularly preferred. A thickness of 20–60 μm is even more preferred.

[0168] Regarding the optical film of the present invention, an optical film with a width of 1 to 4 m is used. It is particularly preferred to use an optical film with a width of 1.4 to 4 m, and even more preferably, from the viewpoint of obtaining a wide optical film, it is 1.6 to 3 m.

[0169] Figure 2 The figure illustrates an example of the apparatus used in the paste preparation step, casting step, stretching step, and drying step of the preferred solution casting film forming method of the present invention.

[0170] Various additive solutions are fed from the feed tank 41, large agglomerates are removed by the filter 44, and the solution is fed into the storage tank 42. Then, various additive solutions are added from the storage tank 42 to the main slurry dissolving tank 1. After the prepared main slurry is filtered, it is cast from the pressure die 30 onto the metal strip (support) 31, dried to form a mesh, and then peeled off at the peeling position 33. After drying while being transported by multiple transfer rollers, it is stretched using the stretching device 34 of the first stretching process and the stretching device 35 of the second stretching process to achieve the desired delay value. Then, in the precipitation suppression zone 36, it is cooled to moderate the film temperature and dried using the drying device 37. Then, while being transported in the drying device 37 with multiple transfer rollers 38, it is dried and wound using the optical film winding device 39 to form an optical film roll 40.

[0171] [2] Materials constituting optical films

[0172] <Cellulose ester resin>

[0173] The optical film of the present invention comprises a cellulose ester resin (hereinafter sometimes referred to as "cellulose ester") with a total acetyl substitution degree in the range of 2.30 to 2.60. By using a cellulose ester with a low total acetyl substitution degree, a wide film can be obtained by stretching at a high stretch ratio, and low phase difference visibility can be obtained because low-stress stretching is possible. In addition, defects such as breakage can be avoided. In the case of cellulose esters with an acetyl substitution degree exceeding 2.60, the cellulose ester becomes ordered, making it difficult to achieve a high stretch ratio.

[0174] Cellulose molecules are composed of multiple linked glucose units, each with three hydroxyl groups. The number of acetyl groups derived from these three hydroxyl groups is called the degree of acetyl substitution. For example, diacetylcellulose (DAC) has an average of 2 to 2.5 acetyl groups bonded to the three hydroxyl groups of its glucose units.

[0175] The cellulose esters used in this invention include carboxylic acid esters with approximately 2 to 22 carbon atoms, which can be esters of aromatic carboxylic acids, and are particularly preferably lower fatty acid esters of cellulose. Lower fatty acids in lower fatty acid esters of cellulose refer to fatty acids with 6 or fewer carbon atoms. The acetyl group bonded to the hydroxyl group can be straight-chain, branched, or form a ring. Furthermore, it can be substituted with other substituents. The number of carbon atoms is preferably selected from acetyl groups with 2 to 6 carbon atoms. The number of carbon atoms in this acetyl group is preferably 2 to 4, more preferably 2 to 3. That is, in this invention, diacetylcellulose is used, which is an essential cellulose ester resin for exhibiting the effects of this invention.

[0176] The degree of acetyl substitution of cellulose esters can be determined according to ASTM D-817-91, with a preferred degree of acetyl substitution of 2.30 to 2.45.

[0177] When the degree of acetyl substitution of cellulose ester is less than 2.30, the water absorption and moisture permeability of the membrane increase, and the protective function of the polarizer may become insufficient.

[0178] The weight-average molecular weight (Mw) of the cellulose ester is preferably 120,000 or higher, with no particular upper limit, but more preferably in the range of 120,000 to 190,000. If within this range, the viscosity of the adhesive during solution casting will not be too high, and defects such as mold streaks during casting are less likely to occur. Furthermore, with the weight-average molecular weight (Mw) within this range, the mechanical strength and other physical properties of the optical film are also excellent.

[0179] A number-average molecular weight (Mn) of 30,000 to 300,000 is preferred because the resulting cellulose ester film has high mechanical strength. A number-average molecular weight of 40,000 to 100,000 is more preferred.

[0180] The ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the cellulose ester (Mw / Mn) is preferably 1.4 to 3.0.

[0181] The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of cellulose esters were determined by gel permeation chromatography (GPC).

[0182] The measurement conditions are as follows.

[0183] Solvent: dichloromethane

[0184] Columns: Shodex K806, K805, K803G (use 3 Showa Denko (Co., Ltd.)

[0185] Column temperature: 25℃

[0186] Sample concentration: 0.1% by mass

[0187] Detector: RI Model 504 (manufactured by GL Science Co., Ltd.)

[0188] Pump: L6000 (manufactured by Hitachi, Ltd.)

[0189] Flow rate: 1.0 ml / min

[0190] Calibration curves: Calibration curves were prepared using 13 samples of standard polystyrene (STK standard polystyrene, manufactured by Tosoh Corporation) with Mw = 1,000,000 to 500. The 13 samples were used at approximately equal intervals.

[0191] The cellulose ester used in this invention can be synthesized using known methods. Specifically, it can be synthesized using the method described in Japanese Patent Application Publication No. 10-45804.

[0192] Cellulose, as a raw material for cellulose esters, is not particularly limited and can include cotton lint, wood pulp (from coniferous trees and broadleaf trees), kenaf, etc. Furthermore, cellulose esters obtained from these sources can be mixed separately in any proportion for use.

[0193] On the other hand, commercially available cellulose esters can be used. Examples of commercially available cellulose esters include Daicel Corporation's L20, L30, L40, and L50, and Eastman Chemical Company's Ca398-3, Ca398-6, Ca398-10, Ca398-30, and Ca394-60S.

[0194] The preferred method for synthesizing cellulose acetate in this invention will be described below.

[0195] Synthesis of Cellulose Acetate

[0196] (Synthesis example 1)

[0197] The sulfate-dissolved pulp (93% α-cellulose content) was beaten (hydrolyzed), then subjected to acetone replacement and drying. For every 100 parts by weight of this pulp, 500 parts by weight of acetic acid were evenly distributed and mixed at 40°C for 30 minutes for pretreatment activation.

[0198] On the other hand, an esterification reaction was carried out using conventional methods with the addition of a mixture of 250 parts by mass of acetic anhydride and 4.0 parts by mass of sulfuric acid. The contents were exothermic due to the reaction of water and acetic anhydride with the raw pulp and the reaction of cellulose and acetic anhydride, which was adjusted by external cooling. Then, 125 parts by mass of organic solvent were added, and the acetylation reaction was carried out under heat preservation.

[0199] Next, after removing the organic solvent used as the reaction solution by heat, 35 parts by mass of a 20% calcium acetate aqueous solution are added to completely neutralize the sulfuric acid in the system and to make calcium acetate in excess (1.09 equivalents relative to sulfuric acid).

[0200] The completely neutralized reaction mixture was maintained at 150°C for 50 minutes, and then allowed to reach 100°C at atmospheric pressure. A dilute aqueous acetic acid solution was added to the reaction mixture with stirring. After separation as sheet-like cellulose acetate, the ester was thoroughly washed with water, removed, and dried. The resulting sheet-like cellulose acetate A had an acetyl substitution degree of 2.4, a number-average molecular weight of 47,500, and a weight-average molecular weight of 166,000.

[0201] (Synthesis example 2)

[0202] In Synthesis Example 1, instead of 35 parts by mass of 20% calcium acetate aqueous solution, 29 parts by mass of 20% magnesium acetate aqueous solution (1.00 equivalent relative to sulfuric acid) were prepared.

[0203] (Synthesis example 3)

[0204] In Synthesis Example 1, the amount of 20% calcium acetate aqueous solution added was changed to 39 parts by mass (1.21 equivalents relative to sulfuric acid).

[0205] (Synthesis Example 4)

[0206] In Synthesis Example 2, the amount of 20% magnesium acetate aqueous solution added was changed to 37 parts by mass (1.28 equivalents relative to sulfuric acid).

[0207] (Synthesis Example 5)

[0208] In Synthesis Example 1, the amount of 20% calcium acetate aqueous solution added was changed to 28 parts by weight (0.98 equivalents relative to sulfuric acid).

[0209] <The sugar esters having furanose or pyranose structures involved in this invention>

[0210] The optical film of the present invention is characterized in that it comprises a compound having all or part of the hydroxyl groups of a compound (A) having one furanose structure or pyranose structure, or a compound (B) having at least two and no more than twelve furanose structures or pyranose structures, esterified with an aliphatic acyl group, i.e., a so-called "glycoester".

[0211] Examples of preferred compounds (A) and (B) can be listed below, but the invention is not limited to these.

[0212] Examples of compound (A) include glucose, galactose, mannose, fructose, xylose, arabinose, etc.

[0213] Furthermore, examples of compound (B) include lactose, sucrose, cellobiose, maltose, cellotrisaccharide, maltotrisaccharide, raffinose, and fructotris. Among these compounds (A) and (B), compounds having both furanose and pyranose structures are particularly preferred. Sucrose is an example.

[0214] There are no particular limitations on the monocarboxylic acid used in the synthesis of compounds that esterify all or part of the hydroxyl groups in compounds (A) and (B) of this invention. Known aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, etc., can be used to synthesize the sugar esters used in this invention. The carboxylic acid used may be one type or a mixture of two or more types.

[0215] Preferred aliphatic monocarboxylic acids include, for example, saturated fatty acids such as acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2-ethylhexanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanic acid, stearic acid, nonadecanic acid, arachidic acid, docosanoic acid, ceric acid, heptadecanic acid, linoleic acid, beeswax acid, and laccosic acid; and unsaturated fatty acids such as undecenoic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, and octenic acid.

[0216] Examples of preferred alicyclic monocarboxylic acids include cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, cyclooctanecarboxylic acid, or their derivatives.

[0217] Details of the methods for manufacturing these compounds are described in Japanese Patent Application Publication No. 8-245678.

[0218] In addition to the esterified compounds of compounds (A) and (B) mentioned above, esterified compounds of oligosaccharides can be used as compounds of the present invention that incorporate at least one of 3 to 12 furanose or pyranose structures.

[0219] Oligosaccharides are manufactured by acting enzymes such as amylase on starch, sucrose, etc. Examples of oligosaccharides applicable to this invention include maltodextrin, isomaltoligosaccharide, fructodextrin, galactodextrin, and xylose oligosaccharide. Oligosaccharides can also be acetylated using the same method as compounds (A) and (B) described above.

[0220] Secondly, an example of the manufacture of sugar ester compounds is described.

[0221] Acetic anhydride (200 ml) was added dropwise to a solution of glucose (29.8 g, 166 mmol) containing pyridine (100 ml) and allowed to react for 24 hours. The solution was then concentrated using an evaporator and placed in ice water. After standing for 1 hour, the solution was filtered through a glass filter to separate the solid and water. The solid remaining on the glass filter was dissolved in chloroform and diluted with cold water until neutral. The organic layer was separated and dried over anhydrous sodium sulfate. After removing the anhydrous sodium sulfate by filtration, the chloroform was removed using an evaporator, followed by drying under reduced pressure to obtain glucose pentaacetate (58.8 g, 150 mmol, 90.9%). It should be noted that the aforementioned monocarboxylic acid can be used instead of the acetic anhydride described above.

[0222] The following are specific examples of the sugar ester compounds involved in this invention, but the invention is not limited thereto.

[0223] [Chemistry 1] Compound 1

[0224]

[0225] Compound 2

[0226]

[0227] Compound 3

[0228]

[0229]

Chemistry 2

[0230] Compound 4

[0231]

[0232] Compound 5

[0233]

[0234] Compound 6

[0235]

[0236] Compound 7

[0237]

[0238]

Transformation 3

[0239] Compound 8

[0240]

[0241] Compound 9

[0242]

[0243]

Chemistry 4

[0244] Compound 10

[0245]

[0246]

Transformation 5

[0247] Compound 11

[0248]

[0249] Compound 12

[0250]

[0251] [Chemical Engineering 6] Compound 13

[0252]

[0253]

Transformation 7

[0254] Compound 14

[0255]

[0256] [Compound]5

[0257]

[0258] Regarding the optical film of the present invention, in order to suppress humidity variations in phase difference and stabilize display quality, it is preferable to contain, in the optical film, a sugar ester in which all or part of the hydroxyl groups of the compound (A) having one furanose or pyranose structure, or the hydroxyl groups of the compound (B) having at least one furanose or pyranose structure, are esterified with aliphatic acyl groups, in a range of 1 to 35% by mass, particularly 10 to 25% by mass. Within this range, the excellent effects of the present invention are exhibited, and precipitation during the storage of the original film is absent, which is therefore preferred. Preferably, a sugar ester with all hydroxyl groups esterified and a sugar ester with one or more residual hydroxyl groups are used in combination. This results in less precipitation and less variation in the viewing angle compared to the case where a sugar ester with all hydroxyl groups esterified is used.

[0259] For example, a mixture of sucrose octaacetate, sucrose heptaacetate, and sucrose hexaacetate is preferred. There is no particular limitation on the mixing ratio; examples include 30:30:30, 40:30:30, 40:50:10, 50:30:20, 60:30:10, 80:10:10, 90:7:3, and 95:5:0. These can be controlled by adjusting the reaction time or the amount of monocarboxylic acid added during sugar esterification, or by mixing the individual components.

[0260] [3] Other additives

[0261] <Polyester>

[0262] In addition to the aforementioned sugar esters, the optical film of the present invention preferably uses polyester, and more preferably a polyester having a structure represented by the following general formula (I). From the perspective of its plasticizing effect, in order to improve brittleness, it is preferable to contain the polyester in the range of 1 to 20% by mass, and more preferably in the range of 5 to 15% by mass.

[0263] General formula (I): B-(GA)nGB

[0264] (In the formula, B represents an aliphatic or aromatic monocarboxylic acid residue. G represents an alkylene glycol residue with 2 to 12 carbon atoms, an aryl glycol residue with 6 to 12 carbon atoms, or an oxoalkylene glycol residue with 4 to 12 carbon atoms. A represents an alkylene dicarboxylic acid residue with 4 to 12 carbon atoms or an aryl dicarboxylic acid residue with 6 to 12 carbon atoms. n represents an integer greater than or equal to 1.)

[0265] The polyester used in this invention is a polyester containing repeating units obtained by reacting dicarboxylic acid and diol, where A represents a carboxylic acid residue in the ester and G represents an alcohol residue.

[0266] The dicarboxylic acid constituting the polyester is an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, or an alicyclic dicarboxylic acid, preferably an aromatic dicarboxylic acid. The dicarboxylic acid can be one type or a mixture of two or more types.

[0267] The diol constituting the polyester is an aromatic diol, an aliphatic diol, or an alicyclic diol, preferably an aliphatic diol, and more preferably a diol with 1 to 4 carbon atoms. The diol may be one type or a mixture of two or more types.

[0268] Preferably, it includes a repeating unit obtained by reacting a dicarboxylic acid containing at least an aromatic dicarboxylic acid with a diol having 1 to 8 carbon atoms; more preferably, it includes a repeating unit obtained by reacting a dicarboxylic acid containing both aromatic and aliphatic dicarboxylic acids with a diol having 1 to 8 carbon atoms.

[0269] The ends of the polyester molecules can be closed (end-sealed) or not. From the viewpoint of reducing the delayed changes of the optical film in response to temperature and humidity changes, it is preferable to close them.

[0270] Specific examples of alkylene dicarboxylic acids constituting A of general formula (I) include divalent groups derived from 1,2-ethanedicarboxylic acid (succinic acid), 1,3-propanedicarboxylic acid (glutaric acid), 1,4-butanedicarboxylic acid (adipic acid), 1,5-pentanedicarboxylic acid (heptanoic acid), and 1,8-octanedicarboxylic acid (sebacic acid). Specific examples of alkenyl dicarboxylic acids constituting A include maleic acid and fumaric acid. Specific examples of aryl dicarboxylic acids constituting A include 1,2-phthalic acid (phthalic acid), 1,3-phthalic acid, 1,4-phthalic acid, and 1,5-naphthalenedicarboxylic acid.

[0271] A can be one type or a combination of two or more types. Preferably, A is a combination of alkylene dicarboxylic acids with 4 to 12 carbon atoms and aryl dicarboxylic acids with 8 to 12 carbon atoms.

[0272] In general formula (I), G represents a divalent group derived from an alkylene glycol with 2 to 12 carbon atoms, a divalent group derived from an aryl glycol with 6 to 12 carbon atoms, or a divalent group derived from an oxoalkylene glycol with 4 to 12 carbon atoms.

[0273] Examples of divalent groups derived from alkylene glycols having 2 to 12 carbon atoms in G include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentanediol), and 2,2-diethyl-1,3-propanediol (…). Divalent groups derived from 3,3-dihydroxymethylpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dihydroxymethylheptane), 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and 1,12-octadecanediol, etc.

[0274] Examples of divalent groups derived from aryl diols having 6 to 12 carbon atoms in G include divalent groups derived from 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), and 1,4-dihydroxybenzene (hydroquinone). Examples of divalent groups derived from oxoalkylene diols having 4 to 12 carbon atoms in G include divalent groups derived from diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol.

[0275] G can be one type or a combination of two or more types. Preferably, G is an alkylene glycol with 2 to 12 carbon atoms.

[0276] In general formula (I), B is a monovalent group derived from a monocarboxylic acid containing an aromatic ring or an aliphatic monocarboxylic acid.

[0277] Monovalent groups derived from monocarboxylic acids containing aromatic rings are carboxylic acids containing an aromatic ring within the molecule. This includes not only carboxylic acids where the aromatic ring is directly bonded to a carboxyl group, but also those where the aromatic ring is bonded to a carboxyl group via an alkylene group or similar pathway. Examples of monovalent groups derived from monocarboxylic acids containing aromatic rings include monovalent groups derived from benzoic acid, p-tert-butylbenzoic acid, o-toluic acid, m-toluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, n-propylbenzoic acid, aminobenzoic acid, acetoxybenzoic acid, phenylacetic acid, 3-phenylpropionic acid, etc.

[0278] Examples of monovalent groups derived from aliphatic monocarboxylic acids include monovalent groups derived from acetic acid, propionic acid, butyric acid, octanoic acid, hexanoic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid, etc. Among these, monovalent groups derived from alkyl monocarboxylic acids having 1 to 3 carbon atoms in the alkyl moiety are preferred, and acetyl groups (monovalent groups derived from acetic acid) are more preferred.

[0279] The weight-average molecular weight of the polyester involved in this invention is preferably in the range of 500 to 3000, more preferably in the range of 600 to 2000. The weight-average molecular weight can be determined using the gel permeation chromatography (GPC) method described above.

[0280] The following are specific examples of polyesters of the present invention having a structure represented by general formula (I), but are not limited thereto.

[0281]

Transformation 8

[0282]

[0283]

Chemistry 9

[0284]

[0285]

Chemistry 10

[0286]

[0287] Specific examples of the synthesis of the polyester involved in this invention are described below.

[0288] <Polyester P1>

[0289] 180g of ethylene glycol, 278g of phthalic anhydride, 91g of adipic acid, 610g of benzoic acid, and 0.191g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230°C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted ethylene glycol was removed by vacuum distillation at 200°C to obtain polyester P1. The acid value was 0.20, and the number average molecular weight was 450.

[0290] <Polyester P2>

[0291] 251g of 1,2-propanediol, 244g of phthalic anhydride, 103g of adipic acid, 610g of benzoic acid, and 0.191g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230°C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted 1,2-propanediol was removed by vacuum distillation at 200°C to obtain polyester P2. The acid value was 0.10, and the number average molecular weight was 450.

[0292] <Polyester P3>

[0293] 330 g of 1,4-butanediol, 244 g of phthalic anhydride, 103 g of adipic acid, 610 g of benzoic acid, and 0.191 g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2 L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230 °C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted 1,4-butanediol was removed by vacuum distillation at 200 °C to obtain polyester P3. The acid value was 0.50, and the number average molecular weight was 2000.

[0294] <Polyester P4>

[0295] 251 g of 1,2-propanediol, 354 g of terephthalic acid, 610 g of benzoic acid, and 0.191 g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2 L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230 °C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted 1,2-propanediol was removed by vacuum distillation at 200 °C to obtain polyester P4. The acid value was 0.10, and the number average molecular weight was 400.

[0296] <Polyester P5>

[0297] 251 g of 1,2-propanediol, 354 g of terephthalic acid, 680 g of p-methylbenzoic acid, and 0.191 g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2 L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230 °C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted 1,2-propanediol was removed by vacuum distillation at 200 °C to obtain polyester P5. The acid value was 0.30, and the number average molecular weight was 400.

[0298] <Polyester P6>

[0299] 180 g of 1,2-propanediol, 292 g of adipic acid, and 0.191 g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2 L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated slowly with stirring under a nitrogen atmosphere until it reached 200 °C. The degree of polymerization was observed while the dehydration condensation reaction was induced. After the reaction was complete, unreacted 1,2-propanediol was removed by vacuum distillation at 200 °C to obtain polyester P6. The acid value was 0.10, and the number average molecular weight was 400.

[0300] <Polyester P7>

[0301] 160g of ethylene glycol, 292g of adipic acid, and 0.191g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated slowly with stirring under a nitrogen atmosphere until it reached 200°C. The degree of polymerization was observed while the dehydration condensation reaction was induced. After the reaction was complete, unreacted ethylene glycol was removed by vacuum distillation at 200°C to obtain <polyester P7>. The acid value was 0.10, and the number average molecular weight was 1000.

[0302] <Polyester P8>

[0303] 251g of ethylene glycol, 244g of phthalic anhydride, 200g of sebacic acid, 610g of benzoic acid, and 0.191g of tetraisopropyl titanate (as an esterification catalyst) were placed in a 2L four-necked flask equipped with a thermometer, stirrer, and slow condenser. The mixture was heated to 230°C under a nitrogen atmosphere while stirring and slowly increasing the temperature. The degree of polymerization was observed during the dehydration condensation reaction. After the reaction was complete, unreacted ethylene glycol was removed by vacuum distillation at 200°C to obtain polyester P8. The acid value was 0.50, and the number average molecular weight was 2000.

[0304] The polyester content in the optical film used in this invention is preferably in the range of 1 to 20% by mass, more preferably in the range of 1.5 to 15% by mass. Within the above range, a plasticizing effect can be achieved, thereby improving the brittleness of the optical film.

[0305] Plasticizers

[0306] In the optical film of the present invention, in addition to the aforementioned sugar esters and polyesters, known plasticizers with a molecular weight of 10,000 or less can also be used within a range that does not impair the effect. There are no particular limitations on the plasticizer, but it is preferably selected from polycarboxylic acid ester plasticizers, glycolate plasticizers, phthalate plasticizers, fatty acid ester plasticizers, and polyol ester plasticizers.

[0307] The polyol ester is an ester (alcohol ester) of aliphatic polyols with two or more members and a monocarboxylic acid, preferably an aliphatic polyol ester with 2 to 20 members. The polyol ester preferably has an aromatic ring or a cycloalkyl ring within its molecule.

[0308] Preferred examples of aliphatic polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutanediol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, trimethylolpropane, pentaerythritol, trimethylolethane, and xylitol. Among these, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferred.

[0309] There are no particular restrictions on the monocarboxylic acid; it can be aliphatic, alicyclic, or aromatic monocarboxylic acids, etc. To improve the membrane's moisture permeability and reduce its volatility, alicyclic or aromatic monocarboxylic acids are preferred. The monocarboxylic acid can be one type or a mixture of two or more. Furthermore, all the OH groups in the aliphatic polyol can be esterified, or some can remain as OH groups.

[0310] Aliphatic monocarboxylic acids are preferably straight-chain fatty acids with 1 to 32 carbon atoms or with side chains. More preferably, the number of carbon atoms in the aliphatic monocarboxylic acid is 1 to 20, and even more preferably 1 to 10. Examples of aliphatic monocarboxylic acids include saturated fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2-ethylhexanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanic acid, stearic acid, nonadecanic acid, arachidic acid, docosanoic acid, tetracosanoic acid, ceric acid, heptadecanic acid, linoleic acid, beeswax acid, and laccosic acid; and unsaturated fatty acids such as undecenoic acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid. Among these, to improve compatibility with cellulose acetate, acetic acid, or a mixture of acetic acid and other monocarboxylic acids, is preferred.

[0311] Examples of alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, and cyclooctane carboxylic acid.

[0312] Examples of aromatic monocarboxylic acids include benzoic acid; aromatic monocarboxylic acids (e.g., tolueneic acid) in which 1 to 3 alkyl or alkoxy groups (e.g., methoxy, ethoxy) are introduced into the benzene ring of benzoic acid; aromatic monocarboxylic acids having 2 or more benzene rings (e.g., biphenylic acid, naphthoic acid, tetrahydronaphthoic acid, etc.), preferably benzoic acid.

[0313] The polycarboxylic acid ester is an ester of an alcohol with a polycarboxylic acid of 2 or more members, preferably 2 to 20 members. The polycarboxylic acid is preferably an aliphatic polycarboxylic acid of 2 to 20 members, or an aromatic polycarboxylic acid of 3 to 20 members, or an alicyclic polycarboxylic acid of 3 to 20 members.

[0314] Examples of polycarboxylic acids include aromatic polycarboxylic acids or their derivatives with three or more elements, such as trimellitic acid, pyromellitic acid, and pyromellitic tetracarboxylic acid; aliphatic polycarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, and tetrahydrophthalic acid; and hydroxy polycarboxylic acids such as tartaric acid, hydroxymalonic acid, malic acid, and citric acid. To suppress volatilization from the membrane, hydroxy polycarboxylic acids are preferred.

[0315] Examples of alcohols include straight-chain or side-chain aliphatic saturated alcohols, straight-chain or side-chain aliphatic unsaturated alcohols, alicyclic alcohols, or aromatic alcohols. The aliphatic saturated alcohols or aliphatic unsaturated alcohols preferably have 1 to 32 carbon atoms, more preferably 1 to 20, and even more preferably 1 to 10. Examples of alicyclic alcohols include cyclopentanol and cyclohexanol. Examples of aromatic alcohols include benzyl alcohol and cinnamyl alcohol.

[0316] There is no particular limitation on the molecular weight of the polycarboxylic acid ester, but it is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. Regarding the molecular weight of polycarboxylic acid ester plasticizers, from the viewpoint of inhibiting precipitation, a larger molecular weight is preferred; from the viewpoint of moisture permeability and compatibility with cellulose acetate, a smaller molecular weight is preferred.

[0317] Examples of polycarboxylic acid esters include triethyl citrate, tributyl citrate, acetylated triethyl citrate (ATEC), acetylated tributyl citrate (ATBC), benzoyl tributyl citrate, acetylated triphenyl citrate, acetylated tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, tributyl trimellitate, and tetrabutyl pyromellitic acid.

[0318] Polycarboxylic acid esters can be phthalate esters. Examples of phthalate esters include diethyl phthalate, di(methoxyethyl) phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

[0319] Examples of glycolates include alkyl phthaloyl alkyl glycolates. Examples of alkyl phthaloyl alkyl glycolates include methyl phthaloyl methyl glycolate, ethyl phthaloyl ethyl glycolate, propyl phthaloyl propyl glycolate, butyl phthaloyl butyl glycolate, octyl phthaloyl octyl glycolate, methyl phthaloyl ethyl glycolate, ethyl phthaloyl methyl glycolate, ethyl phthaloyl propyl glycolate, methyl phthaloyl butyl glycolate, ethyl phthaloyl butyl glycolate, butyl phthaloyl methyl glycolate, butyl phthaloyl ethyl glycolate, propyl phthaloyl butyl glycolate, butyl phthaloyl propyl glycolate, methyl phthaloyl octyl glycolate, ethyl phthaloyl octyl glycolate, octyl phthaloyl methyl glycolate, octyl phthaloyl ethyl glycolate, etc., preferably ethyl phthaloyl ethyl glycolate.

[0320] Ester-based plasticizers include fatty acid esters, citrate esters, and phosphate esters.

[0321] Examples of fatty acid esters include butyl oleate, methyl acetylacetonate, and dibutyl sebacate. Examples of citrate esters include trimethyl acetylacetonate, triethyl acetylacetonate, and tributyl acetylacetonate. Examples of phosphate esters include triphenyl phosphate, tricresyl phosphate, toluene diphenyl phosphate, octyl diphenyl phosphate, biphenyl diphenyl phosphate, trioctyl phosphate, and tributyl phosphate, with triphenyl phosphate being preferred.

[0322] The content of the plasticizer relative to the cellulose ester is preferably in the range of 1 to 20% by mass, more preferably in the range of 1.5 to 15% by mass. If the content of the plasticizer is within the above range, the plasticizing effect can be exhibited, and the plasticizer in the optical film also exhibits excellent impermeability.

[0323] <Ultraviolet absorber>

[0324] When the optical film of the present invention is used as an optical film disposed on the surface side (viewable side) of a liquid crystal display device, it is preferable to contain an ultraviolet absorber from the viewpoint of improving light resistance. The ultraviolet absorber aims to improve light resistance by absorbing ultraviolet light at wavelengths of 400 nm or less, and is particularly preferably 10% or less at a wavelength of 370 nm, more preferably 5% or less, and even more preferably 2% or less.

[0325] The ultraviolet absorbers preferably used in this invention are benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and triazine-based ultraviolet absorbers, with benzotriazole-based ultraviolet absorbers and benzophenone-based ultraviolet absorbers being particularly preferred.

[0326] Examples include 5-chloro-2-(3,5-di-sec-butyl-2-hydroxyphenyl)-2H-benzotriazole, (2-2H-benzotriazole-2-yl)-6-(linear and side-chain dodecyl)-4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, and 2,4-benzyloxybenzophenone. Additionally, there are Tnuvin-type products such as Tnuvin 109, Tnuvin 171, Tnuvin 234, Tnuvin 326, Tnuvin 327, Tnuvin 328, and Tnuvin 928. These are all commercially available products manufactured by BASF Japan and are preferred for use. Among these, halogen-free ultraviolet absorbers are preferred.

[0327] In addition, disc-shaped compounds, such as those having a 1,3,5-triazine ring, are also preferred as ultraviolet absorbers.

[0328] The optical film of the present invention preferably contains two or more ultraviolet absorbers.

[0329] In addition, as a UV absorber, a polymeric UV absorber can also be used, and a polymeric UV absorber as described in Japanese Patent Application Publication No. 6-148430 is particularly preferred.

[0330] Regarding the method of adding ultraviolet absorbers, the ultraviolet absorbers can be dissolved in organic solvents such as methanol, ethanol, butanol, dichloromethane, methyl acetate, acetone, dioxolane, or mixed solvents thereof, and then added to the adhesive, or added directly to the composition of the adhesive.

[0331] For UV absorbers that are insoluble in organic solvents, such as inorganic powders, they are dispersed in organic solvents and cellulose esters using a solvent and a sand mill before being added to the paste.

[0332] The amount of ultraviolet absorber used varies depending on the type of ultraviolet absorber and the conditions of use. When the dry film thickness of the optical film is 15 to 50 μm, the amount used is preferably in the range of 0.5 to 10% by mass, and more preferably in the range of 0.6 to 4% by mass relative to the optical film.

[0333] Antioxidants

[0334] Antioxidants are also known as deterioration inhibitors. When liquid crystal display devices or similar devices are placed in high humidity and high temperature conditions, the optical film may sometimes deteriorate.

[0335] Antioxidants have the function of delaying or preventing the decomposition of optical films due to residual solvents such as halogens or phosphoric acid plasticizers in the optical film, and are therefore preferably contained in the aforementioned optical films.

[0336] As such antioxidants, hindered phenolic compounds are preferred, such as 2,6-di-tert-butyl-p-cresol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylaniline). Examples of tert-1,3,5-triazine, 2,2-thio-diethylethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N′-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrogenated cinnamamide), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-tert-butyl-4-hydroxybenzyl)-isocyanurate, etc.

[0337] Particularly preferred are 2,6-di-tert-butyl-p-cresol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate]. Additionally, hydrazine-based metal passivators such as N,N′-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine and phosphorus-based processing stabilizers such as tris(2,4-di-tert-butylphenyl)phosphite may be used concurrently.

[0338] The amount of these compounds added relative to cellulose esters, by mass ratio, is preferably in the range of 1 ppm to 1.0%, more preferably in the range of 10 to 1000 ppm.

[0339] <Particulate Matting Agent>

[0340] In the case of optical films, in order to improve the surface lubrication, microparticles (matting agents) may be further included as needed.

[0341] The particles can be inorganic or organic. Examples of inorganic particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Among these, silicon dioxide and zirconium oxide are preferred, and silicon dioxide is more preferred to reduce the increase in haze of the resulting film.

[0342] Examples of silica microparticles include AEROSIL R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600, NAX50 (all manufactured by AEROSIL Co., Ltd. of Japan), and Seagate KE-P10, KE-P30, KE-P50, and KE-P100 (all manufactured by Nippon Shokubai Co., Ltd.). Among these, AEROSIL R972V, NAX50, and Seagate KE-P30 are particularly preferred because they maintain low turbidity in the resulting film while reducing the coefficient of friction.

[0343] The primary particle size is preferably in the range of 5–50 nm, more preferably in the range of 7–20 nm. A larger primary particle size significantly improves the slip properties of the resulting film, but easily reduces transparency. Therefore, the particles can be contained as secondary aggregates with a particle size in the range of 0.05–0.3 μm. The size of the primary particles or secondary aggregates can be determined by observing the primary particles or secondary aggregates at a magnification of 500,000 to 2,000,000,000 magnification using a transmission electron microscope, and by calculating the average size of 100 primary particles or secondary aggregates.

[0344] The content of microparticles relative to the cellulose ester resin is preferably in the range of 0.05 to 1.0% by mass, more preferably in the range of 0.1 to 0.8% by mass.

[0345] [4] Polarizers and liquid crystal display devices

[0346] The polarizer using the optical film of the present invention and the liquid crystal display device of the present invention using the optical film of the present invention will be described.

[0347] The polarizer of the present invention is characterized in that it is formed by clamping at least one side of the polarizer using the polarizer protective film of the present invention described above. The liquid crystal display device of the present invention is characterized in that the polarizer of the present invention is bonded to at least one liquid crystal cell surface via an adhesive layer.

[0348] The polarizer of the present invention can be manufactured using conventional methods. Preferably, the polarizer protective film of the present invention undergoes alkaline saponification treatment on the polarizer side, and at least one side of the polarizer, which is prepared by immersion and stretching in an iodine solution, is bonded with a fully saponified polyvinyl alcohol aqueous solution. The polarizer protective film can be used on the other side, or a different polarizer protective film can be used. It is also preferable to use a commercially available cellulose ester film (e.g., KONICA MINOLTA TACK KC4UY: manufactured by Konica Minolta Co., Ltd.).

[0349] Compared to the polarizer protective film of the present invention, the polarizer protective film used for the polarizer on the opposite side via the liquid crystal cell preferably has an in-plane retardation R measured at a wavelength of 590 nm. o 150–350 nm, R t The phase difference is between -100 and 100 nm. These can be manufactured, for example, using the methods described in Japanese Patent Application Publication Nos. 2005-196149 and 2005-275104. Alternatively, a polarizing protective film that also serves as an optical compensation film for further forming an optical anisotropy layer by orienting a liquid crystal compound such as a disk-shaped liquid crystal is preferred. For example, the optical anisotropy layer can be formed using the method described in Japanese Patent Application Publication No. 2005-275083. By using the aforementioned phase difference film in combination with the polarizing protective film of the present invention, a liquid crystal display device with a stable widening effect of viewing angle can be obtained.

[0350] The polarizer, a key component of polarizers, is an element that allows light from a specific polarized wavefront to pass through. Currently, representative polarizers are polyvinyl alcohol (PVA)-based polarizing films, including those dyed with iodine and those dyed with dichroic dyes. For polarizers, products are typically made by preparing a film from an aqueous solution of PVA, uniaxially stretching and dyeing it, or by dyeing and then uniaxially stretching it, preferably after a durability treatment with a boron compound. The film thickness of the polarizer is preferably 5–30 μm, and particularly preferably 10–20 μm.

[0351] Furthermore, it is preferable to use ethylene-modified polyvinyl alcohol with an ethylene unit content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, and a degree of saponification of 99.0 to 99.99 mol%, as described in Japanese Patent Application Publication Nos. 2003-248123 and 2003-342322. Among these, an ethylene-modified polyvinyl alcohol film with a hot water cut-off temperature of 66 to 73°C is preferred. In addition, to reduce color spots, it is further preferable that the difference in hot water cut-off temperature between two points 5 cm apart in the TD direction of the film is 1°C or less; and further, to reduce color spots, it is further preferable that the difference in hot water cut-off temperature between two points 1 cm apart in the TD direction of the film is 0.5°C or less.

[0352] The polarizer using this ethylene-modified polyvinyl alcohol film exhibits excellent polarization performance and durability, and has few color spots, making it particularly suitable for large-scale liquid crystal display devices.

[0353] The polarizer obtained as described above is typically used as a polarizer by attaching a protective film to one or both sides. Examples of adhesives used for attachment include PVA-based adhesives and polyurethane-based adhesives, with PVA-based adhesives being preferred.

[0354] (IPS-mode liquid crystal display device)

[0355] By assembling the polarizer of the present invention into a commercially available IPS (In-Plane Switching) type liquid crystal display device, it is possible to manufacture a liquid crystal display device of the present invention with excellent visibility and an expanded viewing angle.

[0356] In the IPS mode of this invention, the fringe-field switching (FFS) mode is also included. By assembling the polarizer of this invention, a liquid crystal display device of this invention with the same effect can be manufactured.

[0357] When the polarizing protective film of the present invention is provided in a liquid crystal display device, a viewing-side polarizer and a backlight-side polarizer are usually formed on both sides of the liquid crystal cell. Preferably, at least one polarizing protective film is provided between the liquid crystal cell and the viewing-side polarizer or between the liquid crystal cell and the backlight-side polarizer, and the polarizing protective film of the present invention is provided on the liquid crystal cell side.

[0358] Example

[0359] The following examples illustrate the invention in detail, but the invention is not limited to these examples. It should be noted that the use of "parts" or "%" in the examples means "parts by mass" or "% by mass" unless otherwise specified.

[0360] [Example 1]

[0361] (cellulose ester resin)

[0362] Diacetylcellulose 1: acetyl substitution degree 2.45, number average molecular weight 70,000 (recorded as DAC1 in the table).

[0363] Diacetylcellulose 2: acetyl substitution degree 2.30, number average molecular weight 70,000 (recorded as DAC2 in the table).

[0364] Diacetylcellulose 3: acetyl substitution degree 2.60, number average molecular weight 70,000 (recorded as DAC3 in the table).

[0365] Triacetylcellulose: acetyl substitution degree 2.93, number average molecular weight 70,000 (listed as TAC in the table).

[0366] Cellulose acetate butyrate: acetyl substitution degree 1.29, butyryl substitution degree 1.66, degree of polymerization 230, number average molecular weight 70,000 (listed as CAB in the table).

[0367] Cellulose acetate propionate: acetyl substitution degree 0.32, propionyl substitution degree 2.60, degree of polymerization 250, number average molecular weight 70,000 (recorded as CAP in the table).

[0368] (glycoesters)

[0369] Sugar ester 1: Sucrose octaacetic acid ester with the following structure (Ac represents acetyl group).

[0370]

Chemistry 11

[0371]

[0372] Glycoester 2:

[0373] The types and numbers of substituents of aliphatic alkyl (AL) and aromatic alkyl (AR) in the sugar esters used in Japanese Patent Application Publication No. 2014-149325, paragraph number

[0265] , were changed to 6 acetyl groups and 2 benzoyl groups, respectively, to synthesize sugar esters, which are referred to as sugar ester 2.

[0374] It should be noted that in the table, "(number of substituents of AL+AR / total number of OH groups)" represents the total number of substituents of aliphatic alkyl (AL) and aromatic alkyl (AR) groups relative to all OH groups of the sugar esters. For example, "6 / 8" means that 6 out of 8 substituents are AL and / or AR substituents.

[0375] Glycoester 3:

[0376] In International Publication No. 2011 / 135980, paragraph

[0048] [Chemical 5], a sugar ester compound represented by the compound name a3 was used as sugar ester 3. This sugar ester 3 was synthesized by changing the type and number of substituents of the aliphatic alkyl (AL) and aromatic alkyl (AR) groups to benzoyl 6 and acetyl 2, respectively.

[0377] (Polyester 1)

[0378] A mixture of compounds represented by the following structures was used as polyester 1. The number average molecular weight of the mixture was 450, and n = 1.5401.

[0379]

Chemistry 12

[0380]

[0381] <Fabrication of Optical Film 1>

[0382] (Preparation of the main adhesive)

[0383] Prepare the main adhesive with the following composition. First, add dichloromethane and ethanol to a pressure dissolving vessel. While stirring, add diacetylcellulose 1 to the pressure dissolving vessel containing the solvent, and heat while stirring until completely dissolved.

[0384]

[0385] The above-mentioned additive components were placed in a sealed container and dissolved while stirring. The mixture was then filtered using Anji Filter Paper No. 244 manufactured by Anji Filter Paper Co., Ltd., to prepare the main adhesive.

[0386] (Filming of optical film 1)

[0387] The prepared main adhesive was uniformly cast on a stainless steel strip support at a temperature of 22°C and a width of 1.8m using a belt casting apparatus. The cast film thickness was 46.3μm before stretching. The solvent was allowed to evaporate until the residual solvent content was 75%, and then the film was peeled off from the stainless steel strip support with a peel tension of 180N / m.

[0388] Secondly, for the stripped main adhesive 1 mesh, the solvent is evaporated at 35°C. Then, in the first stretching process, a tenter frame is used to stretch the film at 140°C, relative to its original width, with a stretching ratio of 1.12 times (12%) (“TD stretching”). The solvent is evaporated until the residual solvent content is below 3%. At this point, the glass transition temperature of the optical film is set to Tg, which is 155°C.

[0389] Regarding the glass transition temperature mentioned above, the glass transition temperature (Tg) is read from the endothermic peak when the film sample is heated in the temperature range of -30 to 200°C at a heating rate of 10°C / min using a DSC (differential scanning calorimeter).

[0390] Secondly, in the second stretching process, a tenter frame is used to stretch the width by 1.88 times (88%) relative to the original width at a temperature of 215°C. At this time, the residual solvent content at the start of the tenter frame stretching is 0.5%. Therefore, the total stretching ratio of the first and second stretching processes relative to the original width becomes 2 times (100%).

[0391] Then, the optical film, which has been stretched sequentially as described above, is cooled at a temperature of 150°C in a precipitation suppression zone. Next, it is dried at 120°C in a drying zone while being transported by multiple rollers. The resulting optical film is longitudinally cut with a total cut of 150 mm from both ends, resulting in a width of 2500 mm. Furthermore, the ends of the optical film are knurled to a width of 10 mm and a height of 2.5 μm, and then wound onto a core to produce the optical film 1 of this invention. The film thickness is 30 μm, and the roll length is 6000 m.

[0392] <Fabrication of Optical Film 2>

[0393] (Preparation of the main adhesive)

[0394] In the fabrication of optical film 1, polyester was added to the main adhesive to prepare a main adhesive with the following composition. First, dichloromethane and ethanol were added to a pressure dissolving vessel. Diacetyl cellulose 2 was then added to the pressure dissolving vessel containing the solvent while stirring, and heated and stirred until completely dissolved.

[0395]

[0396] Secondly, the film was made in the same manner as the optical film 1. Under the conditions described in Table I, the film was stretched sequentially by TD stretching while passing through the first stretching process, the second stretching process, the precipitation suppression zone and the drying zone. After longitudinal cutting, an optical film 2 with a product width of 2500 mm was obtained.

[0397] <Fabrication of Optical Film 3>

[0398] In the fabrication of optical film 1, polyester was added to the main adhesive to prepare a main adhesive with the following composition. First, dichloromethane and ethanol were added to a pressure dissolving vessel. Diacetylcellulose 3 was then added to the pressure dissolving vessel containing the solvent while stirring, and heated and stirred until completely dissolved.

[0399]

[0400]

[0401] Secondly, the film was prepared in the same manner as the optical film 1. Under the conditions described in Table I, the film was subjected to a successive stretching process using MD stretching and TD stretching while passing through the first stretching process, the second stretching process, the precipitation suppression zone and the drying zone. After longitudinal cutting, an optical film 3 with a product width of 2500 mm was obtained.

[0402] <Fabrication of Optical Films 4-18>

[0403] In the production of optical film 1, as shown in Table I, the addition and amount of polyester, the type and amount of sugar ester, the temperature and stretching ratio of the first stretching process, the temperature and stretching ratio of the second stretching process, the temperature of the precipitation suppression zone, and the changes in the width and film thickness of the slit product were respectively used to produce optical films 4 to 18. Furthermore, optical films No. 12 to 18, in particular, were produced for the following purposes.

[0404] The optical film 12 reduces the total stretch ratio and narrows the longitudinal width.

[0405] The optical film 13 increases the total stretch ratio, making the film thickness of the product thinner.

[0406] The optical film 14 increases the stretching ratio in the first stretching process.

[0407] The optical film 15 is produced by dividing the second stretching process into two parts and performing three successive stretching processes.

[0408] In the first stretching process, the optical film 16 is stretched in the longitudinal direction at a temperature of 140°C (MD stretching) by applying a circumferential speed difference to multiple rollers, and then stretching by 1.12 times (12%) using the roller circumferential speed difference. In the second stretching process, a tenter frame stretching device is used to stretch the film in the width direction by 1.88 times (88%) relative to the original width at a temperature of 215°C.

[0409] The optical film 17 is produced by rapidly cooling the optical film stretched in the second stretching process at a temperature of 100°C in the precipitation suppression zone.

[0410] Optical film 18 is produced by casting the main adhesive onto a stainless steel belt support of a belt casting device to make the cast film thickness 11.2 μm before stretching, and then stretching it at a low ratio (12% on average for both the first and second) to produce an optical film with a thickness of 10 μm.

[0411] <Fabrication of Optical Films 19-21: Comparative Examples>

[0412] In the fabrication of optical film 1, diacetylcellulose 1 was used instead of cellulose ester resin. Using the aforementioned triacetylcellulose, cellulose acetate butyrate, and cellulose acetate propionate, film preparation and stretching were performed in the same manner. The results, as shown in Table II, were "film rupture, cannot be stretched" and "film melted, cannot be stretched," respectively, and the optical film was not obtained.

[0413] <Fabrication of Optical Film 22: Comparative Example>

[0414] In the fabrication of optical film 1, the main paste was prepared without the addition of sugar ester 1, and the film was then formed. As a result, the glass transition temperature Tg of the optical film increased, indicating that "the film fractured and could not be stretched".

[0415] <Fabrication of Optical Film 23: Comparative Example>

[0416] In the fabrication of optical film 1, sugar ester 1 was replaced with sugar ester 3, and the main paste was prepared in the same manner. The film-forming and stretching processes described in Table II were then performed to produce optical film 23.

[0417] <Fabrication of Optical Films 24 and 25: Comparative Example>

[0418] In the fabrication of optical film 10, the temperature of the second stretching process was changed to 185°C. Otherwise, the film-forming and stretching processes described in Table II were performed in the same manner to fabricate optical film 24.

[0419] Similarly, in the fabrication of optical film 10, the temperature of the second stretching process was changed to 230°C. Otherwise, the film-making and stretching processes described in Table II were performed in the same way, and optical film 25 was fabricated. The result was that "the film melted and could not be stretched".

[0420] <Fabrication of Optical Film 26: Comparative Example>

[0421] In the fabrication of the optical film 10, as an online stretching process, the first stretching process was carried out under the temperature conditions of the second stretching process, without the sequential stretching process of the second stretching process. As a result, the film "broke and could not be stretched", and the optical film was not obtained.

[0422] <Fabrication of Optical Films 27-32: Reference Example>

[0423] In the fabrication of optical film 1, a paste prepared by varying the type of cellulose ester resin and the presence or absence of added sugar esters is cast to form a mesh. Then, in the first stretching step, no stretching treatment is performed, and only drying is carried out at 140°C to obtain unstretched optical films 27-32 as reference examples.

[0424] "evaluate"

[0425] For evaluation purposes, unless otherwise specified, the optical film should be conditioned for 24 hours at 23°C and 55% RH and then measured under the same conditions.

[0426] <Delay value>

[0427] The in-plane retardation value R of the optical film o The retardation value R in the thickness direction t The following equations (i) and (ii) are used to derive the result.

[0428] Formula (i)R o =(n x -n y )×d

[0429] Equation (ii)R t ={(n x +n y ) / 2-n z}×d

[0430] In the formula, n x The refractive index n represents the refractive index along the hysteresis axis within the film surface. y The refractive index n represents the refractive index along the advanced phase axis within the film surface. z The refractive index represents the thickness of the film, and d represents the thickness of the film (nm).

[0431] Regarding the refractive index and film thickness mentioned above, the average refractive index of randomly sampled optical films was measured using an Abbe refractometer (4T). Additionally, the average film thickness was measured using a commercially available micrometer.

[0432] Regarding the delay of the optical film, the delay of the film at a wavelength of 590 nm was measured using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Measurement Equipment Co., Ltd.) after the film had been placed in an environment of 23°C and 55%RH for 24 hours.

[0433] The evaluation levels are as follows. R... o and R t When the value of (nm) is expressed in absolute value,

[0434] ◎: 0~2 (nm)

[0435] ○: 3~5 (nm)

[0436] △: 6~10 (nm)

[0437] ×: 11 (nm) and above

[0438] ◎, ○, and △ are not problematic in practical use.

[0439] <Humidity variation of the delay value: ΔR o / ΔRt >

[0440] After placing the above optical film in environments of 23℃·20%RH and 23℃·80%RH for 24 hours, the difference ΔR between the delay values ​​measured at the same time was calculated. o and ΔR t The absolute value is used as an indicator of the fluctuation of the delayed value when the environment changes.

[0441] ΔR o (nm)=|R o (23℃·20%RH)-R o (23℃·80%RH)|

[0442] ΔR t (nm)=|R t (23℃·20%RH)-R t (23℃·80%RH)|

[0443] The evaluation levels are as follows.

[0444] ◎: 0~1 (nm)

[0445] ○: 2~3 (nm)

[0446] △: 3~5 (nm)

[0447] ×: 6 (nm) and above

[0448] ◎, ○, and △ are not problematic in practical use.

[0449] <Determination of Elastic Modulus>

[0450] The determination conditions for the elastic modulus (also known as tensile modulus) of the optical film are set as described below. The elastic modulus is obtained by linear regression between strains of 0.05% and 0.25%.

[0451] For the MD direction, the tensile modulus is determined using the following method according to JIS K7127 (1999).

[0452] 1) Cut the optical film into 100mm (MD direction) × 10mm (TD direction) dimensions to serve as a test piece.

[0453] 2) For this test piece, TENSILON RTC-1225A manufactured by Original Tech Co., Ltd. was used, with the chuck distance between the chucks being 50 mm. The test piece was stretched in the longitudinal direction (MD direction) at a tensile speed of 50 mm / min, and the tensile modulus in the MD direction was measured. The measurement was carried out at 23°C and 55% RH.

[0454] <YI: Yellow Index Value>

[0455] The yellow index value is calculated according to the YI (yellow index: index of yellow hue) of the film as specified in JIS K 7103. As a method for determining the yellow index value, a sample of optical film is prepared, and the tristimulus values ​​X, Y, and Z of the light source color as specified in JIS Z 8701 are calculated using a spectrophotometer U-3300 from Hitachi High Tech Co., Ltd. and the accompanying chroma calculation program, etc., and the yellow index value is calculated according to the definition of the following formula.

[0456] Yellow Index (YI) = 100(1.28X - 1.06Z) / Y

[0457] The evaluation levels are as follows.

[0458] ◎: 0~0.8

[0459] ○: 0.9~1.2

[0460] △: 1.3~1.8

[0461] ×: 1.9 or more

[0462] ◎, ○, and △ are not problematic in practical use.

[0463] <Haze>

[0464] The total haze was measured according to JIS K-7136 using a haze meter (NDH-2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.).

[0465] The evaluation levels are as follows.

[0466] ◎: 0~0.7

[0467] ○: 0.8~1.0

[0468] △: 1.1~1.5

[0469] ×: 1.6 or more

[0470] ◎, ○, and △ are not problematic in practical use.

[0471] <Adopted 13 Determination of longitudinal relaxation time T1 by C-NMR >

[0472] The use of optical films 13 The longitudinal relaxation time T1 of C-NMR was determined as described below.

[0473] Measure 50 mg of membrane sample and perform CCP / MAS analysis using a JEOL RESONANCE JNM-ECA400W membrane analyzer. 13 C1-NMR measurements were performed, and the Torcia method was used to calculate the above... Figure 1The longitudinal relaxation time T1 of the [ring 1] site from the cellulose skeleton.

[0474] It should be noted that the measurement conditions were 23℃, relaxation delay of 3 seconds, cumulative number of measurements of 512, and resonance frequency of 100MHz.

[0475] The composition and evaluation results of the above optical films are shown in Tables I, II and III.

[0476] Table 1

[0477]

[0478] Table 2

[0479]

[0480] Table 3

[0481] Table III

[0482]

[0483] As can be seen from Tables I, II and III, the optical films 1 to 18 involved in the present invention exhibit superior properties such as elastic modulus, YI value and haze, even when stretched over an extremely wide range, compared to the comparative examples. Therefore, they have excellent wide range adaptability, and also excellent delayed manifestation and delayed resistance to environmental changes.

[0484] [Example 2]

[0485] (1) Fabrication of polarizers

[0486] <Fabrication of Polarizing Films 1-18>

[0487] Polarizers 1 to 18 were fabricated using the optical films 1 to 18 prepared above.

[0488] (Making of a polarizing device)

[0489] A 45 μm thick polyvinyl alcohol film was swollen with water at 35 °C. The resulting film was then immersed in an aqueous solution consisting of 0.075 g iodine, 5 g potassium iodide, and 100 g water for 60 seconds, followed by immersion in an aqueous solution consisting of 3 g potassium iodide, 7.5 g boric acid, and 100 g water at 45 °C. The resulting film was then uniaxially stretched at a stretching temperature of 55 °C and a stretching ratio of 5. After washing with water and drying, a polarizer with a thickness of 15 μm was obtained.

[0490] (Preparation of active energy ray-cured adhesive liquid: cationic polymerization type)

[0491] After mixing the following components and degassing, an active energy ray curable adhesive liquid was prepared. Furthermore, triarylsulfonium hexafluorophosphate was incorporated as a 50% propylene carbonate solution; the solid content of triarylsulfonium hexafluorophosphate is indicated below.

[0492]

[0493] (Making of polarizing filters)

[0494] Make a polarizer using the method described below.

[0495] First, as protective film 1, a KC6UA film (manufactured by Konica Minolta Co., Ltd.) was prepared and coated with the above-prepared active energy ray curable adhesive liquid using a micro-gravure coater (gravure roller: #300, rotation speed 140% / line speed) to make the thickness 5μm, thus forming active energy ray curable adhesive layer a.

[0496] Next, the optical film 1 prepared above is coated with the active energy ray curable adhesive liquid prepared above in the same way as above, so that the thickness is 5 μm, forming an active energy ray curable adhesive layer b.

[0497] A polyvinyl alcohol-iodine polarizer, prepared as described above, is placed between layers a and b of the aforementioned active energy radiation-curable adhesive. The layers are then bonded using a roller mill to obtain a laminate consisting of a protective film 1, an active energy radiation-curable adhesive layer, a polarizer, an active energy radiation-curable adhesive layer, and an optical film 1. At this time, the layers are bonded using a roller mill with the hysteresis axis of the optical film orthogonal to the absorption axis of the polarizer.

[0498] Electron beams are irradiated from both sides of the laminate to create polarizer 1.

[0499] The linear velocity was 20 m / min, the accelerating voltage was 250 kV, and the irradiation dose was 20 kGy.

[0500] Polarizers 2 to 18 were fabricated in the same manner, except that optical films 2 to 18 were used instead of optical film 1. In addition, polarizers 23 and 24 of the comparative example were fabricated in the same manner, using optical films 23 and 24 of the comparative example.

[0501] (2) Fabrication of LCD display device

[0502] The polarizers fabricated above are attached to both sides of an IPS-type liquid crystal cell to bring the optical film of the present invention into contact with the liquid crystal cell. The two polarizers are attached in an orthogonal Nicol configuration to obtain a liquid crystal display device. Furthermore, the optical films of the two polarizers use optical films with the same serial number.

[0503] "evaluate"

[0504] <Polarizer Durability>

[0505] For the samples of polarizers prepared above, conditioned for 24 hours at 23°C and 55% RH, the parallel transmittance and orthogonal transmittance were first measured under the same conditions, and the degree of polarization was calculated according to the following formula. Then, each polarizer was subjected to forced degradation at 60°C and 90% RH for 1000 hours, and the parallel transmittance and orthogonal transmittance were measured again, and the degree of polarization was calculated according to the following formula. The change in degree of polarization was determined using the following formula.

[0506] Degree of polarization P = ((H0 - H90) / (H0 + H90))0.5 × 100

[0507] Change in degree of polarization = P0 - P1000

[0508] H0: Parallel transmittance

[0509] H90: Orthogonal transmittance

[0510] P0: Degree of polarization before forced degradation

[0511] P1000: Polarization degree after 1000 hours of forced degradation

[0512] (Evaluation Criteria)

[0513] ○: The rate of change in polarization degree is less than 10%.

[0514] △: The rate of change in polarization is greater than 10% but less than 25%.

[0515] ×: Polarization degree change rate is above 25%

[0516] If the polarization degree change rate is greater than 25%, when assembling the polarizer into the display device, due to environmental changes, uneven display can be confirmed even by visual inspection, and it is judged as a defective product.

[0517] <Evaluation of the front contrast ratio of the display device>

[0518] The front contrast ratio of the IPS-mode liquid crystal display device described above was evaluated using the following method.

[0519] The aforementioned liquid crystal display device was placed on a screen set in a brightly lit room, with the substrate containing electrodes in the substrate constituting the liquid crystal cell positioned on the screen side. Then, using a luminance meter (spectral luminance meter CS-1000: manufactured by Konica Minolta Co., Ltd.) positioned 1 m away from the liquid crystal cell in the normal direction, the luminance was measured for both white and black displays. The luminance ratio (luminance for white display / luminance for black display) was then calculated as the contrast ratio.

[0520] Furthermore, the positive contrast ratio is evaluated based on the following criteria.

[0521] ◎: Contrast ratio of 400 or higher

[0522] 〇: Contrast ratio of 360 or higher but less than 400

[0523] △: Contrast ratio above 320 but less than 360

[0524] ×: Contrast ratio less than 320

[0525] The evaluation results of the above polarizers and liquid crystal display devices are shown in Table IV.

[0526] Table 4

[0527] Table IV

[0528]

[0529] The polarizers using optical films 1-18 of the embodiments exhibit durability ranging from Δ to ○, while the polarizers using optical films 23 and 24 of the comparative examples show poor durability (×). This demonstrates that the optical films of the embodiments exhibit excellent resistance to environmental changes. Therefore, it can be seen that by mounting polarizers using the optical films of the present invention in an IPS-mode liquid crystal display device, a display device can be obtained that suppresses uneven image display even under environmental changes.

[0530] Furthermore, it was confirmed that the liquid crystal display devices 1-18 assembled with polarizers 1-18 using the optical films 1-18 of the embodiments have superior frontal contrast compared to the comparative examples.

Claims

1. A method for producing an optical film, which is a method for producing an optical film containing at least a cellulose ester resin, characterized by include: The process of casting a paste containing at least cellulose ester resin and sugar ester on a support to form a strip film. and The process of stretching the formed elongated film. The total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.

60. The sugar ester is a compound in which all or part of the hydroxyl groups in compound A or compound B have been esterified with aliphatic acyl groups, wherein compound A has one furanose or pyranose structure, and compound B has at least two but no more than twelve furanose or pyranose structures. The optical film has a retardation value R defined by the following formula (i) o in the range of 0 to 10 nm, a retardation value R defined by the following formula (ii) t in the range of -10 to 10 nm, The process of stretching the formed elongated film includes a first step of obtaining a first elongated stretched film, and a second step of further stretching the first elongated stretched film to obtain a second stretched film, wherein the stretching temperature of the second step is in the range of 190 to 220°C. The process of stretching the formed elongated film after the second process has a precipitation suppression zone, the temperature of which is in the range of -100 to -50°C compared to the stretching temperature of the second process. Formula (I) R o = (n x -n y ) x d Formula (ii) R t ={(n x +n y ) / 2-n z}×d In the formula, n x represents the refractive index in the direction of the slow axis in the film surface, n y represents the refractive index in the direction of the fast axis in the film surface, n z represents the refractive index in the thickness direction of the film, the refractive index being measured at 23°C and 55% RH at a wavelength of 590 nm, and d represents the thickness of the film in nm.

2. The method of making an optical film according to claim 1, wherein, The content of the sugar ester is in the range of 10-25% by mass.

3. The method of making an optical film according to claim 1, wherein, The adhesive also contains polyester.

4. The method of manufacturing an optical film according to claim 3, wherein The polyester content is in the range of 5% to 15% by mass.

5. The method of manufacturing the optical film according to claim 1 or claim 2, characterized by, The stretching temperature of the second process is within the range of +60 to +100°C compared to the stretching temperature of the first process.

6. The method of manufacturing the optical film according to claim 1 or claim 2, characterized by, The difference ΔR of the retardation values when measured after the optical film is left in environments of 23°C-20%RH and 23°C-80%RH for 24 hours is also measured o and the absolute value of ΔR t is 5 nm or less.

7. The method of manufacturing the optical film according to claim 1 or claim 2, characterized by, Use of the optical film 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50 to 80 seconds.

8. An optical film manufactured by the method for manufacturing an optical film according to any one of claims 1 to 7, which is an optical film containing at least a cellulose ester resin, characterized in that, The total acetyl substitution degree of the cellulose ester resin is in the range of 2.30 to 2.60, and the optical film also contains sugar esters. The sugar ester is a compound in which all or part of the hydroxyl groups in compound A or compound B have been esterified with aliphatic acyl groups, wherein compound A has one furanose or pyranose structure, and compound B has at least two but no more than twelve furanose or pyranose structures. The optical film has a retardation value R defined by the following formula (i) o R = 0 to 10 nm, a retardation value R defined by the following formula (ii) t R = -10 to 10 nm, The difference ΔR of the retardation values when measured after the optical film is left in environments of 23°C-20%RH and 23°C-80%RH for 24 hours is also measured o and the absolute value of ΔR t is 5 nm or less, And the optical film is adopted 13 The longitudinal relaxation time T1 measured by C-NMR is in the range of 50-80 seconds, Formula (I) R o = (n x -n y ) x d Formula (ii) R t ={(n x +n y ) / 2-n z}×d In the formula, n x represents the refractive index in the direction of the slow axis in the film surface, n y represents the refractive index in the direction of the fast axis in the film surface, n z represents the refractive index in the thickness direction of the film, the refractive index being measured at 23°C, 55% RH, and a wavelength of 590 nm, and d represents the thickness of the film in nm.

9. The optical film of claim 8, wherein, The content of the sugar ester is in the range of 10-25% by mass.

10. A polarizing plate characterized by comprising An optical film according to claim 8 or claim 9 is attached to at least one side of the polarizer.

11. A liquid crystal display device, characterized by comprising: A polarizer according to claim 10 is applied to at least one side of the liquid crystal cell.

12. The liquid crystal display device according to claim 11, wherein It is an IPS-mode liquid crystal display device.

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