TWI808262B - Optical thin film, manufacturing method thereof, optical stack, and liquid crystal display device - Google Patents

Abstract

An optical film, which is an optical film formed of a thermoplastic northylene-based resin containing a northylene-based polymer, wherein the glass transition temperature Tg of the thermoplastic northylene-based resin satisfies formula (1), and the birefringence Δn _R that appears when the thermoplastic northylene-based resin is uniaxially extended to 1.5 times at Tg+15°C satisfies formula (2), the retardation Rth in the thickness direction of the optical film and the thickness of the optical film d satisfies formula (3). (1) Tg≧110℃ (2) Δn _R ≧0.0025 (3) Rth/d≧3.5×10 ^{− 3}

Description

Optical thin film, manufacturing method thereof, optical stack, and liquid crystal display device

The present invention relates to an optical film and its manufacturing method, an optical stack and a liquid crystal display device.

Conventionally, optical films formed of thermoplastic resins are known. For example, Patent Documents 1 to 5 describe optical films made of thermoplastic northylene-based resins.

"Patent Documents" "Patent Document 1": Japanese Patent Laid-Open No. 2005-043740 "Patent Document 2": Japanese Patent Laid-Open No. 2006-235085 "Patent Document 3": Japanese Patent Laid-Open No. 2006-327112 "Patent Document 4": Japanese Patent Laid-Open No. 2008-114369 "Patent Document 5": Japanese Patent Laid-Open No. 2003-238705

In recent years, optical films used in image display devices such as liquid crystal display devices have been required to exhibit excellent retardation, especially, films excellent in exhibiting retardation Rth in the thickness direction. Specifically, the optical film is required to have a large retardation Rth in the thickness direction per unit thickness of the optical film. As a method of obtaining an optical film having a large retardation Rth in the thickness direction per unit thickness using a conventional thermoplastic resin film, stretching at a high stretching ratio can be considered. However, an optical film obtained by stretching at a high stretching ratio tends to have low orientation angle accuracy.

In addition, image display devices are sometimes used in various environments, for example, they may be used in high temperature environments. Therefore, high heat resistance is required for optical films. Accordingly, focusing on the retardation Rth in the thickness direction, it is required to suppress the change in the retardation Rth in the thickness direction even in a high-temperature environment.

The present invention was first made in view of the aforementioned problems, and its object is to provide an optical film that is "an optical film formed of a thermoplastic northylene-based resin that has a large retardation Rth in the thickness direction per unit thickness, has high orientation angle accuracy, and can suppress changes in the retardation Rth in the thickness direction under a high-temperature environment", and an optical stack and a liquid crystal display device including the aforementioned optical film.

The inventors of the present invention have devoted themselves to research in order to solve the aforementioned problems. As a result, the present inventors have found that an optical film having a large retardation in the thickness direction per unit thickness, high orientation angle accuracy, and excellent heat resistance can be produced by using, as a thermoplastic northylene-based resin, which has a glass transition temperature Tg in a specified range and exhibits a specified birefringence Δn _R when stretched under specified conditions, and completed the present invention.

That is, the present invention includes the following.

[1] An optical film formed of a thermoplastic norrylene-based resin containing a norrylene-based polymer, wherein the glass transition temperature Tg of the thermoplastic norrylene-based resin satisfies the following formula (1), and the birefringence Δn _R exhibited when the thermoplastic norrylene-based resin is uniaxially stretched to 1.5 times at Tg+15°C for 1 minute satisfies the following formula (2): The retardation Rth in the thickness direction and the thickness d of the aforementioned optical film satisfy the following formula (3). (1) Tg≧110℃ (2) Δn _R ≧0.0025 (3) Rth/d≧3.5×10 ^{− 3}

[2] The optical film as described in [1], wherein the northylene-based polymer has a molecular weight distribution of 2.4 or less.

[3] The optical film as described in [1] or [2], wherein the northylene-based polymer is selected from the group consisting of polymers containing 25% by weight or more of tetracyclododecene-based monomers and hydrogenated products thereof, The aforementioned tetracyclododecene-based monomer is selected from the group consisting of tetracyclododecene and tetracyclododecene derivatives having substituents bonded to the ring of tetracyclododecene.

[4] The optical film according to any one of [1] to [3], wherein the photoelastic coefficient of the optical film is 8 Brewster or less.

[5] The optical film according to any one of [1] to [4], wherein the optical film has an in-plane retardation Re of 40 nm to 80 nm.

[6] A method for producing an optical film, which is the method for producing an optical film as described in any one of [1] to [5], It includes molding the aforementioned thermoplastic northylene-based resin by extrusion molding or solution casting.

[7] An optical stack comprising the optical film and a polarizing plate as described in any one of [1] to [5].

[8] A liquid crystal display device comprising the optical stack as described in [7].

According to the present invention, it is possible to provide an optical film that is "an optical film formed of a thermoplastic northylene-based resin and having a large retardation Rth in the thickness direction per unit thickness, has high orientation angle accuracy, and can suppress changes in the retardation Rth in the thickness direction under a high-temperature environment", as well as an optical stack and a liquid crystal display device including the aforementioned optical film.

Embodiments and examples are disclosed below to describe the present invention in detail. However, the present invention is not limited to the implementation forms and examples disclosed below, and can be implemented with arbitrary changes within the scope of not departing from the scope of the patent application of the present invention and its equivalent scope.

In the following description, the in-plane retardation Re of the film is the value shown by Re=(nx−ny)×d unless otherwise noted. In addition, the retardation Rth in the thickness direction of the film is a value represented by Rth={[(nx+ny)/2]−nz}×d unless otherwise noted. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) and in the direction giving the maximum refractive index. ny represents the refractive index in the direction perpendicular to the nx direction which is the aforementioned in-plane direction. nz represents the refractive index in the thickness direction. d represents the thickness of the film. Measurement wavelength, unless otherwise noted, is 550 nm.

In the following description, the so-called "elongated" film refers to a film having a length of 5 times or more, preferably 10 times or more, the width of the film, and specifically refers to a film having a length that can be wound into a roll for storage or transportation. The upper limit of the ratio of the length of the film to the width is not particularly limited, but must be made, for example, 100,000 times or less.

In the following description, the term "polarizing plate" includes not only rigid members but also flexible members such as resin films, unless otherwise noted.

[1. Outline of Optical Films]

An optical film related to an embodiment of the present invention is a film formed of a thermoplastic northylene-based resin. The aforementioned thermoplastic northene-based resin includes a northylene-based polymer. Furthermore, the optical film according to this embodiment satisfies the following first to third requirements.

First, the glass transition temperature Tg of the thermoplastic northylene-based resin satisfies the following formula (1). (1) Tg≧110°C

Second, the evaluated birefringence Δn _R of the thermoplastic northylene-based resin satisfies the following formula (2). Here, the evaluation of birefringence means the birefringence that appears when a certain material is stretched 1.5 times free-end uniaxially for 1 minute at a stretching temperature 15° C. higher than the glass transition temperature of the material. (2) Δn _R ≧0.0025

Third, the retardation Rth in the thickness direction of the optical film and the thickness d of the optical film satisfy the following formula (3). (3) Rth/d≧3.5×10 ^{− 3}

The optical film according to the present embodiment that satisfies the aforementioned first to third requirements has a large retardation Rth in the thickness direction per unit thickness d as shown by the formula (3). In addition, this optical film can suppress the change of retardation Rth in the thickness direction under high temperature environment. Furthermore, this optical film has a retardation Rth in the thickness direction that is larger than the thickness d as mentioned above, and can achieve high orientation angle accuracy at the same time.

[2. Thermoplastic northylene-based resins]

The thermoplastic northylene-based resin is a thermoplastic resin containing a northylene-based polymer. A northylene-based polymer is a polymer having a structure obtained by polymerizing a northylene-based monomer and optionally hydrogenating it. Accordingly, a northylene-based polymer generally includes one or more structures selected from the group consisting of a repeating structure obtained by polymerizing a northylene-based monomer and a structure obtained by hydrogenating the repeating structure. Such a northylene-based polymer includes, for example: a ring-opening polymer of a northylene-based monomer, a ring-opening copolymer of a northylene-based monomer and an optional monomer, and hydrogenated products thereof; an addition polymer of a northylene-based monomer, an addition copolymer of a northylene-based monomer and an arbitrary monomer, and hydrogenated products thereof. In addition, the northene-based polymer contained in the thermoplastic northene-based resin may be one type, or two or more types.

The noralene-based monomer system contains a noralene structure in the molecule.作為此降𦯉烯系單體，可列舉例如：雙環[2.2.1]庚-2-烯（俗名：降𦯉烯）、三環[4.3.0.1 ^2,5 ]癸-3,7-二烯（俗名：雙環戊二烯）、四環[4.4.0.1 ^2,5 .1 ^7,10 ]十二-3-烯（俗名：四環十二烯）等不含芳環結構的降𦯉烯系單體；5-苯基-2-降𦯉烯、5-(4-甲基苯基)-2-降𦯉烯、5-(1-萘基)-2-降𦯉烯、9-(2-降𦯉烯-5-基)咔唑等具有芳族取代基的降𦯉烯系單體；1,4-甲橋-1,4,4a,4b,5,8,8a,9a-八氫茀、1,4-甲橋-1,4,4a,9a-四氫茀（俗名：甲橋四氫茀）、1,4-甲橋-1,4,4a,9a-四氫二苯并呋喃、1,4-甲橋-1,4,4a,9a-四氫咔唑、1,4-甲橋-1,4,4a,9,9a,10-六氫蒽、1,4-甲橋-1,4,4a,9,10,10a-六氫菲等於稠環結構中包含降𦯉烯環結構與芳環結構的降𦯉烯系單體；以及此等化合物的衍生物（例如於環具有取代基者）；等。

Examples of substituents include alkyl groups such as methyl groups, ethyl groups, propyl groups, and isopropyl groups; alkylene groups; alkenyl groups; polar groups; As a polar group, a heteroatom or an atomic group having a heteroatom, etc. are mentioned, for example. As a hetero atom, an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, a halogen atom, etc. are mentioned, for example. Specific examples of polar groups include halogen groups such as fluorine, chlorine, bromine, and iodine; carboxyl; carbonyloxycarbonyl; epoxy; hydroxyl; oxygen; alkoxy; ester; silanol; silicon; The number of substituents may be one or two or more. In addition, the types of two or more substituents may be the same or different. However, from the viewpoint of obtaining an optical film with low saturated water absorption and excellent moisture resistance, the northylene-based monomer preferably has less polar groups, and preferably has no polar groups.

The northylene-based monomers may be used alone or in combination of two or more in arbitrary ratios.

The specific types and polymerization ratios of the aforementioned northylene-based monomers are selected as desired so as to obtain a thermoplastic northylene-based resin having a desired glass transition temperature Tg and an evaluated birefringence Δn _R. In general, the glass transition temperature and birefringence development of a northylene-based polymer depend on the type and polymerization ratio of a northylene-based monomer used as a raw material of the northylene-based polymer. Accordingly, the glass transition temperature and birefringence performance of the northylene polymer can be adjusted by properly adjusting the type and polymerization ratio of the northylene type monomer, so the glass transition temperature Tg and the evaluation birefringence Δn _R of the thermoplastic northylene type resin containing the northylene type polymer can be adjusted to satisfy formulas (1) and (2).

From the standpoint of increasing the glass transition temperature and birefringence of the northylene-based polymer to easily obtain the glass transition temperature Tg and evaluate a thermoplastic northylene-based resin with a large birefringence Δn _R , it is preferable to use a tetracyclododecene-based monomer as the northylene-based monomer. Accordingly, the northene-based polymer is preferably selected from the group consisting of polymers of monomers containing tetracyclododecene-based monomers and hydrogenated products thereof. Such a northylene-based polymer generally includes one or more structures selected from the group consisting of a repeating structure obtained by polymerizing a tetracyclododecene-based monomer and a structure obtained by hydrogenating the aforementioned repeating structure (hereinafter referred to as "tetracyclododecene-based structure" as appropriate.).

The tetracyclododecene-based monomer means a monomer selected from the group consisting of tetracyclododecene and tetracyclododecene derivatives. The tetracyclododecene derivative is a compound having a structure in which a substituent is bonded to the tetracyclododecene ring. The number of substituents may be one or two or more. In addition, the types of two or more substituents may be the same or different. As good tetracyclododecene derivatives, for example: 8-ethylenetetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]dode-3-ene (common name: ethylenetetracyclododecene), 8-ethylidetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]dode-3-ene, 8-ethoxycarbonyltetracyclo[4.4.0.1 ^2,5 .1 ^7,1 0 ]dode-3-ene, 8-methyl-8-methoxycarbonyl tetracyclo[4.4.0.1 ^2,5 .1 ^7,10 ]dode-3-ene, etc. The tetracyclododecene-based monomer may be used alone or in combination of two or more.

The proportion (polymerization ratio) of the tetracyclododecene-based monomer contained therein is preferably at least 25% by weight, more preferably at least 27% by weight, particularly preferably at least 29% by weight, and preferably not more than 60% by weight, preferably not more than 60% by weight, more preferably not more than 55% by weight, and most preferably not more than 50% by weight, relative to 100% by weight of the total amount of monomers used as a raw material for a northylene-based polymer. When the polymerization ratio of the tetracyclododecene-based monomer is within the aforementioned range, the glass transition temperature and birefringence development of the northylene-based polymer can be increased, so it is easy to make the glass transition temperature Tg of the thermoplastic nor-thylene-based resin and the evaluation birefringence Δn _R fall within the range of formula (1) and formula (2).

Generally, the ratio of the repeating structure (monomer unit) derived from a certain monomer in the northylene-based polymer is consistent with the ratio of this monomer in all monomers (polymerization ratio). Accordingly, generally, the ratio of the tetracyclododecene-based structure in the northylene-based polymer corresponds to the polymerization ratio of the tetracyclododecene-based monomer to the total amount of monomers. Therefore, it is preferable that the ratio of the tetracyclododecene-based structure to 100% by weight of the northylene-based polymer falls within the same range as the polymerization ratio of the aforementioned tetracyclododecene-based monomer.

Furthermore, from the viewpoint of increasing the glass transition temperature and birefringence development of the northylene-based polymer to easily obtain the glass transition temperature Tg and evaluate a thermoplastic northylene-based resin with a large birefringence Δn _R , it is preferable to use a dicyclopentadiene-based monomer as the northylene-based monomer. Accordingly, the northylene-based polymer is preferably selected from the group consisting of polymers of monomers containing dicyclopentadiene-based monomers and hydrogenated products thereof. Such a northylene-based polymer usually includes one or more structures selected from the group consisting of a repeating structure obtained by polymerizing a dicyclopentadiene-based monomer and a structure obtained by hydrogenating the repeating structure (hereinafter referred to as "dicyclopentadiene-based structure" as appropriate).

The dicyclopentadiene-based monomer means a monomer selected from the group consisting of dicyclopentadiene and dicyclopentadiene derivatives. The dicyclopentadiene derivative is a compound having a structure in which a substituent is bonded to the ring of dicyclopentadiene. The number of substituents may be one or two or more. In addition, the types of two or more substituents may be the same or different. The dicyclopentadiene-based monomer may be used alone or in combination of two or more.

The proportion (polymerization ratio) of the dicyclopentadiene-based monomer contained therein is preferably 50% by weight or more, more preferably 55% by weight or more, more preferably 60% by weight or more, and preferably 80% by weight or less, preferably 75% by weight or less, and most preferably 70% by weight or less, based on 100% by weight of the total amount of monomers used as a raw material for a northylene-based polymer. When the polymerization ratio of the dicyclopentadiene-based monomer is within the aforementioned range, the glass transition temperature and birefringence of the northylene-based polymer can be increased, so it is easy to make the glass transition temperature Tg of the thermoplastic nor-threne-based resin and the evaluation birefringence Δn _R fall within the range of formula (1) and formula (2).

Generally, the ratio of the dicyclopentadiene-based structure in the northylene-based polymer is consistent with the polymerization ratio of the dicyclopentadiene-based monomer to the total amount of monomers. Therefore, it is preferable that the ratio of the dicyclopentadiene-based structure to 100% by weight of the northylene-based polymer falls within the same range as the polymerization ratio of the aforementioned dicyclopentadiene-based monomer.

In particular, when a tetracyclododecene-based monomer and a dicyclopentadiene-based monomer are used in combination as a northylene-based monomer, the ratio of these amounts is preferably within a predetermined range. Specifically, with respect to 100 parts by weight of the tetracyclododecene-based monomer, the amount of the dicyclopentadiene-based monomer is preferably at least 100 parts by weight, more preferably at least 150 parts by weight, more preferably at least 200 parts by weight, preferably not more than 500 parts by weight, preferably not more than 450 parts by weight, and most preferably not more than 400 parts by weight. Accordingly, in the norbene-based polymer, the amount of the dicyclopentadiene-based structure is preferably 100 parts by weight or more, more preferably 150 parts by weight or more, more preferably 200 parts by weight or more, and preferably not more than 500 parts by weight, preferably not more than 500 parts by weight, preferably not more than 450 parts by weight, and most preferably not more than 400 parts by weight, relative to 100 parts by weight of the tetracyclododecene-based structure. When the aforementioned quantitative ratio is in the aforementioned range, the glass transition temperature and birefringence development of the northylene-based polymer can be increased, so it is easy to make the glass transition temperature Tg and the evaluation birefringence Δn _R of the thermoplastic northylene-based resin fall within the range of formula (1) and formula (2).

In the case of using an arbitrary monomer copolymerized with a northylene-based monomer, the kind of the arbitrary monomer is not limited insofar as a thermoplastic northene-based resin having a desired glass transition temperature Tg and evaluated birefringence Δn _R can be obtained. Examples of arbitrary monomers capable of ring-opening copolymerization with a northylene-based monomer include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene, and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene, and cycloheptadiene, and derivatives thereof; and the like. In addition, examples of arbitrary monomers capable of addition-copolymerization with nor-alkene-based monomers include: α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, and 1-butene, and derivatives thereof; cycloalkenes such as cyclobutene, cyclopentene, and cyclohexene, and derivatives thereof; non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene; and the like. Arbitrary monomers may be used alone or in combination of two or more.

The northene-based polymer includes a hydrogenated product of a structure obtained by polymerizing a northene-based monomer and further hydrogenating it. The hydride may be hydrogenated non-aromatic unsaturated bonds in the polymer, hydrogenated aromatic unsaturated bonds in the polymer, or hydrogenated both non-aromatic unsaturated bonds and aromatic unsaturated bonds in the polymer. Among them, a northylene-based polymer in which both non-aromatic unsaturated bonds and aromatic unsaturated bonds in the polymer are hydrogenated is preferable. By using such a hydrogenated northylene-based polymer, the development of retardation Rth in the thickness direction can be effectively improved, and the photoelastic coefficient can be reduced. Accordingly, both a large retardation Rth in the thickness direction and a low photoelastic coefficient can be achieved. Furthermore, it is usually effective to improve the mechanical strength, moisture resistance, heat resistance and other properties of the optical film.

The glass transition temperature of the northylene-based polymer is preferably 110°C or higher, more preferably 112°C or higher, and most preferably 114°C or higher. By using a northylene-based polymer having such a high glass transition temperature, it is possible to suppress loosening of the orientation of the northylene-based polymer in a high-temperature environment. Accordingly, it is possible to suppress a change in the retardation Rth in the thickness direction of the optical film under a high-temperature environment. In addition, a film comprising a northylene-based polymer whose type and polymerization ratio of a northylene-based monomer is adjusted so as to have a glass transition temperature within the aforementioned range tends to exhibit a large birefringence due to stretching, and therefore tends to increase the retardation Rth in the thickness direction of the optical film. The upper limit of the glass transition temperature of the northylene-based polymer is not particularly limited, but it is preferably below 180°C, more preferably below 170°C, and most preferably below 160°C. When the glass transition temperature of the northylene-based polymer is not more than the aforementioned upper limit, the retardation Rth in the thickness direction of the optical film tends to increase.

The glass transition temperature of a northylene-based polymer can be measured using a differential scanning calorimeter in accordance with JIS K 6911 at a heating rate of 10° C./min.

The glass transition temperature of the northylene-based polymer can be adjusted by, for example, the type and polymerization ratio of the northylene-based monomer used as a raw material of the northylene-based polymer.

The northylene-based polymer preferably exhibits large birefringence. Accordingly, a northylene-based polymer preferably has a large estimated birefringence. Specifically, the evaluated birefringence of the northylene-based polymer is preferably at least 0.0025, more preferably at least 0.0026, and most preferably at least 0.0027. By using a northylene-based polymer having such a large estimated birefringence, a large retardation can be expressed even at a low elongation ratio. Accordingly, since the optical film can exhibit a large retardation Rth in the thickness direction at a small stretching ratio, the orientation angle accuracy of the optical film can be effectively improved. The upper limit of the evaluation birefringence of a northylene-based polymer is not particularly limited, but it is preferably not more than 0.0050, more preferably not more than 0.0047, and most preferably not more than 0.0045. When the evaluated birefringence of the northylene-based polymer is not more than the aforementioned upper limit value, the production of the northylene-based polymer can be easily performed.

Evaluation of Norene-Based Polymer Birefringence can be measured by the following method.

A northylene-based polymer was molded to obtain a sheet. The sheet is subjected to free end uniaxial stretching. The so-called free-end uniaxial extension refers to the extension in one direction and does not exert restraint force on the sheet other than the extension direction. The stretching temperature of the aforementioned free-end uniaxial stretching is a temperature 15° C. higher than the glass transition temperature of the northene-based polymer. In addition, the stretching time was 1 minute, and the stretching ratio of the free end uniaxial stretching was 1.5 times. After elongation, the in-plane retardation at the central portion of the sheet was measured at a measurement wavelength of 550 nm, and this in-plane retardation was divided by the thickness of the central portion of the sheet, whereby birefringence was evaluated for evaluation.

Evaluation of the northylene-based polymer The birefringence can be adjusted by, for example, the type and polymerization ratio of the northylene-based monomer used as the raw material of the northylene-based polymer, and the molecular weight distribution of the northylene-based polymer.

The weight average molecular weight Mw of the northylene-based polymer is preferably from 10,000 to 100,000, more preferably from 15,000 to 80,000, and most preferably from 20,000 to 60,000. When the weight average molecular weight is in the aforementioned range, the mechanical strength and formability of the optical film can be highly balanced.

The molecular weight distribution Mw/Mn of the northylene-based polymer is preferably not more than 2.4, more preferably not more than 2.35, and most preferably not more than 2.3. When the molecular weight distribution Mw/Mn of the northylene-based polymer is within the above-mentioned range, the bonding strength of the optical film can be improved, so delamination of the optical film can be suppressed. The so-called molecular weight distribution is the ratio of the weight average molecular weight to the number average molecular weight, and is represented by "weight average molecular weight Mw/number average molecular weight Mn". The lower limit of the molecular weight distribution of the northylene-based polymer is usually 1.0 or more.

The weight average molecular weight and number average molecular weight of a northylene-based polymer can be measured in terms of polyisoprene by gel permeation chromatography using cyclohexane as an eluent. In the case where the northylene-based polymer is insoluble in cyclohexane, toluene may also be used as an eluent in the aforementioned gel permeation chromatography. When the eluent is toluene, the weight average molecular weight and number average molecular weight can be measured in terms of polystyrene.

The stress birefringence of norbene-based polymers is preferably above 2350×10 ^{− 12 Pa − 1} , preferably above 2400×10 ^{− 12 Pa − 1, especially above 2550×10 − 12 Pa − 1, preferably below 3000×10 − 12 Pa − 1 , and preferably below} 2950×10 ^{− 12} Pa ^{− 1 1} or less is better, and 2800×10 ^{− 12} Pa ^{− 1} or less is especially preferable. When the stress birefringence of the northylene-based polymer is greater than or equal to the lower limit value of the aforementioned range, a film containing the northylene-based polymer tends to show a large birefringence due to stretching, and therefore tends to increase the retardation Rth in the thickness direction of the optical film. In addition, when the stress birefringence of the northylene-based polymer is not more than the upper limit of the above-mentioned range, it becomes easy to control the retardation Re and Rth of the optical film, and the in-plane variation of the retardation can be suppressed.

The stress birefringence of a northylene-based polymer can be measured by the following method.

A northylene-based polymer is molded into a sheet to obtain a sheet. After fixing both ends of this sheet with a jig, fix a weight of a specified weight (for example, 160 g) to one side of the jig. Then, in an oven set at a specified temperature (for example, a temperature 5°C higher than the glass transition temperature of the northene-based polymer), set the jig without a fixed weight as the starting point, and hang the sheet for a specified time (for example, 1 hour) for stretching. Slowly cool the stretched sheet back to room temperature. For this sheet, the in-plane retardation at the center portion of the sheet was measured at a measurement wavelength of 650 nm, and the in-plane retardation was divided by the thickness of the center portion of the sheet, whereby the δn value was calculated. Stress birefringence can then be found by dividing this δn value by the stress applied to the sheet (in the above case, the stress applied when the specified weight is fixed).

The stress birefringence of a northylene-based polymer can be adjusted by the type and polymerization ratio of a northylene-based monomer used as a raw material of a northylene-based polymer.

A northylene-based polymer can be produced, for example, by a production method including "polymerizing a northylene-based monomer and optionally an optional monomer in the presence of an appropriate catalyst." In addition, in the case of producing a hydride as a northene-based polymer, the method for producing a northene-based polymer may include, after the above-mentioned polymerization, contacting the obtained polymer with hydrogen in the presence of a hydrogenation catalyst containing a transition metal such as nickel, palladium, or ruthenium to hydrogenate carbon-carbon unsaturated bonds.

The ratio of the norrylene polymer contained in the thermoplastic norrylene resin is arbitrary within the range in which the thermoplastic norrene resin satisfying the formulas (1) and (2) can be obtained. From the viewpoint of making use of the excellent properties of the northylene-based polymer, the proportion of the northene-based polymer contained in the thermoplastic northylene-based resin is preferably 80% by weight to 100% by weight, more preferably 90% by weight to 100% by weight, and most preferably 95% by weight to 100% by weight.

The thermoplastic northene-based resin may contain optional components other than the northene-based polymer. Examples of optional components include ultraviolet absorbers, antioxidants, heat stabilizers, light stabilizers, antistatic agents, dispersants, chlorine scavengers, flame retardants, crystal nucleating agents, strengthening agents, antiblocking agents, antifogging agents, release agents, pigments, organic or inorganic fillers, neutralizers, lubricants, decomposers, metal deactivators, antifouling agents, and antibacterial agents. Optional components may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

The thermoplastic northylene-based resin has a glass transition temperature Tg satisfying the aforementioned formula (1). Specifically, the glass transition temperature Tg of the thermoplastic northylene-based resin is generally 110° C. or higher, preferably 112° C. or higher, and particularly preferably 114° C. or higher. By using the thermoplastic northylene-based resin having such a high glass transition temperature Tg, the relaxation of the orientation of the northylene-based polymer in a high-temperature environment can be suppressed. Accordingly, it is possible to suppress a change in the retardation Rth in the thickness direction of the optical film under a high-temperature environment. In addition, a film containing a thermoplastic northylene-based resin "having a glass transition temperature Tg in the above-mentioned range" generally tends to show a large birefringence due to stretching, and therefore tends to increase the retardation Rth in the thickness direction of the optical film. The upper limit of the glass transition temperature Tg of the thermoplastic northylene resin is not particularly limited, but it is preferably below 180°C, more preferably below 170°C, and most preferably below 160°C. When the glass transition temperature Tg of the thermoplastic northylene-based resin is not more than the above-mentioned upper limit, the retardation Rth in the thickness direction of the optical film tends to increase.

The glass transition temperature Tg of the thermoplastic northylene-based resin can be measured using a differential scanning calorimeter in accordance with JIS K 6911 at a heating rate of 10° C./min.

The glass transition temperature Tg of the thermoplastic northylene-based resin can be adjusted by, for example, the type and polymerization ratio of the northylene-based monomer used as a raw material of the northylene-based polymer, and the content of the northylene-based polymer.

The thermoplastic northylene-based resin has an estimated birefringence Δn _R satisfying the aforementioned formula (2). Specifically, the evaluated birefringence Δn _R of the thermoplastic northylene-based resin is usually not less than 0.0025, preferably not less than 0.0026, particularly preferably not less than 0.0027. By using a thermoplastic northylene-based resin having such a large estimated birefringence Δn _R , a large retardation can be expressed even at a low elongation ratio. Accordingly, since the optical film can exhibit a large retardation Rth in the thickness direction at a small stretching ratio, the orientation angle precision of the optical film can be effectively improved. The upper limit of birefringence Δn _R for evaluation of thermoplastic northylene resin is not particularly limited, but it is preferably 0.0050 or less, more preferably 0.0047 or less, and most preferably 0.0045 or less. When the evaluated birefringence Δn _R of the thermoplastic northylene-based resin is not more than the aforementioned upper limit value, production of the thermoplastic northylene-based resin can be easily performed.

Evaluation of thermoplastic northylene-based resin The birefringence Δn _R can be measured by the following method.

The thermoplastic northylene-based resin is molded to obtain a sheet. The sheet is subjected to free end uniaxial stretching. The above-mentioned stretching temperature of the free end uniaxial stretching is a temperature 15°C higher than the glass transition temperature Tg of the thermoplastic northylene resin (that is, Tg+15°C). In addition, the stretching time was 1 minute, and the stretching ratio of the free end uniaxial stretching was 1.5 times. After stretching, measure the in-plane retardation Re(a) at the center of the sheet at a measurement wavelength of 550 nm, and divide this in-plane retardation Re(a) by the thickness T(a) of the center of the sheet to obtain the estimated birefringence Δn _R .

Evaluation of thermoplastic northylene-based resins The birefringence Δn _R can be adjusted by, for example, the type and polymerization ratio of northylene-based monomers used as raw materials for northylene-based polymers, the molecular weight distribution of northylene-based polymers, and the content of northylene-based polymers.

The stress birefringence C _R of thermoplastic northylene-based resins is preferably above 2350× ^{10 − 12 Pa − 1} , preferably above 2400×10 ^{− 12 Pa − 1, especially above 2550×10 − 12 Pa − 1 ,} preferably below 3000×10 ^{− 12} Pa ^{− 1} , and preferably below 2950×10 ^{− 1} Below 2 Pa ^{− 1} is better, especially below 2800×10 ^{− 12} Pa ^{− 1} . When the stress birefringence _CR of the thermoplastic northylene-based resin is equal to or greater than the lower limit value of the aforementioned range, a film containing the thermoplastic northylene-based resin tends to show a large birefringence by stretching, and therefore tends to increase the retardation Rth in the thickness direction of the optical film. In addition, when the stress birefringence C _R of the thermoplastic northylene resin is below the upper limit of the above-mentioned range, it becomes easy to control the retardation Re and Rth of the optical film, and the in-plane variation of the retardation can be suppressed.

The stress birefringence C _R of a thermoplastic northylene-based resin can be measured by the following method.

The thermoplastic northylene-based resin is molded into a sheet to obtain a sheet. After fixing both ends of this sheet with a jig, fix a weight of a specified weight (for example, 160 g) to one side of the jig. Then, in an oven set at a specified temperature (for example, a temperature 5°C higher than the glass transition temperature Tg of the thermoplastic northylene resin), set the jig without a fixed weight as the starting point, and hang the sheet for a specified time (for example, 1 hour) for stretching. Slowly cool the stretched sheet back to room temperature. For this sheet, measure the in-plane retardation Re(b) at the center of the sheet at a measurement wavelength of 650 nm, and divide this in-plane retardation Re(b) by the thickness T(b) [mm] of the center of the sheet to calculate the δn value. The stress birefringence, C _R , can then be found by dividing this δn value by the stress applied to the sheet (in the above case, the stress applied when the specified weight is fixed).

The stress birefringence C _R of the thermoplastic northylene-based resin can be adjusted by the type and polymerization ratio of the northylene-based monomer used as the raw material of the northylene-based polymer, and the content of the northylene-based polymer.

[3. Characteristics of Optical Films]

The optical film related to this embodiment is a film formed of the above-mentioned thermoplastic northylene-based resin, and its retardation Rth in the thickness direction and thickness d satisfy the aforementioned formula (3). Specifically, the ratio Rth/d is usually at least 3.5×10 ^{− 3} , preferably at least 3.7×10 ^{− 3} , and most preferably at least 4.0×10 ^{− 3} . In this way, the optical film according to this embodiment can increase the retardation Rth in the thickness direction per unit thickness d. Accordingly, the retardation Rth in the thickness direction can be increased while reducing the thickness d. The upper limit of the ratio Rth/d is not particularly limited, but from the viewpoint of effectively suppressing delamination of the optical film, it is preferably 8.0×10 ^{− 3} or less, more preferably 6.0×10 ^{− 3} or less.

The glass transition temperature and birefringence development of a northylene-based polymer generally depend on the type and polymerization ratio of the northylene-based monomer used as the material of the northylene-based polymer. Accordingly, the glass transition temperature Tg and the estimated birefringence Δn _R of the thermoplastic northene-based resin containing the northene-based polymer are related to the type and polymerization ratio of the northene-based monomer used as the material of the northene-based polymer. Accordingly, the glass transition temperature Tg and the estimated birefringence Δn _R of thermoplastic northene-based resins generally reflect the type and polymerization ratio of norrthene-based monomers contained in the thermoplastic northene-based resin as raw materials for northylene-based polymers. According to the studies of the present inventors, it has been found that a thermoplastic northene-based resin comprising a northylene-based polymer using a type and an amount of a northylene-based monomer selected so as to have a glass transition temperature Tg in a predetermined range and to evaluate birefringence Δn _R is excellent in the development of retardation Rth in the thickness direction due to stretching. Accordingly, an optical film having such a high Rth/d can be produced as a stretched film using the thermoplastic northylene-based resin contained in the above-mentioned northylene-based polymer.

The photoelastic coefficient of the optical film related to this embodiment is preferably small. The specific photoelastic coefficient of the optical film is preferably below 8 Brewster, more preferably below 7 Brewster, and most preferably below 6 Brewster. Here, 1 Brewster = 1×10 ^{− 13} cm ² /dyn. When the photoelastic coefficient of the optical film is small, even if the optical film is warped, it is difficult to change the optical characteristics such as retardation. Accordingly, when the optical film is provided in a liquid crystal display device, the occurrence of light leakage due to warping of the optical film can be suppressed. The so-called light leakage refers to the phenomenon that when the liquid crystal display device is set to a black display state, the light that should be shielded leaks from the screen and the screen becomes brighter. The lower limit of the photoelastic coefficient is not particularly limited, but it is preferably above 0.5 Brewster, more preferably above 1.0 Brewster, and most preferably above 1.5 Brewster.

The photoelastic coefficient of the optical film can be measured by an ellipsometer.

An optical film having a small photoelastic coefficient can be realized, for example, by using a thermoplastic northylene-based resin "containing a hydrogenated northylene-based polymer".

The optical film related to this embodiment can achieve high orientation angle accuracy. Specifically, an optical film has a slow axis in an in-plane direction perpendicular to its thickness direction. Moreover, the optical film can suppress the staggering of the direction of the slow axis. Therefore, since the variation of the orientation angle θ which is the angle formed by the slow axis with respect to the reference direction can be suppressed, high orientation angle accuracy can be achieved. When an optical film with high orientation angle accuracy is installed in a liquid crystal display device, it can make display characteristics such as brightness and contrast of the screen uniform in the plane.

The orientation angle accuracy of an optical film can be evaluated by the standard deviation θσ of the orientation angle θ. The smaller the standard deviation θσ of the orientation angle θ of the optical film, the better. Specifically, the standard deviation θσ of the orientation angle θ of the optical film is preferably from 0° to 0.15°, more preferably from 0° to 0.14°, and most preferably from 0° to 0.13°.

The standard deviation θσ of the orientation angle θ of the optical film can be measured by the following method.

The absolute value of the angle between the slow axis of the optical film and a reference direction is measured as the orientation angle θ. This measurement is carried out at a plurality of measurement positions with an interval of 50 mm in the width direction of the optical film and an interval of 10 m in the length direction. The standard deviation θσ of the orientation angle θ can then be calculated from these measurements.

Generally, optical films are produced as stretched films using thermoplastic northylene-based resins. Furthermore, since the thermoplastic northylene-based resin exhibits excellent birefringence, the elongation ratio required for expressing a large retardation satisfying the formula (3) is small. Therefore, when the optical film is produced as a stretched film formed of a thermoplastic northylene-based resin, the stretching ratio can be reduced. With the elongation ratio being so small, the aforementioned optical film can achieve high orientation angle accuracy.

The optical film according to this embodiment is excellent in heat resistance. Specifically, the optical film can suppress a change in retardation Rth in the thickness direction under a high-temperature environment. An optical film excellent in heat resistance is suitable for a liquid crystal display device that may be used in a high-temperature environment.

The heat resistance of the optical film can be evaluated by the rate of change of the retardation Rth in the thickness direction obtained through the endurance test in the high temperature environment. For example, after the retardation Rth0 in the thickness direction of the optical film is measured, the optical film is subjected to a durability test in which the optical film is stored at 85° C. for 500 hours. After the durability test, the retardation Rth1 in the thickness direction of the optical film was measured. Then, the rate of change can be calculated by dividing the change amount Rth0-Rth1 of the retardation in the thickness direction of the optical film obtained through the durability test by the retardation Rth0 in the thickness direction of the optical film before the durability test. According to the optical film related to this embodiment, it is preferable that the change rate of the retardation Rth in the thickness direction can be made 3% or less.

The thermoplastic northylene-based resin contained in the optical film has a high glass transition temperature Tg. Accordingly, even in a high-temperature environment, the molecules of the northylene-based polymer contained in the thermoplastic northylene-based resin are less likely to undergo orientational relaxation. Therefore, it is possible to suppress the variation of the retardation Rth in the thickness direction under a high-temperature environment as described above.

The optical film related to this embodiment preferably has high moisture resistance. Accordingly, the optical film is preferably capable of suppressing a change in retardation Rth in the thickness direction under a high-humidity environment. An optical film excellent in moisture resistance is suitable for a liquid crystal display device that may be used in a high-humidity environment.

The moisture resistance of the optical film can be evaluated by the rate of change of the retardation Rth in the thickness direction obtained through the durability test in a high-humidity environment. For example, after measuring the retardation Rth0 in the thickness direction of the optical film, the optical film is subjected to a durability test of 500 hours of storage at 60° C. and a humidity of 90%. After the endurance test, the retardation Rth2 in the thickness direction of the optical film was measured. Then, the rate of change can be calculated by dividing the change amount Rth0-Rth2 of the retardation in the thickness direction of the optical film obtained through the endurance test by the retardation Rth0 in the thickness direction of the optical film before the endurance test. According to this embodiment, it is preferable that the rate of change of the retardation Rth in the thickness direction can be made 3% or less.

The northylene-based polymer is preferably excellent in moisture resistance, so the optical film is easy to suppress the intrusion of moisture. Accordingly, even in a high-humidity environment, the molecules of the northylene-based polymer contained in the optical film are less prone to orientation relaxation. Therefore, the variation of the retardation Rth in the thickness direction under a high-humidity environment can be suppressed as described above.

The optical film related to this embodiment preferably has a low water absorption rate. For example, the weight-based water absorption of the optical film when immersed in water at 23° C. for 24 hours is preferably 0% to 0.15%, more preferably 0% to 0.10%, and most preferably 0% to 0.05%. With such a low water absorption, the optical film can have excellent moisture resistance as described above.

The optical film related to this embodiment is preferably capable of suppressing delamination. Accordingly, when the optical film is bonded to a film such as a polarizing plate using an adhesive, the optical film can be made difficult to peel off. In view of the fact that conventional stretched films containing nor-alene-based polymers are generally prone to delamination, the fact that the optical film related to this embodiment can suppress delamination is one of the excellent advantages of the optical film.

The in-plane retardation Re of the optical film related to this embodiment is arbitrary depending on the application of the optical film. To reveal a specific range, the in-plane retardation Re of the optical film is preferably above 40 nm, preferably above 45 nm, especially preferably above 50 nm, preferably below 80 nm, preferably below 75 nm, and most preferably below 70 nm. When the in-plane retardation Re of the optical film is not less than the lower limit of the aforementioned range, it is easy to optimize the development of retardation. In addition, when the in-plane retardation Re of the optical film is not more than the upper limit of the above-mentioned range, it is possible to suppress the variation in the retardation in the plane. The in-plane retardation Re can be appropriately selected from the above range according to the design of the image display device.

The retardation Rth in the thickness direction of the optical film related to this embodiment is arbitrary depending on the application of the optical film. To reveal a specific range, the retardation Rth in the thickness direction of the optical thickness is preferably 100 nm or more, more preferably 120 nm or more, especially 150 nm or more, and preferably less than 400 nm, preferably less than 380 nm, and most preferably less than 360 nm. When the retardation Rth in the thickness direction of the optical film is more than the lower limit of the aforementioned range, the oblique contrast of the image display device can be improved. In addition, when the retardation Rth in the thickness direction of the optical film is not more than the upper limit of the above-mentioned range, the retardation Rth in the thickness direction and the in-plane variation of the orientation angle can be suppressed. The retardation Rth in the thickness direction can be appropriately selected from the above range according to the design of the image display device.

The optical film related to this embodiment preferably has a high total light transmittance. The specific total light transmittance of the optical film is preferably 85%-100%, more preferably 87%-100%, and most preferably 90%-100%. The total light transmittance is measured using a commercially available spectrophotometer at a wavelength of 400 nm to 700 nm.

The optical film according to this embodiment preferably has a small haze from the viewpoint of improving the image clarity of a liquid crystal display device incorporating the stacked film. The haze of the optical film is preferably less than 1%, more preferably less than 0.8%, and most preferably less than 0.5%. Haze is measured using a turbidimeter according to JIS K7361-1997.

The optical film related to this embodiment is preferably thin. By using the above-mentioned thermoplastic northylene-based resin, a large retardation Rth in the thickness direction can be obtained even if the optical film is thin. In addition, when the optical film is thin, warping of the optical film can be suppressed, so changes in optical characteristics such as retardation due to warping can be reduced. Accordingly, when the optical film is provided in a liquid crystal display device, the occurrence of light leakage due to warping of the optical film can be suppressed. The specific thickness d of the optical film is preferably not more than 120 μm, more preferably not more than 100 μm, and most preferably not more than 80 μm. The lower limit of the thickness d is not particularly limited, but from the viewpoint of suppressing delamination, it is preferably 20 μm or more, more preferably 30 μm or more, particularly preferably 40 μm or more.

[4. Manufacturing method of optical film]

The above-mentioned optical film can be produced, for example, by a production method including "a step of forming a thermoplastic northylene-based resin to obtain a resin film" and "a step of stretching the resin film". In order to distinguish it from the optical film obtained after stretching, the resin film before stretching will be referred to as "film before stretching" as appropriate below.

In the step of molding the thermoplastic northylene-based resin to obtain a film before stretching, the molding method is not limited. As a molding method, an extrusion molding method, a solution casting method, an inflation molding method, etc. are mentioned, for example. Among them, the extrusion molding method and the solution casting method are preferable, and the extrusion molding method is particularly preferable.

After the unstretched film is prepared, a step of stretching the unstretched film is performed. By this stretching, the molecules of the northylene-based polymer in the film can be oriented, so that an optical film having the above-mentioned optical characteristics can be obtained. The stretching conditions in the step of stretching the pre-stretching film can be set arbitrarily within the range in which a desired optical film can be obtained.

The aspect of stretching the film before stretching may be, for example, uniaxial stretching in which one direction is stretched, or biaxial stretching in which two non-parallel directions are stretched. Furthermore, the biaxial stretching may be simultaneous biaxial stretching in which stretching is performed in two directions at the same time, or sequential biaxial stretching in which stretching is performed in the other direction after stretching in one direction. Among these, biaxial stretching is preferable, and sequential biaxial stretching is preferable from the viewpoint of ease of manufacturing an optical film having a large retardation Rth in the thickness direction.

The stretching direction of the film before stretching can be set arbitrarily. For example, when the film before stretching is a long film, the stretching direction may be vertical, horizontal, or oblique. The term "longitudinal" refers to the length direction of the elongated film, the term "transverse direction" refers to the width direction of the elongated film, and the term "oblique" refers to a direction that is neither parallel nor perpendicular to the longitudinal direction of the elongated film.

The stretching ratio of the film before stretching is preferably not less than 1.4, more preferably not less than 1.5, and preferably not more than 2.2, more preferably not more than 2.1. When the stretch ratio is equal to or greater than the lower limit of the aforementioned range, an optical film having a large retardation Rth in the thickness direction can be easily obtained. In addition, when the stretching ratio is not more than the upper limit of the above-mentioned range, the orientation angle accuracy of the optical film can be easily improved. In the case of biaxial stretching, it is preferable that the overall stretching ratio represented by the product of the stretching ratio in one direction and the stretching ratio in the other direction falls within the aforementioned range.

The stretching temperature of the film before stretching is preferably above Tg°C, more preferably above Tg+5°C, preferably below Tg+40°C, more preferably below Tg+30°C. When the stretching temperature is in the aforementioned range, it is easy to make the thickness of the optical film uniform.

In the above-mentioned production method, the optical film can be obtained by stretching the film before stretching as described above, but the above-mentioned production method may further include an optional process.

For example, the aforementioned manufacturing method may also include a step of trimming the optical film, a step of applying surface treatment to the optical film, and the like.

[5. Optical stack]

An optical stack related to an embodiment of the present invention includes the above-mentioned optical film and polarizing plate. Since the thickness of the optical film can be thinned even if the retardation Rth in the thickness direction is large, the optical stack can be thinned and warpage of the optical stack can be suppressed. Also, since the optical film has high orientation angle accuracy, the optical characteristics of the optical stack can be made uniform in-plane. Furthermore, since the optical film has high heat resistance, the optical stack can also have high heat resistance. Such an optical stack can be suitably applied to image display devices such as liquid crystal display devices.

As the polarizing plate, for example, a film provided with a polarizer layer is used. As the polarizer layer, for example, a film of an appropriate vinyl alcohol-based polymer that has been appropriately treated in an appropriate order and method can be used. Examples of such vinyl alcohol-based polymers include polyvinyl alcohol and partially formalized polyvinyl alcohol. Examples of the treatment of the film include dyeing treatment through dichroic substances such as iodine and dichroic dyes, stretching treatment, and crosslinking treatment. The polarizer layer is one capable of absorbing linearly polarized light having a vibration direction parallel to the absorption axis, especially one with excellent polarization degree. The thickness of the polarizer layer is generally 5 μm˜80 μm, but not limited thereto.

In order to protect the polarizer layer, the polarizer may also have a protective film layer on one side or both sides of the polarizer layer. As the protective film layer, any transparent film layer may be used. Among them, film layers of resins excellent in transparency, mechanical strength, thermal stability, and moisture shielding properties are preferred. Examples of such resins include acetate resins such as cellulose triacetate, polyester resins, polyether resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, thermoplastic northylene-based resins, and (meth)acrylic resins. Acetate resins, thermoplastic northylene-based resins, and (meth)acrylic resins are preferable in terms of small birefringence, and thermoplastic northylene-based resins are particularly preferable from the viewpoint of transparency, low hygroscopicity, dimensional stability, and light weight.

The aforementioned polarizing plate can be manufactured, for example, by laminating a polarizer layer and a protective film layer. When laminating, you can also use bonding agent as needed.

The optical stack may further include any component combined with the optical film and the polarizer. For example, the optical stack may also include a bonding layer for laminating the optical film and the polarizing plate.

The thickness of the optical stack is not particularly limited, but it is preferably above 30 μm, preferably above 50 μm, preferably below 150 μm, and preferably below 130 μm.

[6. Liquid crystal display device]

A liquid crystal display device related to an embodiment of the present invention includes the above-mentioned optical stack. As mentioned above, since the optical film included in the optical stack can be thinned, the optical stack is less likely to be warped. According to this, the occurrence of light leakage caused by changes in the optical characteristics of the optical film in the warped portion can be suppressed. The above-mentioned warping generally tends to occur at the corners of the screen of a liquid crystal display device, but in the liquid crystal display device related to this embodiment, such light leakage at the corners can be suppressed. Moreover, since the optical film can have high orientation angle accuracy, the liquid crystal display device related to this embodiment can make the display characteristics such as luminance and contrast of the screen uniform within the screen surface. Furthermore, since the optical film has high heat resistance, the liquid crystal display device related to this embodiment can suppress the change of display characteristics under high temperature environment.

Generally, a liquid crystal display device includes a liquid crystal cell, and an optical stack is provided on at least one side of the liquid crystal cell. Wherein, the optical stack is preferably arranged in such a way that the liquid crystal unit, the optical film, and the viewing-side polarizer are arranged in sequence. In this configuration, the optical film can function as a viewing angle compensation film.

The liquid crystal unit can be used in any mode such as in-plane switching (IPS) mode, vertical alignment (VA) mode, multi-area vertical alignment (MVA) mode, continuous pyrotechnic alignment (CPA) mode, mixed alignment nematic (HAN) mode, twisted nematic (TN) mode, super twisted nematic (STN) mode, optically compensated bend (OCB) mode, etc.

"Example"

Examples are disclosed below to specifically illustrate the present invention. However, the present invention is not limited to the following examples, and can be implemented with arbitrary changes within the scope not departing from the scope of patent application and the scope of equivalents of the present invention.

In the following descriptions, "%" and "parts" indicating amounts are based on weight unless otherwise noted. The following operations, unless otherwise noted, were carried out in the atmosphere at normal temperature and pressure.

[I. Measuring and calculating methods of physical properties of polymers]

(Measurement method of weight average molecular weight Mw, number average molecular weight Mn and molecular weight distribution Mw/Mn of polymers)

The weight-average molecular weight Mw and the number-average molecular weight Mn of the polymer were measured by gel permeation chromatography (GPC) using cyclohexane as an eluent, and obtained as values in terms of standard polyisoprene.

As standard polyisoprene, standard polyisoprene manufactured by Tosoh Corporation (Mw=602, 1390, 3920, 8050, 13800, 22700, 58800, 71300, 109000, 280000) was used.

The measurement system used three Tosoh columns (TSKgelG5000HXL, TSKgelG4000HXL, and TSKgelG2000HXL) in series under the conditions of a flow rate of 1.0 mL/min, a sample injection volume of 100 μL, and a column temperature of 40 °C.

The molecular weight distribution Mw/Mn was calculated using the measured values of the weight average molecular weight Mw and the number average molecular weight Mn measured by the above method.

(Measuring method of glass transition temperature Tg)

The glass transition temperature Tg was measured using a differential scanning calorimeter ("DSC6220" manufactured by SII NanoTechnology Inc.) in accordance with JIS K 6911 at a heating rate of 10°C/min.

(Measurement method for evaluation of birefringence Δn _R )

The resin was molded into a sheet shape with a length of 50 mm x a width of 100 mm x a thickness of 100 μm to obtain a sample sheet. The sample sheet was uniaxially stretched at the free end using a tensile testing machine ("5564 type" manufactured by Instron Japan Company Limited) equipped with a constant temperature bath. The conditions for this extension are as follows. Extension temperature: Tg+15℃ Chuck spacing: 65 mm Extension ratio: 1.5 times (extension distance 32.5 mm) Extension time: 1 minute Extension speed: 32.5 mm/min

After the stretching treatment, the stretched sample sheet was returned to room temperature to obtain a quantitative test sample.

For this measurement sample, the in-plane retardation Re(a) [nm] at the center of the measurement sample was measured at a measurement wavelength of 550 nm using a retardation meter ("AXOSCAN" manufactured by AXOMETRICS Corporation). And, the thickness T(a) [mm] of the aforementioned center portion of the test sample was measured. Using these measured values Re(a) and T(a), the estimated birefringence Δn _R of the resin was calculated by the following formula (X1). Δn _R ＝Re(a)×(1/T(a))×10 ^{− 6} (X1)

(Measurement method of stress birefringence C _R )

The resin was molded into a sheet shape of 35 mm in length×10 mm in width×1 mm in thickness to obtain a sample sheet. After fixing both ends of this sample sheet with jigs, a 160 g weight was fixed to one jig. Then, in an oven whose temperature has been set to the glass transition temperature (Tg) of the resin + 5°C, set the jig without a fixed weight as the starting point, and hang the sample sheet for 1 hour for stretching. Afterwards, the sample sheet was slowly cooled back to room temperature to obtain a quantitative test sample.

For this measurement sample, the in-plane retardation Re(b) [nm] at the center of the measurement sample was measured at a measurement wavelength of 650 nm using a birefringence meter ("WPA-100" manufactured by Photonic Lattice, Inc.). And, the thickness T(b) [mm] of the aforementioned center portion of the test sample was measured. Using these measured values Re(b) and T(b), the δn value was calculated by the following formula (X2). δn=Re(b)×(1/T(b))×10 ⁻⁶ (X2)

Using this δn value and the stress F applied to the sample, the stress birefringence C _R was calculated by the following formula (X3). C _R =δn/F (X3)

[II. Evaluation method of properties of optical thin film]

(Measurement method of photoelastic coefficient of optical film)

The photoelastic coefficient of the optical film is measured by an ellipsometer.

(Evaluation method of orientation angle accuracy of optical films)

The absolute value of the angle formed by the slow axis relative to the length direction of the optical film is measured as the orientation angle θ. This measurement was performed using a polarizing microscope (polarizing microscope "BX51" manufactured by Olympus Corporation). In addition, the aforementioned orientation angle θ was measured at a plurality of measurement positions with an interval of 50 mm in the width direction of the optical film and an interval of 10 m in the length direction. Calculate the standard deviation θσ of these measurement results as the evaluation index of orientation angle accuracy. The smaller the standard deviation θσ of the orientation angle θ is, the smaller the variation of the orientation angle θ is.

(Evaluation method for delamination of optical films)

An unstretched film ("Zeonor Film" manufactured by Zeon Corporation, thickness 100 μm, glass transition temperature of the resin 160°C, unstretched) formed of a resin containing a northylene-based polymer was prepared as an adherend. Corona treatment was applied to one side of the optical film which is the film to be measured and one side of the aforementioned unstretched film. An adhesive (UV adhesive CRB series manufactured by TOYOCHEM CO., LTD.) was attached to both the corona-treated surface of the optical film and the corona-treated surface of the unstretched film. Bond the surfaces with the adhesive attached to each other. Thereafter, the bonding agent was irradiated with ultraviolet rays using an electrodeless UV irradiation device (manufactured by Heraeus AG) to cure the bonding agent. The aforementioned ultraviolet irradiation was carried out under the conditions of a peak illuminance of 100 mW/cm ² and an integrated light intensity of 3000 mJ/cm ² using a D bulb as a light source. Thereby, a sample film having a layer structure of an unstretched film/adhesive layer/optical film was obtained.

About the obtained sample film, the 90 degree peeling test was implemented by the following procedure.

Cut the sample film into a width of 15 mm to obtain a film sheet. Using an adhesive, attach the optical film side of the film sheet to the surface of the glass slide. At this time, a double-sided adhesive tape (manufactured by Nitto Denko Co., Ltd., model "CS9621") was used as an adhesive. The unstretched film contained in the film sheet was clamped at the end of a high-performance digital load cell ("ZP-5N" manufactured by IMADA Co., Ltd.), and the unstretched film was pulled along the normal direction of the surface of the glass slide at a speed of 300 mm/min. The pulling force was measured as the peel strength. The evaluation of peel strength was performed by the following evaluation criteria. Good: 1.0 N/15 mm or more Bad: Less than 1.0 N/15 mm

(Measurement method of retardation Rth, Re and thickness d of optical film, and evaluation method of Rth/d)

The retardation Rth in the thickness direction of the optical film and the in-plane retardation Re were measured at a measurement wavelength of 550 nm using a retardation meter ("AXOSCAN" manufactured by AXOMETRICS Corporation).

The thickness d of the optical film was measured with a caliper (“ID-C112BS” manufactured by Mitutoyo Corporation).

Divide the measured retardation Rth in the thickness direction by the thickness d to calculate Rth/d.

(Evaluation method for the change rate of retardation Rth in the thickness direction of an optical film after 500 hours at 85°C)

Before the durability test described later, the retardation Rth0 in the thickness direction of the optical film was measured. Afterwards, the durability test of storing the optical film for 500 hours in an environment of 85° C. was carried out. After the durability test, the retardation Rth1 in the thickness direction of the optical film was measured. From these measured values Rth0 and Rth1, the change rate (Rth change rate) of the retardation in the thickness direction of the optical film obtained through the endurance test was calculated by the following formula (X4). Rth rate of change (%) = [(Rth0-Rth1) / Rth0] × 100 (X4)

The smaller the rate of change of Rth, the better the heat resistance of the optical film. Then, the obtained Rth change rate was evaluated by the following evaluation criteria. Good: The rate of change in Rth is 3% or less. Bad: Rth change rate is greater than 3%.

(Evaluation method for the rate of change in retardation Rth in the thickness direction of an optical film after 60°C, 90% humidity, and 500 hours)

Before the durability test described later, the retardation Rth0 in the thickness direction of the optical film was measured. Afterwards, the optical film was subjected to a durability test in which it was stored at 60°C and 90% humidity for 500 hours. After the endurance test, the retardation Rth2 in the thickness direction of the optical film was measured. From these measured values Rth0 and Rth2, the change rate (Rth change rate) of the retardation in the thickness direction of the optical film obtained through the endurance test was calculated by the following formula (X5). Rth rate of change (%) = [(Rth0-Rth2) / Rth0] × 100 (X5)

The smaller the rate of change of Rth, the better the heat resistance and moisture resistance of the optical film. Then, the obtained Rth change rate was evaluated by the following evaluation criteria. Good: The rate of change in Rth is 3% or less. Bad: Rth change rate is greater than 3%.

(Measurement method of water absorption of optical film)

Cut a part of the optical film to prepare a test piece (size: 100 mm×100 mm), and measure the weight w0 of the test piece. Thereafter, this test piece was immersed in water at 23° C. for 24 hours. After dipping, measure the weight w1 of the test piece. Then, the ratio (w1-w0)/w0 of the weight w1-w0 of the test piece increased by immersion to the weight w0 of the test piece before immersion was calculated as the water absorption (%). The smaller the water absorption rate, the better.

[III. Evaluation method of characteristics of liquid crystal display device]

(evaluation of uneven corners)

A durability test was performed in which the liquid crystal display device was stored in an environment of 85° C. for 100 hours. After that, the screen of the liquid crystal display device was set to a black display state, and the presence or absence of light leakage (corner unevenness) around the screen was visually confirmed. Good: Light leakage around the screen was not seen at all. Defective: Light leakage around the screen is conspicuous.

[Example 1]

(1-1) Manufacture of ring-opened polymers:

In a glass reaction vessel whose interior was replaced with nitrogen, 200 parts by weight of dehydrated cyclohexane, 0.75 mol% of 1-hexene, 0.15 mol% of diisopropyl ether, and 0.44 mol% of triisobutylaluminum were placed in the reactor at room temperature and mixed with respect to a total of 100 parts by weight of the monomers described later. Then, while maintaining 45°C, 29 parts by weight of tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), 3 parts by weight of northylene (NB) and 0.02 mol% of tungsten hexachloride (0.65% by weight toluene solution) were continuously added to the reactor in parallel for 2 hours and polymerized. Subsequently, 0.2 mol% isopropanol was added to the polymerization solution to passivate the polymerization catalyst, so that the polymerization reaction was terminated. In the above description, all the amounts indicated by the unit "mol%" are values based on the total amount of monomers as 100 mol%. The obtained northylene-based ring-opened polymer had a weight average molecular weight Mw of 2.8×10 ⁴ and a molecular weight distribution (Mw/Mn) of 2.1. Also, the conversion rate of monomer to polymer was 100%.

(1-2) Production of northylene-based polymers by hydrogenation:

Subsequently, 300 parts of the reaction solution containing the ring-opened polymer obtained in the aforementioned step (1-1) was transferred to an autoclave with a stirrer, and 3 parts of diatomaceous earth-supported nickel catalyst ("T8400RL" manufactured by Nikki Chemical Co., Ltd., nickel loading rate: 57%) was added, and the hydrogenation reaction was carried out at 4.5 MPa and 160°C for 4 hours.

After the hydrogenation reaction, the obtained solution was filtered using RADIOLITE#500 as a filter bed at a pressure of 0.25 MPa ("FUNDABAC filter" manufactured by Ishikawajima Harima Heavy Industries Co., Ltd.) to remove the hydrogenation catalyst and obtain a colorless and transparent solution. The obtained solution was poured into a large amount of isopropanol to precipitate a northylene-based polymer which is a hydrogenated product of a ring-opened polymer. After the precipitated norrylene-based polymer was filtered off, 2.0 parts of a xylene solution in which 0.1 part of an antioxidant [4{3-[3,5-bis(tertiary-butyl)-4-hydroxyphenyl]propionate} neopentylitol ester (manufactured by Ciba Specialty Chemicals, product name "Irganox (registered trademark) 1010")]] was dissolved was added to 100 parts of norrylene-based polymer. Then, it was dried for 6 hours in a vacuum dryer (220° C., 1 Torr) to obtain a thermoplastic northylene-based resin. The weight average molecular weight of the northylene-based polymer was 4.0×10 ⁴ , and the molecular weight distribution Mw/Mn was 2.3.

The glass transition temperature Tg, birefringence Δn _R and stress birefringence C _R of the obtained thermoplastic northylene resin were measured by the method mentioned above. The glass transition temperature Tg of the thermoplastic northylene resin is 110℃, the evaluated birefringence Δn _R is 0.0030, and the stress birefringence C _R is 2600×10 ^{− 12} Pa ^{− 1} .

(1-3) Manufacture of film before stretching:

Put the thermoplastic northylene-based resin obtained in the aforementioned step (1-2) into a twin-screw extruder, and form it into a strand-shaped molded body by hot-melt extrusion. This molded body was finely cut using a strand cutter to obtain pellets of a thermoplastic northylene-based resin.

The pellets were dried at 100°C for 5 hours. Thereafter, the pellets were supplied to an extruder by a conventional method and melted at 250°C. Then, the melted thermoplastic northylene-based resin was discharged from the mold onto a cooling drum to obtain a long film before stretching with a thickness of 110 μm.

(1-4) Manufacture of optical films:

Longitudinal stretching machine using suspension method between rolls is prepared. Using this longitudinal stretching machine, the aforementioned unstretched film was stretched 1.26 times in the longitudinal direction to obtain an intermediate film. The stretching temperature of the aforementioned stretching using a longitudinal stretching machine is 120°C, which is 10°C higher than the glass transition temperature Tg of thermoplastic northylene resin (Tg+10°C).

After that, the above-mentioned intermediate film was supplied to a transverse stretching machine using a tenter method, and stretched 1.43 times in the transverse direction while adjusting the pulling tension and the tension of the tenter chain to obtain a long optical film as a biaxially stretched film. The stretching temperature of the aforementioned stretching using a transverse stretching machine is 120°C, which is 10°C higher than the glass transition temperature Tg of thermoplastic northylene resin (Tg+10°C). The obtained optical film had an in-plane retardation Re of 60 nm, a thickness direction retardation Rth of 320 nm, and a thickness d of 65 μm.

The obtained optical film was evaluated by the method mentioned above.

(1-5) Manufacture of optical stacks:

An unstretched polyvinyl alcohol film (vinylon film with an average degree of polymerization of about 2400 and a degree of saponification of 99.9 mol%) with a thickness of 65 μm was prepared as a strip-shaped raw film. The intermediate guide roller continuously conveys the raw film along the long side, and at the same time, the film is soaked in pure water at 30°C for 1 minute for swelling and at 32°C for 2 minutes in a dyeing solution (a dye solution containing iodine and potassium iodide in a molar ratio of 1:23, with a dye concentration of 1.2 mmol/L) to allow the film to absorb iodine. Thereafter, the film was washed with a 3% aqueous solution of boric acid at 35° C. for 30 seconds. Thereafter, the film was stretched 6.0 times in an aqueous solution containing 3% boric acid and 5% potassium iodide at 57°C. Afterwards, the film was subjected to color correction treatment in an aqueous solution containing 5% potassium iodide and 1.0% boric acid at 35°C. Thereafter, the film was dried at 60° C. for 2 minutes to obtain a strip-shaped polarizer layer with a thickness of 23 μm. The degree of polarization of the polarizer layer was measured with an ultraviolet-visible spectrophotometer ("V-7100" manufactured by JASCO Corporation), and the result was 99.996%.

Acrylic resin ("SUMIPEX HT55X" manufactured by Sumitomo Chemical Co., Ltd.) was supplied to a hot-melt extrusion film forming machine equipped with a T-die. Acrylic resin is extruded from a T-die, and the acrylic resin is formed into a film. Thereby, a strip-shaped protective film layer formed of an acrylic resin and having a thickness of 40 μm was obtained.

Corona treatment was applied to one side of the obtained protective film layer. Thereafter, a UV-curable adhesive ("ARKLS KRX-7007" manufactured by ADEKA Corporation) was applied to the surface of the corona-treated protective film layer to form an adhesive layer. The bonding layer is interposed, and the polarizer layer and the protective film layer are bonded together using pinch rollers. Immediately thereafter, the bonding layer was irradiated with 750 mJ/cm ² of ultraviolet rays using a UV irradiation device to cure the bonding layer. Thereby, a long polarizing plate having a layer structure of polarizer layer/bonding layer (thickness 2 μm)/protective film layer was obtained.

Corona treatment is applied to one side of the optical film. Thereafter, an ultraviolet curing adhesive ("ARKLS KRX-7007" manufactured by ADEKA Corporation) was applied to the surface of the corona-treated optical film to form an adhesive layer. The bonding layer is interposed, and the polarizing plate and the optical film are bonded together using pinch rolls. Immediately thereafter, the bonding layer was irradiated with 750 mJ/cm ² of ultraviolet rays using a UV irradiation device to cure the bonding layer. Bonding was carried out so that the slow axis of the optical film and the absorption axis of the polarizer layer were perpendicular when viewed from the thickness direction. Thus, an elongated optical stacked body having a layer structure of optical film/bonding layer/polarizer layer/bonding layer/protective film layer is obtained.

(1-6) Manufacture of VA type liquid crystal display device:

A VA-type liquid crystal display device (40-type TV "TH-40AX700" manufactured by Panasonic Corporation) was prepared. This liquid crystal display device includes a polarizing plate bonded to the viewing side of the glass surface of the liquid crystal cell. Peel off the polarizing plate on the viewing side from the liquid crystal display device. Afterwards, the elongated optical stack produced by the aforementioned steps (1-5) was cut into an appropriate size for the liquid crystal display device, and the surface on the side of the optical film was bonded to the glass surface of the liquid crystal cell to manufacture a VA-type liquid crystal display device for testing. The aforesaid lamination is carried out in such a way that the "direction of the absorption axis of the polarizing plate on the viewing side originally equipped with the liquid crystal display device" is consistent with the "direction of the absorption axis of the polarizer layer newly bonded to the optical stack of the liquid crystal unit".

The obtained liquid crystal display device was evaluated by the method already mentioned above.

[Example 2]

The combination of monomers used in the aforementioned step (1-1) was changed to 31 parts by weight of tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), and 1 part by weight of norbisene (NB).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.28 times, and the stretching ratio in the horizontal direction was changed to 1.48 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 122.5°C, which is 10°C higher than the glass transition temperature Tg of the thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Example 3]

The combination of monomers used in the aforementioned step (1-1) was changed to 29 parts by weight of tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), and 3 parts by weight of ethylene tetracyclododecene (ETD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.27 times, and the stretching ratio in the horizontal direction was changed to 1.44 times. Furthermore, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 124°C, which is a temperature 10°C higher than the glass transition temperature Tg of thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Example 4]

The combination of monomers used in the aforementioned step (1-1) was changed to 31 parts by weight of tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), and 1 part by weight of ethylene tetracyclododecene (ETD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.30 times, and the stretching ratio in the horizontal direction was changed to 1.50 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 125°C, which is 10°C higher than the glass transition temperature Tg of the thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Example 5]

The combination of monomers used in the aforementioned step (1-1) was changed to 30 parts by weight of tetracyclododecene (TCD) and 70 parts by weight of dicyclopentadiene (DCPD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.256 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 125.5°C, which is 10°C higher than the glass transition temperature Tg of thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Comparative Example 1]

The combination of monomers used in the aforementioned step (1-1) was changed to 31 parts by weight of tetracyclododecene (TCD), 68 parts by weight of dicyclopentadiene (DCPD), and 1 part by weight of norbisene (NB). Next, the polymerization temperature in the aforementioned step (1-1) was changed to 55°C.

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.25 times, and the stretching ratio in the horizontal direction was changed to 1.45 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 122°C, which is 10°C higher than the glass transition temperature Tg of the thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Comparative Example 2]

The combination of monomers used in the aforementioned step (1-1) was changed to 5 parts by weight of tetracyclododecene (TCD), 80 parts by weight of dicyclopentadiene (DCPD), and 15 parts by weight of ethylene tetracyclododecene (ETD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.35 times, and the stretching ratio in the horizontal direction was changed to 1.55 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 114°C, which is 10°C higher than the glass transition temperature Tg of the thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Comparative Example 3]

The combination of monomers used in the aforementioned step (1-1) was changed to 10 parts by weight of methanotetrahydrofluorene (MTF), 40 parts by weight of tetracyclododecene (TCD), and 50 parts by weight of dicyclopentadiene (DCPD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.60 times, and the stretching ratio in the horizontal direction was changed to 1.80 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 138°C, which is a temperature 10°C higher than the glass transition temperature Tg of thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Comparative Example 4]

The combination of monomers used in the aforementioned step (1-1) was changed to 10 parts by weight of methanotetrahydrofluorene (MTF), 40 parts by weight of tetracyclododecene (TCD), and 50 parts by weight of dicyclopentadiene (DCPD).

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.20 times, and the stretching ratio in the horizontal direction was changed to 1.40 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 138°C, which is a temperature 10°C higher than the glass transition temperature Tg of thermoplastic northylene-based resin (Tg+10°C).

Production and evaluation of thermoplastic northylene-based resins, optical films, and liquid crystal display devices were performed in the same manner as in Example 1 except for the above matters.

[Comparative Example 5]

Except having used 50 parts by weight of tetracyclododecene (TCD) and 50 parts by weight of 8-methyltetracyclododecene (MTD) as monomers, the same operation as the step (1-1) of Example 1 was performed to obtain a ring-opened polymer. The weight average molecular weight Mw of the ring-opened polymer was 4.0×10 ⁴ , and the molecular weight distribution Mw/Mn was 2.0. The conversion of monomer to polymer was 100%.

Transfer 300 parts of the polymerization reaction solution containing the ring-opened polymer thus obtained to an autoclave with a stirrer, add 3 parts of diatomaceous earth-supported nickel catalyst (“T8400RL” manufactured by Nikki Chemical Co., Ltd., nickel loading ratio: 57%), and perform hydrogenation reaction at 4.5 MPa and 160° C. for 4 hours.

After the hydrogenation reaction, the obtained solution was filtered using RADIOLITE#500 as a filter bed at a pressure of 0.25 MPa ("FUNDABAC filter" manufactured by Ishikawajima Harima Heavy Industries Co., Ltd.) to remove the hydrogenation catalyst and obtain a colorless and transparent solution. The obtained solution was poured into a large amount of isopropanol to precipitate the polymer. After the precipitated polymer was filtered off, it was dried with a vacuum dryer (220° C., 1 Torr) for 6 hours to obtain a hydrogenated product of the aforementioned ring-opened polymer. The glass transition temperature Tg of the hydrogenated product of the ring-opened polymer was 158°C.

28 parts by weight of the hydrogenated product of the ring-opened polymer, 10 parts by weight of maleic anhydride and 3 parts by weight of dicumyl peroxide were dissolved in 130 parts by weight of tertiary butylbenzene, and reacted at 140° C. for 6 hours. The obtained reaction product solution was poured into methanol to aggregate the reaction product. The aggregate was dried for 6 hours in a vacuum dryer (220° C., 1 Torr) to obtain a hydrogenated maleic acid-modified ring-opened polymer. Hereinafter, this hydrogenated maleic acid-modified ring-opening polymer may be referred to as "polar COP". The maleic acid group content of the polar COP was 25 mol%.

In the aforementioned step (1-3), the aforementioned polar COP is used as the resin of the material of the film before stretching.

In the aforementioned step (1-4), the stretching ratio in the longitudinal direction was changed to 1.62 times, and the stretching ratio in the horizontal direction was changed to 1.82 times. In addition, in the aforementioned step (1-4), the stretching temperature in the longitudinal and transverse directions was changed to 180°C, which was 10°C higher than the glass transition temperature Tg of the hydrogenated maleic acid-modified ring-opening polymer (Tg+10°C).

Production and evaluation of an optical film and a liquid crystal display device were performed in the same manner as in Example 1 except for the above matters.

[result]

The results of the aforementioned Examples and Comparative Examples are shown in Table 1 and Table 2 below. In Table 1 and Table 2 below, the meanings of the abbreviations are as follows. "T" in the monomer column: Tetracyclododecene (TCD). "D" in the monomer column: dicyclopentadiene (DCPD). "N" in the monomer column: norbene (NB). "E" in the monomer column: ethylenetetracyclododecene (ETD). "M" in the column of the monomer: methyl bridge tetrahydrofluorene (MTF). Rth change rate (85°C): The change rate of the retardation in the thickness direction of the optical film obtained through a durability test stored at 85°C for 500 hours. Rth change rate (60°C90%): The change rate of the retardation in the thickness direction of the optical film obtained through the endurance test stored at 60°C and 90% humidity for 500 hours.

"Table 1" [Table 1. Results of Examples]

"Table 2" [Table 2. Results of Comparative Example]

[Reference example 1. Validity of measurement method for peel strength]

An experiment was conducted to evaluate whether it can be said that "the measuring method of the peel strength adopted in the above-mentioned examples and comparative examples reflects the evaluator of the peel strength when the adherend is a polarizing plate."

A polarizing film and an adhesive were prepared by the same method as that described in Example 1 of Japanese Patent Laid-Open No. 2005-70140. Also, the optical film obtained in Example 1 of the present application was prepared as a film to be measured. Corona treatment is applied to one side of the optical film, and the corona-treated side is bonded to one of the surfaces of the polarizing film with an intermediary adhesive. On the other surface of the polarizing film, a cellulose triacetate film is pasted with an intermediary adhesive. Thereafter, it was dried at 80° C. for 7 minutes to cure the adhesive to obtain a sample film. The obtained sample film was subjected to the same 90-degree peeling test as in the above (evaluation method of peeling of optical film). As a result, the same peel strength value as that obtained in Example 1 of the present application was obtained.

From these results, it can be confirmed that the peel strength measurement results obtained by the peel strength measurement methods used in the above-mentioned examples and comparative examples reflect the evaluation of the peel strength when the adherend is a polarizing plate.

none.

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Claims (6)

A kind of optical thin film, its system consists of containing drop

Thermoplastic reduction of ethylenic polymers

An optical film formed of ethylenic resin, wherein the aforementioned

The ethylenic polymer is selected from the group consisting of 100 parts by weight to 500 parts by weight of dicyclopentadiene-based monomers and their hydrogenated products relative to 100 parts by weight of tetracyclododecene-based monomers. The group formed by derivatives of alkenes, the aforementioned drop

The molecular weight distribution of the ethylenic polymer is 2.4 or less, and the aforementioned thermoplasticity decreases.

The glass transition temperature Tg of the ethylenic resin satisfies the following formula (1).

The birefringence △ _{n R} exhibited by vinyl resin under the condition of Tg+15°C and 1 minute uniaxial extension to 1.5 times satisfies the following formula (2), and the retardation Rth in the thickness direction of the aforementioned optical film and the thickness d of the aforementioned optical film satisfy the following formula (3): (1) Tg≧110°C, (2) 0.0050≧△n _R ≧0.0025, (3) Rth/d≧3.5×10 ^-3 . The optical film according to claim 1, wherein the photoelastic coefficient of the optical film is 8 or less Brewster. The optical film according to claim 1, wherein the in-plane retardation Re of the optical film is not less than 40 nm and not more than 80 nm. A method for manufacturing an optical film, which is the method for manufacturing an optical film as described in any one of Claims 1 to 3, comprising reducing the aforementioned thermoplasticity

Vinyl resins are molded by extrusion or solution casting. An optical stack comprising the optical film and a polarizing plate according to any one of Claims 1 to 3. A liquid crystal display device comprising the optical stack as described in Claim 5.